Long-term effects and mechanisms of sulfur-modified nanoscale zero-valent iron in enhancing anaerobic treatment of highly toxic wastewater containing 2,4-dichlorophenol.

Sulfur-modified nanoscale zero-valent iron (S-nZVI) has emerged as a promising additive for enhancing anaerobic treatment of refractory wastewater. However,its long-term effectiveness and role in toxic shock resistance remain unclear. Herein, S-nZVI was first applied to continuous-flow anaerobic reactors treating wastewater containing 2,4-dichlorophenol (2,4-DCP). Due to its unique FeS-dominated nano-interface, S-nZVI endowed the anaerobic system with superior treatment performance and operational stability compared to nanoscale zero-valent iron (nZVI). At 150 mg/L 2,4-DCP, nZVI addition failed to prevent complete reactor collapse, while the S-nZVI group maintained relatively stable 2,4-DCP biodegradation and anaerobic digestion performance. Mechanistic studies revealed that S-nZVI enhanced key enzyme activities,enriched functional microorganisms, and increased microbial electron transport system activity. Furthermore, S-nZVI induced microbial secretion of conductive proteins and established efficient extracellular electron transfer networks. Overall, S-nZVI served as an efficient bioaugmentation additive and promoted microbial electron transfer, improving anaerobic system performance and stability.