Study On The Structure And Flocculation Mechanism Of Microbial Flocculant MBFA₁

The purification, physical and chemical properties, structure and flocculation mechanism ofmicrobial flocculant produced by Aspergillus sojae have been discussed completely in this paper.The most excellent incubate condition of microbial flocculant MBFA1produced byAspergillus sojae is: Czapek’s medium, the rotational speed at130r/min, temperature at30℃,initial pH at6-7and culture time of46h. When the dosage was19.1mg/L, the highestflocculation activity was97.4%. The purified microbial flocculant MBFA1was obtained bycentrifugation， ethanol precipitation， dialysis， gel filtration by Sephadex G-200andfreezing-drying sequentially. The experiment of gel filtration by Sephacryl S-400showed thatpurity of MBFA1was creditable.Study showed that MBFA1was thermal stable, easily dissolved in acid and hot water, butinsoluble in base, cold water and organic solvent. Qualitative analysis and UV resultsdemonstrated that purified MBFA1was mainly composed of polysaccharides. Quantitativeanalysis showed that the content of polysaccharides was91.2%and protein was0.59%. Theelemental analysis showed that33.41%of carbon，7.69%of hydrogen，9.63%of nitrogen and0.39%of sulphur were present in MBFA1. The molecular weight and the mean molecular weightof MBFA1was about1.27×10~4and1.38×10~4determined by Ubbelohde viscosity method andGPC respectively.Complete acid hydrolysis indicated that MBFA1was mainly composed of glucose,arabinose and mannose, with a molar ratio of about100.7∶1∶8.2. Partial acid hydrolysisrevealed that mannose was the end while arabinose, mannose and glucose was branched chainand glucose was main chain. Configuration of monosaccharide may be (1�')、(1�'4)、(1�'4) and(1�'2,6) by periodate oxidation-smith degradation and methylation. IR showed that functionalgroups，such as hydroxyl，amino，carboxyl，hydrogen bond and sulfate，which were beneficialto flocculation，were contained in the structure of MBFA1. It was inferred that the main chain ofMBFA1was compose of (1�'4)-α-Glc and (1�'2,6)-α-D-Glc, branched chain of MBFA1wascompose of (1�'2,6)-α-D-Glc、(1�'4)-α-D-Glc、(1�'4)-β-D-Glc、(1�')-α-Ara、(1�'4)-α-D-Man and the end was compose of (1�')-α-D-Man through polysaccharides signal of NMR.Through the analysis of turbidity removal, particle size, floc morphology, Zeta potential offlocculation of kaolin by MBFA1and experiment of deflocculation of flocs, it can be thought that positive charge of MBFA1neutralized negative charge of kaolin at the initial stage offlocculation, at the same time, MBFA1and kaolin particle became closer and closer because ofvan der Waals forces. With the decrease of distance, functional group of MBFA1like hydroxyl,carboxyl easily combined with kaolin particle to form hydrogen bond and an ionic bond anddense flocs at last. It perhaps existed sweeping, because some kaolin particle easy to be seized atthe process of settlement of flocs.