stable characteristic features (Ahmed 2001a). The polymorphs of metallic zinc
nanoparticles, such as ZnO and ZnS have, been explored for the removal of arsenic.
The structural stability of ZnS at nanoscale is sensitive to natural environmental
conditions due to their ability to adsorb water and aggregation characteristics.
Copper oxide(s) are other class of nanomaterials which do not require pretreatment
and post-pH adjustments during adsorption. It has two types of polymorphs: Cu
I
oxide and Cu
II oxide. Lastly, the bulk Cu 2 O is known to get oxidized into CuO at
ambient conditions; however, nanostructured Cu 2 O has been observed to be fairly
stable (Ram and Mitra 2001).
2.8
Scope of Future Nanoadsorbent Development
The stable characteristics of nanoadsorbents in a wide range of environmental
conditions are expected to be extremely helpful during field-scale applications.
Also, the upgradation of conventional treatment systems by utilizing the
nanoscale-based absorbents as remediation material is required in future scenario
in providing potable water to affected areas. Further studies might be conducted for
synthesizing its nanohybrids using bio-templates and organics to support them on
the different matrices so as to overcome its limitation of dispersion and stability in
the aqueous medium.
2.9
Subsurface Sequestration of Arsenic
Generally, removal of arsenic from the contaminated systems has been categorized
into: ex situ (pump and treat) and in situ (underground treatment) processes. Till
now, pump-and-treat remediation has been practiced on large scale in providing
arsenic-free water to the affected population (Jain and Singh 2012). However, such
technologies have several disadvantages like high operational cost and generation of
toxic sludge (Sarkar et al. 2010). The advantages of in situ removal of contaminants
compared to ex situ technologies include natural treatment of groundwater and low
operational cost. Moreover, the sequestration of groundwater contaminants using in
situ technologies has been considered among sustainable approaches (Kanel 2006).
Therefore, the development of technologies to sequester the arsenic in the subsurface
is gaining a considerable attention. From the last two decades, in situ technologies
such as biosorption, permeable reactive barriers, chemical oxidation and natural
attenuation are being developed. Among these, PRB (permeable reactive barrier),
because of its convenient operation and compactness, makes it easy to manage for
remediation and has been considered as a promising technology (Jain and Singh
2012; Lee et al. 2009).
2 Nanotechnology-Based Treatment Systems for Arsenic Sequestration in. . .
45
nanoparticles, such as ZnO and ZnS have, been explored for the removal of arsenic.
The structural stability of ZnS at nanoscale is sensitive to natural environmental
conditions due to their ability to adsorb water and aggregation characteristics.
Copper oxide(s) are other class of nanomaterials which do not require pretreatment
and post-pH adjustments during adsorption. It has two types of polymorphs: Cu
I
oxide and Cu
II oxide. Lastly, the bulk Cu 2 O is known to get oxidized into CuO at
ambient conditions; however, nanostructured Cu 2 O has been observed to be fairly
stable (Ram and Mitra 2001).
2.8
Scope of Future Nanoadsorbent Development
The stable characteristics of nanoadsorbents in a wide range of environmental
conditions are expected to be extremely helpful during field-scale applications.
Also, the upgradation of conventional treatment systems by utilizing the
nanoscale-based absorbents as remediation material is required in future scenario
in providing potable water to affected areas. Further studies might be conducted for
synthesizing its nanohybrids using bio-templates and organics to support them on
the different matrices so as to overcome its limitation of dispersion and stability in
the aqueous medium.
2.9
Subsurface Sequestration of Arsenic
Generally, removal of arsenic from the contaminated systems has been categorized
into: ex situ (pump and treat) and in situ (underground treatment) processes. Till
now, pump-and-treat remediation has been practiced on large scale in providing
arsenic-free water to the affected population (Jain and Singh 2012). However, such
technologies have several disadvantages like high operational cost and generation of
toxic sludge (Sarkar et al. 2010). The advantages of in situ removal of contaminants
compared to ex situ technologies include natural treatment of groundwater and low
operational cost. Moreover, the sequestration of groundwater contaminants using in
situ technologies has been considered among sustainable approaches (Kanel 2006).
Therefore, the development of technologies to sequester the arsenic in the subsurface
is gaining a considerable attention. From the last two decades, in situ technologies
such as biosorption, permeable reactive barriers, chemical oxidation and natural
attenuation are being developed. Among these, PRB (permeable reactive barrier),
because of its convenient operation and compactness, makes it easy to manage for
remediation and has been considered as a promising technology (Jain and Singh
2012; Lee et al. 2009).
2 Nanotechnology-Based Treatment Systems for Arsenic Sequestration in. . .
45