JP7660643B2 - Biodegradable resin processing method and biodegradable resin processing system - Google Patents

Description

The present invention relates to a method for processing biodegradable resin and a system for processing biodegradable resin.

Research and development into materials to replace conventional plastics has been actively conducted in recent years. Among these, biodegradable plastics, whose main component is polylactic acid (PLA) made from renewable resources, are environmentally friendly biomass plastics that can be decomposed by microorganisms. Biomass plastics are used as a material for shopping bags, replacing conventional plastics that are difficult to decompose, and because they are highly safe for the human body, they are used as medical materials such as dissolving sutures.

In recent years, the demand for biofuels has been increasing due to the sudden rise in the price of petroleum resources, and efforts to convert biomass plastics such as polylactic acid made from renewable resources into methane-containing biogas through methane fermentation have been attracting renewed attention.

Patent Document 1 discloses a waste treatment system that includes a decomposition tank that heats resin-containing waste in the presence of an amine compound to hydrolyze it into monomers, and a methane fermentation section that performs methane fermentation on the monomers obtained in the decomposition tank and organic waste containing refractory solids in a fermentation tank that is supplied with the monomers and organic waste containing refractory solids. Compared to chemical recycling, which regenerates waste plastics into gases that can be used as chemical raw materials or fuels, this method can produce methane without going through a mixed gas that mainly contains hydrogen and carbon monoxide. In addition, by supplying monomers to a fermentation tank in which methane fermentation of organic waste containing refractory solids is being performed, it is possible to achieve both methane fermentation of organic waste containing refractory solids and methane fermentation of monomers in the fermentation tank, enabling efficient methane fermentation.

Patent Document 2 discloses a method for producing methane gas, which includes a step of decomposing polylactic acid resin in a decomposition liquid containing biodegradable enzymes, calcium carbonate, ethanol, and water, and then subjecting the decomposition liquid to methane fermentation. It is described that this method increases the amount of gas generated by about 1.5 times compared to when ethanol is not added. It is also described that the amount of gas generated increases by about 1.3 times compared to when ethanol and calcium carbonate are not added, making this an efficient method for producing methane gas.

JP 2022-170390 A Patent No. 5696971

However, in the waste treatment systems described in Patent Documents 1 and 2, additives such as amine compounds, ethanol, and calcium carbonate are added to the decomposition tank. Therefore, when the decomposition liquid produced in the decomposition tank is added to the fermentation tank, there is a risk that these additives will adversely affect the methanogens in the fermentation tank, reducing the efficiency of methane production.

The object of the present invention is to realize a method and system for processing biodegradable resin that can produce methane with high efficiency without adding any additives other than biodegradable resin and water or water vapor.

The characteristic configuration of the method for treating biodegradable resin of the present invention is as follows:
a decomposition step of mixing waste containing a biodegradable resin with water and hydrolyzing the mixture at a temperature of 120° C. or higher in a sealed decomposition tank to obtain a decomposition liquid containing a decomposition product of the biodegradable resin;
a methane fermentation step of treating the organic waste containing the hardly decomposable solid content and the decomposition liquid in a methane fermentation tank in which methane bacteria are present at a temperature of 30° C. or higher and 60° C. or lower,
In the methane fermentation step, the decomposition liquid is added to the organic waste so that the organic load in the methane fermentation tank is 0.60 g CODCr/L/day or more and 5.0 g CODCr/L/day or less.
The characteristic configuration of the method for treating biodegradable resin of the present invention is as follows:
a decomposition step of mixing waste containing a biodegradable resin with water vapor and hydrolyzing the mixture at a temperature of 120° C. or higher in a sealed decomposition tank to obtain a decomposition liquid containing a decomposition product of the biodegradable resin;
a methane fermentation step of treating the organic waste containing the hardly decomposable solid content and the decomposition liquid in a methane fermentation tank in which methane bacteria are present at a temperature of 30° C. or higher and 60° C. or lower,
In the methane fermentation step, the decomposition liquid is added to the organic waste so that the organic load in the methane fermentation tank is 0.60 g CODCr/L/day or more and 5.0 g CODCr/L/day or less.
The characteristic configuration of the biodegradable resin processing system of the present invention is as follows:
a decomposition device for mixing waste containing a biodegradable resin with water and hydrolyzing the mixture in a sealed decomposition tank at a temperature of 120° C. or higher to obtain a decomposition liquid containing a decomposition product of the biodegradable resin;
a methane fermentation apparatus for treating organic waste containing a hardly decomposable solid content and the decomposition liquid in a methane fermentation tank in which methane bacteria are present at a temperature of 20° C. or higher and 60° C. or lower,
The decomposition liquid is added to the organic waste so that the organic load in the methane fermentation tank is 0.60 g CODCr/L/day or more and 5.0 g CODCr/L/day or less.
The characteristic configuration of the biodegradable resin processing system of the present invention is as follows:
a decomposition device for mixing waste containing a biodegradable resin with steam and hydrolyzing the mixture at a temperature of 120° C. or higher in a sealed decomposition tank to obtain a decomposition liquid containing a decomposition product of the biodegradable resin;
a methane fermentation apparatus for treating organic waste containing a hardly decomposable solid content and the decomposition liquid in a methane fermentation tank in which methane bacteria are present at a temperature of 20° C. or higher and 60° C. or lower,
The decomposition liquid is added to the organic waste so that the organic load in the methane fermentation tank is 0.60 g CODCr/L/day or more and 5.0 g CODCr/L/day or less.

In methane fermentation of organic waste containing difficult-to-decompose solids, such as sewage sludge, the difficult-to-decompose solids are solubilized to convert them into organic matter such as amino acids, sugars, and long-chain fatty acids. These organic matter are then decomposed by anaerobic bacteria into organic compounds such as organic acids and alcohols, and methane is produced from these organic compounds.
Here, since the solubilization of the non-degradable solids proceeds slowly, methane fermentation of organic waste containing non-degradable solids is difficult. Therefore, when only organic waste containing non-degradable solids is subjected to methane fermentation in a fermenter, the volume load on the fermenter cannot be increased, resulting in a low volume load and ineffective use of the fermenter.
However, according to this characteristic configuration, a mixture containing a biodegradable resin and water or steam can be hydrolyzed to produce a decomposition liquid containing a decomposition product of the biodegradable resin. This decomposition liquid is more likely to undergo methane fermentation than organic waste containing a non-degradable solid content. Therefore, by supplying the decomposition liquid to a methane fermentation tank in which methane fermentation of organic waste containing a non-degradable solid content is being performed, in the fermentation tank in which methane bacteria are present, methane fermentation of organic waste containing a non-degradable solid content (production of methane through a solubilization stage of the non-degradable solid content and an acid fermentation stage of the organic matter) and methane fermentation of the decomposition product of the biodegradable resin in the decomposition liquid (production of methane through an acid fermentation stage when the decomposition product is an organic matter, and production of methane based on the organic acid when the decomposition product is an organic acid) can be achieved at the same time. Therefore, methane can be produced more efficiently from the organic waste and the decomposition product in the decomposition liquid than when only organic waste is subjected to methane fermentation.
Furthermore, according to this characteristic configuration, since there is no need to add additives other than the biodegradable resin and water or water vapor, methane fermentation is not inhibited by additives and methane can be produced with high efficiency.
Furthermore, according to this characteristic configuration, by setting the organic load of the decomposition liquid within the above range, a decrease in pH in the fermentation tank is prevented, and there is no adverse effect on methane fermentation, which is preferable.

A further characteristic feature of the method for treating a biodegradable resin of the present invention is that in the decomposition step, 0.30 parts by mass or more and 20 parts by mass or less of water or water vapor is mixed with 1.0 part by mass of the biodegradable resin.
A further characteristic feature of the biodegradable resin treatment system of the present invention is that 0.30 parts by mass or more and 20 parts by mass or less of water or water vapor is mixed with respect to 1.0 part by mass of the biodegradable resin in the decomposition tank.

When organic waste or decomposition liquid containing a large amount of water is added to a methane fermentation tank containing methane bacteria, the ratio of methane bacteria in the methane fermentation tank decreases, methane fermentation becomes difficult to proceed, and there is a risk of reducing the amount of digested sludge generated in the methane fermentation tank. In such a case, it is necessary to carry out an operation to reduce the moisture before and after putting the organic waste or decomposition liquid into the methane fermentation tank, which makes the treatment process complicated.
According to this characteristic configuration, by using a decomposition liquid obtained by mixing an appropriate amount of water with a biodegradable resin in the decomposition process in the methane fermentation process, methane fermentation can be carried out efficiently without concentrating the decomposition liquid.

A further characteristic feature of the method for treating biodegradable resin of the present invention is that at least the portion of the decomposition tank that comes into contact with the decomposition liquid is made of austenitic stainless steel.
A further characteristic feature of the biodegradable resin processing system of the present invention is that at least the portion of the decomposition tank that comes into contact with the decomposition liquid is made of austenitic stainless steel.

According to this characteristic configuration, by using acid-resistant austenitic stainless steel as the material for the parts in contact with the decomposition liquid in the decomposition tank, it is possible to prevent the acid derived from the biodegradable resin generated in the decomposition process from corroding the austenitic stainless steel in the decomposition tank. As a result, it is possible to prevent impurities derived from the decomposition tank from being mixed into the fermentation tank.

A further characteristic feature of the method for treating a biodegradable resin of the present invention is that the hydrolysis temperature in the decomposition step is 120° C. or higher and 170° C. or lower.
A further characteristic feature of the biodegradable resin processing system of the present invention is that the temperature of hydrolysis in the decomposition tank is 120°C or higher and 170°C or lower.

This characteristic configuration can further prevent the acid derived from the biodegradable resin generated in the decomposition process from corroding the austenitic stainless steel in the decomposition tank. As a result, it is possible to prevent impurities from being mixed into the fermentation tank.

A further characteristic feature of the method for treating a biodegradable resin of the present invention is that the biodegradable resin contains at least one of polybutylene succinate and polyhydroxyalkanoate.
A further characteristic feature of the biodegradable resin treatment system of the present invention is that the biodegradable resin contains at least one of polybutylene succinate and polyhydroxyalkanoate.

According to this characteristic configuration, by using the above-mentioned biodegradable resin, the decomposition product contains acid, making acid fermentation unnecessary, and methane fermentation using the decomposition product can be efficiently carried out.

A further characteristic feature of the method for treating a biodegradable resin of the present invention is that the biodegradable resin mixed in the decomposition step contains 0.1 part by mass or more of polylactic acid per 1.0 part by mass of a biodegradable resin other than polylactic acid.
A further characteristic feature of the biodegradable resin treatment system of the present invention is that the biodegradable resin mixed in the decomposition tank contains 0.1 part by mass or more of polylactic acid per 1.0 part by mass of a biodegradable resin other than polylactic acid.

According to this characteristic configuration, in the decomposition process, the decomposition tank contains a predetermined amount of polylactic acid in addition to the biodegradable resin other than polylactic acid, which allows the hydrolysis of the biodegradable resin other than polylactic acid to proceed quickly, and as a result, the decomposition of the waste can proceed more quickly.

FIG. 1 is a schematic diagram of a method for treating a biodegradable resin according to an embodiment of the present invention. FIG. 1 is a block flow diagram of a method for treating a biodegradable resin according to an embodiment of the present invention.

The present invention relates to a method for treating a biodegradable resin, and includes a decomposition step S101 in which waste material containing a biodegradable resin 1 is mixed with water 2 and hydrolyzed in a decomposition tank 11 at a temperature of 120° C. or higher under a pressure of 198 kPa or higher to obtain a decomposition liquid 3 containing a decomposition product of the biodegradable resin, and a methane fermentation step S102 in which an organic waste material 4 containing a hardly decomposable solid content and the decomposition liquid 3 are treated at a predetermined temperature in a methane fermentation tank 21 in which methanogens are present.
<Biodegradable resin>
The biodegradable resin 1 may be any resin having biodegradability, such as a chemically synthesized resin, a microbial resin, a resin using natural products, etc. Specific examples include aliphatic polyesters, polyvinyl alcohol (PVA), celluloses, starches, etc. Examples of aliphatic polyesters include polylactic acid (PLA) resin derivatives, polybutylene succinate (PBS) resin derivatives, polycaprolactone (PCL), polyhydroxybutyrate (PHB) and its derivatives, polyethylene adipate (PEA), polyethylene terephthalate succinate (PETS), polyhydroxyalkanoate (PHA), polyglycolic acid (PGA), polytetramethylene adipate, and condensates of diols and dicarboxylic acids. Examples of polyhydroxyalkanoates include polyhydroxypropionic acid, polyhydroxyvaleric acid, poly-4-hydroxybutanoic acid, PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)), PHBV (poly(3-hydroxybutyrate-co-3-hydroxyvaleric acid)), 3HB4HB (poly(3-hydroxybutyrate-co-4-hydroxybutyrate)), and PHBP (poly(3-hydroxybutyrate-co-3-hydroxypropionic acid)). Examples of celluloses include methyl cellulose, ethyl cellulose, and acetyl cellulose. These may be used alone, as a copolymer, or in combination of two or more kinds. Examples of components that form the copolymer include polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, octanediol, dodecanediol, neopentyl glycol, glycerin, pentaerythritol, sorbitan, bisphenol A, and polyethylene glycol; dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, glutaric acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, and anthracenedicarboxylic acid; hydroxycarboxylic acids such as glycolic acid, L-lactic acid, D-lactic acid, hydroxypropionic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, mandelic acid, and hydroxybenzoic acid; and lactones such as glycolide, caprolactone, butyrolactone, valerolactone, propylolactone, and undecalactone.

In this embodiment, polybutylene succinate and polyhydroxyalkanoate are used as the biodegradable resin 1. By configuring it in this way, acid fermentation is not necessary because these decomposition products contain acid, and methane fermentation using the decomposition products can proceed efficiently.

The biodegradable resin 1 may be a mixture of the above-mentioned biodegradable resin, a general-purpose chemical resin, and additives. Examples of additives include plasticizers, heat stabilizers, light stabilizers, antioxidants, UV absorbers, flame retardants, colorants, pigments, fillers, inorganic fillers, release agents, antistatic agents, fragrances, lubricants, foaming agents, antibacterial and antifungal agents, and nucleating agents.

The biodegradable resin 1 preferably contains a decomposition accelerator, and preferably contains 0.10 to 20 parts by weight, for example 1.0 to 20 parts by weight, of the decomposition accelerator per 100 parts by weight of the biodegradable resin.
If too little decomposition promoter is used, it may be difficult to promote the decomposition of the biodegradable resin, and if more than necessary is used, there is a risk that decomposition of the biodegradable resin will begin during the preparation stage of the resin composition or when it is used as a molded article.

Here, the molded body of biodegradable resin 1 may be a molded body molded by a known molding method. Known molding methods include injection molding, extrusion molding, sheet molding, vacuum molding, air pressure molding, compression molding, cast molding, etc. The layer structure of the obtained molded body is not limited to a single layer structure, but may be a multilayer structure, and the layers constituting the multilayer may be a blend of two or more resins, or may be a mixture with an additive. The multilayer molded body may be molded by co-extrusion molding or co-injection molding using extruders or injectors in a number corresponding to the number of resins, or a film or the like may be attached to the single layer molded body or multilayer molded body in a post-process using an adhesive, thermocompression bonding, extrusion coating, etc.

The decomposition accelerator preferably releases an acid by hydrolysis, and the acid released is preferably one that has a pH (25°C) of 4.0 or less, especially 3.0 or less in an aqueous solution or dispersion at a concentration of 0.0050 g/ml, and is preferably a polymer that is easily hydrolyzed to release an acid when mixed with water. Specific examples include oxalic acid, maleic acid, maleic anhydride, glycolic acid, etc., of which oxalic acid and glycolic acid are preferred. Examples of such decomposition accelerators include polyoxalate, polyethylene maleate, polyglycolic acid, etc. Preferred decomposition accelerators are polyethylene oxalate and polyglycolic acid. These may be copolymers, used alone, or in combination of two or more. Examples of components that form copolymers include polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, octanediol, dodecanediol, neopentyl glycol, glycerin, pentaerythritol, sorbitan, bisphenol A, and polyethylene glycol; dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, glutaric acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, and anthracenedicarboxylic acid; hydroxycarboxylic acids such as glycolic acid, L-lactic acid, D-lactic acid, hydroxypropionic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, mandelic acid, and hydroxybenzoic acid; and lactones such as glycolide, caprolactone, butyrolactone, valerolactone, propylolactone, and undecalactone.

The above-mentioned decomposition accelerator preferably has a glass transition point (Tg) lower than the deactivation temperature of the enzyme used to decompose the biodegradable resin. By using such an accelerator with a low glass transition point, it is possible to more quickly promote the decomposition of the biodegradable resin by the enzyme. The glass transition temperature can be measured, for example, using a DSC6220 (differential scanning calorimetry) manufactured by Seiko Instruments Inc.

The substances contained in the biodegradable resin 1 other than the biodegradable resin are not particularly limited as long as they do not adversely affect methane fermentation.
<Water>
The water 2 contained in the blend may be tap water, ion-exchanged water, well water, distilled water, ultrapure water, etc. Water 2 may contain impurities as long as they do not interfere with the decomposition reaction of the biodegradable resin and the methane fermentation reaction. Water 2 may be liquid or steam.
<Decomposition process>
The method for treating a biodegradable resin of the present invention includes a decomposition step S101 in which a mixture containing the above-mentioned biodegradable resin 1 and water 2 is hydrolyzed at a predetermined temperature in a sealed decomposition tank 11 to obtain a decomposition liquid 3 containing a decomposition product of the biodegradable resin 1.

In the decomposition step S101, when the above-mentioned biodegradable resin 1 and water 2 are used to carry out hydrolysis at a predetermined temperature in a sealed decomposition tank 11, the water 2 may be supplied as steam and mixed with the biodegradable resin 1 in the decomposition tank 11 for hydrolysis, or water may be present in the decomposition tank 11 and heated to produce steam, which is then mixed with the biodegradable resin 1 for hydrolysis.

The decomposition products of biodegradable resin 1 include the oligomers and/or monomers that are the basis of the biodegradable resin, which is a polymer, as well as molecules that are the result of decomposition of decomposition accelerators, general-purpose chemical resins, additives, etc.

When the biodegradable resin 1 contains a resin that takes longer to hydrolyze than polylactic acid, the time required for hydrolysis can be shortened by including polylactic acid in addition to the resin.
That is, in this case, the biodegradable resin 1 contains polylactic acid and a biodegradable resin other than polylactic acid. For example, the biodegradable resin 1 contains polylactic acid and polybutylene succinate, or polylactic acid and polyhydroxyacetic acid. In addition, the biodegradable resin 1 preferably contains 0.1 parts by mass or more of polylactic acid per 1.0 part by mass of the biodegradable resin other than polylactic acid, and if the content of polylactic acid is less than 0.1 parts by mass, the rate of hydrolysis of the biodegradable resin other than polylactic acid becomes relatively slow. In addition, there is no particular limit to the upper limit of the content of polylactic acid per 1.0 part by mass of the biodegradable resin other than polylactic acid, but it is preferable to contain 2.0 parts by mass or less of polylactic acid, more preferably 1.5 parts by mass or less of polylactic acid, and even more preferably 1.0 parts by mass or less of polylactic acid.

As shown in FIG. 1, the decomposition device 10 includes a decomposition tank 11. The decomposition tank 11 includes an inlet section (not shown) into which the biodegradable resin 1 is introduced, an inlet section (not shown) into which water 2 flows, a temperature control section (not shown) for controlling the temperature inside the decomposition tank 11, and a pressure adjustment section (not shown) for controlling the pressure inside the decomposition tank 11. There are no particular limitations on the pressure inside the decomposition tank 11 as long as the hydrolysis reaction of the biodegradable resin 1 proceeds, but it is preferably 800 kPa or less.

In the decomposition tank 11, if the biodegradable resin 1 is polylactic acid (PLA) or its derivatives, a decomposition liquid 3 containing lactic acid, a decomposition accelerator, etc. is produced by hydrolysis. If the biodegradable resin 1 is polybutylene succinate (PBS) or its derivatives, a decomposition liquid 3 containing succinic acid, 1,4-butanediol, a decomposition accelerator, etc. is produced. If the biodegradable resin 1 is polyhydroxybutyrate (PHB) or its derivatives, a decomposition liquid 3 containing 3-hydroxybutyric acid, a decomposition accelerator, etc. is produced.

The material of the decomposition tank 11 is not particularly limited as long as it can promote hydrolysis of the biodegradable resin 1, but it is preferable to use a material with excellent acid resistance such as PTFE or austenitic stainless steel with high acid resistance. Examples of such austenitic stainless steel include SUS316 and SUS316L.
In particular, when austenitic stainless steel is used as the material for the decomposition tank 11, austenitic stainless steel containing 1.0% to 4.0% molybdenum is more preferable because it has particularly high acid resistance. Examples of such austenitic stainless steel include SUS316 and SUS316L.
Furthermore, when austenitic stainless steel is used as the material for the decomposition tank 11, it is preferable that the material contains 8.0% or more of nickel. By using such a construction, the corrosion resistance of the decomposition tank 11 can be improved.
In selecting the decomposition tank 11, it is not necessary that the entire decomposition tank 11 be made of PTFE, austenitic stainless steel containing 1.0% or more of molybdenum, or the like. It is sufficient that at least the material of the portion of the decomposition tank 11 that comes into contact with the decomposition liquid is made of PTFE, austenitic stainless steel containing 1.0% or more and 4.0% or less of molybdenum, or the like.

The biodegradable resin 1 includes those that generate acid when hydrolyzed, such as polylactic acid. In addition, the decomposition promoter contained in the biodegradable resin 1 may contain acid, and acid derived from the decomposition promoter may flow into the decomposition liquid in the decomposition step S101. With the above configuration, the material of the decomposition tank 11 is less likely to corrode when the biodegradable resin 1 is decomposed in the decomposition tank 11. As a result, impurities can be prevented from being mixed into the decomposition liquid, making it less likely to have a negative effect on methane fermentation.

When biodegradable resin 1 and water 2 are mixed, the ratio of biodegradable resin 1 to water 2 is not particularly limited as long as the decomposition reaction of biodegradable resin 1 proceeds, but it is preferable that the water content is 0.30 parts by mass or more and 20 parts by mass or less per 1.0 part by mass of biodegradable resin, and more preferably 1.0 parts by mass or more and 15 parts by mass or less. If the water content is less than 0.30 parts by mass per 1.0 part by mass of biodegradable resin, there is a risk that the decomposition reaction of biodegradable resin 1 will not proceed sufficiently. If the water content is more than 20 parts by mass per 1.0 part by mass of biodegradable resin, the proportion of biodegradable resin 1 will be reduced, and the amount of biodegradable resin that undergoes methane fermentation in the methane fermentation process described below will be reduced, and as a result, the amount of methane obtained will also be reduced.

The temperature of the hydrolysis reaction in the decomposition step S101 is preferably 110°C or higher, and more preferably 120°C or higher. The upper limit of the temperature of the hydrolysis reaction is preferably 170°C or lower, and more preferably 150°C or lower. If the temperature is lower than 110°C, the hydrolysis reaction of the biodegradable resin 1 may not proceed. If the temperature exceeds 160°C, the stainless steel may become susceptible to corrosion.

When austenitic stainless steel containing 1.0% to 4.0% molybdenum is used as the material for the decomposition tank 11, it is preferable that the temperature of the hydrolysis reaction in the decomposition step S101 is 120°C to 150°C. With this configuration, the corrosion rate of the austenitic stainless steel can be made to be corrosion resistant (0.050 to 1.0 mm/year) or completely corrosion resistant (0.050 mm/year or less) as described in the Chemical Industry Handbook (2nd edition), and impurities can be prevented from being mixed into the decomposition liquid.

Furthermore, when using an austenitic stainless steel containing 1.0% to 4.0% molybdenum, it is more preferable that the temperature of the hydrolysis reaction in the decomposition step S101 is 120°C to 150°C, since this makes it possible to make the corrosion rate of the austenitic stainless steel completely corrosion-resistant (0.050 mm/year or less) and further suppresses the mixing of impurities into the decomposition liquid.

In addition, when the biodegradable resin 1 contains a decomposition accelerator, the temperature can be set taking into consideration the temperature conditions under which the decomposition accelerator exerts its effect. In that case, for example, the following can be used as the standard: (glass transition temperature of the decomposition accelerator - 5.0°C) < decomposition temperature < upper limit of the temperature exhibiting enzyme activity. For example, when polyethylene oxalate is used as the decomposition accelerator, decomposition can be promoted under a temperature condition of, for example, 37°C, and when polyglycolic acid is used as the decomposition accelerator, decomposition can be promoted by setting the temperature at, for example, 45°C. In addition, the time for decomposing a biodegradable resin (2.0 cm x 2.0 cm, thickness 100 μm) in the decomposition liquid is preferably 1 to 10 days. More preferably, it is 1 to 7 days. Even more preferably, it is within 4 days. In addition, there are no particular limitations on the stirring conditions of the decomposition liquid, as long as the decomposition liquid is stirred uniformly.

The above process is believed to achieve a high decomposition rate of the biodegradable resin 1, suppress the formation of aggregated precipitates during the decomposition of the biodegradable resin 1, and efficiently produce oligomers and/or monomers. The obtained oligomers can be decomposed into monomers. The oligomers referred to here are polymers in which monomers are bonded, such as dimers, trimers, and tetramers. The oligomers and/or monomers may be linear or have side chains. The oligomers and/or monomers may react with additives such as neutralizers, buffer solutions, medium components, and nutrients, and take the form of a reaction product between the oligomers and/or monomers and the additives.

The biodegradable resin 1 may be a molded body of biodegradable resin. In this case, it may contain general-purpose chemical resins, additives, decomposition accelerators, resins blended when molding the biodegradable resin 1, adhesives, films, etc., contained in the biodegradable resin 1. In addition, when the molded body of the biodegradable resin 1 is a container such as a plate or cup, a straw, a bag, packaging, etc., whose main component is the biodegradable resin 1, it may be organic waste such as food and drink, or waste with moisture attached to the surface of these.

The decomposition liquid 3 may contain substances other than the biodegradable resin 1, and these substances can be removed before being put into the methane fermentation tank 21, or the substances can be removed while methane fermentation is progressing in the methane fermentation tank 21, or the substances can be removed from the treated liquid after the fermentation process.
<Methane fermentation process>
The method for treating biodegradable resins of the present invention further includes a methane fermentation step S102 in which organic waste 4 containing difficult-to-decompose solids and the decomposition liquid 3 obtained in the decomposition step S101 are treated at a predetermined temperature in a methane fermentation tank 21 in which methanogens are present.

As shown in FIG. 1, the methane fermentation apparatus 20 includes a methane fermentation tank 21. The methane fermentation tank 21 includes an addition section (not shown) that adds the decomposition liquid 3 obtained in the decomposition step S101 to the methane fermentation tank 21, an organic waste supply section (not shown) that supplies organic waste 4 containing difficult-to-decompose solids to the methane fermentation tank 21, and a temperature adjustment section (not shown) that can adjust and keep the temperature in the methane fermentation tank 21. The methane fermentation tank 21 may also include a pressure adjustment section (not shown) that adjusts the pressure in the methane fermentation tank 21, a methane bacteria supply section (not shown) that supplies methane bacteria to the methane fermentation tank 21, and a stirring section (not shown) that mixes and stirs the decomposition liquid 3 and organic waste 4 in the methane fermentation tank 21.

Organic waste 4 containing non-degradable solids means waste containing one or more types of solid organic matter. In this embodiment, the organic waste is sewage sludge.

The method of subjecting the decomposition liquid 3 obtained in the decomposition step S101 to the methane fermentation step S102 may be a method of directly adding methane bacteria (including culture liquid if cultured) to the decomposition liquid 3 via a methane bacteria supply section, or a method of first culturing the methane bacteria in a methane fermentation tank or the like and then adding a portion of the decomposition liquid 3 via an addition section. In addition to the batch system, a fed-batch system in which the decomposition liquid 3 or culture liquid of the methane bacteria is added as needed, or a continuous system in which the decomposition liquid 3 is continuously supplied may also be used.

It is preferable to add the decomposition liquid 3 to the organic waste 4 in the methane fermentation tank 21 so that the organic load in the methane fermentation tank 21 is 0.60 g COD Cr/L/day or more and 5.0 g COD Cr/L/day or less. By adding the decomposition liquid within this range to the methane fermentation tank 21, the pH in the methane fermentation tank 21 can be appropriately maintained. As a result, the methanation reaction can proceed with high efficiency.

CODCr is an index that indicates the amount of organic matter in water, and is the amount of oxygen when potassium dichromate oxidizes a target oxidizable substance. In this embodiment, the organic load substantially corresponds to the oligomers and/or monomers that are the basis of the biodegradable resin, which is a polymer, among the decomposition products of biodegradable resin 1, and is more precisely calculated by the following formula (1).

Organic load = Decomposition liquid input amount (mL/L/day) x lactic acid concentration (%) x 1.06 (gCODCr/g lactic acid)...Formula (1)
The specific gravity of the decomposition liquid was set to 1.0.

The methane fermentation apparatus 20 is equipped with a methane fermentation tank 21, in which the organic waste 4 (sewage sludge in this embodiment) and the decomposition products of the biodegradable resin 1 are fermented to produce methane. Specifically, when the subject of methane fermentation is sewage sludge, the organic matter obtained by solubilizing the difficult-to-decompose solids is fermented with acid, and methane is produced from the organic acid thus obtained. On the other hand, when the subject of methane fermentation is lactic acid, succinic acid, or 3-hydroxybutyric acid, methane is produced from the lactic acid, succinic acid, or 3-hydroxybutyric acid. In other words, the methane fermentation apparatus 20 allows methane fermentation of sewage sludge and methane fermentation of lactic acid, succinic acid, or 3-hydroxybutyric acid to be carried out in parallel.

Here, since sewage sludge contains refractory solids, in order to obtain methane by methane fermentation of the sewage sludge, it is necessary to go through a stage of solubilization of the refractory solids, which progresses at a slow rate. Therefore, when methane fermentation of only sewage sludge is performed in the methane fermentation tank 21, the volume load on the methane fermentation tank 21 is low. On the other hand, in the methane fermentation of the decomposition liquid 3 obtained by hydrolysis in the decomposition device 10, the stage of solubilization of the refractory solids is not required, regardless of whether the decomposition liquid 3 is an organic matter or an organic acid. Therefore, in the methane fermentation device 20 of this embodiment, the decomposition liquid 3 is supplied to the methane fermentation tank 21 in which the methane fermentation of sewage sludge is performed in a state where the volume load on the methane fermentation tank 21 is low, so that the methane fermentation of the sewage sludge and the methane fermentation of the decomposition product of the biodegradable resin 1 can be performed simultaneously as described above.

In this way, methane can be efficiently produced from sewage sludge and monomers by effectively utilizing the methane fermentation apparatus 20, which has a low volume load on the methane fermentation tank 21 when only sewage sludge is fermented. Furthermore, when the decomposition product is an organic acid, not only solubilization but also acid fermentation is not required, compared to methane fermentation of only sewage sludge, and methane can be produced even more efficiently.

In this embodiment, when the decomposition liquid is added to the sewage sludge (organic waste 4) in the methane fermentation tank 21, methane fermentation is performed under conditions where the volume load in the methane fermentation tank 21 is 0.60 g COD Cr/L/day or more and 5.0 g COD Cr/L/day or less.

In the methane fermentation step S102 in which the decomposition liquid 3 is fermented into methane, the method of methane fermentation is not particularly limited and may be a wet or dry method. Those skilled in the art can use their ordinary knowledge to set the conditions, etc., as appropriate.

Methanogens are archaea that synthesize methane under anaerobic conditions, and are not particularly limited as long as they are used in methane fermentation in the relevant technical field. For example, (facultative anaerobic bacteria include hydrocarbon decomposition bacteria such as Clostridium, Bacillus, and Staphylococcus, fiber decomposition bacteria such as Plecridium spumarum and Caduceus cellosaehydrogenicus, protein decomposition bacteria such as Clostridium, Proteus, Bacterium, and Bacillus, and Clostridium kluberii. Examples of fat-decomposing bacteria include bacteria from the genera Methanococcus, Methanobacterium, and Methanosarcina. One or more types of these methane fermentation bacteria can be used, and as methane fermentation continues, one or more of these methane fermentation bacteria act depending on the environment to progress the reaction.

In the above methane fermentation step S102, the organic waste 4 may contain other organic substances, such as food processing residues or food waste, for methane fermentation, and nutrient sources for aiding the growth and activity of methane bacteria in the fermentation liquid. In order to increase the efficiency of methane fermentation of the organic substances, pretreatment such as acid decomposition, alkali decomposition, thermal decomposition, steam decomposition, enzymatic decomposition, and decomposition by microorganisms other than methane bacteria may be performed before methane fermentation, and a combination of these pretreatments may be performed.

Methane fermentation can be carried out while stirring appropriately using a stirring unit as necessary. The temperature of methane fermentation is not particularly limited and can be set appropriately by those skilled in the art to a temperature suitable for fermentation, but can be, for example, 20 to 80°C, preferably 35 to 50°C, for example 37°C. In this case, it is preferable to carry out fermentation using a thermostatic chamber to maintain the appropriate temperature.

The treatment time for acid decomposition (acid fermentation) and methane fermentation can be appropriately set by a person skilled in the art depending on the amount of decomposed biodegradable resin, the amount of decomposition liquid, the type of methane bacteria used, and the fermentation temperature, but can be, for example, about 1 to 30 days, preferably 1 to 20 days, and more preferably 1 to 10 days.

When methane fermentation is performed, it is possible to use other organic biodegradation methods, such as hydrogen fermentation, ethanol fermentation, lactic acid fermentation, and acetone-butanol fermentation. For example, when hydrogen fermentation is used in combination, it is possible to take the form of two-stage hydrogen/methane fermentation, and hydrogen and methane can be efficiently recovered by subjecting the organic acids, such as acetic acid, butyric acid, propionic acid, and lactic acid, generated by hydrogen fermentation to methane fermentation.

The methane gas produced often contains various impurities, and can be purified if necessary. Gas purification methods include desulfurization and denitrification, and these processes can be carried out using a gas purification tank, etc., which allows high-purity methane gas to be obtained.

<Biodegradable resin treatment system>
The biodegradable resin treatment system A of the present invention includes the above-mentioned decomposition device 10 and methane fermentation device 20. The decomposition device 10 has a decomposition tank 11, in which waste material containing a biodegradable resin 1 and water 2 are added and mixed. The decomposition tank 11 is sealed, and the contents are hydrolyzed at a decomposition temperature of 120° C. or higher to obtain a decomposition liquid 3 containing decomposition products of the biodegradable resin 1.

The methane fermentation device 20 has a methane fermentation tank 21, in which methane bacteria are present, and treats organic waste 4 containing difficult-to-decompose solids and decomposition liquid 3 at a temperature of 30°C to 60°C. At this time, the decomposition liquid 3 is added to the organic waste 4 so that the organic load in the methane fermentation tank 21 is 0.60 g COD Cr/L/day to 5.0 g COD Cr/L/day.

In the biodegradable resin treatment system A of the present invention, it is preferable to mix 0.30 parts by mass or more and 20 parts by mass or less of water 2 per 1.0 part by mass of biodegradable resin in the decomposition tank 11.

By configuring it in this way, methane fermentation can be carried out using a decomposition liquid in which an appropriate amount of water is mixed with biodegradable resin, so methane fermentation can proceed efficiently without having to concentrate the decomposition liquid.

In the decomposition device 10, the hydrolysis temperature is preferably set to 120°C or higher and 170°C or lower. This configuration can further prevent the acid derived from the biodegradable resin from corroding the austenitic stainless steel in the decomposition tank. As a result, impurities can be prevented from being mixed into the fermentation tank.

The recovered methane gas can be reused for power generation, fuel production, and polymer synthesis. When hydrogen fermentation, ethanol fermentation, lactic acid fermentation, acetone-butanol fermentation, etc. are used in combination, it is possible to obtain the respective fermentation products at the same time, and these can also be reused. The obtained methane gas can be recovered by normal methods and reused according to the purpose. For example, when used for power generation, it can be stored in a gas holder, or it can be directly fed into a fuel cell or gas generator. In addition, the residue and wastewater generated in the fermentation process can also be reused by converting them into fertilizer and animal feed.

The following describes examples of the present invention, but the present invention is not limited to these.

<Hydrolysis treatment of polylactic acid>
(Test Example 1)
1.0 g of polylactic acid pellets (manufactured by Mitsui Chemicals, Inc., LACEA H-100J) and 19 g of water were placed in a PTFE sample decomposition container (manufactured by San-ai Science Co., Ltd., HU-25), and the lid was closed to seal the container. Then, hydrolysis treatment was carried out at 120° C. for 48 hours. The concentration of the obtained aqueous lactic acid solution was measured using high performance liquid chromatography.

(Test Example 2)
The test and measurements were carried out under the same conditions as in Test Example 1, except that the hydrolysis temperature was set to 130°C.

(Test Example 3)
The test and measurements were carried out under the same conditions as in Test Example 1, except that the hydrolysis temperature was set to 100°C.

(Test Example 4)
The test and measurements were carried out under the same conditions as in Test Example 1, except that the hydrolysis temperature was set to 110°C.

The results of Test Examples 1-4 are shown in Table 1. In Test Examples 1 and 2, the lactic acid concentration of the decomposition liquid was 6.3%, while in Test Examples 3 and 4, the lactic acid concentration of the decomposition liquid was 0.0%. From these results, it can be seen that while hydrolysis of polylactic acid proceeds in Test Examples 1 and 2, hydrolysis of polylactic acid does not proceed in Test Examples 3 and 4. Therefore, in order to hydrolyze polylactic acid, the temperature needs to be 120°C or higher.

<Relationship between organic load of digested liquid and methane production>
Example 1
A mixture was obtained by putting 4.0 g of polylactic acid pellets (manufactured by Mitsui Chemicals, Inc., LACEA H-100J) and 16 g of water into a PTFE sample decomposition container (manufactured by San-Ai Scientific Co., Ltd., HU-25).Then, the lid was closed to seal the container, and hydrolysis treatment was carried out at 140°C for 48 hours, to obtain a decomposition liquid with a lactic acid concentration of 24.1%.

Next, 2.0 L of high-temperature anaerobic digestion sludge collected from a general sewage treatment plant was placed into a 3.0 L jar fermenter (NBC-3000, manufactured by Mitsuwa Frontech Co., Ltd.), the nitrogen flow rate was set to 1.0 L/min, the headspace was purged for 5 minutes, the lid was then closed, and the vessel was heated to 55°C to construct a lab-scale methane fermentation tank.

Thickened sludge from the same sewage treatment plant was added at a rate of 100 mL/day so that the retention time in the methane fermentation tank was 20 days, and excess sludge was withdrawn at a rate of 100 mL/day. The methane fermentation tank was operated under these conditions for one month, and after it was confirmed that the methane generation rate had stabilized at 0.90 L/L/day, concentrated sludge was added at a rate of 100 mL/day, and a decomposition liquid with a lactic acid concentration of 24.1% was added so that the organic load was 4.3 g COD Cr/L/day. The withdrawal of excess sludge was adjusted so that the digested sludge volume in the digestion tank was maintained at 2.0 L. This methane fermentation tank was operated continuously for one month, and the methane generation rate and the average pH value of the digested sludge in the methane fermentation tank for the last five days were measured. A compact pH meter (LAQUAtwin pH-11B, manufactured by Horiba, Ltd.) was used as the pH measuring device. The results are shown in Table 2.

Example 2
Methane fermentation was carried out under the same conditions as in Example 1, except that the decomposition liquid with a lactic acid concentration of 24.1% was added so that the organic load was 2.0 g CODCr/L/day. The results are shown in Table 2.

Example 3
Methane fermentation was carried out under the same conditions as in Example 1, except that the decomposition liquid with a lactic acid concentration of 24.1% was added so that the organic load was 0.60 g CODCr/L/day. The results are shown in Table 2.

Example 4
Methane fermentation was carried out under the same conditions as in Example 1, except that the decomposition liquid with a lactic acid concentration of 24.1% was added so that the organic load was 0.30 g CODCr/L/day. The results are shown in Table 2.

(Comparative Example 1)
Methane fermentation was carried out under the same conditions as in Example 1, except that the decomposition liquid with a lactic acid concentration of 24.1% was added so that the organic load was 5.1 g CODCr/L/day. The results are shown in Table 2.

(Reference Example 1)
As a reference example, methane fermentation was carried out under the same conditions as in Example 1, except that the organic load was set to 0.0 g CODCr/L/day, i.e., only digested sludge was used without adding the decomposition liquid. The results are shown in Table 2.

上記の結果から、有機負荷が５．０ｇＣＯＤＣｒ／Ｌ／日を超えると、メタン発生量が低下し、分解液を投入する前のメタン発生量を下回った。これは、ｐＨが低下することで、消化汚泥内の菌の有機物分解活性が低下したためである、と考えられる。

From the above results, when the organic load exceeded 5.0 g COD Cr/L/day, the amount of methane generated decreased and fell below the amount generated before the digestion liquid was added. This is thought to be because the organic matter decomposition activity of the bacteria in the digested sludge decreased due to the decrease in pH.

In addition, in order to increase the amount of methane generated to 1.5 times or more the amount generated in Reference Example 1, in which only sewage sludge was added, it is found that the decomposition liquid should be added at an organic matter load of 0.60 g COD Cr/L/day or more.

<Relationship between the ratio of digested liquid to water and the evaporation residue of digested sludge>
Example 5
In the same manner as in Example 1, a hydrolyzed liquid having a lactic acid concentration of 24.1% was obtained.

Next, 2.0 L of high-temperature anaerobic digestion sludge collected from a general sewage treatment plant was placed into a 3.0 L jar fermenter (NBC-3000, manufactured by Mitsuwa Frontech Co., Ltd.), the headspace inside the jar fermenter was purged with nitrogen at a flow rate of 1.0 L/min for 5 minutes, the lid was then closed, and the vessel was heated to 55°C to construct a lab-scale methane fermentation tank.

Thickened sludge from the sewage treatment plant was added at a rate of 100 mL/day so that the retention time in the methane fermentation tank was 20 days, and excess sludge was withdrawn at a rate of 100 mL/day. The methane fermentation tank was operated under these conditions for one month, and after it was confirmed that the evaporation residue ratio of the digested sludge in the methane fermentation tank was stable at 4.0% and the methane generation rate was stable at 0.90 L/L/day, concentrated sludge was added at a rate of 100 mL/day, and a decomposition liquid with a lactic acid concentration of 24.1% was added to the methane fermentation tank by adjusting the amount of the decomposition liquid added so that the organic load was 0.60 g COD Cr/L/day. The withdrawal of excess sludge was adjusted so that the digested sludge volume in the digestion tank was maintained at 2.0 L. This methane fermentation tank was operated continuously for one month, and the evaporation residue ratio of the digested sludge was measured. The results are shown in Table 3.

Example 6
Polylactic acid pellets (manufactured by Mitsui Chemicals, Inc., LACEA H-100J) were added to a PTFE sample decomposition container (manufactured by San-Ai Science Co., Ltd., HU-25) in an amount of 0.50 g and 19.5 g of water, that is, 1.0 part by mass of polylactic acid (biodegradable resin) was mixed with 39 parts by mass of water to obtain a decomposition liquid having a lactic acid concentration of 3.1%. Thereafter, methane fermentation was performed under the same conditions as in Example 5, except that the decomposition liquid having a lactic acid concentration of 3.1% was added to the methane fermentation tank by adjusting the amount of decomposition liquid input so that the organic load in the methane fermentation tank was 0.60 g COD Cr/L/day. The results are shown in Table 3.

(Example 7)
Polylactic acid pellets (manufactured by Mitsui Chemicals, Inc., LACEA H-100J) were added to a PTFE sample decomposition container (manufactured by San-Ai Science Co., Ltd., HU-25) in an amount of 1.0 g and 19 g of water, that is, 1.0 parts by mass of polylactic acid (biodegradable resin) was mixed with 19 parts by mass of water to obtain a decomposition liquid having a lactic acid concentration of 5.8%. Thereafter, hydrolysis and methane fermentation were performed under the same conditions as in Example 5, except that the decomposition liquid having a lactic acid concentration of 5.8% was added to the methane fermentation tank by adjusting the amount of decomposition liquid input so that the organic load in the methane fermentation tank was 0.60 g COD Cr/L/day. The results are shown in Table 3.

(Example 8)
2.0 g of polylactic acid pellets (manufactured by Mitsui Chemicals, Inc., LACEA H-100J) were added to a PTFE sample decomposition container (manufactured by San-Ai Science Co., Ltd., HU-25), and 18 g of water were added, that is, 9.0 parts by mass of water were mixed with 1.0 parts by mass of polylactic acid (biodegradable resin), and hydrolysis was performed under the conditions to obtain a decomposition liquid having a lactic acid concentration of 11.9%. Thereafter, hydrolysis and methane fermentation were performed under the same conditions as in Example 5, except that the decomposition liquid having a lactic acid concentration of 11.9% was added to the methane fermentation tank by adjusting the amount of decomposition liquid input so that the organic load in the methane fermentation tank was 0.60 g COD Cr/L/day. The results are shown in Table 3.

(Example 9)
10 g of polylactic acid pellets (manufactured by Mitsui Chemicals, Inc., LACEA H-100J) were added to a PTFE sample decomposition container (manufactured by San-Ai Science Co., Ltd., HU-25), and 10 g of water were added, that is, 1.0 part by mass of polylactic acid (biodegradable resin) was mixed with 1.0 part by mass of water to obtain a decomposition liquid having a lactic acid concentration of 60.5%. Thereafter, hydrolysis and methane fermentation were performed under the same conditions as in Example 5, except that the decomposition liquid having a lactic acid concentration of 60.5% was added to the methane fermentation tank by adjusting the amount of decomposition liquid input so that the organic load in the methane fermentation tank was 0.60 g COD Cr/L/day. The results are shown in Table 3.

(Example 10)
15 g of polylactic acid pellets (manufactured by Mitsui Chemicals, Inc., LACEA H-100J) were added to a PTFE sample decomposition container (manufactured by San-Ai Science Co., Ltd., HU-25), and 5.0 g of water were added. In other words, 1.0 part by mass of polylactic acid (biodegradable resin) was mixed with 0.30 parts by mass of water to obtain a decomposition liquid having a lactic acid concentration of 92.3%. Thereafter, hydrolysis and methane fermentation were performed under the same conditions as in Example 5, except that the decomposition liquid having a lactic acid concentration of 92.3% was added to the methane fermentation tank by adjusting the amount of decomposition liquid input so that the organic load in the methane fermentation tank was 0.60 g COD Cr/L/day. The results are shown in Table 3.

(Reference Example 1)
For comparison, as a reference example, methane fermentation was carried out under the same conditions as in Example 5, except that the organic load was set to 0.0 g CODCr/L/day, i.e., only digested sludge was used without adding the decomposition liquid. The results are shown in Table 3.

生分解性樹脂１．０質量部に対して、水の量を０．３０質量部以上２０質量部以下とすれば、分解液を濃縮することなくメタン発酵槽に添加しても、消化汚泥の濃度低下は生じない、すなわちメタン発酵の進行が妨げられないことが分かる。

It has been found that when the amount of water is 0.30 parts by mass or more and 20 parts by mass or less per 1.0 part by mass of biodegradable resin, even if the decomposition liquid is added to the methane fermentation tank without being concentrated, the concentration of the digested sludge does not decrease, i.e., the progress of methane fermentation is not hindered.

In Example 6, the percentage of evaporation residue in the digested sludge was 3.5%, which was lower than in the other Examples. If operation was continued, the amount of methanogens in the digested sludge could decrease, making this unsuitable for long-term operation. However, if operation was continued for a short period of time, it was found that this condition allowed for highly efficient production of methane without the addition of any additives other than biodegradable resin and water.

<<Measurement of corrosion rate>>
Example 11
20 mL of the decomposition solution with a lactic acid concentration of 24.1% obtained in Example 1 was added to a PTFE sample decomposition container (HU-25, manufactured by San-Ai Scientific Co., Ltd.). Next, a SUS304 test piece with a length of 20 mm, width of 15 mm, and thickness of 2.5 mm was immersed, the lid was closed so as to be in a sealed state, and heat treatment was performed at 120°C for 30 days. After 30 days, the corrosion rate (mm/year) was calculated from the weight loss of the test piece. The results are shown in Table 4.

Example 12
Except for the fact that the material of the test piece was SUS316, the corrosion rate (mm/year) was calculated under the same conditions as in Example 11. The results are shown in Table 4.

Example 13
Except for using SUS316L as the material of the test piece, the corrosion rate (mm/year) was calculated under the same conditions as in Example 11. The results are shown in Table 4.

(Example 14)
The corrosion rate (mm/year) was calculated under the same conditions as in Example 11, except that the material of the test piece was SUS316 and the temperature was 140° C. The results are shown in Table 4.

(Example 15)
The corrosion rate (mm/year) was calculated under the same conditions as in Example 11, except that the material of the test piece was SUS316 and the temperature was 160° C. The results are shown in Table 4.

上記の結果から、いずれのステンレス鋼を用いても、化学工学便覧（第２版）に記載の完全耐食（０．０５０ｍｍ/年以下）または耐食性あり（０．０５０ｍｍ/年以上０．１０ｍｍ/年以下）に分類されるため、これらのステンレス鋼を分解槽の材質として用いたとしても耐食性に問題が無いことが分かる。

From the above results, it can be seen that any of the stainless steels used are classified as completely corrosion resistant (0.050 mm/year or less) or corrosion resistant (0.050 mm/year or more and 0.10 mm/year or less) as described in the Chemical Engineering Handbook (2nd edition), and therefore there is no problem with corrosion resistance if these stainless steels are used as the material for the decomposition tank.

In addition, it can be seen that SUS316 and SUS316L, which are austenitic stainless steels containing 1.0% or more molybdenum, have better corrosion resistance than SUS304.

Furthermore, if the processing temperature for SUS316 is 150°C or less, the corrosion rate of the stainless steel is 0.050 mm/year or less, and it is classified as completely corrosion resistant.

These results show that using SUS304, SUS316, and SUS316L as materials for the decomposition tank and hydrolyzing the biodegradable resin at a temperature between 120°C and 170°C reduces corrosion of the decomposition tank and prevents impurities from the decomposition tank from being mixed into the decomposition liquid.

In addition, if SUS316 or SUS316L is used as the material for the decomposition tank, and the hydrolysis temperature is set to 120°C or higher and 150°C or lower, the corrosion rate of stainless steel is 0.050 mm/year or less and it is classified as completely corrosion-resistant, so hydrolysis can be carried out at a high temperature, which is preferable in terms of the efficiency of methane fermentation.

<Relationship between types of biodegradable resins and methane production>
(Example 16)
Hydrolysis and methane fermentation of polybutylene succinate were carried out under the same conditions as in Example 2, except that 4.0 g of polylactic acid was replaced with 4.0 g of polybutylene succinate pellets (Showa Polymer Co., Ltd., Bionolle #1001), and the amount of methane generated over the final 5 days was measured. The results are shown in Table 5.

(Example 17)
Hydrolysis and methane fermentation of polyhydroxybutyric acid were carried out under the same conditions as in Example 2, except that 4.0 g of polyhydroxybutyric acid powder (Biosoft 915, manufactured by Sumitomo Pharma Food & Chemical Co., Ltd.) was used instead of 4.0 g of polylactic acid in Example 2, and the amount of methane generated over the final 5 days was measured. The results are shown in Table 5.

以上の結果から、生分解性樹脂であるポリブチレンサクシネートやポリヒドロキシ酪酸の分解液をメタン発酵に供する場合であっても、メタン発酵によるメタンの生成が可能であることが分かる。

From the above results, it is clear that methane can be produced by methane fermentation even when the decomposition liquid of biodegradable resins such as polybutylene succinate or polyhydroxybutyrate is subjected to methane fermentation.

(Example 18)
2 g of polylactic acid pellets (LACEA H-100J, Mitsui Chemicals, Inc.), 2 g of polyhydroxybutyric acid powder (Biosoft 915, Sumitomo Pharma Food & Chemical Co., Ltd.), and 10 g of water were placed in a PTFE sample decomposition container (HU-25, San-Ai Science Co., Ltd.), the lid was closed to seal the container, and hydrolysis treatment was carried out at 160°C for 5 or 10 hours. The dissolved residue was separated using a metal mesh with a mesh size of 106 μm, and the weight was measured after drying at 40°C for 16 hours. The results are shown in Table 6.

(Example 19)
The weight of the residue after drying was measured under the same conditions as in Example 18, except that the amount of polylactic acid pellets added was 1 g and the amount of polyhydroxybutyric acid powder added was 3 g. The results are shown in Table 6.

(Example 20)
The weight of the residue after drying was measured under the same conditions as in Example 18, except that the amount of polylactic acid pellets added was 0.5 g and the amount of polyhydroxybutyric acid powder added was 3.5 g. The results are shown in Table 6.

(Example 21)
The weight of the residue after drying was measured under the same conditions as in Example 18, except that the amount of polylactic acid pellets added was 0.2 g and the amount of polyhydroxybutyric acid powder added was 3.8 g. The results are shown in Table 6.

(Example 22)
The weight of the residue after drying was measured under the same conditions as in Example 18, except that no polyhydroxybutyric acid powder was added and 2 g of polybutylene succinate was added. The results are shown in Table 6.

(Example 23)
The weight of the residue after drying was measured under the same conditions as in Example 18, except that 1 g of polyhydroxybutyric acid powder and 1 g of polybutylene succinate were added. The results are shown in Table 6.

(Example 24)
The weight of the residue after drying was measured under the same conditions as in Example 18, except that the treatment temperature was 140° C. The results are shown in Table 6.

(Example 25)
The weight of the residue after drying was measured under the same conditions as in Example 18, except that no polyhydroxybutyric acid powder was added, but 2 g of polybutylene succinate was added, and the treatment temperature was 140° C. The results are shown in Table 6.

(Example 26)
Synthesis of biodegradable resin PHBH and decomposition of PHBH
A medium (pH 7.0) was prepared by adding water to 5 g of meat extract, 5 g of peptone, 2 g of yeast extract, _0.5 g _{of KH2PO4} , 1.5 g _{of K2HPO4} , _0.1 g of MgSO4.7H2O to make a total volume of 1 liter, and Aeromonas hydrophila OL-338 strain was added to this medium and cultured with shaking at 30° C. for 48 hours. After the culture was completed, the culture broth was centrifuged to collect the bacterial cells.

Next, a medium (pH 7.0) was prepared by adding water to 25.4 g of β-hydroxycaproic acid, 1.5 g of KH ₂ PO ₄ , 1.5 g of K ₂ HPO ₄ , 0.25 g of MgSO _{4.7H 2} O, and 0.5 g of Tween 85 to make a total volume of 1 liter, and the entire amount of the above-mentioned cells was added to this medium and cultured with shaking at 30°C for 24 hours. After the culture was completed, the cells were washed with distilled water and methanol and dried under reduced pressure to obtain dried cells. The dried cells were extracted with chloroform at 50°C for 2 hours. After the cells were removed, 10 times the amount of methanol was added to the chloroform extract, and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (biodegradable resin PHBH) with a ratio of 3-hydroxybutyrate:3-hydroxyhexanoate=51:49 was precipitated and collected.
Decomposition of biodegradable resin PHBH
The weight of the residue after drying was measured under the same conditions as in Example 18, except that no polyhydroxybutyric acid powder was added and 2 g of PHBH was added. The results are shown in Table 6.

Fermentation of PHBH solution
The CODcr of the obtained PHBH solution was measured, and 30 ml of high-temperature anaerobic digestion sludge and the PHBH solution were added to a 50 ml vial (manufactured by Maruemu Co., Ltd.) so that the COD was 0.05 g COD. The gas phase was purged with nitrogen, the lid was closed, and the mixture was shake-cultured at 55°C and 50 rpm for 20 days, and the amount of biogas generated was measured. The amount of biogas generated was 34 ml. This was almost the same as the amount of biogas generated by adding 0.05 g COD of the PLA solution and shaking cultured for 20 days in the same manner as above, and the amount of biogas generated was 35 ml.

(Example 27)
<Hydrolysis by water vapor>
4 g of water was placed in a PTFE sample decomposition container (HU-25, San-Ai Scientific Co., Ltd.), and then 8 g of 1/8 inch PTFE balls were placed therein. 2 g of polylactic acid pellets (LACEA H-100J, Mitsui Chemicals, Inc.) and 2 g of PBS pellets (Bionolle, Showa Polymer Co., Ltd.) were placed on top of the balls, and the lid was closed to seal the container. Hydrolysis was carried out at 160°C for 5 or 10 hours, and the remaining residue was separated using a metal mesh with 106 μm openings, and the weight was measured after drying at 40°C for 16 hours. The results are shown in Table 6.

Example 17
Hydrolysis of polyhydroxybutyric acid was carried out under the same conditions as in Example 2, except that 4.0 g of polylactic acid was replaced with 4.0 g of polyhydroxybutyric acid powder (Biosoft 915, manufactured by Sumitomo Pharma Food & Chemical Co., Ltd.), and the degree of decomposition was confirmed after 5 hours and 10 hours.

Example 16
In Example 2, 4.0 g of polylactic acid was replaced with 4.0 g of polybutylene succinate pellets (Showa Polymer Co., Ltd., Bionolle #1001). Hydrolysis of polybutylene succinate was carried out under the same conditions as in Example 2, and the degree of decomposition was confirmed after 5 hours and 10 hours.

The above comparative test confirmed that adding PLA causes hydrolysis to proceed more quickly.

表６の実施例１７、１６において、１０時間分解処理後の分解度合いは樹脂投入量のうち５０％以上が分解していないが、４８時間分解処理後は全て溶解したことを確認している。

In Examples 17 and 16 in Table 6, it was confirmed that after 10 hours of decomposition treatment, 50% or more of the resin input was not decomposed, but after 48 hours of decomposition treatment, all of the resin was dissolved.

In Table 6, for the degree of decomposition after 5 hours of treatment and after 10 hours of treatment, if the value of (weight of residue) ÷ 4 g of input amount is less than 10%, it is marked with a ◯, if it is 10% or more but less than 50%, it is marked with a △, and if it is 50% or more, it is marked with an ×.

Although the embodiments and examples of the present disclosure have been described above, it is intended from the outset that the configurations of the above-mentioned embodiments and examples may be appropriately combined or modified in various ways.

The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is indicated by the claims rather than the embodiments and examples described above, and is intended to include the meaning equivalent to the claims and all modifications within the scope.

The present invention can be used in a method for processing biodegradable resins and a system for processing biodegradable resins.

1 Biodegradable resin 2 Water 3 Decomposition liquid 4 Organic waste 10 Decomposition device 11 Decomposition tank 20 Methane fermentation device 21 Methane fermentation tank A Biodegradable resin treatment system S101 Decomposition process S102 Methane fermentation process

Claims (14)

a decomposition step of mixing waste containing a biodegradable resin with water and hydrolyzing the mixture at a temperature of 120° C. or higher in a sealed decomposition tank to obtain a decomposition liquid containing a decomposition product of the biodegradable resin;
a methane fermentation step of treating the organic waste containing the hardly decomposable solid content and the decomposition liquid in a methane fermentation tank in which methane bacteria are present at a temperature of 30° C. or higher and 60° C. or lower,
In the methane fermentation step, the decomposition liquid is added to the organic waste so that the organic load in the methane fermentation tank is 0.60 g CODCr/L/day or more and 5.0 g CODCr/L/day or less. a decomposition step of mixing waste containing a biodegradable resin with water vapor and hydrolyzing the mixture at a temperature of 120° C. or higher in a sealed decomposition tank to obtain a decomposition liquid containing a decomposition product of the biodegradable resin;
a methane fermentation step of treating the organic waste containing the hardly decomposable solid content and the decomposition liquid in a methane fermentation tank in which methane bacteria are present at a temperature of 30° C. or higher and 60° C. or lower,
In the methane fermentation step, the decomposition liquid is added to the organic waste so that the organic load in the methane fermentation tank is 0.60 g CODCr/L/day or more and 5.0 g CODCr/L/day or less. The method for treating a biodegradable resin according to claim 1 or 2, wherein in the decomposition step, 0.30 parts by mass or more and 20 parts by mass or less of water or water vapor is mixed with 1.0 part by mass of the biodegradable resin. The method for treating biodegradable resin according to claim 1 or 2, wherein at least the part of the decomposition tank that comes into contact with the decomposition liquid is made of austenitic stainless steel. The method for treating biodegradable resin according to claim 4, wherein the hydrolysis temperature in the decomposition step is 120°C or higher and 170°C or lower. The method for treating a biodegradable resin according to claim 1 or 2, wherein the biodegradable resin contains at least one of polybutylene succinate and polyhydroxyalkanoate. The method for treating a biodegradable resin according to claim 6, wherein the biodegradable resin mixed in the decomposition step contains 0.1 parts by mass or more of polylactic acid per 1.0 part by mass of a biodegradable resin other than polylactic acid. a decomposition device for mixing waste containing a biodegradable resin with water and hydrolyzing the mixture in a sealed decomposition tank at a temperature of 120° C. or higher to obtain a decomposition liquid containing a decomposition product of the biodegradable resin;
a methane fermentation apparatus for treating organic waste containing a hardly decomposable solid content and the decomposition liquid in a methane fermentation tank in which methane bacteria are present at a temperature of 20° C. or higher and 60° C. or lower,
A biodegradable resin treatment system, in which the decomposition liquid is added to the organic waste so that the organic load in the methane fermentation tank is 0.60 g CODCr/L/day or more and 5.0 g CODCr/L/day or less. a decomposition device for mixing waste containing a biodegradable resin with steam and hydrolyzing the mixture at a temperature of 120° C. or higher in a sealed decomposition tank to obtain a decomposition liquid containing a decomposition product of the biodegradable resin;
a methane fermentation apparatus for treating organic waste containing a hardly decomposable solid content and the decomposition liquid in a methane fermentation tank in which methane bacteria are present at a temperature of 20° C. or higher and 60° C. or lower,
A biodegradable resin treatment system, in which the decomposition liquid is added to the organic waste so that the organic load in the methane fermentation tank is 0.60 g CODCr/L/day or more and 5.0 g CODCr/L/day or less. The biodegradable resin treatment system according to claim 8 or 9, in which 0.30 parts by mass or more and 20 parts by mass or less of water or water vapor is mixed into the decomposition tank per 1.0 part by mass of the biodegradable resin. The biodegradable resin processing system according to claim 8 or 9, wherein at least the part of the decomposition tank that comes into contact with the decomposition liquid is made of austenitic stainless steel. The biodegradable resin treatment system according to claim 11, wherein the temperature of hydrolysis in the decomposition tank is 120°C or higher and 170°C or lower. The biodegradable resin treatment system according to claim 8 or 9, wherein the biodegradable resin includes at least one of polybutylene succinate and polyhydroxyalkanoate. 14. The system for treating a biodegradable resin according to claim 13, wherein the biodegradable resin mixed in the decomposition tank contains 0.1 part by mass or more of polylactic acid per 1.0 part by mass of a biodegradable resin other than polylactic acid.

Images