Studies On Flocculant Of Nitrogenfixing Bacterium

Microbial flocculant is one of new, safe and high efficient flocculants.It has good applied prospect in water and polluted water disposal, food andmedicine production, and other aspects. In this paper, adopting selectivenon-nitrogen culture media, 5 flocculant-producing strains were enriched,isolated and screened, one of which can produce high efficient microbialflocculant (coded F₅, the same to the following). The flocculanting rate of theflocculant produced by F₅ can reach above 98%. The biology characteristics,conditions of producing flocculant, character and application of the flocculantof strain F₅ were studied. The results showed that F₅ can grow very well innon-nitrogen culture media using glucose or saccharose as carbon source. Theaddition of yeast extract can promote the growth of F₅. The colony is round, raised,smooth and colorless crystaline. The cell is rod-shaped and gram-negative, withemdospore and thick capsule. Sequence comparison shows that the similaritiesbetween the 16S rDNA sequence of F₅ and several strains of Bacillus mucilaginosusare 99%. After cultivated three days on the liquid non-nitrogen culture mediawiththe initial pH of 7～7.5, at the temperature of (25～30)℃, the ventilatingaddition (rotating speed of shaking table) of 120 rpm, and other optimalconditions, the flocculanting rate of F₅ fermentation liquor can reach 99.8%.F₅ flocculant has good pH stability and thermostability. The flocculanting testin 0.5% Kaolinite suspension with F₅ flocculant, inorganic flocculant andorganic flocculant were conducted. Result shows the flocculanting rate of F₅flocculant is 42.2% higher than that of an inorganic flocculant, and 71% higherthan that of an organic flocculant. Adding 2 times acetone (V/V) to F₅ fermentingliquor, 43.3 g wet crude product was extracted from 1L fermenting liquid. Thecrude product can still keep high flocculanting activity of 98. 8% when recovered...