Desalination 189 (2006) 110–118 0011-9164/06/$– See front matter © 2006 Elsevier B.V. All rights reserved Presented at the 10th Aachen Membrane Colloquium, 16–17 March 2005, Aachen, Germany. *Corresponding author. Ultrafiltration of aqueous solutions containing organic polymers V. García-Molina a,b* , S. Lyko a , S. Esplugas b , Th. Wintgens a , Th. Melin a a Institut für Verfahrenstechnik, RWTH Aachen, Turmstraße 46, D-52056, Germany Tel. +49 (2) 4180 95428; Fax +49 (2) 4180 92252; email: garcia@ivt.rwth-aachen.de bDepartment of Chemical Engineering, University of Barcelona, Martí i Franquès 1, 08028, Barcelona, Spain Tel. +34 (93) 402 13 12; Fax +34 (93) 402 12 91 Received 20 April 2005; accepted 8 November 2005 Abstract In the last decades, the research done in the field of membrane technology applied to wastewater has drastically increased . However, the applicability of this technology is limited due to the fouling of membranes, directly affecting its performance. In this study, several parameters thought to be in some extent responsible for membrane fouling are evaluated. Ultrafiltration was the selected membrane process and membranes with different molecular weight cut off (MWCO) have been employed. The feed of the experiments consisted of solutions containing humic and fulvic acids, natural organic matter (NOM), alginic acid and cellulose. The influence of different sets of operating parameters, such as applied pressure, concentration of polymer, content of calcium and pH of the feed solution in the performance of the process has been investigated. Keywords: Ultrafiltration; Organic polymers; Water treatment 1. Introduction Ultrafiltration (UF) is a relatively low-pressure membrane process whose use as a water treatment has rapidly increased in the last decade due to stricter regulations for water quality, decreased cost, improved membrane materials and modules, simplicity of installation and improved reliability when compared with conventional treatment processes such as sedimentation and rapid sand filtration [1]. The applications of UF can be ana- lyzed from two different points of view. In some cases, the aim of the process is to recover or con- centrate some valuable substances from a solution — this is common practice in the chemical and pharmaceutical industries [2]. Another application related to this is the concentration of a wastewater stream for further treatment where a higher con- centration is required, as seen in some advanced oxidation processes. The second principal