JP2005238151A - Treatment apparatus and treatment method for organic waste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment method and a treatment apparatus for organic waste, which can simplify a process to treat an organic waste containing ammonia nitrogen and solid matters by methane fermentation and can minituarize a methane fermentation bath. <P>SOLUTION: The treatment apparatus for organic waste is provided with a pretreatment facility 1 for organic waste, a methane fermentation bath 2 for reducing the volume of pre-treated organic waste and recovering methane gas, a dehydration facility 4 for performing solid-liquid separation of organic waste after methane fermentation in the methane fermentation bath 2, and a wastewater treatment facility 5 for treating wastewater separated in the dehydration facility 4, wherein an ammonia removal bath 6 is provided for removing ammonia generated in the methane fermentation bath 6 and organic waste is directly returned to the methane fermentation bath 2 after ammonia-removing treatment in the ammonia removal bath 6. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a processing apparatus and a processing method for organic waste, in particular, simplification of a process for fermenting methane fermentation (anaerobic digestion processing) of organic waste containing ammonia nitrogen and containing solid matter, and The present invention relates to a method and apparatus for treating organic waste that can reduce the size of a methane fermentation tank.

  The treatment and disposal of organic waste has become a major social problem. In particular, due to the implementation of the Food Recycling Law, the treatment of raw garbage and moss has been required to be addressed as an inevitable issue. Under such circumstances, in recent years, many methane fermentation technologies for solid organic waste have been developed in Japan in addition to sewage sludge treatment and manure treatment.

  Among them, many technologies have also been developed for the treatment of ammonia nitrogen, which is a hindrance factor in methane fermentation treatment. For example, Patent Document 1 discloses a waste treatment method in which a part of waste treated with methane fermentation is subjected to hot alkali treatment / ammonia removal treatment, mixed with untreated waste, and again subjected to methane fermentation. Yes. Hereinafter, this technique is referred to as a conventional technique.

  According to this prior art, in order to remove ammonia from some waste treated by methane fermentation and return it to the methane fermentation tank again, the ammonia nitrogen concentration of the waste in this methane fermentation tank is reduced. And solid organic waste can be treated efficiently.

JP 2001-137812 A

  However, the conventional technology mixes waste that has been subjected to methane fermentation treatment with organic waste that has been subjected to pretreatment, returns it to the methane fermentation tank, and performs methane fermentation treatment again, so a large-capacity methane fermentation tank is required. Has the problem of becoming.

  Therefore, an object of the present invention is to provide organic waste that can simplify the process of methane fermentation treatment of organic waste containing ammonia nitrogen and solid matter, and downsize the methane fermenter. The object is to provide a processing method and a processing apparatus for an object.

  The present invention has been made to achieve the above-described object, and is characterized by the following.

  The invention according to claim 1 is a pretreatment facility for organic waste, a methane fermentation tank for reducing the volume of the pretreated organic waste and collecting methane gas, and after methane fermentation by the methane fermentation tank In the organic waste treatment apparatus comprising a dehydration facility for solid-liquid separation of the organic waste and a wastewater treatment facility for treating the wastewater separated by the dehydration facility, the ammonia generated in the methane fermentation tank is removed. An ammonia removal tank to be removed is installed, and the organic waste that has been subjected to ammonia removal treatment by the ammonia removal tank is directly returned to the methane fermentation tank.

  The invention according to claim 2 is a method for treating organic waste in which methane fermentation treatment is performed on an organic waste containing or generating ammonia nitrogen and containing solid matter in a methane fermentation tank. The ammonia nitrogen contained in the organic waste subjected to is removed in an ammonia removal tank, and the organic waste subjected to the ammonia removal treatment is directly returned to the methane fermentation tank.

  The invention according to claim 3 is characterized in that, in the invention according to claim 2, the solid matter concentration of the organic waste used for the methane fermentation treatment and the ammonia nitrogen removal treatment is in the range of 5 to 30%. It is what has.

  The invention described in claim 4 is characterized in that, in the invention described in claim 2 or 3, the method of methane fermentation treatment and ammonia nitrogen removal treatment is a stripping method.

  The invention described in claim 5 is characterized in that, in the invention described in claim 4, in the removal of ammonia nitrogen by stripping, at least one of air, nitrogen, and gas generated by methane fermentation is used. It is.

  The invention according to claim 6 is the invention according to claim 4 or 5, wherein the ammonia nitrogen removal treatment by stripping is maintained within a gas-liquid ratio defined by the following formula (1) within a range of 20 to 1000. It is characterized in that it is performed as described above.

Gas-liquid ratio = G / L = G (V / t) --- (1)
However, in equation (1):
G: Gas flow rate [m ³ / h],
L: amount of organic waste [m ³ / h],
V: Organic waste volume to be treated [m ³ ],
t: Processing time [h]
It is.

  The invention described in claim 7 is characterized in that, in the invention described in any one of claims 4 to 6, the removal of ammonia nitrogen by stripping is performed in a temperature range of 30 to 90 ° C. Is.

  The invention according to claim 8 is the invention according to any one of claims 4 to 7, wherein the ammonia nitrogen removal treatment by stripping is performed under a pressure range of -0.03 to 0.03 MPaG. It has the characteristics.

  The invention according to claim 9 is the invention according to any one of claims 4 to 8, wherein the pH of the organic waste is adjusted to 7 to 10 by adding alkali during the removal of ammonia nitrogen by stripping. It is characterized by adjusting within the range.

  The invention according to claim 10 is the invention according to any one of claims 4 to 8, wherein the pH of the organic waste is adjusted to 7 to 10 by adding alkali during the removal of ammonia nitrogen by stripping. The exhaust gas generated in the ammonia nitrogen removal treatment is cooled to 60 ° C. or lower, and then separated into a treatment gas and a treatment liquid, and the recovered treatment liquid is returned to the ammonia removal tank. It is what has.

  The invention according to claim 11 is the invention according to any one of claims 4 to 8, wherein the exhaust gas generated in the removal process of ammonia nitrogen by stripping is cooled to 60 ° C. or lower, It is characterized in that it is separated into a processing solution and an alkali is added to the recovered processing solution and returned to the ammonia removal tank.

  According to the present invention, it is possible to simplify the process of subjecting organic waste containing ammonia nitrogen and solid matter to methane fermentation and to reduce the size of the methane fermentation tank.

  One embodiment of the organic waste treatment apparatus of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing an organic waste processing apparatus of the present invention, and FIG. 2 is a detailed view of an ammonia removal tank portion.

  As shown in FIG. 1 and FIG. 2, organic waste such as soot or sewage sludge is mixed and pulverized in the pretreatment facility 1 and then sent to the methane fermentation tank 2, where the processing load of the post-process is here. In order to reduce the volume, methane gas is recovered from the viewpoint of resource reuse. The recovered methane gas is sent to the gas purification facility 3 and used for power generation and the like. On the other hand, the organic waste after methane fermentation is sent to the dehydration facility 4 and separated into solid and liquid. The dehydrated cake separated as a solid content in the dehydration equipment 4 is incinerated or composted. On the other hand, the waste water (filtered water) is sent to the waste water treatment facility 5, and the treated water is discharged into a river or the like.

  Part of the organic waste that has been subjected to methane fermentation treatment (anaerobic digestion treatment) in the methane fermentation tank 2 is sent to the ammonia removal tank 6, where at least a part of the ammonia nitrogen contained in the organic waste is contained. Removed. The organic waste from which at least a part of the ammonia nitrogen has been removed is returned to the methane fermentation tank 2.

  Most of nitrogen components such as proteins contained in organic waste change to ammonia nitrogen during the methane fermentation treatment, so the effect is remarkably small even if the removal treatment is performed before that. On the other hand, for the same reason, the ammonia nitrogen removal treatment after the methane fermentation treatment does not remove the methane fermentation inhibition factor. Therefore, by removing ammonia nitrogen in parallel with methane fermentation, in other words, by removing so that the produced ammonia nitrogen does not accumulate beyond the allowable concentration for the activity of methane fermentation bacteria, Can be carried out smoothly.

  The solid waste concentration of the organic waste used for the methane fermentation treatment and ammonia nitrogen removal treatment is preferably within a range of 5 to 30%. If the solid concentration is less than 5%, high methane fermentation efficiency cannot be obtained. The reason why the upper limit of the solid concentration is limited to 30% is as follows. In the case of persimmons, the average solid concentration is about 20%, but in persimmons with a low content of vegetables, fruits and the like containing a lot of water, the solid concentration is about 30%. 30% is an amount that can be processed without dilution even for such a high concentration of soot. When the solid concentration exceeds 30%, (1) the required power for stirring in the ammonia removal tank is increased, and (2) the efficiency of heat exchange when heating and cooling the waste is reduced.

  The removal of ammonia nitrogen by the methane fermentation tank 2 is preferably performed by a stripping method. There are various methods for removing ammonia nitrogen, such as biological denitrification, chlorination, adsorption, and crystallization. The method is not limited in this invention as well, but the concentration of the target solid is high. The stripping method can be said to be optimal because it has a high viscosity (several thousand cP or more) and can be carried out efficiently with a simple equipment at a low cost in a short time and in a small space.

  In the case of the stripping method, it is preferable to use at least one of air, nitrogen gas, and gas mainly composed of methane produced by methane fermentation treatment. These gases are preferable because they do not increase the operation load, but are not limited to the above gases as long as they are safe.

  When the ammonia nitrogen is removed by the stripping method, it is preferable to maintain the gas-liquid ratio defined by the following formula (1) within the range of 20 to 1000.

Gas-liquid ratio = G / L = G (V / t) --- (1)
However, in equation (1)
G: Gas flow rate [m ³ / h],
L: Amount of organic waste [m ³ / h]
V: Organic waste volume to be treated [m ³ ],
t: Processing time [h]
It is.

  The reason why the gas-liquid ratio is limited to the above range is that when the gas-liquid ratio is less than 20, it is difficult to efficiently remove ammonia nitrogen, while when the gas-liquid ratio exceeds 1000, the removal efficiency is high. However, a large-sized blower is required and the operation load becomes heavy. At the same time, the amount of water or steam accompanying the ammonia nitrogen increases, and the load of gas treatment increases.

  The stripping treatment is preferably performed at a temperature in the range of 30 to 90 ° C. This is because when the stripping temperature is less than 30 ° C, it is difficult to efficiently transfer the liquid phase ammonia nitrogen to the gas phase due to the limitation of gas-liquid equilibrium, while when the stripping temperature exceeds 90 ° C. This is because the removal efficiency is increased, but the vapor pressure of water is also increased, and the amount of water or vapor accompanying the ammonia nitrogen is increased.

  The stripping treatment is desirably performed under a pressure in the range of -0.03 to 0.03 MPaG. This is because when the stripping treatment pressure is less than -0.03 MPaG, the ammonia nitrogen removal efficiency is remarkably increased, but the evaporation and scattering of water is also increased. This is because when it exceeds 03 MPaG, a long treatment time is required because the separation rate of ammonia nitrogen is small.

  In the stripping treatment, it is desirable to adjust the pH of the organic waste within the range of 7 to 10 by adding alkali to the organic waste. This is because ammonia nitrogen in the liquid phase is easy to separate and remove by stripping because most of its existence form is free ammonia. However, when the pH is less than 7, the nitrogen nitrogen in the liquid phase has a high abundance ratio as an ammonium ion form due to the restriction of dissociation equilibrium, and thus the removal efficiency is significantly lowered. On the other hand, even if the pH is increased beyond 10, there is no significant change in the form of ammonia nitrogen, and only a large amount of drug is consumed.

  The exhaust gas containing ammonia nitrogen and water or steam generated during the removal process of ammonia nitrogen is cooled to 60 ° C. or less by the condenser 7 and separated into a processing gas and a processing liquid by the gas-liquid separator 8. . At least a part of the collected processing liquid is returned to the ammonia removal tank 6. This makes it possible to maintain a high removal efficiency by suppressing a decrease in the moisture content and an increase in viscosity of the organic waste to be treated as the stripping proceeds. Note that it is more effective that the cooling temperature is lower than the ammonia nitrogen removal temperature, that is, the stripping temperature. The separated processing gas (ammonia carrier gas) is, for example, absorbed into sulfuric acid and recovered as ammonium sulfate.

  In the stripping treatment, instead of adding alkali to the organic waste, alkali or an alkaline aqueous solution is added to the recovered treatment liquid, and the treatment liquid is returned to the ammonia removal tank 6 to adjust the pH during the stripping treatment. May be performed. By adding alkali to the treatment liquid, the pH of the treatment liquid itself is increased, and dissolution of ammonia nitrogen in the exhaust gas can be suppressed. That is, the separation efficiency of ammonia nitrogen and accompanying water can be significantly improved in the cooling separation. Furthermore, although the exhaust gas contains hydrogen sulfide even in a small amount, it can be collected with treated water to which alkali is added in the cooling separation process, so that the treatment load of ammonia nitrogen as the treatment gas is remarkably increased. It becomes possible to reduce.

  In order to perform methane fermentation efficiently, the preferable ammonia nitrogen concentration is 3000 mg / L or less, more preferably 2500 mg / L or less. In particular, when methane fermentation is performed at a high temperature of 50 ° C. or higher, it is desirable to maintain the ammonia nitrogen concentration at 2000 mg / L or lower.

  Agitation of organic waste (treated sludge) in the stripping tank, that is, organic waste (treated sludge), in order to efficiently remove ammonia nitrogen from organic waste with high solids and high viscosity ) Dispersion of the carrier gas in the inside and renewing the gas-liquid interface of the organic waste also produces a high effect. There is no restriction | limiting in particular in the stirring system of the stirrer 9, Either horizontal stirring or vertical stirring may be sufficient. Moreover, a paddle type, a turbine type, a spiral type etc. can be used for a stirring blade. The number, size, and rotation speed of the stirring blade can be arbitrarily selected as long as the organic waste in the stripping tank can be mixed appropriately. For example, the organic matter has a remarkably high solid concentration and viscosity. When processing waste, it is desirable to use a low-speed, high-torque type of several to several tens of revolutions per minute.

Assuming that the amount of organic waste treated is 50 m ³ / day, the methane fermentation treatment time is 20 days, and the amount of waste to be removed from ammonia is 50 m ³ / day, as shown in FIG. In this invention, which returns waste directly to methane fermentation, the effective volume of the methane fermenter is only 1000 m ³ , whereas it is mixed with unfermented organic waste as shown in FIG. Returning, the above-described prior art requires an effective volume that is twice as large as 2000 m ³ . From this, according to this invention, it turns out that simplification of the process which carries out the methane fermentation process of the organic waste containing a solid substance, and size reduction of a methane fermenter can be achieved.

  Hereinafter, the present invention will be described in more detail with reference to an example of organic waste. The organic waste includes organic waste containing sewage treatment sludge, manure, and other ammonia nitrogen in addition to soot.

  100 parts by weight of soot containing 5000 mg / L of ammonia nitrogen was charged into a container equipped with a stirrer having two paddle blades, and a stripping test was performed using air at a temperature of 80 ° C. under normal pressure. . The solid matter concentration of the soot used was 25%, and the specific gravity was approximately 1.0. The exhaust gas is cooled to 40 ° C. with a condenser, caustic soda is added to the treatment liquid separated in the gas-liquid separator, and the organic waste in the stripping tank is circulated through the stripping tank to pH = 8.0. Controlled. Air was blown so that the gas-liquid ratio shown in the above formula (1) was 450, and this state was maintained for 150 minutes. And the soot after completion | finish was extract | collected and the ammonia nitrogen concentration was measured. As a result, the ammonia nitrogen concentration was 704 mg / L, and the ammonia nitrogen removal rate was 86%.

  As a comparative example, the same stripping test as in Example 1 was performed while cooling the exhaust gas to 40 ° C. with a condenser and circulating it in the stripping tank without adding caustic soda to the treatment liquid separated in the gas-liquid separator. . In addition, pH control of the organic waste in a stripping tank was performed while adding the caustic soda aqueous solution directly to a stripping tank. As a result, the ammonia nitrogen concentration of the organic waste in the stripping tank after 150 minutes was 1513 mg / L, and the removal rate of ammonia nitrogen was 70%. Compared with the method of the present invention, the ammonia nitrogen concentration The removal rate was low.

  A stripping test similar to that of the example was performed at a temperature of 70 ° C. As a result, the ammonia nitrogen concentration after 150 minutes was 1593 mg / L, and the removal rate of ammonia nitrogen was 68%.

  A stripping test similar to that of Example 2 was performed at a pressure of -0.02 MPaG. As a result, the ammonia nitrogen concentration after 120 minutes was 921 mg / L, and the removal rate of ammonia nitrogen was 82%.

  The same stripping test as in Example 1 was carried out while maintaining pH 7, 8 and 9. As a result, the ammonia nitrogen concentration after 60 minutes was 4483 mg / L, 2093 mg / L, and 1391 mg / L for pH = 7, 8, and 9, respectively, and the removal rate of ammonia nitrogen was 10% and 58%, respectively. %, And 72%.

It is a block diagram which shows the processing apparatus of the organic waste of this invention. It is detail drawing of an ammonia removal tank part. It is explanatory drawing which shows the processing amount of the organic waste by this invention. It is explanatory drawing which shows the processing amount of the organic waste by a prior art.

Explanation of symbols

1: Pretreatment equipment 2: Methane fermentation tank 3: Gas purification equipment 4: Dewatering equipment 5: Wastewater treatment equipment 6: Ammonia removal tank 7: Condenser 8: Gas-liquid separator 9: Stirrer

Claims (11)

Organic waste pretreatment equipment, methane fermentation tank for reducing the volume of pretreated organic waste and collecting methane gas, and organic waste after methane fermentation by the methane fermentation tank In an organic waste treatment apparatus comprising a dehydration facility for separation and a wastewater treatment facility for treating wastewater separated by the dehydration facility,
An ammonia removal tank for removing ammonia generated in the methane fermentation tank is installed, and the organic waste that has been subjected to the ammonia removal treatment by the ammonia removal tank is directly returned to the methane fermentation tank. , Organic waste treatment equipment. In a method for treating organic waste, in which organic waste containing or producing ammonia nitrogen and containing solid matter is subjected to methane fermentation in a methane fermentation tank,
Ammonia nitrogen contained in the organic waste subjected to the methane fermentation treatment is removed in the ammonia removal tank, and the organic waste subjected to the ammonia removal treatment is directly returned to the methane fermentation tank. Organic waste disposal methods.   The method for treating organic waste according to claim 2, wherein the solid waste concentration of the organic waste subjected to methane fermentation treatment and ammonia nitrogen removal treatment is in the range of 5 to 30%. .   The method of treating organic waste according to claim 2 or 3, wherein the method of methane fermentation treatment and ammonia nitrogen removal treatment is a stripping method.   5. The method for treating organic waste according to claim 4, wherein at least one of air, nitrogen, and a gas generated by methane fermentation is used in the removal of ammonia nitrogen by stripping. 6. The ammonia nitrogen removal treatment by stripping is performed such that the gas-liquid ratio defined by the following formula (1) is maintained within a range of 20 to 1000. Of organic waste.
Gas-liquid ratio = G / L = G (V / t) --- (1)
However, in equation (1):
G: Gas flow rate [m ³ / h],
L: amount of organic waste [m ³ / h],
V: Organic waste volume to be treated [m ³ ],
t: Processing time [h]
It is.   The method for treating organic waste according to any one of claims 4 to 6, wherein the removal of ammonia nitrogen by stripping is performed in a temperature range of 30 to 90 ° C.   The removal of ammonia nitrogen by stripping is performed under a pressure range of -0.03 to 0.03 MPaG, The organic waste according to any one of claims 4 to 7, Processing method.   The alkali waste is added during the removal treatment of ammonia nitrogen by stripping to adjust the pH of the organic waste within a range of 7 to 10, according to any one of claims 4 to 8. , Organic waste disposal methods.   During the removal of ammonia nitrogen by stripping, alkali is added to adjust the pH of the organic waste within the range of 7 to 10, and the exhaust gas generated during the removal of ammonia nitrogen is cooled to 60 ° C or lower. The organic waste processing method according to any one of claims 4 to 8, wherein the processing liquid is separated into a processing gas and a processing liquid, and the recovered processing liquid is returned to the ammonia removal tank. .   After the exhaust gas generated in the removal process of ammonia nitrogen by stripping is cooled to 60 ° C. or lower, it is separated into a processing gas and a processing liquid, an alkali is added to the recovered processing liquid, and the process is returned to the ammonia removal tank. The method for treating organic waste according to any one of claims 4 to 8, characterized in that it is characterized in that

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