Modeling the Biodegradation Kinetics of Perchlorate in the Presence of Oxygen and Nitrate as Competing Electron Acceptors

ABSTRACT

A mathematical model was developed to describe the biodegradation kinetics of perchlorate in the presence of nitrate and oxygen as competing electron acceptors. The rate of perchlorate degradation is described as a function of the electron donor (acetate) degradation rate, the concentration of the alternate electron acceptors, and rates of biomass growth and decay. The kinetics of biomass growth are described using a modified Monod model, and inhibition factors are incorporated to describe the influence of oxygen and nitrate on perchlorate degradation. In order to develop input parameters for the model, a series of batch biodegradation studies were performed using Azospira suillum JPLRND, a perchlorate-degrading strain isolated from groundwater. This strain is capable of utilizing oxygen, nitrate, or perchlorate as terminal electron acceptors. The maximum specific growth rate (μ_max) and half-saturation constant (K _S ^don) for the bacterium when utilizing either perchlorate or nitrate were similar; 0.16 per h and 158 mg acetate/L, respectively. However, these parameters were different when the strain was growing on oxygen. In this case, μ_max and K _S ^don were 0.22 per h and 119 mg acetate/L, respectively. The batch experiments also revealed that nitrate inhibits perchlorate biodegradation by this strain. This finding was incorporated into the model by applying an inhibition coefficient (K _i ^nit) value of 25 mg nitrate/L. Combined with appropriate groundwater transport models, this model can be used to predict perchlorate biodegradation during in situ remediation efforts.

KEYWORDS:

• biodegradation
• bioremediation
• kinetics
• modeling
• nitrate
• perchlorate

ACKNOWLEDGMENTS

We wish to acknowledge the Strategic Environmental Research and Development Program (SERDP) (Project ER-1163) and the Environmental Security Technology Certification Program (ESTCP) (Project ER-0425) for providing financial support for this research. We also wish to thank Martha Arkins for her excellent technical assistance.

Notes

^a = Electron acceptor not added.

^a An average yield of 0.210 mg biomass/mg acetate was used for model simulations.

^b Results from duplicate experiments.