Work along both lines: The p-chloro-m-cresol achieved stable and long-term partial nitrification and inhibited the enrichment of resistance genes

The p-chloro-m-cresol (PCMC) is a versatile preservative with extensive appliance in various pharmaceutical personal care products. In this study, PCMC in-situ anaerobic soaking of activated sludge was implemented to initiate, maintain and restore partial nitrification (PN). The optimal treatment condition was 80 mg/L PCMC and 30 h exposure time, which stably sustained PN for up to 157 days. Results showed that PCMC had a great influence on the content and secondary structures of extracellular polymeric substances, thus enhanced the aggregation and tolerance of bacteria to PCMC. The molecular docking simulation illustrated that PCMC achieved long-term PN by inhibiting nitrite oxidoreductase. The microbial community results showed that PCMC had a stronger inhibitory effect on nitrite oxidizing bacteria, and ammonia oxidizing bacteria was enriched in both quantity and oligotypes which could adapt to PCMC. Meanwhile, PCMC can obviously block the enrichment of some resistance genes without increasing resistance gene transmission burden of system. PCMC is a novel and promising PN inhibitor.