A statistical review of pathogen and indicator log removal values from membrane bioreactor literature

Abstract

In this study, a critical review, gathering all available log removal values (LRV) data reported for membrane bioreactors (MBRs) in recent literature was conducted. One of the key outcomes of this work is that the correlation of MBR operating parameters and LRV was not possible with available literature data, as a full set of operational data was rarely reported. Nevertheless, in excess of 500 virus, 600 bacteria, and 20 protozoa LRV data points were extracted from multiple sources, grouped according to microorganism type, and the LRV performance and variability summarized in the form of normal probability density functions (PDFs). As presented, these LRV PDFs are suitable to permit further probabilistic quantitative microbiological risk assessment activities. In this work, the LRV PDFs were used to propose target pathogens and microbial surrogates by selecting the microorganisms that were most conservatively removed by MBRs. In terms of protozoa, Cryptosporidium was the most conservatively removed pathogen and Clostridium perfringens was the most often reported microbial surrogate. Enterovirus displayed the most conservative overall removal in MBR and was selected as the target pathogen. From the data reported, Escherichia coli was selected as an appropriate microbial surrogate for demonstration of LRV of bacteria.