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Phenolic Wastewater Treatment: Development and Applications of New Adsorbent Materials 325
alum, lime, polymers, or a combination of these chemicals. Sometimes a
combination of coagulation and adsorption processes is used (Nowack
et al., 1999). pH plays an important role in chemical coagulation. The
use of several chemical coagulants and disposal of sludge is a major problem
in this technique. Further, desirable limits for the pollutants are rarely
achieved using coagulation alone.
8.1.1.2 Ion Exchange
Since phenols are weak acids, ion exchange technology can be employed
and can be a potentially attractive process from a recovery point of view,
especially at low concentrations. The exchange process is reversible, and
resins can be regenerated after the recovery of phenols. Resins and zeolites
are widely employed for decontamination of wastewater containing phenol.
However, the process has some limitations in terms of capacity/selectivity,
and the main disadvantages associated with this method include organic and
bacterial fouling and chlorine contamination.
8.1.1.3 Chemical Oxidation
Phenolics can be chemically converted to more oxygenated forms by means
of reactions with oxidizing agents. Chemical oxidation can achieve high
degradation efficiency for phenols, but it needs more energy and may result
in secondary pollution problems. The oxidants that are commonly used in
the chemical oxidation method of water treatment include ozone, chlorine,
hydrogen peroxide, sodium hypochlorite (NaOCl), and potassium perman-
ganate. 4-NP can be degraded into an environmentally friendly compound
by chemical oxidation (Oturan et al., 2000; Stu ¨ber et al., 2005), but this
method cannot recover 4-NP from industrial effluents. Usually, the opera-
tion cost is high and requires trained manpower or advanced reactors
(Langlais et al., 1991). Several chemical oxidation techniques, such as cata-
lytic wet air oxidation (CWAO), hydrogen peroxide promoted CWAO,
wet peroxide oxidation (WPO), and Fenton WPO, have been tested to
remove different aromatic organics belonging to commonly encountered
pollutants. Sometimes chemical oxidation leads to the formation of second-
ary products that are highly acidic, leading to corrosion problems. Although
the addition of Fenton reagent may improve the efficiency, it cannot be used
for treatment of wastewater containing p-nitrophenol due to the formation
of an insoluble complex. The overall oxidation rates are slow, and the use of
chemicals is high. Alternatively, such wastewaters can be treated using fur-
ther advanced oxidation processes (AOPs), where highly reactive free