| It is increasingly recognized that membrane bioreactors (MBRs) are effective in treating municipal and industrial wastewaters. Advantages of using membranes include small footprint and volume requirements, better treated effluent quality, higher volumetric loading and lower sludge yield, comparing with process without using membranes. However, the performance of MBR inevitably deteriorates with operation time, due to the ineluctable fouling caused by the accumulation of soluble and particulate materials onto and/or into the membrane. This major drawback and process limitation has been under investigation ever since the early MBR studies, and remains one of the most challenging issues for further improvement of MBR systems. Thus, the practical applications for MBR are confronted with two primary restrictions (a)low flux,(b) high cost of membrane and (c) progressive membrane fouling.In this work, membrane materials and A/O-MBR process were studied for treating the simulate wastewater from Liao Yang Petrochemical fiber production.The work mainly includes three parts:(1)A modified composite membrane with TiO2/polyvinyl alcohol (PVA) coating on matrix of polyester filter cloth (22μm) was studied in an Anoxic/Oxic (A/O)-MBR process treating a synthetic wastewater as secondary effluent from petrochemical fiber production plant. The effective pore-size of TiO2/PVA/polyester membrane was 5.4μm after coating, and the permeate flux, antifouling properties were studied and compared with that of the commercial PVDF membrane. The results clearly showed that effluent qualities after the TiO2/PVA/Polyester membrane and the commercial PVDF membrane, both in flat frame module, were similar. Both met the basic COD requirements for reuse. Composite membrane had an excellent performance in its high and sustainable flux, low TMP rise during the long-term trial. The composite membrane was only cleaned once, compared with the PVDF for four times cleaning during the 3 month test. Composite membrane has longer extended filtration cycle and requires less frequent cleaning. SEM analysis demonstrated that polyester filter cloth was covered with a non-uniform cake layer formed by sludge deposition and the non-uniform cake layer ensured a stable permeability and reduced the frequency of cleaning. EPS analysis showed that PVDF and composite membrane had little difference in either EPSp or EPSc in low flux stage, both lower than that of sludge flocs. However, in high flow stage, EPS especially LB-EPS had a significant increase on both membranes due to the filamentous bulking and temperature decline. EPSc on composite membrane was 128.56 mg·g-1 VSS, far less than that on PVDF membrane (522 mg·g-1 VSS) due to improved hydrophilicity from immobilized PVA and TiO2.(2)The A/O-MBR system has a better performance on nitrification and denitrification, the TN of effluent maintained at 10 mg/L and the removal rate reached 80%; adjusted the location of return flow, the system can be divided into anaerobic zone-anoxic zone-oxic zone.After nearly 40 days of acclimation training, and the nitrate nitrogen concentration in effluent dropped to 1.012 mg/L, removal rate reached nearly 90% and TP removal rate increased from 10% to 40%. The Nitrogen and phosphorus removal in A/O-MBR system has been enhanced.(3)This work compares the MBRs which with suspensible magnetic composite particles (De/Fe3O4) and without any particles, and investigates the membrane fouling, mixed liquor characteristics and the efficiency of wastewater treatment in those reactors by parallel experiments. The results show that the fouling rate of MBR which with suspensible magnetic composite particles (De/Fe3O4) is lower than the one without any particles. The MBR with particles removes the extracellular polymers (EPS) in the mixed liquid of sludge effectively, and increases the sludge particle size, then improves the mixed liquid characteristics, which could delay the growth of TMP and control the membrane fouling, reduce the frequency of cleaning and the cost of operating.
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