Inactivation of Escherichia coli, Bacteriophage MS2, and Bacillus

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Inactivation of E. coli, Bacteriophage MS2 and Bacillus Spores under UV/H2O2 and UV/Peroxydisulfate Advanced Disinfection Conditions Peizhe Sun, Corey Tyree, and Ching-Hua Huang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b06097 • Publication Date (Web): 25 Mar 2016 Downloaded from http://pubs.acs.org on March 26, 2016

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Environmental Science & Technology

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Inactivation of E. coli, Bacteriophage MS2 and Bacillus Spores under

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UV/H2O2 and UV/Peroxydisulfate Advanced Disinfection Conditions

4

Peizhe Sun, *,a,b Corey Tyree,b Ching-Hua Huang*,a

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a

School of Civil and Environmental Engineering, Georgia Institute of Technology,

6 7 8

Atlanta, Georgia 30332, United States b

Division of Energy and Environment, Southern Research Institute, Birmingham, Alabama 35205, United States

9 10

*Corresponding Authors.

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Phone: 404-894-7694. E-mail: [email protected]

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Phone:404-358-4858. E-mail: [email protected]

13 14 15 16 17

Revised manuscript submitted to

18


19 20 21 22

ACS Paragon Plus Environment


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Abstract: Ultraviolet light (UV) combined with peroxy chemicals, such as H2O2 and

24

peroxydisulfate (PDS), have been considered potentially highly effective disinfection

25

processes. This study investigated the inactivation of E. coli, bacteriophage MS2 and

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Bacillus subtilis spores as surrogates for pathogens under UV/H2O2 and UV/PDS

27

conditions, with the aim to provide further understanding of UV-based advanced

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disinfection processes (ADPs). Results showed that one additional log of inactivation of

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E. coli was achieved with 0.3 mM H2O2 or PDS at 5.2×10-5 Einstein·L-1 photo fluence (at

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254 nm) compared with UV irradiation alone. Addition of H2O2 and PDS greatly

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enhanced the inactivation rate of MS2 by around 15 folds and 3 folds, respectively,

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whereas the inactivation of B. subtilis spores was slightly enhanced. Reactive species

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responsible for the inactivation were identified to be ·OH, SO4·- and CO3·- based on

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manipulation of solution conditions. The CT value of each reactive species was calculated

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with respect to each microbial surrogate, which showed that the disinfection efficacy

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ranked as ·OH > SO4·- > CO3·- >> O2·-/HO2·. A comprehensive dynamic model was

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developed and successfully predicted the inactivation of the microbial surrogates in

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surface water and wastewater matrices. The concepts of UV-efficiency and EE/O were

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employed to provide a cost-effective evaluation for UV-based ADPs. Overall, the present

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study suggests that it will be beneficial to upgrade UV disinfection to UV/H2O2 ADP for

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the inactivation of viral pathogens.


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INTRODUCTION

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Increasing water pollution by infectious biological contaminants is a serious health

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risk around the globe. Recent monitoring studies have detected pathogens in urban

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wastewater influents, including but not limited to adenovirus, enterovirus, and norovirus.1

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Several outbreaks of biological contaminants have also been documented,2-4 among

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which, Escherichia coli (E. coli), Listeria, Salmonella, Heptatis A and Cyclospora were

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the most reported. The U.S. Environmental Protection Agency (USEPA) has listed twelve

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microbial contaminants, including both bacterial and viral pathogens, on the 3rd version

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of the Drinking Water Contaminant Candidate List (CCL), a list of unregulated chemical

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and biological contaminants known or anticipated to occur in public water systems.5

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Some of the microbial contaminants can survive conventional water treatment processes

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(e.g., coagulation/flocculation, activated sludge, and filtration processes) and are likely to

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persist in freshwater with the potential for transmission by a waterborne route.6-8

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Ultraviolet (UV)-based disinfection techniques are being increasingly applied in

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water and wastewater treatment facilities worldwide due to their lower tendency to form

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harmful disinfection byproducts (DBPs) compared to chemical disinfection processes,9-15

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and the ability of UV irradiation to chemically modify the DNA or RNA of

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microorganisms and thus inactivate them.9,16 However, studies have shown that a number

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of microbial contaminants and their surrogates are resistant to UV disinfection including

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adenovirus, bacteriophage MS2, Bacillus subtilis spores, and some antibiotic-resistant

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bacteria and genes.17-21 Therefore, it will be advantageous to develop means to enhance

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the efficacy of UV-based processes for pathogen elimination.

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UV-based

advanced

oxidation

processes

(AOPs),


such

as

UV/H2O2,


65

UV/peroxydisulfate (UV/PDS), and UV/TiO2, have been shown to be highly effective in

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degrading organic micropollutants (e.g., pesticides, pharmaceuticals, and chlorinated

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solvents) in drinking water and wastewater.22-29 Organic contaminants are degraded much

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more effectively and extensively by AOPs than UV alone because highly reactive radical

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and oxidizing species are generated under these designed conditions. In analogy, AOPs

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may hold promise to be more effective than conventional water disinfection processes in

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inactivating pathogens due to these more powerful oxidation capabilities.19,20,30-33

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Especially, radical species, such as hydroxyl radical and carbonate radical, generated in

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AOP or natural conditions, are able to inactive E. coli and MS2.19,30,31,34 Several studies

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have evaluated UV/H2O2 for disinfection purposes. For example, Mamane et al.19

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investigated the inactivation of E. coli, B. subtilis spores, and bacteriophages MS2, T4,

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and T7 using UV (>295 nm) compared to UV/H2O2 AOP. The authors found that

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UV/H2O2 AOP led to an additional one log of inactivation for T7 and additional 2.5 logs

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of inactivation for MS2 phage compared to UV alone. In contrast, inactivation efficiency

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of the other microorganisms was not significantly affected by AOP. Bounty et al.35

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examined the inactivation of adenovirus, one of the most UV-resistant pathogens, using

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UV/H2O2 AOP, and reported that UV inactivation of adenovirus can be significantly

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enhanced by addition of H2O2 due to formation of hydroxyl radicals. The above varying

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outcomes of different microorganisms were likely the results of specific disinfection

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conditions and mechanisms between particular microorganisms and radicals, implying

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that process optimization based on each pathogen of interest would be necessary. Indeed,

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previous studies suggest that viruses are more susceptible to radical attack than bacteria

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and spores.19,34 Whether it is beneficial to upgrade UV disinfection process to UV-based


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advanced disinfection process (ADP) is still not clear based on previous research. In

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addition, there has been little research on applying PDS with UV, another powerful AOP

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option, for disinfection purposes.

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To assess the disinfection potential of UV-based ADP, this study employed three

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microbial surrogates, including E. coli, bacteriophage MS2 and Bacillus subtilis spores as

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representatives for pathogenic bacteria, viruses and protozoa, respectively, to investigate

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the disinfection potency of different radical species generated by UV/H2O2 and UV/PDS

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processes. Dynamic kinetic models were developed to quantitatively evaluate the

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inactivation kinetics of microbial surrogates by the UV-based ADPs to gain mechanistic

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insight. An energy-cost assessment was also conducted to optimize the disinfection

98

efficiency and assess the overall performance of the UV-based ADPs.

99 100 101 102

MATERIAL AND METHODS Chemicals. Sources of chemical and reagents are provided in the Supporting Information (SI) Text S1.

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Microbial surrogates. E. coli (ATCC 15597), bacteriophage MS2 (ATCC 15597-B1)

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and Bacillus subtilis spores (ATCC 6633) were selected as surrogates of pathogenic

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bacteria, viruses and protozoa. Dry powder form of each microbial surrogate was

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purchased from ATCC and revived accordingly. Culture preparation followed the

107

methods by Cho et al.32 Details of stock preparation are described in SI Text S2.

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Experimental setup. The UV-based ADP experiments were conducted with a bench-

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scale collimated-beam UV apparatus (SI Figure S1) equipped with a 4W low-pressure

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UV lamp emitting light predominantly at 254 nm (Philips Co., Netherlands). The



111

spectrum emission of the lamp was characterized by a spectroradiometer (Spectral

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Evolution, SR-1100) (shown in SI Figure S2). The reaction solution (10 mL) was put into

113

a glass petri dish (inner diameter = 5.4 cm) which was placed on a stir plate,

114

perpendicular to the incident light. Therefore, the optical path length was 0.44 cm. The

115

UV fluence rate received in the reaction solution was measured to be 2.2×10-7 Einstein·L-

116

1

117

1.0 mJ·cm-2 was equivalent to 5.5×10-6 Einstein·L-1 (SI Text S3).

·s-1 using potassium ferrioxalate as chemical actinometer. For this experimental setup,

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Most of the experiments were conducted in phosphate buffer solution (3.0 mM PBS

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at pH 7.0) containing 0.3 mM H2O2 or PDS and microbial surrogates, except where stated

120

otherwise. The initial densities of E. coli and B. subtilis spores for each disinfection

121

experiment were around 4×106 CFU/mL and for MS2 were around 3×106 PFU/mL.

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Preliminary tests using dynamic light scattering (Zetasizer Nano ZS instrument, Malvern

123

Instruments) showed that the microbial surrogates (up to ~108 CFU/mL or PFU/mL) were

124

at dispersed state not forming clumps.

125

In the experiments to test the inactivation of microbial surrogates in real water

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matrices, samples of surface water (SW) from a river source and wastewater (WW) from

127

secondary effluent were collected locally at a drinking water treatment plant and a

128

municipal wastewater treatment plant, respectively. The water samples were filtered by

129

glass fiber filters prior to use. The characteristics of the water samples are summarized in

130

SI Table S1, in which inorganic ions were measured by a Dionex DX-100 ion

131

chromatography instrument with conductivity detection and dissolved organic carbon

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(DOC) was measured by a Shimadzu TOC analyzer. The colony-forming-unit (CFU) and

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plague-forming-unit (PFU) of SW and WW were determined, which showed no


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interference with the counting of the microbial surrogates.

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Modeling. Kinetic modeling of radical species was simulated using Simbiology

136

application in Matlab 2014b. Over one hundred elementary reactions (SI Table S2) were

137

considered with rate constants obtained from literature.29,36,37 This model takes into

138

account the effects on ADP from most of inorganic ions, including chloride, sulfate,

139

nitrogen species, carbonate species, and from DOC present in the water matrices. The

140

scavenging effects of pathogens on the radicals were considered much lower than those

141

by the water matrix components and thus neglected in the simulations. Major radical

142

concentrations predicted by this model (under UV/H2O2, UV/PDS and UV/H2O2/NaCO3

143

conditions) were validated using radical probes, such as p-nitroaniline, anisole and

144

nitrobenzene (details shown in SI Text S4, Table S3). The concentrations of radical

145

species presented in this study were all obtained by model simulation at the end of 2 min

146

reaction time. Preliminary test runs showed that the concentrations of major radicals

147

reached pseudo-steady-state within 2 min reaction time.

148 149

RESULTS AND DISCUSSION

150

Inactivation of microbial surrogates by UV, UV/H2O2 and UV/PDS. The E. coli,

151

bacteriophage MS2 and B. subtilis spores were treated under UV, UV/H2O2 and UV/PDS

152

conditions (Figure 1). Control experiments were conducted under the same conditions

153

without UV irradiation, which showed that the microbial surrogates were not inactivated

154

by H2O2 or PDS within 30 min (data not shown). Experiments showed that 4-log

155

inactivation of E. coli was achieved by UV exposure at 10.6 mJ·cm-2 (i.e., 5.2×10-5

156

Einstein·L-1) (Figure 1A). The overall inactivation of E. coli by UV alone presented a lag



157

phase for around 4 mJ·cm-2 followed by a linear loss of bacteria viability over exposure

158

time, which was consistent with literature.9,38 The application of 0.3 mM H2O2 or PDS

159

statistically significantly enhanced the inactivation of E. coli (P < 0.005 by paired t-test).

160

Additional 1-log reduction was achieved at 10 mJ·cm-2, whereas the lag phases were only

161

slightly shortened. The UV dose required to achieve 4-log inactivation were 8.6 and 8.8

162

mJ·cm-2 for UV/H2O2 and UV/PDS, respectively.

163

As for bacteriophage MS2, 4-log inactivation was not achieved till at 85 mJ·cm-2 (i.e.,

164

4.1×10-4 Einstein·L-1) by UV irradiation alone (Figure 1B). The loss of MS2 viability

165

exhibited pseudo-first-order kinetics over UV exposure time. The addition of 0.3 mM

166

H2O2 greatly enhanced the inactivation rate by almost 15 folds, reducing the UV intensity

167

to achieve 4-log inactivation to 6 mJ·cm-2. The inactivation was also enhanced under

168

UV/PDS condition, but less effective than UV/H2O2 condition.

169

B. subtilis spores were inactivated by UV alone, with 4-log inactivation at around 30

170

mJ·cm-2 (i.e., 1.5×10-4 Einstein·L-1) (Figure 1C). The overall inactivation kinetics

171

presented a lag phase followed by a linear relation between –log(N/N0) and UV exposure

172

time. The inactivation of spores was enhanced under UV/H2O2 (P < 0.005), whereas the

173

addition of PDS did not achieve observable difference from UV alone.

174

The inactivation of microbial surrogates by UV irradiation was extensively

175

investigated in prior studies and nicely summarized in a literature review.38 A range of

176

inactivation rates (i.e., log of inactivation per mJ·cm-2 obtained from linear range data)

177

were reported and summarized (E. coli 0.506, MS2 0.055, B. subtilis spores 0.059),38

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which are close to the inactivation rates measured in this study (E. coli 0.550, MS2 0.047,

179

B. subtilis spores 0.128). UV irradiation is effective to inactivate bacteria, primarily due


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to dimerization of adjacent thymine molecules in their DNA.39 On the other hand,

181

viruses, such as bacteriophage MS2, are known to much less susceptible to UV radiation

182

than bacteria.38 The application of the same amount of H2O2 led to different enhancement

183

of the inactivation for E. coli, MS2 and B. subtilis spores, which suggested they have

184

different sensitivity toward reactive species produced under UV/H2O2 condition.

185

Similarly, E. coli and MS2 were subject to inactivation by the radicals produced under

186

UV/PDS condition, whereas the inactivation of B. subtilis spores was not enhanced.

187

Therefore, further studies were conducted in the aim of identifying what reactive species

188

was/were responsible for the inactivation of the microbial surrogates.

189

Contribution of reactive species. In UV/H2O2 and UV/PDS systems, multiple

190

reactive species are generated. The photolysis of H2O2 and PDS produces primary

191

radicals, i.e., hydroxyl radical and sulfate radical. These primary radicals react with water

192

components yielding secondary radicals, such as carbonate radical and superoxide

193

radical. Based on the simulation results (Table 1), hydroxyl radical, sulfate radical,

194

carbonate radical and superoxide radical are present at significantly high concentrations

195

(> 10-13 M) under UV/H2O2 and UV/PDS conditions, which make them potentially

196

important to inactivate microbial pathogens. To elucidate the role of each radical,

197

different combinations of oxidants (i.e., H2O2 and PDS) and radical scavengers (i.e., t-

198

butal alcohol (TBA) and NaHCO3) were employed to create conditions where only one

199

radical species was dominantly higher in concentration (Figure 2). Such conditions were

200

also validated using the kinetic model to calculate the predicted pseudo-steady-state

201

concentrations of radicals (Table 1). Statistical analysis using t-test was employed to

202

assess the experimental results between the radical-dominant conditions and control



203

Page 10 of 38

groups for any significant differences.

204

Hydroxyl radical. It is commonly considered that the dominant radical species

205

generated by UV/H2O2 in a clean water system, such as PBS, is hydroxyl radical due to

206

the direct photolysis of H2O2 (eqn. 1).

207 208 209

−

hυ H 2O2 /HO2 → 2 • OH

(1)

•

OH + HCO3- /CO32− → CO3•− + H2O

(2)

•

OH + H2O2 → HO•2 /O•2− + H2O

(3)

210

However, with the presence of (bi)carbonate from dissolved CO2, carbonate radical

211

will be produced from the reaction between hydroxyl radical with (bi)carbonate (eqn. 2).

212

Additionally, H2O2 can react with hydroxyl radical yielding superoxide radical (eqn. 3).

213

Although carbonate radical and superoxide radical are known not very reactive towards

214

common organic compounds,37 it has been suggested that carbonate radical can inactivate

215

MS234 and superoxide radical contributed to the photoinactivation of E. coli.40 Therefore,

216

the enhancement of the inactivation of microbial surrogates under UV/H2O2 (Figure 1)

217

may not be (only) attributed to hydroxyl radicals. The application of TBA as the hydroxyl

218

radical scavenger is a common approach to study the contribution of hydroxyl radical,

219

whereas TBA also prevents the formation of carbonate radical and superoxide radical

220

(reaction system 3 in Table 1). On the other hand, it is very difficult to create conditions

221

where only hydroxyl radical dominates because: (1) the elimination of (bi)carbonate is

222

difficult to achieve in an open reactor; (2) superoxide radical scavengers, such as 4-

223

hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl

224

hydroxyl radical as well. Therefore, in order to elucidate the contribution of hydroxyl

225

radical, the role of carbonate radical and superoxide radical should be determined first.

(TEMPOL),


potentially

react

with

Page 11 of 38


226

Superoxide radical. Applying eqn. 4-6, a system (UV/10×H2O2/PDS/TBA) where

227

superoxide radical was the major reactive species was created (reaction system 7 in Table

228

1). Essentially, the photolysis of PDS produced sulfate radical (eqn. 4), which reacted

229

with H2O2 yielding superoxide radical (eqn. 5). TBA was used to quench the hydroxyl

230

radical generated from the photolysis of H2O2 (eqn. 6). The application of H2O2 was to

231

produce superoxide radical and to suppress sulfate radical concentration as well (eqn. 5).

232

Concentrations of H2O2 (3 mM) and PDS (0.3 mM) were selected in order to produce a

233

significantly high amount of superoxide radical with minimal hydroxyl and sulfate

234

radical production. •−

235

hν S2O8 → 2 ⋅ SO4

(4)

236

SO•4− + H2O2 → HO•2 /O•2− + SO24−

(5)

237

TBA+ • OH → product

(6)

238

As Table 1 shows, in the superoxide radical dominated condition, the predicted

239

superoxide radical concentration was close to that in the UV/H2O2 system (i.e., ~2×10-8

240

M), while the concentrations of hydroxyl radical and sulfate radical were 2-3 orders of

241

magnitude lower than those in the UV/H2O2 and UV/PDS systems, respectively (reaction

242

system 7 versus 1 and 2). Therefore, negligible inactivation was expected from hydroxyl

243

radical and sulfate radical. For comparison, control experiments (i.e., UV irradiation

244

only) were conducted in PBS with addition of TBA. Preliminary experiments confirmed

245

that TBA (0.1 M) did not have detectable impact on the microbial surrogates (data not

246

shown). Results showed that the superoxide radical dominated condition did not have

247

better inactivation efficiency than the control groups for all microbial surrogates (Figure

248

2A), indicating that superoxide radical has little disinfection potency.

2-



249

Carbonate radical. A carbonate radical dominated system was created by adding 0.1

250

M NaHCO3 into the UV/H2O2 system. The solution pH was maintained at 8.5. The

251

amount of (bi)carbonate ions were sufficient to suppress hydroxyl radical concentration

252

to around 10-15 M (reaction system 6 in Table 1), more than two orders of magnitude

253

lower than that in the UV/H2O2 system. At such concentration, hydroxyl radical was

254

expected to have negligible effects on the inactivation of microbial surrogates. In other

255

words, the contribution from hydroxyl radical was less than 1% of that in the UV/H2O2

256

system. Therefore, carbonate radical was the only important reactive species in the

257

UV/H2O2/NaHCO3 system. To elucidate the contribution of carbonate radical, control

258

groups (i.e., UV irradiation) were conducted in PBS with the addition of NaHCO3.

259

Preliminary experiments confirmed that NaHCO3 (0.1 M) had little impact on the

260

microbial surrogates (data not shown). As shown in Figure 2B, carbonate radical

261

enhanced the inactivation of E. coli and MS2 (P < 0.005), whereas B. subtilis spores were

262

resistant to carbonate radical. The disinfection role of carbonate radical was further

263

confirmed by adding 0.01 mM p-nitroaniline, a carbonate radical scavenger, in the

264

UV/H2O2/NaHCO3 system, in which the inactivation of MS2 was greatly inhibited (SI

265

Figure S3). The carbonate radical concentration in the UV/H2O2/NaHCO3 system was

266

8.64×10-12 M, which was around one order of magnitude higher than that in the UV/H2O2

267

system. Therefore, the inactivation by carbonate radical should be less significant in a

268

low-carbonate UV/H2O2 system. Nevertheless, this result indicates that the inactivation of

269

E. coli and MS2 under UV/H2O2 conditions was partly attributed to carbonate radical.

270

Quantitative discussion is performed in a later section after obtaining CT values.

271

Sulfate radical. Under UV/PDS conditions, both sulfate radical and hydroxyl radical


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272

were produced due to trace amounts of chloride in PBS (eqn. 7 and 8, Table 1). The

273

concentrations of chlorine-containing radicals (i.e., Cl· and Cl2·-), also simulated by the

274

model, were 1-2 orders of magnitude lower than those of sulfate radical and hydroxyl

275

radical and thus could be neglected (data not shown). The reaction between sulfate

276

radical and H2O/OH- can also generate hydroxyl radical (eqn. 9).

277

SO•4− + Cl− → Cl• + SO24−

(7)

278

Cl• + H 2 O/OH− → ClOH•− →• OH + Cl−

(8)

279

SO•4− + H2 O/OH− →• OH + SO24−

(9)

280

To create a condition where sulfate radical is the only important reactive species, 0.1

281

M TBA was added to quench hydroxyl radical formation because TBA reacts with

282

hydroxyl radical ( k = 7.6×108 M-1·s-1) much faster than with sulfate radical ( k = 9.1×105

283

M-1·s-1).37 A higher initial PDS concentration (i.e., 3 mM) was applied to compensate the

284

sulfate radical consumed by TBA (see reaction system 5 versus 4 in Table 1). Control

285

groups (i.e., UV irradiation) were conducted in PBS with TBA but without PDS. As

286

Figure 2C shows, sulfate radical only enhanced the inactivation of MS2 (P < 0.005)

287

whereas no observable contribution was achieved for the inactivation of E. coli and B.

288

subtilis spores. This result suggests that the enhancement of the inactivation of E. coli by

289

UV/PDS in PBS was attributed to the hydroxyl radical produced by the reactions in eqn.

290

7-9.

291

Overall, the results showed that the major reactive species for the inactivation of

292

microbial surrogates are hydroxyl radical, sulfate radical and carbonate radical. Indeed,

293

the second-order rate constants between radicals and biomolecules, including

294

saccharides, amino acids and lipids, suggest that hydroxyl radical and sulfate radical are



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295

the most reactive species (k = ~107–1010 M-1·s-1) whereas carbonate radical can react with

296

biomolecules at the rate 104–108 M-1·s-1.37 Superoxide radical, on the other hand, only

297

reacts with amino acids, and the rates are lower than 10 M-1·s-1.37

298

CT values. The observed loss of viability (-log(N/N0)obs) of pathogens can be

299

expressed as the sum of inactivation contributed by UV irradiation and radical attacks, as

300

shown in eqn. 10, in which, the inactivation by radical attacks was related to the radical

301

concentration multiplied by exposure time (CT, M·min).

302

 N − log  N0

  N  = − log  N  obs  0

  N  − log  UVC  N0 •

= f1 ( I , t ) + f 2 ([ OH ], t ) +

  N    • − log N  OH  0

  N    • − − log N  SO4  0

f 3 ([ SO4•− ], t ) +

f 4 ([CO3•− ], t )

   •−  CO3

(10)

303

In order to quantitatively express the contribution of each reactive species to the

304

inactivation of microbial surrogates, CT profile for each reactive species was obtained by

305

subtracting the inactivation by UV alone from the overall inactivation. Radical

306

concentrations were calculated based on the kinetic modeling results (Table 1). As

307

discussed above, it was difficult to create a system only dominated by hydroxyl radical

308

whereas it was possible for sulfate radical and carbonate radical. Therefore, CT profiles

309

of sulfate radical and carbonate radical were first obtained. The CT profile of hydroxyl

310

radical was then obtained based on the results subtracted of carbonate radical

311

contribution. It is recognized that eqn. 10 is a simplified assumption that does not

312

consider potentially interactive impacts of disinfectant species on the pathogens.

313

However, due to the limited knowledge on the disinfection effects of radical species, eqn.

314

10 served as an initial attempt to quantify the contributions from different radical species.

315

The CT values from eqn. 10 obtained in PBS matrix were then tested in real water

316

matrices to assess the robustness of this simplified model (next section).


Page 15 of 38


317

The CT profile of carbonate radical was obtained from the inactivation results in

318

carbonate radical dominated system (UV/H2O2/NaHCO3), in which carbonate radical

319

concentration was 8.64×10-12 M. Carbonate radical inactivated E. coli and MS2. For E.

320

coli, the CT profile has a slope of 4.35×1010 M-1·min-1 with a lag phase of 5.32×10-12

321

M·min. For MS2, the CT profile has a slope of 2.62×1010 M-1·min-1 (SI Figure S4C).

322

After obtaining the CT profile of carbonate radical, the CT profile of hydroxyl radical

323

can be calculated by subtracting the contribution from carbonate radical from the

324

observed inactivation of microbial surrogates. The slope and lag phase of CT profiles of

325

hydroxyl radical was calculated and shown in Table 2.

326

The CT profile of sulfate radical was obtained from the inactivation results in sulfate

327

radical dominated system (UV/10×PDS/TBA), in which sulfate radical concentration was

328

2.13×10-13 M. As discussed above, sulfate radical only inactivate bacteriophage MS2

329

within the disinfection time. A linear relation was obtained between the loss of MS2

330

viability and CT of sulfate radical (SI Figure S4B). The slope of the CT profile was

331

1.61×1012 M-1·min-1 (Table 2), meaning that exposure of MS2 at (1.61×1012)-1 M sulfate

332

radical for one minute could achieve one log of inactivation.

333

The slope values derived from literature19,30,34 are also included in Table 2 for

334

comparison. Significant differences exist among the studies, possibly due to the

335

employment of different microbial strains or measurement approaches for radical

336

concentrations. It is also worthwhile to note that some of the slope values are higher than

337

the commonly referred diffusion-controlled limits (i.e., 109–1010 M-1·s-1). However, for a

338

reaction between two reactants which are significantly different in size, such as

339

microorganism and radical, the rate limits should be higher than 1010 M-1·s-1. For



340

example, the diffusion-controlled limits for MS2 and hydroxyl radical was estimated

341

above 6.6×1011 M-1·s-1 (i.e., ~4×1013 M-1·min-1). Detailed calculations are shown in SI

342

Text S5.

343

The slopes of CT profiles are indicators of disinfection potency of each radical

344

species. E. coli is more efficiently inactivated by hydroxyl radical than carbonate radical.

345

As for MS2, hydroxyl radical is more efficient than sulfate radical followed by carbonate

346

radical. B. subtilis spores can only be inactivated by hydroxyl radical. The different

347

disinfection efficacy of radicals is expected to partly relate to their oxidizing power and

348

radical charge. Indeed, hydroxyl radical and sulfate radical have higher oxidizing power

349

((E° (•OH/H2O) = 1.9−2.7 V; E° (SO4•−/SO42−) = 2.5−3.1 V) than carbonate radical (E°

350

(CO3•−/CO32−) = 1.63 V at pH 8.4),41 indicating that hydroxyl radical and sulfate radical

351

are more reactive towards biomolecules. However, although sulfate radical has higher

352

oxidizing power than hydroxyl radical, it is less efficient to inactivate microbial

353

surrogates. This difference may be due to the electrostatic repulsion between the surface

354

of microbial surrogates and sulfate radical because they are both negatively charged. In

355

contrast, the non-charged hydroxyl radical likely can more easily attack the

356

microorganism surfaces. Besides oxidizing power and radical charge, hydroxyl radical’s

357

low selectivity in reactions with organic molecules may render higher disinfection

358

potency compared to sulfate radical and carbonate radical, which selectively react with

359

electron-rich molecules.

360

Regarding the difference among the microbial surrogates, MS2 is more vulnerable to

361

radical attack followed by E. coli and B. subtilis spores, meanwhile a lag phase in CT

362

profiles is only observed for E. coli and B. subtilis spores. These observations can be


Page 16 of 38

Page 17 of 38


363

explained by the differences in their repair mechanisms and outer structures. The capsid

364

of MS2 is primarily consisted of proteins, which react with radical species at higher rates

365

than other biomolecules, such as polysaccharides and lipids,37 which are the main

366

building blocks of the outer membranes of E. coli. As for B. subtilis spores, it was

367

suggested that some enzymes on the outer layer can generate pigments which potentially

368

deactivate reactive oxygen species.42. The overall experimental results suggest that it

369

would be beneficial to apply oxidants to enhance UV disinfection of viruses.

370

Inactivation in real water matrices. The inactivation of microbial surrogates was

371

further examined in real water matrices under the similar UV fluence rate (2.2×10-7

372

Einstein·L-1·s-1) and oxidant dose (0.3 mM). Different water samples, including surface

373

water and wastewater secondary effluent, were tested (SI Table S1). Control experiments

374

counting CFU and PFU of spiked microbial surrogates in the SW and WW samples

375

showed comparable results to those spiked in PBS, indicating that the microbial

376

surrogates were negligibly affected by SW or WW components.

377

Experiments showed that, in surface water matrix, the inactivation profiles of E. coli

378

by UV/H2O2 and UV/PDS processes were almost identical to that by UV only (Figure

379

3A), whereas substantially enhanced inactivation of MS2 was achieved with the addition

380

of H2O2 or PDS to UV (Figure 3B). However, in wastewater matrix, the inactivation of

381

either E. coli or MS2 was at similar rates under UV with or without the addition of

382

oxidants (Figure 3C,D). Dynamic kinetic simulations with the input of the real water

383

component data were conducted to predict the concentrations of radical species (Table 1).

384

Specifically, photo-decomposition of nitrate was considered as a source for hydroxyl

385

radical; DOM was considered as scavengers for hydroxyl radical, sulfate radical and



386

carbonate radical; radical reactions involving chloride, (bi)carbonate and sulfate were all

387

included in the kinetic simulations (SI Table S2). The calculated radical concentrations

388

were applied to eqn. 10 to obtain the predicted inactivation profiles of microbial

389

surrogates in the real water matrices. As Figure 3 shows, the predictions agreed well with

390

the experimental results. The good agreement between the predicted and experimental

391

inactivation indicates that the eqn. 10 captures the majority of disinfection actions for the

392

microbial surrogates investigated in this study.

393

Optimization of UV-based ADP. Oxidant dose effect on UV efficiency. Experiments

394

with the real water matrices showed that the UV-based ADP only enhanced the

395

inactivation of MS2 significantly in surface water matrix and great scavenging effects

396

occurred in wastewater matrix. The concentration of oxidants (0.3 mM) did not achieve

397

observable enhancement of the inactivation of E. coli and B. subtilis spores (Figure 4).

398

However, one may assume that a higher oxidant dose would overcome the scavenging

399

effects and achieve measurable inactivation enhancement. To test this hypothesis, model

400

simulations were performed by varying the dose of H2O2 or PDS in UV in surface water

401

and wastewater matrices. The term, UV efficiency (in log·(mJ·cm-2)-1), is defined as the

402

log inactivation of microbial surrogates normalized by the UV dose. The prediction of

403

UV efficiency was performed based on the kinetic model for radical concentrations and

404

eqn. 10 for microbial inactivation.

405

As Figure 4 shows, the increase of H2O2 dose or PDS dose has a great effect on the

406

UV efficiency for MS2, but has little effect on E. coli and B. subtilis spores, suggesting

407

the increase of oxidant dose would not be beneficial to enhance the inactivation efficacy

408

for E. coli and B. subtilis spores. The increase of H2O2 dose up to around 0.25 mM and


Page 18 of 38

Page 19 of 38


409

0.5 mM enables the UV efficiency for MS2 to surpass that for B. subtilis spores in

410

surface water and wastewater, respectively (Figure 4A,C). H2O2 dose up to around 1 mM

411

(for surface water) and 2 mM (for wastewater) renders the UV efficiency for MS2 similar

412

to that for E. coli, which is four times higher than the UV efficiency for MS2 by UV only.

413

Further increase of H2O2 dose yields a tapering increase of UV efficiency for MS2 due to

414

the scavenging effects from H2O2 itself. A similar trend of UV efficiency profile for MS2

415

was also observed at varying PDS dose (Figure 4B,D). However, the effectiveness of

416

PDS is quite different in surface water versus wastewater matrices. Although significant

417

enhancement of UV efficiency for MS2 is obtained in surface water matrix at increasing

418

PDS dose (Figure 4B), the increase of PDS yields limited enhancement in wastewater

419

matrix (Figure 4D). Indeed, the addition of up to 10 mM PDS only triples the UV

420

efficiency for MS2 in wastewater, which is still lower than that for E. coli. Comparing all

421

the simulation results in Figure 4, the investigation suggests that the disinfection efficacy

422

of UV/PDS process is more susceptible to real water matrix effect than the UV/H2O2

423

process.

424

Overall, the change of UV efficiency suggests that it would be beneficial to add a

425

certain amount of H2O2 or PDS to boost the inactivation of MS2 in ADPs. However, the

426

cost of oxidants should also be considered in order to systematically optimize the

427

UV/oxidant ADP.

428

Energy optimization. Based on the discussion above, the application of additional

429

oxidants, especially H2O2, to create ADP condition can achieve substantial enhancement

430

on the inactivation of MS2, but not for E. coli and B. subtilis spores. Therefore, energy

431

optimization was only performed for MS2. In order to optimize ADPs, an economic



Page 20 of 38

432

analysis using the EE/O concept was performed. EE/O is defined as the electric energy to

433

achieve one order of inactivation, which gives a quantitative cost-effective evaluation of a

434

given condition. The electrical energy of UV lamp and the consumption of oxidants

435

would be considered in EE/O evaluation. The overall EE/O can be expressed using eqn.

436

11. EE/O =

437

(P/V) + α ⋅ [Oxidant]  N  −log    N 0 t

(11)

438

where, P/V is the energy input of UV lamps with the unit of kWh·L-1; [Oxidant] is the

439

applied concentration of H2O2 or PDS (mM); α is the unit convertor to translate oxidant

440

amount to energy unit (i.e., 2.27×10-4 kWh·mmole-1 H2O2; 1.64×10-3 kWh·mmole-1 PDS,

441

the unit conversion is detailed in SI Text S6). The term, -log(N/N0)t is the inactivation of

442

MS2 under conditions corresponding to [Oxidant] and P/V values. Therefore, EE/O is

443

with the unit of kWh·L-1.

444

In order to achieve the most cost-effective condition, two alternative strategies are

445

commonly considered, installation of more UV lamps and addition of more oxidant dose.

446

Therefore, P/V and [Oxidant] were varied to predict the EE/O at each given UV and

447

oxidant doses. Applying the scan function of variables in Simbiology, radical

448

concentrations were predicted at UVC dose ranging from 2.4×10-5 to 4.8×10-4 Einstein·L-

449

1

450

by eqn. 10. A detailed demonstration of the calculation of EE/O is provided in SI Text S7.

451

The log(EE/O) at varying UVC doses and oxidant doses in surface water and

452

wastewater were calculated and shown in Figure 5, where cooler colors represent lower

453

EE/O while hotter colors represent higher EE/O. Without addition of oxidants (i.e., at x-

and oxidant dose from 0 to 1 mM. Then, the overall inactivation of MS2 was calculated


Page 21 of 38


454

axis = 0), the EE/O of UV alone is around 5.7×10-5 kWh·L-1. With the addition of H2O2

455

(Figure 5A,B), EE/O shifts to lower values in both surface water and wastewater, with the

456

exception that EE/O decreases then increases at the turning point around 0.05 mM H2O2

457

in wastewater below UVC dose of 1.0×10-4 Einstein·L-1. In UV/PDS ADP, the influence

458

of PDS to decrease EE/O starts to reverse at below 5×10-5 Einstein·L-1 of UVC dose in

459

surface water (Figure 5C), whereas EE/O always increases with the increase of PDS dose

460

in wastewater (Figure 5D). These trends have confirmed that it would be beneficial to

461

add a certain amount of oxidants to improve energy efficiency in the inactivation of MS2.

462

The solid line in Figure 5 presents the UV and oxidant dose combination to achieve

463

certain extent of inactivation. To meet a criteria of 4-log inactivation, certain oxidants

464

must be added at the UV irradiation below 4.2×10-4 Einstein·L-1. In the UV/H2O2 ADP,

465

the most energy-efficient condition is at around 5×10-5 Einstein·L-1 UV and 0.1 mM

466

H2O2 with the EE/O of 1.4×10-5 kWh·L-1 in surface water, and around 1.5×10-4

467

Einstein·L-1 UV and 0.08 mM H2O2 with the EE/O of 2.2×10-5 kWh·L-1 in wastewater.

468

As for UV/PDS ADP, the most energy-efficient condition is at around 1.0×10-4

469

Einstein·L-1 UV and 0.05 mM PDS with the EE/O of 3.5×10-5 kWh·L-1 in surface water,

470

whereas there is no optimal conditions within 5×10-4 Einstein·L-1 UV as the increase of

471

PDS always yields higher EE/O in wastewater. Therefore, based on the overall EE/O

472

evaluation, the UV/H2O2 ADP is more favorable than the UV/PDS ADP in both surface

473

water and wastewater matrices. The typical reduced equivalent dose in the UV

474

disinfection process is below 90 mJ/cm2 (i.e., ~5×10-4 Einstein·L-1), which is just

475

sufficient to achieve 4-log inactivation of MS2. However, the EE/O value (5.8×10-5

476

kWh·L-1) is much higher than the optimal points of UV/H2O2 ADP (i.e., 1.4×10-5 kWh·L-



477

1

for surface water; 2.2×10-5 kWh·L-1 for wastewater). Therefore, by combining UV

478

irradiation and H2O2, nearly two thirds of the energy consumption would be saved.

479

Environmental Implications. This study has demonstrated the disinfection potency

480

of novel UV-based ADPs, as well as provides new information on the effects of radical

481

species on microorganisms. This study is among the first to quantitatively investigate

482

sulfate radical and carbonate radical as reactive species that can inactivate

483

microorganisms. It was also elucidated that superoxide radical exerts negligible effect to

484

inactivate microorganisms. The new knowledge gained from this study is useful for

485

designing optimized UV-based ADPs for water treatment. Specifically, this study

486

suggests that UV/H2O2 is more cost-effective than UV disinfection for virus removal,

487

whereas it is not beneficial to upgrade UV disinfection to UV-based ADP for the

488

inactivation of bacteria and spores. For water treatment facilities to achieve lower EE/O,

489

one can adjust the number of UV lamps and oxidant doses based on the specific water

490

quality using the kinetic model provided in this study.

491

Results of this study are also relevant for certain natural sunlit water systems, where

492

radical species are generated by sunlight-excited photosensitizers. The difference in the

493

resistance of bacteria, viruses and spores to radical species also suggests that the presence

494

of radicals is likely to impact the microorganism community in water systems. In water

495

systems with a higher radical concentration, the microorganisms which are more resistant

496

to radical attack are likely to accumulate over the ones that are more vulnerable.

545 546

ASSOCIATED CONTENT

547

Supporting Information. Text S1-S7, Tables S1−S3 and Figures S1−S4. This material is


Page 22 of 38

Page 23 of 38

548


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

549 550

ACKNOWLEDGMENTS

551

This project was support by the Southern Research Institute. The authors would like to

552

thank Dr. Brian Mastin for his efforts on the initiation of this research.

553 554

REFERENCES

555

(1) Hewitt, J.; Leonard, M.; Greening, G. E.; Lewis, G. D. Influence of wastewater

556

treatment process and the population size on human virus profiles in wastewater. Water

557

Res. 2011, 45 (18), 6267-6276.

558 559

(2) CDC,

List

of

selected

multistate

foodborne

outbreak

http://www.cdc.gov/foodsafety/outbreaks/multistate-outbreaks/outbreaks-list.html.

560

(3) CDC, Viral special pathogens branch (VSPB) - outbreaks.

561

(4) Outbreak

562 563 564 565 566

investigations.

Database,

Worldwide

database

for

nosocomial

outbreaks.

http://www.outbreak-database.com. (5) U.S.

EPA.

U.

S.

Contaminant

candidate

list

3

-

CCL.

http://water.epa.gov/scitech/drinkingwater/dws/ccl/ccl3.cfm. (6) Betancourt, W. Q.; Rose, J. B. Drinking water treatment processes for removal of Cryptosporidium and Giardia. Vet. Parasitol. 2004, 126 (1–2), 219-234.

567

(7) Zhang, K.; Farahbakhsh, K. Removal of native coliphages and coliform bacteria

568

from municipal wastewater by various wastewater treatment processes: Implications to

569

water reuse. Water Res. 2007, 41 (12), 2816-2824.

570

(8) Lucena, F.; Duran, A.; Moron, A.; Calderon, E.; Campos, C.; Gantzer, C.; Skraber,



571

S.; Jofre, J. Reduction of bacterial indicators and bacteriophages infecting faecal bacteria

572

in primary and secondary wastewater treatments. J. Appl. Microbiol. 2004, 97 (5), 1069-

573

1076.

574 575 576 577

(9) Crittenden, J. C. H., K.; Hand, D. W.; Trussell, R. R.; Tchobanoglous, G. Mwh's

Water Treatment: Principles and Design. John Wiley & Sons: 2012. (10) Bove, F.; Shim, Y.; Zeitz, P. Drinking water contaminants and adverse pregnancy outcomes: a review. Environ. Health Perspect. 2002, 110 (Suppl 1), 61.

578

(11) Richardson, S. D.; Plewa, M. J.; Wagner, E. D.; Schoeny, R.; DeMarini, D. M.

579

Occurrence, genotoxicity, and carcinogenicity of regulated and emerging disinfection by-

580

products in drinking water: a review and roadmap for research. Mutat. Res-Rev. Mutat.

581

2007, 636 (1), 178-242.

582 583

(12) Dotson, A. D.; Rodriguez, C. E.; Linden, K. G. UV disinfection implementation status in US water treatment plants. J. Am. Water Works Assoc. 2012, 104 (5), 77-78.

584

(13) Wang, J.-J.; Liu, X.; Ng, T. W.; Xiao, J.-W.; Chow, A. T.; Wong, P. K.

585

Disinfection byproduct formation from chlorination of pure bacterial cells and pipeline

586

biofilms. Water Res. 2013, 47 (8), 2701-2709.

587

(14) Von Gunten, U.; Hoigne, J. Bromate formation during ozonization of bromide-

588

containing waters: interaction of ozone and hydroxyl radical reactions. Environ. Sci.

589

Technol. 1994, 28 (7), 1234-1242.

590 591 592 593

(15) Gerecke, A. C.; Sedlak, D. L. Precursors of N-nitrosodimethylamine in natural waters. Environ. Sci. Technol. 2003, 37 (7), 1331-1336. (16) Setlow, J. K. The effects of ultraviolet radiation and photoreactivation. Compr.

Biochem. 1968, 27


Page 24 of 38

Page 25 of 38

594 595


(17) Setlow, P. Mechanisms for the prevention of damage to DNA in spores of Bacillus species. Annu. Rev. Microbiol. 1995, 49 (1), 29-54.

596

(18) Riesenman, P. J.; Nicholson, W. L. Role of the spore coat layers in Bacillus

597

subtilis spore resistance to hydrogen peroxide, artificial UV-C, UV-B, and solar UV

598

radiation. Appl. Environ. Microbiol. 2000, 66 (2), 620-626.

599

(19) Mamane, H.; Shemer, H.; Linden, K. G. Inactivation of E. coli, B. subtilis spores,

600

and MS2, T4, and T7 phage using UV/H2O2 advanced oxidation. J. Hazard. Mater. 2007,

601

146 (3), 479-486.

602

(20) Nwachuku, N.; Gerba, C. P.; Oswald, A.; Mashadi, F. D. Comparative inactivation

603

of adenovirus serotypes by UV light disinfection. Appl. Environ. Microbiol. 2005, 71 (9),

604

5633-5636.

605

(21) McKinney, C. W.; Pruden, A. Ultraviolet disinfection of antibiotic resistant

606

bacteria and their antibiotic resistance genes in water and wastewater. Environ. Sci.

607

Technol. 2012, 46 (24), 13393-13400.

608

(22) Shemer, H.; Kunukcu, Y. K.; Linden, K. G. Degradation of the pharmaceutical

609

metronidazole via UV, Fenton and photo-Fenton processes. Chemosphere 2006, 63 (2),

610

269-276.

611 612

(23) Chu, W. Modeling the quantum yields of herbicide 2, 4-D decay in UV/H2O2 process. Chemosphere 2001, 44 (5), 935-941.

613

(24) Huber, M. M.; Canonica, S.; Park, G.-Y.; Von Gunten, U. Oxidation of

614

pharmaceuticals during ozonation and advanced oxidation processes. Environ. Sci.

615

Technol. 2003, 37 (5), 1016-1024.

616

(25) Anipsitakis, G. P.; Dionysiou, D. D. Transition metal/UV-based advanced



617 618 619

oxidation technologies for water decontamination. Appl. Catal., B 2004, 54 (3), 155-163. (26) Chan, T. W.; Graham, N. J.; Chu, W. Degradation of iopromide by combined UV irradiation and peroxydisulfate. J. Hazard. Mater. 2010, 181 (1), 508-513.

620

(27) Guan, Y.-H.; Ma, J.; Li, X.-C.; Fang, J.-Y.; Chen, L.-W. Influence of pH on the

621

formation of sulfate and hydroxyl radicals in the UV/peroxymonosulfate system.

622

Environ. Sci. Technol. 2011, 45 (21), 9308-9314.

623

(28) Yao, H.; Sun, P.; Minakata, D.; Crittenden, J. C.; Huang, C.-H. Kinetics and

624

modeling of degradation of ionophore antibiotics by UV and UV/H2O2. Environ. Sci.

625

Technol. 2013, 47 (9), 4581-4589.

626

(29) Zhang, R.; Sun, P.; Boyer, T. H.; Zhao, L.; Huang, C.-H. Degradation of

627

Pharmaceuticals and Metabolite in Synthetic Human Urine by UV, UV/H2O2, and

628

UV/PDS. Environ. Sci. Technol. 2015, 49 (5), 3056-3066.

629

(30) Cho, M.; Chung, H.; Choi, W.; Yoon, J. Linear correlation between inactivation of

630

E. coli and OH radical concentration in TiO2 photocatalytic disinfection. Water Res.

631

2004, 38 (4), 1069-1077.

632

(31) Cho, M.; Chung, H.; Choi, W.; Yoon, J. Different inactivation behaviors of MS-2

633

phage and Escherichia coli in TiO2 photocatalytic disinfection. Appl. Environ. Microbiol.

634

2005, 71 (1), 270-275.

635

(32) Cho, M.; Gandhi, V.; Hwang, T.-M.; Lee, S.; Kim, J.-H. Investigating synergism

636

during sequential inactivation of MS-2 phage and Bacillus subtilis spores with UV/H2O2

637

followed by free chlorine. Water Res. 2011, 45 (3), 1063-1070.

638

(33) Cho, M.; Kim, J.-H.; Yoon, J. Investigating synergism during sequential

639

inactivation of Bacillus subtilis spores with several disinfectants. Water Res. 2006, 40


Page 26 of 38

Page 27 of 38

640


(15), 2911-2920.

641

(34) Mattle, M. J.; Vione, D.; Kohn, T. Conceptual model and experimental framework

642

to determine the contributions of direct and indirect photoreactions to the solar

643

disinfection of MS2, phiX174, and adenovirus. Environ. Sci. Technol. 2014, 49 (1), 334-

644

342.

645 646

(35) Bounty, S.; Rodriguez, R. A.; Linden, K. G. Inactivation of adenovirus using lowdose UV/H2O2 advanced oxidation. Water Res. 2012, 46 (19), 6273-6278.

647

(36) Yang, Y.; Pignatello, J. J.; Ma, J.; Mitch, W. A. Comparison of halide impacts on

648

the efficiency of contaminant degradation by sulfate and hydroxyl radical-based

649

advanced oxidation processes (AOPs). Environ. Sci. Technol. 2014, 48 (4), 2344-2351.

650 651

(37) NIST:

NDRL/NIST

Solution

Kinetics

Database

on

the

Web.

http://kinetics.nist.gov/solution.

652

(38) Hijnen, W.; Beerendonk, E.; Medema, G. J. Inactivation credit of UV radiation for

653

viruses, bacteria and protozoan (oo)cysts in water: a review. Water Res. 2006, 40 (1), 3-

654

22.

655 656

(39) Madigan, M. T.; Martinko, J. M.; Dunlap, P. V.; Clark, D. P. Brock Biology of microorganisms 12th edn. International Microbiology 2008, 11, 65-73.

657

(40) Fisher, M. B.; Nelson, K. L. Inactivation of Escherichia coli by polychromatic

658

simulated sunlight: evidence for and implications of a Fenton mechanism involving iron,

659

hydrogen peroxide, and superoxide. Appl. Environ. Microbiol. 2014, 80 (3), 935-942.

660

(41) Zuo, Z.; Cai, Z.; Katsumura, Y.; Chitose, N.; Muroya, Y. Reinvestigation of the

661

acid–base equilibrium of the (bi) carbonate radical and pH dependence of its reactivity

662

with inorganic reactants. Radiat. Phys. Chem. 1999, 55 (1), 15-23.



663

(42) McKenney, P. T.; Driks, A.; Eichenberger, P. The Bacillus subtilis endospore:

664

assembly and functions of the multilayered coat. Nat. Rev. Microbiol. 2013, 11 (1), 33-44.

665 666


Page 28 of 38

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667 668 669 670

Figure 1. Inactivation of (A) E. coli, (B) bacteriophage MS2 and (C) Bacillus subtilis spores under UV, UV/H2O2 and UV/PDS conditions ([H2O2] = 0.3 mM, [PDS] = 0.3 mM, [PBS] = 3 mM at pH 7.0). UV fluence rate at 2.2×10-7 Einstein·L-1·s-1 was employed. Error bars represent one standard deviation of the means (n = 3).

671 672 673 674 675 676 677 678 679 680

Figure 2. Comparison of the inactivation of microbial surrogates under UV irradiation and UV with different dominated reactive species. Numbers on the bars indicate the corresponding conditions shown in Table 2. (A) superoxide radical dominated condition ((7*): 0.1 M TBA in PBS; (7): 3 mM H2O2, 0.3 mM PDS and 0.1 M TBA in PBS); (B) carbonate radical dominated condition ((6*): 0.1 M NaHCO3 in PBS; (6): 0.3 mM H2O2 and 0.1 M NaHCO3 in PBS); and (C) sulfate radical dominated condition ((5*): 0.1 M TBA in PBS; (5): 3 mM PDS and 0.1 M TBA in PBS). Conditions (5-7) were all under UV fluence rate of 2.2×10-7 Einstein·L-1·s-1. UV fluence (8.9×10-7 – 4.4×10-6 Einstein·L1 -1 ·s ) varied slightly for different conditions as detailed in SI Table S4. Error bars represent one standard deviation of the means (n = 3).

681 682 683

Figure 3. Inactivation of E. coli and bacteriophage MS2 in surface water (SW) or wastewater (WW) (UV fluence rate = 2.2×10-7 Einstein·L-1, [H2O2]0 = 0.3 mM, [PDS] = 0.3 mM). Error bars represent one standard deviation of the means (n=3).

684 685

Figure 4. UVC efficiency (log of inactivation normalized by UV dose) in surface water (SW) and wastewater (WW) at various levels of H2O2 or PDS dose.

686 687 688

Figure 5. Log(EE/O) (in kWh·L-1) for the inactivation of MS2 in surface water (SW) and wastewater (WW) with UV/H2O2 ADP or UV/PDS ADP. Solid lines represent log of inactivation.

689 690

Table 1. Simulated Molar Concentrations (in M) of Reactive Species with Various Components in Solutions

691 692

Table 2. The Disinfection CT (Concentration × Exposure Time) Values of UVC Irradiation and Radical Species.

693



Page 30 of 38

694 1

1

(B) MS2

(A) E. coli

0

0

-log (N/N0)

-log (N/N0)

-1 -2 -3 UV UV/H2O2

-4

UV UV/H2O2

-2

UV/PDS

-3

UV/PDS

-4

-5 -6

-5 0

695

-1

2

4

6

8

10

12

0

20

UV dose (mJ/cm2)

40

60

80

100

UV dose (mJ/cm2)

1

(C) B. subtilis spores

-log (N/N0)

0 -1 -2 -3

UV UV/H2O2

-4

UV/PDS

-5 0

696 697 698 699 700 701

5

10

15

20

25

30

2

UV dose (mJ/cm )

Figure 1. Inactivation of (A) E. coli, (B) bacteriophage MS2 and (C) Bacillus subtilis spores under UV, UV/H2O2 and UV/PDS conditions ([H2O2] = 0.3 mM, [PDS] = 0.3 mM, [PBS] = 3 mM at pH 7.0). UV fluence rate at 2.2×10-7 Einstein·L-1·s-1 was employed. Error bars represent one standard deviation of the means (n = 3).


Page 31 of 38


(A) UV/TBA(/H2O2/PDS)

-log (N/N0)

6

E. coli

4

B. subtilis spores

MS2

2

7*

7

7*

7

7*

7

0

702 (B) UV/NaHCO3(/H2O2)

-log (N/N0)

6

MS2 E. coli B. subtilis spores

4

2

6*

6

6*

6

6*

6

0

703

-log (N/N0)

6

(C) UV/TBA(/PDS)

E. coli

4

B. subtilis spores

MS2

2

5*

704 705 706 707 708 709 710 711 712 713 714

5

5*

5

5*

5

0

Figure 2. Comparison of the inactivation of microbial surrogates under UV irradiation and UV with different dominated reactive species. Numbers on the bars indicate the corresponding conditions shown in Table 2. (A) superoxide radical dominated condition ((7*): 0.1 M TBA in PBS; (7): 3 mM H2O2, 0.3 mM PDS and 0.1 M TBA in PBS); (B) carbonate radical dominated condition ((6*): 0.1 M NaHCO3 in PBS; (6): 0.3 mM H2O2 and 0.1 M NaHCO3 in PBS); and (C) sulfate radical dominated condition ((5*): 0.1 M TBA in PBS; (5): 3 mM PDS and 0.1 M TBA in PBS). Conditions (5-7) were all under UV fluence rate of 2.2×10-7 Einstein·L-1·s-1. UV fluence (8.9×10-7 – 4.4×10-6 Einstein·L1 -1 ·s ) varied slightly for different conditions as detailed in SI Table S4. Error bars represent one standard deviation of the means (n = 3).



Page 32 of 38

1 0

(A) E. coli, SW

0

(B) MS2, SW -2

-log (N/N0)

-log (N/N0)

-1 -2 UV UV/H2O2

-3

-4

UV/PDS UV (model, R2 = 0.9699) UV/H2O2 (model, R2 = 0.9325)

-4 -5

UV UV/H2O2

-6


-8

UV/PDS (model, R2 = 0.9864)


-6

-10 0

1

2

3

4

5

6

0

5

10

15

Time (min)

715

20

25

30

35

Time (min)

1

1

(D) MS2, WW

(C) E. coli, WW

0

0

-log (N/N0)

-log (N/N0)

-1 -2 -3

UV UV/H2O2

-4


-5

-1 -2 UV UV/H2O2

-3


-4


2

UV/PDS (model, R = 0.9325) -6

-5 0

716 717 718 719 720

1

2

3

Time (min)

4

5

6

0

5

10

15

20

25

30

35

Time (min)

Figure 3. Inactivation of E. coli and bacteriophage MS2 in surface water (SW) or wastewater (WW) (UV fluence rate = 2.2×10-7 Einstein·L-1, [H2O2]0 = 0.3 mM, [PDS] = 0.3 mM). Error bars represent one standard deviation of the means (n=3).


Page 33 of 38


721 1.0

2.0

-log(N/N0) / (I0t) (cm /mJ)

0.8

2

0.6 E. coli MS2 B. subtilis spores

0.4

E. coli MS2 B. subtilis spores

1.8

2


(A) SW, UV/H2O2

0.2

1.6

(B) SW, UV/PDS

1.4 1.2 1.0 0.8 0.6 0.4 0.2

0.0 0

2

4

6

8

0.0

10

0

722

4


2

2


0.5 0.4

(C) WW, UV/H2O2

0.3 0.2 0.1 0.0 0

2

4

6

8

10

0.30

E. coli MS2 B. subtilis spores

0.6

6

PDS (mM)

0.7

723

2

H2O2 (mM)

8

10

0.25 E. coli MS2 B. subtilis spores

0.20 0.15 0.10

(D) WW, UV/PDS

0.05 0.00 0

2

H2O2 (mM)

4

6

8

10

PDS (mM)

724 725 726

Figure 4. UVC efficiency (log of inactivation normalized by UV dose) in surface water (SW) and wastewater (WW) at various levels of H2O2 or PDS dose.

727 728 729 730



(A) SW, UV/H2O2

731

(B) WW, UV/H2O2

732


Page 34 of 38

Page 35 of 38


(C) SW, UV/PDS

733

(D) WW, UV/PDS

734 735 736 737

Figure 5. Log(EE/O) (in kWh·L-1) for the inactivation of MS2 in surface water (SW) and wastewater (WW) with UV/H2O2 ADP or UV/PDS ADP. Solid lines represent log of inactivation.



Page 36 of 38

738 739

Table 1. Simulated Molar Concentrations (in M) of Reactive Species with Various Components in Solutions Reaction System

740 741 742 743

•

OH

(M)

SO •4− (M)

CO •3− (M)

HO •2 /O •2− (M)

(1)

UV/H2O2

1.78×10-13

1.64×10-19

4.28×10-13

2.83×10-8

(2)

UV/PDS

3.47×10-13

2.09×10-13

3.53×10-14

6.84×10-14

(3)

UV/H2O2/TBA

2.09×10-17

3.12×10-24

5.67×10-17

2.17×10-11

(4)

UV/PDS/TBA

2.25×10-18

2.17×10-14

2.26×10-15

3.06×10-24

(5)

UV/10×PDS/TBA

2.21×10-17

2.13×10-13

2.22×10-15

3.20×10-22

(6)

UV/H2O2/NaHCO3

1.19×10-15

1.21×10-25

8.64×10-12

8.95×10-8

(7)

UV/10×H2O2/PDS/TBA

2.09×10-16

1.52×10-14

2.59×10-15

2.05×10-8

(8)

UV/H2O2 in SW

1.36×10-14

9.14×10-23

3.86×10-13

(9)

UV/PDS in SW

7.30×10-15

6.60×10-14

1.30×10-13

(10)

UV/H2O2 in WW

2.31×10-15

3.60×10-23

1.20×10-14

(11)

UV/PDS in WW

1.50×10-16

4.17×10-15

2.15×10-13

Solution medium (1-7) was 3.0 mM phosphate buffer at pH 7.0; oxidant concentration was 0.3 mM in most cases or was 3.0 mM in where 10× was indicated; TBA concentration was 0.1 M; NaHCO3 concentration was 100 mM; background total inorganic carbon = 4.78×10-5 M; UV fluence rate was 2.2×10-7 Einstein·L-1·s-1; total simulation time was 120 s.


Page 37 of 38


744 745

Table 2. Disinfection CT (Concentration × Exposure Time) Values of UVC Irradiation and Radical Species Determined in This Study. E. coli

UVC (254 nm) Hydroxyl radical Sulfate radical

B. subtilis spores

CTlag

Slope

CTlag

Slope

CTlag

Slope

1.56×10-5

9.20×104

0

9.10×103

2.96×10-5

4.14×104

2.50×1012 7.55×1012 a 4.25×109 b

0

9.30×1012 4.17×1012 a 1.93×1011 c

1.62×10-13

6.23×1011

Inactivation of Escherichia coli, Bacteriophage MS2, and Bacillus

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