Recycled water production method

Abstract

The purpose of the present invention is to provide a method for producing recycled water, the method being capable of considerably reducing chemical cleaning of a membrane during the production of recycled water from waste water, and being capable of eliminating fouling of the membrane substantially by water washing only. The above are achieved by means of a method for producing recycled water, the method comprising the steps (A) to (D) described below. (A) A step for performing an anaerobic treatment and an aerobic treatment by means of microorganisms on waste water that is discharged during the production process of PHA (B) A step for subjecting the treated water obtained in step (A) to pretreatment filtration by means of a membrane separation activated sludge method (C) A step for subjecting the treated water obtained in step (B) to an alkali treatment (D) A step for filtering the treated water obtained in step (C) by means of an ion removal membrane

Description

[Technical Field]

[0001] The present invention relates to a method for producing recycled water and a method for producing polyhydroxyalkanoic acid (hereinafter also referred to as "PHA"). [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 little adverse impact on ecosystems. Plant-derived biodegradable plastics such as PHA are attracting attention as representative biodegradable plastics. PHA is an aliphatic polyester (thermoplastic polyester) that is produced by microorganisms using natural plant-derived organic acids and oils as a carbon source and accumulates within the cells as an energy storage substance.

[0003] PHA produced by microorganisms is water-insoluble and usually accumulates as granules within microbial cells. Therefore, in order to use PHA as a plastic, a process of separating and extracting PHA from microbial cells is required. For example, Patent Document 1 reports a method for separating and purifying PHA that combines the addition of alkali and high-pressure crushing. Furthermore, Patent Document 2 reports a method for separating and purifying PHA that combines physical cell disruption and chemical treatment with enzymes and surfactants.

[0004] Conventional PHA production methods tend to produce large amounts of wastewater due to cell disruption, centrifugation, etc., and recycling of wastewater is desired to reduce the environmental burden. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 07-31489 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-193940 Summary of the Invention [Problem to be solved by the invention]

[0006] In the separation and purification method of PHA, a filtration membrane is generally used to separate PHA. This filtration membrane requires a membrane capacity recovery treatment by chemical cleaning before repeated use. However, in conventional wastewater recycling technology, there are problems such as the membrane capacity recovery treatment by chemical cleaning causing early deterioration of the filtration membrane, and there is room for improvement.

[0007] Therefore, an object of the present invention is to provide a method for producing recycled water that can significantly reduce the need for chemical cleaning of membranes when producing recycled water from wastewater, and can essentially eliminate membrane fouling by washing with water alone. [Means for solving the problem]

[0008] As a result of intensive research to solve the above-mentioned problems, the inventors have discovered the novel finding that, in a method for producing recycled water from wastewater, by carrying out an alkaline treatment step before the membrane filtration step, membrane fouling can be essentially eliminated by water washing alone, and have completed the present invention.

[0009] Therefore, one aspect of the present invention is a method for producing recycled water, comprising the following steps (A) to (D): (A) a treatment step in which wastewater discharged in a PHA production process is subjected to anaerobic and aerobic treatment using microorganisms; (B) a pretreatment filtration step in which the treated water obtained in step (A) is pretreated and filtered using a membrane separation activated sludge method; (C) an alkali treatment step in which the treated water obtained in step (B) is alkali treated; and (D) a filtration step in which the treated water obtained in step (C) is filtered using an ion removal membrane. [Effects of the Invention]

[0010] According to one aspect of the present invention, a method for producing recycled water can be provided in which, when producing recycled water from wastewater, membrane fouling can be eliminated essentially by cleaning alone, without chemically cleaning the membrane. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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.

[0012] 1. Overview of the Invention A method for producing recycled water according to one embodiment of the present invention (hereinafter also referred to as this production method) comprises the following steps (A) to (D): (A) a treatment step in which wastewater discharged in the PHA production process is subjected to anaerobic and aerobic treatment using microorganisms; (B) a pretreatment filtration step in which the treated water obtained in step (A) is pretreated and filtered using a membrane separation activated sludge method; (C) an alkali treatment step in which the treated water obtained in step (B) is alkali treated; and (D) a filtration step in which the treated water obtained in step (C) is filtered using an ion removal membrane.

[0013] Membrane filtration is a typical method for recycling wastewater. However, membrane filtration can be prone to fouling (clogging) due to minute, highly viscous suspended particles in the wastewater. Therefore, the membranes must be repeatedly cleaned during operation. Generally, there are two known methods for cleaning membranes: (1) physical cleaning, typified by backpressure cleaning, in which filtered water is flushed from the permeate side (secondary side), and (2) chemical cleaning using chemicals.

[0014] The physical cleaning described above uses water to automatically clean periodically (approximately once every 30 minutes to 1 hour), which can remove reversible deposits on the membrane surface or inside. However, physical cleaning cannot completely remove fouling substances adhering to membrane pores, etc., and the transmembrane pressure continues to rise. Therefore, once the transmembrane pressure rises to a certain level, chemical cleaning must be performed to remove the fouling substances from the membrane. However, repeated chemical cleaning not only damages the membrane due to the effects of the chemicals, but also renders it unusable as an ion removal membrane. In other words, a method to extend the usable period of the membrane was desired.

[0015] Therefore, the present inventors have conducted extensive research with the aim of providing a method for producing recycled water that does not require chemical cleaning in order to extend the usable period of the membrane, and as a result, have discovered the following. Certain metal ions cause irreversible membrane fouling. Prior to the filtration process using an ion removal membrane, the treated water is subjected to an alkaline treatment process to precipitate specific fouling substances contained in the treated water as solids in advance, thereby suppressing irreversible fouling on the ion removal membrane. By subjecting the treated water to an alkaline treatment process before carrying out the filtration process using an ion removal membrane, membrane fouling can be eliminated by simply washing with water.

[0016] The method for producing recycled water, which includes the above-mentioned characteristic steps, is unprecedented and represents an extremely excellent technology.

[0017] Furthermore, the present inventors have produced PHA using recycled water obtained by the above-mentioned production method, and have surprisingly succeeded in obtaining PHA with high thermal stability. The present invention will be described in detail below.

[0018] In this specification, "substantially only water washing" means that water washing is the main washing mode, and does not preclude the inclusion of other washing modes in addition to water washing. For example, "substantially only water washing" may include, in addition to water washing, chemical washing in a smaller amount than usual. Preferably, water washing alone is intended.

[0019] [2. Recycled water production method] This production method includes the following steps (A) to (D). Process (A): A process in which wastewater discharged from the PHA manufacturing process is subjected to anaerobic and aerobic treatment using microorganisms. Step (B): A pre-filtration step in which the treated water obtained in step (A) is pre-filtered by a membrane separation activated sludge method. Step (C): An alkaline treatment step in which the treated water obtained in step (B) is subjected to an alkaline treatment. Step (D): A filtration step in which the treated water obtained in step (C) is filtered through an ion removal membrane. (Process (A)) Step (A) in this production method is a treatment step in which wastewater discharged from the PHA production process is subjected to anaerobic and aerobic treatment using microorganisms, and organic matter contained in the wastewater can be decomposed by step (A).

[0020] Anaerobic and aerobic treatment using microorganisms are not particularly limited and can be carried out by common methods used in water treatment. Anaerobic treatment can be carried out, for example, by using acid-producing bacteria to decompose high-molecular-weight carbohydrates, lipids, etc. into organic acids, lower alcohols, etc., and then using granular methanogens to decompose the organic acids, lower alcohols, etc. into methane gas and carbon dioxide. The anaerobic treatment device can be composed of, for example, an acid production tank where the reaction by acid-producing bacteria takes place and an EGSB-type methane production reaction tank where the reaction by methanogens takes place. Aerobic treatment can be carried out, for example, by using an apparatus composed of a denitrification tank (activated sludge treatment tank) and an aeration tank (activated sludge treatment tank) to decompose organic matter that has not been decomposed by anaerobic treatment in the aeration tank using aerobic bacteria. The aerobic treatment apparatus may be composed of, for example, a denitrification tank (activated sludge treatment tank), an aeration tank (activated sludge treatment tank), a second denitrification tank (activated sludge treatment tank), and a reaeration tank (activated sludge treatment tank).

[0021] (Process (B)) Step (B) in this production method is a pre-filtration step in which the treated water obtained in step (A) is pre-filtered by a membrane separation activated sludge method. Step (B) can remove large-particle substances contained in the wastewater that were not decomposed in step (A).

[0022] The pre-filtration step using the membrane bioreactor activated sludge method is not particularly limited and can be carried out by a general method used in water treatment. For example, the pre-filtration step can be carried out in an apparatus in which a membrane bioreactor (MBR) using a UF membrane or MF membrane is installed in an aeration tank (activated sludge treatment tank) or a reaeration tank (activated sludge treatment tank).

[0023] The pores of the MF membrane are not particularly limited, but may be, for example, about 0.4 μm, and the pores of the UF membrane are also not particularly limited, but may be, for example, about 0.05 μm.

[0024] (Process (C)) Step (C) in this production method is an alkaline treatment step in which the treated water obtained in step (B) is alkaline treated. Step (C) allows substances that cause fouling of the ion removal membrane (i.e., fouling substances) to be precipitated in advance in step (D), which will be described later. Therefore, it becomes possible to remove the fouling substances that have adhered to the ion removal membrane in step (D) simply by washing with water.

[0025] More specifically, if the alkaline treatment in step (C) is not performed, the salt concentration of the water that does not pass through the membrane increases during the membrane filtration process in step (D), resulting in the precipitation of crystals on the surface of the ion-removal membrane. As filtration continues, the repeated precipitation of crystals causes the crystals to grow and firmly adhere to the ion-removal membrane, clogging it. Therefore, conventional techniques require chemical cleaning to remove the crystals that have adhered to the membrane surface. However, by performing the alkaline treatment in step (C), the crystals precipitate before membrane filtration, preventing them from firmly adhering to the membrane.

[0026] In other words, this manufacturing method allows the ion removal membrane to be restored essentially by washing with water alone, without the need for chemical cleaning. Therefore, the ion removal membrane is not damaged by chemicals, and irreversible fouling of the ion removal membrane does not occur, allowing the ion removal membrane to be used for a long period of time. In addition, because the chemicals typically used to clean ion removal membranes are highly toxic, avoiding the use of these chemicals is also advantageous from the standpoint of environmental protection.

[0027] In this specification, the term "alkali treatment" refers to adjusting parameters such as pH, fouling index (FI) value, and turbidity of the treated water by adding an alkaline substance to the treated water.

[0028] The method for carrying out the alkaline treatment in step (C) is not particularly limited as long as it is a method that can adjust each parameter of the treated water to a desired value. From the viewpoint of ease of adjustment of each parameter, the alkaline treatment is preferably carried out by adding an alkaline aqueous solution.

[0029] The alkaline aqueous solution used in step (C) is not particularly limited, and examples thereof include aqueous solutions of alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide, aqueous solutions of alkali metal carbonates such as sodium carbonate and potassium carbonate, aqueous solutions of alkali metal bicarbonates such as sodium bicarbonate and potassium bicarbonate, aqueous solutions of alkali metal salts of organic acids such as sodium acetate and potassium acetate, aqueous solutions of alkali metal borates such as borax, aqueous solutions of alkali metal phosphates such as trisodium phosphate, disodium hydrogen phosphate, tripotassium phosphate, and dipotassium hydrogen phosphate, aqueous solutions of alkaline earth metal hydroxides such as barium hydroxide, and aqueous ammonia. From the viewpoint of reducing costs, it is preferable to use an aqueous sodium hydroxide solution.

[0030] In step (C), the pH of the treated water is preferably adjusted to 7.0 to 11.0, more preferably 8.0 to 11.0, and even more preferably 8.5 to 11.0. If the pH is 7.0 or higher, metal salts will precipitate in the treated water. Furthermore, if the pH is 11.0 or lower, deterioration of the ion removal membrane can be prevented.

[0031] In step (C), the turbidity of the treated water is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.3 or more. If the turbidity is 0.1 or more, the solid content has sufficiently precipitated. Furthermore, the upper limit of the turbidity of the treated water is preferably 30 or less, more preferably 20 or less, even more preferably 10 or less, and particularly preferably 5 or less. If the turbidity is 30 or less, the filtration of the treated water is not hindered. The turbidity of the treated water is measured by the method described in the Examples below.

[0032] In step (C), the FI value of the treated water is preferably 4.5 or more, more preferably 5.0 or more, even more preferably 5.5 or more, particularly preferably 6.0 or more, and even more preferably 6.5 or more. If the FI value is within the above range, solids have been sufficiently precipitated in the treated water. There is no particular upper limit to the FI value. Here, the "FI value" is calculated by the following formula (1).

[0033]

number

[0034] In the formula (1), PF represents the clogging factor, T1 represents the time required for 500 mL of treated water to permeate the ion removal membrane, T2 represents the time required for another 500 mL of treated water to permeate the same ion removal membrane after measuring T1, and T represents the time from the start of measuring T1 to the start of measuring T2.

[0035] Conventionally, treated water used for permeation through an ion removal membrane (e.g., an RO membrane) had to be pretreated so that the FI value would be 0 to 4. Therefore, it is surprising that the advantageous effects of the present invention can be obtained by using treated water with a high FI value (e.g., 4.5 or more) that would not normally be permeated through an ion removal membrane (e.g., an RO membrane) in the present production method.

[0036] In the present production method, in addition to step (C), it is preferable that the method further comprises the following step (C'). Step (C'): A precipitation step in which solids containing polyvalent ions are precipitated in the treated water. The multivalent ions are not usually precipitated in the treated water and can cause fouling of the ion removal membrane. Therefore, by carrying out step (C') of precipitating solids containing the multivalent ions before the water passes through the ion removal membrane, fouling of the ion removal membrane can be further suppressed.

[0037] The method for precipitating the solid is not particularly limited, but can be carried out by, for example, adjusting the pH, concentrating, adjusting the temperature, or the like.

[0038] The polyvalent ions are not particularly limited, and examples thereof include divalent or higher cations and divalent or higher anions. The number of types of polyvalent ions contained in the solid is not particularly limited, and may be one type or multiple types. The precipitated solid may be in the form of crystals, particles, rods, or the like.

[0039] In one embodiment of the present invention, the multiply charged ions are Si 2+ , Ca 2+ , PO4 2- , SO4 2- , Mg 2+ , Mn 2+ , Zn 2+ , Fe 2+ , Fe 3+ , Sr 2+ , Cu 2+ , Al 3+ , Sn 3+ It is preferable that the material is one or more selected from the group consisting of:

[0040] In general, Na + , K. + , N.H. 4+ Monovalent ions such as Cl - , NO 3- These anions have high solubility in water and are therefore unlikely to cause fouling, whereas the polyvalent ions have low solubility in water and are prone to precipitate as solids, which can cause fouling of the ion removal membrane.

[0041] In the present production method, step (C) preferably further comprises the following step (C''). Step (C''): A settling and removal step in which the solid matter precipitated in the treated water in step (C') is sedimented and removed. By including step (C'') in the present production method, the frequency of cleaning the ion removal membrane can be further reduced in step (D) described below.

[0042] The method for settling and removing the precipitated solids is not particularly limited, but can be carried out using, for example, a centrifugal settler, a thickener, or the like.

[0043] In one embodiment of the present invention, a scale inhibitor may be added when carrying out step (C). Addition of the scale inhibitor makes it even more difficult for crystals to grow on the surface of the ion removal membrane. Usable scale inhibitors are not particularly limited, but examples include Genesys LF (manufactured by Genesys), PC-191T (manufactured by Katayama Nalco), and Kuriverta N series (manufactured by Kurita Water Industries). The amount of scale inhibitor added is also not particularly limited, but may be, for example, 1 to 50 ppm.

[0044] (Process (D)) Step (D) in this production method is a filtration step in which the treated water obtained in step (C) is filtered through an ion removal membrane. Step (D) makes it possible to remove solids precipitated in step (C). The treated water that has been subjected to step (D) becomes recycled water.

[0045] In this specification, the term "recycled water" refers to water that can be used in the production of PHA, which is obtained by carrying out the steps (A) to (D) on wastewater discharged in the process of producing PHA.

[0046] The ion removal membrane used in step (D) preferably has an MgSO rejection of 60 to 100%, more preferably 70 to 100%, and even more preferably 90 to 100% when subjected to a pressure of 3000 kPa at 20°C. If the MgSO rejection is 60% or higher, the ion permeability of the ion removal membrane will not be high. Furthermore, when the resulting recycled water is used for purifying PHA, a decrease in molecular weight at high temperatures is likely to be suppressed.

[0047] The transmembrane pressure difference of the ion removal membrane in step (D) is not particularly limited, but from the viewpoint of ion removal rate, it is preferably 0.4 MPa to 4.14 MPa, more preferably 0.5 MPa to 2.5 MPa, and even more preferably 0.6 MPa to 2.0 MPa. If the transmembrane pressure difference is 0.4 MPa or more, the amount of permeate and the ion removal rate do not decrease, and if it is 4.14 MPa or less, the membrane is less likely to be damaged. The transmembrane pressure difference of the ion removal membrane is measured by the method described in the Examples below.

[0048] The timing for cleaning the ion removal membrane is not particularly limited, but for example, it is preferably performed when the transmembrane pressure of the ion removal membrane reaches 4.14 MPa or more, more preferably when it reaches 2.5 MPa or more, and even more preferably when it reaches 2.0 MPa or more. By cleaning the ion removal membrane when the transmembrane pressure of the ion removal membrane reaches 4.14 MPa or more, the transmembrane pressure is maintained within the above-mentioned preferred range. The time for cleaning the ion removal membrane is not particularly limited as long as the transmembrane pressure of the ion removal membrane can be sufficiently reduced, but it may be, for example, 30 minutes or more.

[0049] The permeation rate of the ion removal membrane in step (D) is preferably 0.01 to 2000 L / min, more preferably 0.5 to 1500 L / min. A permeation rate of 0.01 L / min or more improves productivity. Furthermore, a permeation rate of 2000 L / min or less makes the ion removal membrane less susceptible to damage.

[0050] The temperature of the treated water during filtration in step (D) is not particularly limited, but is preferably 50° C. or lower, more preferably 45° C. or lower. If the temperature of the treated water is 50° C. or lower, the membrane is less likely to deteriorate. There is also no particular limit to the lower limit of the temperature of the treated water, but from the viewpoint of smooth filtration, it is preferably 1° C. or higher.

[0051] In step (D), it is preferable to periodically wash the ion removal membrane in order to remove the precipitated metal salts.

[0052] Flushing is a preferred method for cleaning ion removal membranes. Flushing is a physical cleaning method in which water is passed through the ion removal membrane at a low pressure and a high flow rate in order to remove initial contamination. While tap water may be used for flushing, recycled water that has passed through the ion removal membrane is preferred from the standpoint of efficiency and cost. The pressure during flushing may be such that the primary pressure of the ion removal membrane is 0.29 MPa or less. The flow rate of the recycled water may be 6 m / min or more.

[0053] As the ion removal membrane, it is preferable to use one or more selected from the group consisting of an NF membrane and an RO membrane, because they have high ion (for example, calcium ion) removal performance, and it is more preferable to use an RO membrane.

[0054] 3. PHA manufacturing method A method for producing PHA according to one embodiment of the present invention (hereinafter also referred to as "the method for producing the present PHA") comprises step (a) of disrupting or solubilizing microbial cells containing PHA, and step (b) of separating the PHA from the composition obtained in step (a), and is characterized in that recycled water produced by the present production method is used in steps (a) and (b). In the method for producing PHA, the use of recycled water produced by the present production method can improve the thermal stability of PHA.

[0055] (Microbial cells containing PHA) In one embodiment of the present invention, microbial cells containing PHA can be obtained by culturing a microorganism capable of producing PHA.

[0056] In one embodiment of the present invention, PHA is a general term for polymers containing 3-hydroxybutyric acid (hereinafter also referred to as "3HB") as a monomer unit. PHA may be poly(3-hydroxybutyric acid), which is a homopolymer containing 3-hydroxybutyric acid as a monomer unit, or may be a copolymer containing 3-hydroxybutyric acid and other 3-hydroxyalkanoic acids as monomer units. Examples of other 3-hydroxyalkanoic acids include 3-hydroxyhexanoic acid (hereinafter also referred to as "3HH"), 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-hydroxypentadecanoic acid, and 3-hydroxyhexadecanoic acid.

[0057] As PHA, poly(3-hydroxybutyric acid), poly(3-hydroxybutyric acid-co-3-hydroxyhexanoic acid), poly(3-hydroxybutyric acid-co-3-hydroxyoctanoic acid), etc. are preferred because they are easily produced industrially, with poly(3-hydroxybutyric acid-co-3-hydroxyhexanoic acid) being particularly preferred. The composition ratio of each monomer unit constituting the two-component copolymer PHBH of 3HB and 3HH is not particularly limited, but when the total of all monomer units is taken as 100 mol%, the 3HH unit may be 1 to 50 mol%, 1 to 25 mol%, or 1 to 15 mol%.

[0058] In one embodiment of the present invention, the microorganism capable of producing PHA is not particularly limited, and may be a microorganism isolated from nature or deposited in a depository institution for strains (e.g., IFO, ATCC, etc.), or a mutant or transformant prepared from such a microorganism. Examples include bacteria of the genera Cupriavidus, Alcaligenes, Ralstonia, Pseudomonas, Bacillus, Azotobacter, Nocardia, and Aeromonas. Particularly preferred are strains such as Alcaligenes lipolytica, Alcaligenes latus, Aeromonas caviae, Aeromonas hydrophila, and C. necator. Furthermore, when a microorganism does not inherently have the ability to produce PHA or produces only a low amount of PHA, a transformant obtained by introducing a target PHA synthase gene and / or its mutant into the microorganism can also be used. The PHA synthase gene used to prepare such a transformant is not particularly limited, but a PHA synthase gene derived from Aeromonas caviae is preferred.

[0059] By culturing the above-mentioned microorganisms under appropriate conditions, microorganisms having accumulated PHA within their cells can be obtained. The culturing method is not particularly limited, and methods such as those described in JP 05-93049 A and WO 2008 / 010296 A can be used. As the microbial cells containing PHA, a bacterial cell culture solution containing PHA-containing microbial cells after the completion of the culture can be used as is, or a sterilized bacterial cell culture solution obtained by heating the bacterial cell culture solution to kill the bacterial cells can be used. The sterilization can be carried out, for example, by heat treatment at a temperature of 50 to 80°C for 5 to 120 minutes.

[0060] (Step (a)) In step (a), the microbial cells containing PHA are disrupted or solubilized. Step (a) can be carried out, for example, by at least one treatment selected from the group consisting of chemical treatment and physical disruption treatment.

[0061] The chemical treatment can be carried out with at least one compound selected from the group consisting of alkaline compounds, proteolytic enzymes, and cell wall-decomposing enzymes.

[0062] The alkaline compound is not particularly limited as long as it can destroy the cell walls of PHA-containing microbial cells and release the PHA from the cells, and examples include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide, etc., alkali metal carbonates such as sodium carbonate, potassium carbonate, alkali metal bicarbonates such as sodium bicarbonate, potassium bicarbonate, alkali metal salts of organic acids such as sodium acetate, potassium acetate, alkali metal borates such as borax, alkali metal phosphates such as trisodium phosphate, disodium hydrogen phosphate, tripotassium phosphate, dipotassium hydrogen phosphate, alkaline earth metal hydroxides such as barium hydroxide, aqueous ammonia, etc. Among these, sodium hydroxide, sodium carbonate, potassium hydroxide, and lithium hydroxide are preferred from the viewpoints of suitability for industrial production and cost reduction.

[0063] The proteolytic enzyme is not particularly limited, but examples thereof include Alcalase, pepsin, trypsin, papain, chymotrypsin, aminopeptidase, carboxypeptidase, etc. Specific proteolytic enzymes that can be used industrially include, for example, "Protease A," "Protease P," and "Protease N" (all manufactured by Amano Enzyme Co., Ltd.), "Alcalase," "Esperase," "Zavinase," and "Evalase" (all manufactured by Novozymes), and are preferably used in terms of decomposition activity.

[0064] The cell wall-degrading enzyme is not particularly limited, and examples thereof include lysozyme, amylase, cellulase, maltase, saccharase, α-glycosinase, β-glycosinase, etc. Among the cell wall-degrading enzymes, lysozyme is preferred in terms of its bacteriolytic effect. Specific examples of cell wall-degrading enzymes that can be used industrially include "Lysozyme" (manufactured by Huayuan Jingmao Co., Ltd., Shandong Province), "Biozyme A," "Cellulase A "Amano" 3," "Cellulase T "Amano" 4," "α-Glucosidase "Amano"" (all manufactured by Amano Enzyme Co., Ltd.), "Termamyl," and "Cellsoft" (all manufactured by Novozymes).

[0065] The above-mentioned enzymatic treatment is preferably carried out in the presence of a surfactant, since this provides a high separation and purification effect. Alternatively, the enzyme may be an enzyme composition containing an enzyme and one or more additives selected from the group consisting of an enzyme stabilizer, a surfactant, and an anti-redeposition agent.

[0066] Examples of surfactants include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. From the viewpoint of highly effective removal of residues resulting from cell membrane disruption, anionic surfactants and / or nonionic surfactants are preferred. For the purpose of removing proteins, etc., it is preferable to use anionic surfactants, and for the purpose of removing fatty acids and oils, it is preferable to use nonionic surfactants. Both anionic surfactants and nonionic surfactants can be used. When both are used, the weight ratio of anionic surfactant / nonionic surfactant is preferably 1 / 100 to 100 / 10, more preferably 5 / 100 to 100 / 20, even more preferably 5 / 100 to 100 / 100, and particularly preferably 5 / 100 to 50 / 100.

[0067] Examples of anionic surfactants include alkyl sulfates, alkylbenzenesulfonates, alkyl sulfate ester salts, alkenyl sulfate ester salts, alkyl ether sulfate ester salts, alkenyl ether sulfate ester salts, α-olefin sulfonates, α-sulfofatty acid salts, esters of α-sulfofatty acid salts, alkyl ether carboxylates, alkenyl ether carboxylates, amino acid surfactants, N-acylamino acid surfactants, etc. Among these, alkyl sulfates having an alkyl group with 12 to 14 carbon atoms, linear alkylbenzenesulfonates having an alkyl group with 12 to 16 carbon atoms, and alkyl sulfates or alkyl ether sulfates having an alkyl group with 10 to 18 carbon atoms are preferred, and as the counter ion, alkali metals such as sodium and potassium, alkaline earth metals such as magnesium, and alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine are preferred.

[0068] Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyalkylene alkyl ethers, fatty acid sorbitan esters, alkyl polyglucosides, fatty acid diethanolamides, alkyl monoglyceryl ethers, etc. Polyoxyethylene alkyl ethers and polyoxyalkylene alkyl ethers are preferred because of their high hydrophilicity and relatively good biodegradability.

[0069] Examples of cationic surfactants include alkyltrimethylammonium salts and dialkyldimethylammonium salts.

[0070] Examples of amphoteric surfactants include carbobetaine and sulfobetaine surfactants.

[0071] Of the surfactants mentioned above, 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 are preferred in terms of cost, amount used, and addition effect.

[0072] The amount of surfactant added is not particularly limited, but is preferably 0.001 to 10 parts by weight, and more preferably 0.001 to 5 parts by weight from the viewpoint of cost, per 100 parts by weight of the bacterial cell culture solution. One type of surfactant may be used alone, or two or more types may be used in combination.

[0073] The enzyme treatment is preferably carried out by, for example, adding an alkaline compound and / or a surfactant to the bacterial cell culture solution and stirring the mixture. The enzyme treatment conditions are preferably controlled to optimize the enzyme used. The required amount of enzyme depends on the type and activity of the enzyme. While not particularly limited, the amount is preferably 0.001 to 10 parts by weight, and more preferably 0.001 to 5 parts by weight, per 100 parts by weight of PHA.

[0074] From the viewpoint of enhancing the crushing effect and facilitating the recovery of PHA, the physical crushing treatment is preferably carried out after adding an alkaline compound, or an alkaline compound and a surfactant. The alkaline compounds and surfactants described above can be used as appropriate. Among the alkaline compounds described above, sodium hydroxide, sodium carbonate, potassium hydroxide, and lithium hydroxide are preferred from the viewpoint of suitability for industrial production and cost reduction. Among the surfactants described above, 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 are preferred in terms of cost, usage amount, and addition effect.

[0075] It is preferable to adjust the pH of the bacterial cell culture solution to 8.0 to 12.5 by adding an alkaline compound. This makes it easy to solubilize bacterial cell (microbial cell) residues, organic matter produced by bacterial cells, organic matter constituting bacterial cells, etc., without affecting PHA. After adding the alkaline compound to the bacterial cell culture solution, it may be treated at a temperature of 20 to 80°C, preferably 20 to 50°C, for 30 minutes to 2 hours.

[0076] The amount of surfactant added is not particularly limited, but is preferably 0.001 to 10 parts by weight, and more preferably 0.001 to 5 parts by weight from the viewpoint of cost, per 100 parts by weight of the bacterial cell culture solution. One type of surfactant may be used alone, or two or more types may be used in combination.

[0077] The equipment used for physical disruption is not particularly limited, but examples include high-pressure homogenizers, ultrasonic disrupters, emulsifying dispersers, and bead mills. Among these, high-pressure homogenizers are preferred from the perspective of disruption efficiency, and more preferred are those in which the suspension is introduced into a pressure-resistant container with a micro-opening and then extruded through the opening under high pressure. Examples of this type of homogenizer include the "PA2K" high-pressure homogenizer manufactured by Nilosoavi. The use of a high-pressure homogenizer exerts a large shear force on the microbial cells, efficiently disrupting them and improving the separability of PHA. Because such equipment applies high pressure at the opening and can instantaneously heat up, it is preferable to cool the bacterial culture medium using a standard low-temperature constant-temperature circulating bath, if necessary, to prevent temperature rise and perform disruption at 20 to 40°C. Performing the treatment at 20 to 40°C allows for treatment with little or no decrease in the molecular weight of the PHA. The disruption pressure during high-pressure disruption is not particularly limited, but from the perspectives of disruption efficiency and cost, 30 MPa to 60 MPa is preferred.

[0078] In step (a), chemical treatment and physical disruption treatment may be used in combination, and in this case, from the viewpoint of enhancing the disruption effect, it is preferable to perform physical disruption treatment after chemical treatment. From the viewpoint of cost, step (a) may be performed by physical disruption treatment alone.

[0079] In step (a), recycled water produced by the present production method can be used as the water. The recycled water can be used, for example, when adding a surfactant, an alkaline compound, etc. The use of recycled water can reduce water consumption, thereby reducing costs. Furthermore, the use of recycled water improves the thermal stability of the resulting PHA.

[0080] The recycled water preferably has a calcium ion concentration of 4.5 mg / L or less, more preferably 3.0 mg / L or less, and even more preferably 2.0 mg / L or less. Having a calcium ion concentration of 4.5 mg / L or less in the recycled water provides the effect of inhibiting thermal decomposition of PHA. Furthermore, the recycled water preferably has a sodium ion concentration of 450 mg / L or less, more preferably 250 mg / L or less, and even more preferably 220 mg / L or less. Having a sodium ion concentration of 450 mg / L or less in the recycled water provides the effect of inhibiting thermal decomposition of PHA.

[0081] (Step (b)) In step (b), the composition obtained in step (a), for example, the PHA in the disruption liquid, is separated. The separation method is not particularly limited, and solid-liquid separation can be performed using methods such as filtration, sedimentation, and centrifugation, and the PHA can be recovered together with the water-insoluble components. Centrifugation is preferred from the viewpoints of industrial mass processing and continuous use.

[0082] The centrifuge is not particularly limited, but a centrifugal settler having a rotating container without holes is preferred, and examples of the type include a separator plate type, a cylindrical type, a decanter type, etc. Since the specific gravity of PHA particles is small compared to water, a separator plate type (intermittent discharge type, nozzle discharge type) that has a large separation and settling area and can obtain high acceleration is preferred, and when the PHA concentration in the crushing treatment liquid is high, a nozzle discharge type is particularly preferred. As a decanter type, a model having a separator plate and a large separation and settling area is preferred.

[0083] In step (b), before separation, 500 to 1000 parts by weight of an aqueous medium may be added to 100 parts by weight of the composition obtained in step (a), for example, the disruption liquid.

[0084] In step (b), the aqueous medium may be recycled water produced by the present production method, or a mixed solvent of the recycled water and a water-miscible organic solvent. The content of recycled water in the aqueous medium is preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, and particularly preferably 85% by weight or more.

[0085] In step (b), the recycled water preferably has a calcium ion concentration of 4.5 mg / L or less, more preferably 3.0 mg / L or less, and even more preferably 2.0 mg / L or less. Having a calcium ion concentration of 4.5 mg / L or less in the recycled water is effective in suppressing thermal decomposition of PHA. The recycled water preferably has a sodium ion concentration of 450 mg / L or less, more preferably 250 mg / L or less, and even more preferably 220 mg / L or less. Having a sodium ion concentration of 450 mg / L or less in the recycled water is effective in suppressing thermal decomposition of PHA.

[0086] The water-miscible organic solvent is not particularly limited, but examples thereof include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, pentanol, hexanol, and heptanol; ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran and dioxane; nitriles such as acetonitrile and propionitrile; amides such as dimethylformamide and acetamide; dimethyl sulfoxide, pyridine, and piperidine. Among these, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, acetonitrile, and propionitrile are preferred because they are easily removable. Furthermore, methanol, ethanol, 1-propanol, 2-propanol, butanol, and acetone are more preferred because they are readily available. Furthermore, methanol, ethanol, and acetone are particularly preferred.

[0087] In step (b), the separated PHA (water-insoluble components including PHA) may be purified by washing it at least once with the aqueous medium described above. The aqueous medium may be, for example, 500 to 1000 parts by weight of the aqueous medium added to 100 parts by weight of the water-insoluble components including PHA. Furthermore, to effectively remove impurities derived from microbial cells and enhance the purification effect, an alkaline compound, a surfactant, a protease, etc. may be added to the aqueous medium.

[0088] (Process (c)) In one embodiment of the present invention, the method for producing a PHA may include a step (c) of drying the PHA separated in step (b). The PHA (dehydrated resin) washed with an aqueous medium and dehydrated can be dried directly to obtain a powdered PHA. The drying method can be appropriately selected and is not particularly limited, but common drying methods such as spray drying, flash drying, fluidized bed drying, and band drying are preferably used.

[0089] In one embodiment of the present invention, a PHA dispersion that has been washed with an aqueous medium and concentrated is added with a dispersant, adjusted to a pH of 7 or less, and then dried to obtain a powdered PHA. Examples of dispersants include water-soluble polymers such as polyvinyl alcohol (PVA), methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, polyacrylic acid, sodium polyacrylate, potassium polyacrylate, polymethacrylic acid, and sodium polymethacrylate; and nonionic surfactants such as polyethylene glycol-polypropylene glycol block ether type (polyoxyethylene-polyoxypropylene block polymer type). An example of a method for adjusting the pH to 7 or less is the addition of an acid. The acid is not particularly limited and may be either an organic acid or an inorganic acid, such as sulfuric acid, hydrochloric acid, phosphoric acid, or acetic acid.

[0090] The molecular weight of the PHA is not particularly limited as long as it exhibits substantially sufficient physical properties for the intended use. For example, from the viewpoint of moldability and strength of molded articles, the weight-average molecular weight of the PHA is preferably 50,000 to 3,000,000, more preferably 60,000 to 1,500,000. The weight-average molecular weight here refers to a value measured from the polystyrene-equivalent molecular weight distribution using gel permeation chromatography (GPC) with a chloroform eluent. The column used in the GPC may be a column appropriate for measuring the molecular weight.

[0091] PHA has high thermal stability, and when heat-treated at 160°C for 20 minutes, the weight-average molecular weight retention is preferably 70% or more, more preferably 73% or more, even more preferably 75% or more, even more preferably 78% or more, and particularly preferably 80% or more. The thermal stability of PHA is measured by the method described in the Examples below.

[0092] PHA has a good color tone, and the yellowness index (YI value) of a sheet having a thickness of 5 mm and press-molded at 160° C. is preferably 20 or less, and more preferably 17 or less.

[0093] PHA can be molded into various types of fibers, threads, ropes, woven fabrics, knitted fabrics, nonwoven fabrics, paper, films, sheets, tubes, plates, rods, containers, bags, parts, foams, and other molded articles. These molded articles can be suitably used in agriculture, fisheries, forestry, horticulture, medicine, hygiene products, clothing, non-clothing, packaging, and other fields.

[0094] In the case of other biodegradable plastics produced by microorganisms, recycled water produced by this manufacturing method can be used in the process of crushing or solubilizing the microbial cells containing the biodegradable plastic and separating the biodegradable plastic.

[0095] 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.

[0096] That is, one embodiment of the present invention is as follows. <1> A method for producing recycled water, comprising the following steps (A) to (D): (A) a treatment process in which wastewater discharged in a polyhydroxyalkanoic acid production process is subjected to anaerobic and aerobic treatment using microorganisms; (B) a pretreatment filtration step in which the treated water obtained in the step (A) is pretreated and filtered by a membrane separation activated sludge method; (C) an alkaline treatment step of alkaline treating the treated water obtained in the step (B); and (D) A filtration step in which the treated water obtained in the step (C) is filtered through an ion removal membrane. <2> In the step (C), the pH of the treated water is adjusted to 7 to 11, the turbidity of the treated water is adjusted to 0.1 or more, and the FI value of the treated water is adjusted to 4.5 or more. <1> The method for producing recycled water according to claim 1. <3> In the step (C), the FI value of the treated water is adjusted to 6.0 or more. <1> or <2> The method for producing recycled water according to claim 1. <4> In the step (C), the alkali treatment is carried out using an aqueous solution of an alkali metal hydroxide, an aqueous solution of an alkali metal carbonate, an aqueous solution of an alkali metal bicarbonate, an aqueous solution of an alkali metal of an organic acid, salt an aqueous solution of an alkali metal borate, an aqueous solution of an alkali metal phosphate, an aqueous solution of an alkaline earth metal hydroxide, and aqueous ammonia; <1> ~ <3> 1. The method for producing recycled water according to any one of the preceding claims. <5> The step (C) further includes the following step (C'): <1> ~ <4> A method for producing recycled water according to any one of the following: (C') a precipitation step of precipitating solids containing polyvalent ions in the treated water. <6> The multivalent ions are Si 2+ , Ca 2+ , PO4 2- , SO4 2- , Mg 2+ , Mn 2+ , Zn 2+ , Fe 2+ , Fe 3+ , Sr 2+ , Cu 2+ , Al 3+ , Sn 3+ One or more selected from the group consisting of <5> The method for producing recycled water according to claim 1. <7> The step (C) further includes the following step (C″): <5> or <6> 2. A method for producing recycled water according to claim 1, (C'') A sedimentation removal step in which the solid matter precipitated in the treated water in the step (C') is removed by sedimentation. <8> In the step (D), the ion removal membrane has an MgSO rejection rate of 60 to 100% when a pressure of 3000 kPa is applied at 20°C. <1> ~ <7> 1. The method for producing recycled water according to any one of the preceding claims. <9> In the step (D), the transmembrane pressure difference of the ion removal membrane is 0.4 to 4.14 MPa. <1> ~ <8> 1. The method for producing recycled water according to any one of the preceding claims. <10> The method comprises a step (a) of disrupting or solubilizing microbial cells containing polyhydroxyalkanoic acid, and a step (b) of separating the polyhydroxyalkanoic acid in the composition obtained in the step (a), and the steps (a) and (b) are carried out in a manner similar to that described above. <1> ~ <9> 10. A method for producing a polyhydroxyalkanoic acid, comprising using recycled water produced by the method according to any one of claims 1 to 9. [Example]

[0097] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0098] [Measurement and evaluation methods] The measurement and evaluation methods used in the examples and comparative examples are shown below.

[0099] (FI value) The FI value is a semi-quantitative index that indicates the degree to which the influent water undergoing membrane treatment causes membrane fouling, and is defined in JIS K3802. For RO membranes, it is recommended that the influent water have an FI value of 5 or less. The calculation method is to measure the time (T1) required for 500 ml of sample water to pass through a 47 mm disc filter with a pore size of 0.45 μm under 0.206 MPa. After 15 minutes of continuous operation, the time (T2) required for another 500 ml sample water to pass through the same filter is also measured, and the FI value is calculated using the following formula (1).

[0100]

number

[0101] In the above formula (1), PF represents the obstruction factor, and T represents the time from the start of measurement of T1 to the start of measurement of T2.

[0102] (Turbidity) 200 mL of the prepared washing water was placed in a dedicated measurement container, and a measuring device (TCR-5Z manufactured by Kasahara Chemical Industries Co., Ltd.) was gently immersed in the container while taking care not to trap air bubbles, and the turbidity was measured.

[0103] (Solid composition analysis) Metal ions contained in the filtrate pretreated by the membrane separation activated sludge method were analyzed using ICP-MS (Agilent Technologies: Agilent 7900). In addition, metal ions contained in the solids adhering to the RO membrane surface were analyzed using ICP-MS (Agilent Technologies: Agilent 7900), and Si·P·SO4 was analyzed using ICP-AES (Shimadzu Corporation: ICPS-7510).

[0104] (thermal stability) Thermal stability was calculated based on the weight-average molecular weight retention of the PHA after heating at 160°C for 20 minutes. If the weight-average molecular weight retention was 70% or more, the thermal stability was judged to be good, and if the weight-average molecular weight retention was less than 70%, the thermal stability was judged to be poor. The weight-average molecular weight retention was calculated using the following formula.

[0105] Weight average molecular weight retention rate (%) = (weight average molecular weight of PHA after heating / weight average molecular weight of PHA before heating) × 100 <Weight average molecular weight of PHA before heating> 10 mg of PHA powder was dissolved in 10 mL of chloroform, and insoluble materials were removed by filtration. The resulting solution (filtrate) was subjected to molecular weight measurement using a Shimadzu GPC system equipped with a Shodex K805L (300 x 8 mm, two connected tubes) (Showa Denko K.K.) and chloroform as the mobile phase. Commercially available standard polystyrene was used as the molecular weight standard sample.

[0106] <Weight average molecular weight of PHA after heating> The PHA powder was preheated at 160°C for 7 minutes and then heated at 160°C for 20 minutes to prepare a PHA sheet. The weight average molecular weight of the PHA after heating was measured in the same manner as in the measurement of the weight average molecular weight of the PHA before heating, except that 10 mg of the PHA sheet was used.

[0107] (Transmembrane pressure) The transmembrane pressure is calculated using the following formula: (RO membrane inlet pressure + RO membrane outlet pressure) / 2 - permeate side (secondary side) pressure Example 1 Wastewater from PHA production underwent anaerobic and aerobic treatment using microorganisms, followed by pretreatment filtration using a membrane bioreactor (MF) membrane. The filtrate pH was adjusted to precipitate solids, and then filtered using an RO membrane. Anaerobic treatment involved acidogenic bacteria in an acidification tank (pH approximately 7.1) to decompose high-molecular-weight carbohydrates and lipids into organic acids and lower alcohols. Granular methanogens then decomposed the organic acids and lower alcohols into methane and carbon dioxide in an EGSB-type methanogenesis reactor (loading capacity 15 kg-CODcr / m3 / d). Aerobic treatment involved a denitrification tank (activated sludge treatment tank), an aeration tank (activated sludge treatment tank), a secondary denitrification tank (activated sludge treatment tank), and a reaeration tank (activated sludge treatment tank). Organic matter not decomposed during anaerobic treatment was decomposed by aerobic bacteria. Pretreatment filtration using the membrane bioreactor was performed using an MF membrane (hollow fiber membrane: PVDF, manufactured by Mitsubishi Chemical Corporation, nominal pore size: 0.4 μm) installed in a reaeration tank (activated sludge treatment tank). Water was passed through the MF membrane at a linear filtration velocity of 0.35 m / day. The pH of the MF membrane permeate was 7, the FI value was 0, and the turbidity was 0 NTU. The MF membrane permeate was collected in a stirring tank, and a scale inhibitor, Genesys LF (manufactured by Genesys), was added to the mixture to a concentration of 2.4 ppm. The pH was adjusted to 8.8 using aqueous sodium hydroxide. Due to the precipitation of solids, the FI value of the water increased to 6 or more, and the turbidity was 0.5 NTU. This water was concentrated four times to produce concentrated water. The water was then pumped to an RO membrane (material: composite polyamide, manufactured by Nitto Denko Corporation, LFC3-LD) at a water temperature of 25°C and a linear filtration velocity of 0.48 m / day. The transmembrane pressure during pumping was 1.5 MPa. Both the water that permeated the RO membrane (also referred to as "recycled water") and the water that did not permeate were returned to the collection tank and circulated. When operated at a constant linear filtration velocity, the transmembrane pressure rose due to fouling, so the water was pumped until the transmembrane pressure reached 2.0 MPa. Then, as a membrane capacity recovery process, a flushing operation was performed for 30 minutes using the permeated water at a feed water linear velocity of 6 m / min or more. After the flushing operation, the concentrated water was pumped at a linear filtration velocity of 0.48 m / day, and the transmembrane pressure reached 1.4 MPa.

[0108] Example 2 Wastewater treatment and RO membrane recovery operations were performed in the same manner as in Example 1, except that the pH was adjusted to 8.9 using sodium hydroxide. The FI value of the water adjusted to pH 8.9 was 6 or more, and the turbidity was 0.5 NTU. The water was then pumped to the RO membrane at a water temperature of 25°C and a linear filtration rate of 0.48 m / day. The transmembrane pressure difference at the start of pumping was 1.6 MPa, and the pumping continued until the transmembrane pressure difference reached 2.0 MPa. After the membrane capacity recovery treatment, the concentrated water was pumped at a linear filtration rate of 0.48 m / day, and the transmembrane pressure difference reached 1.4 MPa.

[0109] Example 3 Wastewater treatment and RO membrane recovery operations were performed in the same manner as in Example 1, except that the pH was adjusted to 9.1 using sodium hydroxide. The FI value of the water adjusted to pH 9.1 was 6 or more, and the turbidity was 0.6 NTU. The water was then pumped to the RO membrane at a water temperature of 25°C and a linear filtration rate of 0.48 m / day. The transmembrane pressure at the start of pumping was 1.4 MPa, and the pumping continued until the transmembrane pressure reached 2.0 MPa. After the membrane capacity recovery treatment, the concentrated water was pumped at a linear filtration rate of 0.48 m / day, and the transmembrane pressure reached 1.3 MPa.

[0110] Example 4 Wastewater treatment and RO membrane recovery operations were performed in the same manner as in Example 1, except that no scale inhibitor was added and the pH was adjusted to 9.1 using sodium hydroxide. The FI value of the water adjusted to pH 9.1 was 6 or more, and the turbidity was 0.7 NTU. The water was then pumped to the RO membrane at a water temperature of 25°C and a linear filtration rate of 0.48 m / day. The transmembrane pressure difference at the start of pumping was 1.6 MPa, and the pumping continued until the transmembrane pressure difference reached 1.9 MPa. After the membrane capacity recovery treatment, the concentrated water was pumped at a linear filtration rate of 0.48 m / day, and the transmembrane pressure difference reached 1.4 MPa.

[0111] Example 5 Wastewater treatment and RO membrane recovery operations were performed in the same manner as in Example 4, except that the pH was adjusted to 9.2 using sodium hydroxide. The FI value of the water adjusted to pH 9.2 was 6 or more, and the turbidity was 0.4 NTU. The water was then pumped to the RO membrane at a water temperature of 25°C and a linear filtration rate of 0.48 m / day. The transmembrane pressure at the start of pumping was 1.4 MPa, and the pumping continued until the transmembrane pressure reached 1.9 MPa. After membrane capacity recovery treatment, the concentrated water was pumped at a linear filtration rate of 0.48 m / day, and the transmembrane pressure reached 1.5 MPa.

[0112] Example 6 Wastewater treatment and RO membrane recovery operations were performed in the same manner as in Example 4, except that the pH was adjusted to 9.2 using sodium hydroxide. The FI value of the water adjusted to pH 9.2 was 6 or more, and the turbidity was 0.3 NTU. The water was then pumped to the RO membrane at a water temperature of 25°C and a linear filtration rate of 0.48 m / day. The transmembrane pressure at the start of pumping was 1.5 MPa, and the pumping continued until the transmembrane pressure reached 2.0 MPa. After membrane capacity recovery treatment, the concentrated water was pumped at a linear filtration rate of 0.48 m / day, and the transmembrane pressure reached 1.6 MPa.

[0113] Comparative Example 1 Wastewater treatment and RO membrane recovery operations were carried out in the same manner as in Example 1, except that pretreatment filtration was performed using a membrane separation activated sludge process using an MF membrane, and then alkali treatment was not performed. The water had an FI value of 0, a turbidity of 0 NTU, and was pumped to the RO membrane at a water temperature of 25°C and a linear filtration speed of 0.48 m / day. The transmembrane pressure at the start of pumping was 1.3 MPa, and the pumping continued until the transmembrane pressure reached 2.3 MPa. Thereafter, after membrane capacity recovery treatment, concentrated water was pumped at a linear filtration speed of 0.48 m / day, and the transmembrane pressure reached 2.2 MPa.

[0114] 〔result〕 For Examples 1 to 6 and Comparative Example 1, the measurement results of the initial transmembrane pressure, the transmembrane pressure at the end of filtration, and the transmembrane pressure after the membrane capacity recovery treatment are shown in Table 1.

[0115] [Table 1]

[0116] Table 1 shows that the transmembrane pressure difference after the membrane capacity recovery treatment was lower in Examples 1 to 6 compared to Comparative Example 1. Since there was no significant difference in the transmembrane pressure difference after the end of liquid transfer, it was shown that the flux rate of the RO membrane was able to be restored to a high value by the membrane capacity recovery treatment. The results of Examples 1 and 4 and Comparative Example 1 suggest that the precipitation of solids, rather than the scale inhibitor, contributes to membrane recovery.

[0117] The metal ion concentrations of the filtrate pre-filtered by the membrane bioreactor in Example 6 are shown in Table 2. The types and concentrations of metal ions in the solid matter adhering to the RO membrane after the liquid transfer in Example 6 are shown in Table 3.

[0118] [Table 2]

[0119] [Table 3]

[0120] Compared to the results in Table 2, the results in Table 3 show a higher proportion of elements that become multivalent ions. This suggests that pH adjustment by alkaline treatment preferentially precipitates low-solubility multivalent ions. This suggests that metal ions do not adhere firmly to the RO membrane, and membrane capacity can be restored by performing membrane capacity restoration treatment using permeate water.

[0121] On the other hand, similar metal salts were also found to adhere to the surface of the RO membrane in the comparative example (data not shown). However, it is presumed that metal ions were concentrated and precipitated on the surface of the RO membrane in the comparative example. Therefore, it is thought that metal salts adhered firmly to the RO membrane surface, and membrane capacity was not restored even when membrane capacity recovery treatment was performed using permeate water.

[0122] Example 7 (Preparation of bacterial culture solution) The cells were cultured using the method described in International Publication No. 2010 / 067543 to obtain a cell culture containing PHA-containing cells. Ralstonia eutropha is currently classified as Capriavidus necator. The repeating unit composition ratio of the PHA contained in the cells (3HB unit / 3HH unit composition ratio) was 92 / 8 to 99 / 1 (mol / mol).

[0123] (Sterilization) The bacterial culture solution obtained above was sterilized by heating and stirring at an internal temperature of 60 to 80°C for 20 minutes.

[0124] (Refining process) Sodium dodecyl sulfate was added to the sterilized bacterial culture solution obtained above to a concentration of 0.2% by weight. Furthermore, washing water containing dissolved sodium hydroxide was added to adjust the pH to 11.0, and the mixture was then incubated at 50°C for 1 hour. Then, high-pressure homogenization was carried out at a pressure of 44 to 54 MPa using a high-pressure homogenizer (Nirosoavi High-Pressure Homogenizer Model PA2K).

[0125] An equal weight of wash water was added to the resulting bacterial cell lysate after high-pressure disruption. After centrifugation, the supernatant was removed and the suspension was concentrated two-fold. To this concentrated aqueous PHA suspension, wash water (pH 11.0) containing added sodium hydroxide was added to the same weight as the removed supernatant, followed by centrifugation. The supernatant was then removed, followed by addition of wash water to form a suspension. 0.2 wt% sodium dodecyl sulfate and protease (Esperase, Novozymes) in an amount equivalent to 1 / 100 the weight of PHA were added, and the suspension was stirred for 2 hours at 50°C and pH 10.0. The supernatant was then removed by centrifugation, and the suspension was concentrated five-fold. To this concentrated aqueous PHA suspension, wash water (pH 11.0) containing added sodium hydroxide was added to the same weight as the removed supernatant, followed by centrifugation. This procedure was repeated five times, and the supernatant was removed to obtain a PHA aqueous suspension with a PHA concentration adjusted to 52 wt%. In this purification treatment step, water obtained by permeating the concentrated water of Example 1 through an RO membrane (recycled water) was used as the washing water.

[0126] (granulation) To the aqueous PHA suspension (solids concentration 52% by weight) obtained above, a dispersant (polyethylene glycol-polypropylene glycol-block ether-type nonionic surfactant, product name "Pronon #208", NOF Corp.) was added at 1 pH (1 part by weight per 100 parts by weight of PHA present in the aqueous suspension), and the solids concentration was then adjusted to 30% by weight with distilled water. After stirring this liquid for 30 minutes, sulfuric acid was added to adjust the pH until it stabilized at 4. The resulting aqueous PHA suspension was dried at 60°C for 12 hours to produce PHA powder.

[0127] Comparative Example 2 Industrial water (Kaneka) was treated with ion exchange resins (Organo, strong acid cation resin and strong basic anion resin) to obtain washing water 2. A PHA powder was obtained in the same manner as in Example 7, except that washing water 2 was used as the washing water in the purification treatment step.

[0128] The thermal stability of the PHA powders obtained in Example 7 and Comparative Example 2 was measured and evaluated as described above. The results are shown in Table 4.

[0129] [Table 4]

[0130] 〔result〕 Table 4 shows that the PHA powder of Example 7 has better thermal stability than the PHA powder of Comparative Example 2. This shows that the use of recycled water of the present invention makes it possible to produce PHA with superior performance (improved thermal stability) compared to the use of conventional cleaning water. [Industrial Applicability]

[0131] The present invention can be suitably used in the field of wastewater treatment and other fields.

Claims

1. A method for producing recycled water, comprising the following steps (A) to (D): (A) a treatment step in which wastewater discharged in a polyhydroxyalkanoic acid production process is subjected to anaerobic and aerobic treatment using microorganisms; (B) a pre-filtration step in which the treated water obtained in the step (A) is pre-filtered by a membrane separation activated sludge method; (C) an alkaline treatment step in which the treated water obtained in the step (B) is alkaline treated; and (D) A filtration step in which the treated water obtained in the step (C) is filtered through an ion removal membrane.

2. 2. The method for producing recycled water according to claim 1, wherein in step (C), the pH of the treated water is adjusted to 7 to 11, the turbidity of the treated water is adjusted to 0.1 or more, and the FI value of the treated water is adjusted to 4.5 or more.

3. The method for producing recycled water according to claim 1 or 2, wherein in step (C), the FI value of the treated water is adjusted to 6.0 or more.

4. 4. The method for producing recycled water according to claim 1, wherein in step (C), the alkaline treatment is carried out using one or more solutions selected from the group consisting of an aqueous solution of an alkali metal hydroxide, an aqueous solution of an alkali metal carbonate, an aqueous solution of an alkali metal bicarbonate, an aqueous solution of an alkali metal salt of an organic acid, an aqueous solution of an alkali metal borate, an aqueous solution of an alkali metal phosphate, an aqueous solution of an alkaline earth metal hydroxide, and aqueous ammonia.

5. The method for producing recycled water according to any one of claims 1 to 4, wherein the step (C) further comprises the following step (C'): (C') A precipitation step of precipitating a solid containing polyvalent ions in the treated water.

6. The multivalent ions are Si ２＋ , Ca ２＋ , P.O. ４ ２－ , S.O. ４ ２－ , Mg ２＋ , Mn ２＋ , Zn ２＋ , Fe ２＋ , Fe ３＋ , Sr ２＋ , Cu ２＋ , Al ３＋ , Sn ３＋ The method for producing recycled water according to claim 5, wherein the organic solvent is one or more selected from the group consisting of:

7. The method for producing recycled water according to claim 5 or 6, wherein the step (C) further comprises the following step (C″): (C'') A sedimentation and removal step in which the solid matter precipitated in the treated water in the step (C') is sedimented and removed.

8. In the step (D), the ion removal membrane has a MgSO ４ The method for producing recycled water according to any one of claims 1 to 5, wherein the rejection rate is 60 to 100%.

9. The method for producing recycled water according to any one of claims 1 to 8, wherein in the step (D), the transmembrane pressure difference of the ion removal membrane is 0.4 to 4.14 MPa.

10. A method for producing polyhydroxyalkanoic acid, comprising: a step (a) of disrupting or solubilizing microbial cells containing polyhydroxyalkanoic acid; and a step (b) of separating the polyhydroxyalkanoic acid from the composition obtained in the step (a), wherein recycled water produced by the method according to any one of claims 1 to 9 is used in the steps (a) and (b).

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