Method for electrically activated persulfate remediation of contaminated river sediments

Abstract

The application provides a method for repairing polluted river sediment by electrically activated persulfate, which comprises the following steps: arranging anode and cathode electrodes in a water area, and adding persulfate at the anode electrode; in the initial operation, the anode electrode is connected to the positive pole of a power supply, and the cathode electrode is connected to the negative pole of the power supply; when the redox potential reaches a threshold value, the positive and negative poles of the power supply are switched. In the repairing process, when the anode redox potential is greater than or equal to 800 mV, the toxic intermediate product generated by the oxidation of the anode plate in the initial stage is reduced by switching the positive and negative poles of the power supply, so that the toxicity of the intermediate product is effectively reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sludge treatment, and particularly relates to a method for repairing river pollution sediment by electrically activated persulfate. BACKGROUND

[0002] With the improvement of industrialization and urbanization, the problem of river sediment pollution has become an issue that cannot be ignored, among which organic pollution is particularly prominent. These organic pollutants mainly come from pesticide and fertilizer residues in agricultural activities, industrial wastewater discharge and urban domestic sewage, etc. These pollutants gradually accumulate in the sediment, which has a serious impact on the water quality and ecological environment of rivers and lakes. The current sediment remediation technology mainly includes ex-situ remediation and in-situ remediation. Although the ex-situ remediation technology can greatly eliminate the impact of sediment on the overlying water quality, it has high operation difficulty and cost, and may cause devastating damage to the benthic ecosystem. The in-situ remediation technology directly carries out on the pollution site without excavating and transporting the sediment, which greatly reduces the risk of secondary pollution and protects the riverbed structure from being damaged. At the same time, the technology cost is relatively low, the operation is simple, and it is more in line with the concept of sustainable development.

[0003] The electrically activated persulfate remediation technology is a kind of in-situ chemical remediation technology for sediment. This technology can accelerate the activation process of persulfate through the action of an electric field, and reduce the amount of chemical reagents used. At the same time, the oxidant can be effectively transported to the pollution area through electro-osmosis and electromigration, which significantly improves the degradation efficiency of organic pollutants in sediment. In recent years, it has attracted widespread attention. However, there are still some limitations in its practical application. A large amount of toxic intermediates such as aldehydes, ketones and sulfides are produced in the process of anodic oxidation of organic matter. These intermediates will cause serious harm to the environmental quality of the pollution area if not treated. SUMMARY

[0004] In view of the deficiencies in the prior art, the application provides a method for repairing river pollution sediment by electrically activated persulfate, to solve the problem of toxic intermediates such as aldehydes, ketones and sulfides produced in the process of anodic oxidation of organic matter.

[0005] The application achieves the above technical purpose through the following technical means.

[0006] A method for repairing river pollution sediment by electrically activated persulfate: arranging anode and cathode electrodes in the water area, and adding persulfate at the anode electrode; when the initial operation, the anode electrode is connected to the positive pole of the power supply, and the cathode electrode is connected to the negative pole of the power supply; when the oxidation-reduction potential reaches the threshold value, the positive and negative poles of the power supply are switched.

[0007] Further, the electrode is a mesh plate structure.

[0008] Further, a plurality of electrodes are arranged in the form of a rectangular array.

[0009] Further, the material of the anode is inert metal, and the material of the cathode is copper, graphite or stainless steel.

[0010] Further, the material of the anode is tin dioxide, lead dioxide or boron-doped diamond.

[0011] Further, the distance between the anode plate and the cathode plate in the same group is 2-2.5 m, the lateral distance between the adjacent two groups of electrodes is 2-3 m, and the longitudinal distance is 1-2 m.

[0012] Further, the electric field strength is 300-400 V / m.

[0013] Further, when the redox potential is greater than or equal to 800 mV, the positive and negative poles of the power supply are switched; when the redox potential is less than or equal to -200 mV, the repair is ended.

[0014] Further, the persulfate salt is sodium persulfate, ammonium persulfate or potassium persulfate, and the ratio of the chemical demand to the persulfate concentration is 4-4.8.

[0015] Further, the electrodes are powered and operated for 8-11 hours per day.

[0016] The beneficial effects of the present application are:

[0017] (1) The present application provides a method for repairing river pollution sediment by electrically activating persulfate salt, when the persulfate salt is added to the system, the sulfate radical is generated by electric activation, and the oxidant is effectively transported to the pollution area by electro-osmosis and electromigration, effectively degrading the organic pollutants in the sediment. At the same time, the acidic environment produced after oxidation is more conducive to the dissolution and migration of heavy metals, and the removal effect of electric repair on heavy metals is enhanced.

[0018] (2) During the repair process of the present application, when the anode redox potential is greater than or equal to 800 mV, the positive and negative poles of the power supply are switched, so that the toxic intermediate products produced by the oxidation of the anode plate in the initial stage are reduced, thereby effectively reducing the toxicity of the intermediate products. For example, taking aldehydes and ketones as examples, the aldehydes and ketones are provided with electrons by the cathode, so that the carbonyl group (C=O) in the molecule is converted into the hydroxyl group (·OH) of alcohol.

[0019] The hydrogen reduction reaction of aldehyde can be written as:

[0020] RCHO + H2→ RCHOH (wherein R is an organic group);

[0021] The hydrogen reduction reaction of ketone can be written as:

[0022] RCOR' + H2→ RCHOR' (wherein R and R' are organic groups).

[0023] (3) In this invention, the electrode is a mesh structure, which helps to distribute the current more evenly, increase the electrolysis area, enhance the electrolyte flow, reduce the residence time of bubbles on the electrode surface, improve electrolysis efficiency and reduce energy consumption. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the electrode arrangement in this invention from a top view. Detailed Implementation

[0025] Embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein similar or identical reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0026] like Figure 1 The diagram shows a top-down view of the electrode layout. The area outlined by the dashed line represents a group of positive and negative electrodes. The electrodes used are mesh structures, with the anode plate made of an inert metal such as tin dioxide, lead dioxide, or boron-doped diamond; the cathode plate is made of copper, graphite, or stainless steel. The spacing between the anode and cathode plates in the same group is 2–2.5 meters. Multiple electrode groups are arranged in a rectangular array, with a lateral spacing (between electrode plates) of 2–3 meters between adjacent groups and a longitudinal spacing (between electrode ends) of 1–2 meters.

[0027] Example 1

[0028] The water quality in an artificial lake in a city park has been declining year by year, with high levels of organic pollutants in the bottom sediment. To address this, an electrode array was deployed as described above. The horizontal spacing between electrode groups is 2 meters, the vertical spacing is 1.5 meters, and the spacing between the anode and cathode plates within the same group is 2.5 meters. The anode is made of tin dioxide, and the cathode is made of copper.

[0029] Each group of electrodes was connected to a power source, and the electric field strength was adjusted to 300V / m via a DC voltage regulator, with a backflow prevention protection device installed. Sodium persulfate was added to the anode of each electrode plate at a ratio of 4:1 (chemical requirement to persulfate concentration). The entire remediation process consisted of two stages:

[0030] Phase 1, Routine Repair Phase: During initial operation, the anode plate is connected to the positive terminal of the power supply, and the cathode plate is connected to the negative terminal. The system is set to operate from 9:00 AM to 6:00 PM daily. The termination of Phase 1 is determined by monitoring whether the oxidation-reduction potential reaches the 800mV threshold.

[0031] Stage 2, electrode replacement stage: after the repair in stage 1 is continued for 4 months, it is found that the redox potential reaches 800 mV; then, the positive and negative positions in each electrode group are replaced, that is, the anode plate is connected to the negative electrode of the power supply, and the cathode plate is connected to the positive electrode of the power supply. During this period, the power is still kept on from 9 am to 18 pm. When the redox potential is ≤-200 mV, it is considered that the repair is completed.

[0032] After 5 months of continuous repair in stage 2, the redox potential reaches -200 mV, and it is found that the water quality of the lake is significantly improved. The organic matter content in the sediment decreases from 8.59% to 1.97%, and the degradation rate reaches 77.1%. After analyzing the organic components of the sediment before and after the repair, it is found that the content of ammonium carbamate in the sediment before the repair is the highest, which has slight toxicity. Secondly, there are benzene, toluene, octanal, benzene ethylamine and other aromatic compounds, which can make the river emit a fishy and pungent odor. After the repair, in addition to a large amount of oxalic acid released from the destroyed plant debris, the main detected substances are mainly alkanes and alkenes.

[0033] The organic components (content greater than or equal to 1%) of the sediment before and after the repair are shown in Table 1 and Table 2:

[0034] Table 1: Organic components of the sediment before the repair

[0035]

[0036]

[0037] Table 2: Organic components of the sediment after the repair

[0038] Name Molecular formula Peak area Relative abundance Oxalic acid C2H2O4 21089976 26.33 Styrene C8H8 6164484 7.70 Hexamethylcyclotrisiloxane C6H18O3Si3 5253104 6.56 Toluene C7H8 3853755 4.81 Methylpropenal C4H6O 2424570 3.03 Benzene C6H6 2277195 2.84 Cyclohexane C6H12 1907009 2.38 Octamethylcyclotetrasiloxane (CH3)8Si4O4 1332934 1.66 Cyclopropane C10H20 1094821 1.37 Cis-9-tricosene C23H46 995266 1.24 1-Tetradecene C14H28 813034 1.02 O-Xylene C8H10 797508 1.00

[0039] Based on Table 1 and Table 2, the relative content changes of various organic pollutants in the sediment before and after the repair are analyzed as shown in Table 3:

[0040] Table 3: Changes in the content of organic matter before and after the repair

[0041] Organic species Before test (%) After test (%) Nitrogen-containing compounds 39.3 1.51 Others 21.57 16.17 Aldehydes, ketones, alcohols, esters 10.99 8.43 Benzene series 9.53 10.61 Olefins 5.36 2.71 Alkanes 4.61 5.67 Heterocycles 3.8 13.88 Silicon-containing substances 3.07 9.26 Carboxylic acids 1.49 29.51 Polycyclic aromatic hydrocarbons 0.28 1.25

[0042] As can be seen from Table 3, the repair method proposed by the present application has the best treatment effect on nitrogen-containing compounds in the sediment, with a degradation rate of 96.15%; the degradation rate of olefins is 48.89%; and aldehydes and alcohol substances can be oxidized to carboxylic acids. At the same time, when the repair is completed, the chemical oxygen demand (COD) and the biological oxygen demand (BOD) of the water body decrease by about 60% and 70%, respectively, and the dissolved oxygen content in the water increases by about 45%, so that the ecological environment is restored and the value of the park landscape is improved.

[0043] Example 2

[0044] A river located near an agricultural area has been affected by agricultural non-point source pollution and nearby small factories for a long time, and a large amount of organic pollutants and some heavy metal pollutants have accumulated in the sediment. The river is repaired according to the technical solution of Example 1. The horizontal spacing between the electrode groups is 2.5 meters, the longitudinal spacing is 2 meters, the spacing between the anode and cathode plates in the same group is 2 meters; the anode plate is made of boron-doped diamond, and the cathode plate is made of graphite; the electric field strength is 400 V / m; ammonium persulfate is added to the anode at a ratio of 4.8 to the chemical demand and the concentration of persulfate; and the power is turned on from 6 to 17 every day. The positive and negative poles of the power supply are exchanged when the redox potential reaches 800 mV in stage 1.

[0045] After a total of 3 months of repair, the water quality of the river has been significantly improved, the content of organic pollutants has been reduced by 80%, the content of heavy metals has been reduced to below the local soil background value, and the local ecological environment has been improved. The change of heavy metal content in the sediment before and after the corresponding repair is shown in Table 4:

[0046] Table 4: Change of organic matter content before and after repair

[0047] Heavy metals Before repair After repair Soil background value of Jiangsu Province Cd 0.329 0.157 0.1 Cu 55.565 29.017 22.3 Cr 129.559 75.835 77.8 As 15.475 9.753 10.6 Mn 377.416 341.536 585.0 Ni 39.821 144.784 26.7 Pb 35.033 23.651 26.2 Zn 118.271 56.348 62.6

[0048] Example 3

[0049] A river located near an industrial area has been receiving industrial wastewater for a long time, and the sediment in the river not only contains high concentrations of organic pollutants, but also contains various heavy metal pollutants. The river is repaired according to the technical solution of Example 1. The horizontal spacing between the electrode groups is 2.8 meters, the longitudinal spacing is 1.8 meters, the spacing between the anode and cathode plates in the same group is 2.2 meters; the anode plate is made of lead dioxide, and the cathode plate is made of stainless steel; the electric field strength is 350 V / m; potassium persulfate is added to the anode at a ratio of 4.5 to the chemical demand and the concentration of persulfate; and the power is turned on from 9 to 17 every day. The positive and negative poles of the power supply are exchanged when the redox potential reaches 800 mV in stage 1.

[0050] After a total of 6 months of repair, the sediment and water quality of the river have reached good environmental standards, the average degradation rate of organic pollutants has exceeded 85%, and the content of heavy metals has been reduced to below the safety threshold. This project effectively improves the health level of the river ecosystem and provides strong support for the environmental governance of the surrounding industrial area.

[0051] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0052] The present application is not limited to the above-described embodiments, and any obvious modifications, replacements or variations made by those skilled in the art without departing from the spirit of the present application fall within the scope of the present application.

Claims

1. A method for remediating contaminated river sediment with electrokinetically activated persulfate, characterized by: The anode and cathode are arranged in water area, and persulfate is added at the anode; during initial operation, the anode is connected to the positive pole of power supply, and the cathode is connected to the negative pole of power supply; when the redox potential reaches a threshold value, the positive and negative poles of power supply are switched, wherein when the redox potential is greater than or equal to 800 mV, the positive and negative poles of power supply are switched; when the redox potential is less than or equal to -200 mV, the repair is ended.

2. The method of remediating contaminated sediment in a river channel by electrokinetically activated persulfate of claim 1, wherein: The electrode is a mesh plate structure.

3. The method of remediating contaminated sediment in a river channel by electrokinetically activated persulfate of claim 2, wherein: The electrodes are arranged in the form of a rectangular array.

4. The method of remediating contaminated sediment in a river according to claim 3, wherein: The material of the anode is inert metal, and the material of the cathode is copper, graphite or stainless steel.

5. The method of remediating contaminated sediment in a river according to claim 4, wherein: The material of the anode is tin dioxide, lead dioxide or boron-doped diamond.

6. The method of remediating contaminated sediment in a river according to claim 3, wherein: The distance between the anode plate and the cathode plate in the same group is 2-2.5 m, the lateral distance between the adjacent two groups of electrodes is 2-3 m, and the longitudinal distance is 1-2 m.

7. The method of electrokinetically activated persulfate remediation of contaminated river sediment according to claim 1, wherein: The electric field strength is 300-400 V / m.

8. The method of electrokinetically activated persulfate remediation of contaminated river sediment according to claim 1, wherein: The persulfate is sodium persulfate, ammonium persulfate or potassium persulfate, and the ratio of the chemical demand to the persulfate concentration is 4-4.

8.

9. The method of electrokinetically activated persulfate remediation of contaminated river sediment according to claim 1, wherein: The electrode is powered on for 8-11 hours per day.

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