Assessment of Turbidity for Assurance of Log Reduction Values by Membrane Bioreactors

Sampling and pathogen analysis can demonstrate very high log reduction values (LRVs) with membrane bioreactor (MBR) systems. However, it has been difficult to gain regulatory approval for these high LRVs as intermittent sampling is not viewed as sufficient to continually assure acceptable water quality. Hazard and critical control point (HACCP) frameworks are increasingly applied to systematically control pathogen risks in water reuse. HACCP frameworks for water reuse require that a significant barrier to pathogens is identified and that this barrier can be monitored to ensure it is functioning nominally - hence pathogen removal is achieved. In this work, a method to correlate MBR filtrate turbidity and pathogen LRV in MBR was investigated and the extent of indicator microorganism relative to total suspended solids transfer was quantified. The relationship between filtrate turbidity and LRV was logarithmic, suggesting that significant increases in turbidity are required to result in marginal reductions in LRV.