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"Demineralization (Water Treatment) Problems"

A discussion started in 2000 but continuing through 2020


Q. I have a problem with a demineralization system. The conductivity of our pure water increase almost 6 times its value. We have tried to recycle the process several times, but the conductivity still higher. Other than regenerated the anion and cation exchanger, we can not find the problem.

My question is:

Do you think that CO2 can be also the problem or what else you recommend me to look for?

Lorena Ramos
Tampa, Florida


A. DI tanks start out at 8-12 meg ohm for tanks that platers use, up to 18 MOhm for lab use.

With use, they rapidly lose their ability to give that quality. As they get to loser and lower quality, the rate of decrease in quality slows down. This is just the nature of the beast.

If you think that you have a CO2 problem, take a reading on a beaker full and boil it for 5 minutes. Cover it and let it cool to original temp. If you have a CO2 problem, you will have better quality water when you take the second readings as you have eliminated the ion.

James Watts
- Navarre, Florida


A. What is the inlet/outlet conductivity of your water?

Is it possible your demineralizer is mechanically malfunctioning? Valves, flappers or chemical delivery system may not be working. Are you drawing the proper volume of chemicals during regen?

How old is your resin? The Anion could become organically fouled or silica fouled over time and may need to be cleaned or replaced.

If the pH of the water is down around 4 you may be seeing CO2 leakage. If it is above 8 you may be seeing Sodium leakage.

John Ring
- Whaton, Illinois, USA


A. Please check your degasifier equipment. If you don't have a degasifier then please to purchase one and fit it at the end after the anion exchanger.This would solve your problem of CO2. Then even if the problem persists use the modern resin conductivity sensor which gives you an output in digital format based on the resin exchange capability and the conductivity of the water.

Please respond about my suggestion.

Atmakury Harish
- Hyderabad, A,P, INDIA


Q. I would like to know the average, minimum and maximum service life of an ion exchanger resin (in general).

What's the frequency in replacing the resin? Annually?

How would you evaluate a resin if it's still functional or not by just merely looking at it? Or is it possible?

Dax Bracero
- Philippines


"I would like to know the average, minimum and maximum service life of an ion exchanger resin (in general)."
A. If your influent is normal quality water, resin may function efficiently +15 years. However, the life of resin depends upon many factors, oxidizing agents in influent may cause very short life.

"What's the frequency in replacing the resin? annually?"
A. You don't need to replace the resin if it is functioning properly. You may need to add some quantity if the resin is lost during backwash.

Mazhar Shah
- Karachi, Sindh, Pakistan

September 24, 2008

Q. Is there any effect if I put degasifier before and after the anion exchanger?
I often see some article that they put degasifier between cation exchanger and anion exchanger. Because degasifier can reduce anion exchanger load to exchange the anion content in the water.
I wish some suggestion for this question.
Thank you.

- Indonesia

April 29, 2009

Q. Sir, ours is a dm plant of 600 m3/hr capacity with 6 streams (cation, anion, mb).
Recently we faced a problem in one of our anion exchangers, i.e., after regeneration silica is not coming down, whereas pH and conductivity are normal (8.5 & 20 micro mho/cm)
Our CO2 inlet to anion exchanger is 17ppm. sodium from cation exchanger is 0.9 ppm?
What could be the reason?

azhagarasan veeraiyan
employee - india

October 3, 2019

Q. Recently While I have change my input feed to DM Plant I am facing issue of high turbidity, reddish brown water from Heat Recovery Steam Generator (300 °C, 16 kg/cm2).

My DM plant is designed with High Pressure Sand Filter, SBA, SAC and MB.

Input feed parameter are
Parameter Inlet Feed
pH 6.8-7.5
Turbidity <10 NTU
M.O Alkalinity as CaCO3 mg/l 80 mg/l
Total Cation/Anion as CaCO3 150 mg/l
(Na + K) as CaCO3 60 mg/l
Calcium hardness as CaCO3 60 mg/l
Total hardness as CaCO3 90 mg/l
Chlorides as Cl 25 mg/l
Sulphates as SO4 35 mg/l
Reactive silica as SiO2 45 mg/l
Colloidal silica as SiO2 Nil mg/l
Total iron + Mn 03-.05 mg/l
Total dissolved solids 150 mg/l
Other heavy metals <0.1 mg/l

Output DM water parameters like pH, Conductivity, silica are same as for previous source.

Kindly suggest the probable cause and/or specific parameters to be checked in system.

Sugat Mittal
- DIGBOI, Assam India

Folks: This is not a consulting service, but a mutual-help public forum. Please try to comment on one of the open questions when posting your own question lest the thread devolve to just a long list of unanswered questions :-)

MB outlet water total residues is very high 15 and conductivity in 0.3

March 17, 2020

Q. MB outlet water total residues is very high 15 and conductivity is 0.3
Total residues value less than 0.4
Please help.

damodharan thangamani
- Sankarapuram, India

March 2020

? Hi Damodharan. I haven't heard that phrase "total residues". Is it the same thing as TDS/total dissolved solids? What are the units? What do you mean the "value" is less than 0.4? Is 0,.4 your target? What are the units of your conductivity, micro mho/cm?


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Ted Mooney, P.E. RET
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