S ¡ For it to beefficient, must have the ability to transport the sewage effectively.
¡ It’s classifiedbased on the type of the wastewater flowing in the pipe: § sanitary sewer – carry only thewater from residential, commercial and industrial with the stormwater excluded. § stormwater sewer -carries the water coming from roofs, paved areas, pavements and roads. § combined sewer – sanitary sewer + stormwater sewer. ¡ Design must be in accordance with § MS 1228:1991: Codeof Practice for Design and Installation of Sewerage system ¡ It’s designed todischarge the wastewater flows as required. ¡ Sewage treatment plant (STP) § converts the sewageinto a form which can be safely discharges to the environment, or reused forvarious compatible purposes. § Effluent dischargemust meet the standard A & B ¡ The diameter of the pipe is§ chosen based on theavailability of the size provided § Consideration ofthe economy § sufficient size tohandle the total discharge, Q. (Q > Peak flow total ) ¡ Lateral sewer§ minimum of 150mmdiameter § receives thechannel sewage from individual buildings to another branch sewer, or directlyto an on-site treatment plant ¡ Reticulation sewer§ 225mm to 300mm.
§ receives thechannel sewage collected from groups of individual properties to branch sewers ¡ Main sewers/ trunk/ outfall sewer§ 450mm to above900mm diameter. § receives sewersfrom branch sewers and transfer flows to large sewage treatment plant. ¡ Branch sewers§ 300mm to 450mmdiameter § receivethe sewage from reticulation sewers and thereafter transfers the flow to smallsewage treatment plants, or to main sewers ¡ The depth of sewers is§ 1.2m below theground surface. § invert depth –minimum of 1.2m ¡ Velocities§ minimum of 0.8 m/s ? self-cleansing? prevents the sludgeto settle in the pipelines § maximum is at 4.0m/s ? prevent scouring ofsewer by erosive action of suspended matter.
¡ The slope§ 1:200 to 1:25 inorder to maintain the velocity. ¡ Design should be:§ Allow easy accessfor inspection and cleaning for the pipe § Made from durablestructure, § cause minimum interferenceto the sewage flow. § minimum of 1.2 m indepth from the ground level § at least at 100mapart of each other for eases of maintenance § Gradients from 1:40 to 1: 110 will should be use to give normally give adequate flow velocities. ¡ Locations are situated§ end of line § intersection ofsewer § changes in gradeand alignment except in curved sewers. ¡ The minimum diameter of manholes constructed from precast concrete Sewer dia. (mm) Chamber dia. (mm) 225-300 1200 375-450 1350 600-750 1500 ¡ Drop manhole § installed to reducethe turbulence in the manholes cause by the elevation differences.
§ if the differencebetween the incoming sewer and manhole invert is more than 500mm § If the differencebetween the incoming sewers is less than 600mm, § invert shall befilleted at the corners to prevent solids deposition ¡ 6 procedure 1. Network sewerplannning2. Sewerage layout plan 3. Determination of population equivalent 4.
Determination of peak flow, discharge, type and size of pipe 5. Determination of velocities 6. Determination ofinvert level and outlet level ¡ Based onMS 1228 :1991 : section 4.3.2 several factors must be condiser in the planning: § Thesewerage pipe must be located in the surrounding area of the road. § The pipe to belocated in private property due to certain topographies must apply forpermission to certain individual before the construction can begin. § Beforeany construction work can begin, the layout and overall existing building, pipeand electrical must first to be determine.
§ During theconstruction work, the separation of sewer and main water should be requires ofminimum horizontal separation of 3 m and a minimum vertical separation of 46 cmfrom water mains. ¡ The system must be drawn to show the location of the pipe and so on.Theprocess involved of: § Preparing thesewerage layout plan to show the flow of sewerage, position of the network,size of pipe and position of manholes ¡ Sewer follow natural drainage ways to minimize excavation and pumpingrequirements. Large trunk sewers are usually constructed in low-lying areasclosely paralleling streams or channels. In general, pipes should crosscontours at right angles. ¡ Located pipe§ place for easy connection for future user § provide access for maintenance.
§ accomplished by placing them in streets or other rights-of-way. ¡ number expressingthe ratio of the sum of the pollution load produced during 24 hours byindustrial facilities and services to the individual pollution load inhousehold sewage produced by one person in the same time. ¡ parameter use toconvert the number of person contributing to volumetric flow rate of wastes ¡ flow rates are measured in cubic meters persecond ¡ calculated for bothexisting land use and for expected future development. Type of establishment Population equivalent Residential 5 per house Commercial 3 per 100m² area Educational Institutions – Day Schools 0.
2 per student – Residential Schools 1 per student (residential) Hospitals 4 per bed Hotels 4 per room Factories 0.3 per employee Market (Wet Type) 3 per stall Market (Dry Type) 1 per stall Petrol Stations 18 per service bay Bus Terminal 4 per bus bay Taxi Terminal 4 per taxi bay Mosque 0.5 per person Church or 0.2 per person Stadium 0.2 per person Swimming Pool or Sports Complex 0.5 per person Public Toilet 16 per WC (water closet) Airport 0.2 per passenger/day Airport 0.
3 per employee Laundry 10 per machine ¡ PE = population equivalent x per capitawastecontribution¡ PE =population equivalent x 225 L/c.d (1) ¡ Cumulative PE = PE 1 + PE2 (2) ¡ Peak flow§ the combination ofinfiltration and inflow, and wastewater flow. § in unit of flowrate per contribution area or unit of flowrate per pipe length.
(4) (5) (6) (7) ¡ flow discharge, Qd depends on the pipe gradient and diameter of thepipe. Pipe area, Apipe = ? r2 (3) Perimeter, P = 2 ? r (4) Hydraulic radius = A/P (5) ¡ Design must be Qd >Peak Flow ? (6) ¡ Manningcoefficient, n § Depend on theselected pipe material Material Manning coefficient, n Concrete 0.013 ? n ? 0.015 Vitrified clay 0.013 ? n ? 0.015 Cast iron 0.013 ? n ? 0.015 Brick 0.015 ? n ? 0.017 Corrugated metal pipe 0.022 ? n ? 0.025 Asbestos cement 0.013 ? n ? 0.015 Earthern channel 0.025 ? n ? 0.030 § Full flow velocityVfull can be calculatedfrom the pipe discharge§ 4m/s > V (fullflow) > 0.8 m/s (7) ¡ Manhole level§ find by groundsurface elevation Fall in sewer = Upper end elevation – Lower end elevation (8) Sewer invert lower end = Gound surface elevation – fall in sewer (9) ¡ However, if ground surface gradient is notsuitable,§ new pipe gradientcan be proposed Fall in sewer = slope x Lower end elevation (10) Sewer invert upper end = Gound surface elevation – cover of pipe – diameter of pipe (11) Criteria Remarks Pipegradient, s 0.5 % ? s ?4 % Full flowvelocity, Vfull 0.8 m/s ? Vfull ? 4 m/s Discharge, Qd PF < Qd