Membrane Fouling and Scaling

By: Gil K. Dhawan Ph.D.k P.E., Applied Membranes, Inc.

The concentration of all materials in the feed water – dissolved and suspended – is highest near the membrane surface. As permeate is removed through the membrane, all impurities are left behind near the membrane surface. The layer of water next to the membrane surface (boundary layer) gets increasingly concentrated in the dissolved and suspended materials. These concentrations reach a certain steady level depending on the feed velocity, element recovery and membrane permeate flux (gallons per square foot of permeate produced per day).

It is important to follow membrane manufacturer’s recommendations on minimum feed flow, maximum element recovery and maximum element flux. These recommendations are based on element size and quality of feed water being treated. The concentrations of the dissolved and suspended solids in the boundary layer control the performance of the membrane. Higher concentrations mean higher osmotic pressure, higher tendency of suspended solids to coagulate and coat the membrane surface, and higher likelihood of scaling to take place. Maintaining proper operating conditions for the membrane is the key preventative step to minimize membrane fouling.
 

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© Applied Membranes, Inc. 2007