Department of Civil and Environmental Engineering, Stanford University, 473 Via Ortega, Stanford, California 94305, United States

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1 Supporting Information for Capture and Reductive Transformation of Halogenated Pesticides by an Activated Carbon-Based Electrolysis System for Treatment of Runoff Yuanqing Li 1 and William A. Mitch 1, * 1 Department of Civil and Environmental Engineering, Stanford University, 473 Via Ortega, Stanford, California 94305, United States *Corresponding author: wamitch@stanford.edu, Phone: , Fax: Pages 1 Text 6 Figures S1

2 Table of Contents Text S1: Materials and methods details Figure S1: Schematics of electrochemical reactor configurations Figure S2: Chlorine formation from 1 mm NaCl in 100 mm phosphate Figure S3: Chloride yield from AC electrolysis of bifenthrin and permethrin S3 S4 S6 S7 Figure S4: Aqueous fipronil decline in Lake Lagunita water during 1 AC electrolysis treatment cycle S8 Figure S5: Effect of saturation with humic acid on AC electrolysis Figure S6: Current and power versus time for AC electrolysis S9 S10 S2

3 Text S1: Materials and Methods Details Materials: Alfa Aesar (Ward Hill, MA) sheet graphite (0.13 mm thickness, catalog number 43078), Norit (Cabot, Alpharetta, GA) Hydrodarco 3000 granular activated carbon (GAC), Fuel Cell Earth (Stoneham, MA) carbon cloth (0.38 mm thickness, yarns/in, carbon content 99%), Chem-Impex International (Wood Dale, IL) fipronil, fipronil sulfone and fipronil sulfide (97.5% purity), Chem Service bifenthrin (98%) and permethrin (98.9%), Fisher (Pittsburgh, PA) Optima grade acetonitrile and methane, and binder-free glass microfiber filters, and Sigma- Aldrich (St. Louis, MO) humic acid sodium salt (technical grade), polyvinylidene fluoride (PVDF) and N-methyl-2-pyrrolidone (NMP) were used as received. Deionized water (18 MΩ) was produced with a Millipore Elix 10/Gradient A10 water purification system. A fipronil stock (10 g/l) was made by dissolving 240 mg of fipronil powder in 24 ml of methanol in an amber glass vial capped with a Teflon-lined septum, and was stored at -20 C. All other chemicals were reagent grade. Analytical methods details: Aqueous samples were analyzed for fluoride, chloride, chlorate and perchlorate using a Dionex ICS-1000 ion chromatography system with a 50 mm NaOH/deionized water (50/50) eluent at a 1 ml/min flow rate with a conductivity detector. Electrode materials were extracted with acetonitrile for analysis of fipronil, fipronil sulfide, fipronil sulfone, bifenthrin, permethrin and other products. For the GAC/graphite electrode, GAC particles were extracted for 2 min at a ratio of 4 ml acetonitrile to 0.2 g GAC. For the GAC/carbon cloth electrode used in the two-cell electrolysis system, the electrode was extracted with 40 ml acetonitrile for 2 min. For the GAC/carbon cloth electrodes used in the single-cell parallel-plate configuration, the electrodes were extracted with 60 ml acetonitrile for 5 min. All of these extraction techniques achieved >95% extraction efficiency for fipronil, bifenthrin and permethrin. To measure the production of DBPs, an aqueous sample (40 ml) was extracted with 3 ml of methyl tert-butyl ether (MtBE) for 2 min. Halogenated DBPs, including 4 trihalomethanes, 4 trihaloacetaldehydes, 3 dihaloacetonitriles, and 2 haloketones were measured by gas chromatography mass spectrometry, as described previously (Zeng and Mitch, 2016); method reporting limits were ~0.2 µg/l. Fipronil, fipronil sulfide and fipronil sulfone were analyzed using an Agilent 1260 high pressure liquid chromatography system equipped with a 6460 triple quadrupole mass spectrometer in the negative ion mode using single ion monitoring. The aqueous samples or acetonitrile extracts (10 µl) were injected onto an Agilent Poroshell 120 EC-C18 column (3 cm 50 mm, 2.7 µm) with isocratic elution using 50% acetonitrile and 50% MilliQ water at a total flowrate of 0.4 ml/min. Fipronil, fipronil sulfide and fipronil sulfone were analyzed in the negative ion single ion monitoring (SIM) mode at 435 m/z, 419 m/z and 451 m/z, respectively. Additional products were tentatively identified in the negative ion mode using full-scan monitoring ( m/z). Bifenthrin and permethrin were analyzed in the positive ion mode using multiple reaction monitoring. For permethrin and bifenthrin, 10 µl of aqueous samples or of acetonitrile extracts was injected into a Synergi Hydro-RP 80 Å column (150 3 mm, 4 µm) and eluted with a gradient method, in which 95% of eluent A (5% ammonium formate in HPLC grade water) and 5% of B (Optima grade methanol) was held for 2 min and then ramped to 23% of A and 77% of B S3

4 over 3 min and held for 2 min, and then ramped to 10% of A and 90% of B over 3 min and held for 5 min, and then ramped to 100% of B over 1 min and held for 4 min, and finally ramped to 95% of A and 5% of B over 2 min and held for 3 min. The fragmentation of bifenthrin was from m/z to m/z in the positive mode. The fragmentation of permethrin was from m/z to m/z in the positive mode. Reference: Zeng, T.; Mitch, W.A. Impact of Nitrification on N-Nitrosamine and Halogenated Disinfection Byproduct Formation within Drinking Water Storage Facilities. Environ. Sci. Technol., 2016, 50, S4

5 Figure S1. Schematics of the electrochemical reactor configurations. A) SEM image of the GAC/carbon cloth electrode surface. Schematics of the B) bench-scale dual-cell reactor, C) bench-scale single-cell reactor, and D) pilot-scale single-cell reactor. A) B) Ag/AgCl Reference Electrode Pt Anode Power Working electrode Cation exchange membrane S5

6 C) Ag/AgCl Reference Electrode Voltage Carbon cloth electrode Carbon cloth electrode insulator D) Power source (AC) Effluent Influent Surface water channel S6

7 Figure S2: Free chlorine formation during single-cell electrolysis using direct current (-1 V vs. S.H.E.) and alternating current (-1 V to +1 V vs. S.H.E. at , and Hz) for a 1 mm chloride solution buffered by 100 mm phosphate at ph 7. Error bars represent the range of experimental duplicates. Some errors are smaller than the symbols. S7

8 Figure S3: Chloride yield during AC electrolysis of 1 mg of permethrin and bifenthrin using a triangular waveform from -1 V to +1 V vs. S.H.E. at Hz at ph 7.0 using 100 mm phosphate buffer. Dechlorination is calculated by dividing the aqueous mass of chloride by the initial mass of chlorine in the fipronil. Error bars represent the range of experimental duplicates. Some errors are smaller than the symbols. S8

9 Figure S4: Aqueous fipronil concentration during the AC electrolysis of Lake Lagunita water spiked with 1 mg (2.3 µmol) fipronil using a triangular waveform from -1 V to +1 V vs. S.H.E. at Hz during a single cycle of 4 h sorption and 4 h AC electrolysis. Error bars represent the range of experimental duplicates. Some errors are smaller than the symbols. 100% AC applied C aq /C 0 50% 0% Time (min) S9

10 Figure S5: Effect of prior saturation with humic acid. Aqueous fipronil concentrations during the AC electrolysis of Lake Lagunita water spiked with 1 mg (2.3 µmol) fipronil using a triangular waveform from -1 V to +1 V vs. S.H.E. at Hz during 1 cycle of 4 h sorption and 4 h AC electrolysis. Fresh = GAC/carbon cloth electrodes rinsed with DI water and heated at 100 for 12 h prior to use. NOM-saturated = GAC/carbon cloth electrodes exposed to 100 mg/l Aldrich humic acid for 72 h prior to use. Error bars represent the range of experimental duplicates. Some errors are smaller than the symbols. S10

11 Figure S6: Single-cell AC electrolysis using a 2.2 cm electrode spacing at Hz. A) Timecurrent profile over A) 1 h and B) 4 h. Time-power profile over C) 1 h and D) 4 h. A) 100 Current (ma) Time (min) B) 100 Current (ma) Time (min) S11

12 C) 0.2 Power (W) Time (min) D) 0.2 Power (W) Time (min) S12