Influence of floc size and structure on membrane fouling in coagulation-ultrafiltration hybrid process--the role of Al13 species.

Coagulation application prior to ultrafiltration process was carried out to increase humic acid (HA) removal and membrane permeability. The [Al(13)O(4)(OH)(24)(H(2)O)(12)](7+) polycation (Al(13) species) was used in the coagulant process and polyaluminum chloride (PACl) was also used for comparison. Characteristics of aggregates pre-coagulated by Al(13) species and PACl were investigated using a laser diffraction particle sizing device. Additionally, membrane fouling was investigated under different coagulation conditions. The various resistances caused by Al(13) and PACl treatment effluents were determined using the membrane fouling index equation. The results indicated that at dose of 1 and 3mg/L, Al(13) produced larger flocs than PACl; while when dosage further increased, the PACl-HA flocs were much larger. The flocs formed by Al(13) were strong and compact, and those formed by PACl were weak and loosely structured with the exception of the flocs generated at 1mg/L. The investigation of membrane fouling demonstrated that Al(13) contributed to the best effluent permeating at 5mg/L and the corresponding dose for PACl was 7 mg/L. The adsorption resistance of effluent pre-treated by Al(13) accounted for a smaller percentage of the total resistances compared with that by PACl.