Patent Application
20100135869
The present invention relates to the ozone generator for detoxifying and disinfecting water. More specifically, the invention relates to the ozone generator for the electrolysis of water forming ozone directly within the water by applying a DC power to an electrode pair in a simple construction
Disinfection and detoxification of drinking water are very important to human health. Regardless of the water source, there must be some form of microorganisms including bacteria, viruses or protozoa present in water. Among them, pathogenic organisms, such as, diarrhea, typhoid, hepatitis and cholera, may result in death. The foregoing and other pathogens must be exterminated for safety. In addition, hazardous organic compounds, acids, bases, fertilizers, and pesticides discharged from factories and farms may get into the water reservoirs designated for public water supply. Many of the chemicals may cause cancers and they require detoxification before the water is consumed.
Water is the most likely source of sickness for people living in the areas with poor or lack of sanitation, such as, wild lands, mountains, lakes, and particularly places hit by natural disasters, for example, earthquake, hurricane, flood or tsunami. Protozoan parasites including Giaradia muris cysts, or Cryptosporidium oocysts, or both can be found in 97% of the surface water in the US. The former microorganism may cause chronicle beaver fever, while the latter may lead to serious cholera-like gastroenteritis in people who drink the infested water. On the other hand, pathogens like Escherichia Coli, Shigella and hepatitis A virus can easily be found in waters contaminated by animal fecal wastes and domestic wastewaters.
There are four primary methods of disinfection, that is, chlorination, chloramination, ozonation, and UV radiation. By far, chlorine is the most widely used disinfectant for killing the water-borne microorganisms in public water supplies around the world. In addition to the distinctive odor and the ineffectiveness of handling the protozoan, the chlorine treatment may generate carcinogens from the reaction of the chlorine with the organics present in the water. In December 2005, the US Environment Protection Agency (EPA) had issued a Purifier Protocol and Standard that prohibits “residues from the disinfectant used for sterilizing drinking water”. Under this guideline, ultraviolet (UV) and ozone (O3) meet such standard as they are chemical-free disinfectants for purifying water. As a matter of fact, in Nice, France, ozone has been used to sterilize/disinfect the public water supply, since as early as 1906. Today, the UV irradiation process is included as one of the standard manufacturing processes in bottled-water and desalination plants. Ozone is listed as “Generally Recognized As Safe” (GRAS) for both potable and bottled water by the US Food and Drug Administration (FDA).
Electrolytic sterilization is a technique that uses an electric current to generate a disinfecting agent in water to serve as bactericide, virucide and or cyst inactivator. Among all chemicals, sodium chloride (NaCl) is the most popular precursor for making sodium hypochlorite (NaOCl) as the disinfectant as disclosed in the U.S. Pat. Nos. 3,622,479; 4,512,865 and 4,761,208. In the electrolytic detoxification, NaOCl is formed in electrochemical cells for removing ammonia (NH3) from water as disclosed in U.S. Pat. Nos. 5,935,392 and 6,348,143. In all of the foregoing reactions, OCl− ion is the oxidant adapted for sterilization or denitrification. Some of the ionic agents may survive the reactions and then become contaminants resulting in an increase of the TDS (Total Dissolved Solids) of the waters treated by OCl−. Many electrolytes specifically prepared to serve as the precursors for various agents formed electrolytically have been disclosed in numerous patents, for example, U.S. Pat. Nos. 5,531,883 and 5,997,702, just to name few. All in all, the chemicals added in the processes of electrolytic sterilization or electrolytic detoxification will become contaminants themselves, therefore leaving the treated water far from clean or safe.
Without adding any chemicals to the water to be treated, the sterilization of water is conducted through a direct electrolysis on sandwiched porous graphite electrodes as disclosed in U.S. Pat. No. 5,744,028, wherein the reaction current is too low to be effective. In U.S. Pat. No. 4,936,979, two alloy electrodes comprised of 88% copper (Cu), 10% tin (Sn) and 2% lead (Pb) are utilized electrolytic sterilization. The electrodes are consumed to provide 1 ppm (parts per million) Cu2+ for killing algae, as well as 0.5 ppt (parts per thousand) Sn2+ and 0.5 ppm Pb2+ for killing bacteria. The foregoing treatment may work for swimming pools, but it is incapable of eliminating the cyst contamination. Although ozone is a much more potent oxidant than OCl−, and applications of the gas are as versatile as from drinking-water sterilization, cleansing of semiconductor wafers as disclosed in U.S. Pat. No. 7,004,181, to medical treatments as disclosed in U.S. Pat. Nos. 5,834,030 and 6,902,670, nevertheless, the oxidizing gas is overwhelmingly generated by corona discharge. The silent discharge method has many problems, for example, a high working voltage, oxygen provision, gas leakage and ozone dissolution. Not only are the foregoing disadvantages absent from the electrolytic generation of ozone, but unique advantages are also present in the in-situ method as elaborated in U.S. Pat. No. 6,984,295. Without chemicals or electricity, ozone is produced via the absorption of 185 nm UV by oxygen as disclosed in U.S. Pat. No. 4,230,571. Recently, UV sterilizers have been fabricated into a hand-held device size for onsite sterilization of potable water. Compared to the aforementioned bulky electrolytic cells, the mini-size UV sterilizer is user-friendly, but the UV lamp is vulnerable to damage under external force.
Accordingly, a first aspect of the present invention provides a robust, chemical-free and compact ozone generator capable of being battery operated suitable for sterilizing/disinfecting and detoxifying waters, e.g., potable waters.
The first aspect of the present invention is directed to an ozone generator that can be immersed in water for in-situ sterilization/disinfection of water and can be made pocket-sized.
In order to realize the object of the first aspect of the present invention, the ozone generator for in-situ sterilization of water, comprising:
a power source, for providing a reaction energy to generate ozone gas within water to be treated;
at least one supercapacitor, for amplifying the reaction energy provided by said power source;
a circuitry, for controlling said supercapacitor to deliver consistent power supply to generate ozone; and
at least a pair of electrodes, for receiving the amplified reaction energy from said supercapacitor for generating ozone within the water to be treated.
The following are preferable or specific embodiments of the first aspect of the present invention. Any combinations of (2) to (10) are preferable or specific embodiments unless any contradictory occurs.
(1) The power source is selected from a group consisting of primary batteries, secondary batteries, fuel cells and solar cells.
(2) The supercapacitor has an operating voltage of at least 2.5V, and at a capacitance of at least 0.5 F.
(3) The zone generator comprises at least two identical supercapacitors, and the control circuitry comprises a switching device which switches said at least two identical supercapacitors to be operated between charging and discharging states.
(4) The switching device comprises a relay or a MOS-FET (metal oxide semiconductor, field effect transistor).
(5) The switching frequency comprises 6 cycles per second or above.
(6) The electrodes have a shape of mesh, screen, or wire network.
(7) The electrodes comprises platinum or boron doped diamond.
(8) The power source is a human-powered generator, and the at least one supercapacitor comprises a supercapacitor in large capacitance to store the energy generated by the said human-powered generator and at least one supercapacitor in small capacitance, for amplifying the reaction energy provided by said power source;
(9) The human-powered generator is a generator that produces electricity through electromagnetic induction.
(10) The supercapacitor for energy storage has a capacitance of at least 6 F.
A second aspect of the present invention has been accomplished to realize an cost-effective and configurable ozone generator in connection with the first aspect of the present invention.
In order to accomplish the object of the second aspect of the present invention, the ozone generator comprises:
at least an anode containing a material with high oxygen evolution potential;
at least a metal cathode;
a constant gap between the said anode and said cathode;
a potential source;
at least one supercapacitor; and
an implementation of the said supercapacitor for power provision.
The following are preferable or specific embodiments of the second aspect of the present invention. Any combinations of the following are preferable or specific embodiments of the second aspect of the second invention, unless any contradiction occurs.
(1) The material is selected from a group of materials containing SnO2, Sb—Ni doped SnO2, Ti, and Pt.
(2) The material is SnO2 or Sb—Ni doped SnO2.
(3) The material is Sb—N doped SnO2.
(4) The Sb—Ni doped SnO2 is one produced from an Sb precursor, an Ni precursor and an SnO2 precursor and a carbon source through sintering.
(5) The cathode is selected from a group of materials containing Pt, stainless steel, and nickel.
(6) The electrode gap is 0.5 mm to 5 mm
The above features of the second aspect of the present invention have been selectively determined through careful consideration of various matters in conjunction with the first aspect of the present invention. Finally, Sb—Ni-doped SnO2 has been determined most preferable as the material with the high oxygen evolution potential, though other materials mentioned below are acceptable in connection with the first aspect of the present invention.
Due to its short lifetime (ca 30 minutes), ozone is unsuitable for storage or shipping. It is produced right before use and at the point of use. Ozone is best generated via the low-voltage electrolytic method. Due to its short lifetime (ca 30 minutes), ozone is unsuitable for storage or shipping. It is produced right before use and at the point of use. Ozone is best generated via the low-voltage electrolytic method. There are three major problems as mentioned below. present in the prior arts of electrolytic ozone including the U.S. Pat. Nos. 5,407,550 to 6,984,295.
That is, a first problem is the anode material that is utilized as the electrocatalyst for forming ozone in electrolyzing water. Platinum and β-PbO2 are the two most widely used ozone-forming materials. However, Pt is prohibitively expensive and less efficient for the ozone formation at ambient temperature, though acceptable. On the other hand, the lead dioxide can produce ozone with a high efficiency at room temperature, but lead is an environmental hazard that is banned in many countries for water treatment.
A second problem for the electrolytic ozone is that an ion-exchange membrane is required for the generation of ozone. Not only the membrane is expensive, but also it severely restricts the scope of utilization of the electrolytic ozone systems containing the membrane. There are so many contaminants as can easily foul the membrane that the material can not be in direct with wastewaters. As a consequence, the electrolytic ozone is implemented in a similar way as the corona discharge wherein the ozone is formed at a separate location followed by the delivery of the gas into the water to be disinfected.
This constitutes a third problem of the electrolytic ozone for its incapability of performing in-situ and instantaneous disinfection. Therefore, an efficient and economic electrocatalyst for the generation of ozone, as well as a convenient and effective implementation of ozonation are urgently needed in connection with the first aspect of the present invention, which has been accomplished by the second aspect of the present invention.
Further, the second aspect of the present invention is to identify a long-term stable anode material containing no noble metal (e.g., Ru, Ir and Pd) for treating wastewater electrochemically in connection with the ozone generator according to the first aspect of the present invention. A bimetal doped tin dioxide (M-SnO2, M=Sb and Ni) thick-film appears to best meet the goal as the electrocatalyst for generating ozone (O3) directly within the waters to be detoxified or disinfected. Using an economical precursor of tin, stannic chloride, together with doping chemicals (Sb and Ni), the doped tin dioxide film can be stepwise grown on different sizes of titanium (Ti) substrates forming the anode electrodes in the desired dimensions and configurations to meet the application needs. Fabrication of the tin dioxide electrodes contains three steps including coating, pyrolysis, and sintering. Actually, a performing and reliable tin dioxide catalyst is built by stepwise epitaxy of nano-size tin dioxide particles into a monolithic structure on the Ti substrate. As the tin dioxide film is deposited layer by layer, the “coating and pyrolysis” steps must be repeated several times before the final sintering treatment. Collectively, the number of pretreatment cycles and the heating conditions determine the durability and performance of tin dioxide film resulted. While Ti metal serves as the film forming substrate and electric conductor for tin dioxide grown atop, the quickly formed surface oxide of Ti, that is, titanium dioxide (TiO2), works as an adhesive bridge between tin dioxide film and Ti metal underneath, as well as a resistant barrier to protect the substrate from the harsh environment of ozone generation. Furthermore, the present inventors discovered that the Sb—Ni doped SnO2 film is more advantageously produced from the precursor of tin, the doping chemicals (Sb and Ni) and a carbon source such as glycerol through coating, pyrolysis, and sintering. With the presence of glycerol, the resulting film is condensed and smooth without crack, exhibiting more excellent performance.
The second aspect of the present invention is to provide an implementation method of the Sb—Ni-doped SnO2 film for the on-line and in-situ detoxification or disinfection of various wastewaters continuously. Please note that hereinafter, Sb—Ni doped SnO2 is referred to as M-SnO2, which includes both the Sb—Ni doped SnO2 and the Sb—Ni doped SnO2 with use of the carbon source. In conjunction with anode, the M-SnO2-coated Ti plate, a metal plate such as a stainless steel plate is employed as cathode. Both electrodes have perforated holes or openings for water to flow through freely. An ozone reactor is constructed by arranging a plural number of anode-cathode pairs in a tandem stack, wherein plates are parallel to one another, using plastic screens, or holding frames for the provision of a constant gap among the electrodes to prevent electric short. Since the electrodes, spacers, and frames are resistant to virtually all chemicals and fine particles, the foregoing O3 reactor can be installed directly in any wastewater to generate ozone therein for in-situ and instantaneous detoxification and disinfection. As the oxidant is improvised, there is no need of delivery and dispersion of O3 gas into the water to be treated. Moreover, there is no air pollutant, for example, NOx, and the floor space of the said reactor is very minimal. The ozone bubbles formed by the said reactor are ultra fine. No disperser system can generate as fine and as uniform bubbles as the reactor using M-SnO2 film. In addition to fast detoxification and disinfection, the fine bubbles facilitate the reaction of ozone with water to form hydrogen peroxide (H2O2), another potent disinfectant. With the synergism of the peroxide, the present invention offers the advanced oxidation process (AOP) to the fast decomposition of organic and inorganic compounds, as well as to the rapid sterilization of microorganisms.
The third aspect of the present invention is further to provide an economical and reliable power provision system for the electrolytic disinfection. Due to the enormous volumes of industrial wastewaters, the ozone reactor demands a large electrode area measured in m2 to meet the throughput requirements of water treatment. For a high treatment capacity, such as, more than 100 CMD (m3/day), a DC current density of 50 mA/cm2, or 500 A/m2, is often needed for the O3 reactor operated at 20 DC V or lower. The power demand of low DC voltage and high DC current is exactly in line with the discharging characteristics of supercapacitor, an energy-storage device that can store electric energy in hundreds farad (F) of capacitance. All of the energy stored in the supercapacitor can be discharged in a split second resulting in peak currents. Hence, the supercapacitor is the best suitable power amplifier for a potential source to deliver the power required for operating the O3 reactor. If the supercapacitor delivers a large quantity of electricity in one discharge, it needs a long period of charging time to refill the lost energy. There is no power can be supplied to the ozone reactor until the capacitor is fully recharged. This means that the conventional application of supercapacitor can not meet the constant power needs of continuous treatments of industrial wastewaters. A technique entitled “charging and discharging swing” (CD Swing) can drive 2 sets of supercapcitors to deliver consistent power to the O3 reactor for continuous detoxification and disinfection of wastewaters. Using supercapcitors and the CD Swing, the power supply for the treatments of industrial wastewaters via the O3 reactor of the present invention may become highly cost-effective.
The ozone generator provided by the first aspect of the present invention, which may be made pocket sized, can effectively perform in-situ sterilization of waters, and can easily be carried by the tourists traveling to places without adequate sanitation facilities, for example.
The second aspect of the present invention can offer a cost-effective technology of performing ozonation using economical electrocatalyst, simple cell design, and efficient power provision. Various ozone generators for various ozonation needs can be easily fabricated based the good scalability and conformability of the fabrication process of Sb—Ni-doped SnO2 electrodes, for example.
The present invention is best understood by reference to the embodiments described in the subsequent sections accompanied with the following drawings.
Now, the first aspect of the present invention will be explained in more detail.
The ozone generator according to the first aspect of the present invention, which may be made pocket-sized, may be driven by DC power, and is capable of generating ozone from within water at any point of use. In order to prolong the service life of the ozone generator, a durable and foul-free electrode is used for generating ozone.
An alkaline battery or rechargeable battery may serve as the main power source for driving the ozone generator to perform electrolysis on water to generate ozone. To minimize the size of the ozone generator, only a few batteries are required. Since the batteries can only deliver a small current, a supercapacitor is adapted to supplement the power deficiency of the battery. In addition, the supercapacitor can also extend the use-time of battery through the “load leveling” effect. Furthermore, two identical groups of supercapacitors are arranged to discharge and re-charge alternatively through a charging-discharging swing, or CD swing approach, so that the power delivered to the electrolysis reaction can be continuous and consistent.
Among the electrode materials available for ozone generation, platinum (Pt) or conducting diamond film (boron-doped diamond, BDD) may be selected for the sake of safety and hygiene. The decay of the foregoing electrode materials does not generate hazardous ingredients into the treated potable water. A plastic screen is disposed between the anode and cathode, which are symmetrical in shape and identical in composition, of the ozone generator to prevent an electrical short. The two electrodes and the plastic screen are fastened together. The electrode is easy to clean and maintain, and can be easily replaced. The ozone generator can also be used as a stirrer during treatment to ensure that all of the water is sterilized or detoxified. No air is required to be injected into the water during the treatment process, ozone is formed due to ionization of the water.
The surface area of the electrodes, the discharge rate of the battery, the capacitance of the supercapacitor, as well as the conductivity of the water to be treated collectively determine the concentration of ozone produced. Generally, the amount of ozone generated is sufficient for sterilization/disinfection of the water but safe for the users to drink. The sterilization time usually ranges around 30-60 seconds, and can kill most of the microbes contained in the water. The ozone generator may be equipped with a switch that can be used to operate the ozone generator for any desired preset time.
The preferred embodiments of the pocket-size ozone generator of the first aspect of the present invention are presented as follows.
In order to produce a sufficient and safe amount of ozone, the maximum operating power for the ozone generator to perform in-situ and rapid sterilization of water is designed at 6 W. Considering the variation of water conductivity from miscellaneous water sources, the operating voltage of the ozone generator is set at 6V. Accordingly, the operating current should be 1 A to deliver the required 6 W power. The targeted current is beyond the allowable or optimal discharge rate of primary batteries and secondary batteries alike. Conventionally, a step-up circuit using DC/DC converter is used for producing high currents from low-current inputs of batteries. Such a converter is often bulky and costly, and therefore not suitable for the pocket size ozone generator shown in
Supercapacitor 500a: (+) pole of 200→404a→404→406→406a→(−) pole of 200
Supercapacitor 500b: (+) pole of 200→408a→408→410→410a→(−) pole of 200
Initially, the terminals of the supercapacitors 500a and 500b carry no polarity before charging. As the supercapacitors 500a and 500b are charged, their terminals will have the same polarity as that of the battery 200. That is, terminals 404 and 406 will serve as the positive and negative electrodes of the supercapacitor 500a, and the terminals 408 and 410 serve as the positive and negative electrodes of the supercapacitor 500b, respectively. The CD swing is initiated by depressing the latch button (not shown), an audible clicking sound is indicative of the switching of the relays 402a and 402b between “closed” and “open” states leading to the switching of the supercapacitors 500a and 500b between charging and discharging states. The operation procedure of the CD swing may be described as follows. The operation procedure of the CD swing includes at least a first cycle, a second cycle and a third cycle.
The First Cycle.
The relay 402a is switched “on” (“open” state) and the relay 402b remains at “closed” state (i.e. “off” state). Meanwhile, the relay 402a changes the contact points of two terminals 404 and 406 of the supercapacitor 500a from 406a/404a to 406b/404b. Thus, the (+) terminal 404 of the supercapacitor 500a is in electrical contact with the two electrodes 600, whereas the supercapacitor 500b remains in parallel with the battery 200. Since the supercapacitor 500b is charged, the battery 200 is prevented from charging the supercapacitor 500b. However, the supercapacitor 500b is also connected in series with the supercapacitor 500a (408→408a→406b→406), the supercapacitors 500a and 500b deliver at the combining voltages of the supercapacitors 500a and 500b, or two times voltage of 200, to the electrodes 600 through (+) pole 404 of the supercapacitor 500a. If the super capacitor 500b releases some of its stored energy, it will be promptly replenished by the battery 200 so that the supercapacitor 500b remains charged ready for assuming the role of discharge.
The Second Cycle.
The relay 402a is “off” (“closed” state) and the relay 402b is “on” (i.e. “open” state). The supercapacitor 500a is connected in parallel with the battery 200 for recharging the energy released in the prior discharging cycle. The contact points of terminals 408 and 410 of the supercapacitor 500b are switched from terminals 408a/410a to 408b/410b. Hence, the supercapacitor 500b will deliver an electric power to the electrodes 600 in conjunction with the supercapacitor 500a. Meanwhile, the supercapacitor 500a is replenished by the battery 200 via their parallel connection.
The Third Cycle and Beyond.
The third cycle includes flow of the first cycle and the second cycle being alternately repeated for every odd-cycle and every even-cycle of CD swing respectively to provide a consistent power supply to the electrodes 600 until the preset sterilization time period has reached (until latch button is turned off) to complete the sterilization.
In the CD swing technique as described above, two identical sets of supercapacitor are employed to reciprocally switch between charging and discharging for continuously supplying consistent power to the electrodes 600 to rapidly generate ozone that is several folds more effective than many other widely used disinfecting chemicals, such as chlorine, chlorine oxide or chloroamines. According to Jensen in “Ozone: The Alternative for Clean Dialysis Water” (DIALYSIS & TRANSPLANTATION, Volume 27, Number 11, pp 708-712, November 1998), the concentration-time value ranges (expressed as mg/L-min) for 99% inactivation of various organisms by O3 at 5° C. is about 0.006-2.0 ppm-min. Thus, an operating voltage of 6V is sufficient to drive ozone generator of the present invention to generate the sufficient amount of O3. For example, about 1 A of operating current and about 0.5 F capacitance for each of the supercapacitors 500a and 500b are required for the compact ozone generator to produce sufficient amount of ozone in about 30-60 seconds. Nevertheless, with the 5V driving-voltage threshold of the relays 402a and 402b, 4 pieces of alkaline batteries are required. Other power sources, for example, rechargeable batteries, fuel cells or solar cells, can also be used for driving the ozone generator of the present invention. Different power sources deliver different voltage outputs, and accordingly the design of the power compartment of the ozone generator should be varied. Regardless of the power source, the power can be amplified by the supercapacitors 500a and 500b and the relay-operated circuit. The relays 402a and 402b have a low-frequency, about 6 cycles per second (6 Hz), mechanically switching devices, and the low frequency will lead to a large fluctuation of output voltage for the power sources using the CD swing. Other disadvantages of the CD swing technique using a relay mat include mechanical wearing due to numerous times of switching, and a fusion of the relay contacts from an excessive current flow through the relay. However, since the ozone generator of the present invention consume significantly less power and has a low-switching operation, the relays can work well for rapid in-situ sterilization of potable waters.
Before the initiation of charging-discharging process, the MOS-FETs L2 and L3 of the supercapacitor 500b are in the “closed” state, the MOS-FETs L1 and L4 of the supercapacitor 500a are in the “open” state, and the MOS-FETs R2 and R3 of the supercapacitor 500a are in the “closed” state and the MOS-FETs R1 and R4 are in the “open” state. Therefore, the supercapacitors 500a and 500b are connected in parallel with battery B, and the supercapacitors CL and CR are charged simultaneously to the same voltage and polarity of 200. Once the CD swing is initiated, the process will be conducted as follows:
The First Cycle
The supercapacitor 500a is in parallel with the battery 200, MOS-FETs L1 and L4 are in the “closed” state and MOS-FETs L2 and L3 of the supercapacitor 500b are in the “open” state. As a result, the supercapacitor 500b and the battery 200 are connected in series, thus, they discharge collectively to the load 718, or the electrodes of the ozone generator. The current delivered to load 718 is monitored by the current sensor 716 so that the power supplied to the ozone generator can be set at a desired level.
The Second Cycle.
The supercapacitor 500b is switched to the parallel configuration with the battery 200 (i.e. the MOS-FETs L2 and L3 are in the “closed” state, and the MOS-FETs L1 and L4 are in the “open” state), thus, the partially discharged supercapacitor 500b is replenished by the battery 200. Meanwhile, the supercapacitor 500a is switched into series connection with the battery 200 (i.e. MOS-FETs R1 and R4 are in the “closed” state, and MOS-FETs R2 and R3 are in the “open” state), thus, the supercapacitor 500a and the battery 200 discharge collectively to load 718 to generate ozone.
The Third Cycle and Beyond.
The third cycle, the first cycle and the second cycle, described above, that are repeated alternatively for every odd-cycle and every even-cycle furthering a CD swing technique, respectively, to provide a consistent power to the electrodes of the ozone generator of the present invention until the preset sterilization period has reached (i.e. until the latch button is depressed off) to complete the sterilization of the potable waters.
Batteries with higher discharge rate than the alkaline batteries, for example, lithium ion battery, are employed with the electrodes as
A prototype ozone generator as shown in
During the sterilization treatment, the water was stirred by the ozone generator. Water from roadside ditch was more contaminated than that from the faucet, therefore, the former consumed more energy to accomplish sterilization. In both cases, as can be inferred from the table above, the waters were effectively sterilized and disinfected.
Conclusion
As it can clearly be seen from the above example and other in-house tests, the compact pocket sized ozone generator provided by the present invention can effectively perform in-situ sterilization of waters, and can easily be carried by the tourists traveling to places without adequate sanitation facilities. A tune of 99% inactivation of microbial and hazardous contaminants present in the potable waters can be achieved in just 30-60 seconds of treatment. The hand-held pocket size ozone generator can be operated by batteries, human power and renewable energies, and it requires no addition of chemicals to the water to be treated. After treatment, the ozone will be converted to oxygen without forming any residues in the treated waters. The amount of ozone is sufficient for sterilization and at a level that is harmless to the users. Thus, no chemicals are required to generate ozone, and the ozone generator only requires the replacement of spent batteries, while the electrodes and human-powered generator may be used a long-period of time.
In the following, preferred and specific embodiments of the second aspect of the present invention will be explained in more detail.
As water becomes scarce, wastewater can become a valuable source for domestic and industrial use of water. In the households, only the potable water provided by the utility company is further purified, whereas the wastewater is simply discharged. Each household pays a fixed fee for the sewage treatment. It is a different situation in the industries for their wastewater discharged to a local wastewater treatment facility is charged according to the amount and types of pollutants released. If the industries can recycle their wastewater, the water retrieved may be used for production and the fee of wastewater treatment can be significantly reduced as well. There are four kinds of technology can be employed for turning wastewater into usable water: physical, chemical, biological, and membrane methods. Among them, chemical and biological treatments are highly effective in killing pollutants by oxidative decomposition, rather than retaining of pollutants which is normally happened in the physical and membrane treatments. Nevertheless, the chemical, particularly, the electrochemical oxidation consumes less energy, occupies smaller space, and generates fewer to none secondary pollution than that of biological oxidation. Electrolytic ozone is an electrochemical oxidation with a dual function that ozone is formed for in-situ ozonation, and many pollutants may be simultaneously oxidized by the anode. The key to the economical viability of electrolytic ozone is the anode material for producing the ozone gas. Only the material with high oxygen evolution potential is suitable for the operation. Several materials including β-PbO2, boron doped diamond (BDD), glassy carbon, gold (Au), graphite, iridium oxide (IrO2), palladium (Pd), and platinum (Pt), have been reported to have the activity on catalyzing the electrolysis of water to ozone. In the foregoing list, Pt and β-PbO2 are two commonly electro-catalysts used to generate ozone from electrolyzing water. Due to high cost and low ozone-formation efficiency (0.5% at room temperature), Pt is less advantageous for industrial wastewater treatment. On the other hand, β-PbO2 has higher current efficiency (13% at room temperature), nevertheless, the material is unstable and hazardous to the environment as the toxic lead ion (Pb2+) may leak into water.
A non-toxic semiconductor, tin dioxide (SnO2), has been widely utilized in the production of sensors, batteries, electrochromic windows, solar cells, and liquid crystal display (LCD). As pointed out in R. Kötz, “Electrochemical Wastewater Treatment Using High Overvoltage Anodes. Part I: Physical and Electrochemical Properties of SnO2 Anodes”, J. Appl. Electrochem., Vol. 21, No. 1, pp 14-20 (1971), pure SnO2 is an n-type semiconductor with a direct band gap of about 3.5 eV. In addition, SnO2 has other unique features: 1) high chemical and electrochemical stability, 2) high electronic conductivity when doped, and 3) high oxygen evolution overpotential. Particularly, the property advantageous to the electrolytic ozone is that the oxygen overpotential of SnO2 is 0.6 V higher than that of Pt. From the cost perspective, SnO2 is also more attractive than Pt. Although SnO2 has been employed for the wastewater treatment as described in U.S. Pat. Nos. 5,364,509; 4,839,007 and 3,627,669, the material requires improvement and the rector or electrolyzer should be more effective. SnO2 can be doped with metal, such as, antimony (Sb), or it can be doped with non-metal, such as, fluorine (F). For enhancing the efficiency of ozone generation, Wang Y-H and his group had doped SnO2 with two kinds of metal in “Electrolytic Generation of Ozone on Antimony- and Nickel-Doped Tin Oxide Electrode”, J. Eelctrochem. Soc., Vol. 152, No. 11, pp D197-D200 (2005). The foregoing article is incorporated herein by reference for developing a proprietary fabrication process in the second aspect of the present invention (See Production process in “Experimental” and so on in Wang Y-H, etc, for example). Generally, the fabrication of Sb—Ni-doped SnO2 electrodes is initiated by preparing an alcohol solution containing the precursors of Sn, Sb, and Ni in a specific atomic ratio, for example, Ni:Sb:Sn=1:10:600, for coating titanium (Ti) substrates. After the solution coated on Ti is converted to a layer of Sb—Ni-doped SnO2 by pyrolysis under 100-300° C., the coating and pyrolysis cycle is repeated at least 10 times. Finally, the repeatedly coated Ti is sintered at 500-600° C. for 30 minutes to 2 hours. Both the number of coating-pyrolysis cycle and the conditions of heating treatment profoundly affect the ozone-forming capability and reliability of the Sb—Ni-doped SnO2 electrodes fabricated. It is found that thicker coating by controlled heating yields electrodes with better quality. The stability of the dopants in the sintered oxide has been examined and validated by Cheng and his group using electrochemical and electron microscopic characterizations. The same group also measured the ozone generation current efficiency of over 30% at room temperature for the Sb—Ni-doped SnO2 electrode. On the other hand, the present invention has identified the following characteristics of the Sb—Ni-doped SnO2 electrode, which are beneficial to the effective use of electrolytic ozone for industrial wastewater treatments:
In the preparation of metal-doped SnO2 film with the carbon source on titanium substrates, the concentration of SnCl4-5H2O used can be from 0.5M to 3M, whereas the dopants SbCl3 and NiCl2-6H2O can be from 2-20 mM and 1-2 mM, respectively. By keeping SnCl4-5H2O in the ethanol solution at the preferred concentration range of 1-2 M, the dopants SbCl3 and NiCl2-6H2O can vary in the corresponding dosages of 4-16 mM and 1-2 mM, respectively, for forming ozone catalyst with good efficiency and good stability. Glycerol is also added at 0.5M to the ethanol solution containing the said three metal salts for facilitating the film formation through pyrolysis. With the presence of glycerol, the resulting film is condensed and smooth without crack. Titanium substrates of desired dimension and configuration are dipped in the precursor solution at desired concentrations for drying at 150-200° C. followed by 5-10 minute sintering at 500-6000° C. The dipping-drying-sintering cycle is repeated 10 times or more so that a metal-doped SnO2 film at 20 μm or higher thickness may be attained. With a thick catalyst layer, the ozone anodes may be submerged directly in various types of wastewater for long-term service of disinfection. The aforementioned ozone anode can work with stainless steel or carbon-base cathode in wastewater to generate ozone therein. No specific electrolyte, such as perchloric acid, sulfuric acid or phosphoric acid, is needed for the said electrode pair to produce the disinfectant.
With the versatile electrodes made of materials with the high oxygen evolution potential, such as SnO2, Sb—Ni-doped SnO2, Sb—Ni-doped SnO2 obtained with use of a carbon source, Ti and Pt, particularly the Sb—Ni doped SnO2 or the Sb—Ni doped SnO2 obtained with use of a carbon source, various ozone reactors can be designed accordingly for cost-effective treatment of various waters.
For households, offices, markets, and laboratories, there are three forms of flow though ozone generator can be devised to meet different ozonation needs.
A portable ozone generator 500 for individual use is devised as shown in
As voltage is required to overcome the electrical resistances of water, electrical connections, and electrode materials for driving power to the Sb—Ni-doped SnO2 electrodes, the electrodes also demand currents of sufficient magnitudes for producing the desired dosage of ozone by electrolyzing the surrounding water. Without side reactions, such as, heat generation and electrode passivation or fouling, the higher the current provided, the more the ozone will be produced. Under a set operation voltage, the current required is proportional to the electrode area. Particularly, the operation current need for industrial ozone reactors, where the electrodes are often measured in m2, will be tremendous. If the ozone generation is operated at the current density of 20 mA/cm2, then every electrode surface area of 1 m2 will need 200 A current. Such huge current demand is beyond the capacity of regular power grids, thus a heavy-duty power line must be ordered from the utility company with installation charge and high leasing fees. Furthermore, a power supply with complex circuitries for stabilizing and further stepping up the currents provided by the power line is needed for operating the industrial electrolytic ozone generators. The foregoing power supply is expensive to own and costly to maintain. Fortunately, the operation-power demand of the electrolytic ozone, i.e. low voltage and high current, is coincident with the electrical properties of supercapacitor, also known as ultracapacitor or electric double layer capacitor (EDLC). The capacitor is a passive energy-storage device with fast charge and discharge rates. The device is also an energy buffer and a power amplifier that can multiply the input power of charging sources to more than 10 times. It is the power amplifying capability and easy implementation that makes supercapacitor ideal for the job of power provisions to the electrolytic ozone for treating miscellaneous industrial wastewaters. Although the capacitor also has other merits, such as, long lifetime and maintenance free, it has some drawbacks as well. From the application perspective, the pulse delivery of power of supercapacitor, that is, the capacitor can only provide power in a pulse mode, appears incompatible with the need of continuous operation in the industrial wastewater treatments. Also, not all energy delivered by supercapacitor is effective. When the voltage of the capacitor has decayed to below the operation voltage of the electrolytic ozone, the discharge power becomes ineffective.
For consistent power delivery and high efficiency of energy use for the operation of electrolytic ozone, the present invention proposes a technique entitled “charging and discharging swing (CD Swing)” as the method of power provision. Two identical sets of supercapacitors and a charging source are needed to conduct the CD Swing. Each set of supercapacitors is allowed to discharge only the effective energy stored in the capacitors. As soon as the first set has delivered its effective energy, the second set will immediately assume the discharging role, and at the mean time the first set will undergo refilling the lost energy. In the next run, the two sets of supercapacitors will switch the positions of charging and discharging, and the reciprocal switching will continue until the operation is terminated. During the CD Swing operation, there is always one set of supercapacitors in series with the charging source for discharging, and the other set is in parallel with the charging source for recharging. Therefore, the output voltage is the sum of the voltages of supercapacitor set and charging source, which equals to the operation voltage of load. In other words, the CD Swing will reduce the use of supercapacitors or charging source to the amount sufficient for providing a voltage that is half of the driving voltage of load.
Before the actuation of CD Swing, L2 and L3 are “closed” for CL (L1 and L4 are “open”) whereas R2 and R3 are “closed” for CR (R1 and R4 are “open”). Therefore, CL and LR are in parallel with the charging source B, and the capacitors are charged simultaneously to the same voltage and polarity of B. When the CD swing operation is in progress, the process will proceed as follows:
With the power amplification of supercapacitors and the operation of CD Swing, various power levels can be provided for ozonation of various waters as described in Table 1:
In the following Examples, Sb—Ni-doped Sn O2 films, which had been produced on Ti plates by using glycerol, were used for electrodes.
A flow-through ozone reactors consisting of 4 pieces of Sb—Ni-doped SnO2 electrodes of 2″ diameter and 4 pieces of 2″-diameter stainless electrodes of 2″ diameter and 4 pieces of 2″-diameter stainless steel plates is constructed as
An ozone generator as
As seen in Table 3 the waters are quantitatively disinfected in both cases.
1.5 liters of 1% ammonia (NH3) water is prepared for ozonation using an ozone reactor as Example 1. Another new 1% NH3 solution is made for ozonation by similar reactor containing the same number pairs and dimensions of electrodes except using platinum coated titanium anode and titanium cathode. The two solutions of ammonia water are independently circulated through either ozone reactor at 2.5 l/min flow and 10 V DC applied to the electrical terminates of either reactor. Only the TDS of the ammonia water during ozonation is measured. Since the ozonation is began, the TDS of solution levels off at 600 ppm after 1 hour and 6 hours ozonation in the SnO2 reactor and Pt-coated Ti reactor, respectively, indicating that the decomposition of ammonia by ozone has been completed in both reactors. Apparently, the SnO2 reactor offers a quicker detoxification than that of Pt-coated Ti reactor. It is also observed that the zone bubbles of the former are finer and more abundant than the latter. Even the Pt-coated Ti reactor presents a stronger smell of O3 odor than the SnO2 reactor, the latter offers a faster killing of contaminants in water. The faster decomposition rate is likely due to the formation of hydrogen peroxide (H2O2) by the reaction between ozone and water, and the possible presence of advanced oxidation process (AOP) from the reaction of ozone and hydrogen peroxide, wherein hydroxyl radical is formed to expedite the decomposition.
Conclusion
Ozone is a powerful and environment friendly disinfectant for water treatment as the gas becomes oxygen after the reaction without leaving any hazardous residue from the agent behind. Due to the cost, space occupation, complexity of system, and potential air pollution, the ozonation using the corona discharge is not affordable to people who has the need ozone treatment. The present invention offers a cost-effective technology of performing ozonation using economical electrocatalyst, simple cell design, and efficient power provision. Various ozone generators for various ozonation needs can be easily fabricated based the good scalability and conformability of the fabrication process of Sb—Ni-doped SnO2 electrodes, for example.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-164343 | May 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/060117 | 5/27/2008 | WO | 00 | 12/22/2009 |
