Accepted Manuscript Transformation of Bromide in Thermo Activated Persulfate Oxidation Processes Junhe Lu, Jinwei Wu, Yuefei Ji, Deyang Kong PII:
S0043-1354(15)00218-3
DOI:
10.1016/j.watres.2015.03.028
Reference:
WR 11224
To appear in:
Water Research
Received Date: 8 January 2015 Revised Date:
23 March 2015
Accepted Date: 27 March 2015
Please cite this article as: Lu, J., Wu, J., Ji, Y., Kong, D., Transformation of Bromide in Thermo Activated Persulfate Oxidation Processes, Water Research (2015), doi: 10.1016/j.watres.2015.03.028. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Transformation of Bromide in Thermo Activated Persulfate
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Oxidation Processes
3 Junhe Lua*, Jinwei Wua, Yuefei Jia, Deyang Kong
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Department of Environmental Science and Engineering, Nanjing Agricultural University,
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Nanjing, 210095, China b
Nanjing Institute of Environmental Sciences, Ministry of Environmental Protection of PRC,
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Nanjing, 210042, China
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*Corresponding author: E-mail: [email protected];
Telephone: (86) 25-84395164; Fax: (86) 25-84395210
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ACCEPTED MANUSCRIPT Abstract Sulfate radicals (SO4-· ) are applied to degrade various organic pollutants. Due to its
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high oxidative potential, SO4-· is presumed to be able to transform bromide to reactive bromine
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species that can react with natural organic matter subsequently to form brominated products
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including brominated disinfection by-products (Br-DBPs). This research was designed to
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investigate the transformation of bromide in thermo activated persulfate oxidation process in the
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presence of humic acid (HA). Significant formation of bromoform and bromoacetic acids was
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verified. Their formation was attributed to the reactions of HA and reactive bromine species
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including Br·, Br2-· HOBr-· , and free bromine resulted from the oxidation of bromide by SO4-· .
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Yields of Br-DBPs increased monotonically at persulfate concentration of 1.0 mM and working
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temperature of 70°C. However, the time-depended formation exhibited an increasing and the
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decreasing profile when persulfate was 5.0 mM, suggesting further degradation of organic
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bromine. HPLC/ICP-MS analysis demonstrated that the organic bromine was eventually
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transformed to bromate at this condition. Thus, a transformation scheme was proposed in which
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the bromine could be recycled multiple times between inorganic bromide and organic bromine
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before being finally transformed to bromate. This is the first study that reveals the
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comprehensive transformation map of bromine in SO4-· based reaction systems, which should be
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taken into consideration when such technologies are used to eliminate contamination in real
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practice.
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Keywords: sulfate radical oxidation; bromide; brominated disinfection by-products; bromate
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ACCEPTED MANUSCRIPT Graphical abstract
SO4·Br2, HBrO
Br-
SO4·-
Br·, Br2·-
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NOM
SO4·-
DBPs
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BrO3-
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ACCEPTED MANUSCRIPT Abbreviations
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PS: persulfate
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PMS: peroxymonosulfate
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DBPs: disinfection by-products
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PFCs: perfluoroalkyl compounds
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PCBs: polychlorinated biphenyls
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MTBE: methyl tert-butyl ether
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PAHs: polycyclic aromatic hydrocarbons
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DOC: dissolved organic carbon
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TOC: total organic carbon
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THMs: trihalomethanes
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HAAs: haloacetic acids
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NOM: natural organic matter
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HA: humic acid
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GC: gas chromatography
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ECD: electron capture detector
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IC: ion chromatography
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ICP-MS: inductively coupled plasma-mass spectrometry
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BRS: bromine radical species
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MBAA: monobromoacetic acid
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DBAA: dibromoacetic acid
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TBAA: tribromoacetic acid
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DHBA: 3,5-dihydroxylbenzoic acid
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TIBr: total inorganic bromine
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1. Introduction
Sulfate radicals (SO4-· ) produced via activation of persulfate (PS)(Adewuyi and Sakyi 2013, Al-Shamsi and Thomson 2013, Furman et al. 2010, Johnson et al. 2008, Liang and Bruell 2008) or
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peroxymonosulfate (PMS)(Anipsitakis and Dionysiou 2003, Costanza et al. 2010, Yao et al. 2012)
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have a one-electron reduction potential of 2.5~3.1 V(Anipsitakis and Dionysiou 2003, Neta et al.
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1988), making it a strong direct electron transfer oxidant similar to hydroxyl radicals (OH·, 2.7 V
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in acid solution and 1.8 V in neutral solution)(Usman et al. 2012). SO4-· based oxidation was
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demonstrated to be a viable way to decompose a broad spectrum of contaminants, including
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polycyclic aromatic hydrocarbons (PAHs)(Usman et al. 2012), polychlorinated biphenyls
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(PCBs)(Rastogi et al. 2009), perfluoroalkyl compounds (PFCs)(Lee et al. 2009), methyl
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tert-butyl ether (MTBE)(Liang et al. 2011), chlorinated solvents(Costanza et al. 2010, Liang and
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Bruell 2008, Waldemer et al. 2006), herbicides(Guan et al. 2013), petroleum hydrocarbons(Yen
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et al. 2011), etc. In addition to the oxidation strength, SO4-· based oxidation systems have a wider
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operational pH range than OH· based ones(Anipsitakis and Dionysiou 2003, Guan et al. 2011).
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Its precursors (PS or PMS) are more stable than that of OH· (H2O2) and thus able to be
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transported to greater distance in the sub-surface(Liang et al. 2008, Liang et al. 2007). Due to
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these advantages, SO4-· based oxidation technologies have attracted increasing attention in
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wastewater treatment and in situ remediation of contaminated soil and ground water.
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The high oxidation potential of SO4-· also enables it to react with various inorganic ions such
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as CO32-, NO3-, Cl-, Br- (Adewuyi and Sakyi 2013, Anipsitakis et al. 2005, Bennedsen et al.
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2012, Fang et al. 2012, Fang and Shang 2012, Wang et al. 2011), which is detrimental to the
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treatment of the targeted contaminants. According to the redox potentials of halides (Br·/Br-, 5
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1.62 V; Cl·/Cl-, 2.41 V)(Huie et al. 1991) and SO4-· (SO4-· /SO42-, 2.5~3.1 V)(Anipsitakis and
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Dionysiou 2003), it is highly possible that reactive halogen species can be generated in
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SO4-· mediated oxidation processes in the presence of halides. For instance, SO4
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chloride ions (Cl-) to chlorine radicals (Cl·, Cl2-· , and ClOH-· ) which can couple to each other to
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form free chlorine (Cl2, HClO)(Anipsitakis et al. 2005, Bennedsen et al. 2012, Yu et al. 2003). −⋅
SO4 SO4 X − → X ⋅, X 2−⋅ → → X 2 / HXO
(1)
oxidizes
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·-
These oxidized halogen species are able to attack a number of organic compounds via addition,
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electron-transfer, or hydrogen-abstraction mechanism(Hasegawa and Neta 1978). When
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electron-rich compounds are present, halogenated intermediates and products can be
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generated(Yang et al. 2014). Bromide (Br-) is theoretically more readily oxidized and expected
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to follow a similar transformation scheme upon oxidation by SO4-· (eq. 1). It was found that
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SO4-· could in fact transform Br- to an even higher oxidation state, bromate (BrO3-)(Fang and
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Shang 2012, Lutze et al. 2014) which is a regulated drinking water disinfection by-product
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(DBP) formed in ozone disinfection process(Miller 1993).
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Generation of the reactive halogen species in SO4-· based treatment processes is of particular concern. It is well recognized that free halogen actively reacts with natural organic matter
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(NOM) resulting in the formation of halogenated DBPs such as trihalomethanes (THMs) and
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haloacetic acids (HAAs) during water disinfection processes(Xie 2003). DBPs are known to
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cause notable health risks and are regulated world widely(Xie 2003). Since both halides and
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NOM are ubiquitous in the environment(Magazinovic et al. 2004), there is a great possibility
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that halogenated by-products are generated when SO4-· is employed to eliminate contaminants.
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For example, Alken found that Cl- strongly interfered with the dissolved organic carbon (DOC)
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products such as chloromethane, chloroform, and methylene chloride(Alken 1992). Since
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bromination reactions are known to proceed at a higher rate than corresponding chlorination
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(Acero et al. 2005), generation of brominated by-products is highly possible. Wang et al. in a
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recent study demonstrated that brominated DBPs (Br-DBPs) could be formed in SO4-· based
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oxidation process in the presence of NOM isolates and Br-27.
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Transformation of Br- in SO4-· based oxidation processes attracted considerable attention
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recently. It appeared that Br- could be converted to either organic form and/or inorganic form
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with higher oxidation state(Fang and Shang 2012, Lutze et al. 2014, Wang et al. 2014). However,
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a detailed map of its transformation is still lacking and the underlying mechanisms that control
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the speciation of products remain unexplored, which comprises the main purposes of the present
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study. We used heat to activate PS because this was the simplest approach to generate SO4-· . In
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addition, possible reactions of Br- induced by photon or metal catalysts could be avoided in this
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system. The results of this study are of relevance to similar oxidation systems involving
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SO4-· and Br-.
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2. Materials and Methods
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2.1 Materials
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All chemicals were of analytical grade or better. K2S2O8 and KBr were purchased from
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Aladdin (Shanghai, China). MTBE was HPLC grade and obtained from Fisher (Waltham, MA).
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THMs and HAAs calibration mixtures were purchased from Sigma-Aldrich (St. Louis, MO).
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BrO3- standard and humic acid (HA) were also from Sigma-Aldrich. Reagent water with a 7
ACCEPTED MANUSCRIPT resistivity of 18.2 MΩ/cm was produced in a Millipore Super-Q Water Purification system. Stock
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solutions of HA, KBr, and PS were prepared by dissolving appropriate amount of the reagents in
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Milli-Q water. Total organic carbon (TOC) of the HA stock was quantified using a Shimadzu
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5050A TOC analyzer.
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2.2 Reaction setup
Transformation of Br- was investigated in a series of EPA vials (42 mL in volume) as batch
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reactors. The vials filled up with solution containing 0.1 mM Br- and 2.0 mg/L HA (as TOC)
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were pre-heated to the working temperature in a water bath before appropriated volume of PS
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stock solution was spiked to each of them to achieve preset concentrations. Since only a tiny
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amount of PS stock solution was added, change of temperature of the reaction solutions thus
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caused was ignored. The vials were headspace free and immersed in a water bath during the
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entire reaction period. After every 15 min 3 vials were taken out and chilled in an ice bath for 10
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min and kept at 5°C in a refrigerator thereafter until further treatment and analysis. One vial was
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for the analysis of Br- and BrO3-, the other two for THMs and HAAs, respectively. It should be
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noted that rapid decrease of temperature could effectively cease the reactions caused by
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PS(Ghauch et al. 2012). Preliminary experiments demonstrated that no DBPs were formed at
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room temperature with other conditions identical. The decomposition of DBPs by PS at room
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temperature was also negligible. Thus, no chemical reagents such as methane or Na2SO3 were
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used to quench the reactions. No buffer was added in order to rule out any interference caused by
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reactions between radicals and buffer species. The reactions were conducted at 50, 60, and 70°C.
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At each temperature level, PS doses of 1.0, 2.0, 3.0, 4.0, and 5.0 mM were tested.
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Formation of free bromine was explored in the presence of 0.1 mM Br- and 2 mg/L HA at 70°C. PS levels of 1.0 and 5.0 mM were selected. Other conditions were same as above except 2
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mL aliquot was taken every 5 min and chilled immediately in an ice bath. Free bromine was
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analyzed using DPD colorimetric method(APHA/AWWA/WEF 2005) by measuring the
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absorbance at 510 nm on a Varian Cary 50 spectrophotometer. Controls with Br- absent were
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also analyzed and the values were used to correct the absorbance created by PS and dissolved
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oxygen induced oxidation of DPD. Standard deviation of this approach was within 5%.
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2.3 DBP and bromate analysis
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THMs and HAAs were extracted with MTBE according to EPA Method 551.1 and 552.2, respectively. DBPs analysis was performed in an Agilent 7890 gas chromatograph (GC)
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equipped with an electron capture detector (ECD) and HP-5 fused silica capillary column (30
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m×0.53 mm i.d., 1.5 µm film thickness). Detailed analytical procedures and instrumental setup
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were specified in Support Information. Br- and BrO3- were separated and quantified using a
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Perkin-Elmer Flexar ion chromatography (IC) coupled with a Perkin-Elmer NexION 300x
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quadrupole-based ICP-MS without additional treatment. The IC was equipped with a Hamiton
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PRP-X100 anion exchange column. An isocratic mobile phase comprised of 20 mM
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NH4NO3-NH4H2PO4 and pH adjusted to 6 was used. The flow rate was 1.5 mL/min. Detailed
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instrumental settings are given in Table S1. Concentrations of bromine species were determined
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by using multipoint standard calibration curves. All the experiments were carried out in
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duplicates or triplicates, and the data were averaged. The standard deviations were usually within
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5-10% unless otherwise stated.
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3. Results and Discussion
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3.1 Formation of organic bromine
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Br- is known to be oxidized by SO4-· to form Br· at a nearly diffusion-limited rate constant of 3.5 × 109 M-1s-1 (eq. 2)(Lutze et al. 2014). Br· rapidly reacts with additional Br- or hydroxyl
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anion yielding dibromide radicals (Br2-· ) or hypobromous radical (HBrO-· ), respectively (eqs. 3
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and 4)(Yang et al. 2014). −⋅
2−
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SO4 + Br − → Br ⋅ + SO4
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Br ⋅ + Br − → Br2
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Br ⋅ +OH − → HBrO −⋅
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Br2 + Br⋅ → Br2 + Br −
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Br2 + Br2 → Br2 + 2 Br −
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Br ⋅ + Br ⋅ → Br2
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Br2 + H 2O ↔ HBrO + H + + Br −
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k = 1.2 × 1010 M-1s-1
(3)
k = 1.06 × 1010 M-1s-1
(4)
k = 2.0 × 109 M-1s-1
(5)
k = 1.9 × 109 M-1s-1
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k = 1.0 × 109 M-1s-1
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k = 1.6 × 1010 M-1s-1
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Given the relatively high concentration of Br-, a significant fraction of SO4-· in the solution was
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expected to be scavenged by Br- and converted to bromine radical species (BRS). It was reported
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that BRS concentrations could exceed that of SO4-· by several orders in SO4-· oxidation processes
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in the presence of seawater level of Br-(Yang et al. 2014). The generated BRS are selective
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oxidants that can be involved in electron-transfer, H abstraction, or addition reactions with
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organic compounds(Hasegawa and Neta 1978). It is generally accepted that electron-transfer and
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H abstraction contribute to the mineralization of contaminants, whereas addition reaction leads to
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the formation of halogenated compounds(Pignatello et al. 2006). In addition to BRS, free
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2014, Neta et al. 1988, Yang et al. 2014). These reactive bromine species (both radical and
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nonradical) could result in the generation of brominated intermediates and products if
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electron-rich compounds are present.
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NOM molecules ubiquitously present in water contain plenty of electron-rich phenolic
moieties. It is widely known that the electron-rich phenolic moieties in NOM molecules react
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with free halogen resulting in the formation of halogenated DBPs such as THMs and HAAs
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during water disinfection processes(Lu et al. 2004, Xie 2003). We presume that the BRS can
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initiate the halogenation of NOM in a similar way and generate Br-DBPs. Since NOM is
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primarily comprised of humic substances (Croué et al. 2000, Ichihashi et al. 1999), commercial
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HA was used to mimic the reactivity of NOM in this research. As shown in Figure 1, formation
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of both bromoform and bromoacetic acids was verified in heated PS solutions in the presence of
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HA and Br-. Among a variety of individual DBPs, bromoform and dibromoacetic acid (DBAA)
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were the dominant species. Monobromoacetic acid (MBAA) and tribromoacetic acid (TBAA)
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were also detected but their yields were at least an order of magnitude lower than that of DBAA
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at identical conditions. Formation of the 4 Br-DBPs generally showed similar trends to the
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change of temperature, reaction time, and PS dose as illustrated in Figure 1. Higher yield of
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DBAA than TBAA is indeed distinct from the distribution pattern of HAAs in bromination using
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free bromine in which TBAA formation is more favored. A similar pattern has also been noticed
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by Wang et al(Wang et al. 2014) and this seems characteristic of the formation of Br-DBPs in
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SO4-· based oxidation processes. Such a result suggests different bromination mechanisms are
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involved in SO4-· mediated bromination processes which warrant further investigation.
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It should be noted that no Br-DBPs were observed in the control experiments with either HA + PS, Br- + PS, or HA + Br- without PS, confirming that reactive bromine species were
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responsible and HA served as the precursor of Br-DBPs. Nevertheless, it is impossible to
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determine the contribution of each of the reactive bromine species (both radical and nonradical)
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because their respective kinetic constant of the reaction with organic matter is unknown. In
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addition, scavenging of SO4-· by Br- greatly reduced the decomposition of the DBP precursor
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(HA) due to its reaction with SO4-· , which made it more available to bromination reactions by
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BRS. Since phenolic moieties are presumed to be the principal electron-rich sites in HA
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molecules liable to the attack of reactive bromine species and generation of Br-DBPs, formation
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of Br-DBPs was further examined using 3,5-dihydroxylbenzoic acid (DHBA) as a HA model
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compound. The data are illustrated in the Supporting Information (Figure S1). It was
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demonstrated that Br-DBPs were also generated and their formation showed similar trends
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concerning the speciation of dominant Br-DBPs and the yields to the change of PS dose and
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reaction time (Figure S1).
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3.2 Influence of PS concentration on Br-DBPs formation
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Time-dependent Br-DBPs formation profile changed dramatically with the change of PS
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concentration as shown in Figure 1. For instance, all the Br-DBPs increased monotonically when
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the initial PS was 1.0 mM. The concentrations of bromoform and DBAA reached 0.38 and 0.72
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µM, respectively, after 2 h at working temperature of 70°C. In contrast, when 5.0 mM PS was
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added to the solution initially, concentrations of Br-DBPs increased at significantly higher rates.
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Their yields reached a temporary maximum at approximately 60 min and decreased thereafter
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(70°C). The maximum concentrations of bromoform and DBAA were 0.11 and 1.01 µM, 12
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at 70°C. Similar trends of Br-DBPs formation were observed with regard to the change of PS
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concentration at a given reaction time and the data were given in the Supporting Information
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(Figure S1). For instance, when Br-DBPs were monitored at the reaction time of 0.5 and 1 h, it
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can be seen that their yields increased monotonically with the elevated PS concentrations (Figure
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S2). However, Br-DBP formation profiles became complicated at the reaction time of 2 h. More
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Br-DBPs were generated when PS increased from 1.0 mM to 2.0 mM. With PS further increased
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to 3.0 mM, DBPs yields declined. No DBPs were found when the PS increased to 4.0 mM.
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Based on these data, it can be inferred that Br-DBPs were not the final products and they
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were most likely degraded by nonselective SO4-· in the solution. To test this, we investigated the
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stability of individual Br-DBPs toward SO4-· and the data are given in Figure 4. It was
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demonstrated that the degradation of Br-DBPs by SO4-· was first order in kinetics (r2 = 0.99).
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Their half-life times were less than 10 min in 1 mM PS solution at 70°C, which corroborates
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their rapid decline after reaching the maximum in 1h (Figure 1). Influence of heating on the
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degradation of Br-DBPs was also investigated and the data can be found in the Supporting
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Information (Figure S3). It was revealed that no appreciable decomposition of bromoform,
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MBAA, and DBAA occurred at 70°C. TBAA was relatively unstable and its half-life was 13 min
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at 70 °C (r2 = 0.98). Because TBAA was a minor DBP species, most of the Br-DBPs should be
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degraded by SO4-· . When Br-DBPs were degraded by SO4-· , organic bromine was probably
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converted back to inorganic Br- which was expected to be oxidized by SO4-· to form reactive
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bromine species and participate to the bromination of HA again.
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3.3 Formation of free bromine and bromate
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Formation of free bromine and BrO3- in UV activated persulfate oxidation systems has recently been documented(Fang and Shang 2012, Lutze et al. 2014). Figure 2a illustrates the
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concentration profiles of nonradical inorganic bromine species in the reaction solutions at 70°C.
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When 5 mM PS was dosed initially, Br- decreased rapidly and became undetectable after 75 min.
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Meanwhile, formation of BrO3- was observed and its concentration kept increasing. More than
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0.09 mM BrO3- was formed after 75 min and the value increased to nearly 0.1 mM after 2 h.
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Since initially 0.1 mM Br- was presented, this suggested that the Br- was quantitatively
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transformed to BrO3-. Formation of free bromine (sum of HBrO/BrO- and Br2) was also detected
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at relatively low level (< 15 µM). However, it exhibited a complicated concentration profile with
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2 temporary maximum appearing at 30 and 75 min (Figure 2a). When the initial PS was 1 mM,
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the transformation of Br- was significantly slower and approximately 0.038 mM still remained in
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the solution after 2 h (Figure 2b). Formation of BrO3- was not observed during the first 1 h and
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its concentration was only 0.022 mM after 2 h. Appreciable free bromine was also found after 1
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h (Figure 2b).
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We assume that Br-, free bromine, and BrO3- were the major inorganic bromine species in the
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reaction solutions because BRS (Br·, Br2-· , etc) were transient and not likely to accumulate(Yang
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et al. 2014). Thus, total inorganic bromine (TIBr) could be calculated as the sum of these
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nonradical inorganic species, which is also given in Figure 2. It can be found that time-dependent
282
change of TIBr showed a “V shape” profile in the solution dosed with 5 mM PS at 70°C (Figure
283
2). It decreased first and reached a temporary minimum (0.051 mM) at 60 min before increasing
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again and finally reaching 0.1 mM which equal to the initial quantity of Br-. Such a “V shape”
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profile is indicative of the formation of organic bromine and precisely coupled with concurrent
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(70°C, 5 mM PS) exhibited an increase and decrease profile with a maximum appeareing at 60
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min. The change of TIBr appeared less complicated in the treatment with 1.0 mM PS. It
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decreased monotonically to approximately 0.05 mM after 2 h, which was also coupled well with
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the concomitant Br-DBP formation (Figure 2b).
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3.4 Reaction scheme
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According to the discussion above, a transformation scheme of Br- in SO4-· oxidation process in the presence of HA can be proposed as shown in Figure 3. Br- was oxidized by SO4-· to form
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reactive bromine species (both radical and nonradical) which attack HA yielding organic
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bromine including Br-DBPs. The organic bromine is not stable toward SO4-· and degraded to
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release Br- again. The released Br- can be oxidized and react with HA again. In this way, Br- is
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cycled multiple times until either the oxidant is depleted or it is converted to BrO3-. The
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treatment with 5 mM PS represents an excessive oxidant scenario in which Br- was quantitatively
299
transformed to BrO3- ultimately. It is noted that the decline of organic bromine was accompanied
300
by the re-accumulation of free bromine (60 – 75 min, Figure1 and Figure 2a), which suggests the
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free bromine formed during this particular period was mostly attributed to the oxidation of
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recycled Br-. The temporary re-accumulation of free bromine also elucidated the intermediate
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role of this species in the formation of BrO3-. This phenomenon is consistent with the finding of
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Fang and Shang (Fang and Shang 2012) and Lutze et al. in their study of the formation of BrO3-
305
in UV activated SO4-· oxidation system. Both of the researches demonstrated that HBrO was the
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key intermediate during the formation of BrO3- although conflicted mechanisms were proposed
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concerning how HBrO was further oxidized.
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When SO4-· is depleted before Br- is completely converted, a portion of Br- will end in form of organic bromine including Br-DBPs. Such a scenario was likely seen in the treatment with 1.0
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mM PS. Comparing the data shown in Figure 1 and 2b, it is evident that the evolution of TIBr
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was also coupled with the concomitant DBP formation. Br-DBPs accumulated while TIBr kept
312
decreasing within the examined reaction period. Further increase of BrO3- was possible with
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prolonged reaction time. According to the stoichiometry relationship as demonstrated in Eq. (9),
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oxidizing 0.1 mM Br- to BrO3- would cost only 0.3 mM PS.
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3S 2 O82− + Br − + 3H 2 O → BrO3− + 6 SO4 + 6 H +
(9)
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However, a significant portion of oxidant was in fact consumed by the organic matter. In this
317
case PS (1 mM) would probably be exhausted before Br- was completely oxidized and organic
318
bromine would be left finally. Fang et al. reported that presence of NOM inhibited the formation
319
of BrO3- in UV/PMS system. They partially attributed this to the inner-filtration effect of NOM
320
to the reactive bromine species(Fang and Shang 2012). In other words, both radical bromine and
321
free bromine were scavenged by the organic matter. This is consistent with the reaction scheme
322
in Figure 3. Moreover, the data in this research demonstrate that such scavenging reactions could
323
result in the formation of Br-DBPs.
324
3.5 Influence of temperature
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Temperature is a key factor that controls the reaction progress. This is reasonable because PS
326
was activated by heat and elevation of temperature facilitates the generation of SO4-· (Ghauch et
327
al. 2012). At 70°C and given the initial PS of 5.0 mM, Br- might have been cycled extensively.
328
The overall reaction had approached to the “end” status within 2 h with regard to the bromine
16
ACCEPTED MANUSCRIPT transformation (Figure 2). When the working temperature decreased to 60°C, the reaction
330
proceeded considerably more slowly (Figure 1). Yields of bromoform and DBAA were 0.54 and
331
0.78 µM after 2 h, respectively. Br-DBPs in the solution were still accumulating at that time.
332
Similar concentration profiles as obtained at 70°C were observed when the reaction was
333
examined over a longer time span (Figure S4). When the temperature was further decreased to
334
50°C, the concentrations of bromoform and DBAA were only 0.17 and 0.19 µM, respectively,
335
after 2 h (Figure 1). Even longer time would be required to allow the reaction to approach the
336
“end” status.
337
3.6 Removal of TOC
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TOC was monitored during the reaction process and the data were shown in Figure 5.
339
Generally, an increase in PS concentration and temperature enhanced the removal of TOC. For
340
solutions with 5.0 mM PS, the residual TOC after 2 h at working temperature of 50, 60, and
341
70°C were 1.27, 0.77, and 0.45 mg/L, respectively. For reaction solutions with 1.0 mM PS, the
342
respective values were 1.75, 1.11, and 0.69 mg/L. According to the data illustrated in Figure 5,
343
TOC underwent a quick reduction phase during the first 15 min, followed by a relatively slow
344
attenuation process. The removal during the first stage accounted for more than 60% of the total
345
removal achieved in 2 h for the treatment with 5.0 mM PS. Because significant amount of DBPs
346
were generated at this stage (Figure 1), degradation of HA by reactive bromine species might
347
contribute some of the TOC removal. However, reactive bromine species reacted with HA
348
primarily via electrophilic addition, which results in the incorporation of bromine to the organic
349
molecules but is not their mineralization(Ichihashi et al. 1999). Thus, the removal of TOC during
350
the first 15 min was more likely contributed to the reactions between HA and SO4-· .
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ACCEPTED MANUSCRIPT 351
SO4-· is believed to react with organics mainly through electron transfer mechanism, which makes it a more selective oxidant than OH· (Ahmed et al. 2012). The fast reduction of TOC
353
during the first 15 min (Figure 5) probably reflects the degradation of the labile sites for
354
SO4-· attacking. It should be noted that Br- concentration was relatively high and its oxidation by
355
SO4-· was also fast (k = 3.5 × 109 M-1s-1), Thus, rapid removal of TOC was concomitant with the
356
generation of reactive bromine species and thus Br-DBPs. After the labile sites were depleted,
357
the remaining organic carbon was relatively recalcitrant toward SO4-· . Nonetheless, oxidation of
358
bromide was less affected. As a result, Br-DBPs were continuously generated but TOC changed
359
slightly. Because the carbon in DBPs only accounted for a tiny fraction of TOC (4 Br-DBPs at 1
360
h accounted for 0.034 mg/L TOC in the treatment with 5 mM PM at 70°C), degradation of
361
Br-DBPs by SO4-· in the second stage did not cause appreciable change of TOC.
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Oxidation of organic matter by SO4-· through electron transfer is expected to produce protons
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according to Eq. 10. Formation of a BrO3- also generates protons according to Eq. 9. Hence,
364
acidification occurred as the reaction proceeded. The pH of the reaction solutions was monitored
365
and found decreasing from 5.8 to approximately 3.5 after 2 h.
367
368
RH + SO4⋅− → R ⋅ + SO4
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2−
+ H+
(10)
4. Conclusions
It was revealed that presence of Br- in thermo activated PS oxidation process results in the
369
formation of Br-DBPs. Among a variety of Br-DBPs, bromoform and DBAA were dominant
370
species. Their yields were an order of magnitude higher than those of MBAA and TBAA.
371
Formation of Br-DBPs was attributed to the generation of reactive bromine species such as Br·,
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ACCEPTED MANUSCRIPT Br2-· , HBrO-· , and free bromine upon oxidation of Br- by SO4-· . With excessive SO4-· , Br-DBPs
373
can be further degraded and Br- eventually transformed to BrO3-. If insufficient SO4-· is provided,
374
partial bromine ends up as organic forms such as Br-DBPs. As such, with initial PS dose of 5
375
mM, time-dependent formation of Br-DBPs exhibited an increase and decrease profile. When PS
376
was 1 mM, Br-DBPs increased monotonically. Such trends were highly coupled with the
377
respective concentration profiles of TIBr. We believe similar reactions scheme occur in other
378
processes involving SO4-· oxidation in the presence of Br- whose concentrations in natural waters
379
range from nearly zero to as high as 4 mg/L(Roccaro et al. 2014). Because both Br-DBPs and
380
BrO3- are highly toxic, particular attention should be paid when SO4-· based oxidation
381
technologies are applied to environmental matrices containing bromide.
382
Acknowledgements
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This research was supported by the Fundamental Research Funds for the Central
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Universities (KYZ201407), 333 Project of Jiangsu Province (BRA2014039), Natural Science
385
Foundation of China (51178224), and the Priority Academic Program Development (PAPD) of
386
Jiangsu Higher Education Institute. The authors would express their gratitude to Dr. Zhu Tang at
387
College of Resources & Environmental Sciences, Nanjing Agricultural University for assistance
388
in HPLC/ICP-MS analysis.
389
Appendix A. Supplementary Data
390
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Detailed DBPs extraction and analysis procedures, ICP/MS operation conditions, and
391
supporting figures. The information can be found in the online version.
392
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Yu, X.-Y., Bao, Z.-C. and Barker, J.R. (2003) Free Radical Reactions Involving Cl•, Cl2-•, and SO4-•
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ACCEPTED MANUSCRIPT 0.8
Persulfate: 1.0 mM
(a)
0.7
70°C
60°C
50°C
Persulfate: 5.0 mM 70°C
60°C
50°C
0.5 0.4
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CHBr3 (µM)
0.6
0.3 0.2 0.1
0
15
30
60
75
0.14
Persulfate: 1.0 mM 70°C 60°C
0.12
Persulfate: 5.0 mM 70°C 60°C
0.08
0.04 0.02 0
15
30
120
(b)
50°C
45
60
Reaction time (min)
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105
50°C
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45
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90
105
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ACCEPTED MANUSCRIPT 1.2
Persulfate: 1.0 mM 70°C 60°C Persulfate: 5.0 mM 70°C 60°C
(c) 1
50°C 50°C
0.6
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DBAA (µM)
0.8
. 0.4
0 0
15
30
45
60
75
Reaction time (min)
90
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0.2
0.18
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(d)
Persulfate: 1.0 mM
70°C 60°C Persulfate: 5.0 mM 70°C 60°C
0.15
0.09
0.06
0
50°C
15
30
45
60
75
90
105
120
Reaction time (min)
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50°C
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120
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Figure 1. Time-dependent formation of DBPs in heated PS solutions in the presence of HA and
513
Br-. [HA]0 = 2.0 mg/L as TOC, [Br-]0 = 0.1 mM, [PS]0 = 1.0 and 5.0 mM, T = 50, 60, and 70°C,
514
no buffer added. (a) bromoform, (b) MBAA, (c) DBAA, (d) TBAA.
515
27
ACCEPTED MANUSCRIPT 0.12 Persulfate: 5.0 mM
(a)
0.08
bromate
0.06
bromide
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Inorganic bromine (mM)
0.10
free bromine
0.04
TIBr
0.02
0.00 15
30
45
60
75
0.12 Persulfate: 1.0 mM
105
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516
90
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(b)
bromate bromide free bromine
0.08
TIBr
0.06
0.04
0.02
0.00
517
15
30
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45
60
75
90
105
120
Reaction time (min)
Figure 2. Change of the concentrations of inorganic bromine species in heated PS solutions.
519
[HA]0 = 2.0 mg/L as TOC, [Br-]0 = 0.1 mM, and 5.0 mM, T = 70°C, no buffer added. (a) [PS]0 =
520
5.0 mM, (b) [PS]0 = 1.0 mM
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ACCEPTED MANUSCRIPT SO4·Br2, HBrO
Br-
SO4·-
Br·, Br2·-
523
NOM
DBPs
SO4·-
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BrO3-
Figure 3. Proposed transformation scheme of bromine in SO4-· mediated reaction processes
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Figure 4. Degradation of individual DBPs in heated PS solutions. [PS]0 = 1.0 mM, T = 70°C, no
527
buffer added.
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ACCEPTED MANUSCRIPT
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ACCEPTED MANUSCRIPT 2.2 2.0 1.8
1.4 1.2 1.0 0.8 0.6
Persulfate: 1.0 mM 70
0.4
60
50
Persulfate: 5.0 mM
0.2
70
60
50
0.0 15
30
45
60
75
90
105
SC
0
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TOC (mg/L)
1.6
120
Reaction time (min)
529
Figure 5. Removal of TOC in heated PS solutions. [HA]0 = 2.0 mg/L as TOC, [Br-]0 = 0.1 mM,
531
[PS]0 = 1.0 and 5.0 mM, T = 50, 60, and 70°C, no buffer added.
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ACCEPTED MANUSCRIPT Br- can be transformed to reactive bromine species by SO4-· ; Reactive bromine species can react with humic substance to form Br-DBPs; Br-DBPs can be further degraded by SO4-· ; Br- is eventually transformed to bromate.
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• • • •
ACCEPTED MANUSCRIPT
Supplementary Data
Transformation of Bromide in Thermo Activated Persulfate
a
a
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Oxidation Processes
a
b
Department of Environmental Science and Engineering, Nanjing Agricultural University, Nanjing, 210095, China
b
Nanjing Institute of Environmental Sciences, Ministry of Environmental Protection of PRC,
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Nanjing, 210042, China
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Junhe Lu *, Jinwei Wu , Yuefei Ji , Deyang Kong
*Corresponding author: E-mail: [email protected];
Telephone: (86) 25-84395164; Fax: (86) 25-84395210
1
ACCEPTED MANUSCRIPT DBPs analysis THMs were analyzed by liquid-liquid extraction according to EPA method 551.1 using a Agilent 7890 gas chromatograph (GC) equipped with an electron capture detector (ECD) and a DB5- fused silica capillary column (30 m × 0.53 mm × 1.5 µm). After a 30 mL sample aliquot was
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extracted with 3 mL MTBE, 1 µL of the extract was injected into the GC. The temperature
program used to separate the analytes was as follows: initial termprature of 35°C held for 12 min,
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then increased at a rate of 8°C /min to 190°C, held for an additional 3 min. The temperature of the injector and detector were 200 and 350°C, respectively. The instrument was calibrated using
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standard deviation of the internal standards was typically near 20%.
HAAs were analyzed using EPA method 552.2. The procedure included liquid-liquid extraction, with subsequent sample derivatization and determination of volatile products by GC
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with ECD detection. A 30-mL sample was adjusted to pH < 0.5 with 98% sulfuric acid and
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extracted with 4 mL MTBE. The HAAs extracted into the MTBE phase were converted to their methyl esters by the addition of acidic methanol followed by slight heating. The acid extract was neutralized by a back extraction with saturated sodium bicarbonate. The target analytes were identified and measured by GC and the column described above. The temperature program was as follows: initial temperature of 35°C held for 12 min, then increased at a rate of 5°C /min to 200°C, and held for 2 min. The analytes were quantified using the procedural standard calibration.
2
ACCEPTED MANUSCRIPT Table S1. ICP/MS settings used for bromate and bromide measurement Settings /Parameters
Value 1300W 0.83mL/min 1.2 mL/min 18 mL/min
Kinetic Energy Discrimination (KED) Analog stage voltage Pulse stage voltage Discrimination threshold Defector voltage Quadrupole rod offset QRO Cell entrance voltage Cell exit voltage Cell rod offset CRO Axial field voltage AFT Rpa Rpq Cell gas A Cell gas B
-1650V 900V 12 -12V -13V -4V -26V -16V 475V 0 0.25 4.7 mL/min 0
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Analyte Internal standard
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Plasma: ICP RF power Nebulizer gas (Ar) flow Auxiliary gas (Ar) flow Plasma gas (Ar) flow
3
Br 78.9183 In 114.904
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ACCEPTED MANUSCRIPT
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Figure S1 Time-dependent formation of DBPs in heated PS solutions in the presence of DHBA. [DHBA]0 = 0.05 mM, [Br-]0 = 0.1 mM, T = 70°C. (a) [PS] 0 = 1.0 mM; (b) [PS] 0 = 5.0 mM
4
ACCEPTED MANUSCRIPT 200 160
0.5
140
1.0 2.0
120 100 80 60 40 20 0 0
1
2
3
4
20 16
0.5
14
1.0
12
2.0
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MBAA (µg/L)
5
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PS (mM)
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CHBr3 (µg/L)
180
10 8 6 4 2
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2
PS (mM)
3
4
5
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Reaction time (h)
200
1.0
150
2.0
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DBAA (µg/L)
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100
50 0
0
1
2
3
PS (mM)
5
4
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Figure S2 Formation of DBPs at varying PS concentrations. [HA]0 = 2.0 mg/L as TOC, [Br-]0 = 0.1 mM, T = 70°C.
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Figure S3 Stability of Br-DBPs at 70°C
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Figure S4 Time-dependent formation of DBPs in heated PS solutions in the presence of HA.
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S0043-1354(15)00218-3
DOI:
10.1016/j.watres.2015.03.028
Reference:
WR 11224
To appear in:
Water Research
Received Date: 8 January 2015 Revised Date:
23 March 2015
Accepted Date: 27 March 2015
Please cite this article as: Lu, J., Wu, J., Ji, Y., Kong, D., Transformation of Bromide in Thermo Activated Persulfate Oxidation Processes, Water Research (2015), doi: 10.1016/j.watres.2015.03.028. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT 1
Transformation of Bromide in Thermo Activated Persulfate
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Oxidation Processes
3 Junhe Lua*, Jinwei Wua, Yuefei Jia, Deyang Kong
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Department of Environmental Science and Engineering, Nanjing Agricultural University,
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Nanjing, 210095, China b
Nanjing Institute of Environmental Sciences, Ministry of Environmental Protection of PRC,
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Nanjing, 210042, China
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*Corresponding author: E-mail: [email protected];
Telephone: (86) 25-84395164; Fax: (86) 25-84395210
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ACCEPTED MANUSCRIPT Abstract Sulfate radicals (SO4-· ) are applied to degrade various organic pollutants. Due to its
22
high oxidative potential, SO4-· is presumed to be able to transform bromide to reactive bromine
23
species that can react with natural organic matter subsequently to form brominated products
24
including brominated disinfection by-products (Br-DBPs). This research was designed to
25
investigate the transformation of bromide in thermo activated persulfate oxidation process in the
26
presence of humic acid (HA). Significant formation of bromoform and bromoacetic acids was
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verified. Their formation was attributed to the reactions of HA and reactive bromine species
28
including Br·, Br2-· HOBr-· , and free bromine resulted from the oxidation of bromide by SO4-· .
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Yields of Br-DBPs increased monotonically at persulfate concentration of 1.0 mM and working
30
temperature of 70°C. However, the time-depended formation exhibited an increasing and the
31
decreasing profile when persulfate was 5.0 mM, suggesting further degradation of organic
32
bromine. HPLC/ICP-MS analysis demonstrated that the organic bromine was eventually
33
transformed to bromate at this condition. Thus, a transformation scheme was proposed in which
34
the bromine could be recycled multiple times between inorganic bromide and organic bromine
35
before being finally transformed to bromate. This is the first study that reveals the
36
comprehensive transformation map of bromine in SO4-· based reaction systems, which should be
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taken into consideration when such technologies are used to eliminate contamination in real
38
practice.
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Keywords: sulfate radical oxidation; bromide; brominated disinfection by-products; bromate
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ACCEPTED MANUSCRIPT Graphical abstract
SO4·Br2, HBrO
Br-
SO4·-
Br·, Br2·-
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NOM
SO4·-
DBPs
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BrO3-
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ACCEPTED MANUSCRIPT Abbreviations
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PS: persulfate
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PMS: peroxymonosulfate
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DBPs: disinfection by-products
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PFCs: perfluoroalkyl compounds
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PCBs: polychlorinated biphenyls
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MTBE: methyl tert-butyl ether
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PAHs: polycyclic aromatic hydrocarbons
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DOC: dissolved organic carbon
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TOC: total organic carbon
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THMs: trihalomethanes
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HAAs: haloacetic acids
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NOM: natural organic matter
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HA: humic acid
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GC: gas chromatography
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ECD: electron capture detector
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IC: ion chromatography
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ICP-MS: inductively coupled plasma-mass spectrometry
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BRS: bromine radical species
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MBAA: monobromoacetic acid
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DBAA: dibromoacetic acid
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TBAA: tribromoacetic acid
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DHBA: 3,5-dihydroxylbenzoic acid
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TIBr: total inorganic bromine
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1. Introduction
Sulfate radicals (SO4-· ) produced via activation of persulfate (PS)(Adewuyi and Sakyi 2013, Al-Shamsi and Thomson 2013, Furman et al. 2010, Johnson et al. 2008, Liang and Bruell 2008) or
73
peroxymonosulfate (PMS)(Anipsitakis and Dionysiou 2003, Costanza et al. 2010, Yao et al. 2012)
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have a one-electron reduction potential of 2.5~3.1 V(Anipsitakis and Dionysiou 2003, Neta et al.
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1988), making it a strong direct electron transfer oxidant similar to hydroxyl radicals (OH·, 2.7 V
76
in acid solution and 1.8 V in neutral solution)(Usman et al. 2012). SO4-· based oxidation was
77
demonstrated to be a viable way to decompose a broad spectrum of contaminants, including
78
polycyclic aromatic hydrocarbons (PAHs)(Usman et al. 2012), polychlorinated biphenyls
79
(PCBs)(Rastogi et al. 2009), perfluoroalkyl compounds (PFCs)(Lee et al. 2009), methyl
80
tert-butyl ether (MTBE)(Liang et al. 2011), chlorinated solvents(Costanza et al. 2010, Liang and
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Bruell 2008, Waldemer et al. 2006), herbicides(Guan et al. 2013), petroleum hydrocarbons(Yen
82
et al. 2011), etc. In addition to the oxidation strength, SO4-· based oxidation systems have a wider
83
operational pH range than OH· based ones(Anipsitakis and Dionysiou 2003, Guan et al. 2011).
84
Its precursors (PS or PMS) are more stable than that of OH· (H2O2) and thus able to be
85
transported to greater distance in the sub-surface(Liang et al. 2008, Liang et al. 2007). Due to
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these advantages, SO4-· based oxidation technologies have attracted increasing attention in
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wastewater treatment and in situ remediation of contaminated soil and ground water.
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The high oxidation potential of SO4-· also enables it to react with various inorganic ions such
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as CO32-, NO3-, Cl-, Br- (Adewuyi and Sakyi 2013, Anipsitakis et al. 2005, Bennedsen et al.
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2012, Fang et al. 2012, Fang and Shang 2012, Wang et al. 2011), which is detrimental to the
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treatment of the targeted contaminants. According to the redox potentials of halides (Br·/Br-, 5
ACCEPTED MANUSCRIPT 92
1.62 V; Cl·/Cl-, 2.41 V)(Huie et al. 1991) and SO4-· (SO4-· /SO42-, 2.5~3.1 V)(Anipsitakis and
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Dionysiou 2003), it is highly possible that reactive halogen species can be generated in
94
SO4-· mediated oxidation processes in the presence of halides. For instance, SO4
95
chloride ions (Cl-) to chlorine radicals (Cl·, Cl2-· , and ClOH-· ) which can couple to each other to
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form free chlorine (Cl2, HClO)(Anipsitakis et al. 2005, Bennedsen et al. 2012, Yu et al. 2003). −⋅
SO4 SO4 X − → X ⋅, X 2−⋅ → → X 2 / HXO
(1)
oxidizes
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·-
These oxidized halogen species are able to attack a number of organic compounds via addition,
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electron-transfer, or hydrogen-abstraction mechanism(Hasegawa and Neta 1978). When
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electron-rich compounds are present, halogenated intermediates and products can be
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generated(Yang et al. 2014). Bromide (Br-) is theoretically more readily oxidized and expected
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to follow a similar transformation scheme upon oxidation by SO4-· (eq. 1). It was found that
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SO4-· could in fact transform Br- to an even higher oxidation state, bromate (BrO3-)(Fang and
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Shang 2012, Lutze et al. 2014) which is a regulated drinking water disinfection by-product
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(DBP) formed in ozone disinfection process(Miller 1993).
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Generation of the reactive halogen species in SO4-· based treatment processes is of particular concern. It is well recognized that free halogen actively reacts with natural organic matter
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(NOM) resulting in the formation of halogenated DBPs such as trihalomethanes (THMs) and
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haloacetic acids (HAAs) during water disinfection processes(Xie 2003). DBPs are known to
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cause notable health risks and are regulated world widely(Xie 2003). Since both halides and
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NOM are ubiquitous in the environment(Magazinovic et al. 2004), there is a great possibility
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that halogenated by-products are generated when SO4-· is employed to eliminate contaminants.
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For example, Alken found that Cl- strongly interfered with the dissolved organic carbon (DOC)
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products such as chloromethane, chloroform, and methylene chloride(Alken 1992). Since
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bromination reactions are known to proceed at a higher rate than corresponding chlorination
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(Acero et al. 2005), generation of brominated by-products is highly possible. Wang et al. in a
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recent study demonstrated that brominated DBPs (Br-DBPs) could be formed in SO4-· based
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oxidation process in the presence of NOM isolates and Br-27.
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Transformation of Br- in SO4-· based oxidation processes attracted considerable attention
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recently. It appeared that Br- could be converted to either organic form and/or inorganic form
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with higher oxidation state(Fang and Shang 2012, Lutze et al. 2014, Wang et al. 2014). However,
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a detailed map of its transformation is still lacking and the underlying mechanisms that control
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the speciation of products remain unexplored, which comprises the main purposes of the present
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study. We used heat to activate PS because this was the simplest approach to generate SO4-· . In
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addition, possible reactions of Br- induced by photon or metal catalysts could be avoided in this
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system. The results of this study are of relevance to similar oxidation systems involving
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SO4-· and Br-.
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2. Materials and Methods
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2.1 Materials
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All chemicals were of analytical grade or better. K2S2O8 and KBr were purchased from
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Aladdin (Shanghai, China). MTBE was HPLC grade and obtained from Fisher (Waltham, MA).
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THMs and HAAs calibration mixtures were purchased from Sigma-Aldrich (St. Louis, MO).
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BrO3- standard and humic acid (HA) were also from Sigma-Aldrich. Reagent water with a 7
ACCEPTED MANUSCRIPT resistivity of 18.2 MΩ/cm was produced in a Millipore Super-Q Water Purification system. Stock
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solutions of HA, KBr, and PS were prepared by dissolving appropriate amount of the reagents in
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Milli-Q water. Total organic carbon (TOC) of the HA stock was quantified using a Shimadzu
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5050A TOC analyzer.
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2.2 Reaction setup
Transformation of Br- was investigated in a series of EPA vials (42 mL in volume) as batch
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reactors. The vials filled up with solution containing 0.1 mM Br- and 2.0 mg/L HA (as TOC)
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were pre-heated to the working temperature in a water bath before appropriated volume of PS
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stock solution was spiked to each of them to achieve preset concentrations. Since only a tiny
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amount of PS stock solution was added, change of temperature of the reaction solutions thus
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caused was ignored. The vials were headspace free and immersed in a water bath during the
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entire reaction period. After every 15 min 3 vials were taken out and chilled in an ice bath for 10
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min and kept at 5°C in a refrigerator thereafter until further treatment and analysis. One vial was
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for the analysis of Br- and BrO3-, the other two for THMs and HAAs, respectively. It should be
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noted that rapid decrease of temperature could effectively cease the reactions caused by
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PS(Ghauch et al. 2012). Preliminary experiments demonstrated that no DBPs were formed at
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room temperature with other conditions identical. The decomposition of DBPs by PS at room
152
temperature was also negligible. Thus, no chemical reagents such as methane or Na2SO3 were
153
used to quench the reactions. No buffer was added in order to rule out any interference caused by
154
reactions between radicals and buffer species. The reactions were conducted at 50, 60, and 70°C.
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At each temperature level, PS doses of 1.0, 2.0, 3.0, 4.0, and 5.0 mM were tested.
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Formation of free bromine was explored in the presence of 0.1 mM Br- and 2 mg/L HA at 70°C. PS levels of 1.0 and 5.0 mM were selected. Other conditions were same as above except 2
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mL aliquot was taken every 5 min and chilled immediately in an ice bath. Free bromine was
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analyzed using DPD colorimetric method(APHA/AWWA/WEF 2005) by measuring the
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absorbance at 510 nm on a Varian Cary 50 spectrophotometer. Controls with Br- absent were
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also analyzed and the values were used to correct the absorbance created by PS and dissolved
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oxygen induced oxidation of DPD. Standard deviation of this approach was within 5%.
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2.3 DBP and bromate analysis
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THMs and HAAs were extracted with MTBE according to EPA Method 551.1 and 552.2, respectively. DBPs analysis was performed in an Agilent 7890 gas chromatograph (GC)
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equipped with an electron capture detector (ECD) and HP-5 fused silica capillary column (30
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m×0.53 mm i.d., 1.5 µm film thickness). Detailed analytical procedures and instrumental setup
168
were specified in Support Information. Br- and BrO3- were separated and quantified using a
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Perkin-Elmer Flexar ion chromatography (IC) coupled with a Perkin-Elmer NexION 300x
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quadrupole-based ICP-MS without additional treatment. The IC was equipped with a Hamiton
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PRP-X100 anion exchange column. An isocratic mobile phase comprised of 20 mM
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NH4NO3-NH4H2PO4 and pH adjusted to 6 was used. The flow rate was 1.5 mL/min. Detailed
173
instrumental settings are given in Table S1. Concentrations of bromine species were determined
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by using multipoint standard calibration curves. All the experiments were carried out in
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duplicates or triplicates, and the data were averaged. The standard deviations were usually within
176
5-10% unless otherwise stated.
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3. Results and Discussion
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3.1 Formation of organic bromine
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Br- is known to be oxidized by SO4-· to form Br· at a nearly diffusion-limited rate constant of 3.5 × 109 M-1s-1 (eq. 2)(Lutze et al. 2014). Br· rapidly reacts with additional Br- or hydroxyl
181
anion yielding dibromide radicals (Br2-· ) or hypobromous radical (HBrO-· ), respectively (eqs. 3
182
and 4)(Yang et al. 2014). −⋅
2−
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SO4 + Br − → Br ⋅ + SO4
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Br ⋅ + Br − → Br2
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Br ⋅ +OH − → HBrO −⋅
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Br2 + Br⋅ → Br2 + Br −
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Br2 + Br2 → Br2 + 2 Br −
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Br ⋅ + Br ⋅ → Br2
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Br2 + H 2O ↔ HBrO + H + + Br −
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k = 1.2 × 1010 M-1s-1
(3)
k = 1.06 × 1010 M-1s-1
(4)
k = 2.0 × 109 M-1s-1
(5)
k = 1.9 × 109 M-1s-1
(6)
k = 1.0 × 109 M-1s-1
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k = 1.6 × 1010 M-1s-1
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Given the relatively high concentration of Br-, a significant fraction of SO4-· in the solution was
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expected to be scavenged by Br- and converted to bromine radical species (BRS). It was reported
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that BRS concentrations could exceed that of SO4-· by several orders in SO4-· oxidation processes
193
in the presence of seawater level of Br-(Yang et al. 2014). The generated BRS are selective
194
oxidants that can be involved in electron-transfer, H abstraction, or addition reactions with
195
organic compounds(Hasegawa and Neta 1978). It is generally accepted that electron-transfer and
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H abstraction contribute to the mineralization of contaminants, whereas addition reaction leads to
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the formation of halogenated compounds(Pignatello et al. 2006). In addition to BRS, free
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2014, Neta et al. 1988, Yang et al. 2014). These reactive bromine species (both radical and
200
nonradical) could result in the generation of brominated intermediates and products if
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electron-rich compounds are present.
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NOM molecules ubiquitously present in water contain plenty of electron-rich phenolic
moieties. It is widely known that the electron-rich phenolic moieties in NOM molecules react
204
with free halogen resulting in the formation of halogenated DBPs such as THMs and HAAs
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during water disinfection processes(Lu et al. 2004, Xie 2003). We presume that the BRS can
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initiate the halogenation of NOM in a similar way and generate Br-DBPs. Since NOM is
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primarily comprised of humic substances (Croué et al. 2000, Ichihashi et al. 1999), commercial
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HA was used to mimic the reactivity of NOM in this research. As shown in Figure 1, formation
209
of both bromoform and bromoacetic acids was verified in heated PS solutions in the presence of
210
HA and Br-. Among a variety of individual DBPs, bromoform and dibromoacetic acid (DBAA)
211
were the dominant species. Monobromoacetic acid (MBAA) and tribromoacetic acid (TBAA)
212
were also detected but their yields were at least an order of magnitude lower than that of DBAA
213
at identical conditions. Formation of the 4 Br-DBPs generally showed similar trends to the
214
change of temperature, reaction time, and PS dose as illustrated in Figure 1. Higher yield of
215
DBAA than TBAA is indeed distinct from the distribution pattern of HAAs in bromination using
216
free bromine in which TBAA formation is more favored. A similar pattern has also been noticed
217
by Wang et al(Wang et al. 2014) and this seems characteristic of the formation of Br-DBPs in
218
SO4-· based oxidation processes. Such a result suggests different bromination mechanisms are
219
involved in SO4-· mediated bromination processes which warrant further investigation.
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It should be noted that no Br-DBPs were observed in the control experiments with either HA + PS, Br- + PS, or HA + Br- without PS, confirming that reactive bromine species were
222
responsible and HA served as the precursor of Br-DBPs. Nevertheless, it is impossible to
223
determine the contribution of each of the reactive bromine species (both radical and nonradical)
224
because their respective kinetic constant of the reaction with organic matter is unknown. In
225
addition, scavenging of SO4-· by Br- greatly reduced the decomposition of the DBP precursor
226
(HA) due to its reaction with SO4-· , which made it more available to bromination reactions by
227
BRS. Since phenolic moieties are presumed to be the principal electron-rich sites in HA
228
molecules liable to the attack of reactive bromine species and generation of Br-DBPs, formation
229
of Br-DBPs was further examined using 3,5-dihydroxylbenzoic acid (DHBA) as a HA model
230
compound. The data are illustrated in the Supporting Information (Figure S1). It was
231
demonstrated that Br-DBPs were also generated and their formation showed similar trends
232
concerning the speciation of dominant Br-DBPs and the yields to the change of PS dose and
233
reaction time (Figure S1).
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3.2 Influence of PS concentration on Br-DBPs formation
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concentration as shown in Figure 1. For instance, all the Br-DBPs increased monotonically when
237
the initial PS was 1.0 mM. The concentrations of bromoform and DBAA reached 0.38 and 0.72
238
µM, respectively, after 2 h at working temperature of 70°C. In contrast, when 5.0 mM PS was
239
added to the solution initially, concentrations of Br-DBPs increased at significantly higher rates.
240
Their yields reached a temporary maximum at approximately 60 min and decreased thereafter
241
(70°C). The maximum concentrations of bromoform and DBAA were 0.11 and 1.01 µM, 12
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243
at 70°C. Similar trends of Br-DBPs formation were observed with regard to the change of PS
244
concentration at a given reaction time and the data were given in the Supporting Information
245
(Figure S1). For instance, when Br-DBPs were monitored at the reaction time of 0.5 and 1 h, it
246
can be seen that their yields increased monotonically with the elevated PS concentrations (Figure
247
S2). However, Br-DBP formation profiles became complicated at the reaction time of 2 h. More
248
Br-DBPs were generated when PS increased from 1.0 mM to 2.0 mM. With PS further increased
249
to 3.0 mM, DBPs yields declined. No DBPs were found when the PS increased to 4.0 mM.
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Based on these data, it can be inferred that Br-DBPs were not the final products and they
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were most likely degraded by nonselective SO4-· in the solution. To test this, we investigated the
252
stability of individual Br-DBPs toward SO4-· and the data are given in Figure 4. It was
253
demonstrated that the degradation of Br-DBPs by SO4-· was first order in kinetics (r2 = 0.99).
254
Their half-life times were less than 10 min in 1 mM PS solution at 70°C, which corroborates
255
their rapid decline after reaching the maximum in 1h (Figure 1). Influence of heating on the
256
degradation of Br-DBPs was also investigated and the data can be found in the Supporting
257
Information (Figure S3). It was revealed that no appreciable decomposition of bromoform,
258
MBAA, and DBAA occurred at 70°C. TBAA was relatively unstable and its half-life was 13 min
259
at 70 °C (r2 = 0.98). Because TBAA was a minor DBP species, most of the Br-DBPs should be
260
degraded by SO4-· . When Br-DBPs were degraded by SO4-· , organic bromine was probably
261
converted back to inorganic Br- which was expected to be oxidized by SO4-· to form reactive
262
bromine species and participate to the bromination of HA again.
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3.3 Formation of free bromine and bromate
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Formation of free bromine and BrO3- in UV activated persulfate oxidation systems has recently been documented(Fang and Shang 2012, Lutze et al. 2014). Figure 2a illustrates the
266
concentration profiles of nonradical inorganic bromine species in the reaction solutions at 70°C.
267
When 5 mM PS was dosed initially, Br- decreased rapidly and became undetectable after 75 min.
268
Meanwhile, formation of BrO3- was observed and its concentration kept increasing. More than
269
0.09 mM BrO3- was formed after 75 min and the value increased to nearly 0.1 mM after 2 h.
270
Since initially 0.1 mM Br- was presented, this suggested that the Br- was quantitatively
271
transformed to BrO3-. Formation of free bromine (sum of HBrO/BrO- and Br2) was also detected
272
at relatively low level (< 15 µM). However, it exhibited a complicated concentration profile with
273
2 temporary maximum appearing at 30 and 75 min (Figure 2a). When the initial PS was 1 mM,
274
the transformation of Br- was significantly slower and approximately 0.038 mM still remained in
275
the solution after 2 h (Figure 2b). Formation of BrO3- was not observed during the first 1 h and
276
its concentration was only 0.022 mM after 2 h. Appreciable free bromine was also found after 1
277
h (Figure 2b).
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We assume that Br-, free bromine, and BrO3- were the major inorganic bromine species in the
279
reaction solutions because BRS (Br·, Br2-· , etc) were transient and not likely to accumulate(Yang
280
et al. 2014). Thus, total inorganic bromine (TIBr) could be calculated as the sum of these
281
nonradical inorganic species, which is also given in Figure 2. It can be found that time-dependent
282
change of TIBr showed a “V shape” profile in the solution dosed with 5 mM PS at 70°C (Figure
283
2). It decreased first and reached a temporary minimum (0.051 mM) at 60 min before increasing
284
again and finally reaching 0.1 mM which equal to the initial quantity of Br-. Such a “V shape”
285
profile is indicative of the formation of organic bromine and precisely coupled with concurrent
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287
(70°C, 5 mM PS) exhibited an increase and decrease profile with a maximum appeareing at 60
288
min. The change of TIBr appeared less complicated in the treatment with 1.0 mM PS. It
289
decreased monotonically to approximately 0.05 mM after 2 h, which was also coupled well with
290
the concomitant Br-DBP formation (Figure 2b).
291
3.4 Reaction scheme
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According to the discussion above, a transformation scheme of Br- in SO4-· oxidation process in the presence of HA can be proposed as shown in Figure 3. Br- was oxidized by SO4-· to form
294
reactive bromine species (both radical and nonradical) which attack HA yielding organic
295
bromine including Br-DBPs. The organic bromine is not stable toward SO4-· and degraded to
296
release Br- again. The released Br- can be oxidized and react with HA again. In this way, Br- is
297
cycled multiple times until either the oxidant is depleted or it is converted to BrO3-. The
298
treatment with 5 mM PS represents an excessive oxidant scenario in which Br- was quantitatively
299
transformed to BrO3- ultimately. It is noted that the decline of organic bromine was accompanied
300
by the re-accumulation of free bromine (60 – 75 min, Figure1 and Figure 2a), which suggests the
301
free bromine formed during this particular period was mostly attributed to the oxidation of
302
recycled Br-. The temporary re-accumulation of free bromine also elucidated the intermediate
303
role of this species in the formation of BrO3-. This phenomenon is consistent with the finding of
304
Fang and Shang (Fang and Shang 2012) and Lutze et al. in their study of the formation of BrO3-
305
in UV activated SO4-· oxidation system. Both of the researches demonstrated that HBrO was the
306
key intermediate during the formation of BrO3- although conflicted mechanisms were proposed
307
concerning how HBrO was further oxidized.
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ACCEPTED MANUSCRIPT 308
When SO4-· is depleted before Br- is completely converted, a portion of Br- will end in form of organic bromine including Br-DBPs. Such a scenario was likely seen in the treatment with 1.0
310
mM PS. Comparing the data shown in Figure 1 and 2b, it is evident that the evolution of TIBr
311
was also coupled with the concomitant DBP formation. Br-DBPs accumulated while TIBr kept
312
decreasing within the examined reaction period. Further increase of BrO3- was possible with
313
prolonged reaction time. According to the stoichiometry relationship as demonstrated in Eq. (9),
314
oxidizing 0.1 mM Br- to BrO3- would cost only 0.3 mM PS.
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2−
3S 2 O82− + Br − + 3H 2 O → BrO3− + 6 SO4 + 6 H +
(9)
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However, a significant portion of oxidant was in fact consumed by the organic matter. In this
317
case PS (1 mM) would probably be exhausted before Br- was completely oxidized and organic
318
bromine would be left finally. Fang et al. reported that presence of NOM inhibited the formation
319
of BrO3- in UV/PMS system. They partially attributed this to the inner-filtration effect of NOM
320
to the reactive bromine species(Fang and Shang 2012). In other words, both radical bromine and
321
free bromine were scavenged by the organic matter. This is consistent with the reaction scheme
322
in Figure 3. Moreover, the data in this research demonstrate that such scavenging reactions could
323
result in the formation of Br-DBPs.
324
3.5 Influence of temperature
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Temperature is a key factor that controls the reaction progress. This is reasonable because PS
326
was activated by heat and elevation of temperature facilitates the generation of SO4-· (Ghauch et
327
al. 2012). At 70°C and given the initial PS of 5.0 mM, Br- might have been cycled extensively.
328
The overall reaction had approached to the “end” status within 2 h with regard to the bromine
16
ACCEPTED MANUSCRIPT transformation (Figure 2). When the working temperature decreased to 60°C, the reaction
330
proceeded considerably more slowly (Figure 1). Yields of bromoform and DBAA were 0.54 and
331
0.78 µM after 2 h, respectively. Br-DBPs in the solution were still accumulating at that time.
332
Similar concentration profiles as obtained at 70°C were observed when the reaction was
333
examined over a longer time span (Figure S4). When the temperature was further decreased to
334
50°C, the concentrations of bromoform and DBAA were only 0.17 and 0.19 µM, respectively,
335
after 2 h (Figure 1). Even longer time would be required to allow the reaction to approach the
336
“end” status.
337
3.6 Removal of TOC
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TOC was monitored during the reaction process and the data were shown in Figure 5.
339
Generally, an increase in PS concentration and temperature enhanced the removal of TOC. For
340
solutions with 5.0 mM PS, the residual TOC after 2 h at working temperature of 50, 60, and
341
70°C were 1.27, 0.77, and 0.45 mg/L, respectively. For reaction solutions with 1.0 mM PS, the
342
respective values were 1.75, 1.11, and 0.69 mg/L. According to the data illustrated in Figure 5,
343
TOC underwent a quick reduction phase during the first 15 min, followed by a relatively slow
344
attenuation process. The removal during the first stage accounted for more than 60% of the total
345
removal achieved in 2 h for the treatment with 5.0 mM PS. Because significant amount of DBPs
346
were generated at this stage (Figure 1), degradation of HA by reactive bromine species might
347
contribute some of the TOC removal. However, reactive bromine species reacted with HA
348
primarily via electrophilic addition, which results in the incorporation of bromine to the organic
349
molecules but is not their mineralization(Ichihashi et al. 1999). Thus, the removal of TOC during
350
the first 15 min was more likely contributed to the reactions between HA and SO4-· .
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ACCEPTED MANUSCRIPT 351
SO4-· is believed to react with organics mainly through electron transfer mechanism, which makes it a more selective oxidant than OH· (Ahmed et al. 2012). The fast reduction of TOC
353
during the first 15 min (Figure 5) probably reflects the degradation of the labile sites for
354
SO4-· attacking. It should be noted that Br- concentration was relatively high and its oxidation by
355
SO4-· was also fast (k = 3.5 × 109 M-1s-1), Thus, rapid removal of TOC was concomitant with the
356
generation of reactive bromine species and thus Br-DBPs. After the labile sites were depleted,
357
the remaining organic carbon was relatively recalcitrant toward SO4-· . Nonetheless, oxidation of
358
bromide was less affected. As a result, Br-DBPs were continuously generated but TOC changed
359
slightly. Because the carbon in DBPs only accounted for a tiny fraction of TOC (4 Br-DBPs at 1
360
h accounted for 0.034 mg/L TOC in the treatment with 5 mM PM at 70°C), degradation of
361
Br-DBPs by SO4-· in the second stage did not cause appreciable change of TOC.
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Oxidation of organic matter by SO4-· through electron transfer is expected to produce protons
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according to Eq. 10. Formation of a BrO3- also generates protons according to Eq. 9. Hence,
364
acidification occurred as the reaction proceeded. The pH of the reaction solutions was monitored
365
and found decreasing from 5.8 to approximately 3.5 after 2 h.
367
368
RH + SO4⋅− → R ⋅ + SO4
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2−
+ H+
(10)
4. Conclusions
It was revealed that presence of Br- in thermo activated PS oxidation process results in the
369
formation of Br-DBPs. Among a variety of Br-DBPs, bromoform and DBAA were dominant
370
species. Their yields were an order of magnitude higher than those of MBAA and TBAA.
371
Formation of Br-DBPs was attributed to the generation of reactive bromine species such as Br·,
18
ACCEPTED MANUSCRIPT Br2-· , HBrO-· , and free bromine upon oxidation of Br- by SO4-· . With excessive SO4-· , Br-DBPs
373
can be further degraded and Br- eventually transformed to BrO3-. If insufficient SO4-· is provided,
374
partial bromine ends up as organic forms such as Br-DBPs. As such, with initial PS dose of 5
375
mM, time-dependent formation of Br-DBPs exhibited an increase and decrease profile. When PS
376
was 1 mM, Br-DBPs increased monotonically. Such trends were highly coupled with the
377
respective concentration profiles of TIBr. We believe similar reactions scheme occur in other
378
processes involving SO4-· oxidation in the presence of Br- whose concentrations in natural waters
379
range from nearly zero to as high as 4 mg/L(Roccaro et al. 2014). Because both Br-DBPs and
380
BrO3- are highly toxic, particular attention should be paid when SO4-· based oxidation
381
technologies are applied to environmental matrices containing bromide.
382
Acknowledgements
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This research was supported by the Fundamental Research Funds for the Central
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Universities (KYZ201407), 333 Project of Jiangsu Province (BRA2014039), Natural Science
385
Foundation of China (51178224), and the Priority Academic Program Development (PAPD) of
386
Jiangsu Higher Education Institute. The authors would express their gratitude to Dr. Zhu Tang at
387
College of Resources & Environmental Sciences, Nanjing Agricultural University for assistance
388
in HPLC/ICP-MS analysis.
389
Appendix A. Supplementary Data
390
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Detailed DBPs extraction and analysis procedures, ICP/MS operation conditions, and
391
supporting figures. The information can be found in the online version.
392
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Yu, X.-Y., Bao, Z.-C. and Barker, J.R. (2003) Free Radical Reactions Involving Cl•, Cl2-•, and SO4-•
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ACCEPTED MANUSCRIPT 0.8
Persulfate: 1.0 mM
(a)
0.7
70°C
60°C
50°C
Persulfate: 5.0 mM 70°C
60°C
50°C
0.5 0.4
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CHBr3 (µM)
0.6
0.3 0.2 0.1
0
15
30
60
75
0.14
Persulfate: 1.0 mM 70°C 60°C
0.12
Persulfate: 5.0 mM 70°C 60°C
0.08
0.04 0.02 0
15
30
120
(b)
50°C
45
60
Reaction time (min)
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105
50°C
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MBAA (µM)
0.1
90
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Reaction time (min)
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509
45
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0
26
75
90
105
120
ACCEPTED MANUSCRIPT 1.2
Persulfate: 1.0 mM 70°C 60°C Persulfate: 5.0 mM 70°C 60°C
(c) 1
50°C 50°C
0.6
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DBAA (µM)
0.8
. 0.4
0 0
15
30
45
60
75
Reaction time (min)
90
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0.2
0.18
105
(d)
Persulfate: 1.0 mM
70°C 60°C Persulfate: 5.0 mM 70°C 60°C
0.15
0.09
0.06
0
50°C
15
30
45
60
75
90
105
120
Reaction time (min)
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0.03
511
50°C
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TBAA (µM)
0.12
120
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Figure 1. Time-dependent formation of DBPs in heated PS solutions in the presence of HA and
513
Br-. [HA]0 = 2.0 mg/L as TOC, [Br-]0 = 0.1 mM, [PS]0 = 1.0 and 5.0 mM, T = 50, 60, and 70°C,
514
no buffer added. (a) bromoform, (b) MBAA, (c) DBAA, (d) TBAA.
515
27
ACCEPTED MANUSCRIPT 0.12 Persulfate: 5.0 mM
(a)
0.08
bromate
0.06
bromide
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Inorganic bromine (mM)
0.10
free bromine
0.04
TIBr
0.02
0.00 15
30
45
60
75
0.12 Persulfate: 1.0 mM
105
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516
90
120
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0
(b)
bromate bromide free bromine
0.08
TIBr
0.06
0.04
0.02
0.00
517
15
30
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0
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Inorganic bromine (mM)
0.10
45
60
75
90
105
120
Reaction time (min)
Figure 2. Change of the concentrations of inorganic bromine species in heated PS solutions.
519
[HA]0 = 2.0 mg/L as TOC, [Br-]0 = 0.1 mM, and 5.0 mM, T = 70°C, no buffer added. (a) [PS]0 =
520
5.0 mM, (b) [PS]0 = 1.0 mM
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28
ACCEPTED MANUSCRIPT SO4·Br2, HBrO
Br-
SO4·-
Br·, Br2·-
523
NOM
DBPs
SO4·-
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BrO3-
Figure 3. Proposed transformation scheme of bromine in SO4-· mediated reaction processes
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Figure 4. Degradation of individual DBPs in heated PS solutions. [PS]0 = 1.0 mM, T = 70°C, no
527
buffer added.
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ACCEPTED MANUSCRIPT
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ACCEPTED MANUSCRIPT 2.2 2.0 1.8
1.4 1.2 1.0 0.8 0.6
Persulfate: 1.0 mM 70
0.4
60
50
Persulfate: 5.0 mM
0.2
70
60
50
0.0 15
30
45
60
75
90
105
SC
0
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TOC (mg/L)
1.6
120
Reaction time (min)
529
Figure 5. Removal of TOC in heated PS solutions. [HA]0 = 2.0 mg/L as TOC, [Br-]0 = 0.1 mM,
531
[PS]0 = 1.0 and 5.0 mM, T = 50, 60, and 70°C, no buffer added.
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ACCEPTED MANUSCRIPT Br- can be transformed to reactive bromine species by SO4-· ; Reactive bromine species can react with humic substance to form Br-DBPs; Br-DBPs can be further degraded by SO4-· ; Br- is eventually transformed to bromate.
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• • • •
ACCEPTED MANUSCRIPT
Supplementary Data
Transformation of Bromide in Thermo Activated Persulfate
a
a
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Oxidation Processes
a
b
Department of Environmental Science and Engineering, Nanjing Agricultural University, Nanjing, 210095, China
b
Nanjing Institute of Environmental Sciences, Ministry of Environmental Protection of PRC,
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Nanjing, 210042, China
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Junhe Lu *, Jinwei Wu , Yuefei Ji , Deyang Kong
*Corresponding author: E-mail: [email protected];
Telephone: (86) 25-84395164; Fax: (86) 25-84395210
1
ACCEPTED MANUSCRIPT DBPs analysis THMs were analyzed by liquid-liquid extraction according to EPA method 551.1 using a Agilent 7890 gas chromatograph (GC) equipped with an electron capture detector (ECD) and a DB5- fused silica capillary column (30 m × 0.53 mm × 1.5 µm). After a 30 mL sample aliquot was
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extracted with 3 mL MTBE, 1 µL of the extract was injected into the GC. The temperature
program used to separate the analytes was as follows: initial termprature of 35°C held for 12 min,
SC
then increased at a rate of 8°C /min to 190°C, held for an additional 3 min. The temperature of the injector and detector were 200 and 350°C, respectively. The instrument was calibrated using
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commercial calibration standards. Five aqueous calibration standards, bracketing the analyte concentration range expected in the samples, were analyzed together with each set of samples. Internal standards were used with samples to check for the extraction efficiency. The relative
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standard deviation of the internal standards was typically near 20%.
HAAs were analyzed using EPA method 552.2. The procedure included liquid-liquid extraction, with subsequent sample derivatization and determination of volatile products by GC
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with ECD detection. A 30-mL sample was adjusted to pH < 0.5 with 98% sulfuric acid and
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extracted with 4 mL MTBE. The HAAs extracted into the MTBE phase were converted to their methyl esters by the addition of acidic methanol followed by slight heating. The acid extract was neutralized by a back extraction with saturated sodium bicarbonate. The target analytes were identified and measured by GC and the column described above. The temperature program was as follows: initial temperature of 35°C held for 12 min, then increased at a rate of 5°C /min to 200°C, and held for 2 min. The analytes were quantified using the procedural standard calibration.
2
ACCEPTED MANUSCRIPT Table S1. ICP/MS settings used for bromate and bromide measurement Settings /Parameters
Value 1300W 0.83mL/min 1.2 mL/min 18 mL/min
Kinetic Energy Discrimination (KED) Analog stage voltage Pulse stage voltage Discrimination threshold Defector voltage Quadrupole rod offset QRO Cell entrance voltage Cell exit voltage Cell rod offset CRO Axial field voltage AFT Rpa Rpq Cell gas A Cell gas B
-1650V 900V 12 -12V -13V -4V -26V -16V 475V 0 0.25 4.7 mL/min 0
AC C
EP
Analyte Internal standard
TE D
M AN U
SC
RI PT
Plasma: ICP RF power Nebulizer gas (Ar) flow Auxiliary gas (Ar) flow Plasma gas (Ar) flow
3
Br 78.9183 In 114.904
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
Figure S1 Time-dependent formation of DBPs in heated PS solutions in the presence of DHBA. [DHBA]0 = 0.05 mM, [Br-]0 = 0.1 mM, T = 70°C. (a) [PS] 0 = 1.0 mM; (b) [PS] 0 = 5.0 mM
4
ACCEPTED MANUSCRIPT 200 160
0.5
140
1.0 2.0
120 100 80 60 40 20 0 0
1
2
3
4
20 16
0.5
14
1.0
12
2.0
M AN U
18
MBAA (µg/L)
5
SC
PS (mM)
RI PT
CHBr3 (µg/L)
180
10 8 6 4 2
TE D
0 0
1
250
2
PS (mM)
3
4
5
EP
Reaction time (h)
200
1.0
150
2.0
AC C
DBAA (µg/L)
0.5
100
50 0
0
1
2
3
PS (mM)
5
4
5
ACCEPTED MANUSCRIPT 10 9
Reaction time (h)
8 1.0
6
2.0
5 4 3 2 1 0 0
1
2
3
4
5
SC
PS (mM)
RI PT
TBAA (µg/L)
0.5
7
AC C
EP
TE D
M AN U
Figure S2 Formation of DBPs at varying PS concentrations. [HA]0 = 2.0 mg/L as TOC, [Br-]0 = 0.1 mM, T = 70°C.
6
ACCEPTED MANUSCRIPT 800 700 CHBr3
MBAA
DBAA
TBAA
500 400 300 200 100 0 10
20
30
Time (min)
40
AC C
EP
TE D
M AN U
Figure S3 Stability of Br-DBPs at 70°C
7
50
SC
0
RI PT
Br-DBPs (µ g/L)
600
60
ACCEPTED MANUSCRIPT 1 0.9
CHBr3
MBAA
DBAA
TBAA
0.8
0.6 0.5 0.4 0.3 0.2 0.1 0 30
60
90
120
150
180
210
Reaction time (min)
240
270
300
330
360
SC
0
RI PT
Br-DBPs (µ M)
0.7
M AN U
Figure S4 Time-dependent formation of DBPs in heated PS solutions in the presence of HA.
AC C
EP
TE D
[HA]0 = 2.0 mg/L as TOC, [Br-]0 = 0.1 mM, [K2S2O8]0 = 5.0 mM, T = 60°C, no buffer added
8
