Promoting nitrogen removal during Fe(III) reduction coupled to anaerobic ammonium oxidation (Feammox) by adding anthraquinone-2,6-disulfonate (AQDS)

Feammox, i.e., Fe(III) reduction coupled to anaerobic ammonium oxidation, is a potential alternative to ammonium removal in natural and artificial ecosystems. However, the efficiency of Feammox is quite low to restrain its practical application in wastewater/solid disposal. In this study, three batch experiments, including control (Fe2O3/AQDS-free), Fe2O3 group (25 mM Fe2O3 only) and AQDS-Fe2O3 group (25 mM Fe2O3 and 0.6 mM AQDS), were conducted in 200 mL serum vials to explore whether AQDS can promote Feammox. Results showed that the nitrogen removal efficiency of the AQDS-Fe2O3 group was 82.6%, compared with 64.3% of the Fe2O3 group and 46.0% in the control. AH2QDS, the reduced state of AQDS, was detected in the AQDS-Fe2O3 group. Another experiment indicated that AH2QDS was oxidized back to AQDS by Fe2O3. These results suggested that AQDS/AH2QDS had been serving as electron shuttles between ammonium and Fe2O3 to successively forward the oxidation of NH4+. X-ray diffraction analysis showed that new Fe(III) species were found in the systems, implying that a Fe(II)/Fe(III) cycle also occurred. In agreement, both iron-reducing and oxidizing bacteria were detected in the systems.