A novel bioflocculant produced by a salt-tolerant, alkaliphilic and biofilm-forming strain Bacillus agaradhaerens C9 and its application in harvesting Chlorella minutissima UTEX2341

•Bacillus agaradhaerens C9 produces 4.65 g/L bioflocculants.•Bacillus agaradhaerens C9 can form biofilm in alkaline condition.•Bioflocculant from Bacillus agaradhaerens C9 flocculates Chlorella minutissima.

A novel bioflocculant MBF-C9 produced by a salt-tolerant, alkaliphilic Bacillus agaradhaerens C9 was investigated in this study. The effects of culture conditions such as initial pH, carbon source, nitrogen source, C/N ratio, and NaCl concentrations on MBF-C9 production were studied. The result showed that 4.65 g/L purified MBF-C9 was extracted with the following optimized conditions: 10 g/L glucose as carbon source, 10 g/L yeast extract as nitrogen source and initial pH 10.2. The MBF-C9 contained 65.42% polysaccharides, 4.70% proteins, and 1.65% nucleic acids. The highest flocculating rate of 95.29% for kaolin suspension was achieved at a dosage of 1.5 mg/L, pH 6.53 and 29 °C, and the highest flocculating rate of 80.63% for Chlorella minutissima UTEX2341 cells was observed at a dosage of 8 mg/L, which is much lower than that used in previous study. In addition, C9 could form biofilm under alkaline condition. Therefore, C9 has the potentials to be used in harvesting microalgae or as a bacterial agent to strengthen the treatment of alkaline wastewater.

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