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.
Highlights
Flocculating agents, widely used in industrial processes such as wastewater treatment, are classified into three groups i.e., inorganic flocculants such as aluminium sulphate; organic synthetic high polymer flocculants such as polyacrylamide (PAM); natural flocculants or bioflocculant such as microbial flocculant [1, 2]
Isolation of flocculant-producing strain ETH-2 of Enterobacter sp
Strain ETH-2 has been deposited into the China Center for Type Culture Collection (CCTCC) (Wuhan, China)
Summary
Flocculating agents, widely used in industrial processes such as wastewater treatment, are classified into three groups i.e., inorganic flocculants such as aluminium sulphate; organic synthetic high polymer flocculants such as polyacrylamide (PAM); natural flocculants or bioflocculant such as microbial flocculant [1, 2]. Synthetic high polymer flocculants have been most frequently utilized due to their flocculating efficiency and low cost, there is increasing evidence of risk to human health and the environment [1,2,3]. Varying types of microorganisms, including bacteria [4,5,6,7,8,9,10], fungi [11, 12] and algae [13, 14], have been isolated from soil and activated sludge, and shown to produce bioflocculant. Recent studies have focused on various bioflocculant producing bacteria including; (Enterobacter aerogenes [4], Halomonas sp. [5], Chryseobacterium daeguense [6], Klebsiella pneumoniae [7], Paenibacillus sp. [8], Corynebacterium glutamicum [9], Bacillus licheniformis [10], et al.)
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