Evaluation of upflow hybrid bioreactor system for treating low-strength nitrogenous wastewater under low-shear environment

Lab-scale upflow bioreactor system without biomass-liquid separation unit was built to treat low-strength nitrogenous wastewater based on intermittent aeration under low-shear environment. Biomass zone formed in the absence of gas bubbles provided simultaneous biomass retention, biodegradation of nitrogenous and carbonaceous compounds, and biomass-liquid separation. Biomass zone was stable as indicated by insignificant biomass washout rates (14–29 mg VSS/day) and relatively constant biomass zone height (26–30 cm) up to the shear gradient of 1.8 s-1. Nitrogen treatment efficiency of wastewater containing 15 mg NH4 + -N/L was 15.3±1.96% under continuous oxygen influx of 95 mg O2 /L/day and autotrophic environment, whereas it increased significantly, 88.2±7.05%, after intermittent aeration (3 hrs air-on and 3 hrs air-off) and organic carbon source were supplied to the bioreactor system. Carbon removal efficiencies for both continuous and intermittent aeration were comparable reported at 85±1.76% and 91±2.1%, respectively.