High pressure

[Wanabe1972]

Guys I have a home built single 4x40 membrane RO. Last year and the beginning of this year the hpp was running underdriven rpm by 3 to 1. It would run .4 GPM concentrate and 1 GPM permeate reducing around 70 percent in a single pass. This was set at 175 psi. I geared the pump to a 1 to 1 to match the motor rpm which was factory recommended rpm. Now the RO makes 1.8 gpm of concentrate and 1 gpm of permeate reducing 35 percent in a single pass but running at 285 psi. What needs to change to get the rejection rate back to the 70s at a tolerable pressure. Does it need a second membrane or am I missing something else. By the way the membrane has always been taken care of with acid and soap washes and the flow matches pretty close to the original specs. Thanks Jeff

[mellondome]

My guess is that your original posted flow rates are backwards. Without dedicated recirculation on a 4in membrane, it is very hard on the membrane to go past 1:1 ratio. Recomendated flow rates would actually be 6:1 to keep the surface from fouling. A second membrane will give you a more concentrated final flow if in series.

[Russell Lampron]

I'm not sure how your homemade RO is set up but you should have a valve that you can open or close to control the concentrate flow. You would need to close it some to slow down the concentrate flow which should increase the permeate flow if the membrane isn't fouled. You should also have a valve on it to control the pressure from the high pressure pump.

[Wanabe1972]

Mellendome the flow rates I posted are correct .4 con to 1 permeate but would foul very quickly and needed to flush the membrane every 30 minutes or so to clear it. I could make it run decent at .5 GPM concentrate to .8 permeate on the first pass and .8 to .5 on a second pass. I regeared the pump to a 1 to 1 to get better flow across the membrane to solve the fowling in which it did but I lost my concentration rate in the process. Russ my system only has one valve on the concentrate side of the membrane close the valve for more permeate open the valve for less permeate. Where would the second valve to control pressure need to be and does it actually change pressure to the membrane or inlet feed rate? Jeff

[bowhunter]

Jeff,

I agree with Mellondome. A membrane will foul quickly if you remove too much permeate per pass without internal recirculation. You should only remove 1/6 of the flow through the membrane as permeate per pass. To add recirculation put a tee in before your permeate needle valve and add a needle valve on the recirculation tubing. Put a tee in your pump supply hose or tubing and connect the recirculation line to the tee on the pump inlet. You use the needle valve on the recirculation line to control the pressure and the needle valve on the concentrate line to control the concentrate flow. You will have to adjust these valves as you start up to get the right flow of concentrate and permeate. You can easily remove 75-80% of the water at 200 psi in one pass, but you need the high recirculation rate through the membrane to prevent fouling. It sounds like your membrane needs a good soap washing followed by an acid wash and it still may be too fouled to clean.

[Wanabe1972]

Ok now I'm really confused. I only have one needle valve and it's on the concentrate side. But your saying I should also have one on the permeate side and to reintroduce permeate I have already removed from the SAP back into the feed pump? I've been doing this all wrong for three years. I will need to draw a picture to show you guys what I've got going on and maybe you can get me straightened out. Jeff

[gmc8757]

Hi Jeff. I think bowhunter meant to say to tee before your concentrate needle valve and send that to a tee on the pump inlet. Only reason I know this is because of Dave...He has helped so many of us with this same exact process. Thank you Dave!

Once you produce permeate..send it to the permeate tank!


Sent from my iPhone using Tapatalk

[Clinkis]

I also have a single xle 4040. The numbers you are getting now sound right. I run mine about 1:2 permeate/concentrate without recirculation.

[mellondome]

If you spend any time with your ro, you will find a sweet spot where further restriction of the concentrate flow doesnt increase the permeate flow. This is usually around 6:1 permeate to concentrate. Most 4x40 we use in maple have a max surface flow rate of 14 g/min across the surface. The closer yoh can get to this, the faster you can remove water because it keeps the surface of the membrane cleaner.

As for your original numbers , you should not push more concentrate then permeate. When you read manufacturers rejection rates, they are talkong about purifying water... and rejecting the concentrate. So if what you stated in your first post is correct, you are concentrating to a higher level than what you previously were.

[Russell Lampron]

Russ my system only has one valve on the concentrate side of the membrane close the valve for more permeate open the valve for less permeate. Where would the second valve to control pressure need to be and does it actually change pressure to the membrane or inlet feed rate? Jeff

I'm not sure how the high pressure valve is plumbed in because my RO is factory made but by adjusting it I can set the high where I want it. I normally run it at 200psi but can go almost to the 500psi high pressure shut off. I set my pressure at 200psi with a concentrate flow of 2gpm and get 2gpm of permeate flow on the first pass when the membrane is clean.


As for your original numbers , you should not push more concentrate then permeate. When you read manufacturers rejection rates, they are talkong about purifying water... and rejecting the concentrate. So if what you stated in your first post is correct, you are concentrating to a higher level than what you previously were.

Actually he is concentrating to a lower level than where he started at. Higher concentrate flow and lower permeate flow equals less water removed and weaker concentrate. If he adjust his concentrate flow lower his permeate flow should go up and his concentrate will be sweeter. That is if the membrane will allow more permeate flow.

[Wanabe1972]

Russ you are right my original setup if SAP was 2 percent it would go to 7 in a single pass at 175 psi now 2 percent SAP goes to 3.5 in a single pass at 285 psi. ????? I don't think the membrane is Fowled as the flow rates at 100 psi are almost the same now as when the membrane was brand new. Jeff

[Russell Lampron]

You need to adjust the concentrate flow down to bring the permeate flow up. I don't know if you have a high pressure cut off switch or not. If you do closing the concentrate flow valve will increase the pressure too much to get good permeate flow. If your high pressure cut off is at 300psi you are pretty much there now.

I am using an NF-270 membrane now but when I was using an XLE I think I was only getting about 1.25gpm on both sides at 250psi. The NF-270 is a faster flowing membrane but can pass sugar at higher pressures and concentrate percentage.

[Russell Lampron]

As for your original numbers , you should not push more concentrate then permeate. When you read manufacturers rejection rates, they are talkong about purifying water... and rejecting the concentrate. So if what you stated in your first post is correct, you are concentrating to a higher level than what you previously were.

I just reread the OP's original post and see that his use of rejection rate is backwards of what it is supposed to be as he is referring to permeate flow as rejection when the opposite is true in regards to maple.

[Super Sapper]

It sounds like your membrane will only do 1 gpm of perm. You increased your total flow so you should foul less but get done sooner with the first pass. It does not look like it will process any faster to your desired concentration except that you will gain in being able to keep processing instead of flushing. I would back off the pressure until you see your permeate drop off and run it a little above that. This will keep you membrane cleaner and run longer. You could also put in a recirculation loop to increase concentration.

[Wanabe1972]

Im going to try this recirculation loop that everyone is talking about. The RO is still set up and will not be moved into my new addition until this summer so im going to play with it and see if i can get the pressure down where i like it.