Partial nitritation for subsequent Anammox to treat high-ammonium leachate

Abstract

Nitrogen removal via autotrophic denitrification, an anaerobic ammonium oxidation (Anammox) process, requires an appropriate NO₂-N/NH₄-N ratio to provide nitrite as an intermediate. In this study, a laboratory-scale Hybrid Sequencing Batch Reactor (HSBR) was implemented for treating high-ammonium raw leachate to yield an appropriate NO₂-N/NH₄-N mixture as a pretreatment for subsequent Anammox. The optimal operating conditions were examined through the long-term operation of the HSBR. The experimental results showed that the prerequisite ratio of NO₂-N/NH₄-N was found with an initial ammonium concentration of 1200 mg/L, dissolved oxygen (DO) of 0.5–1.0 mg/L, sludge retention time (SRT) of 3 days and temperature of 31°C, which is essential for the subsequent Anammox process. Moreover, the inhibition of free ammonia (FA) and free nitrous acid (FNA) were also examined under a constant pH condition, and it was found that AOB (ammonium oxidation bacteria) had a great ability to adapt to a broad FA and FNA concentration, whereas NOB (nitrite-oxidizing bacteria) were inhibited by either FA or FNA concentration to a certain extent. It appears that partial nitritation could be implemented by facilitating FA and/or suppressing FNA concentration.

Keywords:

• partial nitritation
• nitrite accumulation
• ammonium oxidation bacteria (AOB)
• nitrite-oxidizing bacteria (NOB)
• landfill leachate

Acknowledgements

The authors would like to thank the anonymous reviewers for their valuable comments and detailed corrections, which help to improve the quality of our initial manuscript.