Screening Isolates And Optimizing Fermentation Conditions And Application Of A High Efficient Bioflocculant

Two flocculants-producing strains of high flocculating activity were screened from saline lake of Dabancheng in Xinjiang. Experiments studied the culture conditions and influence of medium component having effects on bacteria which take XN-2 as the research object. At the same time, it studied the stain’s flocculating properties for producing of microbial flocculants and its application. The main work is as follows:(I) Two flocculants-producing strains were screened from saline lake of Dabancheng in Xinjiang by the method of serial dilutions and plate streaking. The strain XN-2 which has high flocculating activity was identified as Paenibacillus. Flocculating rates of the XN-2 strain’s fermentation broth is 90% in Kaolin simulated suspending liquid, and the XN-1’s flocculating rates is 90%.(II) The thesis research the optimum combination of carbon source, nitrogen source, pH, culture temperature, fermentation time, inoculation amout based on the stain. The optimal medium:12g glucose,2g yeast extract,1g urea content,pH 7,9% inoculation amout, 31 ℃culture temperature,28 h fermentation time,210 rpm shaker speed. Results show that the optimal medium could promote strain’s capacity of flocculant and cost is lower than the original fermentation medium.(III) Experiments measure the growth curve of bacteria and flocculation rate XN-2.The revelation is that XN-2 produced flocculants mainly in logarithmic growth phase and steady growth and flocculant accumulated mostly in stable phase and decomposed in the decline phase partially. XN-2 flocculants active ingredient is mainly present in the supernatant and it has a capsular polysaccharide, at the same time bacterial cells affect flocculation. The bioflocculant is metabolites of microbial cells so that it was an extracellular flocculant. The purification of 50 mL fermentation of XN-2 strain broth through culture with 48 hours eventually extracted sticky 0.23 g slightly pink solid. Yield of bioflocculant is about 4.6g / L by calculated. It dissolved the bioflocculant according to the concentration of 0.46 g / L in distilled water to the refrigerator for using in the follow-up experiment. Consist of fermentation broth mostly is polysaccharide which Accounted for 64.7% and protein accounted for 1.26% by testing. The flocculant exhibited excellent resistance at high temperature(100 ℃),acidic(pH 4) and alkaline(pH 10),and its activity remained stable.The growth curve, the flocculation rate, glucose consumption curves, polysaccharide content changes during the fermentation exhibited the optimal culture time was 28 h while derived XN-2 glucose utilization substrate consumption law, rule of production for fermentation ingredient of polysaccharide. Polysaccharide corresponded growth of bacteria breeding after experiencing a delay period. As the bacteria enter the decline phase, polysaccharides are decomposed for utilization of bacterial, so fermentation time it should be strictly controlled within 30 h. The pH needed adjusting to ensure an appropriate flocculant production by measuring pH changes during the fermentation and controlling the pH at about 7.(IV) Research results of the practical application for bioflocculant:①For cotton pulp wastewater, strain XN-2 and PAC are better for flocculation and COD removal rate effects. PAC dosage is 8mL, bioflocculant dosage is 4mL with the highest removal efficiency. And the best conditions for flocculation: pH 9, waste water temperature 20 ℃, 2%CaCl23.5mL.Then it measured bioflocculant cotton pulp wastewater flocculation rate is 65%,COD removal efficiency is 54%,while the PAC flocculation rate is 80.2% to cotton pulp wastewater, COD removal rate was 70.8%. Bioflocculant is better than PAC for dosage. PAC is better than the microbial flocculant for wastewater treatment.②For the oily wastewater, Strain XN-2 and PAC are better flocculant for oil removal and COD removal effect. The dosage of PAC and bioflocculant is 8mL and 4mL for the highest removal, At the same time, pH 9, waste water temperature 20 ℃, 2% CaCl2 3.5mL. Then it measured bioflocculant oil wastewater oil removal rate is 68.5%,COD removal efficiency is 44%,while the PAC flocculation rate is 68.5% to oil wastewater, COD removal rate was 58.8%. Microbial flocculant is better than PAC for every aspect.