JP3343662B2 - In-situ treatment method and apparatus for hydrous soil by electroosmosis - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for in-situ treatment of hydrated soil by electroosmosis.

[0002]

2. Description of the Related Art Various types of sludge such as inorganic and organic sludges are subjected to final treatment such as incineration and composting, or transported to a final treatment facility. It is desirable to reduce the volume and volume by dehydrating to a water content suitable for the purpose.For this purpose, natural treatment such as sun drying, mechanical pressing, filtration and chemical treatment with a coagulant have been conventionally used. Used. However, solar drying is not practical for treating large quantities of sludge in terms of site area and processing time. On the other hand, mechanical and chemical treatments increase equipment costs and running costs of power and chemicals, and depending on the type of sludge, it may be difficult to sufficiently dehydrate.

[0003] For this reason, methods for applying the technique of electroosmosis to dewater these sludges have been attempted, and have recently attracted attention in terms of economy and efficiency. In the dehydration treatment using the electroosmosis method, an electrode (anode-cathode) provided opposite to the sludge to be treated, utilizing the fact that soil particles in the sludge are charged to a negative potential with respect to water (zeta potential). The moisture in the sludge is moved to the cathode side by applying a DC voltage during the period (1), and the sludge is dewatered.

Specifically, sludge dewatering by the electroosmosis method is described in, for example, Japanese Patent Application Laid-Open No. 56-60603.
And 500678, etc., transfer the sludge that has been mechanically pre-dewatered to some extent under pressure along a transfer path between a pair of conveyors to which a positive and negative voltage for rotating and rotating relatively is applied, During this time, many methods have been proposed for collecting and discharging the water content of the sludge transferred to the cathode side by electroosmosis.

[0005] According to the sludge dewatering method by electroosmosis, the dewatering efficiency is extremely high, so that the efficiency in the final incineration treatment is improved. There is no hassle of selecting a treatment agent to be suitable.

However, in the conventional sludge dewatering treatment, the sludge to be treated is introduced along a moving path such as a pressurized conveyor or the like, and in some cases, it is combined with a pretreatment for dewatering the sludge to some extent. The need for a mechanical operating unit increases the size of the device, increases equipment costs, and has many problems in terms of operation and maintenance.

In general, sludge to be subjected to dehydration treatment includes organic sludge discharged from sewage treatment plants and factories, as well as inorganic sludge such as dredged sludge from rivers and bays, and sludge derived from residual soil at construction sites. Due to the variety of sources, these sludges are usually transported once to a specific dewatering facility and then treated as a whole. However, in this case, the transportation cost of the sludge accounts for a considerable portion of the sludge treatment cost.

[0008] Therefore, it is desirable that such sludge dewatering treatment be performed on site at the site of generation, and especially in the case of improving soft soil or soil containing harmful substances, they are treated "on site". It is necessary to. However, it is not easy to transport or install such a large-scale facility for each processing site that is distributed and present at various locations.

Therefore, the in-situ treatment technology for soil which can be easily disposed as required for each generation source of the above-mentioned sludge, etc., has a simple structure which does not require labor for operation and maintenance, and is easy to handle. Development is desired.

In the case where the above-mentioned treatment equipment is directly installed at a site where sludge or residual soil is generated, a soil improvement site, or the like to perform dehydration treatment by electroosmosis, the soil near the electrodes is formed by the electrolytic action generated when electricity is supplied. PH value changes. In particular, the pH value on the anode side remarkably shifts to the acidic side with the dehydration treatment,
As a result, in some cases, the metal retained in the form of salts and the like in and around the treated soil itself is ionized and eluted, which may cause secondary contamination around the treated area. Therefore, when treating the hydrated soil by the electroosmosis method, it is necessary to avoid as much as possible the adverse effects of the pH change on the surrounding soil and the like.

It is an object of the present invention to efficiently treat hydrous soil to be treated on site without using large-scale equipment requiring complicated mechanical working parts as in the prior art. It is an object of the present invention to provide a method and apparatus for in-situ treatment of hydrated soil by electroosmosis.

Another object of the present invention is to provide a method for treating a hydrous soil by electroosmosis, in particular, the pH of a treated area inclined toward an acidic side.
Of the present invention is to provide a method and an apparatus for in-situ treatment of hydrated soil, which can restore water to a neutral or specific pH value.

[0013]

The object of the present invention is to provide a method for treating water-containing soil in which electricity is supplied between electrodes provided opposite to a treated area of soil to reduce the water content of the soil by electroosmosis. the result with respect to the central electrode and the central electrode and a plurality of peripheral electrodes are respectively disposed equidistant
Lateral with each peripheral electrode at each vertex centered on the center electrode
The electrode assembly with a regular polygonal cross section is applied to the treated area of the site soil.
A plurality of electrodes are arranged adjacent to each other so as to correspond to each other, and have a polarity such that a current flows from the peripheral electrode to the central electrode or from the central electrode to the peripheral electrode between the central electrode and the peripheral electrodes. A dewatering step of applying a DC voltage in parallel to each of the electrode combinations to transfer water in the soil of the treatment area to the center electrode side by electroosmosis and draining the water, and subsequent to the dehydration step A voltage having a polarity that reverses the direction of the current in the dehydration step is applied between the center electrode and each of the peripheral electrodes, and the pH value of the peripheral electrode side, which has been reduced by energization during the dehydration step, is reduced to a predetermined value. And a pH adjusting step of restoring the value to a value.

[0014] The method of the present invention prior consists of a central electrode of a hollow tubular having a suction drainage channel therein, and a plurality of peripheral electrodes arranged respectively equidistant from the center electrode
The peripheral electrodes are arranged at the vertices with the central electrode as the center point.
An electrode assembly with a regular polygonal cross section is used for treating soil on site.
Multiple electrodes installed adjacent to each other in order to correspond to the area
A combination, a drainage unit connected to the suction drainage channel of the center electrode, a portion connecting each center electrode and each peripheral electrode in parallel with each other, and a center electrode and each peripheral electrode of the electrode combination. A power source for applying a DC voltage from the peripheral electrode to the center electrode,
A water sensor comprising: a pH sensor for measuring an H value; and a power supply control device including at least means for inverting the polarity of the DC voltage of the power supply in accordance with the pH value of soil measured by the pH sensor. It can be implemented by an in-situ soil treatment device.

[0015]

According to the present invention, each of the peripheral electrodes comprises a central electrode and a plurality of peripheral electrodes arranged at equal distances from the central electrode.
Each electrode assembly with a regular polygonal cross section at each vertex
Heart electrode and each peripheral electrode connected in parallel with each other
In order to correspond to the treated area of hydrous soil at the site
A plurality of sets are installed, for example, by applying a DC voltage having a polarity such that a current flowing from each of the peripheral electrodes toward the center electrode is generated, and the water in the soil in the treatment target area is electroosmically transferred to the center electrode side. After the transfer, the water is drained by appropriate means through the suction drainage channel.

In the prior art electroosmosis dewatering equipment, it is necessary to minimize the dewatering time in order to continuously dewater the sludge while moving the sludge during the processing step. The equipment and the compression conveyor complicate the structure and operation and maintenance of the equipment.

However, in the present invention, since the hydrous soil is treated at once at its source, the treatment time is not so limited, and a completely static dehydration treatment only by the electroosmotic action by energization between the electrodes. Thus, the intended purpose is sufficiently achieved.

For example, the water content of various sludges is generally about 80 to 90%, and is usually about 40 to 90% in a normal dehydration treatment so as to be suitable for final treatment such as microbial treatment or incineration.
The water content is reduced to about 50%. According to experiments by the present inventors, when applying the present invention, if the dehydration treatment time is set to about half a day to about one day, such a desired dehydration rate can be obtained at a relatively low voltage of about 20 V. It turned out that it can obtain enough.

In this case, in order to collectively treat the soil in the area to be treated, it is necessary to uniformly supply power to the entire soil in the area to be treated. For this reason, in the present invention, a central electrode (cathode) and a plurality of peripheral electrodes (anodes) facing the central electrode at equal distances from each other are arranged at the respective vertices with the central electrode as a central point. A plurality of sets of electrode assemblies each having a regular polygonal cross section were used, and these were sequentially arranged adjacent to each other so as to correspond to the treatment area of hydrous soil, and a DC voltage was applied in parallel to each electrode assembly. In this way, a uniform dewatering action is caused by electro-osmosis in the entire soil in the treatment area, and water transferred to the respective center electrodes is discharged to perform dehydration. In this case, the cross section of the electrode
For example, to respond to the treated area of water soil without gaps
It is a regular polygon as shown in the embodiment. In this case, the assembly structure
The regular hexagon shown in FIG. 2 is preferable in terms of structural strength and the like.
The same effect can be obtained with an equilateral triangle or square.
It is.

Generally, the rate of dewatering of sludge in hydrous soil is proportional to the voltage applied between the electrodes and inversely proportional to the distance between the electrodes. When dewatering an average sludge to about 40 to 50%, for example, a radius of 1 m is used. Using a combination in which a central electrode is disposed at the center of a regular hexagon and a peripheral electrode is disposed at each vertex thereof, and when a low voltage of about 20 V is applied to the peripheral electrode, the sludge in the treated area can be energized for about 10 to 24 hours. It was confirmed by experiments that the above-mentioned desired dehydration rate was obtained.

In an actual apparatus, for example, a hollow tubular steel pipe or the like is used as a center electrode (cathode), and its lumen is connected to a drainage means such as a pump as a suction drainage channel, while the peripheral electrode (anode) is optional. The electrode assembly can be easily formed by using the above conductive material such as a reinforcing bar.
In this case, the water dehydrated from the soil is discharged through the fine soil particle gaps, so that the soil particles themselves act as a filter, and the wastewater is highly purified, so that no further filtration treatment is required for discharge. On the other hand, the soil after the treatment is dewatered and reduced in volume to about 40 to 50%, which makes it extremely easy to carry out composting and incineration treatment or to transport these to a treatment facility.

Here, in the dehydration treatment by electroosmosis, electrolysis using a water-containing soil component as an electrolyte occurs between the positive and negative electrodes, so that the pH of the region to be treated increases on the center electrode (cathode) side and becomes alkaline, and the peripheral electrode (anode). ) Side, the acid p
H.

In this case, particularly on the acidic side of the anode, conditions are apt to elute metals, so that harmful metals and the like are eluted as ions from compounds contained in the soil to be treated itself or the surrounding soil and the like. It can contaminate the surrounding soil and groundwater or adversely affect the adjacent rock mass and the structure itself.

For this reason, in the present invention, for example, a pH sensor for detecting a pH value is provided near the peripheral electrode (anode), and the polarity of the power supply voltage is inverted at the end of the dehydration step to make the center electrode (cathode) positive. A voltage is applied to cause an electrolytic action between the two electrodes in a state where the polarity is opposite to that in the dehydration step, thereby increasing (recovering) the pH value of the soil near the peripheral electrode to the neutral side. When the pH value reaches an initial value or a preset value, the power supply is stopped by the detection output from the pH sensor, and the entire processing steps are terminated.

In the case where the properties of the hydrous soil are constant and the pH value when the desired dehydration rate is reached can be predicted in advance,
A moisture meter may be used as a means for determining the switching point between the dehydration step and the pH adjustment step and the end point of the pH adjustment step, and in some cases, a pH meter and a moisture meter may be used in combination.

As described above, according to the present invention, an electrode assembly having the above-described simple structure, which is installed in an area to be treated with hydrous soil, a suction pump connected to a suction drainage channel of a center electrode,
Dehydration can be easily performed using a system with a simple structure consisting only of a pH sensor and a power supply with a control circuit.
For this reason, the processing can be performed by installing a processing device at each processing site as needed. Therefore, it is possible to omit the conventional transportation cost from the source to the dehydration treatment facility, the equipment cost required for the pretreatment and the squeezing treatment, and the labor for operating and maintaining them, and the treatment can be performed effectively. .

As described above, one important feature of the present invention is that water-containing soil can be directly dewatered at the treatment site. Therefore, during treatment by electroosmosis, pH change occurs in the treated soil itself and the surrounding soil. May occur. However, in the present invention, the pH following the dehydration step
Since the pH value is restored to the initial value or a predetermined value by the adjusting step, the elution of heavy metal ions and the like due to the change of the pH on the peripheral electrode (anode) side to acidic is prevented, thereby causing a problem of environmental pollution in the surrounding area. Can be avoided.

The present invention is not limited to dewatering sludge and soil,
The present invention can also be applied to soil treatment that should originally be performed in situ, such as improvement of soil containing harmful substances or soft soil having high moisture content. For example, chromium (6
Value) other harmful heavy metal particles,
These compounds are easily discharged to the cathode side during the dehydration by the electroosmosis treatment in the state of being dissolved in the soil water or by dissolving in the soil water from the soil near the positive electrode, which became acidic pH during the electrolytic action, in the soil water. Therefore, it is also effective in detoxifying contaminated soil. In order to render the contaminated soil harmless, it is preferable to purify the dehydrated water and use it repeatedly as a washing liquid. As described above, the soil treatment in the present invention includes dehydration of sludge, improvement of soft soil, regeneration of soil containing harmful substances, and the like.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments. FIG.
FIG. 1 is a view showing an outline of an experimental apparatus for putting the method and apparatus of the present invention into practical use, and FIG. 2 is an explanatory view showing an arrangement of an electrode assembly in a soil treatment area when implementing the present invention.

[0030]

EXPERIMENTAL EXAMPLE The apparatus shown in FIG. 1 was used to confirm the dehydration by the electroosmotic dehydration step in the method of the present invention and the change in pH around the electrode due to the execution of such a step and the recovery of pH by applying a reverse polarity voltage. The following preliminary experiment was conducted.

In a dehydration tank 1 containing 11 kg of inorganic sludge having an initial water content of 49.8% and a pH of 8.2, a stainless steel pipe 2A having an inner diameter of 20 mm and serving as a center electrode 2A having a suction drainage channel in the lumen and a periphery of 250 mm are provided. The electrode assembly 2 composed of a reinforcing rod having a diameter of 5 mm as the peripheral electrode 2B arranged on the same circumference at a distance of the sludge is deposited at a sludge deposition depth (155 mm).
And a 20 V DC voltage (initial current: 0.95 A) was applied from the power supply 3 using the center electrode 2A as a negative electrode and each peripheral electrode 2B as a positive electrode to perform electroosmosis. In the other figures, 2C is a suction / drainage hole formed in the tube wall of the center electrode 2A, 2D is a drainage channel formed using the lumen, 4 is a control unit for reversing the output polarity of the power supply 3, 5 is a suction pump,
Reference numeral 6 denotes a pH sensor.

Table 1 shows the amount of electroosmotic dehydration during 7 hours of energization and the accompanying change in pH value in each part of the sludge.

[0033]

[Table 1] Initial value After 2 hours After 4 hours After 7 hours pH + side 8.2 6.1 5.7 5.2 pH-side 8.2 10.5 11.0 11.4 pH center 8.2 8.2 8.2 8.4 Current (A) 0.95 0.9 0.7 0.5 Voltage (V) 20 20 20 20 Wastewater volume (ml) 0 300 200 250 Wastewater pH ー 11.6 11.7 11.8

In order to restore the pH changed by the electroosmosis treatment, particularly the acidic pH value on the anode side to almost the initial value,
The polarity of the applied voltage between the center electrode 2A and the peripheral electrode 2B was reversed, and electricity was supplied for 4 hours. Table 2 shows the results.

[0035]

[Table 2] Initial value After 2 hours After 3 hours After 4 hours pH + side 11.4 9.5 9.2 8.5 pH-side 5.2 6.5 6.9 7.5 pH Central part 8.4 8.2 8.2 8.2 Current (A) 0.6 0.6 0.6 0.6 Voltage (V) 20 20 20 20 Wastewater volume (ml) 0 100 100 120 Wastewater pH-3.5 5.3 6.5

After 4 hours of energization, as shown in Table 2, (-)
The pH value on the side (in this case, the peripheral electrode 2B) is 5.2 to 7.
5 and almost returned to the original pH value.

Hereinafter, the present invention will be described by way of an example in which dewatering is performed by directly applying the present invention to actual sources of various sludges and the like. The basic configuration of the device is the same as that shown in FIG. In each embodiment, the electrode combination 2 composed of the center electrode (cathode) 2A and the peripheral electrode (anode) 2B is formed in a regular hexagonal shape as shown in FIG. Were connected in parallel (connections between the respective poles were not shown), and these were sequentially installed adjacent to the sludge treatment area. 60,000k of sludge treatment amount in each case
g: The treated area was 30 m ² and the depth was 2 m.

Example 1 Activated inorganic construction sludge having a water content of about 82.2% (pH 8.
6), a plurality of electrode combination bodies 2 shown in FIG.
2,. . . Were sequentially arranged adjacent to each other. In the present embodiment, the distance between the center electrode 2A and the peripheral electrode 2B is 1 m, and the initial value of the total energizing current in the dehydration step from the power supply 3 for these electrode combinations is 10 A, except that it is the same as the experimental example. Equipment and conditions were used.

A DC voltage of 20 V is applied to the center electrode 2A of each electrode assembly 2 from the power source 3 to supply electricity for 10 hours to perform dehydration treatment, and then reverse the polarity for 4 hours.
H adjustment processing was performed. Table 3 shows the results. As shown in Table 3, the water content of the sludge was reduced from the initial value of 82.2% to 35.5%, and the transportation cost was remarkably reduced due to weight reduction and volume reduction. In addition, the positive pH at the time of the dehydration treatment decreased by 4.5,
The pH was restored to almost the original value by the pH adjustment treatment.

Example 2 Dehydration treatment was carried out on organic sewage sludge having a water content of 82.0% in the same manner as in Example 1 for 17 hours. Table 3 shows the results. The water content was reduced to 51.2%, making the water suitable for composting by microbial treatment.

Example 3 A dewatering treatment was performed on river dredged sludge having a water content of 80.8% in the same manner as in Example 1 for 12 hours. Table 3 shows the results. The water content after the treatment was reduced to 41.6%, and the supportability was increased by adding a chemical solidifying agent, so that it became usable for backfilling and the like.

Example 4 Dehydration treatment was carried out on a dredged sludge with a water content of 82.6% in the same manner as in Example 1 for 24 hours. Table 3 shows the results
Shown in The water content after the treatment decreased to 53.3%. In each of Examples 2 to 4, the same pH adjustment treatment as in Example 1 was performed, and as a result, the anode pH was restored to the range of ± 0.2% of the initial value in each case.

[0043]

[Table 3] Example Dehydration time Initial end pH value Moisture content Moisture content Early termination (Hr) (%) (%) (Anode) (Cathode) 1 Inorganic construction sludge 10 82.2 35.5 8.6 4.5 9.3 2 Organic sewage sludge 17 82.0 51.2 6.9 3.8 8.9 3 River dredging sludge 12 80.8 41.6 7.2 4.2 8.8 4 Lake dredging sludge 24 82. 6 53.3 7.4 5.5 9.4 Example 5 In the case of the hydrated soil treatment according to the present invention, when harmful metals and the like are contained in the soil or the water or sewage, these harmful metals are removed during the dehydration by electroosmosis. The present invention can also be applied to detoxification of soil which is removed together with wastewater in an ionic state. When the same method as in each of the above examples was applied to the hydrous soil containing hexavalent chromium, the water content was reduced by the dehydration energization for about 48 hours and the pH adjustment energization of the opposite polarity, and the content of hexavalent chromium was reduced. 0.01p from the initial 20.2ppm
pm or less was confirmed by a dissolution test.

It should be noted that the present invention is not limited to the above embodiment, and various modifications and improvements can be made. For example, in the present invention, it is effective to use the center electrode as the cathode and the peripheral electrode as the anode in the electrode combination, but if necessary, a combination in which the polarities of both electrodes are reversed may be used.

[0045]

As described above, according to the present invention, for example, the moisture content of various sludges can be efficiently reduced to a low moisture content suitable for transportation, incineration, composting and the like.
In particular, in the present invention, the combination with the conventionally proposed mechanical dewatering means is not adopted at all, so the equipment is extremely simplified, and if necessary, it is directly installed on the treatment site to perform the dehydration treatment on the spot Can be. Further, the pH change due to this dehydration treatment is restored to the initial value in the pH adjustment step, and there is no possibility that environmental pollution will occur in the surroundings.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of an experimental apparatus for carrying out the present invention.

FIG. 2 is a layout view of an electrode assembly used for carrying out the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Dehydration tank 2 ... Electrode combination body 2A ... Tubular center electrode (cathode) 2B ... Peripheral electrode (anode) 2C ... Suction drainage hole 2D ... Suction drainage channel 3 ... Power supply 4 ... Control part 5 ... Drain pump, 6 pH sensor

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-50-76657 (JP, A) JP-A-1-189931 (JP, A) JP-A-5-4100 (JP, A) JP-A-62 125811 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C02F 11/12 ZAB

Claims (4)

(57) [Claims] 1. A method for treating water-containing soil in which electricity is supplied between electrodes provided opposite to a treated area of soil to reduce the water content of the soil by electroosmosis. Consisting of a plurality of peripheral electrodes respectively arranged at distance positions, and centered on the central electrode.
The cross section of each peripheral electrode at each vertex at a point is a regular polygon
The electrode assembly to match the area to be treated in the field soil
A plurality of the DC electrodes are sequentially arranged adjacent to each other, and a DC voltage having a polarity such that a current flows from the peripheral electrode to the central electrode or from the central electrode to the peripheral electrode between the central electrode and the peripheral electrodes. A dehydration step of applying water in parallel to each electrode combination to transfer water in soil in the treatment area to the center electrode side by electroosmosis and draining the water, A voltage having a polarity that reverses the direction of the current in the dehydration step is applied between each of the peripheral electrodes, and the pH value of the peripheral electrode side, which has been reduced by energization during the dehydration step, is restored to a predetermined value. a method for in-situ treatment of hydrous soil, comprising a pH adjusting step. 2. A cross section of the electrode assembly having a regular hexagonal shape.
The in-situ treatment method according to claim 1. 3. A central electrode having a hollow tubular shape having a suction drainage passage therein and a plurality of peripheral electrodes arranged at equal distances from the central electrode.
A cross section in which the peripheral electrodes are arranged at each vertex and whose cross section is a regular polygon.
Make sure that the pole assemblies correspond to the treated area of the field soil.
A plurality of electrode combination bodies installed next to each other, drainage means connected to the suction drainage channel of the center electrode, a portion connecting each center electrode and each peripheral electrode in parallel with each other, and the electrode combination A power supply for applying a DC voltage from the peripheral electrode to the central electrode between the central electrode of the body and each peripheral electrode, a pH sensor for measuring a pH value of soil in the treatment area, and a DC voltage of the power supply. A power supply control device including at least means for inverting the polarity in accordance with the pH value of the soil measured by the pH sensor. 4. A cross section of the electrode assembly having a regular hexagonal shape.
The in-situ treatment device according to claim 3.