Screening And Identifying Of A Kind Of Flocculants-producing Bacteria And Studying On Its Flocculation Properties

Microbial flocculants were mainly produced by microorganisms under certain conditions of cultivation, including polysaccharides, proteins and nucleic acid polymers with flocculation activity. By charge neutralization, adsorption, bridging effect and immesh, the flocculants cause the colloid aggregation. Since microbial flocculants are biodegradable, nontoxic, and no secondary pollution, they were deemed as highly promising water treatment chemicals and could be widely used in wastewater treatment, pharmaceutical, food-production and other fields.245 strains were isolated from sludge samples and a new kind of high flocculants-producing bacteria JX18 with flocculation rate of 84% was obtained. It was identified as a Pseudomonas fluorescens based on its morphological, physiological characteristics and the partial sequences of its 16S rRNA.The bacteria entered the logarithmic phase after culturing12 h, reached stationary phase after culturing 40 h, and had a maximum ?occulating activity after culturing 48 h. The further investigation indicated that the optimum flocculants-producing conditions obtained were initial pH 7.0, temperature 30℃, rotation speed 160 r/min. The optimum compent proportion of medium of P. fluorescens JX18 were glucose 7g, peptone 1.3g, KH₂PO₄ 2g, K2HPO₄ 5g, NaCl 0.3g, MgSO₄?7H₂O 0.1g, FeSO₄?7H₂O 0.02g, water 1L according to the single factor experiments and the orthogonal experiment. Optimum cultivation conditions, the flocculation efficiency toward Kaolin clay suspension reached 91.19%.Biomasses, content of flocculant, concentration of glucose in fermentation broth during different time were detected in 5L fermentator. Based on the Logistic equation and Luedeking-Piret equation, the fermentation dynamics models on growth of cell, consumpution of glucose and the content of flocculant were founded. The model could well reflect the changing pattern in growth of cell, the consumpution of glucose and flocculants yield.The further study showed that the materials with flocculation activity were mainly distributed in the fermentation broth. Measurements of chemical and physical analysis revealed that the flocculant is a kind of polysaccharidesthe, accounting for 68% of the crude product. Scanning electron microscopy (SEM) image of the solid-state crude product showed that the flocculant has a linear morphology. It was consisted of glucose, galactose and mannose with the thin layer chromatography (TLC) and high-performance liquid chromatography (HPLC) analysis. As Kaolin suspension modeling waste water, the results of the flocculate properties showed that the flocculant has high heated stability and wide pH serviceable range. At 20¹00℃, the flocculating activity was almost not descended, and the flocculating activity was above 85% at pH 3.0¹0.0. Toward 4g/L Kaolin suspension, the optimum concentration of bioflocculant was 2.5 mg/L, and CaCl₂ was proved to be the best coagulant aid in this flocculating system, in which the optimum concentration was 0.5 g/L.By flocculate property, electron microscopy images and infrared spectra analysis, the initial description of flocculation process are that: kaolin itself is small particulate matter, more evenly dispersed in solution; CaCl₂ is a coagulant aid, the major role of Ca2+ in flocculation is neutralizing negative charge and reducing repulsion of electric charge. Adding the flocculant, bridge and adsorption effect occured. The bioflocculant has a long-linear morphology, and connected the molecule of Kaolin clay together.