Seasonal and Lifecycle Cost Considerations in Evaluating Beneficial Utilization of Digester Gas

Anaerobic digestion is commonly utilized for wastewater residuals stabilization and generates a methane rich biogas stream. This technical paper evaluates seasonal and lifecycle cost considerations for beneficial utilization of this digester gas stream in the form of a case study at the CFPUA James A. Loughlin, Jr. WWTP. Specifically, methodologies for considering seasonal heating demands and long-term loading changes at the treatment facility are analyzed for heating systems using engine driven generator equipment both with and without heat recovery. Lifecycle benefits from the system are estimated from current flow rates of 10-mgd to future flow rates of 16-mgd based on plant design flow. Results indicate that installation of a combined heat and power system produces a significantly higher economic benefit (benefit-tocost ratio = 2.421) than generation of electrical power from digester gas without heat recovery (benefit-to-cost ratio = 1.543).