JP5079834B2 - Methane fermentation method - Google Patents

Description

  The present invention relates to a methane fermentation treatment of organic waste, and more particularly to a methane fermentation treatment capable of stably performing a methane fermentation treatment over a long period of time even when the input load of fat is high.

  In the methane fermentation treatment, organic waste is fermented with methane bacteria under anaerobic condition and converted into methane gas. The organic waste can be decomposed into biogas and water to greatly reduce the amount. In addition, there is a merit that methane gas generated as a by-product can be recovered as energy.

  If a large amount of methane bacteria can be stored in the methane fermentation tank, processing at higher speed becomes possible. As one of the means for storing a large amount of methane bacteria in the methane fermentation tank, the fermentation liquor extracted from the methane fermentation tank is separated into solid and liquid, and the separated sludge separated into solid and liquid is returned to the methane fermentation tank etc. There is a way to do. A typical example of a method for solid-liquid separation of the fermentation broth extracted from the methane fermentation tank is a gravity sedimentation method.

  In addition, in order to increase the efficiency of methane fermentation treatment, it has been conventionally performed to solubilize organic waste and perform methane fermentation treatment.

  For example, the following Patent Document 1 includes a slurrying process for slurrying an organic solid insoluble in water, a solubilization process for converting the slurryed organic solid into an organic substance soluble in water, An anaerobic treatment step of methane fermentation of the solubilized treated product in the presence of sludge containing anaerobic microorganisms, a solubilization treatment step for converting the sludge generated in the anaerobic treatment step into a water-soluble organic substance, There is disclosed a method for treating an organic solid comprising a returning step of returning a solubilized treated product to the anaerobic treatment.

JP 2002-66507 A

  However, fats containing saturated fatty acids such as palmitic acid (melting point 63 ° C.) and stearic acid (melting point 69.9 ° C.) contained in palm oil refining waste liquid etc. are high-temperature methane fermentation whose fermentation temperature is about 55 ° C. Since it was in a solid state without melting, it could not be efficiently contacted with methane bacteria in the tank and the fat was easily discharged out of the tank without being decomposed.

  For this reason, when organic waste containing a large amount of fat having a high saturated fatty acid ratio is subjected to a methane fermentation treatment by increasing the input load, the dispersibility of fat in the methane fermentation tank decreases. In particular, when the fat is 0.2 g / L / day or more in terms of saturated fatty acid, the dispersibility of the fat is remarkably reduced, so that the fat is easily extracted from the methane fermentation tank without being decomposed. And, when solid-liquid separation of the fermented liquor containing a large amount of undegraded fat by gravity sedimentation, the undegraded fat floats on the liquid surface and easily drains as scum, so the liquid property of the waste water deteriorates, There was a problem that the subsequent wastewater treatment required labor. Furthermore, undecomposed fat adheres to the sludge and the sedimentation rate of the sludge is remarkably impaired, so that it is necessary to enlarge the gravity sedimentation tank or to increase the residence time in the tank.

  In the above-mentioned Patent Document 1, in order to increase the efficiency of methane fermentation treatment of solid waste containing organic solids insoluble in water such as beer malt, food waste, and vegetable animal waste, Although it is solubilized, the above problem in the case of subjecting organic waste containing fat having a high saturated fatty acid ratio to methane fermentation treatment with an increased input load has not been studied.

  Therefore, the objective of this invention is providing the methane fermentation method which can decompose | disassemble organic waste which contains fat with a high saturated fatty acid ratio in high concentration efficiently in a short time.

In achieving the above-mentioned object, the methane fermentation method of the present invention is a method in which fat-containing organic waste is put into a methane fermentation tank and subjected to methane fermentation treatment, and a predetermined amount of the fermentation liquid is taken out from the methane fermentation tank. A sludge sedimentation liquid whose sludge concentration becomes higher as it goes downward by gravity sedimentation means is returned, at least a part of the sludge high concentration liquid on the lower layer side of the sludge sedimentation liquid is returned to the methane fermentation tank, and the upper layer side of the sludge sedimentation liquid of the methane fermentation method for discharging at least a portion out of the system of sludge low concentration solution, the sludge sedimentation liquid lower layer side from the extracted sludge-enriched fluid and the organic waste, the organic waste To 100 parts by weight of fat, after mixing in a proportion that the solid content of the sludge concentrate is 500 to 1,000 parts by weight, the fat is dispersed by heating above the melting point of the fat contained therein, The methane fermentation tank Characterized in that the charged load of saturated fatty acids in fat is methane fermentation process by introducing such a 0.2 g / L / day or higher.

  The organic waste of the methane fermentation method of the present invention preferably contains 20 to 35% by mass of fat having a saturated fatty acid ratio of 30% or more in the solid.

  In the methane fermentation method of the present invention, it is preferable that the mixed liquid of the sludge high-concentration liquid and the organic waste is heated to 70 ° C. or higher and then charged into the methane fermentation tank.

  According to the methane fermentation method of the present invention, the high-concentration sludge liquid extracted from the lower layer side of the sludge sedimentation liquid is mixed with organic waste and heated to a temperature equal to or higher than the melting point of the fat contained in the fat, It is dispersed and adheres to the sludge in the high-concentration sludge liquid taken out from the gravity sedimentation means, and can increase the dispersibility of fat in the methane fermentation tank. Thereby, fat becomes easy to contact the methane bacteria in a tank, and the decomposition efficiency of organic waste improves. For this reason, an organic waste containing fat with a high saturated fatty acid ratio and a high melting point is introduced so that the input amount of saturated fatty acid in the fat is 0.2 g / L / day or more and subjected to methane fermentation treatment. However, since fat efficiently contacts and decomposes to methane bacteria in the tank, the decomposition efficiency of organic waste is improved, and the fermentation liquid with a small amount of undecomposed fat is discharged from the methane fermentation tank. . As a result, when the fermentation broth is subjected to gravity sedimentation and solid-liquid separation, scum is difficult to form on the liquid surface, the liquid properties of the supernatant after solid-liquid separation become good, and the supernatant is then drained. The time and effort required can be reduced. In addition, since the fermentation broth extracted from the methane fermentation tank has a small amount of fat, the sedimentation speed of the sludge in the gravity sedimentation means is fast, and sludge can settle in a short time without increasing the size of the gravity sedimentation means. The labor required for liquid separation can be simplified.

It is a schematic block diagram of the methane fermentation apparatus used for the methane fermentation process of this invention. It is a graph which shows the sedimentation characteristic of a fermented liquor. It is a graph which shows the relationship between the input load amount of the saturated fatty acid in fat, and VS decomposition rate.

  One Embodiment of the methane fermentation apparatus used for the methane fermentation process of this invention is described using FIG.

  As shown in FIG. 1, the methane fermentation apparatus mainly includes a pretreatment tank 1, a methane fermentation tank 2, and a gravity sedimentation tank 3.

  The pretreatment tank 1 includes a heating device (not shown) and a stirring device (not shown), and is returned from an organic waste sent from an organic waste supply source and a gravity settling tank 3 described later. This is a treatment tank for mixing the sludge concentrate in the tank and heating it above the melting point of the fat contained in these mixtures (hereinafter referred to as organic waste liquid) to disperse the fat. The pretreatment tank 1 also has a buffering function for stabilizing the inflow of organic waste liquid into the methane fermentation tank 2 described later. The heating device is not particularly limited, and a conventionally known device such as a heater, pressurized steam, a device for heating by exchanging the amount of heat of the organic waste itself to be treated can be used. The stirring device is not particularly limited as long as it can stir the organic waste in the tank, and a conventionally known device such as a stirrer equipped with a stirring blade can be used.

  The pretreatment tank 1 is connected to a pipe L1 extending from the organic waste supply source and a pipe L2 extending from the bottom of the gravity settling tank 3 (which may be connected to the lower portion of the side surface).

  A methane fermentation tank 2 is disposed at the subsequent stage of the pretreatment tank 1. The pretreatment tank 1 and the methane fermentation tank 2 are connected via a pipe L3.

  The methane fermentation tank 2 is a treatment tank that anaerobically treats the organic waste liquid supplied in the tank by the action of anaerobic microorganisms such as methane bacteria and decomposes it into biogas such as methane gas. The methane fermentation tank 2 is provided with a stirring device (not shown) for stirring the fermentation liquid in the tank. Further, from the upper part of the methane fermentation tank 2, a biogas extraction pipe L4 extends and is connected to a gas holder, a gas utilization facility, and the like.

  The stirring device is not particularly limited as long as it can stir the fermentation broth in the tank. For example, a stirrer equipped with a stirring blade may be used. In addition, a gas agitation that forms a path for circulating the fermented liquid in the tank and provides a mechanism for forming an upward flow or a downward flow in the fermented liquid in the tank, or circulates the generated biogas for bubbling. An apparatus may be provided.

  A gravity sedimentation tank 3 is arranged at the subsequent stage of the methane fermentation tank 2. The methane fermentation tank 2 and the gravity sedimentation tank 3 are connected via a pipe L5.

  The gravity sedimentation tank 3 is a treatment tank that gravity settles the sludge in the fermentation liquid taken out from the methane fermentation tank 2 to form a sludge sedimentation liquid whose sludge concentration increases downward. An example is a gravity sedimentation pond. Moreover, the sedimentation speed | rate of sludge can be raised more by arrange | positioning a water flow inclination board to the gravity sedimentation tank 3. FIG. As a gravity sedimentation tank provided with the water flow inclination board, what was described in Unexamined-Japanese-Patent No. 6-63321 etc. is mentioned, for example.

  From the side of the gravity settling tank 3, a pipe L6 for discharging the upper-layer sludge low-concentration liquid (hereinafter also referred to as “sludge separation liquid”) to the outside of the system is connected. Further, a pipe L2 connected to the pretreatment tank 1 extends from the lower part (bottom part in the present embodiment) of the gravity settling tank 3, and a sludge high-concentration liquid (hereinafter also referred to as “sludge concentrate”) on the lower layer side. It is comprised so that at least one part of can be returned to the pretreatment tank 1. FIG.

  Next, the case of using this methane fermentation apparatus will be described as an example to explain the methane fermentation method of the present invention.

  The organic waste used for the methane fermentation treatment of the present invention only needs to contain fat at a high concentration. Among them, fats with a high saturated fatty acid ratio have a high melting point and many solids are formed even at room temperature, so organic waste containing fat with a high saturated fatty acid ratio is preferably used in the methane fermentation treatment of the present invention. It is done. Furthermore, the melting point of saturated fatty acids having 16 or more carbon atoms is 55 ° C. or higher, and fats containing such saturated fatty acids are not dissolved even during the high-temperature methane fermentation treatment, and are easily maintained in a solid state. Organic waste containing fat containing a saturated fatty acid is particularly preferably used in the methane fermentation treatment of the present invention. Examples of main saturated fatty acids having 16 or more carbon atoms contained in organic waste include palmitic acid (16 carbon atoms, melting point 63 ° C.), stearic acid (18 carbon atoms, melting point 69.9 ° C.), and the like. Examples of the organic waste containing fat having a saturated fatty acid having 16 or more carbon atoms include fat and oil drainage discharged from an oil and fat factory, food residues such as ice cream and milk drinks, and the like.

  In addition, the higher the saturated fatty acid ratio of fat, the higher the melting point, and the easier it is to maintain solid properties even at room temperature. Therefore, a fat having a saturated fatty acid ratio of preferably 30% or more, more preferably 40% or more, Organic waste containing 20 to 35%, more preferably 25 to 30% in the solid is preferably used in the methane fermentation treatment of the present invention.

  In addition, the saturated fatty acid ratio of fat means the value which expressed the ratio of the saturated fatty acid in the fatty acid which is a fat component in percentage.

  In the present invention, the organic waste and the sludge concentrate are supplied to the pretreatment tank 1 through the pipe L1 and the pipe L2, respectively. And it heats more than melting | fusing point of the fat contained in these mixtures (organic waste liquid), stirring the organic waste and sludge concentrate supplied to the pretreatment tank 1. As a result, the fat is melted and dispersed and adheres to the sludge surface, so that the dispersibility of the fat in the methane fermentation tank 2 is improved, and the fat is easily brought into contact with the methane bacteria in the tank. Will improve. The details of this reason are not clear, but are presumed to be as follows.

  That is, even if only the organic waste is heated and the fat contained therein is solubilized before the organic waste is put into the methane fermentation tank 2, the fermentation temperature in the methane fermentation tank 2 is the melting point of the fat. Therefore, fat solidifies and precipitates during methane fermentation. When the input load of fat is high, there is a large amount of fat that has a high saturated fatty acid ratio and is easily solidified in the methane fermenter. It becomes fat granules and fat dispersibility decreases. For this reason, the fat is difficult to be decomposed by methane bacteria, and the fat is discharged as a fermentation broth without being decomposed.

  On the other hand, in the present invention, the high-concentration sludge liquid is mixed with organic waste and heated to a temperature higher than the melting point of the fat contained therein, whereby the high-melting-point fat melts and becomes liquid, It is thought that it adheres to sludge such as methane bacteria contained in the liquid. Even if methane bacteria are killed when heated, the dispersion state of high melting point fat is maintained. For this reason, even if the fermentation temperature in the methane fermentation tank 2 is lower than the melting point of fat, the fat adheres to sludge such as methane bacteria and is dispersed in the tank. Even if a large amount of fat with a high melting point is present, it is considered that the fat easily contacted the methane bacteria in the tank. As a result, the decomposition efficiency of the whole organic waste is improved, and it is considered that the fermentation liquid with less undecomposed fat is easily discharged from the methane fermentation tank.

  What is necessary is just to carry out so that the heating temperature of organic waste liquid (The mixture of organic waste and sludge concentrate) may become more than melting | fusing point of the fat contained in organic waste liquid. It can adjust suitably with the kind of fat contained in organic waste liquid, and a saturated fatty acid ratio. For example, in the case of organic waste containing fat having a saturated fatty acid having 16 or more carbon atoms, the organic waste liquid is preferably heated to 60 ° C. or higher, more preferably 60 to 80 ° C. By heating the organic waste liquid to 60 ° C. or higher, fat contained therein can be sufficiently dissolved. Moreover, since energy loss will occur when heating is performed at a higher temperature, the upper limit is preferably set to 80 ° C.

  The heating time of the organic waste liquid may be performed until the fat in the organic waste liquid is completely melted and dispersed, and after rising to the set temperature, 0.1 to 24 hours are preferable, and 0.5 to 2. 0 hours is more preferable.

  The mixing ratio of the organic waste and the sludge concentrate may be such that the solid content of the sludge concentrate is 500 to 1,000 parts by mass with respect to 100 parts by mass of the fat in the organic waste. Preferably, it is 600 to 800 parts by mass. When the solid content of the sludge concentrate is less than 500 parts by mass with respect to 100 parts by mass of fat in the organic waste, the dispersibility of the fat is inferior. There is a tendency that the concentration of substances increases and the efficiency of methane fermentation decreases.

  In the pretreatment tank 1, processing such as pulverization and crushing may be further performed as necessary.

  The organic waste liquid subjected to the fat dispersion treatment as described above is supplied to the methane fermentation tank 2 via the pipe L3, and the input load of saturated fatty acid in the fat is 0.2 g / L / day or more, preferably 0. 4. Supply at 4 to 0.8 g / L / day. Although the methane fermentation treatment can be performed without any problem even when the input amount of saturated fatty acid in fat is less than 0.2 g / L / day, the present invention aims to treat high fat organic waste in a short time. Therefore, the input load of saturated fatty acid in fat is set to 0.2 g / L / day or more. If the input load of saturated fatty acid in fat is 4 to 0.8 g / L / day, methane fermentation can be carried out by increasing the decomposition efficiency of organic waste.

  In addition, the input load amount of the saturated fatty acid in the fat is the amount of saturated fatty acid in the input fat per 1 L of the liquid volume of the methane fermentation tank 2 per day. The amount of saturated fatty acid contained in fat can be calculated by multiplying the total amount of fatty acid by the ratio of saturated fatty acid.

  In the methane fermentation tank 2, the supplied organic waste liquid is retained for a predetermined period while stirring continuously or intermittently by a stirring means (not shown) so that the sludge concentration and temperature of the fermentation liquid in the tank are substantially uniform. Methane fermentation by the action of anaerobic microorganisms such as methane bacteria. Then, the same amount of fermentation liquid as the organic waste liquid supplied to the methane fermentation tank 2 is extracted from the pipe L5 and supplied to the gravity sedimentation tank 3. In addition, biogas such as methane gas generated when methane fermentation of organic waste is taken out of the tank from the pipe L4 and stored in a biogas holder (not shown) or the like.

  In the gravity sedimentation tank 3, the sludge mainly composed of methane bacteria in the fermentation liquid taken out from the methane fermentation tank 2 is gravity settled to form a sludge sedimentation liquid whose sludge concentration increases downward. Then, at least a part of the sludge low-concentration waste liquid on the upper layer side of the sludge sedimentation liquid is discharged through the pipe L6, and at least a part of the sludge low-concentration liquid on the lower layer side of the sludge sedimentation liquid is transferred to the pretreatment tank 1 through the pipe L2. Return it.

  As described above, since the fat is present in the fermented liquid in the methane fermentation tank 2 with good dispersibility, the input load of saturated fatty acid in the fat may be 0.2 g / L / day or more. The fat can be efficiently decomposed by the methane bacteria in the tank, and the decomposition efficiency of the whole organic waste can be increased. For this reason, the fermentation broth extracted from the methane fermentation tank 2 contains almost no undegraded fat. In the gravity sedimentation tank 3, the sludge components are quickly settled to efficiently collect the sludge concentrate. it can. Furthermore, since almost no undecomposed fat is contained, scum is hardly generated on the liquid surface of the gravity settling tank 3, the property of the sludge separation liquid discharged from the pipe L6 is good, and the subsequent wastewater treatment Can be saved.

[Test Example 1]
Example 1
Methane fermentation was performed using the methane fermentation apparatus shown in FIG. As the methane fermentation tank 2, a tank having a volume of 5 L was used. Moreover, the gravity precipitation tank 3 used the tank of the volume 0.5L. As the organic waste, a palm oil refined effluent having a solid concentration of about 35,000 mg / L and a nonvolatile organic matter (VS) concentration of about 30,000 mg / L was used. The amount of fat concentration (chloroform-methanol extraction) in this palm oil refined waste liquid was 10,000 mg / L, and the ratio of palmitic acid and stearic acid to the total fatty acid amount was 40%.
In addition, TS density | concentration (evaporation residue) was measured according to the sewage test method-2.2.9. That is, the amount of solid matter remaining after evaporation of the sample solution at 110 ° C. was divided by the sample solution volume. Further, the VS concentration was determined from the TS concentration (the value obtained by dividing the fermentation liquid (mg / l) by evaporating to dryness at 110 ° C. and dividing the mass of the remaining solid material by the sample liquid volume). It was determined by subtracting the ash concentration obtained by dividing the mass of the remaining solid heated at ± 25 ° C. by the sample volume.
The preconditioning tank 1 is charged with 833 mL of palm oil refining waste liquid per day, and 208 mL of sludge concentrate is returned from the gravity sedimentation tank 3, mixed, heated to 70 ° C., and maintained at 70 ° C. Then, 1,042 mL was charged into the methane fermentation tank 2 in four divided portions per day. In this case, the input load of saturated fatty acid in the fat was 0.67 g / L / day. Further, the same amount of fermentation broth was extracted from the methane fermentation tank 2 and introduced into the gravity precipitation tank 3.
Here, the input load of saturated fatty acid was calculated by the following equation.
Saturated fatty acid input load = fatty acid concentration (10 g / L) × saturated fatty acid ratio (0.40) × input amount of organic waste per liter of fermentation broth (0.167 L / day = 1 L / 6 day)
When the VS concentration of the fermented liquid in the methane fermentation tank 2 after 20 days have passed since the residence time of the organic waste charged into the methane fermentation tank 2 is 6 days, it is 6,000 mg / L. The VS decomposition rate was 80.0%.
Further, the interface between the sludge separation liquid and the sludge separation liquid of the fermentation liquid charged into the gravity settling tank 3 was visually observed to evaluate the sedimentation characteristics of the fermentation liquid. The results are shown in FIG. As shown in FIG. 2, in about 6 hours, the fermentation broth was almost completely separated into the sludge separation liquid and the sludge separation liquid.

(Comparative Example 1)
In Example 1, the mixed liquid of the palm oil refined waste liquid and the sludge concentrate is not heated, but kept at room temperature (20 ° C.) for 1 day and then supplied to the methane fermenter 2. Similarly, methane fermentation treatment was performed.
It was 77,000 mg / L when the VS density | concentration of the fermentation liquid after 20 days passed since the residence time in the methane fermentation tank 2 of the organic waste thrown into the methane fermentation tank 2 became 6 days. The VS decomposition rate was 73%.
Further, the interface between the sludge separation liquid and the sludge separation liquid of the fermentation liquid charged into the gravity settling tank 3 was visually observed to evaluate the sedimentation characteristics of the fermentation liquid. The results are shown in FIG. As shown in FIG. 2, the sludge sedimentation rate was slower than in Example 1, and the separation between the sludge separation liquid and the sludge separation liquid was insufficient even after 8 hours had passed since the addition to the gravity sedimentation tank 3. .

(Comparative Example 2)
Into the preconditioning tank 1, 833 mL of palm oil refining waste liquid is added, heated to 70 ° C., kept at 70 ° C. for one day, and then input to the methane fermentation tank 2 in 833 mL in four divided days. The same amount of fermentation broth was extracted from the methane fermentation tank 2 and introduced into the gravity precipitation tank 3.
When the VS concentration of the fermented liquid in the methane fermentation tank 2 after 20 days have passed since the residence time of the organic waste charged into the methane fermentation tank 2 has reached 6 days, it is 10,200 mg / L. The VS decomposition rate was 64.0%.
From these results, the sludge concentrate and the organic waste containing fat with a high saturated fatty acid ratio are mixed at 70 ° C. or higher, and then put into a methane fermentation tank to perform methane fermentation treatment. The fat decomposition efficiency is improved and the amount of fat in the fermentation liquid drawn out from the methane fermentation tank is reduced, so that the fat can settle in a short time in the gravity sedimentation tank.

[Test Example 2]
In Example 1, methane fermentation was performed by adjusting the amount of organic waste supplied to the methane fermenter so that the input load of saturated fatty acid in fat was 0.2 to 1.0 g / L / day. went. The results are shown in Table 1 and FIG.

  As shown in Table 1 and FIG. 3, the residence time of the organic waste charged into the methane fermentation tank 2 is shortened and the VS decomposition rate is lowered as the input load of saturated fatty acid in fat increases. There was a trend.

1: Pretreatment tank 2: Methane fermentation tank 3: Gravity sedimentation tank L1-L6: Piping

Claims (3)

A fat-containing organic waste is put into a methane fermenter and subjected to methane fermentation treatment. Forming and returning at least part of the sludge high-concentration liquid on the lower layer side of the sludge sedimentation liquid to the methane fermentation tank, and discharging at least part of the sludge low-concentration liquid on the upper layer side of the sludge sedimentation liquid to the outside of the system. In the methane fermentation method,
Wherein the sludge-enriched fluid taken from the lower side of the sludge sedimentation solution and the organic waste, to fat 100 parts by weight of the organic waste in a solid content of the sludge concentrate 500 to 1, After mixing at a ratio of 000 parts by mass, the fat is dispersed by heating above the melting point of the fat contained therein, and the input load of saturated fatty acid in the fat is 0.2 g / A methane fermentation method, wherein the methane fermentation treatment is performed by adding the L / day or more.   The said organic waste is a methane fermentation method of Claim 1 which contains the fat whose saturated fatty acid ratio is 30% or more in 20-35 mass% in solid.   The methane fermentation method according to claim 1 or 2, wherein the mixed liquid of the sludge high-concentration liquid and the organic waste is heated to 70 ° C or higher and then charged into the methane fermentation tank.