Life Cycle Assessment as a Tool for Green Chemistry: Application to Different Advanced Oxidation Processes for Wastewater Treatment

El objetivo de la tesis es contribuir a la aceptacion del Analisis de Ciclo de Vida (ACV) como herramienta metodologica para la evaluacion medioambiental de procesos quimicos disenados siguiendo las pautas de la Quimica Verde. Se pretende asimismo complementar e integrar la evaluacion ambiental con la correspondiente evaluacion economica, tambien desde una perspectiva de ciclo de vida. Con el objetivo de mostrar la potencial utilidad del ACV en este ambito, se llevan a cabo dos casos de estudio en los cuales se evaluan diferentes Procesos Avanzados de Oxidacion (PAOs) para el tratamiento de aguas residuales de la industria conteniendo contaminantes organicos persistentes. Las tecnologias evaluadas son: fotocatalisis en fase heterogenea, fotocatalisis en fase homogenea mediante procesos foto-Fenton, y ozonizacion. El primer caso de estudio se lleva a cabo a partir de datos a escala de laboratorio, mientras que el segundo caso de estudio, de caracter mas detallado, se lleva a cabo mediante datos de planta piloto e industrial. Ambos estudios complementan la dimension ambiental con la dimension economica, utilizando la herramienta Coste del Ciclo de Vida (CCV). A continuacion, se lleva a cabo una discusion sobre la utilidad del ACV en el ambito de los procesos quimicos, dependiendo de la escala de analisis: desde el laboratorio hasta la aplicacion comercial. Finalmente, se presentan las conclusiones globales de la tesis, que pueden resumirse del siguiente modo: - La cuantificacion de los avances alcanzados mediante la aplicacion de los principios de la Quimica Verde requiere herramientas, habiendose mostrado la potencial utilidad del ACV en este ambito mediante dos casos de estudio sobre PAOs. - Se ha mostrado la posibilidad de aplicar el ACV tanto al nivel mas basico de la Quimica Verde (laboratorio) hasta el mas avanzado (aplicacion comercial). Sin embargo los resultados obtenidos mediante ACVs basados en datos de laboratorio no necesariamente coinciden con los obtenidos en un estudio detallado, debido a: 1) falta de optimizacion de los procesos en laboratorio y 2) exclusion de procesos o fases del ciclo de vida que pueden ser relevantes, debido a la falta de datos. Por ello, tales estudios deben ser utilizados unicamente como evaluaciones preliminares. - El ACV despliega su potencialidad en estudios detallados, utilizando datos originados a escala piloto o industrial. Asimismo, el CCV se presenta como un complemento muy apropiado para el ACV, principalmente tambien en el caso de estudios detallados. _________________________________________________ The goal of the thesis is to contribute to the acceptance of Life Cycle Assessment (LCA) as a methodological tool for environmental evaluation of chemical processes designed by following the guidelines of Green Chemistry. This work also intends to complement and to integrate in the same framework the environmental assessment with the respective economic assessment, taking into account a life cycle perspective as well. In order to demonstrate the potential suitability of the LCA tool in this context, two case studies are carried out on the subject of Advanced Oxidation Processes (AOPs) for treating industrial wastewaters containing persistent organic pollutants. In particular, the evaluated AOP technologies are: heterogeneous photocatalysis, homogeneous photo-Fenton, and ozonation. The first case study is carried out by exclusively using data derived from laboratory experiments, while the second case study is more detailed, and carried out by using data from pilot plants and industrial plants. Both studies include, along with the environmental assessment, the corresponding economic assessment, based on Life Cycle Costing (LCC). Following these studies, a discussion is made on the suitability of LCA in the context of chemical processes depending on the scale of analysis. Finally, the overall conclusions of the thesis are outlined, which can be summarised as follows: - In order to assess the advances derived from applying Green Chemistry principles in the design of chemicals and chemical processes, methodological tools are needed. This thesis supports that LCA can be used for such a purpose, as has been shown by means of two case studies on AOPs. - Application of LCA can be carried out at several stages: from the most basic, namely the laboratory scale, to the most advanced, namely commercial application. However, results obtained by means LCA studies based exclusively on laboratory-derived data do not necessarily match the results obtained in a detailed LCAs, mainly due to: 1) lack of optimization of the conditions in which the chemical process takes place in laboratory tests, and 2) excluding relevant operations or life cycle phases which are hardly quantifiable when evaluated from laboratory tests. For this reason, it is suggested that laboratory-derived LCAs should be used only as a means of obtaining preliminary environmental information. - The potential of LCA as a tool is displayed when detailed studies, based on large-scale application data, are carried out. The LCC tool, on the other hand, presents itself as a very suitable complement, mainly when performing detailed studies.