JP2008307486A - Methane fermentation treatment apparatus and control method of methane fermentation tank - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a methane fermentation treatment apparatus and a control method of a methane fermentation tank, which is capable of finding out bad fermentation caused by inhibition, always maintaining in a good condition in the tank, and stabilizing methane fermentation. <P>SOLUTION: In the methane fermentation treatment apparatus 1 having a methane fermentation tank 15 generating a biogas constituted by methane gas as a principal constituent by feeding an organic waste, a slurry feeding amount is controlled by an opening 21 for taking out a part of a fermentation liquid from the methane tank 15, a bacterium number measuring device 23 for measuring a total active bacterium number and a methane fermentation bacterium number in a fermentation liquid taken out, and a control part 24 outputting an alarm to an unstable operational condition of the methane fermentation tank when a rate of the number of methane fermentation bacteria to that of total bacteria in the fermentation liquid measured by the bacterium number measuring device 23 comes to below a predetermined threshold value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a methane fermentation treatment apparatus and a method for controlling a methane fermentation tank.

  Most organic waste such as garbage and sludge is incinerated or landfilled. However, due to problems such as dioxin generation due to incineration, tightness of landfill sites, and bad odors, treatment methods with low environmental impact are required. It has been. In order to solve these problems, a system has been developed in which organic waste is subjected to methane fermentation treatment, and the generated methane gas is generated using a fuel cell or a gas engine.

  In methane fermentation, organic waste is crushed and slurried, and then this slurry is put into a fermentor and fermented with methane bacteria under anaerobic conditions to convert organic waste into methane gas. Various treatment methods and fermenters have been proposed depending on the properties of the input raw materials and operating conditions.

  The methane fermentation method decomposes organic waste into biogas and water, greatly reducing the amount of waste, and is anaerobic and does not require aeration power. There is an advantage that methane gas can be recovered as energy. As a system that efficiently treats organic waste such as garbage by methane fermentation, a system that pulverizes organic waste into a paste and treats it with a high-temperature methane bacterium that exhibits high activity at 50 to 60 ° C. It is disclosed in Patent Document 1, Patent Document 2, and the like. Thermophilic bacteria are 2 to 3 times more active than mesophilic bacteria whose activity increases at a medium temperature of 36 to 38 ° C, and the decomposition rate and digestibility are improved by performing methane fermentation with the high temperature bacteria. I can do it.

In order to maintain a methane fermenter smoothly, it is necessary to measure and manage several factors. The management index of operation includes the temperature in the tank, pH, the amount of activated sludge suspended solids (MLSS), the amount of organic acid, the concentration of ammoniacal nitrogen, the amount of biogas generated. However, it is the anaerobic bacteria that are primarily responsible for fermentation, and if these behaviors can be directly understood, the fermentation state can be diagnosed more reliably.
Japanese Patent Laid-Open No. 10-137730 Japanese Patent Laid-Open No. 13-46997 JP 2004-8078 A

  By the way, what is important in methane fermentation is to efficiently extract methane gas. Therefore, management such as temperature and garbage load is required. Actually, the temperature, pH, MLSS, organic acid amount, ammonia nitrogen concentration, biogas generation amount, etc. are measured and managed for each elapsed day, but there are too many factors to manage and the fermentation becomes unstable. I can't figure out the direct factors that make it happen. Therefore, paying attention to the contents of the methane fermentation tank, that is, the number of active cells, and handling this as a control factor is appropriate for maintaining the steady state of the fermentation tank.

  Until now, in order to grasp the total number of active bacteria present in the methane fermenter, the action of the hydrolase (esterase enzyme) present in the living bacteria and the fluorescence that fluoresces by hydrolysis A method was adopted in which the reagent was put into actual digested sludge, the image observed with a fluorescence microscope was processed, and the bacteria were counted (Patent Document 3). There was a correlation between the total number of active bacteria measured by this method and the amount of gas generated. Therefore, if a decrease in the number of bacteria can be detected, it is possible to control to suppress the input amount of the garbage slurry, and it is possible to operate without breaking the fermentation.

  However, it was difficult to judge the total number of bacteria when the number of bacteria declined, because the organic matter in the garbage was simply reduced, or the influence of the inhibitory substance due to the fluctuation of the ingredients in the garbage. In addition, in order to investigate the decrease in the amount of organic substances, elemental analysis from the TS concentration of the slurry, carbon, hydrogen, and nitrogen is required, which is troublesome. Since it is natural that the number of bacteria decreases due to the small amount of organic matter (it may be considered that there is no nutrition necessary for growth), it is not particularly necessary to take measures such as reducing the amount of slurry. On the other hand, if there is a substance that directly inhibits bacteria such as ammonia nitrogen due to an increase in the amount of protein in the input garbage, it is necessary to take measures such as diluting ammonia quickly, and the number of bacteria has decreased. There is no time to get lost.

  The present invention has been made in view of the above-mentioned problems, and can appropriately determine the number of bacteria in the fermenter so that fermentation failure due to inhibition can be determined. It aims at providing the control method of the methane fermentation processing apparatus which can aim at stabilization of fermentation, and a methane fermentation tank.

  In order to solve the above problems, the present invention provides a fermenter for supplying organic waste and generating biogas containing methane gas as a main component. , A microbial fermentation counter for measuring the total number of active bacteria and methane fermentation bacteria in the extracted fermentation broth, and a methane fermentation bacterium for all active bacteria in the fermentation broth measured by the bacterial count And an alarm output means for outputting an alarm for an unstable operation state of the fermenter when the ratio of the above becomes a predetermined threshold value or less.

  According to the invention, by examining the ratio of methane-fermenting bacteria to the total active bacteria in the fermentation broth, whether the organic matter in the garbage is simply reduced, or the influence of the inhibitory substance due to the fluctuation of the ingredients of the garbage to be introduced It can be determined, and the inside of the tank can always be kept in a good state, and methane fermentation can be stabilized.

  In the region where the ammoniacal nitrogen concentration exceeds 2000 mg / L, the methane bacteria / total bacteria ratio decreases to 0.2 or less, and the acetic acid concentration increases to 1000 mg / L or more. For this reason, in the present invention, when the ratio of the number of methane fermentation bacteria to the total active bacteria becomes 0.2 or less, an operation state alarm for the fermenter is output. Thereby, methane fermentation can be performed more stably by performing recovery operation with respect to a fermenter.

  The methane fermentation treatment apparatus of the present invention further includes adjusting means for adjusting the slurry charged into the fermenter, and the adjusting means is supplied to the fermenter when an alarm is output from the alarm output means. The amount of slurry charged is adjusted. As a result, the ratio of the methane bacteria to the total active bacteria becomes a predetermined value or more again, and the ammonia nitrogen concentration and the acetic acid concentration are lowered, so that stable effect can be achieved.

  Further, when an alarm is output from the alarm output means, an operation of removing a part of the organic acid in the fermenter is performed. As a result, the ratio of the methane bacteria to the total active bacteria becomes a predetermined value or more again, and the ammonia nitrogen concentration and the acetic acid concentration are lowered, so that stable effect can be achieved.

  The present invention provides a method for controlling a methane fermentation tank that supplies organic waste and generates biogas mainly composed of methane gas. In the methane fermentation tank, a part of the fermentation liquid is extracted from the fermentation tank, The total number of active bacteria and the number of methane fermentation bacteria are measured, and based on the measurement result, the ratio of methane fermentation bacteria to the total active bacteria in the fermentation broth is calculated, and the methane fermentation for all active bacteria in the calculated fermentation broth An alarm is output when the proportion of bacteria falls below a predetermined threshold value. According to the present invention, paying attention to the number ratio of all active bacteria and methane fermentation bacteria in the methane fermenter, by appropriately managing the number of bacteria in the fermenter, it is possible to determine the fermentation failure due to inhibition, always The inside of the tank can be maintained in a good state, and methane fermentation can be stabilized.

  In addition, the present invention is characterized in that the alarm is output when the ratio of the number of methane fermentation bacteria to the total active bacteria becomes 0.2 or less. According to the present invention, in the region where the ammoniacal nitrogen concentration exceeds 2000 mg / L, the ratio of methane bacteria / total bacteria decreases to 0.2 or less, and the acetic acid concentration increases to 1000 mg / L or more. By performing the operation, methane fermentation can be performed more stably.

  In addition, the present invention is characterized in that when the alarm is output, the amount of slurry charged to be supplied to the fermenter is adjusted based on the ratio of methane fermentation bacteria to the total active bacteria in the fermentation broth. According to the present invention, by adjusting the amount of slurry supplied from the slurry supply unit to the fermenter, the concentration of organic acid, which is an inhibitory substance in the fermentation liquid, is reduced, and the methane bacteria / total bacteria ratio is also 0.2. Thus, methane fermentation can be performed more stably.

  Further, the present invention is characterized in that when the alarm is output, a part of the organic acid in the fermenter is removed based on a ratio of methane fermentation bacteria to all active bacteria in the fermentation broth. According to the present invention, by removing a part of the organic acid in the fermenter, the concentration of the organic acid that is an inhibitory substance in the fermented liquid is reduced, and the methane bacteria / total bacteria ratio becomes 0.2 or more, so that the methane fermentation is further performed. It can be performed stably.

  According to the present invention, it is possible to determine a fermentation failure due to inhibition by appropriately managing the number of bacteria in the fermenter, always maintaining the inside of the fermenter in a good state, and stabilizing the methane fermentation. A method for controlling a methane fermentation treatment apparatus and a methane fermentation tank can be provided.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of the invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic view of a methane fermenter according to an embodiment of the present invention. As shown in FIG. 1, a methane fermentation treatment apparatus 1 includes a pulverizer 11, a fine pulverizer 12, a slurry adjustment tank 13, a slurry supply pump 14 (adjustment means), a methane fermentation tank 15, a waste liquid treatment tank 17, and a gas holder 18. , A gas utilization system 19, a pump 20, an extraction port (extraction means) 21, a slurry extraction pump 22, a bacteria count meter 23, a control unit (alarm output means) 24, and a dilution water supply pump 25.

  The methane fermentation treatment apparatus 1 supplies organic waste and generates biogas mainly composed of methane gas. Organic waste includes, for example, garbage and surplus sludge from activated sludge. The crusher 11 crushes the input organic waste. The pulverizer 12 pastes the crushed organic waste into a slurry adjusting tank 13 in order to further improve the decomposition rate and digestibility. The slurry adjusting tank 13 adjusts the pasted organic waste to a suitable solid concentration with the dilution water supplied from the dilution water supply pump 25 to perform slurrying. The slurry supply pump 14 sends the organic waste slurried in the slurry adjustment tank 13 to the methane fermentation tank 15.

  The methane fermentation tank 15 generates biogas mainly composed of methane gas from the slurried organic waste. The methane fermentation tank 15 is provided with a fixed filter bed 16 filled with immobilized microorganisms on which anaerobic microorganisms such as methane bacteria are attached and supported. In the methane fermentation tank 15, (1) organic waste is circulated by the slurry supply pump 14, (2) stirring is performed by the stirring blade 15 a, and (3) part of the biogas is stored in the methane fermentation tank 15 by the pump 20. Stirring is performed by a method such as blowing into the lower part and bubbling and stirring, and decomposition by anaerobic microorganisms is performed.

  In this methane fermenter 15, in addition to methane-producing bacteria, there are acid-producing bacteria that decompose (organic acid) solid matter such as garbage before gasification of methane bacteria is possible. In order to efficiently generate biogas, not only the presence of active methane bacteria but also the presence of other acid-producing bacteria becomes important.

  The waste liquid treatment tank 17 treats the fermentation liquid in the methane fermentation tank 15 below the waste water standard and discharges the sewage. The biogas produced by fermentation is collected in the gas holder 18 and used as energy in a gas utilization system 19 such as a gas turbine or a fuel cell.

  The methane fermentation tank 15 is provided with a take-out port 21 that can sample a part of the fermented liquid, and the fermented liquid is taken out from the take-out port 21 every day. The slurry extraction pump 22 sends a part of the fermentation broth in the methane fermentation layer 15 to the bacteria count meter 23 in order to measure the methane bacteria / total active bacteria ratio. The fermented liquor as a sample that has been subjected to a predetermined pretreatment is divided into two parts, and the number of active bacteria is measured by adding a fluorescent reagent on one side, and the number of methane bacteria is measured on the other side. Measure with a fluorescence microscope. The bacterial count meter 23 measures the total number of active bacteria and the number of methane fermentation bacteria in the fermentation liquid taken out from the outlet 21.

  The control unit 24 calculates the ratio of methane-fermenting bacteria to the total number of active bacteria based on the total number of active bacteria and the number of methane-fermenting bacteria (methane bacteria / total active bacteria ratio), and the total activity in the fermentation liquid. When the ratio of the methane fermentation bacteria to the bacteria becomes a predetermined threshold value (for example, 0.2) or less, an alarm for an unstable operation state of the methane fermentation tank 15 is output.

  Here, for example, in order for the control part 24 to stabilize in the methane fermentation tank 15, the ratio of the methane fermentation microbe with respect to all the active microbes in the fermentation liquid measured with the microbe count meter 23 is below a predetermined threshold value. When it becomes, the alarm with respect to the unstable operation state of the methane fermentation tank 15 is output to the slurry supply pump 14. And the slurry supply pump 14 reduces the input organic substance load by adjusting the slurry input amount supplied to the methane fermentation tank 15, and controls the recovery operation for the methane fermentation tank 15. Moreover, the control part 24 controls the recovery operation with respect to the methane fermentation tank 15 by removing a part of the organic acid in the methane fermentation tank 15.

  The measurement of all the active bacteria in the methane fermenter mentioned above is as follows. In order to grasp the total number of active bacteria present in the methane fermenter 15, a fluorescent reagent that emits fluorescence by hydrolysis is utilized using the action of hydrolase (esterase enzyme) present in the body of live bacteria. A method of counting the number of bacteria by processing the image observed with a fluorescence microscope and introducing it into actual digested sludge is adopted (see Patent Document 3). As the fluorescent reagent, a group consisting of 5- (6-) carboxyfluorescein diacetate, 5-carboxyfluorescein diacetate acetoxymethyl estate and the like is used. The ester bond of the fluorescent reagent is hydrolyzed by the esterase enzyme and emits fluorescence. The bacteria measured by this method are considered to contain all bacteria related to fermentation in addition to acid-producing bacteria and methane bacteria.

  Measurement of methane bacteria is as follows. Methane bacteria have a specific fluorescent coenzyme (8-hydroxy-5-diazaflavin derivative) in the body of methane bacteria without fluorescent staining using enzymes like the above all active bacteria, Excitation with a wavelength of 420 nm results in a fluorescence wavelength of 472 nm. It is usually called coenzyme F420 and is known as a simple method for observing methane bacteria. In JP-A-8-154661, this principle is used to measure the fluorescence intensity with a fluorescence spectrophotometer to grasp the activity of methane bacteria and prepare for an unexpected situation. In the present invention, the same means as that for measuring the number of all active bacteria is used, and a method of processing the image observed with a fluorescence microscope and counting the number of bacteria is incorporated.

FIG. 2 is a graph showing the relationship between the methane bacterium / total bacterium ratio in a general 55 ° C. high-temperature methane fermentation experiment, and the ammonia nitrogen concentration and acetic acid concentration that mainly cause inhibition. The ammoniacal nitrogen concentration was analyzed by ion chromatography, and the acetic acid concentration was analyzed by gas chromatography. In the region where the ammoniacal nitrogen concentration exceeded 2000 mg / L, the ratio of methane bacteria / total bacteria decreased to 0.2 or less, and the acetic acid concentration increased to 1000 mg / L or more. Table 1 shows the data of the fermentation broth.

  FIG. 2 and Table 1 show that the inhibition of methane bacteria by ammonia has occurred, and the metabolic function of methane bacteria that produce methane from acetic acid is reduced, indicating a deterioration in fermentation. Usually, when stable fermentation is performed, the acetic acid concentration is 1000 mg / L or less, and since it is always consumed, it must be dealt with so that it returns to an appropriate range. The ratio of methane bacteria / total active bacteria and ammonia nitrogen concentration, and the ratio of methane bacteria / total active bacteria and acetic acid concentration are correlated with each other. By controlling the ratio of methane bacteria / total active bacteria to 0.2 or more, ammonia nitrogen It can be seen that a concentration of 2000 mg / L or less and an acetic acid concentration of 1000 mg / L or less are possible.

  For this reason, when the methane bacteria / total active bacteria ratio is 0.2 or less, the control unit 24 takes measures such as reducing the amount of slurry. Specifically, the control unit 24 sets the threshold value of the methane bacteria / total bacteria ratio to 0.2, and when it becomes lower than that, performs the following response.

When the ratio of methane bacteria / total active bacteria is k <0.2, and the current slurry input amount is q1 (L / D), the control unit 24 calculates the input amount q2 (L / D) in the case of k. Calculate in (1).
・ Q ₂ = q1 × (k / 0.2) (1)

  2 and Table 1, when the methane bacteria / total active bacteria ratio exceeds 0.25, the ammonia nitrogen concentration and the acetic acid concentration are sufficiently lowered. Then, an operation of gradually returning to the original slurry amount may be performed.

  Hereinafter, the Example which performed the tank control of the methane fermentation tank 15 by measurement of the methane bacteria / total active bacteria ratio of this invention is demonstrated. The temperature in the methane fermentation tank 15 is 55 ° C., and the capacity of the methane fermentation tank 15 is 10 liters. The residence time (HRT) is 10 days, and the daily slurry charge is 1 L / d. The organic waste to be input is a slurry obtained by diluting and mixing waste. The solid content concentration (TS) of the slurry is adjusted to 100,000 mg / L.

The fermentation liquor extracted by the slurry extraction pump 22 is quickly taken, and a part thereof is diluted 5 to 20 times, preferably 10 to 15 times with water. After dilution, in order to remove the solid content, the solution is filtered with a filter having a pore size of 20 to 30 μm, and the filtrate is subjected to ultrasonic dispersion treatment. Thereafter, a pH buffer solution may be added to adjust the pH of the sample to be alkaline. As the pH buffer, a reagent adjusted to be alkaline by adding KH ₂ PO ₄ to NaOH or KOH was used.

  The diluted and dispersed fermentation broth sample is divided into two parts, and one of them is added with the fluorescent reagent 5-carboxyfluorescein diacetate to measure the total number of active bacteria, and thoroughly mixed again. The other is used as it is to measure the number of methane bacteria. The sample was hung on a preparation such as a bacteria measuring board (Elma Co., Ltd.) and observed with a fluorescence microscope (E-600, manufactured by Nikon). All active bacteria and methane bacteria were observed with fluorescence, and the observed images were analyzed with commercially available software (Optimas 6.51), and the number of bacteria was counted.

  FIG. 3 shows changes in the operating days of the methane fermenter 15 at 55 ° C. and the ratio of methane bacteria / total active bacteria, ammonia nitrogen concentration, and acetic acid concentration. About 30 days after the start of the measurement, the ratio of methane bacteria / total active bacteria was 0.12, and it was confirmed that the ammonia nitrogen concentration and the acetic acid concentration increased accordingly.

The slurry input amount q ₂ was determined using the above formula (1) for the amount of input raw material slurry.
Q ₂ = 1 × (0.12 / 0.2) = 0.6 (L / d)

Next, the control unit 24 decreased the amount of slurry charged into the methane fermentation tank 15 by controlling the slurry supply pump 14. As a result of this recovery operation, the acetic acid concentration decreased, the ratio of methane bacteria / total active bacteria gradually increased, and the ammonia nitrogen concentration gradually decreased. By measuring the methane bacteria / total active bacteria ratio and adjusting the amount of slurry by setting the threshold value to 0.2, the methane fermentation tank 15 was able to operate stably over a long period of time.
Alternatively, instead of reducing the slurry input amount, the fermentation liquid in the methane fermentation tank 15 may be circulated to the separation unit having a permeable membrane for selectively separating the organic acid, and a part of the organic acid may be removed from the fermentation liquid. Similar effects can be obtained.

  As described above, the threshold of the methane bacteria / total active bacteria ratio is determined by observing the ammonia nitrogen concentration, acetic acid concentration in the methane fermenter 15 and the behavior of the bacteria in the fermenter, and the threshold value is determined. When the value was less than the value, the input amount of garbage was adjusted according to the formula. Thereby, it became possible to realize a methane fermentation tank capable of managing and maintaining a stable fermentation state over a long period of time.

  As described above, according to the present embodiment, when the ratio of methane bacteria and all active bacteria becomes a predetermined value or less, by reducing the amount of slurry to be introduced into the methane fermentation layer 15, or by removing a part of the organic acid, Methane fermentation can be stabilized. By this operation, the ratio of the methane bacteria to the total active bacteria becomes 0.2 or more again, and the ammonia nitrogen concentration and the acetic acid concentration are lowered, so that a stable effect can be achieved.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications may be made within the scope of the gist of the present invention described in the claims. It can be changed. For example, in the said embodiment, when adjusting the slurry input amount supplied to the methane fermentation tank 15 from the slurry supply pump 14 as an example of recovery operation with respect to the methane fermentation tank 15, or removing a part of organic acid in the methane fermentation tank 15 Examples of cases have been described, but the present invention is not limited to these examples.

It is a schematic diagram for demonstrating the structural example of the methane fermentation processing apparatus which concerns on embodiment of this invention. It is a relationship diagram of ammonia nitrogen concentration (NH ₄ ⁺ -N), methane bacteria / total active bacteria ratio, and acetic acid concentration in general methane fermentation. It is the graph which monitored the change of the methane bacteria / total active bacteria ratio, the ammoniacal nitrogen concentration, and the acetic acid concentration in the operation days of a fermenter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Methane fermentation processing apparatus 11 ... Crusher 12 ... Fine pulverizer 13 ... Slurry adjustment tank 14 ... Slurry supply pump 15 ... Methane fermentation tank 15a ... Stirring blade 16. ..Fixed filter bed 17 ... Waste liquid treatment tank 18 ... Gas holder 19 ... Gas utilization system 20 ... Pump 21 ... Removal port 22 ... Slurry extraction pump 23 ... Bacteria count Total 24 ... Control unit 25 ... Dilution water supply pump

Claims (8)

In a methane fermentation treatment apparatus having a fermenter that supplies organic waste and generates biogas mainly composed of methane gas,
Means for removing a portion of the fermentation broth from the fermentor;
A bacterial count counter for measuring the total number of active bacteria and the number of methane fermentation bacteria in the extracted fermentation broth;
An alarm output that outputs an alarm for an unstable operation state of the fermenter when the ratio of methane fermentation bacteria to the total active bacteria in the fermentation broth measured by the microbe count is below a predetermined threshold value And a methane fermentation treatment apparatus. The alarm output means outputs an alarm of an operation state for the fermenter when the ratio of the number of methane fermentation bacteria to the total active bacteria becomes 0.2 or less. Methane fermentation treatment equipment. It further has adjusting means for adjusting the slurry charged to the fermenter,
3. The methane fermentation treatment apparatus according to claim 1, wherein the adjusting unit adjusts a slurry input amount to be supplied to the fermenter when an alarm is output from the alarm output unit. 4. . 3. The methane fermentation treatment apparatus according to claim 1, wherein when an alarm is output from the alarm output unit, an operation of removing a part of the organic acid in the fermenter is performed. In the control method of the methane fermentation tank that supplies organic waste and generates biogas mainly composed of methane gas,
Remove a portion of the fermentation broth from the fermentor,
Measure the total number of active bacteria and the number of methane fermentation bacteria in the extracted fermentation broth,
Based on the measurement results, calculate the ratio of methane fermentation bacteria to all active bacteria in the fermentation broth,
A control method for a methane fermenter, wherein an alarm is output when the ratio of the methane fermentation bacteria to the total active bacteria in the fermentation broth is equal to or less than a predetermined threshold value. 6. The method for controlling a methane fermenter according to claim 5, wherein the alarm is output when a ratio of the number of methane fermentation bacteria to the total active bacteria becomes 0.2 or less. The slurry input amount to be supplied to the fermenter is adjusted based on a ratio of methane fermentation bacteria to all active bacteria in the fermentation liquid when the alarm is output. The control method of the methane fermenter as described in 2. The organic acid in the fermenter is partially removed based on a ratio of methane fermenting bacteria to all active bacteria in the fermentation liquid when the alarm is output. The control method of the methane fermenter of description.

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