JP2012011265A - Methane fermentation residue dehydration system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a methane fermentation residue dehydration system which can stably perform dehydration of methane fermentation residue being not related to fluctuation of concentration of impurity contained in organic waste, and sludge concentration.SOLUTION: The methane fermentation residue dehydration system includes: a methane fermentation tank in which methane fermentation of an organic waste is carried out; an impurity separator which separates an impurity contained in a fermentation residue of the organic waste and a sludge containing liquid; a concentrator which concentrates the sludge in the sludge containing liquid separated by the impurity separator; and a concentrated sludge returning device which returns the concentrated sludge concentrated by the concentrator to the impurity separator, wherein the fermentation residue produced in the methane fermentation tank is supplied to the impurity separator, the sludge containing liquid separated by the impurity separator is supplied to the concentrator, and the concentrated sludge concentrated by the concentrator is returned to the impurity separator by the concentrated sludge returning device.

Description

  The present invention relates to a methane fermentation residue dehydration system and a dehydration method.

  When waste from households, business establishments, etc. is subjected to methane fermentation, organic waste (such as garbage) and non-biodegradable substances (plastic, cloth, metal, etc.) that are sorted before treatment ). The sorted organic waste is used as a raw material for methane fermentation, while impurities are often treated by incineration or the like. In addition, organic waste (such as garbage), which is a raw material for methane fermentation, may be separately collected and used at the discharge source.

  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 preferred when targeting waste discharged from households because of the advantages that it can be processed by simple sorting, a wide range of objects can be processed with low power, and high concentration raw materials. (Patent Documents 1 and 2). Sorting of organic waste and contaminants requires complicated work in order to remove all contaminants, whether by mechanical sorting or by sorting at the discharge source. Therefore, in the dry methane fermentation, the treatment is performed in a state including contaminants, and as a result, the dry methane fermentation residue contains organic matter-based sludge and plastics and other contaminants.

  Conventionally, the fermentation residue is dehydrated by a dry methane fermentation residue dehydration system 10 as shown in FIG. That is, the dry methane fermentation residue generated in the methane fermentation tank 11 is collected by the screw press 12 with impurities and a part of sludge, and the sludge-containing liquid is supplied to the centrifugal dehydrator 13 to be separated into dehydrated sludge and waste water. The

  In the dry methane fermentation, since the waste as a raw material is not finely pulverized before fermentation, impurities and large solid particles are separated from the fermentation residue with relative ease using the screw press 12.

  However, since the methane fermentation tank 11 used for dry methane fermentation is not a complete mixing type but a plug flow (extrusion flow) system, the ratio of impurities and sludge in the fermentation tank is not necessarily uniform and is discharged. The state of the fermentation residue is not stable. Therefore, the operating conditions of the screw press 12 must be changed according to the state of the fermentation residue that is discharged. Moreover, the sludge density | concentration of the isolate | separated sludge containing liquid fluctuates, and the state of a sludge containing liquid also becomes unstable.

  Furthermore, the centrifugal dehydrator 13 has problems such as severe abrasion due to sand and the like, and inability to remove fibers having a small specific gravity.

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

  An object of the present invention is to provide a methane fermentation residue dewatering system capable of stably dewatering a methane fermentation residue regardless of fluctuations in the concentration of contaminants and sludge concentration contained in organic waste.

  The present invention provides a methane fermentation residue dewatering system, which separates a methane fermentation tank for methane fermentation of organic waste; impurities contained in the fermentation residue of the organic waste and sludge-containing liquid Contaminant separating means; concentrating means for concentrating sludge contained in the sludge-containing liquid separated by the contaminant separating means; and concentrated sludge for returning the concentrated sludge concentrated by the concentrating means to the contaminant separating means The fermentation residue generated in the methane fermenter is supplied to the contaminant separation means, the sludge-containing liquid separated by the contaminant separation means is supplied to the concentration means, and the concentration means The concentrated sludge thus concentrated is returned to the contaminant separating means by the concentrated sludge returning means.

  In one embodiment, a flocculant addition means for adding a flocculant to the sludge-containing liquid is further provided.

  In one embodiment, the concentration means is a drum screen or a backing bar screen.

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

  Furthermore, the present invention provides a method for dehydrating a methane fermentation residue, the method comprising obtaining a fermentation residue by subjecting an organic waste to methane fermentation; a contaminant contained in the fermentation residue and a sludge-containing liquid. A step of separating; concentrating the sludge-containing liquid to recover the concentrated sludge; and a step of returning the recovered concentrated sludge to a step of separating the contaminants from the sludge-containing liquid.

  In one embodiment, the method further includes a step of adding a flocculant to the sludge-containing liquid after the step of separating the contaminants and the sludge-containing liquid.

  In one embodiment, the concentration of the sludge-containing liquid is performed using a drum screen or a back bar screen.

  In another embodiment, the separation of the contaminants and the sludge-containing liquid is performed using a screw press.

  According to the present invention, the methane fermentation residue can be stably dehydrated regardless of fluctuations in the concentration of contaminants and sludge concentration contained in organic waste. Furthermore, when the waste water generated by the system of the present invention is further processed, the load on the dehydrator of the waste water treatment facility can be reduced.

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

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

A. FIG. 2 shows an embodiment of the methane fermentation residue dehydration system of the present invention. This methane fermentation residue dehydration system 20 includes a methane fermentation tank 21 for methane fermentation of organic waste; a contaminant separation means 22 for separating contaminants contained in the fermentation residue of organic waste and sludge-containing liquid; A methane fermentation tank 21 comprising a concentration means 23 for concentrating the sludge contained in the sludge-containing liquid separated by the separation means; and a concentrated sludge return means 24 for returning the concentrated sludge concentrated by the concentration means to the contaminant separation means. The fermented residue produced in the above step is supplied to the contaminant separating means 22, the sludge-containing liquid separated by the contaminant separating means 22 is supplied to the concentrating means 23, and the concentrated sludge concentrated by the concentrating means 23 is returned to the concentrated sludge returning means. 24 is configured to be returned to the contaminant separating means 22.

(Methane fermentation tank)
The methane fermentation tank 21 ferments methane from organic waste obtained by simply selecting waste from households, business establishments, and the like. The methane fermentation tank 21 is not particularly limited, and a fermentation tank generally used in the technical field is used.

  As described above, methane fermentation includes dry methane fermentation and wet methane fermentation. In the present invention, the methane fermenter 21 may perform either dry methane fermentation or wet methane fermentation. However, as described above, a wide range of objects that can be processed by simple sorting and high-concentration raw materials are used. Dry methane fermentation is preferred because of the advantage that it can be processed with low power.

(Contaminant separation means)
It is difficult to completely separate organic waste and contaminants. Therefore, since fermentation is performed in a state including impurities, impurities in the dry methane fermentation residue are included. The contaminant separating means 22 is provided for the purpose of separating contaminants contained in the dry methane fermentation residue.

  Examples of the contaminant separating means 22 include a screw press and a coarse screen. Among these, a screw press having a hole diameter (about 2 mm to 5 mm) slightly larger than the hole diameter normally used is preferable. By using a screw press having a slightly larger hole diameter in this way, sludge with a small particle diameter can easily pass through without clogging, and contaminants such as plastic with a large particle diameter cannot pass through. Can be recovered. If the hole diameter is too small, the sludge will clog without passing through, and it may not be possible to stably separate impurities. On the other hand, if the hole diameter is too large, impurities may be clogged.

  The foreign matter separated by the foreign matter separating means 22 is collected in a garbage pit or the like and processed by incineration or the like. On the other hand, the sludge-containing liquid from which the impurities are separated is supplied to the concentration means 23.

(Concentration means)
The concentration means 23 reduces the amount of water in the sludge-containing liquid from which contaminants have been separated, and increases (concentrates) the sludge-containing concentration. Usually, the sludge-containing liquid from which impurities are separated contains about 95% by mass of water. The concentrating means 23 increases the sludge concentration by reducing the water content to about 92% by mass.

  Examples of the concentrating means 23 include a drum screen, a scratch bar screen, and a fine screen. The concentrating means 23 may have a hole diameter smaller than the hole diameter of the contaminant separating means 22 so as not to allow sludge to pass through. Among these, a drum screen and a back bar screen are preferable.

  By using the concentrating means 23, solids having a small specific gravity such as fibers that cannot be removed by the centrifugal dehydrator and remain in the sludge-containing liquid can be concentrated together with the sludge. Therefore, solids having a small specific gravity such as fibers do not remain in the wastewater, and can reduce the load on the dehydrator when treating the wastewater.

(Concentrated sludge return means)
The concentrated sludge return means 24 returns the concentrated sludge concentrated by the concentration means 23 to the contaminant separation means 22.

  The concentrated sludge concentrated by the concentrating means 23 adheres to solids such as fibers contained in the concentrated sludge, thereby forming a floc having a larger particle diameter than the sludge before concentration having a large amount of water. Therefore, flocs having a large particle size are separated and collected by the contaminant separating means 22 by returning the concentrated sludge to the contaminant separating means 22.

  Further, a flocculant adding means described later may be provided in order to stably form the sludge floc.

  Examples of the concentrated sludge return means 24 include a pump, a method of allowing the concentrated sludge to naturally flow down from the concentration means 23 to the contaminant separation means 22.

  Next, another embodiment of the methane fermentation residue dehydration system of the present invention is shown in FIG. The methane fermentation residue dehydration system 30 includes a methane fermentation tank 31 for methane fermentation of organic waste; a contaminant separation means 32 for separating impurities contained in the fermentation residue of organic waste and sludge-containing liquid; Concentration means 33 for concentrating sludge contained in the sludge-containing liquid separated by the separation means; flocculant addition means 35 for adding a flocculant to the sludge-containing liquid; and the concentrated sludge concentrated by the concentration means, Concentrated sludge returning means 34 for returning to the separating means is provided, the fermentation residue generated in the methane fermentation tank 31 is supplied to the contaminant separating means 32, and the sludge containing liquid separated by the contaminant separating means 32 is supplied to the concentrating means 33. The concentrated sludge concentrated by the concentration means 33 is returned to the contaminant separation means 32 by the concentrated sludge return means 34. That is, the methane fermentation residue dehydration system shown in FIG. 3 is provided with a flocculant addition means for adding a flocculant to the methane fermentation residue dehydration system shown in FIG.

  The methane fermentation tank 31, the contaminant separation means 32, the concentration means 33, and the concentrated sludge return means 34 are the methane fermentation tank 21, the contaminant separation means 22, and the concentration means 23 in the methane fermentation residue dewatering system 20 shown in FIG. , And the concentrated sludge return means 24.

(Coagulant addition means)
The flocculant addition means 35 adds a flocculant to the sludge containing liquid separated by the contaminant separation means 32 as necessary.

  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.

B. Method for Dehydration of Methane Fermentation Residue The method for dehydration of methane fermentation residue of the present invention (hereinafter sometimes simply referred to as “dehydration method”) is a step of methane fermentation of organic waste to obtain a fermentation residue (methane fermentation step) ); A step of separating impurities contained in the fermentation residue and sludge-containing liquid (contaminant separation step); a step of concentrating the sludge-containing liquid and recovering concentrated sludge (concentration step); and the collected concentration A step of returning the sludge to the step of separating the contaminants and the sludge-containing liquid (returning step). The dehydration method of the present invention can be performed, for example, in a methane fermentation residue dehydration system as shown in FIG. Hereinafter, each process is demonstrated with reference to FIG.

(Methane fermentation process)
The organic waste supplied to the methane fermentation tank 21 is anaerobically methane-fermented to produce methane fermentation residue and methane gas. In the methane fermentation tank 21, methane fermentation is performed by methane producing bacteria. In the present invention, either dry methane fermentation or wet methane fermentation may be used as described above, and preferably dry methane fermentation.

  The methane fermentation residue produced by methane fermentation is subjected to a contaminant separation step, and 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)
Since it is difficult to completely separate organic waste and impurities, impurities such as plastic remain in the dry methane fermentation residue. Such impurities can be separated using the contaminant separating means 22.

  As the contaminant separation means 22, the above-described screw press, coarse screen, or the like is used, and the contaminants contained in the methane fermentation residue and the sludge-containing liquid are separated. The foreign matter separated by the foreign matter separating means 22 is collected in a garbage pit or the like and processed by incineration or the like. On the other hand, the sludge-containing liquid from which impurities are separated is subjected to a concentration step.

(Concentration process)
Usually, the sludge-containing liquid from which impurities are separated contains about 95% by mass of water. Therefore, in the concentration step, the water content is reduced to about 92% by mass to increase the sludge concentration.

  In the concentration step, the sludge-containing liquid from which impurities are separated is concentrated using the concentration means 23. Examples of the concentration means 23 include the drum screen, the back bar screen, and the fine screen.

  The dehydration method of the present invention preferably includes a step of adding a flocculant before the concentration step. For example, as shown in FIG. 3, the flocculant is added to the sludge-containing liquid from which impurities are separated by the flocculant adding means 35. Since a large sludge floc is formed by adding the flocculant, the sludge floc can be efficiently removed when the concentrated sludge is returned to the contaminant separation step in the return step described later.

  The flocculant is not particularly limited as long as it makes sludge into a favorable floc form. For example, a polymer flocculant is used alone, or a polymer flocculant and an iron-based inorganic flocculant are used in combination. The flocculant is preferably added at a ratio of 0.1 to 1.5 parts by mass with respect to 100 parts by mass of the solid in the sludge-containing liquid from which impurities are separated.

  The concentrated sludge concentrated in the concentration step is supplied to the return step. On the other hand, the separated waste water can be treated and discharged into the natural world such as a river. Or it is reused in methane fermentation equipment.

(Return process)
The concentrated sludge concentrated in the concentration step is returned to the foreign matter separation step and separated together with the foreign matter.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not restrict | limited to a following example.

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. Subsequently, the fermentation residue was extracted from the methane fermentation tank 31 and subjected to the contaminant separation means 32 (screw press) to remove contaminants such as plastic and cloth in the fermentation residue. A polymer flocculant is added to the sludge-containing liquid from which foreign substances have been removed by the flocculant adding means 35 (a ratio of about 1.0% by mass with respect to the solid matter in the sludge-containing liquid) to form a large sludge floc. I let you. Next, a drum screen with a finer mesh size than the screw press was used as the concentration means 33 to reduce the amount of water in the sludge-containing liquid and increase the sludge-containing concentration. The liquid (concentrated sludge) having an increased sludge content concentration was returned to the contaminant separating means 32 (screw press) by the concentrated sludge returning means 34, and the concentrated sludge was dehydrated together with the fermentation residue.

  When the water content of the residue after dehydration (dehydration residue) was measured, it was about 60% by mass, and the power consumption required for dewatering the sludge was about 4.5 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. Next, the fermentation residue is extracted from the methane fermentation tank 11 and dehydrated with a 1.5 mmφ screw press, and then a polymer flocculant is added to the sludge-containing liquid (about 1.0 mass relative to the solid matter in the sludge-containing liquid). %), A large sludge floc was formed. Next, the sludge-containing liquid was dehydrated using the centrifugal dehydrator 13.

  When the water content of the residue after dehydration (dehydrated residue) was measured, it was about 70% by mass, and the power consumption required for dewatering the sludge was about 18 kW.

  Although the dry methane fermentation residue dewatering system of the present invention consumes about 25% of the power consumption of the conventional dry methane fermentation residue dewatering system, the water content in the dehydrated residue is about 10% by mass as compared with the conventional system. I found that there were few. Therefore, it can be seen that the dry methane fermentation residue dehydration system of the present invention can dehydrate the fermentation residue very efficiently.

  According to the present invention, the methane fermentation residue can be stably dehydrated regardless of fluctuations in the concentration of contaminants and sludge concentration contained in organic waste. Therefore, it is useful in the field of processing waste from ordinary households and business establishments.

DESCRIPTION OF SYMBOLS 10 Dry methane fermentation residue dehydration system 11, 21, 31 Methane fermentation tank 12 Screw press 13 Centrifugal dehydrator 20, 30 Methane fermentation residue dehydration system 22, 32 Contaminant separation means 23, 33 Concentration means 24, 34 Concentrated sludge return means 35 Flocculant addition means

Claims (8)

A methane fermentation residue dehydration system,
Methane fermentation tank for methane fermentation of organic waste;
A foreign matter separating means for separating the foreign matter contained in the fermentation residue of the organic waste from the sludge-containing liquid;
A concentration means for concentrating the sludge contained in the sludge-containing liquid separated by the contaminant separation means; and a concentrated sludge return means for returning the concentrated sludge concentrated by the concentration means to the contaminant separation means;
With
The fermentation residue generated in the methane fermenter is supplied to the contaminant separation means, the sludge-containing liquid separated by the contaminant separation means is supplied to the concentration means, and the concentration concentrated by the concentration means A system configured to return sludge to the contaminant separation means by the concentrated sludge return means.   Furthermore, the system of Claim 1 provided with the coagulant addition means for adding a coagulant to the said sludge containing liquid.   The system according to claim 1 or 2, wherein the concentration means is a drum screen or a back bar screen.   The system according to any one of claims 1 to 3, wherein the contaminant separation means is a screw press. A method for dehydrating methane fermentation residues,
Methane fermentation of organic waste to obtain a fermentation residue;
A step of separating impurities contained in the fermentation residue and sludge-containing liquid;
A step of concentrating the sludge-containing liquid to recover the concentrated sludge; and a step of returning the recovered concentrated sludge to a step of separating the contaminants from the sludge-containing liquid;
Including the method.   The method according to claim 5, further comprising a step of adding a flocculant to the sludge-containing liquid after the step of separating the contaminants and the sludge-containing liquid.   The method according to claim 5 or 6, wherein the concentration of the sludge-containing liquid is carried out using a drum screen or a back bar screen.   The method according to any one of claims 5 to 7, wherein the contaminants and the sludge-containing liquid are separated using a screw press.

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