Pulsed electric field for drinking water disinfection

Abstract

The present disclosure relates to a micro-mini pulsed electric field (PEF) device for point-of-use disinfection of drinking water. The pulsed electric field device comprises micro-engineered electrodes and a low-voltage pulsed electric field generator circuit. A pulsed electric field is generated across a micro-gap between the electrodes to achieve disinfection of drinking water.

Claims

1. A tap-mounted device for point-of-use disinfection of water, said device comprising: a plurality of electrodes having a micro-gap between the electrodes, wherein the micro-gap has a micro-gap distance in the range of 10 m to 300 m, the electrodes selected from the group consisting of multi-rod electrodes and jelly-roll type electrodes; a control system; and a low-voltage pulsed electric field generator circuit responsive to the control system, to generate a low-voltage pulsed electric field (PEF) across the micro-gap of the electrodes to provide a voltage of about 5 V up to about 30 V across the micro-gap, thereby providing a pulsed electric field strength at a level effective to increase cell permeability and/or cause an irreversible damage to cells of microorganisms present in the water, wherein the micro-gap establishes a distance between the electrodes sufficient to provide a physical separation between the electrodes while permitting a sufficiently intense pulsed electric field generated across a micro-gap between the electrodes to achieve disinfection of drinking water; wherein the tap mounted device creates a fluid flow path from an inlet to an outlet and the fluid flow path passes through multiple electric fields; wherein the multi-rod electrodes comprise a plurality of positive electrode rods and a plurality of negative electrode rods arranged in a three dimensional array, wherein an area between the electrode rods is open; and wherein the jelly-roll type electrodes have multiple fluid flow paths that run traverse to an axis of the electrodes and each fluid flow path passes through multiple electric fields, the jelly-roll type electrodes including a rolled-up substrate, wherein the substrate has positive and negative electrodes on each side.

2. The device of claim 1 further comprising: a power converter capable of providing a DC power output; and the power converter providing the DC power output to the low-voltage pulsed electric field generator circuit.

3. The device of claim 1, wherein the low-voltage pulsed electric field generator circuit provides an output pulse frequency in the range of about 1 Hertz (Hz) to about 100 Hz.

4. The device of claim 1, wherein the low-voltage pulsed electric field generator circuit provides a pulse width in the range of about 20 nanoseconds to about 100 milliseconds.

5. The device of claim 1, wherein the micro-gap has a micro-gap dimension from about 10 m up to about 100 m.

6. The device of claim 1, wherein the low-voltage pulsed electric field generator circuit generates a pulsed electric field strength of at least 0.5 kV/cm.

7. The device of claim 1, wherein the low-voltage pulsed electric field generator circuit generates an electric field having a pulsed waveform selected from the group of square, sinusoidal, trapezoidal and triangular.

8. The device of claim 1, wherein the electrodes are installed so as to generate an electric field in a direction which is perpendicular or parallel to a water flow between the electrodes.

9. The device of claim 1, wherein the electrodes are made of a conducting material or a carbon-based material.

10. The device of claim 1, wherein the electrodes are coated with a conducting material or a carbon-based material.

11. The device of claim 1, wherein the electrodes are coated electrodes.

12. The device of claim 1, wherein the electrodes are printed electrodes, and the electrodes are printed on both sides of a substrate with the positive electrodes on one side and the negative electrodes on the other side, wherein the substrate is rolled up into a jelly-roll type electrode.

13. The device of claim 1, wherein the negative electrode rods are attached to a negative holding plate at one end and the positive electrode rods are attached to a positive holding plate at one end, wherein the electrode rods are aligned parallel to each other with the positive holding plate on one side of the array and the negative holding plate on the other side of the array.

14. The device of claim 1, wherein a complete perimeter of the electrode rods is directly exposed to the fluid flow path.

15. A method for point-of-use disinfection of water comprising: providing a plurality of electrodes having a micro-gap between the electrodes, wherein the micro-gap has a micro-gap distance in the range of 10 m to 300 m, the electrodes comprising electrodes selected from the group consisting of multi-rod electrodes and jelly-roll type electrodes; providing a control system; providing a low-voltage pulsed electric field generator circuit responsive to the control system; and generating the pulsed electric field (PEF), across the micro-gap of the electrodes to provide a voltage of about 5 V up to about 30 V across the micro-gap, thereby providing a pulsed electric field strength at a level effective to increase cell permeability and/or achieve an irreversible breakdown of cells of microorganisms present in the water, wherein the micro-gap establishes a distance between the electrodes sufficient to provide a physical separation between the electrodes while permitting a sufficiently intense pulsed electric field generated across a micro-gap between the electrodes to achieve disinfection of drinking water; wherein the tap mounted device creates a fluid flow path from an inlet to an outlet and the fluid flow path passes through multiple electric fields; wherein the electrodes are multi-rod electrodes which comprise a plurality of positive electrode rods and a plurality of negative electrode rods arranged in a three dimensional array, wherein the space between the electrode rods is open; and wherein the jelly-roll type electrodes have multiple fluid flow paths that run traverse to an axis of the electrodes and each fluid flow path passes through multiple electric fields, the jelly-roll type electrodes including a rolled-up substrate, wherein the substrate has positive and negative electrodes on each side.

16. The method of claim 15 comprising providing a pulsed electric field strength of at least 0.5 kV/cm.

17. The method of claim 15, further comprising: the generating the pulsed electric field (PEF) comprising providing a DC power output to the low-voltage pulsed electric field generator circuit.

18. The method of claim 15, further comprising using the low-voltage pulsed electric field generator circuit to provide an output pulse frequency in the range of about 1 Hertz (Hz) to about 100 Hz.

19. The method of claim 15, further comprising using the low-voltage pulsed electric field generator circuit to provide a pulse width in the range of about 20 nanoseconds to about 100 milliseconds.

20. The method of claim 15, further comprising: using the low-voltage pulsed electric field generator circuit to provide an output pulse frequency in the range of about 1 Hertz (Hz) to about 100 Hz; and using the low-voltage pulsed electric field generator circuit to generate a pulsed electric field strength of at least 0.5 kV/cm.

21. The method of claim 15, further comprising using the low-voltage pulsed electric field generator circuit to generate an electric field having a pulsed waveform selected from the group of square, sinusoidal, trapezoidal and triangular.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The accompanying diagrams and figures illustrate and explain several characteristics of the present disclosure:

(2) FIG. 1 is a schematic diagram showing a micro-engineered porous electrode system with the installation showing water flow direction perpendicular to the electric (E-) field direction.

(3) FIG. 2 is a schematic diagram showing a micro-engineered multi-rod electrode system with the installation showing water flow direction perpendicular to the E-field direction.

(4) FIG. 3 is a schematic diagram showing a micro-engineered coated-electrode system with the installation showing water flow direction perpendicular to the E-field direction.

(5) FIG. 4 is a schematic diagram showing a micro-engineered printed electrode system with the installation showing the water flow direction perpendicular to the E-field direction.

(6) FIG. 5 is a schematic diagram showing printed electrodes on the substrate for micro-engineered printed electrode system.

(7) FIG. 6 is a schematic diagram showing a micro-engineered porous electrode system with the installation showing water flow direction parallel to the E-field direction.

(8) FIG. 7 is a schematic diagram showing a micro-engineered multi-rod electrode system with the installation showing water flow direction parallel to the E-field direction.

(9) FIG. 8 is a schematic diagram showing a micro-engineered coated-electrode system with the installation showing water flow direction parallel to the E-field direction.

(10) FIG. 9 is a schematic diagram showing a micro-engineered printed electrode system with the installation showing water flow direction parallel to the E-field direction.

(11) FIG. 10 is a schematic diagram showing a miniature pulsed electric field generator with its pulsed form generated by computer simulation.

(12) FIG. 11 is a schematic diagram showing a circuit design of miniature pulsed electric field generator with its pulsed form generated by computer simulation.

(13) FIG. 12 is a schematic diagram showing a circuit design of miniature pulsed electric field generator with its pulsed form generated by computer simulation.

(14) FIG. 13 is a schematic diagram showing a typical device for point-of-use disinfection of water according to the present disclosure.

DETAILED DESCRIPTION

(15) Applicants describe herein a novel micro-mini pulsed electric field device (also called an micro-engineered pulsed electric field device) for disinfection of drinking water comprising a low voltage pulsed electric field generator circuit and micro-engineered electrodes to disinfect microorganisms found in drinking water. An advantage of the present device is that disinfection is achieved while avoiding the excessive use of chemical disinfectants and biocides that could potentially induce resistance and tolerance in microorganisms and possibly alter the taste and quality of the drinking water. The device can be applied not only in a domestic situation, but also in public, commercial and industrial premises where safe drinking water is paramount.

(16) As used herein, disinfection is defined as at least 90% reduction of the number of microorganisms (e.g., the number of colony forming units (CFU) of bacteria) in a sample of water. The disinfection of microorganisms is generally achieved by application of an electric field to the cell wall of microorganisms captured within the electric field. The electric field induces an increase in cell permeability (e.g., pore formation) of the cell wall of the microorganism, and thus causes an irreversible damage to the microorganism through a combination of cell wall collapse, osmotic stress and enhanced transport of residual disinfectants (e.g., chlorine) in water.

(17) Overview

(18) The present disclosure is directed to a point-of-use drinking water disinfection device. The various designs described herein are merely non-limiting examples and it is contemplated that other such designs can be created using design software, e.g., SolidWorks and AutoCAD, and manufactured by a general industrial process

(19) A typical device for point-of-use disinfection of water according to the present subject matter comprises at least a low voltage pulsed electric field generator circuit, micro-engineered electrodes, control system, power supply, and a storage case. The device may further comprise a power converter. A schematic diagram of a non-limiting, exemplary device is shown in FIG. 13. According to FIG. 13, briefly, AC is the preferred power supply. When AC power passes through the converter unit, it is converted into DC power, which can power the PEF generator circuit. The control system is used to control the ON/OFF of the pulse generated by the PEF generator circuit, which pulse is then transmitted to the micro-engineered electrode.

(20) The device can be a stand-alone unit or a tap-mounted unit for point-of-use disinfection of drinking water. A typical stand-alone device has dimensions ranging from 200 mm200 mm200 mm to 300 mm300 mm300 mm; and a tap-mounted unit has dimensions ranging from 30 mm30 mm30 mm to 80 mm80 mm80 mm. An option for tap-mounted unit is an internal rechargeable battery unit to be powered by a dynamo located in the drain through which water is flowing.

(21) Micro-Engineered Electrode System

(22) A micro-engineered electrode system (also referred to as a mini-micro electrode system) is designed to generate intense electric field at low voltage. The electrodes are made of a conducting material or a carbon-based material. Conducting materials of which the electrodes may be made include as non-limiting examples, metals and metal alloy such as stainless steel, aluminum and aluminum alloys, titanium and titanium alloys, copper and copper alloys, tungsten and tungsten alloys, ceramic, glasses and intermetallics including composites such as a metal-metal alloy composite, and coatings thereof. A metal-metal alloy composite can be any combination/mixture of metals, e.g., Fe(Iron)-Al(Aluminium). Non-limiting examples of carbon-based materials of which the electrodes may be made include conducting polymers, carbons, graphite, graphene and carbon nanotubes, including composites and coatings thereof. A carbon-based material composite can be a combination/mixture of the above carbon-based materials, e.g., mixture of graphene with graphite, graphene with carbon nanotubes. Such a carbon-based material composite may also be applied as coating.

(23) A micro-gap having a dimension ranging from about 10 m up to about 300 m, or from about 50 m to about 150 m, is maintained between the electrodes. A physical separation between the microelectrodes is achieved by (a) use of a physical barrier optionally, but not restricted to, insulating materials such as acrylonitrile butadiene styrene, poly(methyl methacrylate), poly(vinyl chloride), polycarbonate, polyphenylsulfone polymer or similar polymer materials; (b) use of a non-electrical conducting protective layer on metal electrodes by electrophoretic deposition, for example by electropolymerization, anodization and electrocoating (e-coating) process; (c) use of microfabrication technology in electrode manufacture to systematically locate and position the electrodes on a solid substrate. A person of skill in the art would readily appreciate what microfabrication techniques are used in the fabrication of electronic devices. Typically, microfabrication techniques involve chemical deposition, photoresist coating, photolithography, patterning and etching.

(24) In terms of the installation of the electrode system within the device, the electrode system, could be installed such that the direction of the electric field generated is either perpendicular or parallel to the water flow.

(25) Low-Voltage Pulsed Electric Field Circuit

(26) A low-voltage pulsed electric field generator with voltage input of less than about 30 V, in particular between about 5 V up to about 20 V, is designed to generate pulsed electric field strength of at least about 0.5 kV/cm to about 20 kV/cm, for example, about 3 kV/cm to about 10 kV/cm. This range of electric field intensity can effectively disinfect drinking water from the tap. The pulsed electric field generator circuit comprises primarily of electrical components including, but not limited to, resistors, capacitors, amplifier, logic gate and IC chips etc. The pulsed electric field generated from the circuit can be simulated by computer software before actual fabrication. The pulsed electric field generated from the circuit has a pulsed waveform, which could be square, sinusoidal, trapezoidal, triangular, etc.

(27) Performance of Micro-Mini Pulsed Electric Field Device

(28) Performance of the micro-mini pulsed electric field device was evaluated as is discussed below with respect to Examples 12 and 13. Tap water containing known concentration of Escherichia coli (E. Coli) was contacted with the different micro-engineered electrode systems in various operating conditions such as different pulse width, pulse frequency, waveform, pulse strength and pulse duration. The low-voltage pulsed electric field circuit generated the pulse and passed to the electrode system for electric field generation. The anti-microbial efficiency was then calculated, in terms of percentage, by counting the Escherichia coli remaining after the disinfection process.

EXAMPLES

Example 1: Micro-Engineered Porous Electrode System (Design 1, Perpendicular Electric Field)

(29) FIG. 1 is a non-limiting schematic diagram showing a micro-engineered porous electrode system (Design 1). The system is installed so that the direction of electric field is perpendicular to the direction of tap water flow. The electrodes in this non-limiting example are in the form of a mesh, but it is also contemplated that the electrodes are in the form of a screen, perforated plates or foils, porous plates and foils, fabrics, papers, micropatterned foils or any materials containing through porosity. Mesh size is defined as the number of squares in one inch horizontally and vertically. Mesh sizes ranging from about 20 mesh to about 200 mesh are suitable. In certain embodiments the mesh size are 40 mesh, 50 mesh or 100 mesh. The electrode materials in this non-limiting example are metals or their alloys, particularly stainless steel, aluminum, brass, titanium and tungsten. It is also contemplated that the electrode materials could be conducting carbons, polymers, ceramics and intermetallics including composites and coating thereof.

(30) A porous barrier made of insulating material with a maximum thickness of 100 m is used to create a micro-gap between the electrodes as shown in FIG. 1. In alternative, the barrier could be a non-electrical conducting protective layer of less than 100 m deposited on the electrodes surface by electrophoretic deposition process (e.g., anodization or E-coating) depending on the electrode material, so that the physical barrier could be omitted. The micro-engineered porous electrodes can have a minimum of two electrodes with or without a separator, but more electrode-separator pairs are contemplated. The number of electrode-separator pairs are constrained mainly by the optimal overall thickness of 10 mm and water pressure drop of not more than 10%. An example of micro-engineered electrodes comprises up to 20 electrode-separator layers with diameter of 10 mm and thickness of 10 mm.

Example 2: Micro-Engineered Multi-Rod Electrode System (Design 2, Perpendicular Electric Field)

(31) FIG. 2 is a non-limiting schematic diagram showing a micro-engineered multi-rod electrode system (Design 2). The system is installed such that the direction of electric field is perpendicular to the direction of tap water flow. The electrodes are in the shape of rods with a diameter of 300 m, but could also be thinner or thicker depending on the mechanical properties of the materials. The term multi-rod electrode system refers to an arrangement comprising a plurality of rod-shaped electrodes. The electrodes could also be in the form of twisted wires, hollow rods, flat plates and rods of different cross-sectionals, including but not limited to, angular shapes with the purpose of creating intense electrical fields. The electrode materials in this non-limiting example are metals or their alloys, particularly stainless steel, aluminum, brass, titanium and tungsten. It could also be contemplated that the electrode materials could be conducting carbons, polymers, ceramics and intermetallics, including composites and coating thereof.

(32) The assembly of the multi-rod electrode system is accomplished using a holding plate, through which half the electrodes are inserted through the top plate and imbedded part-way in the bottom plate. This creates the positive electrodes. The other half of the electrodes are inserted through the bottom plate and imbedded part-way in the top plate to create the negative electrodes as shown in FIG. 2. The distance between the electrodes (i.e., the micro gap dimension/distance) should be less than 300 m. In an alternative embodiment, the distance is 100 m or less.

(33) The overall dimension of the electrode system is from about 10 mm to about 30 mm in diameter, and from about 10 mm to about 50 mm in height, although this is a non-limiting example and other dimensions are contemplated. In more specific embodiments, the electrode system is from about 10 mm and about 15 mm in diameter. In certain embodiments, the electrode system is from about 20 mm to about 40 mm in height.

Example 3: Micro-Engineered Coated-Electrode System (Design 3, Perpendicular Electric Field)

(34) FIG. 3 is a non-limiting schematic diagram showing a micro-engineered coated electrode system (Design 3). The system is installed such that the direction of electric field is perpendicular to the direction of tap water flow. The electrodes in this non-limiting example are in the form of a mesh, but could also be in the form of screen, perforated plates or foils, porous plates and foils, fabrics, papers, micropatterned foils or any materials containing through porosity. Mesh sizes ranging from about 20 mesh to about 200 mesh are suitable. In certain embodiments the mesh size are 40 mesh, 50 mesh or 100 mesh. The electrode materials in this non-limiting example are metals or their alloys, particularly stainless steel, aluminum, brass, titanium and tungsten. It is also contemplated that the electrode materials could be conducting carbons, polymers, ceramics and intermetallics, including composites and coating thereof.

(35) A protective coating of less than 100 m is deposited on the surface of the electrode by electrophoretic deposition (e.g., electropolymerization, anodizing or E-coating) depending on the electrode material. The two coated electrodes are rolled together to give a spiral-wound electrode configuration shown in FIG. 3. One of the electrodes is the positive electrode and the other one is the negative electrode. The overall dimension of the electrode is 10 mm in diameter and 20 mm in height, although this is a non-limiting example and other dimensions are contemplated.

Example 4: Micro-Engineered Printed Electrode System (Design 4, Perpendicular Electric Field)

(36) FIG. 4 is a non-limiting schematic diagram showing a micro-engineered printed electrode system (Design 4). The system is installed such that the direction of electric field generated is perpendicular to the direction of tap water flow. The electrodes (FIG. 5) are printed on a flexible substrate. Materials useful as the flexible substrate include, without limitation plastics, fabrics, and insulated metal foils. The printed electrodes have a size of 50 m and a micro-gap distance of 50 m. For the electrodes pattern A in FIG. 5, the electrodes are printed on both sides of the substrate so that the positive electrodes are on one side and the negative electrodes are on the other side. For the electrodes pattern B and C, parallel positive and negative electrode patterns are printed on both surfaces of the substrate. The electrode materials in this non-limiting example are metals or their alloys, particularly stainless steel, aluminum, brass, titanium and tungsten. It is also contemplated that the electrode materials be conducting carbons, polymers, ceramics and intermetallics, including composites and coating thereof.

(37) A porous barrier made of insulating material with a maximum thickness of 100 m is used to create a micro-gap between the electrodes as shown in FIG. 4. In an alternative embodiment, a non-electrical conducting protective layer of less than 100 m could be deposited on the electrode surface by E-coating process, so that the porous barrier could be omitted. The printed electrode substrate with or without the porous barrier are rolled together to give a spiral-wound electrode configuration shown in FIG. 4. The overall dimension of the electrode is 10 mm in diameter and 10 mm in height, although this is a non-limiting example and other dimensions are contemplated.

Example 5: Micro-Engineered Porous Electrode System (Design 1, Parallel Electric Field)

(38) FIG. 6 shows a non-limiting schematic diagram of a micro-engineered porous electrode system (Design 1). The system is installed such that the direction of electric field is parallel to the direction of tap water flow. The electrodes in this non-limiting example are in the form of a mesh, but could also be in the form of screen, perforated plates or foils, porous plates and foils, fabrics, papers, micropatterned foils or any materials containing through porosity. Mesh size of 40 mesh, 50 mesh and 100 mesh are suitable. The electrode materials in this non-limiting example are metals or their alloys particularly stainless steel, aluminum, brass, titanium and tungsten. It is also contemplated that the electrode material could be conducting carbons, polymers, ceramics and intermetallics including composites and coating thereof.

(39) A porous barrier made of insulating material with a maximum thickness of 100 m is used to create a micro-gap between the electrodes as shown in FIG. 6. In alternative, the barrier could be a non-electrical conducting protective layer of less than 100 m deposited on the electrodes surface by an electrophoretic deposition process (e.g., electropolymerization, anodization or E-coating) depending on the electrode material, so that the physical barrier could be omitted. The micro-engineered electrodes can have a minimum of two electrodes with a separator, but more electrode-separator pairs are contemplated. The number of electrode-separator pairs are constrained mainly by the optimal overall thickness of 10 mm and water pressure drop of not more than 10%. An example of micro-engineered electrodes comprises up to 20 electrode-separator layers with diameter of 10 mm and thickness of 10 mm.

Example 6: Micro-Engineered Multi-Rod Electrode System (Design 2, Parallel Electric Field)

(40) FIG. 7 is a non-limiting schematic diagram showing a micro-engineered multi-rod electrode system (Design 2). The system is installed such that the direction of electric field is parallel to the direction of tap water flow. The electrodes are in the shape of rods with a diameter of 300 m, but could also be thinner or thicker depending on the mechanical properties of the materials. The electrodes could also be in the form of twisted wires, hollow rods, flat plates and rods of different cross-sectionals including, but not limited to, angular shapes with the purpose of creating intense electrical fields. The electrode materials in this non-limiting example are metals or their alloys, particularly stainless steel, aluminum, brass, titanium and tungsten. It is also contemplated that the electrode materials could be conducting carbons, polymers, ceramics and intermetallics, including composites and coating thereof.

(41) The assembly of the multi-rod electrode system is accomplished using a holding plate, through which half the electrodes are inserted through the top plate and imbedded part-way in the bottom plate. This creates the positive electrodes. The other half of the electrodes are inserted through the bottom plate and imbedded part-way in the top plate to create the negative electrodes as shown in FIG. 7. The distance between the electrodes should be less than 300 m. In an alternative embodiment, the distance is 100 m or less. The overall dimension of the electrode system is 10 mm in diameter and 10 mm in height, although this is a non-limiting example and other dimensions are contemplated.

Example 7: Micro-Engineered Coated-Electrode System (Design 3, Parallel Electric Field)

(42) FIG. 8 is a non-limiting schematic diagram showing a micro-engineered coated-electrode system (Design 3). The system is installed such that the direction of electric field is parallel to the direction of tap water flow. The electrodes in this non-limiting example are in the form of a mesh, but could also be in the form of screen, perforated plates or foils, porous plates and foils, fabrics, papers, micropatterned foils or any materials containing through porosity. Mesh size of 40 mesh, 50 mesh and 100 mesh are suitable. The electrode materials in this non-limiting example are metals or their alloys, particularly stainless steel, aluminum, brass, titanium and tungsten. It is also contemplated that the electrode material could be conducting carbons, polymers, ceramics and intermetallics, including composites and coating thereof.

(43) A protective coating of less than 100 m is deposited on the surface of the electrode by an electrophoretic deposition process (e.g., electropolymerization, anodizing or E-coating) depending on the electrode material. The two coated electrodes are rolled together to give a spiral-wound electrode configuration shown in FIG. 8. One of the electrodes is the positive electrode and the other one is the negative electrode. The overall dimension of the electrode is 10 mm in diameter and 20 mm in height, although this is a non-limiting example and other dimensions are contemplated.

Example 8: Micro-Engineered Printed Electrode System (Design 4, Parallel Electric Field)

(44) FIG. 9 is a schematic diagram showing a micro-engineered printed electrode system (Design 4). The system is installed such that the direction of electric field generated is perpendicular to the direction of tap water flow. The electrodes (FIG. 5) are printed on a flexible substrate. Materials useful as the flexible substrate include, without limitation, plastics, fabrics, and insulated metal foils. The printed electrodes have a size of 50 m and a micro-gap distance of 50 m. The electrodes in pattern A shown in FIG. 5 are printed on both sides of the substrate such that the positive electrodes are one side and the negative electrodes are on the other side. For the electrodes pattern B and C, parallel positive and negative electrodes pattern are printed on both sides (surfaces) of the substrate. The electrode materials in this non-limiting example are metals or their alloys, particularly stainless steel, aluminum, brass, titanium and tungsten. It is also contemplated that the electrode materials could be conducting carbons, polymers, ceramics and intermetallics, including composites and coatings thereof.

(45) A porous barrier made of insulating material with a maximum thickness of 100 m is used to create a micro-gap between the electrodes as shown in FIG. 9. In an alternative embodiment, a non-electrical conducting protective layer of less than 100 m could be deposited on the electrode surface by an E-coating process, so that the porous barrier could be omitted. The printed electrode substrate with or without the porous barrier is/are rolled together to give a spiral-wound electrode configuration shown in FIG. 9. The overall dimension of the electrode is 10 mm in diameter and 10 mm in height, although this is a non-limiting example and other dimensions are contemplated.

Example 9: Low-Voltage Pulsed Electric Field Circuit (Design 1)

(46) FIG. 10 is a schematic diagram showing a low-voltage pulsed electric field circuit (Design 1). This design is using Timer (555) to generate a square wave pulse. Timer IC 555 consists of logic gates, flip flop amplifiers and transistors. When an input power is supplied, the amplifier acts as comparator to determine the on/off of the circuit. Flip flop then regulates the input signal with the help of the transistor and gives this IC a constant pulse output. Capacitors in the circuit are present to stabilize the circuit as well as to control the charging and discharging time of the pulse given by Timer IC. Thus pulse width and frequency of the output can be controlled.

(47) Use of the Timer IC 555 provides a short-cut for low voltage pulse generator. It can be appreciated by a skilled artisan that without the Timer IC 555, a few more complex circuits, e.g., logic gates, flip flop and amplifier, would be required in order to replace the built-in design of the Timer IC 555. However, these additional circuits would make the whole circuit large and bulky in size, and therefore challenging or even impossible to achieve a mini and portable finished device.

(48) Pulse width is a critical parameter determining the disinfection performance. Pulse frequency and pulse width are interrelated and a mixture of different pulse widths gives a better disinfection performance. The pulse width and pulse frequency can be adjusted by changing the values of resistors and capacitors in the circuit. Different frequencies and pulsed widths are required for different disinfection environments.

(49) In this design, typically, a pulse frequency of 75 Hz and pulse width of 85 microseconds (s) is generated. For each of the low-voltage generator circuits disclosed herein, the pulse frequency is set in the range of from about 1 Hz to about 100 kHz and the pulse width ranges from about 20 nanoseconds (ns) to about 100 milliseconds (ms) for achieving effective disinfection. In certain embodiments, the pulse frequency is from about 80 Hz to about 100 Hz and the pulse width is from about 50 (s) to 1 ms.

Example 10: Low-Voltage Pulsed Electric Field Circuit (Design 2)

(50) FIG. 11 is a schematic diagram showing a low-voltage pulsed electric field circuit (Design 2). This design is using Timer (555) to generate square wave pulse. Timer IC 555 consists of logic gates, flip flop amplifiers and transistors. When input power is supplied, the amplifier acts as comparator to determine the on/off of the circuit. Flip-flop then regulate the input signal with the help of the transistor and gives this IC a constant pulse output. Capacitors in the circuit are to stabilize the circuit as well as to control the charging and discharging time of the pulse given by Timer IC. Thus pulse width and frequency of the output can be controlled. This is the short-cut for low voltage pulse generator. The pulse width and wave frequency are adjustable by changing the values of resistors and capacitors in the circuit. In certain embodiments, the circuit can generate a high voltage negative pulse with duration less than 100 s if suitable capacitors and resistors are used. In this design, typically, negative pulse with frequency of 70 Hz and pulse width of 104 s is generated.

Example 11: Low-Voltage Pulsed Electric Field Circuit (Design 3)

(51) FIG. 12 is a schematic diagram showing a low-voltage pulsed electric field circuit (Design 3). This circuit uses operational amplifier to generate square wave pulse. R.sub.1, R.sub.2, R.sub.3, R.sub.4 all are involved in controlling the frequency and pulse width. R.sub.1 and R.sub.2 are the feedback design which helps stabilize and control the output range so that the circuit can be stable. C.sub.2 is the key component determining the frequency. The larger the value C.sub.2 has, the longer the discharging time C.sub.2 will be, so the frequency will be shorter. By adding appropriate capacitors and resistors, the circuit generates almost perfect square pulse with short duration. To generate a perfect square waveform pulse when few hundred microseconds of pulse width is desired, logic gates are added to reshape the pulse generate. In this design, typically, pulse with frequency of 80 Hz and pulse width of 200 s is generated.

Example 12: Using a Micro-Engineered Porous Electrode System with Initial E. coli Concentration 104 CFU/ml, Pulse Width of 100 s, Pulse Frequency of 100 Hz and Input Voltage of 5 V

(52) Micro-engineered porous electrode system is used for the disinfection of tap water containing 10.sup.4 CFU/ml of E. coli. Voltage input of 5 V to low-voltage pulsed electric field circuit generates a pulse with frequency of 100 Hz and width of 100 s. The pulse electric field intensity is therefore 0.5 kV/cm. In this embodiment, reduction of 90% of E. coli in the tap water is achieved.

Example 13: Using a Micro-Engineered Porous Electrode System with Initial E. coli Concentration 104 CFU/ml, Pulse Width of 100 s, Pulse Frequency of 100 Hz and Input Voltage of 10 V

(53) Micro-engineered porous electrode system is used for the disinfection of tap water containing 10.sup.4 CFU/ml of E. coli Voltage input of 10 V to low-voltage pulsed electric field circuit generates a pulse with frequency of 100 Hz and width of 100 s. The pulse electric field intensity is therefore 1 kV/cm. In this embodiment, reduction of 90% of E. coli in the tap water is achieved.