Effect of particle size and concentration on the synergistic UF membrane fouling by particles and NOM fractions Jia-yu Tian a,b,n , Mathias Ernst c , Fuyi Cui a , Martin Jekel b a State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, PR China b Department of Water Quality Control, Technische Universität Berlin, Sekr. KF 4, Strasse des 17. Juni 135,10623 Berlin, Germany c Institute for Water Resources and Water Supply, Technische Universität Hamburg-Harburg, Schwarzenbergstr. 95 E, D-21073 Hamburg, Germany article info Article history: Received 29 April 2013 Received in revised form 9 June 2013 Accepted 15 June 2013 Available online 21 June 2013 Keywords: Inorganic particle NOM fractions Ultrafiltration (UF) membrane Synergistic membrane fouling abstract The fouling behavior of different NOM fractions in combination with two micro-particles (0.5–10 μm and ∼45 μm) and one nano-particle (5–15 nm) on UF membrane was investigated. Three NOM models, Aldrich humic acid (HA), bovine serum albumin (BSA) and dextran (DEX) were employed as representa- tives of humic substances, proteins and polysaccharides in natural waters. For all the NOM models, a significant synergistic fouling effect was observed between the organic fraction and the two micro- particles, as evidenced by the proportional increase of fouling resistance with the increase of particle concentration from 10 to 50 mg/L. Whereas at higher particle concentration of 100 mg/L, the synergistic fouling resistance became balanced, or even decreased in comparison with that at 50 mg/L, indicating that there might be a critical concentration range for the micro-particles, in which the particles caused the most pronounced synergistic fouling effect with the NOM fractions. As for the nano-particle of 5–15 nm, much lower synergistic fouling resistance was observed as compared with that of the micro- particles for all the NOM models. This work highlighted the importance of particle size and particle concentration (i.e. mass ratio of particle/NOM) on the combined membrane fouling behavior for UF of natural waters. Besides, the interplay of different NOM fractions in the particle layer also played a crucial role in UF membrane fouling, as demonstrated by the much higher synergistic fouling resistance caused by the HA–BSA–DEX mixture in the presence of different particles, as compared with that by HA alone. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Membrane-based water treatment technology has been accepted as one of the most promising technologies in both drinking water treatment [1–3] and waste water treatment/recla- mation [4–6]. Due to the advantages offered by membrane technology, such as excellent solid/liquid separation capacity, reduced footprint, improved reliability and process simplification, as well as the advances in membrane material and decreased costs, more and more full-scale membrane filtration plants have been constructed or under consideration in recent years. However, up to date, membrane fouling is still a major obstacle limiting further widespread application of membrane technology [7,8]. Membrane fouling has been the research topic of numerous studies for a long time, and substantial progress has been achieved towards better understanding of the membrane fouling behavior [9–11]. At present, it is generally recognized that membrane fouling is determined by 4 factors: (1) membrane properties, such as pore size, hydrophobicity and charges; (2) foulant character- istics, such as molecule weight (MW), charges, hydrophobicity and composition; (3) solution chemistry, such as pH, ion strength and divalent cations; (4) hydrodynamic conditions, such as trans- membrane pressure and cross-flow velocity [12–14]. Membrane fouling is caused by initial membrane-foulants interactions fol- lowed by subsequent foulants-foulants interactions [15]. Several mechanisms have been proposed to describe the fouling behavior, including pore constriction, pore blockage and cake layer forma- tion [16]. In most cases, the fouling behavior is dominated by the combination of different mechanisms, occurring sequentially or simultaneously [17,18]. Natural organic matter (NOM)/effluent organic matter (EfOM) are ubiquitous in natural waters and WWTP secondary effluents, which have been identified as the most detrimental membrane foulants, causing both reversible and irreversible membrane foul- ing in the ultrafiltration (UF) processes. The fouling behavior of NOM on UF membrane has been extensively reviewed in a previous literature [19]. NOM is a complex organic matrix consist- ing of a wide range of organic substances with different MW and chemical properties. In NOM, the hydrophilic biopolymers Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/memsci Journal of Membrane Science 0376-7388/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.memsci.2013.06.016 n Corresponding author at: Harbin Institute of Technology, State Key Laboratory of Urban Water Resource and Environment, 73 Huanghe Road, Nangang District, Harbin 150090, China. Tel.: +86 13796626803; fax: +86 451 86282098. E-mail address: tjy800112@163.com (J.-y. Tian). Journal of Membrane Science 446 (2013) 1–9