MS 1228 1991 -

MS ISO/IEC TR 10037 : 1995

MALAYSIAN

STANDARD

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MS 1228 : 1991 ICS 91.140.80

CODE OF PRACTICE FOR DESIGN AND INSTALLATION OF SEWERAGE SYSTEMS

STANDARDS & INDUSTRIAL RESEARCH INSTITUTE OF MALAYSIA © Copyright 1

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©

SIRIM. No part of this publication may be photocopied or otherwise reproduced without the prior permission in writing of SIRIM

MS 1228

This Malaysian Standard,

which had been approved by

the Building and

Ci’

1991

il Engineering

Industry Standards Committee and endorsed by the Council of the Standards and Industrial Research Institute of Malaysia (SIRIM) was published under the authorit\ of the SIRIM Coun~ii in July, 1991.

S1RIM wishes to draw attention to the fact that this Malaysian Standard does not purport to include all the necessary provisions of a contract.

The Malaysian Standards are subject to periodical review to Leep abreast of’ progress in the industries concerned. Suggestions for improvements will be recorded and in due course brought to the. notice of the Committees charged with the revision of the standards to which they refer.

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The following references relate to the work on this standard: Committee reference

: SIRIM 491/1 1—I

Draft for comment

: Dl 13 (ISC D)

Amendments issued since publication

Arnd.

No.

Date of issue

Text affected

MS 1228 : 1991

CONTENTS

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Page Committee representation

3

Foreword

4

1

General

5

2

Materials

10

3

Design flow and organic loadings

12

4

Sewer and appurtenances

14

5

Sewage pumping stations

21

6

Treatment works

27

7

Disposal of sewage and treated effluent

52

8

Treatment and disposal of sludge

55

1

Equivalent populations

13

2

Design criteria for aerated lagoons

43

3

Common parameters and operating characteristics of single-stage activated sludge system

47

Sludge Loading Rate

62

Tables

4

Appendx A List of references

66

Figures Typical diagram for manhole and inspection chamber

67-74

2

Typical installation of automatic connecting type submersible pump

75

3

Typical diagrams for septic tank

76-77

4

Typical view of a sedimentation tank

78

5

Fixed film media

79

6

Suspended film media

80

2

MS 1228

1991

Committee representation The Building and Civil Engineering Industry Standards Committee under whose supervision this Malaysian Standard was prepared, comprises representatives from the following Government Ministries, trade, commerce and manufacturer associations and scientific and professional bodies. Master Builders’ Association Malaysian Institute of Architects Ministry of Works and Utilities (Public Works Department) Ministry of Housing and Local Government (Housing Division) Institution of Engineers, Malaysia Universiti Teknologi Malaysia Association of Consulting Engineers (Malaysia) Chartered Institute of Building (Malaysia)

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The Technical Committee representatives:

on Building

Services

which

prepared this Malaysian

Standard

consists

of the following

Ir Sugunan Pillay (Chairman)

Bhg. Perkhidmatan }Cejuruteraan Kementerian Kesihotan

Ir. Tan Boo Ir. K. Rishyakaran

Bhg. Perkhidmatan Kejuruteraan Kementerian Kesihatan

Ir. Kazal Sinha Ir. Zulkifli Yahya Ir. Ong Soon Haw

Bhg. Kerajaan Tempatan Kementerian Perumahan dan Kerajaan Tempatan

Ii’. Omar Mohd Yusof/ Ir. Shamsinar Samad/ Ir. Hasnan Hassan

Jabatan Perumahan Negara

Encik Mohsin Ali Rahman

.labatan Bangunan, Institut Tekno}ogi MARA

Encik Ahmad Najuib/ Puan Mariana Mohd Nor

Jabatan Alam Sekitar

Ir. Tee Tong Kher

Persatuan Jurutera Perunding Malaysia

Ir. S. Sivarajah

Majlis Perbandaran lpoh (MPI)

Ir. CD. Ponniah

MINCONSULTANT Bhd.

Encik Eric Baxendale

PAM

Ir. Mahesan Kandiah/ lr. C. Balasundran

Bahagian Perparitan dan Pembentungan Dewan Bandaraya Kuala Lumpur

Encik Ali Maidin/ Puan Mariani Mohammad (Secretary)

Standards and Industrial Research Institute of Malaysia

MS 1228 : 1991

FORE ‘WORD

This

Malaysian Standard Code of Practice was prepared by the Technical Committee on Building

Ser’ices under the authority of the Building and Civil Engineering industry Standards Committee.

In the past, pit privies. conservancy systems and septic tank system were considered satisfactory methods for the disposal of excreta.

However,

numerous studies have indicated thai these

methods. without further treatment of the effluents and sludge hazard.

A

can be an environmental health

number of epidemics of cholera, typhoid. gastroenteritis. infectious hepatitis and the

like have been closely linked with water supply and contaminated with excreta. Furthermore these systems were not designed to receive sullage which were discharged to surface drains with no treatment and were the only practicable means for disposal of sewage in rural areas where the Licensed to Wan Roselan Mustapha / Purchased on 12-July-2007 / Single user license only, copying and networking prohibited

density of population is low.

The provision of a sewerage system to collect and convey all wastewater to a convenient point where the wastewater can be treated prior to disposal is very necessary to protect the environment and the health of the people in general. This code of practice deals with planning, design. installation and testing,

which includes the appurtenances,

sewage pumping stations.

sewage

treatment works, sludge treatment and disposal of effluent. It is intended for use by the design engineer in the planning and the design of sewerage systems, and by the relevant approving authority for the vetting and evaluation of designs, plans and specifications for such works. While this code provides standards/specifications for those experienced in design. it is also recognised that not all sewerage works are designed by such persons. It is, therefore, strongly recommended that

specialist advice be sought where appropriate,

particularly in the design of the sewage

treatment works.

In the preparation of this code, references have been made to various internationally accepted codes of practice and standards, adapting them to local conditions. Considerable assistance and valuable advice have also been derived from a panel of experts and such assistance is hereby ac know ledged.

4

MS 1228: 1991

CODE OF PRACTICE FOR DESIGN AND INSTALLATION OF SEWERAGE SYSTEMS

SECTION 1. GENERAL 1.1 Scope. This code of practice deals with the planning design, construction and installation and testing, of sewerage system, which includes the sewers and sewer appurtenances, sewage pumping stations, sewage treatment works, and all the other works necessary to collect.

convey, treat, and finally dispose domestic sewage and permitted amount of industrial wastewater. This code does not deal with the treatment of industrial effluents (those not permitted to be discharged into the sewerage system) and operation and maintenance. This code is intended to indicate what is considered to be the minimum requirements for the design of sewerage systems and good practices, under normal conditions. However, it is also realised that in certain localities and/or circumstances, there may be special conditions which may Licensed to Wan Roselan Mustapha / Purchased on 12-July-2007 / Single user license only, copying and networking prohibited

require modification to the minimum requirements laid down in this code.

This Code’s recommendations should be supplemented as required by skilled engineering advice based on knowledge of sewerage work practices and of local conditions. 1 .2

Fundamental considerations

1.2.11 Legislations. The existing legislations that affect the provisions under this Code, and that affect the rights and duties of the Local Authorities, who are the final approving authorities of all plans pertaining to sewerage systems, include the following: (a) Local Government Act, 1976. (b) Streets, Drainage and Building Act, 1974: (i) Uniform Building By-laws, 1984. (ii) Drainage, Sanitation and Sanitary Plumbing By-laws, 1976. (c)

Environmental Quality Act, 1974. (i) Environmental Quality (Sewage and Industrial Effluents) Regulations, 1979 PU. (A) 12/79 (ii) Environmental Quality (Clean Air) Regulations, 1978.-PU. (A) 28078 (iii) Environmental Quality (Prescribed Activities) (Environmental Impact Assessment) Order 1987. -

(d) Town and Country Planning Act, 1976. (e)

Factories and Machinery Act. 1967.

(I’)

Electrical Inspectorate Act, 1984.

)

MS 1228 :1991

1.2.2 Safely. sewerage systems pumping station, necessary against

Full consideration shall be given to the safety of the public and operators of in the planning, design and construction of such system. The treatment works. sewer and sewer appurtenances shall be adequately protected and located where unauthorised interference and potential accidents.

Attention is also drawn to the provisions of the Factories and Machinery Act. 1967, with regards to the safety requirements for operators in sewers and sewage works. Reference can be made to the Health and Safety Guidelines No. 2 ‘Safe National Joint Health and Safety Committee for the Water Service, National Water Council. England 1969’ and occupational health and physical safety in the Wastewater Treatment Plant Design by a joint committee of the Water Pollution Control Federation and American Society of Civil Engineers. -

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1.2.3 Location of facilities. All sewer and sewer appurtenances, pumping stations and sewage treatment works shall be located as far from the public right-of-way and habitable buildings as economically practicable. The direction of prevailing winds shall be considered when siting the sewage treatment works. Generally, unless required otherwise by the prevailing~local conditions, the sewage treatment works and pumping station shall be at least 20 m away from any habitable building. For works where noise, odour, aerosols, etc. is a factor the distance should be increased. Location of the final discharge point for treated effluent from sewerage treatment works shall also consider beneficial users of the receiving water course.

Good all weather access roads shall be provided to the sewer appurtenances, pumping stations and sewage treatment works. 1 .2.4

Access.

1 .2.5 Industrial wassewarer. Industrial wastewaters require pretreatment prior to discharge into the sewerage system. Pretreatment is necessary to reduce toxic substances and other materials that may interfere with the normal operation of the sewerage system or may pose a risk to sewage system workers. The stipulation of the pretreatment standard for the discharge of Industrial effluent into the sewerage system is the responsibility of the respective local authority. The Sixth Schedule of the Environmental Quality (Sewage and industrial Effluents) Regulations, 1979 P.U.(A) 12/79, may be used as a guide for discharge of pretreated industrial wastewater into sewerage systems. -

In addition to this, industrial wastewaters shall not contain any of the following: (a) Any liquid, solid or gases, which by itself or in combination with other substances, and which by reason of its quantity is likely or is sufficient to cause fire, explosion or to cause damage to any component of the sewerage system, or be a health hazard or otherwise objectionable, or prevents the entry into the system by the maintenance/repair workers; (b) Any radioactive substances; and (c) Any substances liable to form a viscous or solid coating or deposition on any part of the sewerage system, thereby affecting the performance of the system. 1.3 References. The titles of publications referred to and other standards of interest in this field is given in appendix A. 1 .4

Definitions. For the purpose of this code of practice the following definitions apply:-

1 .4.1

Activated sludge.

aerated. 6

A flocculent microbial mass, produced when sewage is continuosly

MS 1228 : 1991

(g)

particulars of potential outfall location, e.g. tidal or inland waters, rivers, streams, ditches or

soakage, also the proximity, highest known flood level and minimum flow of any stream or other watercourse to which discharge of the effluent is possible; (h) conditions under which the works will be normally operate and be maintained;

(j)

possibility of the need for future extension of the works or of their elimination by a comprehensive scheme; (k) availability of electric power and mains water;

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(m) facilities for eventual disposal of sludge and screenings.

9

MS 1228 : 1991

SECTION 2. MATERIALS 2.] General. All materials used in the construction of any of the works described in this code should comply with the relevant Malaysian Standards. \Vhere no Malaysian Standard exists, materials should be suitable and adequate for the purpose for which they are used and comply with any acceptable international standard. Aggregates. All aggregates shall comply to MS 29* and MS 30**. The grading of the aggregates shall comply to the requirements stated in MS 522:Part it 2.2

2.3 Cement. Cement used for works included in this code should comply with the requirements of MS 522:Part l~and MS l037~. Other type of cement can be used with the prior approval by the relevant authorities.

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2.4 Cement mortar. Cement mortar selection of the correct cement and aggregate for the use in mortars should follow the recommendations of 2.2 and 2.3. A mortar mix having a 1:3 cement/sand ratio is suitable for the following purposes: (i)

brickwork plastering;

(ii)

jointing clay or concrete pipes where flexible joints cannot be used;

(iii)

rendering of inverts and benchings;

(iv)

bedding and haunching manhole covers and frames.

Calcium chloride should not be added to mortars. 2.5

Bricks.

All bricks shall comply to MS 76~and MS 327ss.

2.6

Concrete

2.6.1

General. Concrete works should be in accordance with MS 1 l95:Part l.# All concrete surfaces subjected to acid attack and corrosion should be treated and lined with epoxy or other treatments or constructed with sulphate—resisting cement.. 2.6.2 Adniixiures. Admixtures for promoting workability, for improving strength, for entraining air or for any other purpose should be used only with the prior approval of the relevant authority. Admixtures shall comply with MS 922:Pari 1

MS 29

-

Specification for coarse and fine aggregates from natural sources.

MS 30

-

Methods for sampling and Testing of Mineral Aggregates (Sands and Fillers).

MS 522:Part 1 +

MS 1037 MS 76 MS ~27

-

-

10

Portland Cement.

Specification for bricks and blocks of fire brickearth or shale.

-

Specification for refractory bricks

MS 1195:Part 1 construction. MS 922:Part 1 Admixtures.

Specification of Portland Cement (Ordinary and Rapid-Hardening)

Specification for Sulphate-Resisting

Malaysian Standard Structural Use of Concrete. Part 1:Code of Practice for design and

-

-

Specification

of Concrete Admixtures.

Part

1:Accelerating

Admixtures

and

Water-reducing

\lS 1228: 1991

Calcium chloride as a admixture should not be used in reinforced concrete. prestressed concrete or any concrete made from sulphate-resisting Portland cement. For guidance, reference should be made to MSll95. 2.6.3 Workmanship. Concrete should be mixed in a mechanical mixer until there is a uniform distribution of the materials and the mix is uniform in colour. It should be transported to the

point of placing as rapidly as practicable by methods that will prevent segregation or the loss of any of the ingredients, placed as soon as possible and thoroughly compacted by rodding, tamping or vibration so as to form a void free mass around any reinforcement and into the corners of the

formwork or excavation. Exposed concrete should be cured by keeping at least four days.

it

in a damp condition for

2.7 Plastics. All pipes and fittings should comply with the relevant Malaysian Standards and where practicable should have flexible joints. New plastic products can be used with the prior approval by the relevant authorities.

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2.8 Others. Other materials which are not mention in this code can be used with the prior approval by the relevant authorities and where possible it should comply with all the Malaysian Standard.

MS 1228 : 1991

SECTION 3.

DESIGN FLOW AND ORGANIC LOADINGS

3:1 General. Sewerage systems shall be designed for the estimated ultimate contributary population, except when considering parts of the system that can be readily increased in capacity. The design flow and organic loading shall be estimated on the basis of the estimated contributary population and shall include infiltration flows allowances. 3.2 person.

Average design flow.

The average daily design flow shall be based on 225 litre per

3.3 Design organic loadings. The organic loading from domestic sewage shall be normally based on 55 g of BOD (5 days at 20°C) per person per day, and 68 g of suspended solids per person per day. When existing system is being upgraded, the design of the new facilities shall be based on actual strength of the wastewater flow. Where industrial wastewater is permitted into the sewerage systems. the loadings shall be based on the permissible levels described under the Environmental Quality (Sewage and lndustrial Effluents) Regulations,1979 P.U.(A) 12/79.

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-

3.4 Estimation of sewage flows and organic loading from various premises. The average design daily flow may be estimated from a given premises can be determined by multiplying the estimated equivalent population for that premise by the average daily flow per capita given in 3.2. The equivalent population for the various types of premises given in table I can be used as the minimum, for the purpose of computing the average design daily flows. 3.5 Industrial wastewater. Where industrial wastewater is permitted into a sewerage system, the design flows shall be based on the minimum requirements given in table 2. 3.6 Peak flows. The peak hourly flow, which will required in the design of sewers, pumping stations and components of the treatment plant, shall be determined from the following form ula: Peak flow factor

=

4.7 x

where p is estimated equivalent population, in thousand. 3.7

Infiltration.

While the sewerage system shall be designed cater for unavoidable amount

of infiltration, which arises from faulty joints, cracked sewer pipes and manholes, it is absolutely important that the infiltration into the sewerage system be minimised through proper selection of construction technology and materials, proper supervision of Construction and field testing of the components of system for water—tightness. For guidance, the sewerage system may be designed to cater for a maximum infiltration rate of 50 litre per mm. diameter per km of sewer per day. 3.8 The industrial wastewater flow for light industries including flatted shall be 20 m3 per hectare/day. Other category of industry will be gauge by case basis.

12

factories

MS 1228: 1991

Table 1. Equivalent population No.

Type of Premise/Establishment

Population equivalent (recommended)

Residential

5 per unit*

Commercial: (includes entertainment/recreational centres, restaurants, cafeteria, theatres)

3 per 100 m gross area

Schools/Educational Institutions: -

Day schools/institutions

0.2 per student

—

Fully residential

I per student

-

Partial residential

0.2 per student for non-residential student and 1 per student for

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residential student 4

Hospitals

4 per bed

D

Hotels (with dining and laundry facilities)

4 per room

6

Factories (excluding process wastes)

0.3 per staff

7

Market (wet type)

3 per stall

8

Petrol kiosks/Service stations

18 per service bay

9

Bus terminal

4 per bus bay

‘1 peak flow is equivalent to 225 I/cap

3

MS 1228 : 1991

SECTION 4. SEWER AND APPURTENANCES 4.1 General. Sanitary sewers shall be designed and installed to collect and convey all waste flows both domestic(municipal) wastes and industrial wastes (should be approved by the approving authority) as well as an unavoidable amount of the ground water infiltration to a point of acceptable treatment and ultimate discharge. Rain water from roofs, streets, and other areas and ground water from foundation drains shall be excluded. -

4.2

Pipe Materials for gravity sewers

4.2.1 Choice of materials. Various pipe materials are available and selection should be based on evaluation of the following factors:(a)

Life expectancy

(b) Previous local experience (c)

Resistance to internal and external corrosion and abrasion

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(d) Roughness coefficient (e)

Structural strength

(f)

Cost of supply, transport and ease of installation

(g) Local availability 4.2.2

Ti’pes of pipe material. Common material suitable for sanitary sewers are:-

(a) Vitrified clay pipe (1/C?). Available locally and are manufactured with flexible joints in lengths of 0.6 m to 1.0 m or more and diameter of 100 mm to 300 mm. (b) Reinforced concrete pipe. Available locally in sizes ranging from 150 mm to 3000 mm in diameter. Standard length are 1.83 m for pipe diameter less than 375 mm and lengths of 3.05 in for pipe diameter greater than 375 mm. Several pipe joints are available including the spigot and socket type with rubber rings. (c) Fabricated steel with suiphates resistance cement lining. Available in a wide range of diameter (100 mm to 1500 mm) and lengths up to 9.0 m. Several pipe joints are available such as spigot and socket, flange and mechanical which are commonly used for small diameters up to 750 mm whilst welded joints are used for larger diameter pipes. (d) Cast iron. Available in a variety of diameters and the standard length of 3.66 m. commonly used include both the flanged and the spigot and socket types.

Pipe joints

(e) Asbestos cement pipe. The available pipe diameters range from 100 mm to 600 mm and the standard length is 4.0 rn. Pressure pipes are manufactured in various classes suitable for certain limits of working pressure. Gravity sewers (autociaved only) are manufactured to Suit various loading conditions and required crushing strengths. (f) Plastic pipes. Available in variety of plastics materials such as UPVC. HDPE, PE and PP and with the nominal range from 110 mm up to 630 mm and of pipe length of 6 m. Pipe joints are available including spigot end and socket type with rubber seals as well as jointing by flanges. welding and solvent cementing. (g) Other material. As approved and permitted for their use by the appropriate local authority. 14

MS 1228 : 1991

4.3

Design of sewers

4.3.1

Economy in the design.

While sewers should generally be kept as short as possible, and

unproductive lengths avoided, care should be taken not to restrict potential development. The route and depth of a new sewer should always take account of land where there is the possibility of future development. Where sewers are laid at considerable depths or under highways having expensive foundations and surfaces, it may be cheaper or more convenient to lay shallow rider sewers to receive the local house connections, and to connect the riders at convenient points into the main sewers. 4.3.2 Location of sewers. Adequate access to a sewer for maintenance should be allowed. The following factors should also be considered:-

(a) Location of sewers within streets or alleys right-of-way. (b) if topography dictates, the sewer to be located within the private properties, then adequate access should be provided for maintenance purposes.

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(c) The position of other exsisting or proposed services, building foundation, etc. (d) In relation to water mains, a minimum at 3 m horizontal and 1 m vertical separation respectively to be provided. No sewer line should be above water main unless the pipe is adequately protected. (e) The impact of the construction of the sewer and subsequent maintenance activities upon road users. 4.3.3 Hydraulic design. The most economical design for sewer gradients is obtained when they follow the natural falls of the ground. Sewers should, however, be laid at such gradients as will produce velocities sufficiently high to prevent the deposition of solid matter in the invert. The minimum gradient to be adopted should normally be such that the velocity of flow does not fall

below 0.8 rn/sec at full bore. The maximum gradient to be adopted should be such that the velocity of flow is not greater than 4.0 m/sec when flowing half or full bore in order to prevent scouring of sewer by erosive action of suspended matter. 4.3.4

Structural design

4.3.4.1 Depths of sewers. Sewers should be laid at depths which will accommodate not only all existing properties but also any future properties likely to be erected within the area which the

sewers are designed to serve; in certain cases, the depth of basements may need to be considered. The depth of a sewer will have a significant effect on the cost of its construction. The depth, in conjunction with other factors such as the nature of the ground, presence of groundwater and the proximity of foundations, services etc, may influence the form and method of construction to justify the adoption of alternative layouts with longer routes of sewers. The minimum depth of invert to be adopted shall be 1 .2 m. 4.3.4.2

Size

of sewers. The minimum size of a gravity sewer conveying raw sewage shall be

200 mm in diameter. 15

~vlS1228 : 1991

4.3.4.3 Sewer alignment. Sewers of 600 mm or less in internal diameter shall be laid on a straight alignment and uniform gradient between consecutive manholes. Sewers of larger than 600 mm internal diameters can be laid on curves. In such cases, the curve shall be made by angling the joints by not exceeding 80°/o of the manufacturers recommended deflection angle and the radius of curvature shall not be less than 60 m. The designer shall provide information such as vertical and horizontal alignment for proper construction. 4.3.4.4 Joints. Joints between sewers, sewer-manhole or other appurtenance structures shall be of flexible type and watertight to prevent infiltration and breakages due to differential settlement. 4.3.4.5 Foundation. Foundation is needed to maintain the pipe in proper alignment and sustain the weight of soil above the sewer and any superimposed load.

Bedding for rigid pipes with flexible joints can be classified under two types:(a) Class ~A’ bedding. Where the pipe is embedded in carefully prepared base compacted with 15 mm diameter crusher run extending halfway up to the side of the pipe. The minimum thickness of the crusher run shall be 100 mm or 1/4 of the pipe diameter (whichever is greater). The sidefills and top of the pipe shall be of monolithic 1:2:4 concrete mix with minimum cover of

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tOO mm thick. (b) Class ‘B’ bedding. Where the pipes are embedded in carefully prepared base compacted with 15 mm diameter crusher run extending halfway up the sides of the pipe. The minimum thickness of the crusher run is 100 mm or 1/4 of the pipe diameter (whichever is greater). The remainder sidefills and top of the pipe shall be compacted carefully with selected backfill to a minimum thickness of 300 mm. 4.3.5 Inverted siphons. Inverted siphons shall have not less than two barrels with a minimum pipe size of 150 mm and shall be provided with necessary appurtenances for convenient flushing and maintenance.

The manholes shall have adequate clearance for rodding. In general sufficient head shall be provided and pipe sizes selected to secure flow velocities of at least 0.9 rn/sec for average flow. The inlet and outlet shall be arranged so that the normal flow is diverted to one barrel, and so that either may be out of service for cleaning. Since siphons need more cleaning, they must be avoided as much as practicable. The siphon shall not have sharp bends, either vertical or

horizontal. The rising leg shall be limited to 15% slope, for this reason. There shall be no change in pipe diameter along the length of barrel too. Service connections. Service connections should be of an adequate diameter to reduce the problem of blockage. As it receives only intermittent flows, they are invariably subjected to intermittent stoppages during normal operation and these are removed by wave action rather than by the maintenance of a minimum flow velocity. The minimum gradient of 2% should be provided. The connection should be to the top portion of the main sewer at an angle of approximately of 45° in the direction of flow. The connection should be done with the use of tee junction.

4.3.6

The minimum size of service connection shall be 150 mm. 4.4

Testing of sewers.

The testing of sewers can be done either by air test or water test. The tests should be carried out before backfilling of the sewer trenches. 6

MS 1228 : 1991

Air test

4.4.1

4.4.1.1 General. It provides a rapid test which can be carri~d out after every third or fourth pipe laid. This could then prevent a faulty pipe or a badly made joint passing unnoticed until it is revealed by a test on a completed length.

4.4.1.2 (a)

Procedure. The following test procedure should be adopted:-

Seal the ends of the pipe run with expanding plugs;

(b) Attach U-tube (manometer) and a means of applying the air pressure to one of the plugs; (c)

Apply pressure to achieve a pressure slightly more than 100 mm. of water in the U-tube.

(d) Allow about 5 mm (e)

for stabilization of air temperature.

Adjust air pressure to 100 mm of water.

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Without further pumping, the head of water should not fall by more than 25 mm in period of 5 minutes. 4.4.1.3 Factors affecting the test. There are several possible contributing factors that could effect the apparent failure of the air test:(a) Temperature changes of the air in the pipe due to direct sunshine or cold wind acting on the pipe barrel; (b) Dryness of the pipe wall; (c)

Leaking plugs or other apparatus.

If there is a dramatic fall in pressure, then the pipeline is faulty or the end plugs or other apparatus are leaking. If the failure is marginal, the pipeline should not be rejected on the air test alone and the contractor should be given the opportunity of applying the water test. 4.4.2

Water lest

4.4.2.1 General. Sewers up to and including 750 mm diameter should be tested to an internal pressure represented by 1 .2 m head of water above the crown of the pipe at the high end of the

line. The test pressure should not exceed 6 m head of water at the lower end and if necessary the test on a pipeline can be carried out in two or more stages. The test pressure should be related to the possible maximum level of ground water above the sewer. When pipes larger than 750 mm diameter are to be tested, expert advice, and special equipment rna~’be needed. 4.4.2.2

Procedure. The following test procedure should be adopted:-

(a) Fit an expanding plug. suitably strutted to resist the full hydrostatic head, at the lower end of the pipe and in any branches if necessary. The pipes may need strutting to prevent movement. (b)

Fit a similar plug and strutting at the higher end but with access for hose and standpipe.

17

MS 1228 : 1991

(c)

Fill the system with water ensuring that there are no pockets of trapped air.

(d)

Fill the standpipe of requisite level.

(e)

Leave for at least 2 hours to enable the pipe to become saturated, topping as necessary.

(f) After the absorption period, measure the loss of water from the system by noting the amount of water needed to maintain the level in the standpipe over a further period of 30 mm, the standpipe being topped up at regular intervals of 5 mm. The rate of loss of water should not be greater than 1 litre per hour per metre diameter per linear metre.

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4.4.2.3

Factors affecting the test. Excessive leaking may be due to:-

(a)

Porous or cracked pipe;

(b)

Damaged, faulty or improperly assembled pipe joints;

(c)

Defective plugs;

(d)

Pipes or plugs moving.

4.4.3 Straightness. A sewer should be checked for line and level at all stages construction by either:— (a)

surveyor’s level and staff;

(b) laser beam with sighting targets; (c)

lamp and mirrors.

4.4.4 Infiltration. After stabilized, the sewer should be inspected from the manholes. manholes themselves should be

backfilling is completed and after the groundwater level has checked for infiltration. All inlets should be sealed and the line Any flow from the pipeline coming into the manholes or within investigated to establish its source.

In small pipes the point of infiltration may be located visually with light and mirror or with an inflated rubber plug. When conditions justify it a television camera can be used. The rate of infiltration is dependant upon many factors; a guide to its permissible extent cannot be given; this will depend on the judgement of the engineer. 4.4.5 Freedom from obstruction. As the work progresses the sewer should be checked for obstructions by visual inspection or inserting a mandrel or ~pig’ into the line. A television camera can also be used. 4.5

Manholes

4.5.1

,t’Ianholes location.

Manholes or inspection chamber shall be provided at:-

(a)

The upstream end of all sewers; however this may be replaced by a terminal layout:

(b)

Every change in direction or alignment for sewers > 600 mm;

18

MS 1228 : 1991

(c)

Every change in gradient;

(d)

Every change in size of sewer;

(e)

All intersections and junctions.

(f) Distances of not greater than 100 metres for sewers equal to or more than 00 mm in diameter and 150 metres for sewers equal to or greater than 450 mm in diameter. Greater distances may be permitted in cases where adequate modern cleaning equipments for such spacing is provided, and also in cases where sewers convey pretreated sewage. 4.5.2 Construction. (Typical drawings as shown in Fig. I). Every manhole and inspection chamber shall be of such size and form so as to allow ready access for rodding. The struct should be strong, durable and watertight and shall be constructed as follows:(a) Brickwork in cement mortar at least 225 mm in thickness or concrete (I : 2 : 4 nominal mix) at least 125 mm in thickness or other approved impervious material.

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(b) Internal faces shall be rendered with sulphate resistant cement mortar at least 20 mm thick so as to provide a smooth and impervious surface. (c) Step irons, ladders or other approved fittings shall be of non—corrosive durable material so as to provide safe access to the level of sewer. Cast iron or stainless steel or aluminium alloy is recommended. The interval between steps should be 300 mm with slip prevention surface. ~d) Foundation of every manhole shall be constructed of concrete less than 150 mm in thickness.

(1 : 2 : 4 nominal mix) not

(e) The channel within the manhole shall be formed with half round pipe made of the material as the sewer joining the manhole and shall have a diameter not less than the largest inlet sewer and not more than that of the outlet sewer from the manhole. (1) Every inlet to a manhole shall be discharge into the channel therein with properly made bends constructed within the benching of the manhole. The benching shall have a smooth impervious finish with a minimum slope of 1:12 and so formed as to guide the flow of sewage towards the point of discharge and to provide a safe foothold. (g) Manhole shall be constructed in conjuction with its frame and cover to be watertight. 4.5.3 Dimension and shape. Generally, manholes shall be rectangular, square or circular. The internal horizontal dimension shall be sufficient to perform inspection and cleaning operation without difficulty and a clear opening shall be provided for access to the invert. The minimum dimension required shall depend on whether it is a deep or a shallow manhole. 4.5.4

Frame and cover. The manhole frame and cover shall be of cast iron and shall have:-

(a)

Adequate strength to support superimposed load;

(b)

A good fit between each other such that surface runoff or rainfall will not get into it.

Provision for hinge and/or locking the cover to prevent vandalism and unauthorised access to the manhole. (C)

9

\IS 1228: 1991

Ihe following minimum requirements as to the weight and dimension of the frame and cover are a~folio w

Type of cover and frame

Dimension

Weight

Usage

Light duty

460 mm x 620 mm

54 lbs

Use in domestic premises compound

Medium Duty

Cover 600 mm internal mm. diameter 500 mm Frame 760 mm x 760 mm

250 lbs

Use in domestic drives and similar areas for bearing wheel loads noi exceeding I tonne

As above

530 lbs

Use in all carriagewavs.

-

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Heavy Duty

4.5.5 Deep manhole dimensions. Where deep manholes are required, its internal dimension must be more than 1.5 metre and the manhole may be tapered upwards to a section with minimum internal dimensions of 0.75 metres. In such cases, a minimum headroom of 1.8 in t’rom the base of manhole shall be provided. The opening to the manhole shall be at least 0.6 in. 4.5.6 Shallow manhole dimensions. Where the topography results in a shallow manhole that is in the depth 01’ invert of sewer being from 0.9 in to 1.5 m, a manhole of at least I .0 rn in internal horizontal dimension and a clear opening of’ at least 900 mm shall be used. The dimensions of the manholes at various depths shall be as follows:

Depth

Dimension

Less than 2’

460 mm x 620 rum

Between 2’

-

3’

600 mm x 760 mm

Between 3’

-

5’

760 mm x 760 mm

Greater than 5’

To follow deep manhole

4.5.7 Drop rnwtholes. If an incoming sewer is higher than the outgoing sewer by 600 mm or more. a drop manhole shall be used. \Vhere the difference in elevation between the incoming sewer and manhole invert is less than 600 nim. the invert shall be filleted at the curner~ to prevent solids deposition. 4.5.8 Connecilon bet itoeii manhole and ~eiver. To mini in se damage to the se wer due to differential settlement, the joint between the sewer and the manhole shall be of the flexible t~PC. lu acheive this, a flexible sewer pipe joint just outside the manhole ma~ be used.

20

MS 1228 : 1991

SECTION 5. SEWAGE

PUMPING

STATIONS

5.1 General. Sewage pumping stations should not be subject to flooding and shall be located off the right of way of streets and alleys preferably on land reserved for the purpose and readily accessibility. The pumping station structure is a major part of the cost of the station. It is therefore essential that it is efficient from a structural standpoint, that it is economical to construct, and that the size of the wet-well and dry-well and the space requirements of all equipment to be housed, be carefully determined, with efficient use made of all available spaces. Apart from the pumping facilities which may be required at sewage treatment plants, the principle conditions and factors necessitating the use of pumping stations shall be one or more of the following: (a) The topography of the area or district does not permit drained by gravity into trunk sewers or treatment plants.

(b) Omissions of pumping, although possible, would require excessive construction costs because of the deep excavation required for the installation of a trunk sewer to drain the area.

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(c) Service is required for areas that are outside the natural drainage catchment of the purposed sewage treatment plant.

All safety and other requirements should be met as required under other codes, standards and regulations. Pumping stations should be avoided as far as possible since the installation, operation and maintenance of a pumping station is costly. 5.2

Design details.

(Typical diagram of small pumping station is shown in Fig. 2). The

following design details shall be given consideration in the design of sewage pumping stations:5.2.1 Type. The sewage pumping facility provided may be any one of the following type, the choice depending mainly on the capacity and efficiency required. (a)

Wet-well type with submersible pump units

(b)

Dry-well type

(c) Lift station, using screw-pumps or suction lift pumps. Suction pumps mainly used in sewage treatment plants, and have the advantage of handling variation in flow and all solids without clogging. However, the suction-lift shall not exceed 4.6 in. 5.2.2

Structure

(a) The pumping station substructure shall be of reinforced concrete construction and the exterior wall below ground surface shall be adequately waterproofed and protected against aggresive soils and groundwater. (b) Wet and dry wells, shall be separated.

MS 1228 : 1991

(c)

Suitable facilities shall be provided to facilitate the removal of pumps, motors and any other

equipment in the pumping station. (d) Suitable and safe means of access shall be provided to the dry wells of pump stations, and to wet wells containing either bar screens and/or mechanical equipment requiring inspection or maintenance.

5.2.2.1

Wet well

(a) On small pump stations the practice is to provide, between the cut—in and the cut-out levels, a storage volume equal in litres to 2 to 3 times the peak flow into the wet well in litres per minute merely to protect the starting equipment from overheating and failure caused by too frequent starting and stopping. On larger installations, the effective capacity of the wet well should not exceed 10 mm for the design average 24 h flow. Wet wells that are too large cause

serious maintenance and operation problems because of excessive deposition of gritty and organic material. (b) The wet wells should be narrow but not less than 1.2 m for ready access and should be as

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deep as possible in order that the cut-in level of the last pumps will be below the invert of the inlet channel to the wet-well.

(c) Where continuity of pump station operation is important, consideration should be given to dividing the wet well in two sections properly interconnected to facilitate repairs, cleaning and expansions. (d) Wet wells and suction channels should be designed so that dead areas where solids and scum

may accumulate are avoided. The bottom should have a minimum slope of 1 .5 vertical to I horizontal to the hopper bottom in the direction of flow so that deposits and scum accumulations are carried to the pump suctions by the scouring action of the high velocities at low operating levels.

(e) The wet well should be well lighted with fixtures that are both vapour proof and explosion proof.

5.2.2.2

Dry well

The size of the dry well depends primarily on the number and type of pumps selected and on the piping arrangement. (Totally submerged pumping units do not require dry wells). A good rule of thumb for those installations requiring dry wells is to provide at least 1 .0 m from each of

(a)

the outboard pumps to the nearest side wall and at least 1.2 m between each pump discharge

casing.

Sufficient room is required between pumps to move the pump-off of its base with

sufficient clearance left over between suction and discharge piping and room for on site repairs, inspection, or removal from the pit to the surface for repairs. (b) Depending on the size of the pump station, consideration should be given to the installation of monorails, lifting eyes in the ceiling, and ‘A’ frames for the attachment of portable hoists, cranes and other devices. (c)

22

Provisions should also be made for drainage of the dry well to the wet well.

MS 1228 : 1991

5.2.3

Pump Unit

(a) Minimum number of units. At least 2 Units of pumps shall be provided of which one shall be a standby unit. Constant speed pumps are recommended in view of simplicity of operation and maintenance. If only 2 Units are provided, they shall have the same capacity each being able to handle the design peak flow. Where 3 or more units are installed they shall be designed to fit actual flow conditions and must be of such capacity that with any one unit being out of service,

the remaining units will have capacity to handle maximum sewage flow. (b) Pumps handling raw sewage should be preceeded by readily accessible bar racks or screens with clear spacings not exceeding 30 mm, unless pneumatic ejectors or screw pumps are used, or special devices are installed to protect the pump from clogging or damage. Convenient facilities shall be provided for handling screenings. Where the size of pumping stations warrant, a mechanically cleaned bar screen or communition device is recommended. For larger or deeper stations, duplicate protection units of proper capacity are prefered. (c) Pump openings. Pumps shall be capable of passing spheres of at least 75 mm in diameter. Where a communition or screening device is provided, pumps with smaller-sphere passing

capability may be allowed.

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Pump suction and discharge openings shall be at least 100 mm in diameter. (d) Priming. Except for the self-priming pumps, screw pumps and submersible pumps, the gland of the puma shall be so placed that under normal operating conditions, it will operate under a positive suction head. Pumping rates. The pumps and controls of pumping stations, shall be selected to operate at varying delivery rates to permit discharging sewage from the station to the treatment works at approximately its rate of delivery to the pumping station. The desirable range between the maximum and minimum wet-well levels is 900 mm, while the minimum range shall be 450 mm. Where 2 or more pumps are to operate simultaneously, the difference in level between the start or stop of respective pumps shall not be less than 150 mm.

(e)

Pumping cycle or time between successive starts, of a pump operating over the control range, shall be preferably more than 10 minutes for each pump. (f) Pumping cycle.

5.2.4 Valves. Suitable shut-off valves shall be placed on the discharge line of each pump and its suction line where applicable. A check valve shall be provided on each discharge line. All valves shall be selected such that the closure time is sufficiently provided to minimise surge pressure and water hammer. 5.2.5 Ventilation. Adequate ventilation must be provided for all sections of the pumping stations. Where the pump pit is below the ground surface, mechanical ventilation is required. The ventilation shall be so arranged as to provide completely separate and independant ventilation

for the dry and wet wells. Dampers shall not be used on exhaust or fresh air ducts and fine screens or other obstruction shall be avoided to prevent clogging. Switches for ventilation equipment shall be marked and located conveniently. All intermittently operated ventilating systems shall be interconnected with the respective pit lighting system.

Consideration should also be given to automatic controls where dehumidification equipment where dampness, excessive moisture is a problem. 23

MS 1228 : 1991

(a) Wet wells. Ventilation shall be either intermittent (with at least 30 complete air changes per hour) or continuous (in which case at least 12 complete air changes per hour). Such ventilation shall be accomplished by introduction of fresh air into the wet well by mechanical means. (b) Dry wells. For continuous ventilation, at least 6 complete air changes per hour shall be provided. If intermittent ventilation is proposed, at least 30 complete air changes per hour shall be provided. 5.2.6 Flow measurement. Provision shall be made to install convenient flow measurement equipment whenever such data is required. 5.2.7

Electrical equipment and power supply.

All pump stations should be provided with

electricity from two independent sources (looped supply) and be given priority restoration by the power authority when outages occur. When availability of electrical power supply cannot be assured, the use of standby generators or engine drives as well as in-system storage and by-pass

should be considered. All electrical equipment and light in the wet-well should be explosion proof.

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Adequate lighting and a convenient number of equipment receptacles for power tools shall be provided. The motor starters and controls should be located within a safe and satisfactory control unit.

Separate rooms shall be used for the electrical starters, switches etc. for larger stations.

Such

control units or rooms shall be easily accessible, preferably above flood level, and shall be in accordance to the requirements of other relevant codes and regulations. 5.2.8 shall be station. shall be

Alarm systems. Alarm systems shall be provided for all pumping stations. The alarms activated in cases of power failure, pump failure, or any other malfunctioning of the Where a municipal facility of 24 hours attendance is provided, pumping stations alarms telemetered thereto. Where no such facility exists, an audio-visual device shall be

installed at the station for external observation. 5.2.9 Emergency operation. The objective of emergency operation is to prevent in the case of power failure or pumping station malfunctions, the indiscriminate overflow of raw or partially treated sewage to any waterway and to protect the public by preventing back-up of sewage and

subsequent overflow to basements, streets and other public and private property. (a) Emergency power supply. Provision of an emergency power supply for pumping stations shall be made especially for stations in which interruption due to power is not desirable. This may be accomplished by connection of the station to at least 1 standby generator, driven by petrol or diesel engines. Where generator is used, the unit shall be provided with adequate foundation, and have facilities to remove and perform routine maintenance. Provision shall be made for automatic and manual start-up and cut-off. The generator housing shall be installed with ventilation equipment and lighting. Where internal combustion is used, provision for ventilation of exhaust gases shall be made. (b) Portable pumping equipment. Alternatively, portable pumping equipment could be utilised. The pumping facility shall have the capability to operate between the well and the discharges side of the station, with the station provided with permanent fixtures which will facilitate rapid and easy connection of lines. 24

MS 1228 : 1991

(c) Overflow. Consideration shall be given to the provision of overflow. Such provision of overflow shall be permitted in areas in which the permitted overflow shall not adversely affect the quality of public water supplies and other receiving water bodies. 5.2.10 Instruction and maintenance. Sewage pumping station and shall be provided with a complete set of operation and maintenance instructions, including emergency procedures. maintenance schedules, tools and such spare parts as may be necessary. 5.2.1 1 (a)

Force or pumped mains design

The minimum internal diameter for pumping mains shall be 100 mm.

(b) Pumping main should be so sized such that the velocity in the suction will not exceed 1.50 rn/sec and discharge 2.5 rn/sec. The velocity in the force mains should be at least 0.9

to 1.1 rn/sec. (c) The pumping main shall be of the following materials: i) ii)

Cast iron pipe Asbestos cement pressure pipe

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iii) Steel—pipe with sulphate resisting concrete lining P.V.C pressure pipe

iv) v) vi)

Ductile iron

Other materials approved by the local authority and certified by SIRIM

(d) All joints shall be flexible and watertight (e) The pumping mains shall be provided with such appurtenances as access/inspection chamber, air relief valves and wash out. (f)

The minimum earth cover for pumping mains shall be 1.0 m unless it is concrete surrounded.

(g) The forced mains shall enter the gravity sewer system at a point not more than 600 mm above the flow line of the receiving manhole. (h) The force main and adjoining piping and appurtenances on the discharge side of the pump should be heavy enough to withstand the maximum hydraulic head on the system, including abnormal pressures that may be produced by water hammer and surge pressures. Screening/communiting facilities. Where conventional pumps are used, facilities for screening or communition of solids, which are capable of clogging the pumps and/or pumped mains shall be provided.

5.2.12

Control system

(a) The selection of a control system and a specific control mode is at least as important as the selection of the pump. The factors to be considered in selecting a control system are efficiency. power factor, reliability, operational effects, structural costs and ease of operation. (b) For larger installation, automatic variable speed controls are often more reliable and maintenance free than presumably simpler automatic on off controls. The overall efficiency of a variable speed system may be greater than that of an on off system despite control losses.

25

MS 1228 : 1991

(c) The sophistication and competence of the operating and maintenance personnel is an important consideration when selecting control systems which have to match their training and

experience. 5.2.12.1 Manual control (a) Generally consist of push button stations or selector switches that energize or de—energize the pump motor starter. Manual control systems are rarely used with anything other than constant speed pumps.

5.2.12.2 Automatic control (a) Time. Pumps are started at regular intervals and operate for a preset length of time. Time controlled systems are generally used for sludge pumping. Pressure drop is used to start the pumps on plant water systems. generally served by a standard pressure switch. (b) Pressure.

(c)

Pressure is

Flow. Pumps are turned on as flow exceeds a certain value or turned off when flow drops.

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Influent flow signals are generally from a flow meter or weir with multivolt control. Level. Most of the automatic constant speed systems operate from level signals. Pumps are turned on as levels rise and turned off as they fall. Level detection systems include:

(d)

(e) Automatic switch over. The controlled system shall be designed to ensure automatic switch over of operation between available pumps in each successive cycle. Level detection systems include: (i) Float switches using a rod or tape. Float type controls are economical, simple and reliable when operated in effluent or clear water. When operated in raw wastewater or sludge, maintenance problems can develop from grease coating the float and rods, solids punching the floats, or corrosion of the float, roads or tapes. (ii) Enclosed floats. Enclosed float switches consist of an encapsulated mercury switch that may be either’ open or closed when the float is in the pendant position. As the liquid rises, the position of the float changes the angle of the mercury switch reversing its condition. (iii) Electronic probes. With the use of relays, it is possible to control a single pump or multiple pumps. Enclosed probes in a sealed tube below which is suspended a bladder type container with fluid results in less maintenance problem. (iv) Captive air system. Captive air systems using a diaphragm and small diameter tubing to transmit pressure signals to switches that turn pumps on and off. (v) Pneumatic or air bubbler type control system. This system is generally used for a duplex or

multipump installation.

26

MS 1228 : 1991

SECTION 6. TREATMENT WORKS 6.1

General

6.1.1 General process design considerations. and designed to meet the following aspects:

The treatment works processes shall be planned

(a) the effluent quality requirements as specified in the Third Schedule of the Environmental Quality (Sewage and industrial Effluents) Regulations, 1979. P.U.(A) 12/79 as in Appendix B: (b) the projected effluent flows and characteristics, including anticipated variations in the flows and characteristics; (c) the local environmental and aesthetics requirements, including the proximity to the nearest habitable premise, direction of the prevailing winds, local zoning requirements, socio—economic aspects, and compatibility of the treatment processes with the present and future land and receiving water uses; (d) the availability of land space for the treatment works, including area for future expansion

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and/or upgrading of the treatment processes; (e)

other local conditions such as soil conditions, climatic conditions, topography, etc.;

(f)

the ultimate disposal of the treated effluents, including the access to receiving waters;

(g)

the capitai costs and the operating and maintenance costs of the works;

(h)

the reliability of the process,

including the performance of the process under normal

operating. conditions as well as during unusual or adverse circumstances (a treatment process reliability is the measurement of the--ability of the facility to perform its designated function without failure). The reliability criteria shall include the following: (i) designing the facility for all anticipated circumstances, and this shall include, necessary, bypasses, standby units, and protection against floods;

where

(ii) the mechanical equipment installed shall be easily repaired or replaced without violating the effluent limitations for long period of time (this shall also include adequate backup service and the availability of spare—parts); (iii) units that require to be taken out of service for maintenance purpose on a routine basis shall be duplicated in parallel, so that some treatment can be achieved during the maintenance period: and (iv) the electric power system shall be so designed to cater for breakdowns of the power supp1~i, or to switch the circuitary to standby units in the event of breakdown of any units. Where necessary, power supply shall be obtained from two sources, one of which shall be a standby

generator or another utility sub-station.

(j)

complexity of the processes, including the level of process controls required, and level of trained personnel required; and

(k)

the ultimate disposal of the sludge. 27

MS 1228 :1991

6.1.2

Physical design consideration. Having selected the treatment process to be employed, careful considerations shall be given to the planning and design of the physical facilities. 6.1.2.1

Treatment works layout

6.1.2.1.1 Process units. Careful consideration shall be given to size, shape and the physical arrangement of the process units, depending on the availability of space, the number of units and economics. In selecting the shape of the unit, due consideration shall be given to the aesthetics aspects, without compromising on the functional aspects of the process unit. Wherever practicable, multiple modules that will comprise of a single process will be preferred, as this will facilitate diversion of flows during repairs and/or maintenance of a module. 6.1.2.1.2 Conduits and their identification. In planning the conduits connecting the various process units, provisions shall be made for future expansion, and for isolation of each unit, through the use of valves and other flow control devices. These valves and flow control devices need only have manual operators or nuts that can be controlled by portable manual or power driven operators. Where multiple modules of a single process are employed, proper flow division facility shall be

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provided so as to control both the hydraulic and organic loading on each modules, and shall be designed for easy operation, change, observation and maintenance. All connecting conduits shall be designed to convey the maximum anticipated flows, including when flows are diverted from one Unit to another for maintenance or repair purposes. The conduits shall be designed to avoid pockets and corners where solids can settle and accumulate. For easy indentification of the conduits and piping, these shall be painted with the following colour codes: Chlorine line

-

yellow

Compressed air line

-

green

Fuel gas line

-

orange

Potable water supply line

-

blue

Sewage/effluent line

-

grey

Sludge line

-

brown

6.1.2.1.3

-

-

Plant location

The following items shall be considered when selecting a treatment plant site: (a)

Proximity to residential areas

(b) Direction of prevailing winds

(c) Accessibility by-all weather roads (d) Area available for expansion (e)

28

Local zoning requirements

MS 1228 : 1991

(f)

Local soil characteristics, geology, hydrology and topography available to minimize pumping.

(g)

Access to receiving stream by gravity prefer

(h) Water quality of the receiving water course

(j)

Compatibility of treatment process with the present and planned future land use, including noise, potential odours, air quality, and anticipated sludge processing and disposal techniques. 6.1.2.1.4

Structure to be reinforced concrete

Unless otherwise required, wall, slabs, beams, columns and structure for sewerage plant shall, in general, be in reinforced concrete. Walls shall have minimum thickness of 225 mm. Brickwork may be used in shallow chamber. Where a site must be used which is critical with respect to those items, appropriate measures shall be taken to minimize adverse impacts. The treatment plant should be located in an area not subject to flooding or otherwise ~e adequately protected against flood damage. 6.1.2.1.5

Foundation

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Where necessary,

special foundation (eg.

bakau piling, reinforce concrete piling etc) shall

provided. 6.1.2.1.6

Quality of effluent

The required degree of treatment for sewage treatment plants shall be based on the parameter limits as specified in the Third Schedule and the objectives for the receiving waters as established by the Ministry of Health/Department of Environment. In any case the effluent must be adequately disinfected to destroy disease causing organisms.

6.1.2.1.7

Flow

The sewage treatment plant shall be designed to serve the ultimate contributary population based on an average daily per capita flow of 225 liters, to which must be added an anticipated amount of industrial wastewater and some allowances for infiltration. Where a plant is designed to serve an existing sewerage system, the plant shall be designed on the basis of actual flow measurements, plus allowances for estimated future population and shall be staged as required. i)

Operating equipments

A complete range of tools, accessories and spare parts necessary for the plant operator’s use shall be provided together with the necessary storage space. ii)

Grading a,zcl landscaping

Upon completion of the plant, the ground should be graded. Conrete or hard surfaced walkwa\s should be provided for access to all units. Surface water shall not be permitted to drain into any unit. Landscaping should be provided especially where a plant is located near residential areas.

Lansdcaping should be provided at all such plants to cover the harsh and unpleasant sight of sewage structures.

29

MS 1228 : 1991

6.1.2.1.8

Plant oulfalls

The outfall sewer should be designed to discharge to the receiving waters with the consideration for the following: i)

Preference for freefall or submerged discharged.

ii)

Utilization of cascade aeration of effluent discharge to increase dissolved oxygen.

iii) Limited or complete dispersion across receiving waters. 6.1.2.1.9

Organic loading

The process design of a domestic waste treatment plant shall be on the basis of 55 grams of BOD per capita per day and 68 grams of suspended solids per capita per day. When an existing treatment works is to be upgraded or expanded, the design shall be based upon the actual strength of the wastewater. Domestic waste treatment plants designed to include these industrial waste loads should take into consideration the shock effects of high concentrations and diu-rinal peaks

for short periods of the time on the treatment process particularly for small treatment plants.

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6.1 .2.1 .10

Flow division control

Flow division control facilities shall be provided as necessary to ensure organic and hydraulic loading control to plant process units and shall be designed for easy operator access, change, observation and maintenance. 6.1.2.1.11 i)

PlaNt details

Installation of mechanical equipment

The specifications should be written such that the installation and initial operation of major items of mechanical equipment will be supervised by a representative of the manufacturer. ii) Unit b,vpass

Bypass structure and piping properly located and arranged should be provided so that each unit of the plant can be removed from service independently.

iii) Appropriate effluent sampling The outfall sewer should be so constructed and protected against the effects of floodwater, tide or other hazards as to ensure its structural stability and freedom from stoppage. A manhole should be provided at the shore end of all gravity sewers extending into the receiving waters. Hazards to navigation shall be considered in designing outfall sewers. Provision shall be made for sampling of influent or effluent as well as individual process unit. 6.1.2.1.12

Essential facilities

All plants shall be provided with an alternate source of electric power to allow continuity of operation during power failures. An adequate supply of potable water under pressure should be

provided for use in the laboratory and for general cleanliness around the plant. Toilets, shower, lavatory and locker facilities should be provided in sufficient numbers and convenient location to serve the expected plant personnel. Flow measurement facilities shall be provided at all plants. 30

MS 1228 : 1991

6.1.2.1.13

Safely

Adequate provision shall be made to effectively protect the operator and visitors from hazards.

The following shall be provided to fulfill the particular needs of each plant: (i)

Fencing of the plant site to discourage the entrance of unauthorized persons and animals.

(ii)

Hand rails and guards around tanks, trenches, pits, stairwells and other hazardous structures.

(iii) First aid equipment including CPR. (iv) “No Smoking

signs in hazardous areas.

(v) Protective clothing and equipment. (vi) Portable lighting equipment.

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6.1.2.1.14

Laboratory

All treatment works shall include a laboratory for making the necessary analytical determination and operating control tests, except in individual situations where the omission of a laboratory is approved by the reviewing agency. The laboratory shall have sufficient size, bench-space, equipment and supplies to perform the process control tests necessary for good management of each treatment process included in the design. Measuring devices. Devices should be installed in all plants for indication flow rates of raw sewage or primary effluent, return sludge, and air to each tank unit. Where the design provides for all return sludge to be mixed with the raw sewage (or primary effluent) at one location then the mixed liquor flow rate to each aeration unit should be measured 6.1.3

Evaluation of new treatment processes. ifl the case of a particular new treatment process not included in this code of practice, the designer shall obtain approval of the proposed treatment process to the relevant approving authority. 6.1 .4

6.2

Preliminary treatment

6.2.1

Bar screens.

Bar screens shall be provided upstream of pumps or treatment facility

for protection against clogging and damage. The screening device may he manually-cleaned or mechanically cleaned. 6.2.1.1 Manually or mechanically cleaned screens. Clear opening between bars shall be from 25 mm to 30 mm and shall be placed at a sloped of 10° to 45° to the vertical. Approach velocities sho-uld—norexceèd 0.2 rn/sec and the flow through velocity should not exceed 0.8 m/sec at velocity average rate of flow. The approach channel should be so designed to ensure a good distribution of velocity. Facility for a screened by-pass to be provided in the event of clogging. Where mechanically cleaned screening devices are installed auxiliary manually cleaned screen shall be provided. 31

MS 1228 : 1991

6.2.2 Fine screens. Fine screens, where used for pre-treatment or primary treatment should be installed to manufacturer’s specification and require prior approval of the Local Authority. 6.2.2.1

Disposal of screening.

Screenings should be removed, handled, stored and disposed in a

sanitary manner. 6.2.3 Grit removal. Grit removal facilities may be considered as optional process depending on the nature of sewage to be treated. Grit removal systems may comprise either the Horizontal Constant Velocity Grit Chamber or the Aerated Grit Chamber or Detritor. 6.2.3.1

Horizontal constant velocity grit chamber

(a) The flow through velocity should not exceed 0.23 rn/sec (b) The surface loading rate should not exceed 1500 m2/d/m2. 6.2.3.2

Aerated grit chamber

(a) Maximum detention time to be 3 mm.

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(b) Air rates should be in the range of 4.5 to 12.5 liter/sec/rn of tank (c)

Depth to width ratio of 1:2.

(d) Length to width ratio of 1:2. 6.2.3.3

Detritors

(a) The maximum flow through velocity should not exceed 0.3 rn/sec at peak flows (b) Tangential flow entry into detritor width minimum turbulence. (c) Water depth in tank to be controlled by weir outlet. (d) Reciprocating inclined dewatering systems should be incorporated for washing grit and reducing organic content. Disposal of grit. -Mechanical grit removal system of collecting and disposal of grit in a sanitary manner should be provided. 6.2.3.4

6.3

Primary treatment

Design criteria for septic tanks. (Typical diagrams as in fig. 3). Septic tanks are to be either rectangular or cylindrical chambers sited or constructed below ground level. They are to be of watertight construction so that they neither permit ingress of ground water or engress of sewage to the ground. 6.3.1

32

MS 1228: 1991

6.3.1.1

Capacity.

The capacity of the septic tank should be based on the number of persons or

equivalent population served based on the following formula: C

=

225 P

where C

is the capacity of the tank in litres and

P

is the designed population or equivalent population

The minimum capacity of septic tank should not be less than 2000 litres and should not serve an equivalent population of more than 150. 6.3.2

Rectangular septic tank.

6.3.2.1

Minimum requirements.

Rectangular septic tanks should have the following minimum

dimensions: (a) Minimum liquid depth of 1.25 m but not more than 2.0 rn. Licensed to Wan Roselan Mustapha / Purchased on 12-July-2007 / Single user license only, copying and networking prohibited

(b) Should have width not less than 750 mm, (c) Have a length not less than 2 times its width. (d) Should be roofed and have a minimum water free-board of 250 mm. (e) Adequate opening for desludging and maintenance should be provided. (f) Access for desludging vehicles should be provided. 6.3.2.2 (a)

Arrangement

Tanks less tha,i 1.25 in width

The septic tank shall be constructed with 2 or more compartments, either 2 separated tanks or by dividing a single tank into two by a partition or baffle. (i)

(ii) Where a baffle is used it shall be positioned at a distance of about 500 mm from the inlet

end. The baffle shall extend 150 mm above TWL and shall leave a minimum clearance of about 500 mm at the bottom. (iii) The inlet and outlet shall be a vertical 150 mm diameter cast iron T-~shapeddip pipe with the top limb extending above scum level and the bottom limb extending 500 mm below TWL. (iv) The invert of the inlet dip-pipe should be 75 mm above the invert of outlet dip-pipe. (v)

The floor of the tank should be sloped towards the inlet end at a slope of I to 6.

(b)

Tank greater than 1.25 m width.

(i)

For tanks more than 1.25 m width, the tank shall be of two compartments in series.

The

inlet compartments to have a capacity of twice that of the second compartment. 33

MS 1228 : 1991

(ii) The influent into tanks of more than 1 .25 m width shall discharge into a channel which feeds two or more dip-pipes. The two compartments should also be interconnected by equal number of dip-pipes. (iii) The outlet shall be in the form of weir which should extend the full width of the tank. Scum boards should be placed before the weirs. (iv) The floor of the inlet chamber should be sloped towards the inlet end at a slope of I to 6. (v) The invert of the inlet dip-pipe should be 75 mm above the invert of the outlet dip-pipe. 6.3.3 Other types of septic tanks. As cylindrical septic tanks are precast and factory-made they requires the approval of the relevant Authority on an individual basis.

6.3.4

Design criteria for inihoff tank

6.3.4.1

Sedimentation compartment

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The sedimentation compartment shall have a capacity of not less than 2 hours detention time for average daily flow of 225 litres/cap./day. It shall have a surface overflow rate of not more than 30 m3/m2/day at design peak flow. The sedimentation compartment shall have a length to width ratio of not less than 3 to I. Minimum width shall be 600 mm and depth of not less than 900 mm or more than 2.8

in.

In the sedimentation compartment of the lmhoff Tank the side slopes shall have a slope of not less than 1 .5 times vertical to I horizontal. The compartment shall have a false bottom and communication with the sludge digestion compartment shall be by means of a horizontal slot minimum 150 mm wide running the full width of the tank. A slot overlap of at least 200 mm to be provided. 6.3.4.2

Sludge compartment

The sludge digestion compartment shall have a capacity of not less than 0.04 m3 per capita. The floor of the compartment will have a slope of I vertical to 4 horizontal towards the sludge

draw-off pipe. The sludge draw-off pipe shall be of cast-iron and not less than 100 mm and shall draw off sludge from the bottom of the sludge compartment. Sludge sampling pipes for sludge draw-off above and below the neutral zone shall be provided. The scum compartment shall have a width not less than 450 mm or 25% of the total surface area of the sedimentation compartment, whichever is larger. The scum compartment shall be adequately vented and facilities for adequate removal of gas provided.

34

MS 1228 : 1991

6.3.4.3 Neutral zone. A neutral zone of not less than 300 mm deep shall be provided between the bottom of the sedimentation compartment and the top of the sludge digestion compartment. 6.3.4.4

Inlet and outlet

The inlet may be of minimum 150 mm diameter cast-iron T-shaped dip-pipe with the top limb extending above the scum level and the bottom limb extending 500 mm below the TWL. For wider tanks multiple inlets to be provided. The outlet shall be in the form of weir which should extend the full width of the tank.

Scum boards shall be provided at the inlets and outlets and in the larger tanks at intermediate points.

The scum boards shall be submerged at least 600 mm and extended by at least 450 mm

above TWL. The TWL in the sedimentation tank shall be at least 75 mm below the invert level of the inlet sewer. 6.3.4.5

Reversal

of flow direction.

In large installations with multiple units of sludge

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compartment, provision shall be made for reversal of flow periodically, so as to obtain even distribution of sludge. 6.3.4.6

Effluent.

Effluent from septic and imhoff tanks require secondary treatment in

biological filter or other methods approved by the Local Authority. 6.3.4.7 Slab cover. The roof of the septic and imhoff tanks shall be either covered with a reinforced concrete cast-in-situ slab with adequate openings with air-tights manholes covers for inspection and maintenance or covered with precast reinforced conc.rete slabs fitted with lifting handles and having grooves for jointing with line to prevent emission of smell and breeding of insects. - -

Ventilation. In all septic and imhoff tanks the space between the top of the water level

6.3.5

and the roof shall be: (a)

Adequately ventilated;

(b) Provided with adequate means for dra~vingoff gases; (c) All ventilation provided shall be proofed against the entry of mosquitoes. 6.3.6

Prima,)’ sedimentation tank

6.3.6.1

General.

Sedimentation tanks may provide

the principal degree of wastewater

treatment, or they may be used as a preliminary steps in the further treatment of wastewater. When used as the only means of treatment. these tanks shall be provided for the removal of: (a)

senleable solids capable of forming sludge banks in the receiving waler and;

(b) much of the floating material.

35

MS 1228: 1991

When used as a preliminary step to further treatment the main function of primary sedimentation tank is to reduce the organic loading on the secondary treatment units and are

essentially components of secondary sewage treatment. The efficiency of a sedimentation tank is dependent on the velocity of the flow, which is determined by the tank dimension. Effective flow measurement devices and control appurtenances shall be provided to permit proper proportioning of flow and solids loading to each

unit. Sedimentation tanks may be of the horizontal flow or upward flow or radial flow type. Primary sedimentation tanks could be either rectangular or circular in shape, the circular configurations are recommended for larger flows. 6.3.6.2 Rectangular tanks. The length to width ratio should be 3: 1 or more. The width to depth ratio should be between 1 : 1 to 2.5 : I. Typical depth of rectangular primary sedimentation tank is 2.5 m to 3.0 m. Circular tank. The side water depth should not be under 3 m. The floor slope when used in conjunction with scraper mechanism should be I : 12 or as recommended by supplier of

6.3.6.3

scraper.

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6.3.6.4 Detention time. Detention time should vary with depth of tank and surface loading rate and should be within the range of 90 to 150 mm at Average Daily Flow. 6.3.6.5

Surface loading.

For the rectangular tank the sludge will mainly settle out at the

inlet end of the tank. The settled sewage is collected at the opposite end for treatment. For circular tanks the loading can either be central or peripheral. The surface loading rate at peak flow should not exceed 60 m3/day/m2. 6.3.6.6

Wejr loading. The weir loading rate should be in the range of 150 to 180 m3i’day/rn~.

6.3.6.7

Scraper mechanism and sludge Dumps. Scraper mechanism and sludge pumps for the

collection and transfer of scum and sludge should be approveu bi-~cLcc:li~±ori~’. 6.3.6.8 Primary sedimentation tank with hopper bottom and rectangular (Typical diagrams as in fig. 4). 6.3.6.8.1 Upward flow sedimentation tanks. An upward flow tank is normally square or circular in plan with hopper bottom having steeply sloping sides to provide sludge storage. Sewage enters the tank through a feed pipe and is initially deflected downwards by a stilling box. As the sewage is dispersed into the body of the tank it rises steadily towards a peripheral weir and suspended material fall into the hopper.

[n designing hopper bottom tanks an angle of slope of 60° (giving 51° valley slope) will usually be saListactory. In order to reduce sludge accumulation in the valley angle, a tank of steeper angle of slope of 68° (giving 60° valley slope) may be considered. 6.3.6.8.2

Capacity. The capacity of the hopper should be equivalent to 2 hours detention time

at peak flow. Additional water depth of minimum 400 mm should be provided above the hopper in the vertical side-wall section between the top of the hopper and the TWL. The side-wall height should not be less than 400 mm.

36

MS 1228 : 1991

6.3.6.8.3 Horizontal flow tank. A horizontal flow tank is normally rectangular in plan and should have length of approximately 3 times its width and a depth below TWL of about 1.5 m. This tank should be designed to have a single or multiple hopper conforming to clause 6.3.6.8.1. To facilitate desludging twin tanks should be provided for larger installation. 6.3.6.8.4 Surface loading rate. primary sedimentation tank.

The overflow rate should not be greater than 60 m3/day.’m2

6.3.6.8.5

Solid loading rate. The solid loading rate should be between 2.5 to 6 kg/m2/hr.

6.3.6.8.6

Weir loading rate. The weir loading rate should not exceed 150 m3/day/m.

6.4 Secondary treatment. In waste water treatment plants the preliminary and primary stages of treatment which were described in the earlier chapters of this code can efficiently remove 30% to 40% of the B.O.D. and 6O% to 70% of the influent Suspended Solids (S.S). The fraction remaining are soluble, colloidal or sufficiently small not to settle easily and they

consists of a wide range of organic and inorganic materials.

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The usual way in which the remaining fraction can be further treated is to encourage microorganism to oxidize the organic material in a similar manner to that in the natural process occuring in rivers and streams but at an increased rate. In such secondary treatment the organic material is made to come into contact with microorganisms either in a ~FixedFilm Media’ or a ~SuspendedFilm Media’.

The most commonly used biological process in the fixed film media is the trickling filter and in the suspended film media is the activated sludge with their many varied and modified processes. Other common biological process are the Aerated Lagoon and the Waste Stabilization Pond. 6.4.1

Fixed growth (Typical diagrams as in fig. 5).

6.4.1.1 Mineral media. For sewage treatment plant of 500 persons capacity or less the rectangular type of percolating filter with tipper, chute and channel distribution system of settled sewage may be used. Tipper, chute and channel shall be made of aluminium sheet of minimum 2 mm thickness or of cast iron or stainless steel. The size. capacity, dimension, support shall be approved by the Local Authority. Tipper trough should have a capacity equivalent to 4.5 litres/rn2 of filter surface area.

For sewage treatment plant above 500 persons capacity the circular type percolating filter with dosing syphon and rotary type distributors and ancillaries shall be used. Dosing syphon, rotary distributor equipment shall be of’ approved make, size, capacity and material and designed for 3 x DWF. The distributor arm shall be approximately 150 mm to 300 mm above the media line. The average depth of the media shall not exceed 1.8 m and minimum depth shall not be less than 1.2 m.

MS 1228 : 199]

The media provided shall be inert and resistant to biological attack e.g. granite. limestone or coral. Two sizes of media shall be provided viz. 100 mm single size for the lower one-third and 50 mm single size for the upper two-third 01’ the filter. The loading for the low or standard rate filter shall be as follows: (a)

Hydraulic I 00O x P

°“

litres/day/rn2

(b) Organic (BOD5 ~ 20°C)-80 x P°’1 kgdavi 1000 m3 where P is the designed population. The hydraulic loading rates are not to exceed 4500 litres/day/rn2 and the organic loading rates are not to exceed 400 kg/day/l000 rn3. Good ventilation shall be provided

at the bottom of and through the media.

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Aeration pipes of 100 mm or 150 mm diameter shall be provided extending through the full depth of the media. The size and/or number of opening that will provide the required volume of air shall be based on 0.S% of the surface area of the bed. The inlet openings into the filter underdrains have an unsubmerged gross combined area equal to at least 15 percent of the Surface of the l’ilier. The base slab shall be sloped no flatter than I in 50 and overlaid with approved drainage tiles or pipes. 6.4.1.2 Synthetic media. The synthetic media for trickling filters has extended the range of hydraulic and organic loading well beyond the range of stone media. Two properties that are of interest are specific surface area and percent void space. The ability of synthetic media to handle higher hydraulic and organic loadings is directly attributed to the higher specific surface area and void space of these media compared to stone media. The organic and hydraulic loading should be inaccordance to the manufacturer’s specification.

6.4.2

Rotating biological contact ors IR BC)

6.4.2.1 General. Rotating biological contactors consist of basically high density plastic media discs mounted on the shaft. The shaft is then made to turn slowly at approximately 1 rpm either mechanically through a gear drive system or by the use of air through buoyancy forces exerted on air trapped in air cups fixed to the edge of the discs from an air blow system. The slow rotation of the shaft causes alternating exposure of the media to atmosphere and the wastewater. Biological growths (biofilm) become attached to the surfaces of the discs and eventually form a slime layer (biomass) over the discs. The rotation effects oxygen transfer, keep the biom.ass in an aerobic condition and also causes excess biomass to slough from the discs into the mixed liquor and out of the process basin. This sloughing maintains a uniformly thick biomass and prevents clogging of the discs. RBCs are also available in package units for limited capacit\ which incorporate facilities for primary and secondary settlement together with sludge storage for a period of 4 to 6 months.

38

MS 1228 : 1991

6.4.2.2

Process design

(a) The RBC system requires preliminary treatment, primary and secondary settlement, sludge storage and treatment. (b) The soluble BOD is the controlling factor in design and therefore the approach taken is to determine the amount of the soluble BOD removed per unit of surface area for each stage of a multi-stage RBC system. The soluble BOD shall be taken as 70% of the total BOD for domestic waste. (c) Where primary sedimentation tanks are used also for sludge storage/digestion, an additional increase of 50% of the soluble fraction shall be taken into account in design due to the exertion of the secondary BOD from the digestion process. (d) When the peaks flows are greater than 2.5 DWF, sufficient equilisation volumes shall be provided additionally to primary settling volumes or separate equalisation tanks. (e) Where necessary the RBC systems should be preceeded by fine screens with a maximum clear

spacing of 20 mm.

-

(f) Required media area should be calculated based on the peak loading rate. Licensed to Wan Roselan Mustapha / Purchased on 12-July-2007 / Single user license only, copying and networking prohibited

(g) The RBC should be covered in order to protect media from effect of UV rays and rainfall.

Adequate ventilation should be provided. (h) The limiting design parameters for RBC are summarised below:Rotating Biological Contactor Soluble BOD5 specific loading on first stage

12 to 20 g/day.m2

Tank volumes

5 I/day.m2 of media

Maximum peripherel velocity

0.35 rn/sec

Minimum number of stages

2 stage

Dry sludge removal

0.8 1.1 kg of dry sludge / kg of BOD removed.

Minimum detention in tank

1 hour

6.4.2.3

-

Detail design

6.4.2.3.1 input arrangements and capacity. Wherever possible installations using RBC system should be supplied by gravity and means provided to minimise surges in flow. especially where

package units are used.

Where crude sewage is admitted by pumping, it is important that the-

average frequency of pumping should not be less than four times per hour throughout most of the day.

39

MS 1228: 1991

Septic tanks or other system of sludge tanks built integrally with RBC should be able to hold at least the total volume of sludge deposited in 1-3 months use, dependent on the size of the plant. at the full design loading. They should provide convenient access for desludging and should be sufficiently rigid to withstand pressure from adjoining compartments during desludging. In integral plants, it is desirable for the inlet zone to be baffled or for a weir providing a head loss of 10 mm to 20 mm to be installed to minimise the effect of surges in flow. Treatment is more efficient when longitudinal mixing is minimized in the treatment zone by installation of a number of transverse baffles each providing a head loss of about 10 mm. The design should facilitate the transfer of excess film, shed from the rotating surfaces from the treatment zone to a secondary settlement unit, either by positive mechanical means or by ensuring that sufficient turbulence is induced to carry it forward in the effluent stream.

6.4.2.3.2

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Rotor units and drire mechanisms. The rotational speed (usually 1-3 rpm) and diameter of the rotating structure govern the peripheral velocity, which should not exceed 0.35 rn/sec to avoid stripping of the biomass. Random media, where employed, should be tightly packed for the same reason. Biological film accumulates more thickly on the surfaces nearest the inlet to the treatment zone, and the spacing between adjacent surfaces of discs in this region should be designed to prevent the bridging of gaps between surfaces. 6.4.2.3.3 Construction. The design and alignment of the drive shaft should provide adequate strength to assure long trouble—free life. Failure of power or other interruption of rotation max’, if continued more than 24 hours, allow the biomass on the rotor to become unbalanced due to drainage and drying of the exposed areas. If the rotation recommences without the proper maintenance and cleaning of the discs, severe strain will be placed on the shaft and drive. It is therefore assential that proper provisions for overload protection of the motor is made that automatic restart for the motor is provided after an electrical failure. Structures supporting the rotor bearings and drive should have a adequate long term rigidity to maintain alignment. Bearing, drive chains and sprockets should be protected from moisture and provided with easy access for lubrication and adjustment. Discs shall be durable materials including expanded metal, plastic mesh, GRP. unplasticized polyvinyl chloride or similar materials or high density polystyrene foam. The packing used in rotating cylinders may be similar to random fill media used in high rate biological filters. Rotors are also used with a variety of surfaces disposed in a spiral or honeycomb form.

6.4.2.3.4

Loading and pei’formance of the biological stage. Where full treatment of domestic sewage to the Environmental Quality (Sewage and Industrial Effluents). Regulations 1979 standard is required the loading of the rotating surfaces in the biological zone should not exceed 5 g BOD/m2/day of settled sewage or 7.5 g BOD/m2/day as crude sewage entering an integrated package plant. Higher loadings may be used provided that adequate technical support data has been supplied. The loading should be based on the maximum population to be served. Where quality standards are critical, additional tertiary treatment (polishing) should be provided.

6.4.3

Suspended growth (Typical diagrams as in fig. 6).

6.4.3.1

Waste stabilization pond

6.4.3.1.1

General

40

MS 1228 : 1991

(a) Waste stabilization ponds can be provided in a variety of combination covering anaerobic. facultative and maturation ponds system. A series of ponds produces a better quality effluent than that from a single pond of the same size and it avoids short circuiting of sewage flow. (b) Ponds have considerable advantages as regards to costs and maintenance requirements and the removal of faecal bacteria over all other methods of treating sewage from communities. (c) Anaerobic ponds are designed to recei\’e very high organic loading or to pretreat strong wastes which have a high solids content where the solids settle to the bottom and are digested anaerobically. The partially clarified supernatant liquor can be discharged into a facultative pond for further treatment. (d) Facultative ponds are the most common and they normally receive raw sewage or that which has received only preliminary treatment for example settled effluent from septic tanks and anaerobic pretreatment ponds.

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(e) Maturation ponds are used as a second stage to facultative ponds. Their main function is the destruction of pathogens such as faecal bacteria and viruses. 6.4.3.1.2 Basis of design. The climate of the area (temperature, sunlight, cloud cover, wind. etc) and the nature of the wastewater to be treated (presence of the toxic chemicals. nondegradable substances, sulphates, total dissolved solids, etc) have a considerable effect on pond loadings, and must be taken into account when designing the system. The design loading for the various pond systems shall be as follows:Parameter

Design Criteria

(a) Anaerobic Pond Liquid depth

-

Maximum loading rate

Detention time Sludge accumulation rate

2.5 m 4 rn 0.4 kg BOD/day.m3 minimum 2 days 0.04 m3/year/capita -

(b) Facultative Pond Total surface loading rate Standard A

Standard B

225 kg/ha/day 330 kg/ha/day

Minimum detention time

Standard A Standard B

14 days 9 days

Maximum surface loading rate for the first stage facultative pond. Standard A 330 kg/ha/day Standard B 505 kg/ha/day Minimum free board Liquid depth (minimum) Sludge accumulation rate

0.5 m

1.5

0.04 rn3/vear/capita

41

MS 1228 : 1991

6.4.3.1.3

Design and constructional details

(a) Pond geometry.

Geometry of pond is not necessary rectangular. All corners of pond should

be rounded-up with a minimum radius of 10 rn. (b) impermeable construction. ground water pollution.

The pond should be impermeable so as to avoid percolation and

(c) En2bankn2ent. The inner slope of pond embankment shall have a protective lining of cement rip-rap 0.3 m thick or cast-in situ concrete slab of 75 mm thick extending from top of embankment to a minimum of 0.5 m below liquid surface, or erosion of the embankment by surface wave action can be avoided by placing precast concrete slabs at the top water level. The inner slope shall have a maximum slope of 1 horizontal to 1 vertical if it is pitched with cement rip-rap or rubble pitching and the slope of the embankment is well compacted. The outer slope shall be protected by turfing or rip-rap if subjected to external water wave action. When it is turfed the recommended slope shall be 3 horizontal to 1 vertical.

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All weather roads of enough width (minimum 3.5 m wide) and strength shall be provided for large trucks or lorries to have easy access to the ponds. Surface runoff must be prevented from entering the pond. (d) inlet and outlet structures. In order to minimise hydraulic short circuiting, the inlet and outlet to each pond shall be of multiple units and located in diagonally opposite corners cross

connection between ponds should also be provided. The inlet into the waste stabilization pond shall be preceeded with a scum chamber to arrest scum or other floating materials from entering the pond. A flow measuring device such as venturi or partial flume to measure inflow and a vee-notch to measure final outflow shall be installed if required. in order to reduce the amount of scum the pipe should discharge below the pond surface with a concrete splash pad at the pond base just below the end of inlet pipe to receive the incoming raw sewage. in order to reduce the amount of scum the pipe should discharge below the pond surface and in order to prevent the formation of a sludge bank, the end of the pipe should be sited up to about 1/3 length of the pond away from the embankrnents. (e)

Facilities shall be provided for by-passing to the first, second and subsequent ponds.

6,4.3.2

Aerated lagoons

6.4.3.2.1 General. Aerated lagoons are essentially similar to waste stabilization ponds except that it is mechanically aerated instead of algal oxygenation, much deeper and has a shorter detention time. An advantage that aerated lagoons have is the relative ease with which additional aerators can be added as population increases or as better efficiency is desired. Aerated lagoons are activated sludge units operated without sludge return. lagoon systems are recommended, namely (i)

Completely mixed aerated lagoon system or the aerobic flow through type; and

(ii) Partially mixed or facultative aerated lagoons system.

42

Two basic aerated

MS 1228 : 1991

Floating aerators are most commonly used to supply the necessary oxygen and mixing power.

6.4.3.2.2

Faculialive aerated lagoons. Facultative aerated lagoons are akin to the alga] ponds used for waste stabilization except that the oxygen is derived from mechanical aeration instead of algal photosynthesis. The power input is sufficient for diffusing enough oxygen into the liquid but not sufficient for maintaining all the solids in suspension with the result that suspended solids in the raw sewage entering the lagoons tend to settle down and undergo anaerobic decomposition at the bottom. It is very significantly affected by changes in temperature. It requires lower power to drive the aerator then the completely mixed lagoons. Sludge accumulation will take place at the rate of 0.04 rn3/year/capita. Anaerobic decomposition leads to liquefaction of solids and a non—degradable residue while the original load of grit and inorganic solids entering the lagoon along with raw sewage also settles at the lagoons bottom. The detention time is much larger than the completely mixed lagoons.

6.4.3.2.3

Contpietelv mixed aerated lagoons st’s/em. The lagoons need more power than the facultative type as the surface aerator has to keep the solids in suspension (as in activated sludge aeration tank) in addition to diffusing enough oxygen into the liquid. The wastewater enters at one end and leaves at the other end of lagoons along with the solids under aeration. Hence the solids concentration in the effluent will be the same as the solids concentration in the lagoon itself. The efficiency of BOD removal concentration in the lagoon is not very high since solids are present in the effluent.

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-

-

6.4.3.2.4

The effluents from the aerated lagoons should be further treated.

6.4.3.2.5 Basis of design. lagoons are set out below.

The design criteria for both the completely mixed and facultative

Table 2. Design criteria for aerated lagoons

Aerated Lagoons Parameters

Completely mixed

Falcultative

Minimum detention period

1 day

2.5 days

Oxygen requirement

0.8 1.1 kg 02 consumed/kg BOD removed.

1.5 1.8 kg 02 consumed/kg BOD removed.

Minimum mixing power

5 kw/l000 m3

3 kw/l000 m3

Minimum freeboard

1.0 rn

1.0 rn

Maximum depth

5 m

5 iTt

BOD removal

50%

60% to 70/

Dissolved ox\gen concentration

—

2 mgi

-

-

43

MS 1228 : 1991

6.4.3.2.6 Design details. The construction of aerated lagoons is essentially the same as that of waste stabilization ponds. The major diff’erences are : greater depths (usually 3 m 5 m) steeper embankment slopes and the provision of a complete butyl rubber or polythene or cemente~iriprap lining (minimum 0.5 m thick) to prevent scouring by the turbulence induced by the aerators. -

Where surface aerators are used, it is preferably to have floating units. Where fixed aerators are used (mounted on columns or stilts) it is essential that the liquid level in the lagoon is maintained constant so as to ensure the required degree of submergence of the aerator blades. Electric cable has to be carried overhead to the aerator from the banks of the lagoon. The steel

ropes used to anchor the aerator to the side banks can be used to carry the cable also. For repairs or maintenance the aerator can be pulled in water to the corner of the lagoon where a small loop or arm can be provided to ‘wet-dock’ the aerator and enable lifting it up for inspection. 6.4 .3 .2 .7 Pond geometry. Aerator ~agoons shall be designed to prevent short circuiting to ensure uniform mixing and aeration. The shape of the pond will depend on the selection of the aeration equipment and zone of influence.

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6.4.3.3

Activated sludge

6.4.3.3.1 General. The activated sludge process is an aerobic, biological process which uses micro-organisms in suspension to remove colloidal, suspended and dissolved substances exerting an oxygen demand. Settled sewage is led to ad aeration tank where oxygen is supplied either by mechanical agitation or by diffused aeration. Aeration of the sewage is followed by settlement in the secondary sedimentation tank with part of the resulting sludge recycled to the aeration system to maintain a high cell concentration (2000 8000 mg/I of MLSS) in the aeration tank and the remainder being wasted for further treatment. -

6.4.3.3.2 Type of processes and modification. The activated sludge process is very flexible and can be adopted to almost any type of biological waste treatment problem. Basically the activated sludge processes comprise of:

(a) Conventional activated sludge (b) Contact stabilization (c) Conventional extended aeration (d) Oxidation ditch (a modified extended aeration process) The other modified activated sludge systems that have become standardized vary from the above 4 processes in the way sewage and aeration is introduced into the tank. They include tapered aeration process, continuous flow stirred-tank step aeration, modified aeration, high rate aeration and the pure oxygen system. 6.4.3.3.2.1 Conventional activated sludge. The conventional activated sludge process consists of an aeration tank, a primary and secondary clarifier, and a sludge recycling line. Sludge wasting is accomplished from the recycle or mixed liquor line. Both influent settled wastewater and recycled sludge enter the tank at the head end and are aerated for a period of about 4 to 8 hours. The influent wastewater and recycled sludge are mixed by the action of diffused or mechanical aeration, which is constant as the mixed liquor moves down the tank. During this period. absorption, flocculation and oxidation of the organic matter take place. The mixed liquor is settled in the activated sludge sedimentation tank and the sludge is returned at a rate of 20-50% of the influent flow rate depending on the MLSS maintained in the aeration tank. 44

MS 1228: 1991

6.4.3.3.2.2 Contact stabilization. The contact stabilization process involves treatment in four distinct compartments. In the first compartment, sewage, which will usually be screened or macerated is aerated in contact with activated sludge for a period of 30 to 90 mm, the mixed liquor then passing to the settlement compartment. After settlement the supernatant liquor

treated effluent) is discharged and the sludge is transfered to a third (re-aeration) compartment where it is aerated for a period of 3 to 6 hours during which time oxidation of absorbed organic material occurs. A large proportion of the activated sludge is then recycled to the first (contact) compartment. There may be a fourth (aerobic digester) compartment where surplus sludge is further aerated to oxidize it as completely as possible before being removed for disposal. 6.4.3.3.2.3 Extended aeration. This process is used extensively for prefabricated package plants. It involves treatment in two compartments, an aeration or mixed liquor compartment and a settlement compartment. Sewage, which will usually be screened or macerated, flow to the aeration compartment where it is aerated in admixture with activated sludge. The sludge is separated from the mixed liquor in the settlement compartment which is usually integral with the first compartment but separated from it by partition. The sludge is recycled to the aeration compartment either by gravity pump or air lift. The supernatant liquor (treated effluent) leaves the plant over a weir. Separate sludge wasting generally is provided.

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Operating experience has indicated that problems have developed in many plants where wasting facilities have not been provided. Provisions shall be made to remove excess sludge and this should be treated prior to disposal. 6.4.3.3.2.4 Oxidation ditch. This is basically an extended aeration system and consists essentially of a Continuous shallow channel 1 m to 3 m deep usually forming an oval Circuit in plan. Raw sewage, after screening and grit removal enters the ditch where mechanical rotors (aerator) aerate the liquid and keep it in circulation. The ditch may be followed by a separate settling tank from which the settled sludge may be returned to the ditch by a pump and the excessive solid be sent to a drying bed while the clear supernatant is discharged. In some cases the ditch itself may be used as settling compartment by periodically shutting off the aerators. Excess solids must be removed as sludge on a regular basis. The long sludge age, acheived by recycling more than 95% of the sludge ensures minimal excess sludge production and a high degree of mineralization in the sludge that is produced. Sludge handling and treatment is almost negligible since the small amount of waste sludge can be readily dewatered without odour on drying beds. The ditch should have a concrete lining with side slopes of about I in 1 .5 vertical, A rigid lining should always be provided in the vicinity of the rotor extending to at least 4.5 rn downstream to prevent damage due to the high turbulence in these areas. The same depth below top water level and preferably of the same cross-sectional area should be maintained for the complete circuit. The ditch should be equipped with one or more mechanical aerators arranged to maintain a velocity of flow in the ditch sufficient to keep the activated sludge in suspension. Provision should be made for separate settlement of sludge before discharge of final effluent in the ditch is designed for continous operations.

45

MS 1228: 1991

6.4 .3 .3 .3

Process design

6.4.3.3.3.1

Applicability

(a)

Biodegradable waste. The activated sludge process and its various modification may be used

where sewage is amenable to biological treatment. (b) Operational requirements ..This process requires close attention and competent operating supervision including routine laboratory control. These requirements shall be considered when proposing this type of treatment. (c) Energy requirements. This process requires major energy usage to meet aeration demands. Provisions shall be made for the emergency energy supply. 6.4.3.3.3.2 Specific process selection. The activated sludge process and its several modifications max’ be employed to accomplish varied degrees of removal of suspended solids and reduction of carbonaceous and/or nitrogenous oxygen demand. Choice of the process most applicable will be influenced by the degree and consistency of treatment required, type of waste to be treated, proposed plant size anticipated, degree of operation and maintenance and operating and capital

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costs. All design shall provide for flexibility in operation. 6.4.3.3.3.3 Pretreatment. Where primary sedimentation tanks are not used, effective removal or exclusion of grit, debris, excessive oil or grease, and communition or screening of solids shall be accomplished prior to the acti\’ated sludge process.Where primary sedimentation is used, provision shall be made for discharging raw sewage directly to the aeration tank to facilitate plant start-up and operation during the initial stages of the plants design life. 6.4.3.3.3.4 Capacity~~~The size of the aeration tank or oxidation ditch for any partkul~r adaptation of the process shall be determined by full scale experiment, or rational calculations based mainly on food to microorganism ratio and mixed liquor sus~ehdèdsolids levels. Other factors such as size of treatment plant, diurnal load variations and degree of treatment required shall also be considered when designing for nitrification and denitrification. Calculations should be submitted to justify the basis for design for aeration tank capacity. Calculation using values differing substantially from. those in table 3 should made reference to actual operational plants. Mixed liquor suspended solids levels greater than 5000 mg/i may be allowed providing adequate data is submitted showing the aeration and clarification system capable of supporting such levels. 6.4.3.3.4

Detail design

6.4.3.3.4.1 General requirement. The installation should incorporate the following features: (a)

adequate protection against corrosion;

(b) standby electrical equipment incorporating automatic changeover, where practicable; (c) automatic restarting in the event of power failure; (d) arrangement for the removal and disposal of surplus sludge; (e) adequate control of flow to minimise risk of washout of activated sludge; (f) 46

if below ground level, adequate protection against floatation.

MS 1228 : 1991

Table 3. Common parameters and operating characteristics of single-stage activated sludge system

Process

Loading -

F/M (Kg B0D/

Hydraulic Detention Time (hrs)

02 required kg/kg BOD removed

MLSS

0.8 1.1

-

1500 4000

-

24

1.4 1.6

-

2000 6000

-

0.5-1.5 ~

0.8 1.1

-

0.4 0.6

-

6000 10000

1.4 1.6

-

2000 6000

SRT (days)

kg of BOD/m

0.32 0.92

-

4

0.16 0.4

-

16

0.48 1.12

-

1.44 2.88

-

3

0.16 0.4

-

16

mg/I

Kg MLSS

Conventional

0.15 0.4

-

5

Extended Aeration

0.05 0.15

-

20

Contact

0.15 0.5

-

3

Stabilization

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Oxidation Ditch

6.4.3.3.4.2.

0.5 2.0 0.05 0.15

15

-

-

30

10

-

-

20

-

30

8

-

-

-

6

-

24

1000

-

3000

-

.4eration ta’akg

6.4.3.3.4.2.1 General. Aeration tanks shall be constructed of reinforced concrete or other approved materials. For large plant,the total aeration tank volume required should preferably be divided among two or more units capable of independant operation. If the wastewater is to be aerated with diffused air, the geometry of the tank may significantly affect the aeration efficiency. The depth of wastewater in the tank should be between 3 m and 5 m so that the diffuser can work efficiently. Freeboard from 0.3 m to 0.6 m above the water line should be provided. The width to depth ratio may vary from 1:1 to 2:1. This limits the

width of tank channel to 6 m to 12 m. For tanks with diffusers on both sides or in the centre of the tank, greater widths are permissible so that ~dead spots’ are eliminated or dimensions should be such as to maintain adequate velocities so that deposition of solids will not occur. Triangular baffles or fillets may be placed longitudinally in the corners of the channels to eliminate dead spots and to deflect the spiral flow. Individual tanks should have inlet and outlet gates or valves so that they may be removed for maintainence.

Aeration tanks must have adequate -foundations to prevent settlement or to prevent floatation in saturated soil. 6.4.3.3..’L2.2 Froth-control system. Large quantities of foam may be produced during start up of the process, when the mixed liquor suspended solids is low, or whenever high concentration of surfactants are present in the wastewater. The foaming action produces froth that contains sludge solids, grease and bacteria and the wind may lift the froth off the tank surface and blow it about. Froth controlling systems should be installed to prevent it from foaming. A series of spray nozzles for spraying, cleanwarer or screened effluent or antifoaming chemical additives can be mounted along the top edge ~f the aeration tank opposite the air diffuser. 47

MS 1228 : 199]

6.4.3.3.4.2.3

Arrangement of aeration tanks

(a) Dirnensio/ls. The dimensions of each independent mixed liquor aeration tank or return sludge reaeration tank shall be such as to maintain effective mixing and utilization of air. Ordinarily, liquid depths should not be less than 3 m or more than 5 m. (b) Short-circuiting. For very small tanks with special configuration, the’ shape of the tank and the installation of earation equipment should provide for positive control of short circuiting through the tank.

6.4.3.3.4.2.4

inlets and outlets

(a) Controls. Inlet and outlets for each aeration tank unit shall be suitably equipped with valves. gates, stop plates, weirs or other devices to permit controlling the flow to any unit and to maintain reasonably constant liquid levels. The hydraulic properties of the system shall permit the maximum instantaneous hydraulic load to be carried with any single aeration tank unit out of service. (b) Conduit.

Channels and pipes carrying liquids with solids in suspension shall be designed to

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maintain self-cleansing velocity or shall be agitated to keep such solids in suspension at all rates of flow within the design segment of channels which are not being used due to alternate f’Iow patterns. 6.4.3.3.4.2.5 6.4.3.3.5

Free board. All aeration tanks should have a free board of not less than 0.5 m.

Aeration equipment

6.4.3.3.5.1 General.

There are basically two methods of aerating wastewater i.e.:

(a) introduce air or pure oxygen into the wastewater with submerger porous diffusers or air nozzles and (b) to agitate the wastewater mechanically so as to promote solution of air from the atmosphere. Oxygen requirements generally depend on maximum diurnal organic lO~ding, degree of treatment, and level of suspended solids concentration to be maintained in the aeration tank mixed liquor. Aeration equipment shall be capable of maintaining a minimum of 2 mg/I of dissolved oxygen in the mixed liquor, in the absence of experimentally determined value, the design oxygen requirements for all activated sludge processes shall be in accordance to Table 3. 6.4.3.3.5.2 Diffused air aeration. A diffused air system consists of diffusers (that are submerged in the wastewater). header pipes, air mains and the blowers and appurtenances through which air passes. The efficiency of oxygen transfer depends- on the type and porosity of the diffuser, the size of the bubbles produced, the depth of submersion etc. The diffuser that produces fine bubbles is recommended for its higher transfer efficiency. As there are many different makes of air diffusers available, the recommended design charts and catalogues from the manufacturer should be submitted for evaluation together with the calculation. Having determined the oxygen requirements, air requirements for a diffused air system shall be determined with the following factors:

48

MS 1228 : 1991

(a)

(i)

Tank depth

(ii) Certified aeration device transfer efficiency (iii) Minimum dissolved oxygen concentration in aeration tank. (‘iv) Critical wastewater temperatOre (b)

Normal oxygen requirements for all activated sludge process are as in table 3.

(c) The blowers shall be provided in multiple units, so arranged and in such capacities as to meet the maximum air demand with the single largest unit out of service. The design shall also provide for varying the volume of air delivered in proportion to the load demand of the plant. Aeration equipment shall be easily adjustable in iOcrements and shall maintain solids suspension within these limits. (d) Diffuser systems shall be capable of providing for the diurnal peak oxygen demand or 200% of the design average oxygen demand, whichever is larger. The air diffusion piping and diffuse system shall be capable of delivering normal air-requirements with minimal friction losses.

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All plants employing less than 4 independent aeration tanks shall be designed to incorporate removable diffusers that can be serviced and/or replaced without dewatering the tank. (e) Individually assemble unit diffusers shall be equipped with control valves. Air filters shall be provided in numbers, arrangements, and capacities to furnish at all times and air supply sufficiently free from dust to prevent damage to blowers and clogging of the diffuser system used. 6.4..3.3.5.3

Mechanical aeration system

(a) Oxygen trans/er performance. The mechanisms and drive unit shall be designed for the expected conditions in the aeration tank in terms of the power performance. Certified testing shall verify mechanical aerator performance. -

(b) Design iequirement (i) Maintain a minimum of 2 mg/I of dissolved oxygen in the mixed liquor at au throughout the tanks. (ii)

times

Maintain all biological solids in suspension.

(iii) Meet maximum oxygen demand and maintain process performance with the largest unit’ out of service, and (c) Provide for varying the amount of oxygen transferred in- proportion to the load demand on the plant. 6.4.3.3.6

Return sIL-Idge equipment

49

MS 1228 : 1991

6.4.3.3.6.1 Return sludge rate. The minimum permissible return sludge rate of withdraw) from the final sedimentation tank is a function of the concentration of suspended solids in the mixed liquor entering it. the sludge volume index of these solids, and the length of time these solids are retained in the sedimentation tanks. Since undue retention of solids in the final sedimentation tanks may he deleterious to both the aeration and sedimentation phase of the activated sludge process, the rate of sludge return expressed as a percentage of the average design flow of sludge return should be generally variable on the basis as F, M ratio and MLSS limits as set forth in table 3. 6.4.3.3.6.2 Return sludge pumps. If motor driven return sludge pumps are used, the maximum return sludge capacity shall be obtained with the largest pump out of service. A positive head should be provided on pump suctions. Pumps should have at least 75 mm suction and discharge openings. If air lifts are used for returning sludge from each sedimentation tank hopper, no standby unit will be required provided the design of the air lifts are such to facilitate their rapid and easy cleaning and provided other suitable standby measures are provided. Air lifts should be at least 75 mm in diameter,

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6.4.3.3.6.3 Return sludge piping. Discharge piping should be at least 100 mm in diameter and should be designed to maintain a velocity of not less than 0.60 m/sec when return sludge facilities are operating at normal return sludge rates. Suitable devices for observing, sampling and controlling return activated sludge flow from each sedimentation tank hopper shall be provided. 6.4.3.3.6.4 Waste sludge facilities. Waste sludge control facilities should have a minimum capacity of not less than 25% of the average rate of sewage flow and function satisfactorily at rates of 0.50/o of average sewage flow or a minimum of 45.5 litres/mm. which ever is larger. Means for observing, measuring, sampling and controlling waste activated sludge flow shall be provided. Waste sludge may be discharged to the concentration or thickening tank, primary sedimentation tank, sludge digestion tank, vacuum filters, other dewatering devices or any practical combination of these units. 6.4.3.4 Secondary sedimentation rectangular or circular in shape.

tank.

Secondary sedimentation tank could be either

6.4 .3 .4.1 Rectangular tanks. The length to depth ratio should be 3 : I or more. The width to depth ratio should be between 1:1 to 2.5 : I. The typical depth is about 3 m and where possible the maximum length of tank should not exceed 10 times its depth. 6.4 .3 .4 .2 Circular tanks. The side water depth should not be under 3 m. It is desirable for the radius of the tank not to exceed five times its side water depth. The floor slope when used in conjunction recommended by supplier of scraper. 6.4.3.4.3 flow.

with scraper mechanism should

be 1:12 or as

Detention time. The detention time should be between 90 to 120 mm

at design peak

6.4.3.4.4 Surface loading rate, When used activated sludge processes the surface overflow rate will depend, on the concentration of the MLSS being settled in the sedimentation tank. For concentration of MLSS of 600 mg/I the overflow rate should be in the region of 60 m3/dav1’m2 and for MLSS concentration of 3500 mg/I and above the overflow rate should not exceed 30 m3/day/m2. Both these overflow rates should be at peak flows unless special flow control devices are provided at the inflow of the clarifyer then this overflow rae of the clarifver should be based on the constant flow rate of this device, 50

MS 1228 : 1991

The lower overflow rates to be used for secondary sedimentation tank for biological filter and RBC units. 6.4.3.4.5

Solid loading iaie. The solid loading rate should be between 2.5 to 6.0 kg/m2/hour.

6.4.3.4.6

Weir loading rate. The weir loading should be in the range of ISO to 180 m3/day/m2.

6.4.3.4.7 Scraper mechanism and sludge pump. Scraper mechanism for the collection and transfer or recycle of sludge should be approved by the Local Authority

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6.4.3.4.8 Secondary sedimentation tank with hopper bottom. The design requirements are the same as 6.3.6 except that the surface loading rate is 30 m /day/m.

51

MS 1228 :

1991

SECTION 7. DISPOSAL OF SEWAGE

AND TREATED

EFFLUENTS

7.1 General. After treatment, the disposal of final effluent into inland waters should comply with the requirement of the Environmental Quality Act 1974 and Environmental Quality (Sewage & Industrial Effluents) Regulations l979-P.U.(A) l2~’79. 7.2

Discharge standard for final effluent

7.2.1

Di’~chai’geto inland waters

7.2.1.1 All discharge from sewage treatment systems into any inland waters within the catchment areas specified in the Fourth Schedule*~shall comply with Standard A. as shown in the third column of the Third Schedule, of the Environmental Quality (Sewage & Industrial Effluents) Regulations 1979 P.U.(.A) 12/79. -

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In particular, where sewage is free from and does not include industrial effluents, the following parameter limits of Standard A may be of primary consideration for the purpose of design of the sewage treatment works: Parameter

Limit in mg/I

Biochemical Oxygen Demand (5-Day: 20°C)

20

Suspended Solids

50

7.2.1.2 All discharges from sewage treatment systems into any other inland waters shall comply with Standard B, as shown in the fourth column of the Third Schedule of Environmental Quality (Sewage & Industrial Effleunts) Regulations 1979. In particular, where sewage is free from and does not include industrial effluents, the following parameter limits of Standard B may be of primary consideration for the design of the sewage treatment works: Parameter

Limit in mg/I

Biochemical Oxygen Demand (5—Day~20°C).

50

Suspended Solids

100

7.2.2 Municipal l-f-”aslL-’water Treatment Plant and Marine Outfall for Municipal Seii’agc Discharge. in accordance with the provisions of the Environmental Quality (Prescribed Activities) (Environmental Impact Assessment) Order 1987, the following are listed as prescribed activities and implementation of which are subjected to environmental imp~ctassessment. (a)

The construction of municipal wastewater treatment plant~

(b) The construction of marine outfall for municipal sewage discharge.

‘NOTE. The Fourth Schedule requires periodic updating with respect to new water supply intakes and due attention should be given to new water supply catchnient areas subject to future gazzettrnent.

52

MS 1228: 1991

In the above event, final discharge standards may differ from those specified as Standard A or Standard B of the Environmental Quality (Sewage and Industrial Effluents) Regulations 1979, and may be presàribed on the basis of those recommended following such an assessment. Disposal of Effluent and Sludge onto Land.

7.2.3

In accordance with the respective

provisions of the Environmental Quality (Sewage and Industrial Effluents) Regulations 1979, the following are subject to the prior written permission of the Director-General of Environment Quality: -

(i)

discharge of any effluent in or on any soil or surface of any land under Regulation 9.

(ii) discharge of any solid waste or sludge that is generated from any effluent treatment plant in or on any soil or surface of any land under Regulation 10, 7.3

Marine o~tfaUs

7.3.1

For a proper design, it is essential to obtain detailed data on The fo~1owing:

(a)

Profiles of possible outfall routes:

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(b) Nature of the ocean bottom; (c)

Water density stratification or thermoclines; and

(d)

Patterns of water movement at point of discharge and travel to shore.

(e)

Tides and currents

(f)

Prevailing winds

(g)

Coastal habitation on either side of this proposal outfall site.

Since seawater is denser than sanitary wastewater, this causes the discharged wastewater rises rapidly, normally producing a ~boil’ at the surface. The rising plume mixes with a quantity of seawater which is generally from 10 to 100 or more times the wastewater flow. Dilution increases rapidly as the ‘wastewater field’ moves away from the boil. The required length and depth of the outfall is related to the degree of treatment of the wastewater. The length must be calculated so that time and dilution will protect adequately the beneficial uses of the adjacent waters. 7.3.2 Where the outfall is deep and there is good density stratification (thermocline). the rising plume may pick up enough cold bottom water so that the mixture is heavier than the surface water. The rising plume, therefore, stops beneath the surface, or reaches the surface and then res u bmerges. 7.3.3 The diffuser must be approximately level if it is to accomplish reasonably uniform distribution. For design of the diffuser, the rule of thumb may be used that the total crosssectional area of the ports should not be more than half the cross-sectional area of the pipe. In large diffusers, often exceeding 1 km in length, the diffuser diameter may be stepped down in size toward the end.

53

MS 1228

1991

7.3.4 Outfalls into the open ocean generally are buried to a point where the water is deep enough to protect them from wave action, usually about 10 m. Beyond the buried portion the outfall rests on the bottom. with a flanking of rock to prevent currents from undercutting it where the bottom is soft. 7.3.5 Outfall pipes lines are constructed of reinforced concrete, cast iron ductile iron, steel or other suitable material. Cast iron is sometimes given a cement mortar lining. Steel is more likel\ to be lined with mortar or bituminous material and is sometimes provided wIth cathodic protection. Joints in the pipe should have substantial mechanical strength and be resistant to chemical or biological corrosion. Ball-and-socket joints have been used in iron pipe, while steel pipe is usually welded. Several ingenious joints have been employed in concrete outfalls. The pipe may be placed in trenches on bottoms of soft rock, sand or gravel. On unstable bottoms piling is necessary. Outfalls may employ a number of ports on the sides or top distributed over a long length of the pipe, perhaps as much as a third of its total length. The ports may be plain or may be fitted with Tees to discharge the sewage in low flows. 7.3.6 The implications of bacteriologicl contamination of tidal waters are difficult to quantify which depends on the climatic and environmental conditions. However the effe~ro~~ub!~ health should not be ruled out.

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The effect on the flora and the fauna in the region of discharge- should be considered and could have se~’ereeconomic implications e.g. on fishing. The presence of floating debris and settled solids can cause local problems, screening of effluent should take place long before discharge.

54

and therefore

MS 1228

1991

SECTION 8. TREATMENT AND DISPOSAL OF SLUDGE 8.1 Process selection. The sludge resulting from wastewater treatment operations and processes is usually in the form of a liquid or semisolid liquid which typically contains from 0.25 to 12% solids. The sludge must be disposed of in a manner which does not give rise to nuisance or public health problems. The following factors shall form the basis of all sludge disposal methods and design. (a) There should be no public health hazard at site of disposal which include odour, ground or surface water pollution and nuisance of insects or rodents. (b) After tipping the deposited sludge must remain firm and intact. (c)

Complexity of equipment, financial and staffing requirement.

(d) A back-up method of sludge handling and disposal. (e)

Methods of ultimate sludge disposal.

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There are many methods of sludge treatment processes and an almost infinite number of combinations are possible. The’ more common and suitable processes applicable to Malaysian conditions are: (a)

Preliminary treatment

(b) Thickening (c)

Stabilization

(d)

Dewatering

(e)

Ultimate disposal

8.2

Preliminary treatment

8.2.1 Sludge storage. Sludge storage must be provided to smooth out fluctuation in the rate of sludge production, to allow sludge to accumulate during periods when subsequent sludge processing facilities are not operating and to ensure a uniform feed rate into subsequent treatment. Short term sludge storage may be accomplished in wastewater sedimentation tanks or in sludge thickening tanks. Long term sludge storage may be accomplished in sludge stabilization processes with long detention times (i.e. aerobic or anaerobic digestion) or in specially designed separate tanks. Such tanks may be sized to retain the sludge for a period of several hours to several days. Aeration of the sludge is necessary to prevent septicity. 8.3

Sludge thickening

8.3.1 General. Thickening is a procedure used to increase the solids content of sludge by removing a portion of the liquid fraction and hence volume reduction. The volume reduction obtained by sludge concentration is beneficial to subsequent treatment processes such as digestion, dewatering, drying and combustion from the following stand points:

MS 1228 : 1991

(a)

Capacity of tanks and equipment required;

(b)

Quantity of chemicals required for sludge conditioning;

(c)

Amount of auxiliary fuel required for heat drying or incineration or both.

8.3.2 Design of thickeners. The design of thickeners should consider the type and concentration of sludge, the sludge stabilization processes, the method of ultimate disposal, chemical needs and the cost of operation. Particular attention should be given to the pumping and piping of the concentrated sludge and possible on set of anaerobic conditions. Sludge should be thickened to at least 5% solids prior to transmission to digescors. In designing thickening

facilities it is important to: (a)

provide adequate capacity to meet peak demands.

(b) prevent septicity wiTh its attendant odour problem, during thickening processes. To reduce the size of the units, the use of sludge storage facilities, should be evaluated.

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8.3.2.1 Gravity thickener. Gravity thickener is accomplished in a tank similar in design to a conventional sedimentation tank. Normally a circular tank is used. Dilute sludge is fed to a centre feed well. The feed sludge is allowed to settle and compact, and the thickened sludge is withdrawn from the bottom of the tank. Enough storage space must be provided for the sludge.

Gravity thickening is most effective for untreated primary sludge. The gravity thickener shall be designed with a maximum surface loading rate of 36 m3/m2.d.

The solids loading are as follows: Type of Sludge

(%) Sludge Concentration

Solids Loading kg/m2d

Unthickened

Thickened

Primary sludge

4

6

Activated sludge

0.5

Trickling Filter sludge

1

-

3

4

-

10

50

Primary and activated sludge

3

-

10

3

-

10

80

Primary and trickling filter sludge

4

-

10

4

-

10

100

-

12 2.5

-

-

1.5

12 -

4.0

150 40

In operation, a sludge blanket is maintained at the bottom of the thickener to aid in concentrating the sludge. The sludge volume ratio (volume 01’ sludge blanket held in the thickenner divided by the volume of the thickened sludge removed daily) shall range between 0.5 to 20 days.

56

MS 1228:1991

8.3.2.2 Floatation thickeners. Floatation thickening is most efficiently used for waste sludges from suspended growth biological treatment processes such as the activated sludge process. The degree of the sludge thickeners floatacion

thickening that can be achieved depends on the initial concentration of the sludge and age at which the plant is being operated. Higher loading can be used with t’loauation than are permissible with gravity thickeners. The limiting values for the design of a thickeners (secondary sludge) is summarised below.

Input concentration

=

5000 mg/I

Output concentration

=

4%

Solids loading

=

10 kg/ha.m2

8.4

Anaerobic sludge digestion

8.4.1 General. Primary and secondary sludges are most commonly treated together in a two stage anaerobic digester. The first tank is used for digestion. The second tank is used for storage and concentration of digested sludge and for formation of a relatively clear supernatant. Where a single stage digestion is used, an alternate method of sludge processing or emergency storage to maintain continuity of service shall be provided.

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8.4.2

Process design

8.4.2.1 Tank capacity. The total digestion tank capacity shall be determined by rational calculation based upon such factors as volume of sludge added, its present solids and character, the temperature to be maintained in the digesters, the degree or extend of mixing to be obtained, and the degree of volatile solids reduction required. Calculations should be submitted to justify the basis of design. When such calculations are not based on the above factors, the minimum combined digestion tank capacity outlined below will be required which assume, that a digestion temperature is to be maintained in the range of 30°C to 38°C, that 40% to 50% volatile matter will be maintained in the digested sludge and that the digested sludge will be removed frequently from the system.

Process

Sludge Age

Loading Factor

Detention Time

Completely mixed system

10 days

1.28 kg/m3.day

30 days

Moderately mixed system

14 days

0.6 kg/m3.day

30 days

8.4.3 Detail design. In a two stage tank system, the tanks are made identical, either one can be the primary. In other cases the second tank may be an open tank, an unheated tank. or a sludge lagoon. The tanks may have fixed roofs or floating covers. Any or all of the floating roofs may be of the gas holder or compressed and stored under pressure.

D /

MS 1228 : 1991

8.4.3.1 Depth. For those units proposed to serve as supernatant separation tanks, the depth should be sufficient to allow for the formation of a reasonable depth of supernatant liquor. Tanks shall be circular and range between 6 m to 35 m in diameter. The minimum water, depth should be 7.5 m at the centre and the minimum sidewater depth of 6 m. 8.4.3.2 Maintenance provisions. To facilitate draining, cleaning and maintenance the following features are desirable: (a) Slope. The tank bottom should slope to drain toward the withdrawal pipe, For tanks equipped with.a suction mechanism for withdrawal of sludge, a bottom slope not less than I : 12 is recommended. Where the sludge is to be removed by gravity alone, I : 4 slope is recommended. (b) Access n2anhole. At least two 900 mm diameter access manhole should be provided in the top of the tank in addition to the gas dome. There should be stairways to reach the access manholes. A separate sidewall manhole shall be provided. The opening shall be large enough to permit the uses of mechanical equipment to remove grit and sand.

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(c) Safety. Non sparking tools, safety lights, rubber solid shoes, safety hardness, gas detectors for inflammable and toxic gases, and at least two self-contained breathing units shall be provided for emergency use. 8.4.3.3 Sludge inlets and outlets. Multiple recirculation withdrawal and return points, to enhance flexible operation and effective mixing should be provided, unless mixing facilities are incorporated within the digester. The returns, in order to assist in scum breakup, should discharge above the liquid level and be located near the centre of the tank. Raw sludge discharge to the digester should be through the sludge heater and recirculation return piping or directly to the tank if internal mixing facilities are provided. Sludge withdrawal to disposal should be from the bottom of the tank. This pipe should be interconnected with the recirculation piping to increase versatility in mixing the tank contents, if such piping is provided. 8.4.4

Gas collection, piping and appurtenances

8.4.4.1 General. All portions of the gas system, including the space above the tank liquor, the storage facilities and the piping, shall be so designed that under all normal operating conditions, including sludge withdrawal, the gas will be maintained under positive pressure. All enclosed areas where any gas leakage may occur shall be adequately ventilated. Total gas production is usually estimated form the volatile solids loading of the digester or from the percentage of volatile solids reduction. Typical values are from 0.5 to 0.75 m3/kg of volatile solids added and from 0.75 to 1.15 m3/kg of volatile solids destroyed. 8.4.4.2 Gas collection. Floating covers fit on the surface of the digester contain and allow the volume of the digester to change without allowing air to enter the digester. Gas and air must not be allowed to mix, or else an explosive mixture may result. The covers may also be installed to act as gas holders that store a small quantity of gas under pressure and act as reservoirs. Fixed covers provide a free space between the roof the digester and the liquid surface. storage must be provided so that: (a) 58

When the liquid volume is changed, gas and hot air will be drawn into the digester.

Gas

MS 1228 : 1991

(b) Gas will not be lost by displacement. Gas can be stored either at low pressure in gas holders that use floating covers or at high pressure if gas compressors are used. Gas not used should be burned in a flame. Gas meter should be installed to measure gas produced and gas used or wasted. 8.4.4.3 Safety equipment. All necessary safety facilities shall be included when gas is produced. Pressure and vacuum relief valves and flame traps, together with automatic safety shutoff valves. shall be provided. Water seal equipment shall not be installed. Gas safety equipment and gas compressors should be housed in a separate room with an exterior entrance. 8.4.4.4 Gas piping and condensate. Gas piping shall be of adequate diameter and shall slope to condensate traps at low points. The use of float controlled condensate trap is not permitted. 8.4.4.5 Gas ulitilization equipment. Gas fired boilers for heating digesters shall be located in a separate room not connected to the digester gallery. Such separated room would not ordinarily be classified as a hazardous location. Gas lines to these units shall be provided with suitable flame

traps.

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8.4.4.6 Waste gas. Waste gas burners shall be readily accessible and should be located at least 7.5 m away from any plant structure if placed at ground level, or may be located on the roof of the control building if sufficiently removed from the tank. All waste gas burners shall be equipped with automatic ignition, such as pilot light or a device using a photoelectric cell sensor. Consideration should be given to the use of natural or propane gas to insure reliability of the pilot light. In rembte locations it may be permissible to discharge the gas to the atmosphere through a return bend screened vent terminating at least 3 m above the ground surface, provided that the assembly incorpOrates a flame trap. 8.4.4.7 Ventilation. Any underground enclosures connecting with digestion tanks or containing sludge or gas piping or equipment shall be provided with forced ventilation. 8.4.5 (a)

Digester heating. The heat requirements of digesters consist of the amount needed to: raise the incoming sludge to digestion tank temperatures.

(b) to compensate for the heat losses through walls, floors and roof of the digester. (c)

to make up losses in the piping system.

-

8.4.5.1 Insulation. Wherever possible digestion should be constructed above ground water level and should be suitably insulated to minimise heat loss. 8.4.5.2 Heating facilities. Sludge may be heated by circulating the sludge through external heaters or by heating units located inside the digestion tank. (a)

External’ heating.

Piping shall be designed to provide for the preheating of feed sludge

before introduction to the digesters.

Provisions shall be made in the layout of the piping and

valving to facilitate cleaning of the lines. transfer requirements.

Heat exchanger sludge piping shOuld be sized for heat

59

MS 1228 : 1991

(b) Other heating methods. Other types of heating facilities will also be considered on their own merits. 8.4.5.3 Heating capacity. Heating capacity sufficient to consistently maintain the design sludge temperature shall be provided. Where digested tank gas is used for heating, an auxiliary fuel supply is required. 8.4.5.4

Hot water internal heating control

(a) it/fixing valves. A suitable automatic mixing valve shall be provided to temper the boiler water with return water so that the inlet water to the heat jacket can be held below a temperature at which caking will be accentuated. Manual control should also be provided by suitable by pass valve. (b) Boiler controls. The boiler should be provided with suitable automatic controls to maintain the boiler temperature at approximately 80°C to minimise corrosion and to shut off the main gas supply in the event of pilot burner or electrical failure, low boiler water level, or excessive temperature.

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(c) Thermometers. Thermometers shall be provided to show temperatures of the sludge. hot water feed, hot water return and boiler water. 8.4.6 Supernatant withdrawal. Supernatant piping should not be less than 150 mm in diameter. The piping should be arranged so that withdrawal can be made from 3 or more levels in the digester. A positive unvalved vented overflow shall be provided. Provisions should also be made for sampling at each supernatant draw-off level using a sampling pipes of minimum diameter 37.5 mm and should terminate at a suitably sized sampling sink or basin. 8.5

Aerobic sludge digestion

8.5.1 General. Aerobic digestion can be used to stabilize primary sludge, secondary sludge, or a combination of the two. Digestion is accomplished in single or multiple tanks, design to provide effective air mixing, reduction of the organic matter, supernatant separation, and sludge concentration under controlled conditions. Its advantages over anaerobic digestion are: (a)

volatile solids reduction is approximately equal anaerobic process

(b)

lower BOD concentrations in supernatant liquor

(c)

production of a relatively odourfree, stable end product that can be disposed easily

(d) production of a sludge with excellent dewatering characteristic (e)

recovery of more of the basic fertilizer values in the sludge

Its disadvantages are due to higher power cost associated with supplying the required oxygen and that a uset’ul by-product such as methane is not recovered. 8.5.2 Detail design. Multiple tanks are recommended. A single sludge digestion tank may be used in the case of small treatment plants or where adequate provision is niade for sludge handling and where a single unit will not adversely affect normal plant operations.

60

MS 1228 : 1991

The determination of tank capacities shall be based on rational calculations, including such t’actors as quantity of sludge produced, sludge characteristics, time of aeration, and sludge

temperature. The aerobic digestion tanks shall be designed for effective mixing by satisfactory aeration equipment. Sufficient air shall be provided to keep the solids in suspension and maintain dissolved oxygen between I to 2 mg/I. A minimum mixing and oxygen requirement of 0.35 I/rn3 shall be provided with the largest blower out of service, If diffusers are used, the non-clog type is recommended, and they should be designed to permit continuity of service. The design criteria are summarised below: Parameter

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(a)

Design criteria for aerobic digeser

Hydraulic detention time (i) Activated sludge (ii) Primary sludge or with activated sludge

10 days 15 days

(b) Maximum volatile solids loading

1.6 kg/m3.d

(c)

Dissolved oxygen level in liquid

1

(d)

Energy requirements for mixing (i) Mechanical aerators (ii) Diffuser

20 w/m3 0.35 l/m3.s

8.5.3 Supernatant separation. removal of scum and grease. 8.6

Sludge drying beds

8.6.1

General.

-

2 mg/I

Facilities should be provided for effective collection and

This method of dewatering is most suitable in hot climatic conditions.

In

determining the area of sludge drying beds, consideration shall be given to climatic conditions. the character and volume of sludge to be dewatered, the method and schedule of sludge removal. It may involve pumping if site levels do not permit gravity flow. Requirements for valves, sumps or pump well will depend on particular site conditions. 8.6.2 Design consideration. Air drying of sludge is carried out on under drained clinker ash or grit-sand drying beds consisting of an adequate number of separate bays where drainage and evaporation occur simultaneously. Sludge is laid on the drying beds in a 200 mm 300 mm layer. Sludge bed loadings are computed on a per capita basis or on a unit loading of kg of dry solids per square meter per year. The time required to dry the sludge depends on the climatic condition and in Malaysian condition it should be from 4 to 8 weeks. The area requirements of the drying bed is as the table below: -

61

MS 1228 : 1991

Table 4. Sludge loading rate

8.6.3

T’~pe of sludge

Area (in2/person)

Sludge loading rate kg dry soIids,/m3.~r

Primary digested

0.09

120

Primary and activate.d (digested)

0.16

100

Primary and humus (digested)

0.1

100

Detail ae.sigu

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8.6.3.1 Floor. The floor of the diving be.d may be of concrete laid to a fall of 1:200 and the walls of brick. insitu concrete or precast panels. 8.6.3.2 Wall. Walls should be watertight and its height above the ground should be kept to a minimum in order to avoid obstruction to the passage of air over the surface of the sludge. v~hich assist evaporation of the surface liquor. The outer walls should be curbed to prevent soil from washing into the beds. 8.6.3.3 Underdrainage system. Sludge dewaters by drainage through the sludge mass and supporting sand and by evaporation from the surface exposed to th~ air. Underdrains should be clay pipe or concrete drain tiles at least 100mm in diameter laid with open joints. linderdrains should be spaced at not more than 6 m apart. The tile should be adequately supported and covered with coarse gravel or crushed stone. 8.6.3.4 Sands. The bed shall consist of a bottom layer of 250 mm depth consisting of coarse agregate graded from 28 mm to 40 mm topped with a 225 mm layer of fine to coarse sand. The finished sand surface should be level. compartment. The drying bed area is partitioned into individual beds. in wide by 6 m to 300 m long or a convenient size so that one or two beds will be filled by a normal withdrawal of sludge from the digesters. The size of bed should be such that it is filled to a depth of each not more than 225 mm at one desiudging operation. 8.6.3.5

Bed

approximately 6

The sludge should discharge onto a .precast concrete slab to avoid scouring of the surface of the bed. Decanting devices should be provided for the removal of the supernatant liquor which forms in the initial stages. Not less than two beds should be provided and they should be arranged to facilitate sludge removal. 8.6.3.6 Sludge influent. The sludge pipe to the drying beds should terminate 300 mm abo~e the surface and be so arranged that it will drain. Tracks or roads of sufficient width for transporting awa the dried sludge b big lorries or trucks should be provided. 8.6.3.7 Buffer. To avoid odour nuisance from poorly digested sludge. sludge beds should he located at least 30 m away from dwellings.

MS 1228: 1991

8.7 Mechanical dewatering facilities. Provision shall be made to maintain sufficient continuity of service so that sludge may be dewatered without accumulation beyond storage capacity. The auxilIaries should be provided to ensure facilities should be sufficient to dewater the sludge produced with one largest unit out of service. Unless other standby facilities are available, adequate storage facilities shall be provided. The storage capacity should be sufficient to handle at least a 3 month sludge production. 8.7.1 Auxiliaiv facilities for vacuum filter. There shall be a back-up vacuum pump and filtrate pump installed for each vacuum t’ilter. It is permissible to have an uninstalled back-up vacuum pump or filtrate pump for every three or less vacuum filters, provided that the installed unit can easily be removed and replaced. 8.7.2 Ventilation. Adequate facilities shall be provided for ventilatiort exhaust air should be properly conditioned to avoid odour nuisance.

01’

dewatering and the

8.7.3 Chemical handling enclosures. Lime-mixing facilities should be completely enclosed to prevent the escape of lime dust. Chemical handling equipment should be automated to eliminate the manual lifting requirement.

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8.7.4 Drainage and filtrate disposal. Drainage from beds or filtrate from dewatering units shall be returned to the sewage treatment process at appropriate points. 8.7.5 Other dewatering facilities. If it is proposed dewater or dispose of sludge by other methods, a detailed description of the process and design data shall accompany the plants. 8.8

Sludge disposal on land

8.8.1 Site selection. The programme of land spreading of sludge must be evaluated as an integral system which includes stabilization, storage, transportation, application, soil, crop and groundwater. Sewage sludge is useful to crop and soil by providing nutrients and organic matter. However, sewage sludge contains heavy metals and other substances which could affect soil productivity and the quality of food and as such care should be taken on the application of sludge especially in relation to food crops. By proper selection of the sludge application site, the nuisance potential and public health hazard should be minimized. The following items should be considered and the regulatory agency should be consulted for specific limits: (a)

Land ownership information;

(b) Groundwater table and bed rock location; (c)

Location of dwellings, road and public access~

(d)

Location of wells, springs, creeks, streams, and flood plains;

(e)

Slope of land surface;

(f)

Soil characteristics;

63

MS 1228 : 1991

(g)

Cl imatological information

(h)

Land use plan; and

(.i)

Road weight restrictions.

8.8.2

General limitations to be observed

8.8.2.1 Stabilized sludge. Only stabilized sludge shall be surface applied for agricultural purposes. Stabilized sludge is defind as processed sludge in which the organic and bacterial contents of raw sludge are reduced to level deemed necessary by the regulatory agency to prevent nuisance. odours and public health hazards. 8.8.2.2 Raw vegetables. Sludge should not be applied to land which is used for growing food crops to be eaten raw such as leafed vegetables and root crops.

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8.8.2.3 Minimum pH. No sludge shall he applied on land if the soil pH is less than 6.5 when sludge is applied. The pH shall be maintained above 6.5 for at least two years following end of sludge application. 8.8.2.4 Persistent organic chemicals. At present, sufficient information is not available to establish criteria of sludge spreading with regard to persistent organic chemicals, such as pesticides and polychiorinated biphenyls (PCB) heavy metals and other toxic substances. However, if there is a known source in the sewer system service area which discharge or discharged in the past such chemicals, the sludge should be analysed for such chemicals, and the regulatory agency shall be consulted for recommendations concerning sludge spreading. 8.9

Sludge pumps and piping

8.9.1

Sludge pumps

8.9.1.1 Capacity. Pump capacities should be adequate but not excessive. Provision for varying pump capacity is desirable. 8.9.1.2 Duplicate units, Duplicate units shall be provided where failure of one unit would seriously hamper plant operation. 8.9.1.3 Type. Plunger pumps, screw feed pumps, recessed impeller type centrifugal pumps, progressive cavity pumps, air lift pumps or other types of pumps with demonstrated solids handling capability shall be provided for handling raw and digested sludge. Where centrifugal pumps are used, a parallel plunger type pump should be provided as an alternate to increase reliability of the centrifugal pump. 8.9.1.4 Minimum head. A minimum positive head of 600 mm shall be provided at the suction side of centrifugal type pumps and is desirable for all types of sludge pumps. Maximum suction lifts should not exceed 3.0 m for plunger pumps. 8.9.1.5 Sampling facilities. Unless sludge sampling facilities are otherwise provid-ed. quickclosing sampling valves shall be installed at the sludge pumps. The size of valve and piping should be at least 400 mm.

64

MS

8.9.2

1228:

IYYI

S/uJ~,’cpiping

8.9.2.1 Size and head. Sludge withdrawal piping should have a minimum diameter of 0() mm for gravity withdra~valand lOU mm for pump suction and discharge Itnes. ‘.\ here wthUra~al is by gravity, the available head on the discharge pipe should be adequate to pros ide a least 0.90 m, s velocity. 8.9.2.2 Slope. Gravity piping should be laid on uniform grade and alignment. The slope of gray itv discharge piping should not. be less than 3~/u. Provisions should be made for cleaning. draining, and flushing discharge lines.

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8.9.2.3 Supports. Special consideration should be given to the corrosion resistance and continuing stability of supporting systems located inside the digestion tank.

6)

MS 1228 : 1991

Appendix A List of references

Al. BS 6297:1983 British Standard code of practice for Design and installation of small sewage treatment works ai~dcesspools. -

A2.

Sewerage Master Plans* in Malaysia.

A3. Wastewater Treatment Plant Design by A joint committee of the Water Pollution Control Federation and American Society of Civil Engineers.

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.A4. Recommended standards for sewage works prepared Mississippi River Board of State Sanitary Engineers 1978.

AS.

Sewerage Treatment in Hot Climates by Duncan Mara.

A6.

Wastewater Engineering by Metcalf and Eddy.

.A7.

Wastewater System Engineering by Homer W. Parker.

by

the Great

Lakes.

Upper

AS. Sewerage Procedures and Requirements for Planning Approval, Building Plan Approval And Sewerage Plan Approval by Sewerage Department,Environniental Engineering Division, Ministry of the Environment of Singapore.

As available in the Economic Planning Unit of the Prime Minister’s Department.

66

MS 1228 : 1991

G

H

23314 30

6

3/4j314

20

223/4 28

4

1/2

Key letter

A

B

C

0

B

LI~htduty

18

24

261o/IB

20l5/ie ~28 22 i~n 11/4 1/32 3/32

Key letter

A

C

Heavy duty

20

Medium duty

E

J

K

L

P4

in

1

1/2 i/a

F

C

0

Approx. W.T. of cover and frame

Grade

1io~5

4 1/2 CWI.

A

li/S

1

4

2114 CWT.

B

L

P4

0

Approx. W.T. of cover and frame

Grade

1/4

7/0

3/~CWT,

C

P

0

31/2 3/4

2

3/4

21/2 7/lB

H

J

K

R

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Dimension in inches

Siat.

PLAN (HALF COVER REMOVED I

PLAN I HALF COVER REMOVED)

‘H

4T ~ SECTION 1-1 LIGHT DUTY MANHOLE COVER AND FRAME

A

SECTION 1-~ HEAVY AND MEDIUM DUTY MANHOLE COVER AND FRAME

Figure 1. Typical diagram for manhole and inspection chamber

67

0/2 CI)

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‘0 ‘0

LIGHT

C. I. M.H 9~ ~

2L0~

‘0

‘0

_I

‘.0

SECTION A—A

Figure

SECTION B-B

1. Typical diagram for manhole and inspection chamber (contd.)

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PATTERN C.I.M.Ij COVER l8”x 24 -

6”CONC.SLAB. REINFORCED WITH 6” CR5

5/~M.sBARS AT

611 -l

IN CEMENT.

I?’l CEMENT S.G.W. CHANNEL BE NC H ING (:2:4 CONc.

6’CONC. FOUNDATION (:3:6 MIX.

SECTION C-C

SECTION D-D

Figure I. Typical diagram for manhole and inspection chamber (contd.)

CI)

P.-’ 00

a’.

‘C ‘C

(-I) I.-’

PATTERN C. I.M.H 1 COYER AND FRAME 18X LIGHT

l.~e 00

24

6”CONC. S~.A6 REINFORCEMENT1 ~~WITH 5/8 ~I 1.1.5 BARS Al 6 CES

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‘0

9’ BRICKWORK

BRICKWORi< IN CEMENT.

IN CEMENT

4 S.G.w PIPE 1

12

o0o~~

SECTION E-E

SECTION F-F

Figure 1. Typical diagram for manhole and inspection chamber (con Id.)

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HEAVY DUTY C’IRON COVER AND FRAME

HEAVY DUTY G’IRON COVER AND FRAME

APPROX1’ GEM. RENDERING TO S~T COVER AT CORRECT LEVEL. 9~BRICKWORK IN

CEM MORTAR.

—

(1:2)FLI.JSH POINTED BOTH SIDES.

COM.SLAB RE/HF WITH / B G BARS AT 54 CR5. 58

.i1I(2~BRIcKWORI< CEM. P’IOPTAR (1:2) F LUSH POINT ED BOTHSIDES U’

-—3/4’RENDERIln IN ALUMINA CEM. AND SAND (1:2) ONE RING BRICK

12” ~ CAST IRON DUCI( FOOT BEND

EDGE ARCH

~

I

•__~

~G~IANNEL

91

CONG. FOUNDATION

FORMED IN

BENCHING RENDERED.

SECTION A-A

CONC. BENCH/tIC TO BE LEV~L WITH SOFFIT OF PIPE SLOPEDTO SIDE OF MANHOLE AT ONE INCH IN ONE FOOT.

PRECAST HIGH ALUMINA GRANOLITIC CEMENT CONCRETE CHARNEL

I

SECTION B-B Figure 1. Typical diagram for manhole nut! inspection chamber (contd.)

I.-’ I’.-’

00 ‘0 ‘0

I..-’

I’.-’ 00

HEAVY DUTY C IRON

HEAVY DUTY C IRON COVER AND FRAME.

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COVER AND FRAME

‘0 ‘0

APPROX 1~CEM. RENDERING TO SET COVER AT CORRECT LEVEL. BRICKWORK IN OEM. MORTAR..

CONC.S~.AB RE/HF WITH 11 5/8. ~IM.S BARS AT t~ CR5.. 911

(12) Ft.USF4 POINTED BOTHSIDES.

131/2” BRICKWORK IN CEM. MORTAR. (1: 2 ) FLUSH POINTED BOTHSIDES. 18~BRICKWORK IN CEM MORTAR

(1:2 ) FLUSH POINTED

i8’~BRICKWORK IN GEM. /40R1AR 1)2) FLUSH POINTED BOTH SIDES.

314’ RENDERING IN ALUMINA CEM. AND SAND

•ONE RING BRICK ON EDGE ARCH.

3/4~RENDERING IN ALUMINA CEM. AND SAND (1:2 I.

18~/~CAST IRON DUCK FOOT BEND.

CONC. BENCHING TO BE

LEVEL WITH SOFFIT OF PIPE SLOPED TO SIE~

12” CONG. FOUNDATION

PRECAST HIGH ALUMINA GRANOLffHIC CEM. CONC. CHANNEL.

SECTION A-A

OF MANHOLE AT ONE

INCH IN ONE FOOT.

SECTION B-B

NOTE 18~BRICKWORK TO CHAMBER WHERE INVERT iS GREATER THAN 10’- 0’ DEEP.

Figure I. Typical diagram

for manhole and inspection chamber (conId.)

DUlY C.IRON COVER AND FRAME HEAVY

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HEAVY OJW C.I1~ GOVER AND FRAME

OROJ’ID LEVEL PLACE COVER TO ~ CORR~T LEVEL

~—2I

•.~L_i / 27

•.

— -~

—~

~

:~ONERING BRICK ON E1X~EARCH

r~ I ~

/~ __C__, ,~2 2’ ‘2’ ~. COVER PLATE ~‘

6’~”X59~X9~ CONC. SLAV REINFORCED WITH 5/8 MS. BARS AT 5 CRS WITH H~OKEDENDS _________

2”Chombe~ .~ ‘,/_

///7 I3~/2BRICKWORK IN -

1-2 CEM. MORTAR FLUSH R)INTED EXTERNALLY

~

ONE RING BRICK ON EDGE ARCH ONE RiNG or~,’..,’. ON EDGE ARCH

0.1 BEND— WITH DUCK FOOT

__

9CONC. FOUNDATION

SECTION

Figure 1

I

—

,,

CEM. 9BRICKWORK MCRTAR POINIED BC’TH SIC€S.

7__7

3//. REINOERING ALUMNA

~CAVLMALLEA~

~

.1

.~ .

SECTION B-B

.

Typical diagram for manhole and inspection chamber (contd.) P.-) 00 ‘0 ‘0

(ID

I—’

00

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HEAVY DUTY CIRON COVER L FRAME.

HEAVY DUTY C IRON COVER AND FRAME~~

‘7

/ BRICKWORK IN CEM. MORTAR

~

‘0 rdPC/tD4fl I FVFI

P ~..~-—-—1~6X3~

~ ~ ~-

Ip X9p CONC SLAB REIN~ORCEO WITH 5/8~~MS BARS 2~ AT 6 CR5. WITH HOOK€ ENDS. ONE RING BRICK

~> ll/ /,~

(1:2) FWSI-I POINTED BOTHSIDES—’

C.

‘0

ON EDGES ARCH

IRON ~OP~LAT~

~

/

D

D.

9~X7~6’X9’COtC.SLAB ~ REINFORCEO WITH 5/8 ~I MS BARS AT 6’CRS WITH HIDOXED EN OS.

18 BRICKWORK IN CEM. (1:2 )FLUSH POINTED EXTERNALLY. ONE RING BRICK ON EDGE ARCH

12’ CONC FOUNDATION

SECTION A-A

SECTION B-B

Figtmre I. Typical diagram for manhole amid inspection chamber (could.)

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MS 1228: 1991

1.

Cho~n for lifting purpose

4.

Level switch for start

2

Level sw~fchfor alarm

~.

Level switch ~r motor stop

3.

Cable

Figure 2. Typical installation of automatic connecting type submersible pump 75

MS 1228 : 1991

ccrru~otedperforated

vent pipe

/~

4’~outlet pipe ..........atuminium stoinles steel or ci tipper

half round. channel

y.c

4’~aeration pipe

asaes.os sheets

(1 .nch fa~I

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tnk Ow/c

2 nominal max. size stones — 9 I layer or 6 I_6 gouge stones

perforated precast cone. under drainage tiles

-

ISOMETRIC VIEW OF SEPTIC TANK & FILTER BED .~(e-V2.”T~ i-a”

Figure 3. Typical diagrams for Septic Tank

76

deen channel

MS 1228 : 1991

1 Inlet

~1

Out let

-

Sel:itc FIlter Bed

—Pump

Sump

~LLi

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Typical Single Compartment Septic Tank

Su mp

Typical

Double Compartment SeptK Tank

Figure 3. Typical diagram for Septic Tank (contd.)

77

MS 1228 : 1991

Hydro~totic v~Iyc /000

i000

p ~ip C

Sluice

cO/cc

00

~iudgc draw work

oi/

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pipc

Adju~to~Ic vc~ wotch or çc:)e/ic/ed wc~r rio/cs

~cu (Sb ocr

Dcc kin with rein o cOb/C ~cc/iori9 ovcr took ccntrc aria roddin9 point 0/ e/uo9C out/ct

PLAN Dimcn~ion or~ .n

TYPIC.4.L UPV~RO FLOW

IUn~ctrc~

SEDIMEW~L~JIUN TANK

Figure 4. Typcal view of a Sedimentation Tank

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Licensed to Wan Roselan Mustapha / Purchased on 12-July-2007 / Single user license only, copying and networking prohibited

TANDA-TANDA STANDARD SIRIM Tanda-tanda Standard SIRIM seperti yang tertera di bawah adalah tanda-tanda pengesahan dagangan berdaftar. Tanda-tanda ml hanya boleh digunakan oleh mereka yang dilesenkan di bawah skim tanda pengesahan yang dijalankan oleh SIRIM mengikut nombor Standard Malaysia yang berkaitan. Kewujudan tanda-tanda mi pada atau berkaitan dengan sesuatu barangan adalah sebagai jaminan bahawa barangan tersebut telah dikeluarkan melalui satu sistem penyeliaan, kawalan dan ujian, yang dijalankan semasa pengeluaran. ni termasuk pemeriksaan berkala kerja-kerja pengeluar menurut skim tanda pengesahan SIRIM yang dibentuk untuk menentukan bahawa barangan tersebut .menepati Standard Malaysia. Keterangan—keterangan lanjut mengenai syarat-syarat Iesen boleh didapati dan: Ketua Pengarah, Institut Standard dan Penyelidikan Perindustrian Malaysia, Persiaran Dato’ Menteri, Seksyen 2, Peti Surat 7035, 40911 Shah Alam. Selangor.

SIRIM STANDARD MARKS The SIRIM Standard Marks shown above are registered certification trade marks. They may be used only by those licensed underthe certification marking scheme operated by SIRIM and in conjunction with the relevant Malaysian Standard number. The presence of these Marks on or in relation to a product is an assurance that the goods have been produced under a system of supervision, control and testing, operated during production, and including periodical inspection of the producer’s works in accordance with the certification marking scheme of SIRIM designed to ensure compliance with a Malaysian Standard. Further particulars of the terms of licence may be obtained from: Director-General, Standards and Industrial Research Institute of Malaysia, Persiaran Dato’ Menteri, Section 2, P.O. Box 7035, 40911 Shah Alam, Selangor.

Dicetak dan diterbitkan oleh: Institut Standard dan Penyelidikan Perindustrian Malaysia. Printed and Published by: Standards and Industrial Research Institute of Malaysia.

MS ISO 10202-6 : 1996 INSTITUT STANDARD DAN PENYELIDIKAN PERINDUSTRIAN MALAYSIA Institut Standard dan Penyelidikan Perindustrian Malaysia (SIRIM) telah ditubuhkan hasil dari cantuman Institut Piawaian Malaysia (SIM) dengan Institut Negara bagi Penyelidikan Sains dan Perusahaan (NISIR) di bawah Undang-Undang Malaysia Akta 157 pada 16hb. September 1975:Akta Institut Standard dan Penyelidikan Perindustrian Malaysia (Perbadanan) 1975. Institut ini diletakhak dengan kuasa untuk memamju dan menjalankan penyelidikan perindustrian dan untuk menyedia dan memajukan standard-standard bagi baranganbarangan, proses-proses, amalan-amalan dan perkhidmatan-perkhidmatan; dan bagi mengadakan peruntukan bagi perkara-perkara yang bersampingan atau berkaitan dengan maksud-maksud itu. Satu daripada tugas-tugas Institut ini adalah menyediakan Standard-Standard Malaysia dalam bentuk penentuan-penentuan bagi bahan-bahan, keluaran-keluaran, kaedah-kaedah ujian, kod-kod amalan yang sempurna dan selamat, sistem penamaan dan lain-lain. Standard-Standard Malaysia disediakan oleh jawatankuasa-jawatankuasa perwakilan yang menyelaras keupayaan pengilang dan kecekapan pengeluaran dengan kehendak-kehendak yang munasabah dari pengguna. Ia menuju ke arah mencapai kesesuaian bagi maksud, memudahkan pengeluaran dan pengedaran, kebolehsalingtukaran gantian dan pelbagai pilihan yang mencukupi tanpa pembaziran.

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Standard-Standard Malaysia disediakan hanya setelah penyiasatan yang lengkap menujukkan bahawa sesuatu projek itu disahkan sebagai yang dikehendaki dan berpadanan dengan usaha yang terlibat. Hasil ini berasaskan persetujuan sukarela dan memberi pertimbangan kepada kepentingan pengeluar dan pengguna. StandardStandard Malaysia adalah sukarela kecuali is dimestikan oleh badan-badan berkuasa melalui peraturanperaturan, undang-undang persekutuan dan tempatan atau cara-cara lain yang sepertinya. Institut ini beroperasi semata-mata berasaskan tanpa keuntungan. Ia adalah satu badan yang menerima bantuan kewangan dari Kerajaan, kumpulan wang dari bayaran keahlian, hasil dari jualan Standard-Standard dan terbitan-terbitan lain, bayaran-bayaran ujian dan bayaran-bayaran lesen untuk mengguna Tanda Pengesahan SIRIM dan kegiatan-kegiatan lain yang berhubung dengan Penstandardan, Penyelidikan Perindustrian dan Khidmat Perunding.

STANDARDS AND INDUSTRIAL RESEARCH INSTITUTE OF MALAYSIA The Standard and Industrial research Institute of Malaysia (SIRIM) is established with the merger of the Standards Institution of Malaysia (SIM) and the National Institute for Scientific and Industrial Research (NISIR) under the Laws of Malaysia Act 157 on 16th. September 1975: Standards and Industrial Research Institute of Malaysia (Incorporation) Act 1975. The Institute is vested with the power to provide for the promotion and undertaking of industrial research and for the preparation and promotion of standards for commodities, processes, practices and services; and to provide for matters incidental to or connected with those purposes. One of the functions of the Institute is to prepare Malaysian Standards in the form of specifications for materials and products, methods of testing, codes of sound and safe practice, nomenclature, etc. Malaysian Standards are prepared by representative committees which co-ordinate manufacturing capacity and production efficiency with the user’s reasonable needs. They seek to achieve fitness for purpose, simplified production and distribution replacement interchangeability, and adequate variety of choice without wasteful diversify. Malaysian Standards are prepared only after a full enquiry has shown that the project is endorsed as a desirable one and worth the effort involved. The work is based on voluntary agreement, and recognition of the community of interest of producer and consumer. The use of Malaysian Standards is voluntary except in so far as they are made mandatory by statutory authorities by means of regulations, federal and local by-laws or any other similar ways. The Institute operates entirely on a non-profits basis. It is a grant aided body receiving financial aid from the Government, funds from membership subscriptions and proceeds from sales of Standards and other publications, fees and licence fees for the use of SIRIM Certification Mark and other activities associated with Standardization, Industrial Research and Consultancy Services.

6