Oil spills occur regularly in terrestrial environments and crude oil can contain many compounds that are highly resistant to degradation. Among these compounds are high levels of polycyclic aromatic hydrocarbons (PAHs) which are not only toxic but can also be carcinogenic and/or mutagenic. The first chapter of this dissertation includes an extensive review chapter on the variables affecting the anaerobic degradation of hydrocarbons, with a particular focus on PAHs. Electron acceptors, electron donors, temperature, salinity, pH all play key roles in determining the possibility effective of effective degradation occurring. Thus, by addressing solutions, such as biostimulation, improving environmental variables for optimal growth and enzymatic rates, and increasing the supply of the electron acceptors needed for anaerobic respiration help to remove obstacles to biodegradation. Additionally, the use of co-substrates or techniques such as bioaugmentation can further enhance this endeavor.
Aerobic hydrocarbon degradation also has its challenges, especially for complex aromatic compounds such as PAH.s Electrokinetics (EK) is a remediation technology can be used to make species more accessible such as contaminants, nutrients, electrons acceptors, and electron donors. EK technology can be used to migrate certain contaminants but can also greatly enhance the aerobic degradation of PAHs primarily by increasing bioavailability and nutrient delivery.
Studies were conducted to examine differences in electromigration rates for sand and clay. Two dyes, a red dye with anionic properties (FD&C 40) and a green dye with both anionic and cationic properties, composed of turmeric and Spirulina Blue were analyzed separately. The component of the green dye found to readily migrate is Spirulina Blue, consisting primarily of the protein pigment C-phycocyanin. The red dye in both sand and clay moves towards the anode, as predicted, and the rate between the two media was found to be approximately ten-fold. The green dye, having amphoteric qualities, can accept or donate protons, and can thus become strongly positively or negatively charged depending upon the pH of the system. It was found that due to a shifting pH gradient over time (in sand), this dye was initially anionic and thus migrated towards the anode but ceased migration after 48-72 hours due to a shift to a positive charge. Additional studies were conducted to observe how pH gradients in both sand and soil change over time. It is discovered that the rate at which the pH changes is dependent upon system variables including the current applied, which appears to absent from the literature, and that the initial semi-linear trend does not match the final gradient typically reported.
The final study investigates the potential of EK technology to enhance biodegradation. In order to do so, a sandy soil, spiked with three compounds (fluorene, phenanthrene, fluoranthene) is placed within self-designed electrokinetic setups and an initial experiment shows a high possibility of PAH degradation but is unconfirmable. A second experiment attempts to verify the general findings of the first experiment and employs the use of a surfactant (Brij-35), which is thought to increase microbial movement throughout the contaminated soil and possibly reduce the sorption of PAHs to soil particles, both thereby increasing bioavailability and degradation rates. While biological activity is very apparent in this experiment, no degradation is observed and this may be due to a presence of carbonaceous materials (i.e. organic matter) within the soil. This yields an additional variable that must be taken into consideration in future in-situ studies or remediation projects.
Overall it is found that many factors need to be taken into consideration for both aerobic and anaerobic biodegradation of PAHs. Increasing favorable growth conditions and increasing bioavailability can greatly help with this endeavor. Electrokinetics is an efficient means of ensuring this takes place but very specific designs or methods may be needed and pH gradients and extremes are found to provide significant obstacles to certain implementation but the results found in these experiments may be helpful to shed light on means of maintaining biological or chemical degradation experiments in an in-situ environment.
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