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

•Coagulation performance of three high content Al species was first studied.•Membrane fouling of ultrafiltration would be different because of flocs performance.•The different floc properties and membrane fouling with Al species were discussed.•Alb has the best benefit to alleviate the membrane fouling. Three species of aluminum coagulants mainly consist of mononuclear Al species (Ala), medium polymeric species (Alb) and colloidal species (Alc) 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. Ala coagulant had better UV254 and dissolved organic carbon (DOC) removal efficiency. Furthermore, Ala and Alc were beneficial to form larger flocs with lower strength and looser structure, whereas Alb was prone to form small flocs with higher strength and compact structure. Ultrafiltration experiments indicated that Alb is the most effective Al species to alleviate membrane fouling.