Anaerobic Ammonium Research Articles

Combining Electrochemical Nitrate Reduction and Anammox for Treatment of Wastewater With Low C/N Ratio Nitrate

ABSTRACTThe treatment of high concentration and low C/N ratio of nitrate wastewater is a promising and challenging research topic. Combining electrochemical reduction and anammox is a technology with great development potential for nitrogen removal from wastewater. In this work, Cu─Ag─Co cathode materials were prepared by two‐step electrodeposition method. The effect of current density and initial pH value on nitrate reduction efficiency was investigated in a single chamber electrolytic cell equipped with Cu─Ag─Co cathode and Ti/RuO2─IrO2 anode. The results showed that under the conditions of initial NO3−─N concentration of 500 mg L−1, Na2SO4 concentration of 0.125 mol L−1, current density of 10 mA cm−2, initial pH value of 7, and treatment time of 5 h, NO3−─N removal ratio was 84.5%, the concentration of NO2−─N and NH4+─N was 180.2 mg L−1 and 173.2 mg L−1. Wastewater with a concentration ratio of NO2−─N and NH4+─N of 1.04:1 meets the influent requirements for anaerobic ammonia oxidation. Through the combination process, the final NO3−─N removal ratio was 82.6%, the NO2−─N concentration was 3.2 mg L−1, and the NH4+─N concentration was 26.4 mg L−1. It provided a reference for the treatment of wastewater with low C/N ratio nitrate by combining electrochemical reduction and anammox.

Impact of low temperature on bacterial community dynamics and process efficiency in anaerobic ammonia removal: A network analysis of metagenomic data

The implementation of anaerobic ammonia removal has potential for reducing the operating costs in wastewater treatment plants. However, the application of this process in mainstream treatment presents various challenges, particularly due to the sensitivity of anammox bacteria to low temperatures. To address these challenges, changes in the bacterial community were investigated under decreasing temperatures (from 30 to 12 °C) within a deammonification process conducted in a 10-L sequencing batch reactor (SBR) over a period of 114 days. The aim of the study was to determine which groups of microorganisms are most strongly linked by ecological relationships with anammox bacteria and how these relationships change in response to decreasing temperature. Community dynamics were analyzed by combining metagenomics, network analysis, and specific process rates. The nitrification process was most efficient at 25 °C, as indicated by high values of the ammonia and nitrite utilization rate, and nitrate production rate, all of which declined as the temperature decreased. In contrast, the activity and abundance of anammox bacteria remained stable throughout all phases of the experiment. The decreasing temperature negatively impacted Nitrospira bacteria, the main competitors of anammox in the deammonification system. Despite the reduced process efficiency, the SBR maintained stable functionality even at temperatures as low as 12 °C. Network analysis identified which bacterial groups most frequently co-occurred and interacted, as well as those most sensitive to temperature fluctuations. Among the bacterial nodes, Nitrospira, Phycisphaerae, and Prosthecobacter exhibited the highest degree of connectivity, suggesting that they participate in multiple interactions, such as metabolite exchange, cooperation, or competition. Nevertheless, the temperature node had a greater number of connections than any bacterial node, indicating that this environmental factor had a more important effect on microbial community formation than direct ecological relationships. These results contribute to a comprehensive understanding of the role of anammox bacteria in deammonification systems, their ecological interactions within microbial networks, and their activity under suboptimal temperature conditions, which is crucial for future practical applications.

Full-scale performance and microbial community evolution using dopamine modified ceramic membrane submerged membrane biological reactor in treating young landfill leachate

In this project, ceramic membrane submerged membrane biological reactor (SMBR) was integrated to dissolved air flotation (DAF)-up-flow anaerobic sludge blanket (UASB)-anoxic and aerobic (A/O) system in treating young landfill leachate with a capacity of 300 m3 /day over 185 days’ operation. High removal efficiencies of chemical oxygen demand (COD) (96.8 %), ammonia nitrogen (83.4 %) and total nitrogen (79.6 %) were achieved via DAF-UASB -A/O system. The membrane permeate COD was below 356 mg/L. The permeate turbidity was stable below 11 NTU, met the condition for further ultrafiltration treatment. The SMBR system was operated stability at the flux of 26 LMH because of excellent surface hydrophilicity of the dopamine modified ceramic membrane. Remarkably, immersed chemical cleaning can recover the filterability entirely, indicating the dopamine modified ceramic membrane SMBR can be recognized as fouling–free MBRs. The foulants removal after chemical cleaning on the ceramic membrane was detailly analyzed by scanning electron microscopy coupled with energy dispersive X-ray. The comparative microbial analysis between sludge Day-1 and Day-185 revealed that significant changes of microbial community occurred. Regarding the nitrifying and denitrifying bacteria, Thauera was identified as potential functional specie in simultaneous methanogensis and denitrification process in the UASB reactor. High populations of Proteobacteria, Planctomycetes, Bacteroidetes and Chloroflexi contributed the nitrification and denitrification in the A/O system. The anaerobic ammonia oxidation process might happen due to the identified Planctomycetes. At the genus level, genera, such as Thauera, Phycisphaerae and Betaproteobacteria, with high abundances were functional species ensuring the nitrogen removal in the A/O environment.

Stimulating Acidimicrobium sp. Strain A6 in iron-rich, acidic sediments from AFFF-impacted sites for PFAS defluorination

Per- and polyfluoroalkyl substances (PFAS) are persistent and bioaccumulative contaminants that are widely used in industrial applications and consumer products and pose significant risks to ecosystems and human health. Acidimicrobium sp. Strain A6 (A6), which is common in acidic, and iron rich soils and sediments is capable of both anaerobic ammonium (NH4+) oxidation under iron reduction (Feammox) and defluorination of perfluorinated alkyl substances, such as perfluoroalkyl acids (PFAAs). This study investigates the potential for biostimulating A6 via the supply of NH4+ and ferric iron (Fe(III)) with the goal of defluorinating PFAAs. Sediment samples from acidic, iron-rich, AFFF (aqueous film forming foam) impacted sites were collected and incubated with added Fe(III) and NH4+. Quantitative PCR was used to track A6 numbers as well as dehalogenase and F− ion transporter genes during these incubations; changes in the microbial community structure were tracked through 16S rRNA gene sequencing. The findings reveal that the addition of Fe(III) and NH4+ stimulated the Feammox reaction and A6 growth and enhanced the degradation of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS). Results also show a significant presence and activity of the above-mentioned genes in these incubations. The insights gained from this study could inform bioremediation strategies for PFAS-contaminated environments, especially in geochemical settings that favor the presence of A6.

Functional Genes and Metabolic Pathways of Nitrogen Metabolism Microorganisms in Lake Sediments：A Case Study of Hongfeng Lake, Guizhou Province

The nitrogen cycle is of great importance for material circulation and energy flow in lake ecosystems. It is driven by microorganisms in lake sediments and can contribute to balancing lake ecosystems. In this study, physical and chemical properties of the sediments sampled from Hongfeng Lake in Guizhou Province were assayed and analyzed using metagenomics to reveal relevant microorganisms, functional genes, metabolic pathways, and their relationships throughout nitrogen metabolism. The results showed that bacteria were dominant, and the top three relative abundant genera were Thiobacillus （16.64%）, Rubrivivax（9.43%）, and Nitrospira （7.09%）. Only six pathways, including nitrogen fixation, nitrification, denitrification, assimilatory nitrate reduction, dissimilatory nitrate reduction, and complete nitrification, were detected in total, of which denitrification and dissimilatory nitrate reduction were the primary processes, but anaerobic ammonia oxidation was not detected. Bacteria and archaea participated in these six pathways, while eukaryotes only functioned in dissimilatory nitrate reduction, denitrification, and complete nitrification. Ammonia nitrogen, nitrate nitrogen, and total phosphorus, as main environmental factors affecting the distribution of functional genes for nitrogen metabolism, differentiated with each other in their respective real-world conditions. A positive correlation （95.04%） was observed between the functional genes and microorganisms, and narG, narZ, and nxrA possessed the highest abundance and the highest host genes. On this basis, these findings are expected to further elucidate the nitrogen cycle of typical karst lakes in Guizhou Province.

Macrogenomic analysis of tolerance and degradation mechanisms of polycyclic aromatic hydrocarbon in carbon and nitrogen metabolic pathways and associated bacterial communities during endogenous partial denitrification

The effective production of NO2−-N through endogenous partial denitrification (EPD) provides a promising perspective for the broader adoption and application of anaerobic ammonia oxidation. However, the accumulation of polycyclic aromatic hydrocarbons (PAHs) in the environment may worsen the operational challenges of the EPD system. This study evaluated the resilience of the EPD system to the toxic impacts of phenanthrene (PHE) and anthracene (ANT) through macrogenomic analysis. A control group was maintained under identical conditions for comparison. The results revealed that PHE and ANT had a relatively minimal impact on NO3−-N transformation and organic matter removal but significantly affected PO43−-P removal and NO2−-N accumulation in the EPD process. The PHE system achieved a higher NO2−-N accumulation, with a maximum NO3−-N to NO2−-N conversion ratio of 90.08%. In contrast, the ANT system exhibited higher efficiency in the PO43−-P removal, achieving a peak removal rate of 74.94%. Macrogenomic analysis revealed that PAHs significantly enriched both denitrifying glycogen-accumulating organisms (including Candidatus_Competibacter) and denitrifying polyphosphate-accumulating organisms (such as Thauera, Candidatus_Contendobacter, and Candidatus_Accumulibacter). This enrichment stabilized these organisms, facilitating NO2−-N accumulation and PO43−-P removal. Metabolic pathway analysis indicated that PHE promoted the enrichment of NO3−-N reductase and inhibited NO2−-N reductase activity. However, ANT stimulated oxidative phosphorylation and the phosphate cycle. Moreover, PAH metabolites enhanced the expression of key genes encoding succinate dehydrogenase and isocitrate dehydrogenase in the tricarboxylic acid cycle within the EPD process, leading to increase the synthesis and utilization of acetyl coenzyme-A. Notably, significant differences were observed between the effects of PHE and ANT on these metabolic processes. This study provides new methods for treating PAH-containing wastewater through the combination of EPD and anaerobic ammonia oxidation.

Eco-environmental responses of Eichhornia crassipes rhizobacteria community to co-stress of per(poly)fluoroalkyl substances and microplastics

The stabilization of rhizobacteria communities plays a crucial role in sustaining healthy macrophyte growth. In light of increasing evidence of combined pollution from microplastics (MPs) and per- and polyfluoroalkyl substances (PFASs), Selecting typical floating macrophyte as a case, this study explored their impacts using hydroponic simulations and 16S rRNA high-throughput sequencing. A total of 31 phyla, 77 classes, 172 orders, 237 families, 332 genera, and 125 rhizobacteria species were identified. Proteobacteria (16.19% to 57.70%) was the dominant phylum, followed by Bacteroidota (12.34% to 44.48%) and Firmicutes (11.31% to 36.36%). In terms of α-diversity, polystyrene (PS) MPs and PFASs significantly impacted community abundance (ACE and PD-tree) rather than evenness (Shannon and Pielou) compared to the control. βMNTD and βNTI analyses revealed that PS MPs enhanced deterministic assembly processes driven by F-53B and GenX, while mitigating those induced by PFOA and PFOS. Contamination treatments narrowed the ecological niche breadths at both the phylum (5% (PS) to 49.91% (PS & PFOA)) and genus levels (8% (PS) to 63.96% (PS & PFOA)). Functionally, MPs and PFASs decreased the anaerobic capacity and ammonia nitrogen utilization of rhizosphere bacteria. This study enhances our understanding of the microecological responses of macrophyte-associated bacteria to combined MP and PFAS contamination and offers insights into ecological restoration strategies and mitigating associated environmental risks.

Polystyrene nanoparticles regulate microbial stress response and cold adaptation in mainstream anammox process at low temperature

Nanoplastic pollution has become one of the most pressing environmental issues, and its bioaccumulation in aquatic environment also causes a great difficulty in treatment. Therefore, this work investigated the microbial dynamics of mainstream anaerobic ammonia oxidizing (anammox) process to treat the wastewater containing typical nanoplastics, as well as the fate and regulation mechanism of polystyrene nanoparticles (PS-NPs) with different concentrations. The results showed that 0.1–0.5 mg L-1 of PS-NPs had no significant effect on the nitrogen removal efficiency (NRE). When the concentration of PS-NPs increased from 0.5 mg L-1 to 2 mg L-1, the NRE of R1 with PS-NPs decreased from 94.9 ± 2.3 % to 77.0 ± 1.6 %, while the control reactor R0 maintained a stable NRE. Notably, the relative abundance of Ca. Kuenenia decreased from 17.4 % to 14.8 %, and that of Ca. Brocadia slightly decreased from 5.9 % to 5.0 % in R1. In addition, PS-NPs induced oxidative stress in anammox consortia, leading to the significant increase in reactive oxygen species (ROS) and lactate dehydrogenase (LDH) as well as cell membrane damage. PS-NPs also downregulated the content of heme c and further inhibited anammox activity. Based on the molecular docking simulation and western blotting, cold shock proteins (CSPs) could bind to PS-NPs and reduce the performance of anammox processes at low temperatures.

Novel Anoxic-Anaerobic-Oxic process successfully enriched anammox bacteria under actual municipal wastewater

Anaerobic ammonia oxidation (Anammox) exhibits promise for wastewater treatment,but the enrichment of anammox bacteria (AnAOB) in municipal wastewater treatment plants is a significant challenge. This study constructed a novel Anoxic-Anaerobic-Oxic (AAnO) process with a pure biofilm anoxic zone fed with actual fluctuating municipal wastewater and operated for six months to enrich AnAOB at ambient temperature. High-throughput sequencing (HTS), qPCR, and fluorescence in situ hybridization showed that AnAOB were successfully enriched in the anoxic biofilms, reaching 1.56 % relative abundance on day 75 detected by HTS. During the period from day 130 to day 186, the anammox process contributed to 55.8 ± 19.2 % of the nitrogen removal in the anoxic zone. Phylogenetic analysis revealed this AnAOB species was closely related to Candidatus Brocadia fulgida. This study provides technical support for the application of anammox in mainstream wastewater.

Synergy between Nitrogen Removal and Fermentation Bacteria Ensured Efficient Nitrogen Removal of a Mainstream Anammox System at Low Temperatures.

Simultaneous partial nitrification, anammox, denitrification, and fermentation (SNADF) is a novel process achieving simultaneous advanced sludge reduction and nitrogen removal. The influence of low temperatures on the SNADF reactor was explored to facilitate the application of mainstream anammox. When temperature decreased from 32 to 16 °C, efficient nitrogen removal was achieved, with a nitrogen removal efficiency of 81.9-94.9%. Microbial community structure analysis indicated that the abundance of Candidatus Brocadia (dominant anaerobic ammonia oxidizing bacteria (AnAOB) in the system) increased from 0.03% to 0.18%. The abundances of Nitrospira and Nitrosomonas increased from 1.6% and 0.16% to 2.5% and 1.63%, respectively, resulting in an increase in the ammonia-oxidizing bacteria (AOB) to nitrite-oxidizing bacteria (NOB) abundance ratio from 0.1 to 0.64. This ensured sufficient nitrite for AnAOB, promoting nitrogen removal. In addition, Candidatus Competibacter, which plays a role in partial denitrification, was the dominant denitrification bacteria (DNB) and provided more nitrite for AnAOB, facilitating AnAOB enrichment. Based on the findings from microbial correlation network analysis, Nitrosomonas (AOB), Thauera, and Haliangium (DNB), and A4b and Saprospiraceae (fermentation bacteria), were center nodes in the networks and therefore essential for the stability of the SNADF system. Moreover, fermentation bacteria, DNB, and AOB had close connections in substrate cooperation and resistance to adverse environments; therefore, they also played important roles in maintaining stable nitrogen removal at low temperatures. This study provided new suggestions for mainstream anammox application.

Scavenging of reactive oxygen species in Candidatus Brocadia fulgida through nanocompartments

The antioxidant defense mechanisms for anaerobic ammonia oxidation (anammox) bacteria are still unclear. In this study, the potential antioxidant ability of nanocompartments in Candidatus Brocadia fulgida to typical reactive oxygen species (ROS) was investigated. The results showed that the copies of genes involved in anammox central metabolism were inhibited with hydrogen peroxide (H2O2), while the genes encoded putative anti-oxidative protein (nanocompartments and cargo HAO) up-regulated. The genetically engineered bacteria grew better and maintained the lower ROS levels (65.60 %-78.07 %) and higher electron transport activities (∼5–21 times) than the wild bacteria under H2O2 stimulus. Molecular docking confirmed that nanocompartment proteins could provide diverse sites to bind with H2O2 based on heme as the redox center. Additionally, the nanocompartments induced up-regulation of multiple protective pathways for coping with oxidative stress from H2O2, including antioxidant enzymes and other non-enzymatic pathways. Thus, the heme-containing nanocompartments presented great potential in preventing and relieving oxidative stress.

Crucial role of extracellular polymeric substances from anammox sludge in wastewater phosphorus recovery via magnesium phosphate crystallization

The magnesium phosphate (Mg-P) crystallization based on anaerobic ammonia oxidation is of interest for simultaneous nitrogen and phosphorus removal in wastewater treatment due to cost-effectiveness. Understanding the role of extracellular polymeric substances (EPS) in crystal growth is pivotal for bio-induced Mg-P crystallization. In this work, the effects of EPS in Mg-P crystallization were thoroughly investigated. Results indicated that EPS decreased the initial crystallization rate but slightly improved the final crystallization yield. The maximum removal efficiencies of Mg and P ions increased by 2.8 % and 3.1 %, respectively, when EPS concentration was 80 mg/L. Additionally, the presence of EPS enhanced Mg3(PO4)2·10 H2O production and facilitated the formation of larger rhombic plate-like structures crystals (maximum particle size increased by 215 %). Analysis of EPS composition changes during the crystallization process and characterization of the final crystals suggested that tryptophan-like proteins preferentially involved in the Mg-P crystallization process, while β-sheet proteins potentially influencing crystal morphology. Furthermore, the formation of phosphate ester groups, hydrogen bonding, and COOH-Mg2+ complexes were considered triggering factors for the interaction between EPS and Mg-P crystals. This study elucidated the underlying mechanism of EPS on Mg-P crystallization, further enhancing the understanding of the interaction between inorganic mineralization processes and microorganisms.

Effect of elemental sulfur on anaerobic ammonia oxidation: Performance and mechanism

Biological nitrogen removal processes provide effective means to mitigate nitrogen-related issues in wastewater treatment. Previous studies have highlighted the collaborative efficiency between sulfur autotrophic denitrification and Anammox processes. However, the trigger point induced the combination of nitrogen and sulfur metabolism is unclear. In this study, elemental sulfur (S0) was introduced to Anammox system to figure out the performance and mechanism of S0-mediated autotrophic denitrification and Anammox (S0SAD-A) systems. The results showed that the nitrogen removal performance of the Anammox reactor decreased with the increasing concentrations of NH4+-N and NO2−-N in influent, denitrification occurred when NH4+-N concentration reached 100 mg/L. At stage ⅳ (150 mg/L NH4+-N), the total nitrogen removal efficiency in S0SAD-A system (95.99%) was significantly higher than that in the Anammox system (77.22%). Throughout a hydraulic retention time, the consumption rate of NH4+-N in S0SAD-A was faster than that in Anammox reactor. And there existed a nitrate-concentration peak in S0SAD-A system. Metagenomic sequencing was performed to reveal functional microbes as well as key genes involved in sulfur and nitrogen metabolism. The results showed that the introduction of S0 elevated the abundance of Ca. Brocadia. Moreover, the relative abundance of Anammox genes, such as hao, hzsA and hzsC were also stimulated by sulfur. Notably, unclassified members in Rhodocyclaceae acted as the primary contributor to key genes involved in the sulfur metabolism. Overall, the interactions between Anammox and denitrification were stimulated by sulfur metabolism. Our study shed light on the potential significance of Rhodocyclaceae members in the S0SAD-A process and disclosed the relationship between anammox and denitrification.

Adaptation of the anammox process for high ammonium photovoltaic wastewater treatment

Tunnel Oxide Passivating Contacts (TOPcon) battery in the photovoltaic industry generates high ammonium wastewater during the production process, the adaptability of using the anaerobic ammonia oxidation (Anammox) process for photovoltaic wastewater (PVW) treatment is a research hotspot. Based on the analysis of photovoltaic wastewater quality, the effectiveness of nitrogen removal, sludge characteristics and microbial communities were examined. The results showed that when the influent NH4+-N concentration of PVW was lower than 150 mg·L−1, the nitrogen removal efficiency (NRE) was almost 100 %. In addition, the NRE decreased from 74 % sharply to 20 % when the NH4+-N concentration was increased from 175 mg·L−1 to 200 mg·L−1. The extracellular polymeric substances (EPS) content increased with elevated ammonium concentration in the influent, indicating that microorganisms secreted more EPS to resist elevated nitrogen loading. The main functional populations were Candidatus Kuenenia (0–24 %). The influent ammonium concentration is recommended to be < 200 mg·L−1.

Fe(II)-mediated Fe–N–P metabolism in an anammox-dominated system for enhanced nitrogen removal and Fe–P crystals (FePs) production

Low-carbon and high-efficiency processes for achieving simultaneous nitrogen removal and phosphorus recovery from wastewater are gaining increasing attention from researchers. This study investigated the performance and mechanism of a novel Fe(II)-mediated anaerobic ammonia oxidation (anammox) process characterized by stable nitrogen removal and production of high-value Fe–P crystals (FePs) as byproducts. Fe(II) promotes the synthesis of heme C and enhances the activity of nitrate reduction metabolic genes, which induce nitrate-dependent ferrous oxidation to form a complex Fe–N cycle. In addition, Fe(II) significantly enhanced the phosphorus removal efficiency up to 79.2 ± 6.9% by inducing Fe–P biomineralization. Biomolecular analysis has shown that most iron absorption and transport genes, as well as phosphate transport and regulation genes, are promoted by Fe(II). The composition and microstructure analyses of the anammox granules revealed the formation of FePs that consisted of phosphosiderite (FePO4·2H2O), ludlamite (Fe3(PO4)2·4H2O), and vivianite (Fe3(PO4)2∙8H2O). This study also provides an in-depth illustration of the structural characteristics and formation processes of anammox-FePs granules. Thus, an Fe(II)-induced Fe–N–P metabolic network in an anammox-dominated system was uncovered, offering a feasible approach for simultaneous nitrogen removal and phosphorus recovery.

Gel beads prepared by polyvinyl alcohol cross-linking with phytic acid and Fe as novel microbial carriers for simultaneous partial nitrification, anammox and denitrification

Enhancing the stability of biomass and ensuring a stable activity of anaerobic ammonia oxidizing bacteria are crucial for successful operation of the simultaneous partial nitrification, Anammox, and denitrification (SNAD) process. In this study, gel beads of polyvinyl alcohol/phytic acid (PVA/PA) and polyvinyl alcohol/phytic acid/Fe (PVA/PA/Fe) were prepared as innovative bio-carriers. Theoretical simulations and analyses revealed that these carriers are predominantly connected via hydrogen and borate bonds, with PVA/PA/Fe also featuring metal coordination bonds. The total nitrogen removal efficiency of reactors with PVA/PA/Fe and PVA/PA increased by 13.5 % and 9.0 %, respectively, compared to reactor without carriers. The iron-enriched PVA/PA/Fe carriers significantly improve SNAD by promoting Anammox, Feammox, and nitrate-dependent Fe2+ oxidation reactions, leading to faster nitrogen conversion and higher nitrogen removal rate than reactor without carriers and with PVA/PA. Using of PVA/PA and PVA/PA/Fe gel beads as bio-carriers offers benefits to the SNAD process, including cost-effective and low carbon requirement.

Performances and mechanisms of anaerobic nitrogen removal through Fe (III)/Fe (II) cycle with sponge iron biofilm without external iron addition

Anaerobic ammonia oxidation coupled to Fe (III) reduction (Feammox) plays an important role in the natural nitrogen cycle. However, for its application in wastewater treatment process, the source of iron is a major limitation. In this study, Feammox process was successfully achieved without external iron addition using sponge iron biofilm. The products of Feammox process, nitrate and Fe (II), provided substrates for nitrate dependent ferrous oxidation (NDFO). Therefore, nitrogen removal and Fe (II)/Fe (III) cycle were achieved in reactor and nitrogen removal efficiency by Feammox and NDFO pathways was up to 58.4 %. The X-ray diffraction indicated the sludge contained magnetite and lepidocrocite, which provided Fe (III) for the occurrence of Feammox. Microorganisms related to Feammox process were dominated by Geothrix. It was found Feammox activity was similar at pH of 8 and 7, while inhibited at pH of 6, which was caused by the decrease of Feammox bacteria. And Feammox activity decreased with the decrease of temperature, in which the ammonia removal rate was 2 times faster at 30 °C than at 10 °C. Under micro‑oxygen aeration, the ammonia removal rate improved and Feammox and NDFO processes still played roles in system, nevertheless, under high dissolved oxygen condition, Feammox bacteria-Geothrix and NDFO bacteria Thiobacillus would be gradually eliminated from the system.

Strengthening the enrichment of anaerobic ammonia oxidizing bacteria in biofilms through sludge concentration control

Controlling sludge concentration is an effective means to achieve PN. In this article, the reactor used domestic sewage as raw water and promoted the high enrichment of anammox bacteria by controlling the MLVSS of flocs to 1000–1500 mg/L and increasing the concentration of filler sludge. The measures to reduce the concentration of flocculent sludge increased the proliferation rate of the biofilm and provided sufficient substrate for AnAOB. After 102 days of operation, the abundance of Candidatus Brocadia increased from 0.43% during inoculation to 23.56% in phase VI. The ability of the microbial community to utilize energy metabolism and produce ATP was significantly improved, and the appropriate distribution of anammox bacteria and nitrifying, denitrifying bacteria in the ecological niche led to its high enrichment. In summary, this study proposes a strategy to promote the high enrichment of anammox bacteria in mainstream domestic sewage without adding any chemicals.

Transformation and drive mechanism of nitrogen functional genes at estuaries in dry and wet seasons

The nitrogen cycle plays a vital role in maintaining ecological health and biodiversity. In aquatic systems, nitrogen transformation genes significantly contribute to biological nitrogen cycling. Although the function of these genes is known to be influenced by environmental factors, there is limited research exploring the relationship between nitrogen transformation genes and environmental factors. Therefore, the correlations, between nitrogen transformation genes and environmental factors, were investigated at the estuaries of Chaohu lake (China) in different seasons. The results showed that the values of temperature, pH, organic compounds, nitrogen, and dissolved oxygen were higher in dry season, whereas the abundance of the genes was lower in dry season. In addition, the abundance of the anaerobic ammoxidation gene was much lower than the nitrification gene and denitrification gene. The results indicated that biological nitrification and denitrification were the primary mechanisms for nitrogen removal at estuaries in different seasons, and the reduction of nitric oxide may be a limiting step in the denitrification process. The Co-occurrence Network and Mantel test indicated that, during the dry season, the temperature was the primary driver of ammonification and nitrification functions, the NO3− and NO2− were the primary drivers of denitrification, and the total nitrogen (TN) and NH4+ were the main drivers of anaerobic ammonia oxidation. During the wet season, the dissolved oxygen was the primary driver of ammonification and nitrification functions, the chemical oxygen demand was the primary driver of denitrification, and the TN was the main driver of anaerobic ammonia oxidation. This study provides valuable insights into nitrogen cycling in surface water, contributing to a better understanding of this important process.

Deciphering the anammox microbial community succession with humic acid exposure to optimize large anammox granules for robust nitrogen removal

The robustness of the anaerobic ammonia oxidation (anammox) process in treating wastewater with high concentrations of humic acids (HAs), including landfill leachate and sludge anaerobic digestion liquid, has been paid great attention. This study revealed that the anammox sludge granule size of 1.0–2.0 mm could be robust under the HA exposure with high concentrations. The total nitrogen removal efficiency (NRE) was 96.2% at the HA concentration of 20–100 mg/L, while the NRE was 88.5% at the HA concentration of 500 mg/L, with reduced by 7.7%. The increased extracellular polymeric substances (EPS) content which was stimulated by the HA exposure favored the formation of large granules (1.0–2.0 mm) by enveloping medium and micro granules (0.2–1.0 mm). The abundance of anammox bacteria Candidatus Brocadia was found to be higher (14.2%) in large anammox granules sized 1.0–2.0 mm, suggesting a potentially high anammox activity. However, the abundance of denitrifiers Denitratisoma increased by 4.3% in ultra-large anammox granules sized >2.0 mm, which could be attributed to the high EPS content for heterotrophic denitrifiers metabolism as organic matter. The feedback mechanism of the anammox community for maintaining the ecological function under the HA exposure resulted in a closely related microbial community, with positive and negative correlations in the ecological network increased by 64.3%. This study revealed that the HA exposure of the anammox system resulted in the anammox granules of 1.0–2.0 mm size being the dominant granules with robust nitrogen removal, providing significant guidance for the optimization of anammox granules for an efficient treatment of HA-containing wastewater in anammox applications.