W. W. Eckenfelder is probably one of the leading authorities for applying chemical engineering principles to biological wastewater treatment. One of the basic differences between chemical processes and wastewater treatment processes is the concept of dynamic equilibrium. In chemical processes, the assumption is made that there is no change in the process variables while a material and energy balance is calculated. In a biological system, there is no "steady state" condition that compares to a chemical process. Now Eckenfelder can predict how much oxygen is ultimately required to produce CO2 and some nutrient requirements and measure changes in a number of variables with time. However, factors such as whether the CO2 stays in the water phase as an increase in alkalinity or is scrubbed out with excess air or oxidized hydrogen stays in the water phase or in cells is generally beyond the scope of his analysis.
I hope that this is not discouraging because I believe that his approach is basically better than others.
Ron