JP7716361B2 - Flocculation device and flocculation method - Google Patents

Description

The present invention relates to a flocculation device and flocculation method for flocculating wastewater containing suspended solids.

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 the 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 the wastewater are calculated from these optical measurements. For example, Patent Document 1 describes a coagulation method in which optical measurement values of wastewater discharged from a mixer are obtained using an optical measurement device, and the appropriate injection rate of coagulant is determined based on numerical analysis values calculated from the obtained optical measurements.

International Publication No. 2016/6419

However, this type of flocculation device is equipped with an agitator for agitating the wastewater whose optical measurements are to be measured, as well as a conventional flocculation agitator, and an optical measurement device. As a result, the entire device is larger than conventional flocculation devices, and a large installation space is required. Furthermore, the flocculation device requires additional disposal facilities to dispose of the wastewater measured by the optical measurement device.

The present invention aims to provide a flocculation device and flocculation method that is equipped with an optical measurement device, reduces installation space, and does not require additional equipment for disposing of wastewater after measurement.

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. The measurement system comprises an agitator for agitating 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. The agitator and the optical measurement device are disposed above 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.

In one embodiment, the drain pipe extends vertically.
In one aspect, 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 outlet of the nozzle, the optical sensor, and the inlet of the drain pipe, the inlet of the drain pipe being located below the outlet of the nozzle, 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 aspect, 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.

In one aspect, a coagulation method is provided that includes a coagulation/agitation process in which first wastewater containing suspended solids is subjected to coagulation treatment using a coagulation/agitation mixer, and a measurement process in which optical measurement values of second wastewater containing suspended solids are obtained, the measurement process including a stirring process in which the second wastewater into which a coagulant has been injected is stirred using a stirrer, and an optical measurement process in which the optical measurement values of the stirred second wastewater are obtained using an optical measurement device, the stirrer and the optical measurement device being disposed above the coagulation/agitation mixer, and the second wastewater after the measurement process being allowed to flow into the coagulation/agitation mixer.

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.

FIG. 1 is a schematic diagram illustrating an example of a wastewater treatment apparatus equipped with a measurement system according to an embodiment. FIG. 2 is a schematic diagram showing the configuration of the measurement system shown in FIG. FIG. 3 is a side view showing the agglomeration mixer and measurement system. FIG. 4 is a top view showing the agglomeration mixer and measurement system. FIG. 5 is an enlarged cross-sectional view showing the drain pipe and the opening of the top cover. FIG. 6 is an enlarged schematic diagram showing an optical measurement device of a measurement system according to one embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing an example of a wastewater treatment device equipped with a measurement system according to one embodiment. The wastewater treatment device shown in FIG. 1 is a flocculation device for treating wastewater discharged from a wastewater treatment facility, a water purification facility, or the like. The measurement system, described below, is used to acquire optical measurements for calculating numerical analysis values indicating the properties of the wastewater (e.g., color tone, turbidity, transparency, concentration of suspended solids, and flocculation state of suspended solids). In this embodiment, an appropriate injection rate of flocculant is determined based on the numerical analysis values obtained by numerically analyzing the optical measurements.

In the following, a flocculation device that treats wastewater containing suspended solids, which is an example of wastewater, will be described as an example of equipment equipped with a measurement system. However, the measurement system according to this embodiment may also be installed in other equipment that treats wastewater. For example, the wastewater to be treated may be sludge discharged from a wastewater treatment facility or a water purification facility, wastewater from a wastewater treatment facility, or raw water from a water purification facility. The sludge may be either organic sludge or inorganic sludge.

Examples of organic sludge include organic sludge generated during sewage treatment, human waste treatment, and various industrial wastewater treatment processes. More specifically, examples of organic sludge include primary sedimentation tank sludge, excess sludge, anaerobic digestion sludge, aerobic digestion sludge, human waste sludge, septic tank sludge, digestion supernatant, and coagulation sedimentation sludge. Organic sludge may contain inorganic matter.

Examples of inorganic sludge include inorganic sludge generated during water purification processes, construction wastewater treatment, and various industrial wastewater treatment processes. Here, sludge generated during water purification processes refers to sludge discharged from settling tanks, sludge basins, thickener tanks, etc. at water purification facilities. Inorganic sludge may also contain organic matter.

Examples of wastewater at 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 at water purification treatment facilities include river water, lake water, and groundwater.

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. Furthermore, examples of wastewater from water purification treatment include raw water with an adjusted pH, and raw water injected with an inorganic coagulant.

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 and treating 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 that mixes the wastewater containing suspended solids, and a motor 49 as a drive device for rotating the mixer blade 48. In this embodiment, the rotation speed of the mixer blade 48 of the flocculation mixer 41 is set to approximately 10 to 300 min ⁻¹ . A first supply main pipe 18 extending from the wastewater storage tank 10 is connected to the flocculation mixer tank 42 of the flocculation mixer 41. A first supply main pipe 18 is disposed in the first supply main pipe 18, and a first supply device 14 is disposed in the first supply main pipe 18, and supplies the wastewater stored in the wastewater storage tank 10 to the flocculation mixer 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.

In one embodiment, a line mixer may be used as the coagulation mixer 41. A line mixer is a mixer incorporated into piping. The advantage of a line mixer is that, because the mixer is sealed, two pumps, a sewage pump upstream of the line mixer and a coagulant pump, are all that is needed 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 inside 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 coagulant pump upstream of the mixer, another pump or equipment equivalent to a pump is required. For this reason, it is common practice to send liquid downstream using a height difference without installing a pump.

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

Sewage 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 coagulant is supplied to the coagulation/stirring tank 42 at a predetermined injection rate by the first coagulant injector 24. In the coagulation/stirring tank 42, the first wastewater and the coagulant 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, separating it into filtrate and cake. The cake is recovered from the dehydrator 90.

The flocculation device further includes a measurement system 60 for obtaining optical measurement values of the wastewater containing suspended solids. Figure 2 is a schematic diagram showing the configuration of the measurement system 60 shown in Figure 1. The measurement system 60 includes an agitator 61 separate from the flocculation agitator 41, and an optical measurement device 3 for obtaining optical measurement values of the wastewater agitated by the agitator 61.

The agitator 61 includes an agitation tank 62 to which wastewater containing suspended solids is supplied, an agitator blade 68 that agitates the wastewater containing suspended solids, and a motor 69 that serves as a drive device for rotating the agitator blade 68. A second supply main pipe 19 extending from the wastewater storage tank 10 is connected to the agitation tank 62 of the agitator 61, and a second supply device 15 is disposed in the second supply main pipe 19. The second supply device 15 supplies wastewater stored in the wastewater storage tank 10 to the agitation tank 62 at a predetermined flow rate. The second supply device 15 is, for example, a pump, a valve, or a combination of a pump and a valve. In one embodiment, a line mixer may be used as the agitator 61.

In this embodiment, the agitator 61 is configured as a high-speed agitator that performs high-speed agitation with the rotation speed of the agitating blades 68 set to 300 to 5000 min ^-1 . This high-speed agitation instantly disperses the flocculant in the wastewater, and the flocculant is efficiently and uniformly mixed with the wastewater. As a result, suspended solids contained in the wastewater are efficiently agglomerated.

It is important that the agitator 61 rotates the agitating blade 68 at a rotation speed of 300 to 5000 min ^-1 to agitate the wastewater containing suspended solids and into which the coagulant has been injected at high speed. Preferably, the rotation speed of the agitating blade 68 is 300 to 2000 min ^-1 . More preferably, the rotation speed of the agitating blade 68 is 400 to 1500 min ^-1 . More preferably, the rotation speed of the agitating blade 68 is 500 to 1200 min ^-1 .

When such high-speed mixing is performed, high stress is imposed on the wastewater into which the coagulant has been injected. If the coagulant is not injected at the appropriate injection rate, the flocs will be destroyed before they can grow. Therefore, if the coagulant is not injected at the appropriate injection rate, the flocs will not grow properly. In this embodiment, the control device (described later) acquires optical measurement values from the optical measurement device 3 and determines whether flocs are growing properly from numerical analysis values obtained by numerically analyzing the optical measurement values. This allows the appropriate coagulant injection rate to be determined with high accuracy. As a result, the amount of coagulant used can be reduced. Furthermore, the coagulant injection rate can be appropriately controlled without the operator's experience or intuition. Furthermore, the coagulant injection rate can be appropriately controlled even if the properties of the wastewater containing suspended solids (e.g., the concentration of suspended solids in the wastewater) change.

The rotation speed of the agitator blades 68 is adjusted to 300 to 5000 min-1 based on the type of wastewater containing suspended solids (e.g., wastewater, sludge, etc.), the properties of the wastewater (e.g., SS (Suspended Solids) concentration, viscosity, etc.), and the type of flocculant (e.g., inorganic ^flocculant , organic coagulant, polymer flocculant, etc.). The flocculant to be injected into the wastewater containing suspended solids may be injected into the agitator blades 68, or may be injected into the second supply main pipe 19 located upstream of the agitator tank 62.

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 disposed on the second flocculant supply pipe 27. The second flocculant injection device 25 is a device that injects flocculant into wastewater containing suspended solids at a predetermined injection rate. The second flocculant injection device 25 is, for example, a pump, a valve, or a combination of a pump and a valve.

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. A flocculant is supplied to the agitation tank 62 by the second flocculant injector 25. In the agitation tank 62, the second wastewater and the flocculant are mixed at a high rotation speed of the agitator blades 68 of 300 to 5000 min ⁻¹ , thereby forming flocs of suspended solids. Note that, depending on the injection rate of the flocculant, flocs of suspended solids may not be formed. That is, in the agitator 61, the agitator blades 68 are rotated at high speed to form flocs of suspended solids, but flocs of suspended solids may not be formed depending on the injection rate of the flocculant.

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 that irradiates 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 that can measure the intensity of transmitted light emerging from the second wastewater containing flocs. The optical measurement device 3 may also be a device that can measure transmittance, diffracted light intensity, absorbance, reflected light intensity, etc. The measurement system 60 includes a drain pipe 70 that discharges the second wastewater from the optical measurement device 3.

Figure 3 is a side view showing the agglomeration mixer 41 and measurement system 60. Figure 4 is a top view showing the agglomeration mixer 41 and measurement system 60. Some components are omitted from Figure 4 for the purpose of explanation. The agglomeration mixer 41 further includes a top lid 43 that covers the top of the agglomeration mixer tank 42, and a shaft 45 that connects the agitator blades 48 to a motor 49. The shaft 45 extends through the top 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 agglomeration mixer tank 42.

As shown in FIG. 3, the optical measurement device 3 and agitator 61 of the measurement system 60 are arranged above the aggregating agitator 41. More specifically, the optical measurement device 3 and agitator 61 are arranged above the top cover 43 of the aggregating agitator 41. This arrangement allows the aggregating device to reduce the installation space of the entire device without having to provide additional space for the optical measurement device 3 and agitator 61.

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

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

Figure 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 wastewater and odors from leaking from the coagulation mixing tank 42 to the outside.

Figure 6 is an enlarged schematic diagram showing the optical measurement device 3 of a measurement system 60 according to one embodiment. The optical measurement device 3 includes a nozzle 30 connected to the end of the measurement transfer pipe 72 and an optical sensor 35 that irradiates light onto the second wastewater flowing down from the nozzle 30 to obtain optical measurements. The nozzle 30 is a cylindrical structure that causes the second wastewater flowing down the measurement transfer pipe 72 to flow downward.

The inlet 70b of the drain pipe 70 is located below the outlet 30a of the nozzle 30. The drain pipe 70 is positioned at a distance from the nozzle 30. The nozzle 30 and drain pipe 70 are arranged vertically, with the central axis of the nozzle 30 coinciding with the central axis of the drain pipe 70. An open space is formed between the nozzle 30 and the drain pipe 70 through which the second wastewater flows. Therefore, the second wastewater flows from the nozzle 30 toward the drain pipe 70 and into the atmosphere.

The inlet 70b of the drain pipe 70 is larger than the outlet 30a of the nozzle 30. More specifically, when viewed perpendicular to the central axis 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. In this embodiment, the drain pipe 70 has an inlet section 70c, a first intermediate section 70d, a second intermediate section 70e, and an outlet section 70f. The inlet section 70c includes the inlet 70b of the drain pipe 70 and is located at the top of the drain pipe 70. The funnel-shaped inlet section 70c has an inner diameter that decreases downward, functioning as a reduced diameter section. The first intermediate section 70d is connected to the lower end of the inlet section 70c. The first intermediate section 70d has a cylindrical shape with a constant inner diameter and is configured to guide the second wastewater flowing from the inlet section 70c downward.

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 expanded 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.

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 the transmitted light that reaches the photodetector 35b. 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 period of time, and the measured transmitted light intensity is used as the optical measurement value.

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, numerical analysis device 5, and control device 6 may each be provided separately. Alternatively, the data logger 50 and 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).

Examples of the light source 35a include various lamps (mercury lamps, xenon lamps, krypton lamps, metal halide lamps, halogen lamps, etc.), various lasers (solid-state lasers, semiconductor lasers, liquid lasers, gas lasers, etc.), and various LEDs. Among commercially available optical sensors, LEDs are light sources that can emit relatively high-intensity light, so the light source 35a is preferably an LED. Examples of the photodetector 35b include a CCD, photodiode, phototransistor, photomultiplier tube, photoconductive element, infrared optical sensor, and CMOS. In any case, commercially available products can be used as the optical sensor 35.

As shown in FIG. 6 , the measurement system 60 further includes a box 78 enclosing the outlet 30a of the nozzle 30, the optical sensor 35, and the inlet 70b of the drain pipe 70. The second wastewater discharged from the nozzle 30 flows downward through the atmosphere until it reaches the drain pipe 70. By causing the second wastewater to flow from the nozzle 30 into the drain pipe 70, the atmosphere surrounding the second wastewater also flows into the drain pipe 70 along with the second wastewater. Therefore, according to Bernoulli's theorem, negative pressure is created inside the box 78. The creation of negative pressure inside the box 78 prevents the odor of the second wastewater from diffusing outside the box 78. Furthermore, with this configuration, since the optical sensor 35 is enclosed in the box 78, disturbances such as natural light and wind that affect optical measurements can be eliminated.

Returning to Figure 1, the optical measurement device 3 is electrically connected to a numerical analysis device 5, which is connected to a control device 6. The numerical analysis device 5 may be incorporated into the control device 6. The control device 6 is also connected to a first flocculant injection device 24 and a second flocculant injection device 25.

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 coagulant injection rate based on the numerical analysis values. Examples of numerical analysis values include the mean value, variance, standard deviation, peak area, and peak height of the optical measurement values.

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

Known methods such as transmitted light measurement can be used to calculate SS concentration and turbidity from optical measurement values. Known methods such as transmitted light measurement can be used to calculate chromaticity from optical measurement 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 optical measurement values. 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 measurement values.

The control device 6 determines an appropriate coagulant injection rate from at least one numerical analysis value obtained by injecting a coagulant into the second wastewater, stirring the second wastewater (high-speed stirring), obtaining optical measurement values, and performing numerical analysis based on the optical measurement values at least once. That is, the control device 6 injects a coagulant into the second wastewater containing suspended solids, stirs the second wastewater to form flocs of suspended solids, performs optical measurements on the stirred second wastewater, and numerically analyzes the obtained optical measurement values to obtain numerical analysis values. Furthermore, the control device 6 determines whether the coagulant injection rate is appropriate based on the obtained numerical analysis value. If the injection rate is not appropriate, the control device 6 changes the coagulant injection rate and repeats stirring, optical measurement, and numerical analysis again to determine an appropriate injection rate. Note that depending on the coagulant injection rate, flocs of suspended solids may not be formed.

A method for determining an appropriate coagulant injection rate may use multiple preset injection rates. The control device 6 injects coagulant into second wastewater containing suspended solids at a preset injection rate, agitates the second wastewater to form flocs of suspended solids, performs optical measurements on the agitated second wastewater, and numerically analyzes the obtained measurements to obtain a numerical analysis value. This process is repeated for each of the multiple preset injection rates. The control device 6 compares the multiple numerical analysis values obtained for each of the multiple preset injection rates. In one embodiment, the injection rate that yields the maximum or minimum value is determined to be the appropriate injection rate. In another embodiment, the appropriate injection rate may be the average of the injection rate that yields the largest and the injection rate that yields the second largest numerical analysis value, or the average of the injection rate that yields the smallest and the second smallest numerical analysis value.

In yet another embodiment, the control device 6 may plot multiple numerical analysis values at multiple preset injection rates on a graph where the vertical axis represents the numerical analysis value and the horizontal axis represents the coagulant injection rate, calculate an approximate equation showing the relationship between the multiple injection rates and the multiple numerical analysis values, and determine the appropriate coagulant injection rate based on the obtained approximate equation. For example, the injection rate at which the peak value of the numerical analysis value is obtained can be calculated from the approximate equation, and the obtained injection rate can be used as the appropriate coagulant injection rate.

The determined injection rate is sent from the control device 6 to the first flocculant injection device 24. The first flocculant injection device 24 injects flocculant into the flocculating mixer 41 at the determined injection rate. The first wastewater and flocculant supplied to the flocculating mixer 41 are agitated in the flocculating mixer 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.

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

The purpose of adding diluent to the stirred second wastewater is to reduce the concentration of suspended solids and/or flocs contained 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 diluent, the gaps between the flocs are increased, allowing light to pass through the gaps between the flocs and multiple peaks in the transmitted light intensity are measured. 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 water from various wastewater treatment plants, and seawater.

The configuration of the optical measurement device 3 of the measurement system 60 is not limited to this embodiment, as long as it can acquire measurements for determining the appropriate coagulant injection rate. 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 acquire optical measurements.

The above-described embodiments have been described with the aim of enabling a person of ordinary skill in the art to practice the present invention. Various modifications to 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.

3 Optical measurement device 5 Numerical analysis device 6 Control device 10 Sewage storage tank 11 Coagulant storage tank 14 First supply device 15 Second supply device 18 First supply main pipe 19 Second supply main pipe 24 First coagulant injection device 25 Second coagulant injection device 26 First coagulant supply pipe 27 Second coagulant supply pipe 28 Discharge pipe 30 Nozzle 35 Optical sensor 35a Light source (light projection unit)
35b Photodetector (light receiving unit)
41 Coagulation agitator 42 Coagulation agitation tank 43 Top lid 45 Shaft 48 Agitation blade 49 Motor 50 Data logger 55 Dilution line 60 Measurement system 61 Agitator 62 Agitation tank 68 Agitation blade 69 Motor 70 Drain pipe 72 Measurement transfer piping 75 Sealing member 78 Box 90 Dehydrator

Claims (6)

a coagulation agitator for coagulating the first wastewater, which is wastewater containing suspended solids supplied from the wastewater storage tank ;
a measurement system for obtaining optical measurements of the second wastewater, which is the wastewater containing the suspended solids supplied from the wastewater storage tank ;
A control device is provided that determines an injection rate of a coagulant based on the optical measurement value of the second wastewater and injects the coagulant into the coagulation mixer at the determined injection rate ;
The measurement system includes:
an agitator that agitates the second wastewater into which the coagulant has been injected;
an optical measurement device that obtains the optical measurement values of the stirred second wastewater;
a drain pipe for discharging the second wastewater from the optical measurement device,
the agitator and the optical measurement device are disposed on top of the agglomeration agitator;
An outlet of the drain pipe is located inside the coagulation mixer, and the second wastewater discharged from the drain pipe is configured to flow into the coagulation mixer. The flocculation device of claim 1, wherein the drain pipe extends vertically. The optical measurement device is
A nozzle that causes the second wastewater to flow downward into the atmosphere;
an optical sensor that irradiates light onto the second wastewater flowing down from the nozzle to obtain the optical measurement value;
the measurement system further comprises a box enclosing the nozzle outlet, the optical sensor, and the drain pipe inlet;
The coagulation device according to claim 1 or 2, wherein the inlet of the drain pipe is located below the outlet of the nozzle, and the second wastewater is caused to flow from the nozzle into the drain pipe to create a negative pressure inside the box. The agglomeration device of claim 3, wherein the inlet of the drain pipe is larger than the outlet of the nozzle. The agglomeration agitator comprises:
a coagulation and stirring tank to which the first wastewater is supplied;
an upper lid for covering an upper portion of the flocculation stirring tank;
the drain pipe extends to the inside of the coagulation stirring tank through an opening provided in the upper lid,
The agglomeration apparatus according to claim 1 , wherein the measurement system includes a seal member that seals a gap between the drain pipe and the opening. a coagulation and agitation step of coagulating the first wastewater , which is wastewater containing suspended solids supplied from the wastewater storage tank, using a coagulation and agitation machine;
a measuring step of acquiring optical measurement values of the second wastewater, which is the wastewater containing the suspended matter supplied from the wastewater storage tank ;
a coagulant injection rate determination step of determining an injection rate of a coagulant based on the optical measurement value of the second wastewater;
a flocculant injection step of injecting the flocculant into the flocculating mixer at the determined injection rate ;
The measuring step
a stirring step of stirring the second wastewater into which the flocculant has been injected using an agitator ;
an optical measurement step of obtaining the optical measurement value of the stirred second wastewater by an optical measurement device;
the agitator and the optical measurement device are disposed on top of the agglomeration agitator;
The second wastewater after the measurement step is caused to flow into the coagulation mixer.