A new strategy for the enrichment of ammonia-oxidizing archaea in wastewater treatment systems: The positive role of quorum-sensing signaling molecules

Enrichment of Nitrosocosmicus-AOA in situ and their vertical distribution characteristics in aerated biofilters

Ammonia-oxidizing archaea (AOA) are promising candidates for replacing ammonia-oxidizing bacteria in wastewater treatment. However, limited efforts have been made to enrich copiotrophic-AOA in situ competitively. To this end, two laboratory-scale intermittent aerated biofilters (upflow-aerated biofilter (R1) and downflow-aerated biofilter (R2)) were comparatively employed for the treatment of mainstream wastewater. An extended non-aerobic cycling strategy led to higher residual ammonia-nitrogen levels (0.01-18.7 mg/L), denser biofilms, and facilitated the dominance of Nitrosocosmicus-like AOA (R1: 70.31%; R2: 82.32%). Additionally, the AOA in both biofilters were the main contributors (62%-66%) to the highly efficient nitrification process. Compared with R1, R2 had a higher abundance of Nitrosomonas and Nitrospira, a lower ammonia oxidation rate, and a simpler co-occurrence network of nitrifiers. The protein content induced by intermittent aeration significantly affected the AOA community. Candidatus Brocadia (3.62%-7.82%) was also auto-enriched in both biofilters. Therefore, in situ enrichment of Nitrosocosmicus-dominant nitrifying microorganisms is conducive to developing an environment-friendly, energy-efficient, high ammonia-nitrogen removal AOA-based partial nitrification-anammox process.

Potential directions for future development of mainstream partial nitrification-anammox processes: Ammonia-oxidizing archaea as novel functional microorganisms providing nitrite

The application of ammonia-oxidizing archaea (AOA)-based partial nitrification-anammox (PN-A) for mainstream wastewater treatment has attracted research interest because AOA can maintain higher activity in low-temperature environments and they have higher affinity for oxygen and ammonia-nitrogen compared with ammonia-oxidizing bacteria (AOB), thus facilitating stabilized nitrite production, deep removal of low-ammonia, and nitrite-oxidizing bacteria suppression. Moreover, the low affinity of AOA for ammonia makes them more tolerant to N-shock loading and more efficiently integrated with anaerobic ammonium oxidation (anammox). Based on the limitations of the AOB-based PN-A process, this review comprehensively summarizes the potential and significance of AOA for nitrite supply, then gives strategies and influencing factors for replacing AOB with AOA. Additionally, the methods and key influences on the coupling of AOA and anammox are explored. Finally, this review proposes four AOA-based oxygen- or ammonia-limited autotrophic nitritation/denitrification processes to address the low effluent quality and instability of mainstream PN-A processes.