TOLUENE DIFFUSION AND REACTION IN UNSATURATED PSEUDOMONAS-PUTIDA BIOFILMS

Biofilms are frequently studied in the context of submerged or aquatic systems. However, much less is known about biofilms in unsaturated sy stems, despite their importance to such processes as food spoilage, te rrestrial nutrient cycling, and biodegradation of environmental pollut ants in soils. Using modeling and experimentation, we have described t he biodegradation of toluene in unsaturated media by bacterial biofilm s as a function of matric water potential, a dominant variable in unsa turated systems. We experimentally determined diffusion and kinetic pa rameters for Pseudomonas putida biofilms, then predicted biodegradatio n rates over a range of matric water potentials. For validation, we me asured the rate of toluene depletion by intact biofilms and found the results to reasonably follow the model predictions. The diffusion coef ficient for toluene through unsaturated P. putida biofilm averaged 1.3 x 10(-7) cm(2)/s, which is approximately two orders of magnitude lowe r than toluene diffusivity in water. Our stud ies show that, at the sc ale of the microbial biofilm, the diffusion of toluene to biodegrading bacteria can limit the overall rate of biological toluene depletion i n unsaturated systems. (C) 1997 John Wiley & Sons, Inc.