Effect of Diffusion on the Kinetics of Biodegradation: Experimental Results with Synthetic Aggregates

Abstract

AbstractThe rates of biodegradation in soil often do not conform to the predictions of kinetic models, such as the first‐order and Michaelis‐Menten models, developed to describe metabolic processes occurring in solutions in which microorganisms and their substrates are well mixed. To test whether the kinetics of biodegradation in the presence of aggregates could be described by explicitly accounting for chemical diffusion, studies were conducted in well‐defined experimental systems. The kinetics of biodegradation of low concentrations of 14C‐labeled phenol and glutamate by Pseudomonas sp. Strain K in buffer containing spherical aggregates of kaolinite that exclude bacteria were significantly different from the kinetics measured in the absence of aggregates. Both the biodegradation rate and the percentage of the initial compound degraded were lower in the presence of aggregates than in their absence. Using measurements of biodegradation, diffusion rates, and physical properties of the experimental system as input parameters, the diffusion‐sorption‐biodegradation (DSB) model simulated the biodegradation of phenol and glutamate originating inside aggregates. The model also simulated the initial period of biodegradation of glutamate in an experimental system containing gel‐exclusion chromatography beads. Clay aggregates reduced the concentration of available p‐nitrophenol sufficiently to lower the apparent rate constant for its biodegradation. Microscopic mass‐transfer processes, such as diffusion, may be important to consider in quantitative descriptions of the biodegradation of organic chemicals in soil.