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

Abstract Partial-denitrification (nitrate (NO 3 − -N) → nitrite (NO 2 − -N)) holds great potential in treating NO 3 − -N contained wastewater, by combining with anammox process. In this study, performance of NO 2 − -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 NO 2 − -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 NO 3 − -N to NO 2 − -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 NO 2 − -N (COD/NO 2 − -N) and NO 3 − -N to NO X − -N percentage (NP) in partial-denitrification effluent demonstrated its suitability for subsequent anammox. While, partial-denitrification conducted in SBR was more suitable for low NO 3 − -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 NO 3 − -N contained wastewater.