Efficiency evaluation of sewage treatment plants with different technologies in Delhi (India).

Physical, chemical and microbiological efficiencies of Sewage Treatment Plants (STPs) located in Delhi's watershed in context of different treatment technologies employed in these plants have been determined. There were in all seventeen STPs treating domestic wastewater which were studied over a period of 12 months. These STPs were based on Conventional Activated sludge process (ASP), Extended aeration (Ex. Aeration), physical, chemical and biological removal treatment (BIOFORE) and oxidation pond treatment process. Results suggests that except "Mehrauli" STP which was based on Extended aeration process and "Oxidation pond", effluents from all other STPs exceeded FC standard of 10(3) MPN/100 ml for unrestricted irrigation criteria set by National river conservation directorate (NRCD). Actual integrated efficiency (IE(a)) of each STP was evaluated and compared with the standard integrated efficiency (IE(s)) based upon physical, biological and microbiological removal efficiencies depending upon influent sewage characteristics. The best results were obtained for STPs employing extended aeration, BIOFORE and oxidation pond treatment process thus can be safely used for irrigation purposes.