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28 1. Air and ater Pollution W

w aste The main water treatment techniques are
Separation or clarification tec hniques : grit separation, sedimentation, air flotation, f il-
tration, microfiltration and ultraf and oil–water separation. iltration,
Physico-chemical treatment tec hniques : precipitation, sedimentation, air flotation, f il-
tration, crystallization, chemical oxidation, wet air oxidation, super-critical water oxida-
iltration,
tion, chemical reduction, hydrolysis, nanof reserve osmosis, adsorption, ion
v
exchange, e distillation, rectif e stripping, and incineration.
ication,
aporation,
xtraction,
Biological treatment tec hniques : anaerobic digestion processes, aerobic digestion
ication,
processes, nitrif denitrif and central biological w ication, ater treatment. w aste
Adsorption, ion e and catalysis share a great portion of en xchange, vironmental applica-
ely
v
xtensi
,
tions, as shown in the next section, and more e in Chapter 2. Specif , ically
adsorption and catalysis are eely used for the remoal or destruction of air pollu- v
v
xtensi
tants in gas streams as well as for purifying waters or fresh wxchange has w . Ion e ater aste
a special position among other techniques in the removal of heavy metals from wastewater.
1.4 ENVIRONMENTAL APPLICATIONS OF ADSORPTION,
ION EXCHANGE, AND CATALYSIS
Adsorption, ion e and catalysis are discussed in this book. The fo are among irst tw xchange,
the end-of-pipe techniques, whereas catalysis has a role to play in either pre enting pollu- v
tion during the process or as an end-of-pipe technique of waste treatment. Moreo ion v er ,
exchange is mainly used in wwater treatment, whereas adsorption and catalysis can be aste
found in both wastewater and gas management. Specifically, ion exchange is one of the best
available techniques (BAT) suggested by EC for heavy metal and inorganic salts remo al v
aste from wAs shown in T aters. w a ble 1.12, metal industry is the major source of metal
releases into the environment and ion exchange can be employed as the main pollution
abatement technology. We should again mention that nature does not have any efficient way
of coping with these substances, and as a result, their discharge into the environment should
be minimized. Adsorption is suggested as the BT for both the minimization of contami- A
nants in water that are unsuitable for biological treatment and the remoal of VOCs and v
inorganic compounds from normal waste gas streams. Catalysis is also considered as the
BAT for the destruction of water pollutants that are resistant to biological treatment (as cat-
alytic wet-air oxidation) and for the oxidation of VOCs and inorganic compounds in gas
streams (as catalytic oxidation). Generally, VOCs, sulfur oxides, nitrogen oxides, and v ari-
ous forms of hydrocarbons can be effectively treated by means of these processes.

MULTIPLE CHOICE QUESTIONS

1. CFCs are involved in
(a) photochemical smog
(b) ozone depletion
(c) greenhouse ef fect
(d) both ozone depletion and greenhouse ef fect