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 NO addition, indicating that Fe(II) was anaerobically oxidized to Fe(III). With depletion of NO, 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 NO. During the treatment, anammox bacteria was not detected, but the relative abundance of Geobacter of the NO-added group increased by 13 folds. Isotope experiment in NH-containing reactors found that much more N and N in the NO-added group were produced than those in the control (without NO), confirming that NO induced Fe(II) oxidation to participate in Feammox for NH removal. Also, NO could be produced from partial denitrification of NO, meaning that NO as a more common species might substitute NO to trigger this new anammox process.