Estimation of transport and degradation parameters for naphthalene and anthracene: influence of mass transfer on kinetics.

The method of temporal moment solutions (MOM) for one-dimensional convective-dispersive solute transport involving linear equilibrium sorption and first-order degradation for time pulse sources has been applied to analyze experimental data from a soil microcosm reactor. Estimation of the pore water velocity V for a nonreactive solute was aided by the use of only the first normalized moment while the dispersion coefficient D, first-order degradation rate constant lambda, and the retardation factor R were estimated using both first and second normalized moments. These transport and degradation parameters were compared to those obtained by a transport model using a nonlinear least square curve-fitting program CXTFIT (version 2.0). Results obtained showed that the MOM fits the breakthrough curve with tailing better than the CXTFIT. The initial estimates of these parameters aided the reduction of the dimensionality of the search process of the non- steady-state model. A residual concentration of 1.12E-5 and 1.48 mg/l for naphthalene and 7.67E-4 and 1.61 mg/l for anthracene, in the axial and radial directions, respectively, suggests the preference of naphthalene during the biodegradation process. The surface concentration as depicted using three-dimensional plots showed that there is occlusion of the aromatics (naphthalene and anthracene) within the soil micropores, thereby limiting their bioavailability and in the long run increasing their toxicity.