Troubles with my homemade RO. Sweet in my permeate?

[Steve WI]

For starters THANK YOU ALL who have contributed to MapleTrader! Your selflessness has helped me and I am sure many others from making too many mistakes.

I know its a long read, and that my data collection with an "ish" included is less than exact. What really bothers me is the sugar in my permeate at the end of my last test.

Thanks in advance
Steve

I started with 2.2% sugar water at 54 degrees
2-150GPD membranes in series
10” 5 micron filter
Aquatec 8852 pump with a feed pump

Data. Test one
2.2% in 4% out 9 minutes to run a gallon of concentrate and about 15 min for a gallon of permeate.

Data test two
A tic over 110psi
2.2% in 4.2% out 15 min to run a gallon of concentrate and 7/8 ish gallon of permeate

Data test three
110psi
2.2% in 4% out 12 min for a gallon of concentrate and a little over ½ gallon of permeate

Data test four
2.2% in 3.9% out 10 min per gallon of concentrate and ½ gallon of permeate

Data test five
3% in 5% out 14 min per gallon of concentrate and a little over ½ gallon of permeate

Data test six (pressure climbed a little over 110psi)
3% in 5% out. 17min per gallon of concentrate and ½ gallon of permeate.

Data test seven. (adjusted PSI to 110)
3% in 4.8% out 13 min a gallon of concentrate and ½ gallon of permeate.

Long test.....
Ran the concentrate back into feed tank.
9:30am-11:30am started with 3% sugar water.
3% in 4% out.
4% in 5.2% out 11 min a gallon of sweet 1/3rd ish gallon of permeate
Checked again at 2:00pm.
6.2% in 7.2% out 12 min a gallon of sweet a pint of permeate
Checked again at 3:30pm
7.2% in 8% out 11 min gallon and a splash of permeate.

ISSUE!! 1% sweet in my permeate?

I don't know if I damaged one or both of my membranes? When I started it again tonight with 3% at 110 PSI I couldn't measure any sweet in my permeate?

Thanks for your help
Steve

[SDdave]

Steve,

Not sure if I am going to be a big help on this one. I will try...

First, I assume your using the aquatech 8800 series pump and running in series. About the same as mine as I run 3 100gpd membranes in series. The first thing that pops out is that the pressure isn't high enough yet. I usually run mine at 125 to 130 PSI. There is a set screw on the pump that needs to be adjusted to get a higher PSI, then with the needle valve create enough back pressure to get up to the 125 ish PSI.

Second, How often are you flushing the filters? It would be beneficial to flush and clean after daily use.

Most likely everything is plumbed together correctly as you would have had more sugar in the permeate. Hope that helps some.

SDdave

[Steve WI]

Thanks for the help Dave,

Yes its an 8800 series pump.

I have adjusted the set screw to bring the pressure up to 110.

In the series of tests listed above I did not give it a good flush. I only opened the concentrate valve wide open for a few minutes between a couple of the tests. All of the above tests were done on the same day. So far my end of day flushing has been throwing away the 5 micron filter and running 10-15 gallons of well water through the system with the concentrate valve wide open. When I am working with sap my cleanup will be much more thorough.

Tonight:
I set the pressure at 125 for a few runs. I did notice that every few minutes the pressure would climb? I had to constantly reduce the pressure. The first run at 125 PSI I was getting 1-1 concentrate-permeate. I doubt this will work consistently. Each trial after that I brought down the pressure until I was at 115. I ran two trials, both were at 6 minutes for a gallon concentrate and a 1/2 gallon of permeate. I feel a little more comfortable at this flow. If anything I should open the valve and increase concentrate flow.

Is it right to say that its more important to run your RO at a ratio of 3-1 (or so) and let the sugar content coming out be what it is?
Or is there % increase goal for each pass?

If your membranes are fowled does that mean you can pass sugar into your permeate? Tonight there was no measurable sugar in my permeate.

Thanks again
Steve

[bowhunter]

It sounds to me like you have the permeate and concentrate switched. First of all it's impossible to have no sugar in the concentrate if you have sugar in the feed, so if you truly have no sugar in the concentrate you're measuring the permeate. The concentrate flow across the membrane and the permeate passes though the membrane, if that makes any sense. When I look at your flows, the permeate and concentrate volumes look to be reversed. If your membrane is fouled it will get harder and harder to get permeate to pass through the membrane(s) so you will see reduced permeate flow and you have to raise the pressure to keep the permeate flow up.

[mellondome]

On a small build like this, you will have better long term success if you go for ratios closer to 6to1. This will allow more flow across the membrane surface, keeping it cleaner longer. If you watch flow rates over extended run times , you will find a spot where pressure increase doesn't give measurable permeate increase. This is the optimal pressure / flow rate for water removal.
As for passing sugar, don't know the membranes you are using, but some nano filtration ro membranes will start passing sugar at higher concentrations.

[Clinkis]

I built this exact unit and used it for 3 seasons prior to building a larger one last season. I ran mine around 1.5:1 (60% concentrate and 40% permeate. It would run for 8-10 hours at this rate with no issues with fouling. I would process a 45 gallon drum at a time then flush the permeate back through it then start another 45 gallon drum. worked great. I sold this unit to a friend and he is still using it with the original membranes. I never pass any sugar but I only concentrated to 7-8% max. Some membranes are prone to passing sugar when sugar% gets high.

[Steve WI]

Bowhunter,

I am not sure how I gave you the impression that I had no sugar in my concentrate? It must be how I documented my data. I have noticed slower permeate flow after long test runs.

Mellondome,

After reading your post the other day I did run it with higher concentrate flow. My permeate flow seems to stay consistent. Thanks for the infomration regarding passing sugar at higher concentrations!

Clinkis,

Thanks for sharing your experience with a small unit like this. I'll try your ratio next time I test. I was also wondering if my pump has enough flow to add another membrane in series?

Thanks for the replies!
Steve

[bowhunter]

I misread you last sentence in the first post. Sorry about the confusion. It's not unusual to get the permeate and concentrate on the home ro cartridges reversed sometimes. I think the reason it passed some sugar, if it did, is that you were concentrating around 10% or more. The other test data you provided seems to make sense when you compare the volume of permeate removed and the increase in concentration. I agree with others' advice. Try to keep the ratio of concentrate up to at least 5 to 1 over the permeate on each pass. To keep the ratio the same on each pass the pressure will have to be increased to compensate for the higher sugar content until you reach the limit of your pump. It really isn't a problem if you keep the pressure the same and allow the permeation rate to drop other than making sure you don't start too high and run the ratio so low on the first couple of passes that you prematurely foul the membrane.

[hodorskib]

These little ROs take a little while to get dialed in and I think your smaller tests didn't allow everything to come together. With mine it takes at least an hour before I can set the back pressure correctly and leave it. I try not to go above 7.5% concentrate since I found the membranes foul and the unit slows way down. You can also check to make sure all of your connections are correct. Your concentrate lines should be coming out of the left side of the membrane housing the center one is the permeate line. Keep tinkering you will get it dialed in and it will be all worth the effort.