| Microbial flocculants, a new generation of green water treatment reagent, is becoming a hotspot in the research of environmental engineering and biological engineering.This study screened a bacteria Pannonibacter phragmitetus MB7from printing and dyeing waste water and activated sludge which could produce effective microorganism flocculant. The flocculant was extracted and purified and its chemical composition and properties were analyzed. It also optimized the culture medium of p. phragmitetus MB7strains fermentation and explored the applications of microbial flocculant. The main contents included the following aspects:(1) Screening and identification of bacteria producing efficient microbial flocculantAfter the preliminary screening with Coomassie brilliant blue and Congo red and the second screening experiment with kaolin,37strains with obvious flocculation were gotten. The strain MB7was selected as the follow-up research. Through physiological and biochemical experiments and comparison withl6S rRNA sequence, the MB7strain was identified as Pannonibacter phragmitetus.(2) Extraction, purification and characterization of microbial flocculant produced by P. phragmitetus MB7The high purified microbial flocculants produced by P. phragmitetus MB7after separation and purification was harvested. Ninhydrin reaction and Molish reaction showed that the flocculant was mostly glycoprotein. Furthermore, phenol sulfuric acid method, Bradford method, carbazole reaction, anthrone reaction and Elson-Morgan reaction were used respectively to determine the content of total sugar (95.18%), total protein (4.11%), hyaluronic acid (26.09%), neutral sugar (61.42%) and amino sugars (8.4%), respectively. The weight of flocculant molecular weight of microbial flocculant was1.13×106which was measured by gel permeation chromatography (GPC). Finally Laser Roman spectrum and Fourier infrared spectrum (FTIR) were utilized to explore the reactive group and found that B7flocculant had a large number of reactive groups.(3) Fermentation medium optimization of p. phragmitetus MB7After experiment with different kinds of carbon and nitrogen sources, glucose, peptone and ammonium sulfate was chose as carbon and mixed nitrogen sources for fermentation. The orthogonal test determined the initial optimized concentration of carbon and nitrogen sources were20g/L glucose,1.0g/L ammonium sulfate and2.5g/L peptone.Plackett-Burman experiment found that glucose, ammonium sulfate and initial pH had significant influence on flocculating activity and then the steepest ascent experiment determined the center points of central composite design (CCD) which was28g/L glucose,1.1g/L ammonium sulfate and initial pH8.75. With the help of SAS9.1, CCD experiment was designed and analyzed. Finally, the optimum fermentation medium (g/L) was consisted of28.0glucose,2.5peptone,1.184(NH4)2SO4,0.5KCl,1.0, K2SO40.2, K2HPO4,0.5MgSO4·7H2O,0.01FeSO4, initial pH=8.448.(4) Application research of microbial flocculant B7Microbial flocculant combined and dicyandiamide formaldehyde was used to the treatment of reactive dye printing and dyeing wastewater. The results showed that the decoloring effect of combined treatment process was above90%. The microbial flocculant was also applied to the pretreatment of fermented liquid of E. coil BL21(DE3) and B. subtilis. The flocculating rates could be above85%. Compared with chitosan, microorganism flocculant was more ideal not only in the flocculant dosage but also in treatment effect.To sum up, the flocculant produced by P. phragmitetus MB7strains was mainly glycoprotein with moderate molecular weight and large amount of activity groups and had high flocculating activity. After optimization of fermentation medium, the producing cost was effectively decreased and was more conducive to expand production. The flocculant also exhibited good properties in printing and dyeing waste water treatment and fermentation liquor pretreatment and indicated a certain value for industrial application. |
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