Preparation Of Bacillus Mucilaginosus Bioflocculant And Its Application In Heavy Metal Wastewater

Microbial flocculant(MBF) that originated from microorganisms is a kind of macromolecular substance, such as glycoproteins, proteins, polysaccharides, lipids,glycolipids and so on. Compared with traditional flocculants, MBF has attracted increased attention as a promising substitute for chemical flocculants because of the characteristics of nontoxic, biodegradable and free of secondary pollution risks. They may have a promising application in a variety of industrial processes such as municipal water treatment process,wastewater treatment, downstream processing of food and fermentation industry, etc.Bacillus mucilaginous is a kind of microorganism that can fix nitrogen biologically and produce bioflucculant efficiently in a nitrogen-free environment. This characteristic greatly reduces the cost of fermentation and may have a potential application for actual waste water treatment.In this paper, ninety different strains were isolated from the sample of soil and mixed activated sludge by a selective nitrogen-free medium. Their flocculating activities were tested by the Kaolin suspension method. Among these strains, a bioflocculant-producing bacterium with a flocculating rate exceeding 90%, named MY6-2 was screened out and identified as Bacillus mucilaginosus based on 16 S rDNA sequence, biochemical and morphological characteristics.Single factor experiment and RSM was employed to optimize the culture conditions to maximize the flocculating activity and production of MY6-2. The optimal medium consisted of 0.5%, nitrogen-free; the optimal culture conditions for MY6-2 were 100 mL of broth,initial pH 8, and inoculum size 10%. Consequently, the maximum flocculating rate of 90%was achieved under these culture conditions by adding 0.5 mL fermentation supernatant to100 mL of Kaolin suspension.Through the flocculating substance extracting and its composition analyzing, it is found that the flocculating substance are mainly distributed in the fermented liquid.Using alcohol sinking method, we can get white powdered solid after lyophilization. Through physical,chemical and other methods to analyze that the substance mainly is polysaccharide,and it has a good thermal stability.The optimal flocculation conditions of MBF MY6-2 were as follows: pH > 7.0,flocculant dosage was 0.1mg/100 ml Kaolin suspension, metal cation dosage was 1% of Ca2+3 m L. The flocculation activity can reach more than 90% under this condition. Application results showed that MBF MY6-2 had better flocculation activity in several common suspensions, such as kieselguhr, bentonite, soil, active carbon and starch, compared with polyacrylamide and inorganic salt.The adsorption of Fe3+ from aqueous solution by flucculant MY6-2 was studied by single factors. The result indicated that MY6-2 was an effective adsorbent for Fe3+between the concentration of 60 mg/L to 800 mg/L. The flocculating rate of MY6-2 achieved more than90% in the conditions as follows: pH5.0, temperature 30℃, flocculant dosage 6 mL.