Acid wash on homemade RO

[Clinkis]

I would like to do an acid wash on my 2 post 4x40 MES membrane homemade RO. I think I’ve got a pretty good idea how to do it but what I’m unsure of is how much acid do I use? I bought some Milliard citric acid. How much should I add to how much water? Any advise is appreciated!

[bowhunter]

Citric acid is a really weak acid so it's pretty safe to do. Make a solution of 2/3 of an oz of citric acid per gallon of water. Do the acid wash after you've done a soap wash. You can circulate the citric acid solution or just let the membrane sit in the solution. Also make sure you rinse the membranes thoroughly after the citric acid wash as it is organic and it can grow mold. I believe the pH of this solution is about 2.5 and I don't think you can get citric acid to go much lower.

[Clinkis]

Perfect. That’s what I was looking for. Thx Bowhunter

[Clinkis]

One more quick question. If I’m going to soak it how long should I leave it?

[bowhunter]

I read somewhere that it could soak for several days, but I haven't been able to confirm that. Dow says you can soak the Filmtec membranes overnight. I let mine soak in citric once and I believe it was overnight. You can't do much damage with a citric acid soak other than organic fouling if you let it soak too long.

[maple flats]

On a 4x40 use the amount specified by MES per membrane, after doing a soap wash and a permeate rinse. Let it soak in season for 12-24 hrs. I only use the citric acid if performance drops during the season. After the season do a wash using the soap recommended by MES, then a rinse then an acid wash. Then let it set up to 4 weeks max. Then do another soap wash and a permeate rinse and put it to bed until next year. Add preservative to store it, keep from freezing and never let it dry out.