A general overview of Scaling of Reverse osmosis membranes.
Fahad Maqsood
??Water Operations Professional || Quality Control/Quality Assurance ||Plant Operation & Maintenance || Seawater/Brackish water RO || Industrial Water Treatment || QHSE Enthusiast || NEBOSH Certified(UK)??
Scaling of reverse osmosis membranes occurs when dissolve substances in the feed water reach their maximum solubility limit somewhere in the RO unit. When further concentrated, they precipitate out of the solution and onto a surface. The surface may be a suspended particle in the feed/concentrate stream, the surface of the membrane, the feed water spacer, or any other surface.
The most common RO scales are:
? Calcium Carbonate (CaCO?)
? Calcium Sulfate (CaSO?)
? Barium Sulfate (BaSO?)
? Strontium Sulfate (SrSO?)
? Silica (SiO?)
Other materials can cause scaling, such as metal hydroxides, calcium fluoride, and magnesium salts, but the above five are the most common. If these substances reach their maximum solubility in an RO unit, they precipitate onto a surface as a relatively hard, crystalline layer.
The following are the common symptoms of scaling:
? Normalized filtrate flow (reduced to 25 С) dropped by 10-15% compared to the calculated flow under normal pressure.
? Feedwater pressure with the temperature adjustment was increased by 15% to keep the preplanned flow of the permeate.
?Permeate electrical conductivity was increased by 15%; the salt passage increased by 15%.
? Pressure drop in the RO pressure vessel while product water constant flow and recovery is increased by 15%.