Responses of community structure of amoA -encoding archaea and ammonia-oxidizing bacteria in ammonia biofilter with rockwool mixtures to the gradual increases in ammonium and nitrate

Research advances of ammonia oxidation microorganisms in wastewater: metabolic characteristics, microbial community, influencing factors and process applications

Ammonia oxidation carried out by ammonia-oxidizing microorganisms (AOMs) is a central step in the global nitrogen cycle. Aerobic AOMs comprise conventional ammonia-oxidizing bacteria (AOB), novel ammonia-oxidizing archaea (AOA), which could exist in complex and extreme conditions, and complete ammonia oxidizers (comammox), which directly oxidize ammonia to nitrate within a single cell. Anaerobic AOMs mainly comprise anaerobic ammonia-oxidizing bacteria (AnAOB), which can transform NH₄⁺-N and NO₂^--N into N₂ under anaerobic conditions. In this review, the unique metabolic characteristics, microbial community of AOMs and the influencing factors are discussed. Process applications of nitrification/denitrification, nitritation/denitrification, nitritation/anammox and partial denitrification/anammox in wastewater treatment systems are emphasized. The future development of nitrogen removal processes using AOMs is expected, enrichment of comammox facilitates the complete nitrification performance, inhibiting the activity of comammox and NOB could achieve stable nitritation, and additionally, AnAOB conducting the anammox process in municipal wastewater is a promising development direction.

Step-feeding ratios affect nitrogen removal and related microbial communities in multi-stage vertical flow constructed wetlands

Step-feeding (SF) strategies have been adopted in several types of constructed wetlands (CWs) to enhance nitrogen (N) removal. However, it is unclear how SF affects the N-transforming bacterial communities in CWs. Herein, four multi-stage vertical flow constructed wetlands (MS-VFCWs), each including three vertical flow stages (stage 1-3), were operated under different SF ratios (0%, 10%, 20% and 30%) in the stage 2. The physicochemical influent and effluent parameters, i.e., redox potential (ORP), pH value, chemical oxygen demand (COD), total nitrogen (TN), ammonia (NH₄⁺-N), nitrate (NO₃^--N), and nitrite (NO₂^--N), free-ammonia (FA) concentration, COD/TN ratio, as well as the abundance, structure, and activity of N-transforming bacteria were investigated. Results showed that N removal in a multi-stage vertical flow constructed wetland in the absence of SF was 45.0 ± 7.74%. Alternatively, a combined SF ratio of 20% increased N removal to 61.7% ± 4.50%, accounting for a 37.1% increase compared to the SF ratio of 0%. In the microbial community, FA was determined to be the primary physicochemical parameter governing nitrification processes in MS-VFCWs. Further, partial nitrification processes played an important role in ammonium removal during stage 1, while ammonia-oxidizing archaea were major contributors to ammonium removal in stage 3. Furthermore, abundance of nitrite reductase genes (nirS, nirK) and relative abundance of denitrifying bacteria increased with increasing SF ratio; while the nirS/nirK ratio and the alpha diversity of nirK denitrifiers were significantly affected by SF ratios, and the influent NO₃^--N concentration was related to a shift in denitrifier composition toward strains containing the nirS gene. Autotrophic (e.g., Thiobacillus, Sulfurimonas, Arenimonas, Gallionella and Methyloparacoccus) and facultative chemolithoautotrophic (e.g., Pseudomonas and Denitratisoma) denitrifying bacteria were enriched in stage 2. Hence, the synergy between heterotrophic and autotrophic denitrifying bacteria promoted excellent N removal efficiency with a low COD/TN ratio.

Ammonia oxidizing bacteria and archaea in horizontal flow biofilm reactors treating ammonia-contaminated air at 10 °C

The objective of this study was to demonstrate the feasibility of novel, Horizontal Flow Biofilm Reactor (HFBR) technology for the treatment of ammonia (NH3)-contaminated airstreams. Three laboratory-scale HFBRs were used for remediation of an NH3-containing airstream at 10 °C during a 90-d trial to test the efficacy of low-temperature treatment. Average ammonia removal efficiencies of 99.7 % were achieved at maximum loading rates of 4.8 g NH3 m3 h−1. Biological nitrification of ammonia to nitrite (NO2−) and nitrate (NO3−) was mediated by nitrifying bacterial and archaeal biofilm populations. Ammonia-oxidising bacteria (AOB) were significantly more abundant than ammonia-oxidising archaea (AOA) vertically at each of seven sampling zones along the vertical HFBRs. Nitrosomonas and Nitrosospira, were the two most dominant bacterial genera detected in the HFBRs, while an uncultured archaeal clone dominated the AOA community. The bacterial community composition across the three HFBRs was highly conserved, although variations occurred between HFBR zones and were driven by physicochemical variables. The study demonstrates the feasibility of HFBRs for the treatment of ammonia-contaminated airstreams at low temperatures; identifies key nitrifying microorganisms driving the removal process; and provides insights for process optimisation and control. The findings are significant for industrial applications of gas oxidation technology in temperate climates.

Management of Microbial Communities through Transient Disturbances Enhances the Functional Resilience of Nitrifying Gas-Biofilters to Future Disturbances

Microbial communities have a key role for the performance of engineered ecosystems such as waste gas biofilters. Maintaining constant performance despite fluctuating environmental conditions is of prime interest, but it is highly challenging because the mechanisms that drive the response of microbial communities to disturbances still have to be disentangled. Here we demonstrate that the bioprocess performance and stability can be improved and reinforced in the face of disturbances, through a rationally predefined strategy of microbial resource management (MRM). This strategy was experimentally validated in replicated pilot-scale nitrifying gas-biofilters, for the two steps of nitrification. The associated biological mechanisms were unraveled through analysis of functions, abundances and community compositions for the major actors of nitrification in these biofilters, that is, ammonia-oxidizing bacteria (AOB) and Nitrobacter-like nitrite-oxidizers (NOB). Our MRM strategy, based on the application of successive, transient perturbations of increasing intensity, enabled to steer the nitrifier community in a favorable way through the selection of more resistant AOB and NOB sharing functional gene sequences close to those of, respectively, Nitrosomonas eutropha and Nitrobacter hamburgensis that are well adapted to high N load. The induced community shifts resulted in significant enhancement of nitrification resilience capacity following the intense perturbation.

Microbial community structure of relict niter-beds previously used for saltpeter production

From the 16th to the 18th centuries in Japan, saltpeter was produced using a biological niter-bed process and was formed under the floor of gassho-style houses in the historic villages of Shirakawa-go and Gokayama, which are classified as United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage Sites. The relict niter-beds are now conserved in the underfloor space of gassho-style houses, where they are isolated from destabilizing environmental factors and retain the ability to produce nitrate. However, little is known about the nitrifying microbes in such relict niter-bed ecosystems. In this study, the microbial community structures within nine relict niter-bed soils were investigated using 454 pyrotag analysis targeting the 16S rRNA gene and the bacterial and archaeal ammonia monooxygenase gene (amoA). The 16S rRNA gene pyrotag analysis showed that members of the phyla Proteobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Firmicutes, Gemmatimonadetes, and Planctomycetes were major microbial constituents, and principal coordinate analysis showed that the NO₃⁻, Cl⁻, K⁺, and Na⁺ contents were potential determinants of the structures of entire microbial communities in relict niter-bed soils. The bacterial and archaeal amoA libraries indicated that members of the Nitrosospira-type ammonia-oxidizing bacteria (AOB) and “Ca. Nitrososphaera”-type ammonia-oxidizing archaea (AOA), respectively, predominated in relict niter-bed soils. In addition, soil pH and organic carbon content were important factors for the ecological niche of AOB and AOA in relict niter-bed soil ecosystems.