Revealing the mechanism of zinc oxide nanoparticles facilitating hydrogen production in alkaline anaerobic fermentation of waste activated sludge.

Zinc oxide nanoparticles (ZnO NPs) has been documented to accumulate in waste activated sludge (WAS). Nevertheless, its potential effect on hydrogen accumulation during anaerobic fermentation has never been reported. Such impact exists in anaerobic sludge treatment systems but is unrecognized before. Therefore, this work aims to explore the effect of ZnO NPs on hydrogen accumulation during WAS fermentation while avoiding hydrogen consumption by maintaining pH around 10. Deep insights into the mechanisms of the enhanced hydrogen production after dosing ZnO NPs can then be provided. The 21.1 to 74.0 mL-H 2 /g-VS hydrogen yields were obtained after dosing 0–150 mg/g-TS ZnO NPs into the system, which is 2.5 times higher than the control. The zinc ions released from ZnO NPs did not pose obvious cytotoxic effect on organisms based on the mechanism exploration of this study. The reactive oxygen species (ROS) induced by ZnO NPs facilitated sludge disintegration and improved the biodegradability of released organics, but restrained the bio-processes of hydrolysis and acetogenesis simultaneously. This was further verified by the microbial community analysis, as the abundance of key microbes related to hydrolysis and acetogenesis was reduced evidently in the presence of 150 mg/g-TS ZnO NPs. This study would provide a green and economic strategy for the sustainable engineering application of WAS containing ZnO NPs. [Display omitted] • ZnO NPs at 150 mg/g-TS enhanced hydrogen production by 3.5 folds of control. • ZnO NPs improved sludge disintegration and organics biodegradability. • ZnO NPs reduced the abundance of key hydrolytic microbes and acetogens. • ROS played an essential role in the cytotoxicity rather than the released Zn2+. [ABSTRACT FROM AUTHOR]