Manuel Guisado González

Industrial wastewater advanced oxidation. Part 1. UV radiation in the presence and absence of hydrogen peroxide

The oxidation of two wastewaters collected from distillery and tomato processing plants with UV radiation (254 nm) alone and combined with hydrogen peroxide has been investigated. Distillery wastewaters are refractory to UV radiation but the presence of hydrogen peroxide leads to different COD reductions which indicates that the process is mainly due to the action of radicals. Tomato wastewaters, on the other hand, show a higher reactivity even with UV radiation alone. The quantum yield for tomato wastewaters with an initial COD of 930 mg O2l−1 was found to be 0.7 mol O2 photon−1 and decreased with reaction time. The combined effect of UV radiation and hydrogen peroxide at a 0.01 M concentration on tomato wastewaters leads to about 25% COD reduction while TOC was unchanged. The contribution of radical reactions in this process was higher than 60%.

Fenton Reagent Advanced Oxidation of Polynuclear Aromatic Hydrocarbons in Water

Aqueous oxidation of three polynuclear aromatic hydrocarbons, fluorene, phenanthrene and acenaphthene with the combination of hydrogen peroxide and ferrous ion, Fenton reagent, has been studied. The effect of variables such as concentration of both reactants, pH and presence of bicarbonate ion and humic substances has been investigated. Products resulting from oxidation have also been identified. From experimental results and kinetic data determined the process is confirmed as an advanced oxidation involving the generation of hydroxyl radicals. Oxidation rates are even higher than those from other advanced oxidation systems involving ozone, UV radiation and hydrogen peroxide. Reactivity is in the following decreasing order: Phenanthrene > Fluorene > Acenaphthene.

The use of ultrafiltration and nanofiltration membranes for the purification of cork processing wastewater

Filtration experiments in batch concentration mode (with recycling of the retentate stream) of the cork processing wastewater were performed in laboratory filtration membrane equipment, by using four commercial membranes: two UF membranes with MWCO of 20,000 and 5000 Da, and two NF membranes with an approximate MWCO of 150-300 Da. The filtration experiments of the selected wastewater were performed by modifying the most important operating variables: transmembrane pressure, tangential velocity, temperature, and the nature and MWCO of the membranes. The evolution of the cumulative permeate volumes and permeate fluxes with processing time were analysed, and it was established that the steady-state permeate flux was reached for a volume retention factor of 2. The effect of the mentioned operating conditions on this steady-state permeate flux was discussed. The effectiveness of the filtration treatments was determined by the evaluation of the rejection coefficients for several parameters, which measure the global pollutant content of the effluent: COD, absorbance at 254 nm, tannic content, color, and ellagic acid. Finally, the resistances in series model was used for the evaluation of the resistances to the permeate flux, and it was concluded that the contribution to the total resistance of the fouling resistance (combined external plus internal) was higher than the inherent resistance of the clean membrane.

Kinetic modelling of aqueous atrazine ozonation processes in a continuous flow bubble contactor

The ozonation of atrazine in different waters (ultrapure and surface waters) has been studied in continuous bubble contactors with kinetic modelling purposes. Three ozonation processes have been considered: ozonation alone and combined with hydrogen peroxide or UV radiation. The kinetic models are based on a molecular and free radical mechanism of reactions, reaction rate and mass transfer data and non-ideal flow analysis models for gas and water phases through the contactors (the tanks in series model and the dispersion model). The models predict well the experimental concentrations of atrazine, dissolved ozone and hydrogen peroxide both at non-steady state and steady state regimes. From both experimental and calculated results, atrazine conversions are observed to be highly dependent on the nature of water where ozonation is carried out. As far as removal of atrazine and oxidation intermediates are concerned, ozone combined with UV radiation resulted in the most effective ozonation process among the three studied.

Effect of high salt concentrations on ozone decomposition in water

Abstract Ozone decomposition in water in the presence of different salts has been studied. The stability of ozone varies depending on the salt nature and the pH. At low pH, molecular phosphoric acid has a positive influence upon ozone conversion. At neutral and basic pH, ozone decomposes through a radical mechanism, whose termination step depends on the type of ionic species present. So, at pH 6 in the absence of salts or in the presence of chloride ions it is proposed a second order termination step. In addition, the direct reaction between ozone and chloride ion has to be considered. When there are sulphate, phosphate or carbonate ions present in the water, the termination step changes to first order due to the hydroxyl radical scavenging effect of these ions. Hence, these ions estabilize molecular ozone in water.

Contribution of free radical oxidation to eliminate volatile organochlorine compounds in water by ultraviolet radiation and hydrogen peroxide

Abstract The UV/H 2 O 2 oxidation of trichloroethylene, TCE, and 1,1,1 trichloroethane, TCA, in water was studied. Oxidation rates depend on the initial hydrogen peroxide concentration with maximum values in the presence of concentrations of 10 −2 M which represents rates of about 5 and 250 times higher than those obtained from volatilization alone for TCA and TCE, respectively. In the case of TCE, contribution of direct photolysis is negligible. In natural waters, oxidation rates of TCA and TCE slightly decreases compared to those in laboratory prepared waters. When concentrations of hydrogen peroxide applied are higher than 10 −2 M, TCA is mainly removed by volatilization since hydrogen peroxide consumes most of radicals generated. On the contrary, free radical oxidation continues to be the principal step of removal in the case of TCE since the rate constant of its reaction with hydroxyl radicals is approx. 65 times higher than that of the reaction OH-TCA. Experiments with high concentration of hydrogen peroxide (>10 −2 M) allow to determine the rate constants of TCE-OH and TCA-OH reactions that were found to be 1.8×10 9 and 2.0×10 7 M −1 s −1 , respectively.

Application of photochemical reactor models to UV irradiation of trichloroethylene in water

The UV irradiation of trichloroethylene in water was studied. Degradation rates depend on the initial TCE concentration and nature of the water. Volatilization contribute to the disappearance rate of TCE between 5% and 12% when initial TCE concentration are 25 and 100 μgl−1. respectively. In surface waters containing up to 17 mgl−1 of TOC conversion of TCE is only 54% compared to 80% reached in ultrapure water (with less than 20 μgl−1 of TOC) in 90 min. Degradation rates of TCE decrease with the increase of TOC content of the water. Quantum yields of TCE at 254 nm have been determined from different photochemical kinetic models. Differences between models are likely due to effects (reflection-refraction phenomena) not accounted for in the kinetic equations. From the PSSE model TCE quantum yield has been found to be 1.712±0.041 mol.photon−1.

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.

Kinetic Regime Changes in the Ozonation of 1,3-Cyclohexanedione in Aqueous Solutions

Abstract The reaction between ozone and 1,3-cyclohexanedione in aqueous solutions at different pH was investigated from the point of view of the film theory. The rate of ozone absorption is accompanied by a second order irreversible reaction with 1,3-cyclohexanedione. The kinetic regime of absorption was found to change from fast (the reaction being of pseudo first order) to instantaneous, according to the ozone partial pressure applied. The former kinetic regime allows the determination of the reaction rate constant, while the latter leads to the volumetric mass transfer coefficient of the system.

Application of Gas Absorption Theories to o-Cresol Ozonation in Water

Abstract The reaction rate between ozone and o–cresol in aqueous solution at pH 2 has been studied. According to the absorption theories, the kinetic regime of the process in the experimental conditions investigated, corresponds to an irreversible fast pseudo-first order reaction between non-dissociated o-cresol and ozone. Similar values for the rate constant are deduced from the different theories. Therefore the film theory, having a simple mathematical basis, seems to be the most appropriate model for this kinetic study.