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

CFPUA James A. Loughlin, Jr. WWTP
Wilmington, North Carolina

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. The beneficial utilization of digester gas for electrical power production has been shown to provide the following benefits for the CFPUA James A. Loughlin, Jr. (aka Northside)Wastewater Treatment Plant:
1. Both process configurations, non-CHP and CHP, generate positive economic value based on the lifecycle cost assessment and have an internal rate of return greater than the Owner’s estimated cost of capital (5.5%).
2. The CHP process configuration has the greatest rate of return on invested capital. The marginal rate of return associated with providing full CHP capability is also greater than the cost of capital. An incremental capital investment of $0.14 million dollars was shown
to generate an incremental benefit of approximately $1.32 million dollars. The resultant incremental benefit-to-cost ratio for this marginal expenditure is approximately 9.43 – meaning that each dollar of invested capital is creating $9.43 of present value.
3. The beneficial utilization of digester gas for electrical power production results in reduced greenhouse gas emissions as a renewable energy power source. Estimated GHG emissions reductions range from approximately 890 tons CO2 equivalents (tCO2e) per year under current conditions for a system configured to operate without combined heat and power capability to approximately 2,670 tCO2e per year under future operating conditions with full combined heat and power capability.                                                                                                                                                                                                                      In summary, significant economic and environmental benefits should be available for medium sized (10-mgd to 20-mgd) treatment facilities which have anaerobic digestion process equipment that are not currently beneficially utilizing digester gas beyond process heating demands. Source: WEFTEC 2009 Proceedings

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Posted: August 27th, 2010 | Filed under: Waste Water Treatment | Tags: Cost Savings, Energy Savings, Environmental Impact, Funding Incentives, Reduced Greenhouse Gas Emissions | No Comments »

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