Modelling and design of thin-film slurry photocatalytic reactors for water purification

Photocatalytic oxidation processes are highly effective clean technologies for the degradation and mineralization of a wide variety of priority pollutants in water and wastewater. However, the application of heterogeneous photocatalysis for wastewater treatment on an industrial scale has been impeded by a lack of mathematical models that can be readily applied to reactor design and scale-up. As a results current photocatalytic reactors in research and development have been designed by empirical or semi-empirical methods only.In this paper, a simple and generic mathematical model for steady-state, continuous flow, thin-film, slurry (TFS) photocatalytic reactors for water purification using solar and UV lamps is presented. The model developed is applicable to TFS flat plate and annular photoreactors of (a) falling film design or (b) double-skin design, operating with three ideal flow conditions: (1) falling film laminar flow, (2) plug flow and (3) slit flow. The model is expressed in dimensionless form and scale-up of TFS photocatalytic reactors can be carried out by dimensional analysis. In addition, the model parameters can be estimated easily from real systems and model solutions can be obtained with little computational effort.Comparison of a number of ideal flow systems shows that both falling film laminar flow and plug flow operation modes give higher performance than the slit flow system. Slit flow operation mode results in lower conversions due to the non-correspondence of fluid-residence time and the transversal radiation field. The effect of optical thickness, on reactor performance and the evolution of radial profiles of a model pollutant with photoreactor length are presented for each of the operation modes. The falling film laminar flow system was found to be more efficient than the plug flow system when the reactor conversion is above 80%. For lower reactor conversion the plug flow system was found to be marginally more efficient than the falling film laminar flow system. A methodology for the optimal geometrical design of a highly efficient configuration of TFS photocatalytic reactors is also presented. The mathematical models presented may be used as a tool for the design, scale-up and optimization of these types of photocatalytic reactors.     

体相光催化处理有机废水新工艺

针对工业废水浓度和色度高、光线在废水中的穿透能力有限、催化剂极易中毒等因素,本文以球形微波无极灯为“点光源”填充反应器构建“体光源”,提出体相光催化反应的设想,探索光催化处理工业废水的过程强化作用。分别以甲基橙溶液和含2,4-二氯酸农药废水为研究对象,探索体相光催化反应过程中有机污染物的降解性能;以乙醇水溶液和青霉素废酸水为研究对象,探索体相光催化反应过程热效应与光催化在废水处理中的耦合作用。结果表明,体相光催化反应不仅可以有效地降解水溶液中有机物,2,4-二氯酸农药废水COD_Cr去除率达到83.9%,而且利用反应器运行过程中的热效应能够100%地分离回收青霉素废酸水中的乙酸丁酯,同时去除55.8%的COD_Cr。因此,填充床式体相光催化反应系统能够将微波能、光催化和热效应集成于一体,在实现光催化技术处理有机废水及资源化的实际应用方面有积极意义。     

Methylcellulose fibrils: a mini review

This review covers the recently discovered methylcellulose (MC) fibrils and their impact on MC thermogelation and overall gel strength. The thermogelation of MC aqueous solutions has been studied for nearly 100 years, but it has only recently been attributed to fibril formation at elevated temperatures. The assembly of a fibrillar network explains the general features of MC gels: the unusually high modulus, the turbidity, and the nonlinear rheological behavior at high strains. Recent scattering, atomic force microscopy (AFM) and cryogenic transmission electron microscopy (cryo‐TEM) experimental efforts have led to critical discoveries about the fibril structure. MC fibrils are 60% water by volume when in solution. The length of the fibrils, especially for shorter chains, is closely correlated with the MC chain contour length. On the other hand, the fibril radius does not depend on the temperature, molecular weight or concentration of MC chains but does seem to be correlated with chain stiffness. The discovery of MC fibrils represents a significant departure from the entanglement of polymer chains and localized phase separation based physical model of MC gelation, opens new questions about the mechanism of fibril formation and presents new pathways for stimulus responsive material design. © 2019 Society of Chemical Industry     

Computational fluid dynamics modeling of immobilized photocatalytic reactors for water treatment

A computational fluid dynamics (CFD) model for the simulation of immobilized photocatalytic reactors used for water treatment was developed and evaluated experimentally. The model integrated hydrodynamics, species mass transport, chemical reaction kinetics, and irradiance distribution within the reactor. The experimental evaluation was performed using various configurations of annular reactors and ultraviolet lamp sizes over a wide range of hydrodynamic conditions (350 < Re < 11,000). The evaluation showed that the developed CFD model was able to successfully predict the photocatalytic degradation rate of a model pollutant in the analyzed reactors. In terms of hydrodynamic models, the results demonstrated that the laminar model performs well for systems under laminar flow conditions, whereas the Abe‐Kondoh‐Nagano low Reynolds number and the Reynolds stress turbulence models give accurate predictions for photoreactors under transitional or turbulent flow regimes. The performed analysis confirmed that degradation rates of organic contaminants in immobilized photocatalytic reactors are strongly limited by external mass transfer; as a consequence, the degradation prediction capability of the CFD model is largely determined by the external mass transfer prediction performance of the hydrodynamic models used. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Effective design of photocatalytic reactors: influence of radiative transfer on their performance

The role of radiative transfer on a photocatalytic reaction occurring in an annular reactor has been investigated by modeling the degradation of chloroform contaminating the processed aqueous stream. From the analysis of the resulting effects it is apparent that the crucial factor in assessing the performance of the reactor is the distribution of radiant energy absorption rate which, in turn, depends on the mass of catalyst and on the way it is dispersed within the reactor. An optimization of the reactor is conceivable through a proper selection of the catalyst dispersion.     

银镍共掺催化剂光催化氧化硝基苯废水

在紫外光辐射下,以负载于γ-Al_2O_3上的银镍共掺TiO_2为催化剂、H_2O_2为氧化剂的催化氧化体系处理硝基苯废水。通过单因素实验法,研究了p H、H_2O_2用量、光照强度、温度、反应时间、催化剂用量等因素对该体系催化氧化硝基苯效果的影响。结果表明,对于100 m L 250 mg/L的硝基苯废水,当p H=3,30%H_2O_2投加体积为2.0 m L,反应温度为60℃,光照强度为70 W,催化剂投加量为0.5 g,反应时间为50 min时,该体系对废水中硝基苯的去除率可达到99.3%,COD去除率为69%。     

Photocatalytic reactors for environmental remediation: a review

Research in the field of photocatalytic reactors in the past three decades has been an area of extensive and diverse activity with an extensive range of suspended and fixed film photocatalyst configurations being reported. The key considerations for photocatalytic reactors, however, remain the same; effective mass transfer of pollutants to the photocatalyst surface and effective deployments and illumination of the photocatalyst. Photocatalytic reactors have the potential versatility to be applied to the remediation of a range of water and gaseous effluents. Furthermore they have also been applied to the treatment of potable waters. The scale‐up of photocatalytic reactors for waste and potable water treatment plants has also been demonstrated. Systems for the reduction of carbon dioxide to fuel products have also been reported. This paper considers the main photocatalytic reactor configurations that have been reported to date. Copyright © 2011 Society of Chemical Industry     

光催化氧化-MBR组合工艺在有机废水处理中的应用

对光催化氧化和膜生物反应器技术的研究现状、存在问题及与其它工艺相耦合所达到的处理效果进行了分析;提出将两种工艺加以组合运用,弥补各自缺陷,以达到优化处理和回用生物难降解废水的目的。     

Modified polyether-sulfone membrane: a mini review

Polyethersulfone has been widely used as a promising material in medical applications and waste-treatment membranes since it provides excellent mechanical and thermal properties. Hydrophobicity of polyethersulfone is considered one main disadvantage of using this material because hydrophobic surface causes biofouling effects to the membrane which is always thought to be a serious limitation to the use of polyethersulfone in membrane technology. Chemical modification to the material is a promising solution to this problem. More specifically surface modification is an excellent technique to introduce hydrophilic properties and functional groups to the polyethersulfone membrane surface. This review covers chemical modifications of the polyethersulfone and covers different methods used to enhance the hydrophilicity of polyethersulfone membrane. In particular, the addition of amino functional groups to polyethersulfone is used as a fundamental method either to introduce hydrophilic properties or introduce nanomaterials to the surface of polyethersulfone membrane. This work reviews also previous research reports explored the use of amino functionalized polyethersulfone with different nanomaterials to induce biological activity and reduce fouling effects of the fabricated membrane.     

工业废水活性污泥法设计参数和计算公式的探讨

工业废水种类繁多,并且大部分工业废水的水质特性与城镇污水之间存在较大差别,适用于城镇污水处理设计的参数和计算公式不一定适用于工业废水。对我国现行废水处理设计规范中活性污泥法的主要设计参数进行了汇总,分析了这些规范中存在的一些不足之处,包括以BOD5表征有机物含量的合理性,以泥龄法计算生化池容积和剩余污泥量的局限性,以及A/O法缺氧池(区)容积规定存在的误区等,并对工业废水处理的设计提出了建议。     

Use of dimensionless parameters in design of cascade-connected reactors

General relationships applicable to a wide variety of bacterial mediated wastewater treatment processes have been developed using continuous-flow stirred-tank reactors (CSTR) arranged in series. Monod kinetics and mathematical models of reactors-in-series were used to represent the actual conditions resulting from varying degrees of axial dispersion and wastewater qualities. A numerical method was developed and effluent concentrations from an equivalent reactor series expressed based upon a plug-flow reactor with the same inlet and outlet conditions. Using the numerical results obtained, a nomogram has been derived that enables the required hydraulic and solids residence times for a reactor with a given dispersion number to be determined, when inlet and outlet conditions and the coefficients of Monod kinetics are known.     

组合光催化技术在水处理中的应用

光催化氧化技术被认为是在环境保护领域内一种有前途的新型高级氧化技术,与其他处理技术组合成为处理水中污染物的一个热点。论述了氧化剂、电化学、超声、微波、磁化、生物处理等环境治理技术与光催化氧化组合工艺在水处理中的研究和应用现状,并分析了它们与光催化组合反应的机理,对今后其应用前景进行了展望。     

光催化氧化技术处理油田污水研究进展

随着油田开采的不断深入,油田污水的处理问题也日益显著。近年来,油田污水处理技术层出不穷,光催化氧化技术作为一种新的处理工艺,更是以其独特的优势引起了环保主义者的广泛关注。本文介绍了目前国内外油田污水的主要处理技术,并对光催化氧化技术及其在油田污水处理方面的应用进行了深入的探讨研究。     

First-principles modeling, scaling laws and design of structured photocatalytic oxidation reactors for air purification

First-principles, predictive engineering models provide a sound theoretical basis for quantifying the inherent light energy utilization capabilities and performance limitations of candidate commercial photocatalytic oxidation reactor configurations. In particular, these models provide insight into the similarities and differences between photoreactors based on structured honeycombed monoliths, and those based on reticulated foams or other random catalyst supports.

For honeycombed monoliths, a deterministic first-principles radiation field model provides the channel wall light intensity profile down the length of a single channel in the monolith. A three-dimensional developing flow convection–diffusion reaction model employing this radiation field submodel predicts the velocity and concentration fields. The model shows that light intensity gradients in a monolith of typical dimensions are severe, that only a fraction of the monolith can be effectively photo-activated, and as a consequence process performance is largely controlled by light distribution. For a given light source and photocatalyst combination, reactor performance scales according to the aspect ratio of the channeled monolith, the Reynolds number, and the Dahmköhler number.

For randomly structured monoliths, the radiation field must be determined by probablistic methods. Monte Carlo simulations show that the radiation field in such random porous structure scales according to the pore size distribution and the void fraction, and the photocatalyst film thickness. Reactor performance scales by the radiation field, the Peclet number, the Stanton number, and the Dahmköhler number. The complex interrelationship between the random structure of the monolith and the resulting radiation field and mass transfer behavior makes scaling of these reactor types particularly difficult.     

Hydrodynamics study of two different inverse fluidized reactors for the application of wastewater treatment

We investigated the hydrodynamic characteristics of two types of inverse fluidized bed reactors having different driving force for fluidization: aeration and centrifugal force. In the first reactor, only an upward gas flow allows floating low-density polyethylene beads to sink down into liquid phase and to be uniformly distributed over the entire column. The gas velocity at which the solid concentration is uniform throughout the bed expansion decreases with increasing particle loads. In the second reactor, the particle loads do not greatly affect the critical rotating velocity for the homogeneous distribution of solid particles while the geometry of reactor spacing and the type of impeller are more important for the distribution of particles. For the application of waste-water treatment, the inverse fluidized bed with aeration was found to be more efficient than the second type of reactor.     

pH主导不同反应器处理含砷酸性废水性能比较

分别采用外循环上流式厌氧污泥床(UASB)和厌氧续批式(ASBR)反应器处理模拟含砷酸性废水,考察2种厌氧反应器对模拟含砷酸性废水的处理效果及运行特性。结果表明,外循环UASB较ASBR能更好地应用于模拟废水的处理,外循环UASB和ASBR对COD、SO_4~(2-)和As(Ⅲ)的去除率分别达到74.3%、88.7%、63%和42.8%、73.2%、35%。反应体系对模拟废水的处理效果受pH主导:反应体系pH影响SRB的生长、代谢,进而影响对COD和SO42-的去除效果;As(Ⅲ)主要通过与SRB代谢产物(H_2S/S~(2-))的沉淀作用被去除,pH对AsxSy的溶解度影响较大,进而影响As(Ⅲ)的去除效率。     

焦化废水中挥发酚光催化降解去除影响因素的研究

笔者以紫外光为光源,对焦化废水中挥发酚进行了光催化降解去除的实验研究,系统研究了催化剂用量、焦化废水pH值、温度、搅拌强度等因素对去除焦化废水中挥发酚的影响。结果表明,随着催化剂用量和pH值的增加,挥发酚的去除率先提高后降低;挥发酚的去除率首先随着温度和搅拌强度的增加而提高,当达到一定值后基本不再变化。光催化去除挥发酚过程符合一级动力学反应规律。并且随着挥发酚初始浓度的增加,表观速率常数降低。向废水中曝气可提高挥发酚去除率,但曝气量存在最佳范围。     

Electrocoagulation as a revived wastewater treatment method-practical approaches: a review

This review paper aims to demonstrate electrocoagulation (EC) as a revived technology and introduce recent steps of advanced configurations, along with hybrid approaches for the efficient electrochemical treatment of multi-sourced wastewaters. A brief theoretical background is also provided. Moreover, the practical applications of the process are presented, while no previous research has ever attempted to do so. Through online-based data research, it was found that there are 75 manufacturers of EC systems internationally. Industrial case studies reveal actual process conditions and economical data. America holds 33% of global EC systems' manufacturing share and it is considered the leader in EC innovative designs with a percentage of almost 59%. In America and Europe, composite schemes are nearly equivalent to EC autonomous systems, with respective percentages of 41% and 47%. The performance of a two-stage process combining electro-coagulation (EC) and electro-oxidation (EO) has been proven to be the most successful combination in industrial wastewater treatment, representing 54% of hybrid systems available globally. Most of the commercialized EC systems are of small-medium sizes, accounting for 88% of all systems available worldwide. The latest trends on new reactor and electrode configurations are also presented. EC has great potential for further improvement as there is strong academic background to support water treatment companies for industrial scale ups. Cylindrical type reactors tend to dominate due to the ease of their use and maintenance; meanwhile, hybrid systems of EC with EO, membranes and/or adsorption will continue to expand on the market due to the mature level of these technologies and their ease of adaptation. © 2021 Society of Chemical Industry (SCI).     

非均相光催化水处理管式反应器的放大设计

研究了非均相光催化反应器在放大过程中光辐射能衰减和流体返混对其放大过程设计的影响。结果表明,光辐射能随着光源和反应管的中心距的增加急剧衰减,两者呈1 56次方反比关系;管式反应器中流体的返混程度远小于相同反应体积的环型反应器,这有利于提高水中有机污染物的降解率。建立了一套由3组管式反应器串联且光接触面与光源的距离小于10cm的连续光催化水处理中试装置,并对印染废水进行处理。化学需氧量可从150～180mg/L降至50mg/L以下,处理量为50L/h时的出水优于国家一级排放标准。     

Conceptual design of wastewater treatment plants using a design support system

A case study showed the advantages of using a design support system during the design and retrofit of wastewater treatment plants (WWTP). The Manresa WWTP was chosen to demonstrate these advantages. While the records of the decision‐making process used during the Manresa WWTP design were not available to the authors, its original design objectives and the resulting structure and values for its more important variables were. A simplified but plausible design history focusing on the design decisions and not on the detailed modelling of the WWTP was generated with this information. Using such a design history it is possible (1) to evaluate automatically the compliance of alternative design proposals with respect to the design objectives; (2) to study the influence of the weight of the arguments in the selection of the most adequate proposal; (3) to document the decision‐making process; and (4) to assist the designer in the search of specific items within the historical records during the review of the current design or during the retrofit of the plant. © 2000 Society of Chemical Industry