Biohydrogen fermentation from pretreated biomass in lignocellulose biorefinery: Effects of inhibitory byproducts and recent progress in mitigation strategies

Lignocellulosic biomass (LCB) is expected to play a critical role in achieving the goal of biomass-to-bioenergy conversion because of its wide distribution and low price. Biomass fermentation is a promising method for the sustainable generation of biohydrogen (bioH₂) from the renewable feedstock. Due to the inherent resistant structure of biomass, LCB needs to be pretreated to improve its digestibility and utilization. However, certain intermediates by-products generated during the pretreatment process, such as phenolic compounds, furan derivatives, and aldehydes, have been identified as potent inhibitors of subsequent anaerobic fermentation due to their disruptive effects on the physiological and metabolic functions of hydrogen-producing microbiota. To counteract the negative effects of these inhibitors on bio-H₂ fermentation, various detoxification strategies for LCB hydrolysates have been explored. This review presents a comprehensive analysis of fermentation-inhibitory by-products commonly generated by modern pretreatment protocols and their negative impacts on biohydrogen fermentation. Furthermore, the underlying mechanisms of inhibition upon hydrogen-producing microbes and their impacts on microbial community dynamics are exhibited. State-of-the-art strategies for detoxifying pretreated LCB have been also discussed, along with alternative pretreatment strategies designed to minimize or eliminate the formation of inhibitory by-products. Additionally, this review addresses the significant gap in the economic viability assessments of these processes, offering a detailed evaluation of both the technological and economic feasibility of biomass fermentation. Given the limitations of previous studies, strategies for cost-effective pretreatment and detoxification should be developed in the future to overcome the inhibition of fermentation inhibitors in the bioconversion of biomass to hydrogen.