JPH045516B2 - - 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. Many technologies have been developed to remove SO _x and NO _x from flue gas, but wet treatment methods using various absorbing liquids such as alkali or alkaline earth metal alkaline compounds and sodium sulfite are extremely effective. It is true. In this method, the absorbent liquid is purified to some extent through a process of recovering useful substances, and then the absorbent is injected into it again for reuse. However, it is impossible to reuse 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 generated during the flue gas treatment process.
The compound also contains sulfites and dithionic acid, and if released as is, it will cause water pollution, so it must be purified. Among these compounds, NH ⁺ ₄ , NO ^- ₂ , and 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. It's not that much of a problem. 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 sufficiently removed even by shaking. Dithionic acid is also an oxidizing agent and a catalyst.
It is not easily decomposed even when used in combination with ultraviolet rays, etc. 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 present inventors have invented a method for effectively removing N-S compounds and COD from wastewater, and have already published the method (Japanese Patent Publication No. 57-20877). The gist of the invention disclosed in this publication is that in the treatment of blow wastewater from a wet flue gas desulfurization, denitrification, and desulfurization and denitrification simultaneous treatment equipment, N-S compounds in the wastewater are removed.
After it is decomposed into NH ⁺ ₄ , NO ^- ₂ , NO ₃ , N ₂ O, N ₂ etc. by adding nitrites such as NaNO ₂ or Ca(NO ₂ ) ₂ , it is converted to NH ⁺ ₄ by biological nitrification and denitrification treatment. ,NO ^- ₂ ,
It is characterized by reducing NO ^- ₃ to N ₂ and further removing N-S compounds and dithionic acid that remain without being decomposed even after coagulation and precipitation and filtration by passing water through an ion exchange resin and activated carbon. There is. 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. Weakly basic anion exchange resin (hereinafter abbreviated as WBR) to remove COD from flue gas desulfurization wastewater,
Alternatively, a method of passing water through a strongly basic anion exchange resin (hereinafter abbreviated as SBR) is conventionally known, but it has the following drawbacks. In other words, 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. In this method, the alkali is adsorbed to the resin.
Because COD components are desorbed relatively well, the quality of the treated water is
Regarding COD, it is good. However, since a two-stage application 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 problems ~ are eliminated or significantly reduced. However, this method uses a single ion-exchange resin tower and is based on a down-flow system in which both the water passing step and the regeneration step are carried out in a downward flow, and therefore has the following problems. At low regeneration levels of NaCl2-3 equivalents/-R
Since COD desorption is not as strong as in WBR, the COD in the treated water is 2 to 5 mg/higher than in WBR, making it difficult to maintain the discharge standard value of 10 mg/. Porous WBR mainly composed of tertiary amines including some quaternary amines (e.g.
MP64 (trade name), but has a capacity (through-flow capacity) equivalent to or higher than that of MP64 (trade name), but is a porous type WBR mainly composed of secondary to tertiary amines (e.g.
Capacity (throughflow capacity) is 10 to 15% smaller than Revacit MP62 (trade name). 2.1 when the amount of recycled wastewater with high COD concentration is WBR
/-R, whereas SBR has NaCl5 equivalent / which is considered to be a practical regeneration level using conventional methods.
-R has the same COD of treated water as WBR, but the amount of concentrated waste water is 3.2/-R (15W/V%
(for NaCl) and 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 it has the following 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 present inventors
SBR has better removal performance for N-S compounds than WBR, and in terms of removal performance for COD, which is mainly dithionic acid, when WBR is used for a long period of time, the capacity (throughflow capacity) decreases significantly and annual replenishment is required. As a result, we found that the capacity (through-flow capacity) was not an advantage when it was new, and we conducted further studies to solve the problems mentioned above regarding the method of using SBR. This has led to the completion of the present invention. The present invention provides 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 an SBR, as shown in Figure 1a. The two towers are directly connected in series, and water is passed from the first ion exchange tower to the second ion exchange tower, and regenerant NaCl is passed from the second ion exchange tower to the first ion exchange tower. This is done in the opposite direction to the water flow direction (inter-tower counterflow type). According to this method of passing the regenerant, for example, when the first column and the second column are filled with the same amount of resin, the regeneration level is 3 equivalents/- to the total resin amount.
If regeneration is performed with R, the second column will be regenerated with 6 equivalents/-R, and the quality of the treated water will be very good. Moreover, as shown in FIG. 1b, by regenerating the second column in an inter-column countercurrent type, the quality of the treated water is further improved. moreover,
By collecting the latter part of the regeneration effluent, passing it through the first column, and then passing fresh NaCl from the second column to the first column, even at a regeneration level of 2 to 2.5 equivalents/-R. Good treated water and sufficient capacity can be obtained. Further, the present invention can be carried out by dividing and filling three or more columns, if desired. Thus, the present invention overcomes the traditional drawbacks of SBR and provides many advantages over conventionally used WBR. The advantages of using SBR compared to WBR are listed below. The regenerant cost is 1/4 to 1/5 compared to when using WBR. Since the regenerant is NaCl, NaOH in WBR,
The regeneration time is significantly shorter than in the case of two-stage acid delivery, which is 1/2, and handling is also easier. In addition, the regeneration device is 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.
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 2 shows the case where the second column is regenerated in a counter-current type in an inter-column counter-current type, that is, Figure 1b
This is an example of the case. 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 discharged from the raw water tank 3.
Water is sequentially passed through valves 9, 10, and 11 to a first ion exchange column (hereinafter referred to as the first column) 1 filled with SBR, and then to a second ion exchange column (hereinafter referred to as the second column) 2, N derived from COD and N-S compounds in wastewater is adsorbed and removed. When the water flow is finished, the SBR of the first tower 1 is connected to the valve 12,
13 and backwash with raw water from raw water tank 3. It is not necessary to backwash the SBR in the second column 2 every time, and it is sufficient to perform backwashing once every several cycles to several tens of cycles. In that case, use the treated water in the treated water tank 4 and use the valves 14 and 1.
5 as an opening. When backwashing and settling are completed, the regenerant storage tank 5 is
The NaCl solution is passed through the second column 2 and then the first column 1 in the opposite direction to the water flow direction, but since the second column 2 is a counterflow type, the valves 16, 18, and 19 are opened, and the intermediate water collection is carried out. The liquid is passed through the SBR below the device 29 in an upward flow,
The recycled waste liquid is discharged from the intermediate water collecting device 29. The SBR above the intermediate water collection device 29 is
Since this is a flow prevention layer for SBR, pressurized water or pressurized air (not shown) flows downward from the upper part of the second column 2 between the upwardly flowing chemicals and is discharged from the intermediate water collecting device 29. However, the upper part of the intermediate water collection device 29
SBR also has ion exchange ability, so in order to utilize this ability, the regenerant NaCl is added to the intermediate water collection device 29.
The valve 17 may be opened at the same time as the liquid is passed through the lower SBR in an upward flow, and the liquid is passed through the upper SBR in a downward flow, and both drained liquids are discharged from the intermediate water collecting device 29. FIG. 2 shows an example of this method, which is called a split flow method. In this split flow method, it is possible to regenerate the upper and lower SBRs of the intermediate water collection device 29 individually or at the same time, but when regenerating them individually, balance water etc. are required, and the Not clearly shown in the diagram. When regenerating the second column 2 by a downflow method instead of a countercurrent method, the structure of the second column 2 may be the same as that of the first column 1,
An intermediate water collection device is not required. Note that in the two-column series system, the regenerant is passed through the first column in a forward flow manner, since there is no significant difference in regeneration efficiency between the countercurrent flow method and the forward flow method. Therefore, the concentration of the regenerating agent can be 5 to 25%, but it is preferably 15% or more in order to reduce the amount of regenerated effluent. The valve 20 is designed to dilute the regenerant with the treated water in the treated water tank 4 to a required concentration. The regenerated waste liquid from the second column 2 is passed from the intermediate water collection device 29 to the first column 1 in a downward flow through valves 19, 21, and 22. Since the SBR in the first column 1 is regenerated with NaCl remaining in the regenerated waste liquid in the second column 2, the regenerant can be used effectively. This regenerated waste liquid is received in a concentrated waste liquid storage tank 6. When the passage of the regenerant is completed, the valve 16 is closed and extrusion begins. Since this wastewater is also concentrated, it is received in the concentrated wastewater storage tank 6, but the latter half of the wastewater, which has a relatively low COD concentration, is collected in the recovery tank 7 via the valve 23, and fresh NaCl is passed through it during the next regeneration. Valve 24,2 in front
It is also possible to use it for regenerating the SBR in the first column 1 via 5, 21 and 22. The concentrated waste liquid stored in the concentrated waste liquid storage tank 6 is removed from the valve 26.
It is led to the decomposition tank 8 through the pores, where it is subjected to oxidation treatment such as thermal decomposition and electrolysis, and then discharged outside the system. However, since the solution after decomposition has a high salt concentration, depending on the degree of COD decomposition, part or all of it can be used as a regenerant for SBR in the first column or in the first and second columns, using fresh NaCl if necessary. It is possible to add and use. The liquid after COD decomposition is strongly acidic, so if iron contamination of SBR is a concern, it can also be expected to be effective in iron removal regeneration. When the chemical passage and extrusion are completed, the raw water from the raw water tank 3 is used for washing in the same line as the water passage from the first column 1 to the second column 2, but since the SBR in the second column 2 has been sufficiently regenerated, it cannot be treated. The water quality becomes good within a very short time, and water can be immediately switched on by switching the valve. In addition, in Fig. 2, 27, 28, and 30 are valves, and 31
34 are pumps. Next, examples of the present invention will be described together with comparative examples based on conventional methods. Example 1 and Comparative Example Results of passing the flue gas desulfurization wastewater shown in Table 1 through 4 series of ion exchange equipment (1 and 2 series are examples of the present invention, 3 and 4 series are comparative examples of conventional method) Table 2 shows
It is shown in Table 3.

【table】

[Table] *Product name

【table】

[Table] Example 2 Concentrated regenerated effluent 1 of the second series of Example 1
When H ₂ SO ₄ was added to 10% and heated at 90° C. for 6 hours, S ₂ O ₆ became 0 mg/. 0.5 of this waste liquid is passed from column 2 (countercurrent) to column 1 prior to regeneration in the second train, and fresh NaCl is then added to column 1.
After reducing the amount to an equivalent amount and performing regeneration, the wastewater shown in Table 1 was passed through. The result is that the throughflow capacity is 64.8g/-R.
AsS ₂ O ₆ and COD of the treated water were 2 to 3 mg/, and S ₂ O ₆ was 0 mg/, which were good. Example 3 Extrusion drainage in the first line regeneration of Example 1
0.8 was collected in a separate container, and this liquid was passed through column 1 prior to the next regeneration of the first line. after that,
Fresh NaCl was reduced to 2.5 equivalents and regenerated according to the first series regeneration method, and the wastewater shown in Table 1 was passed through. The results were the same as in the first series of Table 2 for both throughflow capacity and treated water. Example 4 and Comparative Example When the wastewater shown in Table 4 was passed through the ion exchange devices of series 1 to 4 shown in Tables 2 and 3, the results shown in FIG. 3 were obtained.

[Table] Example 5 and Comparative Example A repeated water flow-regeneration test using the flue gas desulfurization wastewater shown in Table 5 in the ion exchange equipment of the 1st and 4th series in Tables 2 and 3. When I went to the 4th
The results shown in the figure were obtained.

[Table] In the present invention, two strong basic anion exchange resin towers are used.
The towers are installed in series and directly connected, and the water is passed through and regenerated in a counter-current manner between the towers, compared to the conventional method in which one strong basic anion exchange resin tower is installed and water is passed through and regenerated. It is possible to regenerate ion exchange resin extremely efficiently, eliminate its drawbacks, obtain treated water of good quality, and make it possible to demonstrate the advantages of strong basic anion exchange resin. It has many advantages over conventional methods that use weakly basic anion exchange resin towers, and is not only superior in resource and energy conservation compared to conventional methods, but also contributes to pollution prevention. It's large.

[Brief explanation of drawings]

1a and 1b are flow sheets showing the basic concept of the present invention, FIG. 2 is a flow sheet showing one embodiment of the present invention, and FIGS. It is a graph that also shows the results of a comparative example using a conventional method. 1...First tower, 2...Second tower, 3...Raw water tank,
4... Treated water tank, 5... Regenerant storage tank, 6... Concentrated waste liquid storage tank, 7... Recovery tank, 8... Decomposition tank.

Claims (1)

[Claims] 1 Flue gas desulfurization and denitrification wastewater is passed through a strongly basic anion exchange resin layer to eliminate COD components and N-S in the wastewater.
In the method of selective exchange adsorption of compounds, two strongly basic anion exchange resin towers are directly connected in series, and in the ion exchange treatment, the wastewater is passed from the first tower to the second tower, and the ion exchange A method for treating flue gas desulfurization and denitrification wastewater, which comprises passing a NaCl solution as a regenerating agent from a second tower to a first tower during resin regeneration processing. 2. The method according to claim 1, wherein the regeneration treatment for the second ion exchange resin column is carried out in a countercurrent manner. 3. The method according to claim 1 or 2, wherein in the regeneration treatment, the regenerated effluent is divided into a first half of the regenerated effluent with a high COD concentration and a second half of the regenerated effluent with a low COD concentration. 4. The method according to claim 3, wherein the regenerated waste liquid having a low COD concentration in the regeneration process is used in advance for the regeneration process of the first ion exchange resin column. 5 The regenerated waste liquid with a high COD concentration in the regeneration process is oxidatively decomposed, and the decomposed liquid obtained by the oxidative decomposition is transferred to either the first ion exchange resin tower or the second ion exchange resin tower. The method according to claim 3, wherein the method is used as a regenerating agent for at least one of the ion exchange resin columns. 6. The method according to claim 5, wherein a NaCl solution added to the decomposition liquid is used as the regenerating agent.