Long-Term Operation of a Pilot-Scale Membrane Bioreactor Treating Brewery Wastewater: Relaxation as a Method for Detection of Membrane Fouling

Fouling control and operation below critical fluxes are relevant for operating membrane bioreactors (MBRs). Within this study, the long-term performance of a pilot-scale MBR was characterized with the aim of achieving maximum operating time without chemical cleaning. The MBR was fed with the effluent from a full-scale anaerobic reactor from a brewery and, combined with an upstream flotation unit, the MBR reduced chemical oxygen demand by 93.6%. During operation, the permeate flux was varied and a dependency of the fouling rate on permeate flux was found, which was not affected by the fluctuations caused by treatment with real wastewater. The fouling was controlled by intermittent 1-min relaxation phases followed by 4-min filtration. Applying this method, the MBR was operated at a flux of 9.5-11.5 L/(m2 h) and a fouling rate below 0.06 kPa/day for 329 days without chemical cleaning until the permeability decreased by >50% to 0.8 L/(m2 h kPa). Based on monitoring the relaxation phases alone, a sudden increase in blockage was found by Day 280, while transmembrane pressure and permeability readings continued without registering major variation for more than 40 days later. This early indication is in industrial scale of special importance because it can be used as an additional method for detecting fouling.