JPS58150495A - Apparatus of circulating type aeration - Google Patents

Abstract

PURPOSE:To save the costs of power and construction work, by providing a vertical straight descending pipe having a nozzle for the injection of aerating air at its lower part and a vertical straight ascending pipe parallelly in a distance apart from or adjacent to each other. CONSTITUTION:Waste water A together with returned sludge B is supplied to the side of the descending pipe 1 of a deaerating tank 5. In the deaerating tank 5, the part of the waste water rising through an ascending pipe 4 is circulated to the side of the descending pipe and let flow downwards together with newly supplied waste water A through the descending pipe 1. Air for aeration and circulation is injected downwards into the waste water through an air- injecting nozzle 2 in the vicinity of the lower part of the descending pipe 1. The flow speed in the descending pipe is made larger than the rising speed of air bubbles. Accordingly, the injected air does not flow backwards into the waste water above the air-injecting nozzle 2 inside the descending pipe 1, while the substantial amount of air is present in the ascending pipe 4. Consequently, the difference of apparent specific gravity is formed between them and utilized as the power to promote the circulation of the waste water through a reactor pipe 3.

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 seventh ultra-deep aeration method is to drill deep vertical holes deeper than the end of the page into the ground, create rising and descending pipes, and circulate wastewater using the difference in apparent specific gravity caused by air blowing. Although this method involves aeration and oxidation under pressure due to the water depth, drilling deep vertical holes deeper than the bottom of the page requires advanced civil engineering technology and the cost of construction is enormous. Therefore, if the amount of wastewater is large, there is an economy of scale, but if the amount of wastewater is less than medium, it becomes 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 involves aerating 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 the tank for pressurization is large. Moreover, when the amount of wastewater to be treated becomes large, the container has a tank-shaped shape, which has the drawback of significantly increasing the manufacturing cost of the container due to its pressure-resistant structure.

The third type of 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. In wastewater treatment where wastewater is subjected to biochemical oxidation under pressure, a descending pipe consisting of a vertical straight pipe with an air blowing pipe for aeration at the bottom is separated from a rising pipe consisting of a vertical straight pipe. or adjacently arranged in parallel, the lower end of the downcomer pipe and the lower end of the riser pipe are connected by a reaction tube forming a water-half-0-shaped flow path, and each of the downcomer pipe and the riser pipe is This is a circulating aeration device characterized by having its upper end 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, (1) is 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 semi-underground. 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). Reaction tube (3
) is a horizontal pipe made of steel or concrete, and its shape is a single-shaped pipe with a long straight pipe section.

The reaction tube (3) may be installed horizontally on the ground, or may be buried underground so shallowly that it cannot be seen. (4) is an ascending pipe, which is a vertical pipe having the same height as the downcomer pipe, which is arranged in parallel with or apart from the downcomer pipe (1), and whose lower end is connected to the reaction pipe (
3) It is connected to the other end, and the upper end is connected to the bottom of the degassing tank (5) like the downcomer pipe (1). A starting air blowing pipe (6) for circulation starting 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. (7) is a defoaming tank consisting of a shallow tank open to the atmosphere, which destroys and removes fine air bubbles remaining in wastewater by mechanical stirring.

(8) is a sludge separation tank, which uses a normal gravity settling system, and the outside of the sludge is extracted from the bottom as a concentrated slurry.
The supernatant water flows out from the top in the form of overflow. (9
) is a return sludge pump, and a normal slurry pump with a set of oven impellers is used.

In the apparatus configured as described above, the wastewater () is supplied to the downcomer pipe (1) side of the deaeration tank (5) together with the returned sludge (). In the degassing tank (5), part of the wastewater that has ascended through the riser pipe (4) circulates to the downcomer side and descends in the downcomer pipe (1) together with the newly supplied wastewater (4). do.

Air for circulation and aeration is injected downward into the wastewater by an air blowing pipe (2) near the bottom of the downcomer pipe (1). The flow velocity in the downcomer is the rising velocity of air bubbles (generally 0.3 m/8θC
), so that the air blown into the wastewater above the air blowing pipe (2) in the descending pipe (1) does not flow back, but there is a considerable amount of air in the rising pipe (4). This causes an apparent difference in specific gravity between the two, which causes the reaction tube (3
) This is the driving force for the sump through which wastewater circulates. Therefore, wastewater can be circulated if the difference in head force between the two is larger than the pressure loss during circulation in the reaction tube (3). In addition, when determining the vertical height of the downcomer pipe (1) and riser pipe (4), it is necessary to take into account the above-mentioned circulation propulsion force as well as the pressure due to the head pressure in the reaction pipe (3). The higher the pressure is, the higher the partial pressure of air (oxygen) in the wastewater becomes, and the concentration of oxygen dissolved in the wastewater increases proportionally, thereby increasing the rate of biological oxidation. The optimum vertical height of the downcomer pipe (1) and riser pipe (4) can be comprehensively determined from the above points of view, but in reality, it is desirable that the height be 10 m or more.

The wastewater that has reached the bottom end of the downcomer tube (1) and contains enough air enters one end of the reaction tube (3), and due to the above-mentioned driving force, it circulates through the reaction tube at a flow rate selected to create a turbulent region. The oxygen transfer rate is improved by stirring the liquid, and while the biochemical oxidation reaction is efficiently performed, the liquid reaches the other end and enters the lower end of the riser pipe (4). 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 boundary of the wastewater treatment plant, or it may be buried shallowly in the ground along the road of the treatment plant, just like a sewage pipe. . 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 the water rises, the pressure due to the water head decreases, so the dissolved air is released and becomes bubbles, which reduce the particle size of the bubbles. The gas also increases in size, reaching a considerable number in the upper part of the riser pipe and entering 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. When the equipment starts operating, 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 deaeration tank (5) is then transferred to the deaeration tank (
7), the fine bubbles remaining in the wastewater are destroyed and defoamed by mechanical stirring. The defoamed wastewater then enters the sludge separation tank (8) and the sludge produced by decomposing organic matter in the reaction tube (3) is transferred to the sludge separation tank (8)' by gravity sedimentation.
The sludge settles to the bottom and is extracted from the bottom, and a part of it is supplied to the deaeration tank (5) as return sludge (b) through the sludge pot (9). 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 manner, is discharged as treated water (D). The descending pipe (1) and rising pipe (4) may be formed by placing two pipes in parallel and spaced apart, or by placing two pipes in parallel adjacently, or depending on the diameter. An adjacent structure in which one large pipe is internally partitioned into two parts may be used.

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, the power cost for the stirring tank can be reduced.

(3) The reaction tube 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: Food processing wastewater (example/) using the apparatus shown in Figure 1
As a result of treating wastewater from a ship's toilet (example), it was confirmed that the following good results were obtained.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing an embodiment to which the apparatus of the present invention is applied. /: descending pipe, 2: air blowing pipe, 3: reaction tube, lI: rising pipe, j: degassing tank, 6: starting air blowing pipe, 7: defoaming tank,
Z: Sludge separation tank, R: Sludge pump, A: Waste water, B: Returned sludge, C: Pressurized air, D = Treated water, E: Excess sludge. Applicant Mitsubishi Kakoki Co., Ltd. Agent Patent Attorney Kentake Hattori

Claims (1)

[Claims] In wastewater treatment, where 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 an ascending pipe (4) consisting of a vertical straight pipe.
The lower end of the descending pipe (1) and the lower end of the rising pipe (4) are connected through a reaction pipe (3) forming a horizontal U-shaped flow path. , and the downcomer pipe (1)
A circulating aeration device characterized in that the upper ends of the rising pipes (4) and the rising pipes (4) are attached to the bottom of the deaeration tank (5).