JPH03181396A - Operating and controlling method for aeration tank - Google Patents

Abstract

PURPOSE:To stabilize purification efficiency of an aeration tank by fetching both the decreasing velocity of dissolved oxygen in the mixed soln. and the measurement result of the concn. of a fungus body into an arithmetic unit and calculating respiratory velocity and estimating the mean respiratory velocity and calculating BOD-MLSS load and feeding back this calculated BOD-MLSS load to operate and control the aeration tank. CONSTITUTION:One part of mixed liquid in an aeration tank 1 is passed through a sampling pipe 5 and sampled by a pump 6 and sent to a measurement device 7 of respiratory velocity. An oxygen densitometer (DO meter) 10 which measures the decreasing velocity of the concn. of oxygen in the mixed liquid in a tank 8 and a fungus body desitometer (MLSS meter) 11 which measures the concn. of the fungus body in the mixed liquid are provided. An arithmetic unit 17 is provided and both the DO meter 10 and the MLSS meter 11 are connected thereto with a signal wire. The arithmetic unit 17 calculates BOD-MLSS load. When this BOD-MLSS load exceeds the preset value, raw water is temporarily stored in an emergency storage tank to decrease load or the amount of the fungus body supplied to the aeration tank 1 is increased. Rise in the concn. of BOD in the treated water is prevented by this treatment.

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 used for activated sludge treatment.

(Conventional technology) The activated sludge treatment method introduces raw water and activated sludge into an aeration tank,
After aerating the mixture by blowing air into it, the treated water is discharged through a settling tank. In the activated sludge treatment method.

Conventionally, its operation was controlled by measuring the amount of dissolved oxygen (DO value) with an oxygen concentration meter (DO meter) installed at the end of the aeration layer, and by controlling the amount of air supplied to the aeration tank so that this DO value remained constant. The amount of bacterial cells (MLSS) or raw water load was controlled.

However, according to this method, there is no point in measuring the dissolved oxygen concentration during the reaction, so the dissolved oxygen concentration must be measured at the end of the aeration tank, and as a result, the raw water inflow and the measurement time are different. There is a problem that even if a gap occurs between the aeration tanks and raw water containing organic matter (BOD) that exceeds the processing capacity of the aeration tank flows in, this cannot be effectively dealt with.

Therefore, for example, Japanese Patent Application Laid-Open No. 82-38297.

The raw water is pre-aerated and introduced into the respiration rate measurement chamber, and activated sludge is mixed into this to measure the dissolved oxygen concentration and bacterial cell concentration (
A high-load raw water measurement method is shown in which the BOD concentration in the raw water is calculated based on the measurement results. If this method is used to control the operation of activated sludge treatment, the BOD concentration of raw water flowing into the aeration tank can be ascertained in advance, so if the raw water load exceeds the processing capacity of the aeration tank, for example, the raw water can be By directing the treated water to an emergency storage tank and leveling the load, it becomes possible to prevent the deterioration of the treated water.

(Problem to be solved by the invention) By the way, the purification efficiency in activated sludge treatment is determined by the total BOD load per unit amount of bacterial cells (MLSS) in the aeration tank.
It is known that the BOD concentration of treated water increases as the BOD-MLSS load increases, depending on the OD-MLSS load. In this BOD-MLSS load, the raw water BOD concentration is S1, and the raw water flow rate is M.

When the aeration tank MLSS concentration is X and the aeration tank volume is V, it is given by the following equation (1).

BOD-MLSS load=S'-M/X@V-(1)
However, according to the operation control using the above-mentioned high-load raw water measurement method, since it is simply used as the BOD concentration concentration S management index of the raw water, fluctuations in the BOD-MLSS load cannot be suppressed, and the aeration tank There was a problem that the purification efficiency became unstable.

The present invention has been made to solve the above-mentioned conventional problems, and its purpose is to
An object of the present invention is to provide an operation control method for an aeration tank that can stabilize the purification efficiency of the aeration tank by using the LSS load as a management index.

(Means for Solving the Problems) In order to achieve the above object, the present invention samples a mixed liquid of raw water and activated sludge from an aeration tank, blows air into it to aerate it, and then Measure the rate of decrease in dissolved oxygen and the concentration of bacterial cells, and then input these measurement results into a calculator to calculate the respiration rate per unit amount of bacterial cells.
The average respiration rate of the aeration tank is estimated from the above calculation results, and the BOD-MLSS of the aeration tank is further calculated based on the above estimation results.
A feature is that the load is calculated and this BOD-MLSS load is fed back to the operation control of the aeration tank.

Generally, the respiration rate in the aeration tank is R, that is, the rate of decrease in dissolved oxygen is 1, and the BOD amount in the aeration tank is S.

If the bacterial cell concentration in the aeration tank is X and the volume of the aeration tank is V, then
It is represented by the following formula (2) (where a.

b is a constant).

R=d02/dt =a. is considered to be constant, so if we integrate equation (2) over the residence time t and transform the equation, we get
The following formula (3) is obtained.

In this equation (3), the left side is the unit cell mass (MLSS)
It represents the rate of decrease in dissolved oxygen per hour, that is, the average respiration rate Ra of the aeration tank. On the other hand, in this equation (3), the above (
By substituting the equation 1), the following equation (4) can be approximately obtained.

Ra = a X (BOD-MLSS load) + b
-<4) That is, the BOD-MLSS load can be calculated by finding the average respiration rate Ra of the aeration tank. Therefore, in the present invention, the dissolved oxygen reduction rate and bacterial cell concentration are measured for the mixed liquid sampled from the aeration tank, and based on these measurement results, the respiration rate R per MLSS is first calculated, and then this R The average respiration rate Ra in the aeration tank is estimated from , and the BOD-MLSS load is calculated by substituting this Ra into equation (4).

By the way, activated sludge treatment methods can be roughly divided into a complete mixing method in which the mixed liquid is retained in an aeration tank for a certain period of time and aerated, and a push flow method in which the mixed liquid is continuously flowed into the aeration tank and aerated. In the former case, the inside of the aeration tank can be considered homogeneous, so if the respiration rate R per MLSS is calculated for the mixed liquid sampled from any part of the aeration tank, this is the average respiration rate of the aeration tank. It represents Ra.

However, in the case of the extrusion flow method, in Figure 5, which shows the relationship between the respiration rate in the aeration tank and the aeration time, the aeration time can be read as the distance $L from the raw water inlet, and therefore the sampling The respiration rate per MLSS differs depending on the location. For this reason, considering boat fishing, unless you sample the mixed liquid countless times from the inlet to the outlet of the aeration tank, find the respiration rate per MLSS for each, and divide the sum by the residence time t, the average It is not possible to determine the respiration rate Ra.However, with such a method, the measurement requires residence time, and it is impossible to manage the operation of activated sludge treatment.Therefore, in the present invention, the method shown in FIG. Focusing on the fact that more than 75% of the organic matter that flows into the aeration tank is removed in the first 20 to 30 minutes, as shown in the figure, the mixed liquid was sampled from several locations near the inlet of the aeration tank, and after each sampling. The respiration rates R1, R2, .

(Function) According to the operation control method of the aeration tank configured as described above,
The BOD-MLSS load is determined by measuring the dissolved oxygen reduction rate and bacterial cell concentration in the mixed liquid sampled from the aeration tank, and this ROD-MLSS load management index is quickly calculated according to the actual condition of the aeration tank. Can control operating conditions.

(Example) Hereinafter, an example of the present invention will be described based on the accompanying drawings.

Embodiment 1 FIG. 1 shows an embodiment of the present invention aimed at a complete mixing type aeration tank. In the figure, l is an aeration tank, 2 is a raw water adjustment tank, and 3 is a settling tank. Raw water is pumped into the aeration tank 1 from the raw water adjustment tank 2, and activated sludge is pumped from the settling tank 3. , and in the mixed liquid of raw water and activated sludge stored in the aeration tank 1,
Air sent from an air source (not shown) is blown through the air pipe 4. The organic matter in the raw water is oxidized and decomposed during the aeration for a predetermined period of time, and after the aeration, the treated liquid is sent to the sedimentation tank 3 for solid/liquid separation, and the supernatant water is discharged as treated water. A portion of the precipitated activated sludge is returned to the aeration tank 1.

A part of the liquid mixture in the aeration tank 1 is sampled by a pump 6 through a sampling pipe 5 and sent to a respiration rate measuring device 7 provided separately. The respiration rate measuring device 7 includes a sealed tank 8 that stores the sampled mixed liquid. This tank 8 includes a stirrer 9 that stirs the mixed liquid, and an oxygen concentration meter (D
A microbial cell concentration meter (MLSS meter) 11 for measuring the bacterial cell concentration in the mixed liquid is provided. The tank 8 also has an air pipe 13 connected to the air source 12, and an air pipe 13 connected to the air source 12.
Air bleed pipe 14 that releases the air inside, and aqua regia pipe 1 that supplies cleaning water for DO meter 1O and MLSS total 11 count 1
5 and a drain pipe 16 for draining the drain. Additionally, a computing unit 17 is separately provided, which includes the D
A total of 10 O and a total of 11 MLSS are connected by one wire.

Hereinafter, the operation of this embodiment will be explained with reference to FIG. 2 as well.

First, a mixed solution of raw water and activated sludge is sampled from the aeration tank 1 using the pump 8 at an appropriate timing (Sl),
This is sent to the tank 8 of the respiration rate measuring device 7 until a small space is left above the tank 8.Next, the mixed liquid in the tank 8 is aerated for a certain period of time by the operation of the air source 12, and the dissolved liquid in the mixed liquid is The oxygen concentration is increased (S2), and after this aeration, the mixed liquid in the aeration tank 1 is sampled again using the pump 6, and this is sent to the tank 8 until it is full. At this time, excess air in the tank 8 is released through the F-bleed pipe 14 (S3), and when the tank 8 is full, all valves are closed to seal the tank 8 (S4).

Next, the DO meter 10 measures the dissolved oxygen concentration rate in the mixed liquid (S5), and the MLSS meter 11 counts 1
The bacterial cell concentration in the mixed liquid is measured (SO), and these measurement results are sent to the computing unit 17. The calculator 17 takes in the measurement results and first calculates the rate of decrease in dissolved oxygen per MLSS, that is, the respiration rate R (S?). In the aeration tank of this complete mixing method, the respiration rate R per MLSS is: Corresponds to the average respiration rate Ra of the aeration tank 1, and the calculator 17 then calculates BOD-ML using the above equation (4).
Calculate the SS load (S8), and this BOD-
! If the IILss load exceeds the set value, either temporarily store the raw water in an emergency storage tank to reduce the load, or use the aeration tank! Prevent the BOD concentration of treated water from increasing by taking measures such as increasing the amount of bacteria supplied to the tank. After the measurement by the respiration rate measuring device 7, the drain pipe 16 is opened to drain the mixed liquid in the tank 8, and the cleaning water is force-fed to the water pipe 15, and the DO meter 10 and the MLSS meter 11 are Prepare for the next measurement.

FIG. 3 shows an investigation of the correlation between the average respiration rate Ra of the aeration tank 1 obtained from the above measurement results and the actually measured 800-MLSS load, and a good correlation is recognized between the two. It is clear from this that there is no problem even if the BOD-MLSS load is calculated using 0).

Embodiment 2 FIG. 4 shows an embodiment of the present invention aimed at an extrusion flow type aeration tank. Note that the same parts as those shown in FIG. Sampling points PI, P2 + P3 + P4 (4 locations in this view)
Set.

Branch pipes 21a and 21b branched from the sampling pipe 5.

21c and 21d as each sampling point) Pt ~
A valve 22a is introduced into P4 and installed in each branch pipe.

22b, 22c, and 22d, the liquid mixture at each sampling point can be independently sampled into the respiration rate measuring device 7 through each branch pipe.

By the way, the respiration rate in the aeration tank l is given by the above equation (2), and the first term on the right side of this equation (2) [a・(dS/
dt )] represents the respiration rate necessary for oxidizing organic matter. Therefore, by setting this first term as Rs, integrating equation (2) over residence time t, and transforming the equation, we can approximately obtain the following (
5) Equation is obtained.

In this equation (5), the left side is the average respiration rate R of the aeration tank
a, and the first term on the right side is the average respiration rate R required for organic matter oxidation.
It is clear that the average respiration rate Ra of the aeration tank can be estimated by finding the respiration rate R° required for organic matter oxidation. However, as mentioned above (by formula 0, BO
It has been found that the D-MLSS load is proportional to the average respiration rate Ra of the aeration tank, and therefore the ROD-MLSS load is proportional to the respiration rate R° required for organic matter oxidation.

On the other hand, the respiration rate in the aeration tank l is as shown in Figure 5.
Although it decreases logarithmically with respect to the aeration time T, in the case of an extrusion flow type activated sludge treatment apparatus, the aeration time T can be read as the distance from the inlet 1a of the aeration tank 1. In this Figure 5, part A (shaded area) shows the amount of oxygen (respiration amount) consumed for organic matter oxidation, and part B (dotted area) shows the amount of oxygen (respiration amount) consumed for controlling the presence of bacteria. each represents. From this, 7 of the organic matter that flowed into the aeration tank 1
It is clear that more than 5% is removed during the first 20 to 30 minutes, ie near the inlet la of the aeration tank l. Therefore, in this example, the above sampling point (Pa) was set at a location where 80% of the amount of oxygen necessary for oxidizing organic matter was consumed.
Sampling points Pl are set near the inlet 1a of the aeration tank l, and other sampling points P 2 + P are set at appropriate intervals between these Pl and P4.
3 (Fig. 4), and each point P1 to P4.
The positions of Ll, L2. L3 (Fig. 4), and the respiration rate per MLSS R1*R2 in the same manner as in Example 1 for the mixed liquid sampled from each point.
+R3R4 is obtained, and the geometric mean stone is calculated based on the following equation (8) and substituted into equation (5), thereby making it possible to estimate the average respiration rate Ra of the aeration tank.

Rs = ((R3 in R2) ・(Ll-L2)
・1/2 + (R4 in R3)・(L2-L3)
・1/2 + (R5 in R4) ・L3・ 1
/2)/Ll
(6) Fig. 6 shows the processing flow of the second embodiment, and the steps STI to ST? Example 1 up to
Steps 61 to S7 are exactly the same, and in the second embodiment, the respiration rate R per MLSS is determined for each measurement while repeating washing in ST8 to STII, and step 5T is performed.
In step 12, the geometric mean n is calculated based on the above equation (6) to estimate the average respiration rate Ra of the aeration tank, and in step 5
In step 713, the BOD-MLSS load is calculated and the process ends.

In addition, FIG. 7 is a result of investigating the correlation between the average respiration rate Ra of the aeration tank l obtained from the above measurement results and the actually measured BOn-MLSS load, and a good correlation is recognized between the two.

(Effects of the Invention) As described above in detail, according to the aeration tank operation control method according to the present invention, it is possible to promptly cope with a decrease in purification efficiency due to fluctuations in BOD-MLSS load. The effect of significantly improving the reliability of activated sludge treatment can be obtained.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the first embodiment of the present invention, Fig. 2 is a flowchart showing the processing flow of the first embodiment, and Fig. 3 is the aeration obtained by calculation in the first embodiment. A graph showing the correlation between the average respiration rate of the tank and the measured 800-MLSS load, Fig. 4 is a schematic diagram showing the second embodiment of the present invention, and Fig. 5 shows the correlation between the respiration rate in the aeration tank and the aeration time. 6 is a flowchart showing the processing flow of the second embodiment, and FIG. 7 is a graph showing the correlation between the average respiration rate of the aeration tank calculated in the second embodiment and the actually measured ROD-
It is a graph showing correlation with MLSS load. l...Aeration tank, 2...Raw water adjustment tank 3
...Sedimentation tank, 5 ...Sampling tube 7
... Respiration rate measuring device, 8 ... Tank 10 ・
・・DO meter, 11 ・IIISS total 2 ・・Air source. 7...Arithmetic unit

Claims (1)

[Claims] (1) Sample a mixed solution of raw water and activated sludge from inside the aeration tank, blow air into it to aerate it, measure the rate of decrease in dissolved oxygen and bacterial cell concentration in this mixed solution, and then:
These measurement results are input into a calculator to calculate the respiration rate per unit amount of microbial cells, and the average respiration rate of the aeration tank is estimated from the calculation results.Further, based on the estimation results, the BOD- Calculate the MLSS load and use this BO
An aeration tank operation control method characterized by feeding back a D-MLSS load to the aeration tank operation control.