Methods for producing reclaimed water

Abstract

The object of the present invention is to provide a method for producing reclaimed water that can significantly reduce the chemical cleaning of membranes during the preparation of reclaimed water from wastewater, and can essentially eliminate membrane fouling using only water cleaning. The present invention solves the above-mentioned problem by providing a method for producing reclaimed water comprising the following steps (A) to (D): (A) a step of performing anaerobic and aerobic treatment on wastewater discharged in the PHA manufacturing process based on microorganisms; (B) a step of pretreatment filtration on the treated water obtained in step (A) by membrane separation activated sludge process; (C) a step of alkali treatment on the treated water obtained in step (B); and (D) a step of filtering the treated water obtained in step (C) by ion removal membrane.

Description

Technical Field

[0001] This invention relates to a method for manufacturing reclaimed water and a method for manufacturing polyhydroxyalkanoates (hereinafter also referred to as "PHA"). Background Technology

[0002] Biodegradable plastics can be completely biodegraded by microorganisms in soil or water, thus entering the natural carbon cycle. Therefore, as environmentally friendly plastic materials that have virtually no adverse impact on ecosystems, they are expected to be actively used. Plant-derived biodegradable plastics such as PHA have attracted considerable attention as representative examples. PHA is an aliphatic polyester (thermoplastic polyester) produced by microorganisms using natural organic acids and oils from plants as carbon sources and stored within cells as an energy storage substance.

[0003] PHA produced by microorganisms is water-insoluble and typically accumulates within microbial cells in the form of particulate matter. To utilize PHA in the form of plastics, a process is required to separate and extract the PHA from the microbial cells. For example, Patent Document 1 reports a method combining alkali addition and high-pressure crushing as a method for separating and purifying PHA. Furthermore, Patent Document 2 reports a method combining physical cell disruption and chemical treatment based on enzymes and surfactants as a method for separating and purifying PHA.

[0004] However, in the previous PHA manufacturing methods, the amount of wastewater generated by cell disruption and centrifugation became very large. In order to reduce the environmental burden, it is desirable to reuse the wastewater.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 07-31489

[0008] Patent Document 2: Japanese Patent Application Publication No. 2008-193940 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] In PHA separation and purification methods, filtration membranes are typically used to separate PHA. These membranes require chemical cleaning to restore their membrane capacity before reuse. However, conventional wastewater reuse technologies suffer from premature membrane degradation due to this chemical cleaning process, indicating room for improvement.

[0011] Therefore, the object of the present invention is to provide a method for producing reclaimed water that can significantly reduce the chemical cleaning of membranes during the preparation of reclaimed water from wastewater, and can essentially eliminate membrane fouling by water rinsing alone.

[0012] Methods for solving problems

[0013] In order to solve the above-mentioned problems, the inventors conducted in-depth research and discovered the following new insights, thereby completing the present invention. The new insights are: by performing an alkali treatment process before the membrane filtration process in the method for producing reclaimed water from wastewater, it is possible to substantially eliminate membrane fouling by water rinsing alone.

[0014] Therefore, one aspect of the present invention is a method for producing reclaimed water, the method comprising the following steps (A) to (D): (A) a treatment step, wherein wastewater discharged in the PHA production step is subjected to anaerobic and aerobic treatment based on microorganisms; (B) a pretreatment filtration step, wherein the treated water obtained in step (A) is pretreated and filtered by membrane separation activated sludge method; (C) an alkali treatment step, wherein the treated water obtained in step (B) is subjected to alkali treatment; and (D) a filtration step, wherein the treated water obtained in step (C) is filtered by ion removal membrane.

[0015] The effects of the invention

[0016] According to one aspect of the present invention, a method for producing reclaimed water can be provided that eliminates membrane fouling substantially by cleaning alone without chemical cleaning of the membrane during the preparation of reclaimed water from wastewater. Detailed Implementation

[0017] The following describes one embodiment of the present invention in detail. It should be noted that, unless otherwise specified, in this specification, "A to B" indicating a numerical range means "A or more and B or less". Furthermore, all documents described in this specification are incorporated herein by reference.

[0018] [1. Summary of the Invention]

[0019] A method for producing reclaimed water according to one embodiment of the present invention (hereinafter also referred to as the manufacturing method) includes the following steps (A) to (D): (A) a treatment step, wherein the wastewater discharged in the manufacturing step of PHA is subjected to anaerobic and aerobic treatment based on microorganisms; (B) a pretreatment filtration step, wherein the treated water obtained in step (A) is subjected to pretreatment filtration by membrane separation activated sludge method; (C) an alkali treatment step, wherein the treated water obtained in step (B) is subjected to alkali treatment; and (D) a filtration step, wherein the treated water obtained in step (C) is filtered by ion removal membrane.

[0020] Membrane filtration is a representative method for wastewater reuse. However, membrane filtration can sometimes become fouled (clogged) by tiny, highly adhesive suspended solids in the wastewater. Therefore, the membrane needs to be cleaned repeatedly while operating. Generally, two known methods for cleaning membranes are (1) physical cleaning, which involves backpressure cleaning by allowing filtered water to flow through the permeate side (secondary side), and (2) chemical cleaning based on chemicals.

[0021] In the aforementioned physical cleaning, reversible deposits on or inside the membrane can be removed by automatically cleaning with water periodically (approximately once every 30 minutes to 1 hour). However, physical cleaning cannot completely remove contaminants adhering to membrane pores, causing the intermembrane differential pressure to continuously rise. Therefore, when the intermembrane differential pressure rises to a certain level, chemical cleaning is required to remove contaminants from the membrane. However, repeated chemical-based cleaning can damage the membrane, rendering it unusable as an ion removal membrane. In other words, a method to extend the usable lifespan of the membrane is desired.

[0022] Therefore, the inventors conducted in-depth research in order to extend the service life of the membrane and to provide a method for producing reclaimed water that does not require chemical cleaning, and as a result, they discovered the following insights.

[0023] Certain metal ions can cause irreversible fouling of the membrane.

[0024] • By performing an alkali treatment process on the treated water before the filtration process based on the ion removal membrane, specific pollutants contained in the treated water are pre-precipitated in the form of solid matter, thereby suppressing irreversible fouling on the ion removal membrane.

[0025] • By pre-treating the treated water with alkali before the filtration process based on ion removal membranes, membrane fouling can be eliminated using only water rinsing.

[0026] The method for producing reclaimed water, including the aforementioned features, is an exceptionally superior technology, unlike anything seen before.

[0027] Furthermore, the inventors used the reclaimed water obtained by the above-described manufacturing method to manufacture PHA, and unexpectedly succeeded in obtaining PHA with high thermal stability. The present invention will now be described in detail.

[0028] It should be noted that in this specification, "substantially water rinsing only" refers to any cleaning method primarily based on water rinsing. Besides water rinsing, other cleaning methods may also be included. For example, "substantially water rinsing only" may include cleaning with chemicals in smaller quantities than usual, in addition to water rinsing. Water rinsing only is preferred.

[0029] [2. Methods for producing reclaimed water]

[0030] This manufacturing method includes the following steps (A) to (D).

[0031] • Process (A): A treatment process that involves microbial-based anaerobic and aerobic treatment of the wastewater discharged during the PHA manufacturing process.

[0032] • Process (B): Pretreatment filtration of the treated water obtained in Process (A) using membrane separation activated sludge method.

[0033] • Process (C): Alkali treatment process for alkali treatment of the treated water obtained in process (B) above.

[0034] • Process (D): A filtration process in which the treated water obtained in process (C) is filtered through an ion removal membrane.

[0035] (Process (A))

[0036] Step (A) in this manufacturing method is a treatment step that performs anaerobic and aerobic treatment based on microorganisms on the wastewater discharged during the manufacturing process of PHA. Through step (A), the organic matter contained in the aforementioned wastewater can be decomposed.

[0037] There are no particular limitations on anaerobic and aerobic treatment based on microorganisms, and both can be carried out using common methods used in water treatment. Anaerobic treatment can be carried out, for example, by utilizing acid-producing bacteria to decompose high molecular weight carbohydrates and lipids into organic acids and lower alcohols, followed by utilizing granular methanogenic bacteria to decompose the organic acids and lower alcohols into methane gas and carbon dioxide. Anaerobic treatment devices can, for example, consist of an acid-generating tank capable of acid-producing bacteria-based reactions and an EGSB-type methane-generating reactor capable of methanogenic bacteria-based reactions. Aerobic treatment can, for example, use a device consisting of a denitrification tank (activated sludge treatment tank) and an aeration tank (activated sludge treatment tank), where undecomposed organic matter from anaerobic treatment is decomposed in the aeration tank by aerobic bacteria. Aerobic treatment devices can, for example, consist of a denitrification tank (activated sludge treatment tank), an aeration tank (activated sludge treatment tank), a second denitrification tank (activated sludge treatment tank), and a re-aeration tank (activated sludge treatment tank).

[0038] (Process (B))

[0039] Step (B) in this manufacturing method is a pretreatment filtration step that uses membrane separation activated sludge method to pretreat the treated water obtained in step (A). Through step (B), large-particle substances contained in the wastewater that was not decomposed in step (A) can be removed.

[0040] The pretreatment filtration process based on membrane separation activated sludge is not particularly limited and can be carried out using general methods used in water treatment. For example, the pretreatment filtration process can be carried out in a membrane bioreactor (MBR) device for membrane separation activated sludge process, where a UF membrane or MF membrane is installed in an aeration tank (activated sludge treatment tank) or a re-aeration tank (activated sludge treatment tank).

[0041] The pore size of the MF membrane is not particularly limited and can be, for example, around 0.4 μm. Similarly, the pore size of the UF membrane is not particularly limited and can be, for example, around 0.05 μm.

[0042] (Process (C))

[0043] Step (C) in this manufacturing method is an alkali treatment step that alkali-treats the treated water obtained in step (B) above. Through step (C), substances that cause contamination of the ion removal membrane in step (D) described later (i.e., pollutants) can be pre-precipitated. Therefore, pollutants adhering to the ion removal membrane in step (D) can be removed solely by water-based rinsing.

[0044] More specifically, in the membrane filtration process based on step (D) without the alkaline treatment in step (C), the salt concentration of the water that does not permeate the membrane increases, resulting in crystallization on the surface of the ion removal membrane. As filtration continues, repeated crystallization leads to crystal growth, causing the crystals to firmly adhere to the ion removal membrane and clog it. Therefore, in conventional techniques, chemical cleaning is required to remove the crystals adhering to the membrane surface. However, by performing the alkaline treatment in step (C), crystallization occurs before membrane filtration, thus preventing the crystals from firmly adhering to the membrane.

[0045] That is, according to this manufacturing method, the ion removal membrane can be restored essentially by water rinsing without chemical cleaning. Therefore, the ion removal membrane is not damaged by chemicals, and irreversible fouling of the ion removal membrane does not occur, allowing for long-term use. Furthermore, since the chemicals commonly used for cleaning ion removal membranes are hazardous, their use is preferably avoided from an environmental protection perspective.

[0046] In this manual, "alkali treatment" refers to adjusting parameters such as pH, pollution index (FI), and turbidity of the treated water by adding alkaline substances to the treated water.

[0047] As for the alkaline treatment method in step (C), any method that can adjust the parameters of the treated water to the desired values ​​is acceptable, and there are no particular limitations. From the viewpoint of easy adjustment of the parameters, alkaline treatment by adding an alkaline aqueous solution is preferred.

[0048] The alkaline aqueous solution used in step (C) is not particularly limited, and examples 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 ammonia. From the viewpoint of cost reduction, aqueous solution of sodium hydroxide is preferred.

[0049] In step (C), the pH of the treated water is preferably adjusted to 7.0–11.0, more preferably to 8.0–11.0, and even more preferably to 8.5–11.0. When the pH is 7.0 or higher, metal salts precipitate into the treated water. In addition, when the pH is 11.0 or lower, deterioration of the ion removal membrane can be prevented.

[0050] In step (C), the turbidity of the treated water is preferably 0.1 or higher, more preferably 0.2 or higher, and even more preferably 0.3 or higher. When the turbidity is 0.1 or higher, the solid components are fully precipitated. Furthermore, the upper limit of the turbidity of the treated water is preferably 30 or lower, more preferably 20 or lower, even more preferably 10 or lower, and particularly preferably 5 or lower. When the turbidity is 30 or lower, it does not impair the filtration of the treated water. It should be noted that the turbidity of the treated water is measured using the method described in the examples described later.

[0051] In step (C), the FI value of the treated water is preferably 4.5 or higher, more preferably 5.0 or higher, even more preferably 5.5 or higher, particularly preferably 6.0 or higher, and even more preferably 6.5 or higher. When the FI value is within the above range, the solid components are fully precipitated into the treated water. There is no particular limitation on the upper limit of the FI value. Here, the "FI value" can be derived by the following formula (1).

[0052] [Mathematical Expression 1]

[0053]

[0054] In equation (1) above, PF represents the clogging factor, T1 represents the time required for 500 mL of treated water to pass through the ion removal membrane, and T2 represents the time required for another 500 mL of treated water to pass through the same ion removal membrane after the measurement of T1. Additionally, T represents the time from the start of the measurement of T1 to the start of the measurement of T2.

[0055] Conventionally, pretreatment is required to ensure that the FI value of the treated water used for permeation of ion removal membranes (e.g., RO membranes) is 0 to 4. Therefore, surprisingly, in this manufacturing method, the advantageous effects of the present invention are achieved by using treated water with a high FI value (e.g., 4.5 or higher) that would normally not permeate the ion removal membrane (e.g., RO membrane).

[0056] The manufacturing method preferably includes the following step (C') in step (C).

[0057] • Process (C'): The precipitation process that removes solids containing multivalent ions from the treated water described above.

[0058] The aforementioned multivalent ions in water treatment typically do not precipitate, becoming a cause of fouling in ion removal membranes. Therefore, by implementing a process (C') that pre-precipitates solid substances containing the aforementioned multivalent ions before they permeate through the ion removal membrane, fouling of the ion removal membrane can be further suppressed.

[0059] There are no particular limitations on the methods for precipitating solid substances; they can be carried out through, for example, pH adjustment, concentration, or temperature adjustment.

[0060] The term "multivalent ion" is not particularly limited and can include, for example, cations with a valence of two or more, and anions with a valence of two or more. The number of different types of multivalent ions contained in a solid substance is not particularly limited; it can be only one type or multiple types. Furthermore, the precipitated solid substance can be in the form of crystals, granules, rods, etc.

[0061] In one embodiment of the present invention, the aforementioned multivalent ions are preferably selected from 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 of them.

[0062] Usually, Na+ K + NH 4+ Ion with monovalent ions, Cl - NO 3- Anions are highly soluble in water and therefore less likely to cause fouling. On the other hand, the aforementioned polyvalent ions have low solubility in water and tend to precipitate out as solids, thus becoming a cause of fouling in ion removal membranes.

[0063] The manufacturing method preferably includes the following step (C”) in step (C).

[0064] • Process (C”): Sedimentation removal process in which solids that have precipitated into the treated water through the above process (C’) are removed by sedimentation.

[0065] By including step (C”) in this manufacturing method, the cleaning frequency of the ion removal membrane can be further reduced in step (D) described later.

[0066] There are no particular limitations on the method for removing precipitated solids by sedimentation, and it can be carried out by, for example, centrifugal sedimentation machines or thickeners.

[0067] In one embodiment of the present invention, a scale inhibitor may be added during step (C). By adding the scale inhibitor, crystals are further made less likely to grow on the surface of the ion removal membrane. The scale inhibitor that can be used is not particularly limited, and examples include: Genesys LF (manufactured by Genesys Corporation), PC-191T (manufactured by Katayama Nalco Corporation), and KURIVERTER N series (manufactured by Kurita Kogyo Co., Ltd.). Furthermore, the amount of scale inhibitor added is not particularly limited and can be, for example, 1 to 50 ppm.

[0068] (Process (D))

[0069] Step (D) in this manufacturing method is a filtration step that filters the treated water obtained in step (C) using an ion removal membrane. Step (D) removes the solids that precipitated in step (C). The treated water from step (D) becomes reclaimed water.

[0070] In this specification, "reclaimed water" refers to water that can be used for the manufacture of PHA obtained by performing the above-described processes (A) to (D) on the wastewater discharged during the manufacturing process of PHA.

[0071] In step (D), the MgSO4 rejection rate of the ion removal membrane under a pressure of 3000 kPa at 20°C is preferably 60-100%, more preferably 70-100%, and even more preferably 90-100%. When the MgSO4 rejection rate is 60% or higher, the ion permeability of the ion removal membrane does not increase. Furthermore, when the obtained reclaimed water is used for PHA purification, it is easier to suppress the decrease in molecular weight at high temperatures.

[0072] The intermembrane differential pressure 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. When the intermembrane differential pressure is 0.4 MPa or higher, the permeate flow rate and ion removal rate will not decrease, and when it is 4.14 MPa or lower, the membrane is less prone to damage. It should be noted that the intermembrane differential pressure of the ion removal membrane is measured by the method described in the examples described later.

[0073] There is no particular limitation on the timing of cleaning the ion removal membrane. For example, it is preferable to clean it when the differential pressure between the membranes reaches 4.14 MPa or higher, more preferably when it reaches 2.5 MPa or higher, and even more preferably when it reaches 2.0 MPa or higher. By cleaning the ion removal membrane when the differential pressure between the membranes reaches 4.14 MPa or higher, the differential pressure can be maintained within the aforementioned preferred range. The cleaning time of the ion removal membrane is not particularly limited, as long as it sufficiently reduces the differential pressure between the membranes, and can be, for example, 30 minutes or more.

[0074] 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. When the permeation rate is 0.01 L / min or higher, productivity is improved. In addition, when the permeation rate is 2000 L / min or lower, the ion removal membrane is less prone to damage.

[0075] The temperature of the treated water during filtration in step (D) is not particularly limited, but it is preferably below 50°C, more preferably below 45°C. When the treated water temperature is below 50°C, the membrane is less prone to degradation. The lower limit of the treated water temperature is not particularly limited, but from the viewpoint of smooth filtration, it is preferably above 1°C.

[0076] In step (D), in order to remove the deposited metal salts, it is preferable to periodically clean the ion removal membrane.

[0077] As a cleaning method for ion removal membranes, rinsing cleaning is preferred. Rinsing cleaning refers to physical cleaning by passing low-pressure, high-flow-rate water through the ion removal membrane to remove initial fouling. The water used for rinsing cleaning can be tap water only; however, from an efficiency and cost perspective, reclaimed water that has passed through the ion removal membrane is preferred. The pressure during rinsing cleaning can be kept below 0.29 MPa (the primary pressure of the ion removal membrane). Alternatively, the reclaimed water flow rate can be 6 m³ / min or higher.

[0078] As the aforementioned ion removal membrane, from the perspective of high ion (e.g., calcium ion) removal performance, it is preferable to use one or more selected from NF membranes and RO membranes, and more preferably to use an RO membrane.

[0079] [3. Manufacturing method of PHA]

[0080] A method for manufacturing PHA according to one embodiment of the present invention (hereinafter also referred to as "the method for manufacturing PHA") includes: a step (a) of breaking down or solubleting microbial cells containing PHA, and a step (b) of separating PHA from the composition obtained in step (a), wherein reclaimed water manufactured by the method is used in both steps (a) and (b). In the method for manufacturing PHA, the thermal stability of PHA can be improved by using reclaimed water manufactured by the method.

[0081] (Microbial cells containing PHA)

[0082] In one embodiment of the present invention, microbial cells containing PHA can be obtained by culturing microorganisms capable of producing PHA.

[0083] In one embodiment of the present invention, PHA is a general term for polymers using 3-hydroxybutyric acid (hereinafter also referred to as "3HB") as a monomer unit. PHA can be a poly(3-hydroxybutyrate) as a homopolymer using 3-hydroxybutyric acid as a monomer unit, or a copolymer using 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, 3-hydroxyhexadecanoic acid, etc.

[0084] From the viewpoint of ease of industrial production, poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-copolymer-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-copolymer-3-hydroxyoctanoate) are preferred as PHAs, with poly(3-hydroxybutyrate-copolymer-3-hydroxyhexanoate) being particularly preferred. The composition ratio of each monomer unit in the copolymer PHBH constituting the above two components, 3HB and 3HH, is not particularly limited. When the total percentage of all monomer units is set to 100 mol%, the 3HH unit can be 1–50 mol%, 1–25 mol%, or 1–15 mol%.

[0085] In one embodiment of the present invention, the microorganism capable of producing PHA is not particularly limited, and microorganisms preserved in naturally isolated microorganisms or strains (e.g., IFO, ATCC, etc.) or mutants or transformants that can be prepared from them can be used. Examples include bacteria of the genera *Cupriavidus*, *Alcaligenes*, *Ralstonia*, *Pseudomonas*, *Bacillus*, *Azotobacter*, *Nocardia*, and *Aeromonas*. Particularly preferred strains include *A. lipolytica*, *A. latus*, *A. caviae*, *A. hydrophila*, and *C. necator*. Alternatively, in cases where the microorganism does not originally possess the ability to produce PHA or has a low production rate, a transformant obtained by introducing the target PHA synthase gene and / or its mutant into the microorganism can be used. The PHA synthase gene used in the preparation of such a transformant is not particularly limited, but is preferably a PHA synthase gene derived from Aeromonas vaginalis.

[0086] By culturing the aforementioned microorganisms under appropriate conditions, microorganisms containing PHA can be obtained. There are no particular limitations on the culturing method; methods listed in, for example, Japanese Patent Application Publication No. 05-93049 and International Publication No. 2008 / 010296 can be used. The PHA-containing microbial cells can be obtained by directly using the culture medium containing PHA-containing microbial cells after culturing, or by heating the culture medium to kill the bacteria and then using the sterilized culture medium. Sterilization can be performed, for example, by heat treatment at a temperature of 50–80°C for 5–120 minutes.

[0087] (Process (a))

[0088] In step (a), the microbial cells containing PHA are broken down or dissolved. Step (a) can be carried out by, for example, at least one treatment selected from chemical treatment and physical disruption treatment.

[0089] Chemical treatment can be carried out using at least one compound selected from alkaline compounds, proteolytic enzymes, and cell wall degrading enzymes.

[0090] Alkaline compounds are only required to disrupt the cell walls of PHA-containing microbial cells, causing the PHA to leak out of the cells. There are no particular limitations; examples include: hydroxides of alkali metals such as sodium hydroxide, potassium hydroxide, and lithium hydroxide; carbonates of alkali metals such as sodium carbonate and potassium carbonate; bicarbonates of alkali metals such as sodium bicarbonate and potassium bicarbonate; alkali metal salts of organic acids such as sodium acetate and potassium acetate; borates of alkali metals such as borax; phosphates of alkali metals such as trisodium phosphate, disodium hydrogen phosphate, tripotassium phosphate, and dipotassium hydrogen phosphate; hydroxides of alkaline earth metals such as barium hydroxide; and ammonia. From the perspective of suitability for industrial production and cost reduction, sodium hydroxide, sodium carbonate, potassium hydroxide, and lithium hydroxide are preferred.

[0091] There are no particular limitations on what constitutes a protein-degrading enzyme, and examples include alkaline protease, pepsin, trypsin, papain, chymotrypsin, aminopeptidase, and carboxypeptidase. Industrially, specific protein-degrading enzymes such as "Protease A," "Protease P," "Protease N" (all manufactured by Amano Enzyme), "Alcalase," "Esperase," "Everlase," and "Everlase" (all manufactured by Novozymes) are preferred from the viewpoint of degradative activity.

[0092] Cell wall degrading enzymes are not particularly limited and can include, for example, lysozyme, amylase, cellulase, maltase, sucrase, α-glucosidase, β-glucosidase, etc. Among these cell wall degrading enzymes, lysozyme is preferred from the viewpoint of lysis efficiency. Specific cell wall degrading enzymes used industrially include, for example, Lysozyme (manufactured by Shandong Huayuan Economic and Trade Co., Ltd.), Biozyme A, Cellulase A "AMANO"3, Cellulase T "AMANO"4, α-Glucosidase "AMANO" (all manufactured by Amano Enzyme), Terminyl, and CellusOFT (all manufactured by Novozymes).

[0093] From the viewpoint of achieving high separation and purification efficiency, the enzyme treatment described above is preferably carried out in the presence of a surfactant. Furthermore, as the enzyme, for example, an enzyme composition containing the enzyme and one or more additives selected from enzyme stabilizers, surfactants, and recontamination prevention agents can be used.

[0094] Examples of surfactants include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. From the viewpoint of high removal efficiency of residues caused by cell membrane disruption, anionic surfactants and / or nonionic surfactants are preferred. For removing proteins, anionic surfactants are preferred; however, for removing fatty acids and oils, nonionic surfactants are preferred. Alternatively, both anionic and nonionic surfactants can be used. When using both, the weight ratio of anionic surfactant to nonionic surfactant is preferably 1 / 100 to 100 / 10, more preferably 5 / 100 to 100 / 20, further preferably 5 / 100 to 100 / 100, and particularly preferably 5 / 100 to 50 / 100.

[0095] Examples of anionic surfactants include: alkyl sulfates, alkylbenzene sulfonates, alkyl sulfate esters, alkenyl sulfate esters, alkyl ether sulfate esters, alkenyl ether sulfate esters, α-olefin sulfonates, α-sulfonyl fatty acid salts, esters of α-sulfonyl fatty acid salts, alkyl ether carboxylates, alkenyl ether carboxylates, amino acid surfactants, and N-acyl amino acid surfactants. Preferably, these are alkyl sulfates with 12 to 14 carbon atoms, straight-chain alkylbenzene sulfonates with 12 to 16 carbon atoms, alkyl sulfate esters with 10 to 18 carbon atoms, or alkyl ether sulfate esters. As counterions, preferred are alkali metals such as sodium and potassium, alkaline earth metals such as magnesium, and alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine.

[0096] Examples of nonionic surfactants include: polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkylene alkyl ethers, fatty acid sorbitan esters, alkyl polyglucosides, fatty acid diethanolamides, and alkyl monoglycerides. From the perspective of high hydrophilicity and good biodegradability, polyoxyethylene alkyl ethers and polyoxyethylene alkylene alkyl ethers are preferred.

[0097] Examples of cationic surfactants include alkyltrimethylammonium salts and dialkyldimethylammonium salts.

[0098] Examples of amphoteric surfactants include carbobetaine type and sulfobetaine type.

[0099] Among the surfactants mentioned above, from the viewpoints of cost, dosage, and additive effect, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium cholate, sodium deoxycholate, and sodium oleate are preferred as anionic surfactants, and polyoxyethylene alkyl ethers and polyoxyalkylene alkyl ethers are preferred as nonionic surfactants.

[0100] There is no particular limitation on the amount of surfactant added, but it is preferably 0.001 to 10 parts by weight relative to 100 parts by weight of bacterial culture medium, and more preferably 0.001 to 5 parts by weight from a cost point of view. One type of surfactant can be used alone, or two or more types can be used in combination.

[0101] Enzyme treatment is preferably carried out, for example, by adding an alkaline compound and / or a surfactant to the bacterial culture medium while stirring. For enzyme treatment conditions, it is preferable to carry out the treatment under conditions that control the optimal value of the enzyme used. The amount of enzyme required depends on the type and activity of the enzyme. While there are no particular limitations, it is preferably 0.001 to 10 parts by weight relative to 100 parts by weight of PHA, and more preferably 0.001 to 5 parts by weight from a cost perspective.

[0102] From the viewpoint of improving crushing efficiency and facilitating PHA recovery, physical crushing is preferably performed after the addition of an alkaline compound, or an alkaline compound and a surfactant. The aforementioned compounds can be appropriately used as alkaline compounds and surfactants. Among the aforementioned alkaline compounds, from the viewpoint of suitability for industrial production and cost reduction, sodium hydroxide, sodium carbonate, potassium hydroxide, and lithium hydroxide are preferred. Among the aforementioned surfactants, from the viewpoint of cost, dosage, and addition effect, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, sodium cholate, sodium deoxycholate, and sodium oleate as anionic surfactants, and polyoxyethylene alkyl ethers and polyoxyalkylene alkyl ethers as nonionic surfactants are preferred.

[0103] Preferably, the pH of the bacterial culture medium is adjusted to 8.0–12.5 by adding an alkaline compound. This facilitates the dissolution of bacterial cell (microbial cell) residues, bacterial-generated organic matter, and organic matter in the cell structure without affecting the pH. After adding the alkaline compound to the bacterial culture medium, the culture is treated at a temperature of 20–80°C, preferably 20–50°C, for 30 minutes to 2 hours.

[0104] There is no particular limitation on the amount of surfactant added, but it is preferably 0.001 to 10 parts by weight relative to 100 parts by weight of bacterial culture medium. From a cost point of view, it is preferably 0.001 to 5 parts by weight. One surfactant can be used alone, or two or more surfactants can be used in combination.

[0105] The apparatus for physical crushing is not particularly limited, and examples include high-pressure homogenizers, ultrasonic crushers, emulsifying dispersers, and bead mills. From the viewpoint of crushing efficiency, a high-pressure homogenizer is preferred, and more preferably a type that extrudes the suspension from the opening by introducing it into a pressure-resistant container with a small opening and applying high pressure. Examples of this type of crusher include, for instance, the "PA2K type" high-pressure homogenizer manufactured by Niro Soavi. When using a high-pressure homogenizer, a large shear force is generated on the microbial cells, thus efficiently destroying them and improving the separability of PHA. Since such a device applies high pressure at the opening, resulting in instantaneous high temperature, it is preferable to cool the bacterial culture medium using a conventional low-temperature constant-temperature circulating bath as needed to prevent temperature rise, performing the crushing treatment at 20–40°C. By treating at 20–40°C, treatment can be carried out without substantially reducing the molecular weight of PHA. The crushing pressure during high-pressure crushing is not particularly limited, but from the viewpoint of crushing efficiency and cost, 30 MPa to 60 MPa is preferred.

[0106] In step (a), chemical treatment and physical crushing treatment can be used in combination. In this case, from the viewpoint of improving the crushing effect, it is preferable to perform physical crushing treatment after chemical treatment. From the viewpoint of cost, it is preferable to perform only physical crushing treatment in step (a).

[0107] In step (a), reclaimed water produced by this manufacturing method can be used as the water. Reclaimed water can be used, for example, when adding surfactants, alkaline compounds, etc. By using the aforementioned reclaimed water, water consumption can be suppressed, thus reducing costs. Furthermore, the thermal stability of the resulting PHA is improved by using reclaimed water.

[0108] The concentration of calcium ions in the reclaimed water is preferably 4.5 mg / L or less, more preferably 3.0 mg / L or less, and even more preferably 2.0 mg / L or less. Maintaining a calcium ion concentration of 4.5 mg / L or less in the reclaimed water helps to inhibit the thermal decomposition of PHA. Furthermore, the concentration of sodium ions in the reclaimed water is preferably 450 mg / L or less, more preferably 250 mg / L or less, and even more preferably 220 mg / L or less. Maintaining a sodium ion concentration of 450 mg / L or less in the reclaimed water helps to inhibit the thermal decomposition of PHA.

[0109] (Process (b))

[0110] In step (b), the composition obtained in step (a), for example, the PHA in the breaking fluid, is separated. The separation method is not particularly limited; solid-liquid separation can be performed using methods such as filtration, sedimentation, or centrifugation to recover the PHA and water-insoluble components. From the viewpoint of enabling large-scale industrial processing and continuous use, centrifugation is preferred.

[0111] There are no particular limitations on the centrifugal separator, but a centrifugal sedimentation machine with a non-porous rotating container is preferred. Types include plate-type, cylindrical-type, and decanter-type. Since the specific gravity difference between PHA particles and water is small, a plate-type separator (intermittent discharge type, nozzle discharge type) with a large separation and settling area and high acceleration is preferred. A nozzle discharge type is particularly preferred when the PHA concentration in the crushing treatment liquid is high. As for decanter-type separators, models with separation plates that increase the separation and settling area are preferred.

[0112] In step (b), 500 to 1000 parts by weight of an aqueous medium may be added to the composition obtained by step (a), for example, 100 parts by weight of the breaking fluid, before separation.

[0113] In step (b), the aqueous medium may be reclaimed water manufactured by this manufacturing method, or a mixture of the aforementioned reclaimed water and a water-miscible organic solvent. The content of reclaimed water in the aqueous medium is preferably 50% by weight or more, more preferably 70% by weight or more, further preferably 80% by weight or more, and particularly preferably 85% by weight or more.

[0114] In step (b), the concentration of calcium ions in the reclaimed water is preferably 4.5 mg / L or less, more preferably 3.0 mg / L or less, and even more preferably 2.0 mg / L or less. Maintaining a calcium ion concentration of 4.5 mg / L or less in the reclaimed water helps to inhibit the thermal decomposition of PHA. The concentration of sodium ions in the reclaimed water is preferably 450 mg / L or less, more preferably 250 mg / L or less, and even more preferably 220 mg / L or less. Maintaining a sodium ion concentration of 450 mg / L or less in the reclaimed water helps to inhibit the thermal decomposition of PHA.

[0115] As a water-miscible organic solvent, there are no particular limitations, but examples include: methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, pentanol, hexanol, heptanol, and other alcohols; acetone, methyl ethyl ketone, and other ketones; tetrahydrofuran, dimethyl ethyl ketone, etc. Ethers such as alkanes; nitriles such as acetonitrile and propionitrile; amides such as dimethylformamide and acetamide; dimethyl sulfoxide, pyridine, piperidine, etc. Among these, from the viewpoint of ease of removal, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, acetone, methyl ethyl ketone, tetrahydrofuran, etc., are preferred. Alkane, acetonitrile, propionitrile, etc. Furthermore, from the perspective of easy availability, methanol, ethanol, 1-propanol, 2-propanol, butanol, acetone, etc., are more preferred. In addition, methanol, ethanol, and acetone are particularly preferred.

[0116] In step (b), PHA can be purified by washing the separated PHA (containing the water-insoluble component of PHA) at least once with the aforementioned aqueous medium. For example, 500 to 1000 parts by weight of the aqueous medium can be added to 100 parts by weight of the water-insoluble component containing PHA. Furthermore, to effectively remove impurities from microbial cells and improve purification efficiency, alkaline compounds, surfactants, proteolytic enzymes, etc., can be added to the aqueous medium.

[0117] (Process (c))

[0118] In one embodiment of the present invention, the method for manufacturing this PHA may include a step (c) of drying the PHA separated in step (b). The PHA (dehydrated resin) washed and dehydrated with an aqueous medium can be directly dried to obtain powdered PHA. The drying method can be appropriately selected and is not particularly limited; conventional drying methods such as spray drying, airflow drying, flow drying, and belt drying are preferred.

[0119] In one embodiment of the present invention, the PHA dispersion can be washed with an aqueous medium, a dispersant is added to the concentrated PHA dispersion, the pH is adjusted to below 7, and then dried to obtain powdered PHA. Examples of dispersants include: water-soluble polymers such as polyvinyl alcohol (PVA), methylcellulose, ethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, 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). As a method for adjusting the pH to below 7, for example, adding an acid can be used. The acid is not particularly limited and can be any acid from organic or inorganic acids; for example, sulfuric acid, hydrochloric acid, phosphoric acid, and acetic acid can be used.

[0120] The molecular weight of PHA is not particularly limited, as long as it exhibits substantially sufficient physical properties for the intended use. For example, from the viewpoint of processability and the strength of the molded body, the weight-average molecular weight of PHA is preferably 50,000 to 3,000,000, more preferably 60,000 to 1,500,000. It should be noted that the weight-average molecular weight here refers to the molecular weight obtained by gel permeation chromatography (GPC) using chloroform eluent to convert the molecular weight distribution of polystyrene. As the chromatographic column in this GPC, a column suitable for determining the above molecular weight can be used.

[0121] PHA exhibits high thermal stability, and after heat treatment at 160°C for 20 minutes, the weight-average molecular weight retention rate is preferably 70% or more, more preferably 73% or more, further preferably 75% or more, even more preferably 78% or more, and particularly preferably 80% or more. It should be noted that the thermal stability of PHA was determined using the method described in the examples below.

[0122] The PHA has a good hue, and the yellowness index (YI value) of the 5 mm thick sheet pressed at 160°C is preferably 20 or less, more preferably 17 or less.

[0123] PHA can be molded into various fibers, filaments, ropes, fabrics, woven materials, non-woven fabrics, paper, films, sheets, tubes, plates, rods, containers, bags, components, foams, and other molded materials. These molded materials are ideally suited for use in agriculture, fisheries, forestry, horticulture, medicine, hygiene products, clothing, non-clothing materials, packaging, and other fields.

[0124] In the case of other biodegradable plastics produced by microorganisms, the reclaimed water produced by this manufacturing method may also be used in the process of breaking down or dissolving the microbial cells containing the biodegradable plastic and separating the biodegradable plastic.

[0125] This invention is not limited to the above-described embodiments, and various modifications can be made 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 this invention.

[0126] That is, one embodiment of the present invention is shown below.

[0127] <1> A method for producing reclaimed water, the method comprising the following steps (A) to (D):

[0128] (A) Treatment process, which involves microbial-based anaerobic and aerobic treatment of wastewater discharged during the manufacturing process of polyhydroxyalkanoates;

[0129] (B) Pretreatment filtration process: The treated water obtained in the above process (A) is pretreated and filtered by membrane separation activated sludge method;

[0130] (C) Alkali treatment process, wherein the treated water obtained in process (B) above is subjected to alkali treatment; and

[0131] (D) Filtration process: The treated water obtained in step (C) above is filtered through an ion removal membrane.

[0132] <2> According to the method for manufacturing reclaimed water described in <1>, in the above-mentioned 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.

[0133] <3> The method for producing reclaimed water according to <1> or <2>, wherein in the above-mentioned step (C), the FI value of the treated water is adjusted to 6.0 or above.

[0134] <4> A method for producing reclaimed water according to any one of <1> to <3>, wherein, in the above-mentioned step (C), the alkali treatment is carried out using one or more aqueous solutions selected from the following: aqueous solution of alkali metal hydroxide, aqueous solution of alkali metal carbonate, aqueous solution of alkali metal bicarbonate, aqueous solution of alkali metal salt of organic acid, aqueous solution of alkali metal borate, aqueous solution of alkali metal phosphate, aqueous solution of alkaline earth metal hydroxide, and ammonia.

[0135] <5> The method for producing reclaimed water according to any one of <1> to <4> further includes the following step (C') in the above-mentioned step (C):

[0136] (C') Precipitation process, in which solid substances containing multivalent ions are precipitated from the above-treated water.

[0137] <6> According to the method for producing reclaimed water described in <5>, wherein the aforementioned multivalent ions are selected from 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 of them.

[0138] <7> The method for producing reclaimed water according to <5> or <6> further includes the following step (C”) in the above-mentioned step (C):

[0139] (C”) Sedimentation removal process, in which the solid matter precipitated into the treated water in the above process (C’) is removed by sedimentation.

[0140] <8> A method for producing reclaimed water according to any one of <1> to <7>, wherein, in the above-mentioned step (D), the MgSO4 rejection rate of the ion removal membrane is 60-100% when a pressure of 3000 kPa is applied at 20°C.

[0141] <9> A method for producing reclaimed water according to any one of <1> to <8>, wherein, in the above-mentioned step (D), the inter-membrane differential pressure of the ion removal membrane is 0.4 to 4.14 MPa.

[0142] <10> A method for manufacturing a polyhydroxyalkanoate, the method comprising:

[0143] The process (a) involves disrupting or solubleting microbial cells containing polyhydroxyalkanoates, and the process (b) involves separating the polyhydroxyalkanoates from the composition obtained in process (a).

[0144] The above-mentioned steps (a) and (b) use reclaimed water produced by any one of <1> to <9>.

[0145] Example

[0146] The present invention will be described in more detail below through embodiments, but the present invention is not limited to these embodiments.

[0147] [Measurement and Evaluation Methods]

[0148] The measurement and evaluation methods in the examples and comparative examples are shown below.

[0149] (FI value)

[0150] The FI value is a semi-quantitative indicator of the degree of fouling caused to the membrane by the influent water intended for membrane treatment, as defined in JIS K 3802. In the case of RO membranes, it is recommended to set the FI value of the influent water to 5 or below. 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 at 0.206 MPa. In addition, after 15 minutes of continuous operation, the time (T2) required for another 500 ml of sample water to pass through the same filter is measured and derived by the following formula (1).

[0151] [Mathematical Expression 2]

[0152]

[0153] In the above formula (1), PF represents the blockage factor, and T refers to the time from the start of the measurement at T1 to the start of the measurement at T2.

[0154] (Turbidity)

[0155] 200 mL of the prepared cleaning water was placed in a dedicated measuring container and the measuring instrument (TCR-5Z manufactured by Kasane Ryukyu Co., Ltd.) was quietly immersed in the container without generating bubbles, and the turbidity was measured.

[0156] (Solid composition analysis)

[0157] Metal ions in the filtrate obtained from pretreatment filtration via membrane separation of activated sludge were analyzed using ICP-MS (Agilent Technologies, Agilent 7900). Additionally, metal ions in the solid components adhering to the RO membrane surface were analyzed using ICP-MS (Agilent Technologies, Agilent 7900), and Si / P / SO4 were analyzed using ICP-AES (Shimadzu Corporation, ICPS-7510).

[0158] (Thermal stability)

[0159] Thermal stability is calculated based on the weight-average molecular weight retention of PHA after heating at 160°C for 20 minutes. A weight-average molecular weight retention of 70% or higher is considered good thermal stability, while a retention of less than 70% is considered poor thermal stability. The weight-average molecular weight retention is calculated using the following formula.

[0160] Weight-average molecular weight retention (%) = (weight-average molecular weight of PHA after heating / weight-average molecular weight of PHA before heating) × 100

[0161] <Weight-average molecular weight of PHA before heating>

[0162] 10 mg of PHA powder was dissolved in 10 mL of chloroform, and insoluble matter was removed by filtration. The molecular weight of this solution (filtrate) was determined using a GPC system manufactured by Shimadzu Corporation, equipped with a "Shodex K805L (300×8 mm, 2 in series)" (manufactured by Showa Denko Corporation), with chloroform as the mobile phase. Commercially available standard polystyrene was used as the molecular weight standard.

[0163] <Weight-average molecular weight of PHA after heating>

[0164] PHA powder was preheated at 160°C for 7 minutes and then heated at 160°C for 20 minutes to prepare PHA tablets. Except for using 10 mg of the PHA tablets, the weight-average molecular weight of the heated PHA was determined by following the same procedure as when determining the weight-average molecular weight of the PHA before heating.

[0165] (Inter-membrane differential pressure)

[0166] The inter-membrane differential pressure is calculated using the following formula.

[0167] (RO membrane inlet pressure + RO membrane outlet pressure) / 2 - Permeation side (secondary side) pressure

[0168] [Example 1]

[0169] Wastewater discharged from PHA production underwent microbial-based anaerobic and aerobic treatment, followed by pretreatment filtration using an MF membrane separation activated sludge process. The pH of the filtrate was adjusted to allow solids to separate, which was then filtered using an RO membrane. Anaerobic treatment was carried out as follows: in an acid-generating tank (pH around 7.1), acid-producing bacteria decomposed high molecular weight carbohydrates and lipids into organic acids and lower alcohols. Subsequently, a methane generation reactor using an EGSB process (loading capacity 15 kg-CODcr / m³) was used. 3 In step / d), granular methanogenic bacteria decompose organic acids and lower alcohols into methane gas and carbon dioxide. Aerobic treatment is carried out using a device consisting of a denitrification tank (activated sludge treatment tank), an aeration tank (activated sludge treatment tank), a second denitrification tank (activated sludge treatment tank), and a re-aeration tank (activated sludge treatment tank), where aerobic bacteria decompose organic matter that has not been decomposed by anaerobic treatment. Pretreatment filtration based on membrane separation activated sludge process is performed in the re-aeration tank (activated sludge treatment tank) using an MF membrane (hollow fiber membrane: PVDF, manufactured by Mitsubishi Chemical Corporation, nominal pore size: 0.4 μm). For the MF membrane, water permeate at a filtration linear velocity of 0.35 m / s. The pH of the MF membrane permeate is 7, the FI value is 0, and the turbidity is 0 NTU. The permeate from the MF membrane was collected in a stirred tank, and 2.4 ppm of Genesys LF (manufactured by Genesys Corporation) as an antiscalant was added. The pH was adjusted to 8.8 using a sodium hydroxide aqueous solution. After solids were precipitated, the water had a FI value of 6 or higher and a turbidity of 0.5 NTU. This water was concentrated four times to prepare concentrated water. Then, it was fed to the RO membrane (material: composite polyamide, manufactured by Nitto Denko Corporation, LFC3-LD) at a water temperature of 25°C and a filtration line velocity of 0.48 m / day. The membrane differential pressure at the time of feed was 1.5 MPa. The water that passed through the RO membrane (also called "reclaimed water") and the non-permeate water were returned to the collection tank for circulation. Operating at a constant filtration line velocity resulted in an increase in the membrane differential pressure due to fouling; therefore, feed was continued until the membrane differential pressure reached 2.0 MPa. Then, as a membrane capacity recovery treatment, a 30-minute flushing operation was performed using permeate water at a supply line velocity of 6 m / min or higher. After the rinsing operation, concentrated water was delivered at a filtration line speed of 0.48 m / day, resulting in a membrane differential pressure of 1.4 MPa.

[0170] [Example 2]

[0171] The pH was adjusted to 8.9 using sodium hydroxide. Otherwise, drainage treatment and RO membrane recovery were performed using the same method as in Example 1. The water adjusted to pH 8.9 had a FI value of 6 or higher and a turbidity of 0.5 NTU. Then, the solution was fed to the RO membrane at a water temperature of 25°C and a filtration linear velocity of 0.48 m / day. The intermembrane differential pressure was 1.6 MPa at the start of the feeding, and feeding continued until the intermembrane differential pressure reached 2.0 MPa. After membrane capacity recovery treatment, concentrated water was fed at a filtration linear velocity of 0.48 m / day, resulting in an intermembrane differential pressure of 1.4 MPa.

[0172] [Example 3]

[0173] The pH was adjusted to 9.1 using sodium hydroxide. Otherwise, drainage treatment and RO membrane recovery were performed using the same method as in Example 1. The water adjusted to pH 9.1 had a FI value of 6 or higher and a turbidity of 0.6 NTU. Then, the solution was fed to the RO membrane at a water temperature of 25°C and a filtration linear velocity of 0.48 m / day. The intermembrane differential pressure was 1.4 MPa at the start of the feeding, and feeding continued until the intermembrane differential pressure reached 2.0 MPa. After membrane capacity recovery treatment, concentrated water was fed at a filtration linear velocity of 0.48 m / day, resulting in an intermembrane differential pressure of 1.3 MPa.

[0174] [Example 4]

[0175] No scale inhibitor was added; the pH was adjusted to 9.1 using sodium hydroxide. Otherwise, drainage treatment and RO membrane recovery were performed using the same method as in Example 1. The water adjusted to pH 9.1 had an FI value of 6 or higher and a turbidity of 0.7 NTU. Then, the solution was fed to the RO membrane at a water temperature of 25°C and a filtration linear velocity of 0.48 m / day. The intermembrane differential pressure was 1.6 MPa at the start of the feed, and feed continued until the intermembrane differential pressure reached 1.9 MPa. After membrane capacity recovery treatment, concentrate was fed at a filtration linear velocity of 0.48 m / day, resulting in an intermembrane differential pressure of 1.4 MPa.

[0176] [Example 5]

[0177] The pH was adjusted to 9.2 using sodium hydroxide. Otherwise, drainage treatment and RO membrane recovery were performed using the same method as in Example 4. The water adjusted to pH 9.2 had a FI value of 6 or higher and a turbidity of 0.4 NTU. Then, the solution was fed to the RO membrane at a water temperature of 25°C and a filtration linear velocity of 0.48 m / day. The intermembrane differential pressure was 1.4 MPa at the start of the feeding, and feeding continued until the intermembrane differential pressure reached 1.9 MPa. Then, after membrane capacity recovery treatment, concentrated water was fed at a filtration linear velocity of 0.48 m / day, resulting in an intermembrane differential pressure of 1.5 MPa.

[0178] [Example 6]

[0179] The pH was adjusted to 9.2 using sodium hydroxide. Otherwise, drainage treatment and RO membrane recovery were performed using the same method as in Example 4. The water adjusted to pH 9.2 had an FI value of 6 or higher and a turbidity of 0.3 NTU. Then, the solution was fed to the RO membrane at a water temperature of 25°C and a filtration linear velocity of 0.48 m / day. The intermembrane differential pressure was 1.5 MPa at the start of the feeding, and feeding continued until the intermembrane differential pressure reached 2.0 MPa. After membrane capacity recovery treatment, concentrated water was fed at a filtration linear velocity of 0.48 m / day, resulting in an intermembrane differential pressure of 1.6 MPa.

[0180] [Comparative Example 1]

[0181] Pretreatment filtration was performed using an MF membrane separation activated sludge process. No alkali treatment was then performed; otherwise, wastewater treatment and RO membrane recovery were conducted using the same method as in Example 1. The water had a FI value of 0 and a turbidity of 0 NTU, and was fed to the RO membrane at a temperature of 25°C and a filtration linear velocity of 0.48 m / day. The intermembrane differential pressure started at 1.3 MPa and continued until it reached 2.3 MPa. After membrane capacity recovery treatment, concentrated water was then fed at a filtration linear velocity of 0.48 m / day, resulting in an intermembrane differential pressure of 2.2 MPa.

[0182] 〔result〕

[0183] For Examples 1 to 6 and Comparative Example 1, the measurement results of the initial intermembrane differential pressure, the intermembrane differential pressure at the end of filtration, and the intermembrane differential pressure after membrane capacity recovery treatment are shown in Table 1.

[0184] [Table 1]

[0185]

[0186] As shown in Table 1, the intermembrane differential pressure decreased after the membrane capacity recovery treatment in Examples 1-6 compared to Comparative Example 1. This indicates that since the intermembrane differential pressure did not differ significantly after the liquid delivery was completed, the RO membrane flux could be restored to a very high value through the membrane capacity recovery treatment. The results of Examples 1 and 4, and Comparative Example 1, suggest that the precipitation of solid components, rather than the scale inhibitor, contributed to the membrane recovery.

[0187] Table 2 shows the metal ion concentrations of the filtrate after pretreatment filtration using the membrane separation activated sludge method in Example 6. Table 3 shows the types and concentrations of metal ions in the solid components adhering to the RO membrane after the filtrate delivery in Example 6.

[0188] [Table 2]

[0189] metal ions Concentration after pretreatment filtration [mg / L] Na 795 K 42 Ca 11 Mg 7 Fe 0.17 Cu 0.06 Al 0.1 Mn 0.04 Sr Less than 0.1 Zn Less than 0.05 Ba Less than 0.01 Co Less than 0.01

[0190] [Table 3]

[0191] metal ions Concentration of metal ions adhering to the RO membrane [wt%] Si 10 Ca 10 Na 6 Mg 2 Mn 0.4 K 0.3 Zn 0.1 Fe 0.06 Sr 0.06 Cu 0.02 Al 0.01 Sn 0.007 P 8 <![CDATA[SO4]]> 5

[0192] Compared to the results in Table 2, the proportion of elements that become multivalent ions is higher in the results in Table 3. Therefore, it can be inferred that low-solubility multivalent ions will preferentially precipitate through pH adjustment based on alkaline treatment. Thus, it can be assumed that metal ions do not firmly adhere to the RO membrane, and membrane capacity can be restored through permeate-water-based membrane capacity recovery treatment.

[0193] On the other hand, in the comparative example, the same metal salt (data not shown) was attached to the same RO membrane surface. However, it can be inferred that in the comparative example, metal ions were concentrated and precipitated on the surface of the RO membrane. Therefore, it can be considered that the metal salt was firmly attached to the RO membrane surface, and even with membrane capacity recovery treatment based on water permeate, the membrane capacity was not recovered.

[0194] [Example 7]

[0195] (Preparation of bacterial culture medium)

[0196] The bacterial cells were cultured according to the method described in International Publication No. 2010 / 067543 to obtain a bacterial culture medium containing PHA. It should be noted that *Ralstonia eutroPHA* is now classified as an insecticidal copper-loving bacterium. The composition ratio of repeating units of PHA in the above-mentioned bacterial cells (3HB unit / 3HH unit ratio) was 92 / 8 to 99 / 1 (mol / mol).

[0197] (Sterilization treatment)

[0198] The bacterial culture broth obtained above was sterilized by heating / stirring at an internal temperature of 60-80℃ for 20 minutes.

[0199] (Purification process)

[0200] Sodium dodecyl sulfate (0.2% by weight) was added to the sterilized bacterial culture medium obtained above. Further, washing water containing dissolved sodium hydroxide was added to bring the pH to 11.0, and the mixture was kept at 50°C for 1 hour. Then, high-pressure crushing was performed using a high-pressure crusher (Niro Soavi PA2K model) at a pressure of 44–54 MPa.

[0201] Washing water of the same weight as the high-pressure-crushed bacterial cell lysate obtained above was added. After centrifugation, the supernatant was removed, and the suspension was concentrated twofold. Washing water with added sodium hydroxide (pH 11.0) of the same weight as the removed supernatant was added to the concentrated PHA aqueous suspension, and centrifugation was performed. Next, after removing the supernatant, washing water was added to suspend the suspension, and 0.2% by weight of sodium dodecyl sulfate and 1 / 100th by weight of PHA protease (Novozymes, Esperase) were added. The suspension was stirred at 50°C and pH 10.0 for 2 hours. Then, the supernatant was removed by centrifugation, and the suspension was concentrated fivefold. Washing water with added sodium hydroxide (pH 11.0) of the same weight as the removed supernatant was added to the concentrated PHA aqueous suspension, and centrifugation was performed. This process was repeated five times, and the supernatant was removed to obtain a PHA aqueous suspension with a PHA concentration adjusted to 52% by weight. It should be noted that in this purification process, water (regenerated water) obtained by passing the concentrated water of Example 1 through an RO membrane was used as the cleaning water.

[0202] (Granulation)

[0203] A dispersant (polyethylene glycol / polypropylene glycol / block ether type nonionic surfactant, trade name "PLONON#208", manufactured by Nippon Oil Co., Ltd.) of 1 pHr (1 part by weight relative to 100 parts by weight of PHA present in the aqueous suspension) was added to the above-obtained PHA aqueous suspension (solid component concentration 52 wt%). Then, the solid component concentration was adjusted to 30 wt% with distilled water. After stirring the liquid for 30 minutes, sulfuric acid was added to adjust the pH to stabilize it at 4. The resulting PHA aqueous suspension was dried at 60°C for 12 hours to prepare PHA powder.

[0204] [Comparative Example 2]

[0205] Industrial water (Kaneka Co., Ltd.) was treated with ion exchange resins (manufactured by ORGANO Co., Ltd., consisting of a strong acidic cation exchange resin and a strong basic anion exchange resin) to obtain cleaning water 2. Cleaning water 2 was used as the cleaning water in the purification process, and otherwise, PHA powder was obtained in the same manner as in Example 7.

[0206] The thermal stability of the PHA powders obtained in Example 7 and Comparative Example 2 was determined and evaluated as described above. The results are shown in Table 4.

[0207] (Table 4)

[0208] Thermal stability [%) Example 7 81 Comparative Example 2 76

[0209] 〔result〕

[0210] As shown in Table 4, the PHA powder of Example 7 exhibits better thermal stability compared to the PHA powder of Comparative Example 2. This demonstrates that, compared to the use of conventional washing water, the regenerated water of this invention enables the production of PHA with superior performance (improved thermal stability).

[0211] Industrial applicability

[0212] This invention is preferably used in the field of drainage treatment and other fields.

Claims

1. A method for producing reclaimed water, the method comprising the following steps (A) to (D): (A) Treatment process, which involves microbial-based anaerobic and aerobic treatment of wastewater discharged during the manufacturing process of polyhydroxyalkanoates; (B) Pretreatment filtration process, in which the treated water obtained in process (A) is pretreated and filtered by membrane separation activated sludge method; (C) An alkali treatment step, wherein the treated water obtained in step (B) is subjected to alkali treatment; and (D) Filtration step, wherein the treated water obtained in step (C) is filtered through an ion removal membrane. In step (C), the FI value of the treated water is adjusted to 6.0 or higher. In step (D), the MgSO4 rejection rate of the ion removal membrane is 60-100% when a pressure of 3000 kPa is applied at 20°C.

2. The method for producing reclaimed water according to claim 1, wherein, In step (C), the pH of the treated water is adjusted to 7-11, and the turbidity of the treated water is adjusted to 0.1 NTU or higher.

3. The method for producing reclaimed water according to claim 1 or 2, wherein, In step (C), the alkali treatment is performed using one or more of the following: 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 ammonia.

4. The method for producing reclaimed water according to claim 1 or 2, wherein the method further comprises the following step (C') in step (C): (C') Precipitation step, in which solid substances containing multivalent ions are precipitated from the treated water.

5. The method for producing reclaimed water according to claim 4, wherein, The multivalent ions are selected from 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 of them.

6. The method for producing reclaimed water according to claim 4, wherein the method further comprises the following step (C'') in step (C): (C'') Sedimentation removal process, in which the solid matter precipitated into the treated water in process (C') is removed by sedimentation.

7. The method for producing reclaimed water according to claim 1 or 2, wherein, In the process (D), the inter-membrane differential pressure of the ion removal membrane is 0.4~4.14 MPa.

8. A method for manufacturing a polyhydroxyalkanoate, the method comprising: The process of disrupting or dissolving microbial cells containing polyhydroxyalkanoates (a), and Step (b) involves separating the polyhydroxyalkanoates from the composition obtained in step (a). The reclaimed water produced by the method of any one of claims 1 to 7 is used in steps (a) and (b).

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