JP6238519B2 - Paddy field repair method - Google Patents

Description

  The present invention relates to a paddy field repair method for repairing a paddy field damaged by a tsunami.

  Development of paddy field restoration methods for effectively restoring paddy fields damaged by tsunamis has been desired. As shown in FIG. 3 (b), a normal paddy field is composed of a subsoil layer (clay layer) formed from clay and the like, and a soil formation layer formed on the subsoil layer and used as a paddy field. It is configured. As shown in FIG. 3 (a), when a paddy field is damaged by a tsunami, sand, fine rubble (cans, stones, concrete pieces, etc.), and salt from seawater accumulate as foreign matter on the soil layer. At the same time, sand, fine rubble and salt are mixed as foreign matter in the soil layer. Therefore, in order to restore the paddy field damaged by the tsunami as a paddy field that can be planted, not only excavating and removing foreign matter accumulated on the soil layer, but also excavating the soil layer mixed with foreign matter, It is necessary to remove the salt and remove foreign substances and return them to the paddy field again. In other words, it is necessary to reuse the soil in which foreign matter is mixed by the tsunami so that it can be reused as a paddy field.

  Conventionally, the dredged sediment from dredged bays or rivers has been reclaimed as liquid cyclones by dredging dredged material from gulf or river dredged by dredging robots and reclaimed sediments by rotary crusher. At the same time, the solid matter settled at the bottom of the hydrocyclone is washed with an aqua screen to separate the earth or sand from which the salt content has been removed, and treated water containing fine particles at the top of the hydrocyclone is added to the thickener tank (sedimentation). It is known to produce a dehydrated cake from the fine particles by solid-liquid separation by agglomeration and precipitation in a tank) (see Patent Document 1).

JP 2000-167432 A

  However, in the conventional recycling method as shown in Patent Document 1, PAC (polyaluminum chloride) or the like is generally used as the flocculant used for the coagulation precipitation. And in this PAC, soluble aluminum exists. Therefore, when a PAC flocculant is added to produce a dehydrated cake, and the dehydrated cake is used as a paddy field, the dissolved aluminum and the fertilizer component (P) combine to reduce the fertilization effect, etc. Affects soil components. For this reason, in the conventional reuse processing method in which the PAC flocculant is added, there is a problem that the treated dehydrated cake cannot be returned to the paddy field as a soil and reused. That is, it has been difficult to restore a paddy field damaged by a tsunami to a paddy field that can be planted using a conventional recycling method.

  Then, an object of this invention is to provide the paddy field restoration method for restoring the paddy field damaged by the tsunami to the paddy field which can be planted.

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

That is, the paddy field restoration method according to the first invention is a paddy field restoration method for repairing a paddy field damaged by a tsunami, and includes a drilling process for excavating a paddy field soil contaminated with a tsunami, and washing water. A cleaning step for cleaning the excavated soil, a fine debris removal step for removing fine debris as the foreign matter from the slurry of the soil after the cleaning step, and a foreign matter from the slurry after the fine debris removal step A fine particle contained in the slurry is added by adding a flocculant composed mainly of a mineral raw material not containing free aluminum ions to the slurry after removing the sand and a slurry after the sand removal step. A fine particle collection step for agglomerating and collecting particles, and collecting the fine particles as fine particles having a particle size usable for paddy fields and returning the collected fine particles to paddy fields What to do That.

A paddy field restoration method according to a second aspect is the paddy field restoration method according to the first aspect, wherein the fine particle fraction collecting step adds chitosan to a flocculant mainly composed of a mineral raw material not containing free aluminum ions. The fine particles contained in the slurry are agglomerated and recovered using the aggregating agent formed.

A paddy field restoration method according to a third aspect is the paddy field restoration method according to the second aspect , wherein the flocculant is mainly composed of hydrous aluminum silicate fine particles made of weathered material of soil or rock (including volcanic discharge). The main component is a mixture of unit particles obtained by destroying an aggregate of mineral particles in a mineral raw material and chitosan particles, and the hydrous aluminum silicate structure in the unit particles remains without being destroyed. The unit particles and the chitosan particles are present in water, and the unit particles have self-aggregation property in the water to be treated excluding suspended substances, and the unit particles and the chitosan particles charge the material to be treated. Neutralize.

  According to the present invention, since the flocculant used in the fine particle collection step is a flocculant mainly composed of a mineral raw material, the collected fine particles do not affect the soil components. Therefore, fine particles (dehydrated cake) collected from the soil excavated from the paddy field damaged by the tsunami can be returned to the paddy field as soil and reused.

It is the schematic which shows the whole structure of the paddy field restoration method which concerns on the Example of this invention. (A) 1st structure of fine grain collection equipment, (b) 2nd structure of fine grain collection equipment, (c) 3rd composition of fine grain collection equipment, (d) Fine grain collection equipment It is the schematic which shows the 4th structure. It is the schematic which shows the paddy field damaged by (a) tsunami, (b) the paddy field after restoration (normal paddy field).

  First, the outline of the paddy field restoration method according to the present invention will be described.

  In the paddy field restoration method according to the present invention, first, foreign matter accumulated in the paddy field damaged by the tsunami is excavated and removed from the paddy field. Here, the foreign matter means sand, salt rubble (cans, stones, concrete pieces, etc.) and salt from seawater (the same applies hereinafter). Furthermore, the soil of the paddy field mixed with foreign matters due to the damage caused by the tsunami is excavated (excavation process). Then, the excavated soil is washed with washing water (washing process). Thereby, the salt which is the said foreign material is removed. Furthermore, the fine rubble as the foreign matter is removed from the soil slurry after the washing (a fine rubble removal step). And the sand which is the said foreign material is removed from the slurry which removed the fine rubble (sand removal process). Further, a flocculant is added to the slurry from which the sand has been removed, so that the fine particles contained in the slurry are agglomerated and recovered after dehydration (fine particle collection step). Here, the collected fine particles are collected as fine particles (dehydrated cake) having a particle size that can be used in paddy fields. The collected fine particles (dehydrated cake) are returned to the paddy field as soil.

  Next, each step of the paddy field restoration method according to the present invention will be described with reference to the drawings.

As shown in FIG. 3A, when a paddy field is damaged by a tsunami, foreign matter due to the tsunami accumulates on the soil layer and also enters the soil layer.
Therefore, as shown in FIG. 1, in the excavation process, first, a layer of foreign matter accumulated in a paddy field damaged by a tsunami is excavated and removed by a heavy machine. Further, the soil 5 mixed with the foreign matter is excavated from the paddy field with a heavy machine.

  In the next washing step, the soil 5 excavated in the excavation step and fresh water as washing water are put into a drum type drum washer (mud washing machine) 10. Then, in the drum washer 10, salt that is a foreign matter mixed in the soil 5 is removed by washing, and the lump portion of the soil 5 is pulverized. Note that the drum washer 10 is an example of a facility for cleaning and thawing the soil 5, and the present invention is not limited to the drum washer 10.

  In the next fine debris removal step, the slurry of the soil 5 after the washing step is put into a fine debris removal screen (vibrating sieve) 20. And the fine rubble which is the foreign material contained in the slurry is removed by the fine rubble removal screen 20. The fine debris removal screen 20 is provided with a screen that can be sieved to a predetermined particle size.

  In the next sand removal step, the slurry from which the fine rubble has been removed in the fine rubble removal step is charged into the sand collection facility 30. And the sand which is a foreign material contained in a slurry is removed by the sand collection equipment 30. FIG. The sand collection facility 30 is provided with a sand dehydrator (not shown) equipped with a vibrating screen, a cyclone and a mud tank. In this sand dehydrator, sand having a predetermined particle size is screened from the slurry by using a plurality of (for example, two types) sieves having different sieve meshes. In addition, for reasons such as sand removal performance in the sand dehydrator, when the sand contained in the slurry cannot be sufficiently removed only by the sand dehydrator, after processing with the sand dehydrator, the sand content is further poured into a static sedimentation tank. It does not matter as a structure to remove. Thus, by removing the sand by sieving to a predetermined particle size in the sand removal step, the slurry from which the sand has been removed is processed in the next fine particle collection step. The load of the fine particle collection process in the particle collection process can be reduced. Further, the removed sand can be used for agricultural land other than construction materials or paddy fields.

  In the next fine particle collection step, the slurry from which the sand has been removed in the sand removal step is charged into the fine particle collection facility 40. And the fine particle content in a slurry is collect | recovered by the fine particle collection equipment 40. FIG. The fine particles collected here are collected as fine particles having a particle size that can be used in paddy fields, and returned to the paddy fields as soil.

  Here, the structure of the fine particle collection equipment 40 will be described. As shown in FIG. 2, the fine particle collection facility 40 can have the following four configurations.

As shown in FIG. 2A, as a first configuration, the slurry from which the sand content has been removed in the sand content removal step is charged into a screw decanter 41. Then, the fine particles in the slurry are collected by the screw decanter 41. Further, the flocculant 50 is added to the slurry processed by the screw decanter 41 to aggregate the fine particles contained in the slurry. And the dehydrated cake is produced | generated by throwing the slurry which added the coagulant | flocculant 50 into the filter press 42. FIG. The filtered water after being processed by the filter press 42 is drained out of the fine particle collection facility 40.
In the first configuration, the fine particles recovered by the screw decanter 41 and the flocculant 50 are added, and the dehydrated cake generated by the filter press 42 is returned to the paddy field as soil. Further, in the first configuration, since the first fine particles are collected by the screw decanter 41 before the flocculant is added to the slurry, the amount of flocculant 50 added to the slurry can be reduced. it can.

  As shown in FIG. 2B, the second configuration is a configuration in which the flocculant 50 added after the processing of the screw decanter 41 in the first configuration is added before the processing of the screw decanter 41. . In the second configuration, as in the first configuration, the fine particles recovered by the screw decanter 41 and the dehydrated cake generated by the filter press 42 are returned to the paddy field as soil.

  As shown in FIG. 2C, the third configuration is a configuration in which the flocculant 50 is added before and after the processing of the screw decanter 41 in the first configuration. In the third configuration, as in the first and second configurations, the fine particles recovered by the screw decanter 41 and the dehydrated cake generated by the filter press 42 are returned to the paddy field as soil.

  As shown in FIG. 2 (d), as a fourth configuration, the flocculant 50 is added to the slurry from which the sand content has been removed in the sand content removal step, and then added to the filter press 42 to generate a dehydrated cake. . And the dehydrated cake produced | generated by the filter press 42 is returned to a paddy field as soil.

Next, the flocculant 50 used in the fine particle collection step will be described. The flocculant 50 is a flocculant (trademark registration No. 5007243: registered trademark “Dronpa”, manufactured by Astec Co., Ltd.) mainly composed of a mineral raw material containing no free aluminum ions, which is manufactured in Japanese Patent No. 5054334, or The flocculant is blended with chitosan.
In the following description, a flocculant composed mainly of a mineral raw material that does not contain free aluminum ions produced in Japanese Patent No. 5054334 (Trademark Registration No. 5007243: Registered Trademark “Dronpa” manufactured by Astec Corporation) A mixture of chitosan and flocculating agent 50 is used.

  The first step of the method for producing the flocculant 50 is a step of selecting after collecting a mineral raw material mainly composed of hydrous aluminum silicate fine particles made of a weathered material of soil or rock (including volcanic discharge). The main raw material of the flocculant 50 is a mineral raw material mainly composed of hydrous aluminum silicate particles made of a weathered material of earth or rock (including volcanic discharge), and includes allophane which is a clay mineral.

  The second step is a step of obtaining unit particles by breaking with a stirring method, a vibration method or a shaking method in a state where the mineral raw material is put in a dispersion treatment container and water is added. In this step, when destroying the aggregate of mineral particles in the mineral raw material, one method selected from a stirring method, a vibration method or a shaking method within a range not destroying the hydrous aluminum silicate structure in the unit particles, or A method combining these is selected and adopted.

  The weathered soil or rock (including volcanic discharge) collected in the first step may be a tightly bound mineral particle aggregate or a relatively weakly coupled mineral particle aggregate. Therefore, one method selected from the stirring method, the vibration method, or the shaking method or a combination of these methods may be selectively used depending on the degree of the binding force.

  Examples of the stirring method include stirring with a stirrer, stirring blade, submersible pump, submerged mixer, and the like. Examples of the vibration method include a high-frequency vibrator, vibration by sound waves, and the like. Examples of the shaking method include reciprocating shaking and swirling shaking.

  The main mineral fine particles contained in soil or rock weathering are hydrous aluminum silicates, which are easily structurally destroyed by mechanical grinding. As a result, problems such as easy elution of aluminum as ions occur. Therefore, it is not preferable to mechanically grind the soil or rock weathered material used as a raw material.

  By performing the second step in this way, unit particles can be obtained by destroying only the mineral particle aggregates without destroying the hydrous aluminum silicate structure. Further, even silt or sand-size minerals contained in the raw material are refined, and they are not added to the water to be treated as new suspended particles.

  The amount of water added in the second step is not particularly limited, but is determined in consideration of the specifications of the apparatus used for injection, the transportation cost of the produced flocculant, and the like.

The third step is a step of mixing the chitosan solution with a solution in which unit particles obtained by the dispersion treatment in water in the second step are dispersed or loosely associated in water. The flocculant 50 is obtained by mixing the solution containing the unit particles obtained in the second step and the chitosan solution.
The thus obtained flocculant 50 (trademark registration No. 5007243: registered trade name “Dronpa” manufactured by Astec Co., Ltd.) containing chitosan as a main component and free aluminum It is characterized by not containing ions. That is, the flocculant 50 is composed of components that do not cause any problems even if mixed in the paddy field.

  For this reason, the added flocculant 50 does not affect soil components such as reduction of fertilization effect due to dissolution of aluminum. Therefore, the dehydrated cake produced by adding the flocculant 50 in the fine particle collection step can be returned to the paddy field as a soil.

  Further, the unit particles (unit particles obtained in the second step) in the flocculant 50 (trademark registration No. 5007243: registered trademark “Dronpa” manufactured by Astec Co., Ltd. and chitosan blended) are suspended. It is characterized by having a self-aggregation property in water to be treated excluding substances. Here, “self-aggregation” means that when it is added to water obtained by removing suspended particles from the water to be treated (for example, water obtained by filtering the water to be treated with a membrane filter), it aggregates itself. To do. Furthermore, unit particles (unit particles obtained in the second step) and chitosan particles in the flocculant 50 (trademark registration No. 5007243: registered trademark “Dronpa” manufactured by Astec Co., Ltd.) Is characterized in that the substance to be treated is neutralized by electrostatic force, and the suspended particles can be efficiently aggregated. Furthermore, the flocculant 50 (trademark registration No. 5007243: registered trademark “Dronpa” manufactured by Astec Co., Ltd.) containing chitosan is mixed with chitosan, so that foreign matter contained in the soil 5 is contained. Even in a slurry containing a salt content, the suspended particles can be more effectively aggregated without reducing the aggregation effect.

  Next, the paddy field restoration method according to the present invention will be described in detail with reference to examples. However, the present invention is not limited to the examples.

Soil 5 before treatment (pre-treatment soil), sand content in the sand removal process (SD sand content), electrical conductivity (EC) (mS / cm) of dehydrated cake in the fine grain recovery process, chlorine concentration The measurement of the component amount (mg / kg) of (mg / kg (dry)) and soil components (N, P, K, Ca) was as follows.
(1) Electrical conductivity (EC)
The electric conductivity (EC) was measured using an electric conductivity meter based on the procedure described in JIS K 0102.3.
(2) Chlorine concentration The chlorine concentration was measured by an ion chromatograph method in accordance with JIS K 01022.35.3.
(3) Amounts of N, P, K, and Ca The amount of N (total nitrogen / solid content) was measured by a neutralization titration method according to the bottom sediment investigation method. The amount of P (total phosphorus / solid content) was measured by a colorimetric test using a UV meter according to the bottom sediment investigation method. Furthermore, the component amounts of K and Ca were measured by ICP emission spectroscopy.

  The soil 5 (soil before treatment) excavated in the paddy field restoration method according to the present invention is a soil obtained by excavating a paddy soil layer having a layer thickness of 10 to 15 cm shown in Table 1 with a heavy machine. The surface mud layer in Table 1 is a layer of starch that has been washed away by the tsunami (the layer containing mud etc.), and the sand layer in Table 1 is the layer of sand that has been washed away by the tsunami. Yes, the soil layer in Table 1 is the original paddy layer. In general, the electrical conductivity of soil (soil) that can be used as paddy fields is 0.4 mS / cm or less (preferably 0.3 mS / cm or less), and the chlorine concentration is 1000 mg / kg (dry) or less. It is said that. Therefore, as apparent from Table 1, it can be said that the soil 5 (soil before treatment) excavated in the present example is not suitable as a paddy field.

  In the washing step, the excavated soil 5 was supplied to the drum washer 10 at 6.5 t / h and washed with water. The washing solid-liquid ratio (soil: water) was set to 1: 1 to 1: 2.

  In the fine rubble removal step, the screen of the first stage screen in the fine rubble removal screen 20 was 20 mm, and the screen of the second stage screen was 5 mm. And the slurry with a particle size of 5 mm or less was sent to the sand removal process of the next process, and others were removed as fine rubble.

  In the sand removal step, a sand dehydrator was used as an apparatus for removing sand. And the sieve of the 1st stage sieve in Sand Dehaida was 2 mm, and the sieve of the 2nd stage sieve was 0.5 mm. Then, a slurry having a particle size of 0.5 mm or less is sent to the fine particle collection step of the next step, and a particle having a particle size larger than 0.5 mm is removed as sand (SD sand), except for construction materials or paddy fields. Used for agricultural land.

  In the fine particle recovery step, the flocculant 50 is added to the slurry from which the sand content has been removed in the sand content removal step, and then added to the filter press 42 to generate a dehydrated cake (the second cake shown in FIG. 2 (d)). 4 configuration). Further, the flocculant 50 added in the fine-grain fraction collecting step is a flocculant (trademark registration No. 5007243: registered trademark “Dronpa”, which is made of a mineral raw material containing no free aluminum ions, which is manufactured in Japanese Patent No. 5054334. “Astech Co., Ltd.) was mixed with chitosan, and 3 kg per 1 m3 of slurry was added. And the particle size of the fine particle part (dehydrated cake) collect | recovered in a fine particle collection process was 0.5 mm or less.

  Soil 5 before treatment (soil before treatment), sand content in the sand removal process (SD sand content), electrical conductivity (EC) (mS / cm) and chlorine concentration of dehydrated cake in the fine grain recovery process Table 2 shows (mg / kg (dry)).

  Soil 5 before treatment (pre-treatment soil), sand content in the sand removal process (SD sand content), dehydrated cake N, P, K, Ca component amount in the fine grain recovery process (mg / kg) ) Is shown in Table 3.

  As is clear from Table 2, the dehydrated cake in the fine particle collection step has an electrical conductivity (EC) of 0.39 mS / cm and a chlorine concentration of 690 mg / kg (dry). In other words, the dewatered cake in the fine particle collection step can be a soil that can be used in paddy fields. In addition, since the electrical conductivity (EC) is 0.20 mS / cm and the chlorine concentration is 190 mg / kg (dry), the sand content (SD sand content) in the sand content removal process can be used as a construction material. Of course, the use of agricultural land is also possible.

  Moreover, as is apparent from Table 3, the amount of soil components (N, P, K, Ca) in the dewatered cake in the fine particle collection step is almost the same as the soil 5 before treatment (soil before treatment). Absent. Therefore, even if the dehydrated cake produced by adding flocculant 50 (trademark registration No. 5007243: registered trademark “Dronpa” manufactured by Astec Co., Ltd. and chitosan blended) is returned to the paddy field as soil, There is no effect on growth.

5 Soil 10 Drum washer 20 Fine debris removal screen 30 Sand removal equipment 40 Fine grain collection equipment 50 Flocculant

Claims (3)

A paddy field restoration method for repairing a paddy field damaged by a tsunami,
An excavation process for excavating paddy field soil contaminated with tsunami,
A washing step of washing the excavated soil with washing water;
A fine rubble removal step for removing fine rubble as the foreign matter from the soil slurry after the washing step;
A sand removal step for removing sand as the foreign matter from the slurry after the fine debris removal step;
By adding a flocculant mainly composed of a mineral raw material not containing free aluminum ions to the slurry after the sand removal step, the fine particles contained in the slurry are aggregated and recovered. Process,
Have
A method for recovering a paddy field, comprising collecting the fine grain part as a fine grain part having a particle size usable for paddy fields, and returning the collected fine grain part to the paddy field. The fine particle collection step uses a flocculant obtained by adding chitosan to a flocculant mainly composed of a mineral raw material not containing free aluminum ions, and agglomerates the fine particles contained in the slurry. It collect | recovers. The paddy field restoration method of Claim 1 characterized by the above-mentioned. The flocculant is
Unit particles obtained by destroying aggregates of mineral particles in mineral raw materials mainly composed of hydrous aluminum silicate fine particles made of weathered soil or rocks (including volcanic emissions) were mixed with chitosan particles The main component,
The hydrous aluminum silicate structure in the unit particles remains without being destroyed,
The unit particles and the chitosan particles are present in water, and the unit particles have a self-aggregation property in water to be treated excluding suspended substances, and the unit particles and the chitosan particles neutralize the material to be treated. The paddy field restoration method according to claim 2 , wherein:

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