부산대학교 도서관

In aquifers polluted with organic compounds, the aqueous phase contaminant plume spreads through the aquifer. Nevertheless, natural attenuation processes at the subsurface can slow the spreading of these plumes and therefore mediate the extent of contamination. One of the natural attenuation processes is biodegradation, which is carried out by indigenous microbial communities. This process is able to degrade contaminant molecules, reducing their concentration in the aquifer. The chemical interfaces present within the organic contaminant plumes are known as plume fringes and at these locations, biodegradation is naturally enhanced by different physical and chemical processes. Previous studies of plume fringes have focused on the biodegradation potential of the planktonic microbial community, yet the role of the biofilm community attached to the sediments are not well understood although likely to be of great relevance. Moreover, these fringes are under the influence of different physical processes, causing the chemical environments at these locations to change relatively rapidly compared to the plume core conditions. The response of biofilms and planktonic communities to alterations in their chemical environment, located at these chemical interfaces have not been explored. This thesis investigates the dynamic responses of microbial communities, both planktonic and attached, to different chemical environments that develop in the chemical interfaces of polluted aquifers. To assess this, different laboratory-based microcosm experiments were carried out using groundwater from a site polluted with phenolic compounds. At this site, field experiments were also developed. The temporal framework of the experiments installed on site in 2014 was extended up to two years. Different chemical analyses were carried out and molecular biology tools were utilised to characterise and assess the microbial communities. The results show that time-scales of microbial attachment in plumes are a stable feature at laboratory and field scales. During the temporal evolution of the experiment it was observed that the attached and planktonic community structures differ over time at chemical interfaces. These differences are sustained when changes in the chemical environment are introduced. The study of the biofilm in these experiments allowed to demonstrate the capacity of this community to be resilient towards changes in their chemical environment. Once established, the community structure of the biofilm remained stable under different environmental chemical changes that are found at the chemical interfaces of polluted aquifers, such as plume advance, plume refreshing and source term variation. This study also considered the variations in chemical interface scenarios introduced by an engineered intervention, such as Pump and Treat (PAT). Using the same study site, where the contaminated aquifer was intervened with a PAT in order to treat the phenolic plume, annual surveys were made for a three-year period to understand the effect of this technology on the planktonic microbial community. With the use of isotope analyses it was possible to demonstrate that the microbial communities remain active after cessation of engineered intervention. The analysis of the microbial community among the different geochemical variables demonstrated that they were under the influence of different gradients of concentration of phenolic compounds. Moreover, the presence of some microbial groups, such as methanogens, could be associated to isotope signatures related to this type of metabolism. This research provides broader insight into the knowledge about the microbial dynamics taking place during biofilm development at chemical interfaces of a polluted aquifer. The robustness of the biofilm community in these environments signals that their influence should be considered in bioremediation applications for the remediation of organic-contaminant plumes.