JPH0579400B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a device for controlling the amount of air supplied to an aeration tank when organic wastewater such as sewage is treated by an activated sludge method.

<Conventional Technology> In sewage treatment plants and the like that treat organic wastewater using the activated sludge method, the aeration tank blower consumes the largest amount of electricity, which is said to account for approximately 40% of the total electricity consumption of the entire treatment plant. Therefore, when considering energy savings for the entire treatment plant, it is most effective to reduce the amount of electricity used by the blower. It is. As an example, as shown in "Energy Saving Aeration Handbook, Published by Science and Technology Development Center, August 1, 1980, pp. 81-98," A so-called inflow water flow proportional control method is used, which is controlled by an on-off valve installed on the suction side of the blower, or a dissolved oxygen concentration meter (hereinafter referred to as DO) is installed in the aeration tank.
Depending on the deviation value between the target value of dissolved oxygen concentration (hereinafter referred to as DO) and the actual DO value, the on-off valve installed on the suction side of the blower is adjusted or the rotation speed of the blower is adjusted. Keeping the DO in the aeration tank constant by adjusting the
There are DO constant control methods, etc. However, the inflow water proportional control method is the most common method;
It focuses only on changes in water quantity, and does not work well against changes in water quality. In addition, the constant DO control method adjusts the amount of air supplied in response to fluctuations in water volume and water quality, but because the length of a normal aeration tank is considerably longer than its width, complete mixing is not possible, and the DO meter is not installed at the correct position. The aeration tank as a whole is subject to considerable variation due to differences in In other words, if the DO meter is installed on the inflow side, the latter stage of the aeration tank will be over-aerated, and conversely, if it is installed on the outflow side, the first stage of the aeration tank will be under-aerated.
Processing function may deteriorate.

In order to solve this problem of constant DO control, there is a so-called tapered aeration method in which the installation density of diffuser plates or diffuser pipes is lowered from the inflow side to the outflow side. However, with this tapered aeration method, it is difficult to determine the tapered ratio at the time of design, and even if the ratio is determined after sufficient preliminary research, it is extremely difficult to respond to subsequent changes in water quality itself. Have difficulty.

<Problems to be Solved by the Invention> The present invention provides a solution that can be applied to the entire aeration tank without causing insufficient aeration in the front stage of the aeration tank or overaeration in the latter stage even if the amount and quality of water flowing into the aeration tank fluctuate. The purpose of the present invention is to provide an air supply amount control device for an aeration tank that can always supply the optimum amount of air and further save energy consumption by always maintaining the air supply amount in the optimum state. It is something.

<Means for Solving the Problems> The present invention divides an aeration tank in an activated sludge method to form a plurality of aeration zones, and provides a distribution pipe with a control valve attached to each aeration zone to supply gas from a blower. An aeration tank which distributes and supplies water to each aeration zone via aeration tank, wherein a dissolved oxygen concentration meter is installed at any position in the aeration tank, and a respirometer is installed in each aeration zone in the aeration tank, The rotation speed of the blower is adjusted based on the deviation between the measured value of the dissolved oxygen concentration meter and the preset target value of the dissolved oxygen concentration meter, and the rotation speed of each corresponding aeration zone is adjusted based on the measured value of each respirometer. Calculate each required air supply amount, then calculate the opening degree of each control valve that can supply that amount based on the required air supply amount of each relevant aeration zone, and adjust the opening degree of each control valve based on the calculation result. The present invention relates to an air supply amount control device for an aeration tank, characterized in that the amount of air supplied to each aeration zone is controlled by adjusting the amount of air supplied to each aeration zone.

The present invention will be explained below based on the drawings.

FIG. 1 is a flow explanatory diagram showing an example of an embodiment of the apparatus of the present invention, in which an aeration tank 3 having an inflow pipe 1 and an outflow pipe 2 is divided into, for example, three aeration zones 4.
a, 4b, 4c, and each aeration zone 4a, 4
b, 4c each have a distribution pipe 6 with a control valve 5.
A large number of air diffuser plates (or air diffuser pipes) 7 are attached to the distribution pipe 6. Each distribution pipe 6 is connected to a blower 9 via a gas main pipe 8.
On the other hand, a DO meter 10 is provided at an arbitrary position in the aeration tank 3, and a respiration rate meter 11 is provided in each of the aeration zones 4a, 4b, and 4c. The converter 12a in the figure is the DO meter 10 or the respiration rate meter 1.
The microcomputer 13 converts the measured value signal of 1, for example, a current signal of 4 to 20 mA, into a voltage signal of 0 to 10 V.
After receiving the voltage signal from a, for example, converting the digital signal from 0 to 4095, the output value for controlling the rotation speed of the blower 9 is calculated via the converter 12b and the inverter 14, and the output value for controlling the rotation speed of the blower 9 is calculated via the converter 12b. It is used to calculate the output value of the opening degree control. The converter 12b converts the signal from the microcomputer 13, for example, a voltage signal of 0 to 10V, into a current signal of 4 to 20mA, and the inverter 14 outputs the signal from the converter 12b, a current signal of 4 to 20mA, for example. The output is converted into a frequency signal of 20 to 50 Hz, and the output value is input to the motor section of the blower 9. The device of the present invention supplies each aeration zone with the optimum amount of air that matches the respiration rate of activated sludge in each aeration zone, so all aeration zones in the aeration tank
The DO values are approximately equal, so the DO meter can be installed at any position in the aeration tank 3.

<Operation of the invention> The present invention calculates the true enzyme requirement per unit volume of each aeration zone based on the respiration rate of activated sludge, and supplies the optimum amount of air to each aeration zone. Organic wastewater such as sewage that has flowed into the aeration zone 4a of the aeration tank 3 through the inflow pipe 1 is supplied from the blower 9 through the main gas pipe 8, the distribution pipe 6, and the diffuser plate 7. Under the aeration conditions, the activated sludge in the aeration tank 3 flows down to the aeration zones 4a, 4b, and 4c in sequence while being processed by the activated sludge, flows out through the outflow pipe 2, and is separated from the activated sludge in a settling tank (not shown). After that, it is discharged outside the system as treated water. The optimal aeration conditions for the aeration tank 3 described above are established as follows.

First, the DO in the aeration tank 3 is measured by the DO meter 10, and the current signal of the measured value is converted into a voltage signal by the converter 12a and inputted to the microcomputer 13, and the input value is converted to a digital signal. preset by that digital signal.
PI is the deviation from the target value of DO (usually 1 to 2 mg/)
The rotation speed of the blower 9 is calculated by calculation (proportional integral calculation) or PID calculation (proportional integral differential calculation). Next, the digital signal of the calculated value is converted into a voltage signal and inputted to the converter 12b, where the voltage signal is output converted to a current signal, and the output is further sent to the inverter 14, where the current signal is converted to a frequency signal and the blower 9 and controls the rotation speed of the blower 9. Note that if you use a blower 9 that maintains an almost constant amount of air even if the pressure on the discharge side changes, such as a displacement type (roots type, etc.), the discharge of the blower 9 can be controlled by controlling the rotation speed of the blower 9. The amount can be effectively controlled. In addition, each respiration rate meter 11 installed in each aeration zone 4a, 4b, and 4c is used to measure the rate at regular intervals (usually 0.5 to 0.5
The current signal of the measured value is converted into a voltage signal by the converter 12a and inputted to the microcomputer 13, which converts the input value into a digital signal. Then, each corresponding aeration zone 4a, 4
Calculate the required air supply amount for b and 4c. Next, the output value of the opening degree of each control valve 5 that can supply the required amount of air is calculated from the required air supply amount, and the output calculation result is converted into a voltage signal and inputted to the converter 12b, where the voltage signal is It converts into a current signal and outputs it to each control valve 5 to adjust the opening degree of each control valve 5. The above operation is shown in the flowchart explanatory diagram of FIG. 2.

Further, calculation of the opening degree of each control valve 5 described above is performed according to the following procedure. Here, i indicates each aeration zone, and in the formulas in each procedure below, i=1 is aeration zone 4a, i=2 is aeration zone 4b, i=
3 indicates the aeration zone 4c.

[Step 1] Input the respiration rate r _i (mg/・hr) Set the respiration rate r ₁ , r ₂ , r ₃ for each aeration zone.

[Step 2] Calculate the required overall oxygen transfer capacity coefficient K _Lai (1/hr) for each aeration zone K _La1 = r ₁ / (C _s − C _p ) K _La2 = r ₂ / (C _s − C _p ) K _La3 = r ₃ / (C _s - C _p ) C _s : Saturated DO at the water temperature in the aeration zone (mg/) C _p : DO target value (mg/) Calculate K _Lai for each aeration zone using the above formula.

[Step 3] Required air supply amount Q _i (N
m ² /min) Since the relationship between the required air supply amount per diffuser plate and K _Lai is a linear function, it is expressed by the following formula.

Q ₁ /N ₁ =A・K _La1 +B Q ₂ /N ₂ =A・K _La2 +B Q ₃ /N ₃ =A・K _La3 +B A, B: Diffusion plate installation water depth and installation density, wastewater properties, water temperature Constant determined by N _i : Number of diffuser plates installed in each aeration zone Substitute K _Lai of each aeration zone obtained in step 2 into the above formula to find Q _i /N _i and Q _i of each aeration zone. .

[Step 4] Calculating the air diffuser plate pressure loss ΔP _di (mmAq) The relationship between the amount of air supplied per air diffuser plate and the pressure loss is roughly shown in Figure 3, but these values were calculated in advance through experiments. ΔP _di corresponding to Q _i /N _i of each aeration zone, that is, ΔP _d1 , ΔP _d2 , ΔP _d3 of each aeration zone, are determined from the table.

[Step 5] Calculate the pressure loss ΔP _A (mmAq) in the gas piping to each aeration zone. Normally, this value is much smaller than ΔP _di , so ignore it.

[Step 6] Pressure loss ΔP _vi to be given to each control valve
Calculation of (mmAq) Assuming that the water level and the installation depth of the diffuser plate are the same in each aeration zone, and the pressure loss of the piping is ignored, the following formula holds true.

ΔP _v1 + ΔP _d1 = ΔP _v2 + ΔP _v2 = ΔP _v3 + ΔP _v3 Here, the values of Q ₁ , Q ₂ , and Q ₃ are compared, and the opening degree of the control valve in the aeration zone with the maximum air supply amount is set as 100%.
For example, if Q ₁ is the maximum, the opening degree of the control valve 5 in the aeration zone 4a is 100%, so ΔP _v1 becomes approximately 0. Therefore, the above equation becomes ΔP _v1 = 0 ΔP _v2 = ΔP _d1 − ΔP _d2 ΔP _v3 = ΔP _d1 − ΔP _d3 , and by substituting ΔP _di obtained in step 4, ΔP _vi of each aeration zone is calculated.

[Procedure 7] Determination of control valve opening degree Di (%) First, calculate each flow velocity u _i (m/sec) in the distribution pipe 6 that distributes gas to each aeration zone.

u ₂ = Q ₂ /60s ₂ u ₃ = Q ₃ /60s ₃ s _i : Cross-sectional area of the distribution pipe 6 of each aeration zone In general, the pressure loss of the control valve is ΔP _vi = e _i・(u _i ² /2g )・ρ e _i : Pressure loss coefficient (-) g : Gravitational acceleration (m/sec ² ) ρ : Density of air (Kg/m ² ) Therefore, ΔP _vi of aeration zones 4b and 4c
is ΔP _v2 = e ₂・(u ₂ ² /2g)・ρ ΔP _v3 = e ₃・(u ₃ ² /2g)・ρ, and e ₂ and e ₃ are calculated from the above formula and prepared in advance by experiment. The control valve opening degree D _i is determined from a table showing the relationship between the pressure loss coefficient e _i and the control valve opening degree D _i (generally shown in FIG. 4).

The opening degree of the control valve 5 obtained in the above manner is converted into a voltage signal of, for example, 0 to 10V, and the converter 1
2b, where the output is converted into a current signal of, for example, 4 to 20 mA, and sent to each control valve 5, and the opening degree of each control valve 5 is adjusted to provide optimal air supply to each aeration zone.

Next, an example of calculating the opening degree of each control valve 5 will be shown.

[Calculation example]

Aeration zone water temperature: 20℃, DO target value: 1mg/
, Number of diffuser plates installed: N ₁ = N ₂ = N ₃ = 60, Diffuser plate installed water depth: 5 m [Step 1] Input of respiration rate r _i From the measured value of the respiration rate meter r ₁ = 30 mg/・hr r ₂ = 25mg/・hr r ₃ = 15mg/・hr [Step 2] Calculation of the required overall oxygen transfer capacity coefficient K _Lai for each aeration zone The saturated DO of the aeration zone at a water temperature of 20℃ is 8.8
mg/, so K _La1 = 30/(8.8-1) = 3.8 (1/hr) K _La2 = 25/(8.8-1) = 3.2 (1/hr) K _La3 = 15/(8.8-1) = 1.9 (1/hr) [Step 3] The constant for calculating the required air supply amount Q _i for each aeration zone is, where A is 24 and B is 10, Q _i /N _i =24K _Lai +10 Therefore, Q ₁ /N ₁ ≒101N/min Q ₂ /N ₂ ≒87N/min Q ₃ /N ₃ ≒56N/min Also, Q ₁ = 6.1Nm ² /min Q ₂ = 5.2Nm ² /min Q ₃ = 3.4Nm ² /min [Step 4 ] Calculation of diffuser plate pressure loss ΔP _di From Figure 3, ΔP _d1 = 470mmAq ΔP _d2 = 390mmAq ΔP _d3 = 270mmAq [Step 5] Calculation of pressure loss ΔP _A of gas piping to each aeration zone Very large compared to ΔP _di Since it is a small value, it is ignored.

[Step 6] Pressure loss ΔP _vi to be given to each control valve
Calculation ΔP _v1 = 0 ΔP _v2 = ΔP _d1 −ΔP _d2 = 80 mmAq ΔP _v3 = ΔP _d1 − ΔP _d3 = 200 mmAq [Step 7] Determination of control valve opening D _i % Assuming that the inner diameter of distribution pipe 6 is 100 mm, s _i = 7.85×10 ^-3 m ² u ₂ = Q ₂ /60s ₂ = 11m/sec u ₃ = Q ₃ /60s ₃ = 7.2m/sec Also e ₂ = ΔP _v2・2g/(u ₂ ²・ρ)≒9 e ₃ =ΔP _v2・2g/(u ₃ ²・ρ)≒50 Note that ρ is 1.5Kg/m ² taking into account the temperature increase by the blower and the water depth of 5m.

Therefore, from FIG. 4, D ₁ =100% D ₂ =58% D ₃ =40%, and the opening degree of the control valve 5 can be determined.

<Effects of the Invention> As explained above, according to the device of the present invention, the optimum air supply amount commensurate with the respiration rate of activated sludge in all the divided aeration zones in the aeration tank, that is, the organic matter decomposition rate. Since it is possible to constantly supply air to each aeration zone, even if the amount and quality of inflow water fluctuates, the optimal amount of air can be quickly achieved. It is possible to prevent this from happening, and it is also possible to save energy consumption by always maintaining the amount of air supplied in an optimal state.

[Brief explanation of the drawing]

Figures 1 to 4 all relate to the device of the present invention, with Figure 1 being an explanatory diagram of the control flow, Figure 2 being an explanatory flowchart, and Figure 3 being the amount of air supplied per diffuser plate. FIG. 4 is an explanatory diagram showing the relationship between the pressure loss coefficient and the opening degree of the control valve. 1...Inflow pipe, 2...Outflow pipe, 3...Aeration tank,
4...Aeration zone, 5...Control valve, 6...Distribution pipe, 7...Diffuser plate, 8...Gas main pipe, 9...Blower, 10...Dissolved oxygen concentration meter (DO meter), 11
... Respirometer, 12... Converter, 13...
Microcomputer, 14...inverter.

Claims (1)

[Claims] 1 An aeration tank in which the aeration tank is divided to form multiple aeration zones, and gas from a blower is distributed and sent to each aeration zone via a distribution pipe with a control valve, and any part of the aeration tank is A dissolved oxygen concentration meter is installed at each aeration zone, and a respiration rate meter is installed in each aeration zone in the aeration tank. At the same time as adjusting the rotation speed of each respirometer, the required amount of air to be delivered to each corresponding aeration zone is calculated based on the measured value of each respirometer, and then each adjustment that can deliver the required amount of air to each aeration zone is performed. An air supply amount control device for an aeration tank, characterized in that the amount of air supplied to each aeration zone is controlled by calculating the opening degree of a valve and adjusting the opening degree of each control valve based on the calculation result.