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.