Interlaced CNT electrodes for bacterial fouling reduction of microfiltration membranes

Transcription

1 Interlaced CNT electrodes for bacterial fouling reduction of microfiltration membranes Supporting Information Submitted Month Day, 217 Qiaoying Zhang 1, Paula Arribas 1, 2, 3, Marielle E. Remillard 1, M. Carmen García- Payo 2, Mohamed Khayet 2, 4, Chad D. Vecitis* 1 1. John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA Department of Applied Physics I, Faculty of Physics, Complutense University of Madrid, Madrid, Spain Campus of International Excellence, Moncloa Campus, Complutense University and Technical University of Madrid (UCM-UPM), Madrid, Spain Madrid Institute for Advanced Studies of Water (IMDEA Water Institute), Alcalá de Henares, Madrid, Spain 2885 Authors contribute equally *Corresponding author: Chad D. Vecitis, vecitis@seas.harvard.edu, Phone: (617) Address: John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 2138 Supporting information: 14 pages, 7 figures, 4 tables, 2 videos Statement of contents: The CNT properties, the membrane preparation before ICE deposition, the permeability change of unpressed and mechanically pressed membranes, the P. fluorescens growth curve, a diagram of the bacterial filtration experimental protocols, the cross-sectional and superficial morphology of the PVDF and ICE-PVDF membranes, the bacterial removal, the morphological and filtration characteristics of the membranes (figures and tables), the Welch s t-test result of the log removal by different membranes, the exponential fitting results of the pressure increase of the membranes, and supplemented movies WEO (in.avi format) showing microbubble generation during BW at 8 V DC. S1

2 CNT properties The CNT used in this study has an average length of 1 μm, an average diameter of 15 nm (5-3 nm), and 5% residual iron according to manufacturer specification. PVDF and PC membrane preparation before ICE deposition It is worth noting that the cleaning procedure of the PVDF membrane explaining in this study (ultrasonication in IPA for 5 min, then in DI for 5 min, and kept in IPA prior to use) was applied before the fabrication of the ICE. PVDF membrane is hydrophobic, then the deposition of the CNT on the membrane surface was easily and better developed when the membrane was previously wet. Then, two different wetting/cleaning experiments were tried, consisting in either only immersed the PVDF membrane in IPA (method 1) or ultrasonicated in IPA (5 min), then in DI (5 min), and kept in IPA (method 2) before ICE fabrication. It was observed by electric conductivity measurements over the ICE that the method 2 reduced the resistivity of the ICE channels about 41 to 53%, thus improving their conductivity. These results were consistent for different volumes of the CNT solution used for ICE fabrication. As high conductivity is desirable for the applied cell potential over the ICE to improve the effectiveness of the bacterial electrochemical filtration, it was decided to use the method 2 as wetting/cleaning procedure. On the other hand, PC membrane was hydrophilic, then wetting step was not necessary for a properly ICE fabrication on the surface. S2

3 Flux (LMH) Permeability (L m -2 h -1 bar -1 ) Flux (LMH) Permeability (L m -2 h -1 bar -1 ) Permeability (L m -2 h -1 bar -1 ) A) unpressed-1 unpressed-2 pressed-1 pressed B) Time (min) Pressure (bar) ed-1 ed B) Pressure (bar) Figure S1: Time-dependent permeability of the unpressed and mechanically-pressed PVDF membranes. A) Permeability change with filtration time for the unpressed and pressed PVDF membranes (after 1 min DI filtration, the unpressed membranes had a similar stable permeability to the pressed membranes) and B) flux and permeability versus pressure for the pressed PVDF membranes. S3

4 OD_ Time (h) Figure S2: Growth curve of the P. fluorescens in TSB by seeding from a TSA plate at 3 C. It can be told that 18 h is mid-to-late exponential phase and is able to provide high biomass yield. S4

5 1) Experiments using 1 7 CFU ml -1 for bacterial density and morphology change evaluation: PVDF or PC ICE- V ICE-DC NaCl V NaCl 2 V NaCl Filtration DI V DI 2 V DI BW 2) Experiments using 1 8 CFU ml -1 for bacterial fouling trend and BW efficacy evaluation: Filtration-1 PVDF ICE- V ICE-DC ICE-AC NaCl V NaCl 2 V NaCl 2 V NaCl DI/NaCl V DI 2 V DI 2 V DI/NaCl BW DI-1 & Filtration-2 & BW-2 & DI-2 Figure S3: Bacterial filtration experimental protocol diagram. Protocol 1 was used to evaluate bacterial removal, surface density, and morphology post-filtration. Protocol 2 was used to evaluate bacterial fouling trend and backwash efficacy. S5

6 CFF (%) DFF (%) Wet curve flow (L min -1 ) Filament resistance ( ) 1/R (1/ ) A) B) C) 181 µm 1 µm 1 µm 5 µm D) CNT 14 µm F) 1/R=.31V+.45 R 2 = µm 5 µm 6.9 E) CNT solution V (ml) 1 µm G) 1 Unpressed PVDF Pressed PVDF Pressed ICE-PVDF J =.185 L min -1 max PWP max = 27 L m -2 h -1 bar d V J max d v (nm) d v (nm) Pressure (bar) Figure S4. Cross-sectional and superficial morphology of the PVDF and ICE-PVDF membranes. SEM images of: A, B) top surface and C, D) cross-section of unpressed and pressed PVDF membranes, respectively, with ICE on D), E) top surface of the ICE. F) Electric resistance of a single ICE filament with S6

7 varying CNT-Nafion volume and G) cumulative pore size distribution (CFF), differential pore size distribution (DFF), and wet curve flow of the unpressed PVDF, pressed PVDF, and pressed ICE-PVDF measured by gas-liquid displacement porometer. S7

8 CFU log removal 7 6 PVDF ICE- V ICE-DC ICE-AC bacteria ml bacteria ml -1 Figure S5. Bacterial removal by the PVDF membranes with or without ICE in the presence or absence of applied voltage. Experiments were completed by filtering 1 7 or 1 8 CFU ml -1 in 155 mm NaCl solution at the flow rate of 1.2 ml min -1 (i.e. J = L m -2 h -1 ). Feed and permeate samples were taken after 3 min of filtration to determine CFU. The error bars are used to describe the ranges of the data instead of confidence intervals. S8

9 Bacterial density (1 5 cm -2 ) A) SEM (PVDF) Filtration Optical microscopy (PC) BW Control ICE-anode ICE-cathode Control ICE-anode ICE-cathode Figure S6. Bacterial density on PVDF and PC membrane surfaces with or without ICE after filtration and BW. Experiments were completed by filtering 1 7 CFU ml -1 in 155 mm NaCl solution for 6 min at the flow rate of 1.2 ml min -1 (i.e. J = L m -2 h -1 ) and BW at the same flow rate for 1 min with DI water. For the PVDF and PC with ICE, 2 V DC and 8 V DC (with the reversed polarity) were applied during filtration and BW, respectively. By optical microscopy, there were 18. ± 2.3 and 3.1 ± CFU cm -2 on the control PC before and after BW. In comparison, the bacterial density increased by 41% on the ICE anode (25.3 ± CFU cm -2 ) and decreased by 9% on the ICE cathode (1.8 ± CFU cm -2 ) after electrochemical filtration at 2 V DC. After BW, the bacterial density further decreased on the anode (.4 ± CFU cm -2 ) and cathode (.3 ± CFU cm -2 ), 87 and 9% lower than the control, respectively. The PVDF, PC, and ICE have notable difference in surface hydrophobicity (DI contact angle was 83.5, 65.9, and 118.7, respectively) and surface roughness (smooth, shiny & very smooth, and rough, respectively), thus the bacterial deposition will vary e.g., there were an order of magnitude greater bacterial density on PVDF versus PC. Plus, the result is also dependent on the bacterial counting technique (SEM and fluorescence microscopy follow very different sample preparation procedures). S9

10 P (bar) 1.4 Control ICE-DC 1.2 ICE-AC Control (BW with NaCl) ICE-AC (BW with NaCl) 1. Cycle 1 Cycle P F-1 End F-1 BW-1 DI-1 P F-2 End F-2 BW-2 DI-2 Figure S7. ΔP values for the control PVDF and the ICE-PVDF in different steps of the bacterial filtration test. Experiments were completed using 1 8 CFU ml -1 filtration for 6 min or up to 1.1 bar in the absence or presence of 2 V DC or AC. A 1 min BW with DI or saline solution was carried out after each filtration cycle in the absence or presence of 8 V DC (for the DC filtration, polarity was reversed in comparison to filtration for the first 5 min and then reversed again for the final 5 min to clean both electrodes) or 8 V AC (for the 2 V AC filtration). DI water was filtered for 1 min after each BW cycle to determine the fouling resistance recovery (FRR) of the process. For all, bacteria filtration, BW filtration and DI water filtration, the flow rates were kept at 1.2 ml min -1 (i.e. J = L m -2 h -1 ). Experimental procedure diagram is displayed in Figure S3, Protocol 2. S1

11 Table S1. Membrane morphology characterization and pure water permeability of PVDF membranes with or without ICE. Membranes Morphological characteristics Filtration characteristics δ (um) ε S (%) ε V (%) d S (nm) d V (nm) PWP (L m -2 h -1 bar -1 ) PVDF unpressed 181 ± ± ± ± ± ± 323 PVDF pressed 119 ± ± ± ± ± ± 71 ICE pressed 14 ± ± ± ± 7 -- ICE-PVDF pressed 123 ± ± ± ± 12 S11

12 Table S2. Welch s t-test summary of the bacterial removal under different conditions. Influent PVDF ICE- V ICE-DC ICE- V CFU ml -1 ICE-DC ICE-AC ICE- V CFU ml -1 ICE-DC ICE-AC S12

13 Table S3. Bacterial density on the PVDF and PC membrane surfaces with or without ICE after 1 7 CFU ml -1 filtration and DI BW. Surfaces Control ICE Conditions Characterization technique SEM for PVDF membranes (1 5 cm -2 ) Optical microscopy for PC membranes (1 5 cm -2 ) Filtration 22.1 ± ± 2.3 BW 86.6 ± ±.5 Filtration anode, 2 V DC 62.8 ± ± 4.9 BW cathode, 8 V 2.7 ± ±.1 Filtration cathode, 2 V DC 25.9 ± ±.3 BW anode, 8 V 21.7 ± ±.1 S13

14 Table S4. Exponential fitting results of the pressure increase of the control PVDF and ICE-PVDF after 1 8 CFU ml -1 filtration and DI BW. Filtration-1 Filtration-2 Membrane k k ΔP (bar) (min -1 ΔP ) (bar) (min -1 ) PVDF.138 ±.3.29 ± ±.6.18 ±.12 ICE- V.14 ± ± ± ±.2 ICE-DC.155 ±.6.19 ± ± ±.5 ICE-AC.121 ± ± ± ±.9 The lowest values in each column are in bold. S14