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

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.Electronic supplementary materialThe online version of this article (doi:10.1007/s11356-016-8211-y) contains supplementary material, which is available to authorized users.

Removal of antibiotic resistance genes in an anaerobic membrane bioreactor treating primary clarifier effluent at 20 °C

“…The 16S rRNA gene copy log removal was consistent with bacterial removal via anaerobic digestion as reviewed by Avery et al 57 and an AnMBR operated at 35°C that also demonstrated a 3-log reduction in total bacteria copy numbers. 58 Changes in abundance of the ARGs and intI1 normalized to 16S rRNA gene copies (Fig. 4) showed no significant difference (ANOVAs, p > 0.85) suggesting no selective removal of any specific gene over another gene.…”

“…These results are consistent with previous observations by Harb and Hong who reported distinct communities within the influent and effluent from an AnMBR operated at 35°C treating real wastewater. 58 Significant differences ( p < 0.01) in dominant genera between membrane feed and membrane final filtrate were determined by DESeq (Fig. 7).…”

Anaerobic Membrane Bioreactor Effluent Reuse: A Review of Microbial Safety Concerns

“…Furthermore, the lower LRV for E. coli seen in this study as compared to a similar AAO MBR, which was examined using culture-based methods [122], illustrates the potential for disparities in results obtained by different detection techniques. Another recent work also employed quantitative digital PCR for the detection of pathogenic bacteria in both a full-scale aerobic MBR and a lab-scale anaerobic MBR treating the same municipal wastewater [123]. Results of the same study targeting total bacteria, Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae showed LRVs of 4.1, 2.7, 1.0, and 3.1, respectively, in the aerobic MBR system and 3.1, 4.2, 1.2, and 3.9, respectively, in the anaerobic MBR [123].…”

“…Another recent work also employed quantitative digital PCR for the detection of pathogenic bacteria in both a full-scale aerobic MBR and a lab-scale anaerobic MBR treating the same municipal wastewater [123]. Results of the same study targeting total bacteria, Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae showed LRVs of 4.1, 2.7, 1.0, and 3.1, respectively, in the aerobic MBR system and 3.1, 4.2, 1.2, and 3.9, respectively, in the anaerobic MBR [123]. In addition to reiterating the potential for variability among pathogenic species, these results also accentuate the potential for improved pathogen removal rates by anaerobic MBRs.…”

“…This variability is likely representative of the same for actual pathogenic bacteria, especially in the case of MBRs [126]. Both quantitative and high-throughput molecular-based analyses of MBR systems have provided valuable insight into this concept, revealing that different MBR system types produce vastly diverse effluent microbial communities [123]. High-throughput microbial analysis specifically has shown the effect that non-microbial emerging contaminants (e.g., antibiotics) can have on reactor microbial communities [74] and has also provided insight into the potential link between ARG levels in anaerobic digesters and associated pathogenic bacterial abundances [64].…”