Triclosan enhances short-chain fatty acid production from sludge fermentation by elevating transcriptional activity of acidogenesis bacteria

Triclosan (TCS) is an emerging contaminant in waste activated sludge (WAS). However, the effects of TCS on WAS anaerobic fermentation is still unknown. Herein, we investigated the impacts of different TCS levels on the short-chain fatty acid (SCFA) accumulation. TCS at 100 mg/kg TSS (total suspended solids) significantly (p < 0.05) enhanced SCFA production by 35.8 +/- 4.1% through increasing the production of propionic and butyric acid, while the higher TCS level inhibited the SCFA production processes. The results of batch tests with real sludge showed that 100 mg/kg TSS TCS enhanced acidogenesis process and had no significant impact on other processes, while higher TCS level caused negative effects on acidogenesis, acetogenesis and methanogenesis. Generally, 2,4-dichlorophenol was considered as the main metabolic product of TCS under anaerobic condition. However, in this study, TCS was found to be converted into (Z)-4-(2,4-dichlorophenoxy)penta-1,3-dien-3-ol, 2,4-dichloro-1-(4 chloro-2-methoxyphenoxy)benzene and other substances, and its hypothetical metabolic pathway were reformulated. The microbial community structure in the WAS anaerobic fermentation system did not significantly change with TCS addition, but 100 mg/kg TSS TCS contributed to the modest enrichment of SCFA producers. Further analyses of key enzyme activity and abundance of enzyme-encoded genes revealed that TCS at 100 mg/kg TSS up-regulated the expression of enzyme-coding genes (i.e. butyrate kinase (BK) and oxaloacetic acid carboxylase (OAATC)), and this is the primary reason for the increased SCFA production. This work provides a new insight for pollutant effects in WAS anaerobic fermentation, which will help to reveal the impact of emerging contaminants and relearn the role of conventional pollutants.