Juan J. Rodriguez

Assessment of the generation of chlorinated byproducts upon Fenton-like oxidation of chlorophenols at different conditions.

Homogeneous Fenton-like (H(2)O(2)/Fe(3+)) oxidation proved to be highly efficient in the degradation of monochlorophenols but some important issues need to be considered depending on the operating conditions. When using the stoichiometric amount of H(2)O(2) and a dose of Fe(3+) in the range of 10-20mg/L, complete breakdown of 4-CP up to CO(2) and short-chain acids was achieved. Nevertheless, when substoichiometric amounts of H(2)O(2) or lower concentrations of iron were used, significant differences between the TOC measured and the calculated from the identified species were found. These differences were attributed to condensation byproducts, including chlorinated species, formed by oxidative coupling reactions. PCBs, dioxins and dichlorodiphenyl ethers were identified. A solid residue was also formed consisting mainly in carbon, oxygen and chlorine including also Fe. The occurrence of these highly toxic species must be carefully considered in the application of Fenton oxidation to wastewaters containing chlorophenols. The possibility of reducing costs by lowering the H(2)O(2) dose below the stoichiometric one needs to take this into account.

Semicontinuous Fenton oxidation of phenol in aqueous solution. A kinetic study.

This work investigates the Fenton oxidation of phenol in a semicontinuous reactor where the overall amount of H(2)O(2) is distributed as a continuous feed upon the reaction time. The experiments were carried out at 25 degrees C and atmospheric pressure, with 100mg/L initial phenol concentration and iron dosages from 1 to 100 mg/L. H(2)O(2) aqueous solution was continuously fed during 4h reaction time up to an overall dose varying within the range of 500-5000 mg/L. The results in terms of evolution of phenol, H(2)O(2) and intermediates, as well as TOC abatement were compared with those obtained in conventional batch operation. It was found that the oxidation rates for phenol and intermediates were lower when adding the H(2)O(2) continuously. However, a higher abatement of TOC was reached at the end of the 4-h reaction time, in spite of a similar overall H(2)O(2) consumption. This is the result of a more efficient OH generation throughout the semicontinuous process, favouring the reaction with the organic species and reducing the occurrence of competitive scavenging reactions involving Fe(2+), H(2)O(2) and OH. Two kinetic models were proposed, one for describing the evolution of phenol, aromatics and H(2)O(2) and the other for TOC. The influence of the operating conditions on the kinetic constants was also studied, looking for the optimal conditions in terms of both, environmental and economic points of view.

Cometabolic biodegradation of 4-chlorophenol by sequencing batch reactors at different temperatures

The simultaneous removal of 4-chlorophenol (4-CP) and phenol in lab-scale sequencing batch reactors at different temperatures has been studied. Phenol feed concentration was fixed at 525 mg/L and 4-CP concentration was increased from 105 to 2100 mg/L at a constant hydraulic residence time (HRT) of 10.5 d. Complete phenol and 4-CP biodegradation was achieved during the aerobic stage working with 4-CP concentrations up to 1470 mg/L in the feed. Both 4-CP and phenol specific initial removal rates were strongly affected by 4-CP feed concentration and temperature. Only at the highest temperature tested (35 degrees C) it was possible to increase the maximum assimilative 4-CP concentration by the biological sludge up to 2100 mg/L, and a significant reduction of the ecotoxicity of the effluents was observed. 4-chlorocatechol (4-CC) was identified as the major intermediate in the aerobic cometabolic 4-CP degradation, being the ecotoxicity of that species substantially lower than that of 4-CP.

Trends in the Intensification of the Fenton Process for Wastewater Treatment: An Overview

The implementation of increasingly stringent regulations for wastewater discharge has enforced research efforts toward either the implementation of novel treatments or the improvement of those presently available. The literature on the use of Fenton oxidation in wastewater treatment has established this method as one of the most effective and suitable process for the abatement of recalcitrant water pollutants. However, despite the many advantages of the conventional Fenton process, there are issues relative to pH modulation, the cost associated to H2O2 and catalyst consumption as well as to sludge disposal that limit a more extended full-scale application. In recent years, several solutions have been developed for the sake of improving Fenton (or Fenton-like) oxidation as a cost-effective technology. This paper presents a thorough review on the different ways of intensifying the Fenton by using radiation, electrochemistry, and/or heterogeneous catalysts, as well as by optimizing the main operating conditions in the conventional homogeneous system. The application of these enhanced technologies to synthetic and real industrial wastewaters is described and discussed.

Enhancement of cometabolic biodegradation of 4-chlorophenol induced with phenol and glucose as carbon sources by Comamonas testosteroni

The biological degradation of phenol and 4-chlorophenol (4-CP) by Comamonas testosteroni CECT 326T has been studied. Phenol and 4-CP were treated alone as a sole carbon and energy source, but only phenol was completely degraded by C. testosteroni. Since the presence of cosubstrates can enhance the toxic compounds removal by pure cultures, phenol and glucose were added as growth substrates for cometabolic transformation of 4-CP. High efficiencies were obtained in all the experiments carried out in presence of both cosubstrates. In spite of the fact that the addition of glucose reduced the lag phase of 4-CP removal, lower phenol concentrations were required to obtain the same degradation efficiencies. The cometabolic transformation of 4-CP was closely related with the extent of phenol removal. The values of the 4-CP/biomass concentration ratio (S/X) obtained for discriminating between complete (S/X ≤ 0.11) and partial 4-CP (S/X ≥ 0.31) transformation showed a narrower range than that reported in the literature. The extent of the cometabolic 4-CP transformation in the presence of phenol could be further enhanced by using glucose as an additional carbon and energy source. However, no significant influence of glucose concentration on 4-CP removal was observed over the concentration range studied.

Comparison of UASB and EGSB performance on the anaerobic biodegradation of 2,4-dichlorophenol

The anaerobic degradation of 2,4-dichlorophenol (2,4-DCP) in upflow anaerobic sludge blanket (UASB) and expanded granular sludge bed (EGSB) reactors using glucose as main carbon source was studied. The performance of both systems was compared in terms of 2,4-DCP and COD removal efficiencies, methane production, stability, granular sludge adaptability as well as reversion of the bacterial inhibition. Both organic and 2,4-DCP loading rates were incrementally varied through the experiments. With loading rates of 1.9 gCODL(-1)d(-1) and 100mg 2,4-DCP L(-1)d(-1), 75% and 84% removal efficiencies of this compound, accompanied by COD consumption efficiencies of 61% and 80% were achieved in the UASB and EGSB reactors, respectively. In these conditions, methane production reached 0.088 L CH(4)g(-1) COD in the EGSB reactor whereas in the UASB reactor was almost negligible. Decreasing the 2,4-DCP loading rate to 30 mgL(-1)d(-1) an improvement in the methane production was observed in both reactors (methanogenic activity of 0.148 and 0.192 L CH(4)g(-1) COD in UASB and EGSB reactors, respectively). Efficiency of dechlorination was improved in both reactors from around 30% to 80% by reducing to one-half the COD due to a decreasing of the 4-chlorophenol concentration accumulated in the effluents of both reactors. The dechlorination efficiency of the UASB reactor was dramatically inhibited at a 2,4-DCP feed concentration above around 210 mgL(-1) because of 2,4-DCP accumulation in the effluent. SEM studies revealed no significant morphological changes in the sludge granules.

Pd-Al pillared clays as catalysts for the hydrodechlorination of 4-chlorophenol in aqueous phase.

Catalysts based on pillared clays with Pd-Al were synthesized from a commercial bentonite and tested for catalytic hydrodechlorination (HDC) using 4-chlorophenol (4-CPhOH) as target compound and formic acid as hydrogen source. Stable Pd-Al pillared clays, with a strong fixation of the active phase to the solid support were obtained since no Pd was detected in the reaction media. The incorporation of Pd to the pillared clay structure yielded catalysts with high activity in the reaction studied reaching a complete removal of the 4-CPhOH under mild conditions of temperature (50-70 degrees C). Phenol was not the only reaction product formed, since a more hydrogenated product such as cyclohexanone was detected in the effluent, which indicates additional hydrogenation of phenol. The influence of the method of introduction of Pd in the pillared clay (ion-exchange or impregnation) and Pd concentration in the catalytic activity were studied as well as other important operating variables such as reaction temperature, catalyst concentration, 4-CPhOH initial concentration and formic acid to 4-CPhOH molar ratio. The catalysts prepared suffered deactivation after three consecutive runs, probably due to carboneous deposits formation since no appreciable Pd leaching was observed.

Interactions of Ionic Liquids and Acetone: Thermodynamic Properties, Quantum-Chemical Calculations, and NMR Analysis

The interactions between ionic liquids (ILs) and acetone have been studied to obtain a further understanding of the behavior of their mixtures, which generally give place to an exothermic process, mutual miscibility, and negative deviation of Raoults law. COSMO-RS was used as a suitable computational method to systematically analyze the excess enthalpy of IL-acetone systems (>300), in terms of the intermolecular interactions contributing to the mixture behavior. Spectroscopic and COSMO-RS results indicated that acetone, as a polar compound with strong hydrogen bond acceptor character, in most cases, establishes favorable hydrogen bonding with ILs. This interaction is strengthened by the presence of an acidic cation and an anion with dispersed charge and non-HB acceptor character in the IL. COSMO-RS predictions indicated that gas-liquid and vapor-liquid equilibrium data for IL-acetone systems can be finely tuned by the IL selection, that is, acting on the intermolecular interactions between the molecular and ionic species in the liquid phase. NMR measurements for IL-acetone mixtures at different concentrations were also carried out. Quantum-chemical calculations by using molecular clusters of acetone and IL species were finally performed. These results provided additional evidence of the main role played by hydrogen bonding in the behavior of systems containing ILs and HB acceptor compounds, such as acetone.

Influence of Water Vapor on the Adsorption of VOCs on Lignin‐Based Activated Carbons

Abstract Activated carbons with a wide range of burn‐off degrees obtained from Eucalyptus kraft lignin have been used to study the influence of the presence of water vapor on VOCs adsorption. The amount adsorbed and the rate of adsorption of both benzene and water vapor increase with activated carbon burn‐off as a consequence of an increase of micropore volume, broadening of micropore size distribution and increasing development of meso‐ and macroporosity. Similar results were found for MEK and methanol. Benzene is only partially desorbed at the adsorption temperature and an appreciable amount of it remains in the carbon, most likely in the narrow micropores. On the contrary, water vapor is completely desorbed at the adsorption temperature and its adsorption profile clearly exhibits two steps with different adsorption rates, associated to water molecules adsorbed on the active sites given rise to cluster formation and further migration and filling of the micropores. Adsorption with mixtures of VOC and water vapor has been carried out. The total amount adsorbed by the carbon, near the equilibrium point, is higher than in the case of the stream containing only the VOC. The adsorption rates for the mixtures streams are similar to that for the corresponding streams containing only the VOC in the case of carbons with a well developed porous structure. However, the presence of water vapor increases the rate of adsorption on the activated carbons with narrower microporosity. Saturation of the activated carbon with water vapor prior to the adsorption of a mixture containing benzene and water vapor has shown little effect on the amount of benzene adsorbed, suggesting that water and benzene molecules are adsorbed in different sites on the carbon surface.

Hydrodechlorination of 4-chlorophenol in water with formic acid using a Pd/activated carbon catalyst

This work reports on the feasibility of hydrodechlorination as a treatment technique for chlorophenols-bearing wastewaters using formic acid as a hydrogen source. 4-Chlorophenol (4-CPhOH) has been used as target compound and the experiments were carried out in batch and continuous mode with a commercial activated carbon-supported Pd (0.5 wt.%) catalyst. The variables studied in the batch runs were HCOOH/4-CPhOH molar ratio (10-1000), temperature (25-75 degrees C) and catalyst concentration (250-1000 mg/L). The continuous experiments were performed in a fixed bed reactor where aqueous solutions of formic acid and 4-CPhOH with molar ratios between 50 and 100 were continuously fed to the reactor, at different space-time values in the range of 10.7-42.8 kg(cat)h/mol. Reaction temperatures from 35 to 100 degrees C were tested and the pressure was fixed at 2.5bar. Conversion values above 99% for 4-CPhOH were obtained in batch experiments, but using a HCOOH/4-CPhOH molar ratio as high as 500. Moreover, most of the phenol produced was adsorbed on the catalyst. Continuous runs were performed to evaluate the efficiency of the catalyst under lower HCOOH/4-CPhOH ratios and to explore the possibility of converting phenol to more hydrogenated products. The results indicated that the HCOOH/4-CPhOH molar ratios needed were an order of magnitude lower than those required in batch runs to achieve conversions of 4-CPhOH close to 95%. Besides, phenol was not the only reaction product formed, since a more hydrogenated product such as cyclohexanone was detected in the effluent, which indicates additional hydrogenation of phenol in contrast to the behaviour observed in batch experiments. A loss of activity was observed in the continuous runs after 20-30 h on stream.