Treating Wet Weather Flows in a Membrane Bioreactor

Membrane bioreactors (MBRs) are a compact biological wastewater treatment process that employ microfiltration (MF) or ultrafiltration (UF) membranes to perform the solids-liquid separation. While using a membrane, instead of gravity sedimentation, for solid-quid separation has significant advantages (e.g. compact footprint, high quality effluent, high MLSS concentrations), there is one potential disadvantage of momentous significance; the ability of the MBR to meet the hydraulic demands at all times. There is no benefit to having membrane treated water quality if basins and emergency storage tanks are overflowing and raw wastewater is popping manhole covers. This paper will discuss a unique problem that occurs when treating wet weather flows with MBRs, sludge deflocculation. Possible reasons for the sludge deflocculation will be explored and present day industry knowledge on the topic discussed.