| Microbial oil is glycerol ester synthesized by microorganism, and it has many important applications in the field of light and food industry, healthcare, energy and chemical industry, and thus it is a hot topic in biochemical engineering. The key issue of its industrialization is finding suitable low-cost substrate to reduce production cost. Because organic acids cannot be removed during distillation process, butanol fermentation wastewater(fermentation broth after distillation) contains some organic acids,and its COD can be usually certain ten thousands mg/L. Oleaginous yeast used for butanol wastewater treatment meamwhile yeast biomass containing many microbial oil and polysaccharidecould been produced, which could both solve the issue of wastewater and obtain certain economic benefits. Nowadays, few researchesfocus the systematical study on substrate metabolism and products accumulation of lipid fermentation on butanol fermentation wastewater, thus the theoretical basis for the optimization and control of this bioconversion technology lacked.To manifest the law of substrate metabolism and products accumulation of lipid fermentation on butanol fermentation wastewater, and elucidate its mechanism, four oleaginous yeasts kept in Lab of Energy and Chemical Engineering of GIEC(Trichosporon cutaneum, Cryptococcus albidus, Trichosporon dermatis, and Trichosporon coremiiforme) were chosen as research objectsin this study. Firstly, the biodegradation effect of yeast with different fermentation mode on butanol fermentation wastewater was studied and the different yeast fermentation mode on actual butanol fermentation wastewater was built. Base on this, the basic issue in the efficient treatment of butanol fermentation wastewater by oleaginous yeast fermentation mode was learned by lump kinetics and other scientific methods. The basic issues included the degradation laws of various organic compounds and the evolution laws of cell growth and products accumulation in the bioconversion process of lipid fermentation. Both mechanisms of substrate metabolism and products accumulation were elucidated then. Finally, the advantages of lump kinetics were shown by comparison with traditionalkinetics in fermentation engineering.Among these four oleaginous yeasts, the treatment of T. cutaneum and T. dermatis gave higher COD removal rate and greater yeast biomass; more lipid content and lipid yield could be obtained for the fermentation of T. coremiiformebut thedegree of unsaturation in its lipid composition was much lower than that of T. dermatis, T. cutaneum and C. albidus.C. albidusgave the lowest biomass and COD degradation for butanol fermentation wastewater treatment.The utilization of acetic acid by these four oleaginous yeasts is low in the media withacetic acid as single carbon source. In the media containing sugars and acetic acid with high COD, T. cutaneum and T. dermatis showed much better effect on the treatment of butanol fermentation wastewater than that of T. coremiiforme and C. albidus. While the effect of sugars and organic acids utilization by T. coremiiforme and C. albidus decreased significantly as the COD increasing. At the same time for COD degradation, could accumulate extracellular polysaccharide products(took some parts of COD). The lipid composition of four oleaginous yeasts was related to the carbon source types in media. Besides microbial oil, these four oleaginous yeasts could also accumulate much cellular polysaccharide and some of protein and ash.For the biomass and lipid content after 5 days’ fermentation, the mode of mix-fermentation showed no superiority, possibly because the early entering into “lipid turnover”physiological phenomenon in mix-fermentation mode. Although the mode of T. dermatis + T. cutaneum showed little improvement of lipid yield, the ratio of oleic acid(C18:1) and linoleic acid(C18:2) could be 29.46% and 39.88%(index of unsaturated fatty acid improved), respectively and this product had more greater potential for industrialization than other single or mix-fermentation. Both synergistic effect of metabolism and competition effect of growth existed in the oleaginous yeasts mix-fermentation mode. Fed-batch mix-fermentation mode had more COD removal rate than that of batch mix-fermentation mode but the more COD removal did not turn into more yeast biomass. In butanol fermentation wastewater, the cell growth rate of different single fermentation or mix-fermentation modes and the “lipid turnover” physiological phenomenon happened in all fermentation modes. Also in butanol fermentation wastewater, the evolution law of polysaccharide was complex in different single or mix-fermentation modes and it is possible that the conversion from lipid to polysaccharide or other products exists. Overall, the evolution of polysaccharide was much more stable in mix-fermentation mode than that of single fermentation mode.In low temperature(23 oC), moderate temperature(28 oC), and high temperature(33 oC), the study on the substrates degradation and products in T. cutaneum and T. dermatis single fermentation or mix-fermentation found that moderate temperature was beneficial for the yeast growth and COD degradation at the early stage of fermentation but showed little effect on the final yeast biomass and COD degradation, and too fast growth rate at moderate temperature affected the lipid accumulation of yeast that the intracellular metabolism preferred to polysaccharide synthesis. By lump method, the whole metabolism network of oleaginous yeasts from substrate to product was divided into five lumps: COD, lipid, polysaccharide, other extracellular products, other intracellular products. The nine rate constants(k1-k9) in kinetics network varied with different single or mix-fermentation modes, and using lump method and lump kinetics could explain the differences of bioconversion in different fermentation modes efficiently. For most fermentation modes, the value of k3, k4, and k9 was all zero, which shown that COD could not turn into polysaccharide or other extracellular products directly and in the process of “lipid turnover”, lipid could not turn into extracellular products directly. Routine fermentation kinetics had well fitting effect on the cell growth, lipid synthesis, and sugar metabolism in typical sugar based medium but it could not reflect the metabolism laws and mechanism of complex material conversion in butanol fermentation wastewater. Lump kinetics break the limitation of routine fermentation kinetics by some fixed empirical equations. It divides the materials in network to various lumps by different properties from the metabolic networks ofhypothesis and by the kinetics analysis, the laws and mechanism of different materials conversion could be obtained, and the complex issues became simple then.By this study, one efficient biological treatment of butanol fermentation wastewater and lipid fermentation substrate could also be obtained andthis study could make the further communication of light industry and chemical engineering and elucidate the basic scientific issues in lipid mixed fermentation in butanol fermentation wastewater. At the same time, the technology built in this work could be the important supplement for today biomass energy production andtheoretical guidance was provided totreatment other alcohol wastewater, organic acid fermentation wastewater and similar such as sugar refinery wastewater, pulping wastewater which contains high concentration organic wastewater. |
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