JP2022175471A - Prediction method of chemical washing period of filtration membrane and use thereof - Google Patents

Abstract

To provide a method capable of appropriately setting a washing period by predicting clogging of a filtration membrane in a simple membrane concentration method.SOLUTION: A prediction method of a chemical washing period of a filtration membrane in membrane filtration of a PHA aqueous suspension includes: (A) a yellowness measurement step measuring yellowness of a filtration membrane penetrated liquid in an early stage of starting of the filtration in a step concentrating the PHA aqueous suspension obtained by the treatment of a microorganism cell through the filtration membrane; and (B) an estimation step estimating the chemical washing period of the filtration membrane by predicting the clogging period of the filtration membrane on the basis of, the measurement result obtained in the step (A).SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to a method for predicting the timing of chemical cleaning of a filtration membrane and its use.

Membrane separation equipment using membrane modules such as microfiltration membranes and ultrafiltration membranes is used in the water treatment field such as seawater desalination, pure water production, water purification and wastewater treatment, and in the food field such as wine and fruit juice concentration. are widely used in various industries. Membrane separators are often automatically operated by presetting time, flow rate, and the like. In such a membrane separation device, when the raw water quality deteriorates rapidly, cleaning cannot catch up with the clogging of the filtration membrane (also referred to as "separation membrane") during filtration under predetermined operating conditions for filtration and cleaning. There is concern that the amount of fresh water produced will decrease, or that the filtration membrane itself will become completely clogged and unusable.

As a technique for predicting clogging of a filtration membrane, for example, Patent Document 1 discloses a method for evaluating fouling of a separation membrane provided in a membrane separation device for obtaining a permeated liquid from a liquid to be treated, wherein the liquid to be treated is centrifuged. The concentration of organic substances in the supernatant liquid and the concentration of organic substances in the permeated liquid of the separation membrane are measured respectively, and the difference or ratio of the measured values, or the rate of change of the difference or ratio of the separation membrane is measured. A method for assessing fouling conditions is described. Further, Patent Document 2 describes a method of operating a membrane filtration plant characterized by predicting changes in filtration differential pressure based on a plurality of parameters and determining operating conditions based on the predicted values. .

JP 2012-200631 A Japanese Patent Application Laid-Open No. 2001-327967

However, with the techniques described in Patent Documents 1 and 2, it is not easy to predict clogging of the filtration membrane, and it is necessary to construct a complex system using multiple detectors such as pressure gauges and turbidity meters. There were some problems.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for estimating clogging of a filtration membrane and appropriately setting the cleaning time in a simple manner in membrane concentration.

As a result of intensive studies by the present inventors to solve the above problems, an aqueous suspension containing polyhydroxyalkanoic acid (hereinafter also referred to as "PHA") (hereinafter also referred to as "PHA aqueous suspension"). ) in the step of concentrating through the filtration membrane, by measuring the yellowness of the filtration membrane permeation liquid at the beginning of filtration (hereinafter also referred to as "initial permeation liquid"), the clogging time of the filtration membrane can be predicted. For the first time, the present invention has been completed.

Therefore, one aspect of the present invention is a method for predicting the timing of chemical washing of a filtration membrane in membrane filtration of an aqueous PHA suspension, comprising: (A) an aqueous PHA suspension obtained by treating microbial cells; In the step of concentrating through a filtration membrane, a yellowness measurement step of measuring the yellowness of the filtration membrane permeate liquid at the beginning of the filtration, and (B) based on the measurement results obtained in the step (A) and an estimating step of estimating the clogging time of the filtration membrane and estimating the chemical cleaning time of the filtration membrane.

ADVANTAGE OF THE INVENTION According to 1 aspect of this invention, blockage of a filtration membrane can be estimated by a simple method, and it becomes possible to set washing time appropriately.

1 is a diagram showing an outline of membrane filtration (concentration) of a PHA aqueous suspension according to one embodiment of the present invention; FIG. FIG. 10 illustrates the relationship between initial permeate yellowness and cycles to membrane blockage, according to one embodiment of the present invention.

One 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". Also, all of the documents mentioned in this specification are incorporated herein by reference.

[1. Overview of the present invention]
According to one embodiment of the present invention, a method for predicting the timing of chemical cleaning of a filtration membrane in membrane filtration of an aqueous PHA suspension (hereinafter referred to as "this prediction method") comprises (A) treating microbial cells; (B) the step (A and an estimation step of estimating the timing of clogging of the filtration membrane and estimating the timing of chemical cleaning of the filtration membrane based on the measurement results obtained in ).

As described above, in the conventional techniques such as those described in Patent Documents 1 and 2, it is not easy to predict clogging of the filtration membrane. There were problems such as the need to build a system.

Therefore, the present inventors have made intensive studies on a method for easily predicting the clogging time of the filtration membrane, and as a result, have succeeded in obtaining the following findings.
• The yellowness of the initial permeate is correlated with the cycles to membrane blockage.
・By measuring the yellowness of the initial permeate, it is possible to predict when the filtration membrane will be clogged and when to wash the filtration membrane with chemicals.

That is, the present invention measures only the yellowness of the initial permeate and can predict membrane clogging with a very simple system. According to the present invention, it is not necessary to continuously monitor or use a plurality of parameters as in Patent Documents 1 and 2, and it is possible to predict when to wash the filtration membrane from a single yellowness measurement. The configuration of this prediction method will be described in detail below.

[2. Prediction Method of Chemical Cleaning Timing of Filtration Membrane]
This prediction method is a method including the following steps (A) to (B).
- Step (A): In the step of concentrating the PHA aqueous suspension obtained by treating the microbial cells through the filtration membrane, the yellowness of the filtration membrane permeate at the beginning of the filtration is measured. Measurement step/step (B): an estimation step of estimating the timing of clogging the filtration membrane and estimating the timing of chemical cleaning of the filtration membrane based on the measurement results obtained in the step (A). , By including the steps (A) and (B), it is possible to predict clogging of the filtration membrane by a simple method, and to appropriately set the cleaning time.

(membrane filtration)
First, membrane filtration (concentration) of a PHA aqueous suspension in this prediction method will be described with reference to FIG. In addition, FIG. 1 shows an example of membrane filtration, and is not limited to this.

As shown in FIG. 1, a PHA aqueous suspension (slurry) 3 is sent from a first container 1 to a filtration membrane 6 . In the first container 1, the PHA aqueous suspension (slurry) 3 to be fed is stirred by a stirrer 2 with blades so that the concentration thereof becomes constant. The PHA aqueous suspension (slurry) 3 is delivered by a PHA aqueous suspension (slurry) delivery pump 4 . A membrane-permeated liquid 10 that has passed through the filtration membrane 6 passes through a yellowness meter 8 to measure the yellowness. A membrane-permeated liquid 10 that has passed through the yellowness index meter 8 is stored in a second container 9 . On the other hand, the PHA aqueous suspension (slurry) 3 that has not passed through the filtration membrane 6 returns to the first container 1 again. One cycle is counted until the PHA aqueous suspension (slurry) 3 reaches a predetermined suspension concentration. During the membrane filtration operation, the pressure before passing through the filtration membrane is measured with the first pressure gauge 5, and the pressure after passing through the filtration membrane is measured with the second pressure gauge 7, and an appropriate pressure is maintained.

In this prediction method, operation is performed until the concentration of the PHA aqueous suspension (slurry) 3 reaches a desired concentration or until the filtration membrane 6 is clogged. In the examples described later, when the initial permeation rate was less than 0.50 L/m ² ·h·kPa, membrane clogging occurred and the operation was considered impossible.

(Step (A))
In the step (A) in this prediction method, the yellowness of the filtration membrane permeate at the beginning of the filtration is measured in the step of concentrating the PHA aqueous suspension obtained by treating the microbial cells through the filtration membrane. This is the step of yellowness measurement.

As used herein, "concentration" means an operation of raising the concentration of PHA in an aqueous PHA suspension to a certain concentration via a filtration membrane.

<PHA>
As used herein, "PHA" has the following formula (1):
[-O-CHR-CH ₂ -CO-] (1)
(Wherein, R is an alkyl group represented by C _n H _2n+1 , and n is an integer of 1 to 15.) General term for polymers or copolymers consisting of one or more units represented by means

In one embodiment of the present invention, the PHA may be a poly(3-hydroxybutyrate) having only 3-hydroxybutyrate as a repeating unit, or a poly(3-hydroxybutyrate) containing 3-hydroxybutyrate and other hydroxyalkanoate It may be a copolymer.

In one embodiment of the present invention, the PHA may be a mixture of a homopolymer and one or more copolymers, or a mixture of two or more copolymers. The form of copolymerization is not particularly limited, and may be random copolymerization, alternating copolymerization, block copolymerization, graft copolymerization, or the like.

In one embodiment of the present invention, PHA includes, for example, poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-3-hydroxypropionate) (P3HB3HP), poly(3 -hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P3HB3HV), poly(3-hydroxybutyrate-co-4- hydroxybutyrate) (P3HB4HB), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate) (P3HB3HO), poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate) (P3HB3HOD) , Poly(3-hydroxybutyrate-co-3-hydroxydecanoate) (P3HB3HD), Poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (P3HB3HV3HH) etc. P3HB3HH, P3HB4HB, and P3HB3HP are preferable from the viewpoint of being able to adjust the melting point to a low level and widening the processing width. Among them, P3HB3HH and P3HB4HB are particularly preferable because they are easy to produce industrially. From the viewpoint of industrial productivity, P3HB and P3HB3HV are also preferable in addition to the above.

PHAs are preferably produced by microorganisms. The PHA-producing microorganism is not particularly limited as long as it is capable of producing PHA. For example, Bacillus megaterium discovered in 1925 was the first P3HB3HH-producing bacterium, and also Capriavidus necator (Old classification: Alcaligenes eutrophus, Ralstonia eutropha). and naturally occurring microorganisms such as Alcaligenes latus. These microorganisms are known to accumulate P3HB3HH in their cells.

In addition, known bacteria producing copolymers of hydroxybutyrate and other hydroxyalkanoates include Aeromonas caviae, which is a P3HB3HH-producing bacterium, and Alcaligenes eutrophus, which is a P3HB4HB-producing bacterium. It is In particular, regarding P3HB3HH, in order to increase the productivity of P3HB3HH, Alcaligenes eutrophus AC32 strain (Alcaligenes eutrophus AC32, FERM BP-6038) (T.Fukui, Y.Doi, J.Bateriol) into which the gene of the P3HB3HH synthase group was introduced. ., 179, p4821-4830 (1997)) are more preferred, and microbial cells obtained by culturing these microorganisms under appropriate conditions and accumulating P3HB3HH in the cells are used. In addition to the above, genetically modified microorganisms into which various PHA-synthesis-related genes have been introduced may be used according to the PHA to be produced, or culture conditions including the type of substrate may be optimized. PHA can also be produced, for example, by the method described in WO 2010/013483.

Since the PHA-containing microorganisms produced by culturing the above microorganisms contain a large amount of bacterial cell-derived components as impurities, a purification step for decomposing and/or removing impurities other than PHA is usually performed. can be implemented. This purification step is not particularly limited, and physical treatments, chemical treatments, biological treatments, etc. that can be considered by those skilled in the art can be applied. method is preferably applicable.

In one embodiment of the present invention, the weight average molecular weight of the PHA is not particularly limited, but from the viewpoint of moldability, the weight average molecular weight is preferably 120,000 to 3,000,000, more preferably 120,000 to 2,500,000. is more preferable, and 150,000 to 1,000,000 is even more preferable. When the weight average molecular weight of PHA is 120,000 or more, sufficient mechanical properties are obtained, and when it is 3,000,000 or less, good moldability is achieved. The weight average molecular weight of PHA was determined by gel permeation chromatography (GPC) ("Shodex GPC-101" manufactured by Showa Denko) using polystyrene gel ("Shodex K-804" manufactured by Showa Denko) as a column and chloroform as the mobile phase. , can be obtained as a molecular weight in terms of polystyrene.

When the PHA in the present production method is PHBH, the composition ratio of 3HB units/3HH units of PHBH is preferably 89/11 to 99.5/0.5 (mol/mol), more preferably 90/10 to 99/1. (mo1/mo1) is more preferred, and 91/9 to 98/2 (mo1/mo1) is even more preferred. When the composition ratio of 3HB units/3HH units is 99.5/0.5 (mol/mol) or less, good moldability and sufficient hardness are obtained, and 89/11 (mol/mol) or more. provides sufficient flexibility.

As used herein, "PHA aqueous suspension" means an aqueous suspension containing PHA after microbial cell treatment. In the aqueous suspension after microbial cell treatment, PHA exists in a dispersed state in the aqueous medium.

<Measurement of yellowness index>
In one embodiment of the present invention, the measurement of yellowness in step (A) is carried out in the step of concentrating the PHA aqueous suspension obtained by treating microbial cells through a filtration membrane. It is carried out by measuring the degree of yellowness of the filtrate permeated through the filtration membrane. The measurement of yellowness in step (A) is performed by the method described in Examples.

As used herein, the term "filtration membrane permeated liquid at the beginning of filtration" means a liquid that has permeated the filtration membrane within a certain period of time immediately after the start of filtration (for example, the supernatant of an aqueous PHA suspension). The "filtration membrane permeated liquid at the initial stage of filtration" is the target for measuring the degree of yellowness in step (A).

In one embodiment of the present invention, the "filtration membrane permeated liquid at the initial stage of filtration" is preferably 1/20 or less of the total permeated liquid amount. That is, according to this prediction method, it is possible to predict the clogging time of the filtration membrane using the "filtration membrane permeated liquid at the beginning of filtration", which is a relatively small amount immediately after the start of filtration.

In the present specification, the term "the amount of permeated liquid equal to or less than 1/20 of the total amount of permeated liquid" means the amount equal to or less than the liquid amount calculated by the following formula.

For example, when the amount of the PHA aqueous suspension at the beginning of the first cycle (before filtration) is 100 kg, the PHA aqueous suspension concentration is 30% by weight, and the target PHA aqueous suspension concentration is 50% by weight, total permeation The amount of permeate that is less than 1/20 of the liquid volume is 2L.

In one embodiment of the present invention, "the amount of permeate that is 1/20 or less of the total amount of permeate" is, for example, 1/25, preferably 1/30, 1/50 is more preferable.

In step (A), the aqueous PHA suspension to be filtered is preferably subjected to the purification treatment described in the above <PHA> section after treatment with microbial cells. This treatment makes it possible to remove from consideration the influence of the medium in which the microorganisms were cultured when evaluating the yellowness index.

Membrane filtration in this prediction method is not particularly limited as long as it is a separation membrane capable of concentrating the PHA aqueous suspension, and examples thereof include dead-end filtration and tangential flow filtration. The membrane filtration is preferably tangential flow filtration from the viewpoint that membrane concentration can be performed while suppressing the phenomenon of PHA particles depositing on the membrane surface.

The pore size of the filtration membrane in this prediction method is not particularly limited as long as it is a pore size that can prevent the passage of PHA particles in the PHA aqueous suspension. The pore size of the filtration membrane is preferably 0.1 to 1.0 μm, more preferably 0.1 to 0.8 μm, even more preferably 0.2 to 0.6 μm. When the pore size of the filtration membrane is 1.0 μm or less, it is possible to avoid a situation in which PHA particles enter the membrane pores and cause clogging. Further, when the pore size of the filtration membrane is 0.1 μm or more, it is possible to avoid a situation in which impurities contained in the PHA aqueous suspension clog the membrane in a short period of time.

The material of the filtration membrane in this prediction method is not particularly limited as long as it has a pore size that does not allow PHA particles to pass through, and examples thereof include ceramics, polypropylene, and polysulfone. From the viewpoint of chemical resistance, the material of the filtration membrane is preferably ceramic.

In one embodiment of the present invention, the PHA particle size/filtration membrane surface opening size in this prediction method is preferably 1.1 to 100, more preferably 1.1 to 40, and 1.1 to 20 is more preferred. When the PHA particle size/filtration membrane surface opening size is 1.1 to 100, there is an advantage that filtration can be performed in an appropriate time. In the present specification, "PHA particle size" means the weight average particle size of PHA. Also, the "PHA particle size" is measured by a static light scattering method.

In one embodiment of the present invention, the PHA aqueous suspension concentration after concentration/the PHA aqueous suspension concentration before filtration in the present prediction method is preferably 1.5 to 2.5, and 1.6 to 2.1 is more preferred, and 1.65 to 1.95 is even more preferred. When the PHA aqueous suspension concentration after concentration/the PHA aqueous suspension concentration before filtration is 1.5 to 2.5, the concentration efficiency is good.

In one embodiment of the present invention, the maximum permeation flow rate/minimum permeation flow rate of the permeation flow rate during constant pressure feeding in the concentration step in the prediction method is preferably 3 to 10, more preferably 3 to 8. , 3 to 6. If the maximum permeation flow rate/minimum permeation flow rate of the permeation flow rate during constant pressure feeding in the concentration step is 3 to 10, there is an advantage that filtration can be performed in an appropriate time. In the present specification, "maximum permeation flow rate/minimum permeation flow rate during constant pressure feeding in the concentration step" refers to the maximum permeation flow rate during constant pressure feeding during the entire period from the start of concentration to the end of concentration. / intended for minimum permeate flux. Further, the maximum permeation flow rate/minimum permeation flow rate of the permeation flow rate during constant pressure feeding is measured by the method described in Examples.

In one embodiment of the present invention, the concentration of the aqueous PHA suspension after concentration/the concentration of the aqueous PHA suspension before filtration is 1.5 to 2.5, and during constant pressure feeding in the concentration step The maximum permeate flow rate/minimum permeate flow rate of the permeate flow rate can be 3-10.

(Step (B))
The step (B) in this prediction method is an estimation step of predicting the clogging time of the filtration membrane based on the measurement results obtained in the step (A), and estimating the chemical cleaning time of the filtration membrane. .

As noted above, the inventors have found that the yellowness of the initial permeate correlates with the cycles to membrane plugging. Therefore, by using the degree of yellowness of the initial permeate as an index, it is possible to predict when the filtration membrane will be clogged, and as a result, it is possible to easily estimate when the filtration membrane will be washed with chemicals.

In this prediction method, the higher the yellowness of the initial permeate, the more impurities that can clog the filtration membrane have passed through the filtration membrane (that is, the impurities are not stopped by the filtration membrane). tend to take longer cycles to occur. In addition, in this prediction method, the lower the yellowness of the initial permeate, the less impurities that can clog the filtration membrane (that is, the filtration membrane stops impurities), so the membrane clogging The cycle to occur tends to be short. Therefore, in one embodiment of the present invention, the higher the yellowness of the initial permeate, the longer the cycle to membrane blockage can be expected. Also, in one embodiment of the present invention, the lower the yellowness of the initial permeate, the shorter the cycle until membrane plugging occurs can be expected.

Further, in one embodiment of the present invention, prediction of the clogging time of the filtration membrane can be performed, for example, as follows, as shown in Examples 1 to 3.

(a) When the yellowness of the initial permeate is 0.6, the clogging time of the filtration membrane is after 3 cycles. That is, it can be estimated that the chemical cleaning time of the filtration membrane is, for example, after 3 cycles of concentration of the PHA aqueous suspension.
(b) When the yellowness index of the initial permeate is 0.9, the clogging time of the filtration membrane is after 4 cycles. That is, it can be estimated that the chemical cleaning time of the filtration membrane is, for example, after 4 cycles of concentration of the PHA aqueous suspension.
(c) When the yellowness of the initial permeate is 1.2, the clogging time of the filtration membrane is after 5 cycles. That is, it can be estimated that the chemical cleaning time of the filtration membrane is, for example, after 5 cycles of concentration of the PHA aqueous suspension.

Further, as shown in Examples 1 to 3, the filtration membrane tends to be washed earlier as the number of times of washing increases.

The chemical used for chemical cleaning is not particularly limited as long as it is a chemical commonly used for cleaning filtration membranes, and examples thereof include sodium hydroxide, surfactants, sulfuric acid, Ultrasil 115, and the like.

The method of cleaning the filtration membrane with chemicals is not particularly limited, and any known method can be used.

[3. Method for Concentrating PHA Aqueous Suspension]
In one embodiment of the present invention, a method for concentrating an aqueous PHA suspension by passing an aqueous PHA suspension obtained by treating microbial cells through a filtration membrane, wherein the filtration is performed by the present prediction method. Provided is a method for concentrating an aqueous PHA suspension (hereinafter referred to as "this concentration method"), which includes a step of estimating the time to wash the membrane with chemicals and washing the filtration membrane. According to this concentration method, clogging of the filtration membrane can be predicted by a simple method, and PHA can be efficiently concentrated.

In this concentration method, "PHA", "concentration", "prediction of chemical cleaning time of filtration membrane", "cleaning of filtration membrane", etc. are described in [2. Prediction Method of Chemical Cleaning Timing for Filtration Membrane].

[4. Production method of PHA]
In one embodiment of the present invention, a method for producing PHA comprising a step of passing an aqueous PHA suspension obtained by treating microbial cells through a filtration membrane to concentrate, wherein the prediction method predicts the time to wash the filtration membrane with chemicals, and provides a method for producing a PHA (hereinafter referred to as "this production method"), which includes a step of washing the filtration membrane. According to this production method, clogging of the filtration membrane can be predicted by a simple method, and PHA can be produced efficiently.

In the present production method, "PHA", "concentration", "prediction of chemical cleaning time of filtration membrane", "cleaning of filtration membrane", etc. are described in [2. Prediction Method of Chemical Cleaning Timing for Filtration Membrane].

In one embodiment of the present invention, the production method may include the following steps before the concentration step.
The step of culturing the microorganisms The step of inactivating (sterilizing) the microorganisms The step of crushing the inactivated (sterilized) microorganisms The step of separating and purifying PHA from the crushed liquid is performed by any known method.

Moreover, in one embodiment of the present invention, the production method may include a step of drying the PHA concentrated in the concentration step. The PHA (dehydrated resin) washed with an aqueous medium and dehydrated can be dried as it is to obtain a powdery PHA. The drying method can be selected as appropriate, and is not particularly limited. For example, general drying methods such as spray drying, airflow drying, fluidized drying, and band drying can be preferably used.

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 to adjust the pH to 7 or less, and then dried to obtain a powdery PHA. Dispersants include, for example, polyvinyl alcohol (PVA), methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, polyacrylic acid, sodium polyacrylate, potassium polyacrylate, polymethacrylic acid, sodium polymethacrylate and the like. Molecules; nonionic surfactants such as polyethylene glycol/polypropylene glycol/block ether type (polyoxyethylene/polyoxypropylene/block polymer type). A method of adjusting the pH to 7 or less includes, for example, a method of adding an acid. The acid is not particularly limited, and may be either an organic acid or an inorganic acid. For example, sulfuric acid, hydrochloric acid, phosphoric acid, acetic acid and the like can be used as appropriate.

The molecular weight of the PHA is not particularly limited as long as it substantially exhibits sufficient physical properties for the intended use. For example, the weight average molecular weight of PHA is preferably from 50,000 to 3,000,000, more preferably from 60,000 to 1,500,000, from the viewpoint of molding processability and strength of molded products. In addition, the weight average molecular weight here refers to that measured from polystyrene conversion molecular weight distribution using gel permeation chromatography (GPC) using a chloroform eluent. As the column in the GPC, a column suitable for measuring the molecular weight may be used.

PHA can be molded into various molded bodies such as various fibers, threads, ropes, woven fabrics, knitted fabrics, non-woven fabrics, paper, films, sheets, tubes, plates, rods, containers, bags, parts, and foams. The molded article can be suitably used in agriculture, fishery, forestry, gardening, medicine, sanitary goods, clothing, non-clothing, packaging and other fields.

The present invention is not limited to the above-described embodiments, and can be modified in various ways within the scope of the claims. Embodiments obtained by appropriately combining technical means disclosed in different embodiments is also included in the technical scope of the present invention.

That is, one embodiment of the present invention is as follows.
<1> A method for predicting the timing of chemical cleaning of a filtration membrane in membrane filtration of an aqueous PHA suspension,
(A) In the step of passing an aqueous suspension containing PHA obtained by treating microbial cells through a filtration membrane to concentrate, measuring the yellowness of the filtration membrane permeate liquid at the beginning of the filtration, yellowness measurement. process and
(B) an estimation step of estimating the timing of clogging the filtration membrane based on the measurement results obtained in the step (A), and estimating the timing of washing the filtration membrane with a chemical agent;
Forecasting methods, including
<2> In the step (A), the filtration membrane permeated liquid at the beginning of the filtration, which is the target for measuring the yellowness index, is a permeated liquid having an amount of 1/20 or less of the total permeated liquid amount, <1> The prediction method described in .
<3> The prediction method according to <1> or <2>, wherein the membrane filtration is tangential flow filtration.
<4> The prediction method according to any one of <1> to <3>, wherein the PHA particle size/the filtration membrane surface opening size is 1.1 to 100.
<5> The PHA aqueous suspension concentration after concentration/the PHA aqueous suspension concentration before filtration is 1.5 to 2.5, and
The prediction method according to any one of <1> to <4>, wherein the maximum permeation flow rate/minimum permeation flow rate of the permeation flow rate during constant pressure feeding in the concentration step is 3 to 10.
<6> A method for concentrating an aqueous PHA suspension, comprising passing an aqueous suspension containing PHA obtained by treating microbial cells through a filtration membrane to concentrate,
A method for concentrating an aqueous PHA suspension, comprising the step of predicting the chemical washing time of the filtration membrane by the prediction method according to any one of <1> to <5>, and washing the filtration membrane.
<7> A method for producing PHA, comprising the step of passing an aqueous suspension containing PHA obtained by treating microbial cells through a filtration membrane for concentration,
A method for producing a PHA, comprising the step of predicting the chemical cleaning time of the filtration membrane by the prediction method according to any one of <1> to <5>, and washing the filtration membrane.

EXAMPLES The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[Measurement and evaluation method]
Measurements and evaluations in Examples and Comparative Examples were carried out by the following methods.

(Yellowness)
Yellowness was measured using a spectrophotometer (U-3900, manufactured by Hitachi High-Tech Science).

(Membrane permeation rate)
The membrane permeation rate was calculated by measuring the weight of the permeated liquid. Specifically, it was calculated by "increased permeate weight per minute" x "specific gravity of water".

[Production Example 1]
(Preparation of cell culture solution)
The KNK-631 strain (see JP-A-2013-009627 and WO 2016/114128) was used for culture production, and a cell culture solution containing cells containing PHA was obtained.

(sterilization)
The cell culture solution obtained above was heated and stirred at an internal temperature of 60 to 80° C. for 20 minutes for sterilization.

(High pressure crushing treatment)
0.2% by weight of sodium dodecylsulfate was added to the sterilized cell culture solution obtained above. Furthermore, after adding sodium hydroxide aqueous solution so that pH might be set to 11.0, it heat-retained at 50 degreeC for 1 hour. Then, high-pressure crushing was performed at a pressure of 450 to 550 kgf/cm ² using a high-pressure crusher (manufactured by Nirosoavi, high-pressure homogenizer model PA2K).

(refinement treatment)
An equal amount of distilled water was added to the crushed liquid obtained above after high-pressure crushing. After centrifugation, the supernatant was removed and concentrated twice. To this concentrated PHA aqueous suspension, the same amount of sodium hydroxide aqueous solution (pH 11.0) as the removed supernatant was added and centrifuged to remove the supernatant. Water is added again to suspend, 0.2% by weight of sodium dodecyl sulfate and 1/100 weight of PHA of protease (Esperase, manufactured by Novozyme) are added, and the mixture is maintained at pH 10.0 at 50°C. Stirring was continued for 2 hours. After that, the supernatant was removed by centrifugation and concentrated 4-fold. Further water was added to adjust the PHA concentration to 27.6% by weight. A portion of the obtained PHA aqueous suspension was extracted, and the yellowness index of the supernatant was measured to be 6.5.

[Example 1]
The PHA aqueous suspension obtained above was placed in a container (the first container 1 in FIG. 1), and a ceramic membrane (Membralox, manufactured by Pall, 03521049A, manufactured by Jabsco) was used to feed the liquid. .2 μm), and subjected to tangential flow filtration (PHA particle size/filtration membrane surface opening size was 8). The membrane permeation linear velocity (supply flow rate to filtration membrane/cross-sectional area of filtration membrane) was set to 3 m/sec, and filtration was performed until the PHA concentration in the aqueous suspension reached 54% by weight. The maximum permeation flow rate/minimum permeation flow rate of the permeation flow rate during constant pressure feeding in the concentration step was 5.6. The initial yellowness of the permeate was 1.2 when the first 1/20th of the expected total permeate volume (0.06 kg) permeated the PHA aqueous suspension volume (2.5 L). . The difference between the yellowness index of the initial PHA aqueous suspension supernatant and the yellowness index of the initial permeate is 5.3. This operation was regarded as one cycle, the aqueous suspension in the container (first container 1 in FIG. 1) was replaced, and the PHA aqueous suspension concentration in the container (first container 1 in FIG. 1) was changed to 27.5. 6% by weight, and 5 cycles of the same operation as the 1st cycle were performed. In the 1st cycle, the initial permeation rate was 0.62 L/m ² ·h·kPa, but in the 5th cycle the initial permeation rate was 0.22 L/m ² ·h·kPa, confirming membrane clogging. rice field. The PHA aqueous suspension concentration after 5 cycles of filtration was 46.5% by weight. Also, the PHA aqueous suspension concentration after concentration/the PHA aqueous suspension concentration before filtration was 1.7. Table 1 shows the initial permeation rate and final permeation rate for each cycle. The membrane permeation rate decreased as the PHA aqueous suspension was concentrated.

[Example 2]
After the operation of Example 1, the membrane was chemically washed using Ultrasil 115 (manufactured by Ecolab), and then the same operation as in Example 1 was performed. The initial yellowness of the permeate was 0.9 when the first 1/20 of the expected total permeate (0.06 L) permeated the PHA aqueous suspension (2.5 kg). . The difference between the yellowness index of the initial PHA aqueous suspension supernatant and the yellowness index of the initial permeate is 5.6. In the first cycle, the initial permeation rate was 0.68 L/m ² ·h·kPa, but in the 4th cycle, the initial permeation rate was 0.39 L/m ² ·h·kPa, confirming membrane clogging. rice field. The PHA aqueous suspension concentration after four cycles of filtration was 48.2% by weight. Table 2 shows the initial permeation rate and final permeation rate for each cycle.

[Example 3]
After the operation of Example 2, the membrane was chemically washed using Ultrasil 115, and then the same operation as in Example 1 was performed. The initial yellowness of the permeate was 0.6 when the first 1/20 of the expected total permeate (0.06 L) permeated the PHA aqueous suspension (2.5 kg). . The difference between the yellowness index of the initial PHA aqueous suspension supernatant and the yellowness index of the initial permeate is 5.9. In the first cycle, the initial permeation rate was 0.82 L/m ² ·h·kPa, but in the third cycle, the initial permeation rate was 0.49 L/m ² ·h·kPa, confirming membrane clogging. rice field. The PHA aqueous suspension concentration after 3 cycles of filtration was 48.5% by weight. The initial and final permeation rates for each cycle are shown in Table 3.

〔result〕
A summary of the results of Examples 1 to 3 is shown in FIG. From FIG. 2, it was found that there is a correlation between the yellowness of the initial permeate and the cycle until membrane clogging occurs. Therefore, by using the yellowness of the initial permeate as an index, the number of cycles until membrane clogging occurs can be predicted.

INDUSTRIAL APPLICABILITY According to the present invention, since clogging of a filtration membrane can be predicted by a simple method, it can be suitably used in the field of membrane separation and other fields.

1 First Vessel 2 Winged Stirrer 3 PHA Aqueous Suspension (Slurry)
4 PHA aqueous suspension (slurry) liquid feeding pump 5 first pressure gauge 6 filtration membrane 7 second pressure gauge 8 yellowness meter 9 second container 10 membrane permeate liquid

Claims (7)

A method for predicting the timing of chemical cleaning of a filtration membrane in membrane filtration of an aqueous suspension of polyhydroxyalkanoic acid, comprising:
(A) In the step of concentrating an aqueous suspension containing polyhydroxyalkanoic acid obtained by treating microbial cells through a filtration membrane, measuring the yellowness of the filtration membrane permeate at the beginning of the filtration, a yellowness measuring step;
(B) an estimation step of estimating the timing of clogging the filtration membrane based on the measurement results obtained in the step (A), and estimating the timing of washing the filtration membrane with a chemical agent;
Forecasting methods, including 2. The method according to claim 1, wherein in the step (A), the filtration membrane permeated liquid at the initial stage of filtration, which is the target of measuring the yellowness, is a permeated liquid having an amount of 1/20 or less of the total amount of permeated liquid. Forecast method. The prediction method according to claim 1 or 2, wherein the membrane filtration is tangential flow filtration. The prediction method according to any one of claims 1 to 3, wherein the polyhydroxyalkanoic acid particle size/the filtration membrane surface opening size is 1.1 to 100. The concentration of the polyhydroxyalkanoic acid aqueous suspension after concentration/the concentration of the polyhydroxyalkanoic acid aqueous suspension before filtration is 1.5 to 2.5, and
The prediction method according to any one of claims 1 to 4, wherein the maximum permeation flow rate/minimum permeation flow rate of the permeation flow rate during constant pressure feeding in the concentration step is 3 to 10. A method for concentrating an aqueous suspension of polyhydroxyalkanoic acid, comprising passing an aqueous suspension containing polyhydroxyalkanoic acid obtained by treating microbial cells through a filtration membrane to concentrate,
A method for concentrating a polyhydroxyalkanoic acid aqueous suspension, comprising the step of predicting the chemical washing time of the filtration membrane by the prediction method according to any one of claims 1 to 5, and washing the filtration membrane. A method for producing polyhydroxyalkanoic acid, comprising the step of passing an aqueous suspension containing polyhydroxyalkanoic acid obtained by treating microbial cells through a filtration membrane to concentrate,
A method for producing polyhydroxyalkanoic acid, which comprises, in the steps, predicting when the filtration membrane should be washed with chemicals by the prediction method according to any one of claims 1 to 5, and washing the filtration membrane.

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