Biodegradation of anionic surfactants in the bioremediation of oil-polluted soil

Abstract

Surfactants are applied as emulsifiers or solubilizers by treatment of polluted soil. Theproblem of secondary pollution has arisen as result of the surfactant-enhanced remediation ofa polluted soil contaminated with hydrophobic organic compounds. Several studies haveshown that the surfactants are biodegradable in aerobic conditions and the biodegradabilitydepended on the chemical properties and concentration of surfactant. A study of the leachingof surfactants from the soil is important, as it is difficult to identify the reason for thereduction of concentration of pollutants in the soil: is it degradation or leaching? Theexperiments were carried out with a fine sandy soil in column tests and CaCO3 was added toincrease soil pH. The soil was treated twice with the bioremediation agent SR-100. The soilpH, the concentrations of anionic surfactant and petroleum hydrocarbons at the differentdepths of soil were determined. The microbial activity of soil fractions was evaluated byrespirometer. The concentration of surfactants was determined colorimetrically as MethyleneBlue active substances (MBAS). The concentration of anionic surfactants decreased in theupper layer of the columns, but it increased in the lower layers. It indicated the leaching ofthe anionic surfactants from soil during experiments of 60 days. The amounts of residualsurfactants were lower in the samples of polluted soil in comparison with unpolluted soil. Thesamples of lower soil fractions had higher microbial activity in comparison with upperfractions. Soil pH was measured as pHH20, pHKcl and pHcac12 instead of the pH of soilsolution, because soil was too dry. The pH of fine sandy soil was 5.8 and during theexperiment the value of pH increased in the lower layer of soil till pHH20 = 7.5.