Production, Characterization, and Flocculation Mechanism of Cation Independent, pH Tolerant, and Thermally Stable Bioflocculant from Enterobacter sp. ETH-2

Abstract

Synthetic high polymer flocculants, frequently utilized for flocculating efficiency and low cost, recently have been discovered as producing increased risk to human health and the environment. Development of a more efficient and environmentally sound alternative flocculant agent is investigated in this paper. Bioflocculants are produced by microorganisms and may exhibit a high rate of flocculation activity. The bioflocculant ETH-2, with high flocculating activity (2849 mg Kaolin particle/mg ETH-2), produced by strain Enterobacter sp. isolated from activated sludge, was systematically investigated with regard to its production, characterization, and flocculation mechanism. Analyses of microscopic observation, zeta potential and ETH-2 structure demonstrates the bridging mechanism, as opposed to charge neutralization, was responsible for flocculation of the ETH-2. ETH-2 retains high molecular weight (603 to 1820 kDa) and multi-functional groups (hydroxyl, amide and carboxyl) that contributed to flocculation. Polysaccharides mainly composed of mannose, glucose, and galactose, with a molar ratio of 1∶2.9∶9.8 were identified as the active constituents in bioflocculant. The structure of the long backbone with active sites of polysaccharides was determined as a primary basis for the high flocculation activity. Bioflocculant ETH-2 is cation independent, pH tolerant, and thermally stable, suggesting a potential fit for industrial application.

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“…As per the analysis of Zeta potential, BFBl imparts the negative charge to the kaolin suspension rather than neutralizing it. Similar results were reported by Tang et al [23]. The FTIR of BFBl showed the presence of different types of functional groups (carboxyl, hydroxyl, and amino group), provided it an anionic nature.…”

“…Similar results were reported by Tang et al . . The FTIR of BFBl showed the presence of different types of functional groups (carboxyl, hydroxyl, and amino group), provided it an anionic nature.…”

“…These groups were preferred for the adsorption process and may serve as binding sites for suspended particles. Tang et al [23] explained this mechanism of bioflocculant with respect to a long backbone of polysaccharides. The polysaccharides with large number of active sites can simultaneously adsorb many particles and form larger flocs.…”

“…The zeta potential is used to analyze the charge difference before and after flocculation of kaolin suspension to find the flocculation mechanism of BFBl. The method was followed as described by Tang et al [23].…”

“…If the net charge of suspension (kaolin + BFBl) was reduced from negative to a positive direction, the mechanism would be charge neutralization. But negative charge impartment suggested a bridging mechanism of flocculation instead of charge neutralization [15,23].…”