Comparison of complete nitritation–denitrification and partial nitritation–anammox for iron oxide wastewater treatment

Abstract

Cost-effective nitrogen removal from iron oxide wastewater is a limitation in the sustainable development of the iron oxide manufacturing industry. Two processes, namely, complete nitritation (in a sequencing batch reactor with zeolite powder, ZSBR) combined with traditional denitrification and partial nitritation (in the same ZSBR) combined with anaerobic ammonium oxidation (anammox), were successfully developed and then compared for long-term nitrogen removal from iron oxide wastewater. Stable and complete nitritation with nitrite accumulation ratio (NAR) > 95.1% was achieved in the ZSBR. Nitrogen removal rates (NRRs) of up to 4.083 ± 0.727 kg N/m3/d were obtained subsequently in a denitrifying upflow sludge blanket reactor at an influent chemical oxygen demand/total nitrogen ratio of 2.5. Efficient partial nitritation was also achieved with effluent NO2−–N/NH4+–N ratios of 1.1–1.5 and NAR > 92.0% in the ZSBR, with a final NRR of 1.175 kg N/m3/d in the subsequent anammox reactor. The addition of zeolite achieved persistent free ammonia inhibition on nitrite oxidizing bacteria in the ZSBR and resulted in efficient and controllable nitrite accumulation. The total chemical cost in the complete nitritation–denitrification process was 3.32 USD/kg NH4+–N, which was 1.14 times higher than that in the partial nitritation–anammox process. Both processes were effective and reliable in achieving nitrogen removal from iron oxide wastewater for the sustainable development of the iron oxide manufacturing industry.