JPH08117738A - Method for purifying raw water for city water - Google Patents

Abstract

PURPOSE: To purify taken-in raw water at low costs, to reduce the consumption of chlorine, and to control the generation of trihalogenomethane. CONSTITUTION: Raw water from an intake is led to a sedimentation basin 3 while being added with acid clay. The water is then added with chlorine and alkali and sent to an admixture basin 4, where polyaluminum chloride is added to the water and the mixture is stirred at a high speed. Next, the water is stirred slowly in a flock forming basin 5, and thereafter, in a chemical precipitation basin 6, a grown-up flock is precipitated and removed. Next, the water is added with chlorine and led to a rapid filtration basin 7, where residual suspended substances are filtered out by a sand layer. Finally, the water, after passing through an activated carbon adsorption tank 9, is added with chlorine and alkali and stored in a water purification basin 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying raw water for tap water.

[0002]

2. Description of the Related Art The amount of rainfall varies every year, but if the amount of rainfall is low, the amount of water in the river will drastically decrease. And in that case, the water becomes extremely polluted, and the turbidity and the odor are extremely deteriorated. Therefore, a large amount of chemicals such as activated carbon, polyaluminum chloride (PAC), and chlorine is required when the raw water for tap water is purified in a water purification plant.

The use of a large amount of these agents increases the cost, and the use of a large amount of chlorine also increases the amount of trihalomethane which is a carcinogenic substance.

[0004]

Thus, the conventional method for purifying raw water for tap water in a water purification plant is to introduce raw water taken from an intake into a sand basin, and add activated carbon powder to the sand basin while the raw water is added. To remove solids such as sand by sedimentation,
Next, add the required amount of chlorine and alkali, then lead to the mixing pond,
In the mixing pond, polyaluminum chloride was added and rapidly stirred, then led to a floc formation pond, and slowly stirred in the floc formation pond so that the suspended solids grow into large particles by the polyaluminum chloride, and then the chemical precipitation pond. Lead to
Flocs that have grown greatly in the chemical sedimentation basin are precipitated and removed, and then the required amount of chlorine is added and then introduced into a rapid filtration basin to remove suspended matter that cannot be removed in the chemical sedimentation basin in the rapid filtration basin. The sand is removed through the sand layer, and finally it is passed through an activated carbon adsorption tank, and after the required amounts of chlorine and alkali have been added, it is stored in a water purification pond.

The present invention has been made to solve the above-mentioned problems in the conventional purification method, and to purify raw water for tap water and reduce chlorine to suppress the amount of trihalomethane generated at a low cost. It is intended to provide a purification method that has made it possible.

[0006]

In order to achieve the above object, the present invention is to replace the activated carbon powder added in the sand basin in the conventional purification method with acid clay.

That is, according to the present invention, the raw water taken in from the intake is guided to a sand basin, and in the sand basin, solid matter such as sand in the raw water is removed by precipitating and removing the solid matter while adding acid clay. After adding chlorine and alkali, lead to a mixing pond, add polyaluminum chloride in the mixing pond and rapidly stir, then lead to a floc formation pond, and in the floc formation pond, suspended solids grow into large particles by polyaluminum chloride The mixture is gently stirred so that it can be introduced into a chemical settling basin, and flocs that have grown significantly in the chemical settling basin can be precipitated and removed, and then the required amount of chlorine can be added, followed by introduction into a rapid filtration basin and the rapid filtration. In the pond, suspended solids that cannot be removed in the chemical sedimentation pond are removed through the sand layer, and finally through the activated carbon adsorption tank, after adding the required amount of chlorine and alkali, they are stored in the clean water pond. It was a method of purifying raw water for tap water.

The acid clay used is a clay whose main constituent is montmorillonite, which is naturally activated in an acidic environment and has adsorptivity.
And its components are SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , CaO, MgO.
, Na ₂ O + K ₂ O, Ig.Loss, etc.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. In the figure, 1 is the intake, 2 is the intake pump building,
3 is a sand basin. 4 is a mixing pond, 5 is a floc formation pond,
6 is a chemical sedimentation tank, 7 is a rapid filtration tank, 8 is an intermediate pump building,
9 is an activated carbon adsorption tank, and 10 is a water purification pond. In addition, 11 is a sludge drainage basin, 12 is a concentration tank, and 13 is a pressure dehydrator.

The specific processing according to this embodiment is performed as follows. The raw water taken in from the intake 1 is first led to the sand basin 3. Then, in the settling basin 3, solid matter such as sand in the raw water is precipitated and removed while adding acid clay. Next, after adding required amounts of chlorine and alkali to the mixing tank 4, polyaluminum chloride (PAC) as a coagulant is added to the mixing tank 4 and rapidly stirred.

Next, it is led to the floc formation pond 5 and is slowly stirred in the floc formation pond 5 so that the suspended matter grows into large particles due to polyaluminum chloride. Next, it is guided to the chemical sedimentation pond 6, and the flocs that have grown greatly in the chemical sedimentation pond 6 are precipitated and removed.

Next, after adding a required amount of chlorine, it is led to the rapid filtration basin 7, and in the rapid filtration basin 7, suspended matter that cannot be removed by the chemical precipitation basin 6 is removed through the sand layer.

Finally, after passing through the activated carbon adsorption tank 9,
The required amounts of chlorine and alkali are added and stored in the water purification pond 10.

[0014]

EFFECTS OF THE INVENTION Since the present invention is to add acid clay in a sand basin that first treats raw water taken in from the intake, most solids and suspended solids are suspended due to the adsorption action of acid clay in the initial stage of treatment. It can absorb and remove things. Therefore, it is not necessary to use a large amount of chemicals in the subsequent processing steps as in the conventional method.
Moreover, since the acid clay is inexpensive, the cost required for the treatment is much lower than that of the conventional method.

Further, since the acid clay contains a large amount of alumina as described above, the amount of polyaluminum chloride as a coagulant can be reduced to less than half of the conventional amount.

Further, in the post-treatment step, as described above, the amount of solids and suspended matter in the raw water is reduced, and the acid clay also contains magnesium.
The amount of chlorine used can also be reduced. Since the amount of chlorine used can be reduced in this way, the amount of trihalomethane generated can be reduced to that extent.

Test examples will be given below to clarify the effect of the present invention. Return the water intake / raw water (refrigerator storage) sent in a 20-liter plastic container to room temperature, shake the plastic container well,
Once transferred to a 3 liter beaker, it was well mixed with a stir bar and collected in a 500 ml tall beaker.
Powdered activated carbon and acid clay were added to each tall beaker in appropriate amounts and stirred for 5 minutes with a magnetic stirrer,
Thereafter, an appropriate amount of PAC was added to each of them, and the mixture was slowly stirred for 5 minutes and allowed to stand. Then add 4% NaOH and adjust the pH
Was adjusted to around 7.0 and allowed to stand for 30 minutes. The supernatant was collected and measured for TOC, odor and turbidity.

The analysis and measurement methods are as follows. pH: Water supply test method 8.3 Glass electrode method (Horiba F-8 used) TOC: Water supply test method 72.3 Combustion oxidation method (Shimadzu TOC-500 used) SS: Water supply test method 25.2 Filtration method Turbid Degree: Clean water test method 3.3.1 Transmitted light measurement method Odor: Clean water test method 6.3 Odor intensity

Further, the raw water intake is the following table.

[0020]

[Table 1]

In Table 1, * 1: TOC is a measured value after filtration, and * 2: odor intensity.

The test results are as follows.

[0023]

[Table 2]

In Table 2, R-0 is the raw water intake, R-1 is the result of the conventional method, and R-2 to R-5 are the results of the present invention. The 6-level odor intensity display by the Environment Agency is as follows.

[0025]

[Table 3]

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

[Explanation of symbols]

 1 Water intake 3 Settling basin 4 Mixing basin 5 Floc formation basin 6 Chemical sedimentation basin 7 Rapid filtration basin 9 Activated carbon adsorption tank 10 Purification basin

Claims (1)

[Claims] 1. The raw water taken in from the intake is led to a sand basin, and in the sand basin, solid matter such as sand in the raw water is removed by precipitation while adding acid clay, and then required amounts of chlorine and alkali are removed. After the addition, the mixture is introduced into a mixing pond, polyaluminum chloride is added in the mixing pond and rapidly stirred, and then the mixture is introduced into a floc formation pond, and slowly suspended in the floc formation pond to grow into large particles by the polyaluminum chloride. The mixture is stirred and then introduced into a chemical sedimentation basin, flocs that have grown greatly in the chemical sedimentation basin are precipitated and removed, and then the required amount of chlorine is added, followed by introduction into a rapid filtration basin, in which the chemical Raw water for tap water, which was stored in a clean water pond after removing suspended solids that cannot be removed in a sedimentation pond through a sand layer and finally through an activated carbon adsorption tank and adding the required amount of chlorine and alkali Purification method.