I have Filmtec RO membranes, which according to Filmtec, are suppose to be cleaned using the high pH caustic cleaner before the low pH acid cleaner. It seems very few people clean their RO in this manner. Normally, it is the opposite, low pH followed by high pH. I was wondering if anyone else has Filmtec membranes and are following their recommendations?

I have always had more sucsess cleanig with low first then high even with Filmtech membranes.Not sure why but most procedures call for high first.

Which cleaner to use first depends on which foulant you need to remove first. If your major foulant is calcium carbonate scale, acid clean first to get rid of the scale. If your major foulant is biofilm, clean first with a high pH cleaner to remove the biofilm..later, you can clean with an acid to remove the scale below the biofilm.

Wouldn't you be doing both by using 1% Minncare? It's low pH takes care of scale and is a disinfectant. Put it this way: What's in the cleaning process that the 1% doesn't have? If you're saying that in the two step process it doesn't matter what the order is then I'm less inclined to believe it's because of a two step process. See what working Sundays does?
Thanks

Years ago Filmtec recommended that Minncare not be used until after acid cleaning. This is because any iron left on the membrane will catalyze membrane deterioration by the Minncare. Also the acidity of a 1% Renalin solution is not sufficient to dissolve carbonate scales.
Florian is correct that the type of fouling will determine whether to use low pH first or last. Practically, only experience on a particular water will verify which type of chemical should be used first.
For 25 years I have used phosphoric acid (1%) heated to 100-110 degrees F. with good results. Subsequent caustic cleaning will remove organic fouling. Sometimes an additional acid cleaning step is valuable after caustic cleaning.
Only testing after each cleaning step for output flux and rejection will verify if the cleaning is successful.

Marcor told me the same thing about the danger of Minncare reacting with iron and eating holes in the membrane.

A tech at Marcor also told me that Minncare will not adequately disinfect a dirty membrane. The foulants will protect some of the bacteria.

What type of RO do you have Stephen, and how do you heat your cleaning solution to 100-110 F? Also, how do you measure flux?
This is for Florian, how do you know what is fouling a membrane? Biofilm or calcium carbonate? I know my incoming water is soft water, typically <1.0ppm for calcium/magnesium. It seems from visual evidence that my high pH is more effective after the acid cleaning.

JD, one way to tell is to send off an old membrane for an analysis. Another way is to test your RO reject water. Keep in mind that if your RO is at 50% reject, the concentration of scalants on your RO membrane is twice as high as your incoming water; 4 times as high for 75% rejection.

If your softener is working well, you should not have calcium scale, or barium scale which require an acid cleaning. If you have high bacteria coming off your carbon, you can have biofilm which will require a caustic clean and disinfection (yes, acid clean membrane before using PAA/peroxide or any oxidizing biocide disinfectant as mentioned above).

JD. The cleaning I mentioned was done in a separate cleaning skid with a jet pump, tank and heater. One module at a time is cleaned this way. While acid cleaning on the RO system can be effective, caustic cleaning of organics is less so. Cleaning works best when the flow is high and the pressure is low. Entraining air into the cleaning solution also helps. The skid is also equipped with a high pressure pump for testing. The flux is merely the output flow standardized to an arbitrary membrane pressure and temperature.

We have 8 membranes 98% reject rate and they were installed in 2000. Only disinfected with PAA. Pre-treatment and your incoming municipal water are probably the biggest factors.