Reduction Of Nitrate In Groundwater Research Articles

Electrical stimulation accelerated phenanthrene biodegradation coupling with nitrate reduction in groundwater

Phenanthrene (PHE) and nitrate co-contamination widely exists in the groundwater. Anaerobic bioremediation of the two suffered from the slow removal rate and limited electron transfer within microbes. Herein electrical stimulation (ES) was proved to stimulate the simultaneous removal of PHE and nitrate anaerobically. High removal of PHE and nitrate (90.94 % and 100 %, respectively) was obtained within 24 h in the ES-bioreactor, two times higher than the control anaerobic bioreactor (32.16 %). ES-bioreactor exhibited a good PHE removal performance within initial PHE ranging from 5 to 25 mg/L. In ES-bioreactor, extracellular polymeric substances increased PHE bioavailability and acted as protective capsules. Nicotinamide adenine dinucleotide (NADH) and cytochrome C (cyt-C) facilitated the extracellular and intracellular electron exchange during PHE biotransformation. ES significantly selected Acetobacterium, PHE-degraders (f_Bacteroidetes_vadin HA17, Limnobacter and Stenotrophomonas) and electrogens (Clostrium_sensu_stricto_13) to participate in PHE decomposition. Acetobacterium decomposed complex organics to acetate, proving accessible substrates for electrogens to maintain an efficient electron flow. Enzymes regulating bacterial chemotaxis, flagellar assembly and carbohydrate metabolism were up-regulated with ES, suggesting the indispensable role of such enzymatic processes in ES-bioreactor. Overall, this work demonstrates ES can promote anaerobic bioremediation of PHE and nitrate in groundwater and, thus, opens up a new bioelectrochemistry application scenario.

Biotransformation of 6:2 Fluorotelomer Thioether Amido Sulfonate in Aqueous Film-Forming Foams under Nitrate-Reducing Conditions.

Despite the prevalence of nitrate reduction in groundwater, the biotransformation of per- and polyfluoroalkyl substances (PFAS) under nitrate-reducing conditions remains mostly unknown compared with aerobic or strong reducing conditions. We constructed microcosms under nitrate-reducing conditions to simulate the biotransformation occurring at groundwater sites impacted by aqueous film-forming foams (AFFFs). We investigated the biotransformation of 6:2 fluorotelomer thioether amido sulfonate (6:2 FtTAoS), a principal PFAS constituent of several AFFF formulations using both quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) and qualitative high-resolution mass spectrometry analyses. Our results reveal that the biotransformation rates of 6:2 FtTAoS under nitrate-reducing conditions were about 10 times slower than under aerobic conditions, but about 2.7 times faster than under sulfate-reducing conditions. Although minimal production of 6:2 fluorotelomer sulfonate and the terminal perfluoroalkyl carboxylate, perfluorohexanoate was observed, fluorotelomer thioether and sulfinyl compounds were identified in the aqueous samples. Evidence for the formation of volatile PFAS was obtained by mass balance analysis using the total oxidizable precursor assay and detection of 6:2 fluorotelomer thiol by gas chromatography-mass spectrometry. Our results underscore the complexity of PFAS biotransformation and the interactions between redox conditions and microbial biotransformation activities, contributing to the better elucidation of PFAS environmental fate and impact.

Numerical groundwater flow and nitrate transport assessment in alluvial aquifer of Varaždin region, NW Croatia

Study regionThe Varaždin alluvial aquifer located in the Drava River valley. Study focusThe study area is characterized by agricultural activity, which raised concerns due to the high nitrate concentration in groundwater. The present study aims to evaluate future nitrate concentrations in groundwater using the numerical groundwater flow and transport modeling. The regional model was generated in GMS software, using the MODFLOW code for steady-state groundwater flow model, and MT3DMS code for nitrate transport model. Advective-dispersive transport was simulated, without a chemical retardation process. The calibrated model was used to investigate the evolution of groundwater nitrate concentrations for the next 20 years under four scenarios: a) current nitrate input; b) zero input from wastewater; c) agricultural input reduced by 50%; d) input from natural vegetation and surface water New hydrological insights for the regionThe scenario analysis demonstrated that reducing the nitrate input from agricultural areas yields a considerable reduction of nitrate in groundwater, while the impact of wastewater is negligible. Neither of the scenarios reached concentrations below threshold value of 50 mg/L for the entire aquifer in the next 20 years. The nitrate concentration in the northern part of the aquifer will remain low, mainly due to the dilution from river. The central part of the aquifer is highly dependent on changing the on-ground nitrate concentration, showing inertia regarding the nitrate attenuation in groundwater.

Are maps of nitrate reduction in groundwater altered by climate and land use changes?

Abstract. Nitrate reduction maps have been used routinely in northern Europe for calculating the efficiency of remediation measures and the impact of climate change on nitrate leaching. These maps are, therefore, valuable tools for policy analysis and mitigation targeting. Nitrate reduction maps are normally based on output from complex hydrological models and, once generated, are largely assumed constant in time. However, the distribution, magnitude, and efficiency of nitrate reduction cannot necessarily be considered stationary during changing climate and land use as flow paths, nitrate release timing, and their interaction may shift. This study investigates the potential improvement of using transient nitrate reduction maps, compared to a constant nitrate reduction map that is assumed during land use and climate change, both for nitrate loads and the spatial variation in reduction. For this purpose, a crop and soil model (DAISY) was set up to provide nitrate input to a distributed hydrological model (MIKE SHE) for an agricultural catchment in Funen, Denmark. Nitrate reduction maps based on an observed dataset of land use and climate were generated and compared to nitrate reduction maps generated for all combinations of four potential land use change scenarios and four future climate model projections. Nitrate reduction maps were found to be more sensitive to changes in climate, leading to a reduction map change of up to 10 %, while land use changes effects were minor. The study, however, also showed that the reduction maps are products of a range of complex interactions between water fluxes, nitrate use, and timing. What is also important to note is that the choices made for future scenarios, model setup, and assumptions may affect the resulting span in the reduction capability. To account for this uncertainty, multiple approaches, assumptions, and models could be applied for the same area. However, as these models are very time consuming, this is not always a feasible approach in practice. An uncertainty of the order of 10 % on the reduction map may have major impacts on practical water management. It is, therefore, important to acknowledge if such errors are deemed acceptable in relation to the purpose and context of specific water management situations.

Simulation of nitrate reduction in groundwater – An upscaling approach from small catchments to the Baltic Sea basin

Simulation of nitrate reduction in groundwater - An upscaling approach from small catchments to the Baltic Sea basin

Review and assessment of nitrate reduction in groundwater in the Baltic Sea Basin

Study regionSix countries within the Baltic Sea Basin: Denmark, Sweden, Finland, Lithuania, Poland and Germany Study focusDuring transport from the field to the sea nitrogen undergoes natural reduction, but with large spatial variations. Mapping this variation would allow more optimal regulation strategies, by imposing most restrictions in areas with low natural reduction. In the present study, a map for spatially variable nitrate reduction in groundwater is developed covering six countries in the Baltic Sea Basin. In contrary to previous studies within the Baltic Sea Basin, the present study provides an independent estimate of the nitrogen reduction in groundwater, based on review of national data and studies. Depending on availability, different approaches were used for the countries ranging from national modelling to expert judgement. Through a joint workshop the assessments were, to the extent possible, harmonised. New hydrological insights for the regionThe review revealed large variations in the hydro-geochemical conditions important for transport and degradation of nitrogen in groundwater. This includes the hydrogeology, the reducing conditions of the subsurface, and the fraction of water transported by drainage systems bypassing the reducing subsurface environments. Significant variations in groundwater reduction between the countries and within most of the countries were thus found, indicating that strategies for nitrogen regulation and mitigation measures may be optimised, if variation in the natural reduction of nitrate is considered.

Nitrate reduction in groundwater and isotopic investigation of denitrification in integrated tree-grass riparian buffers in Taihu Lake watershed, eastern China

Riparian buffer strips can play an important role in reducing nitrate (NO₃⁻) contamination of groundwater from agricultural fields to the adjacent inland water system. Our objective was to investigate the temporal and spatial variation of NO₃⁻ concentrations and delta nitrogen (N) 15 (δ¹⁵N)-NO₃⁻ in groundwater at the integrated poplar-grass buffer strips with three different tree planting densities, and to assess in situ denitrification rate in riparian soils in Taihu Lake watershed of China under a subtropical climate. Nitrate concentrations and δ¹⁵N-NO₃⁻ values in groundwater were monitored along transects of piezometers installed from field edge to ditches at 5 m (16.4 ft) spacing in the integrated poplar-grass buffers. We found that groundwater NO₃⁻ concentrations declined by 67.5% to 88% while the δ¹⁵N-NO₃⁻ values enriched along the subsurface flow paths within the 15 m (49.2 ft) poplar-grass riparian buffers in Taihu Lake watershed throughout the year. Nitrate was removed more efficiently in spring and summer than in autumn and winter owing to vegetation uptake in the growing season combined with high denitrification rates due to higher groundwater table level and soil temperature. The isotopic enrichment factors for NO₃⁻ retention varied seasonally, with the highest absolute value in winter (−8.95‰) and lowest in summer (−4.53‰). The difference between poplar planting densities in buffers did not significantly affect their capacity to reduce groundwater NO₃⁻. Riparian soil denitrification rate was highly seasonal and significantly different in the different soil depths. Our results indicate that the upper soil layer (10 to 35 cm [3.9 to 13.8 in]) in the riparian zones were hot spots for denitrification, and denitrification was strongly influenced by hydrological conditions and soil temperature in the integrated poplar-grass buffers in the Taihu Lake watershed.

Geobacter Sulfurreducens Electrodes for Nitrate Reduction in Ground Water

Nitrate accumulation in ground water is a major global problem, especially in farming communities where fertilizers are used. A nitrate reducing microbial fuel cell fed by hydrogen from a PEM-based water electrolysis cell has been proposed as a low cost alternative to current water treatment methods. To this end, Geobacter sulfurreducens anodes are electrochemically evaluated for their ability to reduce nitrate. G. sulfurreducens was subcultured in a nitrate-based media, then cast on 1 cm2 Toray paper electrodes and immobilized with 4% pectin cross-linked with magnesium chloride. Cyclic voltammograms in Figure 1 demonstrate bioelectrocatalytic nitrate reduction by the G. sulfurreducens anode. Preliminary data gathered from the microbial fuel cell system built by Proton OnSite shows a decrease in nitrate correlating with an increase in ammonia and nitrite with operation. Figure 1

Reduction of nitrate in groundwater by hematite supported bimetallic catalyst

In this study, nitrate reduction of real groundwater sample by 2.2%Cu-1.6%Pd-hematite catalyst was evaluated at different nitrate concentrations, catalyst concentrations, and recycling. Results show that the nitrate reduction is improved by increasing the catalyst concentration. Specific nitrate removal by 2.2%Cu-1.6%Pd-hematite increased linearly with the increase of nitrate concentration showing that the catalyst possesses significantly higher reduction capacity. More than 95% nitrate reduction was observed over five recycles by 2.2%Cu-1.6%Pd-hematite with ~56% nitrogen selectivity in all recycling batches. The results from this study indicate that stable reduction of nitrate in groundwater can be achieved by 2.2%Cu- 1.6%Pd-hematite over the wide range of initial nitrate inputs.

Reduction of Nitrate in Groundwater by Fe(0)/Magnetite Nanoparticles Entrapped in Ca-Alginate Beads

Calcium alginate beads entrapping a mixture of Fe(0) and nanosized magnetite (NMT) were prepared and evaluated for their capability to reduce nitrate in groundwater. Microscopic and spectroscopic analyses of the beads revealed that clusters of Fe(0)/NMT were entirely embedded in alginate polymer matrix containing a large number of carboxylic and hydroxyl functional groups. The extent of nitrate reduction increased with increasing content of Fe(0) and NMT in the beads, but there was a critical NMT mass limit relative to Fe(0) mass where no further increase in nitrate reduction occurred. The beads showed slower nitrate reduction kinetics than bare Fe(0)/NMT but had comparable capacity in overall nitrate removal. Nitrate reduction increased proportionally with an increase in bead dosage to give a maximum removal of 94.5 % at 37.5 g L−1 in 48 h. Nitrate reduction with 50 g L−1 beads achieved completion of two reduction cycles in 72 h to reduce 2.19 mM nitrate to less than 0.71 mM (10 mg-N L−1) in each cycle. The overall results demonstrated that the beads developed in this study have a potential utility in remediation of nitrate in groundwater.

The role of magnetite nanoparticles in the reduction of nitrate in groundwater by zero-valent iron

Magnetite nanoparticles were used as an additive material in a zero-valent iron (Fe(0)) reaction to reduce nitrate in groundwater and its effects on nitrate removal were investigated. The addition of nano-sized magnetite (NMT) to Fe(0) reactor markedly increased nitrate reduction, with the rate proportionally increasing with NMT loading. Field emission scanning electron microscopy analysis revealed that NMT aggregates were evenly distributed and attached on the Fe(0) surface due to their magnetic properties. The rate enhancement effect of NMT is presumed to arise from its role as a corrosion promoter for Fe(0) corrosion as well as an electron mediator that facilitated electron transport from Fe(0) to adsorbed nitrate. Nitrate reduction by Fe(0) in the presence of NMT proceeded much faster in groundwater (GW) than in de-ionized water. The enhanced reduction of nitrate in GW was attributed to the adsorption or formation of surface complex by the cationic components in GW, i.e., Ca2+ and Mg2+, in the Fe(0)–H2O interface that promoted electrostatic attraction of nitrate to the reaction sites. Moreover, the addition of NMT imparted superior longevity to Fe(0), enabling completion of four nitrate reduction cycles, which otherwise would have been inactivated during the first cycle without an addition of NMT. The results demonstrate the potential applicability of a Fe(0)/NMT system in the treatment of nitrate-contaminated GW.

Inhibitory effect of veterinary antibiotics on denitrification in groundwater: a microcosm approach.

Veterinary antibiotics in groundwater may affect natural microbial denitrification process. A microcosm study was conducted to evaluate the influence of sulfamethazine and chlortetracycline at different concentrations (0, 0.01, 0.1, and 1.0 mg/L) on nitrate reduction in groundwater under denitrifying condition. Decrease in nitrate removal and nitrite production was observed with the antibiotics. Maximum inhibition of nitrate removal was observed after seven days of incubation with 0.01 mg/L sulfamethazine (17.0%) and 1.0 mg/L chlortetracycline (15.4%). The nitrite production was inhibited with 1.0 mg/L sulfamethazine to 82.0% and chlortetracycline to 31.1%. The initial/final nitrate concentrations indicated that 0.01 mg/L sulfamethazine and 1.0 mg/L chlortetracycline were most effective in inhibiting activity of denitrifying bacteria in groundwater. After 12 days of incubation, the sulfamethazine biodegradation was observed whereas chlortetracycline was persistent. Sulfamethazine and chlortetracycline in groundwater could inhibit the growth and capability of naturally occurring denitrifying bacteria, thereby threatening nitrate pollution in groundwater.

The effect of granular ferric hydroxide amendment on the reduction of nitrate in groundwater by zero-valent iron

The feasibility of using granular ferric hydroxide (GFH) with zero-valent iron (Fe(0)) for its potential utility in enhancing nitrate reduction was investigated. The addition of 10gL−1 GFH to 25gL−1 Fe(0) significantly enhanced nitrate removal, resulting in 93% removal of 52.2mg-NL−1 in 36-h as compared to 23% removal with Fe(0) alone. Surface analyses of the reacted Fe(0)/GFH revealed the presence of magnetite on the Fe(0) surface, which probably served as an electron mediator for nitrate reduction. Addition of GFH to Fe(0) also resulted in lower solution pH compared to Fe(0). The rate enhancing effect of GFH on nitrate reduction was attributed to the combined effects of magnetite formation and pH buffering by GFH. GFH amendment (100gL−1) significantly increased reduction capacity and longevity of Fe(0) to complete several nitrate reduction cycles before inactivation, giving a total nitrate removal of 205mg-NL−1, while unamended Fe(0) gave only 20mg-NL−1 before inactivation during the first reduction cycle. The overall result demonstrated the potential utility of Fe(0)/GFH system that may be developed into a viable technology for removal of nitrate from groundwater.

Influence of Operating Conditions on Electrochemical Reduction of Nitrate in Groundwater

The influences of current density, initial pH, cation and anion concentrations, and the coexistence of Ca2+ and HCO3- on the efficiency of electrochemical nitrate reduction by a copper cathode and Ti/IrO2 anode in an undivided cell were studied. In the presence of 5 mM of sodium chloride (NaCl), the nitrate-nitrogen concentration decreased from 3.57 to 0.69 mM in 120 minutes, and no ammonia or nitrite byproducts were detected. The nitrate reduction rate increased as the current density increased. The electrochemical method performed well at an initial pH range of 3.0 to 11.0. The rate of nitrate reduction increased as concentrations of Na+, K+, and Ca2+ increased. The anion of the supporting electrolyte decreased the rate of reduction in the order Cl- > HCO3(2-) = CO3(2-) > SO4(2-) at both 5 mM and 10 mM of anion. The coexistence of Ca2+ and HCO3- ions could inhibit nitrate reduction. The concentration of nitrate-nitrogen in polluted groundwater decreased from 2.80 to 0.31 mM after electrolysis for 120 minutes.

Simulation of Nitrate Contamination in Groundwater Caused by Livestock Industry (Case Study: Rey)

With the economic development of many communities and the growing human population more food is needed. The livestock industry is one of the fastest growing industries in developing countries. The development of the livestock industry and the increase of livestock waste happens as a result of the growth in food production. The wastes are stored in a way that contamination of groundwater and surface water pollution in the environment has a significant impact on environment. This study analyses the environmental impact of livestock facilities and nitrate leaching in groundwater. After site sampling and libratory analysis, calibration of a simulation model with observed data was done to show nitrate contamination in “Rey” groundwater. The movement of nitrate into soil and groundwater was simulated by LEACHN. By defining various scenarios and performing sensitivity analysis, we examined precisely the factors affecting ground water contaminations. Along together with the analysis of different scenarios and comparing them with the measured values, seasonal rainfall conditions have greatest impact on the rate of recharge of nitrate to groundwater. Therefore soil with low rainfall shows 44% reduction of nitrate leakage at a depth of 30 cm of soil conditions. Finally, the modeling results and graphs from different scenarios for purpose of nitrate reduction in groundwater were presented. The good match between model results and observed data showed that the model is calibrated to this area and can be used for prediction purposes and further studies.

Ethanol Addition for Enhancing Denitrification at the Uranium Mill Tailing Site in Monument Valley, AZ

Past mining and processing of uranium ore at a former uranium mining site near Monument Valley, AZ has resulted in nitrate contamination of groundwater. The objective of this study was to investigate the potential of ethanol addition for enhancing the reduction of nitrate in groundwater. The results of two pilot-scale field tests showed that the concentration of nitrate decreased, while the concentration of nitrous oxide (a product of denitrification) increased. In addition, changes in aqueous concentrations of sulfate, iron, and manganese indicated that the ethanol amendment caused a change in prevailing redox conditions. The results of compound-specific stable isotope analysis for nitrate–nitrogen indicated that the nitrate concentration reductions were biologically mediated. Denitrification rate coefficients estimated for the pilot tests were approximately 50 times larger than resident-condition (non-enhanced) values obtained from prior characterization studies conducted at the site. The nitrate concentrations in the injection zone have remained at levels three orders of magnitude below the initial values for many months, indicating that the ethanol amendments had a long-term impact on the local subsurface environment.

Enhanced Reduction of Nitrate in Groundwater by Zero-valent Iron with Activated Red Mud

ABSTRACT The objective of this study was to examine the feasibility of using red mud for enhancing the nitrate removal in groundwater by zero-valent iron (Fe(0)). Batch experiments were performed with both untreated and acid-treated red mud in conjunction with Fe(0) system to treat an actual groundwater sample containing 2.52 mM nitrate. Addition of untreated red mud into aqueous solution containing Fe(0) abruptly raised pH value to highly alkaline (11–12.5), leading to inhibition of nitrate reduction. On the other hand, the addition of acid-treated red mud significantly increased nitrate removal, resulting in 164% increase in the 1st-order rate constant (kobs) as compared to Fe(0) alone system when the red mud was dosed at 5 g/L to the solution containing 50 g/L Fe(0). Nitrate removal increased with increasing dose of acid-treated red mud, showing nearly 100% increase in removal efficiency when the dose was increased from 0 to 0.5 g in 20 mL solutions containing 0.2 g Fe(0). The enhancing effect of activated red mud was assumed to be the result from scavenging of the reaction precipitate, thereby minimizing passivation of Fe(0) surfaces, and formation of additional reactive sites (e.g. green rust) for nitrate reduction. The reactions of both untreated and acid-treated red mud in the absence of Fe(0) showed little removal of nitrate, indicating red mud alone lacks reduction or sorption capability for nitrate. Results from this study demonstrated that the potential utility of Fe(0)/activated red mud system may be developed into a viable technology for the removal of nitrate from groundwater.

The role of clay minerals in the reduction of nitrate in groundwater by zero-valent iron

Bench-scale batch experiments were performed to investigate the feasibility of using different types of clay minerals (bentonite, fuller’s earth, and biotite) with zero-valent iron for their potential utility in enhancing nitrate reduction and ammonium control. Kinetics experiments performed with deionized water (DW) and groundwater (GW) revealed nitrate reduction by Fe(0) proceeded at significantly faster rate in GW than in DW, and such a difference was attributed to the formation of green rust in GW. The amendment of the minerals at the dose of 25 g L −1 in Fe(0) reaction in GW resulted in approximately 41%, 43%, and 33% more removal of nitrate in 64 h reaction for bentonite, fuller’s earth, and biotite, respectively, compared to Fe(0) alone reaction. The presumed role of the minerals in the rate enhancement was to provide sites for the formation of surface bound green rust. Bentonite and fuller’s earth also effectively removed ammonium produced from nitrate reduction by adsorption, with the removal efficiencies significantly increased with the increase in mineral dose above 5:1 Fe(0) to mineral mass ratio. Such a removal of ammonium was not observed for biotite, presumably due to its lack of swelling property. Equilibrium adsorption experiments indicated bentonite and fuller’s earth had maximum ammonium adsorption capacity of 5.6 and 2.1 mg g −1, respectively.

Selective Decomposition of Aqueous Nitrate into Nitrogen Using Iron Deposited Bimetals

In the case of the reduction of nitrate in groundwater, the problem is how to convert nitrate [N(+V)] selectively to nontoxic dinitrogen [N(O)] and not to completely reduced ammonia [N(-III)]. Unfortunately, near 100% of the total nitrogen in nitrate is reductively converted to ammonia using naked zerovalent iron (ZVI) thus far reported. In this study, deposition of noble metals (Pt, Pd, and Au) and Cu on iron surface to offer favorable pathways for nitrate reduction was fabricated using either the complete mixing orthe successive method with spontaneous redox reactions. The prepared samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy/energy disperse X-ray spectroscopy, and electrochemical analysis. The formation of N2 from the reduction of nitrate was confirmed by residual gas analyzer coupled to a high vacuum system. Based on the experimental results, the ZVI deposited Pd and Cu closely is suggested to promote the abstraction of oxygen from NOx by adsorbed atomic hydrogen on the Cu surface, and enhance N2 formation on the Pd surface. An optimum N2 selectivity of approximately 30% obtained in the alkaline solution containing nitrate using 0.3 wt.% Pd-0.5 wt% Cu/Fe is evident. For groundwater treatment, iron deposited Pd and Cu could facilitate the development of a process requiring neither a massive addition of chemicals nor complex equipment.

Preparation of Nanoiron by Water-in-Oil (W/O) Microemulsion for Reduction of Nitrate in Groundwater

Nanometer-sized iron particles with monodispersity and narrow size distribution were synthesized by modi-fied microemulsion system using environment-friendly non-ionic surfactants Span 80 and Tween 60 as mixed surfactants. The synthesized iron nanoparticles were characterized by using powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the synthesized particles were mainly composed of α-Fe with an average diameter of 80-90 nm. The chemical activity of the obtained iron nanoparticles was evaluated by the denitrification of nitrate in water. On neutral condition, complete denitri-fication of nitrate was achieved by freshly synthesized nanoiron within 30 min. Ammonia was the main product, with good material balance at the end of the reaction. Two possible reaction pathways for nitrate reduction by nanoiron have been proposed in this study.