JPS6327079B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for fermenting organic waste liquid, and more particularly 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 waste liquids by methane fermentation, organic waste liquids containing high concentrations of BOD components such as excess sludge, human waste, and alcohol distillation waste liquids are heated at 35 to 45°C ( (medium-temperature fermentation) or methane fermentation at about 54℃ (high-temperature fermentation), and generally removes these BOD components over a retention period of about 10 to 50 days, and collects and uses the by-product methane gas as an energy source. Was. However, in this method, the temperature is 37°C or 54°C.
If fermentation is not carried out at a similar temperature, the reaction rate will slow down, so the wastewater must be heated to that temperature or kept warm, and the energy required for this is recovered from the by-product methane. This is by no means small compared to the amount of energy used, and therefore it has the drawback of causing a decline in the energy-saving efficiency of wastewater treatment using methane fermentation, and thus hindering the adoption of the methane fermentation method. Furthermore, in conventional methane fermentation methods, a complete mixing type reaction tank is mainly used, and methane fermentation is 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 was a problem in that it was not possible to maintain a high concentration of microorganisms. In other words, when treating high-concentration organic wastewater with a certain organic load, the residence time in the tank will be longer than when treating low-concentration organic wastewater, and microorganisms will not grow sufficiently in the tank. It is carried out in
In the case of low-concentration organic wastewater, even if the growth rate of microorganisms is constant, as the amount of inflow water increases, the amount of microorganisms that flow out of the tank increases (so-called wash out phenomenon), and the concentration of microorganisms in the tank decreases, causing a reaction. The disadvantage is that the speed also decreases. Therefore, in order to obtain sufficient energy-saving efficiency using low- to high-concentration organic wastewater, it is necessary to have conditions that minimize the outflow of microorganisms, maintain a high concentration of microorganisms in the system, and allow operation at room temperature. becomes. However, as long as a completely mixed reaction tank and planktonic microorganisms are used, methane fermentation of low-concentration organic waste liquid has been considered impossible for the reasons mentioned above. Therefore, the present invention has been made to eliminate such conventional drawbacks, and uses microorganisms fixed to inorganic fine particles to enable methane fermentation even at a low temperature below the conventional medium-temperature fermentation temperature. It has the advantage that there is almost no need for heating or insulating the liquid, and that low-concentration organic waste liquid, which was conventionally considered inefficient, can be treated in a short residence time. That is, the method for methane fermentation of an organic waste liquid of the present invention involves supplying an organic waste liquid to a fermenter filled with supporting particles on which methane bacteria have adhered, and fermenting organic substances in the waste liquid with methane. The method for methane fermentation of waste liquid is characterized in that inorganic fine particles with a particle size of 1 to 75 μm are used as the supporting particles, and the methane fermentation is carried out at a temperature below 35°C while supplying the organic waste liquid in an upward flow. It is something. 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, a fermentation tank is filled with inorganic fine particles, and the methane bacteria are first injected into the reaction tank in small quantities to acclimate the particles to the surface of the particles. At the same time, organic waste liquid is supplied while gradually increasing the organic substrate load. At this time, the concentration of organic acids in the fermenter increases and the pH
When this decreases, methane fermentation is inhibited and the organic matter removal rate and methane gas production rate cannot be increased, and therefore the growth rate of methane bacteria is also low, making it difficult for methane bacteria to adhere to the surface of the carrier particles. For this reason, the pH of the fermenter liquid is usually 6.5~6.5.
Adjust to 8.0, preferably 7.0 to 7.5 to allow methane bacteria to grow faster and adhere to the surface of the supporting particles. By this acclimatization operation, the adhesion of methane bacteria to the surface of the supporting particles is completed in approximately 1 to 6 months, and thereafter, it becomes possible to constantly supply organic waste liquid. The inorganic fine particles used in the present invention include diatomaceous earth, clay, bentonite, calcium carbonate, gypsum, and talc, and preferably diatomaceous earth. These inorganic fine particles usually have a specific surface area of
It is 40,000 m ² /m ³ or more, preferably 60,000 m ² /m ³ or more, and as a result, the methane bacteria concentration can be made higher and the reaction rate can be increased. In addition, inorganic fine particles usually have an average particle size of 100 μm.
Below, preferably 1 to 75 μm, more preferably 1
In the range of ~50μm. Note that diatomaceous earth, which is preferably used in the present invention, is preferably a purified one used for supporting catalysts, but general ones used for adsorbents, superagents, 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 attaching methane bacteria to the surface, it is possible to increase the concentration of methane bacteria in the fermenter. Generally, the concentration of methane bacteria reaches 10000~35000ppm. Next, the organic waste liquid is supplied to the fermenter, and methane fermentation is performed 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. The upward flow can prevent clogging between diatomaceous earth particles. 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 obstructed 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 and to prevent methane bacteria attached to the particle surface from exfoliating excessively, methane gas is released. It is sufficient to perform the minimum expansion or flow necessary for this purpose. 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 allow the generated methane gas to escape easily.
In addition, the methane bacteria on the particle surface are brought into good contact with the wastewater, so that the efficiency of the reaction can be improved. The stirrer should be made of stainless steel or plastic, which does not deteriorate even if it is constantly submerged in water.For example, the shape of the stirrer may be one with multiple stirring blades on the rotating shaft, or one with many stirring blades arranged parallel to the rotating shaft. A shape such as one in which linear members are arranged and fixed to a rotating shaft via a frame is used, which has a shape that has little resistance from waste water or supporting particles and does not cause severe confusion when stirred. In addition, the mixing of organic waste liquid is usually 2 to 5 times
This is carried out using a stirrer that rotates slowly at a speed of about 100 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. In the present invention, methane fermentation of the organic matter in the organic waste liquid is carried out below the mesophilic fermentation temperature. The fermentation temperature can be raised to medium temperature or higher by heating, but since the high microbial concentration is maintained, there is little dependence on the concentration of methane bacteria in the system, so there is no need to intentionally increase the fermentation temperature to medium or high temperature. 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. Furthermore, the organic waste liquid treated in the present invention
Although the BOD concentration is not particularly limited, it is possible to treat high-concentration BOD wastewater extremely efficiently, as well as relatively low-concentration BOD wastewater that is difficult to treat with conventional methods using planktonic microorganisms. The advantages of the present invention can be fully utilized even for wastewater having a BOD of 1,000 ppm. As described above, according to the present invention, methane bacteria are attached to the surface of inorganic thread 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. (a) In the present invention, inorganic fine particles with a particle size of 1 to 75 μm are used as particles for supporting methane bacteria. Specifically, they are diatomaceous earth, clay, bentonite, calcium carbonate, gypsum, and talc. These fine particles usually have a high specific surface area of 40,000 m ² /m ³ or more, and as a result, the concentration of methane bacteria attached to such inorganic fine particles can be reduced to 10,000 to 10,000 m 2 /m 3 or more.
It can be increased to 35,000 ppm, and the reaction rate per fermenter can be increased even at a medium temperature fermentation temperature of less than 35°C. (b) As mentioned in (a) above, we were able to increase the concentration of methane bacteria in the fermenter, so we were able to increase the concentration of methane bacteria in the low-concentration organic waste liquid, which was considered inefficient with the conventional microbial suspension method. It can be operated at a high and stable reaction rate with almost no outflow. Methane bacteria attached to the surface of supporting particles are only separated by contact between particles due to flow, and the concentration of methane bacteria in the fermenter does not decrease even if operated at low concentration and high water volume. . 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. (C) As mentioned in (B), 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. Energy saving efficiency can be significantly improved compared to conventional methods. (d) In the present invention, since the concentration of methane bacteria in the fermenter is high, the fermenter can be made compact. Therefore, compared to the conventional methane fermentation method, the site area required for installing the fermenter can be significantly reduced. (e) However, increasing the concentration of methane bacteria leads to clogging of the methane bacteria carrier. Therefore, in the present invention, in order to provide the contradictory functions of preventing clogging while retaining methane bacteria at a high concentration, organic waste liquid is injected into the methane bacteria supporting particles filled in the fermenter by upward flow. supply. Due to this upward flow, the filled particulate layer becomes an expanded bed or a fluidized bed, and clogging between the particulates can be prevented. If there is minimal expansion or flow at this time,
It is possible to prevent methane bacteria attached to the surface of the fine particles from peeling off as much as possible. Furthermore, when the fine particle layer is used as a fixed bed, by gently stirring the fine particle layer, clogging and detachment of methane bacteria can be prevented. Furthermore, by supplying the waste liquid as an upward flow, the generated methane gas can be released without being hindered by the particles, and the methane bacteria on the surface of the particles can be brought into good contact with the waste liquid, making it possible to improve the efficiency of the reaction. . (F) Furthermore, the method of the present invention can be applied to all kinds of organic waste liquids, and especially when treating low concentration organic waste liquids, the aeration operation in the activated sludge method can be replaced by the methane fermentation method of the present invention. can be replaced with Examples of the present invention will be described below. EXAMPLE As shown in the figure, approximately diatomaceous earth was placed as supporting particles 2 in a fermenter 1 consisting of a vinyl chloride column with a diameter of 0.15 m, an internal volume of 7, and a reaction part volume of approximately 5.
3.3 Filled. An upward flow is formed in the tank by supplying organic wastewater from the wastewater supply pipe 3 at the bottom of the tank through the perforated plate 11 and taking out the treated wastewater from the treated wastewater pipe 4 at the top of the tank. The diatomaceous earth 2 having methane bacteria 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 rotary motor 5. The stirrer used was one in which a large number of vinyl chloride strings were arranged in a frame parallel to the rotation axis. For wastewater, glucose is added to sanitary wastewater to increase BOD concentration.
850 ppm, and methane fermentation was carried out in an anaerobic atmosphere. For about one week after the start of operation, methane bacteria were added little by little, while the wastewater supply rate was gradually increased from 0.2/hr. After about 3 months, a large amount of methane bacteria was observed on the surface of the supporting particles. This enabled steady operation with a wastewater supply rate of 1.5/hr. The treated wastewater was led to a settling tank 7 through a pipe 4 and separated into settled sludge 8 and discharged water 9. Further, the generated gas was stored in a gas holder 10. During steady-state operation, the reaction temperature was changed to three types: 10°C, 20°C, and 30°C, and experiments were conducted for 2.5 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 that lasted about eight months in total.

[Table] (Note 2) The above numbers are the average values for each run.
From the above experimental results, it was found that methane fermentation is possible at temperatures below meso-temperature fermentation, which was considered difficult with conventional methods. Regarding reaction temperature and reaction rate, as the temperature increases, the reaction rate increases. However, the fact that a reaction rate of 2.5 kg/m ³ /day of reaction area was obtained even at a low temperature of 10°C means that the reaction rate is approximately 2 kg in normal medium temperature methane fermentation.
Considering that BOD/reaction area m ³ /day,
It must be said that this is an extremely efficient value. moreover
4.6, 5.5Kg/BOD/reaction part at 20℃ and 30℃
The value of m ³ /day was proved to be very high using the conventional method. Looking at the gas generation rate, the gas generation rate at 20°C was slightly higher than that at 30°C, and no temperature dependence was observed at temperatures around this temperature. As described above, it has been found that the fermentation method of the present invention using diatomaceous earth as a methane bacteria carrier has various advantages that could not be achieved by conventional methods.

[Brief explanation of drawings]

The figure is a system diagram showing an embodiment of the present invention. 1...Fermentation tank, 2...Diatomaceous earth particles.

Claims (1)

[Claims] 1. In a method for methane fermentation of organic waste liquid, in which an 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, the particle size of the supporting particles is 1
A method for methane fermentation of an organic waste liquid, characterized in that the methane fermentation is carried out at a temperature below 35° C. while supplying the organic waste liquid in an upward flow using inorganic fine particles of ~75 μm.