Peracetic acid disinfection kinetics for combined sewer overflows: indicator organisms, antibiotic resistance genes, and microbial community

Abstract

Combined sewer overflows (CSOs) degrade water quality and end-of-pipe treatment is one potential solution for retrofitting this outdated infrastructure. The goal of this research was to evaluate peracetic acid (PAA) as a disinfectant for CSOs using viability based molecular methods for antibiotic resistance genes (ARGs), indicator organism marker gene BacHum, and 16S rRNA genes. Simulated CSO effluent was prepared using 23–40% wastewater, representing the higher end of the range of wastewater concentrations reported in CSO effluent. PAA residual following disinfection was greatest for samples with the lowest initial COD. Treatment of simulated CSO effluent (23% wastewater) with 100 mg∙min/L PAA (5 mg/L PAA, 20 min) was needed to reduce viable cell sul1, tet(G), and BacHum (1.0±0.63–3.2±0.25-log) while 25 to 50 mg•min/L PAA (5 mg/L PAA, 5–10 min) was needed to reduce viable cell loads (0.62±0.56–1.6±0.08-log) in 40% wastewater from a different municipal treatment plant. Increasing contact time after the initial decrease in viable cell gene copies did not significantly improve treatment. A much greater applied Ct of 1200 mg∙min/L PAA (20 mg/L PAA, 60 min) was required for significant log reduction of 16S rRNA genes (3.29±0.13-log). No significant losses of mexB were observed during the study. Data were fitted to a Chick-Watson model and resulting inactivation constants for sul1 and tet(G) > BacHum > 16S rRNA. Amplicon sequencing of the 16S rRNA gene indicated the initial viable and total microbial communities were distinct and that treatment with PAA resulted in marked increases of the relative abundance of select phyla, particularly Clostridia which increased by 1–1.5 orders of magnitude. Results confirm that membrane disruption is a mechanism for PAA disinfection and further treatment is needed to reduce total ARGs in CSO effluent.

Viability-based quantification of antibiotic resistance genes and human fecal markers in wastewater effluent and receiving waters

“…While the vPCR method used in this study reduces signal from extracellular DNA and cells with compromised membranes, this method may be expected to overestimate the viable fraction of cells given that cells may be inactivated without having damaged membranes, which may explain the observations of vPCR/qPCR values above zero. The same viabilitybased method applied here was recently used to demonstrate the disinfection efficiency of PAA on ARG-carrying cells in simulated combined sewer overflow (Eramo et al, 2017b). With PAA disinfection, the fractions of viable-cell sul1 and tet(G) concentrations compared to total sul1 and tet(G) concentrations reached as low as 5.3×10 −3 ± 3.5×10 −3 , or less than 1% (Eramo et al, 2017b), while in this study, the percentage was slightly less than 50%.…”

“…The same viabilitybased method applied here was recently used to demonstrate the disinfection efficiency of PAA on ARG-carrying cells in simulated combined sewer overflow (Eramo et al, 2017b). With PAA disinfection, the fractions of viable-cell sul1 and tet(G) concentrations compared to total sul1 and tet(G) concentrations reached as low as 5.3×10 −3 ± 3.5×10 −3 , or less than 1% (Eramo et al, 2017b), while in this study, the percentage was slightly less than 50%. Differences in disinfectant, concentration, contact time, and the presence of organic matter can affect the disinfection efficiency and may explain the differences in these observations.…”

“…Understanding the ratios of these ARG pools is one step towards better characterizing the hazard posed by ARGs in different compartments. The viability qPCR (vPCR) method used in this study reduces the qPCR signal from DNA originating from nonviable sources in environmental samples (Bae and Wuertz, 2009;Eramo et al, 2017b;Nocker et al, 2007b). This is achieved using propidium monoazide (PMA), a dye that irreversibly intercalates extracellular DNA or DNA in cells with compromised membranes, thereby preventing amplification by qPCR.…”

“…This is achieved using propidium monoazide (PMA), a dye that irreversibly intercalates extracellular DNA or DNA in cells with compromised membranes, thereby preventing amplification by qPCR. Recent applications of this method for targeting ARGs include (1) determining disinfection efficiency of combined sewer overflow effluent with peracetic acid (PAA) (Eramo et al, 2017b) and (2) measuring microbial decay rates in aerobic and anaerobic sludge (Mantilla-Calderon, 2017).…”

Performic Acid Controls Better Clostridium tyrobutyricum Related Bacteria than Peracetic Acid

“…Generally, the disinfection efficiency of PFA is higher than that of PAA. It has been reported that the proportion of enteric clostridia increases when PAA is used as a disinfectant in wastewater treatment, as PAA sensitive non-spore forming microorganisms are destroyed by PAA, but PAA resistant clostridial spores can survive in these conditions [21].…”