Photoelectrotrophic denitrification and iron-sulfur-nitrogen cycle enhance nutrient removal in pyrite-amended...

Pyrite has been widely used as an electron donor for autotrophic denitrification in constructed wetlands; however, its inherently slow dissolution kinetics and restricted electron release often constrain the long-term nutrient removal performance of pyrite-amended constructed wetlands (PCWs). To overcome these shortcomings, this study proposed a novel photocatalysis-enhanced PCW (L-PCW). Results demonstrated that L-PCW significantly outperformed PCW, achieving removal efficiencies of 77% and 88% for total nitrogen and total phosphorus, respectively. Under light irradiation, pyrite generated photoelectrons, driving photoelectrotrophic denitrification and enhancing nitrate reduction. Light exposure also stimulated the production of extracellular polymeric substances, which improved microbial aggregation and photoelectron transfer efficiency. Moreover, light-enhanced pyrite dissolution increased bioavailable iron and sulfur species, enriching iron and sulfur transforming bacteria, which facilitated the iron-sulfur cycle and further promoted nitrogen removal. Enhanced pyrite dissolution also contributed to sustained phosphorus removal, potentially through the formation of iron-phosphorus precipitates. Metabolic pathway analysis demonstrated the upregulation of key functional genes involved in nitrogen metabolism, sulfur metabolism, and the electron transport system, providing genetic evidence for the enhanced nitrogen removal capacity of L-PCW. These findings suggest that L-PCW offers an effective and sustainable strategy for improving nutrient removal in PCWs through the synergistic effects of photocatalysis and microbial processes.