Coupling of partial nitritation and anammox in two- and one-stage systems: Process operation, N2O emission and microbial community

Abstract

Advances in research and technological development in the field of wastewater treatment encourage the implementation of engineered autotrophic nitrogen removal (ANR) systems based on the coupling of partial nitritation (PN) and anaerobic ammonium oxidation (anammox). Such processes can be conducted in two independent dedicated reactors (i.e., two-stage system) or, alternatively, in the same reactor under limited aeration (i.e., one-stage system). In this investigation, both configurations were successfully tested using the sequencing batch reactor (SBR) technology. Processed wastewater was supernatant from a sewage sludge anaerobic digester containing about 1 g NH4+-N/L and 0.3 g PO4-P/L. Pre-conditioning of the supernatant through dilution and magnesium phosphates (e.g., struvite) precipitation favored the anammox process performance under both configurations. The N loading rate (NLR) applied in the PN reactor was ≤1.3 g N/(L·d) with nitrite production efficiencies of about 48%, whereas the N removal rate (NRR) in the anammox reactor was 0.43–0.56 g N/(L·d). On the other hand, in the one-stage reactor, the NRR was approximately 0.27 g N/(L·d). Estimated emissions of nitrous oxide (N2O) in such bioreactors ranged from 0.4 to 4.6% of the N loaded. Comparatively, similar NRRs were achieved for both reactor configurations but the one-stage system used a smaller reaction volume, ran at a lower NLR, and emitted N2O at a lower rate than the two-stage system. The microbial community in both systems was dominated by aerobic ammonium-oxidizing bacteria of the genus Nitrosomonas and the anammox species Ca. Brocadia sinica.