Naphthalene and pyrene degradation in contaminated soil as a function of the variation of particle size and percent organic matter

The effect of soil particle size distribution and percent organic matter on the degradation rate of naphthalene and pyrene in a water medium of 7.05 ml/min at 27 ± 2oC in a soil reactor was studied. Analysis of the pattern of disappearance of these polycyclic aromatic hydrocarbons (PAHs) using various particle sizes showed a rapid decline of concentration of the chemicals during initial stages of bioremediation treatment, followed by a slow reduction rate. The extent of naphthalene and pyrene removal and final concentrations for the period under study differed among the different soil particle sizes. Results show that from an initial 100 mg/l, the concentration of both naphthalene and pyrene decreased in the following sequence clay > silt > fine sand > coarse sand. The degradation of the two PAHs was significantly enhanced by the addition of organic matter to the bulk composite soil. The specific reaction rate constant k was found to increase with decreasing particle size and increase with increasing % organic matter. For both PAHs, coarse sand had the lowest rate constant while clay had the highest. This implies that degradation was faster in the clay fraction than in the other soil fractions. The correlation coefficients obtained using linear regression method was between 0.734 and 0.996 indicating the reliability of the experimental data.