New RO Membrane Rejection only 90%

[Tink]

I just redid my RO unit, and went with a 75GPD DOW Filmtec membrane, and so far my DI has been getting eaten up pretty fast. Here is my set-up and associated readings:

Water feeds into a 5 micron sediment filter
1 micron sediment filter
5 micron carbon filter
.6 micron carbon filter
Hits a booster pump (boosts pressure to 50-55)
Hits the DOW Filmtec 75GPD membrane (has a 550 flow restrictor on the waste water output)
Then to the nuclear grade color changing DI resin from Bulk Reef

My readings are as follows:
Input 167 TDS and 5.25 pH (well water)
After membrane 17TDS
Water Temp after membrane is 60

My tap water uses a Sodium Hydroxide injection unit to raise the pH to 7, and I tried running the RO off that (normally I get the water prior to this injection), but it was even worse (about 260 TDS in and 40 TDS after the membrane)


What's the deal with the crummy 90% rejection rating? I made about 10 gallons of water, and ate up a good 8% of my DI resin.

Any help or tips on getting my rejection rating up to par would be greatly appreciated.

Thanks

 

[flooddc]

What was your reading before you replaced the membrane? 

Also, did you run it for a number of hours or gallons so that it break in? (I forgot how long. Check BRS site for recommendation). It should come down to zero once membrane break in.  If not, can double check to see if it installed correctly. Sometime it not fitted correctly in place.

There was a thread a few months ago with the similar problem here, gotta dig for it!

[Tink]

After I moved to my current house I hadn't hooked up this RO unit, and was buying as needed from the store. Due to this I don't have accurate readings related to how the system performed previously.

 

All above readings were taken after making 10 gallons of finished water. I didn't see a break in period listed on the BRS website, I'll take another look.

 

The membrane seemed to have seated properly, and I had no trouble sealing its housing after the install, so I'm guessing the membrane was installed ok.

[DaveS]

75 gpd only gets 90%. For reefing, if you want more than 50gpd, you typically have to buy the 150gpd and a booster pump.

[flooddc]

I don't have inline TDS so, don't know what the reading should be right after the membrane. But rejection should be around 90+%. Then the rest should be taken care of by your DI resin. 

I recalled seen a video on BRS regarding flushing membrane after installed new one, but my memory getting bad  !

Here is some info on similar topic:

http://wamas.org/forums/topic/59714-when-to-change-rodi-filters/

[Origami]

What's the model number on the membrane? The 1812 is supposed to get 97-98 percent rejection. There's a 100 gpd that routinely gets 90 percent.

 

Sent from my phone

 

[DaveS]

My bad, I was mixing up the 100 with the 75. 100 sux for reefing. No clue what's up with yours Tink.

[Dell2go]

If you let it sit for while then everything needs to be replaced. 

[Tink]

Everything except the housings themselves is brand new.

 

The membrane is model # TW30-1812-75

 

I have flushed the membrane twice, and it has been running for about 6 hours now.

[s2nhle]

Also, when you replace the filters, you have to dump a bucket of water that come out before you will see the better result from TDS.

[Tink]

I've dumped 2 two 5 gallon buckets of finished product, and these numbers are after that.

[Origami]

Just curious. Where did you buy the membrane and when?

 

Sent from my phone

 

 

[Tink]

I purchased it brand new off eBay, came in a sealed package. I'm beginning to wonder about the source though....

 

Just got the membrane this week

[Buckeye Field Supply]

Tink - about half of the time people contat us with odd TDS readings, the problem ends up being bad measurements, rather than actual problems with system performance.  What are you taking your water samples in?  Are you sure you've let your system run long enough to get past the TDS creep period before you took your sample?

 

Be advised that ebay is loaded with counterfit products - we see it all the time - so you might want to take an extra minute to make sure you actually bought the membrane you thought you did.

 

The TW1812-75 has afactory spec of 96 to 98% rejection.  The rejection (and the recovery, and the production) should improve a bit over the first 6 to 24 hours of run time.

 

If membranes are shipped to you dry, rinse if for 10 minutes before use.  If shipped to you wet, rinse it for an hour or as specified on the packaging.

 

Why are you using two carbon blocks on non-chlorinated water?

 

Why with a booster pump are you only at 55 psi?  Is this a non-adjustable off-brand pump?

 

Do you have any other information of the quality of your feedwater?

 

Are you certain your RO membrane is fully seated (fully pushed in)?

 

Russ

[Tink]

I've produced 15 gallons of finished RO product at this time, is that normally considered a sufficient break in period?

 

Samples are taken in a glass shot glass that is rinsed in the water to be tested 3 times before I do the actual test.

 

The 2 carbon blocks were what was included in the BRS filter replacement kit.

 

The pump does appear to be an off brand non-adjustable pump. My pressure reading comes from a gauge between the pump and the RO membrane.

 

I did a few more tests today to see if I could get a better result, but I've had no luck. I put my old RO membrane in ( Axeon TF-1812-100), and 800 flow restrictor and was able to get a result of 15 TDS. I then reinstalled the Filmtec membrane (added a light coat of lubricant to the orings) and 550 flow restrictor and made sure it was fully seated. I even twisted it clockwise as stated in the package. As it stands (after another 5 min flush and 30 min run time) my TDS is at 16.

 

The only other info I have on my feed water is in the following picture of our water test results when the house was purchased last year.

 

 

Here is a picture of the membrane package, it seems pretty legit

 

 

 

I'm at a loss on what could be the trouble

 

 

 

[howaboutme]

I would not buy any RODI replacements from ebay. Buy from any of the big, trusted companies.

[Origami]

Be advised that ebay is loaded with counterfit products - we see it all the time - so you might want to take an extra minute to make sure you actually bought the membrane you thought you did.

That's what I'm wondering about. The last 1812 that I purchased had a hologram sticker on it apparently indicating authenticity. I had noticed that another did not. That, in itself, doesn't prove anything regarding performance, but it may just make you aware of another possibility.

[Tink]

Mine did have a hologram sticker as well. At this rate I'm about to just buy another membrane off Amazon, they're only $30....

[flooddc]

I got my from amazon. It took more about 100 gallons before it settled down. As Russ said, ran it for 24 hours to see if it make any different.

[Tink]

I've seen conflicting reports on which flow restrictor to use. BRS recommends the 550 while I have seen an 800 suggested as well.

 

 

What are you folks using?

[Origami]

I've seen conflicting reports on which flow restrictor to use. BRS recommends the 550 while I have seen an 800 suggested as well.

 

 

What are you folks using?

800 on mine.

[Tink]

So, I ditched the crummy booster pump I had and went with a CDP8800. With the pressure at 84 psi (what it was out of the box), I'm at 131 TDS in and 6 TDS out. A nice improvement for sure, and I hope the output drops at least another point and I'll be at about 96% rejection.

 

Any tips on maybe squeezing a tad more performance out of this sucker (if at all possible)?

[Buckeye Field Supply]

Hopefully you installed your booster pump AFTER your three prefilters.

 

Again, you have no need for two carbon blocks - I'd pull out the 0.6 block and set it aside.  You'll be able to use it some other time.  Its reduces the pressure reaching the membrane by a few psi.

 

Unless you get a guarneteed higher rejection membrane, at 96% your are within spec. 

 

To determine the flow restrictor that is correct for your system, with your water pressure and your water temperature, you have to MEASURE (don't estimate) your waste water to purified water ratio.  How?

 

Line up 7 identical cups (plastic beer cups are perfect for this) in front of your system and turn your system on and let it run for a minute or two.  With your waste water tube in one hand, and your purified water tube in the other hand, how many glasses do you fill with waste water in the time it takes you to fill one with purified?

 

At your pressure with a 75 gpd membrane you are probalbe going to below the target 4:1 ratio.  Because at 85 psi and 60 degrees, a 75 gpd membrane will produce 98 gpd.  So you'd expect a 100 gpd flow restrictor to give you about a 4:1 ratio.  Your current flow restrictor is for a 50 gpd membrane (or for a 75 gpd membrane with cold water and poor pressure).

 

Russ

[Origami]

Hopefully you installed your booster pump AFTER your three prefilters.

 

Again, you have no need for two carbon blocks - I'd pull out the 0.6 block and set it aside.  You'll be able to use it some other time.  Its reduces the pressure reaching the membrane by a few psi.

 

Unless you get a guarneteed higher rejection membrane, at 96% your are within spec. 

 

To determine the flow restrictor that is correct for your system, with your water pressure and your water temperature, you have to MEASURE (don't estimate) your waste water to purified water ratio.  How?

 

Line up 7 identical cups (plastic beer cups are perfect for this) in front of your system and turn your system on and let it run for a minute or two.  With your waste water tube in one hand, and your purified water tube in the other hand, how many glasses do you fill with waste water in the time it takes you to fill one with purified?

 

At your pressure with a 75 gpd membrane you are probalbe going to below the target 4:1 ratio.  Because at 85 psi and 60 degrees, a 75 gpd membrane will produce 98 gpd.  So you'd expect a 100 gpd flow restrictor to give you about a 4:1 ratio.  Your current flow restrictor is for a 50 gpd membrane (or for a 75 gpd membrane with cold water and poor pressure).

 

Russ

Hey Russ. I've seen booster pumps on either side of the three pre-filters depending upon the distributor / source. What's the rationale for preferentially putting it between the prefilters and the membrane vice before the first pre-filter (besides prefilter pressure drop)? Does the recommendation change any if there is another (extra) sediment filter in front of the booster?