Low temperature treatment of municipal sewage in anaerobic fluidized bed reactors

Abstract

The anaerobic fluidized bed reactor (AFBR) appears to be most promising for the treatment of low strength wastes, such as municipal sewage, at low temperature, since the process is able to maintain a large mass of active microorganisms and provides effective removal of TSS. The study is divided in three parts. The objective of the first part is to characterize the effect of decreasing temperature on the performance of two mature AFBR reactors. The second part presents the data from 220 days of operation at 10°C; and in the third part two start-ups, with and without inoculum at 15°C, are evaluated. A gradual temperature decrease from 20 to 5°C, allowing the microorganisms to acclimate to the new lower temperature, did not have a great effect on effluent quality. However a great accumulation of TSS was observed in the top of the fluidized bed. At 10°C, and a hydraulic retention time of 1.5 h, 70% of T COD removal was achieved. It is possible to start-up the AFBR at 15°C without inoculation; however, at least 4 months is required to get good quality effluents.