Leslee Storlie

Leslee Storlie is a Master of Science student in Civil Engineering, emphasizing in the Environmental Engineering program at North Dakota State University. She holds a Bachelor of Science degree in Civil Engineering also from North Dakota State University. Her present research is focused on understanding the unique water quality characteristics and water plant operations that influence the formation of bromate during the ozone disinfection process.

Email: Leslee.Storlie@gmail.com                        
Phone: 651-307-3772

Investigation of Bromate Formation in Ozone Disinfection Systems through Comprehensive Sampling, Water Quality Analysis, and Model Simulation

Fellow:Leslee L Storlie

Advisor: Dr. Wei Lin, Ph.D., Associate Professor, Department of Civil Engineering, North Dakota State University

Matching Support:North Dakota State University

Degree Progress:M.S. in Environmental Engineering expected graduation in May 2013


For many years the primary additive used to disinfect drinking water has been chlorine.  Recently, however, the use of ozone as a disinfection agent has become popular.  Ozone is highly reactive and may form hydroxyl radicals under alkaline conditions, making it one of the strongest oxidants and disinfectants of the oxygen species.  Due to ozone’s high oxidation potential it has the ability to not only disinfect drinking water but also remove inorganic and natural organic substances making it an option for disinfection as well as taste and odor control.  Although ozone has removed many of the dangers associated with the disinfection process it does bring about its own concerns.  Ozone has the potential of oxidizing bromide, found naturally in many source waters, to bromate.

In the early 1990’s, the International Agency for the Research on Cancer (IARC) classified bromate as a possible carcinogen.  As part of the United States Environmental Protection Agency (USEPA) Stage 1 Disinfectants/Disinfection Byproducts Rule a maximum contaminant level (MCL) for bromate was set to 10 ppb for water treatment plants utilizing ozone. 

Unfortunately, knowledge on bromate formation is limited and many municipalities do not have the capability to test for bromate.  To understand the operation of a treatment plant for minimization of bromate, a greater understanding of bromate formation in full-scale water treatment processes is needed.  Once a connection is made between bromate formation and water quality characteristics on a full-scale system, water treatment plant operators would have the ability to estimate the amount of bromate that may form in the resulting drinking water and alter their operating conditions to reduce the formation. The formation of bromate is a common concern that may occur at all water treatment plants that use ozone as a disinfection agent.  In particular, it is a major concern for the Moorhead Water Treatment Plant (WTP) in Moorhead, MN.  During the summer months, ozone demand increases with the increase in temperature, total organic carbon (TOC), and flow rate through the disinfection chambers.  In order to meet proper disinfection contact times, the Moorhead WTP increases the ozone dose and in effect is possibly providing the opportunity for more bromate to form.  Knowledge on bromate formation in a full-scale system is needed to ensure safe drinking water standards are met and to assist municipalities, such as Moorhead, in better understanding their bromate formation.  With the improved understanding, municipalities may be able to remain in compliance through more efficient water plant operation and control.

Project objectives:

The overall goal of this project is to quantify the bromate formation in the disinfection process and identify operational strategies to minimize bromate formation.  The objectives outlined to meet the research goal of this project include the following:

  1. Measuring bromide concentrations in the source waters.
  2. Studying bromate formation in the ozonation process.
  3. Evaluating the impact of operational parameters on bromate formation.
  4. Developing a mathematical model to simulate bromate formation under various operational conditions.


The water plant operation at the Moorhead Water Treatment Plant has been studied in depth through personal part-time operation. Changes in water quality characteristics throughout the change in seasons have been discovered and key insight into the treatment process have provided for a greater idea of how processes can be altered to possibly improve bromate control.

Outside of gaining experience as a water plant operator, one year of historical data from the Moorhead Water Treatment Plant has been analyzed. This data includes pH, TOC, ozone dose, ozone contact time, source water flows, and hardness from locations throughout the treatment process. Through data analysis seasonal patterns have been discovered that give insight into how values will change over the course of a year.

Currently, 10 years of historical TOC data have been compiled and are being analyzed to discover any trending patterns that may have occurred. These trends and the data patterns will be used to refine sampling times and procedures. During times of historically higher TOC levels sampling frequency will be increased to reflect the changes. Bromate and Bromide sampling will begin in the near future after proper DIONEX ICS-3000 Ion Chromatography (IC) system calibration is achieved.

The investigation into bromate formation at the Moorhead WTP is now complete.  Comprehensive sampling was completed in January 2013, data analysis was completed in March 2013, thesis defense was approved in April 2013, and expected graduation is in May 2013. 


The unique parameter of a high pH and the full scale sampling method, allowed for new insights into the factors influencing bromate formation that have not been studied thus far. Through this study it was observed that increases in bromate formation occurred during the summer months at times of increased pH, ozone dose, and bromide concentrations.  Bromate formation was minimal under a range of water quality parameters during the lower temperature months.  In addition, it was suggested that operational controls influenced bromate formation.  With a better understanding of the influence of water quality parameters on bromate formation, a prediction model was developed to assist the treatment facility in minimizing bromate formation through changes in operational control options. 

The research project is applicable to not only the Moorhead WTP but to treatment facilities in this region as well as those in other parts of the United States.  On a regional level, this research will benefit the local water treatment facilities in Fargo and Moorhead as they both use ozone as well as the Red River as their source water.  With this research they will be able to provide the city residents with a much greater quality of drinking water.  It will also assist those plants looking to utilize ozone and could possibly be applied to other cities using the Red River such as Grand Forks.  On a larger scale, the proposed research project will also be utilized.  Due to the lack of research in the Northern portion of the United States, research in this area will be important.  Temperature changes, soil conditions, and much more likely have a large impact on bromide concentrations in source water and will be applicable to more states that differ regionally from the predominant ozone research centers of Nevada and California.  It is also a goal of this research project to publish results in a peer reviewed journal and have the opportunity to assist many more people. 

Lelee Storlie

Dr. Wei Lin


Advisor: Dr. Wei Lin

Assistant Professor of Civil Engineering

North Dakota State University