Biodegradation during contaminant transport in porous media: 6. Impact of sorption on coupled degradation-transport behavior

Bioavailability is one of the critical factors influencing the biodegradation and bioremediation of organic compounds. The bioavailability of many organic contaminants is controlled in part by the nature, magnitude, and rate of sorption/desorption processes. This study investigates the impact of sorption and associated retardation on the bioavailability and biodegradation of aromatic hydrocarbons during transport in porous media. Miscible-displacement experiments were conducted using naphthalene and 2-naphthol as the model sorbing compounds and salicylate, a degradation product of naphthalene, as a nonsorbing reference compound. Two porous media were used, one (Eustis soil, FL, USA) with moderate sorption capacity and one (quartz sand) with no measurable sorption of the compounds. The porous media were sterilized and inoculated with Pseudomonas putida RB1353, an organism that degrades naphthalene and its derivatives. The biodegradation and transport of all three substrates in quartz sand were significantly influenced by microbial lag, the effects of which were observed within two to three pore volumes (3-4.5 h). This was also true for salicylate transport in the Eustis soil system. Conversely, biodegradation lag effects were not observed for naphthalene or 2-naphthol in the Eustis soil system. In addition, the masses of naphthalene and 2-naphthol degraded were significantly greater for the Eustis soil system compared to the quartz sand system. As noted previously, naphthalene and 2-naphthol were sorbed by the Eustis soil but not the quartz sand, while salicylate was not sorbed by either media. These results indicate that the increased residence time associated with sorption of naphthalene and 2-naphthol by Eustis soil enhanced overall biodegradation and obviated the impact of lag on observed transport behavior.