JP3826289B2 - Desalination method - Google Patents

Description

【００１４】
この表から分かるように、塩分含有井戸水に対する海水の混合割合を増すことにより、酸添加量を大幅に低減できる。
【００１５】
実施例２
原水である海水に塩分含有井戸水を１：１の割合で混合し、得られた混合物を逆浸透法により淡水化した。上記混合物のホウ素濃度は３ｐｐｍであり、得られた透過水のホウ素濃度は１．０ｐｐｍ未満であった。
【００１６】
【発明の効果】
第一発明では、塩分含有井戸水に海水を混合し、得られた混合物を逆浸透法により淡水化するので、原水中のスケール成分である重炭酸イオンやカルシウムイオン濃度を低減し、スケール形成抑制に必要な酸の添加量を低減させることができる。また、塩分含有井戸水に海水を加えることにより、井戸での取水量を増す必要がないため、取水量増加に起因する井戸水位低下や水質悪化を招くことなく、既設の井戸をそのまま利用することができる。
【００１７】
第二発明では、原水である海水に塩分含有井戸水を混合することにより、ホウ素除去設備を省略もしくは小型化することができ、メンテナンスを省略し、ｐＨ調整薬品の使用量を低減することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a desalination method using well water containing salt as raw water. The present invention also relates to a desalination method using seawater as raw water. In this specification, water containing salt obtained from a well is referred to as “salt-containing well water”.
[0002]
[Prior art]
Usually, in a seawater desalination apparatus using a reverse osmosis method, pH is adjusted by adding an acid to raw water in order to prevent scale precipitation of calcium carbonate or the like. The amount of acid added is mainly determined by the bicarbonate ion concentration and calcium ion concentration in the raw water.
[0003]
The amount of acid added for adjusting the pH of the reverse osmosis membrane feed water increases as there are more bicarbonate ions and calcium ions in the raw water. For this reason, in desalination using salt-containing well water with a high content of bicarbonate ions and calcium ions as raw water, it is necessary to add a large amount of acid.
[0004]
In addition, when salt-containing well water is treated by the reverse osmosis method, it is necessary to discharge a part of the same water supplied to the reverse osmosis membrane module as concentrated water (brine). Contained well water needs to be taken from the well and supplied to the desalination unit. However, if a large amount of salt-containing well water is acquired from an existing well, there is a concern that the well water level may be lowered or the well water quality may be deteriorated.
[0005]
Moreover, in reverse osmosis seawater desalination facilities, there is a risk that the boron concentration in the permeated water may not comply with the tap water quality standard (boron concentration: 1 ppm or less) due to the aging of the boron removal performance of the reverse osmosis membrane. For example, when seawater having a boron concentration of 4 ppm is used as the raw water, the boron concentration of the permeated water obtained by the reverse osmosis method is 1.5 ppm. Therefore, it is necessary to install a boron removal facility that keeps the boron concentration below the tap water quality standard. However, in the boron removal equipment, it is necessary to adjust the pH by adding caustic soda to treat the boron, so that the pH of the permeated water after boron removal becomes high. For this reason, it is necessary to adjust the pH by adding carbon dioxide gas, sulfuric acid, or the like to the permeated water after boron removal, and to adjust this water to the tap water quality standard.
[0006]
[Problems to be solved by the invention]
In view of the above points, the present invention provides a salt-containing well water desalination method that can reduce the amount of acid addition necessary for suppressing scale formation and that does not cause a decrease in well water level or deterioration in water quality due to an increase in water intake. The purpose is to provide.
[0007]
Another object of the present invention is to provide a seawater desalination method capable of omitting or downsizing a boron removal facility.
[0008]
[Means for Solving the Problems]
How Ru good to the invention comprises a calcium ion and bicarbonate ion, upon desalination by the well water containing salt necessary pH adjustments to prevent scale deposition reverse osmosis, seawater salt content containing well water Here, the desalination method is characterized in that the mixing ratio of seawater to the well water is 20:80 to 80:20 .
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be specifically described based on examples.
[0012]
Example 1
Seawater was mixed with the salt-containing well water containing 260 ppm of calcium ions and 450 ppm of bicarbonate ions, which is the raw water, and the resulting mixture was desalinated by the reverse osmosis method. The required acid addition amount at the same recovery rate (ratio of the production water amount to the supply water amount to the reverse osmosis membrane module) is shown in Table 1 below.
[0013]
[Table 1]

[0014]
As can be seen from this table, the amount of acid added can be greatly reduced by increasing the mixing ratio of seawater to the salt-containing well water.
[0015]
Example 2
Salt water containing salt water was mixed at a ratio of 1: 1 with seawater as raw water, and the resulting mixture was desalinated by a reverse osmosis method. The boron concentration of the above mixture was 3 ppm, and the boron concentration of the obtained permeated water was less than 1.0 ppm.
[0016]
【The invention's effect】
In the first invention, seawater is mixed with the salt-containing well water, and the resulting mixture is desalinated by the reverse osmosis method, so the concentration of bicarbonate ions and calcium ions, which are scale components in the raw water, is reduced, and scale formation is suppressed. The required amount of acid added can be reduced. In addition, it is not necessary to increase the water intake in the well by adding seawater to the salt-containing well water, so existing wells can be used as they are without causing a drop in well water level or deterioration in water quality due to an increase in water intake. it can.
[0017]
In the second invention, by mixing the salt-containing well water with the seawater that is the raw water, the boron removal equipment can be omitted or miniaturized, maintenance can be omitted, and the amount of pH adjusting chemical used can be reduced.

Claims (1)

In order to desalinate well water containing calcium ions and bicarbonate ions and containing salt that requires pH adjustment to prevent scale precipitation by reverse osmosis, seawater is mixed with the salt-containing well water , where the well water The desalination method characterized by the mixing ratio of seawater to 20:80 to 80:20 .