Characterization of a compound bioflocculant produced by mixed culture of Rhizobium radiobacter F2 and Bacillus sphaeicus F6

A compound bioflocculant CBF-F26, produced by mixed culture of Rhizobium radiobacter F2 and Bacillus sphaeicus F6, was investigated with regard to its physicochemical and flocculating properties. It was identified as a polysaccharide bioflocculant composed of rhamnose, mannose, glucose, and galactose, respectively, in a 1.3: 2.1: 10.0: 1.0 molar ratio. The average molecular weight was determined as 4.79 x 10(5) Da by gel-permeation chromatography. Infrared spectrum and X-ray photoelectron spectroscopy revealed the presence of carboxyl, hydroxyl and amino groups in its structure. Thermostability test suggested that CBF-F26 was thermostable and high flocculating activity was maintained. Thermogravimetric property, intrinsic viscosity and surface morphology of CBF-F26 were also studied. CBF-F26 was effective under neutral and weak alkaline conditions (pH 7.0-9.0), and flocculating activities of higher than 90% were obtained in the concentration range of 8-24 mg l(-1) at pH 8.0. The flocculation could be stimulated by cations Ca2+, Zn2+, Fe2+, Al3+, and Fe3+. In addition, the probable flocculation mechanisms were proposed.