Show me your dual RO membrane setups!
- Thread starter mufret
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Here is mine Mike. I originally had a Melev's Reef 100 gpd RODI, and it was time to change the RO Membrane. I heard about the BRS add-on second 75 gpd membrane water saver kit, and since a replacement 100 membrane was about the cost of two 75 GPD units, I converted the 100 gpd unit to a 75 and added the second BRS 75 membrane. Had to buy a new flow restrictor, and I will say this combo works the best with higher water pressures, but I already had an AquaTec booster. This combo gives me a 1:1 product:waste ratio in the summer, and a bit worse in winter, as cold source water makes less RO than warmer source water.
I was told you can't have two different production rate membranes in line with each other. You need two 75s, or 50s, or whatever. Also, the flow restrictor is placed in the waste line coming from the second membrane, not the first. The first membrane's waste line is the input for the second membrane. Remove all other flow restrictors.
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I was told you can't have two different production rate membranes in line with each other. You need two 75s, or 50s, or whatever. Also, the flow restrictor is placed in the waste line coming from the second membrane, not the first. The first membrane's waste line is the input for the second membrane. Remove all other flow restrictors.
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There are instructions there. I had a hard time with some of the tubing because the BRS video orientation was opposite of mine. Finally got through it. One of those purchases you can look back on and feel good about. I don't regret doing this at all. I make a lot of RODI.
There have been arguments against this type setup by Buckeye Field Supply, who posts here and has an RODI business, but is not a sponsor here. I think the gist of his argument is that when you use the first membrane's waste water as the source water for the second, the second membrane is receiving water with about 10% more TDS than the first membrane is, so it fouls much faster than the first. This is an issue in areas of the country with high TDS in their tap water, but is not an issue here, where most of the greater Atlanta area has 36-42 TDS input water, incredibly soft to start with. RO membranes here last for many years before needing replaced.
Here is the second membrane upgrade at $59: http://aquarium.bulkreefsupply.com/search?asug=&view=grid&cnt=12&w=water+saver">http://aquarium.bulkreefsupply.com/search?asug=&view=grid&cnt=12&w=water+saver</a>
The replacement 75 gpd membrane for the 100 gpd unit I changed from was $39, and the flow restrictor was $5. so I think the grand total for my swap from a 100 GPD unit to the twin 75 gpd BRS setup was about $104.
Thanks for the pic and recommendations!
I've ordered 2 new 75 gpd membranes so think I'm good there. I currently have the waste from the first flowing to the input to the second as you detailed. Dave, do you have an auto shut off somewhere in your setup? I currently have that plumbed into my first RO but was wondering if that's were it should be. I do have the restrictor after the second membrane.
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I've ordered 2 new 75 gpd membranes so think I'm good there. I currently have the waste from the first flowing to the input to the second as you detailed. Dave, do you have an auto shut off somewhere in your setup? I currently have that plumbed into my first RO but was wondering if that's were it should be. I do have the restrictor after the second membrane.
mufret;800136 wrote: Thanks for the pic and recommendations!
I've ordered 2 new 75 gpd membranes so think I'm good there. I currently have the waste from the first flowing to the input to the second as you detailed. Dave, do you have an auto shut off somewhere in your setup? I currently have that plumbed into my first RO but was wondering if that's were it should be. I do have the restrictor after the second membrane.
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I don't think anything changes regarding the auto shutoff valve. But watch the BRS Video to be sure.
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If all you want to do is reduce the proportion of feedwater that ends up as waste water, why not spend $4 on a different flow restrictor rather than messing with adding a second membrane?
Russ
Russ
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Those membranes are plumbed in parallel rather than in series, so assuming the correct flow restrictors are installed, each membrane should be something close to a 4:1.
Russ
Edit: What pressure is that 8800 able to generate feeding three 100 gpd membranes?
Russ
Edit: What pressure is that 8800 able to generate feeding three 100 gpd membranes?
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Here's the long version - but as mentioned above, my cautions re scaling the membranes may not be as critical in your location/with your low TDS feedwater.
First - remember that what folks call "waste water" really would be better thought of as "flush water" in that this water serves the important purpose of internally flushing the surface of the semipermeable membrane to keep the membrane from fouling/scaling.
When you configure a system with two membranes in series (the waste from the first membrane going to the "in" port on the second membrane), for this discussion let's say it's two 75 gpd membranes, the system behaves like you have a single long (75 gpd x 2) 150 gpd membrane.
Now - if you use a proper flow restrictor, that is, one for a 150 gpd membrane, you'll have about a 4:1 waste to product ratio. Sounds familiar, right?
If however you don't change the flow restrictor - meaning you keep using the same restrictor you were using when you just had one 75 gpd membrane, then you'll see a waste to product ratio much lower than 4:1. But remember that the recommendation for a ~4:1 ratio comes from the membrane manufacturer. They are telling you that you need about a 4:1 ratio to keep the membrane flushed and keep the membrane from fouling or building up scale. Run the system with a lower ratio and you will foul/scale the membrane(s) quicker than would have otherwise been the case.
Instead of adding a second membrane to lower that ratio, you could have just changed out your flow restrictor ($4) instead. A much less expensive approach to get you to the same endpoint in terms of saving on waste water.
Now, to confuse things just a bit. Filmtec specs call for the 4 to 1 ratio on the basis of assumptions about the water that will be supplied to the membrane. If you have very soft water you MAY be able to get a decent service life from the membrane running at a ratio lower than 4 to 1 (e.g., 3 to 1). Remember that the waste water from the first membrane is about 25% harder than your tap water.
Bottom line: If what you are after is reduced waste water, experiment with a different flow restrictor for $4 instead of messing around with a second membrane plumbed in series.
As a side note, you can also lower the ratio by increasing the pressure delivered to the membrane (with a booster pump), because flow restrictors are sized assuming you are providing factory spec conditions (50 psi and 77 degrees for Filmtec membranes). Increase the pressure and you'll drive more water through the membrane and viola - less waste water. But as I mentioned above, if you do this (just like over-restricting a membrane) - the lower the waste to product ratio, the shorter the lifespan on the membrane.
Makes sense?
Russ
First - remember that what folks call "waste water" really would be better thought of as "flush water" in that this water serves the important purpose of internally flushing the surface of the semipermeable membrane to keep the membrane from fouling/scaling.
When you configure a system with two membranes in series (the waste from the first membrane going to the "in" port on the second membrane), for this discussion let's say it's two 75 gpd membranes, the system behaves like you have a single long (75 gpd x 2) 150 gpd membrane.
Now - if you use a proper flow restrictor, that is, one for a 150 gpd membrane, you'll have about a 4:1 waste to product ratio. Sounds familiar, right?
If however you don't change the flow restrictor - meaning you keep using the same restrictor you were using when you just had one 75 gpd membrane, then you'll see a waste to product ratio much lower than 4:1. But remember that the recommendation for a ~4:1 ratio comes from the membrane manufacturer. They are telling you that you need about a 4:1 ratio to keep the membrane flushed and keep the membrane from fouling or building up scale. Run the system with a lower ratio and you will foul/scale the membrane(s) quicker than would have otherwise been the case.
Instead of adding a second membrane to lower that ratio, you could have just changed out your flow restrictor ($4) instead. A much less expensive approach to get you to the same endpoint in terms of saving on waste water.
Now, to confuse things just a bit. Filmtec specs call for the 4 to 1 ratio on the basis of assumptions about the water that will be supplied to the membrane. If you have very soft water you MAY be able to get a decent service life from the membrane running at a ratio lower than 4 to 1 (e.g., 3 to 1). Remember that the waste water from the first membrane is about 25% harder than your tap water.
Bottom line: If what you are after is reduced waste water, experiment with a different flow restrictor for $4 instead of messing around with a second membrane plumbed in series.
As a side note, you can also lower the ratio by increasing the pressure delivered to the membrane (with a booster pump), because flow restrictors are sized assuming you are providing factory spec conditions (50 psi and 77 degrees for Filmtec membranes). Increase the pressure and you'll drive more water through the membrane and viola - less waste water. But as I mentioned above, if you do this (just like over-restricting a membrane) - the lower the waste to product ratio, the shorter the lifespan on the membrane.
Makes sense?
Russ
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You must have 50 gpd flow restrictors installed on each membrane?
Edit: Or even tighter than that...
Edit: Or even tighter than that...
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Rather than that ASOV, you'd be better off with a 24v solenoid valve with a plug that would allow you to plug it right into the wiring harness that powers the pump.
To get an 8800 pump to work with a 300 gpd system, you'd have to grossly over-restrict the membranes.
Russ
To get an 8800 pump to work with a 300 gpd system, you'd have to grossly over-restrict the membranes.
Russ
