Ammonia Oxidation Research Articles

Investigation on the reduction in unburned ammonia and nitrogen oxide emissions from ammonia direct injection SI engine by using SCR after-treatment system

Currently generated nitrogen oxides (NOx) and unburned ammonia (NH3) can be converted into nitrogen and moisture that are harmless to the human body and environment using selective catalytic reduction (SCR). The concentrations of NOx and unburned NH3 emitted from the ammonia combustion engines are significantly higher than those emitted by engines using existing hydrocarbon fuels. In this study, ammonia, a representative carbon-free fuel, was used in spark ignition engines for existing passenger vehicles to identify the trends in exhaust gases emitted from engines and conduct experiments on after-treatment strategies to reduce NOx and unburned NH3. The addition of oxygen significantly maximized the conversion efficiency of the SCR after-treatment system by changing the concentration of both NOx and NH3 in the exhaust gas.

CePO4 supported Cr catalyst with superior sulfur tolerance for selective catalytic oxidation of ammonia

CePO4 supported Cr catalyst with superior sulfur tolerance for selective catalytic oxidation of ammonia

Electro-nitrification coupled with biological denitrification achieves efficient nitrogen removal from rare earth mine ammonia-nitrate wastewater

Nowadays, ammonia-nitrate wastewater has been posed serious environmental hazards. Electrochemical ammonia oxidation (AOR) technology with environmentally friendly and easy-to-operate features has attracted much attention. In this work, a novel anode catalytic electrode (Ni1Cu1Fe0.5-S/Ti) is prepared by a one-step electrodeposition method for electro-nitrification, and coupled a biological denitrification device for the treatment of real ammonia-nitrate wastewater. The unique three-dimensional layered spherical structure of Ni1Cu1Fe0.5-S/Ti electrode has been verified through physical characterization, and electrochemical tests demonstrated that Ni1Cu1Fe0.5-S/Ti electrode gained an excellent current density of 54.48 mA·cm−2 toward to AOR at 0.65 V vs. Hg/HgO as well as good stability for four times repeated electro-nitrification experiments. The optimal experimental operating conditions were obtained by changing electrode spacing, initial NH4+-N concentration, current density and flow rate. Consequently, 97.7 % total nitrogen (TN) removal efficiency of real wastewater is achieved through electro-nitrification coupled with biological denitrification, providing a new perspective technology for ammonia-nitrate wastewater treatment.

Impact of N loading on Microbial Community Structure and Nitrogen Removal of an Activated Sludge Process with Long SRT for municipal wastewater treatment

Biological nutrient removal process is pivotal in controlling nitrogen and phosphorus from municipal wastewater treatment and reclamation plants in the water environment. The efficiency of municipal wastewater treatment is affected by the fluctuation of influent quality. In this study, the impact of N loading on the removal efficiency and the microbial community structure of activated sludge with long sludge retention time were investigated. The results showed that the effluent NH4+-N and NO2--N concentration were lower than 0.5 mg/L, and the TN removal efficiencies were 79.77% and 65.80%, respectively. The dehydrogenase activity, specific oxygen uptake rate, specific nitrification rate, and specific denitrification rate increased as the N loading increasing. At the phylum level, the most dominant bacterial was affiliated with Proteobacteria in the two systems, accounting for 60.65% and 48.62%, respectively. At the genus level, Acinetobacter, Thauera, and Zoogloea played significant roles in denitrification. The ammonia oxidation bacteria and nitrite-oxidizing bacteria were of the genus Nitrosomonas (r-strategist) and Nitrospira (K-strategist).

Enhancing collaboration of anammox with heterotrophic microbes mediated selectively by iron of different valences: Activities balance, metabolic mechanism, and functional genes regulation

The partial denitrification/anammox (PD/A) process is receiving increasing attention due to its cost-effectiveness advantages. However, effective strategies to alleviate organic matter inhibition and promote anammox activity have been proven to be a big challenge. This study investigated the effects of three types of iron (nano zero-valent iron (nZVI), Fe(II), and Fe(III)) on the PD/A process. It is worth noting that nZVI of 5–50 mg/L and Fe(III) of 5–120 mg/L promoted both PD and anammox activity. Long-term intermittent addition of nZVI (50 mg/L) resulted in a nitrogen removal efficiency of 98.2% in the mixotrophic PD/A system driven by iron and organic matter. The contribution of anammox for nitrogen removal reached as high as 93.8%. The organic carbon demand decreased due to the external electron donor provided by nZVI for PD. Multiple Fe–N metabolic pathways, primarily involving ammonia oxidation by Fe(III) and nitrate reduction by nZVI, play a crucial role in facilitating nitrogen transformation. Conversely, the direct addition of 30–120 mg/L Fe (II) resulted in a significant decrease in pH to below 5.0 and severe inhibition of PD and anammox activity. Following prolonged operation in the presence of nZVI, it was demonstrated that there is an enhancing effect on robust nitrite production for anammox. This was accompanied by a remarkable up-regulation of genes encoding nitrate reductase and iron-transporting proteins dominated by Thauera. Overall, this study has provided an efficient approach for advanced nitrogen removal through organic- and iron-driven anammox processes.

Environmental Adaptability and Roles in Ammonia Oxidation of Aerobic Ammonia-Oxidizing Microorganisms in the Surface Sediments of East China Sea.

This study investigated the community characteristics and environmental influencing factors of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in the surface sediments of the East China Sea. The research found no consistent pattern in the richness and diversity of AOA and AOB with respect to the distance from the shore, indicating a complex interplay of factors. The expression levels of AOA amoA gene and AOB amoA gene in the surface sediments of the East China Sea ranged from 4.49 × 102 to 2.17 × 106 copies per gram of sediment and from 6.6 × 101 to 7.65 × 104 copies per gram of sediment, respectively. Salinity (31.77 to 34.53 PSU) and nitrate concentration (1.51 to 10.12 μmol/L) were identified as key environmental factors significantly affecting the AOA community, while salinity and temperature (13.71 to 19.50°C) were crucial for the AOB community. The study also found that AOA, dominated by the Nitrosopumilaceae family, exhibited higher gene expression levels than AOB, suggesting a more significant role in ammonia oxidation. The expression of AOB was sensitive to multiple environmental factors, indicating a responsive role in nitrogen cycles and ecosystem health. The findings contribute to a better understanding of the biogeochemical processes and ecological roles of ammonia-oxidizing microorganisms in marine sediments.

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.

Effects of biochar and wood vinegar co-application on composting ammonia and nitrous oxide losses and fertility

Composting faces challenges with nitrogen (N) losses through ammonia (NH3) and nitrous oxide (N2O) emissions. In this study, wood vinegar (WV) and biochar (BC) were applied individually or combined into wheat straw and chicken manure composting. Results showed that BC and WV reduced NH3 volatilizations by 22–23 % individually, but their combined application achieved a 59 % reduction. However, this combination increased N2O emissions by 174 %. The BC + WV treatment improved compost quality, evidenced by increased total N content by 22 % and enhanced the biological index, promoting additional dissolved organic matter production. Overall, BC and WV applications improved compost quality, reduced gaseous N losses, and supported the re-utilization of agricultural residues. The combined use of BC and WV significantly enhances compost quality and reduces NH3 emissions, offering a promising solution for sustainable agricultural residue management.

Effects of iron-carbon on nitrogen metabolism of floc and aerobic granular sludge

The aerobic granular sludge (AGS) process had been extensively studied for its simultaneous nitrification and denitrification (SND) capabilities. Iron-carbon (IC) had enhanced AGS nitrogen removal efficiency, but the mechanism remained unclear. In this study, four reactors had been added with 50, 30, 10, and 0 g/L of IC. Total nitrogen removal efficiency increased with IC dosage under the same operation mode. IC enhanced sludge ammonia oxidation rate, denitrification rate, and specific oxygen uptake rate, allowing SND to complete 60 min earlier, potentially reducing wastewater treatment costs. Notably, IC eliminated nitrite accumulation in conventional AGS effluent. IC decreased the abundance of genes and enzyme activities related to NOR expression, while increasing those related to NOS, which may mitigate the potential for nitrous oxide formation by microorganisms. In this study, IC acted as an enzymatic reaction activator, affecting granules more than flocs, with the activity gap gradually decreasing with the IC dosage.

Enhancing anaerobic ammonium oxidation via polymeric ferric sulfate (PFS)-Mediated dual-electron Acceptor: A solution to nitrite deficiency

In addressing the issue of the unstable supply of electron acceptors (nitrite) during Anammox, researchers have often overlooked that the electron transfer process in anammox bacteria (AnAOB) is not restricted to the intracellular, extracellular electron transfer can also serve as an alternative pathway. This study utilized Fe3+ as an adjunctive electron acceptor, coupling Anammox with ferric iron reduction (Feammox) by introducing polymeric ferric sulfate (PFS) in the Anammox system. This approach achieved effective nitrogen removal even when nitrite was deficient. At a NO2–-N to NH4+-N ratio of 0.5, the Feammox-Anammox combined system maintained stable nitrogen removal under the dual electron acceptor, with total nitrogen and NH4+-N removal efficiency of 85 % and 91 %, respectively. The contribution of Feammox and Anammox to NH4+-N removal was 45 % and 55 %, respectively. TEM-EDS confirmed the presence of iron elements across the periphery, periplasm, and cytoplasm of AnAOB, suggesting the involvement of PFS in the metabolic and electron transfer processes. Notably, the introduction of Fe3+ and the limitation of nitrite availability resulted in increased relative abundances of FeOB (Thermomonas) and FeRB (Ignavibacterium) to 30 % and 3.6 %, respectively, indicating that the electron transfer process with Fe3+ as the electron acceptor was continuously intensified, as well as a cycle of Fe3+ / Fe2+ was established. Due to unique nitrogen metabolism mode and high Fe3+ tolerance, the abundance of Candidatus_Brocadia was enriched up to 7.2 %, which alternately dominated the Anammox process with Candidatus_Kuenenia, providing favorable conditions for AnAOB to carry out the extracellular electron transfer process. These findings provide a novel strategy for improving the stability and efficiency of the Anammox process under deficient nitrite supply.

Characteristics and nontargeted metabolomics analysis of anammox granular sludge under short-term exposure to polypropylene and polylactic acid microplastics

A significant quantity of microplastics (MPs) is concealed within biological sludge. Current research predominantly examines the effects of non-biodegradable MPs on traditional sludge. However, the influence of biodegradable MPs on the functional microbial activity of anaerobic ammonium oxidation granular sludge (AnGS) remains inadequately explored. This study specifically investigated the effects of non-biodegradable polypropylene (PP) MPs and biodegradable polylactic acid (PLA) MPs on AnGS under short-term stress. The study found that PP MPs inhibited nitrogen removal performance, reducing nitrogen removal efficiency by 1.14% (100 mesh) and 5.77% (1000 mesh) respectively, along with decreased hydrazine dehydrogenase (HDH) activity. Conversely, PLA promoted denitrification performance, increasing efficiency by 8.21% (100 mesh) and 6.54% (1000 mesh). In response to MPs-induced environmental stress, the secretion of extracellular polymeric substances (EPS) increased in all experimental groups. Additionally, non-targeted metabolomic analysis revealed a decrease in the abundance of KEGG pathways related to carbon and amino acid metabolism in the experimental groups, while the enrichment of terephthalate and benzamide in the PLA groups significantly impacted its process. These findings offered valuable insights into the impact of MPs on anaerobic ammonium oxidation (anammox) and could potentially enhance its application.

Promoting effect of Cu as electron transfer medium on NH3-SCO reaction in asymmetric Ag-Ov-Ti-Sm-Cu ring active site

Selective catalytic oxidation of ammonia (NH3-SCO) has become an effective method to reduce ammonia (NH3) emissions, and is a key part to solve the problem of NH3 pollution. Nevertheless, the optimization of this technology’s performance relies heavily on innovation and the development of catalyst design. In this study, a SmCuAgTiOx catalyst with an asymmetric Ag-Ov-Ti-Sm-Cu ring active site was prepared and applied to the NH3-SCO reaction. The low conversion of Cu-based catalysts in NH3 at low temperature and the inherent low N₂ selectivity of Ag-based catalysts were solved. The successful creation of the asymmetric ring active site improved the catalyst’s reduction performance. Additionally, Cu, acting as an electron transfer medium, plays a crucial role in enhancing electron transfer within the asymmetric ring active site, thus increasing the redox cycle of the catalyst during the reaction. In addition, some lattice oxygen is lost in the catalyst, resulting in the formation of a large number of oxygen vacancies. This process stimulates the adsorption and activation of surface-adsorbed oxygen, facilitating the conversion of NH3 to an amide (NH2) intermediate during the reaction and reducing non-selective oxidation. The N2 selectivity was improved without significantly affecting the performance of Ag-based catalyst. In-situ diffuse reflectance fourier transform infrared spectroscopy (In-situ DRIFTS) analysis reveals that the SmCuAgTiOx catalyst primarily follows an “internal” selective catalytic reduction (iSCR) mechanism in the NH3-SCO reaction, complemented by the imide mechanism. The asymmetric Ag-Ov-Ti-Sm-Cu ring active site developed in this study provides a new perspective for efficiently solving NH3 pollution in the future.

Fabrication of Platinum-Decorated NiCo-Layered Double Hydroxide Nanoflowers for Electrocatalytic Ammonia Oxidation Reaction

The complete anodic oxidation of ammonia is an important part of direct ammonia fuel cells. Fabricating a high-performance electrocatalyst for ammonia oxidation reaction is meaningful for developing a direct ammonia fuel cell. Herein, we designed one platinum-decorated NiCo-layered double hydroxide nanoflower on Ni foam (Pt-NiCo-LDH-Ni foam) and measured the electrocatalytic performance via the cyclic voltammetry (CV) technique. The experimental results demonstrated that the optimized Pt-NiCo-LDH-Ni foam showed great electrocatalytic performance, with a low overpotential with a value of −0.573 V, a high current density of 17.75 mA cm−2 for the ammonia oxidation reaction, and good stability.

Oxidation of Ammonia in Water Microdroplets Produces Nitrate and Molecular Hydrogen.

Water microdroplets containing dissolved ammonia (30-300 μM) are sprayed through a copper oxide mesh with a 200 μm average pore size, resulting in the formation of nitrate (NO3-) and the release of molecular hydrogen (H2). The products result from a redox process that takes place at the liquid-solid interface through contact electrification, where no external potential is applied. Oxidation is initiated by superoxide radical anions (O2-) that originate from the oxygen in the air surrounding the microdroplets and from the hydroxyl radicals (OH•) originating from the water-air interface. Two spin traps (TEMPO and DMPO) capture these radicals as well as NH2OH+•, HNO, NO•, NO2•, and NOOH, which are detected by mass spectrometry. We also directly observed N2O2-• by the same means. We found that the hydrogen atom from the ammonia molecule can be set free not only in the form of H• but also as H2, which is detected using a residue gas analyzer. The oxidation process can be significantly enhanced by a factor of 3 when the sprayed microdroplets are irradiated with ultraviolet light (265 nm, 5 W). 35% of 300 μM ammonia can be degraded within 20 μs, and the nitrate conversion rate is estimated to be 15 nmol·mg-1·h-1.

Unveiling optimal activity and mechanism of in situ Ni reduction Pr2Ni1-xZnxO4 anode for ammonia solid oxide fuel cells

Kinetically sluggish ammonia oxidation and interference of H2 competing with NH3 active sites will suppress the output performance of direct ammonia solid oxide fuel cell (DA-SOFC). Herein, we select Zn2+ doped into Pr2NiO4 as precursor of Pr2Ni1-xZnxO4 (PNZx) that can be destroyed and converted into Pr2O3 together with in-situ Ni reduction, realizing the redistribution of elements in reduction atmosphere. Meanwhile, the foreign Zn2+ as a low-valent element is retained in Pr2O3 lattice due to the high segregation Gibbs free energy to form Ni/Pr2-xZnxO3, which aggravates the change of Pr3+ and Pr4+, thus enhancing the oxygen vacancy concentration. The Zn2+ promotes the reduction of Ni and quenches the adsorption capacity of H2, alleviating the “hydrogen poisoning” behavior. As a result, the maximum powder density of single cell based on PNZ0.1 supported by YSZ electrolyte is 134 mW·cm−2 at 800 ℃, which is more than twice higher than that of Ni/YSZ. Various characterizations reveal that the NH3 reaction path is the synergistic occurrence of ammonia decomposition and ammonia oxidation.

Elevated CO2 and Nitrogen Supply Boost N Use Efficiency and Wheat (T. aestivum cv. Yunmai) Growth and Differentiate Soil Microbial Communities Related to Ammonia Oxidization.

Elevated CO2 levels (eCO2) pose challenges to wheat (Triticum aestivum L.) growth, potentially leading to a decline in quality and productivity. This study addresses the effects of two ambient CO2 concentrations (aCO2, daytime/nighttime = 410/450 ± 30 ppm and eCO2, 550/600 ± 30 ppm) and two nitrogen (N) supplements (without N supply-N0 and with 100 mg N supply as urea per kg soil-N100) on wheat (T. aestivum cv. Yunmai) growth, N accumulation, and soil microbial communities related to ammonia oxidization. The data showed that the N supply effectively mitigated the negative impacts of eCO2 on wheat growth by reducing intercellular CO2 concentrations while enhancing photosynthesis parameters. Notably, the N supply significantly increased N concentrations in wheat tissues and biomass production, thereby boosting N accumulation in seeds, shoots, and roots. eCO2 increased the agronomic efficiency of applied N (AEN) and the physiological efficiency of applied N (PEN) under N supply. Plant tissue N concentrations and accumulations are positively related to plant biomass production and soil NO3--N. Additionally, the N supply increased the richness and evenness of the soil microbial community, particularly Nitrososphaeraceae, Nitrosospira, and Nitrosomonas, which responded differently to N availability under both aCO2 and eCO2. These results underscore the importance and complexity of optimizing N supply and eCO2 for enhancing crop tissue N accumulation and yield production as well as activating nitrification-related microbial activities for soil inorganic N availability under future global environment change scenarios.

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.

Gasdiffusionselektroden für die Elektrokatalytische Oxidation von Gasförmigem Ammoniak: Das Überqueren des Thermodynamischen Tals der Stickstoffdreifachbindung

AbstractDa Ammoniak als vielversprechender Wasserstoffträger immer mehr an Interesse gewinnt, wird auch die elektrochemische Ammoniak‐Oxidationsreaktion (AmOR) immer interessanter. Um die Freisetzung von H2 in einer umgekehrten Haber–Bosch‐Reaktion unter Bildung des energetisch günstigeren N2 zu vermeiden, schlagen wir die Oxidation von Ammoniak zu Nitrit (NO2−) vor, das üblicherweise während des Ostwald‐Prozesses gewonnen wird. Wir untersuchten die anodische Oxidation von gasförmigem Ammoniak, der direkt einer Gasdiffusionselektrode (GDE) zugeführt wird, unter Verwendung verschiedener, in ihrer Zusammensetzung unterschiedlicher Multimetallkatalysatoren, die auf Ni‐Schaum abgeschieden sind, bei gleichzeitiger Bildung von H2 an der Kathode. Dadurch wird die H2‐Menge pro Ammoniakmolekül verdoppelt, während gleichzeitig ein niedrigeres Überpotential als bei der Wasserelektrolyse (1,4–1,8 V gegen RHE bei 50 mA cm−2) angelegt wird. Eine Selektivitätsstudie zeigte, dass einige der Katalysatorzusammensetzungen in der Lage waren, erhebliche Mengen an NO2− zu produzieren. Weitere Untersuchungen mit dem vielversprechendsten Katalysator Nif_AlCoCrCuFe, der in eine GDE integriert ist, zeigten eine Faraday‐Effizienz von bis zu 88 % für NO2− an der Anode, gekoppelt mit einer Faraday‐Effizienz von nahezu 100 % für die kathodische H2‐Produktion.

Gas Diffusion Electrodes for Electrocatalytic Oxidation of Gaseous Ammonia: Stepping Over the Nitrogen Energy Canyon.

As ammonia continues to gain more and more interest as a promising hydrogen carrier compound, so does the electrochemical ammonia oxidation reaction (AmOR). To avoid the liberation of H2 in a reverse Haber-Bosch reaction under release of the energetically more favorable N2, we propose the oxidation of ammonia to value-added nitrite (NO2 -), which is usually obtained during the Ostwald process. We investigated the anodic oxidation of gaseous ammonia directly supplied to a gas diffusion electrode (GDE) using a variety of compositionally different multi-metal catalysts coated on Ni foam under the simultaneous formation of H2 at the cathode. This will double the amount of H2 per ammonia molecule while applying a lower overpotential than that required for water electrolysis (1.4-1.8 V vs. RHE at 50 mA ⋅ cm-2). A selectivity study demonstrated that some of the catalyst compositions were able to produce significant amounts of NO2 -, and further investigations using the most promising catalyst composition Nif_AlCoCrCuFe integrated within a GDE demonstrated up to 88 % Faradaic efficiency for NO2 - at the anode coupled to close to 100 % Faradaic efficiency for the cathodic H2 production.

Nitrogen removal pathways and microbial community structure in the aerobic granular sludge reactor with co-existence of granules and flocs

Granules and floc in the aerobic granular sludge (AGS) reactor undertook different roles in the nitrogen removal process and displayed significant disparities in microbial communities. This study quantified the contribution of different nitrogen removal pathways and analyzed the nitrogen removal mechanisms inside granules and flocs by metagenomics sequencing. The results showed that the AGS reactor performed excellent nitrogen removal efficiency and the removal efficiencies of NH4+-N and total nitrogen were more than 90.0 % and 60.0 %, respectively, with the main nitrogen form of NO2--N in the effluent. Batch experiments indicated that the nitrogen removal pathway was principally shortcut nitrification and denitrification (SCND), accounting for 51.6 %, followed by anaerobic ammonium oxidation (Anammox) accounting for 26.1 % and the remaining 22.3 % was simultaneous nitrification and denitrification (SND). The metagenomic sequencing results pointed out that the abundance of SCND-related genes in the granules was 0.18 %, and the abundance of Anammox-related genes was 0.02 %, which indicated that the granules mainly reduced nitrogen via SCND, and minor nitrogen was removed through Anammox. Inside the flocs, nitrogen was mainly reduced via the unconventional SND pathway (HAND). The in-depth analysis of the nitrogen removal process in the reactor with granules and flocs provides an important reference for further exploring the nitrogen removal mechanism, and supplies foundation for expanding the application of AGS.