Fouling of microfiltration membranes by organic polymer coagulants and flocculants: Controlling factors and mechanisms Sen Wang a , Charles Liu b , Qilin Li a, * a Department of Civil and Environmental Engineering, Rice University, 6100 Main Street, Houston, TX 77005, United States b Pall Corporation, 25 Harbor Park Dr., Port Washington, NY 11050, United States article info Article history: Received 10 March 2010 Received in revised form 4 August 2010 Accepted 7 August 2010 Available online 14 August 2010 Keywords: Polymer flocculant Constant flux Microfiltration Membrane fouling abstract Organic polymers are commonly used as coagulants or flocculants in pretreatment for microfiltration (MF). These high molecular weight compounds are potential membrane foulants when carried over to the MF filters. This study examined fouling of three MF membranes of different materials by three commonly used water treatment polymers: poly(diallyldimethylammonium) chloride (pDADMAC), polyacrylamide (PAM), and poly (acrylic acid-co-acrylamide (PACA) with a wide range of molecular weights. The effects of polymer molecular characteristics, membrane surface properties, solution condition and polymer concentration on membrane fouling were investigated. Results showed severe fouling of microfiltration membranes at very low polymer concentrations, suggesting that residual polymers carried over from the coagulation/flocculation basin can contribute significantly to membrane fouling. The interactions between polymers and membranes depended strongly on the molecular size and charge of the polymer. High molecular weight, positively charged polymers caused the greatest fouling. Blockage of membrane pore openings was identified as the main fouling mechanism with no detectable internal fouling in spite of the small molecular size of the polymers relative to the membrane pore size. Solution conditions (e.g., pH and calcium concentration) that led to larger polymer molecular or aggregate sizes resulted in greater fouling. ª 2010 Elsevier Ltd. All rights reserved. 1. Introduction Microfiltration (MF) has been increasingly applied to drinking water and wastewater treatment due to the small footprint, superior treated water quality, and high level of automation compared to conventional treatment processes. Major limi- tations of the MF technology include inefficiency in natural organic matter (NOM) removal (Vickers et al., 1995), and membrane fouling. Many source waters contain significant amount of NOMda precursor of harmful disinfection byproducts. In addition, membranes can be fouled by NOM over time, leading to loss in water production and requiring more frequent cleaning. As a result, coagulation/flocculation is often used as pretreatment to increase NOM removal and to control membrane fouling. Polymers are widely employed in the coagulation/floccu- lation process in conventional water treatment systems (Bolto and Gregory, 2007). They are known to improve effluent water quality by increasing floc size and strength, reduce alkalinity consumption, and alleviate sludge handling and disposal problems (Gray and Ritchie, 2006; Jin et al., 2003; Taylor et al., 2002; Zhao, 2004). Therefore, polymers are also adopted in the * Corresponding author. Tel.: þ1 713 348 2046; fax: þ1 713 348 5268. E-mail address: Qilin.li@rice.edu (Q. Li). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres water research 45 (2011) 357 e365 0043-1354/$ e see front matter ª 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2010.08.009