JP2730728B2 - Operation control method for batch activated sludge treatment equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an operation control method for a batch activated sludge treatment apparatus.

Conventionally, operation management of a batch activated sludge treatment apparatus has been performed based on the experience of an operation manager having a certain level of technology or more. As a result, the present invention is used in various industries, such as small and medium-sized food manufacturing industries, where it is not expected to have a dedicated operation manager of the activated sludge treatment device. It is very effective in improving the environment as a method of controlling the operation of a wastewater treatment apparatus that always obtains the best water quality.

[Conventional technology]

Batch activated sludge treatment of wastewater has a long history, but this treatment has traditionally been regarded as a simple device in activated sludge treatment equipment. However, this treatment has recently been evaluated in terms of the effect of suppressing filamentous bacteria, the effect of removing phosphorus, and the effect of removing nitrogen, and the batch activated sludge treatment system has been actively reviewed. The conventional general batch-type activated sludge treatment is basically a system in which inflow of raw water, mixing and stirring, aeration treatment, solid-liquid sedimentation separation, and discharge of treated water are carried out in a single tank. Device. The operation control of such batch activated sludge treatment includes water level control, timer control,
In many cases, the control is performed by using the dissolved oxygen concentration (hereinafter referred to as DO), but basically, it completely relied on the experience of the operation manager.

[Problems to be solved by the invention]

The batch activated sludge method is usually operated in a process as shown in FIG. That is, in FIG. 1, the inflow step (1) wastewater is discharged with the operation of the factory and flows into the wastewater treatment system.

(2) The pump that detects the water level when the water level in the pump pit rises starts operating.

Aeration process (3) The aeration device is started by starting the timer.

(4) The pump stops at the end of the factory operation.

(5) The operation of the aeration apparatus is stopped after a lapse of a predetermined time, or the operation of the aeration apparatus is stopped when the DO instruction level of the DO meter is achieved.

(Note) In the batch activated sludge method, which is a variation of the batch type, the aeration is not started until 16:00 in the time chart of FIG. 1 and the aeration starts when the inflow ends.

Sedimentation separation step (6) The sedimentation time is set using a timer or a timer and a sludge interface meter.

Discharge step (7) The discharge of the treated wastewater is controlled by using a timer or a timer together with a sludge interface meter and a water level meter.

The conventional batch activated sludge method is generally operated in the manner described above.However, fluctuations in raw water concentration, water quality, water volume, seasonal fluctuations, MLSS concentration fluctuations, etc. On the other hand, since the operating conditions do not follow, there has been a problem that the processability is not always stable in the operation of the batch type activated sludge treatment apparatus. For this reason, the setting change of the timer, the change of the DO level, etc. are always performed based on the judgment of the operation manager, but the quality of the treated water is affected by the fluctuation of the raw water side and lacks stability.

Therefore, the present invention eliminates the above-mentioned problems of the prior art, and provides a method for controlling the operation of a batch-type activated sludge treatment apparatus in which the processability is stable and stable treated water quality can be obtained without receiving fluctuations on the raw water side. The purpose is to provide.

[Means for solving the problem]

According to the present invention, in operating the batch activated sludge treatment apparatus, the dissolved oxygen concentration in the aeration tank is measured and analyzed which changes according to the progress of the wastewater treatment in the aeration tank, and the concentration of the dissolved oxygen at or above a certain value is measured. The rising gradient that increases with time of dissolved oxygen under a predetermined value, that is, 0.1 to 0.2 mg / l / hr
An operation control method for a batch-type activated sludge apparatus, which controls the operation of the apparatus by setting the time point at which the processing becomes complete as the processing is completed, is provided.

[Action]

Experience shows that DO in the aeration tank is deeply involved in processability. In a continuous activated sludge system, the DO of the aeration tank is controlled to a constant value to ensure the treatment stability. However, in the case of the batch type, since the DO fluctuates due to fluctuations in processability, elapse of the processing time, etc., there is little effect even if control is performed with a constant DO value as in the continuous type. In the case of the batch activated sludge method, the treatability of DO and wastewater in the aeration tank is particularly remarkable.

Fig. 2 shows the inside of the aeration tank when treated by the batch activated sludge method.
It shows the change over time of DO and residual COD. The DO and COD are clearly correlated, and it can be seen that the processing is completed when the DO has risen completely. It is presumed that stable processing performance can be obtained by controlling the operation by focusing on this. However, this cannot be controlled by the DO value. The A value of DO in FIG. 2 is not always constant, and varies every day, such as 8 mg / l or 6 mg / l.

Such fluctuation factors include the amount of aerated air, water temperature, MLSS concentration, load such as COD and BOD. These factors are constantly fluctuating and are difficult to stabilize at wastewater treatment sites. Therefore, if DO control is performed at a certain level, DO is still rising, and pollutants in wastewater typified by COD and BOD are in an undecomposed state.
In some cases, useless aeration may need to be continued as a result of equilibrium without reaching the set value, and there was a problem in using the DO value as a control index. So DO
Instead of the value, a point where DO is stabilized at a certain level is grasped, and it is determined that control can be performed if the point is set as the processing end point.
The control uses a rising gradient of DO (O ₂ mg / l / hr), and the rising gradient gradually decreases, for example, 0.15 mg / l / hr, preferably 0.1
The point at which it became 〜0.2 mg / l / hr was regarded as the processing end point.

However, as is apparent from the graph of FIG. 2, the point where the rising gradient of DO becomes 0.1 to 0.2 mg / l / hr appears twice. 1
The third time, when DO begins to gradually increase from low level,
The second time is when the increased DO converges to a constant value. The processing end point is at the point of time when the second time is high, and is not the first time. Since the first rising gradient always appears at a low DO value (about 3 mg / l or less), a constant value (DO ≒ 3 mg / l)
/ l) The control point may be a time when the rising gradient of DO becomes 0.1 to 0.2 mg / l / hr.

According to the present invention, by performing control using the processing end point as an index by the above means, aeration air amount, water temperature, MLSS concentration, COD, BOD, etc., are not affected by fluctuations, etc. It has become easier to obtain constant and stable treated water quality.

FIG. 6 shows an example of an apparatus for carrying out the present invention.
After the wastewater to be treated is once received in the pump pit, it is pumped into a batch type aeration tank by a pump. The wastewater that has entered the aeration tank is mixed well with the activated sludge in the aeration tank by the air discharged from the blower and blown through the air diffuser. DO as an index of processability is detected by a DO sensor in the aeration tank, and the end point of the process is determined based on the analysis result of the computer. When the treatment is completed and the aeration is stopped, the activated sludge settles at the bottom of the aeration tank. The supernatant water is discharged as treated water by a discharge pump. At that time, the excess sludge is drawn into the excess sludge storage tank by the excess sludge pulling pump, and is stored and completed.

〔Example〕

The control DO gradient of the present invention and the processing status in the DO gradient region before and after the control DO gradient are shown in the following examples, but it goes without saying that the scope of the present invention is not limited to these examples.

Example 1 Controllability and processing conditions in the range of control DO gradient 0.0 to 0.05 mg / l / hr (point where DO increased and reached almost equilibrium) Example 2 Control DO gradient 0.1 to 0.2 mg / l / hr (Slightly before DO rises and becomes equilibrium: control area of the present invention) Example 3 Processability and processing in area of control DO gradient 0.3 to 0.4 mg / l / hr Situation (point at which DO increased linearly and entered the area of the curve) Results Using synthetic sewage, treatment tests were performed under the following conditions, and the treatment properties were compared.

(1) Target water BOD concentration 800mg / l (2) Target water COD concentration 550mg / l (3) MLSS concentration 3200mg / l (4) BODMLSS load 0.25kg / kg ・ D The results are shown in Fig. 3 and Fig. 4. And FIG. 5 and Table-1 and Table-
2 and Table-3.

Comparison of processability (1) SVI value The SVI value at the start of the test was 80 ml / g,
Began to rise gradually and became unstable. In the latter half of the test, the sludge started to become slightly viscous and tended to viscous bulking. Microscopically, almost no filamentous bacteria were found. Comparing Example 1 and Example 2, Example 2 was extremely stable and good, but Example 1 showed a slight but tendency to increase SVI value. It was presumed that it would get even higher as we proceeded.

(2) BOD processability In Example 3, the raw water BOD concentration was 800 mg / l.
Although the treatment was well performed at around mg / l,
The value increased and exceeded 20 mg / l in the second week, and the increasing trend continued. Example 2 was stable at 10 mg / l or less, while Example 1 tended to be slightly higher.

(3) COD processability Although the tendency is almost the same as BOD, the removal rate of Example 3 was abnormally high and the removal rate was 90% or less. Examples 1 and 2 were almost unchanged.

From the above, the DO at the end of aeration is in the range of 6 to 8 mg / l in all three conditions, which is the most conditional as the control concentration in the case of DO control in the conventional batch activated sludge treatment. Good concentration. However, as seen from the examples, in Example 1, the activated sludge was dispersed in the aeration tank because the activated sludge was in the self-digestion region, and the floc tended to be miniaturized. In addition, the water quality was unstable. Embodiment 3 uses DO
Despite the value being 6 mg / l or more, the treatment was not completed, the treated water quality deteriorated, and the properties of the activated sludge also deteriorated over time. In Example 2, the treated water quality was good and stable, and the separation and coagulation properties of the activated sludge were also good, confirming that the control region was the most conditionally superior to the other two examples.

〔The invention's effect〕

Conventional batch-type activated sludge treatment equipment has largely relied on the experience of operation managers.However, the present invention has confirmed the optimum treatment conditions, and it can be easily controlled automatically using a DO meter. It became. As a result, the best processability was always obtained, and the operation and the automatic control at the minimum running cost were made possible without excessive aeration.

[Brief description of the drawings]

FIG. 1 is a time chart showing a normal operation treatment process of a conventional batch activated sludge method, and FIG. 2 is a DO chart in an aeration tank when treated by a batch activated sludge method.
And FIG. 3 is a graph showing the change over time of the SVI value with the control DO gradient as a parameter. FIG. 4 is a graph showing the change of the residual COD with time, and FIG. FIG. 5 is a graph showing the change over time in the COD processability, FIG. 5 is a graph showing the change over time in the BOD processability using the control DO gradient as a parameter, and FIG. 6 implements the present invention. 1 is a drawing showing an example of an apparatus for performing the above. … Wastewater to be treated, Pump pit… Pump …… Aeration tank… Blower, diffuser… Computer… DO sensor… Treatment water… Discharge pump… Excess sludge extraction pump… Excess sludge storage tank

Claims (1)

(57) [Claims] When operating a batch type activated sludge treatment apparatus, the concentration of dissolved oxygen in an aeration tank, which changes with the progress of wastewater treatment in the aeration tank, is measured and analyzed. A method for controlling the operation of a batch activated sludge treatment apparatus in which the operation is controlled when the rising gradient that rises with the time of dissolved oxygen becomes 0.1 to 0.2 mg / l / hr.