JPH07136687A - Operation control method for modified active sludge circulation process in low water temperature period - Google Patents

Abstract

PURPOSE:To provide an operation control method for modified active sludge circulation process which improves nitration efficiency in an aerobic tank even in a low water temperature period and consequently heightens denitrification effect in an anaerobic tank. CONSTITUTION:In a modified active sludge circulation process comprising a step in which raw water is denitrified in an aerobic tanks 1a, 1b by denitrification bacteria, a step in which nitration is conducted through several stages of aerobic tanks 2a, 2b, 2c, 2d by nitration bacteria, and a step in which supernatant from solid-liquid separation in a sedimentation tank is discharged as treated water 11, single or multistage anaerobic-aerobic binary tanks 30a, 30b equipped with a agitation mechanism and an air diffusion pipe with an air capacity control valve are installed between the anaerobic tanks 1a, 1b and the aerobic tanks 2a-2d. A specimen of each tank is extracted to measure NOX-N concentration, and denitrification rate and nitration rate are calculated. In this way, the A:O ratio is determined, and the operation of an agitation mechanism on the side of the anaerobic tanks 1a, 1b and a sludge return ratio from the sedimentation tank to the anaerobic tanks 1a, 1b are controlled.

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 highly efficiently removing organic matter and nitrogen in wastewater by using a modified anaerobic-aerobic activated sludge circulation method in a low water temperature period.

[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.

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 biological biological method for simultaneously removing nitrogen and phosphorus, an anaerobic method is a modification of the conventional activated sludge method.
The aerobic activated sludge method is drawing attention. This anaerobic-aerobic activated sludge method is, for example, as shown in FIG. 3, a biological reaction tank is an anaerobic tank 1a in which dissolved oxygen (hereinafter abbreviated as DO) does not exist.
1b and multi-stage aerobic tanks 2a, 2b, 2c where DO exists
And the anaerobic tanks 1a and 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 the aerobic tank 2
By supplying air from the blower 5 to the air diffuser 4 arranged inside a, 2b, and 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 nitrification solution in the last-stage aerobic tank 2c is transferred to the anaerobic tank 1a using the nitrification solution circulation pump 6.
By feeding the anaerobic tanks 1a and 1b, the denitrification effect is promoted.

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

The denitrifying bacterium is 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.

By using such an anaerobic-aerobic activated sludge treatment method, the same effect as the organic substance removal effect achieved by the normal standard activated sludge method can be obtained, and nitrogen and phosphorus are more effective than the activated sludge method. A high removal rate is achieved.

[0009]

However, in the case of such a conventional anaerobic-aerobic activated sludge treatment method, it is difficult to establish an efficient operation control method, especially in a low water temperature period such as winter season. However, there is a problem that it is difficult to sufficiently enhance both the nitrification efficiency and the denitrification effect in the anaerobic tank.

That is, the operation mode in the anaerobic-aerobic activated sludge method can be roughly classified into a denitrification reaction in the anaerobic tanks 1a and 1b and a nitrification reaction in the aerobic tanks 2a, 2b and 2c. The latter, that is, the nitrification reaction, is the rate-determining reaction. In particular, in order to remove nitrogen efficiently by the anaerobic-aerobic activated sludge treatment method, it is required to maintain denitrification in the anaerobic tank and nitrification in the aerobic tank under the optimum operating conditions, and the nitrogen removing step. Is highly affected by the nitrification process, so that the nitrification process must be performed well in order to perform good nitrogen removal.

This nitrification reaction is caused by the nitrifying bacteria as described above. The activity of the nitrifying bacteria is
It is known that it is easily affected by subtle changes such as water temperature. 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.

When the nitrification progresses satisfactorily, the quality of the denitrification reaction affects the nitrogen removal rate. Therefore, in order to maintain a high nitrogen removal rate, a good balance between the nitrification reaction and the denitrification reaction should be maintained. Required to do so. Also, the aerobic tanks 2a, 2b,
The DO concentration in 2c is constantly changing due to inflow load fluctuations and the amount of water.

In addition to the above, SRT (sludge retention time), M
LSS (active sludge suspended matter concentration), DO (dissolved oxygen concentration), pH, circulation ratio, sludge return ratio, A: O ratio (ratio of anaerobic tank and aerobic tank), etc. are considered. In particular, in order to stably remove nitrogen throughout the year, it depends on how to secure the nitrification efficiency in the low water temperature period.

Therefore, the present invention solves the problems of the anaerobic-aerobic activated sludge treatment, prevents the reduction of the nitrification reaction particularly in the low water temperature period, and enhances the denitrification reaction in the anaerobic tank. It is an object of the present invention to provide an operation control method of the modified activated sludge circulation method that can perform the operation.

[0015]

In order to achieve the above object, the present invention comprises a step of denitrifying raw water with denitrifying bacteria in a multi-stage anaerobic tank, and a step of nitrifying bacteria in a multi-stage aerobic tank. Nitrogenation process, solid-liquid separation in the settling tank to discharge the supernatant liquid as treated water, and activated sludge circulation conversion including a mechanism to return a part of the sludge in the settling tank to the first anaerobic tank. In the method treatment, between the anaerobic tank and the aerobic tank, a single-stage or multiple-stage anaerobic-aerobic dual-use tank equipped with both a stirring mechanism and an air diffuser with an air flow adjusting valve is arranged. by measuring the NO _X -N concentration of the sample was sampled, the denitrification rate by the arithmetic from the increase amount of NO _X -N concentration at the reduction and aerobic tank of NO _X -N concentration in the anaerobic tank and the nitrification The speed was calculated, and from the result, the air flow control valve for the anaerobic-aerobic tank was opened and closed to control A And it determines the O ratio, provides a driving control method to control the sludge return ratio to the anaerobic tank from the driving state of the anaerobic tank side of the stirring mechanism settling tank.

[0016] Also, by deploying turbidimeter to the sedimentation tank, the sludge to the extent that NO _X -N anaerobic tank in and output stage to the extent that ss concentration in the treated water does not exceed the set value does not remain Determine the return ratio.

[0017]

According to the operation control method of the modified activated sludge circulation method, the ratio of the anaerobic tank to the aerobic tank depends on whether the anaerobic-aerobic tank is used as the anaerobic tank or the aerobic tank. By changing the O ratio and supplying air from the blower to the diffuser pipes located inside each aerobic tank determined based on this A: O ratio, the raw water is denitrified under the anaerobic tank or anaerobic conditions. Further, in each aerobic tank, oxidative decomposition of organic matter by activated sludge and nitrification of ammonia by nitrifying bacteria are performed in the presence of oxygen by aeration.

At the time of the above operation, the sample in each tank is sampled to measure NO _X -N, and the amount of decrease in NO _X -N concentration in the anaerobic tank and that in the aerobic tank are measured by the nitrification / denitrification rate calculator. N
The denitrification rate and the nitrification rate are calculated from the increasing amount of the O _X -N concentration, and the control of the A: O ratio and the stirring mechanism in the anaerobic-aerobic tank are calculated from the ratio between the denitrification rate and the nitrification rate. Controlled. Furthermore, by monitoring the turbidity meter installed in the final settling tank, the sludge was returned to the anaerobic tank to such an extent that the ss concentration of the treated water did not exceed the set value and NO _X -N did not remain in the final anaerobic tank. It

Therefore, it is possible to obtain the effect that the operation is continued while updating the A: O ratio and the sludge return ratio of the biological reaction tank itself as the raw water treatment state changes.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific example of the operation control method of the modified activated sludge circulation method in the low water temperature period according to the present invention will be described below with reference to the drawings.

FIG. 2 is a schematic diagram of the experimental apparatus based on this example, and Table 1 shows the nitrification rate (%) and TN obtained based on the operating conditions of the four systems carried out using the experimental apparatus. The removal rate (total nitrogen removal rate) is shown.

[0022]

[Table 1]

First, the construction and operation of the experimental apparatus will be described with reference to FIG. In the figure, 1a and 1b are anaerobic tanks for denitrifying wastewater, and 2a, 2b, 2c and 2d are aerobic tanks having a plurality of stages for nitrification. The anaerobic tanks 1a, 1b and aerobic tanks are shown. The same biological reaction tanks as 2a, 2b, 2c, and 2d are divided and configured by partition plates 13 and 13.

Reference numeral 14 is a first settling basin, 15 is a raw water storage tank, and water level gauges 16 are arranged in both tanks. Initially, the settling tank 14 is provided with a raw water pumping pump P ₁ , and the raw water storage tank 15 is provided with a raw water stirring pump P ₂ and a raw water supply pump P ₃ .

Sludge agitation pumps P ₄ and P ₄ are provided in the anaerobic tanks 1a and 1b, respectively. Also, the aerobic tanks 2a, 2
b, 2c, and 2d have air diffusers 4 as an air blowing mechanism.
4, 4, 4 are arranged, and the air diffusers 4, 4, 4, are provided outside.
Blower 5 and the valve V _1, V ₂ for supplying air to 4,
V ₃ and V ₄ are deployed. P ₅ is a nitrification solution circulation pump.

Reference numeral 7 is a final settling tank, 17 is a treated water storage tank, 1
Reference numeral 8 denotes a surplus sludge storage tank, a stirring mechanism 19 is provided in the final settling tank 7, and a water level gauge 20 is arranged in the treated water storage tank 17. P ₆ is a surplus sludge drawing pump, P ₇ is a sludge returning pump, P ₈ is a treated water discharge pump, and a timer 21 is attached to the surplus sludge drawing pump P ₆ to draw out excess sludge at every predetermined time. Is set to do.

Further, a redox potential meter 22 is arranged in the anaerobic tank 1b, and a similar redox potential meter 23, a pH meter 25, a DO meter 26 and an alkali storage tank 24 are arranged in the aerobic tank 2d.
And are arranged. P ₉ is a chemical injection pump for injecting the alkali in the alkali storage tank 24 into the aerobic tank 2d.

The basic operation of such a device is as follows. First of all, the raw water in the settling basin 14 is the raw water pump P ₁
Is pumped up and stored in the raw water storage tank 15.
The water level in the raw water storage tank 15 is monitored by a water level gauge 16 to control the drive of the raw water pumping pump P ₁ .

The raw water stirred by the raw water stirring pump P ₂ flows into the anaerobic tank 1b from the anaerobic tank 1a as the raw water supply pump P ₃ is driven, and the sludge stirring pumps P ₄ and P ₄ are stirred and denitrified. based on the action of bacteria, NO ₃ -N, NO ₂ -
Reduction of N ions to N ₂ , that is, denitrification, is performed.

Next, the raw water is aerobic tanks 2a, 2b, 2c, 2d.
Flow into the valve and the valves V ₁ , V ₂ , V
Aeration is performed by aeration of the air supplied to the air diffusing pipes ₄ , ₄ , ₄ , ₄ via ₃ , V _4, and NO ₂ -N or NO of ammonia nitrogen NH ₄ -N is generated based on the action of nitrifying bacteria. Oxidation to _3- N, ie nitrification, takes place.

During the above operation, the anaerobic tank 1b and the aerobic tank 2d
The redox potential inside is measured by the redox potential meters 22 and 23, and the pH and DO concentration inside the aerobic tank 2d are measured by the pH meter 25.
And the DO meter 26. The redox potential is
It serves as an index for knowing the strength of the oxidizing power or reducing power of the liquid, and the alkali stored in the alkali storage tank is used as the chemical injection pump P if necessary from the measured redox potential and pH value. It is injected via ₉ into the aerobic tank 2d.

Further, the nitrification solution in the aerobic tank 2d is sent to the anaerobic tank 1a by using the nitrification solution circulation pump P ₅ ,
The denitrification effect of the anaerobic tanks 1a and 1b is promoted. Particularly, phosphorus in the wastewater is released in the anaerobic tanks 1a and 1b, and
It is taken into and removed by the activated sludge in a, 2b, 2c and 2d.

The surplus sludge in the aerobic tank 2d is drawn by the surplus sludge drawing pump P ₆ and temporarily stored in the surplus sludge storage tank 18, and part of the sludge settled in the final settling tank 7 is a sludge return pump P. It is returned to the anaerobic tank 1a by ₇ . Further, the supernatant of the final settling basin 7 is stored in the treated water storage tank 17 and then the treated water discharge pump P ₈ monitored by the water level gauge 20 is driven as treated water 11 into a disinfecting tank (not shown) or the like. It is released after passing through.

The nitrification and denitrification rates in biological nitrogen removal as described above are greatly affected by the water temperature. That is, K _N = a ₁ · exp (b ₁ · T) ··· (1) K _DN = a ₂ · exp (b ₂ · T) · (2) where K _N : nitrification rate (mg-N / g-MLSS · h
r) K _DN : Denitrification rate (mg-N / g-MLSS · hr) a, b: Coefficient T: Water temperature (° C) From the above equations (1) and (2), the high water temperature period is higher than the low water temperature period. It can be seen that both the nitrification rate and the denitrification rate are several times faster.
For example, a ₁ = 0.1197, b ₁ = 0.1295, a ₂ =
0.2870, b ₂ = 0.0687 and water temperature is 15
K _N at ℃ and 25 ℃ are 0.84 and 3.05 mg-, respectively.
N / g-MLSS · hr, K _DN is 0.80,
It is 1.60 mg-N / g-MLSS · hr.

The above-mentioned nitrification means NO ₂ -N or NO ₃ -N of ammoniacal nitrogen NH ₄ -N based on the action of nitrifying bacteria.
Is an oxidation action on the nitrification rate can be regarded as practically zero-order reaction with Michaelis-Menten equation type as an increase rate of decreasing speed or NO _X -N ammoniacal nitrogen _{(NO 2 -N + NO 3 -N} ). Similarly denitrification rate also regarded as practically zero-order reaction as a reduction in the NO _X -N.

Particularly, the growth rate of nitrifying bacteria is low when the water temperature is low, and the SRT required for keeping the nitrifying bacteria in the system becomes long in the low water temperature period. (1st report on evaluation of nitrogen and phosphorus removal process using microorganisms, 1986 1
See January 18, issued by Japan Sewage Works Agency Technical Evaluation Committee).

However, the denitrification rate varies greatly depending on the facility and operating conditions, and as a control factor for more efficient nitrogen removal, as described above, SRT, MLS
S, DO, pH, circulation ratio, sludge return ratio, A: O ratio, etc. must be considered.

Normally, in order to maintain the nitrification efficiency in the low water temperature period, it is necessary to lengthen the SRT, but in order to stabilize the system by SRT control, the normal SRT set value of 2 is set.
Since it takes ~ 3 times the number of days, it is not possible to cope with the quantitative and qualitative changes of inflow water at the time level. Inevitably SR
T is fixed and is usually set to 10 days or more.

Therefore, in the case of this embodiment, by controlling the A: O ratio and the sludge return ratio in the modified activated sludge circulation method, a high nitrogen removal rate (TN removal rate) is secured even in the low water temperature period. The main thing is that.

In the example of FIG. 2, since the reaction tanks are 6 in total, if only the first 1a is an anaerobic tank and the other 5 are aerobic tanks, the ratio of the anaerobic tank to the aerobic tank is The A: O ratio expressed as is 1: 6, and when 1a and 1b are anaerobic tanks, the A: O ratio becomes 1: 3. And we made 4 lines of this equipment, and A: O in the low water temperature period when the average water temperature was 16 ℃.
The ratio is 1: 3 and 1: 6, and the sludge return ratio at this time is 50%
Table 1 shows the results of measuring the nitrification rate and the TN removal rate when the values were 100% and 100%. The HRT (hydraulic retention time) was set to 8 hours as in the case of the standard activated sludge method, and the nitrification solution was circulated only by returning sludge sent to the anaerobic tank 1a using the nitrification solution circulation pump P ₅ . .

From Table 1, when the A: O ratio is the same,
The larger the sludge return ratio, the higher the nitrification rate (1 system <2 system, 3 system
System <4 system) and the sludge return ratio is the same, A: O
The ratio is higher when the aerobic conditions are longer (1 system <3 system, 2
It is understood that the system <4 system). However, regarding the T-N removal rate, no significant difference was observed among the 1 to 3 systems except the 4 system.

That is, in order to secure a high T-N removal rate, it is necessary to set an A: O ratio and a sludge return ratio which can secure a high nitrification rate. By increasing the sludge return ratio,
The circulation amount of nitrate nitrogen increases, and the MLSS concentration in the entire reaction tank is increased to promote DO consumption. However, sludge return amount increases, the NO _X -N amount of circulated is increased possibility of denitrification becomes insufficient occurs, there is a possibility that would increase the load of the final sedimentation tank. Therefore, the main point of the present invention is to determine the A: O ratio based on the ratio between the nitrification rate and the denitrification rate at an arbitrary return ratio and also control the return ratio.

Next, one embodiment of the activated sludge circulation modification method to which the present invention is applied will be described with reference to FIG. In this example, the biological reaction tanks are anaerobic tanks 1a and 1b in which dissolved oxygen (DO) does not exist, anaerobic-aerobic tanks 30a and 30b, and a plurality of aerobic tanks 2a, 2b, 2c and 2d in which DO exists. Due to the partitioning into 6 and more, the biological reaction tank itself has 6 or more compartments (8 compartments in this example)
Is divided into

A stirring mechanism 10 is provided in each of the anaerobic tanks 1a and 1b and the anaerobic-aerobic tanks 30a and 30b, and the anaerobic-aerobic tanks 30a and 30b and the aerobic tanks 2a and 2 are provided.
Air diffusers 4 are provided in b, 2c and 2d, and air is supplied from a blower 5 to each air diffuser.
Incidentally, anaerobic - valves V _5, V ₆ for the air volume adjustment is mounted between the aerobic dual tank 30a, and 30b and the blower 5.

A sampling device 31 is provided in each of the above tanks. 32 NO _X -N measuring device, 33 is nitrification and denitrification rate calculating unit, 34 denotes a controller.

Reference numeral 7 denotes a final settling basin. A stirring mechanism 19 and a turbidity meter 35 are provided in the final settling basin 7, and the value measured by the turbidity meter 35 is input to the controller 34. . P ₇ is a sludge return pump.

According to this embodiment, the A: O ratio naturally varies depending on whether the anaerobic-aerobic tanks 30a and 30b are used as anaerobic tanks or aerobic tanks. That is, since there are a total of eight reaction tanks, the first anaerobic-aerobic both-purpose tank 3
If 0a is an anaerobic tank and the other 5 tanks are aerobic tanks, A: O
The ratio is 3: 5, and if both 30a and 30b are anaerobic tanks, the A: O ratio will be 1: 1. Also, the dual-use tanks 30a, 30
If both b are aerobic tanks, the A: O ratio will be 1: 3.

[0048] The above anaerobic - is to use aerobic dual tank 30a, and 30b or as the anaerobic tank or the aerobic tank, the opening and closing of the air flow rate adjusting valves V _5, V _6, which is controlled by the output of the controller 34 It is determined by the state and the driving state of the stirring mechanism 10.

After the A: O ratio is appropriately set in this way, the raw water 3 flowing into the anaerobic tanks 1a and 1b is first stirred by the stirring mechanism 10 under anoxic conditions to remove the denitrifying bacteria in the activated sludge. Then, air is supplied from the blower 5 to the diffuser pipe 4 arranged inside each aerobic tank determined based on the A: O ratio, and the air flow rate adjusting valves V ₅ and V ₆ are opened. By controlling the degree, the oxidative decomposition of organic matter by activated sludge and the nitrification of ammonia by nitrifying bacteria are carried out in the presence of oxygen by aeration in each aerobic tank.

The supernatant of the final sedimentation tank 7 is treated water 11
As a part of the sludge settled in the final settling tank 7 after being discharged after passing through a disinfection tank or the like outside the drawing, a sludge return pump P
It is returned to the anaerobic tank 1a by ₇ .

During the above operation, the sampling device 31 is used to sample the samples in the first anaerobic tank and the last anaerobic tank, and further in the first aerobic tank and the last aerobic tank, and NO _x − in the sample is sampled. the N was measured by NO _X -N measuring device 32, then the nitrification and denitrification rate calculation unit 33, NO in the anaerobic tank
_The denitrification rate and the nitrification rate are calculated by dividing the decrease amount of the _X- N concentration and the increase amount of the NOx-N concentration in the aerobic tank by the residence time in the anaerobic tank and the aerobic tank, respectively.

From the ratio of the denitrification rate and the nitrification rate thus obtained, the controller 34 controls the A: O ratio based on the opening / closing control of the air flow rate adjusting valves V ₅ and V ₆ , and the anaerobic-
The rotation state of the stirring mechanism 10 in the aerobic tanks 30a and 30b is controlled. Further the final sedimentation tank 7 turbidimeter 35 deployed within and final sludge return pump to the extent that NO _X -N does not remain in the anaerobic tank within which ss concentration in the treated water 11 does not exceed the set value The drive control of P ₇ is performed.

Therefore, the present embodiment is characterized in that the operation is continued while the A: O ratio and the sludge return ratio of the biological reaction tank are updated as needed according to the change in the treatment state of the raw water 3. .

[0054]

As described in detail above, according to the operation control method of the modified activated sludge circulation method according to the present invention, anaerobic-
The A / O ratio can be changed depending on whether the aerobic / aerobic tank is used as an anaerobic tank or an aerobic tank. The A: O ratio can be controlled and the stirring mechanism in the anaerobic / aerobic tank can be changed. By controlling and returning the sludge to the anaerobic tank to such an extent that the ss concentration of the treated water in the final settling tank does not exceed the set value and NO _X -N does not remain in the final anaerobic tank, A: By supplying air from the blower to the air diffuser tubes located inside each aerobic tank determined based on the O ratio, the raw water is denitrified in the anaerobic tank, and in the presence of oxygen due to aeration in each aerobic tank. Oxidative decomposition of organic matter by activated sludge and nitrification of ammonia by nitrifying bacteria are carried out, and the effect of preventing destabilization of the nitrification reaction in the aerobic tank as a whole and promoting the nitrification reaction in the aerobic tank is obtained. To be

Particularly, in order to effectively remove nitrogen by the anaerobic-aerobic activated sludge treatment method, it is required to maintain denitrification in the anaerobic tank and nitrification in the aerobic tank under the optimum operating conditions. Since the nitrogen removal step is highly influenced by the nitrification step, it is required to maintain a good balance between the nitrification reaction and the denitrification reaction in order to maintain a high nitrogen removal rate. The samples in each tank are sampled to measure NO _X -N, and the amount of NO _X -N concentration decrease in the anaerobic tank and N in the aerobic tank are measured by the nitrification / denitrification rate calculator.
The denitrification rate and the nitrification rate are calculated from the increase in the O _X -N concentration, and the A: O ratio and the sludge return rate are controlled from the ratio between the denitrification rate and the nitrification rate. It is possible to increase both the nitrification efficiency in the aerobic tank and the denitrification effect in the anaerobic tank even in the low water temperature period, and the volume of the biological reaction tank is 2 times larger than that of the standard activated sludge method.
There is an effect that it is possible to adopt it under a condition where it is difficult to secure a land such as an urban area, without having to increase the number of times to three times.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram showing an experimental device based on this example.

FIG. 3 is a schematic diagram showing an example of conventional anaerobic-aerobic activated sludge treatment.

[Explanation of symbols]

1a, 1b ... Anaerobic tank 2a, 2b, 2c, 2d ... Aerobic tank 4 ... Diffuser pipe 5 ... Blower 13 ... Partition plate 14 ... First settling tank 15 ... Raw water storage tank 16, 20 ... Water level gauge 17 ... Treated water storage Tank 18 ... Excess sludge storage tank 22, 23 ... Redox potential meter 24 ... Alkali storage tank 25 ... pH meter 26 ... DO meter 30a, 30b ... Anaerobic-aerobic both-use tank 31 ... Sampling device 32 ... NO _X -N measuring device 33 ... Nitrification / denitrification rate calculator 34 ... Controller 35 ... Turbidimeter

Claims (2)

[Claims] 1. A step of denitrifying raw water with denitrifying bacteria in a multi-stage anaerobic tank, a step of nitrifying with nitrifying bacteria in a multi-stage aerobic tank, and a solid-liquid separation in a settling tank to obtain a supernatant. In the activated sludge circulation modified process including a step of discharging the liquid as treated water and a mechanism for returning a part of the sludge in the settling tank to the first-stage anaerobic tank, between the anaerobic tank and the aerobic tank, A single-stage or multiple-stage anaerobic-aerobic both-use tank equipped with both a stirring mechanism and an air diffuser with a valve for adjusting the air flow rate is arranged, and a sample in each tank is sampled to measure the NO _X -N concentration, NO _{X in} anaerobic tank −
Seeking denitrification rate and the nitrification rate from the increase amount of NO _X -N concentration at the reduction and aerobic tank of N concentration by calculation, the results from the anaerobic - performing opening and closing control of the air amount adjusting valve to the aerobic dual tank Of the activated sludge circulation method in the low water temperature period characterized by determining the A: O ratio and controlling the driving state of the stirring mechanism on the anaerobic tank side and the sludge return ratio from the settling tank to the anaerobic tank. Control method. 2. A deployed turbidimeter in the sedimentation tank, the sludge to the extent that NO _X -N anaerobic tank in and output stage to the extent that ss concentration in the treated water does not exceed the set value does not remain The operation control method according to claim 1, wherein the return ratio is determined.