H2O2 process: Kinetic

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Remediation and Control Technologies

Micro-pollutant degradation by the UV/H2O2 process: Kinetic comparison of photoreaction degradation among various radiation sources Mengkai Li, Wentao Li, Dong Wen, James R. Bolton, Ernest R. Blatchley, and Zhimin Qiang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b06557 • Publication Date (Web): 28 Mar 2019 Downloaded from http://pubs.acs.org on March 30, 2019

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Page 1 of 33

Environmental Science & Technology

Submission to Environ. Sci. Technol.

by Li et al.

1 2

Micro-pollutant degradation by the UV/H2O2 process: Kinetic comparison of

3

photoreaction degradation among various radiation sources

4 5

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

6

and Zhimin Qiang,†

7 8

†Key

9

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

11

‡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)

21

1

ACS Paragon Plus Environment


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by Li et al.

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ABSTRACT: Kinetic comparisons of micro-pollutant degradation by ultraviolet

23

(UV) based advanced oxidation processes among various radiation sources are an

24

important issue, yet this is still a challenge at present.

25

comparatively the kinetics of sulfamethazine (SMN) degradation by the UV/H2O2

26

process among three representative radiation sources, including low-pressure mercury

27

UV (LPUV, monochromatic), medium-pressure mercury UV (MPUV, polychromatic),

28

and vacuum UV(VUV)/UV (dual wavelengths causing different reaction mechanisms)

29

lamps.

30

photoreaction system and a previously developed mini-fluidic VUV/UV photoreaction

31

system.

32

SMN degradation rate constant (k′p) followed a descending order of: VUV/UV/H2O2 >

33

MPUV/H2O2 (200300 nm) > LPUV/H2O2, and the k′p of the MPUV lamp was

34

dependent on the wavelength range selected for photon fluence calculation.

35

of potential errors revealed that a shorter effective path-length could have a lower error,

36

and the maximum errors for the MPUV/H2O2 and LPUV/H2O2 processes in this study

37

were 7.4% and 18.2%, respectively.

38

kinetic comparisons of micro-pollutant degradation by UV-AOPs among various

39

radiation sources at bench-scale, which provides useful reference to practical

40

applications.

This study investigated

Experiments were conducted with a newly developed mini-fluidic MPUV

Measured and modeled results both indicate that the photon fluence-based

Analysis

This study has developed a new method for

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by Li et al.

■ INTRODUCTION

42

In past decades, ultraviolet (UV) based advanced oxidation processes (i.e., UV-

43

AOPs) have attracted considerable attention related to their potential for organic

44

pollutant transformation in drinking water, wastewater, and reclaimed water

45

treatment.1-3

46

mechanisms of various emerging pollutants by various UV-AOPs, which demonstrate

47

that UV-AOPs can efficiently degrade most refractive pollutants in water.4-7

48

of the source of UV radiation is critical not only to photoreactor design, in that lamp

49

selection will determine the radiation wavelengths that are available to drive reactions,

50

but to the long-term stable operation as well.

51

Many studies have investigated the degradation kinetics and

Several commercial UV radiation sources are available for UV-AOPs.

Selection

The low-

52

pressure (LP) lamp is characterized by nearly monochromatic emission at 254 nm

53

(LPUV), as well as merits of high photoelectric efficiency and low manufacturing cost.

54

At present, the highest nominal power of an LP lamp (LP amalgam lamp) has reached

55

about 1 kW.

56

electrical parameters, an additional emission line at 185 nm, which is in the vacuum

57

UV (VUV) range, can be output by LP lamps.

58

VUV/UV source.8

59

oxidation.9

60

254 nm) irradiation can lead to a synergistic enhancement effect in UV-AOPs.9,10

61

Hence, VUV/UV is regarded as an emerging high-efficiency radiation source.

62

addition, medium-pressure (MP) mercury lamps are common in commercial UV water

By employing high-purity silica as the LP lamp envelope and appropriate

LP lamps of this type represent a viable

The VUV photolysis of water generates HO for pollutant

Meanwhile, recent studies have found that dual wavelength (i.e., 185 and

3


In



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by Li et al.

63

treatment systems.

They are characterized by compact construction (small footprint),

64

high output power, and a broad UV emission spectrum from 200−400 nm (a spectrum

65

of a representative MPUV is shown in SI Figure S1).

66

efficiency in the critical UV region (200–300 nm) and a short lifetime (about 5000 h)

67

may constrain their applications.

However, low photoelectric

68

Defining an appropriate lamp for a practical UV-AOP application requires

69

integrated consideration of multiple aspects, including kinetics, photoelectric efficiency,

70

lifetime, and stability in long-term operation.

71

based kinetics among various radiation sources by bench-scale tests and model

72

simulations is a critical step, and it should account for the degradation performance by

73

a given UV-AOP under the same exposed photon fluence emitted by various lamps.

74

Note that because the UV photon fluence delivered in various photoreactors is different,

75

time-based kinetics of a photoreaction (unit of reaction rate constant: s−1) cannot be

76

compared among laboratories.11,

77

reaction rate constant: m2 einstein−1) should be used in studies of UV disinfection and

78

UV-AOPs.

12

The comparison of photon fluence-

Hence photon fluence-based kinetics (unit of

79

Kinetic comparisons among various radiation sources represent a significant

80

challenge; most previous research has compared the kinetics of microorganism

81

inactivation and pollutant degradation with a quasi-collimated beam apparatus (qCBA),

82

usually based on LPUV and MPUV lamps.13-15

83

cannot employ a VUV/UV lamp because of its low VUV transmittance in air and the

84

long distance between the lamp and the sample.

However, a conventional qCBA

Moreover, for (photon fluence-based)

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by Li et al.

85

kinetic comparisons among various radiation sources, accurate photon fluence

86

determination is critically important.

87

(PFR) is measured by a radiometer at the center of the solution surface, and several

88

correction factors (e.g., Petri factor, water factor, divergence factor, etc.) are necessary

89

to sequentially calculate the average PFR (PFRave) for the photon fluence calculation.16

90

However, for a polychromatic lamp (e.g., MPUV lamp), non-uniform responses at each

91

wavelength of a radiometer will induce errors.

92

factors required to consider all wavelengths could introduce associated errors.

93

In a qCBA apparatus, the photon fluence rate

Moreover, the multiple correction

Another approach is to use a batch photoreactor that can involve LP, MP, or

94

VUV/UV lamps.

The photon fluence can be determined using an actinometer, such

95

as atrazine or uridine,17,18 whose absorption spectra are shown in SI Figure S1.

96

in photon fluence estimation for LPUV or MPUV lamps are evident in this approach,

97

which are mainly ascribed to: 1) simplifications associated with the Taylor series

98

expansion of the volumetric rate of photon absorption in assessment of photochemical

99

kinetics, 2) difference between the estimated photon fluence by an actinometer and the

100

actual photon fluence in a water sample, and 3) changes in the actual PFR over the

101

reaction course.

Errors

102

Different types of mini-fluidic photoreaction systems, including the mini-fluidic

103

UV photoreaction system19 and the mini-fluidic VUV/UV photoreaction system

104

(MVPS)9 have been developed recently for accurate photoreaction experiments.

105

These systems enable accurate estimation of VUV (185 nm) and UV (254 nm, i.e.,

5



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106

LPUV) photon fluences by using an actinometer, which can facilitate kinetic

107

comparisons among various photoreactions.

108

This study proposed a new method for comparison of the kinetics of micro-

109

pollutant degradation by the UV/H2O2 process (the most commonly used UV-AOP for

110

water and wastewater treatment) among LPUV, MPUV, and VUV/UV lamps.

111

Experimental tests employing an MVPS and a newly developed mini-fluidic MPUV

112

photoreaction system (MMPS), as well as model analysis were carried out.

113

Sulfamethazine (SMN), one of the most frequently detected antibiotics in the

114

environment, was used as a representative micro-pollutant.20,21

115

determination of photon fluences and kinetic parameters under exposure of MPUV (in

116

MMPS) and LPUV (in MVPS) were examined as a means of explaining differences in

117

kinetics observed among these systems.

118

kinetic comparisons among three types of UV lamps for micro-pollutant degradation

119

by a UV-AOP, and it helps select a suitable radiation source for water and wastewater

120

treatment.

121

■ EXPERIMENTAL SECTION

122

Moreover, errors in

This study provides a feasible method for

Photoreactors for Kinetic Determination in UV-AOPs.

The MVPS,

123

incorporating an 8 W LP lamp (Wanhua Co., Zhejiang, China), was utilized in the

124

LPUV and VUV/UV photoreactors in this study (Figure 1).

125

described its construction in detail.9,22

126

and a straight Ti-doped quartz tube (LPUV tube) (each 2.40 mm inner diameter and

127

100 mm length) were placed at 3.0 mm from the LP lamp surface for VUV/UV and

Previous studies have

A straight synthetic quartz tube (VUV/UV tube)

6


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by Li et al.

128

LPUV exposures, respectively.

129

was installed with an MP lamp (500 W, arc length = 100 mm, Foshan Comwin,

130

Guangdong, China).

131

100 mm length) was placed at 3.0 mm from the MP lamp surface for MPUV exposure.

132

Figure 1

133

To obtain an MPUV exposure, an MMPS (Figure 1)

A straight quartz tube (MPUV tube, 2.40 mm inner diameter and

Water samples were collected from the solution container at various experimental

134

times (t, s), so that a range of exposure photon fluences could be obtained.

135

equivalent exposure time (tree, s) was defined as t multiplied by the ratio of the exposure

136

volume of the quartz tube (πr2h, m3) to the total sample volume (V, m3).13

137

photon fluences (einstein m–2) for VUV (Fp,VUV, only 185 nm), VUV/UV (Fp,VUV/UV),

138

LPUV (Fp,LPUV) and MPUV (Fp,MPUV) were calculated as follows:19,22

 r 2h

A reduction

Hence, the

139

tree 

140

Fp, VUV  Ep,0 VUV tree

(2)

141

Fp,VUV/UV  Fp, LPUV  Fp,VUV

(3)

142

Fp, LPUV  Ep,0 LPUV tree

(4)

143

Fp, MPUV  Ep,0 MPUV tree

(5)

V

(1)

t

144

where r and h are the internal radius (1.2 mm) and length (100 mm) of the sample tubes,

145

respectively; and Ep, LPUV , Ep, MPUV and Ep,VUV are the PFRs (einstein m2 s1) in the

146

LPUV (or VUV/UV), MPUV and VUV/UV tubes, respectively.

147

0

0

0

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

148

or higher.

Ultrapure water produced from a Milli-Q system (Advantage A10,

149

Millipore, USA) was used for all solution preparations. 7


SMN was purchased from


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by Li et al.

150

Thermo Fisher Scientific (Fair Lawn, NJ, USA) and dissolved in water buffered with

151

phosphate (5.0 mM, pH 7.0).

152

performance liquid chromatography-tandem mass spectrometry (detailed information

153

is described in SI Text S1).

154

the titanium (IV) oxy-sulfate (TiOSO4, Fluka) method.

155

was quenched by using horseradish catalase (Sigma-Aldrich).

156

Aldrich) was used as an actinometer for photon fluence measurements, whose

157

concentration was analyzed by measuring its absorbance at 262 nm with a Hach

158

DR6000 spectrophotometer.

SMN concentration was analyzed by ultra-high-

H2O2 concentration (Sigma-Aldrich) was determined by The residual H2O2 in samples Uridine (Sigma-

159

Radiation Model. A radiation field (PFR distribution) model (UVCalc® version

160

1, Bolton Photosciences Inc., Edmonton, Alberta, Canada) was chosen to simulate the

161

PFR distributions at various wavelengths and UV transmittances (UVTs).23

162

research has shown good agreement between UVCalc® predictions and experimental

163

measurements in various UV reactors.24-26

164

Photon Absorption Distribution.

Previous

Photon absorption distribution and its

165

variation during the treatment process can strongly impact the kinetic results.27,28

166

Hence, for an accurate simulation, the photon absorption distributions of LPUV (254

167

nm), VUV (185 nm), and each wavelength of the MPUV were calculated (eq 6) and

168

then coupled into the kinetic model.

169

f i,λ 

 i,λ Ci l  i

 i 1

170

i,λ

(6)

 100

Ci l 

where fi,λ and εi,λ are the photon absorption fraction (%) and molar absorption coefficient

8


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171

(cm‒1 M‒1, shown in SI Table S1) of each solution component (i) at a specific

172

wavelength (λ, nm), respectively; and Ci and l′ are the molar concentration (M) of i and

173

effective path-length (cm), respectively.

174

Kinetic Model Simulations for Various Radiation Sources. Kinetic models for

175

the UV/H2O2 process with various lamps were developed, whose principal reactions,

176

rate constants, and parameters are described in SI Table S2.

177

fluence-based) SMN degradation rate constant (k′p) by UV/H2O2 includes the direct

178

photolysis rate constant (k′d,) at the wavelength  and the indirect oxidation (i.e., via

179

HO) rate constant:

180

k p  k d, λ  '

k

The apparent (photon

g

SMN,HO

g

[HO ]ss

(7)

0

Ep

181

where kSMN,HO, [HO]ss, and Ep0 are the second-order reaction rate constant between

182

SMN and HO, steady-state HO concentration, and PFR, respectively.

183

and VUV/UV lamps, their corresponding degradation rate constants (k′p,LPUV and

184

k′p,VUV/UV) can be described as:

For the LPUV

g

185

 k

k

' p,LPUV

k

' p,VUV/UV

' d, λ=254 nm



kSMN,HO [HO ]ss g

(8)

0

Ep,LPUV g

186

 k

' d, λ=254 nm

k

' d, λ=185 nm



kSMN,HO [HO ]ss g

0

Ep,VUV/UV

(9)

187

For the MPUV lamp with emission wavelengths ranging from m to n, the degradation

188

rate constant (k′p,MPUV) is:

189

190

k p,MPUV  '

n

  

m

k d,λ  '

kSMN,HOg [HO

g

]ss

(10)

0 p,MPUV

E

The rate constant k′d, can be expressed as：

9



Page 10 of 33


191

  kd,λ

by Li et al.

 SMN qλo fSMN,λ (1  10 aλl  )

(11)

VEp [SMN]

192

where ΦSMN is the quantum yield of SMN photolysis; and qo, fSMN, and a are the

193

photon flux, photon absorption fraction of SMN, and absorption coefficient of the

194

solution at the wavelength , respectively.

195

(al) < 0.02, a Taylor series expansion can be used to simplify eq 11 with minimal error:

196

197 198

  kd,λ

For circumstances involving absorbance

ln(10) SMN qλo SMN,λ l '

(12)

VEp

For the experimental conditions applied in this study, [HO]ss was estimated as: [HO ]SS 

rHOg

g

2

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

4

2



2

PO 4



[H 2 PO 4 ]

(13)

199

where rHO is the HO formation rate.

200

formation rates were calculated (shown in SI Text S2) and the simplified expressions

201

after Taylor series approximations are shown in eqs 14 and 15:

202

rHO ,LPUV/H O  2

203

2

o  LPUV,H2O2 [H 2 O 2 ]l  ln(10) H 2O2 qLPUV

V

2

rHO ,MPUV/H O  2

For the LPUV and MPUV lamps, their HO

ln(10) H 2O2 l [H 2 O 2 ] V



n =m

qλo λ,H 2O2

(14) (15)

204

where ΦH2O2 is the quantum yield of HO formation with UV/H2O2, which was assumed

205

to be 1.11 mole einstein−1 for the entire wavelength range considered in this study.

206

Eqs 14 and 15 clearly show that the difference in rHO between the LPUV and MPUV

207

lamps was attributable to the incident UV photon flux (i.e., q0) and the solute molar

208

absorption coefficient (i.e., εH2O2,).

209

(rHO,VUV/UV/H2O2) should be the sum of those of the LPUV photolysis of H2O2

For the VUV/UV lamp, its HO formation rate

10


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210

(rHO,LPUV/H2O2), VUV photolysis of H2O2 (rHO,VUV/H2O2), and VUV photolysis of water

211

(rHO,VUV/ H2O); details of this calculation are presented in SI Text S2.

212

213 214

rHOg,VUV/UV/H O  rHOg,LPUV/H O  rHOg,VUV/H O  rHOg,VUV/H O 2

2

2

2

2

2

(16)

2

■ RESULTS AND DISCUSSION Photon Fluence Determination.

The uridine actinometer was used for

215

measurement of the photon fluences, Fp,LPUV and Fp,MPUV.

216

actinometer could facilitate comparisons among the photon fluences of different

217

radiation sources.

218

in the LPUV and MPUV tubes.

219

both LPUV and MPUV could be well expressed by the pseudo-first-order kinetics, with

220

photolysis rate constants (ku) of 1.81  10−4 and 1.51  10−4 s–1, respectively.

221

Therefore, the Fp,LPUV and Fp,MPUV can be determined as follows:

222

Fp,LPUV 

223

Fp,MPUV 

Use of the same

Figure 2 shows the logarithmic decay of uridine as a function of tree The fit lines indicate that the photolysis of uridine by

10ku t 2.303 u  λ

(17)

10 k u t 2.303 u



n  =m

(18)

 λ pλ

224

where pλ and Φu are the relative output ratio at the wavelength  (given in SI Figure S1)

225

and the quantum yield of uridine photolysis, respectively.

226

reported to be 0.020 mole einstein−1 (independent of wavelength).17

227

integrated ε was calculated to be 6620 M−1 cm−1 (for the wavelength range of 200−300

228

nm, SI Table S3), implying that uridine could absorb photons from the LPUV lamp

229

(εLPUV,H2O2 = 8742 M−1 cm−1) 17 more efficiently than those from the MPUV lamp.

11


The value of Φu has been In this study, the

For



Page 12 of 33

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230

the VUV/UV lamp, the determination of Fp,VUV/UV was described in SI Text S3 by using

231

the zero-order degradation rate constant of methanol (i.e., 1.07  10−4 mM min−1).9 Figure 2

232 233

Kinetic Comparison of Micro-pollutant Degradation by UV/H2O2 among

234

Various Radiation Sources.

Figure 3 compares the degradation kinetics of SMN

235

([SMN]0 = 0.10 mg L−1) by UV/H2O2 with the LPUV, VUV/UV and MPUV lamps at

236

various H2O2 doses.

237

order kinetics.

238

comparison of SMN degradation among the three lamps indicated clearly a descending

239

order of the k′p: k′p,VUV/UV > k′p,MPUV > k′p,LPUV at all H2O2 doses.

240

demonstrate that by using the MVPS and MMPS, as well as uridine and methanol as

241

the actinometers, the kinetic comparison of SMN degradation by UV/H2O2 among

242

various radiation sources is feasible, which provides useful reference to practical

243

applications.

All SMN degradation processes were well fitted by pseudo-first-

With an accurate determination of photon fluences, a kinetic

Figure 3

244 245

The results

Without H2O2, the k′p,MPUV (169 m2 einstein–1) was considerably larger than k′p,LPUV

246

(7.6 m2 einstein–1).

247

direct UV photolysis at each λ (i.e., Φ = 0.005, SI Table S2), the low-wavelength

248

photons (200−240 nm) from the MPUV lamp were absorbed more effectively by SMN,

249

thus inducing a higher k′p,MPUV.

250

increased, because an increasing H2O2 dose led to a higher rHO for the indirect HO

251

oxidation of SMN.

Despite the fact that SMN has the same low quantum yield for

With increasing H2O2 dose, both k′p,MPUV and k′p,LPUV

For the VUV/UV/H2O2 process, the VUV photolysis of water and

12


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252

H2O2 could both produce HO, thus enhancing SMN degradation as compared to the

253

LPUV/H2O2 and MPUV/H2O2 processes.

254

produced from the VUV/UV/H2O2 process, but also compete for UV and VUV photons

255

against SMN.

256

which has been explained in a previous study.29

257

Yet H2O2 could not only scavenge HO

Hence, the k′p,LPUV decreased gradually with increasing H2O2 dose,

Comparison between Measured and Modeled Rate Constants.

Figure 4

258

compares the measured and modeled rate constants of SMN ([SMN]0 = 0.10 mg L−1)

259

degradation by UV/H2O2 among various radiation sources as a function of H2O2 dose.

260

The results indicate that with increasing H2O2 dose, both k′p,LPUV and k′p,MPUV increased

261

gradually, while k′p,VUV/UV decreased rapidly, which agrees with the experimental

262

results.

263

increase in the rHO,LPUV/H2O2 and rHO,MPUV/H2O2 for the indirect HO oxidation of SMN.

264

In the H2O2 dose range of 0−30 mg L−1, both the measured and modeled k′p showed a

265

descending order of: k′p,VUV/UV > k′p,MPUV > k′p,LPUV.

Eqs 14 and 15 indicate that an increasing H2O2 dose can lead to a similar

Figure 4

266 267

Effect of MPUV Wavelength Range on Kinetic Determination.

Because of

268

the polychromatic emission feature of the MPUV lamp, the wavelength range selected

269

for the photon fluence calculation in the MMPS will inevitably influence the

270

determination of photon fluence-based rate constants.

271

determination, as mentioned above, adopted a common MPUV/H2O2 wavelength range

272

(i.e., m−n = 200−300 nm).

273

range for H2O2 absorption is 200−280 nm.

The photon fluence

For the UV/H2O2 process, the most effective wavelength Also, for other UV/AOPs (e.g.,

13




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by Li et al.

274

UV/chlorine) whose oxidants have a wider absorption wavelength range (typically

275

200−400 nm), a wider UV wavelength range should be selected for this calculation.

276

In addition, some European researchers have selected the 233−325 nm range for special

277

control of NO2−.30

278

By using the following eq 19, the integrated molar absorption coefficient of uridine

279

(εu) and the PFRave in the MPUV wavelength ranges of 200−300, 200−350 and 200−400

280

nm were calculated individually, as summarized in SI Table S3.

  q      q n

281



m -n

=

o λ

m

n

=

m

(19)

H 2 O2 ， λ o λ

282

It can be seen that for the MPUV lamp, a wider wavelength range induced a lower

283

integrated εu and a higher PFRave.

284

molar absorption coefficient in the 300−400 nm range than in 200−300 nm range.

285

Moreover, a wider wavelength range contains more photons, hence raising the photon

286

fluence.

This is reasonable because uridine has a lower

287

Figure 5 compares the kinetics of SMN degradation by UV/H2O2 among the LPUV,

288

VUV/UV, and MPUV (200−300, 200−350, and 200−400 nm) lamps at an H2O2 dose

289

of 5.0 mg L−1.

290

selected, showing a descending order of: MPUV/H2O2 (200−300 nm) > MPUV/H2O2

291

(200−350 nm) > MPUV/H2O2 (200−400 nm).

292

doses applied (SI Figure S2).

293

efficiently absorbed by H2O2, while other photons are essentially useless in the

294

MPUV/H2O2 process, despite the fact that they are included in the photon fluence

295

calculation.

The k′p,MPUV values were different for different wavelength ranges

The same trend was found for all H2O2

This is because only 200−280 nm photons can be

Therefore, with the same effective absorption of photons, a wider 14


Page 15 of 33



by Li et al.

296

wavelength range led to a lower apparent (photon fluence-based) rate constant of SMN

297

degradation.

298

200−350 nm, the k′p,MPUV was higher than the k′p,LPUV.

299

was found if using the MPUV wavelength range of 200−400 nm.

300

that when carrying out a kinetic comparison among various radiation sources involving

301

a polychromatic UV lamp, it is necessary to define the specific wavelength range

302

responsible for photoreactions of interest.

303

In addition, if using the MPUV wavelength ranges of 200−300 and However, an opposite trend The results imply

Discussion of Potential Errors: Impact of Effective Path-length (l′) on Taylor

304

Series Approximation.

As introduced above, by using the MVPS and MMPS,

305

kinetic comparisons of micro-pollutant degradation by UV-AOPs among the three

306

lamps are feasible.

307

kinetic determinations so as to assess the reliability of the comparisons.

308

errors of the kinetic determinations for the LPUV and MPUV lamps by using uridine

309

actinometer were from the simplifications by Taylor series approximation, PFRave

310

difference between the actinometer and an actual water sample, and PFRave variation

311

during the reaction process.

312

incident VUV photons were absorbed by water during the photon fluence determination

313

(SI Table S3) and SMN degradation processes.

314

the VUV photon fluence than the LPUV and MPUV photon fluences, and the errors

315

aforementioned will not be involved in the k′p,VUV/UV.

Hence, it is relevant to consider the errors associated with the The principal

Because of a high VUV absorbance of water, nearly all

As a result, it is easier to determine

316

The error induced from the simplifications by Taylor series approximation (i.e.,

317

2.303al′/(1-10-al′)) was involved in the photon fluence determination by using the

15




Page 16 of 33

by Li et al.

318

uridine (0.012 mM) actinometer, as well as the kinetic parameter (i.e., k′d,UV and rHO)

319

determination in the solution containing SMN and H2O2.

320

the value of al′ is less than 0.02, the error is nearly equal to 1 (i.e., negligible).

321

study, the errors for both the photon fluence (i.e., using uridine) and kinetic parameter

322

determinations (representative experimental conditions: [H2O2] = 5.0 mg L−1, [SMN]0

323

= 0.10 mg L−1) at various l′ values and wavelengths were calculated (Table 1).

324

results show that a shorter wavelength could induce a larger error than a longer

325

wavelength, and increasing l′ could also raise the error.

326

that bench-scale photoreactors with a relatively shorter l′ will have a lower error than

327

those with a longer l′.

328

the errors for uridine were limited to 1.057 and 1.053, respectively, and for kinetic

329

parameters were limited to 1.005 and 1.096, respectively, under the experimental

330

conditions applied in this study.

331

exists in the qCBA and some batch photoreactors whose l′ values are larger than 15

332

mm, so a correction factor (such as water factor for the qCBA) is necessary.

333

In the conventional view, if In this

The

These observations indicate

For the LPUV (MVPS) and MPUV (MMPS) with l′ of 4.6 mm,

It can be seen clearly that a non-negligible error

Table 1

334

Discussion of Potential Errors: PFRave Difference and Variation. Six annular

335

photoreactors with various radii (i.e., 14.5, 21.5, 31.5, 41.5, 51.5, and 61.5 mm) but the

336

same lamp (8W, length = 100 mm, outer diameter = 23 mm) were simulated.

337

PFRave values (determination of PFRave is shown in a previous study26) at the central

338

cross-sections of these photoreactors containing various solutions (i.e., uridine, WS1,

339

and WS2) individually are shown in Figure S3a−c for three representative wavelengths

16


The

Page 17 of 33



by Li et al.

340

(204, 254, and 296 nm), respectively.

The results indicate that with increasing reactor

341

radius, the PFRave decreased quite rapidly at all three wavelengths, and meanwhile the

342

PFRave difference among various solutions increased slowly.

343

(i.e., standard derivations resulting from PFRave calculations) indicate the

344

nonuniformity of PFR distribution in the central cross-sections of simulated

345

photoreactors.

346

have a spatially-uniform PFR distribution, which facilitates accurate determination of

347

the photon fluence and kinetic parameters.

The error bars of PFRave

Hence, the photoreactor with a small diameter (a short l′) tended to

A quantitative comparison of the PFRave values in three repersentative simulated

348 349

photoreactors (i.e., radii = 14.5, 31.5, and 51.5 mm) is shown in Table 2.

At 204 and

350

254 nm, with increasing reactor radius, the PFRave ratios of uridine to WS1 (RU/WS1) and

351

WS2 (RU/WS2) suggest that a thinner reactor (a shorter l′) could have a lower error (the

352

error means how close the PFRave gets to 1) induced from the UVT difference between

353

uiridine and the water sample.

354

solutions (SI Figure S1), only slight changes in RU/WS1 and RU/WS2 were observed.

355

Taking account of the weighted ratios of various wavelengths on the MPUV output

356

spectrum (SI Figure S1), the RU/WS1 and RU/WS2 for MPUV were also calculated (Table

357

2).

358

with 2.40 mm inner diameter) which were installed close to the lamp, by using uridine

359

as actinometer for WS1 and WS2, PFRave ratios of 0.948 (LPUV for WS1), 0.953

360

(LPUV for WS2), 0.973 (MPUV for WS1) and 0.859 (MPUV for WS2) were obtained.

At 296 nm, because of very similar UVTs of various

It can be seen that for the LPUV (in MVPS) and MPUV (in MMPS) tubes (both

17




Page 18 of 33

by Li et al.

361

Therefore, the LPUV and MPUV lamps had as large as 4.7% and 14.1% errors induced

362

from the PFRave difference in this study, respectively.

363

Table 2

364

The error induced from the UVT variation (which subsequently caused the PFRave

365

variation) during SMN degradation was also evaluated.

The ratios of the initial PFRave

366

to the PFRave when the water sample absorbance [-log10(UVT/100)] decreased to 80%

367

(R80%WS1, R80%WS2) and 50% (R50%WS1, R50%WS2) of the initial absorbance are shown in

368

Table 2.

369

a lower error at each wavelength studied.

370

were as large as 0.5% and 3.6% for a 50% absorbance reduction, respectively.

Once more, the results indicate that a thinner reactor (a shorter l′) would have For the LPUV and MPUV lamps, the errors

371

The three principal errors for the LPUV (in MVPS) and MPUV (in MMPS) lamps

372

discussed above could introduce associated errors of 7.4% and 18.2% by using the error

373

propagation method, respectively.

374

k′p,LPUV and k′p,MPUV (Figure 3) obtained in this study, these errors were acceptable for

375

kinetic comparisons among various UV radiation sources.

376

Potential Applications.

Considering a much larger difference between the

Selection of an appropriate UV radiation source is an

377

important issue in lab-scale photoreaction studies.

A kinetic comparison among

378

various radiation sources at bench-scale can illustrate the performance of a UV-AOP

379

under a given photon fluence, but with differently featured emission spectra of the

380

applied UV sources.

381

test photoreactors with various UV sources.

382

MMPS with low errors on the photon fluence and kinetic parameter determinations,

Therefore, accurate photon fluence determination is critical for Based on the developed MVPS and

18


Page 19 of 33



by Li et al.

383

this study has demonstrated the feasibility of a kinetic comparison of micro-pollutant

384

degradation by UV/H2O2 among three representative radiation sources including the

385

LPUV (monochromatic), MPUV (polychromatic), and VUV/UV (dual wavelengths

386

with different reaction mechanisms) lamps.

387

to other emerging radiation sources, such as UV light-emitting diodes (LEDs) and

388

excimer lamps.

This kinetic comparison is also applicable

389

A kinetic comparison among various radiation sources can reveal their respective

390

performance on micro-pollutant degradation in bench-scale, yet it is insufficient for

391

industrial applications.

392

electricity transmission efficiencies and industrial reactor efficiencies, thus leading to

393

different costs for UV-AOPs.

394

be useful for the cost comparison among various radiation sources.

395

■ ASSOCIATED CONTENT

396

Supporting Information

397

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

398

at DOI:

In fact, different UV radaition sources have different photon-

Nevertheless, an accurate kinetic comparison can still

399

(Text S1) SMN analysis; (Text S2) Calculations of rHO,LPUV/H2O2, rHO,MPUV/H2O2

400

and rHO,VUV/UV/H2O2; (Text S3) Determination of VUV/UV photon fluence

401

(Fp,VUV/UV); (Table S1) Molar absorption coefficients (ε, M−1 cm−1) of various

402

solution components in various wavelength ranges; (Table S2) Rate constants of

403

reactions involved in this study; (Table S3) Integrated εu (M−1 cm−1) and PFRave

404

(einstein m−2 s−1) values in various MPUV wavelength ranges; (Figure S1) 19




Page 20 of 33

by Li et al.

405

Absorption spectra of uridine (0.012 mM), atrazine (0.50 mg L1), H2O2 (5.0 mg

406

L1), water sample 1 (WS1) and water sample 2 (WS2), as well as the output

407

spectra of LPUV and MPUV; (Figure S2) SMN degradation kinetics in

408

LPUV/H2O2, VUV/UV/H2O2, and MPUV/H2O2 (200−300, 200−350, and

409

200−400 nm) processes at H2O2 doses of: (a) 0; (b) 0.50; (c) 5.0; and (d) 20.0

410

mg L−1; (Figure S3) PFR distributions at: (a) 204; (b) 254; and (c) 296 nm in six

411

simulated photoreactors (radii = 14.5, 21.5, 31.5, 41.5, 51.5, and 61.5 mm)

412

containing uridine, WS1, and WS2 individually.

413

■ AUTHOR INFORMATION

414

Corresponding Author

415

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

416

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

417

■ ACKNOWLEDGEMENTS

418

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

419

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

420

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

421

University.

422

■ REFERENCES

423

(1)

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

424

by UV/chlorine: Efficiency, influencing factors, and products. Water Res. 2016, 90,

425

15−23.

20


Page 21 of 33



426

(2)

by Li et al.

Soltermann, F.; Widler, T.; Canonica, S.; von Gunten, U. Photolysis of

427

inorganic chloramines and efficiency of trichloramine abatement by UV treatment of

428

swimming pool water. Water Res. 2014, 56, 280−291.

429

(3)

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

430

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

431

2013, 47 (20), 11726−11733.

432

(4)

Keen, O. S.; Linden, K. G. Degradation of antibiotic activity during UV/H2O2

433

advanced oxidation and photolysis in wastewater effluent. Environ. Sci. Technol. 2013,

434

47 (22), 13020−13030.

435

(5)

Wols, B. A.; Hofman-Caris, C. H. M. Modelling micropollutant degradation in

436

UV/H2O2 systems: Lagrangian versus Eulerian method. Chem. Eng. J. 2012, 210,

437

289−297.

438

(6)

Li Puma, G.; Puddu, V.; Tsang, H. K.; Gora, A.; Toepfer, B. Photocatalytic

439

oxidation of multicomponent mixtures of estrogens (estrone (El), 17 beta-estradiol (E2),

440

17 alpha-ethynylestradiol (EE2) and estriol (E3)) under UVA and UVC radiation:

441

Photon absorption, quantum yields and rate constants independent of photon absorption.

442

Appl. Catal. B-Environ. 2010, 99 (3-4), 388−397.

443

(7)

Fang, J. Y.; Fu, Y.; Shang, C. The roles of reactive species in micropollutant

444

degradation in the UV/free chlorine system. Environ. Sci. Technol. 2014, 48 (3),

445

1859−1868.

446 447

(8)

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

treatment - A review. Water Res. 2014, 52, 131−145.

21




448

(9)

Page 22 of 33

by Li et al.

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

449

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

450

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

451

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

452

(10) Li, M. K.; Hao, M. Y.; Yang, L. X.; Yao, H.; Bolton, J. R.; Blatchley III, E. R.;

453

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

454

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

455

photoreaction system and a pilot photoreactor. Environ. Sci. Technol. 2018, 52,

456

7426−7433.

457

(11) Rosenfeldt, E. J.; Linden, K. G. The ROH,UV concept to characterize and the

458

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

459

2548−2553.

460

(12) Bolton, J. R.; Mayor-Smith, I.; Linden, K. G. Rethinking the concepts of fluence

461

(UV Dose) and fluence rate: The importance of photon-based units - A systemic review.

462

Photochem. Photobiol. 2015, 91 (6), 1252−1262.

463

(13) Afzal, A.; Oppenlander, T.; Bolton, J. R.; El-Din, M. G. Anatoxin-a degradation

464

by advanced oxidation processes: Vacuum-UV at 172 nm, photolysis using medium

465

pressure UV and UV/H2O2. Water Res. 2010, 44 (1), 278−286.

466 467

(14) Guo, H.; Chu, X.; Hu, J. Effect of host cells on low- and medium-pressure UV inactivation of adenoviruses. Appl. Environ. Microbiol. 2010, 76 (21), 7068−7075.

468

(15) Sharpless, C. M.; Linden, K. G. Experimental and model comparisons of low-

469

and medium-pressure Hg lamps for the direct and H2O2 assisted UV photodegradation

22


Page 23 of 33



by Li et al.

470

of N-nitrosodimethylamine in simulated drinking water. Environ. Sci. Technol. 2003,

471

37 (9), 1933−1940.

472

(16) Bolton, J. R.; Linden, K. G. Standardization of methods for fluence (UV dose)

473

determination in bench-scale UV experiments. J. Environ. Eng.-ASCE 2003, 129 (3),

474

209−215.

475

(17) Jin, S. S.; Mofidi, A. A.; Linden, K. G. Polychromatic UV fluence measurement

476

using chemical actinometry, biodosimetry, and mathematical techniques. J. Environ.

477

Eng.-ASCE 2006, 132 (8), 831−841.

478

(18) Yuan, F.; Hu, C.; Hu, X. X.; Qu, J. H.; Yang, M. Degradation of selected

479

pharmaceuticals in aqueous solution with UV and UV/H2O2. Water Res. 2009, 43 (6),

480

1766−1774.

481

(19)

482

photoreaction system for bench-scale photochemical studies. Environ. Sci. Technol.

483

Lett. 2015, 2 (10), 297301.

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

484

(20) Ikehata, K.; Naghashkar, N. J.; Ei-Din, M. G. Degradation of aqueous

485

pharmaceuticals by ozonation and advanced oxidation processes: A review. Ozone-Sci.

486

Eng. 2006, 28 (6), 353−414.

487

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

488

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

489

2013, 262, 189−211.

490

(22) Li, M. K.; Wang, C.; Yau, M.; Bolton, J. R.; Qiang, Z. M. Sulfamethazine

491

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

23




Page 24 of 33

by Li et al.

492

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

493

Res. 2017, 108, 348−355.

494

(23) Bolton, J. R. Calculation of ultraviolet fluence rate distributions in an annular

495

reactor: Significance of refraction and reflection. Water Res. 2000, 34 (13), 3315−3324.

496

(24) Liu, D.; Ducoste, J.; Jin, S.; Linden, K. Evaluation of alternative fluence rate

497

distribution models. J.Water Supp. Res. Technol.-Aqua 2004, 53 (6), 391−408.

498

(25) Li, M. K.; Qiang, Z. M.; Li, T. G.; Bolton, J. R.; Liu, C. L. In situ measurement

499

of UV fluence rate distribution by use of a micro fluorescent silica detector. Environ.

500

Sci. Technol. 2011, 45 (7), 3034−3039.

501

(26) Li, M. K.; Qiang, Z. M.; Bolton, J. R. In situ detailed fluence rate distributions

502

in a UV reactor with multiple low-pressure lamps: Comparison of experimental and

503

model results. Chem. Eng. J. 2013, 214, 55−62.

504

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

505

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

506

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

507

1181−1187.

508

(28) Li, M. K.; Qiang, Z. M.; Pulgarin, C.; Kiwi, J. Accelerated methylene blue (MB)

509

degradation by fenton reagent exposed to UV or VUV/UV light in an innovative micro

510

photo-reactor. Appl. Catal. B Environ. 2016, 187, 83−89.

511

(29) Li, M. K.; Li, W. T.; Bolton, J. R.; Blatchley III, E. R.; Qiang, Z. M. Organic

512

pollutant degradation by VUV/UV/H2O2 process: Inhibition and enhancement roles of

513

H2O2. submitted for publication to Environ. Sci. Technol. 2019, 53, 912−918.

24


Page 25 of 33



by Li et al.

514

(30) Canonica, S.; Meunier, L.; von Gunten, U. Phototransformation of selected

515

pharmaceuticals during UV treatment of drinking water. Water Res. 2008, 42, 1−2,

516

121−128.

25



Page 26 of 33


by Li et al.

Table 1. Errors from the Use of Taylor Series Approximation for Photon Fluence Determination by Uridine as well as Kinetic Parameter Determination for Representative Wavelengths and Various Effective Path-lengths (l′). 2.303al′/(1-10-al′) for photon fluence

2.303al′/(1-10-al′) for kinetic parameter

determination by uridinea

determinationb

l′ (cm) 204 nm

254 nm

296 nm

MPUV

204 nm

(LPUV)

254 nm

296 nm

MPUV

(LPUV)

0.20

1.025

1.025

1.000

1.024

1.080

1.002

1.001

1.042

0.40

1.051

1.049

1.001

1.046

1.163

1.004

1.002

1.084

0.46

1.059

1.057

1.001

1.053

1.189

1.005

1.002

1.096

0.60

1.077

1.074

1.001

1.070

1.250

1.006

1.002

1.126

0.80

1.103

1.100

1.001

1.094

1.342

1.008

1.003

1.168

1.0

1.130

1.126

1.001

1.119

1.437

1.010

1.004

1.210

2.0

1.270

1.261

1.003

1.243

1.966

1.021

1.007

1.422

5.0

1.748

1.723

1.007

1.649

2.575

1.031

1.011

1.632

10.0

2.714

2.652

1.013

2.449

7.745

1.106

1.036

2.979

aIn

solution containing [uridine]0 = 2.93 mg L−1 (0.012 mM).

bIn

solution containing [H2O2]0 = 5.0 mg L−1 and [SMN]0 = 0.10 mg L−1.

26 ACS Paragon Plus Environment

Page 27 of 33



by Li et al.

Table 2. PFRave Ratios of Uridine to Water Samples and PFRave Variation during SMN Degradation at Various Wavelengths in Three Simulated Photoreactors. Wavelengt

Rrlamp (mm)a

RU/WS1

RU/WS2

R80%WS1

R50%WS1

R80%WS2

R50%WS2

3.00

0.960

1.009

1.003

1.007

1.015

1.035

20.0

0.786

1.054

1.015

1.045

1.090

1.222

40.0

0.655

1.093

1.027

1.084

1.159

1.415

254 nm

3.00

0.948

0.953

1.000

1.002

1.002

1.005

(LPUV)

20.0

0.731

0.752

1.000

1.014

1.015

1.029

40.0

0.573

0.604

1.000

1.027

1.027

1.055

3.00

1.001

1.001

1.000

1.001

1.000

1.001

20.0

1.009

1.009

1.003

1.009

1.003

1.004

40.0

1.016

1.016

1.005

1.016

1.005

1.008

3.00

0.973

0.859

1.002

1.002

1.006

0.964

20.0

0.863

0.558

1.019

1.016

1.044

0.814

40.0

0.782

0.424

1.036

1.029

1.082

0.701

h 204 nm

296 nm

MPUV

aReactor

radius (R) minus lamp radius (rlamp, 11.5 mm).




Page 28 of 33

by Li et al.

Figure 1. Schematic illustration of the mini-fluidic VUV/UV photoreaction system (MVPS, left) and mini-fluidic MPUV photoreaction system (MMPS, right).


Page 29 of 33



by Li et al.

tree (s) 0

20

40

60

80

100

120

Experimental time (s) 0

3000

6000

9000

12000

0.00

94.5

3

ln(A262/A262,0)

-0.02 -0.04

94.0 -0.06

MPUV LPUV VUV

-0.08 -0.10 -0.12

[MeOH]  x 10 M)

95.0

93.5

93.0 0

120

240

360

480

600

720

Experimental time (s) 0

1

2

3

4

tree (s)

5

6

7

8

Figure 2. Uridine photolysis kinetics under LPUV (red) and MPUV (black) exposure as well as methanol degradation under VUV exposure (blue).

The solid line for the

MPUV or LPUV lamp represents the pseudo-first-order model fit, while for the VUV source represents the zero-order model fit.



Page 30 of 33


by Li et al.

LPUV/H2O2

VUV/UV/H2O2

0

MPUV/H2O2

(c)

(a)

-4 2

ln([SMN]/[SMN]0)

-1

2

Unit: m einstein k'p,LPUV = 7.6 k'p,VUV/UV = 3331 k'p,MPUV = 169

-8 -12 0

-1

Unit: m einstein k'p,LPUV = 102.7 k'p,VUV/UV = 1874 k'p,MPUV = 359

(b)

(d)

-1

Unit: m einstein k'p,LPUV = 310 k'p,VUV/UV = 1354 k'p,MPUV = 526

-4 2

2

Unit: m einstein k'p,LPUV = 31.5 k'p,VUV/UV = 2761 k'p,MPUV = 176.6

-8 -12 0

2

4

6

0

2 3

4

-1

6

-2

Photon fluence (x 10 einstein m )

Figure 3. SMN degradation kinetics by LPUV/H2O2, MPUV/H2O2 (200−300 nm), and VUV/UV/H2O2 processes at H2O2 doses of: (a) 0, (b) 0.5, (c) 5.0, and (d) 25.0 mg L−1. Conditions: [SMN]0 = 0.10 mg L−1, pH = 7.0.

Solid lines represent the pseudo-first-

order model fits of experimental data.


Page 31 of 33



by Li et al.

6000 Measured and modeled k'p,LPUV Measured and modeled k'p,MPUV Measured and modeled k'p,VUV/UV

4000 3000

2

-1

k'p (m einstein )

5000

2000 1000 0 0

5

10

15

20

25

30

-1

H2O2 (mg L )

Figure 4. Measured and modeled rate constants of SMN degradation by LPUV/H2O2, MPUV/H2O2 (200−300 nm), and VUV/UV/H2O2 processes as a function of H2O2 dose. Conditions: [SMN]0 = 0.10 mg L−1, pH = 7.0.



Page 32 of 33


by Li et al.

0

ln([SMN]/[SMN]0)

-1 -2 -3

LPUV/H2O2 VUV/UV/H2O2 MPUV/H2O2 (200-300 nm) MPUV/H2O2 (200-350 nm) MPUV/H2O2 (200-400 nm)

-4 -5 0

10

20

30 3

40

50 -2

Photon fluence (x 10 einstein m

)

Figure 5. SMN degradation kinetics by LPUV/H2O2, VUV/UV/H2O2, and MPUV/H2O2 (200−300, 200−350, and 200−400 nm) processes. = 0.1 mg L−1, [H2O2] = 5.0 mg L−1, and pH = 7.0.


Conditions: [SMN]0

Page 33 of 33



by Li et al.

TOC ART

ln([SMN]/[SMN]0)

0 -1 -2 -3

LPUV/H2O2 VUV/UV/H2O2 MPUV/H2O2 (200-300 nm) MPUV/H2O2 (200-350 nm) MPUV/H2O2 (200-400 nm)

-4 -5 0

10

20

30 3

MVPS

40

50 -2

Photon fluence (x 10 einstein m

MMPS


)

H2O2 process: Kinetic

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