recirculating waste water from ro/di

[mfinn]

I was at a friends house today and he showed me a small pump mounted above his 5 stage ro/di unit that took the waste water and ran it back through. I didn't have time to get into detail with him about the pump or how it works, etc.
He said it cuts down the ratio of waste water to pure water.

Anyone do this?

 

[jackinfobo]

I never heard of this before, but I would think that it is much harder on the RO membrane. It sounds like he is forcing dirty water back through the unit, which decreases the life of the membrane. I would think the amount of money he is saving will not add up to the cost of a new membrane as it will deteriorate in performance much faster.

 

[cgoulden]

My guess is it is what is called a permeate pump. I use them, although I've not really monitored well enough to validate a reduction in waste water. I use them to get more water in my storage tanks (more preasure). No power connections, basically you connect the waste water to one side of the pump and the supply water to the other (sorry not nearby at the moment and I don't recall if it is before or after the membrane).

 

[TheFishMan65]

That is true, but if he back flushes it often that may help extend the life. The best option I have seen is to add a second RO membrane, I forgot where I saw this, but it doubles the output.

 

[nmcgrawj]

My guess is it is what is called a permeate pump. I use them, although I've not really monitored well enough to validate a reduction in waste water. I use them to get more water in my storage tanks (more preasure). No power connections, basically you connect the waste water to one side of the pump and the supply water to the other (sorry not nearby at the moment and I don't recall if it is before or after the membrane).

Permeate pumps, from my understanding, don't recirculate waste water. They just allow the filter to work as if there is no storage tank there. The waste ratio increases dramatically as backpressure/resistance rises from the storage tank.




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[Gandolfe]

permeating pumps use the waste water to drive the pump as it decreases back pressure form storage tank thus making ro/di more productive. they are non-electrical and go between the output water and the tank if you have one! At least that's my understanding of them

 

[skunkmere]

bigger ro machines use a waste recovery. they route about half the waste or less back into the feed to improve efficiency. now i don't think is worth it unless you want to try saving some water. i use a booster pump to improve my production.

 

[Buckeye Hydro]

Permeate pumps, from my understanding, don't recirculate waste water. They just allow the filter to work as if there is no storage tank there. The waste ratio increases dramatically as backpressure/resistance rises from the storage tank.

You've got it right. The TDS level in the RO water also rises as the backpressure increases.

Russ