Suspended ion exchange pilot program reduces Tampa’s total organic carbon in water
Following a discussion regarding the master planning process for the Tampa, Fla., drinking water facility, a city consultant suggested the possibility of piloting a suspended ion exchange system.
One goal of the discussion was to find options for reducing the total organic carbon at the David L. Tippin Water Treatment Facility. The water treatment facility’s source, the Hillsborough River, has high and variable levels of total organic carbon, which can greatly impact the operations of the facility and the treatment performance.
While looking for a solution with non-proprietary resin and previously piloting other ion exchange technologies known to reduce total organic carbon with some success, Tampa’s consultant researched and suggested the suspended ion exchange pilot, known as SIX.
Sarah Burns, water engineering project coordinator, explained, “SIX will be an additional process in our treatment train; it does not replace an existing process. SIX removes organics via ion exchange, similar to how a water softener works, but with a different type of ion. Organics interfere with the removal of PFAS (per- and polyfluoroalkyl substances) through media filtration. Once we remove the organics via SIX, our existing carbon filters are expected to be able to remove PFAS. We are also currently conducting some bench-scale tests to see if SIX is able to remove PFAS itself. At the time we piloted SIX, we were not able to test for PFAS removals directly because most labs were only able to detect PFAS at 20 parts per trillion. As such, all samples from the Hillsborough River came back non-detectable since the levels in the river are well below 20 parts per trillion.”
After working with a consultant, the city of Tampa, Fla., decided to use a new suspended ion exchange system, known as SIX, to help reduce the amount of total organic carbon in the city’s water. This pilot system concluded in 2021 and was a further process of treatment to help remove additional PFAS in the water. (Photo provided by the city of Tampa, Fla.) 
A full-scale model of the SIX system is currently in the design phase, with SIX being the first stop during the treatment process. This process will improve water quality while saving operation and maintenance costs. The plan is to break ground in 2028 and complete the project in 2032. (Photo provided by the city of Tampa, Fla.) 
Tampa is currently working on bench scale tests in a laboratory to better learn the SIX process’s ability to remove PFAS from water. The pilot program itself showed an average reduction in total organic carbon of over 50% utilizing the SIX system. (Photo provided by the city of Tampa, Fla.)
The city’s current carbon filters are also expected to get some upgrades with testing to begin soon in order to determine what will be required.
These PFAS can be found in normal, everyday projects, such as cleaning products; nonstick cookware; personal care products like shampoo, nail polish and floss; water-resistant fabrics, including umbrellas and raincoats; grease-resistant paper; and stain-resistant coatings such as those on upholstery and carpet. Exposure to these chemicals could result in changes in cholesterol, small changes to infant birth weight, changes to the immune system and changes in response to certain vaccines.
The SIX pilot program concluded in 2021 in Tampa and is no longer ongoing at the water treatment plant. Currently, the city is working on conducting bench-scale tests in a laboratory to better understand the removal capability of PFAS. “As stated, we know SIX removes organics well and organics must be removed before PFAS can be removed via media filtration, but we need more information regarding the direct removal of PFAS via the SIX process,” Burns described. “In short, we know that SIX is a necessary first stop for PFAS removal, but it may directly remove PFAS as well.”
The pilot program itself was a success, with no other difficulties beyond the typical challenges instituting a pilot program incurs. Results of the SIX pilot program showed improvements to overall finished water quality with an average reduction of over 50% of total organic carbon. There were also savings with operations and maintenance at the David L. Tippin Water Treatment Facility in each of the major processes, including reduced solids production, reduced coagulant demand, reduced ozone demand and higher filter throughput. This resulted in an operational savings of $1.4 million.
Currently, Tampa is in the design phase of negotiations for implementing SIX on a full scale. “SIX will be the first process in the treatment train after raw water is pumped in from the river,” Burns stated.
The plan is to break ground in 2028 and have the project completed in 2032. “SIX will benefit the community by improving water quality above and beyond state and federal regulations,” Burns emphasized. “It will also help us save operations and maintenance costs and improve the performance of the facility. Additionally, without SIX, the city would need to install additional filters to achieve the same capacity. The associated capital costs of additional filters exceed the cost of SIX, so there are capital savings as well. Savings are ultimately passed on to the ratepayer.”
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