JP7803365B2 - Wastewater quality measurement system, wastewater treatment equipment, and wastewater quality measurement method - Google Patents

Description

The present invention relates to a wastewater quality measurement system, wastewater treatment equipment, and a method for measuring wastewater quality.

For example, when treating wastewater using aerobic microorganisms to decompose organic matter (such as sludge material and starch), as in the activated sludge process, the amount of organic matter decomposed varies depending on the activity of the microorganisms. In other words, the higher the activity of the microorganisms, in other words, the greater the total number of microorganisms and the higher the metabolic activity of each individual microorganism, the more oxygen in the water they consume, and as a result, the greater the amount of organic matter decomposed. Therefore, it is necessary to change the wastewater treatment conditions, for example, by changing the aeration rate, depending on the amount of organic matter decomposed.

It is known that microbial activity can be estimated from COD (chemical oxygen demand) and BOD (biological oxygen demand). This is because the higher the activity of aerobic microorganisms, the more oxygen they consume in the water. However, as is well known, measuring COD and BOD takes a long time. Therefore, when using COD and BOD as indicators to determine microbial activity, there is a time lag in detecting changes in microbial activity, which can lead to delays in wastewater treatment measures to respond to changes in activity.

Japanese Patent Application Publication No. 11-169840

The present invention was made in consideration of the above circumstances, and aims to provide a wastewater quality measurement system, wastewater treatment equipment, and wastewater quality measurement method that enable the rapid prediction of wastewater COD or BOD.

In order to solve the above problems, the present invention employs the following configuration.
[1] A measurement cell capable of storing test water;
a test water supply unit that supplies the test water collected from wastewater to the measurement cell;
an air supply unit for aerating the test water in the measurement cell;
a dissolved oxygen sensor that measures the dissolved oxygen concentration of the test water from the start of aeration to the end of aeration;
a control unit that controls the operation of the test water supply unit, the air supply unit, and the dissolved oxygen sensor;
The control unit is a first functional unit that calculates a time change in the oxygen consumption rate of the test water based on the dissolved oxygen concentration of the test water measured by the dissolved oxygen sensor from the start of aeration to the end of aeration;
A wastewater quality measurement system having a second functional unit that predicts the BOD or COD of the test water from the time change in the oxygen consumption rate of the test water based on the relationship between the time change in the oxygen consumption rate of the wastewater and the BOD or COD of the wastewater, which has been obtained in advance.
However, the first functional unit determines the time change in the oxygen consumption rate of the test water using the following determination method.
(Determination method)
The dissolved oxygen concentration of the test water is measured multiple times using the dissolved oxygen sensor within the time from the start of aeration to the end of aeration, and the oxygen consumption rate is calculated for each dissolved oxygen concentration using the following formula (1). Based on the relationship between the calculated oxygen consumption rate and time, a linear function y = ax + b is approximated by the least squares method, where x is time and y is the oxygen consumption rate, and the slope a of the linear function is taken as the change in the oxygen consumption rate over time.
qO ₂ =Gvh(Cs-C))...(1)
In equation (1), qO2 _is the oxygen consumption rate (cm·mgO2 _/ min), Gv is the amount of air supplied into the measurement cell (L/min), h is the depth of the test water in the measurement cell (cm), Cs is the saturated dissolved oxygen concentration (mg/L) of the test liquid at the water temperature of the test liquid at the time of measurement, and C is the dissolved oxygen concentration (mg/L) measured by the dissolved oxygen sensor at each measurement time.
[ 2 ] The wastewater quality measurement system according to [1], further comprising a turbidity sensor that measures the turbidity of the test water in a stationary state after aeration is completed.
[ 3 ] The control unit includes a third functional unit that calculates a time change rate of turbidity for each fixed time based on the turbidity of the test water from the start of standing to the end of standing using the turbidity sensor;
The wastewater quality measurement system according to [2] further comprises a fourth functional unit that predicts the particle size distribution of turbidity contained in the test water from the time rate of change of turbidity of the test water based on the relationship between the time rate of change of turbidity of the wastewater and the particle size distribution of turbidity contained in the wastewater, which has been previously obtained.
[ 4 ] The wastewater quality measurement system according to [1], further comprising a sensor cleaning unit that supplies compressed air for cleaning toward the dissolved oxygen sensor.
[ 5 ] The wastewater quality measuring system according to [1], further comprising a cleaning water supply unit that supplies cleaning water to the measurement cell.
[ 6 ] A raw water tank for storing wastewater;
an aeration tank installed downstream of the raw water tank;
a flow path for transporting the wastewater from the raw water tank toward the aeration tank;
[1] to [5] The wastewater quality measurement system according to any one of [1] to [5] ,
A wastewater treatment facility comprising: a test water supply flow path that supplies test water, which is part of the wastewater, from the flow path to the test water supply section of the water quality measurement system.
[ 7 ] A test water supply step of introducing test water collected from wastewater into a measurement cell;
a first measurement step of aerating the test water in the measurement cell and measuring the dissolved oxygen concentration of the test water from the start of aeration to the end of aeration with a dissolved oxygen sensor;
a first calculation step of calculating a time change in the oxygen consumption rate of the test water based on the dissolved oxygen concentration of the test water from the start of aeration to the end of aeration;
A method for measuring the quality of wastewater, comprising: a first prediction step of predicting the BOD or COD of the test water from the time change in the oxygen consumption rate of the test water based on the relationship between the time change in the oxygen consumption rate of the wastewater and the BOD or COD of the wastewater, which has been obtained in advance.
However, the first calculation step is to determine the time change in the oxygen consumption rate of the test water using the following determination method.
(Determination method)
The dissolved oxygen concentration of the test water is measured multiple times using the dissolved oxygen sensor within the time from the start of aeration to the end of aeration, and the oxygen consumption rate is calculated for each dissolved oxygen concentration using the following formula (1). Based on the relationship between the calculated oxygen consumption rate and time, a linear function y = ax + b is approximated by the least squares method, where x is time and y is the oxygen consumption rate, and the slope a of the linear function is taken as the change in the oxygen consumption rate over time.
qO ₂ =Gvh(Cs-C))...(1)
In equation (1), qO2 _is the oxygen consumption rate (cm·mgO2 _/ min), Gv is the amount of air supplied into the measurement cell (L/min), h is the depth of the test water in the measurement cell (cm), Cs is the saturated dissolved oxygen concentration (mg/L) of the test liquid at the water temperature of the test liquid at the time of measurement, and C is the dissolved oxygen concentration (mg/L) measured by the dissolved oxygen sensor at each measurement time.
[ 8 ] A second measurement step of measuring the turbidity of the test water in a stationary state after aeration is completed;
A second calculation step of calculating a time change rate of turbidity for each fixed time based on the turbidity of the test water from the start of standing to the end of standing;
The method for measuring the quality of wastewater according to [7], further comprising a second prediction step of predicting the particle size distribution of turbidity contained in the test water from the time rate of change of turbidity of the test water based on the relationship between the time rate of change of turbidity of the wastewater and the particle size distribution of turbidity contained in the wastewater, which has been previously obtained.
[ 9 ] The method for measuring the quality of wastewater according to [7] or [8], further comprising a cleaning step of supplying cleaning water to the measurement cell after completion of the first measurement step or the second measurement step, injecting compressed air toward the measurement unit of the dissolved oxygen sensor, and then supplying air to the cleaning water in the measurement cell to agitate the cleaning water.
[ 10 ] The method for measuring the quality of wastewater according to [7] or [8], further comprising a cleaning step of supplying cleaning water to the measurement cell after completion of the first measurement step or the second measurement step, supplying air to the cleaning water in the measurement cell to agitate the cleaning water, and then spraying compressed air toward the measurement unit of the dissolved oxygen sensor.
[ 11 ] The method for measuring the quality of wastewater according to [ 9] , further comprising an inspection step of checking the operation of the dissolved oxygen sensor by measuring the dissolved oxygen concentration of the cleaning water with the dissolved oxygen sensor between the start and end of the cleaning step.
[ 12 ] The method for measuring the quality of wastewater according to [ 10] , further comprising an inspection step of checking the operation of the dissolved oxygen sensor by measuring the dissolved oxygen concentration of the cleaning water with the dissolved oxygen sensor between the start and end of the cleaning step.

The present invention provides a wastewater quality measurement system, wastewater treatment equipment, and wastewater quality measurement method that enable rapid prediction of wastewater COD or BOD.

1 is a schematic diagram showing a wastewater treatment facility according to an embodiment of the present invention; 1 is a schematic diagram showing a wastewater quality measurement system according to an embodiment of the present invention; FIG. 1 is a diagram illustrating an example of a method for measuring the quality of wastewater, and is a scatter diagram showing the relationship between the BOD of test water and the change in oxygen consumption rate over time. FIG. 1 is a diagram for explaining an embodiment of a method for measuring the quality of wastewater, and is a scatter diagram showing the relationship between the COD _Cr of test water and the change in oxygen consumption rate over time. FIG. 1 is a diagram illustrating an example of a method for measuring the quality of wastewater, and is a scatter diagram showing the relationship between the BOD of test water and the change in oxygen consumption rate over time. FIG. 1 is a diagram for explaining an embodiment of a method for measuring the quality of wastewater, and is a scatter diagram showing the relationship between the COD _Cr of test water and the change in oxygen consumption rate over time. FIG. 1 is a diagram illustrating a comparative example of a method for measuring the quality of wastewater, and is a scatter diagram showing the relationship between the COD _Cr of test water and the change in oxygen consumption rate over time.

The following describes embodiments of the present invention, including a wastewater quality measurement system, wastewater treatment equipment, and wastewater quality measurement method.

FIG. 1 shows a wastewater treatment facility 1 equipped with a wastewater quality measurement system 10 according to this embodiment.
The wastewater treatment facility 1 shown in FIG. 1 includes a raw water tank 2 , an aeration tank 3 installed downstream of the raw water tank 2 , and a flow path 4 for transporting wastewater from the raw water tank 2 to the aeration tank 3 .

The raw water tank 2 stores the wastewater to be treated. The aeration tank 3 is a tank for aerating the wastewater. The aeration tank 3 is equipped with an air supply mechanism (not shown), which allows air to be supplied to the wastewater. The wastewater is aerated in the aeration tank 3, thereby undergoing biochemical treatment.

A test water supply flow path 5 branches off from the flow path 4 midway. The test water supply flow path 5 is connected to the wastewater quality measurement system 10 of this embodiment. The test water supply flow path 5 supplies test water, which is part of the wastewater, to the water quality measurement system 10.

Next, the water quality measurement system 10 of this embodiment will be described with reference to FIG.
The water quality measurement system 10 comprises a measurement cell 11 capable of storing test water, a test water supply unit 12 that supplies test water to the measurement cell 11, an air supply unit 13 that aerates the test water in the measurement cell 11, a dissolved oxygen sensor 14 that measures the dissolved oxygen concentration of the test water in the measurement cell 11, a control unit 15, a turbidity sensor 16 that measures the turbidity of the test water in the measurement cell 11, a sensor cleaning unit 17, a cleaning water supply unit 18, and a drainage unit 19 that discharges the test water or cleaning water in the measurement cell 11.

The measurement cell 11 is a vertically long container that can store test water during measurement and through which cleaning water can be circulated during cleaning. Connected to the bottom of the measurement cell 11 are a supply flow path L1 for supplying test water or cleaning water to the measurement cell 11, and an air flow path L2 for supplying aeration air to the measurement cell 11. Connected to the top of the measurement cell 11 is a drainage flow path L3 for discharging the test water or cleaning water from the measurement cell 11.

The measurement cell 11 is also equipped with a dissolved oxygen sensor 14 and a turbidity sensor 16. Furthermore, an air flow path L4 is connected near the dissolved oxygen sensor 14 of the measurement cell 11 to supply compressed air for cleaning to the dissolved oxygen sensor 14.

The test water supply unit 12 is composed of a supply flow path L1, an on-off valve 12A provided in the supply flow path L1, and a supply nozzle 12B. The opening and closing operation of the on-off valve 12A is controlled by the control unit 15. The supply flow path L1 is connected to the test water supply flow path 5 shown in Figure 1. This allows the test water supply unit 12 to supply test water collected from wastewater by the test water supply flow path 5 to the measurement cell 11 via the supply flow path L1.

The air supply unit 13 is composed of an air flow path L2, an on-off valve 13A, a flow rate adjustment valve 13B, and a check valve 13C provided in the air flow path L2, and an air nozzle 13D provided at the tip of the air flow path L2. The check valve 13C, the on-off valve 13A, and the flow rate adjustment valve 13B are arranged in the air flow path L2 in order of proximity to the measurement cell 11. The opening and closing operation of the on-off valve 12A and the flow rate adjustment operation of the flow rate adjustment valve 13B are controlled by the control unit 15. The air nozzle 13D is arranged below the measurement cell 11. This allows the air supply unit 13 to supply flow-controlled air to the test water from the bottom of the measurement cell 11 via the air flow path L2, thereby aerating the test water.

The dissolved oxygen sensor 14 measures the dissolved oxygen concentration of the test water stored in the measurement cell 11. In particular, the dissolved oxygen sensor 14 measures the dissolved oxygen concentration of the test water from the start of aeration to the end of aeration. The dissolved oxygen sensor 14 also measures the dissolved oxygen concentration of the cleaning water flowing through the measurement cell 11. The measurement results are sent to the control unit 15.

The turbidity sensor 16 measures the turbidity of the test water stored in the measurement cell 11. In particular, the turbidity sensor 16 measures the turbidity of the test water in a stationary state after aeration has ended. The measurement results are sent to the control unit 15.

The sensor cleaning unit 17 is composed of an air flow path L4, an on-off valve 17A, a flow rate adjustment valve 17B, and a check valve 17C provided in the air flow path L4, and an air nozzle 17D provided at the tip of the air flow path L4. The check valve 17C, the on-off valve 17A, and the flow rate adjustment valve 17B are arranged in the air flow path L4 in order of proximity to the measurement cell 11. The opening and closing operation of the on-off valve 17A and the flow rate adjustment operation of the flow rate adjustment valve 17B are controlled by the control unit 15. The air nozzle 17D is located close to the dissolved oxygen sensor 14. When the measurement cell 11 is filled with cleaning water, the sensor cleaning unit 17 sprays compressed air from the air nozzle 17D at the tip of the air flow path L4 into the measurement cell 11, creating a water flow containing air bubbles toward the dissolved oxygen sensor 14. This allows the sensor cleaning unit 17 to clean the dissolved oxygen sensor 14. As a result, the present invention can prevent dirt from adhering to the dissolved oxygen sensor 14, reducing the frequency of maintenance.

The cleaning water supply unit 18 is composed of a cleaning water flow path L5 and an on-off valve 18A provided in the cleaning water flow path L5. The cleaning water flow path L5 is connected to the supply flow path L1, and the opening and closing operation of the on-off valve 18A is controlled by the control unit 15. This allows the cleaning water supply unit 18 to supply cleaning water into the measurement cell 11 via the cleaning water flow path L5, the supply flow path L1, and the supply nozzle 12B.

The drainage section 19 is composed of a drainage flow path L3 connected to the top of the measurement cell 11. The drainage flow path L3 is an overflow path, and is capable of draining the test water or cleaning water from the measurement cell 11 while maintaining a constant water level in the measurement cell 11.

The control unit 15 controls the operation of the test water supply unit 12, air supply unit 13, dissolved oxygen sensor 14, turbidity sensor 16, sensor cleaning unit 17, and cleaning water supply unit 18.

Specifically, the control unit 15 activates the test water supply unit 12 to supply a portion of the wastewater as test water to the measurement cell 11, and then activates the air supply unit 13 to aerate the test water filled in the measurement cell 11. Between the start and end of aeration, the control unit 15 controls the dissolved oxygen sensor 14 to measure the dissolved oxygen concentration of the test water. After aeration is completed, the test water is allowed to stand in the measurement cell 11 for a certain period of time, during which time the turbidity sensor 16 measures the turbidity of the test water. After the turbidity measurement is completed, the control unit 15 activates the cleaning water supply unit 18 to continuously supply cleaning water into the measurement cell 11, while also activating the sensor cleaning unit 17 to clean the dissolved oxygen sensor 14. Furthermore, the control unit 15 activates the air supply unit 13 to supply air to the cleaning water circulating within the measurement cell 11 to agitate it, thereby cleaning the measurement cell 11. During this cleaning, the control unit 15 inspects the dissolved oxygen sensor 14 by having it measure the dissolved oxygen concentration in the cleaning water and monitoring the measured value.

The control unit 15 also has the following first, second, third, and fourth functional units. Each functional unit performs calculations on the dissolved oxygen concentration and turbidity obtained by the dissolved oxygen sensor 14 and the turbidity sensor 16. Each functional unit is realized as a function provided in a central processing unit (CPU) provided in the control unit 15. The detailed operation of each functional unit will be explained in the explanation of the water quality measurement method.

The control unit 15 may be, for example, a computer equipped with a data input unit that accepts the measurement results of the dissolved oxygen sensor 14 and turbidity sensor 16, a central processing unit, a memory device, a data output unit that outputs commands to the test water supply unit 12, air supply unit 13, sensor cleaning unit 17, and cleaning water supply unit 18, and a display unit. The memory device may store a computer program for operating the control unit 15, and this computer program may be executed by the central processing unit. Furthermore, the test water supply unit 12, air supply unit 13, dissolved oxygen sensor 14, turbidity sensor 16, sensor cleaning unit 17, and cleaning water supply unit 18 may be connected to the control unit 15 via a wired line, a wireless line, or a communication line such as the Internet or a telephone line.

An example of a memory device that stores a computer program for implementing the functions of control unit 15 is a computer-readable recording medium. Examples of computer-readable recording media include portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as hard disks and semiconductor storage devices built into computers. Furthermore, "computer-readable recording media" also includes devices that store a program for a certain period of time, such as volatile memory (RAM) within a computer system that serves as a server or client when a program is transmitted over a network such as the Internet or a communication line such as a telephone line.

Furthermore, the various measurement results obtained by the dissolved oxygen sensor 14 and turbidity sensor 16 may be stored in advance on an external server, and control may be performed by acquiring these results.

The first functional unit has the function of calculating the change in the oxygen consumption rate of the test water over time based on the dissolved oxygen concentration of the test water measured by the dissolved oxygen sensor 14 from the start to the end of aeration.

The first functional unit may also measure the dissolved oxygen concentration of the test water multiple times during the time from the start of aeration to the end of aeration using the dissolved oxygen sensor 14, calculate the oxygen consumption rate for each dissolved oxygen concentration, and determine the change in the oxygen consumption rate over time based on the relationship between the calculated oxygen consumption rate and time.

Furthermore, the first functional unit may use the dissolved oxygen sensor 14 to measure the dissolved oxygen concentration of the test water multiple times during the time from the start of aeration to the end of aeration, calculate the oxygen consumption rate from the dissolved oxygen concentrations at the start and end of measurement, calculate the difference between these rates, and determine the change in the oxygen consumption rate over time by dividing this difference by the time difference between the start and end of measurement.

The second functional unit has the function of predicting the BOD or COD of the test water from the change in the oxygen consumption rate of the test water over time, based on the relationship between the change in the oxygen consumption rate of the wastewater over time and the BOD or COD of the wastewater, which has been previously obtained.

The third functional unit has the function of calculating the rate of change in turbidity over time at fixed intervals based on the turbidity of the test water from the start to the end of the standing period using the turbidity sensor 16.

The fourth functional unit has the function of predicting the particle size distribution of turbidity contained in the test water from the time rate of change of the turbidity of the test water, based on the relationship between the time rate of change of the turbidity of the wastewater obtained in advance and the particle size distribution of the turbidity contained in the wastewater.

Next, the wastewater quality measurement method of this embodiment will be described with reference to Figure 2.

The wastewater quality measurement method of this embodiment sequentially includes a test water supply step in which test water is supplied to the measurement cell 11, a first measurement step in which the dissolved oxygen concentration of the test water is measured, a first calculation step in which the time change in oxygen consumption rate is determined from the dissolved oxygen concentration, and a first prediction step in which the BOD or COD of the test water is predicted.

Furthermore, in the wastewater quality measurement method of this embodiment, after the first measurement step is completed, a second measurement step of measuring the turbidity of the test water, a second calculation step of calculating the time rate of change of turbidity at fixed intervals from the turbidity, and a second prediction step of predicting the particle size distribution of turbidity contained in the test water may be carried out in this order.

Furthermore, the wastewater quality measurement method of this embodiment may include a cleaning step and an inspection step of the dissolved oxygen sensor 14 after the first measurement step or the second measurement step is completed.

Each stage is explained below.

During the test water supply stage, the control unit 15 issues a command to the test water supply unit 12 to open the on-off valve 12A and supply test water from the supply flow path L1 to the measurement cell 11. Once the measurement cell 11 is filled with test water, the control unit 15 issues a command to the test water supply unit 12 to close the on-off valve 12A, thereby stopping the supply of test water to the measurement cell 11. A certain amount of test water is stored in the measurement cell 11.

Next, in the first measurement stage, the control unit 15 issues a command to the air supply unit 13 to open the on-off valve 13A and adjust the flow rate with the flow control valve 13B, while supplying air from the air flow path L2 to the test water in the measurement cell 11. This aerates the test water. Aeration is carried out continuously for a certain period of time. There are no particular restrictions on the aeration time, but it may be in the range of 10 to 300 seconds, for example, or may be 120 seconds. The control unit 15 issues a command to the air supply unit 13 to stop the air supply after the specified time has elapsed.

In the first measurement stage, the control unit 15 issues a command to the dissolved oxygen sensor 14 to measure the dissolved oxygen concentration of the test water during aeration and transmit the measurement results to the control unit 15 in time with the start of aeration. The measurement of the dissolved oxygen concentration continues until the end of aeration. Measurements can be taken at regular intervals, for example, every 0.1 to 30 seconds, or even every second. There are no particular restrictions on the number of measurements, and they can be, for example, 10 to 300 times, or even 90 times. In this way, multiple measurements are taken from the start of aeration to the end of aeration. The measurement can also start a predetermined time after the start of aeration; for example, measurement can start 1 to 20 seconds after the start of aeration, or even 10 seconds later.

The dissolved oxygen concentration measured by the dissolved oxygen sensor 14 increases over time during aeration. However, if the activity of microorganisms in the test water is relatively high, the increase in the dissolved oxygen concentration during aeration will be relatively slow due to the high oxygen consumption by the microorganisms. On the other hand, if the activity of microorganisms in the test water is relatively low, the increase in the dissolved oxygen concentration during aeration will be relatively fast due to the low oxygen consumption by the microorganisms.

Next, in the first calculation stage, the first functional unit of the control unit 15 calculates the time change in the oxygen consumption rate from the dissolved oxygen concentration of the test water during aeration obtained in the first measurement stage. The obtained time change in the oxygen consumption rate is output to the second functional unit.

There are no particular limitations on the method for determining the change in oxygen consumption rate over time, but it may be performed, for example, by either the first or second method described below.

(First Method)
First, in the first measurement stage, the oxygen consumption rate is calculated based on a plurality of dissolved oxygen concentrations measured at regular intervals. The oxygen consumption rate at each measurement time is calculated by the following formula (1).

qO ₂ =G _v h(Cs-C))...(1)

In equation (1), _qO2 is the oxygen consumption rate (cm· _mgO2 /min), _Gv is the amount of air supplied into the measurement cell (L/min), h is the depth of the test water in the measurement cell (cm), Cs is the saturated dissolved oxygen concentration (mg/L) of the test liquid at the water temperature of the test liquid at the time of measurement, and C is the dissolved oxygen concentration (mg/L) measured by the dissolved oxygen sensor at each measurement time.

Next, all measurement results are plotted on an xy plane, with the x-axis representing the elapsed time from the start of measurement and the y-axis representing the oxygen consumption rate. A straight line is drawn based on the plot, showing the change in oxygen consumption rate over time. The slope of the line is then calculated. The slope of the line represents the change in oxygen consumption rate over time. The slope of the line can be calculated from the plot, for example, by approximating a linear function using the least squares method. In this case, the linear function is y = ax + b. y is the oxygen consumption rate _qO2 , x is the elapsed time, a is the slope, which represents the change in oxygen consumption rate over time, and b is the y-intercept.

When actually calculating the change in oxygen consumption rate over time in the control unit 15, plotting the measurement results on the xy plane can be omitted, and the least squares method can be applied to the data group of elapsed time and oxygen consumption rate to directly determine the change in oxygen consumption rate over time, which is the slope of the linear function.

(Second Method)
In the first measurement stage, the dissolved oxygen concentration at the start of measurement _t1 and the dissolved oxygen concentration at the end of measurement _t2 are extracted from a plurality of dissolved oxygen concentration measurements taken at regular intervals. Then, the difference ( _DOE - _DOS ) between the dissolved oxygen concentration _DOS at the start of measurement and the dissolved oxygen concentration _DOE at the end of measurement is calculated. The difference in oxygen consumption rate ( _DOE - _DOS ) is divided by the time from the start of measurement to the end of measurement ( _t2 - _t1 ) to calculate the change in oxygen consumption rate over time ( _DOE - _DOS )/( _t2 - _t1 ).

Next, in the first prediction stage, the second functional unit of the control unit 15 predicts the BOD or COD of the test water from the change in the oxygen consumption rate of the test water based on the relationship between the change in the oxygen consumption rate of the wastewater over time and the BOD or COD of the wastewater, which was previously obtained.

The relationship between the previously obtained change in oxygen consumption rate of the wastewater over time and the BOD or COD of the wastewater can be represented, for example, by a scatter plot of previously measured data on an xy plane with the x-axis representing the change in oxygen consumption rate over time and the y-axis representing COD or BOD. In this case, the COD or BOD is the value measured in accordance with JIS K 0102:2019, and the change in oxygen consumption rate over time can be the value calculated in the first calculation step described above.

When predicting COD or BOD, the relationship between COD or BOD and the time change in oxygen consumption rate can be calculated based on the scatter plot data, and the COD or BOD of the test water can be calculated by inputting the time change in oxygen consumption rate of the test water obtained in the first calculation step into that relationship.

Below, specific examples of COD and BOD prediction are shown.
As an example, Figure 3 shows the relationship between the BOD of the test water and the time change in oxygen consumption rate. The BOD of the test water was measured in accordance with JIS K 0102:2019. The time change in oxygen consumption rate was calculated using the first method described above, measuring the dissolved oxygen concentration of the test water during aeration using the water quality measurement system of this embodiment. As shown in Figure 3, the coefficient of determination ^R2 between the BOD of the test water and the time change in oxygen consumption rate is 0.50, indicating a certain correlation.

FIG. 4 shows, as an example, the relationship between the COD _Cr of the test water and the change in oxygen consumption rate over time. The COD _Cr of the test water was measured in accordance with JIS K 0102:2019. The change in oxygen consumption rate over time was calculated using the first method described above, measuring the dissolved oxygen concentration of the test water during aeration using the water quality measurement system of this embodiment. As shown in FIG. 4, the coefficient of determination ^R2 between the COD _Cr of the test water and the change in oxygen consumption rate over time is 0.58, indicating a certain correlation.

Figure 5 shows, as an example, the relationship between the BOD of the test water and the time change in oxygen consumption rate. The BOD of the test water was measured in accordance with JIS K 0102:2019. The time change in oxygen consumption rate was calculated using the second method described above, measuring the dissolved oxygen concentration of the test water during aeration using the water quality measurement system of this embodiment. As shown in Figure 5, the coefficient of determination ^R2 between the BOD of the test water and the time change in oxygen consumption rate is 0.44, indicating a certain correlation.

FIG. 6 shows, as an example, the relationship between the COD _Cr of the test water and the change in oxygen consumption rate over time. The COD _Cr of the test water was measured in accordance with JIS K 0102:2019. The change in oxygen consumption rate over time was calculated by measuring the dissolved oxygen concentration of the test water during aeration using the water quality measurement system of this embodiment and then using the second method described above. As shown in FIG. 6, the coefficient of determination ^R2 between the COD _Cr of the test water and the change in oxygen consumption rate over time is 0.64, indicating a certain correlation.

On the other hand, as a comparative example, Figure 7 shows the relationship between the COD _Cr of the test water and the change in oxygen consumption rate over time. The COD _Cr of the test water was measured in accordance with JIS K 0102:2019. The change in oxygen consumption rate over time was calculated by measuring the dissolved oxygen concentration of the test water in a stationary state after aeration was completed using the water quality measurement system of this embodiment and using the first method described above. As shown in Figure 7, the coefficient of determination ^R2 between the change in oxygen consumption rate over time calculated from the dissolved oxygen concentration measured after aeration was completed and the COD _Cr of the test water was 0.01, indicating that there is no correlation.

Next, we will explain the second measurement stage, second calculation stage, and second prediction stage. Note that these second measurement stage, second calculation stage, and second prediction stage may or may not be performed.

The second measurement stage begins immediately after the end of the first measurement stage. During the second measurement stage, the air supply from the air supply unit 13 is stopped, and the test water is left stationary. The control unit 15 then issues a command to the turbidity sensor 16 to measure the turbidity of the stationary test water and transmit the measurement results to the control unit 15. The turbidity is measured continuously for a fixed period of time. The measurement time may be, for example, 300 to 1800 seconds, or may be 1430 seconds.

Next, in the second calculation stage, the third functional unit of the control unit 15 calculates the time rate of change of turbidity at regular intervals from the turbidity of the test water obtained in the second measurement stage.

For example, the measurement time of turbidity is divided into three time periods: T0 to T1, T1 to T2, and T2 to T3. T0 is the measurement start time, T3 is the measurement end time, and T1 and T2 are any time periods between T0 and T3. The length of each time period may be the same or different. Furthermore, turbidity D _T0 , D _T1 , D _T2 , and D _T3 at each time period are extracted from the measurement data of the turbidity sensor 16. Then, the time change rate of turbidity in each of the time periods T0 to T1, T1 to T2, and T2 to T3 is calculated.

The rate of change of turbidity over time in the section from T0 to T1 is (D _T1 - D _T0 )/(T1 - T0).
The rate of change of turbidity over time in the section from T1 to T2 is (D _T2 - D _T1 )/(T2 - T1).
The rate of change of turbidity over time in the section from T2 to T3 is (D _T3 - D _T2 )/(T3 - T2).

The position of the turbidity sensor 16 in the measurement cell 11 is fixed, and because turbidity contained in the stationary test liquid settles over time, the turbidity measured by the turbidity sensor 16 decreases over time. Furthermore, according to Stokes' equation, the larger the particle size of turbidity particles, the faster their settling velocity; conversely, the smaller the particle size, the slower their settling velocity. Therefore, the time rate of change in turbidity in the T0-T1 section can be said to indicate the settling velocity of turbidity particles with relatively large particle sizes. Furthermore, the time rate of change in turbidity in the T2-T3 section can be said to indicate the settling velocity of turbidity particles with relatively small particle sizes. Furthermore, the time rate of change in turbidity in the T1-T2 section can be said to indicate the settling velocity of turbidity particles with intermediate particle sizes.

Next, in the second prediction stage, the fourth functional unit of the control unit 15 predicts the particle size distribution of turbidity contained in the test water from the time rate of change of turbidity of the test water, based on the relationship between the time rate of change of turbidity of the wastewater and the particle size distribution of turbidity contained in the wastewater, which was previously obtained.

The relationship between the previously obtained time rate of change in wastewater turbidity and the particle size distribution of turbidity particles contained in the wastewater can be constructed, for example, by using a previously measured particle size distribution of turbidity particles in the wastewater and performing the second measurement step and second calculation step on the same wastewater to determine the time rate of change in turbidity at regular intervals, thereby obtaining the relationship between the particle size distribution of turbidity particles in the wastewater and the time rate of change in turbidity. In this case, the particle size distribution of turbidity particles in the wastewater is a value measured using the scattered light method.

When predicting the particle size distribution of turbidity in wastewater, the relationship between the particle size distribution of turbidity in wastewater and the time rate of change of turbidity, and the equation for the relationship between the particle size distribution of turbidity in wastewater and the time rate of change of turbidity, can be determined in advance, and the particle size distribution of turbidity in the test water can be determined by introducing the time rate of change of turbidity of the test water obtained in the second calculation step into that equation.

Next, we will explain the cleaning stage.

In the cleaning stage, after the first or second measurement stage is completed, the control unit 15 issues a command to the cleaning water supply unit 18 to begin supplying cleaning water to the measurement cell 11. Cleaning water is continuously supplied from the start to the end of the cleaning stage. As the cleaning water is supplied, the test water in the measurement cell 11 is replaced with cleaning water, which is then discharged from the drainage unit 19. Furthermore, cleaning water continues to fill the measurement cell 11 and be discharged from the drainage flow path L3, which serves as an overflow flow path, until the cleaning stage is completed.

Next, the control unit 15 issues a command to the sensor cleaning unit 17, causing compressed air to be sprayed from the air nozzle 17D provided in the measurement cell 11 into the cleaning water in the measurement cell 11. The compressed air is sprayed intermittently. The spray of compressed air creates a water flow containing air bubbles toward the dissolved oxygen sensor 14. This water flow removes foreign matter such as turbidity that has adhered to the dissolved oxygen sensor 14. The removed foreign matter is carried away by the flow of cleaning water and discharged from the measurement cell 11. In this way, the dissolved oxygen sensor 14 is cleaned.

Next, the control unit 15 issues a command to the air supply unit 13 to supply air from the bottom of the measurement cell 11 to the cleaning water inside the measurement cell 11. In this case, the flow rate of the air supply is adjusted by controlling the flow rate adjustment valve 13B to a flow rate that causes turbulent agitation of the cleaning water. As a result, the cleaning water inside the measurement cell 11 is turbulently agitated, removing foreign matter such as turbidity that has adhered to the inner wall of the measurement cell 11. The removed foreign matter is discharged from the measurement cell 11 along with the flow of cleaning water. In this way, the measurement cell 11 is cleaned.

In the above explanation, an example was described in which the dissolved oxygen sensor 14 was cleaned before the measurement cell 11 was cleaned, but the cleaning order is not limited to this; the measurement cell 11 may be cleaned before the dissolved oxygen sensor 14.

Next, we will explain the inspection stage.

During the cleaning stage, cleaning water is continuously supplied to the measurement cell. The quality of the cleaning water is assumed to be nearly constant. Therefore, during the inspection stage, the dissolved oxygen sensor 14 measures the dissolved oxygen concentration of the cleaning water from the start to the end of the cleaning stage to confirm its operation. If the measured dissolved oxygen concentration value is always constant, it can be said that the dissolved oxygen sensor 14 is functioning normally. On the other hand, if the measured dissolved oxygen concentration value changes each time the inspection stage is performed, it is possible that the dissolved oxygen sensor 14 is not functioning normally, and further detailed inspection is required.

As described above, the water quality measurement system and water quality measurement method of this embodiment calculate the time change in the oxygen consumption rate of the test water based on the dissolved oxygen concentration obtained by the dissolved oxygen sensor 14, and then predict the BOD or COD of the test water from the time change in the oxygen consumption rate. This allows COD and BOD to be predicted without the long time required in the past, making it possible to quickly grasp the activity status of microorganisms. As a result, even if the activity status of microorganisms changes during wastewater treatment, this can be detected immediately, and appropriate wastewater treatment measures can be taken in response to the change in activity status.

1...wastewater treatment equipment, 2...raw water tank, 3...aeration tank, 4...flow path, 5...test water supply path, 10...wastewater quality measurement system, 11...measurement cell, 12...test water supply unit, 13...air supply unit, 14...dissolved oxygen sensor, 15...control unit, 16...turbidity sensor, 17...sensor cleaning unit, 18...cleaning water supply unit.

Claims (12)

a measurement cell capable of storing test water;
a test water supply unit that supplies the test water collected from wastewater to the measurement cell;
an air supply unit for aerating the test water in the measurement cell;
a dissolved oxygen sensor that measures the dissolved oxygen concentration of the test water from the start of aeration to the end of aeration;
a control unit that controls the operation of the test water supply unit, the air supply unit, and the dissolved oxygen sensor;
The control unit is a first functional unit that calculates a time change in the oxygen consumption rate of the test water based on the dissolved oxygen concentration of the test water measured by the dissolved oxygen sensor from the start of aeration to the end of aeration;
A wastewater quality measurement system having a second functional unit that predicts the BOD or COD of the test water from the time change in the oxygen consumption rate of the test water based on the relationship between the time change in the oxygen consumption rate of the wastewater and the BOD or COD of the wastewater, which has been obtained in advance.
However, the first functional unit determines the time change in the oxygen consumption rate of the test water using the following determination method.
(Determination method)
The dissolved oxygen concentration of the test water is measured multiple times using the dissolved oxygen sensor within the time from the start of aeration to the end of aeration, and the oxygen consumption rate is calculated for each dissolved oxygen concentration using the following formula (1). Based on the relationship between the calculated oxygen consumption rate and time, a linear function y = ax + b is approximated by the least squares method, where x is time and y is the oxygen consumption rate, and the slope a of the linear function is taken as the change in the oxygen consumption rate over time.
qO ₂ =Gvh(Cs-C))...(1)
In equation (1), qO2 _is the oxygen consumption rate (cm·mgO2 _/ min), Gv is the amount of air supplied into the measurement cell (L/min), h is the depth of the test water in the measurement cell (cm), Cs is the saturated dissolved oxygen concentration (mg/L) of the test liquid at the water temperature of the test liquid at the time of measurement, and C is the dissolved oxygen concentration (mg/L) measured by the dissolved oxygen sensor at each measurement time. The wastewater quality measurement system of claim 1 further comprises a turbidity sensor that measures the turbidity of the test water in a stationary state after aeration has ended. The control unit is a third functional unit that calculates a time change rate of turbidity for each fixed time based on the turbidity of the test water from the start of standing to the end of standing using the turbidity sensor;
The wastewater quality measurement system described in claim 2 further comprises a fourth functional unit that predicts the particle size distribution of turbidity contained in the test water from the time rate of change of turbidity of the test water based on the relationship between the time rate of change of turbidity of the wastewater obtained in advance and the particle size distribution of turbidity contained in the wastewater . The wastewater quality measurement system of claim 1, further comprising a sensor cleaning unit that supplies compressed air for cleaning to the dissolved oxygen sensor. The wastewater quality measurement system of claim 1, further comprising a cleaning water supply unit that supplies cleaning water to the measurement cell. a raw water tank for storing wastewater;
an aeration tank installed downstream of the raw water tank;
a flow path for transporting the wastewater from the raw water tank toward the aeration tank;
The wastewater quality measurement system according to any one of claims 1 to 5 ,
A wastewater treatment facility comprising: a test water supply flow path that supplies test water, which is part of the wastewater, from the flow path to the test water supply section of the water quality measurement system. a test water supply step of introducing test water collected from wastewater into a measurement cell;
a first measurement step of aerating the test water in the measurement cell and measuring the dissolved oxygen concentration of the test water from the start of aeration to the end of aeration with a dissolved oxygen sensor;
a first calculation step of calculating a time change in the oxygen consumption rate of the test water based on the dissolved oxygen concentration of the test water from the start of aeration to the end of aeration;
A method for measuring the quality of wastewater, comprising: a first prediction step of predicting the BOD or COD of the test water from the time change in the oxygen consumption rate of the test water based on the relationship between the time change in the oxygen consumption rate of the wastewater and the BOD or COD of the wastewater, which has been obtained in advance.
However, the first calculation step is to determine the time change in the oxygen consumption rate of the test water using the following determination method.
(Determination method)
The dissolved oxygen concentration of the test water is measured multiple times using the dissolved oxygen sensor within the time from the start of aeration to the end of aeration, and the oxygen consumption rate is calculated for each dissolved oxygen concentration using the following formula (1). Based on the relationship between the calculated oxygen consumption rate and time, a linear function y = ax + b is approximated by the least squares method, where x is time and y is the oxygen consumption rate, and the slope a of the linear function is taken as the change in the oxygen consumption rate over time.
qO ₂ =Gvh(Cs-C))...(1)
In equation (1), qO2 _is the oxygen consumption rate (cm·mgO2 _/ min), Gv is the amount of air supplied into the measurement cell (L/min), h is the depth of the test water in the measurement cell (cm), Cs is the saturated dissolved oxygen concentration (mg/L) of the test liquid at the water temperature of the test liquid at the time of measurement, and C is the dissolved oxygen concentration (mg/L) measured by the dissolved oxygen sensor at each measurement time. A second measurement step of measuring the turbidity of the test water in a stationary state after aeration is completed;
A second calculation step of calculating a time change rate of turbidity for each fixed time based on the turbidity of the test water from the start of standing to the end of standing;
The method for measuring the quality of wastewater described in claim 7, further comprising a second prediction step of predicting the particle size distribution of turbidity contained in the test water from the time rate of change of turbidity of the test water based on the relationship between the time rate of change of turbidity of the wastewater obtained in advance and the particle size distribution of turbidity contained in the wastewater . 9. The method for measuring wastewater quality according to claim 7, further comprising a cleaning step of supplying cleaning water to the measurement cell after completion of the first measurement step or the second measurement step, injecting compressed air toward the dissolved oxygen sensor, and then supplying air to the cleaning water in the measurement cell to agitate the cleaning water. 9. The method for measuring wastewater quality according to claim 7, further comprising a cleaning step of supplying cleaning water to the measurement cell after completion of the first measurement step or the second measurement step, supplying air to the cleaning water in the measurement cell to agitate the cleaning water, and then spraying compressed air toward the dissolved oxygen sensor. 10. The method for measuring the quality of wastewater according to claim 9 , further comprising an inspection step of checking the operation of the dissolved oxygen sensor by measuring the dissolved oxygen concentration of the cleaning water with the dissolved oxygen sensor between the start and end of the cleaning step. The method for measuring the quality of wastewater according to claim 10 , further comprising an inspection step of checking the operation of the dissolved oxygen sensor by measuring the dissolved oxygen concentration of the cleaning water with the dissolved oxygen sensor between the start and end of the cleaning step.