Method and system for treating DNAPL polluted underground water

Abstract

A system for treating DNAPL polluted underground water comprises a first filter material space, a separation space, a dissolved phase treatment space, a treated underground water space and a second filter material space which are sequentially connected through sieve plates in the flowing direction of the underground water. A partition plate for preventing DNAPL phase pollutants from flowing to the dissolved phase treatment space is arranged at the bottom of the sieve plate at the joint of the separation space and the dissolved phase treatment space; the permeable reactive barrier is improved, so that the service life of the active filler is prolonged, and the treatment cost of DNAPL phase pollutants is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the field of remediation and risk control of contaminated groundwater in sites, and specifically to a method and system for treating DNAPL-contaminated groundwater. Background Art

[0002] Dense nonaqueous-phase liquid (DNAPL) refers to a liquid that is insoluble in water and has a density greater than that of water, and is a relatively common type of organic pollutant among many substances causing groundwater pollution. Common DNAPLs such as trichloroethylene, tetrachloroethylene, carbon tetrachloride and other chlorinated organic solvents, coal tar, etc. Since chlorinated organic solvents are good degreasing agents, DNAPL pollution usually occurs in factories that use a large amount of chlorinated organic solvents, such as electronics factories, electronic component cleaning, chemical factories, chemical product manufacturing, dyeing factory paint formulation, pesticide manufacturing factories, commercial dry cleaning, waste solvents used in home decoration, etc., and most DNAPL pollutants have adverse effects on the human body such as carcinogenicity.

[0003] Currently, the main ex-situ treatment technologies for DNAPL pollution are: pumping and treatment technology. In practical engineering applications, when using this technology, extraction wells and above-ground treatment systems need to be built at the site where the contaminated groundwater is located. However, the precise extraction effect of this technology on pollutants is not good, and it will extract groundwater together, resulting in a relatively high disposal cost, and the setting of extraction wells is also a big problem.

[0004] In-situ treatment technologies for DNAPL pollution include: recirculation well technology, in-situ bioremediation technology, in-situ heat treatment technology, biosparging technology, in-situ chemical oxidation technology and permeable reactive barrier technology. Among the above technologies, the permeable reactive barrier technology is considered the most cost-effective technology for reducing, intercepting and remediating pollutants in groundwater. And this technology is to construct a wall composed of active reaction fillers downstream of the contaminated groundwater. The key point of this technology is to construct a wall in the underground aquifer. The wall is composed of active reaction materials. When water flows through the wall, the pollutants carried in the groundwater will interact with the active materials in the wall, reducing the concentration of pollutants in the water, thereby remediating the groundwater.

[0005] In the traditional permeable reactive barrier technology, contaminated groundwater is usually directly flowed into the active filler wall to treat the dissolved pollutants in the groundwater; however, when treating relatively severe DNAPL pollution, the free phase will penetrate the lower layer of fillers, resulting in a reduction in the service life of the active fillers and the need for frequent replacement of fillers, leading to an increase in disposal costs. Therefore, it is necessary to improve the permeable reactive barrier technology so that it can treat contaminated groundwater for a long time, avoid lower layer penetration, and extend the service life of the active fillers. Summary of the Invention

[0006] The present invention aims to provide a method and system for treating groundwater polluted by DNAPL to treat DNAPL-phase pollutants, extend the service life of the activated packing, and reduce the treatment cost.

[0007] To solve the above technical problems, the specific solution adopted by the present invention is as follows:

[0008] A system for treating groundwater polluted by DNAPL includes a first filter media space, a separation space, a dissolved-phase treatment space, a treated groundwater space, and a second filter media space that are sequentially connected through a sieve plate along the groundwater flow direction. A partition for blocking the flow of DNAPL-phase pollutants to the dissolved-phase treatment space is provided at the bottom of the sieve plate where the separation space is connected to the dissolved-phase treatment space.

[0009] The height of the partition is 10 - 60 cm.

[0010] The height of the partition is 30 - 40 cm.

[0011] An extraction module is provided in the separation space. The extraction module includes an extraction metering pump, a phase interface identifier located in the separation space, and a linkage control system. The water suction pipe of the extraction metering pump is located in the separation space, and the water discharge pipe of the extraction metering pump is connected to a collection bucket. The phase interface identifier is located in the separation space, and the phase interface identifier is connected to the linkage control system through a signal transmitter.

[0012] A transfer pump for transporting the DNAPL-phase pollutants in the collection bucket to a waste treatment site for centralized disposal is provided on the collection bucket.

[0013] The installation height of the phase interface identifier is 5 - 30 cm lower than the top of the partition.

[0014] The installation height of the phase interface identifier is 10 - 20 cm lower than the top of the partition.

[0015] A water replenishment module for replenishing water to the separation space is provided in the treated groundwater space. The water replenishment module includes a water replenishment metering pump connected to the linkage control system. The water suction pipe of the water replenishment metering pump is located in the treated groundwater space, and the water discharge pipe of the water replenishment metering pump is located in the separation space.

[0016] The installation position of the water discharge pipe port of the water replenishment metering pump is 10 - 20 cm lower than the top of the separation space.

[0017] The installation position of the water suction pipe port of the extraction metering pump is 2 - 10 cm lower than the phase interface identifier.

[0018] The phase interface identifier is a density meter, a refractive index meter, or an oil-water interface meter.

[0019] The dissolution-phase treatment space is filled with active fillers, and the active fillers are zero-valent iron powder or zero-valent iron particles.

[0020] The dissolution-phase treatment space is filled with adsorbent active fillers or microbial degradation-type materials, and the adsorbent active fillers are activated carbon, molecular sieve or fly ash.

[0021] The first filter media space and the second filter media space have the same structure, and both the first filter media space and the second filter media space are filled with quartz sand.

[0022] A method for treating DNAPL-polluted groundwater uses a system for treating DNAPL-polluted groundwater to conduct site hydrogeological and pollution investigations, determine the distribution of the pollution plume and the direction of groundwater flow. According to the distribution of the pollution plume and the direction of groundwater flow, the first filter media space, the separation space, the dissolution-phase treatment space, the treated groundwater space and the second filter media space are successively installed in the polluted site, so that the polluted groundwater will successively pass through the first filter media space, the separation space, the dissolution-phase treatment space, the treated groundwater space and the second filter media space, and the DNAPL-phase pollutants are blocked by the partition board.

[0023] The DNAPL-phase pollutants blocked by the partition board in the separation space are pumped out by a pumping metering pump for centralized treatment.

[0024] The treated groundwater in the treated groundwater space is replenished into the separation space by a water replenishment metering pump to prevent the groundwater in the dissolution-phase treatment space from flowing back to the separation space after the DNAPL-phase pollutants are pumped out.

[0025] Due to the adoption of the above technical solutions, the present invention has the following beneficial effects:

[0026] By arranging a partition board at the bottom of the sieve plate connecting the separation space and the dissolution-phase treatment space to block the DNAPL-phase pollutants, the entry of the DNAPL phase into the dissolution-phase treatment space is reduced, and further the service life of the active fillers in the dissolution-phase treatment space is increased; the present invention improves the permeable reactive wall to extend the service life of the active fillers, effectively reducing the treatment cost of the DNAPL-phase pollutants; by arranging a water replenishment module, the groundwater in the separation space can be effectively backfilled to prevent the groundwater in the dissolution-phase treatment space from flowing back; a second separation space is also arranged to prevent the failure of the density sensor in the first separation space from causing the inability to pump out the DNAPL-phase pollutants in time. Description of the Drawings

[0027] Figure 1 It is a schematic structural diagram of Embodiment 1 of the present invention;

[0028] Figure 2 It is a schematic structural diagram of Embodiment 2 of the present invention;

[0029] Figure 3 Schematic diagram of the partition structure of the present invention;

[0030] Figure 4 Schematic diagram of the sieve plate structure of the present invention;

[0031] 1. First filter media space; 2. Density sensor; 3. Signal transmitter; 4. Computer control system; 5. Make-up water metering pump; 6. Extraction metering pump; 7. Collection bucket; 8. Delivery pump; 9. Separation space; 10. Partition; 11. Dissolved phase treatment space; 12. Treated groundwater space; 13. Second filter media space; 14. Sieve plate. Detailed implementation manners

[0032] The following briefly describes the usage method of the present invention through two embodiments:

[0033] Embodiment 1

[0034] As Figure 1 shown, a system for treating DNAPL-polluted groundwater includes a first filter media space 1, a separation space 9 adjacent to the first filter media space 1, a dissolved phase treatment space 11 adjacent to the separation space 9, a treated groundwater space 12 adjacent to the dissolved phase treatment space 11, and a second filter media space 13 adjacent to the treated groundwater space 12. As Figure 1 shown, the first filter media space 1, the separation space 9, the dissolved phase treatment space 11, the treated groundwater space 12, and the second filter media space 13 are arranged in sequence from left to right and are connected by a sieve plate 14. When arranged according to the groundwater flow direction, the polluted groundwater first passes through the first filter media space 1. Among them, the first filter media space 1 and the second filter media space 13 have the same structure and both use 3-mm quartz sand as the filter media filler. The first filter media space 1, the separation space 9, the dissolved phase treatment space 11, the treated groundwater space 12, and the second filter media space 13 are connected by a sieve plate 14, and the structure of the traditional sieve plate 14 is as Figure 4 shown.

[0035] As Figure 3 shown, at the bottom of the sieve plate 14 at the connection between the separation space 9 and the dissolved phase treatment space 11, there is a partition 10 for separating the DNAPL phase. The specific structure of the partition 10 is as Figure 3 shown. The partition 10 and the sieve plate 14 are an integral structure. The partition 10 is arranged in the separation space 9 mainly to reduce the DNAPL-phase pollutants entering the dissolved phase treatment space 11, thereby increasing the service life of the dissolved phase treatment space 11.

[0036] As Figure 1As shown in the figure, an extraction module is provided in the separation space 9. The extraction module is mainly used to extract the DNAPL-phase pollutants in the separation space 9 from the bottom of the separation space 9. The extraction module includes an extraction metering pump 6, an interface recognizer located in the separation space 9, and a linkage control system. The linkage control system adopts a computer control system. The water suction pipe of the extraction metering pump 6 is located in the separation space 9. The water outlet pipe of the extraction metering pump 6 is connected to the collection bucket 7. The interface recognizer is located in the separation space 9. The installation position of the port of the water suction pipe of the extraction metering pump 6 is 2-10 cm lower than that of the interface recognizer. The water outlet pipe of the extraction metering pump 6 is connected to the collection bucket 7. The collection bucket 7 is mainly used to store the extracted DNAPL-phase pollutants. The interface recognizer is connected to the linkage control system through a signal transmitter 3. The linkage control system is a computer control system 4.

[0037] The interface recognizer can adopt a density meter, a refractive index meter or an oil-water interface meter. In the present invention, the interface recognizer adopts a density meter, which includes a density sensor 2 and a signal transmitter 3. The density sensor 2 is installed at a position 5-30 cm downward from the top of the partition 10 in the separation space 9.

[0038] A transfer pump 8 is provided on the collection bucket 7 for transferring the DNAPL-phase pollutants in the collection bucket 7 to a waste treatment site for centralized disposal. When the collection bucket 7 is full of stored DNAPL-phase pollutants, it can be used to discharge or transfer the DNAPL-phase pollutants to a waste treatment site for centralized treatment.

[0039] A water replenishment module is provided in the post-treatment groundwater space 12 for replenishing water to the separation space 9. When the extraction metering pump 6 extracts a certain amount of DNAPL-phase pollutants from the separation space 9, in order to prevent the groundwater in the dissolved-phase treatment space 11 from flowing back, it is necessary to replenish water to the separation space 9. The water replenishment module includes a water replenishment metering pump 5 connected to the linkage control system. The water suction pipe of the water replenishment metering pump 5 is located in the post-treatment groundwater space 12. The installation position of the port of the water outlet pipe of the water replenishment metering pump 5 is 10-20 cm lower than the top of the separation space 9. The water outlet pipe of the water replenishment metering pump 5 is located in the separation space 9. The water replenishment metering pump 5 and the extraction metering pump 6 are synchronously controlled through a computer control system. When the extraction metering pump 6 extracts a certain volume of DNAPL-phase pollutants, the water replenishment metering pump 5 will correspondingly replenish the same volume of post-treatment groundwater to the separation space 9.

[0040] The dissolved-phase treatment space 11, mainly an active treatment space composed of active fillers, is located downstream of the separation space 9 and functions to treat the dissolved phase of contaminants in groundwater. The active fillers include zero-valent iron powder and zero-valent iron particles of reducing elemental substances, the adsorption-type active fillers include activated carbon, molecular sieve or fly ash, and the microbial degradation-type materials include specific degradation bacteria screened or mutagenized for characteristic contaminants. It is also possible to use one or a mixture of the above materials.

[0041] The usage method of Example 1 is briefly described as follows:

[0042] For the pollution of dense non-aqueous phase liquids (DNAPLs), site hydrogeology and pollution investigations are carried out to determine the distribution of the pollution plume and the groundwater flow direction. According to the distribution of the pollution plume and the groundwater flow direction, the first filter media space 1, the separation space 9, the dissolved-phase treatment space 11, the treated groundwater space 12, and the second filter media space 13 are installed in the polluted site in sequence. The polluted groundwater will pass through the first filter media space 1, the separation space 9, the dissolved-phase treatment space 11, the treated groundwater space 12, and the second filter media space 13 in sequence.

[0043] Since the density of the DNAPL phase is greater than that of water, the polluted groundwater in the separation space 9 will be stratified, and the DNAPL-phase contaminants will be blocked by the partition plate 10 and cannot enter the dissolved-phase treatment space 11. The contaminants dissolved in the groundwater will enter the dissolved-phase treatment space 11 through the sieve plate 14 above the partition plate 10 for treatment. When the phase interface detector detects the DNAPL-phase contaminants, it will transmit a signal to the linkage control system through the signal transmitter 3. The linkage control system will synchronously control the extraction metering pump 6 and the makeup water metering pump 5 to work. The extraction metering pump 6 will extract the DNAPL-phase contaminants blocked by the partition plate 10 from the separation space 9 into the collection bucket 7. At the same time, the makeup water metering pump 5 will supplement the treated groundwater in the treated groundwater space 12 into the separation space 9 to maintain it, so that the groundwater in the treated groundwater space 12 can enter the separation space 9 again for sedimentation separation. Finally, the polluted groundwater passing through the second filter media space 13 can meet the discharge standard.

[0044] Example 2

[0045] As Figure 2As shown, compared with Embodiment 1, after the separation space 9, a second separation space 9 is provided. A partition 10 with the same structure is provided at the bottom of the sieve plate 14 between the separation space 9 and the second separation space 9 to separate them; on the right side of the second separation space 9 is the dissolved phase disposal space 11, and the second separation space 9 and the dissolved phase disposal space 11 are separated by the partition 10. Density sensors 2 are installed in the second separation space 9 in the same way as in the first separation space 9. The density sensors 2 are connected to the signal transmitters 3, and the signal transmitters 3 are connected to the computer control system 4; the installation positions of the transmission pipelines of the density sensors 2, the extraction metering pumps 6, and the makeup water metering pumps 5 in the second separation space 9 are the same as those of the density sensors 2, the extraction metering pumps 6, and the makeup water metering pumps 5 in the separation space 9.

[0046] The specific usage method of Embodiment 2 is as follows:

[0047] Designed with Embodiment 2, when DNAPL pollution occurs, the DNAPL-polluted groundwater first passes through the first filter medium space 1. The first filter medium space 1 filters the sediment in the polluted groundwater and plays a role in dispersing the water flow; subsequently, the DNAPL-polluted groundwater enters the separation space 9. In the separation space 9, since the density of the DNAPL phase is greater than that of water, stratification occurs. When the upper layer of the DNAPL phase reaches the detection surface of the density sensor 2, the density sensor 2 sends a signal to the computer control system 4 through the signal transmitter 3, and at the same time, the information is transmitted to the computer control system 4; the computer control system 4 sends control instructions to the extraction metering pump 6 and the makeup water metering pump 5. The extraction metering pump 6 extracts the DNAPL pollutants into the collection bucket 7, and the makeup water metering pump 5 simultaneously extracts the treated groundwater with the same volume as the extraction metering pump 6 from the treated groundwater space 12 and injects it into the separation space 9 to maintain the liquid level height of the separation space 9; the pollutants entering the collection bucket 7 are sent to the waste treatment site for centralized disposal under the action of the transfer pump 8.

[0048] When a large amount of leakage occurs in the DNAPL phase, or when the density sensor 2 in the separation space 9 fails, the DNAPL phase enters the second separation space 9. When the lower layer of the DNAPL phase reaches the detection surface of the density sensor 2, the density sensor 2 in the second separation space 9 sends a signal to the computer control system 4 through the signal transmitter 3, and at the same time, the information is transmitted to the computer control system 4; the computer control system 4 sends control instructions to the extraction metering pump 6 and the makeup water metering pump 5. The extraction metering pump 6 extracts the DNAPL pollutants into the collection bucket 7, and the makeup water metering pump 5 simultaneously extracts the treated groundwater with the same volume as the extraction metering pump 6 from the treated groundwater space 12 and injects it into the separation space 9 to maintain the liquid level height of the second separation space 9; the pollutants entering the collection bucket 7 are sent to the waste treatment site for centralized disposal under the action of the transfer pump 8.

[0049] The polluted water dissolved in the groundwater in the upper part of the second separation space 9 enters the dissolved-phase disposal space 11. Under the action of the composite material composed of adsorbent packing activated carbon, zero-valent granular iron, and specific degradation bacteria, the pollutants dissolved in the water are disposed of. The treated groundwater then passes through the treated groundwater space 12 and the second filter media space 13 in sequence. The groundwater after passing through the second filter media space 13 is up to standard and can be discharged.

Claims

1. A system for treating DNAPL-polluted groundwater, characterized in that: It includes a first filter media space (1), a separation space (9), a dissolved-phase treatment space (11), a treated groundwater space (12), and a second filter media space (13) that are sequentially connected along the direction of groundwater flow through a sieve plate (14). At the bottom of the sieve plate (14) where the separation space (9) is connected to the dissolved-phase treatment space (11), there is a partition plate (10) for blocking the flow of DNAPL-phase pollutants to the dissolved-phase treatment space (11).

2. The system for treating DNAPL-polluted groundwater according to claim 1, wherein: The height of the partition plate (10) is 10 - 60 cm.

3. The system for treating DNAPL-polluted groundwater according to claim 1, wherein: The height of the partition plate (10) is 30 - 40 cm.

4. The system for treating DNAPL-polluted groundwater according to claim 1, wherein: An extraction module is provided in the separation space (9). The extraction module includes an extraction metering pump (6), a phase interface identifier located in the separation space (9), and a linkage control system. The water suction pipe of the extraction metering pump (6) is located in the separation space (9), and the water discharge pipe of the extraction metering pump (6) is connected to a collection bucket (7). The phase interface identifier is connected to the linkage control system through a signal transmitter (3).

5. The system for treating DNAPL-polluted groundwater according to claim 4, characterized in that: A transfer pump (8) for transporting the DNAPL-phase pollutants in the collection bucket (7) to a waste treatment site for centralized disposal is provided on the collection bucket (7).

6. The system for treating DNAPL-polluted groundwater according to claim 4, characterized in that: The installation height of the phase interface identifier is 5 - 30 cm lower than the top of the partition plate (10).

7. The system for treating DNAPL-polluted groundwater according to claim 4, characterized in that: The installation height of the phase interface identifier is 10 - 20 cm lower than the top of the partition plate (10).

8. The system for treating DNAPL-contaminated groundwater according to claim 6 or 7, characterized in that: A water replenishment module for replenishing water to the separation space (9) is provided in the treated groundwater space (12). The water replenishment module includes a water replenishment metering pump (5) connected to the linkage control system. The water suction pipe of the water replenishment metering pump (5) is located in the treated groundwater space (12), and the water discharge pipe of the water replenishment metering pump (5) is located in the separation space (9).

9. The system for treating DNAPL-polluted groundwater according to claim 8, characterized in that: The installation position of the port of the water discharge pipe of the water replenishment metering pump (5) is 10 - 20 cm lower than the top of the separation space (9).

10. The system for treating DNAPL-polluted groundwater according to claim 9, characterized in that: The installation position of the port of the water suction pipe of the extraction metering pump (6) is 2 - 10 cm lower than the phase interface identifier.

11. The system for treating DNAPL-polluted groundwater according to claim 10, characterized in that: The phase interface identifier is a density meter, a refractive index meter, or an oil-water interface meter.

12. The system for treating DNAPL-polluted groundwater according to claim 1, characterized in that: The dissolved-phase treatment space (11) is filled with active filler, and the active filler is zero-valent iron powder or zero-valent iron particles.

13. The system for treating DNAPL-polluted groundwater according to claim 1, characterized in that: The dissolved-phase treatment space (11) is filled with adsorptive active filler or microbial degradation-type material, and the adsorptive active filler is activated carbon, molecular sieve, or fly ash.

14. The system for treating DNAPL-polluted groundwater according to claim 1, characterized in that: The first filter media space (1) and the second filter media space (13) have the same structure, and both the first filter media space (1) and the second filter media space (13) are filled with quartz sand.

15. A method for treating groundwater contaminated by DNAPL, characterized in that: Adopt the system for treating DNAPL-polluted groundwater described in any one of claims 1 to 14, conduct site hydrogeological and pollution investigations, determine the distribution of the pollution plume and the direction of groundwater flow, and sequentially install the first filter media space (1), separation space (9), dissolved-phase treatment space (11), treated groundwater space (12), and second filter media space (13) in the polluted site, so that the polluted groundwater will sequentially pass through the first filter media space (1), separation space (9), dissolved-phase treatment space (11), treated groundwater space (12), and second filter media space (13), and the DNAPL-phase pollutants are blocked by the partition plate (10).

16. The method for treating DNAPL-polluted groundwater according to claim 15, wherein: Pump out the DNAPL-phase pollutants blocked by the partition plate (10) in the separation space (9) through the extraction metering pump (6) for centralized treatment, so that the pollutants dissolved in the groundwater above the partition plate (10) enter the dissolved-phase treatment space (11) through the sieve plate (14).

17. The method for treating DNAPL-polluted groundwater according to claim 16, wherein: Supplement the treated groundwater in the treated groundwater space (12) into the separation space (9) through the make-up water metering pump (5) to prevent the groundwater in the dissolved-phase treatment space (11) from flowing back to the separation space (9) after the DNAPL-phase pollutants are pumped out.

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