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 (FeO/AQDS-free), FeO group (25 mM FeO only) and AQDS-FeO group (25 mM FeO 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-FeO group was 82.6%, compared with 64.3% of the FeO group and 46.0% in the control. AHQDS, the reduced state of AQDS, was detected in the AQDS-FeO group. Another experiment indicated that AHQDS was oxidized back to AQDS by FeO. These results suggested that AQDS/AHQDS had been serving as electron shuttles between ammonium and FeO to successively forward the oxidation of NH. 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.