JPS6351077B2 - - Google Patents

Description

Detailed Description of the Invention The present invention is an oxidation date method in which a mechanical surface aerator is installed in an oblong circulation waterway to treat wastewater as activated sludge.
(Dissolved oxygen amount) Control method.

The oxidation date method is to install an oblong circulation waterway (aeration tank), and use a mechanical aerator (hereinafter simply referred to as an aerator) to circulate wastewater (hereinafter referred to as "aeration tank") inside the waterway. This is a method of treating activated sludge by aeration while circulating the mixed liquid of sewage and sludge in an aeration tank. In order to treat wastewater with an activated sludge treatment method such as an oxidation date method, it is required that the wastewater maintain a predetermined DO value. Therefore, the sewage in the aeration tank is
By constantly or timely detecting the DO value, feeding back the detected value to the control device, and changing the rotation speed of the aerator based on that value, or raising and lowering the outflow weir based on that value, the blade of the aerator can be controlled. By changing the immersion depth (hereinafter referred to as automatic control method), the amount of aeration was changed to maintain a predetermined DO value. The characteristics of this oxidation date method are that although it requires a relatively large site, it is easy to maintain and manage, can cope with relatively large fluctuations in inflow load, and can perform advanced treatment (removal of N and P). Therefore, in the middle,
It is suitable as a sewage treatment method for small cities (medium and small scale). However, on the other hand, small and medium-sized sewage facilities have a narrow facility area and a short time to reach the sewage treatment plant. The fluctuations are large, and the fluctuations in water quality (line diagram) are also large. In this way, the sewage (in this specification, refers to the water before being put into the aeration tank) changes depending on the time of day,
When the wastewater is input (inflowed) into the aeration tank, it is required to change the aeration amount, that is, the oxygen supply amount (oxygen dissolved amount) in response to the above fluctuations, in order to maintain the wastewater at a predetermined DO value. Adopting the above-mentioned automatic control method as a control means means that the smaller the sewage treatment facility, the larger the cost of the automatic control equipment will be in the construction cost of the entire facility, and the construction cost will be higher relative to the treatment capacity. Although the oxidation date method has elements suitable for small and medium scale sewage treatment, it imposes a large burden on automatic control equipment. In addition, instead of the automatic control described above, there is also a method of manually controlling the rotation speed, immersion depth, etc. based on successive DO measurement values, but in such a case running costs will be high and it will be difficult to maintain a predetermined DO value. It's difficult.

The present invention has been made in view of the above-mentioned current situation, and is applicable to the oxidation date method in which a vertical shaft type mechanical surface aerator is installed in an oblong circulation waterway to treat wastewater as activated sludge. Without adopting an automatic control method, an outflow weir is installed at the outflow part of the circulation channel to change the water level in the channel according to the amount of inflow water, and the immersion depth of the aerator blade can be adjusted based on the fluctuation of the water level. The purpose of this invention is to provide an inexpensive DO control method that maintains the DO value of wastewater at a predetermined value by varying the amount of aeration.

The outline of the apparatus used to carry out the method according to the present invention will be explained below, and then the DO control method in the oxidation date method of the present invention will be specifically explained. FIG. 2 is a plan view of the entire apparatus for carrying out the oxidation date method according to the present invention, FIG. 3 is a front view of a slit-type outflow weir that constitutes a part of the apparatus shown in FIG. The figure is a side view of an aerator which similarly constitutes a part of the apparatus shown in FIG. 2, and FIG. 5 is a detailed side view of the blade portion of the aerator, showing changes in the immersion depth of the blade.
In the figure, 1 is an aeration tank, 2 is an aerator, 3 is an outflow weir, and 4 is a sewage inlet. In addition, 5 is a settling tank, 6
is a sludge return pump, and 7 is a sludge return port. The aeration tank 1 has an oval outer shape in a plan view,
It is separated along its longitudinal centerline by a central separation wall 1a to form a circulation waterway. This aerator 2 is a vertical surface aerator, and an aeration blade 2a is attached to the lower end of the rotating shaft of an electric motor. In addition, the outflow weir 3 is
A slit plate 3a, which is configured to have only a portion cut out in the center to provide outflow resistance and restrict the outflow of sewage, is attached to the notched recess 1b formed in a part of the aeration tank 1 so as to be freely vertically attached, and a screw mechanism is attached. It is configured so that it can be moved up and down with 3b. Therefore, the aerator 2 is installed at a position adjacent to one end of the central separation wall 1a in the semicircular curved part of the aeration tank 1, and the outflow weir 3 is installed on a part of the outer wall of the aeration tank 1. , as well as sewage inlet 4 and sludge return port 7
is installed in the aeration tank 1. The outflow weir 3 may be of the slit type as explained above, or may be a slit type weir consisting of a slit plate having a triangular cutout depending on the amount of inflow fluctuation, water quality, etc. The flow loss is increased by reducing the diameter, providing a bent portion 9, and providing a water outlet 11 that is movable up and down using a bellows 10 and a screw mechanism 3b', and increasing the height of the water outlet 11. It may be a cylindrical outflow weir 3a' configured to limit the outflow by adjustment. In addition, in the above, each outflow weir (slit plate 3a or water outlet 11) is configured to be able to move up and down by screw mechanisms 3b and 3b' because of the amount of inflow due to the initial setting or subsequent increase in the number of houses. This is to enable adjustment so that an appropriate large variation range or amount of variation of the aeration tank corresponding to the inflow amount can be obtained even if there is an increase in the amount of inflow.

Next, the method according to the present invention will be explained with reference to the above-mentioned apparatus and FIG. 7. If the amount of sewage to be treated changes with time as shown in diagram A in Figure 7, the total amount of inflow to the aeration tank will be from settling tank 5 to aeration tank 1 at a constant rate. The result is as shown in diagram B, which includes the sludge to be returned. In the above state, by providing an outflow weir, the water level in the aeration tank (circulation waterway) is made to fluctuate depending on the amount of inflow. That is, the outflow amount from the aeration tank becomes as shown in diagram C, the water level in aeration tank 1 changes according to the inflow amount, and the immersion depth of the aerator blade remains constant as shown in diagram D. The outflow resistance of the outflow weir 3 is set in advance so as to have a displacement within a range (the width of the notch at the center of the slit plate 3a of the outflow weir, or the width of the slit plate 3).
(a) by moving the water outlet 11 up and down with screw mechanisms 3b, 3b', etc.) so that the water level in the aeration tank 1 (channel) changes according to the inflow amount;
The immersion depth of the blade 2a of the aerator 2 is constant (varies from 5 to 23 cm in the example).On the other hand, when the immersion depth changes, the blade 2a sprays wastewater into the air in response to the change. Use a shape that allows the amount of aeration to change.
That is, for the blade 2a, the required oxygen supply amount (aeration amount) is approximately proportional to the increase or decrease in the immersion depth as shown in FIG. (see). Since the oxygen supply capacity varies depending on the immersion depth D of the blade 2a, the amount of dissolved oxygen in the circulating wastewater varies approximately in proportion to the water level as shown in the diagram E. Therefore, as the amount of sewage inflow changes, the BOD load of the sewage in the aeration tank fluctuates as shown in diagram F in Figure 1, and correspondingly, the amount of dissolved oxygen also fluctuates as shown in diagram E. Therefore, the DO value in the aeration tank can always be maintained within a predetermined appropriate range, as shown in diagram G. In addition, H in FIG. 7 indicates the shaft output of the aerator.

As explained above, according to the present invention, it is possible to always maintain the DO value of wastewater in the aeration tank within a predetermined appropriate range without using an expensive automatic control method in the oxidation date method. Therefore, the oxidation date method can be implemented at low cost, contributing economically to the promotion of the development of sewage treatment facilities in small and medium-sized cities.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing changes in the amount of sewage inflow and water quality with time plotted on the horizontal axis; Fig. 2 is an overall plan view of an apparatus for carrying out the oxidation date method according to the present invention; Figure 3 is a front view of a slit-type outflow weir that forms part of the apparatus shown in Figure 2, and Figure 4 is a side view of an aerator that also forms part of the apparatus shown in Figure 2.
Fig. 5 is a side view showing changes in blade immersion depth of the aerator of Fig. 4, Fig. 6 is a cylindrical outflow weir showing another embodiment of the weir, and Fig. 7 is a vertical axis showing implementation of the present invention. It is a diagram showing various conditions such as inflow/outflow amount, water level fluctuation, DO value, etc. in the aeration tank at 100 ms, with time plotted on the horizontal axis. A...Sewage inflow amount, B...Total aeration tank inflow amount, C
...Aeration tank outflow amount, D...Water level (blade immersion depth), E...Dissolved oxygen amount, F...BOD load amount, G
...DO value, H...Aeration machine shaft output, I...BOD value of inflowing sewage, 1...Aeration tank (circulation waterway), 2...
Aerator, 3...Outflow weir, 4...Sewage inlet, 5...
... Sedimentation tank, 6... Sludge return pump, 7... Sludge return port, 8... Conduit, 9... Bent part, 10... Bellows, 11... Water outlet.

Claims (1)

[Claims] 1. In the oxidation date method, in which a vertical shaft type mechanical surface aerator is installed in an oblong circulation waterway to treat wastewater with activated sludge, the weir itself is installed at the outlet of the circulation waterway without adjustment. An outflow weir is installed that changes the outflow resistance depending on the inflow amount due to its structure, causing the water level in the waterway to fluctuate, and the amount of aeration is adjusted by changing the immersion depth of the aerator blade based on the fluctuation of the water level. By varying the wastewater
A DO control method in an oxidation date method characterized by maintaining a DO value at a predetermined value.