JPH0691292A - Operation control method of aerobic-anaerobic active sludge treatment apparatus - Google Patents

Abstract

PURPOSE:To provide an operation control method of an aerobic-anaerobic active sludge treatment apparatus by which nitrification and denitrification in waste water is promoted to improve a total denitrification ratio. CONSTITUTION:The temperature of water to be treated is measured by a thermometer 15, total nitrogen concentrations of specimens collected from respective reaction tanks are determined by a total nitrogen analyzer 16, and nitrogen components are measured by a nitrogen component analyzer 17. An average sludge retention time(SRT) required is calculated from the relationships between the water temperature and the total denitrification ratio obtained experimentally in advance. The operation of an aerobic-anaerobic active sludge treatment apparatus is conducted by controlling SRT so that the increase in the total nitrogen concentration is prevented. The sludge extracted from the bottom of the final sedimentation pool 4 is led to a sludge separation vessel 11, and the amount of the sludge to be extracted from the pool 4 is controlled by changing the opening of an excessive sludge discharge valve 13 corresponding to the progress of the nitrification reaction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an operation control method for removing organic matter and nitrogen in wastewater with high efficiency by using an anaerobic-aerobic activated sludge treatment device.

[0002]

2. Description of the Related Art Conventionally, various methods have been proposed for efficiently removing organic substances in wastewater such as sewage and removing nitrogen and phosphorus which are considered to be the causative substances of eutrophication. 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.

Although physicochemical methods and biological methods have been proposed as means for removing nitrogen and phosphorus in wastewater, physicochemical methods are not widely used because of the high cost. For example, a phosphorus removal method which has been put into practical use as a physicochemical method includes a coagulation precipitation method and a crystallization method, but this method has a drawback in terms of cost and maintenance.

On the other hand, as a method for biologically removing nitrogen and phosphorus simultaneously, an anaerobic method is a modification of the conventional activated sludge method.
Aerobic activated sludge method is drawing attention. (See, for example, Water Pollution Research, Volume 12, No. 7, 441-448, 1989.) In this method, the biological reaction tank is divided into an anaerobic tank and an aerobic tank, and the anaerobic tank in which dissolved oxygen does not exist is first precipitated. The pond effluent is guided to denitrify by denitrifying bacteria in activated sludge in anoxic condition, and then aeration is performed by aeration in an aerobic tank to oxidize and nitrify organic matter by activated sludge in the presence of oxygen. Nitrification of ammonia by bacteria is performed. A part of the nitrification solution is circulated to the anaerobic tank and used for promoting denitrification.

By using such an anaerobic-aerobic activated sludge treatment method, an effect comparable to the organic matter removal effect achieved by the ordinary activated sludge method can be obtained, and nitrogen and phosphorus are higher than those by the activated sludge method. A removal rate is achieved.

[0006]

However, in the case of a method for removing organic matter and nitrogen in wastewater using such a conventional anaerobic-aerobic activated sludge treatment device, the operation of the anaerobic-aerobic activated sludge treatment device is performed. It cannot be said that the control method is well established, and there is a problem that it is difficult to improve processing efficiency and accuracy.

That is, the following six items can be listed as the main control factors of the above-mentioned anaerobic-aerobic activated sludge treatment method.

(1) Sludge average retention time (sludge retenti
on time, hereinafter abbreviated as SRT) (2) Concentration of suspended solids in activated sludge (mixed liquor suspended s)
solid (hereinafter abbreviated as MLSS) (3) Dissolved oxygen (hereinafter abbreviated as DO) (4) Hydrogen ion concentration (pH) (5) Nitrogen recirculation ratio (6) Anaerobic tank and aerobic Volume ratio of the tank (hereinafter abbreviated as A / O ratio).

Since the above six control factors are often controlled at a constant rate, there is a problem that they are easily affected by changes in the processing state such as changes in flow rate and changes in water quality. That is,
In order to effectively remove nitrogen by anaerobic-aerobic activated sludge treatment, it is necessary to maintain denitrification in an anaerobic tank and nitrification in an aerobic tank under optimal operating conditions. Therefore, the nitrification step must be performed well in order to perform good nitrogen removal.

The above-mentioned nitrification is a reaction that proceeds by the action of nitrite bacteria and nitric acid bacteria. The growth rate of these nitrifying bacteria (generally termed nitrite bacteria and nitric acid bacteria) is BOD (biochemically required). Oxygen), which is considerably smaller than that of decomposing bacteria, keeps nitrifying bacteria in the system when oxidative decomposition of BOD and nitrification are carried out in the same tank as in the circulating anaerobic-aerobic activated sludge method. As described above, the operation is performed while keeping the SRT large.

The SRT of the minimum process required for holding nitrifying bacteria is usually expressed by the following equation.

SRT _C ≧ 1 / μ ... (1) SRT _C : SR necessary for maintaining nitrifying bacteria in the system
T (day) μ: Specific growth rate of nitrifying bacteria (1 day) The growth rate of this nitrifying bacterium is easily affected by the water temperature, and the SRT becomes long in order to keep the nitrifying bacterium in the system in the low water temperature period. As the value of μ, for example, equations (2) and (3) have been proposed.

Μ = 0.062 · exp {0.098 (T-15)} ... (2) μ = 0.11 · exp {0.07 (T-15)} ... (3) When the required SRTs at water temperatures of 15 ° C and 25 ° C are calculated using the above equation (2), they are 16.7 days and 6.2 days, respectively.

On the other hand, if the SRT is too long, there is concern that the nitrogen component may be eluted due to the self-decomposition of sludge. That is, if the SRT is kept operating for a long time, the filamentous fungi with a slow growth rate may be in a condition where they can grow, and bulking may occur or scum due to actinomycetes may occur.

In the anaerobic-aerobic activated sludge method, a long SR is generally used.
Although the process is run at T, it is important that the process is run at the proper SRT for efficient nitrogen removal. However, under the present circumstances, it is often controlled by a constant SRT, and the SRT control according to the processing situation is not performed.

The present invention has been made in view of the above, and mainly promotes nitrification and denitrification of an anaerobic-aerobic activated sludge treatment device by controlling the SRT to an optimum state, and removes total nitrogen. It is an object of the present invention to provide an operation control method capable of increasing the rate.

[0017]

In order to achieve the above object, the present invention provides a step of denitrifying wastewater with denitrifying bacteria in an anaerobic tank, and nitrifying ammoniacal nitrogen with nitrifying bacteria in an aerobic tank. The steps of performing and solid-liquid separation in the final settling tank, returning part of the settled sludge to the anaerobic tank, sending the rest to the excess sludge treatment device for processing, and discharging the supernatant of the final settling tank as treated water. In the anaerobic-aerobic activated sludge treatment device, which comprises a step of refluxing a part of the nitrification liquid in the aerobic tank to the anaerobic bath to promote the denitrification reaction, a reaction constituting the anaerobic-aerobic activated sludge treatment device. Measure the water temperature of the tank, measure the total nitrogen concentration of the sampling liquid collected from each reaction tank, analyze the nitrogen components, and obtain it from the relationship between the water temperature and the total nitrogen removal rate obtained experimentally in advance. Calculate sludge average residence time (SRT) , Anaerobic and to perform operation by controlling the sludge average residence time such that the total nitrogen concentration of the processed water is not increased - to provide a method for controlling the operation of the aerobic activated sludge treatment apparatus.

Further, the sludge derived from the bottom of the final settling basin is connected to a sludge return tank to an anaerobic tank and a sludge distribution tank provided with an excess sludge discharge valve, and the excess sludge discharge valve is connected depending on the nitrification situation. The operation control method of controlling the amount of sludge drawn out from the final settling tank by changing the opening degree of is used.

[0019]

According to the operation control method of the anaerobic-aerobic activated sludge treatment device, the raw water is first denitrified in the anaerobic tank, and then aerated in the aerobic tank. Nitrification of nitrogen takes place. 1 of nitrification liquid in this aerobic tank
The part is returned to the anaerobic tank to promote denitrification in the anaerobic tank.
The liquid discharged from the aerobic tank flows into the settling tank for solid-liquid separation,
A part of the settled sludge returns to the anaerobic tank again, the rest of the sludge is treated as excess sludge, and the supernatant of the settling tank is discharged as treated water.

During the above treatment, the water temperature in the reaction tank is measured as an index, and at the same time, the liquid is sampled from the anaerobic tank and the aerobic tank to measure the total nitrogen concentration (TN concentration) and analyze the nitrogen component. The required average sludge retention time (SRT) is determined from the relationship between the water temperature and the total nitrogen removal rate that have been experimentally determined in advance, and the average sludge retention time is set so that the total nitrogen concentration of the treated water does not increase. Driving is performed.

Further, the sludge discharged from the bottom of the final settling tank is connected to a sludge distribution tank provided with a sludge return valve to the anaerobic tank and a surplus sludge discharge valve, and the surplus sludge discharge valve is connected depending on the nitrification situation. By controlling the opening degree of nitrification and denitrification, the treatment efficiency and accuracy of anaerobic-aerobic activated sludge treatment can be improved.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The anaerobic of the present invention will be described below with reference to the drawings.
An embodiment of the operation control method of the aerobic activated sludge treatment device will be described.

In this embodiment, the water temperature and the total nitrogen concentration (generally referred to as TN concentration) of the reaction tank constituting the anaerobic-aerobic activated sludge treatment device are measured, and the nitrogen component is analyzed to determine the water temperature. Required SR in relation to total nitrogen removal rate
SRT that calculates T and does not increase this total nitrogen concentration
The main goal is to control nitrogen efficiently and economically.

FIG. 2 is a schematic diagram of an experimental apparatus carried out as a preparatory step of the present invention, in which 1 is a raw water preparation tank, 2 is an anaerobic tank for only stirring raw water, 3a, 3b and 3c are aerobic tanks, Four
Is the final sedimentation pond and 5 is a blower. The anaerobic tank 2 and the aerobic tanks 3a, 3b, and 3c, which are reaction tanks, are 7.5 liters each, and four complete mixing tanks each having an effective volume of 30 liters are connected in series to give a water level difference between the tanks. This ensures that there is no backflow from the downstream tank to the upstream tank.

Air blowing members 6, 6, 6 are arranged at the bottom of the aerobic tanks 3a, 3b, 3c, and air is supplied from the blower 5. The final sedimentation tank 4 has an effective volume of 12 liters, and the final sedimentation tank 4 is provided with a stirring mechanism using a motor M ₁ as a drive source.

In the last-stage aerobic tank 3c, 1
A nitrification solution circulation pump P ₅ for returning the part to the anaerobic tank 2 and a return pipe 7 are provided. P ₇ is a pump for withdrawing excess sludge from the final aerobic tank 3c. A sludge return pump P ₆ for returning the sludge to the anaerobic tank 2 is arranged in the middle of the pipe 8 led out from the bottom of the final settling tank 4.

According to such an experimental apparatus, a concentrated stock solution having the composition shown in Table 1 was first prepared in advance, this stock solution was put into the raw water preparation tank 1 using the pump P ₁ , and further, the tap water was supplied using the pump P _2. BOD approx. 200 mg / l after diluting 200 times with water
The raw water of is prepared continuously.

[0028]

[Table 1]

When this raw water is caused to flow into the anaerobic tank 2 by the pump P ₃ , the NO ₃ --N and NO ₂ --N ions are reduced to N ₂ based on the stirring action of the pump P _{4 and} the action of denitrifying bacteria, That is, denitrification is performed. Next, the raw water sequentially flows from the anaerobic tank 2 into the three-stage aerobic tanks 3a, 3b, 3c, and the blower 5 is driven to perform aeration by aeration from the air blowing members 6, 6, 6 and nitrification. Oxidation of ammoniacal nitrogen NH ₄ —N to NO ₂ —N or NO ₃ —N, that is, nitrification, is carried out based on the action of bacteria. Residence time in reaction tank (H
RT) was set to 6 hours, which is the same level as for ordinary urban sewage treatment.

Then, one of the nitrification liquids in the final stage aerobic tank 3c
By the action of the nitrification solution circulation pump P ₅ , 100% is returned to the anaerobic tank 2 from the return pipe 7, that is, the same amount as the inflow amount to the aerobic tank 3c is refluxed, and NO ₃ -N necessary for denitrification, NO ₂ —N or the like is supplied to the anaerobic tank 2. The effluent from the aerobic tank 3c flows into the final settling tank 4 where it is separated into solid and liquid, and 1
The part is returned from the pipeline 8 to the anaerobic tank 2 at 30% via the sludge return pump P ₆ . Therefore, the circulation rate to the anaerobic tank 2 is 1
It will be 30%. The residence time in the final settling tank 4 was 2.5 hours. The supernatant 9 of this final settling basin 4 is discharged as treated water. In this embodiment, SRT (average sludge retention time) 1
Two series were set, a system on day 0 and a system on day 20.

FIG. 3 shows the relationship between the water temperature and the total nitrogen removal rate in the system of SRT 10 days and 20 days when the sludge acclimation progresses favorably and the treatment condition is stable. According to Fig. 3, when the water temperature is around 23 ° C, SRT1
It was confirmed that the total nitrogen removal rate on day 0 was higher than that on day SRT 20, and conversely, the total nitrogen removal rate on day 20 SRT was higher than that on day 10 SRT in the low water temperature period around 23 ° C.

Examples of changes in the composition of nitrogen in the reaction tank during the high water temperature period are shown in FIGS. FIG. 4 shows the nitrogen change in the reaction tank in the system on SRT 10 days, and FIG. 5 shows the nitrogen change in the reaction tank in the system on SRT 20 days. As shown in both figures, the anaerobic tank _{2 NO X -N (NO 2 -N} + NO
_3- N) is almost completely denitrified, and aerobic tanks 3a, 3
In b and 3c, ammoniacal nitrogen (NH ₄ —N) gradually decreases due to nitrification or microbial growth, and NO _x —N is produced in its place, but the production amount differs between 10 and 20 days of SRT. There is.

That is, in the system of SRT 10 days, the aerobic tank 3b
The total nitrogen concentration does not change so much from S. al. To the treated water, but in the system of SRT 20 days, the total nitrogen concentration gradually increases from the aerobic tanks 3b and 3c to the treated water. It is considered that the reason is that the organic component was consumed by denitrification, and the organic component required for cell maintenance and growth was insufficient, and the nitrogen component gradually eluted by autolysis was nitrified.
Therefore, in terms of total nitrogen removal rate, SRT 10 days is more SRT
It is higher than the 20th.

FIG. 1 is a schematic diagram of an anaerobic-aerobic activated sludge treatment device incorporating the control method of this embodiment based on the above findings. That is, 2a and 2b are anaerobic tanks that stir the raw water, and submersible agitators 10 and 10 are arranged at the inner bottoms of the anaerobic tanks 2a and 2b. 3a, 3b, 3c are aerobic tanks, and air blowing members 6, 6, 6 are arranged at the bottoms of the aerobic tanks 3a, 3b, 3c, and air is supplied from the blower 5. Reference numeral 4 denotes a final sedimentation tank, and the final sedimentation tank 4 is provided with a stirring mechanism having a motor M ₁ as a drive source.

In the last-stage aerobic tank 3c, 1
Solution circulation pump P ₅ for returning the part to the anaerobic tank 2a
And a return conduit 7 are provided. In addition, a sludge return pump P is provided in the middle of the pipe 8 which is led out from the bottom of the final settling basin 4.
₆ is provided, and the pipeline 8 is connected to a sludge distribution tank 11. Reference numeral 12 is a sludge return valve for returning a part of the sludge from the sludge distribution tank 11 to the anaerobic tank 2a, and 13 is a surplus sludge discharge valve.

A water temperature gauge 15 is provided in the anaerobic tank 2a. Reference numeral 16 is a total nitrogen analyzer, and the total nitrogen analyzer 16 is adapted to sample the liquid from each of the anaerobic tanks 2a and 2b and the aerobic tanks 3a, 3b and 3c constituting the reaction tank. Reference numeral 17 is a nitrogen component analyzer, and 18 is a controller. A control line 18a of the controller 18 is connected to the blower 5 and the excess sludge discharge valve 13 to output drive signals.

According to this embodiment, as a basic operation, first, raw water flows into the anaerobic tanks 2a, 2b, and NO is generated based on the stirring action of the submersible stirrers 10, 10 and the action of denitrifying bacteria.
₃ -N, reduction to N ₂ in the NO ₂ -N ions, i.e. denitrification is performed. Next, the raw water sequentially flows into the aerobic tanks 3a, 3b, 3c, aeration is performed by aeration from the air blowing members 6, 6, 6 as the blower 5 is driven, and ammonia gas is generated based on the action of nitrifying bacteria. Oxidation of nitrogen NH ₄ —N to NO ₂ —N or NO ₃ —N, ie nitrification, takes place.

Then, one of the nitrification solutions in the aerobic tank 3c at the final stage is
The part is refluxed from the return pipe 7 to the anaerobic tank 2a by the action of the nitrification solution circulation pump P ₅ , and NO ₃ -N, N necessary for denitrification are supplied.
O ₂ —N or the like is supplied to the anaerobic tank 2. The effluent from the aerobic tank 3c flows into the final settling tank 4 for solid-liquid separation, and the sludge that has settled reaches the sludge distribution tank 11 from the pipeline 8 via the sludge return pump P ₆ , and this sludge distribution tank 11 A part of the sludge is removed from the anaerobic tank 2a by operating the sludge return valve 12 attached to the
On the other hand, the excess sludge is extracted from the sludge distribution tank 11 according to the opening and closing of the excess sludge discharge valve 13 and is sent to an excess sludge treatment device (not shown) for treatment. The supernatant 9 of the final settling tank 4 is discharged as treated water.

In the present embodiment, while such anaerobic-aerobic activated sludge treatment is in progress, the anaerobic tanks 2a and 2b and the aerobic tanks 3a, 3b and 3c which constitute the reaction tank as an index are in progress.
The liquid is sampled from the above and sent to the total nitrogen analyzer 16, the total nitrogen concentration (TN concentration) is measured, and each nitrogen component is analyzed by the nitrogen component analyzer 17 in the next stage. Ion chromatography is usually used as the nitrogen component analyzer 17.

The controller 18 is supplied with the water temperature of the raw water detected by the water thermometer 15 provided in the anaerobic tank 2a and the analyzed nitrogen component, and the controller 18 makes a difference between the SRTs shown in FIG. The required SRT is calculated from the relationship between the water temperature and the total nitrogen removal rate by the control, the operation is controlled based on this SRT, and the drive of the blower 5 and the excess sludge are prevented so that the total nitrogen concentration does not rise during the aerobic treatment process. A signal for controlling the opening degree of the discharge valve 13 is emitted.

Normally, the nitrification is promoted by increasing the aeration amount of the aerobic tanks 3a, 3b and 3c, and when the nitrification is carried out smoothly, the circulation ratio of the nitrification liquid from the aerobic tank 3c to the anaerobic tank 2a. It is possible to increase the removal rate of nitrogen by increasing.

Then, NO _x --N is contained in the analyzed nitrogen component.
When ammonia nitrogen other than the above and organic nitrogen remain and nitrification is insufficient, the opening degree of the excess sludge discharge valve 13 is reduced to suppress the amount of sludge drawn out from the sludge distribution tank 11,
Set a large SRT to promote nitrification and denitrification.

Therefore, according to this embodiment, it is possible to set the optimum SRT mainly during operation, and it is possible to improve the treatment efficiency and accuracy of the anaerobic-aerobic activated sludge treatment.

[0044]

As described in detail above, according to the operation control method of the anaerobic-aerobic activated sludge treatment device according to the present invention, the water temperature and the total nitrogen concentration in the reaction tank are measured as indexes and the nitrogen component is also measured. Is analyzed and the required average sludge retention time (SRT) is calculated from the relationship between the experimentally determined water temperature and the total nitrogen removal rate. Is set, and based on this, the operation that enables efficient nitrogen removal can be performed. Particularly, it is possible to obtain an effect that the occurrence of scum due to actinomycetes and bulking associated with long SRT operation is suppressed.

Further, by connecting the sludge derived from the bottom of the final settling tank to the sludge distribution tank and controlling the opening of the surplus sludge discharge valve according to the nitrification situation, nitrification and denitrification are promoted. Comes. Therefore, according to the present invention, the operation control method of the anaerobic-aerobic activated sludge treatment device is established,
It has a great effect that the treatment efficiency and accuracy of wastewater can be improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a basic embodiment of the present invention.

FIG. 2 is a schematic diagram of an experimental device implemented as a preparatory step of the present invention.

FIG. 3 is a graph showing the relationship between water temperature and total nitrogen removal rate depending on the difference in SRT.

FIG. 4 is a graph showing the change in nitrogen in the reaction vessel in the system on SRT 10 days.

FIG. 5 is a graph showing changes in nitrogen in the reaction vessel in the system on SRT 20 days.

[Explanation of symbols]

 2a, 2b ... Anaerobic tank 3a, 3b, 3c ... Aerobic tank 4 ... Final sedimentation tank 5 ... Blower 6 ... Air blowing member 7 ... Return pipe line 10 ... Underwater agitator 11 ... Sludge distribution tank 12 ... Sludge return valve 13 ... Excess sludge discharge valve 16 ... Total nitrogen analyzer 17 ... Nitrogen component analyzer 18 ... Control device

Claims (2)

[Claims] 1. A step of denitrifying waste water with denitrifying bacteria in an anaerobic tank, a step of nitrifying ammoniacal nitrogen with nitrifying bacteria in an aerobic tank, and a sludge which is solid-liquid separated and sedimented in a final sedimentation tank. Part of the water is returned to the anaerobic tank and the rest is sent to the excess sludge treatment device for treatment, and the supernatant of the final sedimentation tank is discharged as treated water, and part of the nitrification liquid in the aerobic tank is returned to the anaerobic tank. In the anaerobic-aerobic activated sludge treatment device including a step of accelerating the denitrification reaction, the water temperature of the reaction tank constituting the anaerobic-aerobic activated sludge treatment device is measured, and the sampling liquid collected from each reaction tank The total nitrogen concentration of
Calculate the required average sludge retention time (SRT) from the relationship between the water temperature and the total nitrogen removal rate, which were experimentally obtained in advance, and control the average sludge average retention time so that the total nitrogen concentration of the treated water does not increase. An operation control method for an anaerobic-aerobic activated sludge treatment device, which is characterized by performing an operation. 2. The sludge discharged from the bottom of the final settling basin is connected to a sludge distribution tank equipped with a sludge return valve to an anaerobic tank and an excess sludge discharge valve, and the excess sludge is discharged depending on the nitrification situation. The amount of sludge drawn from the final settling tank is controlled by changing the opening of the valve.
An anaerobic-aerobic activated sludge treatment device operation control method as described.