Effect of Microbial Surfactants on Hydrocarbon Mineralization in Different Model Systems of Soil

Abstract

By way of microbial degradation of hydrocarbons metabolites may be formed that are more toxic than the substrate hydrocarbon. For example undecanoic acid, which may be formed from undecane, inhibits the elongation of fatty acids in various bacteria (1). Therefore it is necessary to study the effect of microbial surfactants not only on the degradation of hydrocarbons by an original soil population but also on the extent of mineralization. In the first model system, a stirred reactor with 10% soil content of an original soil population, oil degradation capacity could be increased from 25,7 to 46,5 g hydrocarbon mixture per kg soil dry weight and day by lowering the interfacial tension caused by the sophorose lipids added (2). The degradation capacity for a fuel oil also increased from 25,3 to 32,8 g hydrocarbon per kg soil dry weight and day, when sophorose lipids were added. About 90% of this oil could be degraded related to 99% of the defined hydrocarbon mixture (3). Yet after elimination of the model oil the chemical oxygen demand was still about 27% of the initial theoretical value (2). Therefore we examined the extent of mineralization by calculations based on waste air analysis in the stirred reactor with 10% soil content or on hydrogen peroxide usage in fixed bed columns of sieved soil percolated with a mineral salts medium with sufficient hydrogen peroxide (4).