Method for treating wastewater and utilization thereof

Abstract

To provide a wastewater treatment method capable of efficiently removing both organic matter components and nitrogen compound components.SOLUTION: A wastewater treatment method includes the steps for (A) obtaining wastewater with an anionic surfactant concentration of 0 to 1500 mg / L, (B) treating the obtained wastewater with an inorganic coagulant, and (C) treating the wastewater obtained in the step (B) with an anionic polymer coagulant. The pH of the wastewater after the addition of the inorganic coagulant in the step (B) is 4.30 to 5.50.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for treating wastewater generated during the production of polyhydroxyalkanoates from microorganisms and to the use of such wastewater. [Background technology]

[0002] Biodegradable plastics are completely biodegraded by microorganisms in soil or water and incorporated into the natural carbon cycle, making them an environmentally friendly plastic material with almost no adverse impact on ecosystems. Among biodegradable plastics, plant-derived biodegradable plastics such as PHA are attracting attention. PHA is a type of aliphatic polyester (thermoplastic polyester) that can be produced by microorganisms using natural plant-derived organic acids and oils as a carbon source.

[0003] In the PHA production process using microorganisms, wastewater containing large amounts of organic components and nitrogen compounds derived from microbial cell residues, etc. is generated. One method for treating wastewater generated in such a PHA production process using microorganisms is a method of biological treatment and coagulation treatment of such wastewater (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2023-132279 [Patent Document 2] Patent Publication No. 2023-132280 Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned biological treatment and coagulation treatment methods for treating wastewater generated in the PHA manufacturing process using microorganisms were excellent methods for treating the organic components (COD) in the wastewater. However, from the perspective of the efficiency of treating the nitrogen compound components (TN) in the wastewater, there was room for improvement, as a separate denitrification treatment may be required in some cases.

[0006] In light of the above situation, one aspect of the present invention aims to provide a method for treating wastewater that can efficiently remove both organic components and nitrogen compound components in the wastewater generated in a PHA production process using microorganisms. [Means for solving the problem]

[0007] As a result of intensive research to solve the above-mentioned problems, the inventors have discovered that by carrying out a two-stage coagulation treatment using an inorganic coagulant and an anionic polymer coagulant under specific conditions on wastewater generated in a PHA production process using microorganisms, it is possible to efficiently remove both organic components and nitrogen compound components from the wastewater generated in the PHA production process, and have thus completed the present invention.

[0008] That is, one aspect of the present invention includes the following configuration. [1] A method for treating wastewater generated during the production of polyhydroxyalkanoate from a microorganism, comprising: step (A) of obtaining wastewater having an anionic surfactant concentration of 0 to 1500 mg / L; step (B) of treating the wastewater obtained in step (A) with an inorganic flocculant; and step (C) of treating the wastewater obtained in step (B) with an anionic polymer flocculant, wherein in step (B), the pH of the wastewater after addition of the inorganic flocculant is 4.30 to 5.50. [2] The method for treating wastewater according to [1], wherein the inorganic flocculant comprises at least one selected from the group consisting of aluminum sulfate, polyaluminum chloride, and polyferric sulfate. [3] The method for treating wastewater according to [1] or [2], wherein the wastewater generated during the production of polyhydroxyalkanoate from the microorganism is wastewater generated in one or more of the following steps (a) to (c): step (a) of culturing microorganisms that produce polyhydroxyalkanoate; step (b) of crushing and / or solubilizing the microorganisms containing the polyhydroxyalkanoate; and step (c) of separating the polyhydroxyalkanoate from the treated liquid obtained in step (b). [4] The method for treating wastewater according to any one of [1] to [3], wherein the pH of the wastewater obtained in the step (A) is 8.00 to 12.00. [5] The method for treating wastewater according to any one of [1] to [4], wherein the amount of the inorganic flocculant used in the step (B) satisfies the following formula: amount of the inorganic flocculant used in the step (B) / COD concentration in the wastewater obtained in the step (A)=0.30 to 0.50. [6] The method for treating wastewater according to any one of [1] to [5], wherein the wastewater obtained in the step (A) has a COD concentration of 1,000 to 70,000 mg / L and a TN concentration of 10 to 3,600 mg / L. [7] A method for producing polyhydroxyalkanoate, which comprises, as one step, the method for treating wastewater according to any one of [1] to [6]. [Effects of the Invention]

[0009] According to one aspect of the present invention, it is possible to provide a method for treating wastewater that can efficiently remove both organic components and nitrogen compound components in wastewater generated in a PHA production process using microorganisms. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present invention will be described in detail below. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more and B or less." In addition, all documents described in this specification are incorporated herein by reference.

[0011] [1. Wastewater treatment method] A method for treating wastewater according to one embodiment of the present invention (hereinafter, sometimes referred to as "the treatment method") is a method for treating wastewater generated during the production of polyhydroxyalkanoate from microorganisms, and comprises: step (A) of obtaining wastewater having an anionic surfactant concentration of 0 to 1500 mg / L; step (B) of treating the wastewater obtained in step (A) with an inorganic flocculant; and step (C) of treating the wastewater obtained in step (B) with an anionic polymer flocculant, wherein in step (B), the pH of the wastewater after addition of the inorganic flocculant is 4.30 to 5.50.

[0012] This treatment method can efficiently remove both organic and nitrogenous compounds from wastewater generated in a process for producing polyhydroxyalkanoates using microorganisms. Furthermore, as described above, this treatment method does not require biological treatment (e.g., treatment using activated sludge) to treat the wastewater. Therefore, (1) because the treatment tanks and other equipment required for biological treatment are not required, wastewater treatment can be performed in a space-saving and simple process. Furthermore, (2) because even highly concentrated wastewater that is harmful to living organisms can be treated without any problems, it can flexibly respond to fluctuations in wastewater (e.g., concentration, temperature, etc.).

[0013] <Drainage> First, the wastewater to be treated by this treatment method will be described. The wastewater to be treated by this treatment method is wastewater (hereinafter, sometimes simply referred to as "wastewater") generated during the production of polyhydroxyalkanoate (hereinafter, sometimes referred to as "PHA") from microorganisms.

[0014] (PHA) PHA will be described in detail. "PHA" is a general term for polymers containing hydroxyalkanoate as a monomer unit (monomer repeating unit) and is generally biodegradable. In particular, in this specification, "PHA" refers to a (co)polymer containing hydroxyalkanoate repeating units in an amount of 50 mol% or more of all monomer repeating units (100 mol%), and a resin composed of such a (co)polymer. PHA is preferably a (co)polymer containing 60 mol% or more, and more preferably a (co)polymer containing 70 mol% or more, of all monomer repeating units (100 mol%). In this specification, the term "(co)polymer" is used to refer to both a homopolymer composed of only one type of monomer and a copolymer composed of two or more types of monomers.

[0015] Examples of PHA include poly(3-hydroxyalkanoate) (hereinafter sometimes referred to as "P3HA") and poly(4-hydroxyalkanoate). Among them, P3HA is preferred because it is suitable for use in molded articles. In other words, the wastewater to be treated by this treatment method is preferably wastewater generated during the production of P3HA from microorganisms.

[0016] P3HA is a 3-hydroxyalkanoate repeating unit of the formula: [—CHR—CH—CO—O—] (wherein R is C n H 2n+1 where n is an integer of 1 to 15.) as an essential repeating unit. In this specification, "P3HA" refers to a (co)polymer containing 50 mol % or more of the 3-hydroxyalkanoate repeating units out of all monomer repeating units (100 mol %).

[0017] Specific examples of P3HA include homopolymers of one or more monomers selected from the group consisting of 3-hydroxybutanoic acid (hereinafter sometimes referred to as "3HB"), 3-hydroxypropionic acid, 3-hydroxypentanoic acid, 3-hydroxyhexanoic acid, 3-hydroxyheptanoic acid, 3-hydroxyoctanoic acid, 3-hydroxynonanoic acid, 3-hydroxydecanoic acid, 3-hydroxyundecanoic acid, 3-hydroxydodecanoic acid, 3-hydroxytridecanoic acid, 3-hydroxytetradecanoic acid, 3-hydroxyhexadecanoic acid, and 3-hydroxyoctadecanoic acid, or copolymers of two or more of these monomers. Furthermore, P3HA may also be a copolymer of the above-mentioned P3HA-based repeating unit with a repeating unit other than P3HA. For example, P3HA may be a copolymer of the above-mentioned P3HA-based repeating unit and one or more monomers selected from the group consisting of 4-hydroxybutanoic acid, 4-hydroxypentanoic acid, 4-hydroxyhexanoic acid, 4-hydroxyheptanoic acid, 4-hydroxyoctanoic acid, 4-hydroxynonanoic acid, 4-hydroxydecanoic acid, 4-hydroxyundecanoic acid, 4-hydroxydodecanoic acid, 4-hydroxytridecanoic acid, 4-hydroxytetradecanoic acid, 4-hydroxyhexadecanoic acid, and 4-hydroxyoctadecanoic acid.

[0018] More specifically, examples of P3HA include 3HB homopolymers such as poly(3-hydroxybutyrate) (hereinafter sometimes referred to as "P3HB"), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter sometimes referred to as "P3HB3HH"), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (hereinafter sometimes referred to as "P3HB4HB"), and poly(3-hydroxybutyrate-co-3-hydroxypropionate). Among these, P3HB, P3HB3HH, and P3HB4HB are preferred, with P3HB3HH and P3HB4HB being more preferred, due to the ease of industrial production using microorganisms.

[0019] In this specification, "poly(X-co-Y)" refers to a copolymer containing X repeating units and Y repeating units, and is intended to mean a copolymer obtained by copolymerizing a monomer from which the X repeating unit is derived and a monomer from which the Y repeating unit is derived. As described above, the name of a P3HA is determined by the repeating units contained in the P3HA. However, a very small amount (about 1 mol % or less) of a monomer contained in a P3HA may not be reflected in the name of the P3HA, provided that such a monomer does not significantly affect the physical properties of the P3HA. In other words, a P3HA may contain, in addition to the repeating units corresponding to its name, very small amounts of other repeating units.

[0020] (microorganisms) The microorganisms used in this treatment method are microorganisms capable of producing PHA (PHA-producing microorganisms). Examples of PHA-producing microorganisms include bacteria of the genera Cupriavidus, Alcaligenes, Ralstonia, Pseudomonas, Bacillus, Azotobacter, Nocardia, and Aeromonas. In addition to these microorganisms, genetically modified microorganisms in which various PHA synthesis-related genes have been introduced into any microorganism can also be used.

[0021] Among the PHA-producing microorganisms mentioned above, microorganisms capable of producing P3HA (P3HA-producing microorganisms) are preferred for use in the present treatment method. Examples of P3HA-producing microorganisms include Bacillus megaterium, a P3HB-producing bacterium discovered in 1925, and other known naturally occurring microorganisms, such as Cupriavidus necator (formerly classified as Alcaligenes eutrophus and Ralstonia eutropha) and Alcaligenes latus. These microorganisms accumulate P3HB intracellularly.

[0022] Known microorganisms that produce P3HA, a copolymer of 3HB and other hydroxyalkanoic acids, include Aeromonas caviae, which produces P3HB3HH, and Alcaligenes eutrophus, which produces poly(3-hydroxybutyrate-co-4-hydroxybutyrate). In particular, Alcaligenes eutrophus AC32 (FERM BP-6038), which has been transformed with genes encoding P3HA synthases to increase P3HB3HH productivity (T. Fukui, Y. Doi, J. Bacteriol., 179, pp. 4821-4830 (1997)), is a particularly suitable PHA-producing microorganism.

[0023] PHA production using a microorganism can be carried out, for example, by the following procedure.

[0024] (a) a step of culturing a PHA-producing microorganism; (b) a step of crushing and / or solubilizing the cultured PHA-producing microorganism; and (c) a step of separating polyhydroxyalkanoate from the treatment liquid obtained in step (b).

[0025] The wastewater to be treated by this treatment method may be wastewater produced in any of the above processes, or may be a mixture of wastewater produced in two or more of these processes.

[0026] That is, the wastewater generated during the production of polyhydroxyalkanoate from microorganisms that are the target of treatment in this treatment method is preferably wastewater generated in any one or more of the following steps (a) to (c): step (a) of culturing microorganisms that produce polyhydroxyalkanoate, step (b) of crushing and / or solubilizing the microorganisms containing the polyhydroxyalkanoate, and step (c) of separating the polyhydroxyalkanoate from the treatment liquid obtained in step (b).

[0027] The wastewater to be treated by this treatment method may include wastewater generated by cleaning the equipment (culture tanks, etc.) used in the above steps (a) to (c) (or other processes for producing polyhydroxyalkanoates), rainwater that flows into these steps, and other miscellaneous wastewater.

[0028] More specific aspects of steps (a) to (c) will be described in detail in the section [3. Method for producing polyhydroxyalkanoate].

[0029] <Process (A)> This treatment method includes a step (A) of obtaining wastewater having an anionic surfactant concentration of 0 to 1500 mg / L. Step (A) can also be considered as a step of adjusting the anionic surfactant concentration in wastewater generated during the production of polyhydroxyalkanoate from microorganisms to 0 to 1500 mg / L.

[0030] The wastewater generated during the production of PHA from the microorganisms subjected to this treatment method (hereinafter sometimes referred to as "raw wastewater") may contain the anionic surfactant used in the PHA production process (mainly the above-mentioned step (b)). The present inventors have found that if the concentration of the anionic surfactant in the wastewater to be treated exceeds 1500 mg / L, the treatment efficiency of nitrogen compound components in the subsequent steps (B) and (C) is significantly reduced. In other words, they have found that in order to efficiently treat nitrogen compound components in the wastewater, the concentration of the anionic surfactant needs to be 1500 mg / L or less.

[0031] Therefore, from the viewpoint of more efficiently treating nitrogen compound components in the wastewater, the concentration of the anionic surfactant in the wastewater obtained in step (A) is 0 to 1500 mg / L, preferably 0 to 1000 mg / L, and more preferably 0 to 500 mg / L. The concentration of the anionic surfactant in the wastewater in step (A) is a value measured by the method described in the Examples.

[0032] When the concentration of the anionic surfactant in the wastewater to be subjected to step (A) exceeds 1500 mg / L, it is preferable to adjust (reduce) the concentration of the ionic surfactant in step (A) so that the concentration of the anionic surfactant is 1500 mg / L or less. In step (A), the method for adjusting the concentration of the anionic surfactant in the wastewater is not particularly limited, and examples thereof include a method of diluting with water (e.g., pure water, industrial water, etc.) and a method of centrifuging.

[0033] When the concentration of the anionic surfactant in the wastewater to be subjected to step (A) is 1500 mg / L or less, (1) the wastewater may be subjected to the subsequent step (B) without any particular adjustment of the concentration of the anionic surfactant in the wastewater in step (A), or (2) the concentration of the anionic surfactant in the wastewater may be adjusted to be even lower (for example, to 500 mg / L or less) from the viewpoint of further improving the treatment efficiency of nitrogen compound components.

[0034] Examples of anionic surfactants that may be contained in the wastewater subjected to or obtained by step (A) include anionic surfactants that may be used in known PHA production processes. Specific examples include sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonate, sodium cholate, sodium deoxycholate, and sodium oleate. The wastewater from step (A) may contain only one, two or more, or none of these anionic surfactants. When the wastewater from step (A) contains two or more anionic surfactants, the concentration of the anionic surfactant in the wastewater is calculated based on the total amount of the two or more anionic surfactants.

[0035] The pH of the wastewater obtained in step (A) is not particularly limited, but is preferably 8.00 to 12.00, more preferably 9.00 to 11.50, and even more preferably 10.00 to 11.50, because this can improve the coagulation properties of organic components and nitrogen compound components in the subsequent steps (B) and (C). The pH of the wastewater is a value measured by the method described in the Examples.

[0036] When the pH of the wastewater to be subjected to step (A) is outside the above range, step (A) may further include a step of adjusting the pH of the wastewater to within the above range. In step (A), the method for adjusting the pH of the wastewater is not particularly limited, and examples thereof include a method of adding sodium hydroxide.

[0037] The COD (Chemical Oxygen Demand) concentration in the wastewater obtained in step (A) is not particularly limited, but is preferably 1000 to 70000 mg / L, more preferably 5000 to 60000 mg / L, and even more preferably 8000 to 50000 mg / L, because this can improve the COD removal efficiency in the subsequent steps (B) and (C). The COD concentration in the wastewater is an index that indicates the amount (concentration) of organic components in the wastewater, and is a value measured by the method described in the Examples.

[0038] When the COD concentration of the wastewater to be subjected to step (A) is outside the above range, step (A) may further comprise a step of adjusting the COD concentration of the wastewater to fall within the above range. In step (A), the method for adjusting the COD concentration of the wastewater is not particularly limited, and examples thereof include a method of diluting the wastewater with water.

[0039] The TN (total nitrogen) concentration in the wastewater obtained in step (A) is not particularly limited, but is preferably 10 to 3600 mg / L, more preferably 100 to 3000 mg / L, and even more preferably 200 to 2000 mg / L, because this can improve the TN removal efficiency in the subsequent steps (B) and (C). The TN concentration in the wastewater is an index that indicates the amount (concentration) of nitrogen compound components in the wastewater, and is a value measured by the method described in the Examples.

[0040] When the TN concentration in the wastewater subjected to step (A) is outside the above range, step (A) may further comprise a step of adjusting the TN concentration in the wastewater to fall within the above range. In step (A), the method for adjusting the TN concentration in the wastewater is not particularly limited, and examples thereof include a method of diluting the wastewater with water.

[0041] The ratio of the amount of anionic surfactant to the COD concentration in the wastewater obtained in step (A) (amount of anionic surfactant / COD concentration) is not particularly limited, but is preferably 0 to 1.5, more preferably 0 to 1.0, and even more preferably 0 to 0.5, because this can improve the coagulation properties of organic components and nitrogen compound components in the subsequent steps (B) and (C).

[0042] When the ratio of the amount of anionic surfactant to the COD concentration in the wastewater subjected to step (A) is outside the above range, step (A) may further include a step of adjusting the ratio of the amount of anionic surfactant to the COD concentration to fall within the above range. In step (A), the method for adjusting the ratio of the amount of anionic surfactant to the COD concentration in the wastewater is not particularly limited, and examples thereof include methods such as filtration and adsorption.

[0043] <Process (B)> This treatment method includes step (B) of treating the wastewater obtained in step (A) with an inorganic flocculant. Step (B) can also be considered a step of flocculating (primary flocculation) organic components and nitrogen compound components (and anionic surfactants) in the wastewater.

[0044] The inorganic flocculant used in step (B) is not particularly limited as long as it is capable of flocculating (primary flocculation) the organic components and nitrogen compound components (and anionic surfactants) in the wastewater, but aluminum sulfate, polyaluminum chloride, polyferric sulfate, etc. are examples of suitable inorganic flocculants because they are inexpensive and easily available. In other words, the inorganic flocculant used in step (B) is preferably an inorganic flocculant containing at least one selected from the group consisting of aluminum sulfate, polyaluminum chloride, and polyferric sulfate.

[0045] In step (B), the pH of the wastewater after adding the inorganic flocculant is 4.30 to 5.50. The present inventors have surprisingly found that by adjusting the pH of the wastewater obtained after the addition of the inorganic flocculant in step (B) to 4.30 to 5.50, when the wastewater is treated with an anionic polymer flocculant in the subsequent step (C), it is possible to treat (flocculate) a large amount of nitrogen compounds that were difficult to treat (flocculate) by conventional methods.It was not previously known that the pH of the wastewater after the addition of the inorganic flocculant (after primary flocculation) affects the improvement of the efficiency of treating (flocculating) nitrogen compounds when the subsequent polymer flocculant is added (during secondary flocculation), and this is a surprising discovery.

[0046] Therefore, in the step (B), from the viewpoint of treating nitrogen compounds more efficiently, it is preferable to add the inorganic flocculant so that the pH of the wastewater after addition of the inorganic flocculant is 4.30 to 5.50.

[0047] From the viewpoint of treating nitrogen compounds more efficiently, the pH of the wastewater after the addition of the inorganic flocculant in step (B) is preferably 4.30 to 5.20, more preferably 4.40 to 5.00, even more preferably 4.40 to 4.80, and even more preferably 4.40 to 4.70. The pH of the wastewater after the addition of the inorganic flocculant in step (B) varies depending on the pH and surfactant content of the wastewater subjected to step (B), as well as the type and amount of inorganic flocculant added, but can be controlled mainly by adjusting the type and amount of inorganic flocculant added in step (B).

[0048] The amount of inorganic flocculant used in step (B) is not particularly limited as long as it is an amount that allows the pH of the wastewater after addition of the inorganic flocculant to fall within the above range, but it is preferably an amount such that the ratio of the amount of inorganic flocculant used to the COD concentration in the wastewater obtained in step (A) (i.e., supplied to step (B)) is 0.30 to 0.50. In other words, it is preferable that the amount of inorganic flocculant used in step (B) is an amount that satisfies the following formula: Amount of inorganic coagulant used in step (B) / COD concentration in wastewater obtained in step (A) = 0.30 to 0.50.

[0049] By controlling the ratio of the amount of inorganic coagulant used to the COD concentration in the wastewater obtained in step (A) within the above range, the COD removal performance can be further improved. From the viewpoint of further improving the COD removal performance, the ratio of the amount of inorganic coagulant used to the COD concentration in the wastewater obtained in step (A) is more preferably 0.32 to 0.50, and even more preferably 0.40 to 0.50.

[0050] The specific amount of inorganic flocculant used in step (B) is an amount that brings the pH of the wastewater after addition of the inorganic flocculant into the above-mentioned range, and is preferably an amount that brings the ratio of the amount of inorganic flocculant used to the COD concentration in the wastewater obtained in step (A) into the above-mentioned range, but is not particularly limited thereto. For example, the amount is preferably 500 to 40,000 ppm, more preferably 1,000 to 20,000 ppm, and even more preferably 3,000 to 10,000 ppm relative to the wastewater to be treated.

[0051] <Process (C)> This treatment method includes step (C), in which the wastewater obtained in step (B) is treated with an anionic polymer flocculant. Step (C) can also be considered a step in which the organic components and nitrogen compound components (and anionic surfactants) in the wastewater that have been primarily flocculated in step (B) are further flocculated (secondary flocculation) and separated as flocs (solids). In this specification, the wastewater obtained through step (C) may also be referred to as treated water.

[0052] In step (C), the organic components and nitrogen compound components (and anionic surfactants) in the wastewater are coarsely aggregated by secondary aggregation, which allows these components to be precipitated (i.e., coagulated and precipitated), facilitating the separation of these components from the wastewater and the utilization of the separated matter (e.g., for fuel).

[0053] The anionic polymer flocculant used in step (C) is not particularly limited as long as it is capable of further flocculating (secondary flocculation) the organic and nitrogen compound components in the wastewater that have undergone primary flocculation. Examples include sodium acrylate / acrylamide copolymer, alkylsulfonic acid / acrylamide copolymer, sodium alginate, carboxymethylcellulose sodium salt, and sodium polyacrylate.

[0054] The amount of the anionic polymer flocculant used in step (C) is not particularly limited. However, since the anionic polymer flocculant can improve flocculation even when added in a small amount, from the viewpoint of suppressing excessive use and improving economic efficiency, the amount is preferably 1 to 50 ppm, more preferably 1 to 10 ppm, and even more preferably 1 to 5 ppm, relative to the wastewater to be treated.

[0055] In step (C), the method for recovering (separating from the wastewater) the flocculants flocculated by the anionic polymer flocculant is not particularly limited, and for example, a solid-liquid separation operation using a settling tank, a decanter, a filter press, a belt press, a screw press, a pressure flotation device, or the like can be used.

[0056] In step (C), before adding the anionic polymer flocculant, the pH of the wastewater may be adjusted to 5.00 to 7.00, preferably 6.00 to 7.00. By adjusting the pH of the wastewater before adding the anionic polymer flocculant to within the above range, the flocculation properties of organic components and nitrogen compound components in the wastewater can be further improved.

[0057] In step (C), a surfactant treatment agent may be added to the wastewater in addition to the anionic polymer flocculant. Addition of the surfactant treatment agent allows for more efficient flocculation of surfactants (e.g., anionic surfactants), making it easier to remove the surfactant than other surfactant removal methods such as filtration. The timing of adding the surfactant treatment agent in step (C) is not particularly limited, and it may be added before, simultaneously with, or after the addition of the anionic polymer flocculant. However, it is preferable to add the surfactant treatment agent before the addition of the anionic polymer flocculant.

[0058] When a surfactant treatment agent is used in step (C), the amount used (addition amount) thereof is not particularly limited, but is preferably 0 to 500 ppm, more preferably 1 to 400 ppm, and even more preferably 10 to 200 ppm, relative to the wastewater to be treated.

[0059] Examples of surfactant treatment agents that can be used in step (C) include CRYDECODE (Kurita Water Industries Ltd.), SEFFNER N (MP Gokyo Food & Chemical Co., Ltd.), N8105 (Katayama Nalco Co., Ltd.), etc. One of these may be used alone, or two or more may be used in combination.

[0060] According to the present treatment method including the above steps (A) to (C), it is possible to efficiently remove both organic and nitrogenous compounds from wastewater generated in a PHA production process using microorganisms. In this specification, the treatment efficiency of organic and nitrogenous compounds in a wastewater treatment process can be evaluated by the COD removal rate, TN removal rate, and the ratio of TN removal rate to COD removal rate (TN removal rate / COD removal rate) in the treated water (the wastewater obtained in step (C) in the present treatment method).

[0061] Specifically, the COD removal rate of the treated water obtained through this treatment method (i.e., the treated water obtained in step (C)) is not particularly limited, but is preferably 50.0% or more, more preferably 60.0% or more, and particularly preferably 70.0% or more. The higher the COD removal rate of the treated water, the more organic components have been removed from the treated water compared to the wastewater before treatment. The TN removal rate is a value calculated by the following formula: COD removal rate (%) = {1 - (COD concentration (mg / L) of treated water obtained in step (C) / COD concentration (mg / L) of wastewater obtained in step (A))} × 100.

[0062] The COD concentration in the treated water obtained by this treatment method is not particularly limited as long as it is lower than that of the raw wastewater (the wastewater subjected to step (A)), but from the viewpoint of obtaining treated wastewater with a sufficiently reduced environmental load, it is preferably 5000 mg / L or less, more preferably 4000 mg / L or less, and even more preferably 3000 mg / L or less. The lower limit of the COD concentration is not particularly limited, and may be 0 mg / L.

[0063] The TN removal rate of the treated water obtained through this treatment method (i.e., the wastewater obtained in step (C)) is not particularly limited, but is preferably 30.0% or more, more preferably 40.0% or more, and particularly preferably 50.0% or more. The higher the TN removal rate of the treated water, the more nitrogen compound components have been removed from the treated water compared to the wastewater before treatment. The TN removal rate is a value calculated by the following formula: TN removal rate (%) = {1 - (TN concentration (mg / L) of treated water obtained in step (C) / TN concentration (mg / L) of wastewater obtained in step (A))} × 100.

[0064] The TN concentration in the treated water obtained by this treatment method is also not particularly limited as long as it is lower than that of the raw wastewater (the wastewater subjected to step (A)), but from the viewpoint of obtaining treated wastewater with a sufficiently reduced environmental load, it is preferably 400 mg / L or less, more preferably 300 mg / L or less, and even more preferably 200 mg / L or less. Furthermore, the lower limit of the TN concentration is not particularly limited and may be 0 mg / L.

[0065] The ratio of TN removal rate to COD removal rate (TN removal rate / COD removal rate) in the treated water obtained through this treatment method is not particularly limited, but is preferably 30.0% or more, more preferably 40.0% or more, even more preferably 50.0% or more, even more preferably 60.0% or more, and particularly preferably 70.0% or more. A higher ratio of TN removal rate to COD removal rate in a wastewater treatment process indicates that the wastewater treatment process achieves both high treatment efficiency for organic components and high treatment efficiency for nitrogen compound components. The ratio of TN removal rate to COD removal rate can be calculated by dividing the TN removal rate by the COD removal rate.

[0066] <Other processes> The present treatment method may include various steps (other steps) that can be performed in a wastewater treatment process other than the above steps (A) to (C). Examples of such other steps include a step of further removing organic components from the resulting treated water by anaerobic treatment using activated sludge (anaerobic treatment step), a step of further removing nitrogen compound components from the resulting treated water by aerobic treatment using activated sludge (aerobic treatment step), and a step of burning the separated aggregates and using them as an energy source (combustion step). In the present treatment method, one, two or more of these other steps may be performed, or none may be performed. The conditions for performing these other steps can be appropriately determined by those skilled in the art based on known techniques.

[0067] 3. Method for producing polyhydroxyalkanoate In one embodiment of the present invention, there is provided a method for producing polyhydroxyalkanoate (PHA) (hereinafter, sometimes referred to as "the present production method") that includes the present treatment method as one step.

[0068] Since the present production method includes the present treatment method as one step, it is possible to produce PHA while efficiently treating both the organic components and nitrogen compound components in the wastewater generated in the process of the present production method.

[0069] As a specific embodiment of the present production method, any known PHA production process utilizing microbial culture can be applied, except that the present treatment method is included as one step. Preferably, the present production method is a method comprising the following steps (a) to (c): (a) a step of culturing a PHA-producing microorganism; (b) a step of crushing and / or solubilizing the PHA-containing microorganisms cultured in the step (a); Step (c) of separating PHA from the treated liquid obtained in step (b).

[0070] One embodiment of the present production method will be described in detail below, taking as an example a method including steps (a) to (c).

[0071] <Process (a)> The present production method preferably includes step (a), which is a step of culturing a PHA-producing microorganism.

[0072] Regarding the specific aspects of the PHA-producing microorganisms cultured in step (a) and the PHA produced by the PHA-producing microorganisms, the description in the above section [1. Wastewater treatment method] is incorporated as appropriate.

[0073] The cultivation of the PHA-producing microorganism in step (a) can be carried out based on a known method for culturing a PHA-producing microorganism, such as the method described in International Publication No. WO2019 / 142717.

[0074] <Process (b)> The present production method preferably includes step (b), in which the PHA-containing microorganisms cultured in step (a) are disrupted and / or solubilized to remove the PHA accumulated within the microbial cells.

[0075] (Crushing and solubilization) PHA produced by microorganisms accumulates within the cells of the microorganisms. Generally, PHA-producing microorganisms have a cell wall, and in order to recover PHA produced by these microorganisms, the cell wall must be removed by disrupting and / or solubilizing the microorganisms.

[0076] In step (b), the disruption treatment and solubilization treatment are not particularly limited as long as they remove the cell walls of the PHA-producing microorganisms and make them recoverable, and either one of them or both may be performed. When both the disruption treatment and the solubilization treatment are performed, the order in which they are performed is not particularly limited.

[0077] In step (b), an aqueous suspension of PHA-containing microorganisms is preferably used as the target for disruption and / or solubilization. The culture broth containing the PHA-containing microorganisms after completion of the culture can be used as the aqueous suspension, or an aqueous suspension of PHA-containing microorganisms prepared by adding water to the microorganisms recovered from the culture broth can be used. Methods well known to those skilled in the art, such as centrifugation and membrane separation, can be used to recover the microorganisms from the culture broth. Furthermore, the microorganisms may be killed by heating or the like when they are recovered. Here, the heating temperature is preferably 50°C to 80°C. It is preferable to kill the microorganisms during disruption and / or solubilization.

[0078] The disruption and / or solubilization treatment preferably includes at least one treatment selected from the group consisting of chemical treatment and physical disruption treatment, and more preferably includes both chemical treatment and physical disruption treatment.

[0079] Solubilization treatments for microorganisms containing PHA include chemical treatments such as enzyme treatment, alkali treatment, and surfactant treatment. These solubilization treatments may be performed alone or in combination of two or more. When two or more of these solubilization treatments are performed, the order in which they are performed is not particularly limited. Among these, it is preferable to perform two or more selected from the group consisting of enzyme treatment, alkali treatment, and surfactant treatment (particularly alkali treatment and surfactant treatment), and it is preferable to perform all three.

[0080] The enzyme treatment can be carried out according to a conventionally known method, and is not particularly limited thereto. For example, the method described in JP 2012-115145 A (a method in which a PHA-containing microorganism is enzymatically treated to decompose the cell wall and obtain a higher purity) can be used. The enzyme is not particularly limited as long as it can be used in industrial products, but protease and cell wall-decomposing enzymes are preferred. The amount of enzyme added can be selected appropriately. During the enzyme treatment, if the solution pH is outside the optimal pH range for the enzyme, it is preferable to add an acidic or alkaline compound to adjust the pH to within the optimal range. The acidic compound is not particularly limited, and examples thereof include inorganic acids such as nitric acid, sulfuric acid, hydrochloric acid, and phosphoric acid, and organic acids such as acetic acid, formic acid, citric acid, and oxalic acid. The alkaline compound is not particularly limited, and examples thereof include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide; alkali metal carbonates such as sodium carbonate and potassium carbonate; alkali metal bicarbonates such as sodium bicarbonate and potassium bicarbonate; alkali metal salts of organic acids such as sodium acetate and potassium acetate; alkali metal borates such as borax; alkali metal phosphates such as trisodium phosphate, disodium hydrogen phosphate, tripotassium phosphate, and dipotassium hydrogen phosphate; alkaline earth metal hydroxides such as barium hydroxide; and ammonia water.

[0081] The alkali treatment can be carried out, for example, by adding an alkali to an aqueous suspension of PHA-containing microorganisms. Conventional alkalis can be used, and there is no particular limitation as long as they are capable of destroying the cell walls of PHA-containing microorganisms and releasing the PHA from the cells. Examples of alkalis that can be used in the alkali treatment include alkali metal hydroxides, such as sodium hydroxide, potassium hydroxide, and lithium hydroxide; alkali metal carbonates, such as sodium carbonate and potassium carbonate; alkali metal bicarbonates, such as sodium bicarbonate and potassium bicarbonate; alkali metal salts of organic acids, such as sodium acetate and potassium acetate; alkali metal borates, such as borax; alkali metal phosphates, such as trisodium phosphate, disodium hydrogen phosphate, tripotassium phosphate, and dipotassium hydrogen phosphate; alkaline earth metal hydroxides, such as barium hydroxide; and aqueous ammonia. The pH of the aqueous suspension used in the alkali treatment is not particularly limited, but is preferably adjusted to a range of 8.0 to 12.0.

[0082] The surfactant treatment can be carried out according to a conventionally known method, and the method is not particularly limited. For example, the method described in JP 2012-115145 A (a method of adding a surfactant to an aqueous suspension of PHA-containing microorganisms) can be used. The surfactant is not particularly limited as long as it can disrupt the cell walls of PHA-containing microorganisms and release the PHA from the cells. Examples of surfactants include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. From the viewpoint of cleaning performance, anionic surfactants and / or nonionic surfactants are preferred. For the purpose of cleaning and removing proteins, etc., it is preferable to use an anionic surfactant, and for the purpose of cleaning and removing fatty acids and oils, it is preferable to use a nonionic surfactant. Both anionic and nonionic surfactants may be used. Preferred surfactants used in the surfactant treatment include anionic surfactants such as sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, sodium cholate, sodium deoxycholate, and sodium oleate, and nonionic surfactants such as polyoxyethylene alkyl ethers and polyoxyalkylene alkyl ethers, and two or more of these may be used in combination. Among these, sodium dodecyl sulfate (SDS) is preferred from the standpoints of cost, amount used, and additive effect. The surfactant treatment is preferably carried out under alkaline conditions, i.e., it is preferably carried out together with alkaline treatment.

[0083] The amount of surfactant added in the surfactant treatment is not particularly limited, but is preferably 0.001 to 10 parts by weight per 100 parts by weight of PHA, and more preferably 5 parts by weight or less from the viewpoint of cost.

[0084] The physical disruption treatment can be any conventionally known method, and is not limited to any particular method as long as it can separate cellular components other than PHA from the cells and pulverize them. Examples of devices used for the physical disruption treatment include a high-pressure homogenizer, an ultrasonic disrupter, an emulsifying disperser, and a bead mill.

[0085] The enzymes, surfactants, etc. used in step (b) may be contained in the PHA wastewater generated.

[0086] <Process (c)> The present production method preferably includes step (c). Step (c) is a step of separating PHA from the treatment liquid (also referred to as "disruption treatment liquid") obtained in step (b). Step (c) can also be described as a step of recovering only PHA from the treatment liquid containing microbial residues in addition to PHA obtained in step (b).

[0087] Methods for separating PHA from the disruption treatment solution include conventionally known methods such as centrifugation and membrane separation. Among these, centrifugation is preferred because it allows for industrially large-scale processing and continuous use. Centrifugal separation is preferred, as it is a centrifugal settler with a rotating container without holes, and various types include separator plate type, cylindrical type, and decanter type. Because PHA particles have a small specific gravity difference from water, separator plate type (intermittent discharge type, nozzle discharge type) is preferred, as it has a large separation and settling area and can achieve high acceleration. Furthermore, nozzle discharge type is particularly preferred when the PHA concentration in the disruption treatment solution is high. Furthermore, decanter type is generally unsuitable for low acceleration and small differences in solid-liquid specific gravity, but it can also be used by changing the particle size of the PHA. Some decanter type models have separator plates and a large separation and settling area, and such models may be usable without changing the particle size.

[0088] In step (c), after separating and recovering PHA from the disruption solution by the above-mentioned separation method, the PHA can be washed with water, for example, by suspending the PHA in water and then separating the PHA again, to more strictly remove cellular components other than PHA. The pH of this washing is preferably 8.0 to 12.5 (i.e., the washing is with alkaline water).

[0089] (Wastewater treatment process) The present production method includes the present treatment method as one step (wastewater treatment step). The wastewater treatment step is a step in which organic components and nitrogen compound components are removed (separated) by the present treatment method from the various wastewaters generated in the steps of the present production method, specifically, from the above steps (a) to (c). Note that for specific aspects of the "present wastewater treatment method" which is one step of the present production method, the description in the above section [1. Wastewater treatment method] is incorporated by appropriate reference.

[0090] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Example]

[0091] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0092] [Measurement and evaluation methods] The measurements in the examples and comparative examples were carried out by the following methods.

[0093] (pH) The pH of the wastewater was measured using the following method: a glass electrode pH meter (D-210P, manufactured by Horiba, Ltd.) that had been zero-calibrated and span-calibrated was used. After rinsing the electrode with pure water, the pH of approximately 200 mL of the target wastewater was immediately measured.

[0094] (anionic surfactant concentration) The concentration of anionic surfactants in wastewater was measured using the following method: Two separatory funnels (separatory funnel (A) and separatory funnel (B)) were prepared. 50 mL of water, 10 mL of alkaline sodium borate solution, and 5 mL of methylene blue solution were placed in separatory funnel (A), while 100 mL of water, 10 mL of alkaline sodium borate solution, and 5 mL of methylene blue solution were placed in separatory funnel (B). 10 mL of chloroform was added to each separatory funnel and the mixture was vigorously shaken for 30 seconds to separate the layers. The aqueous layer was then washed with 3 mL of chloroform by gentle shaking. This series of operations was repeated until the chloroform layer became colorless, after which 3 mL of 1 mol / L sulfuric acid was added to separatory funnel (B). An arbitrary amount of wastewater of interest was added to separatory funnel (A), 10 mL of chloroform was added, and the mixture was shaken and left for 1 minute. The chloroform layer was then transferred to separatory funnel (B) (extraction operation). Similarly, 10 mL of chloroform was added to the separatory funnel (B), and after shaking and leaving for 1 minute, the entire chloroform layer was transferred to a volumetric flask through a funnel filled with absorbent cotton soaked in chloroform. Another 10 mL of chloroform was added to the separatory funnel (A), and this extraction procedure was repeated, with the entire volume transferred to a volumetric flask. Chloroform was added to this volumetric flask to bring the volume to 50 mL. The absorbance of this solution at a wavelength of 650 nm was measured, and the anionic surfactant concentration was calculated using a calibration curve obtained from the standard solution. This calculated value was used as the anionic surfactant concentration in the target wastewater.

[0095] (COD concentration) The COD concentration in the wastewater was measured by the following method: 2 mL of the test wastewater was added to a chromic acid COD concentration measurement reagent (HACH1227, manufactured by HACH) and heated at 150±5°C for 2 hours. After heating, the absorbance of the heated wastewater was measured at a wavelength of 600 nm, and the COD concentration was calculated using a calibration curve obtained from the standard solution. The calculated value was used as the COD concentration in the target wastewater.

[0096] (TN concentration) The TN concentration in wastewater was measured using the following method: 2 mL of the target wastewater was added to a potassium peroxodisulfate vial containing a persulfate decomposition TN concentration measurement reagent (HACH1402, manufactured by HACH), heated at 105±5°C for 30 minutes, and then mixed with the dedicated reagent. After mixing, the absorbance of the wastewater at a wavelength of 410 m was measured, and the TN concentration was calculated using a calibration curve obtained from the standard solution. The calculated value was used as the TN concentration in the target wastewater.

[0097] Example 1 (PHA production by microorganisms) Ralstonia eutropha, a PHA-producing microorganism described in International Publication No. 2019 / 142717, was cultured by the method described in paragraphs

[0041] to

[0048] of the same document to obtain a fungal culture solution containing PHA-containing fungal cells (microorganisms). Ralstonia eutropha is currently classified as Capriavidus necator.

[0098] The bacterial cell culture solution obtained above was inactivated by heating and stirring at an internal temperature of 60 to 80°C for 30 minutes.

[0099] After this inactivation treatment, the microbial cells were crushed and solubilized with sodium dodecyl sulfate, an ionic surfactant. The resulting solution containing PHA particles and microbial residues was diluted with industrial water and centrifuged six times to separate the PHA.

[0100] (Process (A)) The wastewater generated by the above-mentioned microbial PHA production process was collected, and the pH, COD concentration, TN concentration, and anionic surfactant concentration were measured. The results are shown in Table 1. Since the anionic surfactant concentration of the collected wastewater was 1500 mg / L or less, it was used in the subsequent step (B) without adjusting the concentration, etc.

[0101] (Process (B)) To the wastewater obtained in step (A), 4000 ppm of aluminum sulfate (8% aqueous solution) as an inorganic flocculant was added, and the mixture was stirred at room temperature for 1 minute to react. The pH and other properties of the wastewater after the stirring reaction are shown in Table 1.

[0102] (Process (C)) The wastewater obtained in step (B) was adjusted to a pH of 7.00 by adding an appropriate amount of sodium hydroxide, and then 100 ppm of N8105 (Katayama Nalco Corporation), a surfactant treatment agent, was added. Furthermore, 1 ppm of sodium polyacrylate solution, an anionic polymer flocculant, was added to coagulate and precipitate the organic and nitrogen compounds in the wastewater. After allowing to stand for 1 minute, a small amount of the supernatant liquid of this treated water was sampled, and the COD and TN concentrations were measured. The COD removal rate, TN removal rate, and TN removal rate / COD removal rate were calculated. The results are shown in Table 1.

[0103] [Examples 2 to 6, Comparative Examples 1 to 6] Wastewater generated in a PHA production process from a different batch than that used in Example 1 was used as raw wastewater (subjected to step (A)), and wastewater generated in a PHA production process was treated using the same procedure as in Example 1, except that the amounts of each coagulant, etc. used were changed as shown in Table 1. The COD and TN concentrations in the final treated water were measured, and the COD removal rate, TN removal rate, and TN removal rate / COD removal rate were calculated. The results are shown in Table 1. Note that in none of the Examples and Comparative Examples was the raw wastewater diluted in step (A). Therefore, the content (concentration) of each component in the wastewater after step (A) shown in Table 1 is the content (concentration) of each component in the raw wastewater used in each Example and Comparative Example.

[0104] [Table 1]

[0105] 〔summary〕 As is clear from Table 1, the treatment methods of Comparative Examples 1 to 6 produced low TN removal rates in the resulting treated water, and also produced low TN removal rates relative to the COD removal rate, whereas the treatment methods of Examples 1 to 6, in which an inorganic coagulant was added in step (B) so that the pH of the treated wastewater was within the range of 4.30 to 5.50, produced high COD and TN removal rates in the resulting treated water, and also produced a high TN removal rate relative to the COD removal rate. These results demonstrate that this treatment method can efficiently treat both organic components and nitrogen compound components in wastewater. [Industrial Applicability]

[0106] According to one embodiment of the present invention, a method for treating wastewater generated in a PHA production process can be provided, which can efficiently treat both organic compounds and nitrogen compounds in the wastewater. Therefore, one embodiment of the present invention can be suitably used in wastewater treatment and PHA production.

Claims

1. A method for treating wastewater generated during the production of polyhydroxyalkanoate from microorganisms, comprising: Step (A) of obtaining wastewater having an anionic surfactant concentration of 0 to 1500 mg / L; A step (B) of treating the wastewater obtained in the step (A) with an inorganic flocculant; and and (C) treating the wastewater obtained in the step (B) with an anionic polymer flocculant, In the step (B), the pH of the wastewater after adding the inorganic flocculant is 4.30 to 5.

50.

2. 2. The method for treating wastewater according to claim 1, wherein the inorganic flocculant comprises at least one selected from the group consisting of aluminum sulfate, polyaluminum chloride, and polyferric sulfate.

3. The method for treating wastewater according to claim 1, wherein the wastewater generated during the production of polyhydroxyalkanoate from the microorganism is wastewater generated in any one or more of the following steps (a) to (c): (a) a step of culturing a microorganism that produces polyhydroxyalkanoate; Step (b) of crushing and / or solubilizing the microorganisms containing the polyhydroxyalkanoate; A step (c) of separating the polyhydroxyalkanoate from the treated liquid obtained in the step (b).

4. The method for treating wastewater according to claim 1, wherein the pH of the wastewater obtained in the step (A) is 8.00 to 12.

00.

5. The method for treating wastewater according to claim 1, wherein the amount of the inorganic flocculant used in the step (B) satisfies the following formula: Amount of the inorganic flocculant used in the step (B) / COD concentration in the wastewater obtained in the step (A)=0.30 to 0.

50.

6. 2. The method for treating wastewater according to claim 1, wherein the wastewater obtained in step (A) has a COD concentration of 1,000 to 70,000 mg / L and a TN concentration of 10 to 3,600 mg / L.

7. A method for producing polyhydroxyalkanoate, which comprises the wastewater treatment method according to any one of claims 1 to 6 as one step.

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