JP5392719B2 - Electron donor supplier, method for producing electron donor supplier, and environmental purification method using the same - Google Patents

Description

  The present invention relates to an electron donor supply agent used in biological treatment, a production method thereof, and an environmental purification method using the same, and in particular, even when hydrolyzability is improved, the solid state is obtained in the use environment. And an electron donor supply agent comprising a polylactic acid resin capable of controlling the release rate of the electron donor accompanying hydrolysis, a method for producing the same, and an environment purification method using the same. is there.

  Conventionally, wastewater treatment to prevent eutrophication of rivers and lakes due to the influence of domestic wastewater and factory wastewater, and contamination of the surrounding water environment (groundwater, rivers and lakes) due to the application of nitrogen fertilizer to farmland Has been done.

  Such wastewater treatment is generally carried out by biological treatment which is advantageous in terms of cost. In the wastewater treatment facility, the sewage introduced into the treatment tank is aerated in the presence of activated sludge, and the organic matter (BOD (Biochemical Oxygen Demand) source) contained in the sewage is decomposed by the action of aerobic microorganisms in the activated sludge. The This treatment with activated sludge has a weak function of removing nitrogen components, and nitrogen components such as ammonia tend to remain.

  原因 One of the causative substances of nutrition is nitrate (nitrogen component), and even if organic matter in the wastewater is completely removed, phytoplankton Wastewater treatment loses its meaning by promoting abnormal growth.

  Therefore, in recent years, after activated sludge treatment, nitrification treatment using ammonia as nitrate is performed by nitrifying bacteria, and then nitrogen components are removed by denitrification treatment by denitrifying bacteria under anaerobic conditions. .

  This denitrification treatment uses an organic substance (that is, BOD source) as an energy source and utilizes the reducing action of denitrifying bacteria using nitrate as an electron acceptor. The organic substance as the energy source becomes an electron donor and undergoes a reduction reaction. Supply the necessary electrons. Thereby, nitrate is reduced to nitrogen through nitrous acid, nitric oxide, and dinitrogen monoxide, and as a result, various nitrogen compounds in the wastewater are diffused into the atmosphere as nitrogen gas and removed.

  As described above, this denitrification treatment requires an electron donor that becomes the energy of microorganisms, but most of the organic substances that can become electron donors in the treatment with activated sludge have already been removed. The necessary reducing power will be insufficient. For this reason, at present, low molecular organic substances such as methanol and acetic acid are added to the treatment tank as an electron donor.

  However, since methanol, acetic acid, and the like are liquid, workability is poor and it is difficult to grasp the consumption in the tank. For this reason, it is difficult to accurately determine the timing and amount of addition of the electron donor, and the amount of the electron donor tends to be excessive or insufficient with respect to the original required amount. If the amount of electron donors is insufficient, denitrification may be insufficient, leading to eutrophication of rivers, etc., and if the amount of electron donors is excessive, secondary contamination by the added electron donor may be caused. It can cause.

  Thus, a so-called solid-phase denitrification method using a solid organic substance as an electron donor has been proposed. For example, Non-Patent Documents 1 to 4 show that in this solid-phase denitrification method, poly (3-hydroxybutyric acid) (PHB), polycaprolactone (PCL), and polylactic acid (PLA), which are biodegradable plastics, are activated sludge and wastewater. There have been reports of attempts to remove nitrogen by adding it to the inside.

  Furthermore, it is known that not only nitrogen compounds but also organic chlorine compounds and petroleum hydrocarbons can be decomposed and removed by biological treatment using a biodegradable plastic as an electron donor.

  Patent Document 1 discloses a technique for denitrifying water and soil using polycaprolactone, which is a biodegradable plastic, as an electron donor.

  Patent Document 2 is provided so that one surface of a polymer gel to which microorganisms such as denitrifying bacteria are fixed is in contact with the treatment liquid, and the other surface is in contact with a solid-type biodegradable plastic serving as an electron donor. A bioreactor is disclosed.

  Patent Document 3 discloses a technique in which biodegradable plastic, nitrifying bacteria, and denitrifying bacteria are comprehensively immobilized with polyvinyl alcohol in order to denitrify the treatment liquid. In Patent Documents 2 and 3, polylactic acid is exemplified as one of biodegradable plastics used in the art.

  Here, polylactic acid, which is one of biodegradable plastics, is a general-purpose biodegradable plastic that can be produced by chemical synthesis based on lactic acid produced by fermentation, rather than directly by microorganisms. Production on an industrial basis has begun and its application has been expanded to various fields such as medical treatment, housing, and cars. In addition, it is a biodegradable plastic that is expected to grow in demand in the future.

  In Patent Document 4, as a technology for environmental purification using polylactic acid, a low molecular weight polylactic acid having 2 to 10 repeating units and a polyfunctional alcohol are reacted to form a semi-solid polyester (polylactic acid resin). ), And slowly releasing lactic acid as an electron donor from such polyester, and a technique for decomposing organochlorine compounds by microorganisms is disclosed.

  Patent Document 5 discloses a technique for remediating soil by decomposing organochlorine compounds and petroleum hydrocarbons using known biodegradable plastics made into oligomers by thermal decomposition or hydrolysis. Thus, polylactic acid is exemplified as one of known biodegradable plastics.

JP 2004-209364 A JP 2003-117487 A JP 2003-265170 A Japanese Patent No. 3329899 JP 2006-218457 A

Mller, W.R., Heinemann, A., Schfer, C., Wurmthaler, J., Reutter, T .: Water Supply 10: 7990 (1992) Hiraishi, A. S. T. Khan, S.T .: Appl. Microbiol. Biotechnol. 61: 103109 (2003) Watanabe, A., Uemoto, H., Morisa, M., Saitoh, S., Yoshizaki, R.:Biol.Sci.Space 18: 142-143 (2004) Horiba, Y., Khan, S.T., Hiraishi, A .: Microbes Environ. 20: 25-33 (2005)

  However, biodegradable plastics such as poly (3-hydroxybutyric acid) and polycaprolactone have a problem of high production costs and impracticality. On the other hand, polylactic acid produced as a general-purpose biodegradable plastic is generally difficult to biodegrade and has a problem that it is difficult to become a microbial substrate (ie, an electron donor). It was. In Patent Document 4, a semi-solid polylactic acid resin having biodegradability is proposed, but the manufacturing method is complicated. Further, in Patent Document 5, it has been proposed to use biodegradable plastics oligomerized from high molecular weight biodegradable plastics for environmental purification, but the resulting oligomers have high fluidity, and such There was a problem that it was difficult to apply the low molecular weight polylactic acid obtained by the method to the solid phase denitrification method.

  Furthermore, since there are a wide variety of contamination-causing substances to be purified, when the environment is purified by biological treatment, the decomposition rate at which the microbial community decomposes the contamination-causing substances varies. Here, the supply of the electron donor, that is, the release of lactic acid from polylactic acid proceeds by hydrolysis of polylactic acid, but releases the pollutant causing the removal target according to the decomposition rate of the microorganisms. It is important that If the release rate of lactic acid etc. is too slow compared to the degradation rate of the pollutant causing the removal, the nutrient source will be depleted, the microorganisms will not be able to grow and the degradation of the pollutant will not progress slowly. . On the other hand, if the rate of slow release of lactic acid is too fast compared to the rate of degradation of the pollutant causing the substance to be removed, other microorganisms will also grow with the growth of the microorganisms that degrade the causative agent, often resulting in contamination. It inhibits the growth of microorganisms necessary to decompose the causative substances.

  However, as described above, it is difficult to obtain a solid polylactic acid having biodegradability (hydrolyzability) that can be used as an electron donor supply source. There has been a problem that it is increasingly difficult to obtain an electron donor having a controlled slow release rate. For this reason, it has been difficult to purify the environment by biological treatment using such polylactic acid.

  The present invention has been made in order to solve the above-described problems, and even if hydrolyzability is improved, the present invention can be made into a solid state in a use environment, and an electron donor associated with biodegradation can be obtained. It is an object of the present invention to provide an electron donor supplier containing a polylactic acid resin capable of controlling the release rate, a production method thereof, and an environmental purification method using the same.

  In order to achieve this object, the electron donor supply agent according to claim 1 is used for biological treatment by a microorganism and supplies the electron donor to the microorganism, and has a weight average molecular weight of about 12000. Hereinafter, a polylactic acid resin having a crystallinity of 10% or more and 40% or less and in a solid state at the temperature of the use environment is included. Here, the use environment means an environment in which an electron donor supply agent is charged for biological treatment, and examples include a water treatment tank, a sewage tank, a river, a lake, and a soil. Is done. Further, the temperature of the use environment is a temperature range that the environment can take in nature, for example, a range of 0 ° C. to 40 ° C.

  The electron donor supply agent according to claim 2 is the electron donor supply agent according to claim 1, wherein the polylactic acid resin has a weight average molecular weight of about 9500 or more.

  The method for producing an electron donor supply according to claim 3 is a method for producing an electron donor supply for use in biological treatment by a microorganism and supplying the electron donor to the microorganism, wherein the raw material polylactic acid is used. The molecular weight reduction process for lowering the molecular weight of the resin, the melting process for melting the polylactic acid resin reduced in the molecular weight reduction process at a temperature higher than the melting point, and the melting process And an annealing step of annealing the polylactic acid resin at a temperature lower than the melting point, and an electron donor supply agent is produced using the polylactic acid resin which is crystallized by the annealing step to be in a solid state. .

  The method for producing an electron donor supplier according to claim 4 is the method for producing an electron donor supplier according to claim 3, wherein the molecular weight reduction step has a weight average molecular weight of about 9500 or more and about 12000 or less. Therefore, the raw material polylactic acid resin is made to have a low molecular weight.

  The method for producing an electron donor supplier according to claim 5 is the method for producing an electron donor supplier according to claim 3 or 4, wherein the annealing step has a crystallinity of 10 for the polylactic acid resin. Annealing is performed so as to be not less than 40% and not more than 40%.

  The environmental purification method according to claim 6 is a method for detoxifying a specific component in a substance to be treated by biological treatment, and the electron donor supply agent according to claim 1 or 2 or claims 3 to 5. Biological treatment is performed using the electron donor supply produced by the production method described in any one of the above.

  The environmental purification method according to claim 7 is the environmental purification method according to claim 6, wherein the substance to be treated is an aqueous liquid, the specific component is a nitrogen compound, and the electron donor supply agent is used. The denitrification treatment is performed to remove nitrogen compounds in the liquid.

  The environmental purification method according to claim 8 is the environmental purification method according to claim 7, wherein the polylactic acid contained in the polylactic acid resin has a concentration of about 3 w / v% in the substance to be treated. It is the one that has been thrown into.

  The environmental purification method according to claim 9 is the environmental purification method according to claim 6, wherein the substance to be treated is soil, the specific component is a nitrogen compound, and the electron donor supply agent is used. Denitrification treatment is performed to remove nitrogen compounds in the soil.

  The environmental purification method according to claim 10 is the environmental purification method according to any one of claims 7 to 9, wherein a nitric acid-containing aqueous solution to which acetic acid and lactic acid are added is used, and microorganisms that grow in the aqueous solution are accumulated and cultured. Then, the accumulated cultured microorganism is added to the substance to be treated.

  According to the electron donor supplier according to claim 1, the polylactic acid system having a weight average molecular weight of approximately 12000 or less, a crystallinity of 10% or more and 40% or less, and being in a solid state at the temperature of the use environment It contains resin. Therefore, there is an effect that the polylactic acid-based resin can be made into a solid state while having sufficient hydrolyzability that can be a substrate of microorganisms in biological treatment. As a result, there is an effect that the entire agent can be formed in a solid state dosage form.

  For this reason, it is possible to visually confirm the degree of consumption of the electron donor supply agent introduced into the reaction system by the user or the like, and to easily grasp the amount of consumption (decomposition amount). Therefore, the necessary amount of the electron donor supply can be adjusted appropriately according to the amount consumed, and the necessary reaction can be sufficiently performed, and the occurrence of secondary contamination due to excessive electron donors can be avoided. There is an effect.

  Furthermore, by adjusting the two parameters of the weight average molecular weight and the crystallinity of the polylactic acid resin, this agent is different in the hydrolyzability of the polylactic acid resin, that is, hydrolysis under the same conditions. It can be a group of different speeds. In other words, the agent can be a group having diversity in the supply rate of lactic acid serving as an electron donor.

  For example, when purifying the environment by biological treatment, there are a wide variety of pollutants of interest, and therefore the decomposition rate at which the microbial community decomposes the pollutant (that is, the consumption rate at which the microorganism consumes the electron donor) varies. It becomes. Here, if there is a large difference between the consumption rate at which the microorganism that decomposes the pollutant consumes the electron donor and the supply rate of the electron donor, the electron donor required by the microorganism is insufficient and the pollutant is decomposed. The problem of becoming defective occurs. However, since this agent can have various electron donor supply rates under the same conditions, it is possible to select an appropriate one according to the characteristics of the microorganism that degrades the pollutant and to avoid the occurrence of such problems. effective.

  According to the electron donor supply agent of claim 2, in addition to the effect exhibited by the electron donor supply agent of claim 1, the polylactic acid resin has a weight average molecular weight of about 9500 or more. There exists an effect that a solid state can be favorably maintained below.

  According to the method for producing an electron donor supply according to claim 3, the molecular weight of the raw polylactic acid resin is lowered by the molecular weight reduction step. The low molecular weight polylactic acid-based resin is melted at a temperature equal to or higher than its melting point in the melting step, and then annealed at a temperature lower than the melting point in the annealing step. By this annealing step, the polylactic acid resin is crystallized to be in a solid state. And the electron donor supply agent using this solid-state polylactic acid-type resin is manufactured.

  Accordingly, it is possible to obtain a solid polylactic acid resin having sufficient hydrolyzability that can serve as a substrate for microorganisms in biological treatment, and to provide an electron donor supply using the same. There is. Moreover, since a solid-state polylactic acid-based resin can be used, the electron donor supply agent can be formed in a solid-state dosage form.

  Furthermore, since the polylactic acid-based resin can be prepared by reducing the molecular weight of a high-molecular-weight polylactic acid-based resin, there is no need to bother to newly synthesize from monomers by polymerization. For this reason, for example, wastes of general-purpose polylactic acid resins manufactured with high molecular weight can be used as raw materials, and this agent can be produced at low cost, and polylactic acid resins that are wastes are effective. There is an effect that it can be used.

  According to the method for producing an electron donor supplier according to claim 4, in addition to the effect exhibited by the method for producing an electron donor supplier according to claim 3, the weight average molecular weight is about 9500 in the molecular weight reduction step. Since the raw polylactic acid resin has a low molecular weight so that it is in the range of about 12000 or less, a polylactic acid resin that can maintain a solid state in a use environment can be obtained reliably. There is an effect that can be.

  Here, when a high molecular weight polylactic acid-based resin is modified to lower the molecular weight, generally, the treatment time becomes longer as the molecular weight is lowered, and the obtained polylactic acid-based resin tends to have a wider molecular weight distribution. As a result, the low molecular weight resin tends to be non-crystalline and it is difficult to maintain a solid state. However, the polylactic acid resin of the present agent has a good hydrolyzability because the weight average molecular weight is about 9500 or more even when the high molecular weight polylactic acid resin is reduced in the molecular weight reduction step. A solid state can be maintained.

  According to the method for producing an electron donor supplier according to claim 5, in addition to the effect exhibited by the method for producing an electron donor supplier according to claim 3 or 4, crystallization of a polylactic acid resin by an annealing step Since the annealing is performed so that the degree is 10% or more and 40% or less, there is an effect that it is possible to obtain polylactic acid resins having different hydrolysis rates under the same conditions even with the same molecular weight. For this reason, a group of polylactic acid resins having various hydrolysis characteristics can be produced, and an electron donor supply agent having a hydrolysis rate suitable for a specific application, that is, an electron donor supply rate is provided. it can.

  According to the environmental purification method of claim 6, the electron donor supply agent according to claim 1 or 2 or the electron donor supply agent produced by the production method according to any one of claims 3 to 5 is used. The substance to be treated using a polylactic acid resin that can be handled in a solid state while having sufficient hydrolyzability that can be a substrate for microorganisms in biological treatment. There is an effect that a specific component in the inside can be rendered harmless.

  Here, since the polylactic acid-based resin is decomposed by non-biological hydrolysis, the solid substrate-degrading bacteria do not dominate, and there is an effect that process control depending on the hydrolysis rate can be realized. In other words, since the electron donor that becomes the substrate of the microorganism is supplied by a chemical reaction, the supply rate of the electron donor can be controlled by a simple method such as adjusting the pH, and the electron donation depends on the solid substrate degrading bacteria. Compared to supplying the body, the biological treatment process can be controlled more easily.

  According to the environmental purification method of claim 7, in addition to the effect of the environmental purification method of claim 6, the substance to be treated is an aqueous liquid, the specific component is a nitrogen compound, and the electron donor supply Denitrification treatment is performed to remove nitrogen compounds in the liquid using an agent. Here, the electron donor supply agent used in the present method is the electron donor supply agent according to claim 1 or 2, or the electron donor supply produced by the production method according to any one of claims 3 to 5. Therefore, for example, denitrification treatment of wastewater is performed by solid-phase denitrification using a polylactic acid resin that is sufficiently solid and capable of serving as a substrate for microorganisms and is in a solid state as an electron donor supply source. There is an effect that it can be performed.

  According to the environmental purification method of claim 8, in addition to the effect of the environmental purification method of claim 7, the polylactic acid contained in the polylactic acid-based resin is approximately 3 w / v% in the substance to be treated. Since it is introduced so as to have a concentration, there is an effect that denitrification can be satisfactorily performed at the concentration. Furthermore, since the concentration is specified, it is possible to avoid excessive addition of the electron donor supply agent to the material to be treated, and even if the operator is unfamiliar, the concentration should be used as a guide. Therefore, there is an effect that the denitrification treatment can be performed accurately.

  According to the environmental purification method of claim 9, in addition to the effect of the environmental purification method of claim 6, the substance to be treated is soil, the specific component is a nitrogen compound, and the electron donor supply Denitrification treatment is performed to remove nitrogen compounds in the soil using an agent.

Here, the electron donor supply agent used in the present method is the electron donor supply agent according to claim 1 or 2, or the electron donor supply produced by the production method according to any one of claims 3 to 5. Therefore, for example, decontamination of contaminated soil is performed by solid-phase denitrification using polylactic acid resin, which is sufficiently solid and capable of serving as a substrate for microorganisms, in solid state as an electron donor source. There is an effect that nitrogen treatment can be performed.

  According to the environmental purification method of claim 10, in addition to the effect of the environmental purification method according to any of claims 7 to 9, a nitric acid-containing aqueous solution to which acetic acid and lactic acid are added is used. Accumulating and growing the growing microorganisms and adding the enriched microorganisms to the substance to be treated, so that denitrification should be performed well in microorganisms that detoxify nitrogen compounds using lactic acid as an electron donor in the substance to be treated. There is an effect that can be. There are various substances to be treated, but according to this method, microorganisms having the activity of detoxifying nitrogen compounds can be sufficiently present in the substances to be treated. There is an effect that the denitrification can be promoted even when the microorganism related to the substance is absent or the activity is weak.

It is the figure which showed the relationship between molecular weight and biological nitric acid removal rate. It is the figure which showed the relationship between the crystallinity degree of the polylactic acid (weight average molecular weight = about 10,000) reduced in molecular weight, and a hydrolysis rate. It is the figure which showed the denitrification speed | rate of activated sludge when polylactic acid (weight average molecular weight = about 10,000) with low molecular weight from which crystallinity differs differs was used as a substrate. It is the figure which showed the denitrification speed | rate of the activated sludge when modified polylactic acid (weight average molecular weight = about 10,000, crystallinity 40%) is used as a substrate. It is the figure which showed the nitric acid removal characteristic by the denitrifying bacteria community acclimatized by changing the carbon source.

  Hereinafter, the present invention will be described in detail.

  The electron donor supply agent of the present invention is obtained by modifying a polylactic acid-based resin in combination with a molecular weight and a crystallinity and using it as an electron donor supply source. Is something that can be done. In addition, the electron donor supply agent of the present invention can be in a solid state with sufficient hydrolyzability that can be a substrate for microorganisms in biological treatment.

  The polylactic acid resin in the electron donor supply agent produces lactic acid or a derivative of lactic acid as an electron donor mainly by non-biological hydrolysis, and such lactic acid is an energy source for denitrifying bacteria. As an electron donor, that is, a substrate.

  Here, the polylactic acid-based resin used in the present invention is a polylactic acid homopolymer (for example, poly (L-lactic acid)) or a polylactic acid derivative. The polylactic acid derivative is not particularly limited as long as it has the same degree of crystallinity and biodegradability (hydrolyzability) as polylactic acid. For example, the polylactic acid derivative may be an α carbon of a polylactic acid skeleton (—OCHCH 3 CO—). Atom or atomic group to be bonded is a combination of a hydrocarbon group such as an alkyl group, an aryl group, an allyl group, a vinyl group, a benzyl group, and a formyl group, an alkoxy group, and a derivative thereof other than a combination of a methyl group and hydrogen. The thing which was done is mentioned. In addition, examples of the atomic group include an amino group, a carbamoyl group, and an alkoxycarbonyl group. Further, among the above, those having 1 to 3 hydrocarbon groups, alkoxy groups or hydrogen atoms are preferred. More preferably, the hydrocarbon group and the alkoxy group are linear. More specifically, examples of the atomic group include a methyl group, an ethyl group, a propyl group, a vinyl group, a methoxy group, an ethoxy group, and a propoxyl group. Furthermore, these derivatives can also be used. Atoms and atomic groups that can replace hydrogen atoms of these hydrocarbon groups and alkoxy groups as derivatives include halogen atoms such as chlorine, hydroxyl groups, carboxyl groups, carbonyl groups, amino groups, carbamoyl groups, formyl groups, alkoxycarbonyl groups Etc. Examples of the atoms bonded to the α carbon include halogen atoms such as hydrogen, fluorine, chlorine, bromine and the like.

  The polylactic acid-based resin used in the present invention has molecular weight and crystallinity properties so that it can be controlled as a hydrolysis rate and act as a stable microbially active electron donor. The polylactic acid-based resin is an 11-mer or more and has a weight average molecular weight of 14,000 or less, and preferably a weight average molecular weight of approximately 9500 or more and approximately 12000 or less. .

  A polylactic acid-based resin is non-crystalline and less likely to be in a solid state when it is a 10-mer or less. For this reason, this polylactic acid-type resin needs to be an 11-mer or more. On the other hand, if the weight average molecular weight exceeds 14,000, the hydrolysis rate in an environment such as in water or soil is remarkably reduced, and the production of a substrate serving as a microbial energy source (that is, using the polylactic acid resin as a microbial substrate). It becomes practically impossible. Further, in order to ensure a solid state in the environment and to ensure appropriate hydrolyzability for performing environmental purification by biological treatment, the weight average molecular weight is about 9500 or more and about 12000 in view of solid loss. The following range is desirable.

  Here, the solid loss refers to the solid weight reduced by non-biological hydrolysis. When the weight average molecular weight is about 9500 or less, the solid loss becomes remarkably large.

  In the present invention, the weight average molecular weight is determined by standard polystyrene conversion value using gel permeation chromatography.

  In addition, since the weight average molecular weight is an average value, it is difficult to strictly define the molecular weight range of the polylactic acid resin in a solid state while having sufficient hydrolyzability. For this reason, the lower limit value and the upper limit value are approximately 9500 and approximately 12000, respectively. Specifically, the lower limit value is in the range of 8000 to 9900, and the upper limit value is in the range of 11000 to 14000.

  This polylactic acid resin has a crystallinity of 10% or more and 40% or less. As described above, the present polylactic acid-based resin is reduced in molecular weight to a hydrolyzable molecular weight, but it can be further increased in hydrolyzability linearly by increasing the crystallinity.

  In the present invention, the degree of crystallinity is expressed by the following equation (1), where ΔHcc is the enthalpy of crystallization, ΔHm is the enthalpy of melting, and ΔHm0 is the enthalpy of 100% crystallinity of the standard sample (crystal with infinite crystal thickness). It is prescribed.

Crystallinity (%) = [(ΔHm + ΔHcc) / ΔHm0)] × 100 (1)
In the case of polylactic acid, 135 (J · g−1) is used as ΔHm0. In the present invention, ΔHm0 of the polylactic acid derivative is also set to its crystallinity by using 135 (J · g−1), which is the same as that of polylactic acid. The crystallization enthalpy and the melting enthalpy are determined by DSC analysis of the polylactic acid resin to be measured.

  Here, when the degree of crystallinity is less than 10%, the hydrolysis rate becomes lower than the practical substrate supply rate, so it is desirable to be higher than that. If the degree of crystallinity is 40% or less, it can be obtained by performing a simple heat treatment on a high molecular weight polylactic acid resin produced as a general-purpose biodegradable resin by the modification method described later. For this reason, there exists an advantage that the polylactic acid-type resin used for this invention can be manufactured with a simple manufacturing method, and can be manufactured using the polylactic acid-type resin made into the waste.

  Therefore, in the present invention, the degree of crystallinity of the polylactic acid-based resin is 10% or more and 40% or less. In addition, this polylactic acid-type resin is not limited to what is produced by modifying high molecular weight polylactic acid-type resin, You may synthesize | combine and produce from a monomer.

  Thus, by defining the molecular weight range and crystallinity of the polylactic acid-based resin, it is possible to control the rate of hydrolysis, that is, the rate of liberation of electron donors such as lactic acid according to the change in physical properties. . In particular, when the molecular weight is in the range of about 9500 or more and about 12000 or less and the crystallinity is in the range of 10% or more and 40% or less, the hydrolysis rate can be controlled with higher accuracy, and the product is produced as a general-purpose product. The present polylactic acid resin can be produced by a simple technique using the polylactic acid resin.

  In addition, the polylactic acid-based resin does not impair the biodegradability of polylactic acid (hydrolyzability that can release lactic acid as a substrate at a realistic supply rate at which microorganisms can be an energy source) and is in a solid state (the above crystals It may be a copolymer containing another polymer within a range of a ratio capable of maintaining the degree of conversion. Various polymers can be used as the polymer that forms a copolymer with polylactic acid, but biodegradable polymers are preferably used. Such a biodegradable polymer is not particularly limited. Specifically, poly (3-hydroxybutyric acid), polyhydroxyvalerate, polycaprolactone, polybutylene succinate, polybutylene adipate, polyethylene succinate, polybutylene terephthalate, polyester carbonate, polyglycolic acid, polydioxanone and poly (2 -Oxetanone), starch, cellulose, chitin, chitosan, gluten, and natural rubber, polyethylene glycol, polyvinyl alcohol, polyethylene glycol and polymalic acid. These polymers may be used alone or in combination.

  Furthermore, this electron donor supply agent may be comprised only with polylactic acid-type resin, and may be comprised including additives other than polylactic acid-type resin. Examples of the additive include a pH adjuster, and examples of the pH adjuster include calcium hydroxide, calcium oxide, calcium phosphate, calcium carbonate, magnesium oxide, magnesium phosphate, and magnesium hydroxide. In addition, you may use this pH adjuster 1 type or in mixture of 2 or more types.

  Moreover, the dosage form of the electron donor supply agent of the present invention is not particularly limited, and can be powdery, granular, massive, molded, film, sheet or the like.

  As described above, according to the electron donor supply agent of the present invention, by specifying the molecular weight and crystallinity of the polylactic acid resin, sufficient hydrolyzability that can serve as a substrate for microorganisms in biological treatment. It can be made into a solid state under use environment. For example, if purification treatment of water treatment tanks, sewage tanks, rivers, lakes, soils, etc. is performed throughout the year, the temperature of the use environment naturally rises as the summer temperature rises. However, since the polylactic acid resin of this agent is designed to be in a solid state under the temperature of the usage environment, it can be used in a solid state throughout the year.

  Next, the manufacturing method of the electron donor supply agent of this invention is demonstrated. This production method is configured to produce an electron donor supply agent through a low molecular weight reduction step, a melting step, and an annealing step.

  The low molecular weight reduction step is a step of reducing the molecular weight of the raw material high molecular weight polylactic acid resin. The molecular weight of the raw polylactic acid resin is 150,000 to 300,000 in terms of weight average molecular weight. In the low molecular weight reducing step, the molecular weight of the raw polylactic acid resin is reduced by heating, pressurizing, pulverizing, or the like. Preferably, high temperature and high pressure processing is used. In the high-temperature and high-pressure treatment, the treatment conditions are set at 120 ° C. and 1.05 atm according to the molecular weight and characteristics of the raw polylactic acid resin and the desired target molecular weight, and the treatment is performed for an arbitrary time. In this low molecular weight reduction step, the lower the molecular weight of the polylactic acid resin, the higher the temperature, the higher pressure, and the longer the treatment. Further, by treating under predetermined conditions, a polylactic acid resin having a weight average molecular weight of about 9500 or more and about 12000 or less can be obtained. The low molecular weight reduction step corresponds to the low molecular weight reduction step recited in the claims.

  In this low molecular weight reduction step, the raw polylactic acid resin may be reduced to a target molecular weight by a single treatment, or may be divided into a plurality of times. Further, the treated resin may be subjected to an operation of fractionating the molecular weight to adjust the degree of dispersion of the molecular weight distribution.

  In addition, the weight average molecular weight of the polylactic acid-type resin obtained by the process by a low molecular weight reduction process is calculated | required by a standard polystyrene conversion value using a gel permeation chromatography.

  The melting step is a step of melting the polylactic acid resin whose molecular weight has been reduced in the molecular weight reduction step. In this melting step, the polylactic acid-based resin is heated and melted at a temperature equal to or higher than the melting point. In addition, although heating temperature depends on melting | fusing point of polylactic acid-type resin, this melting | fusing point may be determined by DSC measurement and may be determined based on a weight average molecular weight. The melting step corresponds to the melting step described in the claims.

  The annealing process is a process for crystallizing the polylactic acid-based resin, and heat treatment is performed by holding the melted polylactic acid-based resin at a temperature lower by 20 ° C. to 30 ° C. than the melting point for an arbitrary period of time. This is a step of cooling to room temperature. In the present invention, annealing means not holding annealing for removing residual strain but holding for a certain time for crystallization at an arbitrary temperature below the melting point. In this annealing step, the crystallinity of the polylactic acid resin can be adjusted by changing the holding time. As a result, a solid-state polylactic acid resin having an arbitrary crystallinity in the range of 10% to 40% crystallinity is generated. The annealing step corresponds to the annealing step described in the claims.

  The polylactic acid-based resin obtained through the annealing step has biodegradability suitable as an electron donor supply source in the case of performing biological treatment, and is in a solid state. For this reason, it becomes possible to comprise an electron donor supply agent only by the obtained polylactic acid-type resin. Moreover, you may comprise an electron donor supply agent by adding additives, such as a binder and a pH adjuster, to the obtained polylactic acid-type resin.

  Furthermore, after the annealing step, a molding step for molding the obtained polylactic acid resin or a mixture of the polylactic acid resin and an additive may be provided. This molding process is a process of processing the dosage form of the electron donor supply agent into a molded body. For example, a polylactic acid resin powder is formed into a tablet by press molding or the like. Thus, the handling property can be improved by processing the dosage form of the electron donor supply agent into a molded body.

  Further, before the low molecular weight reduction step, a physical step for appropriately performing pretreatment such as washing and drying of the raw polylactic acid resin may be provided.

  Thus, according to this production method, polylactic acid that is in a solid state while having good biodegradability (hydrolyzability) by a simple method using a polylactic acid resin produced as a general-purpose product. Since the molecular weight range and crystallinity of the resulting polylactic acid resin can be defined, the hydrolysis rate, that is, the rate of liberation of electron donors such as lactic acid can be controlled. A polylactic acid resin that can be produced can be produced, and by containing such a polylactic acid resin, an electron donor supply useful in biological treatment can be produced.

  Next, the environmental purification method of the present invention will be described.

  The environmental purification method of the present invention activates microorganisms using the above-described electron donor supply agent of the present invention, and detoxifies specific components by its reducing action.

  Substances to be treated are aqueous solutions, wastewater, sewage, water from lakes and rivers, and soil. When the substance to be treated is water and denitrification is performed, the electron donor supply agent of the present invention is slightly aerobic after the removal of the BOD source of water and nitrification by nitrifying bacteria. Alternatively, denitrifying bacteria are activated by removing them from the nitrogen component by introducing them into the aqueous phase under anaerobic conditions.

  Here, the concentration of polylactic acid resin in water is preferably within a range where the contained polylactic acid is 1 w / v% to 5 w / v% as a range where nitric acid removal can be achieved practically and effectively. Is approximately 3 w / v%.

  In particular, an electron donor supplier formed of polylactic acid having a weight average molecular weight in the range of about 9500 to about 12000 and having a crystallinity of 40% is optimal for nitrogen removal, and the addition concentration is about 3 w / By setting it as v%, the maximum denitrification efficiency can be obtained.

  The denitrifying bacteria active in such an environment are mainly denitrifying bacterial species (Comamonas spp., Alcaligenes spp., Etc.) belonging to the beta-proteobacterectidae Comamonadaceae and Alcaligenaceae Alcaligenaceae.

  Further, when the material to be treated is soil, the denitrifying bacteria can be activated and the nitrogen component can be removed by pouring or embedding the electron donor supply agent of the present invention into the soil.

  Here, since the polylactic acid-based resin is not dominated by solid substrate-degrading bacteria and is decomposed by non-biological hydrolysis, the pH of the substance to be treated is adjusted as necessary to supply the electron donor. The speed may be adjusted. For this reason, as the environmental purification method using a solid substrate of poly (3-hydroxybutyric acid) or polycaprolactone is superior in biodegradability, the degradation of the polymer depends on the abundance of decomposing microorganisms, and it is removed. There is no difficulty in controlling the nitrogen rate.

  Moreover, under anaerobic conditions, the electron donor supply agent of the present invention can be used as an energy source to activate microorganisms that detoxify organochlorine compounds. Here, the decomposition of the organic chlorine compound by biological treatment proceeds at a very low rate compared to the decomposition of other organic compounds. However, since the electron donor supply agent of the present invention can control the release rate of the electron donor, the microorganism that contributes to the detoxification of the organochlorine compound can change the electron donor according to the rate at which the electron donor is consumed. It can be supplied and the microbial activity of the microorganism can be stably maintained.

  Further, in the environmental purification method of the present invention, a nitric acid-containing aqueous solution to which acetic acid and lactic acid are added is used, and microorganisms that grow in the aqueous solution are accumulated in advance, and the accumulated cultured microorganisms are added to the substance to be treated. It may be.

  In the solid-phase denitrification process using polylactic acid resin as an electron donor source, not only free lactic acid but also its metabolite acetic acid acts as a substrate, so the above-mentioned enrichment culture has affinity for lactic acid and acetic acid. An accumulation culture microorganism in which denitrification microorganisms are accumulated can be obtained. And the said solid-phase denitrification process can be efficiently moved from the first by adding this accumulation | cultivation microorganism.

  Denitrification is a reductive process and requires an electron donor. Therefore, how to secure and control an electron donor that can be easily used by microorganisms is the key to achieving efficient and stable denitrification, but the environmental purification method of the present invention is good. An electron donor supplier formed using a polylactic acid resin that can control the rate of decomposition, that is, the rate of liberation of electron donors such as lactic acid, while having excellent hydrolyzability. Stable denitrification, that is, environmental purification can be achieved.

  Hereinafter, the present invention will be described in detail based on examples. The present invention is not limited to these examples as long as the gist thereof is not exceeded. The measured values shown in the examples were calculated by measuring under the following conditions.

(Measurement of weight average molecular weight)
Using gel permeation chromatography, measurement was performed under the following conditions, and the weight average molecular weight was calculated in terms of standard polystyrene.

Model: Product name HLC8020GPC (manufactured by Tosoh Corporation)
Solvent: Chloroform sample dissolution conditions: 60 ° C., 2 hours temperature: 40 ° C.
Measurement concentration: 50 mg / 50 mL
Injection volume: 100 μL
Column: Two trade names TSKgelGMHHR-H (manufactured by Tosoh Corporation) The column elution volume was calibrated by the universal calibration method using standard polystyrene (manufactured by Tosoh Corporation).

(Measurement of crystallinity)
Melting enthalpy and crystallization enthalpy were measured using a differential scanning calorimeter (manufactured by Shimadzu Corporation, trade name DSC50). 3 mg of the sample was placed in an aluminum pan and measured at a temperature elevation rate of 10 ° C./min. Using the calculated melting enthalpy and crystallization enthalpy, the degree of crystallinity was calculated based on the above formula (1).

(Measurement of nitrate concentration)
Using ion chromatography, the nitrate ion concentration was measured under the following conditions.

Model: Conductivity detector (manufactured by Hitachi High-Technologies Corporation, trade name L7470), pump (manufactured by Hitachi High-Technologies Corporation, trade name L-7110), oven (made by Hitachi High-Technologies Corporation, trade name L7300)
Detector: Trade name Solvent: 2.3M Phthalic acid 2.5M Tris aqueous solution Flow rate: 1.5mL / ml
Temperature: 40 ° C
Injection volume: 100 μL
Column: Trade name # 2720 (manufactured by Hitachi High-Technologies Corporation)

(Measurement of free lactic acid)
Using high performance liquid chromatography (HPLC), the free lactic acid concentration was measured under the following conditions.

Model: Diode array detector (manufactured by Hitachi High-Technologies Corporation, product name L7455), pump (manufactured by Hitachi High-Technologies Corporation, product name L-7100), oven (manufactured by Hitachi High-Technologies Corporation, product name L7300)
Solvent: 0.1% H3PO4 aqueous solution Flow rate: 1.0 mL / ml
Temperature: 40 ° C
Injection volume: 100 μL
Column: Brand name Organic Acid (manufactured by Waters)

Example 1
In Example 1, in order to evaluate the effectiveness of the electron donor supply agent according to the present embodiment, the influence of the change in the weight average molecular weight of the polylactic acid-based resin modified and reduced in molecular weight on the denitrification rate was examined. Tested.

  Polylactic acid (weight average molecular weight 193300) was used as a raw material polylactic acid-based resin, and was subjected to a modification treatment in an autoclave under the conditions shown in Table 1 to reduce the molecular weight.

  The weight average molecular weight of polylactic acid reduced in molecular weight (lower molecular weight reduced polylactic acid) was measured under the above-described conditions using gel permeation chromatography. Table 1 shows the weight average molecular weights of the obtained low molecular weight polylactic acids in the right column in correspondence with the heating temperature and the heating time. The crystallinity of each low molecular weight polylactic acid was 45%.

  Next, a denitrification test using activated sludge was performed under anaerobic conditions using each low molecular weight polylactic acid as a substrate.

  Specifically, as a denitrification test using activated sludge, 100 ml artificial wastewater (0.2% KNO3, 0.2% NH4Cl, 0.7% KH2PO4, 0.85% K2PO4, 0.02% in a 125 ml vial) NaCl, 0.02% MgCl 2 .6H 2 O, 0.045% CaCl 2 .2H 2 O and 0.1% SL 8 solution) were added. At this time, the SL8 solution means 0.5% EDTA · 2Na, 0.1% FeCl2 · 4H2O, 0.03% HBO3, 0.01% CoCl2, 0.005% ZnCl2, 0.003% MnCl2 · 4H2O, It is a solution containing 0.003% NaMoO4 · 2H2O, 0.03% NiSO4 · 6H2O and 0.001% CuCl2 · 2H2O. Furthermore, activated sludge was adjusted and added to these vials so that it might become 2000 mg / ml. The denitrification test was performed three times for each low molecular weight polylactic acid, and the average value and standard deviation of the nitric acid removal rate were calculated. In addition, 1 g of each low molecular weight polylactic acid pellet was added to each vial. All these vial tests were conducted under the conditions of 25 ° C. and a stirring speed of 120 rpm / min.

  Denitrification activity was followed and evaluated by measuring the decrease in added nitrate under the conditions described above using ion chromatography. The results are shown in FIG.

  FIG. 1 is a graph showing the relationship between the weight average molecular weight of the low molecular weight polylactic acid and the biological nitric acid removal rate, wherein the horizontal axis represents the molecular weight and the vertical axis represents the nitric acid removal rate. As can be seen from FIG. 1, when the weight average molecular weight exceeds 14,000, the nitric acid removal rate decreases to near 0 (mg / g / h). That is, it is shown that when the weight average molecular weight exceeds 14,000, the denitrification rate is extremely reduced. In addition, when the weight average molecular weight is approximately 12000 (those with a weight average molecular weight of 11500, a black circle indicated by a in FIG. 1) or less, the nitric acid removal rate exceeds 1 (mg / g / h). It has been shown that sufficient nitric acid removal rates can be obtained.

  On the other hand, among the obtained low molecular weight polylactic acid, the weight average molecular weight was about 10,000 (thickness average molecular weight 9900, black circle shown by b in FIG. 1) was in a solid state, but the weight average molecular weight below that was An approximately 8000 (weight average molecular weight 7900, black circle shown in FIG. 1) was liquefied.

  From the above results, considering the solid loss, it was shown that the range of the weight average molecular weight of about 9500 or more and about 12000 or less is a molecular weight range in which good denitrification can be performed.

(Example 2)
In Example 2, in order to evaluate the effectiveness of the electron donor supply according to the present embodiment, the change in crystallinity of the modified low molecular weight polylactic acid-based resin depends on the hydrolysis rate and the denitrification rate. This is a test of the effect.

  After melting low molecular weight polylactic acid having a weight average molecular weight of approximately 10,000 (weight average molecular weight 9900) at 120 ° C., the crystallinity is about 10%, 20%, 30%, 40% under the conditions shown in Table 2. It changed so that it might become. The crystallinity of the low molecular weight polylactic acid after the treatment under each condition is shown in the rightmost column of Table 2 in association with each condition.

  Thereafter, 100 ml of artificial waste water similar to Example 1 and 1 g of PLA with adjusted crystallinity were added to a 125 ml vial, and the hydrolysis rate in water was evaluated by HPLC measurement of the amount of free lactic acid. The result is shown in FIG. FIG. 2 is a graph showing the relationship between the degree of crystallinity of a low molecular weight polylactic acid (weight average molecular weight = approximately 10,000) and the hydrolysis rate, with the crystallinity on the horizontal axis and the rate of lactic acid release on the vertical axis. Has been. As shown in FIG. 2, the amount of lactic acid liberated (rate) increased linearly as the crystallinity increased.

  Moreover, the denitrification test by the activated sludge similar to Example 1 was done by using these low molecular weight polylactic acids having different crystallinity as a substrate. The denitrification activity was evaluated in the same manner as in Example 1 by following the decrease in nitrate added by ion chromatography. The result is shown in FIG. FIG. 3 is a graph showing the denitrification rate of activated sludge when low molecular weight polylactic acid (weight average molecular weight = approximately 10,000) having a different crystallinity is used as a substrate. Shows the denitrification rate. As shown in FIG. 3, the denitrification rate was higher as the low molecular weight polylactic acid having a higher crystallinity was used as the substrate. Further, a correlation was observed in which the denitrification rate increased linearly in proportion to the crystallinity.

  As described above, both the molecular weight and crystallinity parameters can be controlled by the method for producing an electron donor supply according to the present invention, and the electron donor supply rate and the denitrification rate can be controlled by the electron donor supply according to the present invention. It was shown that can be controlled.

(Example 3)
Example 3 tests the influence which the density | concentration added to a to-be-processed substance has on the denitrification rate about the electron donor supply agent which concerns on this embodiment. The same denitrification test using activated sludge as in Example 1 was performed using low molecular weight polylactic acid (weight average molecular weight = approximately 10,000, crystallinity 40%) as a substrate. The result is shown in FIG.

  FIG. 4 is a graph showing the denitrification rate of activated sludge when modified polylactic acid (weight average molecular weight = approximately 10000, crystallinity 40%) is used as a substrate. The concentration of molecular weight polylactic acid and the denitrification rate are shown on the vertical axis. As can be seen from FIG. 4, the denitrification rate reached a maximum when the low molecular weight polylactic acid concentration was 3 w / v%. The polylactic acid concentration was within 5 w / v%, and the pH in water was kept appropriate (pH 5.0 or higher).

Example 4
In Example 4, in order to evaluate the effectiveness of the environmental purification method using the electron donor supply agent according to the present embodiment, an enrichment culture microorganism that is enriched and cultured in advance with a different carbon source is added to the substance to be treated. The effect of NO on the denitrification rate was tested.

  Sewage activated sludge is collected and peptone (5 gL-1), 10 mM glucose, 10 mM lactate, 10 mM acetate, or 5 mM acetate + 5 mM lactate is the only energy carbon source in an inorganic medium (pH 7.0) containing 20 mM potassium nitrate. As a result, denitrification culture (25 ° C., stationary culture) was carried out using five different media added. Every 23 days, half of the culture solution was taken out and taken up in a fresh medium, and the culture was continued. This batch culture operation was continued for one month and used to examine the nitrate removal characteristics in a medium containing 3% polylactic acid (PLA). The results are shown in FIG.

  FIG. 5 is a diagram showing the nitrate removal characteristics of the denitrifying bacteria community acclimatized by changing the carbon source, with the horizontal axis representing time and the vertical axis representing the remaining amount of nitrate. In FIG. 5, black squares with peptone as the energy carbon source, white squares with glucose as the energy carbon source, black triangles with lactate as the energy carbon source, and acetate The energy carbon source is indicated by a black circle, and the acetate + lactate energy carbon source is indicated by a white circle. As shown in FIG. 5, the fastest removal activity was observed for sludge conditioned with acetic acid + lactic acid.

Claims (10)

In an electron donor supply agent used for biological treatment by a microorganism and supplying an electron donor to the microorganism,
An electron donor supply agent comprising a polylactic acid resin having a weight average molecular weight of about 12000 or less, a crystallinity of 10% or more and 40% or less and being in a solid state at the temperature of the use environment.   The electron donor supply agent according to claim 1, wherein the polylactic acid-based resin has a weight average molecular weight of about 9500 or more. In a method for producing an electron donor supply agent used for biological treatment by a microorganism and supplying an electron donor to the microorganism,
A low molecular weight reducing step for reducing the molecular weight of the raw polylactic acid resin;
A melting step of melting the polylactic acid resin whose molecular weight has been reduced in the low molecular weight step at a temperature equal to or higher than its melting point;
An annealing step of annealing the polylactic acid resin melted by the melting step at a temperature lower than the melting point;
A method for producing an electron donor supply, comprising producing an electron donor supply using a polylactic acid resin crystallized in a solid state by the annealing step.   The low molecular weight step is a step of reducing the molecular weight of the raw polylactic acid resin so that the weight average molecular weight is in the range of about 9500 or more and about 12000 or less. A method for producing an electron donor supply agent.   5. The electron donor according to claim 3, wherein the annealing step is performed such that the crystallinity of the polylactic acid-based resin is 10% or more and 40% or less. A method for producing a supply agent. In an environmental purification method for detoxifying a specific component in a material to be treated by biological treatment,
Characterized by performing a biological process using an electron donor supplying agent produced by the production method according to any one of 5 the electron donor supply agent or claim 3 according to claim 1 young properly 2 Environmental purification method. The substance to be treated is an aqueous liquid,
The specific component is a nitrogen compound,
The environmental purification method according to claim 6, wherein a denitrification treatment for removing nitrogen compounds in the liquid is performed using the electron donor supply agent.   The environmental purification method according to claim 7, wherein the polylactic acid contained in the polylactic acid-based resin is added so as to have a concentration of about 3 w / v% in the material to be treated. The substance to be treated is soil,
The specific component is a nitrogen compound,
The environmental purification method according to claim 6, wherein a denitrification treatment is performed to remove nitrogen compounds in soil using the electron donor supply agent. The nitric acid-containing aqueous solution to which acetic acid and lactic acid are added is used to accumulate and culture microorganisms that grow in the aqueous solution, and the enriched cultured microorganisms are added to the substance to be treated. The environmental purification method according to any one of the above .

Images