Nitrogen Conversion Research Articles

Action Mechanism of Bacillus on Microalgae During Nitrogen Metabolism in Urban Tailwater

To improve deep denitrification of black and odorous water and improve the quality of surface water, we studied the characteristics of nitrogen metabolism and denitrification of urban tailwater by microalgae (Z), Bacillus (Y), and Bacillus microalgae (ZY). The results showed that there was a good removal effect of ammonia nitrogen of group Z and group ZY in urban tailwater. The degradation rate of both groups reached 95%. The best effect on the removal of nitrite nitrogen was of group Z in urban tailwater. The combined action of Bacillus and Micrococcus played a relatively strong and stable effect on the conversion of nitrite nitrogen to nitrate nitrogen in the nitrogen cycle reaction. Bacillus could effectively remove nitrate nitrogen and improve the removal efficiency of nitrate nitrogen by microalgae. Best removal effect of nitrate nitrogen was observed in group ZY in urban tailwater, with a degradation rate as high as 99%, in which the nitrate nitrogen was removed almost completely. The Bacteria with high proportions in Z were Chroococcidiopsis_PCC_7203 (24.38%), uncultured_bacterium-g_norank_f_A4b (23.65%), Exiguobacteriu (7.09%), Leptolyngbya_PCC-6306(9.41%), and Bacillus (1.99%). The bacteria with high proportions in ZY were Brevibacillus (22.94%), Clostridium (8.78%), and Bacillus (4.88%), and the proportion of Chroococcidiopsis_PCC_7203 was only 7.84% in ZY, which was considerably lower than that in Z samples. The conclusions were as follows:microalgae could effectively remove ammonia nitrogen in the system. Bacillus and microalgae had very good removal effect of ammonia nitrogen and nitrate nitrogen. During the nitrogen removal of black and odorous water by algae, the Bacillus inhibited the excessive growth of microalgae and prevented eutrophication and black odor in water. This study can provide data support for the deep treatment of urban tail water and prevention of surface water eutrophication.

Regulatory effect of CaO on glutamate pyrolysis and NOx precursors formation

Pyrolysis is an effective method for safely disposing of sewage sludge via conversion into a usable energy source. However, municipal sludge has a high protein content, which is a major source of NOx precursors. This study investigated the effect of CaO on NOx precursor formation during glutamate pyrolysis and demonstrated that CaO occupies the carboxyl site of glutamic acid at 320 °C, which delays its decomposition and promotes the conversion of glutamic acid from a five- to a six-membered ring. At 400 °C, heterocyclic nitrogen in the tar peaked from 4.87 to 53.87% after adding CaO. As the temperature increases to 480 °C, CaO might promote the conversion of heterocyclic nitrogen into tricyclic piperazine dione in the tar, which subsequently decomposed to produce HCN in large quantities. At 480 °C, CaO contributed to the decrease in pyrrole, pyridine, and quaternary nitrogen in the semi-coke from 24.81%, 12.93%, and 7.43% to 1.91%, 5.97%, and 1.43%, respectively and promoted HCN hydrolysis to form NH3. At 480–680 °C, CaO interacted with NH3 to form CaCN2. The product of CaCxNy decomposition—CaCx—captured NH3. At high temperatures, CaO inhibited HCN release, which might be related to the reaction between CaO and HCN to form CaCxNy, subsequently reconverted into CaO at temperatures above 680 °C. These findings provide novel insights into the influence of CaO on amino acid pyrolysis to produce NOx precursors and the regulation of NOx precursor production.

Enhancement of anaerobic ammonia oxidation process composed of mixed sludge without additional deoxidation by sulfur autotrophic denitrification under mainstream conditions

The practical application of anaerobic ammonia oxidation (anammox) process is hindered because of its strict demand of an anaerobic environment. Due to the slow growth cycle of anammox bacteria and the high cost of wastewater deoxidation, it is difficult to improve the contribution rate of denitrification in anammox pathway. Sulfur oxidizing bacteria (SOB) consume oxygen in the process of oxidizing sulfur elements to provide a better anaerobic environment for anammox bacteria, and sulfur autotrophic denitrification can also remove nitrate produced during the anammox process for deep nitrogen removal. The analysis of cell hydrophobicity and EPS secondary structure were consistent, which showed that the biofilm of A-SAD (anammox- sulfur autotrophic denitrification) system exhibited stronger adhesion and a more stable structure. The functional genes of ammonia oxidation (amoA) and nitrite oxidation (nxrA) were reduced by more than 90 %, implying that SAD provided a favorable anaerobic environment for anammox and reduced the cost of deoxidation in actual operation. The relative abundance of Candidatus_Kuenenia increased nearly threefold, becoming the dominant anammox bacteria in low substrate environment, while other anammox bacteria almost disappeared. The increase of the relative abundance of Thiobacillus and Desulfovibrio were beneficial to the transformation of S0 into bio-sulfur (Bio-S0) through redox, which provided the possibility for the recovery and utilization of sulfur. This experiment provides a comprehensive understanding of the nitrogen and sulfur conversion mechanism for the deoxidation and sulfur recovery of anammox in practical applications.

Self-sacrificed BiOBr template-assisted synthesis of α-Bi2O3/Bi3O4Br heterojunctions with oxygen vacancies for enhanced photocatalytic nitrogen fixation

The catalytic conversion of nitrogen to ammonia is one of the most significant processes in nature and the chemical industry. However, the traditional Haber-Bosch process of ammonia synthesis consumes substantial energy and emits a large amount of carbon dioxide. The efficiency of photocatalytic N2 activation is severely limited by the lack of N2 adsorption sites and poor carrier utilization. Herein, an efficient α-Bi2O3/Bi3O4Br heterojunction is proposed with a photocatalytic nitrogen fixation activity of 238.67 μmol·g−1·h−1. Compared with the BiOBr precursor, α-Bi2O3 and Bi3O4Br, the α-Bi2O3/Bi3O4Br heterojunction with oxygen vacancies can improve the adsorption and activation capacity of N2 and promote the separation efficiency of charge carrier pairs by accommodating photogenerated electrons under visible light through the mechanism of N-type semiconductors. Therefore, oxygen vacancies and heterojunction engineering of semiconductive nanomaterials provide a promising method for the rational design of photocatalysts to enhance the rate of ammonia synthesis under mild conditions.

The nitrogen and carbon footprints of ammonia synthesis in China based on life cycle assessment

The global nitrogen (N) cycle has emerged as an earth system process with more serious artificial disruption than climate change. Artificially synthesized reactive nitrogen (Nr) already accounts for nearly 50% of the total Nr in the earth system. The massive anthropogenic conversion of inert nitrogen (N2) to Nr is a major driver of imbalance and disruption of the earth's N cycle, where the artificial ammonia (NH3) synthesis process is the main trigger. Existing studies on life cycle environmental impacts of ammonia synthesis mainly focused on the greenhouse effect but lacked or underestimated the interference with the nitrogen cycle due to currently incomplete nitrogen footprint frameworks. In addition, the comprehensive evaluation of the nexus between nitrogen and carbon footprint of NH3 synthesis systems is also insufficient. Attempting to solve the above-mentioned problems, life cycle assessment models of seven ammonia synthesis systems were established considering different raw material pathways and production technologies under China's context, assisted by the Brightway2 platform. The general framework of nitrogen footprint accounting (GFNFA) that was established by the authors previously was employed to assess the ammonia synthesis on nitrogen footprint covered all ecosphere. The performance and hotspots of the system nitrogen footprint, carbon footprint (CF) and nitrogen-carbon nexus were then systematically quantified and analyzed. Results indicated that electrolysis-based ammonia powered by renewable and nuclear energy had the lowest Nr emission (0.499–1.148 kg Nr/t NH3) and carbon emission (592.822–1045.494 kg CO2-eq/t NH3). Among the seven ammonia synthesis systems investigated, biomass-based ammonia had the largest Nr emission and system nitrogen accumulation, and it converts the most N2 to Nr per ton ammonia produced, due to the extensive resources consumption and emissions during straw growth and direct Nr emission in gasification process. Thus, it caused the most significant disturbance to the earth's nitrogen cycle. The nexus between nitrogen and carbon footprints was revealed that the system's energy consumption was found to be a common driver through hotspots and contribution analysis. NH3 synthesis efficiency was the most determining factor in the system's Nr and carbon emissions. With a 15% increase in synthesis efficiency, nitrogen and carbon footprints can be reduced by more than 12.5%. This study can help researchers better understand the life cycle impacts of ammonia synthesis systems on earth's nitrogen and carbon cycle from multidisciplinary ecological origins.

Italian ryegrass (Lolium multiflorum L.)-rice (Oryza sativa L.) rotation promotes the nitrogen cycle in the rice rhizosphere through dominant ammonia-oxidizing bacteria

The dominant ammonium bacteria established in different crop rotations are directly related to the conversion and utilization of nitrogen (N) in paddy soil. This study investigated the ammonia oxidation process in the rice rhizosphere of Italian ryegrass (Lolium multiflorum L.)-rice (IRR), celery (Apium graveolens)-rice (CLR) and winter fallow-rice (WFR) rotations in South China through the amoA functional gene analysis based on Miseq high-throughput sequencing platform and qPCR methods. The abundance of amoA gene in IRR was increased by 116.67 % (P < 0.05) and 42.76 % (P > 0.05) compared with CLR and WFR, respectively. Nitrosomonas became the dominant genus in the rhizosphere of IRR, with the highest relative abundance (59.30 %). The contents of soil organic matter, total N and nitrate nitrogen (NO3−-N) in the rice rhizosphere soil in IRR were significantly higher than other two treatments (P < 0.05) by 12.47–14.31 %, 16.88–25.00 %, and 97.48–159.60 %, respectively. Although lower microbial diversity was observed in IRR, the soil fluorescein diacetate hydrolysis enzyme activities and ammonia monooxygenase activities in the rice rhizosphere were higher in IRR than those in CLR and WFR (P < 0.05). Also, the soluble sugar and crude protein of milled rice were highest in IRR among the three rotation treatments (P < 0.05). The ammonia oxidation efficiency of ammonium-oxidizing bacteria was largely dependent on key taxa, such as Nitrosomonas (dominant genus in IRR), rather than the dynamics of AOB community structure. The key amoA-nitrifier taxa of the AOB community developed in IRR are capable of promoting rice production by improving soil N cycle efficiency and reducing the loss of N. Our findings illustrate the regulatory mechanism of IRR on the rice rhizosphere AOB community and reveal the important role of winter ryegrass in promoting soil nitrogen cycling during nutrient transformation of agricultural ecosystems in paddy fields.

Solar-Driven Reforming of Methane and Nitrogen to Methanol and Ammonium on Iron-Modified Zeolite under Ambient Conditions in Water.

Artificial photosynthesis from selective methane oxidation or nitrogen reduction to value-added chemicals provides a promising pathway for the sustainable chemical industry, while still remaining a great challenge due to the extreme difficulty in C-H and N≡N bond cleavage under ambient conditions. Catalysts that can cocatalyze these two reactions simultaneously are rarely reported. Here, Fe-ZSM-5 with highly dispersed extra-framework Fe-oxo species enables efficient and selective photocatalytic conversion of methane and nitrogen to coproduce methanol and ammonia using H2O as the redox reagent under ambient conditions. The optimized Fe-ZSM-5 photocatalyst achieves up to 0.88 mol/molFe·h of methanol products with 97% selectivity. Meanwhile, the productivity of ammonia is 0.61 mol/molFe·h. In situ EPR and DRIFT studies disclose that water serves as a redox reagent to provide hydroxyl radicals for methane oxidation and protons for nitrogen hydrogenation. Quantum chemical calculations revealed that Fe-oxo species play a significant role in the coactivation of methane and nitrogen molecules, which lowers the energy barriers of rate-determining steps for methanol and ammonia generation.

Fe-Single-Atom Catalysts on Nitrogen-Doped Carbon Nanosheets for Electrochemical Conversion of Nitrogen to Ammonia

Fe-Single-Atom Catalysts on Nitrogen-Doped Carbon Nanosheets for Electrochemical Conversion of Nitrogen to Ammonia

Highly dispersed copper-iron nanoalloy enhanced electrocatalytic reduction coupled with plasma oxidation for ammonia synthesis from ubiquitous air and water

Conversion of nitrogen to ammonia at ambient conditions is a promising avenue for future distributed energy storage and fertilizer supply. However, it is currently hindered by the difficult nitrogen activation and competitive hydrogen evolution reaction. Herein, we develop a new strategy of highly dispersed copper-iron (Cu-Fe) nanoalloy enhanced electrocatalytic nitrate reduction to ammonia (NRA), in which nitrate can be derived from nitrogen and oxygen in the air via plasma process. The nitrate obtained by plasma oxidation of air is more than 3 times as much as nitrite, and the total yield rate of nitrate and nitrite is over 137 μmol·h1 by a single electrode of Tesla coil. Highly dispersed Cu-Fe nanoalloy with different ratios of Cu to Fe were prepared for NRA catalysts using the Joule heating method with instantaneous thermal shock, Cu10Fe1 nanoalloy demonstrates the best NRA activity, exhibits an excellent ammonia yield rate of 190.46 μmol·h1·cm2 and Faraday efficiency of 93.74 %. The Kelvin probe force microscope, in situ electrochemical Raman spectroscopy and density functional theory reveal the enhancing effect and tuning mechanism of Fe atom on the adsorption energy and electronic structure of Cu. This work opens up a new pathway for ammonia synthesis from air and water and provides a new strategy for the construction of high-performance NRA catalysts and the analysis of the reaction mechanism.

Characterization and Optimization of Plasma Electrolytic Process for Conversion of Molecular Nitrogen to Ammonia in Aqueous Water at Atmospheric Pressure

Ammonia (NH3) is widely used in the chemical and agricultural industries and is of growing interest as a potential energy carrier. Most of the current global NH3 production utilizes the Haber-Bosch process which has a large environmental and physical footprint. For this reason, there have been substantial efforts to develop an alternative process that can be sustainable and distributed. Recently, plasma-based electrolysis reactors have shown promise to convert molecular nitrogen to various forms of fixed nitrogen such as ammonia, nitrate, and nitrite in water at atmospheric pressure. However, selectivity and control over the products has not been adequately demonstrated. In this work, we studied a plasma formed in pure nitrogen gas or mixtures containing nitrogen gas at the surface of liquid water. Various products were characterized in the liquid phase including ammonium ions, nitrate ions, nitrite ions, and hydrogen peroxide as a function of pH, discharge current, and time. In addition, continuous direct current (DC) was compared to pulsed DC voltage plasma operation. We find that the selectivity to different nitrogen products depends on the solution conditions. These results could be used to inform optimization and scale up of similar plasma-liquid systems for sustainable nitrogen fixation.

(Invited) Next Generation Electrified Membrane Technology for Simultaneous Wastewater Treatment and Production of Nitrogen Fertilizer

Recovery and repurposing of wastewater nitrogen such as nitrate (NO3 −) and nitrite (NO2 −) receive increasing attention as the current approaches of biological nitrogen removal or conversion into nitrogen gas (N2) renders high energy footprints. This study reported the first electrified membrane upcycling of NO3 − into NH3 that further converted into ammonia sulfate (NH4SO4), a liquid fertilizer readily for use. Paired electrolysis was used to couple simultaneous cathodic and anodic electrochemical half-reactions to enable nitrate reduction and eliminate the external acid/base consumption. Under a partial current density of 63.8±4.4 mA·cm−2 on a cathodic membrane made of a mixed-valence copper oxide and a polytetrafluoroethylene (PTFE) hydrophobic substrate, a recovery rate and energy consumption of 3100±91 g-(NH4)2SO4·m−2·d−1 and 21.8±3.8 kWh·kg−1-(NH4)2SO4 were achieved with the synthetic feed solution (150 mM NO3 −) flowing into the cathode chamber and the produced NH3 migrating across the cathodic membrane into a trap and anode chambers filled with the flowing 0.5 M Na2SO4 solution. 99.9% NO3 − was removed in the feed after 5 h operation with a NH3 recovery rate of 99.5%. This electrified membrane process was demonstrated to achieve comparable performances of synergistic nitrate decontamination and nutrient recovery using real nitrate wastewater with durable catalytic activity and stability. Specifically, the required electricity cost for converting 10 to 100 mM NO3 − to (NH4)2SO4 was $675 to $408 ton−1, respectively. The obtained (NH4)2SO4 may be sold as fertilizer at a price of 533 $·ton−1 (according to USDA) and further offset the cost of the NO3 − removal.According to the International Fertilizer Association, in 2018 the U.S. ranked second in nitrogen production, representing 11.6% of global production. However, it still requires the importation of nitrogen fertilizer, to fully meet the national demand. The US Environmental Protection Agency reports that in 2013, ~38 kg of nitrogen per acre per year was used for fertilization, and in 2016, 94 million acres of corn were planted in the US, representing ~40% of US fertilizer demand. Roughly, this equates to ~8.9 billion kg of nitrogen per year needed to meet total US fertilization demand. The nitrogen available in drinking water sources is roughly 65 million kg per year, and the nitrogen available in wastewater sources is roughly 2.4 billion kg per year. Thus, by fully recovering the nitrogen from wastewater 34.3% of the US nitrogen fertilizer requirement could be met. This could also further mitigate the increase in nitrogen fertilizer prices due to blocked nitrogen fertilizer imports and even free the US from nitrogen fertilizer imports. According to U.S. Department of Agriculture, the average U.S. farm price of sulfate of ammonium fertilizers is $533 per ton. Even leaving aside the revenue generated by the treatment of nitrogen-containing sewage, the market size of nitrogen fertilizer produced through sewage is as high as $12.8 billion.

(Invited) Electrifying Nitrogen Transformations: Decarbonizing Ammonia Using Plasma Catalysis and Electrochemical Reduction of Nitrate in Wastewaters

Nitrogen fixation in fertilizers forms the basis of modern agriculture and mediates global food insecurity. Energy-dense nitrogen-based compounds also represent promising carbon-free alternative fuels when synthesized using sustainable energy and materials. However, conventional thermally-activated nitrogen conversion processes consume substantial amounts of fossil fuels as materials and energy inputs, leading to an unsustainable energy and carbon footprint. Therefore, electron-driven approaches are needed to establish fossil-free nitrogen interconversions. Electrochemical and plasma-activated reactions operate under mild conditions, enabling facile coupling to intermittent renewable energy sources to reduce CO2 emissions and reactive nitrogen pollution, facilitating storage and transportation of renewable energy in nitrogen-based fuels.Non-thermal plasma has been used to synthesize ammonia under mild conditions, but the dearth of fundamental understanding of plasma catalytic reactions handicaps the development of efficient plasma catalytic N2 conversion. Therefore, an in situ FTIR reactor was employed in combination with steady-state flow reactor experiments and plasma kinetic modeling to elucidate the surface reaction mechanisms and plasma-catalyst interactions. Ammonia yield can be influenced by plasma-derived intermediates and their interactions with catalyst surfaces, which lead to different reaction pathways. Furthermore, techno-economic analysis was employed to reveal the threshold efficiency required for a plasma process to become environmentally and economically competitive.Beyond electrification of N2 fixation for ammonia synthesis, existing waste streams containing fixed nitrogen as nitrate may be mined for fertilizer or carbon-free renewable energy storage while avoiding the need for H2 as a reagent, via selective nitrate electroreduction to ammonium. Nitrate electrochemical reduction can eliminate the production of concentrated waste streams while avoiding the addition of reductant or hole scavenger chemicals. However, major challenges for nitrate removal from water via electrochemical conversion involve reducing the use of expensive precious metal electrocatalysts while also improving the reaction activity and selectivity, stability, and mass transport of nitrate to electrocatalyst active sites. Therefore, electrochemical membranes were employed as porous flow-through electrodes to address these challenges based on improved mass transport and altered kinetics under flow conditions within membrane pores.Conductive electrified membranes, fabricated using inexpensive materials and green synthesis methods, showed significantly higher nitrate removal efficiency during electrified filtration compared to flow-by mode. The small pore sizes in the membrane reduced the diffusional boundary layer by several orders of magnitude with respect to flow-by mode, overcoming diffusional mass transport limitations. During electro-filtration, the nitrate conversion activity was easily controlled by tuning the permeate flow rate, regardless of applied potential. These multifunctional electrified membranes for reduction of nitrate in wastewaters have the potential to partially displace carbon-intensive industrially synthesized ammonia while simultaneously accomplishing water decontamination.

Light-Driven Electron Uptake from Nonfermentative Organic Matter to Expedite Nitrogen Dissimilation by Chemolithotrophic Anammox Consortia.

Nonphotosynthetic microorganisms are typically unable to directly utilize light energy, but light might change the metabolic pathway of these bacteria indirectly by forming intermediates such as reactive oxygen species (ROS). This work investigated the role of light on nitrogen conversion by anaerobic ammonium oxidation (anammox) consortia. The results showed that high intensity light (>20000 lx) caused ca. 50% inhibition of anammox activity, and total ROS reached 167% at 60,000 lx. Surprisingly, 200 lx light was found to induce unexpected promotion of the nitrogen conversion rate, and ultraviolet light (<420 nm) was identified as the main contributor. Metagenomic and metatranscriptomic analyses revealed that the gene encoding cytochrome c peroxidase was highly expressed only under 200 lx light. 15N isotope tracing, gene abundance quantification, and external H2O2 addition experiments showed that photoinduced trace H2O2 triggered cytochrome c peroxidase expression to take up electrons from extracellular nonfermentative organics to synthesize NADH and ATP, thereby expediting nitrogen dissimulation of anammox consortia. External supplying reduced humic acid into a low-intensity light exposure system would result in a maximal 1.7-fold increase in the nitrogen conversion rate. These interesting findings may provide insight into the niche differentiation and widespread nature of anammox bacteria in natural ecotopes.

Biodegradation of sulfate and elimination of heavy metals by immobilized-microbial bioaugmentation coupled with anaerobic membrane bioreactor

Sulfate-rich metal-laden wastewater (SRMLW) shows a significant threat on the ecological environment and human health. Sulfate-reducing bacteria (SRB) can remove sulfate from wastewater in anaerobic membrane bioreactor (AnMBR). This study constructed recombinant genetic engineered SRB (rSRB) and investigated the sulfate and heavy metals removal efficiency for treating SRMLW by immobilized-microbial bioaugmentation using rSRB (IMrSRB) coupled with AnMBR (Bio-AnMBR). The results show that Bio-AnMBR removed sulfate (99.4%) from SRMLW by upregulating key genes (Sat, DsrAB, AprAB, QmoABC, DsrC and DsrMKJOP) and enzymes (APS reductase, Dissimilatory sulfite reductase, Trithionate reductase and Thiosulfate reductase) in dissimilatory sulfite and sulfate respiration processes. Bio-AnMBR achieved synergistic biodegradation of sulfate and nitrogen by stimulating the activity of these bacteria related to the conversion of nitrogen and sulfate. Microbial analysis indicated that the relatively high abundance of rSRB (79.2%) and functional genes (70.1%) upregulated the activities of key enzymes associated with sulfate metabolism system, thus increasing the production of S (66.4 mg/L) and H2S (23.8 mg/L). Bio-AnMBR significantly improved the tolerance to heavy metals by increasing concentrations of CO32–, S2-, and HS-, which was configured to reduce heavy metals (95.6%) via precipitation of metal sulfide (81.3 mg/L), metal carbonates (30.7 mg/L) and metal hydroxides (18.7 mg/L). Bio-AnMBR increased system stability, shorted hydraulic retention time (HRT), decreased the production of soluble microbial products (SMP), extracellular polymeric substances (EPS) and waste-sludge production (WSP), as well as improved effluent quality. In conclusion, data in this study indicate that application of Bio-AnMBR is a feasible strategy for the treatment of SRMLW.

Effects of solvent phase recycling on microalgae liquefaction in ethanol: Bio-oil production and nitrogen transformation

Liquefaction of microalgae in ethanol offers an eco-friendly bio-oil alternative, but solvent recycling is crucial for sustainability due to extra costs. In this work, Chlorella vulgaris was liquefied in supercritical ethanol at 260 °C, and the solvent phase (SP) separated from bio-oil was recovered and reused. Five liquefaction cycles were performed at identical temperature and pressure conditions to investigate the effects on oil production and nitrogen transformation. The findings demonstrated a gradual increase in water content in recycled SP. Ethanol-water co-solvent as the reaction medium promoted the decomposition and re-polymerization of protein in raw material, thus increasing the bio-oil yield (76.84 %) and higher heating value (33.53 MJ/kg) to some extent. Simultaneously, the relative nitrogen content of bio-oil rose from 8.03 % to 8.52 %, predominantly in the form of nitrogen heterocycles. The potential pathway for nitrogen conversion was revealed, which establishes a theoretical basis for the subsequent denitrification of bio-oil.

Stress response mechanism of wastewater biological nitrogen removal systems to environmentally realistic concentrations of tire wear particles: Contribution of leachable additives

The study quantified the biological nitrogen removal performance, microbial metabolism, microbial community structure, and antioxidant system in a sequencing batch reactor under long-term exposure to 0.1 and 1 mg/L tire wear particles (TWPs), and determined the contribution of leachable additives to the biotoxicity of TWPs. The results showed that long-term exposure to 0.1 and 1 mg/L TWPs inhibited both the nitrification and denitrification processes, reducing ammonia nitrogen (NH4+-N) and total nitrogen (TN) removal efficiency. The TWP leachate (TWPL) primarily contributed to the denitrification inhibition by TWPs, potentially due to the high concentration of zinc ions in the leachable additive. Furthermore, both TWP and TWPL inhibit nitrogen conversion, with TWP inhibiting the generation and transfer of electrons, while TWPL only negatively affects the electron transfer process. This study presents novel insights into the impact of TWPs on biological nitrogen removal, underscoring its broader implications for the geochemical nitrogen cycle.

Ammonia assimilation is key for the preservation of nitrogen during industrial-scale composting of chicken manure

Nitrogen loss from compost is a serious concern, causing severe environmental pollution. The NH4+-N content reflects the release of NH3. However, the nitrogen conversion pathway that has the greatest impact on NH4+-N content is still unclear. This study attempted to explore the key pathways, core functional microorganisms, and mechanisms involved in the transformation of ammonia nitrogen during composting. KEGG (Kyoto Encyclopedia of Genes and Genomes) metabolic pathways revealed that ammonia assimilation was dominated by the glutamate dehydrogenase (GDH) pathway (53.4%), which is crucial for nitrogen preservation. The combined analysis of KEGG, NR species annotation, and co-occurrence network identified 20 easy-to-regulate obligate core nitrogen-transforming functional microorganisms, including 18 ammonia-assimilating bacteria. Furthermore, the effects of environmental parameters on the obligate core functional microorganisms were investigated. The present study results provided a theoretical basis for the utilization of ten ammonia-assimilating bacteria, such as Paenibacillus, Erysipelatoclostridium, and Defluviimonas to improve the quality of compost.

Metagenomic analysis reveals the responses of microbial communities and nitrogen metabolic pathways to polystyrene micro(nano)plastics in activated sludge systems.

Microplastics (MPs) and nanoplastics (NPs) are prevalent in sewage and pose a potential threat to nitrogen biotransformation in wastewater treatment systems. However, investigations on how MPs and NPs affect the microbial nitrogen conversion and metabolism of the activated sludge are still scanty. Herein, the responses of microbiomes and functional genes to polystyrene MPs and NPs in activated sludge systems were investigated by metagenomic analysis. Results indicated that 1mg/L MPs and NPs had marginal impacts on the nitrogen removal performance of the activated sludge systems, whereas high concentrations of MPs and NPs (20 and 100mg/L) decreased the total nitrogen removal efficiency (13.4%-30.6%) by suppressing the nitrogen transformation processes. Excessive reactive oxygen species induced by MPs and NPs caused cytotoxicity, as evidenced by impaired cytomembranes and decreased bioactivity. Metagenomic analysis revealed that MPs and NPs diminished the abundance of denitrifiers (e.g. Mesorhizobium, Rhodobacter and Thauera), and concurrently reduced the abundance of functional genes (e.g. napA, napB and nirS) encoding for key enzymes involved in the nitrogen transformations, as well as the genes (e.g. mdh) related to the electron donor production, thereby declining the nitrogen removal efficiency. Network analysis further clarified the attenuate association between denitrifiers and denitrification-related genes in the plastic-exposed systems, elucidating that MPs and NPs restrained the nitrogen removal by inhibiting the contributions of microorganisms to nitrogen transformation processes. This study provides vital insights into the responses of the microbial community structure and nitrogen conversion processes to micro(nano)plastics disturbance in activated sludge systems.

Transition metal enhanced chromium nitride as composite nitrogen carrier for sustainable chemical looping ammonia synthesis

Chemical looping ammonia synthesis (CLAS) is promising to achieve decentralized ammonia synthesis under ambient pressure. Here, we develop a highly selective composite nitrogen carrier for efficient CLAS based on transition metals (TMs=Co, Ni, Fe) decorated chromium nitride (CrN). Systematic studies indicate that the pristine CrN is extremely inert: only 4.5% lattice nitrogen can be consumed in reacting with H2 (700 °C, 1 bar). Upon loading cobalt, the composite nitrogen carrier achieves lattice nitrogen conversion of 50.7% and ammonia selectivity up to 98.1%. Furthermore, Co-CrN exhibits excellent CLAS performance, attaining an average ammonia production rate of 466.1 μmol g−1 h−1 in 12 chemical loopings, which is ∼10 times that of the pristine CrN. Theoretical calculations reveal that the nitrogen vacancies generated in hydrogenation play a crucial role as activation centers for N2 fixation through a Mars–van Krevelen mechanism. This work provides a novel strategy to optimize nitrogen carriers for enhanced CLAS.

Effect of Nitrogen Application and Microbial Fertilizer on Nitrogen Conversion Processes in Saline Farmland

The nutrient utilization rate of salinized farmland soils is low, the nitrogen loss is high, and soil salinity inhibits the hydrolysis of urea and the release of nutrients. In this work, the effect of microbial fertilizer on the nitrogen transformation characteristics and nitrogen morphology of salinized soils was studied using indoor constant temperature incubation tests with different nitrogen application rates—without (A0) and with microbial fertilizer application (A1 (15 t/ha)) or nitrogen application (N) of 0 kg/ha (N0), 97.5 kg/ha (N1), or 195 kg/ha (N2). The results show the following: (i) When no microbial fertilizer was applied, an increased nitrogen application promoted nitrogen fertilizer’s ammonification and nitrification reactions. Furthermore, the maximum net nitrification rate with the high nitrogen fertilizer application decreased; the apparent ammonification rate and net ammonification rate A0N2 increased by 26.1% and 24.6%, respectively, compared with A0N1 on the first day of incubation; the maximum net nitrification rate of A0N1 was more than that of A0N2; and A0N1 &gt; A0N2 on day 3, while A0N2 &gt; A0N1 on days 3 to 15. At 3 d, the nitrogen conversion process of A0N1 was dominated by the nitrification reaction, while the ammonification reaction dominated in A0N2. (ii) Microbial fertilizers significantly increased the ammonification and nitrification rates under the low N fertilizer application. The intensity of ammonification and nitrification under the low N fertilizer application was greater than that under the high N fertilizer application. The apparent ammonification rate and net ammonification rate of A1N1 increased by 60.9% and 52.6% compared with A0N1 and 21.9% and 21.7% compared with A1N2 on the first day of incubation, and the peak net nitrification rates of A1N1 and A1N2 (28.19 mg/kg d and 11.02 mg/kg d, respectively) and net nitrification rates of A1N1 and A1N2 were 113.7% higher than those of A0N1. The net nitrification rates of A1N1 and A1N2 were 82.3% and 58.6% lower than the maximum net nitrification rates on the 15th day of incubation, respectively. (iii) In saline soils, low-nitrogen microbial fertilizers led to more ammonium nitrogen in the soil, and the high-nitrogen fertilizer application resulted in higher nitrate nitrogen in the soil, leading to nitrogen leaching. Therefore, when applying microbial fertilizer, choosing the most suitable period for reduced chasing is important for the efficient use of fertilizers, the alternative role of biofertilizers, and the study of environmental pollution.