Validating Membrane Bioreactors to Remove Pathogens During Water Reuse: Understanding Key Operational Parameters

Operational parameters that significantly influence log reduction values (LRV) of indicator microorganisms by membrane bioreactors (MBRs) were identified based on analysis of a data set comprised of over 200 site visits to 11 different full scale facilities. High LRV coincided with operation at lower flux, TMP and MLSS and higher operating values of pH, temperature, solids retention time (SRT) and hydraulic retention time (HRT). Higher LRV for virus indicators was favored at lower permeability (i.e. more fouling). Therefore, test plans to determine worst case LRV for MBRs should be conducted under high flux, with clean membranes (low TMP), at short SRT and HRT and under the coldest expected operational conditions. Re-analysis of the Australian validation data and incorporation of new Californian work has suggested that default LRVs of 1.0 for virus and 2.5 for protozoa should be achieved by an MBR, provided filtrate turbidity is maintained below 0.2 NTU.