A review on the utilization of industrial biowaste via hydrothermal carbonization

Abstract A variety of organic waste originating from industrial activities are increasingly accumulating worldwide, especially in developed regions; however, organic waste can potentially be utilized for energy reuse via hydrothermal carbonization. This carbonization is an artificial process that simulates the natural coalification of biomass under moderate conditions and can convert organic waste from harmful to valuable species. The present study provides a comprehensive overview of hydrothermal carbonization, highlighting the current knowledge regarding the technical mechanisms, application advantages, and economic benefits. First, the processing parameters, chemical reactions and carbonization mechanisms mentioned in the recently published literature are extensively discussed. Then, the advantages of hydrothermal carbonization when applied to the derived hydrochar for use as an intermediate feedstock via thermal utilization (e.g., combustion, pyrolysis, or gasification) are detailed. Typical merits related to the upgrading efficiency, environmental safety, and economic benefits are elaborated by summarizing a number of laboratory experiments and large-scale performance tests. Additionally, novel techniques for improving the efficiency of carbonization are described for reference. Finally, potential directions for future studies to establish an efficient and clean mode of utilization, which is important for sustainable industrial development in the near future, are classified and prioritized.