A Case Study of Renewable Natural Gas Techno-Economics and Emissions at a Wastewater Treatment Plant

Renewable natural gas derived from biogas presents a viable pathway for decarbonizing natural gas systems. Wastewater treatment plants equipped with anaerobic digesters often flare or utilize biogas for heat and electricity generation, missing the potential of renewable natural gas. This study investigates the techno-economic feasibility and emission impact of a renewable natural gas system at a small wastewater treatment plant in the Southwestern United States. Due to a lack of existing data on biogas composition and contaminants from plants originating within the United States, samples were tested seasonally for a year, and gas components are reported in this analysis. Using hourly biogas production data, the analysis incorporates costs and renewable fuel credits at 2022 market prices and the cost to remove the biogas contaminants. The results show a 15-year net present value of USD 16.3 million, with a payback period of three years, surpassing the economic performance of combined heat and power systems previously assessed for the same facility. Additionally, renewable natural gas systems achieve a 22% reduction in site emissions compared to combined heat and power systems. These findings highlight renewable natural gas as a profitable and environmentally superior alternative for biogas utilization in small-scale wastewater treatment plants, contingent on access to renewable fuel credits.