| Microbial flocculants (MBF) are biopolymers produced by microorganisms under fermentations and obtained from microorganisms or its secretions through isolation, extraction and purification. Microbial flocculants have quite good development trends and prospects because of its special advantages such as safety, strong effect biodegradable, lack of secondary pollution and so on. Those including fermentations of MBF produced by Bacillus natto, isolation and extraction of MBF, flocculating conditions and characteristics of MBF, compounding of MBF, components and superficial syndrome structures of MBF were focused in the paper.1 Study on optimal fermentations of MBF produced by Bacillus nattoFermentations of MBF produced by Bacillus natto were optimized through single factor experiments, Plackett-Burman screening test design, steepest ascent experiment and response surface method, and the results indicated that the optimal fermentations of MBF produced by Bacillus natto were medium including glucose of 15 g/L, glycerol of 10 g/L, yeast extract of 11.8 g/L, sodium hydrogen phosphate of 3.2 g/L, sodium dihydrogen phosphate of 4 g/L, magnesium sulfate of 0.6 g/L, pH of 6, cultivating conditions including volume of 50 mL/250 mL, inoculum of 3%, temperature of 37℃, shaking speed of 180 r/min, time of 30 h. Results of validating experiments showed that the average flocculating rate of MBF produced by Bacillus natto under optimum fermentations was 96.62 %. Researches on fermentation period of MBF produced by Bacillus natto under optimum fermentations revealed that the optimum time of MBF produced by Bacillus natto was 30 h.2 Study of isolation and extraction of MBFBased on the experiment for distribution of MBF in fermentation broth, main factors affecting isolation and extraction of MBF including centrifugation conditions, pH of fermentation supernatant, precipitant and multiple of precipitant were optimized. The results indicated that the optimal conditions of isolation and extraction of MBF were as follows:pH of supernatant obtained by the centrifugation conditions of 8000 r/min,15 min from fermentation broth, was adjusted to 6, and then 6 times volume of 95% ethanol were added into supernatant and stood in the condition of 4℃for overnight, and then precipitation obtained by the centrifugation conditions of 4000 r/min,15min, was resolved, and dialyzed in the condition of 4℃for overnight, and MBF was gained by freeze drying, and the yield of it were 2.6 g/L3 Study of flocculating conditions and characteristics of MBFFlocculating conditions and characteristics of MBF were investigated. Results of experiment on flocculating kaolin suspension of 100 mL indicated that the optimal dosages of MBF and optimal coagulant (10 g/L CaCl2) were 1 mL and 5 mL respectively. MBF had a wide application of pH, and it could maintain a higher flocculating activity when pH of water bodies flocculated were in the range of 4-9, the flocculating rates were above 80 %, and the flocculating rates of MBF were the highest while pH of water bodies flocculated were in neutral or weak base. MBF had a wide application of temperature, and it could maintain a higher flocculating activity when temperatures of water bodies flocculated were in the range of 4℃-100℃. MBF had a better stability, when it was treated in the range of 4℃-100℃for 15 min and in the boiling water bath of 100℃for 60 min, its flocculating rates could be above 93% and 88% respectively, and its flocculating rates were above 80.91% while MBF was placed within the condition of 4℃for 14 days. Forms of kaolin particles flocculated before and after were observed that kaolin particles flocculated before were uniformity and loose while kaolin particles flocculated after were compacted and aggregated together, which indicated that MBF had a very good flocculating activity to kaolin particles.4 Study of MBF compoundedEffects of MBF compounded with polyaluminium chloride (PAC) and poly-acrylamide (PAM) on flocculating activity to kaolin suspension were researched. Results of MBF compounded with PAC showed that the optimal orders and proportions of MBF/PAC and CaCl2 were MBF of 0.6 mL first, and then CaCl2 of 2 mL, PAC of 0.5 mL when kaolin suspensions of 100 mL were flocculated. Effects of pH and temperatures of water bodies flocculated on the flocculating activity of MBF/PAC were not significant, and compared with the single flocculant, MBF/PAC had a wider range adapted for temperatures and pH of water bodies and higher flocculating activity. Results of MBF compounded with PAM indicated that the optimal orders and proportions of MBF/PAM and CaCl2 were MBF of 0.6 mL first, and then CaCl2 of 2 mL, PAM of 0.1 mL when kaolin suspensions of 100 mL were flocculated. Effect of temperatures of water bodies flocculated on the flocculating activity of MBF/PAM was not significant. MBF/PAM had a higher flocculating activity when pH of water bodies flocculated were in the range of 1-3 and 5-8, which showed that it had a wider range adapted for pH of water bodies, especially in metaacid water bodies. Compared with the single flocculant, MBF/PAM had a wider range adapted for temperatures and pH of water bodies and higher flocculating activity.5 Study of components and superficial syndrome structure of MBFThe qualitation and quantitation of MBF components were determined by the methods of color reactions and instrumental analysises, and superficial syndrome structure of MBF were observed by scanning electron microscope (SEM). The qualitative results of MBF revealed that it contained polysaccharide, protein and other components including alcohols, aldehydes, ketones and carboxylic acids, and polysaccharide of it were consisted of maltose, glucose, galactose, mannose, and protein of it contained 17 amino acids which acidic amino acids of glutamic acid and aspartic acid were the main compositions. The quantitative results of MBF indicated that the contents of polysaccharide, hydrolysis amino acids (protein) and other components were 45.18%, 21.1% and 33.72% respectively. SEM image of MBF powder showed that it had nemaline and lamellar structures, and there were many sunken holes on the surface of it where functional groups of MBF might exist, which might be closely related to its flocculating activity. |
