Coagulation performance and membrane fouling of different aluminum species during coagulation/ultrafiltration combined process

Three species of aluminum coagulants mainly consist of mononuclear Al species (Al_a), medium polymeric species (Al_b) and colloidal species (Al_c) were prepared, separated and purified by organic solvent precipitation method. The effect of different Al species on coagulation performance and membrane fouling were investigated through the coagulation-ultrafiltration hybrid process. The influence of flocs characteristics were also studied to build the relation model between Al species coagulation and membrane fouling mechanisms. The results showed different Al species combined with humic acid (HA) in diverse ways feature distinct floc properties and membrane fouling. Al_a coagulant had better UV₂₅₄ and dissolved organic carbon (DOC) removal efficiency. Furthermore, Al_a and Al_c were beneficial to form larger flocs with lower strength and looser structure, whereas Al_b was prone to form small flocs with higher strength and compact structure. Ultrafiltration experiments indicated that Al_b is the most effective Al species to alleviate membrane fouling.