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K. Dhangar and M. Kumar
with the efficiency ranging from 90 to 99% (Schröder et al. 2010; Tang et al. 2007).
According to the literature, due to smaller pore size and membrane selectivity, reverse
osmosis is more effective as compared to nanofiltration (Tang et al. 2007). The membrane fouling in such filtration processes can be controlled by using pretreatments
such as pre-oxidation and coagulation (Deka et al. 2020).
18.6.3 Redox Processes
The recent redox processes are very popular and promising for removal of PFOS,
as it gives complete mineralization. Various energy sources have been used in redox
processes for PFOS removal.
Photochemical Method: During photochemical processes, an inexhaustible energy
source, solar energy, is used as photocatalytic force to degrade PFOS. PFOS degradation has been carried out using both photo-oxidation and photo-reduction technologies. Though photo-oxidation is commonly used, photo-reduction technology found
more effective for PFOS degradation (Wang et al. 2017). Under mild conditions,
higher defluorination and decomposition are obtained by photochemical methods.
Till date, various photolytic methods such as photocatalysis (Hori et al. 2004), persulfate photolysis (Chen and Zhang 2006; Hori et al. 2005), hydrogen peroxide photolysis (Hori et al. 2004), persulfate photolysis (Chen and Zhang 2006; Hori et al.
2005), alkaline isopropanol photolysis (Yamamoto et al. 2007), direct photolysis
(Yamamoto et al. 2007; Chen and Zhang 2006; Hori et al. 2004) and photo-Fenton
(Tang et al. 2012; Wang et al. 2008; Hori et al. 2007) have been used to effectively
degrade PFOS in water samples.
Sonochemical Method: Sonochemical treatment is effective to degrade PFOS in water
over wide range of concentrations (Vecitis et al. 2008). Ultrasonic irradiation is used
to induce acoustic cavitation, which produces high temperature enough for pyrolysis
at the bubble–water interface (Vecitis et al. 2008). This in situ pyrolysis results faster
and complete degradation of PFOS into fluoride (F
− ), sulfate (SO 4
− ), CO and CO 2 .
Half-life of 30 min has been reported for PFOS degradation via sonochemical method
(Vecitis et al. 2008).
Electrochemical Method: Recently, PFOS has been treated via the first-order kinetics by electrochemical process using a divided electrochemical cell with Ti/RuO 2
anode and boron-doped diamond (BDD) anodes in undivided cells (Zhuo et al. 2011;
Ochiai et al. 2011; Carter and Farrell 2008). During these experimental studies, fluorine was generated, which clearly indicates PFOS defluorination. As most of the
studies have been conducted on synthetic groundwater samples, more future studies
need to be conducted under relevant environmental conditions. Preliminary investigations should be carefully done as some studies noted the perchlorate formation in
K. Dhangar and M. Kumar
with the efficiency ranging from 90 to 99% (Schröder et al. 2010; Tang et al. 2007).
According to the literature, due to smaller pore size and membrane selectivity, reverse
osmosis is more effective as compared to nanofiltration (Tang et al. 2007). The membrane fouling in such filtration processes can be controlled by using pretreatments
such as pre-oxidation and coagulation (Deka et al. 2020).
18.6.3 Redox Processes
The recent redox processes are very popular and promising for removal of PFOS,
as it gives complete mineralization. Various energy sources have been used in redox
processes for PFOS removal.
Photochemical Method: During photochemical processes, an inexhaustible energy
source, solar energy, is used as photocatalytic force to degrade PFOS. PFOS degradation has been carried out using both photo-oxidation and photo-reduction technologies. Though photo-oxidation is commonly used, photo-reduction technology found
more effective for PFOS degradation (Wang et al. 2017). Under mild conditions,
higher defluorination and decomposition are obtained by photochemical methods.
Till date, various photolytic methods such as photocatalysis (Hori et al. 2004), persulfate photolysis (Chen and Zhang 2006; Hori et al. 2005), hydrogen peroxide photolysis (Hori et al. 2004), persulfate photolysis (Chen and Zhang 2006; Hori et al.
2005), alkaline isopropanol photolysis (Yamamoto et al. 2007), direct photolysis
(Yamamoto et al. 2007; Chen and Zhang 2006; Hori et al. 2004) and photo-Fenton
(Tang et al. 2012; Wang et al. 2008; Hori et al. 2007) have been used to effectively
degrade PFOS in water samples.
Sonochemical Method: Sonochemical treatment is effective to degrade PFOS in water
over wide range of concentrations (Vecitis et al. 2008). Ultrasonic irradiation is used
to induce acoustic cavitation, which produces high temperature enough for pyrolysis
at the bubble–water interface (Vecitis et al. 2008). This in situ pyrolysis results faster
and complete degradation of PFOS into fluoride (F
− ), sulfate (SO 4
− ), CO and CO 2 .
Half-life of 30 min has been reported for PFOS degradation via sonochemical method
(Vecitis et al. 2008).
Electrochemical Method: Recently, PFOS has been treated via the first-order kinetics by electrochemical process using a divided electrochemical cell with Ti/RuO 2
anode and boron-doped diamond (BDD) anodes in undivided cells (Zhuo et al. 2011;
Ochiai et al. 2011; Carter and Farrell 2008). During these experimental studies, fluorine was generated, which clearly indicates PFOS defluorination. As most of the
studies have been conducted on synthetic groundwater samples, more future studies
need to be conducted under relevant environmental conditions. Preliminary investigations should be carefully done as some studies noted the perchlorate formation in