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.
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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 or NSF certified products.
All anion resins are adversely impacted by chlorine – Dow Resins Recommended maximum free chlorine levels
Common Anion Resin Applications
PFAS – PFOA, PFOS & genX
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.
- Purolite A592E (residential grade) Purolite A592E
- Purolite A694E (commercial and industrial grade) Purolite PFA694E
According to Purolite, 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.
- Takes up less floor space.
- Extended life
- The Empty bed Contact Times (EBCT) for the resin is 3 minutes vs activated carbon at 7 minutes.
Design & Installation
- Since this is an Ion Exchange product, it is imperative to test for competing ions. PFAS Removal Information Needed for Capacity Rating+System Design
- All carbon and resin tanks should be plumbed in a downflow
- All installations should include a 5-micron prefilter.
- Two treatment vessels plumbed in a lead lag configuration.
- Sample ports located before, between and after the treatment tanks.
- A totalizing water meter to tally total gallons used is recommended when possible.
- Post treatment with a small carbon filter to reduce residual resin odors.
- Purolite A592E resin is non-regenerable and for single use only.
- Proper disposal of activated carbon and resin used to treat for PFAS is always important.
- Small amounts of residential POE resins can be disposed of in the regular trash stream but check with your local authority first.
- Commercially, large amounts of the spent resin can be incinerated by an approved waste hauler.
Tannin, also referred to as TOC (total organic carbon), 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. Tannin water may have iron or color bodies in it. The color tainted water may come or go as it is seasonally affected. For successful outcomes consultation with Urbans Aqua professionals is strongly suggested.
- Tannin types vary by geography. For this reason Urbans Aqua stocks a variety of Purolite anion resins.
- Large molecular weight compounds, use macroporous type 1 anion resin.
- Organic substances, especially tannins and organically bound iron, are found in almost all water supplies.
- Two primary categories of tannin or organics: Humic & Fulvic Acids
- Color of tannin water varies from yellow to dark tea color.
- Organics have a slight negative charge so they react with anion by exchanging chloride. There will be an increase in chlorides, which have a secondary drinking water standard of 250 ppm.
- To avoid fishy odor, use potable grade, rinsed anion resin. The fishy odor from anion resin, especially in the hydroxide (OH) form is due to the release of amines from the resin. Dow Resins Anion Resins Odor
- Regenerate frequently @ 8-10 lbs. per cubic foot to reduce organic fouling of resin.
- Cation for softening and anion resin for tannin reduction can be mixed in one tank to save space. Keep in mind the following:
- Calcium carbonate precipitation may occur.
- Backwash rates for cation and anion are different 5 gpm per sq.ft. vs 2 gpm per sq.ft.
- Use upper screen to prevent resin loss.
- Pre-treat with activated carbon if chlorine levels are high. Chloramine and chlorine will cause breakdown of the resin and increase likelihood of amine (fishy) odor.
- Anion resin will remove alkalinity and the pH will be suppressed during the service cycle. pH adjustment may be required.
- Tannins are a byproduct of decayed vegetation. Decayed plant and animal matter produce humic and fulvic acids.
- Tannins are most prevalent in coastal or low-lying marshy areas. Their presence contributes to a range of color in water from yellow to tea-stain
- Although not a health risk, tannins are aesthetically unpleasing in a water supply. Their yellow color can stain clothing, cause odor in the hot water lines.
- Tannins may contribute to the formation of disinfection byproducts, such as trihalomethanes (THMs), in chlorinated water supplies.
Organically Bound Iron (Heme Iron):
- Iron can complex with organics to produce organically bound or heme iron.
- Heme iron’s presence in water can range from clear to light pink.
- Heme iron is a particularly frustrating substance due to the fact that it masquerades as iron and cannot be removed with conventional oxidation media or cation exchange softeners. This is because the organic binds and encapsulates the iron, effectively altering its ionic properties.
Testing is the first step to effectively treatment of water with tannins and heme iron.
- They are possibly the most difficult contaminants to accurately measure, partly because they fluctuate in concentrations, depending on conditions, such as droughts, floods or seasonal variations and demands on the source water supply.
- Tannin test kits are available from many suppliers.
- A heme iron test kit may be more difficult to obtain. Also, heme iron usually is found in concentrations less than 1 part per million (ppm), making it even more difficult to measure.
- A more comprehensive test is measuring total organic carbon (TOC), which is highly recommended for high-purity applications.
- Most organic test results are expressed in ppm.
- Due to the complex nature of tannin and heme iron, dealers should find several test applications, commonly referred to as pilot studies, in their geographical location. This is the only practical method to determine the best-suited OT resin for your selling territory.
Design & Installation
Ion exchange manufacturers have developed ion exchange resins that effectively and economically remove organics. These resins are commonly referred to as organic traps (OT) or organic scavengers.
- All Organic Trap resins are anionic, and most organics exhibit anionic properties, making them removable by ion exchange. However, in most cases organics are actually adsorbed and desorbed from the resin bead.
- The adsorb/desorb function is more a mechanical process than an ion exchange process. Picture each resin bead as a tiny sponge. As it scavenges organic molecules from the water, the bead swells. When brine is introduced, the resin bead contracts, squeezing the organic out of the bead. Some resins are spongier than others.
- An Organic Trap resin’s capacity is a function of its water retention – the higher the water retention, the higher the capacity.
- Most organic trap resins range from 55 to 64 percent water retention.
- Some high- capacity OT resins are designed with as much as 75% water retention, making them the best performers. Organic Trap resins designed with high water retention sacrifice bead integrity. To obtain high water retention, manufacturers must design resins with lower crosslinking, which is the internal structure that gives resins their strength.
- Unfortunately, the highest-capacity Organic Scavenger resin will ultimately have a shorter life span. Moreover, high-water-retention resins are the most expensive, in some cases costing 50 percent more than standard-capacity OT resins.
Organic Trap Systems – function and resemble the average domestic water softener.
- Choose a quality control valve, which enables you to program the regeneration cycle times.
- Most resin manufacturers recommend design service flow rates of 1 to 4 gallons per minute per cubic foot (gpm/cf). This may be a bit conservative but use common sense when sizing and estimating the service requirements of your application.
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.
- A dual-bed system is possible because OT resins are much lighter than cation resins and will remain at the top of the bed.
- When using a dual bed, the raw water hardness should not exceed 15 grains per gallon and alkalinity should not exceed 250 ppm. High levels of hardness can produce a bicarbonate precipitate that will coat the cation resin, rendering it useless.
- In an upflow brining system, the precipitate will form on the upper screen and control valves, possibly reducing water flow.
Single Bed Organic Trap Systems
A dual bed is not recommended when iron is greater than 3 ppm.
- A single organic trap system should be placed after the water softener and iron removal systems.
- pH values greater than 8.0 should be avoided because OT resins perform better in a slightly acidic environment.
- In any system design, an upper distributor screen is recommended to prevent backwashing the resin to drain, especially if you are using OT in a dual bed.
- OT resins range from 16 to 50 mesh. Choose a distributor screen with a .010-.013 slot size (the industry standard).
- A gravel underbedding is also recommended to help distribution and flow rates. Use 1/4”x1/8” or 1/16”x1/8” gravel.
The most important aspect of an OT system design is the brine cycle. Most organics like tannins take much longer to elute off the resin bead.
- The minimum duration that brine should dwell in the bed is 30 minutes.
- No more than 10 pounds of salt are required to regenerate 1 cubic foot of OT resin.
- OT resins require frequent brining (no less than every three days), so avoid demand-regenerated control valves.
- If possible, program the brine cycle to “stall” 20 minutes into the cycle. This will give the brine a chance to elute the organics off the resin. In some systems, brine stalling is impossible or unnecessary, but it is recommended if it can be incorporated into your system.
- Use the smallest injector possible. A small injector will allow the brine to dwell longer within the resin bed.
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.
- Theoretically, the OT’s ability to dealkalize will starve the bacteria of its meal of sulfates, eliminating the sulfur smell produced in the water.
- Remember, this works only when odor is detected in the hot water.
Anion resins have weak dealkalizing capabilities. If you have low alkalinity, < 50 and low 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.
- The return of color in the conditioned water is the best indication of a fouled resin bed.
- The restoration of a fouled bed is achieved by using commercially available resin cleaners such as phosphoric or citric acids.
- All cleaners should be applied as a warm solution (not to exceed 95 degrees Fahrenheit). The conditioner should be regenerated once before applying resin cleaners.
- When applying the warm acid solution (one pound per cubic foot), periodically check the pH of the drain line.
- When a significant decrease is measured, bypass the system, and allow the solution to soak for a minimum of two to three hours. This should allow enough time for the acid to elute the foulants out of the resin beads.
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.
- The EPA maximum contaminant level (MCL) for nitrate is 10 mg/L as N; maximum contaminant lever set for nitrite is 1.0 mg/L as N.
- Use of a Point of Use (POU) filter is not adequate protection against Nitrate/Nitrite contamination. The USEPA recommends a point of entry (POE) or whole house system.
- Nitrates seriously affect infants- Methemoglobinemia (blue baby syndrome).
- A type 1 or 2 chloride form anion will address the problem broadly and is commonly used by municipalities who carefully monitor effluent. Effectiveness is subject to competing sulfates.
- Nitrate selective resins were developed for applications where there is a high sulfate to nitrate ratio. To assure a successful outcome, use of a nitrate selective resin is strongly recommended.
- Urbans Aqua stocks Purolite A-520E. A520E Bulletin – Nitrate Selective
- Nitrate removal systems are always metered, demand type to monitor water usage.
- Conservatively rate nitrate selective resin at 7,000-10,000 grains. This is based on the ratio of nitrates to nitrates plus sulfates.
- Nitrate resins are sold in the chloride form and regenerated with brine.
- Resin Anion 2014 Nitrate Nitrite Fact Sheet
- Click here for national data on nitrate occurrence from the U.S. Geological Survey. USGS – Nitrates
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)
- Alkalinity is a measure of how much acid can be added to the water without affecting pH.
- Alkalinity may consist of bicarbonate alkalinity, carbonate alkalinity and when pH is more than 8.3 hydroxide alkalinity.
- Dealkalization removes bicarbonate alkalinity, carbonate alkalinity and when pH is more than 8.3 hydroxide alkalinity.
- In water test results alkalinity is stated as “bicarbonate alkalinity” and “carbonate alkalinity”.
- Alkalinity is measured by the quantity of standard sulfuric acid to bring the pH to 4.5. Simply put, how many drops of sulfuric does it take to reduce the pH to 4.5. This drop test is converted to an alkalinity measurement. This is like the drop test used for hard water where each drop indicates a level of hardness.
- Typically, in well water with a pH below 8 there will be bicarbonate alkalinity.
- Type 2 Anion resin in the chloride form is used to dealkalize water. The chloride is exchanged for bicarbonate, carbonate and other anions present in the water. Like a water softener a dealkalizer is regenerated with salt.
- To get extra capacity for bicarbonate removal caustic can be added to the brine regenerate.
- To avoid fishy odor, use potable grade, rinsed anion resin.
- Urbans Aqua stocks Purolite A-300E. A300E Bulletin
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.)
Links to Resin Specifications & Engineering Bulletins:
Urbans Aqua is a stocking wholesaler of Residential & Commercial Water Treatment Equipment and supplies including 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.