JPH10272495A - Treatment of organic waste water containing salts of high concentration - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently purifying waste water contg. salts, etc., to the extent of allowing the direct discharge of the water to rivers, etc., i.e., an efficient treatment method for the org. waste water contg. the salts. SOLUTION: This treatment method treats the org. waste water contg. the salts at a high concn. in the following manner: The waste water described above is subjected to any of a biological treatment, coagulating sedimentation treatment, sand filter treatment or precision filter membrane treatment or the treatment consisting of a combination of >=2 thereof and is then subjected to a desalting treatment by a reverse osmosis membrane, by which the waste water is separated to the reverse osmosis concd. water and the reverse osmosis treated water. The reverse osmosis treated water is recovered and the reverse osmosis concd. water is subjected to a softening treatment for removing calcium and is then subjected to an electrodialysis treatment, by which the water is separated to the electrodialysis concd. water and the electrodialysis desalted water. The electrodialysis desalted water is returned again to the supply side of the reverse osmosis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a treatment method for desalinating organic wastewater containing high concentration of salts and removing organic substances, and more particularly, to a method for removing salts such as night soil and leachate leachate. It can be used for advanced treatment of organic wastewater with a high concentration, desalination treatment, concentration and recovery of salt substances, and recovery and reuse of treated water.

[0002]

2. Description of the Related Art Generally, organic wastewater having a high salt concentration such as human waste and leachate contains a high concentration of pollutants such as salts such as calcium ions and organic substances. Often, biochemical oxygen demand (BOD) or chemical oxygen demand (CO
D) is high, contains many suspended solids (SS), and has a chromaticity attributed to colloidal substances and the like. For this reason, they cannot usually be directly reused for some purpose or directly discharged to rivers. As a method for treating such organic wastewater, a treatment method mainly for removing organic pollutants has been conventionally used. The main treatment methods are, for example, biological treatment for removing BOD, coagulation sedimentation treatment for removing chromaticity, COD and SS, sand filtration and microfiltration for removing turbidity such as SS. There is a film (MF film) treatment. Further, as an advanced treatment method, there is generally a method using ozone or activated carbon.

[0003]

In the above-mentioned method for treating organic wastewater, a combination of these treatments has reached a state of the art in which organic components such as BOD and COD can be sufficiently removed. ing. However, organic wastewater generally contains a variety of salts in addition to organic matter, and in some cases can contain significantly higher concentrations of salts. When treating such wastewater and discharging it to rivers, etc., it is necessary to consider the impact on the water quality protection of the discharge water area and agricultural water, and recently, not only organic pollutants but also such salts There is an increasing need to remove them together from wastewater. Since the conventional methods of purifying organic wastewater are mainly intended to remove organic pollutants therein, there is no effect of removing salts, and the salt concentration of the treated water is almost the same as that of the influent raw water. It has become about.

[0004] A treatment method for removing salts from an aqueous phase containing salts is a well-known technique per se, and examples thereof include a reverse osmosis method, an electrodialysis method, and an evaporation method. In the reverse osmosis method, a salt water in a room partitioned by a semi-permeable membrane (RO membrane) is applied with a mechanical pressure equal to or higher than an osmotic pressure, and water is discharged outside the room through the semi-permeable membrane to obtain desalted water. That is the method. This method has the disadvantage that the efficiency depends on the salt concentration of the saline water. When the concentration of saline water is high, the recovery rate of demineralized water is low. For example, 3.5wt
When desalinating an aqueous solution of NaCl at a rate of 60%
Even if the water recovery rate is as high as 35 to 4 kgf / cm ² ,
0%. To achieve a water recovery of 50% or more, the operating pressure must be 70 kgf / cm ² or more. However, such a high pressure not only increases the processing cost, but also has a limit in consideration of the life of the reverse osmosis treatment apparatus and the like. Further, when the salt water contains calcium ions at a high concentration, there is a risk that calcium scale is deposited on the surface of the semipermeable membrane. Even when the salt concentration is relatively low, the amount of permeated water decreases due to the precipitation of calcium scale on the surface of the semipermeable membrane, and it becomes difficult to treat the treated water at a high recovery rate.

[0005] In the electrodialysis method, basically, a high water recovery rate can be obtained. However, if the water to be electrodialyzed contains calcium ions at a high concentration, calcium scale precipitates in the apparatus. In particular, in the electrodialysis method, calcium scale is easily generated due to a change in pH caused by the movement of hydrogen ions from the anode and hydroxyl ions from the cathode. As with the case of the reverse osmosis method, it is impossible to obtain a high water recovery rate if calcium scale is precipitated. In addition, since organic matter such as COD cannot be removed by this method, it is necessary to remove organic matter by another treatment method such as an activated carbon treatment method in order to obtain high quality treated water. Further, since the evaporation method involves a phase change of the system, there is a problem that the required energy is large and the processing cost is greatly increased. Further, the wastewater is a volatile organic substance or a nitrogen-ammonium salt compound (NH
_{If 4-} N) or the like is contained, they may be mixed into the treated water, and there is a problem that it is difficult to obtain high-quality treated water.

[0006] The present invention sufficiently removes organic components when treating and efficiently purifying organic wastewater containing a high concentration of salts so that it can be reused or discharged directly to rivers and the like. In addition, it is possible to sufficiently remove salts, and to purify the treated water with low salt concentration with high efficiency without causing the problem of reducing the treatment effect such as precipitation of calcium scale during the treatment. It is an object to provide a processing method that can be obtained.

[0007]

That is, the object of the present invention is achieved by the following constitutions. (1) A method for treating organic wastewater containing a high concentration of salts, wherein any one of biological treatment, coagulation sedimentation treatment, sand filtration treatment, and microfiltration membrane treatment is used as a pretreatment for the organic wastewater.
Or a treatment comprising a combination of two or more, followed by a desalination treatment with a reverse osmosis membrane, separating into a reverse osmosis concentrated water and a reverse osmosis treated water, collecting the reverse osmosis treated water, and After performing a softening treatment to remove calcium,
An organic wastewater containing a high concentration of salts, wherein the organic wastewater is subjected to electrodialysis treatment to separate the electrodialysis concentrated water and the electrodialysis demineralized water, and the electrodialysis demineralized water is returned to the reverse osmosis treatment supply side. Processing method. (2) In the softening treatment, the calcium concentration in the treated water is reduced to 1
The method for treating an organic wastewater containing high concentration of salts according to the above (1), wherein the concentration is not more than 00 mg / liter.

(3) The electrodialysis treatment has a desalination rate of 98%.
Thus, the evaporation residue of the electrodialysis demineralized water is 1000 mg /
The method for treating an organic wastewater containing a high concentration of salts according to the above (1) or (2), wherein the treatment is carried out so as to be less than 1 liter. (4) The electrodialysis concentrated water after the electrodialysis treatment has an evaporation residue of 13% by weight or more.
The method for treating an organic wastewater containing a high concentration of salts according to any one of claims 1 to 3.

[0009]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing one embodiment of a treatment apparatus for performing the wastewater treatment method according to the present invention. In the apparatus for treating organic wastewater shown in FIG. 1, the outlet of a treated water inflow pipe 1 extending from an organic matter removal treatment apparatus (not shown) is opened in a reverse osmosis treatment supply tank 2. Reverse osmosis treatment supply tank 2
The reverse osmosis treatment supply pipe 3 is connected to the reverse osmosis treatment device 4. A reverse osmosis treatment water pipe 5 and a reverse osmosis concentrate water pipe 6 extend separately from the reverse osmosis treatment apparatus 4, and the reverse osmosis concentrate water pipe 6 leads the reverse osmosis concentrate to a softening treatment apparatus 7. The reverse osmosis treatment water is recovered from the reverse osmosis treatment water pipe 5 outside the system. The softening device 7 has a softening treatment water pipe 9 for leading the softened treated water to an electrodialysis treatment supply tank 10 and has a sludge discharge pipe 8 for discharging generated mud. An electrodialysis processing supply pipe 11 is connected to the electrodialysis processing apparatus 12 from the electrodialysis processing supply tank 10.
An electrodialysis concentrated water pipe 14 for sending the electrodialysis concentrated water from the electrodialysis processing apparatus 12 is connected to the evaporating and drying processing apparatus 15, and an electrodialysis demineralized water pipe 13 for sending the electrodialysis demineralized water.
Are connected to the reverse osmosis treatment supply tank 2.

In the present invention, the organic wastewater to be treated can be treated even if it is not so high as an organic component. If the organic component enters the electrodialysis treatment, it has an adverse effect. So it can be removed in the reverse osmosis treatment. In addition, the salt concentration in the organic wastewater is not always intended to be a remarkably high concentration, but as described above, a concentration high enough to hinder the discharge, or a higher concentration. It is suitable for high concentration objects. The method for treating organic wastewater of the present invention may be implemented using such an apparatus, for example, as follows.
Organic wastewater is firstly treated as biological treatment, coagulation sedimentation treatment, sand filtration treatment or microfiltration membrane (MF membrane) treatment, or a combination of two or more treatments.
In order to reduce the concentration of the organic substance, it is preferable to perform a treatment in combination with a biological treatment. The pretreated wastewater is temporarily stored in the reverse osmosis treatment supply tank 2 through the treated water inflow pipe 1. Examples of the biological treatment method include a biological activated nitrification denitrification method in addition to the standard activated sludge method. The use of these methods also reduces BOD. Coagulation microfiltration (coagulation MF membrane filtration)
Specific examples of the method include a method of adding an aggregating agent, for example, an inorganic aggregating agent, and aggregating the resultant, followed by filtration with a microfiltration membrane. Using such a method, especially turbid substances such as SS can be removed from wastewater. The coagulation-sedimentation treatment method is a method of adding coagulants and then precipitating aggregates in a sedimentation tank. COD can be reduced by removing chromaticity and SS. The sand filtration method can remove suspended matter such as SS.

The wastewater which has been subjected to the pretreatment for mainly removing organic substances in this way is introduced into the reverse osmosis treatment apparatus 4 from the reverse osmosis treatment supply tank 2 through the reverse osmosis treatment supply pipe 3, where the reverse osmosis treatment ( "RO processing"). In the reverse osmosis treatment, a mechanical pressure of 5 Mpa or more is applied to the wastewater partitioned by a semipermeable membrane (also referred to as an “RO membrane”) to pass water in the wastewater through the RO membrane, thereby obtaining reverse osmosis concentrated water (“ RO concentrated water) and reverse osmosis treatment water, and the reverse osmosis treatment water is recovered through the reverse osmosis treatment water pipe 5. In addition, organic substances that could not be sufficiently removed during the organic substance removal treatment operation will be further filtered through this semipermeable membrane,
Contaminated organic components hardly flow into the recovered desalted water.

The reverse osmosis concentrated water is supplied to a reverse osmosis concentrated water pipe 6.
And introduced into the softening device 7. The softening treatment is, for example, such as replacing a hard water component (poorly soluble salt forming component) of calcium or magnesium in water with a readily soluble salt forming component such as sodium by a lime soda softening method or an ion-exchange hard water softening method. Can be done in a way. In such a softening treatment, the calcium concentration in the reverse osmosis concentrated water is preferably set to 100 mg / liter or less. When the calcium concentration is 100 mg / liter or less, it is possible to effectively prevent the generation of calcium scale in the electrodialysis treatment device 12, so that it is preferable. Sludge generated by the softening treatment is discharged out of the system through a sludge pipe 8.

The softened water containing high-concentration salts from which calcium ions have been removed is temporarily stored in an electrodialysis treatment supply tank 10 through a softened water pipe 9, and further introduced into an electrodialysis treatment apparatus 12 through an electrodialysis treatment supply pipe 11. I do. The introduction and the electrodialysis treatment are preferably performed in a batch system. In the electrodialysis treatment (also referred to as “ED treatment”), a large number of electrodialysis membranes are arranged, and the above-mentioned softened water is supplied to a concentration chamber and a dilution chamber which are alternately formed, or to only a dilution chamber among them. To obtain high concentration electrodialysis concentrated water in the concentration chamber and electrodialysis demineralized water in the dilution chamber.

The electrodialysis demineralized water is supplied to the electrodialysis demineralized water pipe 13.
To the reverse osmosis treatment supply tank 2. Even if organic matter remains in the reflux water, it is filtered by the reverse osmosis treatment device 4,
This is prevented from leaking into the reverse osmosis treatment water. The electrodialysis concentrated water is guided to the evaporating and drying treatment device 15 to be evaporated and dried, and separated into water and salts, and the salts are isolated. In this method, the water to be treated containing calcium is desalted using a reverse osmosis membrane, and the salinity of the water to be treated and organic substances are simultaneously removed at a water recovery rate within a range in which calcium scale does not precipitate. By doing so, high quality treated water (reverse osmosis treated water) is obtained. Further, the reverse osmosis concentrated water having a high calcium concentration is subjected to a softening treatment for the purpose of removing calcium, and the softened water having a sufficiently reduced calcium concentration is subjected to an electrodialysis treatment, preferably in a batchwise manner. By the dialysis treatment, even if the treatment is performed at a high desalting rate and a high water recovery rate, calcium scale is not precipitated, and electrodialysis demineralized water having a low salt concentration and electrodialysis concentrated water having a high salt concentration can be obtained.

Normally, in the electrodialysis treatment, when the batch treatment is carried out, the desalting rate and the treatment efficiency are higher and the salt concentration is higher than in the continuous treatment (13% by weight or more (13% by
000 mg / liter or more))
In addition, the salt concentration ratio between the desalted water and the concentrated water can be 150 or more. The evaporation residue refers to a component remaining in the evaporator as a solid component when water is evaporated. Expressing the change in this concentration in an easily understandable manner, in the demineralized water separated from the concentrated water, salts of 98 wt% or more are reduced, and the salt concentration is reduced to 1000 mg / liter or less.

In the above embodiment, the electrodialysis demineralized water having a low concentration generated in the electrodialysis treatment is returned to the reverse osmosis treatment supply tank 2. By returning in this manner, organic substances such as COD that could not be removed by the electrodialysis treatment can be removed by the reverse osmosis treatment. The salt concentration of the electrodialysis demineralized water, particularly the calcium ion concentration, is lower than that of the water to be treated from the reverse osmosis treatment supply tank 2. Therefore,
The reverse osmosis treatment can be performed in a state where the salt concentration is lower than that of ordinary wastewater. In the reverse osmosis treatment, the permeation flux (permeate amount) basically decreases when the osmotic pressure increases with an increase in the salt concentration of the water to be treated. , The permeation flux of the reverse osmosis treatment does not decrease, and therefore the cost of the reverse osmosis treatment does not increase much, and high-quality reverse osmosis demineralized water can be obtained with a high water recovery rate. Furthermore, even if calcium ions are mixed in the water to be treated, the concentration thereof is low, and there is almost no trouble that the calcium ions are deposited as scale on the surface of the reverse osmosis membrane.

Since the electrodialysis treatment is carried out after removing a large amount of the reverse osmosis demineralized water by the reverse osmosis treatment, the whole volume subjected to the electrodialysis treatment is reduced. It can be obtained efficiently. In addition, prior to the electrodialysis treatment, a softening treatment is performed in advance to reduce the concentration of dissolved calcium. Therefore, the electrodialysis treatment device 12
It is unlikely that calcium ions will precipitate as scales inside and this will cause trouble. Subsequent to the electrodialysis treatment, the salt-concentrated water is subjected to an evaporative drying treatment, where the salts are isolated. The evaporative drying process is intended for high-concentration salt-concentrated water whose volume has been further reduced by electrodialysis.
Therefore, even a treatment that requires a large amount of energy with a phase change can be performed efficiently, and the salt component can be easily isolated as a solid component.

[0018]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples. (Example) Water to be treated, which was obtained by subjecting human waste to biological treatment, coagulation sedimentation treatment and microfiltration membrane treatment, was treated using the treatment apparatus shown in FIG. The operating pressure in the reverse osmosis treatment is a high pressure condition of 5 to 6 MPa, and the sludge after the softening treatment is discharged from the softening treatment device 7 from the drainage pipe 8. Water to be treated after removal of organic substances, treated water obtained by reverse osmosis treatment (referred to as “RO treated water”), treated water obtained by softening treatment (“softened treated water”), electrodialysis treatment The water quality of each of the concentrated waters ("ED concentrated waters") obtained was measured. The measurement results are shown in Table 1.

[0019]

[Table 1]

The presence or absence of calcium scale was determined based on the chemical analysis and the processing performance of each device. The following was found from the above results. Although the chromaticity of the water to be treated, that is, the wastewater subjected to the pretreatment is 150 degrees, the COD is 50 mg / l, the calcium concentration is 60 mg / l, and the concentration of the evaporation residue component is 5600 mg / l, the reverse osmosis treatment is performed. The treated water obtained by the treatment, ie, the RO treated water,
As a result, the COD was 5.0 mg / L, and the concentration of the evaporation residue component was 380 mg / L. Thus, treated water having good water quality was obtained.

Further, by subjecting the RO concentrated water obtained by the reverse osmosis treatment to a softening treatment, the calcium concentration was reduced from 600 mg / L before the treatment to about 65 mg / L, and as a result, the electric power was reduced with respect to the softened water. Even when the salt concentration by dialysis treatment is performed, the calcium concentration of the ED concentrated water is 1
80 mg / liter, and no formation of calcium scale was observed. The ED concentrate has an electrical conductivity of about 130,000 μS / cm and an evaporation residue of 16500
0 mg / liter could be achieved. Since the electrodialysis demineralized water is returned to the reverse osmosis treatment, the water recovery rate indicating the ratio of the treated water amount to the treated water amount is 96.8%, and the concentrated water amount is about 30 minutes relative to the treated water amount. Of 1 or less.

(Comparative Example 1) Only the reverse osmosis treatment was performed on the same water to be treated as in the example. That is, the procedure was the same as that of the example except that the pretreatment was performed and the softening treatment and the electrodialysis treatment were omitted. The water quality was measured for each of the pretreated wastewater (water to be treated), RO treated water obtained by reverse osmosis treatment, and RO concentrated water. Table 2 shows the measurement results.

[0023]

[Table 2]

From the results in Table 2, the following was found. When the reverse osmosis treatment is performed solely on the pre-treated water to be treated, the water recovery rate indicating the ratio of the RO treated water amount (the treated water amount) to the treated water amount is limited to 90.9%, and 96.8% 5.9% less than the example shown. Furthermore, the concentration of the evaporation residue component of the RO concentrated water obtained by the reverse osmosis treatment was only 58,000 mg / liter, which was only about one-third as compared with the electrodialyzed concentrated water (ED concentrated water) of the example. . That is, the amount of the concentrated water is increased about three times as described above, and when this is used for the evaporative drying treatment, the treatment cost is increased as compared with the above. Further, the calcium concentration in the RO concentrated water is 610 mg / liter, and if the concentration is further increased, there is a risk that calcium scale is deposited.

(Comparative Example 2) Only the electrodialysis treatment was performed on the water to be treated which had been subjected to the same pretreatment for removing organic substances as in the example, and the reverse osmosis treatment and the softening treatment were omitted. The water quality was measured for the water to be treated, the ED demineralized water obtained by the electrodialysis treatment, and the ED concentrated water obtained by the electrodialysis treatment.
Table 3 shows the measurement results.

[0026]

[Table 3]

As shown in Table 3, if the water to be treated is subjected to a single treatment of electrodialysis and not subjected to reverse osmosis treatment or softening treatment, the calcium concentration of the electrodialysis concentrated water obtained by the electrodialysis treatment is reduced. It increased to 1800 mg / liter, and the occurrence of calcium scale was recognized to be remarkable. Third
Although not shown in the table, the treatment efficiency was significantly reduced as the number of batch treatments of the electrodialysis treatment was increased as compared with the examples. This is due to the formation of calcium scale. Regarding the quality of the treated water, there was no change in chromaticity and COD before and after the electrodialysis treatment. Also, the water to be treated,
Both electrodialysis demineralized water (ED demineralized water) and ED concentrated water had a chromaticity of 150 degrees and a COD of 50 mg / liter, and there was no removal of organic matter at all. For this reason, it is necessary to remove organic substances by another treatment method in order to obtain treated water of the same level as in the examples.For example, when activated carbon adsorption treatment is used, an increase in equipment or exchange of activated carbon is necessary. This causes an increase in processing cost.

[0028]

According to the present invention, high quality demineralized water (treated water) can be obtained by subjecting treated water, which is an organic wastewater containing a high concentration of salts, to reverse osmosis. After reducing the calcium concentration to 100 mg / liter or less by performing a softening treatment for removing calcium from the concentrated water, even if the softened water is further subjected to electrodialysis treatment, no calcium scale is generated in the treatment. The electrodialysis treatment can be performed at an extremely high concentration and desalination rate. In particular, when the electrodialysis treatment is carried out batchwise, the electrodialysis demineralized water having a high desalting rate and a low salt concentration (evaporation residue 1000 mg / liter or less)
And electrodialysis concentrated water having a high salt concentration (evaporation residue 130
000 mg / liter or more). Further, the electrodialysis demineralized water containing organic substances such as COD and chromaticity is returned to the reverse osmosis treatment and the reverse osmosis treatment is performed again, whereby the organic substances such as COD and chromaticity are removed. As a result, the amount of the electrodialysis concentrated water can be reduced to about 1/30 or less of the amount of the water to be treated, and the energy required in the evaporative drying treatment is smaller than in the case where the reverse osmosis concentrated water is subjected to the evaporative drying treatment. is there.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a wastewater treatment apparatus that performs one embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 Inflow pipe for treated water 2 Reverse osmosis treatment supply tank 3 Reverse osmosis treatment supply pipe 4 Reverse osmosis treatment apparatus 5 Reverse osmosis treatment water pipe 6 Reverse osmosis concentrated water pipe 7 Softening treatment apparatus 8 Drainage pipe 9 Softening treatment water pipe 10 Electrodialysis Processing supply tank 11 Electrodialysis processing supply pipe 12 Electrodialysis processing apparatus 13 Electrodialysis desalinated water pipe 14 Electrodialysis concentrated water pipe 15 Evaporation drying processing apparatus

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C02F 9/00 502 C02F 9/00 502L 502P 504 504A 504E

Claims (4)

[Claims] 1. A method for treating organic wastewater containing a high concentration of salts, wherein the organic wastewater is pretreated as one of biological treatment, coagulation sedimentation treatment, sand filtration treatment, and microfiltration membrane treatment. Or a treatment comprising a combination of two or more, followed by a desalination treatment with a reverse osmosis membrane, separating into a reverse osmosis concentrated water and a reverse osmosis treated water, collecting the reverse osmosis treated water, and After performing a softening treatment for removing calcium, electrodialysis treatment is performed to separate electrodialysis concentrated water and electrodialysis demineralized water, and the electrodialysis demineralized water is returned to the supply side of the reverse osmosis treatment again. A method for treating an organic wastewater containing a high concentration of salts, characterized by comprising: 2. The method for treating organic wastewater containing high concentrations of salts according to claim 1, wherein the softening treatment reduces the calcium concentration in the treated water to 100 mg / liter or less. 3. The electrodialysis treatment according to claim 1, wherein the desalting rate is 98% or more, and the evaporation residue of the electrodialyzed demineralized water is 1000 mg / L or less. A method for treating organic wastewater containing a high concentration of salts. 4. The organic solution containing a high concentration of salts according to claim 1, wherein the concentrated electrodialysis water after the electrodialysis treatment has an evaporation residue of 13% by weight or more. Wastewater treatment method.