Chemical cleaning of membranes from an anaerobic membrane bioreactor treating food industry wastewater

Different chemical cleaning methods were applied to hollow-fiber membranes from an anaerobic membrane bioreactor (AnMBR) treating wastewater with a high oil and grease content. Chemical cleaning methods were assayed in a pilot-scale AnMBR and on single fouled fibers. The effectiveness of the cleaning processes was determined on the basis of overall resistance due to external irreversible fouling and pore-blocking, and from backwash resistance, solely due to pore-blocking. Concentrations of between 500 and 2000 ppm of NaClO, and volumes per unit of membrane area of between 3 and 17.5 L/m2 were employed. Chemically enhanced backwash (CEB) achieved an overall cleaning efficiency of up to 60% by backflushing in situ 6 L/m2 of 2000 ppm. Chemical cleaning in air (CIA) that could be performed in situ reached a cleaning efficiency of up to 80% by employing 10 L/m2 of 1000 ppm NaClO solution. The best results were obtained with dynamic submerged chemical cleaning (SCC) performed out of place in which filtration and backwashing fluxes pass the cleaning solution through the membrane. Non-uniform fouling on the module produced significant reductions in the cleaning efficiency of the backflux-driven chemical methods.