Water Research 39 (2005) 4211–4219 Bacteriophage MS-2 removal by submerged membrane bioreactor Chii Shang à , Hiu Man Wong, Guanghao Chen Department of Civil Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong Received 5 November 2004; received in revised form 10 June 2005; accepted 10 August 2005 Abstract A membrane bioreactor (MBR) may serve as a pre-disinfection or disinfection unit, in addition to its solid/liquid separation and biological conversion functions, to produce sewage effluent of high quality. This bench-scale pilot study focuses on investigating the performance of a submerged MBR in pathogen removal and the factors affecting the removal, using a 0.4-mm hollow-fiber membrane module submerged in an aeration tank and bacteriophage MS-2 as the indicator organism. Removal of the MS-2 phage was found to be contributed by physical filtration by the membrane itself, biomass activity in the aeration tank and bio-filtration achieved by the biofilm developed on the membrane surface. The membrane alone gave poor virus removal (0.470.1 log) but the overall removal increased substantially with the presence of biomass and the membrane-surface-attached biofilm. The contributions of the suspended biomass and attached biofilm to the phage removal are dependent on the inter-related parameters including the concentration of mixed liquor suspended solids (MLSS), the sludge retention time (SRT) and the food to mass (F/M) ratio. The correlations between effluent flux/trans-membrane pressure and virus removal give evidence that phage removal in the MBR is most likely susceptible to both biological and physical factors including the quantity and property of the biomass and the biofilm and the membrane pore size reduction. r 2005 Elsevier Ltd. All rights reserved. Keywords: Bacteriophage; Biofilm; Bioreactor; Disinfection; MBR; Membrane 1. Introduction Membrane separation has long been considered as a ‘‘safe and clean’’ physical means to yield some disinfec- tion credits for water purification and reuse purposes. It reduces the problem associated with the generation of harmful disinfection by-products (DBPs) from chemical disinfection processes (e.g., chlorination or chloramina- tion) by cutting down the chemical dosages. The membrane bioreactor (MBR) technology is similar to conventional activated sludge processes except that membranes (mostly microfiltration membranes) are used to extract effluent. Therefore, much higher concentra- tions of mixed liquor suspended solids (MLSS) (nor- mally 45000 mg/L) and long sludge ages (commonly 420 days) can be kept in the aeration tank since the settlability of the flocs is not a concern. MBRs have demonstrated outstanding performance with respect to its biological conversion and solid removal (common values of effluent: TSSo5mg/L, CODo40mg/L, TNo12mg/L and TPo2.2mg/L) (Churchouse and Brindle, 2002; van der Roest et al., 2002; Wong et al., 2003). MBRs also provide advantages in sludge reduc- tion (Metcalf & Eddy, Inc., 2003) and hence the sludge ARTICLE IN PRESS www.elsevier.com/locate/watres 0043-1354/$-see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2005.08.003 à Corresponding author. Tel.: +85223587885; fax: +85223581534. E-mail address: cechii@ust.hk (C. Shang).