Catalytic ozonation has recently gained significant attention as an effective process used for the removal of organics from water. Unfortunately, despite increasing research efforts in the field of catalytic ozonation and the introduction of new catalysts, the mechanisms of catalytic processes are still largely unknown. An understanding of the mechanisms of catalytic ozonation is vital in order to introduce this technique in water treatment at an industrial scale. Therefore, the main aim of this paper is to provide a short overview of catalytic processes, their recent advances and to identify major directions taken to understand mechanisms governing catalytic processes utilised in water and wastewater treatment. Catalytic ozonation is considered to belong to Advanced Oxidation Processes. However, the results published by several research groups indicate that not all catalytic processes utilise the power of hydroxyl radicals.

The efficiency and mechanisms of catalytic ozonation

The role of surface chemistry in catalysis with carbons

Catalytic ozonation for water and wastewater treatment: Recent advances and perspective.

Activated carbon modifications to enhance its water treatment applications. An overview.

The oxidation of hazardous organic compounds leads to the formation of several by-products, being oxalic acid and oxamic acid final oxidation products refractory to ozonation. The present work aimed to study the ozonation of those carboxylic acids in the presence of activated carbon at different solution pH. For comparative purposes, experiments of adsorption on activated carbon, ozonation, and ozonation in the presence of activated carbon were carried out. In order to clarify the reaction mechanism, some experiments were done in the presence of a radical scavenger. With the aim of evaluating the role of the activated carbon surface chemistry during the ozonation, two activated carbon samples were assessed. A significant synergistic effect between ozone and activated carbon was evidenced in the oxidation of oxalic acid. Oxamic acid was found to be refractory to oxidation at pH 7. On the other hand, at pH 3, the mineralization of oxamic acid was significantly enhanced by the presence of activated carbon. Generally, the presence of activated carbon during ozonation increased the rate of degradation of both carboxylic acids leading to mineralization. Best results were achieved with the most basic activated carbon. In both cases, the efficiency of activated carbon promoted ozonation decreases with the increase of solution pH.

Activated carbon catalytic ozonation of oxamic and oxalic acids

The influence of various factors on aqueous ozone decomposition by granular activated carbons and the development of a mechanistic approach

The ozonation of gallic acid in water in the presence of activated carbon has been studied at pH 5. Hydrogen peroxide, ketomalonic and oxalic acids were identified as by-products. The process involves two main periods of reaction. The first period, up to complete disappearance of gallic acid, during which ozonation rates are slightly improved by the presence of activated carbon. The second one, during which activated carbon plays an important role as promoter, and total mineralization of the organic content of the water is achieved. The organic matter removal is due to the sum of contributions of ozone direct reactions and adsorption during the first period and to a free radical mechanism likely involving surface reactions of ozone and hydrogen peroxide on the carbon surface during the second period. There is a third transition period where by-products concentration reach maximum values and ozonation is likely due to both direct and free radical mechanisms involving ozone and adsorption. Discussion on the mechanism and kinetics of the process is also presented both for single ozonation and activated carbon ozonation.

Gallic acid water ozonation using activated carbon

A mixture of polyphenol compounds (gallic acid, tyrosol, and syringic acid) is treated with ozone in water in the presence of activated carbon (AC). Individual (O3) and combined (O3/AC) ozonations have been carried out following the concentrations of initial compounds, intermediates, ozone, and hydrogen peroxide and total organic carbon (TOC). AC ozonation processes significantly improve both polyphenol conversion and mineralization. Hydrogen peroxide formed during the process seems to play an important role in accelerating the oxidation rate. Different carboxylic acids are formed as intermediate products. Consumption of ozone per unit mass of carbon removed is reduced in the combined ozonation process.

Activated Carbon Promoted Ozonation of Polyphenol Mixtures in Water: Comparison with Single Ozonation

The ozonation of succinic acid in water has been carried out in the presence of four different activated carbons. The influence of some variables, carbon type, particle size, gas flow rate, agitation speed, etc., has been studied for kinetic purposes. Succinic acid has been observed to be a promoter of ozone decomposition in water. Reactivity of ozone with succinic acid is significantly increased in the presence of activated carbon, regardless of its nature, although basic activated carbons present the highest activity. Also, the presence of activated carbon allows the highest mineralization rates. Mass transfer and chemical reactions (bulk water and surface reactions) have been considered for the kinetic study and rate constants of both reactions have been determined at different temperatures. Linear correlations have been obtained between surface reaction rate constants and the pHpzc of activated carbons.

Kinetics of Activated Carbon Promoted Ozonation of Succinic Acid in Water

Pyrolysis kinetic, thermodynamic and product analysis of different leguminous biomasses by Kissinger-Akahira-Sunose and pyrolysis-gas chromatography-mass spectrometry

Inés Giraldez

Papers

The influence of various factors on aqueous ozone decomposition by granular activated carbons and the development of a mechanistic approach

Gallic acid water ozonation using activated carbon

Activated Carbon Promoted Ozonation of Polyphenol Mixtures in Water: Comparison with Single Ozonation

Kinetics of Activated Carbon Promoted Ozonation of Succinic Acid in Water

Pyrolysis kinetic, thermodynamic and product analysis of different leguminous biomasses by Kissinger-Akahira-Sunose and pyrolysis-gas chromatography-mass spectrometry