F W R J
Three Ion Exchange Technologies, One Tough Decision for Florida Utilities Tyler Smith, Chris Reinbold, Vinnie Hart, and Larry Elliott
O
ver the last decade, the ion exchange (IX) process has increasingly become a technology of interest for the removal of natural organic compounds in Florida source waters. Three IX options for municipal treatment plants include: S Fixed bed vessel, which is commonly used throughout Florida and the United States. S Fluidized bed, such as magnetic ion exchange (MIEX), which has seen limited use in Florida and the U.S. (about 12 installations). S Suspended ion exchange (SIX), which has four installations in Europe and is on the verge of its first U.S. installation in Tampa.
Considering Florida’s variability in source water composition and other site-specific considerations, one IX process does not fit all, and each type of IX should be evaluated, considering, among numerous other factors, a utility’s project goals, facility size, operation and maintenance (O&M) aspects, and costs. This article dives into the primary differences, similarities, and pros and cons for the three IX options so that Florida utilities can
consider the most optimal solution for their water quality challenges. Case studies from pilot- and full-scale installations across Florida, varying in size, capacity, and water quality characteristics, were considered. The MIEX is the only patented fluidized bed process (owned by IXOM Watercare Inc.) and uses a magnetized strong base anion exchange resin that is proprietary (the resin and process are both patented). The process was primarily developed to remove dissolved organic carbon (DOC) and the resin’s magnetic properties help facilitate settling (to avoid carryover to downstream processes). The MIEX resin has a mean particle size of 180 to 200 micrometers (µm). The small particle size and macroporous nature increases the available surface area, compared to traditional ion exchange resins. The MIEX process allows water and IX resin to flow through a contact tank with mixing, in which DOC and other negatively charged ions are exchanged for chloride ions. Figure 1 shows the general process flow of MIEX. Raw water flows upward from the bottom of the fluidized
Figure 1. Magnetic Ion Exchange General Process Flow Diagram (courtesy of IXOM Watercare Inc.)
62 July 2022 • Florida Water Resources Journal
Tyler Smith is senior project engineer with Carollo Engineers Inc. in Phoenix. Chris Reinbold is a project manager with Carollo Engineers Inc. in Palm Beach. Vinnie Hart is a project manager with Carollo Engineers Inc. in Denver. Larry Elliott was a vice president with Carollo Engineers Inc. in Orlando (deceased).
bed reactor/tank, where it’s contacted with resin. The resin ideally remains in suspension through the use of an agitator operating at low speeds. A series of tube settlers (or plates) at the top of the reactor vessel separate the resin from the water. Treated effluent overflows into collection launders to downstream treatment. The original treatment scheme had two stages (contact, followed by settling) with resin concentrations in the 10 to 15 milliliter (mL)/L range, while the newer “high rate” systems combine resin contact and settling in the same tank, with increased resin concentrations in the range of 200 to 250 mL/L. Virgin resin is added to the process to make up for quantities of resin that may be inadvertently carried downstream or lost to attrition. At any given time, a small portion of the resin is withdrawn from the reactor vessel, regenerated in semibatch configuration, and returned to the reactor for reuse. The MIEX has multiple full-scale and highrate installations in the U.S.; some of the larger installations include Palm Beach County Water Utilities Dept. (Water Treatment Plant 2; 16.4 mil gal per day [mgd]), Boynton Beach Utilities (20 mgd), and the C.B. Collier Water Treatment Plant in Gadsden, Ala. (24 mgd). Like the other IX technologies discussed, the resin itself has a high affinity for organics to facilitate their removal through ion exchange. In particular, the strong base anion exchange resin is effective at removing hydrophilics, humic substances, building blocks, and low-molecular-weight acids. For Palm Beach County, its full-scale MIEX process was able to reduce raw water total organic carbon (TOC) from 13 to 4 mg/L. A MIEX pilot study conducted for the City of Tampa showed reduction of TOC from 24 to 9 mg/L. Overall, the process has been proven for organics removal in Continued on page 64
