Application of two-phase slug-flow regime to control flux reduction on anaerobic membrane bioreactors treating wastewaters with high suspended solids concentration

The application of anaerobic membrane bioreactors (AnMBR) promoting two-phase slug-flow regime inside tubular membranes was studied, for the treatment of wastewaters containing high content of organic suspended solids. Brewery wastewater was used, which was supplemented with surplus yeast to increase solids concentration. A lab-scale AnMBR was operated with external membrane modules containing inside/out tubular membranes. Biogas was injected inside the membranes in order to promote a slug-flow regime. Membrane filtration provided conditions suitable for COD removal, i.e. biomass and solids retention. Removal levels over 97% were achieved. Reactor was operated at gas superficial velocities in the range of 0.2–0.35 m/s. Liquid superficial velocity was determined by the resulting gas-lift effect. Under these conditions, low flux levels were achieved during reactor operation (below 10 L/m2h), presumably since gas sparging did not provided the required wall shear necessary for preventing deposition of single cells present in the biomass suspension.

► Cake layer formation is the phenomena determining the flux.
► Single cell growth was observed, which largely determined the applicable flux.
► Gas sparging cannot promote flux levels over 10 L/m2 h in AnMBRs.