An evaluation of lime residuals management alternatives for water utilities

Beck, Olivia Roe
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In the United States, some utilities provide lime softening to remove hardness from the drinking water. Lime softening generates residuals as part of the water treatment process, which are inert and non-hazardous. This report provides an environmental and economic evaluation of three lime residuals disposal alternatives: a registered disposal site, beneficially reusing the lime residuals in cement manufacturing, and recalcinating the residuals to reduce the utility’s lime dosage. This report also provides an overview of relevant non-economic factors utilities should consider when selecting a residuals management solution. Because the best alternative for any utility will be specific to that utility’s resources, conditions, and values, this report serves as a framework others might use when evaluating their lime residuals management alternatives. This report found the emissions due to recalcination and the emissions reduction from beneficially reusing the lime residuals in cement manufacturing are orders of magnitude larger than the transportation emissions associated with the registered disposal site. Notably, the emissions due to recalcination will likely be offset by a reduction in lime production, but shifting the emissions from the private sector to a utility might be undesirable. Of the three alternatives, recalcination has the highest capital costs due to the need to purchase a rotary kiln. Cement manufacturing has the highest operations and maintenance costs, and recalcination presents a net savings in operations and maintenance costs due to the chemical savings associated with reduced lime usage. Overall, recalcination is the most financially attractive option, but cement manufacturing provides the most value when considering the social cost of carbon dioxide emissions. Utilities should also consider non-economic factors when assessing lime residuals disposal alternatives, including public perception, managerial impacts, regulatory requirements, and the utility’s values and organizational structure, to assess the full impacts of the alternatives and maximize the likelihood of the selected alternative receiving approval by the public and the utility’s governing body