Quick noob RO/DI system questions

billysprout

Active Member
Review score
+0 /0 /-0
View Badges
Joined
Aug 27, 2021
Messages
307
Reaction score
345
Review score
+0 /0 /-0
Location
10,000 fathoms
Hi friends, just got my spectrapure 70gpd 4-stage (sediment - carbon - ro - di) rodi filter up and running and the membrane is at about 65 psi. Have a couple questions.

* What ratio of RODI water to waste water should I expect? Mine is probably about 3:1 right now.
* How do I improve that ratio or rejection rate if mine is off? e.g. do i lower the pressure, add another filtration step of a specific type, etc
* Can I recirculate waste water through my filter without straining/stressing the system?

Thanks all,
Billy
 
Fritz

Garf

Valuable Member
Review score
+0 /0 /-0
View Badges
Joined
Oct 23, 2020
Messages
1,906
Reaction score
2,442
Review score
+0 /0 /-0
Location
BEEFINGHAM
Hi friends, just got my spectrapure 70gpd 4-stage (sediment - carbon - ro - di) rodi filter up and running and the membrane is at about 65 psi. Have a couple questions.

* What ratio of RODI water to waste water should I expect? Mine is probably about 3:1 right now.
* How do I improve that ratio or rejection rate if mine is off? e.g. do i lower the pressure, add another filtration step of a specific type, etc
* Can I recirculate waste water through my filter without straining/stressing the system?

Thanks all,
Billy
You could certainly add another RO membrane to process the rejected water from the first membrane, but I don’t.
 

Adrift

Well-Known Member
Review score
+0 /0 /-0
View Badges
Joined
Apr 27, 2021
Messages
698
Reaction score
1,941
Review score
+0 /0 /-0
Location
Fort Worth
You could certainly add another RO membrane to process the rejected water from the first membrane, but I don’t.
Agreed the sell the kit at bulk reef supply. Just search water saver. I didnt opt for one either though, price per gallon is pretty cheap. Like running faucets in winter months.
 

Garf

Valuable Member
Review score
+0 /0 /-0
View Badges
Joined
Oct 23, 2020
Messages
1,906
Reaction score
2,442
Review score
+0 /0 /-0
Location
BEEFINGHAM
Agreed the sell the kit at bulk reef supply. Just search water saver. I didnt opt for one either though, price per gallon is pretty cheap. Like running faucets in winter months.
I think it’s a case of deminishing returns, as the pressure across the second membrane will be considerably less than the first, at least in my eyes :)
 

Gtinnel

10K Club member
Review score
+0 /0 /-0
View Badges
Joined
Mar 20, 2020
Messages
10,324
Reaction score
10,447
Review score
+0 /0 /-0
Location
Charleston, WV
I do run a second membrane and am considering adding a third to my system. Whether you can add an extra membrane depends on your source waters tds and your pressure. Your pressure is at the lowest limit recommended for a second membrane.

Your ratio of product:waste looks about right 1:4 is fairly common. Don't get that number and your rejection rate confused they're completely different things. Which one are you trying to improve your rejection rate, or are you wanting to have less waste water.
 
Fritz
OP
B

billysprout

Active Member
Review score
+0 /0 /-0
View Badges
Joined
Aug 27, 2021
Messages
307
Reaction score
345
Review score
+0 /0 /-0
Location
10,000 fathoms
I do run a second membrane and am considering adding a third to my system. Whether you can add an extra membrane depends on your source waters tds and your pressure. Your pressure is at the lowest limit recommended for a second membrane.

Your ratio of product:waste looks about right 1:4 is fairly common. Don't get that number and your rejection rate confused they're completely different things. Which one are you trying to improve your rejection rate, or are you wanting to have less waste water.
sorry, i swapped the ratio. it's 1:3 RODI to waste ratio right now. so WAY lower than the common ratio.

I want to have less waste water, specifically.I'm not in a rush and I want to conserve water cos I'm in california. thanks for clarifying that it's different than rejection rate. ^_^
 

LiveFreeAndReef

Valuable Member
Review score
+0 /0 /-0
View Badges
Joined
Jul 8, 2021
Messages
1,946
Reaction score
2,453
Review score
+0 /0 /-0
Location
New Hampshire
sorry, i swapped the ratio. it's 1:3 RODI to waste ratio right now. so WAY lower than the common ratio.

I want to have less waste water, specifically.I'm not in a rush and I want to conserve water cos I'm in california. thanks for clarifying that it's different than rejection rate. ^_^
1:3/1:4 are the typical Ro/waste ratios
 

Woodyman

Well-Known Member
Review score
+0 /0 /-0
View Badges
Joined
May 25, 2021
Messages
864
Reaction score
877
Review score
+0 /0 /-0
Location
Ohio
sorry, i swapped the ratio. it's 1:3 RODI to waste ratio right now. so WAY lower than the common ratio.

I want to have less waste water, specifically.I'm not in a rush and I want to conserve water cos I'm in california. thanks for clarifying that it's different than rejection rate. ^_^

If your trying to conserve water I would recommend a second membrane, and bump your pressure up to 80-90psi with a booster pump.
 

BZOFIQ

2500 Club Member
Review score
+0 /0 /-0
View Badges
Joined
Jul 31, 2014
Messages
3,046
Reaction score
2,808
Review score
+0 /0 /-0
Location
NYC
I built a system recently with dual membranes and with booster pump running pre membrane at 80 PSI.

I waste 3.5 gallons for every 5 gallons of RO produced. That said my incoming TDS is only at 40 so i get zero out of both 1st and 2nd membrane after few minutes of production.

Using 2x75GPD membranes I produce about 200 GPD.

BTW, the trick was to use one size up more restrictive restrictor if that makes sense, I dont think you want to do that if your incoming TDS is very high
 

BZOFIQ

2500 Club Member
Review score
+0 /0 /-0
View Badges
Joined
Jul 31, 2014
Messages
3,046
Reaction score
2,808
Review score
+0 /0 /-0
Location
NYC
Here is a link to my diagram, ignore the automation that doesn't apply to your system.

 
AS

Gtinnel

10K Club member
Review score
+0 /0 /-0
View Badges
Joined
Mar 20, 2020
Messages
10,324
Reaction score
10,447
Review score
+0 /0 /-0
Location
Charleston, WV
If your trying to conserve water I would recommend a second membrane, and bump your pressure up to 80-90psi with a booster pump.
I couldn't agree more...assuming the OPs source water tds isn't very high.

The tds going into the second membrane will be increased because it's the concentrate (waste) of your first membrane. If your tap water has a high tds to start with you will burn through di quicker and it won't be cost effective to run a second membrane.
 
OP
B

billysprout

Active Member
Review score
+0 /0 /-0
View Badges
Joined
Aug 27, 2021
Messages
307
Reaction score
345
Review score
+0 /0 /-0
Location
10,000 fathoms
thanks everyone! i appreciate the help. my source water TDS is 220 out of the faucet. lol. i want to cut down on waste water specifically, so i don't mind using the extra DI resin. i think i'll add a second membrane and up the pressure for my next project. maybe add a second DI step too since I'm still not tapped into if/when to replace my resin.
 

Gtinnel

10K Club member
Review score
+0 /0 /-0
View Badges
Joined
Mar 20, 2020
Messages
10,324
Reaction score
10,447
Review score
+0 /0 /-0
Location
Charleston, WV
thanks everyone! i appreciate the help. my source water TDS is 220 out of the faucet. lol. i want to cut down on waste water specifically, so i don't mind using the extra DI resin. i think i'll add a second membrane and up the pressure for my next project. maybe add a second DI step too since I'm still not tapped into if/when to replace my resin.
Your source water tds is relatively high (BRS recommends it not be over 300) for a second membrane, so you will likely be okay just make sure to know when your di is depleted. I'd say adding a second di, or even better seperate anion and cation stages is a really good idea.
Are you trying to reduce waste water to save money or is for environmental reasons?
 
OP
B

billysprout

Active Member
Review score
+0 /0 /-0
View Badges
Joined
Aug 27, 2021
Messages
307
Reaction score
345
Review score
+0 /0 /-0
Location
10,000 fathoms
Your source water tds is relatively high (BRS recommends it not be over 300) for a second membrane, so you will likely be okay just make sure to know when your di is depleted. I'd say adding a second di, or even better seperate anion and cation stages is a really good idea.
Are you trying to reduce waste water to save money or is for environmental reasons?
ooh, i think BRS did a video on anion/cation stages. i'll look it up. ^_^

it's purely environmental; water is extremely cheap here. despite the fact that we've been in a drought for almost a decade. lol
 
Avast

What do you use?

  • Gfo

    Votes: 28 5.9%
  • Carbon

    Votes: 171 36.2%
  • Carbon & GFO

    Votes: 153 32.3%
  • Water changes

    Votes: 328 69.3%
Reef Chasers Aquaculture
Top