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While residuals (solids) management is a demanding and costly component of wastewater treatment, wastewater residuals also represent an opportunity for energy recovery and for reducing overall treatment costs. Wastewater utilities are interested in moderating the impacts of volatile electric power costs and in enhancing their environmental sustainability.Water Environment Research Foundation (WERF) developed the Life Cycle Assessment Manager for Energy Recovery (LCAMER) spreadsheet-based tool in 2006 for the purpose of assessing life cycle costs for on-site energy recovery systems using biogas produced by anaerobic digestion of biosolids. The authors completed two case studies to demonstrate the application of the LCAMER Tool. The case studies focused on demonstrating the applicability, effectiveness, and areas of improvement for the LCAMER Tool by evaluating proposed anaerobic digestion and biogas-to-energy improvements for two large wastewater utilities. The case studies discussed in this document include detailed data on biogas generation, estimated energy recovery facility capital and operations and maintenance (O&M) costs, and discussion of potential air emissions from such facilities.

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The Green Bay Metropolitan Sewerage District (GBMSD) will replace their existing solids handling facilities at their Green Bay Facility (GBF). The existing solids handling facilities are challenged by the following:• Aging facilities at the end of their useful life, increasing O&M and decreasing reliability • Pending Federal Clean Air Act Maximum Achievable Control Technology (MACT) air pollution regulations for sewage sludge incinerators that the existing multiple hearth incineration system cannot meet• A system now at full capacity because of the addition of waste activated solids from GBMSD's De Pere FacilityBetween 2008 and 2011, GBMSD and CH2M HILL developed a Solids Management Facility Plan that evaluated numerous solids processing technologies and process trains to respond to these issues. Seventy-three solids unit processes were considered, some were eliminated and the remaining 52 unit processes were used to develop 17 process configurations. Of these seventeen configurations, six alternative configurations were selected and evaluated in detail. The Digestion with Thermal Processing and Electrical Generation alternative was selected and later named the Resource Recovery and Electrical Energy Project, or R2E2.The paper evaluates energy recovery options from the anaerobic digestion and biosolids incineration system and uses for the recovered energy. Recovered energy from anaerobic digestion is converted to electricity and heat, while energy recovered from biosolids incineration is used for partial drying of the biosolids feed and other heating uses. The paper demonstrates the effective use of recovering and utilizing energy to replace a significant portion of purchased power and natural gas.