Molecular-based detection of potentially pathogenic bacteria in membrane bioreactor (MBR) systems treating municipal wastewater: a case study

Moustapha Harb,Pei-Ying Hong

doi:10.1007/s11356-016-8211-y

Abstract

Although membrane bioreactor (MBR) systems provide better removal of pathogens compared to conventional activated sludge processes, they do not achieve total log removal. The present study examines two MBR systems treating municipal wastewater, one a full-scale MBR plant and the other a lab-scale anaerobic MBR. Both of these systems were operated using microfiltration (MF) polymeric membranes. High-throughput sequencing and digital PCR quantification were utilized to monitor the log removal values (LRVs) of associated pathogenic species and their abundance in the MBR effluents. Results showed that specific removal rates vary widely regardless of the system employed. Each of the two MBR effluents’ microbial communities contained genera associated with opportunistic pathogens (e.g., Pseudomonas, Acinetobacter) with a wide range of log reduction values (< 2 to >5.5). Digital PCR further confirmed that these bacterial groups included pathogenic species, in several instances at LRVs different than those for their respective genera. These results were used to evaluate the potential risks associated both with the reuse of the MBR effluents for irrigation purposes and with land application of the activated sludge from the full-scale MBR system.

Highlights

The issue of pathogen presence in treated wastewater effluents has gained attention recently due to an increased interest in reuse applications (Li et al 2013; Zanetti et al 2010)
Despite the high quality and low particulate effluents produced by membrane bioreactor (MBR) systems, it has been observed that 100% rejection of bacteria is not achievable by MBRs when operated with microfiltration (MF) membranes and that log removal rates (LRVs) vary based on the microbial indicator detected (Jong et al 2010; Trinh et al 2012; van den Akker et al 2014)
This species was further identified in five of eight aerobic MBR (AeMBR) activated sludge samples at a phoE gene concentration of 9.7 × 104 ± 3.2 × 104 copies/g. Effluents of both the AeMBR and the anaerobic MBRs (AnMBRs) showed positive detection for K. pneumoniae at 5.9 × 102 ± 6.4 × (3 of 7) and 9.7 × ± 2.0 × 101 (5 of 11), respectively. This resulted in LRVs of 3.1 and 3.9 for K. pneumoniae in the AeMBR and AnMBR systems, respectively

Summary

Introduction

The issue of pathogen presence in treated wastewater effluents has gained attention recently due to an increased interest in reuse applications (Li et al 2013; Zanetti et al 2010). Despite the high quality and low particulate effluents produced by MBR systems, it has been observed that 100% rejection of bacteria is not achievable by MBRs when operated with microfiltration (MF) membranes and that log removal rates (LRVs) vary based on the microbial indicator detected (Jong et al 2010; Trinh et al 2012; van den Akker et al 2014). This variability in microbial removal rates (106 removal) poses an obstacle for reuse purposes, as it means that chlorine disinfection remains necessary for post-MBR effluents. A recent study assessing wastewater treatment practices in China found that the vast majority of sludge treatment processes consisted of only sludge thickening and mechanical dewatering (Jin et al 2014)

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Discussion

Conclusion