JPH0731998A - Slightly anaerobic hydrogen fermentation method for organic waste - Google Patents

Abstract

PURPOSE:To provide the slightly anaerobic hydrogen fermentation method capable of producing the hydrogen being a clean energy high speed and high efficiency. CONSTITUTION:In the slightly anaerobic hydrogen fermentation method subjecting an org. waste 1 to a hydrogen fermentation 7, the org. waste is fermentated while controlling the fermentation liq under the hydrogen fermentation in a slightly anaerobic condition in which an oxidation-reduction electric potential 9 is kept within a range of -100--200mV, and the hydrogen fermentation is executed preferably by a reduced pressure fermentation or while separating hydrogen 12 and gaseous CO2 13 by passing a generated gas to a gas separating membrane 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for biological treatment of organic waste, and more particularly to a method for slightly anaerobic hydrogen fermentation of various sludges containing organic matter such as human waste and sewage sludge.

[0002]

2. Description of the Related Art Conventionally, the treatment and disposal of human waste, sewage sludge and / or various sludges rich in organic matter has low treatment cost, easy operation management, and stabilization of decomposition of organic matter and at the same time energy saving. It is a well-known fact that the methane fermentation method has been adopted due to its advantages such as bioconversion to the substance methane.

The conventional methane fermentation method includes a high temperature methane fermentation method, a medium temperature methane fermentation method and / or a relatively recent technology such as an upflow sludge blanket type methane fermentation method (UASB method). The common treatment technology is to decompose and lower the molecular weight of pollutant organic substances by a three-step biological successive reaction by solid-liquefying bacteria, acid-fermenting bacteria (producing lower carboxylic acids) and methanogenic bacteria, and finally It is a technology that converts methane and carbon dioxide, which are energy substances, into methane fermentation digestion liquid, and microbially oxidizes and stabilizes the remaining organic matter by ordinary aerobic treatment and discharges it to public water bodies.

[0004] The core of this treatment technology is wildly inhabited in various sludges, such as Methanococcus.
occus), methanothrics (Methanothrix), methanosarcina (Methanosarcina), methanoble vivactor (Me
is a methanogenic bioreaction by a so-called methanogenic bacterium such as a carboxylic acid-utilizing methane bacterium such as thanobrevibacter) or a hydrogen-utilizing methane bacterium, and methane is produced by the following biological reaction. Acetic acid ^{_{CH 3 COO - + H 2 O}} = CH 4 + HC
O ₃ ^- ant acid _{^{4HCOO - + 4H + + H 2}} O = 3HC
O ₃ ⁻ + 3H ⁺ + CH ₄ Butyric acid 2CH ₃ (CH ₂ ) ₂ COO ⁻ + HCO
₃ ⁻ + H ₂ O = 4CH ₃ COO ⁻ + H ₂ + CH ₄ hydrogen 4H ₂ + H ⁺ + HCO ₃ ⁻ = CH ₄ +3
H ₂ O

As described above, the methane fermentation method is not only an energy-saving treatment technology, but also can produce an energy substance called methane, and is therefore widely used for the treatment of concentrated organic waste such as human waste and sewage sludge. At the present time, about 550 to 650 treatment sites for human waste treatment total 1250 treatment sites, and sewage treatment treatment total 1200 treatment facilities.
300 to 400 methane fermentation treatment facilities are operating for all (including all) locations.

[0006] However, environmental pollution on a global scale has become apparent over the past few years, and among them, it has been pointed out that global warming caused by various gases is the most threatening future survival of mankind, and a warning is issued. . As the gas that promotes global warming, the largest amount of carbon dioxide is released into the atmosphere from various human production activities, daily activities and natural ecosystems, and the contribution rate to global warming is 45 to 55%. It is said to be. On the other hand, the above-mentioned various activities by human beings and the amount of methane generated from nature are insignificant with respect to the amount of carbon dioxide, but the infrared absorption capacity of methane is far greater than that of carbon dioxide. Large (about two digits larger)
Therefore, the contribution rate of methane gas to global warming is 15 to 20
%, Which is a non-negligible contribution to the rise in the temperature of the earth.

From this point of view, the methane fermentation method as a conventional technique generates methane gas, which has a very serious influence on global warming, in a concentrated and large amount, so that it is completely captured as an energy substance and completely burned. Must. However, in reality, there is no problem in the winter when the outside air temperature is low, and in the summer when the outside temperature is high, the methane gas generated as a heating source for the fermentation tank is obviously a surplus heat source, and in many treatment plants. In many cases, the generated gas is directly emitted to the atmosphere without being used as a heat source.

Further, this methane fermentation technique is characterized in that the carbon dioxide gas produced as a result of a biological reaction is in excessive excess with respect to the absolute amount of hydrogen, which is a substrate of hydrogen-utilizing methanogens. Carbon dioxide, which has absolutely no value as an energy source, always remains at about 40%, which promotes global warming. Further, even if the above-mentioned methane gas is effectively used as energy, when it is burned, it is converted into carbon dioxide gas as shown in the following equation. CH ₄ + 2O ₂ = CO ₂ + 2H ₂ O

From the above, the methane fermentation method, which has been widely applied as a treatment technology for human waste or mainly sewage sludge, has a problem that the generated methane gas leaks into the atmosphere without being used or is intentionally discharged into the atmosphere. Dissipation promotes global warming, and even more troublesome is that even if methane is used as an energy source, it will be converted to carbon dioxide, which is the main cause of global warming, and further promotes global warming. . As detailed above, conventionally, human waste, sewage sludge and / or
Or, various wastewater containing organic matter in a concentrated manner, methane fermentation, which is widely adopted for treatment of sludge, is itself energy-saving and is easy to operate and manage, even if the generated gas is used, Even if it is diffused into the atmosphere without using it, it cannot be said to be an earth-friendly treatment technology because it emits a large amount of methane gas and carbon dioxide gas that negatively contributes to global warming.

[0010]

From the above facts, from the above facts, a new organic waste treatment technology that can contribute to the preservation or improvement of the global environment, especially a new technology that should replace the conventional methane fermentation method, has been available for several years. There is an urgent need for processing technology research and development, and there is a strong social demand for its establishment. The present invention aims to provide a slightly anaerobic hydrogen fermentation method capable of producing the hydrogen, which is a clean energy, at high speed and with high efficiency by improving the above-mentioned fatal defects of the conventional technology, in particular, the methane fermentation method. To do.

[0011]

In order to solve the above problems, in the present invention, in the slightly anaerobic hydrogen fermentation method of hydrogen-fermenting an organic waste, the fermentation liquid in the hydrogen fermentation has an oxidation-reduction potential of -100. Fermentation is performed while controlling so as to be a slightly anaerobic condition in the range of to -200 mV. In the above, hydrogen fermentation is preferably carried out by reduced pressure fermentation or while the generated gas is passed through a gas separation membrane to separate hydrogen and carbon dioxide gas, whereby hydrogen gas is forcibly reacted. The hydrogen partial pressure can be reduced by taking it out of the system.

The organic waste as a raw material is preferably adjusted by slow aeration before fermentation so that the redox potential of the organic waste is within a range in which hydrogen fermentation proceeds without delay. Furthermore, the hydrogen fermentation is divided into a first fermentation that performs vacuum fermentation and a second fermentation that performs atmospheric fermentation, and the fermentation liquid of the second fermentation is adjusted to a redox potential that allows hydrogen fermentation to proceed without delay by slow aeration. However, the fermentation liquor can be combined with the organic waste, or continuously and / or intermittently circulated in the first fermentation. The hydrogen fermentation of the present invention can also be performed by using a redox potential sensor to adjust the air volume of slow aeration so that the redox potential falls within a range suitable for hydrogen fermentation.

As described above, according to the present invention, the redox suitable for the living and growing of the methanogenic bacteria group and the hydrogen-producing bacteria group, which live in the wild, such as human waste and sewage sludge, respectively. By making effective use of the considerable potential difference, the redox potential of the input substrate or the liquid in the anaerobic fermentation tank is artificially adjusted to a range suitable for inhabiting hydrogen-producing bacteria by means such as slow aeration. The hydrogen production method is characterized by adjusting the hydrogen fermentation of organic waste so that it preferentially progresses over the methane fermentation by controlling the above. In addition, high speed and high efficiency can be achieved.

Next, the present invention will be described in detail. In the slightly anaerobic hydrogen fermentation method of the present invention, the hydrogen equilibrium concentration is increased in the liquid phase of the fermenter as a result of the progress of the hydrogen fermentation in preference to the methane fermentation, and naturally, the hydrogen content of the gas phase part of the closed fermenter is increased. The pressure rises. Hydrogen fermentation of organic waste by hydrogen-producing bacteria is an absorbing ergon reaction in which the standard free energy of the biological reaction has a positive value, and the biological reaction is inherently difficult to proceed in the positive direction.

In order to allow this reaction to proceed smoothly in the positive direction, hydrogen, which is a product of hydrogen fermentation, is allowed to successively proceed with other biological reactions in the mixed culture system, whereby the whole biological reaction system is allowed to proceed. As a result, the standard free energy is converted to a degassing ergon reaction with a negative value, or hydrogen in the liquid phase or gas phase is forcibly taken out of the reaction system so that the effect is substantially equivalent to the degassing ergon reaction. Have to operate. Therefore, in the present invention, in order to proceed the hydrogen fermentation of the organic waste without delay, the hydrogen fermentation tank is under reduced pressure conditions and the tank liquid is subjected to reduced pressure fermentation to obtain the equilibrium concentration of hydrogen and the gas in the liquid phase. It is considered that the hydrogen partial pressure in the phase is forcibly reduced so that the hydrogen fermentation substantially proceeds as an ergon reaction.

Further, in the present invention, as another method for smoothly proceeding hydrogen fermentation, the generated gas of hydrogen fermentation is separated into carbon dioxide gas and hydrogen gas by passing through a gas separation membrane, and hydrogen gas is subjected to a biological reaction. It was forcibly taken out of the system to eliminate the above obstacles. As one of the excellent functions of microorganisms, a living environment that is always preferable by a specific microorganism,
Even if living conditions are not given, qualitative conversion at the gene level is performed in the process of culturing under these conditions for a long period of time, gradually adapting to this environment and acclimatizing, and the microorganisms under favorable conditions even in a heterogeneous environment. It has almost the same function as. By effectively utilizing this qualitative conversion, by slowly reducing the degree of decompression of the initially set reduced pressure fermentation tank and / or the amount of hydrogen gas separated in the gas separation membrane, hydrogen fermentation at atmospheric pressure is attempted. Does not hinder the object of the present invention.

The most important essential condition in the present invention is that the ORP of the solution in the fermenter is optimally changed from the absolute anaerobic environment to the slightly anaerobic environment by slow aeration, that is, the ORP is optimal for life and growth of hydrogen-producing bacteria. It is to adjust in the range of −100 to −200 mV. However, if this operation, that is, the slow aeration is directly performed in the hydrogen fermentation tank, the fluctuation range of ORP in the tank becomes unavoidably large, which is not necessarily a preferable living environment for hydrogen-producing bacteria. Although the hydrogen-producing bacterium prefers a slightly anaerobic environment, it is not a so-called aerobic bacterium, and the direct contact of excess oxygen with the bacterium causes the activity of the hydrogen-producing bacterium.
It is a significant impediment to proliferation.

In the present invention, in order to eliminate this inhibiting factor, the ORP of the main fermentation tank is not directly adjusted to a suitable range, but for example, an ORP adjustment tank is provided in front of the main fermentation tank. It is considered that the solution in the main fermentation tank is precisely adjusted by slowly aerating the object to be treated. Further, in the present invention, as another method of eliminating the inhibiting factors, the hydrogen fermentation tank is divided into two, and the first-stage fermentation tank is a reduced pressure fermentation tank,
The next-stage fermenter is an atmospheric fermentor, and the set ORP is operated to be higher than a predetermined ORP by slowly aerating the atmospheric fermenter, and this liquid is subjected to the main fermentation for hydrogen production under reduced pressure. ORP is indirectly fine-tuned by circulating an appropriate amount continuously and / or intermittently in the tank to ensure -100.
It is considered to be in the range of -200 mV.

In addition, in the present invention, in order to more strictly adjust the ORP of the fermenter, an oxidation-reduction potential detection sensor is installed in the main fermentation tanks of the above-mentioned two examples, and this is installed with a blower for slow aeration. By adjusting the aeration air volume,
With this, a mechanism is provided to control the ORP of the biological reaction system so that it is within a range in which hydrogen fermentation surely proceeds.

[0020]

[Action] As is well known, methanogenic bacteria are obligate (absolute)
It belongs to the range of anaerobes and is not only critically hit by the presence of oxygen, it is also unable to survive under these environmental conditions. Therefore, the oxidation-reduction potential (hereinafter abbreviated as ORP) at which these bacteria can survive, live, and act is naturally limited, and is usually rather strictly-
Limited to 350-450 mV. Organic wastes such as human waste and sewage sludge wildly inhabit many methanogens of different genera, and the following species are typical methane bacteria groups.

Methanococcus Methanosarcina Methanothrix Methanobrevibacter Methanomicrobium Methanospirillum Methanospirillum Methananospiran.

These methanogenic bacteria belong to obligate anaerobic bacteria without exception, and not only can they inhabit under the above-mentioned ORP conditions, but the methanogenic bacteria generally have an optimum pH as shown below. Under the conditions, the growth rate is extremely slow even under the optimum temperature condition. Optimum pH ・ ・ ・ ・ ・ 7.8 Optimum temperature ・ ・ ・ ・ ・ 28-33 ℃ Specific growth rate ・ ・ ・ ・ ・ 0.3-0.5day ^-1 As will be described later, the growth characteristics are extremely convenient for stably achieving the objects and objects of the method of the present invention.

Hydrogen-producing fungi belong to the category of facultative anaerobes against methanogenic bacteria, and the presence of oxygen does not necessarily become a decisive obstacle to survival. , Can multiply. Therefore, naturally, the range of viable ORP deviates to the positive side of methanogenic bacteria, and normally -100 to -200 mV is a preferable range of ORP. The hydrogen-producing fungi that wildly inhabit organic waste such as human waste and sewage sludge have been fairly clarified and identified at the present time, but the main ones are listed below. In addition, as a characteristic of hydrogen-producing bacteria, many bacteria produce strong cellulase, and this kind of bacteria decomposes fiber to produce hydrogen.

Clostridium butyricum (Clos
tridium butyricum) Clostridium
thermocellum) Clostridium bifermentans (Clostrid
ium bifermentans) Clostridium sporogenes
orogenes) Clostridium Aerotolerance (Clostridiu
m aerotolerans) Ruminococcus alba Ruminococcus alba Sarcina maxima
Such.

Compared with methanogenic bacteria, these hydrogen-producing fungi fluctuate within a considerable range depending on the target substrate, but as shown below, the specific growth rate under the optimum conditions is usually 1 or more than that of methanogenic bacteria. It is an order of magnitude larger, and even in a chemostat in a continuous system, even if the residence time of the bacteria is 0.5 to 3.0 days, it is not washed out of the system. Optimum pH: 5.5-5.8 Optimum temperature: 25-30 ° C Specific growth rate: 5-15day ^-1

Thus, not only is there a large disparity in the optimum ORP range between methanogenic bacteria and hydrogen-producing fungi, but there is also a large disparity in the optimum pH range and growth rate. Advantageous conditions are provided in order to allow the slightly anaerobic hydrogen fermentation of the invention to proceed in a stable manner prior to the methane fermentation. The amount of hydrogen produced from this innovative new biological production process is large, and it is not only possible to minimize the amount of carbon dioxide gas that is a causative agent of global warming that occurs at the same time It is also possible to treat organic waste by the production treatment process. Therefore, the present invention is a biological hydrogen production method capable of epoch-making treatment of organic waste and hydrogen production, which contributes significantly to global environment conservation and improvement as a total process.

[0027]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Example 1 FIG. 1 shows an example of a process chart for carrying out the method of the present invention. In this example, a mixed sludge (first settling tank sludge + excess activated sludge) is used as an organic waste.
First, in FIG. 1, the sewage mixed sludge 1 is introduced into the ORP adjustment tank 3 via the inflow pipe 2 as a treatment target. The volume of the adjusting tank is not particularly limited, but the retention time of sludge is 0.
Five to one day is enough.

The ORP of the sewage mixed sludge 1 left under anaerobic conditions is usually -350, which is suitable for the progress of methane fermentation.
Methanogenic bacteria, which are in the range of ˜-450 mV and are absolutely anaerobic bacteria, have already started their activities under this environment although they are weak. Therefore, the ORP of the sewage mixed sludge 1 stored in the ORP adjusting tank 3 (either continuous or batch type injection method may be used) up to the ORP suitable for the hydrogen-producing bacteria that are facultative anaerobic bacteria to operate. In order to raise it, it is slowly aerated by the blower 4 and adjusted to -100 to -200 mV, preferably about -150 mV.

However, when the sewage mixed sludge 1 is put into the reduced pressure hydrogen fermentation tank 7 and exposed to anaerobic conditions, the anaerobic level increases and the ORP value becomes lower than the desired value.
It is preferable to set the value closer to the positive value than -200 mV. In any case, OR in the reduced pressure hydrogen fermentation tank 7
In order to strictly set the P value within the optimum ORP range of hydrogen-producing bacteria, in the present invention, the ORP installed in the reduced pressure hydrogen fermentation tank 7 is used.
By electrically interlocking the sensor 9 and the blower 4 for slow aeration, the ORP of the fermentation liquid is controlled so as to always be in the optimum range.

The sewage mixed sludge 1 adjusted to a slightly anaerobic condition by slow aeration is continuously and / or intermittently introduced into the reduced-pressure hydrogen fermentation tank 7 through the transfer pipe 6. As described above, the volume of the reduced pressure hydrogen fermentation tank 7 is designed so that it is inevitably washed out of the tank at the normal growth rate of the methanogen.
It has a volume such that the residence time of the sewage mixed sludge 1 to be treated in the reduced pressure hydrogen fermentation tank 7 is 3 to 5 days. As described above, the growth rate of methanogenic bacteria that normally live wildly in sewage sludge is pH = 7.8, culture temperature 28-
It is in the range of 0.3 to 0.5 day ^{-1 under} the optimum condition of 33 ° C, and the retention time for washing out the methanogens to the outside of the reaction system is calculated within 3.3 days based on this value. .

When anaerobic fermentation is carried out within this short residence time range, so-called acid fermentation-led fermentation, in which acid fermentation is more predominant than methane fermentation, preferentially proceeds, and lower carboxylic acid is added to the fermentation broth. Acid accumulates and the pH of the solution deviates to the acidic side. Thus, by reducing the volume of the reduced-pressure hydrogen fermenter 7, not only the fermentation conditions but also methanogenic bacteria are inevitably washed out of the fermenter, and the pH is further increased.
Since the condition also deviates from the preferable pH of the methanogenic bacterium to a considerably lower side, the optimum environmental condition for the growth of the hydrogen-producing bacterium is automatically provided, which is convenient.

The sewage mixed sludge 1 introduced into the reduced pressure hydrogen fermentation tank 7 has a residence time in the tank of 3 to 5 days, a fermentation temperature of 30 ° C., and an automatically adjusted pH of 5.0 to 6.0. And,
It is preferable to carry out hydrogen fermentation while continuously stirring with the stirrer 8, which is suitable for achieving the object of the present invention. The stirring in the tank does not go against the present invention even if the generated gas is stirred.

When the sewage mixed sludge 1 is treated under the above conditions, organic substances are decomposed as illustrated in the following biological reaction formula,
Lower carboxylic acids and a considerable amount of hydrogen are produced. * (C ₆ H ₁₀ O ₅ ) _n → 4C ₆ H ₁₂ O ₆ → 3CH ₃ (C
_{H 2) 2 COOH + 2CH 3} COOH + 8H 2 + 8CO
₂ * 3CH ₃ (CH ₂ ) ₂ COO ⁻ + 6H ₂ O = 6CH ₃
COO ⁻ + 3H ⁺ + 6H ₂ * 2CH ₃ COO ⁻ + 4H ₂ O = 10H ⁺ + 2H ₂ +4
CO ₂

Therefore, a large amount of generated hydrogen fills the fermentation liquor and the gas phase portion in the reduced pressure hydrogen fermentation tank 7, and not only the equilibrium concentration in the liquid phase but also the hydrogen partial pressure in the gas phase increases. Hydrogen has a biotoxic effect by itself, and hydrogen fermentation is inhibited when the concentration in the liquid phase exceeds a certain limit. Furthermore, as described above, the biological reaction of hydrogen generation by hydrogen-producing bacteria is an absorption ergon reaction in which the standard free energy has a positive value, and the generated hydrogen is forcibly removed from the reaction system to generate a substantial ergon. It is necessary to consider a specific operation that produces the same effect as the reaction. In the present invention, for this purpose, the hydrogen fermenter is subjected to conventional vacuum fermentation conditions. That is, the degree of pressure reduction in the gas phase of the fermenter is usually -3.
It is set to 00 to -400 mmAq, but by constantly maintaining this degree of pressure reduction, hydrogen fermentation proceeds in the positive direction without delay.

As another method of using hydrogen gas generated by hydrogen fermentation outside the biological reaction system, there is a method of using a hydrogen gas separation membrane, and the same effect as under reduced pressure fermentation can be expected. Hydrogen gas has a very small particle size as a gas molecule, and hydrogen can be easily separated from a mixed gas with other gas with a high purity of 99%, so that, for example, already in the petroleum refining industry, chemical industry, and other production processes. Has been put into practical use in. As in the present invention, when the generated gas of hydrogen fermentation of sewage mixed sludge is a mixed gas of hydrogen gas and carbon dioxide gas, hydrogen separation by a gas separation membrane is relatively easy, and usually 5 k
It can be separated as 99% high-purity hydrogen gas at a pressure of g / cm ² or less. As a commercially available hydrogen gas separation membrane, several kinds of materials are sold, but in the examples of the present invention, aromatic polyimide is used as a material capable of separating hydrogen most selectively and effectively. A separation membrane was used.

In the present invention, the gas generated from the reduced-pressure hydrogen fermentation tank 7 is extracted from the gas discharge pipe 10 and passed through the gas separation membrane 11 under reduced pressure to separate the hydrogen gas 12, while the concentrated carbon dioxide. The gas 13 is taken out to another system, and is effectively used, processed and disposed according to the purpose.
Hydrogen-producing bacteria grow normally by reducing the hydrogen partial pressure in the fermenter by vacuum fermentation, gas separation, or a combination of both, but this bacterium is resistant to progressively higher concentrations of hydrogen at the genetic level. Therefore, after a certain period of time from the beginning of operation, vacuum fermentation and gas separation operations gradually return to normal pressure fermentation, or even if the conditions for gas separation are not changed, hydrogen fermentation will continue. Of course, such driving operation is also included in the scope of the present invention without being extremely damped.

The sewage mixed sludge 1 obtained by decomposing organic matter can be easily understood from the above-mentioned biological reaction formula of hydrogen fermentation, so that the lower carboxylic acid (butyric acid 6,000 m 2
g / l or more, acetic acid 500 mg / l or more). Therefore, after the fermented digested liquid is taken out of the system through the outflow pipe 14, the lower carboxylic acid is separated and purified for effective use, or further decomposed by a biological treatment on the assumption that it is released into public water. Need to stabilize. Further, the fermented digested sludge is taken out to the outside by the drawing pipe 15 and treated and disposed by a proper means.

Embodiment 2 FIG. 2 shows another example of a process diagram for carrying out the method of the present invention. In FIG. 2, the hydrogen fermentation tank is divided into two parts, a first fermentation tank 23 for performing reduced pressure fermentation and a second fermentation tank 24 for performing atmospheric fermentation. It is desirable to set the total volume of both fermenters 23 and 24 so that it is 3 to 5 days in which normal methanogenic bacteria are inevitably washed out in terms of growth rate. It is desirable to determine the volume ratio of the second fermenter 24 to be approximately 2: 1, but the present invention is not limited to this ratio.

First, the sewage mixed sludge 21 is introduced into the first fermentation tank through the inflow pipe 22. The fermented liquid that has been hydrogen-fermented in the first fermentation tank (reduced pressure hydrogen fermentation tank) 23 is introduced into the second fermentation tank (normal pressure fermentation) 24 through a transfer pipe, and the hydrogen fermentation is finished in this tank. The second fermenter 24 has a kind of ORP adjusting tank function, and slowly blows air from the bottom of the tank by the blower 32, which is slightly higher than the ORP suitable for hydrogen-producing bacteria (a value close to a positive value). Aerate the liquid in the tank to the specified value. The ORP value of this tank is monitored by an ORP detection sensor 29 provided in the tank. The air supplied from the blower 32 is diffused into the atmosphere together with mainly carbon dioxide gas generated by the gas discharge pipe 30.

Further, the fermented liquor of the second fermenter 24 whose ORP is adjusted to be higher than a value suitable for hydrogen-producing bacteria is continuously or intermittently in the biological reaction system by the fermented liquor circulation pump 33 and the circulation pipe 34. The circulation liquid is circulated as desired, and the circulating liquid is joined to the sewage mixed sludge 21 through the branch pipe 35 or introduced into the first fermentation tank through the branch pipe 36. The main aim of the process illustrated in FIG. 2 is that the process illustrated in FIG.
The ORP of the fermented liquor in the reduced pressure hydrogen fermenter requires a considerable amount of skill to adjust the ORP to a range suitable for the growth of hydrogen-producing bacteria and suitable for suppressing methane fermentation, Opportunity to directly contact oxygen with hydrogen-producing bacteria that play a leading role in the first fermentation tank 23 where main fermentation is performed, as well as being able to accurately control the desired ORP value with a simple operation by liquid circulation. Therefore, there is an advantage that hydrogen fermentation can be carried out smoothly.

Further, in order to perform the ORP adjustment of the first fermentation tank 23 more strictly, the O provided in the first fermentation tank 23 is adjusted.
It is considered that the RP detection sensor 29 and the slow aeration blower 32 are electrically connected and the blower 32 is turned on and off while detecting the ORP value in the tank. As a method of reducing the oxygen partial pressure in the gas phase part of the fermenter by the hydrogen gas in the generated gas, which is an inhibitory factor for hydrogen fermentation, the same method as that illustrated in FIG. 1 is adopted. The generated gas 23 is taken out of the tank by the gas discharge pipe 25, passes through the gas separation membrane under reduced pressure, and is separated into hydrogen gas 27 and concentrated carbon dioxide gas 28. The mechanism of vacuum fermentation is exactly the same as in FIG. The fermented digested sludge is drawn out of the tank by the discharge pipe 37, treated and disposed.

Example 3 In this example, sewage sludge generated from an urban sewage treatment plant as organic waste is subjected to hydrogen fermentation. The sewage sludge used in the experiment was a mixture of the first settling basin sludge concentrated by gravity settling at a certain sewage treatment plant and the excess activated sludge mechanically dewatered so that the solids weight ratio was 2: 1 close to the natural generation ratio. Then, tap water was added to adjust the total solid content of the mixed solution to about 30 g / l, and the mixture was stored in a cool dark place at 3 to 5 ° C so as not to deteriorate during the experiment. Table 1 shows the general properties and composition of the sewage mixed sludge used in the experiment.

[0043]

[Table 1] * ¹ First settling tank sludge: excess activated sludge (mechanical dehydration) = 2:
1 (weight ratio) * ² Centrifugation ... 3,000G, 10 minutes

Regarding the volume of the hydrogen fermentation tank, three cylindrical fermenters having an actual water-filled volume (effective volume) of 5 liters were manufactured, and these were set in a constant temperature water tank of 30 ° C., and the number of fermentation days was 4 days. Medium temperature fermentation was performed. The conditions of each hydrogen fermentation are as follows. Experimental conditions (1) Anaerobic fermentation of control sewage mixed sludge (2) Reduced pressure hydrogen fermentation of mixed sewage sludge Microanaerobic hydrogen fermentation Decompression degree -1,500 mmAq (3) Atmospheric pressure hydrogen fermentation of mixed sewage sludge Hydrogen by hydrogen gas separation membrane Reduction of partial pressure

The hydrogen fermenter used in the examples of the present invention is
Since the effective volume is 5 liters and the scale is small, it is difficult to apply the decompression system of the fermenter according to the present invention to the experimental apparatus of the example as it is, and it is difficult in terms of the apparatus. It will warp and cause trouble. Therefore, in the hydrogen fermentation tank of the experiment (2), the vacuum pump was used to automatically reduce the pressure of the whole tank to substantially -1,500 mmAq, and the fermentation was carried out under reduced pressure. The hydrogen gas separation membrane used in the experiment (3) is a separation membrane made of an aromatic polyimide manufactured by a certain company and has a length of about 290 mm and a diameter of about 5 mm.
It was a 0 mm cylindrical product, and was set in a ready-made separation device and used.

The conditions for hydrogen gas separation are:
Under a reduced pressure condition of 1.5 psig, a mixed gas of hydrogen gas (about 70%) and carbon dioxide gas (about 30%) was sucked from the fermenter, and the purity of the separated hydrogen gas was expected to be 90 to 95%. In the actual operation, the operating time was short because the capacity of the separation device was excessive, and the operation was about 3 min / interruption 57 min.

The sewage mixed sludge tested is slowly aerated before being put into the fermenter (batch type) so that the ORP of the sample sludge is higher than a predetermined ORP.
After adjusting to P-50 to -100 mV, it was put into a fermenter. The ORP of the three hydrogen fermentor solutions is
Each is equipped with an ORP sensor and is suitable for growing hydrogen-producing bacteria while monitoring the ORP value -150m
It was operated with V as the set value.

The injection amount of the sewage mixed sludge into each fermenter was 1.25 liters / day, so that the residence time of sludge in the three fermenters was calculated to be 4 days. The fermented digested liquid was subjected to a centrifugal force of 3,000 G for 10 minutes by using a centrifugal separator to forcibly separate and remove suspended solids, and then used as a sample for water quality analysis. The verification experiment under the above experimental apparatus and experimental conditions is
Table 2 shows the treatment results (average value) for 1 month in the intermediate process, which was continued for 5 months after the operation reached a steady state.

[0049]

[Table 2]

The results obtained by the verification experiment are summarized as follows. (1) As can be easily understood from the experimental results in Table 2,
Even if the mixed sludge of sewage is subjected to anaerobic fermentation (pressure condition almost equal to atmospheric pressure) after adjusting the ORP, hydrogen fermentation does not proceed preferentially, and the number of fermentation days is about 4 to 5 days. Methane fermentation is definitely a priority. (2) Furthermore, the solubilization of organic matter proceeds in such a number of fermentation days, but the decomposition rate of organic matter is low, and methane fermentation is a methane fermentation in which acid fermentation has priority but hydrogen fermentation has priority. Not only is it low in content, but the fermentation digestive juice also contains high concentrations of lower carboxylic acids such as acetic acid and propionic acid.

(3) On the other hand, after making the sewage mixed sludge slightly anaerobic, the degree of pressure reduction of the hydrogen fermentation tank is -1,500 mm.
In the reduced-pressure hydrogen fermentation method in which Aq is continuously set, methane fermentation is obviously suppressed, and hydrogen fermentation proceeds preferentially. The absolute amount of generated gas also increased by about 32% compared to Experiment 1,
Moreover, the generated gas contains hydrogen, which is about 70% of clean energy. Furthermore, naturally, the COD removal rate of the fermented liquor and the organic matter removal rate are far superior to those of Experiment 1.

(4) Further, in Experiment 3, the slightly anaerobic sewage mixed sludge was not subjected to reduced pressure fermentation, but the hydrogen gas in the generated gas was taken out of the system by the gas separation membrane, and the hydrogen partial pressure in the gas phase part of the fermentation tank was adjusted. The hydrogen fermentation was tried by the method of reducing, but Table 2
As shown by the experimental results of 1., there was almost the same effect as the reduced pressure fermentation of Experiment 2, and hydrogen fermentation proceeded prior to methane fermentation. The water quality findings and the gas generation findings as the treatment results are judged to be comparable to the experimental results of Experiment 2.

(5) The reduced-pressure fermentation as a means for giving priority to hydrogen fermentation over methane fermentation and the method for reducing the hydrogen partial pressure by the gas separation membrane are applied to the mixed culture solution for 2 to 3 months at the beginning of the operation. The hydrogen-producing bacterium inside is adapted to the environment of high concentration hydrogen and high hydrogen partial pressure by qualitative conversion at the gene level.
In the examples of the present invention, although no experimental result was particularly presented, when it was tried in the final stage of the verification experiment, the treatment efficiency was reduced by 10 to 15% for about one month, but in this state, equilibrium was reached. Reached (6) It is effective to use titanium citrate together as an auxiliary means for adjusting and maintaining the ORP value of the hydrogen fermentation tank to, for example, −150 mV. Especially when the pH of the mixture is 5.0
It is judged to be practically effective in the range of up to 6.0.

[0054]

As described in detail, the present invention is an innovative invention based on a concept and a concept completely different from the prior art, and has the following operational effects. (1) When treating organic waste under anaerobic conditions, the organic waste, for example, sewage mixed sludge is subjected to slow aeration in advance, which is suitable for the hydrogen-producing bacteria to grow in the ORP of the liquid in the fermentation tank. By performing anaerobic fermentation while adjusting the value to -100 to -200 mV, the so-called methane fermentation that generates a large amount of methane gas and carbon dioxide that promotes global warming is suppressed, and the hydrogen fermentation that generates a large amount of clean energy is performed. You can surely proceed.

Therefore, the present invention can contribute not only to the energy problem that is tight worldwide but also to the prevention of global warming. (2) By the reduced pressure fermentation according to the present invention, or by reducing the hydrogen partial pressure in the hydrogen fermentation tank by separating hydrogen with a gas separation membrane, the absorbed ergon reaction can be substantially converted into the ergon reaction. By this operation, hydrogen fermentation can be reliably advanced in the positive direction.

[Brief description of drawings]

FIG. 1 is a process chart showing an example of a method of the present invention.

FIG. 2 is a process drawing showing another example of the method of the present invention.

[Explanation of Codes] 1, 21: Organic waste, 2, 22: Inflow pipe, 3: OR
P adjusting tank, 4, 32: blower, 5: exhaust, 6: transfer pipe, 7: anaerobic vacuum fermentation tank, 8: stirrer, 9, 29: O
RP sensor, 10, 25, 30: gas exhaust pipe, 11, 2
6: Gas separation membrane, 12, 27: Hydrogen, 13, 28: Concentrated CO ₂ , 14: Outflow pipe, 15, 37: Digested sludge drawing pipe, 23: First reduced pressure fermentation tank, 24: Second atmospheric pressure fermentation tank Three
1: Air supply pipe, 33: Pump, 34: Fermentation liquid circulation pipe, 3
5, 36: Branch pipe

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C12P 3/00 8114-4B

Claims (5)

[Claims] 1. In a slightly anaerobic hydrogen fermentation method of hydrogen-fermenting organic waste, while controlling the fermentation broth in the hydrogen fermentation so that the oxidation-reduction potential is in a range of -100 to -200 mV. A slightly anaerobic hydrogen fermentation method for organic waste, which is characterized by fermentation. 2. The organic waste according to claim 1, wherein the hydrogen fermentation is performed by vacuum fermentation or while the generated gas is passed through a gas separation membrane to separate hydrogen and carbon dioxide gas. Slightly anaerobic hydrogen fermentation method for products. 3. The organic waste is characterized by adjusting the oxidation-reduction potential of the organic waste in advance to a range in which hydrogen fermentation proceeds without delay by slow aeration before fermentation. A slightly anaerobic hydrogen fermentation method for the described organic waste. 4. The redox in which the hydrogen fermentation is divided into a first fermentation in which reduced pressure fermentation is performed and a second fermentation in which atmospheric fermentation is performed, and a fermentation solution of the second fermentation is slowly aerated so that hydrogen fermentation proceeds without delay. 3. The organic waste according to claim 1 or 2, characterized in that the fermentation liquor is adjusted to an electric potential and the fermentation liquor is combined with the organic waste or continuously and / or intermittently circulated in the first fermentation. Slightly anaerobic hydrogen fermentation method for products. 5. The hydrogen fermentation is performed by using a redox potential sensor to adjust the air volume of slow aeration so that the redox potential falls within a range suitable for hydrogen fermentation. The method for slightly anaerobic hydrogen fermentation of organic waste according to any one of 1.