Process for reducing nitrogen oxides through biological treatment

Abstract

The present invention relates to a process for reducing nitrogen oxides through biological treatment, in particular to a method for removing NOx gas from a gas stream (4), the method comprising: i) contacting a solvent system comprising a non-aqueous phase liquid (NAP) capable of acting as a NOx gas-liquid mass transfer vector with the gas stream (4); and ii) subjecting the solvent system of step i) to denitrification by microorganisms, wherein the NOx is selected from nitric oxide (NO), nitrogen dioxide (NO 2 2), and mixtures thereof, and the NAP has a molecular weight of 150 to 550 g / mol and a boiling point of 400 to 700 K. The present invention also relates to the use of NAP for removing NOx gas from a gas stream.

Description

Technical Field

[0001] This application claims the benefit of European Patent Application No. 22382501.9, filed on May 25, 2022.

[0002] The present invention relates to the technical field of NOx removal from exhaust gases. In particular, the present invention relates to a process for reducing nitrogen oxides through a biological treatment using a non-aqueous phase liquid (NAP) as a NOx gas-liquid mass transfer vector.

Background Art

[0003] Worldwide production and industrial use of artificial nitrogen fertilizers, combustion of fuels, and agriculture have led to a significant acceleration of the nitrogen cycle that causes chemical changes in the atmosphere due to increased emissions of trace nitrogen gases such as nitrogen oxides (NOx) and ammonia (NH 3 ) As a result, in the past few decades, only 30-60% of the non-reactive nitrogen species (Nr) produced were due to natural processes.

[0004] Approximately 90-95% of the NOx present in combustion exhaust gases is composed of NO, and the remaining 5-10% is NO 2 . In terms of air quality, high emissions of NOx contribute to both eutrophication and acidification of ecosystems and can lead to adverse health effects such as chronic bronchitis, asthma, and chronic obstructive pulmonary disease. As a result, government agencies are imposing increasingly strict regulations regarding the emissions of these pollutants.

[0005] Strategies developed to control industrial NOx emissions include pretreatment of feedstocks and changes to the combustion process, both of which act as preventive measures aimed at minimizing NOx emissions. Nevertheless, due to the stricter air quality laws and the high concentrations of NOx that can be generated by the combustion process, it is necessary to implement post-treatment or end-of-pipe technologies in which NOx is removed from the flue gas after its formation in the combustion chamber.

[0006] Currently, the main physicochemical post-treatment technologies used to control NOx emissions from combustion gases include selective non-catalytic reduction (SNCR), selective catalytic reduction (SCR), wet and dry scrubbing, and adsorption. However, some of these technologies have drawbacks such as high operating or equipment costs, and significant environmental impacts due to the large amounts of harmful waste (secondary pollutants) they generate that cannot be used in the manufacture of valuable products.

[0007] Biological treatment of NOx is currently attracting attention as an alternative to conventional physicochemical technologies because they are cost-effective, reduce the generation of secondary pollutants, and are thus more environmentally sustainable. The most widely studied biological technology for NOx treatment is biofiltration. This technology is based on the application of nitrification and denitrification processes.

[0008] However, when biofiltration is applied to the removal of NO with very low solubility in water, a relatively long contact time (more than 1 minute) is required to obtain good removal efficiency, resulting in a large reactor volume. For this reason, several alternative processes have been developed to enhance the mass transfer of NO and optimize the performance of the bioreactor.

[0009] One of the bio-based alternative processes is the chemical absorption and biological reduction (CABR) process, which includes a pre-step of biological reduction of NO that performs a chemical absorption or complexation step through the use of a mass transfer vector or chelating agent. Also, technologies such as the membrane bioreactor (MBR) commonly used in water treatment have been implemented. In addition to changing the types of reactors and processes, researchers have also studied various bio-based alternative processes. These include microalgae that use NO as a nitrogen source, and anaerobic ammonium-oxidizing bacteria (Anammox®) that can use NO as an electron acceptor.

[0010] For CABR systems, the most widely used chelating agent is Fe(II)EDTA 2-It is. This compound reacts with NO to form a nitrosyl complex. However, in addition to the complex formation reaction, the presence of oxygen oxidizes Fe(II)EDTA 2- so that another undesirable reaction occurs to produce Fe(III)EDTA - which does not bind to NO. A further drawback of this system is that the chelating agents need to be regenerated before they can be reused. Despite the fact that other studies have focused on other iron chelating agents, there is no evidence in the literature that bio-based technologies using iron complexes have been implemented on an industrial scale, presumably due to the instability of the chelating agents. Furthermore, cobalt-based complexes have also been studied as an option for NO complex formation. However, only a few batch experiments have been conducted and none have been carried out at pilot scale.

[0011] Furthermore, the ability of silicone oil as a mass transfer vector for enhancing nitrous oxide (N 2 O) removal in a denitrification batch assay using a Paracoccus denitrificans culture as the inoculum material is also disclosed in Chapter 7 (2018) of the doctoral thesis of Osvaldo Frutos. However, the authors concluded that no significant enhancement was observed in N 2 O removal regardless of the proportion of silicone oil used. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0012] Therefore, it is derived from what is known in the art that there is still a need to provide a process for removing NOx from flue gas that overcomes the problems of the prior art and can be used on an industrial scale. MEANS FOR SOLVING THE PROBLEMS

[0013] The inventors have found that a non-aqueous phase liquid (NAP) having a specific molecular weight and boiling point is CO 2can be effectively used as a NOx gas-liquid mass transfer vector in the presence of CO 2 As shown in the examples, it has been found that they do not significantly interfere with the selectivity of NAP. Therefore, they are useful for removing NOx gas from gas streams such as flue gas, with high efficiency, particularly in a chemical absorption - biological reduction (CABR) system.

[0014] Furthermore, the NAPs used in the method of the present invention have the advantage that they are not toxic and can therefore be used safely. They are also biocompatible with the microorganisms commonly used in the biological reduction step. Additionally, some of them are short-term non-biodegradable and slightly biodegradable in the long term, and do not cause any reactions when acting as NOx mass transfer vectors. Moreover, their immiscibility with the microbial-containing phase facilitates their separation and recovery. Therefore, they can be directly reused after use without the need to regenerate them.

[0015] Therefore, a first aspect of the present invention relates to a method for removing NOx gas from a gas stream, the method comprising: i) contacting a solvent system comprising a non-aqueous phase liquid (NAP) capable of acting as a NOx gas-liquid mass transfer vector with the gas stream; ii) subjecting the solvent system of step i) to denitrification by microorganisms, wherein NOx is selected from nitric oxide (NO), nitrogen dioxide (NO 2 ), and mixtures thereof, and the NAP has a molecular weight of 150 - 550 g / mol and a boiling point of 400 - 700 K at 101300 Pa.

[0016] A second aspect of the present invention relates to the use of a non-aqueous phase liquid (NAP) for removing NOx gas from a gas stream, particularly in a chemical absorption - biological reduction (CABR) system, wherein the NAP can act as a NOx gas-liquid mass transfer vector, has a molecular weight of 150 - 550 g / mol, a boiling point of 400 - 700 K at 101300 Pa, and a water solubility of 0.1 g / L or less at 298 K and 101300 Pa, and NOx is nitric oxide (NO), nitrogen dioxide (NO 2) and is selected from those and their mixtures.

Brief Description of the Drawings

[0017]

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Mode for Carrying Out the Invention

[0018] All terms used in this application shall be understood in their ordinary meanings known in the relevant technical field, unless otherwise specified. Other more specific definitions of the specific terms used in this application are as described below and are intended to apply uniformly throughout this specification and the entire scope of the claims.

[0019] The term "about" or "approximately" as used in this specification refers to a range of values of ±10% of the specified value. For example, the expressions "about 10" or "approximately 10" include ±10% of 10, that is, 9 to 11.

[0020] The expression "substituted with one or more ~" means that the group can be substituted with one or more, preferably 1, 2, 3, or 4 substituents, as long as the group has sufficient positions where substitution is likely.

[0021] For the purpose of the present invention, the room temperature is 20 to 25 °C.

[0022] “(C 10 ~C 20 ) hydrocarbon” refers to a saturated or unsaturated, branched or straight-chain hydrocarbon chain containing 10 to 20 carbon atoms and optionally one or more double bonds and / or one or more triple bonds. Thus, the term “(C 10 ~C 20 ) hydrocarbon” includes “(C 10 ~C 20 ) alkane”, “(C 10 ~C 20 ) alkene”, and “(C 10 ~C 20 ) alkyne”. This also includes hydrocarbon chains containing single bonds, double bonds, and triple bonds.

[0023] “(C 10 ~C 20 ) alkane” refers to a saturated, branched or straight-chain hydrocarbon chain containing 10 to 20 carbon atoms and only single bonds. Non-limiting examples of alkane groups include n-decane, n-undecane, n-dodecane, n-hexadecane, n-heptadecane, or n-octadecane. “(C 10 ~C 20 ) alkene” refers to an unsaturated, branched or straight-chain hydrocarbon chain containing 10 to 20 carbon atoms and at least one double bond. “(C 10 ~C 20 ) alkyne” refers to an unsaturated, branched or straight-chain hydrocarbon chain containing 10 to 20 carbon atoms and at least one triple bond.

[0024] “(C 1 ~C n) The term "alkyl" refers to a saturated branched or straight-chain hydrocarbon chain containing 1 to n carbon atoms and only single bonds. Non-limiting examples of alkyl groups include methyl, ethyl, propyl, butyl, isopropyl, 1-methylpropyl, 2-methylpropyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, or dodecyl.

[0025] The term "halogen" means fluoro, chloro, bromo, or iodo.

[0026] As used herein, "di(C 1 ~C 10 )alkyl(C 1 ~C 10 )ester" refers to a saturated or unsaturated branched or straight-chain (C 1 ~C 10 )hydrocarbon chain as defined above, with both ends of the chain substituted with -COO(C 1 ~C 10 )alkyl radicals. Non-limiting examples of di(C 1 ~C 10 )alkyl(C 1 ~C 10 )ester groups include diethyl sebacate or dioctyl sebacate.

[0027] As used herein, "(C 1 ~C 12 )ketone" refers to a saturated or unsaturated branched or straight-chain (C 1 ~C 10 )hydrocarbon chain as defined above, whose chemical structure contains a -CO- moiety. Non-limiting examples of (C 1 ~C 12 )ketones include 2-decanone or 2-undecanone.

[0028] As used herein, the term "siloxane" refers to a branched or linear organosilicon oxide polymer, also known as an organopolysiloxane, containing the repeating structural unit -(R 2 -Si-O)-, where R is a monovalent organic radical (e.g., (C1 ~C 6 )alkyl, such as methyl, or C 6 aryl, such as phenyl), and the terminal group is a trimethylsilyl group (-Si(CH 3 )) 3 ). Non-limiting examples of siloxanes include 1,1,1,3,5,5,5-heptamethyltrisiloxane or silicone oil.

[0029] As used herein, the term "chemisorption - biological reduction (CABR) system" refers to an integrated system that includes an absorption tank for chemisorbing NOx from a gas stream and a biological reduction step, in particular, a bioreactor for performing denitrification by microorganisms that convert the absorbed nitrogen species to elemental nitrogen.

[0030] As described above, the first aspect of the present invention relates to a method for removing NOx gas from a gas stream. As used herein, the term "method for removal" refers to a method for complete or partial removal (i.e., reduction in the initial amount) of NOx from a gas stream.

[0031] According to one particular embodiment, optionally in combination with one or more features of the various embodiments described above or below, the NOx contained in the gas stream is completely removed by the process of the present invention.

[0032] According to another particular embodiment, optionally in combination with one or more features of the various embodiments described above or below, 40 - 100 mol%, more specifically 60 - 100 mol%, even more specifically 90 - 100 mol% of the NOx is removed from the gas stream, where % is expressed as the number of moles relative to the total number of moles of NOx initially contained in the gas stream.

[0033] For the purposes of the present invention, as used herein, the term "gas stream" refers to any gas stream, such as flue gas containing undesirable NOx, and the term "NOx" relates to nitric oxide (NO), nitrogen dioxide (NO 2 ), or mixtures thereof.

[0034] In one particular embodiment, optionally in combination with one or more features of the various embodiments described above or below, the gas stream is a multi-component gas mixture, and more specifically the gas stream is carbon dioxide (CO 2 ), oxygen (O 2 ), nitrogen (N 2 ), sulfur oxides (SOx), and nitrogen oxides (NOx), and even more specifically, the gas stream is a flue gas stream.

[0035] As used herein, the term "flue gas" refers to the exhaust gas from any type of combustion process (including, for example, coal, oil, natural gas, petrochemical compounds, waste, or biomass). Typically, a flue gas stream contains 4% - 13% (v / v) carbon dioxide (CO 2 ), 2% - 10% (v / v) oxygen (O 2 ), 77% - 82% (v / v) nitrogen (N 2 ), 0.01% - 0.03% (v / v) nitrogen oxides (NOx), and 0.01% - 0.05% (v / v) sulfur oxides (SOx), where % is expressed as v / v relative to the total volume of the gas mixture (Jin et al., 2005). The compounds contained in the flue gas and their concentrations can vary depending on the fuel composition, combustion system, and operating conditions such as temperature and pressure.

[0036] In one particular embodiment, optionally in combination with one or more features of the various embodiments described above or below, the initial gas stream contains NOx in an amount of 0.005% (v / v) - 0.1% (v / v), particularly 0.01 - 0.05 (v / v) mol% relative to the total number of moles of the gas stream. In a more specific embodiment, the NOx consists of NO. In another more specific embodiment, the NOx consists of a mixture of NO and NO 2 , and even more specifically the NOx consists of a mixture of NO and NO 2 , and the molar ratio of NO:NO 2 is 90:10 - 95:5.

[0037] The first step of the process of the present invention involves contacting a gas stream with a solvent system comprising a non-aqueous phase liquid (NAP) that can act as a NOx gas-liquid mass transfer vector.

[0038] For the purposes of the present invention, the term "NOx gas-liquid mass transfer vector" refers to a liquid substance (i.e., NAP) that can take up or absorb NOx from a gas stream, whereby a significant concentration of NOx (i.e., an amount of 50 mol% or more, particularly 60% or more, relative to the initial content) or NOx contained in the gas stream is completely removed and absorbed into this liquid substance (NAP). A person skilled in the art can readily determine whether a substance is a NOx mass transfer vector by conducting an absorption test that includes contacting a gas stream containing NOx with the substance and measuring the resulting NOx content in the gas stream, as shown in the examples below.

[0039] According to one particular embodiment, optionally in combination with one or more features of the various embodiments described above or below, the NOx absorption capacity of the NAP is at least 0.1 mol NOx / kmol NAP, more specifically 0.1 - 1 mol NOx / kmol NAP, and even more specifically 0.1 - 0.6 mol NOx / kmol NAP.

[0040] As used herein, the term "NOx absorption capacity" refers to the amount of a given NAP required to absorb a given amount of NOx and is expressed as the number of moles of NOx absorbed per kmol of NAP. A person skilled in the art can readily measure the absorption capacity of the NAP by contacting a gas stream containing NOx with a specific amount of NAP and measuring the NOx absorbed, as disclosed in the examples herein. The NOx absorbed corresponds to the value obtained by subtracting the final amount of NOx from the initial amount of NOx contained in the gas stream.

[0041] As used herein, the term "non-aqueous phase liquid (NAP)" refers to an organic liquid having a molecular weight of 150 to 550 g / mol and a boiling point of 400 to 700 K at 101300 Pa. Non-limiting examples of NAP include diethyl sebacate (CAS RN: 110-40-7), 2,2,4,4,6,8,8-heptamethylnonane (CAS RN: 4390-04-9), 1,1,1,3,5,5,5-heptamethyltrisiloxane (CAS RN: 1873-88-7), n-hexadecane (CAS RN: 544-76-3), n-dodecane (CAS RN: 112-40-3), 2-undecanone (CAS RN: 112-12-9), n-heptadecane (CAS RN: 629-78-7), n-octadecane (CAS RN: 593-45-3), silicone oil (CAS RN: 63148-62-9), dioctyl sebacate (CAS RN: 2432-87-3), or perfluoromethyldecalin (CAS RN: 306-92-3).

[0042] In one particular embodiment, optionally in combination with one or more features of the various embodiments described above or below, the NAP has a molecular weight of 170 to 530 g / mol, more specifically 200 to 520 g / mol, more specifically 210 to 430 g / mol, and even more specifically 220 to 410 g / mol.

[0043] In another particular embodiment, optionally in combination with one or more features of the various embodiments described above or below, the NAP has a boiling point of 400 to 700 K at 101300 Pa, more specifically 405 to 600 K, even more specifically 410 to 590 K, and even more specifically 415 to 585 K.

[0044] The NAP used in the method of the present invention is slightly miscible or immiscible in water. If the NAP is immiscible in water, it has the advantage of facilitating phase separation from water. In one particular embodiment, optionally in combination with one or more features of the various embodiments described above or below, the NAP has a water solubility of 0.1 g / L or less, 0.01 g / L or less, 0.0002 g / L or less, 0.0000006 or less, or 0.0000001 g / L or less at 298K and 101300 Pa.

[0045] According to one particular embodiment, optionally in combination with one or more features of the various embodiments described above or below, the NAP has a molecular weight of 150 to 550 g / mol, a boiling point of 400 to 700 K at 101300 Pa, and a water solubility of 0.1 g / L or less at 298K and 101300 Pa, and the NOx is selected from nitric oxide (NO), nitrogen dioxide (NO 2 ), and mixtures thereof.

[0046] In another embodiment, optionally in combination with one or more features of the various embodiments described above or below, the NAP is non-polar. For the purposes of the present invention, the term "non-polar" NAP refers to a NAP that does not act as a proton donor. Generally, non-polar substances have a low HLB (hydrophilic-lipophilic balance) value, particularly 8 or less, more specifically 4 or less, and even more specifically 2 or less.

[0047] In another particular embodiment, optionally in combination with one or more features of the various embodiments described above or below, the NAP is optionally a (C 10 ~C 20 ) hydrocarbon substituted with one or more halogen atoms, a di(C 1 ~C 10 ) alkyl (C 1 ~C 10 ) ester, a (C 1 ~C 12 ) ketone, a siloxane, a perfluoromethyl decalin, and mixtures thereof. More specifically, the NAP is optionally a (C 10 ~C 20)Hydrocarbons, di(C 1 ~C 10 )alkyl(C 1 ~C 10 )selected from the group consisting of esters, siloxanes, and mixtures thereof. More specifically, NAP is selected from the group consisting of 2,2,4,4,6,8,8-heptamethylnonane, n-hexadecane, 1,1,3,3,5,5-hexamethyltrisiloxane, and diethyl sebacate.

[0048] The solvent system used in the process of the present invention may contain only NAP or a mixture of NAP and a liquid phase. In one particular embodiment, optionally in combination with one or more features of the various embodiments described above or below, the solvent system consists of NAP. In another particular embodiment, optionally in combination with one or more features of the various embodiments described above or below, the solvent system contains NAP and a liquid phase. More specifically, the concentration of NAP in the liquid phase is 1 to 60% (v / v), more specifically 2 to 30% (v / v), even more specifically 5 to 10% (v / v) based on the total volume of the solvent system. When present, the aqueous solution may be composed of water or a buffer such as a phosphate buffer or a carbonate buffer.

[0049] The second step of the process involves subjecting the solvent system of step i) containing NOx to denitrification by microorganisms. Denitrification by microorganisms is a process well known in the art. Denitrification occurs when nitrate (NO 3 - ) or nitrite (NO 2 - ) is converted to N 2 gas. This is a reduction process that is thought to occur in four steps: NO 3 - to NO 2 - , NO 2 - to NO, NO to N 2 O, and N 2 O to N 2 , (Niu and Leung, 2010). Thus, NO can be used as an electron acceptor, whereby denitrifying bacteria convert N under anoxic conditions2 It can reduce NO to NO.

[0050] Any denitrification method by microorganisms known in the art, for example, the method disclosed in the following examples, can be used in the second step of this process. Those skilled in the art will be able to determine the specific and optimal assay conditions for denitrification by performing ordinary experiments.

[0051] Microorganisms that can be used in the denitrification step include heterotrophic bacteria of the genera Pseudomonas, Alcaligenes, and Bacillus. Non-limiting examples of microorganisms include Pseudomonas denitrificans, Deferribacter thermophilus (DSM14813), Denitrovibrio acetophilus (DSM12809), Bacillus infernus (DSM10277), Bacillus simplex (DSM1321), Bacillus thermodenitrificans (DSM465), and Bacillus azotoformans (DSM1046).

[0052] Generally, the denitrification step can be carried out in the presence of denitrifying biomass, which is a biomass containing denitrifying microorganisms as disclosed herein. The term "biomass" as used herein refers to a mixture of microorganisms containing several genera with specific detectable microbial activity (metabolism). In the process of the present invention, biomass from different sources can be used to obtain the inoculum material used in the present invention. Those skilled in the art know how to obtain denitrifying biomass, for example, from wastewater treatment plant sludge, sewage sludge, or a bioreactor, by using ordinary methods for concentrating denitrifying biomass, such as supplying nitrite as the sole electron acceptor in an anaerobic sequential batch reactor, as described in the examples.

[0053] According to one specific embodiment, optionally in combination with one or more features of the various embodiments described above or below, denitrification by microorganisms is carried out in the presence of a liquid phase under anoxic conditions by the action of microorganisms capable of producing elemental nitrogen. More specifically, the microorganisms capable of producing elemental nitrogen are in the form of biomass, and the volatile suspended solids (VSS) content is 500 - 5000 mg per liter of the liquid phase, more specifically 1000 - 2000 mg. In a more specific embodiment, the biomass is obtained from the anoxic treatment of wastewater.

[0054] For the purposes of the present invention, the term "anoxic conditions" is generally used herein to refer to the absence of oxygen and the presence of nitrogen species as electron acceptors for microbial metabolism. The term "volatile suspended solids (VSS)" used herein refers to a specific method of quantifying biomass by assimilating the biomass into the volatile portion of the suspended solids, and the volatile portion is the portion that burns out when the total suspended solids are ignited at about 500 - 550 °C.

[0055] Normally, external nutrients for biomass growth, such as external carbon sources, usually compounds such as acetic acid, glucose, lactic acid, or VOCs such as toluene, are used for denitrification (Flanagan et al., 2002).

[0056] According to one specific embodiment, optionally in combination with one or more features of the various embodiments described above or below, the carbon source is added to the biomass such that the atomic ratio of carbon from the carbon source to nitrogen in the nitrate (C:N) is 1:1 - 6:1, more specifically 1:1 - 3:1.

[0057] In one specific embodiment, optionally in combination with one or more features of the various embodiments described above or below, step ii) is carried out at a temperature of 5 - 40 °C, more specifically 20 - 30 °C.

[0058] In one particular embodiment, optionally in combination with one or more features of the various embodiments described above or below, step ii) is carried out at a pH of 6.5 to 9, more specifically 8.0 to 8.5.

[0059] According to another embodiment, optionally in combination with one or more features of the various embodiments described above or below, the method of the present invention is carried out under a pressure in the range of atmospheric pressure (about 101325 Pa) to 161325 Pa, more specifically under substantially atmospheric pressure (101325 Pa).

[0060] According to another embodiment, optionally in combination with one or more features of the various embodiments described above or below, the method of the present invention further comprises step iii) of recovering NAP after step ii) by separating NAP from the microorganisms, in particular by using, for example, a decanter or a sedimentation tank. The recovered NAP can also be reused in a new process for removing NOx from a gas stream.

[0061] The process of the present invention can be implemented in various configurations. Thus, steps i) and ii) are carried out in a single reactor or, alternatively, in different reactors.

[0062] When steps i) and ii) are carried out in different reactors, there are no particular restrictions on the pH or temperature conditions under which step i) can be carried out as long as NAP is not decomposed. In contrast, when the two steps of the method of the present invention are carried out in the same single reactor, the pH and temperature conditions of the reactor are adapted to the action of the microorganisms.

[0063] According to one particular embodiment, optionally in combination with one or more features of the various embodiments described above or below, steps i) and ii) of the method of the present invention are carried out in a single reactor that acts simultaneously as an absorption tank and a bioreactor. More specifically, the temperature of the reactor is 5 to 40 °C, more specifically 20 to 30 °C, and the pH is 6.5 to 9, more specifically 8.0 to 8.5.

[0064] In another specific embodiment, optionally in combination with one or more features of the various embodiments described above or below, steps i) and ii) of the method of the present invention are carried out in different reactors. More specifically, step i) is carried out in an absorption tank at a temperature of 5 to 60 °C, more specifically 20 to 30 °C, and a pH of 4 to 9, more specifically 6.5 to 8.5, and step ii) is carried out in a bioreactor at a temperature of 5 to 40 °C, more specifically 20 to 30 °C, and a pH of 6.5 to 9, more specifically 8.0 to 8.5.

[0065] Two non-limiting examples of possible configurations are shown in FIGS. 8 and 9. In the embodiment shown in FIG. 8, there is physical separation of the absorption of the initial gas stream (e.g., combustion exhaust gas) and subsequent biological treatment of the effluent. The gas (4) to be treated enters a gas-liquid contactor (absorption tank (1)), where the contaminant NOx is transferred from the gas phase to the liquid phase using the mass transfer vector (NAP) as defined herein. The resulting effluent (6) contains the contaminant to be treated and NAP and enters the bioreactor (2). A sedimentation tank (3) is used to separate NAP from the biomass sludge, where NAP (10) is recycled to the absorption tank and the biomass (8) is recycled to the bioreactor.

[0066] In the embodiment shown in FIG. 9, the flue gas (3) passes through a non-biodegradable packing material (1) through which an aqueous solution having a mass transfer vector (NAP) is continuously recycled to supply the nutrients necessary for the activity and growth of microorganisms. Further, gas / liquid mass transfer occurs. A decanter (2) is used to separate NAP from the biomass, where NAP (8) is recycled to the apparatus.

[0067] Throughout the description and claims, the words "comprising", "including" and variations thereof are not intended to exclude other technical features, additives, components or steps. Further, the words "comprising", "including" include the case of "consisting of". Further objects, advantages and features of the present invention will become apparent to those skilled in the art upon examination of the description or will be understood by practice of the invention. The following examples are provided by way of illustration and are not intended to limit the present invention. Reference signs in parentheses in the claims, which are related to the drawings, are intended solely to enhance the understanding of the claims and are not to be construed as limiting the scope of the claims. Further, the present invention covers all possible combinations of the specific preferred embodiments described herein.

[0068] Examples Chemical substances and gases NAP: n-hexadecane (HEX, purity 99%, CAS: 544-76-3), diethyl sebacate (DES, purity 98%, CAS: 110-40-7), 1,1,1,3,5,5,5-heptamethyl-trisiloxane (HTX, purity 97%, CAS: 1873-88-7), 2,2,4,4,6,8,8-heptamethylnonane (HNO, purity 98%, CAS: 4390-04-9), and high-temperature silicone oil (SO, purity 97%, CAS: 63148-52-7) of the highest available purity grade were purchased from Sigma Aldrich (Lyon, France). Nitric oxide (N 2 20% in) and nitrogen were purchased from Linde Gas Espana (Rubí, Catalonia, Spain). CO 2 (≧99.998%) was purchased from Nippon gases Euro-Holding S.L.U (Barcelona, Catalonia, Spain).

[0069] Biomass and growth conditions (nitrate / nitrite-reducing bacteria, NRB) The denitrifying biomass used in this study was taken from an 8-liter Sequencing Batch Reactor (SBR) inoculated with biomass from the anaerobic treatment of a municipal wastewater treatment plant (WWTP) in Manresa, Spain. After inoculation, the denitrifying bacteria were grown in a Sequencing Batch Reactor (SBR) configured to run two 12-hour cycles for two months. Each cycle had a fill time of 13 minutes, an anaerobic reaction time of 11 hours and 15 minutes, a sedimentation time of 30 minutes, and a discharge time of 2 minutes. The reactor also had a pH control system set to pH 8 by adding 1 M HCl. At steady state, the reactor had a total NO of 0.8 g / L 2 - 、1.2 g / L of C 2 H 3 NaO 2 ·3H 2 O, 0.016 g / L of KH 2 PO 4 、0.041 g / L of CaCl 2 、and 1 mL of a trace element solution (0.15 g / L of H 3 BO 3 、0.03 g / L of CuCl 2 ·2H 2 O, 0.18 g / L of KI, 0.12 g / L of MnCl 2 ·4H 2 O, 0.06 g / L of NaMoO 4 ·2H 2 O, 0.12 g / L of ZnSO 4 ·7H 2 O, 0.15 g / L of CoCl 2 ·6H 2 O, and 10 g / L of EDTA.Na 2 O 8 ·2H 2 O).

[0070] 1. Experimental Setup 1.1. Absorption of Nitric Oxide (NO) by Pure NAP Batch tests with pure NAP were conducted in 120 mL amber glass vials with an initial NO concentration of 4500 - 5100 ppmv and different amounts of NAP (DES, SO, HTX, HNO, and HEX). In this experiment, each NAP was added to the vial containing NO. Each NAP was tested individually. The results were compared with a blank containing deionized water instead of NAP. All experiments were carried out in an incubator at 25 °C with stirring at 100 rpm, in quintuplicate for each point. Gas phase analysis (NO and NO 2 ) was performed at the start and end (1 hour) of the experiment.

[0071] 1.2. Absorption of Nitric Oxide (NO) in the Liquid Phase by NAP Batch tests of NAP in contact with the liquid phase were carried out in 500 mL amber glass bottles. The tests were performed using water and phosphate buffer at pH 8 at different ratios of NAP / liquid phase (5, 10, and 20% v / v). An initial NO concentration of 4500 - 6000 ppmv was used. The vials and bottles were pre - prepared in a glove box to maintain an inert atmosphere. In this experiment, each NAP - water or NAP - buffer mixture was added to the vial containing NO. All experiments were carried out in an incubator at 25 °C with stirring at 100 rpm, in triplicate. The results were compared with a blank (deionized water or buffer without NAP). The NO and NO 2 concentrations in the gas phase were measured at the start and end (1 hour) of the test. Also, the liquid phase was monitored for pH, NO 2 - , and NO 3 - at the end of each test.

[0072] 1.3. Toxicity and Short - Term Biodegradation Tests by Denitrifying Bacteria Toxicity and biodegradability tests were carried out using an AER - 500 respirometer (Challenge technology (registered trademark)) to measure N 2 production in the denitrification process. The tests were performed in an inert atmosphere (N 2) It was carried out in a 500 mL glass bottle using 300 mL of biomass from SBR with a solid content concentration of 0.95 TSS / L.

[0073] The toxicity test was carried out by injecting 10 mL of a solution containing an excess amount of carbon source (21.75 g / L of C 2 H 3 NaO 2 ·3H 2 O, 11 g / L of NaNO 2 , 0.4 g / L of KH 2 PO 4 , 1.025 g / L of CaCl 2 , and 25 mL of trace element solution). After injecting the solution, when the N 2 produced by denitrification became stable, 50 mL of each NAP was injected into the bottle. Each test was carried out in duplicate and using a control without NAP.

[0074] The short-term biodegradability test was carried out by injecting 5 mL of a solution with a limited carbon source (7.25 g / L of C 2 H 3 NaO 2 ·3H 2 O, 11 g / L of NaNO 2 , 0.4 g / L of KH 2 PO 4 , 1.025 g / L of CaCl 2 , and 25 mL of trace element solution). After injecting the inorganic medium, when it was observed that the bacteria were producing N 2 , 10 mL of each NAP was injected into the bottle and N 2 was monitored for 6 hours. The test was carried out in duplicate and using a control without NAP.

[0075] 1.4. Long-term biodegradability test The final biochemical oxygen demand (BOD) (long-term biodegradability) test was performed using an OxiDirect® BOD measurement device according to the description of the OECD guideline (301F) for testing chemicals in a respirometry manometric test. The control oxygen consumption due to the pressure change over 28 days was measured.

[0076] The test was conducted in 500 mL glass bottles using 1 mL of biomass from an SBR with a final solids concentration of 0.007 TSS / L, 156 mL of the inorganic medium described in the OECD guideline, and 175 mg of HEX, 169 mg of HNO4, 88 mg of HTX, 66 mg of DES, and 66 mg of SO.

[0077] 1.5. Chemical Absorption and Biological Reduction - CABR Test The CABR batch test was conducted in 120 mL amber glass vials pre-filled with N 2 The experimental conditions were a temperature of 25 °C and stirring at 100 rpm. Four replicates were performed for each point. An initial NO concentration of 4500 - 6000 ppmv was used. Three experiments were conducted with varying relationships between biomass and NAP. In the first experiment, 20 mL of biomass with a concentration of 1.09 g / L was introduced, followed by 2.5 mL of HTX, HNO, and HEX into the same vial. In the second experiment, the biomass concentration was increased to 1.88 g / L and 2.5 mL of NAP was introduced. In the last experiment, 2.7 g / L of biomass and 1 mL of each NAP were injected. The concentrations of NO and NO 2 in the gas phase were measured at the start and end of the test. Also, the liquid phase was monitored for pH, NO 2 - and NO 3 - at the end of each test.

[0078] 1.6. Gas-Liquid Mass Transfer Test in a Two-Phase System (CO 2 / NAP) A gas-liquid mass transfer batch test was conducted to determine the mass transfer rate of CO 2 in the presence of NAP. The first sample was at 6200 - 7100 cm-1 until reaching the transmittance peak area of 2 and then injecting 10 mL of each NAP (HTX, HNO, and HEX). The results were compared with a blank (phosphate buffer at pH 8 instead of NAP). Since preliminary studies found that the phase equilibrium within the system reached within 1 hour, the test time was 1 hour. CO 2 in the gas phase was measured at the start and end of the test. All experiments were conducted in 500 mL amber glass bottles pre-prepared in a glove box to maintain an inert atmosphere, and at least triplicates were performed in an incubator at a temperature of 25 °C and an orbital shaking of 100 rpm.

[0079] 1.7. Gas-liquid mass transfer batch tests in a two-phase system (CO 2 / NO / NAP) CO 2 Gas-liquid mass transfer batch tests with a gas mixture containing CO -1 and NO were conducted to determine the mass transfer rates and selectivities of these gases in the presence of NAP. The first sample was filled with CO 2 until reaching the transmittance peak area of 6388 - 8018 cm -1 and then filled with NO until reaching the transmittance peak area of 73 - 84 cm 2 and then 10 mL of each NAP (HTX, HNO, and HEX) was injected. CO

[0080] 1.8. Gas-liquid mass transfer batch tests in a three-phase system (CO 2 / NO / liquid phase / NAP) CO 2A gas-liquid mass transfer batch test with a gas mixture containing CO and NO was conducted to determine the mass transfer rates and selectivities of these gases in the presence of NAP and the liquid phase. The results were compared with a blank (water or a pH 8 phosphate buffer without NAP). The first sample was filled with CO until reaching the transmittance peak area of 8010 - 8940 cm -1 and then with NO until reaching the transmittance peak area of 11 - 14 cm 2 . Then, 10 mL of each NAP (HTX, HNO, and HEX) was injected. The tests were conducted with a NAP / liquid phase ratio of 10% v / v in a pH 8 phosphate buffer. All experiments were carried out in 500 mL amber glass bottles pre-prepared in a glove box to maintain an inert atmosphere, and at least in triplicate with an orbital shaking of 100 rpm at a temperature of 25 °C in an incubator. The CO -1 and NO in the gas phase were measured at the start and end of the test. Also, the liquid phase was monitored for pH, nitrite (NO 2 ), and nitrate (NO 2 - ) at the end of each test. 3 -

[0081] 2. Analytical Procedures 2.1. Chemical Analysis The concentrations of NO and NO 2 in the gas phase were measured by Fourier transform infrared spectroscopy (FTIR) from a 1 mL aliquot (PerkinElmer Inc., Spain). The removal efficiency of NO in the test was calculated from the difference in NO concentrations at the start and end of each test. The nitrogen compounds and chemical oxygen demand (COD) were analyzed in the liquid sample after centrifugation at 15,000 rpm and filtration (0.22 μm) to separate the NAP found in the sample. Nitrite and nitrate were measured using Hach Lange kits (LCK342 and LCK339 respectively, Hach Lange, Germany). COD was measured using Hach Lange kits (LCK114 and LCK214 respectively, Hach Lange, Germany).

[0082] NO and CO in the gas phase​2 The peak area of 2 was measured by Fourier transform infrared spectroscopy (FTIR). In these experiments, the peak area rather than the concentration was analyzed. Therefore, the test was carried out in terms of the area reduction rate (%), as defined in Equation 1. The nitrogen compounds were analyzed in the liquid sample after centrifugation at 15,000 rpm and filtration (0.22 μm) to separate the NAP found in the sample. NO 2 - and NO 3 - were measured using Hach Lange kits (LCK342 and LCK339, respectively, Hach Lange, Germany).

Number

[0083] The initial area (AREA initial ) is a quantitative measure of the transmittance at a given wavelength (NO = 1730 - 1930 cm -1 , CO 2 = 2230 - 2400 cm -1 ) and correlates with the presence of the compound in the sample at time = 0 h. The final area (AREA final ) is a quantitative measure of the transmittance at the given wavelength (NO = 1730 - 1930 cm -1 , CO 2 = 2230 - 2400 cm -1 ) and correlates with the presence of the compound in the sample at time = 1 h.

[0084] 2.2. Microbial community analysis One sample of the inoculum material in the steady state was taken from the steady state SBR denitrification reactor. DNA extraction from the sample was performed using the DNeasy PowerSoil Pro kit (Qiagen, Germany) according to its principle and handling instructions, and two variable regions (V3, V4) of the 16S rRNA gene were stored at -70 °C. Polymerase chain reaction (PCR) amplification was carried out using the custom-designed fusion primers shown in Table 1.

Table 1

[0085] Bovine serum albumin (BSA) was added to the PCR reaction to neutralize potential inhibitors. PCR products, called amplicons or libraries, were visualized on a 2% agarose gel, purified using the NucleoSpin kit (Macherey-Nagel, Berlin, Germany), and quantified using an Agilent 2100 Bioanalyzer (Agilent Technologies, Santa Clara, CA, USA) and an Agilent High Sensitivity DNA kit (Agilent Technologies). Finally, an equimolar mixture (60 pM) of samples in three pools was prepared and sequenced in three runs. From the equimolar mixture of libraries, the Ion 520 & Ion 530 Kit-Chef (Life Technologies, Carlsbad, CA, USA) and xip 530 were used for sequencing each sample group. Sequencing was performed on a Life Technologies GeneStudio S5 instrument using 850 flows per run. Analysis was performed using QIIME (2-2020.8).

[0086] 2.3. Denitrification ability - qPCR and gene expression The same samples used for the study of the microbiota were used for the study of denitrification gene expression. RNA extraction was performed using the RNeasy PowerSoil Total RNA kit (Qiagen, Germany) according to its principle and handling instructions, and stored at -70 °C until analysis. Three pairs of primers were synthesized from the primer sets shown in Table 2 to selectively amplify the nirS, CnorB, and nosZ genes.

Table 2

[0087] In the table above, Y is C or T, R is A or G, V is A or C or G, H is A or C or T, B is C or G or T, and N is A, C, G, or T (IUPAC nucleotide code). The RNA sample was reverse transcribed using a commercially available polymerase (Super script IV (18090050)), and all three genes were evaluated by real-time quantitative PCR using Thermofisher polymerase, sybrgreen, and an Applied biosystems 7900HT quantitative PCR kit.

[0088] 3. Results 3.1. Absorption of Nitric Oxide (NO) by Pure NAP Figure 1 shows the first screening test. Oxidation of NO to NO 2 was found when using HEX, HTX, HNO, and SO as mass transfer vectors. Furthermore, regarding diethyl sebacate, there was no evidence of an oxidation reaction of NO but there was evidence of an absorption reaction. The best result was obtained with HTX, which had a NO removal efficiency of 49.2% under the research conditions, followed by HEX with a NO removal efficiency of 29.2%.

[0089] Figure 2 shows the gas-phase removal of NO in the presence of pure SO, DES, HTX, HNO, and HEX when increasing the molar concentration of each mass transfer vector. Increasing the molar concentration of various NAPs led to greater removal of NO, thus indicating that the limit of NO removal is due to the amount of absorbent added to the system. HTX, HNO, and HEX reached similar NO removal by adding 0.076, 0.070, and 0.068 moles of absorbent, respectively.

[0090] 3.2. Absorption of Nitric Oxide (NO) in the Liquid Phase by NAP Figures 3 and 4 show the NO absorption when NO was contacted with a mixture of NAP in the liquid phase (water or buffer) at different NAP concentrations. For most of the NAPs, it was observed that the NO absorption was improved when the liquid phase was mixed with the NAP compared to the NAP in its pure state.

[0091] The NAPs that gave the best results in the liquid phase were DES, HTX, and HNO. Furthermore, no significant differences in absorption were observed among them, even when buffer or water was added.

[0092] 3.3. Toxicity tests with denitrifying bacteria All the NAPs studied were found to be non-toxic to denitrifying bacteria in the short-term test.

[0093] 3.4. Biodegradability tests Short-term biodegradability tests showed that all NAPs except DES were non-biodegradable. Furthermore, silicone oil did not decompose in the 28-day test, and hexadecane, heptamethyltrisiloxane, and heptamethylnonane were found to decompose only 8%, 7%, and 1% respectively in the 28-day test. This test also confirmed that DES is completely biodegradable under anoxic and aerobic conditions. However, the decomposed DES is used by denitrifying bacteria as a carbon source.

[0094] 3.5. Chemical Absorption and Biological Reduction - CABR tests Based on the results of abiotic and biotic tests, three absorbents (HEX, HNO, and HTX) were selected to study the integration of chemical absorption and biological NO reduction systems. As shown in Figure 5, it was shown that NO removal improved in the short term (30 minutes or 1 hour) when three mass transfer vectors and enriched denitrifying bacteria were added. It was also observed that increasing the biomass concentration from 1.09 g / L to 1.88 g / L increased NO removal. For example, NRB-HTX reached 100% NO removal efficiency in 3 hours at a biomass concentration of 1.88 g / L, while at 1.09 g / L it only reached 72% NO removal efficiency.

[0095] Furthermore, Figures 6 - 7 show that there was no accumulation of nitrite and nitrate in the system containing NRB-HTX, indicating that NO was converted to NO 2is oxidized, followed by mass transfer from the gas phase to the liquid phase, and it is converted to nitrite or nitrate, and the denitrifying bacteria consume it in their metabolic processes and convert it to nitrogen gas (N 2 ), which is evidence. It has also been proven that there is no accumulation in this system for HEX and HNO.

[0096] 3.6. Microbial community analysis The microbial community structure was analyzed to examine the species present in the CABR test (Example 1.5). In descending order, Thauera (14.37%), Flavobacterium (13.87%), Acinetobacter (7.90%), Cyclobacteriacea (6.41%), Fusibacter (4.41%), Pseudomonas (3.19%), Dechloromonas (2.40%), Rhodobacteraceae (2.25%), Alishewanella (1.75%), and Saprospiraceae (1.74%) were dominant in the samples. It was found that the dominant species in this system were denitrifying bacteria. Thauera, Flavobacterium, and Rhodobacteraceae have been reported as aerobic denitrifying bacteria and may not be inhibited by oxygen. Also, the genera Pseudomonas and Acinetobacter contain the most commonly isolated denitrifying bacteria.

[0097] 3.7. Denitrification ability - qPCR and gene expression As shown in Table 3, the most common gene detected was nosZ. The genera with higher expression of this gene were Thauera, Flavobacterium, and Pannonibacter. The presence of all three genes (nosZ, nirS, and CnorB) was confirmed in Pseudomonas. The genera Streptococcus, Bacillus, Legionella, Streptomyces, and Corynebacterium were found to have the CnorB gene.

Table 3

[0098] This study demonstrates that when all genes are expressed, complete denitrification occurs in the system. It has to be said that even if a certain gene exists in the genome, it is not always expressed. That is, the presence of a gene in the genome does not necessarily indicate its expression because the expression of a certain gene occurs at a given time point or under specific stimuli.

[0099] 3.8. Two-phase systems (CO 2 / NAP) and (CO 2 / NO / NAP) gas-liquid mass transfer tests Figure 10 shows the CO 2 area reduction rate in tests in a two-phase system containing pure CO 2 gas (black) and a gas mixture of NO and CO 2 (gray). The NAP that gave the best results for the peak area reduction of gas-phase CO 2 was HTX (99 ± 0.2% without the gas mixture, 97 ± 0.9% with the NO / CO 2 gas mixture). From these values, it can be concluded that no significant difference was observed when NO was absent from the system. The other two NAPs (HEX and HNO) were found to have a lower CO 2 area percentage difference than the phosphate blank (22 ± 2%). The CO 2 peak area difference reached in the presence of HEX was 11 ± 3% without the gas mixture and 15 ± 2% with the NO / CO 2 gas mixture, and in the presence of HNO, it was 18 ± 3% without the gas mixture and 13 ± 0.3% with the NO / CO 2 gas mixture.

[0100] Figure 11 shows the NO area reduction rate in tests in a two-phase system containing a gas mixture of NO / CO 2 . The NAP with the best NO uptake performance was HTX, which had an area percentage difference of 62 ± 5%, followed by HEX at 31 ± 6% and HNO at 21 ± 4%. The results in Figures 11 and 12 show that in the two-phase system, the selectivity of NAP for CO2 shows it is higher for NO than for

[0101] 3.9. Gas-liquid mass transfer batch test in a three-phase system (CO 2 / NO / liquid phase / NAP) Figure 12 shows the NO area reduction rate in a three-phase system with (black) and without (gray) added liquid phase (phosphate buffer) under the same experimental conditions. As can be seen, for HEX, there was no significant difference in the peak area (28 ± 3% when CO 2 is present and 26 ± 5% when it is not). However, for HNO, the difference was 54 ± 4% when CO 2 is present and 32 ± 4% when it is not, and for HTX, it was 56 ± 7% when CO 2 is present and 70 ± 3% when it is not. According to this result, in the presence of the liquid phase and CO 2 , although there was a difference in the peak area difference for NO, CO 2 did not significantly interfere with the selectivity of NAP, and in actual flue gas, NAP will continue to assist the gas-liquid mass transfer of NO. 2 is present and 70 ± 3% when it is not. According to this result, in the presence of the liquid phase and CO 2 , although there was a difference in the peak area difference for NO, CO 2 did not significantly interfere with the selectivity of NAP, and in actual flue gas, NAP will continue to assist the gas-liquid mass transfer of NO. 2 does not significantly interfere with the selectivity of NAP, and in actual flue gas, NAP will continue to assist the gas-liquid mass transfer of NO.

[0102] Figure 13 shows the analysis of the liquid phase (nitrogen compounds) in the three-phase system. Higher concentrations of nitrogen compounds in the form of NO 2 - and NO 3 - were evident when any of the NAPs were present compared to the NAP-free blank (HEX: 10 ± 1 N mg / L, HNO: 18 ± 2 N mg / L, HTX: 14 ± 2 N mg / L). This confirmed that the NAPs tested improved the transfer of NO from gas to liquid. These results confirmed that when soluble gases (NO 2 ) are generated in the gas phase, they move to the liquid phase through various instantaneous and irreversible reactions with the phosphate buffer to form nitrous and nitric acids.

[0103] Figure 14 shows the CO 2 peak area difference for a test in three phases including a gas mixture of gas (NO) and a liquid phase (phosphate buffer). CO 2 in the presence of NAP was found to have a smaller area difference with NAP than the phosphate blank (19 ± 6%) (HEX: 8 ± 2%, HNO: 3 ± 7%, HTX: 7 ± 2%).

[0104] Prior art documents [Table 4]

Claims

1. A method for removing NOx gas from a gas stream, i) Contacting a gas stream with a solvent system containing a non-aqueous liquid (NAP) that can act as a NOx gas-liquid mass transfer vector, ii) Provide the solvent system from step i) for denitrification by microorganisms. NOx includes nitric oxide (NO), nitrogen dioxide (NO) ２ A method comprising selecting from ), and mixtures thereof, wherein the NAP has a molecular weight of 150 to 550 g / mol and a boiling point of 400 to 700 K at 101300 Pa.

2. The NAP is optionally substituted with one or more halogen atoms (C １０ -C ２０ ) hydrocarbon, di(C １ -C １０ ) alkyl (C １ -C １０ ) ester, (C １ -C １２ ) ketone, siloxane, perfluoromethyldecalin, and mixtures thereof, and the method according to claim 1 selected from the group consisting of.

3. The method according to claim 1, wherein the NAP has a water solubility of 0.1 g / L or less at 298 K and 101300 Pa.

4. The method according to claim 2, wherein the NAP has a water solubility of 0.1 g / L or less at 298 K and 101300 Pa.

5. The method according to claim 1, wherein the NAP is selected from the group consisting of 2,2,4,4,6,8,8-heptamethylnonane, n-hexadecane, 1,1,3,3,5,5-hexamethyltrisiloxane, and diethyl sebacate.

6. The method according to claim 1, wherein the absorption capacity of the NAP is 0.1 to 1 mol NOx / kmol NAP.

7. The method according to claim 1, wherein the solvent system comprises a liquid phase and NAP, and the NAP concentration is 1 to 60% (v / v) of the total volume of the solvent system.

8. The method according to claim 4, wherein the solvent system comprises a liquid phase and NAP, and the NAP concentration is 1 to 60% (v / v) of the total volume of the solvent system.

9. The method according to claim 5, wherein the solvent system comprises a liquid phase and NAP, and the NAP concentration is 1 to 60% (v / v) of the total volume of the solvent system.

10. The method according to claim 1, wherein the denitrification by the microorganism is carried out under oxygen-free conditions in the presence of a liquid phase by the action of a microorganism capable of producing elemental nitrogen.

11. The method according to claim 10, wherein the microorganism capable of producing elemental nitrogen is in the form of biomass obtained from anoxic treatment of a wastewater treatment plant, and the volatile suspended solids (VSS) content is 500 to 5000 mg per liter of liquid phase.

12. The method according to claim 1, wherein steps i) and ii) are carried out in a single reactor, or alternatively, in different reactors.

13. The method according to claim 1, further comprising a further step iii) of recovering the NAP after step ii).

14. The method according to claim 1, wherein step ii) is performed at a temperature of 5 to 40°C.

15. The method according to claim 1, wherein step ii) is performed at a pH of 6.5 to 9.

16. The method according to claim 1, wherein the denitrification by microorganisms is carried out under anaerobic conditions in the presence of a liquid phase by the action of microorganisms capable of producing elemental nitrogen, and step ii) is carried out at a temperature of 5 to 40°C and a pH of 6.5 to 9.

17. The method according to claim 5, wherein the denitrification by microorganisms is carried out under anaerobic conditions in the presence of a liquid phase by the action of microorganisms capable of producing elemental nitrogen, and step ii) is carried out at a temperature of 5 to 40°C and a pH of 6.5 to 9.

18. The method according to claim 1, performed under a pressure in the range of 101325 to 161325 Pa.

19. The use of a non-aqueous liquid (NAP) to remove NOx gas from a gas stream, The aforementioned NAP can act as a NOx gas-liquid mass transfer vector, has a molecular weight of 150-550 g / mol, a boiling point of 400-700 K at 101300 Pa, and a water solubility of 0.1 g / L or less at 298 K and 101300 Pa, and NOx consists of nitric oxide (NO) and nitrogen dioxide (NO). ２ ), and mixtures thereof, selected for use.

20. The use according to claim 19 in a chemical absorption-biological reduction (CABR) system.

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