Nitrification Research Articles

H* Species Regulation by Mn-Co(OH)2 for Efficient Nitrate Electro-reduction in Neutral Solution.

During the electrocatalytic NO3 - reduction reaction (NO3 - RR) under neutral condition, the activation of H2 O to generate H* and the inhibition of inter-H* species binding, are critically important but remain challenging for suppressing the non-desirable hydrogen evolution reaction (HER). Here, a Mn-doped Co(OH)2 (named as Mn-Co(OH)2 ) has been synthesized by in situ reconstruction in the electrolyte, which is able to dissociate H2 O molecules but inhibits the binding of H* species between each other owing to the increased interatomic spacing by the Mn-doping. The Mn-Co(OH)2 electrocatalyst offers a faradaic efficiency (FE) of as high as 98.9±1.7% at -0.6 V vs. the reversible hydrogen electrode (RHE) and an energy efficiency (EE) of 49.90±1.03% for NH3 production by NO3 - RR, which are among the highest of the recently reported state-of-the-art catalysts in neutral electrolyte. Moreover, negligible degradation at -200 mA cm-2 has been found for at least 500 h, which is the longest catalytic durations ever reported. This work paves a novel approach for the design and synthesis of efficient NO3 - RR electrocatalysts.

Efficient nitrate and Cr(VI) removal by denitrifier: The mechanism of S. oneidensis MR-1 promoting electron production, transportation and consumption

When Cr(VI) and nitrate coexist, the efficiency of both bio-denitrification and Cr(VI) bio-reduction is poor because chromate hinders bacterial normal functions (i.e., electron production, transportation and consumption). Moreover, under anaerobic condition, the method about efficient nitrate and Cr(VI) removal remained unclear. In this paper, the addition of Shewanella oneidensis MR-1 to promote the electron production, transportation and consumption of denitrifier and cause an increase in the removal of nitrate and Cr(VI). The efficiency of nitrate and Cr(VI) removal accomplished by P. denitrificans as a used model denitrifier increased respectively from 51.3% to 96.1% and 34.3% to 99.8% after S. oneidensis MR-1 addition. The mechanism investigations revealed that P. denitrificans provided S. oneidensis MR-1 with lactate, which was utilized to secreted riboflavin and phenazine by S. oneidensis MR-1. The riboflavin served as coenzymes of cellular reductants (i.e., thioredoxin and glutathione) in P. denitrificans, which created favorable intracellular microenvironment conditions for electron generation. Meanwhile, phenazine promoted biofilm formation, which increased the adsorption of Cr(VI) on the cell surface and accelerated the Cr(VI) reduction by membrane bound chromate reductases thereby reducing damage to other enzymes respectively. Overall, this strategy reduced the negative effect of chromate, thus improved the generation, transportation, and consumption of electrons. SynopsisThe presence of S. oneidensis MR-1 facilitated nitrate and Cr(VI) removal by P. denitrificans through decreasing the negative effect of chromate due to the metabolites’ secretion.

4-Methyl-1-(prop-2-yn-1-yl)-1H-1,2,3-triazole (MPT): A Novel, Highly Efficient Nitrification Inhibitor for Agricultural Applications

4-Methyl-1-(prop-2-yn-1-yl)-1<i>H</i>-1,2,3-triazole (MPT): A Novel, Highly Efficient Nitrification Inhibitor for Agricultural Applications

Deficient Tin oxide nanofibers with regulated valence for efficient nitrate reduction to ammonia

Electrocatalytic nitrate reduction emerges as a promising process for removal of nitrate and simultaneous production of value-added ammonia, but robust electrocatalysts with high selectivity are required due to the large dissociation energy of N≡O in nitrate. Herein, we propose oxygen deficient Tin oxide nanofibers with regulated bivalence (SnO) and tetravalency (SnO2-δ) as efficient catalysts for nitrate reduction reaction (NitRR). Such quadrivalent catalyst achieves a large NH3 yield of 17.27 mg h−1 mgcat.−1 and an extremely high Faradaic Efficiency (FE) of 95.67 % in 0.1 M PBS with 0.1 M NO3−, which also exhibits excellent electrochemical stability. Material calculations reveal that SnO2-δ exhibits a direct band gap of 0.79 eV, smaller than 1.17 eV for SnO with an indirect band gap, and the potential determining step (*NO2 → *NO) hits a free energy change of only 0.1 eV.

Ti3+ redox dynamics enabling efficient nitrate reduction to ammonia on Ti2O3

The electrochemical nitrate reduction reaction (NO3−RR) demonstrates significant promise as a sustainable pathway for ammonia (NH3) synthesis and regulating the Earth's nitrogen cycle. However, its advancement is currently hindered by low catalytic activity, particularly limited by the sluggish rate-determining step of NO2− formation. Herein, we capitalize on the highly active and versatile redox properties of Ti3+ in Ti2O3, exploiting its spontaneous reduction of NO3− to NO2− to overcome the sluggish rate-determining step. Subsequently, the electrochemical reduction process continuously reduces the generated high valence titanium species back to Ti3+, creating a redox closed loop, and enabling the continuous NH3 synthesis. The catalyst achieves an outstanding NH3 production rate of 19.04 mg h−1 mgcat.–1 with a Faradaic efficiency of 97.8 %. Using in-situ electrochemical electron paramagnetic resonance technology, we explored dynamic changes of Ti3+ in Ti2O3 during the process, while in-situ electrochemical infrared spectroscopy provided insights into intermediates' evolution. Density functional theory calculations confirmed Ti2O3′s highly active NO3−RR.

Competitive enrichment of comammox Nitrospira in floccular sludge

The discovery of complete ammonium oxidation (comammox) has subverted the traditional perception of two-step nitrification, which plays a key role in achieving biological nitrogen removal from wastewater. Floccular sludge-based treatment technologies are being applied at the majority of wastewater treatment plants in service where detection of various abundances and activities of comammox bacteria have been reported. However, limited efforts have been made to enrich and subsequently characterize comammox bacteria in floccular sludge. To this end, a lab-scale sequencing batch reactor (SBR) in the step-feeding mode was applied in this work to enrich comammox bacteria through controlling appropriate operational conditions (dissolved oxygen of 0.5 ± 0.1 g-O2/m3, influent ammonium of 40 g-N/m3 and uncontrolled longer sludge retention time). After 215-d operation, comammox bacteria gradually gained competitive advantages over counterparts in the SBR with a stable nitrification efficiency of 92.2 ± 2.2 %: the relative abundance of Nitrospira reached 42.9 ± 1.3 %, which was 13 times higher than that of Nitrosomonas, and the amoA gene level of comammox bacteria increased to 7.7 ± 2.1 × 106 copies/g-biomass, nearly 50 times higher than that of conventional ammonium-oxidizing bacteria. The enrichment of comammox bacteria, especially Clade A Candidatus Nitrospira nitrosa, in the floccular sludge led to (i) apparent affinity constants for ammonium and oxygen of 3.296 ± 0.989 g-N/m3 and 0.110 ± 0.004 g-O2/m3, respectively, and (ii) significantly low N2O and NO production, with emission factors being 0.136 ± 0.026 % and 0.023 ± 0.013 %, respectively.

Pyrite and humus soil-coupled mixotrophic denitrification system for efficient nitrate and phosphate removal

Pyrite and humus soil-coupled mixotrophic denitrification system for efficient nitrate and phosphate removal

Enhanced Electrocatalytic Nitrate Reduction to Ammonia Using Functionalized Multi-Walled Carbon Nanotube-Supported Cobalt Catalyst.

Ammonia (NH3) is vital in modern agriculture and industry as a potential energy carrier. The electrocatalytic reduction of nitrate (NO3-) to ammonia under ambient conditions offers a sustainable alternative to the energy-intensive Haber-Bosch process. However, achieving high selectivity in this conversion poses significant challenges due to the multi-step electron and proton transfer processes and the low proton adsorption capacity of transition metal electrocatalysts. Herein, we introduce a novel approach by employing functionalized multi-walled carbon nanotubes (MWCNTs) as carriers for active cobalt catalysts. The exceptional conductivity of MWCNTs significantly reduces charge transfer resistance. Their unique hollow structure increases the electrochemical active surface area of the electrocatalyst. Additionally, the one-dimensional hollow tube structure and graphite-like layers within MWCNTs enhance adsorption properties, thus mitigating the diffusion of intermediate and stabilizing active cobalt species during nitrate reduction reaction (NitRR). Using the MWCNT-supported cobalt catalyst, we achieved a notable NH3 yield rate of 4.03 mg h-1 cm-2 and a high Faradaic efficiency of 84.72% in 0.1 M KOH with 0.1 M NO3-. This study demonstrates the potential of MWCNTs as advanced carriers in constructing electrocatalysts for efficient nitrate reduction.

Crystalline modulation of zirconia for efficient nitrate reduction to ammonia under ambient conditions.

Zirconia as a polycrystalline catalyst can be effectively tuned by doping low-valence elements and meanwhile form abundant oxygen vacancies. Herein, the crystalline structures of zirconia are modulated by scandium doping and proposed as a robust catalyst for nitrate reduction to ammonia. The tetragonal zirconia achieves a maximum ammonia yield of 16.03 mg h-1 mgcat.-1, superior to the other crystal forms. DEMS tests unveil the reaction pathway and theoretical calculations reveal the low free energy of -0.22 eV for nitrate adsorption at the tetragonal zirconia.

Octahedral CoS2 electrocatalysts for efficient nitrate reduction to ammonia

Octahedral CoS2 nanocrystals are highly active to ambiently reduce NO3− to NH3 (NO3RR). DFT calculations reveal that CoS2 (111) with high electron supply capacity is responsible for enhanced NO3RR activity.

The Applicability of the Solar Powered Aquaponics Mobile Unit at Sharjah Campus for Sustainable Perspective of Food Security

By recognizing the limitations of conventional farming methods in meeting the escalating global population and the resulting increased demand for food, this study emphasizes the crucial need for sustainable agriculture techniques. This work focuses on establishing a solar-powered aquaponics system as a sustainable, cost-effective, and ecologically responsible approach to ensure food security in the UAE. This paper describes the implemented aquaponics prototype within the mobile learning unit at the Sharjah Campus of the Higher College of Technology by integrating fish and plant cultivation in a closed-loop system to prioritize water conservation and eliminate reliance on soil, align with United Nations sustainable development goals and promoting sustainable farming practices for robust food production in the UAE. The solar energy system was employed for 6 photovoltaic modules for LED lights and 13 photovoltaic modules for the pumping system, with a total installation area of 50 m2. It is found that the power requirements are comparatively lower than the vertical setup, which requires 6 photovoltaic modules for the LED and 14 photovoltaic modules for the pumping system. This paper assesses the functional parameters, including electricity consumption by solar panels and water pump energy usage. Furthermore, investigates the impact of fish and plant interactions on water quality and nitrification efficiency, addressing deficiencies in traditional farming and aquaculture. Monthly evaluations reveal favorable conditions, with pH levels of 6.4-7.2, temperatures between 31.8°C and 34.7°C, and ammonia levels at 1 mg.L-1. Aquatic life exhibits an 83% survival rate and a specific growth rate of 3.92% daily.

Designing Efficient Nitrate Reduction Electrocatalysts by Identifying and Optimizing Active Sites of Co-Based Spinels.

Cobalt-based spinel oxides (i.e., Co3O4) are emerging as low-cost and selective electrocatalysts for the electrochemical nitrate reduction reaction (NO3-RR) to ammonia (NH3), although their activity is still unsatisfactory and the genuine active site is unclear. Here, we discover that the NO3-RR activity of Co3O4 is highly dependent on the geometric location of the Co site, and the NO3-RR prefers to occur at octahedral Co (CoOh) rather than tetrahedral Co (CoTd) sites. Moreover, CoOhO6 is electrochemically transformed to CoOhO5 along with the formation of O vacancies (Ov) during the process of NO3-RR. Both experimental and theoretic results reveal that in situ generated CoOhO5-Ov configuration is the genuine active site for the NO3-RR. To further enhance the activity of CoOh sites, we replace inert CoTd with different contents of Cu2+ cations, and a volcano-shape correlation between NO3-RR activity and electronic structures of CoOh is observed. Impressively, in 1.0 M KOH, (Cu0.6Co0.4)Co2O4 with optimized CoOh sites achieves a maximum NH3 Faradaic efficiency of 96.5% with an ultrahigh NH3 rate of 1.09 mmol h-1 cm-2 at -0.45 V vs reversible hydrogen electrode, outperforming most of other reported nonprecious metal-based electrocatalysts. Clearly, this work paves new pathways for boosting the NO3-RR activity of Co-based spinels by tuning local electronic structures of CoOh sites.

Size-induced d band center upshift of copper for efficient nitrate reduction to ammonia

Electrocatalytic nitrate reduction (NO3RR) technique has emerged as a hotspot in NH3 production, for its practicability, and a series of advanced electrocatalysts with high activity and robust stability needed to be constructed in today's era. In this work, size-tunable Cu nanoparticles on porous nitrogen-doped hexagonal carbon nanorods (Cu@NHC) were reasonably designed and served for catalyzing NO3RR in neutral media. Especially, Cu30%@NHC demonstrated a remarkable electroactivity for NH3 production as it showed a suitable grain size with massive catalytic centers and favorable d band structure with faster *NO3−-to-*NO2− catalytic dynamics. As expected, Cu30%@NHC (3628.28 µg h−1 mgcat.−1) had a much higher NH3 yield than those for Cu20%@NHC (1268.42 µg h−1 mgcat.−1) and Cu40%@NHC (725.03 µg h−1 mgcat.−1). And those collected NH3 products indeed derived from NO3RR process revealed by 15N isotope-labeling and systemic control tests. Moreover, Cu30%@NHC was also durable for NO3RR bulk electrolysis with minor loss in activity. This work offered an effective modifying tactics to boost NO3RR catalysis and could guide the design of other advanced electrocatalysts via size-induced surface engineering.

Enhanced Metal–Support Interfacial Interaction of Pd@FeNi-CoO Composites for Efficient Nitrate Reduction to Ammonia

Enhanced Metal–Support Interfacial Interaction of Pd@FeNi-CoO Composites for Efficient Nitrate Reduction to Ammonia

Aquaponics: A Sustainable Path to Food Sovereignty and Enhanced Water Use Efficiency

This comprehensive review explores aquaponics as an environmentally friendly solution aligned with SDGs and food sovereignty, assessing various aspects from system design to automation, and weighing social, economic, and environmental benefits through literature and case studies. However, challenges persist in obtaining organic certification and legislative recognition, hindering its growth. Achieving remarkable water use efficiency, up to 90%, relies on adaptable fish species like Nile tilapia and carp. Nutrient-rich fish feeds notably benefit low-nutrient-demanding greens. Ensuring water quality and efficient nitrification are pivotal, supported by IoT systems. Despite its efficiency, integrating Industry 4.0 involves complexity and cost barriers, necessitating ongoing innovation. Economies of scale and supportive horticultural policies can bolster its viability. Aquaponics, known for its efficiency in enhancing crop yields while minimizing water use and waste, is expanding globally, especially in water-scarce regions. Aquaponics, pioneered by the University of the Virgin Islands, is expanding in Europe, notably in Spain, Denmark, Italy, and Germany. Asia and Africa also recognize its potential for sustainable food production, especially in water-limited areas. While it offers fresh produce and cost savings, challenges arise in scaling up, managing water quality, and meeting energy demands, particularly for indoor systems. Egypt’s interest in desert and coastal regions highlights aquaponics’ eco-friendly food production potential. Despite the associated high costs, there is a quest for practical and affordable designs for everyday integration. Research in arid regions and industry advancements are crucial for aquaponics’ global food production potential. Deeper exploration of intelligent systems and automation, particularly in large-scale setups, is essential, highlighting the industry’s promise. Practical application, driven by ongoing research and local adaptations, is a key to fully harnessing aquaponics for sustainable food production worldwide.

Tire materials disturb transformations of nitrogen compounds and affect the structure of biomass in aerobic granular sludge reactors

Tire materials (TMs) present a notable hazard due to their potential to release harmful chemicals and microplastics into the environment. They can infiltrate wastewater treatment plants, where their effects remain inadequately understood, raising concerns regarding their influence on treatment procedures. Thus, this study investigated the impact of TMs in wastewater (10, 25, 50 mg/L) on wastewater treatment efficiency, biomass morphology, and microbial composition in aerobic granular sludge (AGS) reactors. TM dosage negatively correlated with nitrification and denitrification efficiencies, reducing overall nitrogen removal, but did not affect the efficiency of chemical-oxygen-demand removal. The presence of TMs increased the diameter of the granules due to TM incorporation into the biomass. The most frequently leached additives from TMs were N-(1,3-dimethylbutyl)-N′-phenyl-1,4-phenylenediamine, benzothiazole (BTH), and 2-hydroxybenzothiazole. In the treated wastewater, only BTH and aniline were detected in higher concentrations, which indicates that tire additives were biodegraded by AGS. The microbial community within the AGS adapted to TMs and their chemicals, highlighting the potential for efficient degradation of tire additives by bacteria belonging to the genera Rubrivivax, Ferruginibacter, and Xanthomonas. Additionally, our research underscores AGS's ability to incorporate TMs into biomass and effectively biodegrade tire additives, offering a promising solution for addressing environmental concerns related to TMs.

A novel combined system for efficient nitrate removal using a continuous flow electrocoagulation and sand filtration (FECF) reactor: Statistical analysis by Taguchi design.

In this study, a new hybrid bench-scale electrocoagulation-sand filtration (FECF) reactor was developed for purifying nitrate-contaminated samples. Before and after electrochemical treatment, two sand filters were included in this continuous system to facilitate the purification procedure, and the contaminated water flows horizontally through the entire system according to a specific hydraulic gradient within the reactor, resulting in water purification. Significant improvement in treatment performance was observed due to the presence of metal hydroxides in the second filter media that were not fully involved in the electrocoagulation treatment. Energy dispersive X-ray (EDX) analysis was performed to detect metal hydroxide species in the sand media, and the need for filter regeneration was evaluated by monitoring changes in the system flow rate. Moreover, an evaluation of the effects of different factors including operating time, current intensity, initial pH, type of anode and cathode, initial nitrate concentration, hydraulic head level inside the reactor, number of electrodes, and NaCl electrolyte concentration on the performance of nitrate removal was conducted through the Taguchi design. Further, ANOVA analysis verified the accuracy of the predicted model, and the variables were classified based on their relative importance in the FECF process. According to the regression model, 97% of nitrates were removed with Al electrodes as anode and Fe as cathode, 70 min purification time, current intensity of 3 A, 100 mg/l initial nitrate concentration, pH 8, electrolyte concentration of 1 g/l, electrode number of 6, and 1.5 cm head level.

Enhancing biocathode denitrification performance with nano-Fe3O4 under polarity period reversal

The presence of excessive concentrations of nitrate poses a threat to both the environment and human health, and the bioelectrochemical systems (BESs) are attractive green technologies for nitrate removal. However, the denitrification efficiency in the BESs is still limited by slow biofilm formation and nitrate removal. In this work, we demonstrate the efficacy of novel combination of magnetite nanoparticles (nano-Fe3O4) with the anode-cathode polarity period reversal (PPR-Fe3O4) for improving the performance of BESs. After only two-week cultivation, the highest cathodic current density (7.71 ± 1.01 A m−2) and NO3−-N removal rate (8.19 ± 0.97 g m−2 d−1) reported to date were obtained in the PPR-Fe3O4 process (i.e., polarity period reversal with nano-Fe3O4 added) at applied working voltage of −0.2 and −0.5 V (vs Ag/AgCl) under bioanodic and biocathodic conditions, respectively. Compared with the polarity reversal once only process, the PPR process (i.e., polarity period reversal in the absence of nano-Fe3O4) enhanced bioelectroactivity through increasing biofilm biomass and altering microbial community structure. Nano-Fe3O4 could enhance extracellular electron transfer as a result of promoting the formation of extracellular polymers containing Fe3O4 and reducing charge transfer resistance of bioelectrodes. This work develops a novel biocathode denitrification strategy to achieve efficient nitrate removal after rapid cultivation.

Highly efficient nitrate removal in sulfur-based constructed wetlands: Microbial mechanisms and environmental risks

Nitrate is widely distributed in groundwater, posing an increasing threat to both water resources and human health. In this study, the treatment performance, removal mechanisms and environmental risks of sulfur-based constructed wetlands (CWs) for purifying nitrate-contaminated groundwater were investigated. Results showed that sulfur-based CWs could achieve the highest nitrate removal (95%). However, sulfate was largely produced as a by-product in sulfur-based CWs, which declined the nitrogen and phosphorus assimilation by plants. Metagenomic analysis indicated that autotrophs denitrifiers (e.g., Thiobacillus) were enriched, and the abundance of nitrate removal genes was enhanced in sulfur-based CWs. Additionally, sulfur cycle was formed in sulfur-based CWs, which explained the highest nitrate removal reasonably. This study provides comprehensive insights into the nitrate removal mechanisms in sulfur-based CWs and the associated environmental risks in purifying the polluted groundwater.

Nitrite improved nitrification efficiency and enriched ammonia-oxidizing archaea and bacteria in the simultaneous nitrification and denitrification process

Simultaneous nitrification and denitrification (SND) is effective and energy-saving for wastewater treatment. As an inevitable intermediate product in the SND process, nitrite affects the efficiency of ammonia oxidation and the composition of nitrifiers. To investigate the impact of nitrite on ammonia oxidation efficiency, two reactors performing SND were respectively operated without nitrite (R1 as control) and with 20 mg N/L nitrite addition (R2 as experimental). The total nitrogen removal efficiency was 74.5% in R1 while 99.0% in R2. With nitrite addition (i.e., 20 mg N/L), the ammonia removal rate in R2 increased to 4.5 times of that in R1. The ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) contributed to respective around 46.9% and 41.8% ammonia removal in R2 based on the results of experiments with specific inhibitors. The number of respective AOA and AOB ammonia monooxygenase gene (amoA) copies increased by 280 and 30 times due to nitrite addition, according to the qPCR results. The high-throughput sequencing results illustrated the increase of dominant AOB species from 0.40% in R1 to 1.59% in R2 and the phylogenetic tree analysis revealed a close link to Nitrosospira multiformis. These results indicated that the ammonia removal efficiency was improved and AOA/AOB were enriched by nitrite addition. The specific nitrite reductases in AOA and AOB boosted the adaptation of nitrite addition. This study demonstrated the positive impacts of nitrite addition on the ammonia removal efficiency and rate in the SND process.