Chemical Denitrification Research Articles

Research progress of nanoscale zero-valent iron in synergistic combinations of denitrifying bacteria for nitrate removal

Nitrate (NO3--N) is a common inorganic nitrogen pollutant in water. Excessive NO3--N can lead to water eutrophication and threaten human health. Nanoscale zero-valent iron (nZVI) has attracted much attention in NO3--N removal due to its high specific surface and excellent electron donor properties. The combination of nZVI and denitrifying bacteria (DNB) demonstrates high efficiency in converting NO3--N into N2. This approach not only substantially enhances the removal rate of NO3--N but also exhibits superior environmental sustainability compared with conventional chemical denitrification methods. Accordingly, it holds substantial promise for mitigating NO3--N pollution and warrants further exploration in the pollution control. Therefore, it is necessary to understand the interaction mechanism between nZVI and DNB for NO3--N removal. This paper details the factors affecting the removal of NO3--N by nZVI combined with DNB, reviews the latest research progress in this field, elaborates on the interaction mechanism between nZVI and DNB for NO3--N removal, and discusses the challenges and future research directions of NO3--N removal by nZVI combined with DNB. This review aims to provide a theoretical basis for the development of efficient approaches for the remediation of NO3--N pollution.

Partitioning denitrification pathways in N2O emissions from re-flooded dry paddy soils

In flooded paddy fields, peak greenhouse gas nitrous oxide (N2O) emission after rewetting the dry soils is widely recognised. However, the relative contribution of biotic and abiotic factors to this emission remains uncertain. In this study, we used the isotope technique (δ18O and δ15NSP) and molecular-based microbial analysis in an anoxic incubation experiment to evaluate the contributions of bacterial, fungal, and chemical denitrification to N2O emissions. We collected eight representative paddy soils across southern China for an incubation experiment. Results show that during the 10-day incubation period, the net N2O emissions were mainly produced by fungal denitrification, which accounted for 58–77% in six of the eight investigated flooded paddy soils. In contrast, bacterial denitrification contributed 6–15% of the net N2O emissions. Moreover, around 11–35% of the total N2O emissions were derived from chemical denitrification in all soil types. Variation partitioning analysis (VPA) and principal component analysis (PCA) demonstrated that initial soil organic carbon (OC) concentrations were the primary regulator of N2O source patterns. Soils with relatively lower OC concentration (7–15 mg g−1) tend to be dominated by fungal denitrification, which accounted for the net N2O production at the end of the incubation period. Overall, these findings highlight the dominance of the fungal denitrification pathway for N2O production in flooded paddy soils, which predominates in soils with relatively lower OC content. This suggests that fungal contribution should be considered when optimizing agricultural management system timing to control N2O emissions in flooded paddy soil ecosystems, and for the relevant establishment of predictive numerical models in the future.

Nitrate and nitrite reduction by adsorbed Fe(II) generated from ligand-promoted dissolution of biogenic iron minerals in groundwater

Chemical denitrification by redox-active Fe(II) species is pivotal in the coupled iron and nitrogen cycles. The reductive dissolution of ferric minerals by ligand can generate Fe(II)-ligand complexes, but their reducing capability for electrophilic pollutants like nitrate and nitrite remains uncertain. Here, biogenic secondary iron minerals (SIM) after dissimilatory iron reduction were reductively dissolved by oxalate and the siderophore desferrioxamine B, and subsequently the partially-dissolved SIM (SIMD) effectively removed NO2− from groundwater via reduction, while exhibiting much lower reactivity towards NO3−. The dissolution and removal processes were well-fitted with the Kabai model and the pseudo-second-order adsorption model, respectively. The equilibrium NO2− removal capacity (qe) of SIMD reached 0.146–0.223 mmol/g, accompanied with the rate constants as 0.433–0.810 g/(mmol·h). The emission of N2O and NO verified the occurrence of chemical denitrification during NO2− removal by SIMD. From the perspective of Fe(II) reactivity, SIMD exhibited higher densities of surface Fe(II) and more negative Eh values than SIM, and these two indicators showed linear correlations with the removal rates. Combined with microscopic, electrochemical and spectral analysis, our results indicated the redox reaction of adsorbed Fe(II)-complexes with NO2− on SIMD surface. The concurrent substance biochar was also considered, as it indirectly influenced dissolution and pollutant removal by shifting the iron mineral phase in SIM from magnetite to goethite. These findings highlight the significant role of reductive dissolution of iron mineral in N transformation, expand the electron pool available to support chemical denitrification, and have implications for Fe and N cycling coupling with pollutant reduction.

Enhanced denitrification driven by a novel iron-carbon coupled primary cell: chemical and mixotrophic denitrification

Iron-carbon micro-electrolysis system is a promising method for promoting electron transfer in nitrate removal. However, many traditional approaches involving simple physical mixing inevitably suffered from the confined iron-carbon contact area and short validity period, leading to the overuse of iron. Here, a ceramsite-loaded microscale zero-valent iron (mZVI) and acidified carbon (AC) coupled-galvanic cell (CMC) was designed to support chemical, autotrophic and heterotrophic denitrification. Long-term experiments were conducted to monitor the nitrogen removal performance of denitrification reactors filled with CMC and thus optimized the denitrification performance by improving fabrication parameters and various operating conditions. The denitrification contributions test showed that the chemical denitrification pathway contributed most to nitrate removal (57.3%), followed by autotrophic (24.6%) and heterotrophic denitrification pathways (18.1%). The microbial analysis confirmed the significant aggregation of related denitrifying bacteria in the reactors, while AC promoted the expression of relevant nitrogen metabolism genes because of accelerated uptake and utilization of iron complexes. Meanwhile, the electrochemical analysis revealed a significantly improved electron transfer capacity of AC compared to pristine carbon. Overall, our study demonstrated the application of a novel mZVI-AC coupled material for effective nitrate removal and revealed the potential impact of CMC in the multipathway denitrification process.Graphical

Selective and effective oxidation of ammonium to dinitrogen in MgO/Na2SO3/K2S2O8 system

The oxidation of ammonium (NH4+) to dinitrogen (N2) with high selectivity and high efficiency is still a challenge. Herein, a novel sunlight induced persulfate (PS)-based AOPs process (MgO/Na2SO3/PS/hv) was proposed by introducing solid base (MgO) and hydrated electron (eaq−), to selectively oxidize NH4+ to N2, with high selectivity and high efficiency at a wide range of pH value. The deprotonation of NH4+ into NH3 by MgO and the generation of •OH and SO4−• by PS activation were responsible for the high efficiency of NH4+ oxidation. The buffering capacity provided by MgO to proton released from PS activation made the NH4+ oxidation possible at a wide pH range. The eaq− from the Na2SO3/hv process was the main active specie to reduce NO2−and NO3− (NOx−) into N2, responsible for high N2 selectivity of NH4+ oxidation. 100% NH4+ could be oxidized within 30 min, and N2 selectivity exceeded 96% at the initial pH range of 3–11 and the initial concentration of NH4+ of 30 mg N/L. This work could offer an efficient AOPs process for selective NH4+ oxidation, which is promising for the chemical denitrification of wastewater ….

Influence of iron species on the simultaneous nitrate and sulfate removal in constructed wetlands under low/high COD concentrations

Nitrate and sulfate are crucial factors of eutrophication and black and odorous water in the surface water and thus have raised increasing environmental concerns. Constructed wetlands (CWs) are the last ecological barrier before effluent enters the natural water body. To explore the simultaneous removal of nitrate and sulfate, the CW microcosms of CW-Con (with quartz sand), CW-ZVI (quartz sand and zero-valent iron), CW-Mag (quartz sand and magnetite), CW-ZVI + Mag (quartz sand, ZVI and magnetite) groups were set up under the low (100 mg/L)/high (300 mg/L) chemical oxygen demand (COD) concentration. Under the high COD condition, CW-ZVI group showed the best performance in nitrate (97.1%) and sulfate (96.9%) removal. Under the low COD concentration, the removal content of nitrate and sulfate in CW-ZVI group was better than CW-Mag group. The reason for this result was that zero-valent iron (ZVI) could be the electron donor for nitrate and sulfate reduction. Meanwhile, ZVI promoted chemical denitrification under high COD concentration according to PCA analysis. In addition, the produced sulfides inhibited the relative abundance of denitrifying bacteria, resulting in the lowest nitrate removal rate in CW-Mag group with sufficient electron donors. This study provided an alternative method to enhance simultaneous sulfate and nitrate removal in CWs.

Nitrate Removal by Zero-Valent Metals: A Comprehensive Review

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 Fe0 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.

Performance of Pd/Sn catalysts supported by chelating resin prestoring reductant for nitrate reduction in actual water

Catalytic hydrogen reduction has appeared as a promising strategy for chemical denitrification with advantages of high activity and simple operation. However, the risk and low utilization of H2 is the disadvantage of catalytic hydrogen reduction. In recent years, catalytic reduction reactions in the presence of sodium borohydride (NaBH4) have been extensively studied. NaBH4 can be used as an electron source to generate electrons on the surface of the catalyst and can catalyze the reduction of pollutants. But it makes commercialization costly and causes significant environmental pollution if widely use NaBH4. In this study, we prepared supported Pd/Sn bimetallic nanoparticles which could adsorb NaBH4 during the preparation of the Pd/Sn bimetallic catalyst as the prestoring reductant. No additional reducing agent is required during nitrate reduction process. The performance and mechanism for nitrate reduction by using Pd/Sn bimetallic nanoparticles were discussed. Moreover, the catalyst D-Pd1/Sn1 reached a complete nitrate removal in the municipal wastewater treatment plant effluent water within 3 h. The results provide a prospect for denitrification in biological wastewater treatment plants.

Insight into the mechanism of chemoautotrophic denitrification using pyrite (FeS2) as electron donor

In this study, denitrification was performed using pyrite as sole electron donor. The nitrate reducing rate ranged from 0.61 to 0.95 mM/d. The production of nitrous oxide (N2O) was observed, accounting for 20% of the total nitrate reduction. The isotope fractionation indicated that N2O production was mainly caused by the bacterial denitrification, instead of chemical denitrification by Fe(Ⅱ). Thiobacillus was the predominant genus, of which relative abundance decreased after the incubation with pyrite. Conversely, other genera belonging to Actinobacteria, like Rhodococcus, increased by more than 10 times. These Actinobacteria-like bacteria lack nitrous oxide reductase, which might be the reason for high N2O production. Furthermore, the predicted microbial functions analysis by PICRUSt2 showed that the genes (menC/E/G) involved in the biosynthesis of electron shuttles (menaquinone-related redox-active molecule), which were remarkably enriched during the process, suggesting that the first step of pyrite oxidation might be driven by the microbial derived electron shuttles.

Selective reduction of nitrate into nitrogen at neutral pH range by iron/copper bimetal coupled with formate/ferric ion and ultraviolet radiation

Nitrate reduction by zero valent iron (Fe0) has been gained increasing attention. However, two key issues, that is, the reduction is efficient only at acidic condition; and the major reduction product is ammonium, which limited the application of Fe0 for the nitrate removal. In this study, to address these issues, a novel system of Fe0@Cu0 bimetal with formate/Fe3+ under UV irradiation was developed for the nitrate reduction. The results showed that 100% nitrate removal efficiency and 98% N2 selectivity were achieved at initial pH of 6.47 by a two-step reduction process: (1) the nitrate was firstly reduced to nitrite, while ammonium was negligible in the Fe0@Cu0/formate/UV system; (2) the accumulated nitrite in the effluent from the first-step reduction could be further reduced to nitrogen by CO2•− radical generated by the reaction of formic acid, Fe3+ and UV radiation. Almost no formate residual was found in the effluent due to the action of photo-induced electron transfer of Fe3+. The optimization of operation conditions and the combination mode of Fe0@Cu0 with formate/formic acid, Fe3+ and UV were investigated. The chemical denitrification mechanism of the Fe0@Cu0 particles was proposed.

Chemical Denitrification with Mg0 Particles in Column Systems

The removal of nitrate from aqueous environments through zero-valent metallic elements is an attractive technique that has gained increasing interest in recent years. In comparison to other metallic elements, zero-valent magnesium (ZVM) has numerous beneficial aspects. Nevertheless, the use of Mg0 particles for nitrate reduction in column systems has not been investigated yet. To overcome the lack of research, in the present study, a wide experimental activity was carried out to develop a chemical denitrification process through ZVM in batch column equipment. Several tests were executed to evaluate the effects of recirculation hydraulic velocity, pH, Mg0 amount, N-NO3− initial concentration and temperature on the process performance. The results show that the process efficiency is positively influenced by the recirculation velocity increase. In particular, the optimal condition was detected with a value of 1 m/min. The process pH was identified as the main operating parameter. At pH 3, abatements higher than 86.6% were reached for every initial nitrate concentration tested. In these conditions, nitrogen gas was detected as the main reaction product. The pH increase up to values of 5 and 7 caused a drastic denitrification decline with observed efficiencies below 26%. At pH 3, the ratio (RMN) between Mg0 and initial nitrate amount also plays a key role in the treatment performance. A characteristic value of about RMN = 0.333 gMg0/mgN-NO3− was found with which it is possible to reach the maximum reaction rate. Unexpectedly, the process was negatively affected by the increase in temperature from 20 to 40 °C. At 20 °C, the material showed satisfactory denitrification efficiencies in subsequent reuse cycles. With the optimal RMN ratio, removals up to 90% were detected by reusing the reactive material three times. By means of a kinetic analysis, a mathematical law able to describe the nitrate abatement curves was defined. Moreover, the relation between the observed kinetic constant and the operating parameters was recognized. Finally, the reaction pathways were proposed and the corrosion reaction products formed during the treatment were identified.

Untangling the nitrate removal pathways for a constructed wetland- sponge iron coupled system and the impacts of sponge iron on a wetland ecosystem

Sponge iron (s-Fe0) is a potential alternative electron donor for nitrate reduction. To gain insight into the mechanism of denitrification in a constructed wetland- sponge iron coupled system (CW-Fe0 system), the removal performance and reduction characteristics of nitrate in constructed wetlands (CWs) with and without s-Fe0 application were compared. Results indicated that s-Fe0 intensified the removal of nitrate with a 6h-HRT. The nitrate removal efficiency was improved by 16–76 % with various influent NO3−-N concentrations (10–30 mg L-1) and at a chemical oxygen demand(COD)/N ratio of 5. The rates of chemical denitrification were positively correlated with the dosage of s-Fe0 and negatively correlated with the influent COD concentration. 16S rDNA sequencing revealed that hydrogen-utilizing autotrophic denitrifier of Hydrogenophaga was highly enriched (accounting for 10 % of the total OTUs) only in CW-Fe0 system. The micro-environment created by s-Fe0 was suitable for heterotrophic denitrifiers of Thauera, Tessaracoccus and Simplicispira. The determination of physiological indicators for plants showed that the application of s-Fe0 causes abiotic stress to wetland plants (Canna indica L.). Nevertheless, s-Fe0 can be used as a substrate for CWs, since it allows a high-efficiency removal of nitrate by mediating chemical denitrification and hydrogen-driven autotrophic denitrification.

Nitrate removal to its fate in wetland mesocosm filled with sponge iron: Impact of influent COD/N ratio

Sponge iron (s-Fe0) is a porous metal with the potential to be an electron donor for denitrification. This study aims to evaluate the feasibility of using s-Fe0 as the substrate of wetland mesocosms. Here, wetland mesocosms with the addition of s-Fe0 particles (CW-Fe) and a blank control group (CW-CK) were established. The NO3−-N reduction property and water quality parameters (pH, DO, and ORP) were examined at three COD/N ratios (0, 5, and 10). Results showed that the NO3−-N removal efficiencies were significantly increased by 6.6 to 58.9% in the presence of s-Fe0. NH4+-N was mainly produced by chemical denitrification, and approximately 50% of the NO3− -N was reduced to NH4+-N, at the COD/ratio of 0. An increase of the influent COD/N ratio resulted in lower ehermical denitrification and higher bio-denitrification. Although chemical denitrification mediated by s-Fe0 led to an accumulation of NH4+-N at COD/N ratios of 0 and 5, the TIN removal efficiencies increased by 4.5%–12.4%. Moreover, the effluent pH, DO, and ORP values showed a significant negative correlation with total Fe and Fe (II) (P < 0.01). High-throughput sequencing analysis indicated that Trichococcus (77.2%) was the most abundant microorganism in the CW-Fe mesocosm, while Thauera, Zoogloea, and Herbaspirillum were the primary denitrifying bacteria. The denitrifiers, Simplicispira, Dechloromonas, and Denitratisoma, were the dominant bacteria for CW-CK. This study provides a valuable method and an improved understanding of NO3−-N reduction characteristics of s-Fe0 in a wetland mesocosm.

Experimental Analysis and Modeling of Nitrate Removal through Zero-Valent Magnesium Particles

The pollution of water by nitrates represents an important environmental and health issue. The development of sustainable technologies that are able to efficiently remove this contaminant is a key challenge in the field of wastewater treatment. Chemical denitrification by means of zero-valent metallic elements is an interesting method to reduce the oxidized forms of nitrogen. Compared to other metallic reactants, zero-valent magnesium (ZVM) has many profitable aspects, but its use for nitrate removal has scarcely been investigated. In the present work, several batch tests were conducted to examine the concurrent effects of pH, initial nitrate concentration and Mg0 quantity on process performance. The experimental results proved that at pH 3, for a given initial nitrate concentration, the dose of ZVM largely influences process efficiency. In particular, with a ratio between Mg0 and initial N-NO3− amount (Mg/NNi) of 0.33 g/mg, it is possible to obtain complete denitrification within 30 min. Beyond this ratio, no further improvement of treatment was observed. The experiments allowed us to identify the nitrogen forms produced during the treatment. Nitrogen gas was generally the main reaction product, but the trends of the different compounds (NO3−, NO2−, NH4+ and N2) notably changed in response to the modification of operating parameters. Moreover, the results demonstrated that, in a highly acidic environment, when treating solutions with a low nitrate concentration, process performances are unsatisfactory even when using a high Mg/NNi ratio. By increasing the process pH to 5 and 7, a significant denitrification decline occurred. Furthermore, at these pH levels, the enhancement of nitrate concentration caused a progressive process deterioration. Through detailed analysis of experimental results, reactions kinetics and new mathematical equations, able to describe the trends of different nitrogen forms, have been defined. Moreover, reactions pathways have been proposed. Finally, the characterization of exhausted material allowed us to identify the corrosion products formed during the treatment.

Identifying and Quantifying the Intermediate Processes during Nitrate-Dependent Iron(II) Oxidation.

Microbially driven nitrate-dependent iron (Fe) oxidation (NDFO) in subsurface environments has been intensively studied. However, the extent to which Fe(II) oxidation is biologically catalyzed remains unclear because no neutrophilic iron-oxidizing and nitrate reducing autotroph has been isolated to confirm the existence of an enzymatic pathway. While mixotrophic NDFO bacteria have been isolated, understanding the process is complicated by simultaneous abiotic oxidation due to nitrite produced during denitrification. In this study, the relative contributions of biotic and abiotic processes during NDFO were quantified through the compilation and model-based interpretation of previously published experimental data. The kinetics of chemical denitrification by Fe(II) (chemodenitrification) were assessed, and compelling evidence was found for the importance of organic ligands, specifically exopolymeric substances secreted by bacteria, in enhancing abiotic oxidation of Fe(II). However, nitrite alone could not explain the observed magnitude of Fe(II) oxidation, with 60-75% of overall Fe(II) oxidation attributed to an enzymatic pathway for investigated strains: Acidovorax ( A.) strain BoFeN1, 2AN, A. ebreus strain TPSY, Paracoccus denitrificans Pd 1222, and Pseudogulbenkiania sp. strain 2002. By rigorously quantifying the intermediate processes, this study eliminated the potential for abiotic Fe(II) oxidation to be exclusively responsible for NDFO and verified the key contribution from an additional, biological Fe(II) oxidation process catalyzed by NDFO bacteria.

Effects of Rhizophora mangle leaf litter and seedlings on carbon and nitrogen cycling in salt marshes \u2013 potential consequences of climate-induced mangrove migration

Background and aimsDue to the production of large amounts of tannins and phenolics by Rhizophora mangle, it was hypothesized that the invasion of this mangrove species in salt marshes due to global warming will result in changes in the cycling of carbon and nitrogen.MethodsLeaf litter and/or seedlings of R. mangle were placed into 1-m2 experimental plots in a Distichlis spicata-dominated salt marsh on the Atlantic Coast of central Florida (USA). An additional litter decomposition experiment was conducted in all plots by adding litter bags containing 10 g of dried D. spicata shoot litter. Seedling growth was measured yearly. One and four years after the start of the experiment, soil samples were collected to determine physical and chemical soil conditions, potential nitrification and denitrification activities and abundances of genes that are related to microbial processes in the nitrogen cycle.ResultsGrowth of R. mangle seedlings was stimulated in the presence of R. mangle litter, while decomposition rates of D. spicata litter were lower in plots with R. mangle litter and seedlings. The presence of R. mangle litter and/or seedlings had no significant effect on potential nitrification and denitrification activities and on the abundances of genes.ConclusionThe colonization of R. mangle into D. spicata-dominated salt marshes will affect the carbon cycle, but not necessarily the nitrogen cycle, which is likely due to the pre-existing nitrogen-limited conditions in the salt marsh.

Nitrogen and oxygen isotopes as indicators of pollution sources in the Faxinal Dam watershed, Southern Brazil

Isotopic signatures of δD-H2O, δ18O-H2O, δ15N-NO3−, δ18O-NO3− and δ15NFertilizer isotopes were used in order to evaluate the impact of agricultural inputs (fertilizers and calcium nitrate) and sewage effluents on the water of tributaries of the Faxinal Dam, which supply the city of Caxias do Sul in Southern Brazil. δ2H and δ18O were identified by spectroscopy laser absorption tunable diode-type cavity ring-down spectroscopy, while the isotopic ratios of 15N and 18O in nitrate were determined by isotopic ratio mass spectrometry, applying the chemical denitrification method. The results showed that most of the analyzed samples are compatible with the Global Meteoric Water Line, Local Meteoric Water Line and Carlos Barbosa Wells and Fountains Tendency Line, except for the Fx-07 sample that presented greater similarity to δ18O values for groundwater. The isotopic signatures of δ15N-NO3− versus δ18O-NO3−, in the great majority of the samples, pointed out the influence and the contribution of the fertilizers. In a monitored affluent, the results show the impact of the direct discharge of domestic sewage, while in the sewage treatment plant there is clear evidence of denitrification. This study demonstrated that isotope application of δ15N-NO3− and δ18O-NO3− is efficient tools for identification of N-NO3− of synthetic fertilizers and domestic sewage.

RETRACTED: Nitrate removal by combined heterotrophic and autotrophic denitrification processes: Impact of coexistent ions

In this current study, sawdust and zero-valent iron (Fe0) were used as co-electron donors to evaluate the effects of coexistent ions on the combined heterotrophic and autotrophic denitrification (HAD) processes. The results showed that HCO3− and SO42− drastically enhanced nitrate removal. The promotion effect derived from both biological and chemical process by HCO3− and chemical process by SO42−. However, Ca2+ ions would remarkably increase nitrate removal due to promoting the electron transfer and the metabolic activities of bacteria, whereas the Cu2+ ions inhibited the biological process due to the deleterious effect on bacteria. Meanwhile, Fe2+ and Fe3+ ions exhibited inhibition effect firstly because of their toxicity to bacteria and promotion subsequently due to their enhancement on Fe0 chemical denitrification. Moreover, byproducts such as nitrite, ammonium, dissolved organic carbon (DOC), etc. were also influenced by common ions.

Use of Nanoscale Zero-Valent Iron (NZVI) Particles for Chemical Denitrification under Different Operating Conditions

The nitrate pollution of waters and groundwaters is an important environmental and health concern. An interesting method to remove the oxidized forms of nitrogen from waters and wastewaters is chemical denitrification by means of metallic iron (Fe0). Particularly advantageous is the use of nanoscopic zero-valent iron particles due to the elevated surface area, which allows reaching extremely high reaction rates. In the present paper, the efficiency of nitrate reduction by means of nanoscopic Fe0 has been investigated under several operating conditions. The iron nanoparticles were synthesized by the chemical reduction of ferric ions with sodium borohydride. The effects of Fe0 dosage, initial N–NO3− concentration and pH on chemical denitrification were identified. In particular, the results of the tests carried out showed that it is possible to reach an almost complete nitrate reduction in treating solutions with a nitrate nitrogen concentration higher than 50 mg/L. Moreover, the process performance was satisfactory also under uncontrolled pH. By means of the trends detected during the experiments, the kinetic-type reaction was identified. Furthermore, a relation between the kinetic constant and the process parameters was defined.

The Effect of the Flood in 2002 on Microflora of the Sandstone Blocks of Charles Bridge in Prague

The flood in 2002 affected salinity and microflora of surface layers of the sandstone blocks of the Charles Bridge in Prague. The microbial decomposition of the organic contaminants causes a significant decrease of pH value which resulted in the chemical denitrification and, consequently, also in the microbial denitrification of nitrites and nitrates on the sandstone block surface.