Sugarcane biochar enhances CO2 conversion to acetic acid by Clostridium thailandense: Linking fermentation performance to genome-based analysis

Abstract

Biogas is a promising renewable energy source, but conventional CO<inf>2</inf> removal technologies are costly and energy-intensive, limiting widespread adoption. Biological CO<inf>2</inf> conversion into acetic acid by acetogenic bacteria via the Wood-Ljungdahl (WL) pathway offers a sustainable alternative for simultaneous biogas upgrading and carbon valorization. However, slow autotrophic growth and low productivity remain critical bottlenecks. Biochar derived from agricultural residues has shown potential to enhance microbial fermentation; however, its role in biological CO<inf>2</inf> fixation to acetic acid has not been investigated. This study evaluated sugarcane leaf biochar (BSL) and bagasse biochar (BSB) for enhancing CO<inf>2</inf> conversion to acetic acid by Clostridium thailandense . BSL demonstrated superior performance, achieving rapid H<inf>2</inf> consumption (89.8% within 48 h vs. 0% for controls) and upgrading biogas from 38.4% to 84.2% CH<inf>4</inf> content while producing 2.0 g/L acetic acid. BSL's higher Fe content (2.1-fold compared to BSB) and superior pH buffering capacity were associated with enhanced bacterial performance, with optimal loading at 15 g/L. Genome-based analysis identified putative transport systems for Fe, Ca, and Mg, suggesting the capacity of C. thailandense to utilize mineral species released from BSL. These minerals may support acetogenic metabolism by supplying physiologically relevant cofactors and by contributing to cellular stability and relief of acid stress, which is consistent with the enhanced biogas upgrading performance observed under BSL supplementation. Overall, BSL represents a promising low-cost functional material for enhancing biological biogas upgrading and acetic acid production through improved mineral availability and fermentation stability.