Optimization of nitrogen and carbon removal with simultaneous partial nitrification, anammox, and denitrification (SNAD) in membrane bioreactor (MBR)

In this study, a membrane bioreactor (MBR) was used to achieve both nitrogen and carbon removal by a simultaneous partial nitrification, anammox, and denitrification (SNAD) process. During the entire experiment, the optimal operating parameters as determined by response surface methodology (RSM) were a C/N value of 1.16, a DO value of 0.84 mg·L-1, and an aerobic time (Tae) of 15.75 min. Under these conditions, the SNAD process achieved efficient and stable nitrogen and carbon removal; the total inorganic nitrogen (TIN) removal efficiency and chemical oxygen demand (COD) removal efficiency were 92.31% and 95.67%, respectively. With the formation of granular sludge, the membrane fouling rate (MFR) decreased significantly from 35.0 Pa·h-1 at SNAD start-up to 19.9 Pa·h-1 during stable operation. Fluorescence in situ hybrid (FISH) analyse confirmed the structural characteristics and the relative ratio of AerAOB, AnAOB, and DNB in the SNAD system.