JP2024044564A - Treatment method for wastewater from civil engineering works - Google Patents

Abstract

[Problem] To provide a method for treating wastewater from civil engineering works, which can efficiently perform coagulation treatment of wastewater from civil engineering works using a coagulation monitoring device. [Solution] This method treats wastewater from civil engineering works using a grit settling tank 1, a relay tank 10, a thickener 20, an inorganic coagulant adding device 17, a polymer coagulant adding device 18, and a discharge tank 30, in which acid is added by an acid adding device 11 when water is being transferred from the grit settling tank 1 to the relay tank 10, and when the pH or interparticle turbidity of the relay tank 10 is equal to or higher than a predetermined value, acid is added even when water is not being transferred from the grit settling tank 1 to the relay tank 10. [Selected Figure] Figure 1

Description

The present invention relates to a method for treating wastewater from civil engineering works, which purifies wastewater discharged from dam construction sites, tunnel construction sites, etc., and in particular to a method for treating wastewater from civil engineering works that includes a coagulation treatment process.

Civil engineering construction sites such as dam construction and tunnel construction produce wastewater containing soil and sand. This wastewater may be alkaline wastewater with a high pH due to the alkaline components in the poured concrete. Also, if it rains on holidays when construction is not taking place, relatively clear drainage may occur. As described above, the water quality of civil engineering wastewater, such as pH and turbidity, varies greatly depending on the construction status and weather.

Patent Document 1 describes that civil engineering work wastewater is subjected to coagulation treatment. When treating civil engineering work wastewater using a flocculant, the civil engineering work wastewater is first treated with a sedimentation tank, then stored in a relay tank, and then introduced into a flocculation treatment tank where it is flocculated, and the flocs are converted into solid-liquid. It is common to separate the water and discharge the clear water.

FIG. 2 is a flowchart showing an example of a civil engineering work wastewater treatment facility for carrying out a civil engineering work wastewater treatment method. Civil engineering work wastewater is introduced into a sand settling tank 1, and while it remains in the sand settling tank 1, relatively large solid particles such as sand settle. The settled sand and the like are appropriately discharged from the discharge section 2. Although not shown, the sand settling tank 1 is provided with a water level gauge. When the water level detected by the water level gauge reaches a predetermined upper limit water level, the pump (in this example, a submersible pump placed a predetermined distance above the bottom of the tank) 3 pumps the water in the sand settling tank 1 through piping 4 to the relay tank. Water is sent (transferred) to 10. When the water level in the sand settling tank 1 drops to a specified lower limit water level, the pump 3 stops.

The relay tank 10 is for temporarily storing water from the sand settling tank 1. The ratio V10/V1 between the volume V10 of the relay tank 10 and the volume V1 of the sand settling tank 1 is usually about 10 to 50.

The relay tank 10 is provided with a sulfuric acid addition device 11, a pH meter 13, and a transfer pump 15. When the pH in the relay tank 10 detected by the pH meter 13 rises to a predetermined upper limit pH (e.g., 8.5) or higher, the sulfuric acid addition device 11 adds a specified amount of sulfuric acid to the relay tank 10. This causes the pH in the relay tank 10 to decrease. Note that acids other than sulfuric acid (e.g., hydrochloric acid, carbon dioxide, etc.) may also be used.

The relay tank 10 is provided with a water level gauge (not shown). When the water level in the relay tank 10 detected by the water level gauge reaches a predetermined upper water level, the water in the relay tank 10 is pumped (transferred) to the thickener 20 via the pipe 16 by the transfer pump 15 (in this example, a submersible pump placed a predetermined distance above the tank bottom). When the water level in the relay tank 10 drops to a specified lower water level, the transfer pump 15 stops.

The pipe 16 is provided with an addition device 17 for an inorganic flocculant (polyaluminum chloride (PAC), sulfuric acid band, etc., in this example, PAC) and an addition device 18 for a polymer flocculant (organic polymer flocculant). There is. The polymer flocculant addition device 18 is provided downstream of the inorganic flocculant addition device 17.

Each of the flocculant addition devices 17, 18 is equipped with a tank for storing an aqueous solution of the flocculant, a chemical injection pump, etc. When the transfer pump 15 is ON, each chemical injection pump operates and each flocculant is added to the pipe 16. When the pump 15 is turned OFF, each chemical injection pump is turned OFF and the addition of each flocculant stops.

The water from the pipe 16 to which each coagulant has been added is stirred and mixed while flowing through the pipe 16, causing the coagulation reaction to proceed, and is then introduced from the pipe 16 into the center core 21 of the thickener 20. The center core 21 is cylindrical and is positioned near the center of the tank body of the thickener 20 with the cylinder axis line running up and down.

The water introduced into the center core 21 from the pipe 16 further undergoes a coagulation reaction, and flocs grow. The water containing the flocs spreads into the thickener 20 from the lower end of the center core 21, and the flocs settle into the thickener 20. The settled flocs are intermittently or continuously pulled out by the sludge removal section 23.

The supernatant water of the thickener 20 is clear water and flows into the discharge tank 30 via the overflow pipe 24. The clear water in the discharge tank 30 is sent to a destination such as a river by a discharge pump 31 and piping 32.

In this water treatment facility for civil engineering wastewater, each transfer pump 3, 15 starts and stops for short periods of time, from 30 seconds to a few minutes (repeatedly turning on and off).

Therefore, if, in the equipment shown in Figure 2, sulfuric acid was added in response to an increase in the pH detected by the pH meter 13, and the coagulant injection control was performed in conjunction with the transfer pump 15 alone, the following problems would occur.

(1) The amount of alkali in the wastewater flowing into the relay tank 10 fluctuates greatly each time the transfer pump 3 is turned on and liquid is sent from the grit settling tank 1. In response to this, the relay tank 10 performs chemical dosing control by turning on/off the chemical dosing pump of the sulfuric acid adder 11 based on a preset threshold value, and sulfuric acid is added at a constant chemical dosing rate. Therefore, when the pH load is small, the pH in the relay tank 10 drops rapidly. Therefore, the pH in the relay tank 10 fluctuates greatly, and as a result, the pH fluctuation in the subsequent stages also becomes large.
(2) In controlling the dosing of coagulants, stabilizing the pH is an important control factor. When the pH fluctuates significantly as described above, the coagulation reaction becomes unstable, and the turbidity of the treated water increases even though coagulants are added.
(3) The concentration of suspended solids (SS) and the coagulation load in the inflow water to the relay tank 10 vary over a wide range, so if a fixed amount of coagulant is injected, when the coagulation load is low, the amount of coagulant added will be excessive, and unreacted chemicals will remain in the treated water. Conversely, when the coagulation load is high, the amount of coagulant added will be insufficient, and the turbidity of the treated water will increase.

One possible solution is to install a turbidity meter in the relay tank 10 and control the amount of chemical added according to the detected turbidity. However, in general, the coagulation load in the inflowing water is not proportional to the SS concentration. (That is, the particle sizes of SS vary widely, and the amount of coagulant required is closely related to the amount of fine particles that do not sink. Therefore, it is difficult to accurately detect the fine particle concentration from the turbidity measured by the turbidity meter.) Therefore, when the amount of coagulant added is controlled based on the value detected by the turbidity meter, coagulation may not be sufficient.

The applicant of this application has proposed an aggregation state monitoring device capable of accurately monitoring the aggregation state in the coagulation treatment water in Patent Documents 2 and 3.

FIG. 3 shows the configuration of the probe portion of the aggregation state monitoring sensor disclosed in Patent Document 3. This probe includes a block 21 having orthogonal surfaces 21a and 21b and an apex 21c where these intersect, a light emitting section 22 provided along the surface 21a that irradiates a laser beam toward the aggregation treatment liquid, and a surface 21b. The light receiving part 23 is provided along the light emitting part 22 and has a light receiving optical axis that is orthogonal to the light emitting optical axis of the light emitting part 22. Further, the aggregation state monitoring sensor 20 includes a light emitting circuit, a detection circuit, and a measuring circuit (not shown) in order to operate the light emitting section 22 to emit light and analyze the light reception signal of the light receiving section 23. The measurement circuit includes a timing circuit, an A/D conversion section, a calculation section, and the like.

Laser light irradiated from the light emitting unit 22 to the measurement area A near the top 21c is scattered by particles in the measurement area A, this scattered light is received by the light receiving unit 23, and is aggregated based on the change in the received light intensity over time. Condition is measured. Note that the block 21 is made of an opaque material.

The light-emitting circuit sends an electrical signal with a constant modulation frequency to the light-emitting unit in response to a signal from the timing circuit, causing it to emit a laser. The light-emitting unit emits laser light in response to the signal from the light-emitting circuit. The light-receiving unit receives scattered light generated when the laser light hits suspended matter in the water, and converts it into an electrical signal. The detection circuit removes the modulation component from the electrical signal from the light-receiving unit, and outputs a received light voltage that corresponds to the intensity of the scattered light.

The measurement circuit transmits a signal for light emission (specific frequency modulated wave) to the light emitting circuit, converts the signal from the detection circuit into a digital signal, performs a logical operation, and outputs information regarding aggregation.

FIG. 4 is a schematic diagram showing a cross section perpendicular to the optical axis of the laser beam L in the measurement area A of FIG. As shown in FIG. 4, five particles exist in the measurement area A at a certain point in time. At this point, the laser beam irradiated onto the measurement area A is scattered by each particle, and scattered light S enters the light receiving section 13. When a predetermined time Δt (preferably selected from 0.1 to 10 mSec, for example, about 1 mSec) has elapsed from this point, the number of particles existing in the measurement area A changes (theoretically, the number of particles Although the number may not change, the number of particles usually fluctuates because the particles undergo Brownian motion and the liquid is continuously injected into the measuring tank 12.)

When the number of particles changes, the intensity of scattered light changes in conjunction with it, and the intensity of light received by the light receiving section 23 changes.

The larger the particle size of the particles, the larger the fluctuation range of the received light intensity when one particle enters and exits the measurement area A. Therefore, the size of the particle size of the particles entering and exiting the measurement area A can be detected from the fluctuation range of this received light intensity. That is, the difference between the received light intensity at a given time t _k and the received light intensity at time t _k+1 after Δt has elapsed is a value proportional to the surface area of the particles that entered and exited the measurement area A during the Δt period.

FIG. 5 shows an example of a temporal change in the aggregation state monitoring sensor output signal (light reception signal intensity) obtained by signal processing the scattered light intensity of the aggregation state monitoring sensor. The output signal in FIG. 5 is a value proportional to the received light intensity (scattered light intensity) of the light receiving section 23, and the unit is, for example, mV.

In this sensor, the light emitting element of the sensor is operated intermittently to reduce wear of the element. As an example, the light emitting element is operated for 200 mSec and then stopped for 1800 mSec, so that the light is emitted once every two seconds. Note that 200 mSec, 1800 mSec, and 2 seconds are examples and are not limited to these.

The first aspect of the method for evaluating the amount of solids in wastewater from the intensity of the light reception signal of the agglomeration state monitoring sensor is to integrate the intensity of the light reception signal over time, as shown in Figure 6, and the larger the integrated value, the greater the amount of solids. This is a method of determining. In FIG. 6, the received light signal intensity is integrated during a light emission period of 200 mSec, such as between time T (mSec) and T+200 (mSec), between T+2000 (mSec) and T+2200 (mSec), and so on. That is, the areas (S ₁ , S ₂ . . . ) of the dotted portions in FIG. 6 are measured over time.

The second aspect of the method for evaluating the amount of solids in wastewater is as shown in FIG. This is a method of determining signal intensities Imin(1), Imin(2), . . . In this method, the minimum received light signal intensity (hereinafter sometimes referred to as the bottom value) Imin during a predetermined time (for example, 10 minutes. There are 300 light emission periods (10 x 60 ÷ 2 = 300) in this 10 minutes). The sum or average value of (1), Imin(2)...Imin(300) is determined, and this value is used as an index value for the amount of solids in the waste water.

In the first and second embodiments, the light emitting element is operated intermittently, but the light emitting element may be operated continuously. In this case, a predetermined period of time (for example, 200 seconds) during which the light emitting element continuously emits light is divided into shorter units (for example, 200 mSec), and the integral value and bottom value of the received light signal intensity in this unit time are calculated. Subsequently, the integrated value and bottom value of the received light signal intensity in this unit time are further integrated or averaged (additional moving average) over a predetermined time. Then, the integrated value or average value obtained over a predetermined period of time is used as an index value of the amount of solids in the waste water.

A third aspect of the method for evaluating the amount of solids in wastewater is a method of detecting the number of peaks of the received light signal intensity in a predetermined time and integrating the signal intensity of each peak, and calculating the amount of solids based on this integrated value. evaluate.

Note that the predetermined time is preferably selected from 200 mSec to 20 minutes, particularly from 200 mSec to 10 minutes, and the above 200 seconds and 10 minutes are just examples.

A fourth embodiment of the method for assessing the amount of solids in wastewater will now be described with reference to Figures 8a and 8b.

FIG. 8a is a graph plotting the received signal strength measured at each of times t ₁ , t ₂ . . . t _z , and the interval between each time Δt (i.e., t _k -t _k-1 ) is, as described above, preferably 0.1 to 10 mSec, for example 1 mSec.

Fig. 8b is an explanatory diagram in which the minimum points _P1 , _P2 ... and the maximum points _Q1 , _Q2 ... are plotted in Fig. 8a, and the differences between the minimum points and the maximum points (hereinafter sometimes referred to as peak differences) _h1 , _h2 ... are plotted. Note that extremely small minimums and maximums whose peak differences are equal to or less than a predetermined value are ignored in the processing because the difference from disturbance is unclear. For example, when _h1 is equal to or less than a predetermined value, if _P1 ≧ _P2 , _P1 and _Q1 are ignored in the data processing, and if _P1 < _P2 , _Q1 and _P2 are ignored, and the data processing is performed so that the difference between _P1 and _Q2 becomes the peak difference.

As described above, the difference _hk between the light receiving signal intensity at any time _tk-1 and the light receiving signal intensity at time _tk is a value correlated to the surface area of the particle that entered and exited the measurement area A between times tk _-1 and _tk .

Therefore, the amount of solids in the wastewater is evaluated based on the sum of all peak differences h ₁ , h ₂ ... _hn during Δt·z seconds from time t ₁ to t _z (z is set to 200, for example, and when Δt=1 mSec, Δt×z is 0.2 seconds).

The turbidity of the liquid between the flocculated particles (flocs) in the wastewater (interparticle turbidity) can also be detected or estimated from the intensity of the light received signal from the flocculation state monitoring sensor. That is, as shown in Figures 4 to 7, the output signal from the flocculation state monitoring sensor shows a peak-bottom type fluctuation in which fluctuations between a peak (maximum) and a bottom (minimum) are repeated as flocs enter and leave the measurement area.

This bottom value is the sensor output value when many flocs have left the measurement area. Therefore, this bottom value is an index value that represents the concentration of fine suspended matter in the liquid between the flocs, i.e., interparticle turbidity, and the lower the interparticle turbidity, the smaller the bottom value. Therefore, when coagulation-treated water obtained by coagulating wastewater from civil engineering works is monitored with a coagulation state monitoring sensor, it can be determined that the lower the bottom value, the better the coagulation is being performed.

JP 2015-139767 A JP 2016-3974 Publication JP 2017-26438 A

The reason for the large pH fluctuations in the relay tank 10 where the pH adjuster is injected is that the inflow operation into the relay tank 10 is frequent and intermittent, and the pH load in the inflow water fluctuates with each inflow.

When the wastewater discharged due to construction is reduced due to holidays, etc., the inflow water will be only water released from the natural world (rainwater, spring water, etc.), and extremely clear water (clear water that does not need to coagulate) will flow in. in many cases. If such clear water is discharged without being subjected to aggregation treatment, it may have less of a burden on the environment. Therefore, it is desirable to judge the necessity of coagulation treatment depending on the quality of the water flowing into the relay tank 10.

It is also necessary to properly assess the effectiveness of the coagulation treatment.

The objective of the present invention is to provide a method for treating wastewater from civil engineering works that can efficiently perform coagulation treatment of wastewater from civil engineering works using a coagulation state monitoring device.

The gist of the method for treating wastewater from civil engineering works of the present invention is as follows:

[1] A grit tank for receiving wastewater from civil engineering works;
a relay tank to which water is transferred from the sand settling tank;
an acid adding device for adding acid to the relay tank;
a thickener to which water is transferred from the relay tank via a pipe;
an inorganic flocculant adding device for adding an inorganic flocculant to the pipe;
a discharge tank into which the supernatant water from the thickener flows;
A method for treating wastewater from civil engineering works using a civil engineering works wastewater treatment facility having the following features:
This method for treating wastewater from civil engineering works is characterized in that, when the pH of the relay tank during transfer from the grit settling tank to the relay tank is less than a preset pH value A, the addition of acid to the relay tank is stopped, and when the pH is A or higher, an amount of acid X is added to the relay tank so that the target pH value becomes A.

[2] When water is not being transferred from the sand settling tank to the relay tank and the pH of the relay tank exceeds a preset predetermined value B, add an amount of acid to the relay tank by the acid addition device. It is added by Y,
The predetermined value A and the predetermined value B have a relationship that satisfies the following formula (1),
A+(0.5-1.5)=B (1)
The method for treating civil engineering wastewater according to [1], wherein the added amount Y is 10 to 90% of the added amount X.

[3] A sensor for detecting interparticle turbidity of water in the relay tank is installed in the relay tank, and particle turbidity detected by the sensor when water is not being transferred from the sand settling tank to the relay tank. When the degree is equal to or higher than a predetermined value C, the acid addition device adds acid to the relay tank in an amount Y,
The method for treating civil engineering wastewater according to [1] or [2], wherein the addition amount Y is 10 to 90% of the addition amount X.

[4] The sensor is an flocculation state monitoring sensor including a measurement light irradiating unit that irradiates a measurement area of the wastewater with measurement light, a scattered light receiving unit that receives scattered light by particles in the wastewater in the measurement area, and an amplitude measuring unit that measures the amplitude of a received light signal obtained in the scattered light receiving unit, and a measurement value calculating unit that monitors and tallys up the occurrence of the measured amplitudes, calculates an occurrence rate or occurrence frequency of a specific amplitude, and calculates an index related to the flocculation of the wastewater that represents the particle size of flocs in the treated water,
The method for treating wastewater from civil engineering works according to [3], characterized in that the interparticle turbidity is detected based on the minimum value of the change over time in the measurement value of the flocculation state monitoring sensor.

[5] A grit tank for receiving wastewater from civil engineering works;
a relay tank to which water is transferred from the sand settling tank;
an acid adding device for adding acid to the relay tank;
a thickener to which water is transferred from the relay tank via a pipe;
an inorganic flocculant adding device for adding an inorganic flocculant to the pipe;
A method for treating wastewater from civil engineering works using a civil engineering works wastewater treatment facility having a discharge tank into which supernatant water flows from the thickener,
The thickener includes a center core that receives water from the piping;
a sensor for detecting interparticle turbidity of water in the center core is installed in the center core;
The inorganic flocculant adding device is operated while water is being transferred from the relay tank to the thickener,
A method for treating wastewater from civil engineering works, comprising operating the inorganic flocculant adding device so that the inter-particle turbidity detected by the sensor reaches a preset value D.

[6] A method for treating wastewater from civil engineering works according to [5], in which, when water is being transferred from the settling tank to the relay tank, if the pH of the relay tank is less than a preset pH value A, the addition of acid to the relay tank is stopped, and if the pH is A or higher, an amount of acid X is added to the relay tank so that the target pH value becomes A.

[7] When water is not being transferred from the settling tank to the relay tank and the pH of the relay tank exceeds a preset value B, an amount of acid is added to the relay tank by the acid adding device,
The predetermined value A and the predetermined value B have a relationship satisfying the following formula (1):
A + (0.5 to 1.5) = B (1)
The method for treating wastewater from civil engineering works according to [6], wherein the amount Y of the acid to be added is 10 to 90% of the amount X of the acid to be added.

According to the method for treating wastewater from civil engineering works of the present invention, the pH control and addition of coagulant during the treatment of wastewater from civil engineering works can be appropriately performed, and the wastewater from civil engineering works can be efficiently coagulated and treated.

It is a flow diagram of civil engineering work wastewater treatment equipment explaining an embodiment. FIG. 1 is a flow diagram of a civil engineering work wastewater treatment facility illustrating a conventional example. It is a block diagram of an aggregation state monitoring sensor. FIG. 2 is a schematic diagram of a measurement area of the aggregation state monitoring sensor. 1 is a graph showing the output of an aggregation state monitoring sensor. It is a graph showing the output of an aggregation state monitoring sensor. 1 is a graph showing the output of an aggregation state monitoring sensor. It is a graph showing the output of an aggregation state monitoring sensor. 1 is a graph showing experimental data. It is a graph showing experimental data. It is a graph showing experimental data. 1 is a graph showing experimental data.

Embodiments will be described below with reference to the drawings.

Figure 1 shows a civil engineering work wastewater treatment facility for carrying out a civil engineering work wastewater treatment method according to an embodiment of the present invention.

In FIG. 1, agglomeration state monitoring sensors 14 and 22 are installed in the relay tank 10 and the center core 21. Further, a controller 12 for controlling the sulfuric acid addition device 11 is installed. A transfer pump operation signal indicating ON/OFF of the transfer pump 3, a detection signal of the pH meter 13, and a detection signal of the aggregation state monitoring sensor 14 are input to the controller 12, and the controller 12 controls the sulfuric acid addition device 11. controlled.

A controller 26 is also installed to control each of the flocculant addition devices 17 and 18. A transfer pump operation signal indicating whether the transfer pump 15 is on or off and a detection signal from the flocculation state monitoring sensor 22 are input to the controller 26, and each of the flocculant addition devices 17 and 18 is controlled by the controller 26.

The rest of the configuration of the equipment in FIG. 1 is similar to the equipment in FIG. 2, and the same reference numerals indicate the same parts.

The agglomeration state monitoring sensors 14 and 22 include an aggregation monitoring device (a coagulation monitoring device that monitors the treatment state of treated water to be agglomerated) disclosed in Patent Document 3 (Japanese Unexamined Patent Publication No. 2017-26438). A measurement light irradiation unit that irradiates a measurement area of treated water, a scattered light reception unit that receives scattered light by particles of the water to be treated in the measurement area, and an amplitude of a light reception signal obtained in the scattered light reception unit. The to-be-treated water includes an amplitude measuring means for measuring, monitors and aggregates the appearance of the measured amplitude, calculates the occurrence rate or frequency of occurrence of a specific amplitude, and represents the particle size of flocs in the to-be-treated water. Agglomeration monitoring device comprising a measurement value calculation unit that calculates an index related to aggregation of It is not something that will be done.

In addition, the coagulation monitoring device of Patent No. 6281534 is
"A coagulation monitoring device for monitoring the treatment state of water undergoing coagulation treatment,
a measurement light irradiation unit that irradiates a measurement area of the water to be treated with measurement light;
a scattered light receiving unit that receives scattered light caused by particles of the water to be treated in the measurement area;
a measurement value calculation unit including an amplitude measurement means for measuring the amplitude of a received light signal obtained from the scattered light receiving unit, monitoring and aggregating the occurrence of the measured amplitude, calculating an occurrence rate or occurrence frequency of a specific amplitude, and calculating an index relating to the aggregation of the water to be treated that represents the particle size of flocs in the water to be treated;
Equipped with
The amplitude measuring means detects a first inflection point where the light receiving signal changes from increasing to decreasing and a second inflection point where the light receiving signal changes from decreasing to increasing, and measures the amplitude from a level difference between the first inflection point and the second inflection point."

In the facility of Figure 1, as in the case of Figure 2, civil engineering wastewater is water discharged from civil engineering work sites at irregular intervals, and flows into the grit tank 1. When the water level in the grit tank 1 reaches a specified upper limit, the transfer pump 3 starts up and transfers the water in the grit tank 1 to the relay tank 10. When the water level in the grit tank 1 falls below the lower limit, the transfer pump 3 stops. The operation time of the transfer pump 3 is usually short, from 1 to 120 minutes, and especially from 0.1 to 30 minutes. However, in the event of rainfall exceeding 20 mm/hour due to a sudden downpour or typhoon, it may take several hours, or in some cases more than 48 hours.

In this embodiment, the sulfuric acid addition device 11 is configured such that when water is being sent from the sand settling tank 1 to the relay tank 10 by the pump 3 (when the pump 3 is ON), the pH detected by the pH meter 13 is If it is less than a preset predetermined value A (a value selected from 6 to 10, especially 7 to 9, for example 8.5), the addition of sulfuric acid to the relay tank 10 is stopped, and the pH meter 13 detects the value. When the pH is greater than A, the controller 12 calculates the amount X of sulfuric acid to be added so that the target value of the pH meter 13 becomes A, and sulfuric acid is added to the relay tank 10 at the amount X. Note that the control by the controller 12 can specifically apply PI or PID control with a predetermined value A (for example, 8.5) as a target value, but is not limited to this.
In one aspect of the present invention, even when the pump 3 is stopped, if the pH value detected by the pH meter 13 exceeds a predetermined value B, sulfuric acid is added in an amount Y. Here, the predetermined value B has a relationship with the predetermined value A as shown in equation (1).
A+(0.5-1.5)=B (1)
Further, the amount Y of acid added is also controlled based on the measured value of the pH meter 13, but the amount Y added is determined by the amount Y being added when the pump 3 is in operation and the wastewater is transferred from the sand settling tank 1 to the relay tank 10. It is preferable to set it to 10 to 90%, preferably 20 to 80%, of the addition amount X, which is the calculation result in the case. With this range, the amount of sulfuric acid to be injected while the pump 3 is stopped can be appropriately set.

Also, the turbidity components of wastewater from civil engineering work sites are mainly alkaline. Therefore, in another aspect of the present invention, when the bottom value of the output of the flocculation state monitoring sensor 14 installed in the relay tank 10 is equal to or greater than the preset value C even when the pump 3 is stopped, sulfuric acid is added at the amount Y even when the pump 3 is stopped. The amount Y of sulfuric acid added at this time is set in the same manner as above.

As shown in FIG. 1, when the water level in the relay tank 10 reaches the upper limit, the transfer pump 15 starts and sends the water in the relay tank 10 into the center core 21 of the thickener 20 via the pipe 16. The operation time of the transfer pump 15 is usually short, about 1 to 120 minutes, and especially about 0.1 to 30 minutes. However, in the event of rainfall exceeding 20 mm/hour due to a sudden downpour or typhoon, it may take several hours, or even 48 hours or more.

While the pump 15 is in operation, an inorganic flocculant and a polymer flocculant are injected into the piping 16 from the flocculant addition devices 17 and 18, and are stirred and mixed in the piping 15 to form the center core. It is released within 21 days.

The flocculated water in the center core 21 flows into the thickener 20 from the bottom of the center core 21, and the flocs sink to the bottom of the thickener 20, where solid-liquid separation takes place.

In one aspect of the present invention, while the pump 15 is operating, the flocculating property is evaluated based on a change in the bottom value (change in turbidity between flocs) of the flocculation state monitoring sensor 22 of the center core 21, and the flocculant addition device Adjust the flocculant injection amount according to step 17. Specifically, based on the bottom value of the sensor 22 (Imin(1), Imin(2), . . . in FIG. 7), the amount of inorganic flocculant added by the flocculant addition device 17 is controlled by PI control or PID control.
Further, the polymer flocculant is added in a constant amount while the pump 15 is operating (if the pump 15 is stopped, the addition of the polymer flocculant is also stopped).

The supernatant liquid after the flocs have settled moves through the overflow pipe 24 to the discharge tank 30. When the water level in the discharge tank 30 reaches a predetermined level or higher, the pump 31 in the discharge tank 30 starts up and the clear water in the tank is discharged into a river or the like. When a predetermined amount of sediment accumulates in the thickener 20, it is pulled out and compressed in a dehydrator or the like to become a dehydrated cake, which is then discarded.

A civil engineering wastewater treatment method according to a preferred embodiment of the present invention has the following characteristics.

(1) When new wastewater flows into the relay tank 10 and the pH detected by the pH meter 13 is equal to or higher than a specified value (predetermined value A set in advance), sulfuric acid or the like is injected. In this case, the amount of sulfuric acid injected is controlled with the specified value as the target value (the amount added at the pH value at this time is X). Note that if the pH is below the specified value, the injection of sulfuric acid is stopped even if wastewater is flowing in (transfer pump 3 is ON).

Conversely, when the inflow of wastewater into the relay tank 10 is stopped, if the interfloc turbidity detected by the flocculation state monitoring sensor 14 is equal to or greater than a specified value (predetermined value C) or if the pH detected by the pH meter 13 is equal to or greater than a specified value (predetermined value B), the amount of sulfuric acid added is calculated and controlled with these specified values as target values. The amount of added Y at this time is set to 10 to 90%, preferably 20 to 80%, of X (the amount of added when wastewater is flowing into the relay tank 10) when the pH value of the relay tank 10 is the same. Note that when the inflow of wastewater into the relay tank 10 is stopped, if the interfloc turbidity is less than the specified value C or the pH is less than the specified value B, the injection of sulfuric acid is stopped.

(2) Since the transfer from the relay tank 10 to the thickener 20 is performed intermittently, the aggregation state monitoring sensor 22 is installed in the center core 21 of the thickener 20, and the bottom value of the sensor 22 is specified while the transfer pump 15 is in operation. The amount of inorganic flocculant added is controlled using the target value.

The following civil engineering work wastewater treatment was performed using the equipment shown in Figure 1 installed at a civil engineering work site. Note that a turbidity meter (manufactured by Optex Co., Ltd.) was installed in the discharge tank 30 to measure the turbidity.

The capacity of each tank in the equipment and the specifications of the sensors are as follows:

Sand settling tank 1: ^100m3 , depth 1m
Relay tank 10: ^10m3 , depth 2m
Thickener 20: ^30m3 , depth 3m
Center core 21: diameter 1m, height of submerged part 1m
Discharge tank 30: ^5m3 , depth 1m
Agglutination state monitoring sensor 14, 22: S.sensingCS-PB manufactured by Kurita Water Industries, Ltd.
Water supply speed of pump 3: 100m ³ /Hr
Water supply speed of pump 15: 100m ³ /Hr
Sulfuric acid concentration: 70% by mass
Inorganic flocculant: PAC (polyaluminum chloride liquid product)
Polymer flocculant: Clifflock PA-331 manufactured by Kurita Water Industries, Ltd.

At this site, the average quality of the wastewater was pH 6.5-7.5 and turbidity 0-50.

[Experimental example 1 (comparative example 1)]
When the pH in the relay tank 10 detected by the pH meter 13 rose to 8.5 or higher, sulfuric acid was added at a rate of 500 L/min, and when the pH detected by the pH meter 13 became 8.3 or lower, the addition of sulfuric acid was stopped.

PAC and polymer flocculant were injected only when the transfer pump 15 of the relay tank 10 was ON. The PAC injection rate was 15 mL/min, and the polymer flocculant injection rate was 2 L/min.

The change in pH over time in the relay tank 10 and the discharge tank 30 is shown in Figure 9, and the turbidity in the discharge tank 30 is shown in Figure 10.

In this comparative example, the addition of sulfuric acid is performed when the pH in the relay tank 10 is ≧8.5, and is stopped when the pH in the relay tank 10 is ≦8.2, and the addition of sulfuric acid is performed when the pH in the relay tank 10 is ≦8.2. , OFF), the pH of both the relay tank and the discharge tank fluctuates greatly (the pH of the discharge tank varies from 5.5 to 9.5, and the pH of the relay tank varies from 6 to 9.5). In addition, since the amount of PAC added was simply injected in a fixed amount when the transfer pump 15 was turned on, the turbidity of the discharge tank did not fall below 30 degrees.

[Experiment Example 2 (Example 1)]
When the transfer pump 3 of the sand settling tank 1 is ON, if the pH of the relay tank 10 is <7.5, the injection of sulfuric acid is stopped, and if the pH is 7.5, the target pH is set to 7.5. The amount of sulfuric acid to be added was injected using PI control, and even when the pump 3 was stopped, when the pH of the relay tank 10 was 8.5, sulfuric acid was added at an amount that was 50% of the PI calculation based on the pH at that time. During shutdown, PAC injection is stopped if pH < 8.5). PAC and polymer flocculant were injected only when the transfer pump 15 of the relay tank 10 was turned on, and the amount of PAC added was controlled by PI based on the bottom value of the flocculation state monitoring sensor 22. The maximum injection volume of PAC was set to 40 mL/min to avoid any residue). In addition, the polymer flocculant injection rate was 2 L/min.

FIG. 11 shows the change over time in the pH in the relay tank 10 and the discharge tank 30 at this time, and FIG. 12 shows the turbidity of the discharge tank.

In addition to carrying out sulfuric acid injection in response to new load inflow depending on the presence or absence of inflow water, even when the transfer pump 3 is stopped, when pH≧8.5, 50% of the PI calculation based on the pH at that time is performed. Since the chemical injection of sulfuric acid was carried out at the addition amount, fluctuations in the pH of both the relay tank 10 and the discharge water tank 30 were suppressed compared to Experimental Example 1.
Furthermore, by controlling the amount of PAC added by PI, it was possible to control the amount of PAC injection depending on the load situation, and there was a lot of turbidity in the wastewater, and the amount of inorganic flocculant added was insufficient even at the maximum injection amount. Although the turbidity rises to a maximum of 50 degrees in this case, the turbidity is relatively low compared to the case of Experimental Example 1, and the discharge tank turbidity is approximately 0 at best.

1 Sand settling tank 10 Relay tank 13 pH meter 14, 22 Aggregation state monitoring sensor 17 Inorganic flocculant addition device 18 Polymer flocculant addition device 20 Thickener 21 Center core 30 Discharge tank

Claims (7)

A grit tank for receiving wastewater from civil engineering works;
a relay tank to which water is transferred from the sand settling tank;
an acid adding device for adding acid to the relay tank;
a thickener to which water is transferred from the relay tank via a pipe;
an inorganic flocculant adding device for adding an inorganic flocculant to the pipe;
a discharge tank into which the supernatant water from the thickener flows;
A method for treating wastewater from civil engineering works using a civil engineering works wastewater treatment facility having the following features:
This method for treating wastewater from civil engineering works is characterized in that, when the pH of the relay tank during transfer from the grit settling tank to the relay tank is less than a preset pH value A, the addition of acid to the relay tank is stopped, and when the pH is A or higher, an amount of acid X is added to the relay tank so that the target pH value becomes A. When water is not being transferred from the sand settling tank to the relay tank, and when the pH of the relay tank exceeds a preset predetermined value B, acid is added to the relay tank in an amount Y by the acid addition device. It is something that
The predetermined value A and the predetermined value B have a relationship that satisfies the following formula (1),
A+(0.5-1.5)=B (1)
The method for treating civil engineering wastewater according to claim 1, wherein the amount Y added is 10 to 90% of the amount X added. A sensor for detecting interparticle turbidity of the water in the relay tank is installed in the relay tank, and when the interparticle turbidity detected by the sensor while water is not being transferred from the grit settling tank to the relay tank is equal to or greater than a preset value C, an amount of acid Y is added to the relay tank by the acid adding device,
3. The method for treating wastewater from civil engineering works according to claim 1, wherein the amount Y is 10 to 90% of the amount X. The sensor includes a measurement light irradiation section that irradiates a measurement region of the wastewater with measurement light, a scattered light reception section that receives scattered light due to particles in the wastewater in the measurement region, and a measurement light reception section that receives measurement light from the scattered light reception section. includes an amplitude measuring means for measuring the amplitude of the received light signal, which monitors and aggregates the occurrence of the measured amplitude, calculates the occurrence rate or frequency of occurrence of a specific amplitude, and determines the particle size of flocs in the water to be treated. A coagulation state monitoring sensor comprising: a measurement value calculation unit that calculates an index related to coagulation of the wastewater representing
4. The method for treating civil engineering work wastewater according to claim 3, wherein the interparticle turbidity is detected based on a minimum value of a change over time of the measured value of the agglomeration state monitoring sensor. A settling tank that receives civil engineering work wastewater,
a relay tank to which water is transferred from the sand settling tank;
an acid addition device that adds acid to the relay tank;
a thickener to which water is transferred from the relay tank via piping;
an inorganic flocculant addition device that adds an inorganic flocculant to the pipe;
In a method for treating civil engineering work wastewater using a civil engineering work wastewater treatment facility having a discharge tank into which supernatant water flows from the thickener,
The thickener includes a center core that receives water from the pipe,
A sensor is installed in the center core to detect interparticle turbidity of water in the center core,
The inorganic flocculant addition device is operated while water is being transferred from the relay tank to the thickener,
A method for treating civil engineering wastewater, comprising operating the inorganic flocculant addition device so that the interparticle turbidity detected by the sensor becomes a predetermined value D. The method for treating wastewater from civil engineering works according to claim 5, wherein, when water is transferred from the settling tank to the relay tank, if the pH of the relay tank is less than a preset pH value A, the addition of acid to the relay tank is stopped, and if the pH is A or higher, an amount of acid X is added to the relay tank so that the target pH value becomes A. When water is not being transferred from the sand settling tank to the relay tank, and when the pH of the relay tank exceeds a preset predetermined value B, acid is added to the relay tank in an amount Y by the acid addition device. It is something that
The predetermined value A and the predetermined value B have a relationship that satisfies the following formula (1),
A+(0.5-1.5)=B (1)
7. The method for treating civil engineering wastewater according to claim 6, wherein the amount Y added is 10 to 90% of the amount X added acid.

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