In normal operation, the membrane in reverse osmosis elements can become fouled by suspended solids, microorganisms and mineral scale. These deposits build up during operation and cause loss in water output or salt rejection, or both. Elements should be cleaned whenever the normalized water output rate drops by 15% from its initial flow rate (the flow rate established during the first 24 to 48 hours of operation) or when salt content in in the product water rises noticeably.
Comparison of Fouled and Clean Membrane
It should be noted that the water output rate will drop if feedwater temperature decreases. This is normal and does not indicate membrane fouling.
For calcium carbonate fouling, here is a quick cleaning procedure:
Buy a 30% concentration of muriatic acid. (This is sold at home improvement stores for cleaning concrete.)
Take your membrane and pressure vessel off-line, plug up the bottom holes of the pressure vessel, and stand it up vertically.
Put on goggles and gloves.
Pour the muriatic acid into the waste or the feed water port.
Let the membrane soak in the solution for 10 minutes.
Drain the solution and then flush the membrane and pressure vessel thoroughly.
Return the membrane and the vessel to the system and see if the membrane's performance has improved.
For a very fine presentation on the causes and treatment of membrane fouling, please seeMembrane Cleaning (PDF file)
For a list of companies that will clean your membranes
(or sell cleaning products), please click here.