RODI issues-high resin and membrane use

Tony44

Amphipod
M.A.S.C Club Member
#1
I have a 150 gpd unit from BRS. My usage of membranes and DI resin are excessive at least according to the recommendations I have seen. Also my TDS from the RO unit to the DI unit seems high, currently 25, I believe they should be in single digits. The membranes were changed in Jan, they had lasted 5 months, my reading were even higher than 25, the sediment filter in March and the carbons in Feb. I typically change the sediment filter each month and the carbons every two months. The DI resin is expired in 30 days. I changed it when the TDS reads 2 on the output. I am on well water here in Elizabeth and have a whole house filter system consisting of 2 sediment filters changed each month and 1 carbon filter 20" changed every 2 months. Recently I checked the TDS at the kitchen and got 168 which I thought was pretty good. This would be water going thru the whole house filters and also feeds the RODI unit. I don't know my water pressure but believe that is high or at least normal considering the force it comes out of the faucet. My think is that if I could get the TDS down going to the DI resin that would solve the high resin use. My other thought is to slow down the flow from the main to the RO unit with a restrictor to say 50 gpd or replace the current restrictor in the lines to the membranes to something like 50 gpd. Anyone else had this problem and have a solution ?
 

jahmic

Reef Shark
M.A.S.C Club Member
#2
What micron size is your sediment and carbon filter on the RO/DI? I recently stepped down in size on my sediment filter to reduce the TDS that was hitting my membrane. Nothing to report yet, but I also noticed I was going through my membrane and DI resin fairly quickly...and my TDS out of the tap ranges from about 65 - 175 depending on the time of year.

Are you flushing your membrane? After replacing my last membrane in a year and blowing through DI resin monthly...I started religiously flushing the membrane after every use. Doing so removes any sediment that could sit there and otherwise damage the membrane. The flush kit is an easy install and should be available on BRS.

I had been purchasing this kit:

http://www.bulkreefsupply.com/brs-4-stage-ro-di-replacement-filter-kit.html

IMO the 5 micron sediment filter followed by a 5 micron carbon block was working the membrane too hard. I now use a 1 micron sediment and am willing to bet my membrane lasts a bit longer this time around.

You should also check your TDS before and after your membrane to confirm that the decrease you see matches the rejection rate of the membrane...if it does not, then your membrane is bad.
 

that0neguy1126

Registered Users
M.A.S.C Club Member
#3
One thing to realize is the 150GPD systems are not very efficient. The 75GPD membranes are normally much more efficient.

Also, what was the output of your RO? 25? That is really really high and would be the reason you burn through DI resin. I would change out the RO filter for a 75 GPD (and change the restrictor as well) and see if that changes anything.
 

Tony44

Amphipod
M.A.S.C Club Member
#4
Thanks for the ideas, the 1 micron sediment seems like a great idea I currently use a 5 micron w/ carbons at 5 micron and .6 micron. This unit has two membranes the part no for Dow Filmtec is TW60-1812-75. It came with TW30-1812-75 but these don't seem to be available anymore. I'll see about getting a 75 gpd restrictor and change out the existing one. The existing restrictor has the number 550 on it whatever that means.
 

jahmic

Reef Shark
M.A.S.C Club Member
#6
http://www.bulkreefsupply.com/instructions/article/Changing-the-flow-restrictor-on-your-membrane

I run the 550 restrictor on my 75gpd membrane as well. It sounds like you are running dual membranes though to get the 150gpd, correct? If so...I'm not sure how that really works as far as what restrictor you need to place inline to get them to function properly...but hopefully someone else can chime in. The 150gpd membranes usually use an inline restrictor instead (see link)...but again, not sure which you really need for 2 membranes.

All that being said...water pressure is likely an issue if you have 2 membranes running. It's my understanding that most people actually need a booster pump to run dual membranes and double their production; you may not be getting enough pressure for your membranes to function properly...especially if that restrictor is not the correct one for your application (not sure on that last bit though).
 
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Tony44

Amphipod
M.A.S.C Club Member
#7
I am running dual membranes to get the 150 gpd. I had also thought that I might have a pressure problem with two membranes. The flow restrictor is in the line to the second membrane and also ties into the flush system. This system is what BRS supplied I have not so far any way changed anything. I wonder if I disconnect one of the membranes and reduce the capacity of the system to I suppose 75 gpd which would be plenty that might solve my problem?
 

jahmic

Reef Shark
M.A.S.C Club Member
#8
That was going to be my next suggestion. I think your membrane may work more efficiently at the correct pressure...as long as it's still good you should see a decrease in the TDS output just after the membrane. The numbers that you are seeing now don't seem to match up with the rejection rate of the membranes so something is definitely up...
 

SynDen

Administrator
Staff member
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#10
Ya that was going to be my suggestion. BRS has great customer service and I am sure they could help you figure out what is going on and how to fix it
 

Tony44

Amphipod
M.A.S.C Club Member
#11
Here are the results from my trials- reducing the membranes from two to one did not help at all just slowed down the unit. The restrictor for 75 gpd and 150 is the same so no change there. I talked w/BRS at length today. Temp can have a big effect on efficiency of the membranes for each 1 deg under 77 deg the efficiency for the membranes goes down 2%. My tap water temp today is 45 deg so there is one problem. I am bleeding in some hot water to bring the feed water as close to 77 as possible so far I have only seen a drop from 30 TDS to 26. CO2 presence in the water can cause high resin usage apparently they have that problem in Minnesota and one of their people goes thru resin every month like I do. However that does not seem to be my problem as the tap water pH is 7.6 and alk 8, these should both be low if CO2 is present. The only other thing I'm going to do is to change the sediment filter to a 1 micron instead of the 5 I have in now, but I don't expect much change other than the membranes may last longer. So I still have the problem I just learned a little more.
 

zombie

Dolphin
M.A.S.C Club Member
#12
You would be surprised how much difference a 1 micron makes vs a 5 micron. I had a 5 micron set up and water came out at 10 ppm before the di and 5 ppm after the di, sediment lasted 2 weeks, carbon and resin lasted 1-2 months. After changing to 1 micron, ppm went down to 3 ppm before the di and 0 ppm after the di. The sediment lasts 1-2 weeks, the carbon 3 months and the di 2-3 months. This is making 100 gallons per week.

You might be an engineer if...You have no life, and you can PROVE it mathematically.
 
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