Nitrogen Transformation Pathways Research Articles

Space heterogeneity of nitrogen removal functional genes, nitrogen transformation pathways and mechanisms in MEBR treating mariculture wastewater

Membrane Electro-Bioreactor (MEBR), exhibited excellent nitrogen removal in mariculture wastewater treatment. However, the differences of microbial community and nitrogen transformation pathways on spatial scale caused by the mass transfer of reactive chlorine species (RCS) generated by electrooxidation were unclear. This study provided new insights into the space heterogeneity of ammonia transformation pathways and mechanisms. The results demonstrated an increase in the reduction of nitrate to nitrite through partial denitrification on the membrane. Coupling with dissimilatory nitrate reduction to ammonium and RCS, higher nitrate (0.3 mgN/L) and TN removal (2.6 mgN/L) was obtained in MEBR. Higher relative abundance of narGHI and nirB were obtained. Ammonia oxidation by biofilters was enhanced in MEBR, that ammonia removal contributed by biofilters was 32.0 %, 5.2 times higher than the membrane. Relative abundance of amoABC and Nitrosomonas in biofilters were the highest. The results will provide theoretical basis for reactor configuration and operation optimization.

Characterization of Microbial Populations in Two Distinct Dairy Manure Management Systems: Seasonal Effect and Implications for Pollutant Gases Emissions.

Following an increase of the demand of dairy products, higher quantities of manure are consequently produced, with the subsequent pollutant gas emission charge associated with its management. The two mostly used housing systems in the northeast of Spain, cubicles (CUB) and compost-bedded pack (CBP), entail different manure management techniques; thus, our main objective was to describe the microbiota present in manure of both systems during two distinct climatic situations (winter, mean temperature of 6.2ºC; and summer, mean temperature of 36.4ºC). The secondary aim was to correlate these microbiological profiles with literature findings on the emission of certain well-known pollutant gases from manure. CBP showed to have higher alpha biodiversity as well as presenting a remarkable clustering by season, but showed lower network complexity than CUB. Firmicutes/Bacteroidetes ratio was found superior in CUB, which also presented a significantly higher abundance of methanogenic genera belonging to Euryarchaeota phylum, such as Methanobrevibacter, Methanosaeta or Methanosarcina. On the other hand, CBP manure presented a significant presence of Corynebacterium, Pseudomonas or Truepera, among other genera, which activity has been linked to nitrogen (N) transformation pathways in manure. Season also had a relevant role to play on the fluctuation of these populations within each housing system under study. These results show how microbial populations change when manure is differently managed, and how these variations can be related to the synthesis of certain pollutant gases upon housing systems.

Isotope analysis of nitrogen removal pathways and N2O production potential in the SDAD-anammox system under different N/S ratios

This study explored the impact of varying nitrate to sulfide (N/S) ratios on nitrogen removal efficiency (NRE) in the sulfide-driven autotrophic denitrification and anammox (SDAD-anammox) system. Optimal nitrogen removal was observed at N/S ratios between 1.5 and 2.0. Isotope tracing results showed that the contribution of anammox to nitrogen removal was enhanced with increasing N/S ratios, reaching up to 37 % at the N/S ratio of 2.5. Additionally, complex nitrogen pathways were identified, including dissimilatory nitrate reduction to ammonium (DNRA). Furthermore, isotope tracing was innovatively applied to investigate N2O emissions, demonstrating that higher N/S ratios significantly reduced N2O emissions, with the lowest emissions at N/S ratio of 2.5. Gene expression analysis indicated that nitrogen and sulfide transformation genes decreased with increasing N/S ratios, while anammox-related genes first increased and then decreased, reflecting the system's microbial dynamics. These findings offer insights into nitrogen transformation pathways and N2O production mechanisms in the SDAD-anammox process.

Plant phenology modulates and undersown cover crops mitigate N2O emissions

Mitigation of N2O emissions, a potent greenhouse gas, remain challenging due to knowledge gaps in plant-mediated nitrogen (N) transformation pathways, which limits ability to identify optimal approaches for efficient N utilization. We set up mesocosms with barley, Italian ryegrass, and barley in combination with Italian ryegrass to assess role of cover crop in N2O emission mitigation. Soil emitted N2O was collected simultaneously from the pots with plants at three growth stages: namely, vegetative, canopy expansion, and grain filling. The gas sample N2O contents, N in microbial biomass (MBN), mineral N content, and phospholipid fatty acid (PLFA) analysis in soils were determined at the three growth stages. Cumulatively, highest N2O was emitted from soil under Italian ryegrass (0.056 mg N g−1 soil) followed by barley (0.0051 mg N g−1 soil) and the least under barley and Italian ryegrass combination (0.0014 mg N g−1 soil). The high emissions under Italian ryegrass occurred at vegetative stage due to high reactive N availability. Strong emissions were observed at canopy expansion stage under barley and were linked to access to the large mineral N proportion redistributed to the lower depth as depicted by highest MBN (0.025 mg N g−1 soil) and decreased extractable N (0.0068 mg N g−1 soil). The high emissions under barley correlated with high fungal/bacterial ratio, pointing towards a fungal role in the emissions. The least soil N2O emissions under barley and Italian ryegrass combination were accompanied by elimination of variations induced by the plant growth stages. Absence of 18:2ω6,9 fungal PLFA biomarker under barley and Italian ryegrass combination indicates a potential inhibition and corresponds with reduced N2O emissions. Together, these results broaden our understanding on how plant-soil interactions drives N2O emissions processes and improves our ability to identify optimal plant-based emission mitigation approaches.

Salt stimulates sulfide−driven autotrophic denitrification: Microbial network and metagenomics analyses

Sulfur autotrophic denitrification (SADN) is a promising biological wastewater treatment technology for nitrogen removal, and its performance highly relies on the collective activities of the microbial community. However, the effect of salt (a prevailing characteristic of some nitrogen−containing industrial wastewaters) on the microbial community of SADN is still unclear. In this study, the response of the sulfide−SADN process to different salinities (i.e., 1.5 % salinity, 0.5 % salinity, and without salinity) as well as the involved microbial mechanisms were investigated by molecular ecological network and metagenomics analyses. Results showed that the satisfactory nitrogen removal efficiency (>97 %) was achieved in the sulfide−SADN process (S/N molar ratio of 0.88) with 1.5 % salinity. In salinity scenarios, the genus Thiobacillus significantly proliferated and was detected as the dominant sulfur−oxidizing bacteria in the sulfide−SADN system, occupying a relative abundance of 29.4 %. Network analysis further elucidated that 1.5 % salinity had enabled the microbial community to form a more densely clustered network, which intensified the interactions between microorganisms and effectively improved the nitrogen removal performance of the sulfide−SADN. Metagenomics sequencing revealed that the abundance of functional genes encoding for key enzymes involved in SADN, dissimilatory nitrate reduction to ammonium, and nitrification was up−regulated in the 1.5 % salinity scenario compared to that without salinity, stimulating the occurrence of multiple nitrogen transformation pathways. These multi−paths contributed to a robust SADN process (i.e., nitrogen removal efficiency >97 %, effluent nitrogen <2.5 mg N/L). This study deepens our understanding of the effect of salt on the SADN system at the community and functional level, and favors to advance the application of this sustainable bioprocess in saline wastewater treatment.

Nitrogen recycling characteristics in multiphase transformation during municipal sludge pyrolysis

The nitrogen content of municipal sludge is as high as 2.5～9.0 wt%, which has become an important problem in pollution control during pyrolysis. Recycling nitrogen from municipal sludge not only enables resource utilization, but also reduces the nitrogen-related pollution. In this study, the transformation pathways of nitrogen to resource material and typical pollutants during the municipal sludge pyrolysis process were analyzed. The results showed that the nitrogen species in municipal sludge were mainly protein-N (64.41%), pyridine-N (19.47%) and inorganic-N (16.13%). After pyrolysis at 300 °C, the peptide bond of protein-N was gradually broken down, resulting in the formation of three nitrogenous intermediates (amine-N, nitrile-N and heterocyclic-N) were produced. These intermediates can be transformed to NH3 for resource recovery or to HCN pollutants. Moreover, the full nitrogen transformation pathways of municipal sludge pyrolysis were constructed by the method of Spearman's correlation coefficient and experiment analysis. It was found that NH3 and HCN were mostly generated from the cracking of three nitrogenous intermediates at 600–800 °C. In addition, there was a prominent effect on the transformation of HCN to NH3 with co-presence of calcium minerals in raw sludge. By adding inorganic calcium minerals, NH3 as a recyclable component was prominently improved by 10.30% at 700 °C, while HCN yield was decreased by 53.02% accordingly under the inhibitory effect. The results systematically provided a theoretical support to the possibility of nitrogen recycling for utilization during municipal sludge pyrolysis, as well as to control the transformation of nitrogen elements into pollutants.

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.

Differences of Nitrogen Transformation Pathways and Their Functional Microorganisms in Water and Sediment of a Seasonally Frozen Lake, China

Nitrogen is one of the most important elements involved in ecosystem biogeochemical cycling. However, little is known about the characteristics of nitrogen cycling during the ice-covered period in seasonally frozen lakes. In this study, shotgun metagenomic sequencing of subglacial water and sediment from Lake Ulansuhai was performed to identify and compare nitrogen metabolism pathways and microbes involved in these pathways. In total, ammonia assimilation was the most prominent nitrogen transformation pathway, and Bacteria and Proteobacteria (at the domain and phylum levels, respectively) were the most abundant portion of microorganisms involved in nitrogen metabolism. Gene sequences devoted to nitrogen fixation, nitrification, denitrification, dissimilatory nitrate reduction to ammonium, and ammonia assimilation were significantly higher in sediment than in surface and subsurface water. In addition, 15 biomarkers of nitrogen-converting microorganisms, such as Ciliophora and Synergistetes, showed significant variation between sampling levels. The findings of the present study improve our understanding of the nitrogen cycle in seasonally frozen lakes.

Nitrogen removal by algal-bacterial consortium during mainstream wastewater treatment: Transformation mechanisms and potential N2O mitigation

This work investigated nitrogen transformation pathways of the algal-bacterial consortium as well as its potential in reducing nitrous oxide (N2O) emission in enclosed, open and aerated reactors. The results confirmed the superior ammonium removal performance of the algal-bacterial consortium relative to the single algae (Chlorella vulgaris) or the activated sludge, achieving the highest efficiency at 100% and the highest rate of 7.34 mg N g MLSS−1 h−1 in the open reactor with glucose. Enhanced total nitrogen (TN) removal (to 74.6%) by the algal-bacterial consortium was achieved via mixotrophic algal assimilation and bacterial denitrification under oxygen-limited and glucose-sufficient conditions. Nitrogen distribution indicated that ammonia oxidation (∼41.8%) and algal assimilation (∼43.5%) were the main pathways to remove ammonium by the algal-bacterial consortium. TN removal by the algal-bacterial consortium was primarily achieved by algal assimilation (28.1–40.8%), followed by bacterial denitrification (2.9–26.5%). Furthermore, the algal-bacterial consortium contributed to N2O mitigation compared with the activated sludge, reducing N2O production by 35.5–55.0% via autotrophic pathways and by 81.0–93.6% via mixotrophic pathways. Nitrogen assimilation by algae was boosted with the addition of glucose and thus largely restrained N2O production from nitrification and denitrification. The synergism between algae and bacteria was also conducive to an enhanced N2O reduction by denitrification and reduced direct/indirect carbon emissions.

Effect of biochar and nitrogen fertilizers on maize seedling growth and enzyme activity relating to nitrification

AbstractMaximizing nitrogen use efficiency (NUE) involves synchronizing the interplay between nitrogen preferential crops and the nitrogen transformation pathways of soil. Biochar may benefit specific N‐preference crops in relatively unsuitable soil environments; however, experimental data are lacking. This study tested eight treatments, consisting of four nitrogen treatments (N0 = control; N1 = NH4Cl; N2 = NaNO3; and N3 = 1:1 ratio of NH4+ and NO3−) each with biochar applied at 0% or 2% (w/w). The results show that biochar and/or nitrogen application enhanced maize seedling biomass and NO3−‐based fertilizer resulted in higher seedling biomass than NH4+‐based fertilizer. With the application of biochar and NH4+‐based fertilizer, maize seedling biomass increased and soil NH4+‐N content was significantly reduced compared with NH4Cl sole application. Correlation analysis and redundancy analysis revealed that SOC content and inorganic nitrogen content were the main factors influencing maize growth and N absorption. Biochar with or without nitrogen fertilizer (except N1 treatment) significantly increased β‐1,4‐glucosidase (BG) activity. Co‐application treatments also resulted in higher vector length, an indicator of C limitation—the increment might add to the risk of microbial C limitation. The activity of ammonia monooxygenase (AMO), a key enzyme in nitrification, decreased with the co‐application of biochar and nitrogen, suggesting the alteration of nitrogen transformation.

Effect of different-sized bulking agents on nitrification process during food waste digestate composting

ABSTRACT Food waste digestate (FWD) disposal is a serious bottleneck in anaerobic digestion plants to achieve a circular bioeconomy. FWD could be recycled into nitrogen-rich compost; however, the co-composting process optimisation along with bulking agents is required to reduce nitrogen loss and unwanted gaseous emissions. In the present study, two different-sized bulking agents, namely, wood shaving (WS) and fine sawdust (FS), were used to investigate their impact on FWD composting performance along with the nitrogen dynamics. The mixing of FWD with different bulking agents altered the physiochemical characteristics of composting matrix and the effective composting performance was observed through reduced ammonium nitrogen and increased seed germination index during 28 days of composting. The carbon loss of 19–22% through CO2 emission indicated similar carbon mineralisation with both types of sawdust; however, the nitrogen transformation pathways were different. Only WS treatment demonstrated the nitrification process, whereas the nitrogen loss was higher with FS. A total nitrogen loss of ∼15% was observed in treatments with FS, whereas WS treatments displayed a nitrogen loss of 12%. The outcome of the present study could significantly contribute to the practical aspect of the FWD composting operation with the promotion of the bio-recycling economy.

Abundance, diversity and changes to environmental variables of comammox Nitrospira in bioretention system

The nitrogen removal of bioretention system (BRS) mainly depends on various microorganisms, among which complete ammonia oxidization bacteria (comammox) are important nitrogen removers. However, the abundance and diversity of comammox Nitrospira in BRS have been rarely studied, and its role in ammonia oxidation is unknown. In this study, 18 field BRSs were investigated to distinguish the abundance and diversity of comammox Nitrospira followed by a mesocosm bioretention experiment to examine the variation in the abundance of comammox Nitrospira after rainfall event. The results showed that: (1) comammox Nitrospira amoA functional genes were widely distributed in the field BRSs with the absolute abundance of 4.72 × 102 to 9.97 × 103 copies∙g−1 dry soil; (2) within 12–24 h after rainfall event, comammox Nitrospira increased rapidly, and its growth rate was even higher than that of ammonia oxidizing bacteria (AOB); (3) a total of 20 operational taxonomic units (OTUs) of comammox Nitrospira amoA genes were detected in the field BRSs. These OTUs were classified as Nitrospira inopinata, Ca. Nitrospira nitrificans, and comammox Nitrospira clade A.2.1 on phylogeny. Except one unique OTU, the other OTUs were phylogenetically similar to the sequences detected in wetlands; (4) different OTUs responded differently to soil physicochemical factors, indicating the environmental adaptability of comammox Nitrospira. These results were helpful to improve the understanding of microbial nitrogen transformation pathways and their roles in BRS.

Dissimilatory nitrate reduction processes in surface sediments of shrimp ponds during the culture period

Intensive aquaculture in estuaries and coasts has resulted in several ecological and environmental problems. Among various nitrogen transformation pathway, dissimilatory nitrate (NO3-) reduction is considered to be highly important in regulating reactive nitrogen. However, there are relatively few studies on the processes and contribution of NOx- reduction in sediment during the shrimp pond culture period. Three sediment NO3- reduction processes, denitrification (DNF), anaerobic ammonium oxidation (ANA), and dissimilatory NO3- reduction to ammonium (DNRA), were surveyed in eight shrimp ponds across three subtropical estuaries using 15N isotope tracing experiments. The rates of DNF, ANA and DNRA ranged from 2.87–18.11, 0.10–1.92, and 0.21–1.25 nmol N g -1 h -1, respectively. DNF was responsible for 64.2–91.6% of the total NO3- reduction. Regarding environmental factors, C and N substrates, as well as salinity, significantly affected NO3- reduction. In general, the N losses were approximately 32.43–131.64 g N m-2 yr-1 for DNF and 2.38–15.85 g N m-2 yr-1 for ANA in this study, indicating that coastal reclamation is a nonnegligible way to remove nitrogen. Our results provide a scientific foundation for understanding the mechanism of nitrogen cycling in the artificial aquatic environment of shrimp ponds.

Low strength wastewater anammox start-up and stable operation by inoculating sponge-iron sludge: Cooperation of biological iron and iron bacteria

The application of anaerobic ammonium oxidation (Anammox) technology in low-strength wastewater treatment still faces difficult in-situ start-ups and unstable operations. Sponge-iron sludge (R1) was used as a novel inoculum to provide a promising solution. Conventional activated sludge (R0) was used as the control. However, little is known about the feasibility and performance during the start-up and operation of Anammox combined with biological iron and iron bacteria in an iron sludge system. Anammox was successfully started both in R1 (87 days) and R0 (89 days) with a low-strength influent (with a nitrogen loading rate (NLR) of 43.64 ± 0.41 g N/(m3⋅d)). During long-term operation, the R0 nevertheless produced higher nitrates (9.7 ± 0.1 mg/L) than expected. In contrast, R1 presented no excess nitrate production (2.1 ± 0.06 mg/L). The total inorganic nitrogen (TIN) removal efficiency increased from 78.2 ± 7.1% in R0 to 86.1 ± 4.3% in R1. The iron sludge in R1 was divided equally into three parts and three different nitrogen-feeding methods were used over the 34 days of operation, as follows: first using a mixture of ammonium (27.15 ± 1.0 mg/L) and nitrite (32.7 ± 1.7 mg/L), then only ammonium (27.15 ± 1.0 mg/L) and lastly only nitrite (32.7 ± 1.7 mg/L) as the influent. R1 was a coupled system composed of Anammox, Feammox, and NOx−-dependent Fe(II) oxidation (NDFO). The contribution of Feammox and NDFO to TIN removal was 27.1 ± 1.2% and 31.9 ± 0.7%. However, Anammox was the primary nitrogen transformation pathway. X-ray diffraction (XRD) analysis shows that iron hydroxide (Fe(OH)3) and iron oxide hydroxide (FeOOH) were generated in R1. The produced Fe(OH)3 and FeOOH were capable of participating in Feammox and formed a Fe(II)/Fe(III) cycle which further removed nitrogen. Therefore, a highly stable and impressive nitrogen removal performance was demonstrated in the iron sludge Anammox system under the cooperation of biological iron and iron bacteria. The study considered the enrichment of norank_c_OM190, Desulfuromonas, and Thiobacillus and their contribution to the Anammox, Feammox, and NDFO processes, respectively. This study provides a new perspective for the start-up and stable operation of low-strength wastewater Anammox engineering applications.

Altered nitrogen transformation pathways and a legacy of sediment organic matter enrichment

Estuaries are ecologically valuable ecosystems that process nutrients through complex biogeochemical processes. Here we identify drivers and inhibitors of nitrogen removal in unvegetated intertidal sandflats at six sites in Manukau Harbour (37° 2.00′S 174° 42.00′E) to quantify the exchange of solutes across the sediment-water interface, with nitrogen removal rates (NRR) measured at two contrasting sites (PI and CB) near and far, respectively, from an historical wastewater treatment plant. Solute fluxes were paired with sediment and macrofauna community data to identify drivers of ecosystem function. Fluxes of oxygen, nitrogen and phosphorous were found to vary among sites, with differences attributed to variation in sediment characteristics (grain size, chlorophyll a, organic content) and macrofauna community structure. Mean NRR was found to vary between sites (PI = 32.2 vs CB = 217.9 μmol N2/m2/h), with bioturbating macrofauna (bivalves Austrovenus stutchburyi and Macomona liliana), microphytobenthic biomass, and exposure to nutrients likely key contributing drivers.

Comparison of Swine Wastewater Treatment by Microalgae and Heterotrophic Nitrifiers: Focusing on Nitrogen Removal Mechanism Revealed by Microbiological Correlation Analysis

Swine wastewater (SW) poses a great threat to the environment due to its high-nutrient profiles if not properly managed. Advanced biological treatment method is an efficient method to treat SW by screening potent microalgae or bacterial strains. In this study, activated sludge, three locally isolated heterotrophic nitrification bacteria and one microalgal strain (Chlorella) were used as inoculums in treating a local SW. Their treatment efficiencies were compared, while the nitrogen removal mechanisms and microbiome profile were explored in detail. It was found that certain heterotrophic nitrification strains had a slight advantage in removing chemical oxygen demand and phosphorus from SW, with the highest removal efficiencies of 83.9% and 76.2%, respectively. The removal efficiencies of ammonia nitrogen and total nitrogen in wastewater by microalgae reached 80.9% and 66.0% respectively, which were far higher than all the heterotrophic nitrification strains. Biological assimilation was the main pathway of nitrogen conversion by microalgae and heterotrophic nitrifying bacteria; especially microalgae showed excellent biological assimilation performance. Correlation analysis showed that Comamonas was highly positively correlated with nitrogen assimilation, while Acidovorax was closely correlated with simultaneous nitrification and denitrification. This study gives a comparison of microalgae and heterotrophic nitrifying bacteria on the nitrogen transfer and transformation pathways.

Microbial community and carbon–nitrogen metabolism pathways in integrated vertical flow constructed wetlands treating wastewater containing antibiotics

This study demonstrates effects of sulfamethoxazole (SMX) on carbon–nitrogen transformation pathways and microbial community and metabolic function response mechanisms in constructed wetlands. Findings showed co-metabolism of SMX with organic pollutants resulted in high removal of 98.92 ± 0.25% at influent concentrations of 103.08 ± 13.70 μg/L (SMX) and 601.92 ± 22.69 mg/L (COD), and 2 d hydraulic retention. Microbial community, co-occurrence networks, and metabolic pathways analyses showed SMX promoted enrichment of COD and SMX co-metabolizing bacteria like Mycobacterium, Chryseobacterium and Comamonas. Relative abundances of co-metabolic pathways like Amino acid, carbohydrate, and Xenobiotics biodegradation and metabolism were elevated. SMX also increased relative abundances of the resistant heterotrophic nitrification–aerobic denitrification bacteria Paracoccus and Comamonas and functional genes nxrA, narI, norC and nosZ involved in simultaneous heterotrophic nitrification-aerobic denitrification. Consequently, denitrification rate increased by 1.30 mg/(L∙d). However, insufficient reaction substrate and accumulation of 15.29 ± 2.30 mg/L NO3–-N exacerbate inhibitory effects of SMX on expression of some denitrification genes.

Microbial community and nitrogen transformation pathway in bioretention system for stormwater treatment in response to formulated soil medium

Bioretention system has been commonly recognized as an emerging management method to control urban rainwater runoff. However, nitrogen conversion mechanisms in bioretention system in response to formulated soil medium remains unknown. In this work, five bioretention columns with different formulated soil medium were established, and results indicated that all bioretention columns achieved high NH4+-N removal rate, but exhibited significantly different NO3--N removal performance. High-throughput sequencing results suggested that nitrification might be achieved by heterotrophic nitrifying bacteria, while Pseudomonas and Rubellimicrobium may be the main denitrifying bacteria, which served as anaerobic and aerobic denitrifier, respectively. Heterotrophic nitrification-anaerobic/aerobic denitrification may the microbial pathways to realize effective nitrogen removal performance in these bioretention systems. Bioretention system with moderate silt content (NC, 10%) displayed higher abundant potential denitrifier, leading to better nitrogen removal performance. Besides, soil adsorption played an important role in nitrogen removal, particularly when activated carbon was added. This work could provide guidance of formulated soil medium optimization for the application of bioretention systems.

Tracing N2O formation in full-scale wastewater treatment with natural abundance isotopes indicates control by organic substrate and process settings

Nitrous oxide (N2O) dominates greenhouse gas emissions in wastewater treatment plants (WWTPs). Formation of N2O occurs during biological nitrogen removal, involves multiple microbial pathways, and is typically very dynamic. Consequently, N2O mitigation strategies require an improved understanding of nitrogen transformation pathways and their modulating controls. Analyses of the nitrogen (N) and oxygen (O) isotopic composition of N2O and its substrates at natural abundance have been shown to provide valuable information on formation and reduction pathways in laboratory settings, but have rarely been applied to full-scale WWTPs.Here we show that N-species isotope ratio measurements at natural abundance level, combined with long-term N2O monitoring, allow identification of the N2O production pathways in a full-scale plug-flow WWTP (Hofen, Switzerland). Heterotrophic denitrification appears as the main N2O production pathway under all tested process conditions (0–2 mgO2/l, high and low loading conditions), while nitrifier denitrification was less important, and more variable. N2O production by hydroxylamine oxidation was not observed. Fractional N2O elimination by reduction to dinitrogen (N2) during anoxic conditions was clearly indicated by a concomitant increase in site preference, δ18O(N2O) and δ15N(N2O). N2O reduction increased with decreasing availability of dissolved inorganic N and organic substrates, which represents the link between diurnal N2O emission dynamics and organic substrate fluctuations. Consequently, dosing ammonium-rich reject water under low-organic-substrate conditions is unfavorable, as it is very likely to cause high net N2O emissions.Our results demonstrate that monitoring of the N2O isotopic composition holds a high potential to disentangle N2O formation mechanisms in engineered systems, such as full-scale WWTP. Our study serves as a starting point for advanced campaigns in the future combining isotopic technologies in WWTP with complementary approaches, such as mathematical modeling of N2O formation or microbial assays to develop efficient N2O mitigation strategies.

The marine nitrogen cycle: new developments and global change.

The ocean is home to a diverse and metabolically versatile microbial community that performs the complex biochemical transformations that drive the nitrogen cycle, including nitrogen fixation, assimilation, nitrification and nitrogen loss processes. In this Review, we discuss the wealth of new ocean nitrogen cycle research in disciplines from metaproteomics to global biogeochemical modelling and in environments from productive estuaries to the abyssal deep sea. Influential recent discoveries include new microbial functional groups, novel metabolic pathways, original conceptual perspectives and ground-breaking analytical capabilities. These emerging research directions are already contributing to urgent efforts to address the primary challenge facing marine microbiologists today: the unprecedented onslaught of anthropogenic environmental change on marine ecosystems. Ocean warming, acidification, nutrient enrichment and seawater stratification have major effects on the microbial nitrogen cycle, but widespread ocean deoxygenation is perhaps the most consequential for the microorganisms involved in both aerobic and anaerobic nitrogen transformation pathways. In turn, these changes feed back to the global cycles of greenhouse gases such as carbon dioxide and nitrous oxide. At a time when our species casts a lengthening shadow across all marine ecosystems, timely new advances offer us unique opportunities to understand and better predict human impacts on nitrogen biogeochemistry in the changing ocean of the Anthropocene.