Dielectric barrier discharge system and method for deeply treating eutrophication of water body

Abstract

The invention discloses a dielectric barrier discharge system and method for deeply treating water eutrophication. The dielectric barrier discharge system and method are used for treating town sewage, industrial wastewater and surface water produced by mass propagation of algae caused by water eutrophication. Comprising a plasma reactor; a ground electrode of the plasma reactor is a metal electrode capable of slowly releasing metal ions into sewage / wastewater to be treated in the discharge process, and the ground electrode is exposed in the sewage / wastewater; a discharge dielectric sheet covers the discharge surface of the high-voltage electrode of the plasma reactor; carrier gas is introduced into a discharge gap between the high-voltage electrode and the upper liquid level of the sewage / wastewater to be treated. According to the invention, nitrogen and phosphorus eutrophication elements in water can be synchronously removed on the basis of removing overgrowing algae microorganisms in water.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a dielectric barrier discharge system and method for deep treatment of water eutrophication. Background Art

[0002] With the rapid development of urbanization and industrialization, natural water bodies have been directly and indirectly affected by human activities, among which eutrophication has become an environmental issue that has attracted widespread attention. Since fertilizers and pesticides used in agricultural activities contain a large amount of nutrients such as nitrogen and phosphorus, these nutrients may enter natural water bodies through runoff or infiltration, causing eutrophication of water bodies. Eutrophication refers to a phenomenon in which the content of nutrients such as nitrogen and phosphorus in water bodies is too high, resulting in excessive reproduction of algae and other aquatic plants and deterioration of water quality. Eutrophication of water bodies will affect water quality, reduce the transparency of water, and make it difficult for sunlight to penetrate the water layer, thereby affecting the photosynthesis of native plants in the water. In addition, a large amount of algae with cyanobacteria and green algae as the dominant species will grow on the surface of eutrophic water bodies, forming a layer of "green scum". These overgrown algae will deplete the dissolved oxygen in the water during their growth, leading to the death of aquatic fish and shrimp.

[0003] The application number is CN202210457087X, and the name of the invention is: A system and method for treating aquaculture wastewater; it uses an SBBR reactor, a biological treatment module, a zeolite treatment module, and an electrochemical oxidation module to jointly treat wastewater; microalgae are removed by inhalation by filter feeders, ammonia nitrogen in the water is removed by a zeolite adsorption system, and an electrochemical oxidation module is used to deeply treat aquaculture wastewater. In its scheme, the efficiency of microalgae inhalation is relatively slow, the repeated use of zeolite requires regeneration, the electrochemical oxidation efficiency is low and incomplete, and it is impossible to remove a large amount of nitrogen and phosphorus elements contained in the wastewater.

[0004] Dielectric barrier discharge plasma technology is to insert an insulating medium between the high voltage electrode and the ground electrode to form a low temperature plasma between the insulating medium and the electrode. Low temperature plasma can produce O3, ·OH, 1 O2、O2 - , H2O2 and other active substances, accompanied by ultraviolet light, ultrasonic cavitation, shock waves and other physical effects, and various physical and chemical reactions with pollutant molecules or microorganisms in the solution, ultimately achieving the purpose of pollutant removal. In the prior art, plasma technology has been widely used in wastewater treatment, but for eutrophic wastewater, it can only kill existing algae microorganisms in the water, and cannot eliminate the risk of algae proliferation from the root, so it needs to be improved. Summary of the invention

[0005] 1. Technical problems to be solved: In view of the above technical problems, the present invention provides a dielectric barrier discharge system and method for deep treatment of water eutrophication, which can simultaneously remove nitrogen and phosphorus eutrophication elements in the water on the basis of removing excessive algae microorganisms in the water.

[0006] 2. Technical solution: A dielectric barrier discharge plasma system for deep treatment of water eutrophication is used for treating urban sewage, industrial wastewater and surface water with massive algae growth caused by water eutrophication; it comprises a plasma reactor; it is characterized in that: the ground electrode of the plasma reactor is a metal electrode that can slowly release metal ions into the sewage / wastewater to be treated during the discharge process, and the ground electrode is exposed and placed in the sewage / wastewater; the discharge surface of the high-voltage electrode of the plasma reactor is covered with a discharge dielectric sheet; the discharge gap between the high-voltage electrode and the upper liquid surface of the sewage / wastewater to be treated is passed with a carrier gas.

[0007] Furthermore, the metal ground electrode is an iron electrode, an aluminum electrode, or a magnesium electrode with a porous foam structure.

[0008] Furthermore, the discharge dielectric sheet is made of insulating material.

[0009] Furthermore, the discharge medium sheet is a quartz sheet or a ceramic sheet.

[0010] Furthermore, it also includes a high-voltage power supply module, a carrier gas output and input module, and a reactor body; the high-voltage power supply module is connected to the high-voltage electrode through a high-voltage power supply line, and a high-frequency AC high voltage difference is established between the high voltage and the metal ground electrode, so that plasma can be generated in the discharge gap; the carrier gas output and input module provides a channel for the carrier gas to enter and exit the reaction area; the reactor body is a container made of insulating material, and its high-voltage electrode and discharge medium sheet are covered on the top of the container, and the ground electrode is fixed to the lower position of the inner cavity of the container; the reactor body is provided with an air inlet and an air outlet for the carrier gas, and an inlet and an outlet for the waste water.

[0011] A method for deep treatment of water eutrophication comprises the following steps: Step 1: urban sewage, industrial wastewater, and surface water to be treated, which are caused by algae proliferation due to eutrophication of water bodies, are introduced into the reactor body of the plasma reactor through the water inlet, and the height of the liquid is lower than the preset height; Step 2: using the gas inlet to continuously input carrier gas into the reaction area inside the reactor body; the carrier gas does not contain nitrogen, which can prevent nitrogen, oxygen and water from reacting to generate nitrous acid and nitric acid and dissolving into water under plasma excitation; Step 3: Power on the plasma reactor, and the reactor starts to treat the wastewater; the power-on time is determined according to the amount of wastewater and the algae biomass, total nitrogen concentration, and total phosphorus concentration in the wastewater; Step 4: Stop discharging and stop supplying carrier gas; stir the sewage / wastewater after the reaction for a preset time, so that the corresponding metal ions released by the ground electrode in the wastewater and the hydroxides generated by the reaction with water in water can fully react with the phosphate ions, ammonium ions and dead algae cell fragments in the wastewater to produce precipitation, adsorption and flocculation behavior to generate precipitation; after standing for a preset time, the upper clear liquid is discharged, and the lower sediment containing rich organic matter and nitrogen and phosphorus nutrients is collected and used as fertilizer for crops.

[0012] Furthermore, the ground electrode is an iron electrode, an aluminum electrode, or a magnesium electrode with a porous foam structure. The wastewater after the reaction in step 4 contains a large amount of metal hydroxides corresponding to the ground electrode, which react fully with the phosphate ions and dead algae cell fragments in the wastewater to produce precipitation, adsorption, and flocculation.

[0013] Furthermore, the carrier gas is a mixture of one or more of helium, argon and oxygen.

[0014] 3. Beneficial effects: (1) The method provides a dielectric barrier discharge system and method for deep treatment of eutrophication of water bodies. The plasma reactor adopts a dielectric barrier discharge structure. Through the electric field and the charge action of the discharge medium tube wall, the reactor body forms a discharge. Because the ground electrode is arranged inside the wastewater to be treated, the plasma is generated at a certain distance above the eutrophic water body polluted by algae through the electric field. At the gas-liquid interface, due to the interaction between the high-energy charged particles in the plasma and the oxygen and nitrogen in the air and the water molecules in the sewage, active substances such as ozone, hydroxyl radicals, singlet oxygen, superoxide anion radicals, hydrogen peroxide, and active nitrogen are generated. These active substances will destroy the cell membrane of algae cells, and after invading the cells, they will also destroy the cell life substances such as proteins, DNA, and chloroplasts in the cells, and finally cause cell death. In addition to the active substances, the physical and chemical effects such as ultrasound and ultraviolet generated by the plasma will also cause damage to the cells. No chemical agents are added in the whole process. The organic matter released into the water body after the algae cells are destroyed can also be degraded and removed by these active substances, which greatly alleviates the deterioration of water quality caused by the death of algae. The cyanobacterial toxins contained in some cyanobacteria can also be degraded. Through the physical and chemical combined effects of this plasma, algae in water bodies can be removed efficiently and environmentally friendly.

[0015] (2) The method provides a dielectric barrier discharge system and method for deep treatment of eutrophication in water bodies. The nitrogen and phosphorus removal process is more environmentally friendly than chemical methods and does not introduce additional anions into the water. During the treatment process, the scheme achieves the simultaneous removal of nitrogen and phosphorus through the selection of electrode materials and metal catalysis. Using iron, aluminum or magnesium as electrode materials can release corresponding metal ions during the electrolysis process. These metal ions react with phosphate and ammonium ions in the water to form insoluble precipitates, thereby removing nitrogen and phosphorus nutrients in the water. Nitrate nitrogen is reduced to nitrogen gas on the electrode surface through a series of charge transfer effects and is separated from the sewage. In addition, the electrolysis process does not introduce additional anions, avoiding the side effects that may be caused by traditional chemical methods, ensuring the environmental protection and high efficiency of the treatment process. At the same time, the active substances generated by the dielectric barrier discharge plasma can convert organic phosphorus in the water into inorganic phosphorus, which reacts with metal ions to precipitate or is adsorbed by metal hydroxides to achieve the purpose of removing organic phosphorus.

[0016] (3) The method provides a dielectric barrier discharge system and method for deep treatment of eutrophication of water bodies. The ground electrode used is a metal electrode with a porous foam structure, and the surface area of ​​the ground electrode is greatly increased. The high specific surface area allows the electrode to fully contact with the wastewater. During discharge, the electrode can quickly release a large amount of metal ions into the wastewater.

[0017] (4) Compared with the electrodes in traditional electrochemical technology, the electrodes in traditional electrochemical technology are prone to passivation, which shortens the electrode life and reduces the processing efficiency. This scheme adopts AC pulse power supply and periodically reverses the electrode polarity, which effectively reduces the electrode passivation phenomenon and improves the cycle performance and service life of the electrode.

[0018] (5) This method can achieve high-efficiency simultaneous removal of algae and nitrogen and phosphorus nutrients in situ, that is, simultaneously complete eutrophication control, reducing the complexity of step-by-step treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a technical principle diagram of the present invention; Figure 2 The schematic diagram of the equipment structure of a specific embodiment is as follows: Figure 3 It is an enlarged view of the iron electrode, aluminum electrode and magnesium electrode of the porous foam structure involved in the present method; Figure 4 It is a diagram showing the effect of treating total phosphorus, algae and other substances in water in a specific embodiment; Figure 5 It is a representation diagram of the inactivation of algae in the treated wastewater in the verification example; Figure 6It is a characterization diagram of metal ion precipitation of the treated wastewater in the verification example; Figure 7 The XRD and XPS images are taken to characterize the precipitate produced in the verification example. DETAILED DESCRIPTION

[0020] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0021] A dielectric barrier discharge plasma system for deep treatment of water eutrophication is used for treating urban sewage, industrial wastewater and surface water with massive algae growth caused by water eutrophication; it comprises a plasma reactor; it is characterized in that: the ground electrode of the plasma reactor is a metal electrode that can slowly release metal ions into the sewage / wastewater to be treated during the discharge process, and the ground electrode is exposed and placed in the sewage / wastewater; the discharge surface of the high-voltage electrode of the plasma reactor is covered with a discharge dielectric sheet; the discharge gap between the high-voltage electrode and the upper liquid surface of the sewage / wastewater to be treated is passed with a carrier gas.

[0022] Furthermore, the metal ground electrode is an iron electrode, an aluminum electrode, or a magnesium electrode with a porous foam structure.

[0023] Furthermore, the discharge dielectric sheet is made of insulating material.

[0024] Furthermore, the discharge medium sheet is a quartz sheet or a ceramic sheet.

[0025] Furthermore, it also includes a high-voltage power supply module, a carrier gas output and input module, and a reactor body; the high-voltage power supply module is connected to the high-voltage electrode through a high-voltage power supply line, and a high-frequency AC high voltage difference is established between the high voltage and the metal ground electrode, so that plasma can be generated in the discharge gap; the carrier gas output and input module provides a channel for the carrier gas to enter and exit the reaction area; the reactor body is a container made of insulating material, and its high-voltage electrode and discharge medium sheet are covered on the top of the container, and the ground electrode is fixed to the lower position of the inner cavity of the container; the reactor body is provided with an air inlet and an air outlet for the carrier gas, and an inlet and an outlet for the waste water.

[0026] A method for deep treatment of water eutrophication comprises the following steps: Step 1: urban sewage, industrial wastewater, and surface water to be treated, which are caused by algae proliferation due to eutrophication of water bodies, are introduced into the reactor body of the plasma reactor through the water inlet, and the height of the liquid is lower than the preset height; Step 2: using the gas inlet to continuously input carrier gas into the reaction area inside the reactor body; the carrier gas does not contain nitrogen, which can prevent nitrogen, oxygen and water from reacting to generate nitrous acid and nitric acid and dissolving into water under plasma excitation; Step 3: Power on the plasma reactor, and the reactor starts to treat the wastewater; the power-on time is determined according to the amount of wastewater and the algae biomass and total phosphorus concentration in the wastewater; Step 4: Stop discharging and stop supplying carrier gas; stir the sewage / wastewater after the reaction for a preset time, so that the corresponding metal ions released by the ground electrode in the wastewater and the hydroxides generated by the reaction with water in water can fully react with the ammonium ions, phosphate ions and dead algae cell fragments in the wastewater to produce precipitation, adsorption and flocculation behavior to generate precipitation; after standing for a preset time, the clear liquid on the upper layer is discharged, and the sediment on the lower layer containing rich organic matter and nitrogen and phosphorus nutrients is collected and used as fertilizer for crops.

[0027] Furthermore, the ground electrode is an iron electrode, an aluminum electrode, or a magnesium electrode with a porous foam structure. The wastewater after the reaction in step 4 contains a large amount of metal hydroxides corresponding to the ground electrode, which react fully with ammonium ions, phosphate ions, and dead algae cell fragments in the wastewater to generate precipitation after precipitation reaction, adsorption, and flocculation.

[0028] Furthermore, the carrier gas is a mixture of one or more of helium, argon and oxygen.

[0029] As attached Figure 1 As shown in the figure, the principle of this application is that the two ends of the AC high voltage power supply are connected to the upper and lower electrodes, wherein the lower electrode is a metal electrode made of iron, magnesium or aluminum. The metal ground electrode is exposed in the eutrophic sewage to be treated, and the sewage contains a large number of algae microorganisms and nitrogen and phosphorus elements. Nitrogen and phosphorus elements are usually in the form of NH4 + 、NO2 - 、NO3 - 、H2PO4 - 、HPO4 2- and PO4 3- The AC high voltage power supply can generate a voltage difference of 10000-20000V between the upper and lower electrodes. A quartz plate (insulating medium) is connected below the high voltage electrode. Due to the existence of the insulating medium, low temperature plasma will be generated in the gap between the sewage and the insulating medium. The active substances (O3, ·OH, 1 O2、O2 - , H2O2) and ultraviolet light, ultrasonic cavitation, shock waves and other physical effects will damage the cell membrane, intracellular structure, protein, and DNA of algae microorganisms in sewage, eventually leading to the death of algae microorganisms. Since an AC power supply is used, the direction of the current will change periodically. When the current direction is upward (electrons downward), the metal atoms in the metal electrode will lose electrons and dissolve into the sewage to be treated in the form of ions. These metal ions react with NH4 +、HPO4 2- PO4 3- Under certain pH conditions, when the metal ground electrode is made of iron or magnesium, Fe 2+ , Fe 3+ Mg 2+ Will be with NH4 + 、HPO4 2- PO4 3- Form MgNH4PO4, Mg3 (PO4) 2, FePO4, Fe3 (PO4) 2 and other precipitation. After standing or filtering, it can be separated from the sewage. When the current direction is downward (electrons are upward), NO2 in the sewage - 、NO3 - It is reduced to N2 through a series of charge transfer reactions on the electrode surface and separated from the sewage. Specific embodiment: As attached Figure 2-4 As shown, it is a device diagram of a plasma reactor of a specific embodiment: in the figure, 1 is a high-voltage electrode terminal, connected to the high-voltage end of the high-voltage power supply module; 2 is a cylindrical metal electrode, connected to the nickel electrode terminal 1, used to produce a downward high-voltage electric field, with a height of 5mm and a radius of 30mm; 3 is a quartz glass sheet, which acts as an insulating medium and is in close contact with the surface of the cylindrical nickel electrode, with a radius of 47mm and a height of 2mm; 4 is a water inlet, which is used to pass the liquid to be treated into the inner cavity of the reactor body, with an inner diameter of 2mm; 5 is an inlet and outlet, which is a channel for the carrier gas to enter or leave the reaction area, and when no special carrier gas is needed, it can be plugged with a rubber stopper. , with an inner diameter of 2mm; 6 is a ground electrode made of metal iron, magnesium or aluminum sheet with a porous foam structure, which is the source of metal ions, and the size of the ground electrode is 50×15×1mm; 7 is a water outlet, which is the channel for the treated sewage to leave the reaction area, with an inner diameter of 2mm; 8 is a polytetrafluoroethylene sleeve, which is used to wrap the ground electrode terminal 9 to prevent the ground electrode terminal 9 from being corroded by sewage, with a radius of 2mm and a height of 9mm; 9 is a ground electrode terminal, which is connected to the ground pole and the top end is connected to the metal electrode 6 with a porous foam structure; 10 is the main body of the reactor, which adopts a dish-shaped glass container with a radius of 45mm, a height of 20mm and a wall thickness of 2mm.

[0031] The steps for treating sewage\wastewater are as follows: assemble the equipment according to the diagram before treatment, connect the high-voltage electrode terminal 1 and the ground electrode terminal 9 to the positive electrode and the ground electrode of the AC high-voltage power supply respectively; plug the gas outlet 7 with a rubber plug, and input the sewage to be treated into the reactor body 10 through a pump provided at the water inlet 4 until the liquid level is about 15 mm; turn on the power (whether to introduce carrier gas as needed); at this time, plasma will be generated in the area above the liquid surface, and turn off the power after treating for about 10 minutes; discharge the treated solution into the container from the water outlet 7, stir for a preset time, and then let it stand for several minutes to allow the insoluble matter to precipitate.

[0032] In the actual treatment process, this system can be connected to other waste liquid treatment devices, or two systems can be connected to achieve circulating treatment of the solution.

[0033] Verification example: The device of the specific embodiment was used to verify the effect of the method on treating total phosphorus and algae. The experimental conditions were: discharge time 10 minutes discharge voltage 14kV waste liquid volume 70ml: the initial concentration of algae was 2.2×10^6 algae cells per milliliter of waste liquid; the initial content of total phosphorus was 6mg / L; the waste liquid was treated with the device in the specific implementation, and the effect diagrams of discharge time and total phosphorus concentration, discharge time and algae cell removal rate were obtained, as shown in the attached figure. Figure 4 (a) and (b) show that the active substances in the system are subjected to ESR analysis, and characteristic peaks of hydroxyl radicals, superoxide anions, and singlet oxygen are obtained, such as Figure 4 As shown in (c)(d)(e).

[0034] Flow cytometry and three-dimensional fluorescence were used to characterize the inactivation of algae. Figure 5 As shown, it can be clearly seen from the results that with the increase of treatment time, the number of damaged cells increased significantly and the characteristic peak of three-dimensional fluorescence disappeared.

[0035] A series of characterizations of the metal ion precipitation and precipitate were carried out, such as the attached Figure 6 As shown, (a) is the precipitation diagram of iron ions, and (b) is the iron ions in phosphorus-containing wastewater; Fe can be detected in pure water. 2+ and Fe 3+ The stable precipitation of Fe 3t The content of Fe 3+ Participated in the precipitation process.

[0036] Figure 7(a) is the XRD spectrum before treatment, (b) is the XRD spectrum of recrystallization at 90 °C after treatment, (c) is the XRD spectrum of the precipitate; (d) is the XPS total spectrum of Fe2p, (e) the XPS total spectrum of P2p, (f) the XPS total spectrum of O1s; From the XRD and XPS characterizations in the figure, it can be concluded that the precipitate produced by the system is mainly composed of FePO4.

[0037] From the above, it can be concluded that this method can efficiently and simultaneously remove high-concentration algae and phosphorus nutrients in the waste liquid in a short time, and there is no need to add additional chemical reagents and no secondary pollution in the whole process.

[0038] Although the present invention has been disclosed as above in terms of preferred embodiments, they are not intended to limit the present invention. Anyone skilled in the art can make various changes or modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection defined by the claims of this application.

Claims

1. A dielectric barrier discharge system for deep treatment of water eutrophication, used for treating urban sewage, industrial wastewater and surface water with large algae growth caused by water eutrophication; including a plasma reactor; characterized by: The ground electrode of the plasma reactor is a metal electrode that can slowly release metal ions into the sewage / wastewater to be treated during the discharge process, and the ground electrode is exposed and placed in the sewage / wastewater; the discharge surface of the high-voltage electrode of the plasma reactor is covered with a discharge dielectric sheet; and a carrier gas is passed through the discharge gap between the high-voltage electrode and the upper liquid surface of the sewage / wastewater to be treated.

2. A dielectric barrier discharge system for deep treatment of water eutrophication according to claim 1, characterized in that: The metal ground electrode is an iron electrode, an aluminum electrode, or a magnesium electrode with a porous foam structure.

3. The dielectric barrier discharge system for deep treatment of water eutrophication according to claim 1, characterized in that: The discharge dielectric sheet is made of insulating material.

4. The dielectric barrier discharge system for deep treatment of water eutrophication according to claim 1, characterized in that: The discharge medium sheet is a quartz sheet or a ceramic sheet.

5. The dielectric barrier discharge system for deep treatment of water eutrophication according to claim 1, characterized in that: It also includes a high-voltage power supply module, a carrier gas output and input module, and a reactor body; the high-voltage power supply module is connected to the high-voltage electrode through a high-voltage power supply line, and a high-frequency AC high voltage difference is established between the high voltage and the metal ground electrode, so that plasma can be generated in the discharge gap; the carrier gas output and input module provides a channel for the carrier gas to enter and exit the reaction area; the reactor body is a container made of insulating material, and its high-voltage electrode and discharge medium sheet are covered on the top of the container, and the ground electrode is fixed to the lower position of the inner cavity of the container; the reactor body is provided with an air inlet and an air outlet for the carrier gas, and an inlet and an outlet for the waste water.

6. A dielectric barrier discharge method for deep treatment of water eutrophication, implemented by using the dielectric barrier discharge system according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1: urban sewage, industrial wastewater, and surface water to be treated, which are caused by algae proliferation due to eutrophication of water bodies, are introduced into the reactor body of the plasma reactor through the water inlet, and the height of the liquid is lower than the preset height; Step 2: using the gas inlet to continuously input carrier gas into the reaction area inside the reactor body; the carrier gas does not contain nitrogen, which can prevent nitrogen, oxygen and water from reacting to generate nitrous acid and nitric acid and dissolving into water under plasma excitation; Step 3: Power on the plasma reactor, and the reactor starts to treat the wastewater; the power-on time is determined according to the amount of wastewater and the algae biomass, total nitrogen concentration, and total phosphorus concentration in the wastewater; Step 4: stop discharging and stop supplying carrier gas; stir the sewage / wastewater after the reaction for a preset time, so that the corresponding metal ions released by the ground electrode in the sewage / wastewater and the hydroxides generated by the reaction with water in water fully react with the phosphate ions, ammonium ions and dead algae cell fragments in the wastewater to generate precipitation, adsorption and flocculation behaviors, and generate precipitation; After standing for a preset time, the clear liquid on the upper layer is discharged, and the sediment in the lower layer containing rich organic matter and nitrogen and phosphorus nutrients is collected and used as fertilizer for crops.

7. The dielectric barrier discharge method for deep treatment of water eutrophication according to claim 6, characterized in that: The ground electrode is an iron electrode, an aluminum electrode, or a magnesium electrode with a porous foam structure. The wastewater after the reaction in step 4 contains a large amount of metal hydroxide corresponding to the ground electrode, which fully reacts with phosphate ions, ammonium ions, and dead algae cell fragments in the wastewater to produce a precipitate after precipitation reaction, adsorption, and flocculation.

8. The dielectric barrier discharge method for deep treatment of water eutrophication according to claim 6, characterized in that: The carrier gas is a mixture of one or more of helium, argon and oxygen.

Images