Why is a resin bed contaminated and how to sanitize it?
Ion exchange resin is susceptible to biological contamination by bacteria or algae. Said contamination notably affects the exchange capacity of the resin and the consumption of regenerant. When this occurs, the root of the problem is usually the feed water to the ion exchange column. When there are indications of biological contamination, it is important to consider preventive measures, such as installing ultraviolet light disinfection equipment at the entrance to the equipment.
If you already have a contaminated column, you can perform a complete system sanitization. However, it is very important to be clear that ion exchange resin is highly susceptible to oxidizing agents such as hydrogen peroxide or other agents used for disinfection of lines, sand filters or others.
The following are two procedures for sanitizing:
Peracetic acid, a derivative of hydrogen peroxide, is a good ally against a wide variety of microbes. Various researches on this subject have shown that peracetic acid is used to an increasing degree in the medical field due to its antibacterial, fungicidal, sporicidal and antiviral action. The work carried out by the Degussa Technical Applications Department, in conjunction with ChemiewerkHomburg AG determined that peracetic acid is suitable as a disinfectant for deionizers due to its broad attack spectrum. Using a 0.1% solution of peracetic acid in water with a reaction time of one hour, a concentration of mold and mildew of 104 – 105 / mL was reduced to almost zero. The short rinse time after using peracetic acid is important (typically 45 minutes or 10 – 15 bed volume, VL or BV in English, 1 BV = 1 liter per liter of resin).
Experiments have shown that in addition to excellent disinfecting action, peracetic acid has minimal effect on the ion exchange properties of cationic or anionic resins.
If peracetic acid is used as a disinfectant, the following procedure should be used for both cationic and anionic resins.
- Make sure the anion resins are completely depleted as peracetic acid works best at pH <8.
- Compose 1 BV of peracetic in an acid solution containing 0.1% peracetic acid.
- Inject 1 BV of disinfectant at a flow rate of 5 BV / h, with discharged displacement to an approved drain for the elimination of chemical residues.
- When all the peracetic acid has been injected, close all valves and retain the sanitizer for at least one hour to submerge the resin and tubing.
- Perform a displacement rinse using raw water for at least 60 minutes at 5 BV / hr, followed by a rapid flush for 30 minutes.
- Regenerate the resin once and return the unit to service.
Sodium hypochlorite is widely available in small carbohydrate and container form. For resin sterilization, a 0.1% chlorine solution should be used. This is achieved by diluting whatever commercial hypochlorite is available.
To prepare the treatment, the following procedures must be followed
- Regenerate the column with brine before treatment to convert all the resin to its spent form (a double or triple regeneration is sometimes necessary).
- Bear in mind that the cationic resin produces chlorine gas if it is not properly depleted before treatment.
- The minimum volume of solution required to treat the litter is 3 BV (ie 3 times the volume of resin installed in the unit).
- Pass the volume of the first bed through the bed at a normal regeneration flow, or approximately 4 BV / hr.
- Retain a portion of the volume of the second bed in the bed for no more than 2 hours.
- Pass the volume of the third bed through the bed at approximately 4 BV / hr.
- Displace the sodium hypochlorite at a rate of approximately 4 BV / h with softened water, then rinse well to remove any traces of sodium hypochlorite. At least 8-10 bed volumes are required.
- Perform a triple regeneration of the resin before returning to service.
Be aware that this form of treatment may break slightly below the cross-linked matrix of the resin. Frequent treatments are not recommended.
The procedure is also not recommended for phenolic and chelate resins.
For anionic resins, the oxidizing effect of sodium hypochlorite is in the amine groups, and therefore disinfection in sodium hypochlorite should only be considered in extreme cases in a specific way.
Proper safety precautions should always be taken when using sodium hypochlorite. In addition, all environmental laws and regulations must be followed for the discharge of waste into drains. All discharge areas must be free of acids or other chemicals that can react negatively with the hypochlorite dilution.
Purolite. (2015). APPLICATION GUIDE: Cleaning Methods for Fouled Ion Exchange Resins. USA