DI Stage for RODI system

[randoma]

I'm tired of re-packing my DI cartridges - I go through two standard 10" cartridges every 2-3 weeks. If I got a pair of 20" 'Big Blue' canisters, would there be any downside to running those full of resin? I was also thinking that it might be a little cheaper to add a third 10" canister and run 3 stage resin instead of the combined resin.

My main concern is water pressure - I have well water and use a small RO booster pump, but it only gets me to about 60psi before the RODI system. I haven't checked pressure on the output, but I expect it is pretty low. The RO system is only rated for 75gpd but I don't know if that makes any difference.

 

[tkeracer619]

I'm tired of re-packing my DI cartridges - I go through two standard 10" cartridges every 2-3 weeks. If I got a pair of 20" 'Big Blue' canisters, would there be any downside to running those full of resin? I was also thinking that it might be a little cheaper to add a third 10" canister and run 3 stage resin instead of the combined resin.

My main concern is water pressure - I have well water and use a small RO booster pump, but it only gets me to about 60psi before the RODI system. I haven't checked pressure on the output, but I expect it is pretty low. The RO system is only rated for 75gpd but I don't know if that makes any difference.

Let's get to the root of your problem instead of throwing DI at it.

Most RODI systems on well water have high levels of CO2 which exhaust DI resin rapidly. This is my first assumption on what is going on here.

There are a few ways to go about fixing this easily and cheaply. What most people do is fill a rubbermaid brute trashcan with the RO water, run a couple of airstones to degas the RO water of excess co2, and then gravity feed that RO water through your DI cartridges into a storage container.

Get a CO2 test kit and see what your well water is reading. My guess is this will resolve your issue and in the long run will save a lot of cash.

Your pressure situation is just fine.

 

[randoma]

Let's get to the root of your problem instead of throwing DI at it.

Most RODI systems on well water have high levels of CO2 which exhaust DI resin rapidly. This is my first assumption on what is going on here.

There are a few ways to go about fixing this easily and cheaply. What most people do is fill a rubbermaid brute trashcan with the RO water, run a couple of airstones to degas the RO water of excess co2, and then gravity feed that RO water through your DI cartridges into a storage container.

Get a CO2 test kit and see what your well water is reading. My guess is this will resolve your issue and in the long run will save a lot of cash.

Your pressure situation is just fine.

Thanks for the reply - I don't know that I'm exhausting resin particularly quickly - I'm making about 150-300 gallons per week, so I'm getting 450-900 gallons out of 2 10x2.5" resin canisters, which seems reasonable to me. My incoming water is ~3-400TDS, ~6-9 going into the DI, 0-1 coming out.

My question is if changing the DI canisters to ones that are nearly 4x the capacity will be too much for my water pressure, although I guess it is more a question of flow rate (haven't measured it, but it is pretty low). I guess a better way to put it - how much more backpressure is there with two 20"x4.5" canisters compared to two 10"x2.5"?

 

[tkeracer619]

A size 1 2.5in cartridge has a cross section surface area of 4.9 while a size 4 has 15.9. So my guess is a size 4 with the same media has about 40% less back pressure at any given cartridge length. Could be wrong though, never tested that.

I still think you should run a CO2 test. Could potentially double the life of the DI you currently have. Also, what membrane do you currently have? Looks like you're getting 98% rejection which is good. When it is time for a membrane change you should look at the spectrapure 99% membrane. Improving rejection, even at 1% would make a big difference. Each time you halve incoming tds into the DI you double it's life.

I get about 2000 gallons out of a single DI cart before it hits 1tds.

Before you go with the size 4 canisters, do the CO2 test. It could make a big difference.

One last thing, if you do go with two size 4 canisters use separate beds. Cation in the first, Anion in the second, and a mixed bed 10" cart for polishing as the 3rd. You can easily regenerate the separate bed carts.

 

[tkeracer619]

Also, I would use...

Cation - Resintech CG8-H (Hydrogen Form)
Anion - Resintech SBG1-OH (Hydroxide Form)
Mixed Bed - Resintech MBD-30

 

[randoma]

Also, I would use...

Cation - Resintech CG8-H (Hydrogen Form)
Anion - Resintech SBG1-OH (Hydroxide Form)
Mixed Bed - Resintech MBD-30

Thank you! Any recommendations for how to test CO2? BRS has a kit that costs $40..

I assume that there should be some way to tell by pH - water coming out of the RO should be ~7ph, but would be lower if there is substantial CO2, I think?

 

[tkeracer619]

Thank you! Any recommendations for how to test CO2? BRS has a kit that costs $40..

I assume that there should be some way to tell by pH - water coming out of the RO should be ~7ph, but would be lower if there is substantial CO2, I think?

You're welcome! I may have one at home you can have if I can find it. Just pay shipping...

 

[randoma]

You're welcome! I may have one at home you can have if I can find it. Just pay shipping...

How could I say no? Thanks!

 

[tkeracer619]

How could I say no? Thanks!

You're welcome!

Found it... I think it's brand new. All I ask is when you're done with it, and someone else needs it, you pass it on.

Shoot me a pm.

 

[Opus123]

If you are getting 9 out of the RO unit, then you should expect around 500 gallons of 0 tds water from a DI cartridge. So if you are getting a steady 9 out of the RO then you aren't that far off from normal DI usage.

 

[alton]

Here is a chart put out by spectrapure. I like your idea of using 20" containers. I use a 20" x 4" for removing high Chloramines.

 

[randoma]

Does anyone know if there is a minimum flow rate for DI cartridges?

 

[tkeracer619]

The lower the better.

 

[randoma]

Got the test kit - thank you, tkeracer! Sorry for taking so long to actually use it - I've been out of town.

At any rate, I get 14ppm CO2 before the DI cartridges. I didn't test after the cartridges. Assuming it is 0 CO2 after, the cartridges, I guess the CO2 is almost tripling the amount of work the DI cartridges are doing?

 

[tkeracer619]

Got the test kit - thank you, tkeracer! Sorry for taking so long to actually use it - I've been out of town.

At any rate, I get 14ppm CO2 before the DI cartridges. I didn't test after the cartridges. Assuming it is 0 CO2 after, the cartridges, I guess the CO2 is almost tripling the amount of work the DI cartridges are doing?

You're very welcome. Hopefully this will help you get this issue sorted...

Here is the formula to figure this out (roughly)

TDS+CO2=Total
CO2/Total=% Exhaustion from CO2

So...
7.5+14=21.5

14/21.5=.65

So basically 65% of your DI is being exhausted by just CO2. That sucks.

I would run the RO into a storage vat, degas it with an airstone, and let gravity pull it through your DI carts. You will probably get close to 1500-3000gal per your two DI carts.

Swap your membrane out to a spectrapure 99% membrane and I bet you get closer to the 3000gal mark. This is a better approach than throwing money at the issue.

 

[randoma]

You're very welcome. Hopefully this will help you get this issue sorted...

Here is the formula to figure this out (roughly)

TDS+CO2=Total
CO2/Total=% Exhaustion from CO2

So...
7.5+14=21.5

14/21.5=.65

So basically 65% of your DI is being exhausted by just CO2. That sucks.

I would run the RO into a storage vat, degas it with an airstone, and let gravity pull it through your DI carts. You will probably get close to 1500-3000gal per your two DI carts.

Swap your membrane out to a spectrapure 99% membrane and I bet you get closer to the 3000gal mark. This is a better approach than throwing money at the issue.

Yep.. That's about the ratio I came up with. Unfortunately I think my wife would kill me if I put another bucket of water in the kitchen/dining room.

It'll have to wait until we get the new house, which will hopefully be soon! (Of course, the new house may not have the same amount of CO2, although it is well water in the same general area...)

That said, I wonder if you couldn't run the water through a wine aerator or something similar.