Reinforced nitrite supplement by cathode nitrate reduction with a bio-electrochemical system coupled anammox reactor

Anammox has been widely used for the treatment of nitrogen wastewater. However, the problem of stable NO₂^- supplement becomes one of the limiting factors. It is an effective method to obtain NO₂^- by denitrifying the NO₃^-, including the by-product of Anammox. In this study, NO₂^- was reinforced by bio-electrochemical system (BES) through the reaction of partial denitrification in situ in an Anammox reactor. Our results showed that both NO₃^- and NO₂^- can be reduced on the cathode with different Coulombic efficiencies. The reduction of NO₃^- amount increased with an increase in Inf-NO₃^-, which was greater than that of NO₂^-. The conversion amount of NO₃^- was 2.50% ± 17.25% to the theoretical Eff-NO₃^-, and the maximum reduction amount was 23.24% with the highest Coulombic efficiency of 3.56%. High throughput results showed that denitrifying bacteria, such as Limnobacter, Thauera, Denitratisoma, Nitrosomonas and Nitrospira, were attached to the cathode surface and in Anammox granular sludge. This study showed that NO₂^- can be supplied by reducing the by-product NO₃^- with denitrification cathode at Anammox environment in-situ.