Using Fe(II)/Fe(III) as catalyst to drive a novel anammox process with no need of anammox bacteria

A novel 'anammox' in the absence of anammox bacteria was confirmed to occur in an anaerobic sludge slurry system, in which Fe(II)/Fe(III) cycle driven by NO -induced Fe(II) oxidation and subsequent NH-induced Fe(III) reduction (Feammox) pushed the nitrogen removal. Results showed that Fe(II) contents significantly (p<0.05) decreased and Fe(III) accordingly increased with NO2- addition, indicating that Fe(II) was anaerobically oxidized to Fe(III). With depletion of NO2-, the Fe(II) content began to increase which was a result of Feammox. Consequently, 96.0% NH-N of the NO -added reactor was removed during 18 days operation, while NH-N content remained essentially unchanged in the control in which NO was not added. X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) analysis indicated that FeOOH was produced from chemical Fe(II) oxidation with NO2-. During the treatment, anammox bacteria was not detected, but the relative abundance of Geobacter of the NOadded group increased by 13 folds. Isotope experiment in-containing reactors found that much more in the added group were produced than those in the control (without ), confirming that induced Fe(II) oxidation to participate in Feammox for removal. Also, NO could be produced from partial denitrification of NO(C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The study confirmed the occurrence of a novel 'anammox' process in the absence of anammox bacteria, driven by NO-induced Fe(II) oxidation and NH-induced Fe(III) reduction (Feammox) in an anaerobic sludge system. The results showed that Fe(II) was anaerobically oxidized to Fe(III) with the addition of NO2-, leading to significant nitrogen removal. XRD and XPS analysis indicated the production of FeOOH from chemical Fe(II) oxidation with NO2-. Additionally, the isotope experiment confirmed the participation of induced Fe(II) oxidation in Feammox for nitrogen removal.