Aspects of microfiltration and reverse osmosis in municipal wastewater reuse

This paper discusses some of the key issues for reclamation of secondary effluent by membranes. The process considered using microfiltration (MF) as pretreatment prior to reverse osmosis (RO). The paper describes the application of ''critical flux'' operation to optimise flux through the MF membrane. Transmission of the polio virus through the 0.2 mu m pore MF membrane was minimised at low pressure, with crossflow and in the presence of biomass; log reductions of 2 were observed. For feed containing significant levels of sewage bacteria, the passage of small (0.2-0.3 mu m sized) bacteria was observed, although log reductions were >4. Bacterial bioadhesion studies of various RO membranes showed significant differences between membranes, the least adsorptive being hydrophilic, Further studies are required to optimise the use of membrane-based reclamation of secondary effluent.