营养性载体基质的物理性质对固态发酵过程的影响
文献类型：学位论文
| 作者 | 段颖异 |
| 学位类别 | 硕士 |
| 答辩日期 | 2012-05-29 |
| 授予单位 | 中国科学院研究生院 |
| 导师 | 陈洪章 ; 王岚 |
| 关键词 | 固态发酵 营养性载体基质 传递性质 菌体生长 过程模拟 |
| 其他题名 | Effect of the Physical Properties of Substrates with Biodegradable Supports on Solid-state Fermentation |
| 学位专业 | 生物化工 |
| 中文摘要 | （1）基于固、液、气三相在决定基质结构变异中的比重，建立三相结构指数用以表征基质结构。三相结构指数同基质传递性质的函数关系能够描述固态发酵基质的物理结构变化对其传递性质的影响，模型决定系数为0.85~0.92。线性相关分析表明，斜卧青霉的生长受到基质保水性、比热容和导热率的共同影响，相关系数分别为0.616，0.73和0.316；斜卧青霉产纤维素酶的能力受到基质导热率和保水性的影响，相关系数分别为0.832和0.224。因此，保水性和导热性是基质结构影响固态发酵效果的主要原因。（2）利用分形维数有效表征发酵基质的不规则形态结构变化，建立了反映固态发酵基质结构随菌体生长变化的分形动力学模型。所建模型能够对不同含水量和纤维长度基质在发酵过程中的形态变化进行表征，所得基质分形维数和菌体量的误差分别为0.541% ~ 5.220% 和0.454‰ ~ 3.885‰。基于基质分形维数的变化速率与菌体比生长速率之间的高度专一性，确立了将数字图像处理和分形动力学模型相结合的发酵在线监控方法。（3）营养性载体基质的密度随菌体生长符合幂函数模型。基质透气率和内部氧气分布证实发酵过程基质经历了“结团-崩解”过程。透气率的变化规律与分形动力学模型相仿。根据孔道迂曲度分形模型计算基质的氧气扩散系数与透气率正相关。营养性载体基质的比热容和热导率随菌体生长均符合幂函数模型。（4）以非饱和多孔介质的传递模型作为固态发酵传递过程建模的基础，将微生物生长动力学和基质物性变化模型并入，形成理论上更符合实际的营养性载体基质固态发酵传递模型。（5）通过实验得出斜卧青霉生长和产酶的热动力学方程。根据发酵不同阶段基质体积、内源热等参数的差异性将发酵过程分为若干段，将各段的模拟结果拼接组成整体模拟结果，形成“分段拼接”的模拟思路。对静置固态发酵纤维素酶过程进行了数值模拟，与实验结果良好吻合。（6）对比静置、强制通风和气相双动态三种操作方式下固态发酵数值模拟结果可知：基质的导热率和对流换热强度是影响发酵基质温度的主要原因。静置固态发酵由于对流散热能力弱和蒸发失水，因而发酵过程温差可达13℃；强制通风和气相双动态能够强化基质内的对流换热进而有效控制发酵基质温度。在气相双动态操作方式下，短纤维基质层的轴向温差随基质高度的变化有显著差异，而长纤维基质的差异不显著。因此，基质的透气率是决定通风操作效果的主要因素。 |
| 英文摘要 | (1) Built three phase structure index (TPSI) to indicate the structural feature of substrates with different particle length and moisture content. The TPSI was proved to have specific relations with the retention ability, permeability, thermal conductivity, volumetric heat capacity of substrates, R2 of the constructed models were between 0.85~0.92. Statistical analysis showed that, moisture content affected the substrates’ thermal conductivity more than fiber length did; both the two factors had significant influence on the retention ability and permeability of substrates. Correlation analysis showed that, Penicillium decumbens growth had significant correlations with the retention ability, volumetric heat capacity and thermal conductivity, coefficients were 0.616, 0.73 and 0.316, respectively. Coefficients of retention ability and thermal conductivity about cellulase production were 0.224 and 0.832. Therefore, retention ability and thermal conductivity of substrates influenced by the three phase structure were the main concerns for improving SSF. (2) Fractal dimension, quantifying the morphological changes of mycelia-matrix from culture images, shows correlations with Penicillium decumbens biomass on lignocellulosic substrates. Kinetic models were constructed to describe the variation of fractal dimension of mycelia-matrix along with fungal growth. Relative errors of the models were 0.541%~5.221% for biomass and 0.454‰~3.885‰ for fractal dimension. Parameters δ and η in fractal kinetic models, which indicate the variation rates of fractal dimension, present significant specificity for specific growth rate of P. decumbens, thus can be used to predict fungal biomass in SSF. With advantages of low cost, reasonable accuracy and well adjustability, the coupling of dynamic imaging and computational modelling show potential in the on-line determination of fungal biomass in SSF. (3) Variations of biodegradable supports’ density with fungal growth accorded with the power function. The substrates’ permeability influenced by fungal growth shared the same models with fractal dimension. During SSF, variations of oxygen distribution within the supports indicated the agglomerate and breakage of substrates, also confirmed the porosity of the fermented substrates. The calculated oxygen diffusion coefficient and permeability had positive relations. Variations of the thermal conductivity and volumetric heat capacity with fungal growth shared similar power functions. (4) Given that the solid-state substrate was a kind of unsaturated porous medium, used the heat and mass transfer models of unsaturated porous medium as the foundation to build the transfer models for SSF, which involved microbial growth kinetics and models of the physical properties variations. The constructed models took both transfer characteristics of the porous media and fungal growth features into account. Therefore, for SSF with variable substrates, the constructed models were better than many of the existing models in describing the heat and mass transfer. (5) Studied the effect of temperature on fungal growth and cellulases production to build the thermal kinetic models for simulation. Based on the least standard deviation method (LSD), analyzed the differences of substrate volume, height, fungal growth and some other parameters between stages in SSF. The whole fermentation process was splitted into 6 stages, and every stage have quite different physical model from others. Simulated the heat and mass transfer in each stage, and combined the results into unity as the final simulation for the whole SSF process. Call this method as “segmentation and integration”. With the new simulation methods, the simulated results of the static SSF in bottles were in good agreement with experimental results. (6) Used the improved transfer models to simulate the fungal growth, cellulase production and temperature distribution in SSF in the enclosed reactor under static, forced aerated and double dynamic aerated operations. The results showed that the thermal conductivity and forced convection played important role in improving SSF. With poor thermal conductivity due to evaporation and weak convection, temperature difference during the static SSF reached 13oC; the forced aeration and double dynamic aeration made strong convection, which strengthened the heat transfer in the substrates, and effectively controlled temperature. Since the convection induced by double dynamic aeration was fiercer than that by forced aeration, fungal growth in former condition was 15% higher than that in the later condition. Under double dynamic aeration mode, temperature difference between 0.4 cm and 4 cm lignocellulosic matrix in SSF was about 4oC. Therefore, when different substrates had the same moisture content, better permeability of substrates with long fibers would improve the heat transfer. To get equivalent productive efficiency, substrates with good permeability should employ weak aeration, and vice versa. |
| 语种 | 中文 |
| 公开日期 | 2013-09-25 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1811]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 段颖异. 营养性载体基质的物理性质对固态发酵过程的影响[D]. 中国科学院研究生院. 2012. |
入库方式： OAI收割
来源：过程工程研究所
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