Performance Evaluation of UASB + Polishing pond Based Sewage Treatment Plant

Abstract

pflow Anaerobic Sludge Blanket Reactor is an extremely fast and effective method for removal of bulk organic compounds from wastewater and has been successfully used to treat variety of industrial as well as domestic wastewaters. Anaerobic reactors hardly produce effluents that comply with usual discharge standards established by environmental agencies. Therefore, the effluents from anaerobic reactors usually require a post-treatment step as a means to adapt the treated effluent to the requirements of the environmental legislation and protect the receiving water bodies. The main role of the post-treatment is to complete the removal of organic matter, as well as to remove constituents little affected by the anaerobic treatment, such as nutrients and pathogenic organisms. The UASB + polishing pond configuration has been studied in this dissertation work. This alternative looks more attractive when the effluent from the pond can be used for agricultural purposes, since the polishing ponds aim mainly at the removal of pathogenic organisms. UASBs are mostly designed using empirical formulas derived either from past pilot scale studies or from performance of already existing STPs elsewhere. Actual performance of the STP can differ from that of design mainly due to differences in sewage characteristics & local conditions. Thus knowing actual performance and capacity of the STP becomes very important. The current study is an attempt in this direction. Samples were collected over four months (Feb to May 09) from four sampling points; raw sewage [P-1], UASB Reactor outlet [P-2], Polishing Pond outlet [P-3] to comment on its design adequacy and to evaluate performance of the STP and its key constituent units. The treated effluent was found almost complying with the prescribed standards. BOD, COD, TSS and MPN of the treated effluent were 33±11 mg/L, 137±43 mg/L, 75±69mg/L and 3.3x106 respectively. Excepting for MPN, if not for the role played by the algal cells in the treated effluent, the treatment process is satisfactory indicating that plant is working properly.