JPS6352560B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a circulating system that mixes and stirs wastewater and oxygen-containing gas under pressure depending on the water depth, increases the amount of dissolved oxygen, and increases the rate of biochemical oxidation of organic matter in the wastewater. Regarding aeration equipment. Conventionally, known wastewater treatment methods for increasing the biochemical oxidation rate include an ultra-deep aeration method, a pressurized aeration method, and a forced circulation aeration method. The first ultra-deep aeration method is to drill a deep vertical hole in the ground to a depth of 100m or more, create a riser pipe and a descender pipe, and circulate wastewater by utilizing the difference in apparent specific gravity caused by air blowing. Although this method involves aeration and oxidation under pressure due to the depth of the water, drilling a deep vertical hole more than 100 meters deep underground requires advanced civil engineering technology and is extremely expensive. Therefore, if the amount of wastewater is large, there are economies of scale and it is economical, but if the amount of wastewater is less than medium, it is economically disadvantageous. Further, there are problems such as it is not suitable for soft ground, and when the concentration of organic matter in wastewater is high, it is difficult to remove the oxidation heat. The second pressurized aeration method aerates wastewater in a pressurized closed tank, but since the wastewater is stirred by air agitation, a large amount of pressurized air is required, and the power cost for raising the pressure is high. Furthermore, when the amount of wastewater to be treated becomes large, the container has a tank-like shape, so the manufacturing cost of the container increases significantly due to its pressure-resistant structure. The third forced circulation aeration method uses a pump to forcefully circulate wastewater within the piping of a pressurized circulation system, and the turbulent flow within the piping agitates the wastewater for biological oxidation. It is necessary to increase the pressure above the pressure inside the reactor and supply it, which poses a problem in that the power cost for this pressure increase and pump circulation increases. As stated above, the present invention provides an improved wastewater treatment device using a circulating aeration method that solves the problems seen in conventional wastewater treatment methods that increase the rate of biochemical oxidation. However, in wastewater treatment in which wastewater is biochemically oxidized under pressure, it is necessary to separate or separate the descending pipe, which is a vertical straight pipe with an air blowing pipe for aeration at the bottom, and the rising pipe, which is a vertical straight pipe. The lower ends of the downcomer pipe and the lower end of the riser pipe are arranged adjacent to each other in parallel, and the lower ends of the downcomer pipe and the lower end of the riser pipe are connected through a reaction tube forming a horizontal U-shaped flow path, and the upper ends of each of the downcomer pipe and the riser pipe are connected. This is a circulating aeration device characterized by being attached to the bottom of the deaeration tank. The configuration of the present invention will be explained below. FIG. 1 is a system diagram showing an embodiment to which the apparatus of the present invention is applied. In the figure, reference numeral 1 denotes a downcomer pipe, which is a vertical pipe made of steel or concrete, and is supported by a frame and installed above ground, or is of a semi-underground type. The upper end of the downcomer pipe 1 is connected to the bottom of a deaeration tank 5, which will be described later, and an air blowing pipe 2 for aeration and circulation is attached downward to the lower part. The lower end of the downcomer tube 1 is connected to one end of the reaction tube 3. The reaction tube 3 is a horizontal tube made of steel or concrete, and its shape is a U-shaped tube with a long straight section. The reaction tube 3 may be installed horizontally on the ground, or may be buried underground so shallowly that it cannot be seen. Reference numeral 4 denotes an ascending pipe, which is a vertical pipe having the same height as the downcomer pipe, and is arranged in parallel with or apart from the downcomer pipe 1, and its lower end is connected to the other end of the reaction tube 3, and its upper end is connected to the downcomer pipe 1. It is also connected to the bottom of the deaeration tank 5. A starting air blowing pipe 6 for starting the circulation is installed upward in the middle of the riser pipe 4. Reference numeral 5 denotes a deaeration tank, which is a round or rectangular water tank that is mounted on the upper ends of the downcomer pipe 1 and the riser pipe 4 so as to connect them, and is open to the atmosphere. Reference numeral 7 denotes a defoaming tank consisting of a shallow tank open to the atmosphere, which removes fine air bubbles remaining in the wastewater by destroying them using mechanical stirring. Reference numeral 8 denotes a sludge separation tank, in which a normal gravity settling type is used, the sludge is extracted from the bottom as a concentrated slurry, and the supernatant water flows out from the top in the form of an overflow. 9 is a return sludge pump, and a normal open impeller type slurry pump is used. In the apparatus configured as described above, wastewater A is supplied together with return sludge B to the downcomer pipe 1 side of the deaeration tank 5.
In the degassing tank 5, a part of the waste water rising up the riser pipe 4 circulates to the downcomer side and descends in the downcomer pipe 1 together with the newly supplied waste water A. Air for circulation and aeration is injected downward into the wastewater near the bottom of the downcomer pipe 1 by means of an air blowing pipe 2.
The flow velocity in the downcomer is the rising velocity of air bubbles (generally 0.3
Therefore, the air blown into the wastewater above the air blowing pipe 2 in the downcomer pipe 1 will not flow back, but since there is a considerable amount of air in the riser pipe 4. This creates an apparent specific gravity difference between the two, which becomes a driving force for the circulation of waste water in the reaction tube 3. Therefore, if the difference in water head due to the difference in apparent specific gravity between the two is larger than the pressure loss during circulation within the reaction tube 3, the wastewater can be circulated. Also, descending pipe 1,
When determining the vertical height of the riser pipe 4, it is necessary to take into account the above-mentioned circulation driving force as well as the pressure due to the water head pressure inside the reaction pipe 3. The higher this pressure is, the more air (oxygen) in the wastewater is As the partial pressure of the wastewater increases, the concentration of oxygen dissolved in the wastewater increases proportionally, and the rate of biological oxidation also increases. Descending pipe 1, rising pipe 4
The optimal vertical height can be determined comprehensively from the above points of view, but in reality, a height of 10 meters or more is desirable. The wastewater that has reached the bottom end of the downcomer pipe 1 and contains sufficient air enters one end of the reaction tube 3, and is refluxed at a flow rate selected to create a turbulent region within the reaction tube due to the above-mentioned driving force, and oxygen is removed by gas-liquid stirring. It reaches the other end and enters the lower end of the riser pipe 4 while increasing the moving speed and efficiently performing the biochemical oxidation reaction. The length of the reaction tube is selected so as to provide an arbitrary residence time depending on the required degree of biochemical oxidative decomposition of organic matter in the wastewater. The shape of the reaction tube 3 may be arbitrary, and for example, it may be installed on the ground along the border of a wastewater treatment plant, or it may be buried shallowly underground like a sewer pipe just along the road of the treatment plant. . These shapes can be formed by appropriately combining straight pipes, curved pipes, etc. The wastewater leaving the reaction tube 3 then enters the lower end of the riser tube 4 and rises inside the reaction tube.As it rises, the pressure due to the water head pressure decreases, so the dissolved air is released and becomes bubbles, and the particle size of the bubbles also increases. At the upper part of the riser pipe, a considerable number of gases enter the degassing tank 5.
Since the deaeration tank 5 is open to the atmosphere, most of the bubbles in the wastewater are removed, and a portion of the wastewater is circulated down to the downcomer pipe 1 together with its activated sludge as described above. At the start of operation of the device, air is injected from the starting air blowing pipe 6 to actively create air bubbles in the upper half of the riser pipe 4 to reduce the apparent specific gravity and provide a driving force for circulation. The wastewater flowing out of the degassing tank 5 then enters the defoaming tank 7, where fine bubbles remaining in the wastewater are destroyed by mechanical stirring and defoamed. The defoamed wastewater then enters the sludge separation tank 8, where the organic matter is decomposed in the reaction tube 3, and the generated sludge is allowed to settle to the bottom of the sludge separation tank 8 using gravity sedimentation, and is extracted from the bottom. 9, the sludge is supplied to the deaeration tank 5 as return sludge B. The supernatant water of the sludge separation tank from which organic components, which are the source of BOD, and solid content such as sludge have been removed in this way, is discharged as treated water D. The format of the downcomer pipe 1 and the riser pipe 4 may be two pipes arranged side by side separated from each other, two pipes arranged side by side next to each other, or one pipe with a large diameter. It may also be an adjoining structure in which the area is internally partitioned into two parts. When wastewater is treated according to the present invention having the above-described structure and function, the following effects can be obtained compared to conventional high-speed oxidation methods. (1) Power costs can be reduced because there is no need to increase the pressure of wastewater and air for biological oxidation to the maximum pressure of the system. (2) Since the gas-liquid is stirred by the turbulent flow itself within the reaction tube, power costs for stirring can be reduced. (3) Reaction tubes can be installed above ground or buried shallowly, reducing civil engineering costs. (4) Since the reaction tube can be installed at the boundary of the treatment plant or along the road, the installation area of the device can be extremely reduced. Example As a result of treating food processing wastewater (Example 1) and marine toilet wastewater (Example 2) using the apparatus shown in FIG. 1, it was confirmed that the following good results were obtained. 【table】

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an embodiment to which the apparatus of the present invention is applied. 1: downcomer pipe, 2: air blowing pipe, 3: reaction pipe,
4: Rising pipe, 5: Deaeration tank, 6: Starting air blowing pipe, 7: Defoaming tank, 8: Sludge separation tank, 9: Sludge pump, A: Waste water, B: Return sludge, C: Pressurized air ,
D: Treated water, E: Surplus sludge.

Claims (1)

[Claims] 1. In wastewater treatment in which wastewater is biochemically oxidized under pressure, a descending pipe 1 consisting of a vertical straight pipe with an air blowing pipe 2 for aeration at the bottom and a rising pipe 4 consisting of a vertical straight pipe are used. The lower end of the downcomer pipe 1 and the lower end of the riser pipe 4 are connected through a reaction pipe 3 forming a horizontal U-shaped flow path, and the lower end of the downcomer pipe 1 and the riser pipe A circulating aeration device characterized in that the upper end of each tube 4 is attached to the bottom of a deaeration tank 5.