Flocculation device and flocculation method

Abstract

To provide a coagulator which has an optical measurement device, can reduce installation space of whole device, and does not require additional facility for discarding foul water after measurement.SOLUTION: A coagulator comprises: a coagulation agitation machine 41 for coagulation processing first foul water including a suspended solid; and a measurement system 60 for acquiring an optical measurement value of second foul water including the suspended solid. The measurement system 60 comprises: an agitation machine 61 for agitating the second foul water into which a coagulation agent is injected; an optical measurement device 3 for acquiring an optical measurement value of the agitated second foul water; and a drain pipe 70 for discharging the second foul water from the optical measurement device 3. The agitation machine 61 and the optical measurement device 3 are provided on an upper part of the coagulation agitation machine 41, and an outlet 70a of the drain pipe 70 is in the coagulation agitation machine 41, and the second foul water discharged from the drain pipe 70 flows into the coagulation agitation machine 41.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a flocculation apparatus and a flocculation method for flocculating wastewater containing suspended solids. [Background technology]

[0002] In order to properly manage the operation of wastewater treatment at various facilities such as wastewater treatment plants and water purification plants, it is necessary to accurately understand the properties of wastewater (e.g., color tone, turbidity, transparency, concentration of suspended solids, and state of aggregation of suspended solids). Therefore, optical measurement values have traditionally been obtained using optical measurement devices, and numerical analysis values indicating the properties of wastewater are calculated from the optical measurement values. For example, Patent Document 1 describes a flocculation method in which optical measurement values of wastewater discharged from a mixer are obtained using an optical measurement device, and an appropriate injection rate of flocculant is determined based on numerical analysis values calculated from the obtained optical measurement values. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2016 / 6419 Summary of the Invention [Problem to be solved by the invention]

[0004] However, such a flocculation device is equipped with an agitator for agitating the wastewater whose optical measurements are to be measured, and an optical measurement device, in addition to a conventional flocculation agitator, etc. Therefore, the entire device is larger than conventional flocculation devices and requires a larger installation space. Furthermore, the flocculation device requires additional disposal facilities to dispose of the wastewater measured by the optical measurement device.

[0005] Therefore, an object of the present invention is to provide a flocculation device and a flocculation method that are equipped with an optical measurement device, reduce installation space, and do not require additional equipment for disposing of wastewater after measurement. [Means for solving the problem]

[0006] In one aspect, a flocculation device is provided, comprising: a flocculation mixer for flocculating first wastewater containing suspended solids; and a measurement system for obtaining optical measurement values of second wastewater containing suspended solids, wherein the measurement system comprises: an agitator for stirring the second wastewater into which a flocculant has been injected; an optical measurement device for obtaining the optical measurement values of the stirred second wastewater; and a drain pipe for discharging the second wastewater from the optical measurement device, wherein the agitator and the optical measurement device are arranged on top of the flocculation mixer, the outlet of the drain pipe is located inside the flocculation mixer, and the second wastewater discharged from the drain pipe is configured to flow into the flocculation mixer.

[0007] In one embodiment, the drain pipe extends vertically. In one embodiment, the optical measurement device includes a nozzle that causes the second wastewater to flow downward into the atmosphere, and an optical sensor that irradiates light onto the second wastewater flowing down from the nozzle to obtain the optical measurement value, and the measurement system further includes a box that encloses the nozzle outlet, the optical sensor, and the drain pipe inlet, the drain pipe inlet being located below the nozzle outlet, and is configured to create negative pressure inside the box by causing the second wastewater to flow from the nozzle into the drain pipe. In one embodiment, the drain pipe inlet is larger than the nozzle outlet. In one embodiment, the coagulation mixer comprises a coagulation mixer tank to which the first wastewater is supplied and a top lid covering the top of the coagulation mixer tank, the drain pipe extends to the inside of the coagulation mixer tank through an opening provided in the top lid, and the measurement system has a sealing member that seals the gap between the drain pipe and the opening.

[0008] In one aspect, a coagulation method is provided, which includes a coagulation and stirring process for coagulating first wastewater containing suspended solids using a coagulation and stirring machine, and a measurement process for obtaining optical measurement values of second wastewater containing suspended solids, wherein the measurement process includes a stirring process for stirring the second wastewater into which a coagulant has been injected using a stirrer, and an optical measurement process for obtaining the optical measurement values of the stirred second wastewater using an optical measurement device, wherein the stirrer and the optical measurement device are arranged above the coagulation and stirring machine, and the second wastewater after the measurement process is flowed into the coagulation and stirring machine. [Effects of the Invention]

[0009] The agitator and optical measuring device of the measurement system are arranged on top of the agglomeration agitator, so that the installation space of the entire apparatus can be reduced. Furthermore, since the outlet of the drain pipe that discharges wastewater from the optical measurement device is located inside the coagulation mixer, no additional equipment is required to dispose of the wastewater after measurement, and the wastewater after measurement can be flowed into the coagulation mixer. [Brief explanation of the drawings]

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

[0011] 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 equipped with a measurement system according to an embodiment. The sewage treatment apparatus shown in FIG. 1 is a flocculation apparatus for treating sewage discharged from a wastewater treatment facility, a water purification treatment facility, or the like. The measurement system described later is used to acquire optical measurement values for calculating numerical analysis values indicating the properties of sewage (for example, color tone, turbidity, transparency, concentration of suspended substances, and flocculation state of suspended substances). In the present embodiment, an appropriate injection rate of a flocculant is determined based on the numerical analysis value obtained by numerically analyzing the optical measurement value.

[0012] Hereinafter, a flocculation apparatus for treating sewage containing suspended substances, which is an example of sewage, will be described as an example of a facility equipped with a measurement system. However, the measurement system 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.

[0013] 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, digested desorbed liquid, flocculation sedimentation sludge, and the like. Organic sludge may contain inorganic substances.

[0014] Examples of inorganic sludge include inorganic sludge generated in water purification treatment, wastewater 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.

[0015] Examples of wastewater for wastewater treatment facilities include wastewater from various industries such as sewage, food industry, drinking water industry, chemical industry, and machinery industry. Examples of raw water for water purification facilities include river water, lake water, and groundwater.

[0016] Furthermore, the wastewater to be treated may be water prepared during processes such as wastewater treatment and water purification. Examples of wastewater from wastewater treatment include wastewater with an adjusted pH, wastewater injected with an inorganic coagulant, wastewater injected with an organic coagulant, and wastewater injected with a metal chelating agent. Examples of wastewater from water purification treatment include raw water with an adjusted pH, raw water injected with an inorganic coagulant, and the like.

[0017] The flocculation apparatus shown in FIG. 1 includes a wastewater storage tank 10, a first supply device 14, a flocculant storage tank 11, a first flocculant injection device 24, and a flocculation mixer 41. The wastewater storage tank 10 stores wastewater containing suspended solids. The flocculation mixer 41 is a device for flocculating the wastewater containing suspended solids. The flocculation mixer 41 includes a flocculation mixer tank 42 to which the wastewater containing suspended solids is supplied, a mixer blade 48 for mixing the wastewater containing suspended solids, and a motor 49 as a drive device for rotating the mixer blade 48. In this embodiment, the flocculation mixer 41 is configured to rotate the mixer blade 48 at a rotation speed of 10 to 300 min -1 A first supply main pipe 18 extending from the wastewater storage tank 10 is connected to the coagulation and mixing tank 42 of the coagulation and mixing machine 41, and a first supply device 14 is disposed in the first supply main pipe 18 to supply the wastewater stored in the wastewater storage tank 10 to the coagulation and mixing tank 42 at a predetermined flow rate. The first supply device 14 is, for example, a pump, or a valve, or a combination of a pump and a valve.

[0018] In one embodiment, a line mixer may be used as the coagulation mixer 41. A line mixer is a mixer incorporated into a pipe. The advantage of a line mixer is that, because the mixer is sealed, two pumps, a sewage pump and a coagulant pump located upstream of the line mixer, are sufficient to send sewage downstream of the line mixer. On the other hand, in the case of a coagulation mixer 41 in which an impeller 48 is installed in the coagulation mixer tank 42, the top of the tank is open, so in order to send liquid downstream of the mixer, in addition to the sewage pump and the coagulant pump located upstream of the mixer, another pump or equipment equivalent to a pump is required. For this reason, it is common to send liquid downstream using a height difference without installing a pump.

[0019] A flocculant is stored in the flocculant storage tank 11. A first flocculant supply pipe 26 extending from the flocculant storage tank 11 is connected to the flocculation stirring tank 42. A first flocculant injector 24 is disposed in the first flocculant supply pipe 26. The first flocculant injector 24 is a device that injects a flocculant into wastewater containing suspended solids at a predetermined injection rate. The first flocculant injector 24 is, for example, a pump, or a valve, or a combination of a pump and a valve.

[0020] Wastewater containing suspended solids is supplied from the wastewater storage tank 10 to the coagulation / stirring tank 42 by the first supply device 14. Hereinafter, the wastewater supplied to the coagulation / stirring tank 42 will be referred to as the first wastewater. A flocculant is supplied to the coagulation / stirring tank 42 at a predetermined injection rate by the first flocculant injector 24. In the coagulation / stirring tank 42, the first wastewater and the flocculant are mixed by the impeller 48, thereby forming flocs of suspended solids. The discharge pipe 28, through which the first wastewater discharged from the coagulation / stirring tank 42 flows, is connected to the coagulation / stirring tank 42, and a dehydrator 90 is connected downstream of the discharge pipe 28. The dehydrator 90 dehydrates the first wastewater in which flocs have formed, and separates it into filtrate and cake. The cake is recovered from the dehydrator 90.

[0021] The flocculation device further includes a measurement system 60 for obtaining optical measurement values of sewage containing suspended substances. FIG. 2 is a schematic diagram showing the configuration of the measurement system 60 shown in FIG. 1. The measurement system 60 includes a stirrer 61 separate from the flocculation stirrer 41, and an optical measurement device 3 for obtaining optical measurement values of the sewage stirred by the stirrer 61.

[0022] The stirrer 61 includes a stirring tank 62 to which sewage containing suspended substances is supplied, a stirring blade 68 for stirring the sewage containing suspended substances, and a motor 69 as a driving device for rotating the stirring blade 68. A second supply source pipe 19 extending from the sewage storage tank 10 is connected to the stirring tank 62 of the stirrer 61, and a second supply device 15 for supplying the sewage stored in the sewage storage tank 10 to the stirring tank 62 at a predetermined flow rate is arranged in the second supply source pipe 19. The second supply device 15 is, for example, a pump, or a valve, or a combination of a pump and a valve. In one embodiment, a line mixer may be used as the stirrer 61.

[0023] In this embodiment, the stirrer 61 is configured as a high-speed stirrer that performs high-speed stirring with the rotation speed of the stirring blade 68 set to 300 - 5000 min -1 By this high-speed stirring, the flocculant is instantaneously dispersed in the sewage, and the flocculant is efficiently and uniformly mixed with the sewage. As a result, the suspended substances contained in the sewage are efficiently flocculated.

[0024] In the stirrer 61, it is important to rotate the stirring blade 68 at a rotation speed of 300 - 5000 min -1 to perform high-speed stirring of the sewage containing suspended substances into which the flocculant has been injected. Preferably, the rotation speed of the stirring blade 68 is 300 - 2000 min -1 More preferably, the rotation speed of the stirring blade 68 is 400 - 1500 min -1 More preferably, the rotation speed of the stirring blade 68 is 500 - 1200 min -1 More preferably, the rotation speed of the stirring blade 68 is 500 - 1200 min

[0025] When performing such high-speed stirring, since high stress is applied to the sewage into which the flocculant is injected, if the flocculant is not injected at an appropriate injection rate, the flocs will be destroyed before they grow. Therefore, if the injected flocculant is not at an appropriate injection rate, the flocs will not grow properly. In this embodiment, a control device described later acquires optical measurement values from the optical measurement device 3, and further determines whether the flocs are growing properly from the numerical analysis values obtained by numerically analyzing the optical measurement values. 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 properly controlled. Furthermore, even if the properties of the sewage containing suspended substances (for example, the concentration of suspended substances in the sewage, etc.) change, the injection rate of the flocculant can be properly controlled.

[0026] The rotational speed of the stirring blade 68 is 300 to 5000 min -1 adjusted based on the type of sewage containing suspended substances (for example, drainage, sludge, etc.), the properties of the sewage (for example, SS (Suspended Solids) concentration, viscosity, etc.), and the type of flocculant (for example, inorganic flocculant, organic coagulant, polymer flocculant, etc.). The flocculant injected into the sewage containing suspended substances may be injected into the stirring blade 68 or may be injected into the second supply pipe 19 arranged upstream of the stirring tank 62.

[0027] In this embodiment, the second flocculant supply pipe 27 extending from the flocculant storage tank 11 is connected to the stirring tank 62. A second flocculant injection device 25 is arranged in the second flocculant supply pipe 27. The second flocculant injection device 25 is a device that injects the flocculant into the sewage containing suspended substances at a predetermined injection rate. The second flocculant injection device 25 is, for example, a pump, or a valve, or a combination of a pump and a valve.

[0028] Wastewater containing suspended solids is supplied from the wastewater storage tank 10 to the agitation tank 62 by the second supply device 15. Hereinafter, the wastewater supplied to the agitation tank 62 will be referred to as the second wastewater. The flocculant is supplied to the agitation tank 62 by the second flocculant injector 25. In the agitation tank 62, the rotation speed of the agitation blades 68 is set to 300 to 5000 min -1 The second wastewater and the coagulant are mixed at a high speed, which causes flocs of suspended matter to form. Note that, depending on the injection rate of the coagulant, flocs of suspended matter may not be formed. That is, in the agitator 61, the agitator blades 68 are rotated at a high speed to form flocs of suspended matter, but depending on the injection rate of the coagulant, flocs of suspended matter may not be formed.

[0029] The measurement transfer pipe 72, through which the second wastewater discharged from the agitator 61 flows, is connected to the agitation tank 62 and the optical measurement device 3. The optical measurement device 3 is a device for irradiating light onto the second wastewater containing flocs formed in the agitator 61 to obtain optical measurement values. In this embodiment, the optical measurement device 3 is a device capable of measuring the intensity of transmitted light emerging from the second wastewater containing flocs. The optical measurement device 3 may also be a device capable of measuring transmittance, intensity of diffracted light, absorbance, intensity of reflected light, etc. The measurement system 60 includes a drain pipe 70 for discharging the second wastewater from the optical measurement device 3.

[0030] Fig. 3 is a side view showing the agglomerating mixer 41 and the measurement system 60. Fig. 4 is a top view showing the agglomerating mixer 41 and the measurement system 60. For the sake of explanation, some components have been omitted from Fig. 4. The agglomerating mixer 41 further includes an upper lid 43 that covers the top of the agglomerating mixed tank 42, and a shaft 45 that connects the agitator blades 48 to a motor 49. The shaft 45 extends through the upper lid 43 and is rotated together with the agitator blades 48 by the motor 49. The central axis of the shaft 45 coincides with the central axis of the agglomerating mixed tank 42.

[0031] 3, the optical measurement device 3 and the stirrer 61 of the measurement system 60 are disposed above the aggregation stirrer 41. More specifically, the optical measurement device 3 and the stirrer 61 are disposed above the top cover 43 of the aggregation stirrer 41. With this arrangement, the aggregation device does not need to have a separate space for arranging the optical measurement device 3 and the stirrer 61, and the installation space of the entire device can be reduced.

[0032] The optical measurement device 3 and the stirrer 61 are arranged outside the shaft 45 in the radial direction of the top cover 43. The stirrer 61 is arranged outside the optical measurement device 3 in the radial direction of the top cover 43. The arrangement of the optical measurement device 3 and the stirrer 61 is not limited to this embodiment. In one embodiment, the optical measurement device 3 may be arranged outside the stirrer 61 in the radial direction of the top cover 43.

[0033] A drain pipe 70 connected to the optical measurement device 3 extends vertically through the top lid 43 of the coagulating mixer 41. An outlet 70a of the drain pipe 70 is located inside the coagulating mixer 41. An opening 43a is formed in the top lid 43, and the drain pipe 70 extends through the opening 43a to the inside of the coagulating mixer tank 42. The second wastewater discharged from the drain pipe 70 flows into the coagulating mixer 41 and joins with the first wastewater in the coagulating mixer tank 42. With this configuration, the coagulating device does not require additional equipment for disposing of the second wastewater after measurement by the optical measurement device 3, and the second wastewater after measurement can be flowed into the coagulating mixer 41.

[0034] 5 is an enlarged cross-sectional view showing the drain pipe 70 and the opening 43a of the top cover 43. The diameter d1 of the opening 43a is larger than the outer diameter d2 of the drain pipe 70. The measurement system 60 has a sealing member 75 that seals the gap between the drain pipe 70 and the opening 43a. The sealing member 75 is, for example, a ring-shaped part such as an O-ring. By including the sealing member 75, the measurement system 60 can prevent sewage and odors from leaking from the coagulation mixing tank 42 to the outside.

[0035] FIG. 6 is an enlarged schematic view showing an optical measurement device 3 of a measurement system 60 according to an embodiment. The optical measurement device 3 includes a nozzle 30 connected to the end of a transfer pipe 72 for measurement, and an optical sensor 35 that irradiates light onto the second sewage flowing down from the nozzle 30 to obtain an optical measurement value. The nozzle 30 is a structure that causes the second sewage flowing through the transfer pipe 72 for measurement to flow downward, and has a cylindrical shape.

[0036] The inlet 70b of the drain pipe 70 is located below the outlet 30a of the nozzle 30. The drain pipe 70 is arranged at a distance from the nozzle 30. The nozzle 30 and the drain pipe 70 are arranged along the vertical direction, and the central axis of the nozzle 30 coincides with the central axis of the drain pipe 70. An open space through which the second sewage flows down is formed between the nozzle 30 and the drain pipe 70. Therefore, the second sewage flows down into the atmosphere from the nozzle 30 toward the drain pipe 70.

[0037] The inlet 70b of the drain pipe 70 is larger than the outlet 30a of the nozzle 30. More specifically, when viewed from a direction perpendicular to the central axes of the nozzle 30 and the drain pipe 70, the inner diameter of the inlet 70b of the drain pipe 70 is larger than the inner diameter of the outlet 30a of the nozzle 30. The drain pipe 70 of the present embodiment has an inflow portion 70c, a first intermediate portion 70d, a second intermediate portion 70e, and an outflow portion 70f. The inflow portion 70c includes the inlet 70b of the drain pipe 70 and is located at the uppermost part of the drain pipe 70. The funnel-shaped inflow portion 70c has an inner diameter that decreases downward and functions as a diameter-reducing portion. The first intermediate portion 70d is connected to the lower end of the inflow portion 70c. The first intermediate portion 70d has a cylindrical shape with a constant inner diameter and is configured to guide the second sewage flowing from the inflow portion 70c downward.

[0038] The second intermediate section 70e is connected to the lower end of the first intermediate section 70d. The second intermediate section 70e has an inverted funnel shape, and its inner diameter increases downward, functioning as an expanding diameter section. The outlet section 70f is connected to the lower end of the second intermediate section 70e. The outlet section 70f includes the outlet 70a of the drain pipe 70 and is located at the bottom of the drain pipe 70. The outlet section 70f has a cylindrical shape with a constant inner diameter. The second wastewater flowing through the drain pipe 70 is supplied to the coagulation mixer 41 from the outlet 70a of the drain pipe 70. The shape of the drain pipe 70 is not limited to this embodiment. In one embodiment, the drain pipe 70 does not have the first intermediate section 70d and the second intermediate section 70e, and the outlet section 70f may be connected to the lower end of the inlet section 70c.

[0039] In this embodiment, the optical sensor 35 is an optical sensor that includes a light source (light-emitting unit) 35a that emits light toward the second wastewater and a photodetector (light-receiving unit) 35b that detects light emerging from the second wastewater, and measures the intensity of transmitted light that reaches the photodetector 35b. The light emitted from the light source 35a and transmitted through the second wastewater containing flocs is detected by the photodetector 35b. The intensity of this transmitted light is measured for a predetermined time, and the measured intensity of transmitted light is used as the optical measurement value.

[0040] The transmitted light intensity, which is an optical measurement value, is measured once or multiple times while changing the coagulant injection rate, thereby obtaining at least one optical measurement value. The transmitted light intensity detected by the photodetector 35b is stored in the data logger 50 and then sent to the numerical analysis device 5, which will be described later. The numerical analysis value calculated by the numerical analysis device 5 is sent to the control device 6, which determines the appropriate coagulant injection rate based on the numerical analysis value. The data logger 50, the numerical analysis device 5, and the control device 6 may each be provided separately. Alternatively, the data logger 50 and the numerical analysis device 5 may be incorporated into the control device 6, which is configured as a single computer or a single programmable logic controller (e.g., a sequencer).

[0041] 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-state 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, CMOS, etc. In any case, commercially available products can be used as the optical sensor 35.

[0042] As shown in FIG. 6, the measurement system 60 further includes a box 78 that surrounds the outlet 30a of the nozzle 30, the optical sensor 35, and the inlet 70b of the drain pipe 70. The second sewage discharged from the nozzle 30 flows down in the atmosphere until it reaches the drain pipe 70. By allowing the second sewage to flow from the nozzle 30 into the drain pipe 70, the atmosphere around the second sewage also flows into the drain pipe 70 together with the second sewage. Therefore, according to Bernoulli's theorem, a negative pressure is formed inside the box 78. By forming a negative pressure inside the box 78, the odor of the second sewage is prevented from diffusing outside the box 78. Furthermore, according to such a configuration, since the optical sensor 35 is surrounded by the box 78, it is possible to eliminate disturbances that affect optical measurement values such as natural light and wind.

[0043] 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. Also, the control device 6 is connected to the first flocculant injection device 24 and the second flocculant injection device 25.

[0044] The optical measurement values obtained from the optical measurement device 3 are sent to the numerical analysis device 5. The numerical analysis device 5 performs numerical analysis on the optical measurement values to obtain numerical analysis values. The obtained numerical analysis values are sent to the control device 6. The control device 6 determines the appropriate injection rate of the coagulant based on the numerical analysis values. Examples of numerical analysis values include the mean value, variance, standard deviation, peak area, peak height, etc. of the optical measurement values.

[0045] The number of optical measurement values equal to or greater than a certain threshold value, or the number of optical measurement values equal to or less than a certain threshold value, may be used as the numerical analysis value. The numerical analysis device 5 may calculate the SS concentration, turbidity, chromaticity, floc particle size, etc. from the optical measurement values, and use these as the numerical analysis value. Here, the floc particle size means the diameter of the floc if the floc is spherical. If the floc is not spherical, the floc particle size means the Stokes diameter or a particle size measured by various measurement methods. The floc particle size may be the average particle size of the floc. Examples of the average particle size include the arithmetic mean diameter, the most common diameter, and the median diameter. The average particle size may be based on the number, mass, or volume.

[0046] Known methods such as transmitted light measurement can be used to calculate SS concentration and turbidity from optically measured values. Known methods such as transmitted light measurement can be used to calculate chromaticity from optically measured values. Known methods such as laser diffraction / scattering and image analysis of images taken with a camera can be used to calculate floc particle size from optically measured values. The floc particle size may be the average floc particle size or the particle size distribution of floc particle sizes. Commercially available measuring devices can be used to perform optical measurements and calculate SS concentration, turbidity, chromaticity, floc particle size, etc. from the obtained optical measured values.

[0047] 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 second sewage, the agitation (high-speed agitation) of the second sewage, 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 second sewage containing suspended substances, agitates the second sewage to form flocs of the suspended substances, performs optical measurement on the agitated second sewage, and 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 agitation, optical measurement, and numerical analysis again to determine an appropriate injection rate. Note that depending on the injection rate of the flocculant, flocs of suspended substances may not be formed.

[0048] 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 second sewage containing suspended substances at a preset injection rate, agitates the second sewage to form flocs of the suspended substances, performs optical measurement on the agitated second sewage, and 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 another embodiment, 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 alternatively, 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.

[0049] In yet another embodiment, the control device 6 may plot multiple numerical analysis values at multiple preset injection rates on a graph whose vertical axis represents the numerical analysis value and whose horizontal axis represents the injection rate of the flocculant, calculate an approximate expression showing the relationship between the multiple injection rates and the multiple numerical analysis values, and determine 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 may be calculated from the approximate expression, and the obtained injection rate may be set as the appropriate injection rate of the flocculant.

[0050] The determined injection rate is sent from the control device 6 to the first coagulant injector 24. The first coagulant injector 24 injects the coagulant into the coagulation mixer 41 at the determined injection rate. The first wastewater and coagulant supplied to the coagulation mixer 41 are agitated in the coagulation agitation tank 42, and flocs are formed in the first wastewater. The first wastewater containing the flocs is sent to the dehydrator 90 and dewatered by the dehydrator 90.

[0051] As shown in Fig. 6, the measurement system 60 may include a dilution line 55 that supplies a diluent to the stirred wastewater, as needed. The dilution line 55 shown in Fig. 6 is connected to the measurement transfer pipe 72 and supplies the diluent to the second wastewater after stirring but before optical measurement. A diluent supply valve (not shown) is disposed in the dilution line 55, and the control device 6 controls the supply of the diluent to the second wastewater after stirring by operating the opening and closing operation of the diluent supply valve as needed.

[0052] The purpose of adding the diluent to the stirred second wastewater is to reduce the concentration of suspended solids and / or flocs in the stirred second wastewater. In second wastewater with a high concentration of suspended solids, there is no difference between the optical measurements when flocs are formed and when they are not formed, which can make it difficult to determine the coagulant injection rate. For example, when the optical measurement device 3 measures the transmitted light intensity of second wastewater with a high concentration of suspended solids, even if the coagulant injection rate is appropriate and flocs are formed, there may be almost no gaps between the flocs, resulting in a nearly constant transmitted light intensity. In contrast, when the stirred second wastewater is diluted with the diluent, the gaps between the flocs are increased, allowing light to pass through the gaps between the flocs, resulting in multiple peaks in the transmitted light intensity. This results in a difference between the transmitted light intensity when flocs are formed and when they are not formed, allowing the appropriate injection rate to be determined. Examples of diluent include pure water, tap water, industrial water, groundwater, treated wastewater from various wastewater treatment plants, and seawater.

[0053] The configuration of the optical measurement device 3 of the measurement system 60 is not limited to this embodiment as long as it can obtain measurements for determining the appropriate injection rate of the coagulant. For example, in one embodiment, the optical measurement device 3 may be configured such that, instead of the nozzle 30, a pair of transparent windows are provided in the measurement transfer pipe 72 through which the second wastewater discharged from the agitator 61 flows, and the optical sensor 35 irradiates light toward one of the transparent windows and detects the light emerging from the other transparent window to obtain optical measurements.

[0054] The above-described embodiments have been described for the purpose of enabling a person of ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments would naturally be possible for a person skilled in the art, and the technical concept of the present invention may 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 concept defined by the claims. [Explanation of symbols]

[0055] 3 Optical measuring device 5. Numerical analysis equipment 6. Control device 10 Sewage storage tank 11 Coagulant storage tank 14 1st supply device 15 Second supply device 18 1st supply pipe 19 2nd supply pipe 24 First coagulant injection device 25 Second coagulant injection device 26 First coagulant supply pipe 27 Second coagulant supply pipe 28 Discharge piping 30 nozzles 35 Optical Sensor 35a Light source (light projector) 35b Photodetector (light receiving part) 41 Coagulation Mixer 42 Coagulation and stirring tank 43 Top lid 45 shaft 48 Mixing blade 49 Motor 50 Data Logger 55 Dilution Line 60 Measurement System 61 Mixer 62 Mixing tank 68 Mixing blade 69 Motor 70 Drain pipe 72 Measurement transfer piping 75 Sealing material 78 boxes 90 Dehydrator

Claims

[

1. ] An agitating mixer for coagulating first sewage, which is sewage containing suspended substances supplied from a sewage storage tank, a measurement system for obtaining an optical measurement value of second sewage, which is the sewage containing the suspended substances supplied from the sewage storage tank, and a control device that determines an injection rate of a coagulant based on the optical measurement value of the second sewage and injects the coagulant into the agitating mixer at the determined injection rate. The measurement system includes a mixer that stirs the second sewage into which the coagulant has been injected, an optical measurement device that obtains the optical measurement value of the stirred second sewage, and a drain pipe that discharges the second sewage from the optical measurement device. The mixer and the optical measurement device are arranged above the agitating mixer, and an outlet of the drain pipe is located inside the agitating mixer and is configured such that the second sewage discharged from the drain pipe flows into the agitating mixer. A coagulation device. [

2. ] The drain pipe extends in the vertical direction. The coagulation device according to claim 1. [

3. ] The optical measurement device includes a nozzle that causes the second sewage to flow downward into the atmosphere, and an optical sensor that irradiates light onto the second sewage flowing down from the nozzle to obtain the optical measurement value. The measurement system further includes a box that surrounds an outlet of the nozzle, the optical sensor, and an inlet of the drain pipe, and an inlet of the drain pipe is located below the outlet of the nozzle and is configured to form a negative pressure inside the box by allowing the second sewage to flow from the nozzle into the drain pipe. The coagulation device according to claim 1 or 2. [

4. ] The inlet of the drain pipe is larger than the outlet of the nozzle. The coagulation device according to claim 3. [

5. ] The agitating mixer includes an agitating mixing tank into which the first sewage is supplied, and an upper lid that covers an upper portion of the agitating mixing tank. The drain pipe extends to the inside of the agitating mixing tank through an opening provided in the upper lid, and the measurement system has a seal member that seals a gap between the drain pipe and the opening. The coagulation device according to any one of claims 1 to 4. [

6. ] A coagulation stirring step of coagulating first sewage, which is sewage containing suspended substances supplied from a sewage storage tank, by an agitating mixer, ​ ​ ​ A measurement step of obtaining an optical measurement value of the second sewage, which is the sewage containing the suspended substances supplied from the sewage storage tank; A flocculant injection rate determination step of determining the injection rate of the flocculant based on the optical measurement value of the second sewage; A flocculant injection step of injecting the flocculant into the agitating mixer at the determined injection rate, The measurement step includes: A stirring step of stirring the second sewage into which the flocculant has been injected by a stirrer; An optical measurement step of obtaining the optical measurement value of the stirred second sewage by an optical measurement device, The stirrer and the optical measurement device are arranged above the agitating mixer, A flocculation method of causing the second sewage after the measurement step to flow into the agitating mixer.

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