Variable Response of Oil-polluted Soils to Biostimulation Treatments Using Nonionic Surfactants and Inorganic Nutrients

We compared the response of oil-polluted desert and marine soils to biostimulation using three nonioinc surfactants (i.e., Triton X-100, Tween-80 and Brij-35) and inorganic nutrients (i.e., N and P) at different ratios. The addition of Tween-80 and Brij-35 resulted in an increase in the produced CO₂ from 2.1 ± 0.01 to 2.5 ± 0.10 and from 0.7 ± 0.01 to ≥1.3 ± 0.02 mg CO₂ g⁻¹ soil after 49 days of incubation in the desert and in the marine soil, respectively. This corresponded to 51% increase in the oil mineralization rate in the marine soil, but only to 20% increase in the desert soil. The addition of inorganic nutrients did not affect CO₂ production in the desert soil but increased the amount of CO₂ produced by the marine soil to reach a maximum of 1.2 ± 0.07 mg CO₂ g⁻¹ soil. The produced CO₂ in the marine soil was comparable at the different N:P ratios. The observed variable response of the two soils to biostimulation could be attributed to differences in their physico-chemical and biological characteristics. The desert soil had higher oil content and lesser nitrate concentrations than the marine soil, and both soils had different textures. The bacterial communities were very different, with no common genera between the two soils. Betaproteobacteria was detected only in the desert soil whereas Deltaproteobacteria and Firmicutes were detected only in the marine soil. We conclude that biostimulation depends on the physico-chemical and biological characteristics of polluted sites, therefore, bioremediation has to be tailored specifically for each type of soil.