5. Energy Evaluation of Household Biogas Project

Biogas plant construction has been boosted in rural China not only due to the immediate merit from biogas production but also due to the succeeding benefit from by-product utilization in agro-industry, both of which are significant strategies to address energy shortage and global warming issues. Combined heat and power and household utilization were prior options in achieving net energy production, provided that power conversion efficiency and biogas production remained at satisfactory levels. A life-cycle energy evaluation of a biogas–digestate utilization system is performed. Besides, energy inputs and outputs within the system boundary are calculated to address the possibility of net energy production by wastewater treatment combined with biogas–sludge use technologies based on input–output analysis. Taking all the life-cycle stages into account, the net energy gain of the entire system is 10,458.024 MJ. Different bioresource use alternatives had a bias toward the efficiency of energy production.