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Old 05-01-2005, 03:33 AM   #1
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RO Configuration Question


I was given a Kent TFC 24 GPD RO unit this last week. After hooking it up I was pretty shocked at the abymsal waste to product ratio. I know it's not great with RO in general, but this was pretty phenomenal.

We have well water, so it's not a per gallon cost issue for us, but I can't abide running that much water down the drain just to make a few gallons. Yes, I realize I can capture it for something like watering plants... but I'm more interested right now is speeding up the RO process and making it easier to run.

I rigged up a pressure gauge today and determined (as I suspected) that my pressure is low. I'm getting just over 20 PSI in the line between the second filter and the membrane. I think 65 is the recommended PSI.

Also, my water temp right now coming out of the pipe is around 61 degrees which, if I recall, is also going to slow down the process.

Considering these factors, it's not real shock that the rate is so horrible.

My question is in regards to the waste water. Is this not just water that couldn't be pushed through the membrane?

Assuming that is the case, why can I not fill a trashcan with maybe 25 gallons of water, drop in a heater to get it in the ideal temp range for the RO and plumb in a booster pump?

My thought is to suck water from can with the pump, push it through the RO at the ideal pressure and feed the product into a second trashcan. The orange hose (waste water) could go back into the source can to be rerun. Over time it seems you would process all of it and closer to a 1:1 ratio.

Add in a water level sensor to run the booster pump and it -seems- like I would have a closed system that could run itself without running the pump dry as it hit the bottom of the source trash can.

I'm sure there is some reason NOT to do this since it seems so logical and I've not heard anyone doing it already. Is the waste water from the RO unit truly "waste" or just the water that couldn't be pushed through the membrane due to pressure, etc?

Any thoughts or explanations would be appreciated.

- Aaron

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Old 05-01-2005, 08:21 PM   #2
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Using a booster is pretty common. 65PSI is the target. What you would be doing by feeding the waste (brine) water back into the the source would be polluting the water all that much more. A TDS meter would be handy here. Your first couple passes would only spit more and more pollution into your source water. Obviously what you end up with is water moved at a really slow pace from one container to another. THat is, there is no magic to RO/DI units. If you push the junk water through it over and over again, you will eventually end up with the junk water on the other side. If you are concerned about water usage, maybe you should check into a tap water filter. Its not RO/DI quality, but there is no waste water produced, just filtered water.


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Old 05-01-2005, 11:23 PM   #3
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Thanks for clarifying this. I wasn't sure if the "waste" water was really waste, per se, or whether it was the unprocessed "overflow" in the course of pushing water through the membrane. Does this mean it is the water that is carrying away things removed from the product water?

In any case, it was a question asked mostly because I'm still learning the ins and outs of RO. My other plan is just to capture the waste water in another trashcan and use it as a cistern, of sorts, for the watering of plants and other useful activities.

- Aaron
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