Nitrification Of Wastewater Research Articles

Enhancing selective nitrate-to-ammonia electrocatalysis with high-performing Ni2P embedded nitrogen phosphide doped carbon (NPC) deposited on CP: Unprecedented performance and stability

One of the biggest challenges to the sustainable manufacture of liquid ammonia and the prevention of worldwide water contamination is the development of effective electrocatalysts for the electrochemical reduction of nitrate (NO3−) to NH3 with high stability. Herein, a highly active and serviceable electrocatalyst is synthesized by pyrolysis, composed of nanostructure nickel phosphide (Ni2P) embedded in nitrogen phosphide doped carbon (NPC) followed by deposition on carbon paper (CP) to improve the electrocatalytic nitrate reduction. Various characterization techniques investigate the crystallinity, morphology, and chemical components of the Ni2P-NPC/CP nanoparticles. The results support the formation of nanostructure Ni2P and strong synergistic interactions between Ni2P and NPC, which resulted in substantial active sites and high electrical conductivity. Excellent performance of Ni2P-NPC/CP nanoparticles is achieved for electrocatalytic NO3− reduction with an NH4+ yield rate of 2.468 mg h−1 mgcat.−1 and Faradaic efficiency (FE) of 84.6% at −1.2 V vs. RHE. Additionally, Ni2P-NPC/CP nanoparticles exhibit exceptional robustness and endurance. Studies using isotope labeling have been carried out, and the results show that nitrate reduction produces ammonia. Ni2P-based electrocatalysts can effectively treat nitrate wastewater to recover ammonia and facilitate its use in diverse industrial applications.

Highly effective removal of nitrate from saline wastewater by glucose-enhanced sulfur autotrophic system

The denitrification performance of the elemental sulfur autotrophic denitrification (S0AD) system requires improvements to broaden its applicability for treating nitrate (NO3−-N) wastewater contaminated with high salinity. Therefore, this work investigated the denitrification performance and mechanism of the glucose-enhanced (C:N ratio = 1) S0AD system with saline wastewater (0–15 g/L). The results showed that by adding glucose, our research successfully constructed the elemental sulfur autotrophic/heterotrophic denitrification (HS0AD) system, which showed a stable NO3−-N removal efficiency above 95 % and lower effluent sulfate generation. The NO3−-N removal efficiency of the HS0AD system was over 95.62 % with wastewater containing different salinity levels. With increasing salinity, the glucose utilization efficiency increased from 65.23 % to 74.35 %. Microbial community analysis showed that adding glucose promoted the growth of the Proteobacteria phylum and stimulated its activity under salt stress. High salinity (≥10 g/L) reduced the microbial diversity at the genus level. However, the growth of salt-tolerant denitrifying bacteria (Thiobacillus and Vitellibacter) still enabled efficient denitrification performance with the system. These microorganisms can resist high salinity stresses by releasing proteins. All results indicated that the glucose-enhanced system shows great nitrate removal potential, even under salt stress. These conclusions provide a theoretical basis for applying a synergistic system to treat saline wastewater contaminated with NO3−-N.

Tailoring Ni 3d orbitals in Ni-Fe/Ni foam heterostructures for enhanced H* adsorption and boosted electrocatalytic nitrate reduction performance

The electrochemical nitrate (NO3−) reduction (ENR) in wastewater, a promising remediation strategy, is often impeded by the essential use of costly noble metals. This study introduces an innovative non-noble Ni-Fe/Ni foam cathode fabricated via one-step electrodeposition technique. Efficient nitrate removal (99.4 %) was achieved with the selectivity of 83.6 % to NH3. The exceptional performance can be ascribed to the augmented active sites and the synergistic interaction between Ni and Fe. The leftward shift of the 3d orbitals density of Ni and the elevation of density at the Fermi level on Ni foam heterostructures, consequent to Fe doping, enhance the adsorption of H*. The addition of reactive chlorine species, generated through anodizing in Cl− mediated system, further improves N2 selectivity by oxidizing intermediate NH4+ product. The coupled anodic oxidation method employed herein achieves nearly 100 % removal efficiency of total nitrogen (TN) for initial concentration of 100 mg/L within 180 min, under the conditions of 1.5 g/L Cl− concentration and a current density of 25 mA cm−2. The findings underscore the potential of the Ni-Fe/Ni foam cathode within a Cl− mediated electrocatalytic framework for nitrate wastewater treatment, providing novel insights into the design of cathode catalysts and anodic coupling strategies for efficient TN removal.

Enzymatic Mesoporous Metal Nanocavities for Concurrent Electrocatalysis of Nitrate to Ammonia Coupled with Polyethylene Terephthalate Upcycling.

Electrochemical upcycling of waste pollutants into high value-added fuels and/or chemicals is recognized as a green and sustainable solution that can address the resource utilization on earth. Despite great efforts, their progress has seriously been hindered by the lack of high-performance electrocatalysts. In this work, bimetallic PdCu mesoporous nanocavities (MCs) are reported as a new bifunctional enzymatic electrocatalyst that realizes concurrent electrocatalytic upcycling of nitrate wastewater and polyethylene terephthalate (PET) plastic waste. Abundant metal mesopores and open nanocavities of PdCu MCs provide the enzymatic confinement of key intermediates for the deeper electroreduction of nitrate and accelerate the transport of reactants/products within/out of electrocatalyst, thus affording high ammonia Faradic efficiency (FENH3) of 96.6% and yield rate of 5.6mgh-1mg-1 at the cathode. Meanwhile, PdCu MC nanozymes trigger the selective electrooxidation of PET-derived ethylene glycol (EG) into glycolic acid (GA) and formic acid with high FEs of >90% by a facile regulation of potentials at the anode. Moreover, concurrent electrosynthesis of value-added NH3 and GA is disclosed in the two-electrode coupling system, further confirming the high efficiency of bifunctional PdCu MC nanozymes in producing value-added fuels and chemicals from waste pollutants in a sustainable manner.

Self-growing nitrogen doped cobalt-copper Co4Cu1N-CN/CF electrode for electrochemical nitrate removal

Selective electrochemical nitrate reduction reaction to nitrogen gas (NO3-N2RR) has emerged as a promising strategy. Herein, a self-growing Co4Cu1N-CN/CF composite electrode was successfully fabricated as cathode for electrochemical nitrate reduction reaction to ammonia (NO3-NH3RR) with the high NH4+-N selectivity (SNH4+-N over 97.8%), which coupled with IrO2-RuO2/Ti anode via hyperchlorination for NO3-N2RR (RTN over 96.1%). Electrochemical and quenching experiments indicated that direct electron transfer (DET) took precedence over indirect reduction (the surface-adsorbed H*) in NO3-NH3RR: Cu sites favored the nitrate to nitrite, and Co sites made for the subsequent reduction to ammonia. Furthermore, the high electron transfer number (n) demonstrated that the excellent performance of Co4Cu1N-CN/CF cathode was attributed to the predominance of DET form NO3－to NH4+ by skipping over some intermediate pathway. This study deepened the understanding of one-step electron reduction in the bimetal synergic NO3-NH3RR reduction and this electrochemical system has practically potential to treat nitrate wastewater efficiently.

Efficient electrocatalytic nitrate reduction using 3D copper foam-supported Co hexagonal nanoparticles in a membrane electrode assembly

Electrocatalytic nitrate reduction reaction (NO3RR) provides a promising route for nitrate recycling and ammonia production. In this work, Co nanoparticle catalyst was developed on a copper foam substrate (CoNPs/CF) by electrodeposition. The CoNPs/CF catalysis exhibits a Faradaic efficiency (FE) of 92.0% at −0.2 V vs. RHE and an NH3 yield rate of 14328.65 μg h−1 cm−2 at −0.5 V vs. RHE. In-suit Raman spectroscopy and theoretical calculations demonstrated that the 3D copper foam structure of the substrate enhances the electron exchange capacity, which promotes the adsorption of nitrate on the cobalt (Co) surface. Moreover, Membrane Electrode Assembly (MEA) is employed with CoNPs/CF, contributing to 98.43 mg h−1 with FE over 80%. Coupled with an air stripping process, this configuration has enabled the successful production of high-purity gaseous NH3 products. This work suggests a practical and viable approach for the conversion of wastewater nitrate into valuable ammonia products.

Electrochemical Reduction of Flue Gas Denitrification Wastewater to Ammonia Using a Dual-Defective Cu2O@Cu Heterojunction Electrode.

Wet flue gas denitrification offers a new route to convert industrial nitrogen oxides (NOx) into highly concentrated nitrate wastewater, from which the nitrogen resource can be recovered to ammonia (NH3) via electrochemical nitrate reduction reactions (NITRRs). Low-cost, scalable, and efficient cathodic materials need to be developed to enhance the NH3 production rate. Here, in situ electrodeposition was adopted to fabricate a foamy Cu-based heterojunction electrode containing both Cu-defects and oxygen vacancy loaded Cu2O (OVs-Cu2O), which achieved an NH3 yield rate of 3.59 mmol h-1 cm-2, NH3 Faradaic efficiency of 99.5%, and NH3 selectivity of 100%. Characterizations and theoretical calculations unveiled that the Cu-defects and OVs-Cu2O heterojunction boosted the H* yield, suppressed the hydrogen evolution reaction (HER), and served as dual reaction sites to coherently match the tandem reactions kinetics of NO3-to-NO2 and NO2-to-NH3. An integrated system was further built to combine wet flue gas denitrification and desulfurization, simultaneously converting NO and SO2 to produce the (NH4)2SO4 fertilizer. This study offers new insights into the application of low-cost Cu-based cathode for electrochemically driven wet denitrification wastewater valorization.

Two-dimensional peak-valley alternating self-supporting electrode accelerating nitrate electrocatalytic reduction: Ammonia synthesis and wastewater treatment

Electrochemical nitrate reduction synthesis of ammonia can use clean energy to convert low-value nitrate pollutants into high value-added ammonia yield. The development of eNitRR catalyst with high activity, high selectivity and stability is the key to achieve distributed small-scale production of nitrate. In this study, a self-supported catalyst (Cu/PTS) with high catalytic activity (for eNitRR) was constructed by anodic oxidation combined with hydrothermal/pyrolysis strategy to realize the embedding of Cu species on the substrate of porous titanium sheet. The ammonia production rate of Cu/PTS catalyzed eNitRR is as high as 7292.43 μg h−1 cm−2 (−1.0 V vs. RHE), the Faradaic efficiency is close to 100 %, reaching 97.34 %, and isotope labeling and Operando ATR-FTIRAS verified and revealed the fact that NO3− to NH3, respectively. Density functional theory calculations well reveal the roles of various components in Cu/PTS and reveal the factors for the enhancement of eNitRR performance. Thanks to the self-supporting characteristics of porous titanium sheet and the surface embedding of copper species, Cu/PTS not only have good electrochemical stability when catalyzing eNitRR, but also can drive eNitRR to operate efficiently in complex water environment. While realizing the purification of nitrate wastewater and the synthesis of ammonia, Cu/PTS can be used as a positive electrode to construct a nitrate–zinc battery to realize the dual functions of self-driven ammonia production and external power supply.

Salinity stress results in ammonium and nitrite accumulation during the elemental sulfur-driven autotrophic denitrification process.

In this study, we investigated the effects of salinity on elemental sulfur-driven autotrophic denitrification (SAD) efficiency, and microbial communities. The results revealed that when the salinity was ≤6 g/L, the nitrate removal efficiency in SAD increased with the increasing salinity reaching 95.53% at 6 g/L salinity. Above this salt concentration, the performance of SAD gradually decreased, and the nitrate removal efficiency decreased to 33.63% at 25 g/L salinity. Approximately 5 mg/L of the hazardous nitrite was detectable at 15 g/L salinity, but decreased at 25 g/L salinity, accompanied by the generation of ammonium. When the salinity was ≥15 g/L, the abundance of the salt-tolerant microorganisms, Thiobacillus and Sulfurimonas, increased, while that of other microbial species decreased. This study provides support for the practical application of elemental sulfur-driven autotrophic denitrification in saline nitrate wastewater.

Advancements in Single Atom Catalysts for Electrocatalytic Nitrate Reduction Reaction

AbstractDue to the urgent demand for nitrate wastewater treatment, the quest for an efficient and environmentally friendly treatment method has emerged as a new research focus. The utilization of single‐atom catalysts (SACs) in electrocatalytic nitrate reduction reaction (NO3RR) for ammonia production is presently recognized as an effective strategy to address pollution issues and obtain high value‐added products. In this review, we summarized the recent research advancements in NO3RR based on SACs. This review includes a comprehensive analysis of the identification and structural determination techniques for SACs, as well as the mechanism of NO3RR over SACs. Furthermore, this review investigates the impact of regulating single atom structures on NO3RR, providing valuable insights for enhancing reaction efficiency. It explores the application of in‐situ technology in real‐time monitoring and control of NO3RR. Finally, perspectives and challenges regarding the application of SACs in NO3RR are presented. Overall, this extensive review offers valuable insights for researchers and industry professionals in the field of nitrate reduction and environmental catalysis.

Deciphering the potential role of quorum quenching in efficient aerobic denitrification driven by a synthetic microbial community

Low efficiency is one of the main challenges for the application of aerobic denitrification technology in wastewater treatment. To improve denitrification efficiency, a synthetic microbial community (SMC) composed of denitrifiers Acinetobacter baumannii N1 (AC), Pseudomonas aeruginosa N2 (PA) and Aeromonas hydrophila (AH) were constructed. The nitrate (NO3−-N) reduction efficiency of the SMC reached 97 % with little nitrite (NO2−-N) accumulation, compared to the single-culture systems and co-culture systems. In the SMC, AH proved to mainly contribute to NO3−-N reduction with the assistance of AC, while PA exerted NO2−-N reduction. AC and AH secreted N-hexanoyl-DL-homoserine lactone (C6-HSL) to promote the electron transfer from the quinone pool to nitrate reductase. The declined N-(3-oxododecanoyl)-L-homoserine lactone (3OC12-HSL), resulting from quorum quenching (QQ) by AH, stimulated the excretion of pyocyanin, which could improve the electron transfer from complex III to downstream denitrifying enzymes for NO2−-N reduction. In addition, C6-HSL mainly secreted by PA led to the up-regulation of TCA cycle-related genes and provided sufficient energy (such as NADH and ATP) for aerobic denitrification. In conclusion, members of the SMC achieved efficient denitrification through the interactions between QQ, electron transfer, and energy metabolism induced by N-acyl-homoserine lactones (AHLs). This study provided a theoretical basis for the engineering application of synthetic microbiome to remove nitrate wastewater.

Spin polarized Fe1−Ti pairs for highly efficient electroreduction nitrate to ammonia

Electrochemical nitrate reduction to ammonia offers an attractive solution to environmental sustainability and clean energy production but suffers from the sluggish *NO hydrogenation with the spin–state transitions. Herein, we report that the manipulation of oxygen vacancies can contrive spin−polarized Fe1−Ti pairs on monolithic titanium electrode that exhibits an attractive NH3 yield rate of 272,000 μg h−1 mgFe−1 and a high NH3 Faradic efficiency of 95.2% at −0.4 V vs. RHE, far superior to the counterpart with spin−depressed Fe1−Ti pairs (51000 μg h–1 mgFe–1) and the mostly reported electrocatalysts. The unpaired spin electrons of Fe and Ti atoms can effectively interact with the key intermediates, facilitating the *NO hydrogenation. Coupling a flow−through electrolyzer with a membrane-based NH3 recovery unit, the simultaneous nitrate reduction and NH3 recovery was realized. This work offers a pioneering strategy for manipulating spin polarization of electrocatalysts within pair sites for nitrate wastewater treatment.

Oxygen vacancy-regulated nanorod array electrodes for boosting the electrocatalytic synthesis of ammonia from nitrate wastewater.

The adsorption of nitrate is the key to enhancing the electrocatalytic nitrate reduction reaction (NitRR). Herein, a typical hydrolysis-coupled redox (HCR) reaction has been designed to prepare unique 3D Cu/Fe2O3 core-shell nanorod array cathodes with controllable oxygen vacancy concentrations for NitRR. The optimal Cu/Fe2O3-13 achieves a high nitrate conversion of 99.10% and ammonia selectivity of 98.30%. The outstanding electrochemical performance is attributed to the enhancement mechanism of OVs and a unique nanorod array structure with a high density of surface-exposed OVs and high-throughput transport pathways for ion-aspects.

Engineering a molecular electrocatalytic system for energy-efficient ammonia production from wastewater nitrate

Electrocatalyst-in-a-box, a novel reactive separation process, enables a molecular catalyst to convert wastewater nitrate into purified ammonia.

A global approach to estimate continuous-time LPV models for wastewater nitrification

In wastewater treatment, understanding and modeling the nitrification process is crucial to implement control. However, the complexity of this process makes it challenging to create simplified models. This study introduces an innovative method for estimating linear parameter-varying (LPV) models in the context of biological nitrification processes. The research focuses on the development of a continuous-time LPV model for a submerged aerated biofiltration system, considering the conversion of ammonium to nitrate in wastewater treatment. The methodology adopts the reinitialized partial moment approach within a global identification framework. The resultant LPV model is structured to capture the dynamics of the biological nitrification process, considering various factors like flow rates, feed concentrations and environmental regulations. Application of this approach to measured data from a wastewater treatment plant, demonstrates its effectiveness in accurately estimating the LPV model parameters. The results not only offer valuable insights into the dynamics and the nonlinear behaviour of the nitrification process but also contribute to the design and optimization of wastewater treatment plants, particularly those employing submerged aerated nitrifying biofilters.

Exploration of a novel electrochemical C[sbnd]N coupling process: Urea synthesis from direct air carbon capture with nitrate wastewater

Direct air capture (DAC) can be used to decrease the CO2 concentration in the atmosphere, but this requires substantial energy consumption. If residual waste carbon (in the form of bicarbonate solution) from DAC can be directly reused, it might present a novel method for overcoming the aforementioned challenges. Electrochemical CN coupling methods for synthesizing urea have garnered considerable attention for waste carbon utilization, but the carbon source is high-purity CO2. No research has been conducted regarding the application of bicarbonate solution as the carbon source. This study proposes a proof-of-concept electrochemical CN coupling process for synthesizing urea using bicarbonate solution from DAC as the carbon source and nitrate from wastewater as the nitrogen source. These results confirmed the feasibility of synthesizing urea using a three-electrode system employing TF and CuInS2/TF as the working electrodes via potentiostatic electrolysis. Under the optimal conditions (initial pH 5.0 and applied potential of −1.3 V vs. Ag/AgCl), the urea yield after 2 h of electrolysis reached 3017.2 μg h−1 mgcat.−1 and an average Faradaic efficiency of 19.6 %. The in-situ attenuated total reflection surface-enhanced infrared absorption spectroscopy indicated a gradual increase in the intensity of the -CONH bond signal on the surface of the CuInS2/TF electrode as the reaction progressed. This implied that this bond may be a key chemical group in this process. The density functional theory calculations demonstrated that *CONH was a pivotal intermediate during CN coupling, and a two-step CN coupling reaction path was proposed. *NH + *CO primarily transformed into *CONH, followed by the conversion reaction of *CONH + *NO to *NOCONH2. This study offers a groundbreaking approach for waste carbon utilization from DAC and holds the potential to furnish technical underpinnings for advancing electrochemical CN coupling methods.

Utilizing the Complexity of Transition Metal Phosphide Surfaces to Tune Nitrate Reduction Selectivity

Electrocatalytic nitrate reduction (NO3RR) is one exciting method of upcycling nitrate in wastewater by conversion to ammonia, an essential component in fertilizers and a potential liquid fuel. Nitrate reduction to NH3 is impeded by the formation of other products such as NO2 - or H2 via the hydrogen evolution reaction (HER). Transition metal phosphide (TMP) nanocrystals have a non-uniform surface charge distribution due to their binary compositions, which leads to a variety of active sites with different binding affinities. We hypothesize that the diversity of active sites on Ni2P can be leveraged to perform complex electrocatalytic reactions such as the NO3RR. Specifically, a diversity of surface sites can create local active site motifs that promote the adsorption of different intermediates, e.g., *NO3 - and *H, that can readily react for the NO3RR. We prepare 5 nm Ni2P and Ni nanocrystals using colloidal syntheses and deposit them onto a carbon support to compare the simpler catalytic surface of Ni with the more complex Ni2P surface. We compare their NO3RR activities with cyclic voltammetry in neutral, buffered aqueous conditions. We also investigate the selectivity between the NO3RR and HER with bulk electrolysis coupled with a colorimetric assay, where Ni2P on carbon shows higher selectivity toward NH3 over NO2 - and H2. With these experiments, we evaluate our hypothesis that the surface complexity of Ni2P will lead to enhanced NO3RR selectivity relative to Ni. This work sets the stage for developing selective electrocatalysts by utilizing ensembles of active sites to drive electrocatalytic selectivity.

A novel pure biofilm system based on aerobic denitrification for nitrate wastewater treatment: Exploring the feasibility of high total nitrogen removal under low-carbon condition

To improve the poor denitrification efficiency of traditional biological treatment for low-carbon wastewater, a novel pure biofilm moving bed biofilm reactor (PH-MBBR) based on heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria was proposed. The start-up of PH-MBBR inoculated with HN-AD bacteria and the operating performances and microbial community composition under various C/N ratios were studied. The results showed that at C/N ratio of only 4, the total nitrogen (TN) removal rate of 10.02 mg/(L·h) was achieved under aerobic conditions. Microbial analysis indicates that the synergistic effect of oligotrophic bacteria Thauera and Azoarcus was the main reason for the high pollutant removal at C/N ratio of 4. Furthermore, the analysis of functional genes and enzymes reveals that NorB and NosZ played important roles in nitrate metabolism in PH-MBBR, and aerobic denitrification pathway was NO3–-N → NO → N2O → N2. This study provides a practical and theoretical basis for low-carbon nitrate wastewater treatment.

Municipal wastewater driven partial-denitrification (PD) aggravated nitrous oxide (N2O) production

Partial Denitrification (PD) provides a new route for nitrate-rich wastewater treatment by combining with energy-efficient anammox. This process was reported to hardly produce N2O despite high nitrite accumulation using acetate as carbon source. This study, however, demonstrated significant N2O would be produced when feeding with real municipal wastewater, the NTR-N2O (NO3−-to-N2O transformation ratio) reached as high as 10%. The supply of feed with a high COD/NO3−-N ratio was unable to alleviate N2O production but was severely aggravated after nitrate was depleted. Excess carbon source resulted in accumulated nitrite further being reduced with NTR-N2O largely improved to 63.4%. Besides, it was observed that acid pH inhibited PD activity and resulted in N2O production significantly increased with the NTR-N2O of 39.9% at an initial pH of 5.5. The increase of pH to alkaline conditions cannot mitigate N2O production. A low feeding proportion of real municipal wastewater for low nitrate wastewater treatment can drastically lower N2O production. The NTR-N2O was only 0.1% at a nitrate concentration of 10 mgN/L (10%), much lower than that at 30 mgN/L with a 30% feeding proportion of municipal wastewater (9.4%). Complex organics and ammonium present in municipal wastewater were supposed to be the primary reasons for the high N2O production. Overall, this work offered a new insight into N2O production during the PD process using the complex organics from wastewater itself.

Ultrafine nano-copper derived from dopamine polymerization & synchronous adsorption achieve electrochemical purification of nitrate to ammonia in complex water environments

Electrochemical-nitrate-reduction-reaction (eNitRR) synthesis of ammonia is an effective way to treat nitrate wastewater and alleviate the pressure of the Haber-Bosch ammonia production industry. How to develop effective catalysts to electrochemically reduce nitrate to ammonia and purify sewage under complex environmental conditions is the focus of current research. Herein, the dopamine polymerization process and the [(C₁₂H₈N₂)2Cu]2+ complex embedding process were run simultaneously in time and space, and ultrafine Cu nanoparticles (Cu/CN) were effectively loaded on nitrogen-doped carbon after heat treatment. Using Cu/CN as the catalyst, the ammonia yield rate and Faradaic efficiency of the electrochemical conversion of NO3− to NH3 are highly 8984.0 µg h−1 mgcat.−1 and 95.6%, respectively. Even in the face of complex water environments, such as neutral media, acidic media, coexisting ions, and actual nitrate wastewater, nitrate wastewater can be effectively purified to form high value-added ammonia. The strategy of simultaneous embedding increases the exposure rate of Cu sites, and the support of CN is also beneficial to reduce the energy barrier of *NO3 activation. This study rationally designed catalysts that are beneficial to eNitRR, and considered the situation faced by practical applications during the research stage, reducing the performance gap between laboratory exploration and industrial applications.