Fouling is a normal phenomenon of most reverse osmosis systems, most foulants can be removed from the membrane by proper cleaner (cleaning agent) and correct cleaning frequency. A foulant layer on the membrane surface or in the membrane element flow channels will increase the concentration polarization of salts at the membrane surface, so that reduce the salt rejection of membrane. The scaling may occur when the solubility product (Ksp) for a compound of limited solubility is exceeded, the results of scaling are decrease in salt rejection, drop in permeate flow or increase in differential pressure.

When to clean RO elements (after data normalization)
. 10~15% decrease in permeate flow rate
. 10~15% increase in differential pressure
. 3~5% decrease in salt rejection