CO2 in well water using up DI resin?
 

Recently got a RODI from Bulk Reef Supply. 75 GPD with a sediment and carbon filters. I'm on a well and took a sample to work at the water plant I work at. Tested out very well, low Fe and Mn, hardness 20 ppm, ph about 6.3, alk about 20 ppm, did have 20 ppm Nitrates and some Phosphates in it as well, but I'd say it's very clean source water. I set up the RODI, and make a can of water and used up 1/2 of my DI Resin. Hokey smokes, this is gonna get expensive quick.

I reread all the instructions, read some stuff in Reefkeeping Mag to be sure I'm doing it right. Yep. But they pointed out that high CO2 will lower the ph and eat up the DI resin. It changes color with ph as well. Now what do I do? I do have plenty of caustic soda at work and can get hydrochloric acid to recharge it, but I'd really like to find a way to get it to last a while. My guess is I'll have to set up another container, buy a pump and let it gas off the CO2 before running it thru the RODI.

Any suggestions would be appreciated.

There are designs for degassing chambers in various places. You might contact one of the filter vendors. If carbon dioxide is the problem, that's about all you can do. Have you double-checked that pH? That's very low. I probably would try aerating a cup of water outside for a few hours, and see how much the pH rose. Also, 20 ppm nitrate is very high, and beyond the limits for drinking water, which would have me worried.

Kind of ironic, isn't it? There's typically a lot of CO2 in well water. It goes right thru the RO membrane like it isn't even there, uses up the ion exchange resin, and then we bubble CO2 back into the water in the calcium reactor to raise the alkalinity.

You could try the Kold Steril system, which would leave the calcium and CO2 intact.

In big commercial systems sodium hydroxide is injected into the RO feed to raise the pH, which causes the CO2 to change into bicarbonate and carbonate ions which are well rejected by the RO membrane. Another alternative are membrane contactors, where the water flows over tiny hollow fibers, which typically have a vacuum on one end and nitrogen fed into the other. The CO2 diffuses thru the fiber and out of the water. As you might guess, neither of these techniques is cheap.

At work we use membrane contactors to degas the RO water before it gets to the electrodeionization stacks. It took five years to get the system "tuned up" but it looks like we will be using about 90 cubic feet less of ion exchange resin this year, which should save about $18,000.

If I wasn't so far behind I'd post a few pictures.

To get back to the original question, if you have a pressurization pump for the RO, you could let the water sit in an open container for a few days, let the CO2 equilibrate with the surrounding air, and then run it thru the RO. As a bonus, the Fe++ or soluble iron, will oxidize to insoluble Fe+++ and settle out in the bottom of the tank, keeping it out of the RO membrane.

Let me know if you give that a try and if so, how it works out.

Can you confirm the tds is dropping across the RO membrane?

Just got back from a Georgia Rural Water Conference at Jekyll Island. First time I've been able to check your responses.

Yes I thought about removing the resin cartridge and checking the TDS of the RO system, to see how much is removed.

I checked the ph and the nitrates again as I first checked them when I moved here in Jan. we use a lot of water, which gets the well moving. Nitrates are down to 5 ppm, good deal. ph is 6.8 - 7.0 range. Still low. We don't have much if any limestone in our soils around here. They use crushed granite for gravel, rip rap etc. Very nice rock they call gravel. Imagine that. I grew up in Illinois with very hard water and limestone everywhere. We have to add Caustic Soda to the Alum to add alkalinity for the coagulation reaction. So I have very soft water with little buffer in it, along with low Fe and Mn.

PerdueWaterGuy, you bring me back to my first water operator classes. Oxidizing "ous" to "ic" to enable the coagulant to remove the Fe and Mn.

So now I get to find a way to engineer a system to remove the CO2. Either another trash can (I have 2 set up already, RODI and Saltwater) with a bubbler and a pump, or a degassing chamber. Something small would be better. Sounds like I have my work cut out for me.

Thank you all for your responses.

TheH and I have put together a calculator for that DI deletion from CO2. It needs the TDS, pH and Alk of the RO water out put.



http://www.hamzasreef.com/Contents/C...IDepletion.php


So now I get to find a way to engineer a system to remove the CO2.

Tap water ==> Caustic Soda solution ==> RO==> DI

CO2 + NaOH ===> HCO3- + Na+




RO to a degassing tube ===> output water to water pump == > DI

http://www.spectrapure.com/gifs/CO2_DIAGRAM.gif

There's another way to get rid of CO2 that might be easier. And you will probably kick yourself for not thinking of it sooner. :-)

How about an old wet/dry filter? Run the RO water over the bioballs or noodles or whatever, and blow a little extra air into the bottom and out the top. Collect the degassed water from the bottom of the filter and pump it thru your DI cartridge.

That technique is pretty common in industry to remove CO2 from water, but those of us in semiconductor and nanotech don't like it because it add can add TOC and bacteria. We prefer much more expensive methods :-)

Tim

This may fall into the category of being crazy, but what if you took the CO2 enriched air from the wet/dry gas stripper, and pumped it into the top of a refugium filled with your favorite macroalgae? Instead of having to breathe the extra CO2, the macro would suck it up instead. Might help replace the alkalinity the macro consumes. If the gas transfer to the water in the refugium was fast enough, you could run the now CO2 depleted air back to the stripper.

Dang. Where did the book with all of the gas transfer equations run off to?

With both of these methods, how do you maintain water pressure through the DI? I guess water pressure is not that important for DI but you still need something to force the water through it; is gravity sufficient for this?

I pulled the DI canister out last night to check the TDS of the RO by itself. Result is 7 TDS. Now I need to do it again, collect a sample, cap it off similar to getting a Dissolved Oxygen sample, and run to my water plant lab and check the ph and alkalinity. I ran an alk with my test kit and it showed Zero, but I might get a better reading titrating it at my lab.
I played with the CO2 calculator with various ph and alk levels. A little here or there makes a big difference. Most were at 50% to 90%. Not a good thing.

Then I get to engineer something to run overnight. Since I'm on a well, I do it at night when nobody is using water, to keep the pressure up.

My problem with some of the things I'm coming up with is I'm rather impatient. I have an auto shutoff for the RODI which works good when I make it at night.

I currently set the RODI in the laundry room next to the washing machine. A line runs to the garage right next to it with an elevated holding tank with 2 valves on it. One valve feeds the saltwater makeup tank, and the other for drawing off topoff water. The RODI has an auto shutoff on it which is great for making water at night. If it floods, it's in the garage keeping me out of trouble.

I could run the RO to can with the auto shutoff. Degass it. and pump it thru the DI to my holding tank. I just need to be able to shut the pump off when it's done. An auto top off maybe? My wheels are turning. Or set up a tank high up on the wall and let gravity run it thru the DI canister. Hey, no pump! I like that idea.

I have 3' of room above the storage tank. Would that give me enough head pressure for a DI canister? I'll have to experiment with it and see.

Yup, you are going to need something to push the water thru the DI cartridge. Either a small pump, or you might be able to raise the tank full of degassed water up a few feet and let the water gravity feed through. Depends on how much resistance the DI cartridge provides to flow. Until the government figures out how to tax it, gravity is free, I'd try that method first.

Well at least I know what the malfunction is. Think I'll keep it simple. Get another trash can, a bubbler, and a small pump. Move the float valve to the new one. And run it thru the DI canister to the RODI storage can. Just have to see how long it takes to run it thru so I can cut off the pump.

I filled a pitcher with RO water, put it in the fridge and tried it out the next day. Tasted real good. Also made coffee with it. I need to get some fittings so we can enjoy super clean water for drinking.

DOH!

I finally remembered something else that may or may not be of help:

Before vacuum degassing membranes got so cheap ($13,600 is cheap in the world of semiconductors) the big semiconductor fabs with CO2 problems used to put a bed of anion exchange resin between the RO and the mixed-bed (DI) resin. The anion resin would soak up the majority of the CO2, extending the life of the DI resin.

I suppose you could get a Kati-Ani, and put anion resin in both chambers, and put it between the RO and the DI cartridge. That way you could avoid more tanks, extra pumps, etc.

Keep us posted on your progress!

Tim

90 gallon tank waiting on remodelling at home
19,000 gallon per day RO at work

Two more things, most folks have water that is good enough quality that you can just run two anion cartrideges (as Spectrapure does in some systems) and let the RO membrane take care of the metals (it will). This efeecively gives you twice as much resin in the same size cartridge so they will last longer.

I have the same problem and and am saving my pennies to buy a Liquicell mini module (and a cheap aquarium air pump). If your CO2 is really high, it will pay for iteself in the long run.

Unfortunately, I don't have one yet so I can't say how well it will work, but after talking with them (and with Spectrapure), I am confident it will take care of the problem for me.

And, by the way, CO2 is especially problematic becasue for each molcule it takes up two active sites on the resin, unlike most contaminants which take up one exchange site.

DI resin and Co2
 

I went from 40gal per cartridge to all most 200 gal by degassing in a container with an air stone for 24 hours, then pumping the water through dual DI using aquatec 6800 RO booster pump from the filter guys, not the normal application for this pump, but with a little finagling it works wonders. I have less than $125.00 for the set up. Jim from the filter guys is familiar with my situation if you would like to contact him.

Depending upon how you set up the storage tank (if it is elevated or not), you could gavity feed through the DI, or you could probably use a pump as small as a maxijet 1200 or something similar to push the degassed RO water through a DI stage.

Russ

same problem here. what is diamater of pipe used in degassing units i have seen pictures of. could one be rigged using a 5 gallon bucket, or does it need to be something larger. i have 2 55 gallon drums i use for water storage. 1 for ro/di water & the other for saltmix. i have low tds from source water & get about 2 after membrane. im either going to set up something or just quit using d/i. i have dual di cartriges & 100 gallons wipes both of them out

+1

Thanks for a good read.

I'm on a well with high TDS, and just invested in a new, updated RO/DI from BRS.

I bought the 6 stage, with 2 stage DI, and a TDS monitor going into the DI, and out of the DI. Going In is about 10, Out is 0. So far so good...

I bought the color changing DI resin, and I noticed it was like woosh! Both filters are brown, in just about 100-150 gallons. The TDS is still reading between 1-0, though. I checked and rechecked, thinking I hooked something up all wrong.

Now I understand the problem is my source well water... :strange:

I also purchased the DIY repack yourself DI resin... At some point, it may just be cheaper for me to buy from a local LFS.

I just wiped out another canister of resin making about 30 gals of water. Working this weekend (Fri - Mon) but next week I want to get another trash can, a pump and a bubbler. Thanks guys.

Just purchased a new home with well water. Burning through DI resin after about 100 gallons. Will be making a degassing chamber this weekend.

Please let us know how much it helps!

setup a large vat with 2 air stones and let it "off gas" for 24-48 hours. I have gotten about 600 gallons out of my single state DI resin so far with only a little changing color.

That's a big improvement. So you've got a factor of 6 so far. Interesting. Thanks for the data.

I want to run something by you guys. I currently have a degassifier setup for my ro/di which has significantly extended the life of my DI resin. Only problem is i get bacterial growth in my degas. chamber which over the course of 50 gallons or so clogs up my resin and my maxijet can't push it through the resin.

I end up having to clean out my degassifier and change out my resin which isnt depleted far too often.

I regenerate my resin, so its not that bad on cost, just a pain in the butt.

Im thinking of going straight from my RO to cation-->anion-->mixed bed, thinking the co2 will deplete the anion resin quickly. But i can easily regenerate a bunch of anion resin at a time. The worst part about regenerating resin is separating it as you have to do it with caustic and then rinse the cation before adding the acid. Would be simple if i didnt have to separate.

Any thoughts? Am i correct in the CO2 will not use up the cation resin?

You could try that. The carbon dioxide should not consume the cation resin, as you stated. Buying the resin in bulk might save enough money that you don't need to regenerate, but that's a personal choice.