Removal of bromate, perchlorate and nitrate from drinking water in an ion exchange membrane bioreactor C.T. Matos, S. Velizarov, J.G. Crespo and M.A.M. Reis CQFB/REQUIMTE, Department of Chemistry, FCT, Universidade Nova de Lisboa, P-2829-516 Caparica, Portugal (E-mail: amr@dq.fct.unl.pt) Abstract The presence of anionic micropollutants, such as bromate, perchlorate and nitrate, in drinking water supplies represents a risk for public health. This work evaluates the applicability of the ion exchange membrane bioreactor (IEMB) concept for their removal. The IEMB concept combines the transport of anionic pollutants, through a dense mono-anion permselective membrane, with their simultaneous biodegradation to harmless products by a suitable microbial culture in a separated biocompartment. The transport of the pollutant counter-ions (anions) is governed by the Donnan equilibrium principle and, therefore, it is possible to enhance it by using a more concentrated driving counter-ion (e.g. chloride) added to the biocompartment. The IEMB process proved to selectively remove nitrate and perchlorate to concentrations below the recommended levels of 4 ppb for ClO 4 2 and 25 ppm of NO 3 2 , from a model polluted stream containing 100 ppb of ClO 4 2 and 60 ppm of NO 3 2 . Transport studies, made under Donnan dialysis conditions, showed bromate fluxes comparable to those obtained for nitrate under similar experimental conditions. However, the rate of biological reduction of bromate was about one order of magnitude slower than that of nitrate. Keywords Bromate; drinking water treatment; ion exchange membrane bioreactor; nitrate; perchlorate Introduction The presence of inorganic anionic micropollutants in water resources represents a risk for public health. The European Union (EU) limits the amount of nitrate in public drinking water supplies to a maximum of 50 ppm but recommends a level below 25 ppm (EC, 1980). There is no drinking water standard for perchlorate but the US Environmental Pro- tection Agency (EPA) recommends the use of a provisional cleanup level in the range of 4 to 18 ppb and (USEPA, 2003); e.g., the California Department of Health Services has set its action level at 6 ppb (CDHS, 2004). The maximum contaminant limit for bromate in drinking water is 10 ppb in the USA and 25 ppb in the EU (Legube et al., 2004). Development of technologies which can selectively remove these anions from water resources to below the imposed limits is an important issue for drinking water treatment. The proposed ion exchange membrane bioreactor (IEMB) concept combines the transport of charged pollutants through a suitable non-porous ion exchange membrane and the abil- ity of some microorganisms to reduce inorganic anions, such as perchlorate, bromate and nitrate to chloride, bromide and nitrogen, respectively. A schematic diagram of the ion transport and bioreduction in the IEMB is shown in Figure 1. The membrane used is positively charged and permits the transport of the target anions from the water stream to a separate biological compartment (biocompartment). This transport is possible due to the driving counter-ion Cl 2 added continuously to the biocompartment. Possible back trans- port of the final products of bioreduction (such as Br 2 ) in the treated water can be easily controlled by regulating the major driving counter-ion concentration (Cl 2 ), as it was demonstrated previously for bicarbonate (Velizarov et al., 2002). At the membrane sur- face contacting the biocompartment, a biofilm is formed due to the anions’ accumulation, Water Science and Technology: Water Supply Vol 5 No 5 pp 9–14 Q IWA Publishing 2005 9