The effects of biostimulation and bioaugmentation on crude oil biodegradation in two adjacent terrestrial oil spills of different age, in a hyper-arid region

This study deals with two adjacent terrestrial oil spills, with similar properties, located in a hyper-arid region in Israel, one from 1975 and the other from 2014. It tests the effect of biostimulation on crude oil degradation in both spills and whether biostimulated sediments from the 1975 spill can bioaugment crude oil degradation in the 2014 spill. Soil hydrophobicity, expressed as Water Drop Penetration Time (WDPT), and Gasoline Range Organics (GRO) and Diesel Range Organics (DRO) content in sediments were measured in one-month ex-situ experiments. No significant reduction in hydrophobicity and GRO + DRO content was observed in non-biostimulated controls. A combined treatment of mineral fertilization at t₀ and maintaining 50% water saturation, significantly accelerated the decrease in hydrophobicity and GRO + DRO content in sediments of both spills. The addition of biostimulated sediments from the 1975 spill failed to accelerate the reduction of GRO + DRO content and hydrophobicity in the 2014 spill. Surprisingly, the GRO + DRO degradation rate in biostimulated sediments from the 2014 spill was 36% higher than in biostimulated sediments from the 1975 spill. Crude oil composition in both spills changes during its degradation and is characterized by an increase in the GRO fraction. To a certain range, WDPT was found to serve as a reliable indicator for oil content in the soil. We conclude that even in a hyper-arid region, oil bio-degradation capabilities develop in a relatively short time. Moreover, while biostimulation was effective in accelerating biodegradation, bioaugmentation with biostimulated sediments from a nearby older spill was found ineffective.