Strontium in Drinking Water: Occurrence, Distribution, and Removal A thesis submitted to the Division of Graduate Studies and Research of the University of Cincinnati in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in the Department of Biomedical, Chemical, and Environmental Engineering of the College of Engineering and Applied Science 2014 Alissa Jo O’Donnell B.S., Civil Engineering, University of Cincinnati, 2011 Committee Members: Dionysios D. Dionysiou (UC), Chair Darren A. Lytle (USEPA) George A. Sorial (UC) ABSTRACT The occurrence and distribution of stable strontium around the United States was not well documented. Data from both the United States Geological Survey and United States Environmental Protection Agency from the past 10 years resulted in 39,256 samples that showed strontium was widely distributed with pockets of very elevated levels (≥ 10 mg/L) located along the Gulf Coast for surface water and in the Midwest for groundwater. Strontium removal data from a number of full-scale ion exchange, iron removal/coagulation, lime softening, and iron-based adsorption plants were examined. Point-of-entry ion exchange and iron removal, and point-of-use reverse osmosis effectiveness were also studied. Cation exchange and lime softening were effective strontium removal strategies, while iron removal/coagulation and iron-based adsorption approaches were not. The effectiveness of conventional coagulation and lime softening treatments on the removal of strontium at the bench-scale was needed. Alum and iron coagulants were able to achieve 18% and 6.0% strontium removal, respectively, from surface water after 0.2 µm vacuum filtering. No significant change in strontium removal was observed with the increase of coagulant dose, initial strontium concentration, pH, or initial turbidity. Lime softening was able to achieve 77% strontium removal after 0.2 µm vacuum filtering. Higher strontium removal efficiencies were seen at higher lime dosages which corresponded to a higher final pH. No significant changes in strontium removal was observed with the increase of initial strontium concentration. i Fundamental studies were conducted with nanopure water to find the mechanism(s) for the lime softening strontium removal efficiencies. When calcium was not initially added, no significant change in strontium removal was observed with the increase of pH or initial strontium concentration. When calcium was initially added, the strontium and calcium removals were significantly increased above pH 11 to 65% and 98%, respectively. When calcium was initially added, a low initial dissolved inorganic carbon greatly reduced both strontium and calcium removal efficiencies to 8.1% and 29%, respectively. Scanning electron microscope images for the fundamental experiments at a pH of 11 showed high spherical vaterite, the least stable polymorph of calcium carbonate, is prevalent in the samples compared to rhombohedron calcite, the most stable polymorph. Strontianite was only found in the sample with the lowest initial calcium concentration. X-ray diffraction patterns revealed that vaterite was shifted, indicating that strontium could be replacing calcium inside the crystal lattice. SEM images also revealed clusters of minerals in a transitional phase at the lowest and highest initial calcium concentrations. The possible mechanism(s) for strontium removal during the lime-soda ash softening treatment process includes surface adsorption into calcium carbonate precipitates, coprecipitation with the calcium carbonate precipitations, or surface-solution ion exchange within calcium carbonate. ii iii ACKNOWLEDGEMENTS First, I would like to thank my thesis committee members: Dr. Darren Lytle from the USEPA and Dr. Dionysios Dionysiou and Dr. George Sorial from UC. You gave me an opportunity to prove that I could accomplish anything, despite all of life’s distractions. You encouraged me to push my limits and were understanding about my need for self-improvement. I would also like to thank Dr. Steven Buchberger from UC who also encouraged me and helped me get into the UC/USEPA traineeship program, which lead me towards my current career path. Secondly, I would like to thank the following staff who spent countless hours helping me. Your contribution was greatly appreciated. Maily Pham and Keith Kelty of the USEPA for their ICP- AES elemental analyses and database management. Bill Kaylor of the National Council on Aging SEE for the alkalinity and chloride analyses. Stephen Harmon of the USEPA for the SEM/EDS/XRD analyses and images. Nicholas Dugan and Jonathan Pressman of the USEPA for their collection of the source waters used in the jar testing experiments. Dan Williams of the USEPA for packing and shipping coolers to different water utility operators. Alex Moix, Dyrian Wandick, and Manelisi Nhliziyo of the USEPA GRO program for their help with a few of the fundamental experimental runs. Emily Nauman of Pegasus Technical Services for the creation of the occurrence, distribution, and USEPA WSWRD studies maps used in this thesis. Christy Mulhen of the USEPA for supply orders, helping me jump through many internal hurdles, and providing me with life advice. Thirdly, I would like to thank my family for their support while completing my degree. To my mother, father and grandmother (Jylene, Tim, and Barb O’Donnell) for their unconditional love iv and support, to my two aunts (Peg Leiter and Mary Ann Darling) who checked up on my wellbeing and encouraged me to keep working hard, and to my late paternal grandfather (Tom O’Donnell) who was always proud of me and told me so regularly. Lastly, I would like to thank my friends for whom this journey to complete my degree would not have been possible. My deepest thanks goes to Andrew Knowles, Cricket Wyatt, Dhawal Chheda, Jananie Rockwood, Jennifer Liggett, Jen Norman, Masud Rana, Nick McCormick, and Ruta Deshpande. When I needed to talk, you were there to listen. When I needed support, you helped get me back on my feet. You always believed in me and wanted the best for me. I am very grateful for having met you all. You taught me so much about myself and I am eternally grateful for our friendships over the years. v TABLE OF CONTENTS ABSTRACT .................................................................................................................................... i ACKNOWLEDGEMENTS ........................................................................................................ iv TABLE OF CONTENTS ............................................................................................................ vi LIST OF FIGURES ................................................................................................................... viii LIST OF TABLES ....................................................................................................................... ix NOTATIONS................................................................................................................................. x CHAPTER 1: INTRODUCTION ................................................................................................ 1 1.1 Problem Statement ................................................................................................................ 1 1.2 Objectives .............................................................................................................................. 1 CHAPTER 2: BACKGROUND .................................................................................................. 3 2.1 Discovery .............................................................................................................................. 3 2.2 Chemical and Physical Properties ......................................................................................... 3 2.3 Industrial Uses ....................................................................................................................... 4 2.4 Health Effects & Regulations ................................................................................................ 4 2.5 Detection ............................................................................................................................... 6 2.6 Occurrence and Distribution ................................................................................................. 6 2.7 Treatment Removal Methods ................................................................................................ 7 2.8 Conventional Drinking Water Treatment .............................................................................. 7 2.9 Lime-Soda Ash Softening Treatment .................................................................................... 9 CHAPTER 3: OCCURRENCE AND DISTRITBUION IN DRINKING WATER ............. 12 3.1 Methodology ....................................................................................................................... 12 3.2 Results & Discussion .......................................................................................................... 13 CHAPTER 4: USEPA STUDIES WITH STRONTIUM IN THE RAW WATER ............... 19 4.1 Methodology ....................................................................................................................... 19 4.2 Results & Discussion .......................................................................................................... 20 CHAPTER 5: JAR TESTING – CONVENTIONAL (SURFACE WATER) ....................... 25 5.1