生物质气化洗焦废水的微生物降解研究以及生物质稀酸水解液的乙醇发酵研究

【作者】 田沈；

【导师】 杨秀山；

【作者基本信息】 首都师范大学 ， 遗传学， 2007， 博士

【摘要】 目前国内外对生物质气化洸焦废水的微生物处理鲜有报道，尚无成熟的工程治理技术和完善的处理工艺。利用理化和生物处理相结合的方法，可提高生物质气化洗焦废水COD的降解效率。该研究首先进行了生物质气化洗焦废水和焦油可否被微生物降解的尝试。结果证明，微生物具有降解生物质气化洗焦废水和焦油COD的能力，但降解速度较慢，一般需4-6d，且底物浓度很低。在证明微生物可降解生物质气化洗焦废水和焦油COD后，为了提高底物浓度和降解速度，对降解生物质气化洗焦废水的微生物进行筛选，筛选实验证明，单一菌种对生物质气化洗焦废水COD的降解速度和降解率低于混合菌种。最后，为了进一步提高处理效率，选用实验室保藏的两株菌，Pseudomonas sp1和Pseudomonas sp2为接种物对生物质气化洗焦废水进行处理，了解该两种菌降解该废水COD的特性。实验结果证明，两株菌的混合使用可提高处理效率，并用包埋法、生物膜法和颗粒活性炭法对该两株菌等量混合接种进行细胞固定化，研究固定化细胞处理生物质气化洗焦废水的特性。结果证明，颗粒活性炭固定化细胞可得到高的COD去除率和短的水力停留时间。同时对芳香族化合物也有较高的去除效果。该文也在实验室条件下，对SBR系统微生物去除生物质气化洗焦废水NH₃-N特性进行研究。在以木质纤维素为原料生产乙醇的研究开发领域中，稀酸水解被认为是最容易实现商业化生产的工艺，国内外在该领域进行了大量和深入的研究，但到目前为止，国内外在用稀酸水解木质纤维素生产燃料乙醇方面还存在着一些问题未能解决，主要集中在两个方面：一是木质纤维素水解得到高浓度的糖和较低浓度发酵抑制剂的水解糖液，此属于化工问题，在本研究中不进行探讨；二是水解糖液的高效乙醇发酵的微生物学问题。在微生物学问题中，主要是高效利用葡萄糖和木糖产乙醇的菌种，特别是高效代谢木糖成乙醇的菌种显得特别重要，因木糖是半纤维素的主要水解产物，而半纤维素是木质纤维素的主要组成成分之一，因此，在以木质纤维素为原料的乙醇商业化生产中，充分利用木糖产乙醇非常重要，木糖的充分利用，可降低乙醇生产成本25％。在微生物学问题中，另一主要问题是要获得耐/分解发酵抑制剂的微生物菌种，因为在木质纤维素稀酸水解过程中，除产生单糖如葡萄糖、木糖、半乳糖、阿拉伯糖、甘露糖外，还同时产生糠醛、羟甲基糠醛、乙酸和酚类化合物等毒性物质，统称为发酵抑制剂，它们严重的影响着微生物的生长和发酵。因此，获得耐/分解发酵抑制剂的乙醇发酵菌种是目前国内外研究的热点问题。在以木质纤维素为原料生产燃料乙醇过程中，上述两个微生物学问题是提高乙醇发酵速率和降低成本的瓶颈。本实验首先通过乙醇耐受实验、木糖发酵实验以及水解液发酵实验对21株菌种进行了筛选。从中筛选到酿酒酵母、嗜鞣管囊酵母和重组大肠杆菌作为供试菌种。将酿酒酵母分别与嗜鞣管囊酵母和重组大肠杆菌组合，得到了两组混合菌种。经过驯化，用驯化后的混合菌种进行了木质纤维素稀酸水解液的乙醇发酵。考察的发酵形式包括批式发酵、补料批式发酵和间隔补料批式发酵，均取得了很好的结果。并用发酵罐进行了补料批式发酵，探讨了该种发酵形式大规模应用的可能性。另外，本实验对筛选出的耐毒酵母菌株进行了水解液的批式发酵实验。通过这些实验，初步获得了一套完整的木质纤维素发酵产乙醇的工艺流程，达到了目的。更多还原

【Abstract】 I here is rarely reported on the biodegradation of biomass gasification wastewater with microorganisms so far in the worldwide, and lacks of the process of treating this kind of wastewater. The treatment efficiency of biomass gasification wastewater can be improved by using combined methods of biology and other physicochemical methods.In the experiment, biodegradability of gasification wastewater and tar was demonstrated by microorganisms at first, the results indicated that microorganisims had the ability to degrade COD in gasification wastewater and tar, but the degradation efficiency was lower with longer (?)action time and lower substrate concentration. In order to increase treatment efficiency, the screening of strain decomposing COD in gasification wastewater was conducted, the results demonstrated that mixted strain gained better COD removal rate than that of single strain. Finally in the lab scale experiment step, two strains of Pseudomonas sp1 and Pseudomonas sp2 preserved in our lab, were used to treat biomass gasification wastewater, the characteristics of degradating COD in the wastewater by the two strains was elucidated, the results demonstrated that mixed culture of the two strains had a high ability to decrease COD concentration in the wastewater, and immobilized cells of the mixed culture were conducted to treat gasification wastewater including the operation of biofilm reactor, entrapped cells reactor, and granular activated carbon adsorption reactor. The results indicated that granular activated carbon adsorption reactor reached to the high removal rate of COD and short hydraulic retention time, as well as the aromatic compounds were degradated efficiently. The paper also reported the excellent nitrogen removal performance from the wastewater using SBR process.Lignocellulosic biomass, a low-cost renewable resource including forestry waste, agricultural residues and municipal solid waste, can be potentially fermented into ethanol by microbial technology that would fulfill increasing demand in fuel. Lignocellulose-derived ethanol is an environmentally friendly liquid fuel, because exhausted carbon dioxide is taken up through growing biomass and therefore makes no net contribution to the atmosphere. However, from the hydrolysis of lignocellulosic materials to detoxification of hydrolysates, from strains’ selection and adaptation to fermentation, there are countless problems that need to be solved and numberless works that need to be done. The aim of this research is to get an effective, simple and low-cost method, and promote the lignocellulose-derived ethanol to be produced on a large scale.In my research, first, the strain selection of both ethanol and inhibitor tolerance were conducted from 21 strains including yeasts and bacterium by the experiments of xylose fermentation, hydrolysates selection and ethanol fermentation. As a result, Saccaromyces cerevisiae, Pachysolen tannophilis and recombinant Escherichia coli was selected for next experiments. Two groups of co-cultures were utilized in the adaptation experiment. One was S. cerevisiae mixed with P. tannophilis, and the other was 5. cerevisiae mixed with recombinant E. coli. After adaptation, two groups of co-cultures were used in the fermentation experiments, including batch fermentation, fed-batch fermentation and intermittent fed-batch fermentation, and some better results were achieved. I also make the fed-batch fermentation with fermentor, from which I examine the feasibility of using fed-batch fermentation on a large scale. In addition, I also study the fed-batch ethanol fermentation of two yeast strains.of toxic-tolerance.According to these experiments, I get an integrated method about ethanol production from lignocellulosic materials and achieve expected results.更多还原