The Research On The Preparation And Characteristic Of Extracellular Bioflocculant

This research screened 6 strains of bioflocculant-producing microorganisms from activated sludge from biological aerated filter by conventional methods. 2 strains with high and stable flocculating activity was obtained after rescreening,which were identified as Bacillus named Bacillus N5 and Streptomyces viridoris named Streptomyces viridoris G15. Taking the 2 strains as the subjects investigated,the effect of the cultural conditions and the medium compositions and proportion on bioflocculant production was studied,and the flocculating characteristic of the bioflocculant produced by strain Streptomyces viridoris G15 was studied also.The experimental results showed that the medium composition and proportion had significant effect on bioflocculant production. The optimum cultural conditions obtained of Bacillus N5 after single factor experiment was:sucrose 20g/L,yeast extract 0.5g/L,urea 0.5g/L,(NH4)2SO40.2g/L,KH2PO45g/L,pH=8,25℃,cultivated for 36 hours in flakes. The optimum compent proportion of medium of Streptomyces viridoris G15 obtained according to the single factor experiment and the orthogonal experiment was:sucrose 20g/L,yeast extract 0.8g/L,urea 0.5g/L,(NH4)2SO40.8g/L,KH2PO45g/L,the optimum cultural conditions was:pH 8,25℃,cultivated for 72 hours in flakes. The effect order on biofocculant production was:KH2PO4 > sucrose> urea>yeast extract>(NH4)2SO4. High inorganic salt ratio was benefical to bioflocculant production,but inhibited if too high;carbon source sucrose and organic nitrogen urea had large effect on bioflocculant production,reasonable C/N ratio was benefical to bioflocculant production.The results of the experiment on the flocculating characteristic of the bioflocculant produced by strain Streptomyces viridoris G15 showed that the flocculating activity of the bioflocculant was due to the secondary metabolic product of G15. The bioflocculant was present in the fermentation liquid mainly and had a high thermostability,7.9 percent was lower after an hour in boiling water. High valent ions could promote the flocculating effect,in which Ca2+ had the best effects. Both the bioflocculant and the coagulant aids had the best dosage. pH and temperature had effect on flocculating activity of the bioflocculant. The bioflocculant was simply purified and the producibility of the crude bioflocculant was 0.8g/L.The study on the bioflocculant produced by Streptomyces viridoris G15 showed that the bioflocculant could keep high flocculating activity in wide range of temperature and in low dosage,which indicated a good utilization prospective of the bioflocculant.