Interlaced CNT Electrodes for Bacterial Fouling Reduction of

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Interlaced CNT electrodes for bacterial fouling reduction of microfiltration membranes Qiaoying Zhang, Paula Arribas, Erin Marielle Remillard, M. Carmen Garcia-Payo, Mohamed Khayet, and Chad David Vecitis Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b00966 • Publication Date (Web): 11 Jul 2017 Downloaded from http://pubs.acs.org on July 12, 2017

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Environmental Science & Technology

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Interlaced CNT electrodes for bacterial fouling reduction of

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microfiltration membranes

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Submitted Month Day, 2017

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Qiaoying Zhang‡1, Paula Arribas‡1, 2, 3, E. Marielle Remillard1, M. Carmen García-

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Payo2, Mohamed Khayet2, 4, Chad D. Vecitis*1

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1. John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138

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2. Department of Applied Physics I, Faculty of Physics, Complutense University of Madrid, Madrid, Spain 28040

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3. Campus of International Excellence, Moncloa Campus, Complutense University and Technical University of Madrid (UCM-UPM), Madrid, Spain 28040

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4. Madrid Institute for Advanced Studies of Water (IMDEA Water Institute), Alcalá de Henares, Madrid, Spain 28805

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‡

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*Corresponding author: Chad D. Vecitis,

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Email: [email protected], Phone: (617) 496-1458,

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Address: John A. Paulson School of Engineering and Applied Sciences, Harvard University,

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Cambridge, MA 02138

Authors contribute equally

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ABSTRACT

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Interlaced carbon nanotube electrodes (ICE) were prepared by vacuum filtering a well-dispersed carbon

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nanotube-Nafion solution through a laser-cut acrylic stencil onto a commercial polyvinylidene fluoride

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(PVDF) microfiltration (MF) membrane. Dead-end filtration was carried out using 107 and 108 CFU mL-1

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Pseudomonas fluorescens to study the effects of the electrochemically-active ICE on bacterial density and

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morphology, as well as to evaluate the bacterial fouling trend and backwash (BW) efficacy, respectively.

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Finally, a simplified COMSOL model of the ICE electric field was used to help elucidate the antifouling

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mechanism in solution. At 2 V DC and AC (total cell potential), the average bacterial log removal of the

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ICE-PVDF increased by ~1 log compared to the control PVDF (3.5-4 log). Bacterial surface density was

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affected by the presence and polarity of DC electric potential, being 87-90% lower on the ICE cathode

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and 59-93% lower on the ICE anode than on the PVDF after filtration, and BW further reduced the

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density on the cathode significantly. The optimal operating conditions (2 V AC) reduced the fouling rate

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by 75% versus the control and achieved up to 96% fouling resistance recovery (FRR) during BW at 8 V

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AC using 155 mM NaCl. The antifouling performance should mainly be due to electrokinetic effects and

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the electric field simulation by COMSOL model suggested electrophoresis and dielectrophoresis as likely

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mechanisms.

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TOC-Abstract art

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KEY WORDS

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Bacterial fouling, Microfiltration membranes, Interlaced carbon nanotube electrodes, Electrophoresis and dielectrophoresis 2 ACS Paragon Plus Environment

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INTRODUCTION

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Microfiltration (MF) is a separation technique widely used in water treatment and industrial processing.

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MF membranes typically have a pore size ranging from 100 nm to 10 µm and remove suspended particles

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and microbial cells by mechanical sieving.1 Accumulation of bacteria on MF membrane surfaces is

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common. At short timescales, high concentration bacteria e.g., during recovery of biochemicals2 or in

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membrane bioreactor systems3, results in concentration polarization and cake layer formation reducing

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permeability. At long timescales, even low bacterial concentrations may result in biofilm formation on

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the membrane surface reducing flux and backwash (BW) efficacy.4 Since biofouling increases operation

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& maintenance (O&M) costs and reduces membrane lifetime, fouling mitigation is of practical

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importance and research interest.

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Bacterial fouling control can be divided into categories such as membrane surface/structure

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modification, boundary condition control, and external force application.5 For instance, modification of

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microporous polysulfone membrane with a sulfonated polyether-ethersulfone/polyethersulfone block

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copolymer,6 and with the addition of silver nanoparticles7,

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sonication,11 and electric-field application12-16 have all been reported to reduce membranes microbial

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fouling. Among these, electrokinetic and electrochemical methods have the advantage of real-time

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automation and control.

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as well as operation at critical flux,9,

10

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The electrokinetics is associated with the electrostatics at the electrode surface and the electric

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field between the electrodes, and both could affect bacterial attachment. Electrostatic,17 electrophoretic,

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and electroosmotic18 mechanisms play an important role in biofouling reduction since most bacteria are

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negatively charged in aquatic systems.19 Dielectrophoresis20, 21 is an alternative detachment mechanism,

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although it has been seldom used for bacterial fouling reduction. The electrochemistry in liquid phase can

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result in direct or indirect bacterial inactivation and affects bacterial growth thus long-term fouling,17, 22

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and that produces gaseous products. For instance, the formation of micro-bubbles at an electro-active

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membrane surface has also been demonstrated to remove the cake layer.13 Among the above mechanisms, 3 ACS Paragon Plus Environment


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dielectrophoresis works under both DC and AC potentials, yet the others are more for DC potential

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studies.

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The electrode material largely determines the performance of electro-active methods. For

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membrane applications, the electrode needs to be anti-corrosive, inexpensive, and porous.5 A carbon

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nanotube (CNT) electrochemical filter14, 22-24 provides a possible solution to membrane surface electrode

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fabrication. CNT electrodes have been observed to inactivate bacteria in the presence of oxidizing22, 23 or

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reducing17 potentials.

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applications possible, also the CNT network has a pore size of 25~100s nm and is relatively stable at low

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electrochemical voltages making it compatible for microfiltration applications.

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The bulk CNT price has decreased to 100 US$ kg-1

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making large scale

In a conventional electrochemical filtration system, the two electrodes are placed parallel, on

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opposite sides,5,

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or both on the feed side28,

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hindering scale-up. Additionally, only one electrode is functional whereas the other is an unutilized

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counter electrode. An alternative is an interlaced electrode design. Du et al. placed 0.6 mm diameter

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metal wires with a 0.03 mm insulating polyurethane coating in an alternating-anode/cathode configuration

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beneath the MF membrane to reduce clay particle fouling at 200 V AC (200 kHz) by dielectrophoresis.30

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However, the insulating layer necessitated the application of high voltages and frequencies and the

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membrane weakened the dielectrophoretic force.

of the membrane, complicating filter design and

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In this work, interlaced CNT electrodes (ICE) on a membrane surface are hypothesized as a

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potential solution to the issues of interlaced metal electrodes below the membrane. First, ICE were

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fabricated by vacuum filtration of a CNT-Nafion solution through a stencil onto a MF membrane. Next,

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the effects of the ICE on bacterial density distribution and morphology were evaluated by dead-end

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filtration of 107 CFU mL-1. Then, ICE anti-biofouling performance was challenged by filtration of 108

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CFU mL-1. Finally, a COMSOL model of the ICE electric field was used to elucidate the underlying anti-

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biofouling mechanisms.


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MATERIAL AND METHODS

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Materials

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CNT (C-grade, multiwalled, powder, >95% purity) was purchased from NanoTechLabs, Inc. (Yadkinville,

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NC) (properties detailed in SI). Nafion 117 solution (~5% in a mixture of lower aliphatic alcohols and

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water) and formaldehyde (ACS reagent, 37 wt. % in water) were purchased from Sigma-Aldrich (St.

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Louis, MO). Pseudomonas fluorescens (P. fluorescens) ATCC 700830 (ATCC, Manassas, VA) was

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utilized in the bacterial fouling experiments. BD Bacto™ tryptic soy broth (TSB), tryptic soy agar (TSA),

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NaCl (reagent grade), isopropyl alcohol (IPA; laboratory grade), and ethanol (EtOH; laboratory grade)

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were purchased from VWR International (West Chester, PA). The fluorescence staining reagent 4’, 6-

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diamidino-2-phenyindole dilactate (DAPI) was acquired from Life Technologies (Grand Island, NY).

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Deionized (DI) water (>18 MΩ) was produced by a Nanopure Infinity ultrapure water system

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(Barnstead/Thermolyne) and was used to prepare solutions and rinse containers.

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Polyvinylidene fluoride (PVDF) membranes (0.3 µm pore size; GE Osmonics JX; hydrophobic)

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and grey polycarbonate (PC) membranes (0.2 µm pore size; 47 mm diameter; hydrophilic) were

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purchased from Sterlitech (Kent, WA). The PVDF membrane was cleaned by ultrasonication in IPA for 5

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min, then in DI for 5 min, and kept in IPA prior to use. The PC membrane was used directly without pre-

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treatment (details in SI). The PVDF membranes were used in most of the fouling experiments while the

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PC membranes were only used for fluorescence microscopy analysis since the former had a too bright

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fluorescence background.

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Fabrication of ICE on membrane surfaces

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ICE were fabricated by vacuum filtering the CNT-Nafion solution through an acrylic stencil onto a

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commercial MF membrane as shown in Figure 1. The CNT-Nafion solution was prepared by probe

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ultrasonicating 60 mg CNT and 300 mg Nafion solution in 30 g IPA at 50% magnitude (~1,000 W L-1)

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for 15 min (Branson Sonifier S450-D). Since the density of the IPA was 0.80 g mL-1, the resulting 5 ACS Paragon Plus Environment


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solution has a concentration of 1.6 mg mL-1 CNT and 0.4 mg mL-1 Nafion. A piece of aluminum foil was

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used to cover the container to avoid excessive solvent evaporation. The solution was well-dispersed and

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stable for up to 2 months. The acrylic stencil was prepared by a laser cutter (VersaLaser). The thickness

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of the acrylic plate was 3 mm, and the filament dimensions were 18×1.5 mm2 with 0.5 mm edge-to-edge

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spacing. The pattern without the two antenna leads covers a total area of 2.1 × 2.1 cm2 of which ~80% is

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covered by ICE. The protective wax paper was kept on the acrylic plate during cutting as well as CNT-

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Nafion solution filtration to help seal the system. After a specific volume (1.0 to 2.2 mL) of the CNT-

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Nafion solution was added to the stencil, ~0.5 bar vacuum was applied and maintained for 5-10 min. The

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samples were then dried in a sterile petri dish at room temperature.

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Membrane characterization

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Membranes were evaluated for differential and cumulative pore size distributions (DFF and CFF,

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respectively), volumetric mean pore size (dV), and wet curve flow with a gas-liquid displacement

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porometer (POROLUXTM 100),31 for volumetric porosity (εV) with a pycnometer and a balance, 32 and for

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superficial mean pore size (dS), porosity (εS), and thickness (δ) with a Zeiss UltraPlus field emission SEM.

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Analysis of the SEM images was completed using Image J (National Institutes of Health, Bethesda, MD).

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Bacterial filtration experiments

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The MF membranes undergo compaction during filtration,33,

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utilized here by compressing the membrane with or without ICE for 45 min (Carver 4386) between two

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pieces of 1.6 mm silicon rubber at a pressure of 4 MPa (40 bar) (the rubber provided a smooth

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compaction surface and reduced the actual pressure exerted on the membranes; parchment paper was

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placed between the membrane and rubber to protect the membrane surface). Compacted membranes had

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a relative constant permeability within the pressure range of 0-1.0 bar for >60 min (Figure S1).

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thus mechanical pre-compaction was

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P. fluorescens was cultured in TSB by seeding from a TSA plate at 30°C and harvested at mid-to-

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late exponential phase (18 h) (Figure S2). After centrifugation and resuspension twice in 155 mM NaCl, 6 ACS Paragon Plus Environment

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the bacterial stock solution was diluted to an optical density of 0.15 at 600 nm (OD600 = 0.15) in saline

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(~108 CFU mL-1 by fluorescence microscopy17). Finally, the solution was either used directly or diluted

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to 107 CFU mL-1.

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All filtration experiments were completed in dead-end mode using a peristaltic pump at a constant

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flow rate of 1.2 mL min-1 with an effective membrane filtration area of 4.4 cm2, thus a filtration flux of J

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= 163.6 L m-2 h-1. The membranes were first wetted with ~8 mL of EtOH:DI 50:50 and then rinsed with

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DI water for 10-30 min. The inlet pressure was monitored and the outlet was open to the atmosphere.

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Prior to bacterial filtration, the pure water permeability (PWP, L m-2 h-1 bar-1) of the membranes was determined by the following equation:

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= ∆/(Δ Δ)

(1)

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where ∆V (mL) is the permeate volume collected over a time ∆t (min), Aeff (cm2) is the effective filtration

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area, and ∆P (bar) is the transmembrane (inlet) pressure.

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Bacterial filtration experiments were carried out with either 107 or 108 CFU mL-1 in 155 mM

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NaCl, with or without ICE, in the presence or absence of applied voltage. DC was applied by a power

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supply (Agilent N5750A) and AC was generated by a customized inverter (DC to square-wave AC) with

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Vrms (2 or 8 V) and frequency (10 kHz) set by an arbitrary waveform generator (Agilent 33120A). The

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current of the system was monitored by the power supply with 1 mA limit of detection. The ∆P was

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recorded during bacterial filtration at 2, 10, and every 10 min afterwards. As the influent concentration

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was high (107-108 CFU mL-1), a 10 min BW was carried out every 60 min or when the ∆P reached 1.1 ±

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0.1 bar. Permeate and feed aliquots were collected in sterile glass vials at 30 min of filtration to count

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CFUs, thus determine bacteria removal.

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Bacterial density and morphology evaluation



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Bacterial filtration experiments were carried out by filtering 107 CFU mL-1 in 155 mM NaCl solution for

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60 min, in the absence (control PVDF membrane) or presence (ICE-DC membranes) of 2 V DC applied

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voltage. BW with DI water without voltage or at 8 V DC (DC polarity inversed with respect to filtration)

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was performed for 10 min after bacteria filtration (see Figure S3, Protocol 1). Both the filtration and BW

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flow rates were kept at 1.2 mL min-1 (i.e. J = 163.6 L m-2 h-1).

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Bacterial fouling trend and BW efficacy evaluation

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Bacterial filtration experiments were carried out by filtering 108 CFU mL-1 in 155 mM NaCl solution for

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60 min, in the absence (control PVDF and ICE-0 V membranes) or presence of 2 V DC or AC applied

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voltage (ICE-DC and ICE-AC membranes, respectively).

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performed in each experiment, and each cycle included a 60-min filtration, a 10-min BW, and a 10-min

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DI water filtration. The BW solution was either DI water or 155 mM NaCl. For filtration in the presence

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of voltage, the BW was carried out in the presence of voltage as well with Vrms = 8 V (DC or AC). The

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DC polarity was reversed in comparison to filtration for the first 5 min and then reversed again for the

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final 5 min to clean both electrodes. In the end, DI water was filtered for 10 min to determine the fouling

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resistance recovery (FRR) following Equation 2 below:35, 36

Up to 2 bacterial filtration cycles were

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% = ( − Δ )/( − ) × 100

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where ∆P0, ∆Pf, and ∆Pc (bar) are the ∆P before fouling, after fouling before BW, and after BW,

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respectively.

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(2)

For all bacteria filtration, BW filtration and DI water filtration, the flow rates were kept at 1.2 mL

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min-1 (i.e. J = 163.6 L m-2 h-1). Experimental procedure diagram is displayed in Figure S3, Protocol 2.

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Bacteria characterization and quantification


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The bacterial concentration in the feed solution prior to fouling experiment was determined by OD600. To

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quantify the bacterial rejection, the feed and permeate aliquots were characterized by the colony-forming

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unit (CFU) method.

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After 107 CFU mL-1 filtration and BW, membranes were examined by fluorescence microscopy

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(PC membranes) and SEM (PVDF membranes) to determine surface bacterial density and morphology.

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After 108 CFU mL-1 filtration and BW, PVDF membranes were only examined by SEM. Fluorescence

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microscopy was completed after staining the samples with DAPI (excitation/emission 358/461 nm) for 2-

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5 min using an inverted microscope (Olympus BX60). SEM of bacterial samples was completed after

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they were fixed with formaldehyde vapor for at least 12 h, dehydrated with 40-to-100% EtOH/DI

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solutions, dried at room temperature, and coated with 2 nm of Pt/Pd (80/20) (EMS 300T D Dual Head

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Sputter Coater).

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RESULTS AND DISCUSSION

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Membrane characterization

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The PVDF and ICE-PVDF membranes were characterized by SEM for cross-sectional and superficial

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morphology (Figure S4A-E), by two-point probe for electric conductivity (Figure S4F), and by capillary

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flow porometry for volumetric pore size distributions and mean pore size (Figure S4G), with results

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summarized in Table S1.

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From the SEM images, the unpressed PVDF membrane had a thickness (δ) of about 181 ± 6 µm,

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a surface porosity (εS) of 15.7 ± 1.4%, and a mean pore size (dS) of 44 ± 4 nm. After mechanical

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compaction, the PVDF membrane δ, εS, and dS decreased to 119 ± 3 µm, 8.1 ± 0.9%, and 31 ± 4 nm,

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respectively. The CNT network after compaction had a thickness of 14 ± 3 µm and was more porous than

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the PVDF regarding surface porosity (εS = 25.5 ± 4.1%) and pore size (dS = 52 ± 10 nm).

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From DFF, the unpressed PVDF had a large wide peak (dv = 722 ± 59 nm), while the pressed

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PVDF peak was narrower and shifted towards smaller values (dv = 412 ± 13 nm). The pressed ICE9 ACS Paragon Plus Environment


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PVDF had two peaks, one similar to the pressed PVDF (dv = 407 ± 15 nm), and the other from the ICE (dv

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= 175 ± 7 nm). The mean pore size of the pressed ICE-PVDF (dV = 245 ± 14 nm) was between the two.

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The volumetric porosity decreased from 39.0 ± 4.5 to 31.4 ± 7.5% upon the addition of ICE.

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The compaction reduced the PWP of the PVDF membranes from 2950 ± 323 to 935 ± 71 L m-2 h-

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bar-1. The pressed PVDF had a stable and similar permeability to the DI-filtration-compacted PVDF

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(Figure S1). The ICE deposition on the PVDF did not significantly change the permeability (902 ± 12 L

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m-2 h-1 bar-1; P value of 0.31; Welch’s t test). The minor decrease in permeability upon ICE deposition

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(~33 L m-2 h-1 bar-1, ~4%) was further confirmed by the wet curve flow (Figure S4G, right).

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The ICE electrical resistance is displayed in Figure S4F. CNT filament resistance decreased

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linearly from 130 ± 18 to 59 ± 6 Ω (2.2-fold) when the volume of the CNT-Nafion solution increased

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from 1.0 to 2.2 mL (1.6 to 3.5 mg CNT).

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pattern area of 2.1×2.1 cm2 and the filaments were l = 18 mm, w = 1.5 mm, h = 14 µm, and 0.5 mm apart.

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The CNT network bulk resistivity ρ (Ω cm) was 0.008 Ω cm, lower than 0.029 Ω cm for a previous CNT-

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Nafion coating17 due to the reduced Nafion/CNT ratio (3-fold). At a resistance of 72.9 Ω, the potential

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drop over a single filament will be negligible (0.07 V given a maximum of 1 mA at 2 V), indicating ICE

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are sufficiently conductive for electrochemical filtration.

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Membrane bacterial removal

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The compacted PVDF membrane (dS = 31 ± 4 nm) removes bacteria by sieving. The control PVDF log

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removal (Figure S5) was 3.5 ± 0.6 and 4.1 ± 0.9 for 107 and 108 CFU mL-1, respectively. In the absence

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of electric potential, the addition of ICE did not significantly alter the log removal, being higher at 4.6 ±

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0.8 for 107 CFU mL-1 and lower at 3.6 ± 0.6 for 108 CFU mL-1. At 2 V DC and AC, the log removal

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increased by ~1 log from the control PVDF to 4.5 ± 0.5 and 4.7 ± 0.6 for 107 CFU mL-1 and 5.1 ± 0.6 and

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5.2 ± 0.9 for 108 CFU mL-1, respectively. However, Welch’s t-test (Table S2) indicated none of the

For the filtration experiments, 2.9 mg CNT was deposited on a


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results had a P-value anode > cathode for the PVDF before and

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after BW. In an attempt to verify the results, another set of experiments were completed with PC

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membranes and the bacterial densities were measured with fluorescence microscopy (discussion in SI).

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For the membrane surface before BW, the bacterial densities on the anode and the control did not follow a

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clear relation i.e., ICE anode density being smaller on PVDF and greater on PC than the control PVDF

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and PC, respectively. However, there was a consistently higher bacterial density on the anode than the

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cathode before and after BW independent of the membrane material, suggesting a likely electrokinetic



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mechanism between the electrode and the deposited bacteria (zeta potential = -10.8 mV),17 which

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generally include electrostatic repulsion by the cathode surface17, electroosmotic motion on electrode

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surface18, as well as electrophoretic and dielectrophoretic motions in the solution (will be discussed in

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ICE electric field modeling). Air bubble evolution due to water splitting 2H2O → 2H2 + O2, 1.23 eV

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NHE and other electrochemical reactions can reduce bacteria on both electrodes,37, 38 yet no visible air

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bubble or gas accumulation could be observed during filtration at 2 V DC. In contrast, during BW at 8 V

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DC, gas bubbles (80% inactivation after 30 s.22 Comparable cell damage and bacterial structure changes were also

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reported on electrically charged CNT UF membranes subjected to a potential of ±1.5 V.15 Therefore,

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notable inactivation of the deposited bacteria on the anode can be expected in this study. The bacteria on

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the ICE cathode retained membrane integrity and morphology after 60 min filtration, in agreement with

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previous findings.17 The morphology change of bacteria partly supported the observed improvement in

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bacterial removal at 2 V DC.

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After BW without voltage, the bacteria remaining on the control PVDF membrane surface were

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still mostly rod-like. In contrast, after electrochemical BW at 8 V DC, cells on the BW anode were

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significantly degraded and those on the BW cathode looked quite rough, but less degraded than the anode

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bacteria. The ICE anode consistently had a greater bacterial density than the cathode in all experiments,

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suggesting that the anodic oxidation did not affect the bacterial density e.g., by breaking down cells, as

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much as the electrokinetic effects.

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Fouling trend and BW efficacy


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∆P values did not change notably during 107 CFU mL-1 filtration and BW experiments used to determine

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bacterial density and morphology changes.

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concentration of 108 CFU mL-1 were completed under similar conditions (i.e., F = 1.2 mL min-1, Aeff = 4.4

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cm2 and J = 163.6 L/m2h) to evaluate the ICE antifouling performance. In an attempt to improve

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performance and test different mechanisms, the experiments were done with 2 V DC and AC. The

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biofouling test sequence was: DI filtration (DI-0, 10-30 min) → bacteria filtration (F-1, 60 min) → BW-1

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(10 min) → DI-1 (10 min) → F-2 (60 min or ∆P = 1.1 bar) → BW-2 (10 min) → DI-2 (10 min) (see

283

Figure S3, Protocol 2). Fouling trends and ∆P values taking during filtration experiment are shown in

284

Figure 3A and Table 1, respectively. Additionally, an empirical exponential fitting of the pressure

285

increase was completed to quantitatively compare fouling rates using Equation 3: 29, 39

Thus, filtration experiments using a higher bacterial

286

Δ = Δ exp ()

(3)

287

where ∆P0 and ∆P (bar) are the transmembrane pressure at time 0 and t (min), and k (min-1) is the fouling

288

rate constant (fitting results summarized in Table S4).

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For all membranes prior to fouling, the PWP was determined (∆PPWP = 0.13 ± 0.02 bar). Over

290

the first bacterial filtration cycle (F-1), the ∆P increased to 0.75, 0.66, 0.54, and 0.25 bar with a fouling

291

rate constant k of 0.029, 0.033, 0.019, and 0.012 min-1 for the control PVDF, ICE-0 V, ICE-DC, and ICE-

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AC, respectively. It is noteworthy that the highest ∆P, and thus the fouling, was obtained using the

293

control PVDF membrane, being 1.4 and 3 times higher than the ICE-DC and ICE-AC, respectively.

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Otherwise, the fouling rate of the ICE-0 V was slightly greater than that of the control PVDF, but that of

295

the ICE-DC and ICE-AC was 34 and 68% lower.

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BW-1 with DI water was then conducted for 10 min to recover the flux in the absence (PVDF and

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ICE-0 V) and presence (ICE-DC and ICE-AC) of 8 V electric potential. Afterwards, DI-1 was performed

298

and the ∆P decreased to 0.64, 0.36, 0.36, and 0.22 bar for the control PVDF, ICE-0 V, ICE-DC, and ICE-

299

AC (Figure 3A, between two plots), respectively. The ∆P value decreased even more (another 6-33%)



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when starting the second bacterial filtration cycle in 155 mM NaCl (see ∆P0 for F-2, Table S3). However,

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this change in pressure was not observed when starting the first bacterial filtration cycle (i.e. ∆P0 for F-1

302

was similar to ∆PPWP for DI-0 prior to membrane fouling). One hypothesis for the difference is that the

303

electrostatic repulsion between the deposited bacteria may decrease during 155 mM NaCl filtration. The

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bacterial zeta potential has been reported to decrease by ~2/3 from solution of low (0.1 mM) to high ionic

305

strength (~150 mM) due to electric double layer (EDL) compaction.40, 41 Bacterial cells, including Gram-

306

positive and Gram-negative, can shrink in response to external ionic shock of 0.1-1 M by a few percent.42,

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43

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permeability in 155 mM NaCl than DI, i.e. ∆P0 for F-2 < ∆P for DI-1.

Thus, P. fluorescens (Gram-negative) fouling layer may become thinner and result in a higher

309

During F-2, the ∆P for all membranes except ICE-AC (∆P = 0.81 bar at the end of F-2) increased

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to 1.1 ± 0.1 bar (maximum allowed). The average time to reach ∆P = 1.1 bar followed the order of

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control PVDF (67 min) < ICE-0 V (85 min) < ICE-DC (100 min) < ICE-AC (projected to be 129 min),

312

and the latter three increased by 27, 49, and 93% from the control PVDF, respectively, resulting in a

313

reduction of membrane fouling and an improvement of the membrane lifetime.

314

The fouling rate constant k for the control PVDF increased 4-fold from F-1 (0.029 min-1) to F-2

315

(0.118 min-1), meanwhile a smaller k increase (1.5 to 2.4-fold) was observed in experiments using ICE-

316

PDVF in the absence and presence of electric potential. In all experiments, the greater k in F-2 is likely

317

caused by the remained bacteria on the membrane surface after BW-1 and DI-1. Otherwise the ICE-

318

PVDF had a lower k increase from F-1 to F-2 due to lesser total deposited bacteria after F-1 and BW-1

319

(Figure 3B-E). As a guideline, Figure S7 summarizes all the ∆P values recorded during cycles 1 and 2 of

320

the bacterial filtration experiment discussed above.

321

The FRR values (Table 1) provided further evidence for the anti-fouling efficacy. Using DI as

322

the BW solution, the FRR was 18 and 43% for the control PVDF in BW-1 and BW-2, respectively, and

323

increased to 57 and 65% for the ICE-0 V.

324

modification was also observed for natural organic matter filtration and was attributed to CNT surface

Increased reversible fouling with UF CNT surface


Page 15 of 26


325

charge and roughness.44 All the ICE-PVDF had a higher FRR (55-216% for BW-1 and 1-51% for BW-2)

326

than the control PVDF, ranking in the order of ICE-0 V > ICE-DC > ICE-AC. Despite the microbubble

327

generation as an attempt to remove deposited bacteria, the ICE-DC had a lower FRR than ICE-0 V, and

328

the bubble generation was very limited for ICE-AC. The reduced FRR for ICE-DC and ICE-AC was

329

probably due to reduced fouling during filtration i.e., there were less deposited bacteria to remove during

330

BW.

331

In an attempt to increase the ICE-AC FRR, BW was also completed using 155 mM NaCl and an

332

FRR ≥ 96% after both BW was observed, being 2-4 fold higher than that of BW using DI (BW using 155

333

mM NaCl was not applied to ICE-DC to avoid electrode oxidation and deterioration at 8 V DC). The

334

FRR increase is confirmed by SEM analysis of the membranes post-BW. As displayed in Figure 3B-E,

335

multilayer bacterial deposits were observed on the control PVDF and ICE-DC post-DI-BW, while sub-

336

monolayer bacterial deposits were observed on the ICE-AC post-DI-BW (mostly individual bacteria) and

337

post-saline-BW (mostly bare CNT surface). Lower magnification SEM (Figs. 3D-2 and 3E-2) of the ICE

338

edge indicated an increasing bacterial density gradient away from the edge with a uniform density >100

339

µm.

340

A higher FRR with 155 mM NaCl BW was observed for the control PVDF as well, 86 and 82%

341

for BW-1 and BW-2, respectively.

Therefore, the FRR increase is primarily attributed to non-

342

electroactive factors. As discussed previously, a reduction in electrostatic repulsion between the deposited

343

bacteria and the bacterial cell shrinkage may result in a thinner fouling layer when using 155 mM NaCl in

344

comparison to DI, which could be removed more easily.

345

ICE electric field modeling

346

The antifouling mechanisms at DC voltages have been discussed in Membrane surface bacterial

347

density and morphology, yet the mechanisms at AC, under which condition best antifouling

348

performance was achieved, should be different due to limited electrostatic, electroosmotic, electrophoretic,



Page 16 of 26

349

and electrochemical effects with frequently-alternating polarity. A simplified COMSOL model of the

350

ICE electric field was used to help elucidate the anti-fouling mechanism in the solution (Figure 4),

351

especially at AC potential. The estimated hydraulic velocity perpendicular to the membrane (v = flow

352

rate/filter area) is ~45 µm s-1. Since the permeability of the ICE-PVDF is very close to that of PVDF after

353

compaction, the velocity field distortion over the membrane surface should be limited and was not

354

considered.

355

The electric field strength during filtration (2 V) at ~0.1-0.5 and 0.8-0.9 mm above the surface is

356

1000 and 500 V m-1, respectively. Assuming the electrostatic mobility of the bacterial cells is -1.0 × 10-8

357

m2 V-1 s-1,40 the bacterial horizontal electro-migration velocity should be ~10 and 5 µm s-1, a magnitude

358

similar to the vertical velocity, in accordance with the hypothesis that electrophoresis is a possible fouling

359

mitigation mechanism at DC potential. Nevertheless, EDL effects for the ICE were not considered in this

360

model, which will develop as soon as the electrode surface gets charged and may greatly reduce the actual

361

electric field strength in the solution.

362

The electric field distribution is non-uniform and its strength decreases with distance from the

363

electrode edges, enabling a dielectrophoretic (DEP) mechanism. Negative dielectrophoresis is likely to

364

occur for the bacteria in 155 mM NaCl and even DI,45, 46 as a result, deposited bacteria would migrate

365

away from the electric field. The DEP force is independent on the direction of the applied electric

366

potential, thus is effective with both DC and AC.47, 48 Since 10 kHz AC effectively overcomes the EDL

367

screening,49 the EDL force will be greater with AC than DC, enhancing the anti-biofouling performance.

368

The bacterial density gradient at the ICE edges provides evidence for DEP during BW at 8 V AC.

369

Bacterial properties and solution conductivity can significantly affect the DEP velocity (8700 - 64 µm s-

370

1 50

371

ICE under experimental conditions here.

372

Summary of antifouling mechanisms

), and quantitative studies are limited. Thus, DEP on the scale of 10s µm s-1 may be possible near the


Page 17 of 26


373

The ICE on PVDF membrane surface showed antifouling properties at DC and AC electric potentials

374

through filtration and BW cycles. For the possible mechanisms involved in this electroactive fouling

375

mitigation approach, we could conclude that: 1) dielectrophoretic effect in the solution between electrodes

376

could be an important antifouling mechanism and is better achieved at AC than DC; 2) electrophoretic

377

effect between electrodes is possible yet has limitation like EDL screening; 3) electrostatic as well as

378

electroosmotic effect at the electrode surface may contribute to the bacterial deposition alteration and thus

379

fouling mitigation; 4) electrochemistry changes bacterial morphology but has less effect on bacterial

380

density than electrokinetics.

381

SUPPORTING INFORMATION

382

The Supporting Information is available free of charge on the ACS Publications website at DOI:

383

XX.XXX/acs.est.XXXXXXX, including the CNT properties, the membrane preparation before ICE

384

deposition, the permeability change of unpressed and mechanically pressed membranes, the P.

385

fluorescens growth curve, a diagram of the bacterial filtration experimental protocols, the cross-sectional

386

and superficial morphology of the PVDF and ICE-PVDF membranes, the bacterial removal, the

387

morphological and filtration characteristics of the membranes (figures and tables), the Welch’s t-test

388

result of the log removal by different membranes, the exponential fitting results of the pressure increase

389

of the membranes, and supplemented movies WEO (in .avi format) showing microbubble generation

390

during BW at 8 V DC.

391

ACKNOWLEDGEMENT

392

We thank Prof. Ralph Mitchell for providing microbial experimental facilities. QZ thanks the U.S.

393

National Science Foundation (Grant CBET-1437209) for financial support. PA is thankful to the Campus

394

of International Excellence, Moncloa Campus (UCM-UPM) for her PhD grant. This work made use of the

395

Center for Nanoscale Systems (CNS) at Harvard University, a member of the National Nanotechnology



Page 18 of 26

396

Infrastructure Network (NNIN), which is in part supported by the National Science Foundation under

397

NSF award number ECS-0335765.

398 399


Page 19 of 26


400

REFERENCES

401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444

1. Van der Bruggen, B.; Vandecasteele, C.; Van Gestel, T.; Doyen, W.; Leysen, R., A review of pressure‐driven membrane processes in wastewater treatment and drinking water production. Environ. Prog. 2003, 22, (1), 46-56. 2. Foley, G., A review of factors affecting filter cake properties in dead-end microfiltration of microbial suspensions. J. Membr. Sci. 2006, 274, (1–2), 38-46. 3. Meng, F.; Chae, S.-R.; Drews, A.; Kraume, M.; Shin, H.-S.; Yang, F., Recent advances in membrane bioreactors (MBRs): Membrane fouling and membrane material. Water Res. 2009, 43, (6), 1489-1512. 4. Cogan, N. G.; Chellam, S., Regularized Stokeslets solution for 2-D flow in dead-end microfiltration: Application to bacterial deposition and fouling. J. Membr. Sci. 2008, 318, (1-2), 379-386. 5. Jagannadh, S. N.; Muralidhara, H. S., Electrokinetics Methods To Control Membrane Fouling. Ind. Eng. Chem. Res. 1996, 35, (4), 1133-1140. 6. Knoell, T.; Safarik, J.; Cormack, T.; Riley, R.; Lin, S. W.; Ridgway, H., Biofouling potentials of microporous polysulfone membranes containing a sulfonated polyether-ethersulfone/polyethersulfone block copolymer: correlation of membrane surface properties with bacterial attachment. J. Membr. Sci. 1999, 157, (1), 117-138. 7. Diagne, F.; Malaisamy, R.; Boddie, V.; Holbrook, R. D.; Eribo, B.; Jones, K. L., Polyelectrolyte and Silver Nanoparticle Modification of Microfiltration Membranes To Mitigate Organic and Bacterial Fouling. Environ. Sci. Technol. 2012, 46, (7), 4025-4033. 8. Liu, Y.; Rosenfield, E.; Hu, M.; Mi, B., Direct observation of bacterial deposition on and detachment from nanocomposite membranes embedded with silver nanoparticles. Water Res. 2013, 47, (9), 2949-2958. 9. Field, R. W.; Wu, D.; Howell, J. A.; Gupta, B. B., Critical Flux Concept for Microfiltration Fouling. J. Membr. Sci. 1995, 100, (3), 259-272. 10. Le-Clech, P.; Chen, V.; Fane, T. A. G., Fouling in membrane bioreactors used in wastewater treatment. J. Membr. Sci. 2006, 284, (1-2), 17-53. 11. Lim, A. L.; Bai, R., Membrane fouling and cleaning in microfiltration of activated sludge wastewater. J. Membr. Sci. 2003, 216, (1-2), 279-290. 12. Guo, L.; Ding, K.; Rockne, K.; Duran, M.; Chaplin, B. P., Bacteria inactivation at a substoichiometric titanium dioxide reactive electrochemical membrane. J. Hazard. Mater. 2016, 319, 137146. 13. Bowen, W. R.; Kingdon, R. S.; Sabuni, H. A. M., Electrically enhanced separation processes: the basis of in situ intermittent electrolytic membrane cleaning (IIEMC) and in situ electrolytic membrane restoration (IEMR). J. Membr. Sci. 1989, 40, (2), 219-229. 14. Zhu, A.; Liu, H. K.; Long, F.; Su, E.; Klibanov, A. M., Inactivation of Bacteria by Electric Current in the Presence of Carbon Nanotubes Embedded Within a Polymeric Membrane. Appl. Biochem. Biotechnol. 2015, 175, (2), 666-676. 15. Ronen, A.; Duan, W.; Wheeldon, I.; Walker, S.; Jassby, D., Microbial Attachment Inhibition through Low-Voltage Electrochemical Reactions on Electrically Conducting Membranes. Environ. Sci. Technol. 2015, 49, (21), 12741-12750. 16. Liu, L.; Liu, J.; Gao, B.; Yang, F., Minute electric field reduced membrane fouling and improved performance of membrane bioreactor. Sep. Purif. Technol. 2012, 86, 106-112. 17. Zhang, Q.; Nghiem, J.; Silverberg, G. J.; Vecitis, C. D., Semi-quantitative performance and mechanism evaluation of carbon nanomaterials as cathode coatings for microbial fouling reduction. Appl. Environ. Microbiol. 2015, AEM. 00582-15.



445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491

18. Poortinga, A. T.; Smit, J.; van der Mei, H. C.; Busscher, H. J., Electric field induced desorption of bacteria from a conditioning film covered substratum. Biotechnol. Bioeng. 2001, 76, (4), 395-399. 19. Hermansson, M., The DLVO theory in microbial adhesion. Colloids Surf., B. 1999, 14, (1–4), 105119. 20. Wang, X.-B.; Huang, Y.; Burt, J.; Markx, G.; Pethig, R., Selective dielectrophoretic confinement of bioparticles in potential energy wells. J. Phys. D 1993, 26, (8), 1278. 21. Markx, G. H.; Huang, Y.; Zhou, X.-F.; Pethig, R., Dielectrophoretic characterization and separation of micro-organisms. Microbiology 1994, 140, (3), 585-591. 22. Vecitis, C. D.; Schnoor, M. H.; Rahaman, M. S.; Schiffman, J. D.; Elimelech, M., Electrochemical multiwalled carbon nanotube filter for viral and bacterial removal and inactivation. Environ. Sci. Technol. 2011, 45, (8), 3672-3679. 23. Rahaman, M. S.; Vecitis, C. D.; Elimelech, M., Electrochemical carbon-nanotube filter performance toward virus removal and inactivation in the presence of natural organic matter. Environ. Sci. Technol. 2012, 46, (3), 1556-1564. 24. Dudchenko, A. V.; Rolf, J.; Russell, K.; Duan, W.; Jassby, D., Organic fouling inhibition on electrically conducting carbon nanotube–polyvinyl alcohol composite ultrafiltration membranes. J. Membr. Sci. 2014, 468, 1-10. 25. De Volder, M. F. L.; Tawfick, S. H.; Baughman, R. H.; Hart, A. J., Carbon Nanotubes: Present and Future Commercial Applications. Science 2013, 339, (6119), 535-539. 26. de Lannoy, C.-F.; Jassby, D.; Gloe, K.; Gordon, A. D.; Wiesner, M. R., Aquatic Biofouling Prevention by Electrically Charged Nanocomposite Polymer Thin Film Membranes. Environ. Sci. Technol. 2013, 47, (6), 2760-2768. 27. Du, F.; Hawari, A.; Baune, M.; Thöming, J., Dielectrophoretically intensified cross-flow membrane filtration. J. Membr. Sci. 2009, 336, (1–2), 71-78. 28. Ibeid, S.; Elektorowicz, M.; Oleszkiewicz, J. A., Novel electrokinetic approach reduces membrane fouling. Water Res. 2013, 47, (16), 6358-6366. 29. Zhang, Q.; Vecitis, C. D., Conductive CNT-PVDF membrane for capacitive organic fouling reduction. J. Membr. Sci. 2014, 459, 143-156. 30. Du, F.; Ciaciuch, P.; Bohlen, S.; Wang, Y.; Baune, M.; Thöming, J., Intensification of cross-flow membrane filtration using dielectrophoresis with a novel electrode configuration. J. Membr. Sci. 2013, 448, 256-261. 31. Khayet, M.; Matsuura, T., Membrane Distillation: Principles and Applications. 2011; p 1-477. 32. Khayet, M.; Feng, C. Y.; Khulbe, K. C.; Matsuura, T., Preparation and characterization of polyvinylidene fluoride hollow fiber membranes for ultrafiltration. Polymer 2002, 43, (14), 3879-3890. 33. Ebert, K.; Fritsch, D.; Koll, J.; Tjahjawiguna, C., Influence of inorganic fillers on the compaction behaviour of porous polymer based membranes. J. Membr. Sci. 2004, 233, (1), 71-78. 34. Arribas, P.; Khayet, M.; García-Payo, M.; Gil, L., Self-sustained electro-spun polysulfone nanofibrous membranes and their surface modification by interfacial polymerization for micro-and ultrafiltration. Sep. Purif. Technol. 2014, 138, 118-129. 35. Lin, J. C. T.; Lee, D. J.; Huang, C. P., Membrane Fouling Mitigation: Membrane Cleaning. Sep. Sci. Technol. 2010, 45, (7), 858-872. 36. Wu, D.; Bird, M. R., The fouling and cleaning of ultrafiltration membranes during the filtration of model tea component solutions. J. Food Process Eng. 2007, 30, (3), 293-323. 37. Hashaikeh, R.; Lalia, B. S.; Kochkodan, V.; Hilal, N., A novel in situ membrane cleaning method using periodic electrolysis. J. Membr. Sci. 2014, 471, 149-154. 38. Dargahi, M.; Hosseinidoust, Z.; Tufenkji, N.; Omanovic, S., Investigating electrochemical removal of bacterial biofilms from stainless steel substrates. Colloid Surf. B 2014, 117, 152-157.


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Page 21 of 26

492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519


39. Vela, M. C. V.; Blanco, S. A.; Garcia, J. L.; Rodriguez, E. B., Analysis of membrane pore blocking models applied to the ultrafiltration of PEG. Sep. Purif. Technol. 2008, 62, (3), 489-498. 40. Vanloosdrecht, M. C. M.; Lyklema, J.; Norde, W.; Schraa, G.; Zehnder, A. J. B., Electrophoretic Mobility and Hydrophobicity as a Measure to Predict the Initial Steps of Bacterial Adhesion. Appl. Environ. Microbiol. 1987, 53, (8), 1898-1901. 41. Poortinga, A. T.; Bos, R.; Norde, W.; Busscher, H. J., Electric double layer interactions in bacterial adhesion to surfaces. Surf. Sci. Rep. 2002, 47, (1), 1-32. 42. Marquis, R. E., Salt-induced Contraction of Bacterial Cell Walls. J. Bacteriol. 1968, 95, (3), 775781. 43. Rojas, E.; Theriot, J. A.; Huang, K. C., Response of Escherichia coli growth rate to osmotic shock. PNAS 2014, 111, (21), 7807-7812. 44. Bai, L. M.; Liang, H.; Crittenden, J.; Qu, F. S.; Ding, A.; Ma, J.; Du, X.; Guo, S. D.; Li, G. B., Surface modification of UF membranes with functionalized MWCNTs to control membrane fouling by NOM fractions. J. Membr. Sci.2015, 492, 400-411. 45. Price, J. A. R.; Burt, J. P. H.; Pethig, R., Applications of a New Optical Technique for Measuring the Dielectrophoretic Behavior of Microorganisms. Biochim. Biophys. Acta. 1988, 964, (2), 221-230. 46. Diaz, R.; Payen, S., Biological cell separation using dielectrophoresis in a microfluidic device. Bio and Thermal Engineering Laboratory–University of California B (ed). http://robotics. eecs. berkeley. edu/% 7Epister/245/project/DiazPayen. pdf 2008. 47. Jones, T. B., Basic theory of dielectrophoresis and electrorotation. Engineering in Medicine and Biology Magazine, IEEE 2003, 22, (6), 33-42. 48. Betts, W. B.; Brown, A. P., Dielectrophoretic analysis of microbes in water. J. Appl. Microbiol. 1999, 85, 201s-213s. 49. Sounart, T. L.; Michalske, T. A.; Zavadil, K. R., Frequency-dependent electrostatic actuation in microfluidic MEMS. J. Microelectromech. S. 2005, 14, (1), 125-133. 50. Auerswald, J.; Knapp, H. F., Quantitative assessment of dielectrophoresis as a micro fluidic retention and separation technique for beads and human blood erythrocytes. Microelectron. Eng. 2003, 67, 879-886.

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Figure 1. Schematic for interlaced CNT electrodes (ICE) fabrication on MF membranes. 1) Top casing, 2) stencil, 3) MF membrane, 4) porous sinter, 5) bottom casing, 6) MF membrane with ICE postfabrication, 7) container casing, 8) pump connection, 9) filtrate container, and 10) base.

525


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526 527 528 529 530 531 532 533


A) Filtration control

B) BW control

C) Filtration anode, 2 V

D) BW cathode, 8 V

E) Filtration cathode, 2 V

F) BW anode, 8 V

10 µm

1 µm

Figure 2. Bacterial density and morphology on membrane surfaces with or without ICE after filtration and BW. SEM images of the control PVDF and ICE surfaces: A) Filtration control PVDF, B) BW control PVDF, C) filtration ICE anode, D) cathodic BW of ICE anode during filtration, E) filtration ICE cathode, and F) anodic BW of ICE cathode during filtration. Experiments were completed by filtering 107 CFU mL-1 in 155 mM NaCl solution for 60 min at the flow rate of 1.2 mL min-1 (i.e. J = 163.6 L m-2 h-1) and BW at the same flow rate for 10 min with DI water. For the ICE-PVDF, 2 V DC and 8 V DC (with the reversed polarity) were applied during filtration and BW, respectively.

534



Page 24 of 26

535 ∆P for DI-1

1.2 A) PVDF ICE-0V ICE-DC ICE-AC

∆P (bar)

0.9

0.6

0.3

0.0

0

10

20 30

40 50 60 0 10 ∆PPWP for DI-0

F-1 t (min)

536

B) PVDF, DI BW

20

30 40

50

60

F-2 t (min)

C) ICE-DC, DI BW

2 µm D-1) ICE-AC, DI BW

2 µm D-2) ICE-AC, DI BW

2 µm E-1) ICE-AC, NaCl BW

20 µm E-2) ICE-AC, NaCl BW

2 µm

20 µm

537

Interlaced CNT Electrodes for Bacterial Fouling Reduction of

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