Slurry-Phase Experiments as Screening Protocol for Bioremediation of Complex Hydrocarbon Waste

Abstract

Flare pits have been used by the upstream oil and gas industry for decades to store and/or burn produced fluids at well sites, compressor stations, and batteries. Waste at such sites, or flare pit (FP) waste, usually contains high levels of hydrocarbons, metals, and salts. At present, bioremediation by land application is the most common method practiced by the oil and gas industry to treat FP waste. High rate slurry-phase and solid-phase biotreatment methods are viable alternatives to the low cost yet inefficient land treatment option. An ultimate biotreatability screening tool is needed to assess the viability of each treatment method. The effects of salinity, nutrient, soil type, and temperature on the ultimate biotreatability of FP waste were investigated using 2 L slurry reactors. The results showed an initial decrease in petroleum concentrations; however, biodegradation decreased or ceased with time, leaving recalcitrant compounds. Within a week, the majority of saturated hydrocarbons degraded to low levels. Aromatics remained stable, while the level of polar compounds fluctuated. Temperature (30–40°C), salinity levels (up to 40 dS/m), and nutrient concentrations (above 350 mg N/L as ammonium nitrogen) exhibited no statistically significant effects on hydrocarbon degradation. The primary effect of waste composition was highly significant; with higher soil clay content resulting in lower biodegradation. Results indicate that slurry phase experiments may serve as a screening tool; however, caution should be exercised because slurries do not contain some of the microflora found in the solid phase (e.g., fungus).