Basic RO things

[Mean_Oscar]

This is a link to a graph of concentrate flow plotted against permeate flow of pure water. It shows almost no improvement in flow rate after about 82 pounds. The instructions to set con and perm flows even works fine.

https://drive.google.com/file/d/1i40efCyQrat193sVnoqp_YAeuJOyu9HB/view?usp=sharing

[maple flats]

That graph will only be accurate with your set up and the condition of the pre filter. As the pre filter builds restriction to flow it will change as well as the density and temperature of the sap will affect it. In fact, with sap you will not get the same results, it will be less!

[Mean_Oscar]

Could not agree more on limitations to accuracy here. This is somebody who does not know what he is doing TRYING to find out.

Considering where to put another pump, I was curious about the drop across membranes. Turns out (R = E / I) it is flow dependent.

https://drive.google.com/file/d/1ThNWZz9jsjNx_6NdVrJ8ZxDr1jWTD8lh/view?usp=sharing

[DRoseum]

What pump are you using? What size membranes? How many taps? Have built many of these small RO units and happy to help.

In general, Pumps in parallel are used to increase flowrate at a steady pressure. Pumps in series are used to increase pressure at a steady flowrate.

For these small units, normally as you scale up in membrane size and number, the pump flowrate at the membrane operating pressure (~100 psi) is the limiting factor. Too low of a flowrate leads to a higher recovery rate at the membrane which increases fouling (reduces performance). Recovery rate is a key concept to understand. It is defined as permeate outflow / input flow and is something you want to keep as low as possible. Obviously you want a lot of permeate outflow (directly related to membrane rating and quantity) ... so that means you have to keep your input flowrate to each membrane as high as possible. Hence why a 2nd pump in parallel makes a lot of sense. You would add this upstream of the filter so both pumps are taking in the same raw sap and both pushing it out through the filter (and membranes) in combination with each other).

I started with a aquatec 8852 and single 400 gpd membrane and scaled up from there multiple times. I am now am working on adding a 2nd Coronwater Typ 8900 pump (a much higher flow rate pump than the aquatec) in parallel to a 5 x 600 gpd setup with low pressure recirculation. The higher flowrates will keep performance higher, especially with the recirc that is driving the concentration levels much higher than a single pass system.

[Mean_Oscar]

Let me add this: There was a sketch of that system in that last post. Are you trying to use Chrome? With Foxfire, you can see the pictures.

Using an 8852-2J03-B423 pump (posted boost limit 80 PSI), last study was with 2 each 75 gpd membranes (rated for 100 PSI), 5 mic housing that leaks around 100 PSI and no taps (that is spring water).
I have housings and membranes to theoretically daisy chain to 1300 gpd....but why do all the fun stuff first.

This all started from trying to soup up my unit to get higher concentrations. Spoiler alert: We have not gotten to the good stuff yet.

From this next study, it looks like on a given system, concentration of solute (more about that later) is huge determinant of how fast you can RO.

https://drive.google.com/file/d/1SHEk44aqDpBhoclhLwsE9Uc_kE0g21qx/view?usp=sharing

[DRoseum]

Yes I can see the diagrams /charts. Yes, concentration level does have impact on membrane performance, along with recovery rate as I noted. Also, not all membranes are created equal and there will be various performance ranges for various concentration levels as a result.

[Mean_Oscar]

Is there a membrane that fits either the smaller of larger housings that is MUCH better than the ubiquitous blue colored ones? All mine are blue.

But talking about getting pressure up, I wondered why the 5 micron was always downstream of the pump. I pulled the 5 mic for a couple of runs and max pressure was 89 v 94 with same set-up. Encouraged, I moved the 5 mic to before the pump but it started the indicated pressure jumping between 80 and 85. It vibrated too so I put it back like it was.

Tried booster pump before main pump and that showed promise. Did 98 and 99 psi vs 93 and 94 but the little pump blew up before I could finish testing.

What did work was putting a vacuum on the permeate line. Only had a half gallon jar for catcher so had to shut down every 7 cups of permeate caught.
https://drive.google.com/file/d/1EXT9q3M6SqpNGdAKjC8QSgKMtWgAYQe3/view?usp=sharing

[Mean_Oscar]

Another question was how do different tree saps RO? Worst misconception was that you could NOT RO black walnut because of the pectin. It worked fine for me and others who risked membranes to try it. Turns out the junk only comes out of solution after you cook it some.

Also puzzling was black birch sap. Kept wondering if I was doing something different or plain wrong. It seemed like it just would not get to anything like the concentration of maple. Limited sample size and lots of other variables. Knew from one analysis that gray birch had mostly fructose and glucose. Was the rumor that it was minerals plugging membranes true? Bought some fructose and glucose from Mr. Amazon and unless he polluted them, the problem is not minerals. A 60-40 fructose-glucose ran like what you see in the graph in green. It is a sorry explanatory graph so you will have to study it. My take is that the fructose and glucose molecules are half the Daltons of sucrose and smaller molecules plug membranes worse.
https://drive.google.com/file/d/1oxlcCsPJ6c2i4X1Es1FVlEWZtNYAWK_g/view?usp=sharing

[Mean_Oscar]

New (to me) phenomenon noted yesterday: ROing 10 gallons of 2% maple in a 5 gallon bucket at 90 PSI across 2 x 200 and 2 x 150 gpd membranes in parallel. Knowing that the lower the Brix, the faster water gets pushed out, I kept diluting with new sap to the top of the 5 gallon bucket trying to keep total liquid between 3.5 and 4.5 gallons. I recorded a 5+% at one point. An hour later after random adds, I got a 2.9%. How on earth could the stuff segregate 40% with all that withdrawing, concentrate coming back in and pouring in more 2% sap? Got long pipette and drew from bottom and it was > 5% there versus < 3% at the surface. After that, I kept the intake as near the top as possible.

[SeanD]

That is what happens with the sweeter, denser concentrate. It sinks to the bottom. I experienced this with a 600 gallon tank, if you can believe it. When I first got my RO, I recirculated back into the collection tank that fed the RO from the bottom of the tank. No matter how I positioned the concentrate line feeding back into the tank, the concentrate would go to the bottom and the pressure on the RO would steadily rise. It's far more efficient to run the sap through separate passes/tanks - but if you are limited on storage, you gotta do what you gotta do.

[Mean_Oscar]

So the best strategy is to run all of 2% sap through making buckets of lets say 3.5% concentrate. Then run all the 3.5% through. That way, you never try to RO 6% concentrate.