Excessive Nitrite Research Articles

Fe/Cl/N triply-doped bamboo-like structure wrapped with Fe3C nanoparticles for electrochemical selective nitrite detection

Nitrite is commonly found in the natural environment and in everyday human activities. However, excessive nitrite consumption can potentially harm human health. Consequently, it is crucial to develop a reliable and sensitive method for nitrite detection. In this work, trichloroacetic acid functionalized Cl-Fe-MIL-88B metal-organic framework is obtained through nucleophilic reaction between animated Fe-MIL-88B and trichloroacetic acid, which is then annealed with melamine in an N2 atmosphere to produce the Fe/Cl/N triply-doped bamboo-like carbon nanotubes (CNTs) wrapped with Fe3C nanoparticles. Owing to the effective doping of Fe/Cl/N elements, the charge distribution and chemical activity of the bamboo-like structure are tailored, greatly improving the conductivity and facilitating electron transfer of the composite for potential electrocatalytic reaction. The Fe3C nanoparticles wrapped inside the CNTs contribute to expose more active sites and provide effective surface area. Accordingly, the Fe/Cl/N doped bamboo-like structure modified glassy carbon electrode shows excellent electrochemical nitrite sensing properties with a high sensitivity of 1060µAcm-2 mM-1, a low detection limit of 0.61µM in a wide linear concentration range of 5-5000μM, as well as good anti-interference and long-term stability. Also, the electrochemical sensor has a satisfactory recovery rate for detecting nitrite ions in spiked milk samples. This work proposes a simple precursor chlorination and pyrolysis strategy to obtain metal-filled bamboo-like structure with high electrical conductivity and electrocatalytic properties, endowing great potential in food safety and environment monitoring.

Conditionally restricted detection of nitrite under acidic conditions by activatable fluorescent probes

As a commonly used food additive, excessive nitrite intake seriously affects people’s health in daily life. As the stomach is the main organ involved in nitrite intake, achieving fast and in situ detection of nitrite in the stomach is of great significance for avoiding the hazards caused by nitrite. However, owing to the poor stability or low sensitivity of existing fluorescent probes under acidic conditions, their application for nitrite detection within the stomach remains challenging. To solve this problem, we developed novel probes specifically designed to maintain stability and demonstrate high sensitivity to nitrite under acidic conditions. Utilizing the optimized probe (DHUROS-11), nitrite levels in environmental and real samples were successfully quantified. Notably, tracing of nitrite within the stomach of mice in real time was realized by using DHUROS-11 as the probe.

Development of an accurate hand-held sensing platform for nitrite detection based on nitrogen-doped carbon dots

As is well known, excessive nitrite can seriously pollute the environment and can harm human health. Although existing methods can be used to determine nitrite content, they still have some drawbacks, such as relatively complicated operation and expensive equipment. Herein, a hand-held sensing platform (HSP) for NO2− determination was developed. First, ammonia-rich nitrogen-doped carbon dots with orange-yellow emission were designed and synthesised, which were suitable as fluorescent probes because of their good optical properties and stability. Then, the HSP based on fluorescence using photoelectric conversion technology was designed and manufactured using three-dimensional printing technology. Under optimum conditions, the voltage (V/V0) of the proposed HSP showed good linearity for NO2− detection in the range of 10–500 μM, with a detection limit of 1.95 μM. This portable sensor showed good stability, accuracy and reliability in detecting actual water and meat samples, which may ensure food safety in practical applications. Moreover, the HSP is compact, portable and easily assembled and is suitable for on-site real-time detection, which shows great application potential and prospects.

Nano-palladium-decorated bismuth sulfide microspheres on a disposable electrode integrated with smartphone-based electrochemical detection of nitrite in food samples

Nitrite (NO2−) is widely used as an additive to extend the shelf life of food products. Excessive nitrite intake not only causes blood-related diseases but also has the potential risk of causing cancers. A disposable screen-printed electrode was modified with nano‑palladium decorated bismuth sulfide microspheres (nanoPd@Bi2S3MS/SPE), and integrated with a smartphone-interfaced potentiostat to develop a portable, electrochemical nitrite sensor. NanoPd@Bi2S3MS was prepared by the hydrothermal reduction of a Bi2S3MS and Pd2+ dispersion and drop cast on the SPE. The nanoPd@Bi2S3MS/SPE was coupled with a smartphone-controlled portable potentiostat and applied to determine nitrite in food samples. The linear range of the sensor was 0.01–500 μM and the limit of detection was 0.0033 μM. The proposed system showed good repeatability, reproducibility, catalytic stability, and immunity to interferences. The proposed electrode material and a smartphone-based small potentiostat created a simple, portable, fast electrochemical sensing system that accurately measured nitrite in food samples.

Optimization of degradation conditions and analysis of degradation mechanism for nitrite by Bacillus aryabhattai 47

Excessive nitrite levels cause significant damage to aquaculture, making it crucial to explore green and reliable nitrite removal technologies. In this study, A Bacillus aryabhattai (designated as the strain 47) isolated from aquaculture wastewater was used as the experimental strain. The nitrite degradation conditions of the strain 47 were optimized, and the optimal conditions are: glucose was 12.74 g/L, fermented special soybean meal was 21.27 g/L, MgCl2 369 mg/L, pH 7.0, incubated at 30 °C with the inoculum size of 2 % and the rotation speed of 170 rpm. Under the optimal conditions, the nitrite concentration of the culture solution was 200 mg/L, and the nitrite removal rate reached 91.4 %. Meanwhile, the mechanism by which Mg2+ enhanced the nitrite degradation ability of the strain 47 was investigated by transcriptomics. An operon structure directed cellular trafficking of Mg2+, and then, the Mg2+-mediated catalytic reaction of multiple enzymes enhanced and improved cellular metabolic processes (e.g. the transport and metabolism of nitrite, central carbohydrate metabolism oxidative phosphorylation). At the same time, with the progress of cell metabolism, cells secreted a series of enzymes related to nitrite transport and metabolism to promote the metabolism of nitrite. And the process of the assimilated nitrate reduction pathway of nitrite degradation in the strain 47 was elaborated at the transcriptome level. This study provided a new insight into nitrite treatment mediated by microbial organisms.

The negative effects of the excessive nitrite accumulation raised by anaerobic bioaugmentation on bioremediation of PAH-contaminated soil

Nitrite accumulation in anaerobic bioaugmentation and its side effects on remediation efficiency of polycyclic aromatic hydrocarbon (PAH)-contaminated soil were investigated in this study. Four gradient doses of PAH-degrading inoculum (10^4, 10^5, 10^6 and 10^7 cells/g soil) were separately supplied to the actual PAH-contaminated soil combining with nitrate as the biostimulant. Although bioaugmented with higher dose of inoculum could effectively improve the biodegradation efficiencies in the initial stage than sole nitrate addition but also accelerated the accumulation of nitrite in soil. The inhibition effects of nitrite swiftly occurred following the rapid accumulation of nitrite in each experiment group, restraining the PAH-degrading functionality by inhibiting the growth of total biomass and denitrifying functions in soil. This study revealed the side effects of nitrite accumulation raised by bioaugmentation on soil microorganisms, contributing to further improving the biodegrading efficiencies in the actual site restoration.

Optimizing waste molasses utilization to enhance electron transfer via micromagnetic carriers: Mechanisms and high-nitrate wastewater denitrification performance

The biological denitrification of high-nitrate wastewater (HNW) is primarily hindered by insufficient carbon sources and excessive nitrite accumulation. In this study, micromagnetic carriers with varying micromagnetic field (MMF) strengths (0.0, 0.3, 0.6, 0.9 mT) were employed to enhance the denitrification of HNW using waste molasses (WMs) as a carbon source. The results revealed that 0.6 mT MMF significantly improved the total nitrogen removal (TN) efficiency at 96.3%. A high nitrate (NO3−-N) removal efficiency at 99.3% with a low nitrite (NO2−-N) accumulation at 25.5 mg/L was achieved at 0.6 mT MMF. The application of MMF facilitated the synthesis of adenosine triphosphate (ATP) and stimulated denitrifying enzymes (e.g., nitrate reductase (NAR), nitrite reductase (NIR), and nitric oxide reductase (NOR)), which thereby promoting denitrification. Moreover, the effluent chemical oxygen demand (COD), tryptophan and fulvic-like substances exhibited their lowest levels at 0.6 mT MMF. Analysis through 16S ribosomal ribonucleic acid gene sequencing indicated a significant enrichment of denitrifying bacteria including Castellaniella Klebsiella under the influence of MMF. Besides, the proliferation of Acholeplasma, Klebsiella and Proteiniphilum at 0.6 mT MMF promoted the hydrolysis and acidification of WMs. This study offers new insights into the enhanced utilization of WMs and the denitrification of HNW through the application of MMF.

Transcriptomic Responses to Nitrite Degradation by Limosilactobacillus fermentum RC4 and Effect of ndh Gene Overexpression on Nitrite Degradation.

The excessive nitrite residue may increase cell damage and cancer risk. Limosilactobacillu fermentum RC4 exhibited excellent nitrite degradation ability. Herein, the molecular mechanism of nitrite degradation by L. fermentum RC4 was studied by integrating scanning electron microscopy analysis, transcriptomics, and gene overexpression. The results demonstrated that the gene profile of RC4 cultured in MRS broth with 0, 100, and 300 mg/L NaNO2 varied considerably; RC4 responded to nitrite degradation by regulating pyruvate metabolism, energy synthesis, nitrite metabolism, redox equilibrium, protein protection, and signaling. High nitrite concentrations affected the morphology of RC4 with a longer phenotype, rough and wrinkle cell and reduced cell surface hydrophobicity. Moreover, an up-regulated expression of gene ndh encoding NADH dehydrogenase, which provides electrons for nitrite reduction by catalyzing NADH, was identified when RC4 was exposed to nitrite. Overexpression of ndh in RC4 increased the nitrite degradation rate by 2-9.5% in MRS broth with 100 mg/L NaNO2. Thus, the findings of this study could be helpful for the application of L. fermentum to reduce nitrite residues and improve food safety in fermented food products.

Electrochemical environmental pollutant detection enabled by waste tangerine peel-derived biochar

Nitrite is widely utilized in food and agricultural fields. Excessive nitrite causes great harm to ecosystems and human health, rendering it one of environmental pollutants. In this work, tangerine peel, as a common agricultural waste in daily life, is considered as a sustainable, renewable and low-cost carbon precursor. Tangerine peel waste has been re-utilized to prepare biochar of iron oxide/nitrogen-doped carbon nanocomposite in constructing electrochemical sensor for nitrite determination. Two electrochemical techniques of linear sweep voltammetry (LSV) and cyclic voltammetry (CV) were practiced for quantifying nitrite. The biochar of iron oxide/nitrogen-doped carbon nanocomposite displayed satisfactory sensing performance in different real environmental samples of soil, spinach and mustard. Agricultural waste to value-added product is becoming increasingly significant. Considering that a lot of tangerine peel is discarded as waste in daily life, the present strategy will be promising to transform a common agricultural waste into value-added product, thus having profound significance in contributing to both the smart farming, pollution alleviation and environmental pollutant monitoring.

Preparation of High-Solid Microfibrillated Cellulose from Gelidium amansii and Characterization of Its Physiochemical and Biological Properties.

Microfibrillated cellulose (MFC) is a valuable material with wide industrial applications, particularly for the food and cosmetics industries, owing to its excellent physiochemical properties. Here, we prepared high-solid microfibrillated cellulose (HMFC) from the centrifugation of Gelidium amansii-derived MFC right after fibrillation. Dispersion properties, morphology, and structural changes were monitored during processing. HMFC has a five-fold higher solid concentration than MFC without significant changes to dispersion properties. SEM images and FTIR spectra of HMFC revealed a stable surface and structure against centrifugal forces. HMFC exhibited 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging activity, although it could not scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH). Moreover, HMFC inhibited the generation of LPS-induced excessive nitrite and radial oxygen species in murine macrophage RAW264.7 cells. Additionally, HMFC suppressed LPS-induced Keap-1 expression in the cytosol but did not alter iNOS expression. HMFC also attenuated the UVB-induced phosphorylation of p38, c-Jun N-terminal kinase (JNK) 1/2, and extracellular-signal-regulated kinase (ERK) 1/2, as well as the phosphorylation of c-Jun in the immortalized human skin keratinocyte HaCaT cells. Therefore, the application of centrifugation is suitable for producing high-solid MFC as a candidate material for anti-inflammatory and anti-oxidative marine cosmeceuticals.

LMOF serve as food preservative nanosensor for sensitive detection of nitrite in meat products

Nitrite (NO2−) is widely present in meat products as a vital food preservative, while excessive nitrite is a serious carcinogen to human beings, developing a sensitive and selective nitrite detection method is of great significance for food safety. Herein, a novel luminescent metal organic framework (LMOF) (Rh6G@MOF-5) is prepared through a facile one-pot synthesis as a fluorescent turn-off sensor for NO2− determination. Upon exposure to NO2−, significant fluorescence intensity decreases linearly along with NO2−concentration in the range of 0–200 μmol/L and the detection limit is estimated to be 0.2 μmol/L. The developed nanocomposite has been shown to be an ultrasensitive and selective nanoprobe for detecting NO2− in meat products, with recoveries ranging from 96.1% to 103.2% with the RSDs less than 4%. Rh6G@MOF-5 nanoprobe offers insight into the fabrication of MOF-based sensors with low cost and convenient operation in analyte detection field.

Sodium nitrite poisoning; A case series of 15 fatalities

To highlight a recent surge in new drug deaths resulting from sodium nitrite (NaNO2) toxicity in which the post mortem blood nitrite (NO2-) and nitrate (NO3) concentrations were measured. The University Hospitals of Leicester (UHL) NHS Trust post-mortem toxicology service receives samples from 27% of Her Majesty's Coroners in England and Wales, analysing approximately 4000 cases per year. We report a series of 15 cases, spanning an 18-month period, in which NaNO2 was the suspected cause of death. NaNO2 is an inorganic sodium salt that has several industrial applications, the most common being preserving meat products. Excess NaNO2 ingestion has also been associated with severe toxicity/death when consumed in excess either accidentally or intentionally. Recently, suicide kits containing NaNO2, and an anti-emetic drug, to assist with ingestion of NaNO2, have become available online. Excessive nitrite ingestion results in iron oxidation within haemoglobin and subsequent production and accumulation of methaemoglobin. Methaemoglobin cannot bind or transport oxygen effectively therefore severe tissue hypoxia and death result. Nitrite is also a vasodilator and can cause coronary ischaemia and stroke as a result of hypotension, tachycardia, and hypoxia. Routine screening was performed on post mortem blood samples received as per usual laboratory protocol; including ethanol analysis by Headspace Gas Chromatography–Flame Ionisation Detection (HS GC-FID), drug screening by High Resolution Accurate Mass–Mass Spectrometry (HRAM-MS) and confirmatory drug quantitation by Liquid Chromatography–Tandem Mass Spectrometry (LC-MS/MS). In this series, the majority of case histories described the presence of NaNO2 at the scene of death/purchase of a suicide kit; therefore aliquots of post mortem blood were referred to a specialist laboratory (William Harvey Research Institute) for quantitative nitrite and nitrate analysis. Measurement was based upon the gas-phase chemiluminescent reaction between nitric oxide (NO) and ozone (O 3 ); NO levels were determined using an NOA 280A, Sievers NO analyser. Fifteen post-mortem cases in which NaNO2 ingestion was considered the most probable cause of death were reported between January 2020 to July 2021; mean age 31 years (range 18 to 49), 8/15 (53%) male. In almost all cases the clinical history described mental health issues, depression, previous suicide attempts/overdose, self-harm or suicidal ideation. Two thirds of the cases listed prescribed anti-depressants/anti-psychotics; these drugs were detected in 6/15 cases. Ethanol was detected in 3/15 cases and anti-emetic drugs in 3/15 cases. Illicit drugs were present in two of the cases at concentrations suggestive of prior use. The mean nitrite and nitrate concentrations were 2106 μmol/L (min–max 1.4–8100) and 7818 μmol/L (14.5–21,100) respectively. Blood reference ranges for nitrite and nitrate are 0.1–0.4 and 20–40 μmol/L respectively. Nitrite was elevated in all but one case, nitrate was elevated in 12/15 (80%) cases. For the majority of cases (9/15) individuals were discovered deceased; 4/15 cases emergency services attended and death occurred either on route to or following hospital admission. The remaining two cases gave insufficient detail regarding circumstances of death. One post mortem report described discolouration on post mortem consistent with the presence of methaemoglobinaemia. The detection and quantitation of nitrite and nitrate during post-mortem toxicological investigations represents a significant challenge analytically and heavily relies upon circumstantial evidence. Even though it still remains a rare cause of death, it is worthwhile considering the possibility of sodium nitrite use in individuals with suicidal ideation given its apparent availability online. The provision of a quantitative nitrite/nitrate analytical service greatly assists in determining the cause of death in these cases.

Coupling diazotization with oxidase-mimetic catalysis to realize dual-mode double-ratiometric colorimetric and electrochemical sensing of nitrite

Nitrite is often utilized as coloring and preservative agents in food industry, but excessive nitrite in drinking water and food causes great threats to human health, requiring convenient and reliable methods for its monitoring. In comparison with common single-signal assays, multimodal detection can not only expand application scenarios but also offer self-correction and self-validation to obtain more reliable results. However, how to achieve the multimodal sensing of nitrite remains a challenge. Here we report a novel dual-mode double-ratiometric colorimetric and electrochemical method for nitrite quantification by coupling diazotization with oxidase-mimicking catalysis. Carbon-supported Mn3O4 particles were explored as an oxidase-like nanozyme with excellent activity to catalyze the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to blue TMBox. On the one hand, the presence of nitrite can induce the diazotization of TMBox, not only decreasing the visible signal of TMBox at 652 nm but also generating a new signal assigned to diazotized TMBox at 445 nm. On the other hand, the existence of nitrite triggers the decrease of the TMB homogeneous electro-oxidation signal, but offers a new electro-oxidation signal attributed to nitrite itself. With such an interesting sensing principle, a dual-mode double-ratiometric colorimetric and electrochemical approach was developed to detect nitrite with good sensitivity and specificity. Reliable applications of the method in monitoring nitrite in several matrices were also demonstrated, implying its great promise in food safety supervision and environmental monitoring.

Ratiometric Colorimetric Detection of Nitrite Realized by Stringing Nanozyme Catalysis and Diazotization Together.

Due to the great threat posed by excessive nitrite in food and drinking water to human health, it calls for developing reliable, convenient, and low-cost methods for nitrite detection. Herein, we string nanozyme catalysis and diazotization together and develop a ratiometric colorimetric approach for sensing nitrite in food. First, hollow MnFeO (a mixture of Mn and Fe oxides with different oxidation states) derived from a Mn-Fe Prussian blue analogue is explored as an oxidase mimic with high efficiency in catalyzing the colorless 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation to blue TMBox, presenting a notable signal at 652 nm. Then, nitrite is able to trigger the diazotization of the product TMBox, not only decreasing the signal at 652 nm but also producing a new signal at 445 nm. Thus, the analyte-induced reverse changes of the two signals enable us to establish a ratiometric colorimetric assay for nitrite analysis. According to the above strategy, facile determination of nitrite in the range of 3.3–133.3 μM with good specificity was realized, providing a detection limit down to 0.2 μM. Compared with conventional single-signal analysis, our dual-signal ratiometric colorimetric mode was demonstrated to offer higher sensitivity, a lower detection limit, and better anti-interference ability against external detection environments. Practical applications of the approach in examining nitrite in food matrices were also verified.

Bioprocess of nitrite accumulation in water - a review

Nitrite is a by-product of the nitrogen cycle. The excessive nitrite not only constrains growth and metabolism of bacteria, but also impairs health of humans and aquatic organisms. On the other hand, the continuous maintaining of nitrite accumulation could achieve the shortcut nitrification process, and reduce energy consumption of biological nitrogen removal to save cost. This article reviews the biological processes and causes of nitrite accumulation in the water environment, and summarizes the factors that affect the accumulation of nitrite, to provide reference for wastewater treatments, including improving the nitrogen removal efficiency, reducing operating costs, decreasing discharge of sewage and nitrite nitrogen in natural water.

A Fast and Highly Selective Nitrite Sensor Based on Interdigital Electrodes Modified With Nanogold Film and Chrome-Black T.

Nitrite is a toxic substance, when excessive nitrite enters the human body, it will be seriously harmful to human. At present, the detection methods of nitrite are complicated to operate and require expensive detection instruments. Therefore, an effective, fast and highly selective nanogold film interdigital electrode sensors that can detect nitrite easily and quickly is developed in the work. Firstly, the variation of the sensitivity of nanogold film nitrite sensors with concentrations (1 mol/L, 10−1 mol/L, 10−2 mol/L, 10−3 mol/L, 10−4 mol/L, and 10−5 mol/L) was measured by experiments. Then, Chrome-black T was modified to the surface of the nanogold film interdigital electrodes by electrochemical polymerization, and the film of chrome-black T had affinity for nitrite ions, so nitrite ions were enriched on the sensor surface. The change law of the impedance signal of the modified nanogold film nitrite sensors after being added to different concentrations of sodium nitrite solution were also concluded. The study demonstrates that the larger the concentration of sodium nitrite solution is added to the modified interdigital electrodes, the smaller impedance and resistance of the modified interdigital electrodes are reflected. Finally, specificity of the modified interdigital electrode sensors has been demonstrated. The novel interdigital electrode sensors can detect the concentration of nitrite solution conveniently and quickly with only 30 s. Therefore, the prospect of applying the novel nanogold film interdigital electrode sensors to the detection of nitrite in blood, body fluid, food and drinking water is promising.

Fast and sensitive fluorescent detection of nitrite based on an amino-functionalized MOFs of UiO-66-NH2

Since excessive nitrite is a serious carcinogen to human beings, it is necessary to generate a convenient and sensitive means for its detection. Owing to this point, thus, UiO-66-NH2 had been successfully employed as a fluorescence turn-off probe for the detection of NO2− through diazotization and reduction. It could detect nitrite sensitively and selectively under acidic conditions (pH ​= ​1.0) at room temperature. The linear range of nitrite was 0–10 ​mM, the detection limit was 77 ​μM, and a short response time (120 ​s) had been displayed by UiO-66-NH2. Whilst, it could specifically recognize nitrite and would hardly be affected by other possibly coexistent interfering substances. Furthermore, quantitative analysis of three real samples also confirmed the reliability and sensitivity of this probe. All these results had shown that the detecting method of UiO-66-NH2 to nitrite was simple in operation, and mild in reaction condition.

The conserved 3' UTR-derived small RNA NarS mediates mRNA crossregulation during nitrate respiration.

Small noncoding RNAs (sRNAs) from mRNA 3′ UTRs seem to present a previously unrecognized layer of bacterial post-transcriptional control whereby mRNAs influence each other's expression, independently of transcriptional control. Studies in Escherichia coli and Salmonella enterica showed that such sRNAs are natural products of RNase E-mediated mRNA decay and associate with major RNA-binding proteins (RBPs) such as Hfq and ProQ. If so, there must be additional sRNAs from mRNAs that accumulate only under specific physiological conditions. We test this prediction by characterizing candidate NarS that represents the 3′ UTR of nitrate transporter NarK whose gene is silent during standard aerobic growth. We find that NarS acts by Hfq-dependent base pairing to repress the synthesis of the nitrite transporter, NirC, resulting in mRNA cross-regulation of nitrate and nitrite transporter genes. Interestingly, the NarS-mediated repression selectively targets the nirC cistron of the long nirBDC-cysG operon, an observation that we rationalize as a mechanism to protect the bacterial cytoplasm from excessive nitrite toxicity during anaerobic respiration with abundant nitrate. Our successful functional assignment of a 3′ UTR sRNA from a non-standard growth condition supports the notion that mRNA crossregulation is more pervasive than currently appreciated.

A colorimetric fluorescent probe for rapid and specific detection of nitrite.

The method of fluorescent probes has been an important technique for detection of nitrite (NO2 - ). As an important inorganic salt, excessive nitrite would threaten humans and the environment. In this paper, a colorimetric fluorescent probe P-N (1,2-diaminoanthraquinone) with rapid response and high selectivity, which could detect NO2 - by visual colour changes and fluorescence spectroscopy is presented. The probe P-N solution (pH 1) changed from pink to colourless with the addition of NO2 - and fluorescence intensity at 639nm clearly decreased. Good linear exists between fluorescence intensities and NO2 - concentrations for the range 0-16μM, and the detection limit was 54nM (based on a 3σ/slope). Moreover, probe P-N could also detect NO2 - in real water samples, and results were all satisfactory. Probe P-N shows great practical application value for detecting NO2 - in the environment.

Efficient nitrogen removal in separate coupled-system of anammox and sulfur autotrophic denitrification with a nitrification side-branch under substrate fluctuation

In order to achieve efficient nitrogen removal, a separate coupled-system of anaerobic ammonia oxidation (anammox) and sulfur autotrophic denitrification (S0-SADN) was established. In this study, the operational feasibility and stability of the coupled-system under substrate fluctuations were investigated. Results showed that the coupled-system improved the total nitrogen removal efficiency (TNRE) to 99.15 ± 0.68%. The tryptophan-like substances in anammox effluent positively impacted the growth of the S0-SADN biofilm. This positive cooperativity boosted the S0-SADN to achieve rapid 12-day startup and stable operation thereafter. The TNRE was determined at 95.27 ± 1.51% and 93.44 ± 0.96% under excessive nitrite and ammonium, respectively. The coupled-system recovered quickly after 21 days of starvation deterioration. To further treat the excessive ammonium, the nitrification side-branch of the coupled-system improved the TNRE to 99.08 ± 0.68%. Extracellular polymeric substances analysis revealed that the anammox and S0-SADN bacteria secreted protein-like substances to resist substrate fluctuation. Microbial community analysis indicated that the stability of bacterial community supported the stability of the coupled-system. These results collectively suggested that the separate coupled-system exhibited excellent performance and provided a platform for practical wastewater treatment in future.