Optical measurement device and optical measurement method

Abstract

To provide an optical measurement device capable of accurately acquiring optical measurements over a long time period using a simple mechanism.SOLUTION: An optical measurement device 3 is provided, comprising a nozzle 30 for allowing wastewater to flow downward to the atmosphere, and an optical sensor 35 configured to irradiate the wastewater flowing down from the nozzle 30 with light to acquire optical measurements.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an optical measurement device and an optical measurement method for obtaining optical measurement values of sewage.

Background Art

[0002] In order to appropriately operate and manage sewage treatment in various facilities such as sewage treatment facilities and water purification facilities, it is necessary to accurately grasp the properties of sewage (for example, color tone, turbidity, transparency, concentration of suspended substances, and aggregation state of suspended substances). Therefore, conventionally, an optical measurement device has been used to obtain optical measurement values, and numerical analysis values indicating the properties of sewage have been calculated from the optical measurement values. For example, Patent Document 1 describes a coagulation method in which an optical measurement value of sewage discharged from a stirrer is obtained using an optical measurement device, and an appropriate injection rate of a coagulant is determined based on a numerical analysis value calculated from the obtained optical measurement value.

[0003] In this coagulation method, in order to obtain an optical measurement value, a pair of transparent windows are provided in a pipe through which the stock solution discharged from the stirrer flows, and the optical measurement device includes a light projecting unit that irradiates light toward one transparent window and a photodetector that receives the light coming out of the other transparent window. The pair of transparent windows function as measurement windows (light transmission parts) of the optical measurement device.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a pipe provided with a light transmission part of an optical measurement device such as a pair of transparent windows, sewage containing foreign matters such as flocs formed by being mixed with a flocculant by a stirrer and surplus flocculant not used for floc formation flows. Therefore, the light transmission part may be contaminated by foreign matters. In this case, it becomes difficult for the optical measurement device to obtain an accurate optical measurement value. Therefore, it is necessary to clean the light transmission part regularly.

[0006] In order to clean the light transmission part, the optical measurement device must be stopped, which also increases the burden on the operator. Therefore, the cleaning frequency of the light transmission part is an important issue. In addition, in order to reduce the burden on the operator, if a mechanism that can automatically clean the light transmission part is provided in the optical measurement device, the optical measurement device becomes complicated and the manufacturing cost increases.

[0007] Therefore, an object of the present invention is to provide an optical measurement device and an optical measurement method that can accurately measure an optical measurement value for a long period of time with a simple mechanism.

Means for Solving the Problems

[0008] In one aspect, an optical measurement device is provided, which includes a nozzle for flowing sewage downward into the atmosphere, and an optical sensor for irradiating light onto the sewage flowing down from the nozzle to obtain an optical measurement value.

[0009] In one aspect, the nozzle includes a nozzle body in which a flow path of the sewage is formed, and a discharge part in which a discharge flow path of the sewage connected to the tip of the flow path of the sewage is formed. The discharge flow path has a diameter smaller than the diameter of the flow path. In one aspect, the diameter of the discharge flow path is in the range of 5 to 30 mm. In one aspect, the flow rate of the sewage flowing down from the nozzle into the atmosphere is in the range of 1 to 10 L / min, or the ratio of the flow rate of the sewage to the cross-sectional area of the discharge port of the nozzle is 1 cm 2 per 0.75 to 7.5 L / min. In one aspect, the optical sensor is disposed near the discharge port of the nozzle and irradiates the sewage immediately after being discharged from the nozzle with light.

[0010] In one aspect, there is provided an optical measurement method in which sewage is caused to flow downward from a nozzle into the atmosphere, and the sewage that has flowed down is irradiated with light from an optical sensor to obtain an optical measurement value.

Advantages of the Invention

[0011] The optical measurement device can obtain an optical measurement value with a simple mechanism of directly irradiating the sewage flowing down from the nozzle with light. That is, the light transmission part contaminated by foreign substances in the sewage does not exist in the sensing zone of the optical sensor. As a result, the cleaning operation conventionally required to obtain an appropriate optical measurement value does not occur, so the optical measurement device can stably obtain an optical measurement value for a long period of time.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an example of a sewage treatment apparatus in which an optical measurement apparatus according to an embodiment is arranged. The sewage treatment apparatus shown in FIG. 1 is a coagulation apparatus for treating sludge discharged from a wastewater treatment facility, a water purification treatment facility, or the like. The optical measurement apparatus described later is used to obtain an optical measurement value for calculating a numerical analysis value indicating the properties of sewage (for example, color tone, turbidity, transparency, concentration of suspended substances, and aggregation state of suspended substances). In the present embodiment, an appropriate injection rate of a coagulant is determined based on a numerical analysis value obtained by numerically analyzing the optical measurement value.

[0014] Hereinafter, a coagulation apparatus for treating a stock solution containing suspended substances, which is an example of sewage, will be described as an example of a facility provided with an optical measurement apparatus. However, the optical measurement apparatus according to the present embodiment may be arranged in other facilities for treating sewage. For example, the sewage to be treated may be sludge discharged from a wastewater treatment facility, a water purification treatment facility, or the like, wastewater in a wastewater treatment facility, or raw water in a water purification treatment facility. The sludge may be either organic sludge or inorganic sludge.

[0015] Examples of organic sludge include organic sludge generated in sewage treatment, night soil treatment, and wastewater treatment of various industries. More specifically, examples of organic sludge include primary sedimentation tank sludge, excess sludge, anaerobic digestion sludge, aerobic digestion sludge, night soil sludge, septic tank sludge, digestion detachment liquid, coagulation sedimentation sludge, and the like. Organic sludge may contain inorganic substances.

[0016] Examples of inorganic sludge include inorganic sludge generated in water purification treatment, drainage treatment of construction works, and wastewater treatment of various industries. Here, the sludge generated in water purification treatment refers to sludge discharged from sedimentation tanks, sludge discharge tanks, thickening tanks, etc. in a water purification treatment facility. Inorganic sludge may contain organic substances.

[0017] Examples of wastewater in wastewater treatment facilities include wastewater from various industries such as sewage, the food industry, the drinking water industry, the chemical industry, and the machinery industry. Examples of raw water in water purification facilities include river water, lake water, and groundwater.

[0018] Furthermore, the wastewater to be treated may be water prepared during the treatment process such as wastewater treatment or water purification treatment. Examples of wastewater in wastewater treatment include wastewater with adjusted pH, wastewater injected with an inorganic flocculant, wastewater injected with an organic coagulant, wastewater injected with a metal chelating agent, and the like. Also, examples of wastewater in water purification treatment include raw water with adjusted pH, raw water injected with an inorganic flocculant, and the like.

[0019] The agglomeration device shown in Fig. 1 has a configuration in which a stock solution storage tank 10, a stirrer 1, and an optical measurement device 3 are connected in series in this order. The stock solution storage tank 10 stores a stock solution (wastewater) containing suspended substances. The stirrer 1 includes a stirring tank 2 to which a stock solution containing suspended substances is supplied, a stirring blade 8 for stirring the stock solution containing suspended substances, and a motor 9 as a driving device for rotating the stirring blade 8. A supply source pipe 18 extending from the stock solution storage tank 10 is connected to the stirring tank 2 of the stirrer 1, and a supply device 7 for supplying the stock solution stored in the stock solution storage tank 10 to the stirring tank 2 at a predetermined flow rate is arranged in the supply source pipe 18. The supply device 7 is, for example, a pump, a valve, or a combination of a pump and a valve.

[0020] In one embodiment, a line mixer may be used as the stirrer 1. A line mixer is a mixer incorporated into a pipe. The advantage of a line mixer is that since the mixer is sealed, if there are two pumps, namely a stock solution pump and a flocculant pump, upstream of the line mixer, the stock solution can be sent downstream of the line mixer. On the other hand, in the case of the stirrer 1 with the stirring blade 8 installed in the stirring tank 2, the upper part of the stirring tank may be open. In this case, in order to send the liquid downstream of the stirrer, in addition to the stock solution pump and the flocculant pump upstream of the stirrer, another pump or a device equivalent to a pump is required. Therefore, usually, it is common not to install a pump and to send the liquid downstream by using the height difference.

[0021] In this embodiment, the stirrer 1 is configured as a high-speed stirrer that performs high-speed stirring with the rotational speed of the stirring blade 8 set in the range of 300 to 5000 min -1 By this high-speed stirring, the flocculant is instantaneously dispersed in the stock solution, and the flocculant is efficiently and uniformly mixed with the stock solution. As a result, the suspended substances contained in the stock solution are efficiently flocculated.

[0022] In the stirrer 1, it is important to rotate the stirring blade at a rotational speed set in the range of 300 to 5000 min -1 to perform high-speed stirring of the stock solution containing suspended substances into which the flocculant has been injected. Preferably, the rotational speed of the stirring blade 8 is set in the range of 400 to 1500 min -1 More preferably, the rotational speed of the stirring blade is set in the range of 500 to 1200 min -1 of the range.

[0023] When performing such high-speed stirring, since a high stress is applied to the stock solution into which the flocculant has been injected, if the flocculant is not injected at an appropriate injection rate, the flocs will be broken before they grow. Therefore, if the injected flocculant does not have an appropriate injection rate, the flocs will not grow properly. In this embodiment, the control device described later acquires an optical measurement value from the optical measurement device 3, and further determines whether the flocs are growing properly from the numerical analysis value obtained by numerically analyzing the optical measurement value. As a result, the appropriate injection rate of the flocculant can be determined with high accuracy. As a result, the amount of flocculant used can be reduced. In addition, even without the experience and intuition of the operator, the injection rate of the flocculant can be appropriately controlled. Furthermore, even if the properties of the stock solution containing suspended substances (for example, the concentration of suspended substances in the stock solution) change, the injection rate of the flocculant can be appropriately controlled.

[0024] The rotation speed of the stirring blade 8 is adjusted within the range of 300 to 5000 min-1 based on the type of the stock solution containing suspended substances (e.g., wastewater, sludge, etc.), the properties of the stock solution (e.g., SS (Suspended Solids) concentration, viscosity, etc.), and the type of the flocculant (e.g., inorganic flocculant, organic coagulant, polymer flocculant, etc.). The flocculant injected into the stock solution containing suspended substances may be injected into the stirring tank 2 or into the supply pipe 18 arranged upstream of the stirring tank 2. -1

[0025] In this embodiment, a flocculant storage tank 11 for storing the flocculant is provided, and a flocculant supply pipe 26 extending from the flocculant storage tank 11 is connected to the stirring tank 2. A flocculant injection device 4 is arranged on the flocculant supply pipe 26. The flocculant injection device 4 is a device that injects the flocculant into the stock solution containing suspended substances at a predetermined injection rate. The flocculant injection device 4 is, for example, a pump, or a valve, or a combination of a pump and a valve.

[0026] In this flocculation device, the stock solution containing suspended substances is supplied from the stock solution tank 10 to the stirring tank 2 by the supply device 7. The flocculant is supplied to the stirring tank 2 by the flocculant injection device 4. In the stirring tank 2, the stock solution and the flocculant are mixed at a high rotation speed with the rotation speed of the stirring blade 8 set within the range of 300 to 5000 min-1, thereby forming flocs of the suspended substances. Note that depending on the injection rate of the flocculant, flocs of the suspended substances may not be formed. That is, in the stirrer 1, the stirring blade 8 is rotated at a high speed to form flocs of the suspended substances, but depending on the injection rate of the flocculant, flocs of the suspended substances may not be formed. -1

[0027] The discharge pipe 28 through which the stock solution discharged from the stirrer 1 flows is connected to the stirring tank 2. In the present embodiment, the optical measuring device 3 is arranged in the discharge pipe 28. The optical measuring device 3 is a device for irradiating light onto the stock solution containing the flocs formed by the stirrer 1 to obtain an optical measurement value. In the present embodiment, the optical measuring device 3 is a device capable of measuring the intensity of the transmitted light coming out of the stock solution containing the flocs. The optical measuring device 3 may be a device capable of measuring the transmittance, scattered light intensity, diffracted light intensity, diffracted / scattered light intensity, absorbance, reflected light intensity, etc.

[0028] Figure 2 is a schematic diagram showing the configuration of the optical measuring device shown in Figure 1. Figure 3 is an enlarged view schematically showing the vicinity of the nozzle shown in Figure 2. As shown in Figure 2, the discharge pipe 28 is divided into a primary side discharge pipe 28A connected to the inlet of the optical measuring device 3 and a secondary side discharge pipe 28B connected to the outlet of the optical measuring device 3. The optical measuring device 3 includes a nozzle 30 connected to the end of the primary side discharge pipe 28A and a tray (liquid receiving part) 32 connected to the tip of the secondary side discharge pipe 28B. The nozzle 30 is a component that causes the stock solution flowing through the primary side discharge pipe 28A to flow downward, and has a cylindrical shape. The tray 32 is arranged below the nozzle 30 and spaced apart from the nozzle 30. The tray 32 is a component for receiving the stock solution flowing down from the nozzle 30, and has a funnel shape in the illustrated example.

[0029] In the present embodiment, the nozzle 30 and the tray 32 are arranged along the vertical direction, and the central axis of the nozzle 30 coincides with the central axis of the tray 32. An open space through which the stock solution flows down is formed between the nozzle 30 and the tray 32. Therefore, the stock solution flows down into the atmosphere from the nozzle 30 toward the tray 32.

[0030] The optical measurement device 3 further includes an optical sensor 35 that irradiates the stock solution flowing down from the nozzle 30 with light to obtain an optical measurement value. In the present embodiment, the optical sensor 35 includes a light source (light projecting unit) 35a that irradiates the stock solution with light, and a photodetector (light receiving unit) 35b that detects the light coming out of the stock solution, and is an optical sensor that measures the intensity of the transmitted light that has reached the photodetector 35b. The light irradiated from the light source 35a and transmitted through the stock solution containing the flocs is detected by the photodetector 35b. The intensity of this transmitted light is measured for a predetermined period of time, and the measured intensity of the transmitted light is used as the optical measurement value.

[0031] The measurement of the intensity of the transmitted light, which is the optical measurement value, is performed once or multiple times while changing the injection rate of the flocculant, whereby at least one optical measurement value is obtained. The intensity of the transmitted light detected by the photodetector 35b is sent to the numerical analysis device 5 described later after being stored in the data logger 50. The numerical analysis value calculated by the numerical analysis device 5 is sent to the control device 6, and the control device 6 determines an appropriate injection rate of the flocculant based on the numerical analysis value. The data logger 50, the numerical analysis device 5, and the control device 6 may be provided separately. Alternatively, the data logger 50 and the numerical analysis device 5 may be incorporated into the control device 6 configured as one computer or one programmable logic controller (e.g., a sequencer).

[0032] Next, with reference to FIGS. 4(a) and 4(b), a measurement example of the intensity of the transmitted light of the stock solution containing the suspended matter by the optical measurement device 3 will be described. FIG. 4(a) shows a measurement example of the intensity of the transmitted light when no flocs are formed in the stock solution because the injection rate of the flocculant is not appropriate, and FIG. 4(b) shows a measurement example of the intensity of the transmitted light when flocs are formed in the stock solution because the injection rate of the flocculant is appropriate. In FIGS. 4(a) and 4(b), the horizontal axis represents the measurement time, and the vertical axis represents the intensity of the transmitted light.

[0033] As shown in Fig. 4(a), when flocs are not formed in the stock solution, the light irradiated from the light source 35a is blocked by the suspended substances and hardly reaches the photodetector 35b. As a result, the measured transmitted light intensity changes with time at a low value. On the other hand, when flocs are formed in the stock solution, the suspended substances are aggregated as flocs. Therefore, as shown in Fig. 4(b), during the measurement of the transmitted light intensity, there are a time when the light irradiated from the light source 35a is blocked by the flocs and does not reach the photodetector 35b, and a time when the light reaches the photodetector 35b through the gaps of the flocs. As a result, a plurality of peaks of the transmitted light intensity are measured. These multiple peaks are used in the numerical analysis described later.

[0034] Examples of the light source 35a include various lamps (such as mercury lamps, xenon lamps, krypton lamps, metal halide lamps, halogen lamps, etc.), various lasers (such as solid lasers, semiconductor lasers, liquid lasers, gas lasers, etc.), and various LEDs. Since an LED is a light source that can irradiate relatively high-intensity light among commercially available optical sensors, the light source 35a is preferably an LED. Examples of the photodetector 35b include CCDs, photodiodes, phototransistors, photomultiplier tubes, photoconductive elements, infrared optical sensors, and CMOSs. In any case, commercially available products can be used as the optical sensor 35.

[0035] In this embodiment, the optical sensor 35 can obtain an optical measurement value by a simple mechanism of directly irradiating light on the stock solution (sewage) flowing down from the nozzle 30. That is, there is no light transmission part contaminated by flocs formed by mixing with the flocculant by the stirrer and foreign substances such as the excess flocculant not used for the formation of the flocs in the sensing zone of the optical sensor 35. As a result, since the cleaning operation conventionally required to obtain an appropriate optical measurement value does not occur, the optical sensor 35 can stably obtain an optical measurement value for a long period of time.

[0036] In order for the optical sensor 35 to obtain appropriate optical measurement values, it is preferable that the stock solution flowing down from the nozzle 30 is rectified (i.e., laminar flow). In order to effectively rectify the stock solution, the nozzle 30 according to the present embodiment includes a nozzle body 30a extending in the vertical direction and a discharge portion 30b connected to the tip of the nozzle body 30a. The end of the nozzle body 30a is connected to the primary side discharge pipe 28A. The nozzle body 30a has a stock solution flow path 30c formed therein. The discharge portion 30b has a discharge flow path 30d formed therein, and the discharge flow path 30d is connected to the flow path 30c of the nozzle body 30a. The central axis of the discharge flow path 30d coincides with the central axis of the flow path 30c.

[0037] When viewed in a cross-section perpendicular to the central axis of the nozzle 30, the flow path 30c and the discharge flow path 30d have a circular shape. Further, the discharge flow path 30d has a diameter d2 smaller than the diameter d1 of the flow path 30c. That is, the discharge portion 30b functions as a reduced-diameter portion with respect to the nozzle body 30a.

[0038] According to the experiments of the inventors, it has been found that the nozzle 30 composed of the nozzle body 30a and the discharge portion 30b has a dramatically improved rectifying effect on the stock solution compared to the nozzle 30 composed only of the nozzle body 30a (i.e., the discharge portion 30b is omitted). Therefore, the nozzle 30 is preferably composed of a nozzle body 30a and a discharge portion 30b that functions as a reduced-diameter portion with respect to the nozzle body 30a.

[0039] Furthermore, according to the experiments of the inventors, it has been found that the cross-sectional shape of the discharge flow path 30d (i.e., the cross-sectional shape perpendicular to the central axis of the discharge flow path 30d) has the highest rectifying effect on the stock solution when it is circular. It has also been found that even if the longitudinal length L of the discharge portion 30b corresponding to the length of the discharge flow path 30d is short, it does not have much influence on the rectifying action of the stock solution flowing down from the nozzle 30. For example, even when the longitudinal length L of the discharge portion 30b is 3 cm, it has been found that the stock solution flowing down from the nozzle 30 is rectified equally compared to the case where a nozzle with a length L of 30 cm is used.

[0040] The flow rate of the stock solution flowing through the nozzle 30 also affects the rectifying effect of the stock solution. Generally, the greater the flow rate of the stock solution flowing through the discharge part 30b of the nozzle 30, the more improved the rectifying effect of the stock solution. That is, by reducing the inner diameter of the discharge part 30b (the diameter of the discharge flow path 30d), the flow rate of the stock solution flowing through the discharge part 30b can be increased, and thereby it is preferable to improve the rectifying effect of the stock solution. Therefore, by using a PVC pipe with a nominal diameter of 13A (inner diameter of 13 mm), which has the smallest inner diameter among commercially available PVC pipes, for the discharge part 30b, a nozzle 30 with a high rectifying effect at low cost can be provided.

[0041] In addition, if the inner diameter of the discharge part 30b is made too small, depending on the properties (size, shape, viscosity, etc.) of the flocs formed in the stock solution, there is a risk that the discharge part 30b will become clogged with flocs. Therefore, the inner diameter of the discharge part 30b should be selected with attention not only to the flow rate of the stock solution but also to the properties of the flocs. For example, the inner diameter of the discharge part 30b may be 5 mm or more, or may be 10 mm or more. Generally, since the diameter of the formed flocs often falls within the range of several mm to a dozen or so mm, it is preferable that the inner diameter of the discharge part 30b be 13 mm or more. Among commercially available PVC pipes, in addition to the pipe with a nominal diameter of 13A, pipes with nominal diameters of 16A, 20A, 25A, or 30A can also be preferably used.

[0042] The stock solution immediately after being discharged from the nozzle 30 is the most rectified. Therefore, as shown in FIGS. 2 and 3, it is preferable to arrange the optical sensor 35 in the vicinity of the discharge port of the nozzle 30. In this case, the optical sensor 35 can irradiate the stock solution immediately after being discharged from the nozzle 30 with light and acquire an optical measurement value.

[0043] As shown in FIG. 2, the optical measurement device 3 may have a box 38 that surrounds the nozzle 30 and the tray 32. The stock solution discharged from the nozzle 30 flows down in the air until it reaches the tray 32. The box 38 prevents the odor of the stock solution from diffusing into the surroundings. Further, in the embodiment shown in FIG. 2, the box 38 surrounds not only the nozzle 30 and the tray 32 but also the optical sensor 38. With such a configuration, it is possible to eliminate disturbances that affect optical measurement values such as natural light and wind.

[0044] Returning to FIG. 1, a numerical analysis device 5 is electrically connected to the optical measurement device 3, and a control device 6 is connected to the numerical analysis device 5. The numerical analysis device 5 may be incorporated in the control device 6. Further, the control device 6 is connected to the flocculant injection device 4.

[0045] The optical measurement value obtained from the optical measurement device 3 is sent to the numerical analysis device 5. The numerical analysis device 5 numerically analyzes the optical measurement value to obtain a numerical analysis value. The obtained numerical analysis value is sent to the control device 6. The control device 6 determines an appropriate injection rate of the flocculant based on the numerical analysis value.

[0046] Examples of the numerical analysis value include the average value, variance, standard deviation, peak area, peak height, etc. of the optical measurement value. The variance of the optical measurement value is a value obtained by statistically analyzing the optical measurement value, and is a quantity indicating the degree of dispersion of the distribution of the optical measurement values obtained during a predetermined measurement time. The standard deviation is the positive value of the square root of the variance. The peak area is the area of the region surrounded by the curve drawn by plotting the optical measurement values obtained during a predetermined measurement time and the reference line (for example, the baseline) on a graph where the vertical axis represents the optical measurement value and the horizontal axis represents the measurement time. The peak area corresponds to, for example, the area of the hatched region in FIG. 4(b). The peak height is the height from the horizontal axis of the peak of the curve drawn by plotting the optical measurement values obtained during a predetermined measurement time on a graph where the vertical axis represents the optical measurement value and the horizontal axis represents the measurement time.

[0047] The number of optical measurement values equal to or greater than a certain threshold, or the number of optical measurement values equal to or less than a certain threshold, may be used as a numerical analysis value. In the numerical analysis device 5, SS concentration, turbidity, chromaticity, floc particle size, etc. may be calculated from the optical measurement values and used as numerical analysis values. Here, the floc particle size means the diameter of the floc when the floc is spherical. When the floc is not spherical, the floc particle size means the Stokes diameter or the particle size measured by various measurement methods. The floc particle size may be the average particle size of the flocs. Examples of the average particle size include the arithmetic mean diameter, the maximum diameter, and the median diameter. Also, the average particle size may be based on the number, mass, or volume.

[0048] As a method for calculating the SS concentration and turbidity from the optical measurement values, known methods such as the transmitted light measurement method can be used. As a method for calculating the chromaticity from the optical measurement values, known methods such as the transmitted light measurement method can be used. As a method for calculating the floc particle size from the optical measurement values, known methods such as the laser diffraction / scattering method and the method of image analysis of an image taken with a camera can be used. The floc particle size may be the average floc particle size or the particle size distribution of the floc particle size. A commercially available measuring device that can perform optical measurement and calculate SS concentration, turbidity, chromaticity, floc particle size, etc. from the obtained optical measurement values can be used.

[0049] The control device 6 determines an appropriate injection rate of the flocculant from at least one numerical analysis value obtained by performing at least once the injection of the flocculant into the stock solution, the stirring (high-speed stirring) of the stock solution, the acquisition of optical measurement values, and the numerical analysis based on the optical measurement values. That is, the control device 6 injects the flocculant into the stock solution containing the suspended substances, stirs the stock solution to form flocs of the suspended substances, performs optical measurement on the stirred stock solution, numerically analyzes the obtained optical measurement values to obtain numerical analysis values. Further, the control device 6 determines whether the injection rate of the flocculant is appropriate based on the obtained numerical analysis values. If the injection rate is not appropriate, the control device 6 changes the injection rate of the flocculant, and repeats stirring, optical measurement, and numerical analysis again to determine an appropriate injection rate. Note that depending on the injection rate of the flocculant, flocs of the suspended substances may not be formed.

[0050] As a method for determining an appropriate flocculant injection rate, a plurality of preset injection rates may be used. The control device 6 injects the flocculant into the sewage containing the suspended substances at the preset injection rate, stirs the sewage to form flocs of the suspended substances, performs optical measurement on the stirred sewage, numerically analyzes the obtained measurement values to obtain numerical analysis values. This is repeated for each of the plurality of preset injection rates. The control device 6 compares the plurality of numerical analysis values obtained at each of the plurality of preset injection rates. In one embodiment, the injection rate at which the maximum value or the minimum value is obtained is determined as the appropriate injection rate. In other embodiments, the average value of the injection rate at which the largest numerical analysis value is obtained and the injection rate at which the second largest numerical analysis value is obtained may be used as the appropriate injection rate, or the average value of the injection rate at which the smallest numerical analysis value is obtained and the injection rate at which the second smallest numerical analysis value is obtained may be used as the appropriate injection rate.

[0051] In still other embodiments, the control device 6 plots a plurality of numerical analysis values at a plurality of preset injection rates on a graph with the vertical axis representing the numerical analysis values and the horizontal axis representing the injection rate of the flocculant, calculates an approximate expression showing the relationship between the plurality of injection rates and the plurality of numerical analysis values, and determines an appropriate injection rate of the flocculant based on the obtained approximate expression. For example, the injection rate at which the peak value of the numerical analysis value is obtained can be calculated from the approximate expression, and the obtained injection rate can be set as the appropriate injection rate of the flocculant.

[0052] The flow rate of the stock solution flowing through the nozzle 30, that is, the flow rate of the stock solution discharged from the nozzle 30, affects the measurement result of the optical measurement value by the optical sensor 35. For example, if the flow rate of the stock solution discharged from the nozzle 30 is too small, the flow of the stock solution is not stable and an accurate measurement result cannot be obtained. On the other hand, if the flow rate of the stock solution discharged from the nozzle 30 is too large, the speed of the flock passing through the sensing zone of the optical sensor 35 exceeds the processing performance of the optical sensor 35, and again, an accurate measurement result cannot be obtained.

[0053] Therefore, the inventors changed the injection rate of the flocculant and the flow rate of the stock solution discharged from the nozzle 30, measured the optical measurement value, numerically analyzed the obtained optical measurement value, and conducted an experiment to confirm whether the appropriate flocculant injection rate determined based on the obtained numerical analysis value matches the appropriate flocculant injection rate determined by the beaker test. In the experiment, a predetermined flocculant was injected into a plurality of sludges at a plurality of injection rates, and then each sludge into which the flocculant was injected was stirred at a rotation speed of the stirring blade of 888 min -1 for a predetermined time. Then, light was irradiated from the light source 35a of the optical sensor 35 onto the stirred sludge flowing down from the nozzle 30 composed of a nozzle body 30a having an inner diameter of 20 mm and a discharge part 30b having an inner diameter of 13 mm to obtain an optical measurement value. Further, the obtained optical measurement value was numerically analyzed to determine an appropriate injection rate of the flocculant.

[0054] FIG. 5(a) is a graph showing an example of experimental results, and FIG. 5(b) is a graph showing another example of experimental results. In FIGS. 5(a) and 5(b), the vertical axis represents the numerical analysis value, and the horizontal axis represents the injection rate of the flocculant. The experimental results shown in the graph of FIG. 5(a) are the experimental results when the flow rate of the stock solution flowing down from the nozzle 30 is set to 0.98 L / min. The experimental results shown in the graph of FIG. 5(b) are the experimental results when the flow rate of the stock solution flowing down from the nozzle 30 is set to 1.47 L / min.

[0055] The plurality of curves drawn in FIGS. 5(a) and 5(b) respectively correspond to the plurality of calculated numerical analysis values. More specifically, the plurality of curves drawn in FIGS. 5(a) and 5(b) respectively correspond to the average value, maximum value, minimum value, and variance of the optical measurement values, and the number of optical measurement values equal to or greater than a predetermined threshold value among the plurality of numerical analysis values. In the graphs of both FIGS. 5(a) and 5(b), it is shown that all the numerical analysis values were judged to be appropriate at the same flocculant injection rate, and this flocculant injection rate was consistent with the flocculant injection rate judged to be appropriate by the beaker test. Therefore, it was found that numerical analysis values capable of determining an appropriate flocculant injection rate can be calculated from the optical measurement values obtained by the optical measurement device 3 according to the above-described embodiment when the flow rate of the stock solution is 0.98 L / min and when the flow rate of the stock solution is 1.47 L / min.

[0056] In the experiment, it was judged that when the flow rate of the stock solution became smaller than 0.98 L / min, the flow of the stock solution flowing down from the nozzle 30 became unstable and accurate measurement results could not be obtained. Also, it was found that when the flow rate of the stock solution became larger than 10 L / min, it became difficult for the optical sensor 35 to detect the flocs. Therefore, from the viewpoint of ensuring that the optical sensor 35 detects the flocs, the flow rate of the stock solution flowing down from the nozzle 30 is preferably in the range of 1 to 10 L / min, particularly in the range of 1 to 3 L / min.

[0057] In a similar experiment, the ratio of the flow rate of the stock solution to the cross-sectional area of the discharge port of the nozzle 30 is 1 cm 2When it is within the range of 0.75 to 7.5 L / min per unit area, it has been found that a numerical analysis value capable of determining an appropriate flocculant injection rate can be calculated from the optical measurement values obtained by the optical measurement device 3 according to the above-described embodiment. Therefore, from the viewpoint of the optical sensor 35 reliably detecting the flock, the ratio of the flow rate of the undiluted solution to the cross-sectional area of the discharge port of the nozzle 30 is 1 cm 2 within the range of 0.75 to 7.5 L / min per unit area, particularly, 1 cm 2 is preferably in the range of 1 to 2 L / min per unit area.

[0058] As shown in FIG. 2, the optical measurement device 3 may include a dilution line 55 that supplies a diluent to the agitated undiluted solution as necessary. The dilution line 55 shown in FIG. 2 is connected to the primary side discharge pipe 28A and supplies the diluent to the undiluted solution after agitation and before optical measurement. A diluent supply valve (not shown) is arranged in the dilution line 55, and the control device 6 controls the supply of the diluent to the undiluted solution after agitation by operating the opening and closing operation of the diluent supply valve as necessary.

[0059] The purpose of supplying the diluent to the undiluted solution after agitation is to reduce the concentration of the suspended substances and / or the concentration of the flock contained in the agitated undiluted solution. In an undiluted solution with a high concentration of suspended substances, there is no difference between the optical measurement value when the flock is formed and the optical measurement value when the flock is not formed. As a result, it may be difficult to determine the injection rate of the flocculant. For example, when the optical measurement device 3 measures the transmitted light intensity of an undiluted solution with a high concentration of suspended substances, even if the injection rate of the flocculant is appropriate and the flock is formed, there is almost no gap between the flocks, and as shown in FIG. 4(a), the transmitted light intensity may become almost constant. On the other hand, when the agitated undiluted solution is diluted with a diluent, the gap between the flocks can be increased, so that light is transmitted through the gap between the flocks, and as shown in FIG. 4(b), a plurality of peaks of the transmitted light intensity are measured. As a result, a difference occurs between the transmitted light intensity when the flock is formed and the transmitted light intensity when the flock is not formed, and an appropriate injection rate can be determined. As the diluent, pure water, tap water, industrial water, groundwater, treated water from various wastewater treatments, seawater, etc. can be used.

[0060] FIG. 6 is a schematic diagram showing another example of a sewage treatment apparatus in which the optical measurement apparatus shown in FIG. 2 is arranged. The sewage treatment apparatus shown in FIG. 6 is a screw press (dehydrator) that squeezes liquid contents such as sludge to separate the liquid contents into filtrate and cake.

[0061] The screw press shown in FIG. 6 includes a cylindrical screen casing (filter cylinder) 61, a screw (not shown) disposed concentrically with the screen casing 61 within the screen casing 61 for transporting sludge (sewage), which is a liquid content, in a predetermined transport direction D, a rotation mechanism (not shown) for rotating the screw, a filtrate receiver 68 for collecting the filtrate that has passed through the screen casing 61, and a drain line 69 connected to the filtrate receiver 68.

[0062] The screen casing 61 is formed of a screen (perforated plate) such as punching metal. The sludge introduced into the screen casing 61 is transported within the screen casing 61 by the rotation of the screw. The sludge is squeezed and dehydrated as it is transported within the screen casing 61. The filtrate that has passed through the screen of the screen casing 61 is collected by the filtrate receiver 68 disposed below the screen casing 61 and discharged from the screw press via the drain line 69.

[0063] In the present embodiment, the above-described optical measurement apparatus 3 is arranged in the drain line 69. The optical measurement apparatus 3 obtains an optical measurement value of the filtrate by directly irradiating the filtrate with light. The obtained optical measurement value is sent to a control device (not shown) of the screw press, and the control device controls the operation of the screw press based on the sent optical measurement value. For example, the control device controls the rotation speed of the screw based on the obtained optical measurement value in order to obtain a cake having an appropriate moisture content.

[0064] The above-described embodiments are described for the purpose of enabling those having ordinary knowledge in the technical field to which the present invention pertains to implement the present invention. Various modifications of the above embodiments can be naturally made by those skilled in the art, and the technical idea of the present invention can also be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope in accordance with the technical idea defined by the claims.

Explanation of Signs

[0065] 1 Stirrer 2 Stirring tank 3 Optical measuring device 4 Coagulant injection device 5 Numerical analysis device 6 Control device 7 Supply device 8 Stirring blade 9 Motor 10 Stock solution tank 11 Coagulant storage tank 18 Supply source pipe 26 Coagulant supply pipe 28 Discharge pipe 30 Nozzle 32 Tray (liquid receiving part) 35 Optical sensor 35a Light source (light projecting part) 35b Photodetector (light receiving part) 38 Box 50 Data logger 55 Dilution line 61 Screen casing (filter cylinder) 68 Filtrate receiver 69 Drain line

Claims

1. A stirrer for stirring sewage, a nozzle for flowing the stirred sewage downward into the atmosphere, an optical sensor for irradiating light on the sewage flowing down from the nozzle to obtain an optical measurement value, a primary discharge pipe extending from the stirrer, with the tip of the nozzle connected thereto, for supplying the stirred sewage to the nozzle, The nozzle, a nozzle body in which a flow path for the sewage is formed, a discharge part in which a discharge flow path for the sewage is formed, connected to the tip of the flow path for the sewage, The nozzle is a nozzle for flowing the sewage pumped from the primary discharge pipe downward from the discharge part into the atmosphere as it is, The discharge flow path has a diameter smaller than the diameter of the flow path, an optical measurement device.

2. The optical measurement device according to Claim 1, wherein the diameter of the discharge flow path is in the range of 5 to 30 mm.

3. The flow rate of the sewage flowing down from the nozzle into the atmosphere is within the range of 1 to 10 L / min, or the ratio of the flow rate of the sewage to the cross-sectional area of the discharge port of the nozzle is 0.75 to ２ 7.5 L / min per cm², the optical measuring device according to claim 1 or 2.

4. The optical measurement device according to any one of Claims 1 to 3, wherein the optical sensor is arranged near the discharge port of the nozzle and irradiates light on the sewage immediately after it is discharged from the nozzle.

5. Further comprising a dilution line connected to the primary discharge pipe for supplying a diluent to the sewage before optical measurement, The optical measurement device according to any one of Claims 1 to 4, wherein the sewage is sewage stirred after injecting a flocculant.

6. From the nozzle, flow the sewage stirred by the stirrer downward into the atmosphere, Irradiate light from an optical sensor on the flowed-down sewage to obtain an optical measurement value, The nozzle, a nozzle body in which a flow path for the sewage is formed, a discharge part in which a discharge flow path for the sewage is formed, connected to the tip of the flow path for the sewage, The nozzle is a primary discharge pipe extending from the stirrer, with its tip connected to the primary discharge pipe for supplying the sewage to the nozzle, The nozzle is a nozzle for flowing the sewage pumped from the primary discharge pipe downward from the discharge part into the atmosphere as it is, The discharge flow path has a diameter smaller than the diameter of the flow path, an optical measurement method.

7. The optical sensor is arranged near the discharge port of the nozzle, The step of obtaining the optical measurement value is a step of irradiating light on the sewage immediately after it is discharged from the nozzle, according to the optical measurement method of Claim 6.

8. The step of obtaining the optical measurement value is performed on the sewage supplied with the diluent, The optical measurement method according to claim 6 or 7, wherein the sewage is sewage that has been stirred after injecting a flocculant.

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