JPS6038083A - Desalination method - Google Patents

Abstract

PURPOSE:To enhance a water recovery ratio by desalting waste water with good efficiency, by supplying water to be treated to an apparatus mounted with a reverse osmosis membrane of which the silica removal ratio of 50% or less, the monovalent ion removal ratio is 50% or more and a divalent ion removal ratio is 80% or more. CONSTITUTION:Water to be treated is supplied to a reverse osmosis membrane apparatus mounted with a reverse osmosis membrane of which the silica removal ratio is 50% or less, the monovalent ion removal ratio is 50% or more and the divalent ion removal ratio is 80% or more and said apparatus is operated under a condition of a water recovery ratio of 75% or more. To the above mentioned reverse osmosis membrane apparatus, the other apparatus using an ion exchange resin such as a strong acidic cation exchange resin, a weak acidic cation exhange resin, a strong basic anion exchange resin and a weak basic anion exchange resin may be provided if necessary. By the aforementioned method, operation exceeding 70% being an conventionally inoperable region is enabled.

Description

[Detailed description of the invention] The present invention relates to a method for desalinating commercial and wastewater.

In recent years, with changes in industrial structure and rapid economic and social development,
The demand for water for various uses is expanding, and efficient use of water is being seriously considered as a solution to water shortages. In order to utilize this water efficiently, there are water treatment systems that utilize, for example, reverse osmosis membranes or ion exchange membranes.

Water usually contains silica (Sin2), calcium, chloride ions, etc. However, the solubility of silica is approximately 100 my/Q concentration, so in conventional reverse osmosis membrane water treatment, silica is blocked by the membrane and concentrated, resulting in silica that exceeds the solubility adhering to the membrane surface. The membrane pores were blocked, often making it impossible to recover the water.

Therefore, the recovery rate of water is generally limited to about 60 to 70 inches, and the current situation is that about 30 to 40% of the remaining water is discarded.

For this reason, there has been a widespread desire in society to recover the remaining 40% of the water that would otherwise be discarded, to the extent that is technically possible9, and to utilize water more effectively.

The purpose of the present invention is to solve the above-mentioned problems by providing a desalination method with an excellent water recovery rate from industrial and waste water.

As a result of extensive research in order to solve the drawbacks of the conventional technology, the inventor of the present invention has found that if a reverse osmosis membrane with a poor silica removal rate is used, it will be possible to reduce the amount of waste due to the unevenness of the membrane surface. Knowledge W
The present invention has been completed.

That is, in the desalination method of the present invention, the water to be treated is treated with silica (S
iOz) removal rate is 50% or less, and the removal rate of -valent ions is 50% or more, and the removal rate of divalent ions is 80% or less.
It is characterized in that it is supplied to a reverse osmosis membrane device equipped with a reverse osmosis membrane with a water recovery rate of 75% or more, and is operated under conditions where the water recovery rate is 75% or more.

The water to be treated that is the target of the method of the present invention may be measured as long as it is normal use/return water, and specific examples thereof include tap water, industrial water, can water, ground water, or sewage. Can be mentioned.

The reverse osmosis membrane used in the present invention can be any membrane as long as it has a silica (St02) removal rate of 50% or less, a -valent ion removal rate of 50% or more, and a divalent ion removal rate of 80% or more. It may be something. Regarding the performance of this reverse osmosis membrane, the silica removal rate is preferably 50% or less, and the lower the better. A specific example of this reverse osmosis membrane is:
Examples include NTR-7250 (trade name, manufactured by Nitto Denko Corporation).

The reverse osmosis membrane device used in the method of the present invention is a device equipped with the above-described reverse osmosis membrane, and other devices may be attached as necessary. Other equipment includes strong acid cation exchange resins, weak acid cation exchange resins, and strong basic anion exchange resins.

Generally known ion-exchange resins such as weakly basic anion-exchange resins are used alone or in combination, and the following are typical treatment apparatuses thereof.

■ A mixed bed column containing a 1■ type strongly acidic cation exchange resin and an OH type strongly basic anion exchange resin.

■ Type Ii strongly acidic cation exchange resin tower - decarboxylation tower - OI
Type I strong basic anion exchange resin tower... (2 bed 3 tower type)
.

(2) H-swollen acidic cation exchange resin tower - OH type weakly basic anion exchange resin tower - decarboxylation tower - OIN type strongly basic anion exchange resin tower... (3 bed 4 tower type).

■ ■(Strong acidic cation exchange resin tower - Decarboxylation tower - OH
Shape strongly basic anion exchange resin tower - H swollen acidic cation exchange resin tower - 〇H type strongly basic anion exchange resin tower... (
4-bed, 5-tower type).

The desalination method of the present invention uses the above-mentioned reverse osmosis membrane device with water recovery rate =
It is operated under conditions of 75% or higher, and is capable of operating at a rate exceeding 70%, which was conventionally impossible. The desalination method may be operated only with the reverse osmosis membrane device used in the present invention, for example, when drinking water is produced by desalinating canned water, and when the quality of the treated water is important. For example, when an ion exchange resin or the like is applied to produce pure water, ultrapure water, etc., it may be applied for pretreatment. In particular, the desalting method of the present invention is suitable for the latter.

According to the desalination method of the present invention, the low water recovery rate of the conventional method using a reverse osmosis membrane can be significantly increased.

Hereinafter, the present invention will be explained in more detail with reference to Comparative Examples and Examples, which will explain the scope of the present invention in a comparative example. Yokohama city water with a silica concentration of about 25 m97Q is stored in a water tank, and the water supply pressure is increased to 15 ky with a high-pressure pump. /cm and supplied to a reverse osmosis membrane device. As a membrane, Membrane B (trade name: 5C-300.0, manufactured by Toshishiku Co., Ltd.) exhibiting a silica removal rate of 81.7% was installed. The water recovery rate of the membrane device was set at 90% and it was operated for approximately 500 hours. The resulting treated water quality is shown in the table.

Example 1 The same procedure as in Comparative Example was carried out, except that Membrane A (trade name: NTR-7250, manufactured by Nitto Denko Corporation) exhibiting a silica removal rate of 26.7% was used as the membrane. The resulting treated water quality is shown in the table.

Further, the amount of permeated water after about 500 hours was the same as the initial value in the device equipped with membrane A, but decreased to about 75 g of the initial value in the device equipped with membrane B.

Further, when both modules were disassembled, no precipitates were observed in Membrane A, whereas scale mainly composed of silica was observed to be deposited in Membrane B.

In this example, the conventional membrane with high silica removal rate only
After 00 hours of operation, the amount of permeated water decreased to the initial value of 75%, and a recovery rate of 90% was judged to be completely impractical. On the other hand, in the case of the membrane of the present invention, there is no decrease in the amount of permeated water even after 500 hours of continuous operation, and furthermore, no silica scale is deposited on the membrane surface, and the recovery rate is 90%, which is sufficient for practical use. .

Example 2 Store groundwater (silica concentration: approx. 45m9/Q) in a water tank and put this water at a pressure of 15! /crrL2, water was supplied to the membrane device equipped with the membrane B with a high silica removal rate used in the comparative example. This membrane was operated for maximum water recovery. As a result, the ability to maintain the amount of permeated water at the same level as the initial value reached a limit of around 70% even if the best conditions were maintained.

The method of the present invention was used to increase the water recovery rate.

First, the same water was supplied at a pressure of 15 to 2 to an apparatus equipped with the Bt membrane with a high silica removal rate used in the comparative example. However, the water recovery rate was set at 50%.

Next, the concentrated water discharged from the membrane device (silica temperature approximately 7
9 mg/Q ) was supplied to the apparatus equipped with Membrane A, which exhibits a low silica removal rate, as used in Example 1, using washing out. Membrane B was operated at a water recovery rate of 80%. With this method, there was almost no decrease in the amount of permeated water, and stable operation was possible over a long period of time. The total book recovery rate using this method is 8
It became 9.4 inches. Therefore, while the conventional method had a recovery rate of about 70% even if the best conditions were maintained, the recovery rate was improved to 89.4% by the method of the present invention, and approximately 20% more water was recovered than in the conventional method.

In addition, this water was then passed through a strong cationic ion exchange resin column,
When water was sequentially passed through the deaeration preparatory and strong basic anion exchange resin columns, pure water having the same quality as conventionally obtained pure water was obtained.

Claims (1)

[Claims] 1 The removal rate of silica (SiO2) from the water to be treated is 50%.
It is supplied to a reverse osmosis membrane device equipped with a reverse osmosis membrane that has a water recovery rate of 75% or more and a removal rate of -valent ions of 50% or more and a removal rate of divalent ions of 80% or more. A desalination method characterized by operating under the above conditions.