Removal Of Nitrogen Oxides Research Articles

Research on a Solar Hybrid Trigeneration System Based on Exergy and Exergoenvironmental Assessments

The environmental performance of a combined cooling, heating, and power system is analyzed in this study at a component-level using a SPECO-based exergoenvironmental analysis. The engine consumes natural gas and produces 168.6 kW net power. The waste heat is recovered by a LiBr-H2O absorption chiller and a heat exchanger, which are used for cooling and heating purposes. The energy system is assisted by a solar field. An environmental Life Cycle Assessment quantifies the environmental impacts of the system, and these data are combined with exergy evaluations. The highest total environmental impact rate, 23,740.16 mPt/h, is related to the internal combustion engine, of which pollutant formation is the primary source of environmental impact. Compared with a non-renewable energy system, the solar-assisted trigeneration system decreased the environmental impact per exergy unit of chilled water by 10.99%. Exergoenvironmental performance can be further improved by enhancing the exergy efficiency of the solution pump and high-pressure generator (HG), and by employing a treatment to remove nitrogen oxides in the reciprocating engine.

Metal-free catalysis for the reaction of nitrogen dioxide dimer with phenol: An unexpected favorable source of nitrate and aerosol precursors in vehicle exhaust

Atmospheric reaction mechanism and dynamics of phenol with nitrogen dioxide dimer were explored by the density functional theory and high-level quantum chemistry combined with statistical kinetic calculations within 220–800 K. The nitric acid and phenyl nitrite, the typical aerosol precursors, are the preponderant products because of the low formation free energy barrier (∼8.7 kcal/mol) and fast rate constants (∼10−15 cm3 molecule−1 s−1 at 298 K). Phenyl nitrate is the minor product and it would be also formed from the transformation of phenyl nitrite in NO2-rich environment. More importantly, kinetic effects and catalytic mechanism of a series of metal-free catalysts (H2O, NH3, CH3NH2, CH3NHCH3, HCOOH, and CH3COOH) on the title reaction were investigated at the same level. The results indicate that CH3NH2 and CH3NHCH3 can not only catalyze the title reaction by lowering the free energy barrier (about 1.4–6.5 kcal/mol) but also facilitate the production of organic ammonium nitrate via acting as a donor-acceptor of hydrogen. Conversely, the other species are non-catalytic upon the title reaction. The stabilization energies and donor-acceptor interactions in alkali-catalyzed product complexes were explored, which can provide new insights to the properties of aerosol precursors. Moreover, the lifetime of phenol determined by nitrogen dioxide dimer in the presence of dimethylamine may compete with that of determined by OH radicals, indicating that nitrogen dioxide dimer is responsible for the elimination of phenol in the polluted atmosphere. This work could help us thoroughly understand the removal of nitrogen oxides and phenol as well as new aerosol precursor aggregation in vehicle exhaust.

Characteristics of PM and PAHs emitted from a coal-fired boiler and the efficiencies of its air pollution control devices

ABSTRACT Sampling and analysis of filterable particulate matter (FPM), FPM2.5, condensable particulate matter (CPM), polycyclic aromatic hydrocarbons (PAHs), sulfur oxides (SOx) and nitrogen oxides (NOx) emitted from a coal-fired boiler equipped with selective catalytic reduction (SCR)+ electrostatic precipitator (ESP) + wet flue gas desulfurization (WFGD) + wet electrostatic precipitator (WESP) as air pollution control devices (APCDs) are conducted. The results show that NOx concentration emitted from the coal-fired boiler is 56 ± 2.17 ppm (with the NOx removal efficiency of 47.2%), which does not meet the best available control technology (BACT) emission standard (≤ 30 ppm). On the other hand, the WFGD adopted has a good removal efficiency for SOx and HCl. Both SOx and HCl emission concentrations are <1 ppm, and removal efficiencies are >99%. The FPM and FPM2.5 emitted from the coal-fired boiler are 0.9 ± 0.06 mg/Nm3 and <0.09 ± 0.006 mg/Nm3, respectively. The overall removal efficiency of FPM achieved with ESP+WFGD+WESP+MGGH is 99.98%. However, high concentration of CPM (37.4 ± 6.3 mg/Nm3) is measured, which is significantly higher than FPM and FPM2.5. The concentrations of 27 PAHs at the WESP inlet and stack are measured as 667 ng/Nm3 and 547 ng/Nm3, respectively while the removal efficiencies of gas- and solid-phase PAHs are 9% and 58%, respectively. The results show that APCDs adopted are not effective in removing PAHs (only 18%), and gas-phase PAHs contribute the most in the total PAH emission. In addition, the benzo(a)pyrene equivalent (BaPeq) concentration emitted from the stack is 28.8 ng-BaPeq/Nm3, and most of it is contributed by 4-6 ring PAHs with high toxic equivalent factors (TEFs). Furthermore, the emission factors of air pollutant emitted from coal-fired boilers equipped with different combinations of APCDs are compiled and compared. The results show that except for CPM and NOx, the emission factors of air pollutant calculated for this coal-fired boiler are lower if compared with other studies.

Effect of Liquid Grounding Electrode on the NOx Removal by Dielectric Barrier Discharge Non-Thermal Plasma

In this paper, an experimental setup was established to study the influence of potassium chloride (KCL) solution as the ground electrode on the nitrogen oxides (NOx) removal efficiency in non-thermal plasma (NTP) generated by dielectric barrier discharging (DBD) reactor. The experimental results show that the KCL solution as the ground electrode has better stability and higher discharge intensity and it is a promising approach to improve NOx removal efficiency. The specific NOx removal efficiency is related to the power frequency, the concentration and temperature of the KCL solution. As the power frequency increases, the NOx removal efficiency first increases and then decreases, and a maximum value is reached at the power frequency of 8 kHz. The NO removal effect is improved as the concentration of the KCL solution increases, especially when the concentration is lower than 0.1 mol/L. Under the same KCL solution concentration and input energy density, the NOx removal efficiency is increased with the solution temperature. In particular, when the power discharge frequency is 8 kHz, the KCL solution concentration is 0.1 mol/L and the solution temperature is 60 °C, the NOx and NO removal efficiency reach 85.82% and 100%, respectively.

Optimization and modeling of efficient photocatalytic TiO2-ZnO composite preparation parameters by response surface methodology

The major focus of this work is the design and optimization of the preparation conditions of binary titanium dioxide-zinc oxide (TiO2-ZnO) composite using response surface methodology (RSM). Calcination temperature and ZnO weight percent (%) with respect to TiO2 were chosen as the key parameters for optimizing the preparation conditions. The evaluation of photocatalytic nitrogen oxides (NOx) removal efficiency was selected for modeling the RSM. Thirteen factorial design runs were first generated with one replicate and 5 center points in order to perform all the experiments. The experimental results on NOx removal efficiency for the composites calcined at 747, 602, and 558 °C containing 5.48%, 3.48%, and 2.1% of ZnO with respect to the weight of TiO2, designated as MaxT(Z%), MedT(Z%) and MinT(Z%) respectively, agree well with RSM predictions. The response coefficient difference between experimental and RSM results of MaxT(Z%), MedT(Z%), and MinT(Z%) were approximately 0.019, 0.044, and 0.11, respectively. The microstructural and optical properties as well the surface composition of MaxT(Z%), MedT(Z%), and MinT(Z%) were evaluated by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS), respectively. The results from the photodecomposition of NOx gas under illuminated UV-light confirmed that the TiO2-ZnO prepared with a 2.1 wt% of ZnO and calcined at 558 °C witnessed the best photocatalytic activity and the reasons for the excellent performance are corroborated with XRD, XPS, and DRS results. This study provides a simple and systematic approach for the optimization and modeling of the binary composite preparation for achieving enhanced photoactivity.

Estimating NOx removal capacity of urban trees using stable isotope method: A case study of Beijing, China

It is widely recognized that green infrastructures in urban ecosystems provides important ecosystem services, including air purification. The potential absorption of nitrogen oxides (NOx) by urban trees has not been fully quantified, although it is important for air pollution mitigation and the well-being of urban residents. In this study, four common tree species (Sophora japonica L., Fraxinus chinensis Roxb., Populus tomentosa Carrière, Sabina chinensis (L.)) in Beijing, China, were studied. The dual stable isotopes (15N and 18O) and a Bayesian isotope mixing model were applied to estimate the sources contributions of potential nitrogen sources to the roadside trees based on leaf and soil sampling in urban regions. The following order of sources contributions was determined: soil > dry deposition > traffic-related NOx. The capacity of urban trees for NOx removal in the city was estimated using a remote sensing and GIS approach, and the removal capacity was found to range from 0.79 to 1.11 g m−2 a−1 across administrative regions, indicating that 1304 tons of NOx could be potentially removed by urban trees in 2019. Our finding qualified the potential NOx removal by urban trees in terms of atmospheric pollution mitigation, highlighting the role of green infrastructure in air purification, which should be taken into account by stakeholders to manage green infrastructure as the basis of a nature-based approach.

Morphology of Organic Carbon Coatings on Biomass-Burning Particles and Their Role in Reactive Gas Uptake

Inorganic salts are a significant component of biomass-burning aerosol (BBA) and have inconsistently been observed to undergo chemical reactions with strong acids and other reactants during atmospheric aging, altering particle hygroscopicity and further reactivity while also liberating reactive halides such as ClNO2(g) and HCl(g) and recycling or removing nitrogen oxides. The condensation of organic carbon to BBA coemitted by wildfires and other biomass combustion processes can affect aerosol particle reactivity with trace gases. These organic coatings along with deliquescence of chloride salts requiring high relative humidities >80% were recently proposed to explain the low observed reaction probability of N2O5(g) with BBA. We performed a series of single-particle analyses to characterize the morphology and composition of laboratory-generated BBA from authentic fuels using transmission and scanning electron microscopies (T/SEM) to test this hypothesis. Stable organic coatings that appear thicker or more oxidized than the particle bulk (likely tar balls) were observed to form on some spherical BBA particles but only when photooxidation was not applied. Inorganic salt components were inconsistently observed to react during simulated photooxidative atmospheric aging, sometimes undergoing chloride displacement reactions with strong acid vapors to produce sulfate and nitrate salts. Particles were also observed where chloride-salt regions were not completely depleted by reaction with strong acids. Organic carbon particle coatings plus the physical phase of chloride salts and deliquescence limitations appear to play a significant role in determining in which particles and fuel types these chloride displacement reactions can occur and the extent of these reactions with acidic vapors.

The low-temperature NO2 removal by tailoring metal node in porphyrin-based metal-organic frameworks

Nitrogen dioxide (NO2) is the most toxic and prevalent form of nitrogen oxides (NOx) pollutant and its removal from ambient air is a pressing challenge. The state-of-the-art deNOx technologies such as selective catalytic reduction (SCR) can only work at elevated temperatures (>250–300 °C), but ineffective for the NOx removal under ambient conditions. The adsorptive removal of NO2 is an alternative approach to SCR, whose success depends on the design of stable adsorbents capable of selectively capturing NO2 with a highly reversible capacity. Here we synthesized and developed five porphyrin-based metal-organic frameworks (PMOFs) as robust ambient NO2 adsorbents, including three aluminum-based (Al-PMOF) isostructures, and two zirconium-based (Zr-PMOFs) isostructures. Of them, Al-PMOF stands out to be the most promising candidate by showing the highest NO2 adsorption capacity (1.85 mmol/g), high stability, and good regenerability (retaining 87% capacity after five cycles of adsorption) at dry conditions. The NO2 adsorption capacity of Al-PMOF was approximately doubled (3.61 mmol/g) at wet conditions. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed the NO2 adsorption mechanism – the hydrogen bonding occurs between bridging hydroxyl (-OH) (attached to the metal node) and NO2 molecules. Our work demonstrates that PMOFs are promising NO2 adsorbents and will provide guidance for designing robust and reusable adsorbents for efficiently removing NO2 at ambient temperature.

Surface plasmon resonance enhanced photocatalysis of Ag nanoparticles-decorated Bi2S3 nanorods for NO degradation

Photocatalysis is an emerging tool used for the reduction of air pollutants. In the atmosphere, nitrogen oxide (NO) is one of the leading pollutants because of its detrimental effects on flora and fauna. This work introduces the photocatalytic NO degradation over Ag nanoparticles-decorated Bi2S3 nanorods. The XRD, FTIR, XPS, SEM, EDS, and TEM demonstrate the existence of the materials, with the morphology of Ag nanoparticles (NPs) loading on Bi2S3 nanorods. The increase in surface area and pore volume of Bi2S3 nanorods thanks to Ag is confirmed by nitrogen adsorption–desorption isotherm using BET. The NO removal efficiency over 3% [email protected]2S3 is 31.12%, while that of pure Bi2S3 is only 11.65%. The band bending and surface plasmon resonance (SPR) enhance the photocatalytic activity are confirmed by DRS and Mott–Schottky plot. The high stability of materials were surveyed by recycle test, XRD, and FTIR. The ESR and trapping experiments support to determine the unique photocatalytic mechanism of [email protected]2S3 via •HO2 radicals. This study provides an unique understanding about of [email protected]2S3 for nitrogen oxides (NOx) degradation under solar light.

Electrochemical removal of NOx by La0.8Sr0.2Mn1−xNixO3 electrodes in solid electrolyte cells: Role of Ni substitution

Electrochemical removal of nitrogen oxides (NOx) by solid electrolyte cells (SECs) is a promising technology due to no required reductant. Herein, a series of La0.8Sr0.2Mn1−xNixO3 (0 ≤ x ≤ 0.5) perovskites were first synthesized and utilized as the electrode materials of SECs. The role of Ni substitution in electrode performance and NOx reduction mechanism were revealed by various experimental characterization and first-principle calculations. The results indicate that the moderate Ni substitution (x ≤ 0.3) increased the NOx conversion of electrodes while reduced the polarization resistance. The further investigation shows that this improvement was attributed to the more surface oxygen vacancies, better reducibility and higher Mn4+ proportion of the Ni-substituted perovskites. The electrochemical impedance spectroscopy (EIS) shows that these changes facilitated the NOx adsorption and dissociation processes on the electrode. According to first-principle calculations, the Ni-substituted perovskite had a lower formation energy of surface oxygen vacancy, while the NO molecule adsorbed on defect surface gained more electrons thus was easier to be reduced and dissociated. Finally, the electrode performance at different operating temperatures and the operational stability were verified.

Toward a viable ecological method for regenerating a commercial SCR catalyst – Selectively leaching surface deposits and reconstructing a pore landscape

Controlling carbon and nitrogen chemistry is essential for human life and civilization. In particular, high-temperature combustion of carbon fuels in the air results in the formation of ecotoxic carbon and nitrogen oxides (NOx). Specifically, NOx needs to be removed from the flue gases of electric power stations. The selective catalyst reduction (SCR) systems support the deNOx (NOx removal) process; however, surface deposits deactivate the SCR system while operating. Moreover, the surface texture is damaged during the exploitation. We show here how this damage reveals itself in the pore landscape of the commercial SCR catalysts. In particular, for the first time, we showed how this could be assessed by a combination of thermoporometry (TPM) and gas physisorption. Accordingly, a correlation between the assessed quality of the pore landscape and the catalyst activity was determined and discussed. We designed a broad collection of new innovative regeneration procedures, which appear to be robust and selective methods for removing surface poisons. The optimal regeneration scheme fully restored the catalyst activity.

Detailed numerical simulations of low-temperature oxidation of NOx by ozone

Limiting gaseous nitrogen oxide (NOx) emissions is a major global concern due to their harmful effect on human health and the environment. During the past decade, low-temperature oxidation by ozone (O3) has emerged as a promising solution for NOx removal in the transportation and energy generation sectors. In the present study, three-dimensional (3D) large eddy simulations (LES) of the turbulent reacting flow inside a NOx-O3 reactor are performed. It is the first publication using LES and detailed finite rate chemistry for such a reactor. Additionally, plug-flow reactor (PFR) simulations are employed to identify the best performing chemical kinetic mechanisms among those available in the literature over the range of conditions studied. Furthermore, results from different experimental works are reviewed to analyze the variability in the literature. Additionally, this will aid in devising a strategy for validation. Time-averaged results obtained from PFR and combined LES-PFR simulations are observed to agree well with experimental results. The species correlation, distribution, and overall flow uniformity in the pure LES simulations are also assessed and the results highlight the benefits of a high mixing efficiency reactor geometry. Moreover, relevant features of the unsteady flow throughout the present reactor are studied. In particular, the analysis of coherent structures and the existence of regions with non-reacted gases and their relation to mixing and NOx oxidation efficiency are evaluated. The present simulations enable a novel understanding of the interplay between mixing and chemistry and highlight, for the first time, details of the oxidation of NOx by O3.

Photocatalytic concrete for NOx degradation: Influence factors and durability

The application of titanium dioxide (TiO2) photocatalyst in concrete is considered a promising method to effective remove nitrogen oxide (NOx) pollutants. However, the influences of application ways on photocatalytic efficiency and catalyst durability should be concerned in detail for its large-scale application. This paper compared the photocatalytic NOx degradation efficiency and durability of conventional TiO2 powder dispersed in cement mortar (TPC), TiO2 supported aggregates mounted on cement mortar surface (TAS) and TiO2 supported aggregates dispersed in cement mortar (TAD), with considering different environmental factors effects such as gas flow rate, NO initial concentration and relative humidity. The photocatalytic efficiency results show that the NOx removal efficiency of TAS is about 1.5 and 1.1 times higher than that of TPC and TAD, respectively, corresponding to the utilization efficiency of TiO2 photocatalysts in TAS is ca. 10 and 16 times higher than in TPC and TAD, respectively. The surface abrasion test suggests that TAS has relatively low photocatalytic efficiency compared with TAD after polishing the sample surface by more than 2 mm, which depends on the mounted thickness of TiO2 supported aggregates. The findings in this work can provide the basis for the application ways of TiO2 supported aggregates in concrete by considering its photocatalytic efficiency, economic efficiency and catalytic durability.

A Review of Photocatalytic Materials for Urban NOx Remediation

NOx is a pervasive pollutant in urban environments. This review assesses the current state of the art of photocatalytic oxidation materials, designed for the abatement of nitrogen oxides (NOx) in the urban environment, and typically, but not exclusively based on titanium dioxide (TiO2). Field trials with existing commercial materials, such as paints, asphalt and concrete, in a range of environments including street canyons, car parks, tunnels, highways and open streets, are considered in-depth. Lab studies containing the most recent developments in the photocatalytic materials are also summarised, as well as studies investigating the impact of physical parameters on their efficiency. It is concluded that this technology may be useful as a part of the measures used to lower urban air pollution levels, yielding ∼2% NOx removal in the immediate area around the surface, for optimised TiO2, in some cases, but is not capable of the reported high NOx removal efficiencies &gt;20% in outdoor urban environments, and can in some cases lower air quality by releasing hazardous by-products. However, research into new material is ongoing. The reason for the mixed results in the studies reviewed, and massive range of removal efficiencies reported (from negligible and up to &gt;80%) is mainly the large range of testing practices used. Before deployment in individual environments site-specific testing should be performed, and new standards for lab and field testing should be developed. The longevity of the materials and their potential for producing hazardous by-products should also be considered.

Constructing anatase TiO2/Amorphous Nb2O5 heterostructures to enhance photocatalytic degradation of acetaminophen and nitrogen oxide

TiO2 nanostructures have been one of the most explored metal oxides photocatalysts to apply for environmental remediation. However, its wide band gap results in the underutilization of sunlight for degradation of pollutants. In order to overcome this handicap, the synthesis of TiO2-based composite has brought extraordinary materials. In this study, we design and prepare TiO2/Nb2O5 heterostructures with different molar ratios by using peroxotitanium and peroxoniobium complex as precursors in aqueous solution. The TiO2 exists in the form of anatase while Nb2O5 is amorphous in the composite, leading to a special crystalline TiO2/amorphous Nb2O5 heterostructures. In particular, Nb element is also doped and Ti3+ ions are formed in the TiO2 lattice, leading to a reduced band gap. The unique TiO2/0.25Nb2O5 (Ti:Nb = 2:1) heterostructures can effectively suppress the recombination of photogenerated electrons and holes, and facilitate the charge transfer, resulting in the optimum photocatalytic performance. The nitrogen oxide removal efficiency by TiO2/0.25Nb2O5 is 77.23% in visible light, which is 3.8-folds and 7.0-folds higher than pure TiO2 and Nb2O5. Photocatalytic degradation of acetaminophen by TiO2/0.25Nb2O5 is 90.6% in visible light, which is approximately 2.5-folds higher than pure TiO2 and Nb2O5.

ZIF-67/CoOOH cocatalyst modified g-C3N4 for promoting photocatalytic deep oxidation of NO

The removal of nitrogen oxides (NOX) by semiconductor photocatalysis is an emerging technology in recent years. However, due to incomplete oxidation, the photocatalytic oxidation of NOX is usually accompanied by the generation of toxic intermediate by-products nitrogen dioxide (NO2), which causes secondary pollution and seriously limits its practical application. To tackle the issue, ZIF-67/CoOOH (ZIF-CH) cocatalyst was constructed via flexible strongly alkali oxidation treatment to modify g-C3N4, in which ZIF-67 was selected as a cobalt source of CoOOH. XRD, SEM, TEM and XPS demonstrated the ZIF-CH was successfully synthesized and anchored on CN. UV–vis, PL, EIS, transfer photocurrent response and DFT indicated that the introduction of ZIF-CH enlarged the response range to visible light, favored the separation and transfer of carriers and improved NO/NO2 adsorption ability. Consequently, the optimized ZIF-67/CoOOH/g-C3N4 (ZIF-CH/CN) exhibited a superior NO removal efficiency of 52.5% without any generation of toxic by-product NO2, and the cycling tests indicated the high stability of ZIF-CH/CN was obtained. In-suit DRIFTS and ESR were used to investigate the reaction pathway by comparing adsorption energy and detecting the reaction intermediates and products. More importantly, this result reveal that amount of hydroxyl radical (·OH) increased after introducing ZIF-CH cocatalyst, which promotes the deep oxidation of NO. These findings could supply a convenient and effective strategy for the design of a cocatalyst to enhance the photocatalytic oxidation performance of NO and inhibit the production of toxic by-product NO2.

Review of Discharge Plasma Treatment of NO X in Diesel Engine Exhaust: Progress in Stand-Alone and Cascaded Measures

This article is intended to provide a comprehensive review of the experimental studies conducted to understand the effect of several parameters involved in the discharge plasma-based nitrogen oxides (NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</sub> ) removal from real diesel engine exhausts, be it stationary or automobile, in addition to simulated ones. In the last two decades, much progress has occurred in the electric discharge-based nonthermal plasma (NTP) treatment of exhaust gas with or without cascading any additional treatment technique, such as catalysts or adsorbents. Most of these studies were conducted with the aim of enhancing the removal of NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</sub> or studying the efficacy of a particular parameter on NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</sub> removal or both. It is now timely to collage the findings of these studies in a way to help the present researchers to understand the effect of various parameters/measures associated with stand-alone and cascaded NTP treatments for NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</sub> removal. It is also intended that the current review helps in moving closer to realizing the application of NTP in the cleansing of gaseous pollutants of diesel exhaust.

Isolated heterotrophic nitrifying and aerobic denitrifying bacterium for treating actual refinery wastewater with low C/N ratio

Heterotrophic nitrifying and aerobic denitrifying bacteria that have been widely isolated from complicated activated sludge microflorae demonstrate dominant advantages in simultaneous removal of ammonium and nitrogen oxides under aerobic conditions. However, owing to the need of organic carbon to support bacterial growth, nitrogen removal of actual industrial wastewater with low carbon-to-nitrogen (C/N) ratio remains a challenge. Here, Pseudomonas mendocina Y7 was identified and presented to effectively remove nitrogen of actual refinery wastewater with low C/N ratio. The isolated bacterium showed high removal efficiency of NH4+-N, NO2--N, and NO3--N up to about 90% in single (100mg/L) or mixed (200mg/L) nitrogen source media at low C/N ratio of 6 when it was cultivated for 12 or 21h. According to PCR amplification, the heterotrophic nitrification and aerobic denitrification capability of strain Y7 was attributed to the functional genes of amoA, hao, napA, and nirS. In activated sludge process for treating actual refinery wastewater with low C/N ratio, compared to abundant accumulation of NO2--N and NO3--N only using the activated sludge, strain Y7 significantly improved the removal efficiency of NH4+‒N and total nitrogen (with influent concentrations of about 40 and 55mg/L) from about 47% and 22% to about 85% and 73%, respectively, without the accumulation of nitrogen oxides. Microbial community structure analysis revealed that strain Y7 could coexist well with other microorganisms in the activated sludge and maintain highly efficient and steady nitrogen removal in continuous treatment system. This discovery provides a promising treatment approach toward actual nitrogen-rich industrial wastewater.

Controlling Nitrogen Oxide and Ultraviolet-A irradiance in ventilation duct system using TiO2 photocatalyst

In this study, we verified the application of TiO2 photocatalysts on ventilation ducts used in buildings and their effects on reducing nitrogen oxide (NOx), which is a typical particulate matter precursor. The TiO2 photocatalyst produces a radical dioxide with a strong acid oxidation power through photochemical reactions with ultraviolet-A (UV-A) rays and removes NOx through oxidation. The removal experiment was conducted by applying TiO2 photocatalyst coatings inside the duct to comply with the conditions of the ISO 22197-1: 2007. In addition, changes in the NOx removal were confirmed through changes in the concentration of NOx and UV-A irradiance inside the duct. At approximately 100 min after switching on the UV-A lamp during the experiment conduced according to ISO 22197-1: 2007, the NOx concentration decreased to 0.053 ppm (by 94.87%). Moreover, it has been confirmed that the trend of reduction is proportional to the changes in UV-A irradiance and NOx concentration, that is, an increase in UV-A irradiance has a significant impact on the reduction of NOx concentration; NOx reduction increases as a secondary function due to an increase in the UV-A irradiance. Through this study, it is believed that NOx, a representative precursor material that generates particulate matter, can be removed through a building ventilation system using a TiO2 photocatalyst.

Water: A promoter of ammonia selective catalytic reduction over copper-exchanged LTA zeolites

Negative effects of water on the hydrothermal stability of ammonia (NH3) selective catalytic reduction (SCR) catalysts are well known. Thus, developing water-resistant, zeolite-based transition metal catalysts like copper (Cu) for mitigating nitrogen oxides from mobile sources is very challenging. Here we show that water markedly facilitates the migration of copper ions from sterically inaccessible sod cage to the readily accessible lta one through six-membered rings within a copper-exchanged high-silica Cu-LTA zeolite. We also show that this ubiquitous molecule promotes the low-temperature SCR activity of the Cu-LTA catalyst with a plausible reaction [H2O-Cu-NH3]+ intermediate. We anticipate that water might play a beneficial role in nitrogen oxides removal over metal-containing zeolites for cleaner air via tuning the active sites and reaction pathways.