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Effect of nitrate on the degradation of bisphenol A byUV/H2O2 and ozone/H2O2 oxidation in aqueous solutionC.G. Parka, E.S. Choia, H.W. Jeonb, J.H. Leea, B.W. Sungb, Y.H. Choa & K.B. Koba Green Environmental Industry Division, Korea Testing Laboratory, Guro-gu, Seoul, 152-718,Korea, Tel. +82 2 860 1678, Fax: +82 2 860 1639b School of Civil & Environmental Engineering, Yonsei University, 134 Shinchondong, Seoul,120-749, Korea.Published online: 05 Aug 2013.

To cite this article: C.G. Park, E.S. Choi, H.W. Jeon, J.H. Lee, B.W. Sung, Y.H. Cho & K.B. Ko (2014) Effect of nitrate on thedegradation of bisphenol A by UV/H2O2 and ozone/H2O2 oxidation in aqueous solution, Desalination and Water Treatment,52:4-6, 797-804, DOI: 10.1080/19443994.2013.827297

To link to this article: http://dx.doi.org/10.1080/19443994.2013.827297

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Effect of nitrate on the degradation of bisphenol A by UV/H2O2and ozone/H2O2 oxidation in aqueous solution

C.G. Parka,*, E.S. Choia, H.W. Jeonb, J.H. Leea, B.W. Sungb, Y.H. Choa, K.B. Kob

aGreen Environmental Industry Division, Korea Testing Laboratory, Guro-gu, Seoul 152-718, KoreaTel. +82 2 860 1678; Fax: +82 2 860 1639; email: parkcg@ktl.re.krbSchool of Civil & Environmental Engineering, Yonsei University, 134 Shinchondong, Seoul 120-749, Korea

Received 9 March 2013; Accepted 30 March 2013

ABSTRACT

The goal of the present study was to investigate the effect of nitrate on the removal ofbisphenol A (BPA) by conducting bench-scale UV/H2O2 and O3/H2O2 operations under avariety of reaction time and initial concentrations of H2O2 and NO

3 N. Also, this study

evaluated the advanced oxidation process processes and determined the optimal conditions,for removing BPA. The practical reaction time and initial H2O2 concentration for the morethan 85% removal of BPA proved to be 2.0min and 150mg/L, respectively, in the presenceor absence of nitrate. The removal efficiency of BPA was improved by the hydroxyl radicalsproduced from nitrate photolysis in the absence of H2O2. In the presence of H2O2, however,nitrate hindered the BPA removal by acting as OH scavengers under the operating condi-tions described above. Also, H2O2 acts as free-radicals scavenger at concentrations aboveoptimum required. In O3/H2O2 process with nitrate addition, more than 75% of the BPAwas removed under the conditions of an initial O3 concentration of 7.5mg/L and H2O2concentration of more than 150mg/L.

Keywords: AOPs; BPA; Hydroxyl radical; Nitrate; Scavenger

1. Introduction

The revolutionized development of resources andtechnologies has produced more chemicals andcompounds which consequently increased the numberof compounds that were identified as possessingpotential environmental threats to the livings. Thisever-increasing number of surreptitious compoundsposes potential environmental threat to theliving organisms [1]. An example is bisphenol A

[2,2-bis(4-hydroxyphenyl)propane; BPA], which iswidely used as a raw material for polycarbonate andepoxy resins and is known to accumulate in naturewithout decomposition causing reproductive damagesto a variety of animal species [2]. BPA and otherendocrine disrupting chemicals (EDCs) manage toenter surface waters through wastewater from BPAproduction factories and/or by agricultural runoff andirrigation return waters [3]. BPA was detected atconsiderably high levels ranging from 0.44 to53 nmol/L in surface waters [4] and 5.7 to 75mmol/L*Corresponding author.

Presented at the Fifth Annual International Conference on Challenges in Environmental Science & EngineeringCESE 2012Melbourne, Australia, 913 September 2012

1944-3994/1944-3986 2013 Balaban Desalination Publications. All rights reserved.

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doi: 10.1080/19443994.2013.827297

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in landfill leachates [5]. Persistent EDCs appear toremain for periods ranging from days to months inthe surface waters into which they are discharged [6].Therefore, in the last decade, there is an increasinginterest in effective remediation technologies forthe destruction of BPA in contaminated waterenvironments [7].

Advanced oxidation process (AOP) employinghydrogen peroxide with UV or O3 is an effectivemethod in the degradation of organic pollutants. InUV/H2O2 or O3/H2O2 process, the oxidation of H2O2generates oxidizing species hydroxyl radical OH,which oxidize various organic compounds quickly [8].Hydroxyl radicals, unlike other oxidants, are capableof oxidizing almost all the reduced materials in trea-ted effluents, without any restriction to specific classesor groups of compounds [9]. Hydroxyl radicals canoxidize a broad range of organic pollutants quicklyand nonselectively [10]. In addition, the advancedH2O2 oxidation process has been found to be veryeffective in the degradation of endocrine disruptors[11]. Typical concentrations of NO3 N are known torange from 2 to 5mg/L in biologically well-treatedwastewater treatment plant effluents. However, thenitrate ion, NO3 , is a well-known strong absorber ofUV light at a wavelength of below 250 nm [12], NO2from NO3 photolysis may interfere with the oxidationreactions of organic chemicals enhanced by hydroxylradicals. Nitrate photolysis has three distinct mecha-nisms, which result in the formation of nitrite (NO2 ),peroxynitrite (ONO2 ), and

NO2. One of these mecha-nisms is the direct route to NO2 formation from NO

3

photolysis, with a low quantum yield [12,13]. The con-siderable production of NO2 can be expected via thetwo other reactions, which produce the intermediatesONO2 and

NO2. These intermediates are eventuallyundergone thermal reactions to NO2 form as a stableproduct [12,14]. The formation of hydroxyl radicalsOH can also be expected, together with one of theintermediates, NO2, from nitrate photolysis. As NO

2

accumulates, it can acts as an OH scavenger. Themechanisms involving H2O2 photolysis have beencritically reviewed [12,15]. H2O2 also influences NO

2

production. Since H2O2 photolysis is another source ofhydroxyl radicals, it might be expected to decreaseNO2 production. H2O2, however, appears to act inpart as a scavenger of hydroxyl radicals. Peroxynitriteions and their conjugate acid, peroxynitrous acid(ONO2H), are strong oxidants. Hydroxyl radicals arealso produced from the decomposition of peroxyni-trous acid. Nitrite and oxygen can be formed from thereaction between peroxynitrous acid and hydrogenperoxide [15]. The literature review conducted on the

reactions related to the UV photolysis of hydrogenperoxide in the presence of nitrate revealed that bothnitrate and hydrogen peroxide appear to act either asOH producers or, at some point in time, as OHscavengers, in an aqueous solution [16].

There were very limited numbers of studies,though, in which the effects of nitrate in an aqueoussolution were systematically determined for the UV/H2O2 and O3/H2O2 process [1720]. In our previousstudies [16,2123], effects of nitrate on the UV photol-ysis were investigated for the degradation of volatileorganic compounds, 2,4-dichlorophenol, DEP, DEHPin aqueous solutions.

The goal of the present study was to investigatethe effect of nitrate on the removal of BPA byconducting bench-scale UV/H2O2 and O3/H2O2operations under a variety of reaction time and initialconcentrations of H2O2 and NO

3 N. Also, this study

evaluated the AOP processes (UV alone, UV/H2O2,and O3/H2O2) and determined the optimal conditions,for removing BPA. Therefore, the results of this studycan provide the referable information about theproper application of ozonation and UV irradiationwith hydrogen peroxide for the removal of BPA. Theidentification of the intermediates from the BPAoxidation was not within the scope of this study.

2. Materials and methods

2.1. Bench-scale AOP system for advanced H2O2 oxidation

All the solvents and reagents used in this study,including bisphenol A (99%, SigmaAldrich, USA),hydrogen peroxide (28% w/w, Duksan, Korea) andKNO3 (99%, Samchun, Korea), were of analyticalgrade. All experiments (UV alone, UV/H2O2, O3/H2O2) were carried out in a bench-scale AOP system(Fig. 1), which consisted of a 28 L raw water tank, a1m3/h capacity raw water feed pump, a 18L UV andO3 reactor, and a maximum 2g/h capacity O3 genera-tor. An O3 generator (Wony Machinery Co., LTD), anO3 injector (Mazzel, USA) and reactor were installed,and connected to the bench-scale AOP system tostudy the BPAs oxidation. The reactor and tank aremade of a stainless steel (STS316L). Also, they wereinterconnected with stainless steel pipes. The UVlamp in the reactor (HanSung Ultraviolet co. LTD)with a nominal power of 65W, emitted radiation at254 nm. All headspaces inside the reactors and pipeswere completely eliminated during the experiments.All the experiments were performed in the batchmode at room temperature, and the pH levels in thereactors were not controlled.

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The aqueous solution (28L) that was poured intothe raw water tank was prepared by dissolving 0.256 gof BPA standard power and 1.01 g of KNO3 in 28 Ldouble-distilled water. To completely mix the solution,the mixture was carefully performed with a stirrer andwas circulated in the raw water tank with the use ofthe installed agitator (IKA-RW 20, IKA-Werke GmbH,& Co.KG) for 2min. Aliquots (799.93 lL) of H2O2 wereinjected before the aqueous solution was circulated tothe UV and O3 reactor, and the UV and O3 reactor wasfilled with the aqueous solution to prevent any head-space inside it. This aqueous solution was againcompletely mixed for a period of time circulated in theUV and O3 reactor, without UV irradiation and O3injection. The UV lamp in the reactor was turned on toinitiate the oxidation reaction. Samples (2mL) wereregularly collected according to the predeterminedschedule.

2.2. Analytical methods

BPA separation and quantification was performedusing high-performance liquid chromatographysystem (HPLC), which is an Infinity 1290 liquid chro-matography from Agilent Technology (Waldbronn,Germany).

The HPLC system consisted of 1290 Infinity(Agilent Technology) systems equipped with a binarypump, autosampler, thermostatted column compart-ment, and variable wavelength detector. A EclipsePlus C18 column (2.1 100mm, 1.8 lm particle size)supplied by Agilent Technology was used for the sep-aration of BPA. Only 100% of acetonitrile was used asa binary mobile phase. The flow rate and the injectionvolume were 0.3mL/min and 1 lL, respectively.

Under these conditions, the separation time was lessthan 2min. These optimal conditions are shown inTable 1. The samples were injected directly intothe chromatograph, without any previous samplepreparation process.

3. Results and discussion

3.1. Effect of nitrate on the UV alone and UV/H2O2processes to degrade BPA

Fig. 2(a) shows the profiles of the removal of BPAas functions of reaction time in the two UV photolysisoperations, into which any H2O2 was not supplied.However, it was added into the one operation as aninitial NO3 N concentration of 5mg/L, and no NO

3

was added into the other operation. The profilesclearly indicate that BPA was removed by the UVphotolysis without any H2O2 and NO

3 N addition,

and the removal efficiency of BPA gradually increasedas the reaction time increased in this UV photolysisoperation. In the UV photolysis without any H2O2addition, the removal efficiency at a reaction of 30minwas about 42.8% with nitrate addition and about

In-line mixer

Pressure gage

Flowmeter

Samplingport

Pump

Stirrer

Bypass

Level sensor

Influent

Valve

Reactor

Inflow watertank

Pump

H2O2tank

UV lamp

Pl

Coolingwaterinlet Coolingwater

outlet

Pl

Pressure gage

Sampling port

Level sensor

Ozone generatorOzone Injector

Ozone Destructor

Air Vent

Fig. 1. Schematic diagram of the bench-scale AOP system for advanced H2O2 oxidation.

Table 1Operational conditions for HPLC

HPLC (Agilent 1290)

Column Agilent Eclipse PlusC18 (2.1 100mm, 1.8 lm)

Column temperature 35C

Mobile phase 100% acetonitrile

Flow rate 0.3mL/min

Injection volume 1 lL

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29.6% without nitrate addition, respectively. It is quiteinteresting to compare the removal efficiencies in thetwo operations. The removal efficiencies in the reactor,where NO3 was present were higher than those in thereactor where NO3 was absent, and these results wereobserved for the tested operation time. It is possiblydue to the oxidation of BPA by hydroxyl radicals, andNO3 can be attributed to the OH radical productionfrom the NO3 absorption of UV [24], even when noH2O2 dissolved in the solution was present in theoperations. The results indicate that NO3 clearly hasenhanced the removal of BPA through the followingnitrate photolysis [13,19,25]:

NO3 hvH !NO2 OH 1

As shown in Fig. 2(b), BPA was rapidly degradedfor the first 0.5min of UV irradiation with H2O2addition and was completely removed at a reactiontime of 2min with an initial H2O2 concentration of150mg/L, and in the absence nitrate addition. Also,with an initial H2O2 concentration of 300mg/L, andin the absence of nitrate, BPA was completelyremoved at a reaction time of 4min. The results indi-cated that the UV photolysis of H2O2 was a moreeffective method for removing BPA than the directUV photolysis. These results clearly show that H2O2photolysis provides another source of hydroxylradicals, as shown in the given chemical reaction [15].

H2O2 hv! 2OH 2

However, the removal efficiency of the BPA wasabout 87.0% with an initial H2O2 concentration of150mg/L and NO3 N concentration of 5mg/L at areaction time of 2min and about 69.0% at s reaction

time of 4min with an initial H2O2 concentration of300mg/L and NO3 N in the UV/H2O2 operation.The adverse effect of NO3 on the removal of BPAcould clearly be shown under the operating condi-tions. The noticeable scavenging effect of nitrate onthe H2O2 photolysis of BPA was the photolysis ofNO3 produced NO

2 ions, which were accumulated

during the reaction, as mentioned earlier [13,24]. Theobserved removal efficiencies of BPA consequentlydecreased due to the OH-radical scavenging of thephoto-chemically generated NO2 , as shown in thefollowing chemical reactions (see (3), (4)) [15]. NO3was also reported to have caused a significant innerfilter effect that could reduce the fraction of theincident UV absorbed by H2O2, which resulted in asignificant reduction in the efficiency of the UV/H2O2system [13]. It is very interesting that the longer thereaction time is, the larger the scavenging effect is.

NO3 hv! NO2 O 3

NO2 OH!NO2 OH 4

3.2. Effect of initial H2O2 concentration on UV/H2O2process to degrade BPA

The effects of the initial H2O2 concentration on theremoval of BPA are shown in Fig. 3(a). The effects ofthe initial H2O2 concentrations on the removal of BPA(4 105mol/L) investigated at five different H2O2concentrations of 50,100, 150, 200, and 300mg/L, withrespect to two initial NO3 N concentrations of 0 and5mg/L, at a reaction time of 2min. About 60.7and 70.5% of the BPA were removed by UVirradiation without nitrate addition, with initial H2O2concentrations of 50 and 100mg/L, respectively.

Time, min

C/C

0

0.0

0.2

0.4

0.6

0.8

1.0

NO3-

-N: 0 mg/L

NO3-

-N: 5 mg/L

Time, min0 10 20 30 40 50 0 1 2 3 4

C/C

0

0.0

0.2

0.4

0.6

0.8

1.0UV/H2O2 (150 mg/L) + NO3--N (0 mg/L)UV/H2O2 (150 mg/L) + NO3--N (5 mg/L)UV/H2O2 (300 mg/L) + NO3--N (0 mg/L)UV/H2O2 (300 mg/L) + NO3--N (5 mg/L)

(a) (b)

Fig. 2. (a) Profiles of the removal of BPA as a function of time with respect to different initial concentrations of NO3 N;initial concentration of BPA: 4 105mol/L; UV intensity: 20mW/cm2, (a) UV irradiation alone, (b) UV irradiation withinitial H2O2 concentrations of 150 and 300mg/L.

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The complete removal of BPA was achieved with ini-tial H2O2 concentration of 150mg/L in the absence ofnitrate. The enhancement of removal by addition ofH2O2 is due to the increase in the hydroxyl radicalconcentration. At low H2O2 concentration, H2O2cannot generate enough hydroxyl radical and theremoval rate is limited [10]. However, the removalefficiency of BPA decreased with increasing initialH2O2 concentration of more than 150mg/L; theaddition of 150300mg/L H2O2 decreases the removalefficiency from 100 to 75.7% in the same operatingconditions. It was reported that high concentration ofH2O2 could restrain the reaction [26]. At the highH2O2 concentration, H2O2 can act as a free-radicalscavenger [27].

H2O2 OH!HO2 H2O 5

In the presence of nitrate (Fig. 3(b)), the removalefficiencies of BPA by UV irradiation, at the initialH2O2 concentrations of 50, 100, and 150mg/L, were50.8, 55.6, and 87.0%, respectively. In the case of initialH2O2 concentration of 150mg/L, the removal efficien-cies of BPA were lower than previous those obtained.The removal efficiencies of BPA were 65.5 and 57.3%,with nitrate addition, at the initial H2O2 concentra-tions of 150 and 300mg/L, respectively. It is sug-gested that H2O2 act as a free-radicals scavenger atconcentrations above optimum required. The removalefficiencies of BPA in the H2O2 photolysis with nitratewere lower than those without nitrate. The scavengingeffect of nitrate was remarkable in the H2O2 photoly-sis under the tested operating conditions. Also, thelargest difference of the removal efficiency due to thescavenging effect of nitrate was about 20.7% with

initial H2O2 concentration of 200mg/L. The impact ofinitial H2O2 concentration on the removal of BPA hasbeen investigated by varying the initial H2O2 concen-tration from 50 to 300mg/L. The results clearly showthat the practical initial concentration of H2O2 formore than 85% removal turned out to be 150mg/L inthe presence or absence of nitrate.

Fig. 3(b) shows the removal efficiencies (%) of BPAas functions of initial H2O2 concentrations (50, 100,150, and 300mg/L) at four different UV doses of6 102, 12 102, 24 102 , and 36 102mJ/cm2 in thepresence of nitrate. The BPA concentration into theUV/H2O2 system was 4 105mol/L with an averageNO3 N concentration of 5.0mg/L. The highest effi-ciency at the H2O2 concentrations of 150mg/L wasshown at all tested UV doses. It appears becausenitrate reacted least as hydroxyl radical scavenger atthe H2O2 concentrations of 150mg/L under testedconditions. These show that the UV photolysis ofH2O2 was most effective for BPA oxidation with theH2O2 concentration of 150mg/L at the UV dose of36 102mJ/cm2 in the aqueous solution containingnitrate of 5mg/L. It is noted that about 87.7% of BPAwas removed under these operating conditions, evenif the relatively high NO3 N concentration of about5.0mg/L was observed in the influent.

3.3. Effect of initial nitrate concentration on UV/H2O2process to degrade BPA

Fig. 4(a) shows the removal efficiencies (%) of BPAas functions of time at the three different NO3 Nconcentrations (0, 2, and 5mg/L) with UV irradiationand no H2O2 addition. The removal efficiencies of BPAby UV irradiation with nitrate addition were higher

Rem

oval

Effi

cien

cy(%

)

0

20

40

60

80

100 NO3--N : 0mg/LNO3--N : 5 mg/L

UV/H2O2(100)

UV/H2O2(150)

UV/H2O2(200)

UV/H2O2(50)

UV/H2O2(300) H2O2 conc. (mg/L)

Rem

oval

Effi

cien

cy (%

)

0

20

40

60

80

100 6 X 102 mJ/cm2

12 X 102 mJ/cm224 X 102 mJ/cm236 X 102 mJ/cm2

50 100 150 300

(a) (b)

Fig. 3. (a) Profiles of the removal efficiencies (%) of BPA as a function of the initial concentrations of H2O2 with respectto different initial concentration of NO3 N in the bench-scale UV/H2O2 operation; reaction time: 2min; initial concentra-tion of BPA: 4 105mol/L; UV intensity: 20mW/cm2. H2O2 concentration for each treatment is given in parentheses.(b) Removal efficiencies (%) of BPA as functions of initial H2O2 concentrations (50, 100, 150 and 300mg/L) at the four dif-ferent UV doses in the bench-scale UV/H2O2 operation; initial concentration of BPA: 4 105mol/L; UV intensity:20mW/cm2; NO3 N concentration: 5.0mg/L.

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than those without nitrate addition. Nitrate could beattributed to the OH radicals production from thenitrate absorption of UV, in the case of no dissolvedH2O2, as previously discussed above. The removal effi-ciencies rather linearly increased, as the NO3 Nconcentration increased. About 24.7, 38.0, and 40.4% ofthe BPA wereRemoved by UV irradiation withoutH2O2 addition, at a reaction time of 20min, with initialNO3 N concentrations of 0, 2, and 5mg/L, respec-tively. Fig. 4(b), on the other hand, the removal effi-ciencies (%) of BPA as functions of time at the threedifferent NO3 N concentrations (0, 2 and 5mg/L)with UV irradiation and H2O2 addition. The removalefficiencies rather linearly decreased, as the NO3 Nconcentration increased due to the scavenging effect ofnitrate. The removal efficiencies of the BPA were 70.5,60.4, and 55.6% in the H2O2 photolysis, at a reactiontime of 2min, with initial NO3 N concentrations of 0,2, and 5mg/L, respectively. Experiment results fromthis study clearly describe that nitrate ions act asproducers of OH radicals in the UV irradiation andabsence of H2O2; however, as scavengers of OHradicals in the UV photolysis and presence of H2O2.Also, the producing and scavenging effects of nitrateincreased, as the NO3 N concentration increased.

3.4. Effect of initial H2O2 concentration on O3/H2O2process to degrade BPA

Fig. 5 shows the effect of H2O2 concentration onoxidation enhancement for an initial BPA concentra-tion (4 105mol/L) in the O3/H2O2 operation. About55.7 and 62.3% of the BPA were oxidized by O3process only without H2O2 addition, with and withoutnitrate addition, respectively. The removal efficienciesincreased with increasing H2O2 concentration;addition of 0150mg/L increased the removal

efficiencies from 55.7 to 100% and from 62.3 to 78.2%,without and with nitrate addition, respectively. Onereason for this significant increase in the oxidationefficiencies in the O3/H2O2 process is the possibleacceleration of the decomposition of ozone with theaddition of H2O2, as the following chemical reactionssuggest [28,29]:

H2O2 ! HO2 H 6

O3 HO2 !OHO2 O2 7

2O3 H2O2 ! 2OH 3O2 8

It was shown that the conjugate base of H2O2could initiate the composition of ozone much morerapidly into hydroxyl radicals than hydroxide ion.

Time (min)

Rem

oval

Effi

cien

cy (%

)

0

20

40

60

80

100NO3

-

-N: 0 mg/LNO3

-

-N: 2 mg/LNO3

-

-N: 5 mg/L

10 20 30Time (min)

Rem

ov

al E

ffici

ency

(%)

0

20

40

60

80

100NO3

-

-N: 0 mg/LNO3

-

-N: 2 mg/LNO3

-

-N: 5 mg/L

1 2 3

(a) (b)

Fig. 4. Removal efficiencies (%) of BPA as functions of time at the three different NO3 N concentrations (0, 2, and5mg/L) in the bench-scale UV/H2O2 operation; initial concentration of BPA: 4 105mol/L; UV intensity: 20mW/cm2,(a) UV irradiation alone, (b) UV irradiation with initial H2O2 concentration of 100mg/L.

Rem

oval

Effi

cien

cy(%

)

0

20

40

60

80

100 NO3--N : 0mg/LNO3--N : 5 mg/L

O3/H2O2(50)

O3/H2O2(100)

O3/H2O2(150)

O3/H2O2(0)

O3/H2O2(300)

Fig. 5. Profiles of the removal efficiencies (%) of BPA as afunction of the initial concentrations of H2O2 with respectto different initial concentration of NO3 N in the bench-scale O3/H2O2 operation; initial concentration of BPA:4 105mol/L; O3 concentration: 7.5mg/L. H2O2 concen-tration for each treatment is given in parentheses.

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However, further increase in initial H2O2 concentra-tion induced a decrease in removal efficiency. Theremoval efficiency of BPA with the initial H2O2concentration of 300mg/L was 89.9%. It was alsonoted that both ozone and hydrogen peroxide appearto act, at some time, as hydroxyl radical scavengers inan aqueous solution, as shown in the followingreactions [30,31]:

OHO3 !HO2 O2 9

H2O2 OH!HO2 H2O 10

HO2 OH!HO2 OH 11

These reactions consider consumption of OHradical to the formation of less reactive perhydroxylradical HO2.

4. Conclusions

It was found that BPA (4 105mol/L) wasremoved in very limited amounts through the directUV photolysis, without addition oxidation byhydroxyl radicals. However, BPA could completely beremoved with an initial H2O2 concentration of150mg/L in the H2O2 photolysis and absence ofnitrate. It is indicated that the UV photolysis of H2O2is a more effective method for removing BPA than thedirect UV photolysis. The practical reaction time andinitial H2O2 concentration for the more than 85%removal of BPA proved to be 2.0min and 150mg/L,respectively, in the presence or absence of nitrate. Theremoval efficiency of BPA was improved by thehydroxyl radicals produced from nitrate photolysis inthe absence of H2O2.In the presence of H2O2, how-ever, nitrate hindered the BPA removal by acting asOH scavengers under the operating conditionsdescribed above. The removal efficiency of BPA wasclearly hindered with initial H2O2 concentration ofmore than 150mg/L. It is noted that H2O2 acts asfree-radicals scavenger at concentrations aboveoptimum required. In O3/H2O2 process with nitrateaddition, more than 75% of the BPA was removedunder the conditions of an initial O3 concentration of7.5mg/L and H2O2 concentration of more than150mg/L.

These findings suggest that the UV/H2O2 processwould likely be more appropriate method comparedwith O3/H2O2 process for removing BPA in thepresence of nitrate.

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