JPH0919687A - Anti-wastewater treatment method - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To treat anti-wastewater with an RO membrane for effective use. SOLUTION: An alkaline agent other than Ca salt is added to the anti-waste water to adjust the pH to 2 to 3.6, and then the anti-waste water is passed through an RO device 5 utilizing the head pressure difference. [Effect] When the pH is 3.6 or less, there is no precipitation of Fe (OH) ₃ and the clogging of the RO film can be prevented. By using an alkaline agent other than Ca salt, it is possible to prevent clogging of the RO film due to CaSO ₄ precipitation. The required energy is reduced by utilizing the head pressure. It is possible to effectively use anti-wastewater and reduce the amount of wastewater treated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating anti-waste water, and more particularly to a method for effectively treating anti-waste water by efficiently treating the anti-waste water with a reverse osmosis membrane (RO membrane) separation device.

[0002]

2. Description of the Related Art Anti-waste water is a large amount of rainwater, spring water, etc. collected from a dormant or abandoned mine. Anti-waste water is acidic with a pH of 2 or less and generally contains heavy metals mainly composed of iron. Also, depending on the type of ore mined, Al, M
It contains n, Zn, Cu, As, Pb, Cd. Conventionally, this anti-waste water is discharged after neutralizing it by adding calcium carbonate or slaked lime to precipitate and separate heavy metals, and it has not been sufficiently utilized by recovering water from the anti-waste water. .

When the amount of anti-waste water is large and the concentration of heavy metals is relatively low, the conventional treatment in which neutralization and precipitation separation treatment are carried out and discharged is not only costly because of the large amount of water but also water resources. It is also disadvantageous in terms of effective use of.

By the way, the RO membrane is currently the mainstream of the desalination technology for canned water, and the RO membrane is used for the treatment of water containing salts and the recovery of water from seawater.

If such an RO membrane can be applied to the treatment of anti-wastewater, the permeated water of the RO membrane can be recovered and used effectively, and the amount of water to be treated for wastewater treatment can be reduced by concentration, which is extremely advantageous. is there.

[0006]

However, the anti-wastewater of Japan, which is rich in sulfide ore, is sulfuric acid-acidified and contains ferrous ions (Fe ²⁺ ).
It has been a factor that hinders the application of the O film.

That is, in general, it is desirable that the RO membrane is treated at pH 6 to 7 to protect the membrane.
Adjusting pH2 following anti wastewater pH 6-7, Fe ²⁺ contained is oxidized to Fe ^3+, further Fe ³⁺ is Fe (O
H) ₃ precipitates and causes the RO membrane to be clogged, so that water cannot pass.

In general, inexpensive slaked lime (Ca (OH) ₂ ) is used for adjusting the pH of anti-waste water.
It is also considered that the addition of (OH) ₂ causes precipitation of CaSO ₄ crystals due to the reaction with SO ₄ ²⁻ in the anti-waste water, which causes water flow inhibition.

It is an object of the present invention to solve the above-mentioned conventional problems and to provide a method for treating RO membranes of anti-waste water, preventing clogging of the membranes, and performing efficient treatment with low energy. .

[0010]

According to the method for treating anti-waste water of the present invention, an alkali agent other than calcium salt is added to the anti-waste water to adjust the pH to 2 to 3.6, and then the head pressure of the anti-waste water is set to the operating pressure. Water is passed through the reverse osmosis membrane separation device.

As shown in Experimental Example 1 below, Fe ²⁺ to F 2
As a result of examining the oxidation rate to e ³⁺ and the solubility of Fe ³⁺ ,
If the pH is 3.6 or less, there is almost no problem of clogging of the RO film due to precipitation of Fe (OH) ₃ . By subjecting the anti-wastewater to RO treatment in such a low pH range, it is possible to stably obtain high-quality permeated water that can also be used as drinking water or agricultural water.

Further, since the anti-waste water is generally discharged from a high place such as a hillside, the head pressure generated due to the difference in height between the anti-waste water discharge port and the installation position of the RO device is the main operating pressure or auxiliary pressure of the RO device. By using it as the operating pressure, the required energy can be reduced.

Of the substances contained in the anti-wastewater, R
Ca ²⁺ , SO ₄ ²⁻ , Fe are responsible for blocking the O film.
²⁺ (or Fe ³⁺ ), which are CaSO ₄ , Fe
It precipitates as (OH) ₃ and causes clogging of the RO film.

As for Fe ²⁺ (Fe ³⁺ ), as described above,
When the pH is 3.6 or less, the problem of clogging of the RO film due to precipitation of Fe (OH) ₃ can be avoided.

On the other hand, for Ca ²⁺ and SO ₄ ²⁻ , when a calcium salt such as Ca (OH) ₂ is used to adjust the pH of the anti-wastewater, precipitation of CaSO ₄ is promoted and the RO membrane is clogged. Therefore, in the present invention, sodium hydroxide (NaOH), magnesium hydroxide (Mg (OH))
₂ ) The pH is adjusted by using an alkaline agent other than calcium salt to prevent the RO film from being blocked due to CaSO ₄ precipitation.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram showing a method of an embodiment of the anti-wastewater treatment method of the present invention.

Reference numeral 1 denotes a neutralization tank in which the alkaline agent is added to the anti-wastewater introduced from the pipe 11 through the pipes 12 and 12a. This neutralization tank 1 is provided with a pH meter 1A,
The anti-waste water is adjusted to pH 2 to 3.6, preferably 2.5 to 3.5 by adjusting the addition amount of the alkaline agent by the valve V _{1 which} is interlocked with the pH meter 1A.

Alkali agents such as NaOH, Mg (O
H) ₂ or the like can be used, but Mg (OH) ₂ is preferable because it is inexpensive. Although Mg (OH) ₂ has a drawback that the reaction rate is slow in the use in the neutral to alkaline range, and is inexpensive, it is generally
Although few examples are used, in the pH adjustment in the range of pH 2 to 3.6, which is the applicable pH range of the present invention, the reaction is almost instantaneously completed, and it can be used without any trouble.

If the adjusted pH in the neutralization tank 1 is less than 2, there is a possibility of causing deterioration of the RO membrane in the latter stage. In addition, if the adjusted pH exceeds 3.6, the problem of clogging of the RO film due to precipitation of Fe (OH) ₃ occurs as shown in Experimental Example 1 below. Therefore, the adjusted pH is 2 to
It is set to 3.6, preferably 2.5 to 3.5.

The pH adjusting water in the neutralization tank 1 is then used in the sand basin 2
The SS content contained in is separated by sedimentation. The separated water in the sand basin 2 is treated by the cartridge filter 4 from the pipe 13, fine SS components that are difficult to separate are removed in the sand basin 2 and further clarified, and then the RO membrane separation device (RO
Water is passed through the device 5 for RO membrane treatment. The RO device 5 is
Any of a low pressure type, a medium pressure type and a high pressure type may be used. Low-pressure type or medium-pressure type requires less energy consumption.

The RO device 5 is installed in a lower area than the neutralization tank 1 and the sand basin 2, and the water head pressure is used as the operating pressure of the RO membrane.

When the operating pressure of the RO membrane cannot be secured only by the head pressure, the booster pump 3 is provided to boost the pressure as shown in the figure.

Generally, the operating pressure required to pass water through the RO membrane is 20 atm or less, 5 to 7 atm for the low pressure RO membrane, and 15 to 17 atm for the medium pressure RO membrane. If the height difference is 50 m, the head pressure difference of 5 atm and 10 atm can be obtained, so if the height difference between the neutralization tank 1 and the sand basin 2 and the RO membrane can be sufficiently secured. No boost pump is required. When the low-pressure RO membrane is used and the height difference is less than 50 m, and when the medium-low pressure RO membrane is used and the height difference is less than 100 m, the boost pump 3 is used together.

In this case, the performance of the booster pump 3 is efficiently exhibited by installing the booster pump 3 at a position where the height difference between the booster pump 3 and the neutralization tank 1 and the sand basin 2 is 20 m or more. Can be made.

As the RO film of the RO device, the adjusted pH is used.
Any RO membrane such as a flat membrane, a tubular membrane, or a hollow fiber membrane made of a synthetic polymer material having high acid resistance such as polyamide or polyvinyl can be used as long as it has sufficient acid resistance. The RO membrane made of polyamide or polyvinyl synthetic polymer exhibits its function sufficiently even at a strong acidity of pH 2 and does not deteriorate in strength, etc., and is stable for long-term use, for example, for 24 months or more. Can be used. Also, these RO membranes do not require a high operating pressure of 30 kg / cm ² or more like the cellulose acetate RO membrane, and can be operated at 5 to 15 kg / cm ² , so that only the head pressure of anti-waste water is sufficient. It is also possible to ensure operating pressure.

The RO device may be of any type such as spiral type or plate-frame type.

The RO device may be provided in a single stage or in multiple stages.

Since the RO membrane permeated water is weakly acidic with a pH of 4 to 5, this permeated water is introduced into the neutralization tank 6 through the pipe 15,
Neutralization is performed with an alkaline agent added from the pipes 12 and 12b. The amount of the alkaline agent added to the neutralization tank 6 is
It is adjusted by interlocking the pH meter 6A provided in the neutralization tank 6 and the valve V ₂ . As the alkaline agent for this neutralization treatment, C
It is possible to use a (OH) ₂ , Mg (OH) ₂ , NaOH or the like.

The neutralized water is discharged from the system through the pipe 16 and is effectively used as recovered water.

On the other hand, the concentrated water of the RO device 5 contains heavy metals in a concentrated form and cannot be discharged as it is. The heavy metals are insolubilized and separated by pH adjustment and aggregation. That is, after adding an alkali agent to concentrated water to generate a metal hydroxide, a flocculant is added to increase flocs, and a treatment such as separation in a precipitation tank is performed. A part of the sludge is returned to the sludge reaction tank, and an alkaline agent is added to and mixed with the sludge to modify the sludge, and then the sludge circulation system (HDS system) in which the alkali-modified sludge is added to the concentrated water is treated.

As shown in the figure, the concentrated water of the RO device 5 is introduced into the neutralization tank 7 through the pipe 17, and the alkaline reformed sludge described below is added through the pipe 18 to neutralize the pH to 7.5 to 8.5. It In addition, 19 is an aeration pipe for oxidizing Fe ²⁺ in concentrated water to Fe ³⁺ .

In the aggregating tank 8, a high-molecular coagulant (polymer) is added to the neutralizing treatment liquid through a pipe 20, and the liquid is introduced into a thickener 9 through a pipe 21 for solid-liquid separation. The supernatant water of the thickener 9 is discharged out of the system as treated water through the pipe 22 and discharged. On the other hand, the separated sludge of the thickener 9 is extracted from the pipe 23, and a part of the sludge is separated from the pipe 23.
It is discharged from the system a and dehydrated. The rest of the separated sludge is sent to the sludge reaction tank 10 through the pipe 23b.

In the sludge reaction tank 10, the sludge is reformed by the reaction between the sludge and the alkaline agent added and mixed through the pipe 24, and the alkali-modified sludge is added to the neutralization tank 7 through the pipe 18 and concentrated water is added. Used for neutralization. At that time, the pH of the neutralization tank 7 is adjusted by adjusting the addition amount of the alkaline agent with the valve V _{3 which} is interlocked with the pH meter 7A provided in the neutralization tank 7.

Here, as the alkaline agent, inexpensive Ca is used.
It is preferable to use (OH) ₂ or Mg (OH) ₂ .

In the treatment of the concentrated water in the RO apparatus, the HDS method, which is used for neutralization after once mixing with the sludge without directly adding the alkaline agent to the concentrated water, provides good dehydration property. Since the reaction product is generated and highly concentrated sludge is obtained, the volume of the generated sludge can be reduced and the sludge dewatering efficiency can be improved.

If the concentrated water of the RO apparatus contains heavy metals such as Cd, adsorption, ion exchange, etc. are performed as necessary.

In the present invention, the concentration ratio of the RO device is
If it is too high, Ca ²⁺ and SO ₄ contained in the anti-waste water
^Since there arises a problem of deposition of membrane-occluding substances such as CaSO ₄ due to the concentration of ^2- , it is usually desirable to set it to 7 times or less, especially 5 times or less.

In the present invention, when a medium-pressure RO membrane is used, high-quality permeated water can be obtained as shown in Table 4 of Example 2 below, and this permeated water may be, if necessary, Mg
It can be used as general purpose water by adding or diluting a small amount of alkali such as (OH) ₂ , Ca (OH) ₂ or NaOH.

When treated with a low-pressure RO membrane, as shown in Table 3 of Example 1 below, the permeated water obtained contains Fe ²⁺ and Cu ²⁺ although the salt concentration is reduced. Therefore, it cannot be used simply by performing neutralization, and after the neutralization, further precipitation treatment or filtration treatment is required.

When carrying out the filtration treatment, space saving can be achieved by applying a tubular type microfiltration (MF) membrane. In this case, the MF membrane separation treatment requires a filtration pressure of 2 to 4 atm, but by utilizing the back pressure on the concentrated water side in the RO membrane separation treatment of the previous stage, an energy source is particularly required. It can be processed without.

[0042]

EXAMPLES The present invention will be described more specifically with reference to experimental examples and examples.

Experimental Example 1 Although the dissolved iron contained in the anti-waste water exists in the form of Fe ²⁺ , the pH of the anti-waste water is weakly acidic to protect the RO membrane during the RO membrane separation treatment of the anti-waste water. ~ When neutralized, Fe ²⁺ reacts with dissolved oxygen and is oxidized to Fe ³⁺ , finally Fe
It becomes (OH) ₃ and closes the membrane. Therefore, Fe in the anti-waste water is dissolved as Fe ²⁺ and is oxidized to Fe ³⁺ ,
Furthermore, it is desired that the precipitation of Fe (OH) ₃ be suppressed.

Therefore, the precipitation characteristics of Fe ³⁺ and Fe ²⁺ to F
The pH dependence of the oxidation reaction to e ³⁺ was examined.

After adding 100 ppm of HCl to an aqueous Fe ₂ (SO ₄ ) ₃ solution (concentration of Fe: 1000 ppm), Mg (OH) ₂ was added to adjust the pH to each pH value.
The dissolved Fe ^{3+ in} the case of reacting overnight was analyzed, and the results are shown in Table 1.

[0046]

[Table 1]

It can be seen from Table 1 that precipitation of Fe (OH) ₃ begins to occur from pH ³ and Fe ³⁺ precipitates almost completely at pH 4 and above.

Next, the anti-wastewater of the A dormant mine with the following water quality is
After adjusting the pH to each pH value with g (OH) ₂ , aeration (2 liters-air / liter-sample solution / minute for 10 minutes with a diffuser) is performed, and the Fe ²⁺ concentration after aeration is measured. Thus, the pH dependence of the oxidation rate of Fe ²⁺ to Fe ³⁺ was investigated, and the results are shown in Table 2.

Water quality of anti-wastewater of A dormant mine pH: 1.6 Fe ²⁺ : 400 ppm Ca ²⁺ : 80 ppm Mg ²⁺ : 15 ppm SO ₄ ^2- : 1200 ppm Cl ⁻ : 20 ppm

[0050]

[Table 2]

From Table 2, it can be seen that the oxidation of Fe ²⁺ is less likely to occur at pH 3, but the oxidation of Fe ²⁺ is more likely to occur from around pH 3.6.

When the results of Table 2 and the results of Table 1 are examined together, even if Fe ²⁺ is oxidized to become Fe ³⁺ , the pH is 3.
If it is 6 or less, the solubility of Fe ³⁺ is high, and Fe (OH)
_It can be seen that there is no problem of RO membrane blockage due to ₃ .

That is, as shown in Table 2, if the pH is 3.6 or less, the oxidation rate of Fe ²⁺ can be suppressed to 50% or less. On the other hand, the solubility of Fe ³⁺ is, as shown in Table 1,
Then, only 4.7 mg / l was dissolved, and Fe ³⁺ was converted to Fe (O
H) ₃ precipitates and causes clogging of the film surface.
Since it is possible to also dissolve 3.6 in 323 mg / l, even Fe ²⁺ is oxidized to Fe ^3+, as long suppressed as Fe ³⁺ generated by oxidation is less than about 300 mg / l, Fe It is possible to prevent the precipitation of (OH) ₃ .

Therefore, the adjusted pH value in the present invention is 3.
It can be said that 6 or less is suitable.

Example 1 An artificial wastewater of the following water quality was prepared by adding salts to the anti-wastewater of the dormant mine B, and Mg (OH) ₂ of 400 p was added to the artificial wastewater.
After adding pm to adjust the pH to 3.0, water was collected by a low pressure RO membrane.

Water quality of artificial wastewater pH: 1.8 Ca ²⁺ : 54.6 mg / l Mg ²⁺ : 10.7 mg / l Fe ²⁺ : 91.0 mg / l Mn ²⁺ : 11.0 mg / l Cu ^{2+ : 30mg / l as 3+: 0.95mg} / l SO 4 2-: 800mg / l Cl -: 185mg / l other: a small amount of Na salt, a Ca salt target water quality and less As0.1mg / l, the concentration ratio is R
The safety was set to 5 times in view of the safety for preventing the precipitation of CaSO ₄ , which causes the scale failure of the O film. As the RO film, a polyvinyl alcohol RO film “NTR-7250” is used.
-S4 "(manufactured by Nitto Denko Corporation) was used, and the other processing conditions were as follows.

Treatment condition Recovery rate = 80% Feed water pressure = 7.0 kg / cm ² Brine pressure = 5.5 kg / cm ² Product water pressure = 0 kg / cm ² Water temperature = 23 ° C. Shows the water quality of RO membrane permeated water and concentrated water. 3 shows.

[0058]

[Table 3]

Example 2 In the same manner as in Example 1, the same treatment was performed by using a medium pressure RO membrane in order to improve the water quality of the RO membrane treated water.

That is, the artificial wastewater prepared in Example 1 was supplemented with Mg.
After adjusting the pH to 3.0 by adding (OH) ₂ 400 ppm, a polyamide RO film “NTR-75” is used as an RO film.
9-HR-S4 "(manufactured by Nitto Denko Corporation).

The concentration ratio is C as in the case of Example 1.
It was set to 5 times in order to prevent precipitation of aSO ₄ . Other processing conditions were as follows.

Treatment condition Recovery rate = 80% Feed water pressure = 17 kg / cm ² Brine pressure = 15.5 kg / cm ² Production water pressure = 0 kg / cm ² Water temperature = 23 ° C. Table 4 shows the water quality of RO membrane permeated water and concentrated water. Show.

As is clear from Table 4, in this example, RO membrane permeated water having a water concentration substantially low and a water quality substantially equal to that of pure water was obtained. This permeate is
After neutralization, it can be used as general purpose water.

Next, the concentrated water thus obtained was successively passed through the neutralization tank 7, the flocculation tank 8 and the thickener 9 shown in FIG. 1 to be processed by the HDS method. The capacity of the neutralization tank 7 and the coagulation tank 8 is 1000 m
1, thickener 9 has a diameter of 200 mm and a capacity of 4500 ml
The sludge reaction tank 10 has a capacity of 100 ml, and 10 g / l of Ca (O 2) is used as an alkaline agent for neutralization.
H) ₂ emulsion was used.

The amount of concentrated water treated was 3 liters / hr, and the pH control value of the neutralization tank 7 was 8.5. Further, 2 ppm of a polyacrylamide polymer (“Cliflock PA331” manufactured by Kurita Water Industries Ltd.) was added to the flocculation tank 8. The amount of separated sludge returned to the sludge reaction tank 10 is 300 ml /
It was set as hr.

As a result, from the thickener 9, the density of 15
A high-concentration sludge that could be concentrated to 220 g / l was obtained after 0 g / l and standing for 3 hours.

The water quality of the obtained treated water was as shown in Table 4, and the harmful metals were almost completely treated.

[0068]

[Table 4]

In the treatment of the concentrated water, when the sludge was not returned and Ca (OH) ₂ was directly injected into the neutralization tank 7, the sludge concentration was 25 g / l, and after standing for 3 hours, the sludge concentration was 35 g / l. Therefore, only sludge with low concentration was obtained.

[0070]

As described above in detail, according to the anti-wastewater treatment method of the present invention, the anti-wastewater is effectively treated by the RO membrane without causing problems such as membrane clogging. Can be used. Moreover, according to the present invention, since the RO membrane treatment is performed by adjusting the pH to 2.5 to 3.6, the amount of the alkaline agent used is small, and the salt concentration hardly increases due to the addition of the alkaline agent, which is advantageous for water recovery. Is. The head pressure of anti-wastewater discharged from high places such as hillsides is RO
Since it is used as the operating pressure for the membrane treatment, the energy required for the membrane separation treatment can be unnecessary or greatly reduced, and the treatment can be performed at low cost. Since the concentrated water that has been concentrated and reduced in volume by the RO membrane is treated as wastewater, the size of the wastewater treatment facility can be reduced. Such an effect is exhibited, which is extremely advantageous industrially.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a method of an embodiment of the anti-wastewater treatment method of the present invention.

[Explanation of symbols]

 1,6,7 Neutralization tank 2 Sand set basin 4 Cartridge filter 5 RO device 8 Coagulation tank 9 Thickener 10 Sludge reaction tank

Claims (1)

[Claims] 1. An anti-waste water, to which an alkaline agent other than calcium salt is added to adjust the pH to 2 to 3.6, and then the water is passed through a reverse osmosis membrane separation device whose operating pressure is the head pressure of the anti-waste water. Anti-wastewater treatment method.