Log removal values in membrane bioreactors: Correlation of surrogate monitoring and operational parameters

Log removal values (LRV) for a range of pathogens in membrane bioreactors (MBRs) were aggregated for 180 sampling events across 11 municipal scale installations. Important correlations were established between LRV for biological (LRVBio) and physical (LRVMem) inactivation with reactor conditions (pH, temperature, solid and hydraulic retention times (SRT, HRT), and mixed liquor suspended solids (MLSS)), membrane properties (pore size and flux), operational variables and filtrate quality. LRVBio correlated positively and significantly between all microorganism indicators and dissolved organic carbon (DOC), becoming a suitable monitoring technique for biological removal. LRVMem correlated positively for protozoa indicators and bacteria consistent with size exclusion as a predominant removal mechanism. Strong correlations between LRV for protozoa, virus and bacteria indicators were established at lower flux, TMP and MLSS, higher pH and temperature and longer solids and hydraulic retention time. The implications of this study provide important guidance for the validation of MBRs producing safe and consistent recycled water.