A thermochemical conversion method known as hydrothermal carbonization (HTC) is appealing, because it may convert wet biomass directly into energy and chemicals without the need for pre-drying. The hydrochar solid product’s capacity to prepare precursors of activated carbon has attracted attention. HTC has been utilized to solve practical issues and produce desired carbonaceous products on a variety of generated wastes, including municipal solid waste, algae, and sludge in addition to the typically lignocellulose biomass used as sustainable feedstock. This study aims to assess the in-depth description of hydrothermal carbonization, highlighting the most recent findings with regard to the technological mechanisms and practical advantages. The process parameters, which include temperature, water content, pH, and retention time, determine the characteristics of the final products. The right setting of parameters is crucial, since it significantly affects the characteristics of hydrothermal products and opens up a range of opportunities for their use in multiple sectors. Findings reveal that the type of precursor, retention time, and temperature at which the reaction is processed were discovered to be the main determinants of the HTC process. Lower solid products are produced at higher temperatures; the carbon concentration rises, while the hydrogen and oxygen content declines. Current knowledge gaps, fresh views, and associated recommendations were offered to fully use the HTC technique's enormous potential and to provide hydrochar with additional useful applications in the future.

Water contamination is one of the most pressing environmental issues of the present. There is a significant amount of interest in the slow pyrolysis of biomass to produce biochar, a solid byproduct that is stable and rich in carbon. Adsorbents manufactured from hydrochars, sometimes referred to as hydrochar created by hydrothermal methods, have been tested for the removal of possible contaminants from wastewater. The hydrothermal processes of hydrothermal carbonization (HTC) and liquefaction (HTL) yield hydrochars, a distinct category of biochar. Because of its peak efficiency, large surface area, large size of pore and capacity to regenerate, hydrochar is an acceptable option for the rehabilitation of a range of pollutants. The formation, activation, identification, and use of biochar and hydrochar were highlighted in this review. The physiochemical properties of the char produced by the two processes are very different, which has an impact on their potential uses in areas like wastewater pollution remediation, soil improvement, greenhouse gas emission and carbon sequestration among others.