Screening Of Flocculant-Producing Beneficial Bacteria And Study On The Flocculating Effect

Microbial flocculant is a sort of flocculatant metabolite produced by microorganisms,Microbial flocculant can be obtained through fermenation, concentration and refining of microorganisms such as bateria and epiphyte.It is the application of microbial technique.It mainly contains glucoprotein, polysaccharides,protein,lipid,Fibrin,DNA,etc.It has many strongpoints such as high safety,wide application,easy decomposition by micro organisms,and harmless to the environment.If microbial flocculant was used to dispose sewage, there would be no pollution in the drains.So it is paid so much attention to by scholars of all countries and has become the focus of research and development.This paper summarized a series of research and development on preparation of microbial flocculants systematically.The isolation of flocculant-producing bacterium,optimization of culture condition for flocculants production,and identification of the bioflocculant-producing bacterium.The composition and characterisitics of microbial flocculants were studied and discussed.The main contents of the research and the results are as follows:In this paper,5 stubs of strains have been sorted and dissolved from the sludge,intestines of the weever and the garden soil.A strain,DK1,with high flocculating activity was screened form sludge.It was identified as Bacillus licheniformis by it is characters and molecular biology(16S rRNA)to find a beneficial bacterium.The culture conditions were optimized for Bacillus licheniformis.The strain could grow in various situations and produce high-effect flocculants.The sudies showed that the optimum carbon sources were lactose and nitrogen sourcesm in the mixture of yeast extract(0.5g/L),ammonium sulfate(0.2g/L),and carbamide(0.5g/L).Under the cultivating conditions with primary pH value7.5～9.5,the liquid pack of 30～60 mL/250mL inoculum size being 3%～6%, at 37℃,on a shaking table at 160r/min.Strain DK1 cultivated for 48～72h can produce a highly efficient flocculant,with a flocculation ratio of 80%being against kaolin clay suspension.The periods of the bioflocculants producing was two days'time.The microbial flocculants produced by Bacillus licheniformis are excreted out of the cell,and the flocculants are mostly distributed in zymolytic medium when cultured in liquid culture mediums,and excreted on the surfac,e of the solid culture medium.Polysaccharides and protein in the secretion were made sure to have a property of flocculant through the method of factor destruction and chemistry analysis.The results of the flocculating experiment on different types of aquaculture with the bioflocculant produced by Bacillus licheniformis indicated that biofiocculant had excellent effect on the water-clarity of aquaculture and could remove indiscerptible COD_(Mn)and BOD₅,and showed excellent effects on the treatment of aquaiculture water.