Reducing nitric oxide into nitrogen via a radio-frequency discharge

Complexing agents-free bioelectrochemical trickling systems for highly-efficient mesothermal NO removal: The role of extracellular polymer substances

The biological treatments are promising for nitric oxide (NO) reduction, however, the biotechnology has long suffered from high demands of NO-complexing agents (i.e., Fe(II)EDTA), leading to extra operation costs. In this study, novel complexing agents-free bioelectrochemical systems have been developed for direct NO reduction. The electricity-driven bioelectrochemical trickling system (ED-BTS, a denitrifying biocathode driven by the external electricity and an acetate-consuming bioanode) achieved approximately 68% NO removal without any NO-complexing agents, superior to the bioanode-driven BTS and open-circuit BTS. The extracellular polymeric substances from the biofilms of ED-BTS contained more polysaccharides, humic substrates, and hydrophobic tryptophan that were beneficial for NO reduction. Additionally, the external electricity altered the microbial community toward more denitrifying bacteria and a higher abundance of NO reduction genes (nosZ and cnorB). This study provides a comprehensive understanding of microbial behaviors on the adsorption and reduction of NO and proposes a promising strategy for mesothermal NO biotreatment.

Study on NO Removal Characteristics of the Fe(II)EDTA and Fe(II)PBTCA Composite System

Fe²⁺ complexation wet denitrification technology has become a research hotspot. It is very important to achieve efficient regeneration of the absorbent and increase NO absorption in the Fe²⁺ complexation system. They are the key to the industrial application of the Fe²⁺ complexation absorption process. In this paper, 2-phosphonate-butane-1,2,4-tricarboxylic acid and ethylenediamine tetraacetic acid were used as ligands to prepare a composite system for the first time. The characteristics of NO removal were investigated under different temperatures, pHs, Fe²⁺ concentrations, O₂ contents, NO concentrations, CO₂ contents, and SO₂ concentrations. Compared with the single ligand, the results show that the denitrification performance of the solution with a complex ligand is significantly improved. In this system, pH 9, 40 °C temperature, and 20 mmol/L Fe²⁺ concentration are the economic ideal conditions for NO removal. The system can realize simultaneous removal of NO and SO₂, but SO₂ in flue gas has a dual effect on the NO removal reaction.

Simultaneous removal of NOx and SO2 from flue gas using combined Na2SO3 assisted electrochemical reduction and direct electrochemical reduction

A method combining Na2SO3 assisted electrochemical reduction and direct electrochemical reduction using Fe(II)(EDTA) solution was proposed to simultaneously remove NOx and SO2 from flue gas. Activated carbon was used as catalyst to accelerate the process. This new system features (a) direct conversion of NOx and SO2 to harmless N2 and SO4(2-); (b) fast regeneration of Fe(II)(EDTA); (c) minimum use of chemical reagents; and (d) recovery of the reduction by-product (Na2SO4). Fe(II)(EDTA) solution was continuously recycled and reused during entire process, and no harmful waste was generated. Approximately 99% NOx and 98% SO2 were removed under the optimal condition. The stability test showed that the system operation was reliable.

Removal dynamics of nitric oxide (NO) pollutant gas by pulse-discharged plasma technique

Nonthermal plasma technique has drawn extensive attentions for removal of air pollutants such as NO_x and SO₂. The NO removal mechanism in pulse discharged plasma is discussed in this paper. Emission spectra diagnosis indicates that the higher the discharge voltage is, the more the NO are removed and transformed into O, N, N₂, NO₂, and so forth. Plasma electron temperature T_e is ranged from 6400 K at 2.4 kV discharge voltage to 9500 K at 4.8 kV. After establishing a zero-dimensional chemical reaction kinetic model, the major reaction paths are clarified as the electron collision dissociation of NO into N and O during discharge and followed by single substitution of N on NO to form N₂ during and after discharge, compared with the small fraction of NO₂ formed by oxidizing NO. The reaction directions can be adjusted by N₂ additive, and the optimal N₂/NO mixing ratio is 2 : 1. Such a ratio not only compensates the disadvantage of electron competitive consumption by the mixed N₂, but also heightens the total NO removal extent through accelerating the NO oxidization process.

Nitric oxide decomposition using atmospheric pressure dielectric barrier discharge reactor with different adsorbents

An NO removal rate of 99% and energy efficiency of 99.4 g NO per kW h were obtained on NaY zeolite using the adsorption–desorption and decomposition process in a self-made coaxial cylinder-type dielectric barrier discharge reactor.

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 additives on the selectivity of byproducts and dry removal of fluorine for abating tetrafluoromethane in a discharge reactor

The removal efficiency of tetrafluoromethane (CF(4)) was significantly enhanced by adding additives (H(2), O(2), H(2)+O(2), H(2)O) in an atmospheric-pressure microwave plasma reactor. However, large amounts of fluorine (F(2)) were produced in this study. Moreover, the selectivity of F(2) was apparently greater than that of HF (in H(2)-based condition) or COF(2) (in O(2)-based abatement). Notably, in an O(2)-rich environment, more F(2) and a larger amount of CO(2) were produced. Subsequently, F(2) can be effectively removed by reacting with CaO to form CaF(2) at 200 degrees C via an in situ dry, chemical absorption process in the low-temperature afterglow discharge zone within the same plasma reactor.

Formation of fluorine for abating sulfur hexafluoride in an atmospheric-pressure plasma environment

In this study, a large amount of toxic and reactive fluorine (F(2)) was produced in the atmospheric-pressure microwave discharge environment by adding additives to abate sulfur hexafluoride (SF(6)). When H(2) was added, the selectivity of F(2) was as high as 89.7% at inlet H(2)/SF(6) molar ratio (R(H2)) = 1. Moreover, the conversion of SF(6) significantly increased from 33.7% (without additive) to 97.7% (R(H2) = 5) at [SF(6)]=1%, and 0.8 kW because the addition of H(2) inhibited the recombination of SF(6). With the addition of O(2), H(2)+O(2) or H(2)O, the selectivity of F(2) was still greater than 81.2%, though toxic byproducts, including SO(2)F(2), SOF(2), SOF(4), SO(2), NO, and HF, were detected. From optical emission spectra, SF(2) was identified, revealing the SF(6) dissociation process might be carried out rapidly through an electron impaction reaction: SF(6)-->SF(2)+4F. Subsequently, F(2) was formed via the recombination of F atoms.