Difusión de contaminantes en vertederos antiguos construidos en terrenos arcillosos

• Autores: Mercedes Regadío García
• Directores de la Tesis: Jaime Cuevas Rodríguez (dir. tes.)
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2012
• Idioma: español
• Tribunal Calificador de la Tesis: María Teresa Sevilla Escribano (presid.), María Isabel Herráez Sánchez de las Matas (secret.), Poul Løgstrup Bjerg (voc.), Francisco Javier Cuadros Ojeda (voc.), José Gumuzzio Fernández (voc.)
• Materias:
  • Ciencias de la tierra y del espacio
    • Geoquímica
    • Geología
      • Geología ambiental
  • Ciencias tecnológicas
    • Ingeniería y tecnología del medio ambiente
      • Control de la contaminación del agua
• Enlaces
  • Tesis en acceso abierto en: digitool-uam.greendata.es
• Resumen

  • An appropriate disposal of waste in landfills is a key issue for protecting, preserving and improving the environment and the human health. The most applied policy for landfilling is the containment strategy (complete isolation of the deposited waste by means of bottom and top liner systems and collection of gas and leachate emissions combined with everlasting aftercare monitoring). Under these conditions, the waste itself remains a source of pollution and the problem is not solved, since if something accidentally fails, the pollutants will be released. For that reason, more and more importance is being attached to the attenuation strategy (included in ¿the multibarrier concept¿ and the European legislation). This strategy considers the landfill and the underlying natural substratum (¿geological barrier¿) act as a biochemical reactor in which natural processes (dilution, dispersion, biodegradation, filtration, redox, precipitation, sorption or ionic exchange reactions) take place and reduce and eliminate the contamination.

    In the present thesis, the response of natural and common Spanish clayey soils to leachate solutions in the long term is investigated both: (i) under a real approach with soil samples below five actual municipal wastes (MW) landfill sites (9-24 years old and no engineered liners) and (ii) under a laboratory approach based on a four-year diffusion experiment with a natural clay compacted in four 0.5 m-height columns; each one in contact with a different leachate. More than 30 parameters were measured in the clayey samples at different depths: physicochemical parameters (electrical conductivity, EC; redox potential, Eh; pH, water soluble organic and inorganic carbon, WSOC/WSIC; ions, alkalinity¿) and geological parameters (exchangeable cations, Ex_cat; cationic exchange capacity, CEC; moisture, h; specific surface area, SSA; mineralogy, microfabric, density). The important quantity of data made it necessary to perform statistical procedures in order to (i) observe correlations within the measured parameters and between them and the attenuation of leachate pollutants (principal component analysis and Varimax rotation) and (ii) to know what effects caused by the different types of leachates on the parameters measured in the clayey materials, are significant (multivariate analysis of variance, between-effects and multivariate tests).

    Although leachates have been in contact with clays for long periods of time, the main soluble components of leachates were attenuated (concentration decrease 90-100%) at depths of only ¿1.5 m from the waste/soil contact within the clay layer. The ratio decrease per meter depth (Dm) and a diffusive flux attenuation capacity (Ac) were defined for each natural substratum to study the differences between them and to compare their performance as a barrier, under normalized conditions of leachate exposure time and quantity of waste per area.

    The most suitable materials were those with ¿47% sheet silicates, characterized by a ratio of illite/smectite between 1.8 and 5, with carbonates and high SSA and density. The observed attenuation depths and the estimated hydraulic conductivity (K) in the studied natural materials proved that the minimum depth and the maximum K of a geological barrier established by Directive 1999/31/EC (1999) are adequate for the pollution control of major soluble species in the leachate. NH4+ was the most indicative parameter of the penetration of landfill leachate pollution and it was effectively retained by exchange reactions. Such ion exchange capacity is interesting for environmental remediation in contaminated sites. The important roles, in the retardation mechanisms, of water entry, sorption, biodegradation, pH buffer capacity, nature of wastes, types of clays, matrix diffusion and precipitation-dissolution equilibrium, have also been discussed.

    Consequently, the long-term effectiveness of several geological barriers beneath MW landfills was analyzed in detail and reliable data relevant to design natural attenuation strategies were presented. The attenuation strategy leads to a more sustainable and more cost-effective waste management concerning (i) liners installation, (ii) drainage and gas collection systems and (iii) post-closure monitoring. Therefore, this strategy results in a more affordable technology for developing countries, where water diseases related to waste pollution kill millions of people, mostly children, per year.

    KEYWORDS Landfills, clays, depth profiles of parameters, natural attenuation.