JP2579873B2 - How to treat tap water - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating tap water which removes lower organochlorine compounds in tap water containing lower organochlorine compounds and improves the Langerian index of tap water.

[0002]

2. Description of the Related Art Conventionally, in order to prevent generation of red water due to corrosion of tap water, caustic soda, soda ash, slaked lime, or the like has been injected into tap water as a countermeasure. However, it is not sufficient to make the pH alkaline by injecting these alkalis, and furthermore, a method of improving the Langelia index of tap water so that a protective film containing calcium carbonate as a main component is formed in the water pipe is proposed. (For example, Japanese Patent Laid-Open No. 2-194983 ). It is said that calcium carbonate is precipitated from water if the tap water index is +,-if it is eluted in water,-if it is 0, it is an equilibrium state where precipitation and elution occur simultaneously. It is said that a value greater than 1 is effective for preventing corrosion.

On the other hand, due to environmental pollution of water sources, there is increasing water source water in which a lower organic chlorine compound, which is a synthetic chemical substance, is dissolved in the water source water to such an extent that it is harmful to the human body. For this reason, perchlorethylene is less than 10 ppb based on water quality,
Trichloroethylene is specified as 30 ppb or less. As a method of removing these lower organic chlorine compounds, a method of performing adsorption treatment or aeration treatment with activated carbon is known.

[0004]

The improvement of the Langelia index of tap water is achieved by dissolving calcium ions in the form of calcium bicarbonate. That is, the improvement of the Langeria index is achieved by dissolving carbon dioxide in tap water, adding slaked lime or calcium carbonate to the solution, and dissolving many calcium ions without increasing the pH significantly by making calcium hydrogen carbonate. . Free carbonic acid is required to improve the Langeria index.

On the other hand, in the activated carbon adsorption method as a method for removing lower organic chlorine compounds such as perchlorethylene and trichloroethylene, the necessary adsorption transfer zone becomes longer because the concentration of lower organic chlorine compounds in water is low, and the apparatus becomes too large. Not preferred. When performing aeration treatment as another method, dissolved free carbonic acid is also removed.

[0006] The present invention is intended to improve the Langeria index by effectively utilizing free carbonic acid contained in a considerable amount of surface water or well water used for tap water, and to remove tap organic chlorine compounds from tap water. It is to propose a processing method.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on improving the Langerian index of tap water and effectively removing lower organic chlorine compounds contained therein, and as a result, have found that lower organic chlorine compounds and free In tap water containing, first, slaked lime or calcium carbonate is dissolved within the amount required to improve the Langerian index, and the dissolved free carbonic acid is replaced with calcium bicarbonate and then aerated.
After, we have reached the present invention to readjust the Langelier index further added slaked lime or calcium carbonate as needed, a carbon dioxide gas.

That is, the constitutional feature of the present invention is that tap water having a water source containing a lower organic chlorine compound and free carbonic acid as a water source has a Langeria index of -1 to +0.8, preferably -0.
After dissolving slaked lime or calcium carbonate in an amount of 5 to +0.5, this water is brought into contact with air to treat tap water.

In another embodiment of the present invention, slaked lime or calcium carbonate is dissolved in tap water whose source is water containing a lower organic chlorine compound and free carbonic acid to obtain a pH of 7 or less.
After contacting the water with air to remove the lower organic chlorine compounds, the amount of slaked lime or calcium carbonate and carbon dioxide gas in such an amount that the Langerial index becomes -1 to +0.8 together with the previously dissolved amount. Is a method of treating tap water.

Hereinafter, the present invention will be described in detail.

The amount of free carbonic acid dissolved in water differs depending on the water source. The water from the groundwater source used for tap water usually contains about 30 ppm of free carbonic acid, and the surface water also contains 10 ppm of free carbonic acid. Contains some free carbonic acid. In addition, the amount of the lower organic chlorine compound dissolved in the water greatly varies depending on the water source. However, the water in the water source around a large city may be dissolved at a water quality standard value or higher and is not removed by ordinary water purification treatment.

In the present invention, slaked lime or calcium carbonate is dissolved in ordinary purified water containing tap water (hereinafter referred to as "raw water") containing such a lower organic chlorine compound and free carbonic acid, and the dissolved free carbonic acid is dissolved. Is treated as calcium bicarbonate so as not to be released by the subsequent aeration treatment, followed by aeration treatment to remove lower organic chlorine compounds.

[0013] Slaked lime is injected as an aqueous solution or powder,
Preferably, it is injected as a 1000 ppm or more aqueous solution of slaked lime. By injecting as an aqueous solution, the injection amount can be easily adjusted and insoluble matter can be avoided. For the production of the slaked lime aqueous solution to be poured, for example, a predetermined amount of slaked lime is charged into a dissolving tank having a stirring means as shown in Japanese Patent Publication No. 63-2890, and the purified water is poured from the lower part of the tank while stirring at a low speed. Then, it can be carried out by taking out the slaked lime aqueous solution of a predetermined concentration from the upper part of the tank.

A slurry of slaked lime or calcium carbonate may be injected in place of the slaked lime aqueous solution, or calcium carbonate may be dissolved by passing raw water through a packed tower of calcium carbonate.

The amount of slaked lime or calcium carbonate dissolved in the raw water is an amount calculated from the Langeria index of the raw water previously determined experimentally and the desired Langeria index after the treatment. If the amount of free carbonic acid dissolved in the raw water is sufficient to improve the Langerian index to a desired value, the entire amount of slaked lime or calcium carbonate calculated from the desired Langerian index is dissolved and subjected to aeration treatment. Also, if the amount of free carbonic acid dissolved in the raw water is insufficient to improve the Langeria index to a desired value, it is preferable that the amount of slaked lime does not remain in a sufficient amount to convert all the free carbonic acid dissolved into calcium bicarbonate. In operation, slaked lime or calcium carbonate is dissolved to such an extent that the pH of the water becomes 7 to 8 and subjected to aeration treatment, and then together with previously dissolved slaked lime or calcium carbonate, the Langeria index is -1 to +0 . Adjust the Langeria index by adding slaked lime or calcium carbonate and carbon dioxide to an amount of 8. After converting the dissolved free carbonic acid into calcium bicarbonate, the raw water is subjected to aeration treatment to remove the dissolved lower organic chlorine compounds. Aeration treatment is a method in which raw water flows from the top of a packed tower such as a Raschig ring and air is supplied from the bottom of the tower , or a method in which air bubbles are generated using a perforated plate or the like from the bottom of the retained or running water, etc. Thus, the water containing the lower organochlorine compound is brought into contact with air to transfer the lower organochlorine compound to the gas phase. Many methods using a known gas-liquid contact device can be applied as the aeration method.
The amount of air that comes into contact with water depends on the gas-liquid contacting device / method, but in most cases it is 30 times or more the volume of water, preferably 4 times.
By contacting air in an amount of 0 to 100 times the volume, 90% or more of the lower organic chlorine compound can be removed.

If slaked lime is dissolved in the water to be subjected to the aeration treatment, it reacts with carbon dioxide gas in the air used for the aeration treatment and becomes calcium carbonate, which precipitates and may adhere to the inside of the gas-liquid contact device. . For this reason, when the amount of free carbonic acid dissolved in the raw water is not enough to improve the Langeria index, slaked lime to be dissolved before aeration is stopped to a pH of about 7 to 8, and after the aeration treatment, the remaining amount of slaked lime is reduced. It is preferable to add slaked lime and a corresponding amount of carbon dioxide gas to adjust to a desired Langeria index.

The air containing the lower organic chlorine compound in the raw water may be discharged through the activated carbon layer by adsorbing the lower organic chlorine compound on the activated carbon.

The water after the aeration treatment as described above is
When the amount of free carbonic acid contained in the raw water is an amount sufficient to improve the Langelia index, the desired water and the amount of the lower organochlorine compound with the desired water are sufficiently smaller than the water quality reference value. Has become. In addition, when dispensing slaked lime or calcium carbonate because the amount of free carbonic acid contained in the raw water is insufficient to improve the Langerian index, add the remaining amount of slaked lime or calcium carbonate and carbon dioxide gas after aeration treatment, and add Adjusting the index improves the desired water.

Next, referring to FIG. 1, one embodiment of the present invention will be described.
An example will be described.

In FIG. 1, reference numeral 1 denotes a slaked lime aqueous solution production tank, in which slaked lime of an amount capable of continuously operating for 30 to 60 hours is previously charged into the tank 1, and water is supplied from a water supply pipe 2 at the lower part of the tank. The slaked lime aqueous solution is continuously taken out from the slaked lime solution taking-out pipe 3 at the upper part, and injected into the raw water pipe 4. The water into which the slaked lime aqueous solution has been injected is sufficiently reacted in the adjusting tank 5 to generate calcium hydrogen carbonate. The water in the adjusting tank 5 is aerated by the aeration device 6
And air is injected from the lower part of the aeration device through the blower pipe 7 and brought into countercurrent contact.

The air containing the lower organochlorine compound in the water in contact with the water is released by adsorbing the lower organochlorine compound on the activated carbon through the activated carbon layer 8 provided at the head of the aerator.

The water that has exited the aeration device 6 has at least 90% of the lower organic chlorine compounds removed. When the injection amount of slaked lime into the pipe 4 is stopped before the aeration until the pH becomes 7 to 8, an aqueous slaked lime aqueous solution is additionally injected from the pipe 9 in such an amount that the Langeria index becomes a desired value. This water is transferred from the pipe 10 to the storage tank 1
Take out to 1. If necessary, slaked lime or calcium carbonate and carbon dioxide gas are added in the process of reaching the storage tank 11 or in the storage tank 11 to adjust the Langeria index. .

Hereinafter, the present invention will be described specifically with reference to examples.

[0024]

[Example] Free carbon dioxide as raw water 50 mg / l, Ca hardness about 4
0 mg / l, water of 50 ppb of perchlorethylene, pH 6.2, and a Langeria index of -2.3 were used. As a device, a slaked lime aqueous solution production tank having a diameter of 0.8 m and a height of 1.44 m, a diameter of 0.1 m, and a height of 0.1 m were used. An apparatus as shown in FIG. 1 comprising an adjusting tank having a height of 0.5 m and an aeration tower having a diameter of 0.05 m and a height of 2.5 m filled with a lashing ring was used.

25 kg of slaked lime is put into a slaked lime aqueous solution production tank, and raw water is supplied from the lower part of the tank while stirring at a low speed to produce a slaked lime substantially saturated aqueous solution (1600 ppm). Inject the aqueous solution,
The water discharged from the adjustment tank was improved to pH 8.0, Ca hardness 100 ppm, total alkalinity 100 ppm, perchlorethylene 50 ppb, and water with a Langeria index of 0.2.

Into the aeration tower, the above water was allowed to flow down from the upper part at 48 liter / Hr, and air was sent from the lower part at 2.4 m ³ / Hr. The water obtained from the bottom of the aeration tower has a pH of 8.5,
The water had a Ca hardness of 100 ppm, a total alkalinity of 104 ppm, perchloroethylene of 2.5 ppb, and a Langeria index of 0.7. The removal rate of perchlorethylene was 95%.

[0027]

According to the method of the present invention, the lower organic chlorine compound is sufficiently reduced from the water quality reference value by an inexpensive method such as aeration while improving the Langeria index by effectively utilizing the free carbonic acid dissolved in the raw water. To a small value.

The method of the present invention is particularly effective for improving tap water using groundwater having a large amount of dissolved free carbonic acid as a water source.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing one embodiment of the present invention.

[Explanation of symbols]

 1 Slaked lime aqueous solution production tank 2 Water supply pipe 3 Slaked lime aqueous solution take-out pipe 4 Raw water pipe 5 Adjustment tank 6 Aeration device 7 Blast pipe 8 Activated carbon layer 9 Pipe 10 Pipe 11 Storage tank

Continuation of the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location C02F 1/58 C02F 1/58 A

Claims (2)

(57) [Claims] The tap water having a water source containing a lower organic chlorine compound and free carbonic acid as a water source has a Langeria index of -1 to +.
A method for treating tap water, comprising dissolving slaked lime or calcium carbonate in an amount of 0.8, and contacting the water with air. 2. A method of dissolving slaked lime or calcium carbonate in tap water using water containing a lower organic chlorine compound and free carbonic acid as a water source to adjust the pH to 7 to 8, and contacting the water with air to remove the lower organic chlorine compound. And then adding slaked lime or calcium carbonate and carbon dioxide gas in an amount such that the Langerial index becomes -1 to +0.8 together with the previously dissolved amount.