Systems and methods for water treatment using venturi plasma discharges

Abstract

The water treatment system includes a venturi injector including a venturi inlet that takes in water to be treated, a venturi throat that includes an orifice in fluid communication with a gas source, a discharge electrode integrated into the gas inlet in fluid communication with the orifice for generating a plasma discharge and thereby producing treated water, and a venturi outlet that discharges the treated water.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 63 / 102,788, filed June 30, 2020, the entire contents of which are incorporated herein by reference. [Background technology]

[0002] Oil and gas production processes generate large amounts of liquid waste. For example, hydraulic fracturing of shale utilizes large amounts of pressurized water to fracture shale formations. The wastewater generated during the drilling phase is called flowback water, while the water generated during the production phase is called produced water. Both flowback water and produced water contain various organic and inorganic components, and discharging produced water can contaminate surface and groundwater and soil. Approximately 250 million barrels per day (i.e., approximately 30 million m per day) of wastewater is generated worldwide. 3 ) of produced water is generated (see Fl-R. Ahmadun et al., "Review of technologies for oil and gas produced water treatment," J. Hazard. Mater., vol. 170, pp. 530-551, 2009), and this volume is expected to continue to grow over the long term, creating a growing need for new methods to robustly and efficiently treat large volumes of produced water. Due to the volatility of oil and gas prices, there is a parallel and urgent need to reduce production costs, including produced water treatment costs.

[0003] A variety of methods are currently available for treating produced water for discharge purposes and for recycling and reuse in subsequent hydraulic fracturing operations. This diverse array of water treatment technologies includes, among other things, de-oiling (removal of dispersed oil and grease), removal of soluble organic matter, disinfection, removal of suspended solid particles, removal of dissolved gases (including hydrocarbon gases, carbon dioxide, and hydrogen sulfide), desalination (removal of sodium and chloride ions), and water softening (reduction of calcium and magnesium hardness) (see F.I.-R. Ahmadun et al.). Similar water treatment objectives can be found in a wide range of applications beyond produced water and flowback water, such as pretreatment of industrial wastewater or process water for discharge or beneficial reuse, municipal wastewater for irrigation reuse, and well water treatment for residential or light commercial use, among other things.

[0004] Plasma arc discharges generate extremely high temperatures of over 2000 K around the arc (see A. Czernichowski et al., "Spectral and electrical diagnostics of gliding arc," Acta Physica Polonica - Series A General Physics, vol. 89, pp. 595-604, 1996, and O. Mutaf-Yardimci et al., "Thermal and nonthermal regimes of gliding arc discharge in air flow," Journal of Applied Physics, vol. 87, pp. 1632-1641, 2000). In addition, plasma discharges directly deposit active plasma species, namely OH, O, O, HO, NO, and OH, into the liquid. xThus, if plasma discharge can be successfully generated in produced water, it can be used for the removal of dispersed oil / grease and soluble hydrocarbons (see N. McIntyre et al., "Uses of ultraviolet / ozone for hydrocarbon removal: Applications to surfaces of complex composition or geometry," J. Vac. Sci. Technol., A: Vacuum, Surfaces, and Films, vol. 9, pp. 1355-1359, 1991), water softening (see Y. Yang et al., "Removal of CaCO3 scales on a filter membrane using plasma discharge in water," Int. J. Heat Mass Transfer, vol. 52, pp. 4901-4906, 2009, and Y. Yang et al., "Mineral Fouling Control by Underwater Plasma Discharge in a Heat Exchanger," J. Heat Transfer, vol. 133, p. 054502, 2011), and disinfection (see H.-S. Kim et al., "Concentration of hydrogen peroxide generated by gliding arc discharge and inactivation of E. coli in water," Int. Commun. Heat Mass Transfer, vol. 42, pp. 5-10, 2013). These active plasma treatment species can be employed for produced water and flowback water from oil and gas exploration, and more broadly, wastewater streams from municipal and many other industrial processes.

[0005] When a voltage gradient (greater than 1 kV / cm) is applied between two electrodes (i.e., an anode and a cathode) separated by approximately 1 cm, free electrons break down the air, creating a plasma discharge that appears similar to lightning. Electrons can also break down liquids with low electrical conductivity (liquids with a conductivity of 0.1 mS / cm or less), generating plasma within the liquid matrix. See Yang, Y., et al., Application of pulsed spark discharge for calcium carbonate precipitation in hard water. Water Res., 2010, 44:3659-3668; Yang, Y., Y. Cho, and A. Fridman, Plasma Discharge in Liquid: Water Treatment and Applications. 2012, New York: CRC Press; and Kim, H. S., et al., Use of plasma gliding arc discharges on the inactivation of E. coli in water. Separation Purification Technology, 2013, 120:423-428.

[0006] However, when the liquid has high conductivity, such as industrial wastewater, seawater, and produced water, which have conductivities exceeding 10 mS / cm, the water itself behaves as an electrical conductor. To overcome the adverse effects of high conductivity, it is necessary to provide an air gap between the anode and cathode, or at least around the discharge (i.e., high-voltage) electrode. One method for providing such an air gap is to use a vortex flow of the liquid in a cylindrical reactor configuration. The vortex flow creates a low-pressure zone in the center of the reactor, where compressed gas is injected through multiple holes in the sidewall of the discharge electrode. See U.S. Patent Application No. 16 / 258,734, entitled "System and Method for Plasma Discharge in Liquid," filed January 28, 2019, and published August 8, 2019, as U.S. Patent Publication No. 2019 / 0241447A1.

[0007] When a discharge electrode (i.e., anode) is surrounded by gas within a liquid reactor, a plasma (either discharge plasma or arc plasma) is generated. The compressed gas within the plasma vortex system not only aids in the generation of the plasma, but also stretches the arc vertically upward, increasing its physical size. Furthermore, the injected gas also cools the discharge electrode, reducing the risk of electrode erosion caused by the high-temperature focal region of the plasma arc. In addition, the vortex flow of the water causes the arc to slide around the circular edge of the discharge electrode, a highly useful process that continuously cools the electrode.

[0008] In one implementation of a plasma vortex system, the discharge electrode is located at the bottom end of a cylindrical reactor, and the ground electrode is at the top end, so that thermal energy from the plasma flows away from the discharge electrode. According to Ohm's law (i.e., V = iR), the current flow in a plasma discharge is determined by the impedance between the two electrodes, which depends not only on the distance between the two electrodes but also on the conductivity of the liquid. Therefore, the plasma power supply should be designed to accommodate varying impedances due to changes in the electrical conductivity of the liquid.

[0009] When a pulsed plasma arc (20-30 kHz) is suspended in a plasma vortex reactor, a steady supply of reactive oxygen / nitrogen species is generated (i.e.

number

[0010] Two drawbacks of vortex-based plasma discharges are the large pressure drop and the large amount of gas required to provide an air gap around the discharge electrode. Furthermore, centrifugal forces generated by the vortex tend to throw the liquid radially within the reactor, while the gas remains in the center of the reactor. Naturally, the liquid and gas do not mix and remain separate. Because the gas contains some useful active plasma species, efficient mixing of the liquid and gas is useful for enhancing the plasma treatment of water or wastewater.

[0011] Therefore, there is a need for a method of generating plasma in a liquid that requires less pressure drop, a smaller gas volume, a smaller footprint, and has improved mixing between the liquid and the gas, resulting in continued improvements in water treatment using pulsed spark or arc discharges with disinfecting capabilities for water, river water, seawater, well water, industrial or municipal wastewater, industrial process water, and produced or flowback water from fracking operations. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] U.S. Patent Application Publication No. 2019 / 0241447 [Non-patent literature]

[0013] [Non-Patent Document 1] Fl-R.Ahmadun et al., “Review of technologies for oil and gas produced water treatment,” J.Hazard.Mater., vol.170, pp.530-551, 2009 [Non-patent document 2] A. Czernichowski et al., “Spectral and electrical diagnostics of gliding arc,” Acta Physica Polonica-Series A General Physics, vol. 89, pp. 595-604, 1996 [Non-patent document 3] O. Mutaf-Yardimci et al., “Thermal and nonthermal regimes of gliding arc discharge in air flow,” Journal of Applied Physics, vol. 87, pp. 1632-1641, 2000 [Non-patent document 4] N. McIntyre et al., “Uses of ultraviolet / ozone for hydrocarbon removal: Applications to surfaces of complex composition or geometry,” J. Vac. Sci. Technol., A: Vacuum, Surfaces, and Films, vol. 9, pp. 1355-1359, 1991 [Non-patent document 5] Y. Yang et al., “Removal of CaCO3 scales on a filter membrane using plasma discharge in water,” Int. J. Heat Mass Transfer, vol. 52, pp. 4901-4906, 2009 [Non-patent document 6] Y. Yang et al., “Mineral Fouling Control by Underwater Plasma Discharge in a Heat Exchanger,” J. Heat Transfer, vol. 133, p. 054502, 2011 [Non-Patent Document 7] H.-S.Kim et al., “Concentration of hydrogen peroxide generated by gliding arc discharge and inactivation of E.coli in water,” Int.Commun.Heat Mass Transfer,vol.42,pp.5-10,2013 [Non-patent document 8] Yang,Y.,et al.,Application of pulsed spark discharge for calcium carbonate precipitation in hard water.Water Res.,2010.44:p.3659-3668 [Non-Patent Document 9] Yang, Y., YICho, and A. Fridman, Plasma Discharge in Liquid: Water Treatment and Applications.2012, New York: CRC Press. [Non-Patent Document 10] Kim,HS,et al.,Use of plasma gliding arc discharges on the inactivation of E.Coli in water.Separation Purification Technology,2013.120:p.423-428 [Non-Patent Document 11] Hijnen, W., E. Beerendonk, and GJMedema, Inactivation credit of UV radiation for viruses, bacteria and protozoan(oo)cysts in water: a review. Water research, 2006.40(1):p.3-22 Summary of the Invention

[0014] Various embodiments disclosed herein relate to methods and apparatus for water treatment using a venturi plasma discharge. According to one or more embodiments, a water treatment system includes a venturi injector including a venturi inlet that takes in water to be treated, a venturi throat including an orifice in fluid communication with a gas source, a discharge electrode integrated into a gas inlet in fluid communication with the orifice for generating a plasma discharge and thereby producing treated water, and a venturi outlet that discharges the treated water. In some embodiments, the discharge electrode can be a cylindrical discharge electrode. In certain embodiments, the venturi throat can be coaxial with the discharge electrode. In some embodiments, the cylindrical discharge electrode can be a hollow cylindrical discharge electrode. In some of these embodiments, the hollow cylindrical discharge electrode can further include an end cap and multiple side openings in the cylindrical wall. In certain embodiments, the end cap can further include a central opening. In other embodiments, the cylindrical discharge electrode can be a solid rod. In certain embodiments, the venturi inlet can include a taper in fluid communication with the venturi throat. In some embodiments, the water treatment system can further include a cylindrical insulator around the cylindrical discharge electrode. In some of these embodiments, the venturi outlet can be a ground electrode. In some other embodiments, the water treatment system can further include a ground electrode disposed upstream of the venturi throat. In these specific embodiments, the water to be treated can have an electrical conductivity in the range of 0.1 mS / cm to 10 mS / cm. In certain other embodiments, the water treatment system can further include a ground electrode disposed downstream of the venturi throat. In these specific embodiments, the water to be treated can have an electrical conductivity in the range of 10 mS / cm to 250 mS / cm. In certain embodiments, the water treatment system can further include a ground electrode disposed in the venturi throat.In some embodiments, the water to be treated can have an electrical conductivity in the range of 0.1 mS / cm to 250 mS / cm. In certain embodiments, the gas can include the gas to be treated. In some embodiments, the discharge electrode can be a cylindrical discharge electrode having a side opening in the cylindrical wall. In some of these specific embodiments, the discharge electrode can further include a central opening in fluid communication with the gas inlet. In certain of these specific embodiments, the water treatment system can further include a cylindrical insulator around the cylindrical discharge electrode and an air gap between the cylindrical insulator and the cylindrical discharge electrode. In some of these specific embodiments, the venturi injector can be a ground electrode. In certain embodiments, the venturi outlet can discharge the treated water to a water holding tank in fluid communication with the venturi inlet. In some embodiments, the water treatment system can further include a gas recirculation system in fluid communication with the gas source.

[0015] According to one or more embodiments, a method of water treatment includes flowing water to be treated through a venturi inlet to a venturi throat including an orifice in fluid communication with a gas source, the venturi throat including a discharge electrode integrated into the gas inlet in fluid communication with the orifice; flowing gas from the gas source through a side opening of the discharge electrode; and generating a plasma discharge, thereby producing treated water. In some embodiments, the method can further include recirculating the gas to the gas source. In certain embodiments, the method can further include recirculating the treated water to the venturi inlet.

[0016] The water treatment systems and methods described herein have many advantages compared to plasma vortex systems, including lower pressure drop, smaller gas volume, smaller footprint, and improved mixing.

[0017] The foregoing and other objects and features will become apparent with reference to the following description and accompanying drawings, which are included to provide an understanding of the present invention and which form a part of this specification, and in which like numerals represent like elements. The drawings are not necessarily drawn to scale, emphasis instead being placed upon illustrating embodiments. [Brief explanation of the drawings]

[0018] [Figure 1A] FIG. 1 illustrates a simplified cross-sectional view of a plasma venturi water treatment system according to one or more embodiments. [Figure 1B] FIG. 1 illustrates a simplified cross-sectional view of a plasma venturi water treatment system according to one or more embodiments. [Figure 1C] FIG. 1 illustrates a simplified cross-sectional view of a plasma venturi water treatment system according to one or more embodiments. [Figure 1D] FIG. 1 illustrates a simplified cross-sectional view of a plasma venturi water treatment system according to one or more embodiments. [Figure 2] FIG. 1 is a simplified perspective view of a discharge electrode for a plasma venturi water treatment system according to one or more embodiments. [Figure 3A] FIG. 1 is a simplified cross-sectional view of another plasma venturi water treatment system according to one or more embodiments. [Figure 3B] FIG. 1 is a simplified cross-sectional view of another plasma venturi water treatment system according to one or more embodiments. [Figure 3C] FIG. 1 is a simplified cross-sectional view of another plasma venturi water treatment system according to one or more embodiments. [Figure 3D] FIG. 1 is a simplified cross-sectional view of another plasma venturi water treatment system according to one or more embodiments. [Figure 3E] FIG. 1 is a simplified top view of a tangential venturi inlet according to one or more embodiments. [Figure 4]1 is a graph of pressure (psig) at the venturi throat as a function of the ratio between the venturi throat diameter D2 and the venturi inlet diameter D1 according to one or more embodiments. [Figure 5] FIG. 1 is a simplified cross-sectional view of a plasma venturi water treatment system including a raw water holding tank and a gas recirculation system according to one or more embodiments. [Figure 6] FIG. 1 is a simplified cross-sectional view of a plasma venturi water treatment system including a raw water holding tank, a treated water holding tank, and a gas recirculation system according to one or more embodiments. [Figure 7] FIG. 1 is a simplified perspective view of a plasma Venturi water treatment system for biological decontamination or disinfection of water used for irrigation, such as drip irrigation, according to one or more embodiments. [Figure 8A] 1 is a photograph of a plasma venturi water treatment system with the plasma discharge turned off, according to one or more embodiments. [Figure 8B] 1 is a photograph of a plasma venturi water treatment system with plasma discharge turned on, according to one or more embodiments. [Figure 9] FIG. 1 is a flow diagram of a method for treating water using a plasma venturi water treatment system according to one or more embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0019] It should be understood that the figures and descriptions of the present invention have been simplified to illustrate relevant elements for a clearer understanding of the present invention, while excluding, for clarity, many other elements found in systems and methods for plasma discharge in liquids. Those skilled in the art may recognize that other elements and / or steps are desirable and / or required in implementing the present invention. However, because such elements and steps are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements and steps is not provided herein. The disclosure herein covers all such variations and modifications to such elements and methods known to those skilled in the art.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described.

[0021] As used herein, each of the following terms has the meaning associated with it in this section.

[0022] The articles "a" and "an" are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element.

[0023] As used herein, "about" when referring to a measurable value such as an amount, duration, etc., is intended to encompass variations of ±20%, ±10%, ±5%, ±1%, ±0.1% from the specified value, as such variations are appropriate.

[0024] As used herein, "HV" means high voltage, such as voltages greater than 1,000V.

[0025] Ranges: Throughout this disclosure, various aspects of the invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Where appropriate, the description of a range should be considered to have specifically disclosed all the possible subranges and individual numerical values ​​within that range. For example, description of a range such as 1 to 6 should be considered to have specifically disclosed subranges such as 1 to 3, 1 to 4, 1 to 5, 2 to 4, 2 to 6, 3 to 6, etc., as well as individual numerical values ​​within that range, e.g., 1, 2, 2.7, 3, 4, 5, 5.3, and 6. This is true regardless of the broadness of the range.

[0026] The purpose of the systems and methods described herein is to disinfect various types of liquids, including water, river / lake water, seawater, well water, industrial or municipal wastewater, industrial process water, and produced or flowback water from fracking operations, and to remove contaminants in wastewater and leachate, and to oxidize and decompose them, without leaving treatment gaps or secondary waste problems. Various embodiments disclosed herein relate to methods and apparatus for water treatment using venturi plasma discharges. According to one or more embodiments, as shown in FIG. 1A , a water treatment system 100 includes a venturi injector 110 having a cylindrical tubular shape. To minimize pressure drop, the cross-sectional area of ​​the injector 110 gradually decreases from an initial diameter D1 at the venturi inlet 120 and then gradually increases to a final diameter D3 at the venturi outlet 140. The diameter D3 of the venturi outlet 140 is typically equal to the diameter D1 of the venturi inlet 120, although it should be noted that other choices for D1 and D3 are possible. See Mazzei Injector Company LLC (Bakersfield, California, USA). The reduced cross-sectional area 130 having diameter D2 is often referred to as the venturi throat 130, where, according to Bernoulli's principle, fluid pressure decreases as fluid velocity increases. See Munson, B., et al., Fundamentals of Fluid Mechanics. 7th ed. 2013, New York: John Wiley & Sons, Inc. Thus, the pressure at the venturi throat 130 is always less than the inlet liquid pressure due to the reduced cross-sectional area. Therefore, as the inlet liquid flow rate increases, the pressure at the venturi throat 130 decreases accordingly. In addition, as the cross-sectional area of ​​the throat decreases, the pressure at the venturi throat 130 also decreases. Because the pressure at the venturi throat can be adjusted relatively easily, the venturi injector 110 can be considered a method for generating an HV plasma discharge in a liquid. There are several properties of Venturi flow that can be useful for generating plasma in liquids.

[0027] The pressure at the throat 130 can be reduced to be well below the inlet pressure of the liquid. Therefore, the venturi throat 130 is an ideal location from which air or other gas can be injected through an orifice 135 that is in fluid communication with a gas source 150. Depending on the level of throat pressure, it may be possible to inject the gas without the use of a compressor.

[0028] Air (or gas) is introduced into the venturi system 100 from a gas source 150 through a gas inlet 155 in fluid communication with the orifice 135 to provide an air gap 186 around the discharge electrode 180, a necessary condition for plasma discharge in water. The introduction of air into the venturi system 100 generally occurs due to reduced pressure at the throat 130, which can be explained by Bernoulli's principle. The Bernoulli equation relates pressure and flow velocity along a streamline as follows:

number

number

[0029] Therefore, in the above Bernoulli equation, V2

number

number

[0030] As an example, consider a water treatment system 100 with a 2-inch inlet diameter D1 delivering a flow rate of approximately 100 gallons per minute (gpm) at an inlet pressure of 40 psig. Note that a flow rate of 100 gpm in a 2-inch diameter pipe results in a flow velocity V1 of 10.2 ft / s. If the throat diameter D2 is 0.8 inches, i.e., D2 / D1=0.4, the pressure drops to approximately 13 psig, as shown in FIG. 4.

[0031] If the throat diameter D2 is further reduced to 0.7 inches, i.e., D2 / D1 = 0.35, the pressure drops to -6 psig (i.e., a hard vacuum), as shown in Figure 4, a significant reduction in throat pressure, and even stronger vacuums are possible at lower values ​​of D2 / D1. This reduction in throat pressure can significantly increase the airflow through the orifice 135 in the venturi throat 130 without the use of a compressor.

[0032] When air or gas (optionally containing droplets, dust, or other aerosolized solids) is injected into the liquid through orifice 135 at throat 130, the high liquid velocity at throat 130 causes the bulk air to break down into a large number of small-sized bubbles, providing improved mixing between the liquid and air compared to plasma vortices, thereby enhancing plasma treatment of the liquid.

[0033] The pressure drop in the liquid flow is significantly smaller in a venturi plasma system than in a plasma vortex system. This is due to the fact that in a plasma vortex system, the centrifugal motion of the vortex flow causes the liquid pressure at the plasma reactor outlet to drop to zero gauge pressure. In contrast, when the cross-sectional area of ​​the venturi injector 110 outlet is increased, Bernoulli's principle restores the liquid pressure at the venturi outlet 140, so the liquid pressure at the venturi injector 110 outlet is still significantly greater than zero gauge pressure.

[0034] The flow reactor geometry of a Venturi plasma system is a tubular configuration compared to the three-dimensional geometry of a Plasma Vortex system. Therefore, the Venturi plasma system has a simpler structure, a smaller footprint, and a lower pressure drop in the connecting piping compared to a Plasma Vortex system.

[0035] To generate a plasma discharge in a liquid, it is necessary to have a grounded electrode in the reactor. In a venturi plasma system, one can consider a grounded electrode 125 located in the venturi throat 130, as shown in FIG. 1A, or an upstream grounded ring electrode 160 near the venturi inlet 120, as shown in FIG. 1B, with an insulating ring 165 provided when the venturi injector 110 is made of metal or other conductive material, as described further below. Alternatively, one can consider a downstream grounded electrode, i.e., a grounded ring electrode 170 near the venturi outlet 140, as shown in FIG. 1C, with an insulating ring 175 provided when the venturi injector 110 is made of metal or other conductive material, as described further below. Because the impedance in a plasma circuit is approximately the sum of the air gap resistance and the liquid resistance, the liquid conductivity is a significant component of the impedance. When a downstream ground 170 is used, the liquid's conductivity can be significantly higher (e.g., 10 mS / cm to 250 mS / cm) because many small bubbles are dispersed in the liquid, reducing the effective conductivity of the liquid-gas mixture. Therefore, when the downstream ground 170 is located, the presence of dispersed bubbles increases the impedance. On the other hand, when an upstream ground 160 is used, the impedance is small because there are few bubbles in the liquid, and therefore it is suitable for liquids with low conductivity (e.g., 0.1 mS / cm to 10 mS / cm). Therefore, the location of the ground electrode 160 or 170 can be used to optimize the plasma impedance depending on the electrical conductivity of the liquid.

[0036] As shown in FIGS. 1A-1C, the discharge electrode 180 is integrated into the gas inlet 155. In some embodiments, the discharge electrode 180 is a cylindrical discharge electrode having side openings 185 in the cylindrical wall. The holes 185 in the side wall of the discharge electrode 180 provide a gap 186 (not shown in FIG. 1B for clarity) around the discharge electrode 180. For example, in one embodiment, the side wall of the discharge electrode 180 has an outer diameter of 32 mm and has 16 circular holes 185 with an inner diameter of 3 mm. Optionally, as shown in FIG. 1B, the end wall of the discharge electrode 180 has one axially centered circular hole 188, e.g., with an inner diameter of 3 mm, for air flow. Therefore, the sum of all openings of the side holes 185 accounts for approximately 94%, while the openings of the holes 188 in the end wall account for 6%. In other words, most of the gas introduced through the gas inlet 155 at the throat 130 flows through the holes 185 in the side wall. Benefits of the high flow through the side holes 185 include efficient cooling of the discharge electrode 180 and a stable air gap 186 between the discharge electrode 180 and the cylindrical insulator 190.

[0037] As shown in FIG. 1D, the orifice 135 can be drilled to position the discharge electrode 180 further into the venturi throat 130. Three ground electrodes 125, 160, and 170 are also shown in FIG. 1D. The discharge electrode 280, detailed in FIG. 2, can be made of two sections 281 and 282, whereby the section 282 closest to the plasma discharge can be made of titanium or other corrosion- and temperature-resistant metal, and the other section 281 can be made of an easily machinable metal such as aluminum. An O-ring 283 provides a gas-tight seal between the gas supply 255 and the cylindrical insulator 290. As discussed above, gas flowing through the side openings 285, shown in the perspective view in FIG. 2 to illustrate the multiple side openings discussed above, sweeps out a gap 286 around the discharge electrode 282 within the lower portion of the cylindrical insulator 290, and a central opening 288 provides additional gas flow. The cylindrical insulator 290 can be made of ceramic or other electrically insulating material suitable for use at high temperatures. The discharge electrode 280 can also be facing upward by turning the plasma processing system shown in Figures 1A-1D upside down (see the photograph shown in Figure 8A). Returning to Figure 1A, the venturi injector 110 can be made of an electrically insulating material, such as plastic, and the ground electrode 125 can be located within the venturi throat 130, or the venturi injector 110 can be made of metal or other electrically conductive material, thereby making the venturi injector 110 the ground electrode 125.

[0038] According to one or more embodiments, as shown in FIG. 3A , a water treatment system 300 includes a venturi injector 310 having a cylindrical-tubular shape in which the cross-sectional area of ​​the injector 310 gradually decreases from an initial diameter D1 at a venturi inlet 320 and then increases to a final diameter D3 at a venturi outlet 340. A reduced-cross-sectional area venturi throat 330 having a diameter D2 is coaxial with a discharge electrode 380. The pressure at the throat 330 can be reduced sufficiently below the liquid inlet pressure, and therefore, the reduced pressure at the throat 330 according to Bernoulli's principle described above allows air or other gas to be injected through an orifice 335 in fluid communication with a gas source 350. Air (or gas) is introduced into the venturi system 300 from the gas source 350 through a gas inlet 355 in fluid communication with the orifice 335 to provide a gap 386 around the discharge electrode 380, a necessary condition for plasma discharge in water. The discharge electrode 380 is integrated into the gas inlet 355, and an orifice 335 is drilled so that the discharge electrode 380 is positioned within the venturi throat 330. In some embodiments, the discharge electrode 380 is a cylindrical discharge electrode. As shown in FIG. 3A, the discharge electrode can be a hollow cylindrical discharge electrode 380. In another aspect, as shown in FIG. 3B, the hollow cylindrical discharge electrode 380 includes an end cap 381 and multiple side openings 385 in the cylindrical wall. Optionally, as shown in FIG. 3C, the end cap 381 includes a central opening 388. In yet another aspect, as shown in FIG. 3D, the cylindrical discharge electrode 380 is a solid rod 380. In embodiments using a solid rod electrode 380, gas flows around the outside of the electrode 380 rather than through the interior of the electrode 380. This gas flow can be parallel to the axis of electrode 380, or it can have a non-zero angular component to its velocity and thereby move along a helical streamline. In such cases, the rotating gas flow may have either a right-handed or left-handed chirality.In embodiments in which both the gas and liquid streams have non-zero angular velocities, the gas and liquid streams may have the same chirality (co-rotation) or opposite chirality (counter-rotation). As shown in Figures 3A-3D, a cylindrical insulator 390 is disposed around the cylindrical discharge electrode 380. The cylindrical insulator 390 may be made of ceramic or other electrical insulating material suitable for use at high temperatures.

[0039] To generate a plasma discharge in a liquid, a grounded electrode must be placed in the reactor and in contact with the liquid. In a venturi plasma system 300, the venturi outlet 340 can be considered to be grounded, as shown in FIG. 3A, or a grounded metal plate 360 ​​can be included between the venturi inlet 320 and the venturi outlet 340, as shown in FIGS. 3B-3D. The grounded metal plate 360 ​​allows the venturi outlet 340 to be made of a non-conductive, optionally transparent, material, thereby allowing for visual observation of the plasma discharge.

[0040] Returning to FIG. 3A, the venturi throat 330 can take the form of an annular gap 331 having a gap length GL. In another embodiment, as shown in FIGS. 3B-3D, the venturi inlet 320 includes a taper 325 in fluid communication with the venturi throat 330. The taper 325 reduces the frictional pressure drop because the axial gap length of the annular gap 331 is significantly reduced. The venturi inlet 320 can be axially perpendicular to the discharge electrode 380, or, as shown in FIG. 3E, the venturi inlet 320 may be oriented tangentially to the discharge electrode 380. An optional taper (not shown) in the venturi inlet 320 leading to the venturi throat 330 maintains circumferential liquid flow while accelerating the liquid velocity.

[0041] As an example, returning to FIG. 3A, consider a water treatment system 300 having a venturi inlet 320 diameter D1=1 inch that delivers a flow rate of approximately 100 gpm. When the venturi throat 330 diameter is D2=1.25 inches and the venturi outlet 340 diameter is D3=1.5 inches, for a gap length GL=0.5 inches, the hydraulic diameter D of the annular gap is h = D3 - D2, resulting in a pressure of -17.5 psig (i.e., a hard vacuum). Such a drop in throat pressure can significantly increase the air flow through orifice 335 in venturi throat 330 without the use of a compressor.

[0042] 5, the venturi outlet 540 discharges the treated water into a water holding tank 505 in fluid communication with the venturi inlet 520, thereby recirculating the water to be treated. In some embodiments, the water treatment system 500 can further include a gas recirculation system 552 in fluid communication with a gas source 550, thereby combining the gas to be treated from the top of the holding tank 505 with gas from the gas source 550, optionally compressed by a gas compressor 551. The required water flow rate and water inlet pressure are provided by a water pump 515.

[0043] Alternatively, as shown in Figure 6, a venturi outlet 640 of the water treatment 600 discharges treated water into a water holding tank 695. Gas from the top of the treated water is combined with gas from a gas source 650 in a gas recirculation system 652 in fluid communication with a gas inlet 655, thereby recirculating the gas to be treated, optionally compressed by a gas compressor 651. The required water flow rate and water inlet pressure from the raw water holding tank 605 is provided to the venturi inlet 620 by a water pump 615.

[0044] According to one or more embodiments, as shown in FIG. 7, a plasma Venturi system 700 is deployed for biological decontamination or disinfection of water used for irrigation, particularly drip irrigation, and can dramatically reduce or eliminate plant pathogens and biofouling on equipment such as emitters or drippers to improve agricultural yield, quality, and importantly, the performance and lifespan of the emitter technology. Plasma Venturi technology also simultaneously reduces mineral fouling or scaling, such as calcium carbonate fouling, through the application of an electric field for electro-coagulation of scale-forming salts. As shown in FIG. 7, air from within the drip irrigation line enters the gas inlet 755 of the Venturi injector 710.

[0045] As shown in FIG. 8A, in one embodiment of the plasma venturi system, a water flow rate in the range of 30 gpm to 38 gpm at 40 psig through a 2-inch venturi injector with a venturi inlet diameter of approximately 40 mm and a D2 / D1 ratio of approximately 0.35 generated a gas inlet flow rate of 2 CFM. As shown in FIG. 8B, a plasma discharge was generated with a current in the range of 2 A to 3 A (current-limited mode). Operating parameters included a water flow rate in the range of 30 gpm to 150 gpm, with a corresponding gas inlet flow rate in the range of 1 cfm to 15 cfm, at an operating pressure in the range of 40 psig to 120 psig, with a maximum current of 4 A and a maximum power of 8 kW for the plasma discharge.

[0046] According to one or more embodiments, as shown in FIG. 9 , a method 900 of water treatment includes flowing 910 water to be treated through a venturi inlet to a venturi throat including an orifice in fluid communication with a gas source, the venturi throat including a discharge electrode integrated into the gas inlet in fluid communication with the orifice; flowing 920 gas from the gas source through a side opening in the discharge electrode; and generating a plasma discharge 930 to thereby produce treated water. The gas flowing through the side opening in the discharge electrode sweeps out an air gap between the cylindrical insulator and the cylindrical discharge electrode. In some embodiments, method 900 can further include recirculating 940 the gas to the gas source. In certain embodiments, method 800 can further include recirculating 950 the treated water to the venturi inlet.

[0047] Further Exemplary Embodiments Example 1 is a water treatment system that includes a venturi injector that includes a venturi inlet that takes in water to be treated, a venturi throat that includes an orifice in fluid communication with a gas source, a discharge electrode integrated into the gas inlet that is in fluid communication with the orifice for generating a plasma discharge, thereby producing treated water, and a venturi outlet that discharges the treated water. Example 2 includes the subject matter of example 1, and further includes a ground electrode disposed upstream of the venturi throat. Example 3 includes the subject matter of either Example 1 or 2, wherein the water to be treated has an electrical conductivity in the range of 0.1 mS / cm to 10 mS / cm. Example 4 includes the subject matter of example 1, further including a ground electrode disposed downstream of the venturi throat. Example 5 includes the subject matter of Example 4, wherein the water to be treated has an electrical conductivity in the range of 10 mS / cm to 250 mS / cm. Example 6 includes the subject matter of example 1, further including a ground electrode disposed in the venturi throat. Example 7 includes the subject matter of Example 1, wherein the water to be treated has an electrical conductivity in the range of 0.1 mS / cm to 250 mS / cm. Example 8 includes the subject matter of any of Examples 1-7, wherein the gas includes a gas to be treated. Example 9 includes the subject matter of any of Examples 1 to 8, wherein the discharge electrode is a cylindrical discharge electrode having a side opening in the cylindrical wall. Example 10 includes the subject matter of example 9, in which the discharge electrode further includes a central opening in fluid communication with the gas inlet. Example 11 includes the subject matter of any of Examples 9-10, further including a cylindrical insulator around the cylindrical discharge electrode. Example 12 includes the subject matter of Example 11, further including an air gap between the cylindrical insulator and the cylindrical discharge electrode. Example 13 includes the subject matter of example 11, in which the venturi injector is a ground electrode. Example 14 includes the subject matter of example 1, in which the discharge electrode is a cylindrical discharge electrode. Example 15 includes the subject matter of example 14, wherein the venturi throat is coaxial with the discharge electrode. Example 16 includes the subject matter of Example 14, in which the cylindrical discharge electrode is a hollow cylindrical discharge electrode. Example 17 includes the subject matter of example 16, in which the hollow cylindrical discharge electrode further includes an end cap and a plurality of side openings in the cylindrical wall. Example 18 includes the subject matter of example 17, wherein the end cap includes a central opening. Example 19 includes the subject matter of Example 14, in which the cylindrical discharge electrode is a solid rod. Example 20 includes the subject matter of any of Examples 14-19, wherein the venturi inlet includes a taper in fluid communication with the venturi throat. Example 21 includes the subject matter of any of Examples 14-19, further including a cylindrical insulator around the cylindrical discharge electrode. Example 22 includes the subject matter of example 21, wherein the venturi outlet is a ground electrode. Example 23 includes the subject matter of any of Examples 1-22, wherein the venturi outlet discharges the treated water into a water holding tank in fluid communication with the venturi inlet. Example 24 includes the subject matter of any of Examples 1-23, wherein the water treatment system further includes a gas recirculation system in fluid communication with the gas source. Example 25 is a method of water treatment, comprising: flowing water to be treated through a venturi inlet to a venturi throat including an orifice in fluid communication with a gas source, the venturi throat including a discharge electrode integrated into a gas inlet in fluid communication with the orifice; flowing gas from the gas source through a side opening in the discharge electrode; and generating a plasma discharge, thereby producing treated water. Example 26 includes the subject matter of Example 25, wherein the gas flowing through the side opening in the discharge electrode sweeps out the air gap between the cylindrical insulator and the cylindrical discharge electrode. Example 27 includes the subject matter of either example 25 or 26, further including recycling the gas to the gas source. Example 28 includes the subject matter of any of Examples 25-27, further including recycling the treated water to the venturi inlet.

[0048] The disclosures of any and all patents, patent applications, and publications cited herein are incorporated herein by reference in their entireties. Although the present invention has been disclosed with reference to specific embodiments, it will be apparent that other embodiments and modifications of the invention may be devised by those skilled in the art without departing from the true spirit and scope of the invention.

Claims

1. 1. A water treatment system comprising: a venturi injector including a venturi inlet for taking in water to be treated; a venturi throat including an orifice in fluid communication with a gas source; a cylindrical discharge electrode integrated into a gas inlet in fluid communication with the orifice to generate a plasma discharge, thereby producing treated water, the venturi throat being coaxial with the cylindrical discharge electrode; a venturi outlet for discharging the treated water.

2. The water treatment system of claim 1 , wherein the cylindrical discharge electrode is a hollow cylindrical discharge electrode.

3. The water treatment system of claim 2 , wherein the hollow cylindrical discharge electrode further comprises an end cap and a plurality of side openings in a cylindrical wall.

4. The water treatment system of claim 3 , wherein the end cap includes a central opening.

5. The water treatment system of claim 1 , wherein the cylindrical discharge electrode is a solid rod.

6. The water treatment system of claim 1 , wherein the venturi inlet includes a taper in fluid communication with the venturi throat.

7. The water treatment system of claim 1 , further comprising a cylindrical insulator around the cylindrical discharge electrode.

8. The water treatment system of claim 7 , wherein the venturi outlet is a ground electrode.

9. The water treatment system of claim 1 , further comprising a ground electrode disposed upstream of the venturi throat.

10. 10. The water treatment system of claim 9, wherein the water to be treated has an electrical conductivity in the range of 0.1 mS / cm to 10 mS / cm.

11. The water treatment system of claim 1 , further comprising a ground electrode disposed downstream of the venturi throat.

12. 12. The water treatment system of claim 11, wherein the water to be treated has an electrical conductivity in the range of 10 mS / cm to 250 mS / cm.

13. The water treatment system of claim 1 , further comprising a ground electrode disposed within the venturi throat.

14. 10. The water treatment system of claim 1, wherein the water to be treated has an electrical conductivity in the range of 0.1 mS / cm to 250 mS / cm.

15. The water treatment system of claim 1 , wherein the gas comprises a gas to be treated.

16. The water treatment system of claim 1 , wherein the discharge electrode is a cylindrical discharge electrode having a side opening in a cylindrical wall.

17. 17. The water treatment system of claim 16, wherein the discharge electrode further comprises a central opening in fluid communication with the gas inlet.

18. 17. The water treatment system of claim 16, further comprising a cylindrical insulator around the cylindrical discharge electrode.

19. 20. The water treatment system of claim 18, wherein the venturi injector is a ground electrode.

20. The water treatment system of claim 1 , further comprising a gas recirculation system in fluid communication with the gas source.

21. The water treatment system of claim 1 , wherein the venturi outlet discharges the treated water to a water holding tank in fluid communication with the venturi inlet.

22. 22. The water treatment system of claim 21, further comprising a gas recirculation system in fluid communication with the gas source.

23. 1. A method for water treatment, comprising: flowing water to be treated through a venturi inlet to a venturi throat including an orifice in fluid communication with a gas source, the venturi throat including a discharge electrode integrated into a gas inlet in fluid communication with the orifice; flowing gas from the gas source through a side opening in the discharge electrode; generating a plasma discharge, thereby producing treated water.

24. 24. The method of claim 23, further comprising recycling the gas to the gas source.

25. 24. The method of claim 23, further comprising recirculating the treated water to the venturi inlet.

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