Soluble microbial products (SMP) in anaerobic chemostats

The production of soluble microbial products (SMP) in anaerobic systems was evaluated using chemostat reactors. Results from steady‐state and tracer experiments with 14C‐glucose and 14C‐acetate showed that significant amounts of SMP were produced during the acidogenesis of glucose, but that SMP did not accumulate during methanogenesis from acetate. In addition, at a retention time of 40 days, SMP comprised almost all of the effluent COD from the glucose‐fed chemostat. For shorter retention 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 from a 14C‐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 evaluated: a model without SMP production, a model with SMP production but no degradation, and a model with SMP production and degradation, The results of this kinetic analysis indicate that the model that includes SMP production and degradation was the only one able to adequately represent the fate of 14C in the tracer experiment. The kinetic parameters were successfully used to predict steady‐state concentrations of SMP and to characterize the formation and degradation characteristics of the SMP. © 1994 John Wiley & Sons, Inc.