CN108262355B - Electric cooperative remediation method for composite contaminated soil based on partitioned electric field - Google Patents

Abstract

The invention relates to a contaminated soil remediation technology, in particular to a composite polluted soil electrodynamic synergistic remediation method based on a partitioned electric field. Specifically, according to the electrokinetic migration-enrichment of heavy metals and chemical oxidation of organic pollutants, the electrode group is energized at intervals, the polarity of the electrodes is controlled, and a subregional electric field is constructed, including the heavy metal migration area/organic pollutants biodegradation-chemical oxidation alternation area, heavy metal enrichment area/organic pollutant biodegradation area, heavy metal precipitation area/organic pollutant biodegradation area. Through the non-isochronous alternating operation of the partitioned electric field, the enrichment of heavy metals and the enhanced degradation of organic pollutants can be realized in space, and the synergistic removal of heavy metals and organic pollutants can be realized in time.

Description

Electrodynamic synergistic remediation method of composite polluted soil based on partitioned electric field

technical field

The invention belongs to the technical field of polluted soil remediation, in particular to a method for electrodynamic synergistic remediation of heavy metal-organic composite polluted soil based on a partitioned electric field.

Background technique

The current soil pollution has changed from single pollution to compound pollution. Pollutants can be divided into heavy metals and organic pollutants. The physicochemical properties and removal mechanisms of the two are quite different. Heavy metals are mainly separated from soil by physical means such as desorption, while organic pollutants are mainly removed from soil by biodegradation.

At present, the remediation technologies of compound polluted soil mainly include phytoremediation, chemical leaching, and electric remediation. A comprehensive comparison of the above three remediation methods shows that phytoremediation has a slow speed and low efficiency, and is not suitable for high-concentration site pollution; chemical leaching has high costs and is likely to cause secondary pollution, and is not suitable for in-situ remediation and low-permeability soils. Electric repair is an economical, safe and efficient repair method. Electric remediation has a good remediation effect on heavy metals and organic pollutants. Its remediation mechanism is specifically under the electrokinetic effect. On the one hand, heavy metals are desorbed from the surface of soil particles, and the heavy metals are directionally migrated and precipitated; Functional microorganisms that accelerate the biodegradation of organic pollutants.

Therefore, according to the mechanism of electrokinetic removal of heavy metals and organic pollutants in soil, if the difference in the reaction process and time of electrokinesis is fully utilized, the synergistic removal of heavy metals and organic pollutants can be achieved, providing an efficient technology for the synergistic remediation of composite polluted soils. .

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for electrokinetic synergistic restoration of heavy metal-organic composite polluted soil based on a partitioned electric field.

In order to achieve the above purpose, the technical solution adopted in the present invention is: an electrodynamic coordinated restoration method for composite polluted soil based on a subregional electric field, comprising the following steps:

The electrode group set in the soil is energized at intervals, the electrode polarity is controlled, and the partitioned electric field is constructed;

Non-isochronous alternate operation of subregional electric fields to achieve synergistic remediation of heavy metal-organic polluted soils.

The electrode groups are in multiple groups and are arranged in sequence; there are intervals between any adjacent electrode groups.

The electrode set includes a pair of electrodes with the same polarity.

The center line of the pair of electrodes is perpendicular to the arrangement direction of the electrode groups.

The interval energization specifically means that when the electrodes of the electrode group arranged in odd or even numbers are energized, the adjacent electrodes of the energized electrodes are not energized.

The control electrode polarity specifically refers to: in an odd-numbered or even-numbered electrode group, the polarity of the adjacent electrode group is opposite; the odd-numbered electrode group has the same polarity as its adjacent even-numbered electrode group.

The construction of the partitioned electric field is as follows:

(1) Between the electrode group P _i and the electrode group P _i+1 electrode is the heavy metal migration area/organic pollutant biodegradation-chemical oxidation alternating area, that is, the Ri area; _i =1, 2, 3...;

(2) The area between the electrode group P _i+1 and the electrode group P _i+2 is the heavy metal enrichment area/organic pollutant biodegradation area, that is, the R _i+1 area;

(3) Between the electrode group P _i+2 and the electrode group P _i+3 electrode is the heavy metal precipitation area/organic pollutant biodegradation area, that is, the R _i+2 area.

The said non-isochronous alternately operating subregional electric field specifically refers to:

Operation mode 1, the electrode group P _i is the positive electrode, the electrode group P _i+2 is the negative electrode, the electrode group P _i+1 and the electrode group P _i+3 are not energized, and the operating time T ₁ is the concentration of heavy metals in R1 in R2. until it exceeds the set value.

The said non-isochronous alternately operating subregional electric field specifically refers to:

Operation mode 2, the electrode group Pi ₊₁ is the positive electrode, the electrode group Pi ₊₃ is the negative electrode, the electrode group _Pi and the electrode group Pi _{+2 are} not energized, and the operating time T2 is when the soil acid-base mutation surface in the _R3 area is stable. After that, the amount of heavy metals precipitated on the acid-base mutation surface is greater than the time required for the set value.

The present invention has the following advantages and beneficial effects:

The invention realizes the enrichment of heavy metals and the enhanced degradation of organic pollutants in space by fully utilizing the directional migration of heavy metals and the chemical oxidation of organic pollutants by electric field through the construction of subregional electric fields and the switching of operation modes, and the realization in time. Synergistic removal of heavy metals and organic pollutants.

Description of drawings

1 is a schematic diagram of an apparatus according to an embodiment of the present invention;

FIG. 2a is a first method of electrode arrangement and polarity switching according to an embodiment of the present invention;

FIG. 2b is a second method of electrode arrangement and polarity switching according to an embodiment of the present invention.

Detailed ways

The present invention will be further described below with reference to specific embodiments and the accompanying drawings.

According to the electrokinetic migration-accumulation of heavy metals and chemical oxidation of organic pollutants, the electrode group is energized at intervals, the electrode polarity is controlled, and a subregional electric field is constructed; the subregional electric field is operated alternately non-isochronously to realize the coordinated restoration of heavy metal-organic contaminated soil. .

The construction method of the partitioned electric field specifically refers to:

(1) Electrode group, specifically including 4 groups of electrodes, which are P1, P2, P3, and P4 in sequence;

(2) Interval energization, specifically, when the interval electrode is energized, the adjacent electrodes of the energized electrode are not energized;

(3) Electrode polarity, specifically, the polarities of the spacer electrodes (P1 and P3, P2 and P4) are opposite, and the polarities of the adjacent electrodes (P1 and P2, P3 and P4) are the same.

According to the different effects of electrokinetics on heavy metals and organic pollutants, the functions of the electric fields in each partition are as follows:

(1) Between the P1 and P2 electrodes is the heavy metal migration area/organic pollutant biodegradation-chemical oxidation alternating area, that is, the R1 area;

(2) Between the P2 and P3 electrodes is the heavy metal enrichment area/organic pollutant biodegradation area, namely the R2 area;

(3) Between the P3 and P4 electrodes is the heavy metal precipitation area/organic pollutant biodegradation area, namely the R3 area.

The non-isochronous alternating operation of the partitioned electric field, specifically:

(1) Operation mode 1, P1 is the positive electrode, P3 is the negative electrode, P2 and P4 are not energized, and the operating time T1 is the enrichment amount of heavy metals in R1 in R2 (from the current value) until it is greater than the set value (eg: ≥80% ) the time required;

(2) Operation mode 2, P2 is the positive electrode, P4 is the negative electrode, P1 and P3 are not energized, and the operating time T2 is when the acid-base mutation surface of the soil in the R3 area is stabilized. The time required to set the value (eg: ≥80%).

As shown in Figure 1, the devices used in electric repair include soil chambers, electrodes, power supplies, and current and voltage monitoring systems. The contaminated soil is mixed with organic pollutant-degrading bacteria, and its moisture content is adjusted to 20% to 30%, and placed in the soil chamber. An appropriate amount of deionized water was added to the soil during the run to balance water loss.

Four groups of electrodes were arranged in the soil chamber, P ₁ , P ₂ , P ₃ , and P ₄ in sequence. In order to keep the voltage constant, two DC power sources are used in the experiment, and the electrodes are connected with the power sources by wires, P1 is connected with the positive pole of the power supply ₁ , P3 is connected with the negative pole of the power supply ₁ , P2 is connected with the positive pole of the power supply ₂ , and P4 is connected with the negative pole of the power supply 2. . _The reaction zone is correspondingly divided into the R1 zone between the P1 and _P2 electrodes, the _R2 zone between the _P2 and _P3 electrodes, and the _{R3 zone} between the _P3 and P4 electrodes _.

The two non-isochronous operating modes of electric repair are:

Operation mode 1: As shown in Figure 2a, turn on the power supply ₁ and turn off the power supply ₂ , that is, the electrode P1 and the electrode _P3 are energized, wherein P1 is the positive electrode, _P3 is the negative electrode, the electrode _P2 and the electrode _P4 are not energized, and the reaction The region range is R ₁ ∪ R ₂ .

_The run time was determined by the heavy metal enrichment in the R2 zone. Specifically, through experiments, the electromigration speed of heavy metals in soil was measured under different pH gradient conditions. When the enrichment of heavy metals in R ₁ in R ₂ ≥ 80%, the operation of mode 1 was terminated, and the running time was recorded as T ₁ .

At the same time, the organic pollutants near the electrode P1 are removed by chemical oxidation, and the organic pollutants in other regions are degraded by biological degradation, forming _a dual effect of chemical oxidation-biodegradation. Therefore, in the reaction process, R ₁ is the heavy metal migration area/organic pollutant biodegradation-chemical oxidation alternating area, and R ₂ is the heavy metal enrichment area/organic pollutant biodegradation area.

Mode ₂ : As shown in Figure 2b, turn off the power supply ₁ and turn on the power supply ₂ , that is, the electrode P2 and the electrode P4 are energized, wherein the electrode P2 is the anode, the electrode _P4 is the cathode, and the electrode _P1 and the electrode _P3 are not energized, The reaction zone range is R ₂ ∪ R ₃ .

The running time was determined by the amount of heavy metal precipitation after the soil acid-base abrupt change surface in the _R3 area was stabilized. Specifically, through batch experiments, it is determined that after the soil acid-base mutation surface is stabilized, when the precipitation amount of heavy metals on the acid-base mutation surface is ≥80%, the mode 2 operation is terminated, and the operation time is recorded as T ₂ .

At the same time, the organic pollutants near the electrode P2 _were removed by chemical oxidation, and the organic pollutants in other areas were degraded by biodegradation, but mainly biodegradation. Therefore, in the reaction process, R ₂ is the heavy metal enrichment area/organic pollutant biodegradation area, and R ₃ is the heavy metal precipitation area/organic pollutant biodegradation area.

Therefore, the synergistic removal of heavy metals and organic pollutants in the soil is realized through the non-isochronous alternate operation of the electrodes P ₁ -P ₃ and the electrodes P ₂ -P ₄ .

Example 1

The polluted soil repaired in this example is self-mixing Cd and pyrene composite polluted soil. The clean soil was collected from 0-20 cm topsoil in Shenbei New District, Liaoning Province, and the soil was loam. The soil from which the stones and plant roots were removed was naturally air-dried and passed through a 20-mesh sieve, and then artificially prepared into a composite polluted soil with a concentration of about 100 mg/kg of Cd and pyrene. The soil pH was measured to be 6.1 after the contaminated soil was air-dried. The pyrene-degrading bacteria stored in the laboratory were activated, and the suspension was mixed with the contaminated soil, and the soil humidity was adjusted to 30% with deionized water, and then loaded into the soil chamber. The specific specifications of the soil chamber are: length 32cm, width 17cm, and height 10cm. An appropriate amount of deionized water was added to the soil during the run to balance water loss.

The repair device used in the embodiment of the present invention is shown in FIG. 1 , and the device mainly includes a soil chamber, an electrode, a power supply, and a voltage and current monitoring system. Four groups of electrodes were set up in the polluted soil, which were P ₁ , P ₂ , P ₃ , and P ₄ in sequence. The electrodes are all stainless steel cylindrical electrodes with a diameter of 1 cm and a height of 10 cm. Electrode P1 and electrode _P4 are placed at _both ends _of the soil chamber, and meet 30cm, the distance between electrode P2 and electrode P1 is _13cm , and the distance between electrode _P3 and electrode P1 is _25cm . In order to maintain a constant voltage gradient, 2 DC power supplies were used in the experiment, in which the voltage of power supply 1 was 25V, and the voltage of power supply 2 was 17V. The electrodes are connected with the power supply by wires, P1 is connected with the positive pole of the power supply ₁ , _P3 is connected with the negative pole of the power supply ₁ , P2 is connected with the positive pole of the power supply ₂ , and P4 is connected with the negative pole of the power supply 2. _The reaction zone is correspondingly divided into the R1 zone between the P1 and _P2 electrodes, the _R2 zone between the _P2 and _P3 electrodes, and the _{R3 zone} between the _P3 and P4 electrodes _.

The electric repair runs for a total of 60 days and is divided into two operating modes:

Operation mode 1: Turn on the power supply ₁ , turn off the power supply ₂ , that is, the electrode P1 and the electrode _P3 are energized, wherein P1 is the positive electrode, _P3 is the negative electrode, the electrode P2 and the electrode _P4 are not energized, and the range _of the reaction zone is _R1∪ R ₂ . Among them, R ₁ is the heavy metal migration area/organic pollutant biodegradation-chemical oxidation alternating area, and R ₂ is the heavy metal enrichment area/organic pollutant biodegradation area.

_The run time was determined by the Cd enrichment in the R2 region. Through experiments, it was determined that under the condition of a voltage gradient of 1V/cm, when Cd was at pH=2.5, 3.5, 4.5, 5, 5.5, 6, and 6.5, the migration speed of Cd in soil was about 10cm/d and 6.6cm/d, respectively. d, 4.9 cm/d, 3.2 cm/d, 1.9 cm/d, 0.2 cm/d, 0 cm/d, and the average moving speed of the acid toward the cathode is about 0.9 cm/d. Based on the above speed calculation, when the enrichment of heavy metals in R ₁ is greater than or equal to 80% in R ₂ , it needs to run for 18 days, that is, the mode 1 time T ₁ =18 days. At the same time, pyrene was removed under the dual action of chemical oxidation and biodegradation.

Operation mode ₂ : Turn off the power supply ₁ and turn on the power supply ₂ , that is, the electrode P2 and the electrode P4 are energized, wherein the electrode P2 is the anode, the electrode _P4 is the cathode, the electrode P1 and the electrode _P3 are not energized, and the range _of the reaction zone is R ₂ ∪R ₃ . Among them, R ₂ is the heavy metal enrichment area/organic pollutant biodegradation area, and R ₃ is the heavy metal precipitation area/organic pollutant biodegradation area.

The running time was determined by the amount of Cd precipitation after the soil acid-base mutation surface in the _R3 area was stabilized. Experiments show that soil pH is stable after 8 days, and when the amount of heavy metal precipitation on the acid-base mutation surface is greater than or equal to 80%, the running time is 12 days, that is, the mode 2 time T ₂ =12 days. At the same time, pyrene is mainly removed by biodegradation.

Therefore, through the alternate operation of the two modes, after a total of 60 days of treatment (T ₁ ×2+T ₂ × ₂ ), the enriched Cd in the R2 area accounted for 85.7% of the total Cd content in the soil, and the pyrene in the soil was 85.7%. The total removal rate reached 68.6%.

Example 2

The difference from Example 1 is that the soil used in the experiment is self-prepared Cd and n-hexadecane composite polluted soil, the Cd concentration is 200 mg/kg, and the n-hexadecane concentration is 500 mg/kg. The total processing time is 60 days, the run time of mode one is 16 days; the run time of mode two is 14 days. After 60 days of treatment, 84.3% of the Cd in the soil was enriched in the R2 zone, and the total removal rate of n _- hexadecane in the soil reached 57.3%.

Example 3

The difference from Examples 1 and 2 is that the pollutants in the soil are various heavy metals and organic substances. The soil used in the experiment is the polluted soil around the smelter. The heavy metal pollutants in the soil are mainly Pb, Cd, Zn, Ni, Cu, etc. The concentrations are 98.73mg/kg, 8.64mg/kg, 105.52mg/kg, 35.68mg/kg , 25.84mg/kg, organic pollutants are mainly polycyclic aromatic hydrocarbons, the total concentration of 16 kinds of EPA priority control polycyclic aromatic hydrocarbons is 563mg/kg. The total processing time was 45 days.

According to the experimental results, under the same pH condition, the migration speed of Cu in the soil is the slowest among the _five heavy metals, so the Cu enrichment in the R2 region is calculated, and the operation time of the mode one is determined, that is, the mode _one time T1 = 25 days. According to the amount of Cu precipitation after the soil acid-base abrupt change surface in the _R3 area was stabilized, the operation time of the second mode was determined, that is, the mode two time T ₁ =20 days.

After 45 days of treatment, the amount of heavy metals Pb, Cd, Zn, Ni, and Cu enriched in the _R2 area accounted for 44.3%, 62.5%, 65.6%, 59.3%, and 32.6% of the total content in the soil, respectively. The removal rate of PAHs reached 36.3%.

The above content is a further detailed description of the present invention in combination with specific preferred implementation cases, and it cannot be considered that the specific implementation of the present invention is limited to this. On the premise of not departing from the concept of the present invention, some simple deductions or substitutions can also be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (4)

1. The electro-dynamic synergistic restoration method of composite polluted soil based on subregional electric field is characterized in that comprising the following steps: The electrode group set in the soil is energized at intervals, the electrode polarity is controlled, and the partitioned electric field is constructed; Non-isochronous alternate operation of subregional electric fields to achieve synergistic remediation of heavy metal-organic contaminated soil; The electrode groups are in multiple groups and are arranged in sequence; there are intervals between any adjacent electrode groups; The interval energization specifically refers to that when the electrodes of the electrode group arranged in odd or even numbers are energized, the adjacent electrodes of the energized electrodes are not energized; The said non-isochronous alternately operating subregional electric field specifically refers to: Operation mode 1, the electrode group P ₁ is the positive electrode, the electrode group P ₃ is the negative electrode, the electrode group P ₂ and the electrode group P ₄ are not energized, and the operating time T ₁ is the enrichment amount of the heavy metals in the R ₁ area in the R ₂ area until more than the time required to set the value; The said non-isochronous alternately operating subregional electric field specifically refers to: Operation mode 2, the electrode group P ₂ is the positive electrode, the electrode group P ₄ is the negative electrode, the electrode group P ₁ and the electrode group P ₃ are not energized, and the operating time T ₂ is that after the soil acid-base mutation surface in the _R3 area is stabilized, the heavy metals are in the acid-base state. The time required for the amount of sedimentation of the abrupt surface to be greater than the set value. 2 . The electrodynamic synergistic remediation method for composite polluted soil based on a partitioned electric field according to claim 1 , wherein the electrode group comprises a pair of electrodes with the same polarity. 3 . 3 . The electrodynamic synergistic remediation method for composite polluted soil based on a partitioned electric field according to claim 2 , wherein the center line of the pair of electrodes is perpendicular to the arrangement direction of the electrode group. 4 . 4. The electrodynamic synergistic remediation method for composite polluted soil based on subregional electric field according to claim 1, is characterized in that: described constructing subregional electric field is as follows: (1) Between the electrode group P _i and the electrode group P _i+1 electrode is the heavy metal migration area/organic pollutant biodegradation-chemical oxidation alternating area, that is, the Ri area; _i =1, 2, 3...; (2) The area between the electrode group P _i+1 and the electrode group P _i+2 is the heavy metal enrichment area/organic pollutant biodegradation area, that is, the R _i+1 area; (3) Between the electrode group P _i+2 and the electrode group P _i+3 electrode is the heavy metal precipitation area/organic pollutant biodegradation area, that is, the R _i+2 area.

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