Occurrence and Removal of Antibiotics in Wastewater Treatment Plants during the COVID-19 Pandemic

To evaluate the presence, removal, and concentration trends of antibiotics in wastewater treatment plants (WWTPs) during the COVID-19 pandemic, monthly influent and effluent samples were collected from four WWTPs in Minnesota to measure 26 antibiotics within six major categories from August 2020 to July 2022. Profiles of the studied antibiotics in each class were dominated by the compounds designated for human use in both influents and effluents. High influent concentrations of azithromycin (123-1031 ng/L) were observed during the initial stages of the COVID-19 pandemic, and levels peaked approximately 3-5 weeks after spikes of weekly COVID hospitalizations and reported cases. The concentration of azithromycin in influents positively correlated with weekly reported COVID cases (Pearson, r = 0.95, p < 0.001) and COVID hospitalizations (Pearson, r = 0.85, p < 0.05) with variably delayed response patterns for large versus small-scale WWTPs in different stages of the COVID-19 pandemic. WWTPs effectively removed most antibiotics (on average 47-88% for sulfamethoxazole and 53-80% for ciprofloxacin), while negative removals were occasionally observed (generally for low influent concentrations). The results of this 2-year study highlight that the COVID-19 pandemic affected the temporal dynamics of antibiotics authorized for the treatment of COVID-19 coinfections.