Resumen de Optimización de un algoritmo para la estimación de indicadores de calidad en el medio hídrico y la aplicación al sistema de medidas y comunicaciones asociado
- español
Esta tesis doctoral comprende las investigaciones llevadas a cabo para el diseño de un prototipo de sistema de medida in situ de concentración de nitratos en agua. El sistema propuesto está basado en el análisis mediante técnicas espectrofotométricas de la respuesta espectral en el ultravioleta y su posterior tratamiento mediante técnicas de programación evolutiva. La aplicación principal del sistema diseñado se encuentra en el seguimiento y control de la contaminación del agua por nitratos. En esta tesis, se analiza la respuesta espectral de la concentración de nitrato y nitrito en agua y se caracteriza la variación de la absorción máxima y de la longitud de onda para la cual se produce. Otro aspecto que se aborda es el modelado de dicha respuesta mediante funciones matemáticas. Igualmente, se expone la aplicación de la programación evolutiva como método para determinar la concentración tanto de nitrato, como de otros contaminantes cuya respuesta sea sensible en el rango de longitudes de onda de la instrumentación disponible. Por último, para resolver el problema de la medida in situ de la concentración de nitrato y nitrito se ha realizado un prototipo en colaboración con el Centro de Investigaciones de la Armada (CIDA)
- English
This thesis comprises the development of a prototype for continuous and online nitrate concentration measurement in water. The proposed system is based on ultraviolet spectrophotometric techniques and the later measures analysis using evolutionary programming. The main application of the proposed system is monitoring nitrate pollution in water. This pollution is a major worldwide problem due mainly to excessive fertilizers used in agriculture. In the European Union, since 1991, Directives 91/271/CEE and 91/676/CEE are aware of this problem. More recently, the Directive 2006/118/CE, has been delivered to specially protect groundwater. Directive 2006/118/CE considers groundwater as a valuable resource to be preserved from chemical pollution and states it as the most sensitive and important drinking water resource in UE. In order to protect the environment and human health, it is necessary to avoid, prevent and reduce the concentration of pollutants in groundwater. The directive encourages the investigations to obtain new criteria about quality and protection of groundwater… this research should be supported as well as the knowledge, experience and results publications in this area. The above mentioned Directives establish a mandatory monitoring of groundwater quality on the basis of pollutant measurement. The control of dissolved oxygen, conductivity and pH is usually made, but the continuous on line measurement of nitrate concentration is a problem to be solved. In 2000, the joint works of departments of Geología, Química Analítica e Ingeniería Química y de Teoría de la Señal y Comunicaciones of Universidad de Alcalá began in a project named “Implantación y gestión de filtros verdes: una alternativa para la depuración y reutilización de aguas residuales (creación de una planta experimental en el filtro verde de Redueña)”. As a new result, in the report of this Project is stated: “following the directive 91/271/CE, the possibility of continuous nitrate pollution measurement in groundwater is considered. The aim is to create a self control irrigation program able to redistribute wastewater in a land application when this water will not be suitable to produce recharge or when nitrate concentration in lixiviate will not be adequate”. So, the main objective in this research has been the creation of a system for continuous and on line measurement of nitrate pollution in water. The measurement of nitrogen in water has been done by using spectrophotometric techniques in ultraviolet wavelengths. First, the influence on light transmission due to nitrate and nitrite ions has been studied. Multiple transmittance measurements have been done using distillate water with known ion concentrations to obtain a variety of responses or patterns. From the study of these patters, the relations between concentration, transmittance and wavelength have been obtained. Later, the responses have been modelled using Fermi and Gaussian functions. But in natural waters, there is a variety of substances apart from nitrogen, whose influence in transmittance is noticed also in ultraviolet wavelengths, especially organic matter. Also turbidity is another source of transmittance variation. Evolutionary programming has been proposed as a selection method of the best adjusting pattern and an algorithm has been stated for simultaneous measurement of multiple pollutants. Finally, the problem of on line measurement has been solved. In cooperation with Centro de Investigaciones de la Armada, a waterproof prototype has been designed for on line measurement.
As a general conclusion, this thesis proposes some devices and algorithms to measure nitrate concentration in water using ultraviolet spectral measurement techniques and evolutionary programming analysis. The following are other conclusions that can also be delivered. Ultraviolet techniques are useful for direct on line measurement of nitrate and nitrite concentrations. As BeerLambert law states, transmittance is proportional to logarithm of concentration, but only in a reduced range. The measurements show, that non linearity effects are significant from 50 mg/l and on. The measurements also show that the maximum absorption wavelength varies with concentration. This variation has also been related to logarithm of concentration. The study of the spectral response shows a Fermi and Gaussian variation of transmittance with wavelength. Fermi function states under maximum absorption wavelength and Gaussian function over that value. Due to other substances interference in ultraviolet, the methods based on one or two wavelengths measurements are not suitable for direct concentration measurement. Multiple wavelengths are more appropriate because they take into account background absorption produced by organic matter and turbidity effects. In spite of other researches proposals about transmittance in a particular site, it is more adequate to allow a simultaneous fitting during spectral deconvolution. Evolutionary programming has been proved as a very useful technique, allowing simultaneous fitting of multiple substances and background absorption. The purposed transmittance modelling has been used to state an estimation method for multiple pollutants based on a combination of experimental and synthetic patterns. The performance of the whole system is limited by transmission losses in optical fibber as well as by their coupling efficiency. In order to optimize it, the final device must integrate optical source and spectrophotometer. The designed prototype has proven its better efficiency compared to traditional tray, but the lenses should be adjusted. Finally, regarding measurement variability and its temporal deviation, the measurements show a good response but it is necessary to introduce some kind of compensation for source emission temporal variation.
