Degradation of polycyclic aromatic hydrocarbons: Model simulation for bioavailability and biodegradation

Abstract

A mathematical model for a one-dimensional convective-dispersive solute transport in a soil matrix is presented. The interplay of linear equilibrium sorption and first order degradation were incorporated into the formulation of the model. The model took into consideration the overall effects of the solid and liquid phase mass transfer resistances. Data from experiments were analysed using the temporal moments method (MOM) and CXTFIT curve-fitting technique. The functional parameters; dispersion coefficient, first order degradation rate constant and the retardation factor were estimated using both first and second normalised moments. The solution to the model equations was achieved by the use of the backward finite difference scheme. Results obtained showed that naphthalene was more selectively degraded than pyrene and anthracene with a residual concentration of naphthalene 1.12E − 5 mg/L, 1.48 mg/L; pyrene 3.11E − 4 mg/L, 1.58 mg/L; and anthracene 7.67E − 4 mg/L, 1.61 mg/L in the axial and radial directions, respectively. Concisely, the modeling results showed the occlusion of these compounds within the fissures and cavities of the soil particles, which renders them not readily bioavailable and thus inaccessible to microbial degradation.Un modèle mathématique pour le transport soluté convectif-dispersif unidimensionnel dans une matrice de solàété présenté. L'action réciproque de la sorption d'équilibre linéaire et la dégradation de premier ordre aété incorporée dans la formulation du modèle. Le modèle prenait en ligne de compte les effets d'ensemble des résistances de transfert de masse des phases liquide et solide. Les données de ces expériences ontété analyséesà l'aide de la méthode temporelle des moments et de la technique CXTFT Les paramètres fonctionnels, le coefficient de dispersion, la constante du taux de dégradation de premier ordre et le facteur de ralentissement ontété estimés faisant appelà la fois aux premier et second moments normalisés. La solution auxéquations du modèle aété obtenueà l'aide du schème de différence finie rétrograde. Les résultats obtenus montraient que le naphtalèneétait plus sélectivement dégradé que le pyrène et l'anthracène où la concentration résiduelle de naphtalèneétait de 1,12E − 5 mg/l, 1,48 mg/l, du pyrène de 3,11E − 4 mg/l, 1,58 mg/l et de l'anthracène de 7,67E − 4 mg/l, 1,61 mg/l en directions axiale et radiale respectivement. En bref, les résultats de modélisation montraient que l'occlusion de ces composés dans les fissures et cavités de particules du sol les rendait moins biodisponibles et ainsi inaccessiblesà la dégradation microbienne.

Remediation of crude oil contaminated soil with locally formulated bioremediation agent

“…This could be traced to the phenomenon of surface adsorption/desorption effects of naphthalene on soil organic carbon and interstitial voids within the micro and sub-micro pores of the soil particle. Reports have also shown that less than the total amount of some aromatics such as naphthalene adsorbed onto soil particles are actually desorbed and released (Nkedi-Kizza et al, 2006;Owabor and Agarry, 2009;Owabor et al, 2010;Owabor et al, 2011). This may therefore, limits their bioavailability for microbial degradation.…”

Mass Transfer: Impact of Intrinsic Kinetics on the Environment

“…The rationale behind this premise is that the small pore spaces internal to aggregates of soil and sediment particles exclude microbes, such that compounds that are dissolved or sorbed within these immobile-water domains must first be transported to the external aqueous phase (i.e., bulk aqueous phase) before they can be metabolized [5]. This premise is supported by several laboratory studies that have found biodegradation to occur only, or predominantly, in the bulk aqueous phase [6], [7]. A variety of factors, including physical characteristics of the sorbent (e.g., particle shapes, sizes, and internal porosities), chemical properties of the sorbates and sorbents, and biological factors (e.g., microbial abundance and affinity for the contaminant) influence availability.…”

“…Studies on mass transfer effects for the evaluation of bioavailability and biodegradation parameters of contaminant solutes in aqueous solid/sediment matrix applicable for biodegradation of the environmentally persistent and recalcitrant chemicals have been extensively investigated using models [7], [9] which incorporates a two-site sorption/desorption kinetics.…”

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

“…Naphthalene and anthracene transport through a saturated and homogeneous porous media in onedimensional uniform flow considering convection, dispersion, linear equilibrium sorption, and firstorder degradation has been described in our earlier paper (Owabor et al 2003). The unsteadystate models characterizing the reactions in both macroporous and microporous systems are intended to predict the concentration in the axial (z) and radial (r) directions using the experimental data from a soil microcosm reactor.…”