System and method for generating plasma-activated liquid and use of the plasma-activated liquid

Abstract

The present invention relates to a system for generating plasma-activated liquid (PAL), which comprises a plasma generator (1) into which a flow of gas (2) is introduced to generate a flow of plasma-activated gas (4), a reactor (6) provided to hold a liquid (7), and a bubble diffuser (10), the reactor (6) comprising an inlet (9) for liquid, an outlet (19) for liquid for the outlet of plasma-activated liquid (18) from the reactor (6), and a gas outlet (13) for the outlet of gas (17) after same has reacted with the liquid (7) inside the reactor (6). The present invention also relates to a method for generating plasma-activated liquid and to the use thereof.

Description

[0001] DESCRIPTION

[0002] System and method for generating plasma-activated liquid, and use of said plasma-activated liquid

[0003] FIELD OF INVENTION

[0004] The present invention relates to the field of producing plasma-activated liquids, such as plasma-activated water. These plasma-activated liquids are used, for example, but not limited to, as disinfectants.

[0005] BACKGROUND OF THE INVENTION

[0006] Plasma is the fourth state of matter. It is composed of positive and negative ions, electrons, excited and neutral atoms, free radicals, molecules in the ground and excited states, and UV photons. Plasma can be classified as thermal (hot) plasma or non-thermal (cold) plasma based on the thermodynamic temperature equilibrium of its constituents. The temperature of cold plasma never exceeds 100 °C. Some widely used non-thermal plasma sources, for example, in food applications, include dielectric barrier discharges (DBDs), plasma jets, and corona discharges.

[0007] The present invention relates to the field of liquid treatment using plasma technology, an area of ​​growing scientific and industrial interest due to its remarkable versatility and effectiveness. This innovative technology harnesses the unique properties of plasma-liquid interaction to induce physical and chemical changes in liquid media, offering advanced solutions to a wide range of challenges in multiple sectors. Plasma technology can be applied, for example, in the treatment of water and wastewater, where it demonstrates significant potential for purification and decontamination. In the biomedical sector, this technology is used for the sterilization of medical instruments and fluids, as well as for wound treatment and the disinfection of biological tissues.Furthermore, the production of plasma-activated fluids opens new avenues for innovative therapies, including cancer treatments, representing a significant advance in modern medicine. On the other hand, in the...

[0008] In the food industry, plasma treatment offers novel methods for decontaminating both solid and liquid foods and food contact surfaces, contributing to extending the shelf life of perishable products. It also allows for the controlled modification of the organoleptic and nutritional properties of beverages, opening new possibilities in food product development. Another important application area for plasma technology is the synthesis and modification of materials, where it facilitates the production of metallic nanoparticles and suspended oxides, as well as the synthesis of carbon nanostructures in liquid media. The functionalization of liquid contact surfaces expands the range of applications, from improving wettability properties to creating surfaces with specific functionalities.In the fields of catalysis and green chemistry, plasma-activated liquids demonstrate considerable potential for activating liquid-phase chemical reactions, synthesizing high-value organic compounds, and improving the efficiency of catalytic processes. This not only contributes to the advancement of sustainable chemistry but also offers new pathways for producing compounds of industrial and pharmaceutical interest. The agricultural and environmental sectors also benefit from this technology through the treatment of irrigation water and nutrient solutions, the stimulation of plant growth using plasma-activated liquids, and the decontamination of soil and groundwater. These applications promise to improve agricultural productivity and contribute to environmental conservation.Finally, the textile and materials industries also benefit from plasma technology, which offers solutions for treating dyeing effluents, modifying the surface properties of fibers and fabrics, and functionalizing polymeric materials in the liquid phase. This not only improves the efficiency of industrial processes but also enables the development of textiles and other materials with advanced properties (Plasma-liquid interactions: a review and roadmap. PJ Bruggeman et al., Plasma Sources Sci. Technol. 25 (2016) 053002).

[0009] Building on prior art, the use of plasma for treating liquids to generate plasma-activated liquids (PALs), such as plasma-activated water (PAW), is known. This technology for generating plasma-activated liquids can be applied to any of the sectors described above, among others. Documents CN115154626, CN114656077, and ES2869598, among others, disclose some systems and methods for generating PAWs known in the prior art. However, these known systems and methods have several drawbacks, such as insufficient performance or high cost, which prevent their industrial-scale implementation from being optimized.

[0010] Therefore, there remains a need in the field for an alternative system and method for generating plasma-activated liquid that allows the production of a solution with a high level of disinfectant, high performance, and reduced cost.

[0011] SUMMARY OF THE INVENTION

[0012] To address the aforementioned problems of the prior art, this document discloses, in a first aspect, a system for generating plasma-activated liquid (PAL) as described in appended independent claim 1. Specifically, the system for generating plasma-activated liquid (PAL), such as plasma-activated water (PAW), according to the first aspect of the present invention comprises:

[0013] - a plasma generator into which a gas flow is introduced to generate a plasma-activated gas flow;

[0014] - a conduit that connects the plasma generator to a reactor;

[0015] - non-return means arranged in the conduit to prevent the fluid from the reactor from flowing back to the plasma generator when the pressure inside the reactor is increased;

[0016] - a reactor arranged to contain a liquid;

[0017] - a bubble diffuser disposed at a gas inlet to the reactor from the duct, to produce plasma-activated gas bubbles within the liquid; the reactor comprising:

[0018] - a liquid inlet that can be plugged for introducing liquid into the reactor;

[0019] - a liquid outlet for the plasma-activated liquid outlet of the reactor; and

[0020] - a gas outlet for the release of gas after its reaction with the liquid inside the reactor.

[0021] A second aspect of the present invention relates to a method for generating plasma-activated liquid (PAL) according to appended independent claim 9. Specifically, the method for generating plasma-activated liquid (PAL), such as plasma-activated water (PAW), according to the second aspect of the invention comprises:

[0022] - introduce a desired volume of liquid to be treated into a reactor;

[0023] - introduce a desired gas flow into a plasma generator; - activate the plasma generator to generate a plasma-activated gas flow;

[0024] - bubbling the plasma-activated gas through the liquid contained in the reactor to produce plasma-activated liquid; and

[0025] - evacuate the plasma-activated fluid.

[0026] According to a third aspect of the present invention, a use of a plasma-activated liquid (PAL), such as plasma-activated water (PAW), as described in independent claim 16, produced by the system according to the first aspect of the invention or by the method according to the second aspect of the invention, as a disinfectant is disclosed.

[0027] The appended dependent claims relate to preferred embodiments of the present invention.

[0028] BRIEF DESCRIPTION OF THE FIGURES

[0029] The present invention will be better understood with reference to the following drawings which illustrate a preferred embodiment of the invention, provided by way of example, and which should not be interpreted as limiting the invention in any way.

[0030] Figure 1 schematically shows the plasma-activated liquid (PAL) generation system according to the preferred embodiment of the present invention.

[0031] Figure 2 shows chromatograms of the reaction products of phenol with the reactive species OH* (benzoquinone), NO* (4-nitrosophenol) and NO2* (2-nitrophenol) contained in different AAPs generated at different overpressures (0, 1 and 3 bar) above atmospheric pressure.

[0032] Figure 3 is a bar chart representing the concentration in mg / l of the products of the reaction of phenol with the reactive species OH* (benzoquinone), NO* (4- nitrosophenol) and NO2* (2-nitrophenol) contained in the different AAPs generated at different overpressures (0, 1 and 3 bar) above atmospheric pressure.

[0033] Figure 4 is a bar graph representing the bacterial inactivation (expressed on a 10-log basis) produced by different AAPs generated at different overpressures (0, 1 and 3 bar), above atmospheric pressure, when they come into contact with a solution artificially contaminated with a concentration of 10 7 Colony-forming units (CFU) of Listeria monocytogenes were inactivated for 5, 15, 30, and 60 minutes. Error bars indicate the standard deviation (inactivation assay performed in triplicate). Relationships marked with an asterisk indicate statistically significant differences (* = p < 0.05; ** = p < 0.001; *** = p < 0.0001). Relationships not marked with an asterisk indicate no statistically significant differences. Figure 4a shows the inactivation assay performed immediately after generating the AAPs, and Figure 4b shows the inactivation assay with the AAPs stored for 24 hours.

[0034] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0035] Throughout the description and claims, the word "comprises" and its variations are not intended to exclude other technical features or components. Furthermore, the word "comprises" includes the case "consists of."

[0036] Throughout this document, the terms “plasma-activated fluid”, “plasma-treated fluid”, “PLF” and “PTF” are used interchangeably and refer to any fluid that has undergone plasma treatment.

[0037] The terms “plasma-activated water,” “plasma-treated water,” “AAP,” and “ATP” are used interchangeably throughout this document and refer to a specific instance of the term “plasma-activated liquid” in which the liquid is water. As those skilled in the art will understand, the term “plasma-activated water” and similar terms, when used throughout this document, are also intended to include the term “plasma-activated liquid” and similar terms in other alternative embodiments of the invention.

[0038] Throughout this document, the terms “plasma-activated gas,” “plasma-ionized gas,” and similar terms are used interchangeably and refer to any gas stream that has undergone plasma treatment. Likewise, the terms “plasma-activated air,” “plasma-ionized air,” and similar terms are used interchangeably throughout this document and refer to a specific instance of “plasma-activated gas” where the gas is air. As those skilled in the art will understand, the term “plasma-activated air” and similar terms, when used throughout this document, are intended to also include the term “plasma-activated gas” and similar terms in other alternative embodiments of the invention.

[0039] For those skilled in the art, other objects, advantages, and features of the invention will become apparent partly from the description and partly from the practice of the invention. The following examples are provided by way of illustration and are not intended to be limiting of the present invention. Furthermore, the present invention covers all possible combinations of embodiments indicated herein.

[0040] As defined above, the present invention is based on a novel system for treating liquids using plasma that improves the efficiency of current devices by increasing the dilution of the functional reactive species generated by the plasma in the liquid. According to a preferred embodiment of the present invention, this increased concentration of dissolved reactive species in the liquid is achieved by increasing the pressure in the mixing reactor of the plasma-activated gas and the liquid.

[0041] In the preferred embodiment described later in this document, it is shown how this increase in the reactive species dissolved in plasma-activated water (PAW) allows for an increase in the disinfectant capacity of said liquid against a solution artificially contaminated with Listeria monocytogenes.

[0042] Before providing a specific description of preferred embodiments of the present invention, a general description of AAP technology will be given. This technology offers numerous advantages over current disinfection methods. First, it is a low-cost technology, as it only consumes electricity and, in many cases, air for plasma generation, and does not require chemicals, filters, or other consumables. Furthermore, unlike the prior art, it is generated at atmospheric pressure and ambient temperature, thus eliminating the need for auxiliary facilities. Additionally, it can be applied using existing tank washing systems (e.g., pressure washers), allowing for simultaneous cleaning and sanitization, resulting in savings of water, energy, and processing time. Finally, it is an environmentally friendly technology because it does not produce toxic chemicals or waste products.However, it is an emerging technology that has not yet been thoroughly studied or applied at an industrial level, and the systems and methods known in the prior art have the disadvantage of relatively low performance and efficiency and / or a relatively high implementation cost.

[0043] Plasma-activated liquids are typically generated by bringing a plasma source into contact with a liquid. This interaction results in the generation and / or transfer of reactive chemical species into the liquid. Plasma-activated solutions can be used, for example, for disinfection purposes in the food industry. The most studied plasma-activated liquid is plasma-activated water (PAW), and numerous publications have demonstrated its antibacterial effects (see, for example, MJ Traylor et al., “Long-term antibacterial efficacy of air plasma-activated water”, J. Phys. D. Appl. Phys. 44 (2011) 472001).

[0044] Atmospheric plasma (AAP) has a different composition and physicochemical properties than water. It typically has an acidic pH, changes in redox potential and conductivity, and the presence of reactive oxygen species (ROS) and nitrogen species (RNS) (A. Mai-Prochnow et al., “Microbial decontamination of chicken using atmospheric plasma bubbles”, Plasma Process. Polym. 18 (2020) 202000052).

[0045] The antimicrobial capacity of AAP occurs through several stages: [a] gas phase: formation of reactive species in the gas phase by the interaction of charged particles (electrons, neutrons, etc.) and ultraviolet radiation with the plasma gas and the surrounding atmosphere, [b] gas-liquid phase: dilution in water of the reactive chemical species generated in the gas phase or those generated by the plasma-liquid interaction, especially those with a relatively long lifetime, such as ozone, atomic oxygen or nitric oxide that act as precursors of other ROS and RNS, such as hydrogen peroxide, nitrates or nitrites, and [c] liquid phase: secondary reactions of the long-lived reactive species, originating, for example, from the instability of nitrites in an acidic medium.These cyclic reactions justify the presence for days of short-lived cytotoxic reactive species, for example, hydroxyl radicals (OH*), acidified nitrites (NO*, NO2*) and peroxynitrites (O=NOOH).

[0046] Some of the most biocidal chemical species in plasma-assisted water (PAW) (OH*, NO*, NO2*, and O=NOOH) are generated after the plasma source is deactivated (short-lived reactive species, or SLS). SLS can be produced during PAW generation (when the plasma comes into contact with the atmosphere and water) but have such a short lifespan (on the order of milliseconds) that their presence in PAW cannot be a consequence of dilution in water. The SLS that are ultimately found in PAW are generated from reactions of long-lived reactive species (hydrogen peroxide, nitrates, and nitrites) produced in PAW after the plasma source is deactivated. The SLS resulting from these secondary reactions are transient reactive species that possess highly cytotoxic properties and cause prolonged antimicrobial activity of PAW, even days after the water is exposed to the plasma discharge.

[0047] The main side reactions arise because nitrites are unstable under acidic conditions (pH < 3.5). Schematics of the main side reactions that take place in the AAP are shown below. Nitrous acid (HNO2), which is in acid-base equilibrium with nitrites [a], decomposes under acidic conditions to form the nitric oxide radical (NO*) and the nitrogen dioxide radical (NO2*) via reaction [b]. The nitrogen dioxide radical (NO2*) further undergoes hydrolysis in aqueous solution to produce nitrite ion (NO2') as the final product via reaction [c]. NO* and NO2* can also react with dissolved oxygen to produce nitrite (NO2') and nitrate (NO3') ions. _) according to the general reactions [d] and [e], respectively. The nitrogen radicals NO* and NO2* formed in these side reactions possess strong cytotoxic properties and are probably one of the main causes of the cytotoxic effects of nitrites under acidic conditions. For this reason, they are called “acidified nitrites.” Furthermore, under acidic conditions, the reaction of nitrites (NO2') with hydrogen peroxide (H2O2) can generate peroxynitrites (O=NOOH) according to reaction [f]. Peroxynitrites can react directly with microorganisms or indirectly by decomposing into OH* and NO2* as shown in reaction [g]. This is one of the pathways for the generation of hydroxyl radicals (OH*).

[0048] NO2- + H + HNO2[a]

[0049] 2 HNO2NO* + NO2* + H2O [b]

[0050] 2 NO2* + H2O NO3- + NO2- + 2 H + [C]

[0051] 4 NO* + O2+ 2 H2O 4 NO2- + 4 H +[d]

[0052] 4 NO2* + O2+ 2 H2O ^ 4 NO3-+ 4 H + [and]

[0053] 9 NO2- + H2O2 + H + ONOOH + H2O [f]

[0054] ONOOH OH* + NO2* [g]

[0055] The formation of acidified nitrites (NO* and NO2*) and OH* radicals through secondary reactions are the key to the long-lasting biocidal properties of AAP.

[0056] Hydroxyl radical (OH*)

[0057] OH* radicals are probably the most important reactive species produced by plasma treatment of aqueous solutions. They can non-selectively oxidize most organic compounds they come into contact with and, through radical recombination, are the main source of hydrogen peroxide in plasma systems. Regarding their biocidal capacity, the outer cell wall of microorganisms, including the cell membrane, is the most affected by OH* radicals. The cell membrane, composed largely of organic compounds such as lipids, proteins, and polysaccharides, is susceptible to attack by OH* radicals. Lipids are the cell membrane macromolecules most vulnerable to oxidation. The reactions of lipids with OH* radicals occur through the removal of hydrogen from the unsaturated carbon bonds of fatty acids, which, in the presence of oxygen, leads to lipid peroxidation.Similarly, OH* radicals can damage membrane proteins by abstracting hydrogen from the alpha carbon of the -CO-NH- peptide bonds between amino acids attached to peptide chains. The attack by OH* radicals leads to peroxidation and cleavage of the protein backbone. The combined effect of these conditions ultimately results in cell death.

[0058] NO* and NO2* radicals (“acidified nitrites”)

[0059] Acidified nitrites possess a significant antimicrobial effect against a wide range of pathogenic organisms, including viruses (such as SARS-CoV-1 and SARS-CoV-2), bacteria, and fungi. Some of the damage they cause to microorganisms includes: oxidation of membrane proteins, reaction with metalloenzymes leading to the consumption of available iron, inactivation of metabolic enzymes, oxidative damage to DNA, lipid peroxidation that damages cell membranes, etc. This multifactorial damage results in severe dysfunction and, ultimately, cell death. Preferred embodiments of the present invention will be described below.

[0060] According to a preferred embodiment of the present invention, a method for generating plasma-activated water (PAW) is disclosed comprising: introducing a desired volume of water to be treated into a mixing reactor; introducing a desired gas flow into a plasma generator to generate the plasma; activating the plasma generator with a set power to generate a plasma-activated gas flow; bubbling the plasma-activated gas to mix it with the water contained in the mixing reactor; throttling the outlet of the plasma-activated gas (once it has passed through the water contained in the reactor) with the consequent increase in pressure and, according to Henry's law, increased dilution of the reactive species in the water, lowering of the pH, generation of secondary reactions, etc.; and evacuating the plasma-activated water through the outlet of the mixing reactor.

[0061] Plasma-activated water can be used for some subsequent purpose (surface disinfection, food curing, seed growth promotion, surgical material sterilization, etc.) or simply disposed of in a controlled manner (water and effluent treatment).

[0062] Although in the preferred embodiment described above the method is applied to the generation of plasma-activated water, those skilled in the art will appreciate that the present invention is not limited to this and can be applied to the generation of any type of plasma-activated liquid (PAL), such as growth medium, buffer solution, oil, etc.

[0063] According to a preferred embodiment of the present invention, the LAP generation method is performed continuously and automatically. The volume of LAP generated can be easily scaled, allowing for the rapid, simple, and economical production of high volumes of plasma-activated fluid.

[0064] As mentioned previously, the reactive species responsible for the disinfectant effect of AAP can be present for a relatively long period.

[0065] 11 prolonged, for example, of vapors for days. Therefore, the method disclosed herein can be carried out regardless of the location where the produced AAP is to be used, and can be performed by an external commercial supplier that generates the required AAP. This possibility is very useful if there are technical limitations that prevent the implementation of the method (i.e., the installation of the system according to the present invention) at the location where the generated AAP is to be used.

[0066] Figure 1 shown schematically depicts a system for generating plasma-activated liquid (e.g., plasma-activated water) according to the preferred embodiment of the present invention.

[0067] The plasma generator (1) (in this case an APPJ-DBD device, atmospheric pressure plasma jet with dielectric barrier discharge, with a power of 700 W) is fed with a gas flow (2) (in this case an air flow of 115 slm of air) with which a plasma jet (3) of about 15 mm in length is generated at the outlet of the plasma generator (1).

[0068] Preferably, air is used as the gas for plasma production since it is the gas that produces the most reactive oxygen and nitrogen species and is also the cheapest.

[0069] The gas flow beyond the plasma jet (3), where the plasma jet is no longer visible, is called plasma-activated gas. This plasma-activated gas flow (4) is conveyed through the conduit (5) to the reactor (6) (in this case, a 30-liter stainless steel tank that can withstand pressures up to 10 bar). This plasma-activated gas flow (4) contains the functional chemical molecules that interact with the liquid (7) contained in the reactor (6). This conduit is equipped with non-return means (8), specifically a non-return valve, to prevent the liquid (7) from the reactor (6) from flowing back to the plasma generator (1) when the pressure inside the reactor (6) is increased. The ionized gas flow is preferably introduced into the reactor (6) through a bubble diffuser (10).In this case, the bubble diffuser (10) consists of a flexible fine bubble diffuser made of EPDM; however, in other embodiments it may consist of a sintered stone or a disc with small holes made of any suitable material.

[0070] The flexible diffuser, when inflated, creates hundreds of tiny holes through which the gas passes. For this diffuser to function, a minimum gas flow is required to inflate and open these holes.

[0071] The small size of the bubble helps dilute the gas in the liquid. The smaller the bubble, the more surface area of ​​the gas is exposed for dilution.

[0072] According to the preferred embodiment, distilled water is used as the liquid to be subjected to plasma activation treatment; however, the invention is not limited to this and any other liquid that can be subjected to plasma activation may be used, such as cell culture medium, buffer solution, oil, etc. The liquid (7) of the reactor (6) (in this case, 5 liters of distilled water, although with the system used in the preferred embodiment of the present invention, up to 25 liters or more can be treated) is introduced through a liquid inlet (9) that can be plugged. Distilled water is suitable for carrying out the tests described herein since it does not have the biocidal effect of chlorine present in tap water. However, according to a further preferred embodiment of the present invention, tap water is used as the starting water for the production of AAP.

[0073] The bubble diffuser (10) is arranged at a gas inlet to the reactor (6) from the conduit (5), and converts the plasma-activated gas flow (4) into fine bubbles (11) within the liquid (7) contained in the reactor (6). Part of this gas (along with the molecules generated by the plasma) dissolves in the liquid (7) contained in the reactor (6). The remaining gas (12), after passing through the liquid (7) contained in the reactor (6), exits through a gas outlet (13) at the top of the reactor (6). According to the preferred embodiment of the present invention, this gas outlet (13) has a valve (14) (in this case, a throttling valve) which, by reducing the gas flow, can increase the pressure of the gas and liquid contained in the reactor (6) (indicated by the arrows (15) in Figure 1). Furthermore, the reactor (6) has a pressure gauge (16) to measure the pressure inside the reactor (6).

[0074] When the valve (14) is fully opened, no overpressure is generated inside the reactor (0 bar reading on the indicator (16)). As the valve (14) is gradually closed and the outflow is restricted, the overpressure can reach 10 bar (in tests performed by the inventors, an overpressure of 3 bar above atmospheric pressure was reached inside the reactor). The gas flow (17) exiting the reactor (6) can optionally be directed to a gas treatment system (e.g., activated carbon filters). Once the liquid (7) contained in the reactor has the target concentration of molecules from the plasma-activated gas, it can be called plasma-treated or activated liquid, PTL or PAL (according to the preferred embodiment of the present invention, plasma-treated or activated water, PTA or PAL) (18).Although reference numbers (7) and (18) are used, those skilled in the art will understand that the liquid (7) and the plasma-activated liquid (18) are both mixed in the reactor (6) during the performance of the plasma activation method of the present invention. At the beginning of the method, all the liquid contained in the reactor (6) will be the starting liquid (7), and it will gradually become plasma-activated as plasma-activated gas (4) is bubbled into the reactor (6) until all or substantially all of the liquid contained in the reactor (6) is plasma-activated liquid (18).

[0075] This plasma-activated liquid (18) is extracted through the liquid outlet (19) at the bottom of the reactor (6), which preferably has a valve (20) that remains closed during the AAP generation method. A cleaning gun (not shown), for example, can be connected to this liquid outlet (19) and used to clean and disinfect a surface using pressurized AAP (the pressure reached inside the reactor).

[0076] The parameters used for the generation of AAP according to the preferred embodiment of the present invention are as follows:

[0077] Table 1 below shows the nomenclature of the three AAP samples produced by the tests described in this document and the pressure reached in the mixing reactor for the production of each of these samples: Table 1

[0078] In the preferred embodiment of the present invention, it is shown how this increase in the reactive species dissolved in plasma-activated water (PAW) allows for an increase in the disinfectant capacity of said liquid against a solution artificially contaminated with Listeria monocytogenes.

[0079] As demonstrated in the examples described below in this document, the physicochemical characteristics of an AAP that significantly reduces the Listeria monocytogenes load were determined to be: pH < 3, EC (electrical conductivity) > 1000 pS / cm, ORP (oxidation-reduction potential) > 500 mV, NOT > 180 mg / l NC>2' > 3 mg / l.

[0080] Examples

[0081] The following describes several application examples of treatment with an AAP generated using the method disclosed in this document.

[0082] 1) Analysis for the quantification of reactive species present in the AAP:

[0083] First, a quantification assay was performed on the reactive species present in a single sample of each AAP prepared as described above.

[0084] The high reactivity of the most biocidal secondary species present in AAP (OH*, NO*, and NO2*) means that their detection and quantification, especially in the liquid phase, must be performed indirectly. The main methods for detecting these species use chemicals that react selectively with these radicals to generate relatively stable products that can be detected spectroscopically by electron paramagnetic resonance, fluorimetry, or high-performance liquid chromatography (HPLC).

[0085] In this case, for the detection and indirect quantification of the reactive species present in the AAP, the method described by Lukes et al. (“Aqueous-phase chemistry and bactericidal effects from an air discharge plasma in contact with water: evidence for the formation of peroxynitrite through a pseudo-second-order postdischarge reaction of H2O2 and HNO2”, Plasma Sources Sci. Technol. 23 (2014) 015019) was used as a reference. This method is based on the reaction between phenol (CeHs-OH) and the OH*, NO*, and NO2* radicals. A solution of phenol in water (« 2 x 10 -2 M) of which 5 ml are taken and mixed with 95 ml of AAP, and the mixture is then heated to 50 °C for 24 hours. Subsequently, the solution is filtered using a 0.45 µm filter disc and subjected to high-performance liquid chromatography (HPLC): 20 pl; C18 column; mobile phase of 1.0 ml / min using the following elution gradient:

[0086] Total time: 16 min; pressure: « 90 bar at 90 / 10, « 60 bar at 60 / 40; DAD detector at 260 nm (reference: 699 nm).

[0087] The reaction products are: benzoquinone (phenol + OH*), 4-nitrosophenol (phenol + NO*) and 2-nitrophenol (phenol + NO2*).

[0088] The retention times are: hydroquinone: « 5 min, 4-nitrosophenol: « 5.4 min, phenol: « 8.2 min and 2-nitrophenol: « 11.2 min.

[0089] For the quantification of reaction products (mg / L), the corresponding calibration curves were prepared from the identified absorbance values ​​of reaction product solutions of known concentrations. Benzoquinone and 2-nitrophenol standards with a purity >98% were obtained from Sigma-Aldrich (Madrid, Spain), and the 4-nitrosophenol standard with a purity >98% was obtained from TCI (Tokyo, Japan). Methanol (>99.5%) was purchased from Scharlab (Sentmenat, Barcelona, ​​Spain).

[0090] Individual stock solutions were prepared at a concentration of 10' 2 M in water-methanol (95-5) and were stored in glass bottles at 8 °C.

[0091] The calibration curves were prepared by dilution with deionized water with the following concentrations: benzoquinone 1.35x10 -5 M, 2-nitrophenol 1,60x10 -4 M and 4- nitrosophenol 2.54x10' 4 M.

[0092] The calibration curves were as follows:

[0093] Chromatograms were obtained from the various AAP samples under study (AAP-Obar, AAP-1bar and AAP-3bar) in which the signals related to the reaction products with phenol of the most important reactive species in relation to the disinfectant / decontaminating capacity of AAP were identified: hydroxyl radicals (OH*; benzoquinone), acidified nitrites (NO*; 4-nitrosophenol and NO2*; 2-nitrophenol) and phenol itself (Figure 2).

[0094] Finally, each of the reactive species present was indirectly quantified (from the reaction products with phenol) using the method described above, and the results are shown in Figure 3.

[0095] Figure 3 shows:

[0096] • For AAP-3bar and AAP-1 bar, the reactive species with the highest concentration is NO* (product of the mixture with phenol, 4-nitrosophenol), followed by NO2* (2-nitrophenol) and OH* (benzoquinone).

[0097] • The AAP-3bar sample has the highest concentration of all biocidal reactive species, followed by AAP-1bar and AAP-Obar.

[0098] 2) Tests relating to the inactivation of a bacterial solution: Analysis of the microbial inactivation of AAP

[0099] A bacterial solution of 10 8CFU / ml. Subsequently, 0.5 ml of bacterial solution was added to 4.5 ml of each AAP and to distilled water (which was the bacterial growth control) in order to make a 1 / 10 dilution and bring the AAP into contact with 10 7 CFU / ml of Listeria monocytogenes. Each assay was performed in triplicate on different days.

[0100] Once the AAP / bacterial contact times had elapsed (5, 15, 30, and 60 minutes in all cases), 1 / 10 dilutions were prepared in distilled water for each sample. Then, 5 µL of each sample were plated onto BHI agar plates and incubated at 37 °C for 24 h.

[0101] Finally, the microbial count was carried out by counting the grown colonies of Listeria monocytogenes after 24 h of incubation, expressing the bacterial population in colony forming units per ml (CFU / ml).

[0102] Results obtained

[0103] To analyze the effectiveness of the AAPs once generated (storage time), the same AAPs were analyzed immediately after being generated (Figure 4a) and after 24 hours (Figure 4b).

[0104] Figure 4a shows the following:

[0105] • Treatments with all AAPs achieve total inactivation (7 log) with AAP / bacterial contact times of 30 and 60 minutes.

[0106] • After 15 minutes of contact, the only treatment achieving complete inactivation was the AAP-3bar sample, which was almost 3 log higher than AAP-1bar and almost 5 log higher than AAP-0bar. The differences in inactivation between the various AAPs were statistically significant in all cases, demonstrating that higher pressure in the mixing reactor resulted in greater bacterial inactivation.

[0107] • For 5 minutes of AAP / bacterial contact, there are no statistically significant differences in inactivation.

[0108] 18 Figure 4b shows the following:

[0109] • The inactivation results of the samples after 24 hours of storage (at room temperature) remain relevant, although slightly lower for some samples and contact times.

[0110] • Treatments with all AAPs achieve total inactivation (7 log) with AAP / bacteria contact times of 60 minutes.

[0111] • For 30 minutes of contact, the only treatment that achieves total inactivation is the AAP-3bar sample, this treatment being 3.5 log greater than AAP-1bar and almost 4.5 log greater than AAP-0bar. The differences in inactivation between the different AAPs are statistically significant in all cases and, as in the results shown in Figure 4a, demonstrate that higher pressure in the mixing reactor leads to greater bacterial inactivation.

[0112] • For 15 minutes of AAP / bacteria contact, the AAP-3bar sample achieves an inactivation 1 log greater than the AAP-Obar sample, this difference in inactivation being statistically significant.

[0113] As can be seen from the previous results, the best treatment was the one with the highest pressure in the mixing reactor, namely AAP-3 bar. It is important to highlight that the greater bacterial inactivation obtained with the AAP-3 bar sample was achieved at no additional cost, as the only adjustment made was to restrict the flow of ionized gas in the mixing reactor. In other words, this greater inactivation did not require any extra energy expenditure. The same plasma power and treatment time (for the same volume of water) were used as those employed for generating the AAP-0 bar and AAP-1 bar samples.

[0114] Based on the results obtained in this example, it is possible to state that at higher pressures in the mixing reactor (ionized gas / liquid), there is a higher concentration of reactive biocidal species present in the AAP (Figures 2 and 3), and therefore, a greater capacity for inactivation of the AAP (Figure 4).

[0115] However, the choice of one or another of the AAPs disclosed herein, all of which fall within the scope of protection of the appended claims, will depend on the preferences and technical constraints of the specific application in which the treatment method disclosed herein is to be used. To determine the pH, EC (electrical conductivity), ORP (oxidation-reduction potential), and NOs' and NO2 concentrations, techniques widely known in the art were used.

[0116] Therefore, the preferred embodiment of the system and method disclosed in the present invention refers to the use of the generated AAP as a disinfectant agent.

[0117] As can be seen from the information provided earlier in this document, the present invention offers several advantages over the prior art, such as: a. Improved efficiency of liquid treatments using plasma, without additional costs, since the pressure increase (one of the main features of the present invention) is obtained simply by restricting the ionized gas at its outlet from the mixing reactor. b. Generation of a large volume per unit of time, much more than most devices known in the prior art. This is of vital importance for the industrial application of the new device. c. The generation of a pressurized liquid allows for pressure cleaning using a disinfectant (plasma-activated water, PWA). d.The disinfectant effectiveness (and presumably the concentration of dissolved biocidal reactive species in the treated liquid) remains constant over time with only a slight decrease in effectiveness. The device and method are easily scalable and can be fully automated.

[0118] This document discloses various embodiments of the device and method of the present invention. However, those skilled in the art will readily understand that the features disclosed in embodiments of the method can be equally applied to embodiments of the device and vice versa.

[0119] Although the invention has been described with reference to a preferred embodiment thereof, those skilled in the art will understand that modifications and variations may be applied to said embodiment without leaving the scope of protection defined by the appended claims.

Claims

CLAIMS 1. System for generating plasma-activated liquid (PAL), comprising: - a plasma generator (1) into which a gas flow (2) is introduced to generate a plasma-activated gas flow (4); - a conduit (5) connecting the plasma generator (1) to a reactor (6); - some non-return means (8) arranged in the conduit (5); - a reactor (6) arranged to contain a liquid (7); - a bubble diffuser (10) disposed at a gas inlet to the reactor (6) from the conduit (5), for producing plasma-activated gas bubbles (4) within the liquid (7); the reactor (6) comprising: - a liquid inlet (9) for introducing liquid (7) into the reactor (6); - a liquid outlet (19) for the outlet of plasma-activated liquid (18) from the reactor (6); and - a gas outlet (13) for the gas outlet (17) after its reaction with the liquid (7) inside the reactor (6).

2. System according to claim 1, characterized in that it further comprises a valve (14) at the gas outlet (13) to reduce the flow of gas (17) leaving the reactor (6), thereby increasing the pressure in the reactor (6).

3. System according to claim 2, characterized in that the valve (14) is a throttling valve.

4. System according to any of claims 2 and 3, characterized in that it further comprises a pressure indicator (16) to indicate the pressure inside the reactor (6).

5. System according to any of claims 2 to 4, characterized in that the valve (14) allows the pressure in the reactor (6) to be increased between 0 and 10 bar above atmospheric pressure, preferably between 0 and 4 bar.

6. System according to any of the preceding claims, characterized in that the bubble diffuser (10) is a flexible fine bubble diffuser made of EPDM.

7. System according to any of the preceding claims, characterized in that the The liquid (7) used is water.

8. System according to any of the preceding claims, characterized in that the gas (2) used is air.

9. Method for generating plasma-activated liquid (PAL), comprising: - introduce a desired volume of liquid to be treated into a reactor; - introduce a desired gas flow into a plasma generator; - activate the plasma generator to generate a plasma-activated gas flow; - bubbling the plasma-activated gas through the liquid contained in the reactor to produce plasma-activated liquid; and - evacuate the plasma-activated fluid.

10. Method according to claim 9, characterized in that it further comprises the step of increasing the pressure in the reactor while the plasma-activated gas is bubbled into the reactor.

11. Method according to claim 10, characterized in that the step of increasing the pressure in the reactor comprises increasing the pressure between 0 and 10 bar above atmospheric pressure, preferably between 0 and 4 bar.

12. Method according to any of claims 10 and 11, characterized in that it further comprises maintaining the reactor under pressure after bubbling the plasma-activated gas into the reactor under increased pressure.

13. Method according to claim 12, characterized in that the reactor is maintained under pressure for at least 1 hour after bubbling the plasma-activated gas into the reactor under increased pressure.

14. Method according to any of claims 9 to 13, characterized in that the liquid introduced into the reactor is water.

15. Method according to any of claims 9 to 14, characterized in that the gas introduced into the plasma generator is air.

16. Use of plasma-activated liquid (PAL) produced by the system according to any of claims 1 to 8 or by the method according to any of the claims 9 to 15, as a disinfectant.

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