JPH06226300A - Method and device for treating water-containing soil on site by electroosmosis - Google Patents

Abstract

PURPOSE:To directly treat water-contg. soil on the treating site with a simple structure and to provide a device capable of treating the soil by electroosmosis without contaminating the environment around the site. CONSTITUTION:An electrode combination 2 consisting of a central electrode 2A and plural peripheral electrodes 2B surrounding the electrode 2A is successively and adjacently arranged in the water-contg. soil treating region. Current and voltage are impressed in parallel between the electrode combinations to dehydrate the soil by electroosmosis, and then the polarity of the impressed voltage is inverted to restore the >= value of the treating region. Since the structure is simple and a mechanically operating part is not needed, the soil is directly treated on the site, and the secondary contamination of the treated soil or its surroundings due to the change in # value is prevented as a current is applied in the reverse direction.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an in situ treatment method and apparatus for hydrous soil by electroosmosis.

[0002]

BACKGROUND OF THE INVENTION In order to subject various sludges such as inorganic and organic sludges to final treatment such as incineration and composting, or to transfer them to a final treatment facility, they must be used in advance. It is desirable to dehydrate and reduce the volume to reduce the water content to a suitable water content.For this reason, natural treatment such as sun drying, mechanical squeezing, filtration treatment and chemical treatment with a coagulant are conventionally performed. It is used. However, sun drying is not practical for treating large amounts of sludge in terms of site area and treatment time. On the other hand, mechanical and chemical treatments increase equipment costs and running costs such as power and chemicals, and depending on the type of sludge, sufficient dehydration may be difficult.

For this reason, a method applying the electroosmosis technique has been attempted for dehydration of these sludges, and attention has been paid in recent years in terms of economical efficiency and efficiency. In the dehydration treatment using the electroosmosis method, the fact that the soil particles in the sludge are negatively charged (zeta potential) with respect to water is utilized, and the electrodes (anode-cathode) provided opposite to each other in the sludge to be treated are used. By applying a DC voltage between the two, the water in the sludge is moved to the cathode side and the sludge is dehydrated.

Concretely, as the dehydration of sludge by such an electroosmotic method, for example, JP-A-56-60603 is used.
As described in No. 500678 and the like, sludge mechanically preliminarily dehydrated to some extent is transferred under pressure along a transfer path between a pair of conveyors to which a positive and negative voltage that relatively rotationally moves is applied, Many methods have been proposed for recovering and discharging the water content of sludge that has moved to the cathode side by electroosmosis during this period.

According to such a sludge dewatering method by electroosmosis, the dewatering efficiency is extremely high, so that the efficiency in the final incineration disposal is improved, and in the case of the chemical dewatering, the subsequent microbial treatment and waste treatment are performed. Nor is there the hassle of choosing a treatment to suit.

However, in the sludge dewatering process of the prior art, the sludge to be treated is introduced along a moving path such as a pressure conveyor, and in some cases, it is combined with a pretreatment for previously dewatering the sludge to some extent, which is complicated. Since a mechanical operating unit is required, the apparatus becomes large in scale, equipment costs increase, and there are many problems in terms of operation and maintenance.

[0007] Generally, the sludge to be dewatered is not only organic sludge discharged from a sewage treatment plant or factory, but also inorganic sludge such as dredged sludge from rivers and bays, and sludge derived from the remaining soil at construction sites. Since there are various sources of such sludge, these sludges are usually transported to a specific dehydration treatment facility and then treated collectively. However, in this case, the sludge transportation cost occupies a considerable part of the sludge treatment cost.

[0008] Therefore, it is desirable to perform such dehydration treatment of sludge on the spot at the site of generation, and in the case of improvement of soft soil or soil containing harmful substances, treat them "on the spot". It is necessary to. However, it is not easy to transport or install such large-scale equipment for each processing site that is distributed and exists in each place.

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

Further, when the above-mentioned treatment equipment is directly installed at a place where sludge or residual soil is generated, a soil improvement place, etc. to perform dehydration treatment by electroosmosis, the soil near the electrodes is electrolyzed by electricity. PH value changes. In particular, the pH value on the anode side shifts significantly to the acid side with dehydration treatment,
As a result, the metal retained in the form of salts or the like in the treated soil itself and its surroundings may be ionized and eluted, which may cause secondary pollution around the treated area. Therefore, when treating the water-containing soil by the electroosmosis method, it is necessary to avoid the adverse effect of the pH change on the surrounding soil and the like as much as possible.

It is an object of the present invention to efficiently treat water-containing soil as an object to be treated on the spot without using a large-scale facility which requires a complicated mechanical operation unit as in the prior art. An object of the present invention is to provide an in-situ method and apparatus for treating water-containing soil by electroosmosis.

[0012] Another object of the present invention is to treat the water-containing soil by electroosmosis, particularly when the pH of the treated area is inclined to the acidic side.
An object of the present invention is to provide an in-situ treatment method and apparatus for water-containing soil capable of recovering water to a neutral or specific pH value.

[0013]

The object of the present invention is to provide a method for treating a water-containing soil in which a water content of the soil is reduced by electroosmosis by applying an electric current between electrodes provided opposite to a treated area of the soil. An electrode combination consisting of a center electrode and a plurality of peripheral electrodes that are arranged at equidistant positions with respect to the center electrode is installed in such a manner that they are sequentially adjacent to a treated area of soil, and the center electrode and each of the peripheral electrodes are arranged. And a DC voltage having a polarity that causes a current to flow from each of the peripheral electrodes to the center electrode or from the center electrode to the peripheral electrode, is applied in parallel to each of the electrode combinations, and Dehydration step of migrating water in the soil of the treatment area to the central electrode side by electroosmosis and draining it, and subsequently to the dehydrating step, between the central electrode and each of the peripheral electrodes of the current in the dehydrating step Reverse direction The polarity of the voltage that is applied,
And an in-situ treatment method for water-containing soil, which comprises a pH adjusting step of recovering a pH value on the side of the peripheral electrode, which has been lowered by energization during the dehydration step, to a predetermined value.

Further, the method of the present invention comprises a hollow tubular center electrode having a suction / drainage channel therein, and a plurality of peripheral electrodes arranged at positions equidistant from the center electrode.
Each center electrode and each peripheral electrode in the area to be treated of soil, an electrode combination sequentially installed in a state of being connected to each other in parallel, and a drainage means connected to the suction drainage channel of the center electrode, A power supply for applying a DC voltage from the peripheral electrode to the center electrode between the center electrode and each peripheral electrode of the electrode combination, a pH sensor for measuring the pH value of the soil in the treated area, and a power supply for the power supply. Set the polarity of the DC voltage to p
It can be carried out by an in-situ treatment apparatus for water-containing soil, comprising: a power supply control apparatus including at least a means for inverting the pH value of the soil measured by the H sensor.

[0015]

In the present invention, first, the center electrode and the peripheral electrodes are connected in parallel to each other by forming the electrode combination body including the center electrode and the plurality of peripheral electrodes arranged at positions equidistant from the center electrode. In this state, a plurality of sets are installed sequentially adjacent to the treated area of the water-containing soil, and for example, a DC voltage of a polarity that causes a current from each of the peripheral electrodes toward the center electrode is applied to the treated area. Water in the soil is transferred to the center electrode side by electroosmosis, and drained by an appropriate means through the suction drainage channel.

In the conventional dehydration treatment equipment by electroosmosis, it is necessary to shorten the dehydration treatment time as much as possible in order to continuously dehydrate sludge while moving it in the treatment process, and the pretreatment used for that purpose Equipment, compression conveyors, etc. made the equipment structure and operation maintenance complicated.

However, in the present invention, since the water-containing soil is treated as a batch at the source, the treatment time is not so limited, and a completely static dehydration treatment is carried out only by the electroosmotic action by energizing the electrodes. By this, the intended purpose is sufficiently achieved.

For example, the water content of various sludges is usually about 80 to 90%, and in order to be suitable for the final treatment such as microbial treatment and incineration, the water content is about 40 to 40% in ordinary dehydration treatment.
The water content is reduced to about 50%. According to the 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 20V. It turned out that it was obtained sufficiently.

In this case, in order to collectively treat the soil in the treated area, it is necessary to uniformly energize the entire soil in the treated area. For this reason, in the present invention, a plurality of electrode combinations comprising a central electrode (cathode) and a plurality of peripheral electrodes (anode) facing each other at equal distances are used around the central electrode, and these are combined in the treated area of the water-containing soil. Are sequentially arranged adjacent to each other, and a DC voltage is applied in parallel to each electrode combination to cause a dehydration action by uniform electroosmosis over the entire soil in the treatment area, and the moisture that has moved to each center electrode side is removed. It is designed to be discharged and dehydrated.

Generally, the dewatering rate of sludge in hydrous soil is proportional to the applied voltage between the electrodes and inversely proportional to the distance between the electrodes, but when dewatering an average sludge to about 40 to 50%, for example, a radius of 1 m. Using a combination of a center electrode and a peripheral electrode at each apex of a regular hexagon, if a low voltage of about 20V is applied to the peripheral electrode, the sludge in the treated area will be heated in about 10 to 24 hours. It was confirmed experimentally that the above-mentioned desired dehydration rate was obtained.

In an actual device, 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 a peripheral electrode (anode) is arbitrarily selected. The electrode assembly can be easily constructed by using the conductive material such as rebar.
In this case, the water dewatered from the soil is discharged through the fine pores of the soil particles, so that the soil particles themselves act as a filter, and the wastewater is highly purified, so that no further filtration treatment is required at the time of discharge. On the other hand, the treated soil is dehydrated and reduced in volume to about 40 to 50%, which makes composting and incineration or transportation to these treatment facilities extremely easy.

During the dehydration treatment by electroosmosis, since electrolysis using a water-containing soil component as an electrolyte occurs between the positive and negative electrodes, the pH of the area to be treated rises on the side of the central electrode (cathode) and becomes alkaline, so that the peripheral electrodes (anode) ) Side, it decreases and acid p
It becomes H.

In this case, particularly on the side of the acidified anode, a condition is apt to elute the metal, so that harmful metal or the like elutes as an ion from the compound contained in the treated soil itself or the surrounding soil. It may contaminate the surrounding soil and groundwater or adversely affect the adjacent bedrock and the structure itself.

Therefore, in the present invention, for example, a pH sensor for detecting the pH value is installed near the peripheral electrode (anode), and the polarity of the power supply voltage is reversed at the end of the dehydration process to make the central electrode (cathode) positive. A voltage is applied to cause an electrolysis action between both 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 electrodes to the neutral side. When the pH value reaches an initial value or a preset value, the energization is stopped by the detection output from the pH sensor and the entire processing step is ended.

When the pH of the water-containing soil is constant and the desired dehydration rate can be predicted in advance,
A moisture meter may be used as a means for determining the switching time point between the dehydration step and the pH adjusting step and the ending time point of the pH adjusting step. In some cases, the pH meter and the moisture meter may be used together.

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

As described above, one of the important features of the present invention is that the water-containing soil can be dehydrated directly at the treatment site. Therefore, during the treatment by electroosmosis, the pH of the treated soil itself and the surrounding soil can be changed. May occur. However, in the present invention, the pH that follows the dehydration step is
Since the pH value is restored to the initial value or the predetermined value by the adjustment process, the elution of heavy metal ions and the like due to the pH of the peripheral electrode (anode) side changing to acidic is prevented, and the problem of environmental pollution around Can be avoided.

In addition to the dehydration treatment of sludge and residual soil, the present invention
It can also be applied to soil treatment that originally needs to be performed on the spot, such as improvement of soil containing harmful substances and soft soil with high water content. For example, chromium (6
Value) Even if it contains other harmful heavy metal particles,
These compounds are easily discharged to the cathode side during dehydration by electroosmotic treatment in the state of being dissolved in soil water or by being dissolved in soil water from the soil near the positive electrode that has become acidic pH during electrolysis. Therefore, it is also effective in detoxifying contaminated soil. In order to render the contaminated soil harmless, it is preferable to purify dehydrated water and repeatedly use it as a cleaning 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]

EXAMPLES The present invention will be described below with reference to examples. Figure 1
FIG. 2 is a diagram 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 diagram showing the arrangement of electrode combinations in a soil treatment area when the present invention is carried out.

[0030]

[Experimental Example] The apparatus of FIG. 1 was used to confirm the dehydration by the electroosmotic dehydration step in the method of the present invention and the pH change around the electrode due to the execution of such step and the pH recovery by the application of the reverse polarity voltage. The following preliminary experiment was conducted.

A stainless steel pipe 2A having an inner diameter of 20 mmφ as a central electrode 2A having a suction / drainage channel in its lumen in a dehydration tank 1 containing 11 kg of an inorganic sludge having an initial water content of 49.8% and a pH of 8.2 and 250 mm around it. The electrode combination 2 made of a reinforcing bar having a diameter of 5 mm as the peripheral electrode 2B arranged on the same circumference at a distance of 5 is the sludge accumulation depth (155 mm)
The central electrode 2A was used as the negative electrode and each peripheral electrode 2B was used as the positive electrode, and a DC voltage of 20 V (initial current 0.95 A) was applied from the power source 3 to carry out electroosmosis. In the other figures, 2C is a suction / drain hole formed in the tube wall of the center electrode 2A, 2D is a drainage channel formed by using a lumen portion, 4 is a control unit for reversing the output polarity of the power source 3, 5 is a suction pump,
6 is a pH sensor.

Table 1 shows the amount of electroosmotic dehydration during 7 hours of energization and the accompanying change in pH value at 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 Central part 8.2 8.2 8.2 8.4 Current (A) 0.95 0.9 0.7 0.5 Voltage (V) 20 20 20 20 Discharged water (ml) 0 300 200 250 Wastewater pH ー 11.6 11.7 11.8

In order to recover the pH changed by the electroosmotic treatment, especially the acidic pH value on the anode side to almost the initial value,
The polarity of the applied voltage between the central electrode 2A and the peripheral electrode 2B was reversed, and electricity was supplied for 4 hours. The results are shown in Table 2.

[0035]

[Table 2] Initial value 2 hours later 3 hours later 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 Discharged water (ml) 0 100 100 120 Wastewater pH ー 3.5 5.3 6.5

After energizing for 4 hours, as shown in Table 2, (-)
The pH value on the side (in this case, the peripheral electrode 2B) is from 5.2 to 7.
It rose to 5, and recovered to almost the initial pH value.

Hereinafter, the present invention will be described with reference to Examples in which dewatering is performed by directly applying it to various sources such as sludge. The basic configuration of the device is similar to that shown in FIG. In each embodiment, an electrode combination 2 including a center electrode (cathode) 2A and a peripheral electrode (anode) 2B is formed in a regular hexagonal shape as shown in FIG. 2, and the center electrode and the peripheral electrode of each combination are formed. Were connected in parallel (the connection between the electrodes is not shown), and these were sequentially installed adjacent to the sludge treatment area. The throughput of each sludge in each case is 60,000k
g: The treated area was 30 m ² and the depth was 2 m.

Example 1 An activated inorganic construction sludge having a water content of about 82.2% (pH 8.
6), a plurality of electrode combinations 2 shown in FIG.
2 ,. ． ． Were sequentially arranged adjacent to each other. In this example, the distance between each central electrode 2A and the peripheral electrode 2B was set to 1 m, and the initial value of the total energizing current in the dehydration process from the power source 3 to these electrode combinations was set to 10 A, which was the same as the above-described experimental example. Equipment and conditions were used.

A DC voltage of 20 V is applied from the power source 3 to the center electrode 2A of each electrode assembly 2 to supply electricity for 10 hours for dehydration treatment, and then the polarity is reversed for 4 hours p.
An H adjustment process was performed. The results are shown in Table 3. As shown in Table 3, the water content of sludge decreased from the initial value of 82.2% to 35.5%, and the transportation cost was remarkably reduced due to the weight reduction and volume reduction. Also, the positive pH during the dehydration process decreased by 4.5,
The pH value was restored to the initial value by the pH adjustment treatment.

Example 2 An organic sewage sludge having a water content of 82.0% was dehydrated for 17 hours in the same manner as in Example 1. The results are shown in Table 3. The water content decreased to 51.2%, and the water content was suitable for composting by microbial treatment.

Example 3 The same procedure as in Example 1 was carried out to dehydrate the river dredged sludge having a water content of 80.8% for 12 hours. The results are shown in Table 3. The water content after the treatment decreased to 41.6%, and by adding a chemical solidifying agent to increase the supporting capacity, it became possible to use it for backfilling.

Example 4 A lake dredged sludge having a water content of 82.6% was dehydrated for 24 hours in the same manner as in Example 1. The results are shown in Table 3.
Shown in. The water content after the treatment was reduced 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 each initial value.

[0043]

[Table 3] Example Dehydration time Initial end pH value Moisture content Moisture content Initial end phase (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 6 7.2 4.2 8.8 4 Lake dredging sludge 24 82. 6 53.3 7.4 5.5 5.5 9.4 Example 5 In the hydrous soil treatment according to the present invention, when harmful metals or the like are contained in soil or water-loam water, these harmful metals are removed during dehydration by electroosmosis. It can also be applied to the detoxification treatment of soil that is removed together with drainage in an ionic state. When the same method as in each of the above-described examples was applied to the water-containing soil containing hexavalent chromium, the water content was decreased by the dehydration energization for about 48 hours and the pH adjustment energization of the opposite polarity, and the content of hexavalent chromium was decreased. 0.01p from the initial 20.2ppm
It was confirmed by the dissolution test that the pH was lowered to pm or less.

The present invention is not limited to the above-described 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 it is also possible to use a combination in which the polarities of both electrodes are reversed, if necessary.

[0045]

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

[Brief description of 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 implementing the present invention.

[Explanation of symbols]

 1 ... Dehydration tank 2 ... Electrode combination 2A ... Tubular center electrode (cathode) 2B ... Peripheral electrode (anode) 2C ... Suction / drainage hole 2D ... Suction / drainage path 3 ... Power supply, 4 ... Control part, 5 ... Drainage pump, 6 ... pH sensor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Katsura Katsura 1-805-1 Kawabe-cho, Ome-shi, Tokyo Lions Mansion 308 Kawabe Kawabe (72) Inventor Tsutomu Moriya 2-31-11-703 Minamisuna, Koto-ku, Tokyo Issue (72) Inventor Kaoru Ichinomiya 3-5-12 Higashi Narashino, Narashino City, Chiba Laforet No. 206

Claims (2)

[Claims] 1. A method for treating a water-containing soil in which a water content of the soil is reduced by electroosmosis by applying an electric current between electrodes provided opposite to a treated area of the soil, wherein the center electrode and the center electrode are equal to each other. An electrode combination consisting of a plurality of peripheral electrodes arranged at a distance position, respectively, is installed in such a manner as to be adjacent to the treated area of the soil, and between the central electrode and the peripheral electrodes. A DC voltage having a polarity that causes a current to flow from the central electrode or the central electrode to the peripheral electrode is applied in parallel to each of the electrode combinations, and water in the soil in the treated area is electroosmotically A dehydration step of transferring to the center electrode side and draining, and a voltage of 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 subsequent to the dehydration step. , The above And a pH adjusting step of recovering the pH value on the side of the peripheral electrode, which has been lowered by energization during the dehydration step, to a predetermined value. 2. A central electrode having a hollow tubular shape having a suction / drainage channel inside, and a plurality of peripheral electrodes arranged at positions equidistant from the central electrode. And an electrode combination that is installed adjacent to each other in the state where the respective peripheral electrodes are connected to each other in parallel, a drainage unit that is connected to the suction drainage channel of the center electrode, a center electrode of the electrode combination, and each periphery. A power supply that applies a DC voltage from the peripheral electrode to the center electrode between the electrodes, a pH sensor that measures the pH value of the soil in the treated area, and a polarity of the DC voltage of the power supply that is measured by the pH sensor. And a power supply control device including at least means for inverting the pH value of the soil to be treated.