Enhancement of nitrogen and phosphorus removal by coupling pyrite-based autotrophic denitrification with an electro-enhanced A2/O process.

Conventional anaerobic-anoxic-oxic (A2/O) processes often exhibit low nutrient removal efficiency and high operational costs when treating carbon-limited wastewater from highway service areas. In this study, a pyrite-based autotrophic denitrification process coupled with an electro-enhanced A2/O system (PE-A2/O) was developed to treat synthetic highway service-area wastewater. At an applied voltage of 1.2 V, the reactor configured with an anoxic anode and an oxic cathode achieved the best nutrient-removal performance. The removal efficiencies of NH4+-N, TN, and PO43--P reached 96.89 ± 3.18%, 94.08 ± 4.99%, and 58.73 ± 3.02%, respectively, representing increases of 25.36%, 28.87%, and 20.20% compared with the control reactor. Pyrite oxidation released Fe2+ and sulfur species that supported autotrophic denitrification, while Fe2+/Fe3+ cycling promoted Fe-mediated phosphate sequestration through precipitation and surface complexation. The PE-A2/O process enriched electroactive genera, including Desulfovibrio and Sulfurospirillum, and denitrifying genera, including Thermomonas and Rhodanobacter. It also increased the relative abundances of genes associated with iron, sulfur, and nitrogen cycling, indicating enhanced functional potential for coupled Fe-S-N transformations. Collectively, this study demonstrates an A2/O-compatible PE-A2/O strategy that integrates pyrite-mediated autotrophic denitrification with electro-enhanced electron transfer, providing a mineral-electrode-microbe pathway for simultaneous nitrogen and phosphorus removal from carbon-limited wastewater.