JPH11253149A - Methane fermentation controller and its control - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a methane fermentation controller and its control, capable of judging whether activity of sludge is kept in good state or not and detecting sign of system failure in early stages. SOLUTION: An organic substrate is fed from a substrate flow inklet 2 into a methane fermentation tank 1. A methane producing rate is calculated by dividing a product of measured gas flow rate with methane concentration with tank effective volume by gas flowmeter 4 and methane densitometer 5 provided between the tank 1 and a gas holder 3. Sludge VSS concentration of the tank 1 is measured by a sludge densitometer 6 and VSS concentration measuring means 7 and specific methane production activity is calculated by a specific methane production activity calculating means 8. A substrate flow rate and the substrate COD of substrate flow inlet 2 are each measured by substrate flowmeter 9 and a substrate COD measuring means 10 and fed to COD volume load calculating means 11 to calculate COD volume load and fed to a specific methane conversion activity calculating means 12. The specific methane conversion activity is compared with a standard value comparing means 13 and whether methane production activity of sludge is good nor not is judged by a judging means 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an indicator of specific methane conversion activity calculated by dividing specific methane production activity by COD volume load, and to the state of methane fermentation or the concentration of methane-producing bacteria or methane in VSS. TECHNICAL FIELD The present invention relates to a methane fermentation control device for controlling the load of methane fermentation by estimating the content ratio of produced bacteria, and a control method thereof.

[0002]

2. Description of the Related Art Conventionally, specific methane production activity has been often used as an index for expressing the activity of sludge in methane fermentation. The specific methane production activity is usually calculated as the COD equivalent methane production per day per sludge VSS unit amount after collecting sludge, putting it in a vial bottle, adding acetic acid or hydrogen as a substrate, and measuring the methane production amount. Is calculated. On the other hand, the specific methane production activity can also be calculated by converting the methane production rate from the methane fermentation tank into COD and dividing by the sludge VSS concentration. Both are called specific methane production activities, but the measurement conditions are different. In the following text, the expression “specific methane production activity” means not the former but the specific methane production activity of the latter methane fermentation tank.

[0003]

In the case of methane fermentation, when an organic substance is overloaded due to a shortened HRT (hydraulic residence time) or an excessive increase in the concentration of organic substances in a substrate, volatile substances, which are intermediate products, are produced. Organic acid concentration increases, lower p
Methanogens are inhibited by H and non-ionized volatile organic acids, and the methane production rate is reduced. A state in which this phenomenon becomes remarkable is called a system failure or sourness, and if the system failure is left untreated, the methane fermentation system is seriously damaged and it takes a long time to recover. Therefore, in the control of methane fermentation, it is necessary to take measures such as early detection of the system failure to reduce the load.

Further, as will be described later, it is not possible to detect a sign of system failure at an early stage only by measuring the specific methane production activity. In an actual example, the specific methane generation activity increases as the load is increased, but it is considered that the system failure has already started when the specific methane generation activity becomes the highest. Therefore, although the specific methane production activity is a good index expressing the activity of sludge in the methane fermentation tank, there is a problem that it is not suitable for judging whether or not the activity of sludge is in a good state.

The present invention has been made in view of the above circumstances, and determines whether or not sludge activity is good.
An object of the present invention is to provide a methane fermentation control device and a control method for detecting a sign of a system failure at an early stage.

[0006]

According to the present invention, in order to achieve the above object, a first invention has a methane fermentation tank to which an organic substrate is supplied, and methane gas fermented in this tank is stored in a storage unit. A gas flow meter and a methane concentration meter are installed in the gas passage connecting the storage part and the methane fermentation tank, and the product of the gas flow rate measured by the gas flow meter and the methane concentration measured by the methane concentration meter is measured. Methane production rate calculating means per tank volume to obtain a methane production rate by dividing by the effective volume of the fermentation tank; VSS concentration measuring means for measuring volatile suspended solids (VSS) of sludge in the methane fermentation tank; The specific methane generation activity is obtained by converting the methane generation rate obtained by the methane generation rate calculation means per COD and dividing by the sludge VSS concentration obtained by the VSS concentration measurement means to obtain the specific methane generation activity. Production activity calculation means, COD volume load calculation means for dividing the product of the substrate input amount supplied to the methane fermentation tank and the substrate COD concentration by the methane fermentation tank volume to obtain a COD volume load, and the specific methane production activity calculation The specific methane conversion activity obtained by the specific methane conversion activity calculation means for obtaining the specific methane conversion activity by dividing the specific methane production activity obtained by the means by the COD volume load obtained by the COD volume load calculation means, Determining means for comparing the specific methane conversion activity with a reference value and determining whether or not the methane generation activity is good or not based on the comparison result.

[0007] A second aspect of the present invention relates to a methane fermentation tank instead of a methane fermentation tank.
Means for calculating methane production rate per tank volume to obtain methane production rate using an ASB tank, and V for measuring volatile suspended solids (VSS) of sludge in the UASB tank
The conversion VS is calculated from the product of the SS concentration measuring means and the value obtained by the VSS concentration measuring means and the effective volume of the UASB tank.
A converted VSS concentration measuring means for obtaining the S concentration, and a methane generation rate obtained by the methane generation rate calculating means per tank volume, which is converted into COD, divided by the converted VSS concentration obtained by the converted VSS concentration measuring means, and the specific methane Specific methane generation activity calculation means for obtaining the production activity; COD volume load calculation means for obtaining the COD volume load by dividing the product of the substrate input amount supplied to the UASB tank and the substrate COD concentration by the UASB tank volume; The specific methane production activity obtained by the methane production activity calculation means is calculated using the COD obtained by the COD volume load calculation means.
D The specific methane conversion activity calculating means for obtaining the specific methane conversion activity by dividing by the volume load, and the value of the specific methane conversion activity obtained by the specific methane conversion activity calculating means are compared with a reference value. Determining means for determining whether the activity is good or not.

The third invention is characterized in that when the value of the specific methane conversion activity falls below a reference value, the hydraulic retention time (HR)
It is characterized in that control is performed so as to reduce the organic substance load by lengthening T).

A fourth invention is characterized in that the reference value is a numerical value of a specific methane production activity intermediate between the specific methane conversion activities before and after the system falls into a system failure.

A fifth invention is characterized in that the concentration of acetic acid-utilizing methane-producing bacteria is estimated from the specific methane-producing activity obtained by the specific methane-producing activity calculating means.

According to a sixth aspect of the present invention, an acetic acid assimilating methanogen concentration / VSS is estimated from the specific methane conversion activity obtained by the specific methane conversion activity calculation means.

A seventh aspect of the present invention is to obtain a methane production rate from a methane gas flow rate and a methane gas concentration generated in a tank.
The methane production rate and sludge VSS concentration or converted VS
After calculating the specific methane production activity from the S concentration, dividing the calculated specific methane production activity by the COD volume load, and calculating the specific methane conversion activity, the specific methane conversion activity is used to determine the quality of the methane fermentation or sludge activity. It is characterized in that a load is controlled for methane fermentation by making a judgment.

The eighth invention compares the specific methane conversion activity before and after the system falls into a system failure, and uses a value obtained from a numerical value of the specific methane production activity intermediate between the obtained values as a reference value. The value of the specific methane conversion activity
It is characterized in that the quality of the methane production activity of the sludge is determined.

According to a ninth aspect of the present invention, the reference value is set in advance, and when the measured value of the specific methane conversion activity is lower than the set reference value, control is performed such that the HRT is lengthened to reduce the load. It is characterized by the following.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a specific methane conversion activity control system of a complete mixed methane fermentation showing a first embodiment of the present invention. In the methane fermentation system of the first embodiment, sludge activity is in a good state. By judging whether or not this was the case, the signs of system failure were detected early, and a new index expressing the sludge activity called specific methane conversion activity was obtained.

Here, the specific methane conversion activity is the specific methane generation activity divided by the COD volume load. In the methane fermentation tank of the complete mixing type shown in FIG. 1, the specific methane conversion activity is measured to determine the quality of the sludge activity.

In FIG. 1, reference numeral 1 denotes a completely mixed methane fermentation tank in which a normal organic substrate such as sewage sludge is used.
It is supplied from the substrate inlet 2. A part of the substrate is converted to methane by the action of anaerobic bacteria contained in the sludge in the tank 1, and the methane is stored in the gas holder 3.

The methane production rate per tank volume is determined by the following equation (1): methane fermentation tank 1 and gas holder 3
Is calculated by dividing the product of the measured gas flow rate and the methane concentration by the effective volume of the methane fermentation tank by the gas flow meter 4 and the methane concentration meter 5 installed between the two.

[0019]

(Equation 1)

The sludge VSS concentration in the methane fermentation tank 1 is as follows:
It is measured by the VSS concentration measuring means 7. In practice, the SS concentration measured by the sensor 6a and analyzed manually or by the sludge concentration meter 6 is added to the VS as shown in the following equation (2).
A method of multiplying the ratio of S / SS is used.

[0021]

[Number 2] methane fermentation tank VSS concentration (kg / m ³⁾ = methane fermentation tank SS concentration ^{(kg / m 3) × VSS} / SS ...... (2) tank ratio of VSS / SS of the sludge is to put a substrate Since the variation is relatively small, such a VSS concentration measurement is possible. Next, the specific methane generation activity is calculated by the specific methane generation activity calculation means 8 by converting the methane generation rate into COD using the following equation (3) and dividing by the sludge VSS concentration.

[0022]

(Equation 3)

The substrate flow rate at the substrate inlet 2 and the substrate CO
D is a substrate flow meter 9 and a substrate COD measuring means 10 respectively.
And is supplied to the COD volume load calculating means 11. The COD volume load calculating means 11 calculates the COD volume load by substituting the substrate input amount, the substrate COD concentration and the value of the methane fermentation tank volume supplied from the following equation (4).

[0024]

(Equation 4)

The specific methane conversion activity is calculated by the specific methane conversion activity calculation means 12 into the following equation (5).
It is calculated by substituting the value of the OD volume load.

[0026]

(Equation 5)

The specific methane conversion activity shows a value higher than a certain value when the properties of the input substrate and the fermentation temperature are within a certain range and the load is not excessive. However, when the system falls into the system failure due to overload, the specific methane conversion activity is significantly reduced. By comparing the specific methane conversion activities before and after falling into the system failure, the value of the intermediate specific methane production activity is experimentally obtained and is assumed to be k. The activity is compared by the reference value comparing means 13, and based on the comparison result, the quality of the methane generation activity of the sludge is judged by the judging means 14. In this way, by comparing the specific methane conversion activity with the reference value by the comparing means 13, it is possible to determine the quality of the methane production activity of the sludge from the level of the reference value. Hereinafter, an example in which the value of k is obtained by actually using the results of a sludge digestion laboratory experiment will be described.

In a medium temperature (36 ° C.) digestion experiment using sewage sludge (mixed centrifugally concentrated and gravity concentrated sludge), HRT was used.
(Hydraulic residence time), load when stepwise increased load, methane production index (methane production rate per tank volume, specific methane production activity, specific methane conversion activity, input C
The chronological changes such as the amount of methane produced per OD), the concentration of acetic acid-utilizing methane-forming bacteria, and the concentration of acetic acid-utilizing methane bacteria / VSS are shown in FIGS.

In FIG. 2 and FIG. 3, in the centrifugal concentrated mixed raw sludge feeding system, the HRT was set to 8 days on the 14th week and to 5 days on the 15th to 17th weeks.
The methane production rate per tank volume was 1.3, 1.4, 1.0 at Weeks 14, 15, 16, and 17, respectively.
5,0.45m ³ / m ³・ day, and specific methane production activity is 0.185,0.2
05, 0.170, 0.020 kg CH ₄ -1 COD / kg VSS · day, the highest value in a series of experiments in the 15th week of HRT 5 days.

However, in the 16th week, both the methane production rate per tank volume and the specific methane production activity decreased. On the other hand, the amount of methane generated per input COD is
At 6 and 17 weeks, they were 0.18, 0.13, 0.10 and 0.04 m ³ / kg, respectively, and decreased rapidly from the 14th to the 15th week, and further decreased after the 15th week. The concentrations of acetic acid assimilating methanogens were 1.1, 1.1, and 14, respectively, at weeks 14, 15, 16, and 17.
It was 0.6,0.05 kg / m ³ , which was at the same level in the 14th and 15th weeks, but decreased rapidly in the 16th week. The acetic acid assimilating methanogen concentration / VSS was 14, 15, 16, 1
Week 7 was 5.7,5.6,3.3,0.2%, respectively, at the same level in weeks 14 and 15, but declined rapidly in week 16. The specific methane conversion activity is as follows:
At week 17, 0.027,0.018,0.015,0.002m ³ /
kgVSS, which decreases from week 14 to week 15,
Then it fell further. The specific methane conversion activity also temporarily decreased to 0.020 m ³ / kg VSS in the seventh week, but then turned upward.

Comprehensively judging from the comparison of various methane generation indices, methane generation progressed smoothly until the 14th week, but on the 15th week immediately before falling into the system failure or the system failure already started. It is thought that he had fallen into a system failure after the 16th week. Therefore, in the case of this experiment, it is considered that methane fermentation can be sustained if the system failure is detected in the 15th week and measures such as reducing the load are taken.

When a methane generation index capable of detecting a decrease in methane generation activity after the lapse of the 15th week is selected, there are specific methane conversion activity and methane generation amount per input COD. Excluded. Of these, the amount of methane generated per input COD has already been used as a methane generation index, but there seems to be no example of using specific methane conversion activity as a methane generation index, and the optimal range of specific methane conversion activity is not known. .

2 and 3, the values of the specific methane conversion activity at the 7th, 14th and 15th weeks were 0.020 and 0.02, respectively.
7,0.018m ³ / kg VSS, and above 0.020m ³ / kg VSS, methane production continues, so under these sludge digestion experimental conditions, it was determined whether methane production could be sustained without falling into the system failure. The value (k) of the specific methane conversion activity, which is a reference for determination, was estimated to be 0.020 m ³ / kg.

In this way, the value of k is determined in advance, and if the measured value of the specific methane conversion activity falls below the value of k, the control is performed such that the HRT is lengthened to reduce the organic substance load. It can be performed.

Next, a second embodiment of the present invention will be described with respect to a specific methane conversion activity control system apparatus in the UASB method shown in FIG. The specific methane conversion activity control system device shown in FIG. 4 measures the specific methane conversion activity in the UASB method to determine whether the sludge (granule) is active or not.

In FIG. 4, reference numeral 21 denotes a UASB tank to which a substrate is supplied from a substrate inlet 22. Reference numeral 30 denotes a substrate flow meter, and 31 denotes a substrate COD measuring means. A part of the substrate is converted to methane by the action of anaerobic bacteria contained in the granular sludge in the UASB tank 21, and the methane is stored in the gas holder 23. The methane production rate per tank volume is U
It is calculated as the product of the gas flow rate measured by the gas flow meter 24 and the methane concentration meter 25 installed between the ASB tank 21 and the gas holder 23 and the methane concentration.

The sludge VSS concentration in the UASB tank 21 is as follows:
It is measured by the VSS concentration measuring means 27. Actually, the SS concentration measured by the manual analysis or the sludge concentration meter 26 for the granular sludge collected from the sludge bed at the bottom of the tank is calculated as VSS / S as shown in the following equation (6).
The sludge VSS concentration in the sludge bed portion is calculated by a method such as multiplying by the ratio of S.

[0038]

[Equation 6] The sludge VSS concentration in the sludge bed portion (kg / m ³ ) = the sludge SS concentration in the sludge portion × VSS / SS (6) Also, the ratio of the sludge bed volume to the UASB tank volume is visually observed or the sludge interface is detected. The measurement is performed using an apparatus that performs the measurement. Alternatively, a measuring instrument such as a sludge concentration distribution meter 28 capable of measuring the sludge SS concentration in the vertical direction is used.
Using these volume ratios, the converted VSS concentration is calculated by the following equation (7).

[0039]

UASB tank converted VSS concentration (kg / m ³ ) = Sludge VSS concentration in sludge bed portion × Sludge bed volume / UASB tank effective volume (7) Next, the specific methane generation activity calculating means 29 calculates (8)
The specific methane generation activity is calculated by converting the methane generation rate into COD using the equation and dividing by the UASB tank converted VSS concentration.

[0040]

(Equation 8)

The substrate flow rate at the substrate inlet 22 and the substrate C
The OD is measured by the substrate flow meter 30 and the substrate COD measuring means 31, respectively, and supplied to the COD volume load calculating means 32. The COD volume load calculating means 32 calculates the substrate input amount and the substrate COD supplied by the following equation (9).
The COD volume load is calculated by substituting the concentration and the value of the UASB tank effective volume.

[0042]

(Equation 9)

The specific methane conversion activity is calculated by the specific methane conversion activity calculating means 29 according to the above equation (5).
It is calculated by substituting the value of the OD volume load.

The specific methane conversion activity depends on the structure of the fermentation tank,
It is affected by the properties of the input substrate and the fermentation temperature. However, when they are within a certain range and the load is not excessive, the value shows a value higher than a certain value. The specific methane conversion activity before and after falling into the system failure is compared, and the numerical value of the specific methane production activity in between these is experimentally obtained, and this is taken as k. Are compared by the reference value comparing means 34, and based on the comparison result, the quality of the methane generation activity of the sludge is judged by the judging means 35. As described above, by comparing the specific methane conversion activity with the reference value by the comparing means 34, it is possible to determine the quality of the methane production activity of the sludge from the level of the reference value.

Next, a high temperature (48-51 ° C.) and a medium temperature (34-36) using an artificial substrate containing acetic acid as a main component were actually used.
° C.) UASB method using the results of laboratory experiments was determined the value of the k, 0.2 m ³ / kg at high temperatures UASB process, mesophilic UAS
In the method B, it was 0.1 m ³ / kg. The value of k is twice as high in the high temperature UASB method as in the medium temperature UASB method.
In the case of the UASB method, it was found to be 5 times higher than in the case of sewage sludge digestion using a completely mixed methane fermentation tank (k = 0.020 m ³ / kg).

Thus, in the UASB method, as in the case of the methane fermentation method using the completely mixed methane fermentation tank, the value of k is determined in advance, and if the measured value of the specific methane conversion activity is k , The HRT can be lengthened to perform control to reduce the COD volume load.

As described above, in the methane fermentation, the specific methane conversion activity includes the methane production rate, the specific methane production activity,
It can be an index expressing the methane production activity of sludge in the same manner as the amount of methane production per input COD. For this reason, even when the methanation rate and methanogenesis activity were measured, when they were at their maximum, the system failed to detect the signs at an early stage because the system failed to start. In the above-described embodiment, by measuring the specific methane conversion activity, before the system failure occurs, the sign can be detected to reduce the load. Also, by measuring the specific methane conversion activity, it becomes possible to easily determine whether or not the sludge activity is in a good state.

Therefore, as a result of correlation analysis between the methane production index and other factors, in the sewage sludge mesophilic digestion experiment, the relationship between the specific methane production activity and the concentration of acetic acid assimilating methanogen shown in FIG. Number r = 0.794, n = 21) and the relationship between specific methane conversion activity and acetic acid assimilating methane bacteria concentration / VSS (correlation coefficient r = 0.770, n = 21) shown in FIG. A close correlation was observed. In addition, in the high-temperature and medium-temperature digestion experiments of sewage sludge, low-temperature methane fermentation of pig manure juice, and UASB experiment of an artificial substrate containing acetic acid as a main component, the specific methane conversion activity and 1 / V shown in FIG.
SS (COD / VSS load / input COD) relationship (r =
0.915, n = 80). This indicates that the specific methane conversion activity is proportional to the acetic acid assimilating methanogen / VSS concentration.

Further, in the UASB method, methanogens /
Since it is known that VSS is higher than that in the case of sludge digestion, it can be explained that the specific methane conversion activity is higher in the UASB method than in the case of sludge digestion.

From the above facts, the significance of measuring the specific methane conversion activity and the effectiveness as an indicator of methane production are recognized.
The following equations (10) and (11), which are regression equations obtained by correlation analysis between specific methane production activity and acetic acid assimilating methane bacteria concentration and specific methane conversion activity and acetic acid assimilating methane bacteria concentration / VSS. The concentration of acetic acid-utilizing methane-producing bacteria and the concentration of acetic acid-utilizing methane-producing bacteria / VSS can also be estimated from the specific methane-producing activity and the specific methane conversion activity using the formula.

[0051]

## EQU10 ## Acetic acid-assimilating methanogen concentration = 4.19 × specific methanogenic activity (kg CH ₄ -COD / kg VSS · day) (kg / m ³ ) +0.276 (10)

[0052]

[Equation 11] acetic acid-utilizing methanogen concentration / VSS = 95.5 × specific methane conversion activity (m ³ / kg VSS) (%) + 1.40 (11)

[0053]

As described above, according to the present invention, by measuring the specific methane conversion activity, it has been impossible to detect the signs of system failure at an early stage. This has the advantage that measures can be taken to reduce the load by detecting the signs before the system failure occurs. Further, according to the present invention, by measuring the specific methane conversion activity, there is an advantage that it can be easily determined whether or not the sludge activity is in a good state.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a specific methane conversion activity control system for a completely mixed methane fermentation showing a first embodiment of the present invention.

FIG. 2 is a characteristic diagram of a change over time of a methane generation index with respect to a load increase in a sludge digestion experiment.

FIG. 3 is a graph showing a change over time in a methane generation index, an acetic acid-utilizing methane-producing bacterium concentration, and the like with respect to a load increase in a sludge digestion experiment.

FIG. 4 is a configuration diagram of a specific methane conversion activity control system in a UASB method showing a second embodiment of the present invention.

FIG. 5 is a characteristic diagram showing a relationship between specific methane production activity and acetic acid-utilizing methane-producing bacteria concentration in a sludge digestion experiment.

FIG. 6 is a characteristic diagram showing a relationship between specific methane conversion activity and acetic acid-utilizing methane-producing bacteria concentration / VSS in a sludge digestion experiment.

FIG. 7 is a characteristic diagram showing the relationship between 1 / VSS and specific methane conversion activity in methane fermentation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Complete mixing methane fermentation tank 2 ... Substrate inflow port 3 ... Gas holder 4 ... Gas flow meter 5 ... Methane concentration meter 6 ... Sludge concentration meter 6a ... Sensor 7 ... VSS concentration measurement means 8 ... Specific methane generation activity calculation means 9 ... substrate flow meter 10 ... substrate COD measuring means 11 ... COD volume load calculating means 12 ... specific methane conversion activity calculating means 13 ... reference value comparing means 14 ... determining means

Claims (9)

[Claims] 1. A methane fermentation tank to which an organic substrate is supplied, wherein a methane gas fermented in the tank is stored in a storage section, and a gas flow meter and a methane fermenter are provided in a gas passage connecting the storage section and the methane fermentation tank. A methane production rate calculation means per tank volume that installs a concentration meter and divides the product of the gas flow rate measured by the gas flow meter and the methane concentration measured by the methane concentration meter by the effective volume of the methane fermentation tank to obtain the methane production rate And volatile suspended solids (VS) of the sludge in the methane fermentation tank.
S) measuring the VSS concentration, and the specific methane production by dividing the methane production rate obtained by the methane production rate calculating means per tank volume into COD and dividing by the sludge VSS concentration obtained by the VSS concentration measuring means. Specific methane production activity calculation means for obtaining activity; substrate input amount and substrate C supplied to the methane fermentation tank
COD volume load calculation means for obtaining the COD volume load by dividing the product of the OD concentration by the methane fermentation tank volume; and the specific methane generation activity obtained by the specific methane generation activity calculation means obtained by the COD volume load calculation means. Specific methane conversion activity calculating means for obtaining the specific methane conversion activity by dividing by the COD volume load, and the specific methane conversion activity value obtained by the specific methane conversion activity calculating means are compared with a reference value. A methane fermentation control device, comprising: determination means for determining whether the activity is good or bad. 2. A UASB tank to which an organic substrate is supplied, wherein a methane gas fermented in this tank is stored in a storage unit, and a gas flow meter and a methane concentration meter are provided in a gas passage connecting the storage unit and the UASB tank. Methane production rate calculation means per tank volume to obtain a methane production rate by dividing the product of the gas flow rate measured by the gas flow meter and the methane concentration measured by the methane concentration meter by the UASB tank effective volume, Volatile suspended matter (VS) of sludge in the UASB tank
S) measuring VSS concentration measuring means, and a converted VS which obtains a converted VSS concentration from a product of a value obtained by the VSS concentration measuring means and a UASB tank effective volume.
S concentration measuring means, and a ratio for obtaining a specific methane production activity by dividing the methane generation rate obtained by the methane generation rate calculating means per tank volume by COD conversion and dividing by the converted VSS concentration obtained by the converted VSS concentration measuring means. Methane production activity calculation means, substrate input amount and substrate CO supplied to the UASB tank
COD volume load calculating means for obtaining the COD volume load by dividing the product of the D concentration by the UASB tank volume; and COD obtained by the COD volume load calculating means by the specific methane generation activity obtained by the specific methane generation activity calculating means. Specific methane conversion activity calculating means for obtaining the specific methane conversion activity by dividing by the volume load, and the specific methane conversion activity value obtained by the specific methane conversion activity calculating means are compared with a reference value. A methane fermentation control device, comprising: determination means for determining the quality of the methane fermentation. 3. The method according to claim 1, wherein when the value of the specific methane conversion activity falls below a reference value, the hydraulic retention time (HRT) is lengthened to reduce the organic matter load. 3. The methane fermentation control device according to 2. 4. The method according to claim 1, wherein the reference value is a numerical value of a specific methane production activity intermediate between the specific methane conversion activities before and after the system falls into a system failure. Methane fermentation control device. 5. The methane fermentation control device according to claim 1, wherein the concentration of acetic acid-utilizing methane-producing bacteria is estimated from the specific methane-producing activity obtained by the specific methane-producing activity calculating means. 6. An acetic acid assimilating methane-producing bacterium concentration / from the specific methane conversion activity obtained by the specific methane conversion activity calculation means.
The methane fermentation control device according to claim 1 or 2, wherein VSS is estimated. 7. A specific methane generation activity is obtained from a methane generation rate from a methane gas flow rate and a methane gas concentration generated in the tank, and then a specific methane generation activity is calculated from the methane generation rate and a sludge VSS concentration or a converted VSS concentration. After calculating the specific methane conversion activity by dividing the activity by the COD volume load, the quality of methane fermentation or sludge activity was judged using the specific methane conversion activity to control the load of methane fermentation. Characteristic methane fermentation control method. 8. The specific methane conversion activity before and after falling into the system failure is compared, and the value obtained from the numerical value of the specific methane production activity in the middle of the obtained values is set as a reference value, which is used as the reference value. The method for controlling methane fermentation according to claim 7, wherein the quality of the methane production activity of the sludge is determined based on the level of the specific methane conversion activity. 9. The method according to claim 1, wherein the reference value is set in advance, and when the measured value of the specific methane conversion activity is lower than the set reference value, control is performed such that the HRT is lengthened to reduce the load. The method for controlling methane fermentation according to claim 7 or 8, wherein