Resumen de Eliminación del color de las aguas residuales procedentes de la tintura con colorantes reactivos
This thesis is based on the study of colour elimination of textile effluents which contain reactive dyes. Reactive dyes are widely used in the dyeing of cotton and other cellulosic fibre. However they exhibit a low degree of exhaustion and low biodegradability, being necessary the application of specific treatments prior to their discharge to the biological treatment. Much of the new methods of colour removal can be classified in three major groups: Advanced oxidation methods (AOM), coagulation with natural products and the selection of specific microorganisms. In this thesis one representative technique of each of these three groups has been selected: treatment by electrochemical oxidation, coagulation with a natural byproduct and enzymatic treatment. The electrochemical oxidation has been applied to synthetic effluents with reactive dyes. The behaviour of the decoloured effluents has been studied, before and after the mixing with the rest of textile wastewater, in order to verify if the electrochemical treatment could affect negatively to the subsequent biological treatment with activated sludge. With this aim the biodegradability of the decoloured effluents has been studied by electrolytic respirometric techniques, which can show inhibitory or toxicity phenomena. The results demonstrate that the electrochemical treatment do not cause problems of inhibition of microbial growth, if the effluent is previously been aerate for 24 hours. This process ensures that the decoloured wastewater can be sent to the biological treatment. The influence of oxidant products generated in the electrochemical treatment has been evaluated in two pilot plants of biological treatment by activated sludge. Consideration has been given to monitoring the microscopic observation of activated sludge as bioindicator of the proper functioning of the treatment plants. It is concluded that the wastewater with reactive dyes can be treated by an electrochemical process to remove colour and the resulting effluent can be treated directly by activated sludge without prior removal of the residual chlorine which can be formed during the electrochemical treatment, only a longer time of adaptation is required in the implementation of the sewage system. A second method of textile wastewater decolourisation has been studied. The use of a natural coagulant extracted from seeds of Moringa oleífera tree in substitution of higher cost methods which require the addition of chemical products. The results obtained with Moringa Oleifera are compared with those obtained using a chemical coagulant and polyelectrolyte. Furthermore, dyeing tests of cotton fabrics were performed with decoloured water. The quality dyeing was compared respect to reference dyeing carried out with clean water. The promising results obtained in this study suggest the use of natural resources in the wastewater textile treatment, mainly in countries with less economic power. Two dyes with different reactive groups (vinylsulphone and chlorotriazine) have been treated with the enzyme laccase in order to study its applicability on the decolourisation of textile effluents. The influence of different parameters is studied, such as the addition of mediator, the concentration of salt and the dye hydrolysis. It is concluded that the addition of mediator or co-substrate is not necessary, the presence of salt in the dye effluent (NaCl) does not inhibit the enzymatic activity and the hydrolysis of the studied dyes does not affect the enzymatic action. 70-90% of decolourisation is obtained, depending on the dye. Finally, it has been carried out the comparative study of the results obtained by the three selected methods of colour removal. It is concluded that the electrochemical treatment is the most efficient, with 95-100% of colour removal, in front of 91-94% obtained by the natural coagulant extracted from Moringa Oleifera and 70-90% of decolourisation reached by the enzymatic treatment.
