Hydrocarbon contamination of soil from accidental spills and negligence represents a major cause of sub-surface contamination. There are numerous physical, chemical and biological techniques available for contaminant remediation. However, many of these methods can be difficult to implement at sites where access to soils, or delivery of treatments, requires substantial excavation works and disruption (for example where contamination is located beneath or adjacent to building structures and underground services). An innovative technology that may provide a solution for the remediation of subsurface contamination without causing interim damage is that of electrokinetic remediation. Electrokinetic remediation is the application of a low voltage, direct current (of the order of mA/cm²) between electrodes placed in a contaminated soil system. The production of an electric field causes a number of electrically-induced processes to occur that can promote soil remediation, principally: electromigration, electroosmosis, electrophoresis, and electrolysis. This study examined the use of electrokinetics coupled with biodegradation to remediate kerosene and transformer oil from sub-surface soils. The principal investigations carried out within this study included: the use of electroosmosis as an in situ flushing technique; use of electrokinetics to deliver surfactants into the soil to promote mobilisation of contaminants within the sub-surface; and the use of electrokinetics to create optimum conditions for biodegradation by the delivery of nutrients and electron acceptors, the removal of toxic metabolites, and by controlling the pH and moisture content of the soil. As an integral part of the research, a field trial was designed and set up to determine whether electrokinetics could be used to promote the biodegradation of transformer oil from the subsurface. This was one of the first field trials in the UK for the electrokinetic remediation of hydrocarbon contaminants. The results of the study support the use of electrokinetics as a field tool for the enhancement of remediation in the sub-surface. Laboratory-scale studies showed the potential to mobilise the more soluble hydrocarbons (such as toluene and xylene) in the soil, to deliver enhancing agents (e.g. surfactants and nutrients) and to remove toxic metabolites. The field-scale experiment demonstrated the concept of a relatively low cost treatment cell on-site and provided some evidence that biodegradation of the transformer oil was promoted. Consequently, it is suggested that electrokinetics, with the correct engineering controls in place, provides a valuable method of optimising the biodegradation of hydrocarbons in the sub-surface.

Hydrocarbon contamination of soils has increased worldwide and bioremediation offers an attractive and environmentally friendly solution to this problem. However, the efficiency and completion of remediation must be assessed using environmental risk assessment criteria. As a result, a variety of indicators have become essential for determining and evaluating recovery of contaminated soils. In this study, microbiological and toxicological assays are used to support traditional chemical analyses, to identify a suite of assays suitable for determining a Soil Recovery Index from Pollution (SRIP). Microbiological assays used are microbial biomass carbon (Cmic), plate counts for culturable degraders and general heterotrophs enzyme activities (dehydrogenase and phosphatase), basal respiration, Substrate Induced Respiration (SIR), and bacterial biosensor. Toxicological response assays of higher organisms include two species of earthworms (Eisenia fetida and Lumbricus terrestris), also, plant assays, including seed germination, root elongation, germination index and plant shoot height performed using two species of plant wheat (Triticum aestivum L.) and white mustard (Brassica alba L.). All assays were applied sequentially to kerosene and diesel amended soils for both incubated and non–incubated treatments. The indicators were discriminated in terms of their sensitivity using a ranking system. The data collected were integrated into a single numeric value to reflect a ‘level of concern’ for each soil treatment. Soil characteristics and hydrocarbon types play key roles in the response of these indicators. The soil that had high organic matter and clay content was less affected by hydrocarbons. For the freshly hydrocarbon amended soils, kerosene was more toxic than diesel, however the opposite was found in the incubated hydrocarbon amended treatments. The most sensitive and robust indicators were basal respiration, bacterial heterotrophs and degraders counts, bacterial biosensors (methanol extracted soils), earthworm survival, mustard root elongation and mustard plant shoot height. Sensitive indicators were inserted into the SRIP. The SRIP indicates the “level of concern” for each soil treatment in a single value.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 223-227). Available also in a digital version from Dissertation Abstracts.

Thesis (M.Sc.). / Written for the Dept. of Natural Resource Sciences. Title from title page of PDF (viewed 2008/07/30). Includes bibliographical references.

Thesis (M.Sc.) - Carleton University, 2007. / Includes bibliographical references (p. 48-50). Also available in electronic format on the Internet.