Pilar Marco

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.

Reactor modelling in the photocatalytic oxidation of wastewater

Two different experimental devices have been tested for the photocatalytic oxidation of phenol, by using TiO 2 suspensions. At the laboratory level, experiments were carried out in microreactors with Xe lamps. At pilot plant scale, the experiments were done at the Plataforma Solar de Almeria (PSA), Spain, by using a high concentrating radiation systems (Heliomans) and solar radiation. Both systems were characterized from the point of view of the radiation field. Kinetic experiments and radiation measurements showed that kinetics are first order with respect to the phenol concentration, and a linear dependence of the reaction rate on the square root of the photonic flow. Kinetic constants (k) were calculated for both systems considering only concentration-time data. Results indicate that k values obtained at the laboratory were ten times greater than these obtained at the PSA. However, results improve when the radiation entering and the radiation absorbed by the catalyst were considered. The fitting of concentration-radiation data drives to values of the kinetic constants more similar for both systems and for all the catalyst concentrations tested. Thus, these new constants can be useful for the change of scale.

Adsorption and Photocatalytic Decomposition of the -Blocker Metoprolol in Aqueous Titanium Dioxide Suspensions: Kinetics, Intermediates, and Degradation Pathways

This study reports the photocatalytic degradation of the -blocker metoprolol (MET) using TiO2 suspended as catalyst. A series of photoexperiments were carried out by a UV lamp, emitting in the 250–400 nm range, providing information about the absorption of radiation in the photoreactor wall. The influence of the radiation wavelength on the MET photooxidation rate was investigated using a filter cutting out wavelengths shorter than 280 nm. Effects of photolysis and adsorption at different initial pH were studied to evaluate noncatalytic degradation for this pharmaceutical. MET adsorption onto titania was fitted to two-parameter Langmuir isotherm. From adsorption results it appears that the photocatalytic degradation can occur mainly on the surface of TiO2. MET removed by photocatalysis was 100% conditions within 300 min, while only 26% was achieved by photolysis at the same time. TiO2 photocatalysis degradation of MET in the first stage of the reaction followed approximately a pseudo-first-order model. The major reaction intermediates were identified by LC/MS analysis such as 3-(propan-2-ylamino)propane-1,2-diol or 3-aminoprop-1-en-2-ol. Based on the identified intermediates, a photocatalytic degradation pathway was proposed, including the cleavage of side chain and the hydroxylation addition to the parent compounds.

Photo-Fenton treatment of valproate under UVC, UVA and simulated solar radiation

The abatement of valproic acid sodium salt (VA) via photo-Fenton process was investigated to evaluate the effect of irradiation type. Three different light sources have been used: UVA (black light blue lamps, BLB reactor), UVC (UVC reactor) and simulated sunlight in a Solarbox (SB). Using the highest concentrations of Fe2+ (10mgL-1) and H2O2 (150mgL-1), 100% of VA degradation was observed in BLB and UVC devices, and 89.7% in Solarbox. Regarding mineralization, 67.4% and 76.4% of TOC conversion were achieved in BLB and UVC, respectively. In Solarbox, mineralization was negligible. Treated solutions under UVA or UVC radiation became biodegradable (BOD5/COD≥0.25), which was not observed in Solarbox where BOD5/COD achieved was only 0.20. Regarding to toxicity (Vibrio Fischeri method), all processes have promoted the overall toxicity reduction of VA solution. Transformation products were identified by a LC-ESI-TOF mass spectrometer, and degradation pathways were proposed. Operating costs and the energy needed by mg of VA removed were estimated and compared, for the different installations, showing that UVA can remove around 3 times more VA than SB and 2 times more VA than UVC, under the same conditions.