Valorization of municipal wastes using co-pyrolysis for green energy production, energy security, and environmental sustainability: A review

Pyrolysis is a potential technology used for the transformation of municipal wastes into energy products such as biofuel. Existing reviews on pyrolysis mainly focus on agroforestry biomass and conventional pyrolysis heating techniques. There is limited literature on the application of recent pyrolysis techniques, types of reactors, key operating parameters, and properties of pyrolysis products from conventional versus recent/novel pyrolysis techniques, and particularly the application of the oil products in fuel engines. Here we focus on the performance of various pyrolysis techniques for valorizing municipal wastes, with an explicit emphasis on the progress and application of co-pyrolysis as a recent technique for value-added products recovery from municipal wastes. We review the main operating parameters of co-pyrolysis, concerns and disputes arisen from the technique, and the resultant liquid fuel properties. In particular, co-pyrolysis using microwave heating shows proficiency to resolve several drawbacks of conventional pyrolysis techniques such as reduced oxygen content and viscosity and increased calorific value of liquid oil, hence promising as a method to generate environmental friendly and sustainable third-generation fuels. Sorting of municipal wastes is recommended as an approach to improve the feasibility of co-pyrolysis by having desired quantity and type of municipal wastes as the feedstock, and more research and development on co-pyrolysis utilizing municipal wastes is necessary to maximize the yield and quality of target pyrolytic products. Thus, we conclude that co-pyrolysis is a feasible and sustainable method for recovering biofuel from municipal wastes to obtain green energy and energy security.