Microbial Indicator as a Performance Evaluation Tool for STP: Case Study

Abstract

Mixed community of microorganisms is key to sewage treatment and few of them may be used as an indicator organism to evaluate the performance of sewage treatment plants (STPs). The aeration tank in the activated sludge process (ASP) forms an artificial ecosystem consist of bacteria and protozoans. Protozoans and E.coli can be used as a reliable microbial indicator to evaluate the performance of sewage treatment plant. In the present research the existing performance of Sanjauli Maliana Sewage Treatment Plant had evaluated in terms of removal efficiency of Total Suspended Solids (TSS), 5-day Biochemical Oxygen Demand (BOD₅) and Chemical Oxygen Demand (COD). The operational parameter of extended aeration ASP has been determined which showed low food/microorganism (F/M) and high mean cell residence time (MCRT) but still the Dissolved oxygen (DO) of aeration tank was very low. In contrary to that, microscopic analysis suggested high food/active microorganism ratio and low MCRT that explained the low DO. The corrective measures were implemented successfully to elevate the performance of STP. The performance evaluation of sewage treatment had been done after 4 weeks and 6 weeks of successful implementation of corrective measures. The removal efficiency of TSS, BOD_5, and COD had increased to 94%, 89%, 92% from 79%, 75% and 83% similarly the total coliform removal has increased by 10 folds after six weeks of implementation of corrective measures. The relative density of ciliates had increased significantly and the relative density of amoeba had decreased. An optimal dose of bleaching powder had been evaluated which may ensure the optimized complete disinfection to reduce the risk of Hepatitis E Virus (HEV) epidemics as well as no stress to the aquatic life. In developing countries like India, these findings may increase the reliability and adaptability of microbial indicators to evaluate the performance of STP which is currently done predominately by physicochemical parameters.