A novel composite consisting of clay, bioflocculant, and inorganic flocculant was designed, and its flocculating effect on harmful algal blooms (HABs) was studied in this study. The extracellular polymeric substances (EPS), produced with a yield of 3.58 +/- 0.11 g/L by a newly isolated Pseudomonas aeruginosa ZjU1, was indicated to be a key component in the composite. The components and functional groups of the EPS were analyzed, and it showed that polysaccharides, proteins, and nucleic acids are the main components; polar functional groups in the EPS are responsible for its flocculating activity. The novel composite was optimized by the response surface methodology and after optimization, the optical components and contents of the composite were Kaolin 2.38 g/L, CaCl2 0.28 g/L, KAI(SO4)(2) 0.09 g/L, and EPS 1.75 mg/L The flocculating rates of the composite were tested, and it could rapidly reach 100 +/- 0.13% within 2 min when OD680 of Microcystis aeruginosa was 0.1; it could reach 100 +/- 0.08% within 5 min for OD680 of M. aeruginosa in HABs up to 1.0. These results suggest that the novel composite will be a highly efficient material for the treatment of HABs caused by M. aeruginosa. (C) 2014 Elsevier B.V. All rights reserved.