(94c) Valorization of Water Treatment Plant Residuals to Biodegradable Deicers

Water softening residuals disposal from the chemical treatment of water supplies is a national problem in the U.S. About 3.1 million tons/yr of lime softening sludge containing calcium carbonate, magnesium hydroxide and other organic and inorganic impurities are generated in the U.S from lime-soda softening to reduce the hardness of water supplies. The current disposal methods principally involve the application of sludges on to agricultural lands or landfilling. These options are expensive due to the high dewatering and transportation costs involved, and the potential deleterious effects on the environment. This research is aimed at the valorization of water plant residuals in the production of a biodegradable and non-corrosive deicing chemical that can be applied onto roads for snow and ice control in winter. Calcium and magnesium acetate deicers can be produced from water plant residuals by reacting the residuals with acetic acid. This reaction is controlled by the mass transfer rate of acetic acid to the calcium carbonate solid, surface reaction rate, and mass transfer rate of the product from the surface. This paper will report results obtained from a study of the reaction process to optimize operating conditions to maximize conversion rates. A freezing point depression model will be presented to predict freezing point depression of the deicer from basic colligative property relationships. This model is found or provide results in good agreement with experimental data.