Studies on Characterization of Bioflocculant Exopolysaccharide of Azotobacter indicus and Its Potential for Wastewater Treatment

Abstract

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.

Production and characteristics of bioflocculant TPT-1 from a consortium of Bacillus pumilus JX860616 and Alcaligenes faecalis HCB2

“…The presence of hydroxyl groups might have built up strong forces of attraction between bioflocculant TPT -1 make-ups and resulted in relatively rigid crystalline solids -whereby hydrogen bonding could occur. Since these strong forces were not dissociable by organic solvents, the bioflocculant TPT -1 was insoluble in all organic solvents (Patil et al, 2011). The solubility of TPT -1 in aqueous solution was due to the principle that "like dissolve like " (Boyd, 2015).…”

“…Thus, polar and charged functional groups of TPT -1 were solvated by aqueous molecules. The hydroxyl groups of the bioflocculant have the probability of forming hydrogen bonds with water, thus making TPT -1 soluble and hydrophilic (Patil et al, 2011).…”

“…TPT -1 was found to be effective at a wide range of pH (pH 3 to 9), with the highest flocculation activity (89%) at pH 3 (Figure 11). However, the decrease in flocculating activity at pH 12, suggested the alkaline degradation of the bioflocculant TPT -1 , which could have resulted from changes that include molecular rearrangements of the polysaccharide chain fragmentation of the bioflocculant (Patil et al, 2011). It was, thus assumed that the slight decrease in flocculation activity was due to OH -ions which might have inhibited the formation of flocs of TPT -1 and Kaolin particles in solution.…”

Effect of synthetic carbon substrates and cane molasses, an agro waste, on exopolysaccharide production by P. fluorescens

“…Due to the presence of many number of hydroxyl groups, strong attractive forces prevail between polysaccharides, which make them insoluble in organic solvents [28]. …”

Flocculation Characteristics of Microalgae Through Combined Flocculants

“…이전 연구결과에서 Aluminium 계열, Ferric계열의 무기 응집제 사용 시 해양 미세조류 높은 응집 효율을 얻을 수 있었다 [13]. 하지만 Aluminium은 Alzheimer 를 유발하는 것으로 알려져 있다 [14][15][16] 해양 미세조류인 Chlorella ellipsoidea의 경우 이전 연구 에서 응집제 중에서 1 g 당 응집 효율이 가장 높았던 Ferric chloride를 선택하였다 [13]. 여기에 생분해성 고분자 응집제 로서 Chitosan, Starch, Sodium alginate, Alginic acid를 혼합 시켜 주었다.…”