Improvement of antibiofouling performance of a reverse osmosis membrane through biocide release and adhesion resistance Hamed Karkhanechi, Fachrul Razi, Isao Sawada, Ryosuke Takagi, Yoshikage Ohmukai, Hideto Matsuyama ⇑ Center for Membrane and Film Technology, Department of Chemical Science and Engineering, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe 657-8501, Japan article info Article history: Received 5 October 2012 Received in revised form 14 December 2012 Accepted 14 December 2012 Available online 25 December 2012 Keywords: RO membrane Antibiofouling Silver nanoparticles Polyzwitterion abstract To improve antibiofouling properties, a commercial reverse osmosis (RO) membrane was modified by surface deposition of a polyelectrolyte multilayers (PEMs) embedded with silver nanoparticles. The mod- ified membrane was further coated with an amphiphilic polyzwitterion, a 2-methacryloyloxyethyl phos- phorylcholine (MPC) copolymer with 2-aminoethyl methacrylate (AEMA). Thus, the modified surface layer consisted of PEMs embedded with silver nanoparticles and polyzwitterion as a top layer. Embed- ding of silver nanoparticles and polyzwitterion coating were confirmed by transmission electron micro- scope (TEM) and X-ray photoelectron spectroscopy (XPS). The effectiveness of biocide release from the modified membranes was evaluated with Pseudomonas putida (P. putida) and Escherichia coli (E. coli) and the anti-adhesion property was studied using P. putida. The silver nanoparticles embedded within PEMs showed biocidal property because of silver ion release, and polyzwitterion at the top layer showed high anti-adhesion properties because of the high hydrophilicity of surface. Thus, the membrane modi- fied by PEMs embedded with silver nanoparticles and polyzwitterion as a top layer showed a high anti- biofouling properties, attributed to the combined effect of biocide release and adhesion resistance. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Reverse osmosis (RO) membranes have been used widely for water desalination and wastewater treatment in industrial, agri- cultural and drinking water production applications [1]. However, fouling is a major problem in RO process as well as in other mem- brane processes. Membrane fouling negatively affects membrane performance by decreasing water permeability. As a result, the costs of membrane processes are increased by higher energy con- sumption and the frequent need for cleaning and maintenance [2–4]. Many studies have been carried out to prevent the fouling in RO processes and various methods have been suggested to control membrane fouling. Membrane fouling can be broadly categorized into inorganic fouling, organic fouling and biofouling [5]. Inorganic fouling is caused by the scale formation at the membrane surface [5] and organic fouling by the deposition of organic foulants (such as surfactants and proteins) on the membrane surface [5,6–9]. Bio- fouling is caused by undesired attachment of microorganism com- munities to the membrane surface, followed by the growth and multiplication of sessile cells, which eventually form a biopolymer matrix or complex structure, regarded as a biofilm on the mem- brane surface [4,10]. Membrane biofouling is a more serious prob- lem than organic fouling, particularly in drinking water production and water treatment, because of the secondary pollutants gener- ated as metabolic products of the bacteria that have attached and grown on the membrane surface [4,11]. In addition, biofouling cannot be removed by chlorine treatment or backwashing [3], while inorganic fouling and organic fouling can be reversed [5]. Generally, the improvement of antibacterial properties has been based on three strategies: biocide leaching (or release killing), con- tact killing and adhesion resistance approaches [12]. In the first strategy (release killing), cytotoxic compounds are released from biocide chemicals embedded into the surface, killing bacteria in the feed solution. Thus, the attachment of bacteria on the mem- brane surface is reduced. Silver (Ag) nanoparticles are a conven- tional biocide, used as a source in the biocide leaching approach. Sawada et al. improved the antibiofouling properties of a polye- thersulfone (PES) membrane by forming an acrylamide surface layer embedded with silver nanoparticles [2]. Other researchers also used Ag nanoparticle as a strong biocide leaching source in their studies [13–16]. In the second approach (contact killing), the surface is modified by antibacterial materials such as antimicrobial peptides and chemicals with quaternary ammonium groups [16–19]. Razi et al. improved the antibiofouling properties of a polyethersulfone (PES) hollow fiber membrane by grafting (2-dimethylamino) ethyl methacrylate methyl chloride quaternary salt (DMAEMAq) onto the membrane surface [17]. 1383-5866/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.seppur.2012.12.016 ⇑ Corresponding author. Tel./fax: +81 78 803 6180. E-mail address: matuyama@kobe-u.ac.jp (H. Matsuyama). Separation and Purification Technology 105 (2013) 106–113 Contents lists available at SciVerse ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur