Combination of anaerobic digestion and sludge biochar for bioenergy conversion: Estimation and evaluation of energy production, CO2 emission, and cost analysis

Abstract

Waste-to-energy technologies involve the conversion of several wastes to useful energy forms like biogas and biochar, which include biological and thermochemical processes, as well as the combination of both systems. Assessing the economic and environmental impacts is an important step to integrate sustainability and economic viability at anaerobic digestion systems and its waste management. Energy production, CO2 emissions, cost analysis, and an overall process evaluation were conducted, relying on findings from both laboratory and pilot-scale experiments. The digestate generated during anaerobic digestion proved to be an effective approach for mitigating some CO2 emissions while managing sludge waste within the anaerobic digestion and CHP system. Incorporating biochar production and application in soil into the process led to a 3.5 % reduction in CO2 emissions, which contributed to a more sustainable form of energy production while offering the potential for the generation of carbon credits through a carbon-negative process. The employment of digestate biochar for energy production seems a feasible way to reduce the amount of residue to final disposal in landfill with a minimal reduction of profit per GWh and a slight increase in the CO2 emissions by 2.7 %.