Colloidal fouling in relation to Reverse Osmosis Membranes
Iron, either soluble form or insoluble form is the main cause of colloidal fouling from within the feed water. The nature of the iron present depends on numerous contributing factors, the main one of which is the PH balance of the water.
Although pre-filters can remove iron oxides, this can be proven ineffective, as the particles can be very small. If the PH of the water rises too much, soluble iron can form insoluble iron oxides.
In reverse osmosis systems, the PH rises from the feed to the reject so that soluble iron can precipitate throughout the system.