Screening Of Bioflocculant-producing Strains And Study Of Characteristics Of Bioflocculant

Bioflocculants (microbial flocculant), which are produced by microorganisms duringtheir growth, have been received considerable scientific and biotechnological attention inrecent years because of their high efficiency, non-toxic, non-secondary pollution of theirdegradative intermediates. In this study, a series of experiments were carried out includingscreening, optimizing fermentation process, studying flocculating characteristics andresearching its application. The main results are as follows:In accordance with the flocculating activity of fermentation liquors to Kaolinsuspension, there were10strains isolated from activated sludge. After shaking flaskfermentation and testing ferment production, the strains B31was acquired to be futurestudied, the flocculating efficiency achieving80.1%. Based on the morphological,physiological and biochemical characterstics, and with reference to “Berger’s BacterialIdentification Manual”, B31was identified as Bacillus polymyxa.Fermentation conditions for flocculant production were optimized using single factorand orthogonal methods. The optimal cultivation conditions for strains B31were15g/Lglucose，0.64g/L urea,2g/L KH2PO4,5g/L K2HPO4,0.1g/L NaCl，0.2g/L MgSO4，pH7.0,30°C, inoculation volume10%,150r/min and72h. Under such conditions, the strainsB31could reach the highest flocculation of89.57%.The bioflocculant MBF B31was separated by organic solvent precipitation. The highproduction yield of crude bioflocculant by cold ethanol precipitation was up to0.7g/L.Crude bioflocculant was purified using Sephacryl S-200gel filtration chromatography.There was only a large single chromatographic peak, the flocculating rate of the purifiedbioflocculant was90.21%and increases very little compared with the crude bioflocculant.According to UV and IR spectra, colorimetric reaction, chemical composition of thebioflocculant was analyzed. It shows that the main ingredient of the bioflocculant isglycoprotein. Its optimal flocculation conditions were of bioflocculant dosage3mL/100mL (10mg/L), pH8.0,5mL CaCl2as coagulant and15min standing time. The resultsshowed the crude bioflocculant could be directly applied without purification, thus saving production time and reducing the cost of treatment.When studying the application of bioflocculants, sweage and car-washingwasterwater were selected as flocculating objects. Results showed that the bioflocculantMBF B31had strong ability of turbidity removal to sweage and car-washing wasterwater.When dealing with sewage, the optimum dosage was2mL/100mL (10mg/L), theturbidity rate reached81.2%, the removal rate of COD was50.2%. And for car-washingwastewater, the optimum dosage was2mL/100mL (10mg/L), the turbidity rate was up to81.2%, the removal rate of COD was50.2%. The strains B31had a good research valueand prospect of utilization.