喷雾接种生物颗粒两相流及其对菌种活性的影响

纯种固态发酵喷雾接种的喷雾系统可能会直接影响微生物的活性,造成微生物的死亡。该文利用固-液两相流理论分析了喷雾接种两相流体中微生物的受力状况,并对该两相流流态特征进行了定性,分析了流体微元体对微生物损伤程度综合衡量参数——黏性能量耗散率公式的理论依据,为后续喷头内部流场仿真奠定了基础。在FLUENT里创建了一个通过流场信息来计算黏性能量耗散率的用户自定义函数,在合理设置边界条件和初始条件的基础上,对在不同孔口尺寸、入口压力条件下空心锥雾喷头的黏性能量耗散率等内部流场进行了数值模拟;设计并制造了一套喷雾接种试验系统,确定了相应的测试试验酵母菌活性的方法。采用CFD仿真和试验验证的方法量化分析了喷头孔口尺寸、喷雾参数等因素对喷雾后生物活性的影响。结果表明,用喷雾接种实现纯种固态发酵过程的自动化、保证接种的均匀性是可行的;接种时喷雾压力越大、喷头孔口尺寸越大,喷头内部流场内能量耗散率极值也越大,菌种死亡率越高,据此可以找到保证接种后微生物存活率的最佳喷雾特性参数。该文的研究为固态发酵喷雾接种或病虫害防治喷施生物农药的应用提供了基础,并可为进一步研究其他喷头对微生物活性的影响提供借鉴。

Solid-liquid two-phase flow of microbial particle spraying inoculation and its influence on microbial viability

Abstract: Solid-state fermentation (SSF) technology has a very wide range of applications on account of the increasing energy shortage at present, especially on account of short fermentation time, low energy cost, high rate yield of product, and reduced environmental pollution for SSF. Currently, solid-state fermentation equipment should also adapt to this extensive demand. In order to create good production conditions, ensure pure solid-state fermentation, and the high quality of products, the inoculating tube must be arranged into the hermetic bioreactor. After sterilization, the nozzle of the inoculation spraying system can spray the microbial strain on the solid substrate, to realize sterilizing, cooling, inoculation, and fermentation inside one solid-state fermentation bioreactor. The microbial viability may be determined by the spraying system of the spraying inoculation of pure-culturing solid-state fermentation that could directly result in the death of the microorganisms.The solid-liquid two-phase flow of the microbial particle spray inoculation fluid system was analyzed. Fluid characteristics of the two-phase flow composed of microorganisms and sterile water was discussed, and the forced state of the microorganism particles was also analyzed. The energy component was deduced, and the theoretical basis, reliability, and practicability of the energy dissipation rate which could quantify the microbial particles' damage within comprehensive hydrodynamic stresses were also discussed and analyzed.The effect of nozzle type and spraying parameters on the results of the spraying inoculation was studied by a simulation using FLUENT. A user-defined function was created in FLUENT to compute the energy dissipation rate from the flow field information. By setting reasonable boundary conditions and initial conditions, simulations of a hollow cone nozzle's flow field of the pressure and energy dissipation rate were conducted for each size of the nozzle and the experimental inlet pressure. A set of spraying inoculation experimental flow devices was designed and manufactured. At the same time, an appropriate test method was determined. Microzyme was selected as the microbial particle in the spraying inoculation experimental system because it was easy to separate the living microzyme from the dead microzyme. It could be dyed with Loeffler basic methylene blue dye and the living microzyme with a strong reducing ability is colorless and the dead or weak dying microzyme is blue under microscope.Experimental and simulation results showed that it was feasible to use a spraying inoculation to realize automation and a pure solid state fermentation process and to ensure uniformity of the inoculation. The best spraying characteristic parameters could be found to ensure microbial viability after inoculation. It could be found that the maximum energy dissipation rate of different size nozzles were different. The larger the hollow cone nozzle size and the inlet pressure were, the higher the maximum energy dissipation rate and the mean mortality of microzyme became. Simulation results showed that the maximum energy dissipation rate in the hollow cone nozzle was not at the outlet, but at the junction of the tangent of two narrow ports and the swirl chamber.The results could provide the foundation for the applications of both the spraying inoculation of pure- culturing solid-state fermentation and the biological pesticide spraying, and could provide the references for studying the effect of other types of nozzles on the microbial viability.