TDS and Water Temp RODI

[piranhaman00]

Hello,

The warmer the water, the higher the conductivity and thus higher the TdS per a conductivity meter. My tap reads 200 when cold and 320 when hot.

An RO unit works more effectively at Warmer temps. How does this increase temp affect the RO efficiency? The true TDS can’t be changing with temp, just the conductivity no? What temp should water be read with conductivity meter for true tds?

 

[Biglew11]

Do not run hot water through rodi unit. Tds of the tap water does fluctuate some with temperature.

Hot water dissolves minerals in your plumbing and hot water heater.

Rodi will produce more clean water the warmer it is so more efficient, but this clean water will contain higher tds, so not as effective.

When measuring tds of tap water measure the cold water of the tap.

Installing a booster pump and running 60-90 psi will increase the efficiency and the rejection rate (good).

 

[Reef.]

Hello,

The warmer the water, the higher the conductivity and thus higher the TdS per a conductivity meter. My tap reads 200 when cold and 320 when hot.

An RO unit works more effectively at Warmer temps. How does this increase temp affect the RO efficiency? The true TDS can’t be changing with temp, just the conductivity no? What temp should water be read with conductivity meter for true tds?

Have you tried letting the hot water go cold and then seeing what reading you get.

though best not use water from the hot tap in rodi systems as the water goes through a different path picking up who knows what...there is a reason we don’t like drinking from the bathroom tap, it just tastes different lol same for hot water.

 

[Randy Holmes-Farley]

Hello,

The warmer the water, the higher the conductivity and thus higher the TdS per a conductivity meter. My tap reads 200 when cold and 320 when hot.

An RO unit works more effectively at Warmer temps. How does this increase temp affect the RO efficiency? The true TDS can’t be changing with temp, just the conductivity no? What temp should water be read with conductivity meter for true tds?

The cheap TDS meters used in line in RO/DI systems are not temperature compensating. They will change conductivity by about 10.8% for each 5 deg C change.

There's a table (Table 1) here for various solutions:

http://www.jenway.com/adminimages/A02_001A_Effect_of_temperature_on_conductivity.pdf

 

[piranhaman00]

Do not run hot water through rodi unit. Tds of the tap water does fluctuate some with temperature.

Hot water dissolves minerals in your plumbing and hot water heater.

Rodi will produce more clean water the warmer it is so more efficient, but this clean water will contain higher tds, so not as effective.

When measuring tds of tap water measure the cold water of the tap.

Installing a booster pump and running 60-90 psi will increase the efficiency and the rejection rate (good).

I use about 80F water, 100F is the max for the membranes, this gives me great efficiency.

The bold is what I was looking for. So using warm water will give water faster but cold water will be lower in TDS thus extending life of system (DI).

Just installed booster pump, 65 to 90psi increase. This question came from initally seeing a great reduction in TDS but I think it was from the water temp I was using through the unit. Yesterday I was making 5gallons/20mins with the BRS 200gph which is 360gpd.

Have you tried letting the hot water go cold and then seeing what reading you get.

though best not use water from the hot tap in rodi systems as the water goes through a different path picking up who knows what...there is a reason we don’t like drinking from the bathroom tap, it just tastes different lol same for hot water.

No but I will, interesting thought.

I didnt think about the different piping, thank you.

The cheap TDS meters used in line in RO/DI systems are not temperature compensating. They will change conductivity by about 10.8% for each 5 deg C change.

There's a table (Table 1) here for various solutions:

http://www.jenway.com/adminimages/A02_001A_Effect_of_temperature_on_conductivity.pdf

Interesting, thank you.


What temp should the water be going through the RODI? Should I just be using cold water?

 

[Randy Holmes-Farley]

I use about 80F water, 100F is the max for the membranes, this gives me great efficiency.

The bold is what I was looking for. So using warm water will give water faster but cold water will be lower in TDS thus extending life of system (DI).

Just installed booster pump, 65 to 90psi increase. This question came from initally seeing a great reduction in TDS but I think it was from the water temp I was using through the unit. Yesterday I was making 5gallons/20mins with the BRS 200gph which is 360gpd.



No but I will, interesting thought.

I didnt think about the different piping, thank you.



Interesting, thank you.


What temp should the water be going through the RODI? Should I just be using cold water?

I would just use ordinary cold water line water.

 

[piranhaman00]

I would just use ordinary cold water line water.

Yes found alot more info on this, thank you!

 

[piranhaman00]

So using cold water instead of warm water lowered my TDS from 9 to 3ppm after RO. but also dropped my production by a lot, with booster pump at 90psi.

It would appear this is "common" knowledge, BRS has a nice video on it. I guess better late than never to learn

 

[Randy Holmes-Farley]

So using cold water instead of warm water lowered my TDS from 9 to 3ppm after RO. but also dropped my production by a lot, with booster pump at 90psi.

It would appear this is "common" knowledge, BRS has a nice video on it. I guess better late than never to learn

Yes, it is well known and understood.

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria by Randy Holmes-Farley - Reefkeeping.com

Various factors, such as temperature and pressure, impact not only the flow rate through the membrane but also the purity of the resulting water. Lower temperatures make the water more viscous and less likely to flow through the small pores, reducing the production of purified water. The effect of temperature on purity is much smaller, with purity decreasing slightly at higher temperatures. Higher line pressure across the RO membrane results in higher rates of production and quality, although a pressure that is too high can damage the membrane. Any backpressure on the effluent will degrade performance. Very high TDS (total dissolved solids) in the source water also leads to higher osmotic backpressure, reducing the membrane's effectiveness. As a rough guide, every 100 ppm of TDS produces 1 psi of osmotic backpressure.