臭氧微气泡处理有机废水的效果与机制

为解决臭氧氧化有机废水氧化效率差、臭氧利用率低这一问题,本文提出了臭氧微气泡处理有机废水的新技术。采用加压溶气法制备的臭氧微气泡处理苯酚配置的模拟废水,通过显微拍摄、动力学分析、紫外-可见吸收光谱、自由基屏蔽等手段对臭氧微气泡的形态大小、氧化效果、传质特性和氧化机制进行了研究,并对臭氧气泡直径和界面压力之间的关系进行了深入探讨。试验与数值计算表明,臭氧微气泡平均粒径为20.37μm,处理初始COD浓度为51.2mg/L的有机废水,COD去除速率分别是使用1μm曝气头和100μm曝气头曝气的1.59倍和3.61倍,臭氧利用率达到99.19%以上,氧化过程是自由基为主的间接氧化过程,污染物最终氧化产物为小分子烃和羧酸。微气泡影响下,臭氧分子传质速率和分解速率均有所提高,而臭氧微气泡表面较高的界面压力是其高效传质的原因之一。     

臭氧微气泡/紫外光处理费托合成水的研究

利用臭氧微气泡/紫外光处理费托合成水，研究臭氧微气泡/紫外光对小分子氧化物脱除过程的影响。首先获得了微气泡的最优粒径分布，再分别对费托合成水及其主要单一组分的水溶液进行氧化处理，并对臭氧微气泡/紫外光体系的氧化效果进行表观动力学分析。结果表明，微气泡可增强气液传质，提高臭氧氧化处理效率，COD降解率随微气泡直径减小呈现先增大后减小的趋势，最佳气泡中位径为25.20μm；在不同紫外光强、氧化体系、反应温度下，臭氧微气泡/紫外光体系氧化费托合成水的COD脱除率均符合准一级反应动力学规律，光强越强、温度越高，反应速率越快；相比单一体系，O₃+UV耦合体系氧化反应速率最快，费托合成水氧化反应活化能为4.088 kJ/mol。在氧化过程中，甲醇转化成甲酸，乙醇转化成乙酸，乙酸转化成甲酸，丙酸转化成乙酸和甲酸。紫外灯功率为1 kW时的设备能耗效率最优，处理时间为2 h时，能耗为58.3 W·h/g。     

数理统计方法在污水生化设计中的应用初探

本文系利用数理统计方法,对埃肯弗尔德(Eckenfelder)公式,在污水生化设计中,如何节约能耗,作了初步探讨。列出了氧传递速率、空气流量及气泡直径与生化装置节能的关系。通过方差分析,发现了气泡直径是影响能耗的主要因素。从而指出了减少能耗,改进生化治理装置的方向和途径。     

基于旋转浮阀的复合曝气器在曝气池中的应用及CFD模拟

基于气体通过阀片后能在阀盖四周形成旋转流场的特点，本文将旋转浮阀应用于曝气池中，以提高其充氧性能。在旋转浮阀四周均匀排布6个气泡石，即旋转浮阀-气泡石复合曝气器；在长宽高为800mm×600mm×910mm的透明有机玻璃池内，以空气-清水为体系，进行曝气实验。为了考察旋转浮阀形成的旋转流场对曝气的影响，以塔内件领域常见的F1浮阀以及气泡石为基准进行实验比较。结果表明，与F1浮阀-气泡石复合曝气器相比，旋转浮阀-气泡石复合曝气器的中心测量点与边界测量点的溶解氧浓度更接近，充氧均匀性指数也更小，说明了旋转浮阀能促进气泡分布均匀，减少传质死区。相比于F1浮阀-气泡石复合曝气器，旋转浮阀气泡石复合曝气器提高了氧总传质系数、氧传质速率、氧传质效率和曝气效率；相比于气泡石曝气器，旋转浮阀-气泡石复合曝气器提高了氧总传质系数、氧传质速率，但降低了氧传质效率和曝气效率。本文还利用CFD模拟流场分布，解释了旋转流场的产生及其提高曝气充氧能力的原因。     

搅拌槽内粘稠物系中气液相间氧传递

以发酵罐中气液相间氧传递为背景，考察了搅拌槽内搅拌器形式、物系流变性质、通气搅拌操作条件等对假塑性粘稠物系中氧传递过程的影响。结果表明，这些因素主要通过改变气体分散状态和相间传质面积来影响氧传递速率。根据气泡在搅拌槽内不均匀分布现象，多层搅拌下气液相间传质过程可以用气泡运动分区分布模型来描述。它说明了采用轴向流桨和涡轮桨组合的搅拌形式在氧传递方面的优越性，为强化发酵罐中供氧指明一条有效途径     

鼓泡塔细胞反应器流体力学与传质特性

以超大规模细胞培养为目的,构建了与细胞培养体系十分接近的冷模实验体系,系统地研究了微载体(Cytodex I)、细胞保护剂(Pluronic F68)和消泡剂(Antifoam C)对鼓泡塔反应器中气、固、液三相流流体力学和氧传质特性的影响。在0.04~0.17 cm/s表观气速范围内采用50 μm孔径的烧结金属滤芯曝气时,在含有0.5和1.0 g/L的Pluronic F68的磷酸盐缓冲溶液冷模体系中,气含率与表观气速成线性增加关系,而气泡直径受表观气速影响较小;相同气速下的冷模体系与空气-水体系相比,气含率显著提高,气泡直径明显减小。在所研究的表观气速范围内微载体均可全悬浮,对气含率有一定增强,但微载体浓度为14%~20%时对气泡大小几乎无影响。消泡剂用量在1.60×10-4时,可以有效抑制泡沫的形成。添加剂对液膜传质系数kL有较大负面作用,抵消了小气泡带来的传质面积增加,总的体积传质系数kLa变化不大。Euler-Euler多相流计算流体力学模型与拟稳态实验数据吻合较好,可用于指导反应器放大设计。     

微曝氧化沟气液两相传质模型构建及传质影响因素分析

基于ANSYS Fluent软件建立了微曝氧化沟气–液两相流动和溶解氧输运模型,对比不同工况下氧体积传质系数的实验测量值和模拟结果,误差在7%以内。采用验证可靠性的模型模拟研究了气泡直径、曝气量和横向流动速度对微曝氧化沟内氧传质的影响。结果表明,气泡直径由1.5 mm增至3 mm时,氧体积传质系数由15.80 h?1降低至5.83 h?1;曝气量由0.5 m3/h增大至2 m3/h时,氧体积传质系数由4.21 h?1增至14.15 h?1,减小气泡直径和增大曝气量能明显提高氧体积传质系数。微曝氧化沟内气–液相间传质及溶解氧的分布受横向流动影响,开启单台和两台推流泵时,氧体积传质系数分别比无横向推流工况增大27.7%和42.4%,横向流动能有效提高气泡羽流内的气含率,增强氧传质效果。     

微气泡耦合生物反应器的研究进展

微气泡具有气液接触面积大、气体溶解速率快、上升速度慢和水中停留时间长等理化特征，非常适合于高气液传质效率需求的生物发酵过程。本文介绍了能够耦合生物反应器的几种微气泡发生装置，分别为微气泡分散器、微孔膜、流体振荡器耦合微孔膜和微气泡曝气搅拌桨；并简述了微气泡发生装置耦合搅拌式生物反应器、气升式生物反应器和生物膜反应器在生物反应过程的应用进展；最后回顾了二氧化碳微气泡在生物反应器的应用研究进展。指出微气泡耦合生物反应器的研究仍处于起步阶段，在放大规律和能耗方面仍处于研究空白。微气泡耦合生物反应器的发展对工业生物技术、石油化工、污水处理和资源再利用等的发展具有重要的意义。     

响应面法优化新型曝气装置的充氧条件

基于静态变螺距螺旋切割原理自主研发了一种高效低耗、易操作的新型溶氧曝气装置。运用响应面法研究了空气流量、液体流量、水体深度对标准氧转移系数、氧利用率和理论动力效率的影响。结果表明,当空气流量为0.5 m~3/h、液体流量为10 m~3/h、水体深度为0.3 m时,新型溶氧曝气装置的标准氧转移系数、氧利用率、理论动力效率分别为1.4394 min~(-1)、37%、7.4388 kg O_2/(kW·h);装置较传统曝气设备具有显著优势。粒径分布测定结果表明,61.31%的气泡粒径集中在0.1μm以下,37.27%的气泡粒径集中在20～75μm,表明新型曝气设备所产生的气泡属于微纳米气泡;该装置可用于水体增氧、养殖、黑臭水体修复和污水处理等方面,应用前景广阔。     

气泡上浮运动与传热传质的耦合模型

针对舰船主机尾气消尾流技术中的气泡上浮运动,分别建立气泡非等温传热、瞬态非平衡传质及其速度、半径等各微分方程,进而构建液体中高温气泡上浮运动的耦合模型。将模型仿真结果与实验、文献研究比对,获得并分析气泡半径及运动速度的误差值,证明模型能够模拟不同温差的气泡在液体中的上浮过程,并得到气泡运动特性的影响规律:传质加速小气泡消失,使中等气泡半径持续减小,但对大气泡影响微弱;气泡运动初期为迅速的非等温传热过程,随气泡半径增大,热流密度变化幅度及热传导效率均下降;压强对气泡运动影响基本保持不变。三者综合作用使非等温传热初期气泡半径迅速下降。随后大气泡平缓增大;中等气泡缓慢地先减小后增大;而小气泡逐渐溶解在液体中。     

Coupling simulation analysis of micro-interface mass transfer in aerobic fermentation

The microbial aerobic fermentation process is a multi-phase biochemical reaction system, and the mass transfer rate of oxygen in air between the gas-liquid two phases has an important impact on the biochemical fermentation process. The transmission characteristics of oxygen in the bubble are the result of the combined influence of the bubble's morphology, movement and system temperature, pressure and physical properties. By establishing a two-component air bubble rising and its oxygen mass transfer coupling model, numerical simulation is used to describe the strengthening effect of the micro-interface system in the aerobic fermentation system. The energy dissipation theory is used to evaluate the energy consumption of the manufacturing microbubble system to obtain a cost-effective bubble shape and a high oxygen utilization rate. The calculation results show that, under the preset working conditions, in a reactor with a certain liquid level, the bubbles with an initial radius greater than 500 μm will escape the system in a short time, resulting in waste of materials; while the initial radius of bubbles is less than 100 μm, its residence time, mass transfer efficiency and oxygen utilization rate will be significantly improved. The generation of small bubbles requires greater energy consumption. Without considering the influence of other factors, if the DO value in the system is maintained at 20% to 30%, the maximum oxygen mass transfer rate can be obtained.     

Development of microbubble aerator for waste water treatment using aerobic activated sludge

In large-scale waste water treatment plants, the aerobic biochemical reactor is the most important process, where the oxygen supply into the microorganisms often limits the overall waste water treatment rate. On the other hand, several kinds of microbubble distributors have been developed to enrich the oxygen dissolution in water. Therefore, the application of microbubbles for a waste water treatment system was investigated in this study.The oxygen absorption performance of typical microbubble generators was compared with typical bubble generators. To evaluate each bubble generator, the liquid-phase volumetric oxygen transfer coefficient, gas hold-up and power consumption per unit liquid volume were measured in a bubble column attached to each bubble generator. All the microbubble generators allowed the oxygen to dissolve faster than the typical aerators. The spiral liquid flow type microbubble generator had the highest oxygen transfer coefficient even at a low air flow rate although it used more energy than the typical distributors.To improve an industrial waste water treatment system, a novel aeration system utilizing a spiral liquid flow type microbubble generator was proposed in this study. The present system has some advantages such as compact size, portability and fast oxygen dissolution rate. To ensure the performance for organic waste water treatment, the effects of the aeration rate, dissolved oxygen concentration and device properties on the specific consumption rate of model organic waste were investigated. For the novel aeration system, the most suitable conditions to treat organic waste were found.     

Evaluation of a novel self-aerating,oscillating baffle column

We describe the operation of a pilot scale oscillating baffle column using a self-aeration system for oxygenation of water. The top baffle has a high constriction ratio and is sufficiently near to the surface of the water such that gas bubbles are generated. This aeration plate is coupled with a series of equally spaced low constriction orifice baffles, which lead to uniform dispersion of entrained air bubbles throughout the liquid volume. Flow visualisation experiments using video and still photography were used to identify two mechanisms for bubble generation: bubble formation under the water surface by surface vortex suction, and bubble generation from the collapse of a surface fountain and subsequent entrainment of bubbles into the bulk. Mass transfer measurements have shown that under most conditions a uniform oxygen concentration could be obtained throughout the column as a result of efficient mixing, and that the sole limitation to mass transfer performance was determined by the aeration mechanism. Initial comparison on the basis of aeration efficiency with other devices reveals a modest oxygen transfer rate, but with low specific power consumption of order 0.3 kW/m³.     

Distribution of the free and oil‐trapped air bubbles in simulated broths containing fungal biomass

The location of air bubbles (i.e. inside oil drops or free in the aqueous phase) was studied by image analysis as a function of the oil and biomass concentrations in a 2 L stirred tank using a simulated fermentation medium (aqueoussalt solution, castor oil, air and fungal biomass) agitated by a Rushton turbine. The solid (fungal) phase plays an important role in defining the location of bubbles, as the percentage (in bubble volume) of bubbles trapped in oil increases threefold when biomass is added to the medium. The bubbles located inside oil drops were found to occupy 60% of the total bubble volume and to be 40% smaller than those which were non‐oil associated. This phenomenon has important implications for oxygen mass transfer in multiphase fermentations.     

Determination of oxygen transfer from single air bubbles to liquids by oxygen microelectrodes

For the investigation of mass transfer from gas bubbles into liquids the concentration gradient of oxygen migrating from air bubbles was measured by means of oxygen microelectrodes. For this purpose a single air bubble was fixed by a platinum wire spiral with the liquid flowing downward. Thus the ascent of the bubble in an aerated liquid was simulated. Liquid-side mass transfer coefficients determined from concentration gradients were higher than values calculated from theory. Sherwood numbers obtained from experimental results for bubbles of larger diameters were distinctly higher than those for smaller bubbles (diameter 1 mm); the difference corresponds approximately to that predicted theoretically between bubbles with mobile and those with rigid interfaces.     

Mass transfer from very small bubbles—the optimum bubble size for aeration

Measurements have been made of mass transfer coefficients K_L of small oxygen bubbles of diameter 100–1000 μm, rising at their terminal veloThe measured coefficients are used together with values from the literature, to calculate the proportion of oxygen transferred from a bubble of air or     

A generalized approach to model oxygen transfer in bioreactors using population balances and computational fluid dynamics

In many biological processes, increasing the rate of transport of a limiting nutrient can enhance the rate of product formation. In aerobic fermentation systems, the rate of oxygen transfer to the cells is usually the limiting factor. A key factor that influences oxygen transfer is bubble size distribution. The bubble sizes dictate the available interfacial area for gas-liquid mass transfer. Scale-up and design of bioreactors must meet oxygen transfer requirements while maintaining low shear rates and a controlled flow pattern. This is the motivation for the current work that captures multiphase hydrodynamics and simultaneously predicts the bubble size distribution.Bubbles break up and coalesce due to interactions with turbulent eddies, giving rise to a distribution of bubble sizes. These effects are included in the modeling approach by solving a population balance model with bubble breakage and coalescence. The population balance model was coupled to multiphase flow equations and solved using a commercial computational fluid mechanics code FLUENT 6. Gas holdup and volumetric mass transfer coefficients were predicted for different superficial velocities and compared to the experimental results of Kawase and Hashimoto (1996). The modeling results showed good agreement with experiment.     

Hydrodynamics and local mass transfer characterization under gas–liquid–liquid slug flow in a rectangular microchannel

Gas–liquid–liquid three-phase slug flow was generated in a glass microreactor with rectangular microchannel, where aqueous slugs were distinguished by relative positions to air bubbles and organic droplets. Oxygen from bubbles reacted with resazurin in slugs, leading to prominent color changes, which was used to quantify mass transfer performance. The development of slug length indicated a film flow through the corner between bubbles and the channel wall, where the aqueous phase was saturated with oxygen transferred from bubble body. This film flow results in the highest equivalent oxygen concentration within the slug led by a bubble and followed by a droplet. The three-phase slug flow subregime with alternate bubble and droplet was found to benefit the overall mass transfer performance most. These results provide insights into a precise manipulation of gas–liquid–liquid slug flow in microreactors and the relevant mass transfer behavior thereof.     

气泡大小对反应器内氧传递系数的影响

在气液反应过程中,气泡的大小对结果往往起了决定性的作用。通过减小气泡的尺寸,可以促进气液传递,加快反应的进程。在气液搅拌式反应器上安装了一种特殊的气体分布器,通过搅拌产生离心场,从而诱导生成泰勒涡柱,使大量进入反应器的空气气泡保持在泰勒涡柱的内部。由于减少了气泡间的凝并作用,气泡尺寸减小,与对照组相比,反应器中最小的气泡尺寸减小了近50%,气泡的比表面积增加近80%。通过对不同通气流量和搅拌速度下气液反应器内氧传递系数的测量,与对照实验比较,使用特殊气体分布器的反应器中,氧的传递系数增加了10%~40%,证明这种气体分布器确实可以增加气液间氧的传递。     

Bubble swarm behaviour and gas absorption in non-newtonian fluids in sparged columns

Mean relative gas hold up, slip velocity, bubble size distribution, and volumetric mass transfer coefficient of oxygen were measured in sparged columns of highly viscous non-Newtonian fluids (CMC solutions) as a function of the gas flow rate, and CMC concentration (fluid consistency index k, and flow behaviour index n).By comparison of the measured bubble swarm velocities with those calculated by relations for single bubbles the bubble swarm behaviour was investigated. It could be shown that small bubbles in swarm have higher rising velocities than single bubbles, expecially in highly viscous media. Large single bubbles rise with high velocity due to the change of their shape caused by the swarm of the smaller bubbles. No large bubbles with spherical cap shape could be observed. The volumetric mass transfer coefficient decreases rapidly with increasing CMC-concentration.A comparison of the volumetric mass transfer coefficients with those measured in mechanically agitated vessels indicates, that the performance of sparged columns is comparable with the one of agitated vessels. Because of their lower energy requirement sparged columns are more economical than mechanically agitated vessels. It is possible to improve the performance of sparged columns by the redispersion of large bubbles in a multistage equipment.