The Synthesis Of Bioflocculant γ-PGA And Study On Its Flocculating Performance And Application

Bioflocculant is a kind of biodegradable macromolecular flocculant secreted from microorganisms. It has been reported that leaf mold, bacteria, microzyme etc. can produce flocculants with various properties. A large number of bioflocculants synthesized by microorganisms were purified and reported to belong to functional proteins (Nocardia amarae YK1, Aspergillus sojae AJ7002), functional polysaccharides (Alcaligenes cupidus KT201, Alcaligenes latus B-16), or glycoprotein (Rhodococcus erythropolis S-1). Compared with traditional inorganic and organic flocculants, it has such advantages: no toxicity, no second pollution, and many sorts of microorganism can produce bioflocculant that it's easy to achieve industrialization through biology engineering and be widely used.A bioflocculant produced by Bacillus subtilis NX-2 showing high flocculant activity, and its synthesis condition, composition, flocculation properties, flocculating mechanism, and application was thoroughly investigated:1. The experiment of distribution of flocculating activity showed that the bioflocculant mostly existed extracellular in the culture broth; the experiment of the nutrition and culture conditions of bioflocculant synthesis showed that the optimum carbon source is glucose, and the optimum nutrition source is yeast extract, fructose and inorganic nutrition source can also be used considering of lowing the cost, the glutamic acid is indispensable to the flocculant produce; it was conformed through the orthogonal experiment that the optimum culture medium comprised glucose 3%,yeast extract 0.8%,K2HPO4·3H2O 0.2%,MgSO4 0.025%,glutamic acid 1%; the optimum volume of medium is 80ml in 500ml shaking flask and the optimum original pH of medium is 7.5.2. 20g/L bioflocculant was got through centrifuging, ethanol precipitation, dialysis, and freeze-dry and identified as poly(γ-glutamic acid) through 1H-NMR and 13C-NMR, belonging to poly amide acid with nylon-4 frame.3. In kaolin suspension, the flocculating activity got highest at the γ-PGA concentration of 20mg/L and was steady to pH with the concentration above 10mg/L. The flocculating activity was synergistically simulated by the addition of cations, Ca2+ was the optimum cation that remarkably promoted the flocculating activity and could lower the cost by dropping the dosage of γ-PGA, while the excessive Ca2+ can restrain the flocculating activity.4. γ-PGA was tested to treat the electric plating waste water that it could remarkably remove the heavy metal ions, such as Cr+3, Ni+2 and Cu+2.