Clarification: Impact on Ultrafiltration Membrane Fouling in Drinking Water Treatment

The impact of different pretreatment conditions (powdered activated carbon [PAC] addition, iron chloride coagulation, and anionic polymer addition) on ultrafiltration membrane fouling was studied. Experiments were carried out at laboratory scale with new membranes and at pilot scale with used membranes. Results show that PAC has a positive effect—or at least, no negative effect—as long as backwashing allows effective removal of the filtration cake. On the other hand, excess PAC can generate irreversible fouling. Iron chloride has no negative impact for either native or used fibers as long as acid backwashes are effective. Inversely, an anionic polymer has a negative impact in every case—causing irreversible membrane fouling—despite its effectiveness in the clarification process. Test results also confirm that aged membranes are more sensitive to fouling than are pristine membranes. Their more hydrophobic structure is caused by the consumption of the hydrophilic agent under the effect of repeated contact with chlorinated water.