JP2010075887A - Cleaning method of contaminated soil and groundwater - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleaning method which shortens a cleaning period inexpensively and is safe in a surrounding environment, in the cleaning method for a contaminated groundwater region including saturated and unsaturated regions incorporating volatile contaminated substances by means of a pumping aeration treatment. <P>SOLUTION: The cleaning method of contaminated soil and groundwater, including a pumping process of pumping up groundwater from a pumping well to the contaminated soil region involving volatile contaminated substances, and a decomposition process of decomposing the volatile contaminated substances by irradiating groundwater pumped up in the pumping process with ultraviolet rays while aerating with ozone gas in an aeration tank, further includes an injection process of returning the groundwater treated in the decomposition process from an injection well to the soil. The ozone is mixed into the groundwater in the injection well to increase the ozone concentration in the groundwater by supplying a gas phase in the aeration tank to the groundwater, to decompose the volatile contaminated substances in the groundwater in the injection well. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for purifying soil and groundwater contaminated with chemical substances such as organic compounds.

  In Japan, pollution prevention has been advocated against heavy metals such as chromium, cadmium, and lead. However, in recent years, contamination of soil and groundwater by chemical pollutants such as petroleum compounds, organic compounds, and agricultural chemicals (fertilizers) has become a serious social problem.

  These pollutions not only directly inhibit the growth of animals and plants, but also cause air pollution due to volatilization and diffusion of pollutants into the atmosphere, and pollutants flow into rivers, lakes, and groundwater along with rainwater. Contamination may spread. There is also a high risk of damage spreading over a wide area in the food chain.

  As a fundamental cleanup measure against these pollutions, for example, excavation of soil containing pollutants, purification on the ground, and backfilling with clean soil are carried out.・ Cleaning with chemicals, etc., or bioremediation to decompose pollutants using the metabolic function of microorganisms have been performed. Also, by injecting solidifying agent into the contaminated soil area, fixing / stabilizing, separating / detoxifying by sucking harmful gas volatilized from pollutants from wells, or by pumping groundwater from which pollutants are leached Treatment methods such as separation and detoxification from soil have also been carried out.

  However, the method of excavating contaminated soil and then purifying and refilling it on the ground is very costly and labor intensive, and is not suitable for treating a large amount of contaminated soil.

  On the other hand, as a method of treating soil in situ, as shown in Patent Document 1 as a method for separation and detoxification from soil by pumping groundwater, contaminated groundwater is pumped from a pumping well and pollutants are removed from the ground. After the purification process, there is a method to drain the purified groundwater from the drain. In this case, in order to shorten the purification treatment period, it is necessary to increase the amount of groundwater to be treated by installing a large number of pumping wells. Therefore, the installation cost of the pumping wells is increased, and the equipment of the purification equipment installed on the ground There is also a cost to increase the capacity.

In Patent Document 2, a well having an opening at a depth corresponding to the saturation zone is provided, and after groundwater flows into the well from this opening, the structure returns to the soil from the opening provided at the height of the unsaturated zone. A method of removing toxic substances by adding an oxidant to a mixed gas containing ozone, blowing it from the ground through pipes into the groundwater in the well, and further irradiating it with ultraviolet rays in the groundwater. In order to shorten the purification treatment period, it is necessary to increase the amount of groundwater to be purified by installing a large number of wells, which increases the cost of installing a pumping well and increases the capacity of purification equipment installed on the ground. It also costs money to make it happen. In addition, since the upper surface of the well is open, unreacted ozone diffuses from the opening to the ground, and depending on the amount, the safety of the surrounding environment is a concern.
JP 2001-029933 A JP 2001-009480 A

  In view of the above-described problems of the prior art, the present invention provides a purification method using a pumped-water aeration process for a contaminated underground region including a saturated zone and an unsaturated zone containing volatile pollutants at a low cost. The object is to provide a purification method that is shortened and safe for the surrounding environment.

  In order to solve the above-described problems, a method for purifying contaminated soil and groundwater provided by the present invention is a method of pumping groundwater from a pumping well to a contaminated soil region containing volatile pollutants, In a contaminated soil and groundwater purification method comprising a decomposition step of decomposing volatile pollutants by irradiating ultraviolet light while aeration tank is aerated with ozone gas in the aeration tank, the groundwater treated in the decomposition step is transferred from the injection well to the soil. It has a back-injection process, and by supplying the gas phase part in the aeration tank to the groundwater in the injection well, ozone is mixed with the groundwater in the injection well to increase the ozone concentration in the groundwater and volatilize in the groundwater in the injection well. It is characterized by decomposing toxic pollutants.

  It has a suction process that sucks the space of the injection well in the injection process, and by supplying the gas discharged from the suction process to the liquid phase part of the aeration tank in the decomposition process, ozone is recycled and unreacted volatilization It is preferable to completely decompose toxic contaminants.

  The volatile contaminant is preferably at least one of trichloroethylene, tetrachloroethylene, dichloroethylene, dichloroethane, and trichloroethane.

  According to the present invention, in a purification method using a pumped water aeration process for a contaminated underground region including a saturated zone and an unsaturated zone containing volatile pollutants, the purification treatment period can be shortened at a low cost, and the surrounding environment can be reduced. A safe purification method can be provided.

  The volatile pollutant to be purified in the present invention includes at least one of trichloroethylene, tetrachloroethylene, dichloroethylene, dichloroethane, and trichloroethane.

An embodiment of the purification method of the present invention will be described with reference to FIG.
In the pumping process, groundwater containing volatile pollutants flowing into the pumping well 6 from the surrounding saturation zone 9 is pumped into the aeration tank 1 by a submersible pump 7 installed at the bottom of the pumping well 6. The pumping well 6 has a non-porous tube 22 at the head and a porous tube 23 other than the head, and the porous tube portion is installed in the soil.

  In the decomposition step, the groundwater in the aeration tank 1 is irradiated with ultraviolet rays generated from the ultraviolet irradiation device 3 and is aerated with a mixed gas containing ozone gas generated from the ozone generation device 2 to decompose volatile pollutants. Ozone is sufficiently dissolved in the groundwater and is supplied to the injection well 12 by gravity flow. The gas in the aeration tank 1 is discharged to the atmosphere via the surplus ozone gas decomposition tank 4.

  In the injection process, groundwater containing volatile contaminants flows into the injection well 12 from the surrounding saturated zone 9, and the volatile contaminants in the groundwater are dissolved in the groundwater supplied from the aeration tank 1. Decomposed by ozone. The injection well 12 is a non-porous tube at the head and a porous tube other than the head, and the porous tube portion is installed so as to be located in the soil.

  The ozone gas mixing pump 17 installed at the bottom of the injection well 12 draws in the groundwater from the groundwater supply line 19 submerged in the injection well, thereby removing excess ozone gas in the aeration tank 1 from the ozone gas supply line 18 connected thereto. Suction. By this operation, surplus ozone gas in the aeration tank 1 is dissolved in the ground water in the injection well 12 and the groundwater is circulated in the injection well 12, so that ozone is spread over the entire ground water in the injection well 12 with a high concentration. This high concentration of ozone accelerates the decomposition of volatile pollutants.

  In the suction process, it is preferable that the gas discharged from the suction process is supplied to the liquid phase part of the aeration tank 1 in the decomposition process by operating the gas suction blower 15.

  As a result, ozone and unreacted volatile pollutants are absorbed into the ground water in the aeration tank 1, where the volatile pollutants are completely decomposed by ozone and ultraviolet irradiation.

  In addition, ozone that has not contributed to this reaction is supplied to the injection well 12 in a state dissolved in groundwater.

  In this way, ozone is effectively recycled without being disposable.

  In order to decompose volatile pollutants in the groundwater in the aeration tank 1, it is necessary to fully study the specifications of the parts related to the decomposition of volatile pollutants such as ozone gas dispersion method and ultraviolet irradiation method in the aeration tank 1 There is. For example, it is necessary to appropriately select the capacity and number of the aeration tanks 1, the residence time in the aeration tank 1 of the pumped water, the bubble forming means for ozone gas aeration, and the like.

  As described above, in order to use ozone gas or ozone-dissolved water everywhere, the equipment in this purification method needs to be made of a material that can withstand the strong oxidizing power of ozone. In particular, in the aeration tank 1, since a high concentration of ozone stays, a measure for preventing corrosion due to ozone is necessary.

  As for the positional relationship between the pumping well 6 and the injection well 12, the pumping well 6 is installed on the downstream side of the groundwater flow 11 in the contaminated area, and the injection well 12 is installed on the upstream side.

  More specifically, it is preferable that the ozone-dissolved groundwater injected from the injection well 12 is installed so as to be in a positional relationship such that volatile pollutants between both wells can be decomposed toward the pumping well 6. The groundwater in which the ozone injected into the injection well 12 is dissolved oozes from the injection well 12 to the surrounding saturated zone, then moves on the groundwater flow 11 and reaches the pumping well 6, and the volatiles in this path The pollutant is decomposed with ozone in the saturation zone 9. By continuing this, the surrounding soil and groundwater of the injection well 12 and the pumping well 6 will be purified.

  One or more pumping wells 6 and injection wells 12 can be installed after considering the purification treatment period and cost.

As shown in FIG. 2, the pumping water having a diameter of 10 cm and a depth of 8 m is applied to the central part of the contaminated soil area contaminated with tetrachlorethylene (hereinafter referred to as PCE) having a depth of about 8 m, a width of about 6 m and a length of about 12 m. A well 6 and an observation well 21 having a diameter of 10 cm and a depth of 8 m were installed 6 m downstream of the groundwater flow 11. Moreover, the 500-liter aeration tank 1 shown in FIG. 3, which is the prior art, an ozone generator 2 for supplying ozone gas with an ozone generation amount of 1.2 g / h and an ozone concentration of 25 g / Nm ³ , and irradiation with ultraviolet rays having a peak wavelength of 254 ± 10 nm An ultraviolet ray irradiation device 3, an excess ozone gas decomposition device 4 filled with an ozone decomposition catalyst 50 L, an activated carbon tank 5 in the overflow line of groundwater in the aeration tank 1, and a 5 L / h submersible pump at the bottom of the pumping well 6 7 was installed. The PCE concentration in the groundwater was monitored by collecting an analytical sample from the observation well 21.

  After the purification was started, as shown in FIG. 4, a tendency to gradually decrease with respect to the initial PCE concentration of 24 ppm in the groundwater was confirmed.

  Since the completion of purification was expected to be 3 years or more after 3 months, two injection wells 12 having a diameter of 15 cm and a depth of 8 m were installed as shown in FIG. 2 in order to promote the purification.

  An overview of the entire facility after the third month of purification is shown in FIG.

  The activated carbon tank 5 was removed, and the overflow line of groundwater in the aeration tank 1 was connected to the ozone-dissolved groundwater inlet 13 located at the head of the injection well 12.

  The gas phase part of the aeration tank 1 and the ozone gas suction port 16 of the injection well 12 were connected by a line. One end of an ozone gas supply line 18 is connected to the ozone gas suction port 16, and the other end of the ozone gas supply line 18 is connected to a portion other than both ends of the groundwater supply line 19.

  A 2.5 L / min ozone gas mixing pump 17 is installed at the bottom of the injection well 12, one end of the groundwater supply line 19 is connected to the suction side of the ozone gas mixing pump 17, and the discharge side of the ozone gas mixing pump 17 is connected to the discharge side of the ozone gas mixing pump 17. An ozone-dissolved groundwater discharge line 20 was connected.

  One end of the groundwater supply line 19 that is not connected to the ozone gas mixing pump 17 is located in the groundwater in the injection well 12.

  An injection well gas suction port 14 and a 0.2 m 3 / h gas suction blower 15 were installed at the head of the injection well 12. Thereafter, the ozone gas mixing pump 17 and the gas suction blower 15 were operated. As a result, the PCE concentration in groundwater decreased rapidly and reached 0.001 ppm about 7 months after the start of purification, so the purification treatment was suspended. Thereafter, monitoring at the observation well was continued for about two months, but no increase in PCE concentration in the groundwater was observed, and it remained below 0.001 ppm.

  The equipment shown in FIG. 3, which is a conventional technology, was installed with the same specifications as in Example 1 for a contaminated soil region contaminated with trichlorethylene having a depth of about 8 m, a width of about 4 m, and a length of about 12 m. Since the completion of purification was expected to be 2 years or more after 3 months with respect to the initial trichlorethylene concentration of 16 ppm in the groundwater, the equipment shown in FIG. As a result, since the concentration reached 0.001 ppm 6 months after the start of purification, the purification treatment was suspended. Thereafter, monitoring was continued for about two months, but no increase in the concentration of trichlorethylene in the groundwater was observed, and it remained below 0.001 ppm.

  From the above, it becomes clear that the treatment period can be shortened by about 70% by using the present invention for ozone aeration and ultraviolet irradiation treatment after pumping, which is a conventional treatment method for volatile pollutants. It was.

  According to the present invention, in a purification method using a pumped water aeration process for a contaminated underground region including a saturated zone and an unsaturated zone containing volatile pollutants, the purification treatment period can be shortened at a low cost, and the surrounding environment can be reduced. Since it can be purified safely, it can be used to repair soil contaminated with volatile pollutants at the factory site.

It is the schematic which shows embodiment of this invention. It is a well arrangement drawing of the example by the purification method of the present invention. It is a conventional purification method. It is a graph which shows a time-dependent change of the tetrachlorethylene density | concentration of groundwater using the purification method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aeration tank 2 Ozone generator 3 Ultraviolet irradiation apparatus 4 Surplus ozone gas decomposition tank 5 Activated carbon tank 6 Pumping well 7 Submersible pump 8 Unsaturation zone 9 Saturation zone (Aquifer)
DESCRIPTION OF SYMBOLS 10 Groundwater level 11 Groundwater flow 12 Injection well 13 Ozone dissolved groundwater inlet 14 Injection well gas suction port 15 Gas suction blower 16 Ozone gas suction port 17 Ozone gas mixing pump 18 Ozone gas supply line 19 Groundwater supply line 20 Ozone dissolved groundwater discharge line 21 Observation well 22 Nonporous tube 23 Porous tube

Claims (3)

  Volatile pollutants by irradiating ultraviolet rays while pumping groundwater pumped from pumping wells and groundwater pumped from the pumping well to the contaminated soil area containing volatile pollutants while aeration tanks aeration with ozone gas In the method for purifying contaminated soil and groundwater, which has a decomposition process for decomposing water, it has an injection process for returning the groundwater treated in the decomposition process from the injection well to the soil, and supplies the gas phase part in the aeration tank to the groundwater in the injection well A method for purifying contaminated soil and groundwater, characterized in that ozone is mixed with groundwater in the injection well to increase the ozone concentration in the groundwater and decompose volatile pollutants in the groundwater in the injection well.   It has a suction step of sucking the space portion of the injection well in the injection step, and recycles ozone by supplying the gas discharged from the suction step to the liquid phase portion of the aeration tank in the decomposition step, The method for purifying contaminated soil and groundwater according to claim 1, wherein unreacted volatile pollutants are completely decomposed.   The method for purifying contaminated soil and groundwater according to claim 1 and 2, wherein the volatile pollutant is at least one of trichloroethylene, tetrachloroethylene, dichloroethylene, dichloroethane, and trichloroethane.