Water Supply and Sewarage Handout

(CEng-4607): Water Supply & Sewerage

Lecture Notes (collection and distribution)

1. DEMAND FOR WATER 1.1. Introduction 1.2. Water Consumption for Various Purposes 1.3. Factors Affecting Consumption 1.4. Periods of Design and Water Consumption Data required 1.1 Introduction In the design of any water works projects it is necessary to estimate the amount of water that is required. This involves:  The determination of people who will be served  The per capita water consumption  Analysis of the factors that may operate to affect consumption It is usual to express water consumption in liters (gallons) per capita per day, obtaining their figure by dividing the total numbers of people in the city in to the total daily water consumption. For many purposes the average daily consumption is convenient. It is obtained by dividing the population in to the total daily consumption averaged over one year. It must be realized, however, that using the total population may in some cases, result in serious in accuracy, since a large proportion of the population may be solved by privately owned wells. A more accurate figure would be the daily consumption per person served. 1.2. Water Consumption for Various purposes The water furnished to a city can be classified according to its ultimate use or end. The uses are:  Domestic  Commercial & Industrial  Public use  Loss and waste Domestic This includes water furnished to houses, hotels, etc, for sanitary, culinary, drinking, washing, batching, and other purposes. It varies according to the living conditions of consumers, the range usually being considered as 75 to 380 liters per capita per day, averaging 190 to 340 per capita. These figures include:  Air conditioning of residences  Irrigation or sprinkling of privately owned gardens and lawns The domestic consumption may be expected to be about 50% of the total in the average city, but where the total consumption in small, the proportion will be much greater.

1 Adama Science and Technology University- Department of Civil Engineering

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(CEng-4607): Water Supply & Sewerage

Lecture Notes (collection and distribution)

Commercial and Industrial Water so classified is that furnished to industrial and commercial plants. Its importance will depend up on local conditions, such as the existence of large industries and whether or not the industries patronize (utilize) the public water works. Self supplied industrial water requirements are estimated to be more than 200 percent of municipal water supply demand. The quantity of water required for commercial and industrial use has been related to the floor area of buildings served. Symons proposes an average of 12.2 m3 / 1000 m2 of floor area per day. In cities of over 25, 000 population commercial consumption may be expected to amount to about 15 percent of the total consumption.

Public Use Public Buildings, such as:  City halls  Jails  Schools As well as public services:  Flushing streets &  Fire protection Require much water for which, usually, the city is not paid. Such water amounts to 50 to 75 liters per capita. The actual amount of water used for extinguishing fires does not figure greatly in the average consumption, but very large fires will cause the rate of use to be higher for short periods.

Losses and Waste This water is some times classified as “un accounted for”, although some of the loss and waste may be accounted for in the sense that its cause and amount are approximately known. Unaccounted for water is due to:  meter and pump slippage  Unauthorized water connections and  Leaks in mains It is apparent that the unaccounted for water, also waste by consumers, can be reduced by careful maintenance of the water system and by universal metering of all water services. In a system 100 percent metered and moderately well maintained the unaccounted for water, exclusive of pump slippage, will be about 10 percent. The total consumption will be the sum of the foregoing uses and the loss and waste. The probable division of this consumption is shown in table 2.

2 Adama Science and Technology University- Department of Civil Engineering

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(CEng-4607): Water Supply & Sewerage

Lecture Notes (collection and distribution)

Table2. Projected consumption of water for various purposes in the year 2000 Use Domestic Industrial Commercial Public Loss & Waste Total

Liters per Percentage capita /day of total 300 44 160 24 100 15 60 9 50 8 670 100

1.3. Factors Affecting Consumption The average daily per capita water consumption varies. The variation depends up on a number of important factors, including:  Size of city  Presence of Industries And Commerce  Quantity of the water  Its price  Climatic Condition  Characteristics of the Population  Whether supplies are metered or  Efficiency of the water works administration  Metering  Variations in rate of Consumption  Fire Demand  Density of Population  Zoning The more important of these factors will be separately treated below, but some can be briefly discussed here. The efficiency of the water works management will affect consumption by decreasing loss and waste. Leaks in water mains and services and unauthorized use of water can be to a minimum by surveyors. A water supply that is both safe and attractive in quality will be used to a great extent than one of poor quality. In this connection it should be recognized that improvement of the quality of water supply will probably be followed by an increase in consumption. Increasing the pressure will have a similar effect. Changing the rates changed for water has little effect up on consumption, at least in prosperous periods. Size of City The effect of size of city is probably indirect. It is true that small per capita water consumption is to be expected in a small city, but this is usually due to the fact that there are only limited uses for water in small towns. On the other hand, the presence of an important water using industry may result in high consumption. 3 Adama Science and Technology University- Department of Civil Engineering

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(CEng-4607): Water Supply & Sewerage

Lecture Notes (collection and distribution)

A small city is likely to have a relatively larger area that is inadequately served by both the water and sewer systems than a large city. Sewerage or its absence will have considerable effect. In the answered home, water consumption will rarely exceed 4 lit/capita/day; while in the average skewered home, it will equal or exceed 300 lit/capita/day. The extension of sewer may, therefore, necessitate additional water supply. Characteristics of the Population Although the average domestic use of water may be expected to be about 300liters per capita per day, wide variations are found. These are largely dependent up on the economic status of the consumers and will differ greatly in various sections of a city. In the high value residential districts of a city or in a suburban community with a similar population the water consumption per capita will be high. In apartment houses, which may be considered as representing the maximum the maximum domestic demand to be expected, the average consumption should be about 380 lit/capita. In area of moderate –or high value single residences even higher consumption may be expected, since to the ordinary domestic demand there will be added an amount for watering lawns. The slum districts of large cities will have lower per capita consumptions, perhaps 100 liters, but consumptions as low as 50 lit/capita have been reported. The lowest figures of all will be found in low-value districts where sewerage is not available and where perhaps a single faucet serves one or several homes. Climatic Conditions Where summers are hot and dry, much water will be used for watering lawns. Domestic use will be further increased by more bathing, while public use will be affected by use in parks and recreation fields for watering grass and for ornamental fountains. On the other hand, in cold weather water may be wasted at the faucets to prevent freezing of pipes, there by greatly increasing consumption. High temperatures may also lead to high water use for air conditioning. Metering Every water works should have some means at the pumping plant of accurately measuring all the water that is delivered to the city, if the meters are of the recording type, valuable information regarding hourly rates of consumption will be available. If all services are metered the difference between the total amount pumped and the sum of service meter readings and any un-metered publicly used water will be the accounted for water. Metering of services consists of placing a rescoring meter in the line leading from the water main to the building served. Consumers are then billed for the water that they used. The alternative to this method is charging by some form of flat rate, which is not related to the actual amount of water used or wasted. The advantages of metering are apparent. Pumping and treatment of water costs money, and wasting of water means a greater cost to be distributed among customers. If services are unlettered, the careful consumers bear some of the burden imposed by the careless and wasteful. It is almost impossible to construct a good system of water charges unless they are based upon actual consumption of water. Lack of service meters has a definite effect upon water consumption in fact; the installation of meters may so reduce consumption that provision of more water may be indefinitely postponed. Comparison of figures in 22 Cites 4 Adama Science and Technology University- Department of Civil Engineering

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(CEng-4607): Water Supply & Sewerage

Lecture Notes (collection and distribution)

90 to 100 present metered, with 13 cites, 20 present metered, showed that the former group had an average consumption of 366 liters; and the latter 824 liters. These were all cites having over 100,000 population. Metering all service of a city should reduce consumption to about 50 percent of the consumption with out meters. Although metering reduces water consumption, there is a tendency for consumption to increase gradually after all services are metered.

Fire demand Although the actual amount of water in a year for fire fighting is small thane rate of use is large. The insurance service office uses the formula F=18c(A)0.s Where f=the required fire flow in gpm(lit/min/3.78) C= a coefficient related to the type of construction A= total flower area ff2(m2x10-76) excluding the basement of the building C ranges from a max of 1.5 for wood frame to a minimum of 0.60for fire resistive construction. The fire flow calculated from the formula is not to exceed 30, 240 lit /min in geared nor 22,680 lit/min for one stray construction .the minim fire flow is not tube less than 1890 lit/min. additional flow may be required to protect nearly by buildings . the total for all purposes for a single fire is not to exceed 45,360 lit/min nor be less than 1990 lit/min. For grouping of single and two-family residences, the following table may be used to determine the required flow. The fire flow must be maintained for a minimum of 4 hours as shown in table –x .most communities will require duration of 10 hours. In order to detmine the max water demand during a fire , the fire flow must be added to the max daily consumption .it is assumed that a community with a population of 22,000 has an average consumption of 600 lit per capita /day and flow directed by a building of orderly construction with a floor area of 1000m2and a height of 6 stories , the calculation is as follows: Average domestic demand=22,000x600=13.2x106 lit/day Maximum daily demand= 1.8x13.2x106=23.76x106lit/day F=18(1) (1000x10.76x6)0.5=17,288 lit/min =24.89x106lit/day Max rate= 23.76x106+24.89x106 =48.65x106 lit/day =2211 lit per capita/day for to24 hours the total flow required during this day would be 23.76+24.89x10/24=34.13x106liters 1551 lit per capital/day The difference between the maximum domestic rate and the values is frequently provides from elevated storage tanks. Table –X, residential fire flows Distance b/n adjacent units/m Required fire flow/lit min 730.5 9.5-30.5 3.4-9.2

1890 2835-3780 3780-5670 5

Adama Science and Technology University- Department of Civil Engineering

2011/12

(CEng-4607): Water Supply & Sewerage

< 3.0

Lecture Notes (collection and distribution)

5670-7560

For continuus construction use 9450 lit/min Periods of design and water consumption data required the economic design period of a structure depends up on its ,fire cost, ease of expansion ,and likely hood of obsolescence in connection with design, the water consumption at the end of the period must be estimated .over design is not conservation since it may burden a relatively .over design is not conservation since it may burden a relatively small community with the cost of extravagant works designed for a far large population. Very appropriately design different segment of the water testament and distribution systems for differing periods using differing capacity criteria. 1 development of source. The design period will depend upon the source .for ground water ,it is easy to drill additional wells ,the design period will be short, perhaps 5 yeas .for surface waters requiring impoundments , the design period will be longer, perhaps as much as 50 years . the design capacity of the source should be adequate to provide the maximum daily demand anticipated during the design period , but not necessarily up on a continuous basis. 2 pipe line from source. The design period is generally long since the life of pipe is long and the cost of material is only a portion of the const of constriction .25 year or more would not be un usual . the design capacity of the pipe line should based up on average consumption of suitable velocities under all anticipated flow conditions 3 water treatment plant. The design period is commonly 10 to 15 years since expansion is generally simple it is considered in the initial design. most treatment units will be designed for average daily flow at the end of the design period since overloads do not result in major flow at the efficiency. Hydraulic design should be based up on max-anticipated flow. 4 pumping plant. the design period is generally 10 years since modification and expansion are easy it initially considered. Pump selection requires knowledge of max flow including fire demand, averge flow, and minimum flow during the design period. 5 amount of storge. The design period may be influenced by cost factors perculiar to the construction of storage vessels, which dictate minimum unit cost for tank of specific size . Design requires knowledge of average consumption , fire demand , maximum hours , maximum week , and maximum month as well as the capacity of the source and pipe lines from the source. 6-distribution system. The deign period is indefinite and the capacity of the system should be sized to accommodate the maximum anticipated development over factors affecting per capital flow should be considered. Maximum hourly flow including fine demand is the basis for design. Variation in rate of consumption The parfait daily water consumption figures discussed above have been base upon annual consumption. The annual average daily consumption, which useful, design tell the fuel story. Climatic conditions, the working day, etc tend to cause wide versions in water use. Though the week Monday will usually have the highest consumption, and Sunday the lowest. Some months will have an average daily consumption higher than the annual average .in most cites the peak month will be July or august. Especially hot, dry weathers will produce a week of maximum 6 Adama Science and Technology University- Department of Civil Engineering

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(CEng-4607): Water Supply & Sewerage

Lecture Notes (collection and distribution)

consumption, and certain days will place still greater demand upon the water system .peak demands also occur during the day, the hours of occurrence depends upon the characteristics start and a minimum about of A.m.A curve showing hourly variation in consumption for a limited area of city may show a characteristic shape .it but there will be a fairly high consumption thorough the working day. The night flow, excluding industries using much water night, is a good indication of the magnitude of the loss and waste. The important of keeping completely record of water pupate of city for each day and fluctuations of demand throughout the day cannot be cover emphasized. So far as possible the information shield is obtained for specific areas. These are the basic data required for planning of water works improvement .if obtained and analyzed, they will also indicate trends in per capita consumptions and hourly demands for which further provision must be made. In the absence of data it is sometimes necessary to estimate the maximum water consumption during a month, week day, or hours. The maximum daily consumption is likely to be 180 percent of the annual average and may rich 200 percent. The formula suggested by R.O Goodrich is consent for estimating consumption and is: P=180t-0.10 Where p=the percentage of the annual average consumption for the time t in days from 2/24 to 360. The formula gives consumption for the maximum day as 180 percent of the average, the weekly consumption 148 percent, and the monthly as 128 percent. These fingers apply particularly to smaller residential cites. Other sites will generally have smaller peaks. The maximum hourly consumption is likely being about 150 percent of the average for that day. Therefore the maximum hourly consumption for a city having an annual average consumption of 670 lit/day per capita would occur on the maximum day and would be 670x80x15, or 1800 lit/day. The fire demand must also be added, according to the method indicated in the following article. Maximum rate of consumption is of less importance than max flow but is required in connection with design use of water, and the proportion of peak demand provided from storage. Usually it eil vary from 25 to 50 percent of the daily average. Peaks of water consumption in certain will affect design of the distribution system. High peaks of hourly consumption can be expected in residential or predominantly residential sections because of heavy use of water for lawn watering especially where underground system are used ,air condition or in other water using appliance .since use of such appliances is increasing peak hourly consumptions are also increasing. Zoning Zoning is that feature of city planning which regulates the height and bulk of building and the uses tp which they may be put. A city plan, therefore, controls the character of districts and prevents, directs or furless changes in then. The advantages of this degree of certainty in the solution of water disturbing and sewerage problems are important. In residential sections the density of population at maximum development will be known. A residential district of high or medium class will not become a slum or apartment house district. 7 Adama Science and Technology University- Department of Civil Engineering

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Lecture Notes (collection and distribution)

Industrial districts will be set aside on the plan and not allowed to encroach upon residential areas. Commercial districts will be largely decentralized, and the main business district will grow in a planed direction. Water mains and sewer systems can then be planned only for actual needs and with some certainty that future changes in the character of districts will over tax ten. Design of Water Distribution Systems The purpose contours and flow patterns of the system. Information on the pressure continuous& flow pattern will the environment engineer to determine if the system cannot meet the demands for which it was designed

8 Adama Science and Technology University- Department of Civil Engineering

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(CEng-4607): Water Supply & Sewerage

Lecture Notes (collection and distribution)

2. METHODS OF FORECASTING POPULATION Prior to design of a water works one must establish the length of time the improvement will serve the community before it is abandoned or enlarged. For example, an impounding reservoir may be constructed of such a capacity that it will furnish a sufficient amount of water for 30 years, or the capacity of a water purification plant may be adequate for 10 years. These periods are known as periods of design, and they have an important bearing up on the amount of funds that may be invested in construction of both water works and sewage works. Since most cities are growing in population, the period of design depends mainly up on the rate of population growth, i.e. the water purification plant mentioned above will just sense the population expected 10 years hence. The problem, according in to forecast as accurately as possible the population 10, 20, or 30 years in the future. It is more difficult to estimate the population in some future year. Several methods are used but it should be pointed out that judgment must be exercised by the engineer as to which method is most applicable. Acknowledge of  The city and its environs  Its trade territory  Whether or not its industries are expanding  The state of development in the surrounding country  Location with regard to rail or water shipment of raw materials and  manufactured goods Will all enter is to the estimation of future population. If course, extraordinary events, such as discovery of a nearby oil field or sudden development of a new industry, upset all calculations of future growth and necessitate hasly extension of existing water and sewage forcotites. Arithmetic Method This method is based up on the hypothesis that the rate of growth is constant. The hypothesis may be tested by examining the growth of the community to determine if approximate equal incremental increases have occurred between recent censuses. Mathematically their hypothesis may be expressed as

dp  k dt dp  the rate of change of population with time K = is & constant. Where dt K is determined graphically or from consideration of actual populations in successive census as

9 Adama Science and Technology University- Department of Civil Engineering

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(CEng-4607): Water Supply & Sewerage

Lecture Notes (collection and distribution)

p  t The population in the future is then estimated from K 

Pt = Po + Kt Where Pt = the population at some time in the future Po = the pn extent population t = the period of the projection Uniform percentage Method The hypothesis of geometric or uniform percentage growth assumes a rate of increase which is proportional to population.

dp

 k' p dt Integration of their equation yields Inp = In Po + k‟t This hypothesis is best tested by plotting recorded population growth on semi log paper. If a straight line can be fitted to the data, the value of k‟ can be determined from its slope. Alternatively K‟ may be estimated from recorded population using Inp  Inpo t In which P& Po are recorded populations separated by a time interval t K' 

Curvilinear Method Their technique involves the graphical projection of the past population growth curve, following whatever tendencies the graph indicates. The communing used variant of this method includes comparison of the projected growth to that of other cities of larger size. The cities chosen for the composition should be as similar as possible to the city being studied. Geographical proximity, likeness of economic base, access to similar transportation systems, and other such factors should be considered. As an example, in figure below, city A, City A (the city being studied) is plotted up to 1970, the year in w/c its population was 000

51,

City B: reach 51, 000 in 1930, and its curve is plotted from 1930 on. Similar curves are drawn for cities C, D, and E from the year in which they reached A‟s 1970 population. A‟s curve can then be continued, allowing it to be influenced by the rates of growth 10 Adama Science and Technology University- Department of Civil Engineering

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(CEng-4607): Water Supply & Sewerage

Lecture Notes (collection and distribution)

of the larger cities. So far as possible the larger cities chosen should reflect conditions as they are in the city being studied.

Fig: Curvilinear method of predicting population. The dashed line is the forecast for city A. Scales A, B, C, D and E apply to the corresponding cities. Logistic Method The logistic curve used in modeling population trends has an S shape. The hypothesis of logistic growth may be tested by plotting recorded population data on logistic paper – on which it will appear as a straight line if the hypothesis valid. In the short term, logistic projection can be made based up on the equation.

Psat

p

 bt

1 a Where; Psate = the situation population of the community a and b = are constants Psat , a and b may be determined from three successive census populations and the equations:

2 Po P1 P2  P1 Po  P2  2

Psat 

a  In

Po P2  P1

2

Psat  Po Po

P P  Ps  1 / n o sat 2 P1 Psat  Po  Where n = the time interval b/n successive census. Substitution of their values in if * permits the estimation of population for any period  t beyond the base year corresponding to Po. b

Declining Growth Method This technique, like the logistic method, assumes that the city has some limiting saturation population, and that its rate of growth is a function of its population deficit

dp dt

 K 11 Psat  P 

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Lecture Notes (collection and distribution)

Following estimation of the saturation population up on some rational basis such as land available and existing population density, K11 may be determined from successive censuses and

P P 1 / n sat n Psat  Po Where P and Po are populations recorded n years apart. Future population can then be estimated using this value and K 11 



P  Po  Psat  Po  1  e k ' ' t



Ratio Method The ratio method of forecasting relies upon the population protection of state or federal demographers and the presumption that the city in question will maintain the same trend in the change of the ratio of its population to that of the larger entity. Application of the method requires calculations of the ratio to the estimated regional population in the year of interest. Accuracy in population estimation is important since if the estimate is to too low the engineering works will quickly be inadequate and redesign, reconstruction, and refinancing will be necessary. Overestimation of population, on the other hand, results in excess capacity which must be financed by a smaller population at a considerably higher unit cos. The selection of an appropriate technique is not always easy and many engineers will test all methods against the recorded growth, consider whatever local factors may be known to have influenced the rate and eliminates those techniques which are clearly in applicable. The growth of a community with limited land area for future expansion might be modeled using the declining growth or logistic technique, while another, with larger rescores of land, power water, and good transportation might be best predicted by the geometric or uniform percentage growth model. In nearly all cases comparison to similar cities is used, and the results obtained by this technique are favored by most engineers.

12 Adama Science and Technology University- Department of Civil Engineering

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(CEng-4607): Water Supply & Sewerage

Lecture Notes (collection and distribution)

3. WATER SOURCES 3.1 Types The origin of all water is rainfall. Water can be collected as it falls as rain before it reaches the ground; or as surface water when it flows over the ground; or is pooled in lakes or ponds; or as ground water when it percolates in to the ground and flows or collects as ground water; from the sea (ocean) in to which it finally flows. Therefore sources of water supply schemes can conveniently be classified as follows: 1. Rain and snow 2. Surface water:  Rivers  Lakes  Pond  Sea water  Impounding reservoirs  Wastewater reclamation 3. Underground sources  Springs Depression springs Contact springs Artesian springs Hot springs  Wells Shallow wells Deep wells Infiltration galleries Infiltration wells Impounding reservoirs: Are artificial lakes formed by the construction of dams across a valley. Wastewater reclamation: Sewage or other waste water may be used as source of water for cooling, flushing water closets (WCS), watering lawns, parks, etc. for fire fighting and for certain industrial purposes after giving the necessary treatment to suit the nature of the use. Springs: Are formed when ground water appears at the ground surface for any reason as a current of flowing water. Types of springs: 1. Depression spring: is a spring formed when the ground surface intersects the water table. 2. Contact spring: is a spring created by a water bearing formation overlying an impervious formation that intersects the ground surface. 3. Artesian spring: is a spring that results from the release of water under pressure from confined water bearing formation either through a fault or fissure reaching the ground surface. It is also known as fracture spring. Wells: Are artificial holes or pits vertically excavated for bringing ground water to the surface.

13 Adama Science and Technology University- Department of Civil Engineering

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Lecture Notes (collection and distribution)

Types of Wells: 1. Shallow wells Shallow wells may be large diameter hand dug wells (diameter 1-4m) and depth  20m. Or machine drilled wells of small diameter (diameter 8-60cm) and depth  60m. 2. Deep wells: Deep wells are most large, deep, high-capacity wells constructed by drilling rig. Construction can be accomplished by cable tool method or rotary method. Drilling rigs are capable of drilling wells 8 to 60cm in diameter and depth  600m.` Infiltration Gallery: An infiltration gallery is a horizontal or nearly horizontal tunnel which is constructed through water bearing strata. It is sometimes referred as horizontal well. Infiltration gallery may be constructed with masonry or concrete with weep holes of 5cm by 10 cm. Infiltration wells: Infiltration wells are shallow wells constructed under the beds of rivers. They are suitable where there are deposits of sand and porous material at least 3m deep in river bed. In the sandy beds of rivers much quantity of water percolates down and gets filtered through it. 3.2 Sources Selection Criteria The choice of water supply to a town or city depends on the following:  Location  Quantity of water  Quality of water  Cost 1. Location: The sources of water should be as near as to the town as possible. 2. Quantity of water: the source of water should have sufficient quantity of water to meet up all the water demand throughout the design period. 3. Quality of water: The quality of water should be good which can be easily and cheaply treated. 4. Cost. The cost of the units of the water supply schemes should be minimum The selection of the source of supply is done on the above points and the source which will give good quality and quantity at least cost will be selected. This economic policy may lead to the selection of both surface and ground water sources to very big cities. For example, the source of the Arbaminch water supply is springs.

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Lecture Notes (collection and distribution)

4. COLLECTION AND DISTRIBUTION OF WATER 4.1 Intakes. Are devices or structures in a surface water source to draw water from this source and then discharge in to an intake conduit through which it will flow in to the water works system. An intake consists of: 

The opening, strainer, or grating through which the water enters, and



The conduit conveying the water, usually by gravity, to a well or sump.

From the well the water is pumped to the mains or treatment plant. Intakes should be so located and designed that possibility of interference with the supply is minimized and where uncertainty of continuous serviceability exists, intakes should be duplicated. The following must be considered in designing and locating intakes: a) The source of supply, whether impounding reservoirs, lakes, or rivers (including the possibility of wide fluctuation in water level). b) The character of the intake surroundings.  Depth of water  Character of bottom  Navigation requirement  The effect of currents floods and storms up on the structure and in scouring the bottom. c) The location with respect to sources of pollution; and d) The prevalence of floating materials such as ice, and vegetation 4.1.1 Types of Intakes. There are different types of intakes, such as reservoir intakes, river intakes and canal intake i) Intakes from Impounding Reservoirs. The water of impounding reservoirs is likely to vary in quality at various levels, making it usually desirable to take water from about a meter from the surface. This, with the fluctuations of water level which may be expected in reservoirs, makes it advisable to have ports at various heights. Where the dam is of earth, the intake is usually a concrete tower located in deep water near the upstream toe of the dam. Access to the tower so that the gates various openings may be manipulated is obtained by means of a foot bridge. The ports may be closed by sluice gates or by gate valves on short lengths of pipe. Where the dam is of masonry, the intake may be a well in the dam structure itself, also with openings at various heights.

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Lecture Notes (collection and distribution)

Fig 4.1a Reservoir Intake Or

Figure 4.1b Tower water intake for a lake or reservoir water supply ii) River Intakes Where rock foundations are available, some cities have built elaborate river intakes, resembling bridge piers with ports at various depths, to allow for great fluctuations in river stage. Small cities may use pipe intakes similar to those described under lake intakes. The bottom must be sufficiently stable. And the water deep enough to allow for a submergence of at least 1m at all times with a clear opening beneath the pipe so that any tendency to form a bar is overcome.

Fig.4.2 River in take 16 Adama Science and Technology University- Department of Civil Engineering

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Lecture Notes (collection and distribution)

River intakes are especially likely to need screens to exclude large floating matter which might injure pumps. River intake is located inside the river so as to get adequate supply in all seasons. Water is drawn from the upstream side of the river, where it is comparatively of better quality. The following are the different types of river intakes: a) Weir intake b) Intake wells c) Pipe intakes d) Intake well with approach channel a) Weir Intake. This consists of a small weir constructed across a river so that river water level in the dry season should also be sufficient to provide water. Intake water may be drawn from the weir through a channel in to a sump well from which it can be pumped to supply. b) Intake Well. This consists of a concrete masonry well located inside a river. A number of penstocks are located at different levels so that water can be drawn in to the well in all seasons. c) Pipe Intakes. These consist of a number of pipes laid horizontally across the river. They are firmly fixed to masonry blocks. The ends of the pipes are fixed with strainers. The water is drawn in to a jack well and then pumped to purification works. This is a cheap and simple arrangement. d) Intake Well with Approach Channel. In case of a very wide river, it is impractical and inadvisable to construct an intake well in the middle of it. Under such conditions, a cross approach channel is constructed so as to connect the river with the intake well. This ensures water supply to the well even during summer. iii) Canal Intakes This consists of a concrete well in the canal. An inlet pipe laid in the canal bed leads in to the well. As the full supply level in the canal is, fairly constant, inlets at different depths are not necessary. The inlet end of the pipe is provided with an enlarged bell mouth, to which is fixed a hemispherical fine screen which prevents floating materials from entering the intake pipe. Also, there is a coarse screen provided so that big floating particles are excluded. The water from the out let of the intake pipe is led to a sump well or supply.

Fig. 4.3 Canal Intake 17 Adama Science and Technology University- Department of Civil Engineering

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Lecture Notes (collection and distribution)

iv) Lake Intakes If the lake shore is inhabited, the intake should be so located that danger of pollution will be minimized. This may require study of currents and effects of winds with particular attention to movements of sewage or industrial wastes, if these are discharged in to the lake. It is also advisable to have the intake opening 2.5m or more above the bottom so that large amounts of silt will not be carried in with the water. Entering velocities must be low, or excessive amounts of floating matter, sediment, fish and ice may be carried in. Entering velocities less than 0.15m/s have been usually used successfully. Offshore winds tend to stir up sediment which will be carried out for long distances. On this account Great Lakes intakes must be located at a distance not less than 600 to 900m from shore.

Figure 4.4 Submerged Lake intakes v) Infiltration Galleries Infiltration galleries are widely used many monsoon countries, such as India, to abstract water from river- bed deposits where surface flow disappears during the dry period but subterranean flow continues. A large diameter concrete caisson or „wet well‟ is sunk in the river bed sediments. The infiltration galleries comprise porous, perforated or un- jointed concrete or asbestos-cement pipes, usually 200-300mm diameter, laid in gravel filtered trenches cut in the river-bed sediments, connected to the wet well in which the pumps are sited. The galleries, of which there may be several many meters long, extend cross- River or up-river to places where it is thought will best pick up the main subterranean flow. 4.2 Methods of Distribution Water is distributed to consumers in several different ways, as local conditions or other considerations may dictate. These methods are:  Gravity Distribution  Distribution by means of pumps with storage (Pumping + Gravity )  Use of Pumps without storage ( Direct Pumping) 1. Gravity Distribution. This is possible when the source of supply is a lake or impounding reservoir at some elevation above the city so that sufficient pressure can be maintained in the mains for domestic and fire service. This is the most reliable method if the conduit leading from source to city is adequate in size and well safeguard against accidental breaks. High pressure for fire fighting, however, may be obtained only by using the motor pumps of the fire department. 18 Adama Science and Technology University- Department of Civil Engineering

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Lecture Notes (collection and distribution)

2. Distribution by means of pumps with storage. In this method the excess water pumped during periods of low consumption is stored in elevated tanks or reservoirs. During periods of high consumption the stored water is drawn up on to augment that pumped. This method allows fairly uniform rates of pumping and hence is economical, for the pumps may be operated at their rate capacity. Since the water stored furnishes a reserve to care for fires and pump breakdowns, this method of operations fairly reliable. Motor pumpers must ordinarily be used for higher fire pressure, although it is possible to close the valves leading to the elevated storage tanks and operate a fire pump at the pumping plant.

3. Use of Pumps without storage. In this method the pumps force water directly in to the mains with no other outlet than the water actually consumed. It is the least desirable system, for a power failure would mean complete interruption in water supply. As consumption varies, the pressure in the mains is likely to fluctuate. To conform to the varying consumption several pumps are available to add water output when needed, a procedure requiring constant attendance. The peak power consumptions of the water plant is likely to occur during periods of otherwise high current consumption and thus increase power cost. An advantage of direct pumping is that a large fire service pump may be used which can run up the pressure to any desired amount permitted by the construction of the mains.

19 Adama Science and Technology University- Department of Civil Engineering

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Lecture Notes (collection and distribution)

4.3 Service Reservoirs (Function and Capacity) 4.3.1 Functions A service reservoir has four main functions: 1. To balance the fluctuating demand from the distribution system, permitting the source to give steady or differently phased output. 2. Provide a supply during a failure or shutdown of treatment plant, pumps or trunk main leading to the reservoir. 3. To give a suitable pressure for the distribution system and reduce pressure fluctuations therein. 4. To provide a reserve of water to meet fire and other emergency demands. It is seldom possible or economic for a source to give a fluctuating output in step with demand. Filtration plants need to be run 24 hours a day with only infrequent, carefully controlled changes of output. Pumps need to be run near their design point for maximum efficiency, whilst electricity tariffs may influence their running times; it is not economical for a long supply main to have an overlarge capacity simply to meet the peak demand of a few hours duration. A technical and economic study of the capital and operating costs of the various options available, including possible silting for a service reservoir is necessary before deciding service reservoir requirements. During the summer months the evening peak may be higher and more prolonged due to garden watering. There will be a slightly different pattern of demand at weekends and on holidays. In the winter there will also be a higher rate through out if a severe frost causes many pipes burst on consumers‟ premises. Position and Elevation of Reservoirs If the service reservoir is to be of maximum value as a safeguarded against break down of the supply to consumers then it should be positioned as near as possible to the area of demand. From the service storage the distribution system should spread directly with such interconnection of mains that, should a break of any one main occur, a supply may be maintained by rerouting the water. It is, of course, not always possible to find a high point which in the center of the distribution area and the best must be done in the circumstances. If the high point is remote from the area of demand the aim should be to feed the demand area by two major mains from the service reservoirs which are interconnected at appropriate points. If there is some high ground which is not quite high enough, then a water tower or several water towers may meet the demand. It is also usually necessary to site the reservoir at such elevation that a steady pressure is maintained at all points of the distribution system, sufficient to give an adequate flow to the top most storey of three or four storey buildings. The elevation at which it is desirable to position a service reservoir depends up on both the distance of the reservoir from the distribution area and the elevation of the highest building to be supplied. 20 Adama Science and Technology University- Department of Civil Engineering

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Lecture Notes (collection and distribution)

If the distribution area varies widely in elevation it may be necessary to use two more service reservoirs at different levels, so that the lower area do not receive an unduly high pressure. Wherever possible the use of non-stand pipes for high pressures should be avoided as such pipes are expensive. Pressure control valves are sometimes installed in inlet mains from service reservoirs in order to reduce the pressure to low laying zones, or to limit increase of pressure at night to reduce leakage. In making a decision to install pressure control devices it should be borne in mind that if the device fails to operate, which it will do if the equipment is not properly maintained, then the downstream mains will be subjected to a sudden increase of pressure and may burst. In addition, excessive wastage of water may also take place through consumers‟ ball valves unaccustomed to working at high heads. Break pressure tanks give better protection to low laying zones and are preferable to pressure reducing devices; however the use of them or pressure reducing valves in pumping schemes represent a direct wastage of pumping energy and more economic alternative should be sought. Types of Service Reservoirs Generally, there are two types of service reservoirs: 1. Surface reservoir (Ground Reservoir or Non-elevated) 2. Elevated reservoir ( Over head Tank)

Accessories of Service Reservoirs The service reservoirs are to be provided with the following accessories: 1. Inlet Pipe : For the entry of water 2. Ladder : To reach the top of the reservoir and then to the bottom of the reservoir, for inspection and cleaning 3. Lightening Conductor : In case of elevated reservoirs for the passage of lightening 4. Manholes : For providing entry to the inside of reservoir for inspection and cleaning 5. Outlet pipe: For the exit of water 6. Outflow Pipe : For the exit of water above full supply level 7. Vent pipes : For free circulation of air 8. Washout pipe : For removing water after cleaning of the reservoir 9. Water level indicator: To know the level of water inside the tank from outside.

21 Adama Science and Technology University- Department of Civil Engineering

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Lecture Notes (collection and distribution)

LIGHTENING CONDUCTOR

MANHOLE LADDER

WATER LEVEL INDICATOR

OVER FLOW PIPE

WASH OUT PIPE INFLOW PIPE

OUTLET PIPE

DITCH

Design Capacity of Service Reservoirs The three major components of service storage are: i) Equalizing or operating storage ii) Fire reserve iii) Emergency reserve Equalizing or operating capacity can be obtained from a mass curve of water consumption rates and pumping supply rates. 1) The capacity can be analytically determined by finding out maximum cumulative surplus during the stage when pumping rate is higher than water consumption rate and adding to this maximum cumulative deficit which occurs during the period when the pumping rate is lower than the demand rate of water. 2) The above figure can be obtained by drawing mass curves of water consumption rates and water pumping supply rates. Example-1 A small town with a design population of 1600 is to be supplied water at 150liters per capita per day. The demand of water during different periods is given in the following table: Time (hr)

03 Demand(1000liters) 20

3-6

6-9

9 -12

12 - 15

15 18

18 -21

21 24

25

30

50

35

30

25

25

Determine the capacity of a service reservoir if pumping is done 24 hours at constant rate. Solution Water supply = 150l/c/d Total water demand = demand * population = 150*1600 = 240,000liters Rate of pumping = 240,000/24 = 10,000lit/hr = 30,000lit/3hr 22 Adama Science and Technology University- Department of Civil Engineering

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Lecture Notes (collection and distribution)

1). Analytical Method Time Pumping 0-3 30,000 3. - 6. 30,000 6. - 9 30,000 9. - 12 30,000 12. - 15 30,000 15. -18 30,000 18. - 21 30,000 21. -24 30,000

Demand 20,000 25,000 30,000 50,000 35,000 30,000 25,000 25,000

Surplus 10000 5000 0 0 0 0 5000 5000

Deficit 0 0 0 -20000 -5000 0 0 0

Cummulative 10000 15000 15000 -5000 -10000 -10000 -5000 0

Maximum cumulative surplus Maximum cumulative deficit Total

= 15,000 liters = 10,000 liters 25,000lit = 25 m3 25 * 4  3.4m If the reservoir is circular with depth, h = 3.0 m, d  3

Time 0-3 3. - 6. 6. - 9 9. - 12 12. - 15 15. -18 18. - 21 21. -24

Pumping 30,000 30,000 30,000 30,000 30,000 30,000 30,000 30,000

Demand 20,000 25,000 30,000 50,000 35,000 30,000 25,000 25,000

Cummulative demand Cummulative Pumping 30,000 20,000 60,000 45,000 90,000 75,000 120,000 125,000 150,000 160,000 180,000 190,000 210,000 215,000 240,000 240,000

Cummulative Demand & Supply

Mass Curve 300,000 250,000

(21. -24), 240,000

200,000 Cummulative demand

150,000 Cummulative Pumping

100,000 50,000 0 0

2

4

6

8

10

Time (Hours)

Example2. If in example -1 pumping is done for: a) Eight hours from 8 hrs to 16 hrs b) Eight hrs from 4 hrs to 8 hrs and again 16 hours to 20 hrs.

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Lecture Notes (collection and distribution)

Solution Total water demand = 240,000lit/hr Rate of pumping = 24,000/8 = 30,00l/h = 90,000lit/3hrs Case I A) Analytical Method

Time 0-3 3-6. 6.-8 8-9. 9. -12 12. 15 15. 16 16. 18 18.21 21. 24

Pumpin g 0 0 0 30000 90000

Deman d 20000 25000 20000 10000 50000

Surplu s 0 0 0 20000 40000

Deficit -20000 -25000 -20000 0 0

Cumulativ e -20000 -45000 -65000 -45000 -5000

90000

35000

55000

0

30000

10000

20000

0

20000

0

25000

0 25000 Maximum cumulative surplus = Maximum cumulativeDeficit = Balancing Storage , S =

For Graphical Method Cummulativ Cummulativ e Demand e supply 20000 45000 65000 75000 125000

0 0 0 30000 120000

50000

160000

210000

0

70000

170000

240000

0

-20000

50000

190000

240000

0

-25000

25000

215000

240000

0

-25000

0

240000

240000

70000 -65000 135000 litres 135 m3

B) Graphical Method

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Lecture Notes (collection and distribution)

Case II A) Analytical Method Time Pumping Demand Surplus 0-3 0 20000 0 3-4. 0 8333 0 4. - 6 60000 16667 43333 6. - 8 60000 20000 40000 8 - 9. 0 10000 0 9.-12 0 50000 0 12. 15 0 35000 0 15. 16 0 10000 0 16.18 60000 20000 40000 18. 20 60000 16667 43333 20. 21 0 8333 0 21. 24 0 25000 0 Maximum cumulative surplus = Maximum cumulative Deficit = Balancing Storage , S =

Deficit Cumulative -20000 -20000 -8333 -28333 0 15000 0 55000 -10000 45000 -50000 -5000

For Graphical Method Cumulative Cumulative Demand supply 20000 0 28333 0 45000 60000 65000 120000 75000 120000 125000 120000

-35000

-40000

160000

120000

-10000

-50000

170000

120000

0

-10000

190000

180000

0

33333

206667

240000

-8333

25000

215000

240000

-25000

0

240000

240000

55000 -50000 105000 litres 105 m3

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Lecture Notes (collection and distribution)

B) Graphical Method: MASS CURVE 300000 Cum m ulative Dem and

CUMULATIVE SUPPLY & DEMAND

250000

Cum m ulative s upply

200000

150000 MAX DEFICIT 100000 Max Surplus 50000

0 0

2

4

6

8

10

12 14 TIM E (HOURS)

16

18

20

22

24

26

Depth and Shape of Service Reservoirs The following are some notes on the salient features of service reservoirs and the alternatives that may be adopted. A. Depth There is an economical depth of service reservoir for any given site. For a given quantity of water either a shallow reservoir having long walls and a large floor area may be constructed or, alternatively. A deep reservoir may be constructed with high retaining walls and a smaller floor area. Depths most usually used are as follows: Size (m3) Depth of water (m) Up to 3500 2.5 to 3.5 3500 to 15,000 3.5 to 5.0 Over 15,000 5.0 to 7.0 These figures don‟t apply to water towers or pre-stressed concrete reservoirs. Factors influencing depth for a given storage are: 1. Depth at which suitable foundation conditions are encountered 2. Depth at which the out let main must be laid 3. Slope of ground, nature and type of back fill 4. The need to make the quantity of excavated material approximately equal to the amount required for backing, so as to reduce unnecessary carting of surplus material to tip. 5. The shape and size of land available B. Shape Circular reservoir is geometrically the most economical shape, giving the least amount of walling for a given volume and depth: it has the attraction of allowing construction of a thin reinforced concrete dome shaped roof, free of all supporting columns, resting on ring beam fixed to the top of the wall for diameters of up to about 60m. 26 Adama Science and Technology University- Department of Civil Engineering

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Lecture Notes (collection and distribution)

However, this shape is seldom adopted. It is unsuitable for division in to two compartments, which would allow one half to be drained for maintenance without taking the whole reservoir out of service.  Its shape frequently does not permit best use of available land, and  Problems of design will arise if it is to be partially buried in sloping ground A rectangular reservoir with a length to width ratio 1.2 to 1.5:  Usually proves most economical when division walls are incorporated  Floors and roof should be sloped to not flatter than 1:250 for drainage ( such slopes should be parallel to maintain uniform column and wall heights)  The total depth of the reservoir must be sufficient to allow the maximum inflow assumed in the design calculation to pass over the over flow weir, with a safety margin of at least 150mm below the under side of roofing beam.  It is good practice to set the over flow weir slightly higher, say by 50mm, than the top water level at which the supply is cut off by a ball valve or an electrode. 4.4 Pipes Used in the Water Distribution System 4.4.1 Pipe Materials For use in transmission and distribution systems, pipe materials must have the following characteristics: Adequate tensile strength and bending strength to withstand external loads. High bursting strength to withstand internal water pressure Ability to resist impact loads to water flow suitable for handling and joining facilities Resistance to both internal and external corrosion The types of pipes used for distributing water include: 1. Cast iron pipe 2. Steel pipe 3. Concrete pipe 4. Plastic pipe A pipe material is selected based on various conditions:  Cost  Type of water to be conveyed  Carrying capacity of the pipe  Maintenance cost  Durability, etc. Asbestos cement pipes Advantages  The inside surface of pipe is smooth  The joining of pipes is very good and flexible  The pipes are ant-corrosive and cheap in cost



5. Asbestos cement pipe 6. Copper pipe 7. Lead pipe

Light in weight to handle and transport

Disadvantage  The pipes are brittle  The pipes are not durable 27

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Lecture Notes (collection and distribution)



The pipes are not laid in exposed places  The pipes can be used only for very low pressure Cast iron pipes Advantages  The cost is moderate  The pipes are easily joined  The pipes are not subjected to corrosion  The pipes are strong and durable  Service connections can be made easily Disadvantage  The breakage of this pipe is large  Carrying capacity decreases with increase in life  The pipes become heavy and uneconomical when their sizes increase (especially beyond 1200mm) Cement Concrete Pipes Advantages o The inside surfaces of the pipes can be made smooth o The maintenance cost is very low o Under normal conditions the pipes are durable o The pipes can be cast in place(in site) o Due to high weight (heaviness) the pipes can resist force of buoyancy when placed under water even when they are empty o Pipes can resist normal traffic loads when placed below roads o There is no danger of rusting and incrustation

Disadvantage o If no reinforcement is provided they cannot resist high pressure o The pipes are and difficult to transport o The pipes are likely to crack during transport and handling o The repair of these pipes are difficult o These pipes are affected by acids, alkaline, and salty waters o These pipes are likely to cause leakage due to porosity

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Lecture Notes (Introduction to water treatment)

Galvanized Iron Pipe Advantages  The pipes are cheap  Light in weight and easy to handle and transport  Easy to join Disadvantage  These pipes are liable to incrustation (due to deposition of some materials inside part of pipe)  Can be easily affected by acidic or alkaline water  Short useful life Plastic Pipes Advantages  The pipes are cheap  The pipes are flexible and possess low hydraulic resistance (less friction)  They are free from corrosion  The pipes are light in weight and it is easy to bend, join and install them  The pipes up to certain sizes are available in coils & therefore it is easy to transport Disadvantage  The coefficient of expansion for plastics is high, the pipes are less resistant to heat  Some types of plastics may impart taste to the water 4.4.2 Determination of Pipe Sizes The size of the pipe is determined by considering the discharge through the pipe and permissible velocity of the flow in the pipe. Q = A*V Where, Q = discharge (m3/s) V = permissible velocity (0.6 to 1.50m/s) A = Cross sectional area of pipe (m2) The size of the pipe used in the water distribution system can be determined by one of the following formulas: 2 1. Darcy –Weisbach formula; h f  fLV 2 gD

2. Hazen-Williams formula; Q  0.278CD 2.63S 0.54 , S  h f

L

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3. Manning‟s Formula;

Q

Lecture Notes (Introduction to water treatment)

1AR 2 / 3 S 1 / 2 n

* The most common pipe flow formula used in design and evaluation of a water distribution system is the Hazen-Williams‟ formula. The water supply pipes sizes available are given in the following table: Metric sizes 10 (mm) English (In) ½

20

25 30

3/4 1

40

50 60

11/4 11/4 2

80 100 150 200 250 300 350 375 400

21/2 3

4

6

8

10

12

14

15

16

Metric sizes (mm) 400 600 450 500 525 450 675 750 900 950 1050 English (In) 16 24 18 20 21 18 27 30 36 38 42 Example-1 Given Total population of a town = 80,000 Average daily consumption of water = 150liters/capita/day If the flow velocity of an outlet pipe from intake  1.5 m/s, determine the diameter of the outlet pipe. Solution

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Lecture Notes (Introduction to water treatment)

Total flow, Q = Demand* Population = 150*80,000 = 12x106 lit/day 

12 X 10 6  0.1389m 3 / sec (24 * 60 * 60 *10 3 )

2 Required pipe area, A  Q  D  Q  D  4Q  0.1389 * 4  343mm

V

4

V

V

1.5 * 

But the pipe size available on the market is 300mm & 350mm, then take D = 350mm Example-2 A town has a population of 100,000 persons. It is to be supplied with water from a reservoir situated at a distance of 6.44km. It is stipulated that one-half of the daily supply of 140lit/capita should be delivered in 6 hours. If the loss of head is estimated to be 15m, calculate the size of pipe. Assume f = 0.04. Solution Total daily supply = 100,000  14,000m 3 3 10

Since half of this quantity is required in 6 hours 14,000 Maximum flow =  0.324m 3 / s (2 * 6 * 60 * 60)

According to the Darcy-Weisbach formula: hf 

 15 

fLQ 2 12.1d 5

Where, hf = 15m, f = 0.04, L= 6440m

0.04 * 6440(0324) 2 0.04 * 6440 * (0.324) 2  d   0.683m  683mm 15 *12.10 12.1* d 5

But available pipe sizes 675mm & 750mm, take 750mm diameter pipe b) What size of pipe line (L = 1000m) should be used to supply 100l/s so that the head loss does not exceed 10m. Use both the three formula, C= 100, n = 0.013, f = 0.035, find also the velocity.

4.4.3 Energy Losses in Pipes Energy loss (head loss) in pipes can be found by one of the following formulas: 1)

Darcy-Weisbach formula hf 

fLV 2 2 gD

Where, hf = head loss (m) F = friction factor (which is related to the relative roughness of the pipe material & the fluid flow characteristics) L = length of pipe (m) V = velocity of flow (m/s)

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Lecture Notes (Introduction to water treatment)

D = diameter of pipe (m) G = Acceleration due to gravity (9081m/s2) The term hf represents the energy loss that occurs in any distribution system. The major loss of energy is due to friction between the moving water and pipe material; however, energy losses also occur from flow disturbance caused by valves, bends in pipes line, and changes in diameter. Exercise-1 Calculate the head loss in 600mm pipe , 1500m long smooth walled concrete ( = 0.001) pipe line carrying a water of 0.30m3/s [Ans, hf = 2.43m) Exercise-2 Calculate the head loss in 200mm pipe, Q = 30l/sec, f = 0.035, L= 1500m [Ans, hf = 12.20m] 2) Hazen-Williams formula; Q  0.278CD 2.63S 0.54 , S  h f

L

Where, C = coefficient that depends on the material and age of the pipe S = Hydraulic gradient (m/m) Table - Values of C for the Hazen-Williams formula Pipe Material C Asbestos Cement 140 Cast Iron  Cement lined 130 – 150  New, unlined 130  5years-old, unlined 120  20 years old, unlined 100 Concrete 130 Copper 130 - 140 Plastic 140 -150 New welded Steel 120 New riveted Steel 100 Monographs shown in fig – solve the equation for C = 100.Given any two of the parameters (Q, D, hf or V) the remaining can be determined from the intersections along a straight line drawn across the monograph. Exercise -3 For Q = 30l/s,D = 200mm,C = 100,L = 1500,Find hf. Solution From nomograph, hf = 12.15m Using the formula, hf = 12.30m 2 / 3 1/ 2 3) Manning‟s Formula; Q  1AR S , R = D/4, S = hf/L

n

Where, n = Coefficient of roughness depending on pipe material, usually n = 0.013 GI pipes

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Lecture Notes (Introduction to water treatment)

n = 0.009  Plastic pipes n = 0.015  Clay concrete pipes Exercise 4. For Q = 30l/s, D = 200mm,n = 0.013,L = 1500 S

hf 10.936n 2 Q 2 10.936n 2 Q 2 10.936(0.013) 2 (30 / 100) 2   hf  * L  *1500  12.550 L D16 / 3 D16 / 3 200 / 100016 / 3

From Nomograph, hf/L = 0.00825  = 0.00825*1500 = 12.38m 4.4.4 Pipe Appurtenances Valves: Used to isolate and drain pipe line sections for test, inspection, cleaning and repair i) Gate valves. Are installed in every main and sub-main to isolate a portion of the network system during a repair. ii) Check-valves (Non-Return valves). Are generally used to prevent reversal of flow when a pump is shot down iii) Air-Relief Valves. In long pipes lines air will accumulate in the high points (summits) of the line and may interfere with the flow. It is necessary, therefore, to place air relief valves at those points where trouble is expected. iv) Pressure regulating valves. These valves automatically reduce pressure on the d/s side to any desired magnitude and are used on lines entering low areas of a city, with out such reductions pressures would be too high. v) Sluice Gates. Are vertically sliding valves which are used to open or close openings in to walls.  Fire hydrants. It is used on mains to provide a connection for fire hazards to fire fighting  Water meters. In most cities, the water furnished to a consumer is measured, and the consumer charged accordingly to the amount of water consumed.

4.5. Pipe Systems 4.5.1 Methods of Laying Distribution Pipes. There are two basic types of networks of pipes which used to distribute water in a city. 1) Branched (Dead-end) pattern 2) Grid-Iron pattern 1. Branching Pattern. This is also known as the tree system of lay out and it consists of one supply main from which sub-mains are taken. The sub-mains again divided in to several branch lines from which service connections are given to the consumers. BRANCH

DEAD-END MAIN

SUB-MAIN

Advantages

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Lecture Notes (Introduction to water treatment)

 The design calculations are simple  Cut off valves required are comparatively less in number  The system is cheap and economical  Laying the water pipes is simple Disadvantages  During repair, a large portion of the distribution system is affected  The pipes terminate at the dead-end and no circulation of air (due to stagnation, pollution may occur)  Common in small scale rural water supply schemes 2.

Grid Pattern. In this pattern, the main, sub-mains and branches are interconnected with each other. LOOP

Advantages  Flow can occur in more than one direction and stagnation does not occur  In case of repairs, a very small portion of the distribution area will be affected  When a fire occurs plenty of water is available for fighting purposes. Disadvantages  The cost of laying the system is high  The procedure for calculating the sizes of pipes and for working out pressures are complicated  A large number of valves are required. Pipe networks (Grid Pattern) A group of interconnected pipes forming several loops or circuits is called a network of pips. Such networks of pipes are commonly used for municipal water distribution systems in cities. The main problem in a pipe network is to determine the distribution of flow through the various pipes of the network such that all the conditions of flow are satisfied and all the circuits are then balanced. The conditions to be satisfied in any network of pipes are as follows: 1. According to the principle of continuity the flow into the junction must be equal to the flow out of the junction. 2. In each loop, the loss of head due to flow in clock wise direction must be equal to the loss of head due to flow in anti-clock wise direction. 3. The Darcy – Weisbach equation must be satisfied for flow in each pipe.  Minor losses may be neglected if the pipe lengths are large. However, if the minor losses are large , they must be taken into account by considering them interims of the head lost due to friction in equivalent pipe lengths

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Lecture Notes (Introduction to water treatment)

 according to Darcy- Weisbach equation the loss of head hf though any pipe discharging at the rate of Q can be expressed as:

H L  KQ n --------------------------------------------------------------------------- (1) Where K = proportionality factor which can be determined for each pipe, knowing the friction factor f, length L, and the diameter D of the pipe. fL ---------------------------------------------------------------------------- (2) K 12.1D 5 n = an exponent having a numerical value ranging from 1.72 to 2.0. For any pipe if Qo is the assumed discharge and Q is the corrected discharge, then: Q  Qo  Q ----------------------------------------------------------------------------- (3) and the head loss for each pipe is

H L  KQ n  K (Qo  Q) n ------------------------------------------------------------ (4) Thus for the complete circuit:



H L   KQ n   K (Qo  Q) n

-------------------------------------------------------- (5) By expanding the terms the terms in the brackets:  KQ n   K (Qon  nQon1Q  ...) ------------------------------------------------------- (6) If Q is small, compared with Qo, all terms of the series after the second one may be dropped. Thus,  KQ n   KQon   KnQon1Q -------------------------------------------------------- (7) For the correct distribution the circuit is balanced and hence  KQ n  0 . Therefore,  KQo n  Q KnQon1  0 --------------------------------------------------------------------- (8)

In the above expression Q has been taken out of the summations as it is same for all the pipes in the circuit. Solving for Q: Q  

 

 

 KQo  KnQo

n n 1



 hL hL n ( ) Q

---------------------------- (9)

In the above expression for the correction the denominator is the sum of absolute terms and hence it has no sign. Further if the head losses due to flow in the clock wise direction are more than the head losses in the due to flow in the anti-clock wise direction, then according to the sign convention adopted, Q will be negative and hence it should be added to the flow in the anti-clock wise direction and subtracted from the flow in the clock wise direction. For pipes common to two circuits or loops a correction from both the loops will be required to be applied. With the corrected flow in all the pipes, a second trial calculation is made for all the loops and the process is repeated till the correction becomes negligible.

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Lecture Notes (Introduction to water treatment)

Procedures can be expressed as follows: 1. Assume any internally consistent distribution of flow. The sum of the flows entering any junction must equal the sum of the flows leaving 2. Compute the head losses in each pipe by means of an equation or diagram. Conventionally, clockwise flows are positive and produce positive head losses. 3. with due attention to sign, compute the total head loss around each circuit: hL = KQn. 4. Compute, without regard to sign, for the same circuit, the sum of: KnQn-1. 5. Apply the corrections obtained from equation (9) to the flow in each line. Lines common to two loops receive both corrections with due attention to sign. Exercise 1 (Design of a dead head-end system with gravity system of distribution) Water is supplied from a reservoir at an elevation of 200m. The elevations of various points in the pipe line are given in brackets. Design the pipes RA, AA2and AB. Assume the minimum pressure in pipes in resident area to be 35m of water and in business districts 50m of water. R ELE. 200m

A1

Q=1000l/s, L=3200m A (100)

Q =180l/s. L =1300m

A2 (90m)

Q=600l/s, L=2000m B1

B(70m)

B2

C1

Q = 430l/s L = 1200m C(55m)

C2

D1

D(54m)

D2

Business District

Exercise-2 Find the floe distribution in the gravity supply system through the following pipe network shown below. Use Hazen – Williams formula (C= 100) . If the pressure at point A is 490.5 KPa, find the pressures at points B & C. Assume all pipe junctions are at the same elevation.

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Lecture Notes (Introduction to water treatment)

250l/s F

A B 75l/s

45 l/s

45 l/s

75l/s

30l/s 100l/s LOOP II

LOOP I

10l/s

10l/s

C

D

E

40l/s

80 l/s 40 l/s

Solution 250l/s F

A B 75l/s

45 l/s

45 l/s

75l/s

30l/s 100l/s LOOP II

LOOP I

10l/s

10l/s

C

D

E

40l/s

80 l/s 40 l/s

Hazen- Williams‟s formula, Q  0.278CD 2.63S 0.54   Q S 2.63   (0.278CD ) 

1 / .54

1.189-3.755

2.566 100-2.566=97.434

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Lecture Notes (Introduction to water treatment)

Exercise-2 C = 100 1st Correction loop I Pipe Diameter D(mm) AD 250 DE 150 EF 200 FA 250

1st Correction loop II Pipe Diameter D(mm) AB 250 BC 200 CD 100 DA 250

2nd Correction loop I Pipe Diameter D(mm) AD 250 DE 150 EF 200 FA 250

2ndCorrection loop II Pipe Diameter D(mm) AB 250 BC 200 CD 100 DA 250

Length L(m) 1000 2000 1000 2000

Flow Q(l/s) 100 10 -30 -75

Slope (m/1000m) 0.025 0.004 -0.008 -0.015 

Q11 =

hL/1.85(hL/Q) 1.189

Length L(m) 2000 1000 2000 1000

Flow Q(l/s) 75 30 -10 -100

Q11 =

hL/1.85(hL/Q) 3.755

Length L(m) 1000 2000 1000 2000

Flow Q(l/s) 97.435 11.189 -28.811 -73.811

Q21 =

hL/1.85(hL/Q) 0.488

Length L(m) 2000 1000 2000 1000

Flow Q(l/s) 78.755 33.755 -6.245 -97.435

Q22=

hL/1.85(hL/Q) 0.783

Slope (m/1000m) 0.015 0.008 -0.031 -0.025 

Slope (m/1000m) 0.024 0.005 -0.008 -0.015 

Slope (m/1000m) 0.016 0.010 -0.013 -0.024 

Head loss hL/Q hL= S*L (m) 25.483 0.255 8.628 0.863 -8.127 0.271 -29.916 0.399 -3.933 1.787

Head loss hL/Q hL= S*L (m) 29.916 0.399 8.127 0.271 -62.164 6.216 -25.483 0.255 -49.603 7.141

Head loss hL/Q hL= S*L (m) 24.285 0.249 10.624 0.949 -7.541 0.262 -29.044 0.393 -1.675 1.854

Head loss hL/Q hL= S*L (m) 32.749 0.416 10.111 0.300 -25.997 4.163 -24.285 0.249 -7.423 5.127

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3rd Correction loop I Pipe Diameter D(mm) AD 250 DE 150 EF 200 FA 250

Length L(m) 1000 2000 1000 2000

Flow Q(l/s) 97.140 11.678 -28.322 -73.322

Q31 =

hL/1.85(hL/Q) 0.099

3rd Correction loop II Pipe Diameter Length D(mm) L(m) AB 250 2000 BC 200 1000 CD 100 2000 DA 250 1000

4th Correction loop I Pipe Diameter D(mm) AD 250 DE 150 EF 200 FA 250

Lecture Notes (Introduction to water treatment)

Flow Q(l/s) 79.537 34.537 -5.463 -97.140

Slope Head loss hL/Q (m/1000m)hL= S*L (m) 0.024 24.150 0.249 0.006 11.499 0.985 -0.007 -7.306 0.258 -0.014 -28.689 0.391  -0.346 1.882

Slope Head loss hL/Q (m/1000m)hL= S*L (m) 0.017 33.354 0.419 0.011 10.549 0.305 -0.010 -20.289 3.714 -0.024 -24.150 0.249  -0.535 4.687

Q32=

hL/1.85(hL/Q) 0.062

Length L(m) 1000 2000 1000 2000

Flow Q(l/s) 97.240 11.777 -28.223 -73.285

Q41 =

hL/1.85(hL/Q) 0.013

4th Correction loop II Pipe Diameter Length D(mm) L(m) AB 250 2000 BC 200 1000 CD 100 2000 DA 250 1000 Q42=

Flow Q(l/s) 79.599 34.599 -5.401 -97.178

Slope Head loss hL/Q (m/1000m)hL= S*L (m) 0.024 24.196 0.249 0.006 11.681 0.992 -0.007 -7.258 0.257 -0.014 -28.662 0.391  -0.044 1.889

Slope Head loss hL/Q (m/1000m)hL= S*L (m) 0.017 33.402 0.420 0.011 10.584 0.306 -0.010 -19.866 3.678 -0.024 -24.167 0.249  -0.047 4.652

hL/1.85(hL/Q) 0.005

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5th Correction loop I Pipe Diameter D(mm) AD 250 DE 150 EF 200 FA 250

5th Correction loop II Pipe Diameter D(mm) AB 250 BC 200 CD 100 DA 250

6th Correction loop I Pipe Diameter D(mm) AD 250 DE 150 EF 200 FA 250

Length L(m) 1000 2000 1000 2000

Flow Q(l/s) 97.247 11.790 -28.210 -73.272

Q51 =

hL/1.85(hL/Q) 0.001

Length L(m) 2000 1000 2000 1000

Flow Q(l/s) 79.605 34.605 -5.395 -97.185

Q52=

hL/1.85(hL/Q) 0.001

Length L(m) 1000 2000 1000 2000 Q61 =

6th Correction loop II Pipe Diameter D(mm) AB 250 BC 200 CD 100 DA 250

Lecture Notes (Introduction to water treatment)

Length L(m) 2000 1000 2000 1000 Q52=

Flow Q(l/s) 97.247 11.790 -28.210 -73.271

Slope (m/1000m) 0.024 0.006 -0.007 -0.014 

Slope (m/1000m) 0.017 0.011 -0.010 -0.024 

Slope (m/1000m) 0.024 0.006 -0.007 -0.014 

Head loss hL/Q hL= S*L (m) 24.199 0.249 11.704 0.993 -7.252 0.257 -28.653 0.391 -0.002 1.890

Head loss hL/Q hL= S*L (m) 33.406 0.420 10.587 0.306 -19.829 3.675 -24.170 0.249 -0.006 4.649

Head loss hL/Q hL= S*L (m) 24.199 0.249 11.705 0.993 -7.252 0.257 -28.652 0.391 0.000 1.890

hL/1.85(hL/Q) 0.000

Flow Q(l/s) 79.605 34.605 -5.395 -97.185

Slope (m/1000m) 0.017 0.011 -0.010 -0.024 

Head loss hL/Q hL= S*L (m) 33.407 0.420 10.587 0.306 -19.824 3.675 -24.170 0.249 0.000 4.649

hL/1.85(hL/Q) 0.000

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Therefore, the flow distribution will be Pipe D(mm) L(mm) Q(l/s) AD 250 1000 97.247 DE 150 2000 11.790 EF 200 1000 -28.210 FA 250 2000 -73.271 AB 250 2000 79.605 BC 200 1000 34.605 CD 100 2000 -5.395 DA 250 1000 -97.185

Lecture Notes (Introduction to water treatment)

S 0.024 0.006 -0.007 -0.014 0.017 0.011 -0.010 -0.024

hL(m) 24.20 11.70 -7.25 -28.65 33.41 10.59 -19.82 -24.17

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Lecture Notes (Introduction to water treatment)

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Lecture Notes (Introduction to water treatment)

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Lecture Notes (Introduction to water treatment)

Figure 4-7 Nomograph for Manning formula, for circular pipes flowing full based on n=0.013

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Lecture Notes (Introduction to water treatment)

5. INTRODUCTION TO WATER TREATMENT 5.1 – Introduction Absolutely pure water is that which contains only hydrogen and oxygen i.e. H 2o and is never found in nature. The water found nature contains a number of impurities in varying amounts. Therefore, removing these impurities up to certain extent so that it may not be harmful to the public health is necessary, .the process of removing the impurities is called water treatment and the Treated water is called wholesome water. The following are the requirement of wholesome water  It should be free from bacteria which may cause diseases  it should be colorless  It should be tasty, odor free and cool.  It should not corrode pipes.  It should not free from all objectionable matter.  It should have dissolved oxygen and free carbonic acid that it may remain fresh. The common impurities found water and their effects as follows:4.2 METHODS OF WATER TREATMENT The common methods of water treatment (water purification) are

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Lecture Notes (Physical, chemical and Biological analysis)

1. Aeration 2. Screening 3. Plain sedimentation 4. Coagulation 5. Filtration 6. Adsorption 7. Softening 8. Disinfection The degree and methods of treatment depend upon  nature of the source  quality of the source  purpose for which it supplied 1. Aeration Aeration may be used to remove undesirable gases dissolved in water i.e. Co2, H2S, etc (degasification) or to add oxygen to water to convert undesirable substance i.e. Iron (Fe 2+) & Manganese to more manageable form (oxidation). The Iron and Manganese may be removed as a precipitate after aeration. Chemically, these reactions may be written as follows: 4 Fe2+ + O2 + 10 H2O 4 Fe (Oh)3+8H+ 4 Mn2+ + O2 + 2 H2O  2 MnO2  + 4H+ Different types of aerators are available  Gravity Aerator  Spray aerator  Air diffuser  Mechanical Aerator 1. Gravity aerators a) Cascade towers (b) Inclined apron possibly shaded with plates 2 spray aerators: - spray droplets of water in to air from stationary or moving orifices or nozzles. 3. Air diffuser 4. Mechanical Aerator 2. Screening Screening usually involves a simple screening or straining operation to remove large solids and floating matter as leaves, dead animals, etc. a) Bar screens- with openings of about 75 mm b) Mesh screens –with opening of 5-20 mm 3. Plain Sedimentation Sedimentation is the removal of particles (silt, sand, clay, etc.) through gravity setting in basins. No chemicals is to enhance the sedimentation process

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Lecture Notes (Physical, chemical and Biological analysis)

4. Coagulation (chemically assisted sedimentation) very fine suspend clay particles are not removed by plain sedimentation .in addition, water also contains electrically charged colloidal matter which are continuously in motion and never settle down due to gravitational forces .such impurities i.e. fine clay and colloidal matter can be removed by the use of chemicals followed by sedimentation and such type of water treatment is called Coagulation. The principle of coagulation can be explained from the following two conditions: 1. Floc formation When coagulants (chemicals) are dissolved in water and thoroughly mixed with it, they produce a think gelatinous precipitate. This precipitate is known as floc and this floc has got the property of arresting suspended impurities in water during downward travel towards the bottom of tank. 2 Electric charges The ions of floc are found to possess positive charge. Hence, they will attract the negatively charged colloidal particles and thus they cause the removal of such particles 3. Flocculation Flocculation is used to denote the process of floc formation and thus follows addition of coagulants .Flocculators are slow stirring mechanisms, which form floc .they mostly consist of paddles which are revolving at very slow speed about 2-3 rpm. The folcculators provide numbers of gentle contacts between the flocculating particles which are necessary for the successful formation of floc. In this operation the floc which has been formed above is allowed to settle and is separated from the water by keeping the water in sedimentation tanks. Coagulation mixing

Flocculation

sedimentation

The following are the most commonly used coagulants: 1) Aluminum sulfate [Al 2(SO4)318H2O] .it is also called Alum It reacts quite quickly giving excellent stable flocs. It reacts with the natural alkalinity in water & if natural alkalinity is not sufficient, lime may be added and forms aluminum hydroxide floc. Chemical Reaction Taking Place i)

Al 2(SO4)3.18H2O + 3Ca (HCO3)22Al(OH)3+3CaSO4+ 6CO2+18 H2O

ii)

Al(SO4)3.18H2O+ 3Ca(OH)22Al(OH)3+3CaSO4+18H2O

iii)

Al2(SO4)318H2O+3Na2CO32Al(OH)3+3Na2SO4+3CO2+18H2o

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Lecture Notes (Physical, chemical and Biological analysis)

2) Sodium aluminates (Na2Al2O4) Chemical Reaction Taking Place i)

Na2Al2O4+Ca(HCO3)2CaAl2O4+Na2CO3+CO2+H2O

ii)

Na2Al2O4+CaSO4CaAL2O4+Na2SO4

iii)

NaAl2O4+CaCl2CaAl2O42NaCl

3) Ferric coagulants  Ferric Chloride Fe Cl3  Ferric sulfate Fe2(SO4)3  Mixture of both (Fe cl3=Fe2(SO4)3) Chemical reaction taking place 2Fe Cl3+3Ca (OH) 22Fe (OH) 3+CaCl2 Fe2 (SO4)3+3Ca (OH) 22Fe (OH) 3+3CaSO4

5 .Filtration The effluent obtained after coagulation does not satisfy the drinking water standard and is not safe. So it requires further treatments. If water is allowed to pass through a bed of sand or fine granular material, the effluent obtained is clear and sparkling with negligible turbidity. This process is known as filtration. Filtration also removes bacteria, taste &odor. Filtration

Pressure Filters

Gravity Filters

Slow Sand Filter

Rapid Sand Filter

1. SLOW SAND FILTERS In slow filters a water tight tank is construct either in stone masonry or brick masonry and a layer of sand is placed over the gravel. The depth of sand varies from 60 to 90 cm. The depth of gravel varies from 30 to 60 cm.

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Lecture Notes (Physical, chemical and Biological analysis)

The water is allowed to enter the filter thought the inlet chamber .it descends through the filter media and during this process, it gets purified. The purpose of cleaning, the top layer of sand is scrapped or removed through a depth of about 15-25 mm. The water is then admitted to the filter. When cleaning of filter had been done for a number of times, the effective depth of filter media of sand is reduced. In order to maintain the efficiency of filter, a fresh layer of about 15 cm depth of graded sand is then added to the filter. The interval between two successive cleanings depends mainly on the nature of impurities present in the water to be treated. It usually varies from 1 to3 months. The rate of filtration for a normal slow sand filter varies 100 to200 lit/hr/m2 of fitter area. Example: find the area of slow sand filters for a town having a design population of 15000 with an average rate of demand as 160 lcpd.

FILTER HEAD

WATER SAND

GRAVEL

TREATED WATER

FILTER FLOOR

UNDER DRAIN CHANNEL

Fig 5. A Typical Section of Slow Sand Filter 2. Rapid sand filters The rapid filter is the most common type used in water treatment to remove non-settle able floc remaining after chemical coagulation and sedimentation. A typical rapid sand filter bed (figure) is placed in a concrete box with a depth of about 2.7 m. The sand filter, about 0.6 m deep, is supported by graded gravel layer containing under drains. During filtration, water passes down ward through the filter bed by a combination of water pressure from above and suction from the bottom. Filters are cleaned by backwashing (reversing the flow) up ward through the bed. Wash troughs suspended above the filter surface collect the back wash water and carry it out of the filter box. The following descriptions of filter operation follow the valve numbering in figure. Initially valves 1 and 4 are opened, and 2, 3, and 5 are closed for filtration. Overflow from the setting Adama Science and Technology University- Department of Civil Engineering

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Lecture Notes (Physical, chemical and Biological analysis)

basing supplied to the filer passes through the bed and under drain system to the clear well underneath. The depth of water above the filter surface is between 0.9 and 1.3m. The under drain pipe is trapped in the clear well to provide liquid connection to the water being filtered, thus preventing backflow of air into the under drain. The maximum head available for filtration is equal to the difference between the elevation of the water surface above the filter and level in the clean; this is commonly 2.7 to 3.7 m. The bed is cleaned by backwashing. Valves 1 and 4 closed (3 remaining closed) and 2 &5 are opened. Clear water flows into filter under drain and passes upward though the bed. The sand layer expands hydraulically about 50 percent and the sand grains are scrubbed by rubbing against each other in the turbulent backwash flow. Dirty wash water is collected by troughs and conveyed to disposal. The first few minutes of filtered water at the beginning of the next run generally wasted to flush the wash water remaining in the bed out through the drain. This is accomplished by opening valve 3 when valve 1 is opened to start filtration (valves 2, 4, and 5 are shut). Finally, opening valve 4 closing 3 permits filtration to proceed again. Example: find the area of rapid sand filters for a town having a design population of 80000 with an average rate of demand as 200 lcpd.

WATER STORAGE TANK

WATER LEVEL WHILE FILTERING WATER LEVEL WHILE WASHING

FROM COAGULATION CLARIFICATION BASIN FILTER RATE CONTROLER

SAND GRAVEL

LATERAL DRAINS MAIN DRAIN

WASH OUT DRAIN

FILTERED WATER STORAGE TANK

Fig 5… Rapid Sand Filter

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Lecture Notes (Physical, chemical and Biological analysis)

Difference between Sand Filters and Rapid Sand Filters Sr.No 1. 2 3 4 5

6 7 8 9

Item Coagulation Compactness

Slow sand filters Not required Requires large area for its installation

Rapid sand filters Essential Requires small area for its installation Construction simple Complicated Economy High initial cost both land & material Cheap and quite economical Method of Scrapping of top layer of 15 to25 mm Agitation and back washing cleaning thickness. Long and laborious method with or with out the help of compressed air short and speedy method Period of 1 to3 months cleaning Rate of 100 to200 lit/hr/m2of filter area filtration Skilled Not essential supervision Suitability The filter can be constructed of local labor and material .it is suitable for small towns and villages where land is cheaply available.

2 to 3 days 3000 to 6000 lit/hr/m2 Essential It is suitable for big cites where land cost is high

3. Pressure Filters Pressure filters have media and under drains contained in a steel tank. Media are similar to those used in gravity filters, and filtration rates from 1.4 to 2.7 lit/m2/sec. Water is pumped through the bed under pressure, and the unit is backwashed by reversing the flow, flushing out the impurities. Pressure filters are not generally employed in lager treatment works; however they are popular in small municipal. Their most extensive application is for treating water for industrial purposes (e.g. pressure filters are in Arbaminch textile factory) 6. Adsorption Adsorption can be defined as the accumulation of substances at the interface between two phases. The material removed from the water is called the adsorbet, and the material providing the solid surfaces is called adsorbent. The adsorbent most commonly used in water treatment is activated carbon. It is manufactured from carbonaceous material such as wood, coal, petroleum residues etc. The activated carbon is used for removal of taste and odors from water as it has excellent properties of attracting impurities such as gases, finely divided solid particles and other liquid impurities.

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Lecture Notes (Physical, chemical and Biological analysis)

7. Softening Softening is the removed or reduction of hardness from the water. Hard water causes the following troubles: 1. Requires more soap for washing clothes 2. The precipitate formed by the action of the soap spoils the cloth 3. Choking and clogging troubles of pipe lines due to precipitation of salt causing hardness 4. Formation of scales in boilers For all these reasons removal of hardness or softening of water is required. There are two methods generally used for softening of water. 1) The lime –Soda Process In the method hardness is removed by using lime [Ca (OH) 2] and soda ash [Na2Co3]. The following are the reactions taking place:1. Ca(HCO3)2+Ca(OH)2CaCO3+2H2O 2. Mg(HCO3)2+Ca(OH)2Mg(OH)2+CaCO3+H2O 3. MgSO4+Ca(OH)2+NaCO3Mg(OH)2+CaCO3+Na2SO4 4. MgCl2+Ca(OH)2+NaCO3Mg(OH)2+CaCO3+2Nacl 2) The ion exchange process In this method hard water is passed thought a bed of zeolite sand (complex silicates of Al & Na), while passing through it Ca &Mg cations get replaced by sodium from the exchanger and the water becomes soft. The sodium from the zeolite sand on getting exhausted and after some time it cannot remove the hardness of the water .but the sodium of the zeolite is generated by applying a solution of sodium chloride (called brine). The reactions involved are: (a) Softening

Na2R

(b)

Ca (OHCO3)2 CASO4 CACI2 Mg (HCO3)2 MgSO4 MgCl2

+

Ca Ca Ca Mg Mg Mg

R

2 NaHCO3 Na2SO4 2NaCl + 2NaHCO 3 Na2SO4 2NaCl

Regeneration CaR+ 2NaCl



Na2R

+

CaCl2 MgCl2

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Lecture Notes (Physical, chemical and Biological analysis)

9. Disinfection Disinfection is the process of killing pathogenic microorganisms in order to avoid water born diseases The disinfection of water can be done by one of the following methods: a) by the boiling of water b) by ultra –violate rays c) by the use of iodine and bromine d) by the use of ozone O3 e) by the use of excess lime f) by the using potassium permanganate [KMnO4] g) by the use of chlorine The most common method of disinfection is the use of chlorine i.e. chlorination. The various chlorine compounds which are available in the market and used as disinfectants are 1. Calcium hypochlorite [ Ca(OCl)2] – power from 2. Sodium hypochlorite [NaOCl] –liquid from 3. Free chlorine Cl2- Gaseous form 5.3. Remarks in Water Treatment 1) The processes selected for the treatment of potable water depend on the quality of raw water supply. 2)

Most ground waters are clear and pathogen-free and not contain significant amounts of organic materials. Such waters may often be used directly with a minimal does of chlorine to prevent contamination in the distribution system.

3)

Other ground waters may contain large quantities of dissolved solids or gases. When these include excessive amounts of iron, manganese, or hardness, treatment methods described in section 5.2 may be required. Treatment systems commonly used to prepare potable water from such ground waters are shown in figures 5.x Surface waters often contain a wide variety of contaminants than ground water, and treatment processes may be more complex. Most surface waters contain turbidity in excess of drinking water standards. Wide variety micro organisms, some of which may be pathogenic are common constituents of surface water. Treatment systems commonly used in treating surface waters are shown in figure 5.y Ground waters like springs can directly be used after chlorination, as in the case of Arbaminch Water Supply.

4)

5)

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Process

Lecture Notes (Physical, chemical and Biological analysis)

Gases to atmosphere

Aeration: Removes undesirable gases and /or oxidation of iron and manganese

1

2

Lime

Softening: Removes calcium and /or magnesium hardness; may be done in one or two stages.

Filtration: Removes residual

Waste stream

Chemicals added

CaCo3 Mg (OH) 2

Soda ash

3

Chlorine

CaCo3 crystals and Mg (OH) 2 floc left over from softening; disinfectant may be added to prevent biological growth on filter medium.

Sludge removal and disposed of possible recovery and reuse of line

Back wash water decanted; sludge combined with sludge from (2) above

4 Disinfection: Destroys pathogens, enough added to provide Storage: provides contact time for disinfection and stores water for peak demands Process

5

Distribution system Chemical added

Adama Science and Technology University- Department of Civil Engineering

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Lecture Notes (Physical, chemical and Biological analysis)

Raw water

Pre-sedimentation: may be necessary if water comes from fast flowing stream. Removes large suspended solids. Chemicals Ammonia may be added to oxidize organics or to arrest their biological oxidation

Mixing, flocculation, settling: removes turbidly by coagulating colloids and settling them out; may also remove colors caused by large organic molecules

Chlorine

Alum Polymers

Filtration: Pohishes to remove remaining turbidity; disinfectant may be added to prevent biological growth on filter medium.

Chlorine

Sludge removed continuously disposal by land filling or other suitable means after dewatering.

2

3 Backwash water decanted, and dewatered sludge disposed of with that from 2 above.

Adsorption: May be necessary if water contains dissolved organics; may contains dissolved organics; may consist of activated carbon columns or activated carbon may be added in powdered from in operation similar to above

Disinfection: Destroys pathogens; enough added to provide residual in the distribution system

Sludge removed periodically and disposed of by spreading on land

1

4

Chlorine

Steam from cleaning cycle condensed and disposed of

5

6 Storage: Provides contact time for disinfection and stores water for peak demand

Typical plant Treating turbid surface water with organics

Distribution system

Adama Science and Technology University- Department of Civil Engineering

2011/12

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Lecture Notes (Physical, chemical and Biological analysis)

6. PHYSICAL, CHEMICAL AND BIOLOGICAL ANALYSIS OF WATER 6.1 SOURCES OF WATER POLLUTION Following are the main sources of water pollution 1. Domestic sewage: If domestic sewage is not properly after it is produced or if the effluent received at the end of sewage treatment is not of adequate standard, there are chances of water pollution. The indiscriminate way of hiding domestic sewage may lead to the pollution of underground sources of water supply such, as wells. Similarly if sewage or partly treated sewage is directly discharged into surface waters such as rivers, the waters of such rivers get contained. 2. Industrial wastes: If industrial wastes are thrown into water bodies without proper treatments, they are likely to pollute the water courses. The industrial wastes may carry harmful substances such as grease, oil, explosives, highly odorous substances, etc. 3. Catchment area: Depending upon the characteristics of catchment area, water passing such area will be accordingly contained. The advances made in agricultural activities and extensive use of fertilizers and insecticides are main factors which may cause serious pollution of surface waters. 4. Distribution system: The water is delivered to the consumers through a distribution of pipes which are laid underground. If there are cracks in pipes or if joints are leaky, the following water gets contaminated by the surrounding substances around the pipes. 5. Oily wastes: The discharge of oily wastes from ships and tankers using oil as fuel may lead to pollution. 6. Radioactive wastes: The discharge of radioactive wastes from industries dealing with radioactive substance may seriously pollute the waters. It may be noted that radioactive substances may not have color, odor, turbidity or taste. They can only be detected by and measured by the use of special precise instruments.

Adama Science and Technology University- Department of Civil Engineering

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Lecture Notes (Physical, chemical and Biological analysis)

7. Travel of water: Depending upon the properties of ground through which water travels to reach the source of water supply; it is charged with the impurities. For instance, ground water passing through peaty land possesses brown color.

6.2 WATER QUALITY CHARACTERISTICS 6.2.1 Physical Characteristics Physical characteristics include:

Adama Science and Technology University- Department of Civil Engineering

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

Solids



turbidity,



color taste,



odor



temperature, and



Foam.

Lecture Notes (Water supply project planning)

Obviously these characteristics may be associated with chemical pollutants and may result from the discharge of chemicals in to the water body. 1. Color: Color is caused by materials in solution or colloidal conditions and should be distinguished from turbidity which may cause an apparent (not true) color. True color is caused by dyes derived from decomposing vegetation. Colored water is not only undesirable because of consumer objections to its appearance but also it may discolor clothing and adversely affect industrial processes. 2. Turbidity: Turbidity is caused by suspended solids. The suspended solids may be dead algae or other organisms. It is generally silt , clay rock fragments and metal oxides from soil. The amount and character of turbidity will depend upon: the type of soil over which the water has run and the velocity of the water. Turbidly is measured by comparing the sample with a standard solution by optical means. Unit for measurement is NTU (Nephelometry turbidity unit). Sedimentation with or without chemical coagulation and filtration are used remove it. 3. Temperature: Temperature increase may affect the portability of water, and temperature above 15 0c is objectionable to drinking water. The temperature of surface waters governs to a large extent the biological species present and their of activity. Temperature has an effect on most chemical reactions that occur in natural water systems. It also has pronounced effect on the solubility of gases in water.

4. Solids: Solids may be present in suspended and /or in solution and may be divided in to organic and inorganic matter.

Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

Suspended solids (SS) are discrete particles which can measured by filtering a sample through a fine paper where as dissolved solids (DS) are due to soluble materials measured by evaporating a filtered sample of water and wighting the residue. Total solids (TS) = SS+DS 5. Foam: Foam form various industrial waste contributions and detergents is primarily objectionable from the aesthetic standpoint. 6. Taste And Odor: The terms taste and odor are themselves definitive of this parameter. Because the sensations of taste and smell are closely related and often confused, awide variety of tastes and odors may be attributed to water by consumers. Substances that produce an odor in water will almost in variably impart a taste as well. The converse is not true, as there are many mineral substances that produce taste but no odor. Many substances with which water comes into contact in nature or during human use may import perceptible taste and odor. These include minerals, metals, and salts from the soil, and products from biological reactions, and constituents of wastewater. Inorganic substances are more likely to produce tastes unaccompanied by odor. Alkaline material imports a bitter taste to water, while metallic salts may give salty or bitter taste. Organic material, on the otter hand, is likely to produce both taste and odor. a multitude of organic chemicals may cause taste & odor problems in water with petroleum-based products being prime offenders. Biological decomposition of organics may also result in taste-and odor-producing liquids and gases in water. Principal among these are the reduced products of sulfur that impart a rotten egg taste and odor. Also certain species of algae secrete an oily substance that may result in both taste and odor. Consumers find taste and odor aesthetically displeasing for obvious reasons. Because water is thought of as tasteless and odorless, the consumer associates taste and odor with contamination and may prefer to use a tasteless, odorless water that might actually pose more of a health threat. Measurement Quantitative tests employ the human taste smell can be used for this purpose. An example is the test for the threshold odor number (TON). Varying amounts of odorous water are poured into containers and diluted with odor free distilled water to make a 200-ml mixture. An assembled panel of five to ten “noses” is used to determine the mixture in which the odor is just barely detectable to the sense of smell. The ton of that sample is then calculated, using the formula A B TON  A Where A is the volume of odorous water (ml) and B is the volume of odor free water required to produce 200 ml mixture. A similar test can used to quantify taste. EPA does not have a maximum standard for TON. A maximum of 3 has been recommended by the public health service and guideline rather that a legal standard. Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

7. Electrical Conductivity The conductivity of a solution depends upon the quantity if dissolved alts present and for dilute solutions, it is approximately proportional to the TDS content. Conductivity (us/m)*(0.6-0.8) =TDS (mg/1) Conductivity measurements are therefore used to determine concentrations of dissolved salt or the concentration of ionized matter in general.

6.2. 2. Chemical Characteristics 1. Dissolved Oxygen (DO) Dissolved oxygen is present in variable quantities water. Its content in surface waters is dependent upon the amount and character of the unstable organic matter in the water. Clean surface waters are normally saturated with DO. The amount of oxygen that water can hold is small and affected by the temperature. The higher the temperature, the smaller the DO. Temperature (0C) DO(mg/1)

0 14.6

10 11.3

20 9.1

30 7.6

Oxygen saturated waters have pleasant taste and waters lacking in DO have an insipid tastes. Drinking water is thus aerated if necessary to ensure maximum DO. For boiler feed water DO is undesirable because its presence increases the risk of corrosion. 2. Oxygen Demand: Organic compounds are generally unstable be oxidized biologically or chemically to stable, relatively inner end produce such as CO2, H20 & NO3. Indicators used for estimation of the oxygen demanding substance in water are biological oxygen demand (BOD), chemical oxygen demand (COD), total oxygen demand (TOD) and total organic carbon (TOC). An indication of the organic content of water can be by measuring the amount of oxygen required for stabilization.

3. Nitrogen The forms most important to water quality engineering include; a) Organic – nitrogen: in the form of proton, amino-acids and urea. b) Ammonia – nitrogen: nitrogen as ammonium salts. e.g. (NH4).CO3

Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

c) Nitrate- nitrogen: an intimidate oxidation stage. Not normally present in large quantity. d) Nitrate- nitrogen: final oxidation product of nitrogen. e) Gaseous nitrogen(N2) The presence of nitrogen compounds in surface waters usually indicate pollution excessive amount of ammonia and organic nitrogen may result form recent sewage discharges or runoff contamination by relatively fresh pollution. Therefore, waters congaing high org-N & ammonia –N levels are considered to be potentially dangerous. While waters in which most of nitrogen is in nitrate from are considered to some what stabilized to constitute prior pollution 4. Hydrogen Sulfide: It is produced in ground water by reduction of sulfates, iron pyrites or decompositions of organic matter. 5. Acidity: Most natural waters are buffered by a carbon dioxide – bicarbonate system. Acidity represent the amount of carbonic acid present .for all practical purposes if pH of the water is below 8.5 some acidity is present. 6. Alkalinity It is defined as the quantity of ions in water that will react to neutralize hydrogen ions. Alkalinity is thus the measure of the ability of water to neutralize acids. By far the most constituents of alkalinity in natural waters are carbonate (CO32-), bicarbonate (HCO3-) and hydroxide (OH). These compounds result from the dissolution of mineral substances in the soil atmosphere. 7.PH: It expresses the moral concentration of the hydrogen ion as its negative logarithm. Pure water is only weakly ionized H2O  H+ +OHAbout 10-7molar concentration of [H] and [OH] are present at equilibrium 1 PH = -log [H+] = log 7 [ H ] 8. Hardness: Hardness is caused by the sum of the alkali earth elements present in water although the major constituents are usually calcium and magnesium. These materials in water react with soap, causing precipitation which as scum or curd on the water surface. Until enough soap has been dissolved to react with all these material s, no lather can be formed. A water that behave like this is said to be „hard „. The hardness compounds are temporary and permanent:

1. Temporary hardness (carbonate hardness)  Calcium bicarbonate (Ca (HCO3)2)  Magnesium bicarbonate (Mg(HCO3)2) 2. Permanent hardness’ (non- carbonate hardness) Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

 calcium sulfate (CaSO4)  Magnesium chloride (MgSo4)  calcium chloride (CaCl2)  Magnesium chloride (Mg cl2) The most usual compounds causing alkalinity, calcium and magnesium bicarbonate, happen also to cause the temporally hardness. Hence, when the alkalinity and hardness are equal, all the hardness is temporary. If the total hardness is greater than the alkalinity, then the excess hardness represents permanent hardness. On the other hand, if the total hardness is less than the alkalinity, the difference indicates the presence of sodium bicarbonate which adds to the alkalinity but doesn‟t increase the hardness. A generally accepted classification of hardness is as follows: Soft Moderately hard Hard Very hard

300 mg/1 as CaCO3

9. Chloride: Chloride may demonstrate an adverse physiological effect when present in concentration greater than 250 mg/1 and with people who are acclimated. However, a local population that is acclimated to the chloride content may not exhibit adverse effect from excessive chloride concentration. Because of high chloride content of urine, chlorides have sometimes been used as an indication of pollution. 10. Fluoride: It is generally associated with a few types of sedimentary or igneous rocks; fluoride is seldom found in surface waters and appears in ground water in only few geographical regions. Fluoride is toxic to humans and other animals in large quantities, while small concentrations can beneficial. Concentrations of approximately 1.0 mg/1 in drinking water help to prevent dental cavities in children. During formation of permanent teeth, fluoride combines chemically with tooth enamel, resulting in harder, stronger teeth that are more resistant to decay. Fluoride is often added to drinking water supplies if quantities for good dental formation are not naturally present. Excessive intakes of fluoride can result in discoloration of teeth. Noticeable discoloration, called mottling, is relatively common when fluoride concentrations in drinking water exceed 2.0 mg/1, but is rare when concentration is less that 1.5 mg/1. Adult tooth are not affected by fluoride, although both the benefits and liabilities of fluoride during teeth formation years carry over into adulthood. Excessive concentrations of grater than 5 mg/1 in drinking water can also result in bone fluorisis and other skeletal abnormalities. 11. Toxic Organic Chemicals These include Polynuclear Aromatic Hydrocarbons (PAH); Pesticides. E.g. DDT; Phenol; etc. 12. Lead, Arsenic and Other Metals: Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

These are toxic substance and are extremely dangerous from public health viewpoint. The presence of lead in excess of 0.1 mg/1 or arsenic in excess of 0.05 mg/1 or Selenium in excess of 0.05 mg/1 or hexavallent Chromium in excess of 0.05 mg/1 shall constitute grounds for rejection of the supply. 6.2.3. Biological Characteristics A feature of most natural water is that they contain a wide variety of micro – organisms forming a balance ecological system. The types and numbers of the various groups of micro – organisms present are related to water quality and other environmental factors. Micro biological indicators of water quality or pollution are therefore of particular concern because of their relationships s to human and animal health. Water polluted by pathogenic micro- organisms may penetrate into private and or public water supplies either before or after treatment. 1. Bacterium: Many are found in water .some bacteria are indicator of pollution but are harmless; other few in number are pathogenic. Bacterial –born diseases include: typhoid fever, cholera, and bacterial dysentery: 2. Viruses These are group of infectious which are smaller that ordinary bacteria and that require susceptible host cells for multiplication and activity. Viral-born diseases include infectious hepatitis and poliomyelitis. 3. Algae: These are small, Chlorophyll bearing generally one–celled plants of varying shapes and sizes which live in water. When present in large numbers they may cause turbidity in water and an apparent color. They cause trouble in water works by undue clogging of filters, but their most troublesome characteristics in the taste and odor that they may cause 4 protozoa: They are the lowest and simplest forms of animal life. Protozoa–born diseases include giardiasis and amebic dysentery. 5 fungi: These are non –chlorophyll bearing plants and they may therefore grow in the absence of light. large numbers die and the decomposition of their will cause disagreeable tastes and odors. 6. Actinomycets: These are related to both bacteria and fungi; and are responsible for earthy, muddy & misty color in water 3.3. EXAMINATION OF WATER QUALITY

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Lecture Notes (Water supply project planning)

Examination of water is made to help informing an opinion of the suitability of a water supply for public and other uses. 1.

Sampling Necessary to obtain a representation sample in a quantity sufficient for analysis complete preservation of sample is practically impossible; however, freezing or adding suitable preservatives may slow down changes in composition. Plastic, glass or metal sample containers are able introduce contamination to sample. Normally plastics are used for chemical analysis (except for oil & grease) and glass for bacteriological analysis.

2. Standard Tests i) Titration (volumetric) method Using burettes, pipits, and other volumetric glass ware, standard solutions are prepared using analytical and distilled or doionized water. APHA recommended determinations to be made by titration method are : Chloride (Cl -), carbonates (CO32-) , bicarbonates (HCO3) , DO, BOD, COD , calcium (Ca++), magnesium (Mg++) , bromide (Br) , hydroxide (OH-), sulfide(S-) , sulfite(SO32), acidity , alkalinity etc. (ii). Colorimetric method (using color as the basis) Measuring amount of color produced by mixing with reagents at fixed wavelength (using spectrophotometer) or comparison with colored standards or discs (comparator). APHA recommended determinations made by colorimetric method are : color , turbidity , iron (Fe++), manganese(Mn++), chlorine (Cl2) , flurried (F-) , nitrate (NO3-) ,nitrite (NO2) , phosphate (PO4---) , ammonia (NH4+) , arsenic , phenols , etc. (iii). Gravimetric method (using weight ad the basis) Using weight of insoluble precipitates or evaporated residues in glassware or metal and accurate analytical balance (+0.001 gm). APHA recommended determinations made by gravimetric methods are: sulfate (SO4), Oil and grease, TDS, TSS, TS, etc. (iv).Electrical method Using probes to measure electrical potential in millivolts against standard cell voltage. APHA recommended determinations made by electrical methods are: pH, Fluoride (F-), DO, nitrate (NO3), etc. (v). flame spectra (emission & absorption) method At fixed wave length characteristics to ions being determined measuring intensity of emission or absorption of light produced by ions exited in flame or heated sources. APHA recommended determinations made by flame spectra methods are ;sodium (Na+ ), potassium (K+) ,lithium (Li+), etc.

6.4 Water Quality Standards Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

Public water supplies are obliged to provide a supply of wholesome water which is suitable and safe for drinking purposes. Potable water is water which is satisfactory for drinking, culinary and domestic purposes. Water quality standards may be set regional, national, or international bodies. Guidelines for drinking water quality have established by the World Health Organization (WHO)as shown in table below. Table WHO Guideline for drinking water quality Parameter Unit Guideline value Microbial quality Fecal coli forms Number/ 100 ml Zero* Coli form organisms Number /100 ml Zero* Inorganic constituents Arsenic Mg/1 0.05 Cadmium Mg/1 0.005 Chromium Mg/1 0.05 Cyanide Mg/1 0.1 Fluoride Mg/1 1.5 Lead Mg/1 0.05 Mercury Mg/1 0.001 Nitrate Mg/1 10 Selenium Mg/1(N) 0.01 Aesthetic Quality Aluminum Mg/1 0,2 Chloride Mg/1 250 Color Mg/1 15 Copper Mg/1 1.0 Hardness True color unit(TCU) 500 Iron Mg/1 0.3 Manganese Mg/1(as caco3) 0.3 PH Mg/1 6.5 to 8.5 Sodium Mg/1 200 Total dissolved solids Mg/1 1000 Sulfate Mg/1 400 Taste and odor inoffensive to most Turbidity NTU consumers Zinc Mg/1 5 5.0

* treated water entering the distribution system Source – Ethiopian building code standard, plumbing services of building (EBCS -9)

Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

7. WATER, WASTE AND HELTH RALATIONSHIPS 7.1 Waterborne Diseases Communicable diseases which may be transmitted by water include

bacterial, viral, and

prozoal infections. The bacterial disease includes typhoid, paratyphoid, salmonellosis, shigellosis, bacillary dysentery, and Asiatic cholera. Viruses cause infectious hepatitis and polimyelitis, while protozoans can cause amoebic dysentery and giardiasis. Schistomiasis is caused by a worm which may be transmitted through water via a snail carrier. Other diseases are not general transmitted by water.

Typhoid, paratyphoid, gastroenteritis, and cholera are transmitted by the fecal and urinary discharges of sick persons and carriers. Through careless disposal of the discharges or inadequate treatment of city sewage, underground water may be affected to contaminate surface supplies. Prevention of water born out breaks of these diseases is primarily a matter of treating the water by methods described in chapter 5 and the placing of adequate safeguards around the water supply system that will prevent chance of contamination.

Gastroenteritis is a clinically identifiable diarrhea disorder but the term is often used to describe outbreaks which are not directly attributable to specific organisms. It resembles food sometimes and apparently some of the organisms that are involved in food poisoning are sometimes waterborne after having reached water by means of bowel discharges. The role of bowel discharges is indicated by the fact that in the past, waterborne typhoid epidemics have been preceded by outbreak of gastroenteritis. On the other hand gastroenteritis has occurred; water borne according to epidemiological evidence, while at the same the water showed no evidence of bacteria pollution. There is now evidence that some gastroenteritis is caused by viral agents. However, it is usual for an outbreak of gastroenteritis to be accompanied by the

Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

presence of coli form organisms in the water. Chemical irritants, the characteristics of which have not been determined, have been blamed for gastroenteritis in a few instances.

It should be recognized by the waterworks man that not all typhoid fever and dysentery is waterborne. The infection may be carried by flies to foods, while carries and the sick may infect foods that they handle. Infected milk has been responsible for many epidemics.

Oysters and other shellfish grown in sewage- polluted water will themselves be polluted and highly dangerous. Infectious hepatitis, also known as epidemic hepatitis, is caused by a virus which has been responsible for several waterborne epidemics but may also be transmitted by direct personal contact, food and milk. Poliomyelitis, also a virus disease, is found in feces of infected persons and in sewage. Hence it has assumed that virus might occur in drinking water. It is possible that some cases may have occurred in this way, but there is no epidemiological evidence connecting outbreaks of poliomyelitis with drinking water or use of swimming pools.

Schistosomiasis organisms are animal parasites which pass part of their life cycle in certain species of water snails. After leaving the snails they are swimming forms known as cercariae, which may be drunk or, more likely, may enter the skin of a person who wades or swims in the water. Coagulation and flirtation do not remove cercariae from water but

chlorination

with a residual of 1 mg/1 will kill them in 10 min.

7.2 Methemoglobinemia This disease causes “blue babies "and has caused some reported cases and deaths. It is caused by nitrates in water consumed by infants under 2 months of age. In children of that age or under the nitrates are reduced in the body to nitrites which react with the oxygen receptor sites on the hemoglobin fraction of the blood and impair its oxygen carrying capacity. This reaction does not occur in older children or adults. The water responsible has had nitrates in excess of 10 mg/1 and in all cases it has been ground water.

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Lecture Notes (Water supply project planning)

High nitrates waters are not uncommon and it is probable that sub clinical cases in addition to more severe cases may occur. One safeguard might be to use nitrate -free water for direct consumption by babies and food formulas. 7.3. Lead Poisoning Lead is sometimes found in water that has been in contact with lead pipes. As lead is a cumulative poison, habitual consumption of such water may result in lead poisoning. This may occur in waters containing over 0.3 to 0.5 mg/1 by weight of lead. The U.S environmental protection agency standard s for water quality, however, places the limit at 0.05 mg/1 the same limit is placed by WHO. The danger of lead poisoning has contributed to the reluctance of water works officials to use lead pipes for service lines. The waters likely to take up lead are soft or acid and include rainwater with its usual high carbon dioxide content, and swamp waters, which may contain humic acids and carbon dioxide. Lead poisoning affects blood formation system, nervous system and the renal system; and may also be fatal. 7.4. Fluorides Waters in certain sections of the country contain fluorides as impurities. Excessive intakes of fluorides can result in discoloration of teeth. Noticeable discoloration, called mottling, is relatively common when fluoride concentrations in drinking water exceed 2.0 mg/1, but is rare when concentrations are less than 1.5mg/1. Adult tooth are not affected by fluoride, although both the benefits and liabilities of fluoride during teeth formation years carry over into adulthood. The teeth of adult moving to an area where the water contains fluoride are not affected. In

USA, the known areas in which mottled enamel occurs include sections of Texas, New

Mexico , Arizona , Colorado , Nevada California, Utah , Oklahoma , Arkansas, Mississippi, Tennessee, Kansas ,Iowa , Illinois ,and the Dakotas. Scattered area also occurs in some of the Atlantic coast states. In our country, the known towns in which enamel occurs include Awassa, Nazareth, Wonji, Methara etc. Excessive concentrations of grater than 5 mg/1 in drinking water can also result in bone fluorisis and other skeletal abnormalities.

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Lecture Notes (Water supply project planning)

8. INTRODUCTION TO WATER- CARRIAGE SANITATION SYSTEMS 8. 1 Introduction If untreated wastes are accumulated or spread everywhere, the decomposition of the organic materials within wastes can lead to the production of malodorous gases, pathogenic organisms or may contain toxic compounds and will pollute our environmental (land, air, water). Therefore, all the solid and liquid wastes have to be collected and conveyed to suitable places for treatment, and are disposed safely. Definition of Terms: Sewage: a combination of the water carried wastes removed from residences, institutions, and commercial and industrial establishments, together with such ground water, surface water, and storm water as may be present. Sewer: Underground conduit (drain) through which sewage is conveyed Sanitary sewer: A sewer carrying domestic sewage only Storm sewer : A sewer carrying storm water only Combined sewer: A sewer carrying domestic sewage and storm water Sullage : Wastewater from bathroom, kitchens, etc. Night soil: Human excreta Sewerage system: The entire science of collecting and conveying sewage by water carriage system through sewers. BOD (Biochemical Oxygen Demand): the quantity of oxygen utilized by a mixed population of microorganisms in the anaerobic oxidation ( of the organic matter in a sample of waste water ) at a temperature of 200C 8.2 Methods of collection and Conveyance There are two methods/systems: 1. Water-carriage system 2. Conservancy system ( Non-water Carriage) Water Carriage System  In this system, water is used as a media of conveying the sewage to the points of treatment and disposal. Therefore it is called water carriage  In this system the excremental matter are mixed up with large quantity of water, are takeout from the city thought properly designed sewerage systems, and disposed after necessary treatment. Merits and Demerits of the Water-carriage system Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

Merits: 1. It is hygienic method because all the excremental matters are collected and conveyed by water only and no human agency is employed for it 2. There is no nuisance in the streets of the towns because all the sewage goes in closed sewers under the ground, the of epidemics (spreading of disease )is reduced 3. Due to more quantity of sewage self cleaning velocity can be obtained even at less gradient 4. Buildings can be designed as one compact unit 5. The usual water supply is sufficient and no additional water is required in water carriage system. 6. This system does not depend on manual labor at every time except when sewers get chocked Demerits  Costly in initial cost  Maintenances of this system is also costly  During monsoon, (wet season) large volume of sewage is to be treated (where as very small volume is to be treated in the remaining period of the year).

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Lecture Notes (Water supply project planning)

Industrial wastes

Separate disposal

Residential & Commercial Wastewater

Segregation & Pretreatment Infiltration & Inflow

Unpolluted Cooling water

Sanitary Sewers

Combined storm & Sanitary Wastewater

Surface drainage Interceptor sewer

Municipal Wastewater treatment plant Overflow by- pass

Treated Effluent

Natural watercourse Fig 8.1 Source of municipal wastewater in relation to collector sewers and treatment

Water Carriage system may be divided in two: a. Sewerage Systems b. Septic Tank 8.3 Types of Sewerage Systems These are broadly classified as follows: 1. Combined system 2. Separate system 3. Partially separate system Combined system : when only one set of sewers are laid, carrying both the sanitary sewage and storm water it is known as combined system. This system is most useful in areas having less sewage to obtain self- cleanings velocity and crowded area (where it is difficult to provided two sewers)

Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

Separate system: When the domestic and industrial sewage are taken in another set of sewers, it is known as separate system. If the rainfall is heavy and it is for short time, it is better to provide separate system, because in combined system self –cleaning velocity will not be available for most of the period of years. Partially separate system: - for this type of system, if a portion of storm water is allowed to enter in the sewers carrying sewage and remaining storm flows in separate system. Merits and demerits of separate system Merits:1. The sewage flows in separate sewer, therefore the quantity of sewage to be treated is less, which results in economical design of treatment plants 2. It is cheaper than combined system, because only sanitary sewage flows in closed sewers and the storm water, which is a foul (unclean), in nature can be taken through open shutters or drains. 3. During disposal, if the sewage is to be pumped, the separate system is cheaper. Demerits 1. Self-cleaning velocity is not available, due to small quantity of sewage; therefore flushing is required at various points. 2. There is always risk that storm water may enter the sanitary sewer and cause overflowing of sewer and heavy load on treatment plant. 3. As two sets of sewers are laid, therefore the maintenance cost is more 4. In busily lanes, lying of two sewers are difficult, which also causes great inconvenience to the traffic during repair.

Merits and Demerits of the Combined System Merits: 1. There is no need of flushing, because self cleaning velocity easily available at every place due to more quantity of sewerage. 2. Rainwater dilutes the sewage therefore; it can be easily and economically treated Demerits: 1. Initial cost is high as compared with separate system. 2. It is no suitable system for areas having rainfall for small periods of the year. Because dry weather flow (rain water) will be small due to which self-cleaning velocity will not be available , resulting in the silting up of the sewers, 3. If the whole sewage is tube disposed of by pumping , it is un economical 4. During heavy rains the over following of sewers will endanger the pubic heath 8.3.1 Separate System Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

This system comprises of :  Sanitary system  Storm water system  Domestic and industrial sewage are taken to one set of sewers  sanitary sewers.  Storm water is taken to another set of sewers  Storm sewers  Sanitary sewage is carried to treatment plants and storm water discharged directly to natural water bodies (rivers, lakes, etc.) 1. Storm Sewer System  It is a system used to collect and convey storm water from streets, roofs .and other sources.  Surface water enters a storm drainage system through inlets located in street gutters or depressed area that collect natural drainage.  Cooling water from industries and ground water seepage that enters footing drains are pumped to the storm sewers, since the pipes are usually set too shallow for gravity flow. INLET

SEWER

A) CURVE INLET

GRATE

SEWER

B) GUTTER INLET

Amount of storm run off The rational method is used to calculate the quantity of runoff for the storm sewer design: Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

Q  0.278 * CIA Where Q = maximum rate of runoff (m3/s) C = Coefficient of runoff based on the type and characteristics of the surface I = Average rainfall intensity (mm/hr), for the period of a given frequency of occurrence having a duration equal to the time required for the entire drainage area to contribute flow. A = Drainage area (km2) Table 8.1 Coefficient of Runoff for Various Areas and Types of Surfaces Description Coefficient 1. Business areas depending on density 0.7 to 0.95 2. apartment dwellings 0.5 to 0.70 3. single family areas 0.30to 0.50 4. parks, cemeteries, play grounds 0.10 to 0.25 5. paved streets 0.80 to 0.90 6. water tight roofs 0.70 to 0.95 7. lawns depending on surface slope and 0.10 to 0.25 character of subsoil Exercise a) What is the maximum population that can be served by a 200mm sanitary sewer laid at minimum grade using a design flow of 1500l/c/d and a flowing full velocity of 0.6m/s? (Answer : 1085 Persons) b) Compute the diameter of storm drain to serve the same population based on:  Population density = 7500persons per km2  Coefficient of runoff, C = 0.40  Time of concentration, tc = 20mm  Full flow velocity, V = 1.5m/s  Rainfall intensity, I for 10 years frequency and duration of 20min = 108mm/hr (Answer: 1200mm) 2. Sanitary Sewer System Sanitary sewers transport domestic and industrial wastes by gravity flow to treatment facilities. Design flow for these sewer systems are based on population served, the per capita quantities. I) Types of Sewers Based on the method (systems) of collection and conveyance, sewers are divided in to three: 1. Sanitary sewers 2. Storm water sewers 3. Combined sewers And on the bases of the function of the sewers, the principal types found in most collection system are  Building sewers  Literal or branch sewers Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

 Main sewers  Trunk sewers  Intercepting sewers Table 8.1 Classification of Sewerage Systems Type of Hydraulic Purpose System Characteristics Sanitary Gravity Sanitary (Gravity) sewers are used to collect wastewater from residential, commercial, industrial, and institutional sources. Allowance must be made for ground water infiltration and unavoidable inflow. Pressure Sanitary (pressure) sewers are used principally to collect wastewater from residential source in location unsuitable for the constriction and /or use of gravity sewers; they are also only to collect wastewater from industrial source because of the large volumes that may be invalid. These systems are usually small and are designed to exclude groundwater infiltration and storm-water inflow vacuum Same as above for pressure systems. Storm gravity Storm –waters are to collect storm water from water Streets roots, roots and other source. Sanitary wastewater is excluded totally. Combined Gravity

Combined sewers are used to collect wastewater from residential. Commercial, institutional, and industrial sources and storm water. Additional and industrial source and storm water. Additional flows come from ground water infiltration and storm water inflow. combined sewers are rarely designed and built the united states today

*Sanitary sewers are known as separate sewers * Pressure and vacuum sewers are seldom used for storm for storm-water flows because of the large quantities involved

Table 8.2 Types of sewers in sewerage systems Types of sewer Purpose

building

Building sewers sometimes called building connections, connect to the building plumbing and used to convey wastewater form the building to lateral or branch sewers or any other sewers except another building sewers building sewers normally being outside the

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Lecture Notes (Water supply project planning)

building foundation.

Lateral branch

or Lateral sewers from the first element of a wastewater collection system and are usually in streets or special easements. They are used to collect wastewater from one or more building sewers and convey it to a main sewer. main Main sewers are used to convey wastewater from one or more lateral to trunk sewers or intercepting sewers. trunk Trunk sewers are large sewers that are used to convey wastewater from main sewers to treatment or other disposal facilities or to large intercepting sewers. intercepting Intercepting sewers are large sewers that are used to intercept a number of main or trunk sewers and convey the wastewater to treatment or other disposal facilities.

Trunk Sewers

Building Sewers

Lateral sewers

Main Sewers Intercepting Sewers

II) Sewer (Pipe Materials) The physical characteristics essential for sewer pipes are: Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

 

Durability for long life Abrasion resistant interior to withstand scouring of wastewater carrying gritty materials.  impervious walls to prevent leakage of water ; and  Adequate strength to resist failure or deformation under backfills and traffic loads. Joints should be durable easy to install and watertight to prevent or entrance of roots. The most important chemical characteristic of pipe materials is resistance to dissolution in water, and corrosion. Pipe surface must be able to withstand both electrochemical and chemical reaction from the surrounding soil and wastewater conveyed in the pipe. Bacterial activity in anaerobic wastewater produces hydrogen sulfides gas; particularly in warm climates when sewers are laid on flat grades. Hydrogen sulfide absorbed in the water condensed on the crown is converted to sulfuric acid by aerobic bacterial action. If the pipe is not chemically resistant, the acid deteriorates it and eventually results in collapse of the crown. The most effective preventive measure is, to select a pipe material resistant to corrosion: such as vitrified clay or plastic. When reinforced concrete pipe is needed for large sizes, and interior protective coatings of coal tar, vinyl or epoxy should be considered. Generation of hydrogen sulfide in a sewer can be reduced by placing the pipe on as steep a gradient as possible and by ventilating if necessary. Corrosion of the pipe bottom is caused by disposal of acidic industrial wastewaters. This problem is best solved by limiting the discharge of acid wastes to the municipal sewer system. In concrete pipes, corrosion resistant liners, such as vitrified clay plates, may be placed in the invert of the sewer for protection.

Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

1. Vitrified Clay Pipe (VCP): It is the most common material used in sanitary sewer pipe. It is manufactured from clay, shale, or combinations of these materials that are pulverized and mixed with a small amount of water. The moistened clay is extruded through dies under high pressure to form the barrel and socket, dried, and then fired in a kiln for verification. Vitrified clay pipe (VCP) is manufactured in both standard and extra strength in diameters from 75.to 1050 mm, and in laying lengths of 0.6 to1.5m depending on diameter. Curves, elbows, and branching fittings. Including single and double tee and wyes, shapes are available in most pipe sizes. 2. Asbestos Cement) Pipe (ACP) This comes in there type: for service connections, gravity sewers and pressure pipe for force mines. The pipe material is composed of cement, Silica and asbestos fibers. It is formed under high pressure and is heat treated to develop strength. Asbestos cement is durable and has smooth surface without lining, but epoxy-lined pipes are available for special applications. Non-pressure sewer pipe is available in the size ranging from 100-to1050 mm diameter in 4m lengths; shorter lengths are available in smaller, and 2 m sections are available in 250 to 525 mm sizes. 3. Plastic Pipe Most frequently used in sewer systems is of PVC (Polyvinyl Chloride Pipe) and PE (polyethylene). PVC pipe is produced in two strength classification in sizes from 100 to 300 mm. A few manufactures make pipe up to 750 mm diameter. The standard length is 6 m with others available. PVC pipe sections have a deep – socket, bell end to accommodate a chemical weld joint. Solvent is spread both on the inside of the bell and on the plain end before they are pushed together. PE pipe is joined by softening the aligned faces of the ends on a suitable apparatus and pressing them together under controlled pressure . PVC pipe is used for building connections, branch sewers, while the popular application of PE pipe has been for long pipelines, often laid under adverse conditions for example, in swamp or underwater crossings 4. Pre-Cast Concrete Sewer Pipe This may be obtained in many sizes with several types of joints. Choice for a particular type of pipe depends on:  Application.  location and  Conditions of installation. Non-reinforced concrete pipe is available in 100 to 600mm diameters in 1m lengths. It is manufactured in standard strength and extra strength grades. The bell and spigot ends are normally jointed by using a rubber ring gasket. Circular reinforced concrete pipes are available in size range from 300 to 2700 mm. pre-cast conduits are also manufactured in elliptical and arch-type shaped. Tongue and groove joins, which are common in reinforced pipes, use a mastic compound or rubber gasket to form watertight seal.

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Lecture Notes (Water supply project planning)

5. Reinforced Concrete Pipe It is used extensively in storm sewer systems for its abrasion resistance, availability in large sizes, high crushing strength and generally; lower cost relative to other types of pipes. since concrete is an alkaline materials subject to attack by acids it should not be used for small sized sanitary sewers where industrial wastes or hydrogen sulfide production is likely to cause internal corrosion . However, reinforced concerted pipe is installed for sanitary trunk sewers where the diameter exceeds the available sizes of vitrified clay pipe. The instillation must be protected by control of acidic, high temperature, or high-sulfate wastes by adding chemicals to control biological growth, maintaining flushing velocities and adequate ventilation, and installation of pipe lining if necessary, epoxy or plastic lining may be cast into the concrete pipe during manufacture; or bituminous or coal-tar epoxy may be painted on the pipe surfaces after installation. 6. Cast –Iron or Ductile –Iron Pipe is used for force mains ,inverted siphons, in pumping stations and treatment plants ,when proper separation from water mains cannot be maintained and where poor sewer foundation conditions exist. Other pipe materials for special applications in waster collection systems are  smooth wall &corrugated steel pipe  bituminize fiber, and  Rein forced resin pipe.

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Lecture Notes (Water supply project planning)

B) Septic Tank 1. In the rural areas and fringe (labor area) areas of suburban town also in case of isolated building and institution, hostels, hotels, hospitals, schools, residential, conies. Underground sewerage system with complete treatment of sewage may be neither feasible nor economical. Under such circumstance septic tanks followed by subsurface disposal of effluent are provided (soak pit) 2.

In the areas having porous soil this method give satisfactory results. The location of septic tank should be as far as possible away from the buildings, and should not be located in swampy (marsh, submerge in water ) area or area prone to flooding

3. The septic tank effluent should not be allowed in to open drainage system because it may cause health hazards, nuisance and mosquito, if the facilities for connection tank should be connected to sewers. 4. A septic tank is a combined sedimentation and digestion tank , where sewage is held for some period (years) and the suspended solids settle down to the bottom this is accompanied Reduction in the volume of sludge and release of gases, like carbon dioxide, methods and hydrogen sulfide, finally decreased in sludge volume. The effect contains considerable amount of dissolved and suspended organic solids (caplet of living or survival) and viable pathogenic that requires careful consideration and disposal of effluent. 5. Septic tanks are recommended for individual houses and small colonies only (300 Persons) because of the unsatisfactory quantity of effluent and difficulty in disposal of effluent. For the satisfactory function of the septic tank, adequate water supply is most essential.

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Lecture Notes (Water supply project planning)

Construction:1. Septic tanks are constructed of brickwork, stone masonry, or concrete or other suitable materials and plastered with rich cement mortar in with some water proofing materials should be mixed up 2. The floor should be 1:2:4 ( Cement : Sand : Aggregate)cement concert and give slope towards the sludge outlet 3. Airtight concert or steel cover should be provided on the top of septic tank 4. Manholes should be provided in the cover for inspection and cleaning of the tank 5. A vent pipe should be installed for the discharge of gases away from the houses 6. the length of the tank should be kept 2-4 times its width Design: The size of a septic tank is based on the number of users and detention time. Detention time (12 - 24 hours) o For small size tank up to 50 users, it is normally assumed 24 hours o For bigger tanks it may be kept up to 16 hours Rate of Flow It is the quantity of wastewater generated from the users. Capacity of Tank: It is determined from the rate of flow and the number of users. Capacity = Q* T Table 8.3 Dimensions of septic tank as per IS.2470 (part I) No of user s 5

Lengt h L (m) 1.5

Breadth B(m)

Liquid depth D(m)

0.75

10

2

0.9

15

2

0.9

20

2.3

1.1

50

4

1.4

1.0 1.0 1.05 1.0 1.0 1.4 1.0 1.3 2.0 1.0 1.3 1.8 1.0 1.3 2.0

Liquid Free capacity(m3 board ) cm 1.12 1.2 1.18 1.8 1.8 2.52 1 .8 2,34 3.6 2.53 3.3 4.55 5.6 7.28 11.2

30 30 30 30 30 30 30 30 30 30 30 30 30 30 30

Adama Science and Technology University- Department of Civil Engineering 2011/12

Sludge to be removed ( m3) 0.18 0.36 0.72 0.36 0.72 1.44 0.54 1.08 2.16 0.72 1,44 2.88 1.8 3.6 7.2

Cleaning intervals

6 month 1 tear 2 year 6 month 1 year 2year 6 months 1 year 2year 6 months 1 year 2years 6 months 1 years 2 years 36

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Lecture Notes (Water supply project planning)

Table 8. 4. The dimensions of large size septic tank as per IS. .2479(part II) No. of user s

Lengt h

Bread th B(m)

Liqui d Depth

L(m)

Liquid Capacit y (m3)

Free board ( cm)

Distance of partition wall from Intel end (m)

Cleanin g interval years

remark

D(m) 100 150 200 250

8.0 10.6 12.4 14.6

2.8 2.7 3.1 3.9

1,04 1.15 1.15 1.15

23.3 32.9 44.2 65.5

45 45 45 45

5.3 7.1 8.3 9.7

2 2 2 2

Tanks for housing colonies

50 100 150 200 300

5 5.7 7.7 8.9 10.7

1.6 2.1 2.4 2.7 3.3

1.4 1.7 1.7 1.7 1.7

11.2 20.4 31.4 41.0 60.0

45 45 45 45 45

3.4 3.8 5.2 6.0 7.2

2 2 2 2 2

Tanks for hostels and boarding

Disposal of septic Tank Effluent The effluent fro septic tank is highly odorous and should be discharged carefully Methods 1. Absorption pits at the bottom of trenches where a layer of broken stones are laid 2. absorption by soak pit of depth 1.2 m to 1.8m having been lined with dry masonry with pointed joints 3. The effluent falls in the pit and is allowed to be absorbed in the surrounding soil Soak Pit: This is also known as Seepage pit, these are circular pits more than one meter in diameter and 1m length below the invert of Intel pipe. Theses are lined with spray bricks or stone and are filled with brickbats or coarse aggregate more than 7.5cm size.

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Lecture Notes (Water supply project planning)

Air Vent

Ground Surface

Inspection & Cleaning Influent

Perforated Pipe

Liquid

Septic Tank

Gravel Bed

Sludge

Absorption (Percolation) Field

Exercise-1 Design a septic tank and soak pit given the following data: rate of water supply per head for a group of houses is 150liters and the population to be served by the septic tank is 500. Assume that the whole amount of water supply is available in the form of sewage.

8.4 Sewage treatment Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

The strength of sewage refers to its capacity to be a hazard to public life and health. This mainly consists of offensive odor; organic matter which can be oxidizes, commonly referred to as biochemical oxygen demand (BOD). Swage with greater BOD is stronger than that with lower BOD. BOD is the amount of oxygen required for biochemical oxidation of the decomposable solids present in sewage at a standard temperature under anaerobic condition. Sewage from separate systems is stronger than that from a combined system due to increased dilution from storm water. Sewage has greater BOD during daytime and during the working day of industries. Sewage treatment is aimed at efficient removal or reducing understandable effects of the impurities contained in the wastewater to tolerable level of the pathogens, suspended solids and other constituents that cause the undesirable effect on health of people, economy, environment or aquatic life. To achieve at the required target, we have different types of treatment processes. However, in areas where there is shortage of finance, lack of skilled labor, and when land is available, stabilization ponds are designed to treat the wastewater.  Stabilization ponds compromise a series of shallow lakes, namely anaerobic, facultative and maturation ponds through which the sewage flows.  Natural physical, chemical and biological process and no machinery do treatment or no energy input is required.  Natural forces (sunshine, wind, temperature and spontaneous plant and animal life) act up on the sewage to treat it. 8.4.1 Design of Stabilization ponds 1. Design of Anaerobic Pond Anaerobic ponds are able to accept high organic loadings and particularly useful for treating strong organic wastewater. Dissolved oxygen is absent and no photosynthesis takes place because of the high turbidity and the dark color of a pond contents and floating materials. The only fundament design condition for an anaerobic pond is to make certain that methane fermentation becomes established. For sewage treatment, temperature in excess of 22 0C it is safe if the following design criteria are adopted.  volumetric loading up to 300g BOD5/m3.d and /or  hydraulic retention time of about 5 days  Assumed BOD removal of 50%  Depth between 2.5 and 5.0 meters. Anaerobic pond installations should comprise at least two units, operated in parallel, in order to permit sludge removal from one of them while the other is still in operation. Since Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

anaerobic ponds are relatively small in volume, the sludge layer builds up quickly. The volume of digested sludge accumulated in anaerobic pond may be assumed to be 40 liters per person per year.

2. Design of Facultative Ponds Facilitative ponds are usually designed on maximum 300 loads per unit area at which the pond will still have a substantial aerobic zone. The area of ponds at mid-depth is given by the equation:

A

I i * Q(10) S

Where, A = the area at mid -depth (m2) Q = the daily wastewater flow to the pond (m3 /day) Ii = the BOD of the influent (mg/l) S = the areal loading rate (kg BOD/ha.d), which varies with temperature of the area. S = 20T -120 Where T = the mean temperature of the coldest month. Facultative pond depth can vary form 1.0 m to 1.5m, which will normally be sufficient to prevent the growth of rooted plants while permitting sun light to penetrate through most of the depth. Detention time in facultative ponds range from 5 to 30 days. 3. Design of Maturation Pond Maturation ponds are designed to achieve the required bacterial removal to give the effluent the desired quality regarding pathogenic organisms. A first -order expression is employed to predict the reduction in bacterial in maturation pond.

Ne 

No (1  k b t R ) n

Where, No = influent bacteria count (per 100ml) Ne = effluent bacteria count (per 100ml) Kb = the rate constant which varies greatly with temperature and also according to the species involved (d-1) tR = retention time in days Kb (t) = kb (20)* (1.19) t- 20 Where kb (20) may be 2.6 /day for coliforms. Experimental work and practical experience shown that a minimum retention period of 5 days in a single maturation pond - Maturation ponds are usually 1.0 to 1.5 meter in depth. Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

8.4.2 Pond Shape and Configuration Irregular shapes in stabilization ponds are avoided because they are likely to cause dead spaces, short circulating and wave amplification, there by disturbing the normal functioning of the units. Rectangular ponds with length to width ratio not greater than 2:1 are used, the longer side being along the direction of the prevailing wind. Sharp corners are avoided at the intersections of embankment slope. The vertices are round of and smoothed out to foster water movement and to avoid dead spaces. The aerobic , facultative and maturation ponds are designed to be in series and each stage in series is broken down in to two ponds in parallel so that cleaning is possible with out interruption of operation. Anaerobic

Facultative

Maturation

8.4.3 Pond Location and Orientation It is recommended that the below mentioned points should be considered during appropriate site location of the ponds:  the flatter the selected area the better  free access for all winds is essential  the pond must not be exposed to flooding  future extension must be considered  the possibility of contaminating local sources of drinking water should be borne in mind  nearest dwellings should be at least 1km from the pond  It must be possible for vehicles to have access to the pond site under all seasonal conditions. If possible, the stabilization ponds should be located so that the direction of the prevailing wind is away from the nearest community, and the ponds should be oriented so that their longest dimension is parallel to that direction.

8.4.4 Stabilization Pond Appurtenances Inlets and outlets: elevated inlets are preferred to inlets at the pond bottom because:  they are free of obstruction at low flows; Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

 

better mixing and dispersion conditions of the influent are attributed to them; and visual observation of approximate flow pattern is possible from any point on the crest of the embankment The outlets are located near the base (toe) of the embankment at the opposite end to the inlet. Flow measurement: Two flow meters should be installed (one on the inlet and the other on the outlet). On the inlet a parshall flume, and on the outlet a V - notch weir. Because comparison of inlet and outlet flows will given an indication of the magnitude of evaporation, seepage or infiltration as well as diluting effect of rainfall and this comparison serves a purpose in the evaluation of pond performance. Slope lining The slope provided is a gentle slope (1/3(33%)); therefore, lining is unnecessary because waves resulting from wind friction will break on the slope and dissipate their energy gently, as on a beach, doing no harm to the embankment. However, a riprap is provided 0.5 m above and 0.5 m below normal water level in the ponds to prevent weed growth Maintenance of stabilization ponds If the waste stabilization ponds are not well maintained they will deteriorate with time and loose their usefulness. The following points are recommended regarding maintenance.  to control appearance of insects such as mosquitoes and files , grass ,water weeds and aquatic plants should be promptly cleared as soon as they appear,  Algal mates accumulating on the surface of facultative ponds should be removed as, they are likely to produce odor problems when they are decayed. The algal mats, either must be sprayed with a jet of water from a hose directed by the operator onto the floating material or they can be removed by a skimmer (if available)  The wastewater stabilization pond site must be surrounded by a so secure but open fence that keeps out intruders and straying animals but doesn‟t prevent wind access to the pond surface.  Trees should not be allowed to grow with in 150m of wastewater stabilization ponds.  Embankments should be inspected for the existence of sign of erosion, crevices, vegetation and holes dug by animal and measures must be taken.  The anaerobic ponds must be desludged every four years. Desludging can be accomplished by emptying the pond down to the top of the sludge layer and taking it out with dragline or calm shell machine.  Pond inlets and outlets should be kept clean and free from obstruction. Recommendation Industrial wastes generated from the textile, abattoir and leather factory should be pretreated to make them free of harmful, toxic materials, acids and alkalis sulfide, Cyanide, Chromium and other toxic metals. Hot fluids that weaken pipe joints and accelerate undesirable chemical reaction should be avoided. The organic load of the industrial wastes must also be reduced and kept equivalent to the municipal wastewater organic load i.e., 472 mg/l. Stabilization Ponds Design Exercise

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Lecture Notes (Water supply project planning)

Example -1. Design a stabilization pond using the following data; Forecasted population= 40,000 Average sewage flow rate =3500m3/d Per-capita BOD5 concentration = 40g/p/d Influent bacterial concentration = 2x107FC/100ml Mean minimum monthly temperature, T= 22 0C Effluent quality requirement = < 5000FC/100ml Solution

40 g / p / d * 40000  457mg / l Influent BOD5 Concentration = 3500m 3 / d Design of the ponds A) Anaerobic pond  Assume volumetric loading = 200g BOD5/m3.d 40 g / p / d * 40000 persons  8000m 3  Then volume of pond= 3 200 g / m .d  Standard sludge accumulation rate = 40l/p/year Then sludge accumulated, for a pond, which is cleaned every 3 years = 40 l/p/year *3 year*40,000pople = 4800, 000liters = 4800m3 v1 4800m 3  1.37  1.5days The required retention time tr   q 3500m 3 There fore liquid volume V2 = 2days * flow rate = 2*3500 = 7000m3 Total volume of sewage = 4800 + 7000 = 10,800m3 If we provide two ponds in parallel: Volume of single pond V2/2 = 11800/2 = 5900m3  Pond depth is 2.5 to 5.0m, take d= 4.0m  Pond area at mid depth = 5900/4 = 1475m2  Take length to width ratio(L:W) = 2:1  A = L*W =2W2 = 1475  W = 27.157  27.50m and L = 54m

B) Facultative Pond Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

 Arial loading rate , S = 20T - 120 = 20*22 -120 = 320Kg BOD /ha.d  If 50% of the BOD5 is removed in anaerobic pond, influent BOD5 to Facultative pond = 0.5*457 = 228.5mg/l I * Q(10) 228.5 * 3500 * (10)   24,992m 2  Mid depth area A  i 320 S  Depth range 1.0 to 1.50m , take 1.50m  Volume of F.P = A*D = 24992*1.50 = 37488m2  Detention time, td = V/Q = 37488/3500 = 10.711days Provide two ponds in parallel  Mid depth area, A = 24992/2 = 12496m2  L:W = 2:1 Single pond at mid depth, A = 2W2 = 12496  W = 79 and L = 158m C) Maturation Pond  Lets provide two maturation ponds in parallel with retention time of 5 days  Kb(t) = Kb(20)*(1.19)T-20, Kb = rate constant  Kb(22) =2.6*(1.19)22-20 = 3.68  3.70 No 2 *10 7 Ne    3854 FC / 100mm (1  kb t R ) n (1  3.7 *1.5)(1  3.7 *10.71)(1  3.7 * 5) 3854FC/100ml < 5000FC/100ml OK! (If Ne > 5000FC/100ml, we would modify tR)    

Volume of each pond = 3500*5/2 = 8750m3 Depth , d = 1.5m  Mid-depth area = 8750/1.5 = 5833m2 L :W = 2:1  W = 54m , L = 108m Side slope = 1/3 69m A.P 4.5m

165.5m F.P 2.0m

42m

153.5m

115.5m M.P 2.0m

103.5m

9. INTRODUCTION TO NON-WATER CARRIAGE SANITATION SYSTEMS

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Lecture Notes (Water supply project planning)

This is the oldest system by which garbage or dry refuse of a town is collected in dustbins, placed along the roads, from where it is conveyed (trucks or covered carts), once or twice a day to the points of deposal. 1. All the for filing, the noncombustible portions of garbage (sand dust clay) are used for filling the low-level areas to reclaim land for further development of town. 2. The combustible portion of garbage (dry levels, waste paper, broken furniture etc) is burnt. 3. The decayed fruits and vegetables, grass and other such things are first dried and then disposed of by burring or in the manufacture of manure (substance especially dung as fertilizer) Garbage or dry refuse of a town is collected in dust bins placed along the roads, form where it is conveyed by trucks or covered carts once or twice in a day to the points of deposal all the for filing the noncombustible portions of garbage such of sand dust clay as be etc are used for filling the low level areas to reclaim lard for Ruther development of town and combustible portion of garbage such as dry levels waste paper, broken furniture etc are burnt .the decayed fruits and vegetables , grass and other such things are first dried and then disposed of by burring or in the manufacture of manure (substance especially dung as fertilizer) Human excreta or night soil is collected separately in privies or conservancy latrines. The liquid and semi liquid wastes are collected in separate pans in same latrine, from where trey are removed through human agency and after removal night soil is taken outside the town in closed animal drawn carts, trucks and is buried in trenches. After 2 to 3 years the buried night soil is converted in to excellent manure, which can be used for growing crops. Waste Disposal in Non-Sewered Areas In case of poor countries , it is not possible to have the water carriage system in all the towns, villages and cities in the rural areas, seated localities and isolated colonies which are not served by the piped water supply, always have a shortage of water, due to which the quantity of wastewater also small . The wastewater from such areas therefore can be easily disposed be developed for the safe collection and deposal of human excreta from such areas under such circumstances. Conservancy is chosen and in such system human excreta is collected in various types of privies Sewerage system (wastewater collection and treatment) is not available for the disposal of sanitary wastes in most towns and all rural areas of our country. Therefore, privies are in use for collection and disposal of night soils. The types of privies that may be adopted are the following: Bore -hole latrines Pour- flush latrines Conventional unimproved pit latrines Ventilated improved pit latrines(VIP) Double tank latrines Septic tank latrines Aqua privy Chemical toilets Working type privy Adama Science and Technology University- Department of Civil Engineering 2011/12

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Lecture Notes (Water supply project planning)

1. Borehole Latrine    

In bore -hole latrine a hole usually not than 45 cm in diameter and 4 m deep is constricted. The hole generally penetrates in the ground water table---. This permits anaerobic digestion of faucal solids and longer use of the pit. The top the hole is ten protected by a slab with slanting foot react adjacent to a slot through which the excreta falls in the hole. The major disadvantage of a borehole latrine is pollution of the ground water.

2. Pour Flush (PF) Latrine  Such toilets comprise water latrines connected directly offset pits  Approximately1-2 liters water poured by hand to flush the excreta in to the pits.  The pit is provided with open brickwork or masonry with suitable openings for dispersion of the effluent to the surrounding subsoil. The pit, therefore, serves as a combined setting, digestion and dispersion tank.  Usually two pits are contracted in parallel so the when the first pit is full, the second pit is put in to operation, when the second pit is nearly full the first can be emptied and the toilet connected to it. A per with alternating pits can , there fore, be used indefinitely  The excavated sable humans from the pit can be applied on land as manure.  The PF may be installed inside the house since it is both from odors and fly &most nuisance. 3. Conventional Unimproved Pit Latrine  The most commonly observed technology around the world, especially rural areas is the pit larine ,  A pit latrine comprise of the pit, squatting plate, and the toilet super structure.  The pit is simply a hole dug into the ground to receive the excreta  When the pit is nearly full, the super structure and the squatting plate are removed and the pit is sealed with soil from a new pit dug nearby.  The unimproved pit latrine described above has both odor and insect problems. 4. Ventilated Improved Pit Latrine (VIP)  The undesirable features of the unimproved pit latrine can be eliminated in the VIP latrine where the external bent pipe is provided to take the foul gases.  The top of the vent pipe should be at least 30 cm above the high point of a slopping roof with a conical roof the vent pipe should extend as high as apex of the roof.  Wind passing across the top of the pipe causes an up draught, which removes bad smells. If the latrine is sited where is no wind , up draught may be encouraged buy putting the pipe on the sunny side of the latrine and painting the outside of the pipe black(unless the pipe itself is back ).air in the pipe is heated and rises.  Any fly which hatch in the pit try to move towards the light; if the superstructure is dark , the fly go towards the top of vent pipe , where , it sees day light.

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

Lecture Notes (Water supply project planning)

It should be noted that in areas where water is carried from distant water points or surface sources, the vip latrine is probably a better choice . For example, thousands of VIP latrines have been constructed in the most marginal areas of the city of Karachi, Pakistan.

5. Double Vault Composting Toilet  This latrine is principally found in vietram and some extent china ..it is particularly suited to densely populated areas where the water table high.  In double vault and the one not in use is sealed so as to create anaerobic conditions the fecal matter is composed and after a minimum sealed off period of 45 days , rendered in to a dark gray harmless, odorless ,nitrogen rich organic manure which is then removed .  Urine is prated from fecal mater by the use of channel in the floor, and around off in to a separate container.  The double viable latrine is now being promoted by un chef in Bangladesh, Burma and Egypt. 6. Aqua Privy  This is made on the similar principle as septic tank. it consists of a water tight tank and a squatting plate above it . a drop 10 cm in diameter goes into the tank below water level.  Like in the septic tank anaerobic digesting takes place with much reduction of solid volume .the effluent is passed to a seepage pit.  The capacity of the tank may be provided at the rate of 0.03 to 0.05 m3 per capita. 7. Chemical Toilet  Chemical toilet usually consists of seat attached to metal cylindrical tank in which a strong solution of caustic soda in water has been put.  The solution of caustic soda sterilizes and liquidities the excreta in the tank and requires replacement only at interval of several months.  The content of chemical toilet when emptied is liquid, sterile and practically free from odor .the discharge can be used as fertilizer.  The tank can be 74 cm in diameter and 150 cm long for one seat. And with additional 90 cm length for each extra seat. 9. Working Type Privy It consists of plat from with a centrally located hole and a squatting arrangement .under the plat from below the whole a container is placed. Excreta gets temporarily collected in the container. From there it may be collected by municipality truck and disused off.

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Lecture Notes (Water supply project planning)

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Lecture Notes (Water supply project planning)

10. WATERT SUPPLY PROJECT PLANNING 10.1 General It has been described earlier that water is required for any living. There are various purposes for which it is required. Without water human cannot survive. Everybody has to arrange water for supplying the water to the community through public tapes or individual house connections the first work is the preparation of the water supply project. The project is prepared after doing /field survey work and collecting the required data. After the preparation of the project, it is sent to the competent authority for sanction of grants for completing the project. When the grants are sanctioned, the government departments dealing with it take up the construction of the project. While planning water supply project, care is taken to insure that it should be economical and efficient scheme meeting the present as well as future requirement for a considerable time. 10.2 Collection of data During preparation of water supply project, following data are collected: a) Geological data: Geological data and survey of the ground water is done in the vicinity of the area, to know the quantity of available water at various depths in the ground. b) Hydrological data: the hydrological and the available surface water sources data in the vicinity of the area are collected to determine the quantity of water available in the surface sources. c) Sanitary conditions of the area: The sanitary conditions of the area and data regarding possible sources of water pollution are collected for deciding the preventive measures against them. d) Topography of the area: survey works have to be done to prepare the topographical map of the area, showing elevations of the various points, density of population in different zones. This map helps in deciding the positions of intake works and treatment plants, type of system to be adopted for conveyance and distribution of water. e) Legal data of lands: Legal data of the lands to be purchased or acquired for the constriction of various units of water works are collected. Legal laws on land zoning, land ownership, water rights, administrative pattern etc, should also be collected, so that the acquisition of land and collection of water may not involve legal complications and delay in the construction of the project. f)

Public opinion: data on the public options are also collected, regarding the start of the project, so that while seeking administrative approval justification can be given.

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Lecture Notes (Water supply project planning)

10.3 Factors to be considered Following factors should be considered and kept in view during of the water supply project:            

Population Per capita requirement Public services Existing water supply Sources of water Conveyance of water Quality of water Treatment works Pumping units for treated water Reservoir Distribution system Economy and reliability

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Lecture Notes (Demand for Water)

(i)

Population: factor affecting the future increase in the population are to be studied and taken into account while determining the future population for the design work. (ii) Per capita requirement: the per capita demand of water should be determined by taking into account the various given in chaptr1 (iii) Public places, parks, institution etc: water is required for the development of parks, fire – infighting and so many other purposes at public places. During preparation of water supply project a provision should be made for the same. (iv) Industries: The water requirement of telecasting industries as well as furor industries should be thoroughly determined and provision made in the project accordingly. (v) Existing water supply: For towns where the project is being made for the expansion of the existing water supply scheme the details of collection, conveyance, treatment and distribution of water should be toughly studied. The spare capacity of the existing water works should alder be utilized. (vi) Source of water: Detailed survey of the various also of water available in the vicinity of the area should be made. survey of the existing sources should also be made whether they are sufficient to meet the requirement of the future e or not .in case the present source of water is well, which cannot cater to the future needs , alternative water source should be considered ,if the flow in the available river is less, the provision of water storage by considered .if the flow in the available river is les , the provision of water storage by construction impounded reservoir should also be considered .if the river bed is sandy , collection of water through infiltration galleries may also be considered. (vii) Conveyance of water: conveyance of water from source to the water treatment units , depends on the relative levels of the two points .it may flow directly under gravity ,if source is at higher elevation .if the water works are at higher elevation ,it is required to be popped .in case the pumping is to be done ,the capacity of the pumps is to be worked out .the rising maintains should be designed . The alignment of the rising main should be such that it should not disturb any structure in the way. (viii) Quality of water: the analysis of the raw water should be made to know the various impurities present in it, and for deciding the treatment of water. (ix) Treatment works. The various sizes and number of tremens units in the water – works shall depend on the quality and quantity of raw water and the desired standard of water. (x)

(xi)

Pumping units for treated water. Number of number of pumps are installed in the pump house for meeting the present water pumping requirement with provision of 50% stand-by pumps for emergency . Additional pumps are installed as and when required. Reservoir. The entire city town should be divided into several zones and a reservoir should be divided for each zone. The height of elevated reservoirs is kept such that it can supply the water to the highest story at the required pressure. As far as possible the location of the reservoir should be at the highest point of the locality.

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Lecture Notes (Demand for Water)

(xii)

Distribution system. The distribution system should be deigned according to the master plan of the town, considering the future development. The designing of the main should be done on 2-3 times the average daily flow. The mains and submains should be laid along the roads of the town. (xiii) Economy and reliability. The water supply scheme should be economical and reliable. It should draw sufficient quantity of ware from the source at cheapest cost and the purification should be done up to desired limit.

1.

2. 3.

4.

5.

10.4 Project drawings All the required drawings of the project are prepared which should express and give all the details of various components of the project. In general the following drawing are prepared and used for estimating and execution of the project. Topographical map. The topographical map of the area showing roads, location of water sources, limit of the town along with its roads, layout of pipes from source to water works etc. is prepared on a scale of 1:500 or so. Site plan. The site plan of the town showing the location of the scheme and the area to be served is also prepared on scale of 1:500 or so. Contour map. The contour map or plan of the entire area is prepared on a scale of 1:100, showing the location of water mains , sub-mains branches, valves ,fire hydrants , pumping stations , service reservoirs ,roads ,streets etc. is prepared . The site plan and the contour plan may also be combined together. In this case the contour lines are drawn on the site itself. Flow diagrams. The flow diagram of the entire scheme is prepared showing the sequence of operations and all aspects of the scheme. The approximate sizes the sequence of operations and all aspects of the scheme. The approximate sizes of operations and all aspects of the distribution mains are also given on these diagrams. Detailed drawing. The detailed drawing of the various units and components of the scheme are prepared all the dimensions including hydraulic and structural details are given on these drawings. The sections of the mains and branches are plotted. The details of the treatment units etc. are also prepared.

10.5 Project Estimates The cost of the water supply project depends on the types of pipe, length of rising mains, type of treatments required, pumping machinery size and design of reserve distribution system etc. The cost of various parts of the water-supply schemes may be taken approximately as follows for guidance Item cost of the item expressed as percentage of the total scheme

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1. 2. 3. 4. 5. 6. 7.

pumping stations reservoirs treatments plants distribution system intake and water works buildings supply water meters and other contingencies 

Lecture Notes (Demand for Water)

18% 6% 10% 50% 2% 9% 5% ---------------------total 100%

The above percentages are for guidance, which can be used for preparation of preliminary estimate for administrative approval. The detailed drawing along with detailed estimating are prepped for the execution of the project and obtaining technical approval. The technical approval or sanction of the project estimate gives a kind of guarantee that the public money will be safely and soundly used on the project. After obtaining all the approvals and allotment of funds, the tenders are called and the work is awarded for execution to suitable agency. 10.6 project report After doing the survey work, preparing drawing and estimates of the water supply scheme, the project is written, the project report should deal with the following points; 1. introduction of the project 2. necessary of the improved, additional or new water supply scheme 3. the area of the city or town with population, industries, cattle to be served 4. the basis of calculation and allowance of water per capital 5. future provisions in the project 6. the quality and quantity of raw water available in the selected sources for the project 7. The possible additional water source which can be used in future for the expansion of the scheme. 8. Nature of the proposed water i.e. intermittent or continuous etc. 9. The method of designing the pipe sizes and the formulae used. 10. Design of all units of water works , intakes overhead service reservoirs 11. Design of disturbing system. 12. The annual cost running the pumps. 13. Recurring expenditure for running the scheme. 14. Cost of treated water ready for distribution and supply rate in per million liters. 15. Design period of the scheme 16. Environmental impact assessment etc. 17. Risk assessment. 18. Mitigation results  how to reduce the risk The project report should also include the justification for the necessity of the scheme, the economical justification for carrying out the scheme including cost - benefit Adama Science and Technology University- Department of Civil Engineering

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Lecture Notes (Demand for Water)

considerations. If there is any other proposal, its pros and cons should also be discussed. The details of the land required to be acquired should also be given in the project report.

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