Combination of natural gums and synthetic surfactants for washing of a soil highly contaminated with crude

Surfactant-enhanced washing has become a very important option for the remediation of soils contaminated with a variety of compounds and elements, i.e., petroleum hydrocarbons, pesticides, dense nonaqueous-phase liquids, metals, and others. The use of biosurfactants has merged as an interesting solution. Many authors have published the use of soil-washing processes by means of biosurfactants produced by different bacteria to clean soils contaminated mainly with petroleum hydrocarbons, metals, and pesticides. The use of natural products produced by plants has been less explored. There are two basic aims of this study: first, to compare the performance of two natural gums (guar and locust bean gum [LBG]) with a synthetic surfactant sodium dodecyl sulfate (SDS), in terms of their total petroleum hydrocarbon (TPH) removal capabilities; second, to evaluate the behavior of these natural products (guar and LBG) combined separately with two synthetic surfactants (SDS or polyethoxylated sorbitan monooleate [TW80]), with respect to both TPH removal and removal efficiencies. When a soil highly contaminated with Mexican crude (about 98,000 mg/kg) was cleaned with guar and LBG, TPH removal values as high as 49.6 and 47.7% were obtained, using gums at concentrations of 0.5%, in comparison with 36.3% of TPH removal, reached by SDS at the same surfactant concentration. Importantly, note that the soil contained TPH-diesel; TPH-gasoline and heavier fractions including benzene, toluene, ethyl benzene and xylene, polyaromatic hydrocarbons; and metals, including high amounts of calcium and magnesium.