Simulation of microbial transport and carbon tetrachloride biodegradation in intermittently‐fed aquifer columns

Abstract

This paper evaluates the microbial transport and degradation processes associated with carbon tetrachloride (CT) biodegradation in laboratory aquifer columns operated with a pulsed microbial feeding strategy. A seven component reactive transport model based on modified saturation kinetics and on a two‐site sorption model was developed to describe the linked physical, chemical, and biological processes involved in CT degradation by Pseudomonas stutzeri KC, a denitrifying bacterium that cometabolically converts CT to harmless end products. After evaluating several expressions for attachment and detachment, we selected a dynamic partitioning model in which strain KC detachment decreases at low substrate concentrations. The resulting model enabled improved understanding of the complex coupled processes operative within our system and enabled us to test a model for field‐scale design and transport studies. Batch studies were used to identify initial degradation and microbial transport processes, and constrained optimization methods were used to estimate a set of reaction rates that best describe the column experiment data. The optimal set of parameters for one column provided a reasonable prediction of solute and microbial concentrations in a second column operated under different conditions, providing an initial test of the model. This modeling strategy improved our understanding of biodegradation processes and rates. The CT degradation rate in the columns was lower than values obtained from batch studies, and processes in addition to the growth and decay of strain KC cells (due to native flora) are necessary to describe the observed nitrate consumption.