Translating GPD permeate to sap

[coach]

Hey guys. Planning on setting up a RO system here. I've got a couple of membranes, and would like to know which one to use. I have a 2.5x40 nanofilteration element, which I understand is the type used in the maple industry. This has a rated permeate flow of 650 GPD at 77F. And I do have a stainless housing for this.

The second membrane I have is 4x40 brackish water RO element. Rated permeate flow is 2200 GPD at 77F. I don't yet have a housing for this one.

If you guys could tell me how the GPD permeate ratings translate to raw sap throughput, then I'd make a decision which one to these to install.

I am assuming the GPD ratings are for 24 hours.

[maple flats]

Sorry, neither membrane rings a bell for me. I suspect the smaller one however if it is what is used in maple, one for brackish water is not likely to be right for maple. You need to realize, your flow will be considerably less, 37 F is generally the temperature used in maple RO's.

[Daveg]

24 hours is correct (an accessory for your RO could include a low-sap-sensor-shutoff so you can run it unattended). I'd assume the 2200GPD can handle more sap than the 650GPD membrane, but I'd make a call to the manufacturer to be sure it's compatible with sugaring. The brackish water membrane relies on salt ions being bigger than water molecules but it might still allow sugar molecules through. It's nice you have the housing for the smaller one.

[bowhunter]

The small one sounds like a nf90 which is suitable for sap. At 250 psi on sap you can probably expect to generate about 50% of the rated capacity of permeate per hour. This assumes removing about 75% of the water from the sap. So 650 per day time 0.5 = 325 per day or 13.5 gallons per hour of permeate. The concentrate produced will be 1/3 of that or 4.5 gallons per hour of 8% concentrate.