JP2022113185A - Organic waste methane fermentation apparatus and method - Google Patents

Abstract

To provide means which efficiently removes a contaminant giving a damage to a membrane from an organic waste to be methane fermented, reduces an organic matter accompanied by the contaminant, and can reduce disposal cost of a residue to be discharged.SOLUTION: There are provided organic waste methane fermentation device and method, wherein an organic waste membrane separation methane fermentation device includes a first sorter for sorting an organic waste charged into a fermentation tank and a second sorter for sorting a fermentation liquid fed to a membrane separation tank from the fermentation tank, where a mesh width of the first sorter is 1.0 mm or more and 10 mm or less, a mesh width of the second sorter is 0.5 mm or more and 3.0 mm or less, the mesh width of the first sorter is larger than the mesh width of the second sorter, and at least a part of a residue sorted by the second sorter is returned to the fermentation tank.SELECTED DRAWING: Figure 1

Description

The present invention relates to an apparatus and method for treating organic waste by membrane separation methane fermentation.

Methane fermentation of organic waste such as raw garbage discarded from households and restaurants, raw garbage discharged from factories for preparing side dishes and cooking, processing plants for agricultural products and marine products, and sewage sludge among municipal solid waste. is being done. Fermentation sludge increases during methane fermentation, so it is pulled out of the fermentation tank, but this also pulls out methane bacteria. Therefore, a membrane separation fermentation method has been developed in which the fermented liquid is sent to a membrane separation tank for membrane separation, and the sludge is returned to the fermentation tank (for example, Patent Document 1).

An outline of this membrane separation fermentation method is shown in FIG. The organic waste to be put into the fermentation tank is pressurized and extruded into a sorting machine (1) having a mesh width of 0.3 to 0.7 mm to separate and remove the residue and put it into the fermentation tank, methane fermentation. A high fermentation temperature of 50 to 57°C is adopted in order to lower the viscosity of the liquid that permeates the membrane. Fermented sludge is taken out from the fermentation tank and circulated between the membrane separation tanks, and this circulation line is also provided with a separator (2). Excess sludge is drawn out from the bottom of the fermenter, dehydrated in a dehydrator, and taken out as a dehydrated cake.

JP-A-2000-24661

In the membrane separation methane fermentation method, it is necessary to avoid contamination of the membrane separation tank with contaminants for stable operation of the membrane separation. In Patent Document 1, garbage is pressurized and extruded through a sieve with slits of 0.3 to 0.7 mm to remove contaminants by compression and pulverization. It also has a screen that is a sorter.

However, when the present inventors examined this method, when the mesh width of the sorting machine, which is a slit sieve, is 0.3 to 0.7 mm, the amount of residue that does not pass through the sorting machine increases, The treatment cost is high, and the residue contains a considerable amount of biodegradable organic matter, so it was found that even the waste that could be effectively used in methane fermentation was disposed of, which was costly to dispose of.

An object of the present invention is to efficiently remove contaminants that interfere with the stable operation of membranes from organic waste subjected to methane fermentation, reduce the amount of organic matter accompanying the contaminants, and reduce the disposal cost of the discharged residue. The purpose is to provide a means for reduction.

In order to solve the above problems, the present invention provides a membrane separation methane fermentation apparatus for organic waste, a first sorter for sorting organic waste to be put into the fermenter, and a membrane separation after leaving the fermenter. A second separator is provided for separating the fermented liquid sent to the tank, the first separator has a mesh width of 1.0 mm or more and 10 mm or less, and the second separator has a mesh width of 0.5 mm or more3. 0 mm or less, the mesh width of the first fractionator is larger than the mesh width of the second fractionator, and at least part of the residue fractionated by the second fractionator is configured to be returned to the fermenter a methane fermentation device for organic waste,
In the membrane separation methane fermentation method for organic waste, the organic waste put into the fermenter is sorted by a first sorter having a mesh width of 1.0 mm or more and 10 mm or less, and the fermenter is discharged into the membrane separation tank. The fermented liquid sent to is separated by a second separator having a mesh width of 0.5 mm or more and 3.0 mm or less and smaller than the first separator, and at least part of the residue separated by the second separator is returned to the fermenter.

That is, as a result of intensive studies, the present inventors found that even if the mesh width of the first sorting machine before feeding into the fermenter is 1.0 mm or more, the amount of residue that can be sorted does not decrease much, but the amount of organic matter mixed in is greatly reduced. It was found that it can be reduced to Then, if the mesh width of the second separator for separating the fermented liquid sent from the fermenter to the membrane separator is 0.5 to 3.0 mm, the contaminants leaked by the first separator can be efficiently removed. It has been found that the membrane separation tank can be operated smoothly for a long period of time without the problem of clogging of the second separator.

According to the present invention, it is possible to efficiently remove contaminants contained in organic waste that damage membranes, to enable methane fermentation to operate stably for a long time, and to discharge most of the organic matter through methane fermentation. The amount of residue generated can be reduced, and the cost of disposal of discharged waste can be reduced.

1 is a block diagram illustrating one embodiment of the present invention; FIG. FIG. 4 is a block diagram illustrating another embodiment of the invention; FIG. 4 is a block diagram illustrating yet another embodiment of the present invention; 1 is a block diagram showing a conventional method of implementation; FIG.

The organic waste that is put into the methane fermentation apparatus of the present invention is methane fermented, and is collected from kitchen garbage discarded from homes and restaurants, factories for preparing side dishes and dishes, and processing plants for agricultural products and marine products. It includes raw garbage discharged and sludge discharged from sewage treatment plants.

Garbage discharged from these households and restaurants is generally put in plastic bags, and raw garbage discharged from manufacturing plants for delicatessens and dishes is often put in cardboard boxes. Combustible waste is crushed with a crusher or the like and the contents are taken out.

The organic waste received in this way is first sorted in order to remove fragments of plastic bags generated during shredding and stones mixed in the organic waste. In the present invention, the mesh width of the first separator to be fed into the fermenter is set to 1.0 mm or more. On the other hand, if the mesh width is larger than 10 mm, the pump for transferring the organic waste to the fermentation tank is likely to be clogged, so the mesh width is preferably 10 mm or less. Therefore, the mesh width of the first sorting machine in the present invention is 1.0 mm or more and 10 mm or less, preferably 2.0 mm or more and 8.0 mm or less, more preferably 3.0 mm or more and 7.0 mm or less. . Types of sorting machines include rotating blade type bag breaking and sorting machines and hammer blade type crushing and sorting machines. The first sorting machine sorts out items such as plastic bag pieces, cardboard pieces, stones, papers, and cloths that cannot be subjected to methane fermentation, and items that hinder the operation of the apparatus.

The organic waste from which unfermentable substances have been removed as residue by the first sorting machine is put into the fermentation tank. On the other hand, the residue is disposed of by incineration or the like.

The fermenter has a closed structure, with a gas discharge port at the top and a sludge extraction port at the bottom. An inlet is provided for the return sludge from the fermenter and is usually also fitted with an agitator to agitate the fermentation liquor. In addition, instruments necessary for fermentation management such as liquid level gauges and thermometers are also installed.

The sludge withdrawal port is connected to a dehydrator where the sludge is dewatered and discharged as a dehydrated cake. Some of the dehydrated cake is used as compost and fuel, but most is incinerated.

As the stirrer, a stirring blade type stirrer such as a paddle type stirrer is used. It is preferable that the stirrer be able to inverter-control the number of revolutions so that the fermented liquid can be gently stirred in order to reduce the load on the second separator. This facilitates sedimentation of the residue with gentle agitation, thereby reducing the amount of residue fed into the second fractionator.

In addition, if the outlet of the fermented liquid from the fermenter in the circulation line between the fermenter and the membrane separation tank is set at a low position, a large amount of sedimentary residue is sent to the second separator. In order to reduce the load, it is preferable to install at a position higher than 1/4, preferably about 1/2 to 3/4, of the liquid level in the fermenter. On the other hand, the position of the inlet of the return sludge from the membrane separation tank may be either high or low.

If the fermented liquid sent from the fermenter to the membrane separation tank is contaminated with large contaminants, they will be caught between the membranes and impair the cleaning performance of the membrane blower, or they will stick to the membrane surface and reduce the effective membrane area. The transmembrane pressure difference is increased by reducing it, and the cleaning frequency is increased. Therefore, a second separator is provided in the line for sending the fermented liquid from the fermenter to the membrane separation tank to remove contaminants that interfere with the stable operation of the membrane separation. If the mesh width of the second separator is too small, it is likely to clog, making it impossible to stably supply the fermented liquid to the membrane separation tank. Also, in order to prevent the sludge concentration in the membrane separation tank from becoming too high, the flow rate of the fermented liquid withdrawn from the fermenter increases, and the drawing pump becomes larger, which is not preferable from the viewpoint of equipment cost. On the other hand, if the mesh width is too large, relatively large contaminants will leak out and interfere with stable operation of membrane separation.

Therefore, it is appropriate that the mesh width of the second sorting machine is 0.5 mm or more and 3.0 mm or less. The mesh width of this second classifier is made smaller than that of the first classifier. The residue separated in the second fractionator also contains a considerable amount of organic matter and is returned to the fermenter. The recycle may be merged into the return side of the circulation line to the fermentor, or it may be recirculated directly to the fermentor.

The second classifier may comprise multiple stages, ie, multiple classifiers connected in series. That is, the residue caught on the side with a large mesh width is heavy and contains rice, which is easy to water. On the other hand, the residue caught on the narrow side of the interstitial width contains small vegetable scraps and is lightweight, so it can be returned without using a pump. By providing a plurality of second sorters, the amount of residue accumulated on the surface of the screen is reduced, and the maintenance of the sorter is facilitated. The mesh width is, for example, 2.0 mm or more and 3.0 mm or less for the front stage, and 0.5 mm or more and less than 2.0 mm for the rear stage.

Bar screens, drum screens, and the like can be used as sorting machines.

The fermented liquid from which contaminants have been removed by the second separator is placed in a membrane separation tank for membrane separation. A plurality of membrane modules are provided in the membrane separation tank, and an air diffuser for cleaning the membranes is installed below them. It is preferable that the membrane has an average pore diameter of about 0.05 to 0.4 μm which does not allow methane bacteria to pass through. Since the methane fermentation is anaerobic, air is not preferable for the air diffuser, and biogas or the like, which is mainly composed of methane and carbon dioxide discharged from the fermentation tank, is used.

In the methane fermentation method using such an apparatus, the organic waste from which unfermentable substances have been removed as residue by the first sorter is placed in a fermenter, and methane bacteria are inoculated to perform methane fermentation. At that time, water is added to the organic waste to adjust the concentration, so that a mixing tank may be provided between the first sorting machine and the fermenter. The concentration is often 4 to 10% by weight of TS. Methane fermentation may be carried out according to a conventional method, and high-temperature fermentation may be carried out using thermophilic bacteria, but it may be carried out at a usual temperature of about 35 to 40°C. During fermentation, it is necessary to maintain the concentration of methane bacteria so that fermentation proceeds smoothly, and the concentration of fermentation sludge should be maintained at about 2 to 5% by volume. Therefore, the fermented liquid is circulated between the fermenter and the membrane separation tank, the water separated by the membrane is drawn out, the sludge is returned to the fermenter, and the excess sludge precipitated in the fermenter is taken out from the sludge withdrawal port. .

The fermented liquid in the fermenter is stirred with a stirrer, but if the stirring is too strong, the sludge that settles in the layer will rise and the load on the second separator will increase. Inverter control the frequency. Since the residue separated by the second separator contains a large amount of organic matter, in principle it is returned to the fermenter.

Fermentation may be performed continuously or batchwise.

FIG. 1 shows the configuration of one embodiment of the present invention. The organic waste is put into a first sorting machine with a mesh width of 1.0 to 10 mm from the left side of the drawing, and unfermentable substances are removed as residues and put into the fermenter. In the fermenter, the fermented liquid is agitated by an inverter-controlled stirrer and circulated between the fermenter and the membrane separator by a pump (not shown). A sludge concentration meter is attached to each of the fermentation tank and the line that sends it to the membrane separation tank, and the sludge concentration of each is measured. The stirring speed of the stirrer is controlled. Contaminants contained in the fermented liquid are then removed by a second separator having a mesh width of 0.5 to 3.0 mm. The removed contaminant residue is combined with the return line to the fermentor. Contaminants are removed from the fermented liquid that has entered the membrane separation tank, water that has permeated the membrane is drawn out, and the fermented sludge is concentrated and returned to the fermenter. In the membrane separation tank, part of the methane gas discharged from the fermentation tank is blown out from below the membrane module by a blower to wash the membrane surface. The sludge that settles in the fermenter is pulled out from the bottom of the fermenter, dehydrated in a dehydrator, and taken out as a dehydrated cake.

The configuration of another embodiment of the invention is shown in FIG. In this embodiment, two machines are connected in series as the second classifier, the former classifier has a mesh width of 2.0 to 3.0 mm, and the latter classifier has a mesh width of 0. 0.5 to 2.0 mm, and the residue separated by the preceding separator is joined to the return line via a pump.

The configuration of yet another embodiment of the invention is shown in FIG. This embodiment is the same as the embodiment shown in FIG. 2 except that the residue separated by the preceding separator is discharged outside the system.

The apparatus shown in FIG. 1 was used. The organic waste was put into a plastic bag from home and discarded, and the collected food waste was put into a hopper, broken with a crusher, and put into the first sorting machine. Then, using a blade type bag-breaking sorter as the first sorting machine, the mesh width was changed from 0.5 mm to 10 mm, and garbage was put in and sorted. Table 1 shows the results obtained.

As a result of the above, if the mesh width is less than 1.0 mm, the ratio of the fractionated residue is large, and the percentage of organic matter is also large. It has been found that the width should be 1.0 mm or more and 10 mm or less.

Therefore, the mesh width of the first sorting machine was set to 10 mm, and the sorted organic waste was placed in a fermenter for methane fermentation. The fermenter is a closed cylinder with a capacity of 10 m ³ and has a funnel-shaped bottom. During the fermentation operation, the fermented liquid is circulated at 1 m ³ /h between the membrane separation tanks, and the organic waste is continuously added, and the sludge accumulated at the bottom is pulled out to reduce the TS concentration of the fermented liquid. It was kept between 2 and 5 wt% (3 wt% as an example). The amount of gas from the fermentation tank supplied to the air diffuser of the membrane separation tank was set at a constant rate of 4 NL/min/m ² ·membrane area.

Table 2 shows the results of examining the number of days from washing the membrane surface until the transmembrane pressure difference reaches 15 kP while changing the mesh width of the second separator from 0.1 mm to 4.0 mm.

As a result of the above, it was confirmed that the interstitial width is preferably 0.5 mm or more and 3 mm or less.

When the SS concentration of the sludge withdrawn from the fermenter exceeds the SS concentration inside the fermenter, the amount of residue generated in the second separator increases, placing a load on the second separator. Therefore, when the SS concentration of the sludge extracted from the fermenter exceeds the SS concentration inside the fermenter, the rotation speed of the stirrer is reduced from 30 rpm to 20 rpm by inverter control, thereby further sedimentation in the fermenter. The SS concentration of the sludge withdrawn from the fermenter was reduced by making it easier to generate.

In addition, the SS concentration of the sludge withdrawn and the SS concentration inside the fermenter were compared when the fermented liquid was withdrawn at a height of 1/4 of the liquid level in the fermenter and when it was at a height of 1/5 of the liquid level. Table 3 shows the measurement results. The number of revolutions of the stirrer was set to 30 rpm in both cases.

As a result of the above, it was confirmed that the fermented liquid withdrawal position is preferably at least 1/4 of the liquid level in the fermenter.

1 to 3, the mesh width of the first sorting machine is 10 mm, the mesh width of the second sorting machine is 0.5 mm in FIG. Table 4 shows the results of measuring the decomposition rate of organic matter in organic waste by performing methane fermentation with a 2.5 mm mesh width at the rear stage and 0.5 mm.

Organic substances were quantified by COD-Cr.

As a result of the above, it was found that the residue separated by the second separator contains a certain amount of organic matter, and by returning this to the fermenter, the decomposition rate of organic matter improves and the amount of methane gas generated increases. .

INDUSTRIAL APPLICABILITY According to the present invention, organic waste can be efficiently methane fermented to generate methane gas, and therefore it can be widely used for methane fermentation of organic waste.

Table 2 shows the results of examining the number of days from washing the membrane surface until the transmembrane pressure difference reaches 15 kPa by changing the mesh width of the second separator from 0.1 mm to 4.0 mm. .

Claims (6)

In a membrane separation methane fermentation apparatus for organic waste, a first sorter for sorting the organic waste to be fed into the fermentation tank and a second sorter for sorting the fermented liquid sent from the fermentation tank to the membrane separation tank. A sorter is provided, the mesh width of the first sorter is 1.0 mm or more and 10 mm or less, the mesh width of the second sorter is 0.5 mm or more and 3.0 mm or less, and the first sorter A methane fermentation apparatus for organic waste, wherein the mesh width is greater than the mesh width of the second classifier and configured to return at least a portion of the residue separated by the second classifier to the fermenter. . 2. The methane fermentation apparatus according to claim 1, wherein the second classifier comprises a plurality of classifiers connected in series. Among a plurality of sorters connected in series, the front-stage sorter has a mesh width of 2.0 mm or more and 3.0 mm or less, and the rear-stage sorter has a mesh width of 0.5 mm or more and less than 2.0 mm. Item 3. The methane fermentation apparatus according to item 2. 4. The methane fermentation apparatus according to any one of claims 1 to 3, wherein the position at which the fermented liquid to be sent from the fermenter to the second separator is at least 1/4 of the liquid level in the fermenter. 5. The methane fermentation apparatus according to any one of claims 1 to 4, wherein an inverter control mechanism for controlling agitation is attached to an agitator for agitating the fermented liquid in the fermenter. In the membrane separation methane fermentation method for organic waste, the organic waste put into the fermenter is sorted by a first sorter having a mesh width of 1.0 mm or more and 10 mm or less, and the fermenter is discharged into the membrane separation tank. The fermented liquid sent to is separated by a second separator having a mesh width of 0.5 mm or more and 3.0 mm or less and smaller than the first separator, and at least part of the residue separated by the second separator is returned to the fermenter.

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