HK1122267A1 - Method and apparatus for determining a coagulant injection rate in a water processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for deciding a flocculating agent infusion rate capable of automatically deciding a proper flocculating agent infusion rate in a short time in a method for treating water which performs coagulation/sedimentation treatment. <P>SOLUTION: After the flocculating agent 20 is injected into test water tanks with a coagulation analyzer including the test water tanks 1A to 1D that store a predetermined amount of raw water, a feed water pump 7, water feed/discharge vales 4, 6 for the raw water and cleaning water, stirrers 3A to 3D, a flocculating agent injection section 21, a detector 30 that measures particle sizes and particle number of floc, and the like, the flocculating agent infusion rate is decided or an infusion amount of the flocculating agent is controlled from an agglomeration starting time after the flocculating agent is dispersed by stirring and a time for an agglomeration of particles to start (agglomeration starting time) is measured. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

Method and device for determining coagulant injection rate in water treatment method

Technical Field

The present invention relates to a method and an apparatus for determining a flocculant injection rate (a ratio of an amount of flocculant to an amount of water to be treated) in a flocculation treatment for treating surface water such as river water and lake water, industrial water, sewage, sludge, plant wastewater, and the like.

Background

A water purification plant using a rapid filtration method generally includes a mixing tank into which a flocculant is injected and rapidly stirred, a flocculation tank in which aggregates (flocs) generated in the mixing tank are grown, a sedimentation tank for settling and removing the grown flocs, and a filtration tank for removing particles or flocs that have not settled completely (see fig. 7 of patent document 2).

The main points of the rapid filtering mode are as follows: the flocculant injection rate is controlled to an appropriate value according to the quality of raw water, and flocs having good settleability are formed. When the flocculation treatment is performed at an inappropriate injection rate, there are problems such as an increase in the loss head of the filtration tank, an increase in the backwashing frequency, and an outflow of particles from the filtration tank due to the remaining flocs from the sedimentation tank and poor flocculation.

The appropriate coagulant injection rate varies depending on not only the turbidity of the raw water but also the alkalinity, pH, water temperature, etc., and is different for each raw water, and therefore, the coagulant injection rate cannot be determined based on the turbidity of the raw water. Therefore, conventionally, in water purification plants, the determination of the flocculation state and the determination or control of the flocculant injection rate have been performed by the following methods.

(1) Beaker test

This method involves extracting raw water to be treated into several beakers at a constant amount, gradually changing the injection rate in each beaker, causing an aggregation reaction by rapid stirring and slow stirring, and determining the turbidity of the supernatant water and the sedimentation state of the flocs after standing for a predetermined time to determine the flocculant injection rate (see fig. 8 of patent document 2).

These operations are usually performed by manual analysis, but an automatic beaker tester which automatically performs the steps from extraction of raw water, injection of a flocculant, setting of the rotation speed and rotation time of a stirrer, and measurement of the turbidity of supernatant water as described in patent document 1 has also been put into practical use (see patent document 1 for details).

(2) Formula of injection rate

The feed-forward control is performed based on an injection rate formula representing the relationship between the turbidity, pH, alkalinity, water temperature, and the like of raw water as parameters and an appropriate coagulant injection rate. The injection rate formula is empirically determined based on beaker tests, sediment water turbidity at the facility of implementation, and the like. The development of this approach is: examples of adding feedforward control based on the turbidity measurement value of the precipitation water, and examples of approximating the results of the beaker test by the operator and the actual operation of the facility by fuzzy control and neural control (paragraphs 0006 and 0007 of patent document 2).

(3) Condensation sensor

In this method, as in the invention method disclosed in patent document 2, a liquid flow of a fluid to be measured is irradiated with a light beam, the average particle diameter and the number concentration of flocs are determined from the average value and the standard deviation of the transmitted light quantity, and the coagulant injection rate is controlled so that the average particle diameter becomes an appropriate value (see patent document 2 for details).

For convenience of explanation, the following patent documents 3 to 6 which disclose the related art of the present invention will be described later.

Patent document 1: japanese laid-open patent publication No. 2-114178

Patent document 2: japanese patent No. 3205450

Patent document 3: japanese patent No. 3672158 (corresponding to US6,184,983)

Patent document 4: japanese patent No. 2824164

Patent document 5: japanese patent laid-open publication No. 10-311784 (corresponding to the publication of patent document 3, US09/037,431)

Patent document 6: japanese laid-open patent publication No. 2002-90284

However, the agglomeration state determination method and the coagulant injection rate determination method using the above-described methods have the following problems.

(1) The method of beaker test of (1) has a problem that a skilled operator is required and different operators are liable to give different results. In addition, there are also the following problems: since the time required for determining the coagulation state and the appropriate coagulant injection rate is as long as about 30 minutes, it is difficult to frequently perform the beaker test, and feedback of the coagulant injection rate to the facility where the beaker test is performed is delayed.

If an automatic beaker tester that automates the beaker test operation is used, the operator's operation can be greatly reduced, but it still takes about 30 minutes to obtain the measurement result, and the problem of a large time lag cannot be solved.

(2) The method of the injection rate formula (2) is different depending on raw water, and therefore, the injection rate formula of each water treatment plant must be managed and cannot be guaranteed to be permanently used. Namely, there is a problem that: when a dam is built on the upstream side of the intake port or a construction is performed on a coastal work, and the influence of heavy rain, the relationship between the water quality and the optimum coagulant injection rate may be lost, and the system is not widespread in terms of area and time.

(3) The method of the coagulation sensor can automatically manage the coagulant injection rate in real time to obtain proper floc particle size, and solves the problems of (1) operators and time lag and (2) universality. However, the appropriate floc particle size varies depending on the quality of raw water, and it is necessary to establish a database in advance for the relationship between the turbidity of raw water and the optimum floc particle size in order to automatically control the flocculant injection rate. Namely, there is a problem that: data from the condensation sensor must be acquired over the entire four seasons, which is time consuming before the official operation.

Although the problems in water purification plants have been described above, it goes without saying that the same problems exist in the coagulation of industrial water, sewage, and plant wastewater.

Disclosure of Invention

The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a flocculant injection rate determining method and device capable of automatically determining an appropriate flocculant injection rate in a short time in a water treatment method for performing flocculation treatment.

In order to solve the above problems, the present invention is a method for determining a ratio of an amount of coagulant injected to an amount of water to be treated (coagulant injection rate) in a water treatment method for performing coagulation treatment by injecting a coagulant into water to be treated, the method comprising the following step (claim 1).

(1) A predetermined amount of water to be treated is extracted into a plurality of test water tanks, and predetermined amounts of flocculant different from each other are injected into the sample water extracted into each of the test water tanks, thereby making each sample water have different flocculant injection rates (flocculant injection step).

(2) The respective sampled waters were measured for the time (agglomeration start time) from when the coagulant was injected into the respective sampled waters until the coagulant was dispersed by stirring and the particles in the respective sampled waters start to agglomerate (agglomeration start time measurement step).

(3) Based on the measured agglomeration start time and the measured coagulant injection rate of each sample water, a fitting line is formed from the relationship between the agglomeration start time and the coagulant injection rate, and the calculation is performed (fitting line calculation step).

(4) An appropriate coagulant injection rate is calculated for the water treatment facility based on the fit line and an appropriate value of the agglomeration start time preset for the water treatment facility (an appropriate coagulant injection rate calculation step).

In addition, although the invention of claim 1 uses a plurality of test water tanks, the agglomeration start time of the sample water having different flocculant injection rates may be measured by repeatedly using 1 test water tank as in the invention of claim 2 described below. That is, the method of determining the coagulant injection rate according to claim 1 is characterized in that the steps (1) and (2) are replaced with the following steps (1a), (2a) and (2 b).

(1a) A predetermined amount of water to be treated was taken out into a single test water tank, a predetermined amount of flocculant was injected into a sample water taken out into the test water tank, and the time (agglomeration start time) from the time when the flocculant was injected until the flocculant was dispersed by stirring and the particles in the sample water started to agglomerate was measured.

(2a) After the above-mentioned step, the test water tank was washed with washing water, the washing water was drained from the test water tank, a predetermined amount of the water to be treated was again extracted into the test water tank, a predetermined amount of the flocculant was injected into a sample water different from the above-mentioned step, and the agglomeration start time was measured.

(2b) The same procedure as described above was repeated a plurality of times while changing the amount of coagulant injected, and the agglomeration start time was measured for each of the sample waters having different coagulant injection rates.

In addition, as in the invention of claim 3 described below, when a database such as a relational expression of the relationship between the agglomeration start time and the coagulant injection rate, which is obtained experimentally in advance, is used, an appropriate coagulant injection rate can be calculated by measuring 1 agglomeration start time using 1 test water tank. That is, a method for determining a ratio of an amount of coagulant injected to an amount of water to be treated (coagulant injection rate) in a water treatment method for performing coagulation treatment by injecting a coagulant into water to be treated, the method comprising the following step (claim 3).

(1) A predetermined amount of water to be treated is extracted into a single test water tank, a predetermined amount of flocculant which is set in advance based on the quality of the water to be treated is injected into a sample water extracted into the test water tank, and the time (agglomeration start time) until the flocculant is dispersed by stirring after the flocculant is injected and the particles in the sample water start to agglomerate is measured.

(2) When the deviation between the measured value of the measured agglomeration start time and the appropriate value of the agglomeration start time preset according to the water treatment facility is within a predetermined range, the coagulant injection rate corresponding to the predetermined amount of the coagulant in the step (1) is determined as an appropriate coagulant injection rate, and when the deviation is larger than the predetermined range, the appropriate coagulant injection rate is calculated by the following procedures (21) to (23).

(21) The relation between the agglomeration start time and the coagulant injection rate is determined by a general formula including 2 constants, and one of the constants is determined based on the water quality of the water to be treated based on a database obtained in advance by an experiment, and a general formula including 1 constant is obtained.

(22) And a calculation formula for determining the relationship between the agglomeration start time and the coagulant injection rate by obtaining another constant based on the general formula including 1 constant, the measured value of the agglomeration start time, and the coagulant injection rate at the time of the measurement.

(23) Based on the above-mentioned operational expression and an appropriate value of the agglomeration start time preset in the water treatment facility, an appropriate coagulant injection rate is calculated.

The embodiment of the invention according to claim 1 or 3 is preferably the invention according to claims 4 to 6 below. That is, the method of determining the coagulant injection rate according to claim 1 or 3 is characterized in that the number of particles in each particle size interval in the sampled water is measured, the time at which the number of particles in a predetermined small particle size interval of the particles present in the sampled water starts to decrease before the coagulant is injected, or the time at which the number of particles in a predetermined particle size interval larger than the predetermined small particle size interval starts to increase due to the start of agglomeration after the coagulant is injected is measured, and the agglomeration start time is determined from at least one of the two times (claim 4).

The method of determining the coagulant injection rate according to claim 1 or 3, wherein the mean particle size and the number of particles in the sample water are measured, the time at which an increase in the mean particle size is observed is measured as a floc growth start time, and the time at which the number of particles counted as flocs starts to increase is measured as a floc increase start time, and the flocculation start time is determined based on at least one of the floc growth start time and the floc increase start time (claim 5).

The method of determining the coagulant injection rate according to claim 1 or 3, wherein the appropriate value of the agglomeration start time preset in the water treatment facility is set based on the retention time of the water to be treated in the mixing tank of the water treatment facility (claim 6).

The retention time of the water to be treated in the mixing tank is determined by the volume of the mixing tank and the amount of the treated water in the actual water treatment facility (implementation facility). In addition, since the coagulant injection rate suitable for the facility varies from time to time depending on the quality of the water to be treated (raw water), it is necessary to extract the water to be treated appropriately into the test water tank and determine the coagulant injection rate suitable for the variation.

The invention relating to the coagulant injection rate determination device is preferably the invention of claim 7 below. That is, an apparatus for carrying out the method for determining the coagulant injection rate according to claim 1 or 3 is characterized by comprising: at least 1 test water tank having a stirrer, a coagulant injection device for injecting predetermined amounts of different coagulants, a caking start time measuring device, and an arithmetic device for calculating an appropriate coagulant injection rate (claim 7).

According to the present invention, in a water treatment method for coagulation treatment, an appropriate coagulant injection rate can be automatically determined in a shorter time than in the conventional method.

Drawings

Fig. 1 is a main system diagram showing an example in which a coagulation analyzer, which is a device for carrying out the coagulant injection rate determination method of the present invention, is connected to a water purification process flow.

FIG. 2 is a schematic structural view of an embodiment of the coagulation analyzer shown in FIG. 1.

Fig. 3 is a schematic side sectional view of the test water tank of fig. 2.

Fig. 4 is a diagram illustrating the change in the number of particles measured after the coagulant is injected into the sample water.

FIG. 5 is a graph showing an example of experimental results of particle number change of particles of 1 to 3 μm, and is used for explaining agglomeration start time.

FIG. 6 is a graph showing an example of experimental results of particle number change of particles of 3 to 7 μm, and is used for explaining agglomeration start time.

Fig. 7 is an explanatory view showing a fit line as a relationship between the agglomeration start time and the coagulant injection rate.

FIG. 8 is an explanatory view showing a comparison between the conventional method and the method of the embodiment of the present invention in terms of the time required for determining the coagulant injection rate.

FIG. 9 is a schematic structural view of an embodiment of the coagulation analyzer shown in FIG. 1, which is different from that of FIG. 2.

FIG. 10 is a graph showing changes in the average particle diameter measured after injecting a flocculant into sampled water, in relation to the growth start time of flocs.

FIG. 11 is a graph showing the change in the average number of flocs measured after injecting a flocculant into sampled water, in relation to the increase start time of the flocs.

FIG. 12 is a graph showing the relationship between the measured value and the appropriate value of the agglomeration start time, and the general formula of the coagulant injection rate and the agglomeration start time, and the injection rate calculation formula after the constants were determined, in relation to example 2.

Detailed Description

Hereinafter, an embodiment of the present invention will be described with reference to fig. 1, and details will be described in the examples, but the present invention is not limited to the embodiment and examples described below.

In the coagulation treatment, as shown in fig. 1, in general, the particles are agglomerated and gradually grown into flocs in the steps from the rapid stirring in the mixing tank after the coagulant is injected to the slow stirring in the floc-forming tank. In this case, the agglomeration is basically started in the mixing tank, and it is important that the agglomeration start time is about the same as the residence time of the mixing tank.

In this case, the treatment after the mixing tank can be performed satisfactorily, and as a result, flocs having high settleability are formed, thereby reducing the turbidity of the precipitation water. The start time of agglomeration is influenced by the water quality such as turbidity, alkalinity, pH, and water temperature of raw water, the stirring intensity, and the coagulant injection rate, and among these factors, the coagulant injection rate can be easily controlled in the facility. That is, if the coagulant injection rate is less than the appropriate amount, the flocculation start time is longer than the retention time of the mixing tank, and a problem occurs in the subsequent floc formation. On the other hand, if the coagulant injection rate is higher than the appropriate amount, the agglomeration start time is shorter than the retention time of the mixing tank, and the coagulant is excessively injected. In the present invention, when a part of the water to be treated (raw water) is caused to flow into the flocculation analyzer shown in FIG. 1, and the flocculation analyzer is controlled so that the flocculation start time becomes a predetermined value with respect to the water quality that changes from moment to moment, the results equivalent to the results of the sedimentation of the flocs in the beaker test, the evaluation of the turbidity of the upper clarified water, and the optimum floc particle size control of the flocculation sensor can be obtained.

That is, if the flocculation analyzer measures the agglomeration start time and controls the flocculant injection rate based on the time, the slow stirring and standing step is not required, and therefore the flocculant injection rate can be automatically determined at about 10 minutes. Therefore, the operation of a skilled operator such as a beaker test is reduced, and the coagulant injection rate control with a smaller time lag than that of an automatic beaker tester can be realized. Further, since it is not necessary to create a database of the turbidity of raw water and the appropriate floc particle size as in the case of the coagulation sensor, the coagulant injection rate control system using the coagulation analyzer has a feature that it can be put into practical use in a short period of time after installation of the device.

Next, a specific method for measuring the agglomeration start time and determining or controlling the coagulant injection rate by the agglomeration analyzer will be described below.

The present invention measures the agglomeration start time using at least either of the two methods described below. A particle counting method of the first method (hereinafter, referred to as a particle counting method) is the same as the method disclosed in patent document 3. The particle counting method irradiates a light beam to sample water flowing in a detector, receives at least one of forward scattered light, side scattered light, backward scattered light, and transmitted light by a photoelectric converter, and measures the number of particles in each particle size section from the number of pulses and the height of each pulse of an electric signal converted by the photoelectric converter in a predetermined time. In the first method of the present invention, the particle number reduction start time is set as the time from when the flocculant addition is started to when the particle number is reduced in the particle size section having a large number of particles, and the particle number increase start time is set as the time at which the particle number is increased in the particle size section having a small number of particles, and the result of calculation of at least one or both of the particle number reduction start time and the particle number increase start time is used as the agglomeration start time.

A variation analysis method of the second method (hereinafter, referred to as a variation analysis method) is the same as the method disclosed in patent document 4. The fluctuation analysis method irradiates a light beam to sample water flowing in a detector from at least one portion, receives at least one of forward scattered light, side scattered light, backward scattered light, and transmitted light by a photoelectric converter, and determines the average particle diameter and the number of particles contained in the sample water from the average value and the standard deviation of an electric signal converted from the output of the photoelectric converter within a predetermined time. In the second method of the present invention, the flocculation start time is set from the start of flocculant addition to the start of an increase in the average particle diameter, and the flocculation start time is set from the start of flocculant addition to the start of an increase in the number of particles counted as flocs.

Patent document 4 discloses a method for determining the average particle diameter and the number of particles from the average value and the standard deviation of the electric signal. Further, as an example of application of this patent, there is also a method of controlling the coagulant injection rate so that the average floc particle diameter becomes an appropriate particle diameter as in the method described in patent document 2. However, it is different from the present invention in the following points. First, in the methods described in patent documents 4 and 2, since the flocculant is continuously injected, suspended particles before flocculation and flocs in various growth processes are mixed. Therefore, the methods of patent documents 4 and 2 cannot measure the time during which the number of particles starts to decrease due to the aggregation of particles, the time during which the size of flocs starts to increase as the flocs start to grow, or the time during which the number of flocs starts to increase as the flocs start to grow (aggregation start time) measured in the present invention. Therefore, the methods of patent document 4 and patent document 2 cannot control the coagulant injection rate based on the agglomeration start time of the present invention, and it can be said that the methods of the present invention are different from the invention methods of patent document 4 and patent document 2.

The apparatus for measuring the agglomeration start time, the number of particles of the flocs, and the average particle diameter by the first method or the second method in the present invention is referred to as an agglomeration analyzer.

The method of controlling the coagulant injection rate of the present invention employs any of the following methods. The first method measures the agglomeration start time at a plurality of different agglomeration agent injection rates using an agglomeration analyzer, derives a relational expression between the agglomeration start time and the agglomeration agent injection rate from the measurement result, and then substitutes a predetermined set value of an appropriate agglomeration start time into the relational expression to obtain an optimum agglomeration agent injection rate.

The second method is to determine a coagulant injection rate that is predicted appropriately using an injection rate equation having at least one of the indices of raw water turbidity, alkalinity, pH, and water temperature as a parameter, and to measure the agglomeration start time at the injection rate using an agglomeration analyzer.

Examples

Example 1

As shown in fig. 1, the coagulation analyzer of the present invention is provided in a pipe for dividing raw water from a water storage well in a water purification process, and the water purification process has the following functions: the raw water taken from the river is sent into a water storage well, the injected coagulant is rapidly stirred in a rapid mixing tank, the aggregate formed in the rapid mixing tank is grown into flocs in a floc forming tank, the flocs are settled in a settling tank, and the upper clear water of the settling tank is filtered in a filtering tank. In some cases, the coagulation analyzer may be connected to a raw water pipe for supplying water to a water quality laboratory in order to perform a beaker test and a raw water quality test.

Here, the present invention is characterized in that an appropriate coagulant injection rate determined from the agglomeration start time measured by the agglomeration analyzer is fed back to the coagulant injection rate in the water purification process.

As shown in FIG. 2, the aggregation analyzer of example 1 comprises a plurality of (4 in this example) test water tanks 1A to 1D for storing a predetermined amount of raw water, water supply and discharge valves 2A to 2E, stirrers 3A to 3D, a raw water inlet valve 4, a raw water drain valve 5, a tap water inlet valve 6, a water supply pump 7, a filter 8, a filter inlet valve 9, a raw water feed valve 10, and a water discharge valve 11, a water level adjustment tank 14 connected to a pipe 13 for discharging water overflowing from the overflow wall 12, a flocculant 20, a flocculant injection part 21, a flocculant injection pipe 22, an injection pipe driving part 23, a stage 24, a detector 30 for measuring the particle size and the particle number of flocs, water intake pipes 31A to 31D, water intake pumps 32A to 32D, a program device 34 for analyzing an electric signal 33 from the detector and controlling the apparatus, and a POD (programmable operation display)35 for displaying the measurement result and the setting condition of an input device.

Here, the detector 30 is configured by a light beam irradiation portion configured by any one of a laser, an LED, and a lamp for irradiating a sample water with a light beam, a photoelectric converter for receiving at least one of forward scattered light, side scattered light, backward scattered light, and transmitted light emitted from particles contained in the sample water and converting the light into an electric signal, and an electronic circuit for measuring the number of particles in each particle diameter section based on the number of pulses and the pulse height of the converted electric signal, as disclosed in patent document 3.

Specific methods for measuring the particle size and the number of particles include the following methods: as an example of an optical system that receives forward scattered light using a semiconductor laser as an irradiation unit, there is a method described in patent document 5 mentioned above for the purpose of measuring the number of particles in sampled water; an example of an optical system that uses a semiconductor laser as an irradiation unit and receives transmitted light is a method described in patent document 6. The detector 30 of the present embodiment employs the particle counting method, but an optical system to which a fluctuation analysis method is applied as described in patent document 4 may be employed.

Next, a specific sequence of the method of measuring the blocking start time will be described below.

First, in order to discharge the sample water remaining in the test water tanks 1A to 1D, the agitators 3A to 3D, the water supply pump 7, and the water intake pumps 32A to 32D are stopped, the raw water discard valve 5 is opened, the raw water inlet valve 4, the tap water inlet valve 6, the filter inlet valve 9, and the raw water feed valve 10 are closed, and the water supply and discharge valves 2A to 2E, and the water discharge valve 11 are opened (hereinafter, referred to as a sample water discharge step).

After the sample water is discharged from the test water tanks 1A to 1D, the tap water inlet valve 6 and the filter inlet valve 9 are opened, and tap water is fed by the water feed pump 7 through the tap water inlet valve 6 and passes through the filter inlet valve 9, whereby the water (hereinafter, referred to as "washing water") is changed into water from which particles are removed by the filter 8. The cleaning water is sent to the test water tanks 1A to 1D and the water level adjustment tank 14 through the water supply and discharge valves 2A to 2E. Further, the drain valve 11 is closed to gradually accumulate the cleaning water in the test water tank, fig. 3 is a side view of the test water tank, and as shown in fig. 3, the water overflowing from the test water tank is discharged through the pipes 15A to 15D (only 15A is shown) (hereinafter referred to as a cleaning water supply step).

Here, the overflow height must be set at a position higher than the water level defined by the height of the overflow wall 12. Further, if the flow meter 16 with a flow switch or an output function is provided, it is possible to automatically detect that the test water tank is full of water. In this step, when the test water tank is cleaned by operating the agitators 3A to 3D in advance, it is effective when the turbidity or chromaticity of the raw water is high.

After the washing water feeding step, that is, after sufficient washing water is fed into the test water tank, the water pickup pumps 32A to 32D are driven, and the washing water is measured by the detector 30. In this case, by storing the level measured by the photoelectric converter and information on the particle size and the number of particles obtained by converting the number or height of pulses generated when the particles pass through the light beam, it is possible to determine contamination of the optical system, deterioration of the filter, and the like, and further to correct the light amount (hereinafter, referred to as a washing water measurement step).

After the washing water measuring step is completed, the drain valve 11 is opened, the water supply pump 7 is stopped, the filter inlet valve 9, the raw water feed valve 10, and the tap water inlet valve 6 are closed, washing water in the test water tank and the water level adjustment tank is discharged (hereinafter, referred to as a washing water drain step), the raw water inlet valve 4 and the raw water feed valve 10 are opened, the raw water discard valve 5 is closed, the water supply pump 7 is driven, the drain valve 11 is closed, and the water supply and drain valves 2A to 2E are opened (hereinafter, referred to as raw water feed steps).

After the test water tank is filled with the raw water, that is, after it is detected whether or not a predetermined time has elapsed or the test water tank is filled with the raw water by the flow meter 16 having a flow switch or an output function, the water supply pump 7 is stopped, the raw water feed valve 10 and the raw water inlet valve 4 are closed, and the raw water discard valve 5 is opened. Then, the water level of each test water tank becomes the height of the overflow wall 12 of the water level adjustment tank 14, and the same volume of test water is specified for each test. Then, the water supply and discharge valves 2A to 2D are closed (hereinafter, referred to as a water level adjustment step).

Here, by using materials having different heights as the overflow wall 12 according to circumstances, the capacity of the test water can be changed.

After the water level is adjusted, the agitators 3A to 3D are driven at a predetermined rotation speed. Next, the water pumps 32A to 32D are driven, the particle number or turbidity of the raw water is measured by the detector 30, and the range of the coagulant injection rate in each of the test water tanks 1A to 1D is set based on the value. At this time, the drainage of the water intake pumps 32A to 32D may be returned to the test water tank. After the raw water is measured for a predetermined time, the flocculant 20 is injected into the test water tanks 1A to 1D in the order of the test water tanks 1A to 1D by the flocculant injection section 21, and the flocculant injection section 21 is constituted by a quantitative pump or a syringe pump. At this time, the flocculant injection pipe 22 is connected to the injection pipe driving section 23, and a predetermined amount of flocculant determined by the above measurement is injected into each test water tank by moving on the stage 24 (hereinafter referred to as flocculant injection step).

After the coagulant is injected, the coagulant is dispersed by stirring, and the particles start to be agglomerated. Fig. 4 shows the change in the number of particles measured by the detector 30 at this time. That is, since the raw water used in the present example contains a large number of particles of 1 to 3 μm, counting by the detector 30 is started before the coagulant is injected, and agglomeration is started about 3 minutes after the coagulant is injected, and the number of particles of 1 to 3 μm is reduced. Then, the number of particles of 3 to 7 μm which are almost absent before the coagulant is injected is increased. This indicates that the particles are clumped together to form a microfloc mass. After a period of time, the micro-flocs further grow into larger flocs, so that the particle number of 3-7 μm is reduced, and the particle numbers of 7-10 μm and 10-15 μm are increased sequentially.

In this apparatus, the particle size range in which the raw water contains many particles can be arbitrarily selected, and 1 to 3 μm is applied to the raw water used in this example. Here, as shown in fig. 5, the time at which the number of particles starts to decrease may be defined as the particle number decrease start time. In this apparatus, the number of particles is output from the detector to the sequencer 34 by the electric signal 33, and therefore the number of particles reduction start time is determined and stored by the sequencer. On the other hand, the particle size range of particles that are hardly contained in the raw water can be arbitrarily selected, and 3 to 7 μm is applied in the case of this example. Here, as shown in fig. 6, the time at which the number of particles starts to increase is defined as a particle number increase start time, and the time is stored in the sequencer (hereinafter referred to as an agglomeration start time measurement step).

In addition, it is possible to use either one of the particle number reduction start time and the particle number increase start time as the blocking start time or an average value of both as the blocking start time.

After the agglomeration start time of each test water tank was measured, the relationship between the respective flocculant injection rates of a to D and the agglomeration start time can be plotted as shown in fig. 7. The aggregation analyzer of the present invention obtains a relational expression (fit line) between the coagulant injection rate and the aggregation start time by a polygonal line approximation formula or a polynomial approximation formula using the data (hereinafter, referred to as a fit line calculation step).

Next, the agglomeration start time, which is set to an appropriate value in advance according to the water treatment facility, is substituted into the above relational expression to calculate an appropriate flocculant injection rate (hereinafter, referred to as an appropriate flocculant injection rate calculation step).

The appropriate value of the agglomeration start time is determined based on the retention time of the mixing tank, but may be corrected in accordance with the actual application of the coagulant injection rate of the facility. The residence time of the mixing tank is determined according to the volume of the mixing tank and the amount of treated water in the plant.

After calculating the coagulant injection rate, returning to the sample water drainage process, and repeating the above processes. In the above description, the example using a plurality of test water tanks was described, but as described above, the agglomeration start time of the sample water having different flocculant injection rates may be measured by repeatedly using 1 test water tank. The appropriate coagulant injection rate calculated as described above may be used as a set value for manually changing the injection rate of the facility to be implemented, or may be used as an input to an injection rate control system of a central monitoring device.

Next, fig. 8 is explained, and fig. 8 is an explanatory view showing a comparison between the conventional method and the method of the present invention in terms of the time required for determining the coagulant injection rate. Compared with the beaker test, the invention can determine the appropriate coagulant injection rate in a short time. This is because: as shown in fig. 8, in the present invention, the slow stirring and standing step required in the beaker test is not required.

Example 2

Next, example 2 will be described with reference to fig. 9 to 12. The coagulation analyzer of the present invention shown in fig. 9 is composed of a test water tank 1 for storing a predetermined amount of raw water, water supply and discharge valves 2 and 2E, a stirrer 3, a raw water inlet valve 4, a raw water drain valve 5, a tap water inlet valve 6, a water supply pump 7, a filter 8, a filter inlet valve 9, a raw water feed valve 10, a water discharge valve 11, a water level adjustment tank 14 connected to a pipe 13 for discharging water overflowing through a bypass pipe 17, a coagulant 20, a coagulant injection part 21, a coagulant injection pipe 22, a detector 36 for measuring the average particle size and the average particle number of flocs, a water intake pipe 31, a water intake pump 32, a program device 34 for analyzing an electric signal 33 from the detector and controlling the apparatus, and POD35 for displaying the measurement results and the setting conditions of the input device.

Here, the detector 36 is configured by a light beam irradiation unit configured by any one of a laser, an LED, and a lamp for irradiating a sample water with a light beam, a photoelectric converter for receiving at least one of forward scattered light, side scattered light, backward scattered light, and transmitted light emitted from particles contained in the sample water and converting the received light into an electric signal, and an electronic circuit for measuring the average particle diameter and the average particle number of flocs from the average value and the standard deviation of the converted electric signal. A specific method for measuring the particle diameter and the number of particles is described in patent document 4. The detector 36 of the present embodiment employs the fluctuation analysis method, but an optical system using the particle counting method described in patent document 3 may be employed.

Next, a method of measuring the blocking start time will be described in the following specific procedure. First, the sample water discharge step, the washing water feed step, the washing water measurement step, the washing water discharge step, the raw water feed step, and the water level adjustment step were performed in the same manner as in example 1. The difference is the following aspects: the number of test water tanks in example 1 was 1, the overflow wall of the water level adjustment tank was an overflow pipe, and there were no stage and no flocculant injection pipe driving unit.

After the water level is adjusted, the mixer 3 is driven at a predetermined rotation speed, and then the water intake pump 32 is driven, and at this time, the drain water of the water intake pump may be returned to the test water tank 1. Next, an appropriately predicted flocculant injection rate is obtained in advance by using an injection rate equation using water quality such as turbidity, alkalinity, pH, and water temperature of raw water as parameters measured by a coagulation analyzer or other devices, and the injection rate is set as the flocculant injection rate of the test water tank 1. Next, the flocculant 20 is injected into the test water tank 1 from a flocculant injection section 21 constituted by a fixed displacement pump or a syringe pump (hereinafter referred to as flocculant injection step).

Next, after the coagulant is injected, the coagulant is dispersed by stirring, and the particles start to be agglomerated. At this time, the average floc particle size measured by the detector 36 changed as shown in FIG. 10. Since the average size of flocs is inputted from the detector to the sequencer 34 by an electric signal 33, the sequencer is set to store the time from the start of flocculant injection to the start of floc growth increase. On the other hand, since the average number of particles of the flocs changes as shown in fig. 11, the floc increase start time is set to be a floc increase start time from the start of the flocculant injection to the start of the floc increase, and the floc increase start time is stored (hereinafter, referred to as an agglomeration start time measurement step).

It is predetermined whether one of the floc growth start time and the floc increase start time is used as the agglomeration start time or an average value of both is used as the agglomeration start time.

If the deviation between the measured value of the measured agglomeration start time and the appropriate value of the agglomeration start time preset in the water treatment facility is within a predetermined range, the flocculant injection rate corresponding to the predetermined amount of the flocculant in the agglomeration start time measurement step is determined as the appropriate flocculant injection rate, and if the deviation is larger than the predetermined range, the step of calculating the appropriate flocculant injection rate is performed in accordance with the procedure (21) to (23) in claim 3. The details thereof are as follows.

That is, first, the general formula of the relationship between the coagulant injection rate and the agglomeration start time is obtained in advance by an experiment or the like. Several formulae are proposed as general formulae, and the formulae are expressed as exponential functions, for example, as the following number 1 (formula (1)).

Number 1

T＝αexp(-βP) (1)

Here, T is the agglomeration start time, P is the coagulant injection rate, and α and 8 are constants that have different values depending on the water quality such as water temperature, pH, alkalinity, turbidity, and the like. Then, one of the constants α is determined based on at least one index of the water quality of the raw water at the time of measurement of the agglomeration start time. The relationship between the water quality parameter and α is obtained in advance by experiments or the like.

Then, the numerical value of α, the measured value of the agglomeration start time, and the coagulant injection rate at the time of measurement are substituted into the general formula, β in the general formula is obtained, and all constants of the general formula (hereinafter referred to as injection rate calculation formula) are determined.

Here, even when the general formula is expressed by a function different from the formula (1), a constant may be determined in advance based on a relationship between the water quality and the constant obtained by an experiment or the like before substituting the measured value of the agglomeration start time and the coagulant injection rate, so that the number of constants with uncertain values in the general formula can be reduced to only one.

Then, the appropriate value of the agglomeration start time is substituted into the injection rate calculation formula to calculate the appropriate coagulant injection rate. The above is a detailed description of the appropriate coagulant injection rate calculation step.

Fig. 12 shows an example of the relationship between the measured value and the appropriate value of the agglomeration start time, the general formula of the coagulant injection rate and the agglomeration start time, and the injection rate calculation formula after the constant is determined in this step. In fig. 12, since the measured value of the agglomeration start time is larger than an appropriate value, the injection rate of the coagulant is corrected (increased). That is, the measured value of the agglomeration start time and the coagulant injection rate at the time of measurement are substituted into the general formula which varies depending on the water quality, and the injection rate calculation formula is determined. Thus, the coagulant injection rate appropriate value can be obtained such that the agglomeration start time becomes an appropriate value. By changing the injection rate of the implementation facility to the appropriate value of the injection rate, the coagulant injection rate determined by the injection rate calculation equation can be corrected.

As described above, according to the method of measuring the agglomeration start time by the agglomeration analyzer of the present invention and controlling the coagulant injection rate based on the measurement time, the slow stirring and standing step is not required, and therefore, the coagulant injection rate can be automatically determined in a time shorter than that of the conventional method.

Claims (6)

1. A flocculant injection rate determining method for determining a flocculant injection rate, which is a ratio of an amount of flocculant injected to an amount of water to be treated in a water treatment method for performing flocculation treatment by injecting a flocculant into the water to be treated, the method comprising the steps of:

(1) coagulant injection step: extracting a predetermined amount of water to be treated into a plurality of test water tanks, and injecting predetermined amounts of coagulant into the sample water extracted into each test water tank, thereby making each sample water have different coagulant injection rates;

(2) an agglomeration start time measurement step: measuring the time from the injection of the coagulant into each of the sample waters until the coagulant is dispersed by stirring and the particles in each of the sample waters start to aggregate, i.e., the time to start aggregation, for each of the sample waters;

(3) fitting line operation procedure: based on the measured agglomeration start time of each sample water and the measured coagulant injection rate, making a fitting line of the relationship between the agglomeration start time and the coagulant injection rate, and performing calculation;

(4) a proper coagulant injection rate calculation step: an appropriate coagulant injection rate is calculated for the water treatment facility on the basis of the fit line and an appropriate value of agglomeration start time preset for the water treatment facility.

2. The coagulant injection rate determining method according to claim 1, wherein the steps (1) and (2) are replaced with the following steps (1a), (2a) and (2b),

(1a) extracting a predetermined amount of water to be treated in a single test water tank, injecting a predetermined amount of flocculant into sample water extracted in the test water tank, and measuring a time from the injection of the flocculant until the flocculant is dispersed by stirring and the start of agglomeration of particles in the sample water, that is, an agglomeration start time;

(2a) after the above-mentioned step, washing the test water tank with washing water, discharging the washing water from the test water tank, extracting a predetermined amount of the water to be treated into the test water tank again, injecting a predetermined amount of coagulant different from the amount of the water to be treated into a sample water different from the above-mentioned step, and measuring the time for starting the agglomeration;

(2b) the same procedure as described above was repeated a plurality of times while changing the amount of coagulant injected, and the agglomeration start time was measured for each of the sample waters having different coagulant injection rates.

3. The coagulant injection rate determination method according to claim 1,

the particle number of each particle size interval in the sampled water is measured, the time at which the particle number of particles in a predetermined small particle size interval of the particles present in the sampled water starts to decrease before the coagulant is injected is measured, or the time at which the particle number of particles in a predetermined particle size interval larger than the predetermined small particle size interval starts to increase due to the start of agglomeration after the coagulant is injected is measured, and the agglomeration start time is determined from at least one of the two times.

4. The coagulant injection rate determination method according to claim 1,

the mean particle diameter and the number of particles in the sampled water are measured, the time at which the increase in mean particle diameter is observed is measured as floc growth start time, and the time at which the increase in mean particle number counted as flocs starts is measured as floc increase start time.

5. The coagulant injection rate determination method according to claim 1,

an appropriate value of the agglomeration start time preset in the water treatment apparatus is set based on the retention time of the water to be treated in the mixing tank of the water treatment apparatus.

6. An apparatus for carrying out the coagulant injection rate determination method according to claim 1, the apparatus comprising: at least 1 test water tank having a stirrer, a coagulant injection device for injecting predetermined amounts of different coagulants, a caking start time measuring device, and a calculating device for calculating an appropriate coagulant injection rate.