Water Softener Resin Disinfection

Table of Contents

Is there bacterial growth that can occur in softener resins?

Water is amazing and the most valuable resource all living beings are gifted. There are so many varieties that exist in water. However, here we will discuss the biological organisms such as mold, bacteria, and algae, which has an excellent ability to attract resin beads. Surface water carries most algae and organisms due to sunlight and surface aeration. In groundwater, it has limited algae due to no sunlight and oxygen, but other bacteria can be consistent there.

While passing water that consists of bacteria and algae through a water softener, they tend to attach to the resin beads because it has a friendly environment for bacteria. Therefore, in some cases, bacterial growth can occur within the bed, resulting in physical fouling of the resin bed. Biofouling refers to the damage of resins due to biological growth.

When can we see bacterial growth in a water softener?

Two occasions can be identified which prepare a friendly environment for the bacteria in a water softener. When softener runs for long periods, there can be absorbent and accumulation of trace of organic matter, nitrates, and ammonia. These groups have microbial feeds, and with time, regeneration of resin beds can support microbial growth.

The other occasion is when water softeners are idle for a long time; months and years, it also acts as a good source of environment for the growth of microbes. In simple words, most problems with biofouling occur because of improper operation or inadequate storage measures.

If your resin is under one of the above two occasions, it will result in a large number of bacterial counts in effluent water than influent water in your water quality report.

What can we do to reduce the growth of bacteria in our softener?

Usually, microbial growth in water softeners is zero or reduced with the regeneration process with the salt or brine solution. Regeneration with acid or base also causes resin pH variations which act as a sanitization process. The normal regeneration process helps inactive microbes within the vessel. In some times, double regeneration may be able to restore resins to usable conditions. If not successful, there should be disinfection procedures to protect the resin bed.

There are several approaches for the disinfection of resin beds. 

What are the disinfection methods?

Within the industry, various types of sterilization methods are used to protect the resin from bacterial growth. The most common methods are,

  1. Disinfection with peracetic acid
  2. Disinfection with chlorine (bleach)
  3. Treatment with hot water
  4. Disinfection with hydrogen peroxide

Disinfection with peracetic acid

Peracetic acid is a highly biocidal oxidizer with strong efficiency in removing micro-organisms in both anion and cation resins. Peracetic acid act as an oxidant for preparing epoxy compounds, a bleaching agent, a sterilizing agent, and a polymerization catalyst for polyester resins in the food processing industry. 

Chemical contact time, dosage (concentration), and temperature should be controlled under certain conditions. Concentrated peracetic acid is hazardous, so it needs to handle with extreme care. There is a standard procedure to treat with acid, and always stick to the relevant procedure given by the supplier. This brief explanation will guide you to have a rough idea of peracetic acid usage in cation resin disinfection. Rinse the resin bed thoroughly with backwashing to remove accumulated debris as the initial step. You can pretreat with HCl if there is any metal contamination. Turn resins into exhausted form and drain the column. Then introduce 0.2% peracetic acid for 30-60 minutes, and thorough rinsing is needed until peracetic is zero within the vessel. Dead microbes need to be washed out with backwashing, regenerate, and again rise thoroughly.

Disinfection with Chlorine

Chlorine dosage for resin disinfection is an intensive method. Chlorine is available as Sodium hypochlorite or as bleach in the market. The sterilization process needs to be carefully controlled due to the high oxidizing ability of chlorine. It will be able to damage or break the Divinylbenzene (DVB) crosslinks in resins. So beads can swell and become mushy. Therefore, chlorine as a disinfectant, concentration, contact time, and temperature should be under comfortable levels. As usual, the procedure, backwash the resin with thorough air scour, pretreat with HCl to remove any metal contamination, and ensure to exhaust the resin with appropriate brine or caustic solution. Then pass 0.1% NaOCl solution downward with 30-40 contact time. Keep for soaking, then perform final rinse until chlorine is not detected in the effluent water. You must strictly adhere to the procedure given by the supplier to clean your water softener resin.

Treatment with Hot water or steam

Steam sterilization is perfect for removing bio residuals after treatment. It occurs no microbes with this step. You must be keen on the tolerance of the resins to the temperature of the steam. Most resins tolerate the water boiling temperature for a short term of period.

Disinfection with hydrogen peroxide

Hydrogen peroxide can use as a disinfectant and a resin cleaner. The most important point is that hydrogen peroxide does not damage ion exchange resins even at high concentrations. Hydrogen peroxide can decompose due to the availability of metal fouling. The reaction is exothermic, and the decomposition rate rapidly increases with elevated temperatures. Precautions need to be taken while using hydrogen peroxide due to runaway reactions and an explosive environment. It is better to prepare the solution lesser than 1%. All the vessels should be vented. Pretreatment is required with iron or metal fouling presence before using hydrogen peroxide. Always be concerned about the solution concentration, contact time period, and the resin environment’s temperature. Usually, start the procedure with backwashing. Treat with brine and consider the pH level to be larger than 6.5. Then release hydrogen peroxide in a sufficient volume with a 1% concentration to reduce the risks to the resin bed. Decomposition of hydrogen peroxide releases oxygen gas, significantly raising the pressure inside the vessel. Slowly pass the solution through the resin bed until 30 minutes. Increasing the contact time by at least one hour for complete sterilization is better. Finally, rinse the resin bed to eliminate all chemicals inside the bed.


  • The primary water source that you use for your water softener can contain lots of ions and microbes. Bacteria, mold, and algae have a remarkable ability to adhere to resins and enhance their generation within the resin beds.
  • Two main occasions can allow microbial growth inside the resin bed; A water softener that is not run for an extended period and a water softener with accumulated organic matters on resins due to long runs for many years.
  • Biofouling is not typically occurring with proper maintenance of the water softener. The regeneration process and backwashing processes prevent the media from bacterial impacts.
  • There are several ways to disinfect polymers. Using peracetic acid, Hydrogen peroxide, bleach, and steam.
  • Each chemical contains its advantages and disadvantages during sterilization. Chemical concentration, dosage, contact time, and ambient temperature are vital points of concern in disinfection procedures.


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