Introduction - Elements of Environmental Engineering: Thermodynamics and Kinetics - page 8

optimization of testing and monitoring strategies, determination of global disper-
sion, and recovery times. To construct F&T models, one needs to obtain a range of
physico-chemical parameters: thermodynamic, kinetic, and toxicological.

1.4.1.3 Design of Separation Processes

Environmentalengineersdesignseparationprocessesfortheisolationofcontaminants
from waste streams before they are discharged to the environment. Both physical and
chemical separation processes are used in environmental engineering. For example,
particulate separation from air and water involve physical separation techniques that
use mechanisms such as aggregation, coagulation, impaction, centrifugal force, and
electromotive force, to name a few. The removal of dissolved gases and vapors from
air and water involve, on the other hand, chemical separation methods. Whereas
mixing of chemicals to form a mixture is a spontaneous process, and, as we will see
in Chapter 2, a thermodynamically favorable process, the reverse, namely, separation
into the component species, requires the expenditure of work. The overall objective
of an environmental separation process is not only to isolate the pollutant, but also to
recycle and reuse where possible the materials separated and separation agents that
were used during the operation.
Invariably, environmental separation processes involve contact between two or
more phases and the exchange of material and energy between them. As an example,
consider the removal of organic contaminants from water by contacting with a solid
phase such as powdered activated carbon. The process has two distinct stages. In

(a) (b)

PF

PF

CF CF

PR

PR

(c)

PF

CF

(e)

(d)

PF

PF

CF

CF

PR

PR

FIGURE 1.4 General separation techniques. CF, contaminated feed, PF, pollutant-free
stream, PR, pollutant-rich stream. (a) Separation by phase creation; (b) separation by phase
addition; (c) separation by barrier; (d) separation by solid agent; and (e) separation by field
gradient. (Modified from Seader, E.D. and Henley, E.J. 1986. Separation Process Principles .
NewYork: John Wiley & Sons, Inc.)