Rapid Start-Up and Long-Term Stability of Anammox with Magnetic Biochar Addition: Performance Improvement, Microbial Community, and Potential Mechanisms

Accelerating the start-up of anaerobic ammonium oxidation (anammox) is the primary condition for its large-scale application. Anammox with magnetic biochar took the shortest start-up time, reducing 15–24 days compared to the control blank (CK) and 6–26 days with pyrolytic biochar. FCS300 (magnetic biochar prepared at 300 °C) could produce the highest levels of heme c (0.123 μmol/g VSS). The extracellular polymeric substances (EPS) in FCS300 had the lowest R ct (12.6 kΩ) and a substantially higher electron-transfer capability (ETC). Candidatus jettenia was the main anammox bacteria (AnAOB) in reactors after the successful start-up, and its distribution was spatially variable on the suspended sludge and the biofilm of the biochar. The findings implied that magnetic biochar might improve electron transfer by shortening the anammox start-up time via an electron shuttle mechanism or direct interspecies electron transfer.