RODI - hot water?

[Jay Hemdal Verified Community Expert]

All,

I make up five gallon batches of RODI through a 4 stage RODI unit that I put on my kitchen sink. Today, because my tap water is so cold, my throughput was abysmal....less than a gallon of product in 2 hours. Thinking I can outsmart it, I adjusted the tap to run warm. I then got two gallons in less than 30 minutes - success! Until I tested the TDS, it was at 5 and is usually zero. I turned the water back to cold to finish the batch. The TDS at the output then dropped to 2.

Do you think I damaged the membrane or the DI cart.?

Thanks,

Jay

 

[homer1475]

Hot water can damage the membrane.

Do you have a TDS reading post membrane before adding the hot water in?

 

[Asm481]

All,

I make up five gallon batches of RODI through a 4 stage RODI unit that I put on my kitchen sink. Today, because my tap water is so cold, my throughput was abysmal....less than a gallon of product in 2 hours. Thinking I can outsmart it, I adjusted the tap to run warm. I then got two gallons in less than 30 minutes - success! Until I tested the TDS, it was at 5 and is usually zero. I turned the water back to cold to finish the batch. The TDS at the output then dropped to 2.

Do you think I damaged the membrane or the DI cart.?

Thanks,

Jay

Membrane will melt at very low temperature.

 

[Jay Hemdal Verified Community Expert]

Membrane will melt at very low temperature.

The feed water temperature never went above 105.

Jay

 

[Jay Hemdal Verified Community Expert]

Hot water can damage the membrane.

Do you have a TDS reading post membrane before adding the hot water in?

No, last time I used it (2 months ago) it was producing 0 TDS.

Jay

 

[spsick]

You may have knocked some buildup loose.

Target temp for RO production is 70° F which requires a tempering valve and absolutely boosts production!

 

[FSP]

105F is getting close but shouldn't be enough to melt the membrane. The 2 month thing is a bigger issue due to microbes if it was left full of water.

 

[Gtinnel]

For most membranes 113 is the temp where the membrane will be damaged.
With warm water your rejection rate will go down while your production rate goes up, so with hotter water it could just be that it allowed more tds through and not that your membrane is damaged. I would expect if your membrane was damaged your tds would be considerably higher than 2 when you went back to cold water.
If your di is color changing does it look depleted, depending upon the tds of your permeate water you may have depleted your di.

 

[Sean Clark]

Pretty sure cold water is recommended for RODI and hot water is not recommended. I am not an expert as to what is cold and what is hot.

 

[punchy7080]

Hot water on the pressure side can also cause the tubing to burst (yes, had this happen at a customer location while filling his tank).

 

[Jay Hemdal Verified Community Expert]

For most membranes 113 is the temp where the membrane will be damaged.
With warm water your rejection rate will go down while your production rate goes up, so with hotter water it could just be that it allowed more tds through and not that your membrane is damaged. I would expect if your membrane was damaged your tds would be considerably higher than 2 when you went back to cold water.
If your di is color changing does it look depleted, depending upon the tds of your permeate water you may have depleted your di.

Thanks, the DI cart. still looks good, but that doesn't explain the 2 TDS getting through (although perhaps there was residual 5 TDS water in the system and I didn't wait long enough for it to flush out).


Jay