Review of microwave pyrolysis of sludge to produce high quality biogas: Multi-perspectives process optimization and critical issues proposal

With the increasing depletion of fossil energy and the development of carbon neutral sustainable concept, the production of high-quality biogas from renewable biomass has important applications. Microwave pyrolysis technology, as a biomass conversion method with the high pyrolysis efficiency, good quality of biogas products and high energy utilization efficiency, has attracted wide attention. However, due to the key defects of microwave pyrolysis technology, it is still in the laboratory scale and has not been applied on a large scale. Therefore, in order to improve the application potential of microwave pyrolysis technology in biomass energy development, this work selects sludge as the representative of biomass, and summarizes 172 related research on the production of high-quality biogas by microwave pyrolysis sludge. In this review, the exploration of key influencing factors, insight into pyrolysis mechanisms from different perspectives, energy consumption and techno-economic analysis are discussed, aiming at optimizing microwave pyrolysis process from multiple perspectives. The key problems and solutions of microwave pyrolysis to generate biogas are investigated and proposed to understand the critical issues that hinder its further development. This review provides new thinking and references for the application and industrialization of microwave pyrolysis technology in producing high-quality biofuels. [Display omitted] •Parameters affecting biogas obtained by microwave pyrolysis of sludge are reviewed.•Mechanisms of microwave pyrolysis of sludge are explored from different perspectives.•Energy consumption and efficiency of microwave pyrolysis process are analyzed.•Critical issues affecting the development of microwave pyrolysis process are proposed.