Pretreatments of lignocellulosic biomass for biohydrogen biorefinery: Recent progress, techno-economic feasibility and prospectives

Abstract

Dark fermentation (DF) of lignocellulosic biomass (LB) is expected to play a critical role in building a green hydrogen supply chain toward the carbon-neutral society. Due to its inherent recalcitrance, biomass demands pretreatment to increase its digestibility. Various pretreatment techniques have been extensively investigated to improve the digestibility of feedstocks. However, no systematic review of pretreatment to promote biohydrogen fermentation has been conducted. Besides, studies analyzing the economic feasibility of pretreatment technologies are lacking. The aim of this review is to analyze the current pretreatment techniques and research results based on different driving forces. Intense thermochemical pretreatment dissolves lignin and hemicellulose and forms various inhibitors that interfere with the physiological and metabolic functions of the microbiota. Moreover, the issues related to the detoxification methods of inhibitors and their impacts on biomass fermentation were highlighted. The possibility of bioaugmentation of hydrogen-producing microflora with genetically engineered or naturally resistant bacteria may serve to be an effective in situ detoxification protocol. Moreover, the recycling techniques related to pretreatment were also discussed. Black liquor is a huge carbon reservoir with great potential to produce products such as biohydrogen and the value-added products generated will help reduce the environmental degradation caused by black liquor. Furthermore, the technical and economic viability of the current pretreatment methods and the prospects were also discussed. Increased costs related with buffering, reduced productivity and energy efficacy are critical factors contributing to the costs of bio-H₂ production. For every 20% increase in H₂ yield, production costs are decreased by 8%.