This thesis is focused οn biogeophysical approaches sensitive to biogeochemical transformations to monitoring contaminated and degraded sites. These approaches are of interest as they have low cost, inexpensive, non-intrusive attributes – making them good candidates as sustainable monitoring tools. There is promise for transfer of these approaches to monitor and eventually help design biological systems such as wastewater treatment, anaerobic digestion, and contaminated land technologies. One of the main interests is the monitoring of natural attenuation at contaminated sites, as well as planning options to accomplish this. The application of geophysical / electrical methods to monitor / investigate microbial mechanisms in the subsurface are likely to have signification implications for the management of contaminated or degraded sites. Biodegradation and natural attenuation are the most favoured approaches to manage contamination. Recent research questions our depth of understanding of the underlying mechanisms of natural attenuation processes, and therefore our ability to adequately monitor and engineer viable remediation solutions. For example, large scale microbially mediated electron transfer across redox boundaries results in ‘geobatteries’ that can be measured using geophysical and bioelectrical methods at landfill and contaminated sites. The size and scale of these geoelectric responses requires the presence of naturally occurring electronic conductors such as bio-precipitates or a combination of extracellular microbial mechanisms and interactions with mineral surfaces. By passing the existing subsurface electronic conductor with a series of large graphite electrodes modifies the geobattery into a large microbial fuel cell or ‘Bio-electrochemical System’ (BES). BESs are engineered environments that manipulate this ability of microbes to oxidize and reduce organic and inorganic matter at an anode and cathode linked via an electronic conductor. The engineered BES can be used as a sensor to investigate and monitor or enhance microbial activity in the subsurface in near real time. The purpose of remediation monitoring is to establish the effectiveness of remediation in preventing contamination, the effectiveness or any remediation taken to eliminate or minimize any risk to human health and environment and that applicable requirements of the remediation have been met. Additionally, biogeophysical approaches could reduce conventional monitoring by reducing the volume of samples, as well as providing data to design and maintain the optimal conditions of sustainable remediation on contaminated or restored sites. In order to achieve the above objectives, bench and field scale BESs were designed to degrade contaminants in groundwater. The power produced (i.e. current and voltage) used as real time biosensor of how the microbial ecology of the system operates. Tank experiments for geophysical (Self-Potential) quantification of physical properties were chosen as engineered case studies in controlled conditions due to Self-Potential sensitivity to biological alterations. Additional, geoelectrical analysis used to determine general peatland health at a restored, actively degrading and an intact (control) location within Garron Plateau at Northern Ireland. Through an analysis of three commonly applied electrode arrays, we provide an insight as to the best performing electrode configuration for near surface geophysical analysis of blanket peatlands and an insight to biogeophysical mechanisms happen in the peat itself. Geophysical analysis correlated with the organic content and patterns associated with is creation or decomposition. Overall, this work demonstrates that, with these approaches, geophysical / electrical methods exhibit significant potential as a monitoring tool of microbial processes on site.
Biogeophysical approaches to monitoring contaminated and restored sites
Kirmizakis, P. (Author). Jul 2020
Student thesis: Doctoral Thesis › Doctor of Philosophy