Synergy between autotrophic denitrification and Anammox driven by FeS in a fluidized bed bioreactor for advanced nitrogen removal

Abstract On the basis of the metabolic synergy between autotrophic denitrification (AuDen) and anaerobic ammonium oxidation (Anammox), the feasibility of a novel ferrous sulfide (FeS)-driven AuDen and Anammox coupled system (FS-DADAS) was investigated. The nitrogen removal performance of FS-DADAS was investigated in a lab-scale fluidized bed bioreactor fed with synthetic wastewater containing NH4+-N and NO3−-N. The results of long-term operation (120 days) demonstrated the promising performance of the system with 100% NO3−-N removal and NH4+-N concentrations lower than 8.11 mg L−1 in the effluent at a nitrogen loading rate of 0.20 g-N·(L·d)−1. Sufficient NO2−-N was provided by the AuDen for Anammox where a high removal rate of total nitrogen (TN) was achieved. The contribution of Anammox to TN removal was at >80%. The reactor could maintain a stable pH with less SO42− production owing to the fact that Fe(II) and S acted as electron donors. FeS gradually transformed into a sheet-like secondary mineral, FeOOH. AuDen (Thiobacillus) and Anammox bacteria (Candidatus Kuenenia) were successfully retained in the bioreactor, with relative abundance values of 18.82%–23.64% and 3.52%–8.67%, respectively. FS-DADAS is a promising technology for the complete removal of TN from wastewaters with low C/N ratios at low energy consumption.