Ion exchange resins contains the traces of nitrates and ammonia that are organic matter and are good feed for microbes hence ion exchange units that are used for longer period of time can be good supportive ground for microbes generation. Also if any ion exchange is left unused for longer period of time, they can also become the good breeding ground of microorganism. Hence, to prevent the resin bed it must be sterilized first.
When demineralizer resin are regenerated with acid or caustic then resins come under the influence of high pH which sanitized the resins to a certain extent. However, if regeneration is done by using salt brine there is very little effect on bacteria. For sterilizing ion exchange resin, some other methods like Steam or Hot Water Sterilization is also used that hardly leaves any remains one of the most effective methods, and the process leaves little or no residual in the resin after treatment. When using these techniques one should make sure that equipment is well designed to tolerate the high temperature.
Chlorine residual in a feed water if left to the resin bed then there will be no problem of biological fouling. But one should take care that resins should not be exposed to oxidants for longer time as it may degrade ion exchange resin.
.Bleaching:
Bleaching is an easy and an inexpensive method for treating resin bed. Exposure to chlorine for short duration makes no harm or to the resin bed. However, some damage do occur hence precaution is needed.
The steps below outline the proper use of bleach to sterilize resin.
Resin column should be backwashed in a normal manner. For cation type resin bleach should be used in hydrogen form. PH of the effluent should be checked properly before adding any bleach. To prevent possible chlorine fumes from forming the pH must be greater than 6.5.
Add the bleach directly in brine tank and pump through the exchanger as a part of the normal brine injection step of regeneration. For Sterilization to be complete and effective, resin and bleach should remain in contact with each other for longer time. The resin, finally should be rinsed properly to remove any disinfection by products that may have formed prior to return to service.
Sterilization by Hydrogen Per Oxide:
Resin can also be sterilized using hydrogen per oxide. Even at higher concentration it does not damage the resin. Hydrogen peroxide can also be used to sterilize resin. However, hydrogen peroxide decomposes due to iron fouling. As the temperature rises this decomposition increased. This can result in faster reaction and may reach to an explosive point.
There are certain precautions that are required before the use of hydrogen peroxide. While using hydrogen peroxide concentration should be kept low. There should be a vent in the tank and it should never be left unattended. The contact of hydrogen peroxide and resin should not last for more than one hour. Iron fouled resin should be well treated before the use of hydrogen peroxide.
Resin Sterilization by Other Oxidant:
For sterilizing resin, apart from chlorine and hydrogen peroxide other oxidants like ozone, potassium permanganate, iodine etc are also used. These oxidants are not only effective but are also safe. Some of the organic biocides are also available that can be used effectively.