December 15, 2017 | Author: Chris Quero | Category: Sewage Treatment, Wastewater, Ph, Filtration, Mole (Unit)
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Manual planta de tratamiento que tiene tecnología MBRR....







Aquatech Engineering Services Limited

GLOSSARY OF TERMS Biochemical Oxygen demand (BOD): The strength of the wastewater is often determined by measuring the amount of oxygen consumed by microorganism like bacteria in biodegrading the organic matter. The measurement is known as the Biochemical Oxygen Demand (BOD). Microorganisms such as bacteria are responsible for decomposing organic waste. When organic matter such as dead plants, leaves, grass clippings, cellulose components, manure, sewage, organic waste like dyes, fats and oils, or even food waste is present in a water supply, the bacteria will begin the process of breaking down this waste. When this happens, bacteria in aerobic process, robbing other aquatic organisms of the oxygen they need to live, consume much of the available dissolved oxygen. If there is a large quantity of organic waste in the water supply, there will also be a lot of bacteria present working to decompose this waste. In this case, the demand for oxygen will be high (due to all the bacteria) so the BOD level will be high. As the waste is consumed or dispersed through the water, BOD levels will begin to decline. Nitrogen and phosphates in a body of water can also contribute to high BOD levels. Nitrates and phosphates are plant nutrients and can cause plant life and algae to grow quickly. When plants grow quickly, they also die quickly. This contributes to the organic waste in the water, which is then decomposed by bacteria. This results in a high BOD level. The temperature of the water can also contribute to high BOD levels. For example, warmer water usually will have a higher BOD level than colder water. As water temperature increases, the rate of photosynthesis by algae and other plant life in the water also increases. When this happens, plants grow faster and also die faster. When the plants die, they fall to the bottom where they are decomposed by bacteria. The bacteria require oxygen for this process so the BOD is high at this location. Therefore, increased water temperatures will speed up bacterial decomposition and result in higher BOD levels. When BOD levels are high, dissolved oxygen (DO) levels decrease because the bacteria are consuming the oxygen that is available in the water. Since less dissolved oxygen is available in the water, fish and other aquatic organisms may not survive. Textile mill wastewater possesses a very high BOD like 400 – 600 mg/l. It is necessary to reduce this BOD value up to a level less than 30 mg/l before discharging them into the environment like canals or rivers. If a water body of high BOD is discharged into the sea or very large river then off course the concentration of BOD decreases due to dilution and have little or no harmful effect on the aquatic life or environment. Therefore if it is possible to discharge a highly toxic effluent in sea or large river no treatment is necessary. Though it was not mentioned, the dissolved oxygen (DO) is a highly significant parameter to define the BOD or COD of a wastewater. The amount of oxygen present in a certain amount of water in dissolved state is known as DO. It is normally expressed as mg/l. Water may contain DO ranging from 0 to 18 mg/l but in most cases of normal waters, DO lies between 7-9 mg/l. Aquatic lives require certain level of DO to survive in the water. In case of wastewater the microorganisms require oxygen to consume the organic wastes. As a result the DO of water decreases tremendously and becomes a threat to the life of aquatic species. Textile effluents possess very 2

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low DO, which is unsuitable for discharging to the environment. During treatment of wastewater air is blown through the effluent when oxygen is dissolved in the effluent as a result DO level raises and as the DO increases the BOD/COD decreases. Chemical Oxygen Demand (COD): This is a means of measuring the ability of wastewater to sustain aquatic life, essential for the preservation of the environment. It also enables proper assessment of treatment plant performance. Aquatic organisms and animals require dissolved oxygen to flourish. The Chemical Oxygen Demand (COD) test gives an indication of the impact of discharge waters on aquatic life by measuring the oxygen depleting nature of the discharge water. COD is based on the fact that nearly all-organic compounds can be fully oxidized to carbon dioxide with a strong oxidizing agent under acidic condition. COD is another common measure of water-borne organic substances — the process of measuring COD causes the conversion of all organic matter into carbon dioxide. For this reason, one limitation of COD is that it cannot differentiate between biologically active and those which biologically inactive. One major advantage of COD over BOD is that COD can be measured in just three hours where as BOD measurement takes at least five days. The value of COD is always higher than BOD, this is because BOD accounts for only biodegradable organic compounds while COD accounts for all organic compounds e.g. biodegradable as well as no biodegradable but chemically oxidisable. Total suspended Solids (TSS): TSS is mainly organic in nature, are visible and can be removed from the wastewater by physical/ mechanical means e.g. screening and sedimentation. TSS is measured by filtering a certain quantity of effluent and then drying the filtrate at certain temperature e.g. 1050C followed by weighing. TSS is expressed as parts per million or in milligram/litre. The pore size of the filter paper is very important in estimating the TSS, the nominal pore size 1.58 micro metre. Total Dissolved Solids (TDS): TDS are the solids that are actually in solution, similar for example to mix sugar into hot coffee. Dissolved solids generally pass through the system unaffected. TDS is the sum total of all of the dissolved things in a given body of water. It is everything in the water that's not actually water. It includes hardness, alkalinity, cyanuric acid, chlorides, bromides, sulfates, silicates, and all manner of organic compounds. Every time we add anything to the water, we are increasing its TDS. This includes not only sanitizing and pH adjusting chemicals, but also conditioner, algaecides, and tile and surface cleaners. TDS also includes airborne pollutants and bather waste as well as dissolved minerals in the fill water. TDS is referred to as the total amount of mobile charged ions, including minerals, salts or metals dissolved in a given volume of water, and is expressed in units of mg per unit volume of water (mg/L), or as parts per million (ppm). Where do Dissolved Solids come from? Some dissolved solids come from organic sources such as leaves, silt, plankton, and dyes and chemicals used in processing, sewage. Other sources come from runoff from urban areas, road salts used on street during the winter, and fertilizers and pesticides used on lawns and farms. 3

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Dissolved solids also come from inorganic materials such as rocks and air that may contain calcium bicarbonate, nitrogen, iron phosphorous, sulfur, and other minerals. Many of these materials form salts, which are compounds that contain both a metal and a nonmetal. Salts usually dissolve in water forming ions. Ions are particles that have a positive or negative charge. Water may also pick up metals such as lead or copper as they travel through pipes used to distribute water to consumers. The effectiveness of water purification systems in removing total dissolved solids will be reduced over time, so it is highly recommended to monitor the quality of a filter or membrane and replace them when required. TDS may be the most misunderstood factor in the whole field of chemical processing and public health. In most cases it is misunderstood because no one knows exactly what effect it is going to have on any particular body of water. TDS is directly related to the purity of water and the quality of water purification systems and affects everything that consumes, lives in, or uses water, whether organic or inorganic, whether for better or for worse. Different standards advise a maximum contamination level (MCL) of 500mg/liter (500 parts per million (ppm)) for TDS, however for domestic water suppliers maintain the TDS within 150 ppm. Off course some water supplies exceed this level. When TDS levels exceed 1000mg/L it is generally considered unfit for human consumption. Most often, high levels of TDS are caused by the presence of potassium, chlorides and sodium. These ions have little or no short-term effects, but toxic ions (lead arsenic, cadmium, nitrate and others) may also be dissolved in the water. At low levels, TDS does not present a problem. In fact, a certain amount of TDS is necessary for water balance. Hardness and Total Alkalinity are both part of TDS. For textile processing the acceptable value of TDS is around 65-150 mg/l. The standards for bath and swimming pool are between 1,000 and 2,000 ppm, with a maximum of 3,000 ppm. For irrigation the acceptable values of TDS are around 1500 ppm. Use of fertilizers increases TDS of the environment. When the water evaporates, it leaves behind all of the solids that had been dissolved in it. This principle is used widely to measure the TDS of a particular body of water. When everything else seems to be all right, and the water still acts unlawfully, check the TDS. High TDS can result in corrosion of metal equipment and accessories, even though the water is balanced. High TDS can cause eye and skin irritation, even though the pH is right and there are no chloramines in the water. High TDS can permit an algae bloom, even with 2-3 ppm chlorine residual. If we drink water of high TDS some of this will stay in the body, causing stiffness in the joints, hardening of the arteries, kidney stones, gall stones and blockages of arteries, microscopic capillaries and other passages in which liquids flow through our entire body.


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Microorganisms - Microscopic living objects, which require energy, carbon and small amounts of inorganic elements to grow and multiply. They get these requirements from the wastewater and the sun, and in doing so help to remove the pollutants. pH – A term used to express the intensity of the acid or alkalinity source. pH represents the effective concentration (activity) of hydrogen ions (H+) in water. This concentration could be expressed in the same kind of units as other dissolved species, but H+ concentrations are much smaller than other species in most waters. The activity of hydrogen ions can be expressed most conveniently in logarithmic units. pH is defined as the negative logarithm of the activity of H+ ions: pH = -log [H+] where [H+] is the concentration of H+ ions in moles per liter (a mole is a unit of measurement, equal to 6.022 x 1023 atoms). Because H+ ions associate with water molecules to form hydronium (H3O+) ions, pH is often expressed in terms of the concentration of hydronium ions. In pure water at 22 C (72 F), H3O+ and hydroxyl (OH-) ions exist in equal quantities; the concentration of each is 1.0 x 10-7 moles per liter (mol/L). Therefore, pH of pure water = -log (1.0 x 10-7) = -(-7.00) = 7.00. Because pH is defined as –log [H+], pH decreases as [H+] increases (which will happen if acid is added to the water). Since pH is a log scale based on 10, the pH changes by 1 for every power of 10 changes in [H+]. A solution of pH 3 has an H+ concentration 10 times that of a solution of pH 4. The pH scale ranges from 0 to 14. However, pH values less than 0 and greater than 14 have been observed in very rare concentrated solutions. The U.S. Environmental Protection Agency (U.S. EPA) sets a secondary standard for pH levels in drinking water: the water should be between pH 6.5 and 8.5. Very high (greater than 9.5) or very low (less than 4.5) pH values are unsuitable for most aquatic organisms. Young fish and immature stages of aquatic insects are extremely sensitive to pH levels below 5 and may die at these low pH values. High pH levels (9-14) can harm fish by denaturing cellular membranes. Changes in pH can also affect aquatic life indirectly by altering other aspects of water chemistry. Low pH levels accelerate the release of metals from rocks or sediments in the stream. These metals can affect a fish’s metabolism and the fish’s ability to take water in through the gills, and can kill fish fry. The term "pH" was originally derived from the French term "pouvoir hydrogène," in English, this means "hydrogen power." The term pH is always written with a lower case p and an upper case H. Sludge-The settable solids separated from the liquid during sedimentation (clarification). The sludge is very toxic in nature and needs to be dealt with very carefully. Under no circumstances it should be mix with the environment again.


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1. INTRODUCTION Aquatech Engineering Services, Dhaka, have prepared this operating and maintenance manual for the Effluent treatment plant installed at ……………………., Chandora, Kaliakoir, Gazipur. It represents the methodology of process operation of the effluent treatment plant and maintenance of the plant equipments. The manual will be helpful to run the effluent plant effectively and efficiently. Every effluent treatment plant is unique with respect to its process flow sheet. This is because the treatment scheme is adopted on the basis of design and input characteristics of the effluent as well as the stipulated pollution level of the treatment. This in turn depends on the type of process, type of generated waste, whether the treated waste will be discharged or recycled, the nature of water receiving body where the treated waste will be discharged (if any) and the pollution laws of the concerned pollution authority. It must therefore be appreciated that effluent treatment plants are tailor- made, and hence the mode of operation would be specific for the treatment envisaged. The operating manual serves as an important guideline for the operating personnel responsible for the start- up and maintenance of the equipment and facilities provided in the plant. The instruction presents in this manual are based on the experience in operation of such plants. However, due to variable nature of the effluents encountered in each plant, certain modification of process operation may be necessary depending on the degree of variation in the raw effluent quality and quantity. This manual includes a brief description of the basis of design of the ETP, the adopted treatment philosophy and the principles of treatment involved. The plant was designed to treat effluents generated from the various sections of the knit fabric dyeing and finishing plant. The scheme envisages treatment of two separate wastewater streams namely the less contaminated water and more contaminated water. The less contaminated effluents are allowed to bypass many stages before uniting together again with mainstream and finally discharged to the environment. This has been done deliberately to reduce the treatment time and operating cost.


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2. Basics of effluent treatment Environmental problems of the textile industry are mainly caused by discharges of wastewater. Textile processing employs a variety of chemicals, depending on the nature of the raw material and end product. Some of these chemicals are different enzymes, detergents, dyes, acids, sodas and salts. Industrial processes generate wastewater containing heavy metal contaminants. Since most of the heavy metals are non-degradable into non-toxic end products, their concentrations must be reduced to acceptable levels before discharging them into the environment. Other wise these could pose threats to public health and/or affect the aesthetic quality of portable water. According to World Health Organization (WHO) the metals of most immediate concern are chromium, zinc, iron, mercury and lead. Various types of treatment processes are adopted to dye or print or finish the textile materials. Different types of textile process could generate different types of effluent. Table 1.1 shows the Characteristics of wastewater produced by a typical knit dyeing industry. Table 1.1: Characteristics of Process Waste Streams of Knit dyeing and finishing.


Processing Unit

Possible pollutants in the waste water

Waste water volume



NaOH,,Waxes, grease Na2Co3, Na2O2, SiO2 And fragments of cloth.

Small 10 L/ kg of cloth



NaOCl, Cl2, NaOH, H2O2, Acids etc.

Mostly washing






Various dyes, salts, alkalies, Acids, Na2S,Na2S2O2 and soap etc. Different finishing agent,

Very small

Nature of waste Water Strongly alkaline, dark color, high BOD (30% of total) Alkaline constitutes, approx 5 % of BOD Strongly colored, fairly BOD (6 % of the total) Low BOD

The above table shows the detail discharges at various stages of processing, however the overall discharges of a Knit Dye house are as follows; Color (organic substance), Na2 SO 4 (inorganic), NaOH, NaHOCl (Sodium hypochlorite), Na2 SO 3, Surfactant (LAS, BIAS, CIAS), (NH)3 SO4, H2O2,CH3COOH (Organic), paraffin (organic), Cellulose, Oil (Organic), Soap (Organic); all these things are COD and BOD. The fate of the above mentioned pollutant chemicals vary, ranging from 100% retention on the fabric to 100% discharge with the effluent. Generally, a wet processing industry generates wastewater possessing various level of toxicity. Textile finishing industry uses large amounts of 7

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water, mainly because of washing operations. If these wastewaters are discharged into the environment they will cause serious and harmful impact not only on under ground and surface water bodies and land in the surrounding area but also will have an adverse effect on the aquatic ecological system. Effluents from textile mills also contain various types of metals, which has a cumulative effect, and higher possibilities for entering into the food chain and may cause various types serious diseases. Due to usage of dyes and chemicals, effluents are dark in colour, which increases the turbidity of water body. This in turn hampers the photosynthesis process, causing the death of many aquatic plants. If aquatic dyes then more oxygen will be required to consume them by bacteria thus causing a reduction of dissolve oxygen in the water. Various types of dyes are used in dyeing of various types of textiles fibres. Fixation capability of different dyes is different. The higher the fixation capacity the lower is the pollution problem. Table 1.2 shows the quantity of unfixed dyes and pollutants of various colouration processes while table 1.3 shows the degree of fixation of various dyes.

Table 1.2: Type of pollution associated with various coloration processes. Fibre Cotton

Dyes Class Direct Dyes


Reactive Dyes


Vats Dyes



Sulphurs Dyes

Disperse Dyes

Type of pollution 1. 2. 3. 1. 2. 3. 1. 2. 3. 1. 2. 3. 4. 1. 2. 3.


Salts Unfixed dye (5 – 30 %) Copper salts, Cationic-fixing agents. Salts Alkali Unfixed dye (10 –40 %) Alkali Oxidizing agents Reducing agents Alkali Oxidizing agent Reducing agent Unfixed dye (20 –40 %) Reducing agent Organic acid Unfixed dye (5 – 20 %

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Table 1.3: Degree of fixation of various dyes. Class of dye Sulphur Vat Azoic Reactive Disperse Pigment 1:2 Metal Complex Dyes on wood Basic Acid

Degree of fixation (%) 60-70 80-95 90-95 50-80 80-92 99 95-99 97-98 80-93

The pollution level of textile wastewater is expressed in terms of BOD, COD, TSS, TDS, heavy metals and also temperature of the discharging effluent. At higher temperature the rate of transfer of gaseous oxygen into dissolved oxygen is reduced on the other hand at high temperature the activities of various aquatic species increases so that they require greater amount of oxygen. Thus at high temperature the demand of oxygen increases while its supply decreases. Various types of dyes and chemicals are used in textile wet processing industry. The pollution capabilities of different chemicals are different. Some are highly polluted while some are less polluted. Table 1.4 shows the pollution capability of various types of dyes and chemicals in textile wet processing.

Table 1.4: Pollution capability of some of the chemicals/ products used in the Textile Industry. General Chemical Type

Difficulty of Treatment

Alkalies, Mineral acids Oxidizing agents Starch sizes, Vegetable oils, fats and waxes Biodegradable surfactants, Organic acids Reducing agents Dyes and fluorescent brighteners Fibres and polymeric impurities Polyacrylate sizes, Synthetic polymer finishes, Silicones Wool grease, PVA sizes, Starch ether and esters, Mineral oil, Surfactants resistant to biodegradation, Anionic and nonionic softeners. Formaldehyde and methylol reactants Chlorinated solvents and carriers 9

Pollution Category

Relatively harmless. Inorganic pollutants.


Readily biodegradable.


Dyes and polymers, Difficult to biodegrade. 3 Difficult to biodegrade, Moderate BOD. Unsuitable conventional

4 for

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Cationic retarders and softeners Biocides Sequestering agents, Heavy metal salts

biological treatment, negligible BOD.


The level of the polluting parameters is very high in textile mill wastewater as compared to the their acceptable values recommended by the Department of Environment, Government of Peoples Republic of Bangladesh (GOB). Off course the acceptable level of the pollutants varies somewhat form country-to-country and even within the country. The main reason for this is the wastewaterreceiving environment. If the effluent is discharged into a very big river or sea in that case vary little or no treatment is necessary as the wastewater will have very little or no effect on such a large water body. However if the same effluent is discharged into a small river or canal in that case off course it will be necessary to treat the wastewater since the effluent will have significant effect on the receiving water. Table 1.5 shows the values of the important pollutants found in the wastewater of the ……………… Apparels Limited Table 1.6 shows the acceptable values of the above pollutants of wastewater suggested by the Department of Environment, GOB. It will be seen in table 1.5, that reference has been made about a range rather than a particular value of the parameters. This is because the characteristics of textile wastewater are not always same which is due to the variation of raw materials, dyes and chemicals etc. For example a factory sometime process 100% cotton and sometime process 50/50 cotton & polyester blend or even 100 % polyester. The three different cases will require different dyes and chemicals. For white goods no dyes are used at all, in that case the effluent characteristics will be different from that of dyed effluent. For sized fabrics the effluent characteristics will be different from that of knit fabrics. The values shown in table 1.5 are presented from our long time experience about the effluent characteristics of similar plants. The ETP is designed in a such a way so that if the your factory changes the processing nature to some other products, even then the etp will be able to handle the treatment efficiency without any problem.


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Hydraulic diagram of the plant


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3. Basis of the Plant Design 3.1 Source The raw effluent shall be discharge to the proposed effluent treatment plant from the dyeing and finishing section of the ……………..Apparels Limited. 3.2 Quantity The quantity of effluent to be treated shall be of the order of = 960 m3 / day. 3.3 Capacity of the Effluent Treatment Plant (ETP). The effluent treatment plant has been designed on the basis of the following • • • • •

Dyeing capacity is 10,000 kg /day Contaminated effluent is 50% Less Contaminated effluent is 50% Operated continuously for 18 hours a day. Flow rate of treatment envisaged is 30 m3 / hr.

3.4 Inlet Effluent Characteristics Sl.No Parameters 1 2 3 4 5 6 7 8




mg/L mg/L mg/L mg/L mg/L Co-pt unit 0 C

8 –14 400 - 600 800 - 1,200 200 - 500 3,000 - 6,000 30 – 60 Dark Mixed 600 C

3.5 Outlet Effluent Characteristics-Bangladesh Standard Sl. No. 1 2 3 4 5 6 7 8

Water quality parameters PH BOD COD TSS TDS Oil & Grease Color Temperature

Unit ---mg/L mg/L mg/L mg/L mg/L Co-pt unit 0 C

Standard value for discharging into * Inland river On land for irrigation 6-9 6-9
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