Kinetics of quinoline biodegradation, sorption and desorption in a clay-coated model soil containing a quinoline-degrading bacterium

Abstract Kinetics of quinoline biodegradation, sorption and desorption in a clay-coated model soil containing a quinoline-degrading bacterium. Studies were initiated to compare the kinetics of quinoline sorption/desorption and biodegradation in order to predict the relative importance of abiotic and biotic processes in the transport of quinoline in columns containing a model soil. Initial biodegradation studies were conducted in a 1-cm-long column containing a quinoline-degrading bacterium (10 9 colony-forming units g −1 porous medium) attached to 100- to 150-μm-diameter glass beads that did not sorb quinoline. At a 155-nmol mL −1 quinoline influent concentration, the maximum consumption rate was 104.7 nmol quinoline min −1 cm −3 pore volume. In contrast, the maximum consumption rate of the first metabolite ( 2 -hydroxyquinoline) was 24.8 nmol mL −1 cm −3 pore volume. In a second experiment, bacteria were mixed with a model soil, consisting of montmorillonite bound to alumina particles (75- to 180-μm diameter). In a 1-cm-long column of the model soil, the quinoline consumption rate at a 155-nmol mL −1 quinoline influent concentration was similar to that obtained in the glass-bead column, showing that the clay does not substantially affect quinoline biodegradation at equilibrium conditions. In a third series of experiments, sorption to the model soil was examined in the absence of microorganisms. The observed desorption rate coefficient for quinoline averaged 1.1·10 −3 s −1 , which was one to three orders of magnitude smaller than was observed for 45 Ca. The slow ion exchange of quinoline on the clay surface is controlled by a site-specific quinoline/montmorillonite interaction and not a larger-scale physical step (i.e. interparticle diffusion). Equilibrium first-order forward (sorption) and reverse (desorption) mass fluxes were 1160 nmol cm −1 cm −3 pore volume with a 155-nmol mL −1 quinoline influent concentration. The initial quinoline mass flux to the clay was estimated as 31,800 nmol cm −1 cm −3 pore volume. Thus, under the experimental conditions, the net rate of decrease of solution-phase quinoline is greater through abiotic processes than through biodegradation. Coefficients obtained from the individual sorption and biodegradation experiments were used in a sorption/biodegradation transport model to quantify any sorption/biodegradation interactions. Breakthrough of quinoline occured more rapidly in the sorption/biodegradation experiments, indicating substantially less sorption compared to sorption experiments. Quinoline sorption was reduced a small amount due to competitive sorption between quinoline and 2 -hydroxyquinoline (biodegradation intermediate), but this effect was too small to account for the substantial decrease in quinoline sorption. Experimental and calculated estimates of biomass coverage on the particles also accounted for some decrease in quinoline sorption, but not the large decrease observed. Therefore other, undefined, processes may contribute to the observed sorption/biodegradation interaction.