Environmental Fluid Mechanics 1:
Mass Transfer and Diffusion

Course Script > Ch 4

Chapter 4:  Physical, chemical and biological transformation

In the previous chapters, concentrations change in response to transport processes, such as diffusion, advection, and dispersion, and we have considered these processes in mass conserving systems.  Now, we would like to look at systems where the mass of a given species of interest is not conserving.  Processes that remove mass can be physical, chemical or biological in nature.  Since the total mass of the system must be conserved, these processes generally change the species of interest into another species; thus, we will call these processes transformation.

This chapter begins by describing the common types of transformation reactions.  Since we are interested in concentration changes, we review reaction kinetics and derive rate laws for first- and second-order systems.  The methods are then generalized to higher-order reactions. Transformation is then added to our transport equation for two types of reactions. In the first case, the reaction becomes a source or sink term in the governing differential equation; in the second case, the reaction occurs at the boundary and becomes a boundary constraint on the governing transport equation. The chapter closes with an engineering application to bacteria die-off downstream of a wastewater treatment plant.

See Lecture 8.




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