JP2020000962A - Treatment method of ns compound affecting cod of desulfurized wastewater - Google Patents

Abstract

To enable removal of all of five NS compounds affecting a COD value by utilizing a part of an existing facility, more particularly, active carbon.SOLUTION: There is provided a desulfurized wastewater treatment method in which desulfurized wastewater, to which powdered active carbon is added and an acid is added so as to adjust a pH to 2 or lower, is subjected to stirring treatment in an acid and active carbon treatment tank. Then, a flocculant and an alkaline solution are added to the desulfurized wastewater after the stirring treatment, thereby causing flocculation in a flocculation tank. Then, a flocculated substance is separated from the desulfurized wastewater in a separation tank, through which wastewater alone is allowed to pass.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a nitrogen-sulfur compound (hereinafter simply referred to as an NS compound) which affects the chemical oxygen demand (hereinafter referred to as COD) of desulfurization wastewater discharged from a desulfurization wastewater treatment facility of a thermal power plant. ). More specifically, the present invention relates to a method for treating NS compounds that affect COD mainly by using activated carbon.

  In a thermal power plant desulfurization wastewater treatment system, an activated carbon packed tower is used for the treatment of organic COD components, and an ion exchange resin is introduced for the treatment of dithionic acid. An unexplained COD increase event of unknown cause has occurred, and there is a problem that effective measures may not be taken in some cases. It is feared that this problem will be exacerbated by the diversification of coal types used, changes in operating conditions, and stricter regulations, and measures are required.

  Therefore, when various studies and experiments were conducted on the unknown COD increase of desulfurization effluent not caused by organic substances or dithionic acid, it was found that NS compounds generated by reaction in flue gas desulfurization equipment were the cause (Non-patent document) 1, 2). There are eight types of NS compounds that may be generated in the desulfurization apparatus (see Table 1 and FIG. 13). They are roughly classified into five types of hydroxylamine NS compounds and three types of sulfamine NS compounds. Since the hydroxylamine-based NS compounds in the inside affect COD, it is desired that all of the five types of NS compounds are to be removed.

.
However, in the case of existing wastewater treatment equipment using activated carbon adsorption, it is not known whether NS compounds in desulfurization wastewater are removed or not. There is little information on the applicability to the compounds, and it was only confirmed that one of the five NS compounds (HATS) was removed (Non-patent Document 4). Can the other four NS compounds be adsorbed? It is not even predictable. Therefore, development of a wastewater treatment method and equipment capable of removing all five types of NS compounds in desulfurized wastewater is required.

  As a conventional NS compound treatment method, a sodium nitrite addition method of treating a hydrolyzate of an NS compound by addition of nitrous acid under acidic conditions (Non-Patent Document 3) or a method of adding sodium hypochlorite There are known a sodium hypochlorite addition method for treating a hydrolyzate of an NS compound and an acid hydrolysis method for hydrolyzing an NS compound under acidity such as sulfuric acid, and these are applied to flue gas desulfurization equipment. Has been proposed (Patent Document 1).

JP 05-31483 A

Shin Aota, Hiroyuki Masaki, Seiichi Oyama. Literature Survey on NS Compounds as Refractory COD Components in Desulfurization Wastewater-Generation Mechanism, Treatment Technology, and Measurement Technology-Central Research Institute of Electric Power Industry V13301. 2013. Arata Aota, Seiichi Oyama. Management technology of NS compounds as difficult-to-process COD components-Synthesis of NS compounds, analysis of analysis conditions, identification of NS compounds in desulfurization effluent-. Central Research Institute of Electric Power Industry Research Report V14002. Monthly issue Takashi Tanaka, Takahisa Yokoyama, Michio Koizumi, Yoshimi Ishihara. Flue Gas Denitrification Wet Reduction Method (Part 5)-Reaction Rate and Reactive Organism of Nitrite and Sulfite-Central Research Institute of Electric Power Industry 278019. Hiraga Yuki, et al. Quantitative analysis and removal of hydroxylamine trisulfonic acid (HATS) in wastewater. Shikoku Electric Power, Shikoku Research Institute, 2015. 102, p.1-5.

  However, in the case of the sodium nitrite addition method, it is necessary to add an excessive amount of sodium nitrite, and sodium nitrite remaining in the wastewater itself also affects COD. With the need for additional processing steps and equipment (so-called oxidation processing steps and equipment). The same applies to the hypochlorous acid addition method, in which it is necessary to add an excessive amount of sodium hypochlorite, and a process / equipment (a so-called reducing agent treatment) for treating hypochlorous acid remaining in the latter stage Process / equipment). For this reason, these treatment methods have many problems as a treatment method of NS compounds generated irregularly, and cannot be said to be preferable.

  In the case of the hydrolysis method, among the five NS compounds, HAODS, HAMS, and HAOMS cannot be treated by themselves because they are relatively stable to acids. In addition, the remaining two NS compounds, HATS and HADS, also produce HAODS and HAMS after hydrolysis. For this reason, the treatment by the acid hydrolysis method alone is completely impossible.

  The present invention focuses on existing wastewater treatment technologies introduced for the treatment of organic COD components and dithionic acid in thermal power plants, and affects COD values by utilizing some of the existing facilities. It is an object of the present invention to provide a treatment method capable of removing all five NS compounds. More specifically, an object of the present invention is to provide a method for treating five types of NS compounds that affect COD using activated carbon.

  As a result of various studies and experiments conducted by the present inventors in order to achieve the object, a normal activated carbon packed column that simply allows activated carbon to pass without adjusting the temperature or pH (that is, at around pH 7 at room temperature). It was common knowledge that the NS compound was not usually removed, but it was found that the NS compound could be adsorbed on activated carbon by adjusting the pH or changing the temperature.

That is, conventionally, it has been considered that an ordinary activated carbon packed tower cannot process NS compounds because HADS and HATS pass through. This seems to be due to the fact that, among the five NS compounds that affect COD, HATS is most accumulated in the desulfurization absorbing solution of the flue gas desulfurization unit and the concentration thereof is greatly affected by the increase in concentration. . HATS, which is one of the hydroxylamine compounds, is a reaction product of bisulfite ion (HSO ₃ ⁻ ) and nitrite ion (NO ₂ ⁻ ) in the desulfurization absorption solution as shown in the production route of FIG. When produced after passing through a certain HADS and the desulfurization absorption liquid and desulfurization effluent are neutral to alkaline, the hydrolysis of HATS is suppressed, so that the form of HATS is maintained without being changed to other hydroxylamine compounds. It is believed that. From this, HATS is presumed to be the main cause of COD increase (Non-Patent Document 1).

  Since HADS as a starting material of the NS compound and HATS having the highest concentration pass through the activated carbon packed column, there was originally a problem that COD did not decrease, and it was thought that activated carbon cannot usually remove NS compounds. As a result of research conducted by the present inventors, it has been found that the removal of some NS compounds can be achieved by simply passing the temperature and pH unadjusted (that is, at room temperature around pH 7), and It has been found that adjusting the pH and pH enables removal of all NS compounds.

  In addition, it was impossible to predict whether or not NS compounds could be adsorbed even with general wastewater treatment technology utilizing ion exchange resins. However, as a result of research and experiments by the present inventors, those that can be treated And the fact that there are some that cannot be processed.

  That is, since the desulfurization effluent contains a very large amount of desulfurization ions, the sulfate ions and the anion exchange resin are in a competitive relationship. Therefore, those that are more easily attached to the ion exchange resin than the sulfate ions can be removed. However, those that do not easily adhere to the ion exchange resin will remain in the wastewater. For this reason, it was found that three types of HADS, HAODS and HATS can be removed, but two types of HAMS and HAOMS are not removed.

  Thus, in the general wastewater treatment using activated carbon and the wastewater treatment using an anion exchange resin, there are NS compounds that can be removed and NS compounds that cannot be removed, and from the knowledge that they have a complementary relationship, By combining these, it was found that all NS compounds could be removed.

    The desulfurization wastewater treatment method of the present invention is based on such a finding, and powdery activated carbon is added to desulfurization wastewater and an acid is added to adjust the pH to 2 or less, and the mixture is stirred in an acid activated carbon treatment tank. After adding a flocculant and an alkaline solution to the desulfurization wastewater and coagulating in a coagulation tank, the desulfurization wastewater and the aggregate are separated in a separation tank so that only the wastewater passes.

  Further, the desulfurization wastewater treatment method according to the second aspect of the present invention is characterized in that after adding an acid to the desulfurization wastewater in an acid treatment tank and stirring to adjust the pH to 2 or less, the desulfurization wastewater after the pH adjustment is passed through an activated carbon packed tower. The wastewater is allowed to pass through, and only the wastewater after the NS compound is attached to and removed from the activated carbon packed tower is allowed to pass.

  In the desulfurization wastewater treatment method according to the present invention, the pH is adjusted to at least 40 ° C., preferably 50 ° C., at the time of pH adjustment before contacting with activated carbon.

  Furthermore, the desulfurization wastewater treatment method according to the present invention is characterized in that an ion exchange resin packed tower and an activated carbon packed tower are connected in series to a desulfurization wastewater path, and ion exchange and activated carbon adsorption are performed continuously.

  According to the desulfurization wastewater treatment method of the present invention, it is possible to remove all NS compounds that affect the COD value by utilizing a part of the existing facilities. More specifically, the present invention can carry out the treatment of all NS compounds that affect COD by utilizing activated carbon, which is a general existing wastewater treatment facility in a thermal power plant.

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows one Embodiment of the processing method of the NS compound which affects COD of the desulfurization wastewater of this invention, (A) is a batch type processing system using activated carbon, (B) is a continuous type processing using activated carbon. (C) is a continuous processing system utilizing an ion exchange resin and activated carbon. It is the schematic which shows an example of the experimental apparatus of the processing method of the NS compound which affects COD of the desulfurization waste water of this invention, (A) is a continuous process using activated carbon, (B) is an ion exchange resin and activated carbon. This is for implementing continuous processing that has been utilized. It is a graph which shows the influence of pH and temperature in the hydrolysis of NS compound, (A) shows HAMS, (B) shows HAOMS, (C) shows HADS, (D) shows HAODS, and (E) shows HATS. It is a graph which shows the change of the removal rate of 5 types of NS compounds in the adsorption test by an ion exchange resin (WBA) column. It is a graph which shows the influence of pH and temperature in activated carbon treatment, (A) shows HAMS, (B) shows HAOMS, (C) shows HADS, (D) shows HAODS, and (E) shows HATS. It is a graph which shows the removal rate and product in activated carbon treatment of HAMS and HAOMS. It is a graph which shows the removal rate in the activated carbon column test of HAMS and HAOMS. It is a graph which shows the processing result of the desulfurization waste water which added the NS compound by the ion exchange resin. It is a graph which shows the processing result of the desulfurization wastewater which added the NS compound by the activated carbon. It is a graph which shows the processing result of HATS by acidic activated carbon processing. It is a graph which shows the processing result of HADS by acidic activated carbon processing. It is a graph which shows the treatment result of NS compound by ion exchange resin and activated carbon treatment. FIG. 3 is a diagram showing the mechanism of formation of an NS compound.

  Hereinafter, the configuration of the present invention will be described in detail based on an embodiment shown in the drawings.

  The desulfurization wastewater treatment method of the present invention focuses on existing wastewater treatment technologies introduced for treating organic COD components and dithionic acid in a thermal power plant, and utilizes a part of existing facilities. This makes it possible to remove all of the five NS compounds that affect the COD value. For example, in a thermal power plant or the like, a general activated carbon packed tower (or including a batch type activated carbon treatment facility) or an ion-exchange resin packed tower is used as a wastewater treatment technology, and in particular, a wastewater treatment technology using activated carbon is utilized. Of the five NS compounds that affect COD.

  Existing activated carbon packing towers (or batch type activated carbon treatment equipment) that are commonly used as existing wastewater treatment technology are desulfurized wastewater at ordinary temperature and pH 7 as they are when ordinary activated carbon treatment is performed, that is, without adjusting pH or temperature. It has been clarified by the present invention that HAMS and HAOMS can be removed even when treating. It is also clear that the other three NS compounds, HADS, HAODS and HATS, can be removed by activated carbon treatment, for example, by heating to at least 40 ° C. at pH 2 by operating under acidic conditions. Was. Further, in some NS compounds, HADS can be removed to a removal rate of about 1.0 and HAODS can be removed almost only by heating to at least 40 ° C., preferably about 50 ° C. even under acidic conditions of about pH 4. Was found.

  On the other hand, in the case of wastewater treatment using an ion exchange resin, it was found that three NS compounds of HADS, HAODS and HATS can be removed, but two of HAMS and HAOMS are not removed. In addition, it has been found that in the ordinary wastewater treatment using activated carbon and the wastewater treatment using an anion exchange resin, there are NS compounds that can be removed and NS compounds that cannot be removed, and that they have a complementary relationship.

  From this, when only the activated carbon packed tower (or the batch type activated carbon treatment equipment is included) is used to remove all five NS compounds, the pH is adjusted or the temperature is changed. It has been found that when the ion exchange resin treatment and the activated carbon treatment are combined, neither pH adjustment nor temperature adjustment to the desulfurization effluent is required.

  FIG. 1A shows one embodiment of a desulfurization wastewater treatment method according to the present invention. This desulfurization wastewater treatment system is a batch treatment (batch treatment) system, which is composed of an acid activated carbon treatment tank 1, a coagulation tank 2, and a separation tank 3. Is added under acidic conditions, for example, to a pH of 2 or less, and the mixture is stirred in the acid activated carbon treatment tank 1 for a predetermined period of time, for example, 2 hours. The coagulant 7 and the alkali solution 8 are added to the desulfurization wastewater 4 after the stirring treatment. After the coagulation and neutralization, the desulfurization wastewater 4 and the aggregate (not shown) are separated in the separation tank 3 so that only the wastewater 9 passes. It is preferable to use, for example, hydrochloric acid as the acid, a sulfate band or polyaluminum chloride (PAC) as the coagulant, and sodium hydroxide or the like as the alkaline solution.

  Here, the stirring treatment in the acid activated carbon treatment tank 1 is performed by adjusting the pH to 2 or less under acidic conditions, and heating the mixture from room temperature to at least 40 ° C, preferably 50 ° C. The concentration of the powdered activated carbon was, for example, 1 w / v% (per dose), but this amount was experimentally adopted as an amount sufficient to achieve the purpose, and is limited to this amount. There is no reason, nor is it an optimized amount. It will be appropriately added as needed. Further, the stirring time varies depending on the capacity of the vessel / column in the case of batch processing, but in the experiment, the purpose was achieved in about 2 hours (per one batch), for example. In the present system, the above-described stirring time, the concentration of the powdered activated carbon, and the like do not show optimum values, and are not particularly limited to these amounts. The temperature of the desulfurization effluent 4 in the acid activated carbon treatment tank 1 is preferably heated in order to promote hydrolysis. However, if the temperature is set as high as, for example, about 50 ° C., removal of NS compounds proceeds, and the reaction proceeds. Although desirable for reducing the size of the tank, it is not always necessary to set the temperature to 50 ° C. From experiments, a sufficient effect was obtained even at 40 ° C.

  The removal of the NS compound is more preferably to promote the hydrolysis by heating, but in some cases, it can be carried out even at room temperature. In the case of the present embodiment, the treatment is performed at pH 2, but the treatment is not particularly limited thereto. For example, a sufficient effect was obtained even at about pH 4. As is clear from the experimental results, if the heating temperature is set higher, for example, if it is set to 50 ° C., a sufficient effect of removing the NS compound can be obtained even at pH 4. On the other hand, of course, since it is hydrolysis, if the temperature is raised to a temperature higher than 50 ° C., the removal effect is further improved, but it is not preferable to heat to a temperature higher than necessary from a thermoeconomic point of view. It is desirable to be about 50 ° C. in relation to the size and capacity of the column of the tower and the processing time.

  FIG. 1B shows another embodiment of the desulfurization wastewater treatment method according to the present invention. This desulfurization wastewater treatment system is a continuous treatment system, and is composed of an acid treatment tank 11 and an activated carbon packed tower 12. The acid 13 is added to the desulfurization wastewater 4 to adjust the pH to 2 or less, and the acid treatment tank 11 is stirred. The desulfurized effluent after the treatment and the stirring treatment is supplied to and passed through the activated carbon packed tower 12, and is brought into contact with activated carbon to remove NS compounds and pass only the effluent 9.

  Here, the stirring treatment in the acid treatment tank 11 is preferably performed after adding an acid such as hydrochloric acid or sulfuric acid to adjust the pH to, for example, 2 and heating the mixture in a temperature range from normal temperature to 50 ° C. It is preferable that the heating temperature be set higher, because hydrolysis can be promoted and the size of the reaction vessel can be reduced. However, it is not always necessary to set the heating temperature to about 50 ° C. In experiments, a sufficient effect was obtained even at 40 ° C. Since the wastewater that has passed through the activated carbon packed tower remains acidic, it is preferable that the wastewater be subjected to a neutralization treatment downstream if necessary.

  FIG. 1C shows still another embodiment of the desulfurization wastewater treatment method according to the present invention. This desulfurization wastewater treatment system enables continuous treatment, and is constituted by an ion-exchange resin packed tower 21 and an activated carbon packed tower 22. In the ion-exchange resin packed tower 21, a part of NS compounds, namely, HADS, HAODS After the removal of HATS and HATS, the activated carbon packed tower 22 removes the remaining part of the NS compound, that is, HAMS and HAOMS, so that only the wastewater 9 passes. Therefore, all five NS compounds can be removed.

  The activated carbon packed tower or the ion-exchange resin packed tower used in the above embodiment is generally provided as existing equipment for wastewater treatment of desulfurization wastewater discharged from the desulfurization wastewater treatment equipment of a thermal power plant. By utilizing a part of the structure, installation space and equipment costs can be reduced. At the same time, the treatment can be carried out in parallel with the treatment of another treatment object, that is, an organic COD component and dithionic acid.

  The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the spirit of the present invention.

  Conducted batch tests using simulated wastewater, column tests, and column tests using actual wastewater to examine the possibility of treatment with ion exchange resin and activated carbon for the five NS compounds that may be generated in desulfurization wastewater. I checked.

[Reagents, etc.]
As NS compounds, five types (HAMS, HAOMS, HADS, HAODS, HATS) which influence the COD increase were tested (Table 1). Of these, HAOMS was obtained from Wako Pure Chemical Industries. Since four types other than HAOMS were not commercially available, they were synthesized. Assuming that each NS compound has a purity of 100%, a 50 mM concentrated solution was prepared using a potassium hydroxide solution (pH 10 to 12) or a buffer solution (pH 2 to 7), and was appropriately diluted before use.

Based on the fact that the NS compound is an anion, the ion exchange resin is a weakly basic anion exchange resin which is also used for removing dithionic acid (S ₂ O ₆ ²⁻ ) which is a COD component of desulfurization effluent. An anion exchange resin type II was used. As the weakly basic anion exchange resin and the strongly basic anion exchange resin type II, Dow Chemical DOWEX Marathon WBA (hereinafter, WBA) and DOWEX Marathon A2 (hereinafter, A2) available as reagents were used. Each ion exchange resin was washed with ultrapure water, a 4% sodium hydroxide solution, 1 mol / L hydrochloric acid and ultrapure water before use, and conditioned.

  As the activated carbon, powdered activated carbon (neutral, Wako Pure Chemical Industries; hereinafter, powdered activated carbon) and crushed activated carbon (particle size: 2 to 5 mm, Wako Pure Chemical Industries, hereinafter, crushed activated carbon) were used. The powdered activated carbon was used as it was, and the crushed activated carbon was used after washing with ultrapure water.

[Degradation characteristics of NS compounds by hydrolysis and nitrous acid addition method]
In order to grasp the degradation characteristics of the five NS compounds by the hydrolysis and nitrite addition methods, batch tests were conducted at the beaker level with different pH and temperature conditions.
1) Hydrolysis NS compounds were hydrolyzed with respect to the five NS compounds under the conditions of pH 2, 4, 7 and room temperature (about 25 ° C.), 40 ° C. and 50 ° C. A 10 mM phosphate buffer was used under the conditions of pH 2 and 7, and a 10 mM acetic acid / sodium acetate buffer was used at pH 4, and a concentrated solution of each NS compound was added to the buffer so that the initial concentration was 0.5 mM. The mixture was allowed to stand at room temperature or in a constant temperature water bath at 40 ° C. and 50 ° C., and the concentration of the NS compound was measured after 1 hour. From the NS compound concentrations before and after the treatment, the decomposition rate (R) was calculated using equation (1).

Here, [A] ₀ and [A] indicate the NS compound concentration [mmol / L] before and after the treatment.
2) Addition method of nitrous acid As in the batch test of acid hydrolysis, pH 2,4,7 were carried out at room temperature (about 25 ° C), 40 ° C and 50 ° C. Sodium nitrite was added to an NS compound solution adjusted to 0.5 mM with a buffer at each pH to a concentration of 5 mM, and the treatment was performed at each temperature. The decomposition rate (R) was calculated from the NS compound concentrations before and after the treatment in the same manner as in the acid hydrolysis.

[Removal characteristics of NS compound by ion exchange resin]
For the adsorption test of the NS compound on the ion exchange resin, a batch test at a beaker level and a column test were performed.

1) Batch test The treatment solution of each NS compound was adjusted to pH 5 with 1 mol / L hydrochloric acid using a 50 mM sodium chloride solution having an NS compound concentration of 0.5 mM. 1 g of the conditioned ion exchange resin (WBA and A2) was added to 50 mL of the treatment solution, and the mixture was stirred for 1 hour at room temperature on a rotating plate, and then the concentration of the NS compound in the treatment solution was analyzed. From the concentration of the NS compound, the removal rate (R) and the distribution coefficient (KdA) were calculated using the equations (1) and (2). The larger the value of the partition coefficient is, the easier it is to adsorb (ion-exchange) the ion-exchange resin, which is an index of the affinity with the ion-exchange resin.

Here, _{[A] R} is the concentration NS compound of an ion exchange resin [mmol / kg-R], V is the solution volume [L], ρ _R is the specific gravity of the ion-exchange resin [kg / L], _{W R} is added The weight [kg] of the ion-exchange resin thus obtained is shown.

2) Column test In the column test, in order to grasp the removal characteristics of the NS compound in the desulfurization wastewater by the ion exchange resin, the NS compound in the wastewater simulating the desulfurization wastewater (simulated wastewater) was treated. For the column test, a column (diameter 10 mm, length 150 mm) packed with conditioned ion exchange resin (WBA) was used. The simulated drainage was prepared using calcium chloride and sodium sulfate, with the components being Ca ²⁺ : 570 mg / L, Na ⁺ : 480 mg / L, Cl ⁻ : 1000 mg / L, SO ₄ ²⁻ : 1000 mg / L, and calcium chloride and sodium sulfate. The pH was set to 5. Before the test, the simulated wastewater was passed at a space velocity (hereinafter, SV) of 20 h- ¹ until the SO ₄ ^2- and Cl ^- concentrations at the column outlet became stable. Thereafter, the wastewater was switched to simulated wastewater containing 0.5 mM of the NS compound, and samples at the inlet and outlet of the column were collected with time to analyze the NS compound. The removal rate (R) was calculated from the concentration of the NS compound using the formula (3).
Here, [A] _in and [A] _out indicate the concentration [mmol / L] of the NS compound at the inlet and outlet of the column.

[Removal properties of NS compounds by activated carbon]
In the adsorption test of the activated carbon, a batch test at the beaker level and a column test were carried out in the same manner as the ion exchange resin adsorption test.

1) Batch test A concentrated solution of each NS compound was added to a 50 mM phosphate buffer (pH 2, 7) or a 50 mM acetic acid / sodium acetate buffer (pH 4) so as to have an initial concentration of 0.5 mM. 0.3 g of powdered activated carbon was added to 30 mL of treated water, and in the treated solution using a buffer solution, stirring was performed at room temperature, 40 ° C., and 50 ° C. using a rotating plate for 2 hours. After stirring, the treatment liquid was filtered with a filter having a pore size of 0.2 μm, and the concentration of the NS compound was analyzed. From the concentration of the NS compound, the removal rate was calculated by the equation (1). For some NS compounds (HAMS and HAOMS), in order to confirm the product after the treatment, a test was conducted with a treatment solution of 0.5 mM in ultrapure water, and sulfate ions (SO ₄ ²⁻ ), ammonia The concentrations of ions (NH ₄ ⁺ ), nitrite ions (NO ₂ ⁻ ), nitrate ions (NO ₃ ⁻ ), hydroxylamine (NH ₂ OH) and total nitrogen (TN) were analyzed. For SO ₄ ^{2-concentration,} to _SO ^{4 2-elution} from the activated carbon, the formula ⁽⁴⁾ _SO 4 ^2- increment minus _SO ^{4 2-a} eluted from the activated carbon with a (ΔSO ₄ ^2-) Calculated.

[Equation 4]
Δ [SO ₄ ²⁻ ] = [SO ₄ ²⁻ ] _t − [SO ₄ ²⁻ ] ₀ − [SO ₄ ²⁻ ] _AC
Here, [SO ₄ ²⁻ ] ₀ , [SO ₄ ²⁻ ] _t , and [SO ₄ ²⁻ ] _AC represent the SO ₄ ²⁻ concentration (mmol / L) eluted from the activated carbon before, after and after the treatment, respectively. Show. [SO ₄ ²⁻ ] _AC was determined from the amount of increase in the SO ₄ ²⁻ concentration by performing the same test on the treatment solution to which the NS compound was not added.

2) Column test The column test of activated carbon was performed for HAMS and HAOMS. A glass column (diameter 25 mm, length 120 mm) filled with about 60 mL of the washed crushed activated carbon was used. HAMS and HAOMS were adjusted to 0.5 mM with ultrapure water and adjusted to pH 7 to obtain treated water. The treated water was passed through the column at a flow rate of SV10 or 5h- ¹ until the NS compound concentration at the column outlet became stable. Thereafter, the treated water at the inlet and outlet of the column was collected, and the NS compound and SO ₄ ^2- concentration were analyzed. From the NS compound and the SO ₄ ²⁻ concentration, the removal rate (R) and the increase in SO ₄ ²⁻ (Δ [SO ₄ ²⁻ ]) were calculated using the formulas (3) and (4).

[Removal of NS compounds in actual wastewater]
1) Actual test wastewater Desulfurization wastewater was collected from one coal-fired power plant, and four types of NS compounds (HATS, HADS, HAODS, HAOMS) except HAMS were added to about 0.5 mM4. A desulfurization effluent containing various NS compounds was prepared (Table 2). Incidentally, HAMS is, Cl ^- for analysis in a high concentration of the waste water is difficult, the addition was omitted. The desulfurization effluent was stored under refrigeration and filtered with a filter having a pore size of 0.2 μm before use. The pH was not adjusted in the treatment with the activated carbon column, and the pH was adjusted to 5 with hydrochloric acid in the treatment with the ion exchange resin column.

2) Column test using actual wastewater In order to confirm the removal of the NS compound in the actual wastewater by the ion exchange resin and the activated carbon, the NS compound in the desulfurization wastewater was treated using a column filled with the ion exchange resin or the activated carbon. In the column test, a glass column (diameter 25 mm, length 120 mm) was filled with about 50 mL of ion exchange resin WBA or about 60 mL of crushed activated carbon. In the treatment with the ion exchange resin, the wastewater was passed at a flow rate of SV20h- ^{1 and in} the treatment with the activated carbon, the wastewater was passed at SV10h- ¹ or 5h- ¹ . After passing water over time collected treatment liquid column outlet, the NS _compound, S _{² O} ^{6 _2-,} were analyzed _SO ^{4 2-.}

[Examination of NS compound treatment method using existing treatment technology]
As a method for treating NS compounds by utilizing existing treatment technologies, a method combining acid hydrolysis and activated carbon treatment (acid activated carbon treatment) and a method combining ion exchange resin and activated carbon (ion exchange resin / fat activated carbon treatment) It was investigated.

FIG. 2 shows an outline of the test apparatus. As shown in FIG. 2 (A), the acidic activated carbon treatment mainly includes an acid treatment tank 11 and an activated carbon column 12. In the treatment step using activated carbon, unlike an ordinary operating condition, an acidic and heated treatment solution is used. Through water. As a treatment solution, a HATS or HADS solution 0.5 mM adjusted to pH 10 or more with 0.1 mol / L sodium hydroxide was used. In the acid treatment tank, the pH was adjusted to 2, and the acid hydrolysis reaction was performed under the conditions of a temperature of 50 ° C and a residence time of 1 hour. For pH adjustment, 2 mol / L phosphoric acid was used so that HAMS and SO ₄ ²⁻ concentration could be analyzed by ion chromatography. The activated carbon column 12 was used by filling a glass column (diameter 25 mm, length 120 mm) with about 60 mL of crushed activated carbon. The flow rate of the treatment liquid was set to SV5h- ¹ (5 mL / min) with respect to the activated carbon column 12. After passing the water, the treatment liquid at the outlet of the acid treatment tank 11 and the column 12 was sampled with time, and the concentration of each NS compound was analyzed. In the drawing, reference numeral 14 denotes a pH control sensor, and 15 denotes a temperature control sensor.

  In the ion-exchange resin / activated carbon treatment, as shown in FIG. 2B, the ion-exchange resin / activated carbon treatment mainly includes an ion-exchange resin column 21 and an activated carbon column 22. Each of the columns 21 and 22 was prepared by filling the above-mentioned glass column with about 50 mL of ion exchange resin WBA and about 60 mL of crushed activated carbon. The treatment liquid used was a simulated wastewater (a wastewater simulating desulfurization effluent) to which HAMS or four types of NS compounds excluding HAMS were added to a concentration of 0.5 mM and adjusted to pH 5 with 1 mol / L sulfuric acid. The flow rate of the treatment liquid was the same as in the acidic activated carbon treatment. After passing the water, the treatment liquid was sampled from each column outlet with time, and the concentration of each NS compound was analyzed.

[Analysis method]
The analysis sample was subjected to various analyses after being filtered through a filter having a pore size of 0.2 μm. The NS compounds and _S 2 _O ^{6 2-analysis,} using ion chromatography (Thermo Fisher Scientific, ICS1600). The analysis conditions were as follows: IonPac AS9-HC was used as a separation column for HAMS and HAOMS, and a 9 mM sodium carbonate solution was used as an eluent. HADS, _HAODS, using IonPac AS16 as separation column in S _{2 O} ^{6 2-analysis,} using a 30mM aqueous solution of sodium hydroxide as the eluent. For HATS analysis, IonPac AS16 was used as a separation column, and an 80 mM aqueous sodium hydroxide solution was used as an eluent. Since the retention time of HAMS is almost the same as that of chloride ion (Cl ⁻ ), when the solution contains Cl ⁻ , the calculation was performed using the TN concentration as an index.

TOC and TN were analyzed using a total organic carbon / total nitrogen analyzer (Toray Engineering). COD was analyzed according to JIS K0102 (2013) COD _Mn . SO ₄ ²⁻ , NO ₃ ⁻ , NO ₂ ⁻ , Cl ⁻ and NH ₄ ⁺ were analyzed using ion chromatography.

[Results and discussion]
[Degradation characteristics of NS compounds by hydrolysis and nitrite addition method]

1) Hydrolysis
FIG. 3 shows the results of examining the effects of pH and temperature on the hydrolysis of NS compounds. It was found that HAMS, HAOMS and HAODS hardly hydrolyzed in the condition range of this report (temperature; room temperature to 50 ° C., pH; 2 to 7, reaction time: 2 hours). HATS and HADS hardly hydrolyze at room temperature at pH 4 or higher, but at pH 2, hydrolysis was confirmed. The hydrolysis proceeded as the temperature increased, and almost all hydrolyzed at 40 ° C. or higher under the condition of pH2. Since the hydrolysis products of HATS and HADS are HAODS and HAMS, respectively, HAODS and HAMS accumulate after hydrolysis.
Therefore, in the hydrolysis under acidic conditions, it is difficult to decompose and remove the NS compound in the desulfurization wastewater.

[Removal characteristics of NS compound by ion exchange resin]

1) Batch test A batch test using two types of ion-exchange resins was performed to determine the partition coefficient of the NS compound in a 50 mM sodium chloride solution, and SO ₄ ²⁻ , NO ₃ ⁻ , and S ₂ O ₆ contained in the desulfurization wastewater were determined. Table ² was compared with ^2- . The distribution coefficient of HADS, HAODS, and HATS, which are divalent or trivalent ions, was about the same as that of S ₂ O ₆ ²⁻ and was found to be larger than that of SO ₄ ²⁻ . On the other hand, the partition coefficients of monovalent HAMS and HAOMS were almost the same as those of NO ₃ ^−, and were smaller than SO ₄ ²⁻ . If the valences are the same, the partition coefficient can be compared as the selectivity of the ion exchange resin. Therefore, the selectivity of the ion exchange resin has a relationship of SO ₄ ²⁻ <HADS <HAODS, S ₂ O ₆ ²⁻ . Also, generally ion exchange resins since it is easy to adsorb higher the valence, there HAMS, HAOMS, tendency such as ^{_{NO 3? <SO 4 2?}} <HATS as selectivity.

2) Column test The desulfurization effluent is a effluent with a high concentration of SO ₄ ²⁻ and Cl ⁻ . In order to examine whether the NS compound in the waste water can be treated with the ion exchange resin, the removal rate of the NS compound in the waste water simulating desulfurization waste water was confirmed using a column filled with the ion exchange resin (FIG. 4). ). It was confirmed that the removal rate of HAMS decreased immediately after passing through the column, and it was hardly removed in the desulfurization wastewater. The removal rate of HAOMS gradually decreased after passing water, and the removal rate was about 0.6 at the end of the test. On the other hand, _SO ^{4 2-high} NS compounds having partition coefficients than _{(HADS, HAODS, HATS) S} 2 O 6 2- and not detected substantially at the column outlet to the end of the study, during the study period, a stable desulfurization effluent Removal was confirmed.

As described above, among the five NS compounds, HADS, HAODS, and HATS of the five NS compounds are not ionized even in the desulfurization wastewater having a high SO ₄ ²⁻ concentration, although the adsorption characteristics may change depending on the material and structure of the base of the ion exchange resin. Removal by exchange resin is possible. On the other hand, it is difficult for HAMS and HAOMS to maintain a high removal rate in the treatment of desulfurization wastewater with an ion exchange resin.

[Removal properties of NS compounds by activated carbon]
1) Batch test In order to evaluate the adsorption characteristics of NS compounds by activated carbon, a batch test using powdered activated carbon was performed (FIG. 5). HAMS and HAOMS had high removal rates regardless of the processing conditions (pH; 2 to 7, temperature; room temperature to 50 ° C.). HAODS, HADS, and HATS tended to have a higher removal rate as the pH was lower and the temperature was higher. It was found that within the range performed in this test, there was a possibility that all NS compounds could be removed under conditions of pH 2 and 40 ° C. or higher. However, the treatment of desulfurization effluent with activated carbon is generally at room temperature and near neutrality, so it is difficult to remove HAODS, HADS and HATS in actual equipment.

When a batch test was performed using HAMS and HAODS diluted with ultrapure water, it was confirmed that after the treatment, the HA42 and HAODS decreased and the SO ₄ ²⁻ concentration increased (FIG. 6). The concentration was about 0.4 mM, and SO ₄ ²⁻ near the initial addition amount (about 0.5 mM) of HAMS and HAODS was detected. Also, _NH in the processing solution ^{_{4 +, NO 2 -, NO}} 3 -, was analyzed the concentration of _NH 2 OH and TN, in HAOMS, confirmed an increase in _NH ^{4 +,} the concentration is about 0.4mM It was found to be about the same as TN and SO ₄ ²⁻ concentrations. This suggests that HAOMS was decomposed into SO ₄ ²⁻ and NH ₄ ⁺ , and it is considered that activated carbon acted as a catalyst such as a hydrolysis reaction. On the other hand, in HAMS, no increase in the concentration of NH ₄ ⁺ or the like was observed, and TN also decreased to 0.04 mM or less. HAMS showed a reaction with activated carbon different from HAOMS, since TN decreased despite an increase in SO ₄ ²⁻ concentration. HAMS is known to react with carbonyl compounds such as ketones and aldehydes to form oximes, and it is possible that HAMS has reacted with functional groups on the surface of activated carbon.

2) Column test The activated carbon treatment in actual wastewater is generally performed by an adsorption tower filled with activated carbon. Therefore, in order to confirm the removal of HAMS and HAOMS by the column packed with activated carbon, 0.5 mM HAMS and HAOMS solution were passed through the column packed with crushed activated carbon at different flow rates (SV10h ^-1 and SV5h ^-1 ). Then, the removal rate was obtained (FIG. 7). Removal rate of HAMS and HAOMS are fast SV10h ^-1 in 0.8 and 0.5 of a flow rate, 0.9 and 0.8 becomes in SV5h ^-1, who HAMS is removal rate than HAOMS tended to be higher . In the batch test, almost all of the HAMS and HAOMS were removed, but in the column test, some remained after the treatment. This is probably due to the fact that the activated carbon column used in this test had a short length of 120 mm for the convenience of the experiment.

As described above, the activated carbon treatment may be applicable as a treatment method for HAMS and HAOMS even under ordinary operating conditions such as water temperature and pH by optimizing the capacity and flow rate of the adsorption tower. However, regarding HAOMS, an increase in NH ₄ ⁺ concentration after the treatment is expected, and it is necessary to separately consider nitrogen treatment depending on the HAOMS concentration in the wastewater.

[Removal of NS compounds in actual wastewater]
1) Ion-exchange resin column treatment Fig. 8 shows the result of passing through a column wastewater obtained by adding four types of NS compounds to desulfurization wastewater collected from a coal-fired power plant. HATS, HADS, and HAODS were not detected until the end of the test, and it was confirmed that HADS and HAODS could be removed by ion exchange resin in the actual wastewater as well as HATS. On the other hand, in the HAOMS, a decrease in the concentration was confirmed after the treatment, and the removal rate was about 59% on average.

From the above, it was found that HATS, HAODS, and HADS among the five NS compounds could be removed from the actual desulfurization wastewater by the treatment with the ion exchange resin. Although the concentration of HAOMS can be expected to be reduced, the removal rate may vary depending on the HAOMS concentration, SO ₄ ²⁻ concentration, etc. of the desulfurization wastewater. In this test, the addition of HAMS was omitted, but HAMS has a distribution coefficient similar to that of HAOMS (Table 3). Is low (FIG. 4), it is considered that the removal rate is the same as or lower than that of HAOMS in actual wastewater.

2) Activated carbon column treatment Fig. 9 shows the results of treating the desulfurized wastewater to which the NS compound was added with the activated carbon column. SO ₄ ^{2-concentration} stable HATS after, HADS and HAODS concentration hardly changes with the pretreatment, the removal rate of the average became 0-7% and low results. On the other hand, in HAOMS, a decrease in concentration was confirmed after the treatment, and removal of HAOMS by activated carbon was confirmed also in actual wastewater. However, since the average removal rate is about 0.6, it is necessary to optimize processing conditions such as column capacity and processing flow rate.

[Method of treating NS compounds using existing treatment technology]
The results of treating HATS and HADS by acidic activated carbon treatment are shown in FIGS. In the treatment solution to which HATS was added, HAODS was produced by hydrolysis in the acid treatment tank, and the concentration of the produced HAODS was reduced by activated carbon treatment (FIG. 10). The average concentrations of HATS and total NS compounds after treatment with activated carbon (average of 600-1800 mL of water flow) are about 0.01 mM and 0.08 mM, respectively. The removal rate of about 98% for HATS and about 83% for total NS compounds Met. In HADS, HAMS was produced in the acid treatment tank together with the decrease in HADS, and decreased after activated carbon treatment. The removal rates of HADS and total NS compounds after the activated carbon treatment were both as high as about 99%.

FIG. 12 shows the results obtained by treating the NS compound using a combination of an ion exchange resin and activated carbon. In the treatment liquids to which the four NS compounds except HAMS were added, almost all of them were removed after the treatment with the ion-exchange resin in all four kinds, and the removal rate was 99% or more on average (average of treated water amount of 600 to 1950 mL). (See FIG. 12A). In the study on the removal characteristics of the NS compound by the ion exchange resin and the removal of the NS compound in the actual wastewater, the treatment of the HAOMS with the ion exchange resin resulted in a part remaining in the treatment liquid. This, SO ₄ ^2-density difference and mock drainage column capacity of the ion exchange resin of the present study is considered to impact of less than the actual waste water. On the other hand, in the treatment solution to which HAMS was added, it was not removed by the ion exchange resin, and a decrease in the concentration was confirmed after the activated carbon treatment (see FIG. 12B). The HAMS removal rate after the activated carbon treatment was about 73% on average (as described above).

  From the above, it is possible to reduce the concentration of HATS or HADS, which is difficult to treat with an activated carbon packed tower under normal operating conditions, by installing an acid treatment tank and treating with activated carbon under acidic conditions. It has been shown that NS compounds can be treated as well. It was also shown that the combination of an ion exchange resin and activated carbon could remove five NS compounds and reduce the concentration.

[Summary of NS compound removal method using existing wastewater treatment technology]
It has been found that NS compounds that can be treated are different with general wastewater treatment techniques such as ion exchange resins and activated carbon. In order to treat all five NS compounds in the desulfurization effluent, a method using activated carbon under acidic conditions, a method combining ion-exchange resin and activated carbon treatment, or an acidic carbon treatment in activated carbon treatment, It is considered that a method of adding powdered activated carbon to the tank or a method of installing an acid treatment tank in front of the activated carbon packed tower can be used.

DESCRIPTION OF SYMBOLS 1 Acid activated carbon treatment tank 2 Coagulation tank 3 Separation tank 4 Desulfurization drainage 5 Powdered activated carbon 6 Acid 7 Coagulant 8 Alkaline solution 9 Drainage 11 Acid treatment tank 12 Activated carbon filling tower 13 Acid 21 Ion exchange resin filling tower 22 Activated carbon filling tower

Claims (5)

  The powdered activated carbon is added to the desulfurization wastewater and the acid is added to adjust the pH to 2 or less, and the mixture is stirred in an acid activated carbon treatment tank. The desulfurization wastewater treatment method, wherein the desulfurization wastewater and the aggregates are separated in a separation tank and only the wastewater is passed.   An acid is added to the desulfurization effluent in an acid treatment tank installed in front of the activated carbon packed tower and stirred to adjust the pH to 2 or less. Then, the desulfurized effluent after pH adjustment is passed through the activated carbon packed tower to remove NS compounds. A desulfurization wastewater treatment method, comprising attaching and removing the activated carbon in the activated carbon packed tower and passing only wastewater.   The desulfurization wastewater treatment method according to claim 1, wherein the desulfurization wastewater is heated to at least 40 ° C. during the pH adjustment.   The desulfurization wastewater treatment method according to claim 3, wherein the acid treatment is heated to 50 ° C.   A desulfurization wastewater treatment method characterized by connecting an ion exchange resin packed tower and an activated carbon packed tower in series to a desulfurization drainage system, and continuously performing ion exchange and activated carbon adsorption.