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Characterisation of exopolymer R-202 isolated from Rhodococcus rhodochrous and its flocculating properties


The characterisation and flocculation behaviour of exopolymer R-202 produced by Rhodococcus rhodochrous were investigated. The water-soluble fraction of this polymer with the molecular weight of about 1.3 × 103 kDa was found to be 62.86% of polysaccharide and 10.36% of protein. Chemical analysis showed the presence of reducing sugars, uronic acids, and amino sugars at the concentrations of 232.41 μg/mg, 45.29 μg/mg and 15.07 μg/mg, respectively. The HPLC analysis revealed that the monosaccharide components of the studied exopolymer were mannose, glucose and galactose at the molar ratio of 12:6:1. The flocculating activity was measured using the kaolin suspension and the basic flocculation parameters of exopolymer were established. The highest flocculating activity of exopolymer R-202 was observed at a dosage of 2 mg/L, a pH value 7.2 and in the presence of 10 mM solutions of salts (NaCl, CaCl2, MgCl2 or FeCl2). This effect depended on the type of ions and increased in the order - Na+ < Ca2+ < Mg2+ < Fe2+. The highest flocculating activity appeared in the presence of Fe2+ ions. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) showed that R-202 is a negatively charged polymer and contains functional groups (hydroxyl, carboxyl, amine, amide) preferred for the flocculation process.