Development and application of techniques to monitor natural attenuation of petroleum hydrocarbons in the environment
The works carried out in this thesis exploited the application of nutrients and microbial additions to environments to enhance natural attenuation of petroleum hydrocarbon contaminant. These sites include former historically site contaminated with solvents [benzene, toluene, ethylbenze, xylene (BTEX)], an intertidal location at the Aberdeen Harbour polluted with diesel, a location at the periphery of the Burgan oil field in Kuwaiti desert contaminated with crude oil, and drill cuttings from the North Sea that was contaminated with paraffin and diesel. The effect of the treatments on the parameters tested was used to determine the performance of natural attenuation in studied environments. The parameters tested include respiration (carbon dioxide production), microbial dehydrogenase activity, microbial population and biomass, bioavailability of contaminants and toxicity testing. In addition, results from gas chromatography (GC-FID) and high performance liquid chromatography (HPLC) complemented biological tests. The treatments resulted in significant changes in the parameters tested and by correlating the observations to the reduction of total petroleum hydrocarbons (TPH) in the environments studied, the success of natural attenuation and bioremediation was confirmed. Techniques were manipulated to suit individual case studies. In response to nutrient and oxygen enhancement of the BTEX contaminated soil, the biomass of degradative microbial population was significantly stimulated. Results of significant increases in respiration and dehydrogenase activity coincided with completed biodegradation of BTEX in the soil. Oxygen that was released from hydrogen peroxide was found to be very effective in achieving significant biodegradation of benzene and toluene when combined with nitrogen and phosphorus. This could have implications for bioremediation of these compounds as the cost of oxygen supply becomes expensive. The bioavailability of BTEX compounds in the soil studied was successfully demonstrated by the used of Pseudomonas putida TVA8 biosensor, a sensor specific to these target molecules. It was observed that concentrations of BTEX that were not detected by HPLC were sensed by the biosensor. The bioremediation of North Sea drill cuttings contaminated with paraffin and diesel was achieved by nutrient additions and inoculation with soil microorganisms. Pre-treatment with steam was observed to be most effective in enhancing the biodegradation of paraffin oil contaminated drill cuttings, while pre-treatment with combined steam and ozone was most effective for enhancing biodegradation of paraffin and diesel contaminated drill cuttings. The metabolic biosensor Saccharomyces cerevisiae W303-1B (lucD) was more sensitive to water extracts of the drill cuttings than Escherichia coli HB101 (pUCD607), suggesting the use of the yeast biosensor in toxicity testing in cases requiring stricter treatment regime.