Energy efficient COD and N-removal from high-strength wastewater by a passively aerated GAO dominated biofilm

Conventional aerobic treatment of high-strength wastewater is not economical due to excessively high energy requirement for compressed air supply. The use of passive aeration avoids the use of compressed air and enables energy efficient oxygen supply directly from the air. This study evaluates a passively aerated simultaneous nitrification and denitrification performing biofilm to treat concentrated wastewater. The biofilm reactor was operated > 5-months under alternating anaerobic/aerobic conditions. For 4-times concentrated wastewater, > 80% COD (2307 mg L^-1 h^-1) and > 60% N (60 mg L^-1 h^-1) was removed at a hydraulic retention time (HRT) of 7 h. A double application in the same reactor enabled > 95% COD and 85% N-removal, at an overall HRT of 14 h which is substantially shorter than what traditional activated sludge-based systems would require for the treatment of such concentrated feeds. Microbial community analysis showed Candidatus competibacter (27%) and nitrifying bacteria (Nitrosomonas, and Nitrospira) as key microbes involved in COD and N-removal, respectively.