Denitrification Activity Research Articles

Distributions, sources, and air-sea fluxes of nitrous oxide in Bohai Bay, China

IntroductionPolluted bays are one of the critical areas for the production and emissions of marine nitrous oxide (N2O), which has a strong effect on global warming and plays a critical role in stratospheric ozone depletion.MethodsIn 2020, the distributions of N2O concentrations and emissions in the water column of Bohai Bay (BHB) were surveyed during two cruises.Results and discussionThe average N2O concentrations were higher in summer compared to autumn, with the oversaturation of N2O in both seasons. A declining gradient of N2O was found from the Hai River and Yellow River estuarine areas to the offshore sea, particularly in summer, implying riverine input was an important source of N2O. The vertical distribution of N2O was uniform in each season owing to the vertical mixing of water columns in the offshore sea, with N2O hotspots at the bottom of the two estuaries in summer and at the surface of the Hai River estuary in autumn. Moreover, the dominant sources of dissolved N2O were analyzed. N2O in the water column was predominately produced by nitrification and coupled nitrification-denitrification on suspended particulate matter. The mixing of water masses, particularly polluted water masses from coastal input, provides high N2O to the entire area of BHB, particularly in summer. Notably, nutrient and organic matter input from the coast could also indirectly drive N2O production by stimulating microbe activities of nitrification and denitrification under the water currents. In addition, statistical analysis revealed that ammonium, dissolved oxygen, and temperature were the dominant controlling factors of N2O in BHB. The annual flux of N2O in BHB was evaluated to be 6.5 Gg, accounting for 0.15% of the global oceanic N2O emission with 0.0044% of the global ocean area. Hence, as a typical polluted bay, BHB acted as a strong N2O source to the atmosphere on a per-unit-area basis.

Insights on the dual role of low-rank coal with high mineral catalysis index (LRC-HMCI) during blending coal for activated carbon production and low-temperature NH3-SCR of NO

The mineral catalysis index (MCI), reflecting the activity of mineral composition in coal, could be used as a meaningful reference to indicate the coal’s application potential. To elucidate the role of low-rank coal with high MCI (LRC-HMCI) on the AC preparation and application, in this investigation, ACs are produced by steam activation after blending Fugu (F) coal, Yangchang (Y) coal and Xiangyuan (X) coal. The as-prepared ACs’ textural evolution and performance were investigated by a series of characterization and low-temperature NO removal tests. The results show that LRC-HMCI promotes the as-prepared AC’s weight loss and burn-off and lowers its yield. The LRC-HMCI could promote the generation of micropores and the transformation from micropores to mesopores/macropores. 6Y-1X-3F-AC’s total BET specific surface area and micropore specific surface area is up to 880 m2/g and 629 m2/g, and the total volume reaches 0.42 cm3/g. LRC-HMCI decreases the AC’s graphitization degree. Meanwhile, LRC-HMCI favors incrementing as-prepared AC’s COO, CO and π–π*. LRC-HMCI also enhances NO removal, and 7Y-1X-2F-AC shows the highest denitrification activity. 2 h’s NO removal rate reaches 45.5%, which is 77.1% higher than 25.7% of Y-AC. The enhanced denitrification is mainly due to the dual role of LRC-HMCI: LRC-HMCI optimizes micropore porosity and improves the surface chemistry properties of AC, which eventually promote the NO and NH3 adsorption; Minerals from LRC-HMCI, particularly Fe-, Ca-, Mg- containing components, could catalyze the NH3-SCR reaction, thus improves the NO removal. The results of this research could guide cost-effective and high-performance AC production through coal blending based on MCI.

Characteristics of denitrification activity, functional genes, and denitrifying community composition in the composting process of kitchen and garden waste

N2O can be easily produced during the co-composting of kitchen waste (KW) and garden waste (GW). This study investigated the effects of the co-composting of KW and GW at different ratios (1:2, 1:1.5, 1:1, and 1.5:1) on the denitrifying activities, functional genes, and community composition of denitrifiers. The results showed that the denitrification activity of KW and GW at a 1:2 ratio was the lowest. The gene abundances of nirS, nirK, nosZI, and nosZII were high on days 12 and 28 under the four different ratios. Network analysis demonstrated that nosZ-type denitrifiers could construct a complex and reciprocal bacterial network to promote the reduction of N2O to N2. Mantel test results revealed that nirS-, nirK-, nosZI-, and nosZII-type denitrifiers were significantly positively correlated with pH, C/N, and moisture content. These findings demonstrated that composting with appropriate proportions of KW and GW could reduce N2O emissions caused by denitrification.

Synergistic between autotrophic and heterotrophic microorganisms for denitrification using bio-S as electron donor

In recent years, biological sulfur (bio-S) was employed in sulfur autotrophic denitrification (SAD) in which autotrophic Thiobacillus denitrificans and heterotrophic Stenotrophomonas maltophilia played a key role. The growth pattern of T.denitrificans and S.maltophilia exhibited a linear relationship between OD600 and CFU when OD600 < 0.06 and <0.1, respectively. When S.maltophilia has applied alone, the NorBC and NosZ were undetected, and denitrification was incomplete. The DsrA of S.maltophilia could produce sulfide as an alternative electron donor for T.denitrificans. Even though T.denitrificans had complete denitrification genes, its efficiency was low when used alone. The interaction of T.denitrificans and S.maltophilia reduced nitrite accumulation, leading to complete denitrification. A sufficient quantity of S.maltophilia may trigger the autotrophic denitrification activity of T.denitrificans. When the colony-forming units (CFU) ratio of S.maltophilia to T.denitrificans was reached at 2:1, the highest denitrification performance was achieved at 2.56 and 12.59 times higher than applied alone. This research provides a good understanding of the optimal microbial matching for the future application of bio-S.

Microwave assisted synthesis of ZnO-TiO2 and its visible light catalytic denitrification activity

Comparing the composite TiO2 prepared by hydrothermal sol gel method and microwave-assisted sol gel method, the microwave-assisted sol gel method with shorter time and better crystallinity was finally used to prepare ZnO-TiO2 materials with different composite ratios. The specific surface area, pore volume and pore size of ZnO-TiO2 composite are significantly larger than those of TiO2. The surface acidity of ZnO-TiO2 composite is stronger. The band structure is conducive to the efficient separation of electrons and holes, and the catalytic reduction activity and selectivity are stronger. The best composite ratio of ZnO and TiO2 is optimized to be 0.2 through photocatalytic denitration experiments. For NOx with an initial concentration of 6.83 mg/m3, under the light source condition irradiated by 65 W energy-saving lamp, the visible photocatalytic removal efficiency is as high as 85%. When the NOx concentration is increased to 13.67 mg/m3 and the ammonia nitrogen ratio is 1:1, the denitration efficiency is as high as 96%, which is 43% higher than that of pure TiO2. According to mechanism analysis, the whole reaction can be divided into adsorption and photocatalysis. Adsorption is the speed control step of the reaction. NO is oxidized to NO2 under the action of adsorbed oxygen, and photogenerated electrons can further reduce NO2 to N2. After NH3 is introduced, NH3 and photogenerated electrons work together to improve NOx removal efficiency.

Evaluation of sludge anaerobic fermentation driving partial denitrification capability: In view of kinetics and metagenomic mechanisms

Partial denitrification (PD) provides a promising approach of efficient and stable nitrite (NO2−-N) generation for annamox. In this study, the feasibility of short-term sludge anaerobic fermentation driving PD was evaluated. It was found that a higher NO2−-N accumulation in nitrate (NO3−-N) reduction was obtained with the 5-days fermented sludge compared to 8 and 15-days fermentation. Moreover, compared to acetate as carbon source, sludge fermentation products (SFPs) induced the higher NO2−-N production with nitrate-to-nitrite transformation ratio (NTR) nearly 100 %. Denitrification activity of fermented sludge were obviously improved with SFPs as electron donor. Metagenomic analysis revealed that Thauera was the dominant bacteria, which was assumed to be the key contributor to PD performance by harboring the highest narGHI and napAB but much lower nirS and nirK. Under the conditions of SFPs and fermented sludge, Thauera was speculated to have higher resistance than other denitrifiers attributed to versatile carbon metabolic capabilities utilizing SFPs with the significantly improved genes for metabolism of complex organic carbon via glycolysis after anaerobic fermentation. A novel integration of sludge fermentation driving PD and anammox for mainstream wastewater treatment and sidestream polishing was proposed to offer a promising application with reduced commercial carbon source consumption and waste sludge reduction.

Effect of plant-self debris on nitrogen removal, transformation and microbial community in mesocosm constructed wetlands planted with Myriophyllum aquaticum

Aquatic macrophytes debris decomposition could release pollutants and nutrients into the water of constructed wetlands (CWs), but their role in nitrogen removal and transformation remains poorly understood. The present study investigated the effects of plant-self debris on nitrogen removal and microbial communities in mesocosm CWs planted with Myriophyllum aquaticum. During the 68-day operation, the plant debris addition did not change the mean removal efficiency of ammonium (NH4+-N) and total nitrogen (TN) of CWs but showed significant differences over the operation time. The NH4+-N and organic nitrogen released from the plant debris decomposition affected the nitrogen removal. The plant debris decreased the effluent nitrate concentration and N2O emission fluxes of the CWs with the increased abundance of denitrifying bacterial genera, indicating that plant debris decomposition increased the denitrification activities via dissolved organic carbon release. High-throughput sequencing indicated that the plant debris altered the distribution and composition of the microbial community in the sediments. Proteobacteria was the dominant phylum (28–52%), and the relative abundance of denitrifying bacteria genera was significantly higher in the sediments with debris addition (37–40%) than in the non-addition (6.6–7.7%). The present study provided new insights into the role of macrophytes in pollutant removal and the plant management strategy of CWs.

Influence of double-layer filling structure on nitrogen removal and internal microbial distribution in bioretention cells

The nitrogen removal effect of traditional bioretention cells on runoff rainwater is not stable. The nitrogen removal effect of bioretention cells can be improved by setting up a layered filling structure, but the effect of changes in filling structure on the nitrogen removal process and microbial community characteristics is still unclear. Two types of porosity fillers were set up in the experiment, and a homogeneous bioretention cell and three bioretention cells with layered fillers were constructed by changing the depth range of the upper and lower layers to analyze the influence of the pore variation of different depth fillers on the nitrogen removal process and microbial community characteristics. The experimental results showed that, compared with the homogeneous filing structure, the layered filling structure can strengthen the adsorption of NH4+-N and the conversion of NO3−-N, so as to increase the removal rates of NH4+-N and NO3−-N by 20.71–81.56% and 9.25%–78.19%, respectively. Although the low porosity filler structure will reduce the nitrification activity and urease activity by 48.63%–66.68% and 8.00%–20.64% respectively, it can increase the denitrification activity by 19.14%–31.92%, thus significantly reducing the nitrate content in the filler. The low porosity filler structure can affect the growth and reproduction of various phylum bacteria such as Proteobacteria, Chloroflexi, Acidobacteria, and genus bacteria such as Nitrospira, Ellin6067, Rhizobacter, Pseudomonas, which can improve the diversity and richness of microorganisms.

Evaluation the role of soluble microbial products for denitrification sludge characteristic under starvation stress

Physiological changes with the assist role of soluble microbial products (SMP) of preserved denitrifying sludge (DS) undergoing long-term stress of starvation under different storage temperature is extremely important. In this study, SMP extracted from DS were added into DS in starvation condition under room temperature (15–20 °C), 4 °C and −20 °C with three different bio-augmentation phases of 10, 15 and 30 days. Experimental results showed that added SMP in room temperature was optimal for preservation of DS under starvation stress with optimized dosage of 2.0 mL mL−1 sludge and bio-augmentation phase of 10 d. SMP was more effective in maintaining the specific denitrification activity of DS, and it was nearly boosted to 94.1 % of control one due to assist of 2 times SMP addition with 10 days interval of each. Under assist of SMP, extracellular polymeric substances (EPS) secretion was enhanced as the defense layer to withstand starvation stress, and the protein may be utilized as an alternative substrate to gain energy, accelerate electron transport and transfer during denitrification process. This investigation revealed the feasibility of SMP as an economical and robust strategy for preservation of DS.

Identification of Fungal and Bacterial Denitrification Inhibitors Targeting Copper Nitrite Reductase.

The usage of nitrification inhibitors is one of the strategies that reduce or slow down the denitrification process to prevent nitrogen loss to the atmosphere in the form of N2O. Directly targeting microbial denitrification could be one of the mitigation strategies; however, until now little efforts have been devoted toward the development of denitrification inhibitors. Here, we have identified small-molecule inhibitors of one of the proteins involved in the fungal denitrification pathway. Specifically, virtual screening was employed to identify the inhibitors of copper-containing nitrite reductase (FoNirK) of the filamentous fungus Fusarium oxysporum. Three series of chemical compounds were identified, out of which compounds belonging to two chemical scaffolds inhibited FoNirK enzymatic activity in low micromolar ranges. Several compounds also displayed moderate inhibition of fungal denitrification activity in vivo. Evaluation of in vitro activity against NirK from denitrifying bacterium Achromobacter xylosoxidans (AxNirK) and in vivo bacterial denitrification revealed a similar inhibitory profile.

Deepened snow in combination with summer warming increases growing season nitrous oxide emissions in dry tundra, but not in wet tundra

Impacts of increased winter snowfall and warmer summer air temperatures on nitrous oxide (N2O) dynamics in arctic tundra are uncertain. Here we evaluate surface N2O dynamics in both wet and dry tundra in West Greenland, subjected to field manipulations with deepened winter snow and summer warming. The potential denitrification activity (PDA) and potential net N2O production (N2Onet) were measured to assess denitrification and N2O consumption potential. The surface N2O fluxes averaged 0.49 ± 0.42 and 2.6 ± 0.84 μg N2O–N m−2 h−1, and total emissions were 212 ± 151 and 114 ± 63 g N2O–N scaled to the entire study area of 0.15 km2, at the dry and wet tundra, respectively. The experimental summer warming, and in combination with deepened snow, significantly increased N2O emissions at the dry tundra, but not at the wet tundra. The deepened snow increased winter soil temperatures and growing season soil N availability (DON, NH4+-N or NO3−-N), but no main effect of deepened snow on N2O fluxes was found at either tundra ecosystem. The mean PDA was 5- and 121-fold higher than the N2Onet at the dry and wet tundra, respectively, suggesting that N2O might be reduced and emitted as dinitrogen (N2). Overall, this study reveals modest but evident surface N2O fluxes from tundra ecosystems in Western Greenland, and suggests that projected increases in winter precipitation and summer air temperatures may increase N2O emissions, particularly at the dry tundra dominating in this region.

Effect of antibiotic and/or heavy metal on nitrogen cycle of sediment-water interface in aquaculture system: Implications from sea cucumber culture

Antibiotics and heavy metals can have a negative impact on the nitrogen (N) cycle and microbial metabolism in coastal aquaculture environment. An indoor simulated culture experiment was conducted to explore how sulfadiazine and lead influence the N cycling in aquatic environment. Specifically, the experiment involved adding sulfadiazine (SDZ), lead (Pb), a combination of SDZ and Pb (SP), and a control group (CK). The fluxes and contents of ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3−-N) and nitrite nitrogen (NO2−-N) in sediment-water interface and sediments, the abundance of N cycle function genes (amoA_AOB, hzsA, nar, nirK, nirS, norB and nosZ) and microbiota in sediments were analyzed. The results showed that the presence of SDZ and Pb inhibited the nitrification function gene and nitrifiers abundance in surface sediment, and thus leading to more accumulation of NH4+ and NO2− in overlying water. Pb exposure increased the abundances of denitrifying bacteria stimulated the first three steps of denitrification in the sediment, resulting in more removal of NO3− from the sediment, but possibly had the risk of releasing more greenhouse gas N2O. Conversely, the presence of SDZ ultimately inhibited denitrification and anammox bacterial activities in the sediment. This study revealed how heavy metal and antibiotic impair the microbial communities and N cycling function gene expression, leading to the deterioration of typical coastal aquaculture environments.

Effects of long-term organic fertilizer substitutions on soil nitrous oxide emissions and nitrogen cycling gene abundance in a greenhouse vegetable field

Intensive vegetable fields, characterized by extremely high nitrogen (N) application rates, emit a large amount of the potent greenhouse gas nitrous oxide (N2O). Short-term substitution of organic fertilizers for chemical fertilizers may mitigate N2O emissions from vegetable fields. However, the long-term impacts, particularly on soil background N2O emissions (excluding effects caused by newly applied fertilizers) in vegetable fields, remain poorly elucidated. Thus, we conducted an 11-year experiment to investigate the long-term fertilization effects on soil background N2O emissions and the abundance of N-cycling genes in a greenhouse vegetable field. The soil capacity for potential denitrification activity (PDA) was further measured to evaluate denitrification potential. The field experiment comprised of four treatments: no fertilization (control, CK), only chemical N fertilizers (CF), 50 % of chemical N fertilizers substituted by organic fertilizers (OL), and 87.5 % of chemical fertilizers substituted by organic fertilizers (OH). The long-term application of chemical fertilizers alone (CF) and organic fertilizer substitutions (OL and OH) increased soil background N2O emissions 30-fold and 10-fold, respectively, with average N2O fluxes of 1.2 ± 3.8, 33.8 ± 5.1, 9.4 ± 2.3 and 10.2 ± 2.7 μg N2O-N m−2 h−1 in the CK, CF, OL and OH treatment, respectively. The CF treatment significantly decreased the abundance of AOA amoA, nirS and nosZ genes, while both the OL and OH treatments increased the abundance of AOB amoA, and the OH treatment also increased nosZ gene abundance. Soil pH was a key determinant of the contrasting responses of N-cycling genes to different fertilizer types. Compared with low fertilizer substitutions (OL), high organic fertilizer substitutions (OH) did not result in more soil background N2O emissions, despite higher potential denitrification activities and soil total N contents. This was due to increased abundance of nosZ gene and likely enhanced N2O consumption activities. Soil NO3−-N concentrations, soil pH, and the abundance of nosZ gene were three main factors in controlling the responses of soil background N2O emissions to long-term fertilization. Overall, this study suggests that in the long-term perspective organic fertilizer substitution is a beneficial practice to mitigate N2O emissions from intensive greenhouse vegetable cropping systems.

Activity of СО&lt;sub&gt;2&lt;/sub&gt;, N&lt;sub&gt;2&lt;/sub&gt; Fixation and Denitrification in the Course of Decay of Coarse Woody Debris Decay of Norway Spruce in the South Taiga

The activity of CO2 efflux, N2 fixation, and denitrification, as well as the physiological state of the community of microorganisms-destructors were assessed depending on the decay stage of the coarse woody debris (CWD) in the incubation experiments with the coarse woody debris of Norway spruce (Picea abies L.) and podzolic soil (Retisol). The coarse woody debris and soil were sampled at the experimental sites of the Central Forest State Reserve (Tver Region, Russia). Maximal CO2 emissions caused by CWD decomposition was associated with the decay stages III and IV. Also, the latter two showed maximal values of such sound indices of microbial activity as substrate induced respiration (SIR, 50 μg С–СО2/(g h)), percentage of easily decomposable С in organic matter (А1, 66%) and metabolic quotient qCO2 (0.78). Unlike the СО2 emission, maximal activity of N2 fixation was at the earlier decay stage II. The values of N2 fixation and denitrification activities indicate a gradual and complicatedly regulated transition process from the properties of bacterial and fungal communities of CDW to those in the soil during stages II, III and IV. The dramatic, more than 3-fold decrease was found only for C : N in CWD during the stages III–IV transition. СО2 emission at the stage V increased dramatically. Nevertheless, the CWD organic matter even at this latest decay stage had lower sustainability than organic matter of podzolic soil.

Activities of CO2 Emission, N2 Fixation, and Denitrification during the Decay of Norway Spruce Coarse Woody Debris in Southern Taiga

Activities of CO2 Emission, N2 Fixation, and Denitrification during the Decay of Norway Spruce Coarse Woody Debris in Southern Taiga

Deciphering community assembly and succession in sequencing batch moving bed biofilm reactor: Differentiation between attached and suspended communities

Elucidating community assembly and succession is crucial to understanding the ecosystem functioning. Herein, the ecological processes underpinning community assembly and succession were studied to uncover the respective ecological functions of attached biofilms and suspended biomass in a sequencing batch moving bed biofilm reactor. Compared with suspended biomass, attached biofilms presented higher relative abundances of Nitrospira (2.94 %) and Nitrosomonas (1.25 %), and contributed to 66.89 ± 11.37 % and 68.11 ± 12.72 % of nitrification and denitrification activities, respectively. The microbial source tracking result demonstrated that early formation of suspended biomass was dominated by the seeding effect of detached biofilms in the start-up period (days 0–30), while self-growth of previous suspended biomass was eventually outcompeted the seeding effect when the reactor stabilized (days 31–120). Null model and ecological network analysis further suggested distinctive ecological processes underpinning the differentiation between attached and suspended communities in the same reactor. Specifically, in the start-up period, positive interactions facilitated early formation of attached (73.84 %) and suspended communities (59.41 %), while homogenous selection (88.89 %) and homogenizing dispersal (65.71 %) governed assembly of attached and suspended communities, respectively. When the reactor stabilized, attached and suspended communities showed low composition turnover as reflected by dominant homogenizing dispersal, while they presented distinctive trends of interspecies interactions. This study sheds light on discrepant ecological processes governing community differentiation of attached biofilms and suspended biomass, which would provide ecological insights into the regulation of hybrid ecosystems.

High performance of the morphologically controlled synthesis carrier of TiO2 for NH3 selective catalytic reduction of NO

TiO2 supported Ni and Ce with different morphologies (particle-like TiO2 (PT), flower-like TiO2 (FT), spherical-like TiO2 (ST), rod-like TiO2 (RT)) were prepared. Ni-Ce/flower-like TiO2 (NCFT) catalyst exhibits the best performance (NO conversion and N2 selectivity both approach to 100% approximately) in 250–450 °C and SO2 resistance (∼80%). The sequence of activities is NCFT > NCST > NCPT > NCRT. The FT carrier provides the largest specific surface area (145.9 m2 g−1), facilitating the dispersion of the active components. In addition, NCFT is abundant in Ni3+ and Ce3+ as well as Oα species, which support excellent redox properties. More weak acid and medium acid sites provided more adsorption sites for NH3-SCR reaction. This is also the main reason that NCFT catalyst has excellent denitrification activity. In-situ infrared results show that the reaction of NCFT catalyst is mainly through E-R mechanism, and NH3 (L) and -NH2 species formed on the catalyst surface were the main ammonia adsorption species and reaction species. Unfortunately, NCFT has not ideal sulfur resistance and stability due to its unique structure, which needs to be further improved.

Microbiome in soils of Mendoza: microbial resources for the development of agroecological management in viticulture

Rhizosphere microorganisms are considered an extension of plants, representing critical actors involved in the promotion of plant nutrient intake from the surrounding environment. Consequently, a great focus is being made on soil microorganisms since they are considered a promising source for crop resilience improvements under a global climate change scenario. To explore bacterial and fungal communities from arid soils in vineyards and their surroundings from two regions with very different climate and tillage histories, an amplicon sequencing analysis was performed. Specifically, Santa Rosa (SR) is in a region commonly known as the first zone, characterised by low altitude (607 m.a.s.l., Winkler V), while Gualtallary (G) is in the Uco Valley Zone, a region with high altitude (1245 m.a.s.l., Winkler III); both in the productive wine region of Mendoza. SR is characterised by its long cultivation history, while G is a recently cultivated region. Topsoil samples were collected and used for bacterial and fungal community profile characterisation. Ascomycota was the predominant phylum (38–97 %) in mycobiome composition, whereas Proteobacteria was the most abundant bacterial phylum (26–34 %) in both regions. Moreover, the main factor explaining microbiome differences between regions was the carbon-to-nitrogen ratio. Anaerolineae and Gammaproteobacteria were a distinctive bacterial class in SR-cultivated soils. Azospirillales were highly abundant in SR uncultivated soils, while Rhizobiales were differentially abundant in G uncultivated soils. Regarding functional analysis, soils from SR showed a higher denitrification activity of nitrifiers as well as glucose-related metabolism, while in G soils, bacterial photosynthesis activities were a differential trait. In addition, Actinobacteria abundance was lower in SR-cultivated soils, indicating a higher susceptibility of this phylum to grapevine crop practices. These results allow the development of hypothetical models of the local microbial resources and their contribution to grapevine nutrition, which is highly important to elaborate recommendations for grapevine management to preserve soil health in vine areas of Mendoza.

Design of bifunctional TiO2-SSZ-13 mixed supports for potassium-resistant vanadia catalysts for NH3-SCR

In this paper, a novel catalyst, SSZ-13 doped V2O5-WO3/TiO2, was designed and synthesized, which owns excellent resistance to potassium poisoning in the selective catalytic reduction of NO by NH3 (NH3-SCR). V2O5-WO3/TiO2-SSZ-13 (30 wt% and 50 wt% SSZ-13 addition) catalysts show more than 80 % NOx conversion at 260–550 °C after K-poisoning. The modified catalyst effectively shields V2O5 as the main active species from K poisoning by preferential reaction of K+ with H+ from Brønsted acid sites (Si-O(H)-Al) of SSZ-13 via ion exchange. Furthermore, SSZ-13 modification also enhances the low-temperature denitrification activity of V2O5-WO3/TiO2 catalyst by producing more polymeric VOx and low-valent VOx. In situ DRIFTS and kinetic studies indicate that the addition of SSZ-13 does not change the reaction mechanism of the vanadia catalyst for NH3-SCR. Physicochemical characterizations coupled with theoretical calculations demonstrate the difference in formation energies of V and K adsorption on TiO2 and SSZ-13, which is the driving force in realizing the directional enrichment of V and K on different supports.

Nitrogen dynamics in soils fertilized with digestate and mineral fertilizers: A full field approach

Highly stabilized digestate from sewage sludge and digestate-derived ammonium sulphate (RFs), were used in a comparison with synthetic mineral fertilizers (SF) to crop maize in a three-year plot trial in open fields. RFs and SF were dosed to ensure the same amount of mineral N (ammonia-N). In doing so, plots fertilized with digestate received much more N (+185 kg ha−1 of organic N) because digestate also contained organic N. The fate of nitrogen was studied by measuring mineral and organic N in soil at different depths, ammonia and N2O emissions, and N uptake in crops. Soil analyses indicated that at one-meter depth there was no significant difference in nitrate content between RF, SF and Unfertilized plots during crop season indicating that more N dosed with digestate did not lead to extra nitrate leaching. Ammonia emissions and N content in plants and grains measured were also similar for both RF and SF. Measuring denitrification activity by using gene makers resulted in a higher denitrification activity for RF than SF. Nevertheless, N2O measurements showed that SF emitted more N2O than RF (although it was not statistically different) (7.59 ± 3.2 kgN ha−1 for RF and 10.3 ± 6.8 kgN ha−1 for SF), suggesting that probably the addition of organic matter with digestate to RF, increased the denitrification efficiency so that N2 production was favoured. Soil analyses, although were not able detecting N differences between SF and Rf after three years of cropping, revealed a statistical increasing of total carbon, suggesting that dosing digestate lead to carbon (and maybe N) accumulation in soil. Data seem to suggest that N2O/N2 emission and organic N accumulation in soil can explain the fate of the extra N dosed (organic-N) in RF plots.