Ammonia Oxidation Research Articles

Adaptation mechanisms of Alcanivorax facilitating its predominance in marine environments

IntroductionAlcanivorax, a typical alkane-degrading bacterium, has demonstrated the ability to utilize inorganic electron donor in some reports. However, a comprehensive analysis of its potentiality to utilize inorganic electron donor is still lacking.MethodsIn this study, genomic and phylogenetic analyzes were used to explore the potential oxidative capacity of inorganic compounds in Alcanivorax. And its functions were verified through physiological experiments.ResultsThe sulfur oxidation-related genes sqr and tsdA are prevalent and have various evolutionary origins. Potential genes for CO oxidation were present in 39 strains, whereas genes associated with iron, hydrogen, and ammonia oxidation were either rare or absent. The physiological functions of Sqr and TsdA were confirmed in six representative strains under heterotrophic conditions. Adding thiosulfate enhanced Alcanivorax growth. However, Alcanivorax bacteria perform sulfide detoxification through Sqr rather than by gaining energy via sulfide oxidation Although no strain was confirmed to be chemoautotrophs, we discovered that the two clades, A. xenomutans and A. profundimaris, can grow under conditions with very low organic matter.DiscussionThe ability to utilize inorganic compounds as a supplementary energy source and adapt to carbon oligotrophic growth may contribute to the prevalence of Alcanivorax in marine ecosystems.

How Ir‐Rh Alloys Improve Electrochemical Ammonia Oxidation Activity Studied by Density Functional Theory

The electrochemical ammonia oxidation reaction (AOR) has applications in hydrogen storage and ammonia waste remediation. Using density functional theory, we investigate the mechanism of AOR on Ir, Rh, and their alloys at varied atomic ratios (Ir75Rh25, Ir50Rh50, and Ir25Rh75) towards N2(g), NO2–(aq), and NO3–(aq) formation. This work introduces a method for computational alloy design by considering both electronic energy and configurational entropy. The structures considered are selective to N2(g) formation and all favoured *N‐N coupling. An Ir50Rh50 alloy was found to reduce the theoretical onset potential for N2(g) formation relative to pure Ir while not exhibiting a downhill coupling step corresponding to catalyst poisoning by *N as shown for pure Rh, consistent with previous experimental work. The formation of NO2–(aq) and NO3–(aq) demand significantly higher potentials, typically limited by the final hydroxylation step before desorption.

"Ca. Nitrosocosmicus" members are the dominant archaea associated with plant rhizospheres.

Ammonia-oxidizing archaea (AOA) are widespread in terrestrial environments and outnumber other ammonia oxidizers in the rhizosphere, possibly exerting an influence on plant growth and development. However, little is known about the selection forces that shape their composition, functions, survival, and proliferation strategies in the rhizosphere. Here, we observed a distinct AOA community on root systems of two different plant species compared to bulk soil. Our results show that the "Ca. Nitrosocosmicus" clade, which possesses functional MnKat genes unlike most other AOA, dominated the rhizosphere soils. Moreover, members of this clade were enriched in H2O2-amended bulk soil, which mimics the ROS stress in root systems. While research on AOA-plant interactions in the rhizosphere is still in its infancy, these findings suggest that "Ca. Nitrosocosmicus" may be an important clade of AOA with potential AOA-plant interaction.

Study on Effect of Calcination and Ag Loading on Ag/TiO2 Catalyst for Low-Temperature Selective Catalytic Oxidation of Ammonia

Study on Effect of Calcination and Ag Loading on Ag/TiO2 Catalyst for Low-Temperature Selective Catalytic Oxidation of Ammonia

Combining Electrochemical Nitrate Reduction and Anammox for Treatment of Wastewater With Low C/N Ratio Nitrate

ABSTRACTThe treatment of high concentration and low C/N ratio of nitrate wastewater is a promising and challenging research topic. Combining electrochemical reduction and anammox is a technology with great development potential for nitrogen removal from wastewater. In this work, Cu─Ag─Co cathode materials were prepared by two‐step electrodeposition method. The effect of current density and initial pH value on nitrate reduction efficiency was investigated in a single chamber electrolytic cell equipped with Cu─Ag─Co cathode and Ti/RuO2─IrO2 anode. The results showed that under the conditions of initial NO3−─N concentration of 500 mg L−1, Na2SO4 concentration of 0.125 mol L−1, current density of 10 mA cm−2, initial pH value of 7, and treatment time of 5 h, NO3−─N removal ratio was 84.5%, the concentration of NO2−─N and NH4+─N was 180.2 mg L−1 and 173.2 mg L−1. Wastewater with a concentration ratio of NO2−─N and NH4+─N of 1.04:1 meets the influent requirements for anaerobic ammonia oxidation. Through the combination process, the final NO3−─N removal ratio was 82.6%, the NO2−─N concentration was 3.2 mg L−1, and the NH4+─N concentration was 26.4 mg L−1. It provided a reference for the treatment of wastewater with low C/N ratio nitrate by combining electrochemical reduction and anammox.

Raman activities of nitrogen reduction and ammonia oxidation intermediates on the high-entropy alloy CoCuFeMoNi catalytic surface.

We developed a computational framework to extract the Raman spectra of nitrogen reduction and ammonia oxidation intermediates on high-entropy alloy (HEA) surfaces, integrating density functional theory with microstructural representations to account for the inherent lattice randomness in these materials. As a case study, we computed the Raman activities of intermediates (N2*, NNH*, N*, NH*, and NH3*) and H* adsorption on CoCuFeMoNi HEA surfaces. A comprehensive map of Raman peaks was generated and assigned to specific vibrational modes. The method highlighted the effects of lattice randomness on the Raman spectra compared to those of adsorbates on single-element catalysts. For instance, our results showed that the adsorbed N2 exhibits Raman modes that are dependent on whether the adsorption is vertical or horizontal. These peak differences could serve as unique fingerprints to identify nitrogen reduction reaction pathways. Moreover, it is also possible to detect surface poisoning by hydrogen, a common issue in reductive environments, due to the high-frequency peaks of H* compared to the typical N-metal stretching and bending frequencies. These results provide valuable references for identifying intermediates in nitrogen reduction and ammonia oxidation reactions, offering insights into reaction mechanisms and potential surface poisoning. This approach is generalizable to other reactions and surfaces in catalysis, provided that the relevant intermediates can be identified.

Pd-W18O49 Nanowire MEMS Gas Sensor for Ultraselective Dual Detection of Hydrogen and Ammonia.

Demand for real-time detection of hydrogen and ammonia, clean energy carriers, in a sensitive and selective manner, is growing rapidly for energy, industrial, and medical applications. Nevertheless, their selective detection still remains a challenge and requires the utilization of diverse sensors, hampering the miniaturization of sensor modules. Herein, a practical approach via material design and facile temperature modulation for dual selectivity is proposed. A Pd nanoparticles-decorated W18O49 nanowire gas sensor is prepared for dual detection of hydrogen and ammonia. The sensor exhibits distinct operating temperatures for ultraselective detection of hydrogen (125°C) and ammonia (225°C), with high responses of 35.3 and 133.8, respectively. This dual selectivity with high sensitivity is attributed to enhanced oxygen adsorption, the chemical affinity of sensing materials for target gases, and distinct reactivity profiles of gases. The proposed sensor is further integrated into a microelectromechanical system, enabling its small size, low power consumption, and rapid temperature modulation. Moreover, the practical feasibility of this sensor platform for smart energy monitoring systems is demonstrated by assessing its sensing properties in electrochemical ammonia oxidation reaction systems. This work can provide a practical approach for developing a single gas sensor with multiple functionalities for application in electronic nose systems.

Modulating N−H Bond Cleavage in Catalytic Ammonia Oxidation Reaction

AbstractThe ammonia oxidation reaction (AOR) exhibits significant potential for environmental remediation and energy utilization. Nevertheless, the complex reaction mechanism of the AOR poses numerous challenges to its application. To overcome these challenges and realize an efficient AOR process, a thorough understanding of every elementary reaction step, especially the cleavage of N−H bonds, is crucial. This review delves into the influence of N−H bond cleavage on the rate and selectivity of AOR, and summarizes the latest advancements in promoting this crucial step. Furthermore, we discuss the challenges faced by N−H bond cleavage and provide insights into the design of efficient catalytic AOR systems.

An Experimental Investigation into Ammonia Oxidation and NOx Emission in a Packed-Bed of Quartz Particles

ABSTRACT The effect of temperature, initial NH3 concentration, equivalence ratio, and flowrate on the characteristics of ammonia (NH3) oxidation and associated NOx formation in a fixed-bed reactor packed with quartz particles has been systematically investigated with a stream of NH3 and O2 in He over a range of furnace set temperatures (900 K – 1400 K), initial NH3 concentrations (2% – 10%), equivalence ratios (ɸ = 0.8, 0.9, 1.0, 1.1), and total flowrates (145 mL/min, 289 mL/min, and 434 mL/min). Benchmark flow reactor experiments, without the quartz particles in the reactor under otherwise similar conditions, were previously performed and served as a reference case for this work. Compared to the flow reactor results, the packed-bed data indicated a lower reaction onset temperature and more gradual NH3 conversion across the temperature range. Both packed-bed and flow reactor experiments indicated that decreasing flowrate, thus increasing residence time, resulted in greater NH3 conversion. NH3 conversion in the fixed-bed reactor was similar for all equivalence ratios at temperatures ≤1200 K, above which NH3 conversion increased with decreasing equivalence ratio, a trend broadly aligned with previous flow reactor experiments. For all conditions examined, NO was the major NOx component and NO2 was insignificant. Across the range of equivalence ratios, NO emission was low, yet noticeable, from 900 K – 1100 K, before spiking at 1200 K. Above 1200 K, NO emissions decreased before drastically increasing again at 1400 K under fuel-lean conditions. At temperatures ≤1300 K, NO was generally found to decrease with decreasing equivalence ratio, while at 1400 K, NO increased with decreasing equivalence ratio. NO emissions were significantly lower in the packed-bed compared to the flow reactor scenario at temperatures ≥1300 K.

Electrochemical Synthesis of Nitrite and Nitrate via Cathodic Oxygen Activation in Liquefied Ammonia.

The electrochemical oxidation of ammonia (NH3) enables decentralized small-scale synthesis of nitrate (NO3-) and nitrite (NO2-) under ambient conditions by directly utilizing renewable energy. Yet, their electrosynthesis has been restricted to aqueous media and low ammonia concentrations. For the first time, we demonstrate here a strategy enabling the direct electrooxidation of liquefied NH3 to NO3- and NO2- by using molecular oxygen, achieving combined Faraday efficiencies above 40%.

An Ambient Measurement Technique for Vehicle Emission Quantification and Concentration Source Apportionment.

We develop a new technique called plume regression where fast response instruments located at the roadside are used to measure exhaust plumes of passing vehicles. The approach is used to generate highly disaggregated vehicle emissions information by vehicle type, which compares well with traditional vehicle emission remote sensing. Additionally, the technique provides valuable new information on ambient concentration source apportionment by vehicle type. The technique is flexible enough to consider a wide range of air pollutants and be deployed at roadside ambient monitoring locations. The new approach is used to quantify emissions and concentration source apportionment for ammonia (NH3) and nitrogen oxides (NOx). We find that emissions of NH3 are generally very well controlled from diesel vehicles including those with selective catalytic reduction systems that use NH3 to reduce emissions of NOx. By contrast, gasoline passenger cars are shown to be the dominant contributor to NH3 emissions, which increase with vehicle mileage. Average fuel-specific NH3 emission factors for gasoline vehicles range from 0.3 to 1.2 g kg-1, while diesel vehicle emission factors remain below 0.06 g kg-1, with the exception of Euro VI buses with the latest regulatory provisions (0.5 g kg-1).

A hybrid oxidation approach for converting high-strength urine ammonia into ammonium nitrate

Nutrient resources contained in human urine have great potential to alleviate global agricultural fertilizer demand. Microbial nitrification is a recognized strategy for stabilizing urine ammonia into ammonium nitrate, a common fertilizer worldwide, but faces a core bottleneck of process instability due to microbial inhibition. This study reports a new approach by developing a hybrid oxidation process involving three stages—microbial ammonia oxidation, chemical nitrite oxidation and microbial nitrite oxidation. Candidatus Nitrosoglobus, a γ-proteobacterial ammonia oxidizer highly tolerant to free nitrous acid, was introduced in the first stage to oxidize half of the total ammonia in the influent (8 g NH4+-N/L) to nitrite. The nitrite was then chemically oxidized by using hydrogen peroxide via a rapid chemical reaction to form nitrate. The third stage, microbial nitrite oxidation, was employed to ensure the complete removal of residual nitrite following chemical oxidation. The overall concept demonstrated in this work showcased the robust performance of the hybrid system. Moreover, the system also had a dual advantage in achieving antimicrobial ability in the first and second stages, making treated urine a safe fertilizer.

Visible light-induced photocatalytic oxidation of gaseous ammonia on C surface-coated N-TiO2 catalyst: synthesis, properties and mechanism

This paper explores an eco-friendly and efficient photocatalytic oxidation (PCO) technology aimed at converting NH3 into N2, which holds considerable importance for environmental conservation and human well-being. Building upon previous investigations of N-TiO2 catalysts, the research group successfully synthesized an N-TiO2 catalyst featuring a carbon layer on its surface via mechanical mixing followed by calcination at 400 °C (denoted as C/N-TiO2(1), 1 represents the molar ratio of N and Ti). The analysis concentrated on the influence of C content on the PCO efficiency of NH3, revealing a peak performance correlated with increasing C levels. Notably, the C/N-TiO2(1) catalyst with 3.0 wt% C exhibited remarkable catalytic performance, achieving a conversion rate of 94 % and selectivity of 98 %. The enhancement of catalytic activity and selectivity is primarily attributed to the co-doping of C and N elements. Experimental results indicate that doping with N alone effectively suppresses the recombination of photogenerated carriers under visible light. Furthermore, the simultaneous doping of C and N significantly reduces the band gap energy of TiO2 (3.18 to 2.90 eV), thereby broadening its photoresponse range. Concurrently, more Ov (Oxygen vacancy) are formed under visible light irradiation, which enhances the PCO performance. More importantly, more acidic sites are introduced to improve the catalyst’s adsorption capacity for NH3. Additionally, the impact of various reaction components on the PCO capability of the 3.0 wt% C/N-TiO2(1) catalyst is examined further. The findings indicate that oxygen anion radicals produced from O2 play a critical role in facilitating NH3-PCO. However, the presence of CO2 and extra H2O could hinder the approach of NH3 molecules to the active sites and decrease the longevity of photogenerated ·OH, consequently reducing catalytic effectiveness. This research introduces fresh insights and optimization approaches for enhancing the activity, selectivity, and stability of catalysts.

A new process for preparing ultrafine WC-Co cemented carbide by doping yttrium within the ammonium metatungstate solution

Ultrafine WC-Co cemented carbide has superior performance of high strength and high hardness, which is widely used in industrial fields. In the traditional process, high temperature carburization method is used to prepare tungsten carbide, and solid-phase mechanical milling method is used to mix grain growth inhibitor (Cr3C2) and tungsten carbide, which easily lead to large WC particle size and uneven WC grain size distribution in WC-Co cemented carbide, thus affecting mechanical properties of the alloy. In the new process, based on the genetic relationship between the particle size of ammonium paratungstate and tungsten carbide, ultrafine ammonium paratungstate uniformly doped with yttrium was firstly obtained by adding a certain amount of ammonia and yttrium oxide into the ammonium metatungstate solution. Then the ammonium paratungstate was calcined to obtain yttrium-doped tungsten trioxide, which was then converted into yttrium-doped ultrafine tungsten carbide powders by introducing carbon monoxide at a low temperature. Finally, the ultrafine WC-Co cemented carbide was prepared by pressure sintering. During the neutralization and crystallization process of ammonium metatungstate solution, the yttrium-doped ultrafine ammonium paratungstate (Fischer particle size 8.4 μm) with narrow particle size distribution and regular morphology was prepared. The yttrium-doped ammonium paratungstate was calcined at 500 °C for 90 min in air atmosphere to obtain yttrium-doped tungsten trioxide powder with a Fischer particle size of 4.5 μm and narrow size distribution. Then the yttrium-doped tungsten trioxide and carbon monoxide gas were reacted at 920 °C for 3h to obtain yttrium-doped ultrafine tungsten carbide powder with a Fischer particle size of 0.32 μm and a specific surface area of 4.44 m2/g, and ultrafine WC-Co cemented carbide with tungsten carbide grain size of 0.28 μm was obtained by pressure sintering. The yttrium uniform distributed effectively inhibited the abnormal growth of tungsten carbide grains. Compared with the WC-Co cemented carbide prepared by solid-phase mechanically mixing tungsten carbide powder and chromium carbide, the yttrium-doped WC-Co cemented carbide had a smaller average tungsten carbide grain size and a more homogeneous microstructure. The prepared yttrium-doped WC-Co cemented carbide had a hardness (HRA) of 94.6, a bending strength of 4841 M, and a coercive force of 42.3 KA/c.

Facet-dependent effect of α-MnO2 on Ag atoms anchoring and low-temperature selective catalytic oxidation of ammonia

Ammonia (NH3) contributes greatly to haze formation, posing significant risks to ecology and health. As a typical NH3 selective catalytic oxidation (NH3-SCO) catalyst, Ag supported catalysts can balance activity and selectivity. In this research, Ag atoms were anchored on the various crystal facets ({310}, {110} and {100}) of α-MnO2 and were studied for the NH3-SCO. The facet-dependence on Ag atoms anchoring mechanism, as well as the anchored Ag structure, have all been revealed in detail. It was found that the capturing of Ag on the facets of α-MnO2 followed the terminal hydroxyl anchoring mechanism, and further confirmed the linear relationship between Ag capturing quantity and the amount of terminal hydroxyl groups. The {310} facet has a strong ability to activate water molecules to produce surface hydroxyl groups, thereby exhibiting a heightened capability to capture Ag atoms; Ag atoms are loaded in the form of fine nanoparticles on the {310} facet, while anchored in a highly dispersed form on the {110} and {100} facets. The anchoring of Ag significantly improves the NH3-SCO performance of α-MnO2, especially, the Ag/α-MnO2 catalyst with Ag anchoring on the {310} facets exhibited the best activity, achieving 100 % conversion and greater than 80 % N2 selectivity at as low temperature as 100 °C. Finally, the adsorption and possible NH3-SCO mechanism of Ag/α-MnO2 catalysts were also explored by in-situ DRIFTS. The aim of this research is to reveal the facet-dependence of α-MnO2on Ag atoms anchoring,and its effect on low-temperature NH3-SCO activity.

Reaction pathway and anti-poisoning mechanism of Pt-based alloy catalysts in the ammonia oxidation reaction

In the electrochemical ammonia oxidation reaction (AOR), the alloying strategy is an effective method to improve the activity of Pt-based catalysts. Nevertheless, its reaction pathway and anti-poisoning mechanisms still need to be studied in detail to improve the understanding. In this study, the OS and GM mechanisms are considered simultaneously to systematically investigate the reaction pathway and anti-poisoning mechanism of Pt and PtM alloys (M = Fe, Co, Ni, Cu, and Zn) by density functional theory. The formation of PtFe, PtCo, PtCu, and PtZn alloys was observed to enhance the kinetics of the AOR. For Pt, PtCo, and PtZn, the GM mechanism is more prevalent in the AOR process due to the lower reaction energy barrier compared to the OS mechanism. Notably, this work demonstrates that the introduction of Fe, Co, Cu, and Zn induces an electronic structure change of Pt atoms, resulting in the weakening of the Pt − N bond and facilitating the desorption of *N and *N2, therefore enhancing the anti-poisoning properties of the OS and GM mechanisms, respectively. This study deepens the understanding of the reaction pathway and anti-poisoning mechanisms of Pt-based alloy catalysts and presents an effective strategy for designing efficient and stable AOR catalysts.

Effect of long-term ammonia deficiency on nitrification performance and microbial dynamics in downflow sponge biofilm reactor

The downflow sponge biofilm (DSB) reactor has a promising nitrification capacity for ammonium (NH4+-N)-polluted raw water treatment. However, the highly fluctuating NH4+-N levels in raw water may pose a challenge to a stable nitrification process. It is unclear how the DSB reactor contends with NH4+-N deficiency. This study evaluated the robustness of a DSB reactor under long-term NH4+-N abundant and NH4+-N deficient conditions. Four NH4+-N deficient periods were investigated, comprising two 14-day partial NH4+-N deficient phases, one 56-day phase involving both partial and complete NH4+-N deficient, and one 90-day complete NH4+-N deficient phase. Repeated 14-day partial NH4+-N deficient phases had no impact on nitrification performance. However, shifting from partial to complete NH4+-N deficient condition resulted in a delay in NOx−-N production when NH4+-N was replenished. Following an additional 90 days of NH4+-N deficient phase, NH4+-N removal performance recovered faster than nitrite (NO2−-N) removal performance, which took 5 and 29 days, respectively. Furthermore, long-term NH4+-N deficiency resulted in a nominal loss of biomass in the DSB reactor. These findings suggested that the nitrification capacity of the DSB reactor is robust when subjected to long-term NH4+-N deficient conditions. The 16S rRNA amplicon sequencing results revealed that the growth of Nitrosomonas was suppressed, but Candidatus Nitrosotenuis predominated in NH4+-N deficient conditions, while Nitrospira persisted throughout the study. The observed persistence of Nitrospira may be attributed to their diverse metabolic capabilities, which include mixotrophy and complete ammonia oxidation metabolisms. Collectively, the co-existence of Ca. Nitrosotenius, Nitrosomonas, and Nitrospira contributed to stable NH4+-N removal performance in the robust DSB reactor. The DSB reactor shows promise for use in raw water treatment with highly fluctuating NH4+-N availability.

Synchronised removal of nitrogen and sulphate from rubber industrial wastewater by coupling of Sulfammox and sulphide-driven autotrophic denitrification in anaerobic membrane bioreactor.

Global rubber industry, growing 4-6 % annually with 13.76 million Mt of rubber produced in 2019, significantly impacts the economy. This study explores coupling sulfate-dependent ammonium oxidation (Sulfammox) and sulfide-driven autotrophic denitrification (SDAD) within an anaerobic membrane bioreactor (AnMBR) to treat high-strength natural rubber wastewater. Over 225 days, the AnMBR system achieved maximal chemical oxygen demand (COD), total nitrogen (TN), ammonium nitrogen (NH4+-N), and sulfate sulfur (SO42--S) removal efficiencies of 58 %, 31 %, 13 %, and 45 %, respectively. TN is predominantly removed through Sulfammox (accounting for 49 % of NH4+-N removal), SDAD, and conventional denitrification pathways. Sulfate removal is achieved via Sulfammox (responsible for 43 % of SO42--S removal), and Dissimilatory sulfate-reducing (DSR) processes (contributing 57 % of SO42--S removal). Microbial analysis identified Desulfovibrio and Sulfurospirillum as key microbes, while metagenomic analysis highlighted crucial sulfur and nitrogen cycling pathways. The findings support Sulfammox and SDAD as promising eco-friendly strategies for treating ammonia- and sulfate-rich industrial wastewater.

Enhanced anammox-mediated nitrogen removal in bioelectrochemical systems at prolonged negative electrode potentials.

Bioelectrochemical anaerobic ammonium oxidation (anammox) systems allow eco-friendly removal of nitrogen from reject wastewater coming from biogas processing as the anammox bacteria have previously shown to have c-type cytochromes acting in the extracellular electron transport (EET) mechanism between the bacteria and electrode. The anammoxosome compartment present in anammox bacteria features a highly curved membrane and contains tubular structures along with electron-dense particles that contain iron, which could enhance the process of EET and enhance nitrogen removal by properly applied potentials. In this study, nitrogen removal was investigated in the electrostimulated anammox nitrogen removal (EANR) cells operated comparatively at open circuit and at applied potentials of - 300mV, - 500mV, and - 700mV vs. Ag/AgCl. At peak performance (at - 700mV vs. Ag/AgCl), the EANR showed up to 140% higher specific nitrogen removal rate (11.2 ± 0.3g N/m2/day) compared to the control reactors without applied potential (8.3 ± 0.2g N/m2/day). The microbial community on the cathode with the applied potential had a higher relative proportion of unclassified Candidatus Brocadia (7.5%) compared to inoculum (> 0.01%), in contrast to cathode without potential (0.74%) and control (0.2%). The EANR system demonstrated to achieve ammonium and nitrite removal efficiencies of 91% and 53%, respectively, during a 24-h test cycle from an initial TN concentration of ~ 100mg N/L. After 150h, it achieved complete removal of all nitrogen compounds, reaching a 100% removal efficiency. The EANR would be very useful in the establishment of field-scale bilateral anammox-bioelectrochemical technology combining microbial fuel cell bioanodes and EANR biocathodes for wastewater treatment.

Space heterogeneity of nitrogen removal functional genes, nitrogen transformation pathways and mechanisms in MEBR treating mariculture wastewater

Membrane Electro-Bioreactor (MEBR), exhibited excellent nitrogen removal in mariculture wastewater treatment. However, the differences of microbial community and nitrogen transformation pathways on spatial scale caused by the mass transfer of reactive chlorine species (RCS) generated by electrooxidation were unclear. This study provided new insights into the space heterogeneity of ammonia transformation pathways and mechanisms. The results demonstrated an increase in the reduction of nitrate to nitrite through partial denitrification on the membrane. Coupling with dissimilatory nitrate reduction to ammonium and RCS, higher nitrate (0.3 mgN/L) and TN removal (2.6 mgN/L) was obtained in MEBR. Higher relative abundance of narGHI and nirB were obtained. Ammonia oxidation by biofilters was enhanced in MEBR, that ammonia removal contributed by biofilters was 32.0 %, 5.2 times higher than the membrane. Relative abundance of amoABC and Nitrosomonas in biofilters were the highest. The results will provide theoretical basis for reactor configuration and operation optimization.