Alfonso Vidal

Photocatalysis with solar energy at a pilot-plant scale: an overview

Abstract Advanced oxidation processes (AOPs) are characterized by a common chemical feature: the capability of exploiting the high reactivity of OH radicals in driving oxidation processes which are suitable for achieving the complete abatement and through mineralization of even less reactive pollutants. This paper reviews the use of sunlight to produce OH radicals. The experimental systems necessary for performing pilot-plant scale solar photocatalytic experiments are described. It outlines the basic components of these pilot plants and the fundamental parameters related to solar photocatalysis reactions. This paper summarizes also most of the research carried out at Plataforma Solar de Almeria (PSA) related with solar photocatalytic degradation of water contaminants. A description is given of how solar photocatalysis could become a significant segment of the wastewater treatment technologies related with the degradation of very persistent toxic compounds. It outlines also the decomposition of organic and inorganic contaminants and different examples are also shown for better comprehension of the ability of solar energy for carrying out oxidation and reduction processes. These examples include chlorophenols, chlorinated solvents, pesticides and cyanide. Besides, the possibility of using the photo-Fenton reaction illuminated with solar light opens the boundary where solar photocatalysis could be applied.

Compound parabolic concentrator technology development to commercial solar detoxification applications

Abstract An EC-DGXII BRITE-EURAM-III-financed project called ‘Solar detoxification technology in the treatment of persistent non-biodegradable chlorinated industrial water contaminants’ is described. The objectives are to develop a simple, efficient and commercially competitive solar water treatment technology based on compound parabolic collectors (CPC) enabling design and erection of turnkey installations. A European industrial consortium, SOLARDETOX, representing industry and research in Spain, Portugal, Germany and Italy has been created through this project. Some of the most up-to-date scientific and technological results are given, including the design of the first industrial European solar detoxification treatment plant, the main project deliverable.

SOLAR PHOTOCATALYTIC DEGRADATION OF WATER AND AIR POLLUTANTS: CHALLENGES AND PERSPECTIVES

Solar photocatalytic oxidation processes (PCO) for degradation of water and air pollutants have recently received increasing attention. Some field-scale experiments have demonstrated the feasibility of using a semiconductor (TiO2) in solar collectors and concentrators to completely mineralize organic contaminants in water and air. Although successful pre-industrial solar tests have been carried out, there are still discrepancies and doubt concerning process fundamentals such as the roles of active components, appropriate modelling of reaction kinetics or quantification of photoefficiency. Challenges to development are catalyst deactivation, slow kinetics, low photoefficiency and unpredictable mechanisms. The development of specific non-concentrating collectors for detoxification and the use of additives such as peroxydisulfate have made competitive use of solar PCO possible. The challenges and perspectives of solar driven PCO as illustrated in the literature and our own results in large solar field loops at the Plataforma Solar de Almeria and CIEMAT laboratories are described.

Photocatalytic degradation of thiocarbamate herbicide active ingredients in water

It has been shown that a wide range of organic compounds in aqueous solutions is photocatalytically oxidized to carbon dioxide in the presence of titanium dioxide with near-UV radiation. The photocatalytic mineralization of thiocarbamate derivative pesticides (EPTC, butylate, molinate, vernolate and cycloate) in water by illuminated TiO2 has been studied. The determination of the effects of various kinetic factors on the photocatalytic degradation and the determination of the nature of the principal intermediates form part of the focus of this study. The degradation rate of these thiocarbamates in a continuous recirculation mode approximates first-order kinetics. It was demonstrated that photocatalyzed degradation of thiocarbamate active ingredients does not occur instantaneously to form carbon dioxide, but through the formation of long-lived intermediate species. Photocatalytic intermediates detected during the degradation of thiocarbamates were identified by GC/MS techniques. Intermediates detected in the photocatalytic oxidation of thiocarbamates in water solutions are in excellent agreement with products identified from the atmospherically important reactions of OH radical with thiocarbamates. Particular attention will be paid to the carbon dioxide formed from the illuminated suspension in order to demonstrate not only apparent destruction but also complete mineralization. The degradation of a two-component mixture was carried out and compared to results obtained with single-component studies.

The use of CPC collectors for detoxification of contaminated water: Design, construction and preliminary results

Abstract Photocatalytic processes in the presence of titanium dioxide provide an interesting way to destroy hazardous organic contaminants. Part of CIEMAT’s efforts to commercialize solar photocatalytic detoxification technology has involved the development of photoreactor designs. Although present treatment costs for the solar water detoxification system are higher than for conventional technologies, potentially greater cost reductions are being investigated through the use of one-sun systems. Aspects of these systems that might realize cost reductions include novel collector materials, the manufacturing process and the economics of scale. These issues are being examined extensively in the one-sun photoreactor research effort. A one-sun compound parabolic concentrator designed by CIEMAT and fabricated by the Instituto de Maquina Herramienta may be constructed at a cost under

Heterogeneous photocatalysis: degradation of ethylbenzene in TiO2 aqueous suspensions

160/m2 with an annual efficiency of 71.3%. Studies reported in this paper also evaluate the performance of the low cost CPC prototype built at a previous stage using a model compound, and explore the feasibility of this concept as the basis for solar photocatalytic oxidation facilities. Our preliminary findings show that the overall treatment cost can be reduced mainly by reducing the unit catalyst cost instead of the unit reactor cost.

Inactivation of titanium dioxide by sulphur: photocatalytic degradation of Vapam®

Abstract Heterogeneous photocatalysis in TiO 2 aqueous suspensions has been used as a technique for the total destruction of organic compounds, such as ethylbenzene, in water. The photocatalytic degradation of ethylbenzene follows pseudo-first-order kinetics in a concentration range between 3 and 50 μM. Studies have shown that a Langmuir-Hinshelwood equation form can describe the initial rate of ethylbenzene disappearance. The objective of our research was to examine the degradation of intermediates species produced by the oxidation of ethylbenzene. The temporal course of the degradation was followed by high performance liquid chromatography. Gas chromatography—mass spectrometry analysis of the reactor solution from a ethylbenzene experiment revealed the presence of several intermediate species, namely 4-ethylphenol, acetophenone, 2-methylbenzyl alcohol, 2-ethylphenol and 3-ethylphenol. The influence of pH on the photocatalytic degradation of ethylbenzene was examined initial 50 /gmM solutions at two different pH values. This study shows that the degradation of ethylbenzene at higher pHs requires a much illumination time to attain quality standards of drinking water.

Laryngeal Mask, Laryngeal Tube, and Frova Introducer in Simulated Difficult Airway

Photocatalytic processes in the presence of titanium dioxide provide an interesting route to destroy hazardous organic contaminants, being operational in the UV-A domain with a potential use of solar radiation. Numerous photocatalytic reactions have been tested showing that organic contaminants in water can be completely mineralized (i.e. converted into CO2, H2O, NO3−, SO42−, etc.) by irradiation in the presence of TiO2. In this paper, the photocatalytic degradation of a monoalkyl dithiocarbamate (Vapam®) by TiO2 illuminated suspensions has been investigated at bench scale. The determination of the effects of various kinetic factors on the photocatalytic degradation and the determination of the nature of the principal intermediates form part of the focus of this study. This research also involves the characterisation of the titanium dioxide surface by X-ray photoelectron spectroscopy to obtain information about the composition and chemical state of the catalyst surface. Preliminary field tests have shown that this pesticide can not be completely mineralized when treating diluted industrial wastes from manufacturing industries. The experimental results presented suggest that inactivation of titanium dioxide by sulphur occurs. These results have significant implications to commercialise solar photocatalytic detoxification technology since the catalyst cost has a major impact on the wastewater cost.

Role of laryngeal mask airway in laparoscopic cholecystectomy

BACKGROUND The use of supraglottic devices is rising in the prehospital management of difficult airway; moreover, we think that patients with multiple trauma or cervical instability can take advantage of these devices without opening or retiring the cervical collar. OBJECTIVE To compare speed and ease of use between Laryngeal Tube S (LTS) and the Ambu AuraOnce laryngeal mask (LMA).Our second objective was to evaluate changing these devices to an endotracheal tube (ETT) using a Frova introducer. METHODS We studied the use of LTS and LMA in an experimental model, represented by a manikin with a rigid cervical collar and a limited mouth opening. This study was carried out in Complutense University of Madrid with 145 2(nd)-year students for the degree in Dentistry who have knowledge of the airway but lack experience in intubation. Number of attempts and time for the devices insertion were measured, as well as time for the exchange maneuver using the Frova introducer. RESULTS Insertion of all devices was possible on the first attempt; time for insertion was LTS 12.2 ± 1.28 s and LMA 6.87 ± 0.97 s. Once these devices were inserted, a Frova introducer is used to perform an exchange by an endotracheal tube; all devices could be exchanged on the first attempt, and exchange time was LTS 26.9 ± 1.2 s and LMA 16.79 ± 1.32 s. Results for both time for insertion and exchange of the LMA were significantly lower than those for the LTS (p < 0.001). CONCLUSION The method used can be considered quick and easy, even for personnel inexperienced in intubation. This exchange maneuver has not been described previously, so we can consider it as a new application of the Frova introducer.

Migraine headache: a rare complication after cervicothoracic block

Laparoscopic cholecystectomy is one of the most commonly performed surgical procedures and the laryngeal mask airway (LMA) is the most common supraglottic airway device used by the anesthesiologists to manage airway during general anesthesia. Use of LMA has some advantages when compared to endotracheal intubation, such as quick and ease of placement, a lesser requirement for neuromuscular blockade and a lower incidence of postoperative morbididy. However, the use of the LMA in laparoscopy is controversial, based on a concern about increased risk of regurgitation and pulmonary aspiration. The ability of these devices to provide optimal ventilation during laparoscopic procedures has been also questioned. The most important parameter to secure an adequate ventilation and oxygenation for the LMA under pneumoperitoneum condition is its seal pressure of airway. A good sealing pressure, not only state correct patient ventilation, but it reduces the potential risk of aspiration due to the better seal of airway. In addition, the LMAs incorporating a gastric access, permitting a safe anesthesia based on these commented points. We did a literature search to clarify if the use of LMA in preference to intubation provides inadequate ventilation or increase the risk of aspiration in patients undergoing laparoscopic cholecystectomy. We found evidence stating that LMA with drain channel achieves adequate ventilation for these procedures. Limited evidence was found to consider these devices completely safe against aspiration. However, we observed that the incidence of regurgitation and aspiration associated with the use of the LMA in laparoscopic surgery is very low.