Separation and Purification Technology 45 (2005) 8–15 Surface modification of polypropylene microporous membranes to improve their antifouling property in MBR: NH 3 plasma treatment Hai-Yin Yu a,b , Meng-Xin Hu a , Zhi-Kang Xu a,∗ , Jian-Li Wang c , Shu-Yuan Wang a a Institute of Polymer Science, Zhejiang University, Hangzhou 310027, China b School of Chemistry and Materials Science, Anhui Normal University, Wuhu 241000, China c Department of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310027, China Received 20 July 2004; accepted 27 January 2005 Abstract To improve the antifouling property of polypropylene hollow fiber microporous membranes (PPHFMMs) in a membrane bioreactor (MBR) for wastewater treatment, PPHFMMs were subjected to surface modification by NH 3 plasma treatment. Structural and morphological changes of the membranes were characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Water contact angle, which reflects the hydrophilicity of the membrane surface, was measured by the sessile drop method. Results of XPS clearly indicated that the plasma treatment introduced nitrogen- and oxygen-containing polar groups on the membrane surface. The water contact angle of the modified membrane reduced with the decrease of the initial NH 3 pressure in the plasma reactor. To assess the relation between the plasma treatment and the membrane fouling in an MBR, membrane filtration for activated sludge was carried out using synthetic wastewater. PPHFMMs after NH 3 plasma treatment showed better flux recovery after cleaning than that of the unmodified membrane. Under the operating conditions with 8–12 h hydraulic retention time and 6.2 g/L sludge concentration in the MBR, the removal efficiency of COD and NH 3 –N was above 95% and around 60%, respectively, for a 350 mg/L COD and a 10–15 mg/L NH 3 –N fed to the bioreactor. © 2005 Elsevier B.V. All rights reserved. Keywords: Membrane bioreactor; Wastewater treatment; Antifouling property; Surface modification; Polypropylene hollow fiber microporous membrane; Plasma treatment 1. Introduction Increasingly the lack of water is a serious problem all over the world because of population growth and the expansion of industry activities. Therefore, there is a growing impetus for wastewater recycle and reuse. Interest in the membrane bioreactor (MBR) technology for wastewater treatment has increased [1–10]. The advantages offered by MBR over conventional treatment technologies are well known. Negative aspects, however, include membrane fouling and concentration polarization (which are to some ∗ Corresponding author. Tel.: +86 571 8795 2605; fax: +86 57 8795 1773. E-mail address: xuzk@ipsm.zju.edu.cn (Z.-K. Xu). extent exacerbated by membrane fouling) [11–15]. When membrane fouling occurs, a thick gel layer (which can be both biological or abiotic in composition) is formed onto the membrane surface and into the membrane pores, which causes the permeate flux to decline quickly. There have been many investigations about the mechanisms of membrane fouling [16,17], processes to restrict fouling [18] and methods to enhance the flux [19]. In general, membrane fouling occurs more seriously on hydrophobic membranes than hydrophilic ones because of hydrophobic interaction between solutes, microbial cells and membrane materials. As a result, much attention has been made to reduce membrane fouling by modifying hydrophobic materials to relative hydrophilic [20–23]. In our previous work [24–26], It was 1383-5866/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2005.01.012