High Nitrate Removal Efficiency Research Articles

Construction of electron-deficient Co on the nanoarrays enhances absorption and direct electron transfer to accelerate electrochemical nitrate reduction

Electrochemical nitrate reduction is a promising remediation strategy for nitrate-contaminated wastewater treatment, in which nitrate adsorption is a prerequisite step in the overall process. Herein, the iron-induced cobalt phosphide was grown in situ on porous nickel foam (Fe-CoP/NF) for the electrochemical nitrate reduction. Structural characterization verified doping of Fe and the uniform nanotube arrays of Fe0.03CoP/NF. Remarkably, the Fe0.03CoP/NF exhibited a high efficiency nitrate removal efficiency (99.3%) and excellent ammonia selectivity (100% selectivity and 0.485mg·h-1cm-2 NH3 yield rate). Both experimental and theoretical results reveal that Fe doping alters the local charge distribution of the Co active centers to form electron-deficient Co. The Co electron-deficient regions were constructed due to the difference in electronegativity between Co and Fe. Furthermore, the formation of electron-deficient centers facilitates the reduction of charge transfer resistance. In particular, Fe0.03CoP/NF maintained an excellent conversion efficiency of nitrate to N2 (99.8%) with 60mM Cl−, and the selectivity of N2 is maintained above 99.1% during long-term operation. This system possesses a low electrical consumption of 1.79 kWh·molN-1. This study designed an enhanced electrocatalyst through enhanced nitrate absorption and direct electron transfer strategies, thus providing a promising and low-power consumption approach for addressing nitrate pollution.

Nutrient removal performance and the nitrogen-sulfur conversion pathways in sulfur-iron based biofilter under acidic/alkaline conditions

The nitrate and phosphate removal in sulfur based (Vp) and sulfur-iron based autotrophic denitrification systems (Sp) with sponge iron as the iron source was investigated under different pH (6–9). In this study, Sp (>98 %) and Vp (>97 %) had higher nitrate removal efficiency at pH 7–8 and the highest phosphate removal efficiency (94.9 % ± 3.57 %) at pH 6. The flow cytometry detection revealed that the cell integrity was damaged due to the formation of iron crusts at pH 6, which resulted in irreversible inhibition in Sp. Electron transfer and nitrogen transformation showed that compared with the sustained inhibition of denitrification at pH 6, the inhibition at pH 9 occurred mainly in the initial 0–2 h due to the enhanced flow of electrons toward the formation of biological element sulfur (Sbio0). Coupled sponge iron promoted the adsorption and reduction of NO2−/N2O and reduced N2O emissions. Metatranscriptomics analysis showed that significant upregulation of key gene expression for nitrogen and sulfur metabolism in Sp, with complex regulatory mechanisms enhancing system stability and performance. Acidic conditions reduced the abundance of denitrification and sulfur oxidation functional genes. However, alkaline conditions (pH of 9) mainly caused the decreased abundance of denitrification functional genes, which was favorable for accumulation of Sbio0. This study provides a theoretical basis for the stable operation and regulation of the sulfur-iron based autotrophic denitrification process.

The stratified response of heterotrophic, autotrophic or mixotrophic denitrification to enrofloxacin stress along different filling heights in up-flow fixed-bed bioreactors

Antibiotics frequently exist in nitrate wastewater and seriously threaten biological denitrification. This study investigated the impact of enrofloxacin (ENR) on autotrophic, heterotrophic, and mixotrophic denitrification processes at various filling heights. The experiments were conducted across four consecutive phases with ENR concentrations of 0, 0.1, 1, and 10 mg/L. As the influent ENR concentration increased, the denitrification performance of the FeS2-based autotrophic denitrification (PAD) system was significantly inhibited at different filling heights, with nitrate removal efficiency (NrE) dropping to 30.42 %. In contrast, the polycaprolactone (PCL)-based heterotrophic denitrification (PHD) and mixotrophic denitrification (PAD+PHD) systems only affected NrE in the lower layer, whereas the middle and upper layers maintained high NrE levels, largely unaffected by ENR stress, reaching up to 98.28 % and 94.02 % respectively. Sulfate reduction was more prominent in the upper and middle layers of the mixotrophic denitrification bioreactor (PHD system). Bacterial diversity indices initially increased and then decreased as ENR concentration rose from 0 to 10 mg/L, with the PHD system showing lower diversity compared to the PAD system. Redundancy analysis (RDA) revealed that the relative abundances of Proteobacteria and Actinobacteriota in the PAD system, and Bacteroidota and Firmicutes in the PHD system, were negatively correlated with ENR concentration. Overall, the PAD system experienced significant stress from ENR at various filling heights, whereas the upper-middle layer of the PHD system demonstrated greater resistance. This highlighted the impact of antibiotic contamination along with the performance of different filling heights and emphasized the need for tailored strategies in wastewater treatment.

Manganese sulfide-sulfur and limestone autotrophic denitrification system for deep and efficient nitrate removal: Feasibility, performance and mechanism

Despite the great potential of sulfur-based autotrophic denitrification, an improvement in nitrate removal rate is still needed. This study used the desulfurized products of Mn ore to develop the MnS-S0-limestone autotrophic denitrification system (MSLAD). The feasibility of MSLAD for denitrification was explored and the possible mechanism was proposed. The nitrate (100 mg/L) was almost removed within 24 h in batch experiment in MSLAD. Also, an average TN removal of 98 % (472.0 mg/L/d) at hydraulic retention time of 1.5 h in column experiment (30 mg/L) was achieved. MnS and S0 could act as coupled electron donors and show synergistic effects for nitrate removal. γ-MnS with smaller particle size and lower crystallinity was more readily utilized by the bacterium and had higher nitrate removal efficiency than that of α-MnS. Thiobacillus and Sulfurimonas were the core functional bacterium in denitrification. Therefore, MnS-S0-limestone bio-denitrification provides an efficient alternative method for nitrate removal in wastewater.

Assessment of nitrate contamination of domestic wells and remedial treatment by electrocoagulation

Natural water contaminated with nitrates can pose serious problems for human health and aquatic ecosystems. Thus, effective, and low-cost treatment systems that can be implemented on both large and small scales are needed. The main goals of this work were to quantify nitrate pollution of groundwater (i.e., underground well water used for drinking purposes), to identify its causes, to evaluate the performance of the electrocoagulation (EC) process in nitrate removal, optimizing the treatment procedure using synthetic water, and to estimate the process cost. A total of thirty domestic wells, located in Sidi Bel Abbes city in North-West Algeria, used for drinking water were subject to sampling. Results indicated that most of the wells had nitrate contents that exceeded the World Health Organization (WHO) guideline value as well as the Algerian permissible limit of 50 mg.L−1, with a maximum NO3- concentration of 162 mg.L−1. The pollution was presumed to be due to agricultural activity, human and animal waste, and the nature of the soil. The EC treatment tests with aluminum electrodes exhibited a high nitrate removal efficiency of 90% at a current density of 5.12 mA.cm−2, electrolysis time 15 min, pH 8.8, agitation speed 400 rpm and at an initial nitrate concentration of 50 mg.L−1. Under optimum operating conditions, nitrate removal was 88% for an initial [NO3-] of 87 mg.L−1 in groundwater. The operating cost was estimated at 0.27 US $/m3 or 0.12 US $/Kg nitrate removed. The findings from this study showed that EC is an economically viable technique for dealing with nitrate contamination for small-scale water treatment applications.

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.

Chitosan-stabilized iron-copper nanoparticles for efficient removal of nitrate.

Chitosan-stabilized iron-copper nanomaterials (CS-nZVI/Cu) were successfully prepared and applied to the nitrate removal. Batch experiments were conducted to examine the effects of experimental parameters on nitrate removal, including Cu loading, CS-nZVI/Cu dosages, initial nitrate concentrations, and initial pHs. From the experimental date, it was concluded that CS-nZVI/Cu has a high nitrate removal efficiency, which can be more than 97%, respectively, at Cu loading = 5%, dosages of CS-nZVI/Cu = 3 g/L, initial nitrate concentrations of 30~120 mg/L, and initial pH values = 2~9. Additionally, the kinetic data for CS-nZVI/Cu were found to fit well with the first-order kinetic model with a rate constant of 0.15 (mg∙L)1-n/min, where n=1. The Langmuir model showed a good fit for NO3- removal, indicating that monolayer chemisorption occurred. The SEM and TEM analyses showed that the addition of chitosan resulted in improved dispersion of the CS-nZVI/Cu. The CS-nZVI/Cu nanomaterials have a more complete elliptical shape and are between 50 and 100 nm in size. The XRD analysis showed that the chitosan encapsulation reduced the oxidation of the iron component and the main product was Fe3O4. The FT-IR analysis showed that the immobilization of chitosan and the iron was accomplished by the ligand interaction. The nitrogen adsorption-desorption isotherm results showed that the CS-nZVI/Cu specific surface area and pore volume decreased significantly after the reaction. Adsorption, oxidation, and reduction are possible mechanisms for nitrate removal by CS-nZVI/Cu. The XPS analysis investigated the contribution of nZVI and Cu in the removal mechanism. Adding copper accelerates the reaction time and rate. In addition, nZVI played a vital role in reducing nitrate to N2. Based on these results, it looks like CS-nZVI/Cu could be a satisfactory material for nitrate removal.

Energy from Waste: Poterioochromonas malhamensis Used for Managing Dairy Effluent and Producing Valuable Microalgal Lipid

Currently, microalgae have become a marvelous and resource-friendly alternative source of advantageous bioproducts, such as lipids, carbohydrates, proteins, or other bioactive compounds. Because of the richness of microalgae in these high-value-added metabolites, still, it is an underdeveloped source of sustainable energy and food. There are some hurdles to profitable production, such as culture contamination and costly harvesting techniques. In the current work, a chrysophyte was isolated from dairy wastewater, identified as Poterioochromonas malhamensis based on its morphology and partial 18S rRNA gene sequences. This isolate was used to remediate dairy waste water (DWW) and to obtain neutral lipids (fatty acids) from microalgae. Microalgal growth was optimized by using different concentrations of DWW, supplemented with all the nutritive requirements for better progression and flourishment. Maximum biomass yield 1.478 g L−1 was achieved by optimized cultural conditions (different concentrations of DWW with BBM media). This strain showed high nitrate and phosphate removal efficiency (87.45% and 88.96%), respectively in 15 days. The experimental results highlighted that the lipid content and the chemical oxygen demand (COD) removal were 31.60% and 88.84%, respectively, and the lipid profile of isolated microalga was C16:0, C16:1, C18:0, C18:1, and C18:2 fatty acids. For growth and treatment purposes, 75% DWW with Bold’s Basal Medium (BBM) media showed better results. This is the first report of DWW treatment using the microalga Poterioochromonas malhamensis, as far as we are aware. Its cultivation prevented the spread of pollution of freshwater sources, remedied the DWW, and generated important lipids for industry.

B-site cation synergy in Mn doped LaCoO3 for enhanced electrocatalysts for electrochemical reduction of nitrate

Electroreduction of nitrate is a promising strategy that has gained more attention in current years. Perovskites are promising catalysts for electroreduction of nitrate due to its special ABO3 structure, which makes it possible to regulate its physical and chemical properties to achieve better nitrate removal efficiency. In this study, we doped Mn cation into the B-site of LaCoO3 and evaluated its performance for electroreduction of nitrate. After appropriate portion of Mn was doped in LaCoO3, optimized Co2+/Co3+ ratio as well as larger surface area and pore structures were acquired. The optimized doped materials LaMn0.6Co0.4O3, which achieved 41.92 % higher nitrate removal efficiency than that of LaCoO3, was in good function under different operating conditions of initial NO3– concentration, cathode potential and pH value and remained outstanding stability after ten consecutive cycles of reaction. Depending on the valence change of Co and Mn of cathode before and after electrocatalysis, we deduced that doped Mn cation not only affected the valence of Co cation but also activated adsorbed oxygen to offer electron and accelerated electron transfer. Generally, this study provided a novel thread to reveal synergism of doped metal cations of perovskites in electroreduction of nitrate.

Volatile fatty acids production from municipal waste streams and use as a carbon source for denitrification: The journey towards full-scale application and revealing key microbial players

Volatile fatty acids (VFAs) production is attracting interest as a sustainable approach to maximize resource recovery from organic wastes. This study explored the interlink between long-term system resilience of VFA production from primary sludge (PS) and external organic waste (OW) without pH control and the microbial community dynamics as well as the effect of substrate variability. The study elucidated the practicality of using VFA-rich effluent as a carbon source for wastewater denitrification. A 15 L bench-scale semi-continuous reactor was operated for 315 days with a feed of 70% v/v PS and 30% v/v OW and scaled up to a 2 m3 pilot-scale continuous reactor operated for 264 days. In the bench-scale study, the system was resilient with VFA production of up to 24,700 ± 400 mg COD/L and a yield of 506 ± 25 mg COD/g VSfed. The VFA composition was dominated by caproic acid up to 62% w/w. In the pilot-scale reactor, substrate variability influenced VFA production with a concentration of up to 21,500 ± 500 mg COD/L. The system was shown to be economically viable. The microbial community was dominated by Lachnospiraceae, Streptococcaceae and Comamonadaceae. The relative abundance of Lachnospiraceae gave a strong positive statistical correlation with caproic acid concentrations. The VFA-rich effluent exhibited a higher specific denitrification rate than methanol and acetate. Moreover, a continuous denitrification experiment with real nitrified wastewater resulted in a high nitrate removal efficiency with a maximum of 98%. The study demonstrates the production of bio-based products from organic wastes as alternatives to fossil-based products.

The synthetic composite materials using PHBV, nZVI and biochar enhanced denitrification performance in water treatment

Solid carbon source (SCS)-based denitrification is a promising technique for nitrogen removal from sewage. However, a sustainable and effective supply of carbon sources, crucial to denitrification performance, has always been challenging. This study developed four synthetic SCSs: biochar (BC), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), PHBV loaded on biochar (BCP), and PHBV loaded on biochar-supported nanoscale zero-valent iron (BCPF), to examine their denitrification efficiency enhancement. Insufficient carbon sources caused low nitrate removal (<45%) in the BC reactor during the entire experiment. At the biofilm formation stage (influent nitrate: 40 mg L-1), the relatively higher nitrate removal in biochar-based SCS reactors than in the P reactor in the first 4 h indicated that the biochar's rapid release of carbon sources played a priming role in denitrification. Then, the subsequent sharp decrease in nitrate removal revealed the biochar's unsustainable release of carbon sources for the denitrifiers. Similar to the P reactor, the nitrate removal in BCP and BCPF reactors gradually increased after 12 h until the 48 h mark, where the high nitrate removal efficiency was stabilized (P: 79.93%−93.74%, BCP: 86.90%−100%, and BCPF: 91.68%−100%), except in the BC reactor. Evidently, the decomposed products from PHBV provided sustainable carbon sources for the denitrifiers. Compared with the P reactor in the continuous running stage, BCP and (especially) BCPF reactors exhibited excellent resistance to load impact. Here, PHBV supplied sustainable carbon sources and electron donors for denitrification, while nZVI served as extra electron donors. The biochar dominantly provided habitats for denitrifiers and functioned as an electron mediator.

Stimulating Nitrate Removal with Significant Conversion to Nitrogen Gas Using Biochar-Based Nanoscale Zerovalent Iron Composites

For efficient and environmentally friendly removal of nitrate from groundwater, biochar-based nanoscale zerovalent iron composites were prepared, where biochar was derived from pine sawdust at 4 different pyrolysis temperatures. The results show that biochar with different pyrolysis temperatures played a great role in both nitrate removal efficiency and nitrate conversion rate to nitrogen gas for the prepared composites. Specifically, the composite with biochar pyrolyzed at 500 °C, ZB12-500, showed the best performance in both nitrate removal and conversion to nitrogen gas. With an initial solution pH from 5 to 10, ZB12-500 maintained high removal efficiencies varying from 97.29% to 89.04%. Moreover, the conversion of nitrate to nitrogen gas increased with the initial nitrate concentration, and it reached 31.66% with an initial nitrate concentration of 100 mg/L. Kinetics analysis showed that the nitrate removal process fit well with a two-compartment first-order kinetic model. Meanwhile, the test of nitrate removal by ZB12-500 in synthetic groundwater showed that HCO3− and SO42− limited nitrate removal but improved nitrate conversion to nitrogen gas. Furthermore, the nitrate removal mechanism suggested that biochar could facilitate electron transfer from zero valent iron to nitrate, which led to high nitrate removal efficiency. In addition, the interaction of ferrous ions and the quinone group of biochar could increase the nitrate conversion to nitrogen gas. Therefore, this study suggests that ZB12-500 is a promising alternative for the remediation of nitrate-contaminated groundwater.

Management and removal of nitrate contamination of water at the source using modified natural nano zeolite

Nitrate is a hazardous substance for human health, the removal of which is an important environmental priority. Therefore, in this study, first, the sources of nitrate pollution of water were investigated, then the structure, role, and application of nanozeolites for the removal of nitrate ions were studied by the analytical method. Also, the presentation of management solutions, identification of polluting industrial sectors, different methods of removal and fabrication of ZSM-5/Fe/Ni nanosorbents, and the determination of optimal conditions for nitrate removal were investigated by experimental design software and graphical analysis of effective parameters. The results of graphical analysis of laboratory method showed us, the highest nitrate removal efficiency at a residence time of 150 minutes, pH 3, 4 g L-1 adsorbent, and 40 mg L-1 nitrate were achieved (%RE:91.5-97.4). Experimental results indicate the high efficiency, absorption capacity, and effectiveness of ZSM-5/Fe/Ni adsorbents for nitrate removal in waters. Finally, the absorbance values or nitrate concentrations between 20-120 mg L-1 were measured by the UV-Vis spectrophotometry. The maximum absorption capacity of ZSM-5/Fe/Ni adsorbents for nitrate was obtained 136.7 mg g-1. The developed method based on a novel ZSM-5/Fe/Ni adsorbents has many advantages such as simple, low cost, high efficiency, and favorite recovery.

Evaluation of N-methylpyrrolidone bio-mineralization mechanism and bacterial community evolution under denitrification environment

With the increasing discharge of wastewater produced from industrial manufacture, the accumulation of recalcitrant and toxic contaminants such as N-methylpyrrolidone (NMP) in ecosystem has raised concerns about their environmental implication. In this study, a denitrification bioreactor was developed and continuously performed for 245 days to realize simultaneous NMP mineralization and nitrate reduction. During long-term experimental period, the approximately 3000 mg L−1 NMP could be thorough degraded along with high nitrate removal efficiency (>97%), the dominant bacteria populations responsible for NMP hydrolysis (Paracoccus, Brevundimonas and Pseudaminobacter) and microbial denitrification (Paracoccus, Hyphomicrobium, Pseudomonas and Pseudoxanthomonas) as well as electron transport (Shewanella) were significantly enriched under denitrification condition. Further enzymatic activity assay revealed the catalytic activities of N-methylhydantoin amidohydrolase (NMA) and succinate dehydrogenase (SDH) were largely enhanced under denitrification environment, indicating that microbial denitrifying distinctly promoted the hydrolysis and mineralization of NMP, which was rather conducive for better NMP removal capacity and long-term stability. In conclusion, this research verified the feasibility of denitrification promoting N-heterocyclic compounds mineralization process and provided theoretical guidance for the engineering application of biodegradation coupled with denitrification treatment.

A new inoculation method of sulfur autotrophic denitrification reactor for accelerated start-up and better low-temperature adaption

Elemental sulfur (S0) autotrophic denitrification (SAD) has been proved feasible for nitrate removal from aquatic environments. The long start-up period up to weeks of the SAD reactor impedes its industrial application. To accelerate the start-up process, this study employed S0 powder packed sequencing batch reactor operated for 10 days to obtain a seed biofilm, which was inoculated into a regular S0 flake packed bed reactor afterwards. Merely two days after inoculation, the reactor inoculated with seed biofilm was well started up and outperformed the control reactor, which was inoculated with regular anaerobic sludge and operated for more than 10 days, delivering much increased denitrification rate of 126 ± 0.68 mg N/(L·d) and a high nitrate removal efficiency of 93.0%. Batch tests during the start-up period showed that the seed biofilm developed well on S0 flakes and delivered improved nitrate removal performance than the control. Extracellular polymeric substance (EPS) analysis revealed an abundant content of protein in tightly bound EPS in the biofilm developed from the seed biofilm, which was recognized as a major contributor to facilitate the biofilm's attachment and growth onto S0 flakes. After operating under moderate temperature, the reactors were tested at a reduced temperature of 15 °C. Results indicated that the reactor inoculated with seed biofilm showed stronger adaptation ability towards low temperature and sustained better denitrification performance than the control, which was attributed to increased protein content in tightly bound EPS produced by the microbes against low-temperature. Determination of the microbial communities in tested reactors when the whole experiment was closing found that sulfur-related genera were dominating in the packed-bed reactor inculcated with seed biofilm, which played an important role in the S0-based denitrification process.

Electrochemical nitrate removal by magnetically immobilized nZVI anode on ammonia-oxidizing plate of RuO2–IrO2/Ti

Ammonium as the major reduction intermediate has always been the limitation of nitrate reduction by cathodic reduction or nano zero-valent iron (nZVI). In this work, we report the electrochemical nitrate removal by magnetically immobilized nZVI anode on RuO2–IrO2/Ti plate with ammonia-oxidizing function. This system shows maximum nitrate removal efficiency of 94.6% and nitrogen selectivity up to 72.8% at pH of 3.0, and it has also high nitrate removal efficiency (90.2%) and nitrogen selectivity (70.6%) near neutral medium (pH = 6). As the increase of the applied anodic potentials, both nitrate removal efficiency (from 27.2% to 94.6%) and nitrogen selectivity (70.4%–72.8%) increase. The incorpration of RuO2–IrO2/Ti plate with ammonia-oxidizing function on the nZVI anode enhances the nitrate reduction. The dosage of nZVI on RuO2–IrO2/Ti plate (from 0.2 g to 0.6 g) has a slight effect (the variance is no more than 10.0%) on the removal performance. Cyclic voltammetry, Tafel analysis and electrochemical impedance spectroscopy (EIS) were further used to investigate the reaction mechanisms occurring on the nZVI surfaces in terms of CV curve area, corrosion voltage, corrosion current density and charge-transfer resistance. In conclusion, high nitrate removal performance of magnetically immobilized nZVI anode coupled with RuO2–IrO2/Ti plate may guide the design of improved electrochemical reduction by nZVI-based anode for practical nitrate remediation.

Effective and selective electroreduction of aqueous nitrate catalyzed by copper particles on multi-walled carbon nanotubes

Drinking-water contamination with nitrate ions is inevitable and wide spreading, which demands feasible removal. Water de-nitration by potentiostatic electroreduction is described here. A novel electrocatalyst based on nano-copper particles, supported onto multi-walled carbon nanotubes (MWCNTs), and spray-deposited onto fluorine doped tin oxide-glass substrates, is described. The Cu/MWCNT/FTO electrode has been characterized by several methods and assessed as a working electrode in aqueous nitrate ion electroreduction, in comparison with MWCNT sprayed on FTO (MWCNT/FTO) with no copper. Comparison with earlier reported electrodes is also described. XRD patterns confirm the presence of nano-copper crystallites, in the electrode, with average size ⁓45 nm. Within 2 h of electrolysis, Cu/MWVNT/FTO exhibits more than 65% removal of nitrate at −1.80 V (vs. SCE). In longer time (7 h) the electrode completely converts the nitrate into N2 (∼65%) and (NH4+) ∼35% with no NO2− ions. The kinetics show 0.76 order with respect to nitrate, and a rate constant 4.53 × 10−2 min−1 higher than earlier counterparts. The new electrode functions under various conditions of temperature, pH, electrolyte type and concentration and inter-electrode spacing, only at ambient applied potential. Moreover, the electrode exhibits stability under nitrate electroreduction conditions, and can be recovered and reused for multiple times without efficiency loss. XRD and EDS results also confirm the electrode stability after multiple reuse. Compared to earlier systems, the Cu/MWCNT/FTO is environmentally stable, safe, non-costly with high nitrate removal efficiency and selectivity.

Nitrate and perchlorate contamination assessment using water samples for bioremediation behavior of nitrate ion with denitrifying bacteria and hypothyroidism of perchlorate ion in rat studies

Perchlorate and nitrate ions are ubiquitous contaminants in the environment released from various activities which is increasingly affected the water quality and consequently the public health and agriculture. The denitrifying bacterial communities are potential drivers of water quality, soil fertility and agriculture productivity. The present study mainly assessed the contamination level of nitrate ion along with perchlorate ions in various water samples collected from fireworks, safety matches manufacturing industry areas around Pullalakkottai, Virudhunagar District, India. Nitrate, perchlorate, calcium, magnesium, sodium, potassium ions in water samples were qualitative and quantitatively analyzed by using various Physico-chemical analytical techniques. The observed maximum contamination values of nitrate and perchlorate ions were found to be 61 mg/L (VP-5), 85.5 mg/L (VP-11) respectively. The highly contaminated five water samples were subjected into bioremediation behavior of nitrate ion using the Pseudomonas sp., Bacillus sp. and Corynebacterium sp. bacterial cultures. The highest nitrate removal efficiency (E) 93.4 % was obtained with Corynebacterium sp. than the Bacillus sp. (83.6 %) and Pseudomonas sp. (80.3 %) cultured in contaminated water sample VP-3. Maximum perchlorate ions contaminated water samples (VP-11) used to examine the hypothyroidism in rat by intravenousinjection of observed days by measuring the T4 hormones level in the blood plasma. It was reduced to nearly half (296 µg/dl) in compared with control (620 µg/dl) for ten days exposure and notable decreasing trend was observed. Disruption of the thyroid can result in developmental disabilities and impair development especially among infants and children.

Adsorption of nitrate from aqueous solution with ZSM-5/Fe nanosorbent based on optimizing of the isotherms conditions before determination by UV-Vis Spectrophotometry

The life-threatening nature of high nitrate concentrations in various water resources motivated the present study to investigate the nitrate adsorption by ZSM-5 nanozeolite and the feasibility of increasing nitrate removal efficiency using iron-doped ZSM-5 (ZSM-5/Fe) nanosorbent. Energy dispersive X-ray diffraction analysis was employed to determine the physical properties of the adsorbent and the presence of iron particles in the nanosorbent structure and BET analysis to measure the specific surface area of the nanosorbent. The optimal adsorption conditions were determined first by modeling the central composite design (CCD) using Design Expert.7 software based on four influential factors . Then, the isotherms of nitrate adsorption under optimized conditions were investigated using the degree of fit of experimental data with Langmuir and Freundlich models for mathematical modeling of the nitrate adsorption process. Based on the test design results, the highest nitrate removal efficiency (%93.1) was reported at the contact time of 150 min, pH value of 3, adsorbent dosage of 4 g/l and initial concentration of 40 mg/l. Analysis of adsorption isotherms also confirmed the greater fit of the experimental data with the Freundlich equation, so that the correction factor of the Freundlich equation was greater than the Langmuir equation.

Performance and enhancement mechanism of redox mediator for nitrate removal in immobilized bioreactor with preponderant microbes

The acceleration of nitrate removal in wastewater treatment by redox mediator (RM) is greatly weakened due to wash-out loss and mass transfer resistance (low hydrophilia) of RM during operation. In this study, an RM reactor with the fixed 1-Amino-4-hydroxyanthraquinone (AHAQ) and three core strains was established and achieved high nitrate removal efficiency (NRE) under low carbon to nitrogen ratio (C/N) and short hydraulic retention time (HRT) conditions, with the maximum efficiency of 99.41% (14.00 mg L−1 h−1) and average improvement by 11.97% (1.41 mg L−1 h−1). This acceleration led to more proportion of carbon consumption by denitrifying bacteria and improved their competitiveness against others in carbon deficiency, although resulting in nitrite accumulation (NIA) in lower C/N. The RM reactor induced the decorrelation tendencies between NRE and active extracellular organics and more sensitive denitrification toward C/N, which favored the stability of effluent organics and biological activities. The increase of oxidative phosphorylation and ubiquinone and other terpenoid-quinone biosynthesis pathway suggested electron transport activity was potentially enhanced by AHAQ. Although the lower C/N deteriorated the reactor NRE, the abundances of amino acids-, fatty acids- and carbohydrate-related metabolisms (45% of the total up-regulating pathways) were enhanced to utilize carbon source effectively. Meanwhile, the enhanced phosphotransferase system facilitated the balance between carbon and nitrogen metabolism. These indicated the changes in biological strategy to grow better and resist the adverse condition. This study highlighted the superior NRE by AHAQ in an immobilized reactor with core strains and more importantly, extended the RM application in wastewater treatment.