JP3455570B2 - Prevention method of soil accumulation in oxidation ditch - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aeration tank of an oxidation ditch, in which the operation of a mechanical aerator is controlled so as to prevent the sediment from spoiling and spoiling. Regarding prevention methods.

[0002]

2. Description of the Related Art In recent years, oxidation ditch has been constructed in various places in small-scale sewers, but this method does not first set a sedimentation tank before the aeration tank, and at the initial stage of surface maintenance Since it is not provided, dirty sand directly flows into the aeration tank, and a large amount of sand flows into it during rainfall. Since this filthy sand has a structure in which organic matter is attached to the surroundings with inorganic fine sand as the core, the specific gravity is lighter than inorganic sand, but is 1.05 to 1.10, which is heavier than activated sludge in the aeration tank. ,
If a flow rate of about 20 cm / sec or more is not applied, it will settle.

[0003]

In particular, in the initial period after the operation of the oxidation ditch, the amount of inflowing water is small, and if all the installed aerators are operated for a long time, they become over-aerated and the activated sludge treatment is dismantled. Therefore, the aerator cannot be fully operated and some of the several aerators must be operated, or the rotation speed must be reduced to operate at low speed, which reduces the flow velocity and turns the sludge into accumulated sludge. However, there is a problem that the organic matter attached to this dirty sand is decomposed. Therefore, it is necessary to adjust the aeration amount according to the inflow amount. Also, since the smaller the scale of the treatment plant is, the larger the temporal fluctuation is. Therefore, the aerator may be operated according to the load fluctuation, and the aerator may be fully operated during the time when the inflow is large in one day. Since the specific sludge has a larger specific gravity than the activated sludge, it cannot be easily rolled up and has the drawback that the accumulated sludge is decomposed.

It is an object of the present invention to provide a method for preventing accumulation of dirty sand in an aeration tank of the oxidation ditch method so as to prevent anaerobic decay.

[0005]

Means for Solving the Problems The present invention has been made to achieve the above object, and in an oxidation ditch in which organic wastewater is biologically treated with activated sludge, mechanical aeration is performed at a water surface position of an aeration tank. One or more machines are installed, and a submersible agitator is installed at the bottom of the water tank on the upstream side of those aerators, and the mechanical aerators are operated at the maximum speed or all units at least once a day. Set a time zone to
The gist is to operate the stirrer according to this time zone to prevent the accumulation of dirty sand.

[0006]

[Function] An underwater type agitator is provided on the upstream side of the bottom of the aerator where dirt is liable to accumulate, and the agitator is operated at the maximum operating speed of the aerators or at the time of full operation when all units are operated. As a result, the accumulated dirty sand is rolled up, so that it is possible to prevent the state of activated sludge and the deterioration of treated water quality due to anaerobic decay of the dirty sand.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for preventing the accumulation of dirt in the oxidation ditch of the present invention will be described below with reference to FIGS. Oxidation Ditch aeration tank 1
Have the required size and shape as shown in FIG.
For example, as shown in FIG. 1, an oval or circular circulating water channel having a required size is formed in the aeration tank 1.
A mechanical surface aerator 3 is provided on the water surface. As shown in the figure, the system of this surface aerator 3 is, in addition to the screw type aerator,
A horizontal axis rotor type and a vertical axis rotor type are generally used, and one or a plurality of two or more aeration tanks are appropriately provided for each tank. Further, at the bottom of the aeration tank 1, an underwater agitator 4 is installed upstream of the aerator 3.

Considering the capacity of the agitator 4 and the installation position / number of the aerators 3, the number of installed units is set to one to a plurality, and in the embodiment of FIG. An aerator and a stirrer are arranged as a set. As a stirrer, a propeller-shaped mechanical stirrer is generally used.
The present invention is not necessarily limited to this, and it is possible to provide another stirring means such as a submersible pump.

Next, the operation and action of the oxidation ditch of the present invention constructed as described above will be explained. By driving the aerator 3 to rotate the screw 31 provided at its tip, negative pressure is generated at the screw tip, but the screw shaft is hollow and the hollow shaft above the water surface is provided with slits. Therefore, air is taken in from this slit, sent to the tip of the screw, atomized by the screw, and jetted into the water. Further, the activated sludge floats due to the stirring water flow obtained by the rotation of the screw, and the inflow sewage and the activated sludge are sufficiently mixed. The water flow pushed out by the aerator eventually reaches the corner part of the aeration tank, makes a half turn along the corner wall surface and the corner guide 2, and reaches the aerator arranged in the straight part of the next circulation water channel and enters the water channel. Form a circulating water stream.

As shown in FIG. 2, the flow in the water depth direction of the aerator 3 is a flow rectified from the water surface to the bottom at a position distant from the aerator 3, but at the position immediately after the aeration, a fine jet of gas is ejected. Since the bubble a advances obliquely downward and floats up, a minute vortex is formed near the bottom of the tank from the lower part of the screw to the downstream due to the effect of the flow accompanying the bubble. Therefore, particles that are heavier than activated sludge such as inflowing sand and silt are likely to settle. Especially in the early stage after the start of operation, the aeration machine cannot be fully operated due to the small amount of inflowing water, and a part of the aeration machine is operated, intermittent operation is performed, or rotation speed control is performed to perform aeration. Due to special operation such as reducing the amount, the circulation flow velocity in the tank becomes smaller than that at full operation. Therefore, the sludge and the sludge adhering to the sludge are accumulated in the lower part of the aerator where the flow velocity is the lowest.

In the present invention, at least 1 sludge is accumulated in the lower part of the aerator having the smallest flow velocity in the water channel in the present invention.
This time, the screw 41 of the stirrer 4 provided on the upstream bottom of the aerator for rotating the aerator to increase the average flow velocity to increase the average flow velocity and to wind up heavy sediment such as dirty sand is rotated and stirred. The machine water flow is applied directly to the sediment.

An example of such an operation schedule is shown in FIG.
Shown in. All of the aerators are operated at the same time according to the time when the amount of inflowing water is large, and they are overflowed and guided to the settling basin, and part of the settled sludge is discharged together with the sludge as excess sludge. Further, when the stirrer is stopped, the bottom flow velocity gradually decreases, so the suspended sediment begins to accumulate at the slowest flow velocity part, that is, at the bottom of the aerator. Therefore, most of the time of the day, the sludge will be accumulated, but once a day, all the aerators are operated at the same time, so the sludge settled at the bottom of the tank is rolled up and floated in the water. Then, since the dissolved oxygen is supplied, it is possible to prevent anaerobic decay of organic matter such as sludge attached to the dirty sand.

In the embodiment, the case of the screw type aerator has been shown, but similarly in the case of the horizontal axis rotor and the vertical axis rotor, the bottom flow velocity is also the lowest in the lower part of the aerator and its adjacent region. Therefore, by providing the stirrer on the upstream side bottom of the aerator and performing the operation of the present invention, the same action and effect can be obtained.

[0014]

The method for preventing the accumulation of dirt in the oxidation ditch of the present invention provides one or a plurality of mechanical aerators at the water surface position of the aeration tank, and the water tank at the bottom of the water tank upstream of these aerators. -Type stirrer is provided, and a time zone for operating the mechanical aerators at the highest speed or for all units is provided at least once a day. Therefore, it is possible to prevent the decomposition of the organic matter that has settled together with the dirty sand and the deterioration of water treatment accompanying it,
In addition, since the agitator, which only compensates for the insufficient flow rate when the aerator is fully operating, is placed at the most appropriate position, the equipment power of the agitator can be reduced, and the agitator can be set to the minimum when the aerator is fully operating Since the operation is limited, the energy consumption can be reduced.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a method for preventing dirt accumulation in an oxidation ditch according to the present invention.

FIG. 2 is a vertical sectional view of the same.

FIG. 3 is a time schedule diagram of an operation according to the present invention.

[Explanation of symbols]

1 aeration tank 2 corner guide 3 screw type aerator 4 stirrer a bubble b sediment

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C02F 3/14-3/26

Claims (3)

(57) [Claims] 1. In an oxidation ditch for biological treatment of organic wastewater with activated sludge, one or more mechanical aerators are provided at the water surface of the aeration tank, and the bottom of the aquarium upstream of these aerators is provided. An underwater stirrer is installed in
Provide a time zone for operating the mechanical aerator at the highest speed or all units at least once during the day, and operate the agitator in accordance with this time zone to prevent the accumulation of dirt. A method for preventing accumulation of foul sand in an oxidation ditch, which is characterized in that 2. The method for preventing accumulation of dirty sand in an oxidation ditch according to claim 1, wherein the mechanical aerator is a screw type. 3. The method for preventing accumulation of dirt in an oxidation ditch according to claim 1, wherein the mechanical aerator is a surface aerator having a horizontal axis or a vertical axis rotor.