JP6681297B2 - Waste treatment method and waste treatment facility - Google Patents

Description

  The present invention relates to a waste treatment method, and more particularly to a method for treating organic waste.

  BACKGROUND ART It has been conventionally known that organic waste such as food waste is subjected to methane fermentation treatment and generated methane gas is used as a resource.

  For example, there has been proposed a method for treating oil-and-fat-containing waste in which organic waste is heated to 40 to 45 ° C to be solubilized and then the obtained liquid organic waste is subjected to methane fermentation at 55 ° C (for example, , Patent Document 1).

Japanese Patent No. 3609332

  However, the methane fermentation reaction may be hindered by the ammoniacal nitrogen produced by the decomposition of the organic waste (hereinafter referred to as ammonia inhibition).

  Particularly, in the method for treating oil-and-fat-containing waste described in Patent Document 1, the liquid organic waste is heated to 55 ° C in the methane fermentation treatment. Such high temperature methane fermentation carried out at 40 ° C. or higher stabilizes methane gas because the methane fermentation reaction is inhibited by a low concentration of ammonia nitrogen as compared with medium temperature methane fermentation carried out at less than 40 ° C. May not be able to be generated.

  On the other hand, Patent Document 1 describes that the temperature condition of the methane fermentation treatment is 35 ° C. or higher and 60 ° C. or lower, and includes the case where the methane fermentation treatment is carried out at an intermediate temperature lower than 40 ° C.

  However, in the method for treating oil-and-fat-containing waste described in Patent Document 1, even if the methane fermentation treatment is carried out at a temperature lower than 40 ° C, the liquid organic waste is heated to 40 ° C or higher in the solubilization treatment. However, there is a problem that the temperature of the methane fermentation treatment cannot be stably maintained below 40 ° C. In particular, when the temperature is high or in an area, liquid organic waste heated to 40 ° C or higher cannot be cooled sufficiently by natural heat radiation, so it is not possible to maintain the temperature of methane fermentation treatment below 40 ° C stably. Have difficulty.

  On the other hand, if a cooling facility is provided in the methane fermentation tank to cool the liquid organic waste after solubilization treatment to less than 40 ° C, the temperature of the methane fermentation treatment can be maintained below 40 ° C. However, there is a problem in that the running cost and equipment cost of the methane gas are required, and the production cost of methane gas increases.

  Therefore, it is considered to carry out each of the solubilization treatment and the methane fermentation treatment at a temperature lower than 40 ° C. However, when the solubilization treatment is performed at a medium temperature lower than 40 ° C, the solubilization of organic matter is higher than that at a high temperature. Is not done efficiently. That is, the medium-temperature solubilization treatment has a problem in that the solubilization rate equivalent to that of the high-temperature solubilization treatment cannot be achieved and the methane gas generation efficiency is reduced.

  Therefore, an object of the present invention is to provide a waste treatment method capable of reducing the production cost of methane gas, suppressing ammonia inhibition of a methane fermentation reaction, and improving the production efficiency of methane gas. To do.

  The present invention [1] includes a medium temperature solubilization step of solubilizing organic waste at a temperature lower than 40 ° C., a methane fermentation step of methane fermenting the solubilized organic waste at a temperature lower than 40 ° C., and the methane fermentation step. A high temperature solubilization step of solubilizing at least a part of the produced fermentation liquor at 45 ° C. or higher and lower than 70 ° C .; and a returning step of returning the fermentation liquor treated by the high temperature solubilization step to the intermediate temperature solubilization step. Includes waste treatment methods including.

  According to such a method, since the temperature of the medium temperature solubilization step is less than 40 ° C, the temperature of the methane fermentation step can be stabilized at less than 40 ° C even without providing equipment for cooling the solubilized organic waste. Can be maintained. Therefore, cost (running cost and facility cost) can be reduced, and ammonia inhibition of the methane fermentation reaction can be suppressed.

  Further, at least a part of the fermented liquor produced in the methane fermentation step is solubilized at 45 ° C. or higher in the high temperature solubilization step. Therefore, it is possible to promote the solubilization of the organic matter contained in the fermentation liquid that has not been solubilized in the medium temperature solubilization step. After that, the fermented liquor is returned to the medium temperature solubilization process together with the newly input organic waste. Therefore, the heat of the methanogen and the fermented liquid contained in the fermentation liquid should be reused in the medium temperature solubilization process. You can Then, the returned fermentation liquor is subjected to methane fermentation together with the organic waste. As a result, the production efficiency of methane gas can be improved.

  However, when the fermented liquid is heated to 70 ° C. or higher in the high temperature solubilization process, the temperature difference between the medium temperature solubilization process and the high temperature solubilization process increases, so the fermentation liquid is returned to the medium temperature solubilization process. In this case, it becomes difficult to maintain the temperature of the medium temperature solubilization step below 40 ° C, and thus it becomes difficult to maintain the temperature of the methane fermentation step below 40 ° C.

Further, in the fermented liquid, the ammoniacal nitrogen maintains an equilibrium state between ammonium ion (NH ₄ ⁺ ) and free ammonia (NH ₃ ) as shown in the following formula (1).
Equation (1)

  When such a fermented liquor is heated to 70 ° C. or higher in the high temperature solubilization step, the solubility of free ammonia in the fermented liquor decreases, so that ammonia gas is released from the fermented liquor. This reduces the concentration of ammoniacal nitrogen in the fermentation broth.

  Ammoniacal nitrogen causes ammonia inhibition when the concentration is high, but is an essential nutrient for the growth of methanogens, and when the concentration is excessively reduced, the methane gas generation efficiency may decrease.

  On the other hand, according to the above method, since the temperature of the high temperature solubilization step is lower than 70 ° C, the medium temperature solubilization step and the methane fermentation step can be stably maintained at lower than 40 ° C, and the solubility of free ammonia in the fermentation liquor is high. Can be suppressed, and the concentration of ammoniacal nitrogen in the fermentation liquid can be suppressed from being excessively decreased.

  The present invention [2] includes the waste treatment method according to the above [1], wherein the fermentation liquor has a pH of less than 9 in the high temperature solubilization step.

However, when the pH of the fermented liquor in the high temperature solubilization step is 9 or higher, the reaction between the hydroxide ion and ammonium ion present in the fermented liquor is promoted as shown in (2) below, and free ammonia and Water and is generated. Then, since ammonia gas is released from the fermentation liquor, the concentration of ammoniacal nitrogen in the fermentation liquor decreases.
Equation (2)

  On the other hand, according to the above method, since the pH of the fermentation liquor in the high temperature solubilization step is less than 9, the hydroxide ion concentration in the fermentation liquor is higher than when the pH of the fermentation liquor is 9 or more. Low. Therefore, the reaction between ammonium ions and hydroxide ions in the fermentation broth can be suppressed, and the concentration of ammonia nitrogen in the fermentation broth can be prevented from excessively decreasing.

  The present invention [3] includes the waste treatment method according to the above [1] or [2], wherein the temperature condition of the intermediate temperature solubilization step is 30 ° C. or higher and 39 ° C. or lower.

  However, if the temperature condition of the medium temperature solubilization step is less than 30 ° C., the organic matter in the organic waste cannot be efficiently solubilized, and the methane gas production efficiency in the methane fermentation step may decrease. is there.

  On the other hand, according to the above method, since the temperature condition of the medium temperature solubilization step is 30 ° C. or higher, the organic matter in the organic waste can be efficiently solubilized.

  Moreover, since the temperature condition of the medium temperature solubilization step is 39 ° C. or lower, the temperature of the methane fermentation step, which is the next step, can be stably maintained below 40 ° C., and the ammonia of the methane fermentation reaction in the methane fermentation step can be maintained. Inhibition can be suppressed.

  As a result, it is possible to stably improve the production efficiency of methane gas in the methane fermentation process.

  In the present invention [4], in the high temperature solubilization step, all of the fermentation liquor produced in the methane fermentation step is heated, and in the returning step, a part of the fermentation liquor treated in the high temperature solubilization step is added. The waste treatment method according to any one of the above [1] to [3], including returning to the medium temperature solubilization step and discharging the rest of the fermentation liquor as an effluent.

  According to such a method, all of the fermentation broth is heated in the high temperature solubilization step, so that the entire fermentation broth can be heat-disinfected, and pathogenic microorganisms and the like in the fermentation broth can be reduced. Then, a part of the fermentation sterilized by heat and sterilization is returned to the medium temperature solubilization step, and the rest of the fermentation liquor is discharged as a discharged liquid. That is, since the discharged liquid is discharged after being heat-sterilized, it can be suitably used as liquid fertilizer.

  The present invention [5] includes the waste treatment method according to any one of the above [1] to [4], wherein the intermediate temperature solubilization step and the methane fermentation step are performed in separate reaction tanks. There is.

  According to such a method, since the intermediate temperature solubilization step and the methane fermentation step are performed in separate reaction tanks, the intermediate temperature solubilization step and the methane fermentation step can be performed under suitable conditions. . Therefore, the solubilization and the processing speed of methane fermentation can be improved.

  In the waste treatment method of the present invention, it is possible to reduce the production cost of methane gas, suppress ammonia inhibition of the methane fermentation reaction, and improve the production efficiency of methane gas.

FIG. 1 is a schematic configuration diagram of an example of a waste treatment facility in which the first embodiment of the waste treatment method of the present invention is implemented. FIG. 2 is a schematic configuration diagram of an example of a waste treatment facility in which the second embodiment of the waste treatment method of the present invention is implemented. FIG. 3 is a schematic configuration diagram of an example of a waste treatment facility in which the third embodiment of the waste treatment method of the present invention is implemented. FIG. 4 is a graph showing the correlation between the residence time and the solubilization rate in Reference Examples 1 and 2. FIG. 5 is a graph showing the correlation between the solubilization temperature and the solubilization rate in Reference Examples 3 and 4.

1. Waste treatment method The first embodiment of the waste treatment method of the present invention is a medium temperature solubilization step of solubilizing an organic waste at a medium temperature solubilization temperature of less than 40 ° C, and a solubilized organic waste (medium temperature). A solubilized liquid) at a methane fermentation temperature of less than 40 ° C., a high temperature solubilization process of solubilizing the fermented liquid produced by the methane fermentation process at a high temperature solubilization temperature of 45 ° C. or higher; And a return step of returning the fermentation liquor (high temperature solubilized solution) treated in the solubilization step to the medium temperature solubilization step.

(1-1) Medium Temperature Solubilization Step In the medium temperature solubilization step, for example, high molecular weight organic matter (eg, carbohydrate, protein, fat, etc.) in organic waste is hydrolyzed by an acid-producing bacterium to produce a low molecular weight organic matter ( For example, after being decomposed into sugars, amino acids and peptides), these low molecular weight organic substances are decomposed into long-chain fatty acids (eg, propionic acid, butyric acid) by acid-producing bacteria.

  The organic waste is a waste containing the above-mentioned polymer organic matter, and is, for example, food waste (for example, agricultural processing waste, marine processing waste, livestock processing waste, kitchen waste (raw garbage), etc.) , Wastewater treatment sludge (for example, human waste sludge, septic tank sludge, sewage sludge, etc.) and the like. The organic wastes can be used alone or in combination of two or more.

  Among the organic wastes, food wastes are preferable, and agricultural processing wastes discarded in the wholesale market are more preferable.

  If necessary, the organic waste is crushed in advance, and then fermentation incompatible substances (for example, metals, plastics, etc.) contained in the organic waste are selected and removed.

  The total nitrogen content (TN) of the organic waste is, for example, 1 g / kg or more, preferably 2 g / kg or more, for example, 8 g / kg or less, and preferably 7 g with respect to 1 kg of the organic waste. / Kg or less, more preferably 5 g / kg or less, and particularly preferably 4 g / kg or less. The T-N can be measured, for example, by pretreating the organic waste by the Kjeldahl method and then performing the neutralization titration method or the summing method.

  Further, the agricultural processing waste has a lower TN than the marine processing waste and the livestock processing waste, and the TN of the agricultural processing waste is, for example, 5 g / kg or less, preferably 4 g / kg or less, More preferably, it is 3 kg or less.

  Further, as will be described later in detail, the newly introduced organic waste is stirred and mixed with a circulating liquid (described later) returned from the high temperature solubilization step (mixing step) before the intermediate temperature solubilization step. As a result, a slurry-like waste-circulating liquid mixture is prepared.

  The pH of the waste-circulating liquid mixture (organic waste) is, for example, 4.0 or more, for example, 6.5 or less, and preferably 6.0 or less.

  When the pH of the waste-circulating liquid mixture (organic waste) is within the above range, the activity of acid-producing bacteria can be improved and the activity of methane-fermenting bacteria can be suppressed in the medium temperature solubilization step.

  The waste-circulating liquid mixture (organic waste) is then adjusted to a moderate solubilization temperature below 40 ° C.

  The medium temperature solubilization temperature is, for example, 30 ° C. or higher, preferably 32 ° C. or higher, more preferably 35 ° C. or higher and lower than 40 ° C., preferably 39 ° C. or lower.

  If the intermediate temperature solubilization temperature is equal to or higher than the above lower limit, the organic matter in the organic waste can be efficiently solubilized, and if the intermediate temperature solubilization temperature is equal to or lower than the above upper limit, methane which is the next step described later. The temperature of the fermentation process can be stably maintained below 40 ° C., and ammonia inhibition of the methane fermentation reaction in the methane fermentation process can be suppressed.

  In order to adjust the temperature of the waste-circulating liquid mixture, if necessary, for example, steam is supplied to the waste-circulating liquid mixture to heat the waste-circulating liquid mixture to the above-mentioned medium temperature solubilization temperature. To do.

  The retention time (hydraulic retention time: HRT) in the medium temperature solubilization step is, for example, 1 day or longer, preferably 2 days or longer, such as 5 days or shorter, preferably 4 days or shorter.

  In addition, in the medium temperature solubilization step, the waste-circulating liquid mixture may be filtered to remove the above fermentation incompatible substances from the waste-circulating liquid mixture, if necessary.

  Furthermore, in the medium temperature solubilization step, nutrient salts may be added to the waste-circulating liquid mixture, if necessary. Examples of the nutrient salt include iron salt, nickel salt, cobalt salt and the like. The nutrient salts can be used alone or in combination of two or more.

  As described above, the waste-circulating liquid mixture is solubilized, and the medium-temperature solubilized liquid (solubilized organic waste) is prepared.

(1-2) Methane fermentation step Next, the medium temperature solubilized liquid (solubilized organic waste) is adjusted to a methane fermentation temperature of less than 40 ° C. In addition, in 1st Embodiment, a middle temperature solubilization process and a methane fermentation process are implemented as a separate process in another reaction tank.

  In the methane fermentation step, for example, the above long-chain fatty acid is decomposed into acetic acid and hydrogen by the symbiotic acetogenic bacterium, and then methane and carbon dioxide are produced by the methanogenic bacterium from acetic acid and hydrogen.

  The methane fermentation temperature is, for example, 30 ° C or higher, preferably 32 ° C or higher, more preferably 35 ° C or higher and lower than 40 ° C, preferably 39 ° C or lower. That is, the temperature range of the methane fermentation temperature is preferably the same as the temperature range of the medium temperature solubilization temperature.

  If the methane fermentation temperature is at least the above lower limit, methane can be stably generated, and if the methane fermentation temperature is at most the above upper limit, ammonia inhibition of the methane fermentation reaction can be suppressed.

  The temperature difference between the methane fermentation temperature and the medium temperature solubilization temperature (= methane fermentation temperature-medium temperature solubilization temperature) is, for example, ± 0 ° C or more, for example, less than ± 10 ° C, preferably ± 5 ° C or less, and further It is preferably ± 3 ° C or lower.

  If the temperature difference between the methane fermentation temperature and the medium temperature solubilization temperature is within the above range, the methane fermentation temperature can be adjusted within the above range without adjusting the temperature (heating or cooling) of the medium temperature solubilization solution before the methane fermentation step. Can be maintained.

  Further, the methane fermentation temperature is within the above temperature range without being adjusted in the methane fermentation step by adjusting the intermediate temperature solubilization temperature as described above in the mesophilic solubilization step. That is, the methane fermentation temperature can be adjusted within the above temperature range with reference to the medium temperature solubilization temperature.

  The residence time (hydraulic retention time: HRT) in the methane fermentation step is, for example, 6 days or longer, preferably 8 days or longer, such as 12 days or shorter, preferably 10 days or shorter.

  As described above, the medium-temperature solubilized liquid is methane-fermented to generate methane gas, and the fermented liquid is prepared.

  The generated methane gas is collected and collected by, for example, a gas holder. In addition, in the first embodiment, all of the fermentation liquid is transported to the high temperature solubilization step.

  The pH of the fermented liquid in the methane fermentation step is, for example, 6.5 or higher, preferably 7.0 or higher, for example 8.2 or lower, and preferably 8.0 or lower.

  When the pH of the fermented liquid is in the above range, methane-fermenting bacteria are activated in the methane fermentation step, and methane can be stably generated.

(1-3) High temperature solubilization step Next, the fermentation liquor is adjusted to the high temperature solubilization temperature. In the high temperature solubilization step, for example, organic substances remaining without being decomposed in both the intermediate temperature solubilization step and the methane fermentation step are solubilized.

  The high temperature solubilization temperature is preferably 45 ° C. or higher, preferably 50 ° C. or higher and lower than 70 ° C., preferably 65 ° C. or lower, more preferably 60 ° C. or lower.

  When the high temperature solubilization temperature is equal to or higher than the above lower limit, it is possible to stably solubilize the organic matter contained in the fermentation liquor that has not been solubilized in the medium temperature solubilization step, and to disinfect the fermentation liquor by heating.

Further, when the high temperature solubilization temperature is equal to or lower than the above upper limit, the production of ammonia gas can be suppressed and the concentration of NH ₄ ⁺ -N in the fermentation liquid can be suppressed from being excessively lowered. Therefore, even in the case of agricultural processing waste, it is possible to secure the NH ₄ ⁺ -N concentration necessary for the growth of methanogens.

  The temperature difference between the high temperature solubilization temperature and the medium temperature solubilization temperature (= high temperature solubilization temperature-medium temperature solubilization temperature) is, for example, + 5 ° C or higher, preferably + 10 ° C or higher, for example, less than + 40 ° C, and preferably , + 30 ° C. or lower, and more preferably + 20 ° C. or lower.

  Further, in order to adjust the temperature of the fermented liquor to a high temperature solubilization temperature, for example, the fermented liquor is heated by a known heat source so as to be in the above temperature range. That is, in the first embodiment, in the high temperature solubilization step, all of the fermentation liquor produced in the methane fermentation step is heated. Although steam can be used as a heat source, ammonia stripping is not performed even when steam is used in the high temperature solubilization process.

  The residence time (hydraulic retention time: HRT) in the high temperature solubilization step is, for example, 0.5 days or more, preferably 1 day or more, for example 3 days or less, preferably 2 days or less.

  As described above, the fermented liquor is solubilized, and the high temperature solubilized liquid (fermented liquid treated by the high temperature solubilization step) is prepared.

  The pH of the high temperature solubilized liquid (fermented liquid) in the high temperature solubilization step is, for example, 4.0 or more, preferably 7.0 or more, for example, less than 9.0, and preferably 8.2 or less.

When the pH of the high temperature solubilized liquid is in the above range, the production of ammonia gas can be further suppressed, and the NH ₄ ⁺ -N concentration in the fermentation liquid can be suppressed from being excessively lowered.

(1-4) Returning Process Next, a part of the high temperature solubilizing liquid is returned to the medium temperature solubilizing process as a circulating liquid, and the rest of the high temperature solubilizing liquid is discharged as an exhaust liquid. The discharged liquid is preferably used as liquid fertilizer and may be transported to a wastewater treatment facility.

  The ratio of the circulating liquid is, for example, 25% by volume or more, preferably 40% by volume or more, for example, 75% by volume or less, and preferably 60% by volume or less, based on the total amount of the high temperature solubilized liquid.

  Specifically, the circulating liquid is mixed with newly introduced organic waste to prepare a waste-circulating liquid mixture, and then returned to the medium temperature solubilization step.

  The mixing ratio of the circulating liquid is, for example, 50 parts by mass or more, preferably 100 parts by mass or more, for example, 200 parts by mass or less, and particularly preferably 100 parts by mass with respect to 100 parts by mass of the organic waste. is there.

  If the mixing ratio of the circulating liquid is at least the above lower limit, the heat of the methanogen and the circulating liquid contained in the circulating liquid can be suitably reused for the medium temperature solubilization step, and if the mixing ratio of the circulating liquid is at most the above upper limit. The temperature of the medium temperature solubilization step can be maintained below 40 ° C.

  As described above, in the first embodiment, the medium temperature solubilization step, the methane fermentation step, the high temperature solubilization step and the returning step are sequentially repeated, and the treatment liquid (waste-circulation liquid mixture, medium temperature solubilization liquid, fermentation liquid, circulation) Liquid) sequentially circulates through these steps.

  Further, those steps may be carried out continuously or intermittently. That is, the treatment liquid may continuously flow into each process without interruption, or the treatment liquid may flow into and stop each process repeatedly.

  Each such step is preferably performed intermittently. Specifically, the treatment liquid is used in each step at a predetermined treatment amount (e.g., every 2 to 3 hours) in a predetermined treatment amount (e.g., 8.0 wt% with respect to the total amount of organic waste treated in one day). (% By mass to 12.5% by mass), the inflow is stopped.

2. Waste Treatment Facility Such a waste treatment method is carried out by the waste treatment facility 1, as shown in FIG. 1, for example.

  The waste treatment facility 1 includes a pretreatment unit 5, a medium temperature solubilization unit 2, a methane fermentation unit 3, a gas holder unit 6, and a high temperature solubilization unit 4.

  The pretreatment unit 5 is a unit for pretreating organic waste, and includes a receiving hopper 7, a crushing device 8, a sorting device 9, a mixing tank 10, and a plurality of (three) pipes 11 (pipe 11A). To 11C) and the first carrier pipe 12.

  The receiving hopper 7 can receive the organic waste to be treated. The receiving hopper 7 is connected to the crushing device 8 by a pipe 11A.

  The crushing device 8 can crush the organic waste from the receiving hopper 7, and for example, a known biaxial crusher can be used. The crushing device 8 is connected to the sorting device 9 by a pipe 11B.

  The sorting device 9 is capable of sorting unsuitable materials for fermentation from the crushed organic waste, and examples thereof include a known wind sorting machine and a rotary blade type sorting machine. The sorting device 9 is connected to the mixing tank 10 by a pipe 11C. Further, the mixing tank 10 is connected to a medium temperature solubilization tank 13 (described later) by a first transfer pipe 12.

  The medium temperature solubilization unit 2 is a unit for medium temperature solubilization of organic waste at less than 40 ° C., and includes a medium temperature solubilization tank 13, a boiler 14, a steam pipe 15, and a second transfer pipe 16. There is.

  Although not shown, the medium-temperature solubilization tank 13 is provided with a known stirring device. Although not shown, the medium-temperature solubilization tank 13 may be provided with an addition unit for adding the above-mentioned nutrient salts to the organic waste. Further, the medium-temperature solubilization tank 13 is connected to the methane fermentation tank 18 (described later) by the second transfer pipe 16.

  The boiler 14 can generate superheated steam, for example, and is connected to the medium temperature solubilization tank 13 by a steam pipe 15. Thereby, the boiler 14 can supply steam into the medium temperature solubilization tank 13 via the steam pipe 15.

  The methane fermentation unit 3 is a unit for methane fermenting the medium-temperature solubilized liquid, and includes a methane fermentation tank 18 and a third carrier pipe 19.

  Although not shown, the methane fermentation tank 18 is provided with a known liquid circulation pump unit. Moreover, the methane fermentation tank 18 is connected to a high temperature solubilization tank 21 (described later) by a third carrier pipe 19. Although not shown, a boiler may be connected to the methane fermentation tank 18 via a steam pipe.

  The high temperature solubilization unit 4 is a unit that solubilizes the fermentation liquid at a high temperature of 45 ° C. or higher, and includes a high temperature solubilization tank 21, a return pipe 24, and a discharge pipe 30.

  Although not shown, the high temperature solubilization tank 21 is provided with a known heat source (for example, a boiler). The high temperature solubilization tank 21 is connected to the mixing tank 10 by a return pipe 24. Thereby, the mixing tank 10, the first carrier pipe 12, the medium temperature solubilization tank 13, the second carrier pipe 16, the methane fermentation tank 18, the third carrier pipe 19, the high temperature solubilization tank 21, and the return. The pipe 24 forms a circulation path. Further, a discharge pipe 30 is connected to the high temperature solubilization tank 21.

  The gas holder unit 6 is a unit that can collect methane gas, and includes a gas holder 26, a first gas pipe 27, a second gas pipe 28, and a gas exhaust pipe 29.

  The gas holder 26 is a known gas holder, and is connected to the methane fermentation tank 18 by a first gas pipe 27 and is connected to the high temperature solubilization tank 21 by a second gas pipe 28. A gas exhaust pipe 29 is connected to the gas holder 26.

  Next, the waste disposal operation in the waste disposal facility 1 will be described.

  In the waste treatment facility 1, first, the above organic waste is put into the receiving hopper 7.

  After that, the organic waste is supplied to the crushing device 8 via the pipe 11A and is broken. Subsequently, the broken organic waste is supplied to the sorting device 9 through the pipe 11B, and the fermentation inappropriate substances are removed.

  Next, the organic waste is supplied to the mixing tank 10 via the pipe 11C. Then, the organic waste is mixed with the circulating liquid returned from the high temperature solubilizing tank 21 in the mixing tank 10 at the above mixing ratio to prepare a waste-circulating liquid mixture.

  Then, the waste-circulating liquid mixture is supplied to the medium-temperature solubilization tank 13 through the first carrier pipe 12, adjusted to the medium-temperature solubilization temperature by the boiler 14, and then maintained for the residence time. As a result, the waste-circulating liquid mixture is solubilized at a mesophilic temperature to prepare a mesophilic solubilized liquid.

  Next, the medium-temperature solubilized liquid is supplied to the methane fermentation tank 18 through the second carrier pipe 16 and then maintained at the above-mentioned methane fermentation temperature for the above-mentioned residence time. As a result, the medium-temperature solubilized liquid is methane-fermented to generate methane gas, and the fermented liquid is prepared.

  The generated methane gas is collected in the gas holder 26 via the first gas pipe 27.

  Further, the fermented liquor is supplied to the high temperature solubilization tank 21 through the third carrier pipe 19 and adjusted to the above high temperature solubilization temperature, and then maintained for the above residence time. As a result, the fermented liquor is solubilized at high temperature to prepare a high temperature solubilized liquid.

  Then, a part of the high temperature solubilized liquid is returned to the mixing tank 10 as a circulating liquid through the return pipe 24 at the above ratio, and the rest of the high temperature solubilized liquid is discharged as a discharged liquid through the discharge pipe 30. To be done.

  The methane gas generated in the high temperature solubilization tank 21 is collected by the gas holder 26 via the second gas pipe 28. The second gas pipe 28 is preferably adjusted so as not to collect ammonia gas. The second gas pipe 28 may be provided with a separation means for separating methane gas and ammonia gas.

3. Function and Effect In the first embodiment of such a waste treatment method, the medium temperature solubilization temperature is lower than 40 ° C. Therefore, it is possible to stably maintain the methane fermentation temperature below 40 ° C. without providing a facility for cooling the medium-temperature solubilized liquid. As a result, the cost (running cost and facility cost) can be reduced, while ammonia inhibition of the methane fermentation reaction can be suppressed.

  Further, the fermented liquid is solubilized at 45 ° C. or higher in the high temperature solubilization step. Therefore, it is possible to promote the solubilization of the organic matter contained in the fermentation liquid that has not been solubilized in the medium temperature solubilization step. After that, the high temperature solubilized fermentation liquor (high temperature solubilized liquid) is returned to the medium temperature solubilization process together with newly introduced organic waste, so that the methanogens and high temperature solubilized liquids contained in the high temperature solubilized liquid are returned. The heat of the lysate can be reused for the mesophilic solubilization step. Then, the returned high temperature solubilized liquid is subjected to methane fermentation again together with the newly input organic waste. As a result, the production efficiency of methane gas can be improved.

Moreover, since the temperature of the high temperature solubilization step is lower than 70 ° C., the medium temperature solubilization step and the methane fermentation step can be stably maintained at lower than 40 ° C., and the NH ₄ ⁺ -N concentration in the fermentation liquor is excessively lowered. Can be suppressed. Therefore, even if the T-N of the organic waste is in the above range, it is possible to secure the NH ₄ ⁺ -N concentration necessary for the growth of the methanogen.

Further, the pH of the fermentation liquid in the high temperature solubilization step is preferably less than 9. Therefore, the reaction between ammonium ions and hydroxide ions in the fermentation broth can be suppressed, and the NH ₄ ⁺ -N concentration in the fermentation broth can be prevented from excessively decreasing.

  In addition, in the first embodiment, all of the fermentation liquid is heated in the high temperature solubilization step. Therefore, all of the fermentation broth can be heat-sterilized, and pathogenic microorganisms and the like in the fermentation broth can be reduced. Then, a part of the fermentation sterilized by heat and sterilization is returned to the medium temperature solubilization step, and the rest of the fermentation liquor is discharged as a discharge. That is, since the discharged liquid is heat-sterilized, the discharged liquid can be suitably used as liquid fertilizer.

  In addition, in the first embodiment, the intermediate temperature solubilization step and the methane fermentation step are performed as separate steps in separate reaction tanks. Therefore, each of the medium temperature solubilization step and the methane fermentation step can be carried out under suitable conditions. As a result, the solubilization and the processing speed of methane fermentation can be improved.

4. Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, the same members as those in the first embodiment described above are designated by the same reference numerals, and the description thereof will be omitted.

  In the first embodiment, all of the fermentation broth is sent to the high temperature solubilization step and heated, but the present invention is not limited to this. In the second embodiment, a part of the fermentation liquor is sent to the high temperature solubilization step as a circulating liquid, and the rest of the fermentation liquor is discharged as an effluent.

  Such a waste treatment method is carried out by the waste treatment facility 40. The waste treatment facility 40 has the same configuration as the waste treatment facility 1 except that the high temperature solubilization unit 4 does not include the discharge pipe 30 and that the methane fermentation unit 3 includes the discharge pipe 31. I have it. That is, the waste treatment facility 40 includes the pretreatment unit 5, the intermediate temperature solubilization unit 2, the methane fermentation unit 3, the gas holder unit 6, and the high temperature solubilization unit 4.

  In the second embodiment, the discharge pipe 31 of the methane fermentation unit 3 is connected to the methane fermentation tank 18. Then, a part of the fermentation liquid subjected to methane fermentation in the methane fermentation unit 3 is supplied to the high temperature solubilization tank 21 via the third carrier pipe 19, and the rest is discharged via the discharge pipe 31.

  According to the second embodiment as described above, the same operational effect as that of the first embodiment can be obtained.

5. Third Embodiment Next, a third embodiment of the present invention will be described with reference to FIG. In addition, in the third embodiment, the same members as those in the above-described first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

In the first embodiment, the medium temperature solubilization step and the methane fermentation step are performed in different reaction tanks, but the present invention is not limited to this. In the third embodiment, the medium temperature solubilization step and the methane fermentation step are performed in a single reaction tank.

  Such a waste treatment method is implemented by the waste treatment facility 50. The waste treatment facility 50 has the same configuration as the waste treatment facility 1 except that the medium temperature solubilization unit 2 is not provided. That is, the waste treatment facility 50 includes the pretreatment unit 5, the methane fermentation unit 3, the gas holder unit 6, and the high temperature solubilization unit 4.

  In the third embodiment, the mixing tank 10 is connected to the methane fermentation tank 18 by the first carrier pipe 12. Further, the boiler 14 is connected to the methane fermentation tank 18 by a steam pipe 15.

  Then, the waste-circulating liquid mixture supplied from the mixing tank 10 to the methane fermentation tank 18 is adjusted by the boiler 14 in the methane fermentation tank 18 to the above-mentioned medium temperature solubilization temperature range and methane fermentation temperature range. . As a result, the waste-circulating liquid mixture is solubilized and methane-fermented to generate methane gas, and the fermentation liquid is prepared.

  According to the third embodiment as described above, the same operational effect as that of the first embodiment can be obtained.

6. Modified Example In the first to third embodiments described above, the circulating liquid is returned to the intermediate temperature solubilization step after being mixed with the organic waste, but the circulating liquid is not limited to this, and the circulating liquid may have an intermediate temperature. It may be directly returned to the solubilization step. In this case, the organic waste and the circulating liquid are mixed in the medium temperature solubilization step.

  In the above-described first embodiment and second embodiment, the methane fermentation temperature is within the above temperature range without being adjusted in the methane fermentation step by adjusting the intermediate temperature solubilization temperature. However, the present invention is not limited to this, and in the methane fermentation step, steam can be supplied to the medium-temperature solubilized solution to adjust the temperature to the above-mentioned methane fermentation temperature.

  In the above-described first to third embodiments, the waste treatment facility includes the crushing device 8, but the crushing device 8 is not limited to this. When the organic waste does not need to be crushed, for example, the above-mentioned wastewater treatment sludge, the waste treatment facility may not include a crushing device.

  These modified examples can also achieve the same operational effects as those of the above-described first embodiment. These first to third embodiments and modifications are particularly suitable when the organic waste contains agricultural processing waste. Further, the first to third embodiments and the modified examples can be appropriately combined.

  Hereinafter, the present invention will be described in more detail with reference to reference examples, but the present invention is not limited thereto. Specific numerical values such as a blending ratio (content ratio), physical property values, parameters, etc. used in the following description are described in the above-mentioned "Description of Embodiments", and a corresponding blending ratio (content ratio). ), A physical property value, a parameter, etc., can be replaced by an upper limit value (a numerical value defined as “below”) or a lower limit value (a numerical value defined as “greater than” or “less than”).

(Reference Example 1) and (Reference Example 2)
A liquid obtained by mixing the organic waste and the fermentation liquid was solubilized at 37 ° C. (medium temperature solubilization temperature) to prepare a medium temperature solubilized liquid (medium temperature solubilization step). The pH of the medium-temperature solubilized solution in the medium-temperature solubilization step was 4.0 to 5.0, and the residence time in the medium-temperature solubilization step was 3 days.

  Next, the medium temperature solubilized liquid was subjected to methane fermentation at 37 ° C. (methane fermentation temperature) to prepare a fermentation liquid (methane fermentation step). The pH of the fermented liquid in the methane fermentation process was 7.0 to 8.0, and the residence time in the methane fermentation process was 9 days.

The fermented liquor after the medium-temperature methane fermentation was collected, subjected to solubilization treatment at the temperature and pH shown in Table 1, and the chemical oxygen demand (COD _cr ) and the soluble chemical oxygen demand (S -COD _cr ) was measured. Moreover, to calculate the solubilization ratio (percentage of _{S-COD cr} for _{COD cr).} The results are shown in Table 1 and FIG.

<Discussion>
As shown in Table 1, the COD _crs of Reference Example 1 (55 ° C.) and Reference Example 2 (37 ° C.) are almost the same value, but the S-COD _cr of Reference Example 1 has a residence time of 1 to 3 days. It was confirmed that, in comparison with S-COD _cr of Reference Example 2, it was about 1.4 times. In FIG. 4, the vertical axis represents the solubilization rate and the horizontal axis represents the residence time. As shown in FIG. 4, it was confirmed that when the fermented liquor was treated at high temperature (55 ° C.), the solubilization of organic substances, which was the limit in the treatment at medium temperature (37 ° C.), was promoted. Therefore, by returning the fermented liquor (high temperature solubilized liquid) treated in Reference Example 1 to the medium temperature solubilization step, improvement in methane gas generation efficiency can be expected.

(Reference Example 3)
The organic waste (garbage) was solubilized at the temperatures shown in Table 2 to prepare a solubilized liquid. The pH of the solubilized liquid in the solubilization step was 4.0 to 5.0, and the residence time in the solubilization step was 3 days. Then, the COD _cr and S-COD _cr of the solubilized solution were measured. The results are shown in Table 2 and FIG.

(Reference example 4)
The organic waste was changed to the fermentation liquor prepared in the same manner as in Reference Example 1, and solubilized at the temperature shown in Table 2 to prepare a solubilized liquid. The pH of the solubilized liquid in the solubilization process was about 8.0, and the residence time in the solubilization process was 3 days. Then, the COD _cr and S-COD _cr of the solubilized solution were measured. The results are shown in Table 2 and FIG.

<Discussion>
As shown in Table 2 and FIG. 5, in Reference Example 3, no significant change was observed in the solubilization rate due to the difference in solubilization temperature (37 ° C. and 55 ° C.), but in Reference Example 4, high temperature (55 ° C. ), The solubilization rate increased by 16.5% as compared with the case of solubilization at medium temperature (37 ° C.).

  In other words, it was confirmed that the organic waste was sufficiently solubilized even at medium temperature solubilization, but the fermentation liquor was not sufficiently solubilized at medium temperature solubilization, and was required to be solubilized at high temperature. .

  The fermentation liquor is solubilized at intermediate temperature before methane fermentation, and it is considered that organic matter that decomposes at intermediate temperature has already been decomposed. It is presumed that the fermented liquor is solubilized at high temperature, so that organic matter that cannot be decomposed by medium-temperature solubilization is solubilized.

1 Waste treatment facility 2 Medium temperature solubilization unit 3 Methane fermentation unit 4 High temperature solubilization unit

Claims (4)

A medium temperature solubilization step of solubilizing the organic waste at a pH of 4.0 or more and 5.0 or less and a temperature of 30 ° C or more and 39 ° C or less ;
A methane fermentation step in which the solubilized organic waste is subjected to methane fermentation at a pH of 7.0 or more and 8.0 or less and a temperature of less than 40 ° C .;
A high temperature solubilization step of solubilizing at least a part of the fermented liquor produced by the methane fermentation step at a pH of 4.0 or higher and lower than 9.0 and at 45 ° C. or higher and lower than 70 ° C .;
And a returning step of returning the fermentation liquor treated in the high temperature solubilization step to the medium temperature solubilization step.   The retention time (hydraulic retention time: HRT) in the medium temperature solubilization step is 1 day or more and 5 days or less,
  The waste treatment method according to claim 1, wherein a retention time (hydraulic retention time: HRT) in the methane fermentation step is 6 days or more and 10 days or less. In the high temperature solubilization step, heating all of the fermentation liquor generated by the methane fermentation step,
In the return process, and returns a part of the fermentation liquid treated by the high-temperature solubilization step to the medium temperature solubilization step, characterized by discharging the remainder of the fermentation liquid as a discharged liquid, according to claim 1 or 2. The waste treatment method described in 2 .   A medium temperature solubilization tank for solubilizing organic waste at a pH of 4.0 or more and 5.0 or less and a temperature of 30 ° C or more and 39 ° C or less
  A methane fermenter for performing methane fermentation of the solubilized organic waste at a pH of 7.0 or more and 8.0 or less and a temperature of less than 40 ° C;
  A high temperature solubilization tank that solubilizes at least a part of the fermented liquor produced in the methane fermentation tank at a pH of 4.0 or higher and lower than 9.0 and at a temperature of 45 ° C. or higher and lower than 70 ° C.,
  And a return pipe for returning the fermented liquor processed in the high temperature solubilization tank to the medium temperature solubilization tank.

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