Carbonization combustion material and method for producing the same

Abstract

To provide a novel biomass-derived combustion material that utilizes micro-plastics in an environment.SOLUTION: The carbonized combustion material of an aspect of the present invention comprises carbide of micro-plastics and carbide of algae adsorbing the micro-plastics.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a carbonization combustion material and a method for producing the same. [Background technology]

[0002] Biomass is organic matter derived from plants and animals that can be used as energy, such as fuel. Examples include wood, dried vegetation, agricultural waste, livestock waste, and sewage sludge. In recent years, methods for using these as energy sources have been explored as an alternative to finite resources such as petroleum. Patent Document 1 discloses a method for producing algal oil using biomass resources.

[0003] On the other hand, in recent years, the environmental impact of microplastics, which are generated when plastics break down, has become a problem. It is said that microplastics enter the human body through the food chain and various other routes, and gradually accumulate. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-041681 [Non-patent literature]

[0005] [Non-Patent Document 1] Convertec, July 2020 issue, pages 2-5 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention aims to provide a novel biomass-derived combustion material that utilizes microplastics from the environment. [Means for solving the problem]

[0007] As a result of diligent research into the aforementioned problems, the inventors of this invention have completed the present invention.

[0008] In other words, according to a first aspect of the present invention, a carbonization combustion material is provided that includes a char of microplastics and a char of algae that have adsorbed the microplastics.

[0009] A second aspect of the present invention provides a method for producing a carbonized combustion material, which includes a carbonization step of carbonizing a material to be carbonized, including algae that have adsorbed microplastics.

[0010] In the first embodiment described above, the microplastics may be microplastics that have been adsorbed and recovered by the algae from the treated water containing the microplastics.

[0011] In the first and second embodiments described above, the algae may be freshwater algae.

[0012] In the first and second embodiments described above, the algae may be characterized in that they secrete an adhesive substance, and the amount of adhesive substance secreted by the algae is such that the volume of the adhesive substance secreted outside the cell is 0.25 times or more and 100 times or less compared to the cell volume.

[0013] In the first and second embodiments described above, the adhesive substance may be a polysaccharide.

[0014] In the first and second embodiments described above, the algae may be at least one selected from diatoms, dinoflagellates, chlorarachnion algae, green algae, red algae, conjugating algae, Euglena algae, and cyanobacteria.

[0015] In the first embodiment described above, the sum of the content of the microplastics and the algae, based on the anhydrous weight before carbonization, may be 20 to 80 wt%.

[0016] In the first embodiment described above, cellulose carbides may be further included.

[0017] In the first aspect, the shape of the carbonized combustion material may be pellet-shaped.

[0018] In the second aspect, as a pre-step of the carbonization step, an adsorption step of allowing algae having the ability to adsorb and recover microplastics to exist in the treated water containing microplastics may be further included.

[0019] In the second aspect, the temperature in the carbonization step may be 200 to 400 °C.

[0020] In the second aspect, as a post-step of the carbonization step, a forming step of compression-molding the carbonized combustion material may be further included.

Advantages of the Invention

[0021] According to the present invention, there is provided a novel biomass-derived combustion material that is useful for household power generation and coal-fired power generation, etc., and utilizes microplastics in the environment.

Brief Description of the Drawings

[0022] [Figure 1] FIG. 1 is a diagram showing the measurement procedure of the amount of the adhesive substance secreted by algae. [Figure 2] FIG. 2 is a magnified photograph of various algae used in the examples. [Figure 3] FIG. 3 is a diagram (photograph) showing the state where precipitates were confirmed after adsorption of microplastics in the examples. [Figure 4] FIG. 4 is a diagram showing the respective components contained in the carbonized samples, the filtration residue before carbonization, and the mixture in terms of the water content standard. [Figure 5] FIG. 5 is a diagram showing the respective components contained in the carbonized samples, the filtration residue before carbonization, and the mixture in terms of the anhydrous standard.

Modes for Carrying Out the Invention

[0023] The present invention will be described in detail below. The method for producing the carbonized combustion material according to this embodiment will be described below, followed by a description of the carbonized combustion material obtained by the above production method according to this embodiment.

[0024] ≪Method for manufacturing carbonized combustion materials≫ The method for producing the carbonized combustion material according to this embodiment includes a carbonization step of carbonizing a material to be carbonized (a composition for carbonized combustion material) that contains algae adsorbing microplastics.

[0025] <Microplastics> The material to be carbided according to this embodiment includes microplastics. "Microplastics" refers to plastic particles with a maximum length of 0.1 μm or more and 5000 μm or less. However, the plastic present (or potentially present) in the material to be carbided according to this embodiment may include not only microplastics, but also plastic particles smaller than 0.1 μm or larger than 5000 μm. Furthermore, in reality, the majority of microplastics (for example, 80% or more, 90% or more, and 95% or more of the total number of particles) are, for example, 0.1 μm or larger, 0.5 μm or larger, 1 μm or larger, 2 μm or larger, 3 μm or larger, 4 μm or larger, 5 μm or larger, 6 μm or larger, 7 μm or larger, 10 μm or larger, 50 μm or larger, 100 μm or larger, 500 μm or larger, 1000 μm or larger, 2500 μm or larger; 2500 μm or smaller, 1000 μm or smaller, 500 μm or smaller, 100 μm or smaller, 50 μm or smaller, 10 μm or smaller, 9 μm or smaller, 8 μm or smaller, 7 μm or smaller, 6 μm or smaller, 5 μm or smaller, 4 μm or smaller, and 3 μm or smaller (maximum length portion). As is well known, microplastics include primary microplastics (plastics manufactured at a micro size: for example, used in facial cleansers, fabric softeners, and slow-release fertilizer capsules) and secondary microplastics (larger plastics that have been broken down into micro-size particles in the natural environment).

[0026] <Algae> The material to be carbonized according to this embodiment includes algae. The algae according to this embodiment have the ability to adsorb and recover microplastics. "Algae having the ability to adsorb and recover microplastics" refers to algae that can reduce the microplastic concentration in the treated water by a predetermined amount (for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%) or more compared to the microplastic concentration in the treated water when the algae are not present (the treated water will be described later). Here, examples of algae that secrete sticky substances include diatoms and brown algae belonging to the stramenopiles, dinoflagellates belonging to the alveolata, chlorarachnion algae belonging to the rhizaria, green algae and red algae belonging to the archaeoplastida, conjugating algae, Euglena algae belonging to the excavata, and cyanobacteria belonging to the bacteria. Algae are known to release various viscous substances extracellularly, and the viscous substances that algae can secrete according to this embodiment are typically polysaccharides, such as agarose and porphyran in red algae such as Gelidium and conjugating algae, and alginic acid and fucose-containing polysaccharides in brown algae such as Laminaria. Incidentally, among the many types of diatoms, Skeletonma tropicum is particularly suitable. Furthermore, cyanobacteria and green algae are suitable because they have excellent growth rates. In addition, Euglena is suitable because it has flagella and can actively adsorb microplastics.

[0027] Other types of algae include those with physical structures that capture microplastics (e.g., porous structures, uneven structures) (e.g., brown algae); and algae that are charged with the opposite charge to microplastics. For example, microalgae vary in shape and size, but some are porous algae with a large surface area, and others form filamentous colonies. These structures also have the function of trapping microplastics. Unlike algae with sticky substances, these types of algae are less susceptible to structural changes due to environmental changes, and are therefore superior in that they can stably retain the captured microplastics.

[0028] For removing microplastics, one type of algae selected from the above-mentioned types may be used, or a combination of two or more specific types of algae may be used. For example, by combining diatoms with algae that grow faster than those diatoms (e.g., cyanobacteria, green algae), a sufficient microplastic adsorption effect can be obtained even in the early stages of cultivation. Furthermore, by combining diatoms with algae larger in size (for example, dinoflagellates and brown algae), it is possible to obtain sufficient adsorption effects for larger microplastics that are difficult to adsorb by diatoms alone.

[0029] The size of the algae according to this embodiment is not particularly limited. However, given that the size of the adsorbed microplastics is between 0.1 μm and 5000 μm, it is preferable that the size be 5000 μm or larger (for example, the size of the connected or clustered algae in the case of algae in groups or clusters). However, the size of the algae may be made to depend on the size of the microplastics present in the treated water. In this case, the expected sizes of the algae are, for example, 0.1 μm or larger, 1 μm or larger, 2 μm or larger, 5 μm or larger, 10 μm or larger, 50 μm or larger, 1000 μm or larger, 500 μm or larger, 1000 μm or larger, 2500 μm or larger, 5000 μm or smaller, 2500 μm or smaller, 100 μm or smaller, 500 μm or smaller, 250 μm or smaller, 100 μm or smaller, 50 μm or smaller, 25 μm or smaller, 20 μm or smaller, 10 μm or smaller, 5 μm or smaller, and 1 μm or smaller. Here, "size" refers to the largest diameter portion (for example, the longest diameter portion in the case of rod-shaped algae). Although algae of various sizes exist in the system, "size" here refers to the average size of 100 randomly selected algae.

[0030] In this embodiment, the amount of adhesive substance secreted by the algae is preferably such that the volume of the adhesive substance secreted outside the cell is between 0.25 and 100 times the cell volume. Within this range, it is possible to provide a means for stably recovering microplastics over a long period of time. The method for measuring the volume of the adhesive substance is as follows: Add 10 μL of microalgae culture solution to a glass slide. Add 10 μL of India ink diluted 5 times, mix the India ink and microalgae culture solution thoroughly, cover with a coverslip, and measure the cell volume of the microalgae and the volume of the extracellular mucilage under microscopic conditions. Following the method of Kishimoto et al. {Kishimoto N., Ichise S., Suzuki K., Yamamoto C.: Analysis of long-term variation in phytoplankton biovolume in the northern basin of Lake Biwa. Limnology 14: 117-128(2013)}, each alga was approximated by an elliptical cylinder, ellipse, rectangular prism, or a combination thereof, and the cell volume was calculated. For the extracellular mucilage volume, the volume including the portion not stained with India ink was calculated, and the extracellular mucilage volume was determined by dividing this by the cell volume. Figure 1 shows the above procedure. In addition, although algae of various sizes exist in the system, the "quantity" referred to here is the average value of the volumes of 100 randomly obtained algae.

[0031] The cell growth rate of the algae used for microplastic removal is preferably 250% or more, more preferably 300% or more, and even more preferably 400% or more. Because the cell growth rate of the algae is within the above range, adhesive substances are secreted rapidly after culturing, allowing the microplastic adsorption effect to be exerted early after culturing. Here, the cell growth rate is calculated according to the following conditions and formula. <Culture conditions> Algae were cultured in 200 ml of culture medium (f / 2, however, sodium nitrate was changed to 750 mg / L, which is 10 times the normal concentration). Table 1 shows the components of culture medium (f / 2). Table 2 shows the components of f / 2 metals contained in culture medium (f / 2).

[0032] [Table 1]

[0033] [Table 2]

[0034] (Cell growth rate) Each algae is cultured using the culture medium described above. The cell count before culture is, for example, 5,000 to 20,000 cells / ml, and typically 10,000 cells / ml. The absorbance at a wavelength of 490 nm is measured using a UV-Vis spectrophotometer 6 hours and 3 days after the start of culture, respectively. The cell growth rate is calculated according to the following formula. Cell growth rate = (absorbance measured after 3 days) / (absorbance measured after 6 hours) × 100 Table 3 shows the cell growth rates obtained for eight types of algae.

[0035] [Table 3]

[0036] The habitat for the algae according to this embodiment can be seawater, freshwater, brackish water, etc., and is not particularly limited, but those that can live in freshwater are preferred. Algae grown in freshwater have a low content of impurities such as chlorine, so harmful gases are less likely to be generated during the carbonization process. As long as the algae can grow in freshwater, their original habitat is not particularly limited, but freshwater algae are preferred because they have good growth efficiency. Examples of freshwater algae include diatoms, green algae, brown algae, dinoflagellates, conjugating algae, and Euglena algae. Furthermore, the algae according to this embodiment may be an algal composition. Specifically, it may be a group of the same or different species of algae.

[0037] The algae according to this embodiment may be algae immediately after being collected from water, or algae that have been dried after collection. Known methods can be used to dry the algae. Examples of methods for drying algae include air drying, filtration, centrifugation, freeze-drying, and spray drying.

[0038] In this embodiment, the lower limit of the sum of the content of algae and microplastics in the carbonized material is preferably 20 wt% or more, more preferably 30 wt% or more, and even more preferably 40 wt% or more, based on the anhydrous weight before carbonization. On the other hand, the upper limit of the sum of the content of algae and microplastics in the carbonized material in this embodiment is preferably 80 wt% or less, more preferably 70 wt% or less, and even more preferably 60 wt% or less. By setting the lower limit of the sum of the respective content rates of algae and microplastics in the material to be carbonized to the above value, a carbonization combustion material that makes full use of algae and microplastics can be obtained. Furthermore, by setting the upper limit of the sum of the respective content rates of algae and microplastics in the material to be carbonized to the above value, a carbonization combustion material can be obtained while suppressing the amount of algae and microplastics used. The algae content in the material to be carbonized is preferably 20 to 80 wt%, and more preferably 30 to 60 wt%, based on the anhydrous weight before carbonization.

[0039] The ratio of algae content to microplastic content in the carbonized material according to this embodiment depends on the amount of microplastic recovered by algae, but is typically 0.001:1 to 0.5:1.

[0040] <Other carbide materials> Components that may be included in the material to be carbonized according to this embodiment include cellulose, which serves as a carbon source for the carbonization combustion material. Examples of materials containing cellulose include woody materials, agricultural waste, livestock waste, and sewage sludge, with wood chips and bamboo chips, which have a stable supply, being more preferable. Specific examples of woody materials and agricultural waste containing cellulose include bark, sawdust, wood powder (also called sawdust), thinned wood, and rice straw discharged during lumbering. While algae contain a large amount of hydrocarbons, they can also contain moisture. Therefore, in order to ensure a smooth carbonization process, it is preferable to reduce the moisture content of the material to be carbonized using a water-absorbing or moisture-retaining material such as sawdust. The moisture content of the material to be carbonized is preferably 40-70 wt%, and more preferably 50-60 wt%. When the moisture content of the material to be carbonized is within this range, spillage is less likely to occur, and the carbonization process can proceed smoothly.

[0041] Components that may be included in the material to be carbonized according to this embodiment include hemicellulose and lignin, which serve as carbon sources for the carbonization combustion material. Each of the cellulose-containing materials described above also contains hemicellulose and lignin.

[0042] Materials that may be included in the carbide material according to this embodiment include plastics that do not fall within the size range of the microplastics described above. Plastic carbides, like the microplastic carbides described later, contain a large amount of fixed carbon. Therefore, carbonization combustion materials containing plastic carbides have a high calorific value. Plastic waste, for example, can be used as the plastic.

[0043] <Carbonization process> The carbonization of the material to be carbonized can be carried out using known methods. One example of a carbonization method is to place the material to be carbonized in a furnace capable of achieving an oxygen-free or low-oxygen state and heat it in an oxygen-free or low-oxygen state for a certain period of time. The carbonization according to this embodiment may be high-temperature carbonization (furnace temperature during heating is, for example, 600 to 800°C) or low-temperature carbonization (furnace temperature during heating is, for example, 200 to 400°C), but low-temperature carbonization is preferred because it reduces the generation of harmful gases. Specifically, the furnace temperature during heating is preferably 200 to 400°C, and more preferably 250 to 400°C. The heating time can be set arbitrarily, depending on the material to be carbonized and the target moisture content. The heating time can be, for example, 10 minutes or more, 20 minutes or more, 30 minutes or more, 1 hour or more, or 3 hours or more.

[0044] The algae and other materials contained in the carbonized material according to this embodiment may contain volatile organic compounds (VOCs). In the case of short-time low-temperature carbonization (also called partial carbonization), volatile organic compounds with boiling points above the furnace temperature remain in the carbonized material, thus improving the energy yield (ratio of fuel energy to raw materials and input energy). On the other hand, the volatile organic compounds (also called combustion gases) that volatilize during carbonization can be recovered separately and used as a liquid combustion material.

[0045] <Adsorption process> The method for producing a carbonized combustion material according to this embodiment may further include an adsorption step, as a pre-step to the carbonization step, in which algae having the ability to adsorb and recover microplastics are placed in the water to be treated that contains microplastics. At this time, it is preferable to appropriately supply air to the water to be treated. This increases the amount of sticky substance secreted from the algae cultivated in the water to be treated, and consequently increases the amount of microplastics adsorbed and recovered by the algae. In other words, the method for producing a carbonized combustion material according to this embodiment allows for the recovery of microplastics from the environment, and the recovered microplastics and the algae used can be reused as a carbonized combustion material.

[0046] "Water to be treated" is not particularly limited and refers to water that contains or may contain microplastics, such as seawater, freshwater, or brackish water. Specific examples of water to be treated include industrial water, industrial wastewater, treated sewage water, domestic wastewater, and agricultural wastewater. More specific examples include wastewater from waste treatment plants and wastewater from power plants. As described above, the algae in this embodiment are preferably freshwater algae, and the water to be treated is preferably freshwater.

[0047] The optimal algal concentration within the system varies depending on factors such as microplastic concentration, microplastic size, and the type of algae used.

[0048] The optimal adsorption time within the system varies depending on the microplastic concentration, microplastic size, type of algae used, and the target microplastic concentration to be reduced. These conditions can be determined, for example, by performing the model experiments described in the examples. The adsorbed algae can be recovered using a filter or similar device installed within the system.

[0049] In the embodiments described above, microplastics are removed from the treated water by algae, but the compounds that can be taken up by the algal cells are not limited to those that can be removed from the treated water. For example, it is possible to remove heavy metals such as cadmium, cobalt, nickel, copper, zinc, and manganese, radioactive substances such as radioactive cesium, radioactive strontium, and radioactive iodine, phosphorus compounds such as reduced phosphorus compounds and phosphate ester compounds, and nitrogen compounds such as ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen from the treated water to perform water treatment (water purification).

[0050] <Forming process> The manufacturing method of the carbonized combustion material according to this embodiment may further include a molding step of compression-molding the carbonized combustion material as a post-process of the carbonization step. Any known method can be used for molding. For example, a pellet molding machine can be used as the molding method. The pellet-shaped carbonized combustion material according to this embodiment is, for example, generally cylindrical, with a diameter D of 3 to 20 mm, a length L of 3 to 50 mm, and a bulk density BD of 500 to 900 kg / m 3 It can be. The pellet-shaped carbonized combustion material according to this embodiment has a diameter (D: 6 ± 1 mm or 8 ± 1 mm), a length (3.15 mm < L ≤ 40 mm), and a bulk density (650 kg / m 3 ≤ BD ≤ 750 kg / m 3 ) preferably in accordance with the quality standards of wood pellets specified by the Japan Wood Pellet Association. When the carbonized combustion material is within such a range, it can be used in general pellet combustion equipment such as pellet stoves and industrial boilers.

[0051] ≪Carbonized Combustion Material≫ The carbonized combustion material according to this embodiment is a carbonized combustion material containing carbide of microplastics and carbide of algae that has adsorbed the microplastics. The microplastics and algae in the carbonized combustion material according to this embodiment are as described above. The carbonized combustion material according to this embodiment can be obtained by the manufacturing method described above.

[0052] The water content of the carbonized combustion material according to this embodiment is preferably 30 wt% or less, more preferably 20 wt% or less, and even more preferably 10 wt% or less. When the water content is within such a range, a large amount of energy can be obtained when the carbonized combustion material is burned.

[0053] The carbonized combustion material according to this embodiment reduces moisture and volatile organic matter through carbonization, and the proportion of fixed carbon may be, for example, 10 wt% or more, 20 wt% or more, 30 wt% or more, 40 wt% or more, 50 wt% or more, or 60 wt% or more on an anhydrous basis. The fixed carbon content in the carbonized combustion material can be measured, for example, in accordance with JIS M 8812:2004. The carbonized combustion material according to this embodiment includes carbonized microplastics and carbonized algae that have adsorbed the microplastics. When microplastics are carbonized, carbonized material mainly composed of hydrocarbons, carbon monoxide, hydrogen, and other gases and fixed carbon is produced. As mentioned above, algae contain a large amount of hydrocarbons and may also contain moisture and volatile organic matter. When algae are carbonized, moisture and some volatile organic matter volatilize, carbonized material is produced, and the remaining volatile organic matter remains. The proportion of fixed carbon in the carbonized material after carbonization is preferably 40 wt% or more on an anhydrous basis. Carbonized combustion materials with this proportion of fixed carbon possess high calorific value. Such carbonized combustion materials utilizing biomass resources can be used as a substitute for fossil fuels such as gasoline.

[0054] The carbonized combustion material according to this embodiment has a calorific value of 10 to 20 megaJ / kg on an anhydrous basis, which is equivalent to that of conventional wood carbonized pellets. The calorific value of the carbonized combustion material can be measured, for example, in accordance with JIS M 8814:2003. The carbonized combustion material according to this embodiment can be used, for example, in household power generation such as small household generators and charcoal stoves, or in coal-fired power generation using large boilers.

[0055] The shape of the carbonized combustion material according to this embodiment may be pellet-shaped. Since the pellet-shaped carbonized combustion material is compacted and has high combustion efficiency per unit volume, it has excellent transport efficiency.

[0056] Furthermore, the carbonized combustion material according to this embodiment can also be used as a soil conditioner. The carbonized combustion material having pores can improve the water permeability and aeration of the soil. It can also adjust the acidity of the soil to a desired pH.

[0057] The embodiments of the present invention have been described above, but these are merely examples, and various other configurations can also be adopted. [Examples]

[0058] <Cultivation of algae> The algae used in the experiment (see Table 4) were cultured in 1 L scale. Turbidity was measured and recorded using a turbidimeter (CO8000 Biowave). For example, for algae of the genus Skeletonema or those approximately 5-10 μm in size, 7000 cells / ml was used as a guideline. If the number of algal cells was greater than 7000 cells / ml, the culture was diluted with culture medium. Conversely, if the number was less, the supernatant was removed after 2-3 hours to adjust the concentration. Then, 19.648 ml of well-suspended culture solution was placed in 70 ml cell culture flasks (3 flasks were prepared). In addition, 19.648 ml of culture medium was placed in new 70 ml cell culture flasks as a control {4 flasks were prepared (one of which was used for calibration curve creation)}. Furthermore, approximately 20 ml of well-suspended culture solution was prepared for baseline correction when measuring absorbance with a UV-Vis spectrophotometer. Next, 352 μl (5.68 × 10⁸ beads / ml) of 2 μm polyvinyl chloride (PVC) bead solution was added to a 70 ml cell culture flask containing culture medium. The mixture was then mixed by pipetting, and the cells were incubated in a 20°C climate chamber for 1 day. Figure 2 shows magnified images of the various algae used. In Figure 2, the dotted lines represent the cell surface, and the solid lines represent the interface of the adhesive substance. Table 5 shows the amount of adhesive component calculated using the method described in the general description.

[0059] [Table 4]

[0060] [Table 5]

[0061] <Microplastic Recovery Test> The flask obtained in the above-mentioned <Algal Culture> (containing the culture of each of the above-mentioned algae at a final concentration of 1 × 10⁷ beads (2 μm) / ml) was removed from the artificial climate chamber without agitation. At this time, a precipitate was observed, as shown in Figure 3. After this, the solution was suspended by swirling and pipetting. Next, a 50 μm cell strainer (pluriStrainer 50 μm) was set and labeled in a 50 ml tube using a connector ring (one for each cell culture flask except those used for the calibration curve). Then, all culture flasks were filtered under reduced pressure using a syringe through each cell strainer (the samples for the calibration curve were not filtered). After that, the primary filtered samples were capped and stored on the lab bench. Finally, a calibration curve was created, and a bead dilution series for the calibration curve was prepared to estimate the bead recovery rate by the algae. Specifically, using a culture medium without added beads as the bead concentration 0, we repeatedly diluted the stock concentration of 1.00 × 10⁷ beads / ml by half to prepare concentrations of 3.13 × 10⁵ beads / ml, 6.25 × 10⁵ beads / ml, 1.25 × 10⁶ beads / ml, 2.50 × 10⁶ beads / ml, and 5.00 × 10⁶ beads / ml.

[0062] <Microplastic Recovery Measurement Test> Absorbance measurements were performed at 267 nm, the fluorescence wavelength of the beads, using a BioSpec-Mini UV-Vis spectrophotometer (Shimadzu Corporation). To estimate the recovery rate of the algae beads, a beads dilution series was measured for a calibration curve, and a linear regression equation was obtained. Absorbance measurements were then performed on the permeate of a 50 μm cell strainer containing algae culture medium + beads solution as the sample, and the bead concentration in the permeate was calculated from the linear regression equation obtained from the calibration curve. The same procedure was repeated for the permeate of a 50 μm cell strainer containing non-cultured medium + beads solution as the control, and the bead concentration in the permeate was calculated from the linear regression equation obtained from the calibration curve. Finally, the bead recovery rate was calculated from the bead concentrations in the sample and the control. The results are shown in Table 6.

[0063] [Table 6]

[0064] <Large-scale cultivation of algae> First, diatoms (Skeletonema tropicum) were pre-cultured in 500 mL cell culture flasks. f / 2 medium (composition described in Tables 1 and 2, except seawater was replaced with sterile water) was used as the culture medium. Algae were seeded into 200 mL of this medium so that the initial algal cell count was 7000 cells / mL. These were placed in a 20°C artificial climate chamber and cultured statically for 14 days to create pre-culture flasks. Twenty of these pre-culture flasks were prepared, yielding a total of 4 L of seed culture medium. Next, 400 L of artificial seawater was prepared for each of two 500 L culture tanks. An air pump (Zensui RLP-100) was connected to each of the culture tanks via a two-way splitter, and air was blown in and stirred at a total airflow of 140 L / min for both tanks. 4 L of seed culture medium was added to one of the 500 L culture tanks, and cultured for 7 days while being stirred with air. Finally, 5g of PVC powder with a particle size of approximately 120μm was added to each of the two 500L culture tanks as microplastics, and cultivation was continued for 3 days while stirring with air to obtain the algal culture solution and the control.

[0065] <Microplastic Recovery Test> 50 mL each was taken from the algal culture medium and control obtained in the above-mentioned <large-scale algal culture>. These were suspended by swirling and pipetting. A 50 μm cell strainer (pluriStrainer 50 μm) was set in a 50 mL tube using a connector ring. Subsequently, the collected algal culture medium and control were filtered under reduced pressure using a syringe through the cell strainer. The primary filtered samples obtained by filtration were sealed and stored on the lab bench. A PVC dilution series for calibration was prepared. Specifically, artificial seawater without added PVC was used as the PVC concentration 0, and a 1.00 × 10⁻⁶ series was prepared. 7 A PVC solution with PVC / mL (number of PVC powders in 1mL) is repeatedly diluted by half to obtain 3.13 × 10⁻¹⁶. 5 PVC / mL, 6.25×10 5 PVC / mL, 1.25 × 106 PVC / mL, 2.50×10 6 PVC / mL, 5.00×10 6 PVC solutions of PVC / mL were prepared.

[0066] <Measurement of microplastic concentration> Using an ultraviolet-visible spectrophotometer BioSpec-Mini (Shimadzu Corporation), the absorbance at 267 nm, which is the fluorescence of PVC, was measured. At this time, a PVC dilution series for the calibration curve was measured to calculate the PVC concentration, and a calibration curve was created to obtain a linear regression equation. Subsequently, the absorbance of the primary filtration sample was measured, and the PVC concentration in the primary filtration sample was calculated from the linear regression equation obtained from the calibration curve. In addition, for baseline correction when measuring the absorbance (OD 267 ), about 200 mL of well-suspended artificial seawater without added diatoms was prepared for baseline correction. The PVC recovery rate by algae was calculated from the PVC concentration in the culture solution in which algae were cultured and the PVC concentration in the control. The PVC recovery rate by algae at this time was 29.4%.

[0067] <Preparation of carbonized samples> From the algal culture solution obtained in the above-mentioned <Large-scale culture of algae>, the surface-layer algae were collected. The algae were filtered using a funnel-shaped filter. 15.14 g of the filtration residue and 5.12 g of sawdust were mixed. At this time, the respective water contents measured using a moisture meter were 83.3 wt% for the filtration residue and 13.5 wt% for the sawdust. The bead weight was about 0.5 g or less, and the sum of the microplastic and algal contents in the mixture was 36 wt% in anhydrous weight. The mixture was placed in a crucible, covered, and left standing in a muffler furnace (Koyo Lindberg KBF-748). The furnace temperature was set to 300 °C and heated for 1 hour to obtain a carbonized sample. In the same manner, samples were heated at 300 °C for 30 minutes and at 400 °C for 1 hour in the furnace respectively to obtain carbonized samples. The weights of each carbonized sample were measured, and the weight yields were measured. The results at this time are shown in Table 7.

[0068]

Table 7

[0069] <Analysis of carbides> Each carbonized sample obtained in the above <Preparation of Carbonized Samples> was molded using a pelletizer to conform to the shape (diameter and length) and bulk density of wood pellets specified by the Japan Wood Pellet Association. The components of each carbonized sample, as well as the filtration residue and mixture before carbonization, were measured in accordance with JIS M 8812:2004. Specifically, the weight loss when the sample was heated at 107°C for 1 hour was considered as water. Next, the weight loss when the sample was placed in a crucible with a lid and strongly heated at 900°C for 1 hour was considered as volatile matter. Finally, the weight loss when the sample was heated at 500-815°C for 3 hours was considered as fixed carbon, and the residue after heating was considered as ash. The results of the ratio of each component at this time are shown in Figure 4. From Figure 4, the water content of all carbonized samples was 10 wt% or less. The results of the ratio of each component at this time based on anhydrous standards are shown in Figure 5. As shown in Figure 5, the proportion of fixed carbon in the carbide of all carbonized samples was approximately 60 wt% on an anhydrous basis. Furthermore, calorific value analysis was performed on the carbonized samples carbonized at a furnace temperature of 300°C for 30 minutes, in accordance with JIS M 8814:2003. As a result, the samples had a calorific value of 17.1 megaJ / kg on an anhydrous basis.

Claims

1. A material comprising: carbonized microplastics adsorbed by algae; and carbonized algae that have adsorbed the microplastics, The aforementioned algae are algae that secrete an adhesive substance, A carbonization combustion material wherein the amount of adhesive substance secreted by the algae is such that the volume of the adhesive substance secreted outside the algae's cells is 0.25 times or more and 100 times or less compared to the cell volume of the algae.

2. The carbonization combustion material according to claim 1, wherein the microplastics are microplastics that have been adsorbed and recovered by the algae from treated water containing microplastics.

3. The carbonization combustion material according to claim 1 or 2, wherein the algae are freshwater algae.

4. The carbonization combustion material according to any one of claims 1 to 3, wherein the adhesive substance is a polysaccharide.

5. The carbonized combustion material according to any one of claims 1 to 4, wherein the algae is at least one selected from diatoms, dinoflagellates, chlorarachnion algae, green algae, red algae, conjugating algae, Euglena algae, and cyanobacteria.

6. The carbonized combustion material according to any one of claims 1 to 5, wherein the sum of the respective content percentages of microplastics and algae, based on the anhydrous weight before carbonization, is 20 to 80 wt%.

7. A carbonized combustion material according to any one of claims 1 to 6, further comprising cellulose char.

8. The carbonization combustion material according to any one of claims 1 to 7, wherein the shape of the carbonization combustion material is pellet-shaped.

9. A method for producing a carbonized combustion material, comprising the steps of: adsorbing microplastics onto algae having the ability to adsorb and recover microplastics into water to be treated containing microplastics; and carbonizing a material to be carbonized including algae that have adsorbed microplastics.

10. The method for producing a carbonized combustion material according to claim 9, wherein the algae are freshwater algae.

11. A method for producing a carbonized combustion material according to claim 9 or 10, characterized in that the algae are algae that secrete an adhesive substance, and the amount of adhesive substance secreted by the algae is such that the volume of the adhesive substance secreted outside the cell is 0.25 times or more and 100 times or less compared to the cell volume.

12. The method for producing a carbonized combustion material according to claim 11, wherein the adhesive substance is a polysaccharide.

13. A method for producing a carbonized combustion material according to any one of claims 9 to 12, wherein the algae is at least one selected from diatoms, dinoflagellates, chlorarachnion algae, green algae, red algae, conjugating algae, Euglena algae, and cyanobacteria.

14. A method for producing a carbonized combustion material according to any one of claims 9 to 13, wherein the temperature in the carbonization step is 200 to 400°C.

15. A method for producing a carbonized combustion material according to any one of claims 9 to 14, further comprising a molding step of compression molding the carbonized combustion material as a post-processing step of the carbonization step.

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