Biodegradability of Venezuelan Crude Oils

Abstract

Abstract Bioremediation represents one of the most promising, cost-effective, and safest technologies to be used for the restoration of crude oil contaminated soils. However, some previous studies have shown that bioremediation is less effective for heavy, low API gravity crude oils. INTEVEP and CHEVRON have independently conducted laboratory studies to evaluate the feasibility of using bioremediation technologies for crude oils (ranging from 9 to 32° API gravity) produced by MARAVEN in Venezuela. The composition of the hydrocarbons in each crude oil was first characterized by Iatroscan, gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS) in order to better understand the potential relationship between API gravity, hydrocarbon composition, and biodegradability. Five percent (w/w) of each oil was applied to a Venezuelan loam soil and fertilizers and organic material (used as bulking agents to improve soil conditions such as moisture holding capacity, tilth, and texture) were added to the oily soil to optimize conditions for biodegradation. Abiotic controls (containing 2% v/w HgCl2 to ensure no microbial activity) and a positive control containing fertilizer, but no crude oil, were also prepared. Biodegradation was measured directly by monitoring the decreases in the percentages of saturated, aromatic, resins and asphaltene fractions via Iatroscan throughout the 4 month incubation time. The initial and final samples were also monitored for losses of total petroleum hydrocarbons by GC and polyaromatic hydrocarbons by GC/MS. Biodegradation was monitored indirectly by measuring the production of CO2, a final breakdown product of hydrocarbon metabolism. Higher microbial activity (c.a. CO2 evolution) was observed in the soil amended with light crude oils (120 mg CO2/h/m2) than in soil amended with heavy crude oils (85 mg CO2/h/m2). Iatroscan, GC, and GC/MS analyses confirmed that the light Venezuelan crude oils (>30°API) were readily biodegraded. The biodegradation potential of each of the crude oils and recommendations for which oil types are most amenable to bioremediation technologies are presented.