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

Abstract

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.