Coupled UASB-activated sludge process for COD and nitrogen removals in municipal sewage treatment in warm climate

Abstract

A laboratory-scale system consisting of an upflow anaerobic sludge blanket (UASB) reactor followed by a modified Ludzack-Ettinger (MLE) activated sludge process was adopted to investigate COD and nitrogen removals in municipal sewage treatment in warm climate. The COD, SCOD, acetic acid (HAc), NH4+-N and PO43−-P conversions in the UASB reactor were investigated. A 35% reduction in volatile suspended solid (VSS) was achieved in the UASB process. The net methane (CH4) production was 0.06 l (g CODremoved)−1. Acids accumulation was not observed. In the MLE activated sludge process, nitrification was almost complete while denitrification was modest. Little excess sludge was produced as the bulk of the COD was removed in the UASB reactor, which reduced the COD mass load to the activated sludge process. The average COD and SCOD of the final effluent of the activated sludge process were 51 and 25 mg l−1, respectively and the average NH4+-N concentration of the final effluent was 3.1 mg N l−1. The results illustrated that the coupled process is feasible for COD and nitrogen removals in municipal sewage treatment in warm climate. However, the low pH of the final effluent (<6 on average) remains an issue to be solved.