annexures - Indian Institute of Technology Roorkee

Chapter - 4 Preparation of Feasibility Report of Sewerage Schemesii.Decentralised SystemWaste water of each sewerage district is carried in sewers or in drains or partly in sewersand partly in drains to a treatment plant designed for that district which constitutes adecentralised treatment system. In the decentralised approach, the Sewerage Districtcould be small envisaging collection, treatment and disposal of wastewater in theneighbourhood itself involving smaller quantity of wastewater.A decentralised system could result in drastically curtailing the length and diameters of trunksewers, in reduction of depth at which the sewers should be laid and in reducing the number ofplaces where IPS should be installed. This may reduce the capital cost.4.3.3 Using Open Drains in Areas Having Septic TanksSome Drainage Areas may have septic tanks. The effluent from the septic tank is partiallytreated and could satisfy conditions for being permitted to flow in open drains. Furtherconveyance and treatment is open to options as below:i. It can be allowed to flow from open street drains to storm water drains. Before drains joinsthe river, the waste water can be taken to a STP for being treated.ii. A network of sewers is laid so that effluent from septic tanks and other waste water iscarried in them to a STP for treatment.iii. For drainage areas that do not have septic tanks, sewers will need to be laid and housesconnected to carry wastewater through a hierarchy of drains to a STP. It has then to behandled as discussed above.4.3.4The status of wastewater management system in the city may be presented in the followingtable. Where necessary a note stating the status of the component, its performance against thedesigned performance and whether it should be repaired, refurbished or modernised, shouldbe appended.Table 4.1: Existing Status of Waste Water ManagementSewageDistrictsDrainageAreaName andnumber ofdrains in thedistrictSewerage Districtscoveredwithsewersand STPState ofSewersState ofSTPSewerage Districts Not CoveredWith Sewer and STPSepticTankDischarge of wastewater in street drainsRemarks4.4 DESIGN PERIODSDesign periods for sewerage mains and STPs have been often debated due to costconsiderations. Keeping in view the resource constraints and optimum utilisation of assets, amodular approach may be followed for these facilities.34