WO2005026063A1

WO2005026063A1 - Circular aerator and wastewater treatment apparatus using the same

Info

Publication number: WO2005026063A1
Application number: PCT/KR2004/002339
Authority: WO
Inventors: Sungwoo Ha
Original assignee: Sungwoo Ha
Priority date: 2003-09-15
Filing date: 2004-09-15
Publication date: 2005-03-24

Abstract

The present invention provides a circular aerator of a water treatment apparatus comprises an aeration pipe; a bubble head generating bubbles by discharging air supplied through an air pipe in the aeration pipe ; a transportation pipe connected to the aeration pipe and forming a passage in which sludge in wastewater rising on the bubbles is passed connected to the aeration pipe ; and a scatter guiding plate having wastewater returning through return holes of the aeration pipe bumped and then returned scattering into the self-oxidation tank to improve turbulent flow. According to such a configuration, since turbulent flow is increased in wastewater held in a self-oxidation tank, air is promptly supplied thereby reducing purification time.

Description

Description CIRCULAR AERATOR AND WASTEWATER TREATMENT APPARATUS USING THE SAME Technical Field

[1] The present invention relates to a circular aerator for purifying waste water and a wastewater treatment apparatus using the same. Background Art

[2] In general, an aerator removing sludge in wastewater rising on bubbles formed by air supply is widely used to purify and treat wastewater. FIG. 1 is an example of such an aerator and shows a configuration, which has ever been disclosed in Korean Registered Patent Publication No. 242777, according to the related art. As shown in FIG. 1, the related art aerator comprises an aeration tank 1 in which wastewater flowed through a supply pipe 7; an aeration pipe 2 provided in the aeration tank 1 and forming return holes 4 and suck-in holes 3 on upper and lower portions, respectively; and a bubble head 6 provided in the aeration pipe 2 and for discharging air flowed in through an air pipe 5 in the aeration pipe 2 to generate bubbles.

[3] In this configuration, if the bubble head 6 begins to discharge air, a fast speed of a current in the direction of rising along with bubble generation in the aeration pipe 2 is formed, whereby a transmural pressure difference of the aeration pipe 2 occurs. Then, wastewater outside of the aeration pipe 2 is rapidly sucked inside the aeration pipe 2 through the suck-in holes 3; sludge contained in such wastewater sucked in rises on bubbles formed by the bubble head 6; the sludge is transferred into a sludge storage tank through a predetermined air pipe (not shown) connected to an upper portion of the aeration pipe and removed; and then the wastewater from which the sludge is removed is returned to the aeration tank 1 through the return holes 4. Accordingly, if such a process is repeated, sludge in wastewater is removed and oxygen in air discharged through the bubbles head 6 is supplied to wastewater thereby improving biochemical oxygen demand or the like and gradually purifying quality of water.

[4] However, such a configuration has a disadvantage that oxygen is not supplied rapidly into the whole wastewater. In other words, since a circulation is accomplished, which wastewater into which oxygen is supplied through the return holes 4 formed on a side of an upper portion of the aeration pipe 2 is quietly flowed out and the wastewater is sucked in again through the suck-in holes 3 formed on a side of a lower portion thereof, a quiet convention current is formed only around the aeration tank 1, thereby taking a considerable time to sufficiently supply oxygen into the whole wastewater. Further, a multi-step wastewater treatment in which wastewater is sequentially passed through each aeration tank 1 by providing this several aeration tanks is generally introduced However, as described above, if oxygen is not supplied rapidly and sufficiently into each of the aeration tanks, a charge that the number of aeration tanks is increased in order to prolong a contact time with oxygen is imposed Moreover, since sludge which is not oxidized yet is contained in wastewater returned to the aeration tank 1 through the return holes 4, an oxidative process on bubbles is passed through repeating the circulation in order to remove the sludge, thereby taking a considerable time to remove the sludge. In addition, such a configuration has a disadvantage that the amount of wastewater circulated through the return holes 4 cannot be actively controlled In other words, in order to sufficiently remove sludge in wastewater, it is necessary that the amount of wastewater circulated through the return holes 4 is increased, thereby ensuring a sludge removing time, while in order to more rapidly supply oxygen into wastewater, the amount of wastewater circulated through the return holes 4 is increased, thereby rapidly circulating a large amount of wastewater in the aeration tank 1. However, since the related art configuration described above has no means to control this, there can be nothing to cope with. Since the related art configuration also has no means to purify and treat except a bubble supply, there is a limit to increase the speed of purification. Disclosure of Invention Technical Problem

[5] To solve the above and/or other problems, the present invention provides a circular aerator and a wastewater treatment apparatus improved to rapidly supply oxygen into wastewater.

[6] Also, the present invention provides a circular aerator and a wastewater treatment apparatus improved to remove sludge from wastewater and to rapidly supply oxygen into wastewater.

[7] Also, the present invention provides a wastewater treatment apparatus improved to prevent water quality deterioration of influent water by wastewater inputted again after removing sludge.

[8] Also, the present invention provides a circular aerator improved to control the amount of wastewater circulated if necessary and to enhance the speed of purification higher than an existing circular aerator. Technical Solution

[9] According to an aspect of the present invention, the present invention provides a circular aerator comprising an aeration pipe provid ed in a self-oxidation tank in which wastewater is held, through which wastewater is flowed in and on one side of which return holes for returning the inflow wastewater to the self-oxidation tank are formed; a bubble head generating bubbles by discharging air supplied through a predetermined air pipe in the aeration pipe; a transportation pipe connected to the aeration pipe and forming a passage in which sludge in wastewater rising on the bubbles is passed; and

[10] turbulent flow increasing means for increasing turbulent flow in wastewater returned through the return holes.

[11] According to another aspect of the present invention, the present invention provides a circular aerator comprising an aeration pipe provid ed in a self-oxidation tank in which wastewater is held, through which wastewater is flowed in and on one side of which return holes for returning the inflow wastewater to the self-oxidation tank are formed; a bubble head generating bubbles by discharging air supplied through a predetermined air pipe in the aeration pipe; a transportation pipe connected to the aeration pipe and forming a passage in which sludge in wastewater rising on the bubbles is passed; turbulent flow increasing means for increasing turbulent flow in wastewater returned through the return holes; and a base net floated on the upper layer of wastewater in the self-oxidation tank, collecting sludge contained in wastewater returned through the return holes and decomposing the sludge using aerobic bacteria.

[12] According to further another aspect of the present invention, the present invention provides a circular aerator comprising an aeration pipe provid ed in a self-oxidation tank in which wastewater is held, through which wastewater is flowed in and on a side wall of which a first return hole for returning the inflow wastewater to the self- oxidation tank are formed; a bubble head generating bubbles by discharging air supplied through a predetermined air pipe in the aeration pipe; and a first openness control means for varying openness of the first return hole.

[13] In this regard, the first openness control means comprises a first rotating member which is provided with a long hole matching the first return hole and provid ed available for rotating on a side wall of the aeration pipe so that openness by matching the first return hole to the long hole is varied in accordance with a rotation angle.

[14] Also, it is preferred that a cohesive agent input means and a surfactant input means for inputting a cohesive agent and a surfactant into the aerator pipe are further comprised, respectively. [15] According to an aspect of the present invention, the present invention provides a wastewater treatment apparatus comprising a plurality of self-oxidation tanks having spaces divided by predetermined partition walls; a plurality of circular aerators for purifying wastewater, the circular aerators provid ed in each of the self-oxidation tanks; and a sludge storage tank holding sludge removed by the circular aerator; and wherein through holes for transferring wastewater is formed on each of the partition walls and each of the through holes is arranged in zigzags in order not to directly confront each through hole of adjacent partition walls.

[16] According to another aspect of the present invention, the present invention provides a wastewater treatment apparatus comprising a plurality of self-oxidation tanks having spaces divided by predetermined partition walls; a plurality of circular aerators for purifying wastewater, the circular aerators provid ed in each of the self- oxidation tanks; and a sludge storage tank holding sludge removed by the circular aerator; and wherein through holes for transferring wastewater is formed on each of the partition walls and each of the through holes is arranged in zigzags in order not to directly confront each through hole of adjacent partition walls; and wherein the circular aerator comprises an aeration pipe provid ed in the self-oxidation tank, through which wastewater is flowed in and on one side of which return holes for returning the inflow wastewater to the self-oxidation tank are formed; a bubble head generating bubbles by discharging air supplied through a predetermined air pipe in the aeration pipe; a transportation pipe connected to the aeration pipe and forming a passage in which sludge in wastewater rising on the bubbles is passed; turbulent flow increasing means for increasing turbulent flow in wastewater returned through the return holes; and a base net floated on the upper layer of wastewater in the self- oxidation tank, collecting sludge contained in wastewater returned through the return holes and decomposing the sludge using aerobic bacteria.

[17] According to further another aspect of the present invention, the present invention provides a wastewater treatment apparatus comprising a plurality of self-oxidation tanks having spaces divided by predetermined partition walls; a plurality of circular aerators for purifying wastewater, the circular aerators provid ed in each of the self- oxidation tanks; a sludge concentration tank for holding sludge removed from the wastewater and concentrating the sludge; a first flow passage in which wastewater is guided to be purified sequentially passing through each of the self-oxidation tanks; a second flow passage in which sludge of wastewater removed by circular aerators in each of the self-oxidation tanks is fed back into at least one of self-oxidation tanks located more upstream than the corresponding self-oxidation tank from the viewpoint of the direction of movement of the first U-shaped pipe; and a third flow passage wherein sludge removed by the circular aerator in a self-oxidation tank in which wastewater is flowed first of all is transferred to the sludge concentration tank.

[18] In this regard, the second flow passage comprises a line for feeding sludge which is removed from the corresponding self-oxidation tank back to an upstream self- oxidation tank just prior thereto.

[19] Also, according to still another aspect of the present invention, it is preferred that a plurality of the self-oxidation tanks comprise first, second, third, and fourth self- oxidation tanks; and wherein the second flow passage comprises a line for feeding back from the second self-oxidation tank to the first self-oxidation tank, a line for feeding back from the third self-oxidation tank to the first self-oxidation tank and a line for feeding back from the fourth self-oxidation tank to the second self-oxidation tank. Advantageous Effects

[20] As described above, the circular aerator and the wastewater treatment apparatus according to the present invention has the following effects.

[21] First, using the scatter guiding plate, turbulent flow in wastewater circulated in an aeration pipe of a circular aerator is maximized, thereby rapidly supplying oxygen into the wastewater and reducing a purification time.

[22] Second, a bubble head comprises a configuration detachably combined with an air pipe, thereby easily replacing only the bubble head if necessary.

[23] Third, an expanding portion is provided in the middle of an aeration pipe to generate big bubbles, thereby easily removing big sludge.

[24] Fourth, through holes of partition walls located among a plurality of self-oxidation tanks are arranged in zigzags, thereby increasing purification efficiency by lengthening flow passage of wastewater.

[25] Fifth, residual sludge in wastewater is decomposed and treated using aerobic bacteria, thereby more higher increasing removal efficiency of the sludge.

[26] Sixth, sludge removed from a corresponding self-oxidation tank is fed back into a self-oxidation tank located upstream thereof, thereby promoting oxidization of the sludge to prevent water quality deterioration of wastewater. Therefore, quality of water in final treatment water can be enhanced

[27] Seventh, the amount of wastewater circulated through return holes is controlled, thereby obtaining desired result such as sludge removal, rapid oxygen supply or the like can be obtained [28] Eighth, a sludge cohesive agent and a sludge surfactant are inputted to an aeration pipe, thereby more rapidly guiding purification work. [29] Ninth, openness of a return hole is automatically controlled, thereby more easily controlling purification work. Description of Drawings [30] FIG. 1 is a vertical cross-sectional view of a circular aerator introduced to the related art wastewater treatment apparatus; [31] FIG. 2 is a lateral cross-sectional view showing a circular aerator and a wastewater treatment apparatus according to a first embodiment of the present invention; [32] FIG. 3 is a vertical cross-sectional view of the circular aerator shown in FIG. 2;

[33] FIG. 4 is an enlarged perspective view of a part of the scatter guiding plate in FIG. 3; [34] FIG. 5 is an enlarged perspective view of a part of the bubble head shown in FIG. 3; [35] FIG. 6 is a view showing a transformable example of the circular aerator shown in FIG. 2; [36] FIG. 7 is a vertical cross-sectional view showing the wastewater treatment apparatus according to a second embodiment of the present invention; [37] FIG. 8 is a plane view showing the wastewater treatment apparatus according to a third embodiment of the present invention; [38] FIG. 9 is a plane view showing the wastewater treatment apparatus according to a fourth embodiment of the present invention; [39] FIG. 10 is a plane view showing the wastewater treatment apparatus according to a fifth embodiment of the present invention; [40] FIG. 11 is a vertical cross-sectional view showing the circular aerator according to the second embodiment of the present invention; [41] FIG. 12 is a perspective view showing the main part of the circular aerator shown in FIG. 11; [42] FIG. 13 is a vertical cross-sectional view showing the circular aerator according to the third embodiment of the present invention; [43] FIG. 14 is a perspective view showing the main part of the circular aerator shown in FIG. 13; [44] FIG. 15 is a perspective view showing the circular aerator according to the fourth embodiment of the present invention; [45] FIG. 16 is a vertical cross-sectional view showing the circular aerator according to the fifth embodiment of the present invention;

[46] FIG. 17 is a perspective view showing the main part of the circular aerator shown in FIG. 16;

[47] FIG. 18 is a vertical cross-sectional view showing the circular aerator according to a sixth embodiment of the present invention;

[48] FIG. 19 is a perspective view showing the main part of the circular aerator shown in FIG. 18; and

[49] FIG. 20 is a perspective view showing the circular aerator according to a seventh embodiment of the present invention. Best Mode

[50] FIG. 2 is a lateral cross-sectional view showing a circular aerator and a wastewater treatment apparatus according to a first embodiment of the present invention.

[51] As shown in FIG. 2, the wastewater treatment apparatus comprises a flow control tank 110 in which wastewater is flowed and stored; a first, second and third self- oxidation tanks 120, 130 and 140 in which the wastewater supplied from the flow control tank 110 is purified and treated; and a sludge storage tank 150 to which sludge removed by purification work from the first, second and third self-oxidation tank 120, 130 and 140. Herein, since the self-oxidation tank is equivalent to the related art aeration pipe, the three self-oxidation tanks in FIG. 2 are shown as an embodiment of the present invention, and not only three self-oxidation tanks but also a plurality of self-oxidation tanks can be arranged to sequentially purify and treat. Reference number, 10a refers to an air input unit for inputting air so that the wastewater in the flow control tank 110 is not rotten.

[52] In this regard, the first, second and third self-oxidation tanks 120, 130 and 140 are divided into each area by main partition walls 112, 122, 132 and 142 and further comprise middle partition walls 121, 131 and 141 dividing each of the areas in half in each of the self-oxidation tanks 120, 130 and 140. Such middle partition walls 121, 131 and 141 form an efficient configuration in which the middle partition walls reduce in half each area of the self-oxidation tanks 120, 130 and 140, whereby the transmural pressure difference of a pipe for flowing in wastewater through the aeration pipe 11 of the circular aerator 10 described below is maximized Further, through holes 112a, 121a, 122a, 131a, 132a, 141a and 142a are formed on each of the partition walls 112, 121, 122, 131, 132, 141 and 142 for transferring wastewater into adjacent areas. This arrangement will be described later. A plurality of circular aerators 10 for purifying and treating wastewater are provid ed in areas divided by each of the partition walls 112, 121, 122, 131, 132, 141 and 142. The circular aerator 10 discharges air supplied through an air pipe 12 from an air blower 190 into wastewater and generates bubbles, thereby removing sludge in the wastewater rising on the bubbles and supplying air into the wastewater.

[53] FIG. 3 shows a vertical cross-sectional view of one circular aerator of such circular aerators 10, the one circular aerator provid ed in a first self-oxidation tank 120 and the rest have configurations like this. Referring to FIG. 3, an aeration pipe 11 of which the lower end floats at a little gap g from the bottom of the self-oxidation tank 120 is provid ed so that wastewater is flowed in the aeration pipe through the gap. A bubble head 13 for discharging air flowed in through an air pipe 12 is provid ed in the aeration pipe 11. In addition, return holes 1 la is formed on a horizontal plane of an upper portion of the aeration pipe 11 so that wastewater is spouted from the inside to the outside of the aeration 11 and returned to the self-oxidation tank 120. A transportation pipe 16 for transporting sludge removed from the wastewater to a sludge storage tank 150 is connected to the upper portion thereof.

[54] In said configuration, if air through the air pipe 12 begins to be supplied, the air is discharged into wastewater flowed in the aeration pipe 11 through air diffusing holes 13a of the bubble head 13. Then, bubbles in the wastewater are generated and the bubbles rise to the upper direction of the aeration pipe 11. In this process, sludge mixed in the wastewater sticks to the bubbles and rises together therewith. Finally, the sludge is discharged into a sludge storage tank 150 through the transportation pipe 16 connected to the upper portion of the aeration pipe 11. Further, the wastewater is discharged through the return holes 11a rising along with rising of the bubbles and a part of the wastewater is flowed in the aeration pipe again through the gap g by pressure difference formed by a generation of current speed In this process, oxygen contained in air is supplied and spread into the wastewater whereby quality of water is gradually improved Meanwhile, in order to rapidly supply such air, the present invention comprises means for inducing to increase turbulent flow in wastewater returning to the self-oxidation tank 120 through the return holes 1 la. In other words, as shown in FIGS 3 and 4, a scatter guiding plate 14 in the shape of a funnel is provid ed in a location confronting the return holes 11a, whereby wastewater discharged through the return holes 1 la is bumped against the scatter guiding plate 14 and then scattered into the self-oxidation tank 120. The reason why the return holes 1 la is formed not on a side of the aeration pipe 11 but on a horizontal plane 1 lb of an upper portion thereof is to maximize an effect that wastewater is not quietly flowed out to the side but spouted upside and scattered just on rising flow. Thus, the turbulent flow in the self- oxidation tank 120 is increased, whereby air is rapidly supplied and spread into the whole wastewater. Time for purifying wastewater is decreased that much. In addition, a rotating plate 15 on which long holes 15a are formed as a means for controlling openness of the return holes 11a, that is, extent of the openness is provid ed available for rotating. The long holes 15a is matched to the return holes 11a and the openness in which wastewater can be spouted matching the return holes 1 la to long holes 15a is changed in accordance with a rotation angle. Accordingly, if necessary, the amount of wastewater returned from the aeration pipe 11 can be controlled by rotating the rotating plate 15.

[55] Further, the aeration pipe 11 comprises an expanding portion 1 lc in which an inner passage is suddenly broadened rising toward the transportation pipe 16. The expanding portion l ie has a function to increase size of bubbles rising. In other words, if the inner passage is suddenly broadened, pressure falls, thereby expanding bubbles. Thus, the bubbles increased at size easily may transport big sludge thereon, thereby enhancing efficiency of removing sludge.

[56] As shown in FIG. 5, the bubble head 13 is detachably combined with the air pipe 12. In other words, since screws 13b and 12a gearing with each other on both sides, fixing and unfixing by tightening or loosening them is carried out. Since if purification treatment work is operated for a long time, air supply can be interrupted due to the sludge sticking to the upper side and piling up thereon, the bubble head 13 is detachably combined with the air pipe 12 in order to separate and replace only the bubble head 13 for this case. Moreover, the reason why the air diffusing holes 13a is formed not on the upper side but on the side is that impediment occurring by sludge sticking is minimized

[57] Further, the transportation pipe 16 comprises a bending portion 16a bent in the shape of reverse U as shown in FIG. 3. This is a means for preventing the sludge removed from the aeration pipe 11 from returning to the aeration pipe 11 flowing backward and the bending portion 16a bent in the shape of reverse U as above is formed, whereby the sludge has difficulty in flowing backward through the bending portion 16a.

[58] As described above, wastewater held in each of the self-oxidation tanks 120, 130 and 140 by the circular aerators 10 is gradually purified and such purification work is continuously operated during wastewater flows from the first self-oxidation tank 120 to the third self-oxidation tank 140. The wastewater finally passing through the third self-oxidation tank 140 flows out a wastewater treatment apparatus passing through a disinfection tank 170 and a discharge tank 180. Since if the sludge stored in the sludge storage tank 150 is left as it is, phosphorus can be generated in an anaerobic condition, it is preferred the sludge is dehydrated and then removed as quickly as possible. However, first-rate water of the sludge storage tank 150 is flowed in the flow control tank 110 again and then goes through purification work again.

[59] Meanwhile, in the present wastewater treatment apparatus, the through holes 112a, 121a, 122a, 131a, 132a, 141a and 142a formed for passing wastewater through the partition walls 112, 121, 122, 131, 132, 141 and 142 and transferring wastewater into each of the self-oxidation tanks 120, 130 and 140 are arranged to increase purification efficiency. In other word, as shown in FIG. 2, a through hole of one partition wall is formed on the left side and a through hole of another partition wall is arranged on the right side, whereby the through holes 112a, 121a, 122a, 131a, 132a, 141a and 142a are arranged in zigzags on the whole. In this way, since each of the through holes 112a, 121a, 122a, 131a, 132a, 141a and 142a do not directly confront each other, The U- shaped passage through which wastewater passes to go over the partition walls 112, 121, 122, 131, 132, 141 and 142 becomes lengthening as shown in a dotted arrow. Accordingly, time for purifying wastewater is sufficiently ensured, whereby it is favorable to increase purification efficiency.

[60] Further, it is preferred that the air supplied through the bubble head 13 is air heated in the range of 30 to 50 °C because ammonia gas generated from wastewater shows an air stripping reaction reacting to hot air, thereby removing a bad smell. In addition, nitrogen in wastewater is decomposed and treated in accordance with a denitrification reaction formula of 2NO + organic carbon → N + 2OH + 4H O. As shown in FIG. 3 2 2 6, ozone (O3) is supplied together with air through the air pipe 12, thereby having a disinfection effect to wastewater. [61] FIG. 7 is a vertical cross-sectional view showing the wastewater treatment apparatus according to a second embodiment of the present invention. In the present embodiment, the circular aerator and the wastewater treatment apparatus as almost same as those of the first embodiment described above are introduced Merely, it is different that a base net 200 is floated on an upper layer of wastewater in order to decompose residual sludge using aerobic bacteria in wastewater. In other words, in the wastewater in the self-oxidation tank 120, the upper layer adjacent to air becomes an aerobic environment, the lower layer becomes an anaerobic environment, and the middle layer therebetween becomes an anoxic layer, respectively. Thus, the upper layer becomes a very good condition in which aerobic bacteria increase. Accordingly, if many base nets 200 are floated on the upper layer, sludge contained in wastewater returning to the self-oxidation tank 120 through the return holes 1 la is collected in the base nets 200 and this sludge is easily decomposed by microorganisms increased in an aerobic environment of the upper lay of wastewater. Therefore, sludge which is not oxidized rising on bubbles is collected in the base net 200 and decomposed by aerobic bacteria, thereby increasing efficiency of removing sludge.

[62] FIG. 8 is a plane view showing the wastewater treatment apparatus according to a third embodiment of the present invention. As shown in FIG. 8, the wastewater treatment apparatus of the present embodiment comprises a flow control tank 350 in which wastewater is flowed and stored; a first, second, third, fourth self-oxidation tanks 310, 320, 330 and 340 in which the wastewater in the flow control tank 350 is supplied and sequentially purified and treated; and a sludge concentration tank 360 in which sludge removed from the wastewater in the first, second, third and fourth self- oxidation tanks 310, 320, 330 and 340by purifying work is held The four self- oxidation tanks in FIG. 8 are shown as an embodiment of the present invention and not only four self-oxidation tanks but also a plurality of self-oxidation tanks can be arranged to sequentially purify and treat.

[63] In this regard, the first, second and third self-oxidation tanks 310, 320, 330 and 340 are divided into each area by partition walls 311, 321, 331 and 341. Further, through holes 31 la, 321a, 331a and 341a are formed on each of the partition walls 311, 321, 331 and 341 for transferring wastewater into adjacent areas. This arrangement will be described later. A plurality of circular aerators 10 for purifying and treating wastewater are provid ed in areas divided by each of the partition walls partition walls 311, 321, 331 and 341. The circular aerator 10 is substantially the same configuration as that of the first embodiment shown in FIG. 3 and discharges air into wastewater and generates bubbles, thereby removing sludge in the wastewater rising on the bubbles and supplying air into the wastewater. As presented in the second embodiment described above, base nets for decomposing residual sludge using aerobic bacteria can be floated on the upper layer of wastewater. In FIG. 8, such base nets are not shown in order to show well a flow passage of the wastewater, but it is considered that the base nets is floated on the upper layer.

[64] As described above, wastewater held in each of the self-oxidation tanks 310, 320, 330 and 340 by the circular aerators 10 is gradually purified and such purification work is continuously operated during wastewater flows from the first self-oxidation tank 310 to the fourth self-oxidation tank 340. The wastewater finally passing through the fourth self-oxidation tank 340 flows out a wastewater treatment apparatus passing through a disinfection tank 370 and a discharge tank 380.

[65] However, in the wastewater treatment apparatus of the present embodiment, sludge removed by the circular aerator 10 in each of the self-oxidation tanks 310, 320, 330 and 340 is not immediately flowed in the sludge concentration tank 360 and is fed back into the self-oxidation tanks 310, 320 and 330 located just adjacent upstream. In other words, a flow passage (1; hereinafter, referred to as 'the first flow passage') in which wastewater flows toward the discharge tank 380 being purified and treated is formed to sequentially flow through the through holes 31 la, 321a, 331a and 341a of each of the partition walls 311, 321, 331 and 341. However, sludge removed by the circular aerator 10 is fed back along with a flow passage (2; hereinafter, referred to as 'the second flow passage') for flowing into the self-oxidation tank located just adjacent upstream. Thus, the sludge removed from the fourth self-oxidation tank 340 is fed back into the third self-oxidation tank 330; the sludge removed from the third self- oxidation tank 330 is fed back into the second self-oxidation tank 320; the sludge removed from the second self-oxidation tank 320 is fed back into the first self- oxidation tank 310; and only the sludge removed from the first self-oxidation tank 310 is flowed in the sludge concentration tank 360 through the third flow passage 303. Also, the sludge deposited in the sludge concentration tank 360 is regularly flowed into the sludge storage tank 390, and first-rate water in the sludge concentration tank 360 is fed back into the flow control tank 350 and then goes through purification work again. Accordingly, since the sludge removed from each of the self-oxidation tanks 320, 330 and 340 except the first self-oxidation tank 310 is not immediately flowed in the sludge concentration tank 360 and fed back into the self-oxidation tank located adjacent upstream, the sludge finally flowed in the sludge concentration tank 360 is mostly the sludge going though various steps of oxidization process described above. Therefore, particles of the sludge flowed in the sludge concentration tank 360 become very small and quality of water returned to the self-oxidation tank through the flow control tank 350 is improved in comparison with the related art.

[66] In other words, wastewater sequentially flows from the first self-oxidation tank 310 to the fourth self-oxidation tank 340 through the first flow passage 301 and then is finally discharged On the contrary, sludge sequentially flows from the fourth self- oxidation tank 340 to the first self-oxidation tank 310 through the second flow passage 302 and then is finally flowed in the sludge concentration tank 360 through the third flow passage 303. In this process, oxidization of the sludge is repeatedly progressed, thereby controlling deterioration of quality of water in wastewater returned to the self- oxidation tank.

[67] Meanwhile, the through holes 31 la, 321a, 331a and 341a of the partition walls 311, 321, 331 and 341 forming the first flow passage 301 are arranged to increase purification efficiency. In other word, as shown in FIG. 2, a through hole of one partition wall is formed on the left side and a through hole of another partition wall is arranged on the right side, whereby the through holes 311a, 321a, 331a and 141a are arranged in zigzags on the whole. In this way, since each of the through holes 31 la, 321a, 331a and 341a do not directly confront each other, The U-shaped passage through which wastewater passes to go over the partition walls 311, 321, 331 and 341 becomes lengthening as shown in a dotted arrow. Accordingly, time for purifying wastewater is sufficiently ensured, whereby it is favorable to increase purification efficiency.

[68] Further, it is preferred that an exit of the transportation pipe 16 forming the second flow passage 302 is arranged on the opposite side of the through hole connected from the corresponding self-oxidation tank to downstream side. In other words, if the through hole of the corresponding self-oxidation tank connected to the self-oxidation on the downstream side is formed on the left side, the exit of the transportation pipe 16 in which sludge is fed back from the self-oxidation tank on the downstream side to the corresponding self-oxidation tank is arranged on the right side. This provides an effect of preventing sludge or the like discharged from the exit of the transportation pipe 16 from being fed back into the self-oxidation tank just on the downstream side through the through holes 311a, 321a and 331a.

[69] Accordingly, the number of oxidization treatment of sludge is increased, thereby controlling deterioration of quality of water in wastewater flowed in and improving quality of final treated water as a result.

[70] FIG. 9 is a plane view showing the wastewater treatment apparatus according to a fourth embodiment of the present invention. A basic configuration and function is the same as that of the wastewater treatment apparatus shown in the third embodiment. Merely, in the present embodiment, the second flow passage 402 for feeding back sludge is formed differently from FIG. 8 In other words, the third embodiment has a configuration in which the sludge removed from the corresponding self-oxidation tank is fed back into the self-oxidation tank just adjacent upstream side, while the present embodiment has the second flow passage 402 for feeding back the third and fourth self-oxidation tanks 330 and 340 into the self-oxidation tank of the two steps ahead Thus, the sludge removed from the fourth self-oxidation tank 340 is fed back into the second self-oxidation tank 320; the sludge removed from the third self-oxidation tank 330 is fed back into the first self-oxidation tank 310; the sludge removed from the second self-oxidation tank 320 is fed back into the first self-oxidation tank 310; and the sludge removed from the first self-oxidation tank 310 is flowed in the sludge concentration tank 360 through the third flow passage 303. This shows that treatment time may be shortened by feeding back skipping over a few steps although an exit for feeding back may be the self-oxidation tank of just the previous step. Accordingly, deterioration of quality of water in wastewater is controlled by the wastewater treatment apparatus according to the present embodiment, thereby improving quality of water in final treatment water.

[71] Next, FIG. 10 is a plane view showing the wastewater treatment apparatus accordin g to a fifth embodiment of the present invention. A basic configuration and function is the same as that of the wastewater treatment apparatus shown in the third and fourth embodiments. Merely, in the present embodiment, the second flow passage 502 for feeding back sludge is formed differently. In other words, the present embodiment has the second flow passage 502 for feeding back all the second, third and fourth self- oxidation tanks 320, 330 and 340 into the first self-oxidation tank 310. In this way, since the sludge is fed back from the fourth self-oxidation tank 340 in which the wastewater is almost final treatment water to the first self-oxidation tank 310, treatment time is shortened Also, a charge for oxidization treatment of the sludge in the first self-oxidation tank 310 is a little decreased Accordingly, deterioration of quality of water in wastewater is controlled by the wastewater treatment apparatus according to the present embodiment, thereby improving quality of water in final treatment water.

[72] By this time, a configuration of the whole wastewater treatment apparatus is mainly described, while transformable embodiments from the circular aerator of the first embodiment shown in FIGS 3 and 4 will be described, hereinbelow.

[73] First, FIGS 11 and 12 show the circular spread of the second embodiment. Referring to FIGS 11 and 12, an aeration pipe 20 of which the lower end floats at a little gap g from the bottom of the self-oxidation tank 100 is provid ed so that wastewater is flowed in the aeration pipe through the gap. A bubble head 22 for discharging air flowed in through an air pipe 21 is provid ed in the aeration pipe 20. In addition, return holes 20a is formed on a side of the aeration pipe 20 so that wastewater is spouted from the inside to the outside of the aeration pipe 20 and returned to the self-oxidation tank 120. A transportation pipe 23 for transporting sludge removed from the wastewater to a sludge storage tank (not shown) is connected to the upper portion thereof. Further, the cohesive agent input means for inputting a cohesive agent to the aeration pipe and promoting sludge cohesion in the wastewater comprises a cohesive agent storing tank 25b in which a cohesive agent is stored; a cohesive agent input pipe 25a connecting the cohesive agent storing tank 25b and the aeration pipe 20; a supply pump 25c supplying a cohesive agent through the cohesive agent input pipe 25 a. Moreover, the surfactant input means for activating bubble generation in the aeration pipe 20 comprises a surfactant storing tank 26b in which a surfactant is stored, a surfactant input pipe connecting the surfactant storing tank 26b and the aeration tank 20, and a supply pump 26c supplying a surfactant through the surfactant input pipe 26a. [74] In said configuration, if air through the air pipe 21 begins to be supplied, the air is discharged into wastewater flowed in the aeration pipe 20 through air diffusing holes 22a of the bubble head 20. Then, bubbles in the wastewater are generated and the bubbles rise to the upper direction of the aeration pipe 20. In this process, sludge mixed in the wastewater sticks to the bubbles and rises together therewith. Finally, the sludge is discharged into a sludge storage tank through the transportation pipe 23 connected to the upper portion of the aeration pipe 20. Further, the wastewater is discharged through the return holes 20a rising along with rising of the bubbles and a part of the wastewater is flowed in the aeration pipe again through the gap g by pressure difference formed by a generation of current speed In this process, oxygen contained in air is supplied and spread into the wastewater whereby quality of water is gradually improved Also, at the same time when bubbles are supplied, a cohesive agent is inputted to the aeration pipe 20 through the cohesive agent input pipe 25a in the cohesive agent input means. As such cohesive agent, any of high molecular cohesive agents usually classified into an anionic system, a nonionic system and a cationic system can be used For example, polyacrylamide may be used, and it is preferred that in order to prevent a pipe from being clogged, the cohesive agent is used storing in a condition of being diluted with water. Such cohesive agent promotes cohesion of sludge rising on bubbles, thereby more rapidly guiding purification work. An experiment shows that if a cohesive is inputted, time taken wastewater to be purified by the desired level is reduced below half rather than a case that the cohesive is not inputted [75] Further, in the surfactant input means, a surfactant is inputted to the aeration pipe 20 through the surfactant input pipe. It is preferred that an anionic surfactant such as sodium alkylsurfate, normal acyclic alkylbenzen or sodium sulfonic aied Such surfactant activates bubbles occurring in the aeration pipe 20, thereby helping purification work proceed rapidly.

[76] In this case, it is preferred that in the point for connecting the cohesive agent input pipe 25a to the aeration pipe 20 of the surfactant input pipe 26a, the connection of the cohesive agent input pipe 25a is arranged in the upper position and the connection of the surfactant input pipe 26a is arranged in the lower position as shown in FIG. 11. The reason is that if the connection of the cohesive agent input pipe 25a is located in the lower position, sludge is cohered in the lower position of the aeration tank 20, whereby the sludge has difficulty in rising toward the aeration pipe 20. Also, if the connection of the surfactant input pipe 26a is located in the upper position, time for guiding bubbles occurring in the aeration pipe 20. In the present embodiment, the cohesive agent input means and the surfactant input means are provided with each separate supply pumps 25c and 26c, but it is possible that this are configured integrating the supply pumps.

[77] Meanwhile, in the outer circumference of the aeration pipe 20 on which the return hole 20a is formed as shown in FIG. 12, a rotating member 24 on which long holes 24a are formed as a means for controlling openness of the return holes 20a, that is, extent of the openness is provid ed available for rotating along with guard rails. The long holes 24a is matched to the return holes 20a and the openness in which wastewater can be spouted matching the return holes 20a to long holes 24a is changed in accordance with a rotation angle of the rotating plate 24. Accordingly, if necessary, the amount of wastewater returned from the aeration pipe 20 can be controlled by rotating the rotating member 24. Reference number, 24b refers to a tightening screw for fixing positions for adjusting the position of the rotating member 24 and then fixing in the adjusted position. Also, reference number, 24c refers to a handle for manually rotating the rotating member 24.

[78] In this configuration, if it is intended that sludge in wastewater is sufficiently removed, the rotating member 24 is located so that the openness becomes low, thereby reducing the amount of wastewater circulating through the return holes 20a. If it is intended that oxygen in wastewater is supplied more rapidly, the openness becomes high by rotating the rotating member 24, thereby increasing the amount of wastewater circulating through the return holes 20a. Further, a cohesive agent is inputted to the aeration pipe through the cohesive agent input means, thereby guiding more rapid purification work.

[79] Next, FIGS 13 and 14 show the circular spread according to the third embodiment. In the present embodiment as same as the second embodiment, the circular aerator comprises an aeration pipe 20 provid ed having a little gap g from the bottom of the self-oxidation tank; a bubble head 22 for discharging air flowed in through an air pipe 21 into the aeration pipe 20; a transportation pipe 23 for transporting sludge removed from the wastewater to a sludge storage tank (not shown); a cohesive agent input means for inputting a cohesive agent to the aeration pipe 20; and a surfactant input means for inputting a surfactant to the aeration pipe 20.

[80] However, in the present embodiment, the return holes (20a and 20b; hereinafter, referred to as 'the first return hole' and 'the second return hole', respectively) for returning wastewater in the aeration pipe 20 into the self-oxidation tank 100 are provid ed on the side and on the horizontal plane of the aeration pipe 20 and the rotating members (24 and 30; hereinafter, referred to as ' the first rotating member' and 'the second rotating member', respectively) for adjusting each of the openness are provided respectively. Herein, the configuration and function of the first return hole 20a and the first rotating member 24 are the same as the first embodiment described above. Also, the basic function that the second return hole 20b and the second rotating member 30 control the amount of discharging wastewater by adjusting the openness of the long hole 31 is same. Merely if the second return hole 20b is formed on the upper horizontal plane of the aeration pipe 20, wastewater is not quietly flowed out to the side but spouted up on flow of rising, thereby maximizing an effect that wastewater supplied with air is rapidly spread into the self-oxidation tank 100. In other words, purification time of wastewater is reduced that much. Reference number, 32 refers to a scatter guiding plate in the shape of a funnel arranged in a location confronting the second return hole 20b and functions that the wastewater spouting through the second return hole 20b is bumped into the scatter guiding plate 32 and then scattered into the self- oxidation tank 100.

[81] Accordingly, the circular aerator controls the amount of wastewater circulated through the first and second return holes 20a and 20b by adjusting the openness rotating the first and second rotating member 24 and 30, thereby obtaining desired result such as sludge removal, rapid oxygen supply or the like can be obtained and further guiding more rapid purification work by inputting the cohesive agent and surfactant. [82] Next, FIG. 15 is a perspective view showing the circular aerator according to the fourth embodiment of the present invention. The basic configuration in which the openness of return holes 20a is adjusted with a rotating member 24 and a cohesive agent and a surfactant is inputted to the aeration pipe 20 is the same as the embodiments described above. However, in the present embodiment, a connecting configuration of the aeration pipe 20 is different from that of the transportation pipe 23. As the embodiment described above, the aeration pipe 20 is not directly connected to the transportation pipe 23 and a temporary holding container 40 is provided in the middle therebetween. Accordingly, bubbles containing sludge spouted up to the aeration pipe 20 are overflowed into the temporary holding container 40 and then transported along with the transportation pipe 23. In the configuration, the bubbles spouted from the aeration pipe 20 can be check directly by sight, thereby adjusting openness checking the condition.

[83] Meanwhile, in the embodiment described above, the rotating member 24 of the first openness control means is manually rotated and may be automatically rotated using a driving motor as embodiments described hereinbelow.

[84] FIGS 16 and 17 show the fifth embodiment in which a driving instrument of the rotating member 24 is automatically modified in the configuration of FIGS 11 and 12. To this end, a gear portion 51 is formed on the outer circumference of the rotating member 24 and a driving gear 52 gearing with the gear portion 51 and a driving motor 54 rotating the driving gear 52 are provided Thus, if the driving motor 54 rotates the driving gear 52 using a reduction gear 53, the rotating member 24 gearing with the gear portion 51 is rotated, thereby controlling the openness of the first return holes 20a.

[85] FIGS 18 and 19 show the sixth embodiment in which driving instruments 61 and 62 of the rotating member 24 are automatically modified in the configuration of FIGS 13 and 14. The driving principle is the same as that of the fifth embodiment.

[86] Also, FIG. 20 shows the circular aerator of the seventh embodiment in which driving instruments 71 and 72 of the rotating member 24 are automatically modified in the configuration of FIG. 15. The driving principle is also same.

[87] Accordingly, if necessary, the automatic instrument is configured to rotate the rotating member 24 as described above, whereby openness of the first return hole 20a is configured to be controlled automatically.

[88] While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Industrial Applicability

[89] As described above, the circular aerator for purifying wastewater and a wastewater treatment apparatus using the same according to the present invention can be used in the field of purifying and treating wastewater.

Claims

[ 1 ] A circular aerator comprising : an aeration pipe provid ed in a self-oxidation tank in which wastewater is held, through which wastewater is flowed in and on one side of which return holes for returning the inflow wastewater to the self-oxidation tank are formed; a bubble head generating bubbles by discharging air supplied through a predetermined air pipe in the aeration pipe; a transportation pipe connected to the aeration pipe and forming a passage in which sludge in wastewater rising on the bubbles is passed; and turbulent flow increasing means for increasing turbulent flow in wastewater returned through the return holes.

[2] The circular aerator of Claim 1, wherein the turbulent flow increasing means comprise a scatter guiding plate confronting the return holes so that wastewater spouting through the return holes is bumped and then scattered into the self-oxidation tank.

[3] The circular aerator of Claim 1, wherein a horizontal plane is provided on an upper portion of the aeration pipe and the return hole is formed on the horizontal plane.

[4] The circular aerator of Claim 1, further comprising openness control means for controlling openness of the return holes.

[5] The circular aerator of Claim 4, wherein the openness control means comprises a rotating plate which is provided with long holes matching the return holes and provid ed available for rotating on the aeration pipe so that openness by matching the return hole to the long hole is varied in accordance with a rotation angle.

[6] The circular aerator of Claim 1, wherein the bubble head is detachably combined with the air pipe.

[7] The circular aerator of Claim 6, wherein each screw thread gearing with each other is formed in the bubble head and the air pipe, respectively so that fixing and unfixing by combination and separation is carried out.

[8] The circular aerator of Claim 1, wherein air diffusing holes through which air formed by the bubble head is discharged is formed on the side of the body thereof.

[9] The circular aerator of Claim 1, wherein the transportation pipe comprises at least one bending portions bent in the shape of reverse U on the part connected to the aeration pipe.

[10] The circular aerator of Claim 1, wherein the lower end of the aeration pipe floats at a predetermined gap from the bottom of the self-oxidation tank so that wastewater is flowed in the aeration pipe through the gap from the bottom thereof.

[11] The circular aerator of Claim 1, wherein the aeration pipe comprises at least one expanding portions in which the inner passage is broadened along the direction from the bubble head to the transportation pipe.

[12] The circular aerator of Claim 1, wherein ozone is supplied together with the air through the air pipe.

[13] A wastewater treatment apparatus comprising: a plurality of self-oxidation tanks having spaces divided by predetermined partition walls; a plurality of circular aerators for purifying wastewater, the circular aerators provid ed in each of the self-oxidation tanks; and a sludge storage tank holding sludge removed by the circular aerator; and wherein through holes for transferring wastewater is formed on each of the partition walls and each of the through holes is arranged in zigzags in order not to directly confront each through hole of adjacent partition walls.

[14] The wastewater treatment apparatus of Claim 13, wherein the circular aerator comprises: an aeration pipe provid ed in a self-oxidation tank in which wastewater is held, through which wastewater is flowed in and on one side of which return holes for returning the inflow wastewater to the self-oxidation tank are formed; a bubble head generating bubbles by discharging air supplied through a predetermined air pipe in the aeration pipe; a transportation pipe connected to the aeration pipe and forming a passage in which sludge in wastewater rising on the bubbles is passed; and turbulent flow increasing means for increasing turbulent flow in wastewater returned through the return holes.

[15] The wastewater treatment apparatus of Claim 14, wherein the turbulent flow increasing means comprise a scatter guiding plate confronting the return holes so that wastewater spouting through the return holes is bumped and then scattered into the self-oxidation tank.

[16] The wastewater treatment apparatus of Claim 14, wherein a horizontal plane is provided on an upper portion of the aeration pipe and the return hole is formed on the horizontal plane.

[17] The wastewater treatment apparatus of Claim 14, further comprising openness control means for controlling openness of the return holes.

[18] The wastewater treatment apparatus of Claim 17, wherein the openness control means comprises a rotating plate which is provided with long holes matching the return holes and provid ed available for rotating on the aeration pipe so that openness by matching the return hole to the long hole is varied in accordance with a rotation angle.

[19] The wastewater treatment apparatus of Claim 14, wherein the bubble head is detachably combined with the air pipe.

[20] The wastewater treatment apparatus of Claim 19, wherein each screw thread gearing with each other is formed in the bubble head and the air pipe, respectively so that fixing and unfixing by combination and separation is carried out.

[21] The wastewater treatment apparatus of Claim 14, wherein air diffusing holes through which air formed by the bubble head is discharged is formed on the side of the body thereof.

[22] . The wastewater treatment apparatus of Claim 14, wherein the transportation pipe comprises at least one bending portions bent in the shape of reverse U on the part connected to the aeration pipe

[23] The wastewater treatment apparatus of Claim 14, wherein the lower end of the aeration pipe floats at a predetermined gap from the bottom of the self- oxidation tank so that wastewater is flowed in the aeration pipe through the gap from the bottom thereof.

[24] The wastewater treatment apparatus of Claim 14, wherein the aeration pipe comprises at least one expanding portions in which the inner passage is broadened along the direction from the bubble head to the transportation pipe.

[25] The wastewater treatment apparatus of Claim 14, wherein ozone is supplied together with the air through the air pipe.

[26] A circular aerator comprising: an aeration pipe provid ed in a self-oxidation tank in which wastewater is held, through which wastewater is flowed in and on one side of which return holes for returning the inflow wastewater to the self-oxidation tank are formed; a bubble head generating bubbles by discharging air supplied through a predetermined air pipe in the aeration pipe; a transportation pipe connected to the aeration pipe and forming a passage in which sludge in wastewater rising on the bubbles is passed; turbulent flow increasing means for increasing turbulent flow in wastewater returned through the return holes; and a base net floated on the upper layer of wastewater in the self-oxidation tank, collecting sludge contained in wastewater returned through the return holes and decomposing the sludge using aerobic bacteria. [27] The circular aerator of Claim 26, wherein the turbulent flow increasing means comprise a scatter guiding plate confronting the return holes so that wastewater spouting through the return holes is bumped and then scattered into the self-oxidation tank. [28] The circular aerator of Claim 26, wherein a horizontal plane is provided on an upper portion of the aeration pipe and the return hole is formed on the horizontal plane. [29] The circular aerator of Claim 26, further comprising openness control means for controlling openness of the return holes. [30] The circular aerator of Claim 29, wherein the openness control means comprises a rotating plate which is provided with long holes matching the return holes and provid ed available for rotating on the aeration pipe so that openness by matching the return hole to the long hole is varied in accordance with a rotation angle. [31] The circular aerator of Claim 26, wherein the bubble head is detachably combined with the air pipe. [32] The circular aerator of Claim 31, wherein each screw thread gearing with each other is formed in the bubble head and the air pipe, respectively so that fixing and unfixing by combination and separation is carried out. [33] The circular aerator of Claim 26, wherein air diffusing holes through which air formed by the bubble head is discharged is formed on the side of the body thereof. [34] The circular aerator of Claim 26, wherein the transportation pipe comprises at least one bending portions bent in the shape of reverse U on the part connected to the aeration pipe. [35] The circular aerator of Claim 26, wherein the lower end of the aeration pipe floats at a predetermined gap from the bottom of the self-oxidation tank so that wastewater is flowed in the aeration pipe through the gap from the bottom thereof. [36] The circular aerator of Claim 26, wherein the aeration pipe comprises at least one expanding portions in which the inner passage is broadened along the direction from the bubble head to the transportation pipe. [37] The circular aerator of Claim 26, wherein ozone is supplied together with the air through the air pipe. [38] A wastewater treatment apparatus comprising: a plurality of self-oxidation tanks having spaces divided by predetermined partition walls; a plurality of circular aerators for purifying wastewater, the circular aerators provid ed in each of the self-oxidation tanks; and a sludge storage tank holding sludge removed by the circular aerator; and wherein through holes for transferring wastewater is formed on each of the partition walls and each of the through holes is arranged in zigzags in order not to directly confront each through hole of adjacent partition walls; and wherein the circular aerator comprises an aeration pipe provid ed in the self-oxidation tank, through which wastewater is flowed in and on one side of which return holes for returning the inflow wastewater to the self- oxidation tank are formed; a bubble head generating bubbles by discharging air supplied through a predetermined air pipe in the aeration pipe; a transportation pipe connected to the aeration pipe and forming a passage in which sludge in wastewater rising on the bubbles is passed; turbulent flow increasing means for increasing turbulent flow in wastewater returned through the return holes; and a base net floated on the upper layer of wastewater in the self-oxidation tank, collecting sludge contained in wastewater returned through the return holes and decomposing the sludge using aerobic bacteria. [39] The wastewater treatment apparatus of Claim 38, wherein the turbulent flow increasing means comprise a scatter guiding plate confronting the return holes so that wastewater spouting through the return holes is bumped and then scattered into the self-oxidation tank. [40] The wastewater treatment apparatus of Claim 38, wherein a horizontal plane is provided on an upper portion of the aeration pipe and the return hole is formed on the horizontal plane. [41] The wastewater treatment apparatus of Claim 38, further comprising openness control means for controlling openness of the return holes. [42] The wastewater treatment apparatus of Claim 41, wherein the openness control means comprises a rotating plate which is provided with long holes matching the return holes and provid ed available for rotating on the aeration pipe so that openness by matching the return hole to the long hole is varied in accordance with a rotation angle. [43] The wastewater treatment apparatus of Claim 38, wherein the bubble head is detachably combined with the air pipe. [44] The wastewater treatment apparatus of Claim 38, wherein each screw thread gearing with each other is formed in the bubble head and the air pipe, respectively so that fixing and unfixing by combination and separation is carried out. [45] The wastewater treatment apparatus of Claim 38, wherein air diffusing holes through which air formed by the bubble head is discharged is formed on the side of the body thereof. [46] The wastewater treatment apparatus of Claim 38, wherein the transportation pipe comprises at least one bending portions bent in the shape of reverse U on the part connected to the aeration pipe. [47] The wastewater treatment apparatus of Claim 39, wherein the lower end of the aeration pipe floats at a predetermined gap from the bottom of the self- oxidation tank so that wastewater is flowed in the aeration pipe through the gap from the bottom thereof. [48] The wastewater treatment apparatus of Claim 38, wherein the aeration pipe comprises at least one expanding portions in which the inner passage is broadened along the direction from the bubble head to the transportation pipe. [49] The wastewater treatment apparatus of Claim 38, wherein ozone is supplied together with the air through the air pipe. [50] A wastewater treatment apparatus comprising: a plurality of self-oxidation tanks having spaces divided by predetermined partition walls; a plurality of circular aerators for purifying wastewater, the circular aerators provid ed in each of the self-oxidation tanks; a sludge concentration tank for holding sludge removed from the wastewater and concentrating the sludge; a first flow passage in which wastewater is guided to be purified sequentially passing through each of the self-oxidation tanks; a second flow passage in which sludge of wastewater removed by circular aerators in each of the self-oxidation tanks is fed back into at least one of self- oxidation tanks located more upstream than the corresponding self-oxidation tank from the viewpoint of the direction of movement of the first flow passage; and a third flow passage wherein sludge removed by the circular aerator in a self- oxidation tank in which wastewater is flowed first of all is transferred to the sludge concentration tank. [51] The wastewater treatment apparatus of Claim 50, further comprising: a flow control tank temporarily storing wastewater supplied to the self-oxidation tank; and wherein first-rate water of the sludge concentration tank overflows into the flow control tank. [52] The wastewater treatment apparatus of Claim 50, wherein the first flow passage comprises through holes formed to transfer wastewater on each of the partition walls; and wherein the second flow passage comprises a transportation pipe for forming a connecting passage for upstream transferring sludge removed by the circular aerators in each of the self-oxidation tanks. [53] The wastewater treatment apparatus of Claim 52, wherein each of the through holes is arranged in zigzags in order not to directly confront each through hole of adjacent partition walls; and wherein an exit of the transportation pipe, the exit which is located on one side is apart from a through hole which is located on the other side and connected downstream in the corresponding self-oxidation tank. [54] The wastewater treatment apparatus of Claim 50, further comprising: a disinfection tank for disinfecting treatment water passing through a plurality of self-oxidation tanks along the first flow passage; a discharge tank for temporarily storing the disinfected water before discharging; and a sludge storage tank for being supplied with sludge concentrated in the sludge concentration tank. [55] The wastewater treatment apparatus of Claim 50, wherein the second flow passage comprises a line for feeding sludge which is removed from the corresponding self-oxidation tank back to an upstream self-oxidation tank just prior thereto. [56] The wastewater treatment apparatus of Claim 50, wherein a plurality of the self- oxidation tanks comprise first, second, third, and fourth self-oxidation tanks; and Wherein the second flow passage comprises a line for feeding back from the second self-oxidation tank to the first self-oxidation tank, a line for feeding back from the third self-oxidation tank to the first self-oxidation tank and a line for feeding back from the fourth self-oxidation tank to the second self-oxidation tank. [57] The wastewater treatment apparatus of Claim 50, wherein a plurality of the self- oxidation tanks comprise first, second, third, and fourth self-oxidation tanks; and wherein the second flow passage comprises a line for feeding back from the second self-oxidation tank to the first self-oxidation tank, a line for feeding back from the third self-oxidation tank to the first self-oxidation tank and a line for feeding back from the fourth self-oxidation tank to the first self-oxidation tank. [58] A circular aerator comprising: an aeration pipe provid ed in a self-oxidation tank in which wastewater is held, through which wastewater is flowed in and on a side wall of which a first return hole for returning the inflow wastewater to the self-oxidation tank are formed; a bubble head generating bubbles by discharging air supplied through a predetermined air pipe in the aeration pipe; and a first openness control means for varying openness of the first return hole. [59] The circular aerator of Claim 58, wherein the first openness control means comprises a first rotating member which is provided with a long hole matching the first return hole and provid ed available for rotating on a side wall of the aeration pipe so that openness by matching the first return hole to the long hole is varied in accordance with a rotation angle. [60] The circular aerator of Claim 59, wherein the first rotating member is provided with a handle so that the first rotation member is manually rotated holding the handle if necessary. [61] The circular aerator of Claim 59, wherein the first rotating member is provided with a gear portion; wherein a driving gear gearing with the gear portion and a driving motor rotating the driving gear are further comprised; and wherein if necessary, the driving motor rotates the driving gear so that the first rotating member geared therewith is rotated [62] The circular aerator of Claim 58, wherein a horizontal plane on which a second return hole is formed is provided on an upper portion of the aeration pipe; and wherein a second openness control means for varying openness of the second return hole is further comprised [63] The circular aerator of Claim 62, wherein the second openness control means comprises a second rotating member which is provided with a long hole matching the second return hole and provid ed available for rotating on the horizontal plane so that openness by matching the second return hole to the long hole is varied in accordance with a rotation angle. [64] The circular aerator of Claim 62, wherein a scatter guiding plate is provid ed for confronting the second return hole; and wherein wastewater spouting through the second return hole is bumped against the scatter guiding plate and then returned scattering into the self-oxidation tank. [65] The circular aerator of Claim 58, wherein the aeration pipe is directly connected to a transportation pipe forming a flow passage of sludge removed rising on the bubbles. [66] The circular aerator of Claim 58, wherein the aeration pipe is connected to a predetermined temporary holding container having a transportation pipe connected thereto; and wherein bubbles containing sludge spouting through the aeration pipe overflow into the temporary holding container and then are discharged through the transportation pipe connected thereto. [67] The circular aerator of Claim 58, further comprising a cohesive agent input means for inputting a cohesive agent to the aeration pipe to promote sludge cohesion in the wastewater. [68] The circular aerator of Claim 67, wherein the cohesive agent input means comprises a cohesive agent storing tank in which a cohesive agent is stored, a cohesive agent input pipe connecting the cohesive agent storing tank and the aeration pipe, and a supply pump supplying a cohesive agent through the cohesive agent input pipe. [69] The circular aerator of Claim 67, further comprising a surfactant input means for inputting a surfactant to the aeration pipe to activate bubble generation in the aeration pipe. [70] The circular aerator of Claim 69, wherein the surfactant input means comprises a surfactant storing tank in which a surfactant is stored, a surfactant input pipe connecting the surfactant storing tank and the aeration tank, and a supply pump supplying a surfactant through the surfactant input pipe. [71] A circular aerator comprising : an aeration pipe provid ed in a self-oxidation tank in which wastewater is held and through which wastewater is flowed in; a bubble head generating bubbles by discharging air supplied through a predetermined air pipe in the aeration pipe; and a cohesive agent input means for inputting a cohesive agent to the aeration pipe to promote sludge cohesion in the wastewater. [72] The circular aerator of Claim 71, wherein the cohesive agent input means comprises a cohesive agent storing tank in which a cohesive agent is stored, a cohesive agent input pipe connecting the cohesive agent storing tank and the aeration pipe, and a supply pump supplying a cohesive agent through the cohesive agent input pipe. [73] The circular aerator of Claim 71, further comprising a surfactant input means for inputting a surfactant to the aeration pipe to activate bubble generation in the aeration pipe. [74] The circular aerator of Claim 73, wherein the surfactant input means comprises a surfactant storing tank in which a surfactant is stored, a surfactant input pipe connecting the surfactant storing tank and the aeration tank, and a supply pump supplying a surfactant through the surfactant input pipe.