Max The New reefer
Active Member
hello folks, I want a RODI machine, I care more about water wasted then anything, Ideally 2:1. Price is not a issue, just under 500 dollars which is pretty reasonable i think.
RODI choosing
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Max The New reefer
Active Member
hmm ok, Idk whats in my water, I have city water, I need either a 5 or 6 stage system, which one? also why does water pressure matter? and whats tds? I literally know nothing about them
ichthyogeek
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Basically, it boils down to what's in your water. If the water is treated with chloramines, you'll want 2 carbon blocks, and if the TDS is incredibly high, you'll want a dual RO membrane. Ask your dad if he can get his hands on a water quality report. It should be available to whoever pays the water bill in your household. It details what gets added into the water, as well as what all is in the water.
TDS = Total Dissolved Solids. They range from ionics (anions and cations like sodium and chloride ions) to small dissolved solids (metabolic byproducts, etc.). The higher the TDS, the more "stuff" is in your water. RODI units essentially remove the "stuff" through a 4 step process (detailed in post below).
TDS = Total Dissolved Solids. They range from ionics (anions and cations like sodium and chloride ions) to small dissolved solids (metabolic byproducts, etc.). The higher the TDS, the more "stuff" is in your water. RODI units essentially remove the "stuff" through a 4 step process (detailed in post below).
ichthyogeek
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So from what I understand, all RODI units derive from the base 4 stage model: sediment, carbon, RO membrane, DI resin. 5 stage usually incorporates an extra carbon block, 6 stage might be an extra DI resin, etc.
Sediment - This is typically a 1-5 micron cartridge made from spun polymer floss. Its purpose is to remove all the "large" particles that are greater than the designated rating. Think rust particles, dirt/sediments, bugs, those kinds of things. Although with modern water purification technology, only the small stuff should be getting through your pipes).
Carbon - This is a similarly sized (1-5 micron) cartridge made of pure carbon. The carbon works to adsorb (not ABsorb, ADsorb) dissolved organics (think proteins, etc.). It also allows for the decomposition of chlorine gas and chloramine (added to kill bacteria!) via electron exchange to create chloride ions (maybe also ammonia for chloramine, unsure about what happens to the -amine part at this stage).
RO membrane - This is where most of the magic happens. It's a membrane that water is forced through. It operate by taking the concept of osmosis, and then brute forcing a reversal. By forcing the water through a ridiculously small membrane, most of the dissolved salts and other TDS stuff left after going through the sediment and carbon stages gets rejected in a high TDS effluent.
DI resin - Any little left over ions that make it past the RO membrane, get sucked up by the De-Ionization resin. The resin is either positively or negatively charged, and therefore binds to negatively or positively charged ions.
Sediment - This is typically a 1-5 micron cartridge made from spun polymer floss. Its purpose is to remove all the "large" particles that are greater than the designated rating. Think rust particles, dirt/sediments, bugs, those kinds of things. Although with modern water purification technology, only the small stuff should be getting through your pipes).
Carbon - This is a similarly sized (1-5 micron) cartridge made of pure carbon. The carbon works to adsorb (not ABsorb, ADsorb) dissolved organics (think proteins, etc.). It also allows for the decomposition of chlorine gas and chloramine (added to kill bacteria!) via electron exchange to create chloride ions (maybe also ammonia for chloramine, unsure about what happens to the -amine part at this stage).
RO membrane - This is where most of the magic happens. It's a membrane that water is forced through. It operate by taking the concept of osmosis, and then brute forcing a reversal. By forcing the water through a ridiculously small membrane, most of the dissolved salts and other TDS stuff left after going through the sediment and carbon stages gets rejected in a high TDS effluent.
DI resin - Any little left over ions that make it past the RO membrane, get sucked up by the De-Ionization resin. The resin is either positively or negatively charged, and therefore binds to negatively or positively charged ions.
ichthyogeek
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From what I understand, water pressure matters, because in order to successfully brute force the water through the RO membrane, sufficient water pressure needs to be applied in order to keep a sustained amount of pressure in the membrane, which allows for effective reverse osmosis.
Also, you've probably seen this, but here, a relatively outdated list of 4 stage membranes:
Keep in mind that the prices are relatively outdated (they fluctuate because that's the capitalist market for ya) by 6 months or so. But the other information (things like micron size, waste:RO water ratio, etc.) should still be accurate. I really need to figure out a way to auto-scrape for pricing....
Also, you've probably seen this, but here, a relatively outdated list of 4 stage membranes:
Keep in mind that the prices are relatively outdated (they fluctuate because that's the capitalist market for ya) by 6 months or so. But the other information (things like micron size, waste:RO water ratio, etc.) should still be accurate. I really need to figure out a way to auto-scrape for pricing....
Max The New reefer
Active Member
ok, that was all very helpful, I'll ask my dad and get back to you!
Opus
2500 Club Member
If water to waste ratio is your main concern, then your best bet is to get a system with a good rejection ratio and then add a flow restrictor you can adjust. Personally I would go with the 99% rejection membrane from Spectrapure but the 98% ones from them or any of the other brand name places will be good. Then get one with a capillary flow restrictor you can cut so you can adjust the water pressure on the RO membrane. You also can get a flow valve that you can adjust manually. You can always buy any of the systems and change out the flow restrictor. Once you have the unit, you will have to manually adjust the flow restrictor until you get to your desired waste ratio. Just realize, as you decrease the amount of waste water, you are decreasing the life of the RO membrane because it is taking on more waste. How much of a decrease, I have no idea. In a normal use scenario, a ro membrane should last 5 to 7+ years. So taking a year or 2 off that is probably OK with you if decreasing the waste water is your main concern.
Also note since we are entering the winter months, the systems are rated with water at around 77 degrees. As the water gets colder the membrane works more efficiently but slower. In the summer months my system fills a 5 gallon jug in around 60 minutes. During the winter it can get to 80 to 90 minutes. I'm in Texas where we have mild winters, not sure what you are looking at as you go further north.
Also note since we are entering the winter months, the systems are rated with water at around 77 degrees. As the water gets colder the membrane works more efficiently but slower. In the summer months my system fills a 5 gallon jug in around 60 minutes. During the winter it can get to 80 to 90 minutes. I'm in Texas where we have mild winters, not sure what you are looking at as you go further north.
ShepherdReefer
5000 Club Member
Great topic. I have been looking for a better RO/DI for the past few weeks. I found a unit from Oceanic Water Systems. It is commercial-grade but produces 400gpd with 0 tds. I have not decided yet.
Opus
2500 Club Member
I looked at the website. I've never heard of them but I wasn't impressed with their information. For one I didn't see where they actually sold a 400gpd membrane but they did have the full blown system. Second, when looking at the 300 gal membrane they state it removes chlorine. That is not really true, chlorine will destroy the ro membrane. They also only rate the membrane at 96% rejection rate. I personally would rather stick with a 100 gpd that gives 99% rejection.
