Supporting Information for. The Roles of Reactive Species in Micropollutant Degradation in the UV/Free Chlorine System

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1 Supporting Information for The Roles of Reactive Species in Micropollutant Degradation in the UV/Free hlorine System Jingyun Fang *,,, ǁ,, Yun Fu, hii Shang *, School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 51075, hina Department of ivil and Environmental Engineering, The Hong Kong University of Science and Technology, lear Water Bay, Kowloon, Hong Kong. ǁ Guangdong Provincial Key Laboratory of Environmental Pollution ontrol and Remediation Technology, Guangzhou 51075, hina SYSU-HKUST Research enter for Innovative Environmental Technology (SHRIET) School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 51075, hina * Addre correspondence to either J. Fang or. Shang. Phone: (J. Fang); (. Shang). Fax: (. Shang). fangjy3@mail.sysu.edu.cn (J. Fang), cechii@ust.h (. Shang). Submitted to Environmental Science & Technology Number of pages (including this page): 17 Number of Texts: 5 Number of Figures: 11 Number of Tables:

2 List of captions: Text S1. Photolysis experiments Text S. Determination of quantum yields of chlorine photolysis at 54 nm Text S3. Derivation of modeling equations Text S4. Elucidating the roles of and other radicals using probe compounds Text S5. Reaction rate constants between l and NOM Table S1. omparison of quantum yields of free chlorine under UV irradiation at 53.7 nm Table S. Oxidant concentrations and contributions to degradation at different values of ph and in the presence of chloride from modeling results Figure S1. Schematic diagram of the large-volume UV irradiator Figure S. Photolysis of dilute H O under UV irradiation at 54 nm. onditions: [H O 0 = 100 μm,. Experiments were performed in duplicate. Error bars indicate the standard deviation of the duplicate experiments. The solid line is the line of best fit Figure S3. (a) Pseudo-first-order rate constants () of degradation and NB degradation under different values of ph in the co-presence of and NB in the UV/chlorine proce. (b) The contributions of and other radicals to degradation in the UV/chlorine proce. onditions: [ 0 = 5 μm, [NB 0 = 5 μm, chlorine dosage = 70 μm Figure S4. degradation in ultrapure water in the UV/chlorine proce at different chlorine dosages. onditions: [ 0 = 5 μm, ph = Figure S5. degradation in ultrapure water in the UV/chlorine proce under different concentrations. onditions: chlorine dosage = 70 μm, ph = Figure S6. degradation in ultrapure water in the UV/chlorine proce under different values of ph. onditions: [ 0 = 5 μm, chlorine dosage = 70 μm Figure S7. Photolysis of dilute free chlorine under UV irradiation at 54 nm at ph 5 and 10. onditions: [chlorine 0 = 70 μm,. Experiments were performed in duplicate. Error bars indicate the standard deviation of the duplicate experiments. The lines are lines of best fit Figure S8. Pseudo-first-order rate constants () of degradation and NB degradation by, - l and l under different values of ph in the co-presence of and NB in the UV/chlorine proce. onditions: [ 0 = 5 μm, [NB 0 = 5 μm, chlorine dosage = 70 μm Figure S9. degradation in ultrapure water in the UV/chlorine proce under different chloride concentrations. onditions: ph = 6.0, [ 0 = 5 μm, chlorine dosage = 70 μm.. 15 Figure S10. degradation in ultrapure water in the UV/chlorine proce in the presence of different concentrations of NOM. onditions: ph = 6, [ 0 = 5 μm, chlorine dosage = 70 μm Figure S11. degradation in ultrapure water in the UV/chlorine proce in the presence of different concentrations of bicarbonate. onditions: ph = 6, [ 0 = 5 μm, chlorine dosage = 70 μm

3 Text S1. Photolysis experiments. 1.1 Effective path length of UV light in the experimental reactor. nce the photochemical reactor was not a standard collimated beam reactor, 1 the UV light was not strictly perpendicular to the water surface. The optical length would depend on the reactor geometry. The reflection and divergence factors of UV light, and the petri factor and the water factor of the reactor should also be considered. 1 It is quite difficult to correct the light attenuation factors in such a system, and thus the effective path length (L) was chosen to characterize the reactor., 3 This parameter indicates the spatially averaged or volume-averaged UV fluence distribution in the reactor rather than the exact UV light distribution. The effective path length (L) was determined by photolysis inetics of dilute H O 4 and the concentration of H O was determined by the peroxidase-catalyzed oxidation of N-N-diethyl-p-phenylenediamine (DPD). 5 For a dilute H O solution, its photolysis follows first-order inetics, 6, 7 and then L could be calculated using eq. S1 and eq. S. d dt t I0 (.303 H O L app )t obs t (S1) V t ln( ) obst (S) 0 where t is the concentration of H O (M) at time t, 0 is the initial concentration of H O ( M in this study), ε is the molar absorption coefficient of H O (M -1 cm -1 ), L is the effective path length (cm), I 0 is the photon flux (E s -1 ), V is the solution volume (L), and Φ app is the apparent quantum yield of H O photolysis (mol E -1 ). At 54 nm, ε = 19.6 M -1 cm -1, Φ app = 1.0 mol E -1, 7 I 0 = ± μe s -1, and V = 0.5 L here. Figure S shows the photolysis inetics of H O, and obs is the slope of the regreion line, which is a function of Φ app, ε, I 0 and L. Thus, for given values of Φ app, ε and I 0, L can be easily computed from the value of obs. For the experimental reactor, the effective path length L of the photoreactor was determined to be 4.9 ± 0.1 cm. The photolysis of dilute H O is dependent on the total quantity of photons absorbed by H O, so the concept of effective path length L involves the influence of reactor geometry, configuration, and physics (i.e., reflection, refraction, scatter,

4 absorbance, and diipation), and thus can represent the spatially averaged or volume-averaged UV fluence rate distribution.,3,4,6 1. Estimation of the average UV fluence rate. For a dilute H O solution, the photolysis of H O in a collimated beam photoreactor can be expreed as follows: 8 d dt t ( app E 110 al al 0 0 ph O )t (.303 appeph O ) where E 0 P is defined as the average UV fluence rate (E s -1 cm - ), a is the solution absorbance for a 1 cm path length (cm -1 ), and L is the effective path length. From eq. S3, obs is a function of E 0 P, Φ app obs t (S3) and ε. For given values of Φ app, ε and I 0, L can be easily computed from the value of obs (shown in Figure S). E 0 P was estimated to be μe s -1 cm -, or about 0.58 mw cm -. In a very dilute solution with high UV transmittance, the average UV fluence rate is approximately equal to the spatially averaged one. For the experimental reactor, the actual UV fluence rate distribution in the photoreactor is influenced by various factors, e.g., reflection, refraction, solution absorbance, and diipation in the photoreactor. 9 0 So the estimated E P is an apparent parameter that represents the average UV fluence rate 10. It was used here to describe the photochemical reactions and for comparisons with other UV-based procees. Text S. Determination of quantum yields of chlorine photolysis at 54 nm. The quantum yields of and photolysis at 54 nm were determined in chlorine solutions at ph 5 and 10, respectively. The concentration of free chlorine can be measured by the DPD colorimetric standard method using a UV-vis spectrophotometer (UV-700, Shimadzu, Japan) to measure sample absorbance at 515 nm. The quantum yield at a single wavelength is a function of both the molar absorption coefficient ε and the time-based first-order rate constant ' 1 1(s ) = 1 1 ( )(Es mol s ) (S4) s s 0 al EP(1 10 ) (S5) al where E P 0 represents the UV fluence rate, a is the solution absorbance for a 1 cm path length, and L is the effective path length. 1 ' was determined by plotting the natural log reduction (ln/ 0 ) of

5 chlorine species (μm) as a function of time (s), as shown in Figure S3. Linear regreion was performed and the corresponding slope was equated to 1 for each chlorine species. The quantum yields of and photolysis under 54 nm light at ambient temperature were determined to be 1.45 and 0.97, respectively. The chlorine decay in the absence of UV light was performed and was subtracted from the system to determine 1. Text S3. Derivation of modeling equations. The steady-state concentration of. The formation rate (F ) and the consumption rate (R ) of can be expreed respectively as follows: F P T T (S6) loh O R Q Q Q Q Q Q Q (S7) l OH P is the rate of formation from photolysis; T loh - and T O - are the rates of production from the transformation of loh and O ; Q, Q l-, Q, Q -, Q OH-, Q and Q are the rates of consumption by benzoic acid (), l -,, -, OH -, and S i. Based on the steady-state consumption, the net rate of change is zero, as expreed in eq. S8, which can be further expreed as eq. S9 by using the reactions in Table 1. F R P T T (Q Q Q Q Q Q Q ) 0 (S8) loh O I 0 A HlO Lf HlO (1 10 ) 4[ loh 15[ O [ H O ( 17[ [ 3[ l [ V [ [ [ [ [ OH [ [ S [ ) l si, where Φ is the quantum yield of photolysis at 54 nm, OH i f HlO L / (S9) A, and A ( )L. The steady-state concentration of can then be expreed as eq. 7 by solving eq. S9. It should be noted that the recombination of (eq 13 in Table 1) is negligible because the steady-state concentration of is extremely small (< 10 1 M). It was not included in eqs S9 and 7. The steady-state concentration of l. milarly, the formation rate (F l ) and the consumption rate (R l ) of l can be expreed as follows:

6 F l P P T l T loh (S10) R l Q Q Q Q Q Q (S11) l OH P and P - are the rates of l formation from and - photolysis; T loh - and T l - are the rates of production from the transformation of loh and l ; Q, Q l-, Q, Q -, Q OH- and Q are the rates of l consumption by, l -,, -, OH - and S i. Based on the steady-state consumption, the net rate of l change is zero, as expreed in eq. S1, which can be further expreed as eq. S13 by using the reactions in Table 1. F R (P P T l l l T loh ) (Q Q l Q Q Q OH Q ) 0 (S1) ( ( 18 I0 A fhlo f ) L(1 10 ) lo lo V [ [ HlO si,l [S i 1 ) OH 1 [ 6 OH 13 [H (S13) where Φ and Φ - are the quantum yields of and - photolysis at 54 nm, f L / A, f L / A, and HlO lo lo lo A ( )L. The steady-state concentration of l can then be expreed as eq. 8 by solving eq. S13. The steady-state concentration of O. The formation rate (F O - ) and the consumption rate (R O -) of O can be expreed as follows: F P T (S14) O OH R Q Q Q (S15) O H O P - is the rate of O formation from - photolysis; T OH is the rate of O production from the transformation of OH ; Q, Q and Q are the rates of O consumption by, H O and S i. Based on the steady-state consumption, the net rate of O change is zero, as expreed in eq. S16, which can be further expreed as eq. S17 by using the reactions in Table 1. F R (P T ) (Q Q Q ) 0 (S16) O O OH

7 I0 f L(1 10 lo lo V [H O[O 15 A si,o ) [S [O i 16 [ ) 0 SS ( 0 [[O (S17) The steady-state concentration of O can then be expreed as eq. 10 by solving eq. S17. The steady-state concentration of l. The formation rate ( F l ) and the consumption rate ( R l ) of l can be expreed as follows: F l T l T loh (S18) F Q Q Q Q (S19) l self decay T l and T loh - are the rates of l production from the transformation of l and loh ; Q, Q self-decay, Q OH- and Q are the rates of l consumption by, self-decay, OH and S i. Based on the steady-state consumption, the net rate of l change is zero, as expreed in eq. S0, which can be further expreed as eq. S1 by using the reactions in Table 1. F R (T T ) (Q Q Q Q ) 0 (S0) l l l loh self decay OH ( si,l 19 [ [S [O i ) 0 (S1) The steady-state concentration of l can then be expreed as eq. 9 by solving eq. S1. rate ( R The steady-state concentration of loh. The formation rate ( F loh ) of loh can be expreed as follows: loh ) and the consumption F T T T (S) loh l l F loh Q Q Q Q Q (S3) self decay H l T, T l and T l - are the rates of loh production from the transformation of, l and l ; Q, Q self-decay, Q H+, Q l- and Q are the rates of loh consumption by, self-decay, H +, l + and S i. Based on the steady-state consumption, the net rate of loh change is zero, as expreed in eq. S4, which can be further expreed as eq. S5 by using the reactions in Table 1. F R (T T T ) (Q Q Q Q Q ) 0 (S4) loh loh l l self decay H l

8 3 4 OH si,loh [ [S OH i 5 13 OH ) 0 6 [H 14 OH ( 7,lOH OH (S5) The steady-state concentration of loh can then be expreed as eq. 11 by solving eq. S5. Text S4. Elucidating the roles of and other radicals using probe compounds. In the UV/chlorine system, when nitrobenzene (NB) and are used simultaneously as the probe compounds, the inetic expreions of NB and degradation could be expreed as follows: d dt d dt ( 17 [ (S6) [ 6 17 SS SS [ NB SS ( 18 otherradicals SS 19 [other radicals ) SS 0 [O SS...) (S7) The first-order degradation rate constant of NB can be used to determine the steady-state concentration of (eq. S6). Then the contribution of and other radicals can be differentiated through eq. S7. Figure S shows the pseudo-first-order rate constants of NB and in the UV/chlorine proce at ph 6 9. The contribution of other reactive species to degradation was significant and even higher than that of. Text S5. Reaction rate constants between l and NOM. The reaction rate constant of l reacting with NOM ( 5 ) can be calculated by eqs S8~33 in Matlab (MathWors). s 0 was obtained experimentally in the presence of NOM. It should be noted that the reaction of NOM with loh - was aumed to be negligible. Thus, 5 was calculated to be (mg/l) -1 s -1 in the presence of 5 mg/l NOM. d[ ( dt [ s [ [O )[ [ (S8) Φε 3 17 pkaph A 10 [chlorine (110 ) I0L 4OH [O [H O pkaph VA pkaph [chlorine 10 [chlorine [ [ pkaph pkaph , (S9)

9 [ [ 1 10 [chlorine 1 10 [chlorine 10 OH [H OH VA ) 10 (1 L I 1) (10 )[chlorine ε 10 ε ( pka-ph 1 pka-ph pka-ph A 0 ph pka ph pka (S30) [ OH (S31) O [H [ [ VA ) 10 (1 L I 1 10 [chlorine ε Φ [O A 0 ph pka - (S3) [H [ OH (S33)

10 Table S1. omparison of quantum yields of free chlorine under UV irradiation at 53.7 nm Quantum yield Initial chlorine conc. References mm Buxton and Subhani, ± ± 0.1 < mm Feng et al., ± ± mm Jin et al., mm Watts et al., ± ± mm This study Table S. Oxidant concentrations and contributions to degradation at different values of ph and in the presence of chloride from modeling results Reactive species onc. (M) ph 6.0 ph 7.5 ph 9.0 s % 0, onc. (M) s % 0, onc. (M) s % 0, ph 6.0 with 1 mm chloride onc. (M) s % 0, 1.04E E E E l 6.45E E E E l.91e E E E O.51E-18 ~0 5.01E-17 ~0 1.36E-16 ~0.51E-18 ~0 loh 5.6E-18 N.A. 1.84E-18 N.A. 1.89E-18 N.A. 7.93E-17 N.A.

11 LPUV lamps Ventilating fan ollimated tube Reagent inlet Sample outlet Magnetic stirrer Figure S1. Schematic diagram of the large-volume UV irradiator ln(/ 0 ) y = x R = Time (min) Figure S. Photolysis of dilute H O under UV irradiation at 54 nm. onditions: [H O 0 = 100 μm,. Experiments were performed in duplicate. Error bars indicate the standard deviation of the duplicate experiments. The solid line is the line of best fit.

12 .005 (a).000 NB.0015 (s -1 ) (b),.0015 other species, (s -1 ) ph Figure S3. (a) Pseudo-first-order rate constants () of degradation and NB degradation under different values of ph in the co-presence of and NB in the UV/chlorine proce. (b) The contributions of and other radicals to degradation in the UV/chlorine proce. onditions: [ 0 = 5 μm, [NB 0 = 5 μm, chlorine dosage = 70 μm / um l 0. 0 um l 50 um l um l 100 um l Time (min) Figure S4. degradation in ultrapure water in the UV/chlorine proce at different chlorine dosages. onditions: [ 0 = 5 μm, ph = 6.0.

13 / um 10 um 0 um Time (min) Figure S5. degradation in ultrapure water in the UV/chlorine proce under different concentrations. onditions: chlorine dosage = 70 μm, ph = / ph 6 ph 7.5 ph Time (min) Figure S6. degradation in ultrapure water in the UV/chlorine proce under different values of ph. onditions: [ 0 = 5 μm, chlorine dosage = 70 μm.

14 ph 5 ph ln (/ 0 ) y = x y = x Time (min) Figure S7. Photolysis of dilute free chlorine under UV irradiation at 54 nm at ph 5 and 10. onditions: [chlorine 0 = 70 μm,. Experiments were performed in duplicate. Error bars indicate the standard deviation of the duplicate experiments. The lines are lines of best fit experimental value NB experimental value modeling - all species modeling value - modeling value - l NB modeling value - 0, (s -1 ) ph Figure S8. Pseudo-first-order rate constants () of degradation and NB degradation by, l and l - under different values of ph in the co-presence of and NB in the UV/chlorine proce. onditions: [ 0 = 5 μm, [NB 0 = 5 μm, chlorine dosage = 70 μm.

15 mm l - 1 mm l - 5 mm l - 10 mm l - 0 mm l - / Time (min) Figure S9. degradation in ultrapure water in the UV/chlorine proce under different chloride concentrations. onditions: ph = 6.0, [ 0 = 5 μm, chlorine dosage = 70 μm / ppm NOM 1 ppm NOM ppm NOM 5 ppm NOM 8 ppm NOM 10 ppm NOM Time (min) Figure S10. degradation in ultrapure water in the UV/chlorine proce in the presence of different concentrations of NOM. onditions: ph = 6, [ 0 = 5 μm, chlorine dosage = 70 μm.

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