Characterisation and biotransformation of heavy oils in the contaminated soil environment

• Main Author: Whittaker, Martin
• Published: University of Edinburgh 1996
• Subjects: 577.27
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.663732

The biotransformation of heavy oils in soil microcosms was studied over a period of 9 months. Over this time, a medium-to-heavy boiling ballast oil and a crude oil exhibited a total reduction in total solvent extractable material (TSEM) of approximately 80%<SUP>w</SUP>/<SUB>w</SUB> and 60%<SUP>w</SUP>/<SUB>w</SUB> respectively. No.6 fuel oil was found to be largely recalcitrant to biotransformation. Abiotic controls indicated that up to 60% of the ballast oil was lost due to microbial activity, and that its microbial half-life was approximately 120 days. Over the 9 months, the %<SUP>w</SUP>/<SUB>w</SUB> of saturates within the ballast oil TSEM decreased from 74.6 to 23.2; the %<SUP>w</SUP>/<SUB>w</SUB> of aromatics increased from 12.5 to 23.0, the %<SUP>w</SUP>/<SUB>w</SUB> of polars increased from 8.6 to 31.3 and the %<SUP>w</SUP>/<SUB>w</SUB> of asphaltenes increased from 4.3 to 22.5. Similar changes were observed for the crude oil. The reliability of several oil biomarker source correlation indices was determined. The most reliable were those comprising ratios of individual hopane isomer pairs, which remained almost constant in both oils even after extensive constant at 0.7 for both oils over the 9 month biotransformation period. Methods of monitoring oil biotransformation through biomarker analysis were also assessed. The most sensitive indicator of oil biotransformation was the ratio of total n-alkanes to 17α(H),21β(H)-hopane. For the ballast oil, this ratio decreased from 748.0 to 8.5 over 9 months. The carbon isotopic composition of individual compounds did not vary significantly with oil biotransformation. However, isotopic characterisation of authentic oil-contaminated groundwater samples showed shifts of 1 - 2‰ in favour of C<SUB>13</SUB> in some progressively weathered samples, although it is not established whether this shift is due to microbial activity. These results are of considerable use to researchers and practitioners in the field of contaminated land assessment elucidating the source terms, weathering characteristics and bioremediation potential of complex heavy oil waste matrices.