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Remediation and Control Technologies

Organic Pollutant Degradation in Water by VUV/UV/H2O2 Process: Inhibition and Enhancement Roles of H2O2 Mengkai Li, Wentao Li, James R. Bolton, Ernest R. Blatchley, and Zhimin Qiang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b05831 • Publication Date (Web): 14 Dec 2018 Downloaded from http://pubs.acs.org on December 16, 2018

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Environmental Science & Technology

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Organic Pollutant Degradation in Water by VUV/UV/H2O2

3

Process: Inhibition and Enhancement Roles of H2O2

4 5

Mengkai Li,†,‡ Wentao Li,† James R. Bolton,ǁ Ernest R. Blatchley, III,‡,+

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and Zhimin Qiang,†

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†Key

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Environmental Sciences, University of Chinese Academy of Sciences, Chinese Academy

Laboratory of Drinking Water Science and Technology, Research Center for Eco-

10

of Sciences, 18 Shuang-qing Road, Beijing 100085, China.

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‡Lyles

12

United States.

13

+Division

14

Lafayette, Indiana 47907, United States.

15

ǁ

16

AB T6G 1H9, Canada.

School of Civil Engineering, Purdue University, West Lafayette, Indiana 47907,

of Environmental & Ecological Engineering, Purdue University, West

Department of Civil and Environmental Engineering, University of Alberta, Edmonton,

17 18

*Corresponding authors.

19

*Phone: +86 10 62849632; e-mail: [email protected] (Z. Qiang)

20

*Phone: 1-765-494-0316; e-mail: [email protected] (E.R. Blatchley III)

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1

ACS Paragon Plus Environment


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ABSTRACT: A vacuum-ultraviolet/ultraviolet (VUV/UV) mercury lamp was found

23

to be a highly efficient radiation source for UV-based advanced oxidation processes

24

(AOPs).

25

Hence, we have investigated sulfamethazine (SMN) degradation by the VUV/UV/H2O2

26

process based on a bench-scale mini-fluidic VUV/UV photoreaction system (MVPS),

27

a pilot reactor, and a model analysis.

28

degradation rate constant (k′app) increased with increasing H2O2 dose, while at the low

29

[SMN]0, k′app decreased with increasing H2O2 dose; this behavior was unexpected.

30

Meanwhile, at low [SMN]0 in a pilot reactor, H2O2 induced just a slight enhancement

31

in the VUV/UV/H2O process.

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for an integrated AOP (i.e., VUV/UV/H2O2) consisting of various component AOPs,

33

H2O2 could inhibit the component AOPs with HO that did not originate from H2O2

34

(e.g., VUV photolysis of water).

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dependent on the contribution comparison between component AOPs that involved

36

HO that did or did not originate from H2O2.

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information regarding the application of the VUV/UV/H2O2 process in water treatment.

If this lamp could enhance the UV/H2O2 process, it would be very attractive.

At high [SMN]0 in the MVPS, the apparent SMN

A numerical simulation of the process suggested that

The apparent H2O2 role in the integrated AOPs was

These results revealed important

38 39

Key words: vacuum-ultraviolet (VUV); VUV/UV/H2O2; advanced oxidation process;

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organic pollutant; water and wastewater treatment.

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■ INTRODUCTION Advanced oxidation processes (AOPs) that generate hydroxyl radicals (HO)1–3 can

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effectively degrade many recalcitrant organic pollutants.

Because they can be

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promoted with no chemical addition, low byproduct formation and small footprint,

48

ultraviolet-based AOPs (UV-AOPs) are regarded as alternative technologies for

49

organic pollutant removal in drinking water, wastewater and reclaimed water

50

treatments.4–7

51

In recent years, low-pressure (LP) mercury (Hg) vacuum-UV/UV (VUV/UV)

52

lamps have become commercially available, with manufacturing and operational

53

expenses that are similar to those of conventional LP Hg UV lamps.8, 9

54

can generate both VUV and UVC (hereafter referred to as UV) radiation without any

55

additional power input, as compared to conventional (LP) UV lamps.10,11

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the additional HO generated by VUV photolysis of water enhances the degradation of

57

organic pollutants in water.

58

VUV/UV/chlorine process, with a VUV/UV Hg lamp used as the radiation source,

59

showed an obvious synergistic effect for organic pollutant degradation.12

60

the application of VUV/UV lamps as the radiation source in UV-AOPs is attractive for

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water and wastewater treatment.

62

These lamps

As a result,

Moreover, recent research has demonstrated that the

Therefore,

UV/H2O2 is currently the most extensively applied UV-AOP in water treatment, in

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which the quantum yield of HO formation is 1.11 (mole einstein-1).13

64

does not absorb UV radiation at 254 nm (emission peak of a conventional LP Hg lamp) 3


However, H2O2


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efficiently because of its low molar absorption coefficient (ε) at 254 nm (i.e., 19 M–1

66

cm–1)14, which obviously limits the performance of the UV/H2O2 process.

67

VUV (185 nm) radiation is absorbed more efficiently by H2O2 (ε = 341 M–1 cm–1).

68

Meanwhile, VUV photolysis of water could generate additional HO.

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combination of VUV/UV and UV/H2O2 processes (i.e., VUV/UV/H2O2), as an

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integrated AOP, involves several component AOPs (CAOPs) that may work together

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in a synergistic manner.

72

this issue.

73

previous study,15 enables accurate determination of kinetic parameters under VUV/UV

74

and UV irradiation. Hence, the use of the MVPS at bench-scale can facilitate UV-AOP

75

investigations.

In contrast,

Therefore, the

However, so far no study has been carried out to examine

A mini-fluidic VUV/UV photoreaction system (MVPS), developed in a

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Kinetic models, which usually assume a steady-state HO concentration, provide

77

an approach to simulate the participating UV-AOPs.16,17 However, most of these

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models neglect the photon absorption distributions of various components in an

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aqueous solution as well as their variations under different conditions.

80

that for organic pollutant degradation by a VUV/UV photo-Fenton process, both UV

81

and VUV photon absorption distributions varied considerably with increasing pollutant

82

concentration, which changed the principal reaction mechanism from indirect HO

83

oxidation to direct VUV photolysis.18

84

absorption distributions and coupling them into the kinetic model are essential for

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accurate prediction of the performance of UV-AOPs, especially an integrated process

86

such as VUV/UV/H2O2.

It was found

Therefore, accurate calculation of photon

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The goal of this study was to examine organic pollutant degradation in water by an

88

integrated AOP (VUV/UV/H2O2) with both bench-scale (i.e., MVPS) and pilot-scale

89

photoreactors; a kinetic model was developed to simulate the performance of

90

VUV/UV/H2O2 in both photoreactors.

91

antibiotic in aquatic environments,19,20 was selected as a model organic pollutant.

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UV and VUV photon absorption distributions were simulated and coupled to the kinetic

93

model for prediction of SMN degradation.

94

explanation for the unexpected effect of H2O2 dose on SMN degradation as observed

95

in the VUV/UV/H2O2 process.

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■ EXPERIMENTAL SECTION

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Bench-Scale Tests.

Sulfamethazine (SMN), a frequently detected The

The simulation results provided an

The MVPS was utilized in this study as a bench-scale

98

photoreactor (SI Figure S1a), whose construction has been described elsewhere.12

99

Two physically identical straight tubes, a synthetic quartz tube (VUV/UV tube with 65%

100

185 nm transmittance) and a Ti-doped quartz tube (UV tube, opaque to VUV

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irradiation), were mounted near an LP lamp (arc length = 200 mm, Wanhua Co.,

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Zhejiang, China) to receive the VUV/UV and UV exposures, respectively.

103

the VUV/UV and UV tubes were located at the same radial distance to the lamp surface,

104

the UV photon fluence rate (Ep,UV) applied to each tube was identical.

105

VUV photon fluence rate (Ep,VUV) were determined to be 3.07 × 10−4 and 0.27 × 10−4

106

einstein m−2 s−1, respectively, in a previous paper.15

107

between the exposure (VUV/UV or UV) tube and the dark region (i.e., the connecting

Because

The Ep,UV and

The test solution was circulated

5



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108

pipes and solution container) of the MVPS during experimental runs.

109

reduction equivalent exposure time (tree, s) was defined as follows:

tree 

110

 r 2h t V

Hence, a

(1)

111

where r and h are the internal radius (1.20 mm) and length (100 mm) of both VUV/UV

112

and UV tubes, respectively; and t and V are the total experimental time (s) and total

113

sample volume (mm3), respectively.21 In addition, the photon fluences (einstein m–2) of

114

VUV (Fp,VUV) and UV (Fp,UV) were equal to the tree times Ep,VUV and Ep,UV, respectively;

115

and the total photon fluence was the sum of Fp,VUV and Fp,UV. Pilot-Scale Tests.

116

To evaluate the practical performance of the VUV/UV/H2O2

117

process, pilot-scale tests were carried out with an annular stainless-steel VUV/UV

118

photoreactor (inner diameter = 35 mm, inner length = 950 mm), which contained a 105

119

W VUV/UV Hg lamp (Foshan Comwin Co. China, arc length = 780 mm) centered

120

inside a high-purity quartz sleeve (outer diameter = 23 mm), as illustrated in SI Figure

121

S1b.

122

L−1), was stored in a tank and pumped through the pilot photoreactor at various flow

123

rates (Qs, m3 h-1).

124

estimate SMN removal efficiency.

125

Deionized water (DI) water (30 L), spiked with trace SMN ([SMN]0 = 0.05 mg

Influent and effluent samples were collected and analyzed to

Chemicals and Analyses. All chemicals used in this study were of reagent grade

126

or higher.

SMN was obtained from Thermo Fisher Scientific (Fair Lawn, NJ, USA)

127

and dissolved in phosphate buffer (5.0 mM) at pH 7.0.

128

Sigma-Aldrich (St. Louis, MO, USA), whose concentration was measured by the

129

Titanium (IV) oxy-sulfate (TiOSO4, Fluka) method on a UV-vis spectrophotometer 6


H2O2 was purchased from

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(Hach DR6000, USA).22

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the residual H2O2 in the samples.

132

liquid chromatography-tandem mass spectrometry (Agilent Technologies, USA).15

133

All solutions used in the bench-scale tests were prepared with ultrapure water produced

134

from a Milli-Q system (Advantage A10, Millipore, USA) unless otherwise stated, and

135

DI water was used for all pilot tests.

136

■ RESULTS AND DISCUSSION

Horseradish catalase (Sigma-Aldrich) was used to quench SMN was analyzed using ultra-high performance

SMN Degradation by VUV/UV/H2O2.

137

Figure 1 shows the kinetics of SMN

138

degradation by VUV/UV/H2O2 in the MVPS at various H2O2 doses and initial SMN

139

concentrations.

140

degradation rate constant of SMN (k′app) by VUV/UV/H2O2 increased as expected with

141

increasing H2O2 dose.

142

H2O2 exhibited an inhibitory effect, that is, the k′app decreased with increasing H2O2

143

dose, which is inconsistent with the conventional opinion concerning micro-pollutant

144

degradation by UV/H2O2.

145

(i.e., [SMN]0 = 0.10 mg L–1, the same Fp,UV in the UV tube of the MVPS), the k′app in

146

the UV/H2O2 process increased monotonically with increasing H2O2 dose (SI Figure

147

S2).

148

values in the VUV/UV/H2O2 process were obviously higher than those in the UV/H2O2

149

process (e.g., at [H2O2]0 = 0 or 5 mg L–1).

150

unexpected inhibitory effect of H2O2 on low-level SMN degradation through model

151

analysis.

At a high [SMN]0 of 5.0 or 20.0 mg L−1 (Figure 1a or 1b), the apparent

Unexpectedly, in the low [SMN]0 cases (0.05 or 0.10 mg L−1),

For comparison, under the same experimental conditions

Because of additional HO formation from VUV photolysis of water, the k′app

Therefore, it is necessary to unravel this

7



Figure 1

152 153

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UV and VUV Photon Absorption Distributions.

The UV photon absorption

154

fractions of H2O2 (fUV,H2O2) and SMN (fUV,SMN), as well as the VUV photon absorption

155

fractions of water (fVUV,H2O), H2O2 (fVUV,H2O2), and SMN (fVUV,SMN) as a function of H2O2

156

dose were calculated (the method is described in SI Text S1) and are shown in Figure

157

2. These values were used as input for the subsequent kinetic model of the

158

VUV/UV/H2O2 process.

Note that the photon absorptions of the buffer solution are

159

not shown in Figure 2.

Figures 2a and 2b show that UV photons (at 254 nm) were

160

mainly absorbed by H2O2 and SMN for the low [SMN]0 cases.

161

degradation mechanisms involving UV (254 nm) included direct UV photolysis and

162

oxidation by HO generated from the UV/H2O2 process. When the H2O2 dose increased

163

from 0 to 30.0 mg L–1, the fUV,H2O2 increased from 0 to 48% (Figure 2a), while the fUV,SMN

164

decreased from 40% to 15% (Figure 2b).

165

was ineffective (quantum yield ΦUV,SMN = 0.005 mole einstein–1)23, indirect HO

166

oxidation was largely responsible for SMN degradation by UV/H2O2.

167

increasing the H2O2 dose should enhance SMN degradation in the UV/H2O2 process.

168

In the high [SMN]0 cases, the fUV,SMN was higher than 90% (Figure 2b), while the fUV,H2O2

169

was lower than 3% (Figure 2a) regardless of H2O2 dose. Because UV photons were

170

mostly wasted on the inefficient direct UV photolysis process, the variation of H2O2

171

dose had little impact on SMN degradation.

172

So the possible SMN

Because the direct UV photolysis of SMN

Figure 2

8


Therefore,

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Similarly, SMN degradation pertinent to VUV (185 nm) included direct VUV

174

photolysis and indirect oxidation by HO generated from VUV photolysis of H2O2 and

175

H2O.

176

decreased (Figure 2c), while the fVUV,H2O2 increased from 0 to 56% (Figure 2d) at each

177

[SMN]0.

178

(Figure 2e), as compared to the decreasing fVUV,H2O (Figure 2c).

179

SMN and H2O2 competed for VUV photons against H2O, which reduced the SMN

180

degradation efficiency because of the low quantum yield for direct VUV photolysis of

181

SMN (ΦVUV,SMN = 0.005 mole einstein–1) as compared to that for VUV photolysis of

182

water (ΦVUV/H2O = 0.33 mole einstein–1). Furthermore, it is noted that under VUV

183

photolysis, water (55.6 M) rather than H2O2 (00.88 mM) mainly accounted for the

184

HO production because of their large concentration difference.12

185

With the H2O2 dose increasing from 0 to 30.0 mg L–1, the fVUV,H2O gradually

Likewise, as [SMN]0 increased from 0.05 to 20.0 mg L–1, fVUV,SMN increased

Kinetic Model Development.

This implies that both

SMN degradation in the integrated

186

VUV/UV/H2O2 process could be ascribed to the indirect oxidation of HO generated

187

from various CAOPs (i.e., UV photolysis of H2O2 (UV/H2O2), VUV photolysis of H2O2

188

(VUV/H2O2), and VUV photolysis of water (VUV/H2O)) as well as the direct UV and

189

VUV photolysis, as illustrated in Figure 3.

190

Table S1. Figure 3

191 192 193 194

The reactions involved are shown in SI

A mathematical model was developed to simulate SMN degradation kinetics in the VUV/UV/H2O2 process: ' kapp  kd,' UV  kd,' VUV  ki'

(2)

9



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

kd,UV [SMN] 

195

o  UV，SMN qUV f UV,SMN (1  10  al )

(3)

V ( Ep,VUV  Ep,UV ) 

kd,VUV [SMN] 

196

o  VUV，SMN qVUV f VUV,SMN (1  10  al )

(4)

V ( Ep,VUV  Ep,UV ) 

' i

k 

197

kSMN,HO [HO ]ss

(5)

Ep,UV  Ep,VUV

198

where k′d,UV, k′d,VUV and k′i are the photon fluence-based rate constants (m2 einstein-1) of

199

SMN degradation by direct UV photolysis, direct VUV photolysis and indirect HO

200

oxidation, respectively; qUV and qVUV are the incident UV and VUV photon fluxes

201

(einstein s1), respectively; a and l′ are the absorption coefficient (cm–1) of the test

202

solution and the effective path-length (cm) of the photoreactor, respectively; and

203

[HO]ss is the steady-state concentration of HO.

o

o

204

The indirect oxidation of SMN involved all HO generated from the UV/H2O2,

205

VUV/H2O2, and VUV/H2O processes (Figure 3); the steady-state HO concentration

206

was calculated as:

207

[HO ]SS 

rHO ,UV/H



2 O2

 rHO ,VUV/H

2 O2

 rHO ,VUV/H

2O

2

k HO , SMN [SMN]  k HO , H O [H 2 O 2 ]  k HO ,HPO 2 [HPO 4 ]  k HO ,H 2

2

4



2

PO 4

[H 2 PO 4 ]



(6)

208

where rHO,UV/H2O2, rHO,VUV/H2O2 and rHO,UV/H2O are the rate constants of HO generation by

209

UV/H2O2, VUV/H2O2 and VUV/H2O2, respectively (whose expressions are described

210

in SI Text S2).

ki  ki, UV/H '

211 212 213

Eq 6 is equivalent to: '

2 O2

'  ki,VUV/H  ki' ,VUV/H2O 2 O2

(7)

and '

ki, UV/H

2 O2



kSMN,HO rHO ,UV/H O / ( Ep,UV  Ep,VUV ) 2

2

2

k HO , SMN [SMN]  k HO , H O [H 2 O 2 ]  k HO ,HPO 2 [HPO 4 ]  k HO ,H 2

2

4

10




2

PO 4



[H 2 PO 4 ]

(8)

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214


' ki,VUV/H  2 O2

kSMN,HO rHO ,VUV/H O / ( Ep,UV  Ep,VUV ) 2

2

2

215

ki' ,VUV/H2O 

2



k HO , SMN [SMN]  k HO , H O [H 2 O 2 ]  k HO ,HPO 2 [HPO 4 ]  k HO ,H PO  [H 2 PO 4 ] 2

4

2

4

kSMN,HO rHO ,VUV/H O / ( Ep,UV  Ep,VUV ) 2

k HO , SMN [SMN]  k HO , H

2

2 O2

[H 2 O 2 ]  k HO ,HPO 2 [HPO 4 ]  k HO ,H 4



2

(9)

PO 4



[H 2 PO 4 ]

(10)

216

where k′i,UV/H2O2, k′i,VUV/H2O2 and k′i,VUV/H2O are the rate constants of SMN degradation by

217

UV/H2O2, VUV/H2O2 and VUV/H2O, respectively.

218

Comparison between Experimental and Modeled Results.

Figure 4 shows the

219

modeled and measured k′app values as a function of H2O2 dose at various initial SMN

220

concentrations.

221

both high (0.05 and 0.10 mg L–1) and low (5.0 and 20.0 mg L–1) [SMN]0 cases.

222

demonstrates that the kinetic model developed based on the CAOPs could simulate well

223

the SMN degradation kinetics.

224

the unexpected inhibitory effect of H2O2 on low-level SMN degradation in the

225

VUV/UV/H2O2 process.

The modeled k′app values agreed well with the experimental results in This

This model will be used later for further analysis of

Figure 4

226 227

For low [SMN]0 cases, H2O2 dose had little impact on the k′d,UV and k′d,VUV (SI

228

Figure S3a), so its inhibitory effect was mainly ascribed to indirect HO oxidation.

229

Figure 5 shows the variations of k′i,UV/H2O2, k′i,VUV/H2O2 and k′i,VUV/H2O as a function of H2O2

230

dose.

231

VUV/UV/H2O2 at [H2O2]0  10 mg L–1; but with increasing H2O2 dose, k′i,VUV/H2O

232

dropped rapidly (Figure 5a).

233

x 107 M–1 s–1, SI Table S1), as well as its competition for VUV photons (i.e., decreasing

234

fVUV,H2O in Figure 2b) that decreased the rHO,VUV/H2O (Figure 3).

At a low [SMN]0, k′i,VUV/H2O contributed mostly to SMN degradation by

This arose from the HO-quenching feature of H2O2 (2.7

11


Therefore, for the


Page 12 of 27

235

CAOP of VUV/H2O in which HO formation was independent on H2O2, H2O2 could

236

inhibit SMN degradation because of its competition for both HO and photons. Figure 5

237 238

Figure 5a also indicates that the k′i,UV/H2O2 and k′i,VUV/H2O2 increased with increasing

239

H2O2 dose as conventionally expected.

240

for the other two CAOPs), in the positive aspect, an increasing H2O2 dose increased the

241

rate of HO formation (rHO,UV/H2O2 and rHO,VUV/H2O2) by absorbing more photons (Figures

242

2a and 2d, discussed in the above section).

243

dose resulted in a stronger competition of H2O2 for both HO and photons, which

244

slowed the SMN degradation rate (Figure 3).

245

play an inhibitory role in the case of a low HO formation rate (e.g., a low Ep,UV) in

246

either UV/H2O2 or VUV/H2O2 process.

247

For UV/H2O2 and VUV/H2O2 (eqs 11 and 12,

In the negative aspect, an increasing H2O2

Hence, one may suspect that H2O2 could

The model simulations could provide more information.

Eqs 8 and 9 clearly show

248

that for the CAOPs in which HO originated from H2O2 (e.g., UV/H2O2 or VUV/H2O2),

249

an increasing H2O2 dose slowed the increase of k′i,UV/H2O2 (or k′i,VUV/H2O2), but it did not

250

inhibit SMN degradation at either a high or a low HO formation rate.

251

previous studies using a quasi-collimated beam apparatus with an LP mercury lamp

252

installed, which outputted a low level of fluence rate (0.05–0.2 mW cm2), the

253

unexpected inhibitory effect of H2O2 did not appear.24,25

In fact, in

254

The experimental and modeled results indicate that H2O2 could strongly inhibit

255

SMN degradation by the CAOPs in which the HO formation was independent of H2O2

256

(e.g., k′i,VUV/H2O).

On the other side, for the CAOPs in which the HO formation

12


Page 13 of 27


257

depended on H2O2 (e.g., k′i,UV/H2O2, k′i,VUV/H2O2), the HO-quenching effect of H2O2 only

258

slowed the increase of SMN degradation rate constant.

259

VUV/UV/H2O2 process consisted of both types of CAOPs as mentioned above.

260

low [SMN]0, the model analysis indicated that the k′i,VUV/H2O played a dominant role, so

261

H2O2 showed an inhibitory effect on the k′app.

The integrated At a

262

Similarly, for high [SMN]0 cases, with increasing H2O2 dose, the k′i,VUV/H2O, k′d,UV

263

and k′d,VUV decreased slightly, while the k′i,UV/H2O2 and k′i,VUV/H2O2 increased (Figure 5b and

264

SI Figure S3b).

265

for UV and VUV photons against H2O2 and water, which lowered the steady-state HO

266

concentration (eq 9), the k′i values (especially the k′i,VUV/H2O) were much lower than those

267

at a low [SMN]0 (Figure 5b).

268

net balance among the k′d,UV, k′d,VUV and k′i.

269

However, because a high SMN concentration could compete strongly

So, the k′app increased with increasing H2O2 dose, as a

Pilot-Scale tests. The MVPS has different geometrical characteristics from most

270

practical photoreactors.

Hence pilot tests were carried out to examine if the

271

unexpected H2O2 inhibitory effect also occurred in pilot photoreactors. Table 1 shows

272

that with increasing H2O2 dose, the efficiency of SMN degradation increased slightly

273

at both flow rates, indicating that H2O2 was not inhibitory in the VUV/UV/H2O2 process

274

in the pilot tests, as it was in the MVPS.

275

SMN degradation either, as was the case for the conventional UV/H2O2 process (SI

276

Figure S2).

277

pilot photoreactor than those of the MVPS. The pilot photoreactor had a more obvious

278

drop of Ep,VUV with a longer l′ than the MVPS (4.6 mm).

Meanwhile, H2O2 did not obviously enhance

This difference could be ascribed to the larger volume and longer l′ of the

13


This implies that the


Page 14 of 27

279

contributions of the CAOPs to SMN degradation (including k′i,UV/H2O2, k′i,VUV/H2O2,

280

k′i,VUV/H2O) could vary in photoreactors with different sizes (e.g., l′ and volume).

281

Therefore, H2O2 played different roles in the MVPS and the pilot photoreactor.

282

Effect of photoreactor size. To examine the effect of the photoreactor size (i.e.,

283

l′) on k′app, five annular photoreactors with the same reactor length (900 mm) and lamp

284

arc length (800 mm) but different inner diameters (29, 35, 45, 55, and 65 mm) were

285

simulated, whose geometric characteristics are summarized in SI Table S2.

286

important to determine l′, which is a crucial parameter in the kinetic model.

287

applied as an actinometer with different concentrations to measure the l′ of a bench-

288

scale batch photoreactor;15 however, this method is inapplicable for a continuous-flow

289

pilot photoreactor with a larger volume.

290

applied to estimate the l′ based on a commercial software package UVCalc® Version 1

291

(SI Text S3).

292

of 29, 35, 45, 55 and 65 mm were calculated to be 3.8, 7.1, 12.5, 17.9 and 23.3 mm,

293

respectively (SI Table S3).

It is

H2O2 was

Therefore, in this study, a new method was

The l′ values of the five simulated photoreactors with inner diameters

294

By using the parameters in SI Tables S2 and S3, the k′app values for SMN (0.10 mg

295

L–1) were calculated as a function of H2O2 dose in the five simulated photoreactors

296

(Figure 5c).

297

with increasing H2O2 dose, while for other three simulated photoreactors with a longer

298

l′, k′app increased with increasing H2O2 dose.

299

apt to induce the H2O2 inhibitory effect.

300

design, an increase of l′ will result in a reduced contribution of k′i,VUV/H2O, whose HO

For the short l′ photoreactors (e.g., l′ = 3.8 and 7.1 mm), k′app decreased

These results imply that a short l′ was

It is suggested that in practical photoreactor

14


Page 15 of 27


301

was not dependent on H2O2, while increasing the contribution of k′i,UV/H2O2, whose HO

302

was dependent on H2O2.

303

enhance reactor performance.

304

efficiency of VUV photons (about 90% of VUV photons were absorbed by the 6 mm

305

solution layer), an increase in l′ could induce higher absorption of UV photons by the

306

solution (i.e., UV/H2O2) and reduce the number of UV photons incident on the

307

photoreactor wall, thereby increasing the SMN degradation efficiency.

308

This information could inform H2O2 addition strategies to In other words, in keeping with the absorption

Discussion on Potential Applications.

In the conventional view, H2O2 can

309

enhance many oxidation processes.

However, this study indicates that the

310

VUV/UV/H2O2 process does not always yield synergistic enhancement of pollutant

311

degradation as has been observed with the VUV/UV/chlorine process, whose combined

312

efficiency was higher than the sum of those of two individual AOPs (i.e., VUV/UV and

313

UV/chlorine).12,20

314

VUV/UV/H2O2) was complex, and it may strongly inhibit the CAOPs in which HO

315

was not dependent on H2O2.

316

simulate the CAOPs that generate HO dependent or independent of H2O2, and

317

determine the apparent role of H2O2 in the VUV/UV/H2O2 process. This approach has

318

the potential to optimize the photoreactor design for pollutant removal in the

319

VUV/UV/H2O2 process by adjusting the l′.

320

also explain why few studies have reported synergistic enhancement on micro-pollutant

321

degradation through the combined application of UV/H2O2 with other AOPs, such as

322

UV/chlorine and UV/persulfate.

Moreover, the H2O2 role in an integrated AOP (e.g.,

The kinetic model described herein can effectively

In addition, the results of this study may

15



323

■ ASSOCIATED CONTENT

324

Supporting Information

325

The Supporting Information is available free of charge on the ACS Publications website

326

at DOI:

327

(Table S1) Kinetic parameters for reactions involved in this study; (Table S2)

328

physical characteristics of five simulated photoreactors; (Table S3) sum of FRs at

329

the inner wall and calculated effective path-length of each simulated photoreactor;

330

(Text S1) calculation of photon absorption distribution; (Text S2) calculation of

331

rHO,UV/H2O2, rHO,VUV/H2O2 and rHO,VUV/H2O; (Text S3) calculation of effective path-

332

length; (Figure S1) schematic diagrams of the mini-fluidic VUV/UV photoreaction

333

system (MVPS) and the pilot VUV/UV photoreactor; (Figure S2) SMN

334

degradation by UV/H2O2 as a function of photon fluence; (Figure S3) modeled

335

SMN degradation rates by UV (k′d,UV) and VUV (k′d,VUV) direct photolysis as a

336

function of H2O2 dose.

337

■ AUTHOR INFORMATION

338

Corresponding Authors

339

*Phone: +86 10 62849632; e-mail: [email protected] (Z. Qiang).

340

*Phone:

341

Notes

342

The authors declare no competing financial interest.

343

■ ACKNOWLEDGEMENTS

1-765-494-0316; e-mail: [email protected] (E.R. Blatchley III)

16


Page 16 of 27

Page 17 of 27


344

This work was financially supported by the National Natural Science Foundation of

345

China (51878653, 21590814, 51525806), the Youth Innovation Promotion Association

346

of Chinese Academy of Sciences, and the Edward M. Curtis Visiting Professorship of

347

Purdue University.

348

■ REFERENCES

349

(1)

Mestankova, H.; Schirmer, K.; Canonica, S.; von Gunten, U., Development of

350

mutagenicity during degradation of N-nitrosamines by advanced oxidation processes.

351

Water Res. 2014, 66, 399−410.

352

(2)

Lee, Y.; Kovalova, L.; McArdell, C. S.; von Gunten, U., Prediction of

353

micropollutant elimination during ozonation of a hospital wastewater effluent. Water

354

Res. 2014, 64, 134−148.

355

(3)

Wang, C.; Klamerth, N.; Messele, S. A.; Singh, A.; Belosevic, M.; El-Din, M.

356

G., Comparison of UV/hydrogen peroxide, potassium ferrate (VI), and ozone in

357

oxidizing the organic fraction of oil sands process-affected water (OSPW). Water Res.

358

2016, 100, 476−485.

359

(4)

Lester, Y.; Ferrer, I.; Thurman, E. M.; Linden, K. G., Demonstrating sucralose

360

as a monitor of full-scale UV/AOP treatment of trace organic compounds. J. Hazard.

361

Mater. 2014, 280, 104−110.

362

(5)

Lester, Y.; Sharpless, C. M.; Mamane, H.; Linden, K. G., Production of photo-

363

oxidants by dissolved organic matter during UV water treatment. Environ. Sci. Technol.

364

2013, 47 (20), 11726−11733.

365

(6)

Kong, X. J.; Jiang, J.; Ma, J.; Yang, Y.; Liu, W. L.; Liu, Y. L., Degradation of 17



366

atrazine by UV/chlorine: Efficiency, influencing factors, and products. Water Res. 2016,

367

90, 15−23.

368

(7)

Guo, M. T.; Yuan, Q. B.; Yang, J., Distinguishing effects of ultraviolet

369

exposure and chlorination on the horizontal transfer of antibiotic resistance genes in

370

municipal wastewater. Environ. Sci. Technol. 2015, 49 (9), 5771−5778.

371

(8)

Xie, P.; Yue, S.; Ding, J.; Wan, Y.; Li, X.; Ma, J.; Wang, Z., Degradation of

372

organic pollutants by Vacuum-Ultraviolet (VUV): Kinetic model and efficiency. Water

373

Res. 2018, 133, 69−78.

374

(9)

Crapulli, F.; Santoro, D.; Sasges, M. R.; Ray, A. K., Mechanistic modeling of

375

vacuum UV advanced oxidation process in an annular photoreactor. Water Res. 2014,

376

64, 209−225.

377 378 379 380 381

(10)

Zoschke, K.; Bornick, H.; Worch, E., Vacuum-UV radiation at 185 nm in

water treatment - A review. Water Res. 2014, 52, 131−145. (11)

Imoberdorf, G.; Mohseni, M., Degradation of natural organic matter in surface

water using vacuum-UV irradiation. J. Hazard. Mater. 2011, 186 (1), 240−246. (12)

Li, M. K.; Qiang, Z. M.; Hou, P.; Bolton, J. R.; Qu, J. H.; Li, P.; Wang, C.,

382

VUV/UV/chlorine as an enhanced advanced oxidation process for organic pollutant

383

removal from water: Assessment with a novel mini-fluidic VUV/UV photoreaction

384

system (MVPS). Environ. Sci. Technol. 2016, 50 (11), 5849−5856.

385

(13)

Goldstein, S.; Aschengrau, D.; Diamant, Y.; Rabani, J., Photolysis of aqueous

386

H2O2: Quantum yield and applications for polychromatic UV actinometry in

387

photoreactors. Environ. Sci. Technol. 2007, 41 (21), 7486−7490.

18


Page 18 of 27

Page 19 of 27

388


(14)

Wang, D.; Bolton, J. R.; Hofmann, R., Medium pressure UV combined with

389

chlorine advanced oxidation for trichloroethylene destruction in a model water. Water

390

Res. 2012, 46 (15), 4677−4686.

391

(15)

Li, M. K.; Wang, C.; Yau, M. L.; Bolton, J. R.; Qiang, Z. M., Sulfamethazine

392

degradation in water by the VUV/UV process: Kinetics, mechanism and antibacterial

393

activity determination based on a mini-fluidic VUV/UV photoreaction system. Water

394

Res. 2017, 108, 348−355.

395

(16)

Rosenfeldt, E. J.; Linden, K. G., The R-OH, R-UV concept to characterize and

396

the model UV/H2O2 process in natural waters. Environ. Sci. Technol. 2007, 41 (7),

397

2548−2553.

398

(17)

Keen, O. S.; McKay, G.; Mezyk, S. P.; Linden, K. G.; Rosario-Ortiz, F. L.,

399

Identifying the factors that influence the reactivity of effluent organic matter with

400

hydroxyl radicals. Water Res. 2014, 50, 408−419.

401

(18)

Wen, D.; Wu, Z. D.; Tang, Y. B.; Li, M. K.; Qiang, Z. M., Accelerated

402

degradation of sulfamethazine in water by VUV/UV photo-Fenton process: Impact of

403

sulfamethazine concentration on reaction mechanism. J. Hazard. Mater. 2018, 344,

404

1181−1187.

405

(19)

Bu, Q. W.; Wang, B.; Huang, J.; Deng, S. B.; Yu, G., Pharmaceuticals and

406

personal care products in the aquatic environment in China: A review. J. Hazard. Mater.

407

2013, 262, 189−211.

408 409

(20)

Li, M. K; Hao, M. Y.; Yang, L.; Yao, H.; Bolton, J. R.; Blatchley, E. R.; Qiang,

Z. M. Trace organic pollutant removal by VUV/UV/chlorine process: Feasibility

19



410

investigation for drinking water treatment on a mini-fluidic VUV/UV photoreaction

411

system and a pilot photoreactor. Environ. Sci. Technol. 2018, 41 (7), 2548−2553.

412

(21)

Li, M. K.; Qiang, Z. M.; Bolton, J. R.; Qu, J. H.; Li, W. T., A mini-fluidic UV

413

photoreaction system for bench-scale photochemical studies. Environ. Sci. Tech. Lett.

414

2015, 2 (10), 297−301.

415

(22)

Eaton, A. D.; Franson, M. A. H.; American Public Health Association,

416

Standard methods for the examination of water and wastewater. 19th ed.; American

417

Public Health Association: Washington, DC, 1995.

418

(23)

Lian, J. F.; Qiang, Z. M.; Li, M. K.; Bolton, J. R.; Qu, J. H., UV photolysis

419

kinetics of sulfonamides in aqueous solution based on optimized fluence quantification.

420

Water Res. 2015, 75, 43−50.

421

(24)

Wols, B. A.; Harmsen, D. J. H.; Wanders-Dijk, J.; Beerendonk, E. F.; Hofman-

422

Caris, C. H. M., Degradation of pharmaceuticals in UV (LP)/H2O2 reactors simulated

423

by means of kinetic modeling and computational fluid dynamics (CFD). Water Res.

424

2015, 75, 11−24.

425 426

(25)

Wu, C.; Linden, K. G., Degradation and byproduct formation of parathion in

aqueous solutions by UV and UV/H2O2 treatment. Water Res. 2008, 42, 4780−4790.

20


Page 20 of 27

Page 21 of 27


Submission to Environ. Sci. Technol.

by Li et al.

Table 1. SMN (0.10 mg L−1) Degradation by VUV/UV/H2O2 in the Pilot Photoreactor at Two Different Flow Rates (Qs). ln([SMN]0/[SMN])

H2O2 dose (mg L–1)

Q = 3.0 m3 h–1

Q = 1.0 m3 h–1

0

2.95 ± 0.03

5.06 ± 0.05

2.5

3.18 ± 0.04

5.17 ± 0.03

5.0

3.26 ± 0.03

5.64 ± 0.29

10.0

3.44 ± 0.01

6.11 ± 0.08

21 ACS Paragon Plus Environment


Page 22 of 27


by Li et al.

[H2O2] 0 (mg L-1) 0.0

0

ln([SMN]/[SMN]0)

5.0

25.0

0.0

(a)

(b)

-0.4

-0.2

-0.8

Unit of m2 einstein-1 k'app = 39.6 k'app = 39.9 k'app = 52.7 k'app = 92.5

-0.4 -0.6

0.50

0

2

-1.2

4

6

0

0

-3

-3

-6

-6 Unit of m2 einstein-1 k'app = 5315 k'app = 4387 k'app = 2978 k'app = 2153

-12

0.0

0.5

1.0

1.5

1

2

3

0

(c)

-9

Unit of m2 einstein-1 k'app = 222.0 k'app = 275.6 k'app = 310.5 k'app = 390.4

-9 -12 2.0

(d)

Unit of m2 einstein-1 k'app = 7443 k'app = 5004 k'app = 3297 k'app = 2453

0.0

0.5

1.0

1.5

2.0

Total photon fluence ( x 103 einstein m-2)

Figure 1 SMN degradation by VUV/UV/H2O2 at pH 7.0 in MVPS as a function of total photon fluence at [SMN]0 = 20.0 mg L–1 (a); 5.0 mg L–1 (b); 0.10 mg L–1 (c); and 0.05 mg L–1 (d).


Page 23 of 27



by Li et al.

100

-1

f VUV,H2O (%)

[SMN]0 (mg L ) 0.05 0.10 5.0 20.0

50 25 0

50 25 0

0

100

f UV,SMN (%)

f VUV, H2O2 (%)

75

10

20

-1

H2O2 dose (mg L )

30

50 25 0 10

20

-1

H2O2 dose (mg L )

30

10

20

10

20

-1

H2O2 dose (mg L )

30

(d)

75 50 25 0

0

-1

30

H2O2 dose (mg L )

100

(b) 75

0

0

100

(a)

f VUV, SMN (%)

f UV,H2O2 (%)

100

(c)

75

(e)

75 50 25 0 0

10

20

-1

30

H2O2 dose (mg L )

Figure 2 UV (254 nm) photon absorptions of H2O2 (a) and SMN (b) as well as VUV (185 nm) photon absorptions of H2O (c), H2O2 (d) and SMN (e) as a function of H2O2 dose in the VUV/UV/H2O2 process. The photon absorption of buffer solution is not shown here.




Page 24 of 27

by Li et al.

Figure 3 Schematic diagram of SMN degradation kinetics by VUV/UV/H2O2.


Page 25 of 27



-1

Modeled and measured k'app, [SMN]0 = 0.05 mg L -1 Modeled and measured k'app, [SMN]0 = 0.10 mg L -1 Modeled and measured k'app, [SMN]0 = 5.0 mg L -1 Modeled and measured k'app, [SMN]0 = 20.0 mg L

8000

6000

4000

2

-1

k ' app (m einstein )

by Li et al.

2000

0 0

5

10

15

20

25

30

-1

H2O2 dose (mg L )

Figure 4 Measured (symbols) and modeled (curves) SMN degradation rate constants as a function of H2O2 dose in the VUV/UV/H2O2 process. Each symbol represents the linear regression of six experimental data points (R2 > 99%).



Page 26 of 27


by Li et al.

k'app (m2 einstein-1)

k' (m2 einstein-1)

k' (m2 einstein-1)

8000 6000

k'i,UV/H2O2

k'i,VUV/H2O2

k'i,VUV/H2O

(a)

k'i,UV/H2O2

k'i,VUV/H2O2

k'i,VUV/H2O

(b)

4000 2000 0 100 80 60 40 20 0 2000

Photoreactors with diameters of (mm): 29 35 45 55

1600

(c) 65

1200 800 400 0

0

5

10

15

20

25

30

H2O2 dose (mg L-1)

Figure 5 Modeled rate constants of SMN degradation by various component AOPs in the MVPS at [SMN]0 = 0.10 mg L–1 (a) and 20.0 mg L–1 (b), as well as modeled k′app in five simulated photoreactors at [SMN]0 = 0.10 mg L–1 (c) in the VUV/UV/H2O2 process.


Page 27 of 27



H2O2 Process

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