Notably, the discharge of fabricated nanoparticles in polluted water might offer
the appropriate substrate for self-conversion to green products. For example, silver
nanoparticle sulfidation is a general approach in contaminated water that gives an
insoluble and less toxic silver form (Levard et al. 2012). The unpredictable actions of
nanoparticles in ecosystem forces the requirement of an effective approach to
manage their potential risk. Few traditional approaches, such as the use of membranes or sorbents, have been developed for the exclusion of nanoparticles while
treating wastewater. Nevertheless, an excellent approach to diminish potential risks
of nanoparticle disposal is to reduce the amounts of solids employed in the remediation of wastewater. The complete recovery of nanoparticles enables their multiple
use to validate the whole approach. There are many factors affecting the possibility
of nanoparticle recycling. Among these various factors, the strategy to remove
pollutants, such as adsorption, degradation, and photocatalysis, has the prime importance. For example, when the surface of nanoparticles is progressively sheltered by
adsorbed species, a revival approach using appropriate chemical reagents, such as,
NaOH must be accompanied. In this case, another issue that needs to be solved is the
handling of the revival reagent that possesses a higher amount of the contaminant.
When nanoparticles behave as catalysts of the reaction, the mild stimulation of
surface characteristics at regular time intervals is sufficient to sustain a high process
yield. There are also some routes in which nanoparticles do not attain saturation in
the loading of pollutants after repeated operations. These kinds of systems must be
designed in such a way that allows the recovery and constant reuse of nanoparticles
to treat wastewater until saturation is reached.
Recovery of exhausted nanoparticles is a necessary step while investigating the
use of nanoparticles in the field of water treatment. The inspiration behind the said
strategy is to assure the lack of nanosized solid particles in the treated water as well
as in the waste streams of the handling process. It is often very difficult to collect the
dispersed nanoparticles due to their extremely small sizes. Moreover, in order to
ensure the absolute separation of nanoparticles from purified water, a costly
nanofiltration system should be designed.
Another relatively more “traditional” strategy to remove used nanoparticles from
water is the process of coagulation. In this process, nanoparticles can be entangled
via the coalesce floc as its sedimentation out of the water takes place. The stability of
nanoparticles can be affected by the coagulating agents via the formation of charged
hydrolytic moieties that help in the neutralization of nanoparticle surface charges.
This approach creates a large aggregation of nanoparticles because of the alleviation
of electrostatic repulsion. The effect of coagulant nature, amount of titania
nanoparticles was explored on the removal of these nanoparticles through primary
water treatment (Petersen et al. 2011). Contrarily, the way of aggregation of ZnO and
titania nanoparticles in polluted water occurs and their hazardous effect on the
oxygen uptake from sludge was investigated using high gradient external magnetic
field. For the same reason, Fe(0) and Fe 2 O 3 nanoparticles are preferentially used
either independently or as support to hold additional active materials. The separation
of nanoparticles from water by using high-gradient magnetic fields is a broadly
investigated field offering several chances of strategy design (Ditsch et al. 2005).
680
B. Akram et al.
the appropriate substrate for self-conversion to green products. For example, silver
nanoparticle sulfidation is a general approach in contaminated water that gives an
insoluble and less toxic silver form (Levard et al. 2012). The unpredictable actions of
nanoparticles in ecosystem forces the requirement of an effective approach to
manage their potential risk. Few traditional approaches, such as the use of membranes or sorbents, have been developed for the exclusion of nanoparticles while
treating wastewater. Nevertheless, an excellent approach to diminish potential risks
of nanoparticle disposal is to reduce the amounts of solids employed in the remediation of wastewater. The complete recovery of nanoparticles enables their multiple
use to validate the whole approach. There are many factors affecting the possibility
of nanoparticle recycling. Among these various factors, the strategy to remove
pollutants, such as adsorption, degradation, and photocatalysis, has the prime importance. For example, when the surface of nanoparticles is progressively sheltered by
adsorbed species, a revival approach using appropriate chemical reagents, such as,
NaOH must be accompanied. In this case, another issue that needs to be solved is the
handling of the revival reagent that possesses a higher amount of the contaminant.
When nanoparticles behave as catalysts of the reaction, the mild stimulation of
surface characteristics at regular time intervals is sufficient to sustain a high process
yield. There are also some routes in which nanoparticles do not attain saturation in
the loading of pollutants after repeated operations. These kinds of systems must be
designed in such a way that allows the recovery and constant reuse of nanoparticles
to treat wastewater until saturation is reached.
Recovery of exhausted nanoparticles is a necessary step while investigating the
use of nanoparticles in the field of water treatment. The inspiration behind the said
strategy is to assure the lack of nanosized solid particles in the treated water as well
as in the waste streams of the handling process. It is often very difficult to collect the
dispersed nanoparticles due to their extremely small sizes. Moreover, in order to
ensure the absolute separation of nanoparticles from purified water, a costly
nanofiltration system should be designed.
Another relatively more “traditional” strategy to remove used nanoparticles from
water is the process of coagulation. In this process, nanoparticles can be entangled
via the coalesce floc as its sedimentation out of the water takes place. The stability of
nanoparticles can be affected by the coagulating agents via the formation of charged
hydrolytic moieties that help in the neutralization of nanoparticle surface charges.
This approach creates a large aggregation of nanoparticles because of the alleviation
of electrostatic repulsion. The effect of coagulant nature, amount of titania
nanoparticles was explored on the removal of these nanoparticles through primary
water treatment (Petersen et al. 2011). Contrarily, the way of aggregation of ZnO and
titania nanoparticles in polluted water occurs and their hazardous effect on the
oxygen uptake from sludge was investigated using high gradient external magnetic
field. For the same reason, Fe(0) and Fe 2 O 3 nanoparticles are preferentially used
either independently or as support to hold additional active materials. The separation
of nanoparticles from water by using high-gradient magnetic fields is a broadly
investigated field offering several chances of strategy design (Ditsch et al. 2005).
680
B. Akram et al.