Membrane bioreactors for use in small wastewater treatment plants: membrane materials and effluent quality

The relative efficiencies of three membrane materials for use in a submerged membrane bioreactor treating domestic wastewater were evaluated. A glass-filled hydrophobic polypropylene membrane allowed no flow through the membrane. A polysulphone membrane (PS, 0.4 mm pore size) did not achieve a steady-state flux although a flux of 7 l m−2h−1 occurred on the last day of the steady-state run. A melt-blown polypropylene membrane (NWPP, 5 μm pore size) gave a steady-state flux of 5 l m−2h−1. Membrane productivity was low due to irreversible fouling in the NWPP membrane and reversible fouling in the PS membrane. It was found that the PP membrane gave a 5-log reduction in total coliforms whereas the PS membrane gave a 9-log reduction. CBOD5, COD, SS, NH3-N and turbidity removal was similar with both the PS and the NWPP membranes. It was concluded that although the NWPP membrane was relatively inexpensive and achieved a high degree of organic matter removal, due to its inability to remove bacteria from the effluent it would be inappropriate to apply it to domestic wastewater in a submerged MBR.