Oil and gas drilling operations create drill cutting wastes around the world. Drill cutting waste includes synthetic drilling fluids typically consisting of petroleum-based compounds mixed with clay-type materials and water. Biological treatment is an effective means of disposing of drill cutting wastes, but proper biodegradation conditions are critical. In this study biological treatment of drill cutting wastes containing Saraline® (synthetic paraffin mineral oil) was examined using a variety of amendments to study the effect of different conditions on the biodegradability of synthetic drill cutting wastes. Soil was collected from a drilling site in Southeast Asia and soil microcosms were incubated in a sealed and controlled environment to mimic the dry season of the field site. Amendments evaluated included native soil as a bulking agent and as a source of inoculum, rice hulls as a bulking agent to improve aeration and moisture retention, and urea as a source of nitrogen fertilizer. All microcosms were maintained with 15 – 20 % moisture and kept at 30oC. Hydrocarbon biodegradation was evaluated using gas chromatographic (GC) analysis of total petroleum hydrocarbon (TPH) concentration of each microcosm. Microcosms were sampled every 30 days for a period of 4 months.

Maximum biodegradation was observed with a 1:1 mixture of soil and drill cuttings containing 1% urea and 10% rice hulls. Biodegradation proceeded with a half-life of about 30 days under these optimal conditions. After 4 months, 91% of the TPH was biodegraded under optimum conditions. Little or no biodegradation was observed for drill cuttings without amendments suggesting addition of soil bulking agent and fertilizer is essential. No decrease in TPH concentration was observed for a control with 1% sodium azide, indicating observed decreases in TPH were due to biodegradation alone. No volatilization was observed in the sealed soil microcosms. A separate volatilization experiment in open containers showed evaporation could contribute significantly to TPH loss in the field.


Civil and Environmental Engineering

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Publisher's website: http://www.battelle.org.



URL: http://digitalcommons.calpoly.edu/cenv_fac/89