JP2006281087A - Processing method of organic waste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method which is capable of independently controlling the retention time of a soluble component such as ammonia, microorganisms such as methane producing bacteria and a recalcitrant solid material and of efficiently processing the draining liquid containing a recalcitrant substance. <P>SOLUTION: The processing method of the organic waste comprises a step of conducting the anaerobic digestion of the organic waste and a step of solid-liquid separating the effluent from the anaerobic digestion step and a step of concentrating the separation liquid solid-liquid separated and feeding back the same to the anaerobic digestion step. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a treatment method using an anaerobic digestion method of a substance to be treated containing a hardly decomposable substance.

  Conventionally, organic waste has been disposed of by incineration after adjusting the moisture content, but from the viewpoint of global environmental conservation, there are a wide range of biological reaction treatment methods for recovering valuable materials such as methane. It is starting to be used. Biological reaction processing methods can be processed under mild conditions, but the processing takes time and the equipment becomes large-scale, and when the object to be processed contains biologically difficult-to-decompose substances, the processing is difficult. There is.

  Garbage is an organic waste that contains a lot of solids. However, in anaerobic treatment of such waste, solids are crushed, and unsuitable materials such as stones, plastic bags, and metal fragments are screened and removed. Anaerobic treatment is performed after removing these by means (see Patent Document 1). Also, shells and eggshells that cannot be removed by pretreatment means are removed by gravity sedimentation from the bottom during the anaerobic treatment, or a screen or dehydrator is mixed between the acid fermentation tank and the anaerobic digester. The removal is performed using the object separation means (see Patent Document 2).

  Organic waste generated from coffee brewers and beer production processes contain persistent substances, which are not difficult to completely decompose like stones, plastic bags, shells and egg shells. , A decomposable substance and a hardly decomposable substance are combined in a physically inseparable state. Therefore, when anaerobic treatment is performed after solid-liquid separation of these wastes in advance as described above, there is a risk that the generation of valuable materials such as methane may be reduced due to a decrease in usable organic matter. There is.

  On the other hand, when a hardly decomposable substance is introduced into the methane fermenter, it cannot be completely decomposed, so undecomposed solids accumulate, resulting in dead volume and increasing the volumetric efficiency of the methane fermenter. Reduce. In order to avoid this, a method of drawing out at an optimum rate in order to prevent accumulation of solid content is known (see Patent Document 1). In this method, methanogenic bacteria are also extracted, resulting in another problem that the decomposition efficiency of the anaerobic digester is lowered. In addition, there may be a case where a solid-liquid separator is introduced between the solubilization tank and the anaerobic digestion tank, but the pH of the solubilization tank is about 4.0 to 5.0. It is known that the decomposition rate of organic matter corresponding to the sludge residence time cannot be obtained because the decomposition rate of the organic matter by the enzyme to be produced is extremely slow. For these reasons, it is considered difficult to apply the anaerobic digestion method to the waste generated from the coffee lees and the beer production process. When applied, the apparatus must be enlarged.

Another problem is that methanogens can be inhibited by high concentrations of ammonia. As disclosed in Patent Document 3, it is preferable to remove the soluble matter and solids contained in the separation liquid by separating the solid components from the object to be treated and the ammonia newly generated in the anaerobic treatment process as disclosed in Patent Document 3. . However, when anaerobic digestion process effluent containing persistent solids is treated by membrane separation, the solid content will wear out the separation membrane due to friction, and as a result, the method cannot be used. There is a problem that it cannot be maintained.
JP-A-11-197639 JP-A-11-77005 Japanese Patent No. 3442288

  The present invention recognizes that the root cause of the above problem is that the residence time of each of soluble components such as ammonia, microorganisms such as methanogens and persistent solids cannot be adjusted independently. From the above, it is possible to independently adjust the residence time of soluble components, microorganisms such as methanogens, and hardly decomposable solids, and to provide a method capable of efficiently treating waste water containing hardly decomposable substances.

In order to achieve the above-mentioned object, the invention of claim 1 is the step of anaerobically digesting organic waste, the step of solid-liquid separation of the effluent from the anaerobic digestion step, and the solid-liquid separation. And a step of concentrating the separated liquid and returning it to the anaerobic digestion step.
The invention of claim 2 is a treatment method by anaerobic digestion of organic waste, wherein the effluent from the anaerobic digestion step is separated into solids by the first separation method, and then by the second separation method. The microorganisms are separated and the return amount to be returned to the anaerobic digestion step is adjusted.
A third aspect of the present invention is the processing method according to the second aspect, wherein the first separation method is performed by a screen or a mesh.
According to a fourth aspect of the present invention, in the processing method according to the second aspect, the second separation method is separated by a separation membrane.

  According to the present invention, the concentration of the methanogen in the anaerobic digestion tank can be maintained at a predetermined level, and the hard-to-decompose solid content can be discharged out of the system, and ammonia as a soluble component is below a predetermined level. Can be adjusted. As a result, it is possible to efficiently separate the easily decomposable substance and the hardly decomposable substance that are combined in a state where they cannot be physically separated.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a process diagram of an anaerobic treatment method according to one embodiment of the present invention. In FIG. 1, coffee grounds (1) which are organic wastes etc. are thrown into the solubilization tank 1 together with the diluent (2). The diluting liquid added at this time may be fresh water, separated water obtained when the solid matter obtained from the solid-liquid separator effluent water or the solid-liquid separator is dehydrated, separated water from the membrane separation treatment, and Furthermore, the water processed by the normal method may be sufficient.

  In the solubilization tank 1, facultative methanogens act on degradable lipids, proteins, and carbohydrates to be decomposed into low molecules having approximately 6 or less carbon atoms. When impurities such as a plastic bag, a metal piece, a shell or an egg shell are included, the solubilization tank 1 is preferably pulled out from the bottom. The effluent water from the solubilization tank 1 containing the decomposed low molecule and the hardly decomposable solid content is introduced into the anaerobic digestion tank 2, and the molecular weight of the hard decomposed solid content is further reduced. The organic material is decomposed into methane and carbon dioxide. Further, the generated gas component is led out of the system and used for applications such as fuel.

  The surplus sludge 12 drawn out from the anaerobic digester is disposed or reused by a known method, and the drawn out effluent is separated by a solid-liquid separation device 3 having a screen or a mesh. It is discarded or reused by dehydration. Here, the mesh width of the screen used and the pore size of the mesh are appropriately determined in consideration of the particle system of the solid matter contained, but in the case of the coffee grinder of the example, about 0.1 to 2 mm is preferable. Is preferably a screen of about 0.4 to 0.5 mm, but as is well known, since it can be crushed to any fineness even with a single coffee grinder, it is equal to or more than 3 times the diameter of the solid matter and is 0.1 mm or more A method of selecting the optimum diameter is preferable.

  The hardly decomposable solid 13 dehydrated by the solid-liquid separation device is discharged out of the system, and the separation liquid discharged from the solid-liquid separation device contains soluble components and microorganisms, which are separated by the membrane separation means 4. To separate. The separation liquid contains a soluble component such as ammonia. A portion 15 of the concentrate that has not passed through the membrane is returned to the anaerobic digester 2. It is known in the literature that ammonia, which is an inhibitory substance, is effectively removed by this treatment. Moreover, the microorganisms, mainly methanogens, are maintained at a preferred concentration by the return process of the concentrate. The remaining concentrate 14 is discarded or reused as it is or through a further concentration / dehydration process.

  This concentration / dehydration step may be performed together with the solid-liquid separation step. As the membrane separation means, an organic flat membrane having submicron level pores is used in the embodiments, but the present invention is not limited to this, and a ceramic membrane may be used in addition to a hollow fiber membrane or a spiral membrane. In order to prevent clogging, the film may be washed by aeration or a dynamic film may be formed, and is appropriately selected according to the object to be processed.

  An example of the above embodiment is shown below. 20 tons of coffee bowl, 1 ton of tea bowl and 0.8 ton of sludge are put into the solubilization tank 1 together with 19 tons of diluted water and solubilized in a residence time of 3 days. The effluent from the solubilization step is introduced into the anaerobic digestion tank 2, and anaerobic digestion is performed under conditions of 55 ° C and sludge residence time of 15 days. As a result, 3.4 tons of biogas containing methane and carbon dioxide is obtained and discharged out of the system. A calorific value of 61,700 MJ / day can be obtained by burning methane contained in this gas in the boiler. Although this heat is used to heat the anaerobic digester, there is still 640 kg / hour of surplus steam, which can be used for various purposes outside the system. Obtaining such energy is a great merit of applying the anaerobic digestion method to the treatment of hardly decomposable substances that have been difficult to apply until now.

  The effluent of the anaerobic digestion tank 2 is dehydrated using a screw press dehydrator as an example of the solid-liquid separator 3, and 9 tons / day of hardly decomposable solids 13 are discharged out of the system. Is disposed of or reused. In this embodiment, a screw press dewatering device is used, but any device can be used as long as it contains microorganisms in the separation liquid and can separate solids. In particular, the solid-liquid separation device 3 having a screen is preferable. The separation liquid of the solid-liquid separation device 3 is introduced into the membrane separation tank 4. In the membrane separation tank 4, an organic flat membrane having pores with an average pore diameter of 0.4 μm (micrometer) is immersed together with an air diffuser for surface cleaning.

  A membrane permeation solution in which soluble components such as ammonia are dissolved is separated from the membrane separation device by 12.8 tons / day. In this embodiment, an organic flat membrane is used. However, any material such as a hollow fiber membrane or a spiral membrane, a ceramic membrane or a metal membrane may be used. Furthermore, although it is preferable to have an air diffuser that diffuses biogas, it is not essential for this treatment method. In addition, depending on the object to be processed, good results may be obtained by forming a dynamic film. From the membrane separation tank, the concentrated sludge containing methanogens is returned to the anaerobic digestion tank. In this embodiment, the flow is returned to the anaerobic digestion tank 2, but the solubilization tank 1 may be used. 15.5 tons of excess sludge 12 is extracted from the anaerobic digestion tank 2 per day and disposed or reused by a known method.

  A second embodiment showing that the volume of the anaerobic digester 2 can be reduced by the treatment method is as follows. When the coffee lees are treated using the corresponding treatment method comprising the solubilization tank 1, the anaerobic digestion tank 2, and the membrane separation tank 4, the sludge residence time (SRT) in the anaerobic digestion tank 2 is set to 15 days, and the organic matter The capacity of the anaerobic digestion tank 2 necessary for decomposing 51% is required for 30 days of the input raw material. On the other hand, when processing is performed using the solubilization tank 1, the anaerobic digestion tank 2, the solid-liquid separation apparatus 3 and the membrane separation tank 4, the organic matter is 47% which is almost equivalent to the control process even if the SRT is set to 10 days. At this time, the volume of the anaerobic digester 2 becomes 15 days of the input raw material. From these comparisons, the volume of the anaerobic digester 2 can be reduced to half.

It is process drawing of the anaerobic processing method which is one of the embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Solubilization tank, 2 ... Anaerobic digestion tank, 3 ... Solid-liquid separator, 4 ... Membrane separation tank, 12 ... Excess sludge, 13 ... Refractory solid substance , 14 ... the remaining concentrate, 15 ... a part of the concentrate.

Claims (4)

Anaerobic digestion of organic waste,
A step of solid-liquid separation of the effluent from the anaerobic digestion step, and a step of concentrating the solid-liquid separated separation solution and returning it to the anaerobic digestion step. Processing method. In the treatment method of organic waste by anaerobic digestion method,
Separating the solids from the effluent from the anaerobic digestion step by the first separation method, then separating the microorganisms by the second separation method, and adjusting the return amount to be returned to the anaerobic digestion step Characteristic processing method. The processing method according to claim 2,
The first separating method is a processing method characterized by separating with a screen or a mesh. The processing method according to claim 2,
The second separation method is characterized in that separation is performed with a separation membrane.

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