Integrating food waste sorting system with anaerobic digestion and gasification for hydrogen and methane co-production

Abstract

Anaerobic digestion (AD) is a potential biotechnology to treat food waste for both energy and resource recovery. However, a high level of contamination in food waste limits their direct use as feedstocks. Therefore, a food waste sorting system followed by anaerobic digestion and gasification is proposed in this study to evaluate the potential of food waste for hydrogen and methane co-production through the thermal-equilibrium model and experimental study. To achieve the H2-rich syngas and methane-rich biogas, the waste sorting system was used to separate the raw waste into pure food waste fraction for AD and discarded waste fraction for gasification. The thermal-equilibrium model is used to predict the content of H2 at different moisture content and air equivalence ratio (ER). The results show that gasification generated the highest hydrogen content at 28.9% with a high moisture content of 55 wt% when the value of ER is 0.35. The highest calorific value of syngas is 5.59 MJ/m3 at the conditions of 60 wt% of moisture content and 0.35 of ER. For the mesophilic AD system, the highest specific methane yield of FW is 557 mL/g VS. Thermophilic AD increased methane yield to 680 mL/g VS while AD of vegetable waste had a negligible production of methane gas. The overall energy performance of the integrated AD and gasification system was assessed in terms of the output of electricity and heat.