Performance of partial-denitrification process providing nitrite for anammox in sequencing batch reactor (SBR) and upflow sludge blanket (USB) reactor

•Partial-denitrification for nitrite production was established in SBR and USB.•NPR of 0.12-2.21 kgN m−3 d−1 in SBR and 0.80-13.85 kgN m−3 d−1 in USB was obtained.•Nitrite production rate achieved 3.54 and 5.58 g N gVSS−1 d−1 in SBR and USB.•Granulation was observed in SBR and USB with diameter of 1.5-2.0 mm and 2.0-3.0 mm.•The suitability of partial-denitrification effluent for anammox was evaluated.

Partial-denitrification (nitrate (NO3−-N) → nitrite (NO2−-N)) holds great potential in treating NO3−-N contained wastewater, by combining with anammox process. In this study, performance of NO2−-N production in partial-denitrification was investigated in two installations: sequencing batch reactor (SBR) and upflow sludge blanket (USB) reactor. Results indicated that partial-denitrification was established successfully in both of SBR and USB, with the NO2−-N production rate (NPR) of 0.13-2.11 kg N m−3 d−1 and 0.90-13.03 kg N m−3 d−1, respectively. The NO3−-N to NO2−-N transformation ratio (NTR) was approximately 83.3% in SBR, while NTR of 51.0%-71.3% was obtained in USB. Sludge granulation was observed in both two reactors during the operation. In SBR, granular diameter of 1.5-2.0 mm was reached with sludge volume index (SVI) of 54.3 mL gSS−1, and 2.0-3.0 mm in USB with SVI of 62.1 mL gSS−1. Additionally, the ratio of COD to NO2−-N (COD/NO2−-N) and NO3−-N to NOX−-N percentage (NP) in partial-denitrification effluent demonstrated its suitability for subsequent anammox. While, partial-denitrification conducted in SBR was more suitable for low NO3−-N wastewater (30 mg L−1), and USB was appropriate for high-strength sewage. Results obtained in this study provide a solid foundation for future applying partial-denitrification combined with anammox process in treating NO3−-N contained wastewater.