2 membranes ro-di

Beam

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hello

few month ago, I had a big problem with dyno's and algae, I identified that the cause was probably my water. I use a Ro-di, and my tds is at zero at the exit, but I know that my water is not top notch despite everything (ICP test)

it was suggested to me to add an extra membrane to my ro-di.
not to recover the waste water, but to make the good water pass through a second membrane.

i have an aquatic life smart buddy booster pump, but i wonder if there will be enough pressure at the outlet of the first membrane to produce water with the second one?

has anyone ever done this?

thanks
 

T-J

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I have horrible city water (500tds) and have a single membrane RODI that ICP tests out just fine.
What did the ICP test show on your RODI water?
Also, to answer your question, I know some people run two membranes. Not sure on the pumps they might use. I'm fortunate enough to not need a pump on my system.
 

KStatefan

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You will have trouble with just running them in series. For the membrane to work properely you need a pressure difference across the membrane and there will not be enough flow coming into the second membrane.
 

BZOFIQ

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I run 2 membranes in series with booster pump at 90 PSI....but my TAP TDS is almost always less than 40.

I don't recommend connecting in series to anybody with incoming TDS in the 100s.
 

Buckeye Hydro

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If you want a double pass RO, then the purified water from the first membrane will need to be run to a tank. Then, after enough water has accumulated, to a booster pump and on to the second membrane.

The purified water won't come out of the first membrane with enough pressure or enough flow to feed a second membrane in real time.

Russ
 

Pod_01

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hello

few month ago, I had a big problem with dyno's and algae, I identified that the cause was probably my water. I use a Ro-di, and my tds is at zero at the exit, but I know that my water is not top notch despite everything (ICP test)

it was suggested to me to add an extra membrane to my ro-di.
not to recover the waste water, but to make the good water pass through a second membrane.

i have an aquatic life smart buddy booster pump, but i wonder if there will be enough pressure at the outlet of the first membrane to produce water with the second one?

has anyone ever done this?

thanks
Just for reference, you cannot get dinoflagellates from RO water. You can have algae and diatom bloom from RO water.
Bad water quality in the reef tank, unhappy corals, strong light can lead to dinoflagellates but RO water not really. The mechanism is bit more complicated.
 

BZOFIQ

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If you want a double pass RO, then the purified water from the first membrane will need to be run to a tank. Then, after enough water has accumulated, to a booster pump and on to the second membrane.

The purified water won't come out of the first membrane with enough pressure or enough flow to feed a second membrane in real time.

Russ

Russ,

Now that I read your post I realized that I misread the original post.

The user wants to double pass the RO and not re-cycle the brine with a second membrane?!?!

...but why would anyone do that instead of RO > DI ? To produce more wastewater? Is it because they're starting with super high TDS?


The setup I mentioned in #4 was designed to minimize waste water and it works extremely well. With your help and feedback I automated pre- and post- flushing of membranes. I produce more clean water then waste and there is nearly no TDS creep in my RO tank because I also dump initially produced water via separate solenoid.
 

RoninNV

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I live in the Vegas area. TDS between 550-600. I run my water thru 1 membrane but use a pump. TDS comes out at 6-15, then I run it thru DI media which comes out at 0 TDS. Just add a DI canister, much easier than adding a 2nd membrane.
 

BZOFIQ

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I live in the Vegas area. TDS between 550-600. I run my water thru 1 membrane but use a pump. TDS comes out at 6-15, then I run it thru DI media which comes out at 0 TDS. Just add a DI canister, much easier than adding a 2nd membrane.

That's what I was thinking but I guess with water coming out high out of the membrane the RO gets used up quickly?
 

BZOFIQ

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FYI for NYC (SI) last night our TDS was at 42. It usually hovers between 37-44, that said there is a lot of sediment and my 20" pre-filter turns kaka-brown relatively fast.
 

BZOFIQ

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My 200GPD ICECAP RODI unit has double ro membranes. Works well at 70psi without the need for a booster pump.

In my understanding, there are different configurations this could be setup, each with different goals/benefits.

1. Additional Membrane run in Parallel
2. Secondary Membrane processing the waste water from the 1st.
3. Secondary Membrane re-processing product water from the 1st.

I'm guessing your setup is #1 with 2 x 100 GPD membranes running in parallel.
 

cdnco2004

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It might be the #2. The benefit of this model over the same model with 1 membrane is not just volume per day but the waste water decreases from 3:1 to 1.5:1. That was the main driver for me in getting this unit. It filters water fast too. My old AcuticLife RO Buddy would do single drip output and would take me 16hrs to fill a 44g brute can. This new unit fills the same container in like 4 hours.
 

Buckeye Hydro

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It might be the #2. The benefit of this model over the same model with 1 membrane is not just volume per day but the waste water decreases from 3:1 to 1.5:1. That was the main driver for me in getting this unit. It filters water fast too. My old AcuticLife RO Buddy would do single drip output and would take me 16hrs to fill a 44g brute can. This new unit fills the same container in like 4 hours.
It's never a good idea to plumb two membranes in series (concentrate from the first feeding the second) unless you have soft, or softened water.
 

cdnco2004

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I am just assuming. Its not something I setup but how it comes from manufacture. All I had to do was mount the unit on wall add filters to the canisters connect incoming water connection, water output connection and waste connection. So I assume they know what they are doing. They say the difference in the 100GPD and 200GPD is the waste output drops to 1.5:1 and the GPD doubles. And like I said, I wanted the wastewater reduction.
 

Buckeye Hydro

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It's never a good idea to plumb two membranes in series (concentrate from the first feeding the second) unless you have soft, or softened water.
This is done routinely in commercial RO systems. Concentrate from one membrane feeding another. Concentrate to permeate ratios on commercial RO's are often 1:1, and can have even less concentrate than that. How is this possible? If you look at the fine print, including required feedwater parameters, you'll see that the feedwater must be soft. Why? Because it is the calcium and magnesium (primarily) that make up hardness, and these will come out of solution and plug the membrane if they are present in the water and if concentrate flow if too limited.

This is why residential systems, where the manufacturer has no idea what the feedwater parameters will be, are typically set at only 15 or 20% recovery (i.e., a 4+ to 1 ratio of concentrate to permeate). Residential membranes are tested by Filmtec assuming a 5.5:1 ratio. The reasons for this design spec don't magically go away if you plumb a second membrane in series. In fact, the situation for the second membrane is actually worse - it's feedwater quality is worse than what reaches the first membrane because about 20% of the pure H2O has been removed.

What is the cost for plumbing two membranes in series with hard water? A shortened life span on the membrane. If that's ok with you that's fine.

If all the user is after is less concentrate, they can simply change out the $4 flow restrictor - you don't need a second membrane to call your system a "water saver."

In most instances the primary beneficiary of a short membrane lifespan is the guy selling you a replacement membrane.

Russ
 
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Troylee

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I live in the Vegas area. TDS between 550-600. I run my water thru 1 membrane but use a pump. TDS comes out at 6-15, then I run it thru DI media which comes out at 0 TDS. Just add a DI canister, much easier than adding a 2nd membrane.
Nice to see another Vegas peep in here! Mine is 570 in Henderson… ugh…
 
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