Removal Of NO3 Research Articles

Biochar immobilized bacteria enhances nitrogen removal capability of tidal flow constructed wetlands.

To improve the nitrogen removal (NR) capability of tidal flow constructed wetlands (TFCWs) for treatment of saline wastewater, biochar, produced from Cyperus alternifolius, was used to adsorb and immobilize a salt tolerant aerobic denitrifying bacteria (Zobellella sp. A63), and then was added as a substrate into the systems. Under low (2:1) or high (6:1) C/N ratio, the removal of NO3--N and total nitrogen (TN) in the biochar immobilized bacteria (BIB) dosing system (TFCW3) was significantly higher (q < 0.05) than that in the untreated system (TFCW1) and the biochar dosing system (TFCW2). At low C/N ratio, the removal rates of NO3--N, TN and chemical oxygen demand (COD) of TFCW3 were 68.2%, 72.6% and 82.5%, respectively, 15-20% higher than TFCW1 and 5-10% higher than TFCW2. When C/N ratio was further increased to 6, the pollutant removal rate of each system was greatly improved, but the removal rate of TFCW3 for NO3--N/TN was still nearly 10% and 5% higher than TFCW1 and TFCW2, respectively. Microbial community analysis showed that aerobic denitrifying bacteria, sulfate reducing bacteria and sulfur-driven denitrifiers (DNSOB) played the most important role of NR in TFCWs. Moreover, biochar bacterial agent significantly increased the abundances of genes involved in NR. The total copy numbers of bacterial 16S rRNA, nirS, nirK, drsA and drsB genes in the TFCW3 were 1.1- to 3.76-fold higher than those in the TFCW1; Especially at low C/N ratio, the copy number of drsA and drsB in the upper layer of TFCW3 were 85.5 and 455 times that of TFCW1, respectively. Thus, BIB provide a more feasible and effective amendment for constructed wetlands to improve the N removal of the saline wastewater by enhancing the microbial NR capacity mainly via aerobic and sulfur autotrophic denitrification.

Catchment controls of denitrification and nitrous oxide production rates in headwater remediated agricultural streams

Heavily modified headwater streams and open ditches carry high nitrogen loads from agricultural soils that sustain eutrophication and poor water quality in downstream aquatic ecosystems. To remediate agricultural streams and reduce the export of nitrate (NO3−), phosphorus and suspended sediments, two-stage ditches with constructed floodplains can be implemented as countermeasures. By extending hydrological connectivity between the stream channel and riparian corridor within constructed floodplains, these remediated ditches enhance the removal of NO3− via the microbial denitrification process. Ten remediated ditches were paired with upstream trapezoidal ditches in Sweden across different soils and land uses to measure the capacity for denitrification and nitrous oxide (N2O) production and yields under denitrifying conditions in stream and floodplain sediments. To examine the controls for denitrification, water quality was monitored monthly and flow discharge continuously along reaches. Floodplain sediments accounted for 33 % of total denitrification capacity of remediated ditches, primarily controlled by inundation and stream NO3− concentrations. Despite reductions in flow-weighted NO3− concentrations along reaches, NO3− removal in remediated ditches via denitrification can be masked by inputs of NO3−-rich groundwaters, typical of intensively managed agricultural landscapes. Although N2O production rates were 50 % lower in floodplains compared to the stream, remediated ditches emitted more N2O than conventional trapezoidal ditches. Higher denitrification rates and reductions of N2O proportions were predicted by catchments with loamy soils, higher proportions of agricultural land use and lower floodplain elevations. For realizing enhanced NO3− removal from floodplains and avoiding increased N2O emissions, soil type, land use and the design of floodplains need to be considered when implementing remediated streams. Further, we stress the need for assessing the impact of stream remediation in the context of broader catchment processes, to determine the overall potential for improving water quality.

Succession of function, assembly, and interaction of microbial community in sequencing biofilm batch reactors under selenite stress

The mechanism of interaction between selenite, a toxic substance, and the microbial community in wastewater is still not well understood. Herein, nine sequencing biofilm batch reactors were used to systematically investigate the response of the microbial community to the continuous selenite stress. The results showed that selenite affected the reactor performance and reduced the biofilm mass. Also, it increased the proportion of the living cells, and changed the protein and polysaccharide composition of the biofilm as well as cellular secretions. Selenite facilitated the removal of NO3–N, according to water-quality and bioinformatics analyses. As such, the selenite was converted into selenium nanoparticles. α-diversity analysis further revealed that 20 μM selenite enhanced the microbial community resilience, while 200 μM selenite had the reverse effect. Community composition analysis showed that Variovorax, Rhizobium, and Simkania had positive correlations with selenite (P < 0.05). Functional prediction suggested that selenite changed the C, N, and S cycle functions. Furthermore, determinism dominated the community assembly process, and the deterministic proportion increased with the increase of selenite concentration. Network analysis showed that selenite improved the stability and positive correlation ratio of the overall microbial network, and accelerated the communication between microorganisms. However, when compared with the 20 μM selenite, the 200 μM selenite boosted the competition and parasitism/predation among microorganisms. Low-abundance genera played a key role in the network of selenite-reducing microbial community. In addition, under selenite stress, biofilm network exhibited better stability and faster information exchange than suspended network, and the positive association between biofilm and suspended microorganisms increased. All in all, this research sheds light on the interaction between selenite and microbial community, as well as provides crucial information on selenium-containing wastewater.

Effects of different electron donors on nitrogen removal performance and microbial community of denitrification system

Biological denitrification is an economical and effective process for the removal of NO3--N from wastewater. During the denitrification process, electron donors such as organic and inorganic compounds are required to provide electrons for the reduction of NO3--N. In this study, the effects of sulfide (sulfur autotrophic denitrification, stage I), sulfide and glucose (sulfur autotrophic-heterotrophic synergistic denitrification, stage II) and glucose (heterotrophic denitrification, stage III) on nitrogen removal performance and microbial characteristics of denitrification system were investigated. After adding 80 mg/L glucose in stage II, advanced nitrogen removal based on sulfur autotrophic and heterotrophic denitrification was achieved with a high NO3--N removal efficiency of 96.0%. The microbial species were marginally reduced as the denitrification system transitioned from sulfur autotrophic denitrification to heterotrophic denitrification, while the abundance of denitrifying bacteria grew dramatically. Comamonas, uncultured_bacterium_f_Burkholderiaceae and Enterobacter increased from less than 2% in stage I to 10.0%, 9.1% and 7.8% in stage III, respectively. In particular, the abundance of sulfur autotrophic denitrifying bacteria (Thiobacillus and Sulfurimonas) did not drop but somewhat increased in stage II. A potential interaction model between sulfur autotrophic and heterotrophic bacteria was proposed. The results of this study provide a novel idea and theoretical basis for improving the nitrogen removal efficiency of the system through biological enhancement or microbial community regulation.

Saturated buffer design flow and performance in Illinois.

There are few peer-reviewed studies documenting saturated buffer annual nitrate (NO3 ) removal or that have assessed the federal practice standard design criteria. Drainage flow, NO3 , and dissolved reactive phosphorus (DRP) were monitored at three saturated buffers in Illinois, USA, for a combined 10 site-years. Nitrate loss reduction averaged 48 ± 19% with removals of 3.5-25.2kg NO3 -N ha-1 annually. Median DRP concentrations at all sampling locations were at the analytical detection limit of 0.01mg L-1 . The current design paradigm (i.e., USDA practice standard) prescribes there should be no flow bypassing the saturated buffer at flow rates that are ≤5% of the peak drainage system flow rate. The drainage coefficient-based and Manning's equation-based peak flow estimates were higher and lower, respectively, than the observed annual peaks in all years. This illustrated inherent uncertainty introduced early in the design process, which can be further compounded by dynamic in-buffer hydrology. The percentage of the observed peak flow rate at which bypass initiated ranged across an order of magnitude between sites (4.4-8.1% of peak flow rate at one site and 42-49% of peak at another) despite the buffers providing relatively similar NO3 removal. Bypass at one site (SB2) was related to the concept of "antecedent buffer capacity filled," which was defined as the 5-d average water depth in the middle control structure chamber expressed as a relative percentage of the bypass stop log height. This design flow analysis serves as a call to further evaluate predictive relationships and design models for edge-of-field practices.

Nitrogen Removal Performance of Novel Isolated Bacillus sp. Capable of Simultaneous Heterotrophic Nitrification and Aerobic Denitrification.

The control of nitrogenous pollutants is a key concern in aquaculture production. Bacillus spp. are commonly used as probiotics in aquaculture, but only a few reports have focused on the simultaneous heterotrophic nitrification and aerobic denitrification (SND) capacity of Bacillus sp. strains. In order to improve nitrogen biodegradation efficiency in the aquaculture industry, the SND capacity of Bacillus sp. strains was evaluated using both individual and mixed nitrogen sources and different sources of organic carbon. Twelve Bacillus sp. isolates were screened from aquaculture pond sediments and shrimp guts for nitrogen biodegradation. Six strains exhibited especially efficient inorganic nitrogen removal capacities in media with individual and mixed nitrogen sources. These strains comprise K8, N2, and N5 (B. subtilis), HYS (B. albus), H4 (B. amyloliquefaciens), and S1 (B. velezensis). The strains grew better when the sole nitrogen source was NH4+-N, but degraded nitrogen in the following order: nitrite nitrogen (NO2--N), ammonium nitrogen (NH4+-N), and nitrate nitrogen (NO3--N). There was no associated NO2--N accumulation, regardless of the nitrogen source. The optimal carbon source for nitrogen removal varied based on different nitrogen sources and associated metabolic pathways. The optimal carbon sources for the removal of NO3--N, NO2--N, and NH4+-N were sodium citrate, sodium acetate, and sucrose, respectively. The application of H4 in recirculating aquaculture water further demonstrated that NO2--N and NH4+-N could be effectively removed. This study thus provides valuable technical support for the bioremediation of aquaculture water.

Eggshell membrane derived nitrogen rich porous carbon for selective electrosorption of nitrate from water

Nitrate (NO3−) is a ubiquitous contaminant in water and wastewater. Conventional treatment processes such as adsorption and membrane separation suffer from low selectivity for NO3− removal, causing high energy consumption and adsorbents usage. In this study, we demonstrate selective removal of NO3− in an electrosorption process by a thin, porous carbonized eggshell membrane (CESM) derived from eggshell bio-waste. The CESM possesses an interconnected hierarchical pore structure with pore size ranging from a few nanometers to tens of micrometers. When utilized as the anode in an electrosorption process, the CESM exhibited strong selectivity for NO3− over Cl−, SO42−, and H2PO4−. Adsorption of NO3− by the CESM reached 2.4 × 10−3 mmol/m2, almost two orders of magnitude higher than that by activated carbon (AC). More importantly, the CESM achieved NO3−/Cl− selectivity of 7.79 at an applied voltage of 1.2 V, the highest NO3−/Cl− selectivity reported to date. The high selectivity led to a five-fold reduction in energy consumption for NO3− removal compared to electrosorption using conventional AC electrodes. Density function theory calculation suggests that the high NO3− selectivity of CESM is attributed to its rich nitrogen-containing functional groups, which possess higher binding energy with NO3− compared to Cl−, SO42−, and H2PO4−. These results suggest that nitrogen-rich biomaterials are good precursors for NO3− selective electrodes; similar chemistry can also be used in other materials to achieve NO3− selectivity.

Simultaneous removal of aromatic pollutants and nitrate at high concentrations by hypersaline denitrification:Long-term continuous experiments investigation

If we can use toxic aromatic compounds as supplementary carbon source, the simultaneous removal of nitrate (NO3−) and aromatic compounds may be achieved at much lower chemical costs. This study uses the expanded granular sludge bed (EGSB) reactors to investigate the hypersaline (> 3%) denitrification performance, the removal of aromatic compounds, i.e., aniline, phenol, and their mixture, and the mechanisms involved in. The four reactors exhibit high removal efficiency of NO3− (> 92.8%) and aromatic compounds (> 73.9%) at 0–1200 mg/L of aromatic compounds. The formation of toxic intermediates such as catechol and azo dyes is revealed by gas chromatography mass spectrometry (GC–MS) with and without N,O-Bis(trimethylsilyl) trifluoroacetamide (BSTFA) derivation, and their toxic effects lead to the lower cell survival ratios after exposing to phenol (64.2% ∼ 68.9%) than to aniline and mixture (72.7% ∼ 78.0%). The stable performance is associated with the more secretion of extracellular polymeric substances (EPS) and the adsorption of pollutants on EPS, and this was indicated from the higher fluorescence intensity in three-dimensional excitation-emission matrix (3D-EEM). Moreover, the Halomonas and Azoarcus show high abundance and play important roles in the removal of both NO3− and aromatic compounds. Besides, quantitative real time PCR (RT-qPCR) results demonstrate the key role of highly abundant nosZ and nirS genes in denitrification. The toxic organics in industrial wastewaters are potentially feasible carbon sources for denitrification even under high-salinity stress.

Cooperative denitrification in biocathodes under low carbon to nitrogen ratio conditions coupled with simultaneous degradation of ibuprofen in photoanodes

A two-chamber microbial photoelectrochemical cell (MPEC) with a denitrification biocathode and an α-Fe2O3/P3HT photoanode was established aimed to enhance nitrate removal from wastewater of low carbon sources and achieve simultaneous ibuprofen degradation. The results demonstrated that the average removal of NO3–-N in the biocathode reached 96.56 ± 0.72% when the COD/NO3–-N was 0.75, and the relative contributions of heterotrophic and autotrophic denitrification were 21.47% and 78.53%, respectively. When there was no organic source in the influent, the maximum removal of NO3–-N was less than 45%. High-throughput sequencing revealed that both heterotrophic bacteria, such as Bacillus, and autotrophic bacteria (e.g., Thermomonas and Hydrogenophaga) dominated in the cooperative denitrification biocathode. Moreover, the functional gene analysis showed that the abundance of genes related to denitrification was highest in the cooperative denitrification biocathode. In addition, the photocatalytic degradation efficiency of ibuprofen in the anode chamber attained 67.95% ± 0.97%.

Nitrate Water Contamination from Industrial Activities and Complete Denitrification as a Remediation Option

Freshwater is a scarce resource that continues to be at high risk of pollution from anthropogenic activities, requiring remediation in such cases for its continuous use. The agricultural and mining industries extensively use water and nitrogen (N)-dependent products, mainly in fertilizers and explosives, respectively, with their excess accumulating in different water bodies. Although removal of NO3 from water and soil through the application of chemical, physical, and biological methods has been studied globally, these methods seldom yield N2 gas as a desired byproduct for nitrogen cycling. These methods predominantly cause secondary contamination with deposits of chemical waste such as slurry brine, nitrite (NO2), ammonia (NH3), and nitrous oxide (N2O), which are also harmful and fastidious to remove. This review focuses on complete denitrification facilitated by bacteria as a remedial option aimed at producing nitrogen gas as a terminal byproduct. Synergistic interaction of different nitrogen metabolisms from different bacteria is highlighted, with detailed attention to the optimization of their enzymatic activities. A biotechnological approach to mitigating industrial NO3 contamination using indigenous bacteria from wastewater is proposed, holding the prospect of optimizing to the point of complete denitrification. The approach was reviewed and found to be durable, sustainable, cost effective, and environmentally friendly, as opposed to current chemical and physical water remediation technologies.

Bioretention system mediated by different dry–wet alterations on nitrogen removal: Performance, fate, and microbial community

In laboratory experiments, the nitrogen migration and transformation in the stormwater bioretention system under different dry–wet alterations were studied. The removal efficiency showed that nitrogen could be removed efficiently in bioretention system under all dry–wet alterations, and the shorter antecedent dry days (ADDs) (1–5 days) were beneficial to the removal of nitrogen before plants decay, compared to the longer ADDs (7–22 days). Using a new method combined with Hydrus-1D model, water transport was simulated and nitrogen migration in bioretention system was quantified, indicating that NH4+-N was mainly removed in the planting layer, and the removal of NO3−-N was occurred in the submerged layer. Fate experiment showed the main fate of the nitrogen was microorganisms (1–5 ADDs) and soil immobilization (7–22 ADDs). Microbial analysis showed that shorter ADDs (1–5 days) were suitable for Firmicutes growth, while Proteobacteria and Actinobacteria accounted for greater abundance under longer ADDs (7–22 days). Canonical correlation analysis (CCA) revealed the relationships between microbial community and environmental factors. Soil moisture content, soil organic matter (SOM), TN (water), root length, and NO3−-N (water) were significantly correlated with bacterial community. This work may give new insights into nitrogen migration and transformation, and can provide a reference for the further mechanism study and construction of stormwater bioretention systems.

Application of Chlorella sp. and Scenedesmus sp. in the Bioconversion of Urban Leachates into Industrially Relevant Metabolites

This paper explores the ability of Chlorella sp. and Scenedesmus sp. to convert landfill leachates into usable metabolites. Different concentrations (0.5, 1, 5, and 10% v/v) of leachate coupled with an inorganic carbon source (Na2CO3, and NaHCO3) were tested to improve biomass production, metabolites synthesis, and removal of NO3 and PO4. The result shows that both strains can effectively grow in media with up to 5% (v/v) leachate, while significantly reducing the concentrations of NO3, and PO4 (80 and 50%, respectively). The addition of NaHCO3 as a carbon source improved the final concentration of biomass, lipids, carbohydrates, and the removal of NO3 and PO4 in both strains.

Influence of ethanol and nitrate on ibuprofen removal in batch reactors under denitrifying conditions

The optimized removal of the anti-inflammatory drug ibuprofen inoculated with activated sludge biomass in batch reactors was evaluated, using the variables ibuprofen (60 – 80 µg L-1), ethanol (130 – 230 mg EtOH L-1) and nitrate (130 – 230 mg NO3- L-1) by rotational central compound design. A higher removal efficiency of ibuprofen (97.5 ± 3.1%) was observed with 95.9 mg NO3- L-1, 109.9 µg IBU L-1 and 110.6 mg EtOH L-1. Under these conditions, complete removal of NO3- (1.1 h-1 speed), 20 ± 2.7% of organic matter removal (366.5 ± 3.5 mg COD L-1)> 90% ethanol removal were obtained. Based on the mass sequencing of the 16 S rRNA gene via the Illumina platform, bacteria related to the degradation of recalcitrant compounds were identified, such as Pseudomonas (1.5%), Zoogloea (1.73%) and Rhodanobacter (1.63%). The enzymes involved in denitrification were also inferred, such as nitrate transporters and several reductases involved in the conversion of intermediates. Although ibuprofen removal occurred in the absence of ethanol (16.5%) and nitrate (15.2%), the optimal removal range (97.5%) as well as the selection of bacteria possibly involved in its degradation pathways was obtained with 110.6 mg EtOH L-1 and 95.9 mg NO3- L-1, achieving removal approximately 5.9 times higher when compared to the assays without ethanol and nitrate.

Enhancing nitrate removal efficiency of micro-sized zero-valent iron by chitosan gel balls encapsulating

The activity of micro-sized zero-valent iron (MZVI) material for nitrate removal in neutral pH and low C/N ratios water needs to be improved. In this study, micro-sized zero-valent iron@chitosan (MZVI@CS) material was synthesized through embedding MZVI particles into chitosan (CS) gel by sol-gel method, and was used for deep removal of NO3−-N in the absence of organic carbon sources and neutral pH. The NO3−-N removal rate of MZVI@CS was 0.37 mg-N·L−1·d−1 (dosage of 1%, initial pH = 7, 25 °C, initial nitrate concentration = 15 mg-N·L−1), which was 11.33 times higher than that of MZVI. The apparent activation energy (Ea) of MZVI@CS with nitrate was 38.23 kJ·mol−1. MZVI@CS can remove nitrate effectively at a low concentration (15 mg-N·L−1). A stable denitration rate (0.37–2.28 mg-N·L−1·d−1) could be maintained under weak acidic, neutral and alkaline conditions (pH = 5–9). More than 80% of reduced nitrate was converted to N2, and only a small amount was converted to NH4+ or NO2−. The gel structure of MZVI@CS eliminated the agglomeration between MZVI particles while the forming of Fe-CS chelates reduced the formation of iron oxide and solved the problems of passivation, hence successfully strengthened the NO3−-N removal efficiency of MZVI. Therefore MZVI@CS has great application potential in NO3−-N deep removal of water bodies with neutral pH and low C/N ratios.

Simultaneous bio-reduction of nitrate and Cr(VI) by mechanical milling activated corn straw

Abundant lignocellulose waste is an ideal energy source for environmental bioremediation, but its recalcitrance to bioavailability makes this a challenging prospect. We hypothesized that the disruption of straw’s recalcitrant structure by mechanochemical ball milling would enhance its availability for the simultaneous bioreduction of nitrate and Cr(VI). The results showed that the ball-milling process increased the quantity of water-soluble organic matter released from corn straw and changed the composition of organic matter by strongly disrupting its lignocellulose structure. The increase in ball-milling time increased the specific surface area of the straw and favored the adhesion of microorganisms on the straw surface, which enhanced the bioavailability of the energy in the straw. Substantially increased removal of NO3--N (206.47 ± 0.67 mg/g) and Cr(VI) (37.62 ± 0.09 mg/g) was achieved by using straw that was ball milled for 240 min, which validated that ball milling can improve the utilization efficiency of straw by microorganisms. Cellular and molecular biological analyses showed that ball-milled straw increased microbial energy metabolism and cellular activity related to the electron transport chain. This work offers a potential way to achieve the win-win goal of utilizing agricultural wastes and remediating environmental pollution.

Sustainable treatment of nitrate-containing wastewater by an autotrophic hydrogen-oxidizing bacterium

Bacteria are key denitrifiers in the reduction of nitrate (NO3−-N), which is a contaminant in wastewater treatment plants (WWTPs). They can also produce carbon dioxide (CO2) and nitrous oxide (N2O). In this study, the autotrophic hydrogen-oxidizing bacterium Rhodoblastus sp. TH20 was isolated for sustainable treatment of NO3−-N in wastewater. Efficient removal of NO3−-N and recovery of biomass nitrogen were achieved. Up to 99% of NO3−-N was removed without accumulation of nitrite and N2O, consuming CO2 of 3.25 mol for each mole of NO3−-N removed. The overall removal rate of NO3−-N reached 1.1 mg L−1 h−1 with a biomass content of approximately 0.71 g L−1 within 72 h. TH20 participated in NO3−-N assimilation and aerobic denitrification. Results from 15N-labeled-nitrate test indicated that removed NO3−-N was assimilated into organic nitrogen, showing an assimilation efficiency of 58%. Seventeen amino acids were detected, accounting for 43% of the biomass. Nitrogen loss through aerobic denitrification was only approximately 42% of total nitrogen. This study suggests that TH20 can be applied in WWTP facilities for water purification and production of valuable biomass to mitigate CO2 and N2O emissions.

Decentralized high-strength wastewater treatment using a compact aerobic baffled bioreactor

Decentralized wastewater treatment is a potential solution to the economic and sustainability issues associated with current wastewater infrastructure requirements for rural and expanding urban settings. However, wastewater produced from small-scale operations (domestic, industrial, agricultural, defense, etc.) are often found to have higher pollution concentrations than municipal wastewater and is referred to as “blackwater” in the study. A baffled bioreactor (BBR) was employed to carry out blackwater treatment. The results of this study showed the removal of organic content and inorganic nitrogen was high in all of the feed amounts tested and increased corresponding to an increase in feed amount. Microbial diversity results supported that the feed amount was the most important factor in treatment performance. The microbial community was more diverse at higher feed amounts than lower feed amounts. A non-metric multidimensional scaling (NMDS) analysis revealed that higher feed amounts enriched Verrucomicrobiaceae, unclassified Sphingomonadales, unclassified Burkholderiales in the microbial community, and facilitated the removal of total solids, total nitrogen, and NO3−. The energy and exergy analyses showed the consumption of 5.02 Wh/L wastewater energy with a universal exergy efficiency of 61% at the feed amount of 3750 LPD. An economic analysis further delineated the treatment cost profiles of the decentralized unit under four different energy case scenarios of electricity from the grid, propane gas engine for remote rural communities, diesel engine (I) using standard U.S. market diesel fuel costs for remote rural communities and scientific research bases, and diesel engine (II) using the fully burdened cost of diesel fuel for military contingency bases and other extreme environmental scenarios.

Removal of nitrate from groundwater by nano-scale zero-valent iron injection pulses in continuous-flow packed soil columns

Injection of zero-valent iron nanoparticles (nZVI) into aquifers has gained increasing attention of researchers for in-situ treatment of NO3−-contaminated groundwater. nZVI has proved efficient in chemically reducing NO3− and, according to recent research efforts, in supporting biological denitrification under favoured conditions. Given the scarce research on nZVI pulsed injection in continuous-flow systems, the objective of this study was to evaluate the effect of nZVI pulses on the removal of NO3− from groundwater in packed soil columns and, more particularly, to elucidate whether or not biotic NO3− removal processes were promoted by nZVI. Three identical columns were filled with aquifer soil samples and fed with the same nitrate polluted groundwater but operated under different conditions: (A) with application of nZVI pulses and biocide spiked in groundwater, (B) without application of nZVI pulses and (C) with application of nZVI pulses. Results showed that the application of nZVI (at 30 mg/L and 78 mg/L doses) resulted in an immediate and sharp removal of NO3− (88–94%), accompanied by an increase in pH (from 7.0 to 9.0–10.0), a drop in redox potential (Eh) (from +420 mV to <100 mV) and a release of Fe(II) and Total Organic Carbon (TOC) in the effluent (to 200 mg/L and 150–200 mg/L, respectively). The released TOC came from the organic polymer used as stabilizer of the nZVI particles. Comparison against the sterilized control column revealed that, under the experimental conditions, no biological denitrification developed and that the removal of NO3− was due to chemical reduction by nZVI. The main by-product of the NO3− removal was NH4+, which at the prevailing pH was partially converted to NH3, which dissipated from the aqueous solution resulting in a net removal of total dissolved N. A mass balance of Fe permitted to quantify the percentage of injected nZVI trapped in the column (>98%) and the NO3− retention capacity of the nZVI particles (13.2–85.5 mg NO3−/g nZVI).

New method for electrochemical ion separation (ElONS) for chloride/nitrate separation using Ag/AgCl electrodes with a cation exchange membrane

Electrochemical ion separation (EIONS) is attracting attention as a new ion separation technology because no by-products are generated during the process. However, conventional EIONS systems have lower selectivity for anions; it has limitations in its application to selective anion extraction. Therefore, it is necessary to develop a new EIONS system with high selectivity for specific anions. In this study, we introduce a highly selective EIONS for Cl- extraction from a mixed solution of Cl- and NO3- using silver/silver-chloride electrodes with a cation exchange membrane. This technique is based on the principle that Ag/AgCl electrodes starts to react with Cl- at a specific potential to remove Cl- from the mixture. As a result, this system removed Cl- with 80 times higher selectivity than its removal of NO3- even at the low cell voltage of 0.3 V. Furthermore, it was found that this system could be operated at a current density as high as 5 mA cm−2, suggesting for rapid extraction. We believe that this system can be feasible for separating Cl- and NO3- electrochemically.

NO3− photolysis-induced advanced reduction process removes NO3− and 2, 4, 6-tribromophenol

Reductive processes are an important type of pollutant removal technology, particularly for organic halogens. NO3− is an anion and pollutant that is commonly present in wastewater. In this study, a novel advanced reduction process (ARP) induced by NO3− photolysis was developed to remove 2,4,6-tribromophenol (TBP) and NO3−. The UV/NO3−/formate acid (FA) process achieved NO3− removal and improved the debromination of TBP (initial TBP concentration = 0.1 mM) (up to 97.8%), however, their coexistence adversely affected the reductive removal of each component. Acidic conditions (pH 3 in this study) benefited the removal of NO3− and the debromination of TBP. Cl− promoted NO3− removal in UV/NO3−/FA, however, it decreased the debromination effect of TBP by 27.8%. Humic acid, a typical dissolved organic matter, suppressed NO3− removal, TBP degradation and debromination under all experimental conditions. Methyl viologen significantly inhibited the performance of ARP, and this verified the role of CO2•- in this ARP. Insufficient reduction and over-reduction of NO3− were observed under different conditions and a greater amount of NH4+ was formed under the influence of TBP. The data also indicated that as much as 80% of the removed NO3− was converted to NO2−, and this is noteworthy. Due to the reductive radicals generated from the oxidation of FA, both oxidative and reductive products of TBP were detected in the effluent. The results of this study provide a potential technology for the reductive removal of organic halogens from NO3−-rich wastewater.