JPH03207490A - Method and device for cleaning acidic river - Google Patents

Abstract

PURPOSE:To efficiently and economically clean acidic river water by passing the acidic river water through a reverse osmosis membrane unit to separate the water to desalted water and concd. water, bringing the desalted water into contact with an alkali material to neutralize the water and discharging this water to the rivers. CONSTITUTION:The raw water taken from the acidic rivers is pressurized and is filtered by a pressure filter 4 and thereafter, the water is pressurized to a high pressure by a high-pressure pump 6 and is passed through the reverse osmosis membrane unit 7, by which the water is separated to the desalted water having the pH higher than the pH of the raw water and the concd. water. The desalted water is introduced into a neutralizing column 10 packed with the alkali material essentially consisting of calcium carbonate or lime by which the desalted water is neutralized. The neutralized and cleaned water is discharged to the rivers. On the other hand, the concd. water is introduced into an iron oxidizing column 11 where an oxidizing agent, such as ozone, is supplied to the water to oxidize the iron to tervalent iron ions. The water is thereafter treated in a neutralizing tank 13 and finally the supernatant liquid of a ferric hydroxide thickener 15 is discharged to the rivers.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention combines the reverse immersion i3 membrane method and an improved iron oxidation/neutralization treatment method to efficiently and economically
This article relates to a method and device for purifying acidic rivers. [Conventional technology] Conventionally, methods for purifying acidic rivers include (1) underground injection method;
(2) Water separation method and (3) Neutralization treatment method are used.
These conventional methods will be explained below.

(1) Underground injection method This is a method in which acidic river water is injected underground and left to the natural purification action underground. The disadvantages of this method are that there is a risk of secondary destruction of nature, and that the effects cannot be clearly predicted. In addition, there are cases where underground injection has destroyed the water retaining layer containing aluminum in the soil, making the land unusable for agriculture.

(2) Separate water conveyance method This method is a method of collecting spring water, which is the cause of acidic rivers, separating it from the river and conveying it to another large river or the main stream downstream. In the case of this method, it leads to contamination of rivers on the confluence side, and there are also many problems such as the cost and land associated with construction of the water channel.

(3) Neutralization method ■ Normal neutralization method A method of neutralization using quicklime and calcium carbonate. In this method, a large amount of by-products including gypsum are precipitated, and since the dewatering properties of this precipitate are poor, large-scale auxiliary equipment such as a mud storage dam for by-products is required. Furthermore, since purified water is neutralized with quicklime and calcium carbonate, it becomes hard water with high calcium hardness, and is often unsuitable not only for drinking water but also for agricultural and industrial purposes.

■ Iron oxidation/neutralization treatment method This method is characterized in that divalent iron ions dissolved in acidic water are oxidized by blowing air with nitrogen oxide in advance to form trivalent iron ions, which are then neutralized. The trivalent iron ions are neutralized by adding calcium carbonate to neutralize them.
Ferric hydroxide [Fe(O
}I)+) precipitates alone. When calcium carbonate is further added after the precipitation of ferric hydroxide has finished, the pH reaches 5.
Aluminum hydroxide (Al(OH)3) precipitates nearby. In this way, this method can separate and recover valuable metals such as iron and aluminum without precipitating by-products such as gypsum (if the 804 ions in the treated raw water are very large, gypsum may precipitate). can do.

The disadvantages of this method are that nitrogen oxides, which cause pollution, are generated during iron oxidation, and if calcium carbonate is added to further raise the pH after aluminum has been precipitated, gypsum may precipitate. , and the purified water has high calcium hardness, making it unsuitable for drinking water or water for agricultural or industrial use.

On the other hand, JP-A No. 63-39696 discloses that seawater is supplied to a reverse immersion i3 membrane device to obtain fresh water as permeated water, and the fresh water is passed through an alkaline material-packed column mainly composed of limestone while introducing air. A permeated water hydration method for desalination of seawater using reverse osmosis is disclosed.

Furthermore, Japanese Patent Application Laid-open No. 63-252588 discloses a wastewater treatment device that is provided with a system for directly flowing brine wastewater from a reverse osmosis membrane device I into a neutralization tank of a comprehensive wastewater treatment device. [Problems to be solved by the invention] As mentioned above, in the conventional method, (1) there is a possibility of secondary natural destruction (in the case of underground water injection method); (2) The cost of countermeasures is enormous, and there is a risk of secondary pollution of the river to which the separated water is directed (in the case of the separated water channel method).

(3) The calcium hardness of the treated water is high, making it insufficient for drinking water, agricultural and industrial water, and unsuitable for the habitat of aquatic organisms (usually in the case of neutralization treatment).

(4) Nitrogen oxides are generated and cause secondary pollution (in the case of iron oxidation/neutralization treatment method).

There were problems such as.

In addition, it is possible to remove dissolved ions in acidic rivers using the reverse permeable membrane method, which is widely applied to seawater desalination.
Although this is an easy concept to achieve, in this case, the treatment of concentrated wastewater becomes a major problem.

The present invention was invented to solve the above problems by combining the reverse osmosis membrane method and an improved iron oxidation/neutralization treatment method. In addition, the above-mentioned Japanese Patent Application Publication No. 6
As shown in Publication No. 3-39696, there is a conventional example of using a reverse osmosis membrane method in seawater desalination and neutralizing the permeate water. While feeding air into the packed tower, it is passed through and neutralized, p
This is a method of conducting Htl control, and the concentrated water is discharged directly into the sea.

The present invention causes environmental pollution. #1 Reverse osmosis membrane concentrated water from river water is also being purified by applying an improved iron oxidation/neutralization treatment method, which is fundamentally different from existing methods.

In addition, the above-mentioned Japanese Patent Application Laid-Open No. 63-252588 describes a reverse osmosis membrane method for acidic river water. There is nothing disclosed or suggested about the technical idea of subjecting l'lM water to iron oxidation and neutralization treatment.

The present invention was made in view of the above points, and it purifies acidic rivers efficiently and economically by effectively combining the reverse osmosis membrane method and an improved iron oxidation/neutralization treatment method. The purpose is to provide methods and revisions. [Means for Solving the Problem] In order to achieve the above object, the method for purifying an acidic river according to claim 1 comprises the steps of ta+~(di, i.e., +8) # raw water taken from an acidic river. After pressurizing and filtering, the process of increasing the pressure to high pressure and passing it through a reverse osmosis membrane unit to separate it into demineralized water having a pH higher than that of the raw water and concentrated water, A process of neutralizing the water by contacting it with an alkaline substance whose main component is calcium carbonate or lime, and discharging this neutralized purified water into rivers, fc) (a+
A step in which the concentrated water of the process is brought into contact with an oxidizing agent such as ozone or hypochlorous acid to oxidize divalent iron ions in the concentrated water to trivalent iron ions. Alternatively, add an alkaline substance mainly composed of lime to precipitate ferric hydroxide, sediment and concentrate the slurry containing this ferric hydroxide, and then separate the dehydrated cake of ferric hydroxide from the concentrated slurry. The method is characterized in that it includes a step of discharging the supernatant liquid from the sedimentation concentration step into a river.

The method of claim 2 is the method of claim 1, in which aluminum hydroxide is precipitated by adding an alkaline substance containing calcium carbonate or lime as a main component to the supernatant liquid of the sedimentation ms step in the dl step, and The method according to claim 3 is characterized in that after the slurry containing aluminum oxide is sedimented and concentrated, a dehydrated cake of aluminum hydroxide is separated from the concentrated slurry, and the supernatant liquid from the sedimentation and illumination condensation step is discharged into a river. In the method of claim 2, air is blown into the supernatant in the step of sedimentation and concentration of the slurry containing aluminum hydroxide, and the supernatant and air are brought into contact with each other to perform decarboxylation treatment, thereby increasing the pH of the slurry. It is characterized by discharging decarbonated purified water into rivers.

The method according to claim 4 is characterized in that in the method according to claim 3, the decarbonated purified water is brought into contact with the desalinated water of step fa) and an alkaline substance containing calcium carbonate or lime as a main component to neutralize the water. The acidic river purification device according to claim 5, as shown in FIG. 1, includes a pressure filter 4 that filters raw water taken from an acidic river, a high-pressure pump 6 that increases the pressure of the filtered raw water to high pressure, A reverse osmosis membrane unit 7 that separates high-pressure raw water into desalinated water and concentrated water, a neutralization tower 10 filled with a lumpy alkaline material mainly composed of calcium carbonate or lime to neutralize the desalted water, and a concentrated water An iron oxidation tower 11 that oxidizes divalent iron ions in concentrated water to trivalent iron ions by bringing water into contact with an oxidizing agent such as ozone or hypochlorous acid, and carbonate the treated water from this iron oxidation tower. A first neutralization tank 13 that adds an alkaline substance mainly composed of calcium or lime to precipitate ferric hydroxide, and a ferric hydroxide thickener 15 that sediments and concentrates the slurry containing this ferric hydroxide. ,
The method is characterized in that it includes a ferric hydroxide component #s17 that separates a dehydrated cake of ferric hydroxide from a concentrated slurry. The apparatus of Claim B is the apparatus of Claim 5, in which the supernatant liquid of ferric hydroxide Schifukuna-15 is introduced, and an alkali containing calcium carbonate or lime as a main component is added to precipitate aluminum hydroxide. An aluminum hydroxide thickener 18 that sediments and concentrates this slurry containing aluminum hydroxide, and an aluminum hydroxide separator 22 that separates a dehydrated cake of aluminum hydroxide from the concentrated slurry are connected to a ferric hydroxide thickener. It is characterized by being installed on the downstream side of the 15. The apparatus according to claim 7 is the apparatus according to claim 6, which further includes a decarboxylation tower 25 which decarbonates by introducing the supernatant liquid of the aluminum hydroxide thickener 18 and bringing the supernatant liquid into contact with air by blowing air into the apparatus. , aluminum hydroxide Schiffner 1
It is characterized by being provided on the downstream side of the 8.

Alkaline substances include CaC such as limestone and dolomite.
A wide range of alkaline substances such as O3-based substances, lime, and others can be applied.

Further, as the reverse osmosis membrane method unit, a circular tube type reverse osmosis membrane device, a spiral type reverse osmosis membrane device, a hollow fiber type reverse osmosis membrane device, a flat membrane type reverse osmosis membrane device, etc. are used. [Operation] After pressurizing raw water taken from an acidic river and filtering it with a pressure filter 4, the pressure is raised to high pressure with a high-pressure pump 6, and passed through a reverse osmosis membrane unit 7, which has a pH higher than that of the raw water. Separate into permeate water (desalinated water) and concentrated water. In addition,
Depending on the quality of the raw water, a flocculant may be injected into the pressure filter.

Desalinated water is introduced into a neutralization tower 10 filled with an alkaline substance containing calcium carbonate or lime as a main component to be neutralized, and this neutralized purified water is discharged into a river. Meanwhile, the concentrated water is transferred to the iron oxidation tower 1.
1 and supply an oxidizing agent such as ozone or hypochlorous acid to oxidize the divalent iron ions in the concentrated water to trivalent iron ions. The treated water from the iron oxidation tower 11 is introduced into the first neutralization tank 13, and an alkaline substance containing calcium carbonate or lime as a main component is added to precipitate ferric hydroxide, which contains the ferric hydroxide. The slurry is introduced into a ferric hydroxide thickener 15 for sedimentation and concentration. The concentrated slurry is then introduced into a ferric hydroxide separator 17 to separate a dehydrated cake of ferric hydroxide. The supernatant liquid of the ferric hydroxide thickener 15 is then discharged into a river or sent to the subsequent aluminum hydroxide thickener 18. In the aluminum hydroxide Schifukuner 18, an alkaline substance containing calcium carbonate or lime as a main component is added to precipitate aluminum hydroxide, and the slurry containing this aluminum hydroxide is precipitated. The concentrated slurry is then introduced into an aluminum hydroxide separator 22 to separate a dehydrated cake of aluminum hydroxide. The supernatant liquid of the aluminum hydroxide solution 18 is then discharged into a river or sent to the subsequent decarboxylation tower 25. In the decarboxylation tower 25, the pH is increased by blowing air to bring the supernatant liquid into contact with the air for decarboxylation treatment. This decarboxylated purified water is either discharged into the river, or sent to one port of the neutralization tower downstream of the reverse osmosis membrane Unisoto 7, where it is neutralized and then discharged into the river. [Embodiments] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. However, unless there is a specific description, the shapes of the structural equipment described in this example, their relative distribution, etc. are not intended to limit the scope of the present invention to these, but are merely illustrative. Just an example. Figure 1 shows an embodiment of the present invention for purifying acidic rivers. In this example, we will explain the case where calcium carbonate is used as the alkaline substance. Moreover, although the present invention is intended to be applied to strongly acidic river water, the present invention will be described with reference to the case of an acidic river with a pH of 2 to 3 as an example.

The apparatus of the present invention consists of a reverse osmosis membrane treatment section 1 and an iron oxidation/neutralization treatment section 2. The reverse osmosis membrane processing section 1 will be explained below. pH2-3
The raw water taken from the acidic river is pumped through the raw water pump 3.
It is pressurized to ~4 kg/cdG, suspended solids are removed by a pressure filter 4, passed through a safety filter 5, and the pressure is increased to 7 to 10 kg/cdG (depending on the salt concentration of the raw water) by a high-pressure pump B, and reverse osmosis is carried out. It is sent to the membrane unit 7. In the permeated water (desalinated water) that has passed through the reverse osmosis membrane unit 7, most of the dissolved ions have been removed, and the pi value has increased to about 4 to 5. By passing it through the column 10, p} can be easily set to about 16 to 7. The purified water leaving the neutralization tower 10 is discharged back into the river. Next, the iron oxidation/neutralization processing section 2 will be explained. The concentrated water from the reverse osmosis membrane unit 7 is sent to the iron oxidation tower 11,
Divalent iron ions are oxidized to trivalent iron ions by oxidizing agents such as ozone and hypochlorous acid (Fe"-=Fe""
). Next, this liquid is transferred to the first neutralization tank 13 using the bomb 12.
By adding calcium carbonate to raise the pH, ferric hydroxide (Fe(OH)3) precipitates. The slurry containing ferric hydroxide is transferred to the ferric hydroxide by bomb 14.
The concentrated slurry is sent to the iron hydroxide separator 15 for sedimentation and concentration, and the concentrated slurry is sent to the ferric hydroxide separator 17 by the bomb 16 for separation and dehydration, and a dehydrated cake of Fe(OR)i is separated and recovered. The separated ice is returned to the ferric hydroxide sinker 15. If the overflow supernatant of ferric hydroxide sinker 15 does not contain aluminum compounds, it can be discharged directly into rivers, but since it usually contains aluminum compounds, the following The aluminum hydroxide thickener 18 is sent to the pump 20, where calcium carbonate is further added to raise the pH.
Precipitate aluminum hydroxide/L/mini'yme (Al(OH)3). This slurry is sent to an aluminum hydroxide separator 22 by a bomb 21, where it is separated and dehydrated, and a dehydrated cake of aluminum hydroxide is separated and recovered. The separated water is returned to the aluminum hydroxide thickener 18. The overflow supernatant liquid from the aluminum hydroxide thickener 18 can be discharged directly into a river, but it is usually sent to the next decarboxylation tower. That is, the overflow supernatant liquid passes through the neutralized liquid tank 23, is sent to the decarboxylation tower 25 by the bomb 24, is brought into contact with air from the air blower 26, is decarboxylated, and the pH is increased. In this case, decarboxylation increases the pH without adding any chemicals. Purified water from the decarboxylation tower 25 is discharged to the outside of the thread by a bomb 27.

In this case, regarding the discharge and treatment of purified water from the decarboxylation tower 25, +11 It is combined with the permeated water (desalinated water) from the reverse osmosis membrane treatment section 1 and sent to the neutralization tower 10 for neutralization treatment, and then returned to the original river. Method of discharging water into (2) A method in which the permeated water (desalinated water) of the reverse osmosis membrane processing unit 1 is not combined with the water and is discharged into another river. However, method (2) is more advantageous in order to effectively utilize permeated water (desalinated water) for agricultural and industrial purposes.

In addition, when the reverse osmosis membrane processing section 1 and the iron oxidation/neutralization processing section 2 are installed in the same place, and when these processing sections 1,
2 may be installed separately in a different location. Figure 2 shows pH 3.0, total dissolved salt concentration 440 ppIl,
The material balance and balance of the reverse osmosis membrane treatment section and the iron oxidation/neutralization treatment section when acidic river water with a calcium hardness of 25 ppm (as CaCOs) is treated according to the flow shown in Figure 1, and the results are scaled up to an actual flow rate. It shows the measured values of each part. From Figure 2, by treating raw water with a pH of 3.0 with a reverse osmosis membrane, desalinated water can be reduced to a pH of 5.0 without the use of chemicals.
It can be seen that the value has increased to 0. In addition, by contacting permeated water (desalinated water) with calcium carbonate, pH 7.
．． Purified water with a total dissolved salt concentration of 23 ppm and a calcium hardness of 15 ppm (as CaCOs) was obtained,
It can be seen that the water can be fully used for drinking and agricultural and industrial purposes. Furthermore, it can be seen that ferric hydroxide and aluminum hydroxide can be efficiently separated by oxidizing and then neutralizing the t-concentrated water from reverse osmosis membrane treatment. [Effects of the Invention] Since the present invention is structured as described above, it has the following effects.

fil Low p}I, for example, by passing acidic water with a pH of 2 to 3 through a reverse osmosis membrane, it is possible to raise the pH to <4 to 5 without using neutralizing chemicals. Also,
Permeated water (desalinated water) produced by the reverse osmosis membrane method has a low concentration of dissolved salts and low hardness, so it can be used not only for agricultural and industrial purposes but also for drinking water with just a simple pH adjustment. ．． (2) Since iron oxidation and neutralization treatment is performed only on concentrated water using the reverse osmosis membrane method, the amount of water handled by the neutralization treatment facility is small and the scale of the facility is small (for example, if the concentration rate is 5 times, the handling The amount of water will be 1/5). (3) Concentrated water obtained by the reverse immersion i3# method is processed in stages by using an iron oxidation/neutralization treatment method (iron oxidation using ozone or a strong oxidizing agent such as hypochlorous acid, or iron oxidation + decarboxylation method). pH
By performing till JB, valuable metals such as iron and aluminum can be separated and recovered without precipitating gypsum. Therefore, large auxiliary facilities such as mud storage dams for by-products such as gypsum are not required.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing an embodiment of the acidic river purification device of the present invention, and FIG. 2 is an explanatory diagram in which experimental data obtained by the method of the present invention is scaled up to an actual scale. 1... Reverse osmosis membrane processing section, 2... Iron oxidation/neutralization processing section, 3... Raw water pump, 4... Pressure filter, 5...
Safety filter, 6... High pressure bomb, 7... Reverse osmosis membrane unit, 8... Block calcium carbonate, 10...
Neutralization tower, 11... Iron oxidation tower, 12... Pump, 13
... 1st neutralization tank, 14 ... Bomb, 15 ... Ferric hydroxide thickener, 16 ... Pump, 17 ... Ferric hydroxide separator, 18 ... Hydroxylation Aluminum thickener, 2ro...pump, 21...pump, 22.
... Aluminum hydroxide separator, 23 ... Neutralized liquid tank, 24 ... Pump, 25 ... Decarbonation tower, 26 ...
Air blower, 27...Pump application person Kawasaki Heavy Industries, Ltd.

Claims (1)

[Claims] 1. The following steps (a) to (d): (a) Raw water taken from an acidic river is pressurized and filtered, then raised to high pressure and passed through a reverse osmosis membrane unit. , a step of separating demineralized water having a pH higher than the pH of the raw water and concentrated water; (b) neutralizing the demineralized water of step (a) by contacting it with an alkaline substance containing calcium carbonate or lime as a main component; (c) The concentrated water from step (a) is brought into contact with an oxidizing agent such as ozone or hypochlorous acid to remove divalent iron ions in the concentrated water. (d) Adding an alkaline substance containing calcium carbonate or lime as a main component to the treated water in step (c) to precipitate ferric hydroxide; A method for purifying an acidic river, comprising the steps of sedimentation and concentration of the slurry, separating a dehydrated cake of ferric hydroxide from the concentrated slurry, and discharging the supernatant of the sedimentation and concentration process into a river. . 2. Add an alkaline substance containing calcium carbonate or lime as a main component to the supernatant liquid of the precipitation and concentration step in step 2 (d) to precipitate aluminum hydroxide, and after settling and concentrating the slurry containing this aluminum hydroxide, concentrate. 2. The method for purifying an acidic river according to claim 1, further comprising separating a dehydrated cake of aluminum hydroxide from the slurry and discharging the supernatant liquid of the sedimentation and concentration process into the river. 3 Air is blown into the supernatant liquid in the sedimentation concentration process of the slurry containing aluminum hydroxide, and the supernatant liquid and air are brought into contact to perform decarboxylation treatment to increase the pH, and this decarboxylated purified water is sent to rivers. 3. The method for purifying an acidic river according to claim 2, wherein the acidic river is discharged into a river. 4. The method for purifying an acidic river according to claim 3, characterized in that the decarboxylated purified water is neutralized by contacting the demineralized water in step (a) with an alkaline substance containing calcium carbonate or lime as a main component. 5 Pressure filter that filters raw water taken from acidic rivers (
4) and a high-pressure pump that boosts the filtered raw water to high pressure (
6), a reverse osmosis membrane unit (7) that separates high-pressure raw water into desalinated water and concentrated water, and a medium filled with bulk alkaline material mainly composed of calcium carbonate or lime to neutralize the desalted water. an iron oxidation tower (11) that oxidizes divalent iron ions in the concentrated water to trivalent iron ions by bringing the concentrated water into contact with an oxidizing agent such as ozone or hypochlorous acid; A first neutralization tank (13) that adds an alkaline substance mainly composed of calcium carbonate or lime to the treated water from the iron oxidation tower to precipitate ferric hydroxide, and a slurry containing the ferric hydroxide. and a ferric hydroxide separator (17) that separates a dehydrated cake of ferric hydroxide from the concentrated slurry. purification equipment. 6. Introduce the supernatant liquid of the ferric hydroxide thickener (15), add an alkaline substance containing calcium carbonate or lime as a main component to precipitate aluminum hydroxide, and precipitate and concentrate the slurry containing this aluminum hydroxide. The aluminum hydroxide thickener (18) and the aluminum hydroxide separator (22) that separates the dehydrated cake of aluminum hydroxide from the concentrated slurry are connected to the ferric hydroxide thickener (15).
6. The acidic river purification device according to claim 5, wherein the device is provided on the downstream side of the acid river purification device. 7. A decarboxylation tower (25) is introduced into which the supernatant liquid of the aluminum hydroxide thickener (18) is decarboxylated by blowing air into it to bring the supernatant liquid into contact with air. 7. The acidic river purification device according to claim 6, wherein the device is provided on the downstream side.