A novel method of simultaneous NH4+ and NO3− removal using Fe cycling as a catalyst: Feammox coupled with NAFO

Abstract

The feasibility of using Feammox coupled with nitrate-dependent Fe(II) oxidizing (NAFO) to cause the simultaneous conversion of NH4+ and NO3− was explored by inoculation with Feammox sludge and the use Fe cycling as catalyst. After 61days operation, the simultaneous conversion of NO3− and NH4+ occurred with the presence of interconversion between Fe(III) and Fe(II). The conversion ratio of NH4+ to NO3− stabilized at 0.9–1. The results of isotopic tracing and microbial diversity analysis indicated that NH4+ was first oxidized to NO2− by Fe(III), then NO3− was reduced to NO2− and N2 by the Fe(II) produced in Feammox process, and finally, the NO2− produced in NAFO process underwent an Anammox process with the remaining NH4+ to yield N2. The results showed the simultaneous continuous conversion process of NO3− and NH4+ with limited Fe as a catalyst was a coupled process of Feammox, Anammox, and NAFO under the anaerobic conditions.