Giving Credit Where Credit is Due – MBR for Potable Water Reuse

Membrane bioreactors (MBR) are well suited for potable water reuse. Two main obstacles impede further implementation: (1) Articulation and comprehension of pathogen removal capabilities; and (2) Pathogen removal monitoring. Two new empirical studies were conducted to address these issues. These studies explored pathogen reduction under normal operation and after cleaning protocols, and the impact of compromised membranes on pathogen removal. The MBRs showed log removal value (LRV) ranges for Enterococci of > 3.4 to > 6.7, Giardia of > 3.3 to > 6.0, Enterovirus > 3.9 to > 8.7 and Norovirus (all three types) were > 2.7 to > 8.2. Pathogen removal efficiencies were not impacted by chemical cleaning protocols, seasonal variation or membrane age. When membranes were intentionally damaged significant pathogen removal was still seen. With effluent turbidity between 0.2 and 2 NTU, LRVs were greater than 2.2, 2.8 and 4.0 for Giardia, Enterovirus and Norovirus respectively. Advances in turbidity monitoring have enhanced the ability to quickly detect breaches and turbidity responded immediately to changes in membrane integrity. Pressure Decay Testing was also evaluated showing no correlation with pathogen removal and limited ability of the membranes to hold pressure. Data from the two studies and literature supports a minimum credit for protozoa of 3.3 and for virus of 2.7 with turbidity monitoring.