KR101066336B1 - Groundwater Purification Method in Extracted Low-Density Non-Aqueous Liquid (LUNPL) for Oil Pollution Recovery - Google Patents

Abstract

The present invention is a method for restoring soil and groundwater in an oil-contaminated area, extracting / recovering LNAPL, which is an oil pollutant in a contaminated area, through a bioslurping process, which is one of soil restoration technologies, and contaminated groundwater The present invention relates to a treatment method for discharging fenton oxide. After oil separation, there are free soil oils and fine soil particles adsorbed to oil components in the oil contaminated groundwater, resulting in deterioration of Fenton's oxidation treatment efficiency. After installing the pretreatment tank capable of removing particles through the front side of the Fenton oxidation tank, the Fenton oxidation tank features the technology of oxidizing and removing organic pollutants in groundwater.

Description

A purifying method of light non-aqueous phase liquid in underground water for remediation of petroleum hydrocarbons -contaminated soil}

The present invention is a method for restoring soil and groundwater in an oil-contaminated area, extracting / recovering LNAPL, which is an oil pollutant in a contaminated area, through a bioslurping process, which is one of soil restoration technologies, and contaminated groundwater The present invention relates to a treatment method for discharging fenton oxide.

There is little data on soil pollution in Korea, and some survey data have recently been reported. In the case of oil pollution, which accounts for the majority of soil pollution in Korea, the main sources of oil pollution are oil accumulation and pollution caused by oil spills from oil manufacturing and storage facilities, military units and oil-related industrial complexes, and transportation processes. It is coming true.

Oil spilled from the oil polluted area drifting on the groundwater layer in the form of LNAPL composed of volatile oil and low-density nonvolatile oil hydrocarbon, etc., and acts as a high concentration oil pollutant that causes groundwater contamination continuously. However, there are few accurate national statistics on the presence and distribution of LNAPL in contaminated soil and the distribution or concentration of complex oil pollutants in groundwater. However, the concentration of soil pollution by oil is increasing every year, especially in TPH, and the level of pollution in military units and oil-related industrial complexes is very serious.

Currently used oil-contaminated soil and groundwater restoration methods are divided into biological treatment methods, physical and chemical treatment methods, and heat treatment methods. Depending on the treatment location, in situ and on situ treatment techniques are used. It is divided into Each of these methods has different advantages and disadvantages. Recently, the selective extraction of the LNAPL layer has been actively researched and commercialized for the bioslurping process that removes oil pollutants, simultaneously degass volatiles through bioventing, and enables in situ biological treatment through underground oxygen supply.

Meanwhile, the Fenton reaction, which is a chemical treatment method generally used for industrial wastewater treatment, is a reaction of oxidizing pollutants using radical hydroxide (OH ·), a powerful oxidant produced by using divalent iron ions and hydrogen peroxide reaction. However, oil contaminants are adsorbed to the colloidal fine particulate matter present in the groundwater, which is not easily removed by the fenton oxidation treatment, which may reduce treatment efficiency. Therefore, there is a need to develop a technology capable of effectively treating the contaminated groundwater generated after oil separation in a conventional bioslurping process while minimizing the deterioration of the Fenton reaction.

An object of the present invention devised to solve the above-mentioned problems of the prior art is to improve the efficiency of fenton oxidation and to minimize the amount of chemicals required by effectively removing fine contaminating particulate matter including fine soil adsorbed in oil. It is to provide a processing device.

The contaminated groundwater treatment apparatus according to the present invention for achieving the above object, in the contaminated groundwater treatment apparatus using Fenton oxidation, the fine colloidal particles adsorbed to oil at the front end of the reaction tank 60 in which the Fenton oxidation reaction is performed It is equipped with a pretreatment tank which electrolyzes and floats, and spontaneously seizes with respect to the particle | grain material whose density exceeds 1.

In the present invention, the fine colloidal particles in the oil-adsorbed particulate matter present in the groundwater after oil-water separation are removed by the flotation principle by electrolysis, and the particles having a higher density than the groundwater are removed by gravity sedimentation. It is possible to reduce the deterioration of the Fenton oxidation efficiency by the material material, it is possible to improve the water quality of the discharged groundwater, thereby reducing the amount of chemicals required for the oxidation treatment. In addition, there is an effect of reducing energy consumption by alternately operating the electric flotation means and gravity sedimentation according to the characteristics of the region and the extraction particle size distribution. In addition, the pretreatment tank according to the present invention does not require a separate air compression device or a compression tank compared to the conventional air flotation method, and thus has good mobility to the contaminated area within the contaminated groundwater site. There is an advantage that the optimal operation is possible according to the distribution characteristic of.

1 is a schematic diagram of a contaminated groundwater treatment system equipped with a Fenton oxidation reactor according to the present invention.
2 is a schematic configuration diagram of a pretreatment tank 30 equipped with an electrolytic flotation device according to the present invention.
3 is a graph comparing the Fenton oxidation treatment efficiency (TOC concentration standard) for groundwater samples after precipitation and filtration according to the present invention.

Hereinafter, the technical configuration of the present invention to be described in more detail.

The present invention is a method for economically and effectively treating the contaminated groundwater generated after oily water separation in the existing bioslurping process, and remains after pre-treatment of the contaminated groundwater containing microparticles after oily water separation through selective operation of electric flotation and gravity settling. Groundwater containing oil pollutants are configured for treatment in a Fenton oxidizer.

As described above, the present invention is a contaminated groundwater purification system composed of a combination of a colloidal particulate matter pretreatment tank in a contaminated groundwater and a Fenton oxidation tank which is a chemical treatment apparatus at a rear stage. The pretreatment tank is based on the electric flotation tank and operates according to the characteristics of the oil polluted area and the soil purification stage. In areas where oil pollution is serious, but in the early stages of purification, high concentrations of LNAPL may be extracted, which may result in high concentrations of colloidal micro-pollutant particles remaining after oil separation. Such colloidal fine particulate matter is difficult to be sufficiently removed by the chemical oxidation with OH. Therefore, it is possible to improve the efficiency of the subsequent fenton oxidation treatment by improving the micro-oil contaminant particle removal efficiency through the voltage control of the electric flotation device according to the present invention. On the other hand, when the concentration of the polluted area is not high, or during the rainy season, the groundwater volume increases or the later purification stage, the pre-treatment tank removes particles through natural sedimentation without operating the electric flotation device and minimizes energy consumption. It is possible.

Hereinafter, a description of the apparatus according to the present invention with reference to the accompanying drawings.

As shown in FIG. 1, the contaminated groundwater treatment system according to the present invention includes a pump 10 for extracting bioslurping, an oil separation tank 20, a pretreatment tank 30 having an electrolysis flotation device, an oil storage tank 40, Settle solids storage tank (50), Fenton oxidation tank (60), pH adjusting tank (70).

1 is an overall configuration diagram of a system for restoring soil contaminated with oil and treating contaminated groundwater in extracted LNAPL according to the present invention. LNAPLs in oil pollution areas are ground-feed to pumps 10 through underground extractors and connectors. LNAPL extracted from the pump (10) is separated from the oil and ground water through the gravity oil separator (20), the oil on the oil separator (20) is the oil storage tank (40), the sedimented solids in the bottom of the sediment solid storage tank Are transferred to 50. In the groundwater discharged from the oil / water separator 20, there are some free oil components and fine colloidal particles to which oil is adsorbed, and the groundwater 31 is a pretreatment tank 30 equipped with an electrolytic flotation means 35. Flows into. 2 is a schematic configuration diagram of a pretreatment tank 30 according to the present invention. As disclosed in the drawings, the electrolytic flotation means 35 installed in the pretreatment tank includes a cathode and an anode which are vertically arranged to cross each other; And a current applying unit, wherein when a voltage is applied between the anode and the cathode by a current applying unit (not shown), basically, the water in the pretreatment bath is electrolyzed to form a hydrogen gas on the cathode side and an oxygen gas on the anode side. Is generated by forming a fine bubble, floating up the oil-absorbed microcolloidal particulate matter in the ground water, and the relatively dense particles can be removed by sedimentation. In addition, the OH radicals generated by the electrolysis means as described above can directly decompose the organic matter in the pretreatment tank, thereby reducing the load in the subsequent Fenton oxidation process and further increasing the decomposition efficiency.

As disclosed in FIG. 2, in the pretreatment tank 30, oil components having a density close to or smaller than 1 and colloidal particles adsorbed with oil are lifted by the microbubbles generated during electrolysis, and then the skimmer 32 is moved from the top. It is preferable to collect and transfer the oil to the oil storage tank 40. Meanwhile, particulate matter having a density greater than 1 present in the groundwater is collected in the lower part of the pretreatment tank by gravity settling and then transferred to the settling solid storage tank 50.

An inclined plate 36 is attached to the upper end of the outlet of the pretreatment tank 30 to reduce the outflow of colloidal micro-oil contaminant particles that rise and then descend, and the particulate matter that falls by gravity. The pretreated ground water is transferred to the Fenton oxidation tank 60 at the rear stage through the outlet 37 and the outlet pipe 33. In the pretreatment tank according to the present invention, the height of the outlet point (end) of the outlet pipe 33 is preferably designed to be equal to the target water level of the pretreatment tank so that the flow is naturally maintained by the same atmospheric pressure as the pretreatment tank. On the other hand, the height of the discharge point of the outlet pipe is preferably formed so that the height can be adjusted in consideration of the water level and residence time of the pretreatment tank. The inlet formed in the pretreatment tank is positioned to be introduced from the upper portion of the pretreatment tank, and the outlet portion is preferably positioned at the top of the electrolytic flotation means 35 and below half of the pretreatment tank 30 to minimize the outflow of fine particles. .

In the Fenton oxidation reactor (60), the pH is maintained at 3-4 to treat organic matter in the pretreated contaminated groundwater, and ferric sulfate (FeSO ₄ ) and hydrogen peroxide (H ₂ O ₂ ) are 1: 5-1: 10. It is mixed with groundwater while injecting Fenton solution within the ratio range. The effluent of the Fenton oxidation tank 60 is discharged after adjusting the pH to 6-7 in the pH adjusting tank 70 before discharge.

The embodiments described below are intended to illustrate the technical idea of the present invention and are not intended to limit the present invention to the ranges disclosed.

Example

After comparing the actual groundwater sample and sedimentation and filtration after real water separation in FIG. 3, the TOC removal efficiency through fenton oxidation was compared for the samples. As disclosed in the graph of FIG. 3, it can be seen that the Fenton oxidation treatment effect is very high in the filter sample from which the particulate matter is most removed. In addition, in Table 1, the COD removal rate through fenton oxidation was compared with respect to groundwater samples before and after the electrical injury pretreatment. The COD removal rate of the pretreatment tank in which the microcolloid particles were removed by the electric flotation was about 76%, and the removal rate was 93% or more through the Fenton oxidation. The COD concentration removed by Fenton oxidation (Fe _S O ₄ : H ₂ O ₂ = 1:10) for the same volume of sample was 46 mg / L (= 530 mg / L-484 mg for pre-treatment samples). / L) or after the pretreatment was 92 mg / L (= 128 mg / L-36 mg / L) was confirmed that about two times the removal rate improvement is achieved. In addition, as shown in Table 2, the COD removal rate through fenton oxidation is affected by the injury time and voltage conditions in the pretreatment of electrical injury. In addition, the removal of dissolved organic matter occurs in addition to the particulate matter during the pre-treatment of the electric flotation, which is caused by the effect of the removal of some dissolved organic matter regardless of the fenton oxidation caused by the radicals generated by the electrolysis. The dissolved organics removal effect was found to increase (Table 3).

<COD concentration of samples before and after electric injury pretreatment and Fenton treatment>

Mg COD / L, before electrical injury pretreatment Mg electrophoretic pretreatment, mg COD / L Before fenton 530 128 After
Fenton 484 36

* Electric injury condition: 25V, injury time 30 minutes

<Fenton oxidation treatment efficiency (%) according to pre-treatment time and voltage condition of electrical injury>

Applied electrical voltage Time 15v 20v 25v 15min 80.5% 81.5% 85.5% 30min 90.5% 91.8% 93.1%

* Result of COD concentration according to voltage change by time after Fenton oxidation

<Dissolved COD removal efficiency according to pretreatment time and voltage conditions in pre-floating step (%)>

Applied electrical voltage Time 15v 20v 25v 15min 7.2% 8.8% 12.4% 30min 15.2% 17.2% 18.6%

As described above, according to the present invention, in the case of the high concentration of the oil pollution area or the initial restoration of the bioslurping process, it is preferable to oxidize the fenton through the electrolysis flotation pretreatment tank 30 as described above, in which the pretreatment tank repairs the groundwater. Depending on the chemical retention time and the fine particle concentration it can be operated by varying the voltage control as described above. On the other hand, when the LNAPL concentration is low, such as low concentration oil pollution area or the late recovery of the bioslurping process, the electrolysis flotation pretreatment tank 30 may be selectively operated. That is, when the microcolloidal oil-adsorbed particles are present at low concentration, the pretreatment tank may be made to remove the particles only by natural sedimentation while the electrolytic flotation means 35 is removed or operated without applying voltage.

10: pump 20: oil / water separator
30: pretreatment tank 40: oil storage tank
50: sedimentation solids treatment tank 60: fenton oxidation reactor
70: pH adjusting tank

Claims (8)

In the contaminated groundwater treatment apparatus using Fenton oxidation,
At the front end of the reaction tank 60 where the Fenton oxidation reaction is carried out, the contaminated groundwater treatment apparatus is provided with a pretreatment tank which electrolyzes and floats the fine colloidal particles adsorbed in oil, and naturally precipitates the particulate matter with a density greater than 1. . The method according to claim 1,
The pretreatment tank has an electrolytic flotation means, the electrolysis flotation means comprising: a cathode and an anode which are vertically arranged to cross each other; And a current applying unit. The method according to claim 1,
An upper end of the pretreatment tank is connected to an oil storage tank 40 for processing oil components and fine colloidal particles adsorbed to the oil, and a stop portion of the pretreatment tank is connected to the Fenton oxidation reactor 60, and a lower end of the pretreatment tank is Polluted groundwater treatment device, characterized in that connected to the sediment solids storage tank (50) for transporting particulate matter by gravity sedimentation. The method according to claim 2,
Contaminated groundwater treatment apparatus characterized in that the inclined plate is installed on the top of the outlet portion formed in the stop of the pretreatment tank so that the outflow of fine colloidal particles and particulate matter adsorbed with oil is reduced. The method of claim 4,
The outflow portion of the pretreatment tank is located above the electrolytic flotation means, and is located below the half of the pretreatment tank. The method according to claim 5,
End portion of the outlet pipe connected to the outlet portion is contaminated groundwater treatment device, characterized in that formed to be adjustable in height. The method of claim 6,
The height of the distal end of the outlet pipe connected to the outlet portion is contaminated ground water treatment apparatus, characterized in that the same height as the target water level of the pretreatment tank. The contaminated groundwater treatment apparatus according to claim 3, wherein a skimmer is further provided between the upper end of the pretreatment tank and the oil storage tank (40).

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