Anion Resin Applications

Anion resin is commonly integrated into water treatment systems to reduce tannin, nitrates or alkalinity.

Urbans Aqua stocks specialty anion resin for quick shipment.

Visit our PDF Library for technical specifications and product manuals on cation resins.

Visit our SDS Library for safety data sheets on cation resins.

In Stock Brands:

Thermax, ResinTech & Purolite

What is Anion Exchange Resin?

Anion exchange resin has a positively charged matrix with exchangeable negative ions (anions). Positively charged ions are fixed and permanently attached. Negatively charged replaceable ions, usually chloride, keep the resin electrically neutral. Because the bead is positively charged only negatively charged ions are attracted or exchanged. For water treatment purposes anion resin comes in the chloride form (Cl-) or hydroxide form (OH).

Anion resin is usually light in color. However, color variation among brands has no impact on its performance. For drinking water applications look for WQA Gold Seal certified products.

All anion resins are adversely impacted by chlorine – Dow Resins Recommended maximum free chlorine levels

Common Anion Resin Applications


Per- and polyfluoroalkyl substances (PFAS) are a group of man-made chemicals that includes PFOA, PFOS, GenX, and many other chemicals. To address this emerging contaminant Purolite has developed a new line of ion exchange resins.

Before selling a PFAS / PFOA system, get a complete water analysis, including TOC.

A properly designed PFAS reduction system should last longer and use less floor space than an equivalent activated carbon system.  This is especially true with larger flow rate applications.


Design & Installation


Organics Reduction (Tannins, Heme Iron)

Tannin, also referred to as TOC (total organic carbon) or as organics, is a catch all term to describe water which is not clear.  Organic substances can have complex molecular structures making their removal from domestic water supplies a difficult and sometimes frustrating challenge. However, specialized anion ion exchange resins can be used to adsorb organics, effectively removing their effect on water. TanninWater with Tannin water may have iron or color bodies in it. The color tainted water may come or go as it is seasonally affectedFor successful outcomes consultation with Urbans Aqua professionals is strongly suggested.


Organically Bound Iron (Heme Iron):

Testing is the first step to effectively treatment of water with tannins and heme iron.

Design & Installation of Systems for the Removal of Organics aka Tannins

 Ion exchange manufacturers have developed ion exchange resins that effectively and economically remove tannins. These resins are commonly referred to as organic traps (OT) or organic scavengers.

Organic Trap Systems – function and resemble the average domestic water softener.

Dual Bed Organic Trap Systems

Since flow rates in many homes are intermittent, the average home may only have a peak flow rate of 6 gpm at different times of day. Therefore, the average OT system may require no more than 1 cf of bed. In some situations, dealers forgo the expense of utilizing a separate OT system and make a dual-bed system by placing as little as one-third (1/3) of a cubic foot of OT resin on top of a cation bed.

Single Bed Organic Trap Systems

A dual bed is not recommended when iron is greater than 3 ppm.

Brine Cycle

The most important aspect of an OT system design is the brine cycle. Tannins, like most organics, take longer to elute off the resin bead.

Potential problems when using organic trap (tannin) resins:

Sulfur Like Odors – If customers are experiencing a sulfur-like odor exclusively from their hot water lines, the problem is most likely sulfate-reducing bacteria. By applying an OT system as a dual bed or as a separate system, the odor will be eliminated.

pH – Anion resins have weak dealkalizing capabilities.  If you have low alkalinity < 50 and TDS < 100 the pH of the water may drop a full point.  There is no easy fix for it.  Be sure to check pH as part of the pilot test. Depending on the result you may need to install an acid neutralizer, which would increase the pH but also the hardness, or a soda ash system to increase pH and avoid the increase in hardness.

Cleaning and Maintaining the Organic Trap Resin Bed

Resin fouling can be avoided with the periodic addition of resin cleaners. However, even the most carefully applied organic trap (OT) system may eventually foul.

If after several cleaning attempts the resin fails to perform, you should consider resin replacement or redesign of the conditioner and pay close attention to why the system fouled.


Although unseen, the incidence of nitrate contaminated water is rising because of past agricultural practices.


Used to reduce alkalinity. “Alkalinity is not the same as pH because water doesn’t not have to be strongly basic (high pH) to have high alkalinity.” (WQA Glossary of Terms Fourth Edition © 2000)

Residential Dealkalization for Reduction of pH

Regardless of which strong base anion resin is being used, knowing the alkalinity in addition to the pH is the only means of determining whether the anion resin will cause a significant drop in pH.

There are exceptions of course. In the case of nitrate select resins, that have a triethyl amine functionality, this amine is more selective for nitrate than it is sulfate. In this case nitrate sloughing will not occur as it will with standard anion resins.

Why Dealkalize Boiler Feed Water

Determining Strong Base Anion Resin Capacity for Dealkalizers – Calculating Kilograins per Cubic Foot (KGr/ft3)

Chloride Removal/Reduction

Strong Base resin in the chloride form will not remove or reduce chlorides. They exchange chloride for alkalinity and contaminants (nitrate, TOC, etc.)


Strong acid cation in the hydrogen form (H+) in combination with strong base anion (SBA) in the hydroxide form (OH), is most often used for demineralization processes such as portable exchange tank (PEDI) operations. In this case, the hydrogen is exchanged for calcium, magnesium and sodium. (For more information please refer to section on demineralization for portable DI exchange operations.)

Radiological Contaminants

Uranium and radium are very easily removed from water because they’re ionically sticky. They will adhere and accumulate on anion and cation resins during the treatment process.  If the system isn’t properly operated and maintained the radiologicals can accumulate resulting in harmful levels of radioactivity.


Radium 226, 228

Links to Resin Specifications & Engineering Bulletins:

Resin Anion Overview Dow Ion Exchange Resins Anion Resins Odor

Resin Anion Overview Dow Ion Exchange Resins Type 1 and Type 2 Strong Base Anion Resins Differences

Resin Overview Dealkalization & Anion SBA Purolite A300 Type 2 Gel

Resin Overview Dealkalization SBA Purolite A300E Type 2 Gel

Thermax Tulsion Anion A-32 Type 2 Gel

ResinTech Anion SBG2-HP Type 2 Gel

Resin Overview Nitrate Selective SBA Purolite A520E Type 1 Macro

ResinTech Select SIR-110-HP

Resin Overview Resin Anion SBA PFA400 Type 1 Gel

Resin Overview Anion SBA Purolite A400 Type 1 Gel

Resin Overview Anion SBA Purolite A-400OH Type 1 Gel

Resin Overview Tannin Reduction SBA Purolite A860 Polyacrylic Macro

Resin Overview Tannin Reduction SBA Purolite A502P Macro Type 1

Resin Overview Tannin Reduction SBA Purolite Tanex Type 1 Macro

Thermax Tulsion A-72 MP N Organics Reduction

Urbans Aqua is a stocking wholesaler of Residential & Commercial Water Treatment Equipment and supplies including Thermax, ResinTech & Purolite Ion Exchange Resin; Calgon & Jacobi Activated Carbon; Filterag Plus; GreensandPlus; Pyrolox Advantage; KDF; Birm; Sand/Gravel; Clack, Fleck & AqMatic valves; Stenner Pumps & Parts. 

We work exclusively with water treatment dealers.