<a href=showthread.php?s=&postid=6850049#post6850049 target=_blank>Originally posted</a> by asnatlas
Most of that waste water that has a TDS reading of 50ppm is then passed back through the membrane again...
I'm a little confused about where the pump is getting water and where it's sending it. I think you're saying it's taking the membrane waste and putting it back through the membrane for another pass.
And you're saying that it won't shorten the membrane life because the membrane waste has the same concentration of TDS as the water coming from the last DI cartridge anyway. (50ppm)
BUT
It's not 50 ppm. It's more. When the water went through the membrane 4 gallons came out as waste and one gallon came out as pure water (0 ppm).
50 parts TDS per 1,000,000 parts water went in.
The membrane took away 1/4 of the water (250,000 parts).
Now its 50 parts TDS per 750,000 parts water coming out as waste.
50 parts per 750,000 = 62.5 parts per million.
So every time the pump sends waste water through the membrane again, the membrane takes out more and more pure water. So the waste water (containing all the junk that didn't pass through the membrane) gets more and more concentrated with TDS. Which cruds up the membrane faster.
well, I THINK I'm right
If I'm wrong, don't tell me
edit: and burning through membranes faster isn't necessarily a bad thing. If it's more cost effective to buy membranes more often and have a lower water bill, then its a good idea.
I saw that link about the pump though. Says it's powered by brine in the waste water and requires no electricity. Sounds too good to be true.:strooper: