JPH0140679B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention deals with the treatment of N-S compounds and
It concerns a method for removing COD. In general, many technologies are being developed to remove SOx and NOx from flue gas, but among these, wet treatment methods that use various absorbing liquids such as alkaline compounds of alkali or alkaline earth metals and sodium sulfite are extremely effective. . This absorbent liquid is purified to some extent through a process of recovering useful substances, and is then reused by injecting absorbent into it. However, it is impossible to recycle the entire amount of the absorption liquid, and several hundred m ³ per day are blown out of the system as wastewater from various processes and for renewal of the absorption liquid. This wastewater contains NH ⁺ ₄ , NO ^- ₂ , NO ^- ₃ , N-S compounds, as well as sulfites and dithionic acid generated during the flue gas treatment process, and if released as is, it could cause water pollution. need to be processed. Among these compounds, NH ⁺ ₄ , NO ₂ ^- ₂ ,
NO ^- ₃ can be easily obtained through biological nitrification and denitrification treatment.
This is less of a problem since it can be reduced to N ₂ or sulfite can be easily converted to sulfate by oxidation. However, N-S compounds consist of amidosulfonates, imidodisulfonates, hydroxylamine monosulfonates, etc., depending on the treatment method, and can be used for oxidizing agents such as Cl ₂ and O ₃ , activated carbon adsorption, or biological treatment. It is a stable compound that is not removed much even when it is shaken. Furthermore, dithionic acid is not easily decomposed even when an oxidizing agent, a catalyst, ultraviolet rays, etc. are used in combination. In this way, even if flue gas desulfurization and denitrification wastewater is subjected to normal oxidation treatment and biological treatment, the N content is due to N-S compounds, and the N content is due to N-S compounds and dithionic acid.
COD is often released into the water without being removed, which is a problem. As a result of repeated research to solve this problem, the inventors have invented and already published a method for effectively removing N-S compounds and COD from wastewater (Japanese Patent Publication No. 57-20877). The gist of this invention is to remove N-S compounds from NaNO ₂ or Ca in the treatment of blow wastewater from wet flue gas desulfurization, denitrification, and desulfurization and denitrification simultaneous treatment equipment.
(NO ₂ ) By adding sulfites such as ₂ , NH ⁺ ₄ , NO ^- ₂ ,
After being decomposed into NO ₃ , N ₂ O, N _2, etc., NH ⁺ ₄ , NO ^- ₂ , NO ^- ₃ is reduced to N ₂ through biological nitrification and denitrification treatment, and even after coagulation and precipitation, it cannot be decomposed even after filtration. It is characterized in that the remaining N-S compounds and dithionic acid are removed by passing water through an ion exchange resin and activated carbon. However, the method using the ion exchange resin of the invention still has various problems, and the problems will be explained below by taking flue gas desulfurization wastewater as an example. To remove COD components from flue gas desulfurization wastewater, weakly basic or medium basic anion exchange resin (hereinafter referred to as
Methods for passing water through a WBR (both abbreviated as "WBR") have been known for some time, but they had the following drawbacks. WBR uses alkali (e.g. NaOH) as a regenerating agent in the regeneration process after water flow is finished, and then WBR
Acid (e.g. HCl, H ₂ SO ₄ ) is passed through to change the salt form. However, conventionally, these chemicals are passed in the same direction as the water passing direction, that is, in a forward flow manner, so even after the regeneration is completed, a small amount of unregenerated WBR remains at the bottom of the column filled with WBR. If the water flow process is started in this state, some COD components will leak from the unregenerated resin. COD to leak
The concentration of the components is affected by the salt concentration of the raw water, and the
As shown in the figure (S ₂ O ₆ concentration of raw water is 1200 mg/), the higher the salt content, the higher the concentration of COD components. Figure 1 shows the case where the regeneration level of NaOH and the regeneration level of sulfuric acid are both 2 equivalents/-R, and when the salt concentration of raw water is 10,000 mg/- or more, S ₂ O ₆ becomes 83
mg/(2 to 3 mg/in COD), making it difficult to maintain the emission standard value of 10 mg/in COD. To solve this problem, it would be possible to increase the NaOH regeneration level and reduce the amount of unrecycled resin remaining, but this would require additional regenerant and chemical costs for neutralizing the recycled waste liquid, and therefore the regeneration Another problem is that it takes a long time and increases the processing cost. The inventors believe that the cause of the deterioration of treated water quality is due to unregenerated water.
Focusing on the fact that WBR is unevenly distributed near the treated water outlet of the WBR packed tower, we realized that if the regenerant is passed in the opposite direction to the water flow direction, that is, in a countercurrent manner, it will always be good regardless of the salt concentration of the raw water. The inventors discovered that treated water can be stably obtained and completed the present invention. Next, one embodiment of the present invention will be described in detail with reference to FIG. Figure 2 is an example of a countercurrent COD adsorption tower with downward flow water and upward flow regeneration method.
The method is not limited to this method, and the same effect can be obtained, for example, in a countercurrent COD adsorption tower using an upward flow water/upward flow regeneration method. However, when applying the upward flow regeneration method, NO-OFF operation is expected to be frequent and the quality of the treated water deteriorates due to disturbance of the resin layer. It is extremely preferable to carry out the ion exchange treatment in a downward flow and to carry out the regeneration treatment in a split manner as shown in the example in FIG. In Figure 2, the wastewater blown from the flue gas desulfurization, denitrification, and desulfurization and denitrification simultaneous treatment equipment undergoes biological treatment.
From raw water tank 1 after pre-treatment such as coagulation sedimentation and filtration.
Valves 8 and 9 to ion exchange resin column 2 filled with WBR
The N content derived from COD and N-S compounds in the wastewater is adsorbed and removed. When the water flow is finished, the upper part of the intermediate water collection device 20
WBR with the regeneration water of the regeneration tank 4 at the valves 10 and 1.
1, 12 for backwashing. The WBR below the intermediate water collection device 20 may be backwashed once every several cycles to several tens of cycles. In that case, valve 10,1
Backwash all layers of WBR through 3 and 12. After backwashing and settling are completed, the valves 14, 13,
The liquid is passed through the intermediate water collecting device 20 to the lower WBR layer through the intermediate water collecting device 20 in an upward flow. At this time, the intermediate water collection device 20
In order to prevent the lower WBR layer from flowing, it is necessary to flow pressurized water or air in a downward direction from the upper part of the column 2, but this is not shown. In addition, the WBR above the intermediate water collecting device 20 also has COD adsorption capacity, and in order to effectively utilize this, the valve 15 is opened at the same time as the NaOH solution is passed in an upward flow. The liquid may be passed through the WBR layer in a downward flow. Both recycled waste liquids are discharged from the intermediate water collection device 20. This method is called a split flow method, and FIG. 2 shows an example thereof. The regenerated liquid discharged from the intermediate water collection device 20 is
The COD is divided into a rich part and a dilute part, and the concentrated waste liquid is stored in a concentrated waste liquid storage tank 7 via a valve 18, and is oxidized and decomposed by thermal decomposition, electrolysis, etc. in a separate concentrated waste liquid treatment device 21. Although not shown, the diluted portion is preferably returned to the preceding pretreatment device. After passing the NaOH solution and extruding it,
In order to change the salt type of the WBR, acid (e.g. N ₂ SO ₄ , HCl) is passed upward from the acid storage tank 6, but this waste liquid has a low COD concentration, so it is stored in the concentrated waste liquid storage tank 7. It is not necessary, and depending on the COD concentration, it can be neutralized and discharged, or it can be returned to the previous pretreatment device. In addition, the liquid oxidized and decomposed in the concentrated waste liquid treatment device 21 exhibits strong acidity, and although it depends on the degree of decomposition, it can be used as an acid for changing the salt type.
2 is a valve for that purpose. In particular, in the method of adding an acid and thermally decomposing the concentrated waste liquid, the concentration of the acid after decomposition is high, so that the acid for changing the salt type is hardly required or only a small amount is required. When acid passage and extrusion are completed, water is washed with raw water from raw water tank 1 using the same line used for water passage, but there is almost no unregenerated resin at the bottom of tower 2, and the process can be shifted to water passage in an extremely short time. . In the figure, 3 is a treated water tank, and 17 and 19 are valves P ₁ , P ₂ , P ₃ , P ₄ and P ₅
is a pump. Next, examples of the present invention will be described together with comparative examples based on conventional methods. Example 1 and comparative example Weakly basic anion exchange resin Revachit MP62
Raw water with the quality shown in Table 1 is passed through a tower filled with (product name) at SV10, and the quality of the treated water is S ₂ O ₆ 100.
mg/, the water flow was stopped (water flow rate 60
/-R). Next, the used ion exchange resin is divided into two parts,
Prepare two 45〓 columns each packed with one column, and
When a regeneration water flow test was conducted using the raw water shown in the table and the conditions shown in Table 2, one using the counterflow method of the present invention and the other using the forward flow method as a comparative example, the results shown in FIG. 3 were obtained.

【table】

[Table] In Fig. 3, A indicates an example, and B indicates a comparative example. In other words, in the case of the counterflow type (this invention), S 2 O ₆ in the treated water shows 0 mg/ from the start of water flow, whereas in the forward flow type, as much as 200 mg/ of S ₂ O 6 leaks at the beginning of water flow, and even after that, the treated water shows less than 45 mg/ I couldn't get water. In addition, the amount of water flow until the S ₂ O ₆ of the treated water increases to 100 mg/- is 60 to 65/-
R was 50 to 55/-R in the comparative example, indicating that the example was more advantageous. Example 2 and Comparative Example Ion exchange treatment and regeneration treatment were carried out under the same conditions as in Example 1, except that the concentration of coexisting salts in raw water and the regeneration level were changed as shown in Tables 3 and 4, respectively.

【table】

[Table] (1) Table 5 shows the results when the regeneration level is 2 equivalents/-R.

[Table] (2) On the other hand, the coexisting salt concentration was 14000 mg/asCaCO ₃
The result when regenerated by the conventional method is the 6th
As shown in the table.

[Table] From the results of Example 2, the present invention has the advantage of being able to treat wastewater containing a high concentration of salts with a high removal rate even at a low regeneration level, and is particularly effective in obtaining highly purified treated water. I understand that there is something. As described above, the present invention improves the drawback of the conventional method in that the quality of treated water deteriorates when raw water containing high salts is passed through it, and also makes it possible to always obtain good treated water even at a low regeneration level. This greatly contributes to pollution prevention, resource conservation, and energy conservation.

[Brief explanation of drawings]

Fig. 1 is a graph showing the ion exchange performance of an ion exchange resin regenerated by a conventional method, Fig. 2 is a flow sheet showing an embodiment of the present invention, and Fig. 3 is a graph showing the results of an embodiment of the present invention. It is. 1... raw water tank, 2... tower, 4... regeneration water tank,
5... Alkali storage tank, 6... Acid storage tank, 7... Concentrated waste liquid storage tank, 21... Concentrated waste liquid treatment device.

Claims (1)

[Scope of Claims] 1 Flue gas desulfurization and denitrification wastewater is passed through a weakly basic anion exchange resin layer or a medium basic anion exchange resin layer to selectively exchange COD components and N-S compounds in the wastewater. After adsorption treatment, COD components and N-
Flue gas desulfurization characterized by performing regeneration treatment by passing an alkali and then an acid through the ion exchange resin layer adsorbing S compounds in a countercurrent manner to the direction of water flow through the ion exchange resin layer in ion exchange treatment. Treatment method for denitrification wastewater. 2. The method according to claim 1, wherein the ion exchange treatment is performed by passing water in a downward flow, and the regeneration treatment is performed by a split method. 3. The alkaline regenerated effluent in the regeneration process is divided into a first half of high COD concentration regenerated effluent and a second half of low COD concentration regenerated effluent, and the high COD concentration regenerated effluent is subjected to oxidative decomposition treatment. Method described. 4. The method according to claim 3, wherein the decomposition liquid obtained by the oxidative decomposition treatment is used as the acid for the regeneration treatment.