Assessing the Efficiency of Humic Substances as Washing Agents for Oil–Contaminated Soils and Peats under Model Experimental Conditions

Two humic preparations of different origins have been compared as washing agents for oil-contaminated soils and peat under model experimental conditions using a sample from the plow horizon of soddypodzolic soil artificially contaminated with oil or diesel fuel and a sample of high-moor peat contaminated with crude oil because of a spill occurred 15 years ago. Soil and peat were washed by shaking with solutions of the humic preparations Gumat Sakhalinskii and Lignogumat in a 1: 10 (m/v) ratio. Control samples were washed with distilled water. Washing with a synthetic surfactant (sodium dodecyl sulfate) was also added to the experimental design. After washing, soil and peat samples were air-dried and used for the determination of the total content of petroleum hydrocarbons; the characterization of their hydrocarbon composition; and the assessment of hydrophobicity from the contact angle and the efficiency of colonization by oil-destructing microorganisms Rhodococcus sp. and Candida sp., which are components of the preparation Bioros recommended for oil contaminations. It has been shown that the extraction efficiency of petroleum hydrocarbons by humic preparations did not differ from the extraction efficiency by water and was less than that by sodium dodecyl sulfate in all cases. No appreciable changes in the contact angles of soil and peat have been observed at the use of water and humic preparations as washing agents, while the contact angle decreased to less than 90o after washing with sodium dodecyl sulfate, which indicated the hydrophobicity of the surface of substrate particles. It has been found that humic preparations favor the colonization of soil and peat by oil-destructing microorganisms Rhodococcus sp. and Candida sp. Based on the obtained results, humic preparations have been recommended for further study as preparations favoring the ability of oil-destructing microorganisms to colonize oil-contaminated substrates.