JPH0527474B2 - - Google Patents

Description

[Detailed description of the invention]

As a method for treating wastewater containing ammonium ions, an electrodialysis device with an ion-exchange membrane as a diaphragm is used. Wastewater containing ammonium ions is passed through one side of the diaphragm, an acid aqueous solution is passed through the other side, and a DC current is applied. An electrodialysis treatment method is known in which ammonium ions in wastewater are exchanged and removed by applying electricity. Sadao Kojima, “Denitrification, dephosphorization technology and eutrophication countermeasures” p.889-892 (1925). However, wastewater containing ammonium ions generally contains dissolved organic matter and organic solids;
When performing electrodialysis treatment, efficient dialysis can be performed at the beginning of operation, but as time passes, the ion exchange membrane becomes contaminated with dissolved organic matter and organic solids, and its dialysis performance deteriorates significantly.
That is, a fouling phenomenon occurs. When this phenomenon occurs, the initial current density cannot be maintained, so
It is necessary to either continue operation by lowering the current density, or to stop operation, drain the remaining liquid in the electrodialysis tank, and then clean the ion exchange membrane with a cleaning agent. However, the processing capacity per hour is greatly reduced, and this is a major problem from the viewpoint of equipment productivity when operated on an industrial scale. In addition, in order to prevent the deterioration of the performance of the ion exchange membrane due to the above-mentioned fouling phenomenon, there is also a method in which the liquid containing dissolved organic matter and organic solids is subjected to clarification or ultrafiltration treatment to remove fouling substances. Although known (same literature as before
(See p.889), introducing such a pretreatment process will increase the total equipment cost and running cost.
From an economic point of view, this is a major drawback. The inventors of the present invention have studied various methods to eliminate the drawbacks of the conventional technology, and have found that by subjecting wastewater containing ammonium ions to Donnan dialysis treatment, high performance can be achieved without the pretreatment process or directly without any reduction in performance. This led to the development of a method to remove ammonium ions. The present invention efficiently exchanges ammonium ions and hydrogen ions by bringing wastewater containing ammonium ions into contact with an aqueous mineral acid solution via a cation exchange membrane. Contact between wastewater containing ammonium ions and an aqueous mineral acid solution (strip solution) through a cation exchange membrane, i.e., contact of the two solutions, for example, one solution on one side of the cation exchange membrane and one solution on the other side. This is done by passing a liquid through one side of the other. If one-time fluid contact is insufficient for Donnan dialysis, circulating fluid contact may be used. It is necessary that the molar concentration of the mineral acid aqueous solution passed through the cation exchange membrane to the side opposite to the wastewater be greater than the total cation concentration contained in the wastewater. The ion exchange reaction in the present invention is based on the Donnan dialysis principle, and the driving force for the reaction is due to the difference in cation molar concentration between the aqueous solutions on both sides via the cation exchange membrane. Hydrogen ions move from the mineral acid side, which has a higher cation molar concentration than the wastewater side, via a cation exchange membrane, and ammonium ions move to the mineral acid side to maintain electrical neutrality on the wastewater side. At this time, anions on the mineral acid side cannot pass through or move even if they come into contact with the cation exchange membrane. Incidentally, if water containing ammonium chloride is brought into contact with hydrochloric acid through a cation exchange membrane instead of waste water containing ammonium ions, the following equation will hold when the ion exchange reaction reaches equilibrium (FGDonnan:
Chem.Rev., page 73 (1925). [C _NH4 ⁺ ] _R / [C _NH4 ⁺ ] _L = [C _H ⁺ ] _R / [C _H ⁺ ] _LHere , [C _NH ⁺ ] and [C _H ⁺ ] are respectively,
It represents the molar concentration of ammonium ions and the molar concentration of hydrogen ions, and the subscripts R and L represent one side and the other side of the cation exchange membrane, respectively. The above equation suggests that the larger the difference in cation molar concentration between the wastewater side and the mineral acid side, the higher the ammonium ion removal rate in the equilibrium state. In the present invention, wastewater containing ammonium ions is
This is wastewater whose main cations are ammonium ions. Dissolved organic matter contained in such wastewater includes dissolved distorted white matter, pigments, sugars, amino acids, organic acids, etc., and organic solids include colloidal distorted white matter, bacterial cells, fibrous matter, etc. It is a substance commonly contained in industrial wastewater, domestic wastewater, etc. Removing ammonium ions from such wastewater is
Contributes to environmental conservation. The ammonium ion concentration in the waste liquid is not particularly limited when treated by the method of the present invention, but
Usually, it is in the range of 100 to 1000 ppm. Furthermore, when ammonium ions are removed from wastewater, they are replaced with hydrogen ions, which may lower the pH of the wastewater, but if necessary, an alkali other than ammonia can be added to adjust the pH. If the wastewater containing ammonium ions is alkaline, hydrogen ions are supplied from the stripping liquid side and the wastewater is neutralized, so the pH of the wastewater from which ammonium ions have been removed is
can be set to around neutrality. Mineral acid aqueous solutions used as stripping liquids include inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid.
The concentration during use is not particularly limited, but it must be higher than the total cation molar concentration in wastewater. Usually a 1-5 molar mineral acid aqueous solution is used. There is no problem if the concentration is higher than this, but depending on the type of mineral acid, if the concentration is too high, the material of the ion exchange membrane may be damaged, so care must be taken. Appropriate concentrations can be determined by those skilled in the art.
It can be easily determined by preliminary experiments. It is easily known from the Donnan dialysis principle (cited in the above document) that in addition to mineral acids, organic acids such as acetic acid formic acid, and inorganic electrolyte aqueous solutions other than ammonium salts such as common salt, sodium sulfate, potassium chloride, and potassium sulfate can be used as the stripping liquid. However, as a result of various studies, the present inventors have found that the rate of dialysis of ammonium ions is much higher when a mineral acid is used as the stripping liquid than when an inorganic electrolyte solution other than an ammonium salt is used. I found out. This is a very important discovery from an industrial perspective, and means that the investment cost for constructing wastewater treatment facilities containing ammonium ions can be significantly reduced. The difference in dialysis rates when the cations in the stripping solution are hydrogen ions derived from mineral acids and cations other than ammonium ions derived from inorganic electrolytes cannot be inferred from the Donnan dialysis principle, and the present inventors' earnest efforts This is the knowledge obtained as a result of research. A simple Donnan dialysis machine consists of creating two chambers by dividing the center of a box-shaped container with a cation exchange membrane, placing waste water in one chamber and mineral acid in the other, and installing a stirrer if necessary. Therefore, it can be easily manufactured. Practically speaking, a filter press type commercially available electrodialysis tank (however, an electrode plate electrode chamber is not required in this case),
A commercially available diffusion dialysis tank can also be used. Examples of the cation exchange membrane include p-styrene sulfonate-divinylbenzene copolymer, p-
Styrene sulfonate-butadiene copolymer, p-
Sulfonic acid-based or carboxylic acid-based materials such as sulfonic acid phenol-formaldehyde copolymer may be used. Examples include Asahi Glass Co., Ltd.'s Selemion CMV membrane and Tokuyama Soda Co., Ltd.'s Neocepta CIM membrane. Using a Donnan dialysis device equipped with a cation exchange membrane in a filter press type, various wastewaters containing various dissolved organic substances and organic solids as mentioned above and having an ammonium ion concentration of 100 to 10,000 ppm are used until the ammonium removal rate reaches 90% or more. After dialysis, no rapid performance deterioration was observed, and just in case, waste water,
Even when the strip solution was replaced with a new one and dialysis was repeated several times, the dialysis performance remained at the same level.
Furthermore, when the device was disassembled and the surface of the cation exchange membrane was observed, no contamination or organic matter adhesion on the membrane surface, which is commonly seen after electrodialysis, was observed. This fact was discovered for the first time by the inventors of the present invention, and it has been found that the drawbacks of the above-mentioned electrodialysis method can be solved at once. Now, by bringing the mineral acid aqueous solution that has absorbed ammonium ions produced in the present invention into contact with water via an anion exchange membrane, only the mineral acid can be recovered by diffusion dialysis to the water side from the mineral acid aqueous solution. The mineral acid aqueous solution obtained in this way is prepared by adding a new required amount of mineral acid as necessary to adjust the concentration.
Use of the mineral acid as a stripping liquid in the present invention is advantageous in that the cost of the mineral acid of the present invention can be reduced. Also, after recovering the mineral acids, a solution of ammonium chloride is produced, which can be used as fertilizer or for other uses. In the present invention, there is provided a diffusion dialysis apparatus for dialyzing only the mineral acid from the mineral acid aqueous solution and recovering it as a new mineral acid aqueous solution by contacting the mineral acid aqueous solution with water through an anion exchange membrane that has absorbed ammonium ions. The cation exchange membrane of the Donnan dialysis apparatus of the invention may be replaced with an anion exchange membrane.
The contact of the two liquids in the diffusion dialysis treatment is carried out in accordance with the contact of the two liquids in the present invention (Donan dialysis treatment). In this case, the anion exchange membrane allows anions to pass through and blocks cations, but in the case of hydrogen ions,
Since the ionic diameter is very small, it specifically passes through the anion exchange membrane, resulting in only the mineral acid being dialyzed. Such an anion exchange membrane may be an amine-based anion exchange membrane such as a quaternary ammonium salt such as paramethyleneamine styrene-divinylbenzene copolymer or paramethyleneamine styrene-butadiene copolymer. Examples include Selemion DMV membrane (Co., Ltd.) and Neocepta AFN membrane (Tokuyama Soda Co., Ltd.). The present invention will be further explained below with reference to Examples, Comparative Examples, and Reference Examples. Comparative Example 1 Strongly acidic cation exchange membrane based on styrene-divinylbenzene copolymer (Asahi Glass Co., Ltd. Selemion)
A filter press type electrodialyzer (Du-ob type, manufactured by Asahi Glass Co., Ltd.) was assembled using 21 sheets of CMV membrane as shown in Fig. 1. The total membrane area was 35.9 ^dm2 . Wastewater 4.0 containing dissolved organic matter and organic solids before being treated by the activated sludge method as wastewater containing ammonium ions was used, and 2N hydrochloric acid 4.0 was used as the mineral acid. The liquid was supplied to the tank, and electricity was applied while circulating the liquid. Note that 0.5N sulfuric acid was used as the polar solution for both negative and positive electrodes. Constant voltage operation was performed for 5 hours at a voltage of 22 V and a current density of 6.7 A/dm ² , and the changes in current density over time were tracked and the results are shown in Table 1.

[Table] After dialysis for 5 hours, the electrodialysis tank was disassembled and the cation exchange membrane surface was observed, and sticky solid matter was observed on the membrane surface on the feed chamber side. Table 2 shows changes in the properties of the feed liquid after 5 hours of dialysis.

[Table] Example 1 Using the same equipment and liquid as in Comparative Example 1, feed liquid and acid solution were circulated through an electrodialysis tank without applying electricity. However, in this case, water was used as the polar solution instead of 0.5N sulfuric acid. Table 3 shows the ammonia nitrogen concentration and
It shows the change in pH over time.

[Table] After 5 hours of dialysis, the apparatus was disassembled and the cation exchange membrane surface was observed, and no co-solid matter was observed on both sides of the membrane surface. Example 2 Assemble a Donnan dialysis machine as shown in Figure 2,
400 ml of the same wastewater as in Comparative Example 1 on the feed chamber side, and 2N HCl or 2N NaCl or
400 ml of 2N KCl was added, and both chambers were stirred at room temperature using a laboratory stirrer (300 rpm), and changes in ammonia nitrogen concentration and pH changes in the feed chamber side were measured over time. The results are shown in Table 4.

[Table] From the above table, it can be seen that the most effective method is to add mineral acid (hydrochloric acid) to the stripping chamber. Example 3 The waste liquid 6.0 used in Example 2 was used as a feed liquid, 3N
Using HCl2.0 as a strip solution, Donnan dialysis was performed for 6 hours without applying electricity using the electrodialysis tank used in Example 1 to obtain a strip solution 2.5 that had absorbed ammonium ions. The increase in liquid volume by 0.5 is due to
This is because water moved from the feed side. Table 5 shows the composition of the strip solution after dialysis.

[Table] Reference Example 1 Incidentally, the commercially available diffusion dialysis shown in Figure 3 incorporates 19 strongly basic anion exchange membranes (Celemion DMV membranes manufactured by Asahi Glass Co., Ltd.) (total membrane area was 39.7 dm ² ). Using a tank (Asahi Glass Co., Ltd. T-ob type dialysis tank), feed the strip solution obtained in Example 3 at a rate of 0.3/hr, and add water for acid recovery to the other side of the membrane.
Acid recovery from the strip solution was accomplished by feeding at a rate of 0.24/hr. Table 6 shows the composition of the recovered hydrochloric acid.

【table】 [Brief explanation of the drawing]

FIG. 1 shows an overview of the device and operation of Comparative Example 1, FIG. 2 shows an overview of the device and operation of Example 2, and FIG. 3 shows an overview of the device and operation of Reference Example 1.

Claims (1)

[Claims] 1 Using a Donnan dialysis device with a cation exchange membrane as a diaphragm, ammonium ions in the wastewater and hydrogen ions in the mineral acid are exchanged by bringing the wastewater containing ammonium ions into contact with an aqueous mineral acid solution through the diaphragm. A method for treating wastewater containing ammonium ions, characterized by: