The application of membrane bioreactor technology to the treatment of wastewater from a multifunctional supermarket

Wastewater from multifunctional supermarkets usually features with large fluctuation of flow and pollutants, and shows significantly different characteristics from domestic wastewater because of its extensive sources and high concentration ofoil substances. Membrane bioreactor (MBR) technology with proper oil pretreatment process is attractive for supermarket wastewater treatment in metropolitans because ofits small footprint, excellent and stable permeate quality, convenient operation, and shock load resistant capability. Operation results oftwo lab-scale MBRs under different organic loads demonstrated that MBR technology could yield excellent permeate quality, but the stable operation cycle was relatively short compared with MBRs for domestic wastewater treatment. Analysis on membrane fouling showed that the high concentration of oil substances (especially oil and grease) in supermarket wastewater was the main cause for membrane permeability deterioration, and the MBR with higher organic load demonstrated better resistant capability for membrane fouling by oil. On the basis oflab-scale MBRs, proper hydraulic retention time (HRT) and more efficient oil pretreatment process were adopted for the design of full-scale supermarket wastewater treatment system. With dissolved-air flotation process as an oil pretreatment process, permeate COD and NH₄-N in the full- scale MBR for supermarket wastewater treatment were respectively 36.8 and 41 mg/L on average, and stable membrane permeability was achieved during 132 day stable operation after 28 day start-up period.