JPH07100487A - Method for controlling operation of intermittent aeration-type activated-sludge process - Google Patents

Abstract

PURPOSE:To eliminate a sensor for control and to operate and control an intermittent aeration method exhibiting stable denitrification and dephosphorization efficiencies only with setting of time by a timer by performing control of aeration and stirring time of the first and the second aeration tanks wholly by means of the timer. CONSTITUTION:After nitrification and absorption of phosphorus are performed under a condition with a dissolved oxygen concn. of 2-3mg/l by setting 30min of the aeration time Ta1 of the first aeration tank 2a, and 70min of the aeration time Ta2 of the second aeration tank 2b, the process is shifted to a stirring process and denitrification and discharge of phosphorus are performed. When the time Ts of one anaerobic-aerobic cycle, 120min, passes through, control by using a timer is performed so as to return both the first and the second aeration tank 2a and 2b to the aeration condition. The aeration time ratio (r) is obtd. by an equation wherein the vol. of the first aeration tank 2a is V1 the vol. of the second aeration tank 2b is V2, the sludge retaining time is (n) days, the specific proliferation rate is mu and Ta1 and Ta2 are set to be (r)>1/(n.u) and Ta1 <=1/2 of Ts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for biologically treating sewage and domestic wastewater, and more particularly to a method for controlling a process for removing nitrogen and phosphorus in wastewater.

[0002]

2. Description of the Related Art Sewage and domestic wastewater are mainly treated to remove organic substances, and a biological treatment method represented by an activated sludge method has been generally used. However, in recent years, eutrophication has become a major problem in closed water areas such as lakes and marshes, and the removal of nitrogen and phosphorus, which cause this, has become important. for that reason,
A treatment method capable of removing nitrogen and phosphorus in addition to organic matter has been developed as an improved method of the activated sludge method. Typical methods are the A ₂ O method, the batch activated sludge method, the intermittent aeration activated sludge method (hereinafter , Abbreviated as intermittent aeration method) and the like.
In these methods, microorganisms are alternately subjected to aerobic and anaerobic conditions to remove organic matter, nitrogen and phosphorus.

Here, the principle of the sewage treatment for the purpose of removing nitrogen and phosphorus will be briefly described. Organic matter in the sewage is decomposed and removed as food for the microorganisms that make up the activated sludge. Under aerobic conditions, nitric acid is used to convert NH ₄ -N (ammonia nitrogen) into NO ₃ -N.
(Nitrate nitrogen), then under anaerobic conditions,
NO ₃ -N is reduced to N ₂ (nitrogen gas) and removed by the action of the denitrifying bacteria. Table 1 summarizes the relationship between nitrification and denitrification.

[0004]

[Table 1] By altering the operating conditions of the aeration tank between aerobic and anaerobic, phosphorus creates activated sludge that has the property of accumulating a large amount of phosphorus in the cells, and this activated sludge is used for removal. That is, since this activated sludge has the property of releasing phosphorus under anaerobic conditions and absorbing phosphorus under aerobic conditions, it absorbs phosphorus under aerobic conditions, and the activated sludge that has absorbed a large amount of phosphorus is treated as excess sludge. Dephosphorization is performed by removing it from the processing system. This relationship can be organized as shown in Table 2.

[0005]

[Table 2] Thus, in removing nitrogen and phosphorus, two conditions, aerobic and anaerobic, are indispensable. Strictly speaking, the anaerobic condition for denitrification and the anaerobic condition for dephosphorization are different, and intermittent aeration According to the method, after denitrification is completed and oxygen molecules due to NO ₃ —N disappear in the aeration tank, phosphorus is released from the activated sludge, which leads to absorption of phosphorus in the next aeration step.

[0006] The intermittent aeration method is a method that has attracted attention because it can set the ratio of aerobic conditions and anaerobic conditions in time and can be applied to existing facilities relatively easily. However, in order to efficiently remove nitrogen and phosphorus in the intermittent aeration method, it is important to control the aeration time (aerobic condition) and the agitation time (anaerobic condition) corresponding to the load, and some control has been performed so far. Methods have been proposed. Examples thereof include methods described in JP-B-63-35317 and JP-A-64-70198, but these methods have problems in control stability and treated water quality.

On the other hand, as a method for greatly improving this problem, the present inventors have proposed a first aeration tank into which waste water flows and a second aeration tank connected in series with the first aeration tank. An apparatus in which two aeration tanks are used and a final settling tank is provided in the subsequent stage and a control method therefor are being applied for by Japanese Patent Application No. 4-146054. FIG. 2 is a schematic diagram showing an intermittent aeration method disclosed in the above-mentioned Japanese Patent Application No. 4-146054 and a main part configuration of an apparatus for explaining an outline of a control system, in which water and air paths are shown by solid arrows, The control signal system is represented by a dotted arrow.

In FIG. 2, the apparatus mainly comprises a first aeration tank 2a and a second aeration tank 2b in which sewage 1 is introduced and organic matter, nitrogen and phosphorus are removed by activated sludge, and activated sludge is separated by gravity sedimentation. It is composed of a final settling tank 4 in which water 3 is obtained, and a returning sludge pump 5 for returning the settled activated sludge to the first aeration tank 2a. The volume ratio of the first aeration tank 2a and the second aeration tank 2b is about 1: 1, and the treated water 3
The total residence time, including the final settling tank 4, is 16 to 32 hours. The control system is a first ORP meter 6a that measures the redox potential in the first aeration tank 2a, a second ORP meter 6b that measures the redox potential in the second aeration tank 2b, and the values of these ORP meters. Based on the first aeration blower 7a, the second aeration blower 7b, the first stirring pump 8a, the second stirring pump 8
It comprises a control device 9 for outputting a control signal to b.

The basic idea when controlling the operation of such an apparatus system is to control the nitrification and denitrification in the first aeration tank 2a for a fixed time to secure the phosphorus release time, and
In the aeration tank 2b, nitrification and denitrification are performed, and one cycle of control is maintained at a predetermined time while preventing the release of phosphorus. The specific method will be described below with reference to FIG.
It will be described with reference to FIG. 3 (a), (b)
Shows the change of ORP with the passage of time, with the aeration start time being zero at any timing during the control.
FIG. 3A is a diagram showing ORP of the first aeration tank, and FIG. 3B is a diagram of ORP in the second aeration tank with respect to time.

First, a method of controlling the first aeration tank 2a will be described. The aeration time for nitrification and phosphorus absorption is T _e ,
The denitrification time is T _f, and the aeration time T _e is adjusted so that the time T _g, which is the sum of T _e and T _f , matches the preset time T _gs . Here, the ORP of the first ORP total 6a
The bending point A appears after the end of denitrification, and the time T _g is measured by detecting the bending point A.
The aeration time T _e is adjusted based on the difference between T _gs and T _g . As a result, since one cycle is maintained at about T _ds time as described later, the phosphorus release time is secured as T _ds −T _gs .

[0011] Next, the control method of the second aeration tank 2b is aeration time for nitrification and phosphorus absorption T _b, the stirring time denitrification progresses and T _C, is the sum of T _b and T _C The aeration time T _b is adjusted so that the time T _d coincides with the preset time T _ds, and at the same time, assuming that one cycle is completed after the time T _d , the first aeration tank 2a and the second aeration tank 2b are simultaneously operated. Return to aeration. It detects the inflection point B from the change in the ORP of the second ORP meter 6b measures a time T _d, is performed by adjusting the aeration period T _b on the basis of the difference between the T _ds and T _d. As a result, since the aeration state is established immediately after the denitrification is completed, phosphorus is not released in the second aeration tank 2b, and a high nitrogen and phosphorus removal rate is obtained.

[0012]

The control method in the intermittent aeration method, which the present inventors have applied for, has been described above. This control method has a high nitrogen and phosphorus removal rate and good stability, but a sensor is used. In order to maintain and maintain in good condition,
It is necessary for the ORP meter to be cleaned at a fairly high frequency of once every 1 to 4 weeks, and for example, there is a problem in applying it to a treatment plant where an administrator is not resident. Subsequent research revealed it.

The present invention has been made in view of the above points, and an object thereof is to set a time by using an intermittent aeration method using a timer, which does not require a control sensor and yet exhibits stable denitrification and dephosphorization efficiency. It is to provide a method of controlling driving only.

[0014]

[Means for Solving the Problems]
Therefore, the operation control method of the intermittent aeration method according to the present invention is
In the intermittent aeration method using the first and second aeration tanks,
The volume of the first aeration tank is V₁, The volume of the second aeration tank to V₂, Exposure
Anaerobic-aerobic consisting of air and stirring _s1
Cycle T_sThe aeration time of the first aeration tank in the_a1, Second aeration tank
Aeration time of T_a2, Sludge retention time of this process (SR
T) is n days, the specific growth rate of nitrifying bacteria is μ, and aeration time is
The ratio r is expressed by r = (V₁・ T_a1+ V₂・ T_a2) / [(V₁+
V₂) ・ T _s], R is less than 1 / (n · μ)
Big and T_a1Is T_sTo be less than 1/2 of T
_a1, T_a2Is set, and T is set in the first aeration tank._a1Time after aeration
Stir and perform T in the second aeration tank._a2Stir after aeration for a period of time
The total time of aeration and stirring in both the first and second aeration tanks is T
_sWhen the time is reached, aeration work from the stirring process in two tanks simultaneously
The timer control for shifting to the step is performed.

[0015]

As described above, in the method of the present invention, the aeration and stirring times of the first and second aeration tanks are all controlled by the timer, so it is not necessary to use the signal from the ORP meter.
For example, the aeration time T _a1 of the first aeration tank is set to 30 minutes to perform nitrification and phosphorus absorption, and thereafter, the process shifts to a stirring step to perform denitrification and phosphorus release. Also, the aeration time T of the second aeration tank
_{When a2} is set to 70 minutes, nitrification is performed, and then denitrification proceeds in the stirring step, and when the preset anaerobic-aerobic cycle time T _s 120 minutes has elapsed, the first and second aeration tanks Both return to the aerated state. There are certain conditions for setting the aeration time, the volume of the first aeration tank is V ₁ , the volume of the second aeration tank is V ₂ , the sludge retention time (SRT) of this process is n days,
Letting the specific growth rate of nitrifying bacteria be μ, the aeration time ratio r = (V ₁
・ T _a1 + V ₂ · T _a2 ) / [(V ₁ + V ₂ ) · T _s ] and r is larger than 1 / (n · μ) and T _a1 is 1/2 or less of T _s. Thus, T _a1 and T _a2 are set. The reason that r is made larger than 1 / (n · μ) is to maintain a certain amount of nitrifying bacteria in the activated sludge, and T _{a1 is set} to T
_The reason why it is set to ½ or less of _s is to end nitrification and denitrification early and secure a sufficient phosphorus release time in the first aeration tank. By performing such timer control, without using a sensor, nitrification,
Times for denitrification, phosphorus release, and phosphorus absorption can be secured, and good nitrogen and phosphorus removal rates can be obtained.

[0016]

First, the basic idea of the present invention will be described. The inventors of the present invention have described the above-mentioned Japanese Patent Application No. 4-146054.
In the process of advancing the control method disclosed in No. 1, when the conditions such as water quality and temperature are relatively stable, the aeration time of the first and second aeration tanks becomes almost constant. It was found that the quality of the treated water was kept good even if it was carried out with a timer without using it. Therefore, the requirements for timer control were considered from the viewpoint of the growth rate of microorganisms, and it was concluded that it is effective to control only by setting the time under the conditions described below.

An embodiment of the control method according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a configuration of a main part for explaining an apparatus and a control system of an intermittent aeration method to which the method of the present invention is applied. 2 that are the same as those in FIG. 2 are denoted by the same reference numerals, and the arrow lines are also handled in FIG.
Is the same as. 1, this device is basically the same as the device shown in FIG. 2, that is, the device disclosed in Japanese Patent Application No. 4-160554, except that the first OR of FIG.
The P total 6a and the second ORP total 6b are not provided.

The operation control method of the present invention in the system shown in FIG. 1 is as follows. For example, after the aeration time T _a1 of the first aeration tank 2a is set to 30 minutes and nitrification and phosphorus absorption are performed under the condition of a dissolved oxygen (DO) concentration of 2 to 3 mg / l,
Transfer to a stirring process to denitrify and release phosphorus. Further, the aeration time T _a2 of the second aeration tank is set to 70 minutes, and D is similarly set.
Nitrogenation was performed under the condition of O concentration of 2 to 3 mg / l, and then denitrification was allowed to proceed in the stirring step. When 120 minutes, which was the time T _s for one cycle of anaerobic-aerobic cycle set in advance, passed, first, Second
Timer control is performed so that both the aeration tank returns to the aeration state.

There are certain conditions for setting the aeration time in each aeration tank, the volume of the first aeration tank 2a is V ₁ , the volume of the second aeration tank 2b is V ₂ , and the sludge retention time (S
RT) is n days, the specific growth rate of nitrifying bacteria is μ, and the aeration time ratio r is r = (V ₁ · T _a1 + V ₂ · T _a2 ) / [(V ₁ +
V ₂ ) · T _s ], and set T _a1 and T _a2 so that r is larger than 1 / (n · μ) and T _a1 is ½ or less of T _s .

The reason why r is made larger than 1 / (n · μ) is to maintain a certain amount of nitrifying bacteria in the activated sludge. Generally, the condition for maintaining nitrifying bacteria in the system is that the SRT is larger than the reciprocal 1 / μ of the specific growth rate μ of nitrifying bacteria, and in the process including anaerobic and aerobic, the ratio of aerobic part to the whole or R · SR, where r is the aerobic time ratio
It is known that T is larger than 1 / μ. In the case of the intermittent aeration method using two aeration tanks to which the method of the present invention is applied,
If r is defined as the aeration time ratio, r = (V ₁ · T _a1 + V ₂
It can be _{calculated as} T _a2 ) / [(V ₁ + V ₂ ) · T _s ]. Therefore, if the SRT is n days, r is 1 /
If it is larger than (n · μ), nitrifying bacteria can be maintained. It should be noted that μ is obtained corresponding to the water temperature, can be easily obtained from the literature, and SRT is obtained as a general management index for the activated sludge method.

Setting T _a1 to ½ or less of T _s is
This is to end the nitrification and denitrification early so as to secure a sufficient phosphorus release time in the first aeration tank 2a. here,
SRT = 20 days, V ₁ = V ₂ , water temperature 20 ° C., μ = 0.2
5 (1 / day), T _a1 = 30 minutes, T _a2 = 70 minutes, T _s = 1
When calculation is performed under the condition of 20 minutes, r = 0.42.
On the other hand, since 1 / (n · μ) is 0.2, r> 1 /
(N · μ), nitrifying bacteria will be maintained in the system. Further, when T _a1 = 30 minutes, denitrification is normally completed in about 30 minutes, and therefore about 60 minutes can be secured for phosphorus release in the first aeration tank 2a, which results in good phosphorus absorption in the aeration step. It is useful. In the second aeration tank 2b, since the aeration time T _a2 = 70 minutes and the denitrification of 50 minutes is secured, the nitrogen removal is good. Anaerobic-Aerobic 1
It is appropriate that the period time T _s is generally about 1 to 3 hours, and the ratio of V ₁ to V ₂ is preferably in the range of 1: 2 to 2: 1.

Next, more specific examples will be described based on the experimental results. The present inventors used the prepared sewage obtained by mixing human waste, canteen drainage, soap water, tap water, sodium acetate, etc., and used an experimental device having the same function as the device shown in FIG. An operation control experiment aimed at simultaneous removal was performed. Table 3 shows the main specifications of the experimental apparatus and the experimental conditions.

[0023]

[Table 3] Table 4 shows an example of the results of this experiment.

[0024]

[Table 4] As can be seen from Table 4, since the nitrogen concentration was relatively high at 42 mg / l, the denitrification time was slightly short in the second aeration tank 2b, and the NO ₃ -N concentration was slightly higher, but TN
The removal rate was 86.9%, the TP removal rate was 93.0%, and the treated water quality was good.

In the control method of the present invention, when the nitrogen concentration is low, stirring may continue even after denitrification in the second aeration tank 2b is completed. However, the dissolved organic matter concentration in the second aeration tank 2b is Since it is low and the amount of phosphorus released is slight, the phosphorus concentration in the treated water 3 does not increase significantly. Further, when the nitrogen concentration is high, the denitrification may not be completed, but since the denitrification is also performed in the first aeration tank 2a and the nitrogen concentration in the second aeration tank 2b is low, the nitrogen concentration in the treated water 3 is low. Does not rise significantly. Of course, water quality analysis, portable DO meter, ORP
It is desirable to inspect the operating condition using a meter, thermometer, etc., and adjust the timer setting if necessary, but this is the same as the management work generally performed in the activated sludge process, and the control according to the present invention In applying the method, the management work load does not increase particularly.

When the above operation control is performed, the control sensor becomes unnecessary, and moreover, the times of nitrification, denitrification, phosphorus release, and phosphorus absorption can be secured, and good nitrogen and phosphorus removal rates can be obtained. . Regarding which of the control method according to the present invention and the control method applied by the present invention described above is applied, when the control of nitrogen and phosphorus regarding the treated water quality is extremely strict, it is preferable to use the control method of the application. Well, when the water quality regulation is relatively loose, it is desirable to use the control method according to the present invention.

[0027]

Although the operation control method of the intermittent aeration type activated sludge method of the present invention has been described above, the method according to the present invention is the method disclosed in Japanese Patent Application No. 4-146054 filed by the present inventors. From the practical point of view. That is, in the present invention, it is possible to perform the control similar to the control method applied by the present inventors without using an ORP meter as a sensor and only by controlling by a timer that sets a certain condition. In particular, the control method according to the present invention eliminates the need for a conventional ORP meter, thus significantly reducing the burden on the operation manager, and ensuring the nitrification, denitrification, phosphorus release, and phosphorus absorption time, thereby ensuring good treated water quality. The great effect of being obtained is obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of main parts of a sewage treatment apparatus to which an operation control method of the present invention is applied.

FIG. 2 is a schematic diagram showing a main configuration of a sewage treatment apparatus to which the control method of the intermittent aeration method applied by the present inventors is applied.

FIG. 3 shows changes in ORP of the first aeration tank and the second aeration tank in the control method of the intermittent aeration method which the present inventors applied for,
(A) is ORP of the first aeration tank, (b) is O of the second aeration tank
Relationship diagram of RP with time

[Explanation of symbols]

 1 Sewage 2a 1st aeration tank 2b 2nd aeration tank 3 Treated water 4 Final settling tank 5 Return sludge pump 7a 1st aeration blower 7b 2nd aeration blower 8a 1st stirring pump 8b 2nd stirring pump 9 Control device

Front page continued (72) Inventor Yasunari Sasaki 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. (72) Inventor Yutaka Mori 1-1 Tanabe Nitta, Kawasaki-ku, Kanagawa-ken Fuji Electric Machinery Co., Ltd. (72) Inventor Shigeru Hatsumata 1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd.

Claims (2)

[Claims] 1. A first aeration tank and a second aeration tank connected in series to the first aeration tank, the aeration state in which waste water is aerated in these two aeration tanks, and aeration is stopped to perform agitation. This is an operation control method of an intermittent aeration type activated sludge method for removing nitrogen and phosphorus in wastewater by repeating the anaerobic state performed, wherein the volume of the first aeration tank is V ₁ and the volume of the second aeration tank is V ₁ .
₂ , T for the time of one cycle of anaerobic-aerobic consisting of aeration and stirring
_s , the aeration time of the first aeration tank within one cycle T _s is T _a1 , the second
The aeration time of the aeration tank is T _a2 , the sludge retention time of this process is n days, and the specific growth rate of nitrifying bacteria is μ.
R = (V ₁ · T _a1 + V ₂ · T _a2 ) / [(V ₁ +
Calculated as _{V 2) · T s],} r is 1 / (n · μ) greater than, and sets the T _a1, T _a2 as T _a1 hours is less than half of T _s time, first The aeration tank performs agitation after aeration for T _a1 hours and the second aeration tank performs agitation after aeration for T _a2 hours, and when the total time of aeration and agitation reaches T _s , the first aeration tank and the second aeration tank An operation control method for an intermittent aeration type activated sludge method, characterized in that the aeration tank and the aeration process are simultaneously transferred from the stirring process to the aeration process. 2. The method according to claim 1, wherein the control time of the first aeration tank and the second aeration tank are all set by using a timer.