Water Treatment - The Drinking Water - page 250

Note: Aeration is rarely effective in processing surface waters, simply
because the odor-producing substances are generally nonvolatile.
Several methods to aerate the water are available. The method selected
depends primarily on the type and concentration of material to be removed
from the water and on the available pressure. Aeration in water treatment
can be accomplished using spray nozzles, cascade systems, multiple-tray
aerators, diffused-air aerators, and mechanical aerators.
Oxidation
Simply stated, oxidation is a reaction in which a substance loses electrons,
thus increasing its charge. A substance that oxidizes another is referred to as
an oxidizing agent or oxidizer . In water treatment, oxidation is used to remove
or destroy undesirable tastes or odors, to aid in removal of iron and manga-
nese, and to help improve clarification and color removal in source water.
Chlorine dioxide, potassium permanganate, and ozone are strong oxidants
capable of destroying many odorous compounds. Because they do not pro-
duce THMs, these chemicals are favored over heavy chlorination.
Note: Atmospheric oxygen through aeration can be used to oxidize the
organic substances responsible for undesirable tastes and odors, but
the process is usually too slow to be of value. If dissolved gases such as
hydrogen sulfide are the cause of taste and odor problems, aeration will
effectively remove them through oxidation and stripping.
Adsorption
When we speak of adsorption, we are referring primarily to a surface phe-
nomenon—the adsorption that results when one substance attaches itself to
the surface of another. The two most common adsorptive media used in water
treatment are activated carbon and activated alumina. These adsorptive mate-
rials are generally most effective for taste and odor control and for removal of
organic pollutants; however, the most important applications of adsorption in
water treatment are the removal of arsenic and organic pollutants.
Adsorption of organic materials using activated carbon has been a com-
mon practice in water treatment for many years. Activated carbon is man-
ufactured from carbonaceous material such as wood, coal, and petroleum
residues. A char is made by burning the material in the absence of air, and
it is then oxidized at higher temperatures to create a very porous structure.
This activation step provides irregular channels and pores in the solid mass,
resulting in a very large surface-area-to-mass ratio. This large surface area
gives activated carbon its effectiveness as an adsorbing agent. The larger the