JPS59173197A - Fermentating method of organic waste liquid - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION In detail, the present invention relates to a method for cleaning organic waste liquid by methane fermentation in a low temperature range and short residence time and recovering methane gas.

Conventionally, when cleaning organic wastewater by methane fermentation, organic wastewater containing high concentrations of BOD components such as excess sludge, human waste, and alcohol distillation wastewater is
Methane fermentation is performed at 5 to 45 degrees Celsius (medium temperature fermentation) or about 54 degrees Celsius (high temperature fermentation), and these BOD components are generally removed over a retention period of about 10 to 50 days, and the by-produced methane gas is used as energy. It was collected and used as a source.

However, in such a method, fermentation must be carried out at a temperature of around 37°C or 54°C, resulting in a decrease in the Get' reaction rate. However, the energy required for this process is by no means small compared to the energy recovered from the by-product methane, which leads to a decrease in the energy-saving efficiency of wastewater treatment by methane fermentation, and ultimately to the adoption of the methane fermentation method. There were drawbacks that hindered the

Furthermore, in the conventional methane fermentation method, a complete mixing type reaction tank was mainly used, and methane fermentation was carried out by floating microorganisms inside the tank.

However, the growth rate of microorganisms that perform methane fermentation is slow, and when a completely mixed reaction tank with planktonic microorganisms is used to treat low-concentration organic wastewater, the microorganisms are removed from the fermenter before they have sufficiently multiplied. Since wastewater is discharged, there is a problem in that it is not possible to maintain a high concentration of microorganisms.

In other words, when treating high-concentration organic waste liquid in a certain organic matter outer cylinder, the retention time in the tank is longer than when treating low-concentration organic waste liquid, and the growth of microorganisms is delayed. However, in the case of low concentration organic waste liquid,
Even if the growth rate of microorganisms is constant, the amount of microorganisms flowing out of the tank increases because the amount of inflow water increases (so-called wash o
This has the disadvantage that the concentration of microorganisms in the tank decreases due to the ut phenomenon), and the reaction rate also decreases. Therefore, in order to obtain sufficient energy-saving efficiency using low- to high-concentration organic wastewater, it is necessary to have conditions in which the outflow of microorganisms is small, the system can maintain a high concentration of microorganisms, and it can be operated at room temperature. Become. However, for the reasons mentioned above, methane fermentation of low-concentration organic waste liquid has been considered impossible unless a complete mixing reactor and planktonic microorganisms are used.

Therefore, the present invention was made to eliminate such conventional drawbacks, and uses microorganisms immobilized on inorganic fine particles.
Methane fermentation can be carried out even at low temperatures below the conventional medium-temperature fermentation temperature, so there is almost no need to heat or insulate the reaction tank, and low-concentration organic waste liquid, which was conventionally considered inefficient, can be processed in a short residence time. It has features such as being able to be processed.

That is, the method for cleaning an organic waste liquid of the present invention involves supplying the organic waste liquid to a fermenter filled with supporting particles on which methane bacteria are attached, and fermenting the organic matter in the waste liquid with methane. The cleaning method is characterized in that inorganic fine particles are used as the supporting particles, and the temperature of the methane fermentation is lower than the mesophilic fermentation temperature.

Hereinafter, the present invention will be explained step by step according to the steps. First, a fermentation tank filled with inorganic fine particles having activated sludge containing organic acid producing bacteria and methane fermenting bacteria (hereinafter referred to as methane bacteria) attached to the surface is prepared. Alternatively, attachment of methane bacteria to inorganic fine particles and methane fermentation are performed in the same fermenter. In the latter case, the fermenter is filled with inorganic fine particles,
In order to acclimatize the microorganisms to the surface of the particles, a small amount of seed sludge for methane fermentation is first injected into the reaction tank. At the same time, organic waste liquid is supplied while gradually increasing the organic substrate load.

At this time, if the organic acid concentration in the fermenter is high or the pH is low, methane fermentation will be inhibited and the organic matter removal rate and methane gas production rate will not increase, so the growth rate of methane bacteria will also be low and the surface of the carrier particles will methane bacteria are difficult to adhere to. .

In this tank, the pH of the fermenter liquid is normally 6.5-8, O
2. Preferably, the temperature is adjusted to 7°0 to 7°5 to allow microorganisms to proliferate more rapidly and adhere to the surface of the supporting particles.

By this acclimatization operation, the attachment of microorganisms to the surface of the supporting particles is completed in about 1 to 6 months, and thereafter, it becomes possible to constantly supply organic waste liquid.

Here, the inorganic fine particles used in the present invention include diatomaceous earth,
Clay, bentonite, calcium carbonate, gypsum, talcum, preferably diatomaceous earth.

These inorganic fine particles usually have a specific surface area of 40.00.
0m2/m3 or more, preferably 60,0007712
As a result, the concentration of methane bacteria can be made much higher and the reaction rate can be increased.

In addition, the inorganic fine particles usually have an average particle diameter of 100 μm or less, preferably 1 to 75 μm, and preferably 1 to 50 μm.
m range.

The diatomaceous earth preferably used in the present invention is preferably a purified one used for supporting catalysts, but general diatomaceous earth used for adsorbents, filtering agents, heat insulating materials, etc. can also be used.

In this way, by using fine particles as microorganism-carrying particles, increasing the specific surface area, and allowing microorganisms to adhere to the surface, it is possible to increase the microorganism concentration in the fermenter. Generally, the concentration of methane bacteria is 10,000 to 35,000
reaches ppm.

Next, organic waste liquid is supplied to the fermenter and methane fermentation is carried out under anaerobic conditions.

This waste liquid is supplied by flowing upward through inorganic fine particles (hereinafter, diatomaceous earth will be explained as an example) filled in the fermenter. By creating an upward flow, clogging between diatomaceous earth particles can be prevented.

Further, diatomaceous earth may be used as a fixed bed, an expanding bed, or a fluidized bed for the wastewater flow. In order to prevent the generated methane gas from being blocked by particles and becoming difficult to escape to the upper part, it is preferable to use a fluidized bed or an expanded bed.

There are no particular restrictions on the expansion or flow state, but in order to reduce the energy required for flow, to prevent microorganisms attached to the particle surface from exfoliating excessively, and to allow methane gas to escape. Just do the minimum necessary expansion or flow.

In the case of a fixed bed, the particle layer is generally gently stirred by a stirrer rotating at low speed to prevent diatomaceous earth particles from adhering to each other, and to ensure that the surface of the rice grains is so that the generated methane gas can escape easily. The methane bacteria are brought into good contact with the wastewater to improve the efficiency of the reaction.

The stirrer is preferably made of stainless steel or plastic, which does not deteriorate even if it is constantly submerged in water, and the shape may be, for example, one with stirring blades arranged in multiple stages on a rotating shaft,
Alternatively, a large number of linear members are arranged flat on a rotating shaft and fixed to the rotating shaft through a frame, and the wastewater has less resistance due to supporting particles and does not cause severe confusion when agitated. shape is used.

In the present invention, methane fermentation of the organic matter in the organic waste liquid is carried out below the mesophilic fermentation temperature.

□Fermentation temperature can be raised to medium temperature or higher by heating.

Since Kiru maintains a high concentration of microorganisms, there is little dependence on the concentration of methane bacteria in the system, so there is no need to carry it to medium-temperature or high-temperature fermentation.

However, when it is necessary to grow methane bacteria in a system at a high concentration, the required concentration can be rapidly increased by raising the temperature to the temperature used for mesophilic fermentation.

Further, although the BOD concentration of the organic wastewater treated in the present invention is not particularly limited, it is possible to treat high-concentration BOD wastewater extremely efficiently and to treat relatively large numbers of organic wastewaters that have been difficult to treat by conventional methods using planktonic microorganisms. Hundreds to several thousand ppm
It is possible to fully utilize the advantage of the present invention, which makes it possible to treat wastewater with a BOD of 100% by employing a fixed microbial membrane.

The organic waste liquid is usually mixed using a stirrer that slowly rotates about 2 to 5 times per minute, and the upward flow of the organic waste liquid is carried out by, for example, circulating the waste liquid in the fermenter using a pump. As described above, according to the present invention, methane bacteria are attached to the surface of inorganic fine particles and methane fermentation is carried out at a temperature lower than the meso-fermentation temperature, so that the present invention has the following excellent advantages.

(b) Since we use a fixed microbial membrane method in which the fermenter is filled with particles with microorganisms attached to the surface, it is possible to increase the concentration of methane bacteria in the fermenter, allowing fermentation to occur even at temperatures below mesophilic fermentation. The reaction rate per tank volume can be maintained high.

(o) As mentioned in (a) above, we were able to increase the concentration of methane bacteria in the fermenter, so we could use low-concentration organic waste liquid, which was considered ineffective with the conventional microbial suspension method, to contain methane bacteria. It can be operated at a high and stable reaction rate with almost no outflow. Methane bacteria attached to the surface of the supporting particles are only peeled off due to contact between particles due to flow, and the concentration of methane bacteria in the fermenter does not decrease even if the fermenter is operated with a low concentration and a high amount of water.

That is, since the present invention employs a fixed microbial membrane method using inorganic fine particles, there is almost no leakage of methane bacteria to the outside of the reaction tank even during high water flow operation, and a high concentration of methane bacteria can be maintained within the fermenter.

e'') As mentioned in (a), since methane fermentation is now possible at a temperature lower than low-medium temperature fermentation, the energy required for heating is greatly reduced compared to conventional methane fermentation.
Therefore, energy saving efficiency can be significantly improved compared to conventional methods. - In the present invention, the fermenter can be made more compact because the concentration of methane bacteria in the fermenter is high. Therefore, compared to the conventional methane fermentation method, the site area required for installing the fermenter can be significantly reduced.

(e) Furthermore, the method of the present invention can be applied to all kinds of organic waste liquids. Particularly when treating low-concentration organic waste liquid, it is possible to replace the aeration operation in the activated sludge method with the methane fermentation of the present invention.

Examples of the present invention will be described below.

EXAMPLE As shown in the diagram, about 3.3 pieces of diatomaceous earth were packed as supporting particles 2 into a fermenter 1 consisting of a vinyl chloride column having a diameter of 0.15 m, an internal volume of 771°, and a reaction partial volume of about 51. An upward flow is formed in the tank by supplying organic wastewater through the wastewater supply pipe 3ρ and the mesh plate 11 at the bottom of the tank, and taking out the treated wastewater from the treated wastewater pipe 4 at the top of the tank. The diatomaceous earth 2 having the microorganisms attached to its surface was made to flow by stirring by a stirrer 6 which was rotated 2 to 5 times per minute by a low-speed rotary motor 5.

The stirrer used had a frame with a large number of vinyl chloride strings arranged in parallel to the rotation axis.

For wastewater, glucose is added to sanitary wastewater to bring the BOD concentration to 8.
50 ppm, and methane fermentation was carried out in an anaerobic atmosphere.

For about a week after the start of operation, methane fermentation seed sludge was added little by little, while the wastewater supply rate was kept at 0.2A! When the amount was gradually increased from /hr, a large amount of microorganisms were observed on the surface of the supporting particles after about 3 months, and steady operation was possible at the wastewater supply rate LM/hr. The treated wastewater was led to a settling tank 7 via a pipe 4 and separated into settled sludge 8 and discharged water 9. Further, the generated gas is stored in the gas holder 10 L ft
C.

In steady operation, the reaction temperature was changed to three types: 10°C, 20°C, and 30°C, and experiments were conducted for 2° and 5 months each. In order to maintain a constant temperature, the entire experimental apparatus was placed in a constant temperature water tank and the temperature of the water in the tank was controlled. Table 1 shows the results of three types of experiments lasting approximately $1 month.

) 10 41 2.5 0.18
20 75 4.6 0゜40
30 90 5.5 0.35
(Note 1) The methane content in the gas was approximately 70% throughout the entire experiment.
%Met.

(Note 2) The above numbers are the average values of each run.

From the above experimental results, it was found that methane fermentation is possible at temperatures as high as medium-temperature fermentation, which was considered difficult with conventional methods.

Regarding reaction temperature and reaction rate, the reaction rate increases as the temperature rises. /F is that the reaction rate is about 2 kgB in normal medium-temperature methane fermentation.
Considering that it is OD/reaction area m3/day, it must be said that this is an extremely efficient value. Further 20°C23
4゜6,5.5 kgBOD/reaction area m3 at 0℃
It was proved that the value per day was much higher than that of the conventional method. Looking at the gas generation rate, the gas generation rate at 20℃ is 30℃
It showed a slightly higher value than that of , but no temperature dependence was observed at temperatures around this range.

As described above, it has been found that the fermentation method of the present invention using diatomaceous earth as a microbial carrier has various characteristics that could not be achieved by conventional methods. 1

[Brief explanation of drawings]

The figure is a system diagram showing an embodiment of the present invention. 1...Fermentation tank, 2. Soil particles. Agent: Patent Attorney Nobuo Kogawa - Patent attorney Teru Noguchiki Patent Attorney Kazuhiko Sai

Claims (1)

[Claims] In an organic waste liquid fermentation method, in which organic waste liquid is supplied to a fermenter filled with supporting particles having methane bacteria attached to the surface thereof, and organic substances in the waste liquid are subjected to methane fermentation, inorganic fine particles are used as the supporting particles. . A method for fermenting an organic waste liquid, characterized in that the temperature of the methane fermentation is lower than the temperature of the mesophilic fermentation.