Apparatus and method for remediating trichloroethylene-polluting soils by integrated rotated migration and PRB

Abstract

Apparatus and method are provided for remediating trichloroethylene-polluting soils by integrated rotated migration and PRB. The apparatus includes a device of electrokinetic remediation, a PRB and a device of injection of surface active agents. The main components of the device of electrokinetic remediation and PRB include cathode, anode, electrode chamber and PRB. A liquid injection pipe is installed between various electrodes and PRBs. The operation of each device is controlled by each control system. The disclosure integrated rotated migration and PRB for remediating contaminants. Surface active agents is helpful for dispersing TCE from soil. The arrangement of the electrode and the PRB greatly shortens distances and time of pollutant migration, which accelerate the speed of remediation and reduce post-processing procedures. In the process of treatment, the three technical methods promote each other, and have the advantages of good repair effect, short time, no secondary pollution and easy operation.

Claims

1. A device for remediating soil, comprising: a device of electrokinetic remediation and Permeable Reactive Barriers (PRBs), wherein the device of electrokinetic remediation comprises: at least two pairs of electrodes including a cathode part and an anode part for each pair, wherein the cathode parts and anode parts are arranged alternately with adjacent parts having different polarities, and forming a radially distributed pattern with an intersection angle between the adjacent parts in a range of 60-90, configured to generate a voltage gradient of 1.5-4.5 V/cm, wherein the trichloroethylene is absorbed by the PRBs distributed in a middle of the intersection angle coaxial with the radially distributed pattern, in a course of rotating migration along the radially distributed pattern, wherein the cathode parts and anode parts are plate electrodes disposed perpendicular to a horizontal plane of the trichloroethylene-polluted soil with an axis of the radially distributed pattern placed at a most polluted region, a stabilized voltage supply, in which electrodes connect with the supply by parallel connection, electrode chambers including an anode chamber and a cathode chamber accommodating the anode parts and cathode parts, respectively, wherein pH of the anode chamber and the cathode chamber are kept at approximately 11 and 3.5, respectively, an electrolytic bath with an anolyte tank for storing alkaline electrolyte and a catholyte tank for storing acidic electrolyte, in which the anolyte tank and the catholyte tank connect with the anode chamber and the cathode chamber respectively by a first peristaltic multi-channel pump to carry the alkaline electrolyte and the acidic electrolyte to the anode chamber and the cathode chamber through channels, a first control system, connected with various electrode chambers via the first peristaltic multi-channel pump to control delivery of the alkaline electrolyte from the anolyte tank to the anode chamber and the acidic electrolyte from the catholyte tank to the cathode chamber, wherein the first control system is further configured to monitor electrolyte saturation of each electrode chamber, an electrolyte treatment tank, connecting with various electrode chambers via a second peristaltic multi-channel pump to receive discharged electrolytes, a second control system, connected with various electrode chambers via the second peristaltic multi-channel pump to control discharge of electrolytes from various electrode chambers to the electrolyte treatment tank upon the electrolyte saturation as monitored by the first control system; and a device of injection configured to inject surface active agents comprising a 0.025 g/L rhamnolipid solution at an injection rate of 1.5-2.5 ml/min, including: a liquid injection pipe, installed in soil between various electrodes and PRBs for injecting surface active agents into polluted soil, a reservoir of surface active agents, connecting with the liquid injection pipe for storing surface active agents, and a third control system, connecting the liquid injection pipe and the reservoir of surface active agents to control injection of surface active agents.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a plan view of a cathode and an anode, an electrode chamber and a PRB in accordance with a mode of carrying out the disclosure;

(2) FIG. 2 is a perspective view of a cathode and an anode and a PRB in accordance with a mode of carrying out the disclosure;

(3) FIG. 3 is a diagram of connection of the device in accordance with a mode of carrying out the disclosure.

(4) Numerals in the drawing represent: 1an anode (where 1-1the first anode part, 1-2the second anode part), 2a cathode (where 2-1the first cathode part, 2-2the second cathode part), 3an anode compartment (where, 3-1the first anode compartment, 3-2the second anode compartment), 4a cathode compartment (where, 4-1the first cathode compartment, 4-2the second cathode compartment), 5 (5-1, 5-2, 5-3, 5-4)PRBs, 6a stabilized voltage supply, 7the first peristaltic multi-channel pump, 8the first control system, 9an anolyte tank, 10a catholyte tank, 11the second peristaltic multi-channel pump, 12the second control system, 13an electrolyte treatment tank, 14a liquid injection pipe, 15the third control system, and 16a reservoir of surface active agents.

DETAILED DESCRIPTION

(5) Further description of the present disclosure in accordance with accompanying drawings and concrete embodiments is as follows, but technician in this field should understand that the scope of the disclosure is not limited to the following concrete embodiments.

(6) According to a mode of carrying out the disclosure, a device for remediating trichloroethylene-polluted soil by rotating-migration and combination of PRB is shown in FIG. 1-3. The overall device is sealed, in which the positive electrode of Stabilized voltage supply 6 connects with first anode part 1-1 and second anode part 1-2 through wires and the negative electrode of Stabilized voltage supply 6 connects with 2-1the first cathode part and 2-2the second cathode part through wires; 1-1the first anode part, 1-2the second anode part, 2-1the first cathode part and 2-2the second cathode part are plate electrodes of coaxial placement that are perpendicular to the horizontal plane, where adjacent electrodes have different polarities and form certain intersection angles; 1-1the first anode part, 1-2the second anode part, 2-1the first cathode part and 2-2the second cathode part are placed in 3-1the first anode compartment, 3-2the second anode compartment, 4-1the first cathode compartment and 4-2the second cathode compartment respectively; Coaxial placement of PRB 5 is carried out between adjacent electrodes; 14a liquid injection pipe is installed between various electrode chambers and PRB 5; 16a reservoir of surface active agents connects with 14a liquid injection pipe through 15the third control system; 9an anolyte tank and 10a catholyte tank connect with 8the first control system by pipes; 8the first control system connects with various electrode chambers by 7the first peristaltic multi-channel pump; 13an electrolyte treatment tank connects with 12the second control system via pipes and 11the second peristaltic multi-channel pump and 12the second control system connects with each electrode chamber.

(7) A device of the disclosure can have two to four pairs of electrodes and two pairs of electrodes is an optimal option. Intersection angles between pairs of electrodes are determined in accordance with pollution degrees of soil. Intersection angles can be properly small for areas with severe pollution and vice versa. An intersection angle between adjacent cathode and anode should range from 60120 with an optimal scope of 6090. Of course, under special circumstances, an intersection angle can be less than 60, such as 25, 20 and 15.

(8) In the mode of carrying out the disclosure shown in the drawings, there are two pairs of electrodes with an intersection angle of about 90.

(9) Generally, electrodes are plates and graphite can be used as both cathode and anode. The size of an electrode relates to the degree of pollution (for example, depths and scopes etc. of polluted soil). Electrodes of proper sizes should be prepared so that the device can cover the entire area of polluted soil after its installation.

(10) Due to radial arrangement of electrodes, pollutants in soil follow rotating routes during their migration. Thus, the device of the disclosure is called a device for remediating trichloroethylene-polluting soil by rotating-migration and combination of PRB.

(11) PRBs are placed between various electrodes in a radial pattern. It would be best to place a PRB in the middle of an intersection angle between cathode and anode. Similarly, PRBs are plates and their sizes are in connection with pollution conditions.

(12) PRBs are PRBs of zero-valent iron and can be padded with adsorbents, such as coarse sand and immobile peat, inside.

(13) With the device above, the method for remediating trichloroethylene-polluted soil by rotating-migration and combination of PRB is used and steps of the method are:

(14) After ensuring that the entire polluted area is covered, install electrode chambers and electrodes. Carry out coaxial placement of four plate electrodes that are perpendicular to the horizontal plane and the co-axis of four plate electrodes should be located in the most polluted area. Polarities of adjacent electrodes are different and they form certain intersection angles. Each electrode lies in an electrode chamber. Coaxial placement of PRB 5 is carried out between adjacent electrodes and a liquid injection pipe is installed between various electrode chambers and PRB 5. The positive electrode of Stabilized voltage supply 6 connects with First anode part 1-1 and Second anode part 1-2 through wires and the negative electrode of Stabilized voltage supply 6 connects with 2-1the first cathode part and 2-2the second cathode part through wires. Installation of other parts is shown in FIG. 3.

(15) Operate each electrode chamber and PRB 5 by 15the third control system at an injection speed of 1.52.5 ml/min and stop operation after 612 h.

(16) Add corresponding alkaline electrolytes and acidic electrolytes in 9an anolyte tank and 10a catholyte tank respectively. After turning on the device of electrokinetic remediation, 9an anolyte tank and 10a catholyte tank deliver electrolytes to corresponding anode compartments and cathode compartments respectively through 7the first peristaltic multi-channel pump and under 8the first control system. After initiating the system of electrokinetic remediation, during rotating-migration, pollutants are absorbed by PRB 5 with a voltage gradient of 1.54.5 v/cm. In the process of remediation, keep monitoring electrolyte saturation of each electrode chamber at the same time. If the electrolyte of an electrode chamber is saturating, extract electrolytes of corresponding electrode chambers and transfer them to 13an electrolyte treatment tank respectively through 11the second peristaltic multi-channel pump and under 12the second control system. After electrifying for 2448 h, turn off Stabilized voltage supply 6.

(17) According to remediation conditions, repetition of steps of surface active agent injection and rotating-migration is feasible. During remediation, keep monitoring the concentration of TCE in the polluted area and evaluating the remediation effects until TCE in soil reaches the environmental standard.

(18) In the method for remediating trichloroethylene-polluted soil by rotating-migration and combination of PRB of the disclosure, adjustment of numbers of electrode pairs, intersection angles between adjacent electrodes, lengths of various electrodes and PRBs, intersection angles between various electrodes and PRBs and replacing times of PRBs can be conducted in accordance with conditions of polluted soil. However, different polarities of adjacent electrodes should be ensured.

Embodiment

(19) (1). Preparation of simulation samples of soil polluted by TCE: gather a soil sample of 1500 g and fire it at a 600 C. with muffle until it reaches constant mass. Screen the sample with a griddle with 1 mm aperture (namely griddle No. 18). Then add TCE in the sample until the concentration of TCE in the sample is 100 mg/kg. Put the sample in a plexiglass box of a radius of 20 cm and a height of 20 cm.

(20) (2). Installation of a device for remediating trichloroethylene-polluted soil by rotating-migration and combination of PRB: as shown in FIGS. 1-3, install the device in the plexiglass box. Both cathode and anodes are graphite plate electrodes with a specification of 15 cm2 cm15 cm (LWH). Coarse sand and immobile peat are padded in PRBs as mediums (with a ratio of 4:1) with a specification of 15 cm2 cm15 cm (LWH).

(21) (3). Operation of the device: first, the injection device of surface active agents is started, in which 0.025 g/L rhamnolipid solution is used as the surface active agent and the injection amount of surface active agents is 2.5 times of the volume of the restored soil. During remediation, pH of the anode compartment and the cathode compartment should be 11 and 3.5 respectively.

(22) Results: after electrokinetic remediation, the concentration of TCE in the polluted area was monitored. According to calculation, the removing rate of TCE in soil was 75.6%. After repeating usage of the device, the rate became 84.3%.

Comparison Embodiment

(23) Compared with the embodiment above, the only difference of these two embodiments is parallel arrangement of a pair of electrodes, PRBs between electrodes and injection pipes between electrodes and PRBs. The area of electrodes is the same as that of the embodiment above, so is the area of PRBs. In addition, experimental environments, experimental procedures and experimental parameters etc. of this embodiment are the same as those of the embodiment above. The result showed that after the first operation, the removing rate of TCE in soil was 57.5% and after repeating usage of the device, the rate became 62.6%.