JP2987103B2 - Intermittent aeration - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating sewage such as sewage and industrial wastewater suitable for nitrification-denitrification, and more specifically to a novel method of controlling intermittent wastewater which is effectively controlled. Regarding the aeration method.

[0002]

2. Description of the Related Art Conventionally, as a method for nitrifying and denitrifying sewage, a batch method or an oxidation ditch method (OD method) is used.
It has been known. However, the batch method may require a plurality of reaction tanks. In this case, not only the installation area of the treatment equipment is increased, but also the adjustment for the fluctuation of the amount of wastewater flowing into the treatment equipment is complicated. In the OD method, a region in an intermediate state that is neither aerobic nor anaerobic occurs in the reaction tank, and wasteful space is generated in the reaction tank.

[0003] To solve these problems of the batch method and the OD method,
As a method that can efficiently perform nitrification-denitrification treatment of sewage without requiring a large installation area, and is easy to operate, and particularly, can efficiently perform nitrification-denitrification treatment of small-scale sewage, Intermittent aeration is known. In the intermittent aeration method, the inside of the reaction tank is alternately switched between an aerobic step and an anaerobic step while continuously supplying sewage into the reaction tank. Regarding nitrogen contained in sewage, in the aerobic process, nitrifying bacteria oxidize ammoniacal nitrogen to nitrate nitrogen in the aerobic process, and in the anaerobic process, nitrate nitrogen is reduced to nitrogen gas by the action of denitrifying bacteria, and From which nitrogen is removed.

On the other hand, regarding phosphorus contained in sewage,
Activated sludge having the property of accumulating a large amount of phosphorus in cells is used. That is, such activated sludge absorbs phosphorus under aerobic conditions and discharges phosphorus under anaerobic conditions. Therefore, phosphorus can be removed from wastewater by absorbing phosphorus under aerobic conditions and removing activated sludge that has absorbed a large amount of phosphorus from the treatment system as excess sludge.

The intermittent aeration method is disclosed in, for example,
798, JP-A-5-50093, JP-A-5-50093
These are known from JP-A-237495 and JP-A-5-237496. In the intermittent aeration method disclosed in Japanese Patent Application Laid-Open No. Hei 1-310798, a stirring device and an aeration device are provided inside a reaction tank, and while continuously stirring wastewater in the reaction tank by the stirring device, an aeration device is used. Aeration intermittently. Thus, the nitrification-denitrification treatment of the sewage is performed by alternately switching the inside of the reaction tank between the aerobic state and the anaerobic state at predetermined time intervals.

In the intermittent aeration method disclosed in Japanese Patent Application Laid-Open No. 5-50093, operation is performed with a predetermined ratio between an anaerobic time period during which air is not supplied and an aerobic time period during which air is supplied in one intermittent cycle. At the same time, when the dissolved oxygen concentration in the reaction tank (hereinafter, sometimes referred to as DO concentration) exceeds a predetermined value during the aerobic time period, the air supply amount and / or the rotation speed of the stirrer are reduced. . JP-A-5-237
In the intermittent aeration method disclosed in Japanese Patent Publication No. 495, during the period of aerobic time, from the start of air supply to the time when the DO concentration in the reaction tank reaches a predetermined value, the supply amount of air and / or the stirrer Is operated with an increased number of revolutions. In the intermittent aeration method disclosed in Japanese Patent Application Laid-Open No. 5-237496, during the period of aerobic time from the start of air supply until the DO concentration in the reaction tank reaches a predetermined value, the amount of air supply and / or Alternatively, the operation is performed while increasing the rotation speed of the stirrer, and when the DO concentration in the reaction tank exceeds a predetermined value, the operation is performed while reducing the air supply amount and / or the rotation speed of the stirrer.

[0007]

The intermittent aeration method disclosed in the above patent publication is a very efficient nitrification-denitrification method for wastewater. However, the load of the sewage flowing into the reaction vessel usually fluctuates. For example, when treating domestic wastewater, the load of inflow sewage from Monday to Friday is generally constant, and the load tends to increase on Saturday and Sunday. Further, since the average temperature of the sewage varies depending on the season, the nitrification reaction rate of the activated sludge varies. In the intermittent aeration method disclosed in the above-mentioned patent publication, the intermittent aeration is automatically performed under optimal operating conditions by following the load fluctuation of the inflow wastewater and the fluctuation of the nitrification reaction rate of the activated sludge. It is difficult.

[0008] Activated sludge absorbs phosphorus when the oxidation-reduction potential (ORP) value is positive under aerobic conditions, and discharges phosphorus when the ORP value is negative under anaerobic conditions.
Generally, when performing continuous aeration, the ORP value is positive. Therefore, phosphorus can be desorbed by absorbing phosphorus under aerobic conditions and removing activated sludge that has absorbed a large amount of phosphorus as excess sludge from the treatment system. In other words, in the intermittent aeration method, the ORP value tends to be negative in the anaerobic step, and phosphorus may be released into the treated sewage.
Further, if the treated sewage is placed in an anaerobic state, it becomes difficult to remove phosphorus even if a coagulant is added to the treated sewage for dephosphorization. The indirect aeration method disclosed in the above patent publication includes
No mention is made of the removal of phosphorus from sewage.

Accordingly, a first object of the present invention is to automatically perform nitrification-denitrification treatment of sewage under optimum operating conditions following changes in the load of inflow sewage and changes in the nitrification reaction rate of activated sludge. It is to provide an intermittent aeration method that makes it possible. Further, a second object of the present invention is the first object, in addition to the first object,
An object of the present invention is to provide an intermittent aeration method capable of surely removing phosphorus from wastewater.

[0010]

The intermittent aeration method according to the first aspect of the present invention for achieving the first object is to continuously supply sewage water into the reaction tank. Is alternately switched to the aerobic process and the anaerobic process, and in the aerobic process,
The intermittent aeration method for treating wastewater by controlling the amount of air supplied to the reaction tank based on the measurement result of the dissolved oxygen concentration in the reaction tank and maintaining the dissolved oxygen concentration in the reaction tank at a predetermined value. Then, a total T ₀ of one day during which the dissolved oxygen concentration in the reaction tank should be maintained at the predetermined value in the aerobic step is obtained in advance, and one cycle of the intermittent aeration cycle including the aerobic step and the anaerobic step is determined. The number of days is M, and the i-th day of the day (however,
In the intermittent aeration cycle (1 ≦ i ≦ M), assuming that the time during which the dissolved oxygen concentration in the reaction tank is maintained at the predetermined value is T _i , (a) calculated based on the following equation (1). Difference Δ
When T is a positive value, the amount of oxygen supplied from the start of the aerobic step in each intermittent aeration cycle on the following day until the dissolved oxygen concentration in the reaction tank reaches the predetermined value is calculated from the start of the aerobic step on the day. (2) When the difference ΔT is a negative value, the dissolved oxygen concentration in the tank is increased from the supply oxygen amount until the concentration reaches the predetermined value. The supplied oxygen amount until the dissolved oxygen concentration reaches the predetermined value,
From the start of the aerobic step on the day, the amount of oxygen supplied to the reaction tank until the dissolved oxygen concentration reaches the predetermined value is reduced. (C) When the difference ΔT is approximately zero, the amount of oxygen supplied in each intermittent aeration cycle on the next day is reduced. The amount of oxygen supplied from the start of the aeration step until the dissolved oxygen concentration in the reaction tank reaches the predetermined value, and the amount of oxygen supplied from the start of the aerobic step on the day until the dissolved oxygen concentration in the reaction tank reaches the predetermined value. It is characterized in that it is the same as the amount.

[0011]

(Equation 4)

As a result of the fluctuation of the average temperature of the sewage depending on the season, the nitrification reaction rate of the activated sludge changes. To cope with this, in the intermittent aeration method according to the first aspect of the present invention, the seasonal correction value ΔT _{0_S} may be added to the right side of the above equation (1). That is, in summer, the water temperature is high,
The nitrification reaction rate of activated sludge is fast. Conversely, in winter, the water temperature is low and the nitrification reaction rate of activated sludge is slow. Therefore, in the summer time required for the total reaction of the activated sludge is shortened, the total value of T _i tends to be a large value. On the other hand, in the winter, the time required for the total reaction of the activated sludge becomes longer, the total value of T _i tends to be a small value.
Therefore, it is desirable to add a correction value ΔT 0 — _S (positive value or negative value) suitable for summer or winter to the right side of the above equation (1). The summer correction value ΔT 0 — _S and the winter correction value ΔT 0 — _S may be obtained by experiments.

In the case of treating domestic wastewater, for example, the load of inflow sewage from Monday to Friday is substantially constant, and the load tends to increase on Saturday and Sunday. In order to reliably cope with such a daily load fluctuation of the sewage flowing into the reaction tank, T ₀ is changed every day,
The value of the day of T ₀ T _{0_1,} when the value of the next day T ₀ was T _{0_2,} it is preferable to obtain the ΔT using Equation (2) below instead of Equation (1). Note that the seasonal correction value ΔT _{0_S}
May be added to the right side of the following equation (2). Thereby, a more stable intermittent aeration method can be performed.

[0014]

(Equation 5)

In the intermittent aeration method according to the first aspect, one day is set as the reference processing cycle. On the other hand, in the intermittent aeration method according to the second embodiment of the present invention described below, N times (where N ≧ 2) of the intermittent aeration cycle is set as the reference processing cycle.

In other words, the intermittent aeration method according to the second aspect of the present invention for achieving the first object has a step of aerating the inside of the reaction tank while continuously supplying sewage to the reaction tank. And the anaerobic step is alternately switched, and in the aerobic step, the amount of air supplied to the reaction tank is controlled based on the measurement result of the dissolved oxygen concentration in the reaction tank, whereby the dissolved oxygen concentration in the reaction tank is adjusted to a predetermined value. This is an intermittent aeration method for treating sewage by keeping the value at a value, and the N of an intermittent aeration cycle including an aerobic process and an anaerobic process.
The total time T _N of the time during which the dissolved oxygen concentration in the reaction tank should be maintained at the predetermined value in the number of times (where N ≧ 2) is obtained in advance, and the intermittent time i (where 1 ≦ i ≦ N) is intermittently determined. in aeration cycle, when the time at which the dissolved oxygen concentration in the reaction vessel held on the predetermined value set to T _i, (i) if the difference ΔT obtained based on equation (3) below is a positive value The amount of oxygen supplied from the start of the aerobic process in this intermittent aeration cycle until the dissolved oxygen concentration in the reaction tank reaches the predetermined value is calculated from the start of the aerobic process N times ago to the last time the dissolved oxygen in the reaction tank. If the oxygen concentration is higher than the average value of the supplied oxygen amount until the oxygen concentration reaches the predetermined value, and (b) the difference ΔT is a negative value, the dissolution of the reaction tank from the start of the aerobic process in the current intermittent aeration cycle is started. The amount of supplied oxygen until the oxygen concentration reaches the predetermined value is determined by starting the aerobic process from N times before to the previous time. Dissolved oxygen concentration of al the reactor is lower than the average value of the supply amount of oxygen until the said predetermined value,
(C) When the difference ΔT is substantially zero, the supply oxygen amount from the start of the aerobic step in the current intermittent aeration cycle until the dissolved oxygen concentration in the reaction tank reaches the predetermined value is calculated from N times before to the previous time. It is characterized in that the average value of the supplied oxygen amount from the start of the aerobic process until the dissolved oxygen concentration in the reaction tank reaches the predetermined value is the same.

[0017]

(Equation 6)

The value of N may be 2 or more, preferably 3 or more and 6 or less. However, the value of N is not limited to this value, and may be appropriately determined depending on the load of the wastewater and the intermittent aeration device.

In the intermittent aeration method of the present invention, the inside of the reaction tank is alternately switched between an aerobic step and an anaerobic step while continuously supplying sewage into the reaction tank. In the aerobic step, air is supplied to the sewage while stirring the sewage in the reaction tank to oxidize organic substances and oxidize (nitrify) ammonia nitrogen to nitrate nitrogen by the action of nitrifying bacteria. The anaerobic step is executed following the end of the aerobic step. In this anaerobic step, the supply of air to the sewage is stopped while the sewage in the reaction tank is continuously stirred. In addition, in the anaerobic process, the stirring of the sewage may be stopped. In the anaerobic process, nitrate nitrogen is reduced to nitrogen gas by the action of denitrifying bacteria, and nitrogen is removed from wastewater. The number M of intermittent aeration cycles each consisting of an aerobic step and an anaerobic step is usually several to several tens of times a day.

In the intermittent aeration method of the present invention, the DO concentration in the reaction tank may be measured with a dissolved oxygen concentration meter (DO meter). The amount of air supplied to the reaction tank is controlled by, for example, calculating the measurement result of the DO meter using a computer composed of a computer, and controlling the frequency of the inverter based on the calculation result. For controlling the amount of air supplied to the wastewater. However, it is not limited to such a method. As a result, the DO concentration in the reaction tank is increased to a predetermined value (D
O ₀ ). Here, D in the reaction tank
O concentration is 0.9 to 1.1 times a predetermined value (DO ₀ ).
In the case where the DO concentration is within the range of 0.95 times to 1.05 times, the DO concentration in the reaction tank is assumed to be maintained at a predetermined value (DO ₀ ). When the DO concentration in the reaction tank is not maintained at a predetermined value (DO ₀ ), the value of the DO concentration in the reaction tank is increasing. Therefore,
In addition to wasting the operation energy of the blower, as shown in FIG. 7, the time of the anaerobic step is shortened, so that it is necessary to extend the intermittent aeration cycle. In FIG. 7,
The change in the DO concentration indicated by the dotted line is a change when the DO concentration in the reaction tank is maintained at a predetermined value (DO ₀ ). In the intermittent aeration method of the present invention, in the aerobic step, the amount of air supplied to the reaction tank is controlled based on the measurement result of the DO concentration in the reaction tank, so that the DO concentration in the reaction tank is set to a predetermined value ( DO ₀ ), it is possible to prevent over-aeration and reduce energy consumption, and to stabilize the time of the anaerobic step as described later.

The predetermined value (DO ₀ ) of the DO concentration is an empirical value or an experimental value in consideration of the water temperature of the sewage, and is a value that can surely confirm the completion of nitrification of the sewage as described later. Generally, the predetermined value (DO ₀ ) is reduced in summer and increased in winter. The predetermined value of DO concentration in summer (DO
₀ ), and 2 mg / liter as a predetermined value (DO ₀ ) of the DO concentration in winter.

The daily total time T ₀ of the time during which the DO concentration in the reaction tank in the aerobic step should be maintained at a predetermined value (DO ₀ ) is as follows:
It can be determined in advance by the following operation and experiment based on the nitrification reaction rate of activated sludge and the like. In the following, regarding the intermittent aeration method according to the second aspect of the present invention, “1 day” or the like in the following description may be appropriately replaced with “N times” or the like. The intermittent aeration method according to the above is mainly described.

In the reaction of activated sludge, ammonia nitrogen is oxidized (nitrified) to nitrate nitrogen by the action of nitrifying bacteria following decomposition of organic matter. Hereinafter, these reactions are collectively referred to as a total reaction of activated sludge. The time per day required for the whole reaction of the activated sludge corresponds to the sum of the decomposition time of the organic matter and the nitrification time. Here, variables are defined as shown in Table 1 below.

[0024]

[Table 1] B ₀ ... BOD total amount (kg / day) = inflow BO
D amount (kg / m ³ ) × inflow sewage amount (m ³ / day) N ₀ ... Total nitrogen amount (kg / day) = inflow total nitrogen amount (kg)
/ M ³ ) × Inflow sewage volume (m ³ / day) K _b ··· BOD decomposition rate (kgBOD / kgMLSS)
· Hr) K _n ··· nitrification rate (kgN / kgMLSS · hr) M L ··· sludge amount in the reactor (kg) = Sludge Concentration (kg
/ M ³ ) × reactor capacity (m ³ ) D _b ··· BOD decomposition time (hr / day) D _n ··· Nitrification time (hr / day)

The BOD decomposition rate (K _b ) is represented by the following equation (4).

[0026]

Equation 7] _{K b = Bo / (M L} × D b) (4)

Therefore, the BOD decomposition time (D _b ) is obtained by modifying the equation (4), further obtaining the BOD decomposition rate (K _b ) by experiment, and calculating the total BOD amount (B ₀ ) and the sludge in the reaction tank. by setting the amount of (M _L) as appropriate, can be obtained from the following equation (5).

[0028]

Equation 8] _{D b = Bo / (M L} × K b) (5)

The nitrification rate (K _n ) is represented by the following equation (6).

[0030]

Equation 9] _{K n = No / (M L} × D n) Equation (6)

Therefore, the nitrification time (D _n ) is obtained by modifying the equation (6), further obtaining the nitrification rate (K _n ) by experiments, and calculating the total amount of nitrogen (N ₀ ) and the amount of sludge (M By appropriately setting _L ), it can be obtained from the following equation (7).

[0032]

Equation 10] _{D n = No / (M L} × K n) Equation (7)

Generally, when denitrification, the amount of nitrogen is 3
Twice the amount of incoming organic matter is consumed. Therefore, considering such a relationship, equation (5) can be modified as follows.

[0034]

Equation 11] _{D b = (Bo-3 ×} No) / (M L × K b) (8)

Accordingly, the time D _TOTAL (hours / day) required for the total reaction per day is the sum of the equations (8) and (7).

[0036]

[Mathematical formula-see original document] D_TOTAL= D_b+ D_n  =(Bo-3 × No)/ (M_L× K_b) +No/ (M_L× K_nEquation (9)

In the intermittent aeration method of the present invention, the formula (9)
Time required for total reaction per day (D
_TOTAL ) to each aerobic step. That is, assuming that the number of intermittent aeration cycles each consisting of an aerobic step and an anaerobic step is M per day, the reaction period D _M in one aerobic step is given by D _M = D _TOTAL / M Equation (10) .

[0038] In the intermittent aeration process according to the second aspect of the present invention, setting the number of daily intermittent aeration cycle, dividing the time required for the entire reaction in such intermittent aeration cycle number (D _{TOTA L)} Thus, the reaction period D in one aerobic step can be obtained.

This reaction period (D _M ) in each aerobic step
Inside, the DO concentration in the reaction tank becomes a low value because dissolved oxygen is consumed in the reaction of the activated sludge (see FIG. 1). When the entire reaction of the activated sludge is completed, the amount of oxygen consumed decreases. As a result, the DO concentration in the reaction tank rises sharply.

The above discussion on the reaction period (D _M )
BOD per day or per unit time
The discussion has been made assuming that the total amount and the total amount of nitrogen are constant. Actually, loads such as the amount of inflow of sewage, the amount of inflow BOD, and the amount of total nitrogen inflow are accompanied. Therefore, the actual reaction period varies.

When the reaction period (D _M ) is fixed, when the load of the inflowing sewage becomes excessive, the entire reaction of the activated sludge is not completed within the reaction period (D _M ). In such a case, the DO concentration in the reaction vessel remains low and cannot be distinguished from the case where the reaction is completed. Therefore, in the prior art or the present invention, an auxiliary period is provided following the reaction period (D _M ), and air is continuously supplied to the wastewater in the reaction tank during the auxiliary period. And
The total of the reaction period (D _M ) and the auxiliary period is defined as the period (hour) of the aerobic step, and the period (hour) of the aerobic step is fixed. By providing such an auxiliary period,
It can be detected whether or not all the reactions of the activated sludge have been completed. That is, since the consumed oxygen amount decreases after the entire reaction of the activated sludge is completed, the DO concentration in the reaction tank rapidly increases. Therefore, if an increase in the DO concentration in the reaction tank is observed within the auxiliary period, it means that the entire reaction of the activated sludge has been completed. Usually, the aerobic process time, which is the sum of the reaction period (D _M ) and the auxiliary period, is 40 to 60 minutes, the reaction period (D _M ) is 10 to 20 minutes, and the auxiliary period is 20 minutes. To 50 minutes. During the auxiliary period, the time for controlling the DO concentration in the reaction tank to DO ₀ is 10 to 4 times.
Preferably, it is 0 minutes. Since the period (time) of the aerobic process is constant, the auxiliary period becomes shorter if the reaction period ( _DM ) becomes longer due to the load fluctuation of the inflow sewage, and the auxiliary period becomes longer if the reaction period ( _DM ) becomes shorter. Become. That is, the time of the auxiliary period varies depending on the load of the inflow sewage.

The load of the incoming sewage is determined by the total BOD (B ₀ ),
Total amount of nitrogen (N _0), BOD decomposition rate (K _b), nitrification rate (K _n), the amount of sludge in the reactor (M _L) and the like of the set value (these a load setting of the inflow wastewater, less FIG. 1 schematically shows a change in the DO concentration in the intermittent aeration cycle when the DO concentration is substantially equal to the load setting value. FIG. 2A schematically shows a change in the DO concentration in the intermittent aeration cycle when the load of the inflow sewage is larger than the load set value, and the intermittent aeration cycle when the load of the inflow sewage is extremely larger than the load set value. FIG. 2B schematically shows the change in the DO concentration at the time. The reaction period in the case shown in FIG. 2A is longer than the reaction period in the case shown in FIG. However, since the period (time) of the aerobic step is constant, the time T _i during which the DO concentration in the reaction tank is maintained at a predetermined value (DO ₀ ) becomes shorter. The reaction period in the case shown in FIG. 2B is longer than the reaction period in the case shown in FIG. However, the period (time) of the aerobic process is because it is constant, the time T _i of DO concentration is maintained at a predetermined value (DO ₀₎ in a reaction vessel is "0". On the other hand, FIG. 3 schematically shows a change in the DO concentration in the intermittent aeration cycle when the load of the inflow sewage is smaller than the load set value. The reaction period in the case shown in FIG. 3 is shorter than the reaction period in the case shown in FIG. 1, but since the period (time) of the aerobic step is constant, the DO concentration in the reaction tank is a predetermined value ( DO ₀ )
Hold time T _i becomes longer. 2 and 3, the broken line indicates a change in the DO concentration (see FIG. 1) in the intermittent aeration cycle when the load of the inflow sewage is substantially equal to the load set value.

A standard value AIR _STD of the supplied oxygen amount from the start of the aerobic step in the intermittent aeration cycle until the dissolved oxygen concentration in the reaction tank reaches a predetermined value (DO ₀ ) is determined in advance by a test. . Then, the set value of the reaction period _DM and the auxiliary period in one aerobic step obtained from the equation (10), the predetermined value of the dissolved oxygen concentration (DO ₀ ), and the standard value of the supplied oxygen amount AIR _STD Repeat the test based on
The time t ₀ during which the concentration of dissolved oxygen in the reaction tank in one aerobic step is maintained at a predetermined value (DO ₀ ) is determined. Then, if this time t ₀ is multiplied by M, the dissolved oxygen concentration in the reaction tank in the aerobic step should be kept at the predetermined value by one.
The total T _{0 of the} days is obtained.

Usually, the time of the anaerobic step is 60 to 80 minutes. In the anaerobic step, a certain period of time is required until the DO concentration in the reaction tank increased in the aerobic step becomes 0 mg / liter. Since the removal of nitrogen from the sewage starts after the DO concentration becomes 0 mg / liter, it is preferable that the DO concentration in the reaction tank be 0 mg / liter in as short a time as possible. In the intermittent aeration method of the present invention,
In the aerobic step, the DO concentration in the reaction tank is adjusted to a predetermined value (D
O ₀ ), the DO concentration in the reaction vessel is 0 mg /
The liter time is generally constant. In the anaerobic step, this state is maintained for 20 to 60 minutes after the DO concentration in the reaction tank has become 0 mg / liter. In the anaerobic step, the sewage in the reaction tank may or may not be stirred. Alternatively, the sewage in the reaction tank may be stirred only immediately before the end of each anaerobic step.

In the intermittent aeration method of the present invention, the dissolved oxygen concentration in the reaction tank in the aerobic step (more specifically, during this auxiliary period) is set to one of the times to be maintained at a predetermined value (DO ₀ ). The total T ₀ of the days is obtained in advance as described above. Alternatively, the total T _N of the time during which the dissolved oxygen concentration in the reaction tank should be maintained at a predetermined value in N times (where N ≧ 2) of the intermittent aeration cycle including the aerobic step and the anaerobic step is obtained in advance. .

Then, the i-th time of the day (provided that 1 ≦ i ≦
In intermittent aeration cycle M), DO concentration in the reactor is determined time T _i which is held at a predetermined value (DO _0). This time T _i can be determined as the time from when the value of the DO meter provided in the reaction tank reaches a predetermined value (DO ₀ ) until the end of the aerobic step. The time of the aerobic step is constant. Then, the difference ΔT is obtained from Expression (1). still,
The total time T _i may be easily performed by using an arithmetic unit such as a sequencer or computer.

When the difference ΔT obtained based on the equation (1) is a positive value, the total time of T _i is shorter than T ₀ . That is, the load of the inflow sewage day is higher than the load set value, because although the total reaction period of the day is greater than D _TOTAL, the total time T _i in assistance time period is shorter than T _0. Therefore, it is expected that the load of incoming sewage on the next day will be higher than the load setpoint. Therefore, the amount of supplied oxygen (AIR ₂ ) from the start of the aerobic step in each intermittent aeration cycle on the next day until the DO concentration in the reaction tank reaches a predetermined value (DO ₀ )
The increase than DO concentration predetermined value of the reaction vessel from the beginning of the day of aerobic step (DO ₀₎ to become up to supply the amount of oxygen (AIR _1). Specifically, for example, based on the value of the difference ΔT, an arithmetic device such as a computer is used to determine the frequency of the inverter required to supply the supplied oxygen amount (AIR ₂ ), and to control the frequency. The amount of air discharged from the blower and supplied to the wastewater in the reaction tank may be controlled. Note that the operating frequency of the inverter is, for example,
Set in advance several levels within the range of 30-100%,
What is necessary is just to comprise so that a predetermined frequency may be selected by the instruction from an arithmetic unit. By performing such an operation,
The oxygen supply amount in the reaction period (D _M ) in each aerobic step on the next day increases, and the reaction period (D _M ) in each aerobic step on the next day can be made shorter than that day. That is,
It is possible to reliably cope with an increase in the load of inflow sewage on the next day.

When the difference ΔT obtained based on the equation (1) is a negative value, the total time of T _i is longer than T ₀ . That is, the load of the inflow sewage day is lower than the load set value, because although the total reaction period of the day is below D _TOTAL, the total time T _i in assistance time period is longer than T _0. Therefore, it is expected that the load of incoming sewage on the next day will be lower than the load set value. Therefore, the supply oxygen amount (AI) from the start of the aerobic step in each intermittent aeration cycle on the next day until the DO concentration of the reaction tank reaches a predetermined value (DO ₀ ).
R ₂ ) is the amount of supplied oxygen (AIR ₁ ) from the start of the aerobic step on the day until the DO concentration in the reaction tank reaches a predetermined value (DO ₀ )
Than to reduce. By performing such an operation, the oxygen supply amount in the reaction period (D _M ) in each aerobic step on the next day is reduced, and the reaction period (D _M ) in each aerobic step on the next day is made longer than that day. be able to. That is, it is possible to reliably cope with a decrease in the load of sewage and to suppress unnecessary energy consumption.

When the difference ΔT is substantially zero, the load of the inflow sewage on that day is substantially equal to the load set value. Therefore, it is expected that the load of incoming sewage on the next day will be approximately equal to the load set point. Therefore, the supply oxygen amount (AIR ₂ ) from the start of the aerobic step in each intermittent aeration cycle on the next day until the DO concentration in the reaction tank reaches a predetermined value (DO ₀ ) is determined by the reaction from the start of the aerobic step on the day. When the DO concentration in the tank reaches a predetermined value (DO
₀ ) may be the same as the supplied oxygen amount (AIR ₁ ).

The difference ΔT and the AIR of the supplied oxygen amount (AIR ₂ ) from the start of the aerobic step in each intermittent aeration cycle on the following day until the DO concentration in the reaction tank reaches a predetermined value (DO ₀ )
The relationship between ₁ and the increase / decrease amount may be obtained in advance by experiments or tests. The difference ΔT is substantially zero when | Δ
It is defined that the value of T / T ₀ | is within 0.1. Note that the value of | ΔT / T ₀ | may be appropriately determined by experiments or the like depending on conditions of the intermittent aeration apparatus, inflow sewage, and the like.

In the intermittent aeration according to the second aspect of the present invention, the same operation as described above may be performed.

In the present invention, since such an operation is performed, the intermittent aeration method corresponding to the load fluctuation of the inflow sewage can be easily performed, and the sewage treatment performance is further stabilized.

As described above, activated sludge absorbs phosphorus when the oxidation-reduction potential (ORP) value is positive under aerobic conditions, and discharges phosphorus when the ORP value is negative under anaerobic conditions. Generally, when performing continuous aeration, O
The RP value is positive. Therefore, phosphorus can be desorbed by absorbing phosphorus under aerobic conditions and removing activated sludge that has absorbed a large amount of phosphorus as excess sludge from the treatment system.
In other words, in the intermittent aeration method, the ORP value tends to be negative in the anaerobic step, and phosphorus may be released into the treated sewage. Further, if the treated sewage is placed in an anaerobic state, it becomes difficult to remove phosphorus even if a coagulant is added to the treated sewage for dephosphorization. In the intermittent aeration method according to the first or second aspect of the present invention for achieving the above second object, a continuous aeration tank is provided downstream of the reaction tank, and the treated sewage treated in the reaction tank is removed. A continuous aeration treatment is performed in the continuous aeration tank. Thereby, the continuous aeration tank is brought into the aerobic state, and the removal of phosphorus from the treated sewage can be surely performed. The residence time of the treated sewage in the continuous aeration tank is 30
Minutes to 60 minutes. When removing phosphorus at a high rate, a coagulant such as PAC (polyaluminum chloride) or ferric chloride may be added to the treated wastewater in the continuous aeration tank.

In the intermittent aeration method according to the first or second aspect of the present invention, the sewage in the reaction tank may or may not be stirred in each anaerobic step. Alternatively,
The sewage in the reaction tank may be stirred just before the end of each anaerobic step. In this case, it is preferable to stir the sewage in the reaction tank for a period (hour) of 10% to 20% of the period (hour) of the anaerobic step immediately before the end of the anaerobic step. Thereby, a reduction in energy consumption in the anaerobic step can be achieved.

[0055]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on embodiments with reference to the drawings.

(Example 1 and Comparative Example 1) FIG. 4 is a conceptual diagram of an intermittent aeration apparatus suitable for carrying out the intermittent aeration method of the present invention. The intermittent aeration apparatus includes a reaction tank 10, a DO meter 11 for measuring the DO concentration of sewage in the reaction tank 10, an arithmetic unit 12, an inverter 13, a blower 14 including a roots blower, and an air diffuser. 15 and an underwater stirrer 16. The diffuser and the underwater stirrer may have an integral structure. The arithmetic unit 12 is configured by a computer, calculates the measurement result by the DO meter 11, and controls the frequency of the inverter 13. Thereby, it is possible to control the amount of air discharged from the blower 14 and supplied to the wastewater in the reaction tank through the air diffuser 15,
The DO concentration in the reaction tank 10 can be kept at a predetermined value (DO ₀ ). In addition, in the i-th intermittent aeration cycle of the day (where 1 ≦ i ≦ M),
DO concentration in the reactor to calculate the sum of the predetermined value (DO ₀₎ to be held time T _i. It should be noted that the time T _i is determined by the value of the DO meter 11 provided in the reaction tank 10 being a predetermined value (D
The time from when O ₀ ) is reached until the aerobic step ends can be determined by the arithmetic unit 12.

The treated sewage treated in the reaction tank 10 flows into the precipitation tank 20 via a pipe. The treated wastewater is solid-liquid separated in the settling tank 20, a part of the sludge is returned to the reaction tank 10 by the sludge pump 21, and the remaining sludge is discharged out of the system. On the other hand, the supernatant is discharged from the upper part of the settling tank 20 as treated water.

Using this intermittent aeration apparatus, the first
A test of the intermittent aeration method according to the embodiment was performed. Example 1
In, when the value of | ΔT / T ₀ | exceeded 0.1, the value of the difference ΔT was evaluated. Also, (2-ΔT / T ₀ )
Was made equal to the value of (AIR ₂ / AIR ₁ ). Note that M
= 12, T ₀ = 240 minutes.

As Comparative Example 1, a test was conducted by a conventional intermittent aeration method in which the inside of the reaction tank was alternately switched between an aerobic step and an anaerobic step while continuously supplying sewage into the reaction tank. In Comparative Example 1, in the aerobic step, the amount of air supplied to the reaction tank was not controlled based on the measurement result of the dissolved oxygen concentration in the reaction tank. Therefore, the operation of obtaining the difference ΔT from the sum of T ₀ and T _i is not performed in Comparative Example 1. The test conditions and test results are shown in Table 2 below.
Shown in

[0060]

Table 1 Example 1 Comparative Example 1 Test Conditions Aerobic Step (min) 40 40 Anaerobic Step (min) 80 80 DO ₀ (mg / liter) 2-Water Temperature (C) 17-19 18-24 Inflowing Sewage ^{BOD (g / m 3) 86~100} 100~133 T-N (g / m 3) 30~ 43 35~ 43 test results treated water ^{BOD (g / m 3) 6.4} 16.3 BOD removal rate ( %) 93.1 85.3 TN (g / m ³ ) in treated water 6.5 7.7 TN removal rate (%) 79.3 74.8

As is clear from Table 2, in Example 1, the BOD removal rate and the TN removal rate were significantly improved as compared with Comparative Example 1.

Example 2, Example 3, and Comparative Example 2 In Example 2, the intermittent aeration apparatus shown in FIG. 5 was used. The intermittent aeration apparatus according to the second embodiment includes a continuous aeration tank 30 downstream of the reaction tank 10. The reactor 10 and the devices attached thereto are the same as in the first embodiment. The continuous aeration tank 30 is provided with an oxidation-reduction potentiometer (ORP meter) 31, a blower 34, and a diffuser 35. In the second embodiment, the treated sewage treated in the reaction tank 10 by the intermittent aeration method described in the first embodiment is continuously aerated in the continuous aeration tank 30. The retention time of the treated sewage in the continuous aeration tank 30 is 30
〜60 minutes. The treated sewage flowing out of the continuous aeration tank 30 flows into the precipitation tank 20 via a pipe as in the first embodiment. The treated wastewater is solid-liquid separated in the settling tank 20, a part of the sludge is returned to the reaction tank 10 by the sludge pump 21, and the remaining sludge is discharged out of the system. On the other hand, the supernatant is discharged from the upper part of the settling tank 20 as treated water.

Using this intermittent aeration apparatus, the first aspect of the present invention
A test of the intermittent aeration method according to the embodiment was performed. Example 2
In, when the value of | ΔT / T ₀ | exceeded 0.1, the value of the difference ΔT was evaluated. Also, (2-ΔT / T ₀ )
Was made equal to the value of (AIR ₂ / AIR ₁ ). Note that M
= 12, T ₀ = 240 minutes.

As Comparative Example 2, a test was conducted by a conventional intermittent aeration method in which the inside of the reaction tank was alternately switched between an aerobic step and an anaerobic step while continuously supplying sewage into the reaction tank. In Comparative Example 2, in the aerobic step, the amount of air supplied to the reaction tank was not controlled based on the measurement result of the dissolved oxygen concentration in the reaction tank. Therefore, the operation of obtaining the difference ΔT from the sum of T ₀ and T _i is not performed in Comparative Example 2. In addition, as Example 3, the same intermittent aeration method as in Example 1 was performed. Here, the difference between Example 3 and Example 1 is that in Example 3, PA was used as a flocculant.
C is added. The amount of PAC added in Examples 2 and ^{3 was} 100 g per 1 m ^{3 of} sewage, assuming that PO ₄ -P = 5 g / m ³ . The test conditions and test results are shown in Table 3 below.

[0065]

Table 2 Example 2 Example 3 Comparative Example 2 Test conditions Aerobic process (min) 40 40 40 Anaerobic process (min) 80 80 80 DO ₀ (mg / liter) 2 2-Water temperature (° C) 18 18 18 continuous aeration no no PAC added added no additive inflow wastewater BOD (g / m ³⁾ 140 Same as at left Same as at left ^{T-N (g / m 3} ) 34.7 Same as at left Same as at left ^{T-P (g / m 3} ) 3.7 No change Same as on the left Test result BOD in treated water (g / m ³ ) 5.6 6.3 14.7 BOD removal rate (%) 96.0 95.5 89.5 TN (g / m ³ ) 6 in treated water 5.5 7.1 9.6 TN removal rate (%) 81.3 79.5 72.3 TP (g / m ³ ) in treated water 0.2 1.3 2.9 TP removal Rate (%) 94.6 64.9 21.6

From Table 3, it can be seen that in Example 2, phosphorus was significantly removed.

Example 4 In Example 4, in the intermittent aeration method according to the first aspect of the present invention, the sewage in the reaction tank was not stirred in each anaerobic step. FIG. 6 shows a conceptual diagram of an intermittent aeration apparatus suitable for implementing the fourth embodiment.

The sludge in the reaction tank 10 quickly takes in the necessary nutrients into the cells. Therefore, when viewed microscopically, the water surrounding the sludge has the same water quality as the treated wastewater. Therefore, if the reaction tank 10 has a structure in which the sewage flowing into the reaction tank 10 is short-circuited and does not flow out to the sedimentation tank 20, even if sludge is settled in the reaction tank 10 in the anaerobic step, the quality of the treated sewage is reduced. Has almost no effect. Therefore, in the anaerobic process, even if the sewage in the reaction tank 10 is not agitated, the quality of the treated sewage is substantially the same as when the sewage in the reaction tank 10 is agitated. In addition, since it is not necessary to stir the sewage in the reaction tank 10, energy consumption can be reduced. As shown in FIG. 6, in the intermittent aeration apparatus according to the fourth embodiment, in order to prevent the sewage flowing into the reaction tank 10 from short-circuiting and flowing out to the sedimentation tank 20, the inflowing sewage is supplied to the reaction tank in the sludge zone. The structure is such that it flows into the fuel cell 10. Actually, in the anaerobic process, a test was performed for the case where the sewage in the reaction tank 10 was not stirred and the case where the sewage was stirred.
There was no significant difference in the quality of the treated sewage.

The degree of energy saving that can be achieved is evaluated below. Sewage for 2,000 people (540m ³
/ Day) is considered. The power consumption of the blower 14 and the underwater stirrer 16 is set to 22 kW and 11 kW.
In addition, the number of times M of intermittent aeration cycle per day is set to 12, the time of the aerobic step is 40 minutes, and the time of the anaerobic step is 80 minutes.

The daily power consumption when the underwater stirrer 16 is operated in the aerobic process and the anaerobic process is as follows. (40 + 80) / 60 × 12 (cycle) × 11 (kW
Hour) = 264 kW / day

On the other hand, only in the aerobic process, the underwater stirrer 1
The daily power consumption at the time of operating No. 6 is as follows. 40/60 × 12 (cycle) × 11 (at kW) = 88
kW / day

Therefore, in this case, the energy can be reduced by 176 kW / day.

Example 5 In Example 5, a test of the intermittent aeration method according to the second embodiment of the present invention was performed using the intermittent aeration apparatus shown in FIG. In the fifth embodiment, when the value of | ΔT / T ₀ | exceeds 0.1, the difference Δ
The value of T was evaluated. The value of (2-ΔT / T ₀ ) was made equal to the value of (AIR ₂ / AIR ₁ ). Note that N = 4,
T ₀ = 20 minutes × 4 cycles = 80 minutes. As a result of the test, in the aerobic process, the BOD in Example 5 was lower than that in the conventional intermittent aeration method in which the amount of air supplied to the reaction tank was not controlled based on the measurement result of the dissolved oxygen concentration in the reaction tank. The removal rate and the TN removal rate were greatly improved.

Although the present invention has been described based on the preferred embodiments, the present invention is not limited to these embodiments.
The conditions of the intermittent aeration apparatus and the intermittent aeration method shown in the examples are merely examples, and can be changed as appropriate.

[0075]

According to the intermittent aeration method of the present invention, it is possible to reliably follow the load fluctuation of the sewage flowing into the reaction tank, and to perform the sewage treatment by the stable intermittent aeration. In addition, it is possible to reduce energy consumption due to intermittent aeration, and to prevent overaeration that may lead to dismantling of sludge and deterioration of water quality due to the demolition. Further, by providing a continuous aeration tank downstream of the reaction tank, phosphorus can be effectively removed from wastewater.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a change in DO concentration in a reaction tank in an intermittent aeration cycle when a load of inflow sewage is substantially equal to a load set value in an intermittent aeration method of the present invention.

FIG. 2 is a diagram schematically showing a change in DO concentration in a reaction tank in an intermittent aeration cycle when the load of inflow sewage is larger than a load set value in the intermittent aeration method of the present invention.

FIG. 3 is a diagram schematically showing a change in DO concentration in a reaction tank in an intermittent aeration cycle when the load of inflow sewage is smaller than a load set value in the intermittent aeration method of the present invention.

FIG. 4 is a conceptual diagram of an intermittent aeration apparatus suitable for performing an intermittent aeration method of the present invention.

FIG. 5 is a conceptual diagram of an intermittent aeration apparatus having a continuous aeration tank suitable for performing the intermittent aeration method of the present invention.

FIG. 6 is a conceptual diagram of another type of intermittent aeration apparatus suitable for performing the intermittent aeration method of the present invention.

FIG. 7 is a diagram schematically showing a change in the DO concentration in the reaction tank when the DO concentration in the reaction tank is not maintained at a predetermined value.

[Explanation of symbols]

 Reference Signs List 10 reaction tank 11 dissolved oxygen concentration meter (DO meter) 12 arithmetic unit 13 inverter 14,34 blower 15,35 air diffuser 16 underwater stirrer 20 sedimentation tank 21 sludge pump 30 continuous aeration tank 31 oxidation-reduction potentiometer (ORP meter)

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-50093 (JP, A) JP-A-5-237495 (JP, A) JP-A-5-237496 (JP, A) 7720 (JP, B2) (58) Field surveyed (Int. Cl. ⁶ , DB name) C02F 3/34 C02F 3/30 C02F 3/12

Claims (6)

(57) [Claims] The present invention is characterized in that while continuously supplying sewage into a reaction tank, the inside of the reaction tank is alternately switched between an aerobic step and an anaerobic step, and in the aerobic step, a measurement result of a dissolved oxygen concentration in the reaction tank is obtained. An intermittent aeration method for treating sewage by controlling the amount of air supplied to the reaction tank based on the control of the dissolved oxygen concentration in the reaction tank at a predetermined value. The total T ₀ of the day during which the dissolved oxygen concentration should be maintained at the predetermined value is determined in advance, and the number of times of the intermittent aeration cycle including the aerobic process and the anaerobic process is defined as M, times th (where, 1 ≦ i ≦ M) in the intermittent aeration cycle, the time at which the dissolved oxygen concentration in the reaction vessel held on the predetermined value when the T _i, in (a) the following formula (1) When the difference ΔT obtained based on the above is a positive value, the difference in the The amount of oxygen supplied from the start of the aeration step until the dissolved oxygen concentration in the reaction tank reaches the predetermined value, and the amount of oxygen supplied from the start of the aerobic step on the day until the dissolved oxygen concentration in the reaction tank reaches the predetermined value. (B) When the difference ΔT is a negative value, the supply oxygen amount from the start of the aerobic step in each intermittent aeration cycle on the following day until the dissolved oxygen concentration in the reaction tank reaches the predetermined value is calculated. And reducing the amount of oxygen supplied from the start of the aerobic step on the day until the dissolved oxygen concentration in the reaction tank reaches the predetermined value. (C) When the difference ΔT is substantially zero, The supply of oxygen from the start of the aerobic step to the time when the dissolved oxygen concentration in the reaction tank reaches the predetermined value, and the supply of oxygen from the start of the aerobic step on the day until the dissolved oxygen concentration in the reaction tank reaches the predetermined value. An intermittent aeration method characterized by the same amount of oxygen. (Equation 1) 2. The seasonal correction value ΔT 0 — _S is _calculated by the above equation (1).
The intermittent aeration method according to claim 1, wherein the intermittent aeration method is added to the right side. 3. changed every day of the week the T _0, T _{0_1} value on the day of T _0, when the value of the next day T ₀ was T _{0_2,} the formula the following formula (2 instead of (1) The intermittent aeration method according to claim 1, wherein the ΔT is obtained by using the above method. (Equation 2) 4. The seasonal correction value ΔT _{0_S} is _calculated by the above equation (2).
4. The intermittent aeration method according to claim 3, wherein the intermittent aeration method is added to the right side of. 5. The reaction tank is alternately switched between an aerobic step and an anaerobic step while continuously supplying sewage into the reaction tank. In the aerobic step, the measurement result of the dissolved oxygen concentration in the reaction tank is obtained. An intermittent aeration method for treating sewage by controlling the amount of air supplied to the reaction tank based on the control of the concentration of dissolved oxygen in the reaction tank at a predetermined value, comprising an aerobic step and an anaerobic step. The total time T _N of the time during which the dissolved oxygen concentration in the reaction tank should be maintained at the predetermined value in N times of the intermittent aeration cycle (where N ≧ 2) is obtained in advance, i times before (where 1 ≦ i) ≦ N) In the intermittent aeration cycle, assuming that the time during which the dissolved oxygen concentration in the reaction tank is maintained at the predetermined value is T _i , the difference ΔT obtained based on the following equation (3) is In the case of a positive value, the reaction tank starts from the start of the aerobic step in the current intermittent aeration cycle. The supplied oxygen amount until the dissolved oxygen concentration reaches the predetermined value is calculated as the average of the supplied oxygen amount from the start of the aerobic process from N times before to the previous time until the dissolved oxygen concentration in the reaction tank reaches the predetermined value. (B) If the difference ΔT is a negative value, the supply oxygen amount from the start of the aerobic step in the current intermittent aeration cycle to the time when the dissolved oxygen concentration in the reaction tank reaches the predetermined value is When the dissolved oxygen concentration in the reaction tank from the start of the aerobic process N times before to the previous time until the dissolved oxygen concentration in the reaction tank reaches the predetermined value is lower than the average value, (c) When the difference ΔT is substantially zero, The amount of oxygen supplied from the start of the aerobic step in the current intermittent aeration cycle to the time when the dissolved oxygen concentration in the reaction tank reaches the predetermined value is calculated from the start of the aerobic step from the previous N times to the previous time. Intermittently providing an average value of the supplied oxygen amount until the concentration reaches the predetermined value. Care method. (Equation 3) 6. A process according to claim 1, further comprising a continuous aeration tank downstream of said reaction tank, wherein the treated sewage treated in said reaction tank is continuously aerated in said continuous aeration tank. 5
The intermittent aeration method according to any one of the above.