Hydrogen Generated by Electrochemical Water Splitting as Electron Donor for Nitrate Removal from Micro-Polluted Reservoir Water

Abstract

Extremely limited organic carbon sources and aerobic environment in micro-polluted reservoir water make conventional denitrification exceptionally challenging. As a result, total nitrogen (TN) concentration in most reservoir waters exceeds standard value year-round. In this study, for the first time, we constructed a mini water-lifting and aeration system (mini-WLAS) to remove nitrate in actual reservoir water. In the mini-WLAS, H₂ was produced through electrolysis of reservoir water without adding any electrolyte, and the ascending water flow carried the generated H₂ from lower layer to upper bacteria layer. The maximum denitrification rate reached 0.29 mg (L·d)^-1 under dissolved oxygen (DO) concentration of 6-8 mg L^-1, 6.04 times higher than that of the control group. There is almost no accumulation of NH₄⁺-N, NO₂^--N, and N₂O, and the concentration of COD_Mn decreased by 55.2%. More importantly, the pH stayed near-neutral steadily throughout the whole process. Microbial community analysis showed that the abundances of hydrogenotrophic denitrifying bacteria (HDB) were 2 orders higher than those in the control system. Some HDB could work under aerobic conditions, providing an explanation for the excellent denitrification performance under high DO. This study provides a novel perspective for TN removal from reservoir water.