The ozonation kinetics of oxalic acid in water in the presence of an activated carbon has been investigated at acid pH. The presence of the activated carbon significantly enhances the degradation rate of oxalic acid if compared to single ozonation and single adsorption. According to total organic carbon measurements, nearly complete mineralization of oxalic acid can be achieved depending on the experimental conditions. The presence of tert-butyl alcohol, which scarcely adsorbs on the carbon surface at the conditions investigated, led to a significant reduction of the oxalic acid removal rate. Consequently, experimental results suggest that the reaction proceeds in the water phase between oxalic acid and oxidant species, likely hydroxyl radicals, coming from the ozone decomposition on the carbon surface. The proposed mechanism yielded a first-order kinetics with respect to ozone, close to the 0.8 order experimentally observed. Also, the energy of activation was found to be approximately 15 kcal mol-1.

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Landfill leachates of the city of Badajoz (in the southwest of Spain) have been treated by wet air oxidation at high temperature (180-270 °C) and pressure (40-70 atm). Typical operating variables such as temperature and oxygen partial pressure have been investigated with no effect of any being found and moderate to low chemical oxygen demand conversions (20-30% depending on initial COD concentration). Initial pH shows a positive influence when acidic conditions are used. Addition of hydrogen peroxide (0.01 M) as a hydroxyl radical promoter is able to provide an additional 15% increase in the final COD removal achieved. If a sulfate radical promoter is used (i.e., Oxone) the process is significantly improved, with COD conversions in the range 60-80%, also depending on the initial COD of the leachates. A first attempt to comprehend the chemistry of this oxidizing system suggests an instantaneous decomposition of Oxone that initiates the radical chain also involving hydroxyl and organic radicals.

This paper deals with the modifications of the chemical surface functionalities and the textural changes of a glassy carbon produced by three oxidizing agents:  ozone, hydrogen peroxide, and oxygen plasma. The chemical surface changes are evaluated by using Fourier transform infrared spectroscopy, temperature-programmed desorption−mass spectrometry, and chemical titrations of the surface functionalities by using the Boehm method. The textural modifications are studied by mercury porosimetry and by N2 and CO2 adsorption at 77 and 273 K, respectively. Ozone is a more effective oxidizing agent than H2O2 and oxygen plasma. It is able to introduce much larger amounts of oxygen functionalities on the surface than the other oxidizing agents. Moreover, the textural characteristics of the original sample remain almost unchanged after the treatments with oxygen peroxide and with oxygen plasma, while ozone produces modifications in surface area and mesoporosity. Nevertheless, ozone modifications of surface area seem to be partially produced by the fixation of the oxygen functionalities at the entrance of the micropores which partially hinder the access of the adsorbates.

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The kinetics of the removal of ozone from air by granular activated carbon (GAC) has been investigated. Twenty GACs with different textural and chemical surface properties were used in this study. The kinetic experiments were carried out in an expanded bed reactor (EBR) and in a packed bed reactor (PBR). A rate equation that takes into account thermal ozone decomposition and removal of ozone by GAC due to chemisorption and catalytic decomposition has been proposed. Deactivation kinetics has also been considered in the reaction model. Intrinsic rate constants for thermal ozone removal (k T), chemisorption of ozone (k 1), and GAC-catalyzed decomposition of ozone (k 2), as well as deactivation rate constants (k d1 and k d2) have been evaluated from dynamic modeling. At the conditions used in this work, ozone was thermally stable only below 323 K. Above this temperature, ozone partially decomposed even in the absence of GAC. Temperature favored the rate of ozone removal by GAC following Arrhenius behavior while air humidity had a negative effect, likely attributed to the blockage of GAC active sites by water. A relationship between k 1 and surface area, volume of pores larger than 3.5 nm, concentration of surface oxygen complexes (SOC), and ash content has been found, while k 2 depends mainly on surface area, basic SOC concentration, and metal content. The activity of the all the GAC samples used decreased with the ozone exposure time. The formation of acidic SOC due to chemisorption of ozone onto GAC has been pointed to as a major reason for the process deactivation. Effective GAC regeneration has been achieved by thermal treatment at 1123 K.