废水好氧生物处理工艺中氧的传质与强化的理论与实践

废水处理好氧生物工艺供氧过程的控制步骤是气液传质作用，即将气体分子氧转化为足够微生物用于氧化污染物的溶解氧（DO），包含碳源BOD5的降解、氨氮的硝化和总氮的去除以及无机COD氧化的共同需求。文章指出DO的传质过程由总传质系数K_La决定，废水性质、生物量、污泥龄、微生物耗氧速率、微生物种群等因素都会影响K_La。DO的浓度梯度是气液固三相氧传质的主要推动力，气液传质受水温、水质、氧分压、气泡大小、液体紊流程度和液膜更新速度等的影响，通过提高氧气分压、增大气泡比表面积、强化气液混合以及无泡供氧等方式及其它们的结合，或者控制污泥流态化程度及其污泥龄，可以获得微生物摄氧能力的提高。本文指出在对水质特征、环境条件、微生物特性、反应器流体特性以及运行参数等优化的基础上，结合一些研究新的方向，如无泡供氧、纯氧/富氧曝气的气泡行为，流场分布、湍流构造、浓度梯度的流体行为，挡板内构件、流态化控制的反应器结构优化，以及充分考虑负荷的HRT和SRT的运行工艺条件，可以实现更加全面的节能目标。

Oxygen dissolution and gas liquid mass transfer in aerobic biological wastewater treatment: theory and practice

Gas-liquid mass transfer is the determining step for aerobic microbiological wastewater treatment. The dissolved oxygen (DO) demand should include the sum of carbonaceous BOD5 degradation, ammonia nitrification, total nitrogen removal and inorganic COD oxidation, which were characterized by wastewater properties. The wastewater properties, biomass of biological reaction, sludge age (SRT), microbial oxygen uptake rate (OUR), microbial populations and microbial growth conditions could comprehensively affect the total mass transfer coefficient K_La. The gradient concentration of dissolved oxygen was the main driving force for oxygen transfer from liquid into solid phase. It is demonstrated that the mass transfer from gas phase into liquid phase is fundamentally affected by water temperature, dissolved constituent, oxygen partial pressure, diameter of oxygen bubble, degree of liquid turbulence and renewal rate of liquid film. From the technical point of view, elevating the partial pressure of oxygen, increasing the specific surface area of bubble, strengthening the mixture of gas and liquid, bubble less aeration and controlling the degree of sludge fluidization or the length of sludge age can be the promising approaches to accelerate oxygen dissolution and enhance the capacity of uptake dissolved oxygen. New methods of energy saving may be attained by the optimization of water quality characteristics, environmental conditions, microbial characteristics, hydromechanics in the reactor and operational parameters.