Sorption and Microbial Degradation of Naphthalene in Soil-Water Suspensions under Denitrification Conditions

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The microbial degradation of naphthalene under den-itrification conditions in soil-water suspensions was de-pendent on solute partitioning between soil and water. Soil-associated naphthalene was in equilibrium with aqueous-phase solute, with the rate of naphthalene deg¬radation being mixed order with respect to aqueous con¬centration. The rate of degradation was modeled by coupling Michaelis-Menten kinetics for aqueous-phase solute with an intraaggregate radial diffusion model for naphthalene sorption and desorption with soil. It was shown by modeling and confirmed by experiment, for the soil suspension particle sizes employed in these tests, that the naphthalene sorption-desorption process was reversible and rapid compared to the rate of microbial degradation. The maximum rate of microbial degradation was propor¬tional to the soil-to-water ratio and independent of nitrate concentration for initial nitrate concentrations greater than several hundred micrograms per gram of soil. Nitrate reduction was described by utilizing the total mass removal of naphthalene and a stoichiometric conversion factor. A coupled solute desorption-degradation model is presented for microbial degradation of hydrophobic organic com-pounds that are desorbed from porous soil aggregates, assuming sorbed solute is inaccessible to microorganisms and that the rate of solute release from the solid is rapid compared to the rate of retarded intraaggregate diffusion. © 1991, American Chemical Society. All rights reserved.

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Environmental Science and Technology