Screening Of The Strains Producing Microbial Flocculant

Microbial flocculant is a polymer with flocculating activity produced by microorganisms during their growth. Its chemical contents include polysaccharide, protein, glycoprotein and nucleic acid. Its molecular weight is about tens of thousands. Comparing with other flocculants, microbial flocculant is safe, high-efficiency and readily biodegradeable. With the enhancement of people's environmental consciousness, the studies of microbial flocculant had drawn more and more attentions. Many microbial with producting flocculant had been found and their chemical composition, structure and mechanism had been studied, however, good-yielding bacterium and new production technique were shortage. So finding high-efficiency microbial flocculant and reducing the cost of production became the key factor giving impetus to industrialized operation of microbial flocculant. In this paper, we carried out a series of experiments including screening, identifying, optimizing fermentation process and studying flocculating characteristics.In accordance with the flocculating activity of fermentation liquors to Kaolin clay suspension, there were 53 strains isolated from activated sludge. After shaking flask fermentation and testing ferment production , the strain 2-21 was acquired to be future studied, which flocculating efficiency achieved 71.8%. With the following identifications of colony morphology, physiological and biochemical characteristics and 16S rDNA gene sequence, the strain 2-21 was preliminarily identified as Stenotrophomonas sp., which had not been reported among flocculant-production strains.Through single factor and orthogonal experiments, the conditions of fermentation which benefited the strain to produce flocculant were optimizied. The optimum culture conditions were as follows: 20.0g/L glucose, 2.0g/L(NH4)2SO4, 9.0g/L K2HPO4·3H2O, 4.0g/L KH2PO4·3H2O, 0.1g/L NaCl, 0.3g/L MgSO4·7H2O, initial pH 7.5～8.0, temperature 30℃, inoculation amount 7%(V/V), rotation speed of rocking bed 180r/min, volume in shake flask 35mL/250mL and culture time 24h. Under the optimum condition, flocculating efficiency achieved 94.3%, enhanced by 53% than the value to the initial.With kaolin clay suspension as test sample, the flocculating characteris- tics of strain 2-21 production was studied. When pH was 4.0 to 7.0, flocculant dosage was 3%(volume fraction), coagulant aid CaCl2 dosage was 0.5g/100mL, the microbial flocculant had an optimal flocculation of Kaolin clay suspension. Result showed that the flocculant of strain 2-21 had effect in the treatment of apple juice, orange juice, fermentation broth of gibberellin and good effect in the treatment of dyeing wastewater, activated carbon and kaolin clay suspension. The strain had a good research value and prospect of utilization.