During the 2018 season I experimented with a better way of cleaning and storing my membranes. In the past as the season went on the performance steadily declined. By following the steps below I have not seen any deterioration in the performance of my system.

Supplies:

• RO Soap - I use CDL “Superflow Green” it comes in a 1.15kg container for under 20 dollars and this is more than enough for two seasons.
• Citric Acid - You can purchase food grade from Amazon or CDL and is under 20 dollars as well.
• Metabisulfite Sodium - RO Membrane Preservative which can be purchased from CDL or other suppliers.
• Digital pH meter to measure from 0-12. I found one on Amazon.com for under 15 dollars.
• A dedicated 5 gallon pail - label RO Wash in big letters or identify it any way you want.
• A dedicated 5 gallon pail - label Acid Wash or however you want to do it.
• Digital thermometer for measuring the temperature of water. Under 20 dollars on Amazon.
• Large bag of Baking Soda

Step One: Mix up your soap solution - RO soap raises the pH level of your permeate. Most residential membranes are rated to be used between 2-11 pH. Check to make sure you know what the range is for your membranes.

• Fill your wash bucket up ⅔ with permeate.
• Fill a pot with 2 ½ gallons of permeate and boil it.
• Pour the boiling permeate into your wash bucket until it is about 1” from the top. Check the temperature - it should not exceed 100º F.
• Mix in your RO soap powder until you get a pH reading of 11 or the upper threshold for your membranes. For me it takes about 1 heaping tablespoon to bring it to 11. The first time add in half that amount mix and then take a reading.

****The RO soap is basically food grade lye with a stabilizer, so make sure you wear gloves so you don’t get it on your hands. I would also wear eye protection to be safe. *****

Step Two: Washing with RO Soap

• Place the intake for your pump in the wash bucket with the RO soap.
• Place both the permeate and concentrate lines in another bucket.
• Turn your system on, make sure your needle valve is wide open, and hold the concentrate line in your hand (just the tubing don’t touch the liquid coming out) and wait until you feel the warm water coming through. At this point move both the concentrate and permeate line into your wash bucket with the soap. By doing this you are removing any sap that is still in the system and it will not change the pH level of your soap solution. This will recirculate the warm soap through the system.
• Let it run this way for 1-2 hours. I have found that 1 hour is plenty during most of the season but as you approach the end and the sap gets cloudy you will want to do 2 hours.
• Pull the feed line out of the soap bucket and wait until you hear the pump go dry. Unplug the system and let the concentrate and permeate lines drip until they stop.

Step Three: Rinsing

• Take a pH reading of your permeate.
• Put your feed tube into your permeate tank and put your concentrate and permeate lines into a barrel. Turn your system on and let it run for about 15 minutes. At this point shut off the system and you need to change the 5 micron filter. Turn the system back on and let run for 45 minutes. After measure the the liquid coming out of the permeate and concentrate lines for a pH level. If it matches your permeate the system has been flushed. I have found that it takes about 30-35 minutes for mine to match but give it another 20 minutes to make sure. I don’t want any off flavors in my next batch of syrup.
• Since you are flushing with permeate you don’t need to change your 5 micron filter for your next run - you can leave it in place surrounded by permeate.

Acid Wash - This should be done at the end of the season or if your system is not responding to the RO Soap Wash. What this means is if you are normally getting 7.5-8% concentrate with a pressure of 125-150 psi and your system can only manage 100 psi and you are only getting 5% or lower concentrate you should do an Acid Wash.

• Fill your Acid bucket up ⅔ with permeate.
• Fill a pot with 2 ½ gallons of permeate and boil it.
• Pour the boiling permeate into your Acid bucket until it is about 1” from the top. Check the temperature - it should not exceed 100º F.
• Mix in your Citric Acid until you get a pH reading of 2-3 or the lowest threshold for your membranes. It took just about 1/4 cup to bring the ph level to 2.4 for me.

****Make sure you are wearing gloves and eye protection this is an acid!****

• Place the intake for your pump in the Acid bucket with the Citric Acid.
• Place both the permeate and concentrate lines in another bucket.
• Turn your system on, make sure your needle valve is wide open, and hold the concentrate line in your hand (just the tubing don’t touch the liquid coming out) and wait until you feel the warm water coming through. At this point move both the concentrate and permeate line into your Acid bucket with the solution. By doing this you are removing any sap/soap/permeate that is still in the system and it will not change the pH level of your acid solution. This will recirculate the warm acid through the system.
• Let it run this way for about an hour then shut the system off and let sit for 1-2 days or up to a week.

You will now need to flush with permeate for 20-30 minutes.

You will now need to do a wash with the RO Soap and flush as detailed above.

We always want to be environmentally friendly so please do not throw the RO Soap or Acid solutions down the drain or out into the yard. You will need to neutralize it first. Start adding Baking Soda to your solutions until you get a normal pH level between 6.5 and 8.5. It is then safe to dispose of.

Storing your membranes in the off season:

The easiest way to do this is to make PVC vessels. 3” PVC pipe works well - I made 2 - 40" canisters because they are easier than one long one. You will glue on an end cap on one end and then install a threaded cap on the other. Plan on doing this well ahead of time. It took about a week of rinsing with water to get the smell from the pvc primer and glue to go away. I found that leaving out in the sun and wind did more than just rinsing with water daily.

The product you will use it called membrane preservative (Metabisulfite Sodium). The mix ratio is 1.1 ounces to 1 gallon of permeate. I fill up my PVC vessels with water and measure how much they hold so I know how much solution to make.

Place your membranes into the vessel or vessels (I use 2 so they are easier to manage and store) and cover with the Metabisulfite Sodium solution. Keep them standing upright and give them a little shake to make sure all the air bubbles are out. Cover and let stand overnight. Open the tops and add additional solution if needed. Give a couple of wraps of teflon tape and seal. Keep them from extreme heat and freezing and they will be safely stored until next season.

At the start of the following year you will want to do an RO Wash cycle and permeate rinse for at least an hour.