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Full-Scale and Bench-Scale Studies on the Removal of Strontium from Water (abstract)
Odonnell, A. AND D. Lytle. Full-Scale and Bench-Scale Studies on the Removal of Strontium from Water (abstract). Presented at AWWA Annual Conference, Boston, MA, June 08 - 12, 2014.
To inform the public of studies on the removal of Strontium from water.
Strontium (Sr) is a natural and commonly occurring alkaline earth metal which has an oxidation state of +2 under normal environmental conditions. Stable strontium is suspended in water and is dissolved after water runs through rocks and soil. It behaves very similar to calcium. Grains, leafy vegetables, and dairy products contributes to dietary strontium. In February 21, 2008, the EPA published a Federal Register notice for the draft Contaminant Candidate List 3. The final list includes 104 chemicals or chemical groups and 12 microbiological contaminants, including strontium, which are known or anticipated to occur in public water systems. These candidates all have the potential to present health risks through drinking water exposure. Federal drinking water guidelines are currently set at 4,000 µg/L because at high levels, infants, children, and adolescents are susceptible to abnormal skeletal development known as rickets (USEPA, 2011). Exacerbated by inadequate calcium levels, strontium substitutes for calcium during bone calcification or displaces calcium from existing calcified matrix (USEPA 1996). Drinking water treatment information in the literature regarding strontium removal from water is minimal. Adsorption, nanofiltration, ion-exchange, and biological treatment have been considered to a limited extent. Given the potential for future regulatory action on strontium, there is an obvious need to examine the effectiveness if drinking water treatment on strontium reduction. Such information will be useful in the regulatory determination process and valuable to water systems that have water supplies with elevated strontium levels. Therefore, the objective of this presentation will be to discuss the effectiveness of conventional coagulation (aluminum and iron) and lime softening to remove strontium from water at the bench level. The effectiveness of chemical doses, pH, or turbidity have on the removal rates will be explored with jar testing. Tests will be conducted with nanopure water for all conditions, river water for alum and ferric chloride coagulation, and ground water for lime softening. In addition, strontium removal data from a number of full-scale ion exchange, iron removal/coagulation, lime softening and iron-based adsorption plants, and distribution of strontium in groundwater sources will be presented. Results showed that strontium is distributed widely across U.S. ground waters with some pockets of very elevated levels located in the midwest. Cation exchange and lime softening can be effective strontium removal strategies, while iron removal/coagulation and iron-based adsorption approaches are not based on full-scale data. Bench-scale results are in agreement with full-scale studies and illustrate the relationship between water quality (e.g., pH, calcium concentration, etc...) and strontium reduction.