A comparative life cycle assessment of electro-anaerobic digestion to evaluate biomethane generation from organic solid waste

Anaerobic digestion is a mature technology, but its application may be constrained by suboptimal feedstock conversion efficiency and associated low biogas production. Electro-anaerobic digestion has been proposed as an innovative technology to boost biogas production performance. This study is the first to assess and compare the life cycle impacts of biomethane production from typical organic solid wastes via conventional and electro-anaerobic digestion within the closed boundary system. The results showed that electro-anaerobic digestion outperformed anaerobic digestion in energy conversion and environmental impact. The energy consumption of electro-anaerobic digestion was reduced by 21.7%–42.6%, the carbon footprint was decreased by 18.0%–42.6%, and the energy conversion ratio was increased by 27.7%–74.3%, as compared to conventional anaerobic digestion. The highest energy conversion ratio (12.8) and the lowest global warming potential (39.6 g CO_2-eq MJ⁻¹) were obtained in the electro-anaerobic digestion of animal manure. Parasitic demand in biogas production was the primary energy consumption process in biomethane production from dry straw, while biogas upgrading was the most significant energy consumption process in other systems. Sensitivity analyses indicated that changes in specific methane yield impacted system performance most. The predicted carbon footprint reduction in the future electricity market demonstrated greenhouse gas emissions for produced biomethane as low as 6.2 g CO_2-eq MJ⁻¹ at complete decarbonization of electricity. As modelled, the theoretical resource of electro-anaerobic digestion of organic solid wastes in China is 82.6% of the natural gas consumption. This study will provide scientific guidance for efficient methanization of organic solid waste for investment in energy projects.