Features of single and combined technologies for lignocellulose pretreatment to enhance biomethane production

Adopting anaerobic digestion (AD) of lignocellulosic biomass to produce biomethane is an effective approach to meet the urgent demand for clean and sustainable energy in energy transition. The pretreatment kinetic mechanism is the key to enhance the lignocellulosic carbon conversion and significantly improve the efficiency of AD. Various pretreatment strategies have been proposed in the literature, while a systematical summarization of these strategies based on different driving forces is still lacking. The purpose of this review is to classify and analyze the current technologies and research achievements on lignocellulose pretreatment technologies according to different driving forces including single ones and combined ones. Features, as well as fundamental modes of conventional and recently emerged pretreatments, have been introduced. Single pretreatment methods driven by physical, chemical, or biological forces have obvious advantages and limitations for the anaerobic transformation of lignocellulosic feedstocks. Recently emerged combined pretreatment technologies powered by multiple forces have synergistic treatment effects which hold greater application potential than those driven by single forces. Besides, a comprehensive evaluation of combined pretreatments is carried out on the basis of pretreatment efficiency, cost, energy consumption, and environmental impact to detect their potential applications in the actual biogas industry. By comprehensively summarizing the current features of single and combined technologies, this review finally provides future research perspectives for biomass pretreatment.