Separation and Purification Technology 52 (2006) 110–116 Decolorization of dye-containing aqueous solutions by the polyelectrolyte-enhanced ultrafiltration (PEUF) process using a hollow fiber membrane module Xiaoyao Tan a,c , Nyi Nyi Kyaw b , W.K. Teo b , K. Li c,∗ a Department of Chemical Engineering, Shandong University of Technology, Zibo 255049, PR China b Department of Chemical & Environmental Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore, Singapore 119260 c Department of Chemical Engineering and Chemical Technology, Imperial College London, London SW7 2AZ, UK Received 1 February 2006; received in revised form 28 March 2006; accepted 28 March 2006 Abstract Polysulfone (PSf) asymmetric hollow fiber membranes with molecular weight cut-off (MWCO) of 13,000 Da have been prepared and employed for removal of the triphenylmethane dyes including malachite green (MG), brilliant green (BG) and new fuchsin (NF) from aqueous solutions. Several water-soluble polymers such as poly(diallydimethyl ammonium chloride) (PDADMAC), poly(sodium-4-styrenesulfonate) (PSS) and polyvinyl alcohol (PVA) have been examined for the polyelectrolyte-enhanced ultrafiltration (PEUF). The experimental results indicate that all the three triphenylmethane-type dyes can be removed effectively using the PSf hollow fiber ultrafiltration membrane with the aid of the anionic PSS polymer. The enhancement is primarily due to the formation of complexes between the anionic polymer and the cationic dye molecules through electrostatic attraction. The cationic and nonionic polymers such as PDADMAC and PVA are not suitable for the decolorization of MG, BG and NF aqueous solutions. The decolorization performances of the PSf membrane module can be fully restored by the back-washing operation using alcohol after each experiment. © 2006 Elsevier B.V. All rights reserved. Keywords: Decolorization; Triphenylmethane dye; Ultrafiltration; Hollow fiber Membrane module 1. Introduction Textile and leather industries generate large amounts of wastewater containing various colorants such as triphenyl- methane dyes, some of which are toxic and potentially carcino- genic and are difficult to degrade biologically [1–5]. Such col- ored wastewater streams could pose serious detrimental effects to both environment and human health, and thus must be treated or decolorized prior to discharge or water recycling. So far, a number of technologies have been developed to treat the wastewater containing dyes, which may be classified into three categories: physical, chemical and biological degradation [5,6]. Physical methods such as precipitation, flocculation [6] or adsorption using bone char and activated charcoal [2,3] do not degrade the pollutants but only transfer them from the liq- uid phase to the solid phase, thus causing secondary pollution ∗ Corresponding author. Tel.: +44 20 7594 5676; fax: +44 20 7594 5629. E-mail address: Kang.Li@imperial.ac.uk (K. Li). or requiring regeneration that is a costly and time-consuming process. Chemical methods including oxidative degradation by chlorine, hydrogen peroxide and ozone, reductive degradation by sodium hydrosulfite, photocatalysis [4,7] and electrochemi- cal treatment require high dosage of chemicals and produce large quantity of sludge, and thus have been proved to be expensive. Moreover, the resulting by-products by chemical degradation may be coloured themselves or/and even toxic [2]. Biodegrada- tion (aerobic or anaerobic) of dyes is cost effective, environmen- tal friendly and does not produce large quantities of sludge [5,8], but it is very selective and thus not suitable for most dyes. For most of these decolorization methods the expensive dyes cannot be recovered because of the destruction of dyes. Obviously, the non-destructive techniques seem to be more attractive since the recovered dyes are more valuable than that of the purified water [9]. Of the available techniques enabling recovery of valuable wastewater components, pressure-driven membrane processes exhibit unique advantages such as energy saving, ease of opera- tion and high efficiency [10–14]. Micro filtration (MF) and ultra- 1383-5866/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2006.03.028