Production And Flocculation Properties Of γ-PGA By Bacillus Pumilus C2

y-poly glutamic acid (y-PGA) is an extracellular polymer of amino acids produced by microorganisms, consisting of D- and L-glutamic acid monomers connected by amide linkages between α-amino and γ-carboxyl groups. γ-PGA has a lot of high activity side-chain free carboxyl with a large number of negative charges since each a-C of repeat unit in the molecular chain has a free carboxyl. It has the application prospect in flocculating purification of waste water by γ-PGA as microbial flocculant. When applied in extreme environments such as high NaCl concentration, high or low temperature, extreme pH, high heavy metals concentration, the flocculating activity of microbial flocculant can be significantly reduced because of the change of spatial conformation. The y-PGAmolecular structure stabilizes, not being destroyed even in extreme condition and suitable for flocculating treatment of sewage with high concent ratio.In this paper, the strain C2 with high flocculating activity to sewage in extreme condition was screened from the sediment of a saltern pool in Dalian and the strain C2 was named Bacillus pumilus C2 after identified by morphological characteristics, physiology biochemistry experiment and 16S rDNA. The structure of flocculation active substance was identified by thin-layer chromatography (TLC),’H-Nuclear magnetic resonance (1H-NMR) and fourier transform infrared spectroscopy (FTIR) and was identified as y-PGA. The optimal fermentation conditions of B. pumilus C2 were 25 g/L sucrose,25 g/L sodium glutamate,10 g/L sodium citrate,10 g/L (NH4)SO4,5 g/L NaCl with the initial pH of 7.0. They-PGA production fermentation in 2.5 L fermentator was proceeded. The kinetics models of cell growth and product formation were established. The established kinetics model of cell growth was dX/dt=0.45×(1-X/221.)X, that of product formation was dP/dt=1.5×dX/dt+0.07X. The study of flocculation property of y-PGA showed that The highest of flocculation activity was obtained when the γ-PGA concentration was 4% and pH was 9.5. γ-PGA has high activity in the conditions of high temperature, and the effect of NaCl concentration is insignificant. After the purification of flue gas desulfurization waste water by y-PGA, the solid content, turbidity and chromaticity were reduced 94.5%,78.1% and 25%, respectively.