Techno-economic and environmental impact assessment of using corn stover biochar for manure derived renewable natural gas production

As an additive to the Anaerobic Digestion (AD), biochar is attracting more research focused on improving digester performance and enhancing biogas yield. Despite the manifold positive impacts, literature data on economic viability and environmental impacts of biochar integration are still scarce. This study performs a comprehensive economic and environmental impacts analysis of biochar use in AD for Renewable Natural Gas (RNG) production. Corn stover biochar is used for the AD of beef manure, and biogas is upgraded to RNG. Process simulation models for AD, biogas upgrading, and RNG compression are developed in Aspen Plus TM. The technoeconomic analysis estimates that biochar addition reduces the minimum RNG selling price by 15% compared to the without biochar scenario. Digestate revenue and RIN credits would further lower the price by 22%. The increased biogas yield offsets the additional capital and feedstock costs for biochar. A cradle-to-gate life cycle assessment shows a 32% reduction in greenhouse gas (GHG) emissions for biochar addition when the biochar mixed with digestate is used for soil application. GHG reductions mostly come from the emission avoidance from conventional manure management and carbon sequestration with manure and biochar. Sensitivity and uncertainty analysis investigates the influence of different economic and process parameters on minimum selling price (MSP) and GHG emissions.