Biotreatment of Flare Pit Waste

Abstract

Abstract The upstream oil and gas industry has used flare pits (FPs) for decades to store and/or burn produced fluids generated at well sites, compressor stations, and batteries. Since produced fluids contain liquid hydrocarbons, process chemicals, crude bitumen, or salt water, FPs usually contain 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 application option. The use of slurry-phase and solid-phase biotreatment in the overall strategy for FP waste remediation is reported in this paper. A laboratory solid-phase bioremediation study was conducted over a period of 270 days to investigate the effects of nitrogen, phosphorus, salinity levels, and incubation temperature on the biodegradation of hydrocarbons in FP pit waste employing a statistical partial factorial experimental design. A soil contaminated with flare pit hydrocarbons was treated with nitrogen (500, 1,250, or 2,000 mg/kg of soil), phosphorus (100, 250, or 400 mg/kg of soil), and salt (yielding electrical conductivities of 0, 20, or 40 dS/m), and incubated at three temperatures (20 °, 30 °, and 40 °C). The highest oil and grease (O&G) reduction of 34% was observed in the soils incubated at 30 °C. Soil temperature had more influence on bioremediation rates than did N or P. The high P levels, up to 400 mg P/kg soil, had no detrimental effect on hydrocarbon biodegradation. High salinity levels reduced the rate of hydrocarbon biodegradation. The slurry-phase biotreatment of flare pit waste using 2 L slurry reactors showed an initial rapid decrease in hydrocarbon concentrations. However, biodegradation decreased with time and eventually ceased, leaving recalcitrant compounds. The nutrient concentrations (above 350 mg N/L, as ammonium nitrogen) did not exhibit statistically significant effects on hydrocarbon degradation. The primary effect of waste composition was highly significant, with higher soil clay content resulting in lower biodegradation. Introduction The produced fluids generated at oil and gas well sites, compressor stations, and batteries contain a variety of liquid hydrocarbons, process chemicals, crude bitumen, and salt water. Until recently, the industry practice was to store and intermittently burn these produced fluids in earthen pits called "flare pits." According to recent estimates, Alberta is home to about 30,000 flare pit (FP) sites(1). In 1996, the provincial government of Alberta banned the disposal of produced fluids in FPs, and requested the oil and gas industry to remediate former FP sites that are posing significant risks to human health and the surrounding environment. Because of the highly complex and variable nature of the waste, remediation of FP waste presents a serious challenge. At present, the most common technique used for remediation of FP sites is bioremediation by land application. Land application is relatively low-tech and less expensive (compared with competing techniques such as incineration). Furthermore, land application is popular in locations such as rural Alberta, because of the nature of the spatial distribution of FP sites.