Comparison of energy production and carbon emissions from varying biogas dispositions from anaerobic co-digestion at a small-scale wastewater treatment plant

This study provides a comparative analysis of energy production and greenhouse gas emissions from five modeled biogas dispositions (uncontrolled release, flaring, boilers, combined heat and power (CHP), and market purification for pipeline injection) for a small-scale (8710 m3 wastewater/day) wastewater treatment plant with anaerobic co-digestion of wastewater sludge, food scraps, and fats, oils, and grease. Using biogas production rates, electricity grid mix data, and thermal energy from natural gas, this study evaluated 100-year Global Warming Potential for each disposition. Analysis revealed that uncontrolled release resulted in the highest emissions (13,600 kg CO2-eq.), while market utilization shows the lowest emissions (486 kg CO2-eq.). Results also indicate that boilers are the most favorable disposition for thermal energy production, generating 22,305 MJ/day (8428 MJ/day beyond digester requirements). CHP produces a surplus of 4300 MJ/day (1190 kWh/day), offsetting ~ 46% of the facility’s electricity requirement; however, CHP produces 2–4 times more CO2-eq./day than boilers. Monte Carlo and sensitivity analyses underscored the importance of biogas production volume and equipment efficiency in determining environmental impact and energy results. This unique analysis informs sustainable practices, providing insights into the potential benefits of anaerobic co-digestion in achieving both energy and carbon neutrality at small-scale facilities.