JPH0476754B2 - - Google Patents

Description

[Detailed Description of the Invention] "Field of Industrial Application" This invention relates to a method and apparatus for producing methane gas by fermentation (methane fermentation) using anaerobic bacteria using urban wastewater, industrial wastewater, etc. as raw materials. be.

``Prior Art'' The conventional method for producing methane by fermentation was carried out as a mere means for treating wastewater, and was carried out using an apparatus as shown in FIG.

First, raw wastewater sent by the pump 1 is mixed with return sludge and sent to the heat exchanger 2 where it is heated. The heated wastewater is placed in fermenter 3. This fermenter 3
has a stirring device 3a, which mixes the sludge and raw wastewater. A part of the wastewater from the fermenter 3 is mixed with the raw material wastewater through a pump 4, and after separating sludge with a dehydrator 5, it is discharged as treated wastewater. A part of the sludge separated and concentrated by this dehydrator 5 is mixed with raw material wastewater by a pump 6 and returned to the fermentation tank 3 via a heat exchanger 2.
Further, methane gas generated in the fermenter 3 passes through a booster 7 and is stored in a gas holder 8, and a part of the stored gas is used to generate heated steam or hot water to be supplied to the heat exchanger 2. In addition, in the said structure, a sedimentation separation tank etc. may be used instead of the dehydrator 5.

"Problems to be Solved by the Invention" The conventional methane production method and apparatus were used as a means of wastewater treatment as described above, and the method and apparatus for producing methane were to maintain a high concentration of suspended solids SS in the fermenter 3,
A strong stirring device 3a was provided in order to thoroughly mix this high SS concentration sludge and wastewater. Also,
Separation devices such as a large settling tank and a dehydrator 5 were installed because the discharged water taken out from the fermenter 3 had a high SS concentration and because the sludge was returned to the fermenter 3 as a starter. As described above, in the conventional method and apparatus, stirring of the fermenter 3, separation of sludge starter bacteria,
There was a problem in that the power costs for returning the wastewater, heating the wastewater, and the associated equipment costs increased.

This invention was made in view of the above circumstances,
The purpose of the present invention is to provide a method and apparatus for producing methane by fermentation, which can economically produce methane gas for energy use and can also treat water such as industrial wastewater and domestic wastewater. .

"Means to solve the problems" In order to solve the above conventional problems, it is necessary to stop stirring the fermenter, which has high running costs, and stop returning SS sludge containing methane-fermenting bacteria to the fermenter.
A drastic solution is required. Also, conventionally,
Methane fermentation requires a large fermenter due to its slow reaction rate, and as a result, a large amount of wastewater remains in the equipment.In order to increase this reaction rate, that is, to reduce the size of the equipment, A solution is needed to increase the concentration of methane-fermenting bacteria in the fermenter. To this end, it is required to maintain a high concentration of methane-fermenting bacteria in the fermenter and to prevent them from flowing out of the fermenter along with the treated wastewater. In order to carry out this, the concept of a bioreactor, which has recently begun to be applied especially in the production of pharmaceuticals, fine chemicals, and amino acids, is used, in which the microorganisms or their enzymes participating in the reaction are contained in a special carrier. It is possible to apply this method. Conventionally, there are carriers (alginate, agar, κ-kanagylan gel, etc.) that have been actually used in the production of amino acids, etc., but these are expensive and very difficult to treat and remove from wastewater. Adaptation to facilities for the purpose of methane fermentation is unthinkable. On the other hand, due to the large volume of the fermentation tank, ceramics, plastic molded products, and heat-fired natural products (ceramics) have mechanical and physical strength.
The use of , etc. is being considered. However, these materials cannot be used economically due to high processing costs.

In contrast, the present inventors applied a bioreactor to methane fermentation, aiming to make it industrially and economically viable.
After extensive investigation and consideration into whether there was a carrier suitable for methane fermentation among inexpensive waste materials, we found that the pores in the stone were relatively large and did not seem to be suitable for microorganisms to attach to and coexist with. We also found that anti-flame rock, which had a low bulk specific gravity and was thought to float in the fermenter and could not be immobilized, is effective as a carrier for methane fermentation bioreactors.

In other words, since anti-flame stone is a natural foam, it does not require energy-intensive heat treatment, and methane-fermenting bacteria, which were used to treat food processing waste liquids and livestock waste, can coexist and multiply in anti-flame stone. This not only makes it possible to generate methane from simulated waste fluids, but also to stimulate the growth of methane-fermenting bacteria, which are said to grow very slowly even when these fluids are continuously poured into a bioreactor made of anti-flint rock.
No out-of-water phenomenon occurred, and it became clear that methane-fermenting bacteria coexisted in the anti-flinder rock and converted the carbon source in the simulated waste liquid into methane gas, etc.

In other words, the apparatus for producing methane gas by fermentation according to the present invention allows methane-fermenting bacteria to coexist and grow in flint-resistant layers of a predetermined particle size, which is used as a methane-fermenting bioreactor, and wastewater is poured into these flint-resistant layers. This produces methane gas. As shown in Fig. 1, this methane gas production device is constructed by filling a reaction tower 10 with anti-flinder stones 9 of a predetermined size (diameter with one side of 8 mm to 50 mm), and allowing methane-fermenting bacteria to coexist in the anti-flame stones 9. , the reaction tower 10 is configured to allow waste water to flow into the interior from the lower end inlet 10a of the reaction tower 10 using a pump 11 and to be discharged from the upper end outlet 10b, and to take out the generated methane gas from the gas exhaust port 10c at the upper end of the reaction tower 10. It is what was done. In FIG. 1, reference numeral 12 indicates a constant temperature bath that supplies hot water for heating the reaction tower 10.

Furthermore, in order to obtain good effects in the above-mentioned apparatus, it is important that the above-mentioned reaction tower has a structure as described below. That is, as shown in FIG. 2, the reaction tower 10 is set to have a cylindrical shape with a ratio of height L to diameter 2R (L/2R) of 1 to 20 (preferably 5 to 10). A conical inlet cover 13 made of a perforated plate 13a such as a wire mesh is provided in the vicinity of the lower end inlet 10a of the reaction tower 10 to prevent the lower surface from entering the crushed stones. It is necessary to set r to the radius R of the reaction tower 10 so that πr ² /πR ² =0.2 to 0.4. In addition, the reference numeral 10d in the figure
indicates the carrier (anti-flinder) supply port, and 13
b indicates a heater in the inlet cover 13; 14 indicates a perforated plate such as a wire mesh for pressing the upper end of the filled anti-flinder layer 15; and 16 indicates the upper end of the anti-flinder layer 15. A down-container is provided in which the treated waste liquid does not leak from the outer edge, flows out from the perforated plate 14, and is taken out from the discharge port 10b.
It shows the cummer. In addition, this reaction tower 10
In this case, it is desirable that the lower part is conical with an angle θ of 45° with respect to the vertical plane of the inner wall surface.
An end plate used for ordinary containers may be used.

In addition, when attaching methane-fermenting bacteria to the flint-proofing stone, the flint-proofing stone is immersed in a liquid containing methane-fermenting bacteria, such as methane fermentation waste liquid, and then treated under reduced pressure to remove the pores in the flint-proofing stone. The air and the liquid containing the methane-fermenting bacteria are replaced, the air in the pores of the anti-flinder stone is degassed, and the methane-fermenting bacteria are allowed to flow into the pores.

In the above configuration, the crushing dimensions of the firestone 9 are set to be 8 mm to 50 mm on one side. Although there is no problem in using crushed stones of 8 mm or less for the fermentation of methane gas itself, crushed stones of 8 mm or less are used. This is because if used, the porosity in the reaction tower 10 will decrease too much, making it difficult for the generated gas to pass through and causing problems.
On the other hand, if crushed stone with a side of 50 mm or more is used, it will be difficult to distribute the waste liquid uniformly.

In addition, the shape and dimensions of the reaction tower 10 are set so that the ratio of height L to diameter 2R (L/2R) is 1 to 20.
If (L/2R) is less than 1, it will be difficult to maintain a uniform linear velocity of the upward wastewater flow distributed in the diametrical direction, and if (L/2R) is greater than 20, it will be difficult to maintain a uniform linear velocity of the upward wastewater flow distributed in the diametrical direction. Maintenance is easier, but the pumping energy required increases, pumping costs,
This is because the strength of the reaction tower makes it difficult to deal with it.

In addition, the lower perforated plate 1 of the inlet cover 13
The reason why the number of meshes in 3a is set to 4 to 10 is to prevent the anti-flame rock 9 of the above dimensions from entering the inlet cover 13, and if it is set to less than 10 meshes, the waste water will not flow smoothly. be.

Furthermore, the reason why the relationship between the radius r of the lower perforated plate 13a of the inlet cover 13 and the radius R of the reaction tower 10 is set to πr ² /πR ² =0.2 to 0.4 is because if it is set outside this range, the inlet cover 13 From reaction tower 1
This is because the flow of wastewater flowing into the tank is not uniform.

It is important to note that when using the reaction tower 10, in order to improve the contact between the dissolved organic matter and the carrier anti-flinder 9 in the reaction tower 10, the introduction of raw waste water into the reaction tower 10 is The average linear velocity in the cross section of the reaction tower 10 is required to be 100 mm/hr or more, preferably 300 mm/hr or more. The flow rate in this case is, for example, the diameter
For a 2m reaction tower, at a linear velocity of 300mm/hr, 1
m ² /hr, indicating that it can be operated with extremely small power.

"Function" As is well known, the anti-flame stone 9 constituting the present invention has the following features:
It has countless pores inside, the hydrogen ion concentration in the water is almost neutral, and it is relatively strong and will not break unless a large impact is applied to it. Further, the crushed surface of the anti-fire stone 9 is amorphous and uneven, and together with numerous pores, it is a favorable environment for the attachment and production of microorganisms. In addition, the anti-flame carrier in which methane-fermenting bacteria are fixed in the pores of the anti-flame stone 9 does not wear out like organic gels and can be used stably for a long period of time. By using such a carrier of anti-flame rock 9, the concentration of bacteria related to methane fermentation in the reaction tower 10 is increased, and the outflow of bacteria (wash, water, etc.) is increased.
This makes it possible to effectively and economically produce methane by increasing the reaction rate per unit volume of methanation of organic matter.

Next, the present invention will be explained in more detail with reference to Examples.

"Example 1" First, the crushed firestone 1 with a side of 8 to 12 mm was placed at a height of
It was placed in a 25 cm glass pressure container with an internal volume of 4.
On the other hand, pour 1 batch of high-temperature methane fermentation waste liquid used for food processing waste liquid treatment into graduated cylinder 1, and leave it for 30 minutes to allow the SS to settle. Obtained. Pour 700ml of the supernatant of this high-temperature methane fermentation waste into the glass pressure-resistant container and seal it tightly, then reduce the pressure inside to 700Torr using gauge pressure to release the air inside the anti-flame stone, and remove the high-temperature methane waste. The operation of fixing it inside was repeated twice. Through this operation, the internal volume of the glass pressure container, which was initially 1.15, became 1.0.

In this way, the crushed stone soaked in the high-temperature methane waste liquid is sieved to separate the waste liquid and crushed stone.
The separated crushed stone was thoroughly drained. After that, this crushed stone was placed in an aqueous solution (buffer solution) 1 containing 0.4 g of K ₂ HPO ₄ and 0.1 g of KH ₂ PO ₄ , washed well, and then sieved to separate it from the buffer solution.
Repeated several times.

In contrast, an implementation apparatus as shown in FIG. 3 was constructed. This device uses the device shown in Figure 2 as a medium (raw material wastewater).
A tank 17, a pump 18, a PH adjustment tank 19, an alkali tank 20, a pump 21, a gas seal tank 22, and a gas meter 23 are installed so as to operate as follows. That is, the PH adjustment tank 19 has a built-in stirrer and is equipped with PH and ORP (oxidation-reduction potential) sensors, and allows liquid to flow in from the reaction tower 10 through a pipe 24. Also,
Based on the signal from the PH sensor, the pump 21 supplies the alkaline solution from the alkaline tank 20 to the tank 19 and controls the pH of the solution returned to the reaction tower 10. The gas generated in the reaction tower 10 passes through a gas pipe 25, passes through a gas seal tank 22, and the amount of gas generated is measured with a gas meter 23. On the other hand, the pH-controlled liquid is returned to the reaction tower 10 by the liquid circulation pump 11. pump 18
In the case of operation in which a culture medium is continuously supplied and methane gas is continuously generated from organic matter contained in the culture medium, the culture medium is supplied from the culture medium tank 17 to the reaction tower 10, and the waste liquid after the reaction is removed from the system by the pump 18. discharge to. In addition, the reaction tower 10 of this implementation apparatus
is made of acrylic and has a height of 750 mm and a diameter (inner diameter) of 50 mm.

800 ml of culture medium was placed in advance in this reaction tower 10,
Filled with the washed crushed stone, and further PH adjustment tank 19
500 ml of culture medium was added to the equipment, such as inside each tube.

The composition of this medium is glucose: 10g, ammonium sulfate: 2.0g,
MgSO ₄ 7H ₂ O; 0.5g, FeSO ₄ 7H ₂ O; 0.1g, K ₂
0.8 g of HPO ₄ , 0.2 g of KH ₂ PO ₄ and 0.1 g of yeast extract were dissolved in tap water.

Finally, adjust the pH to 7.4 using 1N NaOH,
It was operated (circulated) for two weeks at a temperature of 53°C.

The results of this example are shown in FIG. 4 as the amount of gas generated. The total gas generation amount for 14 days was 9.08,
In addition, the concentration of methane gas in the generated gas was 48.5
It was ~53.0%. The oxidation-reduction potential during the operation period was -200 mV or more on the first to second day of operation, but
After that, it showed -400 to -450mV from the third day.
When the total amount of gas generated was calculated using the well-known Buswell formula using glucose as the carbon source, the gas yield was 97.6%.

"Example 2" Using exactly the same procedure as in "Example 1" above, 700 ml of the supernatant of medium-temperature methane fermentation (37°C) waste liquid used for processing livestock waste was infiltrated into 8 to 12 mm anti-firestone crushed stone. , Wash and remove brought-in organic matter and solid matter with a phosphate buffer solution, fill it together with a culture medium into the reaction tower 10 of the same device as described above, and continuously supply hot water at 37°C to the outer cylinder of the reaction tower 10. The pH was adjusted to 7.4 and continuous operation was performed for 15 days. This medium was the same as in "Example 1" and had a total volume of 1250 mι. PH was adjusted with 1N-NaOH.

The state of gas generation during this operation period is shown in FIG. 5, and the total amount of gas generated was 9.05%, and the gas composition was 45.5% to 54.0% methane gas. In addition, the oxidation-reduction potential was -200 mV or more on the first or second day of operation, but from the third day onwards it was -400 mV or more.
It showed -450mV. In addition, when the total gas yield was calculated using glucose as a carbon source according to the well-known Buswell formula, the yield was 97.3%.

“Example 3” Reaction tower 10 of the device used in “Example 1” above
was used as it was from the next day, and continuous operation of methane gas fermentation using a fixed bed using anti-flame rock as a carrier was carried out. Culture medium: glucose; 5g in tap water;
Ammonium sulfate; 1g, K ₂ HPO ₄ ; 0.8g, KH ₂ PO ₄ ; 0.2g,
Add MgSO ₄ 7H ₂ O; 0.5 g, FeSO ₄ 7H ₂ O; 0.1 g, and yeast extract; 0.1 g, adjust the pH of the medium to 7.4 with 1N-NaOH, and then sterilize at 120°C for 10 minutes. I used the one I made. The total amount of liquid in the reaction tower 10 is
The liquid level was adjusted so that the total volume including crushed stone was 960ml and 120ml±50ml during operation. The amount of liquid circulated by the liquid circulation pump 11 is 8 ml/min (480 ml/min).
hr) ±1.5 ml/min. The feed rate of raw material wastewater to the reaction tower 10 and the discharge rate of waste liquid are
The rate was adjusted to 20 ml/hr±2 ml/hr.

The time course of gas generation in this example is shown in Figure 6.The amount of gas generated was low until the fourth day of operation, but from the sixth day onwards, gas generation was approximately 1.6/day. This indicates that about 90% of the typical glucose gas generation is occurring continuously and stably.

"Effects of the Invention" As explained above, according to the present invention, the following excellent effects can be achieved.

a By setting the size of the flint rock to a diameter dimension with one side of 8 mm to 50 mm, that is, by using crushed flint rock with a side of 8 mm or more, when filling the reaction tower with the flint rock, , it is possible to secure a void where the methane gas generated by methane fermentation can easily rise to the top of the reaction tower, and one side of the crushed anti-firestone can be secured.
By setting the diameter to 50 mm or less, it is possible to prevent the uniform flow of wastewater from being disturbed by the anti-firestone.

b When attaching methane-fermenting bacteria to the pores of the anti-flinder stone, the air in the pores and the methane-fermenting bacteria are removed from the pores of the anti-flinder stone by subjecting the flint stone to a reduced pressure treatment in a liquid containing methane-fermenting bacteria. It is possible to replace the liquid contained therein.

Therefore, the methane-fermenting bacteria can be efficiently attached to the pores of the flint rock, and the pores of the flint rock can be efficiently degassed.

That is, when the methane gas production equipment first starts operating, the anti-flinder stone is immersed in a culture solution of methane-fermenting bacteria or a liquid such as waste water in order to cause the methane-fermenting bacteria to adhere to the surface and inside the pores of the anti-flinder stone. In this case, the air remaining in the pores prevents the attachment of methane-fermenting bacteria from being obstructed, and
By replacing the air in the pores with the liquid containing methane-fermenting bacteria through depressurization treatment, the methane-fermenting bacteria are introduced into the pores, and the methane-fermenting bacteria, which grow slowly, can be destroyed in an extremely short period of time. can be attached in large quantities.

Moreover, when filling the reaction tower with the flint-proofing stones, the flint-proofing stones can be easily filled into the reaction tower by preventing the flint-proofing stones from floating due to the inclusion of air.

In addition, stable production of methane gas can be achieved by expelling oxygen, which is a factor that inhibits the production of methane gas by anaerobic methane-fermenting bacteria, from the pores of the anti-flinder stone.

c In addition, in the shape of the reaction tower, by setting the height to diameter ratio to be 1 to 20, that is, by setting the ratio to 1 or more, the linear velocity of the upward wastewater flow distributed in the diametrical direction can be made uniform. In addition, by setting the ratio to 20 or less, it is possible to prevent the pumping energy for raising the wastewater from becoming too large, and to keep the pumping cost in wastewater treatment within an allowable range.

d By setting the mesh size of the perforated plate on the lower surface of the inlet cover to 4 to 10, that is, by setting the mesh size to 4 or more, one side of the inlet cover is designed to ensure easy flow of methane gas and uniform flow of waste water. It is possible to prevent the anti-firestones with a size of 8 mm to 50 mm from clogging the bottom perforated plate, and by setting the mesh size to 10 or less, the flow of waste water from the inlet cover is made smooth. I can do it.

In other words, the size of the firestone is 8 mm to 50 mm on one side.
By using a mesh of 4 to 10 mm and a perforated plate on the lower surface of the inlet cover, smooth and uniform distribution of methane gas and wastewater can be ensured.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of the device of this invention, FIG. 2 is a configuration diagram of the main parts of the device, FIG. 3 is a configuration diagram showing one embodiment of the device, and FIG. 4 is a first diagram of the method of the invention. A graph showing the time course of gas generation in the example, FIG. 5 is a graph showing the time course of gas generation in the second example, and FIG. 6 is a graph showing the time course of gas generation in the third example. The graph in FIG. 7 is a block diagram of a conventional methane gas fermentation device. 9... Anti-flame stone, 10... Reaction tower, 10a... Lower end inlet of the reaction tower, 10b... Upper end outlet of the reaction tower, 13... Inlet cover, 13a... Lower perforated plate of inlet cover, L ... Height of the reaction tower, R ... Radius of the reaction tower, r ... Inlet...
Radius of the bottom perforated plate of the cover.

Claims (1)

[Claims] 1. Methane-fermenting bacteria coexist in anti-flinder stones of a predetermined particle size,
A methane gas production device that produces methane gas by growing and filling a reaction tower with the flint-proofing stone to form a flint-proofing layer as a methane fermentation bioreactor, and flowing wastewater into the flint-proofing layer. , A wastewater inlet for flowing wastewater is provided at the lower end of the reaction tower, and a wastewater outlet is provided at the upper end of the reaction tower, and the ratio (L/2R) of the height L and diameter 2R of the reaction tower is set. A conical inlet cover consisting of a perforated plate with 4 to 10 meshes on the bottom surface is installed at the waste water inlet of the reaction tower, and the reaction tower is set to 8.
When filling anti-flint stones with a diameter of one side of mm to 50 mm and allowing methane-fermenting bacteria to coexist in the anti-flint stones, it is recommended that the anti-flinder stones be subjected to reduced pressure treatment while immersed in a liquid containing methane-fermenting bacteria. A methane gas production device using fermentation. 2. The apparatus for producing methane gas by fermentation according to claim 1, wherein the reaction tower is cylindrical. 3 The radius r of the lower perforated plate of the inlet cover is πr ² /πR ² = 0.2 with respect to the radius R of the reaction tower.
The apparatus for producing methane gas by fermentation according to claim 1 or 2, wherein the methane gas production apparatus is set to 0.4.