Nitrogen Conversion Research Articles

Development of an electrochemical separation-Rhodopseudomonas palustris electrolysis cell-coupled system for resourceful treatment of mature leachate landfill

Electrochemical technology is a promising technique for separating ammonia from mature landfill leachate. However, the accompanying migration and transformation of coexisting pollutants and strategies for further high-value resourceful utilization of ammonia have rarely received attention. In this study, an electrochemical separation-Rhodopseudomonas palustris electrolysis cell coupled system was initially constructed for efficient separation and conversion of nitrogen in mature landfill leachate to microbial protein with synchronously tracking the transport and conversion of coexisting heavy metals accompanying the process. The results revealed that ammonia concentration in the cathode increased from 40.3 to 49.8% with increasing the current density from 20 to 40 mA/cm2, with less than 3% of ammonia transformation to NO2−-N and NO3−-N. During ammonia separation, approximately 95% of HM-DOMs (Cr, Cu, Ni, Pb, and Zn) were released into the anolyte due to humus degradation and further diffused to the cathode. A significant correlation was observed between the releases of HM-DOMs. Cu-DOMs accounted for 70.2% of the total Cu content, which was the highest proportion among the heavy metals (HMs). Among the HMs in anolyte, 57.4% of Pb, 52.5% of Ni, and 50.6% of Zn diffused to the cathode, and most of the HMs were removed in the form of hydroxide precipitations due to heavy alkaline catholyte. Compared with the open-circuit condition, the utilization efficiency of NH4+-N in the R. palustris electrolysis cell increased by 445.1% with 47% and 50% increases in final NH4+-N conversion rate and R. palustris biomass, respectively, due to bio-electrochemical enhanced phototrophic metabolism and acid generation for buffering the strong alkalinity of the electrolyte to maintain suitable growth conditions for R. palustris.

Performance of microbial inoculation and tricalcium phosphate on nitrogen retention and conversion: Core microorganisms and enzyme activity during kitchen waste composting

The substantial release of NH3 during composting leads to nitrogen (N) losses and poses environmental hazards. Additives can mitigate nitrogen loss by adsorbing NH3/NH4, adjusting pH, and enhancing nitrification, thereby improving compost quality. Herein, we assessed the effects of combining bacterial inoculants (BI) (1.5%) with tricalcium phosphate (CA) (2.5%) on N retention, organic N conversion, bacterial biomass, functional genes, network patterns, and enzyme activity during kitchen waste (KW) composting. Results revealed that adding of 1.5%/2.5% (BI + CA) significantly (p < 0.05) improved ecological parameters, including pH (7.82), electrical conductivity (3.49 mS/cm), and N retention during composting. The bacterial network properties of CA (265 node) and BI + CA (341 node) exhibited a substantial niche overlap compared to CK (210 node). Additionally, treatments increased organic N and total N (TN) content while reducing NH4+-N by 65.42% (CA) and 77.56% (BI + CA) compared to the control (33%). The treatments, particularly BI + CA, significantly (p < 0.05) increased amino acid N, hydrolyzable unknown N (HUN), and amide N, while amino sugar N decreased due to bacterial consumption. Network analysis revealed that the combination expanded the core bacterial nodes and edges involved in organic N transformation. Key genes facilitating nitrogen mediation included nitrate reductase (nasC and nirA), nitrogenase (nifK and nifD), and hydroxylamine oxidase (hao). The structural equation model suggested that combined application (CA) and microbial inoculants enhance enzyme activity and bacterial interactions during composting, thereby improving nitrogen conversion and increasing the nutrient content of compost products.

Experimental and kinetic modeling study on laminar flame speeds and emission characteristics of oxy-ammonia premixed flames

The low flame speed and NOx emissions of ammonia are the key to affecting combustion temperature, stability, flame structure, and pollutant control, limiting its application in power generation devices. This study proposes oxy-ammonia combustion (oxygen content in oxidant = 100%, NH3/O2 combustion) as a novel method for significantly enhancing ammonia combustion. A method for measuring the laminar flame speed using the NH* distribution of the Bunsen burner flame is proposed, and the measured data is close to the constant volume combustion bomb. 21 kinetic models were collected and optimized after comparison with the experimental data of constant volume combustion bombs, and results show that Han et al.'s model has higher prediction accuracy for NH3/O2 flames. The preheating temperature was relevant to gas turbine combustors (298.15–500 K), and the equivalence ratio ranged from 0.7 to 1.6. At this extreme condition (oxygen content in oxidant = 100%), the results show that the maximum laminar flame speed reaches 1.25 m/s at ambient pressure and temperature, which is approximately 18 times that of NH3/air combustion, mainly due to the increased reaction rates of OH, H, O and NH2 radicals in the reaction zone (primary ammonia decomposition and H/O radical pool). The NO emission of NH3/O2 combustion at stoichiometric conditions is about 7216 ppmv@15%O2, 1.5 and 13 times that of NH3/air and CH4/air combustion, respectively. NO production and consumption may follow the N2O and NNH mechanism, and HNO is an important precursor for NO formation. Increasing the preheating temperature has less effect on the reaction pathway directions in the reaction network of nitrogen conversion but affects the path flux significantly.

Promoting nitrogen conversion in aerobic biotransformation of swine slurry with the co-application of manganese sulfate and biochar

This study aimed to explore the co-application of MnSO4 (Mn) and biochar (BC) in nitrogen conversion during the composting process. A 70-day aerobic composting was conducted using swine slurry, supplemented with different levels of Mn (0, 0.25%, and 0.5%) and 5% BC. The results demonstrated that the treatment with 0.5MnBC had the highest levels of NH4+-N (3.07 g kg−1), TKN (29.90 g kg−1), and NO3−-N (1.94 g kg−1) among all treatments. Additionally, the 0.5MnBC treatment demonstrated higher urease, protease, nitrate reductase, and nitrite reductase activities than the other treatments, with the peak values of 18.12, 6.96, 3.57, and 15.14 mg g−1 d−1, respectively. The addition of Mn2+ increased the total organic nitrogen content by 29.59%–47.82%, the acid hydrolyzed ammonia nitrogen (AN) content by 13.84%–57.86% and the amino acid nitrogen (AAN) content by 55.38%–77.83%. The richness of Chloroflexi and Ascomycota was also enhanced by the simultaneous application of BC and Mn. Structural equation modeling analysis showed that Mn2+ can promote the conversion of Hydrolyzed Unknown Nitrogen (HUN) into AAN, and there is a positive association between urease and NH4+-N according to redundancy analysis. Firmicutes, Basidiomycota, and Mortierellomycota showed significant positive correlations with ASN, AN, and NH4+-N, indicating their crucial roles in nitrogen conversion. This study sheds light on promoting nitrogen conversion in swine slurry composting through the co-application of biochar and manganese sulfate.

Effects of Intercropping and Nitrogen Application on Soil Fertility and Microbial Communities in Peanut Rhizosphere Soil

The intercropping of peanuts and sugarcane is a sustainable planting model that deserves in-depth research. For this study, two variables, i.e., intercropping status (peanut monocropping or sugarcane/peanut intercropping) and the level of nitrogen fertilization (low, medium, or high), were evaluated to analyze the effects of intercropping and nitrogen application on soil fertility and microbial communities in peanut rhizosphere soil. These analyses revealed that higher nitrogen application led to increased total nitrogen (TN), available nitrogen (AN), and soil organic matter (OM) levels in rhizosphere soil for both monocropped and intercropped peanuts, with a decrease in pH. Monocropped peanuts had higher TN, total phosphorus (TP), and total potassium (TK) levels compared to intercropped peanuts at the same nitrogen level but lower AN content and pH levels. The diversity of microbial communities in the rhizosphere soil of intercropped peanuts was significantly higher than that of monocropped peanuts under high levels of nitrogen fertilizer application. Higher levels of Gemmatimonadetes abundance were observed in intercropping rhizosphere soil, compared to that associated with peanut monocropping under low, middle, and high levels of nitrogen fertilizer application, whereas the opposite trend was observed for Chloroflexi abundance. Nitrospira abundance levels rose gradually in the monocropping treatment group, whereas the opposite trend was evident under intercropping conditions. Further analyses of nitrogen cycle-related genes demonstrated higher levels of nitrogen conversion cycle activity in intercropping peanut rhizosphere soil under low nitrogen levels, whereas nitrogen transformation cycle activity levels were higher in monocropping peanut rhizosphere soil under high levels of nitrogen amendment. It can be concluded that intercropping and nitrogen fertilizer application change the physical and chemical properties of soil, thus affecting the diversity and function of soil microbial communities in the peanut rhizosphere. These results offer a theoretical foundation for more efficient sugarcane/peanut intercropping systems.

Phosphate additives promote humic acid carbon and nitrogen skeleton formation by regulating precursors and composting bacterial communities

This study aimed to compare the effect of different phosphate additives including superphosphate (CP) and MP [Mg(OH)2 + H3PO4] on nitrogen conversion, humus fractions formation and bacterial community in food waste compost. The results showed the ratio of humic acid nitrogen in total nitrogen (HA-N/TN) in CP increased by 49 %. Ammonium nitrogen accumulation was increased by 75 % (CP) and 44 % (MP). Spectroscopic techniques proved that phosphate addition facilitated the formation of complex structures in HA. CP enhanced the dominance of Saccharomonospora, while Thermobifida and Bacillus were improved in MP. Structural equation modeling and network analysis demonstrated that ammonium nitrogen can be converted to HA-N and has positive effects on bacterial composition, reducing sugars and amino acids, especially in CP with more clustered network and synergic bacterial interactions. Therefore, the addition of phosphate provides a new idea to regulate the retained nitrogen toward humification in composting.

Effects of different nitrogen applications and straw return depth on straw microbial and carbon and nitrogen cycles in paddy fields in the cool zone

Straw is an important source of organic fertilizer for soil enrichment, however, the effects of different nitrogen(N) application rates and depths on straw decomposition microorganisms and carbon and nitrogen cycling under full straw return conditions in cool regions of Northeast China are not clear at this stage. In this paper, we applied macro-genome sequencing technology to investigate the effects of different N application rates (110 kg hm−2, 120 kg hm−2, 130 kg hm−2, 140 kg hm−2, 150 kg hm−2) and depths (0–15 cm, 15–30 cm) on straw decomposing microorganisms and N cycling in paddy fields in the cool zone of Northeast China. The results showed that (1) about 150 functional genes are involved in the carbon cycle process of degradation during the degradation of returned straw, of which the largest number of functional genes are involved in the methane production pathway, about 42, the highest abundance of functional genes involved in the citric acid cycle pathway. There are 22 kinds of functional genes involved in the nitrogen cycle degradation process, among which there are more kinds involved in nitrogen fixation, with 4 kinds. (2) High nitrogen application (150 kg hm−2) inhibited the carbon and nitrogen conversion processes, and the abundance of straw-degrading microorganisms and nitrogen-cycling functional genes was relatively high at a nitrogen application rate of 130 kg hm−2. (3) Depth-dependent heterogeneity of the microbial community was reduced throughout the vertical space. At 71 days of straw return, the nitrogen cycling function decreased and some carbon functional genes showed an increasing trend with the increase of straw return depth. The nitrogen cycle function decreased with the increase of straw returning depth. The microbial community structure was best and the abundance of functional genes involved in the nitrogen cycling process was higher under the conditions of 0–15 cm of returning depth and 130 kg hm−2 of nitrogen application.

How do green manure management practices affect ammonia emissions from maize fields?

The use of “green manure”—crops that are cultivated specifically to be incorporated into the soil to increase its organic matter content—has been proposed as an alternative to chemical fertilizer because of its benefits in terms of crop yield. Nonetheless, the differential impacts of green manure on ammonia volatilization remains underexplored. In this study, the influence of various green manure management strategies on ammonia volatilization in maize cultivation were examined. Field experiments conducted from 2020 to 2022, the field experiment applied common vetch after the spring wheat harvest, with five distinct treatments: conventional tillage without green manures as a control (CT); tillage with total green manure incorporation (TG); no-tillage with total green manure mulching (NTG); tillage with only root incorporation (T); and no-tillage with removal of aboveground green manure (NT). The results showed that under TG and NTG, the maize yields were 12.3%-33.2% higher than under CT, and 6.8%-18.8% higher than under T and NT. Compared with CT, all four green manure management practices also significantly increased NH3 emissions in maize fields, and they increased ammonia volatilization by 12.0%-13.7% in NTG and TG compared to root retention patterns, with NTG exhibiting higher rates than TG. NTG significantly increased soil organic matter, total nitrogen, mineral nitrogen, water-filled pore space (WFPS), microbial biomass carbon and nitrogen, and C: N, and it decreased soil pH compared to TG. Regression analysis showed that these factors were correlated with NH3 volatilization. In addition, soil urease and ammonia-oxidation functional genes (amoA) showed differences under green manure management practices. Structural equation modeling showed that NH4+-N had the greatest positive impact on NH3, and urease activity and total nitrogen had positive effects on NH4+-N. Furthermore, microbial biomass carbon and pH had positive and negative effects on urease activity, respectively, both of which were only related to SOM. At the same time, WFPS had a positive impact on total nitrogen. In summary, no-tillage with total green manure mulching increases maize yield but also increases NH3 emissions. NH4+-N formed by the hydrolysis of urea by soil urease and the conversion of total nitrogen were found to be the main reasons for high NH3 emissions. In addition, SOM can promote urease activity, increase NH4+-N content and NH3 volatilization by increasing MBC and decreasing soil pH.

Total nitrogen removal by Fe-activated carbon composite coupled with persulfate

The conversion of nitrate nitrogen (NO3−-N) or ammonia nitrogen (NH4+-N) to dinitrogen (N2) by chemical process for total nitrogen (TN) removal is meaningful, but still a challenge in wastewater treatment. Herein, zero valent iron (Fe0) loaded active carbon (Fe0@AC) was prepared and used to remove TN from the nitrogen-containing wastewater by an efficient chemical reduction coupled with oxidation process (FeR-PSO). In the step of NO3−-N reduction by Fe0@AC, Fe0@AC with 25 wt% Fe0 could reduce 100 % NO3−-N with the initial concentration of 50 mg N/L after 60 min at the Fe0@AC dosage of 9 g/L and initial pH of 3.0, and over 30 % NO3−-N could be reduced to N2. In the subsequent oxidation step, persulfate (PS) and magnesium oxide (MgO) were introduced into the solution after NO3−-N reduction to selectively oxidize NH4+-N to N2. The removal efficiency of NH4+-N and N2 selectivity after 30 min were 100 % and over 90 %, respectively, at the MgO dosage of 8 g/L and the PS dosage of 20.25 g/L. The developed FeR-PSO process could remove 93.40 % of TN from simulated wastewater, and over 90 % of TN from two actual pickle factory wastewaters. The possible mechanisms of NO3−-N reduction and NH4+-N oxidation by FeR-PSO process were proposed. These findings provide new insights for TN removal from NO3−-N containing wastewater or wastewater containing both NO3−-N and NH4+-N by chemical process.

Effects of aeration modes and rates on nitrogen conversion and bacterial community in composting of dehydrated sludge and corn straw.

Aeration is an important factor to regulate composting efficiency and nitrogen loss. This study is aimed to compare the effects of different aeration modes (continuous and intermittent) and aeration rate on nitrogen conversion and bacterial community in composting from dehydrated sludge and corn straw. Results showed that the intermittent aeration mode at same aeration volume was superior to the continuous aeration mode in terms of NH3 emission reduction, nitrogen conversion and germination index (GI) improvement. Intermittent aeration mode with 1200 L/h (aeration 5 min, stop 15 min) [K5T15 (V1200)] and 300 L/h of continuous aeration helped to the conservation of nitrogen fractions and accelerate the composting process. However, it was most advantageous to use 150 L/h of continuous aeration to reduce NH3 emission and ensure the effective composting process. The aeration mode K5T15 (V1200) showed the fastest temperature rise, the longer duration of thermophilic stage and the highest GI (95%) in composting. The cumulative NH3 emission of intermittent aeration mode was higher than continuous aeration mode. The cumulative NH3 emission of V300 was 23.1% lower than that of K5T15 (V1200). The dominant phyla in dehydrated sludge and corn straw composting were Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes. The dominant phylum in the thermophilic stage was Firmicutes (49.39%~63.13%), and the dominant genus was Thermobifida (18.62%~30.16%). The relative abundance of Firmicutes was greater in the intermittent aeration mode (63.13%) than that in the continuous aeration mode (57.62%), and Pseudomonas was dominant in composting with lower aeration rate and the lowest NH3 emission. This study suggested that adjustment to the aeration mode and rate could affect core bacteria to reduce the nitrogen loss and accelerate composting process.

Greenhouse gas emission characteristics during kitchen waste composting with biochar and zeolite addition

Aerobic kitchen waste composting can contribute to greenhouse gas (GHGs) emissions and global warming. This study investigated the effects of biochar and zeolite on GHGs emissions during composting. The findings demonstrated that biochar could reduce N2O and CH4 cumulative releases by 47.7 %and 47.9 %, respectively, and zeolite could reduce the cumulative release of CO2 by 28.4 %. Meanwhile, the biochar and zeolite addition could reduce the abundance of potential core microorganisms associated with GHGs emissions. In addition, biochar and zeolite reduced N2O emissions by regulating the abundance of nitrogen conversion functional genes. Biochar and zeolite were shown to reduce the impact of bacterial communities on GHGs emissions. In summary, this study revealed that biochar and zeolite can effectively reduce GHG emissions during composting by altering the compost microenvironment and regulating microbial community structure. Such findings are valuable for facilitating high-quality resource recovery of organic solid waste.

Effects of adding exogenous microorganisms on nitrogen conversion and its mechanism of action in pig carcass composting

This study aimed to reveal mechanisms of nitrogen changes in a mixed compost of diseased pig carcasses and sawdust after adding exogenous microbial agents. It was found that adding exogenous microbial agents significantly increased the content of various types of nitrogen and the germination index of plants. Microbial dominance of phyla was significantly correlated with indicators of physicochemical properties and copy number of nitrogen-functional genes, with simultaneous nitrogen fixation, nitrification, denitrification, ammonification, and glutamate synthesis during composting. At the end of composting, TKN, NH4+-N, and NO3−-N contents were increased by 1.914–3.082 mg/g, 0.047–0.42 mg/g, and 0.247–0.303 mg/g, respectively, in the experimental groups compared to the control group. Proteobacteria, Bacteroidetes, Firmicutes, Actinobacteria, and Planctomycetes were the five predominant phyla, while Sphingobacterium, and Paenalcaligenes were the two special genera in this experiment. After inoculation with exogenous microbial agents, the levels of nitrate nitrogen were significantly and positively correlated (p < 0.05) with the number of Bacteroidetes, the glnA gene was positively related (p < 0.01) with Planctomycetes, and the amoA, GDH2, and GLUD1-2 genes were positively related (p < 0.05) with Paenalcaligenes. The combined analysis has shown that amoA gene was positively related (p < 0.001) with genes such as nxrA, GDH2 and GLUD1-2, as well as indicators of physicochemical properties such as temperature, organic nitrogen and nitrate nitrogen, while the correlation was negative with genes such as nirB and nirS. Inoculation with exogenous microbial agents can significantly prolong the high-temperature period, which was extended by 5, 6, and 5 days in each experimental group, and the roles of nitrogen-functional genes can also be changed. Meanwhile, we found that the addition of exogenous microbial agents could promote the growth and alteration of microorganisms, which regulated the stability and symbiosis of the nitrogen transformation process.

A DFT study on regulating the active center of v-Ti2XT2 MXene through surface modification for efficient nitrogen fixation

The electrochemical conversion of nitrogen to ammonia provides an encouraging method to substitute the traditional Haber-Bosch process, owing to its high efficiency and mild reaction conditions. The search for high-performance catalysts and comprehension of catalytic mechanisms remains significant challenges. Herein, we conduct a systematic theoretical calculation of the NRR performance and mechanism of 24 Ti2XT2 (X = B, C, N; T = F, Cl, Br, I, O, S, Se, Te) MXenes with a T-vacancy to explore the influence of surface functional terminations and non-metallic center elements. Our findings demonstrate that surface functionalization significantly reduces the limiting potential by altering the rate-determining step. This change ranges from −1.24 V (Ti2NF2) to −0.21 V (Ti2BSe2), signifying the remarkable efficacy of modification of the surrounding environment of the exposed transition metal active center in promoting electrocatalytic performance. Detailed investigation of the charge density difference and orbital interaction reveals that the different NRR performance originates from the surface termination and non-metallic atoms regulate the electronic properties of the active Ti atoms. We also introduce the free energy change of *NNH2 (ΔG*NNH2) as a descriptor to predict the performance of NRR, which exhibits satisfactory linear relationship with free energy change of different intermediates and displays favourable volcano plot with limiting potential. Moreover, we highlight the pivotal role of work function in tuning the energy barrier of the rate-determining step, which can be regulated through the surface modification of MXenes. Our study not only offers a comprehensive understanding of the crucial impact of surface modification on the catalytic activities of defective MXenes, but also provides a rational perspective for designing efficient NRR catalysts.

Influence of low-density polyethylene addition on nitrogen transformation during sludge protein pyrolysis

Co-pyrolysis of sludge and waste plastics is a long-term strategic approach for producing valuable fuels. However, sludge is characterized by a high protein content, which serves as a significant source of nitrogenous components in bio-oil. To improve the quality of pyrolysis products, the present study investigated the effect of low-density polyethylene (LDPE) on nitrogen transformation during the pyrolysis of sludge protein (SP). The study findings indicated that LDPE addition reduced the amount of solid residue owing to the interaction between SP and H radicals generated by LDPE pyrolysis. The thermal weight loss difference consistently remained below 0 when the SP-to-LDPE mixing ratio was 7:3, indicating that LDPE promotes the pyrolysis of SP. For the analysis of nitrogen-containing products during pyrolysis, LDPE addition significantly reduced the levels of nitrogen-containing compounds in the bio-oils of glutamate (Glu), histidine (His), and tyrosine (Tyr). Specifically, at 600°C, Glu, His, and Tyr in the bio-oils decreased by 31.4%, 33.3%, and 34.38%, respectively. No significant changes were observed in the nitrogen content within the pyrolysis char of Glu and His. However, all three amino acids exhibited a significant increase in the formation of NOx precursors due to the attack on the nitrogen positions of the heterocyclic nitrogen species by the H radicals generated by LDPE. This study contributes to research on the impact of LDPE on nitrogen migration and conversion during the pyrolysis of SP, laying the foundation for subsequent studies on pollutant removal reactions.

Looking deeper into the effects of scouring and aeration on membrane aerated biofilms: Analysis of nitrogen conversion, oxygen profiles and nitrous oxide emissions

This study investigated the effects of aeration and scouring strategies on the performance of Membrane Aerated Biofilm Reactors (MABRs) and the distribution of oxygen and nitrous oxide in the biofilm. Four flat sheet MABRs were operated with synthetic feed under different conditions: two with intermittent aeration (iMABR) and two with continuous aeration (cMABR). Scouring was induced by bubbling dinitrogen gas through the reactor bulk at low and high frequencies (LF and HF). In the iMABRs, a partial nitritation biofilm initially developed, but the biofilm adapted to the aeration strategy over time and became nitrifying. The cMABRs directly developed a nitrifying biofilm without a significant phase of partial nitritation. Limiting oxygen availability improved the overall performance with regards to total nitrogen (TN) removal by providing a better environment for anaerobic ammonium oxidation (Anammox) while limiting complete nitrification.Oxygen profiles were measured in the iMABR over time at different biofilms depths, showing that intermittent aeration led to various oxygen concentrations and temporal variations in the oxygen availabilities at different depths of the biofilm. Also, N2O emissions from the MABRs differed greatly between the different systems, but still remained lower compared to other reactor configurations for nitrogen removal, making the MABR technology a worthy alternative. The results showed large differences between the operating strategies of the MABRs and can help to gain more insight into the specific properties of MABRs for nitrogen removal.

Novel ternary composite catalyst 2H/1T-MoS2/Co3O4-Ru for photoelectrocatalytic nitrogen reduction

The conversion of free nitrogen into combined nitrogen is one of the most important processes in nature and chemical production. However, achieving this process in industry requires significant energy consumption and CO2 emissions. Under environmental conditions, the photoelectrocatalytic nitrogen reduction reaction (NRR) has shown enormous potential in reducing energy consumption and environmental pollution. In this study, based on the unique advantages of the Ru element and type II heterojunctions in the field of photoelectrocatalytic nitrogen reduction, trace Ru-doped 2H/1T-MoS2/Co3O4 type II heterojunctions have been successfully prepared for the first time by hydrothermal and photodeposition methods. First-principles calculations demonstrate that doped Ru3+ provides nitrogen adsorption sites and also acts as an electron transfer bridge. The rest of the Ru is anchored by Co3O4, which causes a change in the surrounding electron cloud density, achieving better N2 adsorption and acting as an active centre. The catalyst system achieved a NH3 production rate of 869.8 µmol h−1 g−1 in 0.1 M Na2SO4, and the Faraday efficiency (FE) during the NRR process was as high as 35 %. Therefore, this catalyst has the potential to become a promising photoelectrocatalyst for nitrogen reduction reactions.

Solid-state fermentation of corn straw using synthetic microbiome to produce fermented feed: The feed quality and conversion mechanism

Straw is a typical biomass resource which can be converted into high nutritional value feed via microbial fermentation. The degradation and conversion of straw using a synthetic microbial community (SMC-8) was functionally investigated to characterise its nitrogen conversion and carbon metabolism. Four species of bacteria were found to utilise >20 % of the inorganic nitrogen within 15 h, and the ratio of the diameter of fungal transparent circles (D) to the diameter of the colony (d) of the four fungal species was >1. Solid-state fermentation of corn straw increased the total amino acid (AA) content by 41.69 %. The absolute digestibility of fermented corn straw dry weight (DW) and true protein was 34.34 % and 45.29 %, respectively. Comprehensive analysis of functional proteins revealed that Aspergillus niger, Trichoderma viride, Cladosporium cladosporioides, Bacillus subtilis and Acinetobacter johnsonii produce a complex enzyme system during corn straw fermentation, which plays a key role in the degradation of lignocellulose. This study provided a new insight in utilizing corn straw.

Partial denitrifying phosphorus removal coupling with anammox (PDPRA) enables synergistic removal of C, N, and P nutrients from municipal wastewater: A year-round pilot-scale evaluation

Applying anaerobic ammonium oxidation (anammox) in municipal wastewater treatment plants (MWWTPs) can unlock significant energy and resource savings. However, its practical implementation encounters significant challenges, particularly due to its limited compatibility with carbon and phosphorus removal processes. This study established a pilot-scale plant featuring a modified anaerobic-anoxic-oxic (A2O) process and operated continuously for 385 days, treating municipal wastewater of 50 m3/d. For the first time, we propose a novel concept of partial denitrifying phosphorus removal coupling with anammox (PDPRA), leveraging denitrifying phosphorus-accumulating organisms (DPAOs) as NO2− suppliers for anammox. 15N stable isotope tracing revealed that the PDPRA enabled an anammox reaction rate of 6.14 ± 0.18 μmol-N/(L·h), contributing 57.4 % to total inorganic nitrogen (TIN) removal. Metagenomic sequencing and 16S rRNA amplicon sequencing unveiled the co-existence and co-prosperity of anammox bacteria and DPAOs, with Candidatus Brocadia being highly enriched in the anoxic biofilms at a relative abundance of 2.46 ± 0.52 %. Finally, the PDPRA facilitated the synergistic conversion and removal of carbon, nitrogen, and phosphorus nutrients, achieving remarkable removal efficiencies of chemical oxygen demand (COD, 83.5 ± 5.3 %), NH4+ (99.8 ± 0.7 %), TIN (77.1 ± 3.6 %), and PO43− (99.3 ± 1.6 %), even under challenging operational conditions such as low temperature of 11.7 °C. The PDPRA offers a promising solution for reconciling the mainstream anammox and the carbon and phosphorus removal, shedding fresh light on the paradigm shift of MWWTPs in the near future.

Progress in Single/Multi Atoms and 2D‐Nanomaterials for Electro/Photocatalytic Nitrogen Reduction: Experimental, Computational and Machine Leaning Developments

AbstractThe conversion of atmospheric nitrogen (N2) into ammonia (NH3), known as nitrogen fixation, plays a crucial role in sustaining life on Earth, facing innovation with electrocatalytic and photocatalytic methods. These approaches promise gentler conversions from atmospheric nitrogen to ammonia, diverging from the energy‐intensive Haber‐Bosch process, which requires complex plant infrastructure. Vitality lies in eco‐friendly, cost‐effective, and energy‐efficient pathways. The challenge is that electrocatalysts and photocatalysts for nitrogen reduction have shown low Faraday efficiency, hampered by hydrogen evolution. This work delves into recent strides in electro/photo‐catalytic nitrogen fixation/reduction, deciphering mechanisms, catalysts, and prospects. By unveiling the core principles steering these processes, it dissects efficiency drivers. Experimental and theoretical studies, ranging from density functional calculations/simulations to machine learning‐based catalyst screening, mark the path toward highly efficient catalysts, including single/multi‐atom catalysts embedded in 2D materials. The journey explores diverse catalysts, assessing their performance, spotlighting emerging nanomaterials, heterostructures, and co‐catalyst techniques. Perspectives on future directions and potential applications of electro/photo‐catalytic nitrogen fixation/reduction are offered, by emphasizing their role in sustainable nitrogen management and their implications for global agriculture and environmental sustainability.

Nitrogen Cycling Dynamics: Investigating Volatilization and its Interplay with N2 Fixation

The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems, the conversion of nitrogen can be carried out through both biological and physical processes. Important processes in the nitrogen cycle include fixation, ammonification, nitrification, and denitrification. The majority of Earth's atmosphere (78%) is atmospheric nitrogen, making it the largest source of nitrogen. However, atmospheric nitrogen has limited availability for biological use, leading to a scarcity of usable nitrogen in many types of ecosystems. The nitrogen cycle is of particular interest to ecologists because nitrogen availability can affect the rate of key ecosystem processes, including primary production and decomposition. Human activities such as fossil fuel combustion, use of artificial nitrogen fertilizers, and release of nitrogen in wastewater have dramatically altered the global nitrogen cycle. Human modification of the global nitrogen cycle can negatively affect the natural environment system and also human health. Volatilization and its Relationship to N2 fascination in Nitrogen Cycle in agriculture field is discuss in this paper.