Spectroscopy is the study of matter interacting with electromagnetic radiation (e.g., light). The electromagnetic spectrum in Figure 1 illustrates the many different types of electromagnetic radiation, including gamma rays (γ-rays), X-rays, ultraviolet (UV) radiation, visible light, infrared (IR) radiation, microwaves, and radio waves. The frequency (ν) and wavelength (λ) ranges associated with each form of radiant energy are also indicated in Figure 1.

Introduction to Spectroscopy

Wastewater treatment by means of advanced oxidation processes at basic pH conditions: a review.

Arsenic and antimony in water and wastewater: overview of removal techniques with special reference to latest advances in adsorption

Feasibility of industrial-scale treatment of dye wastewater via bio-adsorption technology

Micro and nanobubble technologies as a new horizon for water-treatment techniques: A review

Ammonia is a major source of water pollution. One of the most common methods for removal of ammonia from water is oxidation. In this work, ozonation of ammonia using microbubbles was studied in a pilot plant. The experimental results indicate that ozone microbubbles were quite effective in oxidizing ammonia. Oxidation of ammonia was effective at high pH and high ozone generation rates. Ozonation was found to occur by direct reaction of ozone with ammonia at the higher pH. However, the hydroxyl radicals were also involved at the lower pH. Bromide ions acted as a catalyst in the ozonation process, and a faster rate of oxidation of ammonia and lower yield of nitrate was observed. The volumetric mass transfer coefficient of ozone in water was determined. It increased with the increasing rate of ozone generation and the pH of the medium.

Removal of Ammonia from Water by Ozone Microbubbles

Microbubble-based methods, in recent times, have been widely used for purification of water and wastewater. Microbubbles have several physicochemi- cal properties, which make them eminently suitable for wastewater treatment. In this review, these properties have been analyzed in detail from the perspective of appli- cation. 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 coef- ficient 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.

Microbubble-aided water and wastewater purification: a review

Concentration of hydroxyl radicals generated from ozone microbubbles was determined by using an indirect method over a wide range of pH (i.e. pH 3–10). p-Chlorobenzoic acid (PCBA) was used as the probe compound to calculate the concentration of hydroxyl radicals. A constant, Rct, was defined as the ratio of OH and O3 exposures, which was employed to estimate the concentration of hydroxyl radicals. The effects of pH and carbonate ions on the generation of hydroxyl radicals were studied. It was observed that the O3 exposure and the depletion of PCBA were higher at acidic pH than at the alkaline pH. At acidic pH, C O 3 2 − acted as the ·OH scavenger only, whereas at alkaline pH, it inhibited ozone decomposition. This changed the values of ·OH exposure, O3 exposure, and hence, Rct. The degradation of phenol was performed at pH 3–10 by using ozone microbubbles. The contributions of ·OH and O3 on the oxidation of phenol were calculated. A mechanism of the generation of ·OH from the ozone microbubbles under acidic and alkaline conditions was developed.

Quantitative prediction of generation of hydroxyl radicals from ozone microbubbles

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

Catalytic ozonation using metal ions is a promising method to enhance the hydroxyl radical generation from ozone. In this study, four common metal ions i.e., Fe(II), Fe(III), Mn(II) and Cu(II) were used as the catalyst in a microbubble reactor. The metal ions increased the decolorization efficiency of the azo dye, Congo Red (CR). The combined use of metal ion and microbubble increased the effective factor to a good extent. Based on the pseudo-first-order reaction rate constant k (min−1), O3 + Cu(III) showed higher value for both with and without microbubbles at acidic pH. The performance of the metal catalyst on the decolorization of CR followed an order Fe(III) < Fe(II) < Mn(II) < Cu(II). The effect of pH, metal ion concentration on the dye oxidation, and the presence of NaCl and CaCO3 were also studied. The pCBA was used as the radical probe to calculate the hydroxyl radical concentration by using an indirect method. From the depletion rate of pCBA it was observed that the generation of hydroxyl radical was more by the use of Cu(II) and the trend was Fe(III) < Fe(II) < Mn(II) < Cu(II). The removal of TOC followed the same order too.

Snigdha Khuntia

Papers

Removal of Ammonia from Water by Ozone Microbubbles

Microbubble-aided water and wastewater purification: a review

Quantitative prediction of generation of hydroxyl radicals from ozone microbubbles

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

Catalytic ozonation of dye in a microbubble system: Hydroxyl radical contribution and effect of salt