JP2004141782A - Water quality control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a water quality control method to perform a control considering water quality fluctuation and seasonal factors and achieve reduction of packs and thus realize a more efficient control method for a water purification plant. <P>SOLUTION: The water quality control method controls the water quality of a supernatant after a flocculant is fed to form flocks and the flocks are precipitated. This water quality control method comprises using the particle diameter and the number of particles as a water quality control index, measuring the particle diameter and the number of particles of suspended substance contained in water on the upperstream side, forming flocks by changing at least one of the injection rate or basicity of the flocculant to be fed to the water on the upperstream side based on the result of the measurement, and obtaining an optimum injection rate and basicity of the flocculant to be fed to the water by measuring the particle diameter and the number of particles of the supernatant after the flocks are precipitated. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to, for example, an improvement of a water quality management method of a water purification plant, and determines an optimum injection rate and a basicity of a flocculant based on the particle size and the number of particles of a suspension contained in raw water to effectively improve turbidity. Water purification management method.
[0002]
[Prior art]
In the water purification plant, suspended substances are aggregated and removed by injecting a flocculant (PAC ... polyaluminum chloride ... hereinafter referred to as a pack) or the like into raw water. By injecting the flocculant, a floc (hereinafter, referred to as a floc) that incorporates the suspended substance is formed. The suspended solids are removed by sedimentation of the floc. The supernatant water of the coagulation-sedimentation process becomes clearer water by the sand filtration process, and is sterilized by chlorine to become tap water. The method of injecting a flocculant to coagulate a suspended substance is an extremely effective method when the suspended substance in raw water is mainly clayey.
Prior art documents related to these series of water purification treatment operations include the following.
[0003]
[Patent Document 1]
Japanese Patent Publication No. 60-43762 [Patent Document 2]
JP-A-04-35702.
[0004]
In the coagulation sedimentation filtration method described above, the floc grows to about 2 to 3 mm in the coagulation operation, and the grown floc is settled and separated in the sedimentation basin. On the other hand, fine flocs of about 50 μm or less that cannot be removed by sedimentation are removed in a filter pond filled with filter sand having an effective diameter in the range of 0.45 to 0.7 mm.
[0005]
In the filter pond, with the lapse of time after the start of filtration, deterrents accumulate in the filter layer, the head loss increases, and the amount of filtered water decreases. For this reason, when the filtration duration time is reached, backwashing operation is performed, and a part of the filtered water is supplied as washing water from the outlet side of the filtration pond, and the contaminants in the filtration layer are discharged together with the washing water. Done. The backwash wastewater is then sent to a drainage pond, where the sludge is settled and separated, and the supernatant water is returned to the raw water.
[0006]
[Problems to be solved by the invention]
It is desirable that the number of backwashing operations is small. To do so, it is necessary to reduce the amount of suspended solids carried to the filtration pond.
In general, at a water purification plant, the amount of pack to be injected is controlled according to the turbidity of raw water flowing into a landing well. That is, the turbidity of the raw water is measured by a turbidity meter, and the amount of the pack to be injected is determined based on the turbidity.
[0007]
However, there is a problem that it is difficult to finely control the outflow of the suspended matter to the filtration pond with the control based on the turbidity.
The present invention has been made in order to solve the above-mentioned problems, and it is intended to capture the content of a suspension by a particle size and perform management in consideration of a pack injection rate and a pack basicity based on the particle size. The purpose of the present invention is to provide a water quality management method in which the amount of suspended solids carried to a filtration pond is reduced.
[0008]
[Means for Solving the Problems]
In order to solve such a problem, in claim 1,
A water quality management method for controlling the water quality of the supernatant water after the floc has settled by introducing a flocculant, wherein the particle size and the number of particles are used as water quality management indices.
[0009]
In claim 2, in the water quality management method according to claim 1,
Measure the particle size and the number of particles in the suspension contained in the raw water, change the injection rate of the flocculant to be added to the raw water based on the measurement results to form flocs, and the particles of the supernatant water after the flocs settle. It is characterized in that the diameter and the number of particles are measured to determine the optimum injection rate of the coagulant to be charged into the raw water.
[0010]
In claim 3, in the water quality management method according to claim 1,
When measuring the particle size and the number of particles of the suspension contained in the raw water and selecting a flocculant to be added to the raw water based on the measurement result, a floc is formed using a flocculant having a different basicity, and the floc is formed. The method is characterized in that the particle size and the number of the supernatant water after sedimentation are measured and the coagulant to be introduced into the water is selected.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is an explanatory diagram of a water purification plant showing an example of an embodiment of the present invention.
In the figure, reference numeral 1 denotes a landing well into which raw water taken in from an intake port flows. Here, a first particle counter is arranged, the suspended matter contained in the raw water is measured, and a pack is loaded according to the measurement result.
[0012]
The raw water into which the packs are introduced is mixed in the rapid mixing pond 2, the growth of the suspension is promoted in the floc forming pond 3, and the larger suspended mass (floc) is settled. The water treated here is sent to the rapid filtration pond via the chemical sedimentation pond 4.
A second particle counter 6 is disposed at an intermediate portion of the chemical sedimentation basin 4, and the output of the second particle counter 6 determines whether the amount of the supplied pack is sufficient or not.
[0013]
FIG. 2 shows the outline of the experiment prior to the implementation. In step (a), 500 ml of raw water was collected in a beaker, and the turbidity and the number of particles by particle size were measured using a turbidimeter and a particle counter (not shown). Measure, then pour the pack. The injection amount of the pack is initially 10 mg / l, and the mixture of the raw water and the pack is put into a jar tester in step (b) and stirred. In the jar tester, the stirring blades are stirred at 150 rpm for 10 minutes, then stirred at 50 rpm for 5 minutes and then allowed to settle for 10 minutes.
Next, in step (c), the beaker is taken out, and the turbidity of the supernatant and the number of particles by particle size are measured in the same manner as in step (a).
[0014]
FIG. 3 is an explanatory diagram showing the relationship of the suspended matter removal rate for each particle size when the injection amount of the above-mentioned pack is changed to 15 mg / l, 20 mg / l, and 25 mg / l. The portion surrounded by a circle P indicates a state where the removal rates of particles of 2 to 10 μm or less overlap.
According to the figure, when the injection amount of the pack is 10 mg / l, the removal rate is about 10% regardless of the particle size, but when the injection amount becomes 15 mg / l, the removal rate of particles of 10 μm or less is 40%. %, And at 20 mg / l and 25 mg / l, the removal rate increases to about 60% and 90%.
[0015]
On the other hand, the removal rate of particles of 10 μm or more is about 20% when the injection amount is 15 mg / l, about 27% at 20 mg / l, and about 60% at 25 mg / l.
In general, the normal injection rate of a water purification plant is about 15 mg / l to 20 mg / l, and 25 mg / l is considered to be excessive injection. However, according to the above results, the normal injection rate contains many particles of 10 μm or more. It can be seen that the removal rate is poor in raw water, and in that case, the injection rate needs to be 25 mg / l or more.
[0016]
FIG. 4 shows the change in the turbidity measured by a turbidimeter and the number of particles measured by a particle counter in the middle part of the sedimentation basin 4 and the particles of 2-3 μm in the water purification plant shown in FIG. And the horizontal axis indicates elapsed time. In the figure, the line indicated by A indicates a change in turbidity in the middle of the sedimentation tank, and B indicates a change in the number of particles in the middle of the sedimentation tank.
[0017]
The vertical line indicated by C indicates the point at which the injection rate of the pack was increased from 14 mg / l to 25 mg / l at about 15:30, and the vertical line indicated by D indicates the pack injection rate of 25 mg / l 1 to 14 mg / l, and the vertical line indicated by E indicates the time when the number of particles reached the maximum value slightly before 20:24.
[0018]
According to the figure, the change in turbidity caused by changing the injection rate is about 0.2 degrees (about 5%), while the change in the number of particles is as large as +350 (about 50%). I understand. This indicates that water quality fluctuation can be more remarkably captured by using a particle number fluctuation more sensitive than turbidity as an index of the degree of purification.
[0019]
By the way, there are various types of packs having different basicities in commercially available packs. A high basicity type (for example, basicity 62) is a high temperature and high turbidity in summer, and a low basicity type (basicity 52) is. It is used for low temperature and low turbidity in winter.
[0020]
FIG. 5 is a diagram showing the relationship between the particle removal rate and the particle size (μm) when the basicity and the injection rate are changed. A is a pack with an injection rate of 15 mg / l and a basicity of 52, B is a pack with an injection rate of 15 mg / l and a basicity of 62, A 'is a pack with an injection rate of 25 mg / l and a basicity of 52, and B' is an injection rate of 25 mg / l 1 shows the removal rate when a pack having a basicity of 62 was injected.
[0021]
In the figure, looking at the cases of A and B injected at 15 mg / l, it can be seen that fine particles of 2 to 10 μm have better removal characteristics in pack B having a higher basicity than pack A having a lower basicity. . However, in the case of large particles of 10 μm or more, the characteristics are reversed, and it is understood that Pack A having a lower basicity has better removal characteristics.
[0022]
On the other hand, in the case of A 'and B' at an injection rate of 25 mg / l, it can be seen that pack B 'having a higher basicity has better removal characteristics at any particle size. In other words, it can be seen that when removing particles of 10 μm or more with Pack B, it is necessary to inject more than usual (15 mg / l).
The foregoing description of the present invention has been presented by way of illustration and example only of particular preferred embodiments. Thus, it will be apparent to one skilled in the art that the present invention may be modified or modified in many ways without departing from its essentials.
[0023]
For example, the injection rate and the basicity of the pack are not limited to those shown in the examples, but can be appropriately adjusted according to the turbidity, turbidity, and temperature. The scope of the present invention defined by the description of the claims is intended to cover alterations and modifications within the scope.
[0024]
【The invention's effect】
As described above, according to the present invention, a floc is formed by adding a flocculant, and in a water quality management method for managing the quality of the supernatant water after the floc has settled, the particle size and the particle size are used as water quality management indices. Using the number, the particle size of the suspension contained in the raw water, the number of particles and the temperature are measured, and the floc is formed by changing at least one of the injection rate or the basicity of the flocculant to be added to the raw water based on the measurement result. Then, the size and number of supernatant water after floc sedimentation were measured to determine the optimal injection rate and basicity of the flocculant to be added to the water. It is possible to reduce the number of packs and realize a more efficient water purification plant management method.
[0025]
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an example of a water purification plant in which the present invention is implemented.
FIG. 2 is an explanatory diagram showing an outline of an experiment prior to implementation.
FIG. 3 is an explanatory diagram showing a pack injection rate and a removal rate of turbid matter by particle diameter.
FIG. 4 is an explanatory diagram showing changes in turbidity measured by a turbidimeter and the number of particles measured for particles of 2 to 3 μm by a particle counter.
FIG. 5 is an explanatory view showing a particle-size-based turbidity removal rate in which basicity is added to a pack injection rate.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Landing well 2 Rapid mixing pond 3 Floc forming pond 4 Chemical sedimentation tank 5 First particle counter 6 Second particle counter 10 Beaker

Claims (3)

A floc is formed by adding a flocculant, and in the water quality control method for controlling the quality of the supernatant water after the floc has settled, the particle size and the number of particles of the suspension are used as a water quality control index. Water quality management method. The particle size and number of the suspension contained in the raw water are measured, the floc is formed by changing the injection rate of the flocculant added to the raw water based on the measurement result, and the supernatant water particles after the floc settles. The water quality management method according to claim 1, wherein the diameter and the number of particles are measured to determine an optimum injection rate of the coagulant to be charged into the raw water. When measuring the particle size and the number of particles of the suspension contained in the raw water and selecting a flocculant to be added to the raw water based on the measurement result, a floc is formed using a flocculant having a different basicity, and the floc is formed. The water quality management method according to claim 1, wherein the particle size and the number of the supernatant water after sedimentation are measured to select a coagulant to be added to the water.

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