Ideal Membrane Specs/ Properties for Hobby Sized RO's?

There's tons of information for 4040 and larger membranes regarding their use for sap, but I can't find much for the smaller 'home' (cartridge) style membranes.
Most membrane manufacturers have a data sheet with there membranes with properties such as:

Min salt rejection %
Stabilized Salt rejection %
max feed silt density index
free chlorine tolerance
max feed water turbidity (in NTU)
PH Range (continuous op, or short term cleaning)
max salinity


Which of these properties is relevant, and are there known limits to any of them that will help determine performance? Is there a chance that a membrane will fail even if it does look good on paper? Any scientific method to picking a membrane?

What size are you looking for? CDL sells replacement membranes for their Nano system and I believe the price is reasonable.

Funny you mention that, that membrane (the nano 600 gpd membrane) is the reason I'm going down this rabbit hole.
I was thinking about building an RO using the same membranes as the nano. I was looking at the membranes sold here https://www.rothsugarbush.com/produc...-gpd-membrane/, and noticed, if you look closely at the label it says "Hikins model 3213-600G"
Hikins is a Chinese brand and the same membranes can be found from a Chinese wholesaler for much less (shipping cost could make up the difference). (Hikins website here: https://hikins.en.alibaba.com/).
This got me thinking, they (Hikins) make 800 gpd membranes in the same housing, or 1000gpd membranes, Why couldn't I design a system using a carbonator pump (rather than diaphragm) and these higher flow membranes that are much cheaper than 4040's?
I just don't want to pick a membrane with the wrong properties and have it fail half way through a season...

I noticed on their website that in order to get that lower price the minimum order was for 100 pieces. Did you see that?

I did see that, but there are other suppliers that produce 600gpd 3213 membranes with no minimum order. Hikins also produces a 1000gpd membrane with a minimum order qty of 2.

Getting back to the original question- Is there any science involved in selecting a membrane for sap? Any papers on the subject?

TFC membranes have been around for many years and there are thousands of manufacturers of the polymer sheet. By changing little things during the manufacturing process the sheets develop different affinities, rejection toleranes, anti fouling properties, cold and hot tolerances, cold and hot efficiencies, chlorine resistance, etc. Sheets aren't necessarily developed for a specific purpose. Sheets are designed and THEN the properties of that sheet are tested in real world applications to determine its effectiveness of performing a specific task. We (The RO Bucket) sourced our membranes by ordering over a dozen different 3012 membranes from a single established manufacturer (They did not have any testing on maple sap, cold temperature performance and anti fouling performance at cold temps). Over the past 4-5 years we have tested these different membranes and determined which ones work the best. We then worked with the manufacturer to select properties that are beneficial to what we are doing and they developed a membrane specifically for us using properties they already had built into their existing sheets.

An off the shelf membrane like CDL uses will probably perform good, but it is not a "maple specific" membrane that has been designed for processing sap. The entire Nano system is manufactured and assembled in China for CDL. I'm sure over time they will further develop their membrane but they are only a couple years into the development of the Nano and they don't have a lot of feedback on what works yet. Just selecting a higher gpd rating membrane is not going to necessarily help your system in the long run. You can tell a lot about a membrane by looking at the cross section of the "wraps". A tightly wound membrane with a lower gpd rating is far superior to a membrane with less windings and a higher gpd rating. This is because it has more surface area, will experience less fouling, and will have more membrane surface for longevity.

Thank you Carl, that's very helpful.

Sounds like the best way to find a good membrane is physical inspection & R&D.

I've also recently heard that it's difficult to concentrate over 5% with a TFC membrane without fouling? If that's the case I might be leaning back towards spending the extra money on a single post 4040 build. That extra 25% will allow me to tap more trees and increase production significantly without upsizing my evaporator.

I should also note, I wouldn't expect any other company to provide tips to a DIY'er on how to build their equipment. Carl's responsiveness and service is second to none! I would buy an RO bucket in a heartbeat, but I'm an engineer, and I love to tinker... sometimes with things I probably shouldn't tinker with :lol: