Clearly affordable

Mississippi Town Leans on Ion Exchange Process to Remove Brown Tint from Water

By Steve Cawood, PE, Regional President and Wheeler Crook, PE, Design Engineer

Discolored tap water had long been a source of frustration for the City of Gautier, Miss., and its citizens. Bathtubs and sinks filled with brown water were hindering growth and stifling economic development. Businesses did not want to move to Gautier, and residents did not like living with the stigma.

Drawing from eight groundwater supply wells, the City endured the brown water problem for some 29 years, much like many other municipalities and water systems in the region. The water comes from the Upper Pascagoula and Lower Graham Ferry aquifers, providing ground water to the system at a production capacity of approximately 4 million gallons per day (MGD).

A color treatability study found that the source of color was total organic carbon – meaning it was not considered a contaminant and thereby complied with the EPA’s Primary Drinking Water Standards. However, ignoring the poor aesthetics of the water was no longer an option. Seen as an impediment to future development, City officials knew something had to be done.

While there were several treatment options available – such as reverse osmosis, ozone, granular activated carbon (GAC), ozone-GAC, ultrafiltration and nanofiltration – many of them would have been too costly, and thereby untenable, for the City.

Devising an Affordable Solution

In 2011, ClearWater Solutions, LLC (CWS), an operations and maintenance company and subsidiary of Goodwyn, Mills and Cawood, Inc. (GMC), enlisted GMC’s team of water resources and treatment experts to help resolve the City’s water issue once and for all.

Initially, GMC was authorized by the City to perform field-scale pilot studies of GAC, pressure filtration and ion exchange systems to analyze the removal of color in groundwater by each process. GMC utilized desktop-sized equipment to determine if each method would work, ensure the feasibility of the technology and collect data to verify the effectiveness in removing the color from the water.

Throughout the process, GMC collaborated with Tonka Water in Minneapolis, Minn., an innovative designer and custom manufacturer of water treatment equipment with tremendous treatment expertise. Since the chemicals used in the process can make a substantial difference in the level of treatment, Tonka’s expertise was needed to provide data and an understanding of the different coagulants and polymers available. The collaboration was instrumental in finding an effective coagulant and polymer.

Ultimately, designers were seeking a solution more economical than reverse osmosis (RO), widely thought to be the most thorough and effective water treatment system available. Due to RO’s accompanying high energy costs, chemical costs, and operation and maintenance costs – primarily the result of having to regularly change the RO membranes – the City needed a less expensive option.

As a result of the pilot, GMC’s team of professionals determined that ion exchange offered comparable clarity to more expensive treatment processes, with significantly reduced annual operations and maintenance costs. Utilizing cutting-edge technology, GMC was able to devise an affordable solution that visibly removed the water’s discoloration. In fact, it significantly reduced the color level from its previous 90 units to less than 5, an undetectable amount. The goal of the project was to achieve color units less than 10.

Final cost of the plant was just $2.1 million, about $300,000 under budget. In contrast, an RO plant would have cost an estimated $5 million. The City of Gautier was subsequently able to refinance old debt and use the savings to pay for the new plant.

Technically speaking, the innovative ion exchange process targets undesired particulates, based upon the type of media and ions within the vessel, through an exchange of ions between two electrolytes or between an electrolyte solution and a complex. In most cases, the term is used to denote the processes of purification, separation and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic “ion exchangers.” Ion exchanges can be unselective or have binding preferences for certain ions or classes of ions, depending on their chemical structure. This can be dependent on the size of the ions, their charge or their structure. In the case of Gautier, ions responsible for color were specifically targeted.

When the treatment facility is in operation, water is pumped through a pressure filter with sand media. On the outlet side of the filter, the water goes through a finishing process incorporating ion exchange.

Design and Construction

The City Council adopted its Clear Water Plan in January 2013, with the purpose of defining the process and timeline for developing a comprehensive water filtration system. A critical component of the plan was the construction of a 1 million gallon-per-day (MGD) ion exchange facility at the public works site on Gautier-Vancleave Road in Gautier.

A raw water pipe system ties four wells to the filtration and ion exchange system, and distributes the treated water through the rest of the city’s water system. The wells represent those with the most significant brownish tint.

Creel Co. General Contractors of Mobile, Ala., was contracted to build the system, and Tonka Water, which assisted GMC during the pilot study, manufactured the water treatment equipment, including the ion exchange vessels. CWS installed the raw water pipe connecting the wells to the filtration system, providing the labor at no additional cost to the City.

In the end, costs were significantly reduced – GMC was able to utilize existing pumps that were at the well sites, so the horsepower of the wells did not need to be increased. Thereby, no filtration and additional construction was required at the well sites. Completed in June 2015, Gautier’s ion exchange water treatment plant is Mississippi’s first such treatment system for municipal water and has already proven to be successful within its first months of operation.

The 1 MGD system, designed by GMC, is operated and maintained by CWS. Today, the operations and maintenance company optimizes the treatment process when necessary to achieve the most economical treatment. The company utilizes an instrument to continuously monitor the raw water on-line to adjust chemicals as needed for color removal.

Through the successful troubleshooting of Gautier’s water quality issue, CWS and GMC locked arms with the City in its effort to find an economical solution. As a result of the success of the Gautier project, all of the entities involved actively promote the use of filtration and ion exchange as an affordable and effective water treatment method.