Tr. Macdonald et al., Mass-transfer limitations for macroscale bioremediation modeling and implications on aquifer clogging, GROUND WATE, 37(4), 1999, pp. 523-531
In engineered in situ bioremediation, substrates are injected into the subs
urface to stimulate microbial metabolism and growth. Models are useful in t
he design and optimization of such systems, such as in devising strategies
to prevent clogging of soil by large bacterial populations around wells, Su
ch models are macroscale, i.e., they do not resolve pore-scale variability;
rather, substrate and biomass concentrations are bulk averages that vary f
rom block to block, These models give unrealistic predictions, in that they
predict monotonically increasing biomass growth everywhere except where th
e Limiting substrate concentration is very small, This work examines the po
ssibility of biofilm mass-transfer limitations at the pore scale using both
the traditional biofilm model as well as previously published results from
an upscaling model, Results from the biofilm model suggest that limitation
s on biofilm growth due to mass-transfer resistance could be significant in
coarse-grained soils with adequate substrate availability, The upscaling a
pproach confirms this result, While these two approaches do not yield ident
ical results, both do agree that coarser grain sizes tend to cause greater
mass transfer resistance. These are the conditions most likely to occur nea
r injection well screens of an enhanced bioremediation system, where cloggi
ng is most commonly observed, The upscaling approach also indicates that th
e degree of mass transfer resistance is reduced at higher ground water velo
cities, which are also most commonly observed near well screens. These resu
lts could be useful for improving macroscale bioremediation models to more
accurately predict rates of biomass growth and aquifer clogging.