Valorization of cannabis waste via hydrothermal carbonization: solid fuel production and characterization

Hydrothermal carbonization (HTC) was employed to convert cannabis waste into valuable solid fuel (hydrochar) under different operating conditions, including reaction temperature (170-230 °C), biomass-water ratio (1:10-1:20), and residence time of 60 min. The produced hydrochar was examined for their fuel properties including calorific value (HHV), proximate and ultimate analysis, thermal stability and combustion behavior, etc. The results revealed higher HTC temperature led to a higher degree of carbonization, which is beneficial for increasing carbon content and HHV of the hydrochar. The HHV of the hydrochar improved significantly up to 24.65 MJ/kg after the HTC compared to 17.50 MJ/kg for cannabis waste. The energy yield of hydrochar from the HTC process was in a range of 70.41-82.23%. The optimal HTC condition was observed at 230 °C and a biomass-water ratio of 1:10, producing high-quality hydrochar with 24.24 MJ/kg HHV and 72.28% energy yield. The hydrochar had similar fuel characteristics to lignite coal with significantly lower ash content. Additionally, recirculation of liquid effluent showed a positive influence on the HHV of hydrochar besides minimizing the release of wastewater from the HTC process. The study revealed that HTC is a promising technique for valorization of cannabis waste into high-value solid fuel, which can be potentially an alternative to coal.