The Water Environment Research Foundation (WERF) and New York State Energy Research and Development Authority (NYSERDA) have conducted a project with Brown and Caldwell, Black & Veatch, Hemenway Inc., and the Northeast Biosolids and Residuals Association (NEBRA) to determine the barriers that wastewater utilities face when implementing anaerobic digestion and combined heat and power (CHP) projects. A number of barriers were identified, but the foremost involved the combination of: Economics. The largest, most widespread barriers to biogas use are economic, stemming from either higher priority demands on limited capital resources or perceptions that the economics do not justify the investment.  Decision making. Public agencies' decision-making practices can also hinder biogas use.Discretionary projects can be easily derailed by numerous factors, specific uncertainties, or requirements to exceed somewhat arbitrary thresholds.This paper uses a simplified case study to evaluate the economics using five methodologies and discusses the benefits and context of each methodology. These methodologies include: 1. Simple Payback; 2. Net Present Value (NPV);

Harnessing available energy from digester gas remains a relatively untapped resource in the wastewater treatment industry. Generating "Green Power" is a major component of the Columbus Biosolids Flow-Through Thermophilic Treatment (CBFT 3 ) project being implemented by Columbus Water Works (CWW). The latest technology in lean-burn, sparkignition combustion engines, including the Advanced Reciprocating Engine Systems (ARES), is being developed by the three major engine manufacturers Caterpillar, Cummins, and Waukesha. Support for the ARES program is being provided by the US Department of Energy.CWW evaluated the use of ARES engines for combined heat and power (CHP) generationa.k.a. cogeneration -for its CBFT 3 Class A biosolids process at the South Columbus Water Reclamation Facility (SCWRF). The proposed use of the high-efficiency engines using digester gas as a fuel source represents the first such application of this technology in the wastewater treatment industry. In addition to generating about 1.3 megawatts (MW) of electricity (equivalent to about 40 percent of the SCWRF consumptive use), the cogeneration system will provide sufficient heat to heat the thermophilic digesters greater than 99 percent of the time. Rigorous life-cycle cost analysis presents an attractive economic payback of 8 to 10 years. This paper describes how CWW used a combination of economic and non-economic factors to evaluate each manufacturer's system as part of a competitive pre-selection process. In broad terms, the following major criteria were used in the selection: 1) capital cost; 2) 10-year maintenance cost (to be contracted with the manufacturer); 3) projected and guaranteed net electrical efficiencies; 4) adequacy of heat production for the thermophilic digester operation; and 5) overall capacity and level of redundancy provided by the proposed system. The results were used to execute a system pre-selection, confirm life-cycle costs, and connect design teams from the project engineering firm (Brown and Caldwell) and the high-efficiency enginegenerator manufacturer (Cummins Power Generation).

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Growing concern over the cost of power and long-term availability of limited fossil fuel resources for the production of electricity have caused electrical utilities and governments to promote "green" or renewable power. Solar, wind, geothermal, biomass, biogas, and low-impact hydroelectricity are current acceptable green-power sources.Digester gas is a renewable, green energy resource that has been used in wastewater treatment plant (WWTP) engines since the 1930s. In the 1980s, many WWTPs added cogeneration with rich-burn engines. In the 1980s and 1990s, utilities either converted their rich-burn engines to lean-burn engines or installed new lean-burn engines to meet air quality requirements.Because digester gas is of finite supply and is dependent on operating parameters such as sludge feed and volatile solids destruction, it is desirable for WWTPs to maximize the efficiency of electricity generation and beneficial reuse of otherwise wasted heat. Recently, a number of projects have used innovative cogeneration technologies, such as fuel cells, gas turbines, microturbines, and Stirling Cycle engines, to harness the energy of digester gas. In addition, advanced reciprocating engine systems (ARES) are currently being developed as another cogeneration technology under an initiative sponsored by the United States Department of Energy (USDOE) and U.S. National Laboratories with three reciprocating engine manufacturers.Columbus Water Works (CWW) is currently evaluating the use of ARES engines for combined heat and power (CHP) generation for its Class A biosolids process named Columbus Biosolids Flow-Through Thermophilic Treatment (CBFT 3 ) at the South Columbus Water Reclamation Facility (SCWRF) that currently treats an average flow between 30 and 35 million gallons per day (mgd). The use of ARES engines as part of the CBFT 3 project would represent one of the lowest capital cost, highest net efficiency CHP technologies. The project is expected to provide a payback between 4 to 7 years, with an even shorter payback period depending on the degree of federal funding secured and avoided capital offsets assumed.Other innovative features of the project include the addition of grease trap waste to the digestion process to increase gas and power production, digester gas pretreatment using multiple unit processes, and heat recovery systems. 3570 WEFTEC®.06

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