Trends and Challenges in Biohydrogen Production from Agricultural Waste

Abstract

Over the past decade, increasing interest has been given to anaerobic fermentative processes for hydrogen production and other high-value by-products. The development of technologies dedicated to energy production from biomass has recently emerged. Indeed, agricultural residues, such as agricultural waste or energy crops, have become economically and technologically attractive for their low-cost and carbohydrate-rich substrates. Moreover, dark fermentation methods present an ingenious solution to process them. However, low hydrogen production yields are often reported because of their rather low biodegradability due to the presence of complex polymers recalcitrant to biodegradation, such as lignocellulose. Hydrogen potentials range between less than 1 ml H₂.g⁻¹ of dry matter for complex lignocellulosic residues and 240 ml H₂.g⁻¹ of dry matter for purified polymers such as starch. Many solutions for increasing hydrogen potential have been proposed such as microbial consortium selection, substrate pretreatment and process parameter optimisation. Consequently, higher hydrogen yields have recently been obtained, reaching 150 ml H₂.g_TVS ⁻¹ for pretreated rice straw. Nevertheless, the only manner to reach viable industrialisation of dark fermentation processes would be to combine this process with other biological energy production techniques such as photofermentation, bioelectrochemically assisted hydrogen production and anaerobic digestion, in a so-called environmental biorefinery concept.