Nitrite Oxidation Research Articles

A hybrid oxidation approach for converting high-strength urine ammonia into ammonium nitrate

Nutrient resources contained in human urine have great potential to alleviate global agricultural fertilizer demand. Microbial nitrification is a recognized strategy for stabilizing urine ammonia into ammonium nitrate, a common fertilizer worldwide, but faces a core bottleneck of process instability due to microbial inhibition. This study reports a new approach by developing a hybrid oxidation process involving three stages—microbial ammonia oxidation, chemical nitrite oxidation and microbial nitrite oxidation. Candidatus Nitrosoglobus, a γ-proteobacterial ammonia oxidizer highly tolerant to free nitrous acid, was introduced in the first stage to oxidize half of the total ammonia in the influent (8 g NH4+-N/L) to nitrite. The nitrite was then chemically oxidized by using hydrogen peroxide via a rapid chemical reaction to form nitrate. The third stage, microbial nitrite oxidation, was employed to ensure the complete removal of residual nitrite following chemical oxidation. The overall concept demonstrated in this work showcased the robust performance of the hybrid system. Moreover, the system also had a dual advantage in achieving antimicrobial ability in the first and second stages, making treated urine a safe fertilizer.

Response of ammonium transformation in bioanodes to potential regulation: Performance, electromicrobiome and implications

Understanding how potential regulation affects ammonium transformation in bioanodes is crucial for promoting their application. This study explored the performance, electrochemical properties, electromicrobiome of bioanodes across potentials from 0.0 V to 0.4 V vs. standard hydrogen electrode (SHE). Higher anode potentials enhanced the performance of electroactive biofilms and ammonium removal but suppressed nitrite oxidation while favoring dissimilatory nitrate reduction (DNRA), leading to increased nitrite accumulation. A reduction in nitrite-oxidizing bacteria (NOB) and an increase in DNRA-related genes resulted in an optimal nitrite-to-ammonium ratio of 1.32 for the Anammox process. Higher anodic potentials (0.3 and 0.4 V) were less effective for TN removal than lower potentials (0, 0.1, and 0.2 V), likely due to increased NOB and denitrification genes at lower potentials enhancing nitrite oxidation and denitrification. These findings indicate that regulating anodic potential effectively directs ammonium transformation in bioanodes, optimizing its conversion to N2 or nitrite.

Immunomodulatory activity of kersen leaf extract (Muntingia calabura) on diabetic rats: analysis of immune response

The immune response to high blood glucose levels leads to an inflammatory response and also produces inflammation mediators. Immunomodulatory functions of Kersen (Muntingia calabura) need further enhancement to ensure that its benefits are more widely recognized by the public. This study aims to determine the immunomodulatory activity of Kersen leaf in inducing and modulating the immune response in diabetic rats. This study was an experimental laboratory with a pre-and post-test with a control group design. The subjects were 30 white rats (Rattus Novergicus Wistar Strain), were treated with extract M. calabura dose 1 (100 mg/kg bw/day), dose 2 (200 mg/kg bw/day), dose 3 (300 mg/kg bw/day). For clinical evaluation, three control groups were formed, including a Normal Control Group, a Diabetes Mellitus (DM) Positive Group, and a DM Positive Group treated with Anti-Diabetic Drugs. The highest amount of IFN-γ concentrations were found in the DM positive control group + antidiabetic drugs (710.3 ± 27.2 ng/mL). The highest number of Nitrit Oxide (NO) concentration was found in the DM positive control group (103.7 ± 10.2 µmol/L). The highest average amount of pancreatic β cell regeneration was found in the normal control group. The DM positive control group and the treatment group had a significant difference (p < 0.05) It means that there is a significant difference in the data of all treatment groups, or these three groups have anti-diabetic activity by repairing or preventing damage to the pancreas organ in DM rats. This study revealed that M. calabura possesses immunomodulatory activity, capable of inducing and modulating immune responses in diabetic rats.

Investigation of Nitrogen Removal in Flue Gas Desulfurization and Denitrification Wastewater Utilizing Halophilic Activated Sludge.

In the process of flue gas desulfurization and denitrification, the generation of high-sulfate wastewater containing nitrogen is a significant challenge for biological wastewater treatment. In this study, halophilic activated sludge was inoculated in a Sequencing Batch Reactor to remove nitrogen from wastewater with a high sulfate concentration (60 g/L). With the influent concentration of 180 mg/L, the removal rate of total nitrogen was more than 96.7%. The effluent ammonium nitrogen concentration was lower than 1.94 mg/L, and the effluent nitrate nitrogen and nitrite nitrogen concentrations were even lower than 0.77 mg/L. The salt tolerance of activated sludge is mainly related to the increase in the content of ectoine in microbial cells. The Specific Nitrite Oxidation Rate is quite low, while the Specific Nitrite Reduction Rate and Specific Nitrate Reduction Rate are relatively strong. In the system, there are various nitrogen metabolic processes, including aerobic nitrification, anaerobic denitrification, and simultaneous nitrification-denitrification processes. By analyzing the nitrogen metabolic mechanisms and microbial community structure of the reaction system, dominate bacteria can be identified, such as Azoarcus, Thauera, and Halomonas, which have significant nitrogen removal capabilities.

Ecological practices increase soil fertility and microbial diversity under intensive farming

Intensive farming offers a potential solution to feed the growing population due to its high productivity. Conventional management (CO) based on inorganic fertilization practices degrades soil quality, but restorative practices including ecological intensification (EI) and organic management results in maintaining soil quality without compromising productivity. In this paper, two different management systems were evaluated: CO, based on inorganic fertilization, and EI, focused on providing organic nutrients to soils to support crops.EI increased soil fertility, together with higher alpha diversity indices, more differentially abundant amplicon sequence variant (ASVs) (247 EI vs. 165 CO) and indicator taxa (60 EI vs. 32 CO). Distinct bacterial taxa were associated with the different management systems, revealing their roles in soil processes and nutrient availability. In the CO treatment, indicator genera such as Nitrospira and Desulfarculaceae were linked to N fertilization and nitrite oxidation, while RB41 was associated with phosphorus availability. Ammoniphilus, PAUC26f, and BSV26 were also indicators of CO management. Conversely, EI treatment promoted bacteria involved in organic matter decomposition and nutrient cycling, such as Halomonas, Chryseolinea and Rhodobacteraceae. Gemmatimonas, Steroidobacter, Altererythrobacter, Acidibacter and Anseongella contribute to carbon and nitrogen cycling. Burkholderiaceae and Rhodopirellula play roles in phosphate solubilization and organic P mineralization, respectively. Numerous taxa with plant growth-promoting (PGP) attributes, such as BIrii41, Pseudomonas, and Lysobacter, were also identified as indicators of the EI treatment.EI associated bacteria were positively correlated with soil organic carbon contents, nitrates, and exchangeable bases, while negatively correlated with CO bacteria. A distance-based multivariate multiple regression (DistLM) demonstrated a strong relationship (r2 = 0.78) between soil physicochemical variables and bacterial community structure, with SOC explaining the most variations in the model. Other significant parameters included potassium (K), electrical conductivity (EC), and nitrates. The results suggest that EI promotes more sustainable soils in terms of fertility and microbial diversity.

Lack of inhibitory effects of 1-Octyne and PTIO on ammonia oxidizers, nitrite oxidizers, and nitrate formation in acidic paddy soils

The feasibility of employing double inhibitors consisting of PTIO and 1-octyne with the 15N pool dilution technique to distinguish comammox process from archaeal and bacterial nitrification remains to be confirmed. As such, we carried out a nitrification inhibition experiment on acidic paddy soils at a pH of 5.0, 5.3, and 5.4 to investigate the effects of 1-octyne and PTIO on nitrate (NO3−) formation, ammonia (NH3)-oxidizing archaea (AOA) and bacteria (AOB), comammox Nitrospira, and nitrite (NO2−)-oxidizing bacteria (NOB) under urea fertilized- and unfertilized- conditions. We observed that 1-Octyne stimulated the growth of comammox Nitrospira clades A and B, and Nitrobacter-like NOB and Nitrospira-like NOB without inhibiting AOB growth. This observation indicates that 1-Octyne has the potential to promote comammox process and NO2− oxidization, and its usage may lead to an underestimation of AOB activity. Unexpectedly, we found that PTIO was incapable of causing a rapid inhibition of AOA growth and NO3− formation. In the short term, PTIO was usually not detrimental to the growth of comammox Nitrospira clades A and B, AOB, and Nitrobacter-like NOB. Instead, increased growth of AOB and Nitrospira-like NOB were observed following its application. Likely due to increased bacterial nitrification and NO2− oxidation and the reaction of PTIO with nitric oxide (NO) produced by non-nitrification processes, increased NO3− formation with PTIO was observable in acidic soils with varying N statuses. These findings highlight the need to develop novel and more efficient inhibition strategies to actualize rate distinction among AOA, AOB, comammox Nitrospira in acidic soils.

Protective effects of nordalbergin against LPS-induced endotoxemia through inhibiting MAPK/NF-κB signaling pathway, NLRP3 inflammasome activation, and ROS production.

Nordalbergin is a coumarin extracted from Dalbergia sissoo DC. To date, the biological effects of nordalbergin have not been well investigated. To investigate the anti-inflammatory responses and the anti-oxidant abilities of nordalbergin using lipopolysaccharide (LPS)-activated macrophages and LPS-induced sepsis mouse model. Production of nitrite oxide (NO), prostaglandin E2 (PGE2), pro-inflammatory cytokines (tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-1β), reactive oxygen species (ROS), tissue damage and serum inflammatory markers, and the activation of the NLRP3 inflammasome were examined. Our results indicated that nordalbergin reduced the production of NO and pro-inflammatory cytokines in vitro and ex vivo. Nordalbergin also suppressed iNOS and cyclooxygenase-2 expressions, decreased NF-κB activity, and attenuated MAPKs signaling pathway activation by decreasing JNK and p38 phosphorylation by LPS-activated J774A.1 macrophages. Notably, nordalbergin diminished NLRP3 inflammasome activation via repressing the maturation of IL-1β and caspase-1 and suppressing ROS production by LPS/ATP- and LPS/nigericin-activated J774A.1 macrophages. Furthermore, nordalbergin exhibited protective effects against the infiltration of inflammatory cells and also inhibited the levels of organ damage markers (AST, ALT, BUN) by LPS-challenged mice. Nordalbergin possesses anti-inflammatory effects in macrophage-mediated innate immune responses, alleviates ROS production, decreases NLRP3 activation, and exhibits protective effects against LPS-induced tissue damage in mice.

Virtual Sensing of Nitrite: A Novel Control for Safe Denitrification in Recirculating Aquaculture Systems (RASs)

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.

Significance of Urea in Sustaining Nitrite Production by Ammonia Oxidizers in the Oligotrophic Ocean

AbstractNitrification, the stepwise oxidation of ammonia to nitrate via nitrite, is a key process in the marine nitrogen cycle. Reported nitrite oxidation rates frequently exceed ammonia oxidation rates below the euphotic zone, raising the fundamental question of whether the two steps are balanced and if alternative sources contribute to nitrite production in the dark ocean. Here we present vertically resolved profiles of ammonia, urea, and nitrite oxidation rates and their kinetic traits in the oligotrophic Subtropical North Pacific. Our results show active urea‐derived nitrogen oxidation (urea‐N oxidation) in the presence of experimental ammonium amendment, suggesting direct urea utilization. The depth‐integrated rates of urea‐N oxidation and ammonia oxidation are comparable, demonstrating that urea‐N oxidation is a significant source of nitrite. The additional nitrite from urea‐N oxidation helps to balance the two steps of nitrification in our study region. Nitrifiers exhibit high affinity for their substrates, and the apparent half‐saturation constants for ammonia and nitrite oxidation decrease with depth. The apparent half‐saturation constant for urea‐N oxidation is higher than that for ammonia oxidation and shows no clear vertical trend. Such kinetic traits may account for the relatively higher urea concentration than ammonium concentration in the ocean's interior. Moreover, a compilation of our results and reported data shows a trend of increased urea‐N oxidation relative to ammonia oxidation from the eutrophic coastal zone to the oligotrophic open ocean. This trend reveals a substrate‐dependent biogeographic distribution of urea‐N oxidation across marine environments and provides new information on the balance and flux of the marine nitrification process.

Identifying the major metabolic potentials of microbial-driven carbon, nitrogen and sulfur cycling on stone cultural heritage worldwide

Microbial activities and biochemical reactions are responsible for the biodeterioration of stone cultural heritage, but information on microbial metabolic potentials remains elusive. Here we profiled microbial community signatures and its functional traits on stone cultural heritage from different climate zones globally using sequencing datasets available publicly. Bacterial community on stone cultural heritage shows a significant separation between BSk (cold semi-arid climate) and Cfb (temperate oceanic climate) with Aw (tropical savanna climate) as a transition region. Importantly, the ubiquity of ammonia oxidizers and nitrite oxidizers on stone cultural heritage under different climates supports the active production and accumulation of nitrates while ammonia/ammonium can be supplied by dinitrogen fixation and dissimilatory nitrate reduction to ammonium (DNRA), together with the hydrolysis of urea, arginine, formamide and cyanate. Sulfate accumulation on stone cultural heritage is mainly resulted from the microbial-driven transformation of organosulfur and thiosulfate, with little dissimilatory reduction of sulfate. Pseudorhodoplanes was identified and reported in elemental sulfur turnover for the first time. Notably, carbon sequestration via the reductive tricarboxylic acid (rTCA) cycle and an incomplete 3-hydroxypropionate/4-hydroxybutynate (HP/HB) cycle other than the Calvin Benson-Bassham (CBB) cycle is also significant on stone cultural heritage under relatively humid climate. These results advance our understanding of microbial metabolic potentials and their genetical partitioning patterns on stone cultural heritage of different climate zones globally.

Predicting aeration time and nitrite accumulation rate variations for Partial Nitritation: A model incorporating nitrogen oxidation rate dynamics

This study aimed to develop a two-step nitrification model to predict variations in aeration time and nitrite accumulation rate (NAR) under fluctuating operational conditions in mainstream partial nitritation (PN) processes. Lab-scale sequencing batch reactors (SBRs) were used to evaluate the ammonia oxidation rate (AOR) and nitrite oxidation rate (NOR) under different solids retention times (SRT) (10, 15, 20, 30, and 50 days) and total volumetric nitrogen loadings (TVNL) (20–60 mg N/L per cycle). A static model was developed to predict consistent AOR and NOR values in the steady state, whereas a dynamic model was established to capture the growth dynamics of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) under unsteady-state conditions. The static model accurately predicted the AOR, NOR, and aeration time at steady state. The dynamic model quantified the relationship between specific growth rates (μ) and food-to-microorganism ratios (F/M) through exponential fitting, successfully capturing AOB and NOB growth dynamics. Validation experiments (SRT = 10 d, TVNL = 60 mg/L per cycle) demonstrated the ability of the dynamic model to predict trends in NAR and aeration time accurately. This study emphasizes the importance of accurately modeling AOR and NOR variations to predict aeration time and NAR, thereby providing valuable insights for aeration control and precise management of AOB and NOB populations in mainstream PN processes.

Enhancing nitrogen removal in low C/N wastewater with recycled sludge-derived biochar: A sustainable solution

Denitrification is an important biological process in wastewater treatment plants (WWTPs). However, a low carbon-to-nitrogen (C/N) ratio limits the availability of organic carbon, potentially reducing denitrification efficiency. This study investigates the impact of sludge-derived biochar on the nitrogen removal of activated sludge for low C/N ratio municipal wastewater. Sludge-based biochar was characterized by its physicochemical properties, revealing that biochar prepared at 400 °C exhibited the highest specific surface area and the most favorable surface functional groups for electron transfer. The results from batch tests showed that adding 4 g/L of biochar dosage enhanced denitrification rates and total nitrogen (TN) removal efficiency the most. Sequencing batch reactors (SBRs) experiments further confirmed that biochar dosgae improved the removal efficiencies of COD, NH4+-N, and TN, achieving stable values of 97.2 ± 1.2 %, 99.2 ± 0.6 %, and 83.8 ± 2.4 %, respectively. Metabolic and electrochemical analyses revealed that biochar addition enhanced the activity of denitrification enzymes, increasing the ammonia oxidation rate by 12.9 ± 0.7 %, nitrite oxidation rate by 14.7 ± 1.2 %, nitrate reduction rate by 36.9 ± 1.5 %, and nitrite reduction rate by 16.4 ± 0.8 %. The relative abundance of denitrification functional genes (amoA, nirS, nirK, narG, nosZ) increased, and the activities of the corresponding enzymes (AMO, NXR, NAP, NIR) rose by 23±6 %, 53±5 %, 260±15 %, and 55±7 %, respectively. This increase in enzyme activity suggested enhanced denitrification processes, which was further supported by the 60.1 ± 3.7 % increase in electron transfer system activity (ETSA), indicating that biochar acted as an electron shuttle. This study proposes a potential sustainable approach for sludge recycling and enhanced wastewater nitrogen removal under low C/N conditions.

Cover crop root exudates impact soil microbiome functional trajectories in agricultural soils

BackgroundCover cropping is an agricultural practice that uses secondary crops to support the growth of primary crops through various mechanisms including erosion control, weed suppression, nutrient management, and enhanced biodiversity. Cover crops may elicit some of these ecosystem services through chemical interactions with the soil microbiome via root exudation, or the release of plant metabolites from roots. Phytohormones are one metabolite type exuded by plants that activate the rhizosphere microbiome, yet managing this chemical interaction remains an untapped mechanism for optimizing plant-soil-microbiome interactions. Currently, there is limited understanding on the diversity of cover crop phytohormone root exudation patterns and our aim was to understand how phytochemical signals selectively enrich specific microbial taxa and functionalities in agricultural soils.ResultsHere, we link variability in cover crop root exudate composition to changes in soil microbiome functionality. Exudate chemical profiles from 4 cover crop species (Sorghum bicolor, Vicia villosa, Brassica napus, and Secale cereal) were used as the chemical inputs to decipher microbial responses. These distinct exudate profiles, along with a no exudate control, were amended to agricultural soil microcosms with microbial responses tracked over time using metabolomes and genome-resolved metatranscriptomes. Our findings illustrated microbial metabolic patterns were unique in response to cover crop exudate inputs over time, particularly by sorghum and cereal rye amended microcosms. In these microcosms, we identify novel microbial members (at the genera and family level) who produced IAA and GA4 over time. Additionally, we identified cover crop exudates exclusively enriched for bacterial nitrite oxidizers, while control microcosms were discriminated for nitrogen transport, mineralization, and assimilation, highlighting distinct changes in microbial nitrogen cycling in response to chemical inputs.ConclusionsWe highlight that root exudate amendments alter microbial community function (i.e., N cycling) and microbial phytohormone metabolisms, particularly in response to root exudates isolated from cereal rye and sorghum plants. Additionally, we constructed a soil microbial genomic catalog of microorganisms responding to commonly used cover crops, a public resource for agriculturally relevant microbes. Many of our exudate-stimulated microorganisms are representatives from poorly characterized or novel taxa, revealing the yet to be discovered metabolic reservoir harbored in agricultural soils. Our findings emphasize the tractability of high-resolution multi-omics approaches to investigate processes relevant for agricultural soils, opening the possibility of targeting specific soil biogeochemical outcomes through biological precision agricultural practices that use cover crops and the microbiome as levers for enhanced crop production.BPG5Z_iDvqR4KrAs2TcSTiVideo

Performance of single PN/A reactor under wide fluctuation of nitrogen load.

Partial nitritation-anammox (PN/A) is a cost-effective technology in high ammonia-nitrogen wastewater treatment. However, PN/A is prone to instability as the ammonia-nitrogen sharply fluctuates. In this study, a packed bed reactor is employed to construct a single-stage PN/A system to investigate the operational characteristics and explore the denitrification mechanism. The effluent NH4+-N concentration, ammonia nitrogen removal rate (ARE), and total nitrogen removal rate (TNR) could be sustained at about 60mg/L, 80%, and over 70%, respectively, when the influent nitrogen load rate (NLR) is changed from 0.733 to 0.879kg-N/m3/day. Both ARE and TNR are decreased when NLR continues increasing to 1.026kg-N/m3/day. The influent NLR decreases from 0.879 to 0.147kg-N/m3/day, and ARE and TNR reached 98% and 85.4%, respectively. Therefore, the denitrification effect of the reactor could be recovered, and the excellent nitrogen removal capacity could be obtained within a wide range of influent NLR. Moreover, the high-throughput sequencing and metagenomic testing indicate that the Proteobacteria and Planctomycetes that the PN/A functional strains (i.e., ammonia-oxidizing bacteria (AOB) and anammox bacteria (AnAOB)) account for 38.8% in the sludge. The relative abundance of Nitrospira containing the nitrite-oxidizing bacteria (NOB) has dropped to 0.01%, and the functional gene nxr of the nitrite oxidation process is also inhibited. The relative expression of the functional gene is dominated by the short-range nitritation and anammox oxidation, which demonstrates that the nitrogen removal is mainly dominated by nitritation-anammox.

Numerical analysis of coupling ozonation in nitrite oxidation through denitrification process for nitrogen removal from wastewater in a bioreactor

Excessive nitrogen in wastewater is released into natural water as a result of urbanization, industrial and agricultural activities, posing a serious threat to the water ecosystem. Elevated nitrogen concentrations in ponds, lakes, and rivers exacerbate eutrophication and algal blooms, compromising ecosystem sustainability and water quality. Within the nitrogen cycle, nitrite is an intermediate component in both nitrification and denitrification processes. Nitrite oxidation and denitrification are related processes that each have distinct functions at various phases and are complimentary by nature. Nitrate is created when nitrite is oxidized, and nitrate is an essential substrate for denitrification. This study evaluates the effects of ozone concentration on nitrite oxidation in bioreactors with four models of different baffle heights. Furthermore, different operating conditions, including fluid velocity and ozone content, were investigated. The normalized averaged source terms and NO3− withdrawal rates were considerably low at shorter baffles compared to taller ones, up to 47.4 % and 58 % less, respectively. A threshold of the baffle height was observed. The performance could increase rapidly before the threshold but a slight change after that. The normalized NO3− concentrations increased by about 59.3 % at the highest inlet velocity compared to the base model. Higher velocity also could increase NO3− withdrawal rates up to 124.4 %. The normalized average source term, the normalized concentration of the product, and the normalized reduction rate in the reactor showed an almost linearly rising relationship with the ozone concentration ratio.

Nitrite-oxidizing bacteria adapted to low-oxygen conditions dominate nitrite oxidation in marine oxygen minimum zones.

Nitrite is a central molecule in the nitrogen cycle because nitrite oxidation to nitrate (an aerobic process) retains fixed nitrogen in a system and its reduction to dinitrogen gas (anaerobic) reduces the fixed nitrogen inventory. Despite its acknowledged requirement for oxygen, nitrite oxidation is observed in oxygen-depleted layers of the ocean's oxygen minimum zones (OMZs), challenging the current understanding of OMZ nitrogen cycling. Previous attempts to determine whether nitrite-oxidizing bacteria in the anoxic layer differ from known nitrite oxidizers in the open ocean were limited by cultivation difficulties and sequencing depth. Here, we construct 31 draft genomes of nitrite-oxidizing bacteria from global OMZs. The distribution of nitrite oxidation rates, abundance and expression of nitrite oxidoreductase genes, and relative abundance of nitrite-oxidizing bacterial draft genomes from the same samples all show peaks in the core of the oxygen-depleted zone (ODZ) and are all highly correlated in depth profiles within the major ocean oxygen minimum zones. The ODZ nitrite oxidizers are not found in the Tara Oceans global dataset (the most complete oxic ocean dataset), and the major nitrite oxidizers found in the oxygenated ocean do not occur in ODZ waters. A pangenomic analysis shows the ODZ nitrite oxidizers have distinct gene clusters compared to oxic nitrite oxidizers and are microaerophilic. These findings all indicate the existence of nitrite oxidizers whose niche is oxygen-deficient seawater. Thus, specialist nitrite-oxidizing bacteria are responsible for fixed nitrogen retention in marine oxygen minimum zones, with implications for control of the ocean's fixed nitrogen inventory.

Photo-generated hydrated electrons for selective reduction of nitrate to dinitrogen: Selectivity and mechanism

The hydrated electron (eaq−) is one of the most admired short-lived reactive species (RSs) for selective reduction of nitrate (NO3−) to nitrogen (N2). However, eaq− donor often exhibits reducibility, which may react with intermediate products, affecting the final product composition of NO3− reduction. Herein, Fe2+, SO32− and the combination of Fe2+ and SO32− were selected as eaq− donors for NO3− photo-reduction to explore the roles of eaq− donors in the product of NO3− reduction. The N2 selectivity achieved through Fe2+/UV, SO32−/UV and Fe2+/SO32−/UV systems was found to be 17.03 %, 45.45 %, and 97.53 % respectively. The main products of NO3− reduction in Fe2+/UV system were nitrite (NO2−) and nitrogen oxide (NOX), while in SO32−/UV system were NO2− and hydroxylamine disulfonate (HON(SO3)22−). Notably, in the Fe2+/SO32−/UV system, various short-lived reactive species (eaq−, SO3•−, etc.) were generated, and eaq− was the main reactive species for NO3− reduction. The generated NO2− and NOX intermediates could be quickly converted to N-S compounds, such as HON(SO3)22− by SO32− and SO3•−, while the generated HON(SO3)22− could be further reduced to N2 by the combined action of Fe3+ from photooxidation of Fe2+, UV and eaq−. Significantly, the Fe2+/SO32−/UV system showed high selectivity and efficiency for removal of NO3− from secondary effluent of municipal domestic sewage. This study helps to design new photo-reduction systems for NO3− removal from nitrogen-containing wastewater/water.

In2O3 electrochemical transistors based on PtAu4/RGO nanocomposites functionalized gate for highly sensitive nitrite detection

Nitrite is commonly found in the environment, but its overuse and potential toxicity pose serious health risks. There is a strong need to develop robust and reliable methods for detecting nitrite. Herein, a novel In2O3 solution-gated electrochemical transistor (SGET) nitrite sensor was designed and fabricated for highly sensitive detection of nitrite. Different thicknesses of In2O3 thin films were prepared by sol–gel method, which were used as the channel of transistors and optimized through evaluating the electronic and electrochemical properties. To improve the catalytic oxidation of nitrite, PtAu4 nanoparticles modified reduced graphene oxide nanocomposites (PtAu4/RGO) were fabricated on the gate of transistors through electrodeposition approach. The developed sensor exhibited exceptional sensing performance in nitrite detection, which featured with low detection limit (0.1 nM nitrite) and ultra-wide linear range from 0.1 nM to 1 mM. The developed In2O3 SGET sensor displayed excellent stability and high resistance to common interfering ions, thereby demonstrating superior anti-interference performance. Nitrite in real samples of natural lake water has been accurately measured, suggesting that the designed sensor could act as an ideal transducer platform for highly sensitive and selective nitrite detection in food and environmental fields.

Porphyrin encapsulated in organic polymers: Electropolymerization and preliminary investigations on electrocatalytic activity

AbstractIn the present work, the incorporation of hydrophobic porphyrins in organic polymers through electrochemically induced polymerization of monomers on conventional electrodes and the preliminary investigations on the electrocatalytic activity of these modified electrodes are explained. Electropolymerized porphyrins show better activity than organic polymers of N‐isopropylacrylamide, triethylene glycol methyl ether methacrylate, and glycerol 1,3‐diglycerolate diacrylate for nitrite oxidation due to the presence of cobalt metal ion. Among the porphyrins investigated, electropolymerized cobalt tetra‐2‐thienylporphyrin requires the least overpotential, due to ease of polymerization and better coating on glassy carbon electrode compared with that of cobalt tetraphenylporphyrin and cobalt tetra‐3‐thienylporphyrin. On encapsulating these porphyrins in organic polymers, improved current and lower overpotential are noticed.

Efficient nitrite determination by electrochemical approach in liquid phase with ultrasonically prepared gold-nanoparticle-conjugated conducting polymer nanocomposites.

An electrochemical nitrite sensor probe is introduced herein using a modified flat glassy carbon electrode (GCE) and SrTiO3 material doped with spherical-shaped gold nanoparticles (Au-NPs) and polypyrrole carbon (PPyC) at a pH of 7.0 in a phosphate buffer solution. The nanocomposites (NCs) containing Au-NPs, PPyC, and SrTiO3 were synthesized by ultrasonication, and their properties were thoroughly characterized through structural, elemental, optical, and morphological analyses with various conventional spectroscopic methods, such as field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller method. The peak currents due to nitrite oxidation were characterized in detail and analyzed using conventional cyclic voltammetry (CV) as well as differential pulse voltammetry (DPV) under ambient conditions. The sensor response increased significantly from 0.15 to 1.5mM of nitrite ions, and the sensor was fabricated by coating a conducting agent (PEDOT:PSS) on the GCE to obtain the Au-NPs/PPyC/SrTiO3 NCs/PEDOT:PSS/GCE probe. The sensor's sensitivity was determined as 0.5μA/μM∙cm2 from the ratio of the slope of the linear detection range by considering the active surface area (0.0316cm2) of the flat GCE. In addition, the limit of detection was determined as 20.00 ± 1.00 µM, which was found to be satisfactory. The sensor's stability, pH optimization, and reliability were also evaluated in these analyses. Overall, the sensor results were found to be satisfactory. Real environmental samples were then analyzed to evaluate the sensor's reliability through DPV, and the results showed that the proposed novel electrochemical sensor holds great promise for mitigating water contamination in the real samples with the lab-made Au-NPs/PPyC/SrTiO3 NC. Thus, this study provides valuable insights for improving sensors for broad environmental monitoring applications using the electrochemical approach.