Optimization of MBBR performance for rural domestic wastewater: Effects of carrier type, operating conditions, and zooplankton regulation

The moving bed biofilm reactor (MBBR) process has shown great potential for rural domestic sewage treatment due to its advantages in operation stability, high mass transfer efficiency, and effective pollutant removal. However, its application in rural of China remains limited. This study evaluated key operational parameters of the MBBR system, including carrier type, filling ratio, air-to-water ratio, hydraulic retention time (HRT), and biofilm management through zooplankton intervention, to optimize its performance for rural wastewater treatment. Results demonstrated that polyurethane (PU) sponge fillers achieved superior removal of total nitrogen (TN) and ammonium nitrogen (NH₄⁺-N) compared to conventional K1 and K3 fillers, while maintaining comparable removal efficiencies for total phosphorus (TP) and chemical oxygen demand (COD). The optimal performance was observed at an air-to-water ratio of 20:1, HRT of 24 h, and a filling rate of 80 %, under which COD, NH₄⁺-N, TN, and TP removal efficiencies reached 94.92 %, 85.61 %, 81.70 %, and 37.19 %, respectively. Zooplankton addition experiments revealed that rotifers enhanced nitrogen and phosphorus removal to some extent, though accompanied by increased effluent turbidity, while paramecium showed minimal impact. Combined addition of both organisms promoted biofilm activity, with rotifers playing a more significant role in controlling biofilm overgrowth. These findings offer practical guidance for the efficient application of MBBR systems in decentralized rural wastewater management.