The occurrence of simultaneous partial nitrification, anaerobic ammonium oxidation and denitrification (SNAD) observed in a single partially aerated full-scale bioreactor treating landfill-leachate is reported in this paper. At present, the full-scale bioreactor is treating an average leachate flow of 304 m3 d-1 with a sludge retention time between 12 and 18 d. The average COD, NH4 +-N and NO3 --N concentrations at the upstream end of the bioreactor, i.e., influent, are 554, 634 and 3 mg L-1, respectively; whereas no NO2 --N is detected in the influent. The percentage removals of COD and NH4 +-N in the bioreactor were 28% and 80%, respectively. A nitrogen mass balance approach was adopted to analyze the performance of SNAD in the full-scale bioreactor. The total nitrogen (TN) removal by combined partial nitrification and anaerobic ammonium oxidation is 68% and the heterotrophic denitrification contributes to 8% and 23% of TN and COD removals, respectively. The red granule in the bioreactor was analyzed by using fluorescence in situ hybridization and polymerase chain reaction. The results of both analytical methods confirm the presence of anaerobic ammonium oxidizing bacteria as the predominant species along with other Planctomycete-like bacteria. Overall, the SNAD process offers the simultaneous removals of nitrogen and COD in the wastewater.
- Partial nitrification