Hi! This is Zilan, I usually go by Z, I'm a second-year PhD student studying environmental engineering at Auburn University. My research focuses on electrified water treatment and circular water economy, with the current target pollutants being selenium.

Coal-fired power plants (CFPPs) consume 396 million tons of coal each year to generate roughly 25% of the U.S.’s net electricity. Domestically produced coal contains on average 1.7 ppm selenium (Se), and once they are burnt about 61% of the oxidized Se in the flue gas are captured by the wet flue gas desulfurization (FGD) scrubber unit. For decades, the generated Se-laden FGD wastewater has been inadequately treated and regulated, releasing ppm-level Se(VI) and Se(IV) oxyanions (e.g., SeO₄^2- & SeO₃^2-) into natural receiving water bodies. These released Se oxyanions can bioaccumulate through the food chain with an enrichment function of 100 times from water to algae and a trophic transfer function of 10 times from algae to fish. Continuous consumption of Se-rich water or fishery products could lead to low fertility, hair loss, and other selenosis symptoms, posing ecological damages, health concerns, and a significant economic loss. Besides the economic incentive, increasingly stringent regulation standards also urge stakeholders to restrain aquatic Se towards a ppb or sub-ppb level (e.g., 29 ppb in FGD wastewater per U.S. EPA).

Direct electrochemical reduction (DER) of selenite has been extensively explored for industrial electroplating, and its high selectivity towards aqueous selenite offers new insight into treating complex Se-laden wastewater. While the benchmark study confirms the feasibility of selenite DER with a gold cathode, the high material cost burdens its industrial applications. In this study, we evaluate six affordable cathode materials on their ability to remove aqueous selenite through DER, including nickel, graphite, copper, iron, stainless steel, and titanium. We focus on their removal efficiency, removal kinetics, Faradaic efficiency, and underlying electroreduction mechanisms. Under a chronoamperometry mode, nickel and graphite exhibit 6-h linear removal kinetics of 186.0 and 213.3 mg Se(IV) m^-2 h^-1 and 24-h removal efficiencies of 70% and 91%, respectively. Graphite’s Faradaic efficiency (3.8%) is slightly higher than nickel’s (2.5%) due to its inert nature and fewer side reactions. We further confirm Se impregnation into graphite is a major Se(IV) removal mechanism, owing to graphite’s porous and layered structure. Compared with other metal cathodes, the corrosion-free graphite does not release metal ions into the water matrix and offers an economically competitive Se(IV) removal on par with that of the gold electrode.