Pure water system higher conductivity in loop 1

[mickawa]

Hello,

As in title, I would like to ask about the reason of higher conductivity of pure water in loop. After EDI device the conductivity is about 0.1 uS/cm, but in loop there is about 0.6uS/cm. The max value is 1.3 uS/cm in temp 25C, so there is no problem. In the other installation we have the similar situation, the conductivity is more or less 0.5 uS/cm higher in loop than just after EDI. In the third system there is the other manufacturer of pure water production device, but the same difference between conductivities. I need to add that in the first system there is no CO2 absorption bed before sterile filter so I thought that is the reason, but in the others installations we have the bed ( and it does not need exchange yet).

I have searched the reason in Net and guidlines and I found nothing clear.

Have You some idea why the water's conductivity in the loop is regulary higher than after the EDI system ?

I know my is english is weak, forgive me mistakes..

Best regards

 

[EdStainless]

Have you done a vacuum degas on a sample?
I suspect dissolved gases.
Perhaps analyze samples from both locations, but do you have a method with enough sensitivity?

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Plymouth Tube

 

[mickawa]

Hello,

I have checked the conductivity of the loop water in two systems after/before thermal sanitisation because of decreasing gas solubility in higher temperature. In fact, the conductivity decreases just after thermal conductivity, but after two days is as before. So you may be right suspecting gases.

I will try to degass and check. I will let you know.

Thanks. Regards.

 

[adirondackweldor]

I maintain a similar system to what you describe, and from our investigation of the same phenomenon, the mere fact of adding water to the PW storage tank on the distribution system will cause the conductivity to rise by a couple tenths. circulation in the distribution loop will cost a couple more tenths. I came to the conclusion (sans testing) that there is quite a bit of gas uptake during filling(we don't use any type of dip tube, it just drops from the nozzle into the tank), and at the liquid/gas interface of the water and head space in the tank. Add ozone sanitization via corona discharge, and oxygen concentrators, and you will get a couple more tenths. If you don't have steady water use, staying below 1 mS/cm can be a challenge.

 

[mickawa]

@Adirondackweldor,

I have a similar system as you described and agree it may be caused by a dissolved gas. I do not know what you mean by "steady water use".

Anyway, the value less than 1 uS/cm can be reached, in our systems the conductivity is about 0.5 uS, 0.4 or 0.7-0.8 uS without any special process. I mounted te CO2 absorption bed but there is no difference in conductivity before/after mounting. I found the concentration of CO2 in the air is about 0.1% v/v, so even without the absorption bed there should be not a strong rising conductivity.

But gases such as oxygen can caused the rising conductivity. If you take a sample of water ( in some open glass and measure you will see increase the conductivity comparison with the water in the loop.

Thanks for your answer.

 

[adirondackweldor]

The steady water use statement has to do with the fact that in the case of our system, if we just circulate water in the distribution loop, and don't use it for processing, I see a steady rise in conductivity over the course of days. I attribute this to our ozone generation system more than anything. CD ozone units are notorious for introducing nitrogen compounds that will play havoc with conductivity in pure water systems. Here is an example of what we found.

RODI skid discharge 0.10 mS/cm(inline)
PW storage tank feed 0.30 mS/cm (grab sample)
PW storage tank contents 0.40 mS/cm (grab sample)
Distribution loop w/o ozone 0.50 ms/cm (inline)
Distribution loop with ozone 0.70-0.90 mS/cm (inline)