New Zero Waste Reverse Osmosis Units

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BBL_Brewer

BBL_Brewer

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I was browsing the net today and stumbled across this article on zero waste reverse osmosis systems. Apparently they are already selling them as well.

http://www.wwdmag.com/membranes-reverse-osmosis/zero-waste-look-future-reverse-osmosis

http://www.costco.com/Premier-Zero-Waste-Reverse-Osmosis-System.product.10034720.html

It's basically your plain Jane RO unit that routes the waste water back into the hot water side of the household plumbing. Makes perfect sense since you don't use hot water for cooking or drinking. This completely eliminates waste water and makes the units 100% efficient. Sounds easy enough, but what I'm not getting is how exactly does it feed the waste water back into the hot water distribution side? At a 4:1 ratio of waste to permeate, that's a lot of waste water that has to go somewhere. If you're not using any hot water while the RO unit is running, where does the water go? I'm thinking that you would have to have a storage tank for the waste water that would feed it back into the water heater or somewhere upstream of the water heater. But the units they are selling don't have such a storage tank. Only the standard pressurized tank for permeate storage and delivery. I suppose as the RO unit uses water and waste is reintroduced into the household plumping that you end up with an equilibrium of water flow. But how would you keep the waste water isolated on the hot water side of the distribution system? Anyone have any bright ideas as to how they might be accomplishing this?
 
There is no excess water to be stored. You are simply moving water around the plumbing and using a small amount that the system will replace.

You are not creating water, only moving it through a couple filters, an RO membrane, and most of it being pumped back into the hot side of the plumbing.

If you put a gallon of water from the cold side of the plumbing through the RO and it generates one quart of RO water then the three quarts of effluent are routed back to the hot side. One quart of water was placed in the RO storage tank and three quarts of water was replaced into the plumbing system resulting in a net usage of one quart of water... and that quart was removed from the plumbing and put in the RO storage tank.

The effluent (waste from the RO process) water is replaced into the hot side plumbing so you are only moving water, there is no excess water.


Sent from my iPad using Home Brew
 
If I got the OP, the question essentially is: will the system end up recycling effluent back to the RO unit input side - because it's pretty clear that it icould do so, given the right plumbing configuration and usage.

The effluent is pumped back into the household hot water line, which runs back through a water heater to a junction with the cold water line downstream of the incoming water supply valve/meter/treatment system, if any.

If nobody is using water for drinking/bathing/cleaning while the RO system is running, eventually 75% of the "water" reaching the RO system input will be from the effluent output "turning the corner" at that junction from the hot side to the cold side.

With a tankless water heating system, that point could occur much sooner than a system with a hot water holding or heating tank, and obviously the larger a tank the longer it would take for the percentage of effluent recycling to reach the maximum possible - the same 75%. And then there's the "loop length" between the RO input and output through the household water system - small homes with short loops would be more likely to have a higher recycling rate than larger homes with long loops.

There's a line in the installation guide that says the system should be installed at least 20' from the water heater. I thought that was curious at the time I read it, now I think there must be some relation to the recycling thing...

[edit] If there's nobody using domestic water there's likely nobody using RO water either, and if the RO tank is full the system isn't drawing water anyway. Practically speaking I'd think the only time the effluent recycling rate could become an issue (assuming there even is an "issue" with high rates of recycling) would be when refilling a completely drawn down RO tank while everyone is out of the household, on a plumbing system with the least holding capacity in the RO "loop"...

Cheers!
 
johnsma22 said:
There is no excess water to be stored. You are simply moving water around the plumbing and using a small amount that the system will replace.

You are not creating water, only moving it through a couple filters, an RO membrane, and most of it being pumped back into the hot side of the plumbing.

If you put a gallon of water from the cold side of the plumbing through the RO and it generates one quart of RO water then the three quarts of effluent are routed back to the hot side. One quart of water was placed in the RO storage tank and three quarts of water was replaced into the plumbing system resulting in a net usage of one quart of water... and that quart was removed from the plumbing and put in the RO storage tank.

The effluent (waste from the RO process) water is replaced into the hot side plumbing so you are only moving water, there is no excess water.


Sent from my iPad using Home Brew
Click to expand...

You're exactly right. The water is essentially being recirculated, only it enters the distribution system on the hot side. But they way they make it sound, it gets used as hot water instead of being recirculated back to the RO unit to get filtered again (which is what I suspect is happening). The only way that the waste water could be used as hot water would be to run hot water while the RO unit is in operation. Or even better, have the system set up so that the RO unit can only operate while the hot water is running. I don't see how that would be advantageous though. If the waste water recirculates back to the RO unit for further filtering the feed water will become more and more saturated with impurities. This will result in poorer water quality in the filtered water and will reduce the life of the membrane. If the RO unit is only in operation while the hot water is running you will use all of the waste water as hot water and none of it will return to the RO unit for further filtering. Problem is, it would take a lot longer to generate large amounts of filtered water this way. A 100 GPD unit can only generate about 50 gallons of water per day. That's 2 gallons per hour. You would have to run a lot of hot water to get 50 gallons of filtered water this way. So where is the advantage here? It's a good marketing strategy, but I'm not buying it. Best case scenario, you save a little money on waste water and have to spend that money on replacing the membrane more often. Why bother?
 
day_trippr said:
If I got the OP, the question essentially is: will the system end up recycling effluent back to the RO unit input side - because it's pretty clear that it icould do so, given the right plumbing configuration and usage.

The effluent is pumped back into the household hot water line, which runs back through a water heater to a junction with the cold water line downstream of the incoming water supply valve/meter/treatment system, if any.

If nobody is using water for drinking/bathing/cleaning while the RO system is running, eventually 75% of the "water" reaching the RO system input will be from the effluent output "turning the corner" at that junction from the hot side to the cold side.

With a tankless water heating system, that point could occur much sooner than a system with a hot water holding or heating tank, and obviously the larger a tank the longer it would take for the percentage of effluent recycling to reach the maximum possible - the same 75%. And then there's the "loop length" between the RO input and output through the household water system - small homes with short loops would be more likely to have a higher recycling rate than larger homes with long loops.

There's a line in the installation guide that says the system should be installed at least 20' from the water heater. I thought that was curious at the time I read it, now I think there must be some relation to the recycling thing...

[edit] If there's nobody using domestic water there's likely nobody using RO water either, and if the RO tank is full the system isn't drawing water anyway. Practically speaking I'd think the only time the effluent recycling rate could become an issue (assuming there even is an "issue" with high rates of recycling) would be when refilling a completely drawn down RO tank while everyone is out of the household, on a plumbing system with the least holding capacity in the RO "loop"...

Cheers!
Click to expand...

Right, you get what I'm saying. But if the loop you described goes full circle then eventually you would be pulling hot water back into the feed for the RO unit. Three problems with that. You're re-filtering waste water, you're sending hot water to the membrane (which isn't optimal) and you're heating that water for no good reason (ie...wasting energy).
 
BBL_Brewer said:
Right, you get what I'm saying. But if the loop you described goes full circle then eventually you would be pulling hot water back into the feed for the RO unit. Three problems with that. You're re-filtering waste water, you're sending hot water to the membrane (which isn't optimal) and you're heating that water for no good reason (ie...wasting energy).
Click to expand...

All true (well, except for the unknown membrane vs hot"ish" water part - jury's still out on that one). Except for incidental/concurrent water consumption in parallel, as long as the RO system is generating there will be "hot" water backing up into the cold side of the loop. It's intrinsic to the design.

Clearly there's an optimal configuration and there's also an optimal operating mode where the recycling is minimized by flushing the loop through parallel water usage...

Cheers!
 
day_trippr said:
Clearly there's an optimal configuration and there's also an optimal operating mode where the recycling is minimized by flushing the loop through parallel water usage...

Cheers!
Click to expand...

Right. I'm just having trouble seeing what that optimal operating mode is and how it would benefit consumers that are using their RO units to generate more than just a few glasses of drinking water in a given day.
 

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