U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings
of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993,
Water-Resources Investigations Report 94-4015
Modeling Steady-State Methanogenic Degradation of Phenols in
Ground Water at Pensacola, Florida
Barbara A. Bekins (U.S. Geological Survey, Menlo Park, Calif.),
E. Michael Godsy (U.S. Geological Survey, Menlo Park, Calif.), and Donald
F. Goerlitz (U.S. Geological Survey, Menlo Park, Calif.)
Field and microcosm observations of methanogenic phenolic-compound degradation
indicate that Monod kinetics theory governs the substrate disappearance
but overestimates the observed biomass. In this paper, we present modeling
results from an ongoing multidisciplinary study of methanogenic biodegradation
of phenolic compounds in a sand and gravel aquifer at Pensacola, Florida.
The aquifer is contaminated with chemicals and wastes used in wood treatment.
Field-disappearance rates of four phenols match those determined in batch
microcosm studies performed by other workers in a related study. The degradation
process appears to be at steady state because the transported contaminants
still are disappearing within 150 meters downgradient of the source even
after a sustained influx over several decades. The existence of a steady-state
degradation profile of each substrate together with a low bacteria density
in the aquifer indicate that the bacterial population is exhibiting no net
growth. This is possibly because of the oligotrophic nature of the biomass
population in which growth and utilization are approximately independent
of the phenolic-compound concentration for most of the concentration range.
Thus, a constant bacteria growth rate should exist over much of the contaminated
area, which may, in turn, be balanced by an unusually high decay or maintenance
rate caused by hostile conditions or predation.