Simultaneous nitrification and denitrification using a novel up-flow bio-electrochemical reactor

Nitrogen removal is a problem in the field of water treatment, especially in the presence of sulfate. Conventional nitrification and denitrification are usually carried out in two separate reactors. In addition, the effect of sulfate on hydrogenotrophic denitrification is not clear. In this study, simultaneous nitrification and denitrification (SND) for nitrogen removal from water was conducted using a single novel up-flow bio-electrochemical reactor (UBER). The influence of dissolved oxygen (DO) on nitrogen removal was investigated. When influent DO was 7.0-8.0 mg L-1, a heterotrophic nitrification zone (with DO 3.2-5.5 mg L-1) and a hydrogenotrophic denitrification zone (with DO 1.6-4.2 mg L-1) were obtained within the reactor, and the removal rates of NH4+-N and TN reached more than 90%. The distribution of DO inside developing biofilms was measured using microelectrodes. When DO in the hydrogenotrophic denitrification zone was 2.9 mg L-1, DO inside the biofilm was just 0.5 mg L-1. The effect of sulfate on hydrogenotrophic denitrification was studied by regulating the S/N ratio of influent water. Simultaneous removal of nitrate and sulfate can be achieved at low S/N, and the removal rates of nitrate and sulfate were similar to 80%. With increasing S/N ratio, sulfide produced by sulfate reduction inhibited both denitrification and further sulfate reduction