The coagulation performance and floc properties of compound bioflocculant (CBF)-aluminum sulfate (AS) dual-coagulant were compared with that of AS in the treatment of synthetic kaolin-humic (HA) water. Results showed that AS-CBF dual coagulant was more efficient for HA removal. The floc formation, breakage and reformation were investigated under different dosages and shear rates. Increasing coagulant dosage resulted in the increase of floc growth rate and size. But the floc recoverability was found to decrease with increasing coagulant dosage. Furthermore, flocs formed by AS-CBF (AS dosed firstly) had faster growth rate, larger size and better recoverability than AS and CBF-AS (CBF dosed firstly) in the dosage range investigated. Similar results were obtained when the shear force was changed. Precipitate charge neutralization was a dominant mechanism of AS, and CBF had good adsorption bridging effect. Due to the combination of two advantages, coagulation efficiency could be enhanced significantly. (C) 2011 Elsevier B.V. All rights reserved.