Pharmaceuticals and Personal Care Products (PPCPs) Impact Enriched Nitrifying Cultures

Abstract

The impact of pharmaceutical and personal care products (PPCPs) on the performance of biological wastewater treatment plants (WWTPs) has been widely studied using whole-community approaches. These contaminants affect the capacity of microbial communities to transform nutrients; however, most have neither honed their examination on the nitrifying communities directly nor considered the impact on individual populations. In this study, six PPCPs commonly found in WWTPs, including a stimulant (caffeine), an antimicrobial agent (triclosan), an insect repellent ingredient (N,N-diethyl-m-toluamide (DEET)), and antibiotics (ampicillin, colistin, and ofloxacin), were selected to assess their short-term toxic effect on enriched nitrifying cultures: Nitrosomonas sp. and Nitrobacter sp. The results showed that triclosan exhibited the greatest inhibition on nitrification with EC50 of 89.1 µg L− 1. From the selected antibiotics, colistin significantly affected the overall nitrification with the lowest EC50 of 1 mg L− 1, and a more pronounced inhibitory effect on ammonia-oxidizing bacteria (AOB) compared to nitrite-oxidizing bacteria (NOB). The EC50 of ampicillin and ofloxacin were 22 and 12.7 mg L− 1, respectively. Additionally, experimental data suggested that nitrifying bacteria were insensitive to the presence of caffeine. In the case of DEET, moderate inhibition of nitrification (< 40%) was observed at the highest concentration tested. These findings contribute to the understanding of the response of nitrifying communities in presence of PPCPs, which play an essential role in biological nitrification in WWTPs. Knowing specific community responses helps develop mitigation measures to improve system resilience.