Coupling pre-concentration and electrochemical degradation processes for the treatment of wastewaters containing organochlorine pesticides
- Autores: Alexandra Raschitor
- Directores de la Tesis: Pablo Cañizares Cañizares (dir. tes.), Javier Llanos López (codir. tes.)
- Lectura: En la Universidad de Castilla-La Mancha ( España ) en 2019
- Idioma: español
- Tribunal Calificador de la Tesis: Silvia Álvarez Blanco (presid.), María José Martín de Vidales Calvo (secret.), Igor Cretescu (voc.)
- Programa de doctorado: Programa de Doctorado en Ingeniería Química y Ambiental por la Universidad de Castilla-La Mancha
- Materias:
- Enlaces
- Tesis en acceso abierto en: RUIdeRA
- Resumen
The water pollution and its management became a hot topic in the scientific community in the last decades and the efforts begun to focus on finding new and better ways to treat the wastewater regardless its provenience. Along the years, there have been many improvements in this aspect but the pollutants have also been upgraded.
Within the last years, the Laboratory of Electrochemical and Environmental engineering from the University of Castilla-La Mancha focusses its efforts on the treatment of the wastewater containing organochlorine compounds using electrochemical technologies. There are currently published dozens of works in which coatings of mineral mixed oxides and conductive diamond are used as electrode materials, demonstrating great efficiency in the removal of various pollutants from wastewater.
The present doctoral thesis is focused on the treatment of the wastewater containing organochlorine compounds reducing the limitations related to the low concentration in which these pollutants are generally found in the environment. For this, the integration of concentration strategies have been investigated in order to reduce the volume of the contaminated stream and increase its concentration, improving the removal efficiency by favouring the mass transfer of the pollutants to the electrodes and the generation of oxidant species, thus minimizing the related operation costs along with the waste generation.
In this respect, the treatment approach for the organochlorine pesticides was chosen according to their formulation and properties. Electrodialysis was used for the concentration of the polar ionic organochlorine pesticides, meanwhile electro-oxidation was applied for their degradation. Furthermore, the removal technique was improved by integrating the electrodialysis with the electro-oxidation in the same cell achieving a simultaneous concentration degradation process that enhances the removal degree and lower the power consumption.
Moreover, a model of the treatment process has been developed in order to predict the efficiency of the integrated system in the treatment of the wastewater containing similar organochlorine compounds and to identify areas for the improvement of the proposed technology.
As for the non-polar organochlorine pesticides, as a first option, the removal was approached by electro-oxidation. To improve the global removal efficiency, it was proceeded to the integration of a concentration step such as ultrafiltration followed by the electro-oxidation of the obtained concentrated stream. Moreover, it was tested a second concentration method, electrocoagulation, that allows to obtain two phases: 1) a diluted phase, free of organic compounds that can be safely discharged and 2) a concentrated stream that contains all the pollutants entrapped into the electrogenerated flocs, stream that is further submitted to a treatment process.
When using electrocoagulation as concentration stage, two options have been considered to confront the treatment of this complex concentrated stream: the treatment as liquid phase and the treatment as solid phase. The treatment as liquid phase consists in dissolving the iron flocs from the concentrated stream and the subsequent application of the electro-oxidation or electroFenton processes.
One its hand, the treatment of the solid waste was approached also by two options: the first one, the use of the ultrasonic irradiation followed by an electro-oxidation stage, and the second, the use of the electrochemical dewatering technique.
The results obtained show that by choosing the appropriate treatment methods it is possible to successfully treat a wastewater containing organochlorine pesticides. The treatment of the polar ionic organochlorine pesticides from the synthetic wastewater by electro-oxidation combined with electrodialysis showed good results achieving a simultaneous concentration and degradation of 2,4 – D and clopyralid, the two model target polar ionic organochlorine pesticides. Removals around 330 mg of pesticide in only 240 minutes have been achieved, without harming the ion exchange membrane. Moreover, it was demonstrated by modelling the process that the removal degree can be further increased by solving the bottleneck of this configuration: the transfer rate of the pollutant through the membranes.
For the treatment of non-polar organochlorine pesticides ElectroFenton applied to the dissolved concentrated flocs obtained from electrocoagulation showed outstanding results in the treatment for both model target pollutants, oxyfluorfen and lindane. In addition, the power consumption for a 30% removal at an applied current density of j = 254.67 A m-2 was reduced from 27.3 (EO) to 7.55 kwh kg-1 (EF) oxyfluorfen and from 93.9 (EO) to 49.5 kwh kg-1 lindane (EF). For the treatment of these compounds as solid phase low frequency ultrasound irradiation followed by EO was the best option achieving removal degrees of 90%.
Moreover by concentrate the wastewater it is possible to reduce its volume by more than 90% and obtain a clean water that can be safely discharged.
