Water treatment method and water treatment device

Abstract

This water treatment method includes subjecting a solution to be treated to anaerobic treatment, the solution containing water and a hardly decomposable nitrogen-containing compound.

Description

Water treatment method and water treatment device

[0001] The present disclosure relates to a water treatment method and a water treatment device.

[0002] When producing a polythiol compound, wastewater containing high concentrations of persistent nitrogen-containing compounds such as dicyandiamide, thiourea, and guanidine is discharged (see, for example, Patent Document 1). Patent Document 1 discloses a wastewater treatment method that can easily reduce the toxicity of thiourea-containing wastewater, and includes a treatment step of reacting dicyandiamide and thiourea under acidic conditions in wastewater containing these compounds.

[0003] Japanese Patent Application Laid-Open No. 2021-107046

[0004] However, there is a need for a water treatment method that can more effectively reduce the concentration of persistent nitrogen-containing compounds in water to be treated that contains persistent nitrogen-containing compounds and water. The water treatment method of the present disclosure provides a water treatment method and a water treatment device that can effectively reduce the concentration of persistent nitrogen-containing compounds in water to be treated that contains persistent nitrogen-containing compounds and water.

[0005] Means for solving the above problems include the following aspects. <1> A water treatment method comprising a step of anaerobically treating water to be treated that contains persistent nitrogen-containing compounds and water. <2> The water treatment method according to <1>, in which the persistent nitrogen-containing compounds include at least one selected from the group consisting of guanidine and dicyandiamide. <3> The water treatment method according to <1> or <2>, in which the anaerobic treatment step anaerobically treats the water to be treated using at least one selected from the group consisting of an anaerobic sludge bed reactor, an anaerobic fluidized bed reactor, and a complete mixing reactor. <4> The water treatment method according to any one of <1> to <3>, in which the anaerobic treatment step anaerobically treats the water to be treated using an upflow anaerobic sludge bed reactor. <5> The water treatment method according to any one of <1> to <4>, wherein the water to be treated further contains thiourea, and further comprises a step of aerobically treating the water to be treated at least either before or after the step of anaerobic treatment. <6> The water treatment method according to any one of <1> to <5>, wherein the water to be treated further contains thiourea, and the step of anaerobic treatment comprises anaerobically treating the water to be treated using at least one reactor selected from the group consisting of an anaerobic sludge bed reactor, an anaerobic fluidized bed reactor, and a complete mixing reactor, and further comprises aerobically treating the water to be treated using at least one reactor selected from the group consisting of a fluidized bed reactor, a suspended bed reactor, a shaking bed reactor, and a trickling filter reactor at least either before or after the step of anaerobic treatment. <7> The water treatment method according to any one of <1> to <6>, wherein the water to be treated further contains thiourea, the anaerobic treatment step comprises anaerobically treating the water to be treated using an upflow anaerobic sludge bed reactor, and further comprises a step of aerobically treating the water to be treated using a downflow suspended sponge reactor at least either before or after the anaerobic treatment step. <8> The water treatment method according to any one of <5> to <7>, comprising a repeating step of alternately repeating the anaerobic treatment step and the aerobic treatment step.<9> The water treatment method according to <8>, wherein the repeating step includes decomposing a portion of the persistent nitrogen-containing compounds into nitrogen gas by alternately repeating the anaerobic treatment step and the aerobic treatment step. <10> The water treatment method according to any one of <2> to <11>, wherein the total concentration of guanidine and dicyandiamide in the water to be treated is 0.1 mg / L to 1000 mg / L. <11> The water treatment method according to any one of <5> to <11>, wherein the total concentration of thiourea in the water to be treated is 0.01 mg / L to 50 mg / L. <12> A water treatment device for carrying out the water treatment method according to any one of <1> to <11>, comprising a reactor that anaerobically treats the water to be treated.

[0006] According to one aspect of the present disclosure, there are provided a water treatment method and a water treatment device that can effectively reduce the concentration of persistent nitrogen-containing compounds in treatment water containing persistent nitrogen-containing compounds and water.

[0007] Fig. 1 is a schematic diagram showing an example of a water treatment device according to the present disclosure; Fig. 2 is a schematic diagram showing another example of a water treatment device according to the present disclosure; Fig. 3 is a schematic diagram showing yet another example of a water treatment device according to the present disclosure; Fig. 4 is a schematic diagram showing yet another example of a water treatment device according to the present disclosure.

[0008] In this disclosure, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In this disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. In this disclosure, when multiple substances corresponding to each component are present in the composition, the amount of each component contained in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified. In the numerical ranges described in stages in this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit of that numerical range may be replaced with a value shown in the examples.

[0009] In this disclosure, upflow means a flow in an upward direction (i.e., against the direction of gravity), and downflow means a flow in a downward direction (i.e., in the direction of gravity).

[0010] [Water Treatment Method] The water treatment method of the present disclosure includes a step of anaerobic treatment of water to be treated containing persistent nitrogen-containing compounds and water. The water treatment method of the present disclosure may include other steps as necessary. According to the water treatment method of the present disclosure, the concentration of persistent nitrogen-containing compounds in water to be treated containing persistent nitrogen-containing compounds and water can be effectively reduced.

[0011] It is known that persistent nitrogen-containing compounds can damage microorganisms used in conventional sludge treatment (see, for example, Appl Biochem Biotechnol 194, 2901-2918 (2022)). For this reason, water to be treated containing persistent nitrogen-containing compounds is sometimes treated by combustion rather than sludge treatment. However, in recent years, from the perspective of aiming for carbon neutrality, it has been considered desirable to avoid combustion treatment.

[0012] In light of the above, the inventors have conducted research and found that the concentration of persistent nitrogen-containing compounds can be effectively reduced by anaerobic treatment of water to be treated that contains persistent nitrogen-containing compounds and water. The water treatment method of the present disclosure is based on this finding. The water treatment method of the present disclosure is particularly suitable as an industrial water treatment method.

[0013] <Water to be treated> The water to be treated, which is the target of water treatment in the water treatment method of the present disclosure, contains persistent nitrogen-containing compounds and water. Examples of the water to be treated include industrial wastewater.

[0014] The persistent nitrogen-containing compound is preferably a compound that, when added at an initial concentration of 100 mg / L, is decomposed to a rate of less than 50% after immersion in activated sludge for 5 days (in other words, a compound that, when added at an initial concentration of 100 mg / L, remains 50% or more of the original compound after immersion in activated sludge for 5 days).

[0015] From the viewpoint of the effect of anaerobic treatment, the persistent nitrogen-containing compound preferably contains at least one selected from the group consisting of guanidine and dicyandiamide. Examples of the water to be treated containing the persistent nitrogen-containing compound in this embodiment include industrial wastewater generated during the production of polythiol compounds (e.g., 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane). Polythiol compounds are produced, for example, as raw materials for urethane resins and thiourethane resins (e.g., thiourethane resins used in the production of eyeglass lenses).

[0016] The total concentration of guanidine and dicyandiamide in the water to be treated is, for example, 0.1 mg / L to 10,000 mg / L, preferably 0.1 mg / L to 7,500 mg / L, more preferably 0.1 mg / L to 5,000 mg / L, even more preferably 0.1 mg / L to 3,000 mg / L, even more preferably 0.1 mg / L to 1,000 mg / L, even more preferably 0.1 mg / L to 400 mg / L, even more preferably 0.1 mg / L to 200 mg / L, and even more preferably 0.1 mg / L to 100 mg / L. Even when the water to be treated contains at least one member selected from the group consisting of guanidine and dicyandiamide at a relatively high concentration as described above, the concentration of these members can be reduced by anaerobic treatment. The lower limit of the total concentration of guanidine and dicyandiamide in the water to be treated may be, for example, 1.0 mg / L, 2.0 mg / L, 5.0 mg / L, or 10.0 mg / L.

[0017] When the water to be treated contains guanidine, the concentration of guanidine in the water to be treated is, for example, 0.10 mg / L to 8000 mg / L, preferably 0.10 mg / L to 6000 mg / L, more preferably 0.10 mg / L to 4000 mg / L, and even more preferably 0.10 mg / L to 2000 mg / L. Even when the water to be treated contains guanidine at a relatively high concentration as described above, this concentration can be reduced by anaerobic treatment. The lower limit of the guanidine concentration in the water to be treated may be, for example, 2.0 mg / L or 5.0 mg / L.

[0018] When the water to be treated contains dicyandiamide, the concentration of dicyandiamide in the water to be treated is, for example, 1.0 mg / L to 2000 mg / L, preferably 1.0 mg / L to 1500 mg / L, more preferably 1.0 mg / L to 1000 mg / L, and even more preferably 1.0 mg / L to 800 mg / L. The lower limit of the concentration of dicyandiamide in the water to be treated may be, for example, 2.0 mg / L or 5.0 mg / L.

[0019] The persistent nitrogen-containing compound may contain compounds other than guanidine and dicyandiamide, such as biguanides.

[0020] The water to be treated may further contain thiourea.

[0021] The water to be treated may further contain an organic substance (preferably an organic acid and / or an alcohol). In this case, the treatment of the water to be treated proceeds more efficiently. Furthermore, from the viewpoint of proceeding with the treatment of the water to be treated more efficiently, in the anaerobic treatment step, an organic substance (preferably an organic acid and / or an alcohol) may first be added to non-treated water containing persistent nitrogen-containing compounds and water, and then the non-treated water to which the organic substance has been added may be anaerobically treated. Examples of organic acids include acetic acid, formic acid, lactic acid, propionic acid, and butyric acid. Only one type of organic acid may be used, or two or more types may be used. Examples of alcohols include methanol and ethanol. Only one type of alcohol may be used, or two or more types may be used.

[0022] <Anaerobic treatment step> In the anaerobic treatment step, it is preferable to anaerobically treat the water to be treated using at least one reactor selected from the group consisting of an anaerobic sludge bed reactor (preferably an upflow anaerobic sludge bed reactor described below), an anaerobic fluidized bed reactor, and a complete mixing reactor.

[0023] In the anaerobic treatment step, it is particularly preferable to use an upflow anaerobic sludge bed reactor (hereinafter also referred to as a UASB reactor) to anaerobically treat the water to be treated. For details of UASB reactors, refer to known documents such as JP 2002-153897 A, JP 2000-210693 A, and Japanese Patent No. 3385490.

[0024] <Aerobic Treatment Step> The water treatment method of the present disclosure may include a step of aerobically treating the water to be treated. In particular, when the water to be treated containing at least one selected from the group consisting of guanidine and dicyandiamide further contains thiourea, it is preferable to include a step of aerobically treating the water to be treated at least either before or after the anaerobic treatment step. The aerobic treatment can also effectively reduce the concentration of thiourea.

[0025] The concentration of thiourea in the water to be treated is, for example, 0.01 mg / L to 200 mg / L, preferably 0.01 mg / L to 100 mg / L, more preferably 0.01 mg / L to 80 mg / L, even more preferably 0.01 mg / L to 50 mg / L, even more preferably 0.01 mg / L to 5 mg / L, and even more preferably 0.01 mg / L to 2 mg / L. Even when the water to be treated contains thiourea at a relatively high concentration as described above, the thiourea concentration can be reduced by aerobic treatment. The lower limit of the thiourea concentration in the water to be treated may be, for example, 0.10 mg / L or 0.15 mg / L.

[0026] Aerobic treatment is preferably carried out using at least one reactor selected from the group consisting of a fluidized bed reactor, a suspended bed reactor, a moving bed reactor, and a trickling filter reactor. Examples of fluidized bed reactors include activated sludge reactors and reactors containing a fluidized bed of immobilized carriers. More specifically, examples of reactors containing a fluidized bed of immobilized carriers include reactors containing a fluidized bed of immobilized carriers that perform aeration by aeration (e.g., a moving bed biofilm reactor (MBBR)). Examples of suspended bed reactors include reactors containing a suspended bed of immobilized carriers, more specifically, reactors containing a suspended bed of immobilized carriers that perform aeration and mixing by an agitator. Examples of suspended bed reactors include reactors containing a suspended bed of immobilized carriers, more specifically, a submerged bioflinge reactor. Examples of trickling filter reactors include downflow suspended sponge reactors. The above-mentioned fluidized bed reactor, the above-mentioned suspended bed reactor, and the above-mentioned swinging bed reactor may each be used in combination with a membrane bioreactor (MBR) in which solid-liquid separation is performed by membrane separation.

[0027] Aerobic treatment is preferably carried out using a downward flow sponge suspended reactor (hereinafter also referred to as "DHS reactor"). For the configuration of the DHS reactor, refer to known documents such as JP 2009-220075 A and JP 2011-212566 A.

[0028] The water treatment method of the present disclosure preferably includes an anaerobic treatment step and an aerobic treatment step, and further includes a step of subjecting the water to be treated that has been subjected to both anaerobic and aerobic treatment to at least one of anaerobic treatment and aerobic treatment (for example, the following repeat step). The step of subjecting the water to at least one of anaerobic treatment and aerobic treatment may be performed on a portion of the total untreated water.

[0029] <Repeating Step> The water treatment method of the present disclosure preferably includes a repeating step in which an anaerobic treatment step and an aerobic treatment step are alternately and repeatedly performed. This allows the concentrations of guanidine, dicyandiamide, and thiourea to be effectively reduced when the water to be treated contains persistent nitrogen-containing compounds including at least one selected from the group consisting of guanidine and dicyandiamide, and thiourea. The repeating step may be performed on a portion of the total untreated water.

[0030] The repeating step preferably includes alternately repeating an anaerobic treatment step and an aerobic treatment step to decompose a portion of the persistent nitrogen-containing compounds and / or thiourea into nitrogen gas. This embodiment has a great advantage in that the persistent nitrogen-containing compounds and thiourea can be treated without combustion.

[0031] It is expected that the repeated process will enable the decomposition of persistent nitrogen-containing compounds and thiourea into nitrogen gas via ammonia produced by anaerobic treatment and nitric acid produced by aerobic treatment.

[0032] The water treatment device according to the present disclosure is a water treatment device for carrying out the water treatment method according to the present disclosure, and includes a reactor for anaerobic treatment of the water to be treated. The water treatment device according to the present disclosure achieves the same effects as those achieved by the water treatment method according to the present disclosure.

[0033] The water treatment device of the present disclosure may include other elements (e.g., a reactor for aerobic treatment of the water to be treated, etc.) as needed. For details of the other elements, please refer to the above-mentioned section "Water Treatment Method" as appropriate.

[0034] Fig. 1 is a conceptual diagram of a water treatment device 100, which is an example of the water treatment device of the present disclosure. The water treatment device 100 shown in Fig. 1 includes a UASB reactor 10, which is an upflow anaerobic sludge bed reactor, a DHS reactor 20, which is a downflow suspended sponge reactor, a substrate tank 30, and a substrate tank 40.

[0035] The water treatment device 100 further includes a circulation path for circulating the water to be treated through the substrate tank 40 → UASB reactor 10 → substrate tank 30 → DHS reactor 20 → substrate tank 40. The water treatment device of the present disclosure does not necessarily have to include a circulation path. An example of a water treatment device of the present disclosure that does not include a circulation path will be described later (water treatment device 200 shown in FIG. 2).

[0036] The circulation path in the water treatment device 100 includes: a pipe 56 connecting the substrate tank 40 and the UASB reactor 10 and having a liquid feed pump P in between; a pipe 51 connecting the UASB reactor 10 (more specifically, a gas-solid-liquid separation device GSS provided downstream of the UASB reactor 10) and the substrate tank 30; a pipe 52 connecting the substrate tank 30 and the DHS reactor 20 and having a liquid feed pump P in between; and a pipe 53 connecting the DHS reactor 20 and the substrate tank 40. In the circulation path, the two liquid feed pumps P are operated to circulate the water to be treated through the path of the substrate tank 40 → UASB reactor 10 → substrate tank 30 → DHS reactor 20 → substrate tank 40.

[0037] The positions where the two liquid feed pumps P are provided are not limited to this example, and they may be provided in any of the pipes that form the circulation path.

[0038] In addition to the piping for forming the circulation path described above, the water treatment device 100 also includes a pipe 55 having one end connected to the middle of the pipe 51 on the outlet side of the UASB reactor 10 and the other end connected to the substrate tank 40. As a result, the water treatment device 100 can also circulate the water to be treated through the route of the substrate tank 40 → UASB reactor 10 → substrate tank 40.

[0039] A water-to-be-treated supply pipe 57 is connected to the substrate tank 40. In water treatment using the water treatment device 100, water-to-be-treated is supplied to the substrate tank 40 from the outside through the water-to-be-treated supply pipe 57.

[0040] The substrate tank 40 is provided with a stirrer for stirring the water to be treated in the tank, and a stirring motor M for rotating the stirrer.

[0041] The water to be treated in the substrate tank 40 is sent to the lower end side of the UASB reactor 10 via the pipe 56 by operating the liquid sending pump P.

[0042] A sludge bed containing anaerobic microorganisms is disposed inside the UASB reactor 10. In the UASB reactor 10, the water to be treated, which is supplied from the lower end side of the UASB reactor 10, passes upward (i.e., in the direction opposite to the direction of gravity) through the sludge bed, and is thereby anaerobically treated by the sludge bed.

[0043] This anaerobic treatment mainly decomposes guanidine and dicyandiamide, and this anaerobic treatment (i.e., decomposition of guanidine and dicyandiamide) produces, for example, ammonia.

[0044] The water to be treated then reaches the upper side of the sludge bed and is then discharged from the upper end side of the UASB reactor 10 .

[0045] The flow rate of the water to be treated passing through the UASB reactor 10 is, for example, 0.24 L / day to 48 L / day, preferably 0.48 L / day to 24 L / day, and more preferably 0.60 L / day to 8 L / day.

[0046] The temperature of the water to be treated when it passes through the UASB reactor 10 is, for example, 15°C to 40°C, preferably 20°C to 35°C.

[0047] The time during which the water to be treated passes through the UASB reactor 10 (specifically, the HRT (hydraulic retention time)) is, for example, 0.5 to 100 hours, preferably 1 to 50 hours, and more preferably 3 to 40 hours.

[0048] The UASB reactor 10 is provided with a gas meter GM as a biogas production amount measuring device for measuring the amount of biogas produced.

[0049] A gas-solid-liquid separator GSS is connected to the upper end of the UASB reactor 10. The water to be treated discharged from the upper end of the UASB reactor 10 via the gas-solid-liquid separator GSS is sent to the substrate tank 30 via a pipe 51. The water to be treated is returned to the substrate tank 40 from the middle of the pipe 51 via a pipe 55 as needed.

[0050] Similar to the substrate tank 40, the substrate tank 30 is provided with a stirrer for stirring the water to be treated in the tank and a stirring motor M for rotating the stirrer.

[0051] The water to be treated in the substrate tank 30 is sent to the upper end side of the DHS reactor 20 through the pipe 52 by operating a liquid sending pump P provided midway through the pipe 52 .

[0052] The water to be treated that is sent to the upper end of the DHS reactor 20 passes downward (in the direction of gravity) through a sponge installed inside the DHS reactor 20. The sponge holds sludge containing aerobic microorganisms. This causes the water to be aerobically treated.

[0053] The flow rate of the water to be treated passing through the DHS reactor 20 is, for example, 0.24 L / day to 48 L / day, preferably 0.48 L / day to 24 L / day, and more preferably 0.60 L / day to 8 L / day.

[0054] The temperature of the water to be treated when it passes through the DHS reactor 20 is, for example, 15°C to 40°C, preferably 20°C to 35°C.

[0055] The time during which the water to be treated passes through the sponge carrier in the DHS reactor 20 (more specifically, the hydraulic retention time (HRT)) is, for example, 0.5 to 100 hours, preferably 1 to 50 hours, and more preferably 3 to 40 hours.

[0056] This aerobic treatment mainly decomposes thiourea. This aerobic treatment (i.e., decomposition of thiourea) produces, for example, nitric acid. The treated water then reaches the lower side of the sponge carrier, is discharged from the lower end of the DHS reactor 20, and is returned to the substrate tank 40 via a pipe 53 connected to the lower end. After water treatment in the water treatment device is completed, the treated water is discharged from the lower end of the DHS reactor 20 to the outside of the water treatment device through a discharge pipe 54.

[0057] 2 is a conceptual diagram of a water treatment device 200, which is another example of the water treatment device of the present disclosure (more specifically, an example without a circulation path). In FIG. 2, elements that are substantially the same as those in FIG. 1 are designated by the same reference numerals, and redundant explanations will be omitted.

[0058] The water treatment device 200 shown in Figure 2 is a one-pass type device without a circulation path. The water treatment device 200 includes a UASB reactor 10, which is an upflow anaerobic sludge bed type reactor, a DHS reactor 20, which is a downflow suspended sponge type reactor, and a substrate tank 40.

[0059] The pathway in water treatment device 200 (hereinafter also referred to as the "single-pass pathway") includes: a pipe 56 connecting substrate tank 40 and UASB reactor 10 and having a liquid feed pump P therebetween; and a pipe 52 connecting UASB reactor 10 (more specifically, a gas-solid-liquid separator GSS provided downstream of UASB reactor 10) and DHS reactor 20 and having a liquid feed pump P therebetween. In the single-pass pathway, the water to be treated supplied to substrate tank 40 through water to be treated supply pipe 57 is fed through the pathway of substrate tank 40 → UASB reactor 10 → DHS reactor 20 by operating the two liquid feed pumps P, and is then discharged to the outside of the water treatment device through discharge pipe 54.

[0060] Water treatment device 200 is similar to water treatment device 100, except that it omits substrate tank 30 and the circulation path for circulating untreated water, and the preferred aspects are also similar.

[0061] Furthermore, as another example of the water treatment device of the present disclosure, there is an example in which the positions of the UASB reactor 10 and the DHS reactor 20 are swapped in the water treatment device 200, with the DHS reactor 20 being placed upstream and the UASB reactor 10 being placed downstream (not shown).

[0062] The water treatment method and water treatment apparatus of the present disclosure have been described above. The water treatment method of the present disclosure can be appropriately combined with other known and used water treatment methods.

[0063] Examples of the present disclosure will be described below, but the present disclosure is not limited to the following examples.

[0064] The water treatment device 100 shown in Figure 1 was prepared. The effective volume of the UASB reactor 10 was 1 L, the effective volumes of the substrate tank 30 and the substrate tank 40 were each 20 L, and the effective volume of the DHS reactor 20 was 1 L.

[0065] The sludge in the UASB reactor 10 was inoculated with seed sludge containing anaerobic microorganisms, specifically, about 1,000 mg TVS (loss on ignition) of activated sludge treating chemical factory wastewater and 37,000 mg TVS (loss on ignition) of granular sludge collected from a UASB reactor treating industrial wastewater.

[0066] The sponge carrier in the DHS reactor 20 was immersed for 1 hour in activated sludge containing aerobic microorganisms for treating chemical factory wastewater while being aerated, to allow the aerobic microorganisms to adhere to the sponge carrier.

[0067] Throughout the experimental period of each of the following examples, MgSO was added to the wastewater as a mineral agent. ４ (16.48mg / L), CaCl ２ ・2H ２ O (46.3 mg / L), MnSO ４ ・5H ２ O (0.0483 mg / L), ZnSO ４ ・7H ２ O (0.035 mg / L), FeCl ３ ・6H ２ O (0.375 mg / L), CuSO ４ (0.0021mg / L), Na２ MoO ４ ・2H ２ O (0.0012 mg / L) and CoCl ２ ・5H ２ O (0.0002 mg / L) was added.

[0068] [Experimental Examples 1-1 and 1-2] In Experimental Examples 1-1 and 1-2, the DHS reactor 20 and the UASB reactor 10 were reconnected in series, and experiments were conducted using the serially connected DHS reactor 20 and UASB reactor 10. In detail, first, in Experimental Example 1-1, the water to be treated was subjected to aerobic treatment using the DHS reactor 20, and then, in Experimental Example 1-2, the aerobically treated water to be treated was subjected to anaerobic treatment using the UASB reactor 10.

[0069] Wastewater (water to be treated) containing guanidine, dicyandiamide, and thiourea at the concentrations shown in the "Before Treatment" column of "Aerobic Treatment" in Experimental Example 1-1 in Table 1 was prepared as the water to be treated by aerobic treatment using the DHS reactor 20. The concentration (value) of each component in Table 1 is expressed in mg / L.

[0070] Throughout all experimental examples, the concentration (value) of each component in Table 1 was determined by quantification using a capillary electrophoresis apparatus (Agilent 7100, Agilent Technologies) and using the aromatics and vitamins analysis running solution 5 as the running solution.

[0071] The DHS reactor 20 in Experimental Example 1-1 was configured such that 36 cylindrical polyurethane sponge carriers, each 32 mm in diameter and 32 mm in height and fitted with a polyethylene plastic net, were randomly packed into an acrylic column 90 mm in diameter and 1,000 mm in height.

[0072] The UASB reactor 10 used in Experimental Example 1-2 was a UASB reactor having a width of 50 mm, a depth of 50 mm, an effective height of 400 mm, and an effective volume of 1 L.

[0073] Under the above conditions, in Experimental Example 1-1, the water to be treated was subjected to aerobic treatment using the DHS reactor 20, and then, in Experimental Example 1-2, the aerobically treated water was subjected to anaerobic treatment using the UASB reactor 10. The HRT (hydraulic retention time) in each reactor was the time (h) shown in Table 1. The concentrations of each component were determined before and after treatment in Experimental Example 1-1 and in Example 1-2. The results are shown in Table 1.

[0074] [Experimental Examples 2-1 and 2-2] In Experimental Examples 2-1 and 2-2, the UASB reactor 10 and the DHS reactor 20 were reconnected in series, and experiments were conducted using the serially connected UASB reactor 10 and DHS reactor 20. In detail, first, in Experimental Example 2-1, the water to be treated was subjected to anaerobic treatment using the UASB reactor 10, and then, in Experimental Example 1-2, the water to be treated that had been subjected to anaerobically treatment was subjected to aerobic treatment using the DHS reactor 20.

[0075] The UASB reactor 10 used in Experimental Example 2-1 was the same as the UASB reactor 10 used in Experimental Example 1-2.

[0076] The DHS reactor 20 in Experimental Example 2-2 was configured such that 44 cylindrical polyurethane sponge carriers, each 32 mm in diameter and 32 mm in height and fitted with a polyethylene plastic net, were randomly packed into an acrylic column 90 mm in diameter and 1,000 mm in height.

[0077] Under the above conditions, in Experimental Example 2-1, the water to be treated was subjected to anaerobic treatment using the UASB reactor 10, and then, in Experimental Example 1-2, the anaerobically treated water was subjected to aerobic treatment using the DHS reactor 20. The HRT (hydraulic retention time) in each reactor was set to the time (h) shown in Table 1. The concentrations of each component were determined before and after treatment in Experimental Example 2-1 and in Example 2-2. The results are shown in Table 1.

[0078] [Experimental Examples 3-1 and 3-2] In Experimental Examples 3-1 and 3-2, the configuration of the water treatment device 100 shown in FIG. 1 was not changed. First, in Experimental Example 3-1, the water to be treated was subjected to anaerobic treatment using the UASB reactor 10. Next, in Experimental Example 3-2, the anaerobically treated water to be treated was subjected to aerobic treatment using the DHS reactor 20.

[0079] The UASB reactor 10 used in Experimental Example 3-1 was the same as the UASB reactor 10 used in Experimental Example 1-2.

[0080] The DHS reactor 20 in Experimental Example 3-2 was configured such that 38 sponge carriers were suspended by a string from the top of an acrylic column having a diameter of 90 mm and a height of 1,000 mm in two rows of 19 carriers each.

[0081] Under the above conditions, in Experimental Example 3-1, the water to be treated was subjected to anaerobic treatment using the UASB reactor 10, and then, in Experimental Example 3-2, the anaerobically treated water to be treated was subjected to aerobic treatment using the DHS reactor 20. The concentrations of each component were determined before and after the treatment in Experimental Example 3-1 and in Example 3-2. The results are shown in Table 1.

[0082]

[0083] As shown in Table 1, the concentrations of guanidine and dicyandiamide in the water to be treated were reduced in each of Experimental Examples 1-2, 2-1, and 3-1, in which the water to be treated was subjected to anaerobic treatment. The results of these Experimental Examples confirmed that the concentrations of persistent nitrogen-containing compounds (particularly guanidine and dicyandiamide) in the water to be treated can be reduced by subjecting the water to anaerobic treatment, which contains water and persistent nitrogen-containing compounds including guanidine and dicyandiamide.

[0084] Furthermore, in Experimental Example 2-2, it was confirmed that the concentration of thiourea was reduced by aerobic treatment of the water to be treated. This confirmed that when the water to be treated contains thiourea, the concentration of thiourea can also be reduced by aerobic treatment of the water to be treated at least either before or after anaerobic treatment.

[0085] [Experimental Example 2X] The water to be treated that had been treated in the order of Experimental Examples 2-1 and 2-2 was further subjected to the anaerobic treatment of Experimental Example 2-1, as described above. As a result, the generation of nitrogen gas was confirmed.

[0086] The results of the above examples show that alternately repeating anaerobic treatment and aerobic treatment can effectively decompose persistent nitrogen-containing compounds including guanidine and dicyandiamide, and thiourea, and that the decomposition can decompose the persistent nitrogen-containing compounds and thiourea into nitrogen gas via ammonia produced by anaerobic treatment and nitric acid produced by aerobic treatment. The ability to decompose the persistent nitrogen-containing compounds and thiourea in the water to be treated into nitrogen gas has a significant advantage in that the persistent nitrogen-containing compounds can be treated without combustion.

[0087] [Experimental Examples 4-1 and 4-2] A water treatment device 300 shown in FIG. 3 was prepared. The water treatment device 300 was obtained by adding the following modifications to the water treatment device 100 (FIG. 1) described above. - Changes in the water treatment device 300 from the water treatment device 100 (see FIG. 3) - The piping (pipes 53 and 54) for forming a circulation path was omitted. - A mixing tank 60 was added between the UASB reactor 10 and the substrate tank 40. The mixing tank 60 is a tank for adding and mixing an additive organic substance (specifically, an organic acid and / or alcohol) to the water to be treated. The substrate tank 40 and the mixing tank 60 were connected by a piping 56 equipped with a liquid feed pump P, and the mixing tank 60 and the UASB reactor 10 were connected by a piping 66 equipped with a liquid feed pump P. - An additive organic substance tank 62 was added to accommodate additive organic substance to be added to the water to be treated. The added organic substance tank 62 and the mixing tank 60 were connected by a pipe 64 equipped with a liquid feed pump P. The DHS reactor 20 was changed to a DHS reactor 23 having a different configuration.

[0088] The UASB reactor 10 used in Experimental Examples 4-1 and 4-2 was a UASB reactor with a width of 100 mm, a depth of 100 mm, an effective height of 500 mm, and an effective volume of 5 L. The DHS reactor 23 in Experimental Examples 4-1 and 4-2 was configured to include: a cylindrical polyurethane sponge carrier loading section with an inner diameter of 131 mm and a height of 810 mm, equipped with three partitions, and located in the center of the flow direction of the water being treated; a water sprinkler section with an inner diameter of 131 mm and a height of 160 mm, located upstream of the flow direction of the water being treated; a sprinkler device for driving the sprinkler section; and a sloped settling tank with an inner diameter of 131 mm and a height of 155 mm, located downstream of the flow direction of the water being treated. The cylindrical polyurethane sponge carrier loading section was randomly packed with 191 cylindrical polyurethane sponge carriers with a diameter of 32 mm and a height of 32 mm, each fitted with a polyethylene plastic net. The effective volume of the cylindrical polyurethane sponge carrier loading section was 5 L. Untreated water introduced into the DHS reactor 23 through the pipe 52 is sprayed onto the cylindrical polyurethane sponge carrier loading section by a spray section for treated water located upstream in the flow direction, passes through the cylindrical polyurethane sponge carrier loading section and the settling tank in this order, and is discharged outside the water treatment device through the pipe 24.

[0089] Using the water treatment device 300, Experimental Examples 4-1 and 4-2 were conducted in this order. Specifically, in Experimental Example 4-1, the water to be treated was subjected to anaerobic treatment using the UASB reactor 10 at 35°C. Then, in Experimental Example 4-2, the anaerobically treated water was subjected to aerobic treatment using the DHS reactor 23 at 25°C. In Experimental Example 4-1, prior to anaerobic treatment using the UASB reactor 10, methanol and acetic acid were added as added organic matter to the water in the mixing tank 60 via the added organic matter tank 62 and the piping 64. In the UASB reactor 10, the water to be treated to which the added organic matter had been added was subjected to anaerobic treatment. This promoted anaerobic treatment. The added organic matter was added at a ratio of 1.5 to the total ammonia nitrogen concentration ("NH4-N" in Table 2) in the wastewater, as a COD concentration. The amounts of organic matter added were methanol 1.3 and acetic acid 0.2 in terms of COD concentration ratio.

[0090] The concentrations of each component were determined before and after the treatment in Experimental Example 4-1 and before and after the treatment in Example 4-2. The results are shown in Table 2.

[0091] [Experimental Examples 5-1 and 5-2] A water treatment device 400 shown in Figure 4 was prepared. The water treatment device 400 was obtained by adding the following modifications to the water treatment device 300 (Figure 3) described above. -Modifications in the water treatment device 400 from the water treatment device 300 (see Figure 4)- The UASB reactor 10 and the piping 51 were connected by a piping 71 equipped with a liquid feed pump P. This formed a circulation path that returned the water to be treated (hereinafter also referred to as UASB-treated water) that had been anaerobically treated in the UASB reactor 10 back to the upstream side of the UASB reactor 10.

[0092] Experimental Examples 5-1 and 5-2 were conducted in this order using the water treatment device 400. Specifically, in Experimental Example 5-1, the water to be treated was subjected to anaerobic treatment using the UASB reactor 10 at 35°C. Then, in Experimental Example 5-2, the anaerobically treated water was subjected to aerobic treatment using the DHS reactor 23 at 25°C. In Experimental Example 5-1, similar to Experimental Example 4-1, methanol and acetic acid were added as additive organic matter prior to anaerobic treatment using the UASB reactor 10. In Experimental Example 5-1, the HRT (h) was changed as shown in Table 2 compared to Experimental Example 4-1. Furthermore, in Experimental Example 5-1, a portion of the water to be treated that had been anaerobically treated in the UASB reactor 10 was circulated by returning it to the upstream side of the UASB reactor 10 via the pipe 71. This facilitated anaerobic treatment by repeatedly performing anaerobic treatment in the UASB reactor 10. Here, the circulation ratio [UASB influent:USAB circulated water], which is the ratio between the "UASB influent," which is the water to be treated supplied from the mixing tank 60 to the UASB reactor 10 through piping 66, and the "USAB circulated water," which is the water to be treated returned to the UASB reactor 10 through piping 71, was adjusted to the ratio shown in Table 2.

[0093] The concentrations of each component were determined before and after the treatment in Experimental Example 5-1 and before and after the treatment in Example 5-2. The results are shown in Table 2.

[0094]

[0095] As shown in Table 2, in each of Experimental Examples 4-1 and 5-1 in which the water to be treated was subjected to anaerobic treatment, the concentrations of guanidine and dicyandiamide in the water to be treated were reduced.

[0096] The disclosure of Japanese Patent Application No. 2023-215080, filed on December 20, 2023, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A water treatment method comprising a step of anaerobic treatment of water to be treated that contains persistent nitrogen-containing compounds and water.

2. The water treatment method according to claim 1, wherein the persistent nitrogen-containing compound comprises at least one selected from the group consisting of guanidine and dicyandiamide.

3. The water treatment method according to claim 1, wherein the anaerobic treatment step uses at least one reactor selected from the group consisting of an anaerobic sludge bed reactor, an anaerobic fluidized bed reactor, and a complete mixing reactor to anaerobically treat the water to be treated.

4. The water treatment method according to claim 1, wherein the anaerobic treatment step uses an upflow anaerobic sludge bed type reactor to anaerobically treat the water to be treated.

5. The water treatment method according to claim 1, wherein the water to be treated further contains thiourea, and further comprising a step of aerobically treating the water to be treated at least either before or after the step of anaerobic treatment.

6. The water treatment method according to claim 1, wherein the water to be treated further contains thiourea, and further comprising a step of aerobically treating the water to be treated using at least one reactor selected from the group consisting of a fluidized bed reactor, a suspended bed reactor, a rocking bed reactor, and a trickling bed reactor, at least either before or after the anaerobic treatment step.

7. The water treatment method according to claim 1, wherein the water to be treated further contains thiourea, the anaerobic treatment step comprises anaerobically treating the water to be treated using an upflow anaerobic sludge bed type reactor, and further comprises a step of aerobically treating the water to be treated using a downflow sponge suspension type reactor at least either before or after the anaerobic treatment step.

8. The water treatment method according to claim 5, further comprising a repeating step of alternately repeating the anaerobic treatment step and the aerobic treatment step.

9. The water treatment method according to claim 8, wherein the repeating step includes decomposing a portion of the persistent nitrogen-containing compounds into nitrogen gas by alternately repeating the anaerobic treatment step and the aerobic treatment step.

10. The water treatment method according to claim 2, wherein the total concentration of guanidine and dicyandiamide in the water to be treated is 0.1 mg / L to 1000 mg / L.

11. The water treatment method according to claim 5, wherein the total concentration of thiourea in the water to be treated is 0.01 mg / L to 50 mg / L.

12. A water treatment device for carrying out the water treatment method according to any one of claims 1 to 11, comprising a reactor for anaerobically treating the water to be treated.

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