Effects of quaternary ammonium disinfectants on human pathogenic bacteria in anaerobic sludge digestion: Dose-response and resistance variation

[Display omitted] •HPBs relative abundance was reduced by low QACs dose but raised at high dose.•Low QACs dose stimulated EPS secretion and enhanced resistance to QACs.•QACs at high dose adversely affected microbial biomass and metabolic functions.•Multiple HPBs developed antibiotic and QACs resistance under QACs stress.•Genes involved in conjugative transfer were promoted by QACs. Sewage sludge is a critical reservoir for biological pollutants, and its harmless disposal remains a major issue. Quaternary ammonium compounds (QACs) as typical household disinfectants are inevitably concentrated in sewage sludge, and have the potential to affect human pathogenic bacteria (HPBs) that remain poorly understood. This study found that the relative abundance of HPBs in digesters was decreased by 10 − 20 % at low QACs dose, but increased by 238 − 591 % at high QACs dose. Mechanistic analysis revealed that low QACs doses promoted functional hydrolytic/fermentative bacteria and their metabolism by stimulating extracellular polymeric substances secretion and enhancing resistance to QACs. Conversely, high QAC doses decreased microbial biomass and developed QACs and antibiotic resistance of HPBs by increasing cell membrane permeability and triggering oxidative stress, resulting in deteriorating sanitation performance. These findings provide advanced insights into the potential function and hazards of exogenous QACs on the biosafety of digestate.