Multiple RO membranes

[alexkharden]

Ok, so I bought a 5 stage 75gpd RO/DI system, too fast, and then regretted it. So now I'm ordering another DI canister, and a "150gpd RO upgrade kit", which basically runs the RO wastewater directly into another membrane and filters it again.

The question I have is, how many times can this be done? 3 RO membranes? 4?

I've tried a bunch of different searches, but I'm not wording the searches correctly or something because I keep coming up with bupkis.

Thanks!

 

[MiddletoM]

i think you can add more than 2 but you have to make sure you are getting 65psi pressure or something like that. may be easier to just get a second RODI system.

 

[Dmorty217]

Get a booster pump with more than one membrane otherwise you won't see the production your looking for. You can have 100 membranes if you wanted that many

 

[albano]

Ok, so I bought a 5 stage 75gpd RO/DI system, too fast, and then regretted it. So now I'm ordering another DI canister, and a "150gpd RO upgrade kit", which basically runs the RO wastewater directly into another membrane and filters it again.

Why do you need another DI canister?

 

[jayball]

The question I have is, how many times can this be done? 3 RO membranes? 4?

I am sure you could use quiet a few with adequite pressure but keep in mind that each subsequent one you add will raise overall TDS, eating your DI resin.

 

[alexkharden]

From what I've read, it allows more compete usage of the first canister. When the first starts to go out, if you only have one, then you're left with the choice of running increasingly high tds water - or changing it out prematurely. With a second one you can use the first one fully while still having good water. Then, when the first one goes out, throw it away, move the second one into the first position, and put the new canister in the second position.

 

[albano]

From what I've read, it allows more compete usage of the first canister. When the first starts to go out, if you only have one, then you're left with the choice of running increasingly high tds water - or changing it out prematurely. With a second one you can use the first one fully while still having good water. Then, when the first one goes out, throw it away, move the second one into the first position, and put the new canister in the second position.

You will probably use the same amount of DI resin with whatever same amount of water that you make...
Do you have a TDS meter with RO unit?

 

[alexkharden]

I am sure you could use quiet a few with adequite pressure but keep in mind that each subsequent one you add will raise overall TDS, eating your DI resin.

That makes sense. So it's a trade off between resin vs waste water. Unless you get resin ridiculously cheap, it's probably best to stick with 2 RO membranes. Unless you have very low tds water to begin with - then it might not be such a bad idea to have more than 2.

 

[alexkharden]

Get a booster pump with more than one membrane otherwise you won't see the production your looking for. You can have 100 membranes if you wanted that many

I did order a booster pump

 

[alexkharden]

You will probably use the same amount of DI resin with whatever same amount of water that you make...
Do you have a TDS meter with RO unit?

Yes, dual TDS with my RO/DI.

 

[outy]

Adding a second membrane is only recommended if you have low TDS incoming.

You have to take into account for proper usage and results you need a 4 to 1 rejection rate or you will just foul membranes quickly.

 

[alexkharden]

I don't mean to be adversarial, but that doesn't sound right.

First, I've seen membranes for sale that have better ratios than 1:4, so that can't be a hard and fast rule in the first place.

Second, I don't think fouling the membrane will be a result. If the water is the correct temp and pressure, then it will function as it should.

Think about it, if my incoming tds is 100 and my ro waste is 130, how will that foul my second membrane any faster than if my initial tds was 130 going to a single membrane?

Maybe I'm wrong.

 

[alexkharden]

Unless your initial tds is like 1000, but then you're going to foul membranes quickly no matter what.

 

[outy]

Unless your initial tds is like 1000, but then you're going to foul membranes quickly no matter what.

I would not add a second membrane if my TDS was over 150.



Also hardness of water maters

say you have 200 going in and 300 coming out add another and you now have300 incoming and 400 coming out of that one.

with each additional one you are raising TDS going to the DI, as actual TDS output of clean water is the BEST out of the first membrane.

 

[outy]

so at 200 TDS in first membrane produces 8 TDS

second membrane has 300 going in and produces 14 TDS


Add another and raise the TDS


You should be following the procedure now

 

[alexkharden]

I would agree with that, certainly, regarding the best water coming from the first membrane. I also considered the increased wear on the DI. Just trying to find a decent balance between water waste, speed of production, DI wear, and membrane wear. I don't know what the tds in my house is yet, as I haven't hooked up my system.

 

[wildman926]

I am sure you could use quiet a few with adequite pressure but keep in mind that each subsequent one you add will raise overall TDS, eating your DI resin.

Please explain how adding additional membranes will raise overall TDS.

 

[alexkharden]

I just took the in line tds meter and dipped the line end into a cup of tap water. It fluctuated between 23 and 67, so I'm going to assume my tds is less than 70.

 

[alexkharden]

Please explain how adding additional membranes will raise overall TDS.

After every membrane the waste water tds will increase. Not the produced ro water.

 

[alexkharden]

I'm not sure about the product water actually. I sent that without thinking.