Low Nitrate Research Articles

Influence of rubber particle inputs on nitrogen removal efficiency of bioretention systems

ABSTRACT Bioretention systems effectively capture rubber particles and other microplastics in stormwater runoff. However, it is uncertain whether long-term particle accumulation affects pollutant removal efficacy. This study investigated the impact of various concentrations of ethylene-propylene-diene-monomer (EPDM) particles (0, 50, 100, and 400 mg/L) on bioretention system nitrogen removal performance. The input of EPDM during short-duration (2 h) rainfall favored the removal of nitrogen, and the total nitrogen effluent concentration of the bioretention system with EPDM was reduced by 0.59–1.52 mg/L compared with that of the system without EPDM. In addition, the input of EPDM reduced the negative effects of drought. During long-duration (24 h) rainfall, higher concentrations of EPDM led to lower nitrate–nitrogen concentrations in the effluent. The bioretention system with EPDM required less time for nitrate–nitrogen removal to reach 50% than that without EPDM input. Microbial community analysis showed that EPDM increased the relative total abundance of denitrifying bacteria (such as Dechloromonas, Zoogloea, Ramlibacter, and Aeromonas) by 7.25–10.26%, which improved the denitrification capacity of the system.

Improving Nutrient Uptake Efficiency in Hydroponic Systems With Phytoremediation of Nitrate‐Nitrogen Contaminated Wastewater

ABSTRACTThis study evaluates the efficacy of a nutrient film technique (NFT) hydroponic system in phytoremediation of nitrate‐nitrogen contaminated wastewater using six plant species: vetiver grass (Chrysopogon zizanioides), golden pothos (Epiprennum aureum), crotons (Codiaeum variegatum), arrowhead plant (Syngonium podophyllum), spinach (Spinacia oleracea), and brinjal (Solanum melongena). This study examines how well different plant species remove nitrate‐nitrogen from wastewater in an NFT hydroponic system. It finds that all plants, but especially money plant and arrowhead plant, successfully lower nitrate levels at influent concentrations of 30 and 90 mg/L. The wastewater had average pH values of 5–6.5, temperature values of 24°C–25°C, electrical conductivity values (EC) of 1.5–2 mS/cm, and total dissolved solids (TDS) between 1062 ± 199.3 and 1400 ± 124.16 mg/L. The system for golden pothos (70.94%–90.3%), crotons (62.5%–83.1%), arrowhead plant (67.25%–90.03%), vetiver grass (45.42%–83.1%), spinach (47.15%–81.71%), and brinjal (59.52%–83.38%) has shown excellent biochemical oxygen demand (BOD5) elimination efficiency. These results suggest that nitrate‐nitrogen contaminated wastewater can be effectively cleaned up by NFT hydroponic systems, which employ certain plant species.

The Arabidopsis PIP1;1 Aquaporin Represses Lateral Root Development and Nitrate Uptake Under Low Nitrate Availability.

Nitrate (NO3 -) deficiency decreases root water uptake and root hydraulic conductance. This adaptive response is correlated with reduced abundance and activity of plasma membrane intrinsic protein (PIP) aquaporins. We therefore screened changes in the root architecture of a complete set of Arabidopsis pip loss-of-function mutants grown under NO3 - deficiency to systematically approach the impact of PIPs under these conditions. NO3 - deprivation led to attenuated responses of specific pip single mutants compared to the strongly altered LR parameters of wild-type plants. In particular, pip1;1 exhibited a lower relative reduction in LR length and LR density, revealing that PIP1;1 represses LR development when NO3 - is scarce. Indeed, PIP1;1 compromises root and shoot NO3 - accumulation during early developmental stages. A fluorescent VENUS-PIP1;1 fusion revealed that PIP1;1 is specifically repressed in the pericycle, endodermis and at the flanks of emerging LRs upon NO3 - deficiency. Thus, LR plasticity and NO3 - uptake are affected by an interactive mechanism involving aquaporins (PIP1;1) and nitrate accumulation during seedling development under NO3 --deficient conditions.

Effects of low and high dietary nitrate intake on human saliva, plasma and skeletal muscle nitrate and nitrite concentrations and their functional consequences

Dietary nitrate (NO3−) supplementation has been shown to reduce blood pressure (BP), improve exercise performance, and alter the oral microbiome. Following a “control” diet (CON), we manipulated dietary NO3− intake to examine the effect of a short-term (7-day) low NO3− diet (LOW) followed by a 3-day high NO3− diet (HIGH), compared to a 7-day standard (STD) NO3− diet followed by HIGH, on saliva, plasma, and muscle [NO3−] and nitrite ([NO2−]), BP, and cycling exercise performance in healthy young adults. We also examined the effect of LOW on the oral microbiome. Saliva [NO3−] and [NO2−], and plasma [NO3−] were significantly lower than CON following LOW (all P < 0.05) but there was no change in plasma [NO2−] or muscle [NO3−] and [NO2−] (all P > 0.05). Following HIGH, saliva and plasma [NO3−] and [NO2−], and muscle [NO3−], were significantly elevated above CON, LOW and STD (all P < 0.05), but there was no difference between CON-LOW-HIGH and CON-STD-HIGH (P < 0.05). BP and exercise performance were not altered following LOW (P > 0.05). HIGH significantly reduced systolic and diastolic BP compared to CON when preceded by STD (both P < 0.05) but not when preceded by LOW (P > 0.05). Peak (+4 %) and mean (+3 %) power output during sprint cycling was significantly improved following HIGH (both P < 0.05), with no differences between CON-LOW-HIGH and CON-STD-HIGH (both P > 0.05). LOW altered the oral microbiome composition, including decreases in relative abundances of phylum Proteobacteria and genus Neisseria. The findings indicate that a short-term low NO3− diet lowers plasma but not skeletal muscle [NO3−]. The maintenance of plasma [NO2−] and muscle [NO3−] and [NO2−] following LOW may be indicative of their importance to biological functions, including BP regulation and exercise performance.

Hysteresis response of carbon release and nitrate reduction in polymer denitrification systems

Polymer denitrification has received much attention in the field of advanced wastewater treatment. It can release carbon source stably during long-term operation, which can be used as electron donor for denitrification. However, the response of the polymer denitrification system to the transient changes of nitrate is not sufficiently disclosed yet. In this study, the response of a polymer denitrification system to nitrate was comprehensively investigated through a series of experiments. Therefore, real-time response and hysteresis response phenomena were identified. The time dependence of microorganisms in the system and the recovery of the hysteresis response were elucidated. The experimental results revealed distinct response patterns before and after the hysteresis tipping point. The denitrifying microorganisms, which showed a high adaptive capacity, exhibited a real-time response over a range of low nitrate concentration variations (∼20–30 mg/L). In contrast, microbial recovery is poor over a range of high nitrate concentration variation (∼35–40 mg/L), which is referred to as a hysteresis response. Finally, the hysteresis response mechanism was revealed by monitoring the recovery of denitrification enzymes, gene and microbial communities. The results showed that transient shocks of high nitrate loads affect microbial community structure stability, denitrifying enzyme activity and gene expression. Meanwhile, the abundance of Microbacterium associated with carbon release was reduced. The combination of these factors leads to a hysteresis response in denitrification and carbon release. This work contributes to a deeper understanding of the hysteresis behavior in polymer denitrification systems, offering critical insights for optimizing system performance and improving nitrogen removal efficiency.

Optimizing Nitrate and Tryptone to Enhance Growth and Triacylglycerol Accumulation in Phaeodactylum tricornutum.

Phaeodactylum tricornutum, a unicellular diatom, is considered a potential feedstock for the production of biofuel and a promising producer for high-value products eicosapentaenoic acid and fucoxanthin. However, a high-efficient cultivating strategy to achieve commercial production of triacylglycerol (TAG) from the diatom is an urgent demand. In this study, we optimized the content and ratio of nitrate and tryptone in the medium to enhance biomass and TAG accumulation simultaneously. Growth with tryptone as the sole nitrogen gave rise to the lowest cell density but the highest TAG content in P. tricornutum relative to nitrate, nitrite, ammonium or urea cultures. In 500 μM NaNO3 cultures, the growth of P. tricornutum increased with the increasing concentration (from 294 to 7056 μM nitrogen) of supplemented tryptone, however supplementation of high tryptone (≥882 μM nitrogen) decreased the neutral lipid content. Elevating nitrogen concentration from 294 to 882 μM via tryptone addition in 250 μM nitrate culture increased cell densities from day 6 to 10 and neutral lipid content on day 10. In particular, supplementing 588 μM nitrogen of tryptone in the 250 μM nitrate culture gave rise to the highest neutral lipid content on days 8 and 10 (increased by 109% and 62% relative to 500 μM nitrate-sole) with a comparable growth to that in 500 μM nitratesole culture from day 2 to 8. In conclusion, we optimized nitrate/tryptone ratio and found that a suitable tryptone addition to a relatively low nitrate culture was favourable to the biomass and TAG accumulation simultaneously in P. tricornutum.

Root endodermal suberization induced by nitrate stress regulate apoplastic pathway rather than nitrate uptake in tobacco (Nicotiana tabacum L.)

Nitrogen levels and distribution in the rhizosphere strongly regulate the root architecture. Nitrate is an essential nutrient and an important signaling molecule for plant growth and development. Hydroponic experiments were conducted to investigate the differences in endodermal suberization in tobacco (Nicotiana tabacum L.) roots at three nitrate levels. Nitrogen accumulation was detected in the roots, shoots, and xylem sap. Nitrate influx on the root surface was also measured using the non-invasive self-referencing microsensor technique (SRMT). RNA-Seq analysis was performed to identify the genes related to endodermal suberization, nitrate transport, and endogenous abscisic acid (ABA) biosynthesis. The results showed that root length, root-shoot ratio, nitrate influx on the root surface, and NiA and NRT2.4 genes were regulated to maintain the nitrogen nutrient supply in tobacco under low nitrate conditions. Low nitrate levels enhanced root endodermal suberization and hence reduced the apoplastic transport pathway, and genes from the KCS, FAR, PAS2, and CYP86 families were upregulated. The results of exogenous fluridone, an ABA biosynthesis inhibitor, indicated that suberization of the tobacco root endodermis had no relevance to radial nitrate transport and accumulation. However, ABA enhances suberization, relating to ABA biosynthesis genes in the CCD family and degradation gene ABA8ox1.

Extraction behaviors of minor actinides and rare earth elements with NTA amide extractants

ABSTRACT Nitrilotriacetamide (NTA amide) has been developed as an extractant for the mutual separation of minor actinides (MA; Am and Cm) and rare earth elements (REs) by solvent extraction. NTA amide is a tertiary amine in which the three carboxyl groups of nitrilotriacetic acid are amidated. NTA amides have six hydrophobic long-chain alkyl groups on the side chains, and they have enhanced solubility in organic solvents, thereby allowing for the use of nonpolar diluents, such as n-dodecane. This study examined the extraction behavior of MA and REs using four NTA amides with six side chains comprising n-octyl groups, 2-ethylhexyl groups, and a mixture of these groups. The results showed that the linear-type hexaoctyl NTA amide (HONTA) had the highest extraction ability for MA. Furthermore, the extraction behavior of MA and REs was different under low and high nitrate conditions, and that of scandium (Sc) was found to be considerably different depending on the side chains.

No Difference between the Efficacy of High-Nitrate and Low-Nitrate Vegetable Supplementation on Blood Pressure after 16 Weeks in Individuals with Early-Stage Hypertension: An Exploratory, Double-Blinded, Randomized, Controlled Trial.

Dietary inorganic nitrate lowers blood pressure (BP) in healthy individuals through improved nitric oxide (NO) bioavailability. However, there is limited evidence examining the long-term effects of dietary nitrate for managing hypertension. We aimed to determine whether the sustained intake of dietary nitrate improved BP and cardiovascular disease (CVD) risk factors in individuals with early-stage hypertension. The Dietary Nitrate (NO3) on BP and CVD Risk Factors (DINO3) Trial was a multi-center, double-blinded, parallel, randomized, controlled trial in participants with elevated BP. Participants were supplemented with high-nitrate (HN) (~400 mg nitrate) or low-nitrate (LN) vegetable powder (~50 mg nitrate) on top of their usual diets for 16 weeks. The primary outcome was office systolic BP at 16 weeks. The secondary outcomes were 24 h ambulatory BP, central BP, heart-rate-corrected augmentation index (AIx75), carotid-femoral pulse wave velocity (cf-PWV), lipids, and high-sensitivity C-reactive protein (hs-CRP). Sixty-six participants were randomized at baseline (39M:27F, age: 51.5 ± 10.8 years, BMI:27.9 ± 3.2 kg/m2). In an intention-to-treat analysis, no differences were observed between HN and LN groups in terms of office systolic BP at 16 weeks (3.91 ± 3.52 mmHg, p = 0.27) or secondary outcomes. In this exploratory study, sustained HN vegetable supplementation did not exhibit more favorable vascular effects than LN vegetable supplementation in individuals with elevated BP.

Field-grown lettuce production optimized through precision irrigation water management using soil moisture-based capacitance sensors and biodegradable soil mulching

AbstractScientists, environmentalists, and farmers are currently in pursuit of sustainable agricultural practices that can effectively ensure global food security while simultaneously mitigating environmental degradation. A field experiment was conducted to elucidate the impact of low-cost capacitance soil moisture-based sensors on lettuce (Lactuca sativa L.) irrigation water conservation, agro-physiological aspects, and nutritional characteristics. The experiment also involved the use of five different types of soil mulching films: white geotextile (WGup), green geotextile (GGup), black plastic (BPup), white geotextile for both above and below ground (WGup-down), green geotextile for both above and below ground (GGup-down), in addition to un-mulched soil (control). The findings demonstrated that the application of WGup, BPup, WGup&amp;down, and GGup&amp;down resulted in a significant improvement in irrigation water conservation, with WGup exhibiting the highest savings at 41.86%, while the control group exhibited the least amount of water savings at 19.87%. Moreover, the highest productivity levels were observed in plants mulched with GGup&amp;down, reaching 47,944.68 kg ha−1, whereas the lowest productivity was recorded in plants mulched with green geotextile GGup at 22,377.89 kg ha−1. In terms of irrigation water productivity (IWP), the order of effectiveness was BPup &gt; GGup-down &gt; WGup &gt; WGup-down &gt; GGup &gt; Control, with BPup achieving the highest IWP at 60.19 kg m−3 and the control treatment reporting the lowest at 27.80 kg m−3. The percentage of the irrigation water applied for crop evapotranspiration (Irc) showed that the control treatment saved the least amount of irrigation water, saving only 19.87%, while the best treatment was WGup, achieved the highest percentage of irrigation water savings at 41.86%. Additionally, mulched plants exhibited higher levels of nutrients (N, P, Ca, Mg, Fe, Mn, and Zn), ascorbic acid (AsA), and total phenol content (TPC), while showing lower nitrate content in the leaves compared to non-mulched plants. Overall, the utilization of soil moisture-based capacitance sensors and biodegradable mulching films has proven to be highly effective and low cost by 16.633 US$ year−1 to enhance irrigation water productivity, growth performance, nutritional quality, and overall productivity of lettuce crops, thereby contributing to the sustainability of lettuce production in arid regions.

High efficiency conversion of low concentration nitrate boosted with amorphous Cu0 nanorods prepared via in-situ reconstruction

Electrocatalytic nitrate reduction reaction (NO3−RR) is a green and competitive method for removing nitrate from water, requiring highly active and long-term stable electrocatalysts. In this work, we report a Cu0 nanorod catalyst with disordered structure (re-Cu NRs), prepared by electrochemical in situ reconfiguration of copper-based nitrides (Cu3N NRs). The amorphous structure allows the exposure of abundant active sites to enhance the electrocatalytic activity because of the disordered atomic arrangement. At a potential of −1.2V vs. Ag/AgCl, the re-Cu NRs catalyst achieved nearly 100% nitrate conversion within 120 min at a low nitrate concentration (50 mg/L), without the accumulation of nitrite. In-situ DEMS detection reveals that the NO3−RR on re-Cu NRs followed the pathway of *NO3− → *NO2− → *NO → *N → *NH → *NH2 → *NH3. Furthermore, combining this proposed pathway with electrochlorination could efficiently transform ammonia into harmless N2 (∼99.41%). Theoretical calculations confirm that the amorphous structure on the surface of re-Cu NRs catalysts can facilitate strongly adsorbed nitrate, weaken the rate-determining step of *NH3 → NH3, and suppress Hydrogen evolution reaction (HER). This study provides a new approach for designing efficient and stable amorphous catalysts for electrocatalytic nitrate reduction.

The bio-cathode of microbial fuel cells systems: Performance analysis under different microbial community conditions

This study aims to investigate the conversion of different microbial community compositions in the cathode chamber in a dual-chamber bioelectrochemical system. A denitrifying bacterial community, or sludge, was enriched for denitrification by microbial consortia and subsequently acclimatized within the cathodic chamber of microbial fuel cells, either within a mixed microbial community sludge microbial fuel cell (M-MFC) or a pure culture of microorganisms in a microbial fuel cell (P-MFC). The bioelectrochemical systems were treated with different nitrate concentrations in the cathodic chamber: the MFC with low concentration nitrate (MFC1, 25 mg/L nitrate; MFC2 50 mg/L nitrate), the MFC with medium concentration nitrate(MFC3, 75 mg/L nitrate; MFC4 100 mg/L nitrate), and MFC with high concentration nitrate (MFC5, 125 mg/L nitrate; MFC6 150 mg/L nitrate; MFC7 175 mg/L nitrate), and the initial COD in the anodic chamber was based on demand(C to N ratio is 5). M-MFC exhibited better-electrogenerated capability than P-MFC. However, P-MFC exhibited better nitrogen removal performance compared to M-MFC. The best performance was attained by both types of MFCs when the nitrate content was 100 mg/L. The maximum output voltages in M-MFC4 and P-MFC4 were 449 mV and 171 mV, respectively. The average conversion rate of M-MFC4 and P-MFC4 were 2.9 mg*L−1 *h−1 and 10.5 mg*L−1 *h−1, respectively. The analysis of the microbial community of two treated MFCs in the cathode chamber in the optimal state indicated that non-electrode denitrification predominantly occurs in P-MFC. The cathode chambers were mostly populated by denitrifying microorganisms. The dominant species in M-MFC were Azonexus, Zoogloea, Ignavibacterium, and Pirellula, and the dominant species in P-MFC were Comamonas, Aeromonas, and Acidovorax. The species was assessed by qPCR analysis, and the results validated the use of a bacterial consortium for domestication as a more suitable method to improve the stability and performance of the MFCs.

Advancing Porphyra linearis (Rhodophyta, Bangiales) culture: low cost artificial seawater, nitrate supply, photosynthetic activity and energy dissipation

Advancing Porphyra linearis (Rhodophyta, Bangiales) culture: low cost artificial seawater, nitrate supply, photosynthetic activity and energy dissipation

Removal of nitrate and phosphate by aquatic plants during aquarium‐based ornamental fish production

AbstractObjectiveThe rising demand for ornamental fish and plants in aquariums is met through industrial production. However, higher production densities may negatively impact water quality (such as ammonia, nitrate, nitrite, and dissolved oxygen levels), thus impacting production. This can be mitigated by utilizing specific aquatic plants to promote sustainable ornamental fish production. This study aimed to determine how the water quality in ornamental fish tanks can be improved using two floating aquarium plant species: Najas grass Najas guadalupensis and Java moss Taxiphyllum barbieri.MethodsThe efficiency of nitrate and phosphate filtration by the two plant species was determined in aquariums containing Endler Guppies Poecilia wingei. The duration of the study was 4 weeks, and the water quality parameters were measured weekly. The growth rates of the two plants were measured at the beginning and end of the study period.ResultNajas grass effectively maintained lower nitrate and phosphate levels while showing robust growth. By week 4, nitrate levels in control tanks rose to 33.75 and 35.00 mg/L in the two independent experiments, while nitrate in tanks with Najas grass only reached 8.75 and 11.50 mg/L. Phosphate levels in control tanks increased to 2.42 and 2.40 mg/L compared to 1.075 and 1.05 mg/L in tanks with Najas grass. In single‐species tanks, Najas grass showed a 1.6‐fold biomass increase, while Java moss showed a 1.2‐fold increase. In tanks with both species, Najas grass biomass increased significantly, whereas Java moss biomass decreased.ConclusionThe superior competitive ability of Najas grass (allelopathy and increased nutrient uptake) underlies the findings of this study and indicates that this species is a better option for maintaining low levels of nitrate and phosphate in aquarium water. This finding can contribute to creating a cleaner and healthier environment for fish species involved in industrial ornamental fish production and trade.

Effects of Dietary Nitrate Supplementation on High-Intensity Cycling Sprint Performance in Recreationally Active Adults: A Systematic Review and Meta-Analysis.

This systematic review and meta-analysis investigated the influence of dietary nitrate supplementation on performance metrics during cycling sprint exercise according to the PRISMA guidelines. Searches were conducted on MEDLINE, PubMed, ScienceDirect, Scopus, and SPORTDiscus databases up to September 2023. Inclusion criteria were healthy recreationally active men and women who consumed nitrate-rich and nitrate-deficient beetroot juice to assess performance outcomes of mean power, peak power, time-to-peak power, and minimum power during 30-s cycling sprints. Risk of bias was assessed using the Cochrane Risk of Bias 2 and TESTEX tools and funnel plots. A random effects model was performed on six studies and showed that dietary nitrate had significant effects on time-to-peak power (SMD: -0.66, 95% CI: -1.127 to -0.192, p = 0.006) but not on mean power, peak power, or minimum power. Subgroup analysis revealed that an acute low nitrate dose improved time-to-peak power (SMD: -0.977, 95% CI: -1.524 to -0.430, p < 0.001) but not after a multiday moderate nitrate dose (SMD: -0.177, 95% CI: -0.619 to -0.264, p = 0.431). These data suggest that acute nitrate supplementation can benefit time-to-peak power during 30-s cycling sprints, but due to the limited availability of data and heterogeneity in methodology, these results should be interpreted with caution. There was insufficient data on women to analyze sex-based differences. Future studies are required to provide insight on how supplementation regimen and population impact the effects of dietary nitrate for enhancing cycling sprint performance.

Transcriptomic responses to shifts in light and nitrogen in two congeneric diatom species.

Light and nitrogen availability are basic requirements for photosynthesis. Changing in light intensity and nitrogen concentration may require adaptive physiological and life process changes in phytoplankton cells. Our previous study demonstrated that two Thalassiosira species exhibited, respectively, distinctive physiological responses to light and nitrogen stresses. Transcriptomic analyses were employed to investigate the mechanisms behind the different physiological responses observed in two diatom species of the genus Thalassiosira. The results indicate that the congeneric species are different in their cellular responses to the same shifting light and nitrogen conditions. When conditions changed to high light with low nitrate (HLLN), the large-celled T. punctigera was photodamaged. Thus, the photosynthesis pathway and carbon fixation related genes were significantly down-regulated. In contrast, the small-celled T. pseudonana sacrificed cellular processes, especially amino acid metabolisms, to overcome the photodamage. When changing to high light with high nitrate (HLHN) conditions, the additional nitrogen appeared to compensate for the photodamage in the large-celled T. punctigera, with the tricarboxylic acid cycle (TCA cycle) and carbon fixation significantly boosted. Consequently, the growth rate of T. punctigera increased, which suggest that the larger-celled species is adapted for forming post-storm algal blooms. The impact of high light stress on the small-celled T. pseudonana was not mitigated by elevated nitrate levels, and photodamage persisted.

The Mitigating Effects of Biostimulant Amendments on the Response of Purslane Plants Grown under Drought Stress Conditions

Portulaca oleracea L. is a wild edible plant with high potential for exploitation in commercial cropping systems due to its nutritional value and great adaptability to abiotic stress conditions. The present study aimed to investigate the response of purslane plants grown under drought stress conditions (100%, 80%, and 60% of field capacity (FC)) and the implementation of biostimulant amendments (control without amendment, plant growth-promoting rhizobacteria (PGPR), mycorrhiza, and effective microorganisms (EMs)) for two consecutive years. In the two-year experiment, the greatest height was recorded in plants grown under no-stress conditions and inoculated with PGPR. The highest branch number, and fresh and dry weight of aboveground and underground parts were observed under no-stress conditions at the mycorrhiza treatment. Moreover, mycorrhiza application in plants growing under 100% FC resulted in the highest N, P, total carbohydrates, and vitamin C and the lowest nitrate and proline contents in leaves. Purslane plants grown under 100% FC and inoculated with PGPR treatment resulted in the highest K and total chlorophyll leaf contents. Additionally, growing plants under mild drought stress (80% FC) combined with biostimulant application (e.g., inoculation with mycorrhiza, PGPR, and EM) may improve plant growth characteristics and mitigate negative stress effects. In general, the applied biostimulant amendments alleviated the adverse effects of drought on plant growth and leaf chemical composition indicating the importance of sustainable strategies to achieve high yield and sufficient quality within the climate change scenario.

(Invited) Understanding Potential Losses and pH Distribution in Electrochemical Nitrate Reduction Reaction to Ammonia

Electrochemical nitrate reduction reaction (NO3 -RR) to ammonia is a promising route to eliminate one of the major pollutants in surface and groundwater. When powered by renewable electricity, electrolysis provides a sustainable method to generate ammonia from nitrate ions, facilitating the transition from a linear to a circular economy. Optimizing the physical and chemical properties of electrolysis cells is crucial to make this process economically viable for widespread implementation. Here, we explore how the choice of current density, conductivity, pH, inter-electrode distance, membrane, catalyst, and buffer solution affect nitrate removal performance and efficiency. We develop a modeling framework to investigate the cell characteristics and fluid dynamics during electrochemical NO3-RR using both laminar and bubbly flows. To obtain more precise results, we employed the bubbly flow model (i.e., Multi-phase Fluid) to take into account how gas production near the electrode surface affects liquid velocity, pH distribution, and, ultimately, potential losses. We exploit mass transfer theory to include the current density effect on migration and diffusion. In the absence of a buffer solution, the Nernstian loss became a significant portion of the polarization loss, which increased with current density. We identified the positive effect of the membrane on energy efficiency to be more significant at smaller inter-electrode distances. This study provides insights into the origin of potential losses and pH distribution, enabling electrochemical cell optimization for renewable fuel synthesis. Next, we will discuss our recent work on designing single atom alloys (SAAs) for selective conversion of low concentration nitrate ions in natural wastewater streams from Dairy farm into ammonia. We benchmarked the catalyst's selectivity, activity, and stability following standard protocols established in the field of nitrogen fixation, including control experiments by using an electrolyte that does not contain nitrate ions and performing experiments under the same operating conditions using nitrogen isotopes (i.e., 14NO3 -, 15NO3 -).

(Invited) Fundamentals of Single Atom Alloy Catalysts for Electrochemical Nitrate Reduction to Ammonia

Electrochemical conversion of toxic nitrate into useful ammonia provides a route to remediating the most frequent water pollutant while simultaneously generating one of the most produced bulk chemicals. While highly desirable, this conversion is plagued by complications including a highly branching reaction pathway - which can produce highly toxic undesirable products, the need to reduce a negatively charged species, a relatively low nitrate concentration, and competition for electrons between nitrate reduction and parasitic hydrogen evolution. Therefore, electrocatalysts must be developed which are highly selective not only for nitrate over other species in the water matrix, but also selective to the desired ammonia product. Single atom alloy catalysts, where a single atom of one element is embedded in a solvating phase of a secondary element, provides an opportunity to engineer catalysts with atomic level precision. In this presentation, we will outline the fundamental behavior of single atom alloy for nitrate reduction. We explore this topic through density functional theory calculations of the reaction mechanisms, including thermodynamics and kinetic aspects. Particularly, we will discuss the effect of single atom identity, effect of matrix element, and pH and potential. We show that the ability of the single atom to localize the N* species drives the reduction towards ammonia formation, as exemplified by Ru in Cu, while facile exchange of N* between the single atom site and the matrix leads to the formation of N2 or other undesirable products, as exemplified by Pd in Cu and Au in Cu, respectively. We also discuss the importance of the selection of the solvating element; for example, Cu is a good solvating metal because it is a good conductor, while minimizing the hydrogen evolution reaction. Further, we discuss the limits of pH and potential on the performance. In general, higher pH and more moderately negative potentials favor nitrate reduction to NH3 or N2, while lower pH and more negative potentials drive H2 evolution, and generation of NOx species.

Efficient Electroreduction of Low Nitrate Concentration via Nitrate Self-Enrichment and Active Hydrogen Inducement on the Ce(IV)-Co3O4 Cathode.

Low concentrations of nitrate (NO3-) widely exist in wastewater, post-treated wastewater, and natural environments; its further disposal is a challenge but meaningful for its discharge goals. Electroreduction of NO3- is a promising method that allows to eliminate NO3- and even generate higher-value NH3. However, the massive side reaction of hydrogen evolution has raised great obstacles in the electroreduction of low concentrations of NO3-. Herein, we present an efficient electroreduction method for low or even ultralow concentrations of NO3- via NO3- self-enrichment and active hydrogen (H*) inducement on the Ce(IV)-Co3O4 cathode. The key mechanism is that the strong oxytropism of Ce(IV) in Co3O4 resulted in two changes in structures, including loose nanoporous structures with copious dual adsorption sites of Ce-Co showing strong self-enrichment of NO3- and abundant oxygen vacancies (Ovs) inducing substantial H*. Ultimately, the bifunctional role synergistically promoted the selective conversion of NH3 rather than H2. As a result, Ce(IV)-Co3O4 demonstrated a NO3- self-enrichment with a 4.3-fold up-adsorption, a 7.5-fold enhancement of NH3 Faradic efficiency, and a 93.1% diminution of energy consumption when compared to Co3O4, substantially exceeding other reported electroreduction cathodes for NO3- concentrations lower than 100 mg·L-1. This work provides an effective treatment method for low or even ultralow concentrations of NO3-.