Studies on characterization of bioflocculant exopolysaccharide of Azotobacter indicus and its potential for wastewater treatment.

Partially characterized bioflocculant exopolysaccharide (EPS) produced from an Azotobacter indicus ATCC 9540 strain reported in our previous study was further characterized, and its flocculant potential was investigated at different pH, temperature, and cations concentrations. Flocculant activity at different concentrations of EPS in the absence of cations was reanalyzed by slight modified flocculant assay. It revealed that flocculant activity increased in a concentration-dependent manner up to a certain limit, with the maximum flocculation of 72% at 500 mg L⁻¹ EPS concentration, even in the absence of cations. At the concentration of 10 mg L⁻¹, CaCl₂ showed more significant activity (92%) than AlCl₃ and MnSO₄. Differential scanning calorimetry study and flocculant assay revealed high temperature stability of EPS up to 97 °C. Molecular weight of the EPS determined by size exclusion chromatography was found to be approximately 2 x 10⁶ kDa. Investigation on flocculation efficacy of the characterized EPS for wastewater treatment of dairy, woolen, starch, and sugar industry suggested it to be effective and stable at wide pH range of 5-10. Wastewater treatment with biopolymer at 500 mg L⁻¹ showed reduction in biochemical oxygen demand (38-80%), chemical oxygen demand (37-79%), and suspended solids (41-68%). This study suggests that Azotobacter polymer has high potential in wastewater treatment as bioflocculant and can be used as a potential alternative to chemical flocculants.