RODI modification. Good or bad?
- Thread starter rob92
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There are a number of quirks here but foremost, I have come to believe that any time you run your flush water to another membrane and squash the 4:1 ratio the results are not that good. Is the intention of this system to make larger amounts of water faster?
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rob92
Active Member
My main reason to cut down on the waste water is because the unit is located in the basement of my parents 100 year old house. I could save it in barrels for when we water the plants and the yard but the system would produce more waste than what we would be able to store. Also I can't run the waste line up to the toilets or washer due to it being 2 floors up and I'm not able to connect it to the dishwasher which is on the next floor up since we never even use it
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rob92
Active Member
I'm not really concerned about paying for the extra water I use since it's only $0.006405 per gallon it's just I would feel better knowing I'm paying for water that I'm able to actually use and not just throw it back into the sewer system
It doesn't work quite like that. The backpressure you will have on the first membrane will basically render it useless. The purpose of running the waste from one membrane into another is to increase the GPD or production rate, it is NOT a water saving device. Many have tried this same idea but long term it does not work since the membranes eventually plug or foul prematurely. The person who perfects this in a cost effective manner will be an instant millionaire guaranteed. It just does not work with todays membrane technologies and materials.
All that waste eventually has to go somewhere, it does not dissapear so after a couple membranes it becomes so concentrated the membrane plugs since you do not have the suggested 4:1 waste ratio to carry it away.
If you want to save water the only proven method is to flush the membrane with stored DI water which is how the Spectrapure UHE systems operate. They use a microrocessor to flush the system with DI on a timed basis then double rinse it and pickle the membrane in DI when it is sitting dormant.
If your tap water is naturally soft or you use softend water AND your TDS is lower than normal (less than 250) you might be able to reduce the waste ratio to 3:1 and in rare cases as low as 2:1 but this is not the norm nationwide. Spectrapure sells 3:1 and 2:1 systems but hey are not for everyone. You need to know your water condition before attempting low waste or you could end up replacing a membrane and DI resin pretty quickly.
All that waste eventually has to go somewhere, it does not dissapear so after a couple membranes it becomes so concentrated the membrane plugs since you do not have the suggested 4:1 waste ratio to carry it away.
If you want to save water the only proven method is to flush the membrane with stored DI water which is how the Spectrapure UHE systems operate. They use a microrocessor to flush the system with DI on a timed basis then double rinse it and pickle the membrane in DI when it is sitting dormant.
If your tap water is naturally soft or you use softend water AND your TDS is lower than normal (less than 250) you might be able to reduce the waste ratio to 3:1 and in rare cases as low as 2:1 but this is not the norm nationwide. Spectrapure sells 3:1 and 2:1 systems but hey are not for everyone. You need to know your water condition before attempting low waste or you could end up replacing a membrane and DI resin pretty quickly.
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How hard is it, thats the biggest factor since membranes love softened water. If its soft you could easily go to 3:1 and possibly 2:1 if its real soft.
Sears, Lowes or HD sell hardness test kits pretty cheap. They are usually next to the water softeners since it is what you use to determine if you need a softener or not.
Engloid
Valuable Member
I also notice that the RO water from the first membrane isn't going into the DI.
I've tried a few ways of doing my RO setup. They said that by running the RO membranes in a chain, it increases GPD, but I couldn't really tell any difference. I just run them parallel (like you have your ones on the right), so that my water all goes through sediment filters, then splits to the RO intake side, then all the waste lines merge and go to a drain.
I've tried a few ways of doing my RO setup. They said that by running the RO membranes in a chain, it increases GPD, but I couldn't really tell any difference. I just run them parallel (like you have your ones on the right), so that my water all goes through sediment filters, then splits to the RO intake side, then all the waste lines merge and go to a drain.
Here is the most common way to plumb a dual membrane system:
http://spectrapure.com/huds/DUAL.pdf
Every major vendor does it this same way where the waste from the first is fed into the second so you basically double the GPD if you are usng identical membranes. It is not intended as a water saving measure since the TDS going into the second membrane is already higher than normal so the downstream membrane would fail prematurely when you reduce the waste.
http://spectrapure.com/huds/DUAL.pdf
Every major vendor does it this same way where the waste from the first is fed into the second so you basically double the GPD if you are usng identical membranes. It is not intended as a water saving measure since the TDS going into the second membrane is already higher than normal so the downstream membrane would fail prematurely when you reduce the waste.
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GHill762
Valuable Member
he has two di cartridges in the picture, one attached to the unit and another separate di for the secondary ro membranes..
More is not better with RO/DI. Everything you add in front of the RO membrane has an associated headloss or pressure drop which reduces the membrane efficiency or rejection rate. The idea is to have as few high quality filters as possible for the job at hand, this will give you the moste efficient, cost effective system. Dual DI on the other hand is downstream of the membrane and a good investment for most.
Engloid
Valuable Member
I disagree. Sediment filters will offer little to no pressure drop, unless you pack them tightly. In other words, pressure will equal out on both sides of the sediment filter, because your biggest restriction is at the membrane. You can bottleneck anything, and pressure will equalize, but once you pass your largest restriction, pressure will drop. If your sediment filter is your largest restriction, something's wrong.
