| Flocculation effect is used to separate starch of the mixed emulsion, protein, and the main methods of extracting and separating organics in sewage disposal. Microbial flocculants is a kind of microbe which has flocculability or microbial secretion. Compared with traditional chemical flocculants, for example aluminums, molysite, polyacrylamide, it has advantages of efficiency, non-toxic, non-secondary pollution. It is the ideal alternative product of chemical flocculants.Steeping liquor was a kind of microbial flocculants. It was invented in long-term production practice. Steeping liquor was a little sour and yellowish-white liquid. It was made of sweet potato (or green beans) starch with milk natural fermentation. Starch particles would rapidly converge greatens, form a mass, and accelerate the separation of starch and other impurities when put steeping liquor in the sweet potato (or green beans) starch. Steeping liquor was good for preventing browning in sweet potato slurry, potato slurry, and mung bean slurry.This subject mainly aimed at Lactobacillus paracasei (short for strain L1) extracted from steeping liquor. It was necessity and advantages in efficiently flocculating sweet potato starch. This subject did research on flocculability and mechanism of action and proclaimed the reason for flocculating starch efficiently. This subject provided theoretical basis for changing the traditional production technology and improving the quality and yield of sweet potato starch.1. Studied flocculation active influence of strain L1 in different carbon sources, nitrogen sources, initial pH value, culture temperature and ventilation, culture period and so on. Glucose, sucrose, maltose and lactose were excellent carbon sources and the optimal nitrogen source was yeast extract or beef extract. Designed orthogonal test based on the single factor experiment and determined optimizing cultivating condition of combining flocculants:its optimal conditions for flocculating activity were 7 for initial pH,25℃for initial temperature and 72h for training time.2. Knew the flocculation rate of fermentation liquor, supernatant fluid and sediment is 72.30%,23.41%,72.37% respectively, based on the detection of flocculation rate. The flocculation rate of sediment was high, and the flocculation effect of supernatant is poor. It showed that flocculation active substances mainly exist in bacteria, rather than metabolite of bacteria cells. Through thermal stability and enzyme stability measurement, it showed that the flocculation active substances were mainly from bacteria surface proteins, instead of sugar. 3. Zeta (ξ) electric potential determine result showed that:in the flocculation process, Zeta (ξ) electric potential varied on pH. When pH value was 4.0, Zeta (ξ) electric potential was lowest (absolute value).Right now, starch particles were unstable and flocculation effect was good. As pH value increased, Zeta potential (absolute value) increased gradually. When pH value was 5.0～6.0, system Zeta (ξ) electric potential (absolute value) was high, the corresponding dispersion stability was good and flocculation effect was poor. Added Na+ to the system causing electrical neutralize effect and compression electric double layer. It made mycelium adsorb starch particles increased, thus it played coagulant function.4. By fermentation liquor treated, particle size distribution of sweet potato starch solution changed obviously. Sweet potato starch particles were smaller by fermentation liquor treated. It explained that the sweet potato starch particles were adsorbed by mycelium, and particle size was smaller, and particle density was increased. Meanwhile, starch particles generated "bridge" phenomenon and form a larger flocculation sinking quickly by gravity in slurry. The results intuitively showed mechanism of fermentation liquor was adsorption bridging mechanism between bacteria and starch particles.5. The combination key testing between Bacteria and starch particles showed that when adding EDTA and HCl, flocculation decomposed largely. When adding carbamide, flocculation had no obviously deflocculating phenomenon. Thus, it was known that flocculation was sensitive to EDTA and HCl while not sensitive to carbamide. Because EDTA and HCl could combine with starch particles, thereby destroyed ionic bond and flocculation had obviously deflocculating phenomenon. But hydrogen bond could form between carbamide and starch particles. So we could speculate that the combination key of flocculants and sweet potato starch was ionic bond. |
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