The Multiple Role of Bromide Ion in PPCPs Degradation under UV

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The multiple role of bromide ion in PPCPs degradation under UV/chlorine treatment Shuangshuang Cheng, Xinran Zhang, Xin Yang, Chii Shang, Weihua Song, Jingyun Fang, and Yanheng Pan Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b03268 • Publication Date (Web): 16 Jan 2018 Downloaded from http://pubs.acs.org on January 16, 2018

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Environmental Science & Technology

ACS Paragon Plus Environment


1

The multiple role of bromide ion in PPCPs degradation under UV/chlorine treatment

2 3

Shuangshuang Cheng1,#, Xinran Zhang1,#, Xin Yang1,*, Chii Shang2, Weihua Song3, Jingyun

4

Fang1, Yanheng Pan1

5 6 7 8

1

9

of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University,

School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory

10

Guangzhou 510275, China

11

2

12

and Technology, Clear Water Bay, Kowloon, Hong Kong

13

3

14

China

Department of Civil and Environmental Engineering, the Hong Kong University of Science

Department of Environmental Science & Engineering, Fudan University, Shanghai 200433,

15

16

# First author

17

*Corresponding author: Tel:+86-2039332690; Email: [email protected] (X. Yang)

18 19 20 21 1


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22

ABSTRACT

23

This study investigated the role of bromide ions in the degradation of nine

24

pharmaceuticals and personal care products (PPCPs) during the UV/chlorine treatment of

25

simulated drinking water containing 2.5 mgC/L natural organic matter (NOM). The kinetics

26

of contributions from UV irradiation and from oxidation by free chlorine, free bromine,

27

hydroxyl radical and reactive halogen species were evaluated. The observed loss rate

28

constants of PPCPs in the presence of 10 µM bromide were 1.6 to 23 times of those observed

29

in the absence of bromide (except for iopromide and ibuprofen). Bromide was shown to play

30

multiple roles in PPCP degradation. It reacts rapidly with free chlorine to produce a trace

31

amount of free bromine, which then contributes to up to 55% of the degradation of some

32

PPCPs during 15 minutes of UV/chlorine treatment. Bromide was also shown to reduce the

33

level of HO• and to change the reactive chlorine species to bromine-containing species, which

34

resulted in decreases in ibuprofen degradation and enhancement in carbamazepine and

35

caffeine degradation, respectively. Reactive halogen species contributed to between 37 and

36

96% of the degradation of the studied PPCPs except ibuprofen in the presence of 10 µM

37

bromide ion. The effect of bromide is non-negligible during the UV/chlorine treatment.

38 39

2



40

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INTRODUCTION Pharmaceuticals and personal care products (PPCPs) have been detected in water sources

41

1-4

42

around the world

. Drinking water treatment primarily relies on adsorptive and oxidative

43

processes to abate dissolved contaminants. Studies have indicated that coagulation,

44

sedimentation, and filtration achieve only minimal removal of PPCPs 5. Free chlorine only

45

selectively reacts with PPCPs bearing phenolic, aniline or amine groups 6. Ultraviolet (UV)

46

light at 254nm photodegrades some PPCPs, but works poorly with UV-resistant PPCPs such

47

as carbamazepine at common disinfection doses (up to 500 mJ cm-2) 7, 8.

48

Advanced oxidation processes (AOPs) are potentially attractive alternatives for removing

49

PPCPs from drinking water 9. Recently the combination of UV irradiation and chlorination

50

(UV/chlorine), one type of AOP, obtained great attention due to the fact that UV/chlorine has

51

exhibited better efficiency in degrading PPCPs than either UV irradiation or chlorination

52

alone

53

upstream of a UV contactor with chlorine contact time varying from seconds to minutes. UV

54

irradiation of free chlorine (HOCl/OCl-) produces highly reactive hydroxyl radicals (HO•) and

55

chlorine radicals (Cl•) 12. Cl• reacts with chloride ion to form dichlorine radicals (Cl2•-) and the

56

reactions of HO• and Cl• with HOCl/OCl- produce oxychlorine radicals (ClO•)

57

presence of HO• and Cl• during UV/chlorine treatment has been directly proved by using

58

electron spin resonance

59

exploring the degradation of reference compounds－benzoic acid and 1,4-dimethoxybenzene

60

14, 15

61

halogen species (RHS, here refers to radicals only) can all degrade PPCPs, but UV irradiation

10, 11

. UV/chlorine application in drinking water can be operated by adding chlorine

13

12

. The

and the existence of Cl2•- and ClO• was indirectly evidenced by

. During the UV/chlorine process, UV irradiation, HOCl/OCl- oxidation, HO• and reactive

3


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62

generally has not contributed significantly to PPCP reduction 8. For chlorine-resistant

63

compounds such as carbamazepine, caffeine, atrazine, DEET, and ibuprofen, HO• and RHS

64

play the dominant roles in their degradation

65

react with electron-rich moieties. The reactivity of RHS with aromatic PPCPs depends on the

66

electron-donating properties of substituents on aromatic ring

67

chlorine adduct formation are reported to be the major mechanisms for chlorine radical

68

reactions

69

aromatic ring) and it can also react with unsaturated compounds to produce Cl adducts (∼106

70

－108 M-1s-1 for double bonds)

71

HO• to yield a hydroxycyclohexadienyl radical with the reaction rate about 1010 M-1s-1 19, 21.

72

Reaction of ClO• with organic compounds is about two or three orders of magnitude slower

73

than that for Cl• 19.

74

16-18

. RHS has been reported to preferentially

15

. Hydrogen abstraction and

19

. Cl2•- can abstract hydrogen slowly from organic compounds (≤107 M-1s-1 on

20

. The addition of Cl• to the benzene ring is similar as that of

In natural waters, bromide is present at concentrations ranging up to tens of µM

22

.

75

The presence of bromide may affect the rate of degradation of PPCPs during UV/chlorine

76

treatment, but this has not been previously investigated. The reaction of bromide with

77

HOCl/OCl- produces free bromine (HOBr/OBr-) (Eq. 1). HOBr is highly reactive towards

78

phenolics and amines

79

phenols

80

17α-ethinylestradiol and benzophenone-3, is considerably faster at bromide concentrations of

81

tens of µgL-1 during chlorination in the dark

82

HO• and Br• and oxybromine radicals (BrO•) can also form (Eq. 2 and 3).

83

than

HOCl

23

, which is about three orders of magnitude more reactive toward 24

.

The

transformation

of

phenolic

compounds,

19, 25-27

including

. The UV irradiation of HOBr generates

HOCl + Br − → HOBr + Cl −

1.6× 103 M-1s-1 4


(1)


84

hv HOBr → HO• + Br •

85

HOBr + HO • → BrO • + H 2O

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(2) 2.0× 109 M-1s-1

(3)

86

Bromide ion is also known to be a HO• scavenger, forming radicals such as BrOH•-, Br•

87

and Br2•- (Eq. 4–7) 28. Meanwhile, bromide also reacts with Cl• and Cl2•- to form ClBr•- (Eq. 8

88

and 9) 29. •

OH + Br − → BrOH • −

1.1× 1010 M-1s-1

(4)

90

BrOH •− + H + → Br • + H 2O

4.4× 1010 M-1s-1

(5)

91

Br • + Br − → Br2

1.2× 1010 M-1s-1

(6)

92

BrOH •− + Br − → Br2•− + OH − 1.9× 108 M-1s-1

(7)

93

Cl • + Br − → BrCl •−

1.2× 1010 M-1s-1

(8)

94

Cl2•− + Br − → BrCl •− + Cl −

4.0× 109 M-1s-1

(9)

89

•−

95

It should be noted that the bromine radicals including BrOH•-, Br•, Br2•- and BrO• have not

96

been directly analyzed by electron spin resonance during UV/chlorine treatment of

97

bromide-containing waters. They are proposed to be present based on the advanced oxidation

98

chemistry involving bromide, which has been extensively studied

99

the mixture of chlorine and bromine radicals in the system, there are no available methods to

100

directly or indirectly obtain their levels currently. Models thus are developed to reflect their

101

steady-state concentrations under varying reaction conditions and they have been used to

102

evaluate UV/hydrogen peroxide, UV/peroxodisulfate and UV/chlorine AOP processes 14, 17, 28,

103

32-34

104

be expected to affect PPCP degradation in the UV/chlorine process. The presence of bromide

105

can either enhance or diminish PPCP degradation and the potential enhancement is a function

28, 30, 31

. Meanwhile, due to

. The above reactions involving bromide can alter the speciation of RHS and would thus

5


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106

of the complex chemistry of the radicals. Increasing bromide concentration has been reported

107

to decrease the degradation rate of phenol during UV/H2O2 treatment. Grebel et al reports that

108

Br2•- accounted for 24% of the phenol destruction while HO• accounted for 75% from model

109

prediction

110

presence of both chloride and bromide due to the dominant formation of ClBr•-, which is

111

highly reactive toward electron-rich moieties 32. Caffeine has been reported to degrade faster

112

in seawater containing both bromide (0.85 mM) and chloride (420 mM) than in fresh water

113

under UV/chlorine treatment

114

directly relevant to UV/chlorine drinking water treatment, but they suggest that bromide must

115

be expected to have great impact on PPCPs degradation during UV/chlorine treatment of

116

drinking water.

33

. The UV/H2O2 degradation of acetaminophen was greatly enhanced in the

17

. Those limited data were obtained under conditions not

117

This study was designed to examine the impact of bromide ions during the UV/chlorine

118

treatment and gain insight into the role of bromide ions in PPCP degradation in this process.

119

The degradation kinetics with and without bromide were evaluated. The contributions to

120

PPCP degradation from UV irradiation and from oxidation by free chlorine (78% HOCl/ 22%

121

OCl- at pH 7.0), free bromine (mainly HOBr at pH 7.0, ∼97%), HO• and RHS were quantified

122

to assess the importance of these reactions and to discover the inherent bromide effects. Nine

123

PPCPs frequently detected in the aqueous environment were tested at a concentration of 500

124

ngL-1 in a 2.5 mgCL-1 natural organic matter (NOM) solution to simulate the feed water in

125

drinking water purification. Two bromide concentrations were tested: 80 µgL-1 (1 µM) and

126

800 µgL-1 (10 µM).

127 6



128

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MATERIALS AND METHODS

129

Chemicals. The nine PPCPs tested were caffeine (CAF), iopromide (IPM), bisphenol-A

130

(BPA), diclofenac (DCF), triclosan (TCS), acetaminophen (ACE), carbamazepine (CBZ),

131

sulfamethoxazole (SMX) and ibuprofen (IBU). All were purchased from Sigma-Aldrich

132

(USA). Their structures and their chemical properties are listed in Table 1. The molar

133

concentrations of the spiked PPCPs are shown in Table S1. An NOM stock solution was

134

prepared by dissolving Suwannee River NOM isolate (Cat. No. 2R101N, International Humic

135

Substances Society) into ultrapure water and filtered by 0.45 µm glass fiber membrane

136

pre-ashed at 500oC. The other chemicals and reagents used are described in the Supporting

137

Information (Text S1).

138

UV/chlorine experiments. Monochromatic UV irradiation at 253.7 nm was applied

139

through an apparatus containing three 10W low-pressure mercury lamps which delivered a

140

quasi-collimated beam. The photo fluence rate at 254 nm received in the reactor was

141

2.24×10-7 E·L-1·s-1 determined according to iodide-iodate chemical actinometry, and the

142

corresponding average UV254 fluence rate was 0.55 mW/cm2

143

diameter was placed directly under the beam.

35

. A cylindrical dish 7 cm in

144

The NOM stock solution was diluted to 2.5 mgL-1 as DOC before each experiment. The

145

stock solutions of the PPCPs were spiked to achieve a concentration of 500 ngL-1 of each

146

tested PPCP (6.32×10-4 µM to 3.31×10-3 µM in molar concentration, Table S1). Bromide was

147

added to some of the samples to achieve a concentration of 1 or 10 µM, as required. All of the

148

samples were buffered to pH 7.0 with 10 mM phosphate buffer. In the UV/chlorine treatment,

149

the chlorine concentration was 70 µM and the accompanied chloride ion addition was 84.5 7


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150

µM. The concentration of chloride ion in NaOCl solution was 84.5 µM. It was determined by

151

subtracting free chlorine concentration from analyzed chloride concentrations in Na2S2O3

152

quenched NaOCl solution. The solution containing NOM, PPCPs and bromide was mixed

153

first. When exposed to the UV light, chlorine was added immediately to the mixing solution

154

and was set as the beginning of the UV/chlorine experiment. UV irradiation alone without

155

free chlorine addition was also tested, as was chlorination at 70 µM in the dark. At different

156

time intervals (0.5-15 min), samples of the mixture being treated were quenched with sodium

157

thiosulfate, followed by solid phase extraction (SPE) for PPCP analysis. The 15-min

158

irradiation corresponded to a fluence of 495 mJ/cm2. The chlorine residuals were recorded in

159

separate tests following these same procedures. In the absence of bromide, the chlorine

160

residuals were analyzed using the DPD ferrous titration method. In the presence of bromide,

161

that same method was used to quantify the total residuals. Bromine residuals were determined

162

by the spectrophotometric phenol red method measuring the absorbance at 592 nm 36. The

163

details are provided in Text S2 in the Supporting Information. Thus, the concentration of free

164

chlorine was obtained by subtracting the bromine concentration from the total residual

165

concentration. The control experiments in the dark were also conducted by dosing 5 mgL-1

166

free chlorine (HOCl/OCl-) or 1 mgL-1 free bromine (HOBr/OBr-) to the NOM solution (2.5

167

mgL-1 as DOC) containing 500 ngL-1 of each PPCP at pH 7.0. The residual free chlorine and

168

bromine concentrations were recorded at different reaction intervals. In order to find the

169

halogenated products, bromide (0, 5, 50, 100 µM), PPCPs (1 mgL-1) and free chlorine (280

170

µM) were spiked or dosed at pH 7.0 at high concentrations compared to the PPCP degradation

171

tests. 8



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172

Determining the rate constants for the PPCPs’ reactions with HOBr. HOBr stock

173

solution was produced by mixing NaOCl with a slight stoichiometric excess of bromide (5%)

174

37

175

at room temperature (23±2°C). The experimental details are provided in Text S3, Table S2

176

and Figure S1 in the Supporting Information.

. The kinetic tests were conducted in the presence of 10 mM phosphate buffer at pH 7.0 and

177

Determining the steady state HO• concentrations. HO• concentrations were inferred

178

indirectly by measuring the depletion of a HO• probe, nitrobenzene (NB). NB (50 nM) was

179

added to the solutions before UV/chlorine treatment. The decay of NB over time was

180

analyzed by HPLC at 265 nm (Dionex U3000). The steady state HO• concentrations were

181

calculated by using Eq. 10.

182

−

d [ NB] = (k HO •, NB [ HO • ]ss + kUV + kvol )[ NB ] = k obs , NB [ NB ] dt

(10)

183

where kHO•,NB is the reaction rate constant between NB and HO•, taken as 3.9 × 109 M-1s-1 14 .

184

kUV and kvol represent the observed first-order rate constants of NB’s disappearance through

185

direct UV photolysis and volatilization, respectively. The details of the tests are presented in

186

Text S4 in the Supporting Information.

187

Modeling of the RHS’ kinetics. Version 5.55 of the Kintecus software was used to

188

model the radical concentration data (Table S4), as the steady-state concentrations of the RHS

189

could not be determined experimentally. Several studies have successfully applied this model

190

to predict the fates of hydroxyl and halogen radicals, confirming good agreements between

191

the modeled results and experimental results

192

constant for the reactions between the RHS and the PPCPs and NOM, the kinetic modeling

193

only considered the reactions involving inorganic components without the incorporation of

32-34, 38, 39

. Because there was no available rate

9


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194

PPCPs and NOM to evaluate the concentrations of inorganic radicals in the initial 5 minutes

195

after the initiation of the reactions. The 5-min scale enables achieving pseudo-steady-state

196

concentrations. It should be noted that many radicals such as BrOH•-, Br•, Br2•- and BrO•

197

haven’t been directly proved during UV/chlorine process. The kinetics model just simply

198

hypothesized based on reactions reported in the literature and the known chemistry of the

199

system

200

radical reactions, but rather as an aid to highlight probable radical reactions. In this study, as

201

NOM, PPCPs and their products may partially scavenge the radicals, this model was merely

202

applied to indirectly reflect the concentrations variance of hydroxyl and reactive halogen

203

radicals in pure solution with/without bromide ions added.

33, 34

-

and the model used here was not intended to provide a means of confirming

204

Calculating the contributions from UV, free chlorine (HOCl/OCl-), free bromine

205

(HOBr/OBr-), HO• and RHS. The degradation of PPCPs during UV/chlorine treatment can

206

involve contributions from UV direct photolysis, oxidation by free chlorine (HOCl/OCl-), HO•

207

and RHS, and free bromine (HOBr/OBr-) oxidation when bromide is present. The degradation

208

of a specific PPCP (expressed as S) can be thus written as in Eq. 11.

209

−

d[S ] = k 'UV [S] + k free chlorine[free chlorine][S] + k free bromine[free bromine][S] + k HO• [HO• ][S] + k RHS[RHS][S] dt (11)

210 211

Where [S] is the concentration of a specific PPCPs; kUV′ is the pseudo–first-order decay

212

rate constant of a PPCP by UV photolysis; kfree chlorine, kfree bromine, kHO•,and kRHS represent the

213

apparent second-order rate constants specific to pH 7 between the PPCP and free chlorine,

214

free bromine, HO• and RHS present, respectively.

215

The remaining concentration of a PPCP ([S]t) at a specific reaction time then can be 10



216

217

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calculated by numerical (stepwise) analysis using Eq. 12. t

t

t

0

0

0

[S]t − [S]0 = − ∫ k 'UV [S]dt − ∫ k free chlorine[free chlorine][S]dt − ∫ k free bromine[free bromine][S]dt t

t

0

0

(12)

− ∫ k HO• [HO• ][S]dt - ∫ k 'RHS[RHS][S]dt 218 219

The removal attributable to each process was calculated separately in Text S5. The fractional removals (R) can thus be expressed as in Eq. 13: t

[S] − [S]t R= 0 = [S]0

∫k 0

' UV

[S]dt

[S]0 t

220

∫k + 0

HO•

t

∫k + 0

[free chlorine][S]dt

free chlorine

[S]0

[HO• ][S]dt [S]0

t

∫k + 0

t

∫k + 0

' RHS

[RHS][S]dt [S]0

[free bromine][S]dt

free bromine

[S]0

(13)

= RUV + R free chlorine + R free bro min e + RHO• + RRHS 221

The contribution percentages attributable from each species hereafter refers to the percentages

222

calculated based on the original concentrations of PPCPs, not the overall removal of PPCPs.

223

Analytical methods. DOC concentrations were measured using a Shimadzu

224

TOC-VCPH analyzer. The SPE procedures followed a revised method proposed by

225

Yang’s group 40 and the details are provided in Text S6 in the Supporting Information.

226

Products analysis is provided in Text S7.

227 228

RESULTS AND DISCUSSION

229

PPCP oxidation kinetics during UV/chlorine treatment. The observed first-order loss

230

rate constants of PPCPs in the absence and presence of 1 and 10 µM bromide at pH 7.0 are

231

shown in Figure 1. The observed loss rate constants in the presence of 1 µM bromide

232

increased by 12 to 210% for majority of the PPCPs except IBU compared to the absence of

233

bromide. This enhancement was enlarged when the bromide concentration increased with

234

exception of IPM and IBU. In the absence of bromide, observed pseudo-first order rate 11


Page 13 of 39


235

coefficients for the PPCPs ranged from 6.1 × 10−4 to 6.6 × 10−2 s−1. IBU, CBZ and CAF had

236

the slowest decay rate constants, which were 5.4 × 10−4, 6.1 × 10−4 and 6.6 × 10−4 s−1,

237

respectively, indicating that they were more resistant compared to other PPCPs. SMX was

238

removed quickly with an observed loss rate constant of 6.6 × 10−2 s−1. SMX features a primary

239

amine that reacts quickly with free chlorine (940 M-1s-1) 6. The other PPCPs, containing either

240

secondary amine (DCF) or a phenolic group (TCS, ACE, BPA), had modest removal rate

241

constants in the range of 10−3 to 10−2 s−1. IPM has iodine and amide groups in its molecule.

242

Iodine can be substituted by a hydroxyl group toward the reaction with HO• 41, 42.

243

In the presence of 10 µM bromide, most of the PPCPs still followed first-order decay

244

kinetics except that CAF, CBZ and IBU had a relatively low correlation coefficient R2

245

(0.88104 M-1s-1).

413

Group II PPCPs have modest to fast overall degradation rates and are primarily degraded

414

by RHS and/or HO• oxidation. They react slowly or not at all with HOCl/OCl- (< 1 M-1s-1)

415

and HOBr. The PPCPs in this group may contain electron rich moieties, but generally weaker

416

electron-donating moieties compared to amine and phenolic moieties. IPM, CAF and CBZ are

417

in Group II.

418

Group III PPCPs have low to modest degradation rates, but they are primary degraded by

419

HO• oxidation. PPCPs in this group do not contain electron-rich moieties. The representative

420

in this study was IBU.

421

Figure 4 illustrates the reaction pathways involved in UV/chlorine treatment when

422

bromide ion is present. The bromide affects the three groups of PPCPs through different

423

reaction mechanisms. Indeed, bromide plays multiple roles. On the one hand, it rapidly reacts

424

with HOCl to produce HOBr. HOBr’s reaction rate constants with primary and secondary

425

amines and phenolic compounds are around one to three orders of magnitude higher than

426

those of HOCl, so a trace amount of bromide in the solution will promote Group I PPCP

427

degradation. On the other hand, bromine radicals form from free bromine photolysis and from

428

bromide’s reaction with HO• and chlorine radicals. The presence of bromide then reduced the

429

levels of HO• and changes the RHS speciation－reducing reactive chlorine species and

430

forming reactive bromine species. The reactive bromine radicals react with electron-rich

431

moieties more selectively than chlorine radicals 45,51, significantly affecting the degradation of

432

Group II PPCPs. Some PPCPs, such as CBZ and CAF, benefit from the presence of reactive 20



Page 22 of 39

433

bromine radicals (e.g. ClBr•- and BrO•). On the contrary, the degradation of some PPCPs, like

434

IPM, was retarded due to the decrease in reactive chlorine radcials. For Group III PPCPs like

435

IBU, the presence of bromide decreased the overall degradation rate due to the decrease in

436

HO• levels.

437

As a result of bromide-involved reactions, brominated transformation products from degradation

were

identified

(Table

S6).

At

a

low

dose

ones

and

438

PPCP

439

of bromide (5 µM), chlorinated products were the

440

brominated products generally contained one bromine atom in their molecules. With

441

increasing bromide concentrations, shifting from chlorinated to brominated products

442

was clearly shown. At a high dose of bromide (50 and 100 µM), brominated products

443

become the dominated ones and the brominated products generally contained one or

444

two bromine atoms. In some products, both chlorine and bromine atoms were present.

445

It should be noted that more chlorinated and brominated products were observed in the

446

presence of UV light (Table S6) than in the absence of UV light (Table S7), which

447

were due to the halogenation reactions from RHS in addition to HOCl/OCl- and

448

HOBr/OBr-. We did not intend to identify of the structures of the transformation

449

products in this study, but further research is needed to improve understanding the

450

formation mechanisms of the brominated products and their associated toxicity.

predominant

451

Environmental implications. Bromide ion is present in water sources at concentrations

452

ranging from ∼10 to >1000 µgL-1 22. It potentially impacts the chemical oxidation treatment of

453

water supplies due to the formation of free bromine and/or reactive bromine radicals. The

454

multiple role of bromide in micropollutant abatement under the UV/chlorine process has been 21


Page 23 of 39


455

demonstrated in this study. Under the UV/chlorine treatment, despite the quenching effect on

456

HO• by bromide and resulting decreases in HO•-driven removal of PPCPs (Group III), faster

457

degradation of many PPCPs (Group I and II) may occur in bromide-rich waters due to free

458

bromine and RHS-mediated reactions. It should be noted that the increase is already

459

significant at 1 µM bromide level. Thus, the bromide effects are expected to be observable for

460

waters with bromide concentrations at sub micromolar or higher levels. This study classified

461

PPCPs into three groups based on their reactive moieties and the contribution of reactive

462

oxidant species. The principles obtained can be applied to predict the degradation

463

performance of other PPCPs in bromide-containing waters under UV/chlorine treatment. This

464

study provides new insights on such reactions and improves the understanding of

465

micropollutant degradation in the UV/chlorine treatment.

466

Although the scope of this study focused on the drinking water treatment, UV/chlorine

467

processes could also be applied for wastewater reclamation or industrial wastewater, where

468

higher amount of bromide will impact the removal efficiency of micropollutants. Future

469

efforts should consider the bromide effects in complicated water matrices and the role of

470

water constituents, such as alkalinity and ammonium N. For example, carbonate can scavenge

471

HO•, Cl•, Cl2•- and BrCl• to form carbonate radicals, which will change the levels and the

472

distribution of the radicals in the UV/chlorine process. The individual contributions from

473

different RHS should also be investigated. Moreover, the transformation byproducts

474

containing bromine can form from the reaction with free bromine and RHS under

475

UV/chlorine conditions in presence of bromide and need further evaluation. Work is on-going

476

in our laboratory to evaluate the yields and risks associated with the formation of these 22



477

Page 24 of 39

byproducts.

478 479

Acknowledgements We thank the National Science Foundation of China (grants 21577178 and 21622706),

480 481

Guangdong’s

Natural

Science

Funds

for

Distinguished

Young

Scholars

(grant

482

2015A030306017), and the Fundamental Research Funds for the Central Universities (grant

483

17lgjc16 and 17lgpy93) for their financial support of this study.

484 485

Supporting information Details of analytical methods and additional figures are included. This material is

486 487

available free of charge via the Internet at http://pubs.acs.org.

488

Information on PPCP and transformation products analysis, bromine reaction rate

489

constants, Kintecus model for radical concentration prediction and etc. (Text S1-S7, Table

490

S1-S6, and Figure S1-S6).

491 492

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665


Table 1. Information on the PPCPs tested.

PPCP

Bisphenol-A (BPA)

pKa

kHO· (109 M-1s-1)

kapp, chlorine pH=7 (M-1s-1)

kapp,bromine pH=7 (M-1s-1) (this study)

9.6, 10.2

6.9 52

62 23

9.4×104

7.9

9.7 53

4.7×102 54

8.6×104

13 56

2.6×104

9.4×102 6

3.0×104

Structure

HO

OH

Cl

OH

Triclosan (TCS)

O

Cl

Cl

H N

Acetaminophen (ACE)

2.2 55

9.71 O

HO

Sulfamethoxazole (SMX)

O NH2

S

O

N

NH

1.69, 5.57

O

5.5±0.7 57

O

Diclofenac (DCF)

Cl

3.89±1.17

OH H N

58

3.8×104

5.9 59

The Multiple Role of Bromide Ion in PPCPs Degradation under UV

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