Effect of mass-transfer limitations on bioavailability of sorbed naphthalene in synthetic model soil matrices

Abstract

External and internal mass-transfer resistances influencing the bioavailability of sorbed naphthalene in a synthetic model matrix for soil aggregates were investigated in batch experiments in mixed reactors. Amberlite® adsorption resins (XAD4 and XAD7) were used as the synthetic model for soil aggregates. The effect of hydrodynamic conditions in the slurry phase on the diffusive transport across a stagnant film surrounding the model particles was studied. In addition, a mechanistic model was developed based on mass balances, diffusion equations, a nonlinear sorption isotherm, and microbial degradation kinetics. Experimental results could be explained well with this model. In the absence of external transfer limitations, intraparticle effective diffusion coefficients of (3.55 ± 0.10) × 10−9 m2/s and (5.29 ± 0.86) × 10−10 m2/s were determined for naphthalene in Amberlite XAD4 and XAD7, respectively.