Nitric Oxide Removal Efficiency Research Articles

Assessment of the Bacterial Community for Denitrifying Removal of Nitric Oxide in a Rotating Drum Biofilter by Denaturing Gradient Gel Electrophoresis

The emission of nitric oxide (NO) to the atmosphere is a major environmental problem. To abate NO emission from the industrial flue gas, a rotating drum biofilter (RDB) was developed for the denitrifying removal of NO. After the start-up period, the RDB could effectively remove NO from the waste gas and the denitrifying removal efficiency could reach 85%. After the addition of CuII(EDTA) to the nutrients, the removal efficiency could increase to 99.1%. To improve the understanding of the relationship between the composition of bacterial population and the performance of the RDB, a denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction-amplified genes coding for 16S rRNA was used to analyze and determine the changes in bacterial communities in the RDB. Results showed that there was a slight change in microbial diversity after the addition of CuII(EDTA) to the nutrient solution, which led to an increase in NO removal efficiency. Eight major bands of 16S rRNA gene fragments obtained from the DGGE gels of biofilm samples were further purified, reamplified, cloned, and sequenced. Phylogenetic analysis identified sixteen types of micro-organisms in the RDB. Sequences of these fragments were compared with those listed in the database of the GeneBank (National Center for Biotechnology Information). Gene analysis of 16S rRNA showed that the major populations were Clostridium sp., β-proteobacterium, γ-proteobacterium, and Cytophaga-Flexibacteria-Bacteroides (CFB) groups. In addition, it was concluded that denitrification was caused by the organism with DNA represented by bands labelled G-5, G-6, and G-8. G-5 was related to a γ-proteobacterium, whereas those labeled G-6 and G-8 were related to a β-proteobacterium.

Photocatalytic activity of titanium dioxide modified concrete materials – Influence of utilizing recycled glass cullets as aggregates

Combining the use of photocatalysts with cementitious materials is an important development in the field of photocatalytic air pollution mitigation. This paper presents the results of a systematic study on assessing the effectiveness of pollutant degradation by concrete surface layers that incorporate a photocatalytic material – Titanium Dioxide. The photocatalytic activity of the concrete samples was determined by photocatalytic oxidation of nitric oxide (NO) in the laboratory. Recycled glass cullets, derived from crushed waste beverage bottles, were used to replace sand in preparing the concrete surface layers. Factors, which may affect the pollutant removal performance of the concrete layers including glass color, aggregate size and curing age, were investigated. The results show a significant enhancement of the photocatalytic activity due to the use of glass cullets as aggregates in the concrete layers. The samples fabricated with clear glass cullets exhibited threefold NO removal efficiency compared to the samples fabricated with river sand. The light transmittance property of glass was postulated to account for the efficiency improvement, which was confirmed by a separate simulation study. But the influence of the size of glass cullets was not evident. In addition, the photocatalytic activity of concrete surface layers decreased with curing age, showing a loss of 20% photocatalytic activity after 56-day curing.

Dynamic model for nitric oxide removal by a rotating drum biofilter

To illustrate the process of nitric oxide (NO) denitrifying removal by a novel rotating drum biofilter (RDB), a dynamic model has been developed and further validated. Based on the mass component profile of NO at the gas–liquid interface combined with a Monod kinetic equation, the model was used to depict the mass transfer-reaction process of NO in RDB, focusing on the concentration distribution of NO in the gas, liquid, and biofilm phases. The NO distribution equation on the biofilm carrier was thereby achieved, as well as a dynamic model for NO elimination in the test system. Additionally, effects of operating parameters such as inlet NO concentration and empty-bed residence time on NO removal efficiency were evaluated through a sensitivity analysis of the model. The model was then modified taking the absorption of NO by nutrition liquid in the bottom of RDB into consideration. The results showed that the simulated data agreed well with the experimental data. The model made it possible to simulate a relatively high NO removal efficiency by RDB.

Modeling and Experimental Study on Nitric Oxide Treatment Using Dielectric Barrier Discharge

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, nonthermal plasma technology was used to remove nitric oxide (NO) from a mixture of air and water vapor. A chemical model was developed to obtain NO removal mechanism and to observe the behavior of the species in the plasma discharge. The influence of water vapor addition on NO removal efficiency was also investigated. Results obtained from the model indicate that the NO removal is mainly achieved by chemical reactions with <formula formulatype="inline"><tex>$\hbox{O}^{\bullet}$</tex></formula>, <formula formulatype="inline"><tex>$ \hbox{N}^{\bullet}$</tex></formula>, and <formula formulatype="inline"><tex>$\hbox{OH}^{\bullet}$</tex></formula> radicals. Experimental results of the NO removal process in a dielectric barrier discharge are also presented. Several experimental parameters such as power, frequency, initial concentration of NO, and specific input energy were tested, and a <formula formulatype="inline"><tex>$\hbox{NO}_{x}$</tex></formula> removal efficiency of approximately 98% was achieved. </para>

The effects of selected parameters on the nitric oxide removal by biofilter

A bench-scale biofilter was used to demonstrate the treatability of off-gas containing nitric oxide (NO) by examining selected operational parameters. After 6 days of operation, the biofilter reached to a steady state and NO reduction was significant, reducing from 200 ppm to 95 and 40 ppm after 6 and 40 days of continuous operation. The oxygen concentrations in the inlet would affect NO removal performance significantly; as oxygen content decreasing from 6% to 0%, the NO removal efficiency increased from 55% to 99%, indicating that oxygen inhibited the progress of denitrification. NO removal was inversely proportional to inlet NO concentration, removal efficiency decreased from 88% to 40 % as NO concentration increasing from 60 to 500 ppm. Column height would significant effect on the NO removal efficiency, under column height = 6.5 m and O 2 = 6% conditions, 90% of removal efficiency was achievable. The effect of glucose added into biofilter would significantly enhance the NO removal efficiencies for both anaerobic and aerobic conditions of which 99% and 55%, respectively.

Ultrasound-Induced Aqueous Removal of Nitric Oxide from Flue Gases: Effects of Sulfur Dioxide, Chloride, and Chemical Oxidant

The effects of sulfur dioxide (SO(2)), sodium chloride (NaCl), and peroxymonosulfate or oxone (2KHSO(5).KHSO(4).K(2)SO(4) with active ingredient, HSO(5)(-)) on the sonochemical removal of nitric oxide (NO) have been studied in a bubble column reactor. The initial concentration of NO studied ranged from about 500 to 1040 ppm. NaCl in the concentration range of 0.01-0.5 M was used as the electrolyte to study the effect of ionic strength. At the low NaCl concentration (0.01 M), the percent fractional removal of NO with initial concentration of 1040 ppm was enhanced significantly, while as the NaCl concentration increased, the positive effects were less pronounced. The presence of approximately 2520 ppm SO(2) in combination with 0.01 M NaCl further enhanced NO removal. However, with a NO initial concentration of 490 ppm, the addition of NaCl was detrimental to NO removal at all NaCl concentration levels. The combinative effect of sonication and chemical oxidation using 0.005-0.05 M oxone was also studied. While the lower concentrations of HSO(5)(-) enhanced NO removal efficiency, higher concentrations were detrimental depending on the initial concentration of NO. It was also demonstrated that in the presence of ultrasound, the smallest concentration of oxone was needed to obtain optimal fractional conversion of NO.

Denitrification removal of nitric oxide in a rotating drum biofilter

A rotating drum biofilter (RDB) was applied and evaluated for nitric oxide (NO) removal by denitrification from a synthesized waste gas using glucose as carbon source. The effects of drum-rotating speed and empty bed residence time (EBRT) on NO removal were investigated under anaerobic conditions . With the increase of drum-rotating speed higher than 0.5 rpm and the decrease of EBRT at a certain feed loading rate, there existed a lower NO removal efficiency influenced by mass transfer. At an EBRT of 65 s and a drum-rotating speed of 0.5 rpm, NO removal efficiency was over 97.9% with inlet NO concentration of 524 ppm. When oxygen existed, NO was removed as the function of denitrification of the main role and chemical oxidation. With the increase of inlet oxygen concentration, denitrification decreased and chemical oxidation increased and the optimal inlet oxygen concentration of about 5.2% was obtained.

Mechanisms of NOx Removal from Flue Gas by Zero Valent Iron

Chemical reaction between nitric oxide (NO) and zero valent iron (ZVI) was studied in a packed-bed column process with high temperatures based on ZVI strong reducing abilities. For six controlled temperatures of 523–773 K and 400 ppm of NO (typical flue gas temperature and concentration), under short empty bed contact time ([EBCT] 0.0226–0.0679 sec), NO was completely removed for temperature of 573–773 K but not for 523 K. Breakthrough curves were conducted for the five working temperatures, and the results indicated that NO reductions by ZVI were varied from 2 to 26.7 mg NO/g ZVI. Higher temperature and longer EBCT achieved better NO removal efficiency. X-ray diffraction (XRD) and electron spectroscopy for chemical analysis (ESCA) were conducted to analyze the crystal structure and oxidation state of the reacted ZVI. Three layers of iron species were detected by XRD: ZVI, Fe3O4, and Fe2O3. ZVI was the most prevalent species, and Fe3O4 and Fe2O3 were less from the XRD analysis. By ESCA, the oxidation state on the reacted ZVI surface was determined, and the species was identified as Fe2O3, which is the most oxidizing species for iron. Therefore, three layers from the ZVI core to the ZVI surface can be identified: ZVI, Fe3O4, and Fe2O3. Combining the results from XRD and ESCA, the mechanisms for ZVI and NO can be proposed as two consecutive reactions from lower oxidation state (ZVI) in the core to higher oxidation state on the iron surface (Fe2O3): (A1) and (A2) Because there was only <5% ZVI used to remove NO comparing to theoretical ZVI used based on the proposed stoichiometry, it can be concluded that the heterogeneous reaction only occurred on the ZVI surface instead of on bulk of the ZVI.

Performance evaluation of biofilters packed with carbon foam and lava for nitric oxide removal

Long-term (>8 months) results of nitric oxide (NO) removal in biofilters, respectively, packed with lava and two different pore sizes of carbon foam (24pores/cm (PPC) and 18 PPC) were measured. During the operation, NO removal efficiency, pressure drops, pH dependence and removal profile were evaluated. NO removal efficiencies were above 93.8%, 79.4% and 58.6% in the biofilters, respectively, packed with 24 PPC carbon foam, 18 PPC carbon foam and lava. The lava-packed biofilter demonstrated higher buffer capacity for change of pH. However, with sufficient nutrient and buffer solution feeding, the biofilter packed with carbon foam showed a higher NO removal efficiency. The pressure drops of the biofilter packed with carbon foam did not exceed 11mmH2O/m. The low-pressure drops made it possible by using carbon foam as packing to conveniently prevent the clogging and channeling problems associated with conventional biofilter operations.

DeNOx Study in Diesel Engine Exhaust Using Barrier Discharge Corona Assisted by V2O5/TiO2 Catalyst

A plasma-assisted catalytic reactor was used to remove nitrogen oxides (NOx) from diesel engine exhaust operated under different load conditions. Initial studies were focused on plasma reactor (a dielectric barrier discharge reactor) treatment of diesel exhaust at various temperatures. The nitric oxide (NO) removal efficiency was lowered when high temperature exhaust was treated using plasma reactor. Also, NO removal efficiency decreased when 45% load exhaust was treated. Studies were then made with plasma reactor combined with a catalytic reactor consisting of a selective catalytic reduction (SCR) catalyst, V2O5/TiO2. Ammonia was used as a reducing agent for SCR process in a ratio of 1:1 to NOx. The studies were focused on temperatures of the SCR catalytic reactor below 200°C. The plasma-assisted catalytic reactor was operated well to remove NOx under no-load and load conditions. For an energy input of 96 J/l, the NOx removal efficiencies obtained under no-load and load conditions were 90% and 72% respectively at an exhaust temperature of 100°C.

Simultaneous removal of NO and SO2 with hexamminecobalt(II) solution coupled with the hexamminecobalt(II) regeneration catalyzed by activated carbon

The wet ammonia desulfurization process can be retrofitted for combined removal of SO2 and NO from the flue gases by adding soluble cobalt(II) salt into the aqueous ammonia solution. Activated carbon is used to catalyze the reduction of hexamminecobalt(III) to hexamminecobalt(II) to maintain the capability of removing NO of the hexamminecobalt solution. The effects of temperature, pH, activated carbon particle size, and superficial liquid flow velocity on hexamminecobalt(III) conversion have been investigated. An apparent activation energy is obtained. According to the experimental results, the catalytic reduction reaction rate increases with temperature. The batch reactor experiments show that the best pH range lies in between 3.5 and 6.5. In a fixed-bed reactor, superficial liquid flow velocity obviously affects the reaction and a high yield of cobalt(II) is obtained at a pH value lower than 9.0. The experiments manifest that the hexamminecobalt solution coupled with catalytic regeneration of hexamminecobalt(II) can maintain a high nitric oxide removal efficiency during a period of time.

Influence of copper content on NO removal of the activated carbon fibers produced by electroplating.

In this study, the activated carbon fibers (ACFs) on which copper metal was deposited by electroplating were used to remove nitric oxide (NO). N(2)/77 K adsorption isotherm characteristics, including the specific surface area and micropore volume, were investigated by BET and T-plot methods. NO removal efficiency was confirmed by gas chromatographic technique. From the experimental results, the copper content supported on ACFs led to an increase in the NO conversion, in spite of the decrease of the specific surface area or the micropore volume of ACFs. Consequently, the presence of Cu on ACFs played an important role in improving the NO reduction into O(2) and N(2), which was mainly attributed to the catalytic reactions of Cz-NO-Cu.

Hollow-Fiber Membrane Bioreactor for Nitric Oxide Removal

This research evaluates the use of a hollow-fiber membrane bioreactor (HFMB) to remove nitric oxide (NO) from combustion gases. In the HFMB, gases containing NO pass through the lumen of microporous hydrophobic hollow-fiber membranes. NO diffuses through membrane pores and partitions into a nitrifying biofilm where it is oxidized to NO3- and other products. The hollow-fiber membranes serve as a support for the microbial population and provide a large surface area for NO and oxygen mass transfer. In this project, nitrifying bacteria were enriched from activated sludge with a liquid NH4+/NO2- feed. After acclimation, an NO/air mixture was introduced to the HFMB at room temperature. NO removal and nitrification rates were investigated at varying liquid velocities. A maximum removal efficiency of 74% was attained at a liquid velocity of 1.5 cm s-1. The effects of gas composition and temperature on mass transfer and biodegradation were investigated using a synthetic combustion gas (15% CO2, 5% O2, 75% N2, 100 ppm NO) at temperatures between 20°C and 55°C. NO removal efficiency was maintained at approximately 70% regardless of gas composition or temperature. Only 9 to 12% of the eliminated nitrogen was recovered as nitrate nitrogen in the effluent. This may have been due to concurrent nitrification/denitrification using an endogenous carbon source.

Studies on nitric oxide removal in simulated gas compositions under plasma-dielectric/catalytic discharges

Application of pulsed electrical discharges for gas cleaning is gaining prominence, mainly from the energy consideration point of view. This present paper presents recent work on applying the electrical discharge plasma technology for treating gaseous pollutants, in general, and nitric oxide, in particular, as this is one of the major contributors to air pollution. The present work focuses attention on pulsed electrical discharge technique for nitric oxide removal from simulated gas compositions and study of effect of packed dielectric pellets, with and without a coating of catalyst, on the removal process. Experiments were conducted in a cylindrical corona reactor energized by repetitive high voltage pulses. The effects of various parameters, viz. pulse voltage magnitude, pulse frequency, initial nitric oxide concentration and gas mixture composition on nitric oxide removal efficiency, are discussed. When the reactors were filled with different dielectric pellets like, barium titanate, alumina, and alumina coated with palladium catalyst, the improvement in nitric oxide removal efficiency is studied and discussed. The power dissipated in the reactor and the energy consumed per nitric oxide molecule removed was calculated. Further results and comparative study of various cases are presented in the paper.

Oxygen effects on thermophilic microbial populations in biofilters treating nitric oxide containing off‐gas streams

AbstractElectricity generation from coal has increased by an average of 51 billion kWh per year over the past 3 years. For this reason cost‐effective strategies to control nitrogen oxides (NOx) from coal‐fired power plant combustion gases must be developed. Compost biofilters operated at 55°C at an empty bed contact time (EBCT) of 13 seconds were shown to be feasible for removal of nitric oxide (NO) from synthetic flue gas. Denitrifying microbial populations in these biofilters were shown to reduce influent NO feeds by 90 to 95% at inlet NO concentrations of 500 ppmv. Oxygen was shown to have a significant effect on the NO removal efficiency demonstrated by these biofilters. Two biofilters were set up under identical conditions for the purpose of monitoring NO removal as well as changes in the microbial population in the bed medium under anaerobic and aerobic conditions. Changes in the microbial population were monitored to determine the maximum oxygen tolerance of a denitrifying biofilter as well as methods of optimizing microbial populations capable of denitrification in the presence of low oxygen concentrations. Nitric oxide removal dropped to between 10 and 20% when oxygen was present in the influent stream. The inactive compost used to pack the biofilters may have also caused the decreased NO removal efficiency compared to previous biofiltration experiments. Analysis of the bed medium microbial population using environmental scanning electron microscopy indicated significant increases in biomass populating the surface of the compost when compared to unacclimated compost.

Simultaneous SOx /NOx removal in a fluidized bed reactor using natural manganese ore

AbstractIn this experiment, the simultaneous removal of SO2 and NO from flue gases was investigated through the use of natural manganese ore as a sorbent‐catalyst in a fluidized bed reactor. Selective catalytic reduction behavior was determined as a function of the sulfation degree within the temperature range from 100 °C to 500 °C. The natural manganese ore showed a high activity in the production of nitrogen and water by the reaction of nitric oxide with ammonia and oxygen up to around 200 °C. At higher temperatures, the nitric oxide removal efficiency decreased due to the oxidation of ammonia by oxygen. With the increase of sulfation degree, the temperature at which the maximum selective catalytic reduction of nitric oxide appears gradually increased, however the maximum nitric oxide removal efficiency decreased. Additionally, we investigated the removal efficiency of sulfur dioxide and nitric oxide with reaction time in a batch fluidized bed reactor within a temperature range of 350 °C to 500 °C. As the reaction temperature increased, the adsorption capacity of sulfur dioxide increased, but the nitric oxide removal efficiency decreased.© 2001 Society of Chemical Industry

Influence of gas flow rate and reactor length on NO removal using pulsed power

A short duration of 100-ns pulsed power has been used to remove nitric oxide (NO) in a mixture of nitrogen, oxygen, water vapor, and NO, simulating flue gases from a power station. The effects of the gas flow rate, the reactor length, and the pulse repetition rate on the percentage of NO removal and its energy efficiency are reported. The percentage of NO removal at a fixed gas flow rate increased with increasing pulse repetition rate due to the increased energy into the discharge. At a fixed pulse rate, the removal of NO increased with decreasing gas flow rate due to the increased residence time of the gas in the discharge reactor, thus facilitating the creation of increased radicals of O and N which then decreased NO. The energy removal efficiency of NO (in mol/kWh) decreased with increasing gas flow rate and increasing removal ratio of NO. The removal of NO increased with increasing energy density (J/I), input into the discharge at different reactor length.

Plasma-Assisted Removal of NO from Gas Streams via Ammonia Injection

Removal of nitric oxide (NO) from gas streams via combined NH3 injection with dielectric barrier discharge (DBD) plasmas was experimentally investigated. Removal of NO was principally achieved via its reaction with NHi radicals generated with DBD plasmas. Removal efficiency of NO was measured as a function of stoichiometric ratio, applied voltage, and inlet NO concentration of the gas stream. Experimental results showed that as much as 80% of NO was removed from gas streams operating at room temperature. Increase in NH3/NO molar ratio and applied voltage enhances NO removal efficiency. NO removal efficiency decreases slightly as oxygen content in the gas stream increases from 0% to 6%, indicating the characteristic of selective reduction in this process. However, 15 ppmv N2O was detected with Fourier transform infrared for gas streams containing 6% by volume O2 and 300 ppmv NO. Results of this study indicated that conventional SNCR process could be operated at a much lower temperature by applying plasma technology to generate NHi radicals. Key words: Plasma; dielectric barrier discharge; NOx removal; selective reduction; NH3 injection

Performance of silica-supported copper oxide sorbents for SO x/NO x-removal from flue gas : II. Selective catalytic reduction of nitric oxide by ammonia

The selective catalytic reduction (SCR) of nitric oxide by ammonia was studied for silica-supported copper oxide particles to be used as a sorbent/catalyst in a continuous process for the simultaneous removal of SO x and NO x from flue gases. The SCR-behaviour was determined as a function of the sulphation degree, i.e. the fraction of copper oxide converted to copper sulphate, at temperatures ranging from 20 to 450°C. Up to 350°C, the fresh catalyst with 0% CuSO 4 showed a high selectivity towards production of nitrogen and water by the reaction of nitric oxide with ammonia and oxygen. At higher temperature, nitric oxide removal efficiencies decreased due to the oxidation of ammonia by oxygen. With an increase of the sulphation degree, the maximum temperature for selective catalytic reduction of nitric oxide gradually increased up to 420°C for a sulphation degree of 80%. In addition, the maximum nitric oxide removal efficiency increased as well. After regeneration of catalyst particles with a sulphation degree of 80%, realised by reduction with hydrogen and subsequent re-oxidation, the catalytic behaviour was similar to that of fresh catalyst particles with a sulphation degree of 5%. This is ascribed to the formation of some Cu 2S during the reduction, which is oxidised to CuSO 4 in the subsequent oxidation step. Since the selectivity towards the reduction of nitric oxide with ammonia is maintained up to about 375°C, a temperature which is very suitable for SO x removal as well, the silica-supported CuO investigated can be applied as a sorbent/catalyst for the simultaneous removal of SO x and NO x from flue gases. The reaction rate constants for SO x and NO x removal appeared to be of the same order of magnitude provided that the reduced sorbent/catalyst enters the absorber directly, i.e. without a separate pre-oxidation.