Capital costs of a MBR (Membrane Bio-Reactor) process are substantially influenced by the membrane cost itself, which contributes around 50% of the total process capital cost. The feasibility of a submerged MBR fitted with three pore-sized NWPP (Non-Woven Poly-Propylene) membranes has been studied. The performance was compared with that of a conventional polysulfone (PS) membrane material. Both the PS and NWPP membranes demonstrated a drastic reduction in permeate flux at the start of operation. Although the NWPP membrane showed a greater fouling propensity than the PS membrane, the difference in flux decline between the two membranes was not great. All membranes produced an effluent extremely low in organic matter and with a low permeate turbidity (<1 NTU), and ammonia removal was higher than 60% in all cases. However, whereas the PS membrane achieved a 7-log reduction in total coliforms, the NWPP membranes achieved only a 2 to 4-log reduction. Consequently, low-cost NWPP membranes can be considered suitable for use in MBR processes for municipal wastewater treatment, but are possibly less suited to domestic wastewater reuse where disinfection is a prerequisite.