Characterization of flocculating agent from the self-flocculating microalga Scenedesmus obliquus AS-6-1 for efficient biomass harvest

In the present work, the extracellular biopolymers from the self-flocculating microalga Scenedesmus obliquus AS-6-1 were studied. It was revealed that the self-flocculation of the microalgal cells was mediated by cell wall-associated polysaccharides with a molecular weight of 127.9 kDa. Sugar compositions analysis indicated that the monomers consist of glucose, mannose, galatose, rhamnose and fructose with the molar ratio of 8:5:3:2:1. Addition of 0.6 mg/L purified flocculating agent resulted in the fast flocculation of freely suspended cells of S. obliquus and Chlorella vulgaris. The flocculating activity is stable between pH 6 and 8 and at 20–60 °C.