EFFECTS OF MICROBIAL METABOLIC LAG IN CONTAMINANT TRANSPORT AND BIODEGRADATION MODELING

A model is introduced for microbial kinetics in porous media that incl udes effects of transients in the metabolic activity of subsurface mic roorganisms. The model represents the microbial metabolic activity as a functional of the history of aqueous phase substrates; this dependen ce is represented as a temporally nonlocal convolution integral. Conce ptually, this convolution represents the activity of a microbial compo nent as a fraction of its maximum activity, and it is conventionally k nown as the metabolic potential. The metabolic potential is used to sc ale the kinetic expressions to account for the metabolic state of the organisms and allows the representation of delayed response in the mic robial kinetic equations. Calculation of the convolution requires the definition of a memory (or kernel) function that upon integration over the substrate history represents the microbial metabolic response. A simple piecewise-linear metabolic potential functional is developed he re; however, the approach can be generalized to fit the observed behav ior of specific systems of interest. The convolution that results from the general form of this model is nonlinear; these nonlinearities are handled by using two separate memory functions and by scaling the dom ains of the convolution integrals. The model is applied to describe th e aerobic degradation of benzene in saturated porous media. Comparativ e simulations show that metabolic lag can be used to consistently desc ribe observations and that a convolution form can effectively represen t microbial lag for this system. Simulations also show that disregardi ng metabolic lag when it exists can lead to overestimation of the amou nt of substrate degraded.