Water Research 38 (2004) 3225–3232 Drinking water denitriﬁcation using a membrane bioreactor Sarina J. Ergas a, *, David E. Rheinheimer b a Department of Civil and Environmental Engineering, University of Massachusetts, 18 Marston Hall, Amherst, MA 01003 5205, USA b Department of Civil and Environmental Engineering, University of California, 760 Davis Hall, Berkeley, CA 94720-1710, USA Abstract A membrane bioreactor (MBR) was investigated for denitriﬁcation of nitrate (NO 3  ) contaminated drinking water. In the MBR, NO 3  contaminated water ﬂows through the lumen of tubular microporous membranes and NO 3  diffuses through the membrane pores. Denitriﬁcation takes place on the shell side of the membranes, creating a driving force for mass transfer. The microporous membranes provide a high NO 3  permeability, while separating the treated water from the microbial process, reducing carryover of organic carbon and sloughed biomass to the product water. Speciﬁc objectives of this research were to develop a model for NO 3  mass transfer in the MBR, investigate the effect of shell and lumen velocity on NO 3  mass transfer and investigate the effects of NO 3  and organic carbon loading on denitriﬁcation rate and product water quality. A mathematical model of NO 3  mass transfer was developed, which ﬁt abiotic mass transfer data well. Correlations of dimensionless parameters were found to underestimate the overall NO 3  mass transfer coefﬁcient by 30–45%. The MBR achieved over 99% NO 3  removal at an inﬂuent concentration of 200 mg NO 3  -N L 1 . The average NO 3  ﬂux to the biomass was 6.1 g NO 3  -N m 2 d 1 . Low efﬂuent turbidity was achieved; however, approximately 8% of the added methanol partitioned into the product water. r 2004 Elsevier Ltd. All rights reserved. Keywords: Nitrate; Denitriﬁcation; Groundwater; Membrane; Bioreactor; Methanol 1. Introduction Worldwide, a signiﬁcant fraction of groundwater used for drinking water exceeds the maximum contaminant limits (MCL) for nitrate (NO 3  ). Sources of NO 3  in groundwater include industrial, food processing, animal and human wastes, and fertilizers. Methemoglobinemia, or Blue Baby Syndrome, is a toxic response to NO 3  exposure. The conventional method for nitrate removal is ion exchange (IEX), while reverse osmosis (RO), which uses ultra-low pressure membranes, has also been used. Both of these processes, however, yield concen- trated waste brines requiring further treatment or disposal. Biological denitriﬁcation is an attractive treatment alternative for NO 3  removal due to the high speciﬁcity of denitrifying bacteria for NO 3  , low cost and high denitriﬁcation rates [1]. Biological denitriﬁcation relies on facultative bacteria that use NO 3  as a terminal electron acceptor under anaerobic conditions. Electron donors used for biological denitriﬁcation have included organic compounds (ethanol, methanol, and acetate), reduced sulfur compounds, and hydrogen [2]. Biological denitriﬁcation processes are conventionally conﬁgured as packed beds; however, post-treatment is generally required in these systems to remove dissolved organic carbon (DOC) and sloughed biomass from the product water. This paper investigates a novel extractive membrane bioreactor (MBR) that has the potential to overcome the limitations of conventional biological denitriﬁcation systems. A conceptual model of the extractive MBR is ARTICLE IN PRESS *Corresponding author. Tel.: +1-413-545-3424; fax: +1- 413-545-2202. E-mail address: ergas@ecs.umass.edu (S.J. Ergas).