JPH09281073A - Method for sensing adherence of microorganism membrane to do-electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for sensing adherence of microorganism membrane to a DO electrode capable of employing a suitable countermeasure such as cleaning by automatically detecting the adhered state of the membrane to the electrode used for a respiratory speedometer. SOLUTION: A respiratory speedometer by an active sludge process aerates active sludge liquid by introducing the air to the liquid, stops the deaeration after DO concentration is raised to a set value, degases it, measures the change of the concentration due to oxygen dissipation of aerobic microorganism of active sludge by using a DO electrode 20 and a DO meter, and calculates the respiratory speed of the sludge from the reducing speed of the DO by the method of least squares. In this case, the method for sensing the adherence comprises the steps of recording the change in the concentration by an automatic recorder, sensing the adherence of a microorganism membrane to the electrode 20 at the time of abrupt reduction in the DO at the degassing step, lifting the electrode 20, and conducting the countermeasure operation such as cleaning.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting microbial film adhesion to a DO electrode used in an apparatus for highly efficiently removing organic matter and nitrogen in wastewater by using a circulating nitrification denitrification method.

[0002]

2. Description of the Related Art Various methods have conventionally been proposed for efficiently removing organic matter in wastewater such as sewage and removing nitrogen and phosphorus which are considered to be the causative agents of eutrophication in closed water areas. . This eutrophication refers to an increase in the concentration of nutrient salts such as N, P in the water area, which activates biological activities using these nutrients as nutrients and changes the ecosystem. In particular, it is known that the above-mentioned eutrophication rapidly progresses when a large amount of domestic wastewater or industrial wastewater flows into lakes and the like.

Recently, it has been required to increase the removal rate of nitrogen, and it is expected that the regulations on nitrogen will be stricter. Therefore, the number of facilities adopting an advanced treatment process capable of removing this will increase. it is conceivable that.

As a biological method for simultaneously removing nitrogen and phosphorus, a circulation type nitrification denitrification method has attracted attention as a modification of the conventional activated sludge method. This circulation type nitrification denitrification method is, for example, as shown in FIG. 5, the biological reaction tanks are anaerobic tanks 1a and 1b in which dissolved oxygen (hereinafter abbreviated as DO) does not exist and a plurality of aerobic tanks 2a in which DO exists. , 2b, 2c, and the anaerobic tanks 1a, 1b are used to agitate the inflowing raw water 3 by an agitation mechanism 10 under anoxic conditions to denitrify by denitrifying bacteria in the activated sludge, and then aerobic. By supplying air from the blower 5 to the air diffuser 4 arranged inside the tanks 2a, 2b, 2c, oxidative decomposition of organic matter by activated sludge and nitrification of ammonia by nitrifying bacteria are performed in the presence of oxygen by aeration. Then, the nitrifying solution in the last-stage aerobic tank 2c is fed into the anaerobic tank 1a by using the nitrifying solution circulating pump 6, whereby the denitrifying effect of the anaerobic tanks 1a and 1b is promoted.

Since the activity of the above nitrifying bacteria decreases as the DO concentration decreases, the DO of the last aerobic tank 2c is measured to obtain D
It is customary that the O controller 12 controls the drive of the blower 5.

The above-mentioned denitrifying bacterium refers to a bacterium that reduces N0 ₂ -N and N0 ₃ -N to N ₂ and NO ₂ by respiration of nitric acid under anaerobic conditions. Also, phosphorus in raw water is anaerobic tanks 1a and 1b.
It is released inside and is taken in and removed by the activated sludge in the aerobic tanks 2a, 2b and 2c. Reference numeral 7 denotes a final settling basin, and the supernatant of the final settling basin 7 is discharged as treated water 11 after passing through a disinfection tank or the like not shown in the figure, and a part of sludge settled in the final settling basin 7. Is returned to the anaerobic tank 1a by the sludge return pump 8, and other sludge is sent from the excess sludge drawing pump 9 to an excess sludge treatment device (not shown) for treatment.

[0007] By using such a circulating nitrification denitrification method, an effect comparable to the organic matter removal effect achieved by a normal standard activated sludge method can be obtained, and nitrogen and phosphorus removal rates higher than those of the activated sludge method. Is achieved.

[0008]

The reactions in the circulation type nitrification and denitrification method are roughly classified into denitrification in an anaerobic tank and nitrification in an aerobic tank. Nitrification is more important than denitrification such as water temperature, DO, pH, etc. It has the characteristic of being easily affected, and is the rate-determining reaction. In order to remove nitrogen particularly efficiently, it is required to maintain denitrification in an anaerobic tank and nitrification in an aerobic tank under optimal operating conditions, and the nitrogen removal step may be affected by the nitrification step. Since it is high, it is necessary that the nitrification process is performed well in order to perform good nitrogen removal.

It is known that this nitrification reaction has a lower rate than the organic substance removal reaction and requires a long residence time, and the activity of nitrifying bacteria is easily affected by subtle changes in pH, water temperature and the like. . In addition, in order to obtain sufficient aeration time, it is necessary to increase the volume of the biological reaction tank by a factor of 2 to 3 compared with the standard activated sludge method, and under conditions where it is difficult to secure land for urban areas. There is a problem that it is difficult to adopt.

In order to promote the nitrification reaction by improving the control reaction, it is necessary to monitor this reaction. However, water quality analysis of nitrogen-related components is not carried out daily in ordinary sewage treatment plants, and there is a problem that this water quality analysis requires much labor and time. For such water quality analysis, a respiration rate meter is used to measure the respiration rate (Nit) of nitrifying bacteria.
A method for measuring -Rr) has been proposed, and an automatic measuring device has been put to practical use. With this method, the respiratory rate can be measured at the shortest intervals of 30 minutes.

Although the automatic respiration rate meter is measured from the rate of decrease of DO, there is a problem that a microbial film is easily attached to the DO electrode for measuring DO. When the microbial membrane adheres to the DO electrode, the microbial membrane itself consumes DO, which causes a problem that the respiration rate of activated sludge, that is, suspended microorganisms cannot be accurately measured.

This respirometer is equipped with an automatic cleaning mechanism using sodium hypochlorite, but the respirometer is compared when the pollutant concentration of the sewage flowing into the sewage treatment plant is high or when the water temperature is high. When it is installed in the front stage of the biological reaction tank of the biological treatment plant, the microbial membrane is likely to adhere to the DO electrode, and the method of frequently pulling up the detection part and manually cleaning the DO electrode is troublesome from the viewpoint of maintenance. Yes, it is inefficient.

Therefore, the present invention solves the problem of the respiration rate meter used in such a circulation type nitrification denitrification method, and shows the state of adhesion of the microbial membrane to the DO electrode used in this respiration rate meter. It is an object of the present invention to provide a method for detecting attachment of a microbial film to a DO electrode that can automatically detect and take appropriate measures such as cleaning.

[0014]

In order to achieve the above object, the present invention aerates the activated sludge liquid by injecting air into the activated sludge liquid, raises the DO concentration to a set value, and then stops the aeration. Deaeration by changing the DO concentration with the oxygen consumption by the aerobic microorganisms in the activated sludge.
In the respiration rate meter in the activated sludge process, in which the respiration rate of the activated sludge is calculated by the least square method from the reduction rate of the DO, the change in the DO concentration is recorded by an automatic recorder. Record and D in the degassing process
PROBLEM TO BE SOLVED: To provide a method for detecting attachment of a microbial film to a DO electrode, which detects that a microbial film is attached to the DO electrode when O is sharply decreased, and pulls up the DO electrode to perform a countermeasure operation such as cleaning. .

According to the method for detecting the attachment of the microbial film to the DO electrode, the change in the DO concentration due to the oxygen consumption by the aerobic microorganism is measured by the DO meter connected to the DO electrode, and the change in the DO concentration is recorded. If a rapid decrease in DO was detected in the degassing process, it was detected that the microbial film had adhered to the DO electrode at that time, and the DO electrode was immediately pulled up and Measures such as cleaning the DO electrode can be taken.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the method for detecting microbial film adhesion to a DO electrode according to the present invention will be described below. FIG. 1 is an example of an apparatus for a respiration rate meter used as an evaluation of activity in an activated sludge process. Briefly explaining the structure and action, 13a is a water intake port, 13b is a drain port, and 14 is a measuring tank. Tubes 15 and 16 forming a water passage are connected to the inlet and outlet sides of the measuring tank 14.

V ₁ is an upper pinch valve, V ₂ is a lower pinch valve, 17, 18 and 19 are air inlets, and the tubes 15 and 16 are in a pinch state by injecting and exhausting air from the air inlets 17 and 19. Then, the activated sludge liquid is opened and closed. Reference numeral 20 is a DO electrode as a dissolved oxygen concentration detector, and 21 is a stirrer.

Reference numeral 22 is an ATU liquid injection pipe, 23 is a tap water injection pipe, and 24 is a cleaning liquid injection pipe. The ATU liquid injection pipe 22 is connected to an ATU addition device (not shown). Further, a third pinch valve V ₃ and an air injection port 25 are arranged between each injection pipe 22, 23, 24 and the upper pinch valve V ₁ . Therefore, each ATU liquid injection pipe 22, tap water injection pipe 23, and cleaning liquid injection pipe 24 are connected to the measuring tank 14 via the third pinch valve V ₃ .

The operation method for measuring the respiration rate of the activated sludge with the above-mentioned structure is as follows. First, as a basic operation, air is introduced from the air injection port 18 into the measurement tank 14 to form an air lift, and the upper pinch valve V ₁ and the lower pinch valve V ₂ are opened so that aerobatic air (not shown) from the water sampling port 13a. The activated sludge liquid in the tank is introduced into the measuring tank 14.

After a lapse of a certain time, the lower pinch valve V ₂ was closed by injecting air from the air inlet 17, the MLSS (active sludge suspended matter concentration) of the activated sludge liquid was measured by a separately installed MLSS meter, and then, The activated sludge liquid sampled by sending air from the air inlet 18 into the measuring tank 14 is aerated to raise the DO concentration to a set value, for example, 5 (mg / l).

When the DO concentration rises to the set value, the aeration is stopped, the upper pinch valve V ₁ is closed by the injection of air from the air injection port 19, and the stirring by the stirrer 21 is started. Then, since the DO concentration decreases with deaeration and oxygen consumption by the aerobic microorganisms of the activated sludge, the DO concentration is measured by the DO electrode 20 and a DO meter (not shown). [Rr] is calculated.

Next, the upper pinch valve V ₁ and the third pinch valve V ₃ are opened to connect the ATU liquid injection pipe 22 to ATU (N
-Allylthiourea) reagent is injected into the measuring tank 14. Then, aeration with air from the air inlet 18 is performed again and D
After increasing the O concentration to the set value, the aeration is stopped, the upper pinch valve V ₁ is closed, and the stirring by the stirrer 21 is performed to decrease the DO concentration due to the oxygen consumption by the activated sludge.
The [ATU-Rr] value is calculated by simultaneously with [Rr] while repeating the process of measuring [Rr] from the decrease rate of DO and calculating [Rr].

Then, the obtained [Rr] value and [ATU-R
[Nit-Rr] is calculated from the difference in the r] values, and the MLSS concentration and [ATU-Rr] and [Nit-R] obtained at the time of water sampling are calculated.
r] to respiration rate per unit sludge volume [Kr], [AT
U-Kr] and [Nit-Kr] are calculated.

To further explain this, the measured [AT
The U-Rr] value is generally used to monitor the progress of nitrification reaction in an aerobic tank. That is, the oxygen utilization rate (Rr) includes the amount of oxygen consumed during oxidative decomposition of organic matter, the amount of oxygen consumed for endogenous respiration of activated sludge, and the amount of oxygen consumed for nitrification reaction. This value is expressed as a value obtained by subtracting the oxygen consumption rate associated with the nitrification reaction from the respiratory rate due to removal of organic substances and endogenous respiration, that is, the total oxygen consumption rate. Therefore, the progress of the nitrification reaction is [Rr] and the nitrification inhibitor N-allylthiourea (chemical formula C ₄ H ₈ N ₂ S,
ATU) difference in Rr measured by adding [ATU-Rr]
Can be obtained from

When the above difference is [Nit-Rr], [Nit-Rr] = [Rr]-[ATU-Rr] (1) That is, the [Nit-Rr] value is the oxygen consumption rate associated with nitrification, and if this value is small, the nitrification reaction will end,
If it is larger, it can be judged that the nitrification reaction has not ended. Since the above [Nit-Rr] represents the oxygen consumption based on the nitrification reaction, it is possible to estimate the nitrification rate in the aerobic tank from this value.

[0026] Normally, the sampled water sampled from the aerobic tank [AT
The oxygen consumption rate [Nit-Rr] value involved in the nitrification reaction is measured by the [U-Rr] value.
Based on the value, it is determined whether or not the nitrification reaction has ended. That is, when the nitrification reaction proceeds smoothly and the concentration of ammonia nitrogen decreases, the above [Nit-Rr] value also sharply decreases, which indicates that the nitrification reaction in the aerobic tank is completed.

On the other hand, the above [ATU-Rr] value is one in which the nitrification reaction in the aerobic tank is not completed when the measured oxygen consumption rate [Nit-rr] value for the nitrification reaction is large. Is judged. At this time, the driving of the stirring mechanism of the anaerobic tank is stopped and the amount of air blown to the aerobic tank is controlled to carry out aeration so as to reach the ideal nitrification rate.

In this way, the respiratory rate [Rr] and [AT
The washing step is performed after measuring the [U-Rr] value. In this case, first, the lower pinch valve V ₂ and the upper pinch valve V ₁
After opening the tap water, tap water is introduced from the tap water injection pipe 23, the sewage in the measuring tank 14 is discharged to an aeration tank (not shown), and then the lower pinch valve V ₂ is closed to replace the inside of the measuring tank 14 with tap water. .

Next, a cleaning liquid such as sodium hypochlorite is introduced into the measuring tank 14 through the cleaning liquid injection pipe 24, and after a certain period of time, the lower pinch valve V ₂ is opened and the measuring tank 14 is opened.
Inject tap water until there is no more cleaning solution inside. When the drain of the washing water is completed, the lower pinch valve V ₂ is closed and the washing process is completed.

After completion of this cleaning step, the lower pinch valve V ₂ is opened again to feed air from the air inlet 18 into the measuring tank 14 for a fixed time. Then, since the measurement tank 14 is filled with air only, the lower pinch valve V ₂ is closed here, and tap water is fed from the tap water injection pipe 23 into the measurement tank 14 through the third pinch valve V ₃ and the state is maintained. While holding, prepare for the next measurement. FIG. 2 is a time chart schematically showing the above steps.

In the present embodiment, the change in the DO concentration due to the oxygen consumption by the aerobic microorganisms in the activated sludge during the above operation is D
A DO meter (not shown) connected to the O electrode 20 is used for measurement, and changes in this DO concentration are continuously recorded by an automatic recorder.

FIG. 3 shows a cycle of the DO measurement value and time when the DO electrode 20 is normal, and FIG. 4 shows a cycle of the DO measurement value and time when the microbial membrane adheres to the DO electrode 20. . As can be seen from FIGS. 2 and 3, when the microbial membrane adheres to the DO electrode, there is almost no section where DO decreases linearly. It is considered that this is because DO in water is consumed by the attached microbial membrane before reaching the diaphragm of the DO electrode.

Therefore, in the aeration process of the time chart, D
Even if O is increased, DO is already greatly reduced in the next degassing step, and the rate of decrease of DO cannot be accurately measured during measurement.

Therefore, in the present embodiment, if it is detected by the automatic recorder that the DO concentration is drastically reduced in the degassing step, it is detected at that point that the microbial membrane is attached to the DO electrode, and immediately. The DO electrode 20 which is the DO detection unit is pulled up, and the DO electrode 2 is manually operated or washed.
It is an operational feature to perform 0 cleaning.

[0035]

As described in detail above, according to the method for detecting the attachment of a microbial membrane to a DO electrode according to the present invention, the change in DO concentration due to oxygen consumption by aerobic microorganisms is measured by a DO meter, and The change in the DO concentration was recorded by a recorder, and if it was detected that the DO decreased sharply in the degassing step, it was detected that the microbial film had adhered to the DO electrode at that time, It is possible to immediately take measures such as pulling up the DO electrode and cleaning the DO electrode.
Therefore, only when the microbial film adheres to the DO electrode, the DO electrode, which is the detection unit, may be pulled up and washed, which is efficient and advantageous in terms of maintenance.

If the pollutant concentration of sewage is high,
Even when the microbial membrane is easily attached to the DO electrode, such as when the water temperature is high, it is possible to automatically detect the attachment state of the microbial membrane to the DO electrode and take appropriate measures such as cleaning. The effect of improving the measurement accuracy of is obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of an operation control method of a modified activated sludge circulation method according to the present embodiment.

FIG. 2 is a chart showing the actual control of the present embodiment.

FIG. 3 is a graph showing a cycle of a DO measurement value and time under normal conditions.

FIG. 4 is a graph showing a cycle of DO measurement value and time when a microbial film is attached.

FIG. 5 is a schematic view showing an example of a conventional circulating nitrification denitrification method.

[Explanation of symbols]

13a ... Water sampling port 13b ... Drainage port 14 ... Measuring tank 15, 16 ... Tube V ₁ ... Upper pinch valve V ₂ ... Lower pinch valve 17, 18, 19, 25 ... Air injection port 20 ... DO electrode 21 ... Stirrer 22 ... ATU liquid injection pipe 23 ... tap water injection pipe 24 ... washing liquid filling tube V ₃ ... third pinch valve

Claims (1)

[Claims] 1. The activated sludge liquid is aerated by injecting air to the activated sludge liquid, and after increasing the DO concentration to a set value, the aeration is stopped to deaerate the activated sludge to reduce oxygen consumption by aerobic microorganisms. The change in the DO concentration with the change of the DO electrode and D
In the respiration rate meter in the activated sludge process, in which the respiration rate of the activated sludge is calculated by the least square method from the reduction rate of the DO, the change in the DO concentration is recorded by an automatic recorder. A DO electrode characterized by recording and detecting that a microbial film has adhered to the DO electrode when DO is rapidly reduced in the degassing step, and pulling up the DO electrode to perform a countermeasure operation such as cleaning. Method for detecting attachment of microbial membranes to skin.