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The retention of nitrite ions in solutions of different concentrations by three cornhusks-based powders was analyzed. Natural cornhusk powder (NCHP), as waste obtained from local market, the alkalized cornhusk powder (ACHP) and the biochar from the original material (CHBC) have been characterized through scanning electron microscopy (SEM) and elemental composition EDAX – TEAM analysis (Energy dispersive analysis X-ray – Texture and ele-mental analytical microscopy) and tested for the removal of nitrite ions. The influence of initial nitrite concentration and contact time was studied under slow stirring rate conditions (150 rpm). For all three adsorbents both Freundlich and Langmuir isotherm equations described the process with R2 > 0.95, denoting physical adsorption and chemisorption on the surface. The estimated retained quantities (mg·g-1) determined from isotherms were 4.4783 (NCHP), 8.3542 (ACHP) and 8.7413 (CHBC). The Ho&McKay model was better adjusted to the adsorption data with R2 > 0.985, while the Lagergren model produced regression factors between 0.61 and 0.88. Considering the biggest concentration of nitrite solution of 50 mg·L-1 and the longest contact time of 150 minutes, the equilibrium capacity qe (mg·g-1) predicted by the Ho&McKay model for the considered adsorbents were: 4.5065 (NCHP), 8.5179 (ACHP) and 8.9445 (CHBC) compared to the obtained qt (mg·g-1) of 4.4384 (NCHP), 8.0685 (ACHP) and 8.5753 (CHBC). The nitrite uptake in the experiments reached a maximum of 2.2192 mg·g-1 on NCHP, 4.0342 mg·g-1 on ACHP and 4.2877 mg·g-1 on CHBC. Considering the cost-effective treatment steps, there is the possibility of valorising an important amount of waste as adsorbent materials.

The retention of nitrite ions in solutions of different concentrations by three cornhusks-based powders was analyzed. Natural cornhusk powder (NCHP), as waste obtained from local market, the alkalized cornhusk powder (ACHP) and the biochar from the original material (CHBC) have been characterized through scanning electron microscopy (SEM) and elemental composition EDAX - TEAM analysis (Energy dispersive analysis X-ray - Texture and ele-mental analytical microscopy) and tested for the removal of nitrite ions. The influence of initial nitrite concentration and contact time was studied under slow stirring rate conditions (150 rpm). For all three adsorbents both Freundlich and Langmuir isotherm equations described the process with R2 > 0.95, denoting physical adsorption and chemisorption on the surface. The estimated retained quantities (mg·g-1) determined from isotherms were 4.4783 (NCHP), 8.3542 (ACHP) and 8.7413 (CHBC). The Ho&McKay model was better adjusted to the adsorption data with R2 > 0.985, while the Lagergren model produced regression factors between 0.61 and 0.88. Considering the biggest concentration of nitrite solution of 50 mg·L-1 and the longest contact time of 150 minutes, the equilibrium capacity qe (mg·g-1) predicted by the Ho&McKay model for the considered adsorbents were: 4.5065 (NCHP), 8.5179 (ACHP) and 8.9445 (CHBC) compared to the obtained qt (mg·g-1) of 4.4384 (NCHP), 8.0685 (ACHP) and 8.5753 (CHBC). The nitrite uptake in the experiments reached a maximum of 2.2192 mg·g-1 on NCHP, 4.0342 mg·g-1 on ACHP and 4.2877 mg·g-1 on CHBC. Considering the cost-effective treatment steps, there is the possibility of valorising an important amount of waste as adsorbent materials. [ABSTRACT FROM AUTHOR]

Traditional denitrification often produces high operating costs and excessive sludge disposal expenses due to conventional carbon sources. A novel electric–magnetic field (MF) 48 mT with Fe0 and C-Fe0 powder in an upflow microaerobic sludge reactor (UMSR) improved nitrogen removal from wastewater without organic carbon resources and gave richness to the heterotrophic bacterial community. In the current study, the reactor was operated for 78 ± 2 days, divided into five stages (without Fe0, with Fe0, coupling with MF, without coupling with MF, and coupling with MF again), at a hydraulic retention time (HRT) of 2.5 h, with an influent loading of ammonium (NH4+-N) 50 ± 2 mg/L, at 25–27 °C, and less than 1.0 mg/L dissolved oxygen (DO). The results demonstrated nitrogen removal efficiency enhanced after coupling with MF on the levels of NO3−-N by 76% with an effluent concentration of 8.7 mg/L, NH4+-N by 72% with an effluent concentration of 13.6 mg/L, and total nitrogen removal (TN) by 76%, respectively. After coupling the MF with the reactor, the microbial community data analysis showed the dominant abundance of ammonia-oxidizing bacteria, heterotrophic nitrifying bacteria, and denitrifying bacteria on the level of Anaerolineaceae_uncultured 2%, which is capable of denitrification that uses Fe2+ as an electron source, Gemmatimonadaceae_uncultured 4%, Hydrogenophaga 4% which is capable of catalyzing hydrogenotrophic denitrification and correlating to nitrate removal, denitrification and desulfurization bacteria SBR1031_norank 18%, anammox-bacteria Saccharimonadales_norank 2%, and (AOM) Limnobacter 3% in the sludge. [ABSTRACT FROM AUTHOR]

Herein, we report the results of a study on combining adsorption and ultrafiltration in a single-stage process to remove nitrite ions from contaminated water. As adsorbent, a surface-modified nanoclay was employed (i.e., Nanomer® I.28E, containing 25–30 wt. % trimethyl stearyl ammonium). Ultrafiltration experiments were conducted using porous polymeric membranes (Ultracel® 10 kDa). The hybrid process of adsorption-ultrafiltration was modeled and optimized using three computational tools: (1) response surface methodology (RSM), (2) artificial neural network (ANN), and (3) support vector machine (SVM). The optimal conditions provided by machine learning (SVM) were found to be the best, revealing a rejection efficiency of 86.3% and an initial flux of permeate of 185 LMH for a moderate dose of the nanoclay (0.674% w/v). Likewise, a new and more retentive membrane (based on PVDF-HFP copolymer and halloysite (HS) inorganic nanotubes) was produced by the phase-inversion method, characterized by SEM, EDX, AFM, and FTIR techniques, and then tested under optimal conditions. This new composite membrane (PVDF-HFP/HS) with a thickness of 112 μm and a porosity of 75.32% unveiled an enhanced rejection efficiency (95.0%) and a lower initial flux of permeate (28 LMH). Moreover, molecular docking simulations disclosed the intermolecular interactions between nitrite ions and the functional moiety of the organonanoclay. [ABSTRACT FROM AUTHOR]

Nitrite-dependent anaerobic methane oxidation (n-DAMO) has been regarded as a promising effective approach to nitrogen removal from wastewater. However, n-DAMO bacteria are very difficult to be enriched in biological wastewater treatment processes. An anaerobic sequencing batch reactor (AnSBR) was introduced in the present study for the enrichment of n-DAMO bacteria with cornfield soil as inoculum. Fed with nitrite (NO2− ) and methane as the specific substrates, a NO2− load removal as high as 46.16 mg/(L·d) was obtained in the AnSBR since the 232nd day of enrichment culturing, though the relative abundance of Candidatus Methylomirabilis referring to n-DAMO bacteria was 2.37% in the acclimatized mixed culture. High-throughput sequencing of the obtained mixed culture revealed that the community structure was complex with the coexistence of n-DAMO bacteria, methanotrophs, heterotrophic denitrifying bacteria and hydrolytic fermentation bacteria. Analysis of interactions among the prevalent microbial populations suggested that Candidatus Methylomirabilis had played a key role in the metabolic network of the mixed culture. The research work presented a novel approach to the enrichment of n-DAMO bacteria from cornfield soil and was helpful in understanding the role of n-DAMO bacteria in complex matrices. [ABSTRACT FROM AUTHOR]

A new facultative anaerobic denitrifier was isolated from anoxic activated sludge and identified as Pseudomonas stutzeri strain HK13. Single-factor experiments indicated that the optimal conditions for nitrate removal were a C/N ratio of 8, an initial pH of 7–10, a shaking speed of 100 rpm, and a temperature of 30–40 °C. When 100 mg/L NO 3 --N and NO 2 --N were used separately as sole nitrogen sources, the strain exhibited efficient denitrification ability with total nitrogen (TN) removal efficiencies of 98.22% and 98.58%, respectively, in 15 h with the corresponding maximum removal rates of 20.03 and 21.77 mg/L/h. And there was no nitrite accumulation finally in the nitrate denitrification system. In addition, 97.42% total oxidized nitrogen (TON) was removed at 20 °C and 93.46% NO 3 --N was reduced at 45 °C, suggesting that strain HK13 had a wide range of temperature and pH to adapt to the environment. Moreover, strain HK13 exhibited a notable ability to tolerate high nitrate loading (initial NO 3 --N > 450 mg/L) with a TON removal amount of over 200 mg/L/day. These findings demonstrate that strain HK13 is effective for nitrogen removal in wastewaters containing high concentrations of nitrate and nitrite. [Display omitted] • Pseudomonas stutzeri HK13 was isolated from anoxic activated sludge and identified. • It possesses efficient denitrification ability. • High removal rates and efficiencies of nitrate and nitrite. • It has a wide range of temperature and pH to adapt to the environment. • It tolerates to high nitrate and nitrite. [ABSTRACT FROM AUTHOR]

The nitrite removal pathway in Acinetobacter sp. TX5 was explored through the key gene identification and the corresponding enzyme purification, after which the capability to reduce nitrite by immobilized beads was investigated in a fixed-bed reactor. Results revealed that a nosZ gene encoding nitrous oxide reductase (N2OR) exists in TX5 cells, and a N2OR responsible for the reduction of N2O to N2 was purified successfully with a molecular weight of 70.05 kDa, a purification fold of 16.30 and a recovery rate of 5.17%. For TX5 immobilization, the optimal values of polyvinyl alcohol (PVA), spent mushroom substrate (SMS) and Aci (TX5) obtained by response surface methodology (RSM) were 6.32%, 2.92% and 4.57%, respectively. In a fixed-bed reactor packed with immobilized TX5, the removal efficiency (RE) achieved 90% (at 50 h) for NO 2 − -N and 85% (at 96 h) for total nitrogen (TN). On the basis of these results, a nitrite removal pathway in TX5 was proposed. Overall, Acinetobacter sp. TX5 might be a promising candidate for nitrite removal with an ability to suppress N2O accumulation. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel HN-AD yeast Candida boidinii L21 was isolated and identified. • Strain L21 effectively eliminated 14–140 mg/L NO 2 –-N. • The nitrogen removal pathway of strain L21 was explored. • Strain L21 efficiently removed 74.52–136.47 mg/L inorganic nitrogen from wastewater. Efficient nitrogen removal yeasts are rarely encountered. Here, a heterotrophic nitrification-aerobic denitrification strain of Candida boidinii L21 was isolated. The optimal removal conditions for strain L21 were glucose as carbon source, C/N of 15, salinity of 10 ppt, pH of 7, shaking speed of 120 rpm, and temperature of 30 °C. Strain L21 removed NH 4 +-N, NO 2 –-N, NO 3 –-N (14–––140 mg/L) and achieved nearly complete NO 2 –-N, removal. Nitrogen balance and enzyme activity analysis indicated the nitrogen removal pathway of strain L21 through assimilation, nitrification, and denitrification pathways. When applied in wastewater and sludge, strain L21 reduced inorganic nitrogen levels within 4 days, with a 58-fold increase in nitrite removal compared to controls. These findings demonstrate that strain L21 holds great potential for enhancing nitrogen removal in wastewater treatment processes, providing valuable insights for improving environmental management practices. [ABSTRACT FROM AUTHOR]

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Herein, we report the results of a study on combining adsorption and ultrafiltration in a single-stage process to remove nitrite ions from contaminated water. As adsorbent, a surface-modified nanoclay was employed (i.e., Nanomer® I.28E, containing 25–30 wt. % trimethyl stearyl ammonium). Ultrafiltration experiments were conducted using porous polymeric membranes (Ultracel® 10 kDa). The hybrid process of adsorption-ultrafiltration was modeled and optimized using three computational tools: (1) response surface methodology (RSM), (2) artificial neural network (ANN), and (3) support vector machine (SVM). The optimal conditions provided by machine learning (SVM) were found to be the best, revealing a rejection efficiency of 86.3% and an initial flux of permeate of 185 LMH for a moderate dose of the nanoclay (0.674% w/v). Likewise, a new and more retentive membrane (based on PVDF-HFP copolymer and halloysite (HS) inorganic nanotubes) was produced by the phase-inversion method, characterized by SEM, EDX, AFM, and FTIR techniques, and then tested under optimal conditions. This new composite membrane (PVDF-HFP/HS) with a thickness of 112 μm and a porosity of 75.32% unveiled an enhanced rejection efficiency (95.0%) and a lower initial flux of permeate (28 LMH). Moreover, molecular docking simulations disclosed the intermolecular interactions between nitrite ions and the functional moiety of the organonanoclay.

Microalgal–bacterial granular sludge (MBGS) process has become a focal point in treating municipal wastewater. However, it remains elusive whether the emerging process can be applied for the treatment of aquaculture wastewater, which contains considerable concentrations of nitrate and nitrite. This study evaluated the feasibility of MBGS process for aquaculture wastewater treatment. Result showed that the MBGS process was competent to remove respective 64.8%, 84.9%, 70.8%, 50.0% and 84.2% of chemical oxygen demand, ammonia–nitrogen, nitrate–nitrogen, nitrite–nitrogen and phosphate–phosphorus under non-aerated conditions within 8 h. The dominant microalgae and bacteria were identified to be Coelastrella and Rhodobacteraceae, respectively. Further metagenomics analysis implied that microbial assimilation was the main contributor in organics, nitrogen and phosphorus removal. Specifically, considerable nitrate and nitrite removals were also obtained with the synergy between microalgae and bacteria. Consequently, this work demonstrated that the MBGS process showed a prospect of becoming an environmentally friendly and efficient alternative in aquaculture wastewater treatment. [ABSTRACT FROM AUTHOR]

The digester reject water is an ammonium-rich sidestream produced from sludge dewatering at wastewater treatment plants (WWTPs). The removal or recovery of nitrogen from this kind of wastewater is conducted by means of biological and membrane processes, air stripping or cation exchangers. The aim of the presented research was to recover the nitrogen contained in digester reject water as nitrite concentrate so that it could be used as a fertilizer or inhibitor of H2S formation in sewers. Digester rejects water that underwent nitritation, microfiltration, nanofiltration was fed through anion exchanger at Janówek WWTP Test Station. To the authors’ knowledge, the recovery of nitrogen in the aforementioned processes from the real reject water as nitrite concentrate has not been performed yet. The conducted research demonstrated the usefulness of Lewatit S 5428 (Lanxess Deutschland GmbH, BU LPT, D-51369 Leverkusen) to obtain at least 2% nitrite concentrate in most eluate samples throughout a few months of exploitation. Nevertheless, the significant changes of the feed constitution during storing and high concentration of chlorides and sulfates in the eluate (even during NaHCO3 regeneration), reduced the possibility of its utility. Only the eluate from the first stage of NaCl regeneration could be used to check its impact on the inhibition of H2S formation. [ABSTRACT FROM AUTHOR]

This study reports the effect of anolytic nitrite concentration on electricity generation and electron transfer in microbial fuel cells (MFCs). Anolytic nitrite enhanced the electricity generation capability of the MFCs at relatively low concentrations (< 60 mg·L−1) but inhibited the activity of anodic electrogenic bacteria at high concentrations. In the anode chamber of the MFC, nitrite was converted to nitrate-releasing electrons before being quickly removed through denitrification. Nitrite alone (in the absence of organic matters) could not perform as an electricity production matrix but promoted electricity production as a co-matrix in the MFC. At an influent nitrite concentration of 60 mg·L−1, the coulombic efficiency of the MFC was minimized at approximately 5.4%, and the charge transfer resistance was also lowest, while the concentrations of extracellular polymeric substances (EPS) and cytochrome c were both maximized. Higher anolytic nitrite concentrations (> 60 mg·L−1) inhibited the production of cytochrome c and EPS and increased the charge transfer resistance, thereby reducing the efficiency of electron transfer in the anodic biofilm. The results provide valuable guidelines for MFC applications in wastewater treatment processes with nitrite-containing influents. [ABSTRACT FROM AUTHOR]

Nitrogen pollution in water bodies is becoming increasingly serious, and how to remove nitrogen from water bodies economically and effectively has become a research hotspot. Especially in recent years, with the gradual expansion of aquaculture in China, the content of nitrite and other nitrogen-containing substances in water bodies has been increasing, which inhibits the growth of farm animals and is one of the causes of eutrophication in water bodies. In this study, a strain of bacteria was isolated from the sludge of an aquaculture fishpond and identified as Pseudomonas stutzeri, which can efficiently degrade nitrite. After continuous domestication in nitrite mixed solution, the nitrite nitrogen reduction capacity of P. stutzeri was significantly improved. Univariate experiments aiming to optimize the degradation conditions indicate that the optimal culture conditions for strain F2 are: medium with a carbon source of sodium succinate; C/N of 18; pH of 8; culture temperature of 28 °C; and shaking speed of 210 rpm in the shaker. Under the optimal culture conditions, the NO2−-N concentration of the culture solution was 300 mg/L, and the nitrite removal rate reached 98.67%. Meanwhile, the results of the nitrogen balance test showed that the strain converted 6.1% of the initial nitrogen into cellular organic nitrogen and 62.3% into gaseous nitrogen.

Nitrite in a water environment is very harmful to humans and aquatic animals. A novel aerobic denitrifying bacterium able to utilize NO2--N as the only nitrogen source was isolated for the purpose of removing nitrite from water, which was identified as Acinetobacter sp. and named as YT03. The growth and denitrification activity of strain YT03 was assessed comprehensively. Results showed that the nitrite in water with an initial concentration of 10 mg L–1 could be completely removed within 6 h by strain YT03, and the optimal conditions for strain YT03 to remove nitrite were as follows: sodium succinate as the carbon source, C/N ratio of 16, pH of 6.5, temperature of 30°C, and shaking speed of 250 rpm. An RNA-Seq transcriptome analysis was used to find genes associated with nitrite removal. Compared with the removal of ammonia nitrogen, 47 genes were significantly differentially expressed, including 20 up-regulated and 27 down-regulated genes, mainly involved in the transport process, biosynthetic process, and so on. And among the differentially expressed genes, C4-dicarboxylate transporter (DctA) and nitrate/nitrite transporter (Nrt) might be of importance for the efficient utilization of carbon and nitrogen sources in aerobic nitrite denitrification with sodium succinate by strain YT03.

A novel Gram-stain-negative strain, designated S37H4 T , was isolated from an intertidal surface sediment sample collected from Zhanjiang City, Guangdong province, south PR China. Cells of the strain were aerobic, non-flagellated, long rod-shaped and motile by gliding. S37H4 T could grow at 4-40 °C, pH 7.0-8.5 and in 2.0-15.0 % NaCl, with optimal growth at 25-30 °C, pH 7.5 and 9.0 % NaCl, respectively. S37H4 T was capable of nitrite removal under high-salt conditions, and there were three denitrification genes, nirK , norB and nosZ, in its genome. The results of phylogenetic analyses based on the 16S rRNA gene and genome sequences indicated that S37H4 T represented a member of the genus Marivirga and formed a subclade with Marivirga lumbricoides JLT2000 T . S37H4 T showed the highest 16S rRNA sequence similarity to M. lumbricoides JLT2000 T (98.3 %) and less than 97.0 % similarity with other type strains of species of the genus Marivirga . The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between S37H4 T and the reference type strains of species of the genus Marivirga were 70.7-74.3 % and 18.2-19.2 %, respectively. The major fatty acids of S37H4 T were iso-C 15 : 0 , iso-C 15 : 1 G, iso-C 17 : 0 3-OH and summed feature 3 (C 16 : 1 ω6 c and/or C 16 : 1 ω7 c ). The major respiratory quinone of this novel strain was MK-7, and the predominant polar lipids were identified as phosphatidylethanolamine, an unidentified aminolipid, an unidentified phospholipid and three unidentified lipids. The results of analyses of phylogenetic, genomic, physiological and biochemical characteristics indicated that S37H4 T represented a novel species of the genus Marivirga , for which the name Marivirga aurantiaca sp. nov. is proposed. The type strain is S37H4 T (= GDMCC 1.1866 T = KACC 21922 T ).

Nitrite in a water environment is very harmful to humans and aquatic animals. A novel aerobic denitrifying bacterium able to utilize NO 2 - -N as the only nitrogen source was isolated for the purpose of removing nitrite from water, which was identified as Acinetobacter sp. and named as YT03. The growth and denitrification activity of strain YT03 was assessed comprehensively. Results showed that the nitrite in water with an initial concentration of 10 mg L–1 could be completely removed within 6 h by strain YT03, and the optimal conditions for strain YT03 to remove nitrite were as follows: sodium succinate as the carbon source, C/N ratio of 16, pH of 6.5, temperature of 30°C, and shaking speed of 250 rpm. An RNA-Seq transcriptome analysis was used to find genes associated with nitrite removal. Compared with the removal of ammonia nitrogen, 47 genes were significantly differentially expressed, including 20 up-regulated and 27 down-regulated genes, mainly involved in the transport process, biosynthetic process, and so on. And among the differentially expressed genes, C4-dicarboxylate transporter (Dct A) and nitrate/nitrite transporter (Nrt) might be of importance for the efficient utilization of carbon and nitrogen sources in aerobic nitrite denitrification with sodium succinate by strain YT03. [ABSTRACT FROM AUTHOR]

The potential for aerobic NO removal by Alcaligenes faecalis strain NR was investigated. 35 mg/L of NO -N was removed by strain NR under aerobic conditions in the presence of NH . N-labeling experiment demonstrated that NO and N were possible products during the aerobic nitrite removal process by strain NR. The key enzyme genes of nirK, norB and nosZ, which regulate the aerobic nitrite denitrification process, were successfully amplified from strain NR. The gene sequence analysis indicates that copper-containing nitrite reductase (NIRK) and periplasmic nitrous oxide reductase (NOSZ) were both hydrophilic protein and the transmembrane structures were absent, while nitric oxide reductase large subunit (NORB) was a hydrophobic and transmembrane protein. According to the three-dimensional structure and binding site analysis, the bulky and hydrophobic methionine residue proximity to the nitrite binding sites of NIRK was speculated to be related to the oxygen tolerance of NIRK from strain NR. [ABSTRACT FROM AUTHOR]

In this work, a mathematical model is developed for a heterogeneously catalyzed reaction in a porous membrane micro-reactor. Hydrogenation of an aqueous nitrite contaminant in water is analyzed as a model reaction. For a straight micro-reactor a numerical algorithm is developed to predict the behavior for non-linear kinetics. This is validated with a semi-analytical solution based on separation of variables under the assumptions of linear kinetics. Predictions of the non-linear model are compared with experimental observations reported in the literature. Analysis shows that the straight reactor is inefficient and catalyst utilization is poor when higher throughputs are required because the system is diffusion limited. A modified design is proposed which incorporates curving of the microchannel to induce passive mixing by generating “Dean Vortices”. The velocity fields are obtained using a perturbation analysis. This is incorporated in solving the convection-diffusion-reaction system which governs the species transport. The non-linear system of equations is solved using an operator splitting technique. The numerical singularity at the center of the curved channel is dealt by transforming the governing equations in the vicinity of r = 0 using Cartesian coordinates. The curving of the reactor results in a significant improvement in conversion for higher flow rates, with enhanced catalyst utilization. The non-monotonic enhancement in Sherwood number is interpreted by analyzing the dynamics of the concentration depletion layer. [ABSTRACT FROM AUTHOR]

The functionalized porous solid ethylenediamine polysiloxane immobilized ligand system P-NN (where P represents [Si-O]n polysiloxane network and NN represents ethylenediamnie group) was prepared by hydrolytic polycondensation of 3-aminopropyl-2-aminoethyltrimethoxysilane with tetraethylorthosilcate (TEOS) in the presence of CTAB surfactant. CTAB was used to enhance the porosity of the material and therefore increases the adsorption capacity of the immobilized ligand system. The functionalized ligand system was investigated as adsorbent for nitrite ions from aqueous solutions. Both batch and column methods were carried out and the effect of various parameters was studied that include contact time, pH, nitrite concentration and temperature in order to investigate the optimum conditions for the nitrite ions removal. The optimum nitrite adsorption was established in acidic medium, at 75°C, and at contact time equals 24 h. The nitrite removal was about 65-100% at 5-50 ppm of initial nitrite concentration. The use of this adsorbent is proved to be repeatable and recyclable. The adsorbent can be considered as a promising material for nitrite removal from different water and waste water and aqueous extracts containing nitrite ions. [ABSTRACT FROM AUTHOR]

Nitrite, at an environmentally relevant concentration, was significantly reduced with iron (hydr)oxides mediated by Shewanella oneidensis MR-1. The average nitrite removal rates of 1.28 ± 0.08 and 0.65 ± 0.02 (mg L −1 ) h −1 were achieved with ferrihydrite and magnetite, respectively. The results showed that nitrite removal was able to undergo multiple redox cycles with iron (hydr)oxides mediated by Shewanella oneidensis MR-1. During the bioreduction of the following cycles, biogenic Fe(II) was subsequently chemically oxidized to Fe(III), which is associated with nitrite reduction. There was 11.18 ± 1.26 mg L −1 of NH 4 + -N generated in the process of redox cycling of ferrihydrite. Additionally, results obtained by using X-ray diffraction showed that ferrihydrite and magnetite remained mainly stable in the system. This study indicated that redox cycling of Fe in iron (hydr)oxides was a potential process associated with NO 2 − -N removal from solution, and reduced most nitrite abiotically to gaseous nitrogen species. [ABSTRACT FROM AUTHOR]

Recirculating aquaculture systems (RAS) normally use nitrifying bacteria to control nitrogen compounds. However, some problems from the nitrification process may arise, creating toxic concentrations for the fish. Nanofiltration (NF) could be the answer for this fluctuation, controlling the quality of water in the required level. In this work, we analyze the capacity of NF 270 membrane to reject nitrite and nitrate ions in two different concentrations and using two different water hardness, based on the concentration detecting in RAS in Chile. In the first test, NF membrane was tested at different transmembrane pressures (TMP) in two types of model solutions, formed by nitrite or nitrate dissolved in deionized water, testing two concentrations, high (H) and low (L), according to the concentration that are dangerous for fish in RAS. In this test, NF 270 membrane rejected approximately 75% of nitrite or nitrate, at the best TMP (19 bar). In the second test, the membrane was tested using nitrite, nitrate, and different qualities of water, based on the water hardness produced by different salts, found in RAS in Chile. This water quality was formulated and classified as soft and hard. There, bivalent cations present in the water are rejected in more than 70% and monovalent cations passed easier through the membrane with a rejection between 50 and 80%, depending on N-molecules concentrations and on the water hardness. We can conclude that this phenomenon is related with the hydrated energy and Donnan exclusion. The rejection of the N-molecules in those conditions depends on the concentration and the hardness of the water. For soft water hardness, the rejection was between 40 and 60% for the N-molecules and for hard water quality, this percentage is in the range of 25–40% at 20 bar of TMP. With these results, a membrane process was proposed to separate the nitrite and nitrate from hard water including different steps that should be tested in a prototype. [ABSTRACT FROM AUTHOR]

The present work seeks to describe a new approach characterized by copper(II) aspirinate complex deposited onto nanotube TiO electrodes as mediator of electron transfer during nitrite reduction, aiming at achieving a faster removal of nitrite to nitrogen species oxides. Thin films of copper aspirinate ([Cu(asp)]) on the Ti/TiO nanotube surface are easily obtained following multi-scans (100 cycles) recorded for the Ti/TiO electrode in 0.1 mol L NaCl, pH 4, containing 5.0 × 10 mol L of the copper coordination compound. The complex showed high adherence while the cyclic voltammograms presented redox peaks at −0.15/+0.15 V, which was attributed to the reduction of Cu(II) to Cu(I). Following 5 min of treatment using photoelectrocatalysis on Ti/TiO-[(Cu)Asp] electrode, a total removal of nitrite was observed, which was found to be at least four times faster compared to Ti/TiO electrode. Concomitantly, we also observed a relatively good conversion to nitrogen-containing gaseous species (56 %) besides the formation of 42 % of ammonia. The results, in effect, also indicate that nitrate and nitrite are not detectable in the treated solution up to levels of 0.5 mg L. The method under consideration has successfully accounted for the maximum limit of nitrite recommended in drinking water which has been set to 1 mg L. [ABSTRACT FROM AUTHOR]

BACKGROUND Nitrite contaminants in groundwater endanger public health since they may cause many diseases such as blue baby syndrome, cancer and hypertension. In this work, novel Pd- CNTs/ Al2O3 catalytic hollow fiber membranes for aqueous nitrite hydrogenation reduction were fabricated by the deposition of carbon nanotubes ( CNTs) and Pd nanoparticles inside porous Al2O3 hollow fibers. A hollow fiber membrane reactor was assembled for nitrite removal from water by catalytic hydrogenation reduction. RESULTS Experimental results indicated that the nitrite hydrogenation rate was highly dependent on hydrogen dissolution in water and adsorption on the catalyst. The nitrite removal increased with increasing H2 partial pressure to balance the nitrite solution, but the influence became very marginal as it approached 1.0 atm. The oxygen in the gas feed lowered the nitrite removal due to the reaction with dissolved hydrogen over the Pd-catalyst. Compared with the conventional diffusion operation of the membrane reactor, the 'flow-through' operation resulted in higher nitrite removals due to the intensified mass transfer rate. CONCLUSION The nitrites in water can be completely removed using the Pd- CNTs/ Al2O3 membrane reactor with flow-through operation. The denitrification should be operated at around 25°C for large reaction kinetics, which is determined by both the temperature and the hydrogen solubility in water. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Acinetobacter junii YB was found to exhibit efficient heterotrophic nitrification and aerobic denitrification ability, with the maximum ammonium, nitrite and nitrate removal rate of 8.82, 8.45 and 7.98 mg/L/h, respectively. Meanwhile, ammonium was found to be removed preferentially in the process of simultaneous nitrification and denitrification in mixed N-sources. The successful PCR amplification of hao , nap A and nir S genes further provided additional evidence of heterotrophic nitrification and aerobic denitrification by strain YB. In addition, orthogonal test showed that dissolved oxygen was the most important determinant of nitrite removal, and the optimal conditions were C/N 15, pH 7.0, 37 °C and 200 rpm. Furthermore, stable nitrogen and organics removal were achieved by one-time dosing of enriched bacteria in a sequencing batch reactor. The inoculation of strain YB significantly improved the denitrification efficiency with minimal accumulation of nitrified products, which demonstrated high potential of the isolate for future practical applications. [ABSTRACT FROM AUTHOR]

The fraction of phytoplankton growth that leads to the rain of organic carbon out of the sunlit surface ocean (“export production”) is central to the ocean׳s sequestration of atmospheric carbon dioxide. Nitrate assimilation has long been taken as a measure of export production; however, this has recently been questioned by suggestions that much of the nitrate in the sunlit layer (the “euphotic zone”) originates from biological nitrogen (N) already in surface waters. This view has been supported by recent observations of euphotic zone nitrate elevated in δ 18 O relative to its δ 15 N, taken as indicative of nitrification (the oxidation of recycled ammonium to nitrite and then nitrate). To evaluate the potential importance of nitrification in the Sargasso Sea euphotic zone, we measured the δ 15 N and δ 18 O of seawater nitrate for samples with ≥0.2 µM nitrate collected on 18 cruises in the Sargasso Sea, and here we present the first large data set to correct for the low but often measurable concentrations of nitrite. Regardless of season, nitrate (i.e., nitrate-only rather than nitrate+nitrite as is commonly reported) δ 15 N and δ 18 O increase in unison from below the base of the euphotic zone toward the surface. This pattern derives from nitrate assimilation by phytoplankton, implying that nitrification is much slower than the upward transport of nitrate into the lower Sargasso Sea euphotic zone. In the twilight zone below the euphotic zone, we observe a rise in nitrate δ 18 O (relative to deeper waters) that is not accompanied by a rise in δ 15 N, suggesting nitrification co-occurring with nitrate assimilation. Nitrification, therefore, does not appear to occur in euphotic zone waters overlapping with nitrate assimilation only in the ~150 m-thick twilight zone layer below it. In net, the data argue for a simpler N cycle for the Sargasso Sea euphotic zone than has recently been suggested, with the rate of euphotic zone nitrate assimilation approximating that of organic carbon export to the deep ocean. [ABSTRACT FROM AUTHOR]

The nitrite removal pathway in Acinetobacter sp. TX5 was explored through the key gene identification and the corresponding enzyme purification, after which the capability to reduce nitrite by immobilized beads was investigated in a fixed-bed reactor. Results revealed that a nosZ gene encoding nitrous oxide reductase (N 2 OR) exists in TX5 cells, and a N 2 OR responsible for the reduction of N 2 O to N 2 was purified successfully with a molecular weight of 70.05 kDa, a purification fold of 16.30 and a recovery rate of 5.17%. For TX5 immobilization, the optimal values of polyvinyl alcohol (PVA), spent mushroom substrate (SMS) and Aci (TX5) obtained by response surface methodology (RSM) were 6.32%, 2.92% and 4.57%, respectively. In a fixed-bed reactor packed with immobilized TX5, the removal efficiency (RE) achieved 90% (at 50 h) for NO 2 - -N and 85% (at 96 h) for total nitrogen (TN). On the basis of these results, a nitrite removal pathway in TX5 was proposed. Overall, Acinetobacter sp. TX5 might be a promising candidate for nitrite removal with an ability to suppress N 2 O accumulation.

This paper describes a simple spectrophotometric procedure for determining NO3--N in water samples. In the proposed method, NO2--N of a water sample is first removed from the water with sulfamic acid. Then, NO3--N is reduced to NO2--N using vanadium (III) chloride and a detection reagent is added. When rapid collection of data is necessary, this method can be adapted to a microtechnique using a 96-well microplate, resulting in a detection limit of 5 NO3--N mg/l. Using a larger volume spectrophotometer cell (5 cm) lowers the detection limit to 0.5 NO3--N mg/l. The proposed method is applicable for routine analysis of water in aquaculture systems and wastewaters in which medium-high NO3--N concentrations are expected. Benefits of the method are reduction of the laborious preparation and avoidance of contact with the harmful substances typical of the cadmium reduction method. [ABSTRACT FROM AUTHOR]

Current generation using nitrite as substrate (pH 6.9, 40 mgN l) in a nitrite-fed microbial fuel cell was investigated under anaerobic and aerobic anodic conditions as an alternative to the biological nitrite oxidation process. Cell current, coulombic efficiency (CE) and power generation of 0.04 mA, 30 ± 2 % and 19.3 ± 3.3 μW m, respectively, were observed under anaerobic conditions while complete nitrite degradation (no current) was obtained under aerobic conditions. Switching from aerobic to anaerobic anode enhanced the CE and power generation (39 ± 1 % and 29 ± 4.3 μW m). [ABSTRACT FROM AUTHOR]

Abstract: Batch test were performed to assess nitrite removal, nitrate formation, CO2 fixation, gaseous nitrogen production and microbial density in activated sludge exposed to volatile fatty acid (VFA) mixtures. Nitrite removal and nitrate formation were both affected by the presence of VFAs, but to different degrees. Nitrate formation rates were reduced to a greater extent (79%) than nitrite removal rates (36%) resulting in an apparent unbalanced nitrite oxidation reaction. Since the total bacterial density and the nitrite oxidizing bacteria (NOB, Nitrospira) concentration remained essentially constant under all test conditions, the reduction in rates was not due to heterotrophic uptake of nitrogen or to a decrease in the NOB population. In contrast to the nitrogen results, VFAs were not found to impact CO2 fixation efficiency. It appeared that nitrite oxidation occurred when VFAs were present since the oxidation of nitrite provides energy for CO2 fixation. However, nitrate produced from the oxidation of nitrite was reduced to gaseous nitrogen products. N2O gas was detected in the presence of VFAs which was a clear indication that VFAs stimulated an alternative pathway, such as aerobic denitrification, during biotransformation of nitrogen in activated sludge. [Copyright &y& Elsevier]

Stringent standards for nitrogen discharge necessitate the implementation of new systems for the sustainable removal of ammonium from wastewater. One of such systems is based on the process of anaerobic ammonium oxidation (Anammox), which is a new powerful tool especially for strong nitrogenous wastewaters. In this study, the Anammox process performance was tested with synthetic wastewater in a completely stirred tank reactor (CSTR). The reactor was operated for 511 days and fed with increasing amounts of ammonium and nitrite. In this period, an increase of ammonium and nitrite utilization rates were observed as a result of the increase of nitrogen loads in the influent. After 272 days, about 60% of the biomass was removed from the reactor and the system was restarted. Throughout 511 days 90% of the ammonium and more than 99% of the nitrite were converted mainly to dinitrogen (N2) and nitrate. The microbial community in the reactor was characterized with Fluorescence in situ Hybridization (FISH). The study showed that the population in the reactor was dominated by the deep-branching planctomycete Candidatus “Brocadia anammoxidans” strain Dokhaven 2. [ABSTRACT FROM AUTHOR]

Nitrogen pollution in water bodies is becoming increasingly serious, and how to remove nitrogen from water bodies economically and effectively has become a research hotspot. Especially in recent years, with the gradual expansion of aquaculture in China, the content of nitrite and other nitrogen-containing substances in water bodies has been increasing, which inhibits the growth of farm animals and is one of the causes of eutrophication in water bodies. In this study, a strain of bacteria was isolated from the sludge of an aquaculture fishpond and identified as Pseudomonas stutzeri, which can efficiently degrade nitrite. After continuous domestication in nitrite mixed solution, the nitrite nitrogen reduction capacity of P. stutzeri was significantly improved. Univariate experiments aiming to optimize the degradation conditions indicate that the optimal culture conditions for strain F2 are: medium with a carbon source of sodium succinate; C/N of 18; pH of 8; culture temperature of 28 °C; and shaking speed of 210 rpm in the shaker. Under the optimal culture conditions, the NO2−-N concentration of the culture solution was 300 mg/L, and the nitrite removal rate reached 98.67%. Meanwhile, the results of the nitrogen balance test showed that the strain converted 6.1% of the initial nitrogen into cellular organic nitrogen and 62.3% into gaseous nitrogen. [ABSTRACT FROM AUTHOR]

Innovative removal of toxic nitrite and ammonia is one of the key approaches for efficient aquaculture biotechnology. This study suggests a fast removal technique of high-levels of nitrite and ammonia using recirculating aquaculture wastewater at 30‰ salinity. Four lab-scale moving bed biofilm reactors (MBBRs; R1, R2, R3, and R4) were operated in parallel for 56 days with different combinations of mature and fresh biofilms on biocarriers at 30% filling ratio. Nitrogen removal efficiency, biofilm physicochemical properties, and microbial analyses were conducted using PCR and sequencing techniques at the region of the 16S ribosomal RNA. The results showed that R4 (using mature biofilms) recorded the highest nitrite and ammonia removal (99.6% and 95.3%, respectively) compared to the control, R1 (94.1% and 89.4%). Meanwhile, the removal rate of ammonia in R4 was significantly the fastest compared to other reactors. Partial Least Squares-Discriminant Multivariate Analysis (PLS-DA) model showed a good prediction with very high accuracy and prediction (Q2 > 0.8) for the first three principal components pertaining to nitrite and ammonia removal. Planktosalinus genus was the most abundant in R4, while proteobacteria phylum was the dominant, followed by Marinobacter and Nitrospina in all reactors. Overall, the use of mature biofilms in MBBR was proven to increase bacterial diversity, enhancing nitrite and ammonia removal efficiency. [Display omitted] • Lab-scale moving bed biofilm reactors (MBBRs) were used in the present study. • Mature biofilms MBBR showed the highest nitrite and ammonia removal efficiency. • MBBR with mature biofilm increased nitrate concentration to 51.7 mg L−1 after 2 days. • Planktosalinus was the dominant genus in all MBBRs, with least number in the control. • New biofilms MBBR showed the highest population of Bacteroidetes (45.92%). [ABSTRACT FROM AUTHOR]

This investigation explores the efficacy of employing ultrasonic cavitation and coupling it with advanced oxidation processes (hydrogen peroxide and Fenton's reagent) for reducing the levels of total ammonia nitrogen in fish pond water containing Tilapia fishes. Ultrasonic cavitation is a phenomenon where the formation, growth and collapse of vaporous bubbles occur in a liquid medium producing highly reactive free radicals. Ultrasonic probe system (20 kHz with 750 W and 1000 W) was used to induce cavitation. Besides, to intensify the process, ultrasonic cavitation was coupled with hydrogen peroxide and Fenton's reagent. Using SERA colour indicator test kits, the levels of ammonium, nitrite and carbonate hardness were measured. The results obtained from this study clearly show that the advanced oxidation processes are more efficient in reducing the ammonium and nitrite levels in fish pond water than using ultrasound alone. The pH and carbonate hardness levels were not affected significantly by ultrasonic cavitation. The optimal treatment time and ultrasound power to treat the water samples were also established. Energy efficiency and cost analysis of this treatment have also been presented, indicating that ultrasonic cavitation coupled with hydrogen peroxide appears to be a promising technique for reducing total ammonia nitrogen levels in the fish pond water. [Display omitted] • Ultrasonic cavitation with AOP efficiently treats fishpond wastewater. • Ultrasonic cavitation is highly energy-efficient and reduces operational cost. • Labour cost and operation downtime can be reduced as maintenance is not needed. • Ultrasonic probes can be switched on and off instantaneously to save time. • Does not use hazardous chemicals and thus safe for aquatic life and humans. [ABSTRACT FROM AUTHOR]

Electrocoagulation (EC) with an aluminum electrode arrangement as anode-cathode was applied to denitrify groundwater and electrooxidation (EO) was examined as a post-treatment step to remove the produced by-products. Initially, EC experiments were performed under batch operating mode using artificially-polluted tap water to investigate the effects of initial pH (5.5, 7.5, 8.5), initial NO 3 −-N concentration (25, 35, 45, 55 mg L−1) and applied current density (10, 20 mA cm−2) on process efficiency. The effect of initial solution pH on ammonium cation concentration was also investigated as their generation (as a by-product) is the main drawback preventing wide-scale application of these treatment processes. Experimental results revealed high nitrate removal percentages (up to 96.3%) for initial pH 7.5 and all initial concentrations and current densities, while the final ammonium concentrations ranged between 5.3 and 9.2 mg NH 4 +-N L−1 (for initial NO 3 −-N of 25 mg L−1). Therefore, EO was examined to oxidize the ammonium cations to nitrogen gas on iridium oxide coated titanium electrodes (IrO 2 /Ti) anode surface. The effects of cathode material (aluminum, stainless steel), total current density and anode surface area (3.3–30 mA cm−2 and 12–36 cm2, respectively) were investigated, and lead to NH 4 +-N percentage removals of between 25% (10 mA cm−2, 12 cm2) and 100% (30 mA cm−2, 24 cm2) for an initial NH 4 +-N concentration of 10 mg L−1. The optimum EC (20 mA cm−2, natural initial pH 7.5–7.8) and EO parameters (30 mA cm−2, 24 cm2 surface area anode, Al cathode) were combined into a hybrid system to treat two real nitrate-polluted groundwaters with initial NO 3 −-N concentrations of 25 and 75 mg L−1. Results revealed that the proposed hybrid treatment system can be used to efficiently remove nitrate from groundwaters. • Two real nitrate-polluted ground water was successfully treated using EC and EO. • Al electrodes were applied to reduce amount of nitrates to ammonium. • Al/cathode and Ti/IrO 2 /anode electrodes were applied to oxidize NH 4 + to N 2. • High nitrate (71.2%–96.71%) and complete NH 4 + removal were achieved. [ABSTRACT FROM AUTHOR]

• Strain MZ-5 showed heterotrophic nitrification and aerobic nitrification capability. • Ammonium was the priority nitrogen source in the mixed N sources. • nap A gene was successfully amplified. • Strain MZ-5 showed good nitrogen removal performance when treating wastewater. Heterotrophic nitrification–aerobic denitrification (HN-AD) has advantages over the traditional nitrogen removal process when removing multiple types of nitrogen in wastewater treatment. Acinetobacter tandoii MZ-5, which is capable of HN-AD, was isolated from the sediment of a polluted river for the first time. It used NH 4 +-N, NO 2 –-N and NO 3 –-N as sole nitrogen sources with maximum removal rates of 2.28, 1.18 and 1.04 mg L−1h−1, respectively. Simultaneous nitrification and denitrification were observed when using mixed N sources and NH 4 +-N was preferentially utilized. High nitrogen removal efficiencies (>90%) were achieved under the following conditions: C/N ratio 11–18, pH 6–8, 25–30 °C and dissolved oxygen 7.35–7.66 mg L−1. Strain MZ-5 was effective at treating wastewater from landfill leachate treatment plants, with NH 4 +-N, NO 3 –-N and total nitrogen (TN) removal efficiencies of 99.28%, 44.85% and 45.31%, respectively. Thus, strain MZ-5 may be a good candidate for wastewater treatment. [ABSTRACT FROM AUTHOR]

Liquid-phase reduction using a solid catalyst provides a potential technique for the removal of nitrites from waters. Activity and selectivity measurements were performed for a wide range of reactant concentrations and reaction conditions in an isothermal semi-batch slurry reactor operating at atmospheric pressure. The effects of catalyst loading and initial nitrite concentration on the reaction rate were alsoinvestigated. The Pd monometallic catalysts were found to be advantageous over the Pd-Cu bimetallic catalyst with respect to both reaction activity and selectivity. Minimum ammonia formation was observed for the Pd(l wt. %)/gamma- Al2O3 catalyst, The reaction kinetics was found to be dependent on the catalyst surface hydroxylation, which has also been confirmed by runs conducted in a continuous-flow monolith reactor. (c) 1998 IAWQ. Published by Elsevier Science Ltd. [ABSTRACT FROM AUTHOR]