WO2001012562A1

WO2001012562A1 - Apparatus for purification of contaminated water by using rotating member

Info

Publication number: WO2001012562A1
Application number: PCT/KR2000/000891
Authority: WO
Inventors: Sunghee Kim; Myungin You; Yeonghee Kim
Original assignee: Ec. Tech Co., Ltd.
Priority date: 1999-08-14
Filing date: 2000-08-11
Publication date: 2001-02-22
Also published as: KR20000072137A; AU6735000A

Abstract

Disclosed is an apparatus for purifying contaminated water using rotating members coated with photocatalytically active titanium oxide films, which is suitable for use in decomposing sparingly decomposable materials, contaminants, and pathogenic bacteria. The apparatus comprises purification means, which is rotatable and coated with photocatalytically active titanium oxide films; power transmission means for transmitting a rotating power to the purification means; oxygen supply means for supplying oxygen to contaminants in accordance with the power transmission of the power transmission means; and light irradiation means for inducing the purification means to be photochemically activated, wherein the titanium oxide coating film is activated by the light irradiation means and catalytically decomposes the contaminants when being brought into contact with them, the purification means is revolved by the operation of the power transmission means, and the oxygen facilitates the decomposition of the contaminants. The purification means is in a semi-submerged structure in which one side of the purification is exposed to the air while the other side is positioned within water. The oxygen supply means utilizes the rotation of the purification means to supply oxygen from the air into the contaminants by natural convention.

Description

APPARATUS FOR PURIFICATION OF CONTAMINATED WATER BY USING ROTATING MEMBER

TECHNICAL FIELD The present invention relates, in general, to an apparatus for purifying contaminated water and, more particularly, to an apparatus suitable for use in decomposing sparingly decomposable contaminants and toxic materials, which takes advantage of the stable and repetitive photocatalytical activation of titanium oxide catalysts immobilized on rotating members at the interface between the air and water.

BACKGROUND ART With great advance m industries, toxic materials increasingly flow m streams or lakes. Particularly, when contaminated streams or lakes are used as water intake sources, sparingly decomposable organic matters may exert fatal influence on the body because they are hardly filtered m ordinary purification processes. Owing to recent increasing tendency to the contamination of water supply sources with protists such as animal and plant planktons and cryptosopondium, extensive and intensive attention has been paid to the purification of the tap water. In a purification process, on the whole, chlorine is provided to sterilize various microorganisms while ozone is used to oxidatively decompose various harmful organic compounds . However, these sterilizers or oxidative decomposers make algae to secrete toxins such as microcystin, anatoxin and saxitoxin, so as to deteriorate the safety of the water. These toxins may be removed by excessive amounts of oxidants. However, they also produce by-products such as trihalomethanes (THMs), known as carcinogens, as a result of the reaction with organic matters remaining in the water. When some of Cyanophyceae, which cause an offensive odor, become dominant species m water supply sources such as rivers or lakes, geosmin (C12H22O, trans-1, 10-dιmethyl-trans- 9-decaol) or 2-MIB (CnH₂oO, 2-methyl-ιso-borneol ) are produced during the metabolism of the microorganisms, giving out a bad smell.

In order to effectively remove such various impurities, water treatment plants typically conduct not only an ordinary water purification process, but also an advanced water purification process which takes advantage of ozone and granular activated carbon (GAC) at present. However, the advanced water purification process suffers from disadvantages of costing a great deal for constructing the facilities and maintaining them. In addition, m spite of such a large-scale investment, the efficiency of the advanced water purification process is sharply decreased three to six months after the feeding of granular activated carbon because it can maintain its absorptive activity only for as much. Furthermore, sterilization by-products of the advanced water purification, for example, trihalomethane, known as a carcinogen, which is generally generated as a result of the sterilizing action of chlorine, and bromate, which results from the ozonolysis m the advanced water purification process are hardly removed, but remain dissolved in the purified water until it reach final users' taps. These harmful materials are rather increasingly produced than reduced because they are reacted for lengthy periods of time during the transportation of the water through waterways to users .

There have been proposed various techniques m order to effectively the secondary contaminants which cannot toe sufficiently removed by prevailing advanced water purification processes. Of them, τ_he most attractive is a photochemical treatment technique for decomposing contaminants. The photochemical treatment technique is advantageous in that the necessary facilities are very simple as compared with those required in conventional water treatment processes and the operation expense is low as no chemicals are used. Also, the photochemical .reatment process enjoys the advantage of producing no secondary pollutions by virtue of using light energy m addition to being very effective. For instance, the photochemical treatment process produces no sludge as well as can effectively decompose organic chlorine compounds most of which are difficult to biologically decompose. In the photochemical process, photocatalysts are typically used and examples thereof include Tι0₂, W0 , ZnO, CdS, and GaAs with prevalence of TiO?.

When contaminants are treated m the presence of titanium oxide, this catalyst is used as being in a powder phase, a pellet phase coated on an immobilized carrier or a hollow bead phase.

When a powder phase of titanium oxide is employed, it is suspended in water for use n treating water contaminants and then reclaimed with the aid of an apparatus. With a large specific area, the titanium oxide m a suspension phase can so sufficiently contact with contaminants as to show a high treatment efficiency. However, a separate apparatus is needed to reclaim the titanium oxide used, costing a great deal for installation. Further, the reclaiming apparatus can be applied only for small-scale facilities, but not for large-scale facilities for water works or wastewater works.

In addition, after being used for duration of time, a powder phase of titanium oxide is so colored or contaminated that it cannot be reused. In this case, the titanium oxide must be reclaimed for disposal and thus, sludge is produced. Further, when too much quantities of a powder phase of titanium oxide are suspended in water, a decrease is brought about m the light transmittance of the water, resulting in a reduction in the production yield of electron holes, which represents the activity of the photocatalyst .

Unlike a powder phase of titanium oxide, a pellet phase or a hollow bead phase of titanium oxide is not difficult to reclaim, but suffers from the serious problem of removing contaminants effectively in practice. In a photocatalytic reaction, one of the most important parameters is reaction efficiency per particle, which has direct connection with the contact opportunity with contaminants. In the case that titanium oxide photocatalysts are stagnant in water or float on the surface of water, the decomposing action of the titanium oxide photocatalysts is actively conducted only on the surface of water because light is illuminated on the surface. In underwater sites, which it is difficult for light to reach, the titanium oxide photocatalysts are so low m catalytic activity as to decompose contaminants at low efficiency.

Based on their decomposition powers, titanium dioxide photocatalysts are experimentally demonstrated to be useful for decomposing contaminants and disclosed in many patents, including Japan Pat. Laid-Open Publication No. Hei . 6-328068. Relating to use of a power, a pellet or a hollow bead phase of titanium oxide in treating water, most of the patents cannot be applied for water treatment facilities in practice owing to the above-mentioned problems. Even if applied, the techniques disclosed in the patents are limited to small- scale facilities.

In order to show high decomposition efficiency, titanium oxide photocatalysts must be activated by light energy and act as decomposers for contaminants m water. However, since presently available titanium oxide photocatalysts float on the surface of water and m water, they have small areas at which the photocatalytic action is actively executed because they cannot receive light m the areas submerged m water. When being present in or on water, the titanium dioxide photocatalysts are intensively activated in the area above the water oy light while being weakly activated in underwater areas because the quantity of the light illuminated on the submerged areas is small. Above or on the surface of water, thus, contaminants are actively decomposed by the activated photocatalysts whereas the decomposition of contaminants is not effectively conducted in underwater sites.

Different from the above-mentioned techniques, there is introduced a technique of treating water by use of an apparatus comprising a spiral glass tube on the inner wall of which titanium oxide is immobilized. However, this apparatus also suffers from the disadvantage of being very low in treatment efficiency because contaminants can be brought into contact with the titanium dioxide photocatalyst immobilized on the inner wall. In addition, the light transmittance is lowered by the contaminants passing through the glass tube, so that a decrease is brought about m the quantity of the light incident on the inner wall, resulting in insufficiently activating the photocatalysts. Further, the floating materials may clog the glass tube, causing a trouble in the apparatus. In fact, this apparatus can be applied only for small-scale facilities.

DISCLOSURE OF INVENTION Therefore, it is an object of the present invention to overcome the above problems encountered m prior arts and to provide an apparatus for purifying contaminated water, which takes advantage of economically favorable, immobilized titanium oxide photocatalysts in decomposing contaminants. It is another object of the present invention to provide an apparatus for purifying contaminated water, which is superior in decomposition efficiency by adopting a semi- submerged structure m which photocatalytically active components are activated m the air and effectively decompose contaminants in water. It is a further object of the present invention to provide an apparatus for purifying contaminated water, which allows oxygen to be introduced into the contaminated water from the air thereby improving the oxidative decomposition of the contaminants.

In accordance with an embodiment of the present invention, there is provided an apparatus for purifying contaminated wastewater using rotating members coated with titanium oxide films, comprising: purification means, which is rotatable and coated with photocatalytically active titanium oxide films; power transmission means for transmitting a rotating power to the purification means; oxygen supply means for supplying oxygen to contaminants m accordance with the power transmission of the power transmission means; and light irradiation means for inducing the purification means to be photochemically activated, wherein the titanium oxide coating film is activated joy the light irradiation means and catalyt cally decomposes the contaminants when being brought into contact with them, the purification means is revolved by the operation of the power transmission means, and the oxygen facilitates the decomposition of the contaminants.

In one version of this embodiment, the purification means is in a semi-submerged structure in which one side of the purification is exposed to the air while the other side is positioned within water. In another version, the oxygen supply means utilizes the rotation of the purification means to supply oxygen from the air into the contaminants by natural convention. In a further version, the purification means comprises a plurality of rotating members, each being coated with the titanium oxide film at a thickness of 0.3- 0.5 μ . Preferably, the titanium oxide film further comprises at least one selected from metals such as copper, platinum, aluminum, gold, zinc and iron and photoactive materials such as Sι0₂, ZnO, SiC, WOj, CdS, GaAs, CuO, and Cu0₂. In still another version, the power transmission means comprises a motor or wafters which can be rotated by natural wind. In still a further version, the light irradiation means utilizes solar light or comprises a UV lamp or a xenon lamp, which generates a wavelength or 400 nm or less , and a reflection panel for reflecting the ι_.ght toward the purification means.

In the apparatus of the present invention, the purification means which rotates in a semi-submerged manner is activated by light and can decompose contaminants at nigh efficiency, along with the oxygen supplied from the air into the water.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken m conjunction with the accompanying drawings, in which:

Fig. 1 shows an apparatus for purifying contaminated water in accordance with a first embodiment of the present invention;

Fig. 2 shows an apparatus for purifying contaminated water in accordance with a second embodiment of the present invention; Fig. 3 shows an apparatus for purifying contaminated water in accordance with a third embodiment of the present invention;

Fig. 4 shows an apparatus for purifying contaminated water in accordance with a fourth embodiment of the present invention;

Fig. 5 is a schematic view showing the mechanism of the photocatalytical reaction;

Fig. 6 is a schematic view showing the formation and reaction path of titanium oxide radicals upon light irradiation;

Fig. 7 is a schematic view showing an experimental equipment for various experiments according to the present invention;

Fig. 8 is a decomposition graph of tnhalomethanes in accordance with Experimental Example I of the present invention;

Fig. 9 is a decomposition graph of stinking materials in accordance with Experimental Example I of the present invention; Fig. 10 is a decomposition graph of chlorophyll a m accordance with Experimental Example I of the present invention;

Fig. 11 is a decomposition graph of colon bacillus m accordance with Experimental Example I of the present invention;

Fig. 12 is a decomposition graph of trihalomethanes in accordance with Experimental Example II of the present invention;

Fig. 13 is a decomposition graph of chlorophyll a and stinking materials m accordance with Experimental Example II of the present invention;

Fig. 14 is a decomposition graph of trihalomethanes m accordance with Experimental Example III of the present invention; Fig. 15 is a decomposition graph of stinking materials in accordance with Experimental Example III of the present invention;

Fig. 16 is a decomposition graph of colon bacillus in accordance with Experimental Example III of the present invention; Fig. 17 is a decomposition graph of pathogenic bacteria m accordance with Experimental Example III of the present invention;

Fig. 18 shows the sterilization effect on pathogenic bacteria in accordance with Experimental Example III of the present invention m photographs;

Fig. 19 is a decomposition graph of an environmental hormone in accordance with Experimental Example III of the present invention; Fig. 20 is a decomposition graph of an environmental hormone showing a comparison between ozone and Experimental Example III of the present invention; and

Fig. 21 is a decomposition graph of a contaminant showing a comparison m decomposing potentials.

BEST MODE FOR CARRYING OUT OF THE INVENTION The present invention may be understood more readily by reference to the following detailed description of preferred embodiments of the invention and the figures. The characteristics of the present invention reside m a purification apparatus of water which is semi-submergible and has such a structure as to increase photoactivity and oxygen inflow to effectively decompose contaminants contained in water. Although being manufactured into various types, the purification apparatus of the present invention will be described, below, m regard to a mobile type and a fixed type.

With reference to Figs. 1 and 2, there are shown mobile types of the apparatus of the present invention while its fixed types are shown in Figs. 3 and 4.

Fig. 1 shows an embodiment of the apparatus for purifying contaminated water according to the present invention. As shown m Fig. 1, the apparatus is comprised mainly of purification means 10 for purifying contaminated water, power transmission means 20 for transmitting power to the purification means 10, light irradiation means 30, and oxygen supply means 40.

As for the purification means 10, it is composed of a plurality of rotating members 10, each made of a circular glass disc on the surface of which titanium oxiαe coating film is applied. In order to form the coating film, first, the circular glass discs are washed with potassium dichromate. After being dried in a dry oven, the washed circular glass discs are coated with titanium oxide m a sol-gel method and thermally treated at 500 °C for four hours. Under the thermal condition of time and temperature, the coating film is changed into an anatase type capable of effectively performing photocatalysis . Only a very trace amount of titanium oxide is consumed whenever the coating is conducted. In detail, titanium oxide is used at an amount of as small as several micrograms, which is no more than one-tens of thousandth of the amount which is consumed when conventional powder phases of titanium oxide are used. On the whole, the more the titanium oxide mducible of photoactivity is, the faster the contaminants are decomposed. In this regard, the amount of the titanium oxide contained within the coating film can be controlled with the number of coating rounds. Although being dependent on coating conditions, the thickness of the coating film preferably amounts to about 0.4-0.45 μm in total after the coating process is repeated about 15 times with a coating rate of about 2-2.5 nm per coating round.

Because tne decomposition of contaminants present m waste water occurs on the surface of the rotating member 10, which is coated with titanium oxiαe, the decomposition is more effective as the surface area of the rotating member 10 is larger. Therefore, although the member is m a plate form in the embodiment, the present invention is not limited thereto. The rotating member 10, which serves as a substrate for a titanium oxide coating film, may have various forms. For instance, it may be formed into a wheel, a screw, a cylinder, an asymptotic cone or another form. In addition, the rotating member may be embossed to increase the surface area. Preferably, as many rotating members as possible are provided to increase the contact area with wastewater. The rotating member 10, even if figured to be of glass in this embodiment, may made of various materials, including metal such as stainless steel or synthetic resins. Optionally, the titanium oxide coating films may be supplemented with metals such as copper, platinum, aluminum, gold, zinc, iron and manganese oxide and/or photoactive materials such as Si0₂, ZnO, SiC, W0₃, CdS, GaAs, CuO, and Cu0₂ to amplify or aid the photoactivity of titanium oxide, thereby increasing the treatment efficiency. The effect of such supplementary materials on the photoactivity of titanium oxide is reported in many documents and well known in the art, so a detail description concerning this is omitted. It is preferred that the purification means 10 consisting of a plurality of rotating members 10 is set to be semi-submerged. That is, at a particular time, one side of the rotating member 10 is positioned m the air while the other side is submerged in wastewater. The reason is that the photocatalyst is allowed to be activated and to have many opportunities to contact with wastewater, so as to effectively decompose contaminants. After being activated by light energy upon the exposure to the air, the coating films on the rotating members are submerged in wastewater by the rotation of the member and thus brought about into contact with the contaminants of the wastewater. In addition, as the rotating members 10 are rotated, the oxygen of the air is introduced into the water, along with the rotating members, and serves as an oxidizer m the wastewater. Therefore, the contaminants can be effectively decomposed without feeding additional oxidizers such as ozone .

Following is a description of the power transmission means 20. The power transmission means 20 functions to transmit power necessary to rotate the rotating members 10. The rotation repeats the exposure to the air and the submergence of the rotating members 10, so that the decomposition of contaminants can be continuously conducted in the water by the members' areas which are activated during the exposure. The power transmission means 2C comprises a support connected to the rotating members 10 ana a power transmission source 20. The power transmission source 20, such as a motor, is installed at one side of the support 22 and transmits power through the support 22 to the rotating members 10.

Alternatively, the power transmission means 20, as shown in Fig. 2, may take advantage of natural wind force. In this case, the power transmission means 20 comprises a support 22' connected to the rotating members 10, a rotating support 24' and wafters 26' . The wafters 26' are installed on the rotating support 24' which is connected to one side of the support 22' . The junction portion between the support 22' and the rotating support 24' employs an engagement structure of gear to transmit to the support 22' the power generated by the revolution of the wafters 26' . In this power transmission structure, therefore, natural wind revolve the wafters 26 to rotate the rotating members 10, so that there can be saved the energy required to operate artificial means. Next, a description will be given of the light irradiation means 30. This means is to irradiate light to activate the titanium oxide photocatalyst, generating a wavelength of 400 nm or less, which is suitable for the photoactivation of titanium oxide. In this regard, the light irradiation means 30 takes advantage of natural light 30' or comprises a UV lamp 30 or a xenon lamp. In tne case of the UV lamp 30 or a xenon lamp, a reflection panel 32 such as aluminum foil is preferably provided to raise the efficiency of the energy. The reflection panel 32 reflects the light energy generated from the artificial light irradiating means 30 such as a UV lamp toward the rotating members 10, greatly decreasing the loss of the electric energy used.

The oxygen supply means 40 functions to feed oxygen, an oxidizer, into the contaminated water to facilitate the oxidative decomposition of contaminants. In order to promote the decomposition of contaminants, various oxidizers may be fed into the wastewater. In the present invention, however, the oxygen of the air is used as an oxidizer. As the purification means 10 is rotated by the power transmission means 20, the oxygen present in the air is introduced into the contaminated water, along with the purification means 10. Thus, the decomposition of contaminants can be effectively performed without feeding an additional oxidizer. Therefore, the rotating purification means 10 serves as the oxygen supply means 40.

In this embodiment, the purification apparatus of water is supported by a buoyant member 50. The buoyant member 50 allows the purification apparatus of water to float on the water as well as to move. By virtue of the buoyant member 50, the purification apparatus can be easily moved to seriously contaminated areas within a wide water supply source and thus, can perform effectively the purification of contaminants. Different from the above mobile type, fixed type purification apparatuses will be explained, below.

Fig. 3 illustrates a fixed type water purification apparatus in accordance with an embodiment of the present invention. As shown in Fig. 3, the fixed type water purification apparatus of this embodiment comprises a fixedly installable reservoir with a volume, which has a water influx tube 102 with a filter 102a at its lower side. Through the filter 102a, solid impurities are removed from the water introduced into the water influx tube 102. The filter 102a can be detachably combined with the water influx tube 102 by a medium such as a bolt. After being used for a predetermined period of time, thus, the filter 102a can be detached from the water influx tube and cleaned for reuse. As a material for the filer 102a, any structure, e.g., a non-woven fabric or a honeycomb structure of a wire screen, may be used if it can filter the solid impurities contained n the water.

At a predetermined height within the reservoir 100, two sets of purification means 10 consisting of a plurality of titanium oxide-coated rotating members are provided. Of course, many sets of the purification means 10 can be provided. In one set of the purification means 10, the titanium oxide-coated rotating members are position on one shaft 12 which is connected to power transmission means 10, e.g, a motor, via a belt 14. Thus, the operation of the power transmission means 20 leads to the rotation of the purification means 10. At a height corresponding to the middle point of the purification means 10, a water efflux tube 104 is provided to the side opposite to the water influx tube 102 in the reservoir 100. Because the water introduced into the reservoir through the water influx tube 102 is discharged through the water efflux tube 104, the water level within the reservoir lies at the height corresponding to the middle point of the purification means 10. In result, the purification means 10 keeps a semi- submerged state in which one side of the purification means is exposed m the air while the opposite side is submerged.

On the ceiling of the reservoir 100, light irradiation means 30, e.g., a UV lamp, is installed while a reflection panel 32, e.g., an aluminum foil, is provided around the light irradiation means 30 to increase the efficiency in transmitting the light generated by the light irradiation means 30 toward the purification means 10, below.

At a lower height of the reservoir 100, there are additionally provided plates 10a which will be submerged m water. Because of being coated with titanium oxide, the plates 10a can be activated by the lignt energy transmitted into the water so as to decompose the contaminants to some degree in the water. Thus, the plates 10 effectively utilize the light and improve the total purification efficiency.

With the aim of smoothly transmitting toward the purification means 10 the water inflow introduced at a pressure through the water influx tube 102, a backflow prevention plate 110 is obliquely formed at the lower side facing the water influx tube 102 m the reservoir 100. The water inflow introduced via the water influx tube 102 is moved upwardly along the slant side of the backflow prevention plate 110. The upward moving of the water flux is somewhat restrained by one of the plates 10a, so that the elevation of the water level occurs all over the water within the reservoir.

A separate space 120 may be provided to the side of the water efflux tube 104 m the reservoir 100. This space 120 is to store the purified water discharged through the water efflux tube 104. From the space 120, the purified water can be removed whenever it is necessary.

In Fig. 3, reference numeral a represents a stabilizer. At a particular site, as described above, the reservoir 100 is fixedly installed m which contaminated water is introduced via the water influx tube 102 ana purified. From the reservoir 100, the purified water is discharged through the water efflux tube 104. Therefore, the reservoir 100 can be designed to have a suitable purification capacity for use m particular purposes. For example, to be used where a large quantity of water is required, like a swimming pool or a water purification spot, the purification capacity of the apparatus can be increased by controlling the quantity of the members, the influx rate of the water influx tube 102, and the efflux rate of the water efflux tube 104.

With reference to Fig. 4, there is shown a water purification apparatus in accordance with another embodiment of the present invention. The water purification apparatus of this embodiment is to strictly purify water on a large scale. This embodiment is characterized in that the water introduced through a water influx tube 102 into a reservoir is allowed to stepwise undergo a plurality of purification means 10 which are activated by respective light irradiation means 30. Hence, the water discharged via the water efflux tube 104 is more strictly purified than is the water m Fig. 3.

Afterwards, the photocatalytic action of the invention will be explained in conjunction with the drawings. In each of the purification apparatuses shown m Figs. 1 to 4, the light energy generated oy the light irradiation means 30 such as natural light or a UV lamp is transferred to one side of the rotating member 10, which is exposed to the air, and activates individual titanium oxide photocatalysts coated on the rotating member 10. Because sufficient light energy is not provided to the opposite side of the rotating member 10, which is submerged m water, the photocatalysts on this side are not sufficiently activated. Under the circumstances, the rotating members 10 are rotated by the power generated by the motor 20 or natural cotton 20' , so that the activated portions of the rotating members 10 enter the water to decompose the contaminants which are in contact with the surfaces. After losing the activation energy as a result of the decomposition, the submerged portions of the members rise to the surface of the water. The portions of the rotating members 10, which are above the surface of the water, are re-activated by the light energy and thus, ready to decompose the contaminants within the water. Since the oxidative decomposition of the activated photocatalyst is performed with in a very short period of time (light transmission and the formation of electrons and holes are conducted for about lO , a higher rotating rate of the rotating members 10 leads to a greater decomposition efficiency. As the rotating members are rotated faster, there is increased the photocatalytically effective surface area which is in contact with the contaminants m the water. In addition, the oxygen of the air is actively supplied into the water as the rotating members 10 are rotated, facilitating the oxidative decomposition of the contaminants without feeding additional oxidizers.

Turning now to Figs. 5 and 6, there is illustrated the photocatalysis mechanism used in the present invention. When a light energy is illuminated on the surface of titanium oxide (Ti0₂) , electrons present in the valance band of the titanium oxide are transferred to the conduction band while positive holes are left in the valance band. Corresponding to the band gap, the light energy necessary for the transference of an electron is about 3.2 eV, which is obtained by using a wavelength of 390 nm or less. Hence, irradiation with a UV beam of 390 nm or less triggers the photochemical reaction illustrated m Fig. 5.

When exposed on the surface, the electrons and positive holes generated through the photochemical reaction are reacted with contaminants to cause a redox reaction. In detail, e^" _CB (electron transferred to the conduction band) and h⁺ _CB (positive hole remaining m the valance band) are diffused over the surface of the titanium oxide. The diffused h⁺ _VB reacts with hydroxyl ions in the water to produce OH radicals and with water molecules to produce Ob radicals and H⁺ ions. Also, the diffused hM directlx oxidizes organic matters. As a result of the reaction of e _CB with the oxygen m the water, there is produced a superoxide radical (0₂ ^"__) which reacts with a water molecule to produce two OH radicals, two hydroxyl ions and one oxygen molecule. When reacting with H⁺, the e^~ _CB produces HO?__. Finally, H₂0₂ is produced, leading to an __OH radical via several reaction routes. The energy that the photons of 40G nm have corresponds to the thermal energy of 30,000 °C at which almost all of organic matters are oxidized into CO and H₂0. In such a submerged type structure of the purification means 10, the exposed surfaces of the light irradiation means 30 are activated through the photochemical reaction, brought into contact with contaminants of the water by the rotation, so as to transfer the energy to the contaminants. Then, the submerged portions of the rotating members rise to the surface of the water and gain photochemical activity. Therefore, an increase in the rotation speed enables the photochemical decomposition to occur with a higher rate. In addition, since the rotation of the purification means 10 introduces the oxygen from the air into the water to increase the oxygen concentration in the water, the photochemical reaction is facilitated so as to increase the decomposition activity against contaminants. Even in the case that the coating film is contaminated with contaminants after being used for a lengthy period of time, the apparatus needs not to be changed with a new one. The removal of the contaminants can be accomplished simply by washing or wiping the coating film. Because the titanium oxide coating film adheres closely to the glass or stainless steel surface, the titanium oxide coating film does not peel off even when it is wiped with a cloth. Therefore, the apparatus according to the present invention can be used semi-permeably . In the following examples, the apparatuses according to the present invention were tested for decomposition potential against various contaminants. In this regard, trihalomethane, which is carcinogenic, resulting from a side effect of the chlorine sterilization, geosmm (C₁₂H₂₂O: trans-1, 10-dιmethyl-trans-9-decaol) , which causes an offensive odor, 2-MBI (CnH₂₀O: 2-methyl-ιso-borneol ) , common bacteria, colon bacillus, chlorophyll a, and microcystm, which is a toxin of Cynophyceae, were selected as indexes to determine the decomposition efficiency of the apparatus according to the present invention. From the concentrations of chlorophyll a and microcystm, algae can be indirectly estimated for the concentration. In addition, the killing effects of the apparatus against various pathogenic bacteria (Salmonella, Shigella, etc) were also examined. All experiments were conducted according to water contamination process assay, Japanese water supply assay, and Standard Methods. Organic matters contained samples or produced materials were identified and analyzed using gas chromatography mass analyzer (GC/MSD) , such as that manufacture by Beaπan, identified as "Star3400CX" .

< EXPERIMENTAL EXAMPLE I >

An apparatus was prepared as shown in Fig. 7 and used for conducting various experiments. Within a batch type reservoir with a volume of 3 L, a plurality of rotating members 10 were supported by a support which was connected to power transmission means, a motor (not shown) . As light irradiation means 30, a 10 W UV lamp was used. For some experiments, seven rotating members, each consisting of a disc with a diameter of about 15 cm and a thickness of about 5 cm, were used at a rotating speed of 24 rpm.

(1) Removal Efficiency of Trihalomethanes Trihalomethanes are hardly removed by conventional advanced water treatment processes which take advantage of ozone and granular activated carbon. Dominant over other trihalomethanes, chloroform (CHC1 ) and dichlorobromo methane (CHCl₂Br) were analyzed for their decomposition with regard to time by use of a gas chromatography mass analyzer (GC/MSD) and the results are given m Fig. 8. As recognized in the graph, trihalomethanes were substantially decomposed after about 60 min and almost completely decomposed after about 120 min.

(2) Removal Efficiency of Stinking Materials

Recently, Anabaena sp . a stinking algae, has frequently appeared at large concentrations (e.g., 450 cells/ml) in various rivers and water purification plants. An experimental data of a water purification plant showed that stinking materials were removed at an efficiency of as low as 50 % even after undergoing an advanced water treatment process usmg granular activated carbon. From the deposited water, obtained from an intermediated step in the water purification process, however, the apparatus of the present invention removed stinking materials at an efficiency of 70-80 % after about 60 mm and decomposed almost all of the stinking materials after 120 mm as shown m Fig. 9.

(3) Removal Efficiency of Chlorophyll a

The water taken from the stream m front of Nosan Watergate, Gangseo-Gu, Pusan, Korea, was measured for chlorophyll a concentration change, from which concentrations of algae can be indirectly estimated, and the result is shown m Fig. 10. As shown m the graph, the concentration of chlorophyll a was 117 ppb at the start and was gradually decreased down to 58 ppb after about 180 mm, which corresponds to a removal efficiency of about 50 %.

(4) Removal Efficiency of General Bacteria and colon bacillus

A water sample prepared by admixing the water taken from the Nakdong River at Mulgeum, Pusan with the sewage taken from the Gamjeon Water-supply reservoir, Sasang-Gu, Pusan, Korea at appropriate amounts was tested using the apparatus of the present invention. In an initial stage, general bacteria was measured to exist at a concentration of 2079 cells per ml, but almost all of them were killed after 10 mine. A positive reaction was detected for colon bacillus at the start, but almost all of them were killed after 10 min, as shown m Fig. 11.

In summary, (1) trihalomethanes, which are sparingly decomposable materials and hardly removed by conventional advanced treatment processes, was removed at 95 % after a reaction period of 60 min and at 99 % after a reaction period of 120 min by the apparatus of the present invention, (2) by use of the apparatus of the present invention, the removal efficiency of stinking materials was raised to 70- 80 % in 60 min, which is higher than that obtained m practical purification plants (about 50 %), (3) the concentration of chlorophyll a, from which the concentration of total algae can be indirectly estimated, was gradually decreased over the reaction period of time and down to about 50 % after 180 min, and (4) general bacteria and colon bacillus were almost completely killed.

< EXPERIMENTAL EXAMPLE II >

In this experimental example, an examination was made of the effect of an increase in the rotation speed of the disc type members on the removal efficiency of contaminants. Fig. 12 shows decomposition results of trihalomethanes chloroform (1) and dichlorobromo methane (2), obtained from the apparatus of Experimental Example I in which the disc type members were operated at a speed of 260 rpm under a UV lamp. For comparison, only a UV lamp was used without rotating the disc type members.

As recognized in the graphs of Fig. 12, chloroform (1) was decomposed at a small efficiency when using a UV lamp only. The decomposition was believed to be attributed to the light energy of the UV lamp. In contrast, almost all of the chloroform was decomposed m 10 mm when the present invention was applied. As compared with the graph of Fig. 8, which was obtained at a rotation speed of 24 rpm, the decomposition effect attributable to an increase m the rotation speed was very excellent. This result was attributed to the fact that increasing the rotation speed brought about an increase m the opportunity of the photoactivated surface area to contact with of contaminants and m the oxygen supply into the contaminated water. As for the dichlorobromo methane (2), it was almost completely decomposed in 10 mm, which was found to be more effective as compared with the decomposition of Fig. 9.

Removal efficiencies of microcystm, which is a toxm of Cynophyceae, and chlorophyll a, which allows algae to be indirectly measured, were measured by use of the apparatus of Experimental Example I, in which disc type members were rotated at a speed of 260 rpm and the results are given n Fig. 13. For this, freeze-dπed Cynophyceae was added m distilled water and experiments were carried out in a batch type. Because only two concentrations were measured at an initial point and after 180 mm, the concentration change therebetween was omitted, which resulted in the schematic linear plot shown m Fig. 13. Therefore, the plot might be in a curved form if the concentration was measured at many time points. Anyway, a decrease in the concentration of chlorophyll a was found from 240 ppb down to 40 ppb m 180 min, corresponding to a removal efficiency of about 83.3 %. This removal efficiency of chlorophyll a was improved at about 33 % by increasing the rotation speed of the members as compared with that of Fig. 10 m which the members were rotated at 24 rpm. Microcystms M-RR and M-LR, which are algal toxins, were measured to be 2.518 ppb and 3.89 ppb, respectively, at an initial point, but neither of them were not detected after 180 min.

< EXPERIMENTAL EXAMPLE III >

In this experimental example, the surface area m which the titanium oxide coating film was m contact with contaminants was enlarged and the photoactivation was boosted by irradiating a stronger light energy. Figs. 14 to 20 gives the results obtained by use of an apparatus comprising a 40 L reservoir and four drum-type rotating members, each having a dimension of 35x40 cm. The rotating members were rotated at a speed of 120 rpm under three 40 W UV lamps.

(1) Removal Efficiency of Trihalomethanes Of trihalomethanes, chloroform (CHC1₃) and trichloro ethylene (CH3CCI3) (a representative material formed during the purification of tap water) were analyzed for their decomposition with regard to time and the results are given in Fig. 14. As recognized in the graph, trihalomethanes were substantially decomposed after about 2 mm and almost completely decomposed after about 5 mm. This decomposition efficiency was higher than that of Experimental Example I and than that obtained when the disc type members of

Experimental Example II was rotated at a speed of 260 rpm. This improved decomposition efficiency is believed to result from the enlarged contact area of the intensively photoactivated titanium oxide coating film on the drum-type members .

(2) Removal Efficiency of Stinking Materials From the deposited water, obtained from an intermediated step in the water purification process, the apparatus of the present invention removed geosmin at an efficiency of 70-80 % after about 30 min and decomposed geosmin almost completely after 60 min as shown in Fig. 15. The removal efficiency of 2-MIB was also approximately twice as much as that obtained in Experimental Example I .

(3) Removal Efficiency of Colon bacillus A sewage sample taken from the Gamjeon Water-supply reservoir, Sasang-Gu, Pusan, Korea was tested m the apparatus of the present invention. A positive reaction was detected for colon bacillus at the start, but almost all of them were killed after 2 mm, as shown in Fig. 16. This removal efficiency was recognized to be high as compared with that of Experimental Example I .

(4) Removal Efficiency of Pathogenic Bacteria

In this experiment, the apparatus of the present invention was tested for the removal efficiency against recently issued pathogenic bacteria Enterococcus faecalis,

Salmonella thyphimuπum, Shigella sonei, and Staphylococcus aureus .

These bacterial strains were obtained from Korean Collection for Type Cultures (KCTC) . Samples cultured at room temperature (25±2 °C) on a pilot scale were taken every two minutes and their cell numbers were counted in a pour plate method (see, Standard Methods for the Examination of Water and Wastewater, 18th ed., Washington, DC, American Public Health Association) . As a culture medium, plate count agar (Difco) was used. The results are given m Table, below.

TABLE: Change in Cell Number of Pathogenic Bacteria

Note: ND: not detected

As apparent from Table and lg 17, Enterococcus faecalis, Shigella sonei and Staphylococcus aureus were completely killed after 2 mm and Salmonella thyphimurium was also killed after 6 mm. Steπli ation of these pathogenic bacteria was clearly identified by comparing the left panel photographs and right panel photographs, which were taken before and after the application of the apparatus of the present invention, respectively, m lg. 18. (5) Removal Efficiency of Environmental Hormones Representative of environmental hormones, bisphenol-A may cause a pain and a dermal damage even if existing at a trace concentration. In addition to causing mutagenesis in chromosomes, bisphenol-A acts just like a female hormone to proliferate breast cancer cells. In this experiment, an examination was made of the decomposition of bisphenol-A, which is fatal to the body.

For use m this experiment, bisphenol-A (Aldrich Chemical Co.) was diluted to 500 μg/L in methanol. Deionized water was obtained through a Milli-Q pure water apparatus .

As apparent from Fig. 19, 50 % or greater of the bisphenol-A was decomposed at 10 mm after the treatment in the apparatus of the present invention and approximately 95 % or greater at 65 mm.

In Fig. 20, the bisphenol-A decomposition efficiency of the present invention is compared with that of a conventional technique using ozone, known as a representative oxidizer. Ozone was fed at a concentration of 2 mg/L into an ozone contact bath while ozone remained at a concentration of 0.7 mg/L in the reactor.

As shown in Fig. 20, the POD drum accordmg to the present invention is superior in bisphenol-A decomposition efficiency to ozone, a strong oxidizer. < EXPERIMENTAL EXAMPLE IV >

In Fig. 21, removal efficiencies of a contaminant were plotted for various techniques with regard to contact time period. As a test contaminant, geosmin, which is a stinking material, was used at a concentration of 10 ppb. In connection to obtaining the removal efficiencies, POD discs which were rotated at a speed of 24 rpm as in Experimental Example I and POD drums which were rotated at a speed of 120 rpm as m Experimental Example III were used in accordance with the present invention. For comparison, various different conditions were adopted. In the following description, reference character G stands for a UV lamp, reference character Pw for titanium oxide powder, reference character POD for an apparatus of the present invention, reference character H-Bead for hollow beads, and reference character Pellet for glass pellets.

As recognized from the data given m Fig. 21, when only light irradiation from a UV lamp was conducted (G) and when titanium oxide-coated hollow beads (H-Bead) and titanium oxide-coated glass pellets (Pellet) were used under the UV light from a UV lamp, geosmin was decomposed at efficiencies of 35.98 %, 36.02 % and 36.57 %, respectively, while the present invention (POD) showed a decomposition efficiency of as high as 97 %. Also, it is apparent that the POD drum is far more effective than the POD disc because the larger surface area of the drum makes the activated titanium oxide to have more frequent opportunity to contact with contaminants. Meanwhile, a 50 ppm suspension of titanium oxide and a 100 ppm suspension of titanium dioxide were measured to show decomposition efficiencies of 89.1 % and 98.8 %, respectively, demonstrating that the contact area of the photocatalytically active component titanium oxide with contaminants is very important in determining the decomposition efficiency. The decomposition efficiency of the POD disc according to the present invention was lower than those of the titanium oxide suspensions . As for the POD drum, its decomposition efficiency was higher than that of the 50 ppm suspension and similar to that of the 100 ppm suspension. However, since the disc and the drum used m the present invention were coated with titanium oxide, the amount of the titanium oxide used was no more than one- several-millionth compared with the suspensions. In contrast to titanium oxide suspensions, the apparatuses of the present invention require no titanium oxide-reclaiming means. Over the suspensions, the apparatuses of the present invention, therefore, have advantages of using lower amounts of titanium oxide, being simpler, and showing higher decomposition efficiencies. It is also obvious that when the drum or the disc is rotated at higher speeds, far better results can be brought about than when the suspensions are used.

In accordance with the present invention, the rotating members coated with titanium oxide have a large surface area and can be applied for the treatment of water m a semi- submerged type as well as for the treatment of air as it is. Therefore, the apparatus of the present invention can be applied for the purification of both water and air and can be improved in decomposition efficiency by increasing the contact area of the catalytically active component with contaminants, for example, by increasing the rotation speed of the rotating members.

Further, during the treatment of water, the rotation of the rotating members introduces oxygen of the air into the water, bringing about an aeration effect to obtain strong oxidizing power.

In addition, the apparatus of the present invention requires no supplementary means such as titanium oxide reclaiming means so that it can be manufactured into a small size. Of course, the apparatus can be manufactured to have a large capacity, depending on the facility scale. Therefore, it can be installed at any sites.

Moreover, when the coating film is contaminated as a result of, for example, use for a long term, the contaminants can be removed simply by wiping the detachable members. Thus, the apparatus can be reused and enjoys the advantage of being used semi-permanently.

The present invention has been described m an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

INDUSTRIAL APPLICABILITY With far superiority in decomposing contaminants m water to conventional suspension, hollow bead, or pellet techniques, as described hereinbefore, the apparatus for purifying contaminated water in accordance with the present invention can be controlled in decomposition efficiency by adjusting the contact area of the catalytically active component with contaminants, for example, by adjusting the coating number, size and number of the titanium oxide coating film and the rotating speed of the purification means. Therefore, the apparatus of the present invention can find numerous applications many fields. For instance, it can be applied for the sterilization of Legionella which usually inhabits cooling towers for large buildings, the removal of secondary contaminants, general bacteria and colon bacillus from tap water stored in reservoirs or tanks, the sterilization of Vibrio bacteria from large aquaria, the sterilization and disinfection of swimming pools, the sterilization and disinfection of small water-supply systems, the advanced treatment of water and wastewater, the treatment of domestic water, and the softening of industrial water. While conventional titanium oxide powders or hallow beads are impossible to apply for the purification of air pollutants even if their contact area is greatly increased or their photoactivity is greatly improved, the apparatus of the present invention can be applied for purification facilities of air pollution because it can be installed at a particularly given site by virtue of the rotating members with a predetermined size.

Claims

CLAIMS :

1. An apparatus for purifying contaminated wastewater using rotating members coated with titanium oxide films, comprising: purification means, which is rotatable and coated with photocatalytically active titanium oxide films; power transmission means for transmitting a rotating power to the purification means; oxygen supply means for supplying oxygen to contaminants in accordance with the power transmission of the power transmission means; and light irradiation means for inducing the purification means to be photochemically activated, wherein the titanium oxide coating film is activated by the light irradiation means and catalytically decomposes the contaminants when being brought into contact with them, the purification means is revolved by the operation of the power transmission means, and the oxygen facilitates the decomposition of the contaminants .

2. The apparatus as set forth claim 1, wherem the purification means is a semi-submerged structure m which one side of the purification is exposed to the air while the other side is positioned within water.

3. The apparatus as set forth in claim 1 or 2, wherem the oxygen supply means utilizes the rotation of the purification means to supply oxygen from the air into the contaminants by natural convention.

4. The apparatus as set forth m claim 3, wherem the purification means comprises a plurality of rotating members, each being coated with the titanium oxide film at a thickness of 0.3-0.5 μm.

5. The apparatus as set forth m claim 4, wherem the titanium oxide film further comprises at least one selected from metals such as copper, platinum, aluminum, gold, zinc and iron and photoactive materials such as Sι0₂, ZnO, SiC, W0₃, CdS, GaAs, CuO, and Cu0₂.

6. The apparatus as set forth m claim 1 or 2, wherem the power transmission means comprises a motor.

7. The apparatus as set forth m claim 1 or 2, wherem the power transmission means comprises wafters which can be rotated by natural wind.

8. The apparatus as set forth m claim 1 or 2, wherem the light irradiation means utilizes solar light or comprises a UV lamp or a xenon lamp, which generates a wavelength of 400 nm or less.

9. The apparatus as set forth m claim 8, wherem the light irradiation means further comprises a reflection panel for reflecting the light toward the purification means.