JPH0118791B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of alleviating corrosiveness by adding an appropriate amount of minerals to water lacking dissolved salts and increasing the pH buffering capacity of the water. Ca and Mg are essential elements for the human body, but it is said that only 10 to 20% of the daily intake comes from drinking water, and people who regularly drink water that is low in dissolved salts, such as distilled water, In some cases, the effect on the human body is considered an issue. In fact, this is a problem encountered in seawater desalination plants using distillation methods, and even in domestic water sources, especially river water with snowy areas upstream, the electrical conductivity is 10μs/cm.
It is not uncommon for water quality similar to distilled water (at 25°C) to be targeted. If the quality of such water is expressed by the Langelier index, which is one of the indicators for evaluating the corrosivity of water, it is -4.
The value is ~-6. In the Langelier index, a positive value indicates a tendency to scale, a negative value indicates a tendency to corrosion, and a value of zero indicates a stable state. Distilled water as mentioned above is extremely corrosive. It can be said that the water quality is likely to cause this. Therefore, in facilities that handle such water, corrosion of equipment and piping, as well as complaints about red water, have become serious problems. In order to reduce the corrosiveness of distilled water or water that is similar to distilled water and which is low in dissolved salts, or to improve water quality so that it is safe to drink regularly, it is necessary to improve the water's hardness and alkalinity by some means. There is a need for a method that can provide the desired pH and maintain the pH within an appropriate range at all times. In the past, pH adjustment was often done by adding alkaline agents such as NaOH, Na ₂ CO ₃ , and Ca(OH) ₂ to alleviate the corrosive nature of water and to deal with red water problems.
Water with a Langelier index of -4 has a small PH buffering capacity, so in order to make the Langelier index zero, the PH must be increased.
It is necessary to set it to about 10. However, there is a standard for the pH of tap water to be between 5.8 and 8.6, and because of the taste of the water, in practice the pH is around 7.5 to 8.0.
Since this is the upper limit of pH setting, these methods can only improve water quality up to a Langelier index of -1.5 to -2.5. In addition, in seawater desalination plants using the distillation method, in order to give the distilled water an appropriate concentration of dissolved salts,
By adding some seawater or by adding dolomite (CaCO ₃ ,
Methods such as passing through a layer of MgCO ₃ minerals) have been used. However, in this case, simply passing distilled water through the dolomite layer will result in a PH of 9 because very few salts will be dissolved and the proportion of ^CO2-3 ions in the _alkalinity components is extremely high. Given the above, measures such as increasing the concentration of dissolved salts by dissolving CO ₂ gas and passing water through it before the dolomite layer, and then adjusting the pH by adding acid after the dolomite layer are recommended. operation management is complicated. The present invention aims to solve the above-mentioned problems of the conventional method and the complexity of operation management. In the present invention, a treated water tank is connected to the bottom of a filling tank filled with a filler whose main component is carbonate, which is a hardness component such as calcium or magnesium, and the raw water is flowed downward from the top of the filling tank. This water quality improvement method is characterized by passing water through the water and aerating gas containing carbon dioxide from the treated water tank so that the pH of the aerated water is within the range of 5.8 to 8.6. Next, to explain the action, in the filling tank, hardness components and alkalinity components are added to the raw water by the reaction between carbonate and carbon dioxide gas dissolved in water, and in the treated water tank, carbon dioxide gas is added to the water. It dissolves in water, adds carbonic acid to the water, and adjusts the pH. Therefore, in the present invention, the filler can be any material whose main component is carbonate, which is a hardness component, such as limestone, marble, or dolomite, and may be a natural mineral or an artificial material with an appropriate amount of mineral added. . Furthermore, in most cases, air, which is the cheapest gas, can be used as the gas containing carbon dioxide gas, but by increasing the content ratio of carbon dioxide gas, the effect of imparting alkalinity and hardness is improved. Next, an embodiment of the present invention will be described based on the drawings. 1 is a filling tank, 1' is a filling material, 2 is a treated water tank, 3 is an aeration pipe, 4 is a blower, 5 is a carbon dioxide gas cylinder, and 6 is an exhaust port. , 7 is a raw water inflow pipe, 8 is a treated water outflow pipe, 9 is a perforated plate for supporting the filler, and 10 is a supply pipe for carbon dioxide-containing gas. The treated water outflow pipe 8 is raised at the upper end position of the treated water tank 2, that is, at the height of the perforated plate 9, so that the treated water outflow pipe 8
The inside is always filled with treated water. Therefore, if raw water is passed in a downward flow from above the filler 1', and a mixed gas of carbon dioxide and air is supplied as a carbon dioxide-containing gas in an upward flow from the aeration pipe 3, Since the mixed gas is aerated in the form of fine bubbles through the aeration pipe 3, the reaction between carbonate as a filler, carbon dioxide gas (carbon dioxide gas from the carbon dioxide gas cylinder 5 and carbon dioxide gas in the air), and water occurs. As a result, hardness components and alkalinity components are added to the raw water. Next, the treated water that flows into the treated water tank 2 is constantly aerated with fresh carbon dioxide gas and air, so free carbon dioxide is further added here and the pH is adjusted, resulting in a pH of 5.8 to 8.6 before the treated water flows out. It is discharged from the pipe 8. In the embodiment described above, the filler 1' is immersed in raw water, but the water level in the filling tank 1 may be set at the perforated plate 9. Next, embodiments of the present invention (all using the apparatus shown in the drawings) will be described. Example 1 This is an example in which the present invention was applied to desalinated seawater obtained by the distillation method.The water quality of this distilled water was as shown in Table 1, and marble was used as the filler and air was used as the ventilation gas. .

[Table] Table 2 shows the results when processing was carried out under the conditions of each SV (space velocity, 1/h) without aeration. It can be seen that when the SV is decreased to increase the amount of dissolution, the pH increases significantly.

[Table] Next, Table 3 shows the treatment results when aeration was performed according to the method of the present invention.

[Table] When ventilation is performed as shown in Table 3, the pH is 8.0 to 8.1.
and within tap water standards, SV2.5~5, G/L ratio 10~
Under 20 conditions, both alkalinity and hardness are 10 to 20 mg/
is increasing. The Langelier index is also −0.8 to −1.3.
improved. Note that the G/L ratio, that is, the gas-liquid ratio, is the ratio between the flow rate of ventilation gas (in a standard state) and the flow rate of raw water. Example 2 An example is shown in which a mixed gas of air and carbon dioxide is used as the ventilation gas in the water quality improvement of Example 1.

【table】

[Table] As shown in Table 4, the treatment effect is further enhanced when carbon dioxide gas is mixed with air and aerated. SV10, G/L
At a ratio of 10, air: carbon dioxide = 1000:2
PH7.8, electrical conductivity 98.0μs/cm, alkalinity 42.1
mg/, hardness improved to 42.6, Langelier index -0.8, PH7.6 when air: carbon dioxide = 1000:3,
Electrical conductivity 122μs/cm, alkalinity 61.8mg/,
The hardness was improved to 62.6mg/, and the Langelier index was -0.6. Example 3 An example of water quality improvement of a water source where red water damage is a problem will be shown. The raw water is river water, and the water quality is as shown in Table 5.

[Table] Treatment was carried out according to the method of the present invention using marble as the filler and air as the aeration gas. processing conditions
SV2.5, G/L ratio 10 PH8.1-8.3, electrical conductivity 89.5μs/cm, alkalinity 27.6mg/, calcium hardness 27.5mg/, magnesium hardness 5.7
mg/, and the Langelier index improved to -0.5 to 0.9. Example 4 Targeting distilled water of the water quality shown in Table 6, the present invention and a gas-liquid cocurrent upward flow type (comparative example ), we compared the treatment effects. Table 7 shows the treatment conditions and treatment results.
Marble with a diameter of 2 to 5 mm was used as the filler.

【table】

[Table] Treatment No. 1 has a G/L ratio by the method of the present invention.
10. When treated at a water flow rate SV of 5 (1/h), an increase in total alkalinity and total hardness of approximately 10 mg/h was observed, and the pH was 8.1, which is lower than the tap water standard.
Treated water within the range of 5.8 to 8.6 is obtained. On the other hand, in treatment No. 2, the G/L ratio and SV were treated under the same conditions as treatment No. 1 using a gas-liquid parallel flow upward flow method, but the increase in total alkalinity and total hardness was Although it is lower than treatment No. 1, the pH is 9.0, which exceeds tap water standards. This is processed
This shows that the CO ₂ usage efficiency is lower than in case No. 1. Processing No. 3 uses a gas-liquid parallel flow upward flow method, and the SV is 5.
(1/h), the G/L ratio is increased to 30, that is, the air amount is increased three times. In this way, if the amount of air is increased, the water quality will be 8.3, which is within the tap water standard, even without providing the treated water tank 2. As is clear from the above examples, the present invention has special effects that cannot be obtained with the gas-liquid parallel flow upward flow system, both in terms of treatment effects and in terms of the power cost of the required amount of air. ing. As described above, the present invention makes it possible to add hardness components, alkalinity components, and free carbonate to raw water in a well-balanced manner through simple operations, and therefore it is possible to easily reduce the negative value of the Langelier index. It is now possible to adjust the pH and keep the pH within the standard of 5.8 to 8.6 at all times, even when the operation is stopped.The structure of the device for carrying out the present invention is also extremely simple, and only air or carbon dioxide can be supplied. This method is extremely effective in practice and has many advantages, such as not requiring any other PH adjustment equipment.

[Brief explanation of drawings]

The drawings are flow sheets illustrating embodiments of the invention. 1... Filling tank, 1'... Filling material, 2... Treated water tank, 3... Aeration pipe, 4... Blower, 5... Carbon dioxide gas cylinder, 6... Exhaust port, 7... Raw water inflow pipe,
8... Treated water outflow pipe, 9... Perforated plate, 10... Supply pipe.

Claims (1)

[Scope of Claims] 1. A treated water tank is provided in communication with the lower part of a filling tank filled with a filler whose main component is carbonate, which is a hardness component such as calcium or magnesium, and the raw water is poured below the upper part of the filling tank. Water is passed through in a countercurrent manner, and gas containing carbon dioxide is aerated from the treated water tank to the treated water.
A water quality improvement method characterized by aeration so that the pH is within the range of 5.8 to 8.6. 2. The method according to claim 1, wherein the aeration treatment is performed by supplying the carbon dioxide-containing gas to an aeration mechanism provided at the bottom of the treated water tank. 3. The method according to claim 2, wherein the aeration treatment is performed using a mixed gas of carbon dioxide and air as the carbon dioxide-containing gas.