High levels of antibiotics released by a pharmaceutical manufacturer negatively impacted wastewater treatment plant performance†

Wastewater treatment plant (WWTP) effluent compliance relies heavily on the performance of biological treatment processes. Biological treatment processes can be compromised by toxic shock events such as upstream spills of high concentrations and/or loads of hydrocarbons and other chemicals from industry wastewater (trade waste). A toxic shock event was observed in the biological treatment at a WWTP, causing untreated wastewater to contaminate the receiving environment. None of the routinely monitored wastewater parameters like heavy metals and organic compounds could be linked to the event. In this study, we investigated the associations between intermittent pulses of elevated concentrations of antibiotics in the influent and toxic shocks to biological wastewater treatment processes. 22 influent samples were analysed for 102 antibiotics and their metabolites. Chemical oxygen demand and nitrogen removal efficiencies in the WWTP's biological treatment process were significantly negatively correlated with concentrations of antibiotics. Seven antibiotics exceeded their predicted no-effect concentrations (PNECs) during this timeframe, also exceeding risk quotients of one to be a likely risk of toxic effects on the WWTP. The combination of correlation and risk quotients exceeding one demonstrated that antibiotics caused the toxic shock event at the WWTP.