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330 Industrial Wastewater Treatment, Recycling, and Reuse
phenol selectively from water, adsorbents are required to possess a hydropho-
bic nature, i.e., zeolites having a high Si/Al ratio. The surfactant-modified
zeolites can also be useful in adsorption of phenol and 4-CP (Kuleyin, 2007).
8.2.1 Biomass as Adsorbent
The use of biomass for wastewater treatment is increasing because of its avail-
ability in large quantities and at low prices. Almost any carbonaceous material
may be used as precursor for the preparation of carbon adsorbents as against
commercial ACs that are usually derived from natural materials such as wood,
coconut shell, lignite, or coal. Coal is the most commonly used precursor for
producing AC (Carrasco-Marı ´n et al., 1996). The adsorption properties
are influenced by the nature of the original vegetation and also by the
physical-chemical changes occurring after deposition (Karaca et al., 2004).
The presence of surface functional groups is an important factor, especially
for adsorption of phenolics due to the chemical nature of the interactions.
Thepresenceofacidicfunctionalgroupsimpartstheabilitytoadsorbphenolic
compounds under oxic conditions, and the presence of oxygen-containing
basic groups such as chromene-type and pyrone-type can be crucial in pro-
moting irreversible adsorption. Notable examples of modifications in this
regard include the presence of molecular oxygen that reportedly increased
the adsorptive capacity of GAC for phenolic compounds by threefold
(Vidic et al., 1993), high-surface-area ACs prepared by chemical activation
of coconut shell with KOH as active agent (Zhonghau and Srinivasan,
1999), AC prepared from agricultural waste by-products such as rubber
seed coat (Rengaraj et al., 2002), tamarind nutshell (Goud et al., 2005) that
can be used for the adsorption of phenol from aqueous solution, and beet
pulp to prepare carbon for phenol adsorption by Dursun et al. (2005). Wu
et al. (2005) prepared carbonaceous adsorbents with controlled pore sizes
from carbonized fir wood (i.e., char) by KOH and steam activation for
the removal of phenols. By changing the KOH/char ratio from 0.5 to 6,
2 1
the KOH-ACs had surface areas ranging from 891 to 2794 m g and
1
3
micropore volume of 0.76-0.82 cm g . As opposed to this, carbons acti-
vated by steam at 900 C for 5 and 7 h had a surface area of 1016 and
2
1
3
131 m g 1 with micropore volume of 0.51 and 0.48 cm g , respectively.
Teng et al. (1998) reported surface modification using phosphoric acid
impregnation followed by carbonization in a nitrogen atmosphere at 400
to 600 C to obtain AC from Australian brown coal. Hobday et al. (1994)
used a range of Victorian brown coal-based material to remove nitrophenol
from an aqueous solution. Das and Sharma (1998) and Ahmaruzzaman and