Mitigating the inhibition of organic matter to mainstream anammox system via electrolytic-enhanced strategy: Efficacy and underlying mechanisms.

Adaptation mechanisms of ANAMMOX bacteria to extreme environments

Hydroxylamine stabilizes low-ammonium comammox-anammox cooperation through selective metabolic regulation of complete nitrification.

In low-ammonium municipal wastewater treatment, the coupling of comammox and anammox represents a promising strategy for energy-efficient nitrogen removal. However, the process exhibits considerable instability under fluctuating influent ammonium concentrations and low-ammonium conditions. Substrate limitation often drives comammox to shift from partial to complete nitrification, thereby disrupting the supply of nitrite to anammox. Moreover, the mechanisms underlying their synergistic interactions at the metabolic regulation level have yet to be elucidated. Herein, a sequencing batch biofilm reactor (SBBR) was operated with stepwise decreased ammonia concentration (33 to 10 mg-N·L-1) and subsequently amended with 5 mg·L-1 hydroxylamine (NH2OH) to probe system performance and microbial synergy. Results demonstrated that NH2OH addition recovered the total nitrogen removal efficiency to 66.7% by selectively enhancing comammox-driven partial nitritation while suppressing complete nitrification, as evidenced by upregulated amoA expression and inhibited nxrAB activity. Additionally, hydroxylamine enhanced the microbial network's resilience in biofilms under substrate-limited conditions and stimulated the expression of dissimilatory nitrate reduction to ammonium (DNRA) genes, providing an alternative nitrogen retention route. The stimulated electron recycling and interspecies communication further reinforced the metabolic coupling between comammox and anammox bacteria. This study elucidates a novel hydroxylamine-mediated regulatory strategy for the comammox-anammox coupling system, providing critical insights into stabilizing synergistic nitrogen removal in carbon-limited mainstream environments.

Underestimated role of modulating sludge structural evolution in hematite-enhanced anammox systems beyond electron transfer capacity and Fe-N coupling.

Anaerobic ammonium oxidation (anammox) represents a promising sustainable nitrogen removal technology, yet the slow growth of anammox bacteria results in suboptimal reaction rates and operational stability, while nitrate accumulation further diminishes total nitrogen removal efficiency. In this study, 1.0 g L-1 hematite was introduced into a bioreactor as a redox-active mineral to overcome these limitations. Hematite amendment enhanced electron transfer capacity, promoted sludge structural evolution, and established Fe-N coupling for diverse nitrogen removal pathways, ultimately improving total nitrogen removal efficiency by 13.4 %. Hematite addition stimulated microbial activity, as evidenced by a 103 % increase in adenosine triphosphate and a 31 % elevation in electron transport system activity, thereby improving electron transfer capacity. Sludge structural evolution was improved, with D50 increasing from 535 ± 18 µm to 1333 ± 96 µm, extracellular polymeric substance-protein content reaching 40.3 ± 6.8 mg g-1 VSS, and microbial viability under shock loading improving from 52.8 % to 58.1 %. Fe-N coupling was confirmed by intensified N2 production attributable to Feammox and NDFO processes, though their quantitative contribution remained minor (<0.1 % of total N2 production), upregulation of the rnfG gene (+136.9 %), and the enrichment of Candidatus Brocadia and iron-reducing bacteria. Partial least squares structural equation modeling (PLS-SEM) analysis suggested that sludge structural evolution accounted for 41.69 % of the observed performance enhancement. The direct contribution of electron transfer capacity was comparatively modest (22.95 %), with its primary influence mediated through an indirect effect on sludge structural evolution (35.36 %). These findings highlight that sludge structural evolution represents a previously underappreciated yet critical pathway in mineral-enhanced anammox systems.

Intensifying mainstream nitrogen removal by coupling acidophilic ammonia oxidation with anammox.

Partial nitritation and anammox (PNA) in membrane-aerated biofilm reactors (MABRs) offers a sustainable pathway for mainstream wastewater treatment; however, its application is often limited by the persistence of nitrite-oxidizing bacteria (NOB). This study demonstrated the feasibility of achieving the acidic PNA process in a lab-scale MABR treating synthetic mainstream wastewater. Long-term operation achieved stable and efficient nitrogen removal at a self-maintained bulk pH of ∼6.5, with a total nitrogen removal efficiency of 89.6 ± 0.9% and a nitrogen removal rate of 1.16±0.03 kg-N/(m3·d) (0.39 g-N/(m2·d)). Acidophilic ammonia-oxidizing bacteria (AOB, 'Candidatus Nitrosoglobus'), predominantly colonized the inner biofilm layer with a lower pH, while anammox bacteria ('Candidatus Brocadia') were mainly distributed in the outer layer. The continuous free nitrous acid (FNA) exposure in the inner layer contributed to NOB suppression, whereas nitrite competition by anammox bacteria in the outer layer further constrained NOB activity. This robust NOB suppression eliminated the need for strict dissolved oxygen limitation, thereby enabling higher oxygen supply and enhancing the acidic PN rate. Meanwhile, anammox bacteria achieved efficient performance that well matched with acidic PN within the mildly acidic microenvironment of the outer biofilm. Overall, this one-stage MABR-based acidic PNA process provides a new avenue towards stable and intensified mainstream nitrogen removal.

Enhancing the Stability of Partial Nitritation Anammox in Mainstream Municipal Wastewater Treatment: Biological Foundations, Control Strategies, and Future Perspectives

Impact of the Fenton pretreatment on enhanced biological phosphorus removal: emphasizing variations in microbial community and metabolism