JPH06304558A - Trihalomethane formation restraining method by low pressure reverse osmosis membrane - Google Patents

Abstract

PURPOSE:To effectively remove a trihalomethane precursor and to easily secure safe potable water in a simple water supply, etc., by adding copper ions to a raw water contg. the trihalomethane precursor before passing the raw water through a low pressure reverse osmosis membrane. CONSTITUTION:In a simple water supply using a shallow well as a water source, raw water contg. a lot of a precursor before the formation of trihalonmethane is drawn by a raw water pump 10. First, the raw water is fed into a filter 12, such as a media filter and turbid matter is removed. Next, after copper sulfate is added (added quantity: 0.1-0.5ppm) to the raw water that has been filtered to decompose bacteria without decomposing the trihalomethane precursor, then the raw water is introduced into a low pressure reverse osmosis membrane 16 through a booster pump 14, and the low pressure reverse osmosis membrane 16, the raw water is separated into a permeated water (potable water) and a concentrate (waste water) and the permeated water is fed to places where it is consumed after a final treatment of adding a post-chlorine agent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention, in a drinking water production plant using river water, lake water, well water, etc. containing a trihalomethane precursor as a water source, keeps bacteria in a sterilized state without decomposing the trihalomethane precursor, By removing the trihalomethane precursor using a low pressure reverse osmosis membrane,
The present invention relates to a method for suppressing the production of trihalomethane.

[0002]

2. Description of the Related Art Trihalomethane is a substance added to the water quality standards of the Ministry of Health and Welfare at the end of 1993, and various treatment methods have been studied. Trihalomethane is a substance produced by decomposing its precursor (humic acid, fulvic acid, hematomelamic acid, etc.) with chlorine, has a small molecular weight, and was very difficult to separate (October 3, 1983).
"Water supply and trihalomethane" issued by Gihodo on 0th
reference).

Conventionally, as a measure for removing trihalomethane, ozone was used instead of chlorine as a bactericide to decompose a trihalomethane precursor into a low molecular weight hydrocarbon compound, and this low molecular weight compound was adsorbed by activated carbon. There was a way to do it. The prior art was investigated for a method of suppressing and removing trihalomethane by a reverse osmosis membrane, but the corresponding publication could not be searched.

[0004]

However, in the conventional method of using ozone as a bactericide and adsorbing with activated carbon, since an ozone generator is used, the apparatus becomes complicated and waste ozone treatment is also required. In addition, it is necessary to regularly replace the activated carbon, resulting in a high maintenance cost.

Since trihalomethane has a small molecular weight as described above and has a low separation efficiency even when a low pressure reverse osmosis membrane is used,
If trihalomethane was produced from the trihalomethane precursor, separation was very difficult. On the other hand, the trihalomethane precursor has a large molecular weight, and if a low pressure reverse osmosis membrane is used, a separation efficiency of 95% or more can be obtained. Therefore, in order to remove trihalomethane, it is advisable to separate its precursor using a low pressure reverse osmosis membrane. The low-pressure reverse osmosis membrane is an intermediate membrane between a seawater desalination reverse osmosis membrane and a UF (ultrafiltration membrane), and is also called a loose reverse osmosis membrane or a nanomembrane.

[0006] Generally, however, a large amount of bacteria are present in rivers and lakes containing a large amount of trihalomethane precursors, and the bacteria are propagated on the membrane surface of the low-pressure reverse osmosis membrane. There was an occasion. On the other hand, in order to prevent bacteria from propagating on the membrane surface of the low-pressure reverse osmosis membrane, ozone may be used in place of chlorine for sterilization.However, the trihalomethane precursor is a hydrocarbon compound of low molecular weight due to ozone. If it is sterilized with chlorine after that, there is a possibility that trihalomethane will be generated.

The present invention has been made in view of the above points, and when producing drinking water from river water, lake water, well water, etc. containing a trihalomethane precursor, the trihalomethane precursor is removed using a low pressure reverse osmosis membrane. In order to prevent bacteria from growing on the membrane surface of the low-pressure reverse osmosis membrane, it is an object of the present invention to provide a method for suppressing trihalomethane production by a low-pressure reverse osmosis membrane to which copper ions are added.

[0008]

In order to achieve the above object, a method for suppressing trihalomethane production by a low pressure reverse osmosis membrane of the present invention is, as shown in FIG. 1, a method in which copper ions are added to raw water containing a trihalomethane precursor. After addition, the raw water is passed through a low pressure reverse osmosis membrane to remove the trihalomethane precursor.

In this case, the amount of copper ions added is 0.1 to 0.1%.
It is preferably 0.5 ppm. That is, when the added amount of copper ions is less than 0.1 ppm, there is a disadvantage that bacteria are easily proliferated on the membrane surface of the low pressure reverse osmosis membrane, while when the added amount of copper ions exceeds 0.5 ppm, There is an inconvenience that the copper ion concentration on the concentrated water side (drainage side) of the reverse osmosis membrane becomes high and the wastewater discharge standard of the Ministry of the Environment cannot be met.

[0010]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to the following examples, and various modifications may be made without departing from the scope of the invention. Is possible. Example 1 FIG. 1 shows an example of an apparatus for carrying out the method of the present invention. This facility is a simple water supply system that uses shallow wells as a water source, and the raw water contains a large amount of trihalomethane precursors.
In FIG. 1, raw water supplied by a raw water pump 10 is first subjected to removal of suspended solids by a filter 12 such as a media filter, and thereafter, in order to kill bacteria without decomposing a trihalomethane precursor, copper sulfate is added to the raw water. Is added. Incidentally, copper sulfate may be added before the suspension is removed, or before and after the suspension is removed. Raw water to which copper sulfate has been added is introduced into the low-pressure reverse osmosis membrane 16 via the booster pump 14. The operating pressure in this case is, for example, 15 to 20 kg / cm ² . The low-pressure reverse osmosis membrane 16 separates the raw water into permeated water (drinking water) and concentrated water (drainage), and to the permeated water (drinking water), a post-chlorine agent is added by about 0.5 mg / l of chlorine. , Final processing is done.

In the flow shown in FIG. 1, 0.2 ppm of copper sulfate, which has a bactericidal effect on bacteria, was added with copper ions without decomposing the trihalomethane precursor. After that, bacteria were formed on the surface of the low-pressure reverse osmosis membrane. It did not propagate and there was almost no deterioration of the membrane performance due to copper ions. Table 1 shows the processing results of the apparatus in Example 1. The trihalomethane production ability is shown by the total concentration of trihalomethane produced when 10 mg / l of sodium hypochlorite is injected into the raw water and the permeated water, respectively.

[0012]

[Table 1]

In the present embodiment, only a device for injecting copper ions and a low-pressure reverse osmosis device are required as special devices, so the equipment is compact, the operation is simple, and small and medium-sized It can be easily applied to simple water supply. Although copper ions are also subject to the water quality standards of the Ministry of Health, 90% or more of the injected copper ions can be separated and removed by the low pressure reverse osmosis membrane, so the water quality standards of the Ministry of Health must be sufficiently cleared. You can

Comparative Example 1 When the apparatus shown in FIG. 1 was operated without the addition of copper sulfate, slime was generated on the surface of the low pressure reverse osmosis membrane one week after the operation.
Since the operation was impossible, the chemical cleaning was performed using a neutral detergent to remove the slime and the operation was restarted, but the slime was generated again and the operation became impossible.

[0015]

Since the present invention is configured as described above, it has the following effects. (1) Since trihalomethane is removed in the form of the precursor before it is produced, the precursor removal rate is high, and since the proliferation of bacteria on the membrane surface can be prevented, so-called trihalomethane precursor is contained in a large amount. Even dirty water sources can be used as drinking water sources. (2) Since the device is simple, it can be applied to measures for removing trihalomethane in small drinking water plants such as simple tap water. (3) Since the low-pressure reverse osmosis membrane has a long life of about 3 years, running costs and maintenance costs are low. (4) Since the operation is simple, the device can be easily operated without requiring special skill.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of an apparatus for carrying out the method of the present invention.

[Explanation of symbols]

 10 Raw Water Pump 12 Filter 14 Booster Pump 16 Low Pressure Reverse Osmosis Membrane

Claims (2)

[Claims] 1. A method for suppressing trihalomethane production by a low pressure reverse osmosis membrane, which comprises adding copper ions to raw water containing a trihalomethane precursor and then passing the raw water through a low pressure reverse osmosis membrane to remove the trihalomethane precursor. . 2. The amount of copper ion added is 0.1 to 0.5 ppm.
The method for suppressing trihalomethane production by the low-pressure reverse osmosis membrane according to claim 1, wherein