MODELING STEADY-STATE METHANOGENIC DEGRADATION OF PHENOLS IN GROUNDWATER

Field and microcosm observations of methanogenic phenolic compound deg radation indicate that Monod kinetics governs the substrate disappeara nce but overestimates the observed biomass. In this paper we present m odeling results from an ongoing multidisciplinary study of methanogeni c biodegradation of phenolic compounds in a sand and gravel aquifer co ntaminated by chemicals and wastes used in wood treatment. Field disap pearance rates of four phenols match those determined in batch microco sm studies previously performed by E.M. Godsy and coworkers. The degra dation process appears to be at steady-state because even after a sust ained influx over several decades, the contaminants still are disappea ring in transport downgradient. The existence of a steady-state degrad ation profile of each substrate together with a low biomass density in the aquifer indicate that the bacteria population is exhibiting no ne t growth. This may be due to the oligotrophic nature of the biomass po pulation in which utilization and growth are approximately independent of concentration for most of the concentration range. Thus a constant growth rate should exist over much of the contaminated area which may in turn be balanced by an unusually high decay or maintenance rate du e to hostile conditions or predation.