Double RO membranes

[mfinn]

I've seen the 2 different ways to use double ro membranes, ( in a series or side by side) but what about adding a ro membrane on the good product water line of the first membrane?
I'm getting a reading of 4-6 TDS coming out of the membrane now and have a extra new ro membrane on the shelf, with all the fittings and container to set up a second ro membrane.
By installing it inline with the good water line, would it help scrub the tds that's making it through the first ro membrane?
I'm just trying to cut down on di resin use.

[Opus123]

Not sure if the pressure is there to make it work. Plus that would waste a lot of water for just dropping tds by 3 or 4.

Have you thought of investing in a 99% rejection rate membrane such as the spectrapure? My tap tds is around 450 and I'm getting a tds of 4 after my membrane. At a 4 tds I should get around 1100 gals of 0 tds out of my DI.

[Jboone82590]

Not sure if the pressure is there to make it work. Plus that would waste a lot of water for just dropping tds by 3 or 4.

Have you thought of investing in a 99% rejection rate membrane such as the spectrapure? My tap tds is around 450 and I'm getting a tds of 4 after my membrane. At a 4 tds I should get around 1100 gals of 0 tds out of my DI.That sounds awesome. Where do u get one at?
I also added an extra membrain and now my TDS is higher then when i had 2 lol

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[HBtank]

People do "water saver setups" with two RO membranes, you use it on the waste water to increase the total system GPM and lower waste volume. I think it is best on lower TDS water (as the waste water is still practical to use in a DI after the second RO), and I believe that is the most common way to use two.

[mfinn]

Not sure if the pressure is there to make it work. Plus that would waste a lot of water for just dropping tds by 3 or 4.

Have you thought of investing in a 99% rejection rate membrane such as the spectrapure? My tap tds is around 450 and I'm getting a tds of 4 after my membrane. At a 4 tds I should get around 1100 gals of 0 tds out of my DI.

I can run my pressure up to 90-100 psi if I need to.
Would there still be that much going to waste after the second membrane? Since it's getting nearly clean water to begin with.

And I'm not spending any extra money on parts. I have everything justt sitting on a shelf.

Yeah I may go to spectrapure.

[tkeracer619]

My incoming TDS is 140. With both spectrapure 99% membranes my out TDS is 0-1.

I'm getting somewhere around 99.5% rejection. It's awesome. Keep in mind every time you cut TDS in half you double the life of your DI (unless there is something else reducing its life).

So with a single 99% membrane you would probably be much better off than where you are now. You wouldn't want to run another membrane on the product water, the backpressure would reduce efficiency of the first membrane.

Regarding dual membranes keep in mind unless you are on softened water you want to keep your waste ratio to 4:1, even with two in series to prevent fouling of the membranes. With special flushing or a softener you can drive the membranes harder. Water quality will suffer though.

[Opus123]

That sounds awesome. Where do u get one at?
I also added an extra membrain and now my TDS is higher then when i had 2 lol

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This is where I got mine but spectrapure sells them directly and I'm sure other online places have them. Just remember if you buy one you need a flow restrictor to match it.

https://premiumaquatics.com/products/spectraselect-90gpd-ro-membrane-99-percent-rejection.html

[Buckeye Hydro]

Fun fact to know and tell...

Filmtec 75 gpd RO membranes used to be rated at 96 to 98% rejection. A few years ago, Filmtec started producing 75's rated at 96 to 99%. If you use a vendor that pays attention to these sorts of things, they should be selling ONLY these 99% 75's.

Russ

[Mark SF]

Fun fact to know and tell...

Filmtec 75 gpd RO membranes used to be rated at 96 to 98% rejection. A few years ago, Filmtec started producing 75's rated at 96 to 99%. If you use a vendor that pays attention to these sorts of things, they should be selling ONLY these 99% 75's.

Russ

Russ,

Totally agree and was a bit disappointed to see that SpectraPure is asking such a high premium for their "hand-selected" 99% rejection membranes. The Dow FilmTec line of products produces a 99% rejection rate with this specific model:

DOW FILMTEC™ BW60-1812-75

That is a 75GPD unit @ 50PSI w/99% rejection for $28.50 Prime on Amazon...SpectraPure wants $60 for theirs! No way...