Bacterial rejection in crossflow microfiltration of sewage

The performance of a low-cost tubular polypropylene microfiltration membrane has been assessed with reference to the disinfection and clarification of real and model municipal wastewaters. Membranes of four different pore sizes were investigated for this duty, these being challenged with both primary and secondary sewage effluent. Further trials on rudimentary:sewage analogues were carried out, the analogues comprising kaolin suspensions and colloidal protein solutions. All membranes were seen to be effective at improving the physiochemical properties of the sewage effluents. Significant bacterial breakthrough was observed at the beginning of a cycle, with rejection rapidly improving to a stable level over the course of the cycle. The effect of increasing solids concentration, in the form of kaolin, was seen to have beneficial effect on flux, this being attributed to the protection of the membrane afforded by the kaolin dynamic layer formed in situ, whilst maintaining high levels of bacterial rejection. Conversely, protein solutions were found to have a markedly deleterious effect on both flux and bacterial rejection, apparently promoting the passage of bacteria through the membrane. The membrane performance against sewage effluents was somewhere between these two extremes.