Page 357 - Industrial Wastewater Treatment, Recycling and Reuse

Phenolic Wastewater Treatment: Development and Applications of New Adsorbent Materials 329

investment and loss in regeneration restricts its use for wide-scale applica-
tion. There has been increased interest in newer biomass-derived adsorbents
that are low-cost materials, but have lower efficiency and capacity compared
to conventional adsorbents. However, by employing different pretreatment
and activation methods, such as charring or chemical treatment with ortho-
phosphoric acid, the performance of these low-cost adsorbents could be
increased significantly.
AC has a complex surface and porous structure. Generally, it has
2 1
45–1800 m g total surface area distributed in micropore (<2 nm), meso-
pore (2-50 nm), and macropore (>50 nm) regions. AC generally exhibits
high adsorption capacity for phenolic compounds and is considerably cost
effective. Due to these reasons, there have been numerous studies on these
materials; for example, Wang et al. (1997) reported adsorption of phenol,
4-CP, and 4-NP and found the adsorptive removal with granular carbon
to be better than that with powder form; Varghese et al. (2004) investigated
the use of AC prepared from water hyacinth for the removal of phenol,
4-CP, and 4-NP with maximum adsorption capacity of 1.20, 1.28, and
1
1.35 mg L , respectively; Jung et al. (2001) reported adsorption of phenol
and chlorophenols on four commercial granular ACs.
As an alternative to conventional adsorbents, a number of low-cost adsor-
bents were developed from materials such as fertilizer waste, wood, and rice
husk by several chemical treatments. Also, several naturally occurring mate-
rials having the characteristics of adsorbents can be similarly low-cost adsor-
bents for the removal of pollutants from waste water, for example, clays,
siliceous materials, zeolites, and bentonites. The adsorption capability, here,
is a result of net negative charge on the structure of minerals that provides the
capacity to adsorb positively charged species. The adsorption properties also
come from their high surface area and high porosity. The use of bentonite for
phenol adsorption from aqueous solutions was reported by Banat and Al-
Asheh (2000). Taha et al. (2003) reported adsorption of phenol in granite
residual soil and kaolinite stating that the residual soil possesses a greater
adsorption capacity compared to kaolinite. Kaleta (2006) reported modified
clarion clay and clinoptylolite as adsorbents for the removal of phenolic com-
pounds from water. Results showed improved capacities by modification of
theclaymaterials.Experimentalresultswerereportedontheadsorptionchar-
acteristics of phenol and m-chlorophenol using organobentonites (Lin and
Cheng, 2000). Removal of phenol from water was also reported by silica
gel, HiSiv 3000, activated alumina, AC, Filtrasorb-400, HiSiv 1000
(Roostaei and Tezel, 2004), and zeolites (Khalid et al., 2004). To adsorb