A comparison of zero-order, first-order, and Monod biotransformation models

Journal Article · Sun Mar 01 04:00:00 EST 1998 · Ground Water

DOI:https://doi.org/10.1111/j.1745-6584.1998.tb01091.x· OSTI ID:577330

Bekins, B A; Warren, E; Godsy, E M ^[1]

---

1. Geological Survey, Menlo Park, CA (United States)

Under some conditions, a first-order kinetic model is a poor representation of biodegradation in contaminated aquifers. Although it is well known that the assumption of first-order kinetics is valid only when substrate concentration, S, is much less than the half-saturation constant, K{sub S}, this assumption is often made without verification of this condition. The authors present a formal error analysis showing that the relative error in the first-order approximation is S/K{sub S} and in the zero-order approximation the error is K{sub S}/S. They then examine the problems that arise when the first-order approximation is used outside the range for which it is valid. A series of numerical simulations comparing results of first- and zero-order rate approximations to Monod kinetics for a real data set illustrates that if concentrations observed in the field are higher than K{sub S}, it may be better to model degradation using a zero-order rate expression. Compared with Monod kinetics, extrapolation of a first-order rate to lower concentrations under-predicts the biotransformation potential, while extrapolation to higher concentrations may grossly over-predict the transformation rate. A summary of solubilities and Monod parameters for aerobic benzene, toluene, and xylene (BTX) degradation shows that the a priori assumption of first-order degradation kinetics at sites contaminated with these compounds is not valid. In particular, out of six published values of K{sub S} for toluene, only one is greater than 2 mg/L, indicating that when toluene is present in concentrations greater than about a part per million, the assumption of first-order kinetics may be invalid. Finally, the authors apply an existing analytical solution for steady-state one-dimensional advective transport with Monod degradation kinetics to a field data set.

• Sponsoring Organization: USDOE
• OSTI ID: 577330
• Journal Information: Ground Water, Journal Name: Ground Water Journal Issue: 2 Vol. 36; ISSN GRWAAP; ISSN 0017-467X
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
54 ENVIRONMENTAL SCIENCES
BENZENE
BIODEGRADATION
COMPARATIVE EVALUATIONS
DATA COVARIANCES
ENVIRONMENTAL TRANSPORT
IN-SITU PROCESSING
MATHEMATICAL MODELS
REMEDIAL ACTION
TOLUENE
XYLENES