Homemade Reverse Osmosis System

Reverse Osmosis is defined as:  a technique for purifying water, in which pressure is applied to force liquid through a semipermeable membrane in the opposite direction to that in normal osmosis.  What does this mean for making maple syrup?  The system will extract/remove water from sap.  Thus concentrating everything else including sugar.  Commercial units can process anywhere from 50 to well over several thousand gallons per hour.  They are also quite costly starting at around 3,000 dollars.  For anyone that makes maple syrup as a hobby - less than 100 taps purchasing a commercial system would not only be costly but also not really necessary.  With a little research and some very generous people, from "mapletrader.com", who were willing to share their knowledge and experience along with information from ESP (Environmental Safety Products, ltd.) I was able to put together a system that is ideal for anyone who collects 120 gallons or less of sap per day.  The total cost for this system ranges from 300-450 dollars depending on how many parts you may already have and how much control you want to have over the process. 

After running this system for several years and talking with others that have built similar systems I would not recommend using all of the pressure gauges and check valves that you can see in the picture below.  Only one pressure gauge is needed and one check valve is optional.  

Please watch this video for more information

Please be aware that my sap runs right around 1.5% sugar.  If yours is higher the maximum concentrate level you will be able to attain is around 8% using 150gpd membranes.  So if you start with 2% sap you will be able to remove 75% of the water, if you have 3 or 3.5% sap you will be able to remove 55-65%.  Basically you will be able to get to a 1:11 or a 1:12 concentrate to syrup ratio regardless of what % your sap starts at.

It is very important to flush the entire system with clean water before you start using it.  The membranes come package with a preservative that would make your first batch of syrup have an off flavor.  See below for directions on how to do this.

The concept is simple and is broken down into 3 stages:
Stage One:  Sap is sent through a small pump and into a 5 micron normal water filter
Stage Two:  Sap passes through four 150 gpd (gallon per day) reverse osmosis membranes
Stage Three:  Pure water is sent to a waste container and the concentrate is sent to another
Stage One:  The size of your initial holding tank is up to you.  I use a 60 gallon barrel since that is what I had.  The whole system will do a maximum of between 120-140 gallons with 40 degree sap concentrating to between 7 and 8% in a 24 hour period so you don't need anything huge.  I also did not want to drill a hole and install a valve in the barrel if this project did not work so I wire tied a section of 3/8" tubing to a 4 foot wooden dowel and just dropped it over the side and down to the bottom of the barrel.  This is my feed line.  It is connected to an Aquatech 8800 booster pump.  This pump is designed to boost and maintain 100psi of pressure with little or no feed pressure.  However, depending on what membranes you use you can actually increase the pump to match the maximum levels for your membranes.  To do this you will want to rotate the small screw on the front of the pump clockwise up to one rotation.  I found one full rotation put me slightly above 125psi so I went with a little over a 3/4 turn and that put me just below 125ps. I left the intake at 3/8" tubing figuring it would help with siphoning over the top of the barrel down to the pump.  The outflow of the pump is reduced to 1/4" tubing which is connected to a 10" standard water filter housing with a 5 micron poly spun filter installed.  I also installed pressure gauges before and after the filter which will give me an idea of when I need to change the filter.  If the pressure is coming in at 120psi with a clean filter it will be leaving at the same pressure if it is lower then the filter is clogging up.  After running for a while this is not necessary I would just have one gauge after the water filter.  It is important to have enough filters on hand for your entire season.  It is important to change the 5 micron filter often.  Early season you can process two days with the same filter (up to 200 gallons) but as the season goes on and the sap gets a little more cloudy you will need to change daily and sometimes more than once a day.  At the beginning of each season I order 1 filter for every 1 1/2 gallons of syrup I plan on making and that usually is enough.  They are readily available at your local Lowe's, Home Depot and some hardware stores if you run short but you will pay up to 5 dollars each.  If you search Amazon.com for 50 packs of 5 micron water filters you can get them with free shipping for about 1.25 each.  They are wrapped in plastic and will last from year to year if you don't open them.
Stage Two:  After leaving the filter it travels into the first membrane housing.  The permeate is connected to the line going to the waste container and the concentrate is connected to the second membrane housing.   This process continues into the 3rd membrane housing and then the 4th.  I have installed a pressure gauge between the 3rd and 4th membranes and a check valve before the needle valve.  It is important to rotate your membranes on a regular basis.  I actually just removed the housing from the lines since it was easier than trying to remove the actual membranes from the housings.  They are very snug and require some effort to remove, while tubing connected with quick connects pop right apart with little or no effort.
Stage Three:  As the sap is pushed through the system permeate or the water you are sending to waste will be extracted after each membrane housing.  I have connected them all together using 1/4" quick connect Tees and have one line going to my waste.  My system is in my garage which also has the waste stack for the entire house going through it.  I installed a check valve on this line as well and plumbed it directly into the stack with an additional line with a T and two ball valves so that I can capture some permeate for rinsing as well as check for any sugar content.  Most people will have a waste container/tank/barrel that they will dump daily.  Since each membrane's concentrate is being fed into the next housing there is only one concentrate line that comes out of the last housing.  This has a 1/4" x 1/4" brass needle valve.  A plastic ball valve does not give you the fine control needed to get the best concentrate levels out. 
Adjusting The Flow:  If your sap temperature is below 40 degrees (F) the flow rate will be very slow less than 2gph (gallons per hour), above 40 degrees and you can see up to a 5-6 gph process rate.  To adjust your flow rate / sugar concentration all you have to do is start closing the needle valve.  The first couple of times you may want to shoot for a 1-2 or a 1-3 ratio of concentrate to permeate.  I use 2 pint mason jars - put one under each line and wait a minute or two and compare.  If I am getting the correct ratio I leave it alone if not adjust and test again.  I have found that you could get a higher ratio but the amount you will process per hour goes down, it is a balance.  As the system runs check occasionally to make sure the flow stays consistent. We had several heavy runs this year with one around 140 gallons.  To process this amount I backed off the needle valve a bit and went to around a 6.5% - 7% concentrate this allowed me to process all 140 gallons in exactly 24 hours.  The difference between 8% and 7% is about 1.5  gallons so it was a small sacrifice in order to process the entire amount. I was still able to reduce that 140 gallons down to around 30 gallons.  Once you get used to it you will be able to collect your sap fill your holding tank then go and do other things like:  sleep, work, activities with the kids, etc. and the next day you will find 50% or more water removed from your sap and it will ready to boil.

This year I will be adding two additional membranes (total of 6) and installing a 150ml flow restrictor.  I am not looking for a higher concentrate level but a faster rate of process.  When I tried the flow restrictor last year with four membranes I was getting just under 5% concentrate levels.  By adding the extra membranes I am hoping to get around 7.5% concentrate while processing around 8 gallons per hour.  I am not sure how it will work out but will post results after the season.  If it works the flow restrictor can replace the needle valve which is not very precise.

Update (February 20, 2017) after processing 100 gallons of 1.5% sap I was only able to achieve a 6% concentrate.  I replaced the flow restictor with a needle valve and have been able to get a 7.5% concentrate while processing just under 10 gallons per hour.  By adding the 5th and 6th membranes the gallons per hour increased from around 6-7gph to 9-10gph.

Flushing the Membranes:
After each run you will want to flush the entire system with permeate - usually 25-30 gallons.  To do this open the needle valve all the way and turn the system on.  This creates turbulence over the membranes that will help release any buildup.  This will not take very long maybe 30 minutes since there is no back pressure.  I use membranes that are rated for 150psi and run my system at around 145ps.  If after flushing my pressure does not return to the 145psi I know it is time to clean them.  I have found that rotating the order of the membranes keeps the last one from fouling quickly.  To do this I disconnect the 1/4" tubing from the housings and then move the entire housing - take the last one and moving it to position one and then moving all the others down the line.

Cleaning the Membranes:  If your system does not return to normal operation after flushing you will need to clean the membranes.
1.  Run 4-5 gallons of clean water/permeate through with the needle valve open all the way.  (use permeate - it is 99.9% pure water)
2.  Mix up 5 gallons of 5% solution of peroxide and water (to do this just put one quart 32oz of standard hydrogen peroxide into a 5 gallon pail and fill up with water/permeate to about an 1" from the top) and run it through again with the valve wide open -  but shut off the system before the last bit goes in.  Leave it off for 10-15 minutes.
3.  Run 10 gallons of clean water/permeate through keeping the needle valve open.

What to do at the end of the season?

I have run consecutive years with the same membranes, 2-years on the 100gpd membranes and then 2 year with 150s.  I check the permeate line for any sugar with a refractometer during each run and it continually read 0%.  With that said I am not sure how many years you can get out of a set of membranes but this is what I do at the end of the year so they are able to be used next year:
1.  I flush the entire system with 10-15 gallons of warm water, if you are on city utilities use a product that many people use to take the chlorine out of water for their fish tanks, excessive exposure to chlorine will break down the membranes.  The product can be found at any pet store or even Walmart for a couple of bucks and will treat several 1,000 gallons. 
2.  Mix up a 5 gallon bucket of warm water and 1 quart of hydrogen peroxide and run it through with the valve open all the way.  Just before the bucket is empty shut off the system for 10-15 minutes so the solution can work through the membranes.
3.  Flush with 20 gallons of water.  Temperature doesn't matter you just want to make sure all of the peroxide solution is flushed out.
4.  Take out each of your membranes and wrap them in two layers of plastic wrap.  Place them in a ziplock bag and store in the bottom of your refrigerator.  You want them to stay moist and cold but never freeze them this will damage the membranes.
5.  At the start of next season check all the O rings for wear and coat them with a silicone grease then repeat the process listed above and you will be back in business.

I think I should be able to get at least three years out of a set of membranes but after two years I will order replacements just in case.  They come sealed in plastic and will be fine if left sealed for at least a year.

Please click on the RO Schematic link below for a drawing of the system.
Bret Hodorski,
Nov 4, 2016, 5:30 AM