STANDARDS & INDUSTRIAL RESEARCH INSTITUTE OF MALAYSIA
MS 1228 : 1991
ICS 91.140.80
CODE OF PRACTICE FOR
DESIGN AND INSTALLATION OF
SEWERAGE SYSTEMS
MALAYSIAN
STANDARD
This Malaysian Standard, which had been approved by the Building and Ci’ 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.
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
MS 1228 : 1991 CONTENTS 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
Tables
1 Equivalent populations 13
2 Design criteria for aerated lagoons 43
3 Common parameters and operating characteristics of single-stage activated
sludge system 47
4 Sludge Loading Rate 62
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
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)
The Technical Committee on Building Services which prepared this Malaysian Standard consists of the following representatives:
Ir Sugunan Pillay Bhg. Perkhidmatan }Cejuruteraan Kementerian Kesihotan (Chairman)
Ir. Tan Boo Bhg. Perkhidmatan Kejuruteraan Kementerian Kesihatan
Ir. K. Rishyakaran
Ir. Kazal Sinha Bhg. Kerajaan Tempatan Kementerian Perumahan dan Kerajaan Tempatan Ir. Zulkifli Yahya
Ir. Ong Soon Haw
Ii’. Omar Mohd Yusof/ Jabatan Perumahan Negara
Ir. Shamsinar Samad/ Ir. Hasnan Hassan
Encik Mohsin Ali Rahman .labatan Bangunan, Institut Tekno}ogi MARA
Encik Ahmad Najuib/ Jabatan Alam Sekitar
Puan Mariana Mohd Nor
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/ Bahagian Perparitan dan Pembentungan Dewan Bandaraya Kuala Lumpur lr. C. Balasundran
Encik Ali Maidin/ Standards and Industrial Research Institute of Malaysia Puan Mariani Mohammad
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 can be an environmental health hazard. A 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 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.
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 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. Full consideration shall be given to the safety of the public and operators of sewerage systems in the planning, design and construction of such system. The treatment works. pumping station, sewer and sewer appurtenances shall be adequately protected and located where necessary against 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.
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.
1 .2.4 Access. Good all weather access roads shall be provided to the sewer appurtenances, pumping stations and sewage treatment works.
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.apply:-1 Activated sludge. A flocculent microbial mass, produced when sewage is continuosly aerated.
(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;
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.
2.2 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
2.3 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.
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- Specification of Portland Cement (Ordinary and Rapid-Hardening) + MS 1037 - Specification for Sulphate-Resisting Portland Cement.
MS 76 - Specification for bricks and blocks of fire brickearth or shale.
MS ~27 - Specification for refractory bricks
MS 1195:Part 1 -Malaysian Standard Structural Use of Concrete. Part 1:Code of Practice for design and
construction.
MS 922:Part 1 - Specification of Concrete Admixtures. Part 1:Accelerating Admixtures and Water-reducing
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 it in a damp condition for at least four days.
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.
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 Average design flow. The average daily design flow shall be based on 225 litre per person.
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.
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 factories shall be 20 m3 per hectare/day. Other category of industry will be gauge by case basis.
Residential
Commercial:
(includes entertainment/recreational centres, restaurants, cafeteria, theatres)
Schools/Educational Institutions:
- Day schools/institutions — Fully residential
- Partial residential
Hospitals
Hotels (with dining and laundry facilities)
Factories (excluding process wastes)
Market (wet type)
Petrol kiosks/Service stations
Bus terminal
0.2 per student I per student
0.2 per student for non-residential student and 1 per student for
residential student
4 per bed 4 per room
0.3 per staff 3 per stall
18 per service bay 4 per bus bay
Table 1. Equivalent population
No. Type of Premise/Establishment Population equivalent
(recommended)
5 per unit*
3 per 100 m gross area
4 D 6 7 8 9
‘1 peak flow is equivalent to 225 I/cap
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 (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. Pipe joints commonly used include both the flanged and the spigot and socket types.
(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.
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.
(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.
~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
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.
4.3.6 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.
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.
4.4.1 Air test
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 Procedure. The following test procedure should be
adopted:-(a) 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 for stabilization of air temperature.
(e) Adjust air pressure to 100 mm of water.
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.
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.
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 backfilling is completed and after the groundwater level has stabilized, the sewer should be checked for infiltration. All inlets should be sealed and the line inspected from the manholes. Any flow from the pipeline coming into the manholes or within manholes themselves should be 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;
(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.
(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 (1 : 2 : 4 nominal mix) not less than 150 mm in thickness.
(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.
(C) Provision for hinge and/or locking the cover to prevent vandalism and unauthorised access to
\IS 1228: 1991
Ihe following minimum requirements as to the weight and dimension of the frame and cover are a~foliow
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
Heavy Duty As above 530 lbs Use in all carriagewavs.
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 betitoeii 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.
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.
(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.
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
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
(a) 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
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.
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.
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.
(e) 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.
(f) Pumping cycle. 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.
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
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.
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 Alarm systems. Alarm systems shall be provided for all pumping stations. The alarms shall be activated in cases of power failure, pump failure, or any other malfunctioning of the station. Where a municipal facility of 24 hours attendance is provided, pumping stations alarms shall be 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.
(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 Force or pumped mains design
(a) 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) Cast iron pipe
ii) Asbestos cement pressure pipe
iii) Steel—pipe with sulphate resisting concrete lining
iv) P.V.C pressure pipe
v) Ductile iron
vi) 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.
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.
(b) Pressure. Pressure drop is used to start the pumps on plant water systems. Pressure is
generally served by a standard pressure switch.
(c) Flow. Pumps are turned on as flow exceeds a certain value or turned off when flow drops.
Influent flow signals are generally from a flow meter or weir with multivolt control.
(d) 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:
(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.
SECTION 6. TREATMENT WORKS
6.1 General
6.1.1 General process design considerations. The treatment works processes shall be planned and designed to meet the following aspects:
(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
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, where necessary, bypasses, standby units, and protection against floods;
(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; andMS 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
provided so as to control both the hydraulic and organic loading on each modules, and shall be designed for easyoperation, 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) Local zoning requirements
(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
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.
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.
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 PlaNt details
i) 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.
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.
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.
6.1.3 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 .4 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.
6.2 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.
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.
(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.
6.2.3.4 Disposal of grit. -Mechanical grit removal system of collecting and disposal of grit in a sanitary manner should be provided.
6.3 Primary treatment
6.3.1 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.
6.3.1.1 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. (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 Arrangement
(a) Tanks less tha,i 1.25 in width
(i) 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.
(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.
