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Nitrate reduction by metallic iron
Abstract
Chemical reduction of nitrate by metallic iron (Fe0) was studied as a potential technology to remove nitrate from water. The effects of pH and the iron-to-nitrate ratio on both nitrate reduction rate and percent removal were investigated. Rate constants and the apparent reaction order with respect to nitrate were determined and a mass balance was obtained. Rapid nitrate reduction by iron powder was observed only at pH≤4. pH control with sulfuric acid significantly prolonged nitrate reduction and increased the percent removal. At high nitrate loadings, both the rate and the percent removal increased with decreasing pH. An iron-to-nitrate ratio of 120 m2 Fe0/mol NO3 or higher was required to completely remove nitrate within an hour. An apparent reaction order of 1.7 with respect to nitrate was observed, which may be partly due to the inhibitory effect of sulfate. Ammonia was the end product of nitrate reduction and accounted for all nitrate transformed under our experimental conditions. Acidity is the principal factor which controls the rate and the extent of nitrate removal by Fe0. The rapid reduction of nitrate at low pH was most likely due to either direct reduction by Fe0 or indirect reduction by surface hydrogen derived from proton. Ferrous species, Fe2+ and Fe(OH)2, were probably not involved in this reaction.
... Generally, and as it was expected, NO 3 − conversion slowly decreased with the increase of the inlet NO 3 − concentration in the feed solution of the system [50,51]. However, it is important to highlight that only a 5% decrease in activity was noticed from inlet NO 3 − concentrations of 90 mg L −1 to 30 mg L −1 , meaning that the catalyst retains its activity at much higher NO 3 − concentrations. ...
... Inlet NO3 − Concentration At this stage, different inlet NO3 − concentrations were studied. The results obtained are presented in Figure 2. Generally, and as it was expected, NO3 − conversion slowly decreased with the increase of the inlet NO3 − concentration in the feed solution of the system [50,51]. However, it is important to highlight that only a 5% decrease in activity was noticed from inlet NO3 − concentrations of 90 mg L −1 to 30 mg L −1 , meaning that the catalyst retains its activity at much higher NO3 − concentrations. ...
... Previous studies reported that NO3 − initial concentrations have a significant effect on the catalytic conversion and corresponding selectivity [50][51][52][53]. No significant differences in conversion were reported for the inlet NO3 -concentration ranges reported in the present work. ...
Nitrate catalytic reduction in a continuous system was studied in the presence of Pd-Cu macrostructured catalysts synthesized through a novel washcoating methodology of the pre-formed bimetallic powder catalyst. The present work aims to understand the behavior of the macrostructured bimetallic catalyst in the presence of different reaction conditions in order to achieve the design of an optimized facility that can produce the best catalytic results: maximum NO3− conversion with enhanced N2 selectivity. The residence time of the inlet solution and the catalyst concentration in the reactor proved to be the parameters that most influenced the conversion and selectivity due to the important role that these parameters play in the hydrodynamic conditions of the reactor. A higher loading of catalyst and lower inlet flow rates allow promoting a higher contact time between the three phases that participate in the reaction (G-L-S). The most efficient reaction conditions (three pieces of the macrostructured catalyst, liquid flow rate of 10 mL min−1, and a total gas flow rate of 200 Ncm3 min−1 (1:1 H2:CO2)) allowed obtaining an NO3− conversion of 51% with a corresponding N2 selectivity of 23%. Also, the conversion results strongly depended on the total gas flow rate used during the reaction since this assists the mixing between the three phases and promotes a greater contact that will contribute to enhanced catalytic results.
... In fact, there is an induction time for the beginning of Alwater reaction in neutral aqueous solution, which results from the hydration process of the Al surface passive oxide film. 45,46,48,51 In this work, a soaking procedure was used to activate Al powder so that Al particle surfaces were covered by a layer of fine nanometer Al(OH) 3 particles. This layer of fine Al(OH) 3 particles is porous (Figure 1b,d) and has low tensile strength so that outside ions and molecules can contact and react with inner Al more easily, leading to shorter induction time for the beginning of Al-water reaction, which was confirmed by many of previous works 41,43,52,53 and also by this work shown in Figure 7. ...
... Figure S1a shows nitrate adsorption in neutral solution using different dosage of Al(OH) 3 powder. It can be seen that there is almost no adsorption of nitrate on Al(OH) 3 surfaces, even if the dosage of Al(OH) 3 powder is 4 g L −1 and the nitrate-N concentration is up to 100 mg L −1 , while the pH value in the solution almost has no change during adsorption test ( Figure S1b). This indicates that the decrease in the induction time for the beginning of Al-water reaction (acceleration of electron transfer from inner Al to the outside) is the reason for increasing nitrate reduction by soaked Al powder. ...
... These indicate that the main byproduct of the reaction of soaked Al with nitrate in neutral solution is ammonia ions. The FTIR spectra of soaked Al powder before and after reaction are given in Figure 8, 59 Figure S3 shows the dependence of ammonia adsorption in aqueous solution on time using Al(OH) 3 powder, indicating that the amount of ammonia-N adsorbed on soaked Al surfaces after reaction is ∼10% of initial nitrate-N concentration. The above results imply that ∼40% of initial nitrate-N was released into air in the form of gas after the reaction, indicating that the left nitrate-N in the reacted solution by soaked Al is obviously lower than those by ZVI, ZVAl, or their alloys reported in previous works. ...
Nitrate is a contaminant widely found in surface water, and a high concentration of nitrate can pose a serious threat to human health. Zero-valent iron is widely used to reduce nitrate in aqueous solution, but an acidic condition is required. Zero-valent aluminum has a much lower redox potential (E0(Al3+/Al0) = -1.662 V) than zero-valent iron (E0(Fe2+/Fe0) = -0.44 V), making it a better choice for reduction of nitrate. However, a passive oxide film covering on Al surfaces inhibits its electron transfer. In this work, metal Al powder was activated by a soaking procedure in deionized water. It was found that nitrate in neutral solution can be efficiently and completely reduced by soaked Al, even if the concentration of nitrate-N was up to 100 mg L-1. Using an optimal soaking time, the soaked Al can remove >90% of nitrate in aqueous solution within ∼2 h at 50 °C. Furthermore, the nitrate reduction efficiency increased with increasing reaction temperature and dosage of Al powder. After reaction, only ∼50% of pristine N content was left in the form of ammonia ions (NH4+) in aqueous solution. Mechanism analyses showed that after soaking, Al particle surfaces were covered by a layer of loose and fine Al(OH)3 grains, which can shorten the induction time for the beginning of the reaction between inner Al and outside ions or molecules. This is the reason why soaked Al has a high efficiency for nitrate removal. The present results indicate that soaking is an effective way to activate Al to remove nitrate in water.
... The use of metallic or zero-valent iron (Fe 0 ) as a chemical removal strategy has received attention. Early studies showed that zero-valent iron can effectively reduce nitrate [10][11][12] because it is a good reductant under anoxic conditions. As a result, it has been used in permeable reactive barriers for the passive reduction of nitrate-contaminated groundwater [9,13]. ...
... The reaction rate dependence on the initial nitrate concentration is uncertain as well. In some studies, the dependence on the initial nitrate concentration was first order [10,19], while others have noted an apparent reaction order of 1.7 [11]. Alowitz and Scherer [12] reported first order dependence on nitrate at lower pH values, which shifted to zero order at a higher pH. ...
... The impact of oxygen (O 2 ) on nitrate reduction by Fe 0 is unclear. As mentioned above, Fe 0 serves as a good reductant and can be coupled to nitrate reduction under anoxic conditions with the concomitant production of ferrous iron (Fe 2+ (aq) ) [11]. The presence of oxygen affects the corrosion of Fe 0 [28], so under oxic conditions, one might expect O 2 to compete with nitrate as an oxidant and impact the amount of nitrate removed from water. ...
Elevated nitrate concentrations in groundwater and surface water supplies can negatively impact the quality of the environment and human health. Recent studies have examined the use of zero-valent iron technology to treat nitrate-contaminated groundwater. Mechanistic aspects of nitrate reduction by zero-valent iron are unresolved. This project investigated the kinetics and mechanism of nitrate reduction by zero-valent iron under anoxic conditions and under oxic conditions. Stirred-batch reactions were studied over environmentally relevant ranges of reactant concentration, pH, and temperature. A complex rate expression was derived with a 1.8 order dependence on nitrate, a 1.4 order dependence on zero-valent iron, and a fractional order (0.8) dependence on proton concentrations under anoxic conditions. An apparent activation energy of 35 kJ mol−1 was observed indicating that nitrate reduction was diffusion controlled under our conditions. Furthermore, the calculated entropy of activation value of −162 J mol−1K−1 indicates that this reaction occurred by an associative mechanism. Under oxic conditions, there was a lag period in nitrate reduction where oxygen was preferentially utilized, leading to a slower rate of nitrate reduction when compared with anoxic conditions. These rate data can be used in predicting nitrate disappearance in nitrate-contaminated groundwater and wastewater treated with zero-valent iron.
... The importance of pH on the chemical denitrification through Fe 0 is shown by several authors. Huang et al. analysed the process considering both uncontrolled and controlled pH conditions [16]. The tests without pH control were conducted for the initial pH values ranging between 2 and 11, with no further corrections. ...
... Consequently, it can be assumed that low pH values are favourable for the process. This was also confirmed by the results of the experiments that were conducted by holding the pH at acid values (2.5, 3, 4, and 4.5) during the entire treatment, in which a significant enhancement in the nitrate removal was achieved [16]. Therefore, the authors supposed that protons directly participate in the chemical reduction of NO 3 -, or that they indirectly promote it [16]. ...
... This was also confirmed by the results of the experiments that were conducted by holding the pH at acid values (2.5, 3, 4, and 4.5) during the entire treatment, in which a significant enhancement in the nitrate removal was achieved [16]. Therefore, the authors supposed that protons directly participate in the chemical reduction of NO 3 -, or that they indirectly promote it [16]. This hypothesis has been confirmed by numerous works in which the mechanisms of chemical denitrification are proposed. ...
Nitrate is a widespread water contaminant that can pose environmental and health risks. Various conventional techniques can be applied for the removal of nitrate from water and wastewater, such as biological denitrification, ion exchange, nanofiltration, and reverse osmosis. Compared to traditional methods, the chemical denitrification through zero-valent metals offers various advantages, such as lower costs, simplicity of management, and high efficiencies. The most utilized material for chemical denitrification is zero-valent iron (ZVI). Aluminium (ZVA), magnesium (ZVM), copper (ZVC), and zinc (ZVZ) are alternative zero-valent metals that are studied for the removal of nitrate from water as well as from aqueous solutions. To the best of our knowledge, a comprehensive work on the use of the various zero-valent materials that are employed for the removal of nitrate is still missing. Therefore, in the present review, the most recent papers concerning the use of zero-valent materials for chemical denitrification were analysed. The studies that dealt with zero-valent iron were discussed by considering microscopic (mZVI) and nanoscopic (nZVI) forms. For each Fe 0 form, the effects of the initial pH, the presence or absence of dissolved oxygen, the initial nitrate concentration, the temperature, and the dissolved ions on the nitrate removal process were separately evaluated. Finally, the different materials that were employed as support for the nanoparticles were examined. For the other zero-valent metals tested, a detailed description of the works present in the literature was carried out. A comparison of the various features that are related to each considered material was also made.
... Decontamination of nitrate can be carried out using biological or physicochemical processes such as adsorption, biological denitrification, reverse osmosis, ion exchange and chemical reduction [10,[13][14][15][16][17][18][19][20][21]. However, these methods suffer some drawbacks. ...
... The first use of zero valent iron, for treatment of nitrate pollution in a controlled laboratory experiment, was studied by Young et al. [157] who used Fe 0 to remove nitrate via reduction process. Then, during the last two decades, numerous researches were carried out on chemical reduction of nitrate by zero valent iron [13,85,[153][154][155][156]158]. Reports have shown the reaction pathways of nitrate reduction by ZVI [13,155,[159][160][161]. Iron reduces nitrate to ammonia, nitrite and nitrogen with relative amounts according to the reaction conditions. ...
... Then, during the last two decades, numerous researches were carried out on chemical reduction of nitrate by zero valent iron [13,85,[153][154][155][156]158]. Reports have shown the reaction pathways of nitrate reduction by ZVI [13,155,[159][160][161]. Iron reduces nitrate to ammonia, nitrite and nitrogen with relative amounts according to the reaction conditions. ...
... En milieu anaérobie, le Fe 0 et le Fe 2+ peuvent réduire les nitrates en produisant du diazote ou de l'ammonium [18,166,167]. Les réactions (13) et (14), correspondent à la réduction des nitrates par le Fe 0 produisant respectivement de l'ammonium et du diazote. Les réactions (15) ...
... En condition abiotique, la réduction des nitrates par le fer est dépendante du pH, elle est favorable à pH acide voire neutre [18,166,167,171]. Dans une étude, la réduction de 0,8 mM de nitrates par le Fe 0 a été complète à pH 2 ou 3 (pH final 4,5). ...
... Dans une étude, la réduction de 0,8 mM de nitrates par le Fe 0 a été complète à pH 2 ou 3 (pH final 4,5). En revanche à pH 4, seulement 0,1 mM des nitrates ont été réduits (pH final 6,5) [166]. Lorsque l'acidité est insuffisante, des précipités d'oxyhydroxydes de fer se forment à la surface du fer réduisant la surface réactive du fer et inhibant la réduction des nitrates [166,167]. ...
En France, il est envisagé de stocker en couche géologique profonde les déchets radioactifs de moyenne activité à vie longue (MAVL). Ces déchets sont chargés en sels de nitrates et après des milliers d'années, le relâchement des nitrates pourrait favoriser la mobilité des radionucléides hors des déchets. Cependant, en présence de matière organique ou d'hydrogène, l'activité bactérienne peut théoriquement réduire les nitrates en espèces azotées plus réduites via la dénitrification. Le 1er objectif de cette thèse est d'évaluer la capacité des bactéries à s'adapter aux conditions physico-chimiques à proximité des déchets, c'est à dire en absence d'oxygène, à pH alcalin entre 9 et 13, en présence de concentrations élevées en nitrates, en présence d'un donneur d'électrons organique (acétate) ou minéral (hydrogène) et en présence de ciment et d'acier solides. Le 2nd objectif est d'évaluer les cinétiques de réduction des nitrates dans les conditions précédemment décrites. La réduction bactérienne des nitrates a été observée jusqu'à pH 11 et 400 mM de nitrates en présence d'acétate et jusqu'à pH 10.5 et 150 mM de nitrates en présence d'hydrogène. En présence d'hydrogène les cinétiques de réduction des nitrates étaient globalement plus ralenties et les bactéries étaient plus sensibles aux pH alcalins que les bactéries qui se développent en présence d'acétate. Ceci s'explique par le fait que l'hydrogène a une solubilité limitée à pression atmosphérique, que l'assimilation de carbone minéral est énergétiquement coûteuse pour les bactéries et enfin qu'en présence d'hydrogène le pH s'élève au cours de l'avancement de la dénitrification. En présence d'acétate le pH s'équilibre autour de 10 grâce aux CO2 produit par l'oxydation de l'acétate. Enfin la présence de ciment solide n'a pas eu de répercussion importante sur l'activité bactérienne, en revanche l'acier solide a stimulé de façon conséquente la réduction des nitrates.
... The high content of nitrates in the drinking waters beyond 50mg/L as the admissible threshold set by the World Health Organization [5] can negatively affect human beings' health. This negative effect can be noticed through pathologies such as methemoglobinemy in infants and the synthesis of carcinogenic nitrosamines and nitrosamides [6,7]. Nitrates can also be responsible for the algae bloom observed on running and smooth expanse of water during the eutrophication [8]. ...
... Response surface and contour plot showing the evolution of nitrate removal rate as a function of adsorbent mass and pollutant concentration at pH = 5The results of the investigated experimental plan on the removal of nitrate aid of corbula trigona seashells permits to obtain the surface of the response and the contour represented on figure(7). This figure shows the effect of the adsorbent mass and its initial concentration, and the pH value settled at center of the domain. ...
This study was about the removal of nitrates in synthetic solutions in batch mode. It put into contribution the use of freshwater seashells (Corbula trigona) as adsorbents. Corbula trigona Adsorbents (ACT) have been characterized by means of analytical techniques such as X-Ray Fluorescence (XRF), Fourier Transform Infrared (FTIR), scanning electron microscopy coupled with the EDX and the X-Ray Diffraction (XRD). This characterization allowed to highlight the elemental composition, the predominant functional groups, the morphology of their surface and to identify the crystal phases. The effects of the different variables which influence the process of the nitrate removal have been studied thanks to a Placket-Burman Design. The concentration of the pollutant, the middle pH and the absorbent mass were the parameters which influenced the studied response. It comes out that the influence of those parameters on the nitrate removal can be respectively rated at 66.16%, 27.05% and 4.21%. The results analysis show that the absorbent mass has a negative impact whereas the pollutant concentration and the middle pH have positively impact the effectiveness. After optimizing the process with the help of the Box-Behnken Design (BBD), the optimum conditions for a removal at 53.76%, of water containing 30mg/L of nitrates, one needs 1.11 g of a pH 2 material. The corbula trigona seashells could be promising in the removal of nitrates and the Box-Behnken Design was the most effective in designing the process and determining the optimum conditions.
... Finally, by calculating the sum of the MA-SHAP values of each Given this condition, this finding confirms that the availability of active sites plays the most critical role in enhancing the reduction process, followed by the presence of enough H + to accelerate iron corrosion and to create new active sites. Most importantly, this finding is able to explain the conflicting results regarding the impact of dissolved oxygen on nitrate reduction rate [39,[84][85][86][87][88]. The preferable oxygen conditions are aerobic conditions, which encourage the production of additional reducers, and anoxic conditions, which prevent the inhibition of denitrification [3]. ...
... Under anoxic conditions, the electrons needed for nitrate reduction come directly from the dissolution of ZVI, which helps avoid the inhibition of denitrification by the formation of iron corrosion products that could lead to surface passivation phenomena [15,85,89]. Under aerobic conditions, dissolved oxygen assists the reduction process by an oxidative attack on the ZVI surface, which increases the reduction rate to a certain extent. ...
... Such lag periods were repeatedly reported in the literature over the years (e.g. Huang et al. 1998, Noubactep et al. 2003, Hao et al. 2005. In Fe 0 /H2O systems, the lag time is indicative of the time required for the generation of FeCPs following Fe 0 immersion into a polluted water. ...
... The presentation until now has demonstrated that no single electron from Fe 0 can be transferred to COCs because of the presence of the universal oxide scale which is never electronically conductive (Table 4). If electrons from Fe 0 were transferred to any COC, there would have not been a lag time between the start of the experiment and the start of reductive transformation of COCs (Schreier and Reinhard 1994, Huang et al. 1998, Hao et al. 2005. Consequently, COCs, O2 and co-contaminants are reduced by Fe II , H2, Fe3O4, green rust, and other reducing species generated in the Fe 2+ can donate one electron and H2 two electrons. ...
The suitability of remediation systems using metallic iron (Fe0) has been extensively discussed during the past 3 decades. It has been established that aqueous Fe0 oxidative dissolution is not caused by the presence of any contaminant. Instead, the reductive transformation of contaminants is a consequence of Fe0 oxidation. Yet researchers are still maintaining that electrons from the metal body are involved in the process of contaminant reduction. According to the electron efficiency concept, electrons from Fe0 should be redistributed to: i) contaminants of concern (COCs), ii) natural reducing agents (e.g., H2O, O2), and/or iii) reducible co-contaminants (e.g. NO3-). The electron efficiency is defined as the fraction of electrons from Fe0 oxidation which is utilized for the reductive transformations of COCs. This concept is in frontal contradiction with the view that Fe0 is not directly involved in the process of contaminant reduction. This communication recalls the universality of the concept that reductive processes observed in remediation Fe0/H2O systems are mediated by primary (e.g., FeII, H/H2) and secondary (e.g., Fe3O4, green rusts) products of aqueous iron corrosion. The critical evaluation of the electron efficiency concept suggests that it should be abandoned. Instead, research efforts should be directed towards tackling the real challenges for the design of sustainable Fe0-based water treatment systems based on fundamental mechanisms of iron corrosion.
... Aside from the previously mentioned concerns, nitrates are generally considered safe at reasonable concentrations, with recommended limits set at less than 50 mg/L for adults and 15 mg/L for infants. However, the biological conversion of nitrates into nitrites introduces additional health risks, including conditions such as methemoglobinemia in infants and pregnant women and potential associations with various types of cancer [6][7][8]. ...
Nitrate contamination in water poses a significant concern for environmental engineers, as it has substantial and direct impacts on water quality, the economy, and public health. Consequently, managing nitrate levels in water sources ranks among the top priorities for water authorities. Currently, various treatment methods, including biological treatments and adsorption, are employed to eliminate nitrate from water or wastewater. A substantial body of literature exists focused on the application of electrocoagulation (EC) for nitrate removal from solutions. This method is favoured for its environmentally friendly attributes and ability to swiftly and cost-effectively remove pollutants. In this study, the EC method was employed to eliminate nitrate from water under varying inter-electrode spacing (I-ES) conditions ranging from 4 to 10 mm and different treatment durations (TD) spanning 5 to 55 minutes. The effects of I-ES and TD on nitrate removal were optimised using Response Surface Methodology (RSM). The study's results demonstrated that the most effective nitrate removal, reaching 91.3%, occurred at an I-ES of 4 mm and a TD of 50 minutes. The agreement between the experimentally observed and predicted removal rates was notably high, with an R2 value of 0.973.
... Nitrate is a pervasive and typical groundwater contaminant [1] originating from sources like industrial and domestic waste [2], extensive use of fertilizers [3], and emissions of animal dung [4]. Moreover, the consumption of nitrate-contaminated groundwater can increase the risk of gastric and esophageal cancers and lead to methemoglobinemia in babies [5,6]. ...
Aggregation and sharp reactivity decrease are the key problems of using nano zero-valent iron (nZVI) as a potential reaction medium for a permeable reactive barrier (PRB). In this study, nZVI particles encapsulated within an acrylonitrile–butadiene–styrene (ABS) matrix (nZVI/(ABS + EC)) was fabricated, which for the first time successfully simultaneously solved the above problems via accurately regulating the distribution of nZVI particles in the ABS matrix and regulating the contact between nZVI particles and the contaminated aqueous environment. In addition, the size and number of the pores throughout the ABS matrix were first regulated by ethyl cellulose (EC) for the purpose of controlling the contact between nZVI particles and the nitrate contaminant, affording apparent rate constants (kobs) for denitrification performance in the range of 0.0423 to 0.0820 min−1. The remediation of simulated nitrate-contaminated solution by nZVI/(ABS + EC) was suitably described by the first-order kinetics model, with kobs ranging from 0.0423 to 0.2036 min−1, and functional relationship models of kobs with the dosages of EC (dEC) and nZVI (dFe) during encapsulation were developed for the quantitative regulation of a sustainable denitrification performance. Results revealed that encapsulation prevents the aggregation of nZVI, rendering a sustainable denitrification performance of the material; the denitrification performance was demonstrated to be affected and quantitatively regulated by the encapsulation and application conditions. Using nZVI/(ABS + EC) as the reaction medium for PRB, the pore blocking of PRB can be avoided, and the sustainable remediation performance can be quantitatively regulated and predicted.
... The formation of concentrated nitrate brine and high costs are two main drawbacks of RO and IE techniques (Ghafari et al. 2008;Xu et al. 2018). Chemical reduction needs a constant supply of additive chemicals (Mollah et al. 2001), whereas biological treatment is limited by its slow degradation rate and requires frequent maintenance (Huang et al. 1998). ...
In this study, a new hybrid bench-scale electrocoagulation-sand filtration (FECF) reactor was developed for purifying nitrate-contaminated samples. Before and after electrochemical treatment, two sand filters were included in this continuous system to facilitate the purification procedure, and the contaminated water flows horizontally through the entire system according to a specific hydraulic gradient within the reactor, resulting in water purification. Significant improvement in treatment performance was observed due to the presence of metal hydroxides in the second filter media that were not fully involved in the electrocoagulation treatment. Energy dispersive X-ray (EDX) analysis was performed to detect metal hydroxide species in the sand media, and the need for filter regeneration was evaluated by monitoring changes in the system flow rate. Moreover, an evaluation of the effects of different factors including operating time, current intensity, initial pH, type of anode and cathode, initial nitrate concentration, hydraulic head level inside the reactor, number of electrodes, and NaCl electrolyte concentration on the performance of nitrate removal was conducted through the Taguchi design. Further, ANOVA analysis verified the accuracy of the predicted model, and the variables were classified based on their relative importance in the FECF process. According to the regression model, 97% of nitrates were removed with Al electrodes as anode and Fe as cathode, 70 min purification time, current intensity of 3 A, 100 mg/l initial nitrate concentration, pH 8, electrolyte concentration of 1 g/l, electrode number of 6, and 1.5 cm head level.
... A new method for the transformation of Azo dyes into easier bio-decomposition compounds with Nanoscale Zero-Valent Iron NZVI has been developed in this study. NZVI is an effective reducing agent for azo dyes [Nam and Tratnyek, 2000;Cao et al., 1999; and it is less cost than chemical methods, effective and environmentally friendly Masciangioli and Zhang, 2003;Chang et al., 2006;Hou et al., 2007;Shu et al., 2007;Fan et al., 2009], NZVI reduction is widely used in treating and remedying and dechlorinate waste waters contaminated with chlorinated compounds [Cheng et al., 2006], nitro aromatic compounds , nitrates [Huang et al, 1998] and heavy metals [Fiedor et al, 1998], and even for the deoxidization of more complex anthropogenic chemicals including pesticides [Fiedor et al, 1998] and dyes [Eykholt and Davenport, 1998;Bigg and Judd, 2001;Weber, 1996;Pereira and Freire, 2006]. The azo bond is cleaved when azo dyes are degraded by NZVI treatment process and an aromatic amines and amino-naphthol compounds are formed along with hydrazo (-NHNH-) as an intermediate . ...
In this study Nanoscale Zero-Valent Iron Fe 0 (NZVI) and Nano Zero Valent-Iron supported on pillared clay(NZVI/PILC) have been prepared and characterizations by physical method such as Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The degradation of acidic aqueous solutions of the Acid red 315 (AR 315) azo dye has been studied by NZVI, pillared clay (PILC) and NZVI-B. The effect of different process parameters, such as solution pH, amount of dosage (NZVI, PILC and NZVI/PILC), time reaction effect and other experimental variable, such as (Azo dye concentration and inorganic salts effect) has been investigated to determined optimization method for removal. The concentration of azo dye measured before and after treatment by using UV-Vis Spectrophotometry method. The experimental results showed that AR 315 azo dye solution (100 mg/L, 1.6×10-4 M) was completely removed by NZVI at optimum conditions (amount of NZVI = 1.0 g, 120 min and pH = 3). While the removal efficiency with NZVI/PILC and PILC were 80% and 0% respectively.
... In recent years, an increasing number of scholars have adopted electrochemical approaches to remove nitrate and evaluate its reduction performance [18][19][20]. So far, researches on catalytic materials for electrochemical reduction of nitrates have primarily involved Cu, Fe, Ni, Sn, Bi, Pt, Pd and Ir [5,[21][22][23][24][25], as well as diamond electrodes [26]. In particular, metallic copper has extremely high catalytic properties and can be effective in the reduction of nitrate to nitrite. ...
... In the c(H 2 SO 4 ) range 1-2 M, the oxalic acid degradation slowly decreased with c(H + ), suggesting that excess H + promotes catalytic reactions to occur. The negative effect of excess H + may result from excess the reactant for sites on the catalyst surface,26,27 and by increasing c(H 2 SO 4 ), the promoting effect of H + hardly increased substantially.In the c(NaNO 3 ) range 0-2 M, oxalic acid degradation decreased with increasing c(NO 3 − ). This result indicates that excess NO 3 − makes a clearly negative contribution to the catalytic reactions, while the same result was obtained by an alternative experiment with potassium nitrate used in order to exclude Na + interference. ...
Large quantities of solutions containing oxalic acid and nitric acid are produced from nuclear fuel reprocessing, but oxalic acid must be removed before nitric acid and plutonium ions can be recovered in these solutions. The degradation of oxalic acid with Pt/SiO2 as a catalyst in nitric acid solutions has the characteristics of a fast and stable reaction, recyclable catalyst, and no introduction of impurity ions into the system. This method is one of the preferred alternatives to the currently used reaction of KMnO4 with oxalic acid but lacks theoretical support. Therefore, this study attempts to clarify the reaction mechanism of the method. First, there was no induction period for this catalytic reaction, and no evidence was found that the nitrous acid produced in the solution could have an effect on oxalic acid degradation. Furthermore, oxidation intermediates (structures of Pt-O) were formed through this reaction between NO3- adsorbed on the active sites and Pt on the catalyst surface, but H+ greatly promoted the reaction. Additionally, oxalic acid degradation through the oxidative dehydrogenation reaction occurred between oxalic acid molecules (HOOC-COOH) and Pt-O, with ·OOC-COOH, which is easily self-decomposable especially in acidic solution, generated simultaneously, and finally CO2 was produced.
... Long HRT allowed for an adequate time for chemical reactions to occur within the reactor (as described by Equations (1)-(3)). Although the accumulated concentration of NO 2 − -N only averaged around 0.35 ± 0.31 mg/L, the highest observed concentration of NH 4 + -N in the effluent was 7.19 ± 0.32 mg/L, which was due to the reaction described by Equation (4), and only Fe 0 was involved this reaction at a long HRT and high iron-to-nitrate ratio [21]. Indeed, there was little biomass attached to the iron surface during this initial stage, so NO 3 − -N could adequately come into contact with the iron, resulting in a high nitrate reduction efficiency, especially at longer HRTs. ...
Due to stricter municipal wastewater discharge standards, there is an increased need for further treatment of nitrate in the secondary effluent of wastewater treatment plants. This is achieved through denitrification by the addition of external carbon sources, which leads to increased costs in wastewater treatment. The aim of this study was to examine the possibility of simultaneous removal of nitrate and phosphorus from simulated secondary effluent by employing a sponge-iron-based denitrifying filter at room temperature. The results indicate that at hydraulic retention times of over 2 h, more than 60% of the nitrate was reduced to ammonia and nitrite via iron-based abiotic nitrate reduction. However, sponge iron easily scaled after two months of operation. Therefore, a little glucose was added to the influent, resulting in a final COD/N ratio of 1:1. Mixotrophic nitrate reduction was observed, and the rust of sponge iron was successfully dissolved. Batch test results demonstrate that biological nitrate denitrification accounted for 70.0% of the total nitrate reduction. Additionally, high-efficiency phosphorus removal through the chemical reaction of released iron and phosphorus was achieved throughout the entire experiment, with removal efficiencies of more than 90% at hydraulic retention times of over 2 h. Moreover, high-throughput sequencing data show that the species diversity obviously increased after adding organic carbon, suggesting the coexistence of heterotrophic and autotrophic denitrifiers. Hence, the sponge-iron denitrifying filter has considerable prospects in the field of secondary effluent treatment and is likely to be the future direction of zero-valent iron application in sewage treatment.
... Also, industrial filing iron waste can be used to add two electrons to a variety of environmental pollutants by converting it into zero-valent iron [10]. It has been demonstrated to be effective in reducing nitro-aromatic chemicals, insecticides, nitrate, and ions of metal as Cr (VI) [11][12][13][14], among other chlorinated solvents [15] studied the capability of zero-valent iron to remove arsenic compounds for the groundwater. Their results showed that more than 98% of arsenate could be removed steadily with a hydraulic resident time of two hours at last, and the effluent meets the drinking water standard. ...
... Removing nitrate from drinking water is carried out mainly by biological, and physicochemical such as electrodialysis (ED) [9], reverse osmosis (RO) [10] or ion exchange (IE) [11], and electro-reduction technologies [6]. The use of biological denitrification [12], which reduces the nitrates to nitrogen using microorganisms in a biological reactor, is generally preferred to physicochemical methods as it completely removes nitrate by converting it into nitrogen gas; however bacterial contamination and sludge formed limits the wide application of this method [13]. ...
Nitrate from the application of nitrogen-based fertilizers in intensive agriculture is a notorious waste product, though it lacks cost-effective solutions for its removal from potential drinking water resources. Catalytic reduction appears to be a promising technique for converting nitrates to benign nitrogen gas. Mesoporous silica SBA-15 is a frequently used catalyst support that has large surface areas and highly ordered nanopores. In this work, mesoporous silica SBA-15 bimetallic catalysts for nitrate reduction were investigated. The catalyst was optimized for the selection of promoter metal (Sn and Cu), noble metal (Pd and Pt) and loading ratios of these metals at different temperature and reduction conditions. The catalysts prepared were characterized by FT-IR, N2 physisorption, XRD, SEM, and ICP. All catalysts showed the presence of cylindrical mesoporous channels and uniform pore structure that remained even after metals loading. In the presence of a CO2 buffer, the catalysts 4Pd-1Cu/SBA-15 and 1Pt-1Cu/SBA-15 reduced at 100 °C under H2 and 1Pd-1Cu/SBA-15 reduced at 200 °C under H2 demonstrated very high nitrate conversion. Furthermore, the forementioned Pd catalysts had higher N2 selectivity (88-87%) compared to Pt catalyst (80%). Nitrate conversion by the 4Pd-1Cu/SBA-15 catalyst was significantly decreased to 81% in the absence of CO2.
... V) . The performance of ZVI in nitrate reduction is highly dependent on the pH of the aqueous solution, and the rapid reaction can occur only when pH < 4 (Huang et al., 1998). To address the shortcomings of ZVI, nanoscale zero-valent iron (nZVI) is proposed as an alternative to ZVI (Ezzatahmadi et al., 2017). ...
Excessive nitrate has been a critical issue in the water environment, originating from the burning of fossil fuels, inefficient use of nitrogen fertilizers, and discharge of domestic and industrial wastewater. Among the effective treatments for nitrate reduction, electrocatalysis has become an advanced technique because it uses electrons as green reducing agents and can achieve high selectivity through cathode potential control. The effectiveness of electrocatalytic nitrate reduction (NO3RR) mainly lies in the electrocatalyst. Iron-based catalysts have the advantages of high activity and low cost, which are well-used in the field of electrocatalytic nitrates. A comprehensive overview of the electrocatalytic mechanism and the iron-based materials for NO3RR are given in terms of monometallic iron-based materials as well as bimetallic and oxide iron-based materials. A detailed introduction to NO3RR on zero valent iron, single-atom iron catalysts, and Cu/Fe-based bimetallic electrocatalysts are provided, as they are essential for the improvement of NO3RR performance. Finally, the advantages of iron-based materials for NO3RR and the problems in current applications are summarized, and the development prospects of efficient iron-based catalysts are proposed.
... As a practical example, biosurfactants can assist in the bioremediation, fragmentation and dispersion process in situations involving oil spills and contamination by metals [13,16,17]. Their use as nanoparticle stabilizers, such as nZVI, has been extensively studied, mainly for the removal of contaminants, such as heavy metals, nitrate and nitrite, from groundwater due to the reduction in the oxidation of these pollutants [18][19][20][21][22][23][24][25][26]. They also can also be used in the pharmaceutical, cosmetic, oil and agricultural industries for solubilization and emulsification, among other processes [14,[27][28][29]. ...
Guava is consumed in natura and is also of considerable importance to the food industry. The seeds and peel of this fruit are discarded, however, guava seeds yield oil (~13%) that can be used for the bioproducts synthesis. The use of a by-product as a carbon source is advantageous, as it reduces the environmental impact of possible harmful materials to nature, while adding value to products. In addition, the use of untested substrates can bring new yield and characterization results. Thus, this research sought to study rhamnolipids (RLs) production from guava seed oil, a by-product of the fructorefinery. The experiments were carried out using Pseudomonas aeruginosa LBI 2A1 and experimental design was used to optimize the variables Carbon and Nitrogen concentration. Characterization of RLs produced occurred by LC-MS. In this study, variables in the quadratic forms and the interaction between them influenced the response (p < 0.05). The most significant variable was N concentration. Maximum RLs yield achieved 39.97 g/L, predominantly of mono-RL. Characterization analysis revealed 9 homologues including the presence of RhaC10C14:2 (m/z 555) whose structure has not previously been observed. This research showed that guava seed oil is an alternative potential carbon source for rhamnolipid production with rare rhamnolipid homologues.
... Regarding the qualifications of the World Health Organization (WHO), the presence of nitrate ions in potable water is a significant environmental problem that fatally affects human health. Nitrates are found in groundwater due to animals' decomposition, nitrogenous fertilizers, industrial processes, and agriculture runoff [1][2][3]. The danger of nitrate to humans is its reduction to nitrite, which is involved in the reduction process of hemoglobin to methemoglobin. ...
The presence of nitrates in water in large amounts is one of the most dangerous health issues. The greatest risk posed by nitrates is hemoglobin oxidation, which results in Methemoglobin in the human body, resulting in Methemoglobinemia. There are many ways to eliminate nitrates from underground water. One of the most effective and selective methods is using zero-valent iron (ZVI) nanoparticles. ZVI nanoparticles can be easily synthesized by reducing ferric or ferrous ions using sodium borohydride. The prepared ZVI nanoparticles were examined by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), electron microscopy (TEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, and zeta potential. We aim to eliminate or reduce the nitrates in water to be at the acceptable range, according to the world health organization (WHO), of 10.0 mg/L. Nitrate concentration in water after and before treatment is measured using the UV scanning method at 220 nm wavelength for the synthetic contaminated water and electrochemical method for the naturally contaminated water. The conditions were optimized for obtaining an efficient removing process. The removal efficiency reaches about 91% at the optimized conditions.
... In particular, the detection of nitrites is important due to their potential to affect human health leading to liver damage, methemoglobinemia, and even cancers [1]. In addition, nitrites cause methemoglobinemia by oxidizing the Fe 2+ of haemoglobin [2]. Furthermore, according to the World Health Organization, the nitrate concentration in drinkable water should not exceed 65.2 µM (3 ppm) [3]. ...
This work is focused on the application of a laser-based technique, i.e., matrix-assisted pulsed laser evaporation (MAPLE) for the development of electrochemical sensors aimed at the detection of nitrites in water. Commercial carbon-based screen-printed electrodes were modified by MAPLE via the application of a newly developed composite coating with different concentrations of carbon nanotubes (CNTs), chitosan, and iron (II) phthalocyanine (C32H16FeN8). The performance of the newly fabricated composite coatings was evaluated both by investigating the morphology and surface chemistry of the coating, and by determining the electro-catalytic oxidation properties of nitrite with bare and modified commercial carbon-based screen-printed electrode. It was found that the combined effect of CNTs with chitosan and C32H16FeN8 significantly improves the electrochemical response towards the oxidation of nitrite. In addition, the MAPLE modified screen-printed electrodes have a limit of detection of 0.12 µM, which make them extremely useful for the detection of nitrite traces.
... When using zero-valent iron, the process consists of direct reduction of nitrate ions by iron [24,25]: ...
The activity of mining enterprises and mining and processing enterprises comes with the generation of wastewater of complex chemical composition in high volumes. Open-pit mining using ammonium nitrate leads to significant pollution of quarry and drainage waters with inorganic nitrogen compounds. Excessive content of inorganic nitrogen causes eutrophication of water bodies and afflicts significant damage to water resources. Biological methods used in treatment of nitrogen-containing wastewater depend significantly on external factors and show insufficiency in quarry wastewater treatment. The development of effective technologies based on physico-chemical treatment methods, in particular on the application of redox methods, is necessary for removing nitrogen compounds from mining wastewater. This paper presents the research results of the application of redox systems consisting of iron scraps and carbon-containing materials to reduce the content of nitrate ions in quarry water of mining enterprises. It was found that strong reducing agents Fe⁰, Fe²⁺, H2 as well as atomic hydrogen, capable of denitrifying water, are formed as a result of electrochemical processes in the redox system. The influence of the examined water pH and mass ratio of current-conducting elements in galvanic couple on efficiency of removing nitrate ions from quarry water was found. The possibility of post-treatment of quarry water, removing ammonium ions with the use of lowland peat, is shown.
... These treatments include adsorption, ion exchange, reverse-osmosis, chemical coagulation, and bacterial assimilation. These treatment processes suffer the challenge of not proffering long-term solutions since the procedures are complicated, and in most cases, secondary pollutants are generated (Huang et al. 1998). Nitrate removal by photocatalysis has been reported as simple, efficient, and cost-effective, and depending on the photocatalyst and reaction condition, N 2 in most times the product (Adamu et al. 2017;Oka et al. 2015). ...
Oxoanions are a class of contaminants that are easily released into the aquatic systems either through natural or anthropogenic activities. Depending on their oxidation states, they are highly mobile, resulting in the contamination of underground water. Above the permissible level in groundwater, they pose as threats to mammals when the contaminated water is consumed. Some of the health challenges caused are cancer, neurological, cardiac, gastrointestinal, and skin disorders. Several treatment technologies have been adopted over the years for the management of these oxoanions present in the aquatic systems. However interesting these treatment technologies might be, they also have their limitations such as cost-effectiveness, the complexity of the process, and generation of secondary pollutants. This work focused on some of the water treatment technologies applied for the removal of oxoanions. Some of the advantages and disadvantages of these treatment technologies are also highlighted. Amongst all the treatment technologies, adsorption is the most applied method for the removal of oxoanions. However, photocatalysis has a higher prospect since it is non-selective and secondary pollutants are not generated after the treatment process. Also, photocatalysis can simultaneously reduce and oxidise oxoanions as well as organic pollutants respectively.
... Besides Fe 2 + , some studies suggested that nitrate is much more easily reduced by Fe 0 than Fe 2 + , especially at low pH [70][71][72][73][74][75] . A UV spectroscopy measurement reported that NO 3 − or Fe 3 + was not detected after iron being immersed in deaerated acidic NaNO 3 , indicating that NO 3 − was all reduced by Fe 0 [76] , probably undergoing a redox reaction as Eq. ...
Nitrate is significant for corrosion process, which has been extensively studied for decades, while some issues remain unclear. Adsorption and reduction mechanisms are widely proposed but separately in literature, and results are inconsistent regarding different corrosion modes and conditions. Adsorption mechanism of nitrate, mostly as competitive adsorption against chloride, is discussed regarding electrode potential, concentration, temperature and alloy composition. However, it has to be based on a premise that nitrate cannot stimulate corrosion, which cannot be fully interpreted by adsorption mechanism. This inadequacy is made up by nitrate reduction mechanism, consuming protons and producing water to lower aggressiveness. Based on these mechanisms, nitrate effect on localized corrosion of carbon steel and stainless steel in aqueous solutions are reviewed in details, including pitting, crevice corrosion and cracking. Nitrate tends to passivate salt-covered pit, but not salt-free pit since proton migration across salt layer is unavailable. However, we suggest that sufficient nitrate may passivate salt-free pit through reduction alone, while further work is required and suggested. Effect of nitrate on crevice corrosion is relatively consistent, which tends to inhibit dissolution against chloride. Nitrate reduction and adsorption are also important for cracking, mostly initiated from intergranular corrosion for carbon steels due to imperfect passivation, and from localized corrosion for stainless steels. Competition between localized corrosion and cracking can interpret inhibitive/non-inhibitive/promoting effect of nitrate. Corrosion products within a local site dissolving in nitrate are also discussed, which inhibit mass transport but enhance stability of dissolution. Nitrate is generally classified as inhibitor but described as dangerous inhibitor.
In one of TotalEnergies North Sea fields, nitrate is continuously injected as the main mitigation of reservoir souring. The nitrate treatment is employed to limit the biogenic generation of H2S, due to reservoir souring. Reservoir souring is caused by the proliferation of SulfateReducing microbes (bacteria and/or archaea).
In parallel, severe corrosion was observed in oil producing well tubing conveying fluids from a reservoir subjected to nitrate treatment. It is known that nitrates can catalyze the corrosion of carbon steels through different mechanisms, in particular electrochemical or microbiological. The challenge was therefore to accurately evaluate the impact of nitrate injection, and its presence in the produced fluids, on the corrosion of the producing well tubing.
The influence of nitrate treatment towards corrosion of carbon steel well tubing has been singled out using an artificial intelligence algorithm. The algorithm employs a method called "Propensity Score Matching" (PSM). PSM is a statistical method commonly used in the medicine field to assess the efficiency of treatment in biased data. This method has been used to compare two reservoirs, one being subjected to nitrate treatment and another that has never been subjected to nitrate treatment.
In this paper a first known use of causal inference in industrial settings is presented. It helped removing biases by comparing only comparable data and to find causal relationship in the data. Outcomes of the multi-faceted study have led to optimized corrosion mitigation approaches and increased well tubing service life.
Bioelectrochemical systems which employ microbes as electrode catalysts to convert chemical energy into electrical energy (or conversely), have emerged in recent years for water sanitation and energy recovery. Microbial biocathodes, and especially those reducing nitrate are gaining more and more attention. The nitrate-reducing biocathodes can efficiently treat nitrate-polluted wastewater. However, they require specific conditions and they have not yet been applied on a large scale. In this review, the current knowledge on nitrate-reducing biocathodes will be summarized. The fundamentals of microbial biocathodes will be discussed, as well as the progress towards applications for nitrate reduction in the context of water treatment. Nitrate-reducing biocathodes will be compared with other nitrate-removal techniques and the challenges and opportunities of this approach will be identified.
The aim of this study was to investigate the effects of hydrophilic sulfur-modified nanoscale zero-valent iron (S-nZVI) as a biocatalyst for denitrification. We found that the denitrifying bacteria Cupriavidus necator (C. necator) promoted Fe corrosion during biocatalytic denitrification, reducing surface passivation and sulfur species leaching from S-nZVI. As a result, S-nZVI exhibited a higher synergistic factor (fsyn = 2.43) for biocatalytic NO3- removal than nanoscale zero-valent iron (nZVI, fsyn = 0.65) at an initial nitrate concentration of 25 mg L-1-N. Based on kinetic profiles, SO42- was the preferred electron acceptor over NO3- when using C. necator and S-nZVI for biocatalytic denitrification. Up-flow column experiments demonstrated that biocatalytic denitrification using S-nZVI achieved a total nitrogen removal capacity of up to 2004 mg L-1 for 127 d. Notably, microbiome taxonomic profiling showed that the addition of S-nZVI to the groundwater promoted the growth of Geobacter, Desulfosporosinus, Streptomyces, and Simplicispira spp in the column experiments. Most of those microbes can reduce sulfate, promote denitrification, and match the batch kinetic profile obtained using C. necator. Our results not only discover the great potential of S-nZVI as a biocatalyst for enhancing denitrification via microbial activation but also provide a deep understanding of the complicated abiotic-biotic interaction.
The ultimate goal of the present study is to design and investigate the bio-geo-filters for nitrate removal from the runoffs. This research uses alternate layers of non-woven geotextile and granular soil to reduce and remove pollution. These layers are of paramount importance in permeability and adsorption capability. Some points have been considered for selecting the materials, including the material capability for pollution removal, their accessibility, and maximal cost-effectiveness. After conducting the permeability tests, the weight mixing ratio of the materials used in permeable reactive barriers (PRB) was considered to be 25% sand, 20% zeolite, 20% iron filings, and 10% poplar wood sawdust. For pH 7, zeolite's maximal nitrate adsorption efficiency is about 69%, sawdust 29%, and iron filings 12%. The investigation of nitrate adsorption through the final prepared PRB for different nitrate concentrations under the optimal pH conditions showed maximal adsorption of about 83% for a nitrate concentration of 150 mg/L. The more the initial nitrate concentration, the more the absorption amount.
Moreover, nitrate was removed with equal amounts of absorbent at optimal pH at different times to determine the equilibrium time. The maximal removal of 100% was obtained at an equilibrium time of 96 hours. In the pollution removal test with biomass grown in the filter environment, the filter decreased the nitrate content up to 99% after nine days, i.e., the final nitrate content was reduced from 100 to 1 mg/L.
Nitrogen and phosphorus in wastewater impose a burden on the environment and cause damages such as eutrophication in closed water bodies. In the former paper, we showed that a pair of iron cathodes is able to reduce nitrate to ammonia via nitrite and discussed the reduction mechanism by comparing with nitrate reduction by ferrous ions dissolved anodically. Here we showed that, in addition to nitrite reduction, nitrite re-oxidation can be caused by hypochlorous acid in the solution generated at anode and by electrically on anode. We also showed that the nitrite oxidation can be suppressed by reducing the size of anode by minimizing the cross section of the nitrite oxidation reaction on anode.
Electrochemically converting nitrate ions back to ammonia can not only eliminate water pollution but also obtain valuable ammonia without a serious carbon footprint, and is thus deemed as an efficient supplement to the traditional Haber-Bosch process. Currently reported catalysts can achieve a single electrode reaction in the electrochemical nitrate reduction reaction. However, the bifunctionality of a single catalyst for both cathodic and anodic reactions has not yet been reported. Herein, we report Fe-doped layered α-Ni(OH)2 with expanded interlayer spacing as an efficient bifunctional catalyst for the nitrate reduction reaction and oxygen evolution reaction. The expanded interlayer spacing facilitates in situ electrochemical potassium ion intercalation between layers. In situ Raman spectroscopy characterization confirms that both the nitrate reduction reaction and oxygen evolution reaction are confined between layers and are triggered by the accumulation of potassium ions. The obtained α-Ni0.881Fe0.119(OH)2 nanosheets deliver an ammonia yield rate of 8.1 mol gcat.-1 h-1 with a NO3--to-NH3 faradaic efficiency of 97.5% at the cathode. The overpotential of oxygen generation at 10 mA cm-2 is reduced to 254 mV at the anode. As a bifunctional catalyst in overall electrolysis, the current density of α-Ni0.881Fe0.119(OH)2 reaches 24.8 mA cm-2 at a voltage of 2.0 V and performs continuously for 50 h with a current retention of 80.2%.
This study uses the electrocoagulation (EC) to remove nitrate from water. Box-Behnken Design method (BBD) was used to evaluate nitrate removal from synthetic water by the EC. BBD was firstly applied to optimise the effects of three parameters; pH of synthetic water (pHSW) (6–10), electrolysing time (ET) (20–80 min), and current density (CD) (1–3 mA/cm2) on nitrate removal. The EC cell is utilised aluminium electrodes to carry out the electrolysing process. The findings of this study generally showed high CD, high ET, and alkaline pHSW are favourable to nitrate removal. It was found the best removal of nitrate (93.2%) was obtained at pHSW, ET and CD of 8, 80 min and 3 mA/cm2, respectively. The results of the statistical analysis showed the removal of nitrate by aluminium electrodes can be accurately forecasted using the BBD methodology, where the R2 of the created model was 0.949, and the maximum difference between the forecasted and actual removal of nitrate was 5.5%. It must be noted the created model is applicable for the studied ranges of the aforementioned factors.KeywordsNitrateElectrocoagulationRemovalBBD
Groundwater nitrate contamination is an emerging threat in stressed regions under intensive farming although, lately, efforts to valorize such residues are highly encouraged. Here, electrochemical nitrate removal has been investigated as a versatile strategy for this purpose, using a reactor equipped with a cheap central Fe-based rotating cylinder electrode (RCE) as cathode and six concentric Ti|IrO2 plates as anodes. The study of the effect of Ecath and rotational speed (ω) on NO3⁻ electroreduction from a synthetic aqueous solution with high conductivity revealed the feasibility of complete nitrate removal, which only required 100-120 min at Ecath = -1.80 V vs Hg|Hg2SO4|sat. K2SO4 within the ω-range of 100-500 rpm. The concentration decays agreed perfectly with a first-order kinetics. NH3 was accumulated as main product, being partly volatilized due to the quick solution alkalization, whereas NO2⁻ was not found. Linear sweep voltammetries demonstrated the high electrocatalytic activity of carbon steel RCE as compared to inactive stainless steel. Koutecky-Levich analysis showed that the reduction process with carbon steel at Ecath from -1.80 V involved 8 electrons. The participation of H radical in the reduction mechanism was ascertained by electron paramagnetic resonance. The mass transport and charge transfer of the RCE reactor were characterized under turbulent flow by means of the dimensionless Damköhler (Da) number, as well as from the Sherwood-Reynolds-Schmidt (Sh-Re-Sc) analysis. A mixed regime with a prevalence of mass transport control was determined at Ecath from -1.8 V. The Sh = 0.70Re0.46Sc0.356 correlation obtained for this reactor may serve to guide the scale-up of electrochemical NO3⁻ removal as more electrocatalytic cathode materials are developed. Successful NO3⁻ elimination from solutions with low conductivity that mimicked groundwater is finally reported.
In this study, an integrated system of Fe⁰ and hydrogenotrophic microbes mediated by nitrate (nitrate-mediated bio-Fe⁰, NMB-Fe⁰) was established to remediate Cd(II)-contaminated sediment. Solid phase characterization confirmed that aqueous Cd(II) (Cd(II)aq) was successfully immobilized and enriched on iron surface due to promoted iron corrosion driven by hydrogenotrophic denitrification and subsequent greater biomineral production such as magnetite, lepidocrocite and green rust. Compared to a Cd(II)aq removal of 21.1% in overlying water of the nitrate-mediated Fe⁰ (NM-Fe⁰) system, the NMB-Fe⁰ system obtained a much higher Cd(II)aq removal of 83.1% after 7 d remediation. The leaching test and sequential extraction results also showed that the leachability of Cd(II) decreased by 75.9% while the residual fraction of Cd(II) increased by 185.7% in comparison with untreated sediment. Besides, the Cd(II)aq removal raised with the increase of nitrate concentration and Fe⁰ dosage, further revealing the promotion effect of nitrate on Cd(II) removal by bio-Fe⁰. This study highlighted the involvement of bio-denitrification in the remediation of Cd(II)-contaminated sediment by Fe⁰ and provided a new insight to enhance its reactivity and applicability for Cd(II) immobilization.
To effectively treat organic pollutants in seawater, this study fabricated different floating photocatalytic spheres by loading TiO2-based photocatalysts to degrade tetracycline in simulated seawater. In photodegradation for tetracycline, the content of the active TiO2 component in the powder photocatalyst played a major role in degrading the performance of the material. A polyurethane porous sponge with a large specific surface area was used as a carrier in loading the powder photocatalyst to avoid the interference of salt ions in seawater for photodegradation. The adsorption ability and performance in tetracycline photodegradation of the PU sponge-filled photocatalytic spheres were significantly higher than those of PMMA photocatalytic spheres under the same conditions. The Pt-deposited P25-A (Pt–P25-A) powder photocatalyst with the strongest visible light response exhibited the highest performance. The rate removal for tetracycline in the simulated seawater by the PU sponge-filled spheres loaded with Pt–P25-A exceeded 80% after 20 h.
To expand the working pH range of NO3⁻-N reduction from aqueous solution, a two-step method including the Al/Cu bimetal and sulfamic acid reduction was developed. In this process, Al/Cu bimetallic materials were prepared by chemical deposition method and characterized by EDS, SEM, XRD and XPS. The NO3⁻-N reduction batch experiment showed that 100% of NO3⁻-N was reduced and converted to N2 at pH of 7, Al/Cu dosage of 30 g/L and EDTA-2Na concentration of 6 mmol/L. When the pH value was adjusted to 3, 5 and 9, NO3⁻-N reduction efficiencies ca. 80-97% were also obtained in the first step, and 100% N2 selectivity was further obtained with the second reduction step at pH of 3, 7 and 9. The kinetics study indicated that the Al/Cu reduction process was in accordance with the pseudo-second order kinetics model.
Zero-valent iron (Fe⁰) has been widely used for the reduction of nitrate, but the end reduction product is mainly ammonium. Here, a novel strategy for selective reduction of nitrate (NO3⁻) to nitrogen gas (N2) with high efficiency and N2 selectivity was investigated using Fe-based material (Fe⁰–Cu⁰–CuFe2O4) combined with citric acid (CA) and ultraviolet (UV) irradiation. In this strategy, the nitrate was firstly reduced to nitrite (NO2⁻) by Fe⁰–Cu⁰–CuFe2O4/UV process, and then the produced NO2⁻ could be further reduced to N2 by carbon dioxide anion radicals (CO2•−) which was generated from CA that was added later. In this process, the selective reduction of NO3⁻ to NO2⁻ was a key step. For this purpose, we synthesized Fe⁰–Cu⁰–CuFe2O4 composite by simple chemical replacement and in-situ growth process, which made it have a delicate structure with good contact between Cu and Fe and CuFe2O4. The selective reduction of NO3⁻ to NO2⁻ in Fe⁰–Cu⁰–CuFe2O4/UV process was due to that the Cu⁰ was the electron enrichment center and the photo-generated hole could suppress the NO3⁻ reduction to NH4⁺ by Fe²⁺. In this proposed strategy, 100% NO3⁻ removal efficiency and 96.3% N2 selectivity were achieved when the initial NO3⁻ concentration was 30 mg N/L and the reduction time was 60 min. The denitrification mechanism of the Fe⁰–Cu⁰–CuFe2O4/UV/CA system was proposed.
Bimetallic catalyst exhibits efficient and potential performance for nitrate reduction towards N2 generation. In this work, Pd-Cu bimetallic catalysts are synthesized based on γ-Al2O3 with different loading sequences and annealing temperatures. The characterization of the catalysts with XRD and STEM indicates that the loading methods affect the dispersity of the catalysts. The catalyst obtains much smaller size and more uniform dispersion by first Cu load with annealing at 900 oC and then Pd load (Cu1%(900 oC)-Pd2.5%/γ-Al2O3). The dispersion of Pd and Cu reach 51.81% and 21.93%, respectively. Then the catalysts are applied for nitrate hydroreduction combined with electrocatalytic in-situ hydrogen production using PPy/Ni cathode to obtain high efficiency of H2 utilization and N2 selectivity. For Cu1%(900 oC)-Pd2.5%/γ-Al2O3, the initial reaction rate for N2 generation is 0.70 mg L⁻¹ min⁻¹ and the TOF based on Pd is 2.13×10⁻³ s⁻¹, which is much higher than the others, due to the best dispersion of Pd-Cu on the support. The loading amount is also optimized and the effects of current and pH are investigated to achieve the optimal performance.
Granules recovered from a highly reduced anaerobic digester were capable of active nitrogen removal in the absence of exogenous electron donors, averaging 0.25 mg mgNO3⁻-N /gVSS/d over 546 days of operation. Electron mass balance indicated that about half the influent nitrate was converted to ammonia via DNRA and another half denitrified. This capacity was associated with an onion-like structure of multiple layers enriched in reduced iron and sulfur, and a complex microbial community shown by metagenomic sequencing to consist of multiple physiological groups and associated activities, including methanogenesis, denitrification, dissimilatory nitrate reduction to ammonia (DNRA), iron oxidation and reduction, and sulfur reduction and oxidation. Nitrate reduction was supported by both entrained organic material and reduced iron and sulfur species, corresponding to 2.13 mg COD/gVSS/d. Batch incubations showed that approximately 15 % of denitrified nitrate was coupled to the oxidation of sulfur derived from both sulfate respiration and granular material enriched in iron-sulfide. Inhibition of sulfate reduction resulted in redirection of electron flow to methanogenesis and, in combination with other batch tests, showed that these granules supported a complex microbial community in which cryptic redox cycles linked carbon, sulfur, and iron oxidation with nitrate, sulfate, iron, and carbon dioxide reduction. This system shows promise for treatment of nitrate contaminated ground water without addition of an external organic carbon source as well as wastewater treatment in combination with (granular) sludge elimination leading in a net reduction of solid treatment costs.
Nitrate is the most common contaminant in groundwater in Korea, as well as across the world. Reduction of nitrate to ammonia is one of the options available to remediate groundwater. In this study, nitrate in groundwater was removed using a zero-valent iron (ZVI) containing biochar synthesized by co-pyrolyzing iron oxide and sawdust biomass. Among the various biogases generated during the pyrolysis of biomass, CO and H2 act as reducing agents to transform iron oxides to ZVI. Approximately 71% of nitrate was reduced to ammonium by ZVI-biochar at initial pH 2.0, and the reduction decreased sharply by the increase in pH. The mass of nitrate-N decreased is exactly same with the mass of ammonia-N formed. However, ammonium remained in the aqueous phase after reduction by ZVI-biochar, and the total nitrogen was not lowered. Acid-washed zeolite adsorbed most ammonium reduced by the ZVI-biochar and maintained the pH to acidic condition to facilitate the reduction of nitrate. The results of this study imply that nitrate-contaminated groundwater can be properly treated within the guidelines of water quality by synthesized ZVI-containing biochar.
Microbial electrochemical snorkel (MES) is a short-circuited microbial fuel cell applicable to water treatment that does not produce energy but requires lower cost for its implementation. Few reports have already described its water treatment capabilities but no deeper electrochemical analysis were yet performed. We tested various materials (iron, stainless steel and porous graphite) and configurations of snorkel in order to better understand the rules that will control in a wetland the mixed potential of this self-powered system. We designed a model snorkel that was studied in laboratory and on the field. We confirmed the development of MES by identifying anodic and cathodic parts, by measuring the current between them and by analyzing microbial ecology in laboratory and field experiments. An important application is denitrification of surface water. Here we discuss the influence of nitrate on its electrochemical response and denitrification performances. Introducing nitrate caused the increase of the mixed potential of MES and of current at a potential value relatively more positive than for nitrate-reducing biocathodes described in the literature. The major criteria for promoting application of MES in artificial wetland dedicated to mitigation of non-point source nitrate pollution from agricultural water are considered.
This work aims to study nitrate ions removal using Borassus aethiopum activated carbon (BA-AC) in a synthetic medium. BA-AC was prepared through artisanal method in order to provide a low-cost activated carbon. Physico-chemical characterization of BA-AC has shown a high-specific surface area (1431 m²/g). Analysis of surface morphology by scanning electron microscopy, mean pore diameter (2.76 nm) and adsorption/desorption isotherm resulted in the mesoporous adsorbent. The existence of functional groups (C = O; C–H; C–OH) was highlighted by Fourier Transform Infrared spectroscopy. A percentage of 60.56% for nitrate ions at pH 4 was reached. Pseudo-second-order kinetic and Langmuir isotherm were the most suitable models to describe adsorption process. The thermodynamic study revealed that adsorption mechanism occurs spontaneously (ΔG° < 0). Enthalpy (ΔH° = 1.89 kJ.mol⁻¹) and entropy (ΔS° = 19.03 J.mol⁻¹K⁻¹) values indicate an endothermic process with an increase of disorder at the solid–liquid interface.
At present, groundwater nitrate pollution in China is serious. The use of microorganisms for biological denitrification has been widely applied, and it is a universal and efficient in situ groundwater remediation technique, but this approach is influenced by many factors. In this study, glucose was adopted as the carbon source, four different concentrations of 0 g/L, 2 g/L, 5 g/L and 10 g/L were considered, and natural groundwater with a nitrate concentration of 300.8 mg/L was employed as the experimental solution. The effect of the carbon source concentration on the nitrate removal rate in groundwater was examined through heterotrophic anaerobic denitrification experiments. The results showed that the nitrate removal rate could be improved by the addition of an external carbon source in the process of biological denitrification, and an optimal concentration was observed. At a glucose concentration of 2 g/L, the denitrification effect was the best.
As the interest in environmentally-friendly energy processes increases, many studies have been focused on producing hydrogen as an alternative energy carrier via catalytic reaction processes. Among several potential reaction processes, water gas shift (WGS) reaction has been studied extensively as a typical catalytic reaction for bulk production of hydrogen. Recently, many studies have been conducted on the formation of an easily reducible active components in order to develop novel catalysts having excellent activities at low temperatures for WGS reaction. In this study, new catalysts based on hydrotalcite with unique interlayered structure were prepared by a hydrothermal synthesis and co-precipitation of copper (Cu) for active metal sites. The catalysts synthesized from different precursors showed that the reduction property of Cu was greatly changed according to the mixed oxide structure generated after calcination. Cu–MgHAlH, the hydrotalcite-based catalyst synthesized using hydroxide precursors, showed the highest redox property and the multiple analysis results confirmed that MgAl2O4 spinel structure is attributed to form easily reducible Cu species. Based on these characteristics, Cu–MgHAlH showed excellent catalytic performance in the WGS reactions between 250 and 400 °C, and it was successfully applied to the sorption-enhanced WGS reaction using catalyst-sorbent hybrid solid pellets. Especially, the hydrotalcite-based catalyst has high potential for application to sorption-enhanced reaction processes using molten salt containing CO2 sorbents because the high reduction properties of Cu species are well maintained in the catalyst when mixed with CO2 sorbents.
This, the first article of a series, presents a summary of the USEPA Water Supply Research Div.'s overall project to evaluate contaminant removal techniques, with specific details on the treatment technology for nitrate and fluoride removal. Subsequent articles will review the treatment technology for the eight other NIPDWR-regulated inorganic contaminants and the radionuclides.
To date it does not appear to have been demonstrated in the literature that halogenated ethylenes can undergo reductive {beta}-elimination to alkynes under environmental conditions. The purpose of this paper is to provide experimental evidence that such pathways may be involved in the reaction of chloroethylenes with zero-valent metals as well as to speculate on the significance of the products that may result. Calculations indicate that reductive {beta}-elimination reactions of chloroethylenes are in fact comparable energetically to hydrogenolysis at neutral pH. Experiments were therefore initiated to assess whether {beta}-elimination reactions of chlorinated ethylenes could occur in the presence of two zero-valent metals, Fe and Zn. 76 refs., 3 figs., 1 tab.
Knowledge concerning the chemical reduction of NO 3 ⁻ to gaseous products, a process of potential practical significance as an antipollution device, is sparse. The influence of pH on chemical reduction of NO 3 ⁻ ‐N (approximate concentration 25 ppm) by Fe ²⁺ in the presence and absence of Cu ²⁺ was studied over a pH range from 6 to 10. After 24‐hours of controlled pH incubations under a helium atmosphere NO 3 ⁻ , NO 2 ⁻ , N 2 O, NO, N 2 , and NH 4 ⁺ were determined. The initial Fe ²⁺ /NO 3 ⁻ mole ratio was 8. Reduction of NO 3 ⁻ was negligible in the absence of Cu ²⁺ , but was pronounced above pH 7 in the presence of approximately 5 ppm Cu ²⁺ . Formation of NH 4 ⁺ increased with pH and was the dominant process at pH 9 and 10. Nitrous oxide and N 2 accumulations were greatest in the pH range from 8 to 8.5 and negligible at pH 6 and 10. Nitrite formation was small except at pH 9 and 10. Trace quantities of NO accumulated during incubation if the pH was allowed to drop below 6.
Levels of Cu ²⁺ and Fe ²⁺ influenced the extent and nature of NO 3 ⁻ reduction at pH 8. Maximum reduction of NO 3 ⁻ (93%) and maximum gas production (equivalent to 61% of the original NO 3 ⁻ ) occurred when the Fe ²⁺ /NO 3 ⁻ mole ratio was 12 and the Cu ²⁺ level was approximately 10 ppm. The N 2 O/N 2 mole ratio in the evolved gases decreased as the Cu ²⁺ level was increased from approximately 1 to 10 ppm and as the Fe ²⁺ /NO 3 ⁻ mole ratio was increased from 8 to 12. Nitrate was relatively stable at a Cu ²⁺ content of 0.1 ppm irrespective of the Fe ²⁺ /NO 3 ⁻ ratio.
We have hypothesized that hydrogen gas intercalated in a palladium lattice is the powerful reducing agent that reductively dechlorinates chlorinated organic compounds that are adsorbed on the surface of palladized electrodes. We have shown that dechlorination of 4-chlorophenol to phenol occurs rapidly on palladized carbon cloth or pal ladized graphite electrodes. The reactions on the palladized carbon cloth and graphite depend on the adsorption of the chlorinated organic compound on the carbon surface and the reaction with hydrogen at the palladium/carbon interface. Palladium was much more effective in promoting the dechlorination reaction than platinum, probably because of its ability to intercalate hydrogen in its lattice.
A kinetic model is presented for the catalytic hydrodehalogenation of chlorinated ethylenes using Pd and H2 under water treatment conditions. All five chlorinated ethylenes, including tetrachloroethylene (PCE) and vinyl chloride, were completely removed from tap water within 10 minutes at room temperature by 0.5 g of 0.5% Pd on alumina and 0.1 atm H2. Ethane accounted for 55–85% of the mass balance in these systems. Ethene was a reactive intermediate whose maximum concentration accounted for less than about 5% of the initial substrate. Palladium on granular carbon was also an effective catalyst, although ethane yield for PCE was somewhat lower than with Pd-alumina (55% versus 85%). The transformation of PCE was first order with respect to both substrate and amount of metal, with a half-life of t12 = 9 min for 0.055 μmole Pd (583 μg of 1% Pd on powdered activated carbon). Addition of ∼10 mg/L of nitrite to the water decreased the rate constant by about 50%. The nitrite concentration decreased by about 25% over the course of the reaction. Addition of nitrate or sulfate had smaller effect on the rate of PCE transformation; chloride had no effect. The presence of oxygen greatly reduced the amount of ethane produced regardless of the catalyst support. Bisulf1de poisoned the catalyst.
In slightly alkaline medium on the action of copper as catalyst ferrous hydroxide reduces nitrate ions to ammonia. The reduction is quantitative and is suitable for the determination of nitrates. Employing distillation with steam the determination can be carried out in 8-10 minutes. Only the As+3, Sb+3 and Sb+5 ions interfere with the method.RésuméEn solution faiblement alcaline, en présence de cuivre comme catalyseur, il est possible de réduire les ions nitriques en ammoniac au moyen d'hydroxyde ferreux. La réduction est quantitative et elle permet un dosage des nitrates. Par distillation à, la vapeur d'eau, Ie dosage dure 8 à 10 minutes. Seuls les ions As+3, Sb+3 et Sb+5, gn̂ent.ZusammenfassungIn schwach alkalischer Lösung kann man in Gegenwart von Kupfer als Katalysator mit Hilfe von Ferrohydroxyd Nitrationen zu Ammoniak reduzieren. Die Reduktion ist quantitativ und ermöglicht eine Bestimmung der Nitrate. Wenn man mit Wasserdampf destilliert, dauert die Bestimmung 8-10 Minuten. Nur die lonen As+3, Sb+3 und Sb+5 stören.
This report is the fourth in a series that summarizes the existing treatment technology to meet the inorganic primary drinking water regulations. Treatment technology for the removal of mercury and chromium from drinking water is presented with emphasis placed on the jar test and pilot plant studies conducted by the Drinking Water Research Division of USEPA. The primary treatment techniques discussed are conventional coagulation, lime softening, activated carbon adsorption, ion exchange, and reverse osmosis. -Author
Flow-through column tests were conducted to investigate the products of degradation of aqueous trichloroethene (TCE) in contact with granular iron metal. The results indicated the degradation process to be pseudo-first-order and the rate constant to be relatively insensitive to the initial concentration of TCE over the range from about 1.3 to 61 mg/L. The principal degradation product was ethene, followed by ethane with substantially smaller amounts of other C1−C4 hydrocarbons. About 3.0−3.5% of the initial TCE appeared as chlorinated degradation products, including the three dichloroethene isomers and vinyl chloride. Although the chloride mass balance was generally between 98 and 102%, a maximum of 73% of the carbon could be accounted for in the identified products. Based on the low concentrations of chlorinated degradation products in the solution phase, it is proposed that most of the TCE remains sorbed to the iron surface until complete dechlorination is achieved.
A combination of new and previously reported data on the kinetics of dehalogenation by zero-valent iron (Fe0) has been subjected to an analysis of factors effecting contaminant degradation rates. First-order rate constants (kobs) from both batch and column studies vary widely and without meaningful correlation. However, normalization of these data to iron surface area concentration yields a specific rate constant (kSA) that varies by only 1 order of magnitude for individual halocarbons. Correlation analysis using kSA reveals that dechlorination is generally more rapid at saturated carbon centers than unsaturated carbons and that high degrees of halogenation favor rapid reduction. However, new data and additional analysis will be necessary to obtain reliable quantitative structure−activity relationships. Further generalization of our kinetic model has been obtained by accounting for the concentration and saturation of reactive surface sites, but kSA is still the most appropriate starting point for design calculations. Representative values of kSA have been provided for the common chlorinated solvents.
The properties of iron metal that make it useful in remediation of chlorinated solvents may also lead to reduction of other groundwater contaminants such as nitro aromatic compounds (NACs). Nitrobenzene is reduced by iron under anaerobic conditions to aniline with nitrosobenzene as an intermediate product. Coupling products such as azobenzene and azoxybenzene were not detected. First-order reduction rates are similar for nitrobenzene and nitrosobenzene, but aniline appearance occurs more slowly (typical pseudo-first-order rate constants 3.5 × 10-2, 3.4 × 10-2, and 8.8 × 10-3 min-1, respectively, in the presence of 33 g/L acid-washed, 18−20 mesh Fluka iron turnings). The nitro reduction rate increased linearly with concentration of iron surface area, giving a specific reaction rate constant (3.9 ± 0.2 × 10-2 min-1 m-2 L). The minimal effects of solution pH or ring substitution on nitro reduction rates, and the linear correlation between nitrobenzene reduction rate constants and the square-root of mixing rate (rpm), suggest that the observed reaction rates were controlled by mass transfer of the NAC to the metal surface. The decrease in reduction rate for nitrobenzene with increased concentration of dissolved carbonate and with extended exposure of the metal to a particular carbonate buffer indicate that the precipitation of siderite on the metal inhibits nitro reduction.
Hydrogen permeation from the gas phase through zone refined iron was measured with the electrochemical technique over 0 to
60°C and 0.01 to 1 atm. The surface impedance problems normally encountered in this pressure-temperature range were eliminated
by a thin layer of electroplated palladium on the input surface of the permeation membrane. The steady state flux was propprtional
to the square root of the pressure and inversely proportional to the membrane thickness. The permeability coefficient was
2.6× 1017 exp ((- 8500 ± 600 cal/mole deg)/RT) atom H/cm s atm1/2, in good agreement with earlier results at higher temperatures. These results can be used to calibrate electrochemical charging
experiments in terms of an effective hydrogen pressure.
The abilities of zero-valent iron powder and hydrogen with a palladium catalyst (H2/Pd-alumina) to hydrodehalogenate 1,2-dibromo-3-chloropropane (DBCP) to propane under water treatment conditions (ambient temperature and circumneutral pH) were compared. DBCP reacted with iron powder (100–200 mesh, 36 g/l) in HEPES-buffered water (pH = 7.0) with a of 2.5 min and in different groundwaters (pH = 8.2–8.7) with a ranging from 41–77 min. Dissolved O2 and NO−3 slowed the transformation, whereas sulfate and nitrite had little effect. Iron removed 60 mg/l of nitrate within 14 min with nitrite as an intermediate. In 75 ml groundwater containing 22.5 mg 1% Pd-alumina catalyst under 10% H2 partial pressure, DBCP was transformed to propane within minutes. The rate in groundwater was slower by about 30% compared to Milli-Qtm water. SO2−4, NO−3, Cl− or O2 added to Milli-Q water only slightly inhibited DBCP transformation by H2/Pd-alumina, while SO2−3 had a much stronger inhibitory affect.
The reduction of nitrate to ammonia occurs with nearly complete conversion at room temperature and pressure under aerobic conditions in the presence of iron and either HCl or a pH buffer. A 50.0 mL solution of 12.5 millimolar nitrate is rapidly reduced to ammonia when exposed to 4.00 g of 325 mesh iron at pH 5.0, 0.05 M sodium acetate/acetic acid. The pseudo-first order rate constant was 0.053 min−1, Under conditions of pH 6.0 buffer, (i.e. 0.1 M 4-morpholineethanesulfonic acid adjusted to pH 6.0) and pH 7.0 buffer (0.1 M 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid adjusted to pH 7.0), the rate constants were 0.0408 min−1 and 0.0143 mint, respectively. In unbuffered solutions there was no loss in nitrate and no production of ammonia. A more concentrated nitrate solution (100 mL of 1.0 M sodium nitrate) was also reduced to ammonia in the presence of 2.5 M HCl with the slow addition of 50.0 g of 325 mesh iron.
Reduction of chlorinated solvents by fine-grained iron metal was studied in well-mixed anaerobic batch systems in order to help assess the utility of this reaction in remediation of contaminated groundwater. Iron sequentially dehalogenates carbon tetrachloride via chloroform to methylene chloride. The initial rate of each reaction step was pseudo-first-order in substrate and became substantially slower with each dehalogenation step. Thus, carbon tetrachloride degradation typically occurred in several hours, but no significant reduction of methylene chloride was observed over 1 month. Trichloroethene (TCE) was also dechlorinated by iron, although more slowly than carbon tetrachloride. Increasing the clean surface area of iron greatly increased the rate of carbon tetrachloride dehalogenation, whereas increasing pH decreased the reduction rate slightly. The reduction of chlorinated methanes in batch model systems appears to be coupled with oxidative dissolution (corrosion) of the iron through a largely diffusion-limited surface reaction.
Anaerobic corrosion of iron metal produces Fe2+, OH-, and H-2(g). Growing interest in the use of granular iron in groundwater remediation demands accurate corrosion rates to assess impacts on groundwater chemical composition. In this study, corrosion rates are measured by monitoring the hydrogen pressure increase in sealed cells containing iron granules and water. The principal interference is hydrogen entry and entrapment by the iron. The entry rate is described by Sievert's law (R = kP(H2)(0.5)), and the rate constant, k, is evaluated by reducing the cell pressure once during a test. For the 10-32 mesh iron used in this study, k initially was 0.015 but decreased to 0.009 mmol kg(-1) d(-1) kPa(-0.5) in 150 d. The corrosion rate in a saline groundwater was 0.7 +/- 0.05 mmol of Fe kg(-1) d(-1) at 25 degrees C-identical under water-saturated or fully-drained conditions. The rate decreased by 50% in 150 d due to alteration product buildup. The first 40-200 h of a corrosion test are characterized by progressively increasing rates of pressure increase. The time before steady-state rates develop depends on the solution composition. Data from this period should be discarded in calculating corrosion rates. Tests on pure sodium salt solutions at identical equivalent concentrations (0.02 equiv/L) show the following anion effect on corrosion rate: HCO3 > SO42- > Cl-. For NaCl solutions, corrosion rates decrease from 0.02 to 3.0 m.
Nitrate-nitrogen reduction was studied in the presence of ferrous iron and a copper catalyst. In a batch system, it was found that the reduction was very fast at pH 8.1 and slow at pH 7.5. A temporary accumulation of nitrate and hydroxylamine was noted. It was found that the reduction of nitrite-nitrogen in the presence of ferrous iron partly continued to ammonium. Decreasing the amount of reagents led to a slower reduction rate but a lower accumulation of nitrite and hydroxylamine. A continuous system was described whereby more than 50% of the initial nitrate could be removed.
The chemical Removal of Nitrate from Water Supplies Using Ferrous Sulfates and Pickle Liquor Aquatic Chemistry The alkalimetric de-termination of nitrate by means of a copper-catalyzed reduction
- R J Sova
- Nebraska-Lincoln
- Nb Lincoln
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Eect of Iron Aging on Reduction Kinetics in a Batch Metallic Iron/Water System Extended Abstract, pre-sented at Division of Environmental Chemistry Chemical re-duction of nitrate by ferrous iron Reduction of Nitrate to Ammonia by Zero-Valent Iron
- A Agrawal
- P G Tratnyek
- R M Allen-King
- D R Burris
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Chemical Removal of Nitrate from Potable Water Supplies, Contribution No. 23
- W J O'brien
The chemical Removal of Nitrate from Water Supplies Using Ferrous Sulfates and Pickle Liquor
- R J Sova
Effect of Iron Aging on Reduction Kinetics in a Batch Metallic Iron/Water System. Extended Abstract, presented at Division of Environmental Chemistry
- R M Allen-King
- D R Burris
- J A Specht
Development of a Chemical Denitrification Process. EPA Water Pollution Control Research Series
- F C Gunderloy
- Jr
- C Y Fujikawa
- V H Dayan