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<br />24 | Final Report Bay Area Clean Water Agencies | City of San Leandro <br />selection, chemical type, fuel type (e.g., coal versus natural gas), location, and others. Research by <br />Falk et al. (2013) is presented in Figure 8-1 that illustrates the potential plant wide increase in GHG <br />emissions at variable nutrient targets for a nominal 10 mgd plant. Target 1 represents secondary <br />treatment and Targets 2 through 5 represent variable nutrient targets with Target 5 being the most <br />stringent. The BACWA Level 2 targets lie somewhere between Targets 1 and 2, and the BACWA <br />Level 3 is comparable to Target 3. The gradual increase in GHG emissions in Falk et al. (2013) from <br />Target 1 to the higher levels is attributed to additional biological treatment facilities, increased energy <br />and chemical use, and additional tertiary nitrogen and phosphorus removal processes. The study <br />findings revealed that a point of diminishing return is reached as nutrient removal objectives <br />approach the technology-best achievable performance where GHG emissions increase rapidly, cost <br />of treatment increase rapidly, while the potential for algal growth reduce marginally. Note, the point <br />of diminishing returns is watershed specific. <br /> <br />Figure 8-1. GHG Emissions Distribution for a Nominal 10 mgd Plant at Various Treatment <br />Targets (Adapted from Falk et al., 2013) <br />The GHG emissions evaluation for the Regional Watershed Permit is not intended to be plant-wide <br />study. Rather, the evaluation focuses on the relative increase in GHG emissions associated with any <br />recommended plant optimization and/or upgrade strategies (e.g., additional oxygen demand <br />associated with nitrification). <br />The GHG emissions accounting focuses on the operating energy and chemical demand for the <br />recommended plant optimization and/or upgrade strategies. The approach relies on the USEPA <br />eGRID values4 for the regional energy production and the GHG emissions associated with chemical <br /> <br />4 http://www.epa.gov/cleanenergy/energy-resources/egrid/ <br />-2,000 <br />0 <br />2,000 <br />4,000 <br />6,000 <br />8,000 <br />10,000 <br />12,000 <br />14,000 <br />16,000 <br />18,000 <br />CO2equivalent tonnes/yrN2O Emissions (w/Data Range as Bars) <br />Biosolids Hauling and CH4 Emissions <br />Deep Well Injection <br />Aeration <br />ChemicalsPumping/ <br />Mixing Miscellaneous <br />Cogeneration