Modeling of an annular photocatalytic reactor for water purification: oxidation of pesticides

Photocatalytic oxidation (PCO) over titanium dioxide (TiO2) is a "green" sustainable process for the treatment and purification of water and wastewater. However, the application of PCO for wastewater treatment on an industrial scale is currently hindered by a lack of simple mathematical models that can be readily applied to reactor design. Current models are either too simplistic or too rigorous to be useful in photocatalytic reactor design, scale-up, and optimization. In this paper a simple mathematical model is presented for slurry, annular, photocatalytic reactors that still retains the essential elements of a rigorous approach while providing simple solutions. The model extends the applicability of the thin-film model of photocatalytic reactors previously presented to include the case of geometrically thick photoreactors (i.e., those reactors in which the thickness of the annular zone is significant as compared to the outer radius of the reactor). The model uses a novel six-flux absorption-scattering model to represent the radiation field in the reaction space, which assumes that scattered photons follow the route of the six directions of the Cartesian coordinates. The model was successfully validated with experimental results from the photocatalytic oxidation of the pesticide isoproturon in an experimental reactor. The mathematical model presented may be used as a tool for the design, scale-up, and optimization of annular photocatalytic reactors for water treatment and purification.     

Evaluation of the intrinsic photocatalytic oxidation kinetics of indoor air pollutants

This paper presents a methodology for the evaluation of the intrinsic photocatalytic oxidation (PCO) kinetics of indoor air pollutants. It combines computational fluid dynamics (CFD) modeling of the fluid flow in the reactor with radiation field modeling and photocatalytic reaction kinetics to yield a rigorous model of a flat-plate, single-pass, flow-through photocatalytic reactor for indoor air purification. This method was applied to model the PCO of trichloroethylene (TCE) in humidified air and to derive kinetic parameters directly from kinetic data in an integral flow reactor. Steady-state PCO experiments of TCE over irradiated TiO2 (Degussa P25) thin films immobilized on glass supports were carried out at different radiation intensities, flow rates, and inlet substrate concentrations. The oxidation rate of TCE was found to be first-order on the incident photon flux and to follow a Langmuir-Hinshelwood type reaction kinetics rate law. Mass transfer resistances were observed at Reynolds numbers less than 46. Apparent quantum yields were found to be up to 0.97 mol Einstein(-1). A comparison of the model prediction with the experimental results in an integral reactor yielded pollutant-specific kinetic rate parameters which were independent of reactor geometry, radiation field, and fluid-dynamics. The kinetic parameters would,therefore, be more universally applicable to the design and scale-up of photocatalytic reactors for indoor air purification.     

同轴静电纺多孔氧化锌薄膜制备及其光催化性能

为制备轻质且具有大比表面积的光催化剂,针对静电纺丝中聚合物载体大都有污染且不可再生的问题,以丝素蛋白为载体,通过同轴静电纺丝制备醋酸锌/丝素(ZnAc/SF)纳米纤维薄膜,然后浸渍于硫化钠(Na₂S)溶液中制备硫化锌(ZnS)/SF纳米纤维薄膜,最后经煅烧得到ZnS/C纳米纤维薄膜和多孔ZnO薄膜。借助X射线衍射仪、X射线光电子能谱仪、扫描电子显微镜、紫外-可见分光光度计对薄膜的结构和性能进行表征,并通过亚甲基蓝催化降解实验研究其光催化性能。结果表明:多孔ZnO薄膜是由10~20 nm颗粒组成的介孔网络组织,具有吸收紫外线能力,比ZnS/C纳米纤维薄膜有更强的光催化作用,对亚甲基蓝的降解效率可达99.5%;多孔ZnO薄膜可进行回收利用,4次循环后降解效率达91%。     

Cellulose-based UVB-shielding Film with High Visible Transparency

Cellulose-based Ultraviolet B (UVB)-shielding films were prepared by coating SnO₂ film onto regenerated cellulose (RGC) film through a magnetron sputtering method. The dependence of the crystalline quality and optical property of the SnO₂ film on the sputtering power was systematically studied. High quality SnO₂ film was grown on RGC film at an optimum sputtering power of 150 W. The optical properties of the composite film can be tailored by adjusting the thickness of the SnO₂ film. The SnO₂/RGC composite film exhibited high visible transparency and excellent UVB-shielding capacity, which can be used for protection against short-wave radiation.     

Baking Studies and Nutritional Value of Bread Supplemented with Full-Fat Sweet Lupine Flour (L. albus cv Multolupa)

Full-fat sweet lupine flour (FFLF) was used to replace 3, 6, 9 and 12% of the wheat flour (WF) in bread. Physical characteristics of the dough, and the chemical composition and biological quality of the breads were investigated. Farinological studies showed that water absorption increased gradually from 60% for WF to 77% for a blend with 12% FFLF. Developing time, weakening of dough and valorimeter value were adversely modified by addition of FFLF. Different levels of FFLF increased in water absorption, loaf volume and loaf weight as compared to all wheat bread. However, specific loaf volume remained constant (3.72) up to 6% FFLF, then decreased. Protein content of wheat bread increased from 10.3% for the control to 11.7% for 9% FFLF bread. PER increased from 1.72 for the control bread to 2.00 for 9% lupine-bread (p<0.01). Bread with 9% FFLF is a possibility for using this legume in human feeding.     

Bread quality and nutritional value of 'Marraqueta' and 'Hallulla' supplemented with full-fat sweet lupin flour (Lupinus albus cv. Multolupa)

'Marraqueta' and 'Hallulla' breads, widely consumed in Chile, were enriched with 6, 9 and 12% full-fat sweet lupin flour (FFLF) containing a small amount of alkaloids (0.025%) and 42.8% protein. Physical characteristics of the dough and the chemical composition and biological quality of the breads were investigated. Farinograph measurements showed that water absorption increased gradually from 61.3% for wheat flour to 79.8% for a blend with 12% FFLF. Developing time, weakening of dough and valorimeter value were not severely modified. Different levels of FFLF increased loaf weight as compared to all wheat bread. Protein content increased from 13.2% for the control to about 16% for 12% FFLF breads. Protein efficiency ratio (PER) values significantly increased (P < 0.01) for 12% FFLF breads: 'Marraqueta' from 1.10±0.09 to 1.59±0.12 and 'Hallulla' from 1.21±0.09 to 1.63±0.07. Apparent digestibility was about 86% and was not changed by FFLF inclusion up to 12%. Twelve per cent FFLF is a recommendable level to enrich 'Hallulla' and 'Marraqueta' in biological quality without affecting the farinological parameters. The results of acceptability tests will be published in due course.     

Long‐chain fatty acid supplemented infant formula does not influence calcium and magnesium bioavailability in weanling rats

The influence of infant formula supplementation with long‐chain‐polyunsaturated fatty acids (LCPUFA) on calcium and magnesium bioavailability was assessed in rats. Two test diets containing a plain, unsupplemented (PF) or supplemented (SF) infant formula as the fat source and a control diet (C) were administered to weaning rats and food intake and body weight gain were monitored for 28 days. In order to assess calcium and magnesium bioavailability, during the last week faeces and urine were collected and apparent absorption and retention were calculated. Food intake and body weight showed no significant differences between PF and SF but were lower in both groups compared with C. Calcium and magnesium intake did not differ between PF and SF, although both parameters were lower compared with C. Calcium absorption efficiency in PF and SF was significantly higher than in C. However, both groups showed higher urinary calcium excretion and thus no differences were observed in calcium retention. Magnesium absorption efficiency was also significantly higher in PF and SF compared with C, but magnesium absorption was significantly lower in SF compared with PF and C. Nevertheless, urinary magnesium excretion and magnesium retention were similar in the three groups. The consumption of a diet containing an infant formula supplemented with LCPUFA compared with the plain formula does not affect calcium and magnesium bioavailability in rats. Copyright © 2005 Society of Chemical Industry     

Effect of oxygen in a thin-film rotating disk photocatalytic reactor

A novel experimental procedure was developed to measure oxygen mass transfer during the oxygenation of water in a thin film of a rotating disk photocatalytic reactor (RDPR). The increase in dissolved oxygen (DO) of initially deaerated water was monitored with time in the reactor vessel at different disk angular velocities after exposure of the reactor to the atmosphere. Oxygenation was predominantly achieved by oxygen mass transport through the thin liquid film carried by the disk and to a much lesser extent by direct oxygenation of the water in the reactor vessel via a surface renewal mechanism. A mathematical model was developed to simulate the phenomenon considering both cases of presence and absence of oxygen mass transport limitations. In the latter case, the model considered that the amount of liquid carried by the disk was saturated with oxygen when returning to the reactor vessel. On the basis of the model and the experimental data, it was proven that mass-transfer limitations existed until the water in the reactor vessel became saturated with oxygen. Results obtained from the model were validated by an alternative analysis using dimensionless groups characteristic to the system. The study revealed that the mass-transfer coefficient increased linearly with disk angular velocity and thus disk Reynolds number. The results showed that oxygen mass-transfer limitations decreased with increasing disk angular velocity, mainly due to an increase in the overall mass-transfer coefficient. In the presence of UV radiation, the influence of oxygen on the photocatalytic oxidation of 4-chlorobenzoic acid was investigated in the RDPR operated in batch and continuous mode. The photocatalytic reactions occurred in a thin film of liquid carried by the disk in the presence of UV radiation and ST-B01 composite spherical ceramic (SiO2/Al2O3) balls coated with anatase TiO2 catalyst. It was found that the initial degradation rate followed Langmuir kinetics with respect to oxygen concentration in the gas phase. When the oxygen concentration in the gas phase surpassed that in air, the degradation rates did not improve significantly, suggesting that operation with air instead of oxygen is most probably a more realistic practical choice. Measurements of DO during the presence and absence of UV radiation suggested that the photocatalytic reactions were mainly oxygen concentration-limited rather than oxygen mass-transfer-limited.     

An Integral Method Analysis of Steam Infusion Heating of a Free Falling Film

An analytical and experimental study of direct contact condensation to a free falling film of liquid was modeled. The thermal energy equation governing the steady state heat transfer was solved by an integral technique. The predictive model for velocity and temperature profiles was verified experimentally. Water was used as the test fluid in a steam infusion unit at flow rates of 1.6-2.3 L/min. The water fell in intact sheets 7.6 x 10^?2 m wide and at an initial thickness of 8.9 x 10^?4 m. Fluid velocity and average fluid temperatures compared well with model predictions within the experimental range.     

异形板外流降膜蒸发器及其研究

文中评述了异形要反外流降膜蒸发器结构及其特点，介绍了异形板上降落液膜传热性能的研究结果和一种新型布液装置及其性能，对于开发和扩大弄形板外流降膜蒸发器在食品工业听的应用具有现实意义。     

Some critical structure factors of titanium oxide nanotube array in its photocatalytic activity

A highly ordered TiO2 nanotube array on Ti substrate was fabricated by using an electrochemical anodic oxidation method. The morphology, crystalline phase, and photoelectrochemical property of the nanotube array were characterized. The photocatalytic activity of the nanotube array was evaluated by the decolorization of methyl orange in aqueous solution using the different light sources. The effects of structure and morphology of the nanotube array on its photocatalytic activity were investigated. It was found that the photoabsorption behavior of the TiO2 nanotube film depended on the structures of the nanotube array. The nanotube array films exhibited a drastically enhanced photocurrent, and a higher photocatalytic activity compared with the TiO2 nanoparticle film prepared by the regular sol-gel method. The experimental results indicated that the film thickness markedly influenced the photocatalytic activity of nanotube array film, and the 2.5 microm-thick TiO2 nanotube array film appeared a maximum photodegradation efficiency to methyl orange. However, for a given nanotube length, the tube diameter was only very slightly affected the photocatalytic efficiency in this work. The explanation for some critical structure factors of TiO2 nanotube array in the photocatalytic activity was discussed as well.     

金属丝径大小对液膜流动影响的CFD研究

精馏过程气液两相流动分布特征对分离效率具有重要影响,为研究金属丝网波纹填料表面液膜流体动力学特性,建立基于VOF法的液膜在金属丝网表面上的气—液两相逆流CFD模型,并根据液膜流动特点考虑了表面张力动量源项和气液界面作用力动量源项。模拟结果与文献流动形式相符,表明文中提出的CFD液膜流动模型具有一定的可靠性。文中主要考察丝径大小对液膜流动的影响,模拟结果表明适当改变丝径的大小有助于改善液膜的稳定,对于提高丝网填料气液之间的传质效率有重要意义。     

Ultraviolet disinfection: similitude in Taylor-Couette and channel flow

The inactivation data for Escherichia coli are recorded for the three reactor geometries of Taylor-Couette flow and flow between either concentric cylinders or a square channel. All of the data are shown to be correlated with the assumption of plug flow. In particular, the effects of nonuniform radiation levels are accounted for by integration across the fluid channel as done previously. However, a new correction factor is introduced that is shown to be inversely proportional to the laminar, velocity boundary thickness to account for the effects of a concentration boundary layer of surviving pathogen. It has also been demonstrated that the common problems of nonuniform radiation levels and concentration boundary layer effects in UV reactors are largely eliminated with the use of Taylor-Couette flow. Moreover, the repetitive exposure of fluid parcels to a small number of lamps in the rotating Taylor-Couette flow decreases maintainance requirements compared to the hydrodynamic equivalent of cross-flow over a tube bank or lamp array. Over a 3-log reduction in the inactivation of E. coli was demonstrated compared to a conventional channel with the same radiation dosage. Moreover, greater than a 2-log reduction was evident compared to flow through concentric cylinders.     

Use of multiwavelength transmission spectroscopy for the characterization of Cryptosporidium parvum oocysts: quantitative interpretation

Combined scattering and absorption properties of suspended particles can be obtained as a function of wavelength by measuring the complete ultraviolet-visible (UV-vis) spectrum. This research reports on the quantitative interpretation of measured UV-vis spectra of Cryptosporidium parvum oocyst suspensions obtained from several commercial sources and evaluated using two different purification techniques. The reproducibility of the measured spectral data was assessed, and the quantitative interpretation of the oocyst spectra in terms of the particle size and the chemical composition of the particles are reported herein. The interpretation model of the spectra is based on light scattering theory, spectral deconvolution techniques, and on the approximation of the wavelength-dependent optical properties of the basic constituents of living organisms. A characteristic set of optical properties for C. parvum oocysts has been determined as a function of wavelength and used for the quantitative interpretation of UV-vis spectra. The results from the spectral deconvolution show quantitative differences among oocyst preparations. These results represent the first step in establishing a set of critical parameters (e.g., oocyst size and chemical composition) necessary for the detection and identification of C. parvum oocysts in water using spectroscopy.     

UV reactor performance modeling by Eulerian and Lagrangian methods

A study was performed to investigate the influence of hydrodynamics on the performance of ultraviolet (UV) reactors. Two general UV disinfection models were developed by integrating fluence rate models and inactivation kinetics within a commercial computational fluid dynamics (CFD) software package to predict reactor performances. Both a particle tracking (Lagrangian) random walk model and a volumetric reaction rate based (Eulerian) model were implemented. Simulations were performed for two characteristic annular single-lamp UV reactor configurations, with inlets concentric (L-shape) and normal (U-shape) to the reactor axis. Two fluence rate models, the infinite line source assumption and the finite line or multiple point source summation (MPSS), were used. First-order inactivation kinetics was assumed for disinfection, with rate constants from MS2 bacteriophage assays. The simulation results provided detailed information on the velocity profiles, reaction rates, range of absorbed dose, and areas of short circuiting of the UV reactors. Model predictions based on both the Lagrangian dose distribution and Eulerian concentration distribution were in good agreement with each other at high flow rates but showed some discrepancies at lower flow rates. Experimental verification of the general models was performed by simulating the disinfection performance of an industrial prototype UV reactor. Results from both integration approaches were shown to be in good agreement with the provided biodosimetry data.     

Effects of photocatalysis on biological decolorization reactor and biological activity of isolated photosynthetic bacteria

In the treatment of synthetic dye wastewater by photosynthetic bacteria under optical irradiation, excessive algal growth and adhesion on the wall of the reactor has been a severe problem. A laboratory scale flow-through model reactor with thin film photocatalysis for improving the efficiency of optical irradiation and controlling algal adhesion is presented. The system showed the efficiency of continuous biodegradation of dye was improved significantly by thin film photocatalysis. Moreover, the effects of photocatalysis on the color removal activity and the growth of isolated photosynthetic bacteria were investigated in batch experiment. Although photocatalytic reactions of TiO2 could inhibit the growth of isolated photosynthetic bacteria, the negative effects of photocatalysis on photosynthetic bacterial growth and decolorant activity were negligible under UV+FL irradiation. These results implicate the possibility of using thin film photocatalysis for controlling algal adhesion and enhancing the decolorant efficiency of photosynthetic bacteria.     

异形竖板降膜蒸发器浓缩耐温淀粉酶溶液的传热性能

研究了异形竖板降膜蒸发器浓缩耐温淀粉酶溶液时的传热性能,得出了传热系数与蒸发温度、单位周边流量,传热温差和酶液浓度之间的实验关联式,分析了一些主要因素对传热性能的影响,并与管式降膜蒸发器的传热性能进行了比较,研究结果表明,异形竖板降膜蒸发器具有良好的传热性能,优于管式降膜蒸发器,适宜浓缩耐温淀粉酶。     

不同冻结方式对金鲳鱼水分、组织结构与品质变化的影响

为研究不同冻结方式对金鲳鱼水分、组织结构与品质变化的影响,本实验以鲜活金鲳鱼为原料,分别采用平板冻结（plate freezer,PF）、螺旋式冻结（spiral freezer,SF）、超低温冻结（cryogenic freezer,CF）和冰柜冻结（ordinary freezer,OF）处理样品,随后通过pH值、挥发性盐基氮（total volatile basis nitrogen,TVB-N）含量、质构特性、色泽、保水性（持水率、蒸煮损失率和汁液损失率）等指标,并结合低场核磁共振与光学显微镜观察,综合评价4 种冻结处理方式对冷冻金鲳鱼水分、组织结构与品质变化的影响。结果发现：整体而言,SF组样品的指标均优于OF组,CF组样品与SF组样品的pH值和TVB-N含量较低,其质构、色泽与保水性变化速率低于PF与OF组。由低场核磁共振结果可知,SF处理对样品水分流失影响最小。由肌肉组织微观结构观察可知,CF组与SF组样品肌原纤维间隙小、分散均匀,组织冰晶细小,金鲳鱼的综合品质较好。因此,与其他冻结方式相比,SF处理的综合效果最佳。     

New insight in characterization of red wine astringency using soft tribology method

The variation of friction coefficient (μ) of model wine and model saliva mixtures with entrainment speed (V_R) on simulated oral surfaces was evaluated by oral tribology. Combined with techniques of dynamic light scattering (DLS), atomic force microscopy (AFM), rheometer, and quartz crystal microbalance with dissipation monitoring (QCM-D), the correlation between characteristics of the model wine and model saliva mixtures (particle size and morphology, suspension viscosity, adsorption film thickness, and viscoelasticity) and the oral lubrication loss was established. The results showed that the higher the concentration of tannin in the model wine, the larger the size of the complexes with the model saliva, and the higher the thickness, viscoelasticity, and roughness of the adsorption film formed, which resulted in the increase of friction coefficient in the boundary lubrication regime. Different from previous results, it is found that the maximum value of the friction coefficient (μ_max) in the boundary regime has the best positive correlation with the astringency perception intensity of the model wine accordingly.