Linking morphological features to anammox communities in a partial nitritation and anammox (PN/A) biofilm reactor

Engineered stable partial nitrification/endogenous partial denitrification-anammox process for enhanced nitrogen removal from low carbon-to-nitrogen ratio wastewater

Addressing the intractable challenges of nitrite instability and slow start-up in anammox for low carbon-to-nitrogen (C/N) ratio wastewater treatment, a one-stage partial nitrification/endogenous partial denitrification-anammox (PN/EPD-A) process in a sequencing batch biofilm reactor was proposed. By synergistically coupling PN and EPD, self-sustained nitrite supply for anammox was achieved. Concurrently, a layered biofilm structure, engineered through tailored aeration and carrier addition, facilitated the rapid enrichment of anammox bacteria. The results demonstrated exceptional performance, achieving a total nitrogen removal efficiency of 83.3 %, with anammox consistently contributing 75.8 % of the nitrogen removed. Microbial community analysis further indicated the stable coexistence of anammox bacteria, ammonia-oxidizing bacteria, and glycogen-accumulating organisms, with their relative abundance reaching 1.36 %, 2.19 % and 9.80 %, respectively. These findings unveiled a robust and efficient strategy to overcome the limitations of anammox technology in low C/N wastewater treatment, paving the way for its broader application in nitrogen removal.

Deciphering key microbes and their interactions within anaerobic ammonia oxidation systems

The stability of anaerobic ammonium oxidation (anammox) performance is inseparably linked to the dynamic equilibrium of microbial interactions. However, understanding of the key microbes within anammox systems remains limited. Through the analysis of 186 16S rRNA datasets combined with various ecological analysis methods, this study identified key microbes in the anammox process. Interactions between Candidatus_Kuenenia and other key microbes are the most significant with greater tolerance to differing water quality, while Candidatus_Jettenia have higher habitat specificity. Under adverse conditions, anammox bacteria can reduce the impact of unfavorable environments by enhancing interactions with certain microbes. This study comprehensively reviews the main functions of key microbes in the anammox system and their interactions, and summarizes several common interaction mechanisms, providing new insights for understanding the startup and stable operation of the anammox process.

Deciphering the dead zone on anammox system in biofilters

In an anammox biofilm reactor, long-term operation inevitably leads to the repeated formation of localized dead zones. Once these dead zones (DZs) occur, the anammox reactor's nitrogen removal efficiency is severely reduced. However, the mechanisms and intrinsic reasons for the transformation of DZs remain unexplored. In this study, the pilot-scale biofilters were classified into biologically active zones (BZs), transition zones (TZs), and DZs. The results indicated that microbial communities undergo accelerated succession from the TZ. Biofilms respond to environmental stress from the DZs by altering the levels of signaling molecules, triggering a series of cascading reactions. These reactions alter the abundance of genes involved in nitrogen removal, promote substance transformation, and speed up the succession of microbial communities. This study demonstrates the objectives and self-healing mechanisms of the anammox biofilm process in the presence of dead zones, which could support the long-term application of anammox technology.

Revealing the Viable Microbial Community of Biofilm in a Sewage Treatment System Using Propidium Monoazide Combined with Real-Time PCR and Metagenomics

Microbial community composition, function, and viability are important for biofilm-based sewage treatment technologies. Most studies of microbial communities mainly rely on the total deoxyribonucleic acid (DNA) extracted from the biofilm. However, nucleotide materials released from dead microorganisms may interfere with the analysis of viable microorganisms and their metabolic potential. In this study, we developed a protocol to assess viability as well as viable community composition and function in biofilm in a sewage treatment system using propidium monoazide (PMA) coupled with real-time quantitative polymerase chain reaction (qPCR) and metagenomic technology. The optimal removal of PMA from non-viable cells was achieved by a PMA concentration of 4 μM, incubation in darkness for 5 min, and exposure for 5 min. Simultaneously, the detection limit can reach a viable bacteria proportion of 1%, within the detection concentration range of 102-108 CFU/mL (colony forming unit/mL), showing its effectiveness in removing interference from dead cells. Under the optimal conditions, the result of PMA-metagenomic sequencing revealed that 6.72% to 8.18% of non-viable microorganisms were influenced and the composition and relative abundance of the dominant genera were changed. Overall, this study established a fast, sensitive, and highly specific biofilm viability detection method, which could provide technical support for accurately deciphering the structural composition and function of viable microbial communities in sewage treatment biofilms.

Formation of autotrophic nitrogen removal granular sludge driven by the dual-partition airlift internal circulation: Insights from performance assessment, community succession, and metabolic mechanism

Granular sludge has been recognized as an effective method for the application and industrialization of the anammox-based process due to its good biomass retention capacity and environmental tolerance. In this study, a one-stage autotrophic nitrogen removal (ANR) dual-partition system with airlift internal circulation was implemented for 320 days. A high nitrogen removal efficiency of 84.6% was obtained, while the nitrogen removal rate reached 1.28 g-N/L/d. ANR granular sludge dominated by Nitrosomonas and Candidatus Brocadia was successfully cultivated. Results showed that activity and abundance of functional flora first increased with granulation process, but eventually declined slightly when particle size exceeded the optimal range. Total anammox activity was observed to be significantly correlated with protein content (R2 = 0.9623) and nitrogen removal performance (R2 = 0.8796). Correlation network revealed that AnAOB had complex interactions with other bacteria, both synergy for nitrogen removal and competition for substrate. Changes in abundances of genes encoding the Carbohydrate Metabolism, Energy Metabolism, and Membrane Transport suggested energy production and material transfer were possibly blocked with further sludge granulation. Formation of ANR granular sludge promoted the interactions and metabolism of functional microorganisms, and the complex nitrogen metabolic pathways improved the performance stability. These results validated the feasibility of granule formation in the airlift dual-partition system and revealed the response of the ANR system to sludge granulation.