JPH11253940A - Purified water treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To treat raw water containing iron, manganese, and organic substances stably and efficiently by a method in which the raw water, after being oxidized with air, is oxidized with ozone and subjected to membrane separation. SOLUTION: In the purification of water, raw water containing iron, manganese, and organic substances is exposed to air from an air diffusing pipe 2 in a raw water tank 1 to be oxidized with air. The most part of oxidation- vulnerable iron is oxidized by the aeration to be deposited. The air oxidized raw water is oxidized with ozone in an ozone column 3. The organic substances is oxidation-decomposed into low molecular weight compounds by the ozone oxidation, and the manganese is oxidized to be deposited as insoluble manganese dioxide. After that, water treated by ozone oxidation is passed through an active carbon column 4 for active carbon treatment, and the low molecular weight compounds are adsorbed/removed. The treated water of the active carbon column 4 is subjected to membrane separation by an UF membrane separator for the solid-liquid separation of the insoluble substances of iron and manganese and other suspended substances.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a water purification method for stably and efficiently treating raw water containing iron, manganese and organic substances.

[0002]

2. Description of the Related Art In recent years, it has been pointed out that odorous substances and harmful substances such as agricultural chemicals and disinfection by-products are mixed in with deterioration of water quality of tap water. Conventionally, in order to cope with these, a water purification treatment method using both ozone treatment and activated carbon treatment has been adopted. Also, as a measure against pathogenic organisms such as cryptosporidium and Giardia, membrane filtration treatments such as ultrafiltration (UF) membranes and microfiltration (MF) membranes have attracted attention. Its introduction is progressing.

[0003] When iron or manganese is mixed in a pipe, it is oxidized and accumulated in the pipe to cause coloring trouble. Conventionally, as a method of treating iron and manganese, a method of oxidizing and insolubilizing and depositing ionic iron and manganese in raw water in an environment in a reduced state such as underground water and performing solid-liquid separation is common. In this case, iron is easily oxidized by air or the like, but manganese is not easily oxidized. Therefore, a catalytic oxidation method (commonly called manganese sand method) using chlorine as an oxidizing agent and hydrated manganese dioxide as an autocatalyst is often used. Has been

However, when the above-mentioned manganese sand method is applied to raw water in which iron, manganese and organic substances coexist to oxidize iron and manganese, the injected chlorine reacts with the organic substances and causes harmful disinfection by-products. There is a problem of producing things.

As a solution to this problem, a treatment method combining an ozone and activated carbon treatment with a membrane filtration treatment has been proposed. In this method, iron and manganese are oxidized and precipitated with ozone, and organic substances are oxidized and decomposed and adsorbed with activated carbon, and then solid-liquid separated by membrane filtration. According to this method, the precursors of disinfection by-products such as trihalomethane are reduced, and iron and manganese are oxidized by ozone and chlorine is not used. Therefore, it is possible to suppress the generation of disinfection by-products due to chlorine. it can. By employing membrane filtration as the solid-liquid separation means, iron and manganese precipitated by oxidation, other suspended substances, microorganisms, and the like can be completely separated.

[0006]

However, the method combining the ozone and activated carbon treatment with the membrane filtration treatment has the above advantages, but has the following disadvantages.

That is, in this method, it is necessary to control the ozone injection rate to an optimum value in response to temporary water quality fluctuations due to seasonal fluctuations, rainfall, etc., but the raw water in which iron, manganese and organic substances coexist is treated with ozone. In this case, there are three control factors. For this reason, selection of the optimal injection rate becomes complicated, and it is difficult to perform stable and efficient processing in response to water quality fluctuation.

[0008] The present invention solves the above conventional problems, and
An object of the present invention is to provide a water purification treatment method capable of stably and efficiently treating raw water containing manganese and organic substances.

[0009]

The water purification method according to the present invention is characterized in that raw water containing iron, manganese and organic matter is oxidized by air, oxidized with ozone, and then subjected to membrane separation.

In the present invention, first, raw water is air-oxidized to oxidize and precipitate most of the relatively oxidizable iron. Thereafter, by oxidizing with ozone, organic substances are oxidized and decomposed to reduce the molecular weight, and manganese is oxidized and precipitated as insoluble manganese dioxide.

These precipitates can be easily removed by subjecting the air-oxidized and ozone-oxidized water to membrane separation.

In the present invention, iron is oxidized in advance by air utilizing the property of iron, which is relatively easy to oxidize, so that the subsequent ozone treatment is mainly intended to oxidize organic substances and manganese. And the amount of ozone used can be reduced.

Further, for the following reasons, the injection of ozone can be easily controlled, and a stable and efficient treatment can be performed.

That is, since iron is relatively easily oxidized, its concentration greatly varies depending on the conditions and conditions of water intake. For example, when the water source is a spring and the residence time underground is short, it is susceptible to rainfall on the ground surface. Therefore, by performing the air oxidation of iron having a large concentration variation in advance in this way, the injection control of ozone in the ozone oxidation is controlled based on the concentration variation of the organic matter and manganese, that is, two types of control factors. The control becomes easy, the control effect is enhanced, and the selection of the optimum injection rate can be easily performed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the water purification treatment method of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of the water purification treatment method of the present invention.

In this method, first, raw water containing iron, manganese and organic matter is aerated in a raw water tank 1 through a diffuser 2 to oxidize the air. Due to this air oxidation, most of the relatively oxidizable iron is oxidized and deposited.

The air oxidizing means may be any means capable of oxidizing most of the iron in the raw water, and its form is not particularly limited.

The residence time of the raw water tank 1 for performing air oxidation is 15
It is preferably set to about 20 minutes.

The raw water that has been oxidized with air is then oxidized with ozone in an ozone tower 3. Due to this ozone oxidation, organic substances are oxidized and decomposed to lower molecular weight, and manganese is oxidized and precipitated as insoluble manganese dioxide.

In this ozone oxidation, if the amount of ozone is small, the oxidation of manganese and organic substances becomes insufficient, and part of the manganese remains ionic and passes through a membrane in a subsequent membrane separation device to lower the quality of treated water. In addition, organic substances also remain in the treated water and deteriorate the treated water quality. Furthermore, insufficient oxidation of organic substances causes a reduction in membrane flux, and also causes the generation of trihalomethane when treated water is sterilized with chlorine. Conversely, if the amount of ozone is too large, the cost is increased, and permanganate ions are generated due to the excessive oxidation of manganese, which increases the load of activated carbon in the subsequent step.

Accordingly, the ozone injection rate is appropriately determined according to the amounts of manganese and organic substances in the raw water, but generally, about 0.5 to 2 mg / L is sufficient. That is, in the normal iron, manganese and organic substance-containing water ozone oxidation and membrane filtration treatment, since ozone is also used for iron oxidation,
Although about 0.5 to 3 mg / L of ozone is required, in the present invention, air oxidation is performed prior to ozone oxidation, so that the amount of ozone required for ozone oxidation can be significantly reduced.

The residence time of the ozone tower 4 is preferably about 10 to 20 minutes.

In the present embodiment, the ozone-oxidized water is passed through the activated carbon tower 4 to remove the organic substances degraded by ozone oxidation by the activated carbon treatment. It is presumed that some of the organic matter adsorbed on the activated carbon is biodegraded by microorganisms attached to the inside of the activated carbon, and the activated carbon can be used continuously for a long period of time. In addition, the activated carbon tower 4 decomposes and removes surplus residual ozone in ozone oxidation and decomposes and removes permanganate generated by peroxidation due to ozone oxidation.

As shown in FIG. 1, the UF membrane separation device 5
When the activated carbon tower 4 is provided at the previous stage, the activated carbon tower 4 is not clogged with the suspended substance in the water, and the suspended substance in the water is trapped as in the case of an upward flow fluidized bed type of granular activated carbon. It is preferable to adopt a type that does not.

The treated water in the activated carbon tower 4 is then subjected to membrane separation in a UF membrane separator 5 to separate solids and liquids of insolubles of iron and manganese and other suspended substances.

Although the UF membrane separator 5 is used in FIG. 1, an MF membrane separator can also be used.

In the method shown in FIG. 1, the activated carbon tower 4 is provided in front of the UF membrane separation apparatus 5, and residual ozone due to ozone oxidation is decomposed and removed in the activated carbon tower 4.
As the membrane of the F membrane separation device 5, a membrane having no ozone oxidation resistance such as polysulfone, polyacrylonitrile, polyethylene, polypropylene, and cellulose acetate can be used. If activated carbon treatment is not performed before membrane separation, UF
Examples of the membrane of the membrane separation device 5 include a metal-inorganic membrane made of stainless steel, copper, aluminum, or the like, an alumina-based ceramic membrane, and other PEEK (polyetheretherketone).
It is necessary to use a film having high ozone oxidation resistance, such as PVDF (polyvinylidene fluoride) or PVDF.

The permeated water of the UF membrane separation device 5 is high-clarity water in which manganese dioxide and other turbid substances are separated into solid and liquid, and is discharged as treated water and sent to the treated water tank 6. On the other hand, the concentrated water is circulated.

FIG. 1 shows an example of an embodiment of the present invention, and the present invention does not depart from the gist thereof.
The method is not limited to the method shown in FIG.

For example, the activated carbon tower may be provided at the subsequent stage of the membrane separation device. In this case, since there is no possibility that the activated carbon tower is clogged by suspended substances, a fixed bed activated carbon tower can be used. is there. However, as described above, when the activated carbon tower is provided at the subsequent stage of the membrane separation device, it is necessary to adopt an ozone oxidation resistant material as the membrane material of the membrane separation device. It is placed before the equipment. In addition, activated carbon treatment, in addition to providing an activated carbon tower,
A method in which powdered activated carbon is directly added to the water supply line may be used.

In FIG. 1, the raw water oxidized with air is directly introduced into the ozone tower 3, but prior to or simultaneously with the ozone oxidation, PAC (polyaluminum chloride), a sulfuric acid band, iron chloride, etc. Alternatively, after performing a flocculation treatment using an inorganic flocculant such as the above to flocculate the colloid particles, solid-liquid separation may be performed.

[0033]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1 Raw water having the quality shown in Table 1 was treated by the method shown in FIG. 1, and the quality of each treated water was examined. The results are shown in Table 1. The processing conditions of each part were as follows.

<Raw water tank> Raw water inflow: 1.2 m ³ / hr Air aeration: 50 Nm ³ / hr Residence time: 50 minutes <Ozone tower> Ozone injection amount: 1.8 mg / L Residence time: 20 minutes <Activated carbon Tower (upflow fluidized bed packed with granular activated carbon)
> SV: 10 hr ^-1 <UF membrane separation device> Effective operating pressure: 0.3 kg / cm ² Comparative Example 1 In order to obtain the same treated water quality as in Example 1 without performing air aeration in the raw water tank, The treatment was carried out in the same manner except that the ozone injection rate in the ozone tower was changed to 2.6 mg / L. The quality of each treated water was examined, and the results are shown in Table 1.

[0036]

[Table 1]

From Table 1, it can be seen that by performing air oxidation prior to ozone oxidation according to the present invention, it is possible to obtain clear and good treated water with a low ozone injection rate.

[0038]

As described in detail above, according to the water purification treatment method of the present invention, raw water containing iron, manganese and organic substances can be treated stably and efficiently to obtain high quality treated water. .

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of a water purification treatment method of the present invention.

[Explanation of symbols]

 Reference Signs List 1 raw water tank 2 diffuser 3 ozone tower 4 activated carbon tower 5 UF membrane separation device 6 treated water tank

Claims (1)

[Claims] 1. A water purification method comprising the steps of: oxidizing raw water containing iron, manganese and organic matter by air, oxidizing with ozone, and then performing membrane separation.