Nitrogen Removal Potential Research Articles

Roles of nitrite in facilitating nitrogen and sulfur conversion in the hybrid bioreactor of Sulfate-reduced ammonium oxidation and anaerobic ammonium oxidation.

The hybrid bioreactor combining sulfate-reducing ammonium oxidation (Sulfammox) and Anammox offered potential for simultaneous nitrogen and sulfur removal, but the removal efficiency and microbial mechanism remain unclear. This study demonstrated that in the hybrid bioreactor, the ammonium utilization rate (AUR) of Sulfammox increased by 5.42 times. The promotion of NO2- on nitrogen and sulfur conversion in Sulfammox could be attributed to: 1) Increasing extracellular polymers substance (EPS) accelerated the stratification of granule sludge; 2) Increasing the relative abundance of Candidatus Brocadia by 29.55 times and Candidatus Anammoxoglobus by 3.17 times; 3) Upregulating the expression of nitrification (amo, hao and nxr) and sulfur metabolism (sat, aprAB dsr and sox) genes, associated with the pathways NH4+→NH2OH→NO2-→NO3- and SO42-→S2-→SO42-. Moreover, Candida Brocadia sapporoensis emerged as a potential specie of Sulfammox, mediating nitrification by hao and nxr, and sulfate reduction by sat and aprAB, thereby enabling electron transfer between nitrogen and sulfur.

Simultaneous nitrogen removal and phosphorus recovery in granular sludge-based partial denitrification/anammox-hydroxyapatite precipitation (PD/A-HAP) process under low C/N ratio and dissolved oxygen limitation.

This study integrates partial denitrification/Anammox (PD/A) with hydroxyapatite (HAP) crystallization in a single reactor, achieving simultaneous nitrogen and phosphorus removal along with phosphorus recovery. By adjusting pH, sludge concentration, low COD/TN ratio, and applying moderate dissolved oxygen stress, the system operated stably and promoted the synergistic growth of HAP and biomass. Results showed a nitrogen removal efficiency (NRE) of 94.13 % and a phosphorus removal efficiency (PRE) of 73.6 %. Metagenomic analysis revealed that under dissolved oxygen stress, The abundance of Candidatus Brocadia increased from 1 % to 26.1 %, significantly boosting anammox activity. indicating enhanced microbial activity. The upregulation of related genes (sdh, suc, hzs) further boosted AnAOB activity. HAP was identified as the main inorganic component of the granule. This process shows strong potential for nitrogen and phosphorus removal with resource recovery in wastewater treatment.

Revealing the nitrogen and phosphorus removal potential: Insights into surface flow and subsurface flow constructed wetlands employing integrated iron and sulfur electron donors

This study investigated the differences in nitrogen (N) and phosphorus (P) removal performance, nitrous oxide (N2O) emissions, and microbial community structure between surface flow (SF) and subsurface flow (SSF) constructed wetlands (CWs) using iron scraps (ISs) and elemental sulfur (S0) as integrated electron donors. Four configurations were examined: control SFCW (SF-C), ISs and S0 SFCW (SF-Fe+S), control SSFCW (SSF-C), and ISs and S0 SSFCW (SSF-Fe+S). The results indicated that both CW types utilizing combined ISs and S0 were effective in removing N, with SF-Fe+S (35.73–72.71 %) exhibiting higher nitrate removal efficiency compared to SSF-Fe+S (10.05–61.27 %). However, SSF-Fe+S (77.88–85.72 %) demonstrated a greater efficiency in removing total phosphorus (TP) than SF-Fe+S (50.78–67.91 %). In addition, both SSFCWs, SSF-C (7.22 mg/m2/d) and SSF-Fe+S (3.39 mg/m2/d) exhibited higher N2O emissions compared to SFCWs, SF-C (3.05 mg/m2/d) and SF-Fe+S (1.94 mg/m2/d). Microbial community analysis revealed distinct differences between CW types; Dechloromonas (22.45 %) and Ferritrophicum (18.23 %) were the dominant genera in SF-Fe+S, whereas Ferritrophicum (37.13 %) and Acinetobacter (21.80 %) predominated in SSF-Fe+S. In addition, TP removal was potentially enhanced by substrate adsorption and coprecipitation through iron (Fe2+ and Fe3+) ions released from ISs corrosion reacting with phosphate (PO43−) ions. The study reveals that the type of CW and the combination of electron donors significantly influence their effectiveness in removing N and P, reducing N2O emissions, and enhancing microbial community composition, thus providing valuable insights.

Nitrifying bacteria for the remediation of organic nitrogen‐contaminated waters: a review

AbstractThe rapid growth of the world's population and its environmental impact has increased the demand for effective water treatment methods. Surface water systems, including rivers, streams, lakes, and ponds, have suffered contamination, leading to the urgent need for effective contaminant removal. Organic nitrogen compounds and nitrates are of particular concern because they pose risks to health and can cause environmental damage. However, traditional water‐treatment methods often prove ineffective for addressing these issues. For this reason, this research focuses on harnessing the capabilities of nitrifying bacteria to denitrify organic nitrogen compounds in water, exploring various bacterial strains, their functions, and their ability to obtain sources of carbon. The study also investigates innovative approaches such as biofilm systems, mixed cultures, and combined processes, which have shown stronger potential for nitrogen removal. Overall, it provides valuable insights into the use of nitrifying bacteria‐based technologies for water remediation in the face of growing environmental challenges.

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.

Characterization of Enterobacter cloacae CAUCoF_BF_01: an autochthonous heterotrophic nitrifying strain from culture ponds for biofloc applications

The biofloc environment needs specific heterotrophic nitrifying bacteria for optimal system performance, hence screening perfect bacterial strains is crucial. Enterobacter cloacae sp. was identified as a novel heterotrophic bacterium isolated from freshwater pond sediment during July, 2022. Through high-throughput sequencing, the isolated bacterium was identified as E. cloacae CAUCoF_BF_01, which demonstrated potential nitrogen removal via heterotrophic nitrification and aerobic denitrification, as well as a preference for different C/N ratios (C/N10, 15, 20, and 25) for consuming nitrogen sources. The bacteria performed superior (p < 0.05) ammonia-N and nitrite-N removal in C/N20, with efficiencies of 91.70% and 91.0%, respectively. C/N15, on the other hand, had higher nitrate-N removal efficiency (69.20%). Furthermore, the optimum temperature for the chosen strain was determined to be 30 °C. This strain, on the other hand, can thrive in temperatures ranging from 20 to 37 °C and pH levels ranging from 6 to 10. Furthermore, the biofilm test reveals that the selected bacterial strain has the potential to form biofilm via extracellular polymeric compound secretion, besides passing ecological safety requirement. The current investigation will be helpful in the development of a successful biofloc-based probiotic for managing system generated ammonia to an optimal level, as well as floc production to maximize system efficiency.

Assessing the effects of NapA gene overexpression on denitrification and denitrogenation in magnetospirillum gryphiswaldense MSR-1.

Previous research on Magnetospirillum gryphiswaldense MSR-1 found that MSR-1 has a good denitrification nitrogen removal ability and specific application prospects in the sewage biological nitrogen removal field. Therefore, this study selected the essential denitrification gene NapA in MSR-1-wt for overexpression, and the overexpressed MSR-1-NapA was successfully constructed. Q-PCR amplification experiment and AGAR gel electrophoresis experiment proved that the relative transcription level of the NapA gene was increased by more than four times, and the denitrification ability of MSR-1-wt and MSR-1-NapA was further determined by enzyme activity experiment, denitrification experiment, and flow cytometry. The results showed that overexpression of the NapA gene increased nitrate reductase activity in MSR-1-NapA by more than four times. In the solution with a nitrate concentration of 118.33 ± 3.23mgN/L, the denitrification efficiency of MSR-1-NapA was superior to that of MSR-1-wt, significantly enhancing both the denitrification and nitrogen removal capacities of MSR-1. This indicates its greater potential for biological nitrogen removal in wastewater treatment.

Increased anaerobic conditions promote the denitrifying nitrogen removal potential and limit anammox substrate acquisition within paddy irrigation and drainage units

Microbial nitrogen (N) removal is crucial for purifying surface water quality in paddy irrigation and drainage units (IDUs). However, the spatiotemporal microbial N removal potential characteristics within these IDUs and the effects of changing anaerobic conditions on this potential remain insufficiently studied. In this study, we investigated the microbial N removal potential of conventional rice-wheat rotation and anaerobically enhanced rice-crayfish rotation IDUs using field measurements, isotope tracing techniques, and quantitative PCR. Our findings reveal that paddy fields were identified as hotspots for anammox activity, contributing to 76.0 %–97.4 % of the total anammox N removal potential in the IDU, while denitrification processes in ditches accounted for 43.5 %–77.4 % of the IDU's denitrification potential. During the rice transplanting period, the anammox N removal potential peaked, representing 35.8 % and 71.8 % of the total anammox N removal potential of the paddy fields in rice-wheat and rice-crayfish IDUs, respectively. An increase in anaerobic conditions diminished the anammox N removal potential while amplifying denitrification capabilities. The N removal potential in paddy fields decreased with increasing depth, contrasting with the relative stability in ditches. Spatiotemporal fluctuations in N removal potentials within these units are influenced by Fe2+ concentration, carbon and N content, WFPS, and pH levels. This study provides a scientific basis for improving nitrogen removal and water quality treatment in IDUs.

Pyrite and Sulfur Autotrophic Denitrification for Simultaneous Nitrogen and Phosphorus Removal and Greenhouse Gas Emission Reduction Potential

Pyrite and Sulfur Autotrophic Denitrification for Simultaneous Nitrogen and Phosphorus Removal and Greenhouse Gas Emission Reduction Potential

Loss of microbial functional diversity following Spartina alterniflora invasion reduces the potential of carbon sequestration and nitrogen removal in mangrove sediments—from a gene perspective

Mangrove ecosystems play an important role in carbon (C) sequestration and nitrogen (N) removal. Although Spartina alterniflora has successively invaded native mangrove habitats during the preceding two decades, the effects of this invasion on the microbial functional potential involved in nutrient cycling remain unclear. In this study, metagenomic sequencing was used to investigate microbial C and N cycling in sediments derived from S. alterniflora and three native mangrove species (Kandelia obovata, Avicennia marina, and Aegiceras corniculatum). Greater differences in functional profiles of C and N cycling-related genes were observed between S. alterniflora and mangrove sediments than between different mangrove sediments. Functional diversity was lower in S. alterniflora sediments than in native mangrove sediments. The growth of Thaumarchaeota and Proteobacteria, was enhanced due to their resilience to diversity loss, while the growth of oligotrophs, such as Chloroflexi and Firmicutes, was inhibited in S. alterniflora sediments. Compared to mangrove sediments, the abundance of genes involved in C fixation and methane production was lower in S. alterniflora sediments. However, S. alterniflora significantly increased the gene abundance of pmo which controlled the oxidation process of CH4 to carbon dioxide. Additionally, genes involved in nitrification were enriched, whereas genes involved in N reduction processes, such as denitrification and dissimilatory nitrate reduction to ammonium, N immobilization, and N mineralization, were depleted in S. alterniflora sediments compared to mangrove sediments. Partial least squares regression models demonstrated that the decrease in soil organic C and increase in pH after S. alterniflora invasion induced the loss of microbial functional diversity, which was the main driver of changes in the abundances of genes involved in C and N cycling. Overall, our findings indicate that S. alterniflora invasion modifies the microbial functional profile of nutrient cycling in native mangrove ecosystems and potentially weakens the capacity of mangroves to sequester carbon and remove nitrogen.

Nitrogen Removal Performance and Microbial Community Structure of IMTA Ponds (Apostistius japonicus-Penaeus japonicus-Ulva)

Denitrification and anaerobic ammonium oxidation (anammox) are key processes for nitrogen removal in aquaculture, reducing the accumulated nitrogen nutrients to nitrogen gas or nitrous oxide gas. Complete removal of nitrogen from aquaculture systems is an important measure to solve environmental pollution. In order to evaluate the nitrogen removal potential of marine aquaculture ponds, this study investigated the denitrification and anammox rates, the flux of nitrous oxide (N2O) at the water–air interface, the sediment microbial community structure, and the gene expression associated with the nitrogen removal process in integrated multi-trophic aquaculture (IMTA) ponds (Apostistius japonicus-Penaeus japonicus-Ulva) with different culture periods. The results showed that the denitrification and anammox rates in sediments increased with the increase of cultivation periods and depth, and there was no significant difference in nitrous oxide gas flux at the water–air interface between different cultivation periods (p > 0.05). At the genus and phylum levels, the abundance of microorganisms related to nitrogen removal reactions in sediments changed significantly with the increase of cultivation period and depth, and was most significantly affected by the concentration of particulate organic nitrogen (PON) in sediments. The expression of denitrification gene (narG, nirS, nosZ) in surface sediments was significantly higher than that in deep sediments (p < 0.05), and was negatively correlated with denitrification rate. All samples had a certain anammox capacity, but no known anammox bacteria were found in the microbial diversity detection, and the expression of gene (hzsB) related to the anammox process was extremely low, which may indicate the existence of an unknown anammox bacterium. The data of this study showed that the IMTA culture pond had a certain potential for nitrogen removal, and whether it could make a contribution to reducing the pollution of culture wastewater still needed additional practice and evaluation, and also provided a theoretical basis for the nitrogen removal research of coastal mariculture ponds.Graphical

Subcuticular and biofilm microbiomes in Holothuria tubulosa and their potential for denitrification

Holothurians, as benthic invertebrates inhabiting marine ecosystems, have a crucial function in that they actively process organic detritus in the sediments. Previous works have provided evidence of the capability of holothurians to reduce nitrate and ammonium concentrations in aquaculture tanks. However, the mechanisms underlying this nitrogen decrease still need to be elucidated and might be related to bacterial symbionts in the holothurians. Here we characterize the community of bacterial symbionts in the biofilm and subcuticle of Holothuria tubulosa and explore the presence of nitrification and denitrification genes. To characterize these bacterial symbionts, we extracted DNA and amplified the V3-V4 hypervariable region of the 16S rRNA gene. We obtained a notable contribution of Bacteroidota, Alphaproteobacteria (mostly Rhodobacterales), and Gammaproteobacteria (mostly Pseudomonadales) both within the biofilm and subcuticle of H. tubulosa. Subsequently, we tested the presence of specific genes encoding enzymes involved in nitrification (i.e. archaeal amoA and bacterial amoA) and denitrification (i.e. nirS and nosZ). Our results confirm the presence of denitrification genes in the holothurian biofilms. These findings indicate that the holothurians house a diverse community of bacterial symbionts, which includes species with the potential for nitrogen removal. Therefore, holothurian holobionts may play a multifaceted ecological role, both processing organic detritus and reducing nitrogen levels in coastal areas. These roles could be extended to sustainable aquaculture, making them valuable ecosystem engineers with significant implications for ecosystem and aquaculture health.

A Continuous Plug-Flow Anaerobic-Multistage Anoxic/Aerobic Process Treating Low-C/N Domestic Sewage: Nutrient Removal, Greenhouse Gas Emissions, and Microbial Community Analysis

The anaerobic-multistage anoxic/aerobic (A-MAO) process has shown good potential for advanced nitrogen removal in recent years, but its greenhouse gas emissions still need to be fully explored. The effects of the influent distribution and external carbon source sodium acetate on nutrient removal, greenhouse gas emissions, and the microbial community structure in a continuous plug-flow A-MAO reactor fed with real low C/N ratio domestic sewage were investigated. The results showed that altering the allocation of carbon source resulted in average chemical oxygen demand (COD) and total nitrogen (TN) concentration in effluent reduced to 26.10 ± 4.86 and 6.65 ± 1.73 mg/L, respectively. Both operations reduced the emission rate of greenhouse gas. While the addition of external car-bon sources leaded to lower N2O emission rates and higher CO2 and CH4 emission rates. The addition of sodium acetate facilitated nitrification and denitrification processes, thereby leading to a reduction in N2O production. Meanwhile, it spurred the growth of methanogenic bacteria and heterotrophic microorganisms, thus boosting the production of CO2 and CH4. Influent distribution promoted the increase of Bacteroidota, Chloroflexi and Acidobacteriota of the reactor. The enrichment of typical hydrolytic bacteria and glycogen accumulating organisms (GAOs) increased the utilization efficiency of carbon sources in the system after the addition of sodium acetate. The significant increase of typical denitrifying bacteria (DNBs) Azospira reduced the N2O emission during heterotrophic denitrification process, which was considered to be an important functional genus for increasing nitrogen loss in this system. The rational utilization of carbon source makes the difference in metabolism function. The study provides a valuable strategy for comprehensively evaluating the pollutant removal and greenhouse gas emission reduction from the A-MAO process.

Immobilized microalgae: principles, processes and its applications in wastewater treatment.

Microalgae have emerged as potential candidates for biomass production and pollutant removal. However, expensive biomass harvesting, insufficient biomass productivity, and low energy intensity limit the large-scale production of microalgae. To break through these bottlenecks, a novel technology of immobilized microalgae culture coupled with wastewater treatment has received increasing attention in recent years. In this review, the characteristics of two immobilized microalgae culture technologies are first presented and then their mechanisms are discussed in terms of biofilm formation theories, including thermodynamic theory, Derjaguin-Landau-Verwei-Overbeek theory (DLVO) and its extended theory (xDLVO), as well as ionic cross-linking mechanisms in the process of microalgae encapsulated in alginate. The main factors (algal strains, carriers, and culture conditions) affecting the growth of microalgae are also discussed. It is also summarized that immobilized microalgae show considerable potential for nitrogen and phosphorus removal, heavy metal removal, pesticide and antibiotic removal in wastewater treatment. The role of bacteria in the cultivation of microalgae by immobilization techniques and their application in wastewater treatment are clarified. This is economically feasible and technically superior. The problems and challenges faced by immobilized microalgae are finally presented.

Synchronous Achievement of Advanced Nitrogen Removal and N2O Reduction in the Anoxic Zone in the AOA Process for Low C/N Municipal Wastewater.

Continuous flow processes for the in situ determination of N2O emissions during low C/N municipal wastewater treatment have rarely been reported. The anaerobic/aerobic/anoxic (AOA) process has recently shown promising potential in energy savings and advanced nitrogen removal, but it still needs to be comprehensively explored in relation to N2O emissions for its carbon reduction advantages. In this study, a novel gas-collecting continuous flow reactor was designed to comprehensively evaluate the emissions of N2O from the gas and liquid phases of the AOA process. Additionally, the measures of enhancing endogenous denitrification (ED) and self-enriching anaerobic ammonium oxidation (Anammox) were employed to optimize nitrogen removal and achieve N2O reduction in the anoxic zone. The results showed that enhanced ED coupled with Anammox led to an increase in the nitrogen removal efficiency (NRE) from 67.65 to 81.96%, an enhancement of the NO3- removal rate from 1.76 mgN/(L h) to 3.99 mgN/(L h), and the N2O emission factor in the anoxic zone decreased from 0.28 to 0.06%. Impressively, ED eliminated 91.46 ± 2.47% of the dissolved N2O from the upstream aerobic zone, and the dissolved N2O in the effluent was reduced to less than 0.01 mg/L. This study provides valuable strategies for fully evaluating N2O emissions and N2O reduction from the AOA process.

Spatial and temporal differences of nitrogen removal potential by denitrification and its management implications of water-based reservoirs in the upper reaches of Taihu Basin: A case study of Lake Tianmuhu

Spatial and temporal differences of nitrogen removal potential by denitrification and its management implications of water-based reservoirs in the upper reaches of Taihu Basin: A case study of Lake Tianmuhu

Simultaneous aerobic nitrogen and phosphate removal by Pseudomonas aeruginosa SNDPR-01: Comprehensive insights on metabolic potential and mechanisms

Versatile metabolic bacteria with simultaneous nitrification–denitrification and phosphate removal (SNDPR) capabilities are promising to reduce the wastewater treatment process from a multi-unit system to a single unit system. Due to the limited study, the metabolic potential and mechanisms of nitrogen (N) and phosphate (P) removal for any SNDPR bacteria remain unknown. In this study, genomic analysis revealed various genes were present in an SNDPR isolate, Pseudomonas aeruginosa SNDPR-01, establishing diverse N- and P-metabolism potential, such as aerobic and anoxic denitrification; dissimilatory nitrate reduction to ammonia; polyphosphate (polyP) metabolism; and utilization of organic P. Phylogenetic analysis predicted that key functional genes related N and P metabolism may co-evolve with chromosomal genes, except for the norB gene, which may originate from horizontal gene transfer. Transcriptomic analysis revealed a partial nitrification and denitrification pathway (NH4+ → NO2– → NO → N2O → N2) to aerobically remove N without the involvement of conventional amoA, hao and napA genes. Unknown genes were confirmed to mediate the oxidation of ammonium to nitrite. Excellent P removal ability was aided by the synthesis of adenosine triphosphate (ATP) and polyP. The formed polyP was utilized under aerobic conditions without accumulation, which is different from traditional polyP accumulation organisms in wastewater treatment plants (WWTPs). This study will deepen the roles of SNDPR bacteria in aerobic ecological niches and enhance their application in WWTPs.

Unveiling the nitrogen and phosphorus removal potential: Comparative analysis of three coastal wetland plant species in lab-scale constructed wetlands

It is well accepted that tidal wetland vegetation performs a significant amount of water filtration for wetlands. However, there is currently little information on how various wetland plants remove nitrogen (N) and phosphorus (P) and how they differ in their denitrification processes. This study compared and investigated the denitrification and phosphorus removal effects of three typical wetland plants in the Yangtze River estuary wetland (Phragmites australis, Spartina alterniflora, and Scirpus mariqueter), as well as their relevant mechanisms, using an experimental laboratory-scale horizontal subsurface flow constructed wetland (CW). The results showed that all treatment groups with plants significantly reduced N pollutants as compared to the control group without plants. In comparison to S. mariqueter (77.2–83.2%), S. alterniflora and P. australis had a similar total nitrogen (TN)removal effectiveness of nearly 95%. With a removal effectiveness of over 99% for ammonium nitrogen (NH4+-N), P. australis outperformed S. alterniflora (95.6–96.8%) and S. mariqueter (94.6–96.5%). The removal of nitrite nitrogen (NO2−-N)and nitrate nitrogen (NO3−-N)from wastewater was significantly enhanced by S. alterniflora compared to the other treatment groups. Across all treatment groups, the removal rate of PO43--P was greater than 95%. P. australis and S. alterniflora considerably enriched more 15N than S. mariqueter, according to the results of the 15N isotope labeling experiment. While the rhizosphere and bulk sediments of S. alterniflora were enriched with more simultaneous desulfurization-denitrification bacterial genera (such as Paracoccus, Sulfurovum, and Sulfurimonas), which have denitrification functions, the rhizosphere and bulk sediments of P. australis were enriched with more ammonia-oxidizing archaea and ammonia-oxidizing bacteria. As a result, compared to the other plants, P. australis and S. alterniflora demonstrate substantially more significant ability to remove NH4+-N and NO2−-N/NO3−-N from simulated domestic wastewater.

Nitrogen metabolism potential in biofilm microbial communities: potential applications in the mariculture wastewater treatment

Marine aquaculture wastewater is one of the major sources of nitrogen pollution in coastal areas, and excessive discharge poses a threat to human health and the marine ecosystem. In order to investigate the nitrogen metabolism potential of microorganisms in marine aquaculture water, metagenomic sequencing was conducted, and microbial communities involved in nitrogen metabolism on composite filler biofilms and their contributions to nitrogen metabolism functions were analyzed based on KEGG annotation. Metagenomic analysis revealed that nitrogen metabolism microorganisms were primarily composed of Proteobacteria, Planctomycetota, Bacteroidota, and Firmicutes. KEGG results indicated the presence of complete nitrogen metabolism pathways within the biofilm. Analysis of nitrogen metabolism modules and relative enzyme abundance showed that the nitrification module was much less abundant compared to denitrification. Denitrification, dissimilatory nitrate reduction, and ammonia conversion to amino acids were the major modules of nitrogen metabolism in the biofilm, reflecting the main nitrogen transformation pathways. The study systematically revealed key driving taxa in the nitrogen cycle within the biofilm. Proteobacteria, Planctomycetota, Bacteroidota, and Verrucomicrobia were identified as the major executors of nitrogen metabolism pathway modules and enzyme functions in the biofilm. This research underscores the diverse microbial communities cooperate to maintain the potential nitrogen removal capacity of the biofilm. This study provide new insights into the critical driving factors of nitrogen cycling in marine aquaculture wastewater, which can serve as a scientific basis for the efficient purification of aquaculture wastewater.

Simultaneous and efficient removal of ammonium and nitrate by a novel isolated Agrobacterium tumefaciens M

A novel nitrogen removal strain M, was isolated and identified as Agrobacterium tumefaciens M. Strain M could remove 100% and 99% of 100 mg/L ammonium and nitrate mainly through assimilation, with elimination rates of 8.61 and 4.60 mg/L/h, respectively. The optimal growth and nitrogen elimination conditions were obtained by a single-factor experiment, including a shaking speed of 150 rpm, pH of 7, C/N ratio of 15, and carbon supply of sucrose (ammonium) and sodium citrate (nitrate). Key genes involved in nitrogen metabolism, including napAB, nirK, norBC, nosZ, nirBD, glnA, and nasAB, were identified in strain M. Moreover, strain M exhibited excellent nitrogen removal efficiencies higher than 90% when ammonium and nitrate coexisted. All results indicated that strain M shows great nitrogen removal potential.