Model coupling intraparticle diffusion/sorption, nonlinear sorption, and biodegradation processes

Diffusion, sorption and biodegradation are key processes impacting the effi ciency of natural attenuation. While each process has been studied individu ally, limited information exists on the kinetic coupling of these processes . In this paper, a model is presented that couples nonlinear and nonequilib rium sorption (intraparticle diffusion) with biodegradation kinetics. Initi ally, these processes are studied independently (i.e., intraparticle diffus ion, nonlinear sorption and biodegradation), with appropriate parameters de termined from these independent studies. Then, the coupled processes are st udied, with an initial data set used to determine biodegradation constants that were subsequently used to successfully predict the behavior of a secon d data set. The validated model is then used to conduct a sensitivity analy sis, which reveals conditions where biodegradation becomes desorption rate- limited. If the chemical is not pre-equilibrated with the soil Drier to thc onset of biodegradation, then fast sorption will reduce aqueous concentrat ions and thus biodegradation rates. Another sensitivity analysis demonstrat es the importance of including nonlinear sorption in a coupled diffusion/so rption and biodegradation model. While predictions based on linear sorption isotherms agree well with solution concentrations, for the conditions eval uated this approach overestimates the percentage of contaminant biodegraded by as much as 50%. This research demonstrates that nonlinear sorption shou ld be coupled with diffusion/sorption and biodegradation models in order to accurately predict bioremediation and natural attenuation processes. To ou r knowledge this study is unique in studying nonlinear sorption coupled wit h intraparticle diffusion and biodegradation kinetics with natural media. ( C) 2001 Elsevier Science B.V. All rights reserved.