Isolation, Screening And Identification Of A Strain Of Microbial Flocculant And Its Flocculation Characteristics

The bioflocculant has received extensive attention of the scholars,because of its numerous advantages,such as non-toxic,harmless,high treatment efficiency.The thesis is mainly focused on the isolation,identification and fermentation of a bioflocculant-producing bacterium.In order to reduce cost of bioflocculant production,the cultivation of bioflocculant-producing bacterium from the common fermentation medium and brewery wastewater medium were optimized.The flocculant characteristic,tolerance and flocculation mechanism of the bioflocculants were further analized.Three screening methods including conventional method,DEHP method,and pyridine method were examined.The results showed that the screening success rate of conventional method was higher than the other two methods.Bioflocculant-production strain OS-1,identified as Klebsiella by 16S rDNA sequence and its biochemical and physiological characteristics,was isolated from soil by the traditional screening method.In order to improve the flocculating effect of bioflocculant on kaolin suspension,the fermentation conditions of Klebsiella sp.OS-1 were optimized.The results showed that the best medium for bioflocculant was:glucose 20 g/L,urea 0.75 g/L,yeast 0.75 g/L,KH2PO42 g/L,K2HPO45 g/L,AICl30.1 g/L,pH natural.The culture condition was 30?,and harvested at 28 hours.In order to reduce cultivation cost of bioflocculant Klebsiella sp.OS-1,carbon source and nitrogen source was replaced by brewery wastewater,and the fermentation condition was further optimized.The results showed that the optimal medium of bioflocculant Klebsiella sp.OS-1 was 15 g/L,KH2PO4 2 g/L,K2HPO45 g/L,and NaCl 0.1 g/L,brewery wastewater CODcr 1013 mg/L,TN 7.2 mg/L,pH 6.5.The culture conditions were as follows:the culture temperature was 35?,the shaking speed was 140 rpm,and the culture time was 40 h.In this paper,flocculant characteristic,tolerance and flocculation mechanism of the bioflocculants produced by the common fermentation medium and brewery wastewater medium were both analyzed.The results showed that the components of the bioflocculant cultured in the common fermentation medium were polysaccharide 78.6%,protein 14.3%.The composition of the bioflocculant produced by brewery wastewater medium were polysaccharide 69.4%,protein 24.5%.The infrared spectrum analysis of the two bioflocculants showed that the flocculant contained amino,carboxyl,hydroxyl and amide groups.To sum up,the two bioflocculants are both carbohydrate flocculants and similar in composition.For bioflocculant produced by common fermentation medium,the optimal dosage is 6.667 mg/L,the optimum temperature is 30?,the temperature tolerance range is 20-70?,the optimum pH range is 5-8,without adding Ca2+,Na+ and other metal cations as the coagulant.For bioflocculant produced by brewery wastewater,the optimal flocculant dosage is 10 mg/L,the optimum temperature is 30?,the temperature tolerance range is of 20-70?,the optimum pH range for 2-7,without adding Ca2+ Na+ and other metal cations as the coagulant.To sum up,the bioflocculant produced by brewery wastewater not only reduces the cost,but also is more adaptable than the common fermentation medium Combined with the results form Zeta potential measurement,the flocculation mechanism of the two kinds of flocculants was preliminarily probably concluded as bridging.