Search Results (81)

Silicon (Si)-based amendments can regulate soil nitrogen (N) cycling and reduce gaseous N losses, but the effect of nano-Si particle size on mineral N dynamics and nitrous oxide (N₂O) emissions under flooded tropical paddy soil conditions remains unclear. This study aimed to elucidate how nano-Si particle size regulates mineral N dynamics and N₂O emissions, with particular emphasis on whether smaller particles promote ammonium N (NH₄⁺-N) dominance and more effectively mitigate N₂O emissions than larger particles. A 30-day flooded incubation experiment was conducted using tropical paddy soil amended with 15 or 50 nm nano-Si particles, each applied at 67 mg kg⁻¹ dry soil, alongside an unamended control. Mineral N dynamics, extracellular enzyme activities, N-cycling functional genes, and N₂O emissions were evaluated. Compared with the control, 15 nm and 50 nm nano-Si significantly increased NH₄⁺-N concentration by 16.4% and 5.25% while reducing nitrate N (NO₃⁻-N) concentration by 40.8% and 23.0%, respectively. The NO₃⁻-N/NH₄⁺-N ratio decreased significantly by 49.8% and 22.1%, indicating a particle-size-dependent shift toward NH₄⁺ dominance. The 15 nm treatment significantly enhanced β-N-acetylglucosaminidase and leucine aminopeptidase activities, supporting organic N turnover and NH₄⁺-N accumulation. It also significantly reduced the abundance of the nitrite reductase gene nirS, involved in denitrification, whereas the N₂O reductase gene nosZ, responsible for N₂O reduction, showed no consistent treatment-specific response. Consistently, cumulative N₂O emissions decreased significantly by 33.6% and 18.2% under 15 nm and 50 nm treatments, respectively. These results indicate that both nano-Si treatments significantly shifted mineral N dynamics toward NH₄⁺-N dominance and reduced cumulative N₂O emissions compared with the control. These responses were consistently stronger under the 15 nm treatment than under the 50 nm treatment, demonstrating that smaller nano-Si particles more effectively limit NO₃⁻-N accumulation, promote NH₄⁺-N retention, and mitigate N₂O emissions in flooded tropical paddy soil. Nevertheless, direct measurements of N-transformation rates, comparisons with conventional Si sources, and field-scale validation are required before practical application. Full article

De novo granulation of autochthonous microorganisms of water and wastewater reduces the start-up periods for cultivating aerobic granular sludge (AGS) and enrichment of degrading strains. However, it has not been demonstrated using refractory carbon compounds. This work investigated the formation of AGS from the seawater microbiome and establishment of pollutant removal pathways by feeding acetonitrile as the sole carbon and nitrogen source. Use of acetonitrile at an organic loading rate of 0.124 kg/m³/day enabled rapid emergence of aggregates and then stable granules (size: 1.3 mm; SVI5: 68 mL/g) within two weeks. TOC removal accompanied by ammonium nitrogen release was consistent and stable at 93% during the 50 days of bioreactor operation. Formation of acetamide and ammonium indicated involvement of nitrile hydratase and amidase enzymes in acetonitrile biodegradation. Ammonium released during acetonitrile biodegradation was removed by partial nitrification and the nitrite denitrification pathway. However, incomplete ammonium removal led to accumulation of up to 120 mg/L NH₄⁺-N by day 50. Phosphate was removed via the enhanced biological phosphate removal pathway. This study shows that de novo granulation permits cultivation of AGS via the de novo granulation approach for simultaneous biodegradation of refractory acetonitrile and biological nutrient removal under saline conditions. Full article

Ammonium nitrogen pollution presents a significant challenge in wastewater treatment. Traditional activated sludge processes often suffer from limitations such as low efficiency and high energy consumption when treating high-ammonium nitrogen wastewater. This study utilized previously screened high-efficiency heterotrophic nitrification aerobic denitrification (HN-AD) bacterial strains (Pseudomonas alcaliphila and Paracoccus versutus) synergistically with microalgae to construct an immobilized bacteria algae symbiotic system (IBAS). The nitrogen removal performance and microbial community response of the system were investigated under different nitrogen sources, carbon to nitrogen (C/N) ratios, and light intensities. Results demonstrated that the system achieved a removal rate of over 95% for nitrite and nitrate. Under conditions of C/N = 15 and high light intensity (335.36 μmol/(m² · s)), the removal rates of NH₄⁺-N, TN, and COD exceeded 90% without nitrite accumulation. Microbial community analysis revealed that high C/N conditions significantly enriched HN-AD functional bacteria (such as Acinetobacter) in the Pseudomonadota phylum and Gammaproteobacteria class. High light intensity promoted the proliferation of microalgae (Chlorella and Halochlorella), enhanced algal bacterial interaction, and improved system stability. This study elucidated the nitrogen removal mechanism of the IBAS under multi-factor regulation, providing a theoretical foundation and demonstrating application potential for low-carbon and high-efficiency wastewater treatment technologies. Full article

Understanding how external nitrogen sources regulate nitrogen fate in river water is critical for improving nitrogen removal and reducing greenhouse-gas risk. Here, short-term microcosm incubations were conducted using source water as the background matrix and seven representative source inputs. By integrating hydrochemical analyses, bacterial community profiling, metagenomics, RT-qPCR, and process-rate measurements, we evaluated source-dependent shifts in nitrogen-cycling pathways. Manure-related inputs generated the highest organic and nitrogen loading, suppressed nitrification, enhanced nrfA (cytochrome c nitrite reductase) abundance and transcription, and promoted DNRA, indicating a shift toward nitrogen retention via ammonium regeneration. In contrast, sewage-related inputs maintained relatively high NO₃⁻ availability, elevated nirS (cytochrome cd1 nitrite reductase) and nosZ (nitrous oxide reductase) expression, and enhanced denitrification, but also increased N₂O production. Metagenomic, transcriptional, and rate-based evidence consistently identified 12 h as a critical window for source-dependent pathway redistribution, highlighting the importance of short-term monitoring for detecting rapid nitrogen-cycle responses following pollution inputs. These findings support source-oriented nitrogen management that considers both nitrogen loading and hydrochemical controls on nitrate fate. Full article

Although numerous studies have focused on the potential application of heterotrophic nitrification–aerobic denitrification (HNAD) bacteria in wastewater treatment, research exploring their potential in aquaculture biofloc systems remains limited. In this study, a promising HNAD strain, identified as Stutzerimonas stutzeri MJ20, was isolated from mature biofloc. This strain efficiently utilized low-cost carbon sources (e.g., glucose) and small-molecule carbon sources (e.g., sodium acetate and sodium succinate). Under conditions with glucose as the carbon source, a carbon-to-nitrogen (C/N) ratio of 15, pH 6–9, temperature 25–35 °C, salinity 0–35‰, and shaker speed of 0–150 rpm, it achieved removal rates of 95–100% for NH₄⁺-N, NO₂⁻-N, and NO₃⁻-N at initial concentrations of 100 mg/L each. Even at higher concentrations (up to 200 mg/L NH₄⁺-N and 500 mg/L for both NO₂⁻-N and NO₃⁻-N), removal rates exceeded 99%. Under mixed nitrogen sources, strain MJ20 demonstrated efficient nitrogen removal, preferentially utilizing NH₄⁺-N, with only minimal and transient accumulation of nitrite and nitrate. Genomic analysis revealed that MJ20 carries key denitrification genes, including napA, nirS, norB and nosZ, and possesses complete pathways for nitrate reduction to nitrogen gas and ammonia assimilation, although typical autotrophic nitrification genes were not detected. Combined genomic data and autotrophic culture experiments indicated that, in addition to utilizing various organic carbon sources, the strain also exhibited certain autotrophic growth capabilities. Furthermore, MJ20 showed strong flocculation ability (flocculation rate > 96% within 16 h), sensitivity to multiple common antibiotics, and no toxicity to zebrafish, demonstrating favorable biosafety. In simulated seawater aquaculture wastewater with a C/N ratio of 5, it achieved a total nitrogen removal rate exceeding 94% within 72 h. These results indicate that strain MJ20 possesses comprehensive advantages, including efficient nitrogen removal, broad carbon source adaptability, strong environmental resilience, minimal accumulation of intermediate nitrogen products, excellent flocculation ability, and high biosafety. These traits highlight its potential for application in biofloc systems and in treating aquaculture tail water with a low C/N ratio. This study provides theoretical insights and practical guidance for screening HNAD bacteria suitable for biofloc systems. Full article

Deammonification, which is based on partial nitritation and anammox (PN/A), is a well-established sidestream treatment for nitrogen removal. However, transferring deammonification to mainstream wastewater treatment remains challenging due to low temperatures, the need to retain slow-growing anammox bacteria (AnAOB), and their competition for nitrite with nitrite-oxidizing bacteria (NOB) and heterotrophic denitrifiers. This work investigates cubic polyurethane foam carriers to promote growth and retention of AnAOB. A moving bed biofilm reactor (MBBR) and an integrated fixed-film activated sludge (IFAS) reactor were compared over a three-year experimental period at lab-scale. The feasibility of the biofilm carriers for deammonification was first evaluated under sidestream conditions, followed by a stepwise transition to mainstream operational conditions. The impact of operational parameters, including dissolved oxygen concentration, pH value, and aeration strategy, was evaluated with respect to the activity of aerobic ammonium-oxidizing bacteria (AOB), NOB, and AnAOB, as well as nitrogen removal rates. Deammonification reached nitrogen removal rates of 0.04–0.12 kg N m⁻³ d⁻¹ (IFAS reactor) and 0.02–0.28 kg N m⁻³ d⁻¹ (MBBR) at subphases with reactor bulk concentrations above 60 mg NH₄-N L⁻¹. Highest nitrogen removal degrees of 77 ± 6% (IFAS) and 76 ± 5% (MBBR) were achieved at reactor bulk concentrations of 96 mg NH₄ L⁻¹ and 97 mg NH₄ L⁻¹, respectively. Lower concentrations triggered NOB activity in both reactors, leading to an increase in nitrate concentration up to 22 mg NO₃-N L⁻¹. AOB and AnAOB activities were on average 6-fold higher on the carriers compared to suspended biomass throughout all experimental phases, demonstrating the feasibility of using cubic polyurethane foam carriers for deammonification. This was also confirmed by fluorescence in-situ hybridization (FISH) measurements. Median nitrogen removal rates over all experimental phases of 0.07 kg N m⁻³ d⁻¹ for the IFAS reactor and 0.05 kg N m⁻³ d⁻¹ for the MBBR were achieved, which are comparable to conventional activated sludge systems performing nitrogen removal via nitrification–denitrification. While at lower nitrogen concentrations, the IFAS reactor yielded superior nitrogen removal rates, peak nitrogen removal rates of 0.28 kg N m⁻³ d⁻¹ were measured in the MBBR configuration. However, controlling NOB activity at lower temperatures and concentrations remains a challenge in MBBR and IFAS configurations. In our study, in the IFAS reactor NOB activities were visible on fewer days than in MBBR. At mainstream-like conditions, higher nitrogen removal rates of IFAS (0.09–0.12 kg N m⁻³ d⁻¹) were achieved compared to the MBBR (0.06–0.09 kg N m⁻³ d⁻¹). This demonstrates the advantage of the IFAS reactor in treating mainstream wastewater via deammonification. As an autotrophic nitrogen removal process, the implementation of deammonification in the mainstream of municipal wastewater treatment plants enables enhanced recovery of biogas from sewage organic matter. The latter would otherwise be consumed during the conventional nitrification-denitrification pathway. Consequently, the overall energy balance for wastewater treatment can be improved, contributing to a more environmentally sustainable process. Full article

Research on heterotrophic bioflocs is extensive, whereas investigations into autotrophic bioflocs remain limited. This study established an in situ autotrophic biofloc (ABF) system for intensive Pacific white shrimp (Penaeus vannamei) farming, aiming for zero water exchange and optimized water quality. A 120-day indoor experiment tested three stocking densities (300 (T1), 250 (T2), and 200 shrimp per m³ (T3)) with no water exchange. Water quality was monitored every two days, and bacterial communities were analyzed on days 10 and 70. The results indicated that ABF maturation was achieved by day 70 across all treatments, marked by three key indicators: (1) synchronous declines in nitrite and nitrate concentrations; (2) concurrent decreases in pH and total alkalinity approaching maturation; and (3) sustained high nitrogen removal efficiency (nitrite < 0.7 mg/L, ammonia < 0.6 mg/L). All density groups displayed similar patterns in both water quality dynamics and microbial community evolution. Bacterial analysis revealed that dominant genera such as Ruegeria, Bacillus, Muricauda, SM1A02, and Nitrospira played critical roles in toxic nitrogen removal, while pathogenic Klebsiella and Vibrio significantly decreased post-maturation. Heterotrophic nitrification and aerobic denitrification microorganisms (HNADMs) were identified as potentially responsible for nitrite accumulation. Nitrite accumulation was found in all groups. T2 and T3 achieved satisfactory breeding performance despite pre-maturation nitrate peaks exceeding 40 mg/L, whereas T1 suffered a low survival rate (27.47%) due to severe nitrite accumulation (>50 mg/L). A biofloc volume (BFV) of 4–8 mL/L effectively managed daily feed inputs of 75–110 g/m³. These findings lay a theoretical and technical foundation for the application of in situ ABF cultivation in intensive farming and enhance the sustainability of aquaculture. Full article

Salinity shock severely impairs the partial denitrification/anammox (PD/A) process, leading to prolonged functional deterioration and slow reactivation of anaerobic ammonium-oxidizing bacteria (anammox). To develop an effective strategy for mitigating salinity-induced inhibition, this study systematically examined the role of exogenous hydroxylamine (NH₂OH) in accelerating PD/A recovery using short-term batch assays and long-term reactor operation. Hydroxylamine exhibited a clear concentration-dependent effect on system reactivation. In batch tests, low-dose hydroxylamine (10 mg/L) markedly enhanced anammox activity, increasing the ammonium oxidation rate to 5.5 mg N/(g VSS·h), representing a 42.5% increase, indicating its potential to stimulate key nitrogen-transforming pathways following salinity stress. During continuous operation, hydroxylamine at 5 mg/L proved optimal for restoring reactor performance, achieving stable nitrogen removal with 87% NH₄⁺-N removal efficiency. The nitrite transformation ratio (NTR) reached approximately 80% within 13 cycles, 46 cycles ahead of the control, while simultaneously promoting the enrichment of key functional microbial taxa, including Thauera and Candidatus Brocadia. Hydroxylamine addition also triggered the production of tyrosine- and tryptophan-like proteins within extracellular polymeric substances, which enhanced protective and metabolic functionality during recovery. In contrast, a higher hydroxylamine dosage (10 mg/L) resulted in persistent NO₂⁻-N accumulation, substantial suppression of Candidatus Brocadia (declining from 0.67% to 0.09%), and impaired system stability, highlighting a dose-sensitive threshold between stimulation and inhibition. Overall, this study demonstrates that controlled low-level hydroxylamine supplementation can effectively reactivate salinity-inhibited PD/A systems by enhancing nitrogen conversion, reshaping functional microbial communities, and reinforcing stress-response mechanisms. These findings provide mechanistic insight and practical guidance for improving the resilience and engineering application of PD/A processes treating saline wastewater. Full article

Anammox is a promising approach for biological nitrogen removal, but the differences in microbial community structure across different systems and their response mechanisms to environmental factors remain unclear. In this study, 206 microbial samples and 2126 environmental factor data points from three different anammox systems, including the upflow anaerobic sludge blanket (UASB), integrated fixed-film activated sludge-partial nitritation/anammox (IFAS-PN/A), and integrated fixed-film activated sludge-simultaneous nitrification, anammox and denitrification (IFAS-SNAD), were analyzed using 16S rRNA sequencing analysis, bioinformatics, and machine learning (ML) techniques. The results revealed significant differences in microbial composition among three systems, evidenced by the enrichment of Candidatus_Brocadia in IFAS-PN/A, the high-diversity community in IFAS-SNAD, and the low-diversity communities dominated by Candidatus_Kuenenia in the UASB. Co-occurrence network analysis demonstrated more tightly connected and complex interactions in IFAS-SNAD networks. Machine learning predictions further showed that the stacked model (ST-RF) achieved the highest accuracy in predicting the nitrogen removal rate (NRR), with determination coefficients (R²) exceeding 0.987 across all testing datasets. Moreover, SHapley Additive exPlanations (SHAP) analysis based on the stacked model revealed that the influence of key environmental factors on NRR varied by system type. These results suggested that NRR of different systems depended on the control of key environmental factors, while the significance of these environmental factors was determined by the type of system. Overall, this study enhanced the ecological and functional understanding of anammox-based processes and provided a data-driven framework for optimizing mainstream nitrogen removal. Full article

In this study, the combined effects of influent carbon-to-nitrogen ratio (C/N = 0.8, 1.5, 2.5, 3.5, 4.5) and nitrate (NO₃⁻-N) concentration (40 and 80 mg/L, labeled as R₄₀ and R₈₀) on the partial denitrification (PD) performance were investigated using an intermittent sequencing batch reactor (SBR) process. With sodium acetate as an additional carbon source, the substrate variation, microbial diversity, and functional bacteria evolution were also explored to reveal the nitrite (NO₂⁻-N) accumulation mechanism at low temperatures (3–12 °C). The results showed that the 3.5-R₄₀ and 2.5-R₈₀ systems both presented the optimal NO₂⁻-N accumulation at a temperature of 10 °C, with the NO₂⁻-N transformation rate (NTR) of 66.89% and 76.79%, respectively. In addition, as the temperature reduced from 10 °C to 5 °C, the NO₂⁻-N accumulation performance was significantly suppressed, where the average effluent NO₂⁻-N of 3.5-R₄₀ (20.00 → 11.00 mg/L) and 2.5-R₈₀ (43.00 → 18.90 mg/L) systems reduced by nearly half. It is worth noting that there was almost no NO₂⁻-N accumulation at a C/N ratio of 0.8, although higher NO₃⁻-N concentration promoted NTR under the same C/N ratio. The high-throughput sequencing showed that the minimum Shannon value of 3.81 and the maximum Simpson value of 0.095 both occurred at a C/N ratio of 2.5, suggesting the downshifted microbial richness. Proteobacteria and Bacteroides increased significantly from 35.31% and 18.34% to 51.69–60.35% and 18.08–35.21%, as compared with the seeding sludge. Thauera and Flavobacterium as the main contributors to NO₂⁻-N accumulation accounted for 31.83% and 20.30% at the C/N ratio of 2.5 under a low temperature of 5 °C. The above discussion suggested that higher temperature (10 °C), lower C/N ratio (2.5–3.5), and higher NO₃⁻-N concentration (80 mg/L) were more favorable for the stable PD formation. Full article

In this study, the distribution patterns of the nitrifying and denitrifying microbiome in a large-scale biofilter (587.24 m³) in a cold freshwater recirculating aquaculture system (RAS) was investigated. Previous studies have revealed that the water quality, nitrification, and denitrification rates in the front (BFF), middle (BFM), and back (BFB) of this biofilter are different. The results showed the highest diversity of the denitrifying microbiome in the BFB, followed by BFF and BFM, whereas nitrifying microbiome diversity remained consistent across different positions. Two genera, Nitrosomonas and Nitrosospira, dominated the nitrifying microbiome, while Pseudomonas, Thauera, Cupriavidus, Dechloromonas, Azoarcus, and Paracoccus comprised the top six denitrifying genera. Principal coordinate analysis indicated a distinct spatial distribution pattern of the denitrifying microbiome but not the nitrifying microbiome. The genera Pseudomonas and Dechloromonas were the biomarkers of the BFF and BFB, respectively. Redundancy analysis showed that nitrite, nitrate, dissolved oxygen, and soluble reactive phosphorus influenced the functional microbiome distribution pattern. Network correlation analysis identified one nitrifying hub (Nitrosospira) in the BFF, five denitrifying hubs (Aromatoleum, Dechloromonas, Paracoccus, Ruegeria, and Thauera) in the BFM, and three denitrifying hubs (Azoarcus, Magnetospirillum, and Thauera) in the BFB. Exclusively negative correlations were found between hubs and its adjacent nodes in the BFF and BFB. This study demonstrates that habitat can shape the distribution patterns of the nitrifying and denitrifying microbiome in the biofilter of the RAS, with the BFF exhibiting greater benefits for the nitrification process. Full article

Increasing the discharge of saline wastewater from an industrial field poses a challenge for applicable Anammox-based technologies. This study established the integrated partial sulfur-driven denitrification and Anammox (SPDA) system to explore the effects of different salinity levels on nitrogen conversion features. The results of batch tests suggested that sulfur-driven denitrification exhibited progressive suppression of nitrate reduction (97.7% → 12.3% efficiency at 0% → 4% salinity) and significant nitrite accumulation (56.4% accumulation rate at 2% salinity). Anammox showed higher salinity tolerance but still experienced drastic TN removal decline (97.6% → 17.3% at 0% → 4% salinity). Long-term operation demonstrated that the SPDA process could be rapidly established at 0% salinity and stabilize with TN removal efficiencies of 98.1% (1% salinity), 72.8% (2% salinity), and 70.2% (4% salinity). The robustness of the system was attributed to the appropriate strategy of gradual salinity elevation, the promoted secretion of protein-dominated EPS, the salinity-responsive enrichment of Sulfurimonas (replacing Thiobacillus and Ferritrophicum) as sulfur-oxidizing bacteria (SOB), and the sustained retention and activity of Brocadia as AnAOB. The findings in this study deepen the understanding of the inhibitory effects of salinity on the SPDA system, providing a feasible solution for saline wastewater treatment with low cost and high efficiency. Full article

Although tropical ecosystems have become increasingly vulnerable to fire over the past century, the mechanisms by which fire disturbance influences N₂O emissions in these regions remain poorly understood. This study investigated the effects of fire on nitrous oxide (N₂O) emissions, the gross nitrification rate (GN), denitrification genes, and carbon (C) and nitrogen (N) fractions in a tropical forest. The results showed that fire increased the GN by 41.5%. The abundance of the nirK and nirS genes encoding nitrite reductase increased by 16.3% and 27.5%, respectively, while the abundance of the nosZI gene encoding N₂O reductase increased by 28%, suggesting a potentially enhanced denitrification capacity. This enhancement in nitrification and denitrification was mainly due to increased easily oxidizable organic C (EOC, +35%), light fraction organic C (LFOC, +32%), hydrolyzable ammonium N (HAN, +13%), and amino sugar N (ASN, +11%), which provided additional substrates for nitrification and denitrification. As a result, soil N₂O emissions increased by 18% in response to fire. Soil N₂O emissions showed a significant and positive linear correlation with GN, EOC, LFOC, HAN, nirK, nirS, and nosZI. Thus, the post-fire increase in N₂O emissions is likely driven by enhanced nitrification and denitrification processes, facilitated by the elevated availability of labile C and N fractions. Our findings provide new evidence for the role of soil C and N fractions in controlling N₂O emission and nitrification–denitrification under fire disturbances in tropical soils. Full article

With the rapid development of the global aquaculture industry, the issue of effluent pollution from aquaculture has become increasingly severe. Effective management of aquaculture effluent is an urgent requirement for the sustainable development of the aquaculture industry, with a key focus on the efficient removal of nitrogen. Heterotrophic bacteria assimilation technology offers advantages such as high efficiency and resource recovery; however, its application in effluent treatment remains limited. Therefore, this study aimed to identify the optimal carbon source for the heterotrophic bacteria assimilation process and to optimize its operating parameters using response surface methodology (RSM). The results revealed that the sucrose group achieved the highest total ammonia nitrogen (TAN) removal rate of 85.1%, significantly outperforming molasses (77.0%) and glucose (62.9%), with microbial biomass also significantly higher than in the other groups. Metagenomic analysis indicated that sucrose promotes the formation of efficient denitrifying microbial communities by enriching the phylum Bacteroidota and the denitrifying functional bacteria Xanthomarina, thereby significantly enhancing denitrification efficiency. The optimal carbon source was determined to be sucrose. Using the optimal parameters of microbial biomass at 1.7 g/L, a hydraulic retention time of 36 h, and a chemical oxygen demand-to-total nitrogen (COD/TN) ratio of 26, the removal rates of total nitrogen (TN), TAN, and nitrite nitrogen (NO₂⁻-N) exceeded 85%, while the removal rate of nitrate nitrogen (NO₃⁻-N) surpassed 60%. A significant interaction was observed between microbial biomass and hydraulic retention time, which notably affected denitrification efficiency (p < 0.05). This study provides theoretical support for the harmless and resourceful treatment of aquaculture effluent, contributing to the green and sustainable development of the aquaculture industry. Full article

The Anaerobic–Swing Aerobic–Anoxic–Oxic (ASAO) process was developed to tackle problems such as temperature sensitivity during the Anaerobic–Oxic–Anoxic (AOA) process. By introducing a swing zone (S zone) with adjustable dissolved oxygen (DO), during the 112-day experimentation period, the ASAO system achieved removal rates of 88.18% for total inorganic nitrogen (TIN), 78.23% for total phosphorus (TP), and 99.78% for ammonia nitrogen. Intermittent aeration effectively suppressed nitrite-oxidizing bacteria (NOB), and the chemical oxygen demand (COD) removal rate exceeded 90%, with 60% being transformed into internal carbon sources like polyhydroxyalkanoates (PHAs) and glycogen (Gly). The key functional microorganisms encompassed Dechloromonas (denitrifying phosphorus-accumulating bacteria), Candidatus Competibacter, and Thauera, which facilitated simultaneous nitrification–denitrification (SND) and anaerobic ammonium oxidation (ANAMMOX). The enrichment of Candidatus Brocadia further enhanced the ANAMMOX activity. The flexibility of DO control in the swing zone optimized microbial activity and mitigated temperature dependence, thereby verifying the efficacy of the ASAO process in enhancing the removal rates of nutrients and COD in low-C/N wastewater. The intermittent aeration strategy and the continuous low-dissolved-oxygen (DO) operating conditions inhibited the activity of nitrite-oxidizing bacteria (NOB) and accomplished the elimination of NOB. Full article