Removal of nitrate from water in a novel ion exchange membrane bioreactor

Biological denitrification in a novel ion exchange membrane reactor (IEMB) has been investigated. The polluted water was separated from the mixed denitrifying culture by a non-porous, mono-anion permselective membrane providing continuous exchange of nitrate for chloride added as a counter-ion to the biocompartment. A removal efficiency of 87% and a surface removal rate of about 1,400 mg NO₃^- m^-2h^-1 was achieved at a nitrate concentration of 150 mg NO₃^- L^-1. The treated water stream was essentially free of ethanol, used as a carbon source, and NO₂^- ions whereas the original water conductivity was completely preserved due to very efficient Donnan exclusion of the cations present in the two solutions from the membrane used. The IEMB process showed higher removal efficiency and better nitrate selectivity compared to a Donnan dialysis process operated under similar conditions.