Figure 3.
Elements and interactions of the process control concept. Control variables (dilution rate D, retention rate R and substrate concentration sin) are used to vary process variables (specific growth rate µ, biomass concentration X) and operational expenditures (Opex). Positive correlation indicated with (+), negative correlation indicated with (−). * Influence of R on Opex is highly dependent on the process. A negative correlation can be seen when biomass has to be disposed of (e.g., for industrial process water treatment or extracellular products). When a product is intracellular, a high bleed stream is desirable.