hodorskib's Small Scale RO Build

[RedMapleCreek]

Why not use two 12v batteries in series to get the 24v to run the pump?

[eustis22]

What is the normal GPH for the 8800 for 4-150? Whats your PSI? I am asking because last year I did not note my PSI but this years is at 100 (which seems low to me) and it took me 14 hours to process approx 75 gallons of 1.5% I did not end up with all that much concentrate (maybe 15-17 gallons?).

[SDdave]

Eustis22,

Rough math says your good to go. 1/4 of total would be around 17 ish. With that you most likely (rough math) ended with 6 to 7% concentrate.

I rebuilt mine from ground up (left it out, froze and cracked) and this year its around 110 PSI. I've always ran around 125 PSI in the past. I check % on concentrate and permeate during run time to double check.

SDdave

[DRoseum]

If plumbed in series, each membrane can cut flow in half (half to permeate and half to concentrate). Therefore if really running each membrane at 50/50, you would get 1/16th of your 75 gallons (1/2 * 1/2 * 1/2 * 1/2 * 75 = 4.6875). Also, that would mean each membrane is in theory doubling the concentration level (1.5% *2*2*2*2 = 24%).

In order to get the 17 gallons you probably weren't really taking 50% of the water out at each membrane. That actually did speed things up, but at the cost of lower concentration. Which is fine...RO is a balance between higher concentration and total time sap sits (bacteria has negative effects over time).

At 50/50 a 150 Gpd membrane at 100psi will only be able to process about 6 gallons of raw sap MAX for ideal conditions (150 Gpd/24hrs/day = 6.25 g/h). Lower temperatures and higher sugar concentrations (like the downstream membranes) decrease performance. Probably safe to assume around 0.6 to 0.75 of that for 40F sap...so more like 4 g/h of sap. And that's the limiting factor for the entire set up if in series.

Depends what your objective is, and while higher concentration is good, you also need to consider time. Bacteria gets concentrated with the sugar. Perhaps you should consider replumbing to have a 2 stage hybrid set up with parallel and series membranes.

Rough math says that 3 membranes (2 in parallel feeding a 3rd in series) all running at 50/50 would take 1.5% to 6% in less time. Reason is you have increased your limiting factor of 4 g/h to approx 8 g/h and are still able to double your concentration 2 times (1.5%*2*2=6%)

I have a detailed post on this topic here:
https://www.sugartree.run/2020/01/di...-hobby-ro.html

[eustis22]

>With that you most likely (rough math) ended with 6 to 7% concentrate.

7%. Which is higher tan what I processed last year so now I feel better about the GPH rate. I get that reducing my concentrate level will speed things up at the cost of %. DR I am off to read your article on parallel --> series. Thanks, everyone.

[wlatrout]

I have a 6-150 setup. Would you go 4 parallel and 2 in series. I see where this could help my situation.

[DRoseum]

I'd give it a try. Feed all 4 in parallel and then have 2 of those each feed another in series. If you try it let us know how it works for you.

[hodorskib]

sorry my account had been suspended for some reason. I have run my 6 membrane system in series, parallel and a combination of both. To process lets say 150 gallons of sap from 1.5% sugar to 7.5-8% it takes the same amount of time in all three setups the only difference is when running in parallel or combination you have to recirculate. I do not do this because I have found that the more times the sap runs through the pump the more it heats up and the lower quality of syrup I make. This has been my experience over the past 7 years.

[DRoseum]

Why do you say it's necessary to recirculate? For purely parallel to get to that high of concentration I would agree. However a combination of parallel feeding to series wouldnt require recirc. You should be able to get from 1.5% to 6% on single pass with only 3 membranes (2 parallel feeding 3rd in series).

[carls47807]

As with Hodorskib, I have found parallel and series setups to process at the same rate (within the precision of the instrumentation I was using). This assumes the pump is the limiting factor in these setups (and if you are running a DC booster, it probably is)

Hypothetical:
Three membranes in parallel processing 24 GPH. Each membrane flows 8 gallons per hour, 4 gallons of concentrate and 4 gallons of permeate. Percent recovery is 50% (at 50/50, past 50/50 and it's even higher). Off the shelf membranes without any fouling resistance are rated for 15% recovery at best.

Three membranes in series processing 24 GPH. Each membrane flows 24 gallons per hour. Each membrane produces an average of 4 gallons of permeate (plus or minus 2 gallons), bringing percent recover to ~17% at 50/50 flow. This is a lot less stress on the membranes and they tend produce permeate efficiently without constant permeate rinsing.

Two membranes in parallel feeding a third membrane in series processing 24gph. The first two membranes flow 12gph and produce 4 gallons of permeate per hour. Recovery on those two membranes is 33% (arguably better than 3 parallel membranes). The third membrane flows at 17% recovery.

Recirculation in a parallel system is necessary to increase the flux across the set of membrane to bring percent recovery down to acceptable levels. Unfortunately, small RO boosters can't achieve necessary recirculation flow rates and maintain optimal pressures. Diaphragm pumps have decreasing exponential flow capabilities past 80psi.