Excess Nitrate Research Articles

Efficiency of Reductive Soil Disinfestation Affected by Soil Water Content and Organic Amendment Rate

Reductive Soil Disinfestation (RSD) is a good method which can restore degraded greenhouse soil and effectively inactivate soil-borne pathogens. However, the approach needs to be optimized in order to facilitate its practical application in various regions. In the present work, we investigated the effect of soil water content (60% water holding capacity (WHC), 100% WHC and continuous flooding) and maize straw application rates (0, 5, 10, and 20 g kg−1 soil) on the improvement of soil properties and suppression of soil-borne pathogens (Fusarium oxysporum, Pythium and Phytophthora). The results showed that increasing the soil water content and maize straw application rate accelerated the removal of excess sulfate and nitrate in the soil and elevated the soil pH. Elevating the water content and maize straw application rate also produced much more organic acids, which could strongly inhibit soil-borne pathogens. Soil properties were improved significantly after RSD treatment with a maize straw amendment rate of more than 5 g kg−1, regardless of the water content. However, RSD treatments with 60% WHC could not effectively inactivate soil-borne pathogens and even stimulated their growth by increasing the maize application rate. RSD treatments of both 100% WHC and continuous flooding could inactivate soil-borne pathogens and increase the pathogens mortality indicated by cultural cells relatively effectively. The inhibited pathogens were significantly increased with the increasing maize application rate from 5 g kg−1 to 10 g kg−1, but were not further increased from 10 g kg−1 to 20 g kg−1. A further increased mortality of F. oxysporum, indicated by gene copies, was also observed when the soil water content and maize straw application rate were increased. Therefore, RSD treatment with 60% WHC could improve soil properties significantly, whereas irrigation with 100% WHC or continuous flooding was a necessity for effective soil-borne pathogens suppression. Holding 100% WHC and applicating maize straw at 10 g kg−1 soil were optimum conditions for RSD field operation to restore degraded greenhouse soil.

Assessment of Potential Nitrite Safety Risk of Leafy Vegetables after Domestic Cooking.

Improper cultivation can easily cause excessive nitrate accumulation in leafy vegetables, and the cooking processes used to prepare them can upset their nitrate/antioxidant balance, affecting their potential nitrite safety risk (PNSR). We investigated the impacts stir-frying, steaming, microwaving, and boiling on the nitrate, nitrite, and antioxidant capacity in water spinach and cabbage, and observed the impacts of storage duration on the PNSR. The antioxidant/in vivo nitrite ratio (A/N) was used to evaluate the nitrite risks in the cooked vegetables. Boiling achieved the highest A/N ratio (1.57) for water spinach, reducing the nitrate content by 25% without significantly affecting the antioxidant capacity. Stir-frying achieved the highest A/N ratio (6.55) for cabbage, increasing the antioxidant capacity by 140% without significantly affecting the nitrate content. Furthermore, it was found that the storage periods for boiled water spinach and stir-fried cabbage should not exceed 12 h and 24 h, respectively. Appropriate cooking methods and limited storage times are thus required for leafy vegetable to prevent adverse health effects.

Overexpression of tomato thioredoxin h (SlTrxh) enhances excess nitrate stress tolerance in transgenic tobacco interacting with SlPrx protein

The thioredoxin (Trx) system plays a vital function in cellular antioxidative defense. However, little is known about Trx in tomato under excess nitrate. In this study, we isolated the tomato gene encoding h-type Trx gene (SlTrxh). The mRNA transcript of SlTrxh in roots and leaves of tomato was induced incrementally under excess nitrate for 24 h. Subcellular localization showed that SlTrxh might localize in the cytoplasm, nucleus and plasma membrane. Enzymatic activity characterization revealed that SlTrxh protein possesses the disulfide reductase function and Cysteine (Cys) 54 is important for its activity. Overexpressing SlTrxh in tobacco resulted in increasing seed germination rate, root length and decreasing H2O2 and O2− accumulation, compared with the wild type (WT) tobacco under nitrate stress. While overexpressing SlTrxhC54S (Cysteine 54 mutated to Serine) in tobacco showed decreased germination rate and root length compared with the WT after nitrate treatment. After nitrate stress treatment, SlTrxh overexpressing transgenic tobacco plants have lower malonaldehyde (MDA), H2O2 contents and Reactive Oxygen Species (ROS) accumulation, and higher mRNA transcript level of NtP5CS, NtDREB2, higher ratio of ASA/DHA and GSH/GSSG, higher activities of ascorbate peroxidase and NADP thioredoxin reductase. Besides, SlTrxh overexpressing plants showed higher tolerance to Methyl Viologen (MV) in the seed germination and seedling stage. The yeast two-hybrid, pull-down, Co-immunoprecipitation and Bimolecular luciferase complementation assay confirmed that SlTrxh physically interacted with tomato peroxiredoxin (SlPrx). These results suggest that SlTrxh contributes to maintaining ROS homeostasis under excess nitrate stress interacting with SlPrx and Cys54 is important for its enzyme activity.

How bacteria remediate soil nitrate for sustainable crop production

Soil secondary salinization has attracted increasing public concern in greenhouse cultivation, and the dominant salt ion is nitrate. In this study, the Bacillus megaterium NCT-2 microbial agent was tested to remediate nitrate for sustainable production of agriculture. To understand the mechanism of microbial agents on remediating nitrate and their contribution to sustainable production, a laboratory 15N tracing study was carried out to quantify the simultaneously operating gross N transformation rates and associated them with copy numbers of key genes in the nitrogen metabolism. The NCT-2 strain showed strong nitrate assimilation (99%) and weak dissimilatory nitrate reduction to ammonium (DNRA) (1%). Mineralization of recalcitrant organic N dominated internal NH4+ production. Ammonium immobilization by NCT-2 strain occurred mainly into the recalcitrant organic N pool (60–67%). No nitrification activity (neither heterotrophic or autotrophic) was detectable in NCT-2 strain. Also the strain did not denitrify and was not involved in nitrous oxide emission. The study showed that NCT-2 strain is able to effectively remediate excessive nitrate in secondary salinized soil without causing any additional N losses, which is extremely conducive to sustainable production of agriculture. With this study the theoretical basis is provided to further develop suitable management tools in using Bacillus megaterium NCT-2 to increase the nitrogen use efficiency in greenhouse cultivation.

Prediction of Nitrate and Phosphorus Concentrations Using Machine Learning Algorithms in Watersheds with Different Landuse

Rapid industrialization and population growth have elevated the concerns over water quality. Excessive nitrates and phosphates in the water system have an adverse effect on the aquatic ecosystem. In recent years, machine learning (ML) algorithms have been extensively employed to estimate water quality over traditional methods. In this study, the performance of nine different ML algorithms is evaluated to predict nitrate and phosphorus concentration for five different watersheds with different land-use practices. The land-use distribution affects the model performance for all methods. In urban watersheds, the regular and predictable nature of nitrate concentration from wastewater treatment plants results in more accurate estimates. For the nitrate prediction, ANN outperforms other ML models for the urban and agricultural watersheds, while RT-BO performs well for the forested Grand watershed. For the total phosphorus prediction, ensemble-BO and M-SVM outperform other ML models for the agricultural and forested watershed, while the ANN performs better than other ML models for the urban Cuyahoga watershed. In predicting phosphorus concentration, the model predictability is better for agricultural and forested watersheds. Regarding consistency, Bayesian optimized RT, ensemble, and GPR consistently yielded good performance for all watersheds. The methodology and results outlined in this study will assist policymakers in accurately predicting nitrate and phosphorus concentration which will be instrumental in drafting a proper plan to deal with the problem of water pollution.

Organic phosphor and lead fluoride based luminescent hybrids

Powder hybrid materials based on the organic phosphor 8-hydroxyquinolate lithium and the inorganic matrix PbF2 have been synthesized. Powder hybrid materials were obtained by co-precipitation from aqueous-alcoholic solutions with ammonium fluoride under various conditions – different concentrations of the organic component, precursor solutions, the order of mixing the reagents: direct precipitation and reverse precipitation, providing a local excess of nitrate or fluorinating agent during the synthesis. Hybrid materials are single-phase powders, whose crystal structure corresponds to the rhombic phase of α-PbF2. All obtained hybrid materials showed effective broadband luminescence in the region of 390–700 nm. The shift of the photoluminescence bands to longer wavelengths relative to the initial Liq is observed, which is characteristic of lead luminescent complexes, which suggests the formation of new optical cents associated with Pbq2 or [PbqF]2, for all obtained hybrid materials. The formation of optical centers occurs as a result of an exchange reaction and the formation of new bonds between lead and organic ligands. Moreover, an increase in the concentration of the initial Pb(NO3)2 solution promotes a more complete course of the exchange reaction (up to 88%). During reverse deposition, a large fraction of Liq is captured by the crystallizing lead fluoride molecularly, and the completeness of the exchange reaction is generally lower than during direct deposition. The photoluminescence intensity during reverse deposition is 3 to 10 times higher than during direct deposition for different concentrations of reagents. The most intense luminescence is provided by the conditions of reverse precipitation with ammonium fluoride of a solution of lead nitrate with a concentration of 0.8 M and a Liq content of 1 wt.%.This research was funded by the Russian Science Foundation, Grant No. 19-79-10003.

Electrocatalytic Nitrate Reduction for Denitrifying Wastewater

Removing excessive nitrate (NO3 −) from wastewater has increasingly become an important research topic in light of the growing concerns over the related environmental problems and health issues. In particular, catalytic/electrocatalytic approaches are attractive for NO3 − removal, because NO3 − from wastewater can be converted to N2 and released back to the atmosphere using renewable H2 or electricity, closing the loop of the global N cycle. However, achieving high product selectivity towards the desirable N2 has proven challenging in the direct NO3 −-to-N2 reaction. In this presentation, we will report our finding on unique and ultra-high electrochemical NO3 −-to-NO2 −activity on an oxide-derived silver electrode (OD-Ag). Up to 98% selectivity and 95% faradaic efficiency of NO2 − were observed and maintained under a wide potential window. Benefiting from overcoming the rate-determining barrier of NO3 −-to-NO2 −during nitrate reduction, further reduction of accumulated NO2 − to NH4 + can be well regulated by the cathodic potential on OD-Ag to achieve a faradaic efficiency of 89%. These indicated the potential controllable pathway to the key nitrate reduction products (NO2 −or NH4 +) on OD-Ag. DFT computations provided insights into the unique NO2 −selectivity on Ag electrodes compared with Cu, showing the critical role of a proton-assisted mechanism. Based on the ultra-high NO3 −-to-NO2 −activity on OD-Ag, we designed a novel electrocatalytic-catalytic combined process for denitrifying real-world NO3 −-containing agricultural wastewater, leading to 95+% of NO3 − conversion to N2 with minimal NOX gases. In addition to the wastewater treatment process to N2 and electrochemical synthesis of NH3, NO2 − derived from electrocatalytic NO3 − conversion can serve as a reactive platform for distributed production of various nitrogen products. Our new research progress along this direction will be briefly presented.

Changes in soil bacterial and fungal communities in response to Bacillus megaterium NCT-2 inoculation in secondary salinized soil.

BackgroundSecondary salinized soil in greenhouses often contains excess nitrate. Inoculation of Bacillus megaterium NCT-2 with nitrate assimilation ability represents an attractive approach for soil remediation. However, the effects of NCT-2 on the structure and function of soil microbial communities have not been explored.MethodsGreenhouse experiments were carried out to investigate changes in soil properties, Brassica chinensis L. growth, bacterial, and fungal community structure and function in response to NCT-2 inoculation.ResultsThe NCT-2 inoculant significantly reduced the nitrate content in B. chinensis and inhibited the rebound of soil nitrate in the later stage. The shifts of bacterial community structure and function by NCT-2 was negligible, and a greater disturbance of soil fungal community structure and function was observed, for example the strong inhibitory effect on ectomycorrhizal fungi. These results indicated that the NCT-2 inoculant likely achieved the remediation effect in secondary salinized soil by shifting fungal community. The present findings add to the current understanding of microbial interactions in response to bacterial inoculation and can be of great significance for the application of NCT-2 inoculants in secondary salinized soil remediation.

Modeling transport, fate, and removal kinetics of nitrate and orthophosphate using recycled adsorbents for high and low-flow stormwater runoff treatment

Excessive nitrate and orthophosphate carried by the stormwater runoff potentially lead to eutrophication in surface water bodies. Various green infrastructures are used that commonly consider the biological treatment of nutrients from the runoff. Due to the leaching and clogging complexities in biological mechanisms, the selection of high-flow, eco-friendly, and recycled adsorbents has been advocated to promote the physiochemical treatment of nutrients as an alternative. In this study, column experiments were conducted to investigate the transport, fate, adsorption equilibria, and reaction kinetics of nitrate (NO3–N) and orthophosphate (PO4–P) onto three recycled adsorbents - recycled concrete aggregate (RCA), recycled crushed glass (RCG), rice husks (RH), and a layered media (LM), under high and low-flow conditions. The non-reactive solute transport in columns was investigated through the bromide tracer test. The HYDRUS-1D model was used to estimate adsorption coefficients and reaction kinetics of pollutants in unsaturated media columns. Our results indicated the maximum superficial pore velocity (v = 4.40 cm/s) and dispersion (α = 2.50 cm) in RCA at the low-flow condition. Overall, NO3–N removal at the exhaustion was low in all columns, ranging between 1 and 25%. Conversely, orthophosphate removal was significant (p < 0.05) in RCA (≤94%) under low flow conditions with increased reaction kinetics (kr,d = 3.45 min−1, kr,s = 0.55 min−1) and enhanced adsorption capacity at saturation (qmax = 1.87E+05–2.33E+05 mg/kg). In conclusion, the dissolved-phase reaction kinetics (kr,d) played a significant role apart from the physisorption for the satisfactory removal of orthophosphate in RCA.

Gibberellic acids promote growth and exopolysaccharide production in Tetraselmis suecica under reciprocal nitrogen concentration: an assessment on antioxidant properties and nutrient removal efficacy of immobilized iron-magnetic nanoparticles.

The present study was aimed to assess the effect of gibberellic acids to enhance the growth, biomass, pigment, and exopolysaccharides production in Tetraselmis suecica under reciprocal nitrogen concentrations. For this study, the seven types of experimental media (N-P, NL-P/2GA3, N0-P/2GA3, NL-P/4GA3, N0-P/4GA3, NL-P/6GA3, and N0-P/6GA3) were prepared with the addition of gibberellic acids under various nitrogen concentrations. The experiment lasted for 15days and the cell density, biomass, chlorophyll 'a', and exopolysaccharides (EPS) concentration of T. suecica were estimated for every 3days. Then the EPS was subjected to the analyses of chemical (carbohydrate, protein, sulfate, and uronic acid), and antioxidant activity. In addition, nutrient removal efficiency was evaluated using different concentration of EPS. The highest DPPH (2,2-diphenyl-1-picrylhydrazyl) (86.7 ± 0.95%) and hydroxyl radical activity (85.7 ± 2.48%) were observed at the EPS concentrations 2.5 and 1.2mg/mL, respectively. The immobilized magnetic Fe3O4-EPS (ferric oxide-exopolysaccharides) nanoparticles (5.0 and 10.0g/L) have efficiently removed the excessive phosphate (89.5 ± 1.65%) and nitrate (73.5 ± 1.72%) from the Litopenaeus vannamei cultured wastewater. Thus, the application of gibberellic acids combined with limited nitrogen concentration could produce higher EPS that could exhibit excellent antioxidant activity, and nutrient removal efficacy in the form of Fe3O4-EPS magnetic nanoparticles.

Application of Anammox-Based Processes in Urban WWTPs: Are We on the Right Track?

The application of partial nitritation and anammox processes (PN/A) to remove nitrogen can improve the energy efficiency of wastewater treatment plants (WWTPs) as well as diminish their operational costs. However, there are still several limitations that are preventing the widespread application of PN/A processes in urban WWTPs such as: (a) the loss of performance stability of the PN/A units operated at the sludge line, when the sludge is thermally pretreated to increase biogas production; (b) the proliferation of nitrite-oxidizing bacteria (NOB) in the mainstream; and (c) the maintenance of a suitable effluent quality in the mainstream. In this work, different operational strategies to overcome these limitations were modelled and analyzed. In WWTPs whose sludge is thermically hydrolyzed, the implementation of an anerobic treatment before the PN/A unit is the best alternative, from an economic point of view, to maintain the stable performance of this unit. In order to apply the PN/A process in the mainstream, the growth of ammonia-oxidizing bacteria (AOB) should be promoted in the sludge line by supplying extra sludge to the anaerobic digesters. The AOB generated would be applied to the water line to partially oxidize ammonia, and the anammox process would then be carried out. Excess nitrate generated by anammox bacteria and/or NOB can be removed by recycling a fraction of the WWTP effluent to the biological reactor to promote its denitrification.

Coupling anammox with heterotrophic denitrification for enhanced nitrogen removal: A review

Anammox has been recognized as the current most cost-effective nitrogen removal process. However, the issue of excess nitrate residue from its effluent remains to be addressed in order to meet the increasingly stringent discharge standard. Other than nitrogen, certain types of wastewater have organic matter that also needs to be removed. Within this context, denitrification can be introduced to reduce nitrate produced in anammox process and improve effluent quality. Meanwhile, the organic content of wastewater can be also controlled. In such integrated system, maintaining the predominant role of anammox is of supreme importance in achieving the stable operation. This study reviews the strategies to establish a competition balance between anammox and denitrification processes by analyzing the kinetics of anammox and denitrifying microorganisms, discussing the favorable conditions in establishing the coupled process, and evaluating the system recovery approaches. Moreover, the dynamics of the microbial communities in response to the organic matters are also presented in order to better understand the complex interactions inside the system and provide a molecular insight in regulating the growth of the two functional bacteria for the stable coexistence. This review offers a guide for future engineering application on anammox coupled denitrification technology for advanced nitrogen removal.

Kinetic and Isotherm Studies of Nitrate Adsorption in Salt Water Using Modified Zeolite

Nitrate is the main form of nitrogen species in natural waters. Excessive nitrate concentration in water is highly undesirable, so that removal of the excessive nitrates in waters is very important. However, the challenge is purposed to remove the excessive nitrates in sea waters by considering anions-rich sea water. Adsorption is a favorable method for the nitrate removal process. Therefore, this research was aimed to study the kinetics and isotherm of nitrates adsorption in salt water. The adsorbent preparation was done by modifying natural zeolite with iron oxide. The adsorbent characterization was carried out by FT-IR spectroscopy and Gas Sorption Analyis methods. The results showed that the modified zeolite have Fe−O group vibrations as indicated by a peak at a wave number of 1404.18 cm−1 and an increased specific surface area. The modified zeolite is capable of adsorbing nitrate ions. The adsorption isotherms studies indicated that the modified zeolite is appropriate to the Dubinin-Radushkevich model. The average adsorption energy value (ED), obtained based on the Dubinin-Radushkevich isotherm &lt;2 kJ/mole, showed that the nitrate adsorption on zeolite surface occurred physically. The most suitable adsorption kinetics model is the pseudo second order with the rate constant of 1.80´10−2 g/mg.min. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Environmental risks for children oral health in Low Danube region

The study was aimed to assess the environmental risks for children oral health in Low Danube region.Material and methods. The study was conducted in 2011-2021. Information on the state of drinking water, the level of environmental safety of food, qualitative and quantitative composition of food was obtained from the reports of territorial institutions of the sanitary-epidemiological service of Odessa region. Actual nutrition was assessed using standard questionnaires. The assessment of the level of environmental and hygienic safety was based on the recommendations of the EPA. Statistical processing was performed by methods of analysis of variance and correlation using specialized software Statistica 10.0.Results. Excessive carbohydrate intake and excessive nitrate load are the main environmental risk factors for dental pathology in children living in the Danube region. Qualitative composition of diets plays a bigger role than mineral composition of drinking water.Conclusion. 1. Drinking water of suboptimal mineral composition was consumed by 41.7% of people, high content of refined carbohydrates was inherent in the diets of 63.0% of surveyed children.2. Children’s diet is characterized with subdeficiency of B vitamins, excessive consumption of refined carbohydrates and a significant nitrate load.

Efficient photochemical denitrification by UV/sulfite system: Mechanism and applications

Denitrification is an effective strategy to control eutrophication caused by excessive nitrate in water. However, the comparatively low efficiency of nitrate removal and N2 selectivity remains a challenge in the denitrification process. Herein, this study proposed a novel photochemical denitrification process by introducing hydrated electron (eaq-) to reduce nitrate in UV/sulfite system. The results indicated that the optimized UV/sulfite system could effectively reduce nitrate to N2 with a nearly 100% denitrification efficiency in 90 min. eaq- was identified as the mainly reactive species to achieve rapid removal of nitrate and nitrite, and the result was verified by quenching and laser flash photolysis tests. Benefiting from the high dispersion of eaq- in water and the rapid reaction rate between eaq- and the target, the generated N2O is susceptible to be reduced, leading to a high selectivity of N2 that was confirmed by 15N-isotopic. Besides, thermodynamic results based on the density functional theory (DFT) calculations suggested that the photochemical denitrification process was exothermic process and tend to transform to N2. Significantly, UV/sulfite system applied in the nickel-plating wastewater showed high denitrification efficiency, demonstrating that the novel photochemical denitrification process is promising for practical wastewater treatment.

Assessment of the Physical, Chemical and Biological Properties of Sachet Water in Mubi Metropolis, Adamawa State North East, Nigeria

Drinking sachet water quality was investigated in Mubi metropolis, Adamawa state, Nigeria, to ensure the continuous supply of clean and safe drinking water for the public health protection. For that reason, detailed biological, physical and chemical analyses of drinking water samples were carried out in different companies that produce sachet water in Mubi metropolis, Adamawa state. A number of parameters such as pH, turbidity, conductivity, total suspended solids (TSS), total dissolved solids (TDS), and heavy metals such as Cu, Zn, Mg, Fe, Cd, Pb, Cr, As, Hg, and Sn were analyzed for each water sample collected period the period of five weeks. The obtained values of each parameter were compared with the standard values set by the World Health Organization (WHO) and local standards such as National Drinking Water Quality Standard (NDWQS). The values of each parameter were found to be within the safe limits set by the WHO and NDWQS. Overall, the water from all the locations was found to be unsafe as drinking water. NAFDAC should carry out regular and frequent surveys of sachet water quality analysis for proper monitoring and management of sachet water production and its quality, Sachet water producing companies should endeavor to carry out proper treatment of the water they produce to ensure it is free of pathogens. Due to the associated effect of excess nitrate in drinking water on infants, it is recommended that some of these sachet waters be avoided for infant’s consumption. This study recommends further studies to investigate the life of sachet water in the area beyond 5 weeks and to critically examine the biological quality of the sachet water produced in the area.

Influence of the subsurface physical barrier on nitrate contamination and seawater intrusion in an unconfined aquifer

Coastal areas are facing not only environmental problems associated with seawater intrusion (SWI) but also health and ecological problems caused by excessive nitrate (NO3−) contamination. The installation of a subsurface physical barrier (SPB) is one of the common methods employed to reduce or prevent SWI, but there are few studies on the impact of SPBs on NP in groundwater. Through laboratory experiments and numerical simulations, the effects of the hydraulic gradient (HG), the nitrate concentration of the set groundwater nitrate pollution source, the relative height of the SPB (HP’) and the relative distance between the SPB and the saltwater boundary on the NP of groundwater in the presence of SWI, subsurface dams and cut-off walls were studied. Evaluation indicators were established to evaluate the degree and shape of the SWI and NP. To better describe the relationship between the velocity distribution and changes in the velocity distribution area and the degree of NP and SWI, the velocity distribution in the presence of SWI and a SPB was summarized separately. The results showed that when there was SPB, low-velocity zones were formed on both sides of the SPB, which not only slowed the migration of NO3− but also changed the shape of the NO3−-contaminated area. The closer to the SPB area the pollutants were, the more obvious the obstruction effect. The obstruction effect of adding the cut-off wall on NP was more obvious than that of adding the subsurface dam wall. The selected HG and Hp’ were important factors affecting NP and SWI. The higher HG was, the more serious the NP, the lower the HG, and the stronger the degree of SWI. Adding SPBs reduces the impact of HGs on NP and SWI. Therefore, the design of SPBs in coastal areas should focus on aspects related to these two factors.

Groundwater quality of an hard rock aquifer in the Subledu Basin of Khammam district, India

Hard rock aquifers of Indian peninsula are loaded with excess nitrate due to heavy use of fertilizers during irrigation and excess fluoride due to the geogenic contamination. This study is focused on the groundwater quality in Subledu Basin in view of the large-scale use of groundwater for both irrigation and drinking purposes as no such study was carried out earlier in the basin. The study area is located at Khammam district, Telangana state, India, which is a hard rock terrain mostly covered with granites and gneisses. Twenty-two groundwater samples were collected covering the entire basin in the month of May 2019 from running hand pumps for analyzing the major anions and cations in the groundwater. The samples were analyzed by using standard gravimetric method for evaluation of total dissolved solids; titrimetric methods to analyze carbonates, bicarbonates and chloride; UV spectrometric method for estimation of nitrate; and ion-selective electrode method for fluoride and spectrophotometer for sulfate and phosphate. These chemical constituents are used to calculate parameters, namely total hardness, sodium adsorption ratio, residual sodium carbonate, sodium percentage, Kelley’s ratio and magnesium hazard. The spatial distribution maps of important chemical constituents are prepared by using the contour maps created by utilizing the inverse distance weighted interpolation tool in the Geographical Information System. The excess fluoride values of 2.84 mg/l, 2.76 mg/l and 1.87 mg/l are observed in the villages of Pocharam, Kistapuram and Turakagudem, respectively, as against the maximum permissible concentration of 1.5 mg/l prescribed by World Health Organization. Excess use of fertilizers for agriculture is causing the nitrate pollution of groundwater in more than 50% of the samples with concentrations ranging from a minimum of 2 mg/l to a maximum of 460 mg/l in the villages of Medidapalle and Bachodu. It is identified that the total hardness is ranging between 200 and 820 mg/l which is very high when compared with the Bureau of Indian Standards. Based on sodium adsorption ratio, residual sodium carbonate, Kelley’s ratio, and sodium percentage analyses, two samples were not suitable for irrigation. Similarly, 13 samples are not suitable for drinking water purposes based on the excess presence of fluoride and nitrate. Groundwater quality maps of Subledu Basin depicting the areas suitable or not for the irrigation as well as for drinking purposes were prepared. From these maps, it is found that groundwater from large parts of the basin is not suitable for drinking purposes while for irrigation purposes it is suitable.

Iron(II) in the world's oxygen deficient zones

Oxygen deficient zones (ODZs) are regions in the marine water column where the concentration of oxygen is very low or zero and respiration occurs using nitrate as the terminal electron acceptor. Under such conditions, iron (Fe) would be predicted to be in the +3 valence state, and its geochemistry would be largely unaffected by the absence of oxygen. In contrast, observations show that Fe(II) is a major and sometimes dominant oxidation state in ODZs, even in the presence of a substantial amount of excess nitrate. Fe(II) plays an important role in Fe transport in ODZs. They are generally enriched in Fe throughout the regions where nitrate reduction is occurring. Here, it is argued that Fe(II) maxima arise as a result of processes common to the Eastern Tropical North and South Pacific as well as the Arabian Sea. Recent work has revealed that lateral advection of Fe(II) from reducing sediments is perhaps the major source and it appears that physical processes that are still poorly understood act over a surprisingly narrow density range. Tracers including iodine and 228Ra have been extremely useful in constraining these processes. The findings reported here have important implications for Fe transport from the continental margin to the ocean interior, and for microbes involved in the nitrogen cycle that have high Fe requirements.

Application of central composite design approach for optimization nitrate removal from aqueous solution by immobilized Pseudomonas putida.

High nitrate concentration is a dangerous pollutant in the environment. Immobilization for the optimum denitrifying bacterial strain isolated from collected wastewater samples was suggested for bioremediation of excessive nitrate concentration from aqueous solutions and its denitrification activity under different pH, nitrate concentration, bacterial beads, temperature and sodium alginate concentration conditions was explored. The active isolate was identified as Pseudomonas putida MT364822.1 by 16S rRNA analysis. Nitrate bioremediation process was optimized by applying response surface methodology based on central composite design approach. Nitrate uptake was significantly affected by variables of study (P-value <0.05). Maximum removal of nitrate (91.1%) was achieved at pH 7, nitrate concentration 400 mg/L, immobilized bacterial beads 3.0 g/L, temperature 35 °C and sodium alginate concentration 2.5% as optimal variable values. For application, immobilized P. putida MT364822.1 removed 82.2% of nitrate from raw fish farm effluent. Storage and reusability experiments showed that the immobilized strain stronger and more stable than the pure strain. The results suggested that immobilized P. putida MT364822.1 is a highly promising and suitable microorganism for use in the bio-removal of nitrate, and the central composite design was more effective in optimizing variables to achieve the best nitrate removal efficiency.