Model Simulations in Support of Field Scale Design and Operation of Bioremediation Based on Cometabolic Degradation

Abstract

This paper addresses questions fundamental to the design and operation of aquifer bioremediation based on cometabolic degradation. A model of a full‐scale, in situ system for bioremediation of chlorinated ethenes relying on cometabolic degradation was developed and applied to a hypothetical aquifer being considered for a large‐scale field demonstration of in situ bioremediation with recirculation. The model was used to identify feasible substrate (electron donor and electron acceptor) delivery schedules. Trichloroethylene (TCE) was the target contaminant. Methane and phenol were considered as electron donors. The delivery of the electron donors and the electron acceptor, oxygen, was varied to evaluate the rate and extent of bioremediation under different substrate delivery schedules. Maximum removal of TCE was predicted when substrates are delivered at ratios near the stoichiometric requirement of electron donor and acceptor for net microbial growth. Additionally, the decrease in TCE removal that results from using substrate delivery schedules other than those achieving the maximum removal of TCE was quantified. This decrease was greater for the methane‐oxygen system because the two gaseous substrates compete for transfer into the recirculated ground water. If one substrate is introduced in excess of the amount required for net microbial growth, it accumulates, thus limiting the ability to introduce the second substrate. This imbalance both limits the introduction of the second substrate and accelerates the accumulation of the substrate added in excess. The phenol‐oxygen system is less sensitive to deviation away from the best observed substrate delivery schedule because phenol is a relatively soluble liquid and its introduction does not compete with the mass transfer of oxygen.

A three‐dimensional model of microbial transport and biodegradation at the Schoolcraft, Michigan, site

“…Numerical models have been used to both design subsurface delivery strategies [ Lang et al , 1997; Hyndman et al , 2000; Scheibe et al , 2001] and evaluate biodegradation processes in laboratory experiments [ Chen et al , 1992; Phanikumar et al , 2002; Kim et al , 2003]. Such models can provide significant insight into the nature and rates of the processes that drive bioremediation when adequate laboratory data are available for model development and calibration.…”

Effect of carbon starvation on toluene degradation activity by toluene monooxygenase-expressing bacteria

“…Biostimulation processes involving the addition of a primary growth substrate commonly utilize pulse injections to improve mixing and spatial distribution (McCarty et al 1998). The addition of pulse injections, however, can result in a condition where organisms experience highly fluctuating substrate concentrations and possible periods of carbon and energy limitations (Lang et al 1997;McCarty et al 1998;Park et al 2001). Accounting for starvation effects, therefore, would be useful for designing the length of the substrate pulse such that deactivation of biodegradation activity is minimized.…”

“…Interestingly, when first-order decay models were applied to experimental data, the first-order rate constant (deactivation rate) for the T4MO-expresing R. pickettii PKO1 bacterium (4.68 d )1 ) was more than an order of magnitude greater than deactivation rates observed for the other oxygenaseexpressing bacteria ( <0.2-0.36 d )1 ) (Costura & Alvarez 2000;Jenkins & Heald 1996;Jones & Morita 1985;Park 2001;Roslev & King 1994). Such a wide range of deactivation rates suggests that deactivation may have a significant influence on the effectiveness of bioremediation processes and the accuracy of in situ biodegradation rate predictions (Lang et al 1997;Park et al 2001). However, the dependence of deactivation rates on biological and environmental factors is currently unclear, complicating the ability to incorporate deactivation information in prediction and design methodologies.…”

Chloroform aerobic cometabolic biodegradation in a continuous‐flow reactor: Model calibration by means of the gauss‐newton method

“…As for the kinetic model, for the initial elaboration of each experimental phase the reaction rates r i were based on the AC model with competitive CAH-growth substrate mutual inhibition and transformation product toxicity proposed by Alvarez-Cohen and McCarty [4] and satisfactorily utilized in numerous studies of CAH AC: [33,39,57,58]…”