JPH0140678B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention deals with the treatment of N-S compounds and
It concerns a method of removing COD. In general, many technologies are being developed to remove SO _x and NO _x from flue gas, but among these, wet treatment methods using various absorbing liquids such as alkaline or alkaline earth metal alkaline compounds and sodium sulfite are extremely effective. It is. 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 , NO ^- ₃
can be easily reduced to N ₂ by biological nitrification and denitrification treatment, and sulfite can be easily converted to sulfate by oxidation, so there is no problem. However, N-S compounds consist of amidosulfonates, imidodisulfonates, hydroxylamine monosulfonates, etc., depending on the treatment method, and are treated with oxidizing agents such as Cl ₂ and O ₃ , activated carbon adsorption, or biological treatment. It is a stable compound that is not easily removed even when exposed to heat. 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 nitrites 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. The method of passing water through a weakly basic anion exchange resin (hereinafter abbreviated as WBR) or a strongly basic anion exchange resin (hereinafter abbreviated as SBR) in order to remove COD from flue gas desulfurization wastewater is well known. However, it had the following drawbacks. The method of using WBR is to pass an alkali solution as a regenerant to desorb the COD components adsorbed on the resin, and then pass a mineral acid (e.g. HCl, H ₂ SO ₄ ) to change the salt type of the resin. Move to water passage. This method is
The alkali desorbs the COD components adsorbed on the resin relatively well, and the quality of the treated water is good in terms of COD. However, since the two-step feeding of alkali and mineral acid is carried out, there are the following problems. Running costs become very high. The playback operation is complicated and the playback time is also long. Equipment such as regenerant storage tanks and installation area will increase. When using alkali, dehydrate it as reclaimed water.
Mg water (e.g. industrial water) and a tank for it are required. The treated water has a slightly acidic pH of 2 to 4, and requires PH adjustment before being discharged. The resin swelling rate from OH type to Cl type (or SO ₄ type) is 30-40%, which is a drastic volume change, and the resin is rapidly refined. The finer resin also causes increased pressure loss. On the other hand, since the method using SBR mainly uses NaCl alone as a regenerating agent, the above-mentioned problems are eliminated or significantly reduced. However, SBR
has the following problems. At a low regenerant level of NaCl2 to 3 equivalents/-R, COD desorption is not as great as in WBR, so the COD of the treated water is 2 to 5 mg/higher than WBR, making it difficult to maintain the discharge standard value of 10 mg/. Porous type WBR mainly composed of tertiary amines including some quaternary amines (for example, Revachit MP64
-Product name) shows the same or higher through-flow capacity, but porous WBR mainly composed of secondary to tertiary amines (e.g. Revachit MP62-Product name)
Capacity is 10-15% smaller than that of 2.1 when the amount of recycled wastewater with high COD concentration is WBR
/-R, SBR is considered to be at a practical regeneration level in the conventional method.With NaCl5 equivalent/-R, the COD of the treated water is the same as WBR, but the amount of concentrated waste liquid is 3.2/-R (15w/v% NaCl). in the case of)
This is about 50% more than WBR. Concentrated wastewater requires further treatment, which increases costs. The reason why SBR has not been used for COD removal until now is because SBR has the above-mentioned drawbacks. In the process of conducting research on reducing the N content and COD contained in wastewater blown from flue gas desulfurization, denitrification, and desulfurization and denitrification simultaneous treatment equipment, the inventors
- SBR has better removal performance for S compounds than WBR, and COD mainly composed of dithionic acid
Even in terms of removal performance, when WBR is used for a long period of time, the through-flow capacity decreases significantly, and the annual replenishment rate is 30 to 40%.
%, and the large throughflow capacity when new is not an advantage.Furthermore, the treated water quality of WBR is good, but this is because the salt concentration of wastewater is 5000mg/
When asCaCO is about ₃ and the salt concentration is 10000
mg/, the treated water quality deteriorates extremely and NaOH
It was newly discovered that the method of using SBR has disadvantages such as having to raise the playback level of the SBR, and as a result of further studies to solve the above-mentioned problems, the present invention was completed. This is what led to this. The inventors believe that when SBR is used at a relatively low regeneration level of 2 to 3 equivalents of NaCl, the reason for the deterioration of treated water quality is that unregenerated SBR remains near the bottom of the tower, that is, near the water collection pipe, even after SBR is regenerated. remains, and if you start flowing water as it is, unregenerated
The disadvantages are that COD components and N-S compounds gradually leak from SBR, and that the concentration of leakage increases as the salt concentration of the wastewater increases. I found that the problem could be resolved by doing this. The present invention is a method for selectively exchanging and adsorbing COD components and N-S compounds in the wastewater by passing flue gas desulfurization and denitrification wastewater through a column filled with SBR, in which a NaCl solution is used as a regenerating agent, and the regenerating It is characterized in that the agent is passed in the opposite direction to the direction of water flow. This prevents unregenerated resin from remaining near the water collection pipes even after the regeneration is complete, making it possible to lower the regeneration level and stably supplying high-quality treated water even for high-salt wastewater. be able to. That is, the present invention eliminates the conventional drawbacks of SBR and provides more advantages than the currently used WBR. The advantages of using SBR compared to WBR are listed below. The regenerant cost is 1/1 compared to using WBR.
It can be significantly reduced by 3 to 1/4. Since the regenerating agent is only NaCl, WBR
The regeneration time is significantly shorter to 1/2 compared to the case of two-stage feeding of NaOH and acid, and handling is also easier. The regeneration equipment is also simpler than WBR, and the installation space is smaller because there are fewer storage tanks and measuring tanks. The pH of the treated water is neutral, between 6 and 8, so there is no need for neutralization, making a neutralization device unnecessary. The volume change due to the ion type of SBR is about 10%, which is significantly smaller than the 30-40% of WBR, and it is physically difficult to miniaturize. Therefore, the resin replenishment rate can be reduced. Next, an embodiment of the present invention will be described in detail with reference to FIG. Figure 1 shows an example of a countercurrent COD adsorption tower with downward flowing water and an upward flow regeneration system, but it is not limited to this type. The same effect can be obtained with a flow-type COD adsorption tower. However, when applying the upward water flow system, the ON-OFF operation becomes frequent and the quality of the treated water may deteriorate due to disturbance of the resin layer, so the downward water flow system is preferable. The wastewater blown from the flue gas desulfurization, denitrification, and desulfurization and denitrification simultaneous treatment equipment undergoes pretreatment such as biological treatment, coagulation sedimentation, and filtration, and then is passed from the raw water tank 1 to the tower 2 filled with SBR via valves 8 and 9. N derived from COD and N-S compounds in wastewater is adsorbed and removed. Since the treated water has a neutral pH, some of it is stored in the treated water tank 3, but it can also be discharged as is. When the water flow is finished, the upper part of the intermediate water collecting device 7
SBR with treated water from treated water tank 3 at valves 10, 11, 1
Backwash through 2. Below the intermediate water collection device 7
SBR only needs to be backwashed once every few cycles to several dozen cycles. In that case, valves 10, 14, 1
Backwash the entire SBR layer through 2. When backwashing and settling are completed, the NaCl solution in the NaCl storage tank 4 is diluted with the treated water in the treated water tank 3 while valves 13, 14,
16 in an upward flow to regenerate the SBR below the intermediate water collecting device 7. At this time, in order to prevent the SBR from flowing, it is necessary to flow pressurized water or pressurized air from the upper part of the tower 2 in a downward flow and discharge it from the intermediate water collecting device 7, but this is not shown. The SBR above the intermediate water collection device 7 also has COD adsorption ability, and in order to effectively utilize this, the NaCl solution is transferred to the intermediate water collection device 7.
At the same time, valve 15 is passed through the lower SBR in an upward flow.
Alternatively, the valve 16 may be opened to allow liquid to flow downward through the SBR at the upper part of the intermediate water collection device 7, and both drained liquids may be discharged through the valve 16. FIG. 1 shows an example of this, and this is called a split flow method. It is possible to regenerate the upper and lower SBRs of the intermediate water collection device 7 individually or at the same time, but when regenerating them individually, balance water etc. (not shown) are required, and the regeneration wastewater is Fluid volume increases. The concentration of the regenerant can be 5 to 25%, but is preferably 15% or more in order to reduce the amount of regenerated effluent. The recycled wastewater discharged from the intermediate water collection device 7 is COD.
It is preferable that the concentrated waste liquid is divided into a rich part and a dilute part, and the concentrated waste liquid is stored in the concentrated waste liquid storage tank 5 via the valve 17, and the dilute waste liquid is returned to the pretreatment process of the ion exchange treatment via the valve 18. . The stored concentrated waste liquid is oxidized and decomposed by a method such as electrolysis or thermal decomposition by adding an acid in a separate concentrated waste liquid decomposition treatment device 6, and then discharged to the outside of the system. but,
The oxidatively decomposed liquid is strongly acidic and can be used as a neutralizing acid in the pretreatment process.
Depending on the degree of COD decomposition, it can be reused as a regenerating agent for the next regeneration. The valve 20 is a valve for this purpose, and can replenish and use NaCl in the NaCl storage tank 4 if necessary. In particular, the solution obtained by adding acid to concentrated wastewater and thermally decomposing it has a high salt concentration, so it is effective as a regenerating agent, and the amount of newly used NaCl can be significantly reduced. When the regenerant passage and extrusion are completed, it is washed with raw water from the raw water tank 1, but since there is almost no unregenerated SBR at the bottom of the tower 2, the process can be started in a very short time. In the figure, P ₁ to P ₄ are pumps,
19 and 21 are valves. Next, an example of the present invention will be shown in comparison with a conventional method. Example 1 and Comparative Example 1 Strongly basic anion exchange resin Dowex MSA
- After passing the wastewater shown in Table 1 through a column filled with 64/-R at SV10, the ion exchange resin was divided into two parts, and two 45〓 columns each filled with 1 were prepared, One was regenerated by the water passage-regeneration method according to the present invention, and the other was regenerated by the conventional method for comparison, and the flue gas desulfurization wastewater shown in Table 1 was passed through, and the results shown in Table 2 were obtained. The regeneration conditions are shown in Table 3.

【table】

[Table] Yes.

[Table] In Example 1, S ₂ O ₆ in the treated water was constantly 0 mg/
On the other hand, in Comparative Example 1, the leakage was 30 mg/leak. Furthermore, the through-flow capacity of Example 1 is also 15 to 20% larger. Further, in Comparative Example 1, an equivalent amount of NaCl6 was required to make the S ₂ O ₆ content of the treated water 0 mg/. Example 2 When H ₂ SO ₄ was added to 1.5% of the concentrated waste liquid from Example 1 to a concentration of 10% and heated at 90°C for 4 hours,
_S2O6 was 97% decomposed _. When 1 equivalent of NaCl was added to this liquid and used as a regenerating agent in Example 1, the S ₂ O ₆ of the treated water was 0 mg/, and the through-flow capacity was 64.5 mg/-.
The result was RasS ₂ O ₆ , which was almost the same as in Example 1. Example 3 and Comparative Examples 2 and 3 In addition to the two columns with the regeneration conditions shown in Table 3, one column packed with a weakly basic anion exchange resin Revachit MP62 (trade name) 1 was used as a comparative example. In addition, when the flue gas desulfurization wastewater shown in Table 4 was passed through, the results shown in Table 5 were obtained. Table 6 shows the playback conditions for Revachit MP62.

【table】

[Table] I couldn't do it.

[Table] Even if flue gas desulfurization wastewater with a high salt concentration is targeted as shown in Table 4, according to the present invention, the S ₂ O ₆ of the treated water is 0.
It was hot. On the other hand, in Comparative Examples 2 and 3, S ₂ O ₆ of the treated water
The amount exceeded 100 mg/ml, making it impossible to apply. Comparative example 2,
In case 3, in order to make the S ₂ O ₆ of the treated water the same as in Example 3, 6 to 7 equivalents of NaCl was added in Comparative Example 2, and 6 to 7 equivalents of NaCl was added in Comparative Example 3.
NaOH3 equivalents and regeneration levels had to be increased. Example 4 and Comparative Examples 4 and 5 When the wastewater shown in Table 7 was passed through three columns under the regeneration conditions shown in Tables 3 and 6, the results shown in FIG. 2 were obtained.

[Table] As described above, the present invention can always stably obtain high-quality treated water even from wastewater containing high salt content, and is inexpensive and easy to handle as a regenerating agent.
Since NaCl can be used at a low regeneration level, it will greatly contribute not only to pollution prevention but also to resource and energy conservation.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing an embodiment of the present invention, and FIG. 2 is a graph showing the results of an example of the present invention. 1... Raw water tank, 2... Tower, 3... Treated water tank, 4
...NaCl storage tank, 5... Concentrated waste liquid storage tank, 6... Concentrated waste liquid decomposition processing device.

Claims (1)

[Claims] 1 Flue gas desulfurization and denitrification wastewater is passed through a strongly basic anion exchange resin layer to remove COD components and N-
After selective exchange adsorption treatment of S compounds,
Regeneration treatment is performed by passing a NaCl solution as a regenerating agent through the ion exchange resin layer that has adsorbed COD components and N-S compounds in a countercurrent manner to the water flow direction to the ion exchange resin layer in ion exchange treatment. A method for treating flue gas desulfurization and denitrification wastewater, characterized by: 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 system. 3 In the above regeneration process, the regenerated effluent is
2. The method according to claim 1, wherein the regenerated wastewater with a high COD concentration is divided into a regenerated wastewater with a high COD concentration and a second half with a low COD concentration, and the regenerated wastewater with a high COD concentration is subjected to oxidative decomposition treatment. 4. The method according to claim 3, wherein the decomposed liquid obtained by the oxidative decomposition treatment is used as a regenerating agent.