JPH0516319B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the operation of an aeration tank in a so-called activated sludge process.

[Conventional technology]

The so-called activated sludge method is a sewage treatment method that utilizes the purification function of microorganisms, and is the most commonly used sewage treatment method for treating various types of wastewater including municipal sewage.

In such an activated sludge method, a flow rate regulating tank and a settling tank are usually installed before and after an aeration tank in which sewage is subjected to aeration treatment.

Then, the wastewater to be treated that flows into the flow rate adjustment tank is
Conventionally, it was handled as follows.

That is, Fig. 4 is a schematic diagram showing the flow rate adjustment tank, where 1 is a flow rate adjustment tank, 2 is a roll water level switch (hereinafter abbreviated as LWL switch), and 3 is a high water level switch (hereinafter abbreviated as HWL switch). ), 4 is an alarm water level switch (hereinafter abbreviated as AWL switch), 5 is two transfer pumps, and normally only one is used to transfer the wastewater to be treated.

Next, these operations will be explained. The liquid level
When the HWL is reached, one pump 5 is activated, and the wastewater to be treated is thereby supplied to an aeration tank (not shown). Then, the liquid level gradually decreases, and when it reaches LWL, the pump 5 stops. Thereafter, when the liquid level rises and reaches HWL, the pump 5 is operated again. In addition, even though the pump 5 is operating due to the large amount of inflow of wastewater to be treated, the liquid level rises.
When AWL4 is reached, two pumps 5 are activated and an alarm is issued.

On the other hand, air is constantly supplied into the aeration tank by a blower, and the sewage to be treated supplied from the flow rate adjustment tank 1 is aerated together with the sludge returned from the settling tank. Then, the mixed liquid in the aeration tank that has been subjected to aeration treatment is transferred from the aeration tank to the settling tank.
Here, it is precipitated. The precipitated supernatant liquid is then discharged as treated water, and the precipitated sludge is returned to the aeration tank.

Note that a metering tank for measuring and adjusting the flow rate to the aeration tank is provided above the flow rate adjustment tank 1.

[Problem that the invention seeks to solve]

In the conventional aeration tank operating method as described above, when the difference between the amount of sewage actually treated (actual amount of sewage) and the planned amount of sewage is small and the sewage to be treated is supplied quantitatively, No particular problem arises.

However, in reality, the actual amount of sewage is significantly smaller than the planned amount of sewage, and the amount of inflow of sewage to be treated is irregular in most cases.

Therefore, the conventional operating method in which the sewage to be treated was transferred from the flow rate adjustment tank to the aeration tank using only a level switch had the following problems.

For example, in FIG. 4, when the liquid level reaches HWL, it gradually decreases due to the operation of the transfer pump 5, and when it reaches LWL, the operation of the transfer pump 5 is stopped. Then, when the liquid level rises to HWL again, the operation of the transfer pump 5 will be restarted. However, if the amount of wastewater to be treated is small at this time, it will take a long time for the liquid level to rise from LWL to HWL, resulting in a state in which no wastewater to be treated is supplied to the aeration tank for a long time. It turns out. In such a state, the microorganisms in the aeration tank will lack nutrients, making it impossible to carry out effective treatment.

In addition, if the above-mentioned measuring tank is installed above the flow rate adjustment tank, it will be possible to adjust the amount transferred to the aeration tank, but if this transfer is too small, it will be difficult to use a triangular shape that functions as an overflow port for the metering tank. The notch becomes clogged with scum, etc., and the transfer stops.

For this reason, the amount of transfer cannot be made that small, and the above-mentioned drawbacks cannot be eliminated.

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide an operation control method that can most effectively exert the processing functions of a processing tank and equipment related thereto.

[Means for solving problems]

As a means for solving the above-mentioned problems, the present invention has a structure in which aeration treatment is carried out every predetermined time period, and in synchronization with this, wastewater to be treated is supplied to an aeration tank during the aeration treatment time. It was adopted.

[Effect]

The operating time of the blower is set in advance so that the wastewater to be treated is introduced into the aeration tank and intermittent aeration treatment is performed. Wastewater to be treated is introduced into the flow rate adjustment tank,
When the level switch detects that the water level is between HWL and LWL, the transfer pump is activated in time with the aeration tank blower operation time, and the wastewater to be treated is advected to the aeration tank. And that water level is LWL
This operation is repeated until the flow rate adjustment tank is reached, and the agitation device installed in the flow rate adjustment tank is operated in conjunction with the operation of the transfer pump to prevent sludge etc. from settling in the flow rate adjustment tank.

On the other hand, the wastewater to be treated advected to the aeration tank is aerated in the aeration tank, and then led to a settling tank where it is subjected to sedimentation treatment. The separated supernatant liquid is then discharged as treated water, and a portion of the settled sludge is returned to the aeration tank as return sludge.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 3.

In Figure 1, 1 is the flow rate adjustment tank, 2 is the LWL
3 is a HLW switch, 4 is an AWL switch, 5 is a transfer pump, 6 is a stirring device, 7 is an aeration tank, 8 is a settling tank, 9 is a control device, and 10 is a blower. Although not shown in the drawing, two transfer pumps 5 are provided, and normally only one is operated.

Further, a metering tank (not shown) is provided between the flow rate adjustment tank 1 and the aeration tank 7.

The operating time of the transfer pump 5, stirring device 6, and blower 10 is set in advance in the control device 9 by a 24-hour timer mechanism or the like, as shown in FIG. 2 or 3. The operation pattern shown in FIG. 2 is a case where the flow rate is adjusted with a metering tank, and the operation pattern shown in FIG. 3 is a case where a metering tank is not used. First, the operation pattern shown in FIG. 2 will be explained.

When the wastewater to be treated is introduced into the flow rate adjustment tank and the LWL switch 2 detects the inflow of the wastewater to be treated, a detection signal is sent to the control device 9. In response to the detection signal, the control device 9 unlocks the operation switches of the transfer pump 5 and the stirring device 6, so that the operation is performed according to the preset operation pattern as described above. Note that the blower 10 provided in the aeration tank 7 is operated intermittently according to the above-described operation pattern, regardless of the flow of wastewater to the flow rate adjustment tank 1. When a predetermined time has elapsed, the stirring device 6 provided in the flow rate adjustment tank 1 starts operating, and then, for example, 30 minutes later, the transfer pump 5 and the blower 10 start operating. And the water level in flow adjustment tank 1 is
If it is within the range from LWL to HWL, this operation is repeated.

In addition, if a metering tank is not used, it is better to operate the transfer pump 5 in several steps for each operation of the stirring device 6 and blower 10, as shown in Fig. 3. . If a metering tank is not used, the water to be treated transferred by the transfer pump 5 will be directly introduced into the aeration tank 7, and the inflow will be larger than when the flow rate is adjusted. The condition in the aeration tank 7 or the settling tank 8 can be stabilized by going to

When the water level in the flow rate adjustment tank 1 falls below LWL, the transfer pump 5 and stirring device 6 are locked by the control device 9 and do not operate regardless of the operation pattern until inflow is detected again. The state is such that only the blower 10 is not operated and is operated according to the operating pattern.

In addition, if the inflow of wastewater to be treated is large and the water level rises while the transfer pump 5 is operating depending on the operation pattern and reaches HWL, the transfer pump 5 is operated regardless of the operation pattern and the water level is lowered to LWL. lower to Furthermore, if the inflow of wastewater to be treated is very large and the water level rises even though the transfer pump 5 is in operation and reaches AWL, the two transfer pumps 5 are operated together from HWL to HWL. The water level is lowered to LWL using one transfer pump.

In addition, in the case of forced operation of the transfer pump unrelated to these operation patterns, there is no need to lower the water level to LWL, and the MWL is between LWL and HWL.
may be set, the water level may be lowered to this point, and then returned to the operating state depending on the operating pattern.

The reason why the stirring device 6 is activated before the transfer pump 5 is activated is that sludge or the like may have settled in the flow rate adjustment tank 1, and the aeration tank 7 may be exposed to extremely high concentrations. This is to prevent treated sewage from being advected and to save on electricity costs compared to constant operation.

Then, the wastewater to be treated which has been subjected to intermittent aeration treatment in the aeration tank 7 is introduced into the settling tank 8. The supernatant liquid separated from the sludge in the settling tank is discharged as treated water.
The settled sludge is returned to the aeration tank 7 as return sludge. A part of the settled sludge is removed as surplus sludge, if necessary.

Since the mixed liquid in the aeration tank is led out from the aeration tank 7 to the settling tank 8 by overflow discharge from the aeration tank 7, it is carried out naturally according to the advection from the flow rate adjustment tank 1 to the aeration tank 7. It will be. Therefore,
When the advection pump 5 is not operating, only the returned sludge flows into the aeration tank 7, and there is little advection of the water to be treated into the settling tank 8, and the settling tank remains stationary, preventing sludge from settling. promoted. Here, when an air lift pump that uses aeration air is used to transfer the return sludge, when the aeration is stopped, the transfer of the return sludge is also stopped.

In accordance with the operating pattern shown in FIG. 2, an experiment was conducted using on/off operation for one cycle t time, and when compared with the conventional operating method, the following findings were made. In this experiment, the water load rate (actual sewage volume/planned sewage volume x 100) was
It was less than 50%.

In the conventional method, wastewater was transferred from the flow rate adjustment tank to the aeration tank over a period of 13 to 14 hours, in order to prevent wastewater from flowing into the aeration tank for too long. However, with this operating method, the transfer time is set to 9 hours, so the amount of sewage to be treated at one time increases compared to conventional methods, which may cause problems such as carryover of sedimentation tank sludge and deterioration of water quality. None of these problems occurred. As mentioned above, the conditions of the settling tank promoted sludge settling, and the sludge interface remained stable, although it fluctuated by about 50 cm between the start and end of aeration.

Regarding water quality, the average BOD value of treated water is 15 based on the conventional method.
mg/, but in this experiment it dropped considerably to 5 mg/. Similarly, the average visibility is 40cm and 100
cm, and the process was quite stable over time.

In addition, the problem of clogging in the triangular notch of the metering tank is almost completely resolved without any problems, as more than a certain amount of sewage is periodically overflowed, and the floating scum and the like are washed away.

〔Effect of the invention〕

As explained above, the present invention supplies wastewater to be treated from the flow rate adjustment tank to the aeration tank intermittently through temporal control, mainly synchronized with the aeration time of the aeration tank. We have minimized the operating time of water pumps, etc., and in addition, we have reduced the amount of sewage to be treated that flows into the aeration tank at a time and distributed it throughout the entire system, so if the actual amount of sewage is significantly less than the planned amount of sewage. Even in this case, it is possible to effectively prevent the deterioration of the purification function of the entire equipment, and it is possible to achieve the effect that energy saving can be achieved. Further, nitrogen contained in the wastewater to be treated can be effectively removed.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram for explaining an embodiment of the aeration tank operation control method according to the present invention, FIG. 2 is a time chart thereof, FIG. 3 is a time chart of another embodiment of the present invention, and FIG. The figure is a schematic diagram of a flow rate adjustment tank. 1 is a flow rate adjustment tank, 5 is a transfer pump, 6 is a stirring device, 7 is an aeration tank, 8 is a settling tank, 9 is a control device,
10 is a blower.

Claims (1)

[Scope of Claims] 1. A method in which wastewater to be treated is introduced into a flow rate adjustment tank, supplied to an aeration tank by a transfer pump disposed in the flow rate adjustment tank, and then subjected to aeration treatment. The treatment is performed every time a predetermined time has elapsed, and in synchronization with this, the transfer pump is controlled to operate during the aeration treatment time, and the wastewater to be treated is supplied to the aeration tank. How to control the operation of an aeration tank.