The effects of drag models and operating condition on the simulation of photocatalytic degradation of pesticides in a fluidized bed reactor.

Fluidized bed reactor can enhance mass transfer and increase reaction rate. Numerical simulation helps to optimize fluidized bed reactors. The present paper models the photocatalytic oxidation of 2,4-dichlorophenoxy acetic acid in a fluidized bed reactor using the Eulerian-Eulerian model. The drag models have influences on the distribution of catalysts particles. The bed expands under the fluid flow and reaches a quasi-steady height at approximately 3s. The asymmetric distribution of catalysts with respect to the axis plane is predicted. The Gidaspow model predicts the nearly same bed expansion with the experimental data, whereas the Syamlal-O ' Brien model overestimates it. The simulation results at two pH values are in accordance with the experimental data. The removal in the continuous stirred tank reactor decreases with the increase in flow rate.

Residence time and the concentration of microorganism in the ozone contactor: a CFD simulation on chamber deflectors.

Disinfection is an important step in deep drinking water treatment technology. This study applies computational fluid dynamics to investigate and optimize the hydrodynamics inside the ozone contactor. ANSYS Fluent was used to solve all the control equations. A step method is used to simulate the residence time distribution. The mean residence time is simulated under the Eulerian framework. The deflectors are installed in chambers to direct flow. The deflectors allow for a more uniform flow and a longer mean residence time within the contactor. The baffling factor showed that the deflectors could reduce the short-circuit effect in the contactor and improve the disinfection efficiency by 34.6% compared to the original reactor. The Morrill factor coefficient is improved by 22.8% compared to the original reactor. According to the Aral-Demirel index, contactors with deflectors are significantly better than other baffle-type contactors. The presence of the deflectors increased the microbial inactivation efficiency from 95.3 to 96.5%. The optimal deflector height should be controlled between 30 and 60 mm.

CFD modeling of ethylene degradation in gas-phase photocatalytic reactors.

Photocatalytic oxidation is a promising technology to degrade volatile organic compounds. The performance of photocatalytic reactors is affected by the hydrodynamics, radiation transfer, mass transfer and reaction kinetics. Baffles may improve the hydrodynamics. The effect of baffles on heterogeneous photocatalytic oxidation of gas-phase ethylene in three annular reactors is simulated using computational fluid dynamics. ANSYS Fluent is used to solve all governing equations. Baffles can improve the uniformity of flow and prolong the residence time. The residence time of the C-type reactor and B-type reactor is 0.5% greater than the unbaffled reactor. Baffles have little effect on the radiation distribution. The concentric arrangement of lamp and the reactor leads to a radial dominance of radiation. The effect of baffles on the diffusion of ethylene is complex. The effective diffusion coefficient at the catalyst surface in the C-type reactor decreases 9.5% and that in the B-type reactor increases 3% with respect to the unbaffled reactor. The outlet ethylene concentration is 4.19 ppmv for the U-type reactor, 3.93 ppmv for the C-type reactor and 3.62 ppmv for the B-type reactor. The optimal performance in the B-type reactor is due to the large diffusion coefficient of ethylene. The arrangement of baffles should enlarge the effective diffusion coefficient at the catalyst surface as far as possible.

Modeling VOCs emission/sorption with variable operating parameters and general boundary conditions.

An integrated model of VOCs emission/sorption from/on dry building materials with a general boundary condition, variable air exchange rate and inlet concentration is developed. An analytical solution is obtained by using the generalized integral transform technique. Good agreements are obtained between the present model and the experimental data. The effects of environmental conditions on the emission are investigated. The emission from two surfaces can increase the concentration of hexanal in the air and decrease the initial emission rate at x=δ with the increase in mass transfer coefficient at x=0. Periodical inlet concentration can lead to the periodic variation of materials between a source and a sink. Ventilation can keep the concentration in the air at a low level and help to decrease the concentration of hexanal in materials. The present model is capable of simulating indoor air quality due to the VOCs emission and sorption.

Contact tracing of syphilis-seropositive pregnant women and syphilis-infection among their male partners in Bao'an district, Shenzhen, China.

BACKGROUND: Untreated male partners are a critical source of maternal re-infection. Contact tracing is a good way to identify infection among partners and reduce risk of mother-to-child transmission related to maternal re-infection. This study aimed to analyze the current situation and related factors of contact tracing of syphilis-seropositive pregnant women and syphilis-infection among their male partners. METHOD: Data of syphilis-seropositive pregnant women and their male partners attending clinic for syphilis-screening were obtained from the Shenzhen Program for Prevention of Congenital Syphilis. Contact tracing rate of syphilis-seropositive pregnant women and syphilis prevalence among male partners were counted, and related factors were also analyzed using a random-effects logistic regression model. RESULT: Of the 1299 syphilis-seropositive pregnant women, 74.1% (963/1299) had their male partners receiving syphilis-screening and 19.1% (184/963) of male partners were syphilis-infected. For pregnant women, being divorced (adjusted odds ratio [AOR] =0.39; 95%CI: 0.17-0.87), seeking for emergency services at their first antenatal clinics visits (AOR = 0.58; 95%CI: 0.44-0.77), reporting willingness to notify partner(AOR = 7.65; 95%CI: 4.69-12.49), multi-partners (AOR = 1.38; 95%CI:1.03-1.86) and having a history of drug abuse (AOR = 0.37; 95%CI: 0.14-1.00)were independently associated with successful contact tracing. For male partners, of minority ethnicity (AOR = 4.15; 95%CI: 1.66-10.34), age at first sex>20(AOR = 0.57; 95%CI: 0.37-0.87), reporting multi-partners (AOR = 1.60; 95%CI: 1.04-2.46), having a history of drug abuse (AOR = 4.07; 95%CI: 1.31-12.64) were independently associated with syphilis-infection. In addition, pregnant women with TRUST titer ≥1:8 (AOR = 2.81; 95%CI: 1.87-4.21), having a history of adverse pregnancy outcomes (AOR = 1.70; 95%CI: 1.14-2.53), reporting multi-partners (AOR = 0.43; 95%CI: 0.29-0.64) and reporting the current partner as the source of syphilis (AOR = 5.05; 95%CI: 2.82-9.03) were independently associated with partners' syphilis-infection. CONCLUSION: Contact tracing is feasible and effective in identifying syphilis-infected partners among syphilis-seropositive pregnant women. Contact tracing is associated with many factors such as women's marital status, services at their first antenatal clinics visit and willingness of partner notification. Partners' ethnicity, age at first sex, multi-partners and history of drug abuse as well as women's levels of TRUST titer were associated with partners' syphilis-infection.

Oxygen-rich bismuth oxychloride Bi12O17Cl2 materials: construction, characterization, and sonocatalytic degradation performance.

In this study, a series of oxygen-rich bismuth oxychloride Bi12O17Cl2 samples were prepared at different calcination temperatures and characterized by X-ray diffraction patterns, UV-Vis diffuse reflectance spectra, scanning electron microscope, X-ray energy dispersion spectroscope, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy. The calcination temperature greatly affected microstructures and band structures of as-prepared samples, further influencing sonocatalytic degradation efficiencies over dye Rhodamine B. Some dependant factors such as ultrasonic power, catalyst dosage, pH value, initial concentration of Rhodamine B, and reaction temperature were systematically investigated and the robust sample Bi12O17Cl2-550 with a favorable microstructure and band structure provided the best sonocatalytic removal efficiency around 90% at the optimal condition. Based upon reactive species entrapping and hydroxyl radical detection experiments, a primary sonocatalysis mechanism was eventually speculated.

In-situ establishment of binary composites α-Fe2O3/Bi12O17Cl2 with both photocatalytic and photo-Fenton features.

A set of binary composites α-Fe2O3/Bi12O17Cl2 were established through an in-situ deposition route and these samples were systematically characterized by a collection of analytical techniques. Scanning electron microscopy, UV-vis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy proved the coexistence of expected two components. High resolution transmission electron microscopy and selected-area electron diffraction indicated the formation of heterojunction domains with the intimate contact of both semiconductors. The degradation behavior of as-synthesized samples was evaluated under visible-light irradiation and the enhanced outcome was observed over dye methyl orange (MO) and colorless 2,4-dichlorophenol (2,4-DCP), mainly attributing to favorable optical and morphological merits, and a suitable well-aligned band structure in these binary composites with a suitable phase composition as well. In addition, these composites showed an obvious photo-Fenton feature that significantly improved the catalytic degradation efficiency over 2,4-DCP when the reagent H2O2 was introduced, indicating the destruction efficiency was controlled by a synergtic effect from both photocatalytic and photo-Fenton degradation routes. Based upon the detection of reactive radical species, a primary synergistic mechanism was eventually speculated.

A visible-light-driven heterojuncted composite WO3/Bi12O17Cl2: Synthesis, characterization, and improved photocatalytic performance.

Novel visible-light-driven WO3/Bi12O17Cl2 heterojuncted photocatalysts with different mass ratios were successfully fabricated by a facile hydrothermal process and were characterized by XRD, UV-Vis DRS, SEM, TEM, HRTEM, XPS, BET, Raman, PL, and ESR techniques. The original morphology of Bi12O17Cl2 was maintained after the addition of WO3 nanoparticles and the specific surface area values of WBx composites were obviously enlarged. The intimate contact of both components in HRTEM confirmed the generation of smooth phase interface. These as-prepared samples were subjected to the photocatalytic degradation of dye rhodamine B (RhB) and tetracycline hydrochloride (TC) under visible light irradiation (λ≥420nm). Under identical conditions, WBx composites showed greatly enhanced photocatalytic performance in comparison to bare WO3 and Bi12O17Cl2. Especially, the sample WB0.5 exhibited the highest photocatalytic removal outcome over RhB among all tested candidates and owned an apparent rate constant about 73.7, 7.1, 15.8 times of those pure WO3, Bi12O17Cl2, and N-doped TiO2, respectively. The enhancement of photocatalytic capability of composites mainly attributed to the suitable morphology, enlarged specific surface areas, strengthened optical property, and favorable well-aligned straddling band-structures. Active species entrapping experiments confirmed holes and superoxide radicals as major oxidative species, by which, a possible photocatalytic mechanism was primarily proposed.

Three dimensional Eulerian-Eulerian simulation on hydrodynamics in dissolved air flotation tank with different turbulence models.

The Eulerian-Eulerian approach is used to simulate the two phase flow of air and water in a dissolved air flotation (DAF) tank. Unsteady simulation is adopted to obtain the quasi-steady result. The two dimensional model cannot capture the three dimensional feature of flow pattern in the tank. The three dimensional model reproduces the stratification structure observed in the experiment and obtains the satisfactory volume fraction of air bubbles in the separation zone. To account for the turbulence effect, four two-equation turbulence models are evaluated. Although all turbulence models capture the stratification structure in the separation zone, the re-normalization group theory (RNG) k-ɛ model obtains the best agreement with the experimental data. The effect of bubble diameter on the performance of DAF tank is simulated. Small air bubbles can form a big range of high volume fraction of air bubbles, which helps to remove the suspended matters.

CFD simulation of an unbaffled stirred tank reactor driven by a magnetic rod: assessment of turbulence models.

A simulation of an unbaffled stirred tank reactor driven by a magnetic stirring rod was carried out in a moving reference frame. The free surface of unbaffled stirred tank was captured by Euler-Euler model coupled with the volume of fluid (VOF) method. The re-normalization group (RNG) k-ɛ model, large eddy simulation (LES) model and detached eddy simulation (DES) model were evaluated for simulating the flow field in the stirred tank. All turbulence models can reproduce the tangential velocity in an unbaffled stirred tank with a rotational speed of 150 rpm, 250 rpm and 400 rpm, respectively. Radial velocity is underpredicted by the three models. LES model and RNG k-ɛ model predict the better tangential velocity and axial velocity, respectively. RNG k-ɛ model is recommended for the simulation of the flow in an unbaffled stirred tank with magnetic rod due to its computational effort.

Poly(vinyl pyrrolidone)-assisted hydrothermal synthesis and enhanced visible-light photocatalytic performance of oxygen-rich bismuth oxychlorides.

A series of novel oxygen-rich bismuth oxychloride (Bi12O17Cl2) were synthesized through a facile poly(vinyl pyrrolidone) (PVP)-assisted hydrothermal route. These obtained Bi12O17Cl2 samples were characterized by various physicochemical techniques. It was found that a proper addition amount of PVP could promote the transformation of Bi12O17Cl2 morphology from irregular clusters to three-dimensional hierarchical flower-like microspheres that were nominated as sample BP2. As-synthesized samples were subjected to a photocatalytic degradation of dye Rhodamine B (RhB) or 2,4-dichlorophenol (2,4-DCP) under visible light. Among all candidates, the sample BP2 with a hierarchical flower-like morphology showed the best degradation efficiency for RhB and 2,4-DCP. The apparent rate constant of sample BP2 in terms of degradation of RhB was nearly 5.7 and 45 times that of unmodified BP0 and N-TiO2. The enhanced photocatalytic performance could be ascribed to synergetic effects including unique hierarchical morphologies, large specific surface area, small particle size, good crystallinity, and suitable band structures. A possible mechanism of catalytic degradation was finally proposed basing upon the active species trapping experiments.