|Ask the Experts|
July 9, 2020
Adding Chlorine to a DI (Deionization) Water System
We have had a recent issue of bacteria accumulation in our DI (Deionization) reservoir. In order to combat this we have put in a floater (similar to one found in swimming pools) containing chlorine tablets. Is this dangerous to use in our system? What limit should the chlorine levels be in the DI reservoir?
|Expert Panel Responses|
The addition of Cl to DI water fundamentally turns it back into city water. The fact you have a DI system would tend to indicate that you need DI! When events like yours occur you need to dump the system, bleach it, rinse thoroughly and start again with a new charge of DI.
Are you using a UV bug killer with your system? If not, you should investigate getting one, if you are, then either the bulb is broken or on its way out.
S T and S Testing and Analysis
Depending on the specific use for the DI water, it may not be necessary. I assume it's for process use, in which case the free chlorine in the water will drastically change the resistivity/conductivity readings of the water. This is due to the fact that the processed water has no buffer to speak of.
Depending on the amount consumed by the bacteria, there may be (probably will be) adequate amount left to initiate corrosion on any substrates cleaned or rinsed with it.
A simpler solution is to install an in-line UV light on the discharge side of the reservoir close to the point of use. This is a common practice to eliminate bacteria in a DI system. Your water consultant should be able to install this at the proper location with minimum down-time to your system.
I would like to caution you from using the DI water that is fine for swimming but very dangerous if you are using the DI water for cleaning of electronic assemblies, boards or components, or feed water for environmental chambers.
To remove the bacteria from the DI system I would recommend using UV light in the DI water loop to destroy the bacteria. I would be very concerned about the contamination of the DI water system that now will leach chlorine into the new clean water. I would ask what is the DI water used for and what quality were you expecting?
President/Senior Technical Consultant
Bacteria growth in DI water storage tanks is a common problem. It is sometimes necessary to clean out the bacteria through a sanitization process. A simple way to do that is to use bleach and allow it to soak for a time, followed by thorough rinsing with DI water to remove the bleach residues. Multiple rinses may be required to remove all of the bleach.
Using a pool chlorinator will have a similar effect on the bacteria as the chemicals in the chlorine tablets dissolve into the water. This causes the water to no longer be De-ionized because ions from the chlorine tablets have been intentionally added to the DI water. The purity of the DI water may be to low for the intended use. For example, the free chlorine in the DI water can potentially cause corrosion or dendritic growth if the DI water is used on circuit board assemblies.
It would be best to use the pool chlorinator only as long as necessary to clean the tank. Then perform thorough rinsing with DI water to remove the chlorine tablet chemicals. Once the DI water purity is back to normal, then it can be used normally.
My colleague Joe Russeau at Precision Analytical Labs(PAL) and myself recommend the following SOP to address bacteria issue:
VP of Advanced Technical Operations
I'm not too familiar with swimming pools and their chemical balance, however the addition of chlorine to the water being used to clean boards may be or should be of some concern.
With enough chlorine added to the system it could lead to an acidic condition which could dry on the boards and this would then create a condition that is susceptible to the absorption of moisture creating a conductive path across conductors which would enhance dendritic growth.
I would suggest getting touch with labs that specialize in the evaluation of cleanliness and have this conversation with them regarding chlorinated residues left behind due to this modified process.
Vice President, Technical Director
Chlorine works large water systems like swimming pools & potable water tanks. If you have a DI water tank and add Cl ion your water is no longer considered to be de-ionized.
Your case requires an expert service to determine the source of the bacteria. The bacteria could be lodged in the water line, or in the filters, or in any other component leading to the tank. The experts will be able to determine the way to remove the bacteria from your system.
Senior Manufacturing Engineer
We assume you're talking about a deionized reservoir for an aqueous cleaner. Adding chlorine will remove bacteria from the cleaner itself but not necessarily from the entire system including the piping and exchange tanks.
It is generally recommended to include an ultraviolet light source in the system since UV light inactivates microorganisms causing them to become sterile. Adding a UV light source in combination with adding chlorine is highly suggested to keep bacteria accumulation under control.
This is not recommended. You may as well just use tap water it would be safer. Most bactericides are chloride or bromine. Both halides are very ionic and will be conductive /corrosive with moisture.
Bacteria and fungus control is an issue in VOC free flux as well. I would suggest that you clean and purge your tank. Run a UV light in a recirculation circuit or place a UV light in the tank. This is dependent on the tank configuration. UV light has to be shielded as it can cause eye damage and other issues so consult a water UV specialist.
After this you will need to add a particulate filter on the exit of the tank.
Deck Street Consultants
If you're adding chlorine to the water after it is deionized, you've defeated the purpose of deionization. Chlorine is very ionic, and in fact is one of the primary soils you want to avoid in electronics. You don't want this in your DI supply.
If you have bacterial growth in the DI reservoir, the system may not be functioning as it should to begin with, since bacterial need nutrients, and deionized water has next to none. I'd take a two-pronged approach:
Just a note on the use of the UV light. If the water becomes stagnant, say the system is shut down for several days over a holiday or a plant shut down, the UV is not doing anything except to the water that is currently directly exposed. Any water in a holding tank or piping can still develop bacterial growth. It is a good idea to have the water circulating past the UV light 24/7.Alan Woodford, NeoTech
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