Studies On The Preparation And Properties Of Extracellular Biopolymeric Flocculant

Based on introduction of the flocculants and their development and application in treatment of wastewater, we have studied about preparation and activity of extracellular biopolymer flocculant (EBF ) in this thesis.Firstly, the extracellular biopolymer flocculants (EBF) were produced by microorganisms, which were isolated from starch wastewater, activated sludge and soil samples, respectively. After being rescreened, 1 stain of bacteria with strong flocculating activity was obtained. According to physiological and morphological characteristics the bacterium was classified into the genus Rarobacter sp. The optimum conditions for production of BF SVI-SD are as following: The water-soluble starch (2%), peptone (2%), KH2PO4 (0.2%), K2HPO4 (0.2%), NaCl (0.05%), (NH4)2SO4 (0.05%), MgSO4-7H2O (0.05%), pH (6.0-8.0), 30~34C, 120 r/min, being cultivated for 50-60 hours in flakes. The strain BF SVI-SD was cultured under this condition produced a strong-activity flocculant. Its relative flocculating efficiency to 4% of kaolin suspension could be over 97%.Secondly, the BF SVI-SD was characterized by UV spectra, IR spectra, SEM, and some chemical, biologic methods. It was identified as polysaccharide consisting of weak acid and neutral sugars. It was nontoxic to human beings and animals. Therefore, it is a kind of safe and environment friendly agent of water treatment.Thirdly, the BF SVI-SD has excellent flocculating properties. It could be used in system which pH value ranges from 4.0 to 9.0, and add only a little dosage. The BF SVI-SD causes aggregation of particles by bridging and charge neutralization. The reason is that the polysaccharide contains abundant hydroxyl groups. It is easy to form hydrogen bond. The effectiveness of the bridging mechanism also depends on the molecular weight of the flocculant and linearly extended biopolymer chains. These chains adsorb other particles leading to the formation of three-dimensional floes.The BF SVI-SD has also been employed for treatment of several kinds of wastewater. It has excellent flocculating properties to treating domestic sewage. The removal efficiencies of COD and turbidity were 63.4% and 97.6%, respectively. Therefore, it has potential application in the fields of treating domestic sewage and foodstuff wastewater.