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Life Cycle Assessment and CostAnalysis of Municipal Wastewater Treatment Expansion Options for Food Waste Anaerobic Co-Digestion
Morellis, B., S. Cashman, S. Arden, Xin Ma, J. Turgeon, J. Garland, AND D. Bless. Life Cycle Assessment and CostAnalysis of Municipal Wastewater Treatment Expansion Options for Food Waste Anaerobic Co-Digestion. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-19/094, 2019.
To explore the environmental impacts and life cycle cost of co-digestion energy recovery from food waste in medium scale wastewater treatment facility. The stakeholders that would be interested in this study and apply the results including local communities; utilities, OW; OWM; Regions; LCA practitioners, decision makers, academia; experts.
This study presents results of a life cycle assessment (LCA) and life cycle cost assessment (LCCA) of a case-study wastewater treatment facility (WWTF) in Massachusetts, the Greater Lawrence Sanitary District (GLSD). The GLSD WWTF is a medium-sized facility that treats an average municipal sewage flowrate of 23.5 million gallons per day (MGD). The WWTF is currently (2017-2018) in the process of installing additional anaerobic digestion (AD) capacity and a combined heat and power (CHP) system to expand energy recovery. The AD and CHP expansion project will allow GLSD to accept up to 92,000 gallons per day of source separated organic (SSO) waste, avoiding landfill and waste-to-energy disposal of food waste, while considerably boosting biogas production. A scenario and sensitivity analysis were included to understand the effect of SSO acceptance rate, AD performance, avoided disposal processes and LCCA parameters on environmental impact and life cycle cost results. Results associated with two co-digestion feedstock scenarios were compared to results for baseline (2016) WWTF operation, prior to co-digestion and the AD and CHP expansion. Results are presented for both a low and base AD performance scenario. Base results consider avoided food waste disposal processes that correspond to 2016 end-of-life disposal pathways in Massachusetts, where approximately 68 and 32 percent of food waste were incinerated and landfilled, respectively. The cost analysis compares the above LCA scenarios across two cost scenarios to establish a low and base estimate of system operating costs over a 30-year period. The study develops life cycle inventory data for the GLSD WWTF based on plant records, engineering design documents and process models of the WWTF. The report presents results for eight environmental impact categories. Results demonstrate that adoption of SSO co-digestion in combination with the AD and CHP expansion project reduce plant-wide environmental impacts and system operating cost in six of eight environmental impact categories when base AD performance is maintained. Water use is negative, indicating an environmental benefit in all scenarios due to on-site and industrial effluent reuse programs. Eutrophication potential is the only impact category that increases because of anaerobic co-digestion in the base AD performance scenario. Eutrophication impact was found to increase by between 10 and 24 percent, depending upon the scenario. Results in all other impact categories respond positively (i.e. yielding reductions in net environmental impact) to anaerobic co-digestion. Reductions in fossil fuel depletion, cumulative energy demand and global warming potential can be particularly dramatic due to their strong link with avoided energy products and disposal processes that yield environmental credits within the analysis. Biogas is a source of non-fossil and low-carbon energy that displaces fossil fuel consumption in the Northeast Regional grid mix as well as on-site natural gas combustion. Net present value (NPV) results decrease moderately with AD expansion under the base scenario. These reductions in system NPV correspond to payback periods for the AD expansion and CHP installation project of ten to 27 years in the base AD performance scenario, depending on the cost and SSO acceptance scenario. Payback periods of less than the 30 year analysis period were not identified within the low AD performance scenario.