Enhanced integrative process of hydrothermal carbonization and anaerobic digestion with hydrochar addition from lignocellulosic waste

This study investigated the combined hydrothermal carbonization and anaerobic digestion process using cow manure and rubberwood waste. Increasing the temperature from 190 to 240 degrees C improved the fuel properties of rubberwood waste, including energy content, ash content, and thermal stability, surpassing those of cow manure. The subsequent anaerobic digestion of the wastewater generated from hydrothermal carbonization of rubberwood waste, containing phenolic and furan contaminants, was chosen and carried out with addition of hydrochar. The addition of 6 g/L of hydrochar resulted in the highest methane yield, which was 27.8% higher than without hydrochar due to inhibition reduced. The recovery of methane through anaerobic digestion accounted for 6.64% of the total revenue, assisting in offsetting energy costs. The rubberwood waste-based integrated process generated a total revenue of 219.41 USD/ton RW. While higher hydrochar dosages improve methane production, the cost of hydrochar should be considered, as allocating a portion of 8.0% for anaerobic digestion affects overall economics. Further optimization, including consideration of wastewater treatment costs, is crucial for maximizing revenue and cost-efficiency in this integrated process.