Pre-denitrification and post-nitrification in an integrated anaerobic/aerobic filter system for advanced treatment of municipal wastewater

The objective of this research was to evaluate the efficacy of pre-denitrification and post-nitrification in a novel biofilter system combining an anaerobic filter with an aerobic filter for the advanced treatment of weak municipal wastewater. Laboratory-scale systems were operated under an empty bed hydraulic retention time of 8 h at ambient temperatures in the range from 17 to 28degreesC. The system recirculating its effluent showed a stable and superior performance without conventional primary and secondary clarification. The system removals of organics, suspended solids, and total nitrogen at a recirculation ratio of three were as high as 98, 97, and 77%, respectively. The upflow anaerobic filter and the following downflow aerobic filter were complementary to one another in a phase-isolated manner of pre-denitrification and post-nitrification. The anaerobic sludge beds retained by the crossflow media in the anaerobic filter played key roles in pre-denitrification, solids capture, and organics removal. The aerobic filter performed not only the complete post-nitrification but also the advanced treatment of organics and solids. The anaerobic sludge bed could also provide supplementary carbon for further denitrification through anaerobic digestion.