18 Perfluorooctanesulfonate (PFOS), Its Occurrence, Fate …
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chloride-containing ground waters (100 mg/L of chloride resulted >1 mg/L increase
in perchlorate) (Donaghue and Chaplin 2013; Pérez et al. 2012).
Plasma Process: According to a recent experimental study, generating plasmas generating within the bubbles in water, PFOS can be decomposed efficiently (Obo et al.
2015). High-voltage direct current of several kilovolts is applied across the bubbles
to generate the plasmas. Due to high surface activity of PFOS, it adheres to air bubbles, and hence, plasmas within the bubble can selectively decompose PFOS. But,
due to smaller contact surface area of plasmas (within 4 mm diameter bubble), the
decomposition/degradation process is slower. Removal can be accelerated by generating multiple plasmas and increasing time as well as energy efficiencies (Obo et al.
2015).
Subcritical Process: Processes carried out in sub/supercritical water are the innovative and environment friendly reaction techniques (Jessop and Leitner 2008). A hot
water with maintained pressure for liquid state is known as subcritical water. Subcritical water possesses various desirable reaction characteristics such as low viscosity,
high diffusivity and hydrolyzing ability for many organic compounds (Hori et al.
2006). According to the reported study (Hori et al. 2006, 2009), pure subcritical
water at ~350 °C was not able to degrade PFOS, but it can be decomposed by adding
reducing agent, zero-valent iron (ZVI) powder, in the medium (water). Commercial
nanoscale ZVI (nZVI) (coated and uncoated) was used to investigate removal of
PFCs, where PFOS showed higher removal efficiency under high dosage of nZVI
(1000 mg/L), acidic condition (pH = 3) and low temperature (20 °C) (Arvaniti
et al. 2015). The mechanism behind PFOS removal was reported as sorption as
well as degradation. No other byproducts were detected by LC–QTOF–MS during
defluorination of PFOS.
18.7 Future Perspectives Toward Research
From the available literature, work regarding PFOS research or knowledge gap has
been identified, and future directions have been proposed accordingly as follows:
1. Till date, PFOS has been studied mostly in its dissolved form; hence, detailed
investigations should be conducted for PFOS in particular phase.
2. Factors causing negative removal efficiency (higher concentration in effluent
than that of influent) of PFOS during biological treatments have not been well
documented. Hence, detailed studies should be conducted for monitoring the
PFOS concentration at various stages of treatment processes.
3. Detailed monitoring studies of advanced treatments on large scale and at normal
conditions are needed.
4. Various factors responsible for solid/water partitioning regarding PFOS need to
be conducted for understanding the fate of PFOS.
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chloride-containing ground waters (100 mg/L of chloride resulted >1 mg/L increase
in perchlorate) (Donaghue and Chaplin 2013; Pérez et al. 2012).
Plasma Process: According to a recent experimental study, generating plasmas generating within the bubbles in water, PFOS can be decomposed efficiently (Obo et al.
2015). High-voltage direct current of several kilovolts is applied across the bubbles
to generate the plasmas. Due to high surface activity of PFOS, it adheres to air bubbles, and hence, plasmas within the bubble can selectively decompose PFOS. But,
due to smaller contact surface area of plasmas (within 4 mm diameter bubble), the
decomposition/degradation process is slower. Removal can be accelerated by generating multiple plasmas and increasing time as well as energy efficiencies (Obo et al.
2015).
Subcritical Process: Processes carried out in sub/supercritical water are the innovative and environment friendly reaction techniques (Jessop and Leitner 2008). A hot
water with maintained pressure for liquid state is known as subcritical water. Subcritical water possesses various desirable reaction characteristics such as low viscosity,
high diffusivity and hydrolyzing ability for many organic compounds (Hori et al.
2006). According to the reported study (Hori et al. 2006, 2009), pure subcritical
water at ~350 °C was not able to degrade PFOS, but it can be decomposed by adding
reducing agent, zero-valent iron (ZVI) powder, in the medium (water). Commercial
nanoscale ZVI (nZVI) (coated and uncoated) was used to investigate removal of
PFCs, where PFOS showed higher removal efficiency under high dosage of nZVI
(1000 mg/L), acidic condition (pH = 3) and low temperature (20 °C) (Arvaniti
et al. 2015). The mechanism behind PFOS removal was reported as sorption as
well as degradation. No other byproducts were detected by LC–QTOF–MS during
defluorination of PFOS.
18.7 Future Perspectives Toward Research
From the available literature, work regarding PFOS research or knowledge gap has
been identified, and future directions have been proposed accordingly as follows:
1. Till date, PFOS has been studied mostly in its dissolved form; hence, detailed
investigations should be conducted for PFOS in particular phase.
2. Factors causing negative removal efficiency (higher concentration in effluent
than that of influent) of PFOS during biological treatments have not been well
documented. Hence, detailed studies should be conducted for monitoring the
PFOS concentration at various stages of treatment processes.
3. Detailed monitoring studies of advanced treatments on large scale and at normal
conditions are needed.
4. Various factors responsible for solid/water partitioning regarding PFOS need to
be conducted for understanding the fate of PFOS.