Abstract:
Ozone is a powerful and versatile oxidant that is good for many applications including sterilization of drinking water, rejuvenation of waste waters, and chemical syntheses. Most of the man-made ozone for the said uses comes from corona discharge of oxygen gas. From the aspects of simplicity, efficiency, voltage level and space area, generation of ozone by water electrolysis has all advantages over the discharge means. It requires an catalyst deposited on the anode of electrolyzer for generating ozone gas directly in water, and the anode material should be affordable, long-lived and reliable. For the said device to become commercially viable, the scale buildup, particularly calcium carbonate, on the cathodes must also be resolved. Tests have shown that the provision of a low vacuum over the electrodes of electrolyzer can assist the device to deliver a consistent ozone throughput for a long period of time. An economical, dependable and self-sustained O 3 -water producing system is devised to fulfill individuals, households, communities, and industries on their water needs.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a technique of generating ozone gas by water electrolysis using low DC voltages. More specifically, the invention relates to a consistent and continuous provision of ozonized water wherein the untreated intake water is the source of ozone gas for personal hygiene, drinking water sterilization, industrial water reuse and desalination. 
       BACKGROUND OF THE INVENTION 
       [0002]    Contaminants in water can be categorized as having chemical or biological nature. In the chemical contaminants, the species may belong to inorganic or organic materials. Together, they impart the contaminated water qualities that can be characterized by a number of major indicators, such as, TDS (Total Dissolved Solids), COD (Chemical Oxygen Demand), TSS (Total Suspended Solids), and TOC (Total Carbon Content). Whereas the biological pollutants include bacteria, viruses and microorganisms like algae, barnacles and spores. Ozone is recognized for its capability of fast and virtually complete eradication of the biological pollutants, and there is no byproduct of the disinfectant left after the treatment. Though at lower reaction rates, ozone can also abate the COD, dissolved and floated alike, in water. Ozone is even claimed to be used as a pretreatment for RO (reverse osmosis) desalination for removing salt and extremely fine particles, that is, for reducing TDS and TSS of seawater, as taught in the U.S. Pat. No. 5,741,416 issued to Tempest Jr. 
         [0003]    Following the widely used corona discharge, the UV radiation of 185 nm wavelength is probably the second choice of technique for ozone generation. Each of the two popular techniques has its disadvantages. In the former, a high-purity oxygen is discharged in an electric filed of 20,000 volt or higher followed by gas-delivery and gas-dispersion into water under the strict control of a bulky equipment system. On the other hand, the said UV may generate ozone via the decomposition of oxygen or water. As the UV ray has a certain travel range, the amount of water that can be affected by the UV radiation is limited, worse yet, the lifetime of UV lamp is short and unpredictable. Using water as the source of ozone, generation of the gas via electrolysis of water has the merits of simplicity, efficiency, compactness and low-volt operation. Furthermore, since ozone is produced directly within water, there is no need of gas-delivery and gas-dispersion, and no air pollution, such as, NOx, which could be formed in the corona discharge. Regardless of the type of electrode materials, hydrogen gas is always generated at cathode and oxygen gas at anode at the electrolysis of water. A catalyst with high oxygen over-potential is required to be on the anode to induce the formation of O 3  besides O 2 . Such catalytic behavior may be found in materials including platinum (Pt), β form lead dioxide (β-PbO 2 ), boron-doped diamond (BDD) and glassy carbon. In the said list of catalysts, Pt is the most frequently investigated as the catalyst on the anode for producing O 3 . 
         [0004]    In the Pt-based electrolytic cells, an ion-exchange membrane is often added for ozone generation as seen in the U.S. Pat. Nos. 5,607,562 issued to Shimamune et al; 6,210,643 to Shiota and 6,787,020 to Kanaya et al, just to name a few. Other Pt-based cells without the membrane can be found in U.S. Pat. No. 4,316,782 issued to Foller et al and U.S. Pat. No. 6,984,295 to Shiue et al. However, the former requires the use of a fluoroanion-containing electrolyte that limits its applications. Though the membrane can increase the O 3 -yield of Pt anode and it can protect the catalyst from harmful anions, but the cell permits the use of a clean water only, otherwise, many water borne pollutants could shorten the service life of the expensive membrane. Even more costly material is the Pt catalyst, it is priced at $1 US or more per 1 cm 2  of Pt film at 3-μm thickness. Pt is so high in price that the industrial-size electrolytic cell for ozonization, whose electrode area measured in m 2 , is beyond people&#39;s reach. Other catalysts in the foregoing list for the electrolytic O 3  are equally unsuitable for practical use, for instance, β-PbO 2  is environmentally hazardous, whereas BDD and glassy carbon are also expensive and inefficient. Thus, an economical and environment friendly catalyst is needed for the commercial ozonization using electrolytic O 3 . 
         [0005]    There are many articles in various journals study antimony doped tin oxide coated on titanium substrate (Ti/SnO 2 —Sb 2 O 5 ) as the anode for the electrolytic sterilization of drinking water and industrial waste stream. The work of Watts et al,  J. Appl. Electrochem ., Vol. 38, pp 31-37 (2008) is cited here as a reference. The article taught that the electrochemical oxidation of organic contaminants, like the phenol compounds, is due to the formation of hydroxy radical (.OH) catalyzed by SnO 2 —Sb 2 O 5  on water electrolysis. It needs ozone to react with hydrogen peroxide (H 2 O 2 ) to form .OH in the advanced oxidation process (AOP). Thus, SnO 2 —Sb 2 O 5  is capable of forming an oxidant stronger than O 3  electrolytically. Furthermore, SnO 2 —Sb 2 O 5  is more affordable and more environment friendly than the aforementioned catalysts. In spite of its high efficiency on eliminating phenol pollutants, SnO 2 —Sb 2 O 5  is prevented from becoming a viable catalyst due to its short service life. This seems a common phenomenon, that is, electrode fouling, for all electrolytic cells involving the electrolysis of water. As the quality issue of the anode materials is important, the buildup of scale, calcium carbonate (CaCO 3 ) in particular, on cathodes also demands an effective solution. Several techniques have been proposed for controlling the scale formation and deposition, such as, anodic polarization in U.S. Pat. No. 4,256,556 issued to Bonnett et el, and polarity reversal in U.S. Pat. No. 5,916,490 to Cho, also in U.S. Pat. No. 4,087,337 to Bennett. Because of its vulnerability to reduction, SnO 2  can serve as anode only, which makes the polarity reversal inapplicable. While most people pay attention to the scale problem, the damages to anode and cathode caused by the adsorption of gas bubbles on the electrodes is overlooked. In the instant invention, a solution for overcoming the interference of scale and bubbles to the operation of electrolytic ozone will be elaborated. 
       SUMMARY OF THE INVENTION 
       [0006]    As one object, the instant invention has added one more metal, namely, nickel (Ni), to SnO 2 —Sb 2 O 5  for forming Sb and Ni doped tin oxide deposited on titanium (Ti/Ni, Sb—SnO 2 ). Using an adequate mole ratio among the three metal atoms, the ternary-metal oxide can catalyze the oxidation of water into oxygen and ozone at high ozone output. Ozone can be generated from any intake raw water without pre-adjustment. Because the lifetime of O 3  is longer than that of .OH, Ni, Sb—SnO 2  is more versatile than SnO 2 —Sb 2 O 5 . Coupling with stainless steel as cathodes, the Ti/Ni, Sb—SnO 2  anodes can form a simple and effective electrolyzer to perform ozonization for various waters. In the said electrolyzer, the anodes and cathodes are stacked alternatively in parallel at 2 mm apart, and the cathodes are disposed at two ends of the stack so that the anodes may be utilized fully. 
         [0007]    Generally, tin chloride (SnCl 4 .4H 2 O) is a preferred precursor for SnO 2 , and the dopants are also in chloro-containing salts for making Ni, Sb—SnO 2 . It is the easy dissolution of chloro-compounds in water for the materials chosen as the sources of the said three metals. Nevertheless, the chloro-containing precursors will emit hydrochloric acid (HCl) fume during the pyrolysis process of film deposition. As more Ni, Sb—SnO 2  film is prepared, more poisonous HCl fume will be generated. The acid fume is harmful to operators and the production equipments. Moreover, the Cl-residue left in the deposited film is detrimental to the quality of catalyst. It is another object of the instant invention to use non-chloro precursors for depositing the Ni, Sb—SnO 2  film on Ti substrate. While Sn and Ni are supplied by their carboxylic acid salts, Sb is obtained from its oxide. A preparation protocol is devised to dissolve two sparingly water-soluble precursors, namely, Sn salt and Sb oxide, into a clear aqueous solution for depositing the Ni, Sb—SnO 2  catalyst by pyrolysis. 
         [0008]    As O 3  is formed via the catalysis of Ni, Sb—SnO 2  on anode, the throughput of O 3  is directly proportional to the total anode surface area disposed in the stack of electrolyzer. At a given water conductivity, the O 3  throughput is also decided by the current density that varies with the DC voltage applied across the anode and cathode. By providing a current density of 20 mA/cm 2  to the electrolyzer of the instant invention, it may produce O 3  at an output of 2 mg/cm 2 ·min. In an O 3  generator equipped with 1 m 2  anode area, it may deliver 1.2 Kg of O 3  per hour upon applying 200A. In order to produce several kilograms of O 3  per day for municipal water sterilization or industrial waste water treatment, the operation current will be in the range of hundreds to thousand ampere. Therefore, it is yet another object of the instant invention to incorporate supercapacitor as the provider of large currents in the power supply system for the Ni, Sb—SnO 2  base ozone generator. Thanks to the power-amplifying capability of supercapacitor, a DC power supply may only need tens ampere current to charge the capacitor for hundreds ampere output. Incorporation of supercapacitor for fulfilling the power needs of the industrial O 3  generators will reduce the cost and size of power supplies required for the ozonization of massive water. 
         [0009]    It is still yet another object of the instant invention to apply a suction over the electrodes of O 3  generator for removing gas bubbles from the electrodes resulting in the prevention of scale buildup. As long as the O 3  generator is in operation, the suction will be on for protecting the electrodes. Either a low-pressure vacuum pump or a Venturi tube is employed for creating the vacuum force required for gas removal. Since there is no barrier or diaphragm blocking the space between the anode and cathode of the generator, all gases formed will be simultaneously withdrawn in one stream from the generator chamber to the points of use. With scales and bubbles being evacuated from the electrode surface, the O 3  generator of the instant invention can perform ozonization at 24 hours a day for many days without interruption. 
         [0010]    The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The instant invention is best understood by reference to the embodiments described in the subsequent sections accompanied with the following drawings. 
           [0012]      FIG. 1  is a schematic diagram of a flow-though ozone generator in a basic configuration; 
           [0013]      FIG. 2  is a schematic diagram of an independent and sustainable ozone generator for continuous and consistent provision of ozonized water; 
           [0014]      FIG. 3  is a schematic diagram of Venturi injector for automatic removal of bubbles and gases from an ozone generator.; 
           [0015]      FIG. 4  is two titration curves for determining the ozone concentration in water of the ozone generator of  FIG. 1  operated with two different voltages. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    There are four recognized methods for making ozone (O 3 ) under controlled conditions, namely, they are: corona discharge, UV radiation, electrolysis and radioactive radiation. The latter is complicated by the presence of harmful isotopes that prohibit the method from commercial use. As early as in 1840, O 3  was discovered as a byproduct of oxygen formed at the anode in electrolyzing sulfuric acid (H 2 SO 4 ) in water. When scientists were looking for commercial use of the electrolytic cell for O 3  formation, they were occupied by the research of different electrolytes and corrosion-resistant anode materials. It is measured that the electrolytic formation of ozone, specified as electrolytic ozone (EO 3 ) thereinafter, can reach at least 10% current efficiency, which is significantly higher than the 4-5% efficiency of corona discharge (CD). In the CD operation, about 80% of the applied electric energy is lost as heat making the generation of ozone inefficient. Due to the misconception that a specific electrolyte is an essential component of EO 3 , people believe that in-situ diffusion of ozone into ultra pure water is required for ozonization. As a result of the diffusion demand, EO 3  can only be in small units with operation cost higher than that of CD. The instant invention can transform the stereotyped status of EO 3  to commercially viable by presenting a novel technique for producing O 3  in high throughputs continuously and consistently using the following components
       1. economical and high-ozone-yield electro-catalyst, namely, Ni, Sb—SnO 2 ,   2. intake raw water as the source of ozone,   3. supercapacitor for providing large currents for industrial applications, and   4. pump or Venturi for creating a vacuum force to remove gas bubbles.       
 
         [0021]    In laboratory, ozone can be produced by electrolysis using a 9 volt battery, a pencil graphite rod cathode, a platinum (Pt) wire anode and a 3 molar (3 M) sulfuric acid electrolyte. The half cell reactions occurring at anode and cathode are as follows: 
         [0000]      Anode: 3 H 2 O→O 3 ↑+6 H + +6 e − (ΔE°=−1.53 V)  (1)
 
         [0000]      2 H 2 O→O 2 ↑+4 H + +4 e − (ΔE°=−1.23 V)  (2)
 
         [0000]      Cathode: 2 H 2 O+2 e − →H 2 ↑+2 OH − (ΔE°=0 V)  (3)
 
         [0000]      Net: 5 H 2 O→O 3 ↑+O 2 ↑+5 H 2 ↑  (4)
 
         [0022]    In the above reactions, reaction (1) and reaction (2) take place simultaneously at the anode but O 2  and O 3  are generated in different proportion. As indicated by the ΔE° values, O 2  is easier than O 3  for generation at anode. Hence, in the electrolysis of pure water using Pt anode, O 2  is more abundant than O 3 . In fact, O 3  is often below the detection limit. When an electro-catalyst is present at the anode to drive the O 2  evolution to a more negative potential level, the evolution of O 3  will become noticeable and useful for treating water. As disclosed in U.S. Pat. No. 4,839,007 issued to Kotz et al., the O 2  overpotential (voltage at commencement of O 2  evolution) of Pt anode is 1.55V, and under the same test condition, the O 2  overpotential of anode coated with antimony doped tin oxide (Ti/SnO 2 —Sb 2 O 5 ) is in the range of 1.75-1.97 V. With higher O 2  overpotential, SnO 2 —Sb 2 O 5  will promote more O 3  formation than Pt. Also, in the treatment of waste water using electrochemical method, SnO 2 —Sb 2 O 5  decomposes a given organic pollutant at the same amount faster than Pt or β-PbO 2 , the O 2  overpotential of the latter is 1.75V. 
         [0023]    Tin oxide can be doped with F, Cl, Sb, Mo, W, Nb, Ta or a mixture of these elements to become conductive. By depositing the doped tin oxide film on a film-forming metal, such as Ti, the resulted anodes are widely used to reduce the COD of waste water via oxidants produced or direct oxidation on the anode. In SnO 2 —Sb 2 O 5  film, Sb mainly serves as a conductivity enhancer to tin oxide rather than catalyzing the formation of O 3 . However, when a second dopant, namely, nickel (Ni), is added to SnO 2 —Sb 2 O 5 , the ternary metal oxide, specified as Ni, Sb—SnO 2  thereinafter, can significantly enlarge the percentage of equ (1) in the anode reactions of water electrolysis, that is, the current efficiency of O 3  generation may reach as high as 30%. For attaining the said efficiency, the mole ratio of Sn:Sb:Ni should be in the ranges from 600:10:1 to 250:10:1. In addition, the concentration of tin ion, as Sn 2+  or Sn 4+ , can be more than 1 molar (1 M), and the Ni, Sb—SnO 2  film is prepared by multiple cycles of brushing, dipping or spraying followed by thermal decomposition or pyrolysis. 
         [0024]    Instead of using chloro-containing precursors for depositing Ni, Sb—SnO 2  film on Ti, the instant invention selects stannous oxalate (SnC 2 O 4 ) for Sn, antimony (III) oxide (Sb 2 O 3 ) for Sb and nickel acetate [Ni(CH 3 COO) 2 .4H 2 O] for Ni. Both of the first two precursors are sparingly soluble in water. In U.S. Pat. No. 4,924,017 (Patent &#39;017) issued to Kobashi et al., SnC 2 O 4  is converted to water-soluble stannic acid [HO(SnO)CO 2 COOH], a compound with acidity as strong as H 2 SO 4 , by reacting with hydrogen peroxide (H 2 O 2 ). Patent &#39;017 is incorporated in its entirety as a reference in the instant invention. Meanwhile, Sb 2 O 3  can also be dissolved together with SnC 2 O 4  in the exothermic oxidation by H 2 O 2 . In order to prepare a transparent solution containing the 3 precursors for depositing Ni, Sb—SnO 2  film on Ti, the following precautions are adopted:
       1. the purity of precursors should be at least 99.8%,   2. the addition of H 2 O 2  to the slurry of precursors should be in portion by portion to avoid over heating that may char the chemicals, and   3. no organic solvent should be added.       
 
         [0028]    As important as the control of solution preparation, the pyrolytic process for converting the solution to the desirable Ni, Sb—SnO 2  film also demands the compliance with a protocol. The key operation parameters include: drying and sintering temperatures, rates and lengths of heating, oxygen supply, annealing control and cleansing of ashes on the coating. Though stannic acid is a strong acid, it permits the deposition of SnO 2  film on stainless steel. Had tin chloride (SnCl 4 .4H 2 O) been used as the precursor of Sn, no SnO 2  film could be plated on stainless steel. Using stainless steel as substrate for titanium, the cost of anodes for EO 3  may be significantly reduced. 
       Flow-Through Ozone Generators 
       [0029]      FIG. 1  shows one of the basic forms of electrolyzer for O 3  generation as proposed by the instant invention. As seen in  FIG. 1 , the O 3  generator  10  is composed of a housing  110  that contains a stack of electrodes formed by juxtaposing two circular anodes represented by  130  and two circular cathodes represented by  150 . A DC power supply  190  is used for applying a voltage to the electrode stack. Both of anodes and cathodes have a number of perforated holes, as represented by  170 , for water to flow through, and for gas bubbles to evolve. During electrolysis, there is more gas bubbles evolved at the edges than other areas of electrodes, which is known as edge effect. There are only circular spacers, not shown in  FIG. 1 , disposed in the gaps of 3 pairs of anodes and cathodes to prevent electric shorts. Without pre-adjustment, raw water can enter the electrolyzer  10  from inlet  120 , and it can exit the electrolyzer casing from outlet  140 . As water passing through the electric field of electrode stack, it will be electrolyzed into micro bubbles of O 3 , O 2  and H 2 . Being a simple design as  FIG. 1 , the O 3  generator  10  is good for assessing the quality of Ni, Sb—SnO 2  film as prepared, as well as for evaluating a formula of coating solution and a deposition protocol, but it is inadequate for long-term ozonization of waters. 
         [0030]    Virtually, in all electrolytic cells using hard water as solvent, the formation of white calcium carbonate (CaCO 3 ), calcium hydroxide [Ca(OH) 2 ], or similar precipitates of magnesium is inevitable. Many places in the electrolytic cells are available for the white fine particles to settle, but they intend to deposit on the cathodes leading to cathode passivation, As the accumulation of scale on the cathode has reached a certain thickness, the desired electrolysis will be completely stopped and the applied energy is wasted. For regenerating the cathode, washing the electrolyzer with hydrochloric acid (HCl) to dissolve the scale is probably the only practical solution. However, the acid dissolution of scale will interrupt the production, and frequent washings may be required if an extremely hard water is employed for electrolysis. Furthermore, the ions of iron (Fe 2+ ) and manganese (Mn 2+ ) present in ground water and seawater of many ports in the world are higher than 0.02 ppm, and these ions can deposit on the anodes as oxides. When the said metals deposit on anode in the form of Fe 2 O 3  or MnO 2 , it can not be removed by any acid, any base, or electricity like polarity reversal resulting in the loss of anodes. Only by depositing new Ni, Sb—SnO 2  film on the original substrates that are cleaned by sand blasting, can the anode be revived. Thus, a convenient and effective way to protect the electrodes, anode and cathode alike, and to impart the generator the capability of delivering long-term and reliable ozonization is required for the EO 3  of the instant invention. 
         [0031]    Generation of hypochlorite (ClO − ) by electrolyzing seawater or sodium chloride solutions has been commercialized for ship ballasts and cooling water equipments for anti-fouling and marine growth prevention. Because calcium is the fifth abundant element in seawater, the electrolytic generation of ClO −  must be interfered by the scale accumulation on the cathodes as well. In U.S. Pat. No. 4,510,026 (Patent &#39;026) issued to Spaziante, a low vacuum, or 0.7 atmospheres (10.3 lb/in 2 , or 10.3 psi), is applied intermittently to a hypochlorite generator for overcoming the scale interference. Patent &#39;026 is also included in its entirety as a reference in the instant invention. During the evolution of H 2  on the cathode, titanium to be exact, in the hypochlorite generator, hydrogen atom (.H) is born first, and the radical is adsorbed on the cathode followed by two combination reactions to H 2  and a metal hydride, respectively, as described in equations (5) to (7): 
         [0000]      H 2 O+e − →.H ad +OH −   (5)
 
         [0000]      2.H ad →H 2   (6)
 
         [0000]      Ti+4.H→TiH 4   (7)
 
         [0032]    Equations (5) to (7) show that the adsorption of .H radical on cathode initiates the formation of titanium hydride resulting in the embrittlement of Ti structure and degradation of cathode. In the same scenario, the adsorption of O 2  and O 3  bubbles on anode may cause the deactivation of Ni, Sb—SnO 2  film, as well as the degradation of anode. Applying a reduced pressure over the electrolyzer submerged in water, less gas will stay in water according to Henry&#39;s Law, and the gas can grow into larger bubbles as well. There is a “blasting effect” along with the removal of gas bubbles from the electrode surface under a reduced pressure. As the bubbles leave the electrodes, any deposit thereon will be lifted up and carried away by water flow, this is the said “blasting effect”. Not only the scale buildup is eradicated, but the degradation of electrodes is also prevented by the application of vacuum over the electrolyzer. 
         [0033]      FIG. 2  shows a preferred embodiment of the EO 3  generator system of the instant invention. There are 3 sections of operation in the O 3  generator  20  of  FIG. 2 . They are the electrolyzer and electrolysis chamber, the DC power unit and the vacuum suction unit. A stack of electrodes constitute the electrolyzer wherein 3 anodes, symbolized by long bars with slanted lines and numbered as  233 , are sandwiched by 4 cathodes, the clear long bars numbered as  235 . Each electrode has a plural number of perforated holes thereon (not shown in  FIG. 2 ), and all electrodes are in parallel separated with a gap of 2 mm fixed by circular insulator-spacers (also not shown in  FIG. 2 ). All anodic plates are linked electrically in a pack, so are all cathodic plates in another electrical pack, for connecting to the positive and negative poles of an outer DC power supply, respectively. Misconnection of the electrical leads with the poles is absolutely prohibited. As no mesh, screen, net, web, membrane or diaphragm is placed among the electrodes, the anodic gases, O 2 /O 3 , and cathodic gas, H 2 , can fully mix, which has no detrimental effect to the functions of O 3 . Ti, in 98-99% purity, is a preferred substrate for the anode, and many iron-base metals including irons, carbon steels, alloy steels and stainless steels can be selected as the substrate for cathode. For treating surface waters, nickel, stainless steel, or aluminum may also be used as the anodic substrate, whereas Ti, aluminum, copper, nickel or magnesium alloy may serve as the cathodic substrate. Both of anode and cathode are flat plates in 0.8-1.0 mm thickness, 7.5 or 10 cm width and 25 or 40 cm length. Nevertheless, other sizes and configuration of electrodes can be fabricated to meet the application needs. In the generator of  FIG. 2 , O 3  is produced in micro-size bubbles that can not be duplicated by any man-made disperser. Because the O 3  reactivity is affected by its bubble size, ozonization by the EO 3  of the instant patent is highly efficient. 
         [0034]    Without pre-adjustment, raw waters, represented by  250 , containing no sticky materials, such as, oils, fats, greases, inks, or varnishes, can enter the electrolysis cell from the inlet  222 . In the electric field of electrolyzer, the intake water will be electrolyzed into O 3  with other gases, and contaminants of water may be subjected to in-situ ozonization, direct oxidation or direct reduction on anodes and cathodes, respectively, or a combination of the foregoing reactions. After the said treatments, the effluent can exit the reaction chamber from the side outlet  224  as ozonized water or purified water. A water pump (not shown in  FIG. 2 ) may be employed to push water in and out of the electrolyzer  20 . The flow of water may also be driven by the pressure in a public tap-water supply line or by gravity force. Block  240 , in dotted square, is a DC power supply unit comprised by one or a bank of supercapacitors  242 , a control circuit C, and a DC power source  244 . Batteries, renewable energies, fuel cells, generators or city lines may serve as the power source  244 . By the maneuver of C,  244  can apply a pre-determined low-current to charge the supercapacitor  242 , then, the capacitor can deliver a current, which is larger than the charging current, to the two electrical leads of electrolyzer  20  for producing a desirable output of ozone. Based on the targeted O 3  outputs, the dimensions and the power rates of the DC power source and those of supercapacitor, as well as the delivery times or delivery frequency of the supercapacitor power to the O 3  generator can be designed and implemented accordingly. 
         [0035]    As seen in  FIG. 2 , a vertical electrolyzer is fully submerged in water, and a room is reserved above water for O 2 /O 3 /H 2  to escape therein. A vacuum pump  260  is employed to apply a reduced pressure over the electrolyzer to draw the escaping gas and bubbles from the chamber into the effluent tube  224  via the suction line  280 . Even the O 3  extracted is mixed with water and water vapor, the mixture can still join the effluent as an ozonized water for various usages. Instead of going to the effluent, the O 3 —H 2 O mixture or only the ozone gas after the removal of moisture by a dehumidifying device can be delivered to other points of use. During ozonization, some fine precipitate may also be generated in water. Thus, adding a filter (not shown in  FIG. 2 ) that can remove sub-micron particles to the generator  20  of  FIG. 2  will make the system more sustainable. Furthermore, the vacuum pump  260  may be replaced by Venturi tube for the purpose of bubble removal.  FIG. 3  shows a design of Venturi injector that may simultaneously replace the effluent tube  224  and the suction line  280  of  FIG. 2 . By constricting the inner diameter of outlet tube  224  in a cone shape section  300 , wherein water must increase the speed for reducing its pressure leading to a partial vacuum created in tube  380 , which is enlarged for clarity sake. Venturi injectors can be operated in a pressure range of 1 to 250 psi (or 0.068 to 17.01 atm), and only a minimum pressure difference is required to initiate the vacuum for sucking gas. Without moving parts, Venturi injectors are maintenance free and electricity free. In facts, they are used for ozone injection in water as seen in the U.S. Pat. No. 5,741,416 to Tempest Jr, U.S. Pat. No. 6,132,629 to Boley, U.S. Pat. No. 6,869,540 to Robinson et al, U.S. Pat. No. 7,416,660 to van Leeuwen et al, and U.S. Pat. No. 7,501,055 to Liou, just to name a few. 
       Supercapacitors (SC&#39;s) 
       [0036]    Supercapacitor (SC) is a passive energy storage device, as well as a power-amplifying electronics. SC can store electric energy between the levels of batteries and conventional capacitors, the latter are the second most used component in electronic circuits. Due to its 3 to 6 orders more of energy stored than the regular capacitors, SC earns the title of “super”. For its large energy content, SC is also named as ultracapacitor. From the perspective of energy storage mechanism, most SC&#39;s rely on the adsorption of ions in a double layer formed at the interface of solid and liquid, namely, the electrode and electrolyte. Hence, the said SC&#39;s are called double layer capacitor or electric double layer capacitor (EDLC). It is the ion adsorption, a physical process, and double layer structure imparting SC the following unique properties:
       Anode and cathode are made identical making SC no polarity before charging. After charging, the electrodes allow electric-short discharge and polarity reversal.   Electric energy is directly filled into, or extracted from, SC without conversion. Thus, the charge and discharge of SC is fast, in seconds, and highly efficient, 90% or higher.   Energy transfer of SC is 100% reversible, the device has many-year lifetime and it is maintenance free.   SC can be operated at 10% extra to the rated voltage, and its current level of charge and discharge has no limitation.   SC can amplify an input current by 10 times or more. A power step-up circuit based on SC can be constructed for low cost and high reliability.   SC is low in cellular voltage (generally, 2.5 V/cell), but it can be fabricated in a single device with working voltage as high as the demands of applications.       
 
         [0043]    Contrary to the high operation voltage and low current of corona discharge (CD), EO 3  is a technique of high operation current and low voltage. Hence, the characteristics of SC are in perfect match with the power requirements of EO 3 . As the price of DC power supply for EO 3  is determined by the current outputs of the equipment, hence, the capital cost and the maintenance fee of EO 3  is profoundly affected by the operation-current needs. Using the advantage of SC, the said costs can be significantly reduced for a power supply with low current outputs can be employed. Incorporation of in the electrolytic ozone is first claimed in U.S. Pat. No. 6,984,295 (Patent &#39;295) issued to Shiue et al. Comparing to Patent &#39;295, the instant invention has made the following improvements:
       (1) Reduction of anode cost by replacing Pt with Ni,Sb—SnO 2  catalyst.   (2) Assurance of EO 3  performance by using vacuum for gas removal.   (3) Fabrication of single SC&#39;s in the required voltages and capacities.       
 
         [0047]    In line with item (3), SC&#39;s can be made in-house in 10V×40F to 30V×20F or other larger power ratings to meet various application needs, such as, public water sterilization, industrial cooling-water antifouling, wastewater treatments and desalination pretreatment. Followings are two practices of the EO 3  system of the instant invention Example 1. 
         [0048]    An ozone generator as  FIG. 1  is constructed using a stack of 2 anodes and 2 cathodes in 10 cm diameter (10 cmφ), and it is disposed in a plastic housing of 12 cmφ by 20 cm height (volume=2.2 L). The total anode area (4 sides) A is calculated as follows: 
         [0000]      A=πr 2 ×4=(3.1416) (5 cm) 2 (4)=314.2 cm 2  
 
         [0049]    4 L (liter) tap water with TDS of 200 ppm is circulated at 4 L/min between the generator and a reservoir. Two different DC voltages, namely, 12V and 16V, are applied to the generator separately. The ozone concentration in water formed under each operation voltage is determined every 5 minutes using potassium iodide (KI) titration at 0.1 equivalent (0.1 N) titrant concentration and starch as the indicator. In the titration, iodide ion (F) is oxidized by O 3  to iodine molecule (I 2 ) that forms a blue complex with starch. With the drop-wise addition of KI, an intense blue color will appear to signify the end point of titration. Table 1 lists the calculated concentrations of O 3  dissolved in water per 5-minute interval, wherein two operation voltages are employed in sequence. 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 O 3  Concentration in Water Formed by Electrolysis 
               
               
                 at 12 V and 16 V, and Calculated from KI Titration 
               
               
                 (4 L tap water, 4 L/minute flow, anode area 314.2 cm 2 ) 
               
             
          
           
               
                   
                 O 3  Concentration (ppm) 
                   
               
             
          
           
               
                 Time 
                 12 Volt 
                 16 Volt 
               
               
                 (min) 
                 3.18 mA/cm 2   
                 6.37 mA/cm 2   
               
               
                   
               
             
          
           
               
                 5 
                 1.05 
                 1.38 
               
               
                 10 
                 1.33 
                 1.71 
               
               
                 15 
                 1.59 
                 1.93 
               
               
                 20 
                 1.79 
                 2.10 
               
               
                 25 
                 1.90 
                 2.27 
               
               
                 30 
                 1.99 
                 2.45 
               
               
                 35 
                 1.99 
                 2.48 
               
               
                 40 
                 2.04 
                 2.49 
               
               
                 45 
                 — 
                 2.49 
               
               
                 50 
                 — 
                 2.49 
               
               
                   
               
             
          
         
       
     
         [0050]    By plotting the ozone concentration as ordinate against time abscissa,  FIG. 4  is resulted. As seen in the figure, the O 3  concentration is leveled off towards the 30-minute mark. Due to no pressure applied to the generator and reservoir, O 3  can escape into atmosphere freely, therefore, a limit to the dissolution of O 3  in water appears as a flat line in  FIG. 4 . Ozone (O 3 ) has a lifetime of about 20 minutes in water, and the gas has a low solubility in water, which is affected by temperature and water content, such as, the presence of oxidizable species. Roughly, about 0.3% of the total O 3  product may dissolve in water, and the rest is in the gas state. Either form of O 3  is effective for sterilization and reduction of COD. As a disinfectant, a low ozone concentration of 0.4 ppm is sufficient for a total kill of most-seen bacteria and pathogens. Hence, O 3  formation using 16V consumes energy excessively for sterilization purpose. Nevertheless, a much higher O 3  dose is required for the COD abatement of industrial wastewaters, which will need a high operation power. By the O 3  concentration formed at 16V in Table 1, the yield of water-borne O 3  per unit area and unit time is assessed as 0.004-0.006 mg/cm 2 ·min, or the overall O 3  yield is in 1.3-2 mg/cm 2 ·min assuming that 0.3% of the total O 3  product dissolves in water. Table 1 indicates that the current density is an important factor to the O 3  yield, other parameters including the quality of catalyst film deposited, the inhibition of scale buildup and the prevention of electrode decay are more crucial to the current efficiency, power consumption, long-term reliability and efficacy of ozonization using the EO 3  technique of the instant invention. 
         [0051]    An ozone generator using 1 anode sandwiched by 2 cathodes with 2 mm gap equipped with a vacuum pump is constructed. Different from the vertical generator of  FIG. 2 , the 8 cmφ×38 cm generator of Exp 2 is placed horizontally. Moreover, about 25% area of the electrodes in this example is intentionally exposed in air for observing the progress of scale deposition on the cathodes. All electrodes are in 7.5 cm width by 25 cm length and 1 mm thickness. 4 L of tap water with TDS of 140 ppm is circulated between the generator and a reservoir at 200 L/hour. A DC voltage of 7.8V is applied to the electrodes in conjunction with a vacuum of 50 cmHg (or 0.66 atm, 9.67 psi) from a 40 W pump powered by 110V×60 Hz. Table 2 summarizes the observations and measurements of each operations in the proof of principle test: 
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Proof of Principle of Vacuum Assisted Ozonization 
               
             
          
           
               
                 # 
                 Operations 
                 Observation/Measurement 
                 Remarks 
               
               
                   
               
               
                 1 
                 Electrolysis 
                 A thin and spotty white deposit 
                 Electrolysis must go with 
               
               
                   
                 without vacuum 
                 on the cathodes 
                 vacuum. 
               
               
                   
                 for 30 min 
               
               
                 2 
                 Electrode exposed 
                 More deposit on the edges of 
                 Water flow removes 
               
               
                   
                   
                 electrodes near the air-water 
                 particles. 
               
               
                   
                   
                 interface 
                 Filter can help. 
               
               
                 3 
                 Water 
                 After 3-hour electrolysis of 4 L 
                 Except sterilization, O 3  can 
               
               
                   
                 hardness/pH 
                 tap water, TDS = 77 ppm, pH = 
                 soften water or Ca/Mg 
               
               
                   
                   
                 6.5 
                 removal 
               
               
                 4 
                 600-hr Non-stop 
                 Current drops from 1.65 A to 
                 The performance is 
               
               
                   
                 Electrolysis 
                 1.55 A (6% decay), very thin 
                 consistent and the anode 
               
               
                   
                   
                 white coat on cathode, anode 
                 has a long lifetime. 
               
               
                   
                   
                 appears intact. 
               
               
                 5 
                 O 3  concentration 
                 2 ppm measured on meter 
                 The power usage is lower 
               
               
                   
                 in water at 600 th   
                 OM-1000 by biotek-ozone 
                 than that of Table 1. 
               
               
                   
                 hour 
                 (www.biotek-ozone.com) 
               
               
                   
               
             
          
         
       
     
         [0052]    In the item 4 of Table 2, during the 25-day straight electrolysis, only 3 L of water is replaced daily. In other words, the fresh water provides more Ca 2+  and Mg 2+  to challenge the anode. Besides the cathodes, white deposit is also found on the water conveying tubes. This indicates that ozone can turn Ca/Mg ions into precipitates, and a filter with sub-micron pores can remove the fine particles to maintain the cleanness of O 3  generator. The removal of bubbles by vacuum is effective on protecting the Ni, Sb—SnO 2  anode, the low operation voltage, 7.8V, has contributed to the lifetime of anode as well. As claimed by Stucki et al in  Pharmaceutical Engineering , Vol. 25, pp 1-7 (2005), in PEM (proton exchange membrane) O 3  cells used for delivering  1  to several hundreds m 3  of sterilized water to pharmaceuticals production, the anodes, β-PbO 2 , have been operated for many years without degradation. Except PEM and pure intake water, a low operation voltage, 3-4 V, is also a factor to the longevity of anode. As only 0.3 to 12 g O 3 /hr output is needed in the foregoing reference, the O 3  generator can be operated at such low voltages. It must take the quality of intake water and the ozonization purpose into account for determining the optimal operation volt for EO 3 . In any situation, the operation voltage of EO 3  should be under 24V DC. A thumb of rule is always applicable to all applications using EO 3 , that is, the operation voltage should be kept as low as possible. Exp 2 provides a direction for the following novel usages of ozonization:
       O 3  can provide sterilization and COD/TDS reduction of waters.   O 3  can replace the chemicals used hugely in RO desalination.   O 3  can perform as a pre- and post-purifier for water treatment.       
 
         [0056]    The application of ozone (O 3 ) is virtually unlimited. All viable applications of O 3  are determined by the cost of gas generation and long-term performance. In addition to affordability, simplicity, compactness and versatility, EO 3  based on Ni, Sb—SnO 2  film as the anodic catalyst also offers a long service-life with the assistance of vacuum. Under the protection of vacuum, the said EO 3  can be integrated with electrocoagulation (EC) into a combinatory technique for a synergistic effect that is more effective in treating waters than either EO 3  or EC alone. When EC adopts iron as anode for delivering Fe 2+  as a coagulant, the ion will be oxidized by O 3  to ferryl species {[Fe(IV)O] 2+ } and ferrate (FeO 4   2− ). These high oxidation states of iron, Fe(IV) and Fe(VI), have an oxidation rate at three orders faster than that of O 3 . Especially among all methods for eliminating the COD contaminants, the combination of EC and EO 3  can provide the quickest and the most complete results. New integration of the EO 3  with other water-treatment techniques for reducing the cost of water treatment is yet to be developed. Through the vacuum transferral of ozone gas from the reaction chamber of EO 3  to its counterpart, the integration can be successfully accomplished. 
         [0057]    Although the present invention has been described with reference to the preferred embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.