Subrata Kumar Majumder

Microbubble-aided water and wastewater purification: a review

Abstract Microbubble-based methods, in recent times, have been widely used for purification of water and wastewater. Microbubbles have several physicochemical properties, which make them eminently suitable for wastewater treatment. In this review, these properties have been analyzed in detail from the perspective of application. Various types of microbubble generators and their operation principles have been discussed. The transport of gas into the aqueous phase has been explained, and the correlations to predict the volumetric mass transfer coefficient have been presented. Many practical applications using ozone, oxygen and air microbubbles, some of which are currently at various stages of commercialization, have been presented. Other important uses of microbubbles for wastewater treatment, namely, removal of fine solid particulate matter and oil, have also been discussed. In addition, directions for future research of microbubble technology and their potential applications have been identified.

Oxidation of As(III) to As(V) using ozone microbubbles

The use of ozone in the treatment of water and wastewater is rapidly increasing due to its high oxidizing power. Arsenic is one the most toxic elements found in water. As(III) and As(V) are the major sources of arsenic poisoning. It is known that As(V) can be more easily removed from water by adsorptive methods than As(III). In this work, oxidation of more toxic As(III) to less toxic As(V) was studied in a pilot-plant by using ozone microbubbles. The microbubbles were effective in dissolving ozone in water. The oxidation was fast over a wide range of pH (e.g., 4-9). The role of hydroxyl radical in the oxidation of As(III) under acidic conditions was investigated by using 2-propanol as the hydroxyl radical scavenger. Under acidic conditions, the addition of 2-propanol slowed down the oxidation, which proves that hydroxyl radicals were involved in the oxidation process. The effect of carbonate ions on the rate of oxidation was investigated. It was found that the generation of carbonate ion radical from the carbonate ion accelerated the oxidation of As(III). The kinetics of oxidation of As(III) by ozone was studied.

A pilot plant study of the degradation of Brilliant Green dye using ozone microbubbles: mechanism and kinetics of reaction

Oxidation of Brilliant Green dye was performed using ozone microbubbles in a pilot plant scale. Decolourisation was very effective at both acidic and alkaline pH. The colour of the aqueous solution was below detectable limit after 30 min at 1.7 mg/s ozone generation rate. The reaction between the dye and ozone was first-order in nature with respect to both ozone and the dye. The enhancement factor increased with increasing dye concentration. The samples were analysed by the ultra-violet–visible (UV–Vis) spectrophotometry, gas chromatography–mass spectrometry (GC–MS) and Fourier transform infra-red (FTIR) spectroscopy. From the GC–MS analysis, 13 intermediates were detected as oxidation products of this dye at various stages of oxidation. The changes in the FTIR spectra showed the destruction of the dye and the formation of new compounds. The oxidation mechanism was divided into two reaction pathways. The mineralisation of Brilliant Green was up to 80% in 60 min, as determined by total organic carbon analysis.

Gas-Newtonian and Gas-Non-Newtonian Slug Flow in Vertical Pipe, Part I: Gas Holdup Characteristics

Studies on two-phase gas-liquid co-current flow with non-Newtonian liquid system has attracted the attention of researchers over the years due to its wide-spread applications and importance in various different processes in chemical and biochemical industries, such as the process of two-phase in oil and gas wells, transportation systems of crude and refined products, and food processing in biochemical engineering and bio-reactors. This article examines the sole objective of experimental studies on gas holdup in Newtonian and non-Newtonian liquid slug flow within a range of gas and liquid flowrate of 0.5×10-4 to 1.92×10-4 m3/s and 1.6×10-4 to 6.7×10-4 m3/s, respectively. The present data was analyzed with different models. To predict gas holdup, correlations have been developed for individual system with Newtonian and non-Newtonian liquid. A general correlation was also developed to predict the gas holdup combing both the Newtonian and non-Newtonian liquid systems. The study of the gas holdup characteristics in gas-Newtonian and non-Newtonian liquid systems may give insight into a further understanding and modeling of this slug flow characteristics in industrial applications.

Dispersion Characteristics of Liquid in a Modified Gas-Liquid-Solid Three-Phase Downflow Bubble Column

The axial dispersion coefficient of liquid in downflow slurry bubble column is estimated experimentally by the residence time distribution (RTD) technique. Its variation with superficial gas and slurry velocities, separator pressure, and slurry concentration is analyzed. The axial dispersion coefficient is correlated in terms of dispersion number with the velocity ratio of slurry to gas, Archimedes number, and Reynolds number by dimensional analysis. The mixing time is represented by the isotropic turbulence theory. We found that the axial dispersion coefficient in this present gas-liquid-solid three-phase downflow bubble column is an order of magnitude higher than that in upflow three-phase system. The dispersion coefficient of bubble motion (Db) and the velocity characteristic factor (k) are analyzed based on velocity distribution theory. The present study may be useful for further understanding and developing of specific multiphase reactor in industrial applications.

Analysis of Particle Recovery in Flotation Column Based on Information Entropy Theory

Quality of mixedness in a flotation column has been analyzed by using information entropy theory. An empirical model with the consideration of geometric and dynamic variable, which affect the quality of mixedness, was developed by dimensional analysis. The efficiency of the particle separation in the floatation column has been enunciated based on the quality of mixedness. The present analysis on the quality of mixedness in flotation column may give insight into a further understanding and modeling of flotation device in industrial applications.

Mass Transfer Characteristics

This chapter deals with the investigations and analysis on the interfacial area and mass transfer coefficient in bubbly flow system. The measurement of the mass transfer phenomena in the bubbly flow system is explained. The efficiency of the mass transfer in the inverse bubbly flow system is analyzed based on the dispersion coefficient of bubble motion and the velocity characteristic factor. The same is also analyzed by the information entropy theory and with the maximum mixedness factor. The mass transfer coefficient and the interfacial area of bubble–liquid are enunciated with the different models.

Heat Transfer Characteristics

In this chapter, the mechanisms of heat transfer in bubbly flow with different models are enunciated. The heat transfer coefficient and its measurement techniques in conventional and inverse bubbly flow system are described. The effects of different operating and geometric variables on the heat transfer coefficient are explained. The analogy of heat, mass, and momentum transfer in bubbly flow is also analyzed in this chapter.

Adsorption of As(V) on zirconium-based adsorbents

AbstractAdsorption of As(V) on zirconium impregnated activated carbon and amorphous zirconium oxide has been reported in this work. The adsorption of As(V) on both of these adsorbents was fast and effective. The As(V) adsorption capacity of amorphous zirconium oxide was larger than that of zirconium–activated carbon. Characterization of these adsorbents was performed by various methods (viz. SEM, EDX, XRD, and FTIR). The electric charge on the surface of these adsorbents in aqueous media was measured at different pH. The adsorption of As(V) followed a pseudo-second-order kinetics. However, from the intra-particle diffusion model, it was found that film-diffusion and intra-particle diffusion took place simultaneously during adsorption. Langmuir, Freundlich, and Redlich–Peterson adsorption isotherms were fitted to the experimental data. The adsorption of As(V) on these adsorbents was found to be spontaneous and endothermic in nature. The thermodynamic parameters (viz. changes in Gibbs free energy, enthalpy,...

Gas Holdup and Frictional Pressure Drop In a Modified Slurry Bubble Column

Abstract This article presents the analysis of gas holdup, pressure drop and bubble size of gas-liquid-solid flow in a modified downflow slurry bubble column. The analysis is done based on the Lockhart-Martinelli principle. The Lockhart-Martinelli model is modified and incorporate to predict the frictional pressure drop and gas holdup of three-phase flow in the modified bubble column. The effects of operating variables such as slurry flow rate, gas flow rate, slurry concentration and particle diameter on frictional pressure drop and gas holdup are investigated. To predict the gas holdup, Sauter mean bubble diameter and pressure drop, correlations have also been developed as function of different dimensionless groups by introducing the operating variables and physical properties. The studies of the pressure drop in the downflow slurry bubble column may give insight into a further understanding and modeling of the three-phase flow characteristics in industrial applications.