Polish Journal of Chemical Technologt, 5, 2, 40 - 43, 2003 Water Tieatment Using the New Concept of Ion Exchange Membrane Bioreactor Svetlozar Velizarov, Maria A. Reis and João G. Crespo CQFB / REQUIMTE, Department of Chemístry, Faculdade de Ci4ncias e Tecnologia, Unlversidade Nova de Llsboa, P-2829-516 Caparica, Portuga| tel.: +351 21 294 8385; fax: +jSI 21 294 8385; E-mail: jgc@dq.fct.unl.pt The ion exchange membrane bioreactor (ÌEMB) is a new concept for treating water, contaminated wiú inorganic charged pollutants, which uses a non-porous ion exchange membrane as a barrier between the water stream and a biocompartment, A suitable driving çounter-ion is added to the biocompartment, providing tle coupled çounter-diffrrsion of the tmget contaminating ion, where úe latter undergoes and a biode$adation (biofansfor- mation) to harmless product(s) by a mixed microbial culture. Transpod of co-ions through the membrane is negligible due to tleir electrostatic repulsation (Donnan exclusion) from the similarly chmged membrane surface. A case study based on nitrate as the target pollutant and chloride as the driving counter-ion is presented in order to show ttre potential of the IEMB process for drinking wateÍ denitrification. The effeçts of the mo$t important process variables on the flux and removal were studied, The biofilm developing on the membrane surface, contacting the ÌEMB biocompartment, was found to serve as a teactive banier for cmbon source penetration into the treated water. Keywords: ion exchange membrane bioreactor; donnan dialysis; membrane transport; water treatment. TNTRODUCTION A number of charged inorganic compormds, e.g. arions such as nitate, perchlorate, bromate, fluoride, as well as cations, such as heavy metals, have been found in potentially hamftl concentrations in numerous water sources, The maximum al- lowed concenlations ofthese compounds me generally set by the drinking water quality reguJatory standards in the relatively low mg'Lì to mg'Lr range, Besides the drinking water pro- duction, water of defined ion composition is required in the mmufrctwing of a number of food products, in úe fresh water fisheries and sea aqumiums, Tleated water of an extemely low conductivity (< 0.05 mS cmr) is used in the electronic industry and for the production ofclean boiler feedwater. Nowadays, membrane sqlaration processe$ such as reverse osmosis (RO), nanofiltration (NF), ultraÍïltration (UF), microfiltration (MF), and elechodialysis (ED) are widely used in all areas of water teatmentl. FuÍhermore, Donnan dialysis (DD), a process úat similarly to ED uses ion exchange mem- branes, although without applying m exiernal'electric potential difference across the membrane wiú electrodes, has been successfrlly tested recently for defluoridation of drinking wateÉ 3. However, because ions al€ not removedbut only fiansfened, and, usually, concentated by all these processes, new water treatment stategies are needed. Combinations of biological teatment such as denitification, performed by a microbial culture, which in the presence of a suitable electron donor reduces nitrate to harmless gaseous nitrogor, and a simúaneous membrane filtration (UF or MF) of the treated water have been studied by several authorsa - 6. More recently, a dialysis process utilizing a low-porosify (0.02 mm) hydrophobic membrane has been also tested. Unfortu- nately, besides úeir relatively low selectivity for niFate, these processes were genemlly found adequate for microbial cells retention only, while residual nutrients (oryanic and/or inor- ganic) were often detected in tbe treated water, thus çausing its secondary pollution. Such water would require an extensive post-treatrnent to meet the standmd criteria, The so+alled ion exchange membrane bioreactor (IEMB) concqrt has been recently introduced and proved to be sútable for fhe tansport and removal of mono-valent anions firom water streamss - t I . The IEMB concept is illusüated in Figure I for the case of drinking water denitrification. This integrated process combines continuous Donnan dialysis of nitrate from the water streâm, through a non-porous, mono-anion permselective membrane, with its simultaneous bioreduction to nitrogen by a mixed anoxic cúture, to which a carbon sowce (eúanol) is supplied, Figurel. A schematic diagrarn of úe ion transport mechanism in úe ion-exchange urembrane bioreactor Co-ions (potassium) as well as multi-valent anions are re- jected by the mono-anion permselective membrane. The Don- nan dialysis t5rye of operation requires the presence in úe biocompartment of the so-called driving cormter-ions, able to exchange with the target countef,-ion (nitate) removed from the water streanl in orderto keep electroneutality, Chloride, which provedto be a sútable driving counter-ion, ìs shown in TlrÃlEd r|EbÍ Et- F..r....-...,.r H0ft- [,r.t:F+l*lr+--ffi =- t(' -Eq cl- Hçft- Hq