Anaerobic filter for polishing effluent of UASB reactor treating strong sewage at 23 degrees C.

Anaerobic filter (AF) was used for polishing effluent of UASB reactor treating strong sewage at an average water temperature of 23 degrees C. The UASB-AF system was operated with sludge discharge taking place only from the AF reactor. It was hypothesized that better removal of suspended COD (COD(ss)) fraction from the system can be achieved by increasing sludge discharge frequency from the AF reactor. For this purpose, sludge discharge frequencies of once, twice and thrice per day from the AF reactor were investigated. Results showed that average total COD (COD(tot)) removal efficiency of the system increased from 62% when sludge was discharged once per day from the AF reactor up to 67% when sludge was discharged twice and thrice per day. However, the increase in COD(tot) removal was not due to increased removal of COD(ss) fraction; but mainly due to development of an active biomass on the filter media, which increased removal efficiency of soluble COD fraction. The AF reactor had also an evidence of pathogens reduction. The AF reactor achieved 1-2 log reduction in Fecal Coliform counts.