JPS6321297Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a water quality monitoring device, and its purpose is to provide a water quality monitoring device that can accurately monitor and control the quality of treated water by measuring the concentration distribution of low-concentration sludge. There is something to do.

The purpose of a sewage treatment plant is to treat the discharged water so that it does not cause water pollution in downstream water areas, and the quality of the treatment is evaluated based on the quality of the discharged water. BOD (biological oxygen demand) is often used as an evaluation item for treated water. By the way, there is a strong correlation between the BOD and SS (suspended solids) of effluent water in a treatment plant under relatively stable operating conditions, as shown in Figure 1. This indicates that the main cause of the BOD of the effluent is either the SS in the final settling tank that is not completely settled and flows out, or the sludge that has settled once but is thrown up by the water flow in the settling tank.

Therefore, as a water quality monitoring device, discharge control is performed by monitoring the settling state of sludge in the final settling tank, but instruments for measuring the settling state of sludge include a sludge interface meter or a sludge concentration distribution meter. . The sludge interface meter is an instrument that measures the sludge level in the final settling tank pit by using the attenuation of ultrasonic waves by sludge, and detects the position of the interface by following the detection end to the position of the sludge interface. A sludge concentration distribution meter measures the distribution of sludge concentration from the water surface to the bottom by moving the sensor up and down at a constant speed and in a constant cycle, recording changes in the amount of attenuation of ultrasonic waves during that time.

Figure 2 shows part of a typical sewage treatment process. The sewage 1 that has undergone preliminary treatment in the final settling tank is aerated in the aeration tank 2 to which activated sludge is added, and organic matter in the sewage is removed by the action of aerobic microorganisms.
The mixed solution of purified water and activated sludge from the aeration tank 2 is sent to the sedimentation tank 3 where it is mixed with purified water (supernatant water) 4 and activated sludge (sediment).
The purified water 4 is discharged as overflow water 6, and the activated sludge 5 is sent to the aeration tank 2 by the return sludge pump 7, and is sent to the initial settling tank by the excess sludge pump 8. The sludge interface meter (or sludge concentration distribution meter) 9 has its detection end 10 immersed in the sedimentation tank 3 and detects a position at a certain concentration (for example, 8000 ppm) as the sludge interface 51.
The concentration distribution of settled sludge is measured by driving the 0 up and down at a constant speed.

Therefore, it is possible to control the return sludge pump and surplus sludge pump using a sludge interface meter or a sludge concentration distribution meter to adjust the amount and concentration of settled sludge in the settling tank to appropriate values.

However, the lower limit of sludge concentration that can be measured with an ultrasonic sludge concentration distribution meter is about 500 to 1000 ppm. Furthermore, the state of low-concentration sludge suspended in supernatant water above the sludge interface cannot be detected by an ultrasonic sludge concentration distribution meter. In addition, the BOD of treated water quality is
This is caused by the outflow of SS on the order of ppm to several + ppm.

Therefore, for proper water treatment, it is necessary to measure the concentration and concentration distribution of minute SS components suspended in supernatant water.
It becomes necessary to monitor. Currently, there are no suitable process instruments to directly measure SS, and methods using turbidity meters are often used. Essentially, SS measures mass and turbidity measures opacity of light, so they are different.

However, in the case of treated water from a sewage treatment plant, the third
As shown in Fig. 4, a high correlation is obtained between the two. Figure 3 shows the relationship between the SS of the secondary treated water and the turbidity meter reading (white circles), and the relationship between the SS of the sand-filtered tertiary treated water using the secondary treated water as raw water and the turbidity meter reading. (black circle) is shown. Figure 4 shows the results of a test made by mixing treated water and final sedimentation sludge to create a simulated test water with a high SS concentration.

As mentioned above, turbidity is correlated with SS and BOD, and it is very important to measure the turbidity distribution of supernatant water in a sedimentation pond.

However, current sampling type turbidimeters are mainly commercially available as process instruments, and immersion type turbidimeters are mainly portable types. Furthermore, since direct current light (for example, tungsten lamp light emitted by a direct current power supply) is used as a light source, it is affected by stray light, and furthermore, since visible light is used, errors occur in the case of colored liquids.

By the way, if you measure the water discharged from the final sedimentation basin using a commercially available turbidity meter, you can obtain information about BOD based on the relationship shown in Figure 1, but you cannot obtain information about measures to prevent it. However, using the device of the present invention, this becomes possible. That is, in the settling state of sludge in the final settling tank, there is almost no SS at a water depth of 1 to 2 m, and the visually visible sludge interface is usually at a depth of 2 m or more. However, although methods that use ultrasonic waves can in principle measure concentrations of 500 to 1000 ppm or more, in reality they are not reliable.
The concentration is over 3000ppm. Therefore, if it is possible to know the distribution of SS or turbidity between water depths of 0 to 2 m or 0 to 3 m, it is currently possible to extract sludge from the final settling tank using signals from an ultrasonic sludge interface meter or concentration distribution meter. However, it is possible to control sludge extraction to minimize the SS overflow by using the signal from the device of the present invention. Furthermore, it is possible to investigate the relationship between the SS distribution at water depths of about 0 to 3 m and the treatment method, and there is a possibility that a more qualitatively improved treatment method can be elucidated. FIG. 5 shows a conceptual diagram when the water quality monitoring device of the present invention is applied to a final sedimentation tank. The mixed solution of activated sludge and purified water obtained in the aeration tank flows into the settling tank and is separated into supernatant water 11 and settled sludge 12, forming a sludge interface 12A. However, depending on the state of the sludge and the state of the flow within the sedimentation basin, sludge 13 that has not been completely settled may float and mix in the overflow water 15 that passes over the overflow plate 14. In such a sedimentation tank, in order to detect turbidity from suspended matter floating in supernatant water, a turbidity detection end 19 is connected by a wire 18 from a drive mechanism of a measurement unit 17 provided on the ground 16 side. The detection end 19 is suspended in water, and the detection end 19 is controlled to move up and down under suspension control by a drive mechanism. Further, the detection signal at the turbidity detection end 19 is taken into the measurement section 17 via the cable 20, and calculations for turbidity detection are performed.

Note that the speed of elevation of the detection end 19 is controlled at a slow speed (for example, 500 m/min) so as not to disturb the state of suspended matter in the test water and the state of the interface.
In addition, the measurement range of the turbidity detection end 19 is 0 to 10 ppm,
It is made to be about 0 to 100 ppm or 1000 ppm.

FIG. 6 shows a block diagram of the measuring section 17. The drive control section 21 indicated by a dashed line block is 22 to 25.
The detection end elevation control circuit 22 controls the operation of a drive motor 23, and the motor 23 drives the hoisting drum 24. The drum 24 raises and lowers the detection end 19 by winding or unwinding the wire 18.

The position of the detection end 19 is detected by the detector 25 from the rotation angle of the motor 23 or the drum 24, and this detection signal is used as a speed control signal of the control circuit 22 and is also sent to the indicator recorder 27 as the detection end position signal 26. be included. The indicator recorder 27 takes in the output of the calculator 29 which obtains the detection signal of the detection end 19 as the turbidity output 28, and records the turbidity distribution in the supernatant water as an indication based on the detection end position signal.

In addition, instead of controlling the detection terminals 19 to move up and down to indicate and record the turbidity distribution as described above, a plurality of detection terminals 19 are provided at regular intervals at positions at different water depths, and the signals from each detection terminal are sequentially captured. By doing so, it is possible to have a configuration in which the drive control section 21 is omitted.

FIG. 7 shows a block diagram of the turbidity detection terminal 19 and the arithmetic unit 29, in the case of a scattered light measurement method in which near-infrared light is used as a light source and this light source is modulated in an alternating current manner. The bottom surface of the case of the turbidity detection end 19 is made of transparent glass 30, and a light emitting diode 31 that is pulse-driven at a constant frequency and duty ratio is provided in the case so as to illuminate the suspended matter 13.
A light-receiving element 32 that converts the reflected light from light-to-electricity from light to electricity.
A light receiving element 33 that converts direct light from the light emitting diode 31 into an electrical signal is also provided. Light receiving element 32
The input light includes light emitted from the light emitting diode 31 that is scattered and reflected by the suspended object 13, as well as external light such as sunlight (DC type) and fluorescent lamp light (AC type), and its electrical output The signal is taken into the computing unit 29 as a waveform in which pulsating current is superimposed on the output waveform of the light emitting diode 31, as shown in the figure.

The arithmetic system of the arithmetic unit 29 includes a filter circuit 34, a rectifier circuit 35, and an amplifier 36, and by passing the electric signal from the light receiving element 32 through the filter circuit 34, the DC component and the power frequency are removed, as well as their harmonic components. As a result, a pulse signal (shown in the figure) proportional to the pulse light output level of the light emitting diode 31 is extracted. This signal is rectified by the rectifier circuit 35 and converted into direct current, and amplified by the amplifier 36 to output turbidity.
8 and is sent to the indicating instrument side.

The drive system of the arithmetic unit 29 includes a light emission output control circuit 37 for the light emitting diode 31, and this control circuit 37
Negative feedback control is performed in which the pulse output level for driving the light emitting diode 31 is controlled to be constant using the amount of light received by the light emitting element 33 as a feedback amount.

The features of this turbidity detector are (1) Since it uses near-infrared light as the detection light, it is completely unaffected by the coloration of the sample water, which is a problem with general turbidity meters, and outputs proportional to SS. can be obtained.

(2) The influence of stray light can be removed by measuring the light emitted from the light source in a blinking state and extracting only the alternating current component in the output of the light receiving element.

This advantage is especially important in this device because the influence of sunlight changes depending on day and night or the depth position of the detection end.

(3) Since a near-infrared light emitting diode is used, the life is long, and since the light output of the light emitting source is controlled by a comparison light receiving element, stable measurements can be performed over a long period of time.

Although the case where a scattered light type turbidity detector is used has been described above, it is also possible to use other detection methods, for example, a transmitted light measurement type turbidity meter as shown in FIG.

In FIG. 8, reference numeral 38 is a light emitting unit that has light emitting diodes 31 and 33 in FIG. Water turbidity is detected. The light receiving element 32 shown in FIG. 7 is provided in the light receiving section 39. As shown in FIG.

Although the above description has been made regarding the case where the present invention is applied to the final sedimentation tank of a sewage treatment plant, it is of course applicable to a water quality monitoring device that performs coagulation sedimentation using a primary sedimentation tank or the addition of chemicals.

As described above, the water quality monitoring device according to the present invention is
By measuring the distribution of sludge floating in low-concentration sample water such as supernatant water from a sedimentation tank, it is possible to predict deterioration in the quality of effluent water due to sludge overflow and to appropriately control the quality of effluent water before discharge. By controlling the flow of treated water within the pond, efficient control of treated water becomes possible. In addition, since the turbidity detector uses a turbidity measurement method that modulates near-infrared light in an alternating current manner and removes extraneous light, measurement accuracy is not affected by colored sample water and extraneous light does not affect the measurement accuracy. High-precision measurement is possible without being affected by the strength of light, and since semiconductor elements such as light emitting diodes can be used, long-life measuring instruments can be realized.

[Brief explanation of the drawing]

Figure 1 shows the relationship between SS and BOD of treated water.
Figure 2 is a diagram illustrating the sewage treatment process, Figures 3 and 4 are diagrams showing the relationship between SS and turbidity, Figure 5 is a conceptual diagram of the water quality measurement system in the water quality monitoring device of the present invention, and Figure 6 is a diagram illustrating the sewage treatment process. 5 is a block diagram of the measuring section 17 in FIG. 5, FIG. 7 is a block diagram of the turbidity detector in FIG. 5, and FIG. 8 is another configuration diagram of the turbidity detector. 11...Supernatant water, 12...Sludge, 13...Sludge, 17...Measurement section, 19...Turbidity detection end, 21
... Drive control section, 22 ... Elevation control circuit, 23 ...
... Motor, 24 ... Drum, 25 ... Position detector, 27 ... Indication recorder, 29 ... Turbidity calculator,
31... Light emitting diode, 32, 33... Light receiving element, 34... Filter circuit, 35... Rectifier circuit,
36...Amplifier, 37...Light emission output control circuit, 3
8... Light emitting section, 39... Light receiving section.

Claims (1)

[Scope of utility model registration request] a detection end for irradiating treated water with blinking near-infrared light and detecting reflected light or transmitted light in the treated water; and means for arranging this detection end in supernatant water of a sedimentation tank at a plurality of water depth positions; A computing unit that controls the emission intensity of the near-infrared light to a certain extent and extracts an alternating current component from the light detection signal, and a supernatant water turbidity distribution for each water depth is determined from the output of the computing unit for the water depth position of the detection end. A water quality monitoring device comprising means for monitoring the quality of treated water and controlling inflow and discharge based on the correlation between turbidity distribution and suspended solids in supernatant water or biological oxygen demand.