Question replacing RODI filters

[avilamillar]

I have a 180G Spectrapure MAXCAP RODI System. It has the sediment filter, then carbon, 2 RO membranes on top, then 2 DI resins.

I replaced the sediment and carbon filter about 2 months ago. RO membranes and DIs about 4 months ago.

It has 2 TDS meters, the first one reads 545 for the water coming in and 13 for the out. The second reads 7 for the in and 2 for the out. I like to use water with 0 TDS because if I dont algae starts to appear. Which filters am I supposed to change here? just the DI?

Thanks.

[Squiers007]

More than likely just the DI needs to be replaced. Can you give a bit more information about where in the system the meters are reading from (I.e. before the sediment filter and after the RO, etc.)

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[CoryDude]

Yeah, the DI filter resin needs to be replaced every few months. I'd recommend the color changing resin. It makes life much easier.

Just to make sure I'm correct in understanding your set up; water supply to unit ---> tds meter (545 reading) ---> micron filter ---> carbon filter----1st ro membrane---> 2nd tds meter (13 reading)----> 1st di resin ----> 3rd tds meter (7 ppm) ---> 2nd ro membrane ----> 2nd di resin ----> 4th tds meter (2ppm).

The first ro membrane is showing a 97% rejection rate which is pretty good. Your final reading of 2 ppm is a 99.6% rejection rate which is good.

If you really want a 100% rejection rate, I'd run the water like this; water supply in ---> sediment filter ---> carbon filter ---> 1st ro filter ---> 2nd ro filter ----> 1st di cannister ---> 2nd di cannister. When you replace the di, swap the di cannisters and replace the di in the cannister that was first in line before you swapped them. Like I said, use the color changing di resin to help you out.

[avilamillar]

Im not 100% but what I see is this:

Water supply --> micron filter --> carbon filter --> tds 545 --> 1st RO --> 2nd RO --> tds 13-->1st DI --> tds 7 --> 2nd DI --> tds 2 --> water out.

I just went into my BRS account and it looks like I actually got the color changing DI resin last time. I was sure I have gotten the normal one and that's why it looked brown. I guess it's brown because I need to replace it...

RO membranes still look good right? from 545 to 13.

Thanks

[BuckeyeHydro]

Couple of comments on this thread:


The first ro membrane is showing a 97% rejection rate which is pretty good. Your final reading of 2 ppm is a 99.6% rejection rate which is good.

If you really want a 100% rejection rate, I'd run the water like this; water supply in ---> sediment filter ---> carbon filter ---> 1st ro filter ---> 2nd ro filter ----> 1st di cannister ---> 2nd di cannister. When you replace the di, swap the di cannisters and replace the di in the cannister that was first in line before you swapped them.
"Rejection Rate" is a term that applies to performance of the RO membrane only. So doesn't make sense to talk about rejection rate once the water passes through a DI.

Are you using identical mixed bed resin cartridges?

Looks like both your DI carts are past their useful life.

Your RO stages are producing water at 13 ppm from a feedwater ppm of 545 - that's abour a 97.5% rejection rate so that's pretty good.

Are your membranes plumbed in series (waste from the first feeding the second) or in parallel (both fed by the system prefiltered feedwater)?

Russ

[avilamillar]

Couple of comments on this thread:


"Rejection Rate" is a term that applies to performance of the RO membrane only. So doesn't make sense to talk about rejection rate once the water passes through a DI.

Are you using identical mixed bed resin cartridges?

Looks like both your DI carts are past their useful life.

Your RO stages are producing water at 13 ppm from a feedwater ppm of 545 - that's abour a 97.5% rejection rate so that's pretty good.

Are your membranes plumbed in series (waste from the first feeding the second) or in parallel (both fed by the system prefiltered feedwater)?

Russ

I am using identical resins. I'm using the ones that BRS sells and they are plumbed in series. From what I've read 90G RO membranes should have a rejection rate of about 98% so I guess mine are still good. Now just one more question. When it reaches what % of rejection should I change the RO membrane?

Thanks

[BuckeyeHydro]

When your rejection rate drops, or when the production falls below what it should be given your pressure and temperature (you can use the calculator on our website to figure out how fast your system should produce water - your system uses two 75 gpd membranes) you'll know one or both of the membranes need to be replaced. How low should you let the rejection rate go? That's really up to you. You would weigh the cost of a new membrane or two against the cost of going through resin faster than you otherwise would.

Russ

[avilamillar]

When your rejection rate drops, or when the production falls below what it should be given your pressure and temperature (you can use the calculator on our website to figure out how fast your system should produce water - your system uses two 75 gpd membranes) you'll know one or both of the membranes need to be replaced. How low should you let the rejection rate go? That's really up to you. You would weigh the cost of a new membrane or two against the cost of going through resin faster than you otherwise would.

Russ

Thanks for the help. My unit actually uses 90 gpd membranes but im looking into switching to 75 gpd because they have a better rejection rate and they are also cheaper.

Thanks again.

[BuckeyeHydro]

Here's a secret if you promise not to tell: those 90's are really 75's.

One membrane manufacturer (Filmtec) tests and reports their membrane's performance under a set of conditions that include 50 psi. Most other manufacturers use 60 psi.

But if you take a Filmtec 75 gpd membrane and run it at 10 psi higher (60 psi), guess what it will produce:
http://i224.photobucket.com/albums/dd293/BuckeyeFS/75gpd60psi.jpg

[avilamillar]

Awesome. Thanks :) so if I change to the filmtec 75gpd membrane I wont even have to change the flow restrictor right? I'm running a bit over 40psi

[BuckeyeHydro]

I'd need a little more info to tell if your flow restrictor would need to be changed. Feel free to give us a call when you are in front of the system.

Russ
513-312-2343