CN1538939A

CN1538939A - Method for killing of microorganism in water by UV-TiO2 photocatalytic reaction and reactor for killing of micro-organisms

Info

Publication number: CN1538939A
Application number: CNA028154770A
Authority: CN
Inventors: ��ʱ��; 金时郁; 金仲坤; 金龙昊; 李荣祥
Original assignee: Chosun University
Current assignee: Chosun University
Priority date: 2001-08-06
Filing date: 2002-08-06
Publication date: 2004-10-20
Anticipated expiration: 2022-08-06
Also published as: WO2003014030A1; CN1301917C; KR100439195B1; KR20030012956A

Abstract

There are disclosed a method for killing of microorganisms in the water by UV-TiO2 photocatalytic reaction and a reactor for killing of microorganisms.

Description

By UV-TiO2Method for killing microorganisms in water by photocatalytic reaction and reactor for killing microorganisms

Technical Field

The present invention relates generally to water disinfection by photocatalytic reactions. More particularly, the present invention relates to an apparatus for water sterilization and a method for inactivating or destroying microorganisms and organic substances in water using the same, which comprises the steps of adding hydrogen peroxide to contaminated water, introducing the contaminated water added with hydrogen peroxide into a photocatalytic reactor containing porous beads on which a photocatalyst is immobilized, injecting air thereinto, and applying UV rays thereto.

Background

Typically, areas with low levels of rainfall face shortages of drinking water as well as water for irrigation. Particularly in korea, annual rainfall has recently decreased, resulting in a shortage of fresh water. Most korean farmers are using conventional irrigation systems, which are inefficient due to economic problems introduced into modern furrow irrigation, which efficiently supplies water to a desired area, but require high investment costs for its establishment. Therefore, to solve this difficulty in the field of irrigation for crop cultivation, water, in particular waste water, must be recycled. In addition, the recycling of wastewater is necessary for the continuous use of seawater or fresh water in large aquariums. To recycle the waste water, first, it is most important to kill the microorganisms in the water.

Chlorine has been widely used in conventional wastewater recirculation systems for water disinfection in order to control the growth of bacteria, viruses and algae. However, this water disinfection is disadvantageous because carcinogenic Trihalomethanes (THMs) are produced and chlorides remain. In particular, residual chloride is problematic in the production of pure water or ultrapure water. In addition, the high-tech purification process using ozone for water disinfection is uneconomical in terms of high investment costs required for its establishment and management. Recently, attempts have been made to use a photocatalyst, titanium dioxide (TiO)₂) Sterilization, which is inexpensive in its set-up and maintenance.

Using titanium dioxide (TiO)₂) The disinfection of the photocatalyst is based on the following protocol.

[ scheme 1]

[ scheme 2]

[ scheme 3]

According to scheme 1, when TiO is irradiated with photons having sufficient band gap energy or more₂When in use, photons (hv) excite electrons from the valence band (valence band) to the conduction band overcoming the band gap and leaving an electron vacancy in the valence band, a hole (h)⁺). Conduction band electron (e)^- _CB) And valence band hole (h)⁺ _VB) Then diffused and transferred to TiO₂Of (2) is provided. The excited electrons and the generated holes can react with H in water₂O，OH^-Organic substance and O₂Participate together in the redox process.

Referring to scheme 2, diffused holes (h)⁺ _VB) With OH in water^-Reacting to produce OH radicals (OH), or with water molecules (H)₂O) reaction to produce OH and H⁺And direct oxidation of organic materials.

Referring to scheme 3, electron (e)^- _CB) Reacts with oxygen in water to produce peroxide free radical (O)₂ ^-Cndot.). Peroxide radical and waterMolecular reaction to produce OH, OH^-And oxygen molecules. When the water contains hydrogen peroxide, the hydrogen peroxide absorbs UV energy to produce OH, or with e^- _CBOr the dissolved oxygen reacts to produce OH. The OH radicals (OH.) produced participate in the oxidation of organic substances.

However, TiO photocatalyst is used₂And the sterilization method according to the reaction mechanism as described above have several disadvantages as follows. When powdered titanium dioxide is added to water containing contaminants, TiO is used₂Continuous treatment of the water of the powder results in a suspension for re-suspending the TiO₂The consumption of a large amount of electrical energy by the powder, and in addition, the photocatalyst should be recovered from the treated water. When mixing TiO₂TiO at the end of the lamp life when coated directly on an ultraviolet lamp₂And likely to be undesirably discarded along with the lamp. In addition, when TiO is used₂When coating the inside of the reactor, the coating operation is very difficult if the reactor is large in size. In addition, in-use TiO₂After coating, the reactor should be heat treated above 500 ℃, thus limiting the materials that can be used in reactor manufacture. In addition, when TiO is added₂When fixed to glass beads, TiO₂The film was gradually eroded from the surface of the glass beads by a continuous stream of water.

Disclosure of Invention

In order to solve the problems encountered in the background art, intensive and thorough research into a reactor for water sterilization by photocatalytic reaction and a method of inactivating or destroying microorganisms and organic substances contained in water using the same resulted in the finding that an apparatus comprising a photocatalytic reactor and a method of using the same for water sterilization, in which contaminated water is sterilized by a method of adding hydrogen peroxide to water to be treated, introducing the water to which hydrogen peroxide is added into a photocatalytic reactor comprising porous beads on which a photocatalyst is fixed, injecting air into the photocatalytic reactor and applying UV rays into the photocatalytic reactor, operating time for sterilization is shortened and sterilization efficiency is improved due to the introduction of air and hydrogen peroxide, and the reactor can be constructed in a small size, thus allowing it to be installed in a narrow place and removed, thus facilitating its cleaning, thus, the present invention has been completed.

It is therefore an object of the present invention to provide an apparatus for water disinfection comprising a photocatalytic reactor comprising porous beads on which a photocatalyst is immobilized and equipped with an ultraviolet lamp for UV irradiation and an inlet for injecting air thereinto.

It is another object of the present invention to provide a method for effectively inactivating microorganisms in contaminated water using the apparatus for water disinfection.

Brief Description of Drawings

The above and other objects, features and other advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which

FIG. 1 is a sectional view showing the construction of a device for disinfecting water according to a first embodiment of the present invention;

FIG. 2 is a side view showing a photocatalytic reactor included in the apparatus of the present invention;

fig. 3 is a view of an apparatus for water sterilization having several photocatalytic reactors arranged in parallel according to another embodiment of the present invention.

FIG. 4 shows the immobilization of TiO₂A photograph of the bead of (a);

FIGS. 5a and 5b show the immobilization of TiO₂The sterilization activity of the porous beads and the glass beads of (1), wherein the number of viable cells and the sterilization rate (%) for E.coli are plotted against time in FIGS. 5a and 5b, respectively;

FIGS. 6a and 6b are graphs showing the sterilization effect and viability of each UV lamp according to the diameter of a photocatalytic reactor, in which the number of living cells and the sterilization rate (%) for E.coli are plotted against time in FIGS. 6a and 6b, respectively;

FIGS. 7a and 7b are graphs in which the number of living cells and the sterilization rate (%) for E.coli are plotted against time in FIGS. 7a and 7b, respectively, when air is injected into the photocatalytic reactor;

FIG. 8 is a graph showing the effect of hydrogen peroxide concentration on the sterilization efficiency of Escherichia coli when a photocatalytic reaction occurs, in which the sterilization rate (%) at different hydrogen peroxide concentrations is plotted against time;

FIG. 9 is a graph showing the effect of the concentration of hydrogen peroxide on the sterilization efficiency of Escherichia coli when a photocatalytic reaction is not induced, in which the sterilization rate (%) at different hydrogen peroxide concentrations is plotted against time;

FIG. 10 is a graph showing the effect of hydrogen peroxide concentration on bean sprouting;

FIGS. 11a and 11b are graphs in which the number of living cells of E.coli and the sterilization rate (%) are plotted against time in FIGS. 11a and 11b, respectively, when the volume of treated water is doubled and a photocatalytic reaction is induced;

FIGS. 12a and 12b are graphs in which the number of viable cells and the bactericidal rate (%) against bacteria in water for bean sprouting are plotted against time; and

fig. 13a and 13b are graphs in which the number of viable cells and the fungicidal rate (%) against fungi in water used for bean sprouting were plotted against time.

^*Brief description of the reference

100: the device 10: photocatalytic reactor

11: photocatalyst-immobilizing porous bead

12: the ultraviolet lamp 13: water outlet

14: water inlet 15: internal frame

16: the outer frame 17: o-shaped ring

18: the locking device 20: first water storage pool (water respiroir)

21: water supply pipe 22: water supply pump

30: intake pipe 31: air pump

40: ultraviolet stabilizer

41: the circuit 50: filter

51: the second water storage tank

Best Mode for Carrying Out The Invention

The present invention relates to a device for disinfecting water, which will be described in detail with reference to the accompanying drawings.

Fig. 1 shows the construction of a device for water sterilization according to a preferred embodiment of the present invention.

As shown in fig. 1, an apparatus 100 for water sterilization, in which water is sterilized by a photocatalytic reaction, comprises a photocatalytic reactor 10 containing porous beads 11 on which a photocatalyst is immobilized. The ultraviolet lamps 12 are axially installed in the photocatalytic reactor 10 at regular intervals, when hatched with cross lines, as best seen in fig. 2, such that the lamps 12 are located at the center and ends of the cross shape, thereby generating OH radicals when the photocatalyst-immobilized porous beads 11 are exposed to UV irradiation from the ultraviolet lamps 12. An air inlet pipe 30 is axially installed inside the lower layer of the photocatalytic reactor 10, and air from an air pump 31 is injected into the inside of the photocatalytic reactor 10 through the air inlet pipe 30. The water inlet 14 and the water outlet 13 are installed at the lower portion and the upper portion of the photocatalytic reactor 10, respectively, and are diagonally located on the outer shell of the reactor 10 when cut along the longitudinal axis, thereby increasing the residence time of water in the photocatalytic reactor 10. A filter 50 for preventing the undesired discharge of the photocatalyst-immobilized porous beads 11 from the reactor 10 is installed in each of the water inlet 14 and the water outlet 13. The housing of the reactor 10 has a sealed structure with inner and

outer frames

15 and 16. The inner frame 15 and the outer frame 16 are equipped with each other by means of a locking device 18, which locking device 18 has an O-ring 17 made of rubber, sandwiched between the two

frames

15 and 16.

The inner and

outer frames

15 and 16 of the photocatalytic reactor 10 are made of transparent acrylic resin (acryl), thus allowing a user to visually observe the inside of the photocatalytic reactor 10 and check abnormality and replacement time of the ultraviolet lamp 12.

The porous beads 11 may be formed by using photocatalyst-immobilized beads such as dolomite beads or bentonite beads. In detail, such asAs shown in fig. 4, porous beads 11 made of muscovite were prepared by baking muscovite having high porosity at 800 ℃, coating the surface thereof with a photocatalyst, and then heat-treating at 1400 ℃. The photocatalyst is TiO₂. By having a large surface area, the photocatalyst-immobilized porous beads 11 can effectively inactivate or destroy microorganisms and organic substances. Preferably the porous beads have a diameter of 6-10 mm. When the diameter is below this range, the porous beads are closely packed together, thereby blocking the flow of water in the photocatalytic reactor. In contrast, when the diameter is above this range, the total surface area of the porous beads is reduced, thereby decreasing the sterilization efficiency.

In particular, the photocatalyst-immobilized porous beads 11 serve as a catalyst in a method of sterilizing water when exposed to ultraviolet light. After the photocatalyst-immobilized porous beads 11 are used several times, microorganisms and organicsubstances adsorbed in the pores of the porous beads 11 can be easily removed by heat treatment, thus allowing their semi-permanent use.

The photocatalyst-immobilized porous beads 11 filled inside the photocatalytic reactor are advantageous compared to conventional glass beads coated with a photocatalyst, as follows. Porous beads have excellent absorption capacity for microorganisms and organic substances due to their porosity, have improved sterilization efficiency due to their large surface area, and can be used semi-permanently. In contrast, glass beads have a short life span due to easy desorption of the photocatalyst, which is caused by a continuous water flow.

According to an embodiment of the present invention, when water sterilization is performed in a photocatalytic reactor using photocatalyst-immobilized porous beads and glass beads, referring to fig. 5a and 5b, TiO is immobilized₂Has a specific coating of TiO₂The glass beads of (2) have a greater sterilization capacity.

Ultraviolet lamps 12 are installed at regular intervals in the photocatalytic reactor 10, wherein the interval between the ultraviolet lamps affects the sterilization efficiency in the contaminated water. Since OH radicals (OH) as strong oxidants are generated when ultraviolet light from the ultraviolet lamps 12 is irradiated onto the photocatalyst-immobilized porous beads 11, the ultraviolet lamps 12 should be installed in a line to allow all the porous beads 11 to be exposed to the ultraviolet light. The interval between the ultraviolet lamps 12 may be changed according to the size of the photocatalytic reactor 10. According to the embodiment of the present invention, when the sterilization of water is performed in the cylindrical photocatalytic reactor 10 in which the ultraviolet lamps 12 are arranged at regular intervals and which has a diameter of 20cm and a length of 72cm, the most effective sterilization isachieved when the ultraviolet lamps 12 are arranged at intervals of 55 to 80 mm. However, when a large amount of contaminated water is sterilized, the interval between the ultraviolet lamps 12 may be changed according to the size of the photocatalytic reactor 10.

According to the prior art, the electrodes of the ultraviolet lamp are placed in the photocatalytic reactor, and thus the ultraviolet lamp needs to be covered with expensive quartz in order to prevent the electrodes of the ultraviolet lamp from contacting water. However, according to the present invention, the ultraviolet lamp 12 can be installed without a quartz tube because the electrodes of the ultraviolet lamp 12 extend to the outside of the photocatalytic reactor 10, allowing a complete sealing effect of the reactor 10, thereby reducing the material cost. Since the inner and

outer frames

15 and 16 are made of transparent acrylic resin, the inside of the photocatalytic reactor 10 is visible, thus allowing a user to visually check any abnormality of the lamp 12 and to determine when to replace the existing lamp 12 with a new one. Furthermore, the inner and

outer constructions

15 and 16 are equipped with locking means 18 to maintain the gas tightness of the photocatalytic reactor 10. The locking means 18 is released as necessary so that the ultraviolet lamp 12 is replaced with a new one only by releasing the locking means 18. The locking device 18 may be selected from conventional nuts and bolts, and other types of detachable locking devices.

In order to inject air into the photocatalytic reactor 10, an air inlet pipe 30 is installed at a lower portion of the photocatalytic reactor 10. The air inlet tube 30 is finely perforated to prevent it from being clogged with the photocatalyst-coated porous beads 11, and is connected to an air pump 31 which may or may not have a regulator, so as to control the air pressure. Air from the air pump 31 is introduced into the photocatalytic reactor 10 through the air inlet pipe 30, thereby increasing the amount of dissolved oxygen in water. However, since the inflow of a large amount of air generates warm flow in water and thus increases the reaction efficiency of water, it is preferable that the air pump 31 is powerful.

In order to prevent the photocatalyst-immobilized porous beads 11 from flowing out into the water supply pipe 21, filters 50 made of plastic are installed in the water inlet 14 and the water outlet 13. The pore size of the filter 50 may vary depending on the size of the porous beads.

The apparatus for water sterilization 100 according to the present invention further comprises a water supply pipe 21 through which water is injected into the photocatalytic reactor 10, and an ultraviolet stabilizing device 40 controlling the operation of the ultraviolet lamp 12.

As described above, the apparatus 100 for water sterilization according to the present invention comprises the photocatalytic reactor 10 including the photocatalyst-immobilized porous beads 11, the ultraviolet lamp 12, and the inlet pipe 30. In order to sterilize a large amount of contaminated water, as shown in fig. 3, a plurality of photocatalytic reactors 10 may be manufactured in a large size or in a small size and then arranged in parallel. Such manufacture of the photocatalytic reactor according to size and arrangement may be modified by those skilled in the art, and the apparatus 100 for water disinfection may be used to disinfect and then recycle various waters including agricultural water and seawater or fresh water used in aquaria.

According to another aspect of the present invention, a method of passivating or destroying microorganisms and organic matter in contaminated water using the above-described apparatus 100 is provided.

The method for disinfecting water by photocatalytic reaction comprises the steps of: adding hydrogen peroxide into water to be treated; introducing water to which hydrogen peroxide is added into a photocatalytic reactor 10 containing porous beads 11 on which a photocatalyst is immobilized; and injecting air into the photocatalytic reactor 10 through the air inlet pipe 30, and applying ultraviolet rays into the photocatalytic reactor 10 to induce a photocatalytic reaction.

The water from the first water storage tank 20 flows into the photocatalytic reactor 10 through the water inlet 14 installed at the lower portion thereof, circulates therein, and then flows out through the water outlet 13, which is stimulated by the water supply pump 22. The water in the photocatalytic reactor 10 is sterilized by OH radicals, which are generated when ultraviolet rays are irradiated onto the porous beads 11, and the sterilized water is stored in the second water storage tank 51.

In addition, in order to improve the sterilization efficiency, a small amount of hydrogen peroxide is added to the water in the first water storage tank 20. The concentration of hydrogen peroxide may vary depending on the volume of water, and is preferably 25 to 50mg/L, wherein the minimum amount of hydrogen peroxide is preferably used because of possible problems in terms of economy and stability when hydrogen peroxide is used at a high concentration. As shown in fig. 8, when water is treated with hydrogen peroxide of various concentrations, the sterilization efficiency in water increases with the concentration of hydrogen peroxide, thereby shortening the time required for water sterilization.

As shown in fig. 9, in which the sterilization efficiency without exposure to UV by adding hydrogen peroxide was compared with the sterilization efficiency with exposure to UV, it was confirmed that hydrogen peroxide alone could not effectively inactivate microorganisms in water, whereas high sterilization efficiency could be obtained by using hydrogen peroxide together with exposure to ultraviolet rays.

In addition, much higher sterilization efficiency can be obtained by increasing the amount of dissolved oxygen in water due to the use of the air inlet tube 30 and the air pump 31. When air is introduced from the air pump 31 into the photocatalytic reactor 10 through the air inlet pipe 30, the amount of dissolved oxygen in the water is increased, resulting in the formation of warm flow and thus increasing the contact of contaminants and OH radicals in the water. The volume of air injected into the photocatalytic reactor used in the present invention is 30L/min, wherein it is preferable that the air pump is as powerful as possible without adversely affecting the operation of the photocatalytic reactor.

As shown in fig. 7, when air is introduced into the photocatalytic reactor, the sterilization efficiency of water is higher in the initial stage than when sterilization is performed without using air. According to the example of the present invention, during the first 1 minute, a sterilization rate of 95% or 90.6% was observed when air was injected or not injected, respectively. This result is due to the fact that the introduced air generates a warm flow and thus increases the level of dissolved oxygen, which results in an increased production of OH radicals and thus a more efficient disinfection.

As is evident in table 1 below and fig. 10, the water treated with hydrogen peroxide is stable. Table 1 shows the effect of hydrogen peroxide on the sprouting of beans.

[ Table 1]

Unit (%)	H₂O₂Concentration (mg/L)
Unit (%)	H₂O₂Concentration (mg/L)						Sky	0	10	50	100	500	1000
1	71.67	20.00	53.33	60.00	78.33	50.00	Sky	0	10	50	100	500	1000
1	71.67	20.00	53.33	60.00	78.33	50.00	2	90.00	86.67	76.67	86.67	93.33	95.00
3	91.67	88.33	80.00	88.33	93.33	95.00	2	90.00	86.67	76.67	86.67	93.33	95.00

As is evident from Table 1, the germination rate decreased slightly at a concentration of 50mg/L hydrogen peroxide, but recovered over time. As is apparent from fig. 10, the total length of the bean sprouts increases with the concentration of hydrogen peroxide. The total length of bean sprouts was significantly increased at a concentrationof hydrogen peroxide of 500mg/L, with a significance level of 5%. There was no significant difference in the length of hypocotyls between bean sprouts grown in water which had not been treated with hydrogen peroxide or treated with 100mg/L of hydrogen peroxide, but the length of hypocotyls was significantly increased at 500mg/L of hydrogen peroxide. Further, the length of the roots of the bean sprouts increases with the addition of hydrogen peroxide. There was no significant difference in hypocotyl thickness between the bean sprouts treated with or without hydrogen peroxide. These results indicate that water treated with hydrogen peroxide is stable.

When the volume of the treated water is doubled, the apparatus 100 for water sterilization, which comprises the photocatalytic reactor 10 containing the photocatalyst-immobilized porous beads 11, as shown in fig. 11a and 11b, also shows excellent sterilization efficiency, in which the initial sterilization efficiency is slightly lower but is restored soon. In addition, the treatment of a large amount of water can be achieved using several photocatalytic reactors 10 arranged in parallel.

The invention will be explained in more detail with reference to the following examples in conjunction with the accompanying drawings. However, the following examples are provided only to illustrate the present invention, and the present invention is not limited thereto.

<example 1>method for water sterilization using photocatalytic reactor

The optimum conditions for water disinfection were determined using various reactors, and the optimum conditions were as follows. Use of a photocatalytic reactor 10 having a length of 720mm and a diameter of 200mm, fixed TiO 8mm in diameter₂And an ultraviolet lamp 12 emitting maximum ultraviolet light of 39W at 254nm, adding hydrogen peroxide of 0-75mg/L and injecting air through an inlet pipe 30at a rate of 30L/min to sterilize water. In all experimental and comparative examples of the present invention, the sterilization efficiency was evaluated by collecting samples at regular intervals, serially diluting the samples, applying 100. mu.l of the finally diluted samples on a solid medium to allow the growth of bacteria and fungi, and then counting the colonies grown on the medium.

<experimental example 1>measurement of E.coli viability per ultraviolet lamp according to the diameter of photocatalytic reactor

In order to determine the optimum size of the photocatalytic reactor for obtaining the maximum sterilization efficiency of each ultraviolet lamp, the inhibition level of growth of E.coli was investigated in the photocatalytic reactor 10 having 55, 80 or 110mm diameter in which one ultraviolet lamp 12 was installed.

In the process of fixing TiO₂After the porous beads of (1) were added to each of the photocatalytic reactors 10, the buffer solution containing E.coli was circulated in the photocatalytic reactor 10 exposed to ultraviolet rays for 15 minutes. The resulting sterilization efficiencies are given in table 2 below and in fig. 6a and 6 b.

[ Table 2]]

Number of viable Escherichia coli Eye (cell/ml)	0min	1min	15min
Number of viable Escherichia coli Eye (cell/ml)	0min	1min	15min	55mm	7.1×10³	375	13
80mm	7.3×10³	823	21	55mm	7.1×10³	375	13
80mm	7.3×10³	823	21	110mm	7.1×10³	3.1×10³	201

As shown in Table 2 and FIGS. 6a and 6b, in the photocatalytic reactor 10 having a diameter of 55mm, the initial cell number of E.coli after 1min (7.1X 10)³One cell/ml) to 375 cells/ml and to 13 cells/ml after 15 minutes, which showed 95% and 99.8% bactericidal efficiency, respectively. In a photocatalytic reactor 10 having a diameter of 80mm, the initial cell number of E.coli after 1min (7.3X 10)³Individual cells/ml) to 823 cells/ml, and to 21 cells/ml after 15 minutes, whichshowed sterilizing efficiencies of 88.6% and 99.7%, respectively, in which the initial sterilizing activity was lower than that when a photocatalytic reactor having a diameter of 55mm was used, but was restored to a level similar to that of the photocatalytic reactor having a diameter of 55mm after 15 minutes. However, when a photocatalytic reactor having a diameter of 110mm was used, the initial cell number of E.coli (7.1X 10) after 1min³Individual cell/ml) to 3.1X 10³One cell/ml, which decreased to 201 cells/ml after 15 minutes, showed sterilization efficiencies of 57.5% and 97.2%, respectively, which were much lower than when photocatalytic reactors having diameters of 55mm and 80mm were used. These results show that photocatalytic reactors with diameters of 55mm and 80mm provide high disinfection efficiency, however with diameters of 55mm and 80mm110mm photocatalysisThe reactor gives a significantly lower disinfection efficiency. Therefore, the most suitable size of the photocatalytic reactor for each ultraviolet lamp 12 is 55mm to 80mm in diameter.

<Experimental example 2>Effect of air injection on inactivation of Escherichia coli

The viability of E.coli was studied for 15min using an air pump 31 to inject air into the photocatalytic reactor 10 through an air inlet pipe 30 at a rate of 30L/min, and compared with the case where no air was injected. The results are given in table 3 below, and in fig. 7a and 7 b.

[ Table 3]]

Number of viable Escherichia coli Eye (cell/ml)	0min	1min	15min
Number of viable Escherichia coli Eye (cell/ml)	0min	1min	15min	Without injection of air	7.1×10³	668	70
By injecting air	7.1×10³	357	13	Without injection of air	7.1×10³	668	70

As shown in Table 3 and FIGS. 7a and 7b, when air was not injected, the initial cell number of E.coli after 1min (7.1X 10)³One cell/ml) to 668 cells/ml, showing a bactericidal efficiency of 90.6%, which was reduced to 70 cells/ml after 15 minutes. In contrast, when air was injected, the initial cell number of E.coli after 1min (7.1X 10)³Individual cells/ml) to 357 cells/ml, showing 95% bactericidal efficiency, to 13 cells/ml after 15 minutes. It was found that the sterilization efficiency when air was introduced was higher than that when air was not introduced. It is considered that this result is caused by the fact that the injected air generates warm current in the water of the photocatalytic reactor 10 in which the photocatalytic reaction occurs, thus causing the OH radicals to react more efficiently, and increasing the amount of dissolved oxygen and thus generating the OH radicals.

<Experimental example 3>H₂O₂Influence of injection on growth of Escherichia coli

Hydrogen peroxide was added to the water in the photocatalytic reactor 10 in amounts of 10, 15, 20 and 25mg/L, and air was added at a rate of 30L/min using an air pump 31 to evaluate the viability of E.coli for 15 min. The results are given in table 4 below and fig. 8.

[ Table 4]

Live large intestine rodNumber of bacteria Eye (cell/ml)	0min	1min	15min
Live large intestine rodNumber of bacteria Eye (cell/ml)	0min	1min	15min	Without addition of H₂O₂	7.3×10³	267	13
H₂O₂，10mg/L	7.5×10³	242	14	Without addition of H₂O₂	7.3×10³	267	13
H₂O₂，10mg/L	7.5×10³	242	14	H₂O₂，15mg/L	9.2×10³	203	5
H₂O₂，20mg/L	8.5×10³	157	0	H₂O₂，15mg/L	9.2×10³	203	5
H₂O₂，20mg/L	8.5×10³	157	0	H₂O₂，25mg/L	8.5×10³	82	After 10min 0

As shown in Table 4 and FIG. 8, the initial cell number of E.coli after 1min when hydrogen peroxide was not added (7.3X 10)³One cell/ml) to 267 cells/ml and after 15 minutes to 13 cells/ml, which showed 96% and 99.8% bactericidal efficiency, respectively. When added in an amount of 10mg/LIn the case of hydrogen peroxide, the initial cell number of E.coli after 1min (7.5X 10)³One cell/ml) to 242 cells/ml, showed a sterilization efficiency of 96.7% which was slightly higher than that without hydrogen peroxide addition, and after 15min, showed a sterilization efficiency of 99.8% which was similar to that without hydrogen peroxide addition. When hydrogen peroxide was added in an amount of 15mg/L, the initial cell number of E.coli after 1min (9.2X 10)³One cell/ml) to 203 cells/ml, showing 97.8% bactericidal efficiency. When hydrogen peroxide was added in an amount of 20mg/L, the initial cell number of E.coli after 1min (8.5X 10)³Individual cells/ml) to 157 cells/ml, showing 98% sterilization efficiency, and showing complete sterilization efficiency at 15min later. Initial cell number of E.coli after 1min (8.5X 10) when hydrogen peroxide was added in an amount of 25mg/L³Individual cells/ml) to 82 cells/ml, showed 99% sterilization efficiency, and showed complete sterilization efficiency after 10 min. These results indicate that high disinfection efficiency is achieved by adding small amounts of hydrogen peroxide.

<experimental example 4>measurement of sterilizing efficiency when volume of treated water is doubled

The amount of water treated in the photocatalytic reactor 10 was doubled while adding hydrogen peroxide in amounts of 20, 25, 30 and 50mg/L, and air was injected at a rate of 30L/min using an air pump 31 to evaluate the viability of E.coli for 15 min. The results are given in table 5 below and fig. 11.

[ Table 5]]

Number of viable cells

0min

1min

2min

5min

15min

(cells/ml)
(cells/ml)						Without addition of H₂O₂	3.2×10⁴	1.5×10⁴	1.2×10⁴	1.8×10³	37
H₂O₂，20mg/L	3.8×10⁴	1.1×10⁴	7.0×10³	1.8×10³	15	Without addition of H₂O₂	3.2×10⁴	1.5×10⁴	1.2×10⁴	1.8×10³	37
H₂O₂，20mg/L	3.8×10⁴	1.1×10⁴	7.0×10³	1.8×10³	15	H₂O₂，25mg/L	3.1×10⁴	2.2×10⁴	1.5×10³	2×10²	4
H₂O₂，30mg/L	3.5×10⁴	1.9×10⁴	1.0×10³	82	2	H₂O₂，25mg/L	3.1×10⁴	2.2×10⁴	1.5×10³	2×10²	4
H₂O₂，30mg/L	3.5×10⁴	1.9×10⁴	1.0×10³	82	2	H₂O₂，50mg/L	3.4×10⁴	1.1×10⁴	8.5×10³	13	1

As shown in Table 5 and FIG. 11, when hydrogen peroxide was not added, the initial cell number of E.coli after 1min (3.2X 10)⁴Individual cells/ml) to 1.5X 10⁴Individual cells/ml, 1.2X 10 after 2 minutes⁴Individual cells/ml, 1.8X 10 after 5 minutes³One cell/ml, and 37 cells/ml after 15 minutes, which showed bactericidal efficiencies of 51%, 62.3%, 94.3%, and 99.8%, respectively. When hydrogen peroxide was added in an amount of 20mg/L, the initial cell number of E.coli after 1min (3.8X 10)⁴Individual cell/ml) to 1.1X 10⁴Individual cells/ml, 7.0X 10 after 2 minutes³Individual cells/ml, 1.8X 10 after 5 minutes³One cell/ml, and 15 cells/ml after 15 minutes, inactivated 69.3%, 81.8%, 95.3%, and 99.9% of E.coli cells, respectively. When hydrogen peroxide was added in an amount of 25mg/L, the initial cell number of E.coli after 1min (3.1X 10)⁴Individual cell/ml) to 2.2X 10⁴Individual cells/ml, 1.5X 10 after 2 minutes³One cell/ml, and 4 cells/ml after 15 minutes, which showed bactericidal efficiencies of 92.8%, 95.2%, and 99.98%, respectively. When hydrogen peroxide was added in an amount of 30mg/L, the initial cell number of E.coli after 1min (3.5X 10)⁴Individual cell/ml) to 1.9X 10⁴One cell/ml, 82 cells/ml after 5 minutes, and 2 cells/ml after 15 minutes, which showed 94.4%, 99.7%, and 99.99% bactericidal efficiency, respectively. In addition, when hydrogen peroxide was added in an amount of 50mg/L, the initial cell number of E.coli after 1min (3.4X 10)⁴Individual cell/ml) to 1.1X 10⁴One cell/ml, 13 cells/ml after 5 minutes, and 1 cell/ml after 15 minutes, which showed sterilization efficiencies of 96.6%, 99.96%, and 99.99%, respectively.

<Experimental example 5>measurement of Disinfection efficiency of aquatic bacteria for sprouting of beans

In this test, instead of the buffer containing E.coli, water more practically used for bean sprouting was used, and the disinfection efficiency in water was evaluated. Air was injected into the photocatalytic reactor 10 at a rate of 30L/min and hydrogen peroxide was added in different amounts of 25, 50 and 75 mg/ml. The viability of the bacteria in the water was assessed for 90 min. The results are given in table 6 below and in fig. 12a and 12 b.

[ Table 6]]

Efficiency of disinfection	1min	15min	30min	90min
Efficiency of disinfection	1min	15min	30min	90min	Without addition of H₂O₂	82.9％	99.7％	99.1％	99.5％
H₂O₂，25mg/L	82.6％	99.4％	99.5％	99.9％	Without addition of H₂O₂	82.9％	99.7％	99.1％	99.5％
H₂O₂，25mg/L	82.6％	99.4％	99.5％	99.9％	H₂O₂，50mg/L	88.2％	99.8％	99.9％	99.99％
H₂O₂，75mg/L	91.2％	99.8％	99.99％	Complete disinfection	H₂O₂，50mg/L	88.2％	99.8％	99.9％	99.99％

Water bag for 4 hours of bean sproutingContaining 4.0X 10⁴Individual cells/ml of bacteria. As shown in Table 6 and FIGS. 12a and 12b, when no hydrogen peroxide was added, the initial number of viable bacteria was reduced to 6.8X 10 after 1min³One cell/ml, 123 cells/ml after 15 minutes, showed bactericidal efficiencies of 82.9% and 99.7%, respectively. The number of viable bacteria increased to 343 cells/ml after 30min, but decreased to 220 cells/ml after 90min, showing 99.5% bactericidal efficiency. When hydrogen peroxide was added in an amount of 25mg/L, it was found that the sterilization efficiency was 82.6%, 99.4%, 99.5% and 99.9% after 1, 15, 30 and 90min, respectively, wherein the sterilization efficiency in the initial stage was slightly lower than that without hydrogen peroxide, but after 90min, it increased to a level higher than that without hydrogen peroxide. Furthermore, no reduction in the sterilization efficiency was observed during the sterilization process, although this phenomenon was observed without adding hydrogen peroxide.

However, when hydrogen peroxide was added in an amount of 50mg/L, the sterilization efficiencies were found to be 88.2%, 99.8% and 99.99%, respectively, after 1, 15 and 90 min. When added in an amount of 75mg/L, hydrogen peroxide showed bactericidal activity of 91.2%, 99.8% and 99.99% after 1, 15 and 30min, respectively, and complete inactivation of the bacteria was observed after 90 min.

It was found that the disinfection efficiency for all bacteria was slightly lower than for E.coli alone and the total number of live bacteria was slightly higher than for E.coli alone. However, these results are due to the following reasons. That is, there is a limit to the growth of E.coli in a buffer containing no nutrients, however, the bacteria may continuously proliferate due to the presence of bean-derived organic acids in water. In addition, when hydrogen peroxide is added in amounts higher than 50mg/L, a much higher disinfection efficiency of the bacteria is observed.

<Experimental example 6>measurement of Disinfection efficiency of aquatic fungus for Bean sprouting

The same method as in experimental example 5 was used to evaluate the fungicidal activity against fungi in the water used for bean sprouting. The results are given in table 7 below and in fig. 13a and 13 b.

[ Table 7]]

Efficiency of disinfection	1min	15min	90min
Efficiency of disinfection	1min	15min	90min	Without addition of H₂O₂	69.3％	99.6％	99.7％
H₂O₂，25mg/L	71.1％	99.5％	99.88％	Without addition of H₂O₂	69.3％	99.6％	99.7％
H₂O₂，25mg/L	71.1％	99.5％	99.88％	H₂O₂，50mg/L	90％	Complete disinfection	-
H₂O₂，75mg/L	93.7％	Sterilizing completely after 4min		H₂O₂，50mg/L	90％	Complete disinfection	-

The water used during the 4 hours of bean germination contained 1.0X 10⁴Individual cells/ml of fungus. As shown in table 7 and fig. 13, the fungicidal efficiencies were 69.3%, 99.6% and 99.7% after 1, 15 and 90 minutes, respectively, when no hydrogen peroxide was added. When added in an amount of 25mg/L, hydrogen peroxide shows fungicidal efficiencies of 71.1%, 99.5% and 99.88% after 1, 15 and 90 minutes, respectively. When added in an amount of 50mg/L, hydrogen peroxide shows a fungicidal efficiency of 90% and 99.8% after 1 and 10 minutes, respectively, and completely inactivates the fungi in water after 15 min. When hydrogen peroxide was added in an amount of 75mg/L, the fungicidal efficiency was found to be 93.7% after 1min, and no viable fungi were observed after 4 min.

<Comparative example 1>In the use of fixed TiO₂Measurement of the Disinfection efficiency with porous beads or glass beads

In this test, muscovite and glass beads of high porosity were used as TiO₂An immobilized carrier material. To fix TiO₂Porous beads of, i.e. immobilising TiO₂The disinfection efficiency of the dolomite mother beads and the coating TiO₂The disinfection efficiency of the glass beads of (1) was compared, wherein TiO₂As photocatalyst in the use of immobilized TiO₂After filling the photocatalytic reactor 10 with the porous beads or glass beads, the reaction was carried out by adding air at a rate of 30L/min and exposing the mixture toultraviolet raysColi for 15min and evaluated for viability. The results are given in table 8 below and in fig. 5a and 5 b.

[ Table 8]]

Number of viable cells (cells) /ml)

0min

1min

15min

Porous bead	7.2×10³	370	1
Porous bead	7.2×10³	370	1	Glass bead	7.1×10³	357	13

As shown in table 8 and fig. 5a and 5b, in which TiO was to be immobilized₂The disinfection efficiency of the dolomite mother beads and the coating TiO₂When using coated TiO, the disinfection efficiency of the glass beads of (1) was compared₂The initial cell number of E.coli (7.1X 10) in the case of the glass beads of (4)⁴Individual cells/ml) decreased to 357 cells/ml after 1min and 13 cells/ml after 15min, showing 95% and 99.8% bactericidal efficiency, respectively.

When using fixed TiO₂The number of viable bacteria in the muscovite mother beads is from 7.2X 10 after 1min³The reduction of one cell/ml to 370 cells/ml, 1 cell/ml after 15min, showed 95% and 99.9% bactericidal efficiency, respectively, indicating that the TiO was immobilized₂The disinfection efficiency of the dolomite mother beads is slightly higher than that of the coated TiO₂The glass beads of (1).

In addition, TiO on glass beads was found₂Gradually desorbed from the surface of the glass beads by a continuous stream of water, thus requiring the use of TiO₂The used glass beads are subjected to a new coating step. In contrast, TiO, in contrast to glass beads₂The photocatalyst is more easily impregnated into porous beads such as muscovite powder with high porosity. Furthermore, the TiO is fixed by treatment at high temperature₂Porous beads of (3), TiO not observed₂Desorption from the porous beads.

<Comparative example 2>In the presence of H₂O₂Determination of the Disinfection efficiency without exposure to UV light

For comparison, hydrogen peroxide (H) was added₂O₂) And sterilization efficiency with or without exposure to ultraviolet rays, hydrogen peroxide was added to water in an amount of 25mg/L, and the viability of E.coli was evaluated. The results are given in fig. 9.

As shown in FIG. 9, 25mg/L H was added when simultaneously exposed to UV light₂O₂No viable E.coli could be detected after 5min when the sterilization was performed. In contrast, when ultraviolet rays were not supplied, it was found that the sterilization efficiency was only 51% even after 15 min. TheseThe results indicate that excellent disinfection efficiency is achieved not by hydrogen peroxide alone, but by the addition of hydrogen peroxide with simultaneous exposure to ultraviolet light.

INDUSTRIAL APPLICABILITY

As described above, the apparatus for sterilizing water according to the present invention can shorten the time required for water sterilization and improve sterilization efficiency by adding hydrogen peroxide and air. In addition, the device can be made in a small size as needed, thus allowing it to be installed in a narrow place. In addition, the device is easy to remove, thereby facilitating its cleaning. Therefore, devices for water disinfection are very useful in inactivating or destroying microorganisms and organic contaminants in water.

Claims

1. A device for water disinfection by photocatalytic reaction, comprising:

a first reservoir for storing water to be treated;

a photocatalytic reactor comprising porous beads on which a photocatalyst is immobilized and equipped with a water inlet, a water outlet, an ultraviolet lamp and an air inlet tube;

a water supply pump connected between the first water storage tank and the photocatalytic reactor;

the air is led into an air pump of the photocatalytic reactor through an air inlet pipe; and

a second water reservoir for storing disinfected water from said photocatalytic reactor treatment.

2. The apparatus according to claim 1, wherein each of said water inlet and said water outlet is equipped with a filter to prevent said photocatalyst-immobilized porous beads from flowing out of said photocatalytic reactor.

3. The apparatus according to claim 1, wherein the water inlet and the water outlet are installed at upper and lower portions of the photocatalytic reactor, respectively, and are positioned diagonally to each other to increase residence time of water in the interior of the photocatalytic reactor.

4. The device according to claim 1, wherein said photocatalyst is TiO₂。

5. The device according to claim 1, wherein said porous beads are made of muscovite and have a diameter of 6-10 mm.

6. The apparatus according to claim 1, wherein said ultraviolet lamps are axially installed in said photocatalytic reactor at regular intervals.

7. The apparatus according to claim 1, wherein the ultraviolet lamp is installed in such a manner that an electrode of the ultraviolet lamp protrudes to the outside of the photocatalytic reactor.

8. The apparatus of claim 1, wherein the inlet pipe is installed at a lower portion of the photocatalytic reactor and is finely perforated at regular intervals.

9. The apparatus of claim 1, wherein the photocatalytic reactor has a sealing structure that sandwiches the O-ring between the inner frame and the outer frame.

10. The apparatus according to claim 1, wherein the photocatalytic reactor is equipped with a sealed transparent acrylic window to allow a user to observe the inside of the reactor with naked eyes.

11. The apparatus of claim 1, wherein the photocatalytic reactor is designed such that two or more reactors are arranged in parallel.

12. A method for water disinfection by photocatalytic reaction using the device of claim 1, comprising the steps of: adding hydrogen peroxide into the polluted water;

introducing the contaminated water with the hydrogen peroxide added thereto into a photocatalytic reactor containing porous beads on which a photocatalyst is immobilized;

injecting air into the photocatalytic reactor; and

ultraviolet light is applied to the photocatalytic reactor.

13. The method according to claim 12, wherein the hydrogen peroxide is added to the water in an amount of 25-50 mg/L.