Simultaneous in-situ excess sludge reduction and removal of organic carbon and nitrogen by a pilot-scale continuous aerobic-anaerobic coupled (CAAC) process for deeply treatment of soybean wastewater

A pilot-scale continuous aerobic-anaerobic coupled (CAAC) process was constructed and implemented for simultaneous excess sludge reduction and removal of organic carbon and nitrogen from the anaerobic effluent generated by an internal circulation (IC) reactor for treating soybean wastewater. When the hydraulic retention time (HRT) was shortened to 1.3 days, the average removal efficiencies for chemical oxygen demand (COD), NH4+-N, and total nitrogen (TN) reached 86%, 91%, and 67%, respectively. The mixed liquor suspended solids (MLSS) in the effluent generated by the CAAC process amounted to only 24 mg/L on average. The sludge production rate was estimated to be 0.1582 g MLSS/g COD, which is only 32% of that achieved by the conventional activated sludge process. The denaturing gradient gel electrophoresis (DGGE) analysis result showed that some fermentative and acetogenic bacteria were detected in anoxic and anaerobic zones. Such populations are associated with the anaerobic digestion and in-situ reduction of activated sludge.