A New Approach to Controlling Halogenated DBPs - ACS Publications

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Removal of Intermediate Aromatic Halogenated DBPs by Activated Carbon Adsorption: A New Approach to Controlling Halogenated DBPs in Chlorinated Drinking Water Jingyi Jiang, Xiangru Zhang, Xiaohu Zhu, and Yu Li Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b06161 • Publication Date (Web): 15 Feb 2017 Downloaded from http://pubs.acs.org on February 16, 2017

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Environmental Science & Technology

1

Removal of Intermediate Aromatic Halogenated DBPs by Activated Carbon Adsorption: A New

2

Approach to Controlling Halogenated DBPs in Chlorinated Drinking Water

3

Jingyi Jiang, Xiangru Zhang*, Xiaohu Zhu and Yu Li

4 5

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

6

Kong, China

7

S Supporting Information

8

ABSTRACT:

9

disinfection

During of

chlorine

drinking

10

chlorine may react

11

organic matter (NOM) and bromide

12

ion

13

halogenated disinfection byproducts

14

(DBPs). To mitigate adverse effects

15

from

16

activated carbon (GAC) adsorption

17

has been considered as one of the best available technologies for removing NOM (DBP

18

precursor) in drinking water treatment. Recently, we have found that many aromatic halogenated

19

DBPs form in chlorination, and they act as intermediate DBPs to decompose and form

20

commonly known DBPs including trihalomethanes and haloacetic acids. In this work, we

21

proposed a new approach to controlling drinking water halogenated DBPs by GAC adsorption of

22

intermediate aromatic halogenated DBPs during chlorination, rather than GAC adsorption of

23

NOM prior to chlorination (i.e., traditional approach). Rapid small-scale column tests were used

24

to simulate GAC adsorption in the new and traditional approaches. Significant reductions of

25

aromatic halogenated DBPs were observed in the effluents with the new approach; the removals

26

of total organic halogen, trihalomethanes, and haloacetic acids by the new approach always

27

exceeded those by the traditional approach; and the effluents with the new approach were

28

considerably less developmentally toxic than those with the traditional approach. Our findings

29

indicate that the new approach is substantially more effective in controlling halogenated DBPs

30

than the traditional approach.

in

raw

DBP

water

with

water,

to

exposure,

natural

generate

granular

1

ACS Paragon Plus Environment


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31

INTRODUCTION

32

Chlorine is the most widely employed disinfectant in inactivating pathogens, but it may react

33

with natural organic matter (NOM) and bromide in raw water to generate unintended

34

halogenated disinfection byproducts (DBPs) in drinking water.1–6 In fact, bromide is present in

35

raw waters worldwide. Bromide levels up to 2‒4 mg/L have been detected in some raw waters.7,8

36

Once adopting chlorine to disinfect bromide-containing waters, the formed brominated DBPs

37

along with chlorinated DBPs are likely to exert potential health risks on consumers.

38

Epidemiological studies have reported that human ingestion of chlorinated drinking water

39

containing halogenated DBPs is somewhat related to increased spontaneous abortions, stillbirth,

40

birth defects, bladder cancer, and colorectal cancer.9,10 Toxicological studies have also shown

41

that trihalomethanes (THMs), haloacetic acids (HAAs) and other DBPs are genotoxic or

42

carcinogenic in laboratory creatures.1,11 Among all halogenated DBPs, brominated DBPs are of

43

increasing concern because they are usually tens-to-hundreds of times more toxic than their

44

chlorinated analogs.1 A collective parameter, total organic halogen (TOX), has been widely used

45

as a quantitative surrogate and a toxicity indicator for the overall halogenated DBPs in

46

disinfected waters.11–15

47

Because of concerns over the adverse effects of DBPs, the U.S. EPA has regulated four

48

THMs (THM4) and five HAAs (HAA5) in the Disinfectants/DBPs Rule with maximum levels at

49

80 and 60 µg/L, respectively.16 In response to the regulation, various strategies have been carried

50

out for controlling halogenated DBPs, especially THMs and HAAs, in chlorinated drinking

51

waters. Generally, there are three major strategies, including source control, alternative

52

disinfectants, and precursor removal.17 Source control involves environmental management

53

policies and engineering techniques to lower NOM and bromide concentrations in source waters.

54

In water utilities, the second and third options are often adopted. Alternative disinfectants 2


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55

including chloramines, chlorine dioxide, and ozone could be adopted to replace chlorine, but the

56

formation of other DBP species can still pose a health risk to the consumers.17 Precursor removal

57

aims at lowering the NOM concentration in raw water prior to disinfection. NOM level in raw

58

water can be determined with dissolved organic carbon (DOC) measurement. Since the

59

formation of regulated THMs and HAAs somewhat depends on the raw water DOC level,

60

removal of DOC presumably leads to the reduction of THM or HAA precursors.18‒20 Among all

61

treatments concerning raw water DOC removal, granular activated carbon (GAC) adsorption is

62

recommended in the Disinfectants/DBPs Rule by U.S. EPA as one of the best available

63

technologies for water utilities.16,17 Moreover, GAC adsorption has been reported to remove the

64

precursors of some emerging DBPs in NOM.20‒22 However, considering the size exclusion effect,

65

high molecular weight humic substances (a major fraction in NOM) in raw water may be unable

66

to diffuse into micro-pores and even block some meso-pores in GAC particles, resulting in rapid

67

saturation of a GAC filter and ineffective control of DBP precursors.23 Despite many efforts

68

made to control the formation of halogenated DBPs, most previous studies focused on

69

controlling DBP precursors and few of them investigated the treatment of halogenated DBPs

70

already formed. This is most likely because there is hardly a panacea to effectively and

71

economically treat various halogenated DBPs simultaneously. It has been reported that a point-

72

of-use carbon filter was effective in removing THMs, but it was not effective in removing HAAs

73

unless biological degradation occurred.24‒27

74

Recently, an innovative precursor ion scan (PIS) scheme for fast selective detection of polar

75

halogenated DBPs using an electrospray ionization-triple quadrupole mass spectrometer (ESI-

76

tqMS) has been developed.28 By setting PIS of m/z 79/81 or 35/37, almost all polar brominated

77

or chlorinated DBPs in a water sample can be selectively detected.28‒30 By applying ultra

3



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performance liquid chromatography (UPLC) with the ESI-tqMS, many new halogenated DBPs

79

have been detected and identified, and most of them are aromatic halogenated DBPs, which can

80

be classified into five groups: halo-1,4-hydrobenzoquinones, halo-4-hydroxybenzaldehydes,

81

halo-4-hydroxybenzoic acids, halo-salicylic acids, and halo-phenols.29,30 At about the same time,

82

Li’s team has also identified another group of aromatic halogenated DBPs, halo-benzoquinones,

83

in drinking water.31,32 More importantly, it has been demonstrated that these aromatic

84

halogenated DBPs act as intermediate DBPs which further decompose during chlorination to

85

form commonly known DBPs,29,30,33 including the regulated THMs and HAAs. Compared to

86

humic substances in NOM, intermediate aromatic halogenated DBPs are generally lower in

87

molecular weight and smaller in size. Thus, in comparison with the traditional GAC treatment

88

aiming at the NOM adsorption, intermediate aromatic halogenated DBPs may access to the

89

micro-pores of GAC particles and make better use of the total pore volumes of GAC particles.

90

Moreover, NOM molecules usually contain both hydrophobic and hydrophilic entities,19 while

91

aromatic compounds (including aromatic halogenated DBPs) are usually hydrophobic and have

92

relatively high affinity towards GAC.34 Accordingly, we hypothesized that, in comparison to the

93

GAC adsorption of NOM prior to chlorination (i.e., traditional approach), a significant reduction

94

of overall halogenated DBPs, as well as the regulated THMs and HAAs, could be achieved by

95

the GAC adsorption of already-formed intermediate aromatic halogenated DBPs during

96

chlorination (i.e., new approach). Notably, it has been demonstrated that aromatic halogenated

97

DBPs usually presented tens-to-hundreds times higher development toxicity than aliphatic

98

halogenated DBPs.35‒37 Considering the higher developmental toxicity of aromatic halogenated

99

DBPs solely, it is also essential to remove them from drinking water.

100

The objectives of this work were to determine the feasibility of removing halogenated DBPs,

4


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especially intermediate aromatic ones, during chlorination by GAC adsorption, and to validate

102

that the new approach (i.e., GAC adsorption during chlorination for intermediate aromatic

103

halogenated DBP removal) is more effective in removing halogenated DBPs than the traditional

104

approach (i.e., GAC adsorption prior to chlorination for NOM removal). To simulate GAC

105

filter’s operation for both approaches, the rapid small scale column test (RSSCT) was used.

106

RSSCT is a scaled-down version of a pilot or full-scale fixed-bed GAC filter and can be applied

107

to predict the similar breakthrough curve of a pilot or full-scale system.38‒40 The removals of

108

aromatic halogenated DBPs, THMs, HAAs, and TOX with both approaches were evaluated and

109

compared. Comparative developmental toxicity of the treated waters against the embryos of

110

Platynereis dumerilii was studied. This bioassay is a sensitive in vivo metric and has been

111

successfully employed in comparing the developmental toxicity of numerous DBP species and

112

DBP mixtures in disinfected waters.13,35,36,41,42

113 114

MATERIALS AND METHODS

115

Chemicals, Reagents and Seawater. A NaOCl stock solution (>50000 mg/L as Cl2) was

116

supplied by Allied Signal. The working solutions were prepared by diluting the commercial

117

stock and calibrated by the DPD/FAS titration method.43 Suwannee River NOM (SRNOM,

118

2R101N) was supplied by the International Humic Substances Society. Standards for THM4 and

119

nine HAAs (HAA9) were purchased as two mixtures (2000 mg/L for each species) from Supelco.

120

3,5-Dichloro-4-hydroxybenzaldehyde (97%), 3,5-dichloro-4-hydroxybenzoic acid (98%), 3,5-

121

dichlorosalicylic acid (99%), 3-bromo-5-chloro-4-hydroxybenzaldehyde (95%), and 3,5-

122

dibromosalicylic acid (98%) were purchased from International Laboratory USA. 3,5-Dibromo-

123

4-hydroxybenzaldehyde (98%) was purchased from Alfa Aesar. 3,5-Dibromo-4-hydroxybenzoic

124

acid

(≥98%)

was

purchased

from

Indofine

Chemical

Company.

2,6-Dibromo-1,45



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hydrobenzoquinone (97%), 2,4,6-trichlorophenol (98%), 2,4,6-tribromophenol (99%), 2,6-

126

dichloro-4-nitrophenol (98%), and 2,6-dibromo-4-nitrophenol (98%) were purchased from

127

Aldrich. Methanol, acetonitrile (ACN), methyl tert-butyl ether (MtBE), and other chemicals

128

were reagent grade or higher and supplied by Aldrich. Bituminous coal-based GAC (Calgon

129

Filtradsorb 300, F300) was obtained from Calgon Carbon Corporation (Tianjin, China).

130

Prepacked coconut-based GAC column TXAPPC (Mitsubishi, Japan) was used for TOX

131

measurement. Ultrapure water (18.2 MΩ·cm) was provided by a Cascada I water purification

132

system (PALL). Seawater was collected locally, filtered with a 0.45-µm membrane, steam

133

autoclaved at 121 ºC for 20 min, and cooled to room temperature prior to culturing P. dumerilii

134

and conducting toxicity test (Supporting Information, SI).

135

RSSCT. The RSSCT was conducted for both approaches. The proportional diffusivity-

136

RSSCT was adopted to determine the appropriate column operation parameters, with which the

137

DBP breakthrough with the co-loading of background NOM could be predicted as accurately as

138

possible.38 A brief summary of parameters and assumptions used in the RSSCT is shown in the

139

SI and Table S1. The column was prepacked with virgin grounded Calgon F300 whose mean

140

particle diameter was 76 µm (170 × 230 mesh). It was designed to meet the restrictions set by

141

previous studies.39,40 Specifically, to limit the dispersion effect, the minimum Reynolds number

142

of the small column was set at 0.54; to mitigate the wall and channeling effects, the ratio of the

143

column inner diameter (ID) to the mean particle diameter of GAC was larger than 50. A typical

144

empty bed contact time of 10 min was chosen to simulate a pilot-scale system. The operation

145

temperature was kept at 20 ± 1 °C and the flow rate was 6.93 ± 0.04 mL/min.

146

Experimental Set-up of the New and Traditional Approaches and Collection of Influent and

147

Effluent Samples. The configurations of the influent generation and the GAC adsorption (i.e.,

148

RSSCT) system are shown in Figure 1. All the experimental set-up (including the pump head, 6


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fittings, tubing, and tanks) in contact with water was made of Teflon, stainless steel, or glass. By

150

feeding different working solutions, the system can be used to simulate the new approach (i.e.,

151

GAC adsorption during chlorination) and the traditional approach (i.e., GAC adsorption prior to

152

chlorination). In the new approach, the chlorine addition was conducted through a stainless-steel

153

static mixer (FMX8442S, Omega, U.S.) which enabled the fully mixing of two working

154

solutions. “NOM feed” and “Chlorine feed” was at a 1:1 (v/v) ratio, indicating a simulated raw

155

water containing 3 mg/L SRNOM as C, 90 mg/L NaHCO3 as CaCO3 for alkalinity, and 2 or 0

156

mg/L KBr as Br− was reacted with 5 mg/L NaOCl as Cl2. The relatively high bromide

157

concentration in the simulated raw water was used to amplify the production of brominated

158

DBPs.29,30 Bromide in surface waters can reach up to 2 mg/L in Israel and 4.13 mg/L in

159

Australia.7,8 After the chlorine addition, the chlorinated water then traveled along a Teflon tubing

160

(11.5 m × 4.8 mm ID, with a hydraulic retention time of 30 min). The 30-min chlorination was

161

conducted to simulate a typical disinfection scenario in utilities. The CT value, an index for

162

evaluating disinfection efficiency, was 103.4 or 129.8 mg/L as Cl2 × min for the bromide-

163

containing or bromide-free simulated raw water, respectively. They were above the CT values

164

required for the 3-log reduction of protozoa Giardia lambila (61‒88 mg/L as Cl2 × min at pH 8‒

165

9)44 and the 2-log reduction of viruses (2‒30 mg/L as Cl2 × min at pH 7‒9).45 Besides,

166

intermediate aromatic halogenated DBPs have been reported to form at relatively high levels in a

167

30-min chlorinated simulated raw water.29 Peristaltic pumps (Masterflex Model 7524-65, Cole-

168

Parmer Instrument, U.S.) with Teflon diaphragm pump heads (Masterflex Model 77390-00,

169

Cole-Parmer Instrument, U.S.) were used to distribute the chlorinated water to GAC column via

170

foil-wrapped Teflon tubing so that the chlorination was conducted in darkness. The effluent

171

samples were collected intermittently during the whole RSSCT operation. The effluent pH

7



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values ranged from 8.5 to 8.7. No chlorine residual was detectable in all effluent samples after

173

GAC adsorption, which was consistent with Snoeyink et al.46 To simulate the traditional

174

approach, one of the working solutions, “Chlorine feed”, was substituted by ultrapure water. The

175

effluent samples were also collected intermittently during the whole RSSCT operation. Then, the

176

effluent samples were subjected to chlorination in darkness under the same CT values as the new

177

approach (Tables S2 and S3 for chlorination of bromide-containing and bromide-free effluent

178

samples, respectively) so that the disinfection efficiencies in both approaches were kept the same.

179

The pH values of all the effluent samples were not further adjusted during chlorination (pH 8.4‒

180

8.7). After 30-min chlorination, chlorine residuals in all the effluent samples were measured and

181

quenched with 105% of the required stoichiometric amount of 0.1 M Na2S2O3. For both

182

approaches, the influent samples were also collected before the GAC adsorption. To compare the

183

influent water samples with the two approaches, the influent DBP level with the traditional

184

approach was referred to the DBP level in the influent sample that was dosed with 5 mg/L

185

NaOCl as Cl2 for a 30-min contact time in darkness.

186

Regarding daily maintenance of the system, all the working solutions were refilled every 16

187

h and the flow rate was measured and calibrated every 8 h. The end-points of RSSCT operation

188

of both approaches were set at a time when the effluent DOC level reached up to approximately

189

100% of the influent DOC level, which was around a throughput of 12000 bed volumes (BVs).

190

Later, to obtain a nearly complete TOX, THM4, and HAA5 breakthrough profile, the RSSCT

191

operation with the new approach was prolonged to a throughput of 22500 BVs. Parallel RSSCT

192

operations were conducted and reproducible breakthrough profiles were obtained, with details

193

shown in the SI and Figure S1.

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It needs pointing out that coagulation (often used in combination with flocculation and

195

sedimentation) is a treatment unit that is designed to remove suspended solids. Due to the

196

absence of suspended solids in the simulated raw waters, coagulation was not involved in both

197

approaches. SRNOM is a well-characterized standard reference material from the International

198

Humic Substances Society. SRNOM, rather than coagulated SRNOM, has been widely used in

199

DBP studies.29,30,47–50 The advantage of using SRNOM directly in this study is that it provided a

200

good starting material for better comparison of the two approaches and for convenient

201

verification of the results in other laboratories. (It needs mentioning that, at the request of a

202

reviewer, we also conducted a test with the coagulated SRNOM and compared the TOX

203

formation with both approaches. The details are shown in SI and Figure S2.)

204

It should be noted that the chlorination in the new approach was for primary disinfection.

205

This is different from prechlorination, in which a low dosage of chlorine is applied at the very

206

beginning of a drinking water treatment to control biological fouling, odor, or reduced iron or

207

manganese.

208

Subsequent Chlorination of Effluents with the New and Traditional Approaches. Since there

209

was no detectable chlorine residual in the effluent with the new approach, an extra addition of

210

chlorine to the effluent was conducted to keep a certain disinfectant residual in the distribution

211

system (i.e., subsequent chlorination). The bromide-containing effluent was selected to study the

212

levels and toxicity of halogenated DBPs under such subsequent chlorination. Firstly, the

213

bromide-containing effluent samples with the traditional approach were collected and chlorinated

214

as aforementioned. After a 30-min chlorination, their chlorine residuals were measured (Table

215

S4). Then, the same levels of chlorine were compensated back to the corresponding effluent

216

samples with the new approach. To simulate the chlorination in the distribution system, the pH

9



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values for all the samples were adjusted to 8.5 and the contact time was 1 d. After 1-d subsequent

218

chlorination, the chlorine residuals in all the effluent samples with the new and traditional

219

approaches were measured and quenched with 105% of the required stoichiometric amount of

220

0.1 M Na2S2O3. A control sample was generated by chlorinating the corresponding bromide-

221

containing simulated raw water with a chlorine dose of 5 mg/L NaOCl as Cl2 and a contact time

222

of 1 d and 30 min in darkness.

223

Sample Pretreatment. For each sample, it was divided into three aliquots. The first aliquot

224

was subjected to DOC, TOX, THM and HAA analyses. The second aliquot was extracted and

225

concentrated following a previous method for MS analysis.13,29,30 Briefly, the 1-L sample was

226

adjusted to pH 0.5 with sulfuric acid and was dosed with 100 g Na2SO4. The sample was then

227

extracted with 100 mL of MtBE. The upper organic layer was transferred and concentrated to 0.5

228

mL by rotary evaporation. The 0.5-mL MtBE extract was added with 20 mL of ACN for solvent

229

exchange and the mixture was rotoevaporated to 1.0 mL. The 1.0-mL solution in ACN was

230

preserved at 4 °C and it was mixed with ultrapure water at 1:1 (v/v) ratio prior to MS analysis.

231

The third aliquot was used in the developmental toxicity assay. In brief, the sample was

232

concentrated following the same liquid-liquid-extraction procedure stated above, except that the

233

0.5-mL MtBE extract (after rotary evaporation) was dried out by nitrogen gas. The solid was

234

preserved at 4 °C and dissolved in seawater 30 min before the toxicity test as a toxicity test stock

235

solution. Notably, because it has been proved that the volatile fraction of a DBP mixture has little

236

contribution to the overall developmental toxicity,41 this bioassay could still reveal the toxic

237

potency of the DBP mixtures despite the loss of volatile DBPs during the sample pretreatment.

238

Measurement of DOC, TOX, THMs and HAAs. DOC was measured using a TOC-VSH

239

analyzer (Shimadzu). TOX was determined according to Standard Method 5320B43 with an off-

10


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line ion chromatograph (Dionex).51,52 The detection of THMs and HAAs followed EPA methods

241

551.1 and 552.2 (SI) using a gas chromatograph with an electron capture detector (7890A,

242

Agilent).

243

(UPLC/)ESI-tqMS Analysis. An ESI-tqMS system (Waters) was applied to analyze the

244

pretreated samples. The ESI-tqMS instrumental parameters were optimized and set according to

245

previous studies (SI).13,53 The detection of overall polar brominated or chlorinated DBPs was

246

achieved by conducting PIS of m/z 79/81 or 35/37, respectively. Intermediate aromatic

247

halogenated DBPs were analyzed with Zhai and Zhang’s procedure29 using UPLC (Acquity,

248

Waters) coupled with ESI-tqMS. A Waters HSS T3 column (1.8 µm particle size, 100 × 2.1 mm)

249

was used for pre-separation. Other parameters for the instrument setting are shown in the SI. For

250

a molecular ion detected by PIS, the multiple reaction monitoring (MRM) mode was used to gain

251

the retention time and the isotopic abundance ratio in the UPLC/ESI-tqMS analysis. To verify

252

the presence of a specific halogenated DBP in a pretreated sample, the corresponding standard

253

compound and the sample spiked with the corresponding standard compound were analyzed with

254

the same MRM mode.

255

Comparative Developmental Toxicity Bioassay with the Embryos of a Polychaete P. dumerilii. A

256

recently developed acute toxicity bioassay with the embryos of a polychaete P. dumerilii was

257

adopted in this study.35 The details of stock cultural conditions of P. dumerilii and the

258

developmental toxicity assay are shown in SI. Briefly, the 12-h embryos of P. dumerilii were

259

exposed to a series of bromide-containing or bromide-free effluent samples with both new and

260

traditional approaches (concentrated by a same concentration factor) for another 12 h. After 24-h

261

post-fertilization, the normal embryos should develop into the first larval stage. According to the

11



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embryo’s normal development percentage, the response profiles of effluent samples with the new

263

and traditional approaches were obtained.

264 265

RESULTS AND DISCUSSION

266

Characteristics of Influents with the New and Traditional Approaches. Water quality

267

parameters including DOC, THMs, HAAs, and TOX of four RSSCT influents are shown in

268

Table S5. By keeping the same hydraulic conditions and CT values, the DBP levels in the

269

influent with the new approach were approximately the same as those in the chlorinated influent

270

with the traditional approach. Since brominated DBPs are of great health concern,1,2,11,35,37 the

271

effective control of halogenated DBPs in chlorinated bromide-containing water may be of great

272

significance in safe drinking water production.

273

The New Approach Reduced the Levels of Polar Halogenated DBPs, Especially Aromatic Ones,

274

More Effectively than the Traditional Approach. With the aid of PIS, almost all polar brominated

275

or chlorinated DBPs in a water sample were revealed. Figure S3 displays the ESI-tqMS PIS m/z

276

79 spectrum of the bromide-containing influent with the new approach. Various polar

277

brominated DBPs were selectively detected. Figure 2 shows the ESI-tqMS PIS spectra of m/z 79

278

of the RSSCT effluent samples collected from the traditional and new approaches. As the BVs of

279

water treated with either approach increased from 300 to 12000, various brominated DBPs (e.g.,

280

m/z 171/173 for bromochloroacetic acid and m/z 215/217 for dibromoacetic acid) broke through

281

out of the column and their peak intensities increased in the collected effluent samples. But with

282

the new approach (Figure 2h‒n), the intensities of the two HAAs in the effluent samples were all

283

significantly lower than those in the corresponding effluent samples with the traditional approach

284

(Figure 2a‒g). With the same instrument setup, the total ion intensity (TII) in the PIS m/z 79

285

spectrum of a sample can reflect the total level of polar brominated DBPs in the sample and the 12


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TII values of different samples can be compared. By summing up the intensities of ions within

287

m/z 80–600 in each PIS m/z 79 spectrum, the TII change of overall polar brominated DBPs could

288

be obtained.30 The TII levels of brominated DBPs in the effluent samples with the new approach

289

were always significantly lower than the corresponding effluent samples with the traditional

290

approach (Figure S4), indicating that the new approach removed considerably more brominated

291

DBPs than the traditional approach. A similar trend was also observed during treatment of the

292

bromide-free simulated raw water. Figure S5 presents the chlorinated DBPs (detected by

293

conducting ESI-tqMS PIS of m/z 35) in the bromide-free influent sample with the new approach.

294

Figure S6 shows the ESI-tqMS PIS m/z 35 spectra of the bromide-free effluent samples with the

295

traditional and new approaches. Figure S7 shows the change of TII of overall polar chlorinated

296

DBPs (the sum of the intensities of ions within m/z 36‒600 in each ESI-tqMS PIS m/z 35

297

spectrum)30 in the bromide-free effluents with both approaches.

298

Because of the complexity of the DBP composition in water samples, a molecular ion or ion

299

cluster in a PIS spectrum likely corresponds to more than one homolog. Therefore, a UPLC was

300

used to separate the overlapped homologs prior to ESI-tqMS analysis. Thirteen polar brominated

301

DBPs in the bromide-containing influent and effluent samples were detected and identified by

302

the UPLC/ESI-tqMS, and the details are given in the SI and Table S6. These DBPs have been

303

reported in previous studies, including commonly known HAAs and intermediate aromatic

304

halogenated DBPs.29,30 The intermediate aromatic brominated DBPs, including 3-bromo-5-

305

chloro-4-hydroxybenzaldehyde,

306

hydroxybenzoic

307

nitrophenol, and 2,6-dibromo-1,4-hydrobenzoquinone, were used to investigate the GAC

308

adsorption of aromatic halogenated DBPs. For every aromatic brominated DBP in Table S6, the

acid,

3,5-dibromo-4-hydroxybenzaldehyde,

3,5-dibromosalicylic

acid,

2,4,6-tribromophenol,

3,5-dibromo-42,6-dibromo-4-

13



Page 14 of 31

309

UPLC/ESI-tqMS MRM analysis of it in the effluent samples was conducted. The area of a peak

310

in the MRM chromatogram of a sample can reflect the corresponding DBP level in the sample.35

311

By setting the peak area of an aromatic brominated DBP in the RSSCT influent sample as the

312

reference level (100%), the normalized peak areas of the corresponding DBP in the effluent

313

samples with the new and traditional approaches were calculated. Figure S8 illustrates the peak

314

area changes of intermediate aromatic brominated DBPs in the effluent samples with both

315

approaches. The normalized peak areas of them in the effluent samples with both approaches

316

kept increasing from the beginning to the end of the RSSCT operation, but the ones with the new

317

approach were always substantially below the corresponding ones with the traditional approach.

318

For instance, at 12000 BVs, the normalized peak areas of seven aromatic brominated DBPs

319

(Figure S8) in the effluent samples with the new approach were about 5‒45% while those with

320

the traditional approach were about 70‒100%. A similar trend was also observed during

321

treatment of the bromide-free simulated raw water. Table S7 summarizes the polar chlorinated

322

DBPs detected in the bromide-free influent and effluent samples. Figure S9 shows the

323

normalized peak area changes of five aromatic chlorinated DBPs (including 3,5-dichloro-4-

324

hydroxybenzaldehyde, 3,5-dichloro-4-hydroxybenzoic acid, 3,5-dichlorosalicylic acid, 2,4,6-

325

trichlorophenol, and 2,6-dichloro-4-nitrophenol) in the bromide-free effluent samples with the

326

new and traditional approaches. It needs emphasizing that, although the adsorption of individual

327

aromatic halogenated DBPs onto GAC might vary from each other, it was evident that the new

328

approach reduced the levels of aromatic halogenated DBPs more significantly than the traditional

329

approach.

330

The rather high removals of aromatic halogenated DBPs by the new approach relative to the

331

traditional approach may be ascribed to the different adsorption mechanisms of the two

14


Page 15 of 31


332

approaches. In the traditional approach, GAC adsorption of DBP precursor (NOM, as quantified

333

by DOC) occurred. Due to the size-exclusion effect,23 the GAC was saturated by NOM relatively

334

quickly. As shown in Figure S1, the effluent’s DOC level reached almost 80% breakthrough

335

(BV80%) after 2500 BVs. Meantime, a quick increase of the aromatic halogenated DBP levels in

336

the effluent samples with the traditional approach was observed. While in the new approach,

337

GAC adsorption of aromatic halogenated DBPs occurred. Compared to large NOM molecules,

338

these small aromatic halogenated DBPs broke through out of the GAC column much slowly.

339

Their levels in the effluent samples reached around 1‒30% breakthrough after 2500 BVs

340

(Figures S8 and S9). Also, polar halogenated DBPs (represented by TII) were removed

341

significantly by the new approach compared to the traditional approach (Figures S4 and S7).

342

The New Approach Showed a Higher Removal of DBPs (including THM4, HAA5, HAA9, and

343

TOX) than the Traditional Approach. Various DBPs together with the remaining NOM were in

344

the influent with the new approach. Since each DBP was at a trace level in water, it could be

345

viewed as an organic micropollutant. It has been reported that during GAC column operation,

346

when the influent NOM was at mg/L levels and the influent micropollutant was at ng/L to low

347

µg/L levels, normalized breakthrough profile (C/C0) of the micropollutant was similar regardless

348

of the influent micropollutant level.54‒57 Thus, the normalized THM4, HAA5, HAA9 and TOX

349

breakthrough curves were used to reflect the degree of DBP treatment during RSSCT operations

350

despite different DBP concentrations in the bromide-containing and bromide-free influents.

351

Treatment of the bromide-containing raw water was elaborated here. Figure 3a‒d illustrates

352

the breakthrough curves of the THM4, HAA5, HAA9 and TOX, respectively, with the new and

353

traditional approaches. The removals of THM4, HAA5, HAA9, and TOX by the new approach

354

always exceeded those by the traditional approach. For instance, the BV25% of THM4, HAA5,

355

HAA9, and TOX occurred at approximately 19500, 4000, 5600, and 1000 BVs respectively of 15



Page 16 of 31

356

water treated with the new approach. In contrast, the corresponding BV25% of THM4, HAA5,

357

HAA9, and TOX occurred around 150, 150, 200, and 250 BVs respectively of water treated with

358

the traditional approach. The new approach also extended the GAC service time. The nearly

359

complete breakthrough points (BV80%) of HAA5 and TOX were shifted from 2700 and 4000 BVs

360

with the traditional approach to 7500 and 21000 BVs with the new approach, respectively.

361

Significant reductions of THM4 and HAA9 were even observed in the effluent sample at 22500

362

BVs of water treated with the new approach, which was almost twice of the RSSCT operation

363

time with the traditional approach. Similar trends were also observed during treatment of the

364

bromide-free simulated raw water. The corresponding breakthrough profiles of THM4, HAA5

365

(=HAA9), and TOX are presented in Figure 3f‒h.

366

Traditionally, the utilities target 20‒50% DOC removal (i.e., 80‒50% DOC breakthrough) in

367

operating GAC filters for DBP precursor control.58 Similar to DOC breakthrough analysis, the

368

maximum acceptable effluent TOX concentration or TOX breakthrough point was set at the BV

369

when the effluent TOX concentration reached BV50% in this study. The DBP removal was

370

calculated as the ratio of the mass of DBP removed by the GAC relative to the total mass of DBP

371

passed through the GAC at breakthrough. When the bromide-containing influent was treated by

372

the new approach, effluent’s TOX level reached its BV50% at 5900 BVs (Figure 3d). At that

373

treated volume, the removals of THM4, HAA5, HAA9, and TOX were 96.9%, 78.2%, 88.6%, and

374

63.2% respectively with the new approach, and 29.6%, 30.7%, 31.2%, and 37.6% respectively

375

with the traditional approach. Similarly, the breakthrough point was at 3350 BVs (BV50% of TOX

376

in the effluent with the new approach, Figure 3h) during treatment of the bromide-free influent.

377

The removals of THM4, HAA5 (=HAA9), and TOX were 84.6%, 83.1%, and 71.6% respectively

378

with the new approach, and 29.5%, 26.3%, and 27.9% respectively with the traditional approach.

16


Page 17 of 31


379

In summary, the DBP removals increased by 25.6‒67.3% from the traditional approach to the

380

new approach. Besides, with the new approach, the BV50% of TOX in the bromide-containing

381

waters treated by the new approach was substantially longer than that in the bromide-free waters,

382

suggesting an enhanced adsorption of brominated DBPs over chlorinated DBPs during the GAC

383

adsorption. Chemicals with high logarithm of the octanol‒water partition coefficients (log P) are

384

considered to be relatively hydrophobic and tend to have high GAC adsorption coefficients.59 As

385

shown in Tables S6 and S7, brominated DBPs (e.g., 2,4,6-tribromophenol with a log P of 4.404)

386

have higher log P values than their chlorinated analogs (e.g., 2,4,6-trichlorophenol with a log P

387

of 3.769), and thus brominated DBPs had higher GAC adsorption capacities than their

388

chlorinated analogs. Accordingly, the new approach removed halogenated DBPs more

389

effectively in treating the bromide-containing raw water than in treating the bromide-free raw

390

water.

391

(It needs mentioning that for the bromide-containing raw water, coagulation removed 9.9%

392

of TOX, coagulation with the traditional approach removed 33.9% of TOX, and coagulation with

393

the new approach removed 63.6% of TOX (Figure S2). The results indicated that even with

394

coagulation, the new approach still showed a significantly better control of overall halogenated

395

DBPs than the traditional approach.)

396

The New Approach Produced Less Toxic Finished Waters than the Traditional Approach.

397

Since the levels of aromatic halogenated DBPs and TOX in the effluent samples with the new

398

approach were substantially lower than those in the effluent samples with the traditional

399

approach, the effluent samples with the new approach were expected to be less toxic than the

400

corresponding effluent samples with the traditional approach. The embryo’s normal development

401

percentages of the bromide-containing and bromide-free effluent samples are shown in Figure 3e

402

and 3i, respectively, with different approaches. A lower normal developmental percentage 17



Page 18 of 31

403

indicates a higher toxic potency. For both bromide-containing and bromide-free waters treated,

404

the normal developmental percentages of embryos in the effluent samples with the new approach

405

were considerably higher than those in the corresponding effluent samples with the traditional

406

approach, indicating that the effluent with the new approach was less toxic than the

407

corresponding one with the traditional approach.

408

The New Approach Generated Less DBP-containing and Less Toxic Finished Waters during

409

Subsequent Chlorination than the Traditional Approach. For the new approach, a certain residual

410

chlorine (3‒4 mg/L as Cl2, Figure S10) was present in the influent. When the chlorine-containing

411

water passed through a GAC column, the chlorine residual could be quickly consumed by the

412

reductive carbon surface at the top of the GAC column.46 To inactivate microbial growth in the

413

water distribution system, an extra addition of chlorine is essential to keep a disinfectant residual

414

in the effluent with the new approach. We viewed this extra chlorine addition after the new

415

approach as a trade-off or a necessary sacrifice in order to lower the halogenated DBP levels and

416

potential health risks in finished water. Figure 4 shows the levels of DBPs (including THM4,

417

HAA5, HAA9, and TOX) and the corresponding developmental toxicity in the 1-d subsequently

418

chlorinated effluents with the new and traditional approaches. Compared to the halogenated DBP

419

levels in the control sample (Table S8), less halogenated DBPs produced in the 1-d subsequently

420

chlorinated effluent samples with both approaches. But compared to the traditional approach, the

421

subsequently chlorinated effluents with the new approach always presented lower levels of

422

THM4, HAA5, HAA9, TOX, and developmental toxicity. Because both approaches showed

423

similar breakthrough profiles of DOC (i.e., DBP precursor) (Figure S11), the differences in the

424

levels of halogenated DBPs and toxicity might be attributed to the effective adsorption of

425

intermediate aromatic halogenated DBPs (i.e., precursors of aliphatic halogenated DBPs) with

426

the new approach. With the additional removal of those aromatic intermediates, the levels of 18


Page 19 of 31


427

halogenated DBPs and the corresponding developmental toxicity in the effluent samples with the

428

new approach were reduced more substantially (than those in the corresponding effluent samples

429

with the traditional approach) in the subsequent chlorination.

430

Notably, for a different source water with a different water matrix, a different chlorination

431

scenario may be selected with which the disinfection goal can be met and meantime relatively

432

high levels of intermediate aromatic halogenated DBPs can be formed. A good idea could be to

433

use surrogates such as differential absorbance and differential fluorescence indices,60–63 whose

434

slopes may help to identify the optimal point to enhance the removal of intermediate aromatic

435

halogenated DBPs. As such, the method for quantifying the formation of overall aromatic

436

halogenated DBPs needs to be studied, and the association between overall aromatic halogenated

437

DBP formation and differential absorbance/fluorescence indices needs to be established.

438 439

ASSOCIATED CONTENT

440

Supporting Information.

441

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

442

Additional details, Tables S1‒S8 and Figures S1−S11 (PDF)

443 444

AUTHOR INFORMATION

445

Corresponding Author

446

*Phone: +852 2358 8479; fax: +852 2358 1534; email: [email protected].

447

ORCID

448

Xiangru Zhang: 0000-0001-6382-0119

449

Notes

450

The authors declare no competing financial interest. 19



Page 20 of 31

451 452

ACKNOWLEDGMENTS

453

This study was financially supported by the Research Grants Council of Hong Kong, China

454

(projects 16213014 and IRS15EG14). The authors thank Long Pan for his assistance in the THM

455

and HAA measurement, Dave Ho for his daily maintenance of the TOX analyzer, and Dr.

456

Adriaan Dorresteijn for providing parental P. dumerilii.

457 458

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activated carbon. In Water Quality and Treatment: A Handbook on Drinking Water;

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Edzwald, J. K. Ed.; McGraw-Hill: New York, NY, 2011.

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(60) Korshin, G. V.; Wu, W. W.; Benjamin, M. M.; Hemingway, O. Correlations between

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differential absorbance and the formation of individual DBPs. Water Res. 2002, 36 (13),

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3273‒3282.

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(61) Roccaro, P.; Vagliasindi, F. G.; Korshin, G. V. Changes in NOM fluorescence caused by

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chlorination and their associations with disinfection by-products formation. Environ. Sci.

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Technol. 2009, 43 (3), 724‒729.

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(62) Roccaro, P.; Vagliasindi, F. G.; Korshin, G. V. Quantifying the formation of nitrogen-

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containing disinfection by-products in chlorinated water using absorbance and fluorescence

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indexes. Water Sci. Technol. 2011, 63 (1), 40–44.

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(63) Yan, M.; Korshin, G. V.; Chang, H. S. Examination of disinfection by-product (DBP)

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formation in source waters: A study using log-transformed differential spectra. Water Res.

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2014, 50, 179‒188.

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Page 28 of 31

Figure 1. Schematic flow setups of the influent feeding and GAC adsorption (RSSCT) system which simulated the new and traditional approaches. (a) “NOM feed” was filled with the NOM working solution (6 mg/L SRNOM as C, 180 mg/L NaHCO3 as CaCO3, and 0 or 4 mg/L KBr as Br−). (b) “Chlorine feed” was filled with the chlorine working solution (10 mg/L NaOCl as Cl2) for the new approach, while it was filled with ultrapure water for the traditional approach. (c) Chlorination pipe line was made of PTFE with an ID of 4.8 mm and a length of 11.5 m. (d) Glass filter-disc’s pore size was 50 µm.

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Figure 2. ESI-tqMS PIS m/z 79 spectra of the bromide-containing effluent samples with the traditional approach collected at (a) 300 BVs, (b) 1000 BVs, (c) 2500 BVs, (d) 4000 BVs, (e) 6500 BVs, (f) 9000 BVs, and (g) 12000 BVs, respectively; ESI-tqMS PIS m/z 79 spectra of the bromide-containing effluent samples with the new approach collected at (h) 300 BVs, (i) 1000 BVs, (j) 2500 BVs, (k) 4000 BVs, (l) 6500 BVs, (m) 9000 BVs, and (n) 12000 BVs, respectively. The y-axes are on the same scale with a maximum intensity of 1.10×106. “×2” in charts a‒n indicates that the spectra in the m/z range of 100‒200 are magnified by 2 times, and “×8” in charts a‒n indicates that the spectra in the m/z range of 220‒400 are magnified by 8 times.

29



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Page 30 of 31

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Figure 3. The breakthrough profiles of THM4, HAA5, HAA9, TOX, and embryos’ normal development percentages in the effluent samples with the traditional approach ( ) and the new approach ( ): (a‒e) treatment of the bromide-containing simulated raw water, and (f‒i) treatment of the bromide-free simulated raw water. The bromide-containing and bromide-free effluent samples were concentrated by 140 and 310 times, respectively, in testing the developmental toxicity. The embryo’s normal development percentage in the control sample was 82.4%. Each parameter was measured in duplicate.

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Figure 4. (a) THM4, (b) HAA5, (c) HAA9, (d) TOX, and (e) embryos’ normal development percentages of the 1-d subsequently chlorinated effluent samples with the traditional approach ( ) and the new approach ( ). The raw water contained 2 mg/L Br−. For the developmental toxicity test, the effluent samples were concentrated by 220 times, and the embryo’s normal development percentage in the control sample was 81.1%. Each parameter was measured in duplicate.

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A New Approach to Controlling Halogenated DBPs - ACS Publications

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