Subsurface as a bioreactor: interaction between physical heterogeneity and microbial processes

• Autores: Núria Perujo Buxeda
• Directores de la Tesis: Xavier Sánchez Vila (dir. tes.), Anna M. Romaní (dir. tes.)
• Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2018
• Idioma: español
• Tribunal Calificador de la Tesis: Francesc Sabater Comas (presid.), Daniel Fernández (secret.), Gabrielle Weigelhofer (voc.)
• Programa de doctorado: Programa de Doctorado en Ingeniería Ambiental por la Universidad Politécnica de Catalunya
• Materias:
  • Ciencias de la vida
    • Microbiología
      • Procesos microbianos
  • Ciencias de la tierra y del espacio
    • Hidrología
      • Hidrobiología
  • Ciencias tecnológicas
    • Ingeniería y tecnología del medio ambiente
      • Tecnología de aguas residuales
    • Procesos tecnológicos
      • Circulación a través de medios porosos
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• Resumen

  • Infiltration systems are water treatment technologies where water vertically percolates through porous media while several biogeochemical processes occur. Biofilms are the main responsible for those biogeochemical processes due to their ability to colonize sediments as well as due to their role in transformation of organic matter and nutrients in aquatic ecosystems and subsurface environments. However, an excessive biofilm growth in sand filtration systems can significantly reduce their infiltration capacity (bio-clogging), thus constraining the processes that occur therein. Sediment grain size distribution influences the performance of these systems since it determines hydrological characteristics in subsurface sediments influencing biofilm growth as well as the process rates of biogeochemical processes in depth. Furthermore, sediment grain size can also influence the occurrence and depth-extension of bio-clogging. The main objective of this doctoral thesis is to study the influence of grain size distributions on biogeochemical processes and on bio-clogging in depth in sand infiltration systems used as potential tertiary treatments for the removal of organic matter and nutrients in water. To achieve this objective, two infiltration experiments have been carried out: (a) a laboratory-scale columns experiment using 5 sediment grain size distributions used as potential infiltration systems (Chapter I) and (b) an outdoor infiltration experiment in sediment tanks using two sediment grain size distributions (Chapter II and Chapter III).

    The results of this thesis show how sediment grain size distribution influences biofilm establishment and growth, biogeochemical rates as well as occurrence of bio-clogging in surface sediments and in depth. Accordingly, coarse sediments (coarse system) allow higher biomass in depth but they do not have the ability to remove dissolved phosphorous; however, due to high input loads they showed higher process rates. Grain size distribution of coarse sediment in the upper layer and fine sediment in the bottom layer (coarse-fine system) promotes the accumulation of biomass at the interface of the two sediment layers which results in a hot-spot of microbial activity. In addition, it promotes nutrient accumulation in sediments (dissolved phosphorous removal) possibly due to the fact that its flow velocities are smaller than those of a coarse system and therefore the contact time between the water and sediment increases by promoting the assimilation and adsorption of nutrients in the porous medium. Biomass establishment in fine sediments (fine system) results in greater bio-clogging due to lower initial porosity compared to systems with coarse sediment on the surface. This lower porosity results in less space available to colonize, and due to this, biofilm in the top layer of the monolayer fine system could reach the maturity state earlier than the bilayer coarse-fine system. That, together with the lower flows in the fine system, favours the detachment of biofilm in the top layer and its transport in depth. EPS accumulation in depth (due to live bacteria release or due to transport from upper sediment layers) is the main factor causing K variations in depth (potential to cause deep-clogging). Results also showed that mixed sediments of fine and coarse sands (mixture system) and the fine-coarse system achieve similar performance than fine system reaching similar biomasses between them and lower process rates than the other grain size distributions studied