Activated carbon as an insoluble electron shuttle to enhance the anaerobic ammonium oxidation coupled with Fe(III)...

Anaerobic ammonium oxidation coupled with Fe(III) reduction (Feammox) is an autotrophic biological nitrogen removal (BNR) technique in treating low-C/N wastewater. However, the nitrogen removal rate of Feammox is limited by the extracellular electron transfer. In this study, wood activated carbon (AC) was chosen as electron shuttle to enhance the start-up of the Feammox process. Within an operational period of 150 days, the NH₄⁺-N removal efficiency reached 97.9-99.5% with a volumetric loading rate (VLR) of 0.04-0.06 kg N m^-3 d^-1. Batch experiments indicated that compared with Fe₂O₃-AQDS and Fe₂O₃ groups, Fe₂O₃-AC group showed higher catalytic performance and TN removal efficiency reached 85.7%. Quinone (CO) and phenolic (-OH) chemical groups of AC were equipped with electron transfer capacity (76.51 ± 9.27 μmol e^- g^-1). Moreover, Fe(II)/Fe(III) species and the secondary iron minerals were found in our system. Microbial analysis showed that Proteobacteria and Acidobacteriota, which observed with relatively high abundance, were played an important role in the integrated Feammox system. This study demonstrates the significant influence of AC on Feammox process and provides an enhanced biological nitrogen removal strategy for practice engineering application.