Utilization of Organosolv Waste Waters as Liquid Phase for Hydrothermal Carbonization of Chaff

Organosolv wastewater was used as the liquid source during the hydrothermal carbonization (HTC) of chaff at 200 °C for 4 h and compared to a control HTC of chaff in water. The produced hydrochars had a carbon content of 58 wt % and a higher heating value (HHV) of 23 MJ kg^–1 independently of the employed liquid source. Concentrations of inorganic elements were analyzed as well as organic acids in the process water. The use of organosolv wastewater had no negative effects on the HTC process and hydrochar properties. Subsequently, the HTC process waters were used for biomethane production. Performing HTC in organosolv water led to a doubling of the biomethane yield as compared to water as liquid source. The use of this industrial wastewater in combination with the solid agricultural waste chaff has the potential of increasing the sustainability of the HTC process by the disposal of two waste stream sources at the same time as well as by reducing the amount of contaminated waters that would eventually have to be treated.