Photocatalysis for the Degradation of Ionic Surfactants in Water: The Case of DPC
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1171-S07-19
Photocatalysis for the Degradation of ionic surfactants in Water: the case of DPC Alberto Naldonia, Claudia L. Bianchia, Silvia Ardizzonea, Giuseppe Cappellettia, Luca Ciceria, Alessandro Schibuolaa, Carlo Pirolaa and Marco Pappinib a
Dipartimento di Chimica Fisica ed Elettrochimica, Università degli Studi di Milano, Via Golgi 19, 20133 Milan, Italy b C.I.G.A., Via Golgi 19, 20133 Milan, Italy
ABSTRACT Traditional techniques to remove contaminants (carbon adsorption, incineration, biological activity and chemical treatment) have a lot of disadvantages. Advanced Oxidation Processes (AOP’s) are used as alternative processes in the degradation of surfactants and in general for wastewater treatment. They are based on the generation of OH·, one of the most powerful oxidant known (E° = 2.73 V) and capable to react non-selectively with any organic compound. In the present work, the degradation of a cationic surfactant (dodecylpyridinium chloride (DPC)) was performed. The photodegradation reaction was investigated both in a slurry reactor and in a vessel where the photocatalyst (P25 by Degussa) was anchored onto an aluminum surface to avoid the final filtration of the powder at the end of the reaction. Moreover a new photoreactor was built on purpose to investigate the influence of the pressure on the degradation process. INTRODUCTION Surfactants are wetting agents that lower the surface tension of a liquid, allowing easier spreading, and lower the interfacial tension between two liquids. The surfactants present in detergent products remain chemically unchanged during the washing process and they are discharged down the drain with the dirty wash water. In the vast majority of cases, the drain is connected to a sewer and ultimately to a waste water treatment plant, where the surfactants present in the sewage can be removed by biological and physical-chemical processes. European Law now requires efficient treatment of urban waste water and all but the smallest conurbations would have been complied before the end of 2005 [1]. Environmental remediation of surface water containing detergents, dyes and pesticides is particularly complex also due to the necessity of avoiding biodegradation processes especially when cationic surfactants are present. Consequently, the literature is rich in studies which show different approaches (called advanced oxidation processes) for the degradation of such molecules. The most valuable and attractive ability to degradate and to mineralize completely or nearly so, organic pollutants is at the very basis of photocatalytic reactions applied to environmental remediation efforts. Many studies have been published on the use of TiO2 as a photocatalyst for the decomposition of organic compounds [2]. Many authors have already investigated the degradation of ionic surfactants by photocatalysis, especially anionic molecules, and their conclusion was that the photodegradation
of the surfactant depends on many factors such as: pH, flow rate, loading of photocatalyst, and the presence and quan
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