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Environmental and cost life cycle assessment of disinfection options for municipal wastewater treatment
Cashman, S., A. Gaglione, J. Mosley, L. Weiss, N. Ashbolt, T. Hawkins, J. Cashdollar, X. Xue, Cissy Ma, AND S. Arden. Environmental and cost life cycle assessment of disinfection options for municipal wastewater treatment. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-14/377, 2014.
The study intends to answer the following research questions: 1. What are the net life cycle impacts associated with the collection and treatment of municipal wastewater? 2. What are the contributions of each life cycle stage to the net result for each impact category? What are the contributions of each step in the wastewater management system? 3. What are the contributions of specific environmental releases to the net result for each technology and impact category? 4. What is the effect of plausible parameter variability? What parameters associated with wastewater characteristics have the greatest effect on net greenhouse gas and human health impact results?
This document summarizes the data collection, analysis, and results for a base case wastewater treatment (WWT) plant reference model. The base case is modeled after the Metropolitan Sewer District of Greater Cincinnati (MSDGC) Mill Creek Plant. The plant has an activated sludge system but is not removing nitrogen or phosphorus and uses sodium hypochlorite for disinfection prior to discharge to the Ohio River. Sludge at the Mill Creek Plant is incinerated in fluidized bed reactors. The Mill Creek plant receives a large amount of industrial waste and UV may not provide sufficient disinfection. EPA obtained the data used to develop the base case from MSDGC and supplemented the data with publicly-available data where necessary. Results of the base case analysis show normalized WWT results are dominated by eutrophication. Eutrophication impacts are from release of ammonia and phosphorus emissions in wastewater effluent. Sludge incineration makes the largest contribution to global warming potential, much of which is related to biogenic CO2 emissions from combustion of the sludge. Excluding biogenic carbon dioxide emissions more than halves the overall carbon footprint of treating wastewater in the base case. Aeration is the life cycle stage that consumes the most electricity, making it the largest contributor for many impacts including energy demand, fossil depletion, acidification, blue water use, ozone depletion, human health cancer, and human health criteria. The impacts driven by electricity consumption are sensitive to the electricity usage and electricity grid sensitivity analyses conducted. Overall, primary disinfection with sodium hypochlorite only contributes zero to 6 percent for most impact categories, with the exception of blue water use, ozone depletion, metal depletion, and human health noncancer. Upstream processes associated with production of the sodium hypochlorite have relatively high impacts for these categories. Wastewater collection accounts for 33 percent of the total cost, followed by plant-wide overhead cost, which accounts for 20 percent of the cost, sludge thickening and dewatering, which accounts for 19 percent of the cost, and aeration, which accounts for 14 percent of the cost. The base case WWT LCA and cost model developed here can serve as a framework for examining different disinfection technologies and treatment methods. EPA plans to compare base case results to an alternative using peracetic acid as the disinfecting agent in future work.