Vincenzo Caprio

Advanced oxidation processes (AOP) for water purification and recovery

Abstract All advanced oxidation processes (AOP) are characterised by a common chemical feature: the capability of exploiting the high reactivity of HO radicals in driving oxidation processes which are suitable for achieving the complete abatement and through mineralization of even less reactive pollutants. The different AOP are considered and critically presented according to their specific features with reference, whenever possible, to their real applications for water pollution abatement. The experimental apparatus and working procedures which can be adopted for carrying out waste water treatments by AOP application are examined. Some remarks upon treatment economics are provided on the basis of the main parameters affecting the AOP costs.

PARACETAMOL OXIDATION FROM AQUEOUS SOLUTIONS BY MEANS OF OZONATION AND H2O2/UV SYSTEM

Paracetamol oxidation from aqueous solutions is studied by means of ozonation and H(2)O(2) photolysis. Both oxidative systems are able to destroy the aromatic ring of the substrate with a partial conversion of the initial carbon content into carbon dioxide. For the adopted experimental conditions mineralization degrees up to 30% and 40% are observed with ozonation and H(2)O(2) photolysis, respectively. Main reaction intermediates and products are identified for both systems by HPLC and GC-MS analyses and a kinetic characterization is achieved.

The ozonation of pyruvic acid in aqueous solutions catalyzed by suspended and dissolved manganese

Abstract Reaction mechanisms and kinetics of manganese-catalyzed ozonation of pyruvic acid in aqueous solution are investigated. Experiments performed in the pH range 2.0–4.0 show that the reactivity is strongly enhanced by heterogeneous and homogeneous catalytic mechanisms, which are activated by suspended MnO 2 particles and by dissolved Mn ions, respectively. Homogeneous mechanisms and related kinetics are elucidated.

The kinetics of Mn(II)-catalysed ozonation of oxalic acid in aqueous solution

The Mn(II)-catalysed ozonation of oxalic acid in aqueous solution is investigated at pH = 0 and pH = 4.7. Experiments are performed in both semi-batch and batch conditions by following the kinetic development of the ozonation processes. At pH = 0 first-order kinetics with respect to both ozone and Mn(II) are observed with no dependence upon the oxalic acid concentration. A rate constant of 6.2 × 104 l mol−1 min−1 and equimolar consumptions of ozone and oxalic acid are evaluated. At pH = 4.7 higher initial reactivities are observed whereas the low ozone to oxalic acid molar consumption ratios indicate the intervention of molecular oxygen in the oxidation process thus confirming its radical evolution. Reaction mechanisms are proposed to explain the observed reactive behaviours of the investigated systems.

Oxidation of 3,4-dihydroxybenzoic acid by means of hydrogen peroxide in aqueous goethite slurry

The oxidation by H2O2 of 3,4-dihydroxybenzoic acid (3,4-DHB) in aqueous/goethite slurry at varying operating conditions (catalyst load, temperature, pH, substrate and hydrogen peroxide starting concentration) is investigated. At adopted catalyst loads the observed kinetic developments are consistent with a non-radicalic oxidation mechanism involving the interaction between hydrogen peroxide and 3,4-DHB acid both adsorbed on the active sites of the catalyst. The temperature dependence of rate parameters for the proposed model is also assessed.

Photocatalytic oxidation of 4-nitrophenol in aqueous TiO2 slurries : an experimental validation of literature kinetic models

The photocatalytic oxidation of 4-nitrophenol in the presence of solid TiO2 has been studied in an annular reactor. The experiments have been performed in both acidic and basic solutions (pH = 3 and 8.5) at different catalyst loads and temperatures. The concentration–time data have been correlated with the rate equation: −d[R]/dt = k0k2[R]/(1 + k2[R]) in order to evaluate the unknown parameters. The laws of dependence of the parameters k0 and k2 on catalyst load and temperature have been interpreted in the terms of detailed kinetic models proposed in the literature. The results throw some light on the different reaction mechanisms occurring on varying the operating conditions. © 2000 Society of Chemical Industry

The oxidation of metol (N-methyl-P-aminophenol) in aqueous solution by UV/H2O2 photolysis

The oxidation of metol (N-methyl-p-aminophenol) in aqueous solution by means of a UV/H2O2 system has been studied in the pH range 3.0–9.0. The results of the present investigation indicate that the pH, H2O2 and substrate concentration and oxygen presence significantly influence the system behaviour. Toxicity tests show that the H2O2 photolytic process is capable of reducing the toxicity of metol aqueous solutions. The kinetic constant of the attack of HO radicals to the substrate has been also estimated through the adoption of a simplified model.

Kinetic modeling of pyruvic acid ozonation in aqueous solutions catalyzed by Mn(II) and Mn(IV) ions

The ozonation of pyruvic acid (2-ketopropionic acid) in aqueous solutions, catalyzed by Mn(II) and Mn(IV) ions, has been studied at three different pH values (pH = 1.1, 2.0 and 3.0). A mathematical model of the unsteady operation of the experimental reactor has been developed, which takes into account the reactions occurring in the liquid phase and the ozone mass transfer from the gas bubbles. Those reactions have been described with two alternative kinetic models, both made out of four elementary steps. The two kinetic models correlate the experimental data with a fair accuracy, respectively at the lowest and at the highest pH examined. In particular, at pH = 3.0, the ozonation results are inhibited by the acetate ions produced by the reaction itself. This effect has been correctly described in the terms of a complex formed with the low oxidation-state manganese, which successively reacts with the dissolved ozone.

Quinoline ozonation in aqueous solution

Abstract The oxidation of quinoxaline by ozone in aqueous solution is investigated. The chemical and kinetic evolution of the oxidation process at varying pH are followed by means of semi-batch and batch ozonation experiments. Results indicate that quinoxaline ozonation can develop according to both radical and ionic mechanisms whose relative occurrence can be varied by means of addition to the reacting system of radical scavengers or ozone decomposition promoters. It is shown that each mechanism involves an initial attack of ozone to both the homocyclic and heterocyclic rings of quinoxaline. Pyrazinedicarboxylic acid is formed as a stable final product in ionic ozonation, whereas it appears as an intermediate still reactive towards ozone in radical ozonation. Despite this, the radical ozonation of quinoxaline appears to be more selective than ionic zonation with respect to production of pyrazinedicarboxylic acid. Reaction schemes are proposed to account for the observed kinetic behaviors and product form...

Photochemical degradation of benzotriazole in aqueous solution

Photochemical degradation of benzotriazole is investigated in aqueous solution at 25°C and pH values varying in the range 3–11. The quantum yields at different pH values are evaluated by analysing the kinetics of the reacting system. Reaction kinetics are markedly affected by pH because of its influence upon benzotriazole dissociation. A mathematical method that takes into account the presence of intermediates and of the pH has been developed.