Hydrothermal carbonization of household wet waste - characterization of hydrochar and process wastewater stream

In the present study, household wet waste (HWW) pretreatment was explored using hydrothermal carbonization (HTC) to enhance resource recovery opportunities. The pretreatment was performed at 200 °C for 1-8 h duration in a 2 L high pressure reactor. After HTC, the recovered solid hydrochar (HC) showed high calorific value of ∼ 27 MJ/kg compared to 18 MJ/kg of HWW. Moreover, it contained significant amount of oxygen containing acidic functional groups, hence the waste derived HC may also be utilized as adsorbent in wastewater treatment and soil conditioner. The process wastewater (PW) contained several value-added organics including proteins and furfurals. The HTC reaction kinetics showed the conversion of HWW to primary HC as the fastest step (rate constant = 0.0126 min^-1). Moreover, the biochemical methane potential test on PW revealed generation of significant amounts of biogas with 55-75% methane. The total energy production from HC and PW was estimated as ∼ 3.3 MJ/kg of HWW.