Search Results (91)

Ammonia-oxidizing bacteria (AOB) are key to the nitrogen cycle, but their resistance to nitrite (NO₂⁻-N) accumulation is unclear. This study examined N.eA1, an AOB from the completely autotrophic nitrogen removal over nitrite (CANON) process, assessing its adaptive responses to NO₂⁻-N. The ammonia oxidation and N₂O emission were evaluated at varying NO₂⁻-N levels, and 3D fluorescence, extracellular polymeric substances (EPS), and soluble microbial products (SMP) analysis were used to probe stress responses. Cellular respiration and key enzyme activities were measured, and proteomics was applied to study protein expression changes. Results showed that higher NO₂⁻-N levels boosted N₂O production, inhibited nitrification, and stimulated denitrification in N.eA1. At 100 mg·L⁻¹ NO₂⁻-N, EPS rose and SMP fell, with ammonia monooxygenase (AMO) suppressed and nitrite reductase (NIR) as well as nitric oxide reductase (NOR) enhanced. Gene expression analysis revealed decreased AMO, hydroxylamine oxidoreductase (HAO), and energy transport-related enzymes, but increased NIR and NOR genes. The downregulation of electron transport complex genes offered insights into molecular adaptation to nitrite stress of N.eA1, highlighting the interplay between metabolic and genetic responses, which is essential for developing sustainable and efficient nitrogen management strategies. Full article

With increasing wastewater treatment demands and decarbonization goals, synergistic reduction in pollutants and green house gas (GHG) emissions is crucial. High process emissions like N₂O pose significant challenges, yet optimized carbon reduction strategies for conventional plants are lacking. This study developed three mathematical models to quantify the impact of dissolved oxygen (DO), influent salinity, and C/N ratio on direct emissions (CH₄, N₂O) and indirect emissions. Response Surface Methodology (RSM) optimized these factors to minimize GHG emissions under three accounting scenarios: (1) plants with CH₄ reuse systems: salinity = 0.5 g L⁻¹, DO = 3.67 mg L⁻¹, C/N = 12.75; (2) plants focusing solely on direct emissions: salinity = 0.5 g L⁻¹, DO = 3.35 mg L⁻¹, C/N = 3; and (3) plants assessing total emissions: salinity = 0.5 g L⁻¹, DO = 2.5 mg L⁻¹, C/N = 7.18. Key findings indicated that increasing salinity exacerbated greenhouse gas emissions. Elevated DO levels in the aerobic stage reduced N₂O emissions but increased indirect emissions in the A²/O process. Higher C/N ratios promoted anaerobic CH₄ production, but sufficient carbon reduced N₂O by enabling complete heterotrophic denitrification. A 60−day continuous GHG emissions monitoring campaign was conducted at a WWTP to validate the actual emission reductions achievable under the identified optimal control conditions. An analysis and comparison of operational and economic costs were also performed. The findings provide practical insights into sustainable GHG emission management and offer potential solutions to advance the synergistic reduction in GHG emissions and pollutants. Full article

Nitrous oxide (N₂O) emissions from paddy soils significantly contribute to global warming; however, the regulatory mechanisms of microbial denitrification remain poorly understood. This study investigated the biotic and abiotic drivers of N₂O production and reduction across seven paddy soils spanning China’s major rice-growing regions, using integrated qPCR, incubation experiments, and multivariate analyses. Results demonstrated niche partitioning among denitrifying microorganisms. Pearson correlation analysis demonstrated significant positive correlations between potential N₂O production rates and the abundances of denitrification genes (nirS, nirK, and fungal nirK), as well as between N₂O reduction rates and nosZ gene abundances (both clade I and II). Key soil chemical properties, including pH, total carbon (TC), and NH₄⁺-N content, showed significant relationships with both potential N₂O production rates and reduction rates. Furthermore, random forest analysis identified nirS, fungal nirK, TC, and pH as key predictors of N₂O production, while nosZ (clade I and II), TC, and pH governed N₂O reduction. Structural equation modeling revealed that nirS-type bacteria predominantly drove N₂O production, whereas nosZ II-encoded microorganisms primarily mediated N₂O reduction. Moreover, TC exhibited direct positive effects on both processes, while pH indirectly influenced N₂O production by regulating nirS abundance and affected reduction via nosZ Ⅱ modulation. These findings provide a mechanistic framework for mitigating agricultural denitrification-derived N₂O emissions through a targeted management of soil carbon and pH conditions to optimize complete denitrification. Full article

To date, the nitrogen metabolism pathways and salt-tolerance mechanisms of halophilic denitrifying bacteria have not been fully studied, and full-scale engineering trials with saline fly ash-washing wastewater have not been reported. In this study, we isolated and screened a halophilic denitrifying bacterium (Marinobacter sp.), GH-1, analyzed its nitrogen metabolism pathways and salt-tolerance mechanisms using whole-genome data, and explored its nitrogen removal characteristics under both aerobic and anaerobic conditions at different salinity levels. GH-1 was then applied in a full-scale engineering project to treat saline fly ash-washing leachate. The main results were as follows: (1) Based on the integration of whole-genome data, it is preliminarily hypothesized that the strain possesses complete nitrogen metabolism pathways, including denitrification, a dissimilatory nitrate reduction to ammonium (DNRA), and ammonium assimilation, as well as the following three synergistic strategies through which to counter hyperosmotic stress: inorganic ion homeostasis, organic osmolyte accumulation, and structural adaptations. (2) The strain demonstrated effective nitrogen removal under aerobic, anaerobic, and saline conditions (3–9%). (3) When applied in a full-scale engineering system treating saline fly ash-washing wastewater, it improved nitrate nitrogen (NO₃⁻-N), total nitrogen (TN), and chemical oxygen demand (COD) removal efficiencies by 31.92%, 25.19%, and 31.8%, respectively. The proportion of Marinobacter sp. increased from 0.73% to 3.41% (aerobic stage) and 2.86% (anoxic stage). Overall, halophilic denitrifying bacterium GH-1 can significantly enhance the nitrogen removal efficiency of saline wastewater systems, providing crucial guidance for biological nitrogen removal treatment. Full article

The nitrogen cycle is the key to the healthy operation of river ecosystems and plays an important role in maintaining the ecological balance, purifying water quality, and promoting the circulation of material. The Xisha River was chosen as the research object to analyze the water quality condition from 2021 to 2023, and the microbial diversity of nitrogen metabolism, functional genes, and metabolic pathways in the water body were analyzed using macro-genomics technology. The results showed that total nitrogen (TN) was the main exceedance factor in the water body, and ammonia nitrogen (NH₃-N), TN, and total phosphorus (TP) were the key factors affecting the water quality. The downstream station (W2) exhibited the most significant water quality changes, while the upstream station (W5) showed the highest biodiversity and abundance. The top five genera in abundance in the water body were unclassified__c__Actinomycetia, unclassified__p__Bacteroidota, Paenisporosarcina, Candidatus_Planktophila, and unclassified__c__Betaproteobacteria. The five most abundant nitrogen metabolism genes were K01915 (nitrate reductase), K00265 (nitrite reductase), K01673 (ammonium transporter), K00266 (nitrite reductase), and K02575 (nitrate reductase), each contributing to critical nitrogen cycling processes such as denitrification, nitrification, and nitrogen assimilation. The six major nitrogen metabolism pathways were denitrification (M00529), anisotropic nitrate reduction (M00528), anisotropic nitrate reduction (M00529). anisotropic nitrate reduction (M00530), complete nitrification (M00804), nitrate assimilation (M00615), methylaspartate cycling (M00740), and assimilatory nitrate reduction (M00531). TN was identified as the primary environmental factor influencing both microbial communities and nitrogen metabolism genes. Co-occurrence network analysis identified K01915 (nitrate reductase), K00459 (ammonium transporter), K01673 (ammonium transporter), and K00261 (nitrate reductase) as pivotal genes involved in nitrogen metabolism. This study reveals the microbial-driven nitrogen cycle and lays the foundation for mitigating nitrogen pollution in the Xisha River. Full article

Deep-sea chemosynthetic ecosystems, including cold seeps and hydrothermal vents, are widely spread in global oceans. Campylobacterota are important primary producers in deep-sea hydrothermal vents and serve as a vital food source for local invertebrates. However, the nutrients that these bacteria can provide to their hosts are unclear. To date, research on Campylobacterota in cold seeps is very limited. Consequently, little is known about the biological features and ecological potential of Campylobacterota in cold seeps. In the present work, we examined the diversity, growth, metabolic characteristics, and nutrient production of Campylobacterota in a deep-sea cold seep. Over 1000 Campylobacterota ASVs, especially autotrophic Sulfurovum and Sulfurimonas, were identified. By optimizing the culture medium, 9 Sulfurovum and Sulfurimonas strains were isolated, including three potentially novel species. Two novel species were characterized and found to exhibit unique morphological features. These two novel strains possessed complete reverse tricarboxylic acid pathways. One novel strain, FCS5, was a psychrotolerant autotroph with denitrification and phosphorus-removing capacity. FCS5 could grow in the absence of vitamins. Consistently, metabolomics and transcriptome analyses indicated that FCS5 produced multiple vitamins, which regulated the expressions of a large number of genes associated with carbon fixation and multiple-nutrient synthesis. Besides vitamins, autotrophic Campylobacterota also produced abundant free amino acids, fatty acids (short-chain, medium, and long-chain), and proteins. This study indicates that the cold seep abounds with Campylobacterota, which are capable of providing various nutrients for the chemosynthetic ecosystem. In addition, these bacteria may have wide applications, such as in wastewater treatment and carbon emission reduction. Full article

Microbial communities in wastewater treatment plants (WWTPs) play a crucial role in the decontamination of polluted water. An uncultured order-level lineage AKYH767 of the phylum Bacteroidota has been consistently detected in microbial consortia of activated sludge at WWTPs worldwide, but its functional role remains elusive. Representatives of AKYH767 were also detected in soils and freshwater bodies, which may be their natural reservoirs. Here, we obtained ten high-quality metagenome-assembled genomes, including one closed circular genome, of AKYH767 bacteria from metagenomes of the wastewater and activated sludge and used genomic data to uncover the metabolic potential of these bacteria and to predict their functional role. The cells of the AKYH767 bacteria were inferred to be rod-shaped and non-motile. Genome-based metabolic reconstruction predicted the Embden–Meyerhof pathway, the non-oxidative stage of the pentose phosphate pathway, and the complete tricarboxylic acid cycle. A facultatively anaerobic chemoheterotrophic lifestyle with the capacity to oxidize low organic substrates through aerobic respiration was suggested. Under anaerobic conditions AKYH767 bacteria can perform different steps of denitrification. They have limited capacities to hydrolyze carbohydrates and proteinaceous substrates but can utilize fatty acids. A peculiar property of AKYH767 bacteria is the presence of the phenylacetyl-CoA pathway for the utilization of phenylacetate, and about half of the genomes encoded the benzoate degradation pathway. Apparently, in bioreactors at WWTPs, the AKYH767 bacteria could be involved in the denitrification and biodegradation of aromatic compounds. Based on phylogenetic and genomic analyses, the novel AKYH767 bacterium is proposed to be classified as Candidatus Pollutiaquabacter aromativorans, within the candidate order Pollutiaquabacterales. Full article

Anaerobic ammonium oxidation (anammox) technologies have attracted substantial interest due to their advantages over traditional biological nitrogen removal processes, including high efficiency and low energy demand. Currently, multiple side-stream applications of the anammox coupling process have been developed, including one-stage, two-stage, and three-stage systems such as completely autotrophic nitrogen removal over nitrite, denitrifying ammonium oxidation, simultaneous nitrogen and phosphorus removal, partial denitrification-anammox, and partial nitrification and integrated fermentation denitritation. The one-stage system includes completely autotrophic nitrogen removal over nitrite, oxygen-limited autotrophic nitrification/denitrification, aerobic de-ammonification, single-stage nitrogen removal using anammox, and partial nitritation. Two-stage systems, such as the single reactor system for high-activity ammonium removal over nitrite, integrated fixed-film activated sludge, and simultaneous nitrogen and phosphorus removal, have also been developed. Three-stage systems comprise partial nitrification anammox, partial denitrification anammox, simultaneous ammonium oxidation denitrification, and partial nitrification and integrated fermentation denitritation. The performance of these systems is highly dependent on interactions between functional microbial communities, physiochemical parameters, and environmental factors. Mainstream applications are not well developed and require further research and development. Mainstream applications demand a high carbon/nitrogen ratio to maintain levels of nitrite-oxidizing bacteria, high concentrations of ammonium and nitrite in wastewater, and retention of anammox bacteria biomass. To summarize various aspects of the anammox processes, this review provides information regarding the microbial diversity of different genera of anammox bacteria and the engineering aspects of various side streams and mainstream anammox processes for wastewater treatment. Additionally, this review offers detailed insights into the challenges related to anammox technology and delivers solutions for future sustainable research. Full article

Carbonate rock dissolution (CRD) in karst areas generates abundant ions, which contribute significantly to nitrogen (N) transformation in paddy ecosystems. However, little is known about the microbial mechanisms by which CRD ions (Ca²⁺, Mg²⁺, HCO₃⁻/CO₃²⁻, and OH-) regulate N balance. In this experiment, rice pot studies were conducted using karst soil (S1), karst soil with removed carbonate minerals (S2), non-karst soil (S3), and non-karst soil with additional carbonate minerals (S4). The effects of CRD on N-metabolizing microorganisms and functional genes in N metabolism were investigated using metagenomic sequencing technology. Six N metabolism pathways, including N fixation, nitrification, denitrification, dissimilatory nitrate reduction to ammonia (DNRA), assimilatory nitrate reduction to ammonia (ANRA), and complete nitrification (comammox) were revealed. Compared with S3, the relative abundance of the denitrification module (M00529) in S1 clearly increased by 1.52%. Additionally, compared to S3, the relative abundance of the complete nitrification (comammox) module (M00804) in S4 decreased by 0.66%. Proteobacteria and Anaeromyxobacter were significant contributors to variations in N metabolism. Key factors that influenced variations in N metabolism included Ca²⁺, Mg²⁺, and pH. This study explored the effects of CRD on N-metabolizing microorganisms and functions, which was of great significance to the N cycle in karst paddy ecosystems. Full article

In this study, porous glass with controllable layered structure was successfully prepared by the phase-separation method, with the aim to develop a high-performance high-temperature catalytic (denitrification) material. Glass compositions with different R values (n (Na₂O)/n (B₂O₃)) were designed based on the phase diagram of sodium borosilicate glass. The layered porous structure was obtained by heat treatment in the phase-separation temperature range and acid-leaching treatment to remove the boron-rich phase. For the adsorption and separation process, the layered pore is very ideal, due to its high contact area, high storage capacity and easy mass transfer characteristics, which means it has high adsorption capacity and separation efficiency. The experimental results show that the thickness of the silicon layer can be precisely controlled in the range of 2–23 μm by adjusting the heat treatment time (1.25–10 h), and the material has excellent high-temperature stability (the pore structure parameters do not change significantly after calcination at 600 °C for 10 h). V₂O₅ (multiphase redox catalyst) can be uniformly loaded by the impregnation method, and the layered structure can be completely retained. The formation process of the layered structure was studied by infrared, Raman spectroscopy and SEM analysis. This study provides a new strategy for the development of customizable porous materials. Full article

The investigation of metabolic pathways and regulatory mechanisms in newly discovered species can offer valuable insights into the nitrogen removal function of heterotrophic nitrification–aerobic denitrification (HN-AD) bacteria. To investigate the nitrogen removal mechanism of a new genus, Delftia, we analyzed the complete genome, metabolic pathways, and the related genes of Delftia sp. B7. We further examined the nitrogen removal capacity of Delftia sp. B7 under various nitrogen sources and real wastewater. Our results demonstrate the presence of several genes in Delftia sp. B7, including narGHI, nasAB, nirK, nirS, nirBD, norBC, nosZ, nxrAB, gdhA, glnA, gltBD, amt, and nrt. These genes encode enzymes that facilitate ammonia assimilation, assimilatory nitrate reduction to nitrite, HN-AD, and dissimilatory nitrate reduction (DNRA) in Delftia sp. B7. Specifically, we propose an HN-AD pathway in Delftia sp. B7, NH₄⁺-N → NH₂OH → NO₂⁻-N → NO₃⁻-N → NO₂⁻-N → NO → N₂O → N₂, which accounts for the majority of nitrogen removal. Here, the transformation of NH₄⁺-N to NO₂⁻-N was achieved by unknown enzymes or by another pathway. When treating municipal wastewater, Delftia sp. B7 was able to remove 45.62 ± 1.29% of TN. These findings provide a theoretical basis for utilizing microbial resources to mitigate nitrogen contamination. Full article

Recirculating aquaculture system (RAS) technology is seen worldwide as a solution for sustainable fish production. However, there are still deficiencies in the process technology imperiling consistent operation and thus economic results. Drawbacks are linked to essential processes of the water treatment systems such as denitrification. Nitrogenous waste needs to be removed from RAS process water to maintain an adequate production environment for fish and to mitigate the environmental impact of discharged process water. At present, denitrification lacks reliable process control, especially regarding the organic carbon feed to heterotrophic denitrification processes. An investigation into heterotrophic denitrification in an experimental RAS resulted in the discovery of a virtual sensor based on measurements of the oxidation reduction potential (ORP). The virtual sensor responds to an insufficient carbon feed to denitrification. It is based on the oxidation of nitrite in an ozone-enhanced foam flotation installed downstream of the denitrification. The sensor essentially delivers a binary signal denoting either a complete or an incomplete denitrification process. The virtual sensor can be used for reliably controlling heterotrophic denitrification. It requires an upgraded process chain employing ozone-enhanced foam flotation (protein skimmer) downstream of the denitrification. However, the virtual sensor does not require any additional instrumentation. Full article

Anaerobic digestion (AD) produces useful biogas and waste streams with high levels of dissolved methane (CH₄) and ammonium (NH₄⁺), among other nutrients. Membrane biofilm reactors (MBfRs), which support dissolved methane oxidation in the same reactor as simultaneous nitrification and denitrification (ME-SND), are a potential bubble-less treatment method. Here, we demonstrate ME-SND taking place in single-stage, AD digestate liquid-fed MBfRs, where oxygen (O₂) and supplemental CH₄ were delivered via pressurized membranes. The effects of two O₂ pressures, leading to different O₂ fluxes, on CH₄ and N removal were examined. MBfRs achieved up to 98% and 67% CH₄ and N removal efficiencies, respectively. The maximum N removal rates ranged from 57 to 94 mg N L⁻¹ d⁻¹, with higher overall rates observed in reactors with lower O₂ pressures. The higher-O₂-flux condition showed NO₂⁻ as a partial nitrification endpoint, with a lower total N removal rate due to low N₂ gas production compared to lower-O₂-pressure reactors, which favored complete nitrification and denitrification. Membrane biofilm 16S rRNA amplicon sequencing showed an abundance of aerobic methanotrophs (especially Methylobacter, Methylomonas, and Methylotenera) and enrichment of nitrifiers (especially Nitrosomonas and Nitrospira) and anammox bacteria (especially Ca. Annamoxoglobus and Ca. Brocadia) in high-O₂ and low-O₂ reactors, respectively. Supplementation of the influent with nitrite supported evidence that anammox bacteria in the low-O₂ condition were nitrite-limited. This work highlights coupling of aerobic methanotrophy and nitrogen removal in AD digestate-fed reactors, demonstrating the potential application of ME-SND in MBfRs for the treatment of AD’s residual liquids and wastewater. Sensor-based tuning of membrane O₂ pressure holds promise for the optimization of bubble-less treatment of excess CH₄ and NH₄⁺ in wastewater. Full article

When municipal solid waste (MSW) is placed in a landfill, it undergoes anaerobic decomposition, leading to the production of landfill gas, which primarily consists of methane (CH₄) and carbon dioxide (CO₂). Reducing methane emissions is essential in the fight against climate change. It must be implemented at global and European levels, as set out in 2030 in the impact assessment of the climate goal plan. This assessment states that to achieve the goal by 2030 and to reduce greenhouse gas emissions by at least 55%, the methane emissions must be reduced, considering the goals of the Paris Agreement. The Glasgow Climate Pact includes a global mitigation target of the year 2030: to reduce CO₂ emissions by 45%, and the emissions of methane and other greenhouse gasses. For that purpose, looking for new, more advanced ways of managing such waste is necessary. The main objective of this experimental study was to evaluate the influence of aeration, probiotic introduction, and water supply on the production of landfill gasses (CO₂, CH₄, N₂, H₂, etc.) in five different landfill models during the management of MSW and to propose the best solutions for reducing environmental pollution. The results of the research showed that the first and second models of landfills, using only anaerobic conditions, can be used for the treatment of MSW for the production of biogas (CH₄, CO₂), as up to 40–60% of it was released during the 120-experiment period. The third landfill model can be applied in old, already closed landfills, where the rapid stabilization and aeration of MSW are required to minimize pollutant emissions (N₂, etc.) and unwanted odors and shorten biodegradation processes. The results of the fourth and fifth landfill models, in which aerobic–anaerobic conditions were applied, showed that the developing nitrification–denitrification processes resulted in complete nitrogen removal (from 20% to 0%), and overall waste stabilization improved the biodegradation of the MSW. Later, relatively good (on average, 30%) results of biogas (CH₄, CO₂) emissions are achieved during anaerobic condition formation results. Summarizing all experiment results of all landfill models for the further evaluation of the processes, all models can be applied in real practice depending on where they will be used and what result they want to achieve. Full article

Ecological floating beds, with their compact footprint and mobility, offer a promising solution for sustainable surface water remediation in rural areas. However, low removal efficiency and instability still limit its application. In this study, iron–carbon-based fillers were integrated into ecological floating beds to investigate their impact and mechanisms in removing pollutants, including carbon, nitrogen, phosphorus, and heavy metals. Results indicate that all five fillers (activated carbon, iron–carbon fillers, sponge iron, activated carbon + iron–carbon fillers, and activated carbon + sponge iron) can completely remove orthophosphate, and the sponge iron filler system can completely remove nitrate. Then, fillers were applied to ecological floating beds, and the iron–carbon microelectrolysis (activated carbon + sponge iron filler)-enhanced ecological floating bed showed superior removal efficiency for pollutants. It achieved 95% removal of NH₄⁺-N, 85% removal of NO₃⁻-N, 75% removal of total phosphorus, 90% removal of chemical oxygen demand, and 90% removal of heavy metals. Typical nitrifying bacteria Nitrospira, denitrifying bacteria Denitratisoma, and a variety of bacterial genera with denitrification functions (e.g., Rhodobacter, Dechloromonas, Sediminibacterium, and Novosphingobium) coexisted in the system, ensuring efficient and robust nitrogen removal performance. These findings will provide support for the sustainable treatment of surface water in rural areas. Full article