RODI Levels Seem High

[AaronFReef]

I just finished building and testing my frankenstein RODI system. First problem I noticed was I had reversed the brine and clean lines on both membranes but I reversed that and fixed it. Noticed that with my TDS meter (not pictured but now added to the white teed clean output line from the membranes). I let my membranes flow (teed into the drain) for a while to see what my ppm TDS settled out on and it actually only dropped to mid 20's. With the second membrane flushing (and therefore bypassed) I get a TDS of low teens. I realize putting brine into my second membrane will raise my TDS out of my averaged output, but I was surprised at how high it was. Should I worry about 20 TDS coming out of my RO and into my 3 part DI system? Seems like I would use lots of resin, no? My PSI was 80 by the way. Perhaps its too high? I do get 0 ppm on my DI output, but worry something is wrong that will cost me lots of resin.

 

[cwalton00]

What do you mean by brine?

 

[Flippers4pups]

Brine?

 

[Water Dog]

I think he means waste line.

 

[AaronFReef]

The waste of an RO is sometimes called the brine since it concentrates the salt. Sorry for the confusion.

 

[cromag27]

the correct term is indeed brine. if you don’t need the second membrane i’d do away with it. yes, this is an adverse effect of have dual membrane, which means you’ll burn through your di faster. 80psi is not too high.

 

[Opus]

Hard to say if there is an issue since you didn't give the tds of your tap water. My tap tds is around 450 and I get 2 tds after my membrane but I'm running a spectrapure. At 20 a normal DI cartridge will give you around 220 gallons of 0 tds water. Not sure on your 3 stage setup.

 

[AaronFReef]

Great thanks you two. Yeah my TDS is 450 in too. I’ll be okay with a few hundred gallons of use before new resin I suppose. Sounds normal.

 

[cromag27]

Great thanks you two. Yeah my TDS is 450 in too. I’ll be okay with a few hundred gallons of use before new resin I suppose. Sounds normal.

i get much much more than that. but i’m using spectrapure’s newest resins and i don’t run dual membranes. a few hundred gallons is nothing.

 

[cromag27]

so you’re rejection rate is 95.5% right now. your membranes are shot.

 

[AaronFReef]

Weird. They’re brand new. Maybe because I ran them wrong for a minute with the flow restrictors on the clean lines and the waste flowing freely.... thanks for running those numbers for me.

 

[Water Dog]

At an incoming TDS of 450, even BRS, the only proponent of the (wasteful IMO) double membrane setup advises against it. If you got a standard Dow Filmtec 75 gpd membrane at a 98% rejection rate, you should get 9 tds after the RO membrane. If you went with the Spectrapure 99% membrane, you should get around 4 to 5 tds.

4-5 tds will allow your DI set up to last a lot longer than if you are pushing your current 20 tds though it. IMO, get rid of the second RO membrane and make sure the current membrane that you’re using is running to spec.

 

[AaronFReef]

Okay. Thanks! Will do.

 

[Opus]

Great thanks you two. Yeah my TDS is 450 in too. I’ll be okay with a few hundred gallons of use before new resin I suppose. Sounds normal.

I would do like others suggest and just go with 1 membrane. I don't see how you could have ruined a new membrane in a few minutes but I guess it is possible. What brand membranes do you have?

As for DI usage. My 2 tds will get me around 2200 gallons of 0 tds water compared to 220 you will get at your current 20 tds.

 

[AaronFReef]

They are Dow filmtec 75 gpd. This is basically the BRS special. All from their parts. I suppose I could go parallel and put both membranes from the carbon and tee their clean lines together. Twice the waste instead of half but well water is cheap I guess.

 

[Water Dog]

Ugh, wait, are you really on well water? The excess CO2 in well water will really deplete your DI resin. However, there are some relatively simple solutions to combat CO2 in well water.

 

[AaronFReef]

I’ve read and heard about those but I think I’d rather avoid the pain of a CO2 scrubber (dissipation tank) so decided I’d pay a bit more for resin. I may eventually install one but right now while my equipment room addition is under construction I’m doing a temporary mixing station outdoors right behind my tank and that means I want to be able to shut stuff down easier. But I’d rather not have additive reasons my DI is being used up too quick and will split the membrane setup back apart.

 

[TMB]

Is the picture above still how you have everything currently hooked up? or have you changed anything since that pic?

 

[AaronFReef]

It has changed considerably since the pic.

 

[cromag27]

stick with one membrane and replace everything with spectrapure. you will save money in the long run. their membranes and di are far superior.

just a few other things, make sure you aren’t operating the rodi unit in extreme temperatures and sanitize it once per 12 months. adjust the waste appropriately (4:1 - 3:1).