Predicting the degradation potential of Acid blue 113 by different oxidants using quantum chemical analysis.

In this work, quantum chemical analysis was used to predict the degradation potential of a recalcitrant dye, Acid blue 113, by hydrogen peroxide, ozone, hydroxyl radical and sulfate radical. Geometry optimization and frequency calculations were performed at 'Hartree Fock', 'Becke, 3-parameter, Lee-Yang-Parr' and 'Modified Perdew-Wang exchange combined with PW91 correlation' levels of study using 6-31G* and 6-31G** basis sets. The Fourier Transform-Raman spectra of Acid blue 113 were recorded and a complete analysis on vibrational assignment and fundamental modes of model compound was performed. Natural bond orbital analysis revealed that Acid blue 113 has a highly stable structure due to strong intermolecular and intra-molecular interactions. Mulliken charge distribution and molecular electrostatic potential map of the dye also showed a strong influence of functional groups on the neighboring atoms. Subsequently, the reactivity of the dye towards the oxidants was compared based on the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy values. The results showed that Acid blue 113 with a HOMO value -5.227 eV exhibits a nucleophilic characteristic, with a high propensity to be degraded by ozone and hydroxyl radical due to their lower HOMO-LUMO energy gaps of 4.99 and 4.22 eV respectively. On the other hand, sulfate radical and hydrogen peroxide exhibit higher HOMO-LUMO energy gaps of 7.92 eV and 8.10 eV respectively, indicating their lower reactivity towards Acid blue 113. We conclude that oxidation processes based on hydroxyl radical and ozone would offer a more viable option for the degradation of Acid blue 113. This study shows that quantum chemical analysis can assist in selecting appropriate advanced oxidation processes for the treatment of textile effluent.

Application of doped photocatalysts for organic pollutant degradation - A review.

Advanced oxidation process involves production of hydroxyl radical for industrial wastewater treatment. This method is based on the irradiation of UV light to photocatalysts such as TiO2 and ZnO for photodegradation of pollutant. UV light is used for irradiation in photocatalytic process because TiO2 has a high band gap energy which is around 3.2 eV. There can be shift adsorption to visible light by reducing the band gap energy to below 3.2 eV. Doped catalyst is one of the means to reduce band gap energy. Different methods are used for doped catalyst which uses transition metals and titanium dioxide. The band gap energy of three types of transition metals Fe, Cd and Co after being doped with TiO2, are around 2.88 ev, 2.97ev and 2.96 ev, respectively which are all below TiO2 energy. Some of the transition metals change the energy level to below 3.2 eV and the adsorption shifts to visible light for degradation of industrial pollutant after being doped with titanium dioxide. This paper aims at providing a deep insight into advanced oxidation processes, photocatalysts and their applications in wastewater treatment, doping processes and the effects of operational factors on photocatalytic degradation.

Investigation of mass transfer intensification under power ultrasound irradiation using 3D computational simulation: A comparative analysis.

This paper aims at investigating the influence of acoustic streaming induced by low-frequency (24kHz) ultrasound irradiation on mass transfer in a two-phase system. The main objective is to discuss the possible mass transfer improvements under ultrasound irradiation. Three analyses were conducted: i) experimental analysis of mass transfer under ultrasound irradiation; ii) comparative analysis between the results of the ultrasound assisted mass transfer with that obtained from mechanically stirring; and iii) computational analysis of the systems using 3D CFD simulation. In the experimental part, the interactive effects of liquid rheological properties, ultrasound power and superficial gas velocity on mass transfer were investigated in two different sonicators. The results were then compared with that of mechanical stirring. In the computational part, the results were illustrated as a function of acoustic streaming behaviour, fluid flow pattern, gas/liquid volume fraction and turbulence in the two-phase system and finally the mass transfer coefficient was specified. It was found that additional turbulence created by ultrasound played the most important role on intensifying the mass transfer phenomena compared to that in stirred vessel. Furthermore, long residence time which depends on geometrical parameters is another key for mass transfer. The results obtained in the present study would help researchers understand the role of ultrasound as an energy source and acoustic streaming as one of the most important of ultrasound waves on intensifying gas-liquid mass transfer in a two-phase system and can be a breakthrough in the design procedure as no similar studies were found in the existing literature.

A comparative fluid flow characterisation in a low frequency/high power sonoreactor and mechanical stirred vessel.

This study aims at analysing the jet-like acoustic streaming generated under low-frequency and high-power ultrasound irradiation and comparing it with fluid streaming generated by traditional mechanical mixing. The main characteristics of fluid flow, which include radial, axial and tangential terms of velocity and their effects on fluid flow pattern, pressure distribution, axial mixing time and turbulence intensity were considered at different power inputs. Both 3D CFD simulation and Particle Image Velocimetry (PIV) were used in this study. The CFD results indicated that the jet-like acoustic streaming reached the velocity magnitude of 145 cm/s at 400 W, which reduced the mixing time to 1.38 s. However, the minimum mixing time of 3.18 s corresponding to the impeller rotational speed of 800 RPM was observed for mechanical stirring. A uniform axial flow pattern was generated under ultrasound irradiation whereas the tangential flow pattern was more prominent in the stirred vessel. Besides, the highest turbulence was observed in the vicinity of the ultrasound transducer and impeller with the values of 138% and 82% for the ultrasonicator and stirred vessel, respectively. The predicted fluid flow pattern under ultrasound irradiation was in a reasonable agreement with that obtained from PIV, with a reasonable accuracy.

Influence of ultrasound power on acoustic streaming and micro-bubbles formations in a low frequency sono-reactor: mathematical and 3D computational simulation.

This paper aims at investigating the influence of ultrasound power amplitude on liquid behaviour in a low-frequency (24 kHz) sono-reactor. Three types of analysis were employed: (i) mechanical analysis of micro-bubbles formation and their activities/characteristics using mathematical modelling. (ii) Numerical analysis of acoustic streaming, fluid flow pattern, volume fraction of micro-bubbles and turbulence using 3D CFD simulation. (iii) Practical analysis of fluid flow pattern and acoustic streaming under ultrasound irradiation using Particle Image Velocimetry (PIV). In mathematical modelling, a lone micro bubble generated under power ultrasound irradiation was mechanistically analysed. Its characteristics were illustrated as a function of bubble radius, internal temperature and pressure (hot spot conditions) and oscillation (pulsation) velocity. The results showed that ultrasound power significantly affected the conditions of hotspots and bubbles oscillation velocity. From the CFD results, it was observed that the total volume of the micro-bubbles increased by about 4.95% with each 100 W-increase in power amplitude. Furthermore, velocity of acoustic streaming increased from 29 to 119 cm/s as power increased, which was in good agreement with the PIV analysis.

Simulation for supporting scale-up of a fluidized bed reactor for advanced water oxidation.

Simulation of fluidized bed reactor (FBR) was accomplished for treating wastewater using Fenton reaction, which is an advanced oxidation process (AOP). The simulation was performed to determine characteristics of FBR performance, concentration profile of the contaminants, and various prominent hydrodynamic properties (e.g., Reynolds number, velocity, and pressure) in the reactor. Simulation was implemented for 2.8 L working volume using hydrodynamic correlations, continuous equation, and simplified kinetic information for phenols degradation as a model. The simulation shows that, by using Fe(3+) and Fe(2+) mixtures as catalyst, TOC degradation up to 45% was achieved for contaminant range of 40-90 mg/L within 60 min. The concentration profiles and hydrodynamic characteristics were also generated. A subsequent scale-up study was also conducted using similitude method. The analysis shows that up to 10 L working volume, the models developed are applicable. The study proves that, using appropriate modeling and simulation, data can be predicted for designing and operating FBR for wastewater treatment.