STUDY OF THE ELECTROCHEMICAL REDUCTION, OXIDATION AND OXIDO-REDUCTION FOCUSED ON THE DECOLORATION / DEGRADATION OF TEXTUILE DYEBATHS CONTAINING REACTIVE DYES WITH AZO GROUPS AS CROMOFORE

     Nowadays, the total industrial water consumption in the developed countries is about 59 %, as reported in the First World Water Development Report, Water for People, Water for Life (March 2003). More than 80 % of the dangerous wastes of the world are produced in the industrialized countries and, in developing countries, a 70 % of wastewaters are flowed into rivers without any pre-treatment. As a consequence, a great contamination of rivers is produced.
     According to these dates, the treatment and reuse of wastewaters from the industrial sector in the world are especially relevant and ever more in countries whose assessment of water resources is in the reds. This is the case of Spain, the european nation with a greater water deficit.
     
     The textile industry uses huge quantities of water. Wastewaters from the different  manufacturing processes are potentially toxic and highly coloured due to the high content of organics compounds. Among these compounds we can find non-fixed dyes.  As a result, it is neccesary a pretreatment before throwing them away. This problem is particularly pronounced in the case of reactive dyes. 
     
     In this Doctoral Thesis the feasibility of the electrochemical treatment of textile wastewaters containing reactive dyes is studied. The main objective is to achieve decoloured solutions with an organic matter content significatively lower tan the initial value. The application of the electrochemical treatment provides for water reuse in the different textile processes in such a way that scarcity of water, environmental pressures on a juridical and legislative scale and the increase of water cost could be solved. 
     
     On the one hand, this research work is focused on the characterization of stainsless steal electrodes as well as semiconductive electrodes of Ti/SnO2-Sb-Pt by Cyclic Voltammetry (CV). Moreover, a chemical and electrochemical characterization by means of Scanning Electronic Microscopy (SEM) and Energy-dispersive X-ray (EDX) of Ti/SnO2-Sb-Pt electrodes has been carried out. This confirmed the increase of the electrocatalaytic activity by means of doping with antimony as well as the more compact layer obtained when introducing low quantities of platinum.
     
     On the other hand, the application of these electrodes to the electrochemical treatment of synthetic solutions containin different reactive dyes has been estudied. The studied processes were oxidation, reduction and oxido-reduction in the presence of Na2SO4 as electrolyte and different applied current densities. Besides, in the more relevant cases, the feasibility of the use of NaCl as electrolyte has been considered. It has been employed two types of electrochemical cells as well as different work conditions. 
     The estudy of physico-chemical parameters such as the Total Organic Carbon (TOC), the Chemical Oxygen Demand (COD), the Carbon Oxidation State (COS) and the Average Current Efficiency (ACE) allowed to determinate the optimum conditions for the degradation and decoloration of this type of wastewaters.
     Likewise, several techniques of instrumental analysis have been employed such as Fourier Transform Infrared Attenuated Total Reflection (FTIR-ATR), UV-Visible Espectroscopy, High Performance Liquid Chromatography (HPLC), X-Ray Photoelectronic Espectroscopy (XPS) and Gas Chromatography-Mass Espectrometry (GC-MS). 
     The assays done during this Doctoral Thesis show that the studied dyes are fragmented following different mechanism as a function of the process carried out. The molecular structure, the applied current density and the type of electrolyte determinate the efficiency of the process. All the studied cases follow a pseudo-first order kinetics.