Centralised –Decentralised transportation system

1. Centralised –Decentralised transportation system M.K. PANDEY/P. Jenssen

2. Sewer lines Wastewater treatment plant Centralised system • Collection system 70 - 90 % • Treatment 10 - 30 % (Otis 1996, Mork et al. 2000) • The cost of conventional gravity system is up to 4 times higher than the cost of treatment and disposal Wastewater treatment plant

3. House hold human waste and wastewater Department of Plant and Environmental Sciences } { Urine Excreta ＋ Feaces ＋ Flush ＋ Anal cleansing Wastewater Black water ＋ Greywater Or Sewage

4. House hold human waste and wastewater • Important constituents • Organic matter • Neutrients- Nitrogen, Phosphorus, Potassium • Pathognes Department of Plant and Environmental Sciences } { Urine Excreta ＋ Faeces ＋ Flush ＋ Anal cleansing Wastewater Black water ＋ Greywater Or Sewage

5. Wastewater transportation • Wastewater transported to treatment plant as quickly as possible • Self cleansing velocity should be maintained at low flow • Velocity should not be higher than the maximum allowable velocity – to prevent wear and tear of the pipes • Formation of Hydrogen sulphide, airlock should be prevented • Should not be close to W/S lines • Proper selection of type and shape of sewer Department of Plant and Environmental Sciences

6. Conventionalgravitysewer • Pollution due to combined sewer overflow • Large dia sewer • Interference to other infrastructure • Contamination of water distribution system • High chances of system failure Department of Plant and Environmental Sciences WW Treatment Plant G.L Over flow structure Pumping system River

7. Types ofconventionalsewerage system • Combined sewer • Storm and sanitary sewage (wastewater) collected in one sewer • Suitable at places where rainfall is evenly distributed throughout the year • Overflow structure required to divert the flow more than the design flow • Large dia sewer required • Large volume of wastewater to be treated • Plumbing work reduced in houses • Separate sewer – Storm sewage and sanitary sewage conveyed in separate sewer • Chances of clogging • Prone to formation of H2S • Partially separate system • Rainwater from houses and yards discharged into sanitatry sewers Department of Plant and Environmental Sciences

8. Sewer lines Wastewater treatment plant Investment Cost • Collection system 70 - 90 % • Treatment 10 - 30 % (Otis 1996, Mork et al. 2000) • The cost of conventional gravity system is up to 4 times higher than the cost of treatment and disposal Wastewater treatment plant

9. Decentralized system Collection in a septic tank and transport the effluent wastewater to nearby treatment system Department of Plant and Environmental Sciences • Soak pit • Constructed wetland • Infiltration system • Pond system • Sand filter Septic tank (S.T) Natural Treatment Compost or transport to faecal sludge treatment facilities.

10. Decentralized system Low flush or pour flush Collection and treatment of blackwater and Greywater separately Department of Plant and Environmental Sciences • Soak pit • Constructed wetland • Infiltration system • Pond system • Sand filter Settling tank and greese tap Septic tank (S.T) Natural Treatment Compost or Transport to faecal sludge treatment facilities

11. Decentralized system Low flush or pour flush Collection and treatment of urine, faeces and greywater separately Department of Plant and Environmental Sciences Urine Settling tank and greese tap Natural Treatment Faeces

12. Decentralized system- STEG 50 mm to 200 mm 50 mm • Septic tank effluent gravity (STEG) • Can be laid in variable grade - because no solid to settle • Uniform slope with no high points to prevent airlock • H2S formation • Air release valve in high points • Clean out ports at junction 100 mm

13. Decentralized system- STEP • Septic tank effluent pump (STEP) and pressure sewer with grinder pumps • Sewer are under pressure – pressure generated by high head turbine pump • Advantage in high groundwater and rocky soil and rolling terrain - can follow the terrain • If grinder pumps used- septic tank not required

14. Decentralized system- Vaccum sewer • Vacuum sewer • Vacuum applied to transport sewage

15. Hydraulics of wastewater collection system • Velocity and headloss are two governing parameter • Hazen williams equation (1) • Where • V= Velocity of flow, m/s • C = Hazen –williams coefficient, 150 may be used PVC pipe • R = Hydraulic Radius, (wetted area/wetted perimeter), m • (e.g for pipe flowing full • D = inside dia of sewer, m • S = Slope of energy gradeline, m/m, • hf = head loss due to friction, m • L = Length of pipeline

16. Hydraulics of wastewater collection system • Manning`s equation (2) • Where V= Velocity of flow, m/s n = Manning’s coefficient, 0,013 to 0.009 may be used for PVC pipe R = Hydraulic Radius, (flowing full) D = inside dia of sewer, m S = Slope of energy grade line, m/m, hf = head loss due to friction, m L = Length of pipeline Sewer line (gravity sewers) are designed as a open channel or flowing just full

17. Hydraulics of wastewater collection system • The velocity should be less than 1.5 m/s to avoid excessive frictional loss. • No minimum velocity required for STEG system – (but usually kept at 1m/s)

18. Information's required for design and layout of STEG collection system • Site characteristics • Topography of the area • Depth of soil • Depth of water table • Depth of freezing zone • Equivalent dwelling unit (EDU) • Residence with given number of residents e.g if 1 EDU is defined as residence with 4 person then 8 person residence is 2EDU

19. Information's required for design and layout of collection system • Peak flow rates • collection system based on peak flow rates • 1.3 to 1.9 lit/min/EDU (USA) • 0.8 to 1.2 lit/min/EDU (Norway)

20. STEPS for the design of Sewer collection system • Prepare a longitudinal profile • Select a pipe size • Calculate the velocity using Hazen Williams equations • Calculate the pipe cross sectional area and determine the actual capacity • Check for the surcharged condition

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