JP7162975B2 - Method for treating NS compounds that affect COD of desulfurization wastewater - Google Patents

Description

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

In the desulfurization wastewater treatment system of thermal power plants, an activated carbon filled tower is introduced for the treatment of organic COD components, and an ion exchange resin is introduced for the treatment of dithionic acid. It is a problem that there are cases where the phenomenon of increasing COD of unknown cause occurs, and effective countermeasures cannot be taken. It is feared that this problem will become more serious as the types of coal used are diversified, operating conditions are changed, and regulations are strengthened, and countermeasures are required.

Therefore, various studies and experiments were conducted on the increase in COD of desulfurization wastewater, which is not caused by organic matter or dithionic acid, and it was found that the cause was NS compounds generated by reaction in flue gas desulfurization equipment (non-patent document 1, 2). There are eight types of NS compounds that can be generated in the desulfurization apparatus (see Table 1 and FIG. 13), which are roughly divided into five types of hydroxylamine-based NS compounds and three types of sulfamine-based NS compounds. Since the hydroxylamine-based NS compounds in the group affect COD, it is desired that all five types of NS compounds be targeted for removal.

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However, in the case of existing wastewater treatment facilities using activated carbon adsorption, it is not clear whether or not NS compounds are removed from desulfurization wastewater. There is little information on the applicability to compounds, and only one of the five NS compounds (HATS) was confirmed to be removed (Non-Patent Document 4). It is unpredictable whether or not Therefore, there is a demand for the development of wastewater treatment methods and equipment capable of removing all five types of NS compounds in desulfurization wastewater.

Conventional methods for treating NS compounds include a sodium nitrite addition method (Non-Patent Document 3) in which a hydrolyzate of an NS compound is treated by adding nitrous acid under acidic conditions, and a method by adding sodium hypochlorite. A sodium hypochlorite addition method for treating hydrolysates of NS compounds and an acid hydrolysis method for hydrolysates of NS compounds under acidic conditions such as sulfuric acid are known, and these methods should be applied to flue gas desulfurization equipment. has been proposed (Patent Document 1).

JP-A-05-31483

Arata Aota, Hiroyuki Masaki, Seiichi Oyama. Literature survey on NS compounds as difficult-to-treat COD components in desulfurization wastewater - Formation mechanism, treatment technology, measurement technology - Central Research Institute of Electric Power Industry Research Report V13301. 2013. Arata Aota, Seiichi Oyama. Control technology for NS compounds as difficult-to-treat COD components -Synthesis of NS compounds and examination of analysis conditions, Identification of NS compounds in desulfurization wastewater-. Central Research Institute of Electric Power Industry Research Report V14002. monthly issue Tanaka, T., Yokoyama, T., Koizumi, M., Ishihara, Y. Flue gas denitrification wet reduction method (5th report) -Reaction rates and reactive organisms of nitrite and sulfite-. Central Research Institute of Electric Power Industry Research Report 278019. 1978. Yuki Hiraga, et al. Quantitative Analysis and Removal Method of Hydroxylamine Trisulfonic Acid (HATS) in Wastewater. Shikoku Electric Power Company, Shikoku Research Institute Annual Report.

However, in the case of the sodium nitrite addition method, it is necessary to add an excessive amount of sodium nitrite, and the sodium nitrite itself remaining in the wastewater also affects COD. This entails the problem of further requiring a treatment process/equipment (so-called oxidation treatment process/equipment). In addition, the same is true for the hypochlorous acid addition method, and it is necessary to add an excessive amount of sodium hypochlorite. process/equipment). For this reason, these treatment methods have many problems as treatment methods for NS compounds that occur irregularly, and cannot be said to be preferable.

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

The present invention focuses on the existing wastewater treatment technology that has been introduced for the treatment of organic COD components and the treatment of dithionic acid in thermal power plants, and utilizes part of the existing equipment to affect the COD value. An object of the present invention is to provide a treatment method capable of removing all five types of NS compounds. More specifically, the object of the present invention is to provide a method for treating five NS compounds that affect COD using activated carbon.

In order to achieve this object, the inventors of the present invention conducted various studies and experiments, and as a result, a normal activated carbon packed tower that simply allows activated carbon to pass through without adjusting the temperature or pH (that is, at around pH 7 at room temperature) It was common knowledge that the NS compounds were not usually removed in the conventional method, but it was found that the NS compounds could be adsorbed onto the activated carbon by adjusting the pH or changing the temperature.

That is, conventionally, it was thought that NS compounds could not be treated in ordinary activated carbon-packed towers because HADS and HATS pass through them. Among the five types of NS compounds that affect COD, HATS is the most accumulated in the desulfurization absorption liquid of the flue gas desulfurization unit, and it is thought that this has a large effect on the increase in concentration. . HATS, which is one of the hydroxylamine compounds, is a reaction product of hydrogen sulfite ions (HSO ₃ ⁻ ) and nitrite ions (NO ₂ ⁻ ) in the desulfurization absorbent, as shown in the production route of FIG. When the desulfurization absorbent and desulfurization effluent are neutral to alkaline, the hydrolysis of HATS is suppressed, so it does not change to other hydroxylamine compounds and maintains the form of HATS. It is believed that From this, HATS is presumed to be the main factor of COD increase (Non-Patent Document 1).

Since HADS, which is the starting material for the NS compounds, and HATS, which has the highest concentration, pass through the activated carbon packed tower, there was originally a problem that the COD did not decrease, and it was thought that the NS compounds could not normally be removed with activated carbon. , as a result of research by the present inventors, it was possible to remove some of the NS compounds simply by passing the temperature and pH unadjusted (that is, at room temperature and around pH 7), and that the temperature It has been found that all NS compounds can be removed by adjusting the pH.

The desulfurization wastewater treatment method of the present invention is based on such knowledge, and comprises adding powdered activated carbon to desulfurization wastewater containing NS compounds that affect the COD value of HAMS, HAOMS, HADS, HAODS, and HATS, and adding an acid. It is added to adjust the pH to 2 or less, stirred for 2 hours in an acid activated carbon treatment tank within the range of room temperature to 50 ° C., a flocculant and an alkaline solution are added to the desulfurized waste water after the agitation treatment, and flocculated in the flocculation tank. After that, the desulfurization waste water and the aggregates are separated in a separation tank, and only the waste water is allowed to pass through.

Further, in the desulfurization wastewater treatment method according to the second aspect of the invention, acid is added to desulfurization wastewater containing NS compounds that affect the COD value of five kinds of HAMS, HAOMS, HADS, HAODS, and HATS in the acid treatment tank. The pH was adjusted to 2 or less by stirring at 50° C. for 1 hour , and then the pH-adjusted desulfurization effluent was passed through the activated carbon packed tower at a flow rate of SV5h ⁻¹ to remove the NS compound from the activated carbon packed tower. It is attached to the activated carbon inside and removed, allowing only waste water to pass through.

Further, in the desulfurization wastewater treatment method according to the present invention, the water is heated to at least 40°C, preferably 50°C during pH adjustment before contact with activated carbon.

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 part of the existing equipment. More specifically, the present invention can utilize activated carbon, which is a common existing wastewater treatment facility in thermal power plants, to treat all NS compounds that affect COD.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram showing one embodiment of a method for treating NS compounds that affect the COD of desulfurization wastewater according to the present invention, in which (A) is a batch type treatment system using activated carbon, and (B) is a continuous treatment using activated carbon. System (C) is a continuous treatment system utilizing ion exchange resin and activated carbon. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram showing an example of an experimental apparatus for the method of treating NS compounds that affect the COD of desulfurization wastewater according to the present invention, where (A) is a continuous treatment using activated carbon, and (B) is an ion exchange resin and activated carbon. It is intended to perform an active continuous process. 1 is a graph showing the effects of pH and temperature on the hydrolysis of NS compounds, (A) HAMS, (B) HAOMS, (C) HADS, (D) HAODS, and (E) HATS, respectively. 4 is a graph showing changes in the removal rate of five NS compounds in an adsorption test using an ion exchange resin (WBA) column. It is a graph which shows the influence of pH and temperature in activated carbon treatment, (A) HAMS, (B) HAOMS, (C) HADS, (D) HAODS, and (E) HATS, respectively. 1 is a graph showing removal rate and products in activated carbon treatment of HAMS and HAOMS. 1 is a graph showing removal rates in activated carbon column tests for HAMS and HAOMS. 4 is a graph showing the results of treating desulfurized wastewater to which an NS compound was added using an ion-exchange resin. 4 is a graph showing the results of treating desulfurization wastewater to which an NS compound was added with activated carbon. It is a graph which shows the processing result of HATS by acid activated carbon processing. It is a graph which shows the processing result of HADS by acidic activated carbon processing. 4 is a graph showing the results of treatment of NS compounds by ion-exchange resin/activated carbon treatment. FIG. 2 is a diagram of the formation mechanism of NS compounds.

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

The desulfurization wastewater treatment method of the present invention focuses on the existing wastewater treatment technology that has been introduced for the treatment of organic COD components and the treatment of dithionic acid in thermal power plants, and utilizes a part of the existing equipment. It makes it possible to remove all five NS compounds that affect the COD value. For example, in thermal power plants, etc., we utilize general activated carbon packed towers (or batch-type activated carbon treatment equipment) and ion exchange resin packed towers as wastewater treatment technology. Therefore, all five NS compounds that affect COD are treated and used.

A general activated carbon packed tower (or batch-type activated carbon treatment facility) as an existing wastewater treatment technology is used when normal activated carbon treatment is performed, that is, desulfurized wastewater is treated at normal temperature and pH 7 without adjusting pH or temperature. It has been clarified by the present invention and the like that HAMS and HAOMS can be removed even when treating . In addition, it is clear that the other three NS compounds, HADS, HAODS and HATS, can also be removed by activated carbon treatment by heating under acidic conditions, for example, by heating to at least 40°C at pH 2. was made Furthermore, in some NS compounds, HADS can be removed to a removal rate of about 1.0, and HAODS can be almost removed simply by heating to at least 40°C, preferably about 50°C, even in an acidic environment of about pH 4. I came to know.

On the other hand, in the case of wastewater treatment with an ion exchange resin, three types of NS compounds, HADS, HAODS, and HATS, can be removed, but two types, HAMS and HAOMS, are not removed. They also found that there are NS compounds that can be removed and NS compounds that cannot be removed by normal wastewater treatment with activated carbon and wastewater treatment with an anion exchange resin, and that they are in a complementary relationship.

Therefore, in order to remove all five types of NS compounds, when using only an activated carbon packed tower (or a batch-type activated carbon treatment facility), it is necessary to adjust the pH or change the temperature. It was found that when ion exchange resin treatment and activated carbon treatment are combined, it is not necessary to adjust the pH or temperature of the desulfurization effluent.

FIG. 1(A) shows an embodiment of the desulfurization wastewater treatment method according to the present invention. This desulfurization wastewater treatment system is a batch treatment (batch treatment) system, and is composed of an acid activated carbon treatment tank 1, a flocculation tank 2, and a separation tank 3. Powdered activated carbon 5 is added to desulfurization wastewater 4, and acid 6 is added to adjust the pH to 2 or less under acidity, for example, and stirred in the acid activated carbon treatment tank 1 for a predetermined time, for example, 2 hours. After flocculation and neutralization, desulfurization waste water 4 and aggregates (not shown) are separated in a separation tank 3, and only waste water 9 is allowed to pass through. It is preferable to use, for example, hydrochloric acid as the acid, aluminum sulfate or polyaluminum chloride (PAC) as the coagulant, and sodium hydroxide as the alkaline solution.

Here, the stirring treatment in the acid-activated carbon treatment tank 1 is carried out by heating from room temperature to at least 40° C., preferably 50° C., under acidic conditions, preferably adjusted to pH 2 or less. The concentration of the powdered activated carbon was, for example, 1 w/v% (per dose), but this amount was experimentally adopted as a sufficient amount to achieve the purpose, and a specific amount limited to this amount was used. No reason, and not an optimized amount. It will be added appropriately as needed. In the case of batch processing, the stirring time varies depending on the capacity of the container and column, but in the experiment, the purpose was achieved with, for example, about 2 hours (per batch). In this system, the above-described stirring time, powdered activated carbon addition concentration, and the like do not indicate optimum values, and are not particularly limited to these amounts. Further, the temperature of the desulfurization waste water 4 in the acid-activated carbon treatment tank 1 is preferably heated in order to promote hydrolysis. Although it is desirable to make the tank smaller, it is not always necessary to set the temperature to 50°C. Experiments have shown that even 40°C is sufficiently effective.

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

FIG. 1(B) 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. An acid 13 is added to the desulfurization wastewater 4 to adjust the pH to 2 or less, and the mixture is stirred in the acid treatment tank 11. After the desulfurization treatment and stirring, the desulfurized waste water is supplied to the activated carbon packed tower 12 and passed through it to contact with the activated carbon to remove the NS compounds and allow only the waste water 9 to pass through.

Here, the stirring treatment in the acid treatment tank 11 is preferably carried out after adjusting the pH to, for example, 2 by adding an acid such as hydrochloric acid or sulfuric acid, and heating in the temperature range from normal temperature to 50°C. It is preferable to set the heating temperature higher because hydrolysis is promoted and the reaction vessel can be made smaller. Since the waste water that has passed through the activated carbon-filled tower remains acidic, it is preferable to neutralize the waste water downstream, if necessary, before discharging the waste water.

FIG. 1(C) 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 composed of an ion-exchange resin-filled tower 21 and an activated carbon-filled tower 22. In the ion-exchange resin-filled tower 21, part of the NS compounds, ie, HADS and HAODS and HATS are removed, the remaining part of the NS compounds, that is, HAMS and HAOMS are removed in the activated carbon packed tower 22, and only the waste water 9 is allowed to pass. Therefore, removal of all five NS compounds is possible.

The activated carbon-filled tower or ion-exchange resin-filled tower used in the above embodiments is generally provided as existing equipment for wastewater treatment of desulfurized wastewater discharged from the desulfurized wastewater treatment equipment of thermal power plants. It is possible to reduce the installation space and equipment cost by utilizing a part of the karari. At the same time, it can be treated in parallel with the treatment of other objects to be treated, that is, organic COD components and dithionic acid.

Although the above embodiment is an example of the preferred embodiment of the present invention, the present invention is not limited to this, and can be modified in various ways without departing from the gist of the present invention.

Batch tests using simulated waste water, column tests, and column tests using actual waste water were conducted to investigate the possibility of treatment with ion-exchange resin and activated carbon for 5 types of NS compounds that may be generated in desulfurization waste water. and investigated.

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

Based _on the fact that NS compounds _are ^anions , ion exchange resins are weakly basic anion exchange resins and strongly basic Anion exchange resin type II was used. Weakly basic anion exchange resin and strongly basic anion exchange resin type II used Dow Chemical DOWEX Marathon WBA (hereafter WBA) and DOWEX Marathon A2 (hereafter A2) available as reagents. All ion exchange resins were conditioned by washing with ultrapure water, 4% sodium hydroxide solution, 1 mol/L hydrochloric acid and ultrapure water before use.

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 Chemicals; hereinafter crushed activated carbon) were used. Powdered activated carbon was used as it was, and crushed activated carbon was used after washing with ultrapure water.

[Decomposition characteristics of NS compounds by hydrolysis and nitrous acid addition method]
In order to understand the degradation characteristics of five NS compounds by hydrolysis and nitrous acid addition, beaker-level batch tests were carried out under different pH and temperature conditions.
1) Hydrolysis Five NS compounds were hydrolyzed under the conditions of pH of 2, 4 and 7 and room temperature (about 25°C), 40°C and 50°C. A 10 mM phosphate buffer was used at pH 2 and 7, and a 10 mM acetic acid/sodium acetate buffer was used at pH 4. A concentrated solution of each NS compound was added to the buffer to an initial concentration of 0.5 mM. It was allowed to stand in a constant temperature water bath at room temperature or at 40°C or 50°C, and the concentration of the NS compound was measured after 1 hour. A decomposition rate (R) was calculated from the NS compound concentrations before and after the treatment using the formula (1).

ここで、［Ａ］_０と［Ａ］は処理前後のＮＳ化合物濃度［ｍｍｏｌ／Ｌ］を示す。
2）亜硝酸添加法
酸加水分解の回分試験と同様に、ｐＨ ２，４，７、温度を室温（約２５℃）、４０℃、５０℃の条件で実施した。各ｐＨの緩衝液で０．５mMに調製したＮＳ化合物溶液に亜硝酸ナトリウムを５ mMになるように添加し、各温度で処理を行った。酸加水分解と同様に処理前後のＮＳ化合物濃度から分解率（Ｒ）を算出した。

Here, [A] ₀ and [A] indicate the NS compound concentration [mmol/L] before and after treatment.
2) Nitrous acid addition method Similar to the acid hydrolysis batch test, the conditions were pH 2, 4, 7 and room temperature (about 25°C), 40°C, and 50°C. Sodium nitrite was added to NS compound solutions adjusted to 0.5 mM with buffers of each pH to 5 mM, and the treatment was carried out 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 compounds by ion exchange resin]
A beaker-level batch test and a column test were carried out for the adsorption test of the NS compound to the ion exchange resin.

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

ここで、［Ａ］_Ｒ はイオン交換樹脂中のＮＳ化合物濃度［ｍｍｏｌ／ｋｇ－Ｒ］、Ｖは溶液量［Ｌ］、ρ_Ｒはイオン交換樹脂の比重［ｋｇ／Ｌ］、Ｗ_Ｒは添加したイオン交換樹脂重量［ｋｇ］を示す。

Here, [A] _R is the concentration of the NS compound in the ion exchange resin [mmol/kg-R], V is the volume of the solution [L], ρ _R is the specific gravity of the ion exchange resin [kg/L], and _WR is the added The weight of the ion-exchange resin [kg] is shown.

ここで、［Ａ］_ｉｎと［Ａ］_ｏｕｔはカラム入口と出口のＮＳ化合物の濃度［ｍｍｏｌ／Ｌ］を示す。 2) Column test In the column test, NS compounds in wastewater simulating desulfurization wastewater (simulated wastewater) were treated in order to understand the removal characteristics of the NS compounds in the desulfurization wastewater by the ion exchange resin. A column (diameter 10 mm, length 150 mm) filled with conditioned ion exchange resin (WBA) was used for the column test. The simulated wastewater was prepared with Ca ²⁺ : 570 mg/L, Na ⁺ : 480 mg/L, Cl ⁻ : 1000 mg/L, SO ₄ ²⁻ : 1000 mg/L using calcium chloride and sodium sulfate. A pH of 5 was used. Before the test, simulated waste water was passed through the column outlet at a space velocity (hereinafter referred to as SV) of 20 h ^-1 until the SO ₄ ^2- and Cl ^- concentrations stabilized. Thereafter, the system was switched to simulated waste water containing 0.5 mM NS compound, and samples were taken at the column inlet and outlet over time to analyze the NS compound. The removal rate (R) was calculated using the formula (3) from the concentration of the NS compound.

Here, [A] _in and [A] _out indicate the concentration [mmol/L] of the NS compound at the column inlet and outlet.

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

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

[Formula 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 are the SO ₄ ^2- concentration (mmol/L) before treatment, after treatment, and eluted from activated carbon, respectively. show. [SO ₄ ^2- ] _AC was determined from the amount of increase in SO ₄ ^2- concentration by conducting the same test on the treatment solution to which no NS compound was added.

2) Column test A column test of activated carbon was performed on HAMS and HAOMS. A glass column (25 mm diameter, 120 mm length) packed with about 60 mL of 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 SV 10 or 5 h ^-1 until the NS compound concentration at the column outlet stabilized. Thereafter, the treated water at the column inlet and outlet was sampled and analyzed for NS compound and SO ₄ ^2- concentrations. From the NS compound and the SO ₄ ^2- concentration, the removal rate (R) and SO ₄ ^2- increment (Δ[SO ₄ ^2- ]) were calculated using equations (3) and (4).

[Removal of NS compounds in actual wastewater]
1) Tested actual wastewater Desulfurization wastewater was collected from one coal-fired power plant, and four NS compounds (HATS, HADS, HAODS, HAOMS) other than HAMS were added to about 0.5 mM. A desulfurization effluent containing NS compounds was prepared (Table 2). The addition of HAMS was omitted because it is difficult ^to analyze waste water with a high Cl 2 -concentration. The desulfurization effluent was stored in a refrigerator, filtered through a filter with a pore size of 0.2 μm before use, and used without pH adjustment in the treatment with an activated carbon column, and adjusted to pH 5 with hydrochloric acid in the treatment with an ion-exchange resin column.

2) Column test using actual wastewater In order to confirm the removal of NS compounds in actual wastewater by ion-exchange resin and activated carbon, NS compounds in desulfurization wastewater were treated using a column filled with ion-exchange resin or activated carbon. For the column test, a glass column (25 mm diameter, 120 mm length) filled with about 50 mL of ion-exchange resin WBA or about 60 mL of crushed activated carbon was used. Wastewater was passed at a flow rate of SV 20h ^-1 for treatment with ion exchange resin, and at SV 10h ^-1 or 5h ^-1 for treatment with activated carbon. After the passage of water, the treated liquid at the column outlet was sampled over time and analyzed for each NS compound, S ₂ O ₆ ^2- and SO ₄ ^2- .

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

A schematic of the test apparatus is shown in FIG. As shown in FIG. 2(A), the acidic activated carbon treatment is mainly composed of an acid treatment tank 11 and an activated carbon column 12. In the treatment process using activated carbon, unlike normal operating conditions, an acidic and heated treatment solution is used. water through. A 0.5 mM HATS or HADS solution adjusted to pH 10 or higher with 0.1 mol/L sodium hydroxide was used as the treatment liquid. In the acid treatment bath, the pH was adjusted to 2, and the acid hydrolysis reaction was carried out under the conditions of a temperature of 50° C. and a residence time of 1 hour. 2 mol/L phosphoric acid was used for pH adjustment so that HAMS and SO ₄ ²⁻ concentrations could be analyzed by ion chromatography. As the activated carbon column 12, a glass column (25 mm in diameter, 120 mm in length) filled with about 60 mL of crushed activated carbon was used. The flow rate of the treated liquid was set to SV5h ⁻¹ (5 mL/min) with respect to the activated carbon column 12 . After the passage of water, the treated liquids at the outlets of the acid treatment tank 11 and the column 12 were sampled over time, and the concentration of each NS compound was analyzed. In the figure, reference numeral 14 is a pH control sensor, and 15 is a temperature control sensor.

The ion exchange resin/activated carbon treatment is mainly composed of an ion exchange resin column 21 and an activated carbon column 22 as shown in FIG. 2(B). Each of the columns 21 and 22 was used by filling about 50 mL of the ion exchange resin WBA and about 60 mL of crushed activated carbon in the glass column described above. The treatment solution used was simulated waste water (effluent simulating desulfurization waste water) to which HAMS or four NS compounds other than HAMS were added to a concentration of 0.5 mM, and was 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 the passage of water, the treated liquid was sampled from each column outlet over time, and the concentration of each NS compound was analyzed.

[Analysis method]
The analytical sample was filtered through a filter with a pore size of 0.2 μm and then subjected to various analyses. Ion chromatography (Thermo Fisher Scientific, _ICS1600 ) was used for analysis of ^NS compounds and _S2O62- . HAMS and HAOMS were analyzed using an IonPac AS9-HC separation column and a 9 mM sodium carbonate solution as an eluent. HADS, HAODS, and S ₂ O ₆ ²⁻ were analyzed using IonPac AS16 as a separation column and 30 mM sodium hydroxide aqueous solution as an eluent. For analysis of HATS, IonPac AS16 was used as a separation column, and 80 mM sodium hydroxide aqueous solution was used as an eluent. Since the retention time of HAMS is almost the same as that of chloride ions (Cl ^- ), the TN concentration was used as an indicator when the solution contained Cl ^- .

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

[Results and discussion]
[Decomposition characteristics of NS compounds by hydrolysis and nitrous acid 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 under the conditions of this report (temperature: room temperature to 50°C, pH: 2 to 7, reaction time: 2 hours). HATS and HADS are hardly hydrolyzed at pH 4 or higher at room temperature, but hydrolysis was confirmed at pH 2. These hydrolysis proceeded at higher temperatures, and almost all hydrolyzed at 40°C or higher under pH 2 conditions. Since the hydrolyzates of HATS and HADS are HAODS and HAMS, respectively, HAODS and HAMS are accumulated after hydrolysis.
Therefore, it is difficult to decompose and remove NS compounds in desulfurization effluent by hydrolysis under acidic conditions.

[Removal characteristics of NS compounds by ion exchange resin]

₁ ) Batch test A _batch test was performed using _two types of ion _- exchange resins ^to determine the partition coefficient of the ^NS compound in a 50 mM sodium chloride solution. ^2- and are compared in Table 3. It was found that the partition coefficients of HADS, HAODS and HATS, which are divalent or trivalent ions, are comparable to that of S ₂ O ₆ ^2- and larger than that of SO ₄ ^2- . On the other hand, the distribution coefficients of monovalent HAMS and HAOMS were similar to those of NO ₃ ^- and smaller than that of SO ₄ ^2- . If the valences are the same, the partition coefficient can be compared as the selectivity of the ion-exchange resin, so the selectivity of the ion-exchange resin has a relationship of SO ₄ ^2- <HADS<HAODS, S ₂ O ₆ ^2- . In addition, since ion exchange resins generally tend to adsorb more easily as the valence number increases, the selectivity tends to be HAMS, HAOMS, NO ₃ ^? < SO ₄ ^{2 ?} < HATS.

2) Column test Desulfurization effluent has a high concentration of SO ₄ ^2- and Cl ^- . In order to investigate whether such NS compounds in wastewater can be treated with an ion exchange resin, we used a column filled with ion exchange resin to confirm the removal rate of NS compounds in wastewater simulating desulfurization wastewater (Fig. 4). ). It was confirmed that the removal rate of HAMS rapidly decreased after passing water through the column, and that HAMS was hardly removed in the desulfurization effluent. With HAOMS, the removal rate gradually decreased after passing water, and the removal rate was about 0.6 at the end of the test. On the other hand, NS compounds (HADS, HAODS, HATS) and S ₂ O ₆ ^2- , which have higher partition coefficients than SO ₄ ^2- , were hardly detected at the column outlet until the end of the test. Confirmed removal from

From the above, although the adsorption characteristics may change depending on the material and structure of the matrix of the ion exchange resin, among the five NS compounds, ^HADS , _HAODS , and HATS are ion 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 ion exchange resins.

[Removal characteristics of NS compounds by activated carbon]
1) Batch Test In order to evaluate the adsorption properties of NS compounds by activated carbon, a batch test was carried out using powdered activated carbon (Fig. 5). HAMS and HAOMS showed high removal rates regardless of treatment conditions (pH: 2 to 7, temperature: room temperature to 50°C). HAODS, HADS and HATS tended to have higher removal rates at lower pH and higher temperatures. It was found that all NS compounds could be removed under conditions of pH 2 and 40° C. or higher within the scope of this test. However, since desulfurization waste water is generally treated with activated carbon at room temperature and near neutrality, 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 HAMS and HAODS decreased and SO ₄ ^2- concentration increased after treatment (Fig. 6). Its concentration was about 0.4 mM, and SO ₄ ²⁻ close to the initial addition amount (about 0.5 mM) of HAMS and HAODS was detected. Further, when the concentrations of NH ₄ ⁺ , NO ₂ ⁻ , NO ₃ ⁻ , NH ₂ OH and TN in the treatment liquid were analyzed, HAOMS confirmed an increase in NH ₄ ⁺ with a concentration of about 0.4 mM. It was found to be comparable to 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 for hydrolysis reaction and the like. On the other hand, in HAMS, no increase in concentration of NH ₄ ⁺ was observed, and TN decreased to 0.04 mM or less. HAMS showed a decrease in TN in spite of an increase in SO ₄ ^2- concentration, suggesting a different reaction with activated carbon than HAOMS. HAMS is known to react with carbonyl compounds such as ketones and aldehydes to form oximes, and it is possible that HAMS reacted with functional groups on the surface of activated carbon.

2) Column test In actual wastewater treatment with activated carbon, treatment using an adsorption tower filled with activated carbon is common. Therefore, in order to confirm the removal of HAMS and HAOMS by a column packed with activated carbon, 0.5 mM HAMS and HAOMS solutions were passed through a column packed with crushed activated carbon at different flow rates (SV10h ^-1 , SV5h ^-1 ). and the removal rate was determined (Fig. 7). The removal rates of HAMS and ^HAOMS were 0.8 and 0.5 at high flow rate SV10h ^-1 and 0.9 and 0.8 at SV5h-1, and HAMS tended to have a higher removal rate than HAOMS. . Batch tests removed almost all HAMS and HAOMS, while column tests resulted in some remaining after treatment. This is probably because the activated carbon column used in this test was as short as 120 mm in length for the convenience of the experiment.

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

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

From the above, it was found that out of the five NS compounds, HATS, HAODS, and HADS can be removed from actual desulfurization waste water by treatment with an ion exchange resin. A reduction in the concentration of HAOMS can be expected, but the removal rate may vary depending on the concentration of HAOMS and SO ₄ ^2- concentration in the desulfurization effluent. Although the addition of HAMS was omitted in this test, HAMS has a partition coefficient similar to that of HAOMS (Table 3). (Fig. 4), it is considered that the removal rate in actual wastewater is similar to or lower than that of HAOMS.

2) Activated Carbon Column Treatment FIG. 9 shows the results of treating the desulfurization wastewater to which the NS compound was added using an activated carbon column. After the SO ₄ ^2- concentration stabilized, the concentrations of HATS, HADS and HAODS were almost the same as before treatment, and the average removal rate was as low as 0-7%. On the other hand, in HAOMS, a decrease in concentration was confirmed after the treatment, and removal of HAOMS by activated carbon was also confirmed in actual wastewater. However, since its average removal rate is about 0.6, it is necessary to optimize treatment conditions such as column capacity and treatment flow rate.

[Method for treating NS compounds using existing treatment technology]
The results of treating HATS and HADS by acidic activated carbon treatment are shown in FIGS. 10 and 11. FIG. In the treatment solution containing HATS, HAODS was produced by hydrolysis in the acid treatment tank, and the concentration of the produced HAODS was reduced by the activated carbon treatment (Fig. 10). The average concentrations of HATS and total NS compounds after activated carbon treatment (average of 600 to 1800 mL of water flow) were approximately 0.01 mM and 0.08 mM, respectively, with a removal rate of approximately 98% for HATS and approximately 83% for total NS compounds. Met. In addition, in HADS, HAMS was generated as HADS decreased in the acid treatment tank, and decreased after activated carbon treatment. A high removal rate of about 99% was obtained for both HADS and total NS compounds after the activated carbon treatment.

FIG. 12 shows the result of treating the NS compound with a combination of ion exchange resin and activated carbon. In the treatment solutions to which four types of NS compounds were added, excluding HAMS, most of them were removed after treatment with ion exchange resin, and the removal rate was 99% or more on average (average of treated water volume 600 to 1950 mL). (See FIG. 12(A)). In a study on the removal characteristics of NS compounds by ion exchange resins and the removal of NS compounds in actual waste water, the treatment with HAOMS ion exchange resins resulted in a portion of NS compounds remaining in the treated liquid. This is thought to be due to the difference in the column capacity of the ion exchange resin used in this test and the SO ₄ ²⁻ concentration of the simulated wastewater being lower than that of the actual wastewater. On the other hand, in the treated liquid containing HAMS, it was not removed by the ion exchange resin, and the concentration was confirmed to decrease after the activated carbon treatment (see FIG. 12(B)). The removal rate of HAMS after activated carbon treatment averaged about 73% (same as above).

From the above, it is possible to reduce the concentration of HATS and HADS, which are difficult to treat with an activated carbon packed tower under normal operating conditions, by installing an acid treatment tank and performing activated carbon treatment under acidic conditions. Possibility of processing NS compounds including It was also shown that the combination of ion-exchange resin and activated charcoal can also remove five types of NS compounds and reduce their concentrations.

[Summary of methods for removing NS compounds using existing wastewater treatment technology]
It was found that common wastewater treatment technologies such as ion exchange resin and activated carbon can treat different NS compounds. In order to treat all five types of NS compounds in desulfurization wastewater, there are methods using activated carbon under acidic conditions, methods combining treatment with ion-exchange resin and activated carbon, and methods under acidic conditions and heating in activated carbon treatment. 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 is considered to be able to cope with this problem.

1 acid activated carbon treatment tank 2 flocculation tank 3 separation tank 4 desulfurization waste water 5 powdered activated carbon 6 acid 7 flocculant 8 alkaline solution 9 waste water 11 acid treatment tank 12 activated carbon packed tower 13 acid 21 ion exchange resin packed tower 22 activated carbon packed tower

Claims (4)

Powdered activated carbon is added to desulfurization effluent containing NS compounds that affect the COD value of HAMS, HAOMS, HADS, HAODS, and HATS, and acid is added to adjust the pH to 2 or less . After stirring in an acid-activated carbon treatment tank for 2 hours , adding a flocculating agent and an alkaline solution to the desulfurized waste water after the stirring process and flocculating it in the flocculating tank, the desulfurized waste water and the flocculate are separated in a separation tank. A desulfurization wastewater treatment method, characterized in that only wastewater is allowed to pass through. In an acid treatment tank, acid is added to desulfurization effluent containing five NS compounds that affect the COD value of HAMS, HAOMS, HADS, HAODS, and HATS . After decomposition , the pH-adjusted desulfurization waste water is passed through the activated carbon packed tower at a flow rate of SV5h ⁻¹ to remove the NS compounds by attaching them to the activated carbon in the activated carbon packed tower, and only the waste water is allowed to pass through. A desulfurization wastewater treatment method characterized by: 2. The desulfurization waste water treatment method according to claim 1 , wherein the desulfurization waste water is heated to at least 40[deg.] C. during the pH adjustment. 2. The desulfurization wastewater treatment method according to claim 1 , wherein the acid treatment is performed by heating to 50.degree.

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