The production of soluble microbial products (SMP) in anaerobic system
s was evaluated using chemostat reactors. Results from steady-state an
d tracer experiments with C-14-glucose and C-14-acetate showed that si
gnificant amounts of SMP were produced during the acidogenesis of gluc
ose, but that SMP did not accumulate during methanogenesis from acetat
e. In addition, at a retention time of 40 days, SMP comprised almost a
ll of the effluent COD from the glucose-fed chemostat. For shorter ret
ention times, as low as 10 days, the SMP concentration remained almost
constant, but its significance in the effluent COD was reduced due to
the accumulation of intermediate volatile fatty acids. The results fr
om a C-14- tracer experiment in the glucose-fed chemostat were used to
evaluate the importance of including SMP formation and degradation in
kinetic modeling of the methanogenic chemostats. Three models were ev
aluated: a model without SMP production, a model with SMP production b
ut no degradation, and a model with SMP production and degradation. Th
e results of this kinetic analysis indicate that the model that includ
es SMP production and degradation was the only one able to adequately
represent the fate of C-14 in the tracer experiment. The kinetic param
eters obtained from fitting the model to the tracer experiment were su
ccessfully used to predict steady-state concentrations of SMP and to c
haracterize the formation and degradation characteristics of the SMP.
(C) 1994 John Wiley & Sons, Inc.