Growth Kinetics Study of a Bacterial Consortium Producing Biosurfactants, Constructed with Six Strains Isolated from an Oily Sludge

Abstract

We investigated the ability of a bacterial community constructed with six strains isolated from an oily sludge, to utilize diesel oil at high concentrations. The consortium was able to grow at concentrations up to 84 g diesel oil/L and had produced biosurfactants during its active growth phase; these compounds, in their crude form, reduced the surface tension of distilled water from 72 mN/m to 31 mN/m, with a corresponding Critical Micelle Concentration value γ CMC = 81 mg/L. The plot of specific growth rates obtained from the growth curves versus initial concentrations was found to fit adequately the experimental data by the Andrews inhibitory model, which resulted in the following kinetic constants: μ max = 0.535 d - 1 ± 0.063, K S = 18.68 g/L ± 3.59 and K I = 29.02 g/L ± 4.96, reflecting the slow biodegradation rate. At 25.2 g diesel oil/L, close to the optimal concentration S * = 23.28 g/L ± 4.23, the consortium metabolized diesel oil faster than each strain did individually, suggesting that the process was stimulated by a synergistic interaction between the members of the consortium.