Troubleshooting an RO/DI system

A

alcmaeon

New member
Hey Folks

I have been running a RO/DI system for about a year now and I can't get 0 TDS. I also have the algae to prove it. I'm not here to slam the folks the system comes from; I just want to understand how to get to 0 TDS. I did communicate with the manufacturer with many emails where they gave me suggestions and we worked through all of the possibilities including replacement of all filter media (I'm on my third set of most of the filters, my fourth DI and my second RO membrane). However nothing worked.

I replaced everything including that last DI and the 2nd RO membrane on about April 1st.

I assume this is significant: I can get down to about 3-4 TDS when everything is fresh but very rapidly (couple weeks) that reading begins to climb.

The system is (in this order) a 10 micron sediment, 10 micron carbon, 5 micron carbon, 50 gpd RO membrane (Filmtec) and than a splitter sending one branch to the inline DI cartridge, the other branch goes to a drinking taste filter. Each branch has separate out lines.

I am measuring the TDS with a HM digital TDS and temp meter, which may not be the most precise meter but it should be giving a good baseline measured against its own previous performance.

So as of today, TDS is as follows:
Raw city water at 63 degrees Fahrenheit: 350ppm
Drinking water out line: 90ppm
DI outline: 79ppm
RO waste line 486 ppm

Again this is with every filter, the DI and RO all fresh on April 1st. The drain filter shoots out a healthy stream of water and when it is attached to the sink drain I can hear it gurgling away. The raw city water tends to range from about 350 to 390ppm.

The system is set up per the directions and double checked via email with the manufacturer. From everything I can find on this forum and all over the rest of the web this system should be working. However I am starting to think I am just throwing good money after bad. Is 350ppm all that hardcore? I donââ"šÂ¬Ã¢"žÂ¢t get stains in my toilets or sinks. Should I be replacing the sediment and carbon filters monthly? The manufacturer didnââ"šÂ¬Ã¢"žÂ¢t think so. Any add on components that might help?

Thoughts? Suggestions?
 
a guess: water is getting past the membrane and exhausting the DI resin really fast...
 
Can you think of a way to test that out?
I was trying and I couldn't. Lol, I am in need of sleep at the moment!

I do know that when I changed out the RO the last time I had to grip the membrane with pliers and pull it slowly out as my fingers were not strong enough. Which should indicate that the seals were strong. --and this is ongoing so the high TDS readings predate my using the pliers on the old membrane.
 
You definitely have water bypassing the membrane. There is absolutely no reason you should have an RO only TDS above 8 maximum if it is in fact a Filmyec membrane. My raw water averages 630 and my TDS never goes above 13 with RO only and my RO/DI is 0 for over 250 gallons per resin refill.
I would venture to guess your membrane is not sealed correctly. It could be a defective housing, seal or o-rings, or even a bad membrane.
 
Does carbon filter chloramine like it does chlorine? I can't remember. If the water supply has chloramine and it's getting through and degrading the membrane?

Just trying to brain storm here...
 
To effectively remove chloramines you need to use catalytic carbon in place of or in addition to carbon blocks. Normal carbon removes the chlorine portion but lets the ammonia through. RO membranes will not be destroyed by ammonia but they do not do a good job of removing it either, thats where the catalytic carbon comes in. www.purelyh2o.com among others sells catalytic carbon.
 
Thanks, I was actually just reading about that... Do you think it could be an issue for him?
 
No. I suspect a bad plastic casting on the RO housing or something similar that allows raw water past the membrane. A Filmtec RO membrane should be giving him 98% rejection for at least 2 years of very heavy use and 3 or 4 years or normal use without DI even. With his raw water TDS at 350, RO should be 7 TDS or less and a good large capacity vertical DI should last him 400 to 500 gallons before he sees a TDS of 1 or 2.
 
AZ Rat, as usual, is on the right track. One indication of membrane bypass is an low waste to permeate ratio. What is your ratio?

The other thing that sometimes is the culprit is that folks don't do a careful job of measuring the tds. Can you tell us how you're doing that?
 
alcmaeon,

I didn't catch this if it was already mentioned, but how well is your TDS meter working? Have you calibrated it? Do you have a friend with 0 tds that you could test your probe against?

Jack
 
Hey All

Thanks for putting your brains on this for me.

The chlorimane question is my first thought, tomorrow I will call the water company and find out what they are using. I had assumed it was chlorine but I will make sure.


Regarding the TDS meter, I have nobody close to check there water with it so I ran up to the little water store at our Safeway and got some purified water that they measured at 0 TDS right in front of me. Back my house the HM meter also measured the store water at 0. Yep, I know, time to upgrade TDS meters. At the same time it should be a good measure against its own past readings. The ratios I gave above are typical.

Unresistible: "One indication of membrane bypass is an low waste to permeate ratio" Lol, I don't even know what that means! Thats why I came to you guys though, for the education. What is it and how do I measure it?
 
And we may have a winner! Though it makes me unhappy that neither I nor the manufacturer managed to think up such an obvious and easy answer. Right after I posted the last response I went to our water districts website and found:

" ACWD began providing chloramination treatment to most of Fremont, Newark and Union City as part of its long-range water quality program."

I am in Fremont. So I will go that route and see what happens.

Thanks again everyone.
 
Chloramines probably still are not your problem. Yes you will not be removing all the ammonia but normal carbon will be removing the chlorine portion that could damage your membrane. You still have other issues. Even if you have chloramines the residual is going to be in the neighborhood of 0.5 to 1.0 mg/L which is much less than what you are seeing.
 
I like having you around AZDesertRat! I've learned a bunch in the past few days:) Thanks...
 
<a href=showthread.php?s=&postid=7364697#post7364697 target=_blank>Originally posted</a> by alcmaeon
Hey All

Unresistible: "One indication of membrane bypass is an low waste to permeate ratio" Lol, I don't even know what that means! Thats why I came to you guys though, for the education. What is it and how do I measure it?
Click to expand...

AzRat suggestted what you might be seeing it water bypassing the RO membrane in the RO housing. When that happens, unpurified water bypasses the membrane and finds its way to the purified water (permeate) port. So where you think you should be getting purified water, you may be getting a mix of purified water and unpurified water.

If this is the case, you may see a waste to permeate ratio that is lower than 4:1 - i.e., you're might have too much water coming out of the permeate port. What is the ratio of waste water to permeate on your system?
 
Pull the membrane out again and check the condition of the two rubber orings at the far end of the membrane.

Do you have the membrane installed with the brine seal near the end of the RO housing that unscrews?
 
i had the same problem with my RO. all it was "was a bad seat" as told by the customer service line i called. i pulled it out and put it back in and pushed REALLY HARD to properly seat it. The guy on the phone said it had to be 1/8 out further than the outer caseing on my Coralife. but anyway....i was blown away at how hard i had to push to seat the membrane. So....check clearances and push and seat! is my advice.
 
Actually :)

Actually :)

What this sounds like to me is a cracked housing.
From time to time when you insert the membrane into the housing the permeate slot will crack. This is an area where the molding seals together and unfortunately is the only thing separating the permeate from the concentrate (good water from bad) If this happens the two water flows are mixed together in the housing and you end up with the type of water you are getting. What you will need to do is remove the membrane housing and shine a flashlight into the shaft. You will see a round nipple. Look around the edges of the nipple for a crack. If you see a crack there replace the housing and you should be OK. If this proves not to be the case give me acall and we can troubleshoot the system. Good Luck!
 
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