Screening Of The Strains Producing Microbial Flocculant

Microbial flocculants are a kind of biological macromolecular materials withcertain flocculating activity, mainly produced by microorganisms. Compared withinorganic flocculants and organic synthetic polymer flocculants, microbial flocculantsare safe, non-toxic, and easily degraded by microorganism. In addition, they have afunction of adsorbing heavy metal. That makes microbial flocculants become a hot fieldof research and development at home and abroad. The paper concentrates on thescreening and identification strains by the method of limitting oxygen, the optimizationof culture medium and cultivation conditions, the separation and identification ofproducts and the flocculation properties. The main results are as follows:4strains with high flocculating activity were isolated from6samples and theirflocculation rates were nearly80%. A bacteria strain130, which had stableperformance and the highest flocculating activity, with average flocculation rate of81.3%was chosen. Based on its morphological, physiological characteristics and thepartial sequences of its16S rDNA, it was identified as a Rheinheimera sp.. That strainwas a kind of facultative anaerobic bacteria strains.The flocculant produced by Rheinheimera sp.130was mainly distributed in thefermentation broth. After extraction and purification, measurements of chemicalanalysis, UV absorption spectrum and infrared spectrometer analysis revealed that theflocculant was a kind of polysaccharide. UV absorption spectrum analysis showed thatprotein and nucleic acid were not the active ingredient of the flocculant. Infraredspectrometer analysis showed the presence of carboxyl, hydroxyl and other polar groupsin its molecules. The content of neutral saccharide was about69.4%and that of uronicacid was about6.84%.The optimum medium of fermentation were glucose35g/L, soybean meal1g/L,K2HPO4·3H2O5g/L, KH2PO4·12H2O2g/L, MgSO4·7H2O0.1g/L, FeSO4·7H2O0.03g/L; The optimum cultural conditions was: initial pH of7, the cultivate temperature of37℃, liquid volume of50/250mL, shaking revolution of120r/min, inoculation contentof2%and fermentation time of84h. Compared with the flocculating efficiency of theinitial, it increased from81.3%to89.72%under the optimum medium and conditions.The results of the experiments on the flocculating properties of the flocculantproduced by Rheinheimera sp.130showed that, the dosing quantity of flocculant for the suspension with4g/L kaolin was0.75mL. Ca2+and Al3+of high cations could have asignificant role in promoting the flocculation, especially Ca2+as a coagulant had a stableand clear function for the flocculation. The optimum dosing quantity of1%CaCl2was1mL. There were wide ranges of pH and temperature for the flocculation. Theflocculation rate was above80%in pH8-10and that was stable at the temperaturerange of0-70℃.