Eliminación de amoniaco y materia orgánica de lixiviados de vertedero mediante electro-oxidación en ánodos de diamante dopado con boro
- Autores: Ángela Anglada
- Directores de la Tesis: Inmaculada Ortiz Uribe (dir. tes.), Ana María Urtiaga Mendia (dir. tes.)
- Lectura: En la Universidad de Cantabria ( España ) en 2011
- Idioma: español
- Tribunal Calificador de la Tesis: Ángel Irabien Gulías (presid.), Manuel Andrés Rodrigo Rodrigo (secret.), Dionisis Mantzavinos (voc.), Eloy García Calvo (voc.), Christos Comninellis (voc.)
- Materias:
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- Resumen
Nearly all the known physicochemical and biological processes have been explored for the treatment of recalcitrant landfill leachate. However, none has emerged as a panacea. Among the processes studied, electrochemical oxidation has proved to be capable of eliminating both the organic and NH4+ contaminant load. Nevertheless, despite the high removal ability of the electrode materials tested, they present several major drawbacks, e.g. release of toxic metal ions due to dissolution of the electrode, surface corrosion or fast deactivation of the electrode surface- that limit their practical application. In this context, high quality boron-doped diamond (BDD) electrodes have emerged as a promising alternative as they possess several technologically important characteristics including an inert surface with low adsorption properties, remarkable corrosion stability even in strong acidic media, and extremely high oxygen evolution overpotential.
In this thesis, firstly, the fundamentals involving electrochemical oxidation are laid down. Then, a brief overview of the developments of electrochemical oxidation by means of BDD anodes in wastewater treatment is given. The application of BDD anodes to the remediation of ammonia contaminated effluents, the understanding of the electrochemical reaction mechanisms involved in the electro-oxidation of multi-component mixtures, and the potential for formation of undesired oxidation by-products such as chlorinated organics and inorganic ions (ClO3-, ClO4-, NO3-, NO2-) stand out among the issues that still need to be tackled before the full-scale implementation of this technique.
Based on the above considerations, this thesis focuses on the elimination of organic compounds and ammonium by electrochemical oxidation by means of BDD anodes within the frame of landfill leachate treatment.
Landfill leachate is a complex wastewater of unknown detailed composition that contains, among others, high concentrations of organic pollutants, ammonia nitrogen and chloride ions. Keeping this observation in mind, the intricate reaction scenarios that are created when multi-component mixtures are electro-oxidized by means of BDD anodes are described in Chapter 2. The fulfilment of this objective is pursued by performing a series of experiments with synthetic wastewaters contaminated with ammonia and/or different model organic compounds (phenol, formic acid and methanol). In order to elucidate whether direct or chlorine-mediated oxidation pathways are involved in the oxidation of these pollutants, tests in absence/presence of NaCl have been carried out. Three electrochemical techniques have been used to clarify the reaction mechanisms: voltammetry, chronoamperometry and galvanostatic electrolysis. The results have demonstrated that a high interaction between the oxidation of ammonia and organic compounds exists in presence of chloride ions in the effluent.
Chapter 3 deals with the electro-oxidation of leachate from two different municipal landfill sites by means of BDD anodes at laboratory scale. The effect of current density and wastewater composition (pH and concentration of Cl-, COD and NH4+) on the elimination of COD and NH4+ has been assessed at laboratory scale. Moreover, an in-depth study of the formation of chlorinated organic compounds and nitrate ions has been furnished. Afterwards, the use of electro-oxidation in the treatment of highly-strength saline industrial effluents is studied.
A simple and novel mathematical model has been proposed to describe the removal of COD and NH4+ from landfill leachate by electrochemical oxidation. These models consider the different reaction pathways for organic matter (direct, ¿OH mediated oxidation and indirect oxidation in the bulk) and for ammonium oxidation (chlorine mediated mechanisms) that were observed to influence the elimination of these pollutants in the fundamental study carried out in Chapter 2. The model is highly versatile as it is capable of describing the electro-oxidation of leachates with different origins and from various treatment processes, providing a tool for process design. In Chapter 4 this model is used to scale-up the electro-oxidation process. A pilot plant with a total BDD anode area of 1.05 m2 was designed, built and finally operated on the landfill site. Furthermore, experimental validation of the model proposed in Chapter 3 is provided which involves the re-calculation of the parameters affected by the change of scale. Finally, an estimation of the energy consumption of the process is made.
