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).
- Type 1 has the trimethylamine functionality on it. Unless properly cycled it may give off a fishy smell.
- Type 2 has a different amine, dimethylethanolamine, DMEA.
- Type 2 resin has much higher capacity and more efficient regeneration.
- Type 2 resin for industrial purposes may give off a plastic smell. This odor comes from trapped amine left from production.
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
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.
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. 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 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.
- All Organic Trap resins are anionic, and most organics exhibit anionic properties, making them removable by ion exchange. However, in most cases tannins 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.
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.
- Theoretically, the resin’s ability to dealkalize starves 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.
pH – 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
- Strong base anion resin (SBA) used for nitrate removal will remove alkalinity and could potentially form calcium carbonate scale on the resin and on wetted surfaces including valves. However, there is no need to soften water before a nitrate system until hardness exceeds 10 grains even if alkalinity is high. There won’t be enough hardness to form scale
- What happens when a customer has high hardness, 12-14 grains, and nitrates above allowable limits and this customer doesn’t want to buy a softener? How does the hardness affect the anion resin?
- As discussed above, calcium carbonate scale will deposit on the resin and wetted surfaces and impede flow.
- Drain lines may clog with the built-up scale.
- High heat areas such as water heaters or boilers will scale.
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
Residential Dealkalization for Reduction of pH
- For residential dealkalization a Type 2, WQA Gold Seal certified resin is required (Purolite A-300E). There is no residual odor because the resin is cycled with acid and caustic and rinsed with hot water.
- Softening is done to prevent calcium and magnesium based scales. There are two components in this scale, calcium and magnesium hardness, and alkalinity, which is bicarbonate alkalinity, HCO3-1.
- When you combine calcium (Ca+2) and the bicarbonate alkalinity (HCO3-1), calcium carbonate (CaCO3) is formed, and that’s the scale that you then form.
- By reducing one of those components, you reduce the potential for forming that calcium carbonate scale.
- Alkalinity can exist as bicarbonate, HCO3-1; it can exist as carbonate which is CO3-2 and it can also exist as hydroxide.
- In about 95 percent of the cases we face in home residential treatment, your alkalinity is primarily bicarbonate. It’s not carbonate, it’s not hydroxide.
- In some of the higher pH applications, where your pH is 8 and higher, you’re going to have some carbonate in there along with the bicarbonate.
- Applying an A300E type of strong base anion will remove that alkalinity from the water.
- One thing to keep in the back of your mind is that the resin wants to come into equilibrium with the water, which means it wants to have the same concentration of ions on the resin as it does in the water.
- High alkalinity – >200ppm in the water and your pH is up around 8 or so.
- The resin’s going to take out enough alkalinity to drop that pH maybe one unit. Leaving it in the neutral or above region. It’s not going to create a corrosive environment by dropping below 7.
- Low alkalinity – 50 to 100,
- The resin is going to remove all the alkalinity, so your pH is going to be 5, 5.5 or 6. If there is copper in the home you will begin to see blue stains.
- High alkalinity – >200ppm in the water and your pH is up around 8 or so.
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.
- Where there is low alkalinity pH equilibrium is difficult to attain.
- It takes a very, very long time for any kind of a pH rise to happen, because with every regeneration the process starts over again.
- An important factor in this is selectivity of the resin for specific ions.
- Cation Selectivity –
- In softening the cation resin has a greater selectivity for calcium and magnesium and would rather be on the resin than sodium.
- Calcium and magnesium bump the sodium off as it goes onto the resin, so your softened water is going to have an equivalent amount of sodium in the water to the hardness that is removed.
- Anion Selectivity –
- Like cation resin the selectivity for ions is a function of the atomic weight of the resin but also the valence. The selectivity for most anion resins goes as follows:
- Sulfate, which is divalent, is going to have a greater selectivity for the anion resin, than bicarbonate and chloride and nitrate, which are all monovalent.
- Once you start treating initially, the anion takes everything out. You’re taking sulfate, alkalinity, and nitrate out and exchanging for chloride.
- As time goes on, the sulfate being taking out is going to be bumping off the alkalinity as well as the nitrate that has been removed during the initial part of the run.
- Ultimately, as the resin gets closer to exhaustion, it’s going to be primarily in the sulfate form, but it’s really going to be in the form of in equilibrium with the water.
- But as a sulfate knocks off the alkalinity, you’re going to see pH start rising again. Unfortunately, that’s not going to happen until the end of the run, so you’re going to have to do something to combat that dealkalization from taking place.
- What we typically recommend is putting a neutralizer or some type of chemical pH control after the anion resin, to restore the pH.
- Selectivity of both cation and anion resins are important planning your ion exchange application. Selectivity for standard anions and cations are governed by valence and molecular weight of the ions you want to remove. The higher the valence the higher the selectivity and for equal valence the higher molecular weight ion will have the higher selectivity.
- In softening with a cation resin in Na form, the resin is more selective for divalent Ca and Mg, therefore the exchange for the monovalent Na on the resin. Since Ca has a higher molecular weight than Mg, the Ca has a greater affinity for the resin than Mg. The cation will have even higher selectivity for trivalent Al.
- In the case of dealkalization with strong base anion in the chloride form the same principals hold true. The selectivity is greatest for divalent So4 (sulfate) compared to NO3 (nitrate), HCO3 (bicarbonate alkalinity) and Cl (chloride). This is why chloride is exchanged from the anion by the other anions in the water
- Like cation resin the selectivity for ions is a function of the atomic weight of the resin but also the valence. The selectivity for most anion resins goes as follows:
- Cation Selectivity –
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
- Ion Exchange is used to prevent scale formation and control corrosion.
- Bicarbonate alkalinity and calcium magnesium hardness, when combined, will form calcium carbonate which will scale up industrial, commercial, and residential boilers.
- For industrial boilers you will want low hardness and alkalinity. This is accomplished by treating makeup with a softener and dealkalizer.
- Reducing alkalinity and hardness reduces the amount of boiler blow down so you don’t have to use as many chemicals for scale and corrosion control.
- There is a second benefit – if you don’t take bicarbonate alkalinity out from the boiler feed water, that alkalinity will flash off with the steam as carbon dioxide (CO2). When that steam condenses it is typically brought back to the boiler as condensate. The CO2 in the steam will condense as carbonic acid dropping the pH to an acidic, corrosive condition.
- How does a water treatment guy combat that carbonic acid that forms? More chemicals. They feed neutralizing amines to the boiler feed water, which also flash over with the steam to neutralize the carbonic acid when it forms in the condensate. The benefit from that is corrosion control. Without it, you’re going to corrode the piping, so you’re going to see copper and iron coming back in the condensate. And ultimately that’s going to go back into boiler feed water and back into the boiler, and you’re going to have copper and iron deposits in the boiler, which we want to avoid. Copper will cause pitting on boiler tubes and may ultimately lead to tube failure.
Determining Strong Base Anion Resin Capacity for Dealkalizers – Calculating Kilograins per Cubic Foot (KGr/ft3)
- Range is between 4 and 10 Kgr/ft3 or 4,000 and 10,000 grains/ft3. There are dealkalization capacity curves on specification sheets but it’s necessary to have a water analysis.
- The capacity of A300E or any type 2 anion resin for dealkalization is based on the percent of alkalinity of all the anions in the water. To determine you would need to know sulfate, alkalinity, nitrate, and chloride.
- For example, using a capacity curve, if you have 100 ppm total anions and 60 ppm is alkalinity, that’s probably going to give you about 8,000 grains per cubic foot.
- In an industrial environment if you add a little caustic to the brine you will get higher capacity. There are separate curves shown on the spec sheets for this. The caustic addition to the NaCl increases capacity about 10-15%.
- Adding extra salt doesn’t get you extra capacity – e.g., typically 5 pounds per cubic foot per regeneration is adequate. Bumping it up to 10 pounds does not increase capacity. Ditto for caustic. Adding more than a 0.25 pound of caustic per cubic foot will not increase capacity.
- The caustic is fed separately from the brine into the NaCl dilution water with a chemical feed pump.
- It is important to note that softened water should be used for brine make up. Otherwise, you will form calcium carbonate in the brine. This is especially important if you are using caustic.
Strong Base resin in the chloride form will not remove or reduce chlorides. They exchange chloride for alkalinity and contaminants (nitrate, TOC, etc.)
- Anion resin used in the home is regenerated with NaCl (salt).
- As water passes through any anion resin in the chloride form it is exchanging chloride for anions which have a greater affinity for the SBA – nitrate, sulfate, etc.
- When the resin is exhausted it is regenerated with 10% NaCl. The resin is overwhelmed by the high concentration of chlorides and the nitrates, sulfates etc. are exchanged off as the chloride goes back on the SBA exchange sites.
- If you have 450 ppm of chloride coming in, it’s going to increase to a much higher level, equivalent to the amount of sulfate, nitrate anions that you take out of the water.
- This same problem will occur if you are trying to reduce sulfates – SO4.
- Adding sodium carbonate into the brine tanks may reduce chloride but it’s not a real strong science so it’s not recommended.
- Membrane technology – Reverse Osmosis is the only practical way to reduce chlorides in residential water.
- Demineralization: A strong acid cation (SAC) in hydrogen (H) form followed by a strong base anion (SBA) resin in hydroxide (OH) form following will remove all ions including chloride but acid and caustic will be necessary for regeneration. This is not practical for home use.
- Mixed bed resin: A mixed bed composed of SBA in hydroxide form and SAC in H form will also remove all ions including chlorides however, as with demineralization it is not practical for home use.
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.)
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.
- Type II anion resin, which is also used for dealkalization and NON-selective nitrate removal.
Radium 226, 228
- Cation resin, which is also used for water softening.
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.