Dihydroxy-Substituted Coumarins as Fluorescent Probes for Nanomolar-Level Detection of the 4-Amino-TEMPO Spin Label.

This paper reports on dihydroxycoumarins as fluorescent probes suitable for the detection and determination of the nitroxide radical, namely 4-amino-TEMPO. Since 4-amino-TEMPO is used as a spin label for the detection of various radicals and damage caused by these species, its determination under physiological conditions might help us to understand the mechanism of the oxidative stress. Among different coumarins studied, only dihydroxy-substituted derivatives show high sensitivity, specificity, and selectivity for the nitroxide radical. In this assay, dihydroxy-substituted coumarins under the action of 4-amino-TEMPO show a very fast and significant increase in fluorescence intensity and lifetime. Among them 6,7-dihydroxycoumarin (esculetin) exhibits the strongest fluorescence enhancement (up to 40 times), with an estimated limit of detection equal to 16.7 nM-a significantly lower value when compared with UV-Vis or electron paramagnetic resonance (EPR) spectroscopy. The method is characterized by an easy procedure of sample preparation and very short time of analysis. The mechanism of the interaction between 6,7-dihydroxycoumarin and 4-amino-TEMPO has been examined with the use of a series of complementary techniques, such as steady-state and time-resolved fluorescence spectroscopy, UV-Vis spectroscopy, electron paramagnetic resonance spectroscopy, potentiometric titration, and high-performance liquid chromatography. It has been proven that the only route of the reaction in the system studied is a proton transfer from the molecule of esculetin to the amino group of the nitroxide. Biological studies performed on prostate cancer cells, breast cancer cells, and normal skin fibroblasts revealed significant anticancer properties of 6,7-dihydroxycoumarin, which caused a considerable decrease in the viability and number of cancer cells, and affected their morphology, contrary to normal fibroblasts. Furthermore, the experiment performed on prostate cancer cells showed that fluorescence emission of esculetin is closely related to intracellular pH-the higher pH, the higher observed fluorescence intensity (in accordance with a chemical experiment). On the other hand, the studies performed in different pH levels revealed that when pH of the solution increases, the observed fluorescence intensity enhancement under the action of 4-amino-TEMPO decreases (better sensing properties of esculetin towards the nitroxide in lower pH).

Photo-assisted SCR removal of NO by upconversion CeO2/Pr3+/attapulgite nanocatalyst.

The emission of nitrogen oxides has caused severe harm to the ecosystem; thus, the development of low-cost and high-efficiency denitrification catalysts and new methods are of great significance. In this work, a co-precipitation method was employed to prepare Pr-doped CeO2/attapulgite (CeO2/Pr3+/ATP) nanocomposites. X-ray diffraction (XRD), photoluminance spectroscopy (PL), ultraviolet-visible diffuse reflectance (UV-Vis), Fourier transform infrared (FT-IR), and high-resolution transmission electron microscopy (HRTEM) were utilized to characterize the products. Results showed that the CeO2/Pr3+ nanoparticles were uniformly coated on the surface of ATP and demonstrated outstanding upconversion effect which converted the visible light to ultraviolet light. The upconversion luminescence of CeO2/Pr3+/ATP was strongest when the molar doping amount of Pr was 1 mol%, and the photo-SCR denitrification achieved the highest of 90% conversion and 95% selectivity when the loading amount of CeO2/Pr3+ was 40 wt%. The ATP and CeO2/Pr3+ constructed an indirect Z-type heterojunction structure mediated by oxygen vacancy which benefited the separation of charge carriers and enhanced the reduction-oxidation potentials, both are responsible for the remarkable denitrification performance.

Simultaneous removal of PCDD/Fs and NOx from the flue gas of a municipal solid waste incinerator with a pilot plant.

The pilot-scale plant on the simultaneous removal of PCDD/Fs and NOx from the flue gas of a municipal solid waste incinerator is presented. In order to research the influence of temperature on the catalytic decomposition of PCDD/Fs and the selective catalytic reduction of NOx, the experiments were performed at 220 °C, 260 °C, and 300 °C, and the congener profiles of PCDD/Fs for the samples collected at the inlet and outlet were illustrated. Noteworthy, the detailed congener distributions of PCDD/Fs in the gas-phase and particle-phase of the inlet and 300-outlet (decomposition temperature = 300 °C) samples are presented, and the removal efficiencies η(g-I-TEQ) and η(p-I-TEQ) reached to 94.94% and 99.67%, respectively. The effect of the SCR process on the removal of PCDD/Fs was also studied at a relatively low temperature of 220 °C. Additionally, the NOx emissions and the SCR efficiencies were investigated.

Evaluation of an oil-producing green alga Chlorella sp. C2 for biological DeNOx of industrial flue gases.

NOx, a significant portion of fossil fuel flue gases, are among the most serious environmental issues in the world and must be removed in an additional costly gas treatment step. This study evaluated the growth of the green alga Chlorella sp. C2 under a nitrite-simulated NOx environment and the removal rates of actual flue gas fixed salts (FGFSs) from Sinopec's Shijiazhuang refinery along with lipid production. The results showed that nitrite levels lower than 176.5 mM had no significant adverse effects on the cell growth and photosynthesis of Chlorella sp. C2, demonstrating that this green alga could utilize nitrite and NOx as a nitrogen source. High concentrations of nitrite (88.25-176.5 mM) also resulted in the accumulation of neutral lipids. A 60% nitrite removal efficiency was obtained together with the production of 33% algae lipids when cultured with FGFS. Notably, the presence of nitrate in the FGFS medium significantly enhanced the nitrite removal capability, biomass and lipid production. Thus, this study may provide a new insight into the economically viable application of microalgae in the synergistic combination of biological DeNOx of industrial flue gases and biodiesel production.

Spray absorption and electrochemical reduction of nitrogen oxides from flue gas.

This work developed an electrochemical reduction system which can effectively scrub NO× from flue gas by using aqueous solution of Fe(II)(EDTA) (ethylenediaminetetraacetate) as absorbent and electrolyte. This new system features (a) complete decomposition of NOX to harmless N2; and (b) fast regeneration of Fe(II)(EDTA) through electrochemical reaction. The Fe(II)(EDTA) solution was recycled and reused continuously during entire process, and no harmful waste was generated. The reaction mechanism was thoroughly investigated by using voltammetric, chromatographic and spectroscopic approaches. The operating conditions of the system were optimized based on NOX removal efficiency. Approximately 98% NO removal was obtained at the optimal condition. The interference of SO2 in flue gas and the system operating stability was also evaluated.

[Effects of gaseous compositions the on simultaneous removal of NO(x) and SO2 from simulated flue gas by ammonia absorption].

The effects of NO(x) oxidation ratio, O2 and SO2 concentrations in simulated flue gas as well as addition of S(IV) oxidation inhibitor NaS2O3 on the simultaneous removal of SO2 and NO(x) by ammonia absorption were investigated under the conditions of pH 5.9-6.1 and aqueous S(IV) concentration > or = 1.0 mol x L(-1). The research results showed that NO2 could be effectively absorbed by ammonium sulfite, but the NO absorption was negligible. Therefore, NO oxidation is the premise of NO(x) removal. Aqueous S(IV) concentration is a key factor affecting NO2 absorption removal, the higher the O2 concentration or the lower the SO2 concentration, the faster the aaqueous S(IV) concentration decreased, which resulted in a faster decrease of NO2 removal efficiency. S(IV) oxidation was inhibited to some extent by the addition of oxidation inhibitor S2O3(2-) into the absorption solution. As a result, the decrease of NO2 removal efficiency became slower.

Experimental study on removal of NO using adsorption of activated carbon/reduction decomposition of microwave heating.

Experimental studies were carried out on flue gas denitrification using activated carbon irradiated by microwave. The effects of microwave irradiation power (reaction temperature), the flow rate of flue gas, the concentration of NO and the flue gas coexisting compositions on the adsorption property of activated carbon and denitrification efficiency were investigated. The results show that: the higher of microwave power, the higher of denitrification efficiency; denitrification efficiency would be greater than 99% and adsorption capacity of NO is relatively stable after seven times regeneration if the microwave power is more than 420 W; adsorption capacity of NO in activated carbon bed is 33.24 mg/g when the space velocity reaches 980 per hour; adsorption capacity declines with increasing of the flow rate of flue gas; the change in denitrification efficiency is not obvious with increasing oxygen content in the flue gas; and the maximum adsorption capacity of NO was observed when moisture in flue gas was about 5.88%. However, the removal efficiency of NO reduces with increasing moisture, and adsorption capacity and removal efficiency of NO reduce with increasing of SO2 concentration in the flue gas.

Effect of solution pH on SO2, NO(x), and Hg removal from simulated coal combustion flue gas in an oxidant-enhanced wet scrubber.

This paper presents a study on the simultaneous removal of SO2, NO(x) and Hg (both Hg0 and Hg2+) from a simulated flue gas by oxidant injection in a bench-simulated wet limestone scrubber for a wide range of slurry pH. The slurry pH strongly influenced the chemical mechanism in the scrubber and, therefore, affected pollutant removal. This paper also examines the potential ClO2(gas) reemission from a developed multipollutant scrubber at different slurry pHs. To better understand the chemical mechanisms at each slurry pH and to apply a mass balance to the process, detailed product ion analyses were performed for all experiments. Ion analysis covered three different chlorine species (chlorite, chloride, chlorate), sulfate, nitrite and nitrate. Different NO(x) removal efficiencies and mechanisms were found in acidic and alkaline pHs in the multipollutant scrubber. The acidic solution was favorable for NO and Hg0 oxidation, but increasing the slurry pH above 7.0 was disadvantageous for NO and Hg oxidation/removal. However the rate of NO(x) absorption (by percentage) was higher for the alkaline solution.

Enhanced biological removal of NOχ from flue gas in a biofilter by Fe(II)Cit/Fe(II)EDTA absorption.

A mixed absorbent had been proposed to enhance the chemical absorption-biological reduction process for NO(x) removal from flue gas. The mole ratio of the absorbent of Fe(II)Cit to Fe(II)EDTA was selected to be 3. After the biofilm was formed adequately, some influential factors, such as the concentration of NO, O(2), SO(2) and EBRT were investigated. During the long-term running, the system could keep on a steady NO removal efficiency (up to 90%) and had a flexibility in the sudden changes of operating conditions when the simulated flue gas contained 100-500 ppm NO, 100-800 ppm SO(2), 1-5% (v/v) O(2), and 15% (v/v) CO(2). However, high NO concentration (>800 ppm) and relative short EBRT (<100s) had significant negative effect on NO removal. The results indicate that the new system by using mixed-absorbent can reduce operating costs in comparison with the single Fe(II)EDTA system and possesses great potential for scale-up to industrial applications.

Simultaneous desulfurization and denitrification from flue gas by Ferrate(VI).

An innovative semidry process has been developed to simultaneously remove NO and SO2 from flue gas. According to the conditions of the flue gas circulating fluidized bed (CFB) system, ferrate(VI) absorbent was prepared and added to humidified water, and the effects of the various influencing factors, such as ferrate(VI) concentration, humidified water pH, inlet flue gas temperature, residence time, molar ratio of Ca/(S+N), and concentrations of SO2 and NO on removal efficiencies of SO2 and NO were studied experimentally. Removal efficiencies of 96.1% for SO2 and 67.2% for NO were obtained, respectively, under the optimal experimental conditions, in which the concentration of ferrate(VI) was 0.03 M, the humidified water pH was 9.32, the inlet flue gas temperature was 130 °C, the residence time was 2.2 s, and the molar ratio of Ca/(S+N) was 1.2. In addition, the reaction mechanism of simultaneous desulfurization and denitrification using ferrate(VI) was proposed.

Simultaneous removal of NO(x) and SO2 in exhausted gas through landfill leachate.

Simultaneous removal of NO(x) and SO2 from exhausted gas were investigated by studying co-culture of sulfate reducing bacteria and anaerobic denitrifying bacteria, separated from landfill leachate. When H2S, generated by sulfate reducing bacteria was chosen as the sole electron donor for anaerobic denitrifying bacteria, the co-culture system demonstrated a faster NO removal rate, higher stability and better permanence. When the feed gas flow rates of N2 and SO2 were maintained constant at 0.1 m3/h and 16 ml/min respectively, the maximum NO-removal rate could be achieved at over 92% with NO feed gas kept between 2-6 ml/min, while the SO2 removal rate was always above 95%. Long-term continuous removal of NO exhibited an evident periodicity of five days, however, the fluctuation range of NO-removal was decreasing. Moreover, the decrease of the gas flow rate and the increase in NO inlet concentration could contribute to a higher NO- removal rate.

Experimental aspects of combined NOx and SO2 removal from flue-gas mixture in an integrated wet scrubber-electrochemical cell system.

The objective of this work was to study the effect of some operating conditions on the simultaneous removal of NO(x) and SO2 from simulated NO-SO2-air flue-gas mixtures in a scrubber column. The gaseous components were absorbed into 6M HNO3 electrolyte in the scrubber in a counter-current mode, and were oxidatively removed by the Ag(II) mediator oxidant electrochemically generated in an electrochemical cell set-up. The integration of the electrochemical cell with the scrubber set-up ensured continuous regeneration of the Ag(II) mediator and its repeated reuse for NO(x) and SO2 removal purpose, thereby avoiding: (1) the usage of chemicals continuously for oxidation and (2) the production of secondary waste. The influences of packing material (raschig glass rings, raschig poly(vinylidene) fluoride rings, Jaeger tri-pack perfluoroalkoxy spheres), feed concentrations of NO and SO2 (100-400 ppm NO and 100-400 ppm SO2), superficial gas velocity (0.061-0.61ms(-1)) and liquid velocity (0.012-0.048 ms(-1)) were investigated. The raschig glass rings with high surface area provided highest NO removal efficiency. NO and NO(x) showed decreasing abatement at higher feed concentrations. The removal of nitrogen components was faster and also greater, when SO2 co-existed in the feed. Whereas the gas flow rate decreased the removal efficiency, the liquid flow rate increased it for NO and NOx. The flow rate effects were analyzed in terms of gas/liquid residence time and superficial liquid velocity/superficial gas velocity ratio. SO2 removal was total under all conditions.

Evaluation of constructed wetlands by wastewater purification ability and greenhouse gas emissions.

Domestic wastewater is a significant source of nitrogen and phosphorus, which cause lake eutrophication. Among the wastewater treatment technologies, constructed wetlands are a promising low-cost means of treating point and diffuse sources of domestic wastewater in rural areas. However, the sustainable operation of constructed wetland treatment systems depends upon a high rate conversion of organic and nitrogenous loading into their metabolic gaseous end products, such as N2O and CH4. In this study, we examined and compared the performance of three typical types of constructed wetlands: Free Water Surface (FWS), Subsurface Flow (SF) and Vertical Flow (VF) wetlands. Pollutant removal efficiency and N2O and CH4 emissions were assessed as measures of performance. We found that the pollutant removal rates and gas emissions measured in the wetlands exhibited clear seasonal changes, and these changes were closely associated with plant growth. VF wetlands exhibited stable removal of organic pollutants and NH3-N throughout the experiment regardless of season and showed great potential for CH4 adsorption. SF wetlands showed preferable T-N removal performance and a lower risk of greenhouse gas emissions than FWS wetlands. Soil oxidation reduction potential (ORP) analysis revealed that water flow structure and plant growth influenced constructed wetland oxygen transfer, and these variations resulted in seasonal changes of ORP distribution inside wetlands that were accompanied by fluctuations in pollutant removal and greenhouse gas emissions.

Control of diesel soot and NOx emissions with a particulate trap and EGR.

The exhaust gas recirculation (EGR), coupled with a high-collection efficiency particulate trap to simultaneously control smoke and NOx emissions from diesel engines were studied. This ceramic trap developed previously provided the soot cleaning efficiency of 99%, the regeneration efficiency reaches 80% and the ratio of success reaches 97%, which make EGR used in diesel possible. At the presence of EGR, opening of the regeneration control valve of the trap was over again optimized to compensate for the decrease of the oxygen concentration in the exhaust gas resulted from EGR. The results indicated the cleaning efficiency and regeneration performance of the trap were maintained at the same level except that the back pressure increased faster. A new EGR system was developed, which is based on a wide range oxygen (UEGO) sensor. Experiments were carried out under steady state conditions while maintaining the engine speed at 1600 r/min, setting the engine loads at 0%, 25%, 50%, 75% and 100% respectively. Throughout each test the EGR rate was kept at nine different settings and data were taken with the gas analyzer and UEGO sensor. Then, the EGR rate and engine load maps, which showed the tendencies of NOx, CO and HC emissions from diesel engine, were made using the measured data. Using the maps, the author set up the EGR regulation, the relationship between the optimal amounts of EGR flow and the equivalence ratio, sigma, where sigma = 14.5/AFR.

NOx removal from flue gas by an integrated physicochemical absorption and biological denitrification process.

An integrated physicochemical and biological technique for NO(x) removal from flue gas, the so-called BioDeNO(x) process, combines the principles of wet absorption of NO in an aqueous Fe(II)EDTA(2-) solution with biological reduction of the sorbed NO in a bioreactor. The biological reduction of NO to di-nitrogen gas (N(2)) takes place under thermophilic conditions (55 degrees C). This study demonstrates the technical feasibility of this BioDeNO(x) concept in a bench-scale installation with a continuous flue gas flow of 650 l.h(-1) (70-500 ppm NO; 0.8-3.3% O(2)). Stable NO removal with an efficiency of at least 70% was obtained in case the artificial flue gas contained 300 ppm NO and 1% O(2) when the bioreactor was inoculated with a denitrifying sludge. An increase of the O(2) concentration of only 0.3% resulted in a rapid elevation of the redox potential (ORP) in the bioreactor, accompanied by a drastic decline of the NO removal efficiency. This was not due to a limitation or inhibition of the NO reduction, but to a limited biological iron reduction capacity. The latter leads to a depletion of the NO absorption capacity of the scrubber liquor, and thus to a poor NO removal efficiency. Bio-augmentation of the reactor mixed liquor with an anaerobic granular sludge with a high Fe(III) reduction capacity successfully improved the bioreactor efficiency and enabled to treat a flue gas containing at least 3.3% O(2) and 500 ppm NO with an NO removal efficiency of over 80%. The ORP in the bioreactor was found to be a proper parameter for the control of the ethanol supply, needed as electron donor for the biological regeneration process. The NO removal efficiency as well as the Fe(III)EDTA(-) reduction rate were found to decline at ORP values higher than -140 mV (pH 7.0). For stable BioDeNO(x) operation, the supply of electron donor (ethanol) can be used to control the ORP below that critical value.

Removal of NOx from lean exhaust gas by storage/reduction on H3PW12O40 x 6H2O supported on Ce(x)Zr4-xO8.

We have demonstrated the interest of using Zr-Ce mixed oxides as supports for the system H3PW12O40 x 6H2O (HPW) and Pt for the storage (absorption into HPW and adsorption on Zr-Ce support)-reduction of NOx. Zr-Ce oxides adsorb NOx (mainly NO2) as nitrates, which are desorbed thermally as NO2 and NO (12 mg of NOx x g(-1)). On (HPW-Pt)/Zr-Ce system, NO and NO2 are stored equimolarly by substitution of water molecules of the HPW structure. The Zr/Ce support molar ratio has an important influence on the quantity of NOx stored with a maximum for the system Zr/Ce = 0.5. The presence of Pt has no influence on storage capacity but rather on its efficiency, and it is essential when reducing. Pt strongly accelerates both NOx desorption and reduction processes. Reduction of NOx occurs with H2, CO, or an H2/CO mixture. With H2, NO2 is reduced to NO. With CO, it seems reasonable that the mechanism of NO2 reduction concerns its reaction with CO to produce CO2 and NO. Addition of H2 to CO accelerates the reduction process. However, the difference between NOx stored and desorbed implies also the presence of another reduction step. This could be related to an NO interaction with an active site which produces its decomposition with nitrogen as product. The catalytic system proposed is highly selective since no N2O formation was detected.

Biological removal of NOx from flue gas.

BioDeNOx is a novel integrated physico-chemical and biological process for the removal of nitrogen oxides (NOx) from flue gas. Due to the high temperature of flue gas the process is performed at a temperature between 50-55 degrees C. Flue gas containing CO2, O2, SO2 and NOx, is purged through Fe(II)EDTA2- containing liquid. The Fe(II)EDTA2- complex effectively binds the NOx; the bound NOx is converted into N2 in a complex reaction sequence. In this paper an overview of the potential microbial reactions in the BioDeNOx process is discussed. It is evident that though the process looks simple, due to the large number of parallel potential reactions and serial microbial conversions, it is much more complex. There is a need for a detailed investigation in order to properly understand and optimise the process.

Simultaneous removal of nitrogen oxide/nitrogen dioxide/sulfur dioxide from gas streams by combined plasma scrubbing technology.

Oxides of nitrogen (NOx) [nitrogen oxide (NO) + nitrogen dioxide (NO2)] and sulfur dioxide (SO2) are removed individually in traditional air pollution control technologies. This study proposes a combined plasma scrubbing (CPS) system for simultaneous removal of SO2 and NOx. CPS consists of a dielectric barrier discharge (DBD) and wet scrubbing in series. DBD is used to generate nonthermal plasmas for converting NO to NO2. The water-soluble NO2 then can be removed by wet scrubbing accompanied with SO2 removal. In this work, CPS was tested with simulated exhausts in the laboratory and with diesel-generator exhausts in the field. Experimental results indicate that DBD is very efficient in converting NO to NO2. More than 90% removal of NO, NOx, and SO2 can be simultaneously achieved with CPS. Both sodium sulfide (Na2S) and sodium sulfite (Na2SO3) scrubbing solutions are good for NO2 and SO2 absorption. Energy efficiencies for NOx and SO2 removal are 17 and 18 g/kWh, respectively. The technical feasibility of CPS for simultaneous removal of NO, NO2, and SO2 from gas streams is successfully demonstrated in this study. However, production of carbon monoxide as a side-product (approximately 100 ppm) is found and should be considered.

Removal of NOx from flue gas with radical oxidation combined with chemical scrubber.

In this paper, removal of NOx (namely DeNOx) from flue gas by radical injection combined with NaOH solution (26% by weight of NaOH in water) scrubbing was investigated. The experimental results showed that the steady streamer corona occurs through adjusting the flow rate of the oxygen fed into the nozzles electrode. The vapor in the oxygen has influence on the V-I characteristics of corona discharge. Both HNO2 and HNO3 come into being in the plasma reactor and the DeNOx efficiency in the plasma reactor is more than 60%. The overall DeNOx efficiency of the whole system reaches 81.7% when the NaOH solution scrubbing is collaborated.

Removal of NOx from flue gas with iron filings reduction following complex absorption in ferrous chelates aqueous solutions.

A novel process for removal of nitrogen oxides (NOx) from flue gases with iron filings reduction following complex absorption in iron-ethylenediaminetetraacetic acid aqueous solution is proposed. The reaction mechanism involved in the process is discussed briefly. The parameters influencing the process, including the concentration of ferrous chelates, initial pH, amount of iron filings, temperature, flow rate of the flue gas, and inlet nitric oxide concentration and oxygen content of the flue gas, are researched in detail. The optimal NOx removal conditions are established. The regeneration and circular utilization of the absorption solution also is studied.