Toward Universal Half-Saturation Coefficients: Describing Extant K(s) as a Function of Diffusion.

Area of Science:

• Environmental Engineering
• Biochemical Engineering
• Applied Physics

Background:

• Bacterial kinetic parameters, such as K(s), are often assumed constant in water resource recovery facilities.
• Observed K(s) values can vary significantly, leading to the attribution of these changes to biological characteristics like "K-strategists."
• The influence of physical processes on apparent kinetic parameters is often overlooked.

Purpose of the Study:

• To investigate the role of diffusion as a dominant factor influencing observed bacterial kinetic parameters (K(s)).
• To challenge the notion that intrinsic biological characteristics are the primary drivers of apparent K(s) variations.
• To demonstrate the applicability of diffusion models in understanding bacterial kinetics within water resource recovery systems.

Main Methods:

• Application of the "porter-diffusion" model, originally developed for aquatic systems, to four distinct biological processes.
• Modeling bacterial kinetic effects using a physics-based approach.
• Analysis of systems with low substrate concentrations.

Main Results:

• Diffusion was identified as the dominant mechanism influencing apparent K(s) across all four modeled biological processes.
• The study provides evidence that physical transport phenomena, specifically diffusion, are more influential than intrinsic biological factors.
• The "porter-diffusion" model effectively describes bacterial kinetic effects in the studied systems.

Conclusions:

• Observed K(s) values are not constant and are strongly influenced by diffusion.
• The physics of the system, particularly diffusion, is the dominant mechanism affecting apparent K(s) in water resource recovery facilities.
• For treatment processes with low substrate concentrations, variable K(s) values or explicit modeling of diffusion are recommended.