Microbial Modification Enhances Organic Sulfur Removal Capability of Chelated Iron Solution for Natural Gas

Feedstock natural gas typically contains sulfur compounds, such as hydrogen sulfide (H₂S), carbonyl sulfide (COS), and methyl mercaptans (MeSH), which require removal before pipeline transportation. The chelated iron process, a liquid-phase oxidation method, is widely employed for desulfurizing refinery gas, natural gas, and biogas due to its low capital investment, operational simplicity, and cost-effectiveness. While highly efficient for H₂S removal, the chelated iron process exhibits limited effectiveness against organic sulfur compounds like COS and MeSH, restricting its applicability. Certain microorganisms demonstrate strong organic sulfur removal capabilities. While biodesulfurization effectively treats low-sulfur streams, its standalone configuration shows inadequate removal for high-concentration H₂S, primarily due to microbial inhibition at elevated sulfur loads. This study has developed a novel desulfurization technology that integrates biological desulfurization with chelate iron desulfurization, namely, the biochelated iron system. Desulfurizing strain TYWJ-1 was isolated from a purification facility. Its optimal growth conditions were determined using Box-Behnken response surface methodology (RSM), and its sulfur compound removal mechanisms were elucidated through whole-genome analysis. Compared to chelated iron solution, the biochelated iron system significantly enhanced removal efficiency of H₂S, MeSH, and COS. For ternary mixtures (H₂S/COS/MeSH), chelated iron achieved 100% H₂S removal but only 34.6-35.8% for COS and 58.0-59.1% for MeSH removal at 9.62-10.03 min EBRT. The biochelated iron system significantly outperformed the conventional one, achieving 100% H₂S, 55.2-55.7% COS, and 94.7-96.5% MeSH removal under identical conditions. The biochelated iron system maintained stable multisulfur compound removal performance throughout a 10 day continuous operation. Critically, TYWJ-1 remained viable and metabolically active within the chelated iron solution. The biochelated iron system represents a pioneering advancement within liquid-phase oxidation desulfurization. It offers applicability to a wider range of gas compositions and achieves a superior desulfurization performance. This integrated approach holds significant promise as a next-generation liquid-phase oxidation technology for the efficient purification of diverse fuel gases.