多相厌氧生物反应器的介尺度研究

Multiphase bioreactors are widely used in various industries such as chemical engineering, energy and environmental protection etc. The multiphase anaerobic bioreactors generate clean energy biogas (methane: about 60%), and simultaneously stabilize and reduce organic substances. Upflow anaerobic reactors are the largest number of anaerobic reactor and are typical gas (biogas)-liquid (wastewater)-solid (granules, i.e. anaerobic microorganisms) three-phase reactors. The anaerobic granules generate biogas and purify pollutants. .Since the anaerobic reaction in granules (at atom and molecular scale) is significantly affected by diffusion of organic substances (at molecular scale) and flow (at macro scale), there exists complicated structure and behavior at meso scale, i.e. “single anaerobic granule- granules -reactor”. From this view, the anaerobic reactor consists of huge number of complex space-time structures between reactor (macro scale) and single granule (micro scale). Flow is key to the meso structure and behavior, while the gas flow is the most important factor of flow. .In order to find out the solutions to improve the efficiency of reactors and to scale up the reactors, this project aims at investigating the relation among the flow-mass transfer- reaction in multiphase bio-reactors with upflow anaerobic reactors as study object, including the identification of the typical meso structure and its impact factors and study about the properties of the flow field and working mechanism of its impact factors, and the relationship between flow regime and reaction rate of granules at single granule, granules and reactor levels, and development of the association model to connect the three levels etc..The study will be conducted focusing on the experiment with an original on-line method jointly developed by our French partner from CNRS and us. The method combined microdevice and quantitative image analysis technique with the image acquisition approaches including some advanced equipments to obtain the flow and shear rate fields around granules such as Particle Image Velocimetry (PIV，resolution 50μm), Micro Particle Image Velocimetry (MPIV, resolution 500nm) and high-speed camera (500 FPS) etc. Since the flow field within the reactor could be controlled well, the microdevice is good for the study about coupling effects of hydrodynamic and biological processes in multiphase reactors. The reviewers of our papers published in the mainstream journal such as Environmental Science and Technology (top environment journal) wrote that“The approach is original and quite appealing”and“it is the first time that such study is performed at such a small scale”. .We have satisfactory research experience about the study at meso scale including 2 ordinary projects and 1 international project granted by NSFC and 1 project from Fok Ying Tung Education Foundation since 2007. And our meso research is jointly conducted with our French partner and so will this project.

多相生物反应器是化工、能源和环保领域常见反应器。多相厌氧生物反应器可生产清洁燃料沼气，同时实现有机物稳定化和减量化和资源化。而升流式厌氧反应器是目前数量最多的厌氧反应器，它依赖厌氧颗粒污泥完成产沼气和净化有机物。由于颗粒污泥的厌氧生物反应（原子分子水平）受有机质传质扩散（分子群水平）和流动（宏观统计水平）的影响导致升流式反应器中形成了“颗粒污泥-颗粒污泥群-反应器”的典型介尺度结构和行为。本课题响应指南中科学问题三“建立颗粒尺度上反应-传递-流动跨尺度关联的理论与调控方法”，以升流式厌氧反应器为对象，探索多相生物反应器的“污泥-污泥群-反应器”时空上流动-传质-反应的关系，包括：识别典型的介尺度结构及其主要影响因素；掌握这个尺度下各层面流场的特征以及主要影响因素的影响机制；掌握流态分布及流态与颗粒污泥反应速率的关系；建立各层面的关联机制，从而找到提高反应器效率的要点和反应器放大的关键。

多相生物反应器是化工、能源和环保领域常用的反应器。多相厌氧生物反应器可产生清洁能源沼气，同时实现有机物稳定化、减量化和资源化。升流式厌氧反应器是目前使用最广泛的厌氧反应器，它依赖颗粒污泥完成产气和净化有机物。由于颗粒污泥中发生的厌氧反应受到分子群水平的传质和宏观统计水平的流动的影响导致反应器中出现了“颗粒污泥-颗粒污泥群-反应器”的典型介尺度结构。课题响应指南中科学问题三建立跨尺度关联的理论和调控方法，取得了以下成果：（1）识别出污泥、污泥群和反应器这个介尺度结构的影响因素主要有两个方面，分别是颗粒污泥的外部环境和颗粒污泥的物理特性。（2）首次获得了颗粒污泥受到的剪切力的情况，并提出了厌氧反应器水力状况形成的模式。进一步识别出气泡就是剪切速率的主要来源，颗粒污泥受到的剪切速率与气泡密度线性正相关。（3）在真实反应器中，对流扩散和分子扩散同时发挥作用。对流扩散对颗粒污泥的传质有促进作用，但分子扩散仍然发挥了重要的影响。首次从颗粒污泥内部结构研究了传质过程。（4）取得了有机负荷为4.32-8.30 kg COD/(m3.d)之间，反应器各处的分子扩散和对流扩散系数。从传质状况看，升流式反应器由下而上就是由高效区、中效区和低效区组成。（5）升流式反应器的优化就在于缩小低效区，扩大高效区。采用大颗粒污泥有利于高效反应。上述研究结果对于掌握厌氧反应器中的介尺度现象和调控机制十分重要。