Jaime Giménez

Comparison of different advanced oxidation processes for phenol degradation.

Advanced Oxidation Processes (O3, O3/H2O2, UV, UV/O3, UV/H2O2, O3/UV/H2O2, Fe2+ /H2O2 and photocatalysis) for degradation of phenol in aqueous solution have been studied in earlier works. In this paper, a comparison of these techniques is undertaken: pH influence, kinetic constants, stoichiometric coefficient and optimum oxidant/pollutant ratio. Of the tested processes, Fenton reagent was found to the fastest one for phenol degradation. However, lower costs were obtained with ozonation. In the ozone combinations, the best results were achieved with single ozonation. As for the UV processes, UV/H2O2 showed the highest degradation rate.

Degradation of 32 emergent contaminants by UV and neutral photo-fenton in domestic wastewater effluent previously treated by activated sludge

This study focuses on the removal of 32 selected micropollutants (pharmaceuticals, corrosion inhibitors and biocides/pesticides) found in an effluent coming from a municipal wastewater treatment plant (MWTP) based on activated sludge. Dissolved organic matter was present, with an initial total organic carbon of 15.9 mg L(-1), and a real global quantity of micropollutants of 29.5 μg L(-1). The treatments tested on the micropollutants removal were: UV-light emitting at 254 nm (UV(254)) alone, dark Fenton (Fe(2+,3+)/H(2)O(2)) and photo-Fenton (Fe(2+,3+)/H(2)O(2)/light). Different irradiation sources were used for the photo-Fenton experiences: UV(254) and simulated sunlight. Iron and H(2)O(2) concentrations were also changed in photo-Fenton experiences in order to evaluate its influence on the degradation. All the experiments were developed at natural pH, near neutral. Photo-Fenton treatments employing UV(254), 50 mg L(-1) of H(2)O(2), with and without adding iron (5 mg L(-1) of Fe(2+) added or 1.48 mg L(-1) of total iron already present) gave the best results. Global percentages of micropollutants removal achieved were 98 and a 97% respectively, after 30 min of treatments. As the H(2)O(2) concentration increased (10, 25 and 50 mg L(-1)), best degradations were observed. UV(254), Fenton, and photo-Fenton under simulated sunlight gave less promising results with lower percentages of removal. The highlight of this paper is to point out the possibility of the micropollutants degradation in spite the presence of DOM in much higher concentrations.

Ultrasonic treatment of water contaminated with ibuprofen

The application of ultrasound (US) waves for remediation of wastewater is an area of increasing interest and promising results. The aim of this paper is to evaluate the influence of several parameters of the US process on the degradation of ibuprofen (IBP), a widely used non-steroidal anti-inflammatory recalcitrant drug found in water. Applied US power, dissolved gas, pH and initial concentration of IBP were the parameters investigated under sonication (300 kHz). Ultrasound increased the degradation of IBP from 30 to 98% in 30 min. Initial rate of IBP degradation was evaluated in the range of 1.35 and 6.1 micromolL(-1)min(-1) for initial concentrations of 2 to 21 mgL(-1) or 9.7 micromolL(-1) to 101 micromolL(-1), respectively. Under air and oxygen the degradation rate of IBP was 4 micromolL(-1)min(-1) being higher than that when argon was used. The most favorable degradation pH was acidic media. Complete removal of IBP was achieved but some dissolved organic carbon (DOC) remained in solution showing that long-lived intermediates were recalcitrant to the US irradiation. However, chemical and biological oxygen demands (COD and BOD(5)) indicated that the process oxidize the ibuprofen compound to biodegradable substances removable in a subsequent biological step.

Degradation of the emerging contaminant ibuprofen in water by photo-Fenton

In this study the degradation of the worldwide Non-Steroidal Anti-Inflammatory Drug (NSAID) ibuprofen (IBP) by photo-Fenton reaction by use of solar artificial irradiation was carried out. Non-photocatalytic experiments (complex formation, photolysis and UV/Vis-H(2)O(2) oxidation) were executed to evaluate the isolated effects and additional differentiated degradation pathways of IBP. The solar photolysis cleavage of H(2)O(2) generates hydroxylated-IBP byproducts without mineralization. Fenton reaction, however promotes hydroxylation with a 10% contamination in form of a mineralization. In contrast photo-Fenton in addition promotes the decarboxylation of IBP and its total depletion is observed. In absence of H(2)O(2) a decrease of IBP was observed in the Fe(II)/UV-Vis process due to the complex formation between iron and the IBP-carboxylic moiety. The degradation pathway can be described as an interconnected and successive principal decarboxylation and hydroxylation steps. TOC depletion of 40% was observed in photo-Fenton degradation. The iron-IBP binding was the key-point of the decarboxylation pathway. Both decarboxylation and hydroxylation mechanisms, as individual or parallel process are responsible for IBP removal in Fenton and photo-Fenton systems. An increase in the biodegradability of the final effluent after photo-Fenton treatment was observed. Final BOD(5) of 25 mg L(-1) was reached in contrast to the initial BOD(5) shown by the untreated IBP solution (BOD(5)<1 mg L(-1)). The increase in the biodegradability of the photo-Fenton degradation byproducts opens the possibility for a complete remediation with a final post-biological treatment.

Low-concentrating CPC collectors for photocatalytic water detoxification: comparison with a medium concentrating solar collector

The photocatalytic oxidation of 2,4-Dichlorophenol (DCP), using TiO 2 suspensions under solar radiation, has been studied at pilot-plant scale at the Plataforma Solar de Almeria (PSA). Two different reactor designs were tested: a medium concentrating radiation system called a Parabolic-Trough-Collector Reactor, PTCR, equipped with two motors (azimuth and elevation) to adjust the position of the module perpendicular to the sun, and a low-concentrating radiation system, the Compound-Parabolic-Concentrator Reactor, CPCR, facing south and inclined 37 degrees. Substrates were dissolved in water to required mg L −1 levels in a reservoir tank. In both cases, 0.2 g L −1 of the suspended TiO 2 catalyst was used in a 250 L solution of the contaminant, which was recirculated through the photoreactors using a centrifugal pump and an intermediate reservoir tank. The advantages and disadvantages of the two types of photoreactors in DCP oxidation are compared and discussed. The strong potential of photocatalytic peroxydisulphate-assisted degradation in high DCP concentrations was demonstrated in both systems, and chemical actinometry (the decomposition reaction of oxalic acid by radiated uranyl salts) in the CPC reactor is compared with the results obtained in the PTC.

Mineralization enhancement of a recalcitrant pharmaceutical pollutant in water by advanced oxidation hybrid processes

Degradation of the biorecalcitrant pharmaceutical micropollutant ibuprofen (IBP) was carried out by means of several advanced oxidation hybrid configurations. TiO(2) photocatalysis, photo-Fenton and sonolysis - all of them under solar simulated illumination - were tested in the hybrid systems: sonophoto-Fenton (FS), sonophotocatalysis (TS) and TiO(2)/Fe(2+)/sonolysis (TFS). In the case of the sonophoto-Fenton process, the IBP degradation (95%) and mineralization (60%) were attained with photo-Fenton (FH). The presence of ultrasonic irradiation slightly improves the iron catalytic activity. On the other hand, total removal of IBP and elimination of more than 50% of dissolved organic carbon (DOC) were observed by photocatalysis with TiO(2) in the presence of ultrasound irradiation (TS). In contrast only 26% of mineralization was observed by photocatalysis with H(2)O(2) (TH) in the absence of ultrasound irradiation. Additional results showed that, in the TFS system, 92% of DOC removal and complete degradation of IBP were obtained within 240 min of treatment. The advanced oxidation hybrid systems seems to be a promising alternative for full elimination/mineralization for the recalcitrant micro-contaminant IBP.

Photocatalytic reduction of chromium(VI) with titania powders in a flow system. Kinetics and catalyst activity

The photocatalytic reduction of chromium(VI) with titania powders has been studied using a continuous flow system. The kinetics and the influence of catalyst concentration and pH on the reaction rate have been analyzed. Kinetic results show a half-order reaction at pH lower than 4, and a first-order reaction for pH above 4. Deactivation of titania was found when reduction of chromium(VI) was carried out at pH higher than 4, due to the fouling of titania caused by chromium hydroxides. A model for catalyst deactivation has been developed. It describes the performance of the catalyst at the different experimental conditions tested. Furthermore, the results obtained in the kinetic studies are supported by data from electronic microscopy and adsorption techniques.

Photocatalytic degradation of phenol: Comparison between pilot-plant-scale and laboratory results

Abstract The photocatalytic oxidation of phenol, using TiO2 suspensions, has been studied at pilot-plant-scale with solar radiation, at the Plataforma Solar de Almeria (PSA), Spain, and at the laboratory level with Xe lamps, at the University of Barcelona (UB). Two different reactor designs were tested at the PSA: a high concentrating radiation systems (Heliomans) and a low concentrating radiation systems (CPCs). Both were characterized from the point of view of the radiation field. The factors relating the solar radiation arriving at the radiation entering the photoreactors have been determined. Kinetic experiments were performed. In all the cases, the reaction rate shows linear dependence on the square root of the photonic flow entering the photoreactors. The kinetics is the first order with respect to the phenol concentration. The kinetic constants have been determined and compared for all the systems tested (laboratory and pilot-plant-scale). The efficiencies of Heliomans and CPCs modules have been compared.

Effects of radiation absorption and catalyst concentration on the photocatalytic degradation of pollutants

Abstract This study is dealing with the reaction rate dependence on catalyst concentration and light absorption in photocatalytic processes. Models relating the reaction rate to the absorbed radiation by the catalyst (titania in suspension) are proposed. To apply these models, the system is divided into layers and each layer is divided into cells, assuming that there is only one particle (agglomerate) of catalyst in each cell. The extensive reaction rate can be calculated as the sum of the reaction rate in each cell, being this proportional to the light absorbed by each particle. Two different models are proposed for light propagation through the reaction medium (exponential and probabilistic model). The extinction coefficients have been estimated by using transmittance measurements related to sedimentation rates changing according to catalyst concentration and pH. The integration of these models, taking into account the expression of the reaction rate, allows to obtain equations that can explain the trends observed in the photocatalytic treatment of Cr(VI) and phenol, by using TiO2 (Degussa-P25) in suspension.

Photocatalysis and radiation absorption in a solar plant

Abstract Recently, many papers have appeared in literature about photocatalytic detoxification. However, progress from laboratory data to the industrial solar reactor is not easy. Kinetic models for heterogeneous catalysis can be used to describe the photocatalytic processes, but luminic steps, related to the radiation, have to be added to the physical and chemical steps considered in heterogeneous catalysis. Thus, the evaluation of the radiation, and its distribution, inside a photocatalytic reactor is essential to extrapolate results from laboratory to outdoor experiments and to compare the efficiency of different installations. This study attempts to validate the experimental set up and theoretical data treatment for this purpose in a Solar Pilot Plant. The procedure consists of the calibration of different sunlight radiometers, the estimation of the radiation inside the reactor, and the validation of the results by actinometric experiments. Finally, a comparison between kinetic constants, for the same reaction in the laboratory (artificial light) and field conditions (sun light), is performed to demonstrate the advantages of knowing the radiation inside a large photochemical reactor.