UV Photolysis of Chloramine and Persulfate for 1,4-dioxane Removal

Subscriber access provided by UNIV OF DURHAM

Remediation and Control Technologies

UV Photolysis of Chloramine and Persulfate for 1,4-dioxane Removal in Reverse Osmosis Permeate for Potable Water Reuse Wei Li, Samuel Patton, Jamie M. Gleason, Stephen Peter Mezyk, Kenneth P Ishida, and Haizhou Liu Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b06042 • Publication Date (Web): 13 Apr 2018 Downloaded from http://pubs.acs.org on April 15, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 35

Environmental Science & Technology

ACS Paragon Plus Environment


1

UV Photolysis of Chloramine and Persulfate for 1,4-dioxane Removal in

2

Reverse Osmosis Permeate for Potable Water Reuse

3

Wei Li,†‡ Samuel Patton,†‡ Jamie M. Gleason,ǁ Stephen P. Mezyk,ǁ

4

Kenneth P. Ishida§ and Haizhou Liu†‡*

5

†

Department of Chemical & Environmental Engineering, University of California, Riverside, CA 92521 USA

6

7

‡

Environmental Toxicology Program, University of California, Riverside, CA 92521 USA §

8

CA 92708 USA

9

10 11

Research & Development Department, Orange County Water District, Fountain Valley,

ǁ

Department of Chemistry and Biochemistry, California State University, Long Beach, CA 90840, USA

12

13

* Corresponding author, phone (951) 827-2076; fax (951) 827-5696

14

Email: [email protected]

15

16

Submitted to Environmental Science & Technology

1


Page 2 of 35

Page 3 of 35


17

Abstract

18

A sequential combination of membrane treatment and UV-based advanced oxidation processes

19

(UV/AOP) has become the industry standard for potable water reuse. Chloramines are used as

20

membrane anti-fouling agents and therefore carried over into the UV/AOP. In addition,

21

persulfate (S2O82-) is an emerging oxidant which can be added into a UV/AOP, thus creating

22

radicals generated from both chloramines and persulfate for water treatment. This study

23

investigated the simultaneous photolysis of S2O82- and monochloramine (NH2Cl) on the

24

removal of 1,4-dioxane (1,4-D) for potable water reuse. The dual oxidant effects of NH2Cl and

25

S2O82- on 1,4-D degradation were examined at various levels of oxidant dosage, chloride, and

26

solution pH. Results showed that a NH2Cl-to-S2O82- molar ratio of 0.1 was optimal, beyond

27

which the scavenging by NH2Cl of HO•, SO4•-, and Cl2•- radicals decreased the 1,4-D

28

degradation rate. At the optimal ratio, the degradation rate of 1,4-D increased linearly with the

29

total oxidant dose up to 6 mM. The combined photolysis of NH2Cl and S2O82- was sensitive to

30

the solution pH, due to a disproportionation of NH2Cl at pH lower than 6 into less photo-

31

reactive dichloramine (NHCl2) and radical scavenging by NH4+. The presence of chloride

32

transformed HO• and SO4•- to Cl2•- that is less reactive with 1,4-D, while the presence of

33

dissolved O2 promoted gaseous nitrogen production. Results from this study suggest that the

34

presence of chloramine can be beneficial to persulfate photolysis in the removal of 1,4-D;

35

however, the treatment efficiency depends on a careful control of an optimal NH2Cl dosage

36

and a minimal chloride residue.

2



37

Introduction

38

Potable water reuse provides a viable solution to water scarcity by treating municipal

39

wastewater.1,2 UV-based advanced oxidation processes (UV/AOPs) have become an integral

40

part of the treatment train to degrade trace organic contaminants.3-9 For example, 1,4-dioxane

41

(1,4-D), a solvent widely used in production of adhesives, dyes, textiles and cosmetics, has

42

been widely detected in wastewater and classified as a potential human carcinogen. 10 - 13

43

Because small and neutral trace organic contaminants like 1,4-D can pass through reverse

44

osmosis (RO) membranes, UV/AOP typically takes place after membrane treatment to

45

ultimately eliminate recalcitrant trace contaminants from RO permeate.

46

Chloramine is often added to the feed water to minimize membrane bio-fouling. Due to their

47

small molecular sizes and neutral charge, chloramines also pass through RO membranes and

48

are carried over to downstream UV/AOP step where they undergo photolysis.14 In addition,

49

hydrogen peroxide (H2O2) is the default oxidant added to the UV/AOP step to produce

50

hydroxyl radicals (HO•). Although possessing a high oxidative capacity, HO• is not selective

51

and can readily be scavenged by bicarbonate and chloride which adversely affects its efficiency.

52

6,15

53

In recent years, persulfate (S2O82-) has also been considered as an alternative oxidant in

54

UV/AOP.6, 16-20 The primary quantum yield of SO4•- from S2O82- is higher than that of HO•

55

from H2O2 (0.7 vs. 0.5), while both SO4•- and HO• have similar oxidizing power (2.5-3.1 V vs.

56

1.9-2.8 V), respectively.

57

contaminants, especially electron-rich contaminants in recycled water.6, 27 , 28 Therefore,

58

UV/S2O82- can potentially have a higher efficiency and a lower energy footprint than UV/H2O2

21 - 26

Furthermore, SO4•- is more selective towards organic

3


Page 4 of 35

Page 5 of 35


59

in water reuse. Given the existence of de facto UV/NH2Cl because of NH2Cl carry-over and

60

the future application of UV/S2O82-, it is important to understand the unique radical generation

61

under photolysis in mixtures of NH2Cl and S2O82-.

62

The mechanism on the simultaneous photolysis of NH2Cl and S2O82- is not well developed.

63

NH2Cl has a relatively high UV molar absorbance coefficient (371 M-1cm-1 at 254 nm) and a

64

quantum yield comparable to H2O2.4,29-31 NH2Cl can also act as a self-scavenger and will

65

decrease its radical yield upon UV irradiation.14 Furthermore, the presence of ammonium in

66

wastewater, and as a photo-degradation product of NH2Cl, may also act as a scavenger for

67

radicals including Cl•.31,32 Most prior studies have examined chloramine photolysis in aquatic

68

conditions unrelated to potable reuse.8,29-31 Our recent study showed that photolysis of NH2Cl

69

in RO permeate produces both HO• and Cl2•- that promote 1,4-D degradation.14 Furthermore,

70

SO4•- produced from S2O82- photolysis can react with NH2Cl to generate secondary radicals,

71

but the extent of radical propagation reactions in RO permeate with the dual oxidants remains

72

unknown.

73

The objectives of this study were to quantify the formation of reactive radicals during the

74

simultaneous photolysis of NH2Cl and S2O82- solutions, to examine the impact of oxidant

75

dosage, pH, and chloride on the degradation of 1,4-D, and to develop a kinetic model to predict

76

the radical yield and transformation of primary radicals (e.g. SO4•- and Cl•) to secondary

77

radicals including Cl2•- and HO•.

78

Materials and Methods

4



Page 6 of 35

79

All chemicals used were reagent grade and purchased from Fisher Scientific or Sigma Aldrich.

80

All solutions were prepared using deionized water (DI) (resistivity < 18.2 MΩ, Millipore

81

System). A fresh 50 mM NH2Cl stock solution was prepared daily by slowly titrating NaOCl

82

with (NH4)2SO4 at 1:1.2 molar ratio and buffered with 4 mM borate at pH 8.8.33 The prepared

83

NH2Cl solution was equilibrated for 3 hours in the dark and its concentration was verified

84

using the standard DPD method with KMnO4.34 An equal-molar chloride residue always co-

85

existed with NH2Cl due to chloramine equilibrium chemistry, which was confirmed by a

86

Dionex-1000 ion chromatography equipped with a conductivity detector.

87

persulfate stock solution was prepared daily using Na2S2O8. Most experiments were conducted

88

using N2-purged water to minimize dissolved O2. In some experiments, DI water was purged

89

with ambient air for 20 minutes to ensure an air-saturated solution. The solution pH was

90

adjusted to a targeted value between 5 to 8 with phosphate buffer, which also maintained the

91

ionic strength constant at 50 mM. Chloride concentration in the mixture was adjusted to a final

92

value between 0.2 and 4 mM.

93

To start a UV experiment, solutions of NH2Cl ranging between 0 and 6 mM and S2O82-

94

between 2 and 4 mM were mixed with 1,4-D at a final concentration of 250 µM. In addition,

95

10 µM benzoic acid (BA) and 20 µM nitrobenzene (NB) were added as radical probe

96

compounds to collectively calculate the radical steady-state concentrations. The concentrations

97

of oxidants and 1,4-D used in this study were higher than those observed in RO permeate in

98

order to observe the reaction kinetics. In the fixed chloride experiments, chloride concentration

99

was adjusted to a final concentration of 4 mM. To examine the effect of NH4+ on Cl• and Cl2•-

100

scavenging, the NH4+ concentration was adjusted between 0 and 6 mM with 100 mM

101

(NH4)2SO4 stock solution. At the same time, chloride concentration was set at 4 mM. The

5


A 100-mM

Page 7 of 35


102

prepared reaction solution was quickly mixed, transferred to multiple 8-mL quartz tubes with

103

no headspace, and placed in a carousel UV reactor (ACE Glass) equipped with a low-pressure

104

monochromatic (λ=254 nm) mercury lamp (Philips TUV6T5, 6W). The UV fluence was

105

measured by a multimeter equipped with a thermopile 919P sensor (Newport Power meter) and

106

determined to be 1.4 mW/cm2.

107

Samples were withdrawn from the UV reactor at pre-determined time intervals. The NH2Cl

108

concentration was measured immediately using the DPD colorimetric method.34 The presence

109

of S2O82- in the sample had no interference with this measurement. The S2O82- concentration

110

was measured using KI titration on a Horiba UV spectrometer after NH2Cl was removed by

111

air-purging the solution for 30 minutes.35,36 The concentrations of 1,4-D, BA and NB were

112

measured by an Agilent 1200 liquid chromatography equipped with a diode array detector and

113

a Zorbax Eclipse SB-C18 column (4.6×150mm, 5-µm particle size). To quantify the generation

114

of nitrogen species during NH2Cl photolysis, total nitrogen (TN) was measured by a TOC

115

analyzer coupled with a nitrogen detector (OI Analytical, Inc.); ammonium, nitrite, and nitrate

116

were measured using colorimetric methods with phenate, sulfanilamide and nicotinamide

117

adenine dinucleotide phosphate, respectively,34 and no interference from persulfate was

118

observed. Gaseous nitrogen formation was calculated based on the loss of TN; the remaining

119

fraction of nitrogen was attributed to organic nitrogen.

120

The steady-state concentrations of SO4•-, HO•, and Cl2•- were calculated based on the

121

competitive decay kinetics of probe compounds (Text S1 and Table S1). All calculations were

122

based on experimentally observed pseudo first-order rates of 1,4-D, BA and NB. The second-

123

order rate constants of each radical with 1,4-D, BA and NB were obtained from the prior

6



124

literature. The direct photolysis of 1,4-D, NB and BA was experimentally determined to be

125

negligible. A kinetics model was developed using the Kintecus software (calculations for direct

126

photolysis rate was presented in Text S2, and all reactions of the model are listed in Table

127

S2). 37 The model development and optimization can be found in Text S3 and prior

128

literature.18,38 Laser flash photolysis studies were conducted to determine the rate constants of

129

SO4•-, Cl• and Cl2•- with NH2Cl and NHCl2 (Text S4 and Figures S1-S3).

130

Results and Discussion

131

Impact of NH2Cl dosage on UV/S2O82-

132

The effect of NH2Cl on 1,4-D degradation by UV photolysis of S2O82- was investigated by

133

fixing the S2O82- and 1,4-D concentrations at 2 mM and 0.25 mM, respectively. The UV

134

fluence-normalized rate constant39-42 of 1,4-D degradation increased from 7.5×10-4 to 9.7×10-4

135

cm2•mJ-1 when the NH2Cl dosage increased from 0 to 0.2 mM; however, the rate decreased to

136

5.3×10-4 cm2•mJ-1 when the NH2Cl dosage was increased further to 4 mM (solid bars in Figure

137

1A and Figure S4A). Photolysis of S2O82- generated SO4•-, which quickly reacted with Cl- to

138

form Cl• (Reactions 1-2 in Scheme 1; all subsequent referred reactions are shown in Scheme 1).

139

Cl• was further transformed into Cl2•- (Reaction 3) and finally resulted in HO• production

140

(Reactions 4-6). Experimental data from competition kinetics with probe compounds and

141

branching ratio calculations showed that HO• contributed the most to 1,4-D degradation in

142

UV/S2O82- and NH2Cl, followed by SO4•- and Cl2•- (Figure 1A and Text S5). Cl2•- was assumed

143

to be the major radical that contributes to 1,4-D degradation other than HO• and SO4•-. This

144

assumption was made based on prior laser flash photolysis study14 and branching ratio

145

calculations (Text S5.4). The laser flash photolysis study revealed a second-order rate constant 7


Page 8 of 35

Page 9 of 35


146

of 3.3×106 M-1s-1 between Cl2•- and 1,4-D (Text S4), and branching ratio calculation indicated

147

that approximately 3-25% of Cl2•- contributed towards 1,4-D (Text S5.4). Because Cl•

148

predominately reacted with Cl- and NH2• had negligible reactivity with 1,4-D,14 Cl• and NH2•

149

were not considered as important to 1,4-D degradation. Experimental results showed that the

150

contribution of HO• reached a maximum at the optimal NH2Cl dosage of 0.2 mM –

151

corresponding to a NH2Cl-to-S2O82- molar ratio of 0.1:1, and decreased by 27% when the

152

NH2Cl dosage increased to 4 mM. The contribution of SO4•- to 1,4-D degradation dropped

153

significantly to negligible levels when the NH2Cl-to-S2O82- ratio increased above 0.1,

154

accompanied by a substantial increase in the contribution of Cl2•- to 1,4-D removal (solid bars

155

in Figure 1A).

156

As the concentration of NH2Cl increased from 0 to 4 mM, UV photons were preferentially

157

absorbed by NH2Cl as compared to S2O82-, which resulted in an increase in the photolysis rate

158

of NH2Cl and a decrease in the photolysis rate of S2O82- (Figure S4B). The percentage of light

159

absorbed by NH2Cl and S2O82- in the mixture system was calculated (Text S6 and Table S7).

160

For instance, in the presence of 0.1 mM NH2Cl, S2O82- absorbed 98% of UV photons if no

161

monochloramine were present, but only 49% of light in the presence of 4 mM NH2Cl.

162

Therefore, the contribution of S2O82- to 1,4-D degradation decreased by 50% with 4 mM

163

NH2Cl addition. Meanwhile, NH2Cl photolysis produced Cl• and NH2• (Reaction 7) that are

164

less reactive with 1,4-D compared to SO4•- and HO•.14 As a result, the rate of 1,4-D

165

degradation was reduced when the concentration of NH2Cl increased from 0.2 to 4 mM (Figure

166

1A). In contrast, an increase in S2O82- dosage in the presence of a constant NH2Cl level always

167

increased radical concentrations (Figure S5).

8



Page 10 of 35

168

In addition, when the NH2Cl-to-S2O82- ratio was higher than 0.1, the experimentally observed

169

1,4-D degradation rate with both oxidants was 10% to 40% lower than the theoretically

170

summed value as if both oxidants existed separately and no radical scavenging by oxidants

171

occurred (striped bars in Figure 1A, calculation provided in Text S6 and Table S7). Compared

172

to theoretical values, the mixing of NH2Cl and S2O82- led to a strong scavenging effect on SO4•-

173

and Cl2•-, especially with higher dosages of NH2Cl. Furthermore, the degradation rate of 1,4-D

174

was positively correlated with the photolysis rate of S2O82-, but inversely correlated with that of

175

NH2Cl (Figure 1B). These trends strongly suggested that in the mixed oxidant system, S2O82-

176

did not strongly scavenge radicals. S2O82- was the driving force for the radical generation and

177

1,4-D removal. In contrast, increasing NH2Cl dose was not beneficial to the treatment, due to

178

the scavenging effects of NH2Cl on major radicals.

179

Radical distribution in UV photolysis of S2O82 and NH2Cl

180

Impacts of NH2Cl on the radical generation and scavenging pathways in UV/S2O82- were

181

elucidated in Scheme 1. When the NH2Cl dosage was increased up to 0.2 mM, [SO4•-]ss

182

decreased by 75%, and [HO•]ss increased by 2-fold (Figure 1C). Since 1,4-D is more reactive

183

with HO• than with SO4•-, the overall degradation rate of 1,4-D was enhanced.43 However, as

184

the NH2Cl concentration increased from 0.2 to 4 mM, both [HO•]ss and [SO4•-]ss decreased

185

substantially, and [Cl2•-]ss increased by 4-fold (Figure 1C). This trend resulted from the

186

scavenging effects of NH2Cl on HO• and SO4•- (Reactions 8-9).

187

In addition, the co-existence of chloride with NH2Cl also transformed SO4•- and Cl• to Cl2•-

188

(Reactions 2-3). HO• reacts with NH2Cl with a rate constant of 5.1×108 M-1s-1, 44 and the

9


Page 11 of 35


189

second-order rate constant between SO4•- and NH2Cl of 2.4 × 107 M-1s-1 was measured by laser

190

flash photolysis (Text S4). For instance, up to 68% of HO• and 7% of SO4•- were scavenged by

191

4 mM NH2Cl (Texts S5.1 and S5.2, Tables S3-S4). Cl• was less affected by the presence of

192

NH2Cl (Text S5.3 and Table S5). Cl2•- was scavenged by NH2Cl (Reaction 10, Text S5.4 and

193

Table S6); however, more Cl2•- was produced with increasing NH2Cl dosage, thus [Cl2•-]ss

194

reached a plateau after NH2Cl reached 2 mM (Figure 1C). As 1,4-D is more reactive with HO•

195

and SO4•- than with Cl2•-, the overall loss rate slowed down significantly at the higher NH2Cl

196

concentrations (solid bars in Figure 1A). Although the concentrations of 1,4-D and oxidants

197

utilized in this study were higher than the concentrations used in the real treatment processes,

198

the calculated steady-state radical concentrations were comparable to those observed in real

199

AOPs (~10-10 and 10-13 M).

200

In addition, the co-existence of chloride with NH2Cl acts as a scavenger to transform SO4•- and

201

Cl• to Cl2•- (Reactions 3-4). To eliminate the confounding effects of chloride, the initial NH2Cl

202

dosage was varied but the chloride level was fixed at 4 mM. These data showed that the 1,4-D

203

degradation rate decreased by 43% with increasing NH2Cl concentrations (Figure S6). This

204

trend further confirmed that scavenging reactions with NH2Cl decreased the radical

205

concentrations (i.e., Reactions 8-10).

206

Products from photolysis of S2O82- and NH2Cl

207

The major products of NH2Cl photolysis were ammonium, nitrate, gaseous nitrogen and

208

organic nitrogen (Figure 2). The formation of ammonium likely resulted from the oxidation of

209

NH2Cl by NH2• (Reaction 11). The NHCl• radical is also formed via HO•, SO4•- and Cl2•-

210

reactions with NH2Cl (Reactions 8-10). Recombination of this radical and its eventual 10



Page 12 of 35

211

oxidation can produce N2 gas (Reactions 12-13). A small amount of nitrate was produced

212

throughout the experiment, possibly due to the reaction between NH2Cl and nitrite or H2O.31,45

213

Organic nitrogen was likely the degradation products from the interaction of NH2• and NHCl•

214

with 1,4-D. 46 - 48 Another possible pathway is that dissolved O2 reacts with NH2• forming

215

intermediate products NH2O2•, which reacted with other radicals such as SO4•-, HO•, and Cl• to

216

form nitrate.40 The formation of NO2• from nitrate photolysis subsequently resulted in the

217

formation of organic nitrogen.49-51

218

In the absence of S2O82-, photolysis converted 60% of NH2Cl to NH4+, 32% to organic nitrogen,

219

3% to gaseous nitrogen and 5% to nitrate, respectively (Figure 2). In contrast, in the presence

220

of S2O82-, NH2Cl photolysis generated more gaseous nitrogen and less organic nitrogen species.

221

SO42-, with a 2:1 stoichiometry, was the only sulfur species observed from S2O82- photolysis

222

(Figure S7). SO4•- directly oxidizes NH2Cl (Reaction 9) and yields N2 gas (Reaction 13). SO4•-

223

could also withdraw elections from NH3 or NH4+ and oxidize them to N2.52 Consequently, the

224

gaseous nitrogen formation almost doubled with the inclusion of S2O82- (Figure 2). The

225

presence of O2 reacted with NH2• and promoted the formation of nitrate and subsequent

226

organic nitrogen. The results suggest that O2 and S2O82- aid in the production of more highly

227

oxidized nitrogen species.

228

Impact of total oxidant dosage on 1,4-dioxane degradation

229

The effect of total oxidant dosage on 1,4-D degradation was examined at two NH2Cl-to-S2O82

230

molar ratios, specifically 0.1:1 and 1:1. The 0.1:1 ratio generally achieved 33% to 240% more

231

1,4-D removal as compared to the 1:1 ratio (Figure 3A). The [SO4•-]ss was approximately 5

232

times higher at the 0.1:1 ratio (Figure 3B), and [HO•]ss was 70% to 300% higher when the total 11


Page 13 of 35


233

oxidant dosage exceeded 4 mM (Figure 3C). At the optimal ratio of 0.1:1, when the total

234

oxidant (i.e., S2O82- and NH2Cl) dosage exceeded 6 mM, major scavenging by S2O82- reduced

235

the [HO•]ss by 15% (Reaction 14, Figure 3C), and consequently 1,4-D degradation rate

236

dropped by 15% (Figure 3A). In contrast, at the NH2Cl-to-S2O82- ratio of 1:1, the 1,4-D

237

removal rate exhibited a bell-shape curve with the maximal rate observed at 4 mM (Figure 3A).

238

At this oxidant ratio, more SO4•- was transformed to Cl2•- that was less reactive with 1,4-D.

239

Despite the conversion of Cl2•- to HO• (Reactions 3-7), the 1:1-ratio generally resulted in

240

higher [Cl2•-]ss concentration and lower [SO4•-]ss compared to 0.1:1-ratio (Figures 3B and 3C).

241

At the NH2Cl-to-S2O82- ratio of 1:1, when the total oxidant dosage exceeded 6 mM, more than

242

90% of HO• was scavenged by NH2Cl and Cl- (Text S5.1), which resulted in a 30% decrease of

243

[HO•]ss (Figure 3D).

244

Impact of chloride on the photolysis of S2O82- and NH2Cl, and 1,4-D removal

245

An increase of chloride concentration from 0.2 to 2 mM slowed 1,4-D degradation by 28%,

246

and preferentially reduced the contribution from HO• (Figure 4A). There was a 40% and 80%

247

reduction in [HO•]ss and [SO4•-]ss, respectively, whereas [Cl2•-]ss increased by 240% (Figure

248

4B). The change of radical distribution was attributable to the chloride-assisted conversion of

249

HO• and SO4•- to Cl2•- (Reactions 3-4). Up to 87% of HO• and 97% of SO4•- were scavenged

250

by 2 mM of chloride (Texts S5.1 and 5.2); however, the ClOH•- quickly dissociated to generate

251

HO• (Reactions 5-7). The presence of 2 mM chloride accelerated the reaction between HO• and

252

Cl- (Reaction 15) and also accelerated the reaction of HClOH• with Cl- (Reaction 16).

253

Approximately 9% of HClOH• was scavenged by 2 mM chloride forming Cl2•- (Text S7).

254

These two reverse reactions led to elevated [Cl2•-]ss and reduced [HO•]ss. 12



Page 14 of 35

255

Impact of pH on the photolysis of S2O82- and NH2Cl, and 1,4-D removal

256

RO permeate is typically acidic due to the application of acids as the scale inhibitors to the feed

257

water. Therefore, it is important to understand the effect of a wider range of pH on the

258

performance of UV/AOP (Figure 5A). The experimental data at the higher pH 8 showed

259

enhanced treatment efficiency. The increase of 1,4-D degradation kinetics from pH 5 to 8 was

260

accompanied by an increase of [HO•]ss and [SO4•-]ss (Figure 5B). The enhancement observed at

261

higher pHs (e.g. pH 7 and 8) was likely due to the increased stability of NH2Cl. NH2Cl

262

disproportionates into NHCl2 at pH 5 via an acid catalyzed reaction, which is further converted

263

to trichloramine (NCl3).53,54 Dark control experiments showed that approximately 36% and 11%

264

of NH2Cl decayed into NHCl2 after 20 minutes at pH 5 and 6, respectively (Figure S8).

265

Furthermore, the disproportionation of NH2Cl also generates NH4+ which scavenges Cl•

266

(Reaction 17).31,32

267

To further test the hypothesis that NH4+ could scavenge reactive chlorine species, additional

268

UV/S2O82- experiments were conducted by varying the NH4+ concentration between 0 and 6

269

mM with a constant chloride concentration of 4 mM. The presence of NH4+ up to 6 mM

270

decreased the 1,4-D degradation by up to 30% (Figure S9). Collectively, the disproportionation

271

of 0.2 mM NH2Cl to 0.14 mM NH4+ scavenged Cl• and Cl2•- (Reactions 17-18), and resulted in

272

approximately 10% decrease of 1,4-D degradation rate at pH 5 compared to pH 8.

273

Environmental Implications

274

The study demonstrated the application of an alternative oxidant, S2O82- in UV/AOP for 1,4-D

275

removal for potable reuse. The findings suggest that UV/S2O82- is an efficient UV/AOP

276

technology that may help the water utility to comply with ever strengthening regulations. 13


Page 15 of 35


277

Specifically, UV/S2O82- can be operated efficiently in the presence of monochloramine, a

278

disinfectant that is widely used in recycled water treatment trains. With careful control of the

279

NH2Cl-to-S2O82- molar ratio at 0.1:1, the overall UV/S2O82- performance is enhanced. However,

280

beyond this optimal ratio, the performance is hindered, because high NH2Cl dosage has a

281

photon filtering effect and also significantly scavenges generated radicals, which decreases the

282

yields of HO• and Cl2•-. In addition, UV/S2O82- decreases the formation of undesirable NH2Cl

283

decay products, ammonium, and organic nitrogen, and promoted gaseous nitrogen production.

284

Although the concentration of chloride is relatively low in RO permeate, its presence may slow

285

down 1,4-D degradation through the transformation of reactive HO• and SO4•- to less reactive

286

Cl2•-. Elevated pH could enhance treatment efficiency. Results from this study elucidate the

287

fundamental mechanisms of radical generation during the unique photolysis of dual oxidants,

288

quantify the effects of incidental presence of NH2Cl on the application of S2O82- in water reuse,

289

and assist in the development of more efficient UV/AOP technologies.

290

Acknowledgment

291

This work was supported by grants to H.L. from the U.S. National Science Foundation (CHE-

292

1611306), and to W.L from the U.S. National Science Foundation Graduate Research

293

Fellowship and UC Riverside IGERT Water Sense Fellowship. We thank Alex Numa from UC

294

Riverside and Guadalupe Lara from La Verne University for participation in this project. Laser

295

flash photolysis studies were conducted at the Notre Dame Radiation Research Laboratory,

296

which is supported by Office of Basic Energy Sciences within the U.S. Department of Energy.

297

Supporting Information Section

14



Page 16 of 35

298

Additional description of monochloramine preparation, calculations of steady-state

299

concentration and branching ratio of reactive radical species, tables of reactions for model

300

development, and figures of 1,4-D first-order decay and oxidant decay, the effect of pH on 1,4-

301

D degradation in UV/S2O82 and UV/NH2Cl are provided in the Supporting Information Section.

15


Page 17 of 35


302 303

Scheme 1 Radical generation and reaction pathways in UV photolysis of persulfate and

304

monochloramine. All reactions are listed in Table 1.

16



305

Page 18 of 35

Table 1 Rate constants and elemental reactions for Scheme 1.

No.

Rate Constant (M-1 s-1)

Reaction ௛ఔ

1 2

Sଶ Oଶି ሮ 2SO∙ି ସ ଼ ሱ ∙ି ି ∙ SOସ + Cl → SOଶି ସ + Cl

3

Cl∙ + Clି → Cl∙ି ଶ ି . Cl∙ି ଶ + Hଶ O → Cl + HClOH

4 5

HClOH . → H ା + ClOH .ି

6

ClOH .ି → Clି + OH ∙

7

NHଶ Cl ሱሮ NHଶ. + Cl∙ NHଶ Cl + OH . → NHCl. + Hଶ O

௛ఔ

8

Reference*

See Text S3

Calculated

3.1×108

55

8.5×109

56

1.3×10

3a

57

1.0×10

8a

57

6.1×10

9a

58

See Text S3

Calculated

5.1×108

59

9

ି . NHଶ Cl + SO∙ି ସ → NHCl + HSOସ

(2.4±0.2)×107

Measured

10

NHଶ Cl + Clଶ∙ି → NHCl. + H ା + 2Clି

(6.5±3.5)×106

Measured

11

NHଶ Cl + NHଶ∙ → NHCl. + NHଷ

(1.0±0.8)×105

Measured

∙ି . ∙ 12 NHCl. + SO∙ି ସ /OH /Clଶ /Cl → Nଶ + Prodcut 13 NHCl. + NHCl. → Nଶ + 2HCl ∙ି . ି 14 Sଶ Oଶି ଼ + OH → Sଶ O଼ + OH

1.0×109 1.0×109

Assumedb Assumedb

1.4×107

60

15

OH ∙ + Clି → ClOH .ି

4.3×109

61

16

HClOH . + Clି → Cl∙ି ଶ + Hଶ O

5.0×109

57

17

NHସା + Cl. → NHଶ. + HCl + H ା

(1.3±0.5)×105

Measured

18

. NHସା + Cl.ି ଶ → NHଶ + HCl + HCl

(1.3±0.5)×105

Measured

19

1,4 − D + Cl∙ି ଶ → product 1,4 − D + SO∙ି ସ → product 1,4 − D + OH . → product

3.3×106

14

4.1×107 3.1×109

62 63

20 21 306

a

rate constants are in unit of s-1

307

b

Rate constants are assumed based on known reactivity of the species with other compounds.

17


Page 19 of 35


308

kNH Cl (x10-6 M•cm2•mJ-1) 2

0

2

4

6

B k1,4-D (x10-4 cm2•mJ-1)

10

8

6 S2O82Persulfate NH2Cl Monochloramine 4 1.6

309

2.0

kS O ( 2

8

2-

2.4 x10-7

M•cm2•mJ-1)

18


2.8


Page 20 of 35

310 311

Figure 1 Impact of NH2Cl dosage on the treatment of 1,4-dioxane by UV/ S2O82-/NH2Cl. (A)

312

Contribution of radicals to 1,-4-dioxane degradation; (B) Correlation between 1,4-D

313

degradation rates and oxidants photolysis rates; (C) Steady-state radical concentrations. [S2O82-

314

]=2 mM, [1,4-dioxane]=250 µM, [Cl-]=0-4 mM, [benzoic acid]=10 µM, [nitrobenzene]=20 µM,

315

pH=5.8. UV dose=2760 mJ•cm-2. Assumption on Cl2•- contribution in Figure 1A was based on

316

the laser flash photolysis study and branching ratio calculations (Text S5.4). Dashed lines in

317

figure 1C represent the modeled results. In Figure A, the theoretical calculations did not

318

considered radical scavenging reaction by NH2Cl (Reactions 8-10 in Table 1).

19


Page 21 of 35


N 2-purged

Air-saturated

Distribution of Nitrogen Products

100%

Organic c Organi nitrogen n nitroge

80%

Gaseous N2 60%

nitrogen

40%

NO3NO3-

20%

NH4+ NH4

0%

319

UV/NH 0 2Cl

UV/S2 O822-+NH2 Cl

UV/NH 0 2Cl

UV/S2 O28 2 +NH2 Cl

320

Figure 2 Impact of persulfate and dissolved oxygen on the distribution of nitrogen products

321

during UV photolysis of NH2Cl. [S2O82-]=0 or 2 mM, [NH2Cl]=2 mM, [Cl-]=2 mM, [1,4-

322

dioxane]=250 µM, pH=5.8, UV dose=2760 mJ•cm-2. Gaseous nitrogen formation was obtained

323

by subtracting the final total nitrogen from the initial total nitrogen, and organic nitrogen was

324

determined as the difference between total nitrogen and other nitrogen species including NH4+,

325

NO3-, gaseous nitrogen and NH2Cl.

20



326

327

21


Page 22 of 35

Page 23 of 35


328

329 330

Figure 3 Impact of zetal oxidant dosage on the treatment of 1,4-dioxane by UV/S2O82/NH2Cl.

331

(A) Effect of total oxidant dosage on 1,4-dioxzne degradation rates; (B-D) Steady-state

332

concentration of SO4•-, HO• and Cl2•-, respectively. [1,4-dioxane]=250 µM, [Cl-]=0-4 mM,

333

[benzoic acid]=10 µM, [nitrobenzene]=20 µM, pH=5.8, UV dose=2760 mJ•cm-2. Assumption

334

on Cl2•- contribution in Figure 3A was based on the laser flash photolysis study and branching

335

ratio calculations (Text S5.4) 22



Page 24 of 35

336

337 338

Figure 4 Impact of chloride on 1,4-dioxane treatment by UV/S2O82-/NH2Cl. (A) Impact of

339

chloride on 1,4-dioxane degradation rate and radical contribution; (B) steady-state

340

concentrations of radicals. [S2O82-z=2 mM, [NH2Cl]=0.2 mM, z1,4-dioxane]= 250 µM,

341

[benzoic acid]=10 µM, [nitrobenzene]=20 µM, pH=5.8. UV dose=2760 mJ•cm-2. Assumption

23


Page 25 of 35


342

on Cl2•- contribution in Figure 4A was based on the laser flash photolysis study and branching

343

ratio calculations (Text S5.4). Dashed lines in Figure B represent the modeled results.

344

345 346

Figure 5 Impact of pH on 1,4-dioxane treatability by UV/S2O82-/NH2Cl. (A) Impact of pH on

347

1,4-dioxane degradation rate and radical contribution; (B) steady-state concentration of radicals.

348

[S2O82-]=2 mM, [NH2Cl]=0.2 mM, [Cl-]=0.2 mM, [1,4-dioxane]=250 µM, [benzoic acid]=10

349

µM, [nitrobenzene]=20 µM. UV dose=2760 mJ•cm-2. Assumption on Cl2•- contribution in 24



Page 26 of 35

350

Figure 5A was based on the laser flash photolysis study and branching ratio calculations (Text

351

S5.4).

Dashed

lines

in

Figure

B

25

represent


the

modeled

results.

Page 27 of 35

352


References

1 National Research Council of the National Academies. Water reuse: potential for expanding the nation’s water supply through reuse of municipal wastewater. The national Academies Press. Washington DC. 2012. 2 Sedlak, D. L. Water 4.0: the past, present, and future of the world’s most vital resource. Yale University Press. New Haven, CT. 2014. 3 Bahnmüller, S.; Loi, C.; Linge, K.; von Gunten, U.; Canonica, S. Degradation rates of benzotriazoles and benzothiazoles under UV-C irradiation and the advanced oxidation process UV/H2O2. Water Research. 2015, 74, 143-154. 4 Watts, M. J.; Linden, K. G. Chlorine photolysis and subsequent OH radical production during UV treatment of chlorinated water. Water Research. 2007, 41 (13), 2871-2878.   5 An, D.; Westerhoff, P.; Zheng, M.; Wu, M.; Yang, Y.; Chiu, C. A. UV-activated persulfate oxidation and regeneration of NOM-Saturated granular activated carbon. Water Research. 2015, 73, 304-310. 6 Yang, Y.; Pignatello, J. J.; Ma, J.; Mitch, W. A. Effect of matrix components on UV/H2O2 and UV/S2O82− advanced oxidation processes for trace organic degradation in reverse osmosis brines from municipal wastewater reuse facilities. Water Research. 2016, 89, 192-200. 7 Remucal, C. K.; Manley, D. Emerging investigators series: the efficacy of chlorine photolysis as an advanced oxidation process for drinking water treatment. Environmental Science: Water Research & Technology. 2016, 2 (4), 565-579.

26



Page 28 of 35

8 Soltermann, F.; Widler, T.; Canonica, S.; von Gunten, U. Photolysis of inorganic chloramine and efficiency of trichloramine abatement by UV treatment of swimming pool water. Water Research. 2014, 56, 280-291. 9 von Sonntag, C. Advanced oxidation processes: mechanistic aspects. Water Science and Technology. 2008, 58 (5), 1015-1021. 10 Mohr, T. K.; Stickney, J. A.; DiGuiseppi, W. H. Environmental investigation and remediation: 1, 4-dioxane and other solvent stabilizers. CRC Press. 2016. 11 Adamson, D. T.; Piña, E. A.; Cartwright, A. E.; Rauch, S.; Anderson, R. H.; Mohr, T.; Connor, J. A. 1,4-Dioxane drinking water occurrence data from the third unregulated contaminant monitoring rule. Science of the Total Environment. 2017, 596-597, 236-245. 12 Zenker, M. J.; Borden, R. C; Barlaz, M. A. Occurrence and treatment of 1,4-dioxane in aqueous environments. Environmental Engineering Science. 2003, 20 (5), 423-432. 13 International Agency for Research on Cancer. IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans, Vol 71. 1999; pp 589-602. 14 Patton, S.; Li, W.; Couch, K.; Mezyk, S.; Ishida, K.; Liu, H. The impact of the UV photolysis of monochloramine on 1,4-dioxane removal: implications on potable water reuse. Environmental Science & Technology Letters. 2017, 4 (1), 26-30. 15 Grebel, J.; Pignatello, J.; Mitch, W. Effect of halide ions and carbonates on organic contaminant degradation by hydroxyl radical-based advanced oxidation processes in saline waters. Environmental Science & Technology. 2010, 44 (17), 6822-6828.   16 Lutze, H. V.; Kerlin, N.; Schmidt, T. C. Sulfate radical-based water treatment in the presence

27


Page 29 of 35


of chloride: formation of chlorate, inter-conversion of sulfate radicals into hydroxyl radicals and influence of bicarbonate. Environmental Science & Technology. 2015, 72, 349-360. 17 Mark, G.; Schuchmann, M. N.; Schuchmann, H. P.; Von Sonntag, C. The photolysis of potassium peroxodisulphate in aqueous solution in the presence of tert-butanol: a simple actinometer for 254 nm radiation. Journal of Photochemistry and Photobiology A: Chemistry. 1990, 55 (2), 157-168. 18 Li, W.; Jain, T.; Ishida, K.; Remucal, C. K.; Liu, H. A mechanistic understanding of the degradation of trace organic contaminants by UV/hydrogen peroxide, UV/persulfate and UV/free chlorine for water reuse. Environmental Science: Water Research & Technology. 2017. 3 (1), 128-138. 19 Yang, Y.; Pignatello, J. J.; Ma, J.; Mitch, W. A. Comparison of halide impacts on the efficiency of contaminant degradation by sulfate and hydroxyl radical-based advanced oxidation processes (AOPs). Environmental Science & Technology. 2014, 48 (4), 2344-2351. 20 Zhang, R.; Sun, P.; Boyer, T. H.; Zhao, L.; Huang, C. H. Degradation of pharmaceuticals and metabolite in synthetic human urine by UV, UV/H2O2, and UV/PDS. Environmental Science & Technology. 2015, 49 (5), 3056-3066. 21 Minisci, F.; Citterio, A.; Giordano, C. Electron-transfer processes: peroxydisulfate, a useful and versatile reagent in organic chemistry. Accounts of Chemical Research. 1983, 16 (1), 27-32. 22 Baxendale, J. H.; Wilson, J. A. The photolysis of hydrogen peroxide at high light intensities. Transactions of the Faraday Society. 1957, 53, 344-356.

28



23 Buxton, G. V.; Greenstock, C. L.; Helman, W. P.; Ross, A. B. Critical review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals (•OH/•O−) in aqueous solution. Journal of Physical and Chemical Reference Data. 1988, 17 (2), 513-886. 24 Neta, P.; Madhavan, V.; Zemel, H.; Fessenden, R. W. Rate constants and mechanism of reaction of sulfate radical anion with aromatic compounds. Journal of the American Chemical Society. 1977, 99 (1), 163-164. 25 Peyton, G. R. The free-radical chemistry of persulfate-based total organic carbon analyzers. Marine Chemistry. 1993, 41 (1-3), 91-103. 26 Yang, Q.; Choi, H.; Chen, Y.; Dionysiou, D. Heterogeneous activation of peroxymonosulfate by supported cobalt catalysts for the degradation of 2,4-dichlorophenol in water: the effect of support cobalt precursor and UV radiation. Applied Catalyst B: Environmental. 2008, 77 (3), 300-307. 27 Fang, G. D.; Dionysiou, D. D.; Wang, Y.; Al-Abed, S. R.; Zhou, D. M. Sulfate radical-based degradation of polychlorinated biphenyls: effects of chloride ion and reaction kinetics. Journal of Hazardous Materials. 2012, 227, 394-401. 28 Qian, Y.; Guo, X.; Zhang, Y.; Peng, Y.; Sun, P.; Huang, C. H.; Niu, J; Zhou, X; Crittenden, J. C. Perfluorooctanoic acid degradation using UV–persulfate process: modeling of the degradation and chlorate formation. Environmental Science & Technology. 2015, 50 (2), 772781. 29 De Laat, J.; Boudiaf, N.; Dossier-Berne, F. Effect of dissolved oxygen on the photodecomposition of monochloramine and dichloramine in aqueous solution by UV irradiation at 253.7 nm. Water Research. 2010, 44 (10), 3261-3269. 29


Page 30 of 35

Page 31 of 35


30 Cooper, W. J.; Jones, A. C.; Whitehead, R. F.; Zika, R. G. Sunlight-induced photochemical decay of oxidants in natural waters: Implications in ballast water treatment. Environmental Science & Technology. 2007, 41 (10), 3728-3733. 31 Li, J.; Blatchley, E. R. UV photodegradation of inorganic chloramines. Environmental Science & Technology. 2008, 43 (1), 60-65. 32 Zhang, X.; Li, W.; Blatchley, E. R.; Wang, X.; Ren, P. UV/chlorine process for ammonia removal and disinfection by-product reduction: comparison with chlorination. Water Research. 2015, 68, 804-811. 33 Choi, J.; Valentine, R. L. Formation of N-nitrosodimethylamine (NDMA) from reaction of monochloramine: a new disinfection by-product. Water Research. 2002. 36 (4), 817-824. 34 American Public Health Association (APHA), Standard Methods for the Examination of Water and Wastewater 18th ed., American Public Health Association: Washington, DC, USA, 1992. 35 Liang, C.; Huang, C. F.; Mohanty, N.; Kurakalva, R. M. A rapid spectrophotometric determination of persulfate anion in ISCO. Chemosphere. 2008, 73 (9), 1540-1543. 36 Holzwarth, G.; Balmer, R. G.; Soni, L. The fate of chlorine and chloramines in cooling towers Henry's law constants for flashoff. Water Research. 1984, 18 (11), 1421-1427. 37 Lanni, J. C., Kintecus, Windows version 4.55. www.kintecus.com. 2012. 38 Li, W.; Orozco, R.; Camargos, N.; Liu, H. Mechanisms on the Impacts of Alkalinity, pH, and Chloride on Persulfate-Based Groundwater Remediation. Environmental Science & Technology. 2017, 51 (7), 3948-3959.

30



39 Lester, Y.; Ferrer, I.; Thurman, E. M.; Linden, K. G. Demonstrating sucralose as a monitor of full-scale UV/AOP treatment of trace organic compounds. Journal of Hazardous Materials. 2014, 280, 104-110. 40 Rosenfeldt, E. J.; Linden, K. G.; Canonica, S.; Von Gunten, U. Comparison of the efficiency of OH radical formation during ozonation and the advanced oxidation processes O3/H2O2 and UV/H2O2. Water Research. 2006, 40 (20), 3695-3704. 41 He, X.; Mezyk, S. P.; Michael, I.; Fatta-Kassinos, D.; Dionysiou, D. D. Degradation kinetics and mechanism of β-lactam antibiotics by the activation of H2O2 and Na2S2O8 under UV254nm irradiation. Journal of Hazardous Materials. 2014, 279, 375-383. 42 Chen, P. J.; Linden, K. G.; Hinton, D. E.; Kashiwada, S.; Rosenfeldt, E. J.; Kullman, S. W. Biological assessment of bisphenol A degradation in water following direct photolysis and UV advanced oxidation. Chemosphere. 2006, 65 (7), 1094-1102.

43 Eibenberger, J. Pulse radiolytic investigations concerning the formation and the oxidation of organic radicals in aqueous solutions. INIS. 1980. 15 (08) 95. 44 Gleason, J. M.; McKay, G.; Ishida, K. P.; Mezyk, S. P. Temperature dependence of hydroxyl radical reactions with chloramine species in aqueous solution. Chemosphere. 2017, 187, 123129. 45 Vikesland, P. J.; Ozekin, K.; Valentine, R. L. Effect of natural organic matter on monochloramine decomposition: pathway elucidation through the use of mass and redox balances. Environmental Science & Technology. 1998, 32 (10), 1409-1416.

31


Page 32 of 35

Page 33 of 35


46 Stefan, M. I.; Bolton, J. R. Mechanism of the degradation of 1, 4-dioxane in dilute aqueous solution using the UV/hydrogen peroxide process. Environmental Science & Technology. 1998, 32 (11), 1588-1595. 47 Farnia, G.; Tomat, R.; Vianello, E. Relative reactivities of aliphatic alcohols and amines towards aminyl radicals. Journal of the Chemical Society, Perkin Transactions. 1975, 2 (7), 763-768. 48 Lisitsyn, Y. A.; Kargin, Y. M. Electrochemical amination of unsaturated and aromatic compounds. Russian Journal of Electrochemistry. 2000, 36 (2), 89-99. 49 Men'kin, V. B.; Makarov, I. E.; Pikaev, A. K. Pulse radiolysis study of reaction rates of OH and O-radicals with ammonia in aqueous solutions. High Energy Chemistry (English Translation. 1989, 22 (5), 333-336. 50 Mack, J.; Bolton, J. R. Photochemistry of nitrite and nitrate in aqueous solution: a review. Journal of Photochemistry and Photobiology A: Chemistry. 1999, 128 (1), 1-13. 51 Ridd, J. H. The range of radical processes in nitration by nitric acid. Chemical Society Reviews. 1991, 20 (2), 149-165. 52 Deng, Y.; Ezyske, C. M. Sulfate radical-advanced oxidation process (SR-AOP) for simultaneous removal of refractory organic contaminants and ammonia in landfill leachate. Water Research. 2011, 45 (18), 6189-6194. 53 Vikesland, P. J.; Ozekin, K.; Valentine, R. L. Monochloramine decay in model and distribution system waters. Water Research. 2001, 35 (7), 1766-1776. 54 Schmalz, C.; Frimmel, F. H.; Zwiener, C. Trichloramine in swimming pools–formation and mass transfer. Water Research. 2011, 45 (8), 2681-2690.

32



55 Chawla, O. P.; Fessenden, R. W. Electron spin resonance and pulse radiolysis studies of some reactions of SO4•-. The Journal of Physical Chemistry. 1975, 79 (24), 2693-2700. 56 Yu, X. Y.; Barker, J. R. Hydrogen peroxide photolysis in acidic aqueous solutions containing chloride ions. I. Chemical mechanism. The Journal of Physical Chemistry A. 2003, 107 (9), 1313-1324. 57 McElroy, W. J. A laser photolysis study of the reaction of SO4- with Cl- and the subsequent decay of Cl2- in aqueous solution. Journal of Physical Chemistry. 1990, 94 (6), 2435-2441. 58 Jayson, G.; Parsons, B.; Swallow, A. J. Some simple, highly reactive, inorganic chlorine derivatives in aqueous solution. Their formation using pulses of radiation and their role in the mechanism of the Fricke dosimeter. Journal of the Chemical Society. Faraday Transaction 1: Physical Chemistry in Condensed Phases. 1973, (69), 1597- 1607.

59 Poskrebyshev, G. A.; Huie, R. E.; Neta, P. Radiolytic reactions of monochloramine in aqueous solutions. The Journal of Physical Chemistry A. 2003, 107 (38), 7423-7428.

60 Buxton, George V.; G. Arthur Salmon; and Nicholas D. Wood. A pulse radiolysis study of the chemistry of oxysulphur radicals in aqueous solution. Physico-Chemical Behaviour of Atmospheric Pollutants. Springer Netherlands. 1990. 245-250. 61 Jayson, G.; Parsons, B.; Swallow, A. J. Some simple, highly reactive, inorganic chlorine derivatives in aqueous solution. Their formation using pulses of radiation and their role in the mechanism of the Fricke dosimeter. Journal of the Chemical Society. Faraday Transaction 1: Physical Chemistry in Condensed Phases. 1973, (69), 1597- 1607.

33


Page 34 of 35

Page 35 of 35


62 Huie, R. E.; Clifton, C. L.; Kafafi, S. A. Rate constants for hydrogen abstraction reactions of the sulfate radical, SO4−: Experimental and theoretical results for cyclic ethers. The Journal of Physical Chemistry. 1991, 95 (23), 9336-9340. 63 Eibenberger, J. Pulse radiolytic investigations concerning the formation and the oxidation of organic radicals in aqueous solutions. INIS. 1980, 15 (08) 95.

34


UV Photolysis of Chloramine and Persulfate for 1,4-dioxane Removal

Recommend Documents