Exogenous hydrogen supply improves in-situ biogas upgrading of sewage sludge: Performance and mechanisms

Abstract

In-situ biogas upgrading is a promising approach for enhancing carbon dioxide capture and efficient resource use. Recent investigations have highlighted that exogenous hydrogen can be used to purify biogas. However, the effects of exogenous hydrogen supply on in-situ biogas upgrading remain poorly understood. This study investigated the effects of direct and indirect hydrogen supply on in-situ biogas upgrading and elucidated potential underlying mechanisms. Significant enhancements were observed in methane production efficiency and biogas upgrading using an exogenous hydrogen supply. Batch tests showed that adding 10 g/L coarse zero valent iron (cZVI) resulted in a high cumulative methane yield of 286.4 mL/g-volatile solids (VS) and methane content of 95.5%, representing a 2.2-fold and 1.5-fold increase, respectively, compared to results in the absence of cZVI. In semi-continuous tests, the use of hollow fibers to enhance hydrogen diffusion led to an increased methane production rate (52.0 mL/g-VS·d), while less hydrogen was more favorable for biogas purification (92.0% methane). Further analysis revealed that an exogenous hydrogen supply enhances cooperative interactions between hydrolysis microbes, acetogenesis microbes, and methanogens to promote methane production and biogas upgrading. These findings provide valuable insights into the impact of exogenous hydrogen supply on in-situ biogas upgrading during anaerobic digestion of sewage sludge, informing future development of strategies for enhancing methane production and biogas upgrading from waste sources.