Abstract
Combined sewer overflows (CSOs) degrade water quality through the release of microbial contaminants in CSO effluent. Improved understanding of the partitioning of microbial contaminants onto settleable particles can provide insight into their fate in end-of-pipe treatment systems or following release during CSO events. Sampling was performed across the hydrograph for three storm events as well as during baseflow and wet weather in three surface waters impacted by CSO. qPCR was performed for select antibiotic resistance genes (ARG) and a marker gene for human fecal indicator organisms (BacHum) in samples processed the partitioning of microbial contaminants on settleable particles versus suspended in the aqueous phase. Amplicon sequencing was performed on both fractions of storm samples to further define the timing and partitioning of microbial contaminants released during CSO events. Samples collected at the CSO outfall exhibited microbial community signatures of wastewater at select time points early or late in the storm events. CSOs were found to be a source of ARG. In surrounding surface waters, sul1 was higher in samples from select locations during wet weather compared to baseflow. Otherwise, ARG concentrations were variable with no differences between baseflow and wet weather conditions. The majority of ARG at the CSO outfall were observed on the attached fraction of samples: 64–79% of sul1 and 59–88% of tet(G). However, the timing of peak ARG and human fecal indicator marker gene BacHum did not necessarily coincide with observation of the microbial signature of wastewater in CSO effluent. Therefore, unit processes that remove settleable particles (e.g., hydrodynamic separators) operated throughout a CSO event would achieve up to (0.5–0.9)-log removal of ARG and fecal indicators by removing the attached fraction of measured genes. Secondary treatment would be required if greater removal of these targets is needed.
Highlights
Outdated sewer infrastructure results in the release of 26 × 106 m3 of untreated wastewater to New Jersey (NJ) surface waters each year (New Jersey Future, 2017)
Samples collected during baseflow and during or immediately following rainfall events in local waterways were analyzed to provide a broader understanding of antibiotic resistance genes (ARG) during wet weather events in Combined sewer overflows (CSOs) impacted waters
The total 16S rRNA gene copy normalized sul1 and tet(G) concentrations observed during the three storm events were within the range observed during the baseflow and wet weather sampling in the Passaic River, Hudson River, and Raritan Bay (Figure 5)
Summary
Outdated sewer infrastructure results in the release of 26 × 106 m3 of untreated wastewater to New Jersey (NJ) surface waters each year (New Jersey Future, 2017). End-of-pipe treatment of CSO effluent is a potential solution for improving water quality at a lower cost than upgrading combined sewer systems to separate sanitary systems, which is estimated to cost $40.8 billion in the United States (United States Environmental Protection Agency, 2016). Understanding the timing and partitioning of microbial contaminants on settleable particles in CSO effluent on settleable particles is needed for designing and operating end-of-pipe treatment systems. Understanding the timing and potential for removal of indicator organisms is pertinent for meeting water quality regulations of the Clean Water Act. because correlations between indicator organisms and pathogens are often weak (Harwood et al, 2005) and different microbes associate with particles at different rates (Suter et al, 2011), targeting a broader range of microbial contaminants is of interest
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