Denitrification Activity Research Articles

Research progress of Mn-based low-temperature SCR denitrification catalysts.

Selective catalytic reduction (SCR) is a efficiently nitrogen oxides removal technology from stationary source flue gases. Catalysts are key component in the technology, but currently face problems including poor low-temperature activity, narrow temperature windows, low selectivity, and susceptibility to water passivation and sulphur dioxide poisoning. To develop high-efficiency low-temperature denitrification activity catalyst, manganese-based catalysts have become a focal point of research globally for low-temperature SCR denitrification catalysts. This article investigates the denitrification efficiency of unsupported manganese-based catalysts, exploring the influence of oxidation valence, preparation method, crystallinity, crystal form, and morphology structure. It examines the catalytic performance of binary and multicomponent unsupported manganese-based catalysts, focusing on the use of transition metals and rare earth metals to modify manganese oxide. Furthermore, the synergistic effect of supported manganese-based catalysts is studied, considering metal oxides, molecular sieves, carbon materials, and other materials (composite carriers and inorganic non-metallic minerals) as supports. The reaction mechanism of low-temperature denitrification by manganese-based catalysts and the mechanism of sulphur dioxide/water poisoning are analysed in detail, and the development of practical and efficient manganese-based catalysts is considered.

Optimizing roof-harvested rainwater storage: Impact of dissolved oxygen regime on self-purification and quality dynamics

Roof-harvested rainwater presents a promising, unconventional, and sustainable water resource for both potable and non-potable uses. However, there is a significant gap in understanding the quality evolution of stored rainwater under varying dissolved oxygen conditions and its suitability for various applications. This study investigated the evolution of rainwater quality under three distinct storage conditions: aerated, open, and sealed. Additionally, the microbial community and metabolic functions were analyzed to systematically evaluate the self-purification performance over long-term storage durations. The results indicate that aerated storage enhances microbial carbon metabolism, leading to a degradation rate of 54.4 %. Sealed and open storage conditions exhibited primary organic matter degradation during the early and late stages, respectively. Roof-rainwater harvesting (RRWH) systems showed limited denitrification activity across all three dissolved oxygen conditions. The maximum accumulation of NO3-N during the storage period reached 5.23 mg/L. In contrast, sealed storage demonstrated robust self-purification performance, evidenced by a comprehensive coefficient of 15.83 calculated by Streeter-Phelps model. These findings provide valuable insights into the mechanisms governing rainwater quality changes under various storage conditions, emphasizing the necessity for developing effective management strategies for the storage and utilization of roof-harvested rainwater.

Applications of different forms of nitrogen fertilizers affect soil bacterial community but not core ARGs profile.

The objective of this study was to investigate the impact of various chemical nitrogen fertilizers on the profile of antibiotic resistance genes (ARGs) in soil. A microcosm experiment was conducted with four treatments, including CK (control with no nitrogen), AN (ammonium nitrogen), NN (nitrate nitrogen), and ON (urea nitrogen), and the abundance of ARGs was assessed over a 30-day period using a metagenomic sequencing approach. The levels of core ARGs varied between 0.16 and 0.22 copies per cell across different treatments over time. The abundance of core ARGs in the ON treatment closely resembled that of the CK treatment, suggesting that environmentally friendly nitrogen fertilizers, particularly those in controlled release formulations, may be preferable. The core ARG abundance in the AN and NN treatments exhibited noticeable fluctuations over time. Overall, chemical nitrogen fertilizers had minimal effects on the core ARG profile as determined by principal component analysis and clustering analyses. Conversely, distinct and significant changes in bacterial communities were observed with the use of different nitrogen fertilizers. However, the influence of nitrogen fertilizers on the core ARGs is limited due to the unaffected potential bacterial hosts. Nitrogen-cycling-related genes (NCRGs), such as those involved in nitrogen-fixing (nifK, nifD, nifH) and denitrification (narG, napA, nirK, norB, nosZ) processes, exhibit a positive correlation with ARGs (rosA, mexF, bacA, vanS), indicating a potential risk of ARG proliferation during intense denitrification activities. This study indicates that the application of chemical nitrogen has a minimal effect on the abundance of ARGs in soil, thereby alleviating concerns regarding the potential accumulation of ARGs due to the use of chemical nitrogen fertilizers.

Novel control strategy employing anaerobic/aerobic/anoxic/aerobic/anoxic mode to enhance endogenous denitrification and anammox for municipal wastewater treatment

Anaerobic/Aerobic/Anoxic (AnOA) process utilizes endogenous denitrification to remove nitrogen. However, low endogenous denitrification activity critically restricts its application owing to insufficient carbon sources. In this study, a novel control strategy employing anaerobic/aerobic/anoxic/aerobic/anoxic (AOAOA) mode was introduced to treat low Carbon/Nitrogen (C/N) ratio municipal wastewater over 262 days. The concentration of total inorganic nitrogen (TIN) was only 3.9 ± 2.0 mg/L in the effluent, with a high nitrogen removal efficiency (NRE) of 94.3 %. The relative abundance of Candidatus Competibacter increased from 1.2 % to 2.3 %, ensuring an efficient endogenous denitrification process. Additionally, Candidatus Brocadia enriched from 0.02 % to 0.6 %, contributing to 63.1 % nitrogen removal during the anoxic stage in Phase Ⅲ. This study presents a promising approach for enhancing endogenous denitrification and anammox in the AnOA process, contributing to sustainable wastewater treatment.

Application of flow airlift fluidized bed (CAFB) - Aerobic denitrification bioreactor using polycaprolactone (PADR) as organic carbon source and biofilm carrier for synthetic marine aquaculture wastewater treatment

Aerobic denitrification, a novel method for complete nitrate removal process, relies on a constant carbon supply, and carbon availability can be a limiting factor for the process. Three biodegradable polymers - polybutylene succinate (PBS), polycaprolactone (PCL), and polylactic acid (PLA) were used as carbon source of aerobic denitrifying bacteria, Halomonas venusta for treating recirculating aquaculture wastewater in batch tests, respectively. The group utilizing PCL displayed the greatest efficiency in nitrate removal. Afterwards, a continuous flow airlift fluidized bed (CAFB) - aerobic denitrification bioreactor using PCL(PADR) as bio-carriers and carbon source was started up. The effect of shifting temperature on the nitrate removal and microbial community of CAFB-PADR was investigated under different hydraulic retention times (HRT). The results showed that no significant difference was detected in denitrification activity at 25 and 30 °C condition, where the denitrification rate was 1.1–1.8 times higher than that at 15 °C. However, the nitrogen removal efficiency was above 50 % and there was barely accumulation of nitrite at 15 °C, indicating the good nitrate removal performance in CAFB-PADR at all three temperature conditions. Microbial composition analyses revealed that as the temperature decreased, the relative abundance of Gammaproteobacteria increased, while those of Alphaproteobacteria and Bacteroidia diminished decreased. The existence of denitrifying function genera (Marinobacter, Pseudomonas, Halomonas and Hydrogenophaga) ensured the rapid removal of nitrogen in the biofilter. When the temperature dropped to 15 °C, Pseudomonas progressively took the position of Marinobacter, both of which had denitrification and degradation activities. The relative abundance of the denitrifying bacteria Halomonas that we inoculated has been less than 1 % since phase II. Overall, the PCL-supported CAFB-PADR demonstrated in this study shows potential for removing high concentrations of nitrate from recirculating marine aquaculture wastewater.

Comparing low-temperature NH3-SCR activity, operating temperature window and kinetic properties of the Mn-Fe-Nb/TiO2 catalysts prepared by different methods

In order to overcome the shortcomings of traditional V-based catalysts, such as poor low-temperature activity, narrow temperature window, and toxicity. Therefore, the Mn-Fe-Nb/TiO2 catalysts were prepared using impregnation (IM), citric acid complexation (CA), co-precipitation (CP), hydrothermal synthesis (HY), and sol–gel (SG) methods to develop novel NH3 selective catalytic reduction (NH3-SCR) catalysts with excellent low-temperature activity, a wide temperature window, and environmental friendliness. Their NH3-SCR catalytic activity was evaluated, followed by a detailed analysis of their morphology, structure, specific surface area, chemical state, redox properties, acidity, and interactions using X-ray diffraction (XRD), Bruaner-Emmet-Teller (BET), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), NH3 temperature-programmed desorption (NH3-TPD), and Fourier transform infrared spectroscopy (FTIR) techniques. The 5Mn-7Fe-4Nb/TiO2-SG catalyst, prepared via sol–gel, exhibited the highest denitrification (de-NOx) activity and the widest operating temperature window, achieving over 80% Nitric oxide (NO) conversion at 180–350 °C and a peak conversion of 97% at 250 °C. The XRD, BET, SEM, and HR-TEM characterization results showed that the catalyst prepared using the sol–gel method had the smallest particles, the highest specific surface area, and the greatest dispersion. XPS and NH3-TPD results revealed that the catalyst prepared using the sol–gel method possessed the highest surface adsorbed oxygen (Oα) content and the largest number of acidic sites. H2-TPR and FTIR analyses indicated that the catalyst prepared using the sol–gel method enhanced the reduction capacity and possessed the strongest interaction forces among support-active-promoter components. Steady-state kinetic tests confirmed that in the NH3-SCR reaction, the rate-determining step was the adsorption activation of NO on the catalyst surface. The sol–gel method reduced the activation energy for de-NOx reactions, enhancing the low-temperature activity of the catalyst.

Response of the performance and succession of denitrification consortium under the variation of nutritional conditions: Mechanisms and characteristics

In the process of wastewater treatment, biomass was typically subjected to variation of nutrient condition. This study investigated the effects of different nutrient condition on denitrification performance and bacterial communities. The results showed that under carbon-to-nitrogen ratio (C/N) was 4, denitrifying sludge (DS) exhibited excellent denitrification performance with influent nitrate (NO3--N) concentration in the range of 88.8 ± 9.04–297.5 ± 6.63 mg L−1, maintained total nitrogen removal efficiency (TNRE) of 98.1 ± 1.75 %. While, as influent NO3--N concentration reached 408.9 ± 9.56 mg L−1, the denitrification performance was inhibited, and this inhibition was reversible. Under appropriate substrate level (215.0 ± 13.01 mg L−1), the specific denitrification activity (SDA) elevated to 300 % of its original value. Additionally, under starvation stress, although the relative abundance of some starvation-resistant bacteria (such as Actinobacteriota and Lentimicrobium) increased, the TNRE decreased by 7.3 %. During the recovery phase, despite extracellular polymeric substances (EPS) promoted, the TNRE decreased to 78.3 ± 4.7 %. Starvation stress was less favorable to DS for activity recovery than that of feast condition. These findings contribute to elucidating the mechanisms for DS to respond of different nutrient condition.

Synergetic effects of chlorinated paraffins and microplastics on microbial communities and nitrogen cycling in deep-sea cold seep sediments

Chlorinated paraffins (CPs) and microplastics (MPs) are commonly found in deep-sea cold seep sediments, where nitrogen cycling processes frequently occur. However, little is known about their combined effects on sedimentary microbial communities and nitrogen cycling in these environments. This study aimed to investigate the synergistic impacts of CPs and MPs on microbial communities and nitrogen cycling in deep-sea cold seep sediments through microcosm experiments. Our results demonstrated that the presence of CPs and MPs induced significant alterations in microbial community composition, promoting the growth of Halomonas. Furthermore, CPs and MPs were found to enhance nitrification, denitrification and anammox processes, which was evidenced by the higher abundance of genes associated with nitrification and denitrification, as well as increased activity of denitrification and anammox in the CPs and MPs-treatment groups compared to the control group. Additionally, the enhanced influence of CPs and MPs on denitrification was expected to promote nitrate-dependent and sulfate-dependent anaerobic oxidation of methane, thereby resulting in less methane released into the environment. These findings shed light on the potential consequences of simultaneous exposure to CPs and MPs on biogeochemical nitrogen cycling in deep-sea cold seep sediments.

Understanding Partial Denitrification-hydroxyapatite (PD-HAP) coupled granules to enhance process stability and phosphorus removal by investigating the size effect of granules

The innovative Partial Denitrification-hydroxyapatite (PD-HAP) coupled granule offers a promising biotechnology for supplying nitrite to Anammox while simultaneously removing phosphorus. This study systematically examined the characteristics, biomass activity, and microbial community of PD-HAP granules of various sizes to enhance system stability and phosphorus removal efficiency. The results showed that larger granules had higher inorganic mineral and extracellular polymeric substances (EPS) content. These factors contributed to their denser structure, smoother surfaces, and better settling velocities compared to smaller granules. In contrast, smaller granules exhibited higher denitrification activity due to their greater biomass content and more efficient mass transfer. Calcium and phosphorus were identified as the primary inorganic constituents, mainly in the form of HAP, and were especially abundant in larger granules. Granules larger than 3.0 mm demonstrated a higher capacity for phosphorus removal. This was due to their significantly greater tightly bound EPS (T-EPS) content, which led to increased HAP and phosphorus levels. All granule sizes maintained a nitrate-to-nitrite transformation ratio (NTR) above 80 %, primarily due to the dominance of Flavobacterium (65.8 %-74.9 %). Although larger granules had lower denitrification activity, they still achieved an excellent NTR (above 85 %). They also showed superior settling velocity (174.9 m/h) and stronger phosphorus removal capacity (54.1 mg/g SS) compared to smaller granules. Maintaining a dominant proportion of granules larger than 3.0 mm could be an effective strategy to enhance both system stability and phosphorus removal. This study provides valuable insights into the PD-HAP coupled granular process, promoting efficient nitrite production and effective phosphorus removal.

The role of halophyte-induced saline fertile islands in soil microbial biogeochemical cycling across arid ecosystems

Halophyte shrubs, prevalent in arid regions globally, create saline fertile islands under their canopy. This study investigates the soil microbial communities and their energy utilization strategies associated with tamarisk shrubs in arid ecosystems. Shotgun sequencing revealed that high salinity in tamarisk islands reduces functional gene alpha-diversity and relative abundance compared to bare soils. However, organic matter accumulation within islands fosters key halophilic archaea taxa such as Halalkalicoccus, Halogeometricum, and Natronorubrum, linked to processes like organic carbon oxidation, nitrous oxide reduction, and sulfur oxidation, potentially strengthening the coupling of nutrient cycles. In contrast, bare soils harbor salt-tolerant microbes with genes for autotrophic energy acquisition, including carbon fixation, H2 or CH4 consumption, and anammox. Additionally, isotope analysis shows higher microbial carbon use efficiency, N mineralization, and denitrification activity in tamarisk islands. Our findings demonstrate that halophyte shrubs serve as hotspots for halophilic microbes, enhancing microbial nutrient transformation in saline soils.

How does CO2 supply shape the biofilm microenvironment in denitrifying H2-based membrane biofilm reactor: A modeling study

CO2 supply to a hydrogen-based membrane biofilm reactor (H2-based MBfR) is an imperative approach for maintaining its performance. The supply modes (via bulk liquid or membrane) and dosages of CO2 can largely determine the efficiency of H2-based MBfR, but their effects on the biofilm microenvironment remain unclear. To bridge this knowledge gap, a denitrifying H2-based MBfR equipped with an in-situ pH microsensor was constructed, and an expanded model was developed by incorporating the modified denitrification kinetic algorithm, based on the measured pH gradients in the biofilm. Results showed that the greatest NO3− removal was achieved at an influent CO2 concentration of 50 mg/L and a CO2 fraction of 20 %. The carbon source constituted a decisive factor, limiting the denitrification activity in the inner and outer layers of the biofilm when CO2 was supplied below the optimum dosage (50 mg/L or 20 %) via bulk liquid and membrane, respectively. Increasing the CO2 dosage to 100 mg/L or 30 % enabled the sufficient carbon source, but led to low-pH inhibition in the entire biofilm. The outcomes of this research provided mechanistic insights into the denitrification behaviors of H2-based MBfR, and the developed model could help devise CO2 supply strategies for the management of the reactor.

Enhanced denitrification performance of Mo/Mn co-doped 5 %Fe/TiO2 catalysts via citric acid-assisted impregnation

This study investigates the denitrification performance of Fe5Mn3Mo3/TiO2 catalysts prepared using citric acid-assisted impregnation (CA) and conventional impregnation (IM) methods in the context of NH3-selective catalytic reduction (SCR) reaction. Specifically, the influence of citric acid quantity on the catalytic activity is studied, with a special emphasis on Fe5Mn3Mo3/TiO2-0.5CA variant. Our results demonstrate that Fe5Mn3Mo3/TiO2-0.5CA exhibits superior low-temperature activity and prolonged stability compared to the conventional impregnation method. Remarkably, operating temperature window based on 80 % denitrification activity is T80 = 190–405 °C. Furthermore, the Fe5Mn3Mo3/TiO2-0.5CA maintains a noteworthy 98 % NO conversion at 300 °C for a duration of 100 hours. The excellent performance is attributed to the highly dispersed nature of the active species, the large specific surface area, the low apparent activation energy, and a robust interaction between the active components and the substrate. XPS analysis reveals a significantly higher Oα/(Oα+Oβ) ratio for Fe5Mn3Mo3/TiO2-0.5CA, underscoring the effectiveness of citric acid modification in promoting the formation of Fe2+ species. This research provides valuable insights into the design and optimization of catalysts for efficient denitrification processes.

Rapid start-up of mainstream partial denitrification /anammox and enhanced nitrogen removal through inoculation of precultured biofilm for treating low-strength municipal sewage

This study investigated the rapid start-up of mainstream partial denitrification coupled with anammox (PD/A) and nitrogen removal performance by inoculating precultured PD/A biofilm. The results showed mainstream PD/A in the anaerobic-anoxic-aerobic (A2O) process was rapidly established within 30 days. Nitrogen removal efficiency (NRE) improved by 23.8 % contrasted to the traditional A2O process. The mass balance showed that anammox contribution to total nitrogen (TN) removal were maintained at 37.9 %∼55.7 %, and reducing hydraulic retention time (HRT) strengthened simultaneously denitrification and anammox activity. The microbial community showed that the dominant bacteria such as denitrifying bacteria (DNBs) and glycogen accumulating organisms (GAOs) both in biofilm and flocculent sludge (floc), integrating with anammox bacteria (AnAOB) in biofilm might lead to enhanced nitrogen removal. Overall, this study offered a fast start-up strategy of mainstream PD/A with enhanced nitrogen removal, which are valuable for upgradation and renovation of existed municipal wastewater treatment plants (WWTPs).

Selective catalytic reduction of NOx by NH3 at low temperature over Mn0.5Zr(0.5-x)Fex catalyst with different Fe/Zr ratios

ABSTRACT Through a basic co-precipitation technique, a series of Mn0.5Zr(0.5-x)Fex ternary oxide catalysts with different Fe/Zr ratios have been prepared and applied to the selective catalytic reduction of NOx. The results of catalytic activity test show that the Mn0.5Zr0.2Fe0.3 catalyst with a molar ratio of Fe/Zr of 3:2 has the most effective denitrification activity at low temperature and displays considerable tolerance to SO2 and H2O. The Mn0.5Zr0.2Fe0.3 catalyst exhibits a combination of physical and chemical attributes, including an elevated specific surface area and a homogeneously distributed active component, which collectively furnish additional points of interaction for the reacting gases, thus improving the catalytic performance. In addition, the high Mn4+/Mnn+ and Fe2+/Fen+ ratios, strong redox capacity, and more acidic sites on the surface of the catalyst also have positive effects on its denitrification performance. Meanwhile, the reaction process on Mn0.5Zr0.2Fe0.3 catalyst is driven by the Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms. This study provides an important reference for the design of Mn-based catalysts with high denitration performance and excellent resistance to SO2 and H2O.

Feasibility study of denitrification catalyst prepared from badam shell biochar

Badam shells are a common type of fruit shell waste, yet there is scarce research on using them to produce biochar and applying it in the field of denitrification. This study aimed to utilize badam shells as raw material to produce biochar and evaluate the feasibility of badam shell biochar (BC) as a carrier for denitrification catalysts. Badam shells were carbonized under a N2 atmosphere at 600 °C for 120 min to prepare badam shell biochar. After treating BC with acid (H3PO4 or HNO3), Mn or Fe is loaded to obtain denitrification catalysts (BC-HN-Mn, BC-HN-Fe, BC-HP-Mn, and BC-HP-Fe). These catalysts exhibit high denitrification activity within the temperature range of 100–300 °C (>80 %, and exceeding 90 % at 250–300 °C). Moreover, they are characterized by a large number of acidic sites and adsorbed oxygen species distributed on their surface, demonstrating excellent resistance to sulfur dioxide poisoning and maintaining high denitrification activity under low oxygen conditions. This study provides a reference for the application of badam shell in Selective catalytic reduction (SCR) technology.

Carcass decay inhibits denitrification indirectly by regulating the microbiota and physicochemical properties in a model water system

Abstract Animal carcass decomposition is involved in nitrogen (N) cycle in the aquatic ecosystems, for example denitrification, volatilization and leaching. The denitrification process is a crucial part of the nitrogen cycle, helping to alleviate biological toxicity resulting from nitrate accumulation. However, it is still unknown whether and how cadaver decay affects the denitrifiers and their activity in river water. In this study, six denitrifiers (encoding napA, narG, nirK, nirS, norB and nosZ, respectively) and denitrifying activity were investigated in a model water system with nitrogen pollution from corpse decomposition using high‐throughput sequencing, real‐time quantitative PCR and denitrifying enzyme activity (DEA) assay. Cadaver decay increased the quantity and altered the composition of denitrifying microbiota. Multiple regression on distance matrices revealed that corpse decay had a significantly greater impact on the denitrification communities than temperature. To our surprise, the DEA decreased in the contaminated water by cadavers. The multiple regression models revealed that the abundance of denitrifying taxa and the gene copies may jointly predict changes in DEA, with highest contribution coming from the norB‐type Hydrogenophaga. Further, the partial least squares path model (PLS‐PM) showed that corpse decay indirectly inhibited DEA via the denitrification community and water physicochemical properties. Synthesis and applications. This study provides important insights into how cadaver decomposition can reduce denitrification activity in water systems. These findings can assist us in scientifically managing and remediating polluted water bodies.

Soil physicochemical and microbial properties affect nitrogen cycling in technogenically transformed coal dump soils

Mining industrial sectors deteriorate local and regional environmental quality, contributing to global ecosystem contamination. The activities of microorganisms and enzymes involved in nitrogen cycling processes were investigated in coal dump soils that had undergone technogenic transformations and reclamation. Compared to the background uncontaminated soil, the heavy metal concentrations increased to high contamination levels (the contents of mobile forms of Zn, Ni, and Cu were 66.9; 35.6; 12.9 mg/kg, respectively), salinity increased to 0.1–2.41 %. The activities of nitrification and denitrification as well as the abundance of ammonifiers reduced due to high concentrations of mobile forms, the presence of coal particles, and the salinity of soil samples. The urease activity decreased due to reduced content of soluble organic matter in disturbed soils (2.3 times lower than the background soils). Mechanical reclamation leads to a 4-fold decrease in soil toxicity levels; however, it does not enhance nitrogen cycling activity. The activity of nitrification and urease decreased by >4 times as compared to the soil of the protected area. Microbial community composition of coal mine soils was similar to that of undisturbed soil. Nitrifiers in coal mine soil were represented by the genera Nitrososphaera, Candidatus Nitrosocosmicus, Nitrosospira, Nitrosomonas, Nitrosococcus, Nitrospira, Nitrobacter. The results indicated that the disruption of nitrification process led to low nitrate content in technogenically transformed coal dump soils.

The nature of synergy effects between VOx and TiO2 in low temperature NH3-SCR reaction

In this study, we investigated the low-temperature activity of selective catalytic reduction of NO by NH3 (NH3-SCR) with the effect of different vanadium oxide (VOx) loading in the VOx/TiO2 catalyst. By calculating the specific rate of activity, it was found that the fastest specific rate of activity was achieved when the loading of V2O5 reached 10 wt%, and the nitrogen oxides (NOx) conversion of the above optimal catalyst reached over 80 % in the temperature range of 180–465 °C. The effects of preparation method, calcination temperature, and support on the aggregation state of the vanadium species and the SCR activity of the catalyst were also investigated on the basis of the ideal ratio. Combining the activity and characterization results, it is found that the impregnation method and calcination at 410 °C are more favorable for the moderate dispersion of the vanadium species on the TiO2 surface, producing more highly reactive polymorphic VOx, which is more readily dispersed on the surface of the TiO2 support and interacts more strongly with the TiO2. The interaction between the two can promote the transfer of electrons, resulting in the production of more active O species and low-valent vanadium. The aforementioned species can enhance the catalyst's low- temperature denitrification activity.

Catalytic enhancement of microbial denitrification by FeVO4@biochar: Insight into the extra cellular polymeric matrix mechanism

The biological denitrification is being considered as one of the best methods for nitrate removal from wastewaters, however it suffers with lower efficiency which needs to be improved effectively. The present study was aimed to prepare FeVO4@biochar and investigated its role as electron shuttle in enhancing the biological denitrification through various batch experiments. Significantly higher rates of denitrification were observed after addition of FeVO4@biochar in different concentrations and the highest efficiency was observed in 15 wt% FeVO4@biochar (BF-15) where 87.6 % denitrification was achieved after 7 days (from 100 mg/L to 12.7 mg/L of nitrate) compared to pure biochar (65.7 mg/L; 34.3 %) and sludge (72.7 mg/L; 27.3 %). FeVO4@biochar increased the transfer of external electron to bacteria and enhanced the denitrification activity. The variations in NAR (nitrate reductase), NIR (nitrite reductase) and ETSA (electron transport system activity) were investigated to understand the changes in microbial-community during denitrification. The FeVO4@biochar and extracellular polymeric substance (EPS) both acted as the media for electron transport along with the decreased repulsions between nitrate and the catalyst surface that further provides higher nitrate reduction efficiency. The electroactive bacteria could easily utilize the photogenerated electrons from FeVO4@biochar and facilitate excellent denitrification. The microbial-diversity analysis revealed Bacteroidota, Firmicutes, Proteobacteria, Chloroflexi, Desulfobacterota, Acidobacteriota, Actinobacteriota, and Gemmatimonadota were observed as the most predominant phyla actively participated in enhanced denitrification. This study suggested that the addition of photoactive catalyst strongly enhanced the electron transfer during denitrification and provides new ideas to the biological denitrification

Study on Novel SCR Catalysts for Denitration of High Concentrated Nitrogen Oxides and Their Reaction Mechanisms

With the rapid development of industrialization, the emission of nitrogen oxides (NOx) has become a global environmental issue. Uranium is the primary fuel used in nuclear power generation. However, the production of uranium, typically based on the uranyl nitrate method, usually generates large amounts of nitrogen oxides, particularly NO2, with concentrations in the exhaust gas exceeding 10,000 ppm. High concentrations of nitrogen dioxide are also produced during silver electrolysis processing and the treatment of waste electrolyte solutions. Traditional V-W/TiO2 NH3-SCR catalysts typically exhibit high catalytic activity at temperatures ranging from 300 to 400 °C, under conditions of low NOx concentrations and high gas hourly space velocity. However, their performance is not satisfying when reducing high concentrations of NO2. This study aims to optimize the traditional V-W/TiO2 catalysts to enhance their catalytic activity under conditions of high NO2 concentrations (10,000 ppm) and a wide temperature range (200–400 °C). On the basis of 3 wt% Mo/TiO2, various loadings of V2O5 were selected, and their catalytic activities were tested. Subsequently, the optimal ratios of active component vanadium and additive molybdenum were explored. Simultaneously, doping with WO3 for modification was selected in the V-Mo/TiO2 catalyst, followed by activity testing under the same conditions. The results show that: the NOx conversion rates of all five catalysts increase with temperature at range of 200–400 °C. Excessive loading of MoO3 decreased the catalytic performance, with 5 wt% being the optimal loading. The addition of WO3 significantly enhanced the low-temperature activity of the catalysts. When the loadings of WO3 and MoO3 were both 3 wt%, the catalyst exhibited the best denitrification performance, achieving a NOx conversion rate of 98.8% at 250 °C. This catalyst demonstrates excellent catalytic activity in reducing very high concentration (10,000 ppm) NO2, at a wider temperature range, expanding the temperature range by 50% compared to conventional SCR catalysts. Characterization techniques including BET, XRD, XPS, H2-TPR, and NH3-TPD were employed to further study the evolution of the catalyst, and the promotional mechanisms are explored. The results revealed that the proportion of chemisorbed oxygen (Oα) increased in the WO3-modified catalyst, exhibiting lower V reduction temperatures, which are favorable for low-temperature denitrification activity. NH3-TPD experiments showed that compared to MoOx species, surface WOx species could provide more acidic sites, resulting in stronger surface acidity of the catalyst.