Can i run recirculate concentrate through my RO membranes?

[Fun4stuff]

I have a homemade RO setup. Nothing fancy. I have been running my sap through twice.

Can i just set it up so it recirculates? So that the concentrate tube dumps back into my sap bucket... and run it through until I reach a certain brix (e.g. i usually get 6-8 brix after running it through twice).

[wobbletop]

Yes.

Although I believe the higher concentrate sap is heavier so sinks to the bottom so if your input line is sitting at the bottom, it may not be as efficient.

[Russell Lampron]

You can do that, I did it that way for years. The thing that I didn't like about it was that I was recirculating it in my raw sap tank because it was all that I had at the time. I would be diluting my concentrate every time that I had to add raw sap to the tank. I have since set up a designated sweet tank and only run 2 passes, the first into the sweet tank and the 2nd into the head tank. If the bucket that you refer to is like my sweet tank recirculate like you are doing until you get to the brix that you want.

[DrTimPerkins]

Note that each time you run liquid through an RO it will warm up, so recirculating or running it through twice will end up heating the sap/concentrate a good bit, accelerating the growth of microbes. Therefore, it should be boiled fairly soon and it will produce somewhat darker syrup.

[Fun4stuff]

Thanks all! Good tips noted.

[Waynehere]

We have a 500 gal head tank that we recirculate. It is one of the old long tanks, so in one end and out the other. Usually takes about 2-3 hrs to take out 3-400 gal of perm, then we fire up the evaporator while the RO is almost done. 2 hrs of boiling and done for the night. Works pretty well and I can walk away and leave it for the first couple of hours. I have a light inside the sap shack and outside so I can see if it is running or not.

[jrgagne99]

You can also install a poor-man's "internal" recirculation. Tee it in so you're pulling from the concentrate outlet (upstream of your main restrictor needle valve) and re-introduce it to your flow somewhere downstream of feed pump and preferably downstream of the particulate filter too. You need a needle valve on this leg to dial in the recirculation flowrate and membrane pressure. Use the main needle valve, together with your recirc need valve, to control the membrane pressure and concentrate outlet flow rate. I use this setup to get to 8% in "one pass" with my 4"x40" single post, although a lot of the sap is recirculating within the RO rather than going all the back to the raw sap tank.

This setup was a game changer for me because I can run straight from the RO and into the evaporator without even needing a concentrate tank. It also means that I start getting boilable concentrate 5 minutes after walking into the sugarhouse, so that I can fire up the boiler right away without having to wait for a full single-pass to finish beforehand.

[Keitha333]

I do this from time to time when sap is coming too quick for my storage and I can do it overnight. One thing that I noticed is that it did pass some sugar into my permeate when it was more concentrated. THought it was my membrane failing but then I would check my permeate line when not recirculating and it was and has been fine....