Evaluation of factors affecting biological treatability of flare pit waste in western Canada

Abstract

The upstream oil and gas industry used flare pits (FPs) for decades to store and/or burn produced fluids generated at well sites, compressor stations, and batteries. FPs usually contain high levels of hydrocarbons, metals, and salts that could inhibit the microbial activity during bioremediation. Slurry- and solid-phase laboratory treatability experiments demonstrated that they serve as a potential effective screening tool for developing treatability predictions for FP waste.

Slurry-phase experiments investigated the effects of salinity, nutrient, soil type, and temperature on the ultimate biotreatability of FP waste. The primary effect of soil type was highly significant; with higher clay content resulting in lower biodégradation. Temperature (30°C/40°C), salinity (up to 40 dS/m) and nutrient (up to 700 mg N/L) did not show any statistically significant primary or interaction effects on hydrocarbon degradations. The major portion of the hydrocarbons was biodegraded within 10 to 70 days resulting in overall Oil and Grease (O&G) removal of 18 to 40%.

Two separate slurry biotreatment experiments based on factorial design studied the effects of two metals (cadmium and zinc) and their interaction effects with salinity on hydrocarbon biodégradations in FP waste. The results showed 42 - 52.5% hydrocarbons were removed in the slurries spiked with Cd, and 47 - 62.5% in the slurries spiked with Zn. The Analysis of Variance (ANOVA) showed that primary effect of cadmium and cadmium-salinity interaction effect were statistically significant. Zinc's primary effect and zinc-salinity interaction effect on hydrocarbon degradations were statistically insignificant, but its quadratic effect was significant.

Solid-phase bioremediation study employing a statistical fractional factorial experimental design investigated the effects of nitrogen (500, 1,250, or 2,000 mg/kg of soil), phosphorus (100, 250, or 400 mg/kg of soil), salinity (0, 20, or 40 dS/m), and incubation temperature (20°, 30°, and 40° C) on hydrocarbons biodégradation in the soil contaminated with FP hydrocarbons over a period of 270 days. The highest O&G reduction was 34% in the soils incubated at 30° C Soil temperature had significant influence on biodégradation rates. High phosphorus levels (up to 400 mg P/kg) had no detrimental effect, while high salinity levels reduced the hydrocarbon biodégradation.