Study On The Cultural Conditions And Flocculanting Characteristic On Microbial Flocculants Produced By Aspergillus Niger

Microbial flucculants are natural polymers used for water treatment whichproduced by microorganisms during their growth, they are composed mainly byglycoprotein, polysaccharide, protein, nucleic acid and so on. Because of their highefficiency, safety and biodegradability, this kind of flocculants overcome theenvironmental problems caused by the inorganic and synthetic polymer flocculants.The studies of microbial flocculants have drawn more and more attentions.The paper concentrates on the optimization of culture medium and cultivationcondition of Aspergillus niger (A80) isolated, identificated by our laboratory. Theflocculants produced by A80was precipitated by ethanol and purified by hexadecyltrimethyl ammonium bromide. The flocculanting characteristic and chemicalcomposition of microbial flocculants was analysed. infrared spectrum and gelfiltration chromatography was used to identify the features groups and molecularweight, which aimed to analyse flocculation mechanism from the point ofcomposition and groups and provide guidance for industrial use of microbialflocculants. The main results are as follows:1) The optimal cultural conditions were as follows:100g/L sucrose as carbonsource,1.6g/L yeast extract as nitrogen source, initial pH of culture medium5-6.2) Experiment on flocculation efficiency changed with incubation time showedthat the microbial flocculants produced by A80reached the maximum activity whencultivated after48h. The results of flocculation active distribution indicated thatflocculant activity of microbial flocculants mainly exist in the fermented liquid withmycelium played a small supporting role.With kaolin clay suspension as test sample,when fermentation broth of A80obtained on the48hours, initial pH was5.0,flocculant dosage was2.5%(volume fraction), the microbial flocculant had anoptimal flocculation of Kaolin clay suspension (93.6%). The microbial flocculantshad good stability on temperature and pH change, when pH changed from2to10and temperature changed from4℃to100℃, the flocculant activity maintained at70%above.3) Analysis on pure flocculant products indicated that: this bioflocculant mainlycomposed by acidic polysaccharides (polysaccharide content accounts for88.3%),next was nucleic acid with content of11.64%(w/w) and very little protain. SEMshowed that its appearance presents a catenuliform, membranous with villousprojection. FT-TR demonstrated that it contains the typical characteristic groups andbases of polysaccharide, like carboxyl group, hydroxyl and so on. What’s more, theresult of GPC shows that the Mw of the MBF is7.858×104Da.