Water Science and Engineering 2015, 8(2): 139e144
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Water Science and Engineering
journal homepage: http://www.waterjournal.cn
Degradation of bisphenol A using electrochemical assistant Fe(II)-activated
peroxydisulfate process
Chun-wei Yang*
College of Environmental Science and Engineering, Jilin Normal University, Siping 136000, PR China
Received 22 October 2013; accepted 17 December 2014
Available online 15 April 2015
Abstract
Degradation of bisphenol A (BPA) in aqueous solution using sulfate radicals was investigated using the Fe(II)-activated peroxydisulfate
(PDS) process, electrochemical process, electrochemical process with 2.5 mmol/L Na2S2O8 without Fe(II), and electrochemical assistant Fe(II)activated PDS process. It was found that the electrochemical assistant Fe(II)-activated PDS process performed best in the degradation of BPA.
The variables considered to influence the degradation efficiency of BPA were the initial concentration of Fe2þ, the initial concentration of
Na2S2O8, and the current density. More than 97% of the BPA removals were achieved within 120 min under the optimum operational condition.
The degradation of BPA was accompanied by the formation of phenol, hydroquinone, and small-molecule compounds such as succinic acid. The
electron transfer was the principal step in the oxidation of BPA.
© 2015 Hohai University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://
creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords: Sulfate radicals; Peroxydisulfate; Advanced oxidation; BPA
1. Introduction
Bisphenol A (BPA) is a compound widely used in the
production of polycarbonate plastics and epoxy resin (Morgan
et al., 2014; Mei et al., 2011). It is an endocrine-disrupting
chemical (EDC) that affects the endocrine system and produces an adverse effect on aquatic life, animals, and potentially human. There is increasing evidence that EDCs can alter
endocrine functions and may disrupt the growth, development,
and reproduction of the human body by interfering with the
production of the endocrine system. Accordingly, because of
the contribution of estrogenic chemicals to the development of
This work was supported by the Natural Science Foundation of Jilin
Province (Grant No. 20140101215JC), the Key Program in Science and
Technologies of Jilin Province (Grant No. 20150204049SF), and the Key
Laboratory of Industrial Ecology and Environmental Engineering, the Ministry
of Education of China (Grant No. KLIEEE-13-07).
* Corresponding author.
E-mail address: [email protected] (Chun-wei Yang).
Peer review under responsibility of Hohai University.
hormone-dependent cancers, disorders of the reproductive
tract, and other effects, they are often referred to as environmental estrogens (Tyler and Denys, 2014; Branco and Lemos,
2014). BPA has become a controversial issue because it was
detected in different environmental media (aquatic environment, soil, sediment, and air), food, and the human body
(Huang et al., 2012; Suzuki et al., 2004). Therefore, the
development of a process for BPA degradation has aroused
significant interest (Cui et al., 2009; Li et al., 2008).
The electrochemical process is one of the advanced
oxidation processes (AOPs) developed in recent years for
wastewater treatment (Lei et al., 2013; Li et al., 2005).
Effectiveness of electrochemical oxidation for wastewater
treatment depends largely upon the properties of the anodes
and the organic substances involved in the process (Jin et al.,
2014; Chen et al., 2005). Traditional electrodes, such as
graphite, are not effective for wastewater treatment (Souza
et al., 2014). Recently, there has been a growing interest in
using sulfate radicals to treat organic contaminants
(Anipsitakis and Dionysiou, 2004; Rastogi et al., 2009).
http://dx.doi.org/10.1016/j.wse.2015.04.002
1674-2370/© 2015 Hohai University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://
creativecommons.org/licenses/by-nc-nd/4.0/).
140
Chun-wei Yang / Water Science and Engineering 2015, 8(2): 139e144
Sulfate radicals could be produced from peroxydisulfate
(PDS) or peroxymonosulfate via thermal, photochemical,
radiolysis, or redox decomposition (Eqs. (1) through (4))
(Zhao et al., 2010).
Heating
ð1Þ
S2 O2
8 /2SO4
Illuminating
ð2Þ
2
S2 O2
8 þ e /SO4 þ SO4
ð3Þ
nþ
2
ðnþ1Þþ
S2 O2
8 þ M /SO4 þ SO4 þ M
ð4Þ
S2 O2
8 /2SO4
where M denotes the transition metal.
The Fe(II)-activated PDS process has been used in wastewater treatment, especially for in situ chemical oxidation
using sulfate radicals (Ahmed et al., 2012; Liang et al., 2004).
However, there have existed critical limitations in the application of the Fe(II)-activated PDS process because the reaction
requires acid conditions, and the efficiency has been too low.
Evidence of the latter is that some of the sulfate radicals
produced react with excess Fe2þ thereby lowering the concentration of sulfate radicals that are available to degrade
contaminants in the system (Eqs. (5) and (6)).
2þ
2
3þ
S2 O2
8 þ Fe /SO4 þ SO4 þ Fe
ð5Þ
2
2þ
3þ
SO
4 þ Fe /SO4 þ Fe
ð6Þ
Therefore, for water treatment, it would be interesting to
develop environmentally benign methods with environmental
and economic considerations. The electrochemical assistant
Fe(II)-activated PDS process has been established, offering a
new method of solving problems. In the electrolytic cell,
pollutants are destroyed by the action of the Fe(II)-activated
PDS process in bulk together with anodic oxidation at the
anode surface. Simultaneously the electrochemical reduction
of Fe3þ to Fe2þ at the cathode surface (Eq. (7)) enhances
Eq. (5). Moreover, the oxidation of regenerated Fe2þ to Fe3þ
may occur at the same time (Eq. (8)) on the anode surface in
order to maintain the appropriate Fe2þ concentration.
FeðOHÞ
2þ
Fe /Fe
2þ
þ e /Fe2þ þ OH
3þ
þe
ð7Þ
ð8Þ
As a result, our research focuses on the destruction of BPA,
as an EDC, using the electrochemical assistant Fe(II)-activated
PDS process in an effort to propose sulfate radicals-based
AOPs as an alternative to the most common and established
electro-Fe(II)-activated PDS system for the decomposition of
EDCs. In this study, the reaction mechanism and the products
of BPA degradation were also evaluated. From the environmentally friendly point of view, the electrochemical assistant
Fe(II)-activated PDS process for wastewater treatment provides a promising alternative as a novel technology for elimination of contaminants.
2. Materials and methods
2.1. Chemicals
BPA was obtained from the Shanghai Third Chemical Reagent Factory in China. Sodium sulphate (anhydrous, with a
purity of 99%), sodium peroxydisulfate (analytical reagent
grade, with a purity of 99%), and ferrous sulfate (analytical
reagent grade, with a purity of 99%) were purchased from the
Shenyang Chemical Reagent Factory in China. All sample
solutions were prepared with deionized water from the ion
exchange system.
2.2. Procedures and equipment
Experiments were performed at room temperature (20±1) C
in a 100 mL beaker supplied with a magnetic stirrer under
constant potential conditions using a ATTEN APR-6402
potentiostat/galvanostat (Shenzhen, China). Graphite plates
(2.5 cm 4.5 cm 0.5 cm) were used as cathode and anode
electrodes with the electrode spacing maintained at 1 cm. The
aqueous solutions were agitated continuously with a magnetic
stirrer at a velocity of 75 rpm. The initial concentrations of BPA
and Na2SO4 were 35 mg/L and 25 mmol/L, respectively. A
series of experiments was conducted to investigate the optimal
iron catalyst concentration, current density, and sodium peroxydisulfate concentration. The pH of BPA solutions was not
adjusted during the reaction.
2.3. Analytical methods
The concentration of BPA was determined using highperformance liquid chromatography (HPLC) incorporating a
high-pressure pump (Shimadzu LC-6A) and a UV detector
(Waters 481 detector). In the HPLC analysis, a Vydac C18
column (with a size of 1.0 mm 150 mm and a mean particle
size of 5 mm) and a mobile phase of methanol/water (with a
volume ratio of 3:1) at a steady flow rate of 1 mL/min were
used. The injection volume was 2 mL. The retention time of
BPA was 4.62 min. Measurements were made in triplicate in
each experiment with errors less than 5%.
3. Results and discussion
3.1. Preliminary studies on treatment method
Preliminary experiments were performed to compare the
effect of different combinations of treatment methods,
including the Fe(II)-activated PDS process, electrochemical
process, electrochemical process with 2.5 mmol/L Na2S2O8
without Fe(II), and electrochemical assistant Fe(II)-activated
PDS process, as shown in Fig. 1. The initial concentrations
of BPA and Na2SO4 were 35 mg/L and 25 mmol/L, respectively. These experiments were carried out at room temperature (20±1) C and neutral pH. In the Fe(II)-activated PDS
Chun-wei Yang / Water Science and Engineering 2015, 8(2): 139e144
Fig. 1. Variation of BPA concentration with time with different
processes.
process the concentrations of Fe(II) and PDS were 0.2 and
2.5 mmol/L, respectively. The current density in the electrochemical process and electrochemical assistant Fe(II)activated PDS process was maintained at 3.6 mA/cm2. In the
electrochemical assistant Fe(II)-activated PDS process the
concentrations of Fe(II) and PDS were 0.2 and 2.5 mmol/L,
respectively. The reaction duration was kept at 30 min. The
Fe(II)-activated PDS process, electrochemical process, electrochemical process with 2.5 mmol/L Na2S2O8 without Fe(II),
and electrochemical assistant Fe(II)-activated PDS process had
minimum BPA concentrations with a decreasing order of
30.69, 24.17, 19.54, and 14.27 mg/L, respectively. It was
clearly seen that the best and efficient treatment method for
the degradation of BPA was the electrochemical assistant
Fe(II)-activated PDS process.
The removal rate of BPA only reaches 12.3% after a 30-min
treatment with the Fe(II)-activated PDS process because the
Fe(II)-activated PDS process only has high efficiency at a
relatively high temperature (50e70 C) and acid condition
(with pH values from 2 to 4) (Huang and Huang, 2009).
Therefore, it is not efficient to treat BPA with the Fe(II)activated PDS process. The existence of PDS could enhance
the efficiency of the electrochemical process because sulfate
radicals can be produced through PDS reaction at the cathode
electrode surface (Eq. (3)). BPA could also be removed by the
anode during the electrochemical reaction. The concentration
of BPA decreased to 19.54 mg/L after a 30-min treatment with
the electrochemical process with 2.5 mmol/L Na2S2O8 without
Fe(II). By contrast, the concentration of BPA reached
14.27 mg/L with the electrochemical assistant Fe(II)-activated
PDS process due to the coupling of electrochemical and
Fe(II)-activated PDS processes. Therefore, the electrochemical
assistant Fe(II)-activated PDS process is feasible and practical
in the treatment of BPA. Further investigations of process
factors should be considered.
141
assistant Fe(II)-activated PDS process. Other operating parameters apart from the initial concentration of Fe2þ were kept
the same (the BPA and Na2S2O8 concentrations and the current density were 35 mg/L, 2.5 mmol/L, and 3.6 mA/cm2,
respectively). It was observed that the BPA removal rate
increased with the initial concentration of Fe2þ, especially
below 1.0 mmol/L (Fig. 2), and the influence of the initial
concentration of Fe2þ was less pronounced when it reached
1.0 mmol/L. When the Fe2þ concentration was greater than
1.0 mmol/L the remaining Fe2þ could react with sulfate radicals (Eq. (6)). Finally, the BPA removal rate remained steady
even when the initial concentration of Fe2þ increased. Taking
into account the practical application of this process, the
optimal initial concentration of Fe2þ in the following experiments was set as 1.0 mmol/L.
3.3. Influence of initial concentration of Na2S2O8 on
BPA removal rate
The initial concentration of Na2S2O8 has a significant effect
on the degradation of BPA with the electrochemical assistant
Fe(II)-activated PDS process. The effect of the initial concentration of Na2S2O8 was essentially investigated and the
results are shown in Fig. 3. The initial concentration of
Na2S2O8 varied from 0.5 to 4.5 mmol/L while other experimental parameters remained constant (the BPA and Fe2þ
concentrations were 35 mg/L and 1.0 mmol/L, respectively,
and the current density was 3.6 mA/cm2). It was clearly seen
that the increase of the initial concentration of Na2S2O8 from
0.5 to 2.5 mmol/L improved the BPA removal rate from 46.1%
to 61.36% after 30 min of treatment, as high concentration can
accelerate the generation of sulfate radicals and decomposition
of organic pollutants. However, when the initial concentration
of Na2S2O8 increased from 2.5 to 4.5 mmol/L, the removal
rate of BPA remained almost steady, from 61.36% to 62.45%.
The results show that the optimal initial concentration of
Na2S2O8 was 2.5 mmol/L for the degradation of BPA using the
electrochemical assistant Fe(II)-activated PDS process.
3.4. Influence of current density on BPA removal rate
Experiments were conducted to determine the effect of
current density on the removal of BPA using the electrochemical assistant Fe(II)-activated PDS process while other
experimental parameters were kept constant (the BPA, Fe2þ,
3.2. Influence of initial concentration of Fe2þ on BPA
removal rate
In order to evaluate the effect of the initial concentration of
Fe2þ on the degradation of BPA, six discrete values between
0.1 and 1.8 mmol/L were used with the electrochemical
Fig. 2. Effects of initial concentration of Fe2þ on BPA removal rate.
142
Chun-wei Yang / Water Science and Engineering 2015, 8(2): 139e144
Fig. 3. Effects of initial concentration of Na2S2O8 on BPA removal
rate.
and Na2S2O8 concentrations were 35 mg/L, 1.0 mmol/L, and
2.5 mmol/L, respectively). The values of current density
applied were 0.9, 1.8, 3.6, 5.4, 7.2, and 9.0 mA/cm2. As shown
in Fig. 4, the removal rate increased from 31.97% to 61.36%
with the increase of current density from 0.9 to 3.6 mA/cm2
within 30 min. However, when the current density was greater
than 3.6 mA/cm2, the BPA removal rate decreased to 50.31%
for current densities from 3.6 to 9.0 mA/cm2. This may be
explained by the fact that high current density may lead to a
decrease of the concentrations of sulfate radicals and Fe2þ,
and then influence the removal rate of BPA. Furthermore, the
results revealed that there was an optimum current density
(3.6 mA/cm2) in treating the BPA solution.
3.5. Kinetics studies of BPA removal
Fig. 5. Variations of BPA concentration and removal rate with reaction time.
ln
C
¼ kt
C0
ln
C
¼ 0:030 5t
C0
ð9Þ
ð10Þ
where C is the concentration of BPA at reaction time t, and C0
is the initial concentration of BPA.
3.6. Reaction products from oxidation of BPA
It is necessary to study the kinetics of BPA removal under
optimal conditions. The degradation process of BPA was
observed when the BPA, Fe2þ, and Na2S2O8 concentrations
were 35 mg/L, 1.0 mmol/L, and 2.5 mmol/L, respectively, and
the current density was 3.6 mA/cm2 at ambient temperature
and neutral pH. The results are shown in Fig. 5. The optimal
BPA removal rate reached 97.67% within 120 min of treatment. The electrochemical assistant Fe(II)-activated PDS
process is operative in the degradation of BPA.
The kinetics of the BPA removal process followed the firstorder reaction of the BPA concentration. Fig. 6 presents the
calculation of the pseudo first-order rate constant k, for BPA
degradation with the electrochemical assistant Fe(II)-activated
PDS process within the 120-min treatment. The first-order
kinetics of the removal rate are expressed in Eq. (9). The
degradation process of BPA follows Eq. (10).
The reaction products from the oxidation of BPA using the
electrochemical assistant Fe(II)-activated PDS process were
identified by means of HPLC. Fig. 7 shows the BPA degradation process in separate reaction time.
The results indicated that after the 120-min reaction the
BPA concentration was very low, but hydroquinone, phenol,
and succinic acid were found using the standard addition
method. The concentration of BPA decreased with the reaction
time but the peak height of intermediate products remained
steady. Previous reports (Cui et al., 2009; Li et al., 2008) have
shown the degradation pathways of BPA. Hydroquinone was
one of the key intermediate products through isopropylidene
bridge cleavage. Then succinic acid could be discovered
through aromatic ring cleavage. The degradation pathway of
hydroquinone was determined because hydroquinone and
succinic acid were detected throughout the reaction with the
electrochemical assistant Fe(II)-activated PDS process.
Fig. 4. Effects of current density on BPA removal rate.
Fig. 6. Degradation kinetics of BPA.
Chun-wei Yang / Water Science and Engineering 2015, 8(2): 139e144
143
Fig. 7. HPLC chromatograms of BPA in water at different reaction time.
Nevertheless, the results also indicated that the concentrations of intermediate products hydroquinone and phenol were
very low. Therefore, during the oxidation of BPA, electron
transfer was assumed to be the key step of the sulfate radical
attack. A sulfate radical mediated attack on BPA leads to the
formation of organic radicals via electron transfer from the
organic compounds to the sulfate radicals. The degradation of
BPA through a hydroxylation reaction of hydroxyl radicals did
not prevail in this process. The results regarding reaction intermediates indicated that succinic acid was the primary intermediate from BPA degradation and the electron transfer
was the principal step in the oxidation of BPA.
4. Conclusions
The electrochemical assistant Fe(II)-activated PDS process
was proven to be feasible and effective in the treatment of BPA
solution. The influence of some operational parameters on the
degradation of BPA was discussed. This promising and ecofriendly oxidation system is likely a useful contribution to
the field of AOPs. The main conclusions are as follows:
(1) The removal rate of BPA was strongly dependent on the
initial concentration of Fe2þ, the initial concentration of
Na2S2O8, and the current density.
(2) Investigation of the mechanism of the degradation of
BPA with the electrochemical assistant Fe(II)-activated PDS
process suggested that this process obeyed the first-order
kinetics.
(3) The formation of intermediates, such as hydroquinone
and succinic acid, showed that electron transfer was the
foremost step in the oxidation of BPA.
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