Sandra Contreras

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.

Contribution of the ozonation pre-treatment to the biodegradation of aqueous solutions of 2,4-dichlorophenol

The effect of ozonation on the biodegradability of 100-ppm aqueous solutions of 2,4-dichlorophenol has been investigated. BOD at 5, 10 and 21 days, BOD/COD and BOD/TOC ratios and the average oxidation state are presented. Biodegradability measured as BOD5/COD ratio was increased from 0 of the original solution to 0.25 at the moment of removing all the initial compound (corresponding to an ozone dose of 0.12 g L-1, 0.48 for BOD21/COD ratio). To test the effect of this pre-treatment, the biological oxidation of these pre-ozonated solutions was performed in two semi-continuous stirred tank reactors, one with non-acclimated sludge and one with acclimated-to-phenol sludge. The study showed that the TOC content of the pre-treated solution could be removed up to 68% by an aerobic biological treatment as well as co-digested with municipal wastewater (TOC removal up to 82%), with similar operating retention times to a municipal wastewater plant (12-24 h). Kinetic studies based on Monod model have also been carried out. Pseudo-first-order kinetic constants were found to be in the range of 0.5-0.8 L g TVSS-1 h-1.

Influence of H2O2 and Fe(III) in the photodegradation of nitrobenzene

Abstract The influence of H 2 O 2 and Fe(III) in the degradation of nitrobenzene in aqueous solutions combined with UV radiation has been studied. A major efficiency is achieved when UV is combined with H 2 O 2 or Fe(III). Likewise, H 2 O 2 and Fe(III) concentration has an important effect on the degradation. Nitrophenol isomers are detected as the major intermediate products.

Rate equation for the degradation of nitrobenzene by ‘Fenton-like’ reagent

Abstract This paper describes the effect of temperature and initial concentration of H 2 O 2 , Fe(II), PhNO 2 and dissolved oxygen on the degradation rate of PhNO 2 in homogeneous aqueous solution by ‘Fenton-like’ reagent ([H 2 O 2 ] o ≫[Fe(II)] o ). The oxidation products o -, m - and p -nitrophenol were found as intermediates in the ratio 1:1.3–2.8:1.4–2.7 as compared with PhNO 2 when conversion of the latter was less than 25%. This fact suggests that hydroxylation of PhNO 2 was promoted by HO radicals. The reaction was investigated in a completely mixed-batch reactor under a wide range of experimental conditions: pH ∼3.0; 278–318 K; 1.5 2 O 2 ] o o 2 ] o 2 ] o 2 was determined to be 59.7 kJ mol −1 . The degradation rate of PhNO 2 follows pseudo-first-order kinetics. The results of this study demonstrate that the degradation rate of PhNO 2 in the ‘Fenton-like’ system could be predicted with sufficient precision by the equation R D =1.05×10 11 exp(−59.7/ RT )[H 2 O 2 ] o 0.68 [Fe(II)] o 1.67 [PhNO 2 ] o −0.32 . The second-order rate constant for the overall rate of H 2 O 2 decomposition by Fe(III) was found to be 0.83 M −1 s −1 at 298 K. The value of the steady-state HO radical concentration in the ‘Fenton-like’ reaction was found to be ∼10 −13 M, as estimated by two independent methods.

Simultaneous in situ generation of hydrogen peroxide and Fenton reaction over Pd–Fe catalysts

High mineralization degree of organic compounds can be achieved by a novel environmentally-friendly full heterogeneous Pd-Fe catalytic system, which involves in situ generation of hydrogen peroxide from formic acid and oxygen, and oxidation of organic compounds by Fenton process in a one-pot reaction.

Hydrogen substitutes for the in situ generation of H2O2: An application in the Fenton reaction

This study investigates the ability of formic acid, hydrazine and hydroxylamine to act as H(2) substitutes in conducting phenol degradation by Fenton reaction using in situ generated hydrogen peroxide. The processes were performed with semi-heterogeneous (Pd/Al(2)O(3)+soluble Fe(2+)) and fully heterogeneous (FePd/Al(2)O(3)) catalytic systems under ambient conditions. In contrast to bulk H(2)O(2) production conditions, hydrazine is able to produce H(2)O(2)in situ followed by phenol degradation using Pd/Al(2)O(3)+Fe(2+) at pH 3 without the need for halide ions. However, a degree of mineralization exceeding 37% could not be achieved. The significant production of in situ H(2)O(2) at the inherent acidic pH of hydroxylammonium sulfate in the presence of Pd/Al(2)O(3)+Fe(2+) was also found to differ from the bulk production of H(2)O(2), in which no H(2)O(2) was detected. A remarkable degree of mineralization (ca. 65%) as well as fast phenol degradation during the reaction started at pH 7 over FePd/Al(2)O(3) may be an advantage of using hydroxylamine. On the other hand, using formic acid, H(2)O(2) was produced at a moderate rate, thereby achieving higher efficiency in the mineralization of phenol. Most importantly, the catalysts were more stable in the presence of formic acid than hydrazine or hydroxylamine.

Size and aspect ratio control of Pd2Sn nanorods and their water denitration properties

Monodisperse Pd2Sn nanorods with tuned size and aspect ratio were prepared by co-reduction of metal salts in the presence of trioctylphosphine, amine, and chloride ions. Asymmetric Pd2Sn nanostructures were achieved by the selective desorption of a surfactant mediated by chlorine ions. A preliminary evaluation of the geometry influence on catalytic properties evidenced Pd2Sn nanorods to have improved catalytic performance. In view of these results, Pd2Sn nanorods were also evaluated for water denitration.

State of the art of produced water treatment

Produced water (PW) is the wastewater generated when water from underground reservoirs is brought to the surface during oil or gas extraction. PW is generated in large amounts and has a complex composition, containing various toxic organic and inorganic compounds. PW is currently treated in conventional trains that include phase separators, decanters, cyclones and coarse filters in order to comply with existing regulation for discharge. These treatment trains do not achieve more restrictive limitations related to the reuse of the effluent (reinjection into extraction wells) or other beneficial uses (e.g., irrigation). Therefore, and to prevent environmental pollution, further polishing processes need to be carried out. Characterization of the PW to determine major constituents is the first step to select the optimum treatment for PW, coupled with environmental factors, economic considerations, and local regulatory framework. This review tries to provide an overview of different treatments that are being applied to polish this type of effluents. These technologies include membranes, physical, biological, thermal or chemical treatments, where special emphasis has been made on advanced oxidation processes due to the advantages offered by these processes. Commercial treatments, based on the combination, modification and improvement of simpler treatments, were also discussed.

Assessment of cationic surfactants mineralization by ozonation and photo-Fenton process.

Aqueous solutions of two important quaternary ammonium compounds--16-BAC (benzyl-dimethyl-hexadecylammonium-chloride) and 18-BAC (benzyl-dimethyl-stearylammonium-chloride)--were treated by the ozonation and photo-Fenton processes at different ozone doses and hydrogen peroxide concentrations, respectively. During the photo-Fenton experiments, two different types of lamps were used--a UV mercury vapor medium pressure lamp and a xenon lamp, which simulates solar radiation. The total organic carbon removal was monitored to follow the mineralization of the surfactants. According to the experimental results, after 90 minutes of treatment, the photo-Fenton process achieved up to 80% of mineralization when the UV lamp was used. The efficiency of the photo-Fenton with the xenon lamp was lower. The ozonation process reached, at most, 50% mineralization at the used conditions (ozone dose = 7.57 g/h).

Sequential Ozonation and Biological Oxidation of Wastewaters: A Model Including Biomass Inhibition by Residual Oxidant

We modeled the potential impact of a residual oxidant (ozone in the present case, known to be a strong bactericide) on the performance of a combined chemical and biological water treatment. This model is fashioned by adapting a recent model for the kinetics of ozone disinfection to an activated sludge system performing in the presence of ozone residuals. Our new model allows prediction of the bioreactor performance under different substrate loadings and residual oxidant concentrations, helping to identify regimes where air stripping would be necessary before the second step.