Coupling anammox and feammox via polymeric ferric sulfate: An efficient and aeration-saving way for nitrogen removal

To address the issue that Fe3+ precipitate would inhibit microbial metabolic activity, and to further promote the total nitrogen removal efficiency (TNRE), polymeric ferric sulfate (PFS) was added to coupling anammox and feammox. The results showed that PFS could hydrolyze part of the extracellular polymeric substances (EPS), making the spatial structure of microbial aggregations loose and porous, which probably alleviated the potential Fe(OH)3's inhibition. Meanwhile, the hydrolyzed EPS, such as aromatic amino acid, e.g., tryptophan, associated with protein-like substances, could be used as electron donors for denitrification to remove NO3−-N produced by anammox. Thus, TNRE achieved up to 95.60% when the NO2−-N/NH4+-N ratio was 0.9 in the influent flow. Coupling feammox, 9.53% of oxygen demand could be saved in the upstream partial nitrification process because of the reduction of NO2−-N/NH4+-N in the influent flow. The total nitrogen removed by anammox was 72.44%, feammox was 16.34% and denitrification was 6.82%, with 4.40% remaining in the effluent. The addition of PFS selected two possible feammox bacteria, norank_f__Bacillaceae and norank_f__Acidimicrobiaceae.