Effective role and mechanism of scrap iron filings in controlling hydrogen sulfide production in septic tanks.

Long-term anaerobic conditions in septic tanks exacerbate the release of hazardous gases, such as hydrogen sulfide (H2S), which degrades urban air quality. While traditional iron salt addition effectively inhibits H2S production, its large-scale application imposes economic burdens and challenges for low-carbon emission reduction. To address this issue, this study proposes the use of scrap iron filings (SIFs) as a source of Fe2+ and Fe3+ ions and evaluates their efficacy in sulfide control through a long-term laboratory-scale septic tank reactor. Experimental results demonstrated that the addition of SIFs reduced the average concentration of dissolved sulfides by 45.6 % and gaseous H2S by 92.6 %. Microbial community analysis of septic tank sediments revealed a significant decrease in sulfate-reducing bacteria (SRB) and an increase in sulfur-oxidizing bacteria (SOB), indicating that SIFs influence microbial activity by suppressing sulfide generation while enhancing sulfide oxidation. Furthermore, the addition of SIFs slightly increased the carbon-to-nitrogen (C/N) and carbon-to-phosphorus (C/P) ratios in the effluent, potentially improving subsequent nitrogen and phosphorus removal in wastewater treatment. These findings suggest a promising strategy for reducing hydrogen sulfide emissions and corrosion in septic tanks.