Effects of salinity on the performance, microbial community, and functional genes among 4-chlorophenol wastewater treatment

Chlorophenols frequently occur alongside salinity in industrial wastewater; thus, the effects of low concentrations of salinity (NaCl, 100 mg/L) on sludge performance, microbial community, and functional genes were deeply analyzed among 4-chlorophenol (4-CP, 2.4-4.0 mg/L) wastewater treatment. The influent 4-CP was effectively degraded, but the efficiencies for PO₄^3--P, NH₄⁺-N, and organics reduction were slightly inhibited by NaCl stress. Long-term NaCl and 4-CP stress significantly stimulated the secretion of extracellular polymeric substances (EPS). The abundances of predominant microbes at different taxonomic levels were affected by NaCl, and the increased relative abundances of functional genes encoding proteins contributed to resist NaCl and 4-CP stress. The functional genes associated with phosphorus metabolism and nitrogen metabolism in nitrification were unaffected, but the functional genes in denitrification increased in diversity under NaCl stress in 4-CP wastewater treatment. This finding acquires useful insight into the wastewater treatment with low chlorophenols and low salinity.