Control of Living Processes 2

Consider the differences in the ways that organisms respond to fixing dilution rate and fixing nutrient concentration. There must be a very roundabout scheme for adjusting metabolic rates so that the consumption of limiting nutrient matches the feed rate to reach the exact concentration of S that determines the specific growth rate coefficient equal to the dilution rate. Actual experiments show undershoot or overshoot when a chemostat is disturbed, and the system tends to be quite unstable at high dilution rates.

Control of an auxostat is complicated by requiring sensors and pumps but is simple in terms of response. The concentration of limiting nutrient will adjust quickly to the new set point and usually without overshoot or undershoot if the controller is tuned properly.

Go "with the flow"