JPS6238015B2 - - Google Patents

Description

[Detailed description of the invention]

In recent years, methane fermentation and anaerobic digestion methods have attracted attention as a means of economically recovering energy from biomass resources and wastes with high moisture content such as organic sludge, human waste, kitchen waste, industrial waste, and garbage. ing. This methane fermentation gas usually contains methane 45
Contains ~75%, carbon dioxide gas 25~55%, and 20~
Contains 4000 μ/m of hydrogen sulfide. When using methane gas as an energy source, hydrogen sulfide is oxidized and becomes sulfur dioxide gas or sulfuric acid mist, which corrodes boilers and combustion furnaces and becomes a source of air pollution, so it must be thoroughly removed.
Also, when methane fermentation gas is stored in a gas holder, there is a risk of corrosion of the gas holder, blower, etc. Also, when stirring the inside of the methane fermentation tank,
In many cases, a method is adopted in which the generated gas is bubbled in the tank, but if there is a large amount of hydrogen sulfide in the gas, there is a risk that the slurry to be treated in the tank will contain a large amount of sulfide, inhibiting methane fermentation. Because there is
It is desirable to desulfurize the recycled gas. For the desulfurization of methane fermentation gas, various methods and devices have been used for a long time to target the digestion gas of sewage sludge and human waste. It is broadly divided into dry type and wet type. In the dry type, iron powder, iron chilico, a mixture of iron and granules that reduce ventilation resistance, activated carbon, etc. are mainly used. The activated carbon has been desorbed and reused. Therefore, two or more absorption devices are required to be used alternately, and devices for oxidation and desorption are also required. Desulfurization with iron is expected to remove 70-85%. Wet desulfurization equipment is usually carried out by sending methane fermentation gas to a scrubber that is isolated from the air, and scrubbing with caustic soda, soda carbonate, chlorinated water, etc. Hydrogen sulfide is fixed and removed as soda sulfide and sulfur, and desulfurization removes about 80 to 99%.
Although these methods depend on the H ₂ S concentration, they consume a large amount of chemicals, especially caustic soda, which absorbs carbon dioxide gas from the gas, so its consumption is large. Another method is to desulfurize using organic chemicals. As described above, none of the conventional methods are economical and highly efficient in industrial implementation, and there are serious problems in practical implementation in this kind of large-scale field. The present inventor has been conducting research to solve this conventional problem. On the other hand, for more than 10 years, the present inventor has been using activated sludge, which is produced by treating sewage, human waste, organic industrial wastewater, etc., to remove various malodorous components.
We have been researching and developing biological oxidation and deodorization technology. For this reason, the inventor came up with a completely new idea that activated sludge treatment could be applied to desulfurization of methane fermentation gas. However, if the methane fermentation gas is treated aerobically, air will be mixed in and diluted, creating a risk of explosion and reducing its value as a fuel gas. Therefore, in activated sludge treatment, it is necessary to avoid mixing air into the methane fermentation gas. Furthermore, activated sludge must be maintained aerobically. Therefore, it is considered difficult to directly apply activated sludge treatment technology to methane fermentation gas in which oxygen is absent or in a very small amount. However, the inventor of the present invention has continued to conduct intensive research and has determined that methane fermentation gas is brought into contact with an activated sludge mixture kept aerobically and/or a culture solution containing hydrogen sulfide oxidizing bacteria in a gas-liquid contact device with air cut off. They discovered the surprising fact that by doing so, methane fermentation gas can be efficiently desulfurized without introducing air, and also succeeded in developing a new device for this purpose, leading to the completion of the present invention. That is, the present invention involves introducing an activated sludge mixture kept aerobically and/or a culture solution containing hydrogen sulfide oxidizing bacteria and methane fermentation gas into a gas-liquid contacting device in a state where air is shut off, and bringing them into contact with each other. The desulfurization method using activated sludge for methane fermentation gas is characterized by a method in which the container is divided into two parts by providing a partition wall, one of which is used as a gas-liquid contacting part with air cut off, and the other part is used as an aeration part. A methane fermentation gas introduction section is provided at the bottom of the liquid contact section, and an air introduction section is provided at the bottom of the aeration section, and the activated sludge mixture and/or hydrogen sulfide oxidation kept aerobically from the aeration section is provided at the top of the partition wall. An opening is provided at the bottom of the partition wall for introducing the culture solution containing bacteria into the gas-liquid contact section, and an opening is provided at the bottom of the partition wall for introducing the culture solution containing activated sludge mixture and/or hydrogen sulfide oxidizing bacteria from the gas-liquid contact section into the aeration section. This invention relates to a desulfurization device for methane fermentation gas, which is characterized in that each opening is provided. According to the present invention, hydrogen sulfide in methane fermentation gas can be efficiently removed without mixing air, so problems of corrosion of boilers and air pollution during combustion are solved, and there is no mixing of air. Therefore, the value of the methane fermentation gas as a fuel gas does not decrease, and the methane fermentation gas after treatment can be suitably and effectively used as various energy sources. The present invention will be explained below using the drawings. FIG. 1 is a flow sheet of one embodiment of the method of the present invention, in which 1 is a methane fermentation tank, 2 is a gas-liquid contact device with air cut off, 3 is an aeration device, and 4 is a gas holder. . Occurred in methane fermentation tank 1
Methane gas containing H ₂ S is introduced into the lower part of the gas-liquid contact device 2 via the pipe 5 and the blower 6, and rises inside the gas-liquid contact device 2. On the other hand, activated sludge or a mixed liquid containing hydrogen sulfide oxidizing bacteria, which has been sufficiently aerated in an aeration device (aeration tank) 3 and held aerobically, is introduced into the contact device 2 by a pump 7, whereupon methane gas containing hydrogen sulfide is introduced into the contact device 2. in countercurrent contact with the hydrogen sulfide to decompose and remove hydrogen sulfide. Methane gas from which hydrogen sulfide has been decomposed and removed is transferred to the gas holder 4 through a pipe 8. Note that air is introduced into the aeration device 3 through a pipe 9. Further, the mixed liquid is discharged from the lower part of the gas-liquid contact device 2. The mixed liquid discharged at this time may be returned to the aeration tank 3 and recycled, or may be directly discharged from the system. If the activated sludge method is used in a sewage treatment facility, human waste treatment facility, organic industrial wastewater treatment facility, etc., and the surplus sludge is subjected to methane fermentation, the final settling tank of the activated sludge treatment facility The drawn sludge is put into the aeration tank 3, aerated until dissolved oxygen is included in the mixed liquid, and then sent to the gas-liquid contact device 2. Part or most of the mixed liquid discharged from there is transferred to the aeration tank 3. The waste can be returned to its original state, or all of it can be returned to the aeration tank of the original treatment facility (exclusion from the system). If the facility has a sludge reaeration tank, that reaeration tank can be used instead of the aeration tank 3. If you want to perform methane fermentation on sludge, kitchen waste, crushed garbage, etc., or collect and use the gas generated from a waste landfill, you need to transport surplus activated sludge from a nearby activated sludge treatment facility. , aeration tank 3
The mixed liquid discharged from the gas-liquid contacting device 2 is also returned to the aeration tank 3 for circulation. If activated sludge is difficult to obtain, a culture solution containing nutrients such as nitrogen, phosphoric acid, magnesium, and iron, or a digestion and desorption solution from methane fermentation is placed in the aeration tank 3 and sent to the gas-liquid contact device 2 for circulation. As the product is used, hydrogen sulfide oxidizing bacteria will naturally grow and desulfurization will occur. It can be used by adding separately cultured hydrogen sulfide oxidizing bacteria to the culture solution. In addition, when implementing the method of the present invention, the gas-liquid contact device 2
It is also possible to use a device in which the aeration tank 3 and the aeration tank 3 are integrated. This device is a newly developed device by the present inventor, and its basic structure is that one large tank is divided into two by a partition wall, and one is used as a gas-liquid contact device and the other as an aeration tank, so that the air in the aeration tank is The structure is such that only the aerated activated sludge in the aeration tank is introduced into the gas-liquid contact device, and that it can be circulated back to the aeration tank after contact with the gas. An example is shown in FIG. In Fig. 2, 10 is a gas-liquid contact part, 11 is an aeration part,
Reference numeral 12 denotes a methane fermentation gas introduction pipe, and the gas rises in the gas-liquid contact section 10 from its tip 13 serving as the gas introduction section. Further, an air introduction pipe 14 is inserted into the aeration section 11, and air is introduced from a lower end 15 serving as an air introduction section. Gas-liquid contact part 10
An activated sludge mixture 16 is introduced into the aeration section 11. The activated sludge mixture aerated and aerobically maintained in the aeration section 11 is circulated to the gas-liquid contact section 10 through openings 18 and 19 provided at the upper and lower parts of the partition wall 17. Since the activated sludge mixture flows by introducing a large amount of air for aeration, the circulation flow path varies depending on the position of the air introduction pipe 14, but when the pipe 14 is located away from the partition wall 17 as shown in FIG. In this case, there is a flow path in the aeration section 11 as shown by "→". That is, in the circulation flow path, as air is introduced from the lower end 15 of the pipe 14, the activated sludge mixture flows upward and then to the left, and the aeration section 1 below the opening 18 flows.
The activated sludge mixture is introduced into the gas-liquid contacting part 10 through the upper opening 18 along the guide plate 21 provided on the first side, and is inevitably returned from the activated sludge mixture through the lower opening 19. In the gas-liquid contact section 10, the introduced activated sludge mixture is brought into contact with the gas introduced from the methane fermentation gas introduction pipe 12, and the gas desulfurized by the contact is discharged from the gas discharge pipe 20. Here, since the pipe 14 is installed apart from the partition wall 17 and the guide plate 21 also functions as a baffle plate, it is possible to completely prevent air from entering the gas-liquid contact portion 10. In addition, the methane fermentation gas introduced from the tip 13 of the pipe 12 will hardly escape to the aeration part 11 side if the pipe 12 is installed at a position away from the partition wall 17 as shown in FIG. Accordingly, by providing the baffle plate 22 below the guide plate 21 on the gas-liquid contacting part 10 side, it is possible to completely prevent the gas from escaping to the aeration part 11 side. In Fig. 2, "..." indicates the movement of gas. In addition, in the present invention, the gas-liquid contact device 2 uses a method in which methane fermentation gas is injected in the form of bubbles from the bottom of a tank filled with an activated sludge mixture or a hydrogen sulfide oxidizing bacteria culture solution, in the same way as the aeration tank 3. You can pick it up. The mixed liquid may be sprayed into a closed scrubber so that it can be discharged from the bottom, and then the methane fermentation gas may be sent in an upward flow from the bottom to bring it into contact with the scrubber. Particular care must be taken to prevent air from entering the contact device. Sewage, human waste, organic industrial wastewater, etc. usually contain a small amount of sulfide, and the mixed liquid in the activated sludge aeration tank used to treat them is inhabited by some hydrogen sulfide oxidizing bacteria. The growth of this bacterial group will be inhibited unless it is kept under aerobic conditions at a level where dissolved oxygen is detected in the mixed solution. Aeration tank 3
is similar to an aeration tank for activated sludge treatment,
Therefore, when the mixed liquid in which the dissolved oxygen has been sufficiently dissolved and the redox potential has been increased is sent to the gas-liquid contacting device 2 and brought into contact with the methane fermentation gas, H ₂ S in the gas dissolves into the mixed liquid together with carbon dioxide gas, and at the same time, A portion of the dissolved oxygen is consumed by dissolving and oxidizing H ₂ S, and is discharged as a mixed liquid with a low redox potential. H ₂ S in the methane fermentation gas is removed by being dissolved in the mixed liquid through contact, and a gas containing almost no H ₂ S is discharged from the device. Gas-liquid contact device 2
In the aeration method, bubbles are brought into contact with the water from a depth of 1 meter, and even if the time required for the bubbles to rise is several seconds, sufficient removal is achieved. The shorter the residence time of the mixed liquid in the gas-liquid contact device 2, the safer it is, and it is sufficient to discharge the mixed liquid before the dissolved oxygen disappears (usually within 5 minutes).
The H ₂ S is dissolved in the mixed solution and returned to the aeration tank 3 in a partially oxidized form, or returned to the activated sludge aeration tank of this treatment, where it is further oxidized and decomposed and converted from sulfite ions to sulfate ions. changes up to. If the catalytic converter and aeration tank are cycled and used repeatedly, there is a risk that sulfate ions will accumulate in the mixed liquid and the pH will tilt towards the acidic side. Because it partially dissolves and exhibits a strong buffering capacity, it is difficult for the pH to drop below 5 even after long periods of circulation.
Therefore, the ability to oxidize and decompose hydrogen sulfide usually does not decrease even with circulating contact, but sometimes the pH is checked and
It is desirable to replace the mixed liquid when it becomes 5 or less. In addition, if sulfate ions become concentrated in the mixed solution (several thousand mg/), the decomposition ability will decrease, so if activated sludge is constantly replenished and some of it is discharged, such dangers can be avoided. There is no gender. Activated sludge produced by treating sewage containing a lot of H ₂ S, such as human waste, can be used immediately for desulfurization, but even when using general activated sludge or a culture solution of hydrogen sulfide oxidizing bacteria as described above, It often takes several days for hydrogen sulfide oxidizing bacteria to grow and become dominant under the conditions of the equipment. Therefore, when using new sludge or culture solution, it is necessary to circulate it between the contact device and the aeration tank and let it acclimate for several days. When ordinary activated sludge is allowed to acclimate for two days and then brought into contact with methane fermentation gas in an aeration manner, H ₂ S in the gas is significantly removed. It is clear that the degree of removal varies depending on the H ₂ S concentration in the gas, the amount of mixed liquid supplied, the concentration of mixed liquid, etc. The amount of H ₂ S supplied per day per 1 kg of (MLVSS) is also important. the
Table 1 shows the results of examining the H ₂ S removal effect using the method described above while changing the H ₂ S load. The necessary degree of H ₂ S removal from methane fermentation gas varies depending on the purpose of the purified gas and the H ₂ S concentration in the gas, but is at least 80%.
It seems necessary to remove the If you try to expect that efficiency, H ₂ S10 per 1 kg of suspended solids in the mixed solution per day.
It appears that the load must be kept below 100 g. When the load is less than 2.5g/MLSS-Kg/day, _H2S is
More than 99% can be removed. When this is carried out using a hydrogen sulfide oxidizing bacterial culture solution, the H ₂ S load per kilogram of suspended solids in the culture solution can be approximately 10 times that of activated sludge.

[Table] * This value is the concentration at the end of the experiment under each load condition.
Example 1 Activated sludge produced at a sewage treatment facility was used in a methane fermentation device that generates approximately 1000 ^Nm3 of sewage sludge methane fermentation gas (50% methane, 40% carbon dioxide, 10% nitrogen, 100μ/H ₂ S/day) per day. The gas was desulfurized using The gas-liquid contact for this purpose is carried out by the aeration method, and a sealed gas-liquid contact tank with a volume of approximately 4 m ³ and a water depth of 1.5 m is installed. Approximately 40 m ³ of gas per hour is pumped into it using a rotary blower, and the gas is pumped into the activated sludge mixture. It was diffused. The activated sludge was extracted from the final settling tank of the sewage treatment facility at a rate of 120 m ³ per hour and sent to an aeration tank with a capacity of 40 m ³ where it was sufficiently aerated using a diffused air system, and the suspended solids concentration of the mixed liquid was 8000 mg/hour. It was hot. The mixed liquid is pumped into the upper part of the contact tank at a rate of 2 m ³ per minute, and discharged from the lower part of the tank. 1/10 of the discharge is returned to the aeration tank of the original facility, and the rest is used for the aeration of this desulfurization equipment. I put it back in the tank. As a result, the amount of H ₂ S in the methane fermentation gas was approximately 10 μ/cm, and desulfurization was achieved with a removal rate of approximately 90%. In that case
The H ₂ S load per 1 kg of MLSS was approximately 6.6 g/day. Example 2 Methane fermentation gas (methane) from concentrated waste liquid from fish processing
60%, carbon dioxide gas 35%, nitrogen 4%, _H2S1000μ /
), which generates approximately ^200Nm3 per day, desulfurizes the gas by recycling activated sludge brought in by tank truck from a nearby wastewater treatment facility as much as possible. The gas-liquid contact device used a closed aeration tank with a volume of about 2 m ³ and a water depth of 1.5 m, and 8.3 Nm ³ of methane fermentation gas per hour was pumped into the tank using a rotary blower for aeration. Activated sludge was received in a sufficiently aerated aeration tank with a volume of approximately 0 m ³ , and half of the old sludge was removed every month and replaced with new sludge. The concentration of suspended solids in the mixed solution was approximately 6000 mg/. 5 minutes per minute
m ³ was pumped into the upper part of the contact tank, the same amount was withdrawn from the lower part and circulated to the aeration tank. As a result, the amount of H ₂ S in the processing gas was approximately 50 μ/cm, and an H ₂ S removal rate of approximately 95% could be achieved. MLSS in that case/
The H ₂ S load per kg was approximately 7.0 g/day. The pH of the mixed solution during circulation was maintained at 5.2 to 6.8.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing one embodiment of the method of the present invention, and FIG. 2 shows an example of a desulfurization apparatus used in carrying out the method of the present invention.

Claims (1)

[Scope of Claims] 1. An activated sludge mixture maintained aerobically or/and a culture solution containing hydrogen sulfide oxidizing bacteria and methane fermentation gas are introduced into a gas-liquid contact device with air blocked and brought into contact. A method for desulfurizing methane fermentation gas using activated sludge. 2. During the above contact, apply less than 10 g of hydrogen sulfide per 1 kg of suspended solids (MLSS) in the activated sludge mixture per day, and 100 g per day for hydrogen sulfide oxidizing bacterial culture solution.
The desulfurization method according to claim 1, characterized in that the contact is carried out as follows. 3. Divide the container into two parts by providing a partition wall, one of which will be used as a gas-liquid contact part with air cut off, and the other part will be used as an aeration part, and a methane fermentation gas introduction part will also be installed at the bottom of the gas-liquid contact part. An air introduction section is provided at the bottom of the aeration section, and an activated sludge mixture kept aerobically from the aeration section and/or a culture solution containing hydrogen sulfide oxidizing bacteria is introduced into the air-liquid contact section at the top of the partition wall. methane fermentation gas characterized in that openings are provided at the lower part of the partition wall for introducing the activated sludge mixture and/or the culture solution containing hydrogen sulfide oxidizing bacteria from the gas-liquid contact section into the aeration section. desulfurization equipment.