Influence of increasing anode surface area on nitrite-absent ammonium oxidation in a continuous single-chamber...

Reducing energy consumption in conventional nitrogen removal processes is a crucial and urgent requirement. This study proposes an efficient electrode-dependent bio-electrochemical anaerobic ammonium (NH₄⁺-N) oxidation (BE-ANAMMOX) process, employing a carbon brush as the electron acceptor and voltage of 0.8 V. The applied voltage facilitated the removal of NH₄⁺-N with a maximum removal efficiency of 41% and a Coulombic efficiency of 40.92%, without the addition of nitrite (NO₂^--N). Furthermore, the NH₄⁺-N removal efficiency demonstrated an increase corresponding to the increase in the anodic surface area. The bio-electrochemical NH₄⁺-N removal achieved remarkable reductions, eliminating the need for O₂ and NO₂^--N by 100%, lowering energy consumption by 67%, and reducing CO₂ emissions by 66% when treating 1 kg of NH₄⁺-N. An analysis of the microbial community revealed an increase in nitrifiers and denitrifiers, including Exiguobacterium aestuarii, Alishewanella aestuarii, Comamonas granuli, and Acinetobacter baumannii. This intricate process involved the direct conversion of NH₄⁺-N to N₂ by ANAMMOX bacteria through extracellular electron transfer, all without NO₂^--N. Thus, bio-electrochemical NH₄⁺-N removal exhibits promising potential for effective nitrogen removal in wastewater treatment facilities.