Operation of partial nitrification to nitrite of landfill leachate and its performance with respect to different oxygen conditions

• Stable partial nitrification of leachate can be achieved under 1.0–2.0 mg L−1 DO condition.
• Decrease the DO to 0.5–1.0 mg L−1 led to the effluent unsuitable for an anammox reactor.
• A reduction of ammonia conversion whereas an increase of COD removal is noticed when DO > 3.0 mg L−1.
• There is a continuous rise in effluent nitrate even under the FA inhibition range when DO > 2.0 mg L−1.

The coupled system of partial nitrification and anaerobic ammonium oxidation (Anammox) is efficient in nitrogen removal from wastewater. In this study, the effect of different oxygen concentrations on partial nitrification performance with a sequencing batch reactor (SBR) was investigated. Results indicate that, partial nitrification of landfill leachate could be successfully achieved under the 1.0–2.0 mg L−1 dissolved oxygen (DO) condition after 118 d long-term operation, and that the effluent is suitable for an Anammox reactor. Further decreasing or increasing the DO concentration, however, would lead to a decay of nitrification performance. Additionally, the MLSS concentration in the reactor increased with increasing DO concentration. Respirometric assays suggest that low DO conditions (<2 mg L−1) favor the ammonia-oxidizing bacteria (AOB) and significantly inhibit nitrite oxidizing bacteria (NOB) and aerobic heterotrophic bacteria (AHB); whereas high DO conditions (>3 mg L−1) allow AHB to dominate and significantly inhibit AOB. Therefore, the optimal condition for partial nitrification of landfill leachate is 1.0–2.0 mg L−1 DO concentration.