Effect of hydrothermal carbonization as pretreatment on energy recovery from food and paper wastes

In this study, food waste (FW) and paper wastes were subjected to hydrothermal carbonization (HTC) with a purpose to improve energy recovery potential. FW is suggested as the suitable feedstock for production of hydrochar (HC) having highest calorific value (29.6 MJ/kg). Carbon content in FW derived HC was increased from 50% to similar to 72% whereas energy retention efficiency was found to be 5.74 times of that in FW. Wastewater recovered after HTC of FW was rich in carbohydrates with chemical oxygen demand of similar to 56,000 mg/L which may further be subjected to anaerobic treatment for biogas generation. Energy balance calculations showed that the solid and liquid fractions recovered after HTC of FW yielded highest energy output (2950 kJ/kg FW) compared to incineration (2217 kJ/kg FW), anaerobic digestion (2605 kJ/kg) and in-vessel composting. HTC process can be adopted as decentralized facility by institutions where highly moisturized wastes are generated.