Nonequilibrium Sorption and Aerobic Biodegradation of Dissolved Alkylbenzenes During Transport in Aquifer Material: Column Experiments and Evaluation of a Coupled-Process Model

We investigated the effect of simultaneous sorption and aerobic biodegradation on the transport of several dissolved alkylbenzenes in an aquifer material and evaluated the performance of a coupled-process transport model. First-order biodegradation rate constants decreased with decreasing number of C in the alkyl groups and exhibited a correlation with molecular structure as measured by molecular connectivity. For three series of isomers, the rate constant for the isomer with a substituent in the ortho position was smaller than the rate constants for the other isomers. Predictions obtained with the coupled-process model, wherein sorption was assumed to be rate limited, matched the breakthrough curves better than did predictions obtained with a model wherein sorption was assumed to be instantaneous. Accordingly, the assumptions upon which use of the model was based, e.g., biodegradation occurs only in solution and without a significant acclimation period, and can be simulated with a first-order equation, appear to be valid.