Diffusiophoretic water filtration device with closed channel structure

Abstract

A diffusiophoretic water filtration device includes a pressurized gas chamber receiving a pressurized gas; an inlet manifold receiving a colloidal suspension including colloidal particles in water; a flow chamber having an inlet and an outlet, the flow chamber receiving the colloidal suspension at the inlet from the inlet manifold, the colloidal suspension flowing between the inlet and at least one outlet in a flow direction; and a horizontal sheet separating the gas chamber and the flow chamber, the sheet being made of a gas permeable membrane, the gas capable of permeating the membrane, the membrane being water impermeable, the gas being carbon dioxide and permeating the membrane upwardly from the gas chamber in a direction normal to the membrane so as to induce diffusiophoretic motion on at least some of the colloid particles opposite to or in the direction normal to the membrane, the sheet covering a top of the pressurized gas chamber. The flow chamber is a closed flow chamber having an air permeable cover and a channel structure contacting the colloidal suspension, so as to define a thickness between the cover and the horizontal sheet; and the at least one outlet has a first outlet spaced above a second outlet, the first outlet for receiving water having a higher concentration of some of the colloid particles than a second outlet.

Claims

1. A method for operating a diffusiophoretic water filtration device including a pressurized gas chamber receiving a pressurized gas; an inlet manifold receiving a colloidal suspension including colloidal particles in water; a flow chamber having an inlet and an outlet structure, wherein the outlet structure comprises at least one outlet, the flow chamber receiving the colloidal suspension at the inlet from the inlet manifold, the colloidal suspension flowing between the inlet and the at least one outlet in a flow direction; and a horizontal sheet separating the pressurized gas chamber and the flow chamber, the horizontal sheet being made of a gas permeable membrane, the pressurized gas capable of permeating the gas permeable membrane, the gas permeable membrane being water impermeable, the pressurized gas being carbon dioxide and the pressurized gas permeating the gas permeable membrane upwardly from the pressurized gas chamber in a direction normal to the gas permeable membrane so as to induce diffusiophoretic motion on at least some of the colloidal particles opposite to or in the direction normal to the gas permeable membrane, the horizontal sheet covering a top of the pressurized gas chamber; the flow chamber being a closed flow chamber having an air permeable cover and a channel structure contacting the colloidal suspension, so as to define a thickness between the air permeable cover and the horizontal sheet; and the at least one outlet having a first outlet spaced above a second outlet, the first outlet for receiving water having a higher concentration of some of the colloidal particles than the second outlet, the method further comprising clamping the horizontal sheet to the air permeable cover via at least one longitudinally extending clamp; providing carbon dioxide in the pressurized gas chamber at at least 120 kPa; providing the colloidal suspension to the inlet of the flow chamber at at least 1 mbar to flow the colloidal suspension through the flow chamber and induce diffusiophoretic motion on the colloidal particles in the flow chamber; and removing water having a reduced colloidal particle content at the second outlet.

2. The method as recited in claim 1, wherein the colloidal suspension further includes non-colloidal particles larger than the colloidal particles, and further comprising inducing diffusiophoretic motion on the non-colloidal particles in the flow chamber.

3. The method as recited in claim 1, wherein the at least one longitudinally extending clamp contacts a top of the air permeable cover.

4. The method as recited in claim 3, wherein the at least one longitudinally extending clamp further contacts a bottom of at least one flange of the pressurized gas chamber.

5. The method as recited in claim 4, wherein the pressurized gas chamber is formed of metal and the at least one flange extends laterally.

6. The method as recited in claim 1, wherein the at least one longitudinally extending clamp includes at least two longitudinally extending clamps.

7. The method as recited in claim 1, wherein the horizontal sheet is a PDMS sheet.

8. The method as recited in claim 1, wherein a thickness of the horizontal sheet is from 10 micrometers to 25 micrometers.

9. The method as recited in claim 1, wherein the horizontal sheet is at least 5 cm wide by 5 cm long.

10. The method as recited in claim 1, wherein the horizontal sheet preferably has a Shore A of between 40 and 60, and a tensile elongation of at least 1000 psi.

11. The method as recited in claim 1, wherein the inlet manifold comprises a water pressure regulator.

12. The method as recited in claim 1, wherein the air permeable cover is made in one piece of PDMS together with a channel structure of longitudinally extending microchannels, each of the microchannels having a thickness equal to or less than 1 mm.

13. The method as recited in claim 1, claim 1, wherein the channel structure is provided separately from the cover, and is sandwiched by the horizontal sheet and the air permeable cover.

14. The method as recited in claim 13, wherein the air permeable cover is made of PDMS and the channel structure of a plastic.

15. The method as recited in claim 1, wherein the at least one outlet includes a movable splitter for altering a size of the first outlet.

16. The method as recited in claim 1, further comprising stretching the sheet over the pressurized gas chamber.

17. A method for operating a diffusiophoretic water filtration device including a pressurized gas chamber receiving a pressurized gas; an inlet manifold receiving a colloidal suspension including colloidal particles in water; a flow chamber having an inlet and an outlet structure, wherein the outlet structure comprises at least one outlet, the flow chamber receiving the colloidal suspension at the inlet from the inlet manifold, the colloidal suspension flowing between the inlet and the at least one outlet in a flow direction; and a horizontal sheet separating the pressurized gas chamber and the flow chamber, the horizontal sheet being made of a gas permeable membrane, the pressurized gas capable of permeating the gas permeable membrane, the gas permeable membrane being water impermeable, the pressurized gas being carbon dioxide and permeating the gas permeable membrane upwardly from the pressurized gas chamber in a direction normal to the gas permeable membrane so as to induce diffusiophoretic motion on at least some of the colloidal particles opposite to or in the direction normal to the gas permeable membrane, the horizontal sheet covering a top of the pressurized gas chamber; the flow chamber being a closed flow chamber having an air permeable cover and a channel structure contacting the colloidal suspension, so as to define a thickness between the air permeable cover and the horizontal sheet; and the at least one outlet having a first outlet spaced above a second outlet, the first outlet for receiving water having a higher concentration of some of the colloidal particles than the second outlet, the method further comprising providing carbon dioxide in the pressurized gas chamber at at least 120 kPa; providing the colloidal suspension to the inlet of the flow chamber at at least 1 mbar to flow the colloidal suspension through the flow chamber and induce diffusiophoretic motion on the colloidal particles in the flow chamber; splitting the flow after the inducing of the diffusionphoretic motion into a first outlet flow having a reduced colloidal particle content and a second outlet flow having an increased colloidal particle content using a splitter; moving the splitter to alter a distance between the splitter and the horizontal sheet; and removing the water having the reduced colloidal particle content at the second outlet.

18. The method as recited in claim 17, wherein the moving step is a function of the reduced colloidal particle content in the first outlet flow or the increased colloidal particle content in the second outlet flow.

19. A method for operating a diffusiophoretic water filtration device including a pressurized gas chamber receiving a pressurized gas; an inlet manifold receiving a colloidal suspension including colloidal particles in water; a flow chamber having an inlet and an outlet structure, wherein the outlet structure comprises at least one outlet, the flow chamber receiving the colloidal suspension at the inlet from the inlet manifold, the colloidal suspension flowing between the inlet and the at least one outlet in a flow direction; and a horizontal sheet separating the pressurized gas chamber and the flow chamber, the horizontal sheet being made of a gas permeable membrane, the pressurized gas capable of permeating the gas permeable membrane, the gas permeable membrane being water impermeable, the pressurized gas being carbon dioxide and the pressurized gas permeating the gas permeable membrane upwardly from the pressurized gas chamber in a direction normal to the gas permeable membrane so as to induce diffusiophoretic motion on at least some of the colloidal particles opposite to or in the direction normal to the gas permeable membrane, the horizontal sheet covering a top of the pressurized gas chamber; the flow chamber being a closed flow chamber having an air permeable cover and a channel structure contacting the colloidal suspension, so as to define a thickness between the air permeable cover and the horizontal sheet; and the at least one outlet having a first outlet spaced above a second outlet, the first outlet for receiving water having a higher concentration of some of the colloidal particles than the second outlet, the method further comprising providing carbon dioxide in the pressurized gas chamber at at least 120 kPa; receiving the colloidal suspension in the inlet manifold and spreading the colloidal suspension widthwise; maintaining a height of the colloidal suspension in the inlet manifold to regulate an inlet pressure of the colloidal suspension; providing the colloidal suspension to the inlet of the flow chamber at the inlet pressure, the inlet pressure being at least 1 mbar to flow the colloidal suspension through the flow chamber and induce diffusiophoretic motion on the colloidal particles in the flow chamber; and removing the water having the reduced colloidal particle content at the second outlet.

20. The method as recited in claim 19, further comprising sand filtering the colloidal suspension upstream of the inlet manifold.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) One schematic embodiment of the water filtration system of the present invention is shown by reference to:

(2) FIG. 1, which shows a schematic view of the system;

(3) FIG. 2, which shows an embodiment of the water filtration device of the present invention schematically;

(4) FIG. 3 shows a schematic top view of the water filtration device of FIG. 2;

(5) FIG. 4 shows a schematic cross sectional view a first embodiment of a flow chamber including a sheet and one piece cover and channel structure;

(6) FIG. 5 shows a schematic cross sectional view of a second embodiment with a flow chamber including two sheets and a sandwiched channel structure;

(7) FIG. 6 shows an inlet area of the flow chamber of FIG. 5 schematically;

(8) FIG. 7 shows an outlet area of the flow chamber of FIG. 5 schematically; and

(9) FIG. 8 shows a variable outlet splitter.

DETAILED DESCRIPTION OF AN EMBODIMENT

(10) FIG. 1 shows a water filtration system 100 for cleaning river water, which may contain various particles such as colloidal plastic or metallic particles, and other bioparticles such as bacteria and viruses. Many of these particles are charged negatively or positively. Any type of water with charged colloidal particles may be filtered using the present invention. Colloidal particle as defined herein is any particle that can form a colloid or colloidal suspension in water. Such colloidal particles typically range in sizes of a micrometer or less, but larger sizes are possible. The present invention is not limited to filtering colloidal particles, but can also be used to filter larger particles that are impacted by diffusiophoresis, for example even up to 100 nanometers in size or larger, from water. Preferably the particles to be filtered are less than 250 nanometers in size, even if not colloidal. These non-colloidal particles can have very low sedimentation rates, and thus the present invention can aid in sedimentation or forcing these larger particles downwardly.

(11) Water filtration system 100 includes a pump 110 pumping water from a river. The pump 110 pumps the water through a sand filter 120 to remove larger particles and impurities. The water with suspended colloidal particles, i.e. a colloidal suspension, then passes to the water filtration device 200 of the present invention.

(12) Water filtration device 200 is designed to remove positively charged colloid particles and other particles, the removal of which can significantly increase the water quality.

(13) Water filtration device 200, shown in FIG. 2 schematically, has an inlet manifold 210 receiving pond water with colloidal particles, preferably having passed through a preliminary filter or sedimentation device, such as sand filter 120. However, water filtration device 200 could be upstream of sand filter 120, thereby removing bacteria and other particles that can foul the sand filter 120. Separate water filtration devices 200 could also be both upstream and downstream of sand filter 120.

(14) Inlet manifold 210 spreads the water with colloidal particles in the widthwise direction (into the page in FIG. 2) from a pipe received from sand filter 120. In this example the water with colloidal particles is spread in the inlet manifold to a width of 1 m, and is maintained at a depth d of 1 cm, which height thus regulates the pressure of the suspension that flows into a flow chamber 212. Larger heights can provide larger pressures, and thus faster velocities through the flow chamber 212. The height or a pump can also be used to set the input pressure to a setpoint, for example 1 mbar.

(15) A pressurized gas chamber 220 receives a pressurized gas, such as carbon dioxide, from for example pressurized canisters or an industrial source. Gas chamber 220 has gas tight walls 226, over which sheet 222 can be stretched taut and fastened to in a gas tight manner, for example with fasteners and a sealant. The pressurized gas thus can exit in a uniform manner through the sheet 222. Sheet 222 thus defines the top of gas chamber 220 and the bottom of flow chamber 212.

(16) The colloidal suspension flows from inlet manifold 210 to flow chamber 212 via an exit. Flow chamber 212 can have water tight sidewalls extending from and sealed with respect to sheet 222, and may have a microfluidic or fluid structure therein as will be described. The colloidal suspension thus flows between inlet manifold 210 and two outlets 230, 240 in a flow direction, and, with the closed flow chamber 212 of the present invention, the sheet 222 preferably is in a horizontal orientation to gain the benefit of any gravitational effects on the colloidal particles as they congregate. Other particles present in the water, for example up to 100 nanometers or larger in the largest dimension, can also be impacted positively by gravitational effects.

(17) However, other orientations, even vertical, are possible especially for microfluidic chamber structures where the input pressure is the primary velocity driver.

(18) The carbon dioxide gas permeates the sheet or membrane 222 in a direction normal to the sheet or membrane 222, the normal direction being vertical in the embodiment shown, so as to induce diffusiophoretic motion on positively charged colloidal particles opposite to the direction normal to the membrane, here toward the sheet 222. Negatively charged colloidal particles can move away from the sheet 222, and possibly be filtered, split or suctioned from the top of the suspension. The removal of negatively charged colloidal particles is optional and not necessary in this embodiment.

(19) Outlet 240 thus has water having a higher concentration of positively charged colloidal and other particles, defined as waste water although it can be re-used or refiltered, than a second outlet 230, which can be defined as having filtered water.

(20) A splitter 250, extending widthwise in a wing-shaped manner with a trailing edge of the wing facing the stream, is moveable upwardly or downwardly in this embodiment, and can alter the dimensions of the outlet 240, and thus outlet 230. This adjustment can be a function of the water quality of the filtered water for example, and provides highly advantageous control of water quality, for example as the sources to be filtered are impacted, for example by rainwater.

(21) The splitter 250 may be keyed for example for rotation about a shaft 401 (FIG. 3), the shaft at one end having a worm gear 402 (FIG. 3) movable for example by a worm driven by a motor and controller. Very fine distance gradations thus can be achieved. In the example show, splitter 250 first can be located at 150 micrometers above the sheet 222 and a bottom of the outlet 240, so that for example 350 micrometers of a 500 micrometer thick stream passes above the splitter. The distance then can be adjusted as a function of the colloidal particle distribution in the thickness direction in the stream, and the front edge of the splitter can rotate so that the distance for example can move from about 100 micrometers above the sheet 222 to about 200 micrometers, for example. Splitting of between 20 percent and 40 percent of a 500 micrometer thick stream thus is possible.

(22) FIG. 3 shows a schematic top view of the water filtration device of FIG. 2, showing channels 300, 301, which extend a length l in the flow direction F, and a width w in a crosswise direction and have a thickness t (FIG. 2). The exit of inlet manifold 210 extends past front walls 309 of the channels, so the input pressure extant in inlet manifold 210 is transferred to the channels 300, 301. As the depth of the water is typically much larger than the thickness t of the channels 300, 301, the pressure in channels 300, 301 can generally be estimated as the pressure at the exit of the inlet manifold 210.

(23) FIG. 4 shows a schematic cross sectional view a first embodiment of a flow chamber 212 including a sheet 222 and one piece cover and channel structure 310, having channels 300, 301 therein. Each channel 300, 301 can for example be of a thickness of 500 micrometers, width of 900 micrometers and extending approximately a meter in length. The cover and channel structure 310 thus may be etched for example via soft lithography into a single piece of PDMS material for example. The straight channels however also permit mechanical or laser cutting. A PDMS barrier b between the channels in the width direction of 100 micrometers can be provided, so that for a width of 1 m, 1000 microchannels can be provided, if for example the two edge barriers are 50 micrometers wide. The single piece 1 m?1 m cover and channel structure can be laid over the PDMS sheet 222, which due to the air pressure from gas chamber 220, presses against the cover from below and forms stable microchannels. The gas chamber can be formed for example of metal, and may have longitudinally extending flanges 221 on both lateral sides. Longitudinally extending clamps 400, 402 thus can contact the top of the one piece cover and channel structure 310 and the bottom of the flange 221. Clamps 400, 402 could be for example a two part structure tightenable for example with bolts or screws or made of an elastic material that springs back to provide the clamping action.

(24) The FIG. 4 embodiment provides microchannels for excellent fluid velocity control, and is easily detachable and cleanable. The cover for example can be removed and the channels and the PDMS sheet sprayed with high velocity water. The device can then be quickly reassembled. A distance 311 between an outer surface of the cover facing air, and the top of the channel structure can be for example 10 to 25 micrometers.

(25) FIG. 5 shows a schematic cross sectional view of a second embodiment with a flow chamber including sheet 222, a cover 330 formed as a second sheet and a sandwiched channel structure 320 forming channels 302, 303. In the second alternate embodiment, the channel structure 320 is provided separately from cover 330, and is sandwiched by the sheet 222 and the cover 330. In this embodiment, cover 300 may be similar to sheet 222 described above, and channel structure 320 may be for example a rectangle made of PVC or other plastic material, or PDMS or other polymer material, with longitudinally extending channels open on the top and bottom to define longitudinally extending holes. Channel structure 320 thus has a thickness t for example of 500 micrometers, and the holes formed by channels 302, 303 can be 900 micrometers wide and extending approximately a meter in length. At the front end, channel structure 320 can be connected so that the inlet is provided by placing a colloidal suspension supply over the holes formed by channels 302, 303, and the rear end can have an outlet structure to divide the outlet stream by connecting the holes at a certain height, for example extending in a V-shape to a rear thickness of 25 micrometers between 125 and 150 micrometers.

(26) FIG. 6 shows an inlet area of the flow chamber of FIG. 5 schematically, with the front end of the channel structure 320 shown, and displaying how cover 330 is offset slightly to the rear with respect to sheet 222 to form the inlet distance iw for the channel structure 320. The inlet distance iw preferably is at least as large as thickness t to reduce fouling.

(27) FIG. 7 shows an outlet area of the flow chamber of FIG. 5 schematically, with for example the rear of the channels 302, 303 (FIG. 6) of channel structure 320 being connected by a fixed splitter, for example at a height of 150 micrometers. The outlet area can be manufactured for example by micromachining or lasering the PVC material.

(28) FIG. 8 shows a variable outlet splitter 250 rotatable around a shaft 401, with the rear end of channels 304 (similar to 302, 303 in FIG. 6) connected at top connector to keep the channels 304 properly spaced.

(29) The second embodiment also may be clamped in a similar manner to the first embodiment so that the cover 330, channel structure 320 and sheet 222 are clamped to form flow chamber 212. All of the parts can be easily disassembled and cleaned, for example with clean water sprayed at high pressure.

(30) In the two embodiments shown, on one example, the thickness of the channels is 500 micrometers, the width 900 micrometers and the length 1000 mm. Sheet 222 is approximately 1 m?1 m. An input pressure can be for example 1 mbar, or about 1 cm of input depth. Each channel can produce a flow velocity of about 0.00132457 m/s and a flow rate of 0.0357633 mL/min, and has laminar flow with a Reynolds number of about 0.85. The dwell time of the colloidal suspension in the flow chamber 212 is approximately 755 seconds. The colloidal particle diffusiophoretic velocity will vary with colloidal particle zeta potential and concentration gradients over the thickness of the flow chamber, and the exact velocity for each colloid will vary. However, colloidal particle diffusiophoretic velocities of between 1 to 10 micrometer per second are typical, as stated in the Origins of concentration gradients for diffusiophoresis noted above at page 4687. Thus most positively charged colloidal particles, even if at the top of the input stream at the beginning of flow chamber 212, will move, by the time the fluid has moved through the flow chamber 212 to outlet 240. A diffusiophoretic velocity of 1 micrometer per second would move colloidal particles by 755 micrometers, which is larger than the thickness of the fluid, and thus congregate the positively charged colloidal particles at the bottom of the stream at the outlet 240.

(31) The flow rate overall for 1000 microchannels thus is 35.76 mL/min or 2.146 liters per hour, and with a slitter height of 150 micrometers, a filtered water to waste water split ratio is 70% to 30%, and a filtered water output is 1.5 liters per hour.

(32) The embodiment channel structure described above has a minimum distance of 500 micrometers, which for most colloidal suspensions is sufficient to reduce fouling. Smaller channel thicknesses of 20 micrometers or even smaller could be possible depending on the application, but thicknesses of 100 micrometers or more are preferred. The concentration gradients and diffusiophoretic velocities at higher thicknesses may be smaller, but the laminar flow and length of the flow chamber can compensate for these effects. A thickness of 600 micrometers for example instead of 500 micrometers, with other sizes remaining the same, increases the flow rate to almost 3.91/h, with 2.7 liters per hour of filtered water, almost doubling output. The dwell time is 555 seconds, also leading to most positively charged colloidal particles moving via diffusiophoresis to congregate at the bottom of the stream by the time they reach outlet 240.

(33) To maintain concentration gradients and laminar flow however, channel thicknesses of 1 mm or less are preferred, and sufficient to reduce most fouling.

(34) The present device allows for a simply-constructed, relatively large flow rate water filtration device that can be generally free of fouling and easy to clean and maintain, all with a low energy consumption. Particles that become lodged in the channel structure can be removed during cleaning, and blockages are reduced. Thus even smaller channel structures, such as 20 micrometer thickness channel structures or smaller could be used, depending on the colloidal particles to be filtered.

(35) The present invention also provides that the partially filtered colloidal suspension, without the positively charged colloidal particles, can pass to a negative charged colloid filter in which air is present at the bottom and carbon dioxide at the top. In this case the sheet and pressurized gas chamber can be on the top, and move the negatively charged colloidal particles downwardly through diffusiophoretic motion. This optional downstream filter can be used with or without first attempting removal of the negatively charged colloidal particles from the positively charged colloidal particle filter described in detail herein, and can be added depending on the type of colloidal suspension being filtered.