Along with the growing energy demand and the rising concerns over the environmental impacts of fossil fuels, much attention has been recently drawn toward the possibility of exploiting organic or biodegradable wastes, including lignocellulosic wastes (LWs), as the sources of renewable energy. Notably, the anaerobic digestion (AD) of such wastes can mitigate environmental damage, and then produce biogas and bioenergy for low-income rural communities, which is particularly worthwhile in developing countries. Nevertheless, progress in this field has been hindered by a multitude of challenges, e.g., the floating of such wastes on the top of reactors, which typically obstructs gas flow, high carbon-to-nitrogen ratio (CNR), and brings about an almost complex structure of LWs as well as their poor degradability because of high lignin content. In spite of that, many problems can be tackled by adopting appropriate methods, including providing mixing in reactors, reducing CNR, balancing inoculum-to-substrate ratio (ISR), and performing chemical and biological pretreatments. Against this background, the present study aimed to review the related literature on the AD of LWs to identify the existing challenges, and reflect on the strategies to deal with them for the purpose of improving bioenergy production from this type of waste.

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