Wastewater quality measurement system, wastewater treatment equipment, and wastewater quality measurement method

Abstract

To provide a water quality measurement system that quickly predicts COD or BOD of wastewater.SOLUTION: There is provided a wastewater quality measurement system 10 including a measurement cell 11 capable of storing test water, a test water supply unit 12 that supplies the test water collected from wastewater 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 a dissolved oxygen concentration of the test water from a start of aeration to an end of aeration, and a control unit 15 that controls operation of the test water supply unit 12, the air supply unit 13, and the dissolved oxygen sensor 14. The control unit 15 has a first functional unit that calculates a time change in an 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 measured by the dissolved oxygen sensor 14, and a second functional unit that predicts BOD or COD of the test water from the time change in the oxygen consumption rate of the test water based on a previously acquired relation between the time change in the oxygen consumption rate of the wastewater and the BOD or COD of the wastewater.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a wastewater quality measurement system, a wastewater treatment facility, and a method for measuring the quality of wastewater. [Background technology]

[0002] For example, when treating wastewater by using aerobic microorganisms to decompose organic matter (such as sludge material or starch), as in the activated sludge process, the amount of organic matter decomposed varies depending on the activity of the microorganisms. That is, 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 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, such as changing the aeration rate, depending on the amount of organic matter decomposed.

[0003] 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 or BOD as an indicator to determine microbial activity, there is a time lag in detecting changes in microbial activity, which can sometimes result in delays in wastewater treatment measures to respond to changes in activity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-169840 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a wastewater quality measurement system, a wastewater treatment facility, and a method for measuring the quality of wastewater, which enable rapid prediction of the COD or BOD of wastewater. [Means for solving the problem]

[0006] 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 change in the oxygen consumption rate of the test water over time using the following determination method. (Determination method) The dissolved oxygen sensor is used 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. The oxygen consumption rate for each dissolved oxygen concentration is calculated 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 using the least squares method, where x is time and y is the oxygen consumption rate. The slope a of the linear function is used to determine the change in the oxygen consumption rate over time. qO 2 =Gvh(Cs-C)) …(1) In equation (1), qO 2 is the oxygen consumption rate (cm mgO 2 / 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 has been completed. [ 3The control unit includes a third functional unit that calculates a time rate of change of turbidity at regular intervals based on the turbidity of the test water from the start to the end of the standing time using the turbidity sensor; Further, a fourth functional unit is provided that predicts the particle size distribution of turbidity matters 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 matters contained in the wastewater, which has been previously obtained. 2 ] A wastewater quality measurement system according to the present invention. [ 4 The wastewater quality measuring 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 measuring 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] ~ [5] The wastewater quality measurement system according to any one of the preceding claims, 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 sensor is used 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. The oxygen consumption rate for each dissolved oxygen concentration is calculated 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 using the least squares method, where x is time and y is the oxygen consumption rate. The slope a of the linear function is used to determine the change in the oxygen consumption rate over time. qO 2 =Gvh(Cs-C)) …(1) In equation (1), qO 2 is the oxygen consumption rate (cm mgO 2 / 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; and a second prediction step of predicting the particle size distribution of turbidity matters 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 matters contained in the wastewater, which has been previously obtained. 7 ] A method for measuring the quality of wastewater described in [ 9 After the first measurement step or the second measurement step is completed, a cleaning step is performed in which cleaning water is supplied to the measurement cell, compressed air is sprayed toward the measurement unit of the dissolved oxygen sensor, and then air is supplied to the cleaning water in the measurement cell to agitate the cleaning water. 7 ]or[ 8 ] A method for measuring the quality of wastewater described in [ 10 After the first measurement step or the second measurement step is completed, a cleaning step is performed in which cleaning water is supplied to the measurement cell, air is supplied to the cleaning water in the measurement cell to agitate the cleaning water, and then compressed air is sprayed toward the measurement unit of the dissolved oxygen sensor. 7 ]or[ 8 ] A method for measuring the quality of wastewater described in [ 11 and 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. 9 ] A method for measuring the quality of wastewater described in [ 12and 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. 10 ] A method for measuring the quality of wastewater described in [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a wastewater quality measurement system, a wastewater treatment facility, and a method for measuring the quality of wastewater, which enable rapid prediction of the COD or BOD of wastewater. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing a wastewater treatment facility according to an embodiment of the present invention; [Figure 2] 1 is a schematic diagram showing a wastewater quality measurement system according to an embodiment of the present invention; [Figure 3] FIG. 1 is a diagram for explaining an embodiment of a method for measuring the quality of wastewater, and is a scatter plot showing the relationship between the BOD of test water and the change in oxygen consumption rate over time. [Figure 4] 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 CODCr of test water and the change in oxygen consumption rate over time. [Figure 5] FIG. 1 is a diagram for explaining an embodiment of a method for measuring the quality of wastewater, and is a scatter plot showing the relationship between the BOD of test water and the change in oxygen consumption rate over time. [Figure 6] 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 CODCr of test water and the change in oxygen consumption rate over time. [Figure 7] FIG. 1 is a diagram illustrating a comparative example of a method for measuring the quality of wastewater, and is a scatter plot showing the relationship between the CODCr of the test water and the change in oxygen consumption rate over time. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a wastewater quality measuring system, a wastewater treatment facility, and a wastewater quality measuring method according to embodiments of the present invention will be described.

[0010] 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 sending wastewater from the raw water tank 2 to the aeration tank 3.

[0011] 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 is capable of supplying air to the wastewater. The wastewater is aerated in the aeration tank 3, thereby undergoing biochemical treatment.

[0012] A test water supply flow path 5 branches off midway through the flow path 4. A wastewater quality measurement system 10 of this embodiment is connected to the end of the test water supply flow path 5. The test water supply flow path 5 supplies test water, which is part of the wastewater, to the water quality measurement system 10.

[0013] Next, the water quality measuring system 10 of this embodiment will be described with reference to FIG. The water quality measurement system 10 includes 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.

[0014] The measurement cell 11 is a vertically long container that can store test water during measurement and through which wash water can be circulated during cleaning. A supply flow path L1 for supplying test water or wash water to the measurement cell 11 and an air flow path L2 for supplying air for aeration to the measurement cell 11 are connected to the bottom of the measurement cell 11. In addition, a drainage flow path L3 for discharging the test water or wash water from the measurement cell 11 is connected to the top of the measurement cell 11.

[0015] 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 to the measurement cell 11 near the dissolved oxygen sensor 14 to supply compressed air for cleaning to the dissolved oxygen sensor 14.

[0016] 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 a 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.

[0017] The air supply unit 13 is composed of an air flow path L2, an on-off valve 13A, a flow rate control 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 control 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 control operation of the flow rate control 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.

[0018] 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.

[0019] 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 result is sent to the control unit 15.

[0020] The sensor cleaning unit 17 comprises an air flow path L4, an on-off valve 17A, a flow rate control 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 control valve 17B are arranged in the air flow path L4 in order of proximity to the measurement cell 11. The control unit 15 controls the opening and closing operation of the on-off valve 17A and the flow rate control operation of the flow rate control valve 17B. 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. Therefore, the present invention can suppress the adhesion of dirt to the dissolved oxygen sensor 14, and can reduce the frequency of maintenance.

[0021] 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.

[0022] 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 discharging the test water or cleaning water in the measurement cell 11 while maintaining a constant water level in the measurement cell 11.

[0023] The control unit 15 controls the operations of the test water supply unit 12 , the air supply unit 13 , the dissolved oxygen sensor 14 , the turbidity sensor 16 , the sensor cleaning unit 17 , and the cleaning water supply unit 18 .

[0024] 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 flowing through the measurement cell 11 to agitate it, thereby cleaning the inside of the measurement cell 11. During this cleaning, the control unit 15 inspects the dissolved oxygen sensor 14 by making the dissolved oxygen sensor 14 measure the dissolved oxygen concentration in the cleaning water and monitoring the measured value.

[0025] The control unit 15 also includes 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.

[0026] The control unit 15 may be, for example, a computer equipped with a data input unit that receives the measurement results of the dissolved oxygen sensor 14 and the turbidity sensor 16, a central processing unit, a memory device, a data output unit that outputs commands to the test water supply unit 12, the air supply unit 13, the sensor cleaning unit 17, and the 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. The test water supply unit 12, the air supply unit 13, the dissolved oxygen sensor 14, the turbidity sensor 16, the sensor cleaning unit 17, and the cleaning water supply unit 18 may be connected to the control unit 15 by wired or wireless lines, or via a network such as the Internet or a communication line such as a telephone line.

[0027] Furthermore, a computer-readable recording medium can be exemplified as a memory device that stores a computer program for realizing the functions of control unit 15. 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) inside a computer system that serves as a server or client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line.

[0028] Furthermore, various measurement results obtained by the dissolved oxygen sensor 14 and the turbidity sensor 16 may be stored in an external server in advance, and control may be performed by acquiring these results.

[0029] The first functional unit has a function of determining the amount of change in the oxygen consumption rate of the test water with time based on the dissolved oxygen concentration of the test water measured by the dissolved oxygen sensor 14 from the start of aeration to the end of aeration.

[0030] In addition, the first functional unit may use the dissolved oxygen sensor 14 to measure the dissolved oxygen concentration of the test water multiple times within the time from the start of aeration to the end of aeration, 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.

[0031] 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 divide this difference in oxygen consumption rate by the time difference between the start and end of measurement to determine the change in the oxygen consumption rate over time.

[0032] The second functional unit has the function 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 previously obtained.

[0033] The third functional unit has a function of determining the rate of change of turbidity over time at fixed intervals based on the turbidity of the test water from the start to the end of the standing still period using the turbidity sensor 16.

[0034] 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 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.

[0035] Next, the method for measuring the quality of wastewater according to this embodiment will be described with reference to FIG.

[0036] The method for measuring the quality of wastewater in this embodiment sequentially includes a test water supply step of supplying test water to the measurement cell 11, a first measurement step of measuring the dissolved oxygen concentration of the test water, a first calculation step of determining the time change in oxygen consumption rate from the dissolved oxygen concentration, and a first prediction step of predicting the BOD or COD of the test water.

[0037] In addition, the method for measuring the water quality of wastewater of this embodiment may, after completing the first measurement step, sequentially carry out a second measurement step in which the turbidity of the test water is measured, a second calculation step in which the time rate of change of turbidity at regular intervals is calculated from the turbidity, and a second prediction step in which the particle size distribution of turbidity contained in the test water is predicted.

[0038] Furthermore, in the method for measuring the quality of wastewater according to this embodiment, a cleaning step and an inspection step of the dissolved oxygen sensor 14 may be performed after the first measurement step or the second measurement step is completed.

[0039] Each stage will be explained below.

[0040] In 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 the 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.

[0041] 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 supply air from the air flow path L2 to the test water in the measurement cell 11 while adjusting the flow rate with the flow rate control valve 13B. 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, and may be 120 seconds. The control unit 15 issues a command to the air supply unit 13 to stop the air supply after the predetermined time has elapsed.

[0042] Furthermore, in the first measurement stage, in synchronization with the start of aeration, 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. The measurement of the dissolved oxygen concentration continues until the end of aeration. The measurement may be performed at regular intervals, for example, every 0.1 to 30 seconds, or may be every second. The number of measurements is not particularly limited, and may be, for example, 10 to 300 times, or may be 90 times. In this way, multiple measurements are performed from the start of aeration to the end of aeration. The measurement may also be started a predetermined time after the start of aeration, for example, 1 to 20 seconds after the start of aeration, or may be started 10 seconds later.

[0043] The dissolved oxygen concentration measured by the dissolved oxygen sensor 14 increases over time during aeration, but if the activity of the 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 the 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.

[0044] 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.

[0045] There are no particular limitations on the method for determining the time change in oxygen consumption rate, and for example, it may be performed by either the first method or the second method described below.

[0046] (First method) First, in the first measurement stage, the oxygen consumption rate is calculated based on multiple dissolved oxygen concentrations measured at regular intervals. The oxygen consumption rate at each measurement time is calculated using the following formula (1).

[0047] qO2=G v h(Cs-C)) …(1)

[0048] In equation (1), qO2 is the oxygen consumption rate (cm mgO2 / min), and G v is the amount of air supplied to 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.

[0049] 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 line is drawn based on this plot to show 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.

[0050] 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.

[0051] (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 the multiple dissolved oxygen concentration measurements taken at regular intervals. S and the dissolved oxygen concentration DO at the end of the measurement E Difference with (DO E -DO S ) is calculated. E -DO S ) by the time from the start to the end of the measurement (t2 - t1), the change in the oxygen consumption rate over time, DO E -DO S) / (t2-t1).

[0052] Next, in the first prediction stage, the second functional section of the control section 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 has been previously obtained.

[0053] 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 can be a 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.

[0054] When predicting COD or BOD, a relationship equation between COD or BOD and the time change in oxygen consumption rate is 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 the oxygen consumption rate of the test water obtained in the first calculation step into the relationship equation.

[0055] Below are some specific examples of COD and BOD predictions. FIG. 3 shows, as an example, the relationship between the BOD of the test water and the time change in the oxygen consumption rate. The BOD of the test water is a value measured in accordance with JIS K 0102:2019. The time change in the oxygen consumption rate was calculated by measuring the dissolved oxygen concentration of the test water during aeration using the water quality measurement system of this embodiment and using the first method described above. As shown in FIG. 3, the coefficient of determination R 2 is 0.50, which indicates that there is a certain correlation.

[0056] As an example, FIG. 4 shows the COD of the test water. Cr The relationship between the COD of the test water and the change in the oxygen consumption rate over time is shown. Cris a value measured in accordance with JIS K 0102:2019. The time change in the oxygen consumption rate 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 first method described above. As shown in Figure 4, the COD of the test water Cr and the coefficient of determination R between the time change in oxygen consumption rate 2 is 0.58, which indicates that there is a certain correlation.

[0057] FIG. 5 shows, as an example, the relationship between the BOD of the test water and the time change in the oxygen consumption rate. The BOD of the test water is a value measured in accordance with JIS K 0102:2019. The time change in the oxygen consumption rate was calculated by measuring the dissolved oxygen concentration of the test water during aeration using the water quality measurement system of this embodiment and using the second method described above. As shown in FIG. 5, the coefficient of determination R 2 is 0.44, which indicates that there is a certain correlation.

[0058] As an example, FIG. 6 shows the COD of the test water. Cr The relationship between the COD of the test water and the change in the oxygen consumption rate over time is shown. Cr is a value measured in accordance with JIS K 0102:2019. The time change in the oxygen consumption rate 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 Figure 6, the COD of the test water Cr and the coefficient of determination R between the time change in oxygen consumption rate 2 is 0.64, which indicates a certain correlation.

[0059] On the other hand, as a comparative example, Figure 7 shows the COD of the test water. Cr The relationship between the COD of the test water and the change in the oxygen consumption rate over time is shown. Cris a value measured in accordance with JIS K 0102:2019. The time change in the oxygen consumption rate 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 then calculating it using the first method described above. As shown in Figure 7, the time change in the oxygen consumption rate calculated from the dissolved oxygen concentration measured after aeration was completed and the COD of the test water Cr The coefficient of determination R 2 is 0.01, which indicates that there is no correlation.

[0060] Next, the second measurement stage, the second calculation stage, and the second prediction stage will be described. Note that the second measurement stage, the second calculation stage, and the second prediction stage may or may not be performed.

[0061] The second measurement stage begins immediately after the end of the first measurement stage. In the second measurement stage, the supply of air from the air supply unit 13 is stopped, and the test water is left standing still. Then, the control unit 15 issues a command to the turbidity sensor 16 to measure the turbidity of the test water in the standing state and transmit the measurement results to the control unit 15. The turbidity measurement is carried out continuously for a fixed period of time. The measurement time may be, for example, 300 to 1800 seconds, or may be 1430 seconds.

[0062] Next, in the second calculation stage, the third functional section of the control section 15 calculates the time change rate of the turbidity for each fixed time period from the turbidity of the test water obtained in the second measurement stage.

[0063] For example, the measurement time of the 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, the turbidity D at each time is calculated from the measurement data of the turbidity sensor 16. T0 , D T1 , D T2 , D T3 Then, the time rate of change of turbidity in each of the intervals T0 to T1, T1 to T2, and T2 to T3 is calculated.

[0064] The time rate of change of turbidity in the period T0 to T1 is (D T1 -D T0 ) / (T1-T0). The time rate of change of turbidity in the section T1 to T2 is (D T2 -D T1 ) / (T2-T1). The time rate of change of turbidity in the section T2 to T3 is (D T3 -D T2 ) / (T3-T2).

[0065] The position of the turbidity sensor 16 in the measurement cell 11 is fixed, and turbidity contained in the test liquid in a stationary state settles over time, so the turbidity measured by the turbidity sensor 16 decreases over time. According to Stokes' law, 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 interval T0-T1 can be said to suggest the settling velocity of turbidity particles with relatively large particle sizes. Furthermore, the time rate of change in turbidity in the interval T2-T3 can be said to suggest the settling velocity of turbidity particles with relatively small particle sizes. Furthermore, the time rate of change in turbidity in the interval T1-T2 can be said to suggest the settling velocity of turbidity particles with intermediate particle sizes.

[0066] Next, in the second prediction stage, the fourth functional section of the control section 15 predicts the particle size distribution of the 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.

[0067] The relationship between the previously obtained time rate of change in turbidity of the wastewater and the particle size distribution of the turbidity particles contained in the wastewater can be established, for example, by obtaining the time rate of change in turbidity for a certain period of time by performing the second measurement step and the second calculation step on the same wastewater, and then obtaining the relationship between the particle size distribution of the turbidity particles in the wastewater and the time rate of change in turbidity. In this case, the particle size distribution of the turbidity particles in the wastewater is a value measured by the scattered light method.

[0068] 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 relational equation between the particle size distribution of turbidity in wastewater and the time rate of change of turbidity are first determined, 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 the relational equation.

[0069] Next, the cleaning step will be described.

[0070] 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 start 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. The 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.

[0071] 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 manner, the dissolved oxygen sensor 14 is cleaned.

[0072] 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 in the measurement cell 11. The amount of air supplied in this case is adjusted to a flow rate that causes turbulent agitation of the cleaning water by controlling the flow rate adjustment valve 13B. This causes turbulent agitation of the cleaning water inside the measurement cell 11, removing foreign matter such as turbidity adhering to the inner wall of the measurement cell 11. The removed foreign matter is discharged from the measurement cell 11 with the flow of cleaning water. In this way, the measurement cell 11 is cleaned.

[0073] In the above explanation, an example has been described in which the dissolved oxygen sensor 14 is cleaned before the measurement cell 11 is cleaned, but the cleaning order is not limited to this, and the measurement cell 11 may be cleaned before the dissolved oxygen sensor 14 is cleaned.

[0074] Next, the inspection stage will be described.

[0075] 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 check its operation. If the measured value of the dissolved oxygen concentration is always constant, it can be said that the dissolved oxygen sensor 14 is functioning normally. On the other hand, if the measured value of the dissolved oxygen concentration 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.

[0076] As described above, according to the water quality measurement system and water quality measurement method of this embodiment, the time change in the oxygen consumption rate of the test water is determined based on the dissolved oxygen concentration obtained by the dissolved oxygen sensor 14, and the BOD or COD of the test water is predicted from the time change in the oxygen consumption rate. This makes it possible to predict COD or BOD without the long time required in the past, and therefore makes 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. [Explanation of symbols]

[0077] 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...measuring 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

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 measuring system according to claim 1 , further comprising a turbidity sensor that measures the turbidity of the test water in a stationary state after aeration has been completed.

3. 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.

4. The wastewater quality measuring system according to claim 1 , further comprising a sensor cleaning unit that supplies compressed air for cleaning to the dissolved oxygen sensor.

5. The wastewater quality measuring system according to claim 1 , further comprising a cleaning water supply unit that supplies cleaning water to the measuring 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; 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.

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 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. 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.

10. 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.

11. 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.

12. 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.

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