Supporting Information. Removal of Persistent Organic Contaminants by Electrochemically Activated Sulfate

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1 Supporting Information Removal of Persistent Organic Contaminants by Electrochemically Activated Sulfate Ali Farhat a, Jurg Keller a, Stephan Tait a, Jelena Radjenovic a,b a Advanced Water Management Centre, The University of Queensland, Queensland 4072, Australia b Catalan Institute for Water Research (ICRA), Scientific and Technological Park of the University of Girona, H 2 O Building, Emili Grahit 101, Girona, Spain Number of pages: 12 Number of texts: 3 Number of tables: 4 Number of figures: 3 * Corresponding author: Jelena Radjenovic, Catalan Institute for Water Research (ICRA), Scientific and Technological Park of the University of Girona, Girona, Spain Phone: ; Fax: ; jradjenovic@icra.cat S1

2 Text S1 Chemical Analysis of Target Organic Contaminants An Alltima C18 Column, mm, particle size 5 μm, from Alltech Associates Inc. (Deerfield, IL, U.S.A.) was used at 40 C for the chromatographic separation. For the positive mode, Milli-Q grade water with 0.1% formic acid was eluent A, whereas acetonitrile with 0.1% formic acid was used as eluent B. Starting with 5% eluent B, the elution gradient was increased to 60% by 5 min, raising to 90% by 13 min, and further increasing to 100% of eluent B by 15 min. It was kept constant for 2 min, before returning to the initial conditions at 5% by 18 min, where the column was left to re-equilibrate for 5 min, completing the chromatographic analysis in 23 min. For the negative mode, a mixture of acetonitrile and methanol (ratio 1:1 by volume) was eluent A, and Milli-Q grade water with 1 mm ammonium acetate was eluent B. Starting with 95% eluent B, the elution gradient was decreased to 10% by 7 min, kept constant at 10% until 10 min, followed by further decreasing to 0% of eluent B by 12 min. It was kept constant for 3 min, before returning to the initial conditions at 95% by 16 min, where the column was left to re-equilibrate for 5 min, completing the chromatographic analysis in 21 min. Diatrizoate, carbamazepine, DEET, and iopromide were detected and quantified using the positive mode; whereas tribromophenol, triclopyr, and triclosan were quantified using the negative mode. The settings for the compound-dependent parameters of each transition are summarized in Text S3 Energy Consumption Energy consumption was calculated using the average cell voltage. Since target contaminants are present at low concentrations, it was decided to express the consumption of energy as electric energy per order (E EO ) as a more appropriate parameter to estimate energy efficiency of the electrochemical system. It primarily estimates the electric energy, kwh m -3, consumed to reduce S2

3 the concentration of the organic contaminant by one order of magnitude in a unit volume of treated solution. The electric power was calculated from the applied current (I, A) and the average cell voltage (U, V) per volume of treated solution (V, L), and then multiplied by the reaction time (t, h) required to achieve the corresponding order of magnitude of removal as per the following formula. 3 E EO = U. I. t V. log C o C (1) S3

4 Table S1. The source-dependent parameters were as follows: curtain gas (CUR), 30V; nitrogen collision gas (CAD), high; source temperature (TEM), 700 C; ion source gases GS1 and GS2, 62V; ion spray voltage, 5500V, and entrance potential (EP), 10V. S4

5 Text S2 Analysis of Hydrogen Peroxide and Persulfate Hydrogen peroxide (H 2 O 2 ) concentration was quantified with ammonium metavanadate. 1 This method was tested for different concentrations of H 2 O 2 in the presence or absence of persulfate (S 2 O 2-8 ). Further investigation for any possible interferences of S 2 O 2-8 in the measurement was conducted by adding different concentrations of S 2 O 2-8 to the H 2 O 2 solution (0.6mM; 20 mg L -1 ), Figure S2-A. The ammonium metavanadate method was found to be insensitive to the presence of S 2 O 2-8 in the investigated concentration range (i.e., from 1 to 50 mg L -1 S 2 O 2-8 ). Thus, this method was used for the measurement of H 2 O 2 concentration in the solution. Persulfate was detected with a ferrous/thiocyanate method at acidic ph. 2 This method was found to be susceptible to H 2 O 2 interference. The addition of H 2 O 2 in the range of 1.0 mg L -1 to 50 mg L without any addition of S 2 O 8 ions significantly colored the solution and reported a linear increase in the absorbance, similar to that of S 2 O 2-8 without any addition of H 2 O 2. Moreover, the absorbance values reported for H 2 O 2 (0.6mM; 20 mg L -1 ) significantly increased from 1.42 to 2.27 as concentration of added S 2 O 2-8 increased from 0 to 50 mg L -1 (Figure S2-B), signifying that both oxidants were detected. Thus, this method was used for determining a combined concentration of H 2 O 2 and S 2 O 2-8 in the solution. S5

6 Text S3 Energy Consumption Energy consumption was calculated using the average cell voltage. Since target contaminants are present at low concentrations, it was decided to express the consumption of energy as electric energy per order (E EO ) as a more appropriate parameter to estimate energy efficiency of the electrochemical system. It primarily estimates the electric energy, kwh m -3, consumed to reduce the concentration of the organic contaminant by one order of magnitude in a unit volume of treated solution. The electric power was calculated from the applied current (I, A) and the average cell voltage (U, V) per volume of treated solution (V, L), and then multiplied by the reaction time (t, h) required to achieve the corresponding order of magnitude of removal as per the following formula. 3 E EO = U. I. t V. log C o C (1) S6

7 Table S1 The optimized compound-dependent MS parameters: declustering potential (DP), collision energy (CE) and cell exit potential (CXP) for each compound and each transition of the negative and positive mode. Organic compound Q1 Mass (Da) Q3 Mass (Da) DP CE CXP Carbamazepine DEET Diatrizoate Iopromide Tribromophenol Triclopyr Triclosan S7

8 Table S2 Electric energy consumption per order (E EO ), expressed as electric energy, kwh m -3, consumed to reduce the concentration of the organic contaminant via electrooxidation in Na 2 SO 4 and NaNO 3 anolytes (ph 2; 9 ms cm -1 ; and 200 A m -2 ) by one order of magnitude in a unit volume of treated solution. Organic compound Electric energy consumption per order (E EO ), kwh m -3 E Na2SO4 E NaNO3 Carbamazepine DEET Diatrizoate Iopromide Tribromophenol Triclopyr Triclosan S8

9 Table S3 Apparent rate constants (h -1 ) for chemical oxidation of target organic contaminants with non-activated K 2 S 2 O 8 determined in Na 2 SO 4 solutions (ph 2, 9 ms cm -1, 40 mm). Organic compound Oxidation rate constant k S2O8 2-, h -1 Carbamazepine DEET Diatrizoate Iopromide Tribromophenol Triclopyr Triclosan S9

10 Table S4 Bimolecular rate constants (k, M -1 s -1 ) for oxidation of target organic contaminants with homogeneously generated OH and SO 4 - radicals. k SO4 -, M -1 s -1 Ref. k OH, M -1 s -1 Ref. Carbamazepine DEET Diatrizoate Iopromide Tribromophenol - - Triclopyr Triclosan S10

11 Potentiostat for Current feeder + Data Acquisition Sampling point Anolyte Peristaltic pump Catholyte Magnetic Stirrers Figure S1 Schematic diagram of cation exchange membrane (CEM)-divided electrolytic cell, operated in batch mode. S11

12 Absorbance 0.20 A S 2 O 8 2- concentration (ppm) Absorbance 2.5 B S 2 O 8 2- concentration (ppm) Figure S2 Absorbance measured at 450 nm for 0.6 mm solution of hydrogen peroxide with the addition of increasing persulfate concentrations using the (A) metavanadate method, 1 and (B) ferrous/thiocyanate method. 2 S12

13 Oxidant Concentration (mm) Electrolysis Time (min) Figure S3 Electrochemical generation of the oxidants: persulfate ( ) and hydrogen peroxide ( ) in electrooxidation with Na 2 SO 4 anolyte (40 mm, ph 2, 9.0 ms cm -1 ) at 200 A m -2. S13

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