Anammox granule destruction and reconstruction in a partial nitrification/anammox system under hydroxylamine stress

Multi-omics reveals mechanism of hydroxylamine-enhanced ultimate nitrogen removal in pilot-scale anaerobic/aerobic/anoxic system

Hydroxylamine (HA) dosing is an effective strategy for promoting partial nitrification (PN); however, its impact on endogenous denitrification remains underexplored. In this study, long-term continuous HA dosing (1.4 mg/L) was introduced for over 110 days in a pilot-scale anaerobic/aerobic/anoxic (AOA) system treating municipal wastewater (66.7-75 m3/d). The HA dosing significantly increased the nitrite accumulation ratio to 67.6 ± 5.0 % (p<0.001) and reduced the effluent total inorganic nitrogen concentration from 6.2 ± 2.0 to 2.4 ± 1.1 mg/L (p<0.001), achieving a nitrogen removal efficiency of 87.4 ± 4.5 % (p<0.001) at a hydraulic retention time of 8 h. During the HA dosing, aerobic nitrogen removal contribution increased from 2.4 ± 3.4 % to 25.8 ± 8.1 % (p<0.001), and the anoxic nitrogen removal rate improved from 1.63 ± 0.11 to 2.35 ± 0.13 mg N/(L·h) (p<0.001). Enhanced nitrogen removal was not only achieved through the rapid establishment of PN but also driven by the long-term impact of HA dosing on microbial community dynamics. Multi-omics analyses revealed that HA disrupted the polyphosphate (poly-P) cycle, evidenced by enhanced transcription of ppx (poly-P degradation) and suppressed ppk (poly-P synthesis), thereby reducing energy availability for phosphate-accumulating organisms (PAOs) and shifting the carbon source competition toward glycogen-accumulating organisms (GAOs), with Ca. Competibacter abundance increased from 0.16 % to 1.13 % (p < 0.001). The economic analysis demonstrated that HA reduced sludge production by 11.2 % and saved operating costs by 31.4-42.8 % compared to conventional carbon sources. These findings highlight the potential of HA dosing to achieve sustainable and highly efficient wastewater treatment.

Autotrophic biological nitrogen removal in a non-aerated algae-partial nitritation /anammox system: Long-term performance and microbial community

This study demonstrated the long-term process stability of algal-partial nitritation/anammox (A-PN/A) in an operational operation condition and gained insight into the mechanism during the photoperiod. Results showed that an efficient nitrogen removal characteristic was obtained under the operational conditions: algae (Oocystis borgei) to PN/A sludge mass ratio of 1:5, light intensity of 2000 lux, and photoperiod of 12:12. Moreover, in a long-term operation, the total inorganic nitrogen removal efficiency could be stabilized at 86 %. Based on Flow cytometry analysis and high-throughput sequencing, the proportion of Chlorophyta exhibited a distinct upward trend, which could provide oxygen for ammonia-oxidizing bacteria and protect anammox bacteria from photooxidative damage. In a typical light-dark cycle assay, unexpectedly, little nitrite accumulated in a typical photoperiod, indicating the partial nitritation and anammox process co-occurred in the whole experiment. There was a higher nitrogen removal rate and higher transcript levels of amoA and hzsA in light period than dark period. While the dark period played a key role in the suppression of nitrite-oxidizing bacteria genus Nitrospira and nxrB inhibition to maintain stable A-PN/A, which was proved by whole-light batch experiments.

Deciphering the key role of biofilm and mechanisms in high-strength nitrogen removal within the anammox coupled partial S0-driven autotrophic denitrification system

Anammox coupled partial S0-driven autotrophic denitrification (PS0AD) technology represents an innovative approach for removing nitrogen from wastewater. The research highlighted the crucial role of biofilm on sulfur particles in the nitrogen removal process. Further analysis revealed that sulfur-oxidizing bacteria (SOB) are primarily distributed in the inner layer of the biofilm, while anammox bacteria (AnAOB) are relatively evenly distributed in inner and outer layers, with Thiobacillus and Candidatus Brocadia being the dominant species, respectively. Except for anammox and PS0AD processes, 15N isotope labeling tests determined that sulfur reshaped nitrogen metabolism pathways, providing solid evidence for the occurrence of sulfammox process. SOB and AnAOB collaborate in nitrogen and sulfur conversion, with SOB-drived PS0AD processes reducing nitrate to nitrite for AnAOB to remove ammonia. Conversely, the nitrate produced from anammox process can be reused by SOB. Metagenomic analyses verified that SOB drove the PS0AD process through encoding soxBYZ gene, while AnAOB might play an important role in simultaneously driving the anammox and sulfammox processes. These findings underscore the importance of biofilm and clarify the nitrogen-sulfur cycle mechanisms within the coupled system.

Novel anammox granules formation from conventional activated sludge for municipal wastewater treatment through flocs management

The direct integration of anammox process into municipal wastewater treatment has caused widespread concern, but the lack of anammox seeds limited its real application. This study successfully cultivated anammox granules (322.0 μm) from conventional activated sludge treating municipal wastewater. Through ultra-low floc sludge retention times of 8d, nitrifiers on flocs were eliminated and partial nitrification was realized. Furthermore, highly bacteria-enriched granules were initially formed, with Nitrosomonas and Ca. Competibacter 4-fold higher than that of flocs. Specific staining results revealed the microbial interaction with Ca. Brocadia, considering that Ca. Competibacter and Nitrosomonas correspondingly identified in the inner and outer layers of granules. The percentage of Ca. Brocadia present on the granules increased substantially from 0.0 % to 3.0 %, accompanied by a nitrogen removal rate of 0.3 kg·m-3·d-1. Our findings revealed a valuable reference for the anammox bacteria in-situ enrichment under mainstream conditions, which provides theoretical guidance for anammox-based processes practical application.