Fe(Ⅲ)/Fe(Ⅱ) Cycle Enables Biological Nitrate Ammoniation at Low C/N Ratio for Reactive Nitrogen Recovery

Abstract

The recovery of reactive nitrogen from industrial wastewater by biological ammoniation is a promising strategy of sustainable wastewater treatment. However, the low C/N ratio of pickling wastewater restricts nitrate towards ammonium, resulting in nitrogen loss. Here, we have proven the feasibility of nitrate ammoniation utilizing the Fe(Ⅲ)/Fe(Ⅱ) cycle at low C/N ratios, where partial organic electrons were employed to reduce Fe(Ⅲ) and the regenerated Fe(Ⅱ) facilitated ammoniation. It achieved the nitrate reduction efficiency of 96 ± 2% and ammoniation efficiency of 49 ± 2% for 3 cycles. Iron, acting as electron carriers, contributed to the upregulation of nrfA and the downregulation of nirK. Electroactive bacteria Geobacter spp. was sustained at high abundance (~23%) by the iron cycle. These findings provided a novel approach to recover active N using the iron cycle from wastewater, which has broader implications for sustainable circular economy and the ecology of carbon, iron and nitrogen cycle.

Keywords: Nitrogen recovery, C/N ratio, Dissimilatory nitrate reduction to ammonium, Iron cycle, Geobacter