JP5654754B2 - Dry methane fermentation residue dehydration system - Google Patents

Description

  The present invention relates to a dehydration system and a dehydration method for dry methane fermentation residues.

  When waste from households, offices, offices, etc. is subjected to methane fermentation, the waste is separated and sorted at the time of collection or before processing, and is not biodegradable with organic waste (such as garbage). Sorted into substances (plastics, cloth, metals, etc.). The sorted organic waste is used as a raw material for methane fermentation, while impurities are often treated by incineration or the like.

  Methane obtained by methane fermentation of organic waste is used as a biogas for fuels. On the other hand, the methane fermentation residue generated after methane fermentation is dehydrated and separated into sludge and waste water.

  In general, methane fermentation includes dry methane fermentation and wet methane fermentation. Dry methane fermentation is preferably performed when solid waste is targeted because it can be processed by simple sorting, has a wide range of objects, and can process high-concentration raw materials with low power. Conventionally, the dry methane fermentation residue produced in the methane fermentation tank 11 is dehydrated by the dehydrating means 12 and separated into dehydrated sludge and wastewater by the dry methane fermentation residue dehydrating system 10 having the configuration shown in FIG.

  By the way, since dry-type methane fermentation has the above characteristics, simple selection can be performed before fermentation. Simple sorting can remove relatively large contaminants such as plastic, but not all contaminants are removed. Further, even when performing separate collection, complete separation is not necessarily performed at the emission source. Therefore, dry methane fermentation is performed in a state including impurities, and as a result, impurities are included in the dry methane fermentation residue.

  In the fermenter 11, when the sludge density | concentration is maintained constant, a foreign material and sludge are in a mixed state, without isolate | separating. However, when the sludge density | concentration in the fermenter 11 falls, a contaminant and sludge isolate | separate and a contaminant precipitates in the lower part in the fermenter 11. FIG. Further, when a large amount of contaminants such as plastic having a small specific gravity is included, the floating in the upper part of the fermenter 11. In order to prevent such impurities from floating or settling, the sludge concentration in the fermenter 11 may be increased. In order to increase the sludge concentration, it is conceivable to reduce the amount of dilution water for diluting the raw material. However, in order to prevent ammonia inhibition, a predetermined amount of dilution water is required, and the dilution water cannot be reduced below the required amount.

  Therefore, it is effective to return the residue after fermentation into the fermenter 11 (Non-Patent Document 1). However, if the residue containing impurities is returned to the fermenter 11, the content of impurities in the fermenter 11 is increased.

  Further, in recent years, as described in Patent Document 1 and Patent Document 2, fermentation residues after dry methane fermentation are used as additives for horticultural corrosive soil, compost, and the like. However, if the dry methane fermentation residue contains impurities, it cannot be used as it is as compost (compost).

  Therefore, a system that effectively removes impurities from the dry methane fermentation residue is desired.

JP-A-4-231395 JP-A-6-319526

Proceedings of the 13th Annual Meeting of the Waste Science Society 2002 “Operation Report of Organic Waste Recycling Demonstration Plant (Part 3)”

  The present invention can efficiently perform dry methane fermentation while maintaining a constant sludge concentration even when using raw materials containing impurities such as plastics, cloths, and metals, and has a stable dewatering capacity. An object of the present invention is to provide a dry methane fermentation residue dehydration system capable of operating a dehydrator.

  The present invention provides a dry methane fermentation residue dehydration system, wherein the dry methane fermentation residue dehydration system comprises a methane fermentation tank for dry methane fermentation of organic waste; and impurities contained in the fermentation residue of the organic waste. A debris separating means for separating; a dehydrating means for dehydrating the fermentation residue from which the impurities have been separated; and a dehydrated sludge returning means for returning the dehydrated sludge after dehydration to the methane fermentation tank. The resulting organic waste fermentation residue is supplied to the contaminant separation means, the fermentation residue from which the contaminant has been separated is supplied to the dehydration means, and at least one of the dewatered sludge recovered by the dehydration means. The section is configured to be returned to the methane fermentation tank by the dewatered sludge returning means.

  In one embodiment, a flocculant adding means is provided between the contaminant separating means and the dehydrating means.

  In one embodiment, the fermentation residue of the organic waste is withdrawn from the upper part or the lower part of the methane fermenter and supplied to the contaminant separating means.

  In one embodiment, the contaminant separating means is a screw press.

  In a further embodiment, the dehydrating means is a screw press, a centrifugal dehydrator, a rotary press, or a belt press.

  Furthermore, the present invention provides a method for dehydrating a dry methane fermentation residue, the method comprising supplying organic waste to a methane fermenter; obtaining the fermentation residue by subjecting the organic waste to dry methane fermentation A step of separating impurities contained in the fermentation residue; a step of dehydrating the fermentation residue from which the impurities are separated to obtain dehydrated sludge; and returning at least a part of the dehydrated sludge to the methane fermentation tank Comprising the steps of:

  In one embodiment, the method further includes a step of adding a flocculant to the fermentation residue from which the impurities are separated after the step of separating the impurities.

  In one embodiment, the fermentation residue of the organic waste is withdrawn from the upper part or the lower part of the methane fermenter and subjected to a step of separating the impurities.

  In one embodiment, in the step of separating the impurities, the impurities are separated by a screw press.

  In a further embodiment, in the step of obtaining the dewatered sludge, the fermentation residue from which the impurities are separated is dehydrated by a screw press, a centrifugal dehydrator, a rotary press, or a belt press.

  According to the present invention, it is possible to efficiently perform dry methane fermentation while maintaining a constant sludge concentration even when using raw materials containing impurities, and the dehydration apparatus can be operated with a stable dewatering capacity. . Furthermore, according to the present invention, since the dewatered sludge obtained after dehydration does not contain impurities, it can be used as it is as a raw material for compost or the like.

It is a systematic diagram which shows the embodiment of the conventional dry-type methane fermentation residue dehydration system. It is a systematic diagram showing one embodiment of the dry methane fermentation residue dehydration system of the present invention. It is a systematic diagram which shows the other embodiment of the dry-type methane fermentation residue dehydration system of this invention.

  A dry methane fermentation residue dehydration system and a dry methane fermentation residue dehydration method of the present invention will be described with reference to the accompanying drawings.

A. Dry Methane Fermentation Residue Dehydration System FIG. 2 shows an embodiment of the dry methane fermentation residue dehydration system of the present invention. This dry methane fermentation residue dehydration system 20 includes a methane fermentation tank 21 for dry methane fermentation of organic waste; a contaminant separation means 23 for separating contaminants contained in the fermentation residue of organic waste; A dehydrating means 22 for dehydrating the fermentation residue, and a dewatering sludge returning means 24 for returning the dehydrated sludge after dehydration to the methane fermentation tank 21. The fermentation residue of the organic waste produced in the methane fermentation tank 21 is supplied to the contaminant separation means 23, the fermentation residue from which the impurities are separated is supplied to the dehydration means 22, and the dehydration recovered by the dehydration means 22. At least a part of the sludge is configured to be returned to the methane fermentation tank 21 by the dehydrated sludge return means 24.

(Methane fermentation tank)
The methane fermentation tank 21 performs dry methane fermentation of organic waste obtained by simple sorting of waste from households, offices, business establishments, etc. or organic waste collected separately. The methane fermenter 21 is not particularly limited, and a general fermenter such as a horizontal cylindrical fermenter is used.

  In the methane fermentation tank 21, dry methane fermentation is performed. Dry methane fermentation may be performed at a high concentration of about 15 to 40% by mass of the sludge in the methane fermentation tank. Therefore, as described above, dry methane fermentation has the advantages that it can be processed by simple sorting, can process a wide range of objects, and high-concentration raw materials with low power. In the present invention, the “sludge concentration” means not only the concentration of sludge but also the concentration including fine paper pieces and fiber pieces contained in the sludge.

(Contaminant separation means)
The simple sorting of waste cannot separate all impurities. In addition, the organic waste collected separately includes impurities. Therefore, since fermentation is performed in a state including impurities, the dry methane fermentation residue (the fermentation residue of organic waste) includes impurities. The contaminant separating means 23 is provided for the purpose of separating contaminants contained in the dry methane fermentation residue.

  Examples of the contaminant separation means 23 include a screw press, a fine screen, a link chain type dehydrator, a bar screen, a drum type screen, and a dust remover. Among these, a screw press is preferable.

  The foreign matter separated by the foreign matter separating means 23 is collected in a garbage pit or the like and processed by incineration or the like. On the other hand, the dry methane fermentation residue from which impurities are separated is supplied to the dehydrating means 22.

(Dehydration means)
The dehydrating means 22 separates the dry methane fermentation residue from which impurities have been separated into dehydrated sludge and waste water.

  The dehydrating unit 22 may have a finer solid-liquid separation surface than the contaminant separating unit 23. Examples thereof include a screw press, a centrifugal dehydrator, a rotary press, and a belt press. Among these, a screw press is preferable.

  For example, when a screw press is used as the contaminant separation means 23, a screw press, a centrifugal dehydrator, a rotary press, or a belt press with a finer solid-liquid separation surface can be preferably used as the dehydrating means 22.

  The dry methane fermentation residue dehydration system of the present invention may include secondary dehydration means (not shown) in the subsequent stage of the dehydration means 22 as necessary. For example, when a bar screen, a drum-type screen, or a dust remover is used as the contaminant separating means 23, a screw press is used as the dehydrating means 22, and a screw press with a finer solid-liquid separation surface is used as the secondary dehydrating means. It may be used.

  At least a part of the dewatered sludge separated by the dewatering means 22 (or the secondary dewatering means) is returned to the methane fermentation tank 21. Thus, by returning at least a part of the dewatered sludge to the methane fermentation tank 21, when the sludge concentration in the methane fermentation tank 21 decreases, the sludge concentration can be increased, and the sludge concentration in the methane fermentation tank 21. Can be kept constant. Therefore, separation of contaminants and sludge in the methane fermentation tank 21 can be prevented.

(Dehydrated sludge return means)
The dewatered sludge returning means 24 returns at least a part of the dehydrated sludge separated by the dewatering means 22 (or the secondary dewatering means) to the methane fermentation tank 21. The dehydrated sludge is not necessarily returned directly to the methane fermentation tank 21. That is, the dewatered sludge may be supplied to the methane fermentation tank 21, and the preceding stage of the methane fermentation tank 21, for example, an intermediate storage tank (not shown) for storing raw materials, a raw material dilution tank (not shown), an intermediate storage tank or You may return to the raw material supply line (not shown) etc. which connect the dilution tank and the methane fermentation tank 21. FIG.

  Examples of the dewatered sludge return means 24 include a piston pump, a screw conveyor, and a belt conveyor.

  Next, another embodiment of the dry methane fermentation residue dehydration system of the present invention is shown in FIG. This dry methane fermentation residue dehydration system 30 includes a methane fermentation tank 31 for dry methane fermentation of organic waste; a contaminant separation means 33 for separating contaminants contained in the fermentation residue of organic waste; A dehydrating means 32 for dehydrating the fermentation residue; a dehydrated sludge returning means 34 for returning the dehydrated sludge after dehydration to the methane fermentation tank 31; and a flocculant adding means 35. The organic waste fermentation residue generated in the methane fermentation tank 31 is supplied to the contaminant separation means 33, and the fermentation residue from which the contaminants have been separated is supplied to the dehydration means 32, and the dewatered sludge recovered by the dehydration means 32. At least a part of the dewatering sludge is returned to the methane fermentation tank 31 by the dewatered sludge returning means 34, and the flocculant adding means 35 is provided between the contaminant separating means 33 and the dewatering means 32. ing.

  The methane fermentation tank 31, the contaminant separation means 33, the dehydration means 32, and the dewatered sludge return means 34 are the methane fermentation tank 21, the contaminant separation means 23, the dehydration means 22, and the dehydration in the dry methane fermentation residue dehydration system 20 described above. It can be the same as the sludge return means 24.

(Coagulant addition means)
The flocculant addition means 35 can add a flocculant as needed to the dry methane fermentation residue from which impurities have been separated.

  The flocculant adding means 35 can be, for example, a means for adding the flocculant by mechanical control, a means for manually adding the flocculant, or the like. The flocculant will be described later.

  In the dry methane fermentation residue dehydration system of the present invention, when the dry methane fermentation residue is supplied from the methane fermentation tanks 21 and 31 to the contaminant separation means 23 and 33, the dry methane fermentation residue is preferably the methane fermentation tank 21, It is comprised so that it may be extracted from the upper part or the lower part of 31.

  For example, the methane fermentation tank 21, 31 side of the line connecting the methane fermentation tanks 21, 31 and the contaminant separation means 23, 33 branches, and one branched end is connected to the upper part of the methane fermentation tanks 21, 31. The remaining ends are connected to the lower parts of the methane fermentation tanks 21 and 31. Opening / closing means (for example, a valve) is provided between the branch point and the upper and lower connecting portions of the methane fermentation tanks 21 and 31. The opening / closing means such as a valve may be a manual type or an automatic type such as a machine control.

  Here, the “upper part of the methane fermentation tank” means a position where the dry methane fermentation residue can be extracted from the vicinity of the upper layer of the dry methane fermentation residue present in the methane fermentation tank. It is not necessary to be the top of 31 or the like.

  Even if the foreign matter floats, the foreign matter can be preferentially removed from the methane fermentation tanks 21 and 31 by extracting the dry methane fermentation residue from the upper part of the methane fermentation tanks 21 and 31.

  On the other hand, the “lower part of the methane fermenter” means the vicinity of the bottom in the methane fermenter, for example, from the bottom of the methane fermenter 21, 31 to a height of about a quarter. It is not necessary to be the lowest part (bottom part) of 31.

  Even if impurities are precipitated, impurities can be preferentially removed from the methane fermentation tanks 21 and 31 by drawing out the dry methane fermentation residue from the lower part of the methane fermentation tanks 21 and 31.

B. Method for dehydrating dry methane fermentation residue The method for dehydrating a dry methane fermentation residue of the present invention (hereinafter sometimes simply referred to as “dehydration method”) is a step of supplying organic waste to a methane fermentation tank (organic waste). Product supply step); a step of subjecting the organic waste to dry methane fermentation to obtain a fermentation residue (dry methane fermentation step); a step of separating impurities contained in the fermentation residue (contaminant separation step); Including a step of dehydrating the fermentation residue from which water is separated to obtain dehydrated sludge (dehydration step); and a step of returning at least a portion of the dehydrated sludge to the methane fermentation tank (return step). The dehydration method of the present invention can be performed, for example, in a dry methane fermentation residue dehydration system as shown in FIG. Hereinafter, each process is demonstrated with reference to FIG.

(Organic waste supply process)
In the dehydration method of the present invention, the organic waste is supplied to the methane fermentation tank 21. As described above, the organic waste is obtained by simple sorting or separate collection from wastes from homes, offices, offices, and the like.

  The supply method of the organic waste is not particularly limited, and is supplied to the methane fermentation tank 21 by a general supply method.

(Dry methane fermentation process)
The organic waste supplied to the methane fermentation tank 21 is subjected to anaerobic dry methane fermentation to produce a dry methane fermentation residue and methane gas. In the methane fermentation tank 21, dry methane fermentation is performed by methane producing bacteria.

  The dry methane fermentation residue is subjected to a contaminant separation process. In the dehydration method of the present invention, when the dry methane fermentation residue is subjected to the contaminant separation step, the dry methane fermentation residue is preferably drawn from the upper part or the lower part of the methane fermentation tank 21.

  On the other hand, methane gas is recovered by a methane gas recovery device (not shown) provided in the methane fermentation tank 21 and used as biogas.

(Contaminant separation process)
In the simple sorting, all the impurities cannot be separated, and the waste collected separately includes the impurities, so that impurities such as plastic remain in the dry methane fermentation residue. Such impurities can be separated using the contaminant separating means 23.

  As the contaminant separation means 23, for example, the above-described screw press, fine screen, link chain type dehydrator, bar screen, drum type screen, dust remover, etc. are used, and only the contaminants are separated from the dry methane fermentation residue. .

(Dehydration process)
In the contaminant separation step, the dry methane fermentation residue from which the contaminants have been separated is subjected to a dehydration step.

  The dry methane fermentation residue from which the impurities are separated is separated into dehydrated sludge and waste water by the dehydrating means 22.

  As the dry methane fermentation residue from which impurities are separated, those having a finer solid-liquid separation surface than the impurities separating means 23 can be used. For example, dehydration is performed using the above-described screw press, centrifugal dehydrator, rotary press, belt press, or the like. Among these, it is preferably dehydrated using a screw press.

  The dehydration method of the present invention may include a step of adding a flocculant before the dehydration step. For example, as shown in FIG. 3, the flocculant is added to the dry methane fermentation residue from which impurities are separated by the flocculant adding means 35. By adding the flocculant, a large sludge floc is formed, so that even when the sludge concentration is low, stable dehydration can be achieved.

  Examples of the flocculant include an aluminum-based inorganic flocculant, an iron-based inorganic flocculant, and a polymer flocculant. The flocculant is preferably added in a proportion of 0.1% by mass to 1.5% by mass, more preferably 0.4% by mass to 0.6% by mass, with respect to the dry methane fermentation residue from which impurities are separated. Is done.

  At least a part of the dewatered sludge separated in the dehydration step can be returned to the methane fermentation tank 21 in the return step described later, and the remaining dewatered sludge can be used as a raw material for compost or the like.

  On the other hand, the separated wastewater can be treated and discharged into the natural world such as sewers and rivers.

  After the dehydration step, a secondary dehydration step may be included as necessary.

(Return process)
At least a part of the dehydrated sludge separated by the dehydration step is returned to the methane fermentation tank 21 by the dehydrated sludge return means 24.

  The dehydrated sludge is preferably 100: 1 to 100: 30, more preferably 100: 3 to 100: 20, so that the dry methane fermentation residue and the dehydrated sludge extracted from the methane fermentation tank 21 have a volume ratio of 100: 1 to 100: 20. Returned to the methane fermentation tank 21.

  Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to the following examples.

Example 1
Using the dry methane fermentation residue dehydration system of the present invention shown in FIG. 3, the dry methane fermentation residue was dehydrated.

  Organic waste was supplied to the methane fermentation tank 31, and dry methane fermentation was performed. The fermentation residue was extracted from the methane fermenter 31 and subjected to the contaminant separation means 33 (screw press) to remove contaminants such as plastic and cloth in the fermentation residue. A polymer flocculant (a ratio of about 0.4% by mass with respect to the solid content of the fermentation residue) was added to the fermentation residue from which impurities were removed by the flocculant addition means 35 to form a large sludge floc. Next, the fermentation residue was dehydrated by using, as the dehydrating means 32, a screw press that was finer than the screw press used as the contaminant separating means 33.

  When the water content in the fermentation residue (dehydrated residue) after dehydration was measured, it was about 60%, and the electric power (power consumption) required for dehydration of the fermentation residue was about 3.0 kW.

(Comparative Example 1)
The dry methane fermentation residue was dehydrated using the conventional dry methane fermentation residue dehydration system shown in FIG.

  Organic waste was supplied to the methane fermentation tank 11, and dry methane fermentation was performed. The fermentation residue is extracted from the methane fermenter 11 and dehydrated with a 1.5 mmφ screw press, and then a polymer flocculant (a ratio of about 1.0% by mass with respect to the fermentation residue) is added to the filtrate to remove a large sludge floc. The fermentation residue was dehydrated using a centrifugal dehydrator as the dehydrating means 12.

  When the water content in the fermentation residue (dehydration residue) after dehydration was measured, it was about 80%, and the electric power (power consumption) required for dehydration of the fermentation residue was about 14.7 kW.

  In the dry methane fermentation residue dehydration system of the present invention, the water content in the dehydrated residue is less than that of the conventional dry methane fermentation residue dehydration system, even though it consumes only about 20% of the electric power of the conventional dry methane fermentation residue dehydration system. Was found to be about 20% less. Therefore, the dry methane fermentation residue dehydration system of the present invention can dehydrate the fermentation residue very efficiently.

  According to the present invention, it is possible to efficiently perform dry methane fermentation while maintaining a constant sludge concentration even when using raw materials containing impurities, and the dehydration apparatus can be operated with a stable dewatering capacity. . Therefore, it is useful in the field of processing waste such as household and office work. Furthermore, according to the present invention, since the dewatered sludge obtained after dehydration does not contain impurities, it can be used as it is as a raw material for compost.

10, 20, 30 Dry methane fermentation residue dehydration system 11, 21, 31 Methane fermentation tank 12, 22, 32 Dehydration means 23, 33 Contaminant separation means 24, 34 Dehydrated sludge return means 35 Coagulant addition means

Claims (10)

A dry methane fermentation residue dehydration system,
A methane fermentation tank for dry methane fermentation of organic waste;
A foreign matter separating means for separating the foreign matter contained in the fermentation residue of the organic waste;
Dehydrating means for dehydrating the fermentation residue from which the impurities have been separated; and dewatering sludge returning means for returning the dehydrated sludge after dehydration to the methane fermentation tank;
With
The fermentation residue of the organic waste generated in the methane fermenter is supplied to the contaminant separation means, the fermentation residue from which the contaminant is separated is supplied to the dehydration means, and the recovery residue recovered by the dehydration means A system wherein at least a portion of the dewatered sludge is configured to be returned to the methane fermentation tank by the dewatered sludge return means.   The system according to claim 1, wherein a flocculant addition unit is provided between the contaminant separation unit and the dehydration unit.   The system according to claim 1 or 2, wherein a fermentation residue of the organic waste is drawn from an upper part or a lower part of the methane fermenter and supplied to the contaminant separation means.   The system according to any one of claims 1 to 3, wherein the contaminant separation means is a screw press.   The system according to any one of claims 1 to 4, wherein the dehydrating means is a screw press, a centrifugal dehydrator, a rotary press, or a belt press. A method for dehydrating dry methane fermentation residues,
Supplying organic waste to the methane fermenter;
A step of subjecting the organic waste to dry methane fermentation to obtain a fermentation residue;
Separating impurities contained in the fermentation residue;
Dehydrating the fermentation residue from which the impurities have been separated to obtain dehydrated sludge; and returning at least a portion of the dehydrated sludge to the methane fermentation tank;
Including the method.   The method according to claim 6, further comprising a step of adding a flocculant to the fermentation residue from which the impurities are separated after the step of separating the impurities.   The method according to claim 6 or 7, wherein the fermentation residue of the organic waste is extracted from an upper part or a lower part of the methane fermenter and subjected to a step of separating the impurities.   The method according to any one of claims 6 to 8, wherein in the step of separating the contaminants, the contaminants are separated by a screw press.   The fermentation residue from which the impurities are separated in the step of obtaining the dewatered sludge is dehydrated by a screw press, a centrifugal dehydrator, a rotary press, or a belt press. Method.

Images