JPH07116684A - Controlling method for intermittent aeration type activated sludge method - Google Patents

Abstract

PURPOSE:To control an operation so that the removal ratio of nitrogen and phosphorus contained in drainage is drastically enhanced in the case of performing drainage treatment. CONSTITUTION:In an intermittent aeration type activated sludge method, drainage is introduced into an aeration tank and both an aerobic state for performing aeration and an anaerobic state for stopping aeration and performing agitation are alternately repeated. Thereafter treated water is discharged from the final settling basin and a part of activated sludge is pulled out as excess sludge. Nitrogen and phosphorus contained in drainage are removed. In the case of controlling the intermittent aeration type activated sludge method, an ORP gauge is provided in a reaction tank and the occurrence time of an inflection point is measured by detecting the inflection point on an ORP curve in the aeration and agitation processes. The aeration time in the aeration and agitation processes of the next time is decided according to the occurrence time of the inflection point in the aeration and agitation processes up to now. As a result, since time allocation of nitrification, denitrification, absorption of phosphorus and discharge of phosphorus is made proper, the removal ratio of nitrogen and phosphorus is drastically enhanced.

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 serious problem in closed water areas such as lakes and marshes, and removal of nitrogen and phosphorus, which cause this, has become important. Therefore, a treatment method capable of removing nitrogen and phosphorus in addition to organic substances has been developed as an improved method of the activated sludge method. Typical methods include the A ₂ O method, the batch activated sludge method, and the intermittent aeration activated sludge method. (Hereinafter, abbreviated as intermittent aeration method) and the like. These methods are collectively called anaerobic aerobic activated sludge method because microorganisms are alternately subjected to aerobic and anaerobic conditions to remove organic matter, nitrogen and phosphorus.

First, the principle of 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. Nitrogen oxidizes NH ₄ —N (ammonia nitrogen) into NO ₃ —N (nitrate nitrogen) under aerobic conditions, and then NO ₃ under anaerobic conditions by denitrifying bacteria. -N is reduced to N ₂ (nitrogen gas) and removed. The relationship between nitrification and denitrification can be summarized as follows.

[0004]

[Table 1] Reaction Nitrogen morphological change Reaction conditions Microbial nitrification reaction Ammonium nitrogen → Nitrate nitrogen Aerobic (with dissolved oxygen) Nitrifying bacteria Denitrification reaction Nitrogen nitrogen → Nitrogen gas Anaerobic (without dissolved oxygen) Denitrifying bacteria Phosphorus By altering the operating conditions of the aeration tank between aerobic and anaerobic alternately, activated sludge having the property of accumulating a large amount of phosphorus in the cells is produced, 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 follows.

[0005]

[Table 2] Phosphorus concentration in the reaction tank Reaction conditions Phosphorus removal Phosphorus release Increase Anaerobic (No dissolved oxygen) -Phosphorus absorption Decrease Aerobic (Dissolved oxygen) Activated sludge extraction In this way, nitrogen and phosphorus are removed. Two conditions, aerobic and anaerobic, are essential, but strictly speaking, the anaerobic condition for denitrification and the anaerobic condition for dephosphorization are different, and NO ₃ is left in the aeration tank after denitrification is completed. The release of phosphorus from the activated sludge occurs after the elimination of oxygen molecules due to -N, which leads to the absorption of phosphorus in the subsequent aeration step.

Next, the intermittent aeration method, which is one of typical anaerobic aerobic activated sludge methods for small-scale sewage treatment, will be described. The intermittent aeration method has a long history of development and has a single aeration tank where the actual equipment is already in operation, and a two-tank intermittent aeration method that uses two aeration tanks that are currently being developed. There is a law. The 2-tank intermittent aeration method is Japanese Patent Application No. 4-23395.
The method is described in detail in Japanese Patent Publication No. 3 and is expected from the fact that the removal rate of nitrogen and phosphorus is high both theoretically and experimentally, but there are still few actual-scale operation examples. On the other hand, the single-tank intermittent aeration method is capable of removing a considerable amount of nitrogen and phosphorus, and has a simple device configuration.

An operation control method for simultaneous removal of nitrogen and phosphorus in the single tank intermittent aeration method is disclosed in Japanese Patent Laid-Open No. 4-1974.
Although it is described in Japanese Patent Publication No. 97, its outline can be summarized as follows. FIG. 3 is a schematic diagram showing a main part configuration of an apparatus used in the single tank intermittent aeration method. FIG. 3 shows the apparatus configuration, water and air paths as solid arrows,
The control signals are represented by dotted arrows. In FIG.
This device mainly comprises an aeration tank 2 in which sewage 1 flows in and is treated by intermittent aeration, and a final settling basin 4 in which activated sludge and treated water 3 are separated. The control system includes a DO meter 5 for measuring the dissolved oxygen concentration, and a control device 7 for outputting a control signal for operating and stopping the aeration blower 6 based on the DO measurement value. The aeration stirring device 8 has the functions of an air diffuser and a stirring device, and is normally operated continuously.

In this apparatus, one processing cycle (hereinafter,
(Sometimes simply referred to as a cycle) for about 2 hours,
Aeration and agitation are performed within one cycle, and DO is 0.
Time of 2 mg / l or less (anaerobic level time: A), and 0.
The operation is usually controlled so that the ratio A / B to the time of 5 mg / l or more (aerobic level time: B) is 0.5 to 1.0. In that case, the nitrogen removal rate is 80 to 90%.

[0009]

In order to efficiently remove nitrogen and phosphorus in the single tank intermittent aeration method, aeration for promoting nitrification and phosphorus absorption within one cycle, stirring for promoting denitrification, and subsequent phosphorus release. 3 of stirring to proceed
It is necessary to properly maintain the time allocation of the process. But,
The above method of controlling the ratio of A / B focuses on controlling the apparent distribution of the aeration time and the stirring time, and it is sufficient to deal with the time distribution of the denitrification process and the phosphorus release process in the stirring time. Has not been done. Therefore, in the above method of controlling A / B, although the nitrogen removal rate is good, there is a problem that the phosphorus removal rate decreases and becomes unstable when the raw water quality, the water temperature, or the like changes.

The present invention has been made in view of the above-mentioned problems, and an object thereof is a single-tank system capable of always obtaining high denitrification and dephosphorization efficiency regardless of changes in raw water quality and operating conditions. It is to provide a control method of the intermittent aeration method.

[0011]

In order to solve the above-mentioned problems, the control method of the present invention has an ORP meter installed in an aeration tank for operation control of the intermittent aeration type activated sludge method, and the treatment up to the present time is performed. Based on the appearance time of the inflection point on the ORP curve in the cycle, the sum of the aeration time of the next processing cycle and the denitrification time in the stirring step is controlled to a predetermined time, and this predetermined time is currently It is determined based on the sum of the aeration time and the denitrification time in the treatment cycles up to, or based on the average value of the sum of the aeration time and the denitrification time in several cycles of the treatment cycles to date.

[0012]

The present invention detects the ORP inflection point by performing the control as described above, so that the denitrification time and the phosphorus release time can be measured, and the aeration time can be set for each cycle. Therefore, as a result, the aeration, denitrification, and phosphorus release time in one cycle can be determined. Therefore, by adjusting the aeration time of the next cycle based on the appearance time of the inflection point of the cycle up to the present time, it is possible to always maintain an appropriate ratio of aeration, denitrification, and phosphorus release time. As a result, good treated water quality with high removal rates of organic substances, nitrogen, and phosphorus can be obtained.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the control method of the single tank intermittent aeration 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 of an apparatus and a control system of a single tank type intermittent aeration method to which the present invention is applied. The same reference numerals are used for the portions in common with FIG. 3 in FIG.
Is the same as. In FIG. 1, this device is basically the same as the device shown in FIG. 3 except that the DO meter 5 is not provided and an ORP meter 9 is installed in the aeration tank 2 instead.

The control method of the present invention in this system is as follows:
A description will be given with reference to FIG. 2 together with the change in water quality due to control. 2 (a) is the elapsed time related to the change of the NO _X -N (nitrite nitrogen and the sum of the nitrate nitrogen to produce with the nitrification), FIG. 2 (b) PO ₄ -P (orthophosphoric acid 2) the relationship between the change in phosphorus and the elapsed time, FIG. 2C is a diagram showing the relationship between the change in the ORP and the elapsed time, and FIG. 2C also shows the operating conditions of the aeration tank 2 and the biological reaction. Is also shown.

As described above, FIG. 2 (c) shows a change in ORP with the passage of time while the aeration start time is set to zero at an arbitrary timing during execution of the control method according to the present invention. The main point of the control method of the present invention is to fix one cycle time T _S2 and adjust the sum of the aeration time T _N and the denitrification time T _D (T _N + T _D ) within that time, and adjust the aeration time T _N. To control the time T _S1 set in advance. That is, in FIG. 2C, one cycle time T _S2
Is set to 2 hours, and T _S1, which is the set value of the sum of the aeration time and the denitrification time, is 1.5 hours. Aeration time T _N
Is set to 1 hour in advance as a result of the calculation described later. Looking at the change in ORP, the bending point A appears 25 minutes after the start of stirring after the end of aeration. Since the bending point A has the property of appearing when the denitrification is completed, the bending point A
By detecting (detection method will be described later), the time T _D , that is, the denitrification time can be determined to be 25 minutes. As a result, since one cycle time T _S2 is 2 hours, the phosphorus release time T _P becomes the remaining 35 minutes. In this way, the denitrification time T _D and the phosphorus release time T _P can be determined by detecting the inflection point of the ORP.

By the way, the denitrification time T _D is 25 minutes,
T _N + T _D is 85 minutes, which is 5 minutes shorter than the set value of T _S1 . Therefore, in the next cycle, the aeration time T _N is adjusted so that T _N + T _D approaches T _S1 . Specifically, the method of adjusting the aeration time T _N is based on the following equation (1).

[0017]

[Formula 1] T _{N, n} = T _{N, n-1} + K ₁ [T _S1 − (T _N + T _D )] (1) where T _{N, n} : aeration time T _{N, n-1} in the next cycle : aeration period K ₁ in the current cycle: constant T _S1: set value of the sum between the aeration period and de窒時T _N + T _D: sum time T _N + T _D between aeration time and de窒時in the current cycle, the current The average value (moving average) of the sum of the aeration time and denitrification time of several cycles up to the above cycle may be used.

By performing such control, the water quality
Aeration time and denitrification regardless of fluctuations in operating conditions
The phosphorus release time can be maintained at a constant ratio during
As described below, a stable and high nitrogen and phosphorus removal rate can be obtained.
You can Here, each time setting will be described. 1 service
Uccle time T_S22 hours is appropriate,
The longer the time, the greater the fluctuations in the treated water quality, and the shorter the time, the greater
It becomes technically difficult to detect the curved point A. Also aeration
Time and denitrification time T_N+ T _DIs the phosphorus release time T_PTo
Decide in consideration. That is, from the conventional knowledge, the phosphorus release time
May require 20-40% of the processing time
I know, so 1 cycle time T_S220-40% of
To calculate the phosphorus release time and the remaining time to T_N+ T
_DAnd In the case of FIG. 2, the set T_P30 minutes
And T_S2Is 2 hours, so the phosphorus release time is treated
Equivalent to 25% of the time.

The bending point A is detected as follows. That is, OR with the passage of time with the step time being Δt
The slope of the P curve is obtained, and the latest slope is α2 and the slope before Δt time is α1, and α2 / α1 is calculated. When the slope of the ORP curve is almost constant, α2 / α1 is about 1, but
At the bending point, α2 / α1 rapidly increases to 1.5 to 3. Therefore, a threshold value β is set, and when (α2 / α1)> β, it is determined that the bending point appears.

Next, the water quality change in the aeration tank 2 when the above control is performed will be described. In FIG. 2 (a),
NO _X -N is increased in advanced nitrification aeration time T _N, often are all ammonium nitrogen nitrification before the aeration period is completed, an increase in the NO _X -N stops.
Subsequently, in the denitrification step, NO _X -N becomes nitrogen gas and is removed. Further, as shown in FIG. 2 (b), PO ₄ -P is absorbed by activated sludge at the aeration time T _N and decreases, and when the denitrification ends, the phosphorus release reaction proceeds and increases. When the PO ₄ -P concentration changes in this way, the phosphorus concentration in the activated sludge is increasing, and therefore phosphorus removal can be achieved by extracting excess sludge. Further, the water quality in the aeration tank 2 varies as shown in FIGS. 2A and 2B, but since the sewage 1 continuously flows into the aeration tank 2, the treated water 3 that has passed through the sedimentation basin 4 The water quality will be this average value and maintained at a low level.

It is well known that organic matter is removed by activated sludge in the aeration-stirring cycle, and detailed description thereof will be omitted. By the way, in the control method of the present invention, when phosphorus removal is unnecessary, the set value of T _P may be reduced to give priority to denitrification. Further, the sewage 1 is generally continuously inflowed, but it may be allowed to flow only during the stirring time, and in that case, the control method of the present invention can be applied without any problem. The DO for the aeration time is adjusted to 2 to 3 mg / l by adjusting the air amount, but it is desirable to control it to about 2 mg / l in order to further stabilize the water quality. However, DO control is not an essential element in the method of the present invention.

[0022]

In the conventional control method of the single tank intermittent aeration method, the ratio of the aeration time and the stirring time was controlled, but the time distribution of the denitrification process and the phosphorus release process in the stirring time was controlled. Since it was not present, the nitrogen removal rate was good, but there was a problem that the phosphorus removal rate would decrease if the raw water quality, water temperature, etc. changed.

The control method of the present invention made to cope with this has the following advantages. That is, in the control method of the present invention, an ORP meter is installed in the aeration tank, and
By detecting the appearance time of the inflection point on the P curve, the denitrification and phosphorus release times are measured, and the aeration time per cycle is determined so that an appropriate phosphorus release time can be secured. Is. Moreover, the aeration time is always corrected and calculated based on the current cycle time distribution.

As a result, by implementing the control method of the present invention, it is possible to quickly respond to changes in raw water quality and operating conditions,
While securing a predetermined phosphorus release time per cycle,
Since the aeration time can be set, stable simultaneous removal of nitrogen and phosphorus at a high rate can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a main part of an apparatus to which a method of the present invention is applied.

Water in the aeration tank of Figure 2 apparatus in which the method of the present invention is applied, shows a change in the ORP, (a) is NO _X -N,
(B) is a relationship diagram of PO ₄ -P and (C) is ORP with time.

FIG. 3 is a schematic diagram showing a main part configuration of an apparatus to which a conventional method is applied.

[Explanation of symbols]

 1 Sewage 2 Aeration tank 3 Treated water 4 Final settling tank 5 DO meter 6 Aeration blower 7 Controller 8 Aeration stirrer 9 ORP meter

Claims (3)

[Claims] 1. A treatment cycle in which an aerobic state in which aeration is performed and an anaerobic state in which aeration is stopped and stirring is repeated in this order in an aeration tank into which wastewater flows, and then this treated water is treated in a final settling tank. When controlling the intermittent aeration type activated sludge method that removes nitrogen and phosphorus in wastewater by discharging a part of the activated sludge as surplus sludge, an ORP meter is installed in the aeration tank, and the treatment up to now is performed. An intermittence characterized by detecting a bending point on an ORP curve in a cycle and controlling the sum of the aeration time of the next processing cycle and the denitrification time in the stirring step to a predetermined time based on the appearance time of the bending point. Control method of aeration type activated sludge method. 2. The control method according to claim 1, wherein the sum of the aeration time in the next treatment cycle and the denitrification time in the stirring step is based on the sum of the aeration time and the denitrification time in the current treatment cycle. A control method of an intermittent aeration type activated sludge method characterized by making a decision. 3. The control method according to claim 1, wherein the sum of the aeration time of the next treatment cycle and the denitrification time in the stirring step is calculated as the sum of the aeration time and denitrification time of several treatment cycles up to the present. A control method for an intermittent aeration type activated sludge method, which is characterized in that it is determined based on an average value of sums.