KR100231950B1 - Sewage treatment process and apparatus - Google Patents

Abstract

The present invention provides a wastewater treatment method and apparatus that can effectively remove Se (especially hexavalent Se) in wastewater and can achieve compliance with the elution standards at low cost. And / or reduced to a simple substance Se, followed by solid-liquid separation.

Description

Drainage treatment method and device

The present invention relates to a wastewater treatment method and apparatus. Specifically, the present invention relates to a wastewater treatment method and apparatus capable of effectively removing Se, in particular hexavalent Se, from sewage containing Se (selenium).

In general, wet flue gas desulfurization systems are widely used in thermal power generation facilities. In such flue gas desulfurization systems, flue gas is generally contacted with an absorbent slurry (e.g., limestone slurry) to absorb sulfur oxides in the flue gas stream, and The gypsum formed as a by-product is separated from the slurry, but since the harmful substances contained in the flue gas stream melt in the wastewater discharged from the flue gas desulfurization system, it is necessary to remove these harmful substances before discharge or reuse. In particular, in the flue gas from the flue gas desulfurization apparatus for coal boilers, the harmfulness of Se contained in the coal at a content of up to about 10 mg / kg has become a problem in recent years, and it is desired to remove it from the waste water and treat it harmlessly. .

In addition, Se has similar toxicity to arsenic compounds, and there are examples of obstacles and emission regulations overseas, so it was added to the new regulations in February 1994 in Japan, and the environmental standard (0.01mg / l) and drainage standard ( 0.1 mg / l) and the elution criteria (0.3 mg / l) for landfill disposal were established. In addition, Se exists in a tetravalent state (main form: selenic acid SeO ₃ ^2- ) and a hexavalent state (main form: selenic acid SeO ₄ ^2- ), and in particular, hexavalent valent Se has high solubility (20 ° C.). Solubility in 95%) easily soluble in water.

In addition, the current flue gas desulfurization apparatus is usually provided with a wastewater treatment apparatus, and the wastewater purification treatment is performed in this apparatus. However, in the conventional wastewater treatment apparatus, the coagulation sedimentation treatment, the COD (chemical oxygen demand) treatment, the denitrification treatment by microorganisms, and the like are sequentially performed, and no Se removal treatment has been considered.

In addition, conventionally, a method of removing tetravalent Se contained in drainage or the like has been used, and in this method, tetravalent Se is converted into FeCl ₃ , Fe ₂ (SO ₄ ) ₃ , and a chelating agent (for example, Japan's Miyoshi Resin (Myoshi Resin) product: Epolas MX-7) or a polymer heavy metal scavenger (e.g., Japanese Miyoshi resin product: Epoflock L-1), solid-liquid separation (solvent extraction) have. However, no effective removal method has been found for the conventional hexavalent Se.

For this reason, in the past, when Se (particularly hexavalent Se) is contained in the waste water, in order to comply with the above dissolution standards, desulfurization waste water or the like is diluted with a large amount of water. There was a problem that a treatment was required.

Accordingly, it is a first object of the present invention to provide a wastewater treatment method and apparatus capable of effectively removing Se (particularly hexavalent Se) and complying with the above elution criteria at low cost.

1 is a schematic block diagram of an apparatus for performing the first embodiment of the present invention.

2 is a schematic block diagram of an apparatus for performing the second embodiment of the present invention.

* Explanation of symbols for main parts of the drawings

10: desulfurization system 20: drainage treatment device

2a: drainage treatment device A: desulfurization drainage

B: Treatment completion drain

A second object of the present invention is to provide a method for treating sewage containing sewage, comprising a microbial wastewater treatment step of reducing hexavalent Se in the wastewater to tetravalent Se and / or single Se and solid-liquid separation. do.

Another object of the present invention includes a denitrification process and a selenium reduction process using an active mud having selenium reducing ability to reduce selenium from hexavalent Se to tetravalent Se and / or single Se with a denitrifying ability. By doing this, microbial treatment of wastewater is performed.

Another object of the present invention is to add a treating agent for separating tetravalent Se from the drain. Further improvement is obtained by adding the treating agent before or after the separation step followed by the second solid-liquid separation step.

Moreover, another improvement that adopts the principle of the present invention is given to the sewage treatment apparatus containing Se. Also included are microbial drainage treatment means for reducing hexavalent Se present in the waste water to tetravalent Se and / or single Se and means for solid-liquid separation of the obtained liquid.

In an embodiment of the present invention, the microbial treatment means for drainage is a selenium reduction using microorganisms having denitrification and denitrification ability and an active mud with selenium reducing ability to reduce selenium from hexavalent Se to tetravalent Se and / or single Se. Means;

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described.

In FIG. 1, the desulfurization system 10 is shown in block form, which is a conventional system. As an example, the desulfurization system 10 includes an absorption tower in which a tank for supplying limestone slurry is formed at the bottom, and the absorbent slurry in the tank of the absorption tower is sent to the tower main body of the absorption tower by a circulation pump, and the tower main body is provided. By contacting the flue gas passing through the part with gas-liquid, the sulfur oxides in the flue gas stream are absorbed and removed. In the case of the tank oxidation system, the absorbent slurry which is in contact with the flue gas and flowed down into the tank is oxidized by the air sucked into the tank, and a solid gypsum as a by-product is generated in the tank. In this case, a portion of the slurry in the tank is continuously discharged and solid-liquid separated, so that gypsum having a low water content is continuously collected, while most of the separated water is circulated as water constituting the limestone slurry newly supplied into the tank. Used as In addition, part of the separation water is discharged out of the system of the desulfurization apparatus as so-called desulfurization wastewater (A). This is an essential treatment in order to prevent excessive impurities from flowing into the slurry from the flue gas stream and accumulate excessively in the circulation water constituting the slurry, and desulfurization performance is impaired. In this desulfurization wastewater A, a considerable amount of Se flows from the flue gas continuous stream, especially for coal boilers. For example, hexavalent Se contains about 0.3 mg / l.

Desulfurization drainage (A) is applied to the wastewater treatment apparatus 20 in accordance with the principles of the present invention. Water is discharged as the treated wastewater B through the coagulation sedimentation apparatus 21, the COD treatment apparatus 22, the microorganism treatment apparatus 23, and the tetravalent Se removal apparatus 24.

The coagulation sedimentation step is a process for recovering fine solid particles that could not be separated during the solid-liquid separation process for collecting solid gypsum in the desulfurization system 10. The COD treatment apparatus 22 makes the COD value below the reference value. In order to remove the inorganic soil material, a process is carried out. This COD treatment step can be carried out by a known method such as boiling wastewater at a high temperature to thermally decompose the contaminant or selectively adsorb a specific contaminant with an adsorptive resin. Partially or all of the tetravalent Se contained in the wastewater reacts with the coagulant in the coagulation sedimentation apparatus 24, becomes selenite, and is precipitated and removed from the solid phase. Also in the 21 and the COD treatment apparatus 22, they are discharged to the downstream side toward the microbial treatment apparatus 23 as they are dissolved in the wastewater.

In the microbial treatment apparatus 23, each treatment of aerobic treatment (aerobic microbial treatment), anaerobic treatment (anaerobic microbial treatment), and precipitation treatment (solid-liquid separation) is performed in sequence. Aerobic treatment in the apparatus 23 is, nitrite bacteria (by the oxidation of NH ₄ ⁺ NO ₂ ^- bacteria in the nature to produce) and jilsangyun (NO ₂ ^- bacteria in the nature to produce ^- by oxidizing the NO ₃₎ An activated mud containing an activated mud is used, and drainage after passing through the COD treatment apparatus 22 is introduced into the mixing or stirring tank in which the active mud is suspended or suspended, and if necessary, blows air and aeration Exposure). In this aerobic treatment, NH ₄ ⁺ in the waste water is oxidized by nitrite bacteria in active mud to NO ₂ ⁻ after a considerable residence time, and this NO ₂ ⁻ is oxidized by nitric acid bacteria in active mud and NO ₃ ^−. Becomes In addition, the wastewater after the aerobic treatment is finished is precipitated as necessary, and the downstream side (eg, agitation tank described later in the anaerobic treatment) in a state in which the active mud used for the aerobic treatment is not sent to the anaerobic process. Is discharged.

Next, the anaerobic treatment step is performed in the apparatus 23 using the active mud. The active mud contains a microorganism having Se reducing ability to reduce hexavalent Se to tetravalent Se and / or single Se and denitrifying bacteria (bacteria having the property of reducing NO ₃ ⁻ to produce N ₂ ). The agitation vessel in which the active mud is suspended or suspended is introduced into the agitation tank and stirred, and the anaerobic environment is maintained while supplying nutrients such as acetate. In this anaerobic treatment, the oxygen in NO ₃ ⁻ in the waste water is reduced by denitrification bacteria in the active mud to be N ₂ , and at the same time by the microorganism having Se reducing ability, the oxygen in the hexavalent Se in the waste water (main form: Selenic acid SeO ₄ ^2- ) is reduced to tetravalent Se (main form: selenic acid SeO ₃ ^2- ) or to a single Se.

In the settling section of the microorganism processing apparatus 23, the wastewater after the anaerobic treatment is introduced into, for example, a sedimentation separator and the like, and is sent to a wake (tetravalent Se removal step) after the mud (solid content) is removed. At this time, the generated N ₂ becomes a gas and is released into the atmosphere. Moreover, since Se has extremely low solubility, most of it precipitates as mud, and since tetravalent Se also has low solubility compared with hexavalent Se, some precipitate as mud. For this reason, most of Se except a small amount of tetravalent Se dissolved in the waste water is introduced into the mud and removed from the waste water. In addition, the mud removed by the precipitation treatment may be treated as industrial waste, but, for example, by adding and treating a tetravalent Se separation or eluting treatment agent, dewatering it by centrifugal sedimentation, etc. It is also easy to handle, and there is little problem of Se separation or elution.

In the tetravalent Se removal apparatus 24, each of the separation or the elution treatment (the tetravalent Se separation or the elution treatment) and the coagulation sedimentation treatment (solid-liquid separation) are sequentially performed. Separation or dissolution is introduced into the agitation tank after drainage of the microorganism treatment step, and a trivalent Fe such as FeCl ₃ or Fe ₂ (SO ₄ ) ₃ or the like is used to separate or elute tetravalent Se into the agitation tank. The compound contained) is added to the wastewater. According to this treatment, tetravalent Se (main form: selenic acid SeO ₃ ^2- ) contained in the wastewater is treated with, for example, (1), (2) or (3), (4) It causes a reaction represented by to become precipitated or eluted iron selenite (Fe ₂ (SeO ₃ ) ₃ ).

or

For this reason, when this wastewater is solid-liquid separated by the flocculation sedimentation apparatus 24 in the next flocculation sedimentation process, tetravalent Se will isolate | separate into solid phase as iron selenite, and will separate or elute in the discharged mud, and will mix. Therefore, almost no Se is contained in the treated wastewater B discharged as the wastewater treatment apparatus, and the above discharge standard is sufficiently satisfied. In addition, the sludge removed by the flocculation sedimentation treatment may be treated as industrial waste, but, for example, dehydration by centrifugal sedimentation or the like to make a cake shape makes it easy to handle. In addition, since most of Se is separated or eluted in this sludge bundle, even if it is discarded as a cake shape, the elution standard of Se can be fully satisfied.

In addition, although the example which demonstrated the addition of the treatment agent which isolate | separates or precipitates tetravalent Se into the waste water after the mud after a microorganism treatment process separates, the said treatment agent is added to the waste water before segregation of a mud after a microorganism treatment process, Alternatively, the eluted Se may be separated from the mud in the subsequent solid-liquid separation process.

According to the wastewater treatment method as described above, the hexavalent Se, which was conventionally impossible to remove, is also sufficiently removed from the wastewater, as demonstrated in the embodiments described later, so that it can easily meet the drainage standard (0.1 mg / L). . In addition, since reduction of hexavalent Se can be performed simultaneously with a denitrification process, the structure of the apparatus 23 for a microorganism processing process is the same as the structure of the conventional drainage apparatus which performed the nitriding process (aerobic process) and the denitrification process. It can be realized as it is (the apparatus structure except active mud), and in this case, the present invention can be easily applied to the existing apparatus easily and at low cost only by installing the apparatus for the step of removing tetravalent Se. Moreover, compared with the case where reduction and denitrification of hexavalent Se are performed in a separate process, the whole processing time can be shortened significantly.

In addition, depending on the Se concentration in the wastewater, the capacity of the microbial treatment tank, and the management of the metabolic state, the concentration of Se (mainly tetravalent Se) remaining in the wastewater after the microbial treatment process is increased by Se removal in the microbial treatment process. The tetravalent Se removal process is not necessary because it is below the emission threshold.

Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, a treatment agent 26 for separating or eluting tetravalent Se is added to the wastewater in the microbial treatment step of the microbial treatment apparatus 23 'and mixed. The desulfurization system 10, the flocculation and precipitation apparatus 21, and the COD treatment apparatus 22 are as shown in FIG. A treatment agent 26 (eg, FeCl ₃ or Fe ₂ (SO ₄ ) _3, etc.) for separating or eluting tetravalent Se is introduced into the mixing tank 27 in the aerobic treatment as shown in FIG. 2. Or into the mixing tank 28 in the anaerobic treatment.

In the anaerobic treatment, tetravalent Se originally dissolved in the waste water, and in the anaerobic treatment, most of the tetravalent Se produced by reduction of the hexavalent Se causes a reaction represented by the treatment agent 26 and the reaction formula 1 to be mixed in the aerobic treatment. In the tank 27 or the mixing tank 28 in the anaerobic treatment, it becomes iron selenite (Fe ₂ (SeO ₃ ) ₃ ), separated or eluted, and separated from the sludge produced in the subsequent treatment 29. Eluted tetravalent Se is removed.

Therefore, most of Se is not contained in the treated wastewater B, and the above discharge standards are sufficiently satisfied. In this case, the tetravalent Se removal step after the microbial treatment step becomes unnecessary, and the drainage treatment device having a configuration substantially the same as that in the conventional configuration in which the device configuration for the tetravalent Se removal step is eliminated may be used. For this reason, the apparatus configuration becomes extremely simple, and the se removal function can be added to the existing equipment without causing an increase in equipment cost of the wastewater treatment apparatus. In addition, since there is no tetravalent Se removal process after the microorganism treatment process, the overall treatment time is further shortened.

In this case, since most of Se is insolubilized and exists in the sludge generated in the precipitation treatment of the microbial treatment step, it is not a problem even if the liquid is separated into a liquid to form a cake shape and disposed as it is.

Further, as the treatment agent 4 is separated or eluted Se, it may be added to not containing a divalent Fe (for example FeSO _4). Also in this case, by the forced oxidation by aeration in natural oxidation or aerobic treatment, divalent Fe becomes trivalent Fe, and the reaction shown by the said Reaction Formula 1 also arises, and tetravalent Se can be separated or eluted. .

EXAMPLE

The following describes the method of the present invention in more detail. In the experiments in the following examples, the hexavalent Se concentration was about 10 ppm in the active mud containing the denitrification bacteria used for the denitrification treatment using a flue gas desulfurization system, and in a closed anaerobic environment for 14 days. I used to be tamed. In addition, the microorganisms used for denitrification were isolated and found to belong to Pseudomonas genus. More specifically, the denitrifying bacteria belong to the species of aeruginosa of the genus Pseudomonas. The microorganisms used herein were assigned to the International Trade Organization, Bioindustry and Industrial Technology Institute (1-3 1-3, Tsukubashi Higashi, Ibaraki, Japan), September 9, 1996, in accordance with the Treaty of Budapest. Deposited as BP-5661 (Pseudomonas SR-34) and FERM BP-5662 (SR-25).

Example 1

The reduction test of hexavalent Se in the wastewater was conducted. The test conditions are as shown in Table 1 below, 50 ml of the active mud and 450 ml of desulfurization waste water were mixed and stirred in a flask, sealed to an anaerobic environment, and maintained at 25 ° C. for 24 hours, after which solids were precipitated and only supernatant water was The sediment was collected and analyzed for the concentration of Se or hexavalent or tetravalent Se in the supernatant procedure and the concentration of nitrogen (No ₃ ⁻ ). The analysis results are shown in Table 2 below.

From the analysis results of Table 2, it can be seen that the concentration of tetravalent Se significantly decreased, and the concentration of tetravalent Se, which could hardly be measured in the wastewater before treatment, increased.

Then, FeCl ₃ is added to the supernatant after the reduction treatment, mixed and stirred, followed by coagulation precipitation treatment, whereby the total Se concentration in the liquid phase becomes 0.08 mg / l, which can sufficiently meet the emission standard (0.1 mg / l).

Example 2

Subsequently, 450 ml of the active clay 50 ml desulfurization drainage (8 ppm of hexavalent Se concentration before treatment) was placed in a flask, and 0.5 mg of FeSO ₄ was added as a treating agent to separate or elute. After stirring for 24 hours, solids were precipitated, and only the supernatant was collected, and the concentration of Se or tetravalent Se in the supernatant was analyzed. The result was that neither hexavalent Se or tetravalent Se could be measured and was hardly present in the liquid flux. In addition, pH in the process was 7-7.8.

The present invention is not limited to the above-described form of the present invention and various aspects may be present. For example, as a treatment agent for separating or eluting Se, a chelating agent (for example, Japanese Miyoshi resin: Epoleas MX-7) or a polymer heavy metal collecting agent (in addition to FeCl ₃ or Fe ₂ (SO ₄ ) ₃ exemplified) For example, Japanese Miyoshi Resin Products: EPOFLOCK L-1) and the like can be used. As described above, a compound (FeSO ₄ ) containing divalent Fe may be added as a treatment agent.

As described above, when the concentration of Se (mainly tetravalent Se) remaining in the drainage water after the microbial treatment step becomes lower than a desired value by the Se removal action in the microbial treatment step, the tetravalent Se removal step Is not necessary. In addition, the wastewater treatment method and apparatus of the present invention can be applied to any wastewater as long as it contains waste water containing not only desulfurized wastewater but also hexavalent Se.

According to the above-described wastewater treatment method and apparatus, Se is reduced from hexavalent Se to tetravalent Se and / or single Se by microbial treatment, so that the liquid can be easily separated into solids and a large amount of Se can be removed as a solid. . The single Se has extremely low solubility, and the tetravalent Se also has a low solubility in comparison with the hexavalent Se, so that many Se can be removed as a solid by this treatment. For this reason, the density | concentration of hexavalent Se which was impossible with the conventional method or apparatus can be reduced specially.

In order to achieve the advantages of the present invention, it is not necessary to make changes in the conventional wastewater treatment apparatus, but active mud must be changed. Removal of hexavalent Se can be performed by the original equipment utilizing the present invention. In addition, in this configuration, since the hexavalent Se reduction and denitrification occur in the same process, the overall reaction time can be significantly shortened.

According to the wastewater treatment method described above, an active mud containing at least a microorganism having denitrification ability and a microorganism having Se reducing ability to reduce hexavalent Se to tetravalent Se and / or single Se is used in the microbial treatment apparatus. In this way, the denitrification treatment is performed together with the reduction of Se, thereby simplifying the configuration of the wastewater treatment apparatus. That is, for example, when the Se removal treatment is carried out in a separate process using an active mud separate from the denitrification treatment, it is necessary to install a separate Se removal treatment dedicated device (for example, a microbial treatment mixing tank). The same apparatus can be shared if it is the structure of this invention. In other words, if the existing wastewater treatment apparatus has been denitrified by microorganisms in the past, the treatment method of the present invention can be carried out as it is without changing the apparatus configuration and changing the used active mud. , Hexavalent Se can be removed. In this configuration, since the denitrification treatment can be performed at the same time as the reduction of Se, the treatment time required for the overall drainage treatment is also shortened.

According to the wastewater treatment method described above, in the microbial treatment, a treatment agent for separating or eluting tetravalent Se is added to the wastewater. Thus, by reducing the tetravalent Se present in the untreated wastewater or the hexavalent Se in the microbial treatment, Most of the generated tetravalent Se is separated or eluted, and can be removed by solids removal treatment (for example, precipitation treatment). Therefore, after the treatment, the total Se concentration in the drainage flow can be further reduced, and the regulation values such as the drainage standard can be observed with a large margin. In this case, since the treatment agent is added to the wastewater in the microbial treatment, it can be carried out only by providing an apparatus for adding the treatment agent to the treatment tank in the microbial treatment, and a stirring tank for mixing the treatment agent in the wastewater. Since there is no need to separately install a lamp or the like, the equipment cost of the wastewater treatment apparatus is inexpensive, and the retrofit of the existing apparatus is also extremely easy.

According to the wastewater treatment method described above, in the tetravalent Se removal step, a treatment agent for separating or eluting tetravalent Se is added to the wastewater after the microbial treatment. For this reason, the tetravalent Se which existed from the beginning in the untreated wastewater or the tetravalent Se generated by reduction of the hexavalent Se in microorganism treatment, and the majority of the tetravalent Se dissolved in the wastewater isolate | separates or elutes, It is removed in the separation process. Therefore, after the treatment, the total Se concentration in the drainage flow can be further reduced, and the regulation values such as the drainage standard can be observed with a large margin.

Claims (18)

A sewage treatment method comprising Se, comprising a microbial treatment step of draining water to reduce hexavalent Se present in the waste water to at least one of tetravalent Se and single se, and a step of separating solid-liquid. The method of claim 1, wherein the microorganism treatment process, the denitrification process using a microorganism having a denitrification ability and the active mud with selenium reducing ability to reduce hexavalent Se to tetravalent Se and selenium reduction process, characterized in that Wastewater treatment method. The method of claim 1, wherein the microorganism treatment process, the denitrification process using a microorganism having a denitrification ability and the active mud with selenium reduction ability to reduce the hexavalent Se to a single Se and a selenium reduction process characterized in that Treatment method. The method for treating waste water according to claim 1, wherein a treatment agent for separating tetravalent Se is added to the waste water. The wastewater treatment method according to claim 2, wherein a treatment agent for separating tetravalent Se is added to the wastewater. The wastewater treatment method according to claim 3, wherein a treatment agent for separating tetravalent Se is added to the wastewater. 5. The method for treating wastewater according to claim 4, wherein a second solid-liquid separation process is performed after adding a separating agent to the wastewater before the separating process. A sewage treatment apparatus containing Se, comprising a means for separating microorganisms and solid-liquid separation of hexavalent Se present in the wastewater to at least one of tetravalent Se and single se. 9. The wastewater according to claim 8, wherein the microorganism treating means comprises denitrification and selenium reducing means using microorganisms having denitrification ability and active mud having selenium reducing ability to reduce hexavalent Se to tetravalent Se. Processing unit. 9. The wastewater treatment according to claim 8, wherein the microorganism treating means comprises denitrification and selenium reducing means using microorganisms having denitrification ability and active mud having selenium reducing ability to reduce hexavalent Se to elemental Se. Device. 9. The apparatus of claim 8 having means for adding a treating agent to separate tetravalent Se in the drain. 10. The apparatus of claim 9 having means for adding a treating agent to separate tetravalent Se in the drain. 11. The apparatus of claim 10 having means for adding a treating agent to separate tetravalent Se in the drain. 12. The apparatus of claim 11 having means for adding said treating agent to the drainage prior to separating the liquid from the solid. 12. The wastewater treatment apparatus according to claim 11, further comprising means for adding the treating agent to the drainage after separating the liquid from the solid, and means for separating the liquid from the solid again. The method for treating wastewater according to claim 1, wherein the microbial treatment of wastewater uses bacteria belonging to the genus Pseudomonas. The wastewater treatment method according to claim 1, wherein the microbial treatment process of wastewater comprises Pseudomonas genus SR-34 and FERM BP-5661. The wastewater treatment method according to claim 1, wherein the microbial treatment process of wastewater uses SR-25 and FERM BP-5662.

Images