A New Denitrification Pathway in Oxygen-Rich Aquatic Environments through Long-Distance Electron Transfer

Abstract The lack of electron donors in oxygen-rich aquatic environments limits the ability of natural denitrification to remove excess nitrate, leading to eutrophication of aquatic ecosystems. Herein, we demonstrate that electron rich substances in river or lake sediments could participate in long-distance electron rebalancing to reduce nitrate in overlying water. A microstructure containing Dechloromonas and consisting of an inner layer of green rust and an outer layer of lepidocrocite forms in the sediment-water system through synergetic evolution and self-assembly. The microstructure enables long-distance electron transfer from the sediment to dilute nitrate in the overlying water. Specifically, the inner green rust adsorbs nitrate and reduces the kinetic barrier for denitrification via an Fe(II)/Fe(III) redox mediator. Our study reveals the mechanism of spontaneous electron transfer between distant and dilute electron donors and acceptors to achieve denitrification in electron-deficient aquatic systems.