ELSEVIER Desalination 167 (2004) 153-158 DESALINATION www.elsevier.com/locate/desal Effects of mixed liquor suspended solid concentrations on membrane bioreactor efficiency for treatment of food industry wastewater S. Katayon a, M.J. Megat Mohd Nool ~*, J. Ahmad b, L.A. Abdul Ghani a, H. Nagaoka c, H. Aya c ~Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia Tel. +603 (8) 946-6381; Fax +603 (8) 656-7129; email: megatj@eng.upm.edu.my bKolej Universiti Sains dan Teknologi Malaysia, Trengganu, Malaysia CMushashiInstitute of Technology, Tokyo, Japan Received 27 January 2004; accepted 10 February 2004 Abstract This study investigated the impact of mixed liquor suspended solid (MLSS) concentrations on the performance of a membrane bioreactor for treating food industry wastewater. The membrane bioreactor was mainly made up of an activated sludge reactor and microfiltration hollow-fibre membrane. Two experimental procedures consisting of low and high MLSS concentrations were set up. The process at low MLSS concentrations provided a higher degree of treatment in terms of suspended solids (99.2%) and turbidity (99.73%) removals. The mean flux value of process at low MLSS concentrations (5.03 L/m2.h) was found higher than those at high MLSS concentrations (2.27 L/m~.h). Furthermore, the effectiveness of MLSS concentrations was greatly influenced by the position of the membrane modules. Higher turbidity and suspended solids removals and higher flux values were obtained with a horizontally positioned membrane module compared to a vertically placed membrane module. Keywords." Membrane bioreactor; Activated sludge; Wastewater treatment; MLSS; Mixed liquor suspended solids; Microfiltration *Corresponding author. Presented at the EuroMed 2004 conference on Desalination Strategies in South Mediterranean Countries: Cooperation between Mediterranean Countries of Europe and the Southern Rim of the Mediterranean. Sponsored by the European Desalination Society and Office National de l 'Eau Potable, Marrakech, Morocco, 30 May-2 June, 2004. 0011-9164/04/$- See front matter © 2004 Elsevier B.V. All rights reserved doi;10.1016/j. desal.2004.06.124