An organic compound destruction apparatus and method are provided, and more particularly, discharge arcs generated between a pair of electrodes in a plasma reactor destroy undesired or contaminant organic molecules in a liquid.
Per-and-polyfluoroalkyl substances (“PFAS”) are a group of man-made chemicals that are persistent in the environment and human body, which can lead to adverse human health effects. PFAS molecules have been commonly used as stain repellants and fire-fighting foams which were emitted into the air and water by industrial processes used to manufacture fluoro chemicals. PFAS molecules have also entered the ground and surface water through disposal of waste and sewage sludge, and as a result of fire-fighting use. Most existing PFAS removal approaches, however, do not destroy PFAS but instead merely generate solid waste and wastewater with high concentrations of PFAS.
U.S. Patent Publication No. 2018/0222781 is entitled “Water Purification using Porous Carbon Electrode” which published to Liu et al. on Aug. 9, 2018. This device uses an electrolysis chemical reaction process in an electrolyte solution to break contaminants into small and stable molecules by using an electric current flowing between parallel electrodes. Furthermore, U.S. Patent Publication No. 2021/0379602 entitled “Electrode Apparatus for Creating a Non-Uniform Electric Field to Remove Polarized Molecules in a Fluid,” invented by common inventor Fan, discloses removing PFAS from water with electrodes. These patent publications are incorporated by reference herein.
Raj Kamal Singh, et al., “Breakdown Products from Perfluorinated Alkyl Substances (PFAS) Degradation in a Plasma-Based Water Treatment Process,” Environmental Science & Technology (2019), 53, 2731-2738, teaches a plasma reactor for the destruction of PFAS, but merely uses a discharge energy spark or arc that is generated between a longitudinal high voltage electrode and the liquid solution in a vessel. A similar arrangement is disclosed in U.S. Patent Publication No. 2016/0228844 entitled “Enhanced Contact Electrical Discharge Plasma Reactor for Liquid and Gas Processing,” published to Mededovic, et al, on Aug. 11, 2016, which is incorporated by reference herein. These conventional centerline arc approaches, however, do not efficiently and quickly destroy all types of PFAS in the liquid, especially short-chain PFAS. In addition, the arcs flow from the electrode to the liquid, which becomes part of the circuit. This leads to intensive heating to the solution, which is undesirable.
In accordance with the present invention, an organic compound destruction apparatus and method are provided. In another aspect, a laterally oriented discharge arc generated between electrodes in a plasma reactor destroys an undesired or contaminant organic molecule in a liquid solution. A further aspect of the electrodes includes a center electrode and a closed-loop outer electrode. Another aspect includes a system which uses electrodes and at least one magnet, which is preferably a closed-loop magnet, to drive the laterally oriented arc across a horizontal plane in a plasma reactor to destroy organic compounds, such as PFAS molecules, in a liquid. Still another aspect includes a system which uses a grid or mesh electrode to create a discharge arc in a plasma reactor to destroy organic compounds, such as PFAS molecules, in a liquid. A further aspect causes bubbles that carry PFAS molecules to rise and interact with a generally horizontally extending electrical discharge between an electrode and a horizontally offset outer electrode/magnet assembly.
In another aspect, an apparatus and method use a non-uniform electric field to concentrate PFAS around an active electrode in a liquid, in combination with gas bubbles generated around this active electrode to enhance the capture and transport of PFAS to the liquid surface. Still another aspect of the present apparatus and method employ a center electrode and a closed-loop magnet assembly-based outer electrode above the liquid surface to generate plasma arcs in between the electrodes, allowing effective plasma interaction with the gas bubbles that carry PFAS and rise within a liquid. A laterally elongated and substantially solid, central electrode is provided in another configuration of the present apparatus and method, in combination with a closed-loop surrounding electrode and a magnet assembly, to laterally orient an electrical arc therebetween in a plasma reactor.
The present apparatus and method are advantageous over traditional approaches. For example, the present system efficiently destroys a majority of PFAS molecules in less than sixty minutes and consumes low electrical power with negligible or substantially no heating to the liquid solution, thereby being cost effective to operate in a large-scale commercial system. Moreover, the present use of plasma effectively breaks the strong C—F bonds within PFAS molecules, thereby generating superior performance as compared to conventional remediation such as electrochemical oxidation, which consumes significantly more electric energy and requires much longer process time (e.g., many hours). Additional advantages and features of the present apparatus and method will be observed in the following description and appended claims, taken in conjunction with the accompanying drawings.
An organic compound destruction apparatus and method include a primarily laterally and horizontally oriented discharge arc, which is generated between a center electrode and a closed-loop outer electrode in a plasma reactor, to destroy undesired organic compounds in a liquid. This can be generally observed in
Apparatus 27 includes an upper and central electrode 31, coaxially surrounded by at least one ring magnet 33 or multiple adjacent magnets, a gas injector 35, and a holding tank 37. In this embodiment, upper central electrode 31 is a solid, metallic rod being elongated in a longitudinal direction spaced above a liquid solution in tank 37. The liquid solution includes PFAS in water 23. In contrast, gas injector 35 is a hollow tube which upwardly projects from and is located near the bottom of the solution through an aperture in a bottom of tank 37. Upper central electrode 31 and gas injector 35 are coaxially aligned in this configuration. A proximal end of gas injector 35 is connected to a gas supply and acts to flow gas, such as argon, therethrough and into the solution which creates upwardly rising bubbles 39 therein. Alternate gases include a mixture of argon plus oxygen, nitrogen, air, and the like.
As can best be observed in
The laterally oriented arc 41 covers at least a majority, if not an entire, upper surface area of tank 37. PFAS molecules attach to and rise with the gas bubbles 39 from the liquid solution into an upper air (preferably not vacuum) area 25 located between water 23 and a distal end of upper central electrode 31. Therefore, arc 41 will contact the PFAS-gas bubbles and destroy at least a majority, and more preferably all, of PFAS molecules 21 as they are transported to the leachate surface. The plasma arc destruction of PFAS is synergistically beneficial since the rotating arc covers almost the entire upper surface of tank 37. Furthermore, the plasma arc is between center electrode 31 and a side electrode in horizontal plane, there is no electric current going through the liquid to cause heating and evaporation of the liquid. This feature enables effective capture of PFAS by the gas bubbles and safe processing.
An optional surfactant can be added into the liquid solution to more effectively transport certain types of PFAS molecules to the liquid surface. It is alternately envisioned that contaminant organic molecules other than PFAS may be destroyed by use of the present apparatus and method, such as 1,4-dioxane, benzene, and the like.
Reference should now be made to
In this configuration, a synergistically combined hollow, metallic lower center electrode and gas injector 35 are mounted to bottom 103 via a sealed insulator 111. An optional gas manifold 113 made of electrically insulative material is coupled to a middle portion of lower center electrode/gas injector 35, inside tank 37, such that the gas longitudinally flows through lower center electrode/gas injector 35, along a lateral length of manifold 113, and is then emitted into the solution via outlet holes 115 spaced along both the manifold and the lower center electrode/gas injector. The lower center electrode/gas injector and manifold form a generally+shape. Gas bubbles 39 are formed from the exiting gas, which thereby upwardly carry the PFAS molecules.
In a preferred option, the apparatus includes at least one pair of co-axial electrodes consist of lower center electrode/gas injector 35 and lower peripheral electrode 131 inside the liquid. Lower peripheral electrode 131 is inwardly spaced from tank 37. An exemplary diameter of the lower center electrode/gas injector is 1-10 mm, while an exemplary diameter of lower peripheral electrode is 10-100 mm. In one version, lower peripheral electrode 131 is a curved and solid tube, while in a second version, the lower peripheral electrode is a tubular-shape metallic grid with openings between the elongated and crossing mesh strands to allow liquid flow therethrough. An electrical circuit 133, including a low-voltage direct current power source 135, is connected to both lower center electrode/gas injector 35 and lower peripheral electrode 131.
Lower center electrode/gas injector 35 and peripheral electrode 131, advantageously create a non-uniform electric field between them. This electric field can effectively drive the PFAS toward the lower center electrode/gas injector. Meanwhile, the gas flows simultaneously from the side wall holes of the lower center electrode/gas injector to generate the bubbles. Since the PFAS molecules are concentrated around the center electrode due to this non-uniform electric field, there is an improved ability of the adjacent gas bubbles to catch the PFAS molecules and transport them to the surface of the liquid solution, where the plasma is generated and interacts with the bubbles. Thus, the non-uniform electric field due to the laterally offset co-axially structured lower electrodes, in combination with the bubbling action and plasma, creates a synergistic and multifunctional system for transporting the contaminants for subsequent destruction.
In this embodiment, multiple cylindrical or bar magnets 141 are arranged adjacent to each other to collectively define a circular assembly, co-axially surrounding neck 107 of tank 37. The permanent magnets in this embodiment have a North-South axis being substantially vertical and parallel to the longitudinal centerline of electrodes 31 and 35. The magnets may be separate parts as shown in
A metallic carrier 147, preferably stainless steel, has an inner clamping segment 149 and an outer retention segment 151. Inner segment 149 has an inverted U-cross-sectional shape which is secured over distal end 109 of the tank and clamped onto its neck 107. Retention segment 151 holds magnets 141 and shunts 143 and 145. Carrier 147, concentrically surrounding upper central electrode 31, acts as an electrode, to generate the plasma arc with the upper central electrode.
Upper central electrode 31 is mounted through an electrically insulative lid (not shown). The lid spans across the otherwise open distal end 109 of the tank. An electrical circuit 161, including a high-voltage power source 163, is connected to upper central electrode 31 and an outer wall of magnet carrier 147. Power source 163 supplies a greater voltage than does power source 135, with power source 163 preferably being at least 10 kV amplitude and power source 135 preferably being 0.5-50 V. All of the electrodes are metallic, such as graphite, copper, stainless steel, nickel or an alloy thereof, by way of non-limiting examples.
Electrical arc 41 (see
The embodiment of
Referring now to
In this exemplary embodiment, gas injector 35 also acts as a lower center electrode and may be one or multiple spaced apart hollow, upwardly elongated active electrodes, aligned along a vertical plane defined by the longitudinal orientation of upper central electrode 231. Lower center electrode/gas injector 35 may include concentrically spaced apart pairs of electrodes like peripheral electrodes 181a and 181b illustrated in
Still another embodiment of the PFAS treatment and destruction reactor apparatus is illustrated in
Referring now to
Lower center electrode 329 preferably is a hollow tube with gas emitting holes to create gas bubbles 39 in the solution. Peripheral electrode 341 is preferably metal mesh. The co-axial electrodes 329 and 341 are laterally placed in the same direction as is upper central electrode 213.
Grid 371 includes openings 391 between crossing metallic strands 393 of the mesh material. Each mesh opening size is 0.5-10 mm, by way of non-limiting example. Electrical arcs 395 may be discharged from any of the grid strands, and each arc is oriented in a primarily vertical direction between the associated mesh strand and an adjacent PFAS-carrying bubble 39 moving from the liquid surface to the plasma region 25. The arc can be generated from any point on the grid strands depending on where the gas bubble rises, thereby beneficially providing full surface area coverage and rapid arc-to-PFAS interaction timing. In the preferred version of this grid embodiment, no magnets are needed.
While various embodiments have been disclosed, it should be appreciated that additional variations of the electrode apparatus and method are also envisioned. For example, additional or different gas manifold and electrode shapes and sizes may be used although certain of the present advantages may not be fully realized. Electrodes made of porous metals or other electrically conductive materials can be also used. While certain tank shapes have been disclosed it should be appreciated that alternate shapes may be used (for example, rectangular, octagonal, oval or other cross-sectional shapes) although all of the present advantages may not be fully achieved. Different electrical circuits and solution chemistry can also be provided. It is also noteworthy that any of the preceding features may be interchanged and intermixed with any of the others. Accordingly, any and/or all of the dependent claims may depend from all of their preceding claims and may be combined together in any combination. Variations are not to be regarded as a departure from the present disclosure, and all such modifications are entitled to be included within the scope and sprit of the present invention.
This application claims priority to U.S. provisional patent application Ser. No. 63/331,937, filed on Apr. 18, 2022, which is incorporated by reference herein.
This invention was made with government support under 1724941 and under 1917577 awarded by the National Science Foundation. The government has certain rights in the invention.
Number | Date | Country | |
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63331937 | Apr 2022 | US |