F. Javier Rivas

Fenton-like oxidation of landfill leachate

Abstract The treatment of stabilized leachates by means of Fentons like reagent [Fe(III)–H2O2] has been studied. It has been demonstrated that the oxidation state of the catalyst does not influence the efficacy of the process in terms of chemical oxygen demand depletion profiles. The abrupt increase in temperature experienced in oxidation experiments involves a wastage of hydrogen peroxide diminishing the fraction of this reagent addressed at removing COD. If temperature is kept constant, the hydrogen peroxide uptake is 10 mg of H2O2 consumed per mg of COD abated (from 15 to 30°C). Working temperatures above 30°C does not lead to additional COD conversion, contrarily, the percentage of wasted H2O2 is increased. A rough economic analysis of the process indicates that this treatment can be a suitable alternative to deal with this type of effluents.

Removal of emergent contaminants: integration of ozone and photocatalysis.

A mixture of nine pharmaceuticals has been treated by means of the systems: UV-B(313 nm), O(3), UV-B(313 nm) + TiO(2), O(3) + UV-B(313 nm), and O(3) + UV-B(313 nm)+TiO(2). Simple photolytic or ozonation processes lead to a deficient total organic carbon (TOC) elimination after 120 min of exposure (25 and 30% conversions, respectively). Addition of a photocatalyst such as titanium dioxide significantly enhanced the mineralization degree, a 60% TOC conversion was obtained. A TiO(2) load optimum around 0.25 g L(-1) was observed. No loss in photoactivity was experienced after 2 reuses. Due to ozone photodegradation, the combination of ozone and radiation increased the generation of hydroxyl radicals. As a consequence, TOC removal was increased to a value in the proximity of 85%. The most complex system, O(3) + UV-B(313 nm) + TiO(2), achieved the highest TOC abatement (95%). Use of ozone in photocatalytic processes involves an increase in hydroxyl radical generation.

Wet peroxide degradation of atrazine

The high temperature (150-200 degrees C), high pressure (3.0-6.0 MPa) degradation of atrazine in aqueous solution has been studied. Under these extreme conditions atrazine steadily hydrolyses in the absence of oxidising agents. Additionally, oxygen partial pressure has been shown not to affect atrazine degradation rates. In no case mineralisation of the parent compound was observed. The addition of the free radical generator hydrogen peroxide to the reaction media significantly enhanced the depletion rate of atrazine. Moreover, partial mineralisation of the organics was observed when hydrogen peroxide was used. Again, oxygen presence did not influence the efficiency of the promoted reaction. Consecutive injections of hydrogen peroxide throughout the reaction period brought the total carbon content conversion to a maximum of 65-70% after 40 min of treatment (suggesting the total conversion of atrazine to cyanuric acid). Toxicity of the effluent measured in a luminometer decreased from 93% up to 23% of inhibition percentage. The process has been simulated by means of a semi-empirical model.

Advanced oxidation of polynuclear aromatic hydrocarbons in natural waters

Abstract The advanced oxidation of some polynuclear aromatic hydrocarbos, PAHs (fluorene, phenanthrene and acenaphthene) in surface waters where they were added was studied with ozone alone or combined with hydrogen peroxide or UV radiation (254 nm) or with the combination of the latter two. The influence of water nature (surface and organic‐free waters) and type of oxidation was investigated. Oxidation rates in surface waters are generally slower than those in organic‐free waters. PAHs are in any case removed from surface waters at high oxidation rates with half life ranging from less than 1 minute when ozone is used in combination to UV radiation to 1 to 3 minutes for the other advanced oxidations. Application of UV radiation alone lead to the lowest degradation rates with half lifes of more than 6 minutes. Among the PAHs studied, fluorene is the one with the lowest oxidation rates regardless of type of advanced oxidation applied.

Direct, radical and competitive reactions in the ozonation of water micropollutants

Abstract Contribution of direct and radical reactions in the ozonation of three water micropollutants: ortho‐chlorophenol, mecoprope and atrazine, including competition of secondary reactions, are evaluated. Consumption rates of ozone due to these contributions are determined at different ozone partial pressure and pH. In the ozonation of ortho‐chlorophenol the oxidation is due to the direct reaction with ozone and an important fraction of the ozone absorbed (up to 60%) is also consumed by intermediate compounds. The pesticides studied, mecoprope and atrazine, show different behaviour for the ozone consumption. Thus, radical reactions are the main pathway for the elimination of atrazine, at any pH, and mecoprope at pH = 12. The influence of secondary reactions on the consumption of ozone is also important. Concentration of hydroxyl and superoxide ion radicals are determined from the kinetic data.

Aqueous Ozone Decomposition Onto a Co2O3-Alumina Supported Catalyst

Abstract The aqueous ozone decomposition in the presence of a Co2O3-Alumina catalyst was investigated. Activity and estability assays were conducted by reusing the same catalyst in consecutive runs. The catalyst was shown to significantly increase the ozone abatement rate without loss in activity after five consecutive experiments. The process can be acceptably simulated by a double homogeneous–heterogeneous decomposition mechanism. An increase in the working temperature resulted in an opposite effect by increasing the extension of the homogeneous decomposition and lowering the extension of the heterogeneous decomposition. Similarly, different trends were observed by adding two distinct free radical scavengers (terc-butyl alcohol and carbonates).

Impacts of Changing Operational Parameters of In Situ Chemical Oxidation (ISCO) on Removal of Aged PAHs from Soil

Abstract The removal efficiency of two different types of peroxide addition, catalyzed hydrogen peroxide (CHP) and sodium percarbonate (SPC) were compared on a highly PAH-contaminated soil from a wood impregnation site. In an attempt to simulate real in situ reagents delivery, experiments have been carried out in acrylic columns. The main parameters affecting contaminant removal were the reagent’s temperature and the total addition of peroxide (gH2O2/gPAHs). The highest removal efficiency was 64% for CHP and 53% for SPC. CHP treatment is affected to a greater extent by the mobilization of PAHs out of the soil matrix at low peroxide dosages. SPC treatment showed less contaminant mobilization and lower sensitivity to changes in operational parameters. Acenaphthene and fluorene showed high removal efficiencies probably, caused by their higher solubility and lower Koc. The rest of the low molecular weight PAHs proved recalcitrant to the CHP treatment. Channelling effects and the inefficient decomposition of hydrogen peroxide led to the uneven distribution of the reaction.