The influence of dilution rate, temperature, and influent substrate concentration on the efficiency of steady-state biomass production in continuous microbial culture.

The efficiency of steady-state biomass production was defined as the ratio of the biomass produced at steady state to the biomass that would be produced if influent substrate were completely and permanently incorporated. The scope of analysis was confined to microbial growth processes described by a Monod reaction mechanism. A thermo-kinetic analysis of this mechanism with coefficient values estimated from experimental data showed: (table; see text) (1) As the dilution rate was increased, the efficiency passed through a single peak. Raising the temperature did not markedly change the peak efficiency, but did broaden and shift the peak toward higher dilution rates. In contrast, elevating the influent substrate concentration significantly improved the peak efficiency while still broadening and shifting the peak toward higher dilution rates. (2) As the temperature was raised, the efficiency also showed a single peak. Increasing the dilution rate did not significantly alter the peak value or breadth, but did shift the peak to higher temperatures. In contrast, elevating the influent substrate concentration substantially improved the peak efficiency and caused the peak to shift toward lower temperatures without broadening. (3) As the influent substrate concentration was elevated, the peak efficiency improved and asymptotically approached unity. These results suggested that relatively high influent substrate concentrations, low temperatures, and moderate dilution rates would be needed to optimize the efficiency of steady-state biomass production by Monod processes with coefficient values similar to those used in this paper.