someone posed this question to me which i did not know how to answer. I have a ro with a recovery rate of 75%. is there a standard that my permeate and concentrate flow shoild be at to achieve 75%?

so to add to my previous post. stamped on my ro is perm 2.08 and conc. .69 for a recovery rate of 75%. This is not what my readings are now, should i reset them to that? hardly seems like much flow.

What are your current permeate and concentrate flows at? Is your RO still at the original configuration or have membranes been added at some point?

First some more info is needed.

What machine do you have (manufacturer / model) and how many membranes are there?

What are the current permeate and concentrate flows, operating pressures (whatever is displayed by the machine) and feed water temperature?

What is the water quality (TDS / Conductivity) and percent rejection?

Perm = 2.8
Conc = 2.9

Original configuraton, but I think the guy
before me messed with the flow settings. I need
to know in my mind this is right.

That doesn't make a whole lot of sense. What is stamped on your RO equals 2.77 and the readings you gave equals 5.7. The readings you say the RO is displaying now equals a 50% recovery. Even if you adjusted the flows back to a 75% setting, you permeate would be approx 4.3 and concentrate at 1.4. I would venture that at some point additional membranes were added or high flow type membranes were put in.

quote:

Originally posted by G2:
Perm = 2.8
Conc = 2.9

Original configuraton, but I think the guy
before me messed with the flow settings. I need
to know in my mind this is right.

These flows do not indicate a 75% recovery regardless of any other factors. Assuming 5.7 gpm feed at 75% recovery your permeate flow would be 4.28 gpm and concentrate flow 1.42 gpm.

You stated that the previous guy messed with the settings - based on what limited info you provided I'd say that's likely.

Again what make and model RO do you have and how many membranes? Have membranes been added since the unit was originally installed?

That is why i am askig, makes no sense.
Started with 2 membrane, still have 2. I can
promise you what is on the machine and original literature = 75%. The idiot that worked here changed it at some point 2 summers ago according to old logs i am looking at. How did you come up with 4.3 and 1.4? just curious.

Jombi - If you do the math, a permeate flow of 2.08 with a concentrate flow of .69 IS a 75% recovery setting.

G2 - If you add 2.8 + 2.9 that equals 5.7gpm. 75% of 5.7 equals 4.275 (4.3) which would be your permeate setting since you want to recover 75%. If you subtract 4.3 from 5.7, you get 1.4 which would be the concentrate.

gotchya

For 75% recovery, your permeate flow will be 3x as high as your concentrate flow (3 x 0.69 = 2.07). For 50% recovery, your permeate flow will equal your concentrate flow (2.8 permeate ~= 2.9 concentrate).

% Recovery = Permeate flow / (permeate flow + concentrate flow) x 100%

2.8 gpm through 2 membranes is a little high, but if your water meets the AAMI limits, this is not a big problem. If you reduce your concentrate flow, your membranes may foul more frequently. You can reduce your concentrate flow by adjusting its flow restrictor. But, in doing so, you will increase the membrane pressure, which will increase the permeate flow...unless you also open the orifice that controls your recycle flow. Increasing the permeate flow will increase the velocity of the water towards the membrane surface, causing particles/bacteria to be held onto the membrane surface (not get washed off with the concentrate)...fouling your RO membrane. I would suggest talking to your 510k vendor before adjusting anything.

If your cleaning frequency on your RO is good, then I would not adust it. If you are having to clean the RO too much, I definitely would not suggest decreasing the concentrate flow.

Don't forget adjusting your recovery means you need to have your pre treatment looked at. You should not adjust your recovery until the 510k company you recieved the system from, verifies that the pretreatment is sized correctly. This can be a BIG problem if you go from 75% to 50% recovery. Just a FYI