SELECTION AND DESIGN OF APPROPRIATE STP TECHNOLOGY FOR A TOWN IN TAMIL NADU

Abstract

There are many Sewage Treatment technologies available for the treatment and reuse of sewage in India. Sometimes, it is difficult to select a technology that is appropriate for the desired treatment in the specific region such as rural, urban or metropolitan area. The important factors affecting the selection of STP technology are the volume of daily flow, sewage characteristics, degree of treatment needed, disposal of the effluent, area of land required for the plant, capital cost of installation, power required for the treatment, annual operation and maintenance cost. The Techno Economic Analysis tools such as Life Cycle Cost Analysis, Benefit Cost Ratio and Internal Rate of Return are used to take final decision. The study highlights the application of the Techno Economic Analysis tools for the selection of appropriate technology of sewage treatment and aims to provide guidance/methodology in'the appropriate STP technology selection for urban planners and decision makers. Kancheepuram a town in Tamil Nadu, a historic temple city is identified for the case study. Five municipal sewage treatment technologies that are mostly used in India are selected for analysis. Three major decision variables/parameters that affect the selection are taken into account for analysis; capital cost, annual maintenance cost, and land cost. The selection of technology is made by calculating the benefit cost ratio, assuming a discount rate of 10% and the cost benefit analysis or Life cycle cost analysis. It is found that the Waste Stabilization Pond is the most economical and cost effective technology to treat municipal sewage where the cost of land is below Rs. 62 Lakhs per ha (i.e., Rs. 62 per sqft or Rs. 620/sqm). Beyond Rs. 62 Lakhs to Rs. 190 Lakhs per ha the Upflow Anaerobic Sludge Blanket (UASB) with final polishing pond is economical. Above Rs. 190 Lakhs per ha Moving Bed Biofilm Reactor (MBBR), Sequencing Batch Reactor (SBR) & Activated Sludge Process (ASP) are found to be economical. For the Kancheepuram town the WSP is selected for the municipal sewage treatment as the land cost is Rs. 1.50 Lakhs per ha. (i.e., Rs. 1.5 per sqft or Rs. 15/sqm). The WSP is designed for actual conditions and the cost estimation been worked out.