Roles of Heavy Metals during Pyrolysis and Gasification of Metal-Contaminated Waste Biomass: A Review

Abstract

The presence of contaminates (i.e., heavy metals) in biomass through various sources (industrial activities and municipal solid waste) from its growth to end use has become a nuisance. Over the past years, biofuel production from metal-contaminated waste biomasses (MCWBs) has attracted more attention on account of the potential roles in addressing both energy and environmental concerns. This review considers the migration and transfer behaviors of heavy metals into various output streams, including solid products (i.e., biochar), tar and syngas from MCWBs, i.e., contaminated energy crops, plants, industrial wastes, and municipal solid waste, and using thermochemical processes (gasification and pyrolysis). In addition, the authors also shed light on the transfer mechanisms of heavy metals (however, the availability of the literature on the transfer mechanisms of heavy metals during thermal process is very limited) and usability of products (bio-oil, biochar, and syngas), including a comparison of gasification and pyrolysis processes in regard to the conversion of MCWBs into bioenergy. In the end, techno-economic assessments and future perspectives are presented. This review will be helpful to promote future research and may aid in the scale-up of the current practices to visualize MCWBs as potential opportunities instead of nuisances.