José A. Peres

Removal of COD from olive mill wastewater by Fenton's reagent: kinetic study.

This work describes the application of Fentons reagent (H(2)O(2)/Fe(2+)) to the removal of chemical oxygen demand (COD) from olive mill wastewater (OMW) in a laboratory-scale batch reactor. The effect of different operational conditions, namely, hydrogen peroxide and ferrous ion concentrations, temperature and initial pH were evaluated. ORP, pH and dissolved oxygen were on-line monitored. Working with an initial pH equal to 3.5, a temperature of 30 degrees C, a molar ratio H(2)O(2)/Fe(2+)=15 and a weight ratio R=H(2)O(2)/COD=1.75 makes possible a COD conversion of 70%. A kinetic study was carried out using a modified pseudo-first-order model. The experiments performed at different temperatures allowed the calculation of the Arrhenius equation parameters and the global activation energy for the pseudo-first-order reaction (28.2 kJ/mol).

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.

Mature landfill leachate treatment by coagulation/flocculation combined with Fenton and solar photo-Fenton processes

This work reports the treatment of a mature landfill leachate through the application of chemical-based treatment processes in order to achieve the discharge legal limits into natural water courses. Firstly, the effect of coagulation/flocculation with different chemicals was studied, evaluating the role of different initial pH and chemicals concentration. Afterwards, the efficiency of two different advanced oxidation processes for leachate remediation was assessed. Fenton and solar photo-Fenton processes were applied alone and in combination with a coagulation/flocculation pre-treatment. This physicochemical conditioning step, with 2 g L(-1) of FeCl3 · 6H2O at pH 5, allowed removing 63% of COD, 80% of turbidity and 74% of total polyphenols. Combining the coagulation/flocculation pre-treatment with Fenton reagent, it was possible to reach 89% of COD removal in 96 h. Moreover, coagulation/flocculation combined with solar photo-Fenton revealed higher DOC (75%) reductions than single solar photo-Fenton (54%). In the combined treatment (coagulation/flocculation and solar photo-Fenton), it was reached a DOC reduction of 50% after the chemical oxidation, with 110 kJ L(-1) of accumulated UV energy and a H2O2 consumption of 116 mM. Toxicity and biodegradability assays were performed to evaluate possible variations along the oxidation processes. After the combined treatment, the leachate under study presented non-toxicity but biodegradability increased.

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.

Ozonation kinetics of winery wastewater in a pilot-scale bubble column reactor

The degradation of organic substances present in winery wastewater was studied in a pilot-scale, bubble column ozonation reactor. A steady reduction of chemical oxygen demand (COD) was observed under the action of ozone at the natural pH of the wastewater (pH 4). At alkaline and neutral pH the degradation rate was accelerated by the formation of radical species from the decomposition of ozone. Furthermore, the reaction of hydrogen peroxide (formed from natural organic matter in the wastewater) and ozone enhances the oxidation capacity of the ozonation process. The monitoring of pH, redox potential (ORP), UV absorbance (254 nm), polyphenol content and ozone consumption was correlated with the oxidation of the organic species in the water. The ozonation of winery wastewater in the bubble column was analysed in terms of a mole balance coupled with ozonation kinetics modeled by the two-film theory of mass transfer and chemical reaction. It was determined that the ozonation reaction can develop both in and across different kinetic regimes: fast, moderate and slow, depending on the experimental conditions. The dynamic change of the rate coefficient estimated by the model was correlated with changes in the water composition and oxidant species.

Tertiary treatment of pulp mill wastewater by solar photo-Fenton.

This work reports on pulp mill wastewater (PMW) tertiary treatment by Fenton (Fe(2+)/H(2)O(2)) and solar photo-Fenton (Fe(2+)/H(2)O(2)/UV) processes in a pilot plant based on compound parabolic collectors (CPCs). Solar photo-Fenton reaction is much more efficient than the respective dark reaction under identical experimental conditions. It leads to DOC mineralisation, COD and total polyphenols (TP) removal higher than 90%. The solar photo-Fenton experiment with 5mg Fe L(-1) reaches 90% of DOC mineralisation with 31kJ L(-1) of UV energy and 50mM of H(2)O(2). The initial non-biodegradability of PMW, as shown by respirometry assays and BOD(5)/COD ratio, can be changed after a solar photo-Fenton treatment. Experiments with 20 and 50mg Fe L(-1) revealed that solar photo-Fenton can reach the same DOC degradation (90%), however, consuming less H(2)O(2) and time. Diluting the initial organic load to 50% also diminishes the dosage of H(2)O(2) and the necessary reaction time to achieve high DOC removals. Accordingly, solar photo-Fenton can be considered an alternative or complementary process to improve the performance of a biologic treatment and, subsequently, achieve legal limits on discharge into natural waters.

Solar Photochemical Treatment of Winery Wastewater in a CPC Reactor

Degradation of simulated winery wastewater was studied in a pilot-scale compound parabolic collector (CPC) solar reactor. Total organic carbon (TOC) reduction by heterogeneous photocatalysis (TiO(2)) and homogeneous photocatalysis with photo-Fenton was observed. The influence of TiO(2) concentration (200 or 500 mg/L) and also of combining TiO(2) with H(2)O(2) or Na(2)S(2)O(8) on heterogeneous photocatalysis was evaluated. Heterogeneous photocatalysis with TiO(2), TiO(2)/H(2)O(2) and TiO(2)/S(2)O(8)(2-) is revealed to be inefficient in removing TOC, originating TOC degradation of 10%, 11% and 25%, respectively, at best. However, photo-Fenton experiments led to 46% TOC degradation in simulated wastewater prepared with diluted wine (WV) and 93% in wastewater prepared with diluted grape juice (WG), and if ethanol is previously eliminated from mixed wine and grape juice wastewater (WW) by air stripping, it removes 96% of TOC. Furthermore, toxicity decreases during the photo-Fenton reaction very significantly from 48% to 28%. At the same time, total polyphenols decrease 92%, improving wastewater biodegradability.

Characteristics of p-hydroxybenzoic acid oxidation using Fenton's reagent.

Abstract The objective of this work was to investigate the oxidation of p-hydroxybenzoic acid by the Fentons reagent. Batch experiments were carried out to investigate the influence of the most important process variables: hydrogen peroxide and ferrous salt concentrations, pH, and temperature. The optimal results obtained indicate that p-hydroxybenzoic acid can be effectively degraded using Fentons oxidation within 10-min reaction time by using a molar ratio H2O2: p-hydroxybenzoic acid of 4:1 and H2O2:Fe2+ of 15:1, at 30°C and pH = 3.0. The behavior of ORP and pH along the reaction time for different values of R (molar ratio H2O2: p-hydroxybenzoic acid) was also discussed. A pseudo-first order model was applied to describe the oxidation kinetics of p-hydroxybenzoic acid by Fentons reagent.