JP2006247568A - Methane fermentation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a methane fermentation method which enables the monitor of a methane fermentation condition and maintenance of a stable methane fermentation condition. <P>SOLUTION: In the methane fermentation method where organic waste is charged to a methane fermentation tank containing anaerobic microorganisms mainly comprising methane bacteria to be subjected to methane fermentation, and hydrogen sulfide in the produced biogas is desulfurized with a wet desulfurizer, methane gas concentration and carbon dioxide gas concentration in the biogas are measured to calculate hydrogen sulfide concentration in the biogas, and operation control of the methane fermentation is carried out from the calculated value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a methane fermentation treatment method for treating organic waste such as manure, raw garbage, food processing residue and the like using anaerobic microorganisms.

  Most organic waste such as garbage is incinerated or landfilled, but due to problems such as the generation of dioxins associated with incineration, tightness of landfill sites, and foul odors, treatment methods with low environmental impact are required. Yes. In order to solve these problems, research and development have been conducted on a system in which organic waste is subjected to methane fermentation, 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.

  In the methane fermentation treatment, organic waste is pulverized and slurried, and then this slurry is put into a fermenter and fermented with methane bacteria under anaerobic conditions to decompose the organic waste into biogas and water. This method is advantageous in that the amount of organic waste can be greatly reduced and methane gas produced as a by-product can be recovered as energy. In addition, since it is anaerobic and does not require aeration power, it is an energy-saving treatment method.

  Here, in the methane fermentation treatment, since it is necessary to efficiently decompose organic waste and take out methane gas, it is important to optimally control the fermentation state in the methane fermentation tank.

  As a method for improving the fermentation efficiency in the methane fermenter, there is an adjustment of the addition amount of a metal salt serving as a nutrient such as methane bacteria. As nutrients, it is widely known to add nickel, cobalt or the like to the methane fermentation tank.

  Moreover, organic acids, such as propionic acid, are contained in the organic waste used for methane fermentation treatment. It is known that the activity of methane bacteria decreases due to the accumulation of organic acids. Usually, microorganisms capable of decomposing organic acids such as sulfate-reducing bacteria are introduced and decomposed into carbon dioxide, hydrogen sulfide and the like.

  However, it is known that hydrogen sulfide generated by the decomposition of the organic acid is highly toxic and corrosive, and inhibits methane fermentation and the like at a high concentration.

  In order to reduce this hydrogen sulfide, for example, in Patent Document 1 below, the growth of sulfate-reducing bacteria in the fermenter is monitored, or the number of sulfate-reducing bacteria is monitored, and the monitoring result is used as an index for the methane fermenter. Nutrients are added.

In Patent Document 2 below, the methane gas content and the hydrogen sulfide content in the biogas are measured, and the hydrogen sulfide generation amount is suppressed by supplying and stopping the oxygen-containing gas or oxygen according to the measured value. ing.
JP 2002-282826 A JP 2003-136089 A

  In Patent Documents 1 and 2, in order to maintain a stable fermentation state in the methane fermentation treatment, the hydrogen sulfide concentration in the methane fermentation treatment tank is reduced. At that time, the hydrogen sulfide concentration in the biogas is measured. The process according to the measurement result is performed.

  However, since the amount of hydrogen sulfide in the biogas is very small, the measuring instrument is relatively expensive. Moreover, since the measurement means is a batch type, continuous measurement in real time cannot be performed, and convenience is lacking.

  Therefore, an object of the present invention is to provide a methane fermentation treatment method capable of monitoring the methane fermentation state and maintaining a stable fermentation state with a simple analysis technique.

  In achieving the above-mentioned object, the methane fermentation treatment method of the present invention introduces an organic waste into a methane fermentation tank containing anaerobic microorganisms mainly composed of methane bacteria, and performs methane fermentation. In the methane fermentation treatment method for desulfurizing hydrogen sulfide in a desulfurization apparatus, the methane gas concentration or carbon dioxide concentration in the biogas is measured to calculate the hydrogen sulfide concentration in the biogas, and methane is based on the value. It is characterized by controlling the operation of fermentation.

  As a result of various studies, the present inventors have found that the methane gas concentration and carbon dioxide concentration in biogas obtained by methane fermentation of organic waste are correlated with the hydrogen sulfide concentration in biogas. . The methane gas concentration and the carbon dioxide gas concentration in the biogas can be measured in real time by the non-dispersive infrared absorption method, and these measuring instruments are relatively inexpensive.

  Therefore, according to the present invention, the hydrogen sulfide concentration in the methane fermentation tank can be calculated by a relatively simple method, and the operation is performed so that the hydrogen sulfide concentration in the tank can be reduced according to the calculated hydrogen sulfide concentration. A stable methane fermentation treatment state can be maintained by appropriately controlling the state.

  Moreover, in this invention, it is preferable to increase the input of the nutrient salt of methane bacteria added to a methane fermentation tank according to the increase amount of the hydrogen sulfide concentration in the said biogas calculated.

  It is known that methane bacteria and sulfate-reducing bacteria have a competitive relationship in using hydrogen in the methane fermentation tank. Therefore, when the hydrogen sulfide concentration in the biogas is high, it can be estimated that the activity of methane bacteria is reduced.

  Therefore, using the hydrogen sulfide concentration in biogas as an activity guideline for methane bacteria, if this hydrogen sulfide concentration is increased, methane bacteria can be activated by adding trace metals that are nutrient salts of methane bacteria, As a result, the concentration of hydrogen sulfide in the methane fermentation tank can be reduced, and a stable methane fermentation state can be maintained.

  Further, in the present invention, based on the calculated hydrogen sulfide concentration in the biogas and the amount of sulfur inflow into the desulfurization device calculated from the amount of biogas generated actually measured, sulfur to the desulfurization material It is preferable to determine the replacement time by calculating the adsorption amount in advance.

  According to this, by stabilizing the generation amount of hydrogen sulfide, it is possible to stabilize the load of the desulfurization device, and to design an optimal replacement time for the desulfurization material to be filled in the desulfurization device. Reduction of the amount used and optimization of the desulfurization process can be expected.

  According to the present invention, since the hydrogen sulfide concentration in the biogas is calculated based on the methane gas concentration and the carbon dioxide concentration in the biogas, the methane gas concentration or the carbon dioxide concentration can be calculated in real time with a relatively simple device. It is possible to measure and constantly monitor the transition of hydrogen sulfide concentration in biogas. Moreover, the methane fermentation treatment state can be stabilized by stabilizing the hydrogen sulfide concentration in the biogas by a method such as determining the amount of nutrient added according to the calculated hydrogen sulfide concentration.

  Furthermore, since the hydrogen sulfide concentration in the biogas can be stabilized, the amount of desulfurization in the desulfurizer can be estimated by taking into account the amount of biogas generated, and the size and processing capacity of the desulfurizer. Optimal design such as can be done. Moreover, the optimal replacement | exchange time of a desulfurization material can be designed, and the consumption of a desulfurization material can be reduced.

  Hereinafter, the present invention will be described in more detail with reference to the drawings. The schematic block diagram of one Embodiment of the methane fermentation processing apparatus which can be used for the methane fermentation processing method of this invention is shown by FIG.

  First, the methane fermentation treatment apparatus of FIG. 1 will be described. The methane fermentation treatment apparatus includes a pulverizer 1 for treating organic waste into a paste, a slurry adjusting tank 2 for slurrying and storing the paste, and methane. A fermentation tank 3, a waste liquid treatment tank 4 for treating the fermented liquid after the methane fermentation treatment, a dry desulfurizer 5 for removing hydrogen sulfide from the biogas obtained by the methane fermentation treatment, and a nutrient storage tank 6 It is mainly composed of.

  A pipe 1 a from the pulverizer 1 is connected to the slurry adjustment tank 2 via the paste supply pump 10, and a pipe 2 a from the slurry adjustment tank 2 is connected to the methane fermentation tank 3 via the slurry supply pump 11. . A pipe 6 a extending from the nutrient salt storage tank 6 for adding a nutrient salt such as a metal salt into the methane fermentation tank 3 is connected to the methane fermentation tank 3 via the nutrient salt supply pump 20.

  On the bottom of the methane fermentation tank 3, a pipe 4 a for extracting the slurry after the methane fermentation treatment is connected to the waste liquid treatment tank 4 via the slurry extraction pump 12.

  The waste liquid treatment tank 4 only needs to be capable of denitrification treatment, for example, an activated sludge tank for performing a biological treatment method for removing organic matter and nitrogen by microorganisms, or after aeration treatment with ammonia and catalytic combustion with air. An apparatus that performs an ammonia stripping method that renders nitrogen gas harmless can be used.

  A pipe 5a for taking out the generated biogas is connected to the upper part of the methane fermentation tank 3, and is connected to a dry desulfurizer 5 for desulfurizing hydrogen sulfide in the biogas.

  Between the pipe 5a and the dry desulfurizer 5, a measuring device 7 for measuring the methane gas concentration or the carbon dioxide gas concentration in the biogas is disposed. Here, the measuring device 7 is not particularly limited as long as it is a measuring device that can be used for detecting methane gas or carbon dioxide gas, and examples thereof include a non-dispersed infrared absorption measuring device.

  And the measured value from this measuring device 7 is comprised so that it may input into the calculator 30, and it supplies nutrient salt from the nutrient salt supply pump 20, or increases supply amount according to a measured value. Can do.

  In the measuring device 7, when the methane gas concentration in the biogas is measured, the arithmetic processing and control by the arithmetic unit 30 are performed as shown in the flowchart of FIG.

  First, in step S1, the methane concentration in the biogas measured by the measuring device 7 is input to the computing unit 30 as a measured value.

  And it progresses to step S2 and it is judged whether a measured value is more than predetermined, and if it is more than predetermined value, it will progress to step S3 and the supply amount of the nutrient salt from the nutrient supply pump 20 will be set. The methane fermentation process is performed in the same amount.

  On the other hand, when the measured value is less than or equal to the predetermined value, the process proceeds to step S4, where nutrient salt is supplied from the nutrient salt supply pump 20, or the supply amount is increased. The above processing is repeated at predetermined intervals, and control can be performed so that the measured value in step S2 is equal to or greater than the predetermined value.

  Further, in the measuring device 7, when the concentration of carbon dioxide in the biogas is measured, the calculation processing and control by the calculator 30 are performed as shown in the flowchart of FIG.

  First, in step S <b> 11, the carbon dioxide concentration in the biogas measured by the measuring device 7 is input to the computing unit 30 as a measured value.

  Then, the process proceeds to step S12, and it is determined whether or not the measured value is equal to or less than a predetermined value. If the measured value is equal to or less than the predetermined value, the supply amount of the nutrient salt from the nutrient salt supply pump 20 remains the set amount in step S13. Methane fermentation treatment is performed.

  On the other hand, when the measured value is equal to or larger than the predetermined value, the process proceeds to step S14, where nutrient salt is supplied from the nutrient salt supply pump 20, or the supply amount is increased. The above processing is repeated at a predetermined interval, and control can be performed so that the measured value in step S12 is less than or equal to the predetermined value.

  Thus, the computing unit 30 is configured to supply nutrient salts into the methane fermentation tank according to the measured value.

Next, the methane fermentation processing method of this invention using this processing apparatus is demonstrated.
The organic waste is first stored in the pulverizer 1 and is subjected to processing such as crushing and pulverization to form a paste. Then, the pasted organic waste is stored in the slurry adjustment tank 2 via the paste supply pump 10. Here, it is diluted with moderate water and slurried.

  Next, this slurry is put into the methane fermentation tank 3 by the slurry supply pump 11 to perform methane fermentation.

  The methane fermentation tank 3 is provided with a fixed filter bed or the like filled with immobilized microorganisms on which anaerobic microorganisms such as methane bacteria (not shown) are attached and supported, and the slurry is subjected to methane fermentation and anaerobic. Organic waste is decomposed by microorganisms. In addition, the same amount of fermentation broth as the slurry supplied at regular intervals is drawn from the bottom of the methane fermentation tank 3 by the slurry extraction pump 12, and the inside of the methane fermentation tank 3 is always filled with a fixed amount of slurry. .

  The biogas generated by the methane fermentation treatment is desulfurized by a dry desulfurizer 5 filled with an iron-based catalyst such as iron oxide and a desulfurization material such as (manufactured by Tetsugen: TG refiner), and hydrogen sulfide is removed.

  Here, the biogas is measured at the measuring device 7 by measuring the concentration of methane gas or carbon dioxide in the biogas, and the measured value is input to the computing unit 30. The computing unit 30 performs arithmetic processing and control based on the input measurement value, adjusts the amount of nutrient salt supplied from the nutrient salt supply pump 20 as necessary, and puts the methane fungus in the methane fermentation tank 3. The nutrient salt is added or increased, and the methane gas concentration is controlled to be a predetermined value or higher, or the carbon dioxide gas concentration is controlled to be a predetermined value or lower.

  For example, in order to control the hydrogen sulfide concentration in the methane fermentation tank to be 600 ppm or less, the carbon gas concentration is 42% or more, although it depends on the processing capacity of the dry desulfurizer 5 and the scale of the methane fermentation tank. The feed amount of the nutrient salt of methane bacteria is controlled so that the carbon dioxide gas concentration is 42% or less by supplying the nutrient salt from the nutrient salt supply pump 20 or increasing the nutrient salt supply amount. . Alternatively, when the methane gas concentration becomes 58% or less, the methane bacterium is supplied so that the methane gas concentration becomes 58% or more by supplying the nutrient salt from the nutrient salt supply pump 20 or increasing the supply amount of the nutrient salt. To control the amount of nutrient input.

  Then, the desulfurized biogas is collected in a gas holder (not shown) and is effectively used as a fuel for a power generator such as a fuel cell power generation device or a gas engine or a boiler. In this embodiment, the methane gas concentration or carbon dioxide concentration in the biogas before the desulfurization treatment is measured, but the methane gas concentration or carbon dioxide concentration after the desulfurization treatment may be measured.

  As described above, the present invention calculates the hydrogen sulfide concentration in the biogas by measuring the methane gas concentration or the carbon dioxide concentration in the biogas, and performs the operation control of the methane fermentation based on the value. It is said.

  The methane fermentation treatment was performed for 82 days, of which the operation was performed for 45 days with a residence time of 4 days, and when the hydrogen sulfide concentration, methane gas concentration, and carbon dioxide concentration in the biogas were measured, the measurement results shown in FIG. 4 were obtained. It was. FIG. 4 shows the relationship among the staying days indicating the operational load, the methane gas concentration in the biogas, the carbon dioxide gas concentration, and the hydrogen sulfide concentration in the elapsed days.

  And the relationship between the hydrogen sulfide concentration and the methane gas concentration in the staying days of 4 days has a negative correlation as shown in FIG. 5, and the carbon dioxide gas has a positive correlation as shown in FIG. It was found that the hydrogen sulfide concentration in the biogas is highly correlated with the methane gas concentration or the carbon dioxide concentration in the biogas. 5 and 6 are obtained by extracting and plotting the data of the staying days of 4 days from the measurement results of FIG.

  That is, as the carbon dioxide concentration increases or the methane gas concentration decreases, the hydrogen sulfide concentration increases. On the other hand, as the carbon dioxide concentration decreases or the methane gas concentration increases, the hydrogen sulfide concentration decreases and the concentration decreases. Stabilize. Here, the hydrogen sulfide concentration in the biogas is measured using a gas sulfide detector for hydrogen sulfide, and the methane gas concentration and carbon dioxide gas concentration are measured using a gas chromatograph (trade name; “P200” manufactured by Agilent Technologies). It was measured.

  Therefore, the hydrogen sulfide concentration in the biogas can be calculated by measuring either the methane gas concentration or the carbon dioxide concentration without directly measuring the hydrogen sulfide concentration in the biogas.

  Then, using the hydrogen sulfide concentration in the biogas as an activity guideline for methane bacteria, when this hydrogen sulfide concentration increases, the methane bacteria are added by a method such as adding trace metals that are nutrient salts of methane bacteria. By activating it and reducing the hydrogen sulfide concentration in the methane fermentation tank, a stable methane fermentation state can be maintained.

  Thus, since the methane gas concentration and carbon dioxide concentration in biogas can be detected continuously, the transition of the hydrogen sulfide concentration in the concentration biogas can be calculated by calculating the hydrogen sulfide concentration from the methane gas concentration or carbon dioxide gas. Can be monitored, the concentration of hydrogen sulfide in biogas can be stabilized by a method such as controlling the supply amount of nutrient salts of methane bacteria, and the methane fermentation treatment state can be stabilized.

  In addition, by stabilizing the hydrogen sulfide concentration in the biogas, it is possible to calculate the hydrogen sulfide concentration in the biogas and the amount of sulfur inflow into the desulfurizer from the measured amount of biogas generated, Therefore, the amount of sulfur adsorbed on the desulfurization material can be calculated in advance, so that the amount of desulfurization treatment in the desulfurization apparatus can be estimated, and the optimum replacement time of the desulfurization material can be designed, so that the consumption of desulfurization material can be reduced. Therefore, the operation cost and maintenance cost can be reduced.

  The methane fermentation treatment method of the present invention is suitably used for methane fermentation treatment of organic waste such as raw garbage, food processing residue, surplus sludge such as activated sludge treatment.

It is a schematic block diagram which shows one Embodiment of the methane fermentation processing apparatus used for this invention. It is a flowchart figure which shows the arithmetic processing by the calculating unit 30, and the control method when the methane gas density | concentration is measured with the measuring device. It is a flowchart figure which shows the arithmetic processing by the calculator 30, and the control method when a carbon dioxide gas concentration is measured with the measuring device. It is a test result which shows the time-dependent change of the hydrogen sulfide density | concentration in biogas, methane gas density | concentration, and a carbon dioxide gas density | concentration. It is a graph which shows the relationship between the methane gas density | concentration and the hydrogen sulfide density | concentration in the residence days. It is a graph which shows the relationship between the carbon dioxide gas density | concentration and hydrogen sulfide density | concentration in the residence days.

Explanation of symbols

1: Crusher 2: Slurry adjustment tank 3: Methane fermentation tank 4: Waste liquid treatment tank 5: Dry desulfurizer 6: Nutrient salt storage tank 7: Measuring instrument 20: Nutrient supply pump 20
30 calculator

Claims (3)

In the methane fermentation treatment method in which organic waste is put into a methane fermentation tank containing anaerobic microorganisms mainly composed of methane bacteria and methane fermentation is performed, and hydrogen sulfide in the obtained biogas is desulfurized by a desulfurization apparatus.
A methane fermentation treatment method characterized in that a methane gas concentration or a carbon dioxide gas concentration in the biogas is measured to calculate a hydrogen sulfide concentration in the biogas, and methane fermentation operation control is performed based on the value.   The methane fermentation treatment method according to claim 1, wherein the input amount of nutrient salts of methane bacteria added to the methane fermentation tank is increased according to the calculated increase amount of the hydrogen sulfide concentration in the biogas. Based on the calculated concentration of hydrogen sulfide in the biogas and the amount of sulfur inflow into the desulfurizer calculated from the amount of biogas generated actually measured, the sulfur adsorption amount to the desulfurization material is calculated in advance. The methane fermentation treatment method according to claim 1 or 2, wherein the replacement time is determined by the method.