Evaluation of Different Pretreatment Processes of Lignocellulosic Biomass for Enhanced Biomethane Production

Lignocellulosic biomass is the most abundant source of organic materials available, yet it remains highly underutilized as a source of renewable energy products. The complex and rigid properties of lignocellulosic materials make the biomass difficult to digest, and thus it does not offer a significant energy yield once digested through anaerobic digestion (AD). Several pretreatment methods have been developed over the past years to improve the digestibility of lignocellulosic biomass and enhance its energy yield potential. This Review examines the latest technologies and methods used in the pretreatment of lignocellulosic biomass for more efficient AD and energy yield in the form of methane gas. Such pretreatment processes include mechanical, irradiation, thermal, chemical, biological, and combined pretreatment. A comparison between the different types of available pretreatment methods shows that the different methods have been successful in achieving an improvement in the methane yield from lignocellulosic substrates on a laboratory scale. There is a clear variation in the energy requirements, reaction times, and methane improvement for each method. However, more research is necessary to assess the applicability and feasibility of such methods on full-scale facilities. In addition, the optimum choice of a pretreatment process will remain highly dependent on the substrate type and economic feasibility.