JPH0747353A - Water purification method - Google Patents

Abstract

PURPOSE:To remove hydrophobic gaseous materials contained in water, particularly trihalomethane to the maximum and to always supply safe water by removing the hydrophobic gaseous materials from water on the primary side by permeation through a gaseous material permeable high polymer membrane whose gaseous pressure at its secondary side is made negative. CONSTITUTION:In a hydrophobic gaseous material removing device 1, a group of thin tubes 9 constituted by collecting a lot of thin tubes 9 of a bundled body consisting of capillary tubes formed of a gaseous material permeable high polymer material membrane is housed in a tank 10, and one end and the other end of the group of thin tubes 9 are made to communicate with a water inflow pipe 11 and an outflow pipe 12, respectively. The tank 10 is communicated with an air suction pipe 13, and to the free end of the air suction pipe 13, a vacuum pump 14 is connected. When the tank 10 is evacuated, differential pressure is caused between both the sides of the high molecular material membrane, allowing the hydrophobic gaseous materials to be separated from water. Here, in the case water to be treated is city water and when residual chlorine in water is removed before trihalomethane is removed, the effect to lower trihalomethane is increased.

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 water capable of removing hydrophobic gaseous substances contained in water, especially trihalomethane.

[0002]

2. Description of the Related Art The water purification process generally performed at present is to sterilize and disinfect the tap water raw water taken from a river or the like to sterilize and disinfect inorganic and organic pollutants. After a certain concentration of chlorine is left in the treated water after injection, activation such as sterilization is prevented, and then a coagulant is injected to carry out a coagulant precipitation treatment for removing suspended matter in the raw water. Therefore, the rapid filtration method is used.

By the way, tap water contains a substance called trihalomethane (hereinafter referred to as "THM") which is harmful to the human body.

This THM is produced by reacting chlorine and humin in tap water.

[0005] Over the year from April 1981 to March 1982, the THM content of tap water sampled at the Yodogawa water system faucet was investigated by the liaison group analysis group which considered the Yodogawa water problem.

[0006] As a result, it was found that the THM value was higher at the downstream sampling point than at the upstream of the Yodo River.

This indicates that the THM content value is proportional to the distance from the upstream water treatment plant to the water sampling point.

That is, the longer the contact time between chlorine and humic acid in tap water, the more THM is produced.

However, in the water purification plant, there is an obligation to add a standard amount of chlorine to the tap water in order to maintain the bactericidal action as described above.

Therefore, if tap water is used at a point away from the water treatment plant, chlorine and humin react as described above while flowing over a long distance from the water treatment plant to the point of use.
Is generated.

Therefore, while drinking such tap water, THM may gradually accumulate in the human body and may harm the human body.

An activated carbon treatment method is known as a method for removing THM from tap water. This is to remove THM by adsorbing it on activated carbon, and a high THM removal rate can be obtained. However, in order to implement this activated carbon treatment method, it is necessary to install an activated carbon filtration pond, etc., and it is difficult to perform it easily with the existing water purification equipment mainly based on the rapid filtration method. It is effective against the THM, but naturally it is not effective against the THM generated between the water treatment plant and the faucet.

Further, in Japanese Patent Laid-Open No. 58-137409, a flocculant is injected even before chlorine is injected to microflocify the humic substance, which is a precursor of THM, and contact with chlorine is injected later. THM by blocking
Although a method of suppressing the production is described, THM can be reduced only by about 40% by this method.

In Japanese Patent Application Laid-Open No. 58-174207, TH
Note that the amount of M produced increases at high pH values (eg, pH 7.5 to 8.0 or higher).
It is described that the production of THM is reduced by controlling the pH value to be weakly acidic (for example, about pH 6.0 to 6.5). It is considered that THM generation reaction is delayed in this method due to the reaction equilibrium, and that THM is generated in a large amount if the contact time between chlorine and humic substances is sufficiently long.

Therefore, it is difficult to always set the THM contained in tap water below a certain reference value in the above-mentioned prior art.

In view of the above circumstances, it is an object of the present invention to provide a method for purifying water in which hydrophobic gaseous substances contained in water, particularly THM, are maximally removed and safe water is always supplied. To do.

[0017]

The above-mentioned objects can be achieved by the present invention described below.

That is, the present invention is characterized in that hydrophobic gaseous substances are permeablely removed from water on the primary side through a gaseous substance permeable polymer membrane having a negative pressure on the secondary side. Regarding purification methods.

It is preferable that the membrane of the polymer substance is in the shape of a hollow fiber, which is suitable for large-scale processing. As a material for the membrane, a silicone rubber resin is preferable from the viewpoint of gas permeability and durability.

The above method of the present invention is particularly suitable for removing THM among hydrophobic gaseous substances. Furthermore, it is preferable to remove THM by the above-mentioned method after removing residual chlorine of water, because the THM removal rate increases.

By providing water circulating means to repeatedly purify water, clean and safe water having a high degree of purification can be supplied.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The water to which the purification method of the present invention is applied may be of any type such as river water, ground water, well water, etc., but is preferably for drinking, and is particularly purified for drinking at a water purification plant. Tap water is preferred.

According to the present invention, water is passed through one of the membranes of a gas-permeable polymer and a pressure is applied to the side filled with water, or the other side (not filled with water) is evacuated. , Separates hydrophobic gaseous substances from water by providing a pressure difference on both sides of the membrane.

At this time, it is preferable to apply a negative pressure or vacuum to the side of the polymer membrane which is not filled with water. This is because the pressurizing means such as a pump may momentarily generate a pressure larger than the set pressure when the switch is turned on, which may impose a burden on the membrane and shorten its life.However, the vacuum pump gradually turns on when the switch is turned on. This is because the negative pressure is applied and the burden on the membrane is small.

The film of the gaseous substance-permeable polymer substance used in the present invention is a non-porous film having no pores on its surface. The gas removal according to the present invention selectively permeates depending only on the gas permeability which is a characteristic of the polymer membrane.

As the polymer film, silicone rubber resin, polyolefin resin, tetrafluoroethylene resin, polyvinyl alcohol resin, polyacrylonitrile resin, polyimide resin, polysulfone resin, etc. can be used. Considering the gas permeability, particularly the selective permeability to THM and durability, the silicone rubber resin is most preferable.

In recent years, a polymer material membrane formed into a hollow fiber shape has been attracting attention from the viewpoint of handleability. In the present invention, the polymer material membrane is formed into a hollow fiber shape, and water is supplied from one end to the other end. A device for removing the hydrophobic gaseous substance as shown in FIG. 1 may be considered.

A hydrophobic gaseous substance removing apparatus 1 which is an example of an embodiment for achieving the water purification method of the present invention is a capillary tube composed of an assembly of capillaries formed of a polymer film as described above ( Hollow fiber membranes), for example, 100 to
A thin tube group 9 formed by collecting 200 pieces is housed in a tank 10. One end of the thin tube group 9 communicates with a water inflow pipe 11 and the other end communicates with an outflow pipe 12.

An intake pipe 13 is connected to the tank 10, and a vacuum pump 14 is connected to the free end of the intake pipe 13.

Hydrophobic gaseous substances in water can be removed by the method described above. Hydrophobic gaseous substances include oxygen and THM, and removal of oxygen can prevent the generation of red water.
Safe water can be secured by removing THM which is a carcinogen.

Here, when the water to be treated is tap water, the effect of reducing THM is enhanced by removing residual chlorine in the water prior to removing THM. As a method for removing chlorine, a known method can be applied, and examples thereof include a method of adsorbing with activated carbon and a method of irradiating with ultraviolet rays to decompose.

The present invention maximizes its effect by incorporating a circulation means for repeatedly supplying water purified by the above-mentioned hydrophobic gaseous substance removing device to the hydrophobic gaseous substance removing device. Therefore, the hydrophobic gaseous substance contained in water can be minimized.

Therefore, if water is circulated for a certain period of time (for example, 1 hour) or more, it is possible to supply water of substantially stable water quality at any time, and particularly for THM, the standard value of 30 ppb or less set by the World Health Organization (WHO) The water can be stably supplied.

For example, an example of an embodiment for purifying tap water by the method of the present invention is a tap water purifying apparatus as shown in FIG.

The tap water sent from the water purification plant 6 is stored in a water receiving tank 7 installed in the basement of the building or the like, and up to an elevated water tank 8 installed on the roof of the building by a pumping pump (not shown). Pumped.

The high water tank 8 and the hydrophobic gaseous substance removing device 1 are connected by a water guiding pipe 2, and a water guiding pump 15 and a foreign matter filter 3 are attached on the way. At this time, the amount of water sent by the water transfer pump 15 is 0.5 to
It is about 1000 t / h, preferably 1 to 300 t / h.

The free end of the water guiding pipe 2 is connected to the inflow pipe 11 of the hydrophobic gaseous substance removing device 1.

Next, one end of the circulation pipe 4 is connected to the outflow pipe 12 of the apparatus 1 for removing hydrophobic gaseous substances, and the other end is connected to the elevated water tank 8 and is branched to supply water pipe 5.
Connect with.

The free end of the water supply pipe 5 is connected to the faucet 16 of each household.

Therefore, when the faucet 16 is closed,
The tap water circulates in the circulation pipe 4 and the water guide pipe 2, but when the faucet 16 is opened, the circulated tap water flows through the water supply pipe 5 and flows out from the faucet 16.

Since the device of the present invention can thus be used immediately before the faucet at the end of the water supply pipe, it is possible to provide tap water in which THM is substantially removed and a minimum remains.

The present invention can be applied not only to the removal of hydrophobic gaseous substances from water but also to the removal of a desired gas from other liquids.

[0043]

In the method of the present invention, by applying a negative pressure, the hydrophobic gas-like substance is removed from the water passing through the polymer film due to the gas permeability which is a characteristic of the hydrophobic gas-permeable substance permeable polymer film. Can be removed. In particular, THM, which is a carcinogen, can be selectively permeated and removed to provide safe water (drinking water) with low THM. Further, by incorporating a circulation means, safe water with stable water quality can be provided.

[0044]

EXAMPLES The present invention will be described in more detail with reference to examples.

<Example 1> A water purifying apparatus using the present invention shown in FIG. 2 was installed on the roof of the safety car No. 2 building in Akasaka, Minato-ku, Tokyo. In the following examples, DO means dissolved oxygen.

The tap water currently used in this building and the treated water of the apparatus of the present invention are used as test water. The operating conditions of the apparatus are such that the deaerator operating time is 1 hour, the flow rate is 5 t / h, and bubbles may be present.

(Sample Collection and Transportation) A 100 ml graduated cylinder with a ground-in stopper was gently collected without bubbling, 10 drops of phosphoric acid (1 + 10) was added to adjust the pH to 2, and sodium sulfite (0.5 w / v%) was added. Was added to dechlorinate, filled with water, cooled with ice and transported.

(Quantification of THM by solvent extraction method) 40 ml or 30 ml as test water was placed in a 50 ml graduated cylinder equipped with a stopper, and 10 ml or 20 ml of n-hexane was collected.
ml was added, and the mixture was vigorously shaken and then left still, and 2 μl of the n-hexane layer was measured by ECD-GC. Three specimens were prepared for each, and two specimens (one specimen was a spare) were measured by the same operation.

The conditions of the gas chromatogram are as follows.

Apparatus: Shimadzu GC-3BE (electron capture type detector) column 20% CD-550 / AW-DMCS φ3 m
m × 3.0 m Setting conditions: Sample inlet temperature 200 ° C. Column temperature 120 ° C. and 140 ° C. Detector temperature 200 ° C. Carrier gas Ultra-high purity nitrogen (0.8 kg / cm ² ) Commercial standard solution (Wako Pure Chemical Industries) under these conditions Manufactured organic halide standard solution B: chloroform, bromodichloromethane, dibromochloromethane, bromoform, trichloroethylene,
Typical gas chromatograms when tetrachloroethylene, including 1,1,1-trichloroethane are measured) are shown in FIGS. 3 (a) and 3 (b) and their retention times are shown in Table 1.

[0051]

[Table 1]

At the same time, a calibration curve (THM (ng) / (peak area)) was prepared using the standard solution (organic halide standard solution B manufactured by Wako Pure Chemical Industries), and the value (an obtained from the calibration curve was obtained.
From g), the THM amount was calculated using Formula 1.

[0053]

[Equation 1]

The results are shown in Tables 2 and 3 and FIG. 4, and it can be seen that the THM amount is reduced by using the method of the present invention. In the safety car No. 2 building, which was tested this time, no bromoform was found in THM.

[0055]

[Table 2]

[0056]

[Table 3]

(In the table, the% value indicates the degree of decrease with respect to raw water.)

<Embodiment 2> In Embodiment 1, the operating conditions of the water purifier operating device were such that no activated carbon filter was used, the deaerator operating time was 1 hour, the flow rate was 6 t / h, and the other operations were in accordance with Example 1. THM quantification was performed.

The results are shown in Tables 4 and 5 and FIG. 5, and the THM amount was reduced by using the method of the present invention.

[0060]

[Table 4]

[0061]

[Table 5]

(In the table, the% value indicates the degree of decrease with respect to raw water.)

<Embodiment 3> In Embodiment 1, the operating conditions of the water purifier were set to 5 t / h without using an activated carbon filter.
THM was quantified in the same manner as in Example 1 except that water after one pass and after continuous operation for 2 hours was set to a vacuum degree of 720 mmHg and the test water was used.

The results are shown in Tables 6 and 7 and FIG. 6, and the THM amount was reduced by using the method of the present invention.

[0065]

[Table 6]

[0066]

[Table 7]

(In the table, the% value represents the reduction rate with respect to the sample water sample B. However, * indicates the degree of reduction with respect to the sample water sample D _0. )

Example 4 Residual chlorine content in tap water and T
The relationship with the amount of HM was investigated. The results are shown in the graph of FIG.

As can be seen from this graph, as chlorine in tap water decreases, the amount of THM also decreases accordingly.
In particular, when the residual chlorine amount in tap water decreases to 0.4 ppm or less, the THM amount also begins to decrease remarkably.

Therefore, if the residual chlorine is previously reduced to 0.4 ppm or less before the THM is removed by the method of the present invention, not only delicious water with no chlorine smell can be provided, but also The THM removing effect can be further enhanced.

[0071]

According to the present invention, the following effects can be expected. That is, the hydrophobic gaseous substance can be permeated and removed from water by a simple method in which a negative pressure is applied to the secondary side through the gaseous substance-permeable polymer membrane. Therefore,
Oxygen is removed by the method of the present invention, generation of red water in water can be prevented, THM which is a carcinogen can be removed, and safe water can be secured.

In the method of the present invention, a large amount of water can be treated by using a hollow fiber polymer membrane. Further, among the polymer membranes, the silicone rubber resin is excellent in gas permeability, particularly THM selective permeability. Therefore, by adopting this, it is possible to provide treated water at low cost.

The present invention is an epoch-making method capable of selectively permeating and removing THM, which is a carcinogen, to provide safe water. That is, conventionally, when tap water is used at a location away from the water purification plant, THM is generated by the reaction of chlorine and humin before the tap water reaches the faucet, and the human body continues to drink such tap water. Accumulation of trihalomethanes in the area could cause harm to the human body.

On the other hand, the present invention can remove trihalomethane itself. Therefore, drinking tap water purified by the method of the present invention does not cause any harm to the human body such as cancer.

If chlorine is removed in advance before the method of the present invention, the THM removing effect is enhanced, and safer water can be provided, and moreover, delicious water with no odor of chlorine can be provided. . By providing the circulation means, the hydrophobic gaseous substance contained in water is removed to the minimum extent by repeatedly applying the method of the present invention.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a hydrophobic gaseous substance removing apparatus according to an embodiment of the present invention.

FIG. 2 is a flow chart explanatory view of a water purifier used in Examples 1 to 3, which is a water purifier incorporating the above embodiment of the present invention.

FIG. 3 is a gas chromatogram when a commercially available standard solution (organic halide standard solution B manufactured by Wako Pure Chemical Industries, Ltd.) is measured in Example 1. (A) is a chromatogram when measured at a column temperature of 120 ° C, and (b) is a chromatogram when the column temperature is 140 ° C.

[Fig. 4] Fig. 4 shows T according to the operating time of the water purifier in Example 1.
It is a line graph which shows HM amount.

[Fig. 5] Fig. 5 is a graph showing T accompanying the operation time of the water purification device in the second embodiment.
It is a line graph which shows HM amount.

[Fig. 6] Fig. 6 is a graph showing T with the operating time of the water purifier in Example 3.
It is a line graph which shows HM amount.

FIG. 7 is a graph showing the relationship between residual chlorine in water and trihalomethane.

[Explanation of symbols]

 1 ... Hydrophobic Gaseous Substance Removal Device 2 ... Water Transfer Pipe 3 ... Foreign Material Filter (Activated Carbon) 4 ... Circulation Pipe 5 ... Water Supply Pipe 6 ... Water Purification Plant 7 ... Water Receiving Tank 8 ... Inflow pipe 12 Outflow pipe 13 Intake pipe 14 Vacuum pump 15 Water transfer pump 16 Faucet

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location // B01D 61/36 8014-4D

Claims (6)

[Claims] 1. A method for purifying water, characterized in that a hydrophobic gaseous substance is permeated and removed from water on the primary side through a gaseous substance-permeable polymer membrane having a negative pressure on the secondary side. 2. The method for purifying water according to claim 1, wherein the polymer film has a hollow fiber shape. 3. The method for purifying water according to claim 1, wherein the film of the polymer substance is made of a silicone rubber resin. 4. The method for purifying water according to claim 1, wherein the hydrophobic gaseous substance is trihalomethane. 5. A method for purifying water, comprising removing trihalomethane by the method according to claim 4 after removing residual chlorine of water. 6. A water purification method comprising water circulation means, wherein the water purification method according to claim 1 is repeatedly performed.