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Oxidation of bisphenol A by UV/S2O : Comparison withUV/H2O2Sung-Hwan Yoon a , Seongpil Jeong a & Seockheon Lee aa Water Environmental Centre, Korea Institute of Science and Technology (KIST) , 39-1Hawolgok-dong, Seongbuk-gu, Seoul , 136-791 , Republic of KoreaAccepted author version posted online: 27 May 2011.Published online: 19 Dec 2011.

To cite this article: Sung-Hwan Yoon , Seongpil Jeong & Seockheon Lee (2012) Oxidation of bisphenol A by UV/S2O :Comparison with UV/H2O2 , Environmental Technology, 33:1, 123-128, DOI: 10.1080/09593330.2011.579181

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Environmental TechnologyVol. 33, No. 1, January 2012, 123128

Oxidation of bisphenol A by UV/S2O28 : Comparison with UV/H2O2Sung-Hwan Yoon, Seongpil Jeong and Seockheon Lee

Water Environmental Centre, Korea Institute of Science and Technology (KIST), 39-1Hawolgok-dong, Seongbuk-gu, Seoul 136-791, Republic of Korea

(Received 4 September 2010; accepted 3 April 2011 )

The UV/S2O28 process was applied to decompose bisphenol A (BPA), which is a representative endocrine-disrupting chem-ical (EDC), and was comared with the UV/H2O2 process. The BPA degradation efficiency by UV/S2O28 was increasedby increasing S2O28 concentration or decreasing BPA concentration. The presence of humic acid caused an inhibitoryeffect. The BPA oxidation rate by UV/S2O28 was increased in the following order: neutral pH (pHi = 7) < acidic pH(pHi = 4) < basic pH (pHi = 10). The main oxidizing species in the UV/S2O28 system was sulphate radical (SO

4 ),

whereas the main oxidizing species in the UV/H2O2 system was OH radical (OH). Compared with UV/H2O2, the

UV/S2O28 process showed higher performance for not only BPA degradation but also its mineralization, which meansthat SO4 is a more effective oxidant for BPA than the OH

. The results shown in this study imply that the SO4 -basedUV/S2O28 process can be an excellent alternative process for the widely used UV/H2O2 process, with higher remediationperformance.

Keywords: endocrine-disrupting chemical; bisphenol A, UV/S2O28 , UV/H2O2, sulphate radical, OH radical.

IntroductionEndocrine-disrupting compounds (EDCs) are natural andsynthetic chemicals that cause adverse effects on humansand animals by influencing the endocrine system. Theyinclude natural estrogens, synthetic estrogens and anthro-pogenic chemicals, and they have been reported to be asignificant cause of reproductive and sexual disturbance inanimals [1,2]. Various EDCs are released into the aquaticenvironment, mainly via the effluents of sewage treatmentplants (STPs). The detected concentrations of EDCs inthe aquatic environment are known to range from ng/Lto g/L level [3,4]. Even with those low concentrations,EDCs can pose a serious threat to the endocrine sys-tem of humans and animals. The widespread existence ofEDCs in the aquatic environment implies that EDCs arenot sufficiently removed by conventional water treatmentprocesses (e.g. activated sludge, activated carbon, chlori-nation). Because of the highly hazardous effects on humansand animals, it is necessary to remove EDCs more effec-tively from STPs and drinking water treatment plants. Forthis purpose, advanced oxidation processes (AOPs) havebeen recommended owing to the high potential for theoxidation of persistent micropollutants such as EDCs, phar-maceutically active compounds and personal care products

Corresponding author. Email: seocklee@kist.re.kr

[5,6]. Generally, AOPs not only decompose EDCs but alsoreduce their estrogenic activities [79].

A lot of studies have shown that AOPs are very effec-tive for the oxidative removal of EDCs [10]. Advancedoxidation processes, which use the hydroxyl radical (OH,EOH = 2.7 V as normal hydrogen electrode [NHE]) or sul-phate radical (SO4 , E

SO4 = 2.53.1 V as NHE) as the

main oxidizing species, include O3, O3/H2O2, UV/H2O2,UV/TiO2, Fe(II)/H2O2, UV/Fe(III)/H2O2, ultrasonic oxi-dation, electrochemical oxidation, electron-beam radiation,and UV/S2O28 . Most previous studies on the removal ofEDCs by AOPs employed OH-induced processes (e.g.O3, O3/H2O2, UV/H2O2, UV/TiO2, UV/Fe(III)/H2O2)[1115]. Several AOP studies using SO4 -induced pro-cesses have been conducted for the removal of somepersistent organic pollutants (e.g. butylated hydroxyanisole,atrazine, 2,4-dichlorophenol) [1619]. However, littleresearch has been conducted using SO4 -induced pro-cesses (e.g. UV/S2O28 , heat/S2O

28 ) for the oxidative

removal of EDCs. That is the reason why this study wasconducted.

In this study, bisphenol A (BPA) was selected as thetarget EDC because of its frequent detection in the aquaticenvironment. Although it has been recently reported that

ISSN 0959-3330 print/ISSN 1479-487X online 2012 Taylor & Francishttp://dx.doi.org/10.1080/09593330.2011.579181http://www.tandfonline.com

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BPA has an insignificant hazardous effect on humans at theconcentration range commonly encountered in the aqueousenvironment (less than 1 g/L), BPA is still considered tobe one of the most typical EDCs [20]. It is a key monomer inthe production of polycarbonate plastics and epoxy resins.The aim of this work was to compare the UV/S2O28 processand the UV/H2O2 process for the oxidation of BPA.

ExperimentalMaterialsAll the chemicals except humic acid (HA) were of reagentgrade and used as received. Only HA sodium salt purchasedfrom Sigma-Aldrich was of technical grade. Sodium per-sulphate (Na2S2O8) was used as the source of persulphate(S2O28 ). Ultrapure water (18.2 Mcm) was obtained usinga laboratory water-purifying system (Millipore). A 6 Wlow-pressure mercury lamp (Philips, G6T5, = 254 nm)was used as the light source.

Photochemical experimentsDisodium hydrogen phosphate (Na2HPO4) was added formaintaining a desired pH, and 0.1 M H2SO4 and 0.2 MNaOH were used for pH adjustment. Experiments werecarried out using a cylindrical borosilicate glass reac-tor (50 mm i.d. 230 mm height). An aqueous solution(250 mL) containing BPA and an oxidant (S2O28 or H2O2)was poured into the reactor. The solution was irradi-ated with UV-C light ( = 254 nm) with magnetic stir-ring. Sample aliquots were intermittently withdrawn foranalysis. Sodium thiosulphate (Na2S2O3) was immedi-ately added as a quenching reagent into every samplebefore high-performance liquid chromatography (HPLC)and total organic carbon (TOC) analyses, in order tostop the potential reaction between BPA and persulphate([Na2S2O3]/[persulphate] > 10).

AnalysisThe concentration of BPA was measured using a Shimadzuhigh-performance liquid chromatography (HPLC) systemwith a fluorescence detector. A C-18 reverse-phase col-umn served as the stationary phase, with 1 mL/min ofthe eluent consisting of 50% acetonitrile and 50% 10 mMphosphoric acid. An excitation wavelength of 229 nm andan emission wavelength of 309 nm were used to detectthe fluorescence. Mineralization efficiency was determinedusing a Shimadzu TOC analyser. The S2O28 concentra-tions were determined by the iodometric spectrophotometermethod [21], and H2O2 concentrations were measured bythe 2,9-dimethyl-1,10-phenanthroline (DMP) method [22].An Orion 250 pH meter was used for the pH measurements.A HACH DR 5000 spectrophotometer was employed forthe absorption measurements.

Results and discussionEffects of BPA concentration and S2O28 concentrationThe dependence of the BPA degradation efficiency oninitial BPA concentration at 100 M S2O28 and initialpH 4.0 is shown in Figure 1a. The BPA concentration waschanged from 10 to 40 M. The required reaction timeto achieve a certain efficiency of BPA degradation (e.g.90%) increased with the increase in BPA concentration.The effect of S2O28 concentration at 40 M BPA and ini-tial pH 4.0 is shown in Figure 1b. The S2O28 concentrationwas changed from 100 to 400 M. In this case, the requiredreaction time decreased with the increase in S2O28 concen-tration. That is, the BPA degradation by UV/S2O28 couldbe accelerated by increasing the ratio of [S2O28 ]/[BPA].The increase of [S2O28 ]/[BPA] in the UV/S2O

28 process

causes a higher amount of SO4 radicals to react with BPAfor a given amount of BPA, and thus the required reactiontime is shortened.

Effects of humic acid (HA) and pHThe effect of HA is shown in Figure 2. The dissolvedorganic carbon (DOC) concentration of HA stock solution

Irradiation time (min)

0 5 10 15 20

[BP

A] t

/ [B

PA

] 0

0.0

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0.4

0.6

0.8

1.0

10 M BPA 20 M BPA 40 M BPA

effect of BPA concentration

Irradiation time (min)0 5 10 15 20

[BP

A] t

/ [B

PA

] 0

0.0

0.2

0.4

0.6

0.8

1.0

100 M S2O82-

200 M S2O82-

400 M S2O82-

effect of S2O82- concentration

A

B

Figure 1. Effect of (a) BPA concentration ([S2O28 ]0=100 M)and (b) S2O28 concentration ([BPA]0 = 40 M) on BPA degra-dation. pHi = 4 (with 0.2 mM Na2HPO4).

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Irradiation time (min)0 1 2 3 4 5 6

[BP

A] t

/ [B

PA

] 0

0.0

0.2

0.4

0.6

0.8

1.0

HA-DOC = 0 mg/L HA-DOC = 8.5 mg/L HA-DOC = 17 mg/L

Figure 2. Effect of humic acid on BPA degradation. [BPA]0 =10 M, [S2O28 ]0 = 100 M, pHi = 4 (with 0.2 mM Na2HPO4).

0 1 2 3 4 5 60.0

0.2

0.4

0.6

0.8

1.0

pH 4pH 7pH 10

Irradiation time (min)

[BP

A] t

/ [B

PA

] 0

Figure 3. Effect of pH on BPA degradation. [BPA]0 = 10 M,[S2O28 ]0 = 100 M, pH adjusted with 0.2 mM Na2HPO4.

was 85 mg/L. With this HA stock solution, a desiredconcentration of HA-DOC was prepared. The BPA degra-dation efficiency decreased with the increase in HA-DOCconcentration. In 6 min, the BPA degradation efficien-cies corresponding to 0, 8.5 and 17 mg/L HA-DOC were96.0%, 62.3% and 40.2%, respectively. The presence ofHA-DOC showed an inhibitory effect on the BPA degrada-tion by UV/S2O28 , since HA-DOC acted as a competitivescavenger for SO4 radicals and also decreased the lightpenetration in the solution.

The effect of pH is shown in Figure 3. Usually, in theUV/S2O28- system, the pH drops to an acidic value owing tothe formation of proton (H+) and SO24 [23]. However, inour experiments, the pH drop was insignificant because ofthe pH-buffering effect of 0.2 mM Na2HPO4: pH < 0.3.The BPA degradation efficiency by UV/S2O28 increasedin the following order: neutral pH (pHi = 7) < acidic pH(pHi = 4) < basic pH (pHi = 10). Although we do nothave a clear explanation for this result, we assume that the

Irradiation time (min)

[BP

A] t

/ [B

PA

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w/o alcoholsw/ 10 mM t-butanolw/ 10 mM ethanol

UV/S2O82-

Irradiation time (min)

0 1 2 3 4 5 6

0 1 2 3 4 5 6

[BP

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/ [B

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0.0

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0.4

0.6

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1.0

w/o alcoholsw/ 10 mM t-butanolw/ 10 mM ethanol

UV/H2O2

A

B

Figure 4. Effects of t-butanol and ethanol on the BPA degrada-tion by (a) UV/S2O28 ([S2O

28 ]0 = 500 M) and (b) UV/H2O2

([H2O2]0 = 500 M). [BPA]0 = 50 M, pHi = 7 (with 5 mMNa2HPO4).

highest efficiency at the basic pH is attributable to the mostrapid dissociation of S2O28 to SO

4 . The higher efficiency

at the acidic pH than at the neutral pH also seems dueto the more rapid decomposition of S2O28 and formationof SO4 . The acid- and base-catalysed decomposition ofpersulphate is a well-known phenomenon [24,25]. How-ever, it seems that this pH dependence (pHi7 < pHi4