Pyrolysis and hydrothermal carbonization of biowaste: A comparative review on the conversion pathways and potential applications of char product

Pyrolysis and hydrothermal carbonization have (HTC) received a great deal of attention and are regarded as representative thermal techniques in the dry and wet conversion of biowaste. With this regard, understanding the formation pathways and physicochemical properties of the solid product, namely biochar and hydrochar, will guide the applications in the field of renewable energy and the environment. In this review, the influence factors and the pathways of biowaste transformation during pyrolysis and HTC were compared coupled with the detailed formation mechanism of hydrochar and biochar, and typical physicochemical properties and potential applications in soil remediation, wastewater treatment, and biofuel production were discussed. We also present new perspectives on the biochar and hydrochar applications concerning the unique properties, and the future challenges and outlook on thermal conversion techniques towards biowaste valorization as a green process were presented.