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

Abstract

Surfactants are applied as emulsifiers or solubilizers by treatment of polluted soil. The
problem of secondary pollution has arisen as result of the surfactant-enhanced remediation of
a polluted soil contaminated with hydrophobic organic compounds. Several studies have
shown that the surfactants are biodegradable in aerobic conditions and the biodegradability
depended on the chemical properties and concentration of surfactant. A study of the leaching
of surfactants from the soil is important, as it is difficult to identify the reason for the
reduction of concentration of pollutants in the soil: is it degradation or leaching? The
experiments were carried out with a fine sandy soil in column tests and CaCO3 was added to
increase soil pH. The soil was treated twice with the bioremediation agent SR-100. The soil
pH, the concentrations of anionic surfactant and petroleum hydrocarbons at the different
depths of soil were determined. The microbial activity of soil fractions was evaluated by
respirometer. The concentration of surfactants was determined colorimetrically as Methylene
Blue active substances (MBAS). The concentration of anionic surfactants decreased in the
upper layer of the columns, but it increased in the lower layers. It indicated the leaching of
the anionic surfactants from soil during experiments of 60 days. The amounts of residual
surfactants were lower in the samples of polluted soil in comparison with unpolluted soil. The
samples of lower soil fractions had higher microbial activity in comparison with upper
fractions. Soil pH was measured as pHH20, pHKcl and pHcac12 instead of the pH of soil
solution, because soil was too dry. The pH of fine sandy soil was 5.8 and during the
experiment the value of pH increased in the lower layer of soil till pHH20 = 7.5.