Shortcut nitrification/denitrification through limited-oxygen supply with two extreme COD/N-and-ammonia active landfill leachates

Shortcut nitrification/denitrification (N/DN) was carried out through limited dissolved oxygen supply (DO, 0.5-0.8 mg/L) with active air-stripping treated (COD/N of 10.1 and 615.7 mg N/L ammonia) and raw leachate (COD/N of 2.2 and 3596.3 mg N/L ammonia). The reactor demonstrated robust performance, achieving maximum removal rates of 5.33 kg COD/m(3)/d and 1.2 kg N/m(3)/d under 0.6 mg/L DO supply. 16S rRNA gene amplicon sequencing analysis revealed that Nitrosomonas holding around 1.0% responded to ammonia oxidation, while nitrite oxidizing bacteria were suppressed. For the air-stripping treated leachate, abundant and diverse denitrifying populations (e.g. Paracoccus, Pseudomonas, Roseimaritima, and Thauera) were likely responding for total nitrogen (TN) and COD removal. Feeding the raw leachate, apart from heterotrophic denitrifiers contributing to auxiliary COD and TN removal, lithotrophic denitrifiers using sulfur and/or sulfide as electron donors were associated with sulphur reducing bacteria, suggesting that the changing of feeding strength propelled a remarkable shift of denitrifying populations. An unexpected observation was found that Candidatus Anammoximicrobium sp., previously reported in dilute wastewaters, proliferated and accounted for 0.63% whilst the reactor was fed with active raw leachate (rich in ammonia nitrogen and COD). Functional profiles prediction suggested that methyl compounds metabolization and aromatic compounds degradation might actively perform. This study validated that the shortcut N/DN could be achieved by a limited oxygen supply for high COD/N wastewaters (e.g., over 9) and leads to immediately beneficial to the treatment of relevant wastewaters.