| Potato starch wastewater which belongs to high concentration organic wastewater, richin nutrition, can be absorbed by microorganism, has the potential for microbial fermentationmedium. This study attempts to take advantage of bioconversion effect of microbial, achievethe goal of potato starch wastewater recycling use. This experiment selects activated sludgefrom sewage treatment plant and starch processing wastewater lagoons for strains separatingmaterials. Screening strains that could ferment potato starch wastewater and producingflocculants. Optimizing the nutritional composition and fermentation conditions that the strainfermented potato starch wastewater to produce bioflocculant. The flocculation characteristics,nature and flocculation mechanism of MBF-CA have been studied also. The main conclusionsobtained were as follows:1. In the trial, according to the ability of strains fermenting potato starch wastewater andproducing flocculants, one high yield strain was obtained, named as F5. The flocculation rateof fermentation broth against Kaolin clay suspension was82.6%. F5was identified asCandida anglica by the study of colony morphology observation, microstructure observation,physiological and biochemical characteristics test and the26S rDNA sequence analysis. Thestrains of Candida anglica have been collected by the Chinese general microbiologymicrobial preservation management committee center, the strains preserved numbers isCGMCC No.7032.2. The flocculation rate of fermentation broth against Kaolin clay suspension asevaluation index. The results showed that under the conditions of pH value5.6, inoculum size8%(volume fraction),150r/min and28℃f or48h, the best nutritional compositions were:1mL/100mL glycerin as adding carbon sources,0.05g/100mL(NH4)2SO4as nitrogen source,0.1g/100mL MgCl2and0.1g/100mL KH2PO4. The test showed that Candida anglica couldgrow well in non-sterilization potato starch wastewater as basic substrate, and couldaccumulate flocculation active substance within48h effectively.1.36g flocculant can beextracted from1L fermentation liquor.3. Based on the research of the flocculation characteristics for MBF-CA, figured out thatthe best coagulant aid is CaCl2. In100ml of0.5%(W/V) of kaolin suspension, the optimaldosing quantity of coagulant aid is0.04g, the best flocculant dosing quantity is0.04g. Theoptimum mixing time is3min under180r/min. When the system responses6min,fermentation broth against Kaolin clay suspension basic settlement completely within6min.Within20℃to40℃, the flocculanthas high flocculating activity. In addition, the flocculant has a strong thermal stability, pH stability and storage stability.4. The result showed that MBF-CA is composed of polysaccharide and protein secretedby Candida anglica to the outside of the cell. The mass fraction of polysaccharide and proteinin MBF-CA is98.75%and0.52%respectively. The major flocculating active ingredient ofMBF-CA is polysaccharide, protein at trace levels is not present flocculating active. Thechemical bond between MBF-CA with kaolin particles is ionic bond. MBF-CA in water isnegatively charged. It can compress kaolin particles electric double layer. Flocculantmolecular containing sugar characteristic peak, and contains a lot of-OH,-COOH. Thosechemical groups are advantageous to the solubility for MBF-CA in water and make molecularat full stretch, increase the effective length of molecular, it is good for adsorption and bridgingrole.5. Based on the analysis of the results, the flocculating mechanism of MBF-CA can bespeculated as follows: MBF-CA could adsorb multiple colloid particles at the same time byionic bonding forming a three-dimensional network structure, form a bridging role betweenthe particles, under the action of gravity, the flocculation settling down. Those particles notbeen adsorbed will be settled because the role of enmeshment from flocculation, too. The keyflocculation mechanism is adsorption bridging role, enmeshment role could speed up thesystem response. |
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