Methanogenesis suppression for VFAs recovery in anaerobic digestion: A review of mechanisms and trends

Volatile fatty acids (VFAs), as intermediate products of anaerobic digestion, are attracting increasing attention due to their potential applications as effective carbon sources and precursors for high-value biofuels and biochemicals. Methanogenesis inhibition is a key to VFAs production, yet current strategies are limited by poor mechanistic insight and potential toxicity. This study has systematically evaluated the existing methanogenesis inhibition strategies qualitatively and quantitatively, with a focus on elucidating the inhibitory mechanisms and factors. Bayesian mixed effects model provides robust statistical evidence that these inhibition methods reliably suppress methanogenesis and enhance VFAs production across diverse conditions. Particularly, chemical inhibition methods have consistently performed well in methane inhibition (highest density interval HDI 1.99–6.11) and VFAs accumulation (HDI 0.016, 0.079). However, chemical inhibitors may lack selectivity and have the potential to accidentally inhibit non-target microbial communities. In contrast, operational and physical inhibition methods are effective in promoting VFAs accumulation (HDIs 0.063, 0.153 and 0.026, 0.111), but their impact on methane inhibition was unstable with HDIs that are either wide or crossing zero, possibly due to methanogens recovery and subsequent VFAs consumption. Biological inhibition has limited effectiveness in both areas with HDIs crossing zero, likely because it is still in the early stages of development and requires further research. By integrating microbial, physicochemical, and systems-level insights, this work offers a perspective on the rational design of carbon redirection strategies toward VFAs production using anaerobic biotechnology.