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question about R/O units


MissDeffiance
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I have an Air/Water/Ice brand unit (they're a club sponsor, too) that I'm happy with. I hear that using a pre-filter pump to raise the water pressure to the proper level helps with efficiency, but really RO/DI units are very inefficient. It's just the way they work :-( It's a bummer too, I pay more for my tank in my water bill than in my electricity bill.

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I have an Air/Water/Ice brand unit (they're a club sponsor' date=' too) that I'm happy with. I hear that using a pre-filter pump to raise the water pressure to the proper level helps with efficiency, but really RO/DI units are very inefficient. It's just the way they work :-( It's a bummer too, I pay more for my tank in my water bill than in my electricity bill.[/quote']

 

Yeah, Andy is right, other than keeping the feed pressure (and temperature) optimal, there isn't a whole lot to be done about efficiency. If you choose a low rejection rate (of solutes) membrane, which might slightly decrease your overall water use, you will then saturate your DI resin more quickly. This is the nature of RO unfortunately.

 

I have been trying to come up with ways to mitigate the water use by saving the RO reject for watering plants etc. since it's actually better than tap water as it's already gone through a sediment filter and at least one carbon filter. Whatever "contaminants" that make it through those would only be about 30% more concentrated than before it goes through the RO so really, this is pretty good water to be putting down the drain! I have been thinking about hooking up the reject line to a big rain barrel or something for re-use.

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Save the waste water and use it for...

 

flushing toilets by turning off the water line to the toilet and pouring the water into the back tank after a flush...

 

laundry by filling up the laundry tub with the waste instead of the automatic fill...

 

watering plants...

 

watering the pets...

 

soaking DIY rock (this is what I do with most of mine).

 

I am sure you could think of 1000s of uses for a bucket of water. :)

 

BTW, I traded my old RO/DI unit in to Waves, and bought one of their new ones. It was more expensive than just changing out the membrane and resin, but I got a much better unit.

 

dsoz

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wow, i had no idea ithey even had waste water. i thought it just forced the water thru it and then you change the filters. glad i asked about that one. I'm thinking the ZERO waste thing sounds good. My water bill is already around $100. a month and thats without my tank running. As far as units go(to get back to the original question) i found this one at http://www.melevsreef.com/rodi.html Looks like a good deal from what i've seen at other places.

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Yeah, manufacturers specs usually state 60 - 70% efficient but those are ideal numbers seldom seen in the real world -- kind'a like car MPG specs.

 

It's the RO portion of the filter that's so inefficient; clean water passes through the membrane, while the waste water carries away the impurities that are left behind. The DI side is very efficient, the DI resin removes the remaining impurities as the water passes through it.

 

Some folks with really good tapwater choose to just do the DI portion (with carbon, I guess), but I think they're leaving themselves open to a LOT of risk... just because their water is relatively pure today doesn't mean it'll be the same way forever. It's not like the city will tell you ahead of time if they're going to flush the system with a massive dose of whatever.

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Good clarification Andy - the reverse osmosis membrane is the only part of the typical system that has water loss, all the others are throughput filters/resins where you get out (in terms of water volume!) is what you put in.

 

Bob/Blown - I am curious about the "zero waste" setups. The only thing I can imagine is some sort of loop system where the "reject" water (carrying a higher concentration of contaminants than the original input) is fed back through the RO membrane and partially diluted with some "fresh" water to make up volume/flow. While more efficient in terms of water use, I can't see this working too well in terms of water purity... you would jack up the concentration of contaminants in the retentate so high the rejection rate of the membrane would start to suffer and you dump it all on the DI resin. I must be missing something here... sorry for the digression :D

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Couldn't you just recycle the waste water back through the system? I was thinking of building a system with holding tanks for the water and use a pump to run it through the RO/DI unit and have the waste water return to the holding tanks then it would continue to run through the system and not waste as much water. You could then just fill the holding tanks with a few gallons of water, depending on use and size of holding tanks, maybe once a week.

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Couldn't you just recycle the waste water back through the system? I was thinking of building a system with holding tanks for the water and use a pump to run it through the RO/DI unit and have the waste water return to the holding tanks then it would continue to run through the system and not waste as much water. You could then just fill the holding tanks with a few gallons of water' date=' depending on use and size of holding tanks, maybe once a week.[/quote']

 

In theory yes, as long as you have a pump to provide the appropriate feed pressure - and I presume this is sort of what the zero loss systems do. I wonder, however, what impact this has on the effectiveness and life span of the RO membrane and DI resin for the reasons mentioned above. You would probably have to calculate the trade off between water consumption and membrane/resin replacement. Of course, if you can save and use the reject water for something else as Dennis suggested, then it's still a zero loss without compromising your filtration setup!

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Some "zero waste" systems just plumb the waste water into your house's hot water line. Re-running waste water through the RO/DI unit is supposed to be murder on filter cartridges...

 

Ahh! That makes more sense... thanks Andy! Hmmm.... I wonder if I can figure out a way to do that (plotting)

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If your really serious about the waste water issue read the information and the new unit that spectrapure has out. NO it's not cheep. It is state of the art though. I had a long talk with tec support about the unit. It has a micro processor in it. Membrane flushing system that flushes wi ro water, not tap water as the other flush systems do. If for no other reason at least read about it to understand how it works. To bring things up to speed with the new technology.http://www.spectrapure.com/low_waste_systems.htm

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If your really serious about the waste water issue read the information and the new unit that spectrapure has out. NO it's not cheep. It is state of the art though. I had a long talk with tec support about the unit. It has a micro processor in it. Membrane flushing system that flushes wi ro water' date=' not tap water as the other flush systems do. If for no other reason at least read about it to understand how it works. To bring things up to speed with the new technology.[url']http://www.spectrapure.com/low_waste_systems.htm[/url]

 

Will do - thanks Blaine!

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Zero waste uses a pump to boost the waste water back into the hot water side. Its not that bad in price. Ill get a retail price and let you know. You should be able to find them from someone that sells systems.

 

As far as waste, its 3-1. 3 gallons down the drain, 1 gallon made. If yours is doing 9-1 or whatever its junk or not working correctly. There is no reason it should be doing that.

 

This is one of the units we sell, comes as a zero waste system.

http://www.watts.com/pro/_productsFull.asp?catId=2242&parCat=2269&pid=5595&ref=2

 

Anyhow hopefully I dont get yelled at, didnt want to come across trying to sell stuff. I see these posts here quite a bit but usually just stay quiet. Jody (Reefboy) can help you or get you the stuff from me. :)

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