Optimization of coagulation process and its influence on membrane fouling for Anaerobic-Anoxic-Oxic-Anoxic Membrane...

As part of sewage treatment, coagulation could remove phosphorus from the effluent of the Anaerobic-Anoxic-Oxic-Anoxic (A²OA) biological process. The importance in investigating the influence of coagulation on Anaerobic-Anoxic-Oxic-Anoxic Membrane Bioreactor (A²OA-MBR) should be emphasized. In this study, systematic optimization of coagulation parameters for greater pollutant removal was conducted in terms of coagulant dosage, coagulation residence time and stirring hydraulic conditions. Coagulation process could remarkably remove turbidity, phosphorus, chemical oxygen demand, humic-like, protein-like and polysaccharide-like substances from secondary effluent and A²OA sludge-liquid mixture. Furthermore, the influence of coagulation on membrane fouling development during the ultrafiltration of secondary effluent and A²OA sludge-liquid mixture was investigated based on optimum coagulation parameters. Coagulation simultaneously reduced reversible membrane fouling and the irreversible one by 86 % and 16 %, respectively. According to excitation-emission matrix and attenuated total reflection-fourier transform infrared spectra, membrane fouling was primarily influenced by the cake layer, although pore fouling might be aggravated by A²OA processes. Besides, the feasibility of coagulation-assisted A²OA-MBR was also assessed using hollow fiber membranes. It exhibited excellent potential in alleviating membrane fouling, while regular cleaning twice a day was not enough to suppress transmembrane pressure increase during direct domestic wastewater ultrafiltration. Additionally, both polysaccharide-like and protein-like foulants were vital components for membrane fouling during wastewater treatment.