Joaquín R. Domínguez

Kinetic model for phenolic compound oxidation by Fenton's reagent.

A kinetic model is developed for the oxidation of phenolic compounds by Fentons reagent. In the first stage a rigorous kinetic model is applied to calculate the different kinetic rate constants for the oxidation process of p-hydroxybenzoic acid. In a second phase a competitive method is applied to calculate these kinetic constants for another 10 phenolic compounds present in agroindustrial and pulp paper wastewaters. These 10 phenolic compounds were: beta-resorcylic acid, 3-(4-hydroxyphenyl)-propionic acid, ferulic acid, protocatechuic acid, caffeic acid, p-coumaric acid, vanillic acid, syringic acid, veratric acid and 3,4,5-trimethoxybenzoic acid.

Oxidation of p-hydroxybenzoic acid by UV radiation and by TiO2/UV radiation: comparison and modelling of reaction kinetic

The phenolic compound p-hydroxybenzoic acid is very common in a great variety of agroindustrial wastewaters (olive oil and table olive industries, distilleries). The objective of this work was to study the photocatalytic activity of TiO2 towards the decomposition of p-hydroxybenzoic acid. In order to demonstrate the greater oxidizing power of the photocatalytic system and to quantify the additional levels of degradation attained, we performed experiments on the oxidation of p-hydroxybenzoic acid by UV radiation alone and by the TiO2/UV radiation combination. A kinetic model is applied for the photooxidation by UV radiation and by the TiO(2)/UV system. Experimental results indicated that the kinetics for both oxidation processes can be fitted well by a pseudo-first-order kinetic model. The second oxidation process can be explained in terms of the Langmuir-Hinshelwood kinetic model. The values of the adsorption equilibrium constant, K(pHB), and the second order kinetic rate constant, k(c), were 0.37 ppm(-1) and 6.99 ppm min(-1), respectively. Finally, a comparison between the kinetic rate constants for two oxidation systems reveals that the constants for the TiO2/UV system are clearly greater (between 220-435%) than those obtained in the direct UV photooxidation.

Treatment of black-olive wastewaters by ozonation and aerobic biological degradation

Abstract The degradation of the organic pollutants present in black-olive wastewater was carried out by ozonation, aerobic biological degradation, and the combination of two successive steps: an aerobic biological process followed by an ozonation. Contaminant removal was followed by means of global parameters directly related to the concentration of organic compounds in those effluents: chemical oxygen demand and total aromatic and phenolic contents. In the ozonation, an approximate kinetic study was performed to determine the apparent kinetic constants for the COD reduction, k COD , and for the total aromatic reduction, k A . In the aerobic biological degradation, the kinetic study was performed using the Monod model applied to the experimental data. In the combined process, a higher overall reduction in COD and aromatic content was achieved by the successive stages, and there was improved removal of the organic material during the second treatment. This enhancement was reflected in an increase in the apparent kinetic constants in the ozonation of the wastewater that had previously been treated aerobically, relative to the values obtained for the kinetic parameters in the single process experiment which were carried out under the same operating conditions.

Comparison of the degradation of p-hydroxybenzoic acid in aqueous solution by several oxidation processes

A comparative study is made of 12 methods of chemical oxidation applied to degrading p-hydroxybenzoic acid in aqueous solution. The oxidation processes tested were: UV, O3, UV/TiO2, O3/Fe2+, O3/H2O2, O3/UV, UV/H2O2, H2O2/Fe2+, H2O2/Fe2+/O3, UV/H2O2/O3, H2O2/Fe2+/UV and O3/UV/H2O2/Fe2+. The 12 processes were ranked by reactivity. In a kinetic study, the overall kinetic rate constant was split up into three components: direct oxidation by UV irradiation (photolysis), direct oxidation by ozone (ozonation), and oxidation by free radicals (mainly OH*).

Kinetics of the reaction between ozone and phenolic acids present in agro-industrial wastewaters

The kinetics of the ozonation of three phenolic acids is investigated from ozone absorption experiments in a semi-continuous reactor. After the evaluation of stoichiometric ratios for the individual reactions between ozone and each phenolic acid, the oxidation of p-hydroxybenzoic acid by ozone is performed in a first stage. The influence of the operating variables on the degradation process is established, and the application of a mass transfer with chemical reaction model based on the film theory leads to the determination of the reaction orders and kinetic rate constants. The experimental absorption rates obtained agree well with those calculated theoretically. In the second stage, a mixture of ferulic acid (4-hydroxy-3-methoxycinnamic acid), beta-resorcylic acid (2,4-dihydroxybenzoic acid) and p-hydroxybenzoic acid is ozonated under different experimental conditions. The kinetic study is performed by means of a competitive method that takes p-hydroxybenzoic acid as reference compound. The application of this model allows to determine the kinetic rate constants for each compound, which are correlated as a function of pH and temperature. The results obtained support that the kinetic regime of absorption is fast and pseudo-first order with respect to ozone, a condition required by the competitive method used.

Aerobic biological treatment of black table olive washing wastewaters: effect of an ozonation stage

Abstract The present work is a study of oxidative degradation of the organic matter present in the washing waters from the black table olive industry. Pollutant organic matter reduction was studied by an aerobic biological process and by the combination of two successive steps: ozonation pretreatment followed by aerobic biological degradation. In the single aerobic biological process, the evolution of biomass and organic matter contents was followed during each experiment. Contaminant removal was followed by means of global parameters directly related to the concentration of organic compounds in those effluents: chemical oxygen demand (COD) and total phenolic content (TP). A kinetic study was performed using the Contois model, which applied to the experimental data, provides the specific kinetic parameters of this model: 4.81×10 −2 h −1 for the kinetic substrate removal rate constant, 0.279 g VSS g COD −1 for the cellular yield coefficient and 1.92×10 −2 h −1 for the kinetic constant for endogenous metabolism. In the combined process, an ozonation pretreatment is conducted with experiments where an important reduction in the phenolic compounds is achieved. The kinetic parameters of the following aerobic degradation stage are also evaluated, being 5.42×10 −2 h −1 for the kinetic substrate removal rate constant, 0.280 g VSS g COD −1 for the cellular yield coefficient and 9.1×10 −3 h −1 for the kinetic constant for the endogenous metabolism.

Kinetics of p-hydroxybenzoic acid photodecomposition and ozonation in a batch reactor

The decomposition of p-hydroxybenzoic acid, an important pollutant present in the wastewaters of the olive oil industry, has been carried out by a direct photolysis provided by a polychromatic UV radiation source, and by ozone. In both processes, the conversions obtained as a function of the operating variables (temperature, pH and ozone partial pressure in the ozonation process) are reported. In order to evaluate the radiation flow rate absorbed by the solutions in the photochemical process, the Line Source Spherical Emission Model is used. The application of this model to the experimental results provides the determination of the reaction quantum yields which values ranged between 8.62 and 81.43 l/einstein. In the ozonation process, the film theory allows to establish that the absorption process takes place in the fast and pseudo-first-order regime and the reaction is overall second-order, first-order with respect to both reactants, ozone and p-hydroxybenzoic acid. The rate constants are evaluated and vary between 0.18x10(5) and 29.9x10(5) l/mol s depending on the temperature and pH.

Ozonation of black-table-olive industrial wastewaters: effect of an aerobic biological pretreatment

The present work is a study of oxidative degradation of the organic matter present in the washing waters from the black-table-olive industry. This oxidation is performed by an ozonation process, by an aerobic biological degradation process, and by another ozonation of biologically pretreated washing waters. In the ozonation process, a second-order kinetic reaction with respect to ozone and COD or aromaticity has been deduced. The kinetic rate constants were correlated as a function of temperature by Arrhenius-type equations. In the aerobic biological treatment, a kinetic study was performed using the Contois model, giving a value of 4.8 10−2 h−1 for the kinetic bioreaction constant. Likewise, a cell yield coefficient of 0.30 g VSS g COD−1 and a kinetic constant for the endogenous metabolisme of 1.2 10−2 h−1 were deduced. Finally, in the ozonation of biologically pretreated wash-waters, the deduced kinetic rate constants for COD and aromaticity were, respectively, 4.5 and 2.4 times higher that those corresponding to the ozonation of wash-waters without biological pretreatment. © 2000 Society of Chemical Industry

Advanced Photochemical Degradation of Emerging Pollutants: Methylparaben

This paper addresses the oxidation by ultraviolet radiation of methylparaben, a ubiquitous and suspicious preservative which is massively added to cosmetics and personal care products. Experiments included pH and temperature variation, as well as several experimental conditions such as presence/absence of hydrogen peroxide, titanium dioxide, or some different water matrix (surface water or ground water). Results were evaluated under the line source spherical emission model, so quantum yield was the adequate target variable for explaining the process. A modified Arrhenius correlation including pH level was used for modelling the whole system.

Combined treatment of olive mill wastewater by Fenton's reagent and anaerobic biological process

This work presents the application of Fentons reagent process combined with anaerobic digestion to treat an olive mill wastewater (OMW). Firstly, OMW was pre-treated by chemical oxidation in a batch reactor with Fentons reagent, using a fixed H2O2/COD ratio of 0.20, pH = 3.5 and a H2O2/Fe2+ molar ratio of 15:1. This advanced oxidation treatment allowed reaching reductions of 17.6 and 82.5% of chemical oxygen demand (COD) and total polyphenols (TP), respectively. Secondly, OMW treatment by anaerobic digestion was performed using previously adapted microorganisms immobilized in Sepiolite. These biological tests were carried out varying the substrate concentration supplied to the reactor and COD conversions from 52 to 74% were obtained. Afterwards, Fentons reagent followed by anaerobic digestion was applied to OMW treatment. This combined process presented a significant improvement on organic load removal, reaching COD degradations from 64 to 88%. Beyond the pollutant load removal, it was also monitored the yield of methane generated throughout anaerobic experiments. The methane produced ranged from 281 cm3 to 322 cm3 of CH4/g COD removed. Additionally, a methane generation kinetic study was performed using the Monod Model. The application of this model allowed observing a kinetic constant increase of the combined process (kFN = 0.036 h−1) when compared to the single anaerobic process (kF = 0.017 h−1).