Tracking the nitrogen transformation in saline wastewater by marine anammox bacteria-based Fe(II)-driven autotrophic denitratation and anammox

Marine anammox bacteria-based Fe(II)-driven autotrophic denitratation and anammox (MFeADA) was investigated for nitrogen removal from saline wastewater for the first time. The study demonstrated that varying influent doses of Fe(II), which participate in the Fe cycle, significantly influenced nitrogen removal performance by altering the fate of nitrite. When 50 mg/L Fe(II) was added, the nitrogen removal was mainly performed by the anammox and Fe(II)-driven autotrophic denitratation (FeAD). As the Fe(II) rose to 100-150 mg/L, the anammox, FeAD and Feammox mainly occurred. Optimal nitrogen removal efficiency, reaching 93 %, was achieved at an influent Fe(II) concentration of 150 mg/L. As the Fe(II) reached 250 mg/L, however, nitrate was directly reduced to dinitrogen gas by the excessive Fe(II) through the Fe(II)-driven autotrophic denitrification (FeADN). Candidatus Scalindua (4.1 %), Marinicella (5.3 %) and SM1A02 (31.8 %) were the dominant functional microbes. In addition, the normalized nitrate reductase abundance was about 3.1 times that of nitrite reductase, leading to the occurrence of FeAD, which achieved a stable nitrite supply for marine anammox bacteria. This novel study can promote the practical implementation of the MFeADA process in nitrogen-laden saline wastewater treatment.