Patent Application
20190345044
The present disclosure relates to an apparatus and method for filtration of drinking water. More particularly, the present disclosure relates to a drinking water filter having a reactive electrochemical membrane that is powered by direct current.
Micropollution in natural waters such as rivers and groundwater aquifers prevents these potentially potable sources from being used as drinking water. In the United States, for example, many hazardous waste sites are contaminated with trichloroethylene (TCE), a potentially carcinogenic compound. TCE and 2,4,6-trichlorophenol (TCP), a carcinogenic and persistent pollutant, represent the large class of chlorinated organics responsible for the contamination of many potential drinking water sources around the world. Other emerging and environmentally persistent organic micropollutants include polyromantic hydrocarbons (PAHs), organophosphate flame retardants, endocrine disrupting compounds (EDCs), pesticides, herbicides, pharmaceuticals and personal care products (PPCPs). Chloroform is a common contaminant in drinking water, as a byproduct of chlorination processes.
Recent studies have indicated that aeration, chlorine dioxide, dissolved air flotation, coagulation, flocculation, sedimentation, granular filtration, and microfiltration are all ineffective for removing poly- and perfluoroalkyl substances (PFASs) including perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). Activated carbon and anion exchange are less effective at removing shorter chain PFASs. The most effective treatment technologies are nanofiltration and reverse osmosis, which are associated with high initial capital investment and operational cost. Ultrafiltration with lower operation pressure than nanofiltration, is usually used for separation of bacteria, which are retained or rejected by the membranes. However, the biofouling of ultrafiltration membrane is a problem for the wide application of this method. And sole ultrafiltration cannot remove emerging contaminants especially those with small molecular sizes. These removal methods do not result in complete degradation and destruction of pollutants, but rather a separation and concentration of PFASs.
Likewise, microbial contamination (e.g., bacteria, viruses, and protozoan) is a global problem for drinking water security. Pathogenic microorganisms such as pervasive SARS, Ebola virus, avian influenzas, and pneumonia cause severe diseases and threaten general public safety and human health. Many waterborne diseases in the US are associated with the opportunistic pathogen Legionella, which may originate from drinking water contamination in distribution systems and premise plumbing. Conventional disinfectants (e.g., chlorine, chlorine dioxide, or ozone) can eliminate a wide spectrum of undesirable microorganisms; however, they also render the rise of more than 600 different disinfection byproducts (DBP) and increase microbial resistance to disinfectant chemicals. Many DBPs (e.g., trichloromethane, bromine-dichloromethane, dibromomethane and tribromomethane) are potentially carcinogenic. Conventional disinfection methods are becoming less efficient due to the evolution of antibiotic-resistant strains or genes. UV irradiation is an effective, safe, and environmentally friendly disinfection method but the lack of persistent antibacterial capacity generally causes high risk of regrowth, particularly in poor sanitation. Due to water quality regulations, water utilities may need to implement alternative treatment technologies to remain in full regulatory compliance.
In one embodiment, a method of purifying drinking water or tap water employs an electrochemically reactive membrane system. The application of a direct current (DC) generated reactive species at the membrane surface could oxidize soluble trace level organic compounds such as disinfection byproducts and pathogenic microbes. This method may also reduce membrane fouling and energy consumption for backwash and flux recovery.
Compared to other membrane filtration processes, the electrochemically reactive membrane filtration system has increased efficiency of contaminants degradation and removal, as well as water purification and disinfection. The electrochemically reactive membrane filtration system operates at relatively lower transmembrane pressures (thus requires low pumping pressures to filtrate water) compared to polymeric microfiltration or ultrafiltration of similar pore sizes with low potential of membrane fouling.
The method also preserves Ca2+, Mg2+, and other trace elements. A traditional reverse osmosis (RO) membrane, on other hand, removes all beneficial elements together with other potentially harmful suspended or soluble particles from the water. Such a process consumes large amounts of power, and results in a permeate having a low pH. Additionally, the RO process removes trace elements that are beneficial to the human health such as Ca2+, Mg2+. Hence, drinking RO treated water in the long term may cause calcium loss or other potential health risks. On the contrary, an electrochemically reactive membrane does not have such problems.
The disclosed method has a low energy consumption. Both ultrafiltration and microfiltration do not have high demand of water pressure or power.
In one embodiment, the disclosed system employs electrochemical oxidation and membrane filtration. The electrochemically reactive membrane filtration is scalable and battery-operated or DC powered. The electrochemically reactive membrane serves as both filter and anode that permits degradation of pollutants and permeate passage under DC currents. Water permeates through electrochemically reactive membrane filters under a mild hydraulic pressure that may be provided from a peristaltic pump or from the tap water pressure itself. The water treatment performance largely relies on the degradation kinetics of different pollutants in water on the porous electrode filters (e.g., Fe/Pd, Cu/Pd, Ni/Pd, Al/Pd, Carbon/Pd, boron-doped diamond, and TiO2/Al2O3). For example, the membranes may be synthesized from conductive titanium-based materials (e.g., substoichiometric titanium dioxide or Ti4O7) and any kinds of membranes with materials displaying high conductivity, or combinations thereof. The sizes of the electrode could vary.
The application of a DC generated reactive species at the electrochemically reactive membrane surface oxidizes soluble organic compounds. There are additional benefits of electrochemically reactive membranes such as reduced membrane fouling, reduction of organic (toxic) compounds in permeate and energy consumption for backwash and flux recovery, and water purification.
One particular type of filter configuration includes tubular system dead-end filtration. Another particular type of filter configuration includes planar cross flow filtration system. Other configurations may also be employed. Any combination and/or permutation of the embodiments is envisioned. Other objects and features will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the present disclosure.
In the accompanying drawings, structures are illustrated that, together with the detailed description provided below, describe exemplary embodiments of the claimed invention. Like elements are identified with the same reference numerals. It should be understood that elements shown as a single component may be replaced with multiple components, and elements shown as multiple components may be replaced with a single component. The drawings are not to scale and the proportion of certain elements may be exaggerated for the purpose of illustration.
Exemplary electrochemically reactive membrane filtration systems are disclosed below. The systems include subsystems and components to measure and control process variables, such as permeate flux and pressure, for effective performance. The apparatus could employ sensors or other condition detection and control subsystems or components that might be required to process at a particular rate or at a particular scale.
The rod 115 serves as a counter or auxiliary electrode. It should be understood that other counter or auxiliary electrodes could be used. In one embodiment, the rod 115 is cylinder-shaped with a diameter of 3 mm and made of stainless steel and fixed at a bottom latch 120 by a holder 125. The holder 125 includes an aperture for holding the rod 115 in place and preventing movement or displacement. In one embodiment, the holder is constructed of stainless steel. However, other electrically conductive materials may be employed.
In alternative embodiments, the rod could have other shapes and dimensions and could be made of any other suitable material. For example, the rod may be constructed of any anti-corrosive conductive materials (e.g., stainless steel, copper, platinum).
A DC power source is wired to the electrochemically reactive membrane filter 110 and the stainless-steel rod 115 to provide electricity. The electrochemically reactive membrane filter 110 thus acts as both a filter and an electrode. Exemplary DC power sources include, without limitation, DC generators and AA or AAA batteries with output voltage of 3 V or higher and the total dischargeable energy of 2000 or more milli-Amp hours (mAh).
At least two chemical mechanisms are involved on the electrochemically reactive membrane filter 110, namely, (1) direct anodic oxidation, where water pollutants are oxidized after adsorption on the electrochemically reactive membrane surface, and (2) indirect electrolysis, in which organic pollutant oxidation is mediated by the reactive radicals generated on the electrochemically reactive membrane surface. For the second mechanism, radicals such as hydroxyl radicals could be formed via water oxidation at an anode surface when the electric potential is supplied. During this indirect oxidation, the agents produced on the anode, which are responsible for oxidation of inorganic and organic matters, may be chlorine and hypochlorite, hydrogen peroxide, and ozone. Moreover, during electrolysis, two species of active oxygen can be electrochemically produced on the electrochemically reactive membrane. One is the chemisorbed “active oxygen” (oxygen in the oxide lattice), while the other is the physisorbed “active oxygen” (adsorbed hydroxyl radicals).
One pair of top side connector 130 and a bottom side connector 135 provides an electrical path for the positive of DC power source to the electrochemically reactive membrane filter 110 through the tubular electrochemically reactive membrane filtration system 100. Another pair of top side connector 140 and bottom side connector 145 provides an electrical path for the negative of DC power source to the stainless-steel rod 115 through the tubular electrochemically reactive membrane filtration system 100.
In one embodiment, the electrochemically reactive membrane filter 110 is a 10-cm long one-channel tubular electrode made of porous electrode materials as mentioned above with the outer and inner diameters of 10 mm and 6 mm. It should be understood that the use of such configurations of the electrochemically reactive membrane electrode is merely exemplary, and that other titanium suboxide or any other suitable material with suitable geometry or physical configurations may also be applicable.
A top inlet conduit 150 of the system is configured to be attached to a residential tap water faucet by screw thread. Raw water flows into the electrochemically reactive membrane filter 110 under a mild hydraulic pressure provided from a peristaltic pump or from the tap water pressure itself. Outlet conduit 155 is connected to the side of the tubular electrochemically reactive membrane filtration system 100 for permeate withdraw. A bottom cap 160 of the electrochemically reactive membrane system is removable. In filtration mode, the bottom cap 160 is sealed to allow water to pass through the membrane surface only. In flush mode the bottom cap 160 is removed to allow water to flush out the fouling on the inner side of electrochemically reactive membrane filters 110.
To mitigate surface fouling and extend the effective filtration period, a DC power supply could be used to generate surface radicals and oxidative chemicals that are antimicrobial and helpful for membrane surface cleaning or defouling. For example, under DC polarization from 50 A·m−2 to 250 A·m−2 or approximately 10 to 22 V of cell voltage, 0.0045 mM to 0.022 mM chlorine may be generated on the cathode surface within two hours in the presence of Meanwhile, 8 μM to 55 μM H2O2 can also be generated on the anode surface under the same condition.
A first O-ring 215 is disposed between the planar electrochemically reactive membrane filter 205 and the mesh 210. The first O-ring 215 may be constructed of insulation and water stopping material. A second O-ring 220 is disposed beneath and attached with the planar electrochemically reactive membrane filter 205. The second O-ring 220 may be constructed of stainless-steel or another metal. A third O-ring 225 is fixed under the second O-ring 220 to support the planar electrochemically reactive membrane filter 205. The third O-ring 225 may be constructed of insulation and water stopping material. In alternative embodiments, any number of O-rings, gaskets, or other sealing devices may be employed.
A cover 230 is capped on top of the planar electrochemically reactive membrane filtration system 200. The cover 230 may be constructed of a transparent material, such as glass or a polymeric material, for observation.
The planar electrochemically reactive membrane filtration system 200 is closed with several fasteners, such as bolts 235. When the system 200 is closed, the O-rings 215, 220, 225 seal the planar electrochemically reactive membrane filter 205. Other exemplary fasteners include, without limitation, screws, rivets, and adhesive. Alternatively, the planar electrochemically reactive membrane filtration system 200 may be closed by welding or braising.
The mesh 210 serves as a counter or auxiliary electrode. It should be understood that other counter or auxiliary electrodes could be used. In one embodiment, the mesh 210 is round-shaped and made of stainless steel. It will be understood that the mesh could have other shapes and could be made of any other suitable material. For example, the mesh may be constructed of any anti-corrosive conductive materials (e.g., stainless steel, copper, and platinum).
In one embodiment, the planar electrochemically reactive membrane filter 205 is a 47-mm diameter electrode made of Ti4O7. While the use of Ti4O7 is exemplary, the electrochemically reactive membrane could be made of any other titanium suboxide or any other suitable material displaying high conductivity and electrochemical activity. The length, inner diameter, and outer diameter of the electrode could vary.
The second O-ring 220 serves as conductive material connecting between the planar electrochemically reactive membrane filter 205 with DC power. It should be understood that other conductive material could be used.
A direct current (DC) power source, such as DC generator or batteries, is wired to the electrochemically reactive membrane and the stainless-steel mesh 210. The planar electrochemically reactive membrane filter 205 thus acts as both a filter and an electrode. At least two chemical mechanisms are involved on the planar electrochemically reactive membrane filter 205, namely, (1) direct anodic oxidation, where water pollutants are oxidized after adsorption on the electrochemically reactive membrane surface, and (2) indirect electrolysis, in which organic pollutant oxidation is mediated by the current-generated reactive radical species.
A side connector 240 provides an electrical path for the positive of DC power source to the planar electrochemically reactive membrane filter 205 through the planar electrochemically reactive membrane filtration system 200. Another side connector 245 provides an electrical path for the negative of DC power source to the stainless steel mesh 210 through the planar electrochemically reactive membrane filtration system 200.
Raw water flows into the planar electrochemically reactive membrane filter 205 under a mild hydraulic pressure provided from a peristaltic pump or from the tap water pressure itself through an inlet conduit 250. The permeate flows through the planar electrochemically reactive membrane filter 205 and flows out from permeate outlet conduit 255. The concentrated raw water flows out through discharge outlet conduit 260 to be recirculated or discharged.
In the illustrated embodiments, each of the filtration systems 100, 200 include a single electrochemically reactive membrane filter and do not include any filters other than the electrochemically reactive membrane filter. Testing has shown that a single electrochemically reactive membrane filter connected to a DC power source is sufficient to remove multiple pollutants (e.g., bacteria, dye, and chemical additives) from drinking water, without removing desirable trace metal elements. In alternative embodiments, multiple electrochemically reactive membrane filters may be employed. In still other embodiments, additional filters may be employed, such as those discussed above.
To the extent that the term “includes” or “including” is used in the specification or the claims, it is intended to be inclusive in a manner similar to the term “comprising” as that term is interpreted when employed as a transitional word in a claim. Furthermore, to the extent that the term “or” is employed (e.g., A or B) it is intended to mean “A or B or both.” When the applicants intend to indicate “only A or B but not both” then the term “only A or B but not both” will be employed. Thus, use of the term “or” herein is the inclusive, and not the exclusive use. See, Bryan A. Garner, A Dictionary of Modern Legal Usage 624 (2d. Ed. 1995). Also, to the extent that the terms “in” or “into” are used in the specification or the claims, it is intended to additionally mean “on” or “onto.” Furthermore, to the extent the term “connect” is used in the specification or claims, it is intended to mean not only “directly connected to,” but also “indirectly connected to” such as connected through another component or components.
While the present application has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the application, in its broader aspects, is not limited to the specific details, the representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant's general inventive concept.
The present application claims the benefit of U.S. Provisional Patent Application No. 62/669,105, filed May 9, 2019, the content of which is hereby expressly incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62669105 | May 2018 | US |
