Mechanistic study of wheat straw-enhanced sulfur release and denitrification in a pyrite-based bioretention system:...

In order to improve pyrite-driven sulfur/iron release and overcome the limitations of slow sulfur/iron release and low denitrification efficiency in pyrite (FeS₂)-based bioretention systems for urban non-point source pollution control, this study innovatively created a mixotrophic bioretention system (WPB) by incorporating wheat straw (WS). The iron-sulfur-carbon multi-element cycles and synergistic denitrification mechanisms were thoroughly examined using a 180-day simulated rainwater runoff experiment. The results demonstrated that the continuous organic carbon release from WS achieved an average NO₃^--N removal efficiency of 85.06 %, a 15.08 % improvement over the pure pyrite system (PB). According to a study of the microbial community, WS encouraged the cooperative development of a multi-pathway denitrification network that was dominated by Sulfurimonas (0.6 %, sulfur cycling), Denitratisoma (3.9 %, heterotrophic denitrification), Braceroidetes_vadinHA17 (7.2 %, heterotrophic denitrification), Geobacter (4.0 %, iron reduction), and Thiobacillus (0.38 %, sulfur oxidation). Microscopic characterization revealed a 2.3-fold increase in etch pit density (7-12 pits/μm²) and Fe/S elemental loss rates of 9.9 % and 22.7 %, respectively, suggesting that WS significantly altered the pyrite surface. Additionally, the analysis of microbial extracellular polymeric substances (EPS) revealed that the loosely bound EPS (LB-EPS) content rose by 40% (to 92-61 μg/g) and the Zeta potential dropped by 34.6%, both of which improved microbial aggregation and biofilm stability. This research offers vital theoretical and technical underpinnings for creating stable and effective pyrite-based bioretention systems.