Removal of mono-valent oxyanions from water in an ion exchange membrane bioreactor: Influence of membrane permselectivity

The ion exchange membrane bioreactor (IEMB) proved to be an effective technology for the removal of nitrate and perchlorate from polluted drinking water when using a mono-anion permselective membrane such as Neosepta ACS. Aiming at reducing the cost of the system, this study evaluates the use of a lower-cost anion exchange membrane, which exhibits no preferential mono-anion permselective properties. With this purpose an Excellion I-200 membrane was tested, for the removal of anionic micropollutants, such as nitrate and perchlorate from drinking water supplies. The impact of the lower anion permselectivity of this membrane on the quality of the treated water was determined. It was demonstrated that differences between the membrane properties are responsible for the different permselectivities observed towards multi-valent and mono-valent anions. The use of Excellion I-200 resulted in a less selective removal of perchlorate and nitrate, allowing anions such as sulphate and phosphate species to be transported. When treating 3.1 l/m2 h of water contaminated with 100 μg/l of perchlorate and 60 mg/l of nitrate, lower removal degrees were obtained (85% of perchlorate and 88% of nitrate), compared with 96% of perchlorate and 99% of nitrate achieved with the Neosepta ACS membrane, operating under the same conditions. However, the Excellion I-200 membrane shows no target anion flux decline during a relatively long period of operation (1 month) and no secondary contamination of the treated water by the carbon source used. These characteristics are essential for a membrane to be successfully used in the IEMB system. Additionally, the selection of the membrane depends on the latter characteristics and on the water quality requirements.