NL2031159B1 - A Method for Removing Organochlorine Compounds in soil by Chelating Agent-Enhanced Advanced Oxidation Under Electrokinetic Remediation - Google Patents

Abstract

The present invention relates to the field of remediation technology of soil contamination, and specifically relates to a method of removing organochlorine compounds in soil by chelating agent-enhanced advanced oxidation under electrokinetic remediation, the method comprising the following steps: 1) transferring contaminated soil to an electrokinetic remediation device, adding oxidant and glutamic acid N,N-diacetic acid to the soil, while setting nano zero-valent iron near the anode of the electrokinetic remediation device; 2) adjusting pH of electrolyte and start the electrokinetic remediation device for the removal of organochlorine compounds in the soil. The oxidant is at least one of persulfate, hydrogen peroxide, permanganate and hypochlorite. The method of the present invention is based on the combined treatment of electrokinetic remediation, nano-zero-valent iron, oxidant and glutamate N,N- diacetic acid for the synergistic removal of organochlorine contaminants in soil, which can achieve a significant increase in the removal rate of organochlorine contaminants in soil, as well as the in-situ removal of organochlorine contaminants.

Description

1 001879P-NL

A Method for Removing Organochlorine Compounds in soil by Chelating

Agent-Enhanced Advanced Oxidation Under Electrokinetic Remediation

Technical Field

The present invention belongs to the field of soil pollution remediation technology, specifically, it relates to an in-situ remediation method for organochlorine compound contaminated soil.

Background Technology

Organochlorine compounds are kinds of organic pollutants that are important and difficult to degrade, raising wide concern due to their high residual, high ecotoxicity and strong bioresidual properties. Organochlorines are easily adsorbed on soil and river sediments due to their high lipid solubility and hydrophobicity. The existing degradation methods for organochlorines include gas extraction, incineration, solidification/stabilization, biodegradation, chemical oxidation, chemical reduction, and chemical leaching. Although gas extraction is convenient and fast, it is only applicable to volatile pollutants in organochlorines. Incineration is a primitive degradation method, but it may cause secondary pollution. Oxidants are always used in chemical oxidation method, including Fenton's reagent, ozone, potassium permanganate, persulfate, ferrate, etc. However, most oxidants have poor dechlorination ability for organochlorine pollutants, while chemical reduction technology has strong dechlorination reduction ability for organochlorine pollutants, but the reduction rate is slow and the degradation is incomplete, and even toxic intermediates are easily produced. Biodegradation has a long remediation cycle and is greatly influenced by the environment. Chemical drenching could not completely degrade organochlorine in soil.

Therefore, the combination of chemical oxidation and biological methods has been widely studied to achieve complete degradation of organochlorine compounds. After searching, relevant applications in the prior art have been disclosed, such as Chinese

Patent Application No. 201611095749.4 with application publication date of May,24 2017, which discloses the remediation method for contaminated soil by organochlorine pesticide. It used chemical reagents with chemical reduction properties and slow- release carbon biomass to remediate organochlorine pesticide contaminated soil through a combination of periodic anaerobic fermentation, chemical reduction

2 001879P-NL dechlorination and aerobic biodegradation. Although the method of this application has the advantages of environmental protection and environmental friendliness, and also improves the efficiency of remediation and reduces the remediation cycle to a certain extent, the method requires the use of a rototiller to rototill the contaminated soil pile 2-3 times after the agent is applied, so that the agent is fully mixed with the contaminated soil, which is a tedious operation step.

In order to solve the problem of complete degradation of organochlorine compounds, more researchers have also found that the use of nano zero-valent iron as soll organochlorine dechlorination reductant can effectively reduce and dechlorinate organochlorine in soil, which is now widely used in the remediation of sewage and organochlorine contaminated soil sites. After searching, the Chinese patent application

No. 201611199336.0 with publication date of May 31, 2017, discloses a method of degrading organochlorine in soil using nano-zero-valent iron in combination with potassium ferrate, the specific scheme of which is as follows: by adding a certain amount of nano-zero-valent iron and potassium ferrate to the organochlorine- contaminated soil with a certain pH and liquid-solid ratio, putting it into a constant temperature oscillator at room temperature. After shaking for 6-24 hours, the degradation rate of organochlorine in the treated soil can reach more than 70%. The method of this application uses chemical reduction method to dechlorinate the organochlorine pollutants, which can degrade part of the organochlorine pollutants, and then uses Fe(VI) in potassium ferrate to further oxidize and degrade the dechlorination products of organochlorine, so as to achieve rapid and complete degradation of organochlorine pollutants. However, the method of this application aiming at the degradation rate of organochlorine still needs to be improved.

Therefore, based on the shortcomings of the prior art, there is an urgent need to invent a soil remediation method with high degradation efficiency for organochlorine compounds.

Content of the invention 1. The problem to be solved

In response to the shortcomings of the existing technology in the removal efficiency of organochlorine pollutants in soil, the present invention provides a combination

3 001879P-NL treatment of glutamic acid N,N-diacetic acid, electrokinetic remediation, nano zero- valent iron, and oxidant to synergistically remove organochlorine pollutants in soil, which can achieve a substantial increase in the removal rate of organochlorine pollutants in soil, and at the same time can achieve the removal in situ. 2. Technical solutions

In order to solve the above problems, the technical solution adopted in the present invention is as follows.

The present invention provides a method for removing organochlorine compounds in soil by chelating agent-enhanced advanced oxidation under electrokinetic remediation, in the following steps: 1) transferring contaminated soil to an electrokinetic remediation device, adding oxidant and glutamic acid N,N-diacetic acid to the soil, setting nano-zero valent iron near the anode of the electrokinetic remediation device; the basic principle of the electrokinetic remediation device described in the present invention is to induce an electrochemical reaction process by applying a low direct current to the electrodes placed in the soil, and the reactor can be assembled or by using conventional electrokinetic remediation devices in the prior art. 2) Adjusting the pH of the electrolyte and starting the electrokinetic remediation device for the removal of organochlorine compounds in soil.

As a further improvement of the present invention, the oxidant is at least one of persulfate, hydrogen peroxide, permanganate and hypochlorite.

As a further improvement of the present invention, the pH of the electrolyte in step 2) is adjusted to 4 to 5. The purpose of this step is that, due to the presence of transition metal ions such as Fe? in the soil, which are soluble and dominant under acidic conditions, while metals such as iron are relatively insoluble or have low solubility in most aqueous systems under pH > 5 conditions.

4 001879P-NL

As a further improvement of the present invention, the nano zero-valent iron is set at a position of 5cm from the anode plate.

As a further improvement of the present invention, the contaminated soil contains iron oxides of any one or combination of rhodochrosite, hematite or magnetite.

As a further improvement of the present invention, the molar concentration of glutamic acid N,N-diacetic acid is 1 mol/L.

As a further improvement of the present invention, the mass concentration of the hydrogen peroxide is 5%.

As an even further improvement of the present invention, the organochlorine compounds comprise one of 1,3 5-trichlorobenzene (1,3,5-TCB), 1,2,4- trichlorobenzene (1,2,4-TCB), 1,2, 3-trichlorobenzene (1,2,3-TCB), 1,2,4,5- tetrachlorobenzene (1,2,4,5-TCB), pentachlorobenzene (PeCB), hexachlorobenzene (HCB) Any one of 4,4-DDT (4,4,-DDE), 2,4'-DDT (2,4,-DDT) or 4,4,-DDT (4,4,-DDT).

As a further improvement of the present invention, the electrode material of the electrokinetic remediation device is one of graphite, iron, titanium, stainless steel or alloy. 3. Beneficial effects

Compared with the prior art, the beneficial effects of the present invention are. (1) The method of the present invention for removing organochlorine compounds in soil by chelating agent-enhanced advanced oxidation under electrokinetic remediation, using electrokinetic remediation in combination with advanced oxidation for the removal of organochlorine compounds in soil, and at the same time setting nano zero- valent iron near the anode of the electroremediation device, on the one hand using nano-zero-valent iron with high specific surface area and reaction activity to activate the oxidant more rapidly and effectively to degrade pollutants, at the same time, it accelerates the cyclic reaction of Fe?* and Fe? in the soil, and continuously supplies

Fe?* to the system, thereby improving the efficiency of advanced oxidation reactions;

001879P-NL and on the other hand, when it was used for organochlorine compound removal, the nano-zero-valent iron can make the organic chlorinated organic pollutants firstly reduce and dechlorinate, and then the oxidation reaction process is carried out, which can degrade the chlorinated organic pollutants more efficiently and specifically by 5 using the dual effect of reduction and oxidation in the system. (2) The chelating agent-enhanced advanced oxidation under electrokinetic remediation method of the present invention for the removal of organochlorine compounds in soil, using the combination treatment of glutamate N,N-diacetic acid, electrokinetic remediation, nano zero-valent iron and oxidant, serves several purposes: 1) the use of glutamate N,N-diacetic acid itself is good for the solubility of iron in soll (producing more Fe?*), therefore, they synergize and at the same time strengthen the removal of organic compounds by advanced oxidation and oxidant oxidation; (2) The combination of glutamic acid N,N-diacetic acid and electrokinetic remediation treatment effectively promotes the migration of oxidant and dissolved Fe?" in the system, thus significantly increasing the dual effect of reduction and oxidation of organochlorine compounds present in the system, thus achieving a significant increase in the removal rate of organochlorine compounds.

Description of the accompanying drawings

FIG. 1 is a design diagram of the electrokinetic remediation device in Example 1 of the present invention; and

FIG. 2 is a diagram of the actual use of the electrokinetic remediation device in

Example 1 of the present invention.

FIG. 3 is a schematic diagram of nano zero-valent iron.

In the figure: 1, removable cover plate; 2, liquid storage chamber; 3, electrode chamber; 4, stable flow orifice spacer.

Specific embodiments

The present invention is further described below in conjunction with specific embodiments.

6 001879P-NL

Example 1

Instruments and reagents: accelerated solvent extraction instrument (Thermo

Scientific, USA), YK-AD5050 power supply of Guangzhou Post and

Telecommunications Equipment Co., Ltd, constant voltage 2V cm’ and GC-uECD (Agilent 7890A/5975C, USA, 7693 autosampler) detector, ethyl acetate (chromatographic pure), acetonitrile (chromatographic pure), and n-hexane (chromatographic purity) were purchased from J.T. Baker Company (USA). A GC-

UECD with autosampler was used for the qualitative and quantitative analysis of organochlorine contaminants.

This example shows the effect of hydrogen peroxide (H2O2) and chelating agent GLDA in advanced oxidation combined with electrokinetic remediation to remove organochlorine compounds in soil.

Step 1): Organochlorine compound contaminated soil samples were taken from a contaminated site downstream of a pesticide plant wastewater treatment system in

China, and soil samples were taken from topsoil, the contaminated soil containing iron oxides of one or combination of rhodochrosite, hematite or magnetite. The soil was ground and sieved through a 2 mm sieve and stored at 4°C for use. Another part of the soil was taken to determine the physicochemical properties and mineral composition of the soil, and the physicochemical properties of the soil are shown in Table 1. In this procedure, soil acid digestion was used for the analysis of inorganic elements (As, Cd,

Co, Cr, Cu, Mn, Ni, Pb, Zn) in the soil, and Agilent 7700x and PE Optima8000 were used for the quantitative determination of trace elements and other elements. The raw conductivity of the soil was determined as follows: 10 g of dry soil samples were added to 50 mL of distilled water, shaken for 30 min, and the supernatant was measured using a conductivity meter (DDB 303A). pH was determined: weighing 10 g of dry soil samples dissolved in 25 mL of 1 M KCI solution, and pH was determined using a pH meter (pH/ISE meter 410P-01).

7 001879P-NL

Table 1 Physicochemical properties of soils

Chemical element or Concentration Unit properties pH 6.82 -

EC 542.0 uS/cm

Cr 66.3 mg kg”!

Co 12.8 mg kg’

Ni 53.6 mg kg’!

Cu 81.3 mg kg!

Zn 608.5 mg kg’

As 12.60 mg kg’!

Cd 2.61 mg kg’!

Pb 102. 6 mg kg’!

Mn 535.0 mg kg’

P 755.0 mg kg’!

Al203 7.97 %

CaO 3.27 %

Fe203 4.12 %

K2Ô0 1.76 %

MgO 0.94 %

Na20 1.07 %

Step 2): Assemble the electrokinetic remediation device. The electrokinetic remediation test was conducted in a reactor consisting of five compartments, and the reactor is shown in Figure 1.

Parameters of the assembled electrokinetic remediation device: The electrokinetic remediation device in this embodiment uses the YK-AD5050 power supply from

Guangzhou Post & Telecom Equipment Co., Ltd. with a constant voltage of 2 V cmt.

The soil treatment capacity of the central compartment is 2 dm? (height = 10 cm, length = 20 cm, width = 10 cm). The electrode cells have a capacity of 0.6 dm? (6 cm x 10 cm x 10 cm) and each electrode cell is connected to a reservoir with a capacity of 0.6 dm? (6 cm x 10 cm x 10 cm), the reservoir being intended to collect a possible excess of electrolyte to avoid its overflow on the experimental bench. The removable cover plate 1 is used to facilitate the picking and placing of the soil with the addition of reagents, the reservoir 2 is used to store the electrolyte liquid, and the electrode chamber 3 is equipped with the graphite plate electrodes, the graphite plate electrode parameters: length = 110 mm, width = 60 mm, thickness = 10 mm. the soil chamber is divided into three parts: S1, S2 and S3 (from anode to cathode) to monitor the homogeneity of the

8 001879P-NL treatment. A steady flow orifice spacer 4 was used as a membrane filter to separate the soil chamber from the electrode cell. Removable nano zero-valent iron (nZVI) was set at a distance of 5 cm on the anode side. The nano zero-valent iron (nZVI) was used as described by filling nano zero-valent iron powder in folded A4 paper and then inserting the A4 paper into the contaminated soil along the longitudinal section of the remediation device. Figure 3 shows a picture of nano zero-valent iron and Figure 2 shows the actual use of the electrokinetic remediation device in Example 1 of the present invention.

Two groups were set up, where group “a” was the group with the addition of 5% hydrogen peroxide solution by mass concentration, and group “b” was the group with the addition of GLDA solution with a molar concentration of 0.1 mol/L and 5% (by mass concentration) hydrogen peroxide solution, and the pH of electrolyte was adjusted to about 5 (transition metal ions such as Fe? are soluble and dominant under acidic conditions, and under pH = 5 conditions, iron and other metals are relatively insoluble or have low solubility in most aqueous systems).

Step 3) Start the electrokinetic remediation device for electrokinetic remediation treatment: where the group settings are labeled as: group “a”: EK+ H202 (5%, ) + nZVl, group “bp”: EK+ H202 (5%) + GLDA (0.1 M) + nZVl. Record the changes before changing the solvent daily. Collect soil samples after 7 days to test the removal rate of organochlorine contaminants in the soil.

Step 4) 0.5 g of soil was mixed and stirred with 3 g of diatomaceous earth at 100°C and 1500 psi, and extracted with a mixture of hexane/acetone (5:1, v/v). The extraction solution was concentrated to 1 mL by rotary evaporator at 50°C. The concentrated solution was extracted by SPE (sulfated silica/sodium sulfate anhydrous) and eluted with hexane for 15 mL. The eluate was then concentrated to 1 mL and detected by

GC-uECD for organochlorine compounds.

Comparison example

This embodiment is basically the same as Example 1, with the difference that the mobile nano zero-valent iron (nZVI) is not provided at the anode in this comparison example.

9 001879P-NL

Three groups were set up for the experiment. Group 1 was a comparison group with only 0.1 mol/L GLDA solution added, Group 2 was a comparison group with only 5% hydrogen peroxide solution added, and Group 3 was a comparison group with both 0.1 mol/L GLDA solution and 5% hydrogen peroxide solution added.

The specific settings of the embodiments and the comparison groups are shown in

Table 2.

Table 2 Specific settings for each group for the example 1 and comparison example

Processing Soil (kg) Solvent Voltage Conditions (Vem)

Grout 20 ~~ 5%H.0. 2 pH50, 7days

Group 2 2.0 0.1 M GLDA 2 pH 5.0, 7days

Group 3 2.0 5% H202 + 0.1 M GLDA 2 pH 5.0, 7days

Group a 2.0 5% H20:2 + nZVI 2 pH 5.0, 7 days 5% H202 + 0.1 M GLDA+

Group b 2.0 2 pH 5.0, 7 days nZVI

The average removal rate statistics for each organochlorine pollutant are shown in

Table 3.

Table 3 Average removal rate statistics of each organochlorine pollutant 2 1,3,5- 1,2,4- 1,2,3- Dichloro-

Trichloro- Trichloro- Trichloro- Pentachloro- diphenyl-

Group benzene benzene benzene benzene trichloro- (1,3,5- (1,2,4- (1,2,3- (PeCB) ethane

TCB) TCB) TCB) (2,4 -

DDT) 5% H202 49.74% 5528% 40.82% 52.91% 45.13% 0.1 M GLDA 10.35% 15.25% 897% 12.43% 9.97%

10 001879P-NL 24 - 1,3,5- 1,2,4- 1,2,3- Dichloro-

Trichloro- Trichloro- Trichloro- Pentachloro- diphenyl-

Group benzene benzene benzene benzene trichloro- (1,3,5- (1,2,4- (1,2,3- (PeCB) ethane

TCB) TCB) TCB) (24 -

DDT) 5%H302+01M

GLDA 60.62% 59.62% 66.61% 62.57% 65.07% 5% H202 + nZVI 5261% 73.67% 53.07% 61.96% 65.67% 5% H202 + 0.1M

GLDA+ nZVI 69.43% 77.02% 68.35% 71.28% 72.02%

The results show that for organochlorine compounds such as 1,3,5-TCB, the removal rate of treatment with H202 alone is about 49.7%, because H202 is a strong oxidant that can attack and destroy the organic matter in the soil, easily contacting the contaminants and thus oxidizing the organochlorine compounds; on the other hand, there are some iron oxides and other components in the contaminated soil itself, and according to the nature of the test soil, it is known that the Fe Os content in the test soil is as high as 4.2%, and the electrochemical reaction process can be induced under the condition that the electrokinetic remediation device applies low direct current to the electrode placed in the soil, thus generating divalent iron ions (Fe?*) and thus inducing the Fenton reaction to generate HO-, so the organic pollutants in contaminated soil can also be oxidized by hydroxyl radicals generated by Fenton-like reactions occurring in the soil.

The removal rate of organochlorine compounds 1,3,5-TCB was about 52.6% after the

H2O: treatment and the simultaneous installation of nano zero-valent iron (nZVI) that could be moved at the anode cell (5 cm from the anode cell) of the electrokinetic remediation device, which improved the removal rate to some extent (by 2.9%) . because the reasons are: on the one hand, the addition of nZVI accelerates the Fe?* and Fe cyclic reaction in the Fenton-like reaction in the soil, which provides a continuous supply of Fe?* to the system; on the other hand, nZVI can reductively dechlorinate organochlorine pollutants (dechlorination occurs when organochlorine

11 001879P-NL compounds come into contact with nZVI), and the system has both oxidation and reduction effects, which can degrade organochlorine pollutants more efficiently and specifically.

On the basis of H202 treatment (without nZVI), GLDA was added to the soil simultaneously, and the removal rate of 1,3,5-TCB pollutants was 60.6%, which was 10.9% higher than that of 5% H20: treatment alone, mainly because glutamic acid N,N- diacetic acid could maintain soluble Fe?*. Although its solubility for organochlorine compounds in soil is poorer, but it contributes to the degradation of organochlorine compounds due to the enhanced Fenton-like reaction process. In the comparison example, the addition of GLDA to the soil alone showed an electric removal of 10.4% of organochlorine contaminants in the absence of oxidants. This result indicates that comparing to the H202 treatment alone, the increase in efficiency of the combination of H202 and glutamic acid N,N-diacetic acid is mainly reflected in the enhanced effect of glutamic acid N,N-diacetic acid on the Fenton-like reaction, and the increase in treatment efficiency is reflected in the joint contribution of H202 and glutamic acid N,N- diacetic acid (52.6% + 10.4% = 63%).

The electrokinetic remediation treatment applied to the contaminated soil by simultaneously adding GLDA to the soil in addition to the H202 treatment and installing nano zero-valent iron on the anodic side revealed that the above combined treatment showed a substantial increase in the removal of 1,3,5-TCB among organochlorine compounds, reaching 69.4%, an increase of 19.7% (compared to Hz202 treatment alone). This result indicates that there is a synergistic effect between GLDA, nano zero- valent iron and oxidant in the treatment system when electrokinetic remediation treats organochlorine compounds 1,3,5-TCB in soil, substantially increasing the removal rate of organochlorine pollutants and showing essentially the same result for other organochlorine pollutants except for organochlorine compounds such as 1,3,5-TCB.

Therefore, it can be concluded that the combination treatment of glutamate N,N- diacetic acid, electrokinetic remediation, nano zero-valent iron, and oxidant of the present invention synergistically removes organochlorine pollutants in soil, and can achieve a substantial increase in the removal rate of organochlorine pollutants in soil, while enabling in situ removal.

12 001879P-NL

The foregoing description of the disclosed embodiments enables a person skilled in the art to implement or use the present invention. A variety of modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the invention will not be limited to these embodiments shown herein, but will be subject to the widest scope consistent with the principles and novel features disclosed herein.

Claims (9)

13 001879P-NL Conclusions 1. A method for the removal of organic chlorine compounds from soil by advanced oxidation using chelating agents in combination with electrokinetic remediation, characterized by : the specific steps of: 1) transferring contaminated soil to an electrokinetic remediation device, adding of an oxidant and glutamic acid N,N-diacetic acid to that soil, and simultaneously setting nano-zero-valent iron near the anode of that electrokinetic remediation device; 2) adjustment of the pH of the electrolyte and activation of the electroremediation unit for the removal of organic chlorine compounds from the soil. 2. A method for the removal of organic chlorine compounds from soil by advanced oxidation using chelating agents in combination with electrokinetic remediation according to theorem 1, characterized by the fact that the oxidizing agent is at least one of the following substances: persulphate, hydrogen peroxide , permanganate and hypochlorite. The method of advanced oxidative synergistic electroremediation with chelating agents for the removal of organic chlorine compounds from the soil according to claim 1 or 2, provided that the pH of the electrolyte is adjusted to 4 to 5 in step 2). 4. The method for the removal of organic chlorine compounds from soil by chelating agent-enhanced advanced oxidative synergistic electroremediation according to theorem 3, provided that said zero-valent iron nanoparticles are located at a distance of 5 cm from the anode plate. The method of chelating agent-enhanced advanced oxidative synergistic electrokinetic remediation for the removal of organic chlorine compounds from soil according to claim 4, provided that the contaminated soil contains iron oxides of one or a combination of rhodochrosite, hematite or magnetite. 14 001879P-EN The method of chelating agent-enhanced advanced oxidative synergistic electroremediation for the removal of organic chlorine compounds from soil according to claim 1 or 2, provided that: said glutamic acid N,N-diacetic acid has a molar concentration of 1 mol/L. 7. The chelator-enhanced advanced oxidative synergistic remediation method for the removal of organochlorine compounds from soil according to claim 6, characterized in that: said hydrogen peroxide is present at a concentration of 5% by mass. 8. The method of chelating agent-enhanced advanced oxidative synergistic electroremediation for the removal of organic chlorine compounds from soil according to theorem 7, characterized in that said organic chlorine compounds are 1,3,5-trichlorobenzene, 1,2,4-trichlorobenzene, 1 ,2,3-trichlorobenzene, 1,2,4,5-tetrachlorobenzene, pentachlorobenzene, hexachlorobenzene, 4,4-DDT, 2,4 or 4,4-DDT. -DDT or one of the 4,4 -DDT. 9. The method for the removal of organic chlorine compounds from soil by means of chelator-enhanced advanced oxidation synergistic electrokinetic remediation according to statement 8, provided that the electrode material of said electrokinetic remediation device is one of the following materials: graphite, iron, titanium, stainless steel or an alloy.