What’s Clogging Your Membrane?

by Ryan Lessing, Watts Water Quality

Want to know what’s clogging your commercial RO membranes? The next time your RO stops producing water, try using your senses to determine why.

  • Smell:Does the membrane have a fishy or moldy odor when removed from the housing? If it does it’s likely that bacteria/bio film is present. Cut the membrane lengthwise and unroll it like a roll of paper towels.
  • Feel: The membrane material should feel like clean wet plastic. If there’s slime or a slippery film present it means the membrane could be bio-fouled. If the membrane’s texture feels like sand paper it means a mineral fouling is present.

To test mineral fouling, unroll and dry a sample of membrane, scrape up a sample of the mineral, put it into a beaker, and soak it in RO water with a pH of 4 (adjusted with muratic acid) for one hour. Then readjust the pH back to 7 with baking soda and use a field kit to test for hardness and/or iron. Is hardness present? If yes, your softener isn’t working all the time. Then scrape up a second sample of scale and put a drop of vinegar on it. If it foams it is carbonate; if not it could be sulfate.

  • Sight: Is there discoloration on the membrane surface? A red/brown discoloration indicates possible iron fouling while grey/brown indicates possible silt fouling.

Source: Watts Email Newsletter.

Pure Water Gazette Fair Use Statement