JP4185348B2 - Water quality management method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to, for example, improvement of a water quality management method for a water purification plant, and determines an optimum injection rate and basicity of a flocculant based on the particle size and the number of particles of a suspension contained in raw water, thereby effectively improving turbidity. It relates to the water purification management method.
[0002]
[Prior art]
In a water purification plant, a suspended substance is aggregated and removed by injecting a flocculant (PAC ... polyaluminum chloride ... hereinafter referred to as a pack) into raw water. By injecting the flocculant, an agglomerate (hereinafter referred to as a floc) incorporating the suspended solids is formed. Suspended substances are removed by precipitation separation of the floc. The supernatant water of the coagulation sedimentation process becomes clearer water by sand filtration, and is sterilized by chlorine to become tap water. The method of injecting a flocculant to agglomerate the suspended material is a very effective method when the suspended material in the raw water is mainly clayey.
Prior art documents related to these series of water purification operations include the following.
[0003]
[Patent Document 1]
Japanese Patent Publication No. 60-43762 [Patent Document 2]
Japanese Patent Laid-Open No. 04-35702.
[0004]
In the coagulation sedimentation filtration method described above, flocs grow to about 2 to 3 mm in the coagulation operation, and the grown flocs are settled and separated in a sedimentation basin. On the other hand, fine flocs of about 50 μm or less that could not be removed by sedimentation separation are removed in a filtration basin filled with filtration sand having an effective diameter in the range of 0.45 to 0.7 mm.
[0005]
In the filtration pond, the detained matter accumulates in the filtration layer with the passage of time from the start of filtration, the head loss increases, and the amount of filtered water decreases. For this reason, backwashing operation is performed at the time when the filtration continuation time is reached, and a part of the filtrate water is supplied as wash water from the outflow side of the filter basin, and the detained matter in the filtration layer can be discharged together with the wash water. Done. The backwash wastewater is then sent to a drainage basin, and after the sludge is settled and separated, the supernatant water is returned to the raw water.
[0006]
[Problems to be solved by the invention]
The smaller the number of backwash operations, the better. This requires less suspension to be carried to the filter basin.
By the way, generally in the water purification plant, the injection amount of the pack is controlled according to the turbidity of the raw water flowing into the landing well. That is, the turbidity of raw water is measured with a turbidimeter, and the amount of pack injected is determined based on the turbidity.
[0007]
However, in the control based on turbidity, there is a problem that it is difficult to finely control the outflow of the suspension to the filtration pond.
The present invention has been made to solve the above-described problems, and captures the content of the suspension by the particle size, and performs management in consideration of the injection rate of the pack and the basicity of the pack based on the particle size. The purpose is to provide a water quality management method that reduces the amount of suspended matter transported to the filtration basin.
[0008]
[Means for Solving the Problems]
In order to solve such a problem, in claim 1,
Raw water taken from the intake port is stored, and a landing well into which at least one of the two types of basicity of about 52 and basicity of about 62 is introduced, and the flocculant disposed at the subsequent stage of the landing well, The mixing pond that mixes the raw water that has been added, the floc formation pond that is placed downstream of this mixing pond to grow and sink flocs, and the treated water from the flock formation pond that flows after the floc formation pond flows in. In the water quality management method for a water purification plant including a chemical sedimentation basin, a first particle counter is provided in the landing well, a second particle counter is disposed in the chemical sedimentation basin, and the suspended matter measured by the first particle counter is measured. Of the particle size,
When the particle size is 2 to 10 μm , a flocculant having a basicity of about 62 is introduced at an injection rate of about 15 mg / l,
When the particle size is 10 μm or more, a flocculant having a basicity of approximately 52 is injected at an injection rate of approximately 15 mg / l, or an flocculant having a basicity of approximately 62 is injected at an injection rate of approximately 25 mg / l.
The amount of the flocculant injected into the landing well is adjusted according to the output of the second particle counter.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
Drawing 1 is an explanatory view of a water purification plant which shows an example of an embodiment of the present invention.
In the figure, 1 is a receiving well, and raw water taken from the intake port flows in. Here, a first particle counter is arranged, the suspended matter contained in the raw water is measured, and a pack is inserted according to the measurement result.
[0012]
The raw water charged with the pack is mixed in the rapid mixing pond 2, and the growth of the suspension is promoted in the flock formation pond 3, so that a large suspension lump (floc) settles. The water treated here is sent to the rapid filtration basin through the chemical sedimentation basin 4.
A second particle counter 6 is disposed in the middle part of the chemical sedimentation basin 4, and it is determined whether the amount of packs supplied is excessive or insufficient based on the output.
[0013]
FIG. 2 shows an outline of the experiment prior to the implementation. In step (a), 500 ml of raw water is collected in a beaker, and the turbidity and the number of particles by particle size are measured using a turbidimeter and a particle counter (not shown). Measure, then inject the pack. The injection amount of the pack is 10 mg / l at first, and the mixed solution of the raw water and the pack is put into a jar tester in the step (b) and stirred. In the jar tester, the stirring blade is stirred at a rotation speed of 150 rpm for 10 minutes, and 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 as in step (a).
[0014]
FIG. 3 is an explanatory diagram showing the relationship of the suspension removal rate for each particle size when the injection amount of the pack is changed to 15 mg / l, 20 mg / l, and 25 mg / l. In addition, the part enclosed with the circle mark P has shown the state with which the removal rate of the particle | grains below 2-10 micrometers overlapped.
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 is 15 mg / l, the removal rate of particles of 10 μm or less is 40%. The removal rate is improved to about 60% and 90% at 20 mg / l and 25 mg / l.
[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 over-injected. However, in the above results, many particles of 10 μm or more are included in the normal injection rate. It can be seen that the raw water has a poor removal rate, in which case the injection rate must be 25 mg / l or more.
[0016]
FIG. 4 shows the change in the number of particles measured for turbidity measured with a turbidimeter at the intermediate part of the sedimentation basin 4 with a turbidimeter and particles with a particle counter of 2 to 3 μm in the water purification plant shown in FIG. The abscissa indicates the elapsed time. In the figure, the line indicated by A indicates the turbidity change in the middle of the settling basin, and B indicates the change in the number of particles in the middle of the settling pond.
[0017]
The vertical line indicated by C indicates the time when the injection rate of the pack was increased from 14 mg / l to 25 mg / l around 15:30, and the vertical line indicated by D indicates the pack injection rate of 25 mg / l slightly before 18 o'clock. The time point when the particle number was decreased from 1 to 14 mg / l is shown, and the vertical line indicated by E shows the time point when the number of particles reached the maximum value slightly before 20:24.
[0018]
According to the figure, the change in turbidity by changing the injection rate is about 0.2 degree (about 5%), while the change in the number of particles is greatly changed to +350 (about 50%). I understand. This indicates that water quality fluctuations can be captured more significantly by using particle number fluctuations that are more sensitive than turbidity as an index of purification.
[0019]
By the way, there are various types of packs with different basicity in the commercially available packs. A type with a high basicity (for example, basicity 62) is a high temperature / high turbidity in summer and a type with a low basicity (basicity 52) Used for low temperatures and low turbidity in winter.
[0020]
FIG. 5 is a graph showing the relationship between the particle removal rate and the particle size (μm) when the basicity and the injection rate are changed. A is an injection rate 15 mg / l and a basicity 52 pack, B is an injection rate 15 mg / l and a basicity 62 pack, A 'is an injection rate 25 mg / l and a basicity 52 pack, B' is an injection rate 25 mg / l The removal rate in the case of injecting a basicity 62 pack at 1 is shown.
[0021]
In the figure, looking at the cases of A and B injected at 15 mg / l, it can be seen that the fine particles of 2 to 10 μm have better removal characteristics of pack B with a higher basicity than pack A with a lower basicity. . However, in the case of large particles of 10 μm or more, the characteristics are reversed, and it can be seen that Pack A having a lower basicity has better removal characteristics.
[0022]
On the other hand, in the case of A ′ and B ′ having an injection rate of 25 mg / l, it can be seen that the pack B ′ having a higher basicity is superior in removal characteristics at any particle size. In other words, it is found that when particles of 10 μm or more are to be removed with the pack B, it is necessary to inject more than usual (15 mg / l).
The foregoing description of the present invention has only shown certain preferred embodiments for purposes of illustration and illustration. Accordingly, it will be apparent to those skilled in the art that the present invention can be modified and modified in many ways without departing from the essence thereof.
[0023]
For example, the injection rate and basicity of the pack are not limited to those shown in the examples, and can be appropriately adjusted according to turbidity, turbidity, and temperature. The scope of the present invention defined by the description in the appended claims is intended to include modifications and variations within the scope.
[0024]
【The invention's effect】
As described above, according to the present invention, the raw water taken from the intake port is stored, and the receiving well into which at least one of the flocculants of the basicity of about 52 and the basicity of about 62 is charged, Arranged downstream of this landing well and mixing the raw water charged with the flocculant, a floc-forming pond disposed downstream of the mixing basin for growing and sinking flocs, and disposed downstream of the floc-forming pond In the water quality management method for a water purification plant including a chemical sedimentation basin into which treated water from the flock formation pond flows, a first particle counter is provided in the landing well, and a second particle counter is provided in the chemical sedimentation basin, Of the suspended particle size measured by the first particle counter,
When the particle size is 2 to 10 μm , a flocculant having a basicity of about 62 is introduced at an injection rate of about 15 mg / l,
When the particle size is 10 μm or more, a flocculant having a basicity of approximately 52 is injected at an injection rate of approximately 15 mg / l, or an flocculant having a basicity of approximately 62 is injected at an injection rate of approximately 25 mg / l.
Since the amount of the flocculant injected into the landing well is adjusted according to the output of the second particle counter, it is possible to manage in consideration of water quality fluctuations and seasonal factors, and more efficient by reducing packs. A water treatment plant management method can be realized.
[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 turbidity by particle size.
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 diagram showing the removal rate of turbidity by particle size in which basicity is added to the pack injection rate.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Landing well 2 Rapid mixing basin 3 Flock formation pond 4 Chemical sedimentation basin 5 1st particle counter 6 2nd particle counter 10 Beaker

Claims (1)

Raw water taken from the intake port is stored, and a landing well into which at least one of the two types of basicity of about 52 and basicity of about 62 is introduced, and the flocculant disposed at the subsequent stage of the landing well, The mixing pond that mixes the raw water that has been added, the floc formation pond that is placed downstream of this mixing pond to grow and sink flocs, and the treated water from the flock formation pond that flows after the floc formation pond flows in. In the water quality management method for a water purification plant including a chemical sedimentation basin, a first particle counter is provided in the landing well, a second particle counter is disposed in the chemical sedimentation basin, and the suspended matter measured by the first particle counter is measured. Of the particle size,
When the particle size is 2 to 10 μm , a flocculant having a basicity of about 62 is introduced at an injection rate of about 15 mg / l,
When the particle size is 10 μm or more, a flocculant having a basicity of approximately 52 is injected at an injection rate of approximately 15 mg / l, or an flocculant having a basicity of approximately 62 is injected at an injection rate of approximately 25 mg / l.
A water quality management method characterized by adjusting an amount of the flocculant injected into the landing well according to an output of the second particle counter.

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