Physical, geochemical and microbial parameters driving the improvement of water quality in Managed Aquifer Recharge
LECTURA DE TESIS
Programa de Doctorado en Ingeniería del Terreno
Thesis in Geothecnical Engineering and Geo-Sciences will be defended
"Physical, geochemical and microbial parameters driving the improvement of water quality in Managed Aquifer Recharge".
Carme Barba Ferrer
Thesis advisors: Dr. Albert Folch / Dr. Francisco Javier Sánchez
The defense will take place: friday, november 16th 2018, 11:00
UPC, Campus Nord
Building C1 . Classroom: 002
C/Jordi Girona, 1-3
Worldwide water demand has been increasing over time, mainly due to population growth and society development. In addition, climate change is causing a significant alteration of the periodicity and intensity of precipitation and climate related events. All this implies significant challenges for a sustainable exploitation of water resources specially during water scarcity periods.
Therefore, Managed Aquifer Recharge (MAR) represents a feasibly solution to deal with future water management challenges through the storage of available water in aquifers.
The present dissertation is focused on the study of microbial, biogeochemical and physical processes related to MAR ponds, regarding both quantity and quality aspects. The knowledge about these processes has allowed to identify key issues affecting the correct operation of infiltration ponds, laying the foundations for the optimization of quantity and quality targets.
Two different sites in Llobregat River Basin were chosen as a investigation framework.
The first part of this thesis was developed in Sant Vicenç dels Horts MAR system (Barcelona), where an innovative treatment for emerging contaminants had been proved successfully. A reactive layer was put in the bottom of infiltration pond, promoting different redox conditions below the pond and enhancing the removal of dissolved organic matter as well as emergent organic contaminants. In this thesis, further work has been carried out, by investigating the role of microbial community in this removal, by means of a microbial fingerprinting study between two different scenarios. Which were (1) when no-recharge was present and (2) during a long recharge period. The microbial fingerprinting study confirmed that microbial diversity during recharge period fitted in Intermediate Disturbance Hypothesis approach. Furthermore, sequencing of prominent bands evidenced the presence of principally degradative-like microorganisms during recharge. A multivariate statistical analysis including hydrochemical, soil grain-size distribution, operational and microbial variables was also performed. Most relevant variables affecting microbial populations were identified. Likewise, the correlations between some microbial prints in the system revealed the presence of some classes and species involved in biodegradation pathways.
The second investigation was focused on the study of redox processes from the infiltration pond to the aquifer, passing through the vadose zone. The study was placed in Castellbisbal MAR system (Barcelona). This facility has a conventional surface infiltration pond without the effect of the reactive layer. The infiltration path was widely monitored and four sampling campaigns were carried out in four different moments along a one-year study. Results from in situ redox potential measurements, temperature evolution, operating conditions (water levels, flow rate and infiltration rate), characterization of the organic matter and hydrochemical composition of water were collected and analyzed. Especially, operating conditions and redox potential, where it was observed that evolution in the first meter of the infiltration profile had been related to clogging development in the pond bottom.
Finally, results from monitoring tasks were used as the basis to construct a flow and heat transport model simulating recharge process. The flow model included the decrease of hydraulic conductivity caused by clogging periods. In addition, a heat transport model was capable to calculate the modifications of hydraulic conductivity due to temporal temperature evolution. Taking into account results of heat transport model, two batch-type biogeochemical models were suggested to explain redox processes in winter and summer scenarios. Furthermore, models were capable to explain the fate of the different fractions of dissolved organic matter, and the corresponding change of degradation rates due to temperature changes amongst different scenarios.