Study on the Electrochemical Nitrogen Removal Efficiency in the Bio-electrochemical Denitrification Part of CANNED Process

The electrochemical nitrogen removal efficiency in a bio-electrochemical denitrification part of Complete Autotrophic Nitrite-nitrification and Electrochemical Bio-denitrification Combined Process (CANNED) was studied before the biofilm inoculation stage under pure electrochemical conditions, which was 24 h HRT and 0.052 mA/cm² electric current density, when the influent nitrogen forms were NO₂^--N, NH₄⁺-N and NO₂^--N+NH₄⁺-N, respectively. The results were shown as follows: When only NO₂^--N was added and the NO₂^--N influent concentration increased from 100 mg /L to 400 mg /L, NO₂^--N was removed partially by the bio-electrochemical part but the NO₂^--N removal efficiency reduced gradually from 40% to about 20%, which was might due to the oxidation of HClO produced from the influent constant Cl^- concentration. When only NH₄⁺-N was added and the influent NH₄⁺-N concentration increased from 100 mg/L to 400 mg/L, the bio-electrochemical part NH₄⁺-N removal efficiency was kept about 35%. This was mainly because that NH₄⁺-N was supplied in the form of NH₄Cl in the influent and the concentration of Cl^- and HClO reacted with NH₄⁺-N increased with the NH₄⁺-N increasing accordingly. When NO₂^--N and NH₄⁺-N were both added, the removal efficiency of each individual ion was almost the same as the NO₂^--N and NH4+-N were added separately. The results showed that NH₄⁺-N and NO₂^--N were removed partially by the influent Cl^- and there was no electrochemical interaction of the NH₄⁺-N and NO₂^--N removal under the electrochemical conditions in the bio-electrochemical part of CANNED.