ms 1228 1991 sewer design
DESCRIPTION
Sewer Design According to Malaysian StandardTRANSCRIPT
MS ISO/IEC TR 10037 : 1995
1
STANDARDS & INDUSTRIAL RESEARCH INSTITUTE OF MALAYSIA
MS 1228 : 1991 ICS 91.140.80
CODE OF PRACTICE FOR DESIGN AND INSTALLATION OF SEWERAGE SYSTEMS
MALAYSIANSTANDARD
© Copyright
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© SIRIM. No part of this publication may be photocopied or otherwise reproduced
without the prior permission in writing of SIRIM
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MS 1228 1991
This Malaysian Standard, which had been approved by the Building and Ci’ il Engineering
Industry StandardsCommittee and endorsed by the Council of the Standards and Industrial
ResearchInstitute 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 Standarddoes not purport to
include all the necessaryprovisionsof a contract.
The Malaysian Standardsare subject to periodical review to Leep abreast of’ progress in the
industriesconcerned.Suggestionsfor improvementswill be recordedand in due course brought to
the. notice of the Committeeschargedwith the revision of the standardsto which they refer.
The following referencesrelate to the work on this standard:
Committeereference : SIRIM 491/11—I
Draft for comment : Dl 13 (ISC D)
Amendmentsissued since publication
Arnd. No. Date of issue Text affected
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MS 1228 : 1991
CONTENTS
Page
Committeerepresentation 3
Foreword 4
1 General 5
2 Materials 10
3 Design flow andorganicloadings 12
4 Sewerandappurtenances 14
5 Sewagepumping stations 21
6 Treatmentworks 27
7 Disposalof sewageand treatedeffluent 52
8 Treatmentanddisposalof sludge 55
Tables
1 Equivalentpopulations 13
2 Design criteria for aeratedlagoons 43
3 Commonparametersandoperatingcharacteristicsof single-stageactivatedsludgesystem 47
4 SludgeLoading Rate 62
Appendx A List of references 66
Figures
Typical diagramfor manholeand inspectionchamber 67-74
2 Typical installationof automaticconnectingtype submersiblepump 75
3 Typical diagramsfor septictank 76-77
4 Typical view of a sedimentationtank 78
5 Fixed film media 79
6 Suspendedfilm media 80
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MS 1228 1991
Committeerepresentation
The Building and Civil Engineering Industry Standards Committee under whose supervision this Malaysian Standard wasprepared, comprises representatives from the following Government Ministries, trade, commerce and manufacturerassociations 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 followingrepresentatives:
Ir Sugunan Pillay Bhg. Perkhidmatan }Cejuruteraan Kementerian Kesihotan(Chairman)
Ir. Tan Boo Bhg. Perkhidmatan Kejuruteraan Kementerian KesihatanIr. K. Rishyakaran
Ir. Kazal Sinha Bhg. Kerajaan Tempatan Kementerian Perumahan dan Kerajaan TempatanIr. Zulkifli YahyaIr. Ong Soon Haw
Ii’. Omar Mohd Yusof/ Jabatan Perumahan NegaraIr. Shamsinar Samad/Ir. Hasnan Hassan
Encik Mohsin Ali Rahman .labatan Bangunan, Institut Tekno}ogi MARA
Encik Ahmad Najuib/ Jabatan Alam SekitarPuan 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 Lumpurlr. C. Balasundran
Encik Ali Maidin/ Standards and Industrial Research Institute of MalaysiaPuan Mariani Mohammad(Secretary)
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MS 1228 : 1991
FORE‘WORD
This Malaysian StandardCode of Practice was preparedby the Technical Committee on Building
Ser’ices under the authority of the Building and Civil Engineeringindustry StandardsCommittee.
In the past,pit privies. conservancysystemsand septic tank systemwere consideredsatisfactory
methods for the disposal of excreta. However, numerous studies have indicated thai these
methods.without further treatmentof the effluents and sludge can be an environmental health
hazard. A number of epidemicsof cholera, typhoid. gastroenteritis.infectious hepatitis and the
like have been closely linked with water supply and contaminatedwith excreta. Furthermore
these systemswere not designedto receivesullage which were dischargedto surfacedrains with
no treatmentand were the only practicablemeansfor disposal of sewage in rural areaswhere the
density of population is low.
The provision of a seweragesystem to collect and convey all wastewaterto a convenientpoint
where the wastewatercan be treatedprior to disposalis very necessaryto protectthe environment
and the health of the people in general. This code of practice deals with planning, design.
installation and testing, which includes the appurtenances,sewagepumping stations. sewage
treatmentworks, sludge treatmentand disposalof effluent. It is intendedfor use by the design
engineer in the planning and the design of seweragesystems,and by the relevant approving
authority for the vetting and evaluationof designs,plans and specificationsfor such works. While
this code provides standards/specificationsfor those experiencedin design. it is also recognised
that not all sewerageworks are designed by such persons.It is, therefore, strongly recommended
that specialist advice be sought where appropriate, particularly in the design of the sewage
treatmentworks.
In the preparationof this code, referenceshave been made to various internationally accepted
codesof practice and standards,adapting them to local conditions. Considerableassistanceand
valuable advice have also been derived from a panel of experts and such assistanceis hereby
acknowledged.
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MS 1228: 1991
CODE OF PRACTICE FORDESIGN AND INSTALLATION OF SEWERAGE SYSTEMS
SECTION 1. GENERAL
1.1 Scope. This code of practice deals with the planning design, construction andinstallation and testing, of seweragesystem,which includes the sewersandsewerappurtenances,sewagepumping stations, sewage treatment works, and all the other works necessaryto collect.convey, treat, and finally dispose domestic sewage and permitted amount of industrialwastewater. This code does not deal with the treatment of industrial effluents (those notpermitted to be dischargedinto the seweragesystem)and operationand maintenance.
This code is intended to indicate what is consideredto be the minimum requirementsfor thedesign of seweragesystemsand good practices,under normal conditions. However, it is alsorealisedthat in certainlocalities and/or circumstances,there may be specialconditions which mayrequire modification to the minimum requirementslaid down in this code.
This Code’s recommendationsshould be supplementedas required by skilled engineeringadvice
basedon knowledgeof seweragework practicesandof local conditions.
1 .2 Fundamentalconsiderations
1.2.11 Legislations. The existing legislations that affect the provisions under this Code, andthat affect the rights and dutiesof the Local Authorities, who are the final approvingauthoritiesof all planspertaining to seweragesystems,include the following:
(a) Local GovernmentAct, 1976.
(b) Streets,DrainageandBuilding Act, 1974:(i) Uniform Building By-laws, 1984.(ii) Drainage,Sanitationand SanitaryPlumbing By-laws, 1976.
(c) EnvironmentalQuality Act, 1974.(i) EnvironmentalQuality (Sewageand Industrial Effluents)
Regulations,1979 - PU. (A) 12/79(ii) EnvironmentalQuality (Clean Air) Regulations,1978.-PU.(A) 28078(iii) EnvironmentalQuality (PrescribedActivities)
(EnvironmentalImpact Assessment)Order 1987.
(d) Town andCountry Planning Act, 1976.
(e) Factoriesand MachineryAct. 1967.
(I’) Electrical InspectorateAct, 1984.
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MS 1228 :1991
1.2.2 Safely. Full consideration shall be given to the safety of the public and operators ofsewerage 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 wherenecessary against unauthorised interference and potential accidents.
Attention is also drawn to the provisions of the Factories and Machinery Act. 1967, with regardsto the safety requirements for operators in sewers and sewage works. Reference can be made tothe Health and Safety Guidelines No. 2 ‘Safe National Joint Health andSafety Committeefor theWater Service, National Water Council. England - 1969’ and occupational health and physicalsafety in the Wastewater Treatment Plant Design by a joint committee of the Water PollutionControl Federation and American Society of Civil Engineers.
1.2.3 Location of facilities. All sewer and sewer appurtenances,pumping stations and sewagetreatmentworks shall be locatedas far from the public right-of-way and habitable buildings aseconomically practicable. The direction of prevailing winds shall be consideredwhen siting thesewagetreatmentworks. Generally, unlessrequiredotherwiseby the prevailing~local conditions,the sewagetreatmentworks and pumping station shall be at least 20 m away from any habitablebuilding. For works wherenoise,odour, aerosols,etc. is a factor the distanceshould be increased.Location of the final dischargepoint for treatedeffluent from seweragetreatmentworks shallalso considerbeneficial usersof the receiving water course.
1 .2.4 Access. Good all weatheraccessroadsshall be provided to the sewer appurtenances,pumping stationsandsewagetreatmentworks.
1 .2.5 Industrial wassewarer. Industrial wastewatersrequire pretreatmentprior to dischargeintothe seweragesystem.Pretreatmentis necessaryto reducetoxic substancesandother materialsthatmay interfere with the normal operation of the seweragesystemor may pose a risk to sewagesystemworkers.
The stipulation of the pretreatment standard for the discharge of Industrial effluent into thesewerage system is the responsibilityof the respectivelocal authority. The Sixth Scheduleof theEnvironmental Quality (Sewage and industrial Effluents) Regulations,1979 - P.U.(A) 12/79,may be used as a guide for dischargeof pretreatedindustrial wastewaterinto seweragesystems.In addition to this, industrial wastewatersshall not containany of the following:
(a) Any liquid, solid or gases, which by itself or in combination with other substances,andwhich by reason of its quantity is likely or is sufficient to cause fire, explosion or to causedamage to any component of the seweragesystem, or be a health hazard or otherwiseobjectionable,or preventsthe entry into the systemby the maintenance/repairworkers;
(b) Any radioactivesubstances;and
(c) Any substancesliable to form a viscous or solid coating or deposition on any part of theseweragesystem,therebyaffecting the performanceof the system.
1.3 References.The titles of publicationsreferred to and otherstandardsof interest in thisfield is given in appendixA.
1 .4 Definitions. For the purposeof this codeof practicethe following definitions apply:-
1 .4.1 Activated sludge. A flocculent microbial mass, producedwhen sewageis continuosly
aerated.
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(g) particulars of potential outfall location, e.g. tidal or inland waters, rivers, streams,ditches orsoakage,also the proximity, highestknown flood level andminimum flow of any streamor otherwatercourseto which dischargeof the effluent is possible;
(h) conditionsunder which the works will be normally operateand be maintained;
(j) possibility of the need for future extension of the works or of their elimination by acomprehensivescheme;
(k) availability of electric power andmains water;
(m) facilities for eventualdisposalof sludge andscreenings.
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MS 1228 : 1991
SECTION 2. MATERIALS
2.] General. All materials used in the constructionof any of the works described in thiscode should comply with the relevantMalaysianStandards.
\Vhere no Malaysian Standard exists, materials should be suitable and adequate for the purposefor 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 theaggregatesshall comply to the requirementsstated in MS 522:Part it
2.3 Cement. Cement used for works included in this code should comply with therequirementsof MS 522:Part l~and MS l037~.
Other type of cementcan be used with the prior approvalby the relevant authorities.
2.4 Cement mortar. Cement mortar selection of the correct cementand aggregatefor theuse in mortars should follow the recommendationsof 2.2 and 2.3. A mortar mix having a 1:3cement/sand ratio is suitable for the following purposes:
(i) brickwork plastering;
(ii) jointing clay or concrete pipes where flexible joints cannot be used;
(iii) renderingof inverts andbenchings;
(iv) beddingandhaunchingmanholecoversand frames.
Calcium chloride should not be addedto 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 concretesurfaces subjected to acid attack and corrosion should be treated and lined with epoxy or othertreatmentsor constructedwith sulphate—resisting cement..
2.6.2 Adniixiures. Admixtures for promoting workability, for improving strength, forentraining air or for any other purpose should be used only with the prior approval of therelevantauthority. Admixtures shall comply with MS 922:Pari 1
MS 29 - Specification for coarseand fine aggregatesfrom 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 andconstruction.
MS 922:Part 1 - Specification of Concrete Admixtures. Part 1:Accelerating Admixtures and Water-reducing
Admixtures.
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Calcium chloride as a admixture should not be used in reinforced concrete. prestressedconcreteor any concretemadefrom sulphate-resistingPortlandcement.For guidance,referenceshould bemade to MSll95.
2.6.3 Workmanship. Concreteshould be mixed in a mechanicalmixer until there is a uniformdistribution of the materials and the mix is uniform in colour. It should be transportedto thepoint of placing as rapidly as practicable by methodsthat will preventsegregationor the loss ofany of the ingredients,placed as soonas possibleand thoroughly compactedby rodding, tampingor vibration so as to form a void free mass around any reinforcement and into the corners of theformwork or excavation.Exposedconcreteshould be cured by keeping it in a dampcondition forat least four days.
2.7 Plastics. All pipes and fittings should comply with the relevant Malaysian Standardsand where practicable should have flexible joints. New plastic products can be used with theprior approval by the relevant authorities.
2.8 Others. Other materials which are not mention in this code can be used with the priorapproval by the relevant authorities and where possible it should comply with all the MalaysianStandard.
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MS 1228 : 1991
SECTION 3. DESIGN FLOW AND ORGANIC LOADINGS
3:1 General. Seweragesystemsshall be designed for the estimatedultimate contributarypopulation, except whenconsideringparts of the systemthat can be readily increasedin capacity.
The design flow and organic loading shall be estimatedon the basisof the estimatedcontributarypopulationand shall include infiltration flows allowances.
3.2 Average design flow. The averagedaily design flow shall be based on 225 litre perperson.
3.3 Design organic loadings. The organic loading from domestic sewageshall be normallybased on 55 g of BOD (5 days at 20°C) per person per day, and 68 g of suspended solids perpersonper day. When existing systemis being upgraded,the design of the new facilities shall bebasedon actualstrengthof the wastewaterflow.
Where industrial wastewateris permitted into the seweragesystems.the loadingsshall be basedonthe permissible levels described under the Environmental Quality (Sewage and lndustrialEffluents) Regulations,1979- P.U.(A) 12/79.
3.4 Estimation of sewageflows and organic loading from various premises.The averagedesigndaily flow may be estimated from a given premises can be determined by multiplying theestimatedequivalent population for that premiseby the averagedaily flow per capita given in3.2. The equivalent population for the various types of premisesgiven in table I can be usedasthe minimum, for the purposeof computing the averagedesign daily flows.
3.5 Industrial wastewater. Where industrial wastewateris permitted into a seweragesystem,the design flows shall be basedon the minimum requirementsgiven in table2.
3.6 Peak flows. The peak hourly flow, which will required in the design of sewers,pumping stationsand componentsof the treatmentplant, shall be determinedfrom the followingformula:
Peakflow factor = 4.7 x
where p is estimatedequivalentpopulation, in thousand.
3.7 Infiltration. While the seweragesystemshall be designedcater for unavoidableamountof infiltration, which arisesfrom faulty joints, crackedsewerpipes and manholes,it is absolutelyimportant that the infiltration into the sewerage system be minimised through properselection ofconstructiontechnologyandmaterials,propersupervisionof Constructionand field testingof thecomponents of system for water—tightness.
For guidance, the seweragesystemmay be designedto cater for a maximum infiltration rate of50 litre per mm. diameter per km of sewer per day.
3.8 The industrial wastewater flow for light industries including flatted factoriesshall be 20 m3 per hectare/day.Other categoryof industry will be gaugeby casebasis.
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MS 1228: 1991
Residential
Commercial:
(includesentertainment/recreationalcentres,restaurants,cafeteria,theatres)
Schools/EducationalInstitutions:
- Day schools/institutions
— Fully residential
- Partial residential
Hospitals
Hotels (with dining and laundryfacilities)
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-residentialstudent and 1 per student forresidentialstudent
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 grossarea
4
D
6
7
8
9
‘1 peak flow is equivalent to 225 I/cap
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SECTION 4. SEWER AND APPURTENANCES
4.1 General. Sanitary sewersshall be designedand installed to collect and convey all wasteflows - both domestic(municipal) wastes and industrial wastes (should be approved by theapproving authority) as well as an unavoidable amount of the ground water infiltration to a pointof acceptable treatment and ultimate discharge. Rain water from roofs, streets,and other areasandground 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 basedon evaluation of the following factors:-
(a) Life expectancy
(b) Previous local experience
(c) Resistanceto internal and externalcorrosionand abrasion
(d) Roughnesscoefficient
(e) Structural strength
(f) Cost of supply, transportand easeof installation
(g) Local availability
4.2.2 Ti’pes of pipe material. Commonmaterial suitablefor sanitarysewersare:-
(a) Vitrified clay pipe (1/C?). Available locally and are manufacturedwith flexible joints inlengthsof 0.6 m to 1.0 m or more and diameterof 100 mm to 300 mm.
(b) Reinforcedconcretepipe. Available locally in sizes ranging from 150 mm to 3000 mm indiameter. Standardlength are 1.83 m for pipe diameterless than 375 mm and lengths of 3.05 infor pipe diametergreaterthan 375 mm. Severalpipe joints are available including the spigot andsockettype with rubber rings.
(c) Fabricated steel with suiphates resistance cement lining. Available in a wide range ofdiameter(100 mm to 1500 mm) and lengths up to 9.0 m. Severalpipe joints are available such asspigot and socket, flange and mechanicalwhich are commonly used for small diametersup to750 mm whilst weldedjoints areusedfor larger diameterpipes.
(d) Cast iron. Available in a variety of diametersand the standardlength of 3.66 m. Pipe jointscommonly usedinclude both the flangedand the spigot andsockettypes.
(e) Asbestoscementpipe. The availablepipe diametersrangefrom 100 mm to 600 mm and thestandard length is 4.0 rn. Pressure pipes are manufactured in various classes suitable for certainlimits of working pressure. Gravity sewers (autociaved only) are manufacturedto Suit variousloading conditions and required crushingstrengths.
(f) Plastic pipes. Available in variety of plastics materials such as UPVC. HDPE, PE and PPand with the nominal range from 110 mm up to 630 mmand of pipe length of 6 m. Pipe jointsare available including spigot end and socket type with rubber seals as well as jointing by flanges.welding and solventcementing.
(g) Other material. As approvedand permitted for their use by the appropriatelocal authority.
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MS 1228 : 1991
4.3 Design of sewers
4.3.1 Economy in the design. While sewersshould generally be kept as short as possible, andunproductive lengths avoided, care should be taken not to restrict potential development.Therouteand depth of a new sewershould always take accountof land where there is the possibilityof future development.
Where sewers are laid at considerabledepths or under highways having expensivefoundationsand surfaces, it may be cheaperor more convenient to lay shallow rider sewers to receive thelocal houseconnections,and to connectthe riders at convenientpoints into the main sewers.
4.3.2 Location of sewers. Adequateaccessto a sewerfor maintenanceshould be allowed. Thefollowing factors should also be considered:-
(a) Location of sewerswithin streetsor alleys right-of-way.
(b) if topographydictates,the sewerto be locatedwithin the private properties,then adequateaccessshould be provided for maintenancepurposes.
(c) The positionof other exsistingor proposedservices,building foundation,etc.
(d) In relation to water mains, a minimum at 3 m horizontal and 1 m vertical separationrespectively to be provided. No sewer line should be above water main unless the pipe isadequatelyprotected.
(e) The impact of the constructionof the sewerandsubsequentmaintenanceactivitiesupon roadusers.
4.3.3 Hydraulic design. The mosteconomicaldesignfor sewergradientsis obtainedwhen theyfollow the natural falls of the ground. Sewersshould, however, be laid at such gradientsas willproducevelocities sufficiently high to prevent the deposition of solid matter in the invert. Theminimum gradient to be adoptedshould normally be such that the velocity of flow doesnot fallbelow 0.8 rn/sec at full bore. The maximum gradient to be adopted should be such that thevelocity of flow is not greaterthan 4.0 m/secwhen flowing half or full bore in order to preventscouringof sewerby erosive action of suspended matter.
4.3.4 Structural design
4.3.4.1 Depths of sewers. Sewersshould be laid at depthswhich will accommodatenot only allexisting propertiesbut also any future propertieslikely to be erectedwithin the area which thesewersare designedto serve; in certaincases,thedepthof basementsmayneedto be considered.
The depth of a sewerwill havea significant effect on the costof its construction. The depth, inconjunctionwith other factorssuch as the natureof theground, presenceof groundwaterand theproximity of foundations,servicesetc, may influence the form and method of construction tojustify the adoptionof alternativelayoutswith longer routesof sewers.
The minimum depthof invert to be adoptedshall be 1 .2 m.
4.3.4.2 Size of sewers. The minimum size of a gravity sewer conveyingraw sewageshall be
200 mm in diameter.
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4.3.4.3 Sewer alignment. Sewersof 600 mm or less in internal diameter shall be laid on astraight alignment and uniform gradientbetweenconsecutivemanholes.Sewersof larger than 600mm internal diameterscan be laid on curves. In such cases,the curve shall be made by anglingthe joints by not exceeding 80°/o of the manufacturersrecommendeddeflection angle and theradius of curvature shall not be less than 60 m. The designershall provide information such asvertical and horizontal alignment for proper construction.
4.3.4.4 Joints. Joints betweensewers,sewer-manholeor other appurtenancestructuresshall beof flexible type and watertight to prevent infiltration and breakages due to differentialsettlement.
4.3.4.5 Foundation. Foundation is needed to maintain the pipe in proper alignment and sustainthe weight of soil above the sewerand any superimposedload.
Bedding for rigid pipes with flexible joints can be classifiedunder two types:-
(a) Class ~A’bedding. Where the pipe is embeddedin carefully preparedbasecompacted with15 mm diameter crusher run extending halfway up to the side of the pipe. The minimumthicknessof 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 oftOO mm thick.
(b) Class ‘B’ bedding. Where the pipes are embeddedin carefully preparedbasecompactedwith15 mm diametercrusherrun extendinghalfway up the sidesof the pipe. The minimum thicknessof the crusher run is 100 mm or 1/4 of the pipe diameter (whichever is greater).The remaindersidefills and top of the pipe shall be compactedcarefully with selectedbackfill to a minimumthicknessof 300 mm.
4.3.5 Inverted siphons. Inverted siphons shall have not less than two barrels with a minimumpipe size of 150 mm and shall be provided with necessaryappurtenancesfor convenientflushingand maintenance.
The manholes shall have adequate clearance for rodding. In general sufficient head shall beprovided and pipe sizes selected to secure flow velocities of at least 0.9 rn/sec for average flow.The inlet and outlet shall be arrangedso that the normal flow is diverted to one barrel, and sothat either may be out of service for cleaning. Since siphons need more cleaning, they must beavoided as much as practicable. The siphon shall not have sharp bends, either vertical orhorizontal.The rising leg shall be limited to 15% slope, for this reason.There shall be no changein pipediameteralong the length of barrel too.
4.3.6 Service connections. Service connectionsshould be of an adequatediameter to reducethe problem of blockage. As it receivesonly intermittent flows, they are invariably subjectedtointermittent stoppagesduring normal operationand theseare removedby wave action rather thanby the maintenanceof a minimum flow velocity. The minimum gradient of 2% should beprovided. The connection should be to the top portion of the main sewer at an angle ofapproximatelyof 45° in the direction of flow. The connectionshould be done with the use of teejunction.
The minimum size of serviceconnectionshall be 150 mm.
4.4 Testing of sewers.
The testing of sewerscan be doneeither by air test or water test. The testsshould be carried outbefore backfilling of the sewer trenches.
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4.4.1 Air test
4.4.1.1 General. It provides a rapid test which can be carri~dout after every third or fourthpipe laid. This could then preventa faulty pipe or a badly madejoint passingunnoticed until itis revealedby a test on a completedlength.
4.4.1.2 Procedure. The following test procedure should be adopted:-
(a) Seal the endsof the pipe run with expandingplugs;
(b) Attach U-tube (manometer)and a meansof applying the air pressureto one of the plugs;
(c) Apply pressureto achievea pressureslightly 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 mmof water.
Without further pumping, the headof water should not fall by more than 25 mm in period of 5minutes.
4.4.1.3 Factors affecting the test. There are severalpossiblecontributing factors that couldeffect the apparentfailure of the air test:-
(a) Temperaturechangesof the air in the pipe due to direct sunshineor cold wind acting on thepipe barrel;
(b) Drynessof 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 otherapparatusare leaking. If the failure is marginal, the pipeline should not be rejectedon the air testalone and the contractorshould be given the opportunity of applying the water test.
4.4.2 Water lest
4.4.2.1 General. Sewersup to and including 750 mm diametershould be tested to an internalpressurerepresentedby 1 .2 m head of water above the crown of the pipe at the high end of theline. The test pressureshould not exceed6 m headof water at the lower endand if necessarythetest on a pipeline can be carriedout in two or more stages.The test pressureshould be related tothe possiblemaximum level of ground water abovethe sewer.
When pipes larger than 750 mm diameterare to be tested, expert advice,and special equipmentrna~’be needed.
4.4.2.2 Procedure. The following testprocedureshould be adopted:-
(a) Fit an expandingplug. suitably strutted to resist the full hydrostatic head, at the lower endof the pipe and in any branchesif necessary.The pipes may need strutting to preventmovement.
(b) Fit a similar plug and strutting at the higher end but with accessfor hoseand standpipe.
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(c) Fill the systemwith water ensuringthat thereare no pocketsof trappedair.
(d) Fill the standpipeof requisite level.
(e) Leave for at least 2 hours to enable the pipe to becomesaturated,topping as necessary.
(f) After the absorption period, measurethe loss of water from the systemby noting the amountof water needed to maintain the level in the standpipe over a further period of 30 mm, thestandpipebeing topped up at regular intervals of 5 mm.
The rate of lossof water should not be greater than 1 litre per hour per metrediameterper linearmetre.
4.4.2.3 Factorsaffecting the test. Excessiveleaking may be due to:-
(a) Porousor crackedpipe;
(b) Damaged,faulty or improperly assembledpipe joints;
(c) Defective plugs;
(d) Pipesor plugs moving.
4.4.3 Straightness. A sewershould be checkedfor line and level at all stagesconstructionbyeither:—
(a) surveyor’s level and staff;
(b) laserbeamwith sighting targets;
(c) lamp and mirrors.
4.4.4 Infiltration. After backfilling is completed and after the groundwater level hasstabilized,the sewershould be checkedfor infiltration. All inlets should be sealedand the lineinspected from the manholes. Any flow from the pipeline coming into the manholesor withinmanholesthemselvesshould be investigatedto establishits source.
In small pipes the point of infiltration may be located visually with light and mirror or with aninflated rubber plug. When conditions justify it a television cameracan be used. The rate ofinfiltration is dependantupon many factors;a guide to its permissibleextentcannot be given; thiswill dependon the judgementof the engineer.
4.4.5 Freedom from obstruction. As the work progressesthe sewer should be checked forobstructionsby visual inspectionor inserting a mandrelor ~pig’ into the line. A televisioncameracan also be used.
4.5 Manholes
4.5.1 ,t’Ianholes location. Manholesor inspection chambershall be provided at:-
(a) The upstreamend of all sewers;however this may be replacedby a terminal layout:
(b) Every changein direction or alignment for sewers> 600 mm;
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(c) Every changein gradient;
(d) Every changein size of sewer;
(e) All intersectionsand junctions.
(f) Distances of not greater than 100 metres for sewers equal to or more than 00 mm indiameter and 150 metres for sewers equal to or greater than 450 mm in diameter. Greaterdistancesmay be permitted in caseswhere adequatemoderncleaning equipmentsfor such spacingis provided, and also in caseswhere sewersconvey pretreatedsewage.
4.5.2 Construction. (Typical drawings as shown in Fig. I). Every manhole and inspectionchambershall be of such sizeand form so as to allow ready accessfor rodding. The struct shouldbe strong, durable and watertight and shall be constructedas follows:-
(a) Brickwork in cementmortar at least 225 mm in thicknessor concrete(I : 2 : 4 nominal mix)at least 125 mm in thicknessor other approved impervious material.
(b) Internal facesshall be renderedwith sulphateresistantcementmortar at least 20 mm thick soas to provide a smooth and impervious surface.
(c) Stepirons, laddersor otherapprovedfittings shall be of non—corrosivedurable material so asto provide safe accessto the level of sewer. Cast iron or stainlesssteel or aluminium alloy isrecommended.The interval betweenstepsshould be 300 mm with slip prevention surface.
~d) Foundationof every manhole shall be constructedof concrete (1 : 2 : 4 nominal mix) notless than 150 mm in thickness.
(e) The channel within the manholeshall be formed with half round pipe madeof the materialas the sewer joining the manholeand shall have a diameternot less than the largest inlet sewerand not more than that of the outlet sewerfrom the manhole.
(1) Every inlet to a manhole shall be dischargeinto the channel therein with properly madebends constructed within the benching of the manhole. The benching shall have a smoothimpervious finish with a minimum slope of 1:12 and so formed as to guide the flow of sewagetowardsthe point of dischargeand to provide a safe foothold.
(g) Manhole shall be constructedin conjuction with its frame and cover to be watertight.
4.5.3 Dimensionand shape.Generally, manholesshall be rectangular,square or circular. Theinternal horizontal dimension shall be sufficient to perform inspection and cleaning operationwithout difficulty and a clear openingshall be provided for accessto the invert. The minimumdimension required shall dependon whether it is a deepor a shallow manhole.
4.5.4 Frame and cover. The manholeframe and cover shall be of cast iron and shall have:-
(a) Adequatestrengthto support superimposedload;
(b) A good fit betweeneachother such that surfacerunoff or rainfall will not get into it.
(C) Provision for hinge and/or locking the cover to prevent vandalismand unauthorisedaccesstothe manhole.
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\IS 1228: 1991
Ihe following minimum requirementsas to the weight and dimensionof the frame and cover area~folio w
Type of coverand frame
Dimension Weight Usage
Light duty 460 mm x 620 mm 54 lbs Use in domesticpremisescompound
Medium Duty Cover 600 mm internalmm. diameter500 mmFrame - 760 mm x
760 mm
250 lbs Use in domesticdrives andsimilar areasfor bearingwheel loads noi exceedingI tonne
Heavy Duty As above 530 lbs Use in all carriagewavs.
4.5.5 Deep manhole dimensions. Where deep manholesare required, its internal dimensionmust be more than 1.5 metre and the manhole may be tapered upwards to a section withminimum internal dimensions of 0.75 metres. In such cases, a minimum headroom of 1.8 in t’romthe baseof manholeshall be provided. The opening to the manholeshall be at least0.6 in.
4.5.6 Shallowmanholedimensions. Where the topography results in a shallow manhole that isin the depth 01’ invert of sewerbeing from 0.9 in to 1.5 m, a manholeof at least I .0 rn in internalhorizontal dimension and a clear opening of’ at least900 mm shall be used.
The dimensionsof the manholesat various depthsshall 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 deepmanhole
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 incomingsewer and manhole invert is less than 600 nim. the invert shall be filleted at the curner~toprevent solids deposition.
4.5.8 Connecilon betitoeii manhole and ~eiver. To mini in se damage to the sewer due todifferential settlement, the joint between the sewerand the manholeshall be of the flexible t~PC.lu acheivethis, a flexible sewer pipe joint just outside the manholema~be used.
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MS 1228 : 1991
SECTION 5. SEWAGE PUMPING STATIONS
5.1 General. Sewage pumping stations should not be subject to flooding and shall be locatedoff the right of way of streetsand alleys preferably on land reservedfor the purposeand readilyaccessibility.
The pumping station structure is a major part of the cost of the station. It is therefore essentialthat it is efficient from a structural standpoint, that it is economical to construct, and that thesize of the wet-well and dry-well and the spacerequirementsof all equipment to be housed,becarefully determined, with efficient use made of all available spaces.
Apart from the pumping facilities which may be required at sewage treatment plants, theprinciple conditions and factors necessitatingthe use of pumping stationsshall be one or more ofthe following:
(a) The topography of the area or district does not permit drained by gravity into trunk sewersor treatment plants.
(b) Omissions of pumping, although possible, would require excessiveconstructioncosts becauseof the deepexcavation 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 purposedsewagetreatmentplant.
All safety and other requirementsshould be met as required under other codes, standardsandregulations.
Pumping stations should be avoided as far as possible since the installation, operation andmaintenanceof a pumping station is costly.
5.2 Design details. (Typical diagram of small pumping station is shown in Fig. 2). Thefollowing design details shall be given consideration in the design of sewage pumping stations:-
5.2.1 Type. The sewagepumping facility provided may be any one of the following type, thechoice dependingmainly on the capacity and efficiency required.
(a) Wet-well type with submersiblepump units
(b) Dry-well type
(c) Lift station, using screw-pumpsor suction lift pumps. Suctionpumps mainly used in sewagetreatmentplants, and have the advantageof handling variation in flow and all solids withoutclogging. However, the suction-lift shall not exceed4.6 in.
5.2.2 Structure
(a) The pumping station substructure shall be of reinforced concrete construction and theexterior wall below ground surface shall be adequately waterproofed and protected againstaggresivesoils and groundwater.
(b) Wet and dry wells, shall be separated.
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(c) Suitablefacilities shall be provided to facilitate the removalof pumps,motorsand any otherequipment in the pumping station.
(d) Suitableand safe meansof accessshall be provided to the dry wells of pump stations, and towet wells containing either bar screensand/or mechanical equipment requiring inspection ormaintenance.
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 perminute merely to protect the starting equipment from overheating and failure caused by toofrequent starting and stopping. On larger installations, the effective capacity of the wet wellshould not exceed 10 mm for the design average 24 h flow. Wet wells that are too large causeserious maintenance and operation problems because of excessive deposition of gritty and organicmaterial.
(b) The wet wells should be narrow but not less than 1.2 m for ready access and should be asdeep as possible in order that the cut-in level of the last pumps will be below the invert of theinlet channel to the wet-well.
(c) Where continuity of pump station operation is important, consideration should be given todividing the wet well in two sections properly interconnected to facilitate repairs, cleaning andexpansions.
(d) Wet wells and suction channels should be designedso that dead areas where solids and scummay accumulate are avoided. The bottom should have a minimum slope of 1 .5 vertical to Ihorizontal to the hopper bottom in the direction of flow so that deposits and scum accumulationsare carried to the pump suctions by the scouring action of the high velocities at low operatinglevels.
(e) The wet well should be well lighted with fixtures that are both vapour proof and explosionproof.
5.2.2.2 Dry well
(a) The size of the dry well dependsprimarily on the numberand type of pumpsselected and onthe piping arrangement. (Totally submerged pumping units do not require dry wells). A goodrule of thumb for those installations requiring dry wells is to provide at least 1 .0 m from each ofthe outboard pumps to the nearestside wall and at least 1.2 m between each pump dischargecasing. Sufficient room is required between pumps to move the pump-off of its base withsufficient clearance left over between suction and discharge piping and room for on site repairs,inspection,or removalfrom the pit to the surfacefor repairs.
(b) Depending on the size of the pump station, considerationshould be given to the installationof monorails, lifting eyesin the ceiling, and ‘A’ frames for the attachmentof portable hoists,cranesand otherdevices.
(c) Provisions should also be made for drainage of the dry well to the wet well.
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5.2.3 Pump Unit
(a) Minimum numberof units. At least 2 Units of pumps shall be provided of which one shall bea standby unit. Constant speedpumpsare recommendedin view of simplicity of operation andmaintenance. If only 2 Units are provided, they shall have the samecapacity each being able tohandle the design peak flow. Where 3 or more units are installed they shall be designedto fitactual flow conditionsand 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 screenswith clear spacings not exceeding 30 mm, unless pneumatic ejectors or screw pumps are used, orspecial devices are installed to protect the pump from clogging or damage. Convenient facilitiesshall be provided for handling screenings. Where the size of pumping stations warrant, amechanically cleaned bar screen or communition device is recommended. For larger or deeperstations, duplicate protection units of proper capacity are prefered.
(c) Pump openings. Pumps shall be capable of passing spheres of at least 75 mmin diameter.Where a communition or screening device is provided, pumps with smaller-sphere passingcapability may be allowed.
Pump suction and discharge openings shall be at least 100 mmin diameter.
(d) Priming. Except for the self-priming pumps, screw pumps and submersible pumps, thegland of the puma shall be so placed that under normal operating conditions, it will operateunder a positive suction head.
(e) Pumping rates. The pumps and controls of pumping stations, shall be selected to operate atvarying delivery rates to permit discharging sewage from the station to the treatment works atapproximately its rate of delivery to the pumping station. The desirable range between themaximum 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 orstop of respective pumps shall not be less than 150 mm.
(f) Pumping cycle. Pumping cycle or time between successive starts, of a pump operating overthe 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 andits suction line where applicable. A check valve shall be provided on each discharge line. Allvalves shall be selected such that the closure time is sufficiently provided to minimise surgepressure and water hammer.
5.2.5 Ventilation. Adequate ventilation must be provided for all sections of the pumpingstations. Where the pump pit is below the ground surface, mechanical ventilation is required.The ventilation shall be so arrangedas to provide completelyseparateand independantventilationfor the dry and wet wells.
Dampers shall not be used on exhaust or fresh air ducts and fine screens or other obstruction shallbe avoided to prevent clogging. Switches for ventilation equipment shall be marked and locatedconveniently. All intermittently operated ventilating systems shall be interconnected with therespective pit lighting system.
Consideration should also be given to automatic controls where dehumidification equipment
where dampness, excessive moisture is a problem.
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(a) Wet wells. Ventilation shall be either intermittent (with at least 30 complete air changesperhour) or continuous(in which case at least 12 complete air changesper hour). Such ventilationshall be accomplishedby 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 beprovided. If intermittent ventilation is proposed,at least 30 complete air changes per hour shallbe provided.
5.2.6 Flow measurement. Provision shall be made to install convenient flow measurementequipment whenever such data is required.
5.2.7 Electrical equipment and power supply. All pump stations should be provided withelectricity from two independentsources(loopedsupply) and be given priority restorationby thepower authority when outages occur. When availability of electrical power supply cannot beassured, the use of standby generators or engine drives as well as in-system storage and by-passshould 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 beprovided.
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. Suchcontrol units or rooms shall be easily accessible, preferably above flood level, and shall be inaccordance to the requirements of other relevant codes and regulations.
5.2.8 Alarm systems. Alarm systems shall be provided for all pumping stations. The alarmsshall be activated in cases of power failure, pump failure, or any other malfunctioning of thestation. Where a municipal facility of 24 hours attendance is provided, pumping stations alarmsshall be telemetered thereto. Where no such facility exists, an audio-visual device shall beinstalled at the station for external observation.
5.2.9 Emergencyoperation. The objective of emergency operation is to prevent in the case ofpower failure or pumping station malfunctions, the indiscriminate overflow of raw or partiallytreated sewage to any waterway and to protect the public by preventing back-up of sewage andsubsequent overflow to basements, streets and other public and private property.
(a) Emergencypower supply. Provision of an emergency power supply for pumping stationsshall be made especially for stations in which interruption due to power is not desirable. Thismay be accomplished by connection of the station to at least 1 standby generator, driven bypetrol or diesel engines.
Where generatoris used, the unit shall be provided with adequatefoundation, and havefacilitiesto remove and perform routine maintenance. Provision shall be made for automaticand manualstart-up and cut-off. The generatorhousing shall be installed with ventilation equipment andlighting. Where internal combustion is used, provision for ventilation of exhaust gases shall bemade.
(b) Portable pumping equipment. Alternatively, portable pumping equipment could be utilised.The pumping facility shall havethe capability to operatebetweenthe well and the dischargessideof the station, with the station provided with permanent fixtures which will facilitate rapid andeasyconnectionof lines.
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(c) Overflow. Consideration shall be given to the provision of overflow. Such provision ofoverflow shall be permitted in areas in which the permitted overflow shall not adverselyaffectthe quality of public water supplies and other receiving water bodies.
5.2.10 Instruction and maintenance. Sewage pumping station and shall be provided with acomplete set of operation and maintenance instructions, including emergency procedures.maintenanceschedules,tools and such sparepartsas may be necessary.
5.2.11 Force or pumpedmainsdesign
(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 notexceed 1.50 rn/sec and discharge 2.5 rn/sec. The velocity in the force mains should be at least 0.9to 1.1 rn/sec.
(c) The pumping main shall be of the following materials:
i) Cast iron pipeii) Asbestos cement pressure pipeiii) Steel—pipe with sulphate resisting concrete liningiv) P.V.C pressure pipev) Ductile ironvi) 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 mmabovethe flow line of the receiving manhole.
(h) The force main and adjoining piping and appurtenanceson the dischargeside of the pumpshould be heavy enough to withstand the maximum hydraulic head on the system, includingabnormal pressures that may be produced by water hammer and surge pressures.
Screening/communiting facilities. Where conventional pumps are used, facilities for screening orcommunition of solids, which are capable of clogging the pumps and/or pumped mains shall beprovided.
5.2.12 Control system
(a) The selection of a control systemand a specific control mode is at least as important as theselectionof the pump. The factors to be consideredin selectinga control systemare efficiency.power factor, reliability, operationaleffects, structuralcosts and easeof operation.
(b) For larger installation, automatic variable speed controls are often more reliable andmaintenancefree than presumablysimpler automaticon off controls. The overall efficiency of avariable speedsystemmay be greaterthan that of an on off systemdespite control losses.
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(c) The sophistication and competenceof the operating and maintenancepersonnel is animportant consideration when selecting control systems which have to match their training andexperience.
5.2.12.1 Manual control
(a) Generally consist of push button stations or selector switches that energize or de—energize thepump motor starter. Manual control systems are rarely used with anything other than constantspeedpumps.
5.2.12.2 Automatic control
(a) Time. Pumpsare started at regular intervals and operate for a presetlength of time. Timecontrolledsystemsare generallyusedfor sludgepumping.
(b) Pressure. Pressure drop is used to start the pumps on plant water systems. Pressure isgenerally served by a standard pressure switch.
(c) Flow. Pumps are turned on as flow exceedsa 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 automaticconstantspeedsystemsoperatefrom level signals. Pumpsareturned on as levels rise and turned off as theyfall. Level detectionsystemsinclude:
(e) Automatic switch over. The controlled system shall be designedto ensureautomaticswitchover of operation betweenavailable pumps in each successivecycle. Level detection systemsinclude:
(i) Float switchesusing a rod or tape. Float type controls are economical,simple and reliablewhen operated in effluent or clear water. When operatedin raw wastewateror sludge,maintenanceproblemscan developfrom greasecoating the float and rods, solids punching thefloats, or corrosionof the float, roadsor tapes.
(ii) Enclosedfloats. Enclosedfloat switchesconsistof an encapsulatedmercuryswitch that maybe either’ open or closed when the float is in the pendant position. As the liquid rises, theposition of the float changes the angle of the mercury switch reversing its condition.
(iii) Electronic probes. With the use of relays, it is possibleto control a single pump or multiplepumps. Enclosed probes in a sealed tube below which is suspended a bladder type container withfluid results in less maintenance problem.
(iv) Captive air system. Captive air systemsusing a diaphragm and small diameter tubing totransmit pressuresignalsto switchesthat turn pumpson andoff.
(v) Pneumaticor air bubbler type control system.This systemis generally used for a duplex ormultipump installation.
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SECTION 6. TREATMENT WORKS
6.1 General
6.1.1 General processdesign considerations. The treatmentworks processesshall be plannedand designedto meet the following aspects:
(a) the effluent quality requirementsas specified in the Third Schedule of the EnvironmentalQuality (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 flowsand characteristics;
(c) the local environmental and aestheticsrequirements,including the proximity to the nearesthabitable premise, direction of the prevailing winds, local zoning requirements, socio—economicaspects, and compatibility of the treatment processeswith the present and future land andreceiving 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 conditionssuch 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 maintenancecosts of the works;
(h) the reliability of the process, including the performance of the process under normaloperating.conditions as well as during unusual or adversecircumstances(a treatmentprocessreliability is the measurementof the--ability of the facility to perform its designatedfunctionwithout failure). The reliability criteria shall include the following:
(i) designing the facility for all anticipated circumstances, and this shall include, wherenecessary,bypasses,standbyunits, and protectionagainst floods;
(ii) the mechanicalequipmentinstalled shall be easily repairedor replacedwithout violating theeffluent limitations for long period of time (this shall also include adequatebackupserviceandthe availability of spare—parts);
(iii) units that require to be taken out of servicefor maintenancepurposeon a routine basis shallbe duplicated in parallel, so that sometreatmentcan be achievedduring the maintenanceperiod:and
(iv) the electric power systemshall be so designed to cater for breakdownsof the power supp1~i,or to switch the circuitary to standby units in the event of breakdownof any units. Wherenecessary,power supply shall be obtained from two sources,one of which shall be a standbygenerator or anotherutility sub-station.
(j) complexity of the processes,including the level of processcontrols required, and level oftrained personnelrequired; and
(k) the ultimate disposalof the sludge.
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6.1.2 Physical designconsideration. Having selectedthe treatmentprocessto be employed,careful considerationsshall be given to the planning and designof the physical facilities.
6.1.2.1 Treatmentworks layout
6.1.2.1.1 Processunits. Careful consideration shall be given to size, shape and the physicalarrangementof the processunits, dependingon the availability of space,the numberof units andeconomics. In selecting the shapeof the unit, dueconsiderationshall be given to the aestheticsaspects, without compromising on the functional aspects of the process unit. Whereverpracticable,multiple modulesthat will compriseof a single processwill be preferred,as this willfacilitate diversion of flows during repairsand/or maintenanceof a module.
6.1.2.1.2 Conduits and their identification. In planning the conduits connecting the variousprocess 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 devicesneed only have manual operators or nuts that can be controlled by portable manual or powerdriven operators.
Where multiple modules of a single process are employed, proper flow division facility shall beprovided so as to control both the hydraulic and organic loading on eachmodules,and shall bedesignedfor easyoperation, change,observationandmaintenance.
All connectingconduits shall be designedto conveythe maximum anticipated flows, includingwhen flows are diverted from one Unit to another for maintenanceor repair purposes. Theconduits shallbe designedto avoid pocketsand cornerswhere solids can settleandaccumulate.
For easy indentification of the conduits and piping, these shall be painted with the followingcolour codes:
Chlorine line - - yellow -
Compressedair line - green
Fuel gas line - orange
Potable water supply line - blue
Sewage/effluentline - grey
Sludgeline - brown
6.1.2.1.3 Plant location
The following items shall be considered when selecting a treatment plant site:
(a) Proximity to residentialareas
(b) Direction of prevailing winds
(c) Accessibility by-all weatherroads
(d) Area available for expansion
(e) Local zoning requirements
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(f) Local soil characteristics,geology,hydrology and topographyavailable to minimize pumping.
(g) Access to receivingstreamby gravity prefer
(h) Water quality of the receiving water course
(j) Compatibility of treatment processwith the presentand plannedfuture land use,includingnoise, potential odours,air quality, and anticipatedsludge processinganddisposaltechniques.
6.1.2.1.4 Structure to be reinforcedconcrete
Unless otherwiserequired,wall, slabs, beams,columnsand structurefor sewerageplant shall, ingeneral, be in reinforced concrete. Walls shall haveminimum thicknessof 225 mm. Brickworkmay be usedin shallow chamber.
Where a sitemust be usedwhich is critical with respectto thoseitems, appropriatemeasuresshallbe taken to minimize adverseimpacts. The treatment plant should be located in an area notsubject to flooding or otherwise~e adequatelyprotectedagainstflood 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 degreeof treatment for sewagetreatmentplants shall be basedon the parameterlimits as specified in the Third Scheduleand the objectivesfor the receiving waters as establishedby the Ministry of Health/Departmentof Environment. In any case the effluent must beadequatelydisinfectedto destroydiseasecausingorganisms.
6.1.2.1.7 Flow
The sewagetreatmentplant shall be designedto serve the ultimate contributary populationbasedon an averagedaily per capita flow of 225 liters, to which must be addedan anticipatedamountof industrial wastewaterand some allowancesfor infiltration. Where a plant is designedto servean existing seweragesystem, the plant shall be designedon the basis of actual flow measurements,plus allowancesfor estimatedfuture populationand shall be stagedas required.
i) Operating equipments
A complete rangeof tools, accessoriesand spareparts necessaryfor the plant operator’suseshallbe provided togetherwith the necessarystoragespace.
ii) Grading a,zcl landscaping
Upon completion of the plant, the ground should be graded. Conreteor hard surfaced walkwa\sshould be provided for accessto all units. Surfacewater shall not be permitted to drain into anyunit. Landscapingshould be provided especiallywhere a plant is located near residential areas.Lansdcapingshould be provided at all such plants to cover the harsh and unpleasantsight ofsewagestructures.
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6.1.2.1.8 Plant oulfalls
The outfall sewer should be designedto dischargeto the receiving waters with the considerationfor the following:
i) Preferencefor freefall or submergeddischarged.
ii) Utilization of cascadeaerationof effluent dischargeto increasedissolvedoxygen.
iii) Limited or completedispersionacrossreceiving waters.
6.1.2.1.9 Organic loading
The processdesign of a domesticwastetreatmentplant shall be on the basisof 55 gramsof BODper capita per day and 68 grams of suspendedsolids per capita per day. When an existingtreatmentworks is to be upgradedor expanded,the design shall be basedupon the actualstrengthof the wastewater. Domestic waste treatment plantsdesigned to include these industrial wasteloads should take into considerationthe shock effects of high concentrationsand diu-rinal peaksfor short periods of the time on the treatmentprocessparticularly for small treatmentplants.
6.1.2.1 .10 Flow division control
Flow division control facilities shall be provided as necessaryto ensureorganic and hydraulicloading control to plant processunits and shall be designedfor easyoperator access, change,observation and maintenance.
6.1.2.1.11 PlaNt details
i) Installation of mechanicalequipment
The specificationsshould be written such that the installationand initial operationof major items
of mechanical equipment will be supervised by a representative of the manufacturer.ii) Unit b,vpass
Bypass structureand piping properly locatedand arrangedshould be provided so that each unitof the plant can be removedfrom service independently.
iii) Appropriateeffluent sampling
The outfall sewershould be so constructedandprotectedagainsttheeffects of floodwater, tide orother hazardsas to ensureits structuralstability and freedomfrom stoppage. A manholeshouldbe provided at the shoreendof all gravity sewersextendinginto the receivingwaters. Hazardstonavigation shall be consideredin designingoutfall sewers. Provision shall be madefor samplingof influent or effluent as well as individual processunit.
6.1.2.1.12 Essentialfacilities
All plants shall be provided with an alternate source of electric power to allow continuity ofoperation during power failures. An adequatesupply of potable water under pressureshould beprovided for use in the laboratory and for generalcleanlinessaround the plant. Toilets, shower,lavatory and locker facilities should be provided in sufficient numbersand convenientlocation toservethe expectedplant personnel. Flow measurement facilities shall be provided at all plants.
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6.1.2.1.13 Safely
Adequateprovision shall be made to effectively protect the operator and visitors from hazards.The following shall be provided to fulfill the particular needsof eachplant:
(i) Fencingof the plant site to discouragethe entranceof unauthorizedpersonsandanimals.
(ii) Hand rails and guardsaround tanks, trenches,pits, stairwells and otherhazardousstructures.
(iii) First aid equipmentincluding CPR.
(iv) “No Smoking signs in hazardous areas.
(v) Protectiveclothing andequipment.
(vi) Portable lighting equipment.
6.1.2.1.14 Laboratory
All treatmentworks shall include a laboratoryfor making the necessaryanalytical determinationand operatingcontrol tests, except in individual situationswherethe omissionof a laboratory isapprovedby the reviewing agency. The laboratory shall have sufficient size, bench-space,equipmentand supplies to perform the processcontrol tests necessaryfor good managementofeach treatment process included in the design.
6.1.3 Measuringdevices. Devicesshould be installed in all plants for indication flow ratesof raw sewage or primary effluent, return sludge, and air to each tank unit. Where the designprovides for all return sludge to be mixed with the raw sewage(or primary effluent) at onelocation then the mixed liquor flow rate to eachaerationunit should be measured
6.1 .4 Evaluation of new treatment processes. ifl the case of a particular new treatmentprocess not included in this code of practice, the designer shall obtain approval of the proposedtreatment process to the relevant approving authority.
6.2 Preliminary treatment
6.2.1 Bar screens. Bar screensshall be provided upstreamof pumpsor treatmentfacility
for protectionagainstclogging and damage.
The screeningdevicemay he manually-cleanedor mechanicallycleaned.
6.2.1.1 Manually or mechanicallycleanedscreens.Clear openingbetweenbars shall be from25 mmto 30 mmand 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 averagerate of flow.
The approachchannelshould be so designedto ensurea 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 screenshall be provided.
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6.2.2 Fine screens. Fine screens, where used for pre-treatmentor primary treatmentshouldbe installed to manufacturer’s specification and require prior approval of the Local Authority.
6.2.2.1 Disposalof screening. Screeningsshould be removed,handled, storedanddisposedin asanitary manner.
6.2.3 Grit removal. Grit removal facilities may be consideredas optional processdependingon the nature of sewage to be treated. Grit removal systemsmay compriseeither the HorizontalConstant Velocity Grit Chamberor the AeratedGrit Chamberor Detritor.
6.2.3.1 Horizontal constant velocity grit chamber
(a) The flow through velocity should not exceed0.23 rn/sec
(b) The surfaceloading rate should not exceed1500 m2/d/m2.
6.2.3.2 Aeratedgrit chamber
(a) Maximum detention time to be 3 mm.
(b) Air ratesshould 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 exceed0.3 rn/secat peakflows
(b) Tangentialflow entry into detritor width minimum turbulence.
(c) Water depth in tank to be controlled by weir outlet.
(d) Reciprocating inclined dewatering systemsshould be incorporated for washing grit andreducing organic content.
6.2.3.4 Disposal of grit. -Mechanicalgrit removal systemof collecting and disposal of grit in asanitary manner should be provided.
6.3 Primary treatment
6.3.1 Design criteria for septic tanks. (Typical diagramsas in fig. 3). Septic tanks are to beeither rectangularor cylindrical chamberssited or constructedbelow ground level. They are tobe of watertight construction so that they neither permit ingress of ground water or engressofsewageto the ground.
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6.3.1.1 Capacity. The capacity of the septic tank should be basedon the number of persons orequivalentpopulation servedbasedon the following formula:
C = 225 P
where
C is the capacity of the tank in litres and
P is the designedpopulation or equivalentpopulation
The minimum capacityof septic tank should not be less than 2000 litres and should not servean
equivalentpopulationof more than 150.6.3.2 Rectangularseptic tank.
6.3.2.1 Minimum requirements. Rectangularseptic tanks should have the following minimum
dimensions:
(a) Minimum liquid depth of 1.25 m but not more than 2.0 rn.
(b) Should havewidth not less than750 mm,
(c) Have a length not less than2 times its width.
(d) Should be roofedandhavea minimum water free-boardof 250 mm.
(e) Adequateopeningfor desludgingandmaintenanceshould be provided.
(f) Accessfor desludgingvehiclesshould be provided.
6.3.2.2 Arrangement
(a) Tanksless tha,i 1.25 in width
(i) The septic tank shall be constructed with 2 or more compartments, either 2 separated tanksor 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 inletend. The baffle shall extend 150 mm above TWL andshall leave a minimum clearanceof about500 mm at the bottom.
(iii) The inlet andoutlet shall be a vertical 150 mm diametercastiron T-~shapeddip pipe with thetop limb extendingabovescumlevel and the bottom limb extending500 mm below TWL.
(iv) The invert of the inlet dip-pipe should be 75 mm abovethe invert of outlet dip-pipe.
(v) The floor of the tank should be sloped towardsthe inlet endat 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 compartmentsin series. The
inlet compartmentsto havea capacityof twice that of the secondcompartment.33
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(ii) The influent into tanks of more than 1 .25 m width shall dischargeinto a channelwhich feedstwo or moredip-pipes. The two compartmentsshould also be interconnectedby equalnumberofdip-pipes.
(iii) The outlet shall be in the form of weir which should extend the full width of the tank.Scum boardsshould 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 precastand factory-madethey requires the approval of the relevantAuthority on an individual basis.
6.3.4 Design criteria for inihoff tank
6.3.4.1 Sedimentation compartment
The sedimentationcompartmentshall have a capacityof not less than 2 hours detention time foraveragedaily flow of 225 litres/cap./day.
It shall havea surfaceoverflow rateof not more than 30 m3/m2/dayat design peakflow.
The sedimentation compartment shall have a length to width ratio of not less than 3 to I.
Minimum width shall be 600 mm anddepthof not less than900 mm or more than2.8 in.
In the sedimentation compartment of the lmhoff Tank the side slopesshall have a slope of not
less than 1 .5 times verticalto I horizontal.
The compartment shall have a false bottom and communication with the sludge digestioncompartmentshall be by means of a horizontal slot minimum 150 mm wide running the fullwidth of the tank.
A slot overlap of at least 200 mmto be provided.
6.3.4.2 Sludge compartment
The sludge digestioncompartmentshall havea capacityof not less than0.04 m3 per capita.
The floor of the compartment will have a slope of I vertical to 4 horizontal towardsthe sludgedraw-off pipe.
The sludge draw-off pipe shall be of cast-iron and not less than 100 mm and shall draw offsludgefrom the bottom of the sludgecompartment.
Sludgesamplingpipesfor sludgedraw-off aboveandbelow the neutral zoneshall be provided.
The scum compartmentshall havea width not less than 450 mm or 25% of the total surfaceareaof the sedimentation compartment, whichever is larger.
The scum compartmentshall be adequatelyvented and facilities for adequateremoval of gasprovided.
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6.3.4.3 Neutral zone. A neutral zone of not less than 300 mm deep shall be provided betweenthe 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 diametercast-ironT-shapeddip-pipe with the top limb
extendingabovethe scum level and the bottom limb extending500 mm below the TWL.
For wider tanks multiple inlets to be provided.
The outlet shall be in the form of weir which should extendthe full width of the tank.
Scum boardsshall be provided at the inlets and outlets and in the larger tanks at intermediatepoints. The scum boards shall be submerged at least 600 mmand extended by at least 450 mmabove TWL.
The TWL in the sedimentationtank shall be at least 75 mm below the invert level of the inletsewer.
6.3.4.5 Reversal of flow direction. In large installations with multiple units of sludgecompartment, provision shall be made for reversal of flow periodically, so as to obtain evendistribution of sludge.
6.3.4.6 Effluent. Effluent from septic and imhoff tanks require secondary treatment inbiological 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 areinforced concrete cast-in-situ slab with adequate openings with air-tights manholes covers forinspection and maintenance or covered with precast reinforced conc.rete slabs fitted with liftinghandles and having grooves for jointing with line to prevent emission of smell and breeding ofinsects. - -
6.3.5 Ventilation. In all septic and imhoff tanks the space between the top of the water leveland the roof shall be:
(a) Adequately ventilated;
(b) Provided with adequate means for dra~ving off gases;
(c) All ventilation provided shall be proofed against the entry of mosquitoes.
6.3.6 Prima,)’ sedimentationtank
6.3.6.1 General. Sedimentation tanks may provide the principal degree of wastewatertreatment, 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.
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When used as a preliminary step to further treatment the main function of primarysedimentation tank is to reduce the organic loading on the secondary treatment units and areessentially components of secondary sewage treatment.
The efficiency of a sedimentationtank is dependenton the velocity of the flow, which isdetermined by the tank dimension. Effective flow measurement devices and controlappurtenances shall be provided to permit proper proportioning of flow and solids loading to eachunit. 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 circularconfigurations are recommended for larger flows.
6.3.6.2 Rectangular tanks. The length to width ratio should be 3: 1 or more. The width todepth ratio should be between 1 : 1 to 2.5 : I. Typical depth of rectangular primarysedimentation tank is 2.5 m to 3.0 m.
6.3.6.3 Circular tank. The side water depth should not be under 3 m. The floor slope whenused in conjunction with scraper mechanism should be I : 12 or as recommended by supplier ofscraper.
6.3.6.4 Detention time. Detention time should vary with depth of tank and surface loadingrate 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 theinlet end of the tank. The settled sewage is collected at the opposite end for treatment. Forcircular tanks the loading can either be central or peripheral. The surface loading rate at peakflow 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:l i~±ori~’.6.3.6.8 Primary sedimentation tank with hopper bottom and rectangular (Typical diagramsas in fig. 4).
6.3.6.8.1 Upward flow sedimentation tanks. An upward flow tank is normally square orcircular 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 weirand suspended material fall into the hopper.
[n designing hopper bottom tanks an angle of slope of 60° (giving 51° valley slope) will usually besaListactory. In order to reduce sludge accumulation in the valley angle, a tank of steeper angleof slope of 68° (giving 60° valley slope) may be considered.
6.3.6.8.2 Capacity. The capacityof the hopper should be equivalent to 2 hours detention timeat peak flow.
Additional water depth of minimum 400 mmshould be provided above the hopper in the verticalside-wall section between the top of the hopper and the TWL. The side-wall height should notbe less than 400 mm.
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6.3.6.8.3 Horizontal flow tank. A horizontal flow tank is normally rectangular in plan andshould 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 desludgingtwin tanks should be provided for larger installation.
6.3.6.8.4 Surface loading rate. The overflow rate should not be greater than 60 m3/day.’m2
primary sedimentationtank.
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 primarystages of treatment which were described in the earlier chapters of this code can efficientlyremove 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 theyconsists of a wide range of organic and inorganic materials.
The usual way in which the remaining fraction can be further treated is to encourage micro-organism to oxidize the organic material in a similar manner to that in the natural processoccuring in rivers and streams but at an increased rate.
In such secondary treatment the organic material is made to come into contact with micro-organisms either in a ~Fixed Film Media’ or a ~Suspended Film Media’.
The most commonly used biological processin the fixed film media is the trickling filter and inthe 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 diagramsas in fig. 5).
6.4.1.1 Mineral media. For sewage treatment plant of 500 persons capacity or less therectangular type of percolating filter with tipper, chute and channel distribution system of settledsewagemay be used.
Tipper, chute and channel shall be madeof aluminium sheetof minimum 2 mm thicknessor ofcast iron or stainlesssteel. The size. capacity,dimension,support shall be approvedby the LocalAuthority.
Tipper trough should have a capacity equivalentto 4.5 litres/rn2 of filter surfacearea.
For sewagetreatmentplant above 500 personscapacity the circular type percolating filter withdosing syphon and rotary type distributors and ancillaries shall be used. Dosing syphon, rotarydistributorequipmentshall be of’ approvedmake, size,capacityand material anddesignedfor 3 xDWF. The distributor arm shall be approximately150 mm to 300 mm above the media line.
The averagedepth of the media shall not exceed 1.8 m and minimum depth shall not be less than1.2 m.
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The media provided shall be inert and resistant to biological attack e.g. granite. limestone orcoral. Two sizesof media shall be provided viz. 100 mm single size for the lower one-third and50 mm single size for the upper two-third 01’ the filter.
The loading for the low or standardrate 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 designedpopulation.
The hydraulic loading rates are not to exceed4500 litres/day/rn2 and the organic loading rates arenot to exceed400 kg/day/l000 rn3.
Good ventilation shall be provided at the bottom of and through the media.
Aeration pipes of 100 mm or 150 mm diameter shall be provided extending through the fulldepth of the media. The size and/or numberof opening that will provide the required volume ofair shall be basedon 0.S% of the surfacearea of the bed.
The inlet openings into the filter underdrainshave an unsubmergedgrosscombined area equal toat least 15 percentof the Surfaceof the l’ilier.
The baseslab shall be sloped no flatter than I in 50 and overlaid with approveddrainagetiles orpipes.
6.4.1.2 Syntheticmedia. The synthetic media for trickling filters has extendedthe range ofhydraulic and organic loading well beyond the range of stone media. Two properties that are ofinterest are specific surfaceareaand percentvoid space.The ability of synthetic media to handle higher hydraulic and organic loadings is directlyattributed to the higher specific surfacearea and void spaceof these media compared to stonemedia.
The organicand hydraulic loading should be inaccordanceto the manufacturer’sspecification.
6.4.2 Rotating biological contactors IR BC)
6.4.2.1 General. Rotating biological contactorsconsistof basically high density plastic mediadiscs mountedon the shaft. The shaft is then made to turn slowly at approximately 1 rpm eithermechanicallythrough a geardrive systemor by the useof air through buoyancyforces exerted onair trapped in air cups fixed to the edgeof the discs from an air blow system. The slow rotationof the shaft causes alternating exposure of the media to atmosphereand the wastewater.Biological growths (biofilm) becomeattached to the surfacesof the discs and eventually form aslime layer (biomass)over the discs. The rotation effects oxygen transfer, keep the biom.assin anaerobic condition and also causesexcess biomass to slough from the discs into the mixed liquorand out of the processbasin. This sloughing maintains a uniformly thick biomassand preventsclogging of the discs.
RBCs are also available in packageunits for limited capacit\ which incorporate facilities forprimary andsecondarysettlementtogetherwith sludge storagefor a period of 4 to 6 months.
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6.4.2.2 Processdesign
(a) The RBC system requires preliminary treatment, primary and secondary settlement,sludgestorageand treatment.
(b) The soluble BOD is the controlling factor in design and therefore the approachtaken is todeterminethe amount of the soluble BOD removed per unit of surfacearea for each stageof amulti-stageRBC system. The soluble BOD shall be taken as 70% of the total BOD for domesticwaste.
(c) Where primary sedimentationtanks are used also for sludge storage/digestion,an additionalincreaseof 50% of the soluble fraction shall be taken into account in design due to the exertionof the secondaryBOD from the digestion process.
(d) When the peaks flows are greater than 2.5 DWF, sufficient equilisation volumes shall beprovided additionally to primary settling volumesor separateequalisationtanks.(e) Where necessarythe RBC systemsshould be preceededby fine screenswith a maximum clear
spacingof 20 mm. -
(f) Requiredmediaarea should be calculatedbasedon the peak loading rate.
(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 parametersfor RBC are summarisedbelow:-
RotatingBiological Contactor
SolubleBOD5 specific loadingon first stage 12 to 20 g/day.m2
Tank volumes 5 I/day.m2 of media
Maximum peripherelvelocity 0.35 rn/sec
Minimum numberof stages 2 stage
Dry sludge removal 0.8 - 1.1 kg of drysludge / kg of BOD removed.
Minimum detention in tank 1 hour
6.4.2.3 Detail design
6.4.2.3.1 input arrangementsand capacity. Wherever possible installations using RBC systemshould be supplied by gravity and means provided to minimise surges in flow. especiallywherepackageunits are used. Where crude sewageis admitted by pumping, it is important that the-averagefrequencyof pumping should not be less than four times per hour throughout most of theday.
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Septic tanks or other system of sludge tanks built integrally with RBC should be able to hold atleast the total volume of sludge depositedin 1-3 months use, dependenton the size of the plant.at the full design loading. They should provide convenientaccessfor desludgingand should besufficiently rigid to withstand pressurefrom adjoining compartmentsduring desludging.
In integral plants, it is desirable for the inlet zone to be baffled or for a weir providing a headloss of 10 mm to 20 mm to be installed to minimise the effect of surges in flow. Treatment ismore efficient when longitudinal mixing is minimized in the treatmentzone by installation of anumberof transversebaffles eachproviding a head loss of about 10 mm.
The design should facilitate the transferof excessfilm, shed from the rotating surfacesfrom thetreatmentzone to a secondarysettlementunit, either by positive mechanicalmeansor by ensuringthat sufficient turbulenceis induced to carry it forward in the effluent stream.
6.4.2.3.2 Rotor units and drire mechanisms. The rotational speed (usually 1-3 rpm) anddiameterof the rotating structure govern the peripheral velocity, which should not exceed0.35rn/sec to avoid stripping of the biomass. Random media, where employed, should be tightlypacked for the samereason. Biological film accumulatesmore thickly on the surfacesnearesttheinlet to the treatment zone, and the spacing between adjacent surfaces of discs in this regionshould be designedto prevent the bridging of gapsbetweensurfaces.
6.4.2.3.3 Construction. The design and alignment of the drive shaft should provide adequatestrengthto assurelong trouble—freelife. Failure of power or other interruption of rotation max’,if continued more than 24 hours, allow the biomass on the rotor to become unbalanceddue todrainage and drying of the exposed areas. If the rotation recommenceswithout the propermaintenanceand cleaning of the discs,severestrain will be placed on the shaft and drive. It istherefore assential that proper provisions for overload protection of the motor is made thatautomatic restartfor the motor is provided after an electrical failure.
Structuressupporting the rotor bearingsand drive should have a adequatelong term rigidity tomaintain alignment. Bearing, drive chains and sprocketsshould be protected from moisture andprovided with easyaccessfor lubrication and adjustment.
Discs shall be durable materials including expanded metal, plastic mesh, GRP. unplasticizedpolyvinyl chloride or similar materials or high density polystyrenefoam. The packing used inrotating cylinders may be similar to random fill media usedin high rate biological filters. Rotorsare also used with a variety of surfacesdisposedin a spiral or honeycombform.
6.4.2.3.4 Loading and pei’formance of the biological stage. Where full treatmentof domesticsewage to the Environmental Quality (Sewage and Industrial Effluents). Regulations 1979standardis required the loading of the rotating surfacesin the biological zone should not exceed5 g BOD/m2/day of settled sewageor 7.5 g BOD/m2/day as crude sewageenteringan integratedpackageplant. Higher loadingsmay be used provided that adequatetechnical support data hasbeen supplied. The loading should be based on the maximum population to be served. Wherequality standardsare critical, additional tertiary treatment(polishing) should be provided.
6.4.3 Suspendedgrowth (Typical diagramsas in fig. 6).
6.4.3.1 Waste stabilization pond
6.4.3.1.1 General
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(a) Waste stabilization pondscan be provided in a variety of combination covering anaerobic.facultative and maturation ponds system. A seriesof ponds producesa better quality effluentthan that from a single pond of the samesize and it avoidsshort circuiting of sewageflow.
(b) Ponds have considerableadvantagesas regards to costs and maintenancerequirementsandthe removalof faecal bacteriaover all other methodsof treating sewagefrom communities.
(c) Anaerobic ponds are designed to recei\’e very high organicwastes which have a high solids content where the solids settle toanaerobically. The partially clarified supernatantliquor can bepond for further treatment.
loading or to pretreat strongthe bottom and are digesteddischarged into a facultative
(d) Facultativepondsare the most common and they normally receive raw sewageor that whichhas received only preliminary treatment for example settled effluent from septic tanks andanaerobicpretreatmentponds.
(e) Maturation pondsare used as a secondstageto facultative ponds. Their main function is thedestruction of pathogenssuch as faecalbacteriaand viruses.
6.4.3.1.2 Basisof design. The climate of the area(temperature,sunlight, cloud cover, wind.etc) and the nature of the wastewaterto be treated (presenceof the toxic chemicals. non-degradablesubstances,sulphates,total dissolvedsolids, etc) have a considerableeffect on pondloadings, and must be taken into account when designingthe system. The design loading for thevarious pond systemsshall be as follows:-
Parameter
(a) AnaerobicPond
Design Criteria
Liquid depth -
Maximum loading rateDetention timeSludge accumulationrate
(b) FacultativePond
Total surfaceloading rateStandard AStandardB
Minimum detention timeStandardAStandardB
2.5 m - 4 rn0.4 kg BOD/day.m3
minimum 2 days0.04 m3/year/capita
225 kg/ha/day330 kg/ha/day
Maximum surfaceloading rate for the first stagefacultative pond.Standard A 330 kg/ha/dayStandard B 505 kg/ha/day
Minimum free boardLiquid depth (minimum)Sludgeaccumulationrate
14 days9 days
0.5 m1.50.04 rn3/vear/capita
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6.4.3.1.3 Design and constructionaldetails
(a) Pond geometry. Geometryof pond is not necessaryrectangular. All cornersof pond shouldbe rounded-upwith a minimum radius of 10 rn.
(b) impermeableconstruction. The pond should be impermeable so as to avoid percolation andground water pollution.
(c) En2bankn2ent. The inner slope of pond embankmentshall havea protective lining of cementrip-rap 0.3 m thick or cast-in situ concrete slab of 75 mm thick extending from top ofembankmentto a minimum of 0.5 m below liquid surface, or erosion of the embankmentbysurfacewave action can be avoided by placingprecast concrete slabs at the top water level. Theinner slope shall havea maximum slope of 1 horizontal to 1 vertical if it is pitched with cementrip-rap or rubble pitching and the slope of the embankmentis well compacted.
The outer slope shall be protected by turfing or rip-rap if subjected to external water waveaction. When it is turfed the recommendedslope shall be 3 horizontal to 1 vertical.
All weather roads of enough width (minimum 3.5 m wide) and strength shall be provided forlarge trucks or lorries to haveeasyaccessto the ponds. Surfacerunoff must be preventedfromentering the pond.
(d) inlet and outlet structures. In order to minimise hydraulic short circuiting, the inlet andoutlet to each pond shall be of multiple units and located in diagonally oppositecorners crossconnectionbetweenpondsshouldalso be provided.
The inlet into the wastestabilizationpond shall be preceededwith a scum chamberto arrestscumor other floating materialsfrom entering the pond. A flow measuringdevice such as venturi orpartial flume to measureinflow and a vee-notchto measurefinal outflow shall be installed ifrequired.
in order to reduce the amount of scum the pipe should dischargebelow the pond surfacewith aconcretesplashpad at the pond basejust below the end of inlet pipe to receive the incoming rawsewage. in order to reducethe amount of scum the pipe should dischargebelow the pond surfaceand in order to prevent the formation of a sludge bank, the end of the pipe shouldbe sited up toabout 1/3 length of the pond away from the embankrnents.
(e) Facilities shall be provided for by-passing to the first, secondand subsequentponds.
6,4.3.2 Aerated lagoons
6.4.3.2.1 General. Aerated lagoons are essentially similar to waste stabilization ponds exceptthat it is mechanicallyaerated instead of algal oxygenation, much deeper and has a shorterdetention time. An advantagethat aeratedlagoonshave is the relative easewith which additionalaeratorscan be added as population increasesor as betterefficiency is desired.
Aerated lagoons are activated sludge units operatedwithout sludge return. Two basic aeratedlagoon systemsare recommended,namely
(i) Completely mixed aeratedlagoon systemor the aerobic flow through type; and
(ii) Partially mixed or facultative aeratedlagoonssystem.
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Floating aeratorsare most commonly usedto supply the necessaryoxygen and mixing power.
6.4.3.2.2 Faculialive aeratedlagoons. Facultative aeratedlagoons are akin to the alga] pondsused for wastestabilization except that the oxygen is derived from mechanicalaeration insteadofalgal photosynthesis.The power input is sufficient for diffusing enough oxygen into the liquidbut not sufficient for maintaining all the solids in suspensionwith the result that suspendedsolidsin the raw sewageentering the lagoonstend to settle down and undergoanaerobicdecompositionat the bottom. It is very significantly affected by changesin temperature. It requires lowerpower to drive the aerator then the completelymixed lagoons.
Sludgeaccumulationwill take place at the rate of 0.04 rn3/year/capita. Anaerobic decompositionleads to liquefaction of solids and a non—degradableresiduewhile the original load of grit andinorganic solids entering the lagoon along with raw sewagealso settlesat the lagoonsbottom. Thedetentiontime is much larger than the completelymixed lagoons.
6.4.3.2.3 Contpietelv mixed aerated lagoons st’s/em. The lagoons need more power than thefacultative type as the surfaceaeratorhas to keep the solids in suspension(as in activated sludgeaeration tank) in addition to diffusing enough oxygen into the liquid. The wastewaterentersatone end and leavesat the other end of lagoons along with the solids under aeration.- Hence thesolids concentration in the effluent will be the same as the solids concentration in the lagoonitself. The efficiency of BOD removalconcentrationin the lagoon is not very high since solidsare presentin the effluent. -
6.4.3.2.4 The effluents from the aeratedlagoonsshould be further treated.
6.4.3.2.5 Basis of design. The design criteria for both the completely mixed and facultativelagoonsare set out below.
Table 2. Design criteria for aerated lagoons
Parameters
Aerated Lagoons
Completely mixed Falcultative
Minimum detentionperiod 1 day 2.5 days
Oxygen requirement 0.8 - 1.1 kg 02consumed/kgBODremoved.
1.5 - 1.8 kg 02consumed/kgBODremoved.
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
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6.4.3.2.6 Design details. The constructionof aeratedlagoons is essentially the same as that ofwastestabilization ponds. The major diff’erences are : greaterdepths (usually 3 m - 5 m) steeperembankmentslopes and the provision of a completebutyl rubber or polytheneor cemente~irip-rap lining (minimum 0.5 m thick) to prevent scouring by the turbulenceinducedby the aerators.
Where surfaceaeratorsare used, it is preferably to have floating units. Where fixed aeratorsareused(mountedon columnsor stilts) it is essentialthat the liquid level in the lagoon is maintainedconstantso as to ensurethe required degreeof submergenceof the aeratorblades.
Electric cable has to be carried overheadto the aeratorfrom the banksof the lagoon. The steelropesused to anchorthe aeratorto the side bankscan be used to carry the cable also. For repairsor maintenancethe aeratorcan be pulled in water to the cornerof the lagoonwhere a small loopor arm can be provided to ‘wet-dock’ the aeratorandenablelifting it up for inspection.
6.4.3.2 .7 Pond geometry. Aerator ~agoonsshall be designed to prevent short circuiting toensure uniform mixing andaeration. The shapeof the pond will dependon the selection of theaerationequipmentandzoneof influence.
6.4.3.3 Activatedsludge
6.4.3.3.1 General. The activatedsludge processis an aerobic, biological processwhich usesmicro-organismsin suspensionto removecolloidal, suspendedand dissolvedsubstancesexertingan oxygendemand. Settled sewageis led to ad aerationtank where oxygen is suppliedeither bymechanicalagitationor by diffused aeration. Aerationof the sewageis followed by settlementinthe secondarysedimentationtank with part of the resulting sludge recycled to the aerationsystemto maintaina high cell concentration(2000 - 8000 mg/I of MLSS) in the aerationtank andthe remainderbeing wastedfor further treatment.
6.4.3.3.2 Typeof processesand modification. The activatedsludge processis very flexible andcan be adoptedto almost any type of biological waste treatmentproblem. Basically the activatedsludgeprocessescompriseof:
(a) Conventionalactivatedsludge
(b) Contactstabilization
(c) Conventionalextendedaeration
(d) Oxidation ditch (a modified extendedaerationprocess)
The other modified activatedsludge systemsthat have becomestandardizedvary from the above4 processesin the way sewageand aeration is introduced into the tank. They include taperedaerationprocess,continuousflow stirred-tankstepaeration,modified aeration, high rate aerationand the pure oxygensystem.
6.4.3.3.2.1 Conventionalactivatedsludge. The conventionalactivatedsludge processconsistsofan aerationtank, a primary and secondaryclarifier, and a sludge recycling line. Sludge wastingis accomplishedfrom the recycle or mixed liquor line. Both influent settled wastewaterandrecycledsludge enter the tank at the headend and are aeratedfor a period of about 4 to 8 hours.
The influent wastewaterand recycled sludge are mixed by the action of diffused or mechanicalaeration, which is constantas the mixed liquor moves down the tank. During this period.absorption, flocculation and oxidation of the organic matter take place. The mixed liquor issettled in the activatedsludge sedimentationtank and the sludge is returned at a rate of 20-50%of the influent flow ratedependingon the MLSS maintainedin the aeration tank.
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6.4.3.3.2.2 Contact stabilization. The contact stabilization processinvolves treatment in fourdistinct compartments. In the first compartment, sewage, which will usually be screenedormaceratedis aeratedin contactwith activatedsludge for a period of 30 to 90 mm, the mixedliquor then passing to the settlement compartment. After settlement the supernatantliquortreated effluent) is dischargedand the sludge is transferedto a third (re-aeration)compartmentwhere it is aeratedfor a period of 3 to 6 hours during which time oxidation of absorbedorganicmaterial occurs. A large proportionof the activatedsludge is thenrecycled to the first (contact)compartment. There may be a fourth (aerobic digester)compartmentwhere surplus sludge isfurther aeratedto oxidize it as completelyas possiblebefore being removedfor disposal.
6.4.3.3.2.3 Extendedaeration. This processis usedextensively for prefabricatedpackageplants.It involves treatment in two compartments, an aeration or mixed liquor compartmentand asettlementcompartment. Sewage, which will usually be screenedor macerated,flow to theaeration compartment where it is aeratedin admixture with activated sludge. The sludge isseparatedfrom the mixed liquor in the settlementcompartmentwhich is usually integral with thefirst compartmentbut separatedfrom it by partition. The sludge is recycled to the aerationcompartmenteither by gravity pump or air lift. The supernatantliquor (treatedeffluent) leavesthe plant over a weir. Separatesludgewastinggenerallyis provided.
Operatingexperiencehas indicated that problemshave developedin many plantswhere wastingfacilities have not beenprovided. Provisionsshall be made to remove excesssludge and thisshould be treatedprior to disposal.
6.4.3.3.2.4 Oxidation ditch. This is basically an extendedaeration system and consistsessentiallyof a Continuousshallow channel 1 m to 3 m deep usually forming an oval Circuit inplan.
Raw sewage,after screeningand grit removal entersthe ditch where mechanicalrotors (aerator)aerate the liquid andkeep it in circulation. The ditch may be followed by a separatesettling tankfrom which the settledsludge may be returnedto the ditch by apump and the excessivesolid besent to a drying bedwhile the clear supernatantis discharged. In some casesthe ditch itself maybe used as settling compartmentby periodically shuttingoff the aerators. Excesssolids must beremovedas sludgeon a regular basis.
The long sludgeage, acheivedby recycling more than95% of the sludge ensuresminimal excesssludge production and a high degree of mineralization in the sludge that is produced.Sludge handlingand treatmentis almost negligible since the small amountof waste sludgecan bereadily dewateredwithout odour on drying beds.
The ditch should havea concretelining with side slopesof about I in 1 .5 vertical, A rigid liningshould always be provided in the vicinity of the rotor extendingto at least 4.5 rn downstreamtopreventdamagedue to the high turbulencein theseareas.
The same depth below top water level and preferablyof the samecross-sectionalarea should bemaintainedfor the completecircuit. The ditch should be equippedwith one or more mechanicalaeratorsarranged to maintain a velocity of flow in the ditch sufficient to keep the activatedsludgein suspension.
Provision should be madefor separatesettlementof sludge before dischargeof final effluent inthe ditch is designedfor continousoperations.
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6.4.3.3 .3 Processdesign
6.4.3.3.3.1 Applicability
(a) Biodegradablewaste. The activatedsludge processand its various modification may be used
wheresewageis amenableto biological treatment.(b) Operational requirements..This process requires close attention and competent operatingsupervision including routine laboratory control. These requirementsshall be considered whenproposing this type of treatment.
(c) Energy requirements. This processrequiresmajor energy usageto meet aeration demands.Provisionsshall be madefor the emergencyenergysupply.
6.4.3.3.3.2 Specific processselection. The activatedsludge processand its several modificationsmax’ be employed to accomplish varied degreesof removal of suspendedsolids and reductionofcarbonaceousand/or nitrogenousoxygen demand.Choice of the processmost applicable will beinfluenced by the degree and consistencyof treatmentrequired, type of waste to be treated,proposedplant size anticipated,degreeof operation and maintenanceand operating and capitalcosts. All designshall provide for flexibility in operation.
6.4.3.3.3.3Pretreatment.Where primary sedimentationtanks are not used,effective removal orexclusionof grit, debris,excessiveoil or grease,and communitionor screeningof solids shall beaccomplishedprior to the acti\’atedsludgeprocess.Whereprimarysedimentationis used,provisionshall be madefor dischargingraw sewagedirectly to the aerationtank to facilitate plant start-upandoperationduring the initial stagesof the plants design life.
6.4.3.3.3.4Capacity~~~The size of the aeration tank or oxidation ditch for any partkul~radaptationof the processshall be determinedby full scaleexperiment, or rational calculationsbased mainly on food to microorganismratio and mixed liquor sus~ehdèdsolids levels. Otherfactorssuch as size of treatmentplant, diurnal load variations and degreeof treatmentrequiredshall also be consideredwhen designingfor nitrification and denitrification. Calculationsshouldbe submitted to justify the basis for design for aerationtank capacity. Calculationusing valuesdiffering substantiallyfrom. those in table 3 should madereferenceto actual operationalplants.Mixed liquor suspended solids levels greater than 5000 mg/i may be allowed providing adequatedata is submittedshowing the aerationandclarification systemcapableof supportingsuch levels.
6.4.3.3.4 Detail design
6.4.3.3.4.1 Generalrequirement. The installationshould incorporatethe following features:
(a) adequateprotectionagainstcorrosion;
(b) standbyelectrical equipmentincorporatingautomaticchangeover,wherepracticable;
(c) automaticrestartingin the eventof power failure;
(d) arrangementfor the removal and disposalof surplussludge;
(e) adequatecontrol of flow to minimise risk of washoutof activatedsludge;
(f) if below ground level, adequateprotectionagainst floatation.
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Table 3. Common parameters and operating characteristics ofsingle-stageactivated sludge system
Process Loading-
HydraulicDetentionTime (hrs)
02 requiredkg/kgBOD removed
MLSSmg/I
F/M(Kg B0D/Kg MLSS
SRT(days)
kg ofBOD/m
Conventional
ExtendedAeration
Contact
Stabilization
OxidationDitch
0.15 -
0.4
0.05 -
0.15
0.15 -
0.5
0.5 -
2.0
0.05 -
0.15
5 - 15
20 - 30
3 10
-
20 - 30
0.32 -
0.92
0.16 -
0.4
0.48 -
1.12
1.44 -
2.88
0.16 -
0.4
4 - 8
16 - 24
0.5-1.5~
3 - 6
16 - 24
0.8 -
1.1
1.4 -
1.6
0.8 -
1.1
0.4 -
0.6
1.4 -
1.6
1500 -
4000
2000 -
6000
1000 -
3000
6000 -
10000
2000 -
6000
6.4.3.3.4.2. .4eration ta’akg
6.4.3.3.4.2.1 General. Aeration tanks shall be constructedof reinforced concrete or otherapprovedmaterials. For large plant,thetotal aeration tank volume required should preferably bedivided among two or more units capableof independantoperation.
If the wastewateris to be aeratedwith diffused air, the geometry of the tank may significantlyaffect the aerationefficiency. The depth of wastewaterin the tank should be between3 m and5 m so that the diffuser can work efficiently. Freeboardfrom 0.3 m to 0.6 m above the waterline should be provided. The width to depth ratio may vary from 1:1 to 2:1. This limits thewidth of tank channelto 6 m to 12 m.
For tanks with diffusers on both sidesor in the centreof the tank, greaterwidths are permissibleso that ~deadspots’ are eliminatedor dimensionsshould be such as to maintain adequatevelocitiesso that deposition of solids will not occur. Triangular baffles or fillets may be placedlongitudinally in the cornersof the channelsto eliminate dead spotsand to deflect the spiral flow.
Individual tanks should have inlet and outlet gatesor valves so that they may be removed formaintainence.
Aeration tanks must have adequate-foundationsto prevent settlementor to prevent floatation insaturatedsoil.
6.4.3.3..’L2.2 Froth-control system. Large quantities of foam may be producedduring start upof the process, when the mixed liquor suspended solids is low, or wheneverhigh concentrationofsurfactantsare presentin the wastewater. The foaming action producesfroth that contains sludgesolids, grease and bacteria and the wind may lift the froth off the tank surfaceand blow it about.
Froth controlling systems should be installed to prevent it from foaming. A series of spraynozzles for spraying, cleanwarer or screenedeffluent or antifoaming chemical additives can bemounted along the top edge ~f the aeration tank opposite the air diffuser.
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6.4.3.3.4.2.3 Arrangement of aeration tanks
(a) Dirnensio/ls. The dimensions of each independent mixed liquor aeration tank or returnsludge reaeration tank shall be such as to maintain effective mixing and utilization of air.Ordinarily, liquid depthsshould not be less than 3 m or more than 5 m.
(b) Short-circuiting. For very small tanks with special configuration, the’ shapeof the tank andthe installation of earation equipment should provide for positive control of short circuitingthrough the tank.
6.4.3.3.4.2.4 inlets and outlets
(a) Controls. Inlet and outlets for eachaerationtank unit shall be suitably equippedwith valves.gates, stop plates, weirs or other devices to permit controlling the flow to any unit and tomaintain reasonablyconstant liquid levels. The hydraulic propertiesof the system shall permitthe maximum instantaneous hydraulic load to be carried with any single aeration tank unit out ofservice.
(b) Conduit. Channels and pipes carrying liquids with solids in suspension shall be designed tomaintain self-cleansingvelocity or shall be agitatedto keepsuch solids in suspensionat all ratesof flow within the design segment of channels which are not being used due to alternate f’Iowpatterns.
6.4.3.3.4.2.5 Free board. All aeration tanks should havea free boardof not less than 0.5 m.
6.4.3.3.5 Aeration equipment
6.4.3.3.5.1 General. There are basically two methodsof aerating wastewateri.e.:
(a) introduce air or pure oxygen into the wastewaterwith submergerporous diffusers or airnozzlesand
(b) to agitatethe wastewatermechanicallyso as to promotesolution of air from the atmosphere.
Oxygen requirements generally depend on maximum diurnal organic lO~ding, degree oftreatment, and level of suspendedsolids concentration to be maintained in the aeration tankmixed liquor. Aeration equipment shall be capable of maintaining a minimum of 2 mg/I ofdissolved oxygen in the mixed liquor, in the absenceof experimentallydetermined value, thedesign oxygen requirementsfor all activated sludge processesshall be in accordanceto Table 3.
6.4.3.3.5.2 Diffused air aeration. A diffused air systemconsistsof diffusers (that are submergedin the wastewater).headerpipes, air mainsand the blowers and appurtenancesthrough which airpasses.
The efficiency of oxygen transfer depends-on the type and porosity of the diffuser, the size ofthe bubbles produced, the depth of submersion etc. The diffuser that producesfine bubbles isrecommended for its higher transfer efficiency. As there are many different makes of airdiffusers available, the recommended design charts and cataloguesfrom the manufacturer shouldbe submitted for evaluation together with the calculation. Having determined the oxygenrequirements,air requirementsfor a diffused air system shall be determinedwith the followingfactors:
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(a) (i) Tank depth
(ii) Certified aerationdevice transferefficiency
(iii) Minimum dissolvedoxygen concentrationin aeration tank.
(‘iv) Critical wastewatertemperatOre
(b) Normal oxygen requirementsfor all activatedsludge processare as in table 3.
(c) The blowers shall be provided in multiple units, so arrangedand in such capacitiesas to meetthe maximum air demand with the single largest unit out of service. The design shall alsoprovide for varying the volume of air delivered in proportion to the load demandof the plant.Aeration equipment shall be easily adjustablein iOcrementsand shall maintain solids suspensionwithin theselimits.
(d) Diffuser systemsshall be capableof providing for the diurnal peakoxygen demandor 200%of the design averageoxygen demand,whichever is larger. The air diffusion piping and diffusesystemshall be capableof delivering normal air-requirementswith minimal friction losses.
All plants employing less than 4 independentaeration tanks shall be designed to incorporateremovablediffusers that can be servicedand/or replacedwithout dewateringthe tank.
(e) Individually assembleunit diffusers shall be equipped with control valves. Air filters shallbe provided in numbers, arrangements,and capacities to furnish at all times and air supplysufficiently free from dust to prevent damageto blowers and clogging of the diffuser systemused.
6.4..3.3.5.3 Mechanicalaerationsystem
(a) Oxygen trans/er performance. The mechanismsand drive unit shall be designed for theexpectedconditions in the aeration tank in terms of the power performance. Certified testingshall verify mechanicalaeratorperformance. -
(b) Design iequirement
(i) Maintain a minimum of 2 mg/I of dissolved oxygen in the mixed liquor at au timesthroughoutthe tanks.
(ii) Maintain all biological solids in suspension.
(iii) Meet maximum oxygen demandand maintain processperformancewith the largest unit’ outof service,and
(c) Provide for varying the amount of oxygen transferredin- proportion to the load demandonthe plant.
6.4.3.3.6 Return sIL-Idge equipment
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6.4.3.3.6.1 Return sludge rate. The minimum permissible return sludge rate of withdraw) fromthe final sedimentationtank is a function of the concentrationof suspendedsolids in the mixedliquor entering it. the sludge volume index of thesesolids, and the length of time thesesolids areretained in the sedimentationtanks. Since undue retention of solids in the final sedimentationtanks may he deleteriousto both the aeration and sedimentation phase of the activated sludgeprocess,the rate of sludge return expressedas a percentageof the averagedesign flow of sludgereturn should be generally variable on the basis as F, M ratio and MLSS limits as set forth intable 3.
6.4.3.3.6.2 Return sludge pumps. If motor driven return sludge pumps are used, the maximumreturn sludge capacity shall be obtained with the largest pump out of service. A positive headshould be provided on pump suctions. Pumps should have at least 75 mm suction and dischargeopenings. If air lifts are used for returning sludge from each sedimentation tank hopper, nostandby unit will be required provided the design of the air lifts are such to facilitate their rapidandeasycleaningand provided othersuitable standbymeasuresare provided. Air lifts should beat least75 mm in diameter,
6.4.3.3.6.3 Return sludge piping. Discharge piping should be at least 100 mm in diameter andshould be designed to maintain a velocity of not less than 0.60 m/secwhen return sludge facilitiesare operating at normal return sludge rates. Suitable devices for observing, sampling andcontrolling return activatedsludge flow from eachsedimentationtank hoppershall be provided.
6.4.3.3.6.4 Waste sludge facilities. Waste sludge control facilities should have a minimumcapacity of not less than 25% of the averagerate of sewageflow and function satisfactorily atrates 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 beprovided. Waste sludge may be dischargedto the concentration or thickening tank, primarysedimentation tank, sludge digestion tank, vacuum filters, other dewatering devices or anypractical combinationof theseunits.
6.4.3.4 Secondary sedimentation tank. Secondarysedimentation tank could be eitherrectangularor circular in shape.
6.4.3.4.1 Rectangulartanks. The length to depth ratio should be 3 : I or more. The width todepth ratio should be between1:1 to 2.5 : I. The typical depth is about 3 m and where possiblethe maximum length of tank should not exceed10 times its depth.
6.4.3.4.2 Circular tanks. The side water depth should not be under 3 m. It is desirablefor theradius of the tank not to exceedfive times its side water depth.
The floor slope when used in conjunction with scraper mechanism should be 1:12 or asrecommendedby supplier of scraper.
6.4.3.4.3 Detention time. The detention time should be between90 to 120 mm at design peakflow.
6.4.3.4.4 Surfaceloading rate, When usedactivated sludge processes the surface overflow ratewill depend, on the concentration of the MLSS being settled in the sedimentationtank. Forconcentration of MLSS of 600 mg/I the overflow rate should be in the region of 60 m3/dav1’m2and for MLSS concentration of 3500 mg/I and above the overflow rate should not exceed 30m3/day/m2. Both theseoverflow ratesshould be at peakflows unless specialflow control devicesare provided at the inflow of the clarifyer then this overflow rae of the clarifver should be basedon the constantflow rate of this device,
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The lower overflow rates to be used for secondarysedimentationtank for biological filter andRBC units.
6.4.3.4.5 Solid loading iaie. The solid loading rateshould be between2.5 to 6.0 kg/m2/hour.
6.4.3.4.6 Weir loading rate. The weir loading should be in the rangeof ISO to 180 m3/day/m2.
6.4.3.4.7 Scraper mechanismand sludge pump. Scraper mechanism for the collection andtransferor recycle of sludge should be approvedby the Local Authority
6.4.3.4.8 Secondarysedimentationtank with hopper bottom. The design requirementsare thesameas 6.3.6 except that the surfaceloading rate is 30 m /day/m.
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SECTION 7. DISPOSAL OF SEWAGE AND TREATED EFFLUENTS
7.1 General. After treatment, the disposal of final effluent into inland waters shouldcomply with the requirementof the EnvironmentalQuality Act 1974 and Environmental Quality(Sewage& Industrial Effluents) Regulations l979-P.U.(A) l2~’79.
7.2 Dischargestandardfor 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 thecatchmentareasspecified in the Fourth Schedule*~shall comply with StandardA. as shown in thethird column of the Third Schedule, of the Environmental Quality (Sewage & IndustrialEffluents) Regulations1979 - P.U.(.A) 12/79.
In particular, where sewage is free from and does not include industrial effluents, the followingparameterlimits of Standard A may be of primary considerationfor the purposeof design of thesewagetreatmentworks:
Parameter Limit in mg/I
Biochemical Oxygen Demand 20(5-Day: 20°C)
SuspendedSolids 50
7.2.1.2 All dischargesfrom sewagetreatmentsystemsinto any other inland waters shall complywith StandardB, as shown in the fourth column of the Third Scheduleof Environmental Quality(Sewage& Industrial Effleunts) Regulations1979.
In particular, where sewageis free from and does not include industrial effluents, the followingparameterlimits of Standard B may be of primary considerationfor the design of the sewagetreatmentworks:
Parameter Limit in mg/I
Biochemical Oxygen Demand 50(5—Day~20°C).
SuspendedSolids 100
7.2.2 Municipal l-f-”aslL-’water Treatment Plant and Marine Outfall for Municipal Seii’agcDischarge. in accordancewith the provisionsof the EnvironmentalQuality (Prescribed Activities)(Environmental Impact Assessment)Order 1987, the following are listed as prescribedactivitiesand implementationof which are subjectedto environmentalimp~ctassessment.
(a) The constructionof municipal wastewatertreatmentplant~
(b) The constructionof marine outfall for municipal sewagedischarge.
‘NOTE. The Fourth Schedulerequires periodic updating with respect to new water supply intakes and due attention shouldbe given to new water supply catchnientareassubject to future gazzettrnent.
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In the above event, final discharge standards may differ from those specified as Standard A orStandard B of the EnvironmentalQuality (Sewageand Industrial Effluents) Regulations1979, andmay be presàribed on the basis of thoserecommendedfollowing such an assessment.
7.2.3 Disposal of Effluent and Sludge onto Land. In accordancewith the respectiveprovisionsof the EnvironmentalQuality (Sewageand Industrial Effluents) Regulations 1979, thefollowing are subject to the prior written permission of the Director-General of EnvironmentQuality:-
(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 generatedfrom any effluent treatment plant inor 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 dataon The fo~1owing:
(a) Profiles of possible outfall routes:
(b) Nature of the ocean bottom;
(c) Waterdensitystratification or thermoclines;and
(d) Patternsof water movementat point of discharge and travel to shore.
(e) Tides and currents
(f) Prevailing winds
(g) Coastalhabitation on either side of this proposal outfall site.
Since seawater is denser than sanitary wastewater, this causes the discharged wastewater risesrapidly, normally producing a ~boil’ at the surface. The rising plume mixes with a quantity ofseawaterwhich is generally from 10 to 100 or more times the wastewaterflow. Dilution increasesrapidly as the ‘wastewaterfield’ movesaway from the boil. The required length and depth of theoutfall is related to the degree of treatment of the wastewater. The length must be calculatedsothat time and dilution will protectadequatelythe beneficial usesof the adjacentwaters.
7.3.2 Where the outfall is deep and there is good densitystratification (thermocline). the risingplume may pick up enough cold bottom water so that the mixture is heavier than the surfacewater. The rising plume, therefore, stops beneath the surface, or reaches the surface and thenres u bmerges.
7.3.3 The diffuser must be approximately level if it is to accomplish reasonably uniformdistribution. For design of the diffuser, the rule of thumb may be used that the total cross-sectionalareaof the ports should not be more than half the cross-sectionalarea of the pipe. Inlarge diffusers, often exceeding 1 km in length, the diffuser diameter may be steppeddown insize toward the end.
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7.3.4 Outfalls into the open ocean generally are buried to a point where the water is deepenough to protect them from wave action, usually about 10 m. Beyond the buried portion theoutfall rests on the bottom. with a flanking of rock to prevent currents from undercutting itwhere the bottom is soft.
7.3.5 Outfall pipes lines are constructedof reinforced concrete,cast iron ductile iron, steel orothersuitable material. Cast iron is sometimesgiven a cementmortar lining. Steel is more likel\to be lined with mortar or bituminous material and is sometimes provided wIth cathodicprotection. Joints in the pipe should have substantialmechanical strength and be resistant tochemical or biological corrosion. Ball-and-socketjoints have been used in iron pipe, while steelpipe is usually welded. Several ingeniousjoints have been employed in concreteoutfalls. Thepipe may be placed in trenches on bottoms of soft rock, sand or gravel. On unstable bottomspiling is necessary. Outfalls may employ a number of ports on the sides or top distributed over along length of the pipe, perhapsas much as a third of its total length. The ports may be plain ormay be fitted with Tees to dischargethe sewagein low flows.
7.3.6 The implicationsof bacteriologicl contaminationof tidal waters are difficult to quantifywhich dependson the climatic and environmentalconditions.However the effe~ro~~ub!~ healthshould not be ruled out.
The effect on the flora and the fauna in the region of discharge-should be consideredand couldhave se~’ereeconomic implications e.g. on fishing.
The presenceof floating debris and settled solids can cause local problems, and thereforescreeningof effluent should take place long before discharge.
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SECTION 8. TREATMENT AND DISPOSAL OF SLUDGE
8.1 Process selection. The sludge resulting from wastewatertreatment operationsandprocessesis usually in the form of a liquid or semisolid liquid which typically containsfrom 0.25to 12% solids. The sludge must be disposedof in a mannerwhich does not give rise to nuisanceor public health problems. The following factors shall form the basis of all sludge disposalmethodsand design.
(a) There should be no public health hazardat site of disposal which include odour, ground orsurface water pollution and nuisance of insects or rodents.
(b) After tipping the depositedsludge 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.
There are many methods of sludge treatment processesand an almost infinite number ofcombinations are possible. The’ more common and suitable processesapplicable to Malaysianconditions are:
(a) Preliminary treatment
(b) Thickening
(c) Stabilization
(d) Dewatering
(e) Ultimate disposal
8.2 Preliminary treatment
8.2.1 Sludgestorage. Sludge storagemust be provided to smooth out fluctuation in the rateofsludge production, to allow sludge to accumulate during periods when subsequentsludgeprocessing facilities are not operating and to ensure a uniform feed rate into subsequenttreatment.
Short term sludge storage may be accomplished in wastewatersedimentationtanks or in sludgethickening tanks. Long term sludge storagemay be accomplishedin sludge stabilization processeswith long detention times (i.e. aerobic or anaerobicdigestion) or in specially designedseparatetanks. Such tanks may be sized to retain the sludge for a period of several hours to several days.Aeration of the sludge is necessaryto prevent septicity.
8.3 Sludge thickening
8.3.1 General. Thickening is a procedureused to increasethe solids content of sludge byremoving a portion of the liquid fraction and hence volume reduction. The volume reductionobtained by sludge concentration is beneficial to subsequent treatment processessuch asdigestion, dewatering, drying and combustionfrom the following stand points:
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(a) Capacity of tanks and equipment required;
(b) Quantity of chemicals required for sludge conditioning;
(c) Amount of auxiliary fuel required for heatdrying or incineration or both.
8.3.2 Design of thickeners. The design of thickeners should consider the type andconcentration of sludge, the sludge stabilization processes, the method of ultimate disposal,chemical needsand the cost of operation. Particular attention should be given to the pumpingand piping of the concentratedsludge and possibleon set of anaerobicconditions. Sludgeshouldbe thickened to at least 5% solids prior to transmission to digescors. In designing thickeningfacilities it is important to:
(a) provide adequatecapacity to meetpeakdemands.
(b) prevent septicity wiTh its attendantodour problem, during thickening processes.To reduce
the size of the units, the use of sludge storagefacilities, should be evaluated.
8.3.2.1 Gravity thickener. Gravity thickener is accomplishedin a tank similar in design to aconventional sedimentation tank. Normally a circular tank is used. Dilute sludge is fed to acentre feed well. The feed sludge is allowed to settle and compact, and the thickened sludge iswithdrawn from the bottom of the tank. Enough storage space must be provided for the sludge.Gravity thickening is most effective for untreatedprimary sludge.
The gravity thickener shall be designedwith a maximum surface loading rate of 36 m3/m2.d.The solids loading are as follows:
Type of Sludge (%) Sludge Concentration Solids Loadingkg/m2d
Unthickened Thickened
Primary sludge
Activated sludge
Trickling Filter sludge
Primary and activated sludge
Primary and trickling filter sludge
4 - 12
0.5 - 2.5
1 - 3
3 - 10
4 - 10
6 - 12
1.5 - 4.0
4 - 10
3 - 10
4 - 10
150
40
50
80
100
In operation, a sludge blanket is maintainedat the bottom of the thickener to aid in concentratingthe sludge. The sludge volume ratio (volume 01’ sludge blanket held in the thickenner divided bythe volume of the thickenedsludge removeddaily) shall range between0.5 to 20 days.
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8.3.2.2 Floatation thickeners. Floatation thickening is most efficiently used for wastesludgesfrom suspendedgrowth biological treatmentprocessessuch as the activated sludge process. Thedegreeof thickening that can be achieveddependson the initial concentrationof the sludge andthe sludge ageat which the plant is being operated. Higher loading can be used with t’loauationthickeners than are permissible with gravity thickeners. The limiting valuesfor the design of afloatacion thickeners (secondarysludge) is summarisedbelow.
Input concentration = 5000 mg/I
Outputconcentration = 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 twostageanaerobicdigester. The first tank is usedfor digestion. The secondtank is usedfor storageand 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 maintaincontinuity of serviceshall be provided.
8.4.2 Processdesign
8.4.2.1 Tank capacity. The total digestion tank capacity shall be determined by rationalcalculation based upon such factors as volume of sludge added, its presentsolids and character,the temperatureto be maintained in the digesters,the degreeor extendof mixing to be obtained,and the degree of volatile solids reduction required. Calculationsshould be submitted to justifythe basisof design.
When such calculationsare not basedon the abovefactors, the minimum combined digestion tankcapacity outlined below will be required which assume,that a digestion temperature is to bemaintained in the range of 30°C to 38°C, that 40% to 50% volatile matter will be maintained inthe digested sludge and that the digestedsludge will be removedfrequently from the system.
Process Sludge Age Loading Factor Detention Time
Completelymixedsystem
Moderately mixed system
10 days
14 days
1.28 kg/m3.day
0.6 kg/m3.day
30 days
30 days
8.4.3 Detail design. In a two stage tank system, the tanks are made identical, either one canbe the primary. In other cases the second tank may be an open tank, an unheatedtank. or asludge lagoon. The tanks may have fixed roofs or floating covers. Any or all of the floatingroofs may be of the gas holder or compressedand stored underpressure.
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8.4.3.1 Depth. For those units proposed to serve as supernatant separation tanks, the depthshould be sufficient to allow for the formation of a reasonabledepth of supernatant liquor.Tanks shall be circular and range between6 m to 35 m in diameter. The minimum water,depthshould be 7.5 m at the centreand the minimum sidewaterdepth of 6 m.
8.4.3.2 Maintenance provisions. To facilitate draining, cleaning and maintenance the followingfeaturesare desirable:
(a) Slope. The tank bottom should slope to drain toward the withdrawal pipe, For tanksequipped with.a suction mechanism for withdrawal of sludge, a bottom slope not less than I : 12is recommended. Where the sludge is to be removed by gravity alone, I : 4 slope is recommended.
(b) Accessn2anhole. At least two 900 mm diameteraccessmanhole should be provided in thetop of the tank in addition to the gas dome. There should be stairways to reach the accessmanholes. A separatesidewall manhole shall be provided. The openingshall be large enoughtopermit the usesof mechanicalequipmentto remove grit and sand.
(c) Safety. Non sparking tools, safety lights, rubber solid shoes,safety hardness,gas detectorsfor inflammable and toxic gases,and at least two self-containedbreathingunits shall be providedfor emergencyuse.
8.4.3.3 Sludge inlets and outlets. Multiple recirculation withdrawal and return points, toenhanceflexible operation and effective mixing should be provided, unlessmixing facilities areincorporated within the digester. The returns, in order to assist in scum breakup, shoulddischarge 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 returnpiping or directly to the tank if internal mixing facilities are provided. Sludge withdrawal todisposal should be from the bottom of the tank. This pipe should be interconnectedwith therecirculation piping to increaseversatility 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, thestorage facilities and the piping, shall be so designedthat under all normal operating conditions,including sludge withdrawal, the gas will be maintained under positive pressure. All enclosedareaswhereany gas leakagemay occur shall be adequatelyventilated.
Total gas production is usually estimatedform the volatile solids loading of the digesteror fromthe percentageof volatile solids reduction.
Typical values are from 0.5 to 0.75 m3/kg of volatile solids addedand from 0.75 to 1.15 m3/kg ofvolatile solids destroyed.
8.4.4.2 Gas collection. Floating covers fit on the surfaceof the digestercontain and allow thevolume of the digesterto changewithout allowing air to enter the digester. Gasand air must notbe allowed to mix, or else an explosivemixture may result. The covers may also be installed toact as gas holders that store a small quantity of gas under pressureand act as reservoirs.
Fixed covers provide a free space between the roof the digester and the liquid surface. Gasstoragemust be provided so that:
(a) When the liquid volume is changed,gas and hot air will be drawn into the digester.
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(b) Gaswill not be lost by displacement.
Gas can be stored either at low pressure in gas holders that use floating covers or at high pressureif gas compressors are used. Gas not used should be burned in a flame. Gas meter should beinstalled 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.Pressureand vacuumrelief valves and flame traps, togetherwith automatic safety shutoff valves.shall be provided. Water seal equipment shall not be installed. Gas safety equipment and gascompressorsshould be housedin a separateroom with an exterior entrance.
8.4.4.4 Gaspiping and condensate.Gas piping shall be of adequatediameterand shall slope tocondensatetraps at low points. The useof float controlled condensatetrap is not permitted.
8.4.4.5 Gas ulitilization equipment. Gas fired boilers for heatingdigestersshall be located in aseparateroom not connectedto the digestergallery. Such separatedroom would not ordinarily beclassified as a hazardous location. Gas lines to these units shall be provided with suitable flametraps.
8.4.4.6 Waste gas. Wastegas burnersshall be readily accessibleand should be locatedat least7.5 m away from any plant structureif placed at ground level, or may be located on the roof ofthe control building if sufficiently removedfrom the tank.
All waste gas burners shall be equipped with automatic ignition, such as pilot light or a deviceusing a photoelectric cell sensor. Consideration should be given to the use of natural or propanegas to insure reliability of the pilot light.
In rembte locations it may be permissible to discharge the gas to the atmosphere through a returnbend screenedvent terminating at least 3 m abovethe ground surface,provided that the assemblyincorpOrates a flame trap.
8.4.4.7 Ventilation. Any underground enclosures connecting with digestion tanks or containingsludge or gaspiping or equipment shall be provided with forced ventilation.
8.4.5 Digester heating. The heat requirementsof digestersconsistof the amount neededto:
(a) 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 leveland should be suitably insulated to minimise heat loss.
8.4.5.2 Heating facilities. Sludge may be heated by circulating the sludge through externalheatersor by heating units locatedinside the digestion tank.
(a) External’ heating. Piping shall be designedto provide for the preheating of feed sludgebefore introduction to the digesters. Provisionsshall be made in the layout of the piping andvalving to facilitate cleaning of the lines. Heat exchangersludge piping shOuldbe sized for heattransfer requirements.
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(b) Other heating methods. Other types of heating facilities will also be considered on their ownmerits.
8.4.5.3 Heating capacity. Heating capacity sufficient to consistentlymaintain the designsludgetemperatureshall be provided. Where digestedtank gas is used for heating, an auxiliary fuelsupply 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 boilerwater with return water so that the inlet water to the heatjacketcan be held below a temperatureat which caking will be accentuated. Manual control should also be provided by suitable by passvalve.
(b) Boiler controls. The boiler should be provided with suitable automatic controls to maintainthe boiler temperature at approximately 80°C to minimise corrosion and to shut off the main gassupply in the event of pilot burner or electrical failure, low boiler water level, or excessivetemperature.
(c) Thermometers. Thermometersshall be provided to show temperaturesof the sludge. hotwater feed, hot water return and boiler water.
8.4.6 Supernatant withdrawal. Supernatantpiping should not be less than 150 mm indiameter. The piping should be arranged so that withdrawal can be made from 3 or more levelsin the digester. A positive unvalved ventedoverflow shall be provided. Provisionsshould also bemade for sampling at each supernatantdraw-off level using a sampling pipes of minimumdiameter 37.5 mmand should terminate at a suitably sized sampling sink or basin.
8.5 Aerobic sludge digestion
8.5.1 General. Aerobic digestioncan be used to stabilize primary sludge, secondarysludge, ora combination of the two. Digestion is accomplishedin single or multiple tanks, design toprovide effective air mixing, reduction of the organic matter, supernatant separation, and sludgeconcentrationundercontrolled conditions. Its advantagesover anaerobicdigestionare:
(a) volatile solids reduction is approximately equal anaerobic process
(b) lower BODconcentrations 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) recoveryof more of the basic fertilizer values in the sludge
Its disadvantages are due to higher power cost associated with supplying the required oxygen andthat a uset’ul by-productsuch as methaneis not recovered.
8.5.2 Detail design. Multiple tanks are recommended. A single sludge digestion tank may beused in the case of small treatment plants or where adequateprovision is niade for sludgehandling and where a single unit will not adversely affect normal plant operations.
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The determination of tank capacities shall be based on rational calculations, including sucht’actors as quantity of sludge produced, sludge characteristics, time of aeration, and sludgetemperature.
The aerobic digestion tanks shall be designed for effective mixing by satisfactory aerationequipment. Sufficient air shall be provided to keep the solids in suspension and maintaindissolved 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 typeis recommended, and they should be designed to permit continuity of service. The design criteriaare summarisedbelow:
Parameter Design criteria for aerobic digeser
(a) Hydraulic detention time(i) Activated sludge 10 days(ii) Primary sludge or with activated sludge 15 days
(b) Maximum volatile solids loading 1.6 kg/m3.d
(c) Dissolved oxygen level in liquid 1 - 2 mg/I
(d) Energy requirements for mixing(i) Mechanicalaerators 20 w/m3
(ii) Diffuser 0.35 l/m3.s
8.5.3 Supernatant separation. Facilities should be provided for effective collection andremovalof scum and grease.
8.6 Sludge drying beds
8.6.1 General. This method of dewatering is most suitable in hot climatic conditions. Indetermining the area of sludgedrying beds, considerationshall be given to climatic conditions.the character and volume of sludge to be dewatered, the method and schedule of sludgeremoval. It may involve pumping if site levels do not permit gravity flow. Requirements forvalves, sumpsor pump well will dependon particular site conditions.
8.6.2 Design consideration. Air drying of sludge is carried out on under drained clinker ashor grit-sand drying beds consisting of an adequate number of separate bays where drainage andevaporationoccur simultaneously.
Sludge is laid on the drying beds in a 200 mm- 300 mm layer. Sludgebed loadingsare computedon a per capitabasis or on a unit loading of kg of dry solids per squaremeter per year. The timerequired to dry the sludge dependson the climatic condition and in Malaysian condition it shouldbe from 4 to 8 weeks. The arearequirementsof the drying bed is as the table below:
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Table 4. Sludge loading rate
T’~ pe of sludge Area(in2/person)
Sludge loading ratekg dry soIids,/m3.~r
Primary digested
Primary and activate.d(digested)
Primary and humus(digested)
0.09
0.16
0.1
120
100
100
8.6.3 Detail ae.sigu
8.6.3.1 Floor. The floor of the diving be.d may be of concrete laid to a fall of 1:200 and thewalls of brick. insitu concreteor precastpanels.
8.6.3.2 Wall. Walls should be watertight and its height above the ground should be kept to aminimum in order to avoid obstruction to the passageof air over the surfaceof the sludge. v~hichassist evaporationof the surface liquor. The outer walls should be curbed to prevent soil fromwashing into the beds.
8.6.3.3 Underdrainage system. Sludge dewaters by drainage through the sludge mass andsupportingsand and by evaporationfrom the surfaceexposedto th~air. Underdrains should beclay pipe or concretedrain tiles at least 100mm in diameter laid with open joints. linderdrainsshould be spaced at not more than 6 m apart. The tile should be adequatelysupported andcovered with coarse gravel or crushed stone.
8.6.3.4 Sands. The bed shall consist of a bottom layer of 250 mmdepth consisting of coarseagregategraded from 28 mm to 40 mm topped with a 225 mm layer of fine to coarsesand. Thefinished sand surfaceshould be level.
8.6.3.5 Bed compartment. The drying bed area is partitioned into individual beds.approximately6 in wide by 6 m to 300 m long or a convenientsize so that one or two beds willbe filled by a normal withdrawal of sludge from the digesters. The size of bed should be suchthat it is filled to a depth of eachnot more than 225 mm at one desiudgingoperation.
The sludge should dischargeonto a .precastconcreteslab to avoid scouring of the surfaceof thebed. Decanting devices should be provided for the removal of the supernatant liquor whichforms in the initial stages. Not less than two beds should be provided and they should bearranged to facilitate sludge removal.
8.6.3.6 Sludgeinfluent. The sludge pipe to the drying bedsshould terminate 300 mm abo~e thesurfaceand be so arrangedthat it will drain. Tracks or roadsof sufficient width for transportingawa the dried sludge b big lorries or trucks should be provided.
8.6.3.7 Buffer. To avoid odour nuisancefrom poorly digested sludge. sludge beds should helocatedat least 30 m away from dwellings.
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8.7 Mechanical dewatering facilities. Provision shall be made to maintain sufficientcontinuity of service so that sludge may be dewatered without accumulation beyond storagecapacity. The auxilIaries should be provided to ensure facilities should be sufficient to dewaterthe sludge produced with one largest unit out of service. Unless other standby facilities areavailable, adequatestoragefacilities shall be provided. The storagecapacity should be sufficientto handleat least a 3 month sludge production.
8.7.1 Auxiliaiv facilities for vacuum filter. There shall be a back-up vacuum pump andfiltrate pump installed for each vacuum t’ilter. It is permissible to have an uninstalledback-upvacuum pump or filtrate pump for every three or less vacuum filters, provided that the installedunit can easily be removedand replaced.
8.7.2 Ventilation. Adequate facilities shall be provided for ventilatiort 01’ dewateringand theexhaustair should be properly conditioned to avoid odour nuisance.
8.7.3 Chemicalhandling enclosures. Lime-mixing facilities should be completely enclosed toprevent the escape of lime dust. Chemical handling equipment should be automated to eliminatethe manual lifting requirement.
8.7.4 Drainage and filtrate disposal. Drainage from beds or filtrate from dewatering unitsshall 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 othermethods,a detaileddescriptionof the processand design datashall accompanythe plants.
8.8 Sludge disposal on land
8.8.1 Site selection. The programmeof land spreadingof sludge must be evaluated as anintegral system which includes stabilization, storage, transportation, application, soil, crop andgroundwater. Sewagesludge is useful to crop and soil by providing nutrients and organic matter.However, sewage sludge contains heavy metals and other substances which could affect soilproductivity and the quality of food and as such careshould be taken on the application of sludgeespeciallyin relation to food crops.
By proper selection of the sludge application site, the nuisance potential and public health hazardshould be minimized. The following itemsshould be consideredand the regulatory agencyshouldbe consultedfor specific limits:
(a) Land ownershipinformation;
(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) Slopeof land surface;
(f) Soil characteristics;
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(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 agriculturalpurposes. Stabilized sludge is defind as processedsludge in which the organic and bacterialcontentsof raw sludge are reducedto level deemednecessaryby the regulatory agency to preventnuisance.odoursand public health hazards.
8.8.2.2 Raw vegetables. Sludge should not be applied to land which is used for growing foodcrops to be eatenraw such as leafed vegetablesand root crops.
8.8.2.3 Minimum pH. No sludge shall he applied on land if the soil pH is less than 6.5 whensludge is applied. The pH shall be maintainedabove 6.5 for at least two years following end ofsludge application.
8.8.2.4 Persistent organic chemicals. At present, sufficient information is not available toestablish criteria of sludge spreading with regard to persistent organic chemicals, such aspesticides and polychiorinated biphenyls (PCB) heavy metals and other toxic substances.However, if there is a known source in the sewer system service area which dischargeordischargedin the past such chemicals, the sludge should be analysedfor such chemicals,and theregulatory agencyshall be consultedfor recommendationsconcerningsludge spreading.
8.9 Sludge pumps and piping
8.9.1 Sludgepumps
8.9.1.1 Capacity. Pump capacitiesshould be adequatebut not excessive. Provision for varyingpump capacity is desirable.
8.9.1.2 Duplicate units, Duplicate units shall be provided where failure of one unit wouldseriously 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 demonstratedsolidshandling capability shall be provided for handling raw and digestedsludge. Where centrifugalpumps are used, a parallel plunger type pump should be provided as an alternate to increasereliability of the centrifugal pump.
8.9.1.4 Minimum head. A minimum positive head of 600 mm shall be provided at the suctionside of centrifugal type pumpsand is desirable for all types of sludge pumps. Maximum suctionlifts should not exceed 3.0 m for plunger pumps.
8.9.1.5 Sampling facilities. Unless sludge samplingfacilities are otherwise provid-ed. quick-closing sampling valves shall be installed at the sludge pumps. The size of valve and pipingshould be at least 400 mm.
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8.9.2 S/uJ~,’cpiping
8.9.2.1 Size and head. Sludge withdrawal piping should have a minimum diameter of 0() mmfor gravity withdra~valand lOU mm for pump suctionand dischargeItnes. ‘.\ here wthUra~alisby gravity, the available head on the discharge pipe should be adequate to pros ide a least0.90 m, s velocity.
8.9.2.2 Slope. Gravity piping should be laid on uniform grade and alignment. The slope ofgrayitv discharge piping should not. be less than 3~/u. Provisions should be made for cleaning.draining, and flushing dischargelines.
8.9.2.3 Supports. Special consideration should be given to the corrosion resistance andcontinuing stability of supporting systemslocated inside the digestion tank.
6)
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MS 1228 : 1991
Appendix A
List of references
Al. BS 6297:1983 - British Standardcode of practice for Design and installation of smallsewagetreatmentworks ai~dcesspools.
A2. SewerageMasterPlans* in Malaysia.
A3. WastewaterTreatment Plant Design by A joint committee of the Water Pollution ControlFederationand American Societyof Civil Engineers.
.A4. Recommended standards for sewage works prepared by the Great Lakes. UpperMississippi River Board of State SanitaryEngineers1978.
AS. SewerageTreatmentin Hot Climates by Duncan Mara.
A6. Wastewater Engineering by Metcalf and Eddy.
.A7. Wastewater System Engineering by Homer W. Parker.
AS. SewerageProceduresand Requirementsfor Planning Approval, Building Plan ApprovalAnd Sewerage Plan Approval by SewerageDepartment,EnvironnientalEngineering Division,Ministry of the Environmentof Singapore.
As available in the Economic Planning Unit of the Prime Minister’s Department.
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Key letter A C E G H J K L P4 0 P 0 R Approx. W.T. ofcover and frame
Grade
Heavy duty 20 23314 30 6 3/4j314 in 1 31/2 3/4 2 1io~5 4 1/2 CWI. A
Medium duty 20 223/4 28 4 1/2 1/2 i/a 3/4 21/2 7/lB li/S 1 4 2114 CWT. B
Key letter A B C 0 B F C H J K L P4 0 Approx. W.T. ofcover and frame
Grade
LI~htduty 18 24 261o/IB 20l5/ie ~28 22 i~n 11/4 1/32 3/32 1/4 7/0 3/~CWT, C
Dimension in inches
SECTION 1-1LIGHT DUTY MANHOLE COVER
AND FRAME
4T ~ A
SECTION 1-~HEAVY AND MEDIUM DUTY MANHOLE
COVER AND FRAME
Figure 1. Typical diagram for manhole and inspection chamber
Siat.
PLAN (HALF COVER REMOVED I PLAN I HALF COVER REMOVED)
‘H
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‘0
_I
Figure 1. Typical diagram for manhole and inspection chamber (contd.)
0/2
LIGHT C. I. M.H
CI)
‘0‘0
9~ 2L0~~
‘0
‘.0
SECTION A—A SECTION B-B
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- 6”CONC.SLAB. REINFORCED WITH5/~M.sBARS AT 6” CR5
IN CEMENT.
S.G.W. CHANNEL
Figure I. Typical diagram for manhole and inspection chamber (contd.)
PATTERN C.I.M.Ij COVERl8”x 24
611
-l
I?’l CEMENT
BE NC H ING(:2:4 CONc.
SECTION C-C
6’CONC. FOUNDATION (:3:6 MIX.
SECTION D-D
CI)
P.-’
00
‘C‘Ca’.Li
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UN
IVE
RS
ITI T
UN
HU
SS
EIN
ON
N M
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IA /
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10-O
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008
/ Sin
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only
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and
net
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9’ BRICKWORKIN CEMENT BRICKWORi< IN CEMENT.
4 S.G.w PIPE
SECTION F-F
LIGHT PATTERN C. I.M.H1COYER AND FRAME 18X 24 6”CONC. S~.A6 REINFORCEMENT
~~WITH 5/8 ~I 1.1.5 BARS Al 61
CES
(-I)
I.-’l.~e00
‘0
1 12
o0o~~
SECTION E-E
Figure 1. Typical diagram for manhole and inspection chamber (conId.)
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HEAVY DUTY C’IRONCOVER AND FRAME
HEAVY DUTY G’IRONCOVER AND FRAME
APPROX1’ GEM. RENDERING TO S~TCOVER AT CORRECT LEVEL.
9~BRICKWORK IN CEM MORTAR. —
(1:2)FLI.JSH POINTED BOTH SIDES.
U’
.i1I(2~BRIcKWORI< CEM. P’IOPTAR(1:2) F LUSH POINT ED BOTHSIDES
-—3/4’RENDERIln IN ALUMINACEM. AND SAND (1:2)
12” ~ CAST IRONONE RING BRICK DUCI( FOOT BEND
EDGE ARCH
~ I •__~ 91 CONG. FOUNDATION
~G~IANNEL FORMED IN
BENCHING RENDERED.
SECTION A-A
PRECAST HIGH ALUMINA GRANOLITIC I
CEMENT CONCRETE CHARNEL
Figure 1. Typical diagram for manhole nut! inspection chamber (contd.)
COM.SLAB RE/HFWITH
5/8
B G BARS AT 54 CR5.
CONC. BENCH/tIC TO BE LEV~LWITH SOFFIT OF PIPE SLOPEDTOSIDE OF MANHOLE AT ONEINCH IN ONE FOOT.
SECTION B-B
I.-’I’.-’00
‘0‘0
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APPROX 1~CEM. RENDERING TO SETCOVER AT CORRECT LEVEL.
HEAVY DUTY C IRONCOVER AND FRAME.
BRICKWORK IN OEM. MORTAR..(12) Ft.USF4 POINTED BOTHSIDES.
18~BRICKWORK IN CEM MORTAR(1:2 ) FLUSH POINTED
314’ RENDERINGINALUMINA CEM. AND SAND
•ONE RING BRICKON EDGEARCH.
18~/~CASTIRON DUCKFOOT BEND.
911 CONC.S~.AB RE/HFWITH 5/8. ~IM.S BARS ATt~
11CR5..
i8’~BRICKWORK IN GEM./40R1AR 1)2) FLUSHPOINTED BOTH SIDES.
3/4~RENDERING INALUMINA CEM. ANDSAND (1:2 I.
SECTION A-A SECTION B-B
CONC. BENCHING TO BELEVEL WITH SOFFIT OFPIPE SLOPED TO SIE~OF MANHOLE AT ONEINCH IN ONE FOOT.
18~BRICKWORK TO CHAMBER WHEREINVERT iS GREATER THAN 10’- 0’ DEEP.
I..-’
HEAVY DUTY C IRONCOVERAND FRAME
I’.-’
00
‘0‘0
131/2” BRICKWORKIN CEM. MORTAR.(1: 2 ) FLUSH POINTED BOTHSIDES.
12” CONG. FOUNDATION
PRECAST HIGH ALUMINA GRANOLffHICCEM. CONC. CHANNEL.
NOTE
Figure I. Typical diagram for manhole and inspection chamber (conId.)
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HEAVY OJW C.I1~GOVER AND FRAME
6’~”X59~X9~CONC. SLAVREINFORCED WITH 5/8 MS. BARSAT 5 CRS WITH H~OKEDENDS _________
I3~/2BRICKWORK IN1-2 CEM. MORTARFLUSH R)INTEDEXTERNALLY ~
HEAVY DUlY C.IRONCOVER AND FRAME
OROJ’ID LEVEL
PLACE COVER TO ~ ~—2ICORR~T LEVEL •.~L_i •. —
-~ :~ONERING
/ 27 —~ ~ BRICK ONE1X~EARCH
~‘ r~I ~ 9BRICKWORK/~ __C__, ,~2 CEM. MCRTAR~. COVER 2’ POINIED BC’TH‘2’ PLATE SIC€S.
2”Chombe~ .~ I
‘,/_ ,, — 7__7///7
3//. REINOERINGALUMNA
- ~CAVLMALLEA~ ~
__ .19CONC. FOUNDATION .~ .
SECTION SECTION B-B
Figure 1 . Typical diagram for manhole and inspection chamber (contd.)
P.-)
00
‘0‘0
ONE RING BRICKON EDGE ARCH
ONE RiNG or~,’..,’.ON EDGE ARCH0.1 BEND—
WITH DUCKFOOT
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(ID
HEAVY DUTY C IRONCOVER AND FRAME~~
I—’00
‘0rdPC/tD4fl I FVFI ‘0
‘7 ~ P Ip p~..~-—-—1~6X3~ X9 CONC SLAB/ ~ ~> ll/
2~REIN~ORCEOWITH 5/8~~MS BARS
BRICKWORK IN CEM. MORTAR ~ ~- /,~ AT 6 CR5. WITH HOOK€ ENDS.(1:2) FWSI-I POINTED BOTHSIDES—’ ONE RING BRICK
ON EDGES ARCH
~OP~LAT~ ~
/
9~X7~6’X9’COtC.SLAB~ D.REINFORCEO WITH 5/8 ~I MSBARSAT 6’CRS WITH HIDOXEDENOS.
18 BRICKWORK IN CEM.(1:2 )FLUSH POINTEDEXTERNALLY.
ONE RING BRICKON EDGEARCH
12’ CONC FOUNDATION
SECTION B-B
HEAVY DUTY CIRONCOVER L FRAME.
C. IRON
D
SECTION A-A
Figtmre I. Typical diagram for manhole amid inspection chamber (could.)
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MS 1228: 1991
1. Cho~nfor lifting purpose
2 Level sw~fchfor alarm3. Cable
4. Level switch for start
~. Level switch ~r motor stop
Figure 2. Typical installation of automatic connectingtype submersible pump
75
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MS 1228 : 1991
ISOMETRIC VIEW OF SEPTIC TANK & FILTER BED.~(e-V2.”T~i-a”
ccrru~otedperforated
asaes.os sheets (1 .nch fa~I
- deen channel
Figure 3. Typical diagrams for Septic Tank
/~
half round.y.c channel
vent pipe
4’~outlet pipe..........atuminium stoinles steel or ci tipper
4’~aeration pipe
tnk Ow/c
2 nominal max. size stones —
I I9 layer or 6 _6 gouge stones
perforated precast cone.under drainage tiles
76
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MS 1228 : 1991
Inlet Sel:itc
~LLi
-
—Pump Sump
Typical Double Compartment SeptK Tank
Figure 3. Typical diagram for Septic Tank (contd.)
Out let
FIlter Bed
1 ~1
Typical Single Compartment Septic Tank
Su mp
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MS 1228 : 1991
Hydro~totic v~Iyc
PLANDimcn~ion or~ .n IUn~ctrc~
TYPIC.4.L UPV~RO FLOW SEDIMEW~L~JIUNTANK
Adju~to~Ic vc~ wotch orçc:)e/ic/ed wc~r rio/cs
~cu (Sb ocr
Dcc kin9
with rein o cOb/C~cc/iori ovcr tookccntrc aria roddin9 point0/ e/uo9C out/ct
Figure 4. Typcal view of a Sedimentation Tank
/000 i000
p ~ip C
Sluice cO/cc
00 ~iudgc draw oi/pipc work
78
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8
C) -4 C) 0 m Ill
I 0 m m z w 0 I- 0 C)
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3,-
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00Q
(I)
00
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TANDA-TANDA STANDARD SIRIM
Tanda-tanda Standard SIRIM seperti yang tertera di bawah adalah tanda-tanda pengesahan daganganberdaftar. Tanda-tanda ml hanya boleh digunakan oleh mereka yang dilesenkan di bawah skim tandapengesahan yang dijalankan oleh SIRIM mengikut nombor Standard Malaysia yang berkaitan. Kewujudantanda-tanda mi pada atau berkaitan dengan sesuatu barangan adalah sebagai jaminan bahawa barangantersebut telah dikeluarkan melalui satu sistem penyeliaan, kawalan dan ujian, yang dijalankan semasapengeluaran. ni termasuk pemeriksaan berkala kerja-kerja pengeluar menurut skim tanda pengesahan SIRIMyang 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.
The SIRIM Standard Marks shown above are registered certification trade marks. They may be used onlyby those licensed underthe certification marking scheme operated by SIRIM and in conjunction with the relevantMalaysian Standard number. The presence of these Marks on or in relation to a product is an assurance thatthe 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 schemeof 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.
SIRIM STANDARD MARKS
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MS ISO 10202-6 : 1996
6
INSTITUT STANDARD DAN PENYELIDIKAN PERINDUSTRIAN MALAYSIA
Institut Standard dan Penyelidikan Perindustrian Malaysia (SIRIM) telah ditubuhkan hasil dari cantuman InstitutPiawaian Malaysia (SIM) dengan Institut Negara bagi Penyelidikan Sains dan Perusahaan (NISIR) di bawahUndang-Undang Malaysia Akta 157 pada 16hb. September 1975:Akta Institut Standard dan PenyelidikanPerindustrian Malaysia (Perbadanan) 1975. Institut ini diletakhak dengan kuasa untuk memamju danmenjalankan penyelidikan perindustrian dan untuk menyedia dan memajukan standard-standard bagi barangan-barangan, proses-proses, amalan-amalan dan perkhidmatan-perkhidmatan; dan bagi mengadakan peruntukanbagi perkara-perkara yang bersampingan atau berkaitan dengan maksud-maksud itu.
Satu daripada tugas-tugas Institut ini adalah menyediakan Standard-Standard Malaysia dalam bentukpenentuan-penentuan bagi bahan-bahan, keluaran-keluaran, kaedah-kaedah ujian, kod-kod amalan yangsempurna dan selamat, sistem penamaan dan lain-lain. Standard-Standard Malaysia disediakan olehjawatankuasa-jawatankuasa perwakilan yang menyelaras keupayaan pengilang dan kecekapan pengeluarandengan kehendak-kehendak yang munasabah dari pengguna. Ia menuju ke arah mencapai kesesuaian bagimaksud, memudahkan pengeluaran dan pengedaran, kebolehsalingtukaran gantian dan pelbagai pilihan yangmencukupi tanpa pembaziran.
Standard-Standard Malaysia disediakan hanya setelah penyiasatan yang lengkap menujukkan bahawa sesuatuprojek itu disahkan sebagai yang dikehendaki dan berpadanan dengan usaha yang terlibat. Hasil ini berasaskanpersetujuan sukarela dan memberi pertimbangan kepada kepentingan pengeluar dan pengguna. Standard-Standard Malaysia adalah sukarela kecuali is dimestikan oleh badan-badan berkuasa melalui peraturan-peraturan, 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 bantuankewangan dari Kerajaan, kumpulan wang dari bayaran keahlian, hasil dari jualan Standard-Standard danterbitan-terbitan lain, bayaran-bayaran ujian dan bayaran-bayaran lesen untuk mengguna Tanda PengesahanSIRIM dan kegiatan-kegiatan lain yang berhubung dengan Penstandardan, Penyelidikan Perindustrian danKhidmat Perunding.
STANDARDS AND INDUSTRIAL RESEARCH INSTITUTE OF MALAYSIA
The Standard and Industrial research Institute of Malaysia (SIRIM) is established with the merger of theStandards 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 ofMalaysia (Incorporation) Act 1975. The Institute is vested with the power to provide for the promotion andundertaking 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 materialsand products, methods of testing, codes of sound and safe practice, nomenclature, etc. Malaysian Standards areprepared by representative committees which co-ordinate manufacturing capacity and production efficiency withthe user’s reasonable needs. They seek to achieve fitness for purpose, simplified production and distributionreplacement 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 desirableone and worth the effort involved. The work is based on voluntary agreement, and recognition of the communityof interest of producer and consumer. The use of Malaysian Standards is voluntary except in so far as they aremade mandatory by statutory authorities by means of regulations, federal and local by-laws or any other similarways.
The Institute operates entirely on a non-profits basis. It is a grant aided body receiving financial aid from theGovernment, funds from membership subscriptions and proceeds from sales of Standards and otherpublications, fees and licence fees for the use of SIRIM Certification Mark and other activities associated withStandardization, Industrial Research and Consultancy Services.
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