JPS5912629B2 - How to purify municipal waste compost - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a purification method for producing compost from municipal waste.

When municipal waste is composted through aerobic fermentation, non-compostable materials such as soft plastics, metals, and cloth contained in the municipal waste can be separated to some extent by sorting, magnetic sorting, wind sorting, etc. Brittle non-compostable materials such as glass, ceramics, and hard plastics generally have small particle sizes, and especially when they are crushed as a pretreatment, they become finer in the process and are difficult to separate from compostable materials.

In the past, various attempts have been made to remove these brittle non-composted materials, such as a repulsion type separation method that takes advantage of the difference in elasticity between composted materials and foreign materials, and an air separation method that uses the difference in specific gravity. Even if relatively good results are obtained when the particle size of the foreign material is large, when the particle size is small, it is substantially separated, f)
3 It was impossible.

However, these foreign substances, such as brittle non-compostable materials such as glass, ceramics, and hard plastics, do not decompose naturally, so they only accumulate in the soil, and are dangerous to agricultural operations, so they must be virtually completely removed. In other words, the removal of these foreign substances is extremely important as an essential condition for putting urban compost into practical use.

In view of the above, the present invention provides, by performing electrostatic separation,
Glass, ceramics, and ceramics with relatively small particle sizes, which were previously difficult to manufacture.
The purpose is to make it possible to accurately separate brittle non-compostable materials such as hard plastics, to easily and reliably purify them, and to make composting in urban areas practical.

The present invention provides a method for refining municipal waste compost in which urban waste is fermented and composted, in which at least non-brittle compost such as soft plastics, metals, cloth, etc. The compound is removed to obtain a mixture of composted material and brittle non-composted material such as glass, ceramics, hard plastic, etc., and the moisture content of the mixture is 50.
In the range of 5% or more, the compost is sieved through a screen with a mesh size of 15 wl1 or less and 5 M or more, and then separated into compostable materials and brittle non-compostable materials by an electrostatic separation process, and only the composted materials are taken out as compost. This is a method for refining municipal waste compost.

The present invention was made by focusing on the following findings obtained based on research and experiments conducted by the inventors.

(1) The average moisture content of municipal waste compost is generally about 40% to 5.
The moisture content is around 0%, but composted material has a high moisture content.
-Brittle foreign materials such as glass, ceramics, and hard plastics do not absorb moisture, so there is a significant difference in electrical resistance between them.

According to the inventors' measurements, as shown in Figure 1, in the range where the co-average water content is less than 50% or more, the lower limit of the electrical resistance value of brittle foreign materials such as glass, ceramics, hard plastics, etc. was found to be higher than the upper limit of the electrical resistance value of the composted material.

As a result, the well-known electrostatic separation method, in which two types of substances with different electrical resistances are charged and separated by the action of a high-voltage electrostatic field, has been found to be able to separate composted materials and brittle foreign matter even for compost made of a variety of materials. It was predicted that this would be possible with high precision in the separation of

(2) Municipal waste is crushed and sieved in advance to remove non-compostable materials such as soft plastics, metals, cloth, and wood, and brittle foreign materials such as glass, ceramics, and hard plastics are composted from garbage and paper. After the mixed raw materials were composted by aerobic fermentation, they were further sieved through a 5 wl 1 mesh sieve, and the moisture content was variously adjusted, and a test was conducted using the electrostatic separator shown in FIG. 2.

In the figure, 8 is a raw material, 9 is a diaphragm, 10 is a high voltage electrode, 11 is a ground electrode, 12 is a partition, 13 is a composted material, and 14 is a non-composted material that is a brittle foreign material.

As a result, although it was impossible to separate the composted material from the brittle foreign matter group under conditions of complete dryness (moisture content 0), it was not possible to separate the composted material from the brittle foreign material group under conditions of complete dryness (moisture content 0). 100
It has been found that it is possible to separate the composted material with % purity.

FIG. 3 shows the relationship between the average moisture content and the yield of composted material (100% purity) when the applied ρ voltage is 3 and ■.

When the average moisture content exceeds 50%, the composted material tends to adhere to foreign matter and the apparent specific gravity of the composted material increases, so even if the partition position is adjusted appropriately, the yield of the composted material will decrease. decreases significantly.

The optimal average moisture content for electrostatic separation is generally in the range of 35% to 5%, but it is often industrially difficult to adjust the moisture content to less than 10%, so in practice it is recommended to use 35%. It is preferable to adjust the amount below to 10% or more.

In terms of handling, transportation, commercial value, etc. of compost, it is generally preferable that the moisture content is 40 or less, and this condition also coincides with the moisture content that is highly desired in illegal practices.

Note that the yield of composted material when the average moisture content is high (around 50 parts) tends to be improved more than the results shown in FIG. 3 by increasing the applied voltage and decreasing the particle size.

(3) To simplify the explanation, a uniform horizontal electrostatic field (voltage E
), ignoring air resistance and considering the behavior of the composted material (conductive material).If the specific gravity of the composted material is γ and the particle size is d, then the electric force J1 in the horizontal force direction is f1'oc d
2.Ee Since the vertical southward gravity f2 is f2d3.multidot.r, the angle .theta. that the resultant force F makes with respect to the vertical force direction as shown in FIG.

In order to improve the separation accuracy, it is preferable to increase θ to a greater extent than dγ, that is, to increase the voltage E and decrease the particle diameter d and specific gravity γ, but for practical purposes, the voltage is generally limited to 40 to 50 KV or less. The specific gravity γ is defined by the water content.

Therefore, it is preferable to reduce the particle size as much as possible, and in this respect, illegal activities aimed at separating brittle foreign substances that are easily divided into fine particles are much more difficult than with conventional repulsion methods or wind power methods. There are also reasons why it is advantageous.

- In order to increase the power and composting speed, it is generally preferable for the particle size of the compost to be small, and extremely small particle sizes are disadvantageous in terms of sieve clogging, power consumption, aeration, etc.

Considering both the electrostatic separation accuracy and composting conditions described above, it is desirable that the mesh size of the sieve is 15M or less and 5 or more meshes.

As described above, the method of the present invention not only enables highly accurate separation of brittle foreign substances in compost, which was previously difficult, but also provides optimal adjustment conditions for moisture content and particle size when applying illegal methods. It has basically been clarified that the conditions match well with the operating conditions for composting and the conditions for increasing commercial value.

To explain the present invention with reference to the drawings in accordance with an embodiment, municipal waste is first crushed and sieved into non-compostable materials A group such as soft plastics, metals, cloth, wood, etc., as well as stable waste,
A mixture of compostable materials B such as paper and foreign materials (brittle non-compostable materials) group C such as glass, ceramics, and hard plastics (B+
C) Separate into groups.

In this case, the mesh size of the sieve is preferably around 30M. If necessary, a considerable portion of the paper can be transferred to Group A.

Next, the (B+C) group is subjected to aerobic fermentation in a fermenter 2 to adjust the average moisture content to 50% or less (preferably 35% or less), and then subjected to a secondary crushing/sieving machine 3 having a mesh size of 15 pores or less and 5 haze or more. The remaining non-composted materials A' group are removed by this process, and the particle size of the (B+C) group is adjusted.

Although the crushing and sieving machines of the primary crushing and sieving machine 1 and the secondary crushing and sieving machine 3 can function by directly connecting the crushing machine and the sieving machine, known selective crushing and sorting as shown in FIG. It is better to use a machine.

This is a cylindrical screen 1 rotated by a drive device 17.
5 and a scraping plate 16 which is rotated by a drive device 18 at a speed different from that of the cylinder, and the raw material is sent in the axial direction to repeat crushing and sieving in an integrated manner. The (B+C) group and the A group are easily selected.

In addition, between the process of primary crushing/sieving machine and fermenter 2, (B+
C) Some metals mixed into the group (conductive non-composted material)
The small pieces may be removed using a magnetic separator, a repulsion type separator, etc. (falling is also not shown).

The moisture content and particle size of the (B+C) group that has passed through the secondary crushing/sieving machine 3 have been adjusted to a range that allows electrostatic separation, so the electrostatic separator 4 almost completely removes the brittle non-compostable C group. can be removed to separate compost B with extremely high purity.

As shown in FIG. 8, the electrostatic separator 4 may be a known composite cylindrical type having both a corona electric field and an electrostatic field.

That is, the (B+C) group that has fallen into the grounded rotating cylinder 20 via the conveyor 19 passes through a corona electric field and then further passes through an electrostatic field to become conductive composted material B and insulating brittle non-composted material C group. They are separated as shown in the figure.

21 is a brush, 22 is a corona discharge electrode, 23 is a compost hopper, and 24 is a foreign matter hopper.

As the electrostatic separator 4, in addition to the above-mentioned composite cylindrical type, known methods such as a pure electrostatic cylindrical type, a corona discharge type cylindrical type, a method of dropping in a horizontal electric field, a frictional charging type, etc. can be used. .

FIG. 6 shows another embodiment of the invention, in which it is intended to increase the yield of compost B.

As shown in FIG. 3, according to the experimental results, the yield of extracted material in electrostatic separation is highest when the average moisture content is about 10% to 15%.

On the other hand, although it depends on the moisture content of the raw materials left for fermentation, the average moisture content of the compost leaving the primary fermentation tank is generally around 40% to 50%, and even if it is left to cure indoors for about 10 days, it still retains moisture. The rate is 30
It only decreases to around 35%.

Therefore, if this is to be reduced industrially to 10% to 15%, heat drying is required.

In this embodiment, heat drying is carried out for this purpose to increase the yield, and at the same time, the heat is effectively used to dehydrate the mixed sludge.

That is, in this example, when attempting to compost organic sludge with a high moisture content such as livestock waste (electrified manure) or sewage sludge, aerobic fermentation is difficult at a moisture content of 70 parts or more. Focusing on the fact that some dehydration is required as a pretreatment and that these organic sludges do not contain problematic foreign substances and do not need to be separated, the composted material B purified after heating and drying and this The moisture content is adjusted by mixing with organic sludge [2] and re-fermented.

By adopting such a method, the energy used for heating and drying to increase the yield of composted municipal waste B can be effectively used for dewatering organic sludge with a high moisture content, which is rational. become a target.

To explain with reference to Fig. 6, as in the embodiment shown in Fig. 5, municipal solid waste passes through a primary crusher/sieve machine 1, a fermenter 2, a secondary crusher/sieve machine 3, and is sorted into groups (B+C), and then water content is adjusted. Tank 5
After lowering the moisture content, it is applied to the electrostatic separator 4.

The moisture adjustment tank 5 may be formed by a long-term indoor curing deposition method or a heat drying method, and is determined by taking into consideration equipment costs, operating costs, yield of compost B, etc.

The compost B purified by the electrostatic separator 4 is further mixed with the high water content organic sludge (contains no foreign matter) in a mixing tank 6 to adjust the water content to 70% or less, and then transferred to a re-fermenter. Ferment it again in I to obtain high quality compost.

The present invention makes it possible to remove brittle non-compostable materials such as glass, ceramics, and hard plastics from compost, which has been considered extremely difficult in the past, even when the particle size of the brittle non-compostable materials is small. It is possible to provide a method for refining municipal waste compost that makes it possible, accurately separates it, and purifies it easily and reliably, making it practical.
In terms of practical waste treatment, its effective use, and pollution prevention, it has extremely effective effects.

[Brief explanation of the drawing]

The drawings relate to embodiments of the present invention, and Fig. 1 is a graph showing experimental results, Fig. 2 is an explanatory diagram of the experimental apparatus, and Fig. 3 is a graph showing experimental results.
The figure is a graph showing the experimental results, Figure 4 is an explanation diagram of the operation, and Figure 5 is a graph showing the experimental results.
6 is a flow sheet of a different embodiment, FIG. 7 is an explanatory diagram of a crushing/sieving machine, and FIG. 8 is an explanatory diagram of an electrostatic separator. 1...Primary crushing/sieving machine, 2...Fermentation tank, 3...Secondary crushing/sieving machine, 4...
Electrostatic separator, 5...Moisture adjustment tank, 6...
・Mixing tank, 7... Re-fermenting tank, 8... Raw material, 9... Vibration plate, 10... High voltage pole, 11... ...Grounding electrode, 12...Partition,
13... Composted material, 14... Non-composted material, 15... Cylindrical screen, 16...
- Scraping board, 17.18... Drive device, 19...
... Conveyor, 20 ... Ground rotating cylinder, 21
...Brush, 22...Corona discharge electrode,
23... Composted material hopper, 24... Foreign material hopper. 145-

Claims (1)

[Claims] 1. In a method for refining urban waste compost by fermenting and composting urban waste, at least at the time of magnetic application before or after the composting fermentation process, at least non-brittle non-compostable materials such as soft plastics, metals and cloth are removed. A mixture of composted materials and brittle non-composted materials such as glass and ceramic hard plastics is obtained, and when the moisture content of the mixture is in the range of 50 parts or less and 5 parts or more, the mixture is sieved through a screen with a mesh size of 15 parts to 58 parts. A method for refining municipal waste compost, which comprises separating the compost into compostable materials and brittle non-compostable materials using an electrostatic separation process, and extracting only the compostable materials as compost.