JP2016112556A - Method for biologically treating water to be treated by using aerobic fluidized bed - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for biologically treating water to be treated by using an aerobic fluidized bed, in which when the water to be treated, which water contains a thiocyanate ion and an ammonium ion, is treated biologically, the thiocyanate ion can be removed selectively and efficiently without oxidizing the ammonium ion.SOLUTION: When the biological treatment is performed continuously on the water to be treated, which water contains the thiocyanate ion and the ammonium ion, the method for biologically treating the water to be treated by using the aerobic fluidized bed comprises the steps of: charging a fluidized carrier, on which microbes are fixed, in a biological treatment tank; aerating the fluidized carrier-charged biological treatment tank to compose the aerobic fluidized bed; acclimatizing microbes in the biological treatment tank while monitoring the thiocyanate ion and a nitrite ion in the treated water in the biological treatment tank or the treated water to be discharged from the biological treatment tank; controlling the hydrological residence time; and removing the thiocyanate ion selectively while suppressing generation of the nitrite ion.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for continuously treating to-be-treated water containing thiocyanate ions and ammonium ions by biological treatment, and in particular, without constituting ammonium aerobic fluidized bed and oxidizing ammonium ions. The present invention relates to a biological treatment method for water to be treated that selectively removes thiocyanate ions.

  As treated water containing thiocyanate ion and ammonium ion (ammonia nitrogen), for example, coke oven wastewater (another water) generated in coke production process, coal gasification wastewater generated in coal gasification process, acetylene purification process There is a waste water that is generated, but for such treated water, for example, if the breakpoint method by chlorination suitable for the treatment of ammonium ions is applied, harmful gases such as hydrogen cyanide derived from thiocyanate ions and harmful Such intermediates are known to be difficult to process.

Therefore, some studies have been made and proposed in the past regarding methods for treating water to be treated containing such thiocyanate ions and ammonium ions.
For example, in Patent Document 1, when a coke oven gas liquid (anhydrous water) is biologically treated, a denitrification tank in an oxygen-free condition and a nitrification tank in an aerobic atmosphere are used, and a subsequent nitrification tank is used in the preceding denitrification tank. A method has been proposed in which thiocyanic acid in the coke oven gas liquid is circulated as a hydrogen donor by circulating the nitrification liquid from the tank, and this method uses thiocyanate ions and nitric acid or nitrous acid in an oxygen-free denitrification tank. In addition, ammonia nitrogen is oxidized to nitric acid or nitrous acid in a nitrification tank in an aerobic atmosphere. However, in this method, it is necessary to install at least two treatment tanks (in the embodiment, two denitrification tanks and two nitrification tanks are used), and this is applied to facilities having existing treatment tanks. In addition, if the thiocyanic acid component used as a hydrogen donor in an oxygen-free denitrification tank is insufficient, it is necessary to separately add a chemical such as methanol that causes high processing costs. Furthermore, as disclosed in Non-Patent Document 1, this method has a remarkably slow removal rate compared to the case of removing thiocyanate ions under aerobic conditions.

  Moreover, in patent document 2, the 1st process of making ozone act on the wastewater containing ammoniacal nitrogen and a thiocyanate ion, and the 2nd process of making a chlorine-type oxidizing agent act on the treated water in this 1st process are included. And a method of removing ammoniacal nitrogen in the second step after removing thiocyanate ions in the first step. However, in this method, the ozone treatment performed in the first step is an extremely expensive treatment method, and a harmful by-product may be generated in some cases.

  Furthermore, in Patent Document 3, when treating the coal gasification wastewater generated in the coal gasification step, the pH is adjusted to 3-6 after removing suspended substances by coagulation sedimentation treatment, and then hydrogen peroxide or the like is used. There is disclosed a method of removing ammonia by irradiating ultraviolet rays in the presence of an oxidizing agent to remove thiocyanate ions and the like, further adjusting the pH to 7 or more and aeration with water vapor or air. However, even in this method, it is necessary to perform ultraviolet irradiation in the presence of an oxidizing agent such as hydrogen peroxide in order to remove thiocyanate ions and the like.

  Patent Document 4 discloses a COD concentration simulation method and apparatus in biological treatment of aqueous water, which is built on the basis of an activated sludge model as a water quality simulation method and is generated in the coke production process. A new activated sludge model that can be applied to water containing ions has been proposed. However, this method does not propose a new method for biological treatment of safe water.

  By the way, when trying to treat thiocyanate ions and ammonium ions simultaneously with activated sludge, a reaction occurs in which the thiocyanate ions are removed and at the same time the ammonium ions are oxidized to nitrite ions, and the thiocyanate ions are removed. However, ammonium ions are oxidized to nitrite ions and remain in the treated water. And since this nitrite ion is a component (160mg / L) of chemical oxygen demand (COD) that has a low allowable limit in the effluent standard, the fact that nitrite is contained in the treated water From the point of view, it is not desirable.

JP 09-290,290 A JP 11-033,571 JP 2007-216,225 JP 2011-045,872

D. Y. Sorokin et al., Microbiol. , 2004, 150, 2435-2442

  Since the present inventors can biologically treat thiocyanate ions in treated water, expensive chemicals and equipment are used for treating treated water containing thiocyanate ions and ammonium ions. And it was considered preferable to perform the treatment by a biological treatment that does not generate harmful gases and by-products. However, as described above, in the aerobic atmosphere, microorganisms remove thiocyanate ions and at the same time oxidize ammonium ions to nitrite ions, so it is necessary to treat thiocyanate ions while suppressing the oxidation to nitrite ions. However, in the conventional biological treatment under the aerobic condition where dissolved oxygen is present, such a treatment method has not been reported.

  The present invention has been made in view of such circumstances, and in the biological treatment of water to be treated containing thiocyanate ions and ammonium ions, the thiocyanate ions can be selectively and efficiently oxidized without oxidizing the ammonium ions. It is an object of the present invention to provide a biological treatment method for water to be treated by an aerobic fluidized bed that can be removed well.

In order to achieve the above object, the present inventors have made various studies and obtained the following findings.
First of all, it was found that microorganisms that remove thiocyanate ions in the water to be treated have adhesion, and for these adherent microorganisms, thiocyanate ions were more rapidly absorbed in an aerobic atmosphere than in anoxic conditions. It was confirmed that it could be removed. And from these findings, in the process of studying biological treatment with an aerobic fluidized bed, surprisingly, in the process of habituation of microorganisms, removal of thiocyanate ions and oxidation of ammonium ions to nitrite ions However, if the hydraulic residence time after the acclimation treatment in the biological treatment tank is shorter than the hydraulic residence time during the acclimation treatment, the microorganism that decomposes thiocyanate ions Microorganisms that easily stay in the aerobic fluidized bed and are difficult to flow out and microorganisms that decompose ammonium ions are difficult to stay in the aerobic fluidized bed and easily flow out. As a result, oxidation of ammonium ions to nitrite ions is suppressed, and thiocyanate It was found that acid ions are selectively removed.

  Furthermore, after the hydraulic residence time has been shortened, oxidation of ammonium ions to nitrite ions can be suppressed, and even if the hydraulic residence time is extended, the production of nitrite ions can be suppressed for a while. Therefore, even if the hydraulic residence time is changed in accordance with the quality of the wastewater and the amount of wastewater, the hydraulic residence time may be reduced during the acclimation treatment in some cases. It was found that thiocyanate ions can be selectively removed while suppressing the generation of nitrite ions even when the length is further extended.

In addition, the hydraulic retention time after acclimation treatment in the biological treatment tank is shorter than the hydraulic retention time during acclimation treatment, and thiocyanate ions are removed by selective removal of thiocyanate ions. In the treated water after that, thiocyanate ions are removed as much as possible, and the production of nitrite ions is suppressed as much as possible. For example, breakpoint method by chlorine oxidation, ammonia stripping method, zeolite A conventional treatment method suitable for the treatment of ammonium ions such as an adsorption method can also be easily applied.
The present invention has been made based on these findings.

That is, the gist of the present invention is as follows.
(1) An aerobic fluidized bed by continuously introducing water to be treated containing thiocyanate ions and ammonium ions into a biological treatment tank charged with a fluid carrier and aeration to fix microorganisms on the fluid carrier. Comprising a continuous treatment of the water to be treated by biological treatment of the aerobic fluidized bed,
In the biological treatment tank, while monitoring the treated water in the biological treatment tank or the thiocyanate ions and nitrite ions discharged from the tank, microorganisms are fixed on the fluid carrier and aerobic flow is performed. Introducing water to be treated by changing the hydraulic residence time stepwise or continuously from the first stage treatment to the Nth stage treatment of the microbe-acclimation treatment constituting the floor,
The hydraulic residence time after the second stage treatment is shorter than the hydraulic residence time of the previous stage treatment until the removal of thiocyanate ions in the treated water and the suppression of the formation of nitrite ions in the treated water are confirmed. Control to be
A biological treatment method of water to be treated by an aerobic fluidized bed, wherein thiocyanate ions are selectively removed while suppressing generation of nitrite ions.
(2) The hydraulic residence time after the second stage treatment is controlled after the removal of thiocyanate ions in the treated water and the suppression of the formation of nitrite ions in the treated water. (1) The biological treatment method of water to be treated by an aerobic fluidized bed as described in (1) above, which is performed so as to be shorter than the hydraulic residence time of the stage treatment.
(3) The control of the hydraulic residence time after the second stage treatment has been continued even after the removal of thiocyanate ions in the treated water and the suppression of the formation of nitrite ions in the treated water have been confirmed. The biological treatment method of water to be treated by an aerobic fluidized bed according to (1) or (2), wherein the treatment is performed so as to maintain a physical residence time.
(4) The hydraulic residence time after the second stage treatment is controlled after the thiocyanate ion in the treated water is confirmed after the removal of thiocyanate ions in the treated water and the suppression of the formation of nitrite ions in the treated water. The aerobic flow according to (1) or (2), wherein the aerobic flow is performed so as to extend or shorten the hydraulic residence time of the pretreatment depending on the concentration of acid ions and nitrite ions Biological treatment method of water to be treated by floor.
(5) In any one of the above (1) to (4), the introduction of water to be treated into the biological treatment tank is performed by changing the hydraulic residence time stepwise. The biological treatment method of to-be-treated water by an aerobic fluidized bed as described in 1.
(6) The pH value of the treated water in the biological treatment tank or the treated water discharged from the tank is monitored, and the thiocyanate ion of the treated water in the biological treatment tank or the treated water discharged from the tank. When the concentration is equal to or higher than a predetermined value and the pH value of the treated water is further reduced to less than 7.0, the pH value in the biological treatment tank is adjusted to a range of 7.0 to 8.5. The biological treatment method of water to be treated by an aerobic fluidized bed according to any one of (1) to (5), which is characterized by the above.

  According to the present invention, when water to be treated containing thiocyanate ions and ammonium ions is continuously treated by biological treatment, no harmful chemicals or by-products are produced without using expensive chemicals or equipment. The thiocyanate ions can be selectively removed while suppressing the production of nitrite ions at a higher speed than the conventional biological treatment by the activated sludge method, etc. It is possible to reduce the processing cost and to suppress the generation of harmful by-products.

FIG. 1 shows the hydraulic residence time, thiocyanate ion concentration (mgSCN / L), and nitrite ion concentration (mgN / L) with respect to the operating days in the biological treatment of treated water by the aerobic fluidized bed of the present invention. ) Is an explanatory diagram conceptually showing the relationship. FIG. 2 is an explanatory diagram for explaining a configuration example of a biological treatment facility for water to be treated by an aerobic fluidized bed according to an embodiment of the present invention. FIG. 3 is a graph showing the results of examining the removal rate of thiocyanate ions by activated sludge in an aerobic atmosphere and oxygen-free conditions. FIG. 4 is a graph showing the results of examining the influence of the pH value during treatment in the treatment of thiocyanate ions in an aerobic fluidized bed. FIG. 5 is a conceptual diagram of the biological treatment tank used in Example 1, showing a case without a fluid carrier (a) and a case with a fluid carrier (b). FIG. 6 is a graph showing the results of Example 1 using artificial waste water (treated water), the results of monitoring thiocyanate ions, nitrite ions, and pH values corresponding to the number of operating days; It shows the result of controlling the hydraulic residence time. FIG. 7 is a graph showing the results of Example 2 using artificial waste water (treated water), the results of monitoring thiocyanate ions, nitrite ions, and pH values corresponding to the number of operating days; It shows the result of controlling the hydraulic residence time.

  First, in the biological treatment method of water to be treated according to the present invention, how thiocyanate ions are removed from the water to be treated, and how generation of nitrite ions due to oxidation of ammonia ions is suppressed. In the case of control where the hydraulic residence time is increased stepwise, the hydraulic residence time, thiocyanate ion concentration (mgSCN / L), and nitrite ion concentration (mgN / L) relative to the number of operating days The relationship will be described with reference to FIG.

  First, in the microorganism habituation process (first stage process) for establishing microorganisms on the fluid carrier 10 in the biological treatment tank 1 to form an aerobic fluidized bed, microorganisms that decompose thiocyanate ions into the fluid carrier 10. And microorganisms that oxidize ammonia ions gradually settle, thiocyanate ions in the treated water are gradually removed and are no longer detected in the treated water, and ammonia ions are oxidized to increase the concentration of nitrite ions in the treated water . Next, when the biological treatment is continued with the hydraulic residence time being longer than that in the first stage treatment (second stage treatment), the microorganisms that decompose thiocyanate ions remain in the aerobic fluidized bed and remain in the thiocyanate. Although the removal of the ions is continued, the microorganisms that decompose the ammonia ions do not stay in the aerobic fluidized bed and are discharged, and the production of nitrite ions is suppressed and the nitrite ion concentration gradually decreases. In the biological treatment in the second stage treatment, immediately after the hydraulic residence time is shortened, the thiocyanate ion concentration temporarily increases due to disturbance of the hydraulic residence time change. Acclimatization of microorganisms that decompose acid ions occurs, and thiocyanate ions are removed stably again. Thereafter, when the biological treatment is continued by making the hydraulic residence time shorter than the second stage treatment (third stage treatment), the change in the hydraulic residence time is changed as in the second stage treatment. Although the thiocyanate ion concentration temporarily increases due to disturbance, the removal of thiocyanate ions is stabilized again, and the generation of nitrite ions is suppressed. After stabilization of thiocyanate ion removal and suppression of nitrite ion formation (after the third stage treatment), even if the hydraulic residence time fluctuates, the generation of nitrite ion is suppressed for a while. However, thiocyanate ions can be selectively removed.

  The relationship between the hydraulic residence time, the thiocyanate ion concentration, and the nitrite ion concentration with respect to the number of operating days shown in FIG. 1 is as follows, for example, as shown by the two-dot chain line in the figure. The same applies to the case where the hydraulic residence time is continuously changed (increased) in the treatment.

Hereinafter, the method of the present invention will be described in detail based on a configuration example of a biological treatment facility for water to be treated by the aerobic fluidized bed of the present invention shown in FIG.
In FIG. 2, a biological treatment facility for water to be treated is configured based on a biological treatment tank 1 and a sedimentation tank 2. The biological treatment tank 1 is continuously introduced with water to be treated through a pipe 3, and the biological treatment tank 1 is loaded with a fluid carrier 10 for fixing microorganisms. An unillustrated microbial seeding source inhabited by microorganisms capable of removing thiocyanate ions of pollutants is introduced. In addition, air is sent into the tank from the air pump 9 and aerated to form a swirling flow in the biological treatment tank 1, and the fluid carrier 10 flows on the swirling flow. Microbial acclimatization treatment (first stage treatment) is performed during a predetermined hydraulic residence time in the tank 1, and microorganisms derived from the microbial inoculation source or the water to be treated are fixed on the fluid carrier 10 and aerobic flow. A floor is formed. And while the to-be-treated water introduced into the biological treatment tank 1 is retained in the biological treatment tank 1 for a predetermined hydraulic residence time, thiocyanate ions are removed to become treated water, The treated water is fed into the sedimentation tank 2 through the pipe 4, further solid-liquid separated in the sedimentation tank 2, and the supernatant part becomes the final treated water. It is designed to be discharged outside the processing facility.

  Here, in the biological treatment tank 1, a separator that prevents the fluid carrier 10 forming an aerobic fluidized bed from being taken out of the tank by the treated water in the vicinity of the inlet of the treated water pipe 4. 11, a pH meter 8 for measuring the pH value in the biological treatment tank 1, and an alkali supply for adjusting the pH by supplying alkali to the tank according to the pH value measured by the pH meter. A pump 7 is provided. Furthermore, suspended matter containing activated sludge (such as a microbial seed source) that has passed through the separator 11 and settled in the settling tank 2 is sent back to the bottom of the settling tank 2 into the water to be treated. A piping 6 is provided.

  In the present invention, the water to be treated is wastewater containing thiocyanate ions and ammonium ions, for example, coke oven wastewater (another water) generated in the coke production process, and coal gasification process. Examples include generated coal gasification wastewater, washing wastewater generated in the acetylene purification step, and the like.

In the present invention, the fluid carrier 10 used for fixing microorganisms is inserted into the biological treatment tank 1 and flows along with the flow in the tank by aeration. There is no particular limitation on the shape, size, material, etc., as long as it can form an aerodynamic fluidized bed. Industrial wastewater treatment facilities, food wastewater treatment facilities, industrial water treatment facilities, wastewater disposal site wastewater The conventionally well-known commercially available thing used so far at a processing facility, a community plant, a septic tank, etc. can be used. For example, for plastic fluid carriers, a plurality of manufacturers have a porous cubic shape, a skeleton-like spherical shape, a small cylindrical shape, a tubular shape, etc., and a size of an external shape (2 to 30) mm × (2 -30) mm or 2 to 30 mmφ, 2 to 30 mm in length, and a catalog value with a specific surface area of 300 to 6000 m ² / m ³ and a specific gravity of 1.0 ± 0.5 is commercially available . The fluid carrier 10 preferably has a large specific surface area, has a porosity that allows microorganisms to enter (usually, microorganisms have a diameter of about 1 μm), and is easily attached to microorganisms.

  Further, the amount of the fluid carrier 10 used also flows with the flow in the tank by aeration, and forms an aerobic fluidized bed in the biological treatment tank 1 and can sufficiently come into contact with the treated water in the tank. As long as it is used, it may be the amount of a conventionally known commercial product that has been used in industrial wastewater treatment facilities, food wastewater treatment facilities, industrial water treatment facilities, waste disposal site wastewater treatment facilities, community plants, septic tanks, etc. For example, in the case of a plastic fluid carrier, the volume ratio in the biological treatment tank 1 is preferably 5% (V / V) or more and 50% (V / V) or less. More preferably, it is 10% (V / V) or more and 30% (V / V) or less.

  For the microorganisms to be fixed on the fluid carrier 10, microbial seed sources such as activated sludge, soil, natural seawater, etc., inhabited by microorganisms capable of removing thiocyanate ions are used, and only one of them is used. Alternatively, two or more kinds may be used in combination, and activated sludge is preferably used from the viewpoint that microorganisms are present at a high concentration. Furthermore, if activated sludge of a biological treatment facility from which thiocyanate ions are removed can be used, it is more preferable because the amount of microorganisms that remove thiocyanate ions is considered to be large. The input of this microbial seeding source can be set in consideration of the concentration of thiocyanate ions and ammonium ions in the treated water, the nature of the treated water such as other pollutants, and the surrounding environment. Considering the outflow to the outside of the tank inside, it is preferable to add a large amount. Furthermore, if the fluid carrier 10 can be brought into contact with a high-concentration microorganism seed source before being charged into the biological treatment tank 1, microorganisms can be fixed on the fluid carrier in a short period of time. More preferred. For example, the use of return sludge and precipitated sludge in biological treatment equipment that removes thiocyanate ions is considered to have a high concentration of microorganisms that remove thiocyanate ions. And the fluid carrier are previously accommodated in a container and immersed therein, whereby microorganisms can be attached to the fluid carrier in advance.

  In the present invention, after water to be treated, a fluid carrier 10 and a microbial seed source are placed in the biological treatment tank 1, the inside of the tank is aerated to form an aerobic fluidized bed. Water to be treated is introduced by changing the hydraulic residence time stepwise (continuously) from microbial acclimation treatment (first stage treatment) for fixing the fluid to the surface of the fluid carrier 10 to the Nth stage treatment. However, at that time, regarding the hydraulic residence time after the second stage treatment, until the removal of thiocyanate ions in the treated water and the suppression of the production of nitrite ions in the treated water are confirmed, the biological treatment tank 1 The thiocyanate ions are selectively removed while controlling the generation of nitrite ions to be shorter than the hydraulic residence time of the immediately preceding pretreatment in FIG.

  Here, the aeration for constituting the aerobic fluidized bed provides sufficient fluidity to the fluid carrier 10 by supplying sufficient oxygen into the tank and forming a swirl flow in the tank, The microorganism attached to the fluid carrier 10 can efficiently remove thiocyanate ions to be processed, and is usually performed by sending air using the air pump 9 or the like. Pure oxygen can also be used as a part or instead of air.

  In addition, the microorganism acclimation treatment (first stage treatment) for fixing the microorganisms on the surface of the fluid carrier 10 can be performed in the same manner as the conventional method, and the treatment time or treatment period is also treated. Depending on the type of target water to be treated (components and concentration of pollutants contained in the water to be treated), the microbial seeding source and fluid carrier 10 used, and the surrounding environment, etc. The thiocyanate ion concentration in the treated water discharged from the biological treatment tank 1 over time reaches a target value (for example, zero (0 mg / L), water quality standard value of waste water, etc.) and reaches a predetermined period (for example, 1 It is good that the thiocyanate ion treatment is confirmed to be stable and it does not increase during a period of about a week), and a predetermined hydraulic residence time (first stage) Processing) May be adjusted to handle thiocyanate is in the activated sludge method, for example, about 24 hours.

  In the present invention, microorganisms are sufficiently fixed on the surface of the fluid carrier 10 to form a desired aerobic fluidized bed, and the treated water in the biological treatment tank 1 or the treated water discharged from this tank is used. After the thiocyanate ion concentration is stabilized and the above-described microorganism adaptation process (first stage process) is completed, the thiocyanate ion concentration and nitrous acid in the treated water in the biological treatment tank 1 or the treated water discharged from this tank Until the thiocyanate ions are removed while monitoring the ion concentration while suppressing the generation of nitrite ions, the first stage treatment immediately before the hydraulic residence time after the second stage treatment in the biological treatment tank 1 It is controlled so as to be shorter than the hydraulic residence time. And the control which shortens the hydraulic residence time after the 2nd step process in this biological treatment tank 1 is processing after processing in biological treatment tank 1 according to the kind of treated water, the surrounding environment, etc. Set target values of thiocyanate ion concentration and nitrite ion concentration (for example, zero (0 mg / L) and drainage standard value) for water, and set the above thiocyanate ion and nitrite ion below these target values. Monitor it. In addition, about control which shortens the hydraulic residence time after the 2nd step process in this biological treatment tank 1, in addition to the target value of said thiocyanate ion concentration and nitrite ion concentration, chemical oxygen of treated water A target value (e.g., drainage standard value) of the required amount (COD) is set, and the thiocyanate ion, nitrite ion and the above-mentioned target values of thiocyanate ion concentration, nitrite ion concentration and COD concentration are set. Monitoring of COD may be performed, and this also has the advantage that wastewater standards can be more reliably observed in the treatment of wastewater containing COD components other than thiocyanate ions and nitrite ions.

  Here, the thiocyanate ion, nitrite ion, and COD concentration measurement method performed for monitoring thiocyanate ion, nitrite ion, and COD in the biological treatment tank 1 will be described. In addition, there is no particular limitation as long as the concentration of COD and COD can be measured continuously or periodically. For example, the ion chromatography method is used for the thiocyanate ion concentration, and the method of JIS K102043.1.1 is used for the nitrite ion concentration. Further, regarding COD, the method of JIS K1020 17 can be exemplified.

  In the present invention, microorganisms that remove thiocyanate ions can be preferentially retained in the biological treatment tank 1 by controlling to shorten the hydraulic residence time after the second stage treatment in the biological treatment tank 1. . This is thought to be due to the fact that the growth rate of microorganisms that remove thiocyanate ions is faster than the growth rate of microorganisms that oxidize ammonium ions. When shortened, the amount of inflow thiocyanate ions increases and microorganisms that remove thiocyanate ions grow preferentially over microorganisms that oxidize ammonium ions, predominately occupy the surface of the flow carrier 10, It is presumed that the place where the microorganisms that oxidize live on the surface of the fluid carrier 10 disappears and flows out of the biological treatment tank 1 and decreases. The control for shortening the hydraulic residence time after the second stage treatment in the biological treatment tank 1 is performed by adjusting the target values of the thiocyanate ion and nitrite ion after treatment, and if necessary, the target value of the post-treatment concentration of COD. It is adjusted according to.

In the present invention, the control for shortening the hydraulic residence time after the second stage treatment in the biological treatment tank 1 is preferably performed while monitoring thiocyanate ions and nitrite ions (and, if necessary, COD). For example, in the case of stepwise control in which the hydraulic residence time after the second stage treatment is stepwise shortened to a predetermined value, it is recommended that To implement.
That is, first, after confirming that the thiocyanate ion concentration in the treated water did not increase for a certain period of time (for example, about one week) and stabilized below the target value by the microorganism treatment of the first stage, the second stage treatment was performed. Reduce the hydraulic retention time at the moment (for example, to about 3/4 of the original 24 hours), observe the trend of the thiocyanate ion concentration and nitrite ion concentration (and COD concentration) afterwards, When the thiocyanate ion concentration of the treated water does not increase beyond the target value, the treatment is performed for a certain period of time (for example, about one week) with the reduced hydraulic residence time during the second stage treatment. If the thiocyanate ion concentration of the treated water rises above the target value, the hydraulic residence time during the second stage treatment is changed to the hydraulic residence time during the first stage treatment. Return to microbial acclimatization process again It is carried out. Next, after the treatment is continued for a certain period of time (for example, about one week) with the reduced hydraulic residence time during the second stage treatment, the hydraulic residence time during the second stage treatment is again slightly reduced (for example, The third stage process is performed in the same manner as in the second stage process, and the same operation as described above is repeated until the Nth stage process. By this operation, the nitrite concentration (and COD concentration) of the treated water gradually decreases. This operation may be terminated when all of the thiocyanate ion concentration and the nitrite ion concentration (and COD concentration) of the treated water have stably achieved the target value for a certain period (for example, about one week). Furthermore, if the operation is continued, it is possible to process at higher speed, but there is a limit to the amount of microorganisms that can be fixed on the carrier, so there is a limit to the hydraulic residence time that can be shortened. is necessary. According to such a stepwise control method, for example, the hydraulic residence time after the second stage treatment is reduced to about three times that during the first stage treatment (microbe acclimation treatment) (24 hours → 8 hours). As described above, find the hydraulic residence time after the second stage treatment in which all of the thiocyanate ion concentration and nitrite ion concentration (and COD concentration) in the treated water achieve the target values. Can be operated.

  By the way, components other than thiocyanate ions and ammonium ions are also contained in coke oven drainage and the like. For example, when activated sludge of coke oven wastewater treatment equipment is used as a microbial seed source capable of removing thiocyanate ions, microorganisms that decompose components other than thiocyanate ions and ammonium ions are also present in the activated sludge. there is a possibility. In such a case, the appropriate hydraulic residence time varies depending on the growth rate difference (magnitude relationship) between the microorganism, the microorganism that removes thiocyanate ions, and the microorganism that oxidizes ammonium ions. In such a case, the thiocyanate ion concentration and the nitrite ion concentration (further, the COD concentration) can be processed so as to achieve the target values.

  That is, the inventors examined water to be treated containing phenol and thiosulfate ions as COD components other than thiocyanate ions and ammonium ions. In this study, the operation of the present invention shortened the hydraulic residence time, and as a result, conditions under which thiocyanate ions were removed and nitrite ions were not completely generated could be confirmed. However, a phenomenon was observed in which the removal rate of thiocyanate ions began to decrease as the confirmed hydraulic residence time was maintained. Therefore, when the microbial acclimatization treatment was performed again with the hydraulic retention time slightly extended based on the method of the present invention, the thiocyanate ion removal rate recovered, and nevertheless the production of nitrite ions continued. And found that it was suppressed. From this fact, once the microorganisms are acclimatized to such an extent that nitrite ions are not completely formed, the thiocyanate ion concentration and nitrite ions continue even if the hydraulic residence time is changed or fluctuated. It has been found that the concentration (and also the COD concentration) can be processed to achieve the target value.

  Therefore, according to the present invention, the thiocyanate ions are removed by making the hydraulic residence time after the second stage treatment in the biological treatment tank 1 shorter than the hydraulic residence time at the previous stage treatment, It is possible to suppress the production of ions almost completely. Further, after the treatment is continued for a certain period of time (for example, about one week) with the reduced hydraulic residence time, the hydraulic residence time is extended. Even if the thiocyanate ion concentration rises temporarily, the hydraulic residence time is temporarily extended because the effect of suppressing the production of nitrite ions can be maintained for a certain period (for example, about 2 months). This can increase the removal rate of thiocyanate ions. If the nitrite ion concentration in the treated water rises above the target value, the hydraulic residence time is shortened again, and if the treatment is continued for a certain period (for example, about one week), Generation of nitrite ions can be suppressed. The extension or shortening of the hydraulic residence time is carried out by appropriately selecting either one while monitoring thiocyanate ions and nitrite ions (and, if necessary, COD). In addition, according to the present invention, not only can it be applied to waste water containing COD components other than thiocyanate ions and ammonium ions as described above, but also the amount of waste water has changed and the hydraulic residence time has fluctuated. Even in this case, thiocyanate ions can be removed while stably suppressing the production of nitrite ions.

  Furthermore, in the present invention, when ammonium ions in the water to be treated are oxidized to produce nitrite ions, and the pH value of the treated water is lowered and the removal rate of thiocyanate ions is deteriorated, the pH value is adjusted. By adjusting to the range of 7.0 to 8.5, the removal rate of thiocyanate ions can be recovered. However, adjustment of the pH value promotes oxidation of ammonium ions and increases in nitrite ions. Therefore, it is not necessary to adjust pH unless the removal rate of thiocyanate ions decreases. Here, the method for adjusting the pH value is not particularly limited. For example, the pH value in the biological treatment tank 1 is monitored by the pH meter 8, and when the pH value falls below the set value, alkali supply is performed. What is necessary is just to drive the pump 7, for example, introduce | transduce sodium hydroxide solution in the biological treatment tank 1, and maintain pH value more than a predetermined setting value.

  The treated water treated in the biological treatment tank 1 is introduced into the settling tank 2, and is separated into suspended substances such as activated sludge and treated water by gravity sedimentation in the settling tank 2, and a part of the suspended substances. Is returned to the biological treatment tank 1. However, this sedimentation tank 2 does not need to be installed when there is almost no suspended matter in the treated water discharged from the biological treatment tank 1 depending on the type of water to be treated.

  Hereinafter, the biological treatment method of the water to be treated by the aerobic fluidized bed of the present invention will be specifically described based on test examples and examples.

[Test Example 1: Culture test of microorganisms capable of removing thiocyanate ion]
In a solvent obtained by mixing industrial water and natural sea water at a volume ratio of 2: 3, the solutes for the culture test shown in Table 1 are dissolved at the concentrations shown in Table 1, and the aerobic conditions shown in Table 1 respectively. A culture test solution A used below and a culture test solution B used under anoxic conditions were prepared. In addition, about the density | concentration of sodium nitrite in the culture test liquid B, the quantity required in order to remove a thiocyanate ion with a density | concentration of 100 mg / L was calculated and determined.

  Next, 20 mL each of the culture test solution A and the culture test solution B prepared above were placed in two 100 mL-vial bottles, and each vial was sealed with a rubber stopper and covered with an aluminum cap. Moreover, about the vial bottle which prepared the culture solution B used under anaerobic conditions, a nitrogen purge was performed for 5 minutes to remove oxygen in the gas phase and dissolved oxygen in the culture solution B in the vial, For each vial, inject 1 mL of a microbial species plant source dispersion that has been confirmed to remove thiocyanate ions, and refill nitrogen for 5 minutes or more for vials charged with culture solution B used under anoxic conditions. Purge was performed to remove oxygen in the gas phase in the vial and dissolved oxygen in the culture broth B.

Each vial prepared in this manner was set on a shaker, and a culture test was conducted at room temperature and a culture period of 5.5 hours under reciprocal shaking at 150 rpm.
In these culture tests, samples for analysis were collected at the start of culture and at the end of culture, the thiocyanate ion concentration was measured, and the thiocyanate ion removal rate per hour was determined. The results of the obtained aerobic culture test and anoxic culture test are shown in FIG.

  As is clear from the results shown in FIG. 3, the thiocyanate ion removal rate when cultured under aerobic conditions is 2.8 times faster than when cultured under anoxic conditions. It was found that it was necessary to operate under aerobic conditions in order to remove ions at high speed.

[Test Example 2: Confirmation test on influence of pH in biological treatment containing thiocyanate ion and ammonium ion]
Prepare artificial wastewater (treated water) having the solute composition shown in Table 2 and charge 50 ml of treated water into each of six 100 mL-plastic bottles, and each plastic using hydrochloric acid aqueous solution or sodium hydroxide aqueous solution. The pH of the water to be treated in the bottle was adjusted to 6.0, 6.5, 7.0, 7.5, 8.0, and 8.5, respectively. In addition, in the water to be treated in each of these plastic bottles, five microorganism fixing fluid carriers in which the fixation of microorganisms having thiocyanate ion removal ability in Example 1 shown below was confirmed were inserted, and each plastic bottle was Were placed on a shaker and subjected to a culture test at room temperature and a culture period of 6 hours under reciprocal shaking at 150 rpm.

In these culture tests, the concentration of thiocyanate ions contained in the water to be treated before the test and the treated water after the test was measured, and the thiocyanate ion removal rate per hour was calculated. The result is shown in FIG.
As is clear from the results shown in FIG. 4, when the pH during biological treatment is less than 7.0, the thiocyanate ion removal rate tends to be slow, and the thiocyanate ion removal rate at pH 7.5 is reduced. When it was set to 100%, it decreased to 81% at pH 6.0.
For this reason, it has been found that it is preferable to adjust the pH to 7.0 or higher if necessary when the pH is lowered due to the production of nitrite ions due to oxidation of ammonium ions.

[Example 1]
In a solvent obtained by mixing industrial water and natural seawater at a volume ratio of 2: 3, solutes shown in Table 2 were dissolved at concentrations shown in Table 2 to prepare artificial drainage (treated water).

  Further, as shown in FIG. 5, an integrated biological treatment having a structure in which a biological treatment region 20 a and a sedimentation region 20 b are separated from each other by a partition wall 23 and communicated with each other below the partition wall 23. Two devices 20 are prepared, and a sponge carrier 21 [fluid carrier (AQ-1 manufactured by Kanto Inoac)] having a size of 10 mm × 10 mm × 10 mm is placed in a biological treatment region 20a of one biological treatment device 20 in a volume ratio of 20 % (v / v) is added to prepare a biological treatment apparatus 20 (Example 1) with a fluid carrier (b), and the other biological treatment apparatus 20 has a sponge in the biological treatment region 20a. Without introducing the carrier 21, a biological treatment apparatus 20 (control example) without a fluid carrier (a) was prepared.

  Into each biological treatment device 20 without the fluid carrier prepared in this way (a) and with the fluid carrier (b), the above-mentioned treated water 24 is allowed to flow and activated sludge is introduced as a microbial seed source, At the time of the microorganism habituation treatment (first stage treatment) for fixing microorganisms on the sponge carrier, the treated water 24 is allowed to flow so that the hydraulic retention time is 24 hours, and the treated water in each biological treatment apparatus 20 Air aeration 22 was performed on 24 to form an aerobic fluidized bed, and microorganisms were acclimatized.

  Immediately after the start of this biological treatment operation, thiocyanate ion removal was observed, but there was a gradual decrease in pH, and the thiocyanate ion removal was unstable. After 69 days, the treatment was continued while adjusting the pH to around 7.5 using a 5 wt% -sodium hydroxide aqueous solution, and the microorganisms were treated at the stage where the thiocyanate ion removal rate was stable at 98% or more (No. 1). 1-stage processing) was completed. Nitrite ions were increasing at the end of this microorganism habituation treatment (first stage treatment).

  After the completion of the microorganism adaptation process (first stage process), thiocyanate ions and nitrite ions are measured by measuring the thiocyanate ion concentration and the nitrite ion concentration of the treated water in the biological treatment region 20a of each biological treatment device 20. And monitoring the pH value of the treated water in the biological treatment area 20a of each biological treatment device 20 while monitoring the pH value, the hydraulic residence time in the area from the 90th day after the start of operation. The amount of inflow of the water to be treated 24 is increased so that it becomes 18 hours (second stage treatment), and from the 111th day after the operation is started, the water staying in the region is 12 hours so that the hydraulic residence time is 12 hours. Further increase the inflow amount of the treated water 24 (third stage treatment), and further increase the inflow amount of the treated water 24 so that the hydraulic residence time in the region becomes 8 hours from the 118th day after the start of operation (the third stage treatment). 4-stage processing), finally 132 days I continued driving to my eyes.

  During this time, in the second stage treatment, the hydraulic residence time in the region was shortened to 18 hours, so that a tendency to reduce the production of nitrite ions began to be observed while maintaining the thiocyanate ion removal rate at a high value. In addition, by reducing the hydraulic residence time in the region to 12 hours in the third stage treatment, the generation of nitrite ions is almost completely suppressed while maintaining the thiocyanate ion removal rate at a high value. Furthermore, even when the hydraulic residence time in the region is shortened to 8 hours in the fourth stage treatment, the thiocyanate ion removal rate can be maintained at a high value while suppressing the generation of nitrite ions. It was confirmed.

In the biological treatment in Example 1, the measurement results of thiocyanate ion, nitrite ion, and pH value with respect to the operating days are shown in FIG.
In addition, in the biological treatment of Example 1 and the control example, the thiocyanate ion and the sub-aqueous water were treated with respect to the treated water on the 8th to 10th day after the start of operation in which the hydraulic residence time in the region was reduced to 8 hours. The results of examining the concentration of nitrate ions are shown in Table 3.

Here, comparing the case of using the biological treatment apparatus 20 with the fluid carrier of Example 1 (b) and the case of using the biological treatment apparatus 20 without the fluid carrier of the control example (a), It was as follows.
That is, in both cases of Example 1 and the control example, the thiocyanate ions were removed from the start of operation during the microorganism acclimation treatment (first stage treatment), but nitrite ions were oxidized by the oxidation of ammonium ions. Production was also confirmed.
However, when the hydraulic residence time in the subsequent region was controlled to be short, the production of nitrite ions could be suppressed in both cases of Example 1 and the control example. Regarding removal, when the hydraulic residence time in the region was reduced to 12 hours, the thiocyanate ion removal rate was up to about 77% in the control example, whereas in Example 1, it was stable at 90% or more. In addition, when the hydraulic residence time in the region was reduced to 8 hours, the thiocyanate ion removal rate was only about 62% in the control example, whereas in Example 1, it was 90%. That was stable.

[Example 2]
In a solvent obtained by mixing industrial water and natural seawater at a volume ratio of 2: 3, the solutes shown in Table 4 were dissolved at the concentrations shown in Table 4 to prepare artificial drainage (treated water). In Example 2, in addition to the solute of Example 1, phenol and thiosulfate ions as main COD components contained in coke oven wastewater were added.

  Further, as shown in FIG. 5, an integrated biological treatment having a structure in which a biological treatment region 20 a and a sedimentation region 20 b are separated from each other by a partition wall 23 and communicated with each other below the partition wall 23. A device 20 was prepared. Also, put a sponge carrier (fluid carrier (AQ-1 manufactured by Kanto Inoac)) of 10 mm x 10 mm x 10 mm in a plastic bottle and high-concentration activated sludge as a microbial seeding source. The microorganism was attached to the sponge carrier by immersing it with a lid.

  The sponge carrier 21 and activated sludge prepared in this way are introduced into the biological treatment region 20a of the biological treatment apparatus 20 so that the volume ratio of the sponge carrier 21 is 20% (v / v). (Example 2) was prepared.

  In the microorganism treatment process (first stage treatment) in which the above-described treated water 24 flows into the biological treatment apparatus 20 thus prepared and the microorganisms are fixed on the sponge carrier, the hydraulic treatment of the treated water 24 is performed. The residence time was 24 hours and air aeration 22 was performed on the water to be treated 24 in each biological treatment apparatus 20 to form an aerobic fluidized bed, thereby acclimatizing the microorganisms. Further, the treatment was performed while adjusting the pH to around 7.5 using a 5 wt% -sodium hydroxide aqueous solution.

  In the biological treatment in Example 2, the measurement results of thiocyanate ion, nitrite ion, and pH value with respect to the operating days are shown in FIG. Immediately after the start of this biological treatment, thiocyanate ion removal was observed, and then the thiocyanate ion removal rate was stable at 99% or more. finished. During the microorganism acclimation treatment (first treatment), 22% or more of the ammonia in the water to be treated was oxidized to nitrite ions.

  The microorganism acclimatization process (first stage process) was completed 71 days earlier than Example 1 in which the microorganisms were not previously fixed on the sponge carrier. This is because the pH was adjusted and the sponge carrier 21 was rubbed well in advance and covered with a lid overnight.

  After the completion of the microorganism acclimation process (first stage process), the thiocyanate ion concentration and the nitrite ion concentration of the treated water in the biological treatment region 20a of the biological treatment apparatus 20 are measured to determine the thiocyanate ion and nitrite ion concentration. While monitoring, while measuring the pH of the treated water in the biological treatment area 20a of the biological treatment apparatus 20 and monitoring the pH value, the hydraulic residence time in the area is 18 from the 19th day after the start of operation. The amount of inflow of the water to be treated 24 is increased so as to become time (second stage treatment), and then the water to be treated 24 is set so that the hydraulic residence time in the region becomes 12 hours from the 39th day after the start of operation. The inflow amount of the water to be treated 24 was further increased so that the hydraulic residence time in the region was 8 hours from the 46th day after the start of operation (third stage treatment). 4-stage processing). After that, from the 74th day, the inflow amount of the water to be treated 24 is reduced so that the hydraulic residence time in the region becomes 10 hours (fifth stage treatment), and further from the 96th day, the hydraulic residence time in the region. The amount of inflow of the water to be treated 24 was reduced (sixth stage treatment) so as to be 24 hours, and the operation was continued until the 151st day.

  During this time, in the second stage treatment, the hydraulic residence time in the region was shortened to 18 hours, so that a tendency to reduce the production of nitrite ions began to be observed while maintaining the thiocyanate ion removal rate at a high value. Further, by shortening the hydraulic residence time in the region to 12 hours, it was possible to further suppress the formation of nitrite ions while maintaining the thiocyanate ion removal rate at a high value.

  However, when the hydraulic residence time in the region is shortened to 8 hours in the fourth stage treatment, the thiocyanate ion removal rate after a while while suppressing the production of nitrite ions almost completely. Decreased. This is because the microorganisms that decompose phenol and thiosulfuric acid that were not contained in the water to be treated in Example 1 lived on the surface of the sponge carrier 21, and therefore live on the surface of the microorganism sponge carrier 21 that removes thiocyanate ions. As a result, the removal rate is considered to have decreased.

  Thus, since the thiocyanate ion removal rate has increased beyond the target value, in the fifth stage treatment, the hydraulic residence time is set to the condition of the fourth stage treatment (hydraulic residence time is 12 hours. The biological treatment was carried out at 10 hours close to). As a result, it was possible to almost completely suppress the formation of nitrite ions while maintaining the thiocyanate ion removal rate at 94% or more.

  Therefore, in the sixth stage treatment, when the hydraulic residence time was extended to 24 hours, the thirocyanate ion removal rate was maintained at a high value, but more surprisingly, the remaining 76 days. As a result, the production of nitrite ions could be suppressed almost completely.

  In the biological treatment of Example 2, the concentration of thiocyanate ions and nitrite ions was examined for the treated water on the 13th day after the start of operation in which the hydraulic residence time in the region was shortened to 10 hours. The results are shown in Table 5.

Here, the results of Example 1 and Example 2 were as follows.
That is, in both cases of Examples 1 and 2, thiocyanate ions were removed from the start of operation during the acclimation treatment (first stage treatment), but nitrite ions were oxidized by oxidation of ammonium ions. Generation was also confirmed.
However, when control is performed to shorten the hydraulic residence time in the subsequent region, in Example 1, the hydraulic residence time is shortened to 8 hours, and in Example 2, the hydraulic residence time is reduced. After shortening the time to 10 hours, in both cases, the thiocyanate ion removal rate was stable at 90% or more, and the production of nitrite ions could be suppressed.
Furthermore, in Example 2, the hydraulic residence time was maintained at 10 hours and then extended to 24 hours, but the suppression of nitrite ion production was maintained.

  From the results of Examples 1 and 2 above, if the biological treatment of the water to be treated that constitutes the aerobic fluidized bed of the present invention is used, thiocyanate ions are simply selected while suppressing the production of nitrite ions. The thiocyanate ions can be processed at high speed by shortening the hydraulic residence time. In addition, once the hydraulic residence time has been shortened and the microorganisms have been acclimatized, the generation rate of thiocyanate ions can be suppressed for a while even if the hydraulic residence time is extended again. If the water content decreases, the hydraulic residence time is extended, and if the amount of nitrite produced increases, the hydraulic residence time is shortened, and the thiocyanate ion and nitrite ion concentrations are reduced. It was found that thiocyanate ions can be selectively removed while suppressing the production of nitrite ions by appropriately selecting and carrying out monitoring.

  DESCRIPTION OF SYMBOLS 1 ... Biological treatment tank, 2 ... Sedimentation tank, 3-6 ... Piping, 7 ... Alkaline supply pump, 8 ... pH meter, 9: Air pump, 10 ... Fluid carrier, 11 ... Separator, 20 ... Biological treatment apparatus, 20a ... Biological Treatment area, 20b ... Sedimentation area, 21 ... Sponge carrier (fluid carrier), 22 ... Air diffuser, 23 ... Partition, 24 ... Water to be treated, 25 ... Final treated water.

Claims (6)

An aerobic fluidized bed is formed by continuously introducing water to be treated containing thiocyanate ions and ammonium ions into a biological treatment tank charged with a fluid carrier and aeration to fix microorganisms on the fluid carrier. A method for continuously treating the water to be treated by biological treatment of the aerobic fluidized bed,
In the biological treatment tank, while monitoring the treated water in the biological treatment tank or the thiocyanate ions and nitrite ions discharged from the tank, microorganisms are fixed on the fluid carrier and aerobic flow is performed. Introducing water to be treated by changing the hydraulic residence time stepwise or continuously from the first stage treatment to the Nth stage treatment of the microbe-acclimation treatment constituting the floor,
The hydraulic residence time after the second stage treatment is shorter than the hydraulic residence time of the previous stage treatment until the removal of thiocyanate ions in the treated water and the suppression of the formation of nitrite ions in the treated water are confirmed. Control to be
A biological treatment method of water to be treated by an aerobic fluidized bed, wherein thiocyanate ions are selectively removed while suppressing generation of nitrite ions.   After the second stage treatment, the hydraulic residence time is controlled by the removal of thiocyanate ions in the treated water and the suppression of the formation of nitrite ions in the treated water. 2. The biological treatment method for water to be treated by an aerobic fluidized bed according to claim 1, wherein the treatment time is shorter than the hydraulic residence time.   The control of the hydraulic residence time after the second stage treatment was continued after the removal of thiocyanate ions in the treated water and the suppression of the formation of nitrite ions in the treated water. The biological treatment method for water to be treated by an aerobic fluidized bed according to claim 1 or 2, wherein the treatment is performed so as to maintain time.   After the second stage treatment, the hydraulic residence time is controlled by confirming the removal of thiocyanate ions in the treated water and the suppression of the formation of nitrite ions in the treated water. The water to be treated by the aerobic fluidized bed according to claim 1, wherein the water is treated so as to be extended or shortened with respect to the hydraulic residence time of the pretreatment according to the concentration of nitrite ions. Biological treatment method.   The aerobic flow according to any one of claims 1 to 4, wherein introduction of water to be treated into the biological treatment tank is performed by changing the hydraulic residence time stepwise. Biological treatment method of water to be treated by floor.   The pH value of the treated water in the biological treatment tank or the treated water discharged from the tank is monitored, and the thiocyanate ion concentration of the treated water in the biological treatment tank or the treated water discharged from the tank is predetermined. When the pH value of the treated water decreases to less than 7.0, the pH value in the biological treatment tank is adjusted to a range of 7.0 to 8.5. The biological treatment method of the to-be-processed water by the aerobic fluidized bed of any one of Claims 1-5.

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