Abstract:Wastewater treatment plants (WWTPs) have been identified as potential sources of antibiotic resistance genes (ARGs) but the effects of tertiary wastewater treatment processes on ARGs have not been well characterized. Therefore, the objective of this study was to determine the fate of ARGs throughout a tertiary-stage WWTP. Two ARGs, sul1 and bla, were quantified via quantitative polymerase chain reaction (qPCR) in solids and dissolved fractions of raw sewage, activated sludge, secondary effluent and tertiary effluent from a full-scale WWTP. Tertiary media filtration and chlorine disinfection were studied further with the use of a pilot-scale media filter. Results showed that both genes were reduced at each successive stage of treatment in the dissolved fraction. The solids-associated ARGs increased during activated sludge stage and were reduced in each subsequent stage. Overall reductions were approximately four log 10 with the tertiary media filtration and disinfection providing the largest decrease. The majority of ARGs were solids-associated except for in the tertiary effluent. There was no evidence for positive selection of ARGs during treatment. The removal of ARGs by chlorine was improved by filtration compared to unfiltered, chlorinated secondary effluent. This study demonstrates that tertiary-stage WWTPs with disinfection can provide superior removal of ARGs compared to secondary treatment alone.

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A systematic investigation of SARS-CoV-2 genome concentrations in nine Southern California wastewater treatment plants (WWTPs) was carried out. The goal was to compare the variability of the viral concentration among different WWTPs that serve different communities and to correlate the concentration of virus in wastewater with the community level COVID-19 epidemic. The results showed that there were significant differences in viral concentration detected in different plants. However, the variability of SARS-CoV-2 concentration cannot easily be explained by the COVID-19 case reports because a large number of sewer-shed characteristics have important influences on the quantifiable viral concentration in the sewage samples. The results from year-long tracking of SARS-CoV-2 concentration in two large WWTPs, however, matched fairly well with the county level COVID-19 case reports. This suggests continuous monitoring of SARS-CoV-2 in the same treatment plant can offer insights into community level trends of COVID-19 and can serve as an alert for a possible resurgence of the disease. Amplicon-based sequencing targeting two SARS-CoV-2 single nucleotide polymorphism (SNP) mutations was shown as a proof-of-concept for identifying SARS-CoV-2 variants in wastewater. The outcomes of this research contribute to the advancement of wastewater-based epidemiology for COVID-19 and other infectious diseases.