150
P. Sahu
will be reached in 3 min. (Darracq et al. 2014; Xie et al. 2011). But this mechanism has some drawbacks such as scaling and fouling, which need maintenance or
replacement, and due to non-selective nature of this membrane filtration technologies,
demineralization of target water can take place.
6.7.2.4 Ion Exchange
Another ex situ technology that is used to eliminate ClO 4
− from groundwater and
surface water is ion exchange technology. Synthetic ion exchange resins are generally
used as strongly basic ion exchange media. The removal efficiency of the media
depends on stability of media, its exchange capacity and its regeneration capacity.
For example, strongly basic ion exchange media are very effective to remove ClO 4
−
from ClO 4
− contaminated water if concentration of ClO 4
− is <50 mg/L. Positively
charged functional groups of perchlorate resins are initially dosed with anions like
chloride ion. These positively charged functional groups attract ClO 4
− anion present
in perchlorate contaminated water, due to its stronger attractive force and replaces
ClO 4
− anion with Cl
− (Mihelcic 1999), and thus, ion exchange process removes the
ClO 4
− ion, populating the treated water with chloride ions. But coexisting anions of
ClO 4
− may occupy the available sites, and as a consequence, perchlorate removal
efficiency will be reduced (Ye et al. 2012). Study of Darracq et al. (2014) reveals
that out of five different resins that are A532E, A520E, A400E, PWA-5 and PSR-2,
A532E and PSR-2 show the best performance in removing ClO 4
− from groundwater
and drinking water systems. They can treat ClO 4
− contaminated water containing
10–10,000 µg/L ClO 4
− (Table 6.2). Problems associated with this technology are of
two folds (i) high cost and (ii) disposal after a single use.
6.7.2.5 Electrochemical Reduction
Nontoxic chloride ions are produced by electrochemical reduction of ClO 4
− (Logan
2001). Electrochemical reduction of ClO 4
− anion has been conducted in a cell with
Ni electrode and a Pt counter electrode in concentrated solutions of hypochlorous acid
(Rusanova et al. 2006). Electrodes such as Ti, Rh, Pt, Ir, Ru and Sn are also capable
of reducing ClO 4
− ions (Brown 1986; Lang et al. 2008). For example, study of Wang
et al. (2009) reveals that in the presence of Ti anode, ClO 4
− in aqueous solutions
shows significant reduction from 200 mg/L to 20 mg/L within 8 h. The presence of
titanium metal as a chemical reductant can remove ClO 4
− in water (Lee and Kramer
2007). The activity of titanium was enhanced by eliminating the localized surface
oxide film using electrochemically induced pitting corrosion. The activity of pitting
corrosion is enhanced by higher current. Higher current dissolves more transitory
titanium metal ions near the pits, and it results in a higher rate of ClO 4
− reduction.
The surface of the bare Ti(0) inside the pits induces further electrochemical reactions,
increasing the current. This increased current causes faster conversion of chloride to
chlorine (Srinivasan and Viraraghavan 2009).
P. Sahu
will be reached in 3 min. (Darracq et al. 2014; Xie et al. 2011). But this mechanism has some drawbacks such as scaling and fouling, which need maintenance or
replacement, and due to non-selective nature of this membrane filtration technologies,
demineralization of target water can take place.
6.7.2.4 Ion Exchange
Another ex situ technology that is used to eliminate ClO 4
− from groundwater and
surface water is ion exchange technology. Synthetic ion exchange resins are generally
used as strongly basic ion exchange media. The removal efficiency of the media
depends on stability of media, its exchange capacity and its regeneration capacity.
For example, strongly basic ion exchange media are very effective to remove ClO 4
−
from ClO 4
− contaminated water if concentration of ClO 4
− is <50 mg/L. Positively
charged functional groups of perchlorate resins are initially dosed with anions like
chloride ion. These positively charged functional groups attract ClO 4
− anion present
in perchlorate contaminated water, due to its stronger attractive force and replaces
ClO 4
− anion with Cl
− (Mihelcic 1999), and thus, ion exchange process removes the
ClO 4
− ion, populating the treated water with chloride ions. But coexisting anions of
ClO 4
− may occupy the available sites, and as a consequence, perchlorate removal
efficiency will be reduced (Ye et al. 2012). Study of Darracq et al. (2014) reveals
that out of five different resins that are A532E, A520E, A400E, PWA-5 and PSR-2,
A532E and PSR-2 show the best performance in removing ClO 4
− from groundwater
and drinking water systems. They can treat ClO 4
− contaminated water containing
10–10,000 µg/L ClO 4
− (Table 6.2). Problems associated with this technology are of
two folds (i) high cost and (ii) disposal after a single use.
6.7.2.5 Electrochemical Reduction
Nontoxic chloride ions are produced by electrochemical reduction of ClO 4
− (Logan
2001). Electrochemical reduction of ClO 4
− anion has been conducted in a cell with
Ni electrode and a Pt counter electrode in concentrated solutions of hypochlorous acid
(Rusanova et al. 2006). Electrodes such as Ti, Rh, Pt, Ir, Ru and Sn are also capable
of reducing ClO 4
− ions (Brown 1986; Lang et al. 2008). For example, study of Wang
et al. (2009) reveals that in the presence of Ti anode, ClO 4
− in aqueous solutions
shows significant reduction from 200 mg/L to 20 mg/L within 8 h. The presence of
titanium metal as a chemical reductant can remove ClO 4
− in water (Lee and Kramer
2007). The activity of titanium was enhanced by eliminating the localized surface
oxide film using electrochemically induced pitting corrosion. The activity of pitting
corrosion is enhanced by higher current. Higher current dissolves more transitory
titanium metal ions near the pits, and it results in a higher rate of ClO 4
− reduction.
The surface of the bare Ti(0) inside the pits induces further electrochemical reactions,
increasing the current. This increased current causes faster conversion of chloride to
chlorine (Srinivasan and Viraraghavan 2009).