RO Rejection Rate based on Pressure

[johanasu]

If you increase from 40 to 60 to 80 PSI, should you note an increase in rejection rate for each step up?

 

[evolved]

Assuming you're also tuning the flow restrictor at each step, yes.

 

[johanasu]

Any idea what kind of improvement you are likely to see?

 

[evolved]

Usually enough to justify the cost of a booster pump in saved DI cost.

An actual number, not sure.

 

[johanasu]

Our school water pressure is 44PSI and I am getting 92% rejection. I am hoping a booster pump to 70+ PSI will get me up over 96% rejection... we shall see!

 

[m-six hundred]

Ouch, good luck. Maybe make water art home and bring it to the school.

 

[johanasu]

I've been lugging RODI for the current tanks, 20 20 30 40 and 14. Not going to lug it back and forth for the 150 as well

We had a RODI system donated, and the money for a booster pump, just getting the paperwork sorted for the booster (taking forever).

 

[reefstew]

This is a good question to be answered by Jeremy or Charles at Spectrapure. They have a forum on here so that might be a good place to ask.

 

[azjohnny]

IME increased water pressure has increased water production and TDS removal. I run my Maxcap at 100 psi and get 168 gpd ( 7 gph) with a 99% rejection rate with a Spectrapure Select Plus membrane

Spectrapure suggests not to go over 80 psi. I have run @ 100psi for about 3 yrs now with no issues

 

[azjohnny]

Our school water pressure is 44PSI and I am getting 92% rejection. I am hoping a booster pump to 70+ PSI will get me up over 96% rejection... we shall see!

Do you ever flush the membrane? with a rejection rate you could be fouling the membrane.

What is the bad/good ratio of the water?

 

[johanasu]

There is a manual flush in place that I used when I received the system (donated) used. I have adjusted the ratio to 4:1 as the system is sold by BRS as a "water saver" and it is run around 2.25:1 by default.

The interesting thing about these dual membrane systems is that you use the waste water from the first membrane to drive the second membrane. If I have 400+ incoming TDS to the first membrane, I am going to have 500+ incoming TDS to the second membrane(waste water from the first membrane). Then the two RO outputs are combined to a single output at 31 TDS. So I'm wondering if the first membrane is putting out 20 TDS and the second is producing 40 TDS that is combined to average 30-31 TDS. 20 from 400 is 95% and 40 from 500 is 92%. Not bad at 42 PSI.

The really odd thing is when I run the RO membranes singly, there must be a glitch in the setup, as I was getting higher output TDS than the two combined...so strange...

Hopefully we'll get our hands on a booster pump and I can update if it helps the rejection rates.

 

[johanasu]

Well I took it all apart and re-assembled it. Adjusted the flow restrictor to be 4:1, secured all connections, did another flush and now I am here:

 

[azjohnny]

If I have 400+ incoming TDS to the first membrane, I am going to have 500+ incoming TDS to the second membrane

If your incoming TDS is 400 the waste water will be higher than 500. My feed is around 650 and the waste is around 950. Remember the waste is a concentrated brine

 

[azjohnny]

Well I took it all apart and re-assembled it. Adjusted the flow restrictor to be 4:1, secured all connections, did another flush and now I am here:

Your final TDS should be lower than 22. Based on your 400 ppm TDS that is only a 95% rejection rate.

Is that with a booster pump?

By improving your rejection rate by 2% you will double the life of your DI

 

[azjohnny]

Here is a link to Spectrapure's Reef Central page there is a lot of good info in the stickies

http://reefcentral.com/forums/forumdisplay.php?f=229

 

[johanasu]

95% at 42psi isn't too bad. Not to mention the rejection rate through a dual membrane system is actually higher than that. Remember what you said, the secondary membrane is getting feed water over, 550 tds, maybe higher. So the combined TDS of the primary and secondary membrane outputs at 22TDS is actually pretty solid. If it gets even better with a booster pump that will be great.

If you assume 50% of the total output from each membrane, and each membrane functioning at the same rejection rate, then the rate is higher than 95%. If you combine 410TDS into the first membrane and let's say 600TDS at the second membrane. That averages to 505 TDS and 96% rejection which is the minimum for most RO membranes. If I can get up to 98% @ 60 or 80 PSI then I will be happy.

 

[fishntyme1]

Where is AZDESERTRAT!!!!!!! He knows all about this. He makes water so pure if you drink it Charlie Sheen will appear and call it tigers blood.

Most pressures from city water need a booster pump for a dual setup.

 

[Buckeye Hydro]

Here's some actual data from some test runs with a "98%" rejection 75 gpd Filmtec membrane we did a while back. You'll see that at the lower end of the pressure range, say at about 45 psi and below, an increase in pressure has a reasonably large affect on rejection. About 60 psi, adding pressure changes rejection only a little (that is, the curve in the graph flattens out).

Russ

 

[briankmarsh1980]

i run my spectrapure maxcap 90 at 80 to 100 psi depending on the year. i get about 240gpd now with a 99 percent rejection out of the membrane i run my unit at a 3 to 1 ratio.
i do however have a second membrane piggybacked.