Continuing in this series let’s talk about ion exchange resin (IXR). IXR is a staple of the water treatment industry and for the water engineer it serves as an effective tool for treating water for virtually every application imaginable. Much of IR is created from a plastic bead in which chemically active exchange sites are attached to the bead. The exchange sites enable one charged particle to be held on the bead with a less offensive charged particle being released into the water.
Water softening resin, for instance holds sodium ions, then in the presence of iron, calcium and magnesium, it releases sodium and holds (exchanges) the iron, calcium and magnesium. IXR comes in three forms. Cation, to remove positively charged ions, Anion, to remove negatively charged ions, and Mixed Bed, to remove both positive and negative ions.
In home water filters IXR presents a few challenges:
- Given the volume of water that can pass through a home filter, the capacity to remove contaminants is not high. Filters exhaust quickly, especially on tap water that has a lot of dissolved inorganic solids.
- When anion resin exhausts in the filter a fish-like odor is frequently given off. The smell comes from nitrogenous compounds called amines, and varies greatly dependent on the incoming water. THe odor can impregnate pitchers and create a lasting odor and even taste.
- The global demand for IXR is explosive, varied and often causes great delays in having orders filled. This fluctuating supply and demand makes it next to impossible for home water filter manufacturers to deliver a consistent, non-varying product. Indeed, one of the common complaints about current home water filters is that the capacity in terms of gallons per filter is not predictable or dependable.
- IXR products are largely plastic, and of a very small, spherical shape, with the size of a sand particle. They require hydrocarbons to manufacture and are not environmentally friendly.