Reducing RO waste

[Ben Rhau]

Hi all,

Thanks for your help on my question about RO and chloramines. I have questions about what configurations are sensible to reduce waste water.

I see two ways to reduce the amount of wastewater produced by the RO unit:

• Using a booster pump. This is purported to reduce the waste ratio to approach 1:1.
• Using two membranes in series. This is purported to reduce the waste roughly by half.

My questions are:

1. If the water pressure is sufficiently high (> 60psi) is there still a benefit to using the booster pump? Is added pressure the only thing that reduces waste? And if so, what pressure is needed to approach a 1:1 ratio?
2. If I connect two membranes in series and there is sufficient water pressure (> 60psi) would a booster pump reduce the waste further, or are there diminishing returns to combining these two methods?

I understand that both methods put a lot of load on the membranes (particularly the second membrane). Essentially what I'm trying to get at is whether it makes sense to get a booster pump, an additional membrane, or both.

Cheers

 

[MacZ]

If the water pressure is sufficiently high (> 60psi) is there still a benefit to using the booster pump? Is added pressure the only thing that reduces waste? And if so, what pressure is needed to approach a 1:1 ratio?

About 5-6 bar (80-90psi) is what I find recommended in my circles locally.

If I connect two membranes in series and there is sufficient water pressure (> 60psi) would a booster pump reduce the waste further, or are there diminishing returns to combining these two methods?

Depending on the membrane model you might need the pump just to get it through both membranes. So to a degree both together can make for the ideal result.

 

[Ben Rhau]

Once again found <some info from the reef community> that jibes with what you are saying. Sounds like a single membrane with a pump to get it to 90psi is the way to go. Thanks!

 

[Apistoguy52]

Psi will help produce more GPD ( I run my membrane at 200psi, and the gpd output is 3x the listed output), but the waste water ratio should remain somewhat static. If you’ve got fairly soft water to begin with, tightening up the restrictor on the waste water line will improve the ratio of product to waste ( at the risk of clogging the membrane at a faster rate if it isn’t flushed regularly)