Biostimulation Treatments of Hydrocarbon-Contaminated Soil in Semiarid Patagonia, Argentina

Abstract Bioremediation is considered an appropriate technology for decontamination of polluted natural environments. The successful application of bioremediation depends on appropriate hydrocarbon-degrading microorganisms and environmental conditions in situ. Las Heras is a place located in northwest Santa Cruz (Patagonia, Argentina) with a very intensive activity of oil industry. In this region the conditions most likely to limit hydrocarbon degradation include cold and fluctuating temperatures, low moisture contents, low nutrient levels and alkaline pH. In this work we describe three representative cases of biostimulation treatments (nutrients and water addition) applied to soils with different pollution states: Case A (1680 m3) exhibited high values of total petroleum hydrocarbons (TPH 33510 mg/kg); Case B (480 m3) showed high values of total petroleum hydrocarbons (TPH 27754 mg/kg) and polyaromatic hydrocarbons (PAH 1.64 μg/1 in lixiviate); and Case C (1680 m3) exhibited high PAH values (PAH 1.94 μg/l in lixiviate). The controlled addition of nitrogen and phosphorous sources and water increased bacterial counts of soil in all cases and resulted in a significant elimination of hydrocarbons: 32 % TPH in Case A after 7 months of treatment (from May to December 2005); 39 % TPH and 88 % PAH in Case B after 5 months (from October 2005 to February 2006) and 90 % of PAH after 3 months of treatment (from May 2005 to July 2005) were removed. In addition, we performed a comparative evaluation of natural attenuation, biostimulation and bioaugmentation (inoculation of bacterial strains) for bioremediation of PAH-contaminated soil in situ. Both, biostimulation and bioaugmentation promoted significant degradation (> 90 %) of PAH after 6 weeks of treatment, whereas attenuation resulted in a reduced degradation rate (67 %). In conclusion, this study suggests that autochthonous bacterial communities from semiarid soils in Patagonia have the potential to degrade hydrocarbons after amelioration of unfavorable environmental conditions.