Effects of individual and complex ciprofloxacin, fullerene C60, and ZnO nanoparticles on sludge digestion: Methane production, metabolism, and microbial community

Antibiotics and nanoparticles, emerging contaminants, present great environmental risks and human health concerns. Sludge adsorption, a biological wastewater treatment removal mechanism, targets ciprofloxacin (Cip) antibiotics, C60, and ZnO, leaving complex pollution in sludge anaerobic digestion. This study investigated the mechanisms through which individual and combined ZnO, Cip, and C60 affect sludge anaerobic digestion by studying their effects on CH4 production, metabolism, and microbial community. ZnO was generally more toxic to CH4 production than Cip. The ZnO + Cip complex was more influential (>29%) than ZnO or ZnO + C60, with short-lasting acute and additive toxicity effects on methanogenesis and degradation of protein and carbohydrate. ZnO + C60 and ZnO + Cip exerted apparent additional complex effects on Firmicutes, Aminicenantes, Chloroflexi, and Parcubacteria. These results would potentially aid toxicity control related to complex pollution, and improve energy production and reduce pollution risks when used in land applications.