JP4822800B2 - Methane fermentation treatment method for garbage or food residue - Google Patents

Description

  The present invention relates to a method for methane fermentation treatment of garbage or food residues, which comprises treating garbage or food residues by methane fermentation.

  Incineration and landfill disposal have been carried out as a method for treating organic waste such as garbage and sludge. In recent years, however, in view of consumption of large amounts of heavy oil, incineration of dioxins, and shortage of landfill disposal sites. Therefore, there is a demand for a processing method with a low environmental load. As a treatment method with a low environmental load, a method for methane fermentation treatment of organic waste has been developed (see, for example, Patent Literature 1 and Patent Literature 2). Such a methane fermentation treatment method is, for example, organic. After waste is pulverized into a paste or slurry, these are supplied to the methane fermentation facility and fermented with methane bacteria under anaerobic conditions to convert organic waste into methane gas. . The methane fermentation treatment method can decompose organic waste into biogas and water, greatly reducing the amount of waste, and does not require aeration power because it is fermented under anaerobic conditions. There is an advantage that methane gas in biogas can be recovered as energy.

In the methane fermentation treatment method, various pretreatments are performed prior to supplying organic waste to the methane fermentation facility in order to efficiently perform methane fermentation in the methane fermentation facility and improve the processing capacity. In addition, subcritical water treatment has been studied as an example of pretreatment (see, for example, Patent Document 3 and Patent Document 4). For example, Patent Document 3 includes rice husks, lawn, pruned branches, and hay that are discharged in agriculture and forestry. Cellulose / Lignin High C / N Ratio Low C / N Ratio Waste and Manure / Manure High C / N Ratio Low Moisture Waste Prior to Methane Fermentation Treatment, Cellulose / Lignin High C / N As a subcritical water treatment for hydrothermally treating a specific low-moisture waste near or below the critical point of water (374.1 ° C., 22.04 MPa), the pressure (Gaesh pressure) 2 to 22 MPa, It describes that the treatment is performed under conditions of a temperature of 200 to 650 ° C. and a treatment time of 1 minute to 10 hours. In Patent Document 4, as a food disposal method, particularly for baked confectionery and dairy products including bread and dough, 150 to 300 ° C. and subcritical water conditions of about the saturated vapor pressure according to the temperature. (For example, refer to Patent Document 4).
JP 2002-119937 A JP 2004-130206 A JP 2003-94022 A JP 2003-251306 A

  On the other hand, among organic waste, raw garbage from general households, and business-use garbage and food from restaurants, hotels, inns, supermarkets, convenience stores, food manufacturing, food sales, food distribution, etc. As for residues, these garbage and food residues are inherently more degradable than other organic wastes, and considerable heating energy is required to perform subcritical water treatment. Therefore, in consideration of cost-effectiveness, pretreatment by subcritical water treatment has been made unnecessary due to the idea that the cost is rather high.

  However, due to the abundant eating habits in recent years, a large amount of garbage and food residues have been generated as waste, and interest in recycling of waste and environmental problems has been improved. Since recovery has become established, it is desired to develop a treatment method that can treat raw garbage and food residues more efficiently and at low cost, and can also be used effectively as a resource.

  The present invention has been made paying attention to such a conventional problem, and methane of garbage or food residue that can be efficiently processed at low cost while collecting garbage or food residue as an energy source. An object is to provide a fermentation treatment method.

  As a result of intensive research, the present inventor has found that raw garbage or food residue is treated as a raw garbage when it is supplied to a methane fermentation facility after being subjected to a subcritical water treatment in a specific low temperature zone and in a short time. Alternatively, the present inventors have experimentally found that food residues can be fermented with high efficiency, whereby food waste or food residues can be processed quickly at low cost.

The present invention has been made based on such knowledge, and in the method of methane fermentation treatment of raw garbage or food residue by treating raw garbage or food residue by methane fermentation, the raw garbage or food residue is treated with methane fermentation equipment. Prior to supply to the sub-critical water treatment temperature of 120 to 140 ° C. , the pressure at the sub-critical water treatment temperature is 0.2 to 0.5 MPa, and the garbage or food for 2.5 to 10 minutes. The above object is achieved by providing a method for methane fermentation treatment of garbage or food residue in which the residue is treated with subcritical water in a closed space .

Moreover , it is preferable that the moisture content of the said garbage or food residue is 80 to 90% in the methane fermentation processing method of the garbage or food residue of this invention.

According to the behavior analysis method of the present invention, according to the method of methane fermentation of food waste or food residue of the present invention, the food waste or food residue is sufficiently profitable even when considering cost-effectiveness, It can be efficiently processed at low cost while being recovered as an energy source.

  The method for methane fermentation treatment of garbage or food residue according to a preferred embodiment of the present invention preferably treats garbage or food residue having a water content of 80 to 90% as organic waste, for example, as shown in FIG. , A processing method used for processing in a methane fermentation treatment facility including a pretreatment facility 10, a methane fermentation facility 11, an energy recovery facility 12, and the like.

That is, the method of methane fermentation treatment of garbage or food residue according to the present embodiment is for supplying garbage or food residue to the methane fermentation facility 11 in the methane fermentation treatment method of treating garbage or food residue by methane fermentation. Prior to this, the garbage or food residue is pretreated by subcritical water treatment in the pretreatment facility 10 at a subcritical water treatment temperature of 120 to 140 ° C. for 2.5 to 10 minutes.

  Here, in the present embodiment, in the methane fermentation treatment facility, raw garbage or food residue (hereinafter referred to as “hydrated food residue”) that is a processing target is input to the receiving device 10 a of the pretreatment facility 10. After that, it is pulverized by a predetermined amount by the pretreatment device 10b and unsuitable for fermentation is removed and stored as a slurry. The hydrated food residue in the form of slurry is supplied to the methane fermentation tank 11a of the methane fermentation facility 11 as necessary, and methane fermentation treatment is performed. Methane fermentation is a series of processes in which organic substances are assimilated by various microorganisms and converted to methane (CH4). For example, solid organic substances are decomposed into water-soluble low-molecular substances such as carbohydrates, amino acids, and fatty acids ( Solubilization process), further decomposed to produce lower fatty acids such as acetic acid, propionic acid and butyric acid, decomposed into acetic acid and hydrogen gas, etc., and produced methane from acetic acid and hydrogen gas In the anaerobic atmosphere, the hydrated food residue is fermented through these processes by the action of methane bacteria.

  In addition, biogas mainly composed of methane gas generated by methane fermentation is supplied to, for example, the power generation device 12a of the energy recovery facility 12 through the gas holder 11b, the desulfurization device 11c, and the like to generate electricity or supply heat. It will be used effectively. On the other hand, the digested liquid and digested sludge, which are residues from the methane fermentation tank 11a, are sent to the digested liquid processing system 13a of the digested liquid processing facility 13, the liquid fertilizer storage tank 14a of the liquid fertilizer storage facility 14, etc. As a result, it will be returned to farmland, discharged into rivers and transported to sewage treatment plants.

And in this embodiment, the pretreatment by the subcritical water treatment of the hydrated food residue is performed on the hydrated food residue that has been pulverized into a slurry form in the pretreatment device 10b of the pretreatment facility 10, for example, 120 to 140 It is carried out by subjecting to a hydrothermal reaction treatment at a subcritical water treatment temperature of ° C. for 2.5 to 10 minutes.

Here, the pretreatment by the subcritical water treatment of the water-containing food residue needs to be performed at a subcritical water treatment temperature of 120 to 140 ° C. When the subcritical water treatment temperature is lower than 112 ° C. , the decomposition to the precursor of methanation becomes insufficient, and when it is higher than 140 ° C. , the decomposition becomes excessive. Further, by setting the subcritical water treatment temperature to 120 to 140 ° C., a decomposition state more suitable as a precursor for methane formation is realized.

Incidentally, subcritical water treatment is performed in the preprocessing facility 10 in a closed space provided pretreatment apparatus 10b of the pressure in the closed space (gauge pressure), and 120 to 140 ° C. The subcritical water treatment temperature In this case, the pressure in the closed space (gauge pressure) is particularly preferably 0.2 to 0.5 MPa.

Further, in the present embodiment, pretreatment with subcritical water treatment temperature 120 to 140 ° C. of hydrous food residue, it is necessary to perform 2.5-10 minutes and are preferably carried out between 5 and 7.5 minutes. If the subcritical water treatment time is shorter than 2.5 minutes, the decomposition of the methanation into precursors is insufficient, and if it is longer than 10 minutes, the decomposition becomes excessive. Further, by setting the subcritical water treatment time to 5 to 7.5 minutes, a decomposition state more suitable as a precursor for methane production is realized.

  Moreover, it is preferable that a water-containing food residue performs a subcritical water process in the state which made the moisture content 80-90%. By performing subcritical water treatment in a state where the water content of the water-containing food residue is 80 to 90%, a decomposition state more suitable as a precursor for methane production is realized. In addition, although raw garbage or food residue originally has a considerable moisture content of about 70 to 95%, when the moisture content of the hydrated food residue that has been pulverized into a slurry is less than 80%. It is preferable to perform a subcritical water treatment by adding an appropriate amount of water as appropriate and maintaining the water content of the water-containing food residue at 80 to 90%.

And according to the methane fermentation processing method of the garbage or food residue of this embodiment, it becomes possible to efficiently process the garbage or food residue at low cost while collecting it as an energy source. That is, in this embodiment, prior to supplying the hydrated food residue to the methane fermentation facility, the above-mentioned specific low temperature band and short-time subcritical water treatment are performed in the closed space in the pretreatment facility 10. Since it performs as a process, compared with the case where methane fermentation is performed without performing a subcritical water process, for example, the processing speed by about 1.8-2.0 times methane fermentation, for example, 1.2 times-1 it is possible to obtain a generation of gas by methane fermentation of approximately .5 times, even when considering cost-effectiveness, it becomes possible to construct an inexpensive processing system to meet the sufficient profitability, a large amount of garbage Or it becomes possible to process a food residue efficiently and promptly.

  In addition, according to the present embodiment, it is possible to efficiently ferment hydrated food residue with methane and recover more biogas as an energy source, reduce fermentation residue after methane fermentation, and ferment It is also possible to reduce the burden of residue processing, which makes it possible to process garbage or food residues more inexpensively and efficiently.

  The present invention is not limited to the above-described embodiment, and various modifications can be made. For example, the method for methane fermentation treatment of raw garbage or food residue of the present invention can be employed in various other known methane fermentation treatment facilities and methane fermentation treatment systems in addition to the methane fermentation facility having the configuration shown in FIG. .

  Hereinafter, although this invention is demonstrated still in detail based on the Example and comparative example which were done by the laboratory experiment, this invention is not limited to these.

[Relationship between subcritical water treatment temperature and gas generation rate]
As food waste or food residue, a simulated food residue having the composition and water content shown in Table 1 was used. As Comparative Example 1, the amount of gas generated was measured by methane fermentation without pretreatment by subcritical water treatment. Moreover, as Examples 1-4, after performing the pretreatment by subcritical water treatment for the time shown in Table 2 at the treatment temperature shown in Table 2, methane fermentation was performed and the amount of gas generated was measured. The measurement results are shown in Table 2 as a ratio with the amount of gas generated in Comparative Example 1. Furthermore, as Comparative Examples 2 and 3, after pretreatment by subcritical water treatment for the time shown in Table 2 at the treatment temperature shown in Table 2, methane fermentation was performed and the amount of gas generated was measured. The measurement results are shown in Table 2 as a ratio with the amount of gas generated in Comparative Example 1. Furthermore, the measurement result of the gas generation amount in Table 2 is shown in FIG. 2 as a chart.

  According to the gas generation ratio shown in Table 2 and FIG. 2, it is found that in Examples 1 to 4 according to the present invention, the gas generation is remarkably increased.

[Relationship between subcritical water treatment temperature and amount of organic acid as precursor of methanogenesis]
As food waste or food residue, a simulated food residue having the composition and water content shown in Table 1 was used, and as Example 5, pretreatment by subcritical water treatment was performed at the treatment temperature shown in Table 3 for the time shown in Table 3. Later, the amount of organic acid (mg / liter) was measured. Table 3 shows the measurement results. Further, as Comparative Examples 4 to 6, after the pretreatment by the subcritical water treatment for the time shown in Table 3 at the treatment temperature shown in Table 3, the amount of organic acid (mg / liter) was measured. Table 3 shows the measurement results. Furthermore, the measurement result of the amount of organic acid in Table 3 is shown in FIG. 3 as a chart.

  According to the measurement results of the amount of the organic acid shown in Table 3 and FIG. 3, it is found that in Example 5 according to the present invention, the amount of the organic acid that is the precursor of methane formation is remarkably increased.

[Relationship between fermentation time and gas generation]
As food waste or food residue, the simulated food residue with the composition and moisture content shown in Table 1 was used, and as Comparative Example 7, methane fermentation was carried out without pretreatment by subcritical water treatment, and the fermentation time and gas generation amount The relationship was measured. Moreover, as Comparative Example 8, methane fermentation was performed after pretreatment by subcritical water treatment at a treatment temperature of 200 ° C. for 5 minutes, and the relationship between fermentation time and gas generation amount was measured. The measurement results are shown as a chart in FIG.

  According to the measurement result of the relationship between the fermentation time and the gas generation amount shown in FIG. 4, in Comparative Example 8 in which pretreatment by subcritical water treatment was performed for 5 minutes at a treatment temperature of 200 ° C., no pretreatment was performed. Compared with the comparative example 7 fermented with methane, the amount of gas generated is only slightly increased, and it is assumed that the hydrous food residue is excessively decomposed.

  As food waste or food residue, the simulated food residue with the composition and moisture content shown in Table 1 was used, and as Comparative Example 9, methane fermentation was carried out without pretreatment by subcritical water treatment, and the fermentation time and gas generation amount The relationship was measured. As Example 6, methane fermentation was performed after pretreatment by subcritical water treatment at a treatment temperature of 120 ° C. for 5 minutes, and the relationship between fermentation time and gas generation amount was measured. As Example 7, pretreatment by subcritical water treatment was performed at a treatment temperature of 120 ° C. for 10 minutes, followed by methane fermentation, and the relationship between fermentation time and gas generation amount was measured. As Example 8, methane fermentation was performed after pretreatment by subcritical water treatment at a treatment temperature of 140 ° C. for 10 minutes, and the relationship between fermentation time and gas generation amount was measured. As Example 9, methane fermentation was performed after pretreatment by subcritical water treatment at a treatment temperature of 160 ° C. for 5 minutes, and the relationship between fermentation time and gas generation amount was measured. As Comparative Example 10, methane fermentation was carried out after pretreatment by subcritical water treatment at a treatment temperature of 180 ° C. for 10 minutes, and the relationship between fermentation time and gas generation amount was measured. The measurement results are shown as a chart in FIG.

  According to the measurement results of the relationship between the fermentation time and the gas generation amount shown in FIG. 5, in Examples 6 to 8 according to the present invention, good results are obtained with respect to the gas generation rate and the gas generation amount, and the pretreatment is performed. Compared with the comparative example 9 which is not, the generation rate of gas by methane fermentation of about 1.8 times to 2.0 times, for example, and the generation of gas by methane fermentation of about 1.2 times to 1.5 times, for example It turns out that the quantity is obtained. On the other hand, in Example 9, compared with Examples 6-8, both the generation rate of gas and the amount of gas generation have decreased, and partial excessive decomposition | disassembly by pre-processing of a water-containing food residue is estimated. . In Comparative Example 10, only the same gas generation rate and gas generation amount as those in Comparative Example 11 in which no pretreatment was performed can be obtained, and excessive decomposition due to pretreatment of the water-containing food residue is estimated.

It is explanatory drawing which shows the general | schematic structure of the methane fermentation processing facility which carries out methane fermentation processing of garbage or a food residue using the methane fermentation processing method which concerns on preferable one Embodiment of this invention. It is a chart which shows the measurement result of the generation amount of gas. It is a chart which shows the measurement result of the quantity of organic acid. It is a chart which shows the measurement result of the relationship between fermentation time and gas generation amount. It is a chart which shows the measurement result of the relationship between fermentation time and gas generation amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Pretreatment equipment 10a Receiving device 10b Pretreatment equipment 11 Methane fermentation equipment 11a Methane fermentation tank 11b Gas holder 11c Desulfurization equipment 12 Energy recovery equipment 12a Power generation equipment 13 Digestive liquid treatment equipment 13a Digestive liquid treatment system 14 Liquid fertilizer storage equipment 14a Liquid fertilizer storage tank

Claims (2)

In the method of methane fermentation treatment of garbage or food residue, which treats garbage or food residue by methane fermentation,
Prior to supplying the garbage or food residue to the methane fermentation facility, the subcritical water treatment temperature is 120 to 140 ° C. , and the pressure at the subcritical water treatment temperature is 0.2 to 0.5 MPa . A method for methane fermentation treatment of garbage or food residue, wherein the garbage or food residue is treated with subcritical water in a closed space for 5 to 10 minutes. The method for methane fermentation treatment of garbage or food residue according to claim 1 , wherein the moisture content of the garbage or food residue is 80 to 90%.

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