Ultrafiltration of aerobic granular sludge bioreactor effluent: Fouling potentials and properties

Abstract

The integration of low-pressure membrane filtration and aerobic granular sludge (AGS) reactor leads to a novel environmental biotechnological process with great potential to control membrane fouling and demonstrate good wastewater treatment performance. However, membrane fouling mechanisms in the AGS-based membrane bioreactor (MBR) lack systematic elaboration. In the present work, a bench-scale AGS reactor was operated for 8 months to investigate the effects of granule evolution, initial water flux, and membrane material on membrane fouling behavior and reversibility. After 143 days of operation, complete granulation was successfully achieved in the AGS reactor, which showed 97.6 ± 1.7% organic degradation, 94.3 ± 2.0% NH3-N removal, 90.6 ± 0.8% total nitrogen removal, and 98.9 ± 1.0% PO4-P removal. The remarkable AGS effluent quality reduced the fouling layer formation compared to the filtration occurred before complete granulation. The combined cake-complete model demonstrated that the dominant fouling mechanism is cake layer formation. The polyethersulfone (PES) membrane exhibited a better antifouling performance than the polyvinylidene fluoride membrane, regardless of the AGS effluent composition. The experimental data suggest the existence of a threshold flux for fouling reversibility when PES membrane is applied to treat the AGS effluent. Combining physical cleaning and operating under the threshold flux can effectively control the fouling degree in treating the AGS effluent by UF membrane. This, in turn, can reduce the operating cost caused by chemical cleaning and membrane replacement. Overall, the results provide comprehensive insights into the membrane fouling mechanisms and control strategy in a side-stream AGS-MBR and will contribute to the large-scale application of AGS-MBR technology in wastewater treatment.