JPS591396B2 - How to treat water containing boron and COD - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating water containing boron and COD, and particularly to a method for treating flue gas desulfurization wastewater containing boron and COD.

Flue gas desulfurization wastewater, for example, flue gas desulfurization wastewater in a lime-gypsum process, contains boron and COD.

The boron contained in such wastewater is usually in the form of BO or borofluoride, and COD is in the form of dithionic acid,
Soluble COD such as polythionic acid and NS compounds.

Conventionally, methods for removing boron from such wastewater include a method of exchange adsorption with an anion exchange resin and a method of forming an insoluble precipitate with an aluminum compound. Treatment can be performed by using these alone or in combination, but anion When using exchange resin, there was a drawback that a large amount of regenerant was required.

In addition, as a method for removing COD, SS-based and metal-based COD
A certain amount of COD can be removed from D by air oxidation, neutralization, coagulation, etc. However, soluble COD such as dithionic acid, polythionic acid, and NS compounds cannot be removed by the above treatment methods. Adsorption treatment is performed using exchange resin.

However, if such wastewater is treated with an anion exchange resin to remove boron and COD at the same time, the optimum pH for the ion exchange reaction is different, resulting in poor treatment efficiency and the need for a large amount of regenerant. There were drawbacks.

This invention is intended to improve the above points, and O
By using weakly basic anion exchange resins of H type and SO4 type, ion exchange can be carried out efficiently.
The purpose of this study is to propose a method for treating water containing boron and COD that can reduce the amount of regenerant.

This invention involves an ion exchange process in which water containing boron and COD is passed through an OH type weakly basic anion exchange resin layer and then passed through an SO4 type weakly basic anion exchange resin layer. Sulfuric acid is passed through the weakly basic anion exchange resin layer, and sodium hydroxide is passed through the SO4 type weakly basic anion exchange resin for regeneration, and the recycled waste liquid is discharged from the OH type weakly basic anion exchange resin layer. S0
The regenerated waste liquid discharged from the S04 weakly basic anion exchange resin layer is placed in the OH type 4 weakly basic anion exchange resin layer.
This is a method for treating water containing boron and COD, which is characterized by including a regeneration step of passing the liquid through a weakly basic anion exchange resin layer.

In this invention, the water containing boron and COD to be treated includes boron in an ion-exchangeable form such as BOR- or borofluoride, and soluble COD such as dithionic acid, polythionic acid, or NS compound. This is water that contains COD in an ion-exchangeable form, and includes the aforementioned lime-gypsum process flue gas desulfurization wastewater.

When flue gas desulfurization wastewater contains a large amount of fluorine and heavy metals, it is desirable to remove these by pretreatment such as adding slaked lime, and when the content of boron is high, it is recommended to remove fluorine and heavy metals. It is desirable to lower the boron content by performing pretreatment such as addition.

Further, when the raw water contains hardness components such as calcium salts, especially when slaked lime is added in pretreatment, it is desirable to soften the water to remove the hardness components as a measure against resin scaling.

As a softening method, there is a method of adding carbonate, bicarbonate, or carbon dioxide gas to raw water and separating unnecessary precipitates such as CaCO3 that are generated.

In the ion exchange step, raw water that has been pretreated as described above is passed through an OH type weakly basic anion exchange resin layer to exchange and adsorb boron, and then passed through an SO4 type weakly basic anion exchange resin. to exchange and adsorb COD.

pH of water supplied to the OH type weakly basic anion exchange resin layer
is preferably 9 or more, and the pH of the water supplied to the SO4 type weakly basic anion exchange resin layer is preferably 7 or less.

When boron is exchange-adsorbed using a weakly basic aniline exchange resin, the SO4 form can also be exchange-adsorbed, but the OH form has better exchange-adsorption efficiency and is less affected by pH.

In the case of SO4 form, the adsorption power is weak below pH 11.
Even if it is 12, the amount of adsorption is smaller than that of the OH type.

Further, in the case of the OH type, it is less affected by pH than the SO4 type, but the exchange adsorption efficiency is better at pH 9 or higher.

This point will be made clear by the experimental examples described below.

On the other hand, regarding the exchange adsorption characteristics of COD by a weakly basic anion exchange resin, the exchange adsorption efficiency of the S04 type is better than that of the OH type, and the raw water pH is preferably 7 or less.

As mentioned above, the raw water flow order is as follows: First, the raw water is made to pH 9 or more and passed through the OH type weakly basic anion exchange resin layer, and then the water is passed through the SO4 type anion exchange resin layer with the pH adjusted to 4 to 7. It's convenient because of the relationship.

In other words, if the above-mentioned pretreatment is performed to remove fluorine, heavy metals, large amounts of boron, etc., or if softening treatment is performed, highly alkaline pretreated water is generated, so treatment under highly alkaline conditions is not recommended. If the boron exchange adsorption step is carried out, it is advantageous because the treatment can be carried out in a highly alkaline state.

There are no particular limitations on the concentration of boron and COD in the raw water supplied to the ion exchange step, but if it contains a high concentration of boron, it is desirable to remove it to some extent through pretreatment as described above.

The boron concentration of raw water suitable for ion exchange is 200 m1i/
is below the level.

In addition, the water flow rate in the ion exchange process is OH type, S0
All four types are about SVI~10h-'.

The OH type and S04 type weakly basic anion exchange resins that have exchanged and adsorbed boron and COD in the ion exchange step are each successively regenerated.

(The OH-type weakly basic anion exchange resin that has exchanged and adsorbed boron is directly hydroxylated.) When regenerated with IJium, the resin becomes OH.
Although it can be shaped, the regeneration efficiency (boron elution efficiency) is poor, and sulfuric acid regeneration has better regeneration efficiency.

On the other hand, for the S04 type weakly basic anion exchange resin that has exchanged and adsorbed COD, the regeneration efficiency is better with sodium hydroxide than with sulfuric acid.

Therefore, in the regeneration process, sulfuric acid is passed through the OH type weakly basic anion exchange resin layer and sodium hydroxide is passed through the S04 type weakly basic anion exchange resin layer for regeneration. In order to return the recycled waste liquid discharged from the OH type weakly basic anion exchange resin layer to the S04 type weakly basic anion exchange resin layer,
The recycled waste liquid discharged from the O4 type weakly basic anion exchange resin layer is passed through the OH type weakly basic anion exchange resin layer.

By carrying out such a regeneration method, the regeneration efficiency can be increased and the form of the resin can be converted by effectively utilizing the excess sulfuric acid and sulfur hydroxide in the regeneration waste liquid.

In this case, the eluted boron and COD are not exchanged and adsorbed onto the resin again.

The sulfuric acid used for regeneration is about 20 to 100y7 at about 1 to 8t/l-R, and the sodium hydroxide is about 20 to 10
0'? / of about 0.3 to 1.5 t/l-R is used, and after passing the liquid at SVo of about 5 to 4 h', extrusion, washing with water, etc. are carried out according to a conventional method.

The OH type and Sq type weakly basic anion exchange resins that have undergone the regeneration process as described above are again subjected to an ion exchange process, and raw water is passed through them to remove boron and COD.

In the present invention, since water containing boron and COD is passed through the OH type weakly basic anion exchange resin layer and then through the S04 type weakly basic anion exchange resin layer, boron and COD are efficiently removed. In addition, when performing pretreatment, it is possible to maintain the high alkalinity of the pretreated water and perform efficient exchange adsorption, and it is also possible to perform efficient regeneration by making effective use of the regenerant. .

That is, sulfuric acid is passed through the OH type weakly basic anion exchange resin layer, sulfuric acid is passed through the S04 type weakly basic anion exchange resin layer, and then the recycled waste liquid is passed through the other resin layer. By doing so, we can improve the regeneration efficiency and
The regenerant can be used effectively.

Next, the effects of the present invention will be specifically explained using experimental examples and examples.

Experimental Example Filtered supernatant water (pH 11,
8, B 106”?/l, Ca 3.Q77v/,
/, ) with sulfuric acid in SO4 form or hydroxylated with l-IJ
5v3 to weakly basic anion exchange resin made into OH form with um.
Table 1 shows the results of water flow at h-'.

Note that the pH of the flowing raw water was adjusted with sulfuric acid.

From the results in Table 1, it can be seen that the OH type weakly basic anion exchange resin is good for removing boron, and it is desirable to run the resin at a pH of 9 or higher.

Example When flue gas desulfurization wastewater was decalcified by adding sodium carbonate and I-IJ hydroxide, the pH was 11.8 and the boron content was 106/7. Supernatant water with a COD of 50 mti/l was obtained.

After this water was passed through the OH type weakly basic anion exchange resin layer, sulfuric acid was added to adjust the pH to 4.5, and the water was passed through the S04 type weakly basic anion exchange resin layer.

The water flow rate was 3h-1 in both cases.

04, boron 0.7TIg/l as final treated water,
Treated water with C0D6.0/l was obtained (water flow rate 401
/l-R).

This operation was further continued, and when the water flow rate was 581/l-R, the COD became 107IIIi/l, so the operation was interrupted and regeneration was performed.

reproduction! Tun OH type weakly basic anion exchange resin with sulfuric acid 50%
After passing an aqueous solution of 3 t/l-R at S V 2 h-', pure water was subsequently passed through at 1 t/l-R under the same conditions.

The properties of the recycled waste liquid (hereinafter referred to as recycled waste liquid A) were as follows.

pH0.5 Boron: 13001117/l Sulfuric acid:
22700m'i/1%COD: 17m? /l The results show that approximately 10% of the boron adsorbed on the resin was dissolved by sulfuric acid.

It is also seen that at pH 9 or higher, the OH type weakly basic anion exchange resin selectively adsorbs boron and hardly adsorbs COD.

On the other hand, for the S04 type weakly basic anion exchange resin, a sodium hydroxide aqueous solution of 80 t/l was added at SV2 h-' for 1.
2t/l-R, followed by pure water 1t/l under the same conditions.
-R was washed with water.

As a result, a recycled waste liquid (hereinafter referred to as recycled waste liquid B) having the following properties was obtained.

pH12.7 Boron: 23■/l Sodium hydroxide:
18000■/l COD: 1080■/1゜From now on, C adsorbed on the S04 type weakly basic anion exchange resin
It can be seen that almost 100% of OD is eluted.

After treating both resins as described above, the recycled waste liquid A is
4 type weakly basic anion exchange resin layer, on the other hand, O
The solution was passed through each of the H-type weakly basic anion exchange resin layers, and both were washed with 1 t/l of pure water to convert each resin layer into an S04-type and an OH-type.

As a result, recycled waste liquid A exhibited the following properties.

pH 1,2 Boron: 101077v/l COD near 711fl/l In addition, recycled waste liquid B showed the following properties.

pH 3,7 Boron: 167/lg/1 COD near 20m
1!7/l As a result, considering the dilution rate, boron, C
It can be seen that OD is ion-exchanged without being readsorbed.

After completing the regeneration in this way, water flow was restarted again.

As a result, at a flow rate of 40t/l-H, the boron content in the final treated water was 0.9■/l, and the COD was 6.1■/l.
It was l.

This is almost the same in performance as the initial state, and it can be seen that the above regeneration was almost completely performed.

Claims (1)

[Claims] 1. An ion exchange step in which water containing boric acid and COD is passed through an OH type weakly basic anion exchange resin layer and then passed through an SO4 type weakly basic anion exchange resin layer; During regeneration, sulfuric acid is added to the OH type weakly basic anion exchange resin layer.
Then, sodium hydroxide is passed through each of the SO4 type weakly basic anion exchange resin layers for regeneration, and the recycled waste liquid discharged from the OH type weakly basic anion exchange resin is transferred to the SO4 type weakly basic anion exchange resin layer. A method for treating water containing boron and COD, comprising a regeneration step of passing recycled waste liquid discharged from an SO4 type weakly basic anion exchange resin layer through an OH type weakly basic anion exchange resin layer. 2. The method for treating water containing boron and COD according to claim 1, wherein the water containing boron and COD is flue gas desulfurization wastewater. p of water supplied to the 30H type weakly basic anion exchange resin layer
3. The method for treating water containing boron and COD according to claim 1 or 2, wherein H is 9 or more and the pH of the water supplied to the SO4 type weakly basic anion exchange resin layer is 7 or less. The method for treating water containing boron and COD according to any one of claims 1 to 3, wherein the water supplied to the 40H type weakly basic anion exchange resin layer is pre-softened water.