System and method for treating storage tank cleaning wastewater through electric flocculation coupling ultraviolet synergistic electro-Fenton

Abstract

The invention discloses a system and a method for treating storage tank cleaning wastewater through electric flocculation coupled ultraviolet synergistic electro-Fenton. The system sequentially comprises an electric flocculation treatment unit and an electro-Fenton unit according to the treatment sequence of the storage tank cleaning wastewater, the electric flocculation treatment unit comprises an electric flocculation reactor and a bilateral aeration system, and the bilateral aeration system performs bilateral aeration in the electric flocculation reactor; the electro-Fenton unit comprises an electro-Fenton reactor, an aeration system and an ultraviolet system, the aeration system aerates the electro-Fenton reactor, and the ultraviolet system performs ultraviolet radiation on the electro-Fenton reactor. According to the invention, treatment is carried out by coupling electric flocculation with an electro-Fenton process, so that the treatment cost is low, practicability and high efficiency are realized, and the method can be widely applied to treatment of storage tank cleaning wastewater; the technical problems that in the prior art, the pollutant concentration of the storage tank cleaning wastewater is high, the biodegradability is poor, the treatment effect of a conventional process is unstable, secondary pollution is serious, and a biochemical method is difficult to operate are solved.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a system and method for treating organic matter and ammonia nitrogen in tank cleaning wastewater by electrocoagulation coupled with ultraviolet radiation and electro-Fenton electrotreatment. Background Technology

[0002] During the long-term storage and transportation of crude oil, small amounts of mechanical impurities, silt, heavy metal salts, and heavy components such as paraffin and asphalt will gradually settle and accumulate at the bottom of the storage tank due to density differences, forming a gel-like deposit, commonly known as tank bottom sludge. As storage time extends, the sludge continues to accumulate, not only exacerbating tank corrosion and reducing effective oil storage capacity, but also affecting normal production operations. Therefore, regular cleaning and maintenance of the storage tanks are necessary.

[0003] Taking a 100,000 cubic meter crude oil storage tank as an example, depending on the cleaning process, the amount of sludge generated in a single cleaning operation is approximately 500 to 2,000 tons. The treated sludge generally undergoes two-phase or three-phase separation pretreatment before being disposed of as hazardous waste, while the wastewater is treated on-site. However, this wastewater is complex, exhibiting typical characteristics of being difficult to biodegrade and highly toxic. Its typical water quality indicators are as follows: Chemical Oxygen Demand (COD) 300–2500 mg / L, Ammonia Nitrogen 30–100 mg / L, Total Dissolved Solids (TDS) 500–2000 mg / L, and Petroleum Concentration 200–500 mg / L. Currently, wastewater treatment in storage areas primarily employs a physicochemical treatment process mainly based on "oil removal—air flotation—filtration," which has limited treatment capacity and is insufficient to handle such high-concentration, difficult-to-degrade wastewater. If the wastewater is directly discharged into the sewage treatment system, not only will a large amount of chemicals need to be added, which will easily cause secondary pollution, but it will also have a strong impact on the treatment facilities and seriously affect the quality of the effluent. If biological treatment is used, the conditions for biological operation cannot be met due to intermittent water flow and poor biodegradability.

[0004] Electrochemical oxidation technology, as a highly efficient and environmentally friendly wastewater treatment method, has shown significant advantages in degrading organic pollutants and ammonia nitrogen. It has attracted considerable attention due to its simple operation, controllable process, good economic efficiency, mild reaction conditions, and strong adaptability to water quality fluctuations. However, several bottlenecks remain in its engineering applications, such as electrode passivation, short service life, the need for external reagents like iron salts in the electro-Fenton process, large sludge production, and potential secondary pollution. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a system and method for treating tank cleaning wastewater using electrocoagulation coupled with ultraviolet radiation and electro-Fenton electrotherapy.

[0006] In a first aspect, the present invention provides a system for treating tank cleaning wastewater by electrocoagulation coupled with ultraviolet radiation and electro-Fenton synergy, which is achieved by the following technical solution.

[0007] A system for treating tank cleaning wastewater by electrocoagulation coupled with ultraviolet radiation and electro-Fenton irradiation, comprising, in the order of wastewater treatment, an electrocoagulation treatment unit and an electro-Fenton unit; the electrocoagulation treatment unit includes an electrocoagulation reactor and a bilateral aeration system, wherein the bilateral aeration system aerates the electrocoagulation reactor from both sides; the electro-Fenton unit includes an electro-Fenton reactor, an aeration system, and an ultraviolet system, wherein the aeration system aerates the electro-Fenton reactor, and the ultraviolet system irradiates the electro-Fenton reactor with ultraviolet light.

[0008] Furthermore, the electrocoagulation reactor employs a soluble anode, which is selected from at least one of iron and aluminum electrodes; the cathode of the electrocoagulation reactor is selected from at least one of graphite, stainless steel, iron, and aluminum electrodes; the current in the electrocoagulation reactor is a pulsed current or a direct current with a density of 10 mA / cm³. 2 -50mA / cm 2 .

[0009] Furthermore, the anode of the electro-Fenton reactor is selected from at least one of lead dioxide electrode, platinum electrode, carbon-based material, and boron-doped diamond electrode; the cathode of the electro-Fenton reactor is a carbon-based composite hydrophobic agent, wherein the carbon-based material is selected from at least one of carbon black, graphene, graphite felt and its modified electrode materials, and the hydrophobic agent is selected from at least one of fluoropolymer polytetrafluoroethylene and non-fluorinated hydrophobic agent polydimethylsiloxane; the current density of the electro-Fenton reactor is 20 mA / cm². 2 -90mA / cm 2 .

[0010] Furthermore, the electrocoagulation reactor is provided with staggered electrode groups and / or parallel electrode groups, the electrode spacing of the electrode groups is 20 mm-50 mm, and the electrode plane forms an angle of 45°-90° with the water flow direction; the electro-Fenton reactor is provided with at least one of staggered electrode groups, parallel electrode groups, and tubular electrode groups, the electrode spacing of the electrode groups is 20 mm-50 mm.

[0011] Furthermore, the bilateral aeration system and the aeration system are selected from at least one of blower aeration, jet aeration, and dissolved air aeration.

[0012] Furthermore, the ultraviolet system is selected from at least one of an external irradiation system and an internal irradiation system.

[0013] Furthermore, the system also includes a clarification and sedimentation unit disposed between the electrocoagulation treatment unit and the electro-Fenton unit, wherein the clarification and sedimentation unit is selected from at least one of the following: sedimentation separation unit, magnetic powder sedimentation separation unit, air flotation unit, and filtration unit.

[0014] Secondly, the present invention provides a method for treating tank cleaning wastewater by electrocoagulation coupled with ultraviolet radiation and electro-Fenton electrotherapy, which is achieved by the following technical solution.

[0015] A method for treating tank cleaning wastewater by electrocoagulation coupled with ultraviolet radiation and electro-Fenton treatment, using the above-mentioned system, specifically includes the following steps: passing the tank cleaning wastewater into an electrocoagulation treatment unit for electrocoagulation treatment to obtain electrocoagulated effluent; passing the electrocoagulated effluent into an electro-Fenton unit for electro-Fenton treatment to obtain purified effluent.

[0016] Furthermore, a method for treating tank cleaning wastewater by electrocoagulation coupled with ultraviolet radiation and electro-Fenton treatment, using the above-mentioned system, specifically includes the following steps: the tank cleaning wastewater is fed into an electrocoagulation treatment unit for electrocoagulation treatment to obtain electrocoagulated effluent; the electrocoagulated effluent is fed into a clarification and sedimentation unit for clarification treatment to obtain clarified effluent; and the clarified effluent is fed into an electro-Fenton unit for electro-Fenton treatment to obtain purified effluent.

[0017] By adopting the above technical solution, this invention can efficiently remove organic matter and ammonia nitrogen from tank cleaning wastewater through electrocoagulation coupled with ultraviolet synergistic electro-Fenton system treatment and filtration process. At the same time, it solves the passivation problem of traditional electrocoagulation plates and the problem of traditional electro-Fenton requiring additional reagents, thus solving the existing problem of tank cleaning wastewater treatment.

[0018] Furthermore, the pH during the electrocoagulation process is 7-9; the aeration rate during the electrocoagulation process is 0.05-0.2 L / min; and the electrocoagulation time is 0.5 h - 1 h.

[0019] Furthermore, the pH during the electro-Fenton treatment process is 5-8; the aeration rate during the electro-Fenton treatment process is 0.05-0.2 L / min; and the ultraviolet radiation dose during the electro-Fenton treatment process is 500-5000 mJ / cm². 2 The electro-Fenton treatment time is 1-2 hours.

[0020] The present invention achieves the following beneficial effects: (1) The electrochemical treatment system for tank cleaning wastewater provided by the present invention addresses the treatment needs of pollutants such as petroleum, ammonia nitrogen and COD in tank cleaning wastewater. It uses electrocoagulation coupled with electro-Fenton process for treatment, which is not only low in treatment cost but also practical and efficient. It can be widely used to treat tank cleaning wastewater and solves the technical problems of high pollutant concentration, poor biodegradability, unstable treatment effect of conventional process, serious secondary pollution and difficulty in operation of biochemical method in the prior art.

[0021] (2) Green and environmentally friendly: This invention solves the problem of easy passivation of traditional electrocoagulation electrode plates, solves the problem of needing to add other chemical reagents in traditional electro-Fenton, extends the life of anode and cathode plates, and reduces the use of chemical reagents and the risk of secondary pollution, which meets the requirements of green and environmentally friendly.

[0022] (3) The organic matter removal rate of the purified water after the present invention is ≥ 50%, the ammonia nitrogen removal rate is ≥ 80%, and the TDS removal rate is ≥ 50%. Attached Figure Description

[0023] Figure 1 This is a flowchart of the processing of the present invention; Figure 2 This is a diagram of the air-assisted electrocoagulation treatment device of the present invention; Figure 3 This is a diagram of the UV-coordinated electro-Fenton treatment device of the present invention. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments. like Figure 1 As shown, a method for treating tank cleaning wastewater by electrocoagulation coupled with ultraviolet radiation and electro-Fenton electrotherapy includes the following steps: (1) The wastewater from tank cleaning was treated by air-assisted electrocoagulation with bilateral external aeration to obtain the first treated wastewater; (2) Filter the first treated wastewater in step (1) to obtain the second treated wastewater; (3) The second wastewater in step (2) is subjected to ultraviolet-assisted electro-Fenton treatment to obtain treated wastewater.

[0025] In step (1), the air-assisted electrocoagulation treatment with bilateral external aeration uses soluble metal plates as anodes and cathodes to conduct electrochemical experiments. During the process, the metal electrodes generate flocculant hydroxides and other substances, which flocculate suspended matter, oil, organic matter and other colloidal particles in the solution into precipitates and remove them for subsequent processes.

[0026] In step (2), the clarification and sedimentation unit removes the precipitate generated by flocculation in step (1) from the tank cleaning wastewater.

[0027] In step (3), a large amount of hydrogen peroxide is generated during the electro-Fenton treatment. Ultraviolet light can effectively homogenize the hydrogen peroxide, generating more oxidizing hydroxyl radicals and superoxide radicals, which more thoroughly decompose the organic matter in the tank cleaning wastewater into carbon dioxide and water, thereby removing it from the wastewater. At the same time, the ammonia nitrogen in the tank cleaning wastewater is oxidized, converting it into nitrogen gas or other inorganic nitrogen compounds to achieve the effect of removing ammonia nitrogen.

[0028] In this embodiment, as Figure 2 and Figure 3 The diagrams show the air-assisted electrocoagulation and UV-coordinated electro-Fenton systems used in the treatment of tank cleaning wastewater. The air-assisted electrocoagulation system employs bilateral external aeration, continuously refreshing the solution and airflow on the anode and cathode surfaces to mitigate the passivation of the anodes and cathodes during electrocoagulation. In the UV-coordinated electro-Fenton system, the addition of UV light effectively homogenizes H2O2, generating more potent hydroxyl radicals. An in-situ photoelectric-Fenton system is constructed, eliminating the need for additional ferrous ions and significantly enhancing the oxidation capacity. This allows for more thorough decomposition of organic pollutants into CO2 and H2O, reducing the accumulation of toxic intermediates.

[0029] Preparation Example The preparation method of graphite felt composite hydrophobic agent polytetrafluoroethylene (PTFE / CNT / GF) electrode is as follows: PTFE / CNT / GF electrodes were prepared using a combination of impregnation and sintering methods. First, graphite felt was pretreated by ultrasonication in ultrapure water. After drying in an oven, pure graphite felt was obtained. Next, propanol, polytetrafluoroethylene dispersion, and carbon nanotubes (the mass ratio of carbon nanotubes to solid polytetrafluoroethylene was 4:1) were added to a beaker, stirred, and ultrasonicated. The treated graphite felt was then immersed in the above solution and subsequently dried in an oven. Afterward, it was placed in a muffle furnace and heated from 25°C to 600°C at a rate of 5°C / min and held for 30 minutes. After cooling, the PTFE / CNT / GF electrode was obtained.

[0030] Example 1 A system for treating tank cleaning wastewater by electrocoagulation coupled with ultraviolet radiation and electro-Fenton treatment, comprising, in the order of wastewater treatment, an electrocoagulation unit, a clarification unit, and an electro-Fenton unit: The electrocoagulation treatment unit is used to generate metal hydroxide flocs through anodic dissolution, thereby oxidizing, adsorbing, flocculating, and separating suspended solids, colloids, petroleum and COD in water by flotation. The electrocoagulation treatment unit includes an electrocoagulation reactor, which uses a soluble anode, which is an iron electrode. The cathode of the electrocoagulation reactor is an iron plate, and the aeration system uses a double-sided blower aeration. The electro-Fenton unit degrades petroleum hydrocarbons, ammonia nitrogen, and COD in water through direct and indirect oxidation. The electric Fenton unit includes an electric Fenton reactor, the anode of which is a lead dioxide electrode, the cathode is polytetrafluoroethylene (PTFE) composite hydrophobic agent prepared in the preparation example, the aeration system is blower aeration, and the ultraviolet system is internal ultraviolet irradiation. The clarification and precipitation unit is located between the electrocoagulation treatment unit and the electro-Fenton unit; The clarification and sedimentation unit uses a sedimentation + filtration unit. After adding 0.3 mL of 0.1% PAM to settle the flocs, the filtration accuracy is 30 μm. The specific steps for treating wastewater from tank cleaning are as follows: Wastewater quality from crude oil storage tank cleaning: suspended solids 30 mg / L, COD 1353 mg / L, ammonia nitrogen 48.4 mg / L, petroleum hydrocarbons 89 mg / L.

[0031] After settling and separation, the wastewater from the crude oil storage tank cleaning process is filtered through a 20-mesh screen to remove some suspended solids before entering the electrocoagulation unit for electrocoagulation treatment. The current density for electrocoagulation treatment is 20 mA / cm³. 2 The electrocoagulation treatment time was 1 hour, the electrode spacing of the electrode group in the electrocoagulation treatment was 40 mm, the electrode plane was at a 90° angle with the water flow direction, and the aeration rate was 0.1 L / min, resulting in the tank cleaning wastewater after electrocoagulation treatment. The tank cleaning wastewater after electrocoagulation treatment enters the clarification and sedimentation unit for clarification treatment to obtain clarified tank cleaning wastewater. The clarified tank cleaning wastewater enters the electro-Fenton unit for electro-Fenton treatment, with a current density of 20 mA / cm². 2 The electro-Fenton treatment time was 1 hour, the electrode spacing of the electro-Fenton treatment electrode group was 20 mm, the aeration rate was 0.1 L / min, and the ultraviolet dose was 500 mJ / cm². 2 The wastewater from the tank cleaning process, after being treated with electro-Fenton, is the final effluent.

[0032] The final effluent quality obtained in this embodiment is as follows: suspended solids 12 mg / L, COD 198 mg / L, ammonia nitrogen 9.8 mg / L, and petroleum hydrocarbons 5 mg / L.

[0033] Example 2 This embodiment uses the same system as in Embodiment 1. The specific treatment steps for the tank cleaning wastewater are as follows: Wastewater quality from crude oil storage tank cleaning: suspended solids 54 mg / L, COD 270 mg / L, ammonia nitrogen 69.7 mg / L, petroleum hydrocarbons 95 mg / L.

[0034] The wastewater from cleaning crude oil storage tanks is first filtered through a 20-mesh screen to remove some suspended solids before entering the electrocoagulation treatment unit for electrocoagulation treatment. The current density of the electrocoagulation treatment is 30 mA / cm³. 2 The electrocoagulation treatment time was 40 min, the electrode spacing of the electrocoagulation electrode group was 25 mm, the aeration rate was 0.1 L / min, and the electrode plane was at a 90° angle to the water flow direction, resulting in the tank cleaning wastewater after electrocoagulation treatment. The tank cleaning wastewater after electrocoagulation treatment enters the clarification and sedimentation unit for clarification treatment to obtain clarified tank cleaning wastewater. The clarified tank cleaning wastewater enters the electro-Fenton unit for electro-Fenton treatment, with a current density of 30 mA / cm². 2 The electro-Fenton treatment time was 1 hour, the electrode spacing of the electro-Fenton treatment electrode group was 25 mm, the aeration rate was 0.1 L / min, and the ultraviolet dose was 1500 mJ / cm². 2 The wastewater from the tank cleaning process, after being treated with electro-Fenton, is the final effluent.

[0035] The final effluent quality obtained in this embodiment is as follows: suspended solids 9 mg / L, COD 49 mg / L, ammonia nitrogen 9.8 mg / L, and petroleum hydrocarbons 3 mg / L.

[0036] The above results show that the method of the present invention does not require the addition of a large amount of chemical reagents, has low treatment cost and strong adaptability, can effectively cope with water volume fluctuations and low temperature operating conditions, solves the problems of substandard effluent and secondary pollution caused by traditional processes, can ensure stable and compliant discharge of tank cleaning wastewater, and eliminates environmental risks for enterprises.

[0037] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A system for treating storage tank cleaning wastewater by electric flocculation coupled with ultraviolet and synergistic electro-Fenton, characterized in that: The treatment sequence of the storage tank cleaning wastewater comprises, in sequence, an electrocoagulation treatment unit and an electro-Fenton unit; the electrocoagulation treatment unit comprises an electrocoagulation reactor and a double-side aeration system, and the double-side aeration system performs double-side aeration on the electrocoagulation reactor; the electro-Fenton unit comprises an electro-Fenton reactor, an aeration system and an ultraviolet system, the aeration system performs aeration on the electro-Fenton reactor, and the ultraviolet system performs ultraviolet irradiation on the electro-Fenton reactor.

2. The system for treating storage tank cleaning wastewater by electric flocculation coupled with UV synergistic electro-Fenton according to claim 1, characterized in that: The electric flocculation reactor adopts a soluble anode, and the soluble anode is at least one of an iron electrode and an aluminum electrode; the cathode of the electric flocculation reactor is at least one of a graphite electrode, stainless steel, an iron electrode and an aluminum electrode; the electric current of the electric flocculation reactor is pulse current or direct current, and the density is 10 mA / cm 2 - 50 mA / cm 2 .

3. The system for treating storage tank cleaning wastewater by electric flocculation coupled with UV synergistic electro-Fenton according to claim 1, characterized in that: The anode of the electro-Fenton reactor is at least one of a lead dioxide electrode, a platinum electrode, a carbon-based material, and a boron-doped diamond electrode; the cathode of the electro-Fenton reactor is a carbon-based material composite hydrophobic agent, the carbon-based material is at least one of carbon black, graphene, graphite felt, and a modified material electrode thereof, and the hydrophobic agent is at least one of a fluorine-containing polymer polytetrafluoroethylene and a non-fluorine hydrophobic agent polydimethylsiloxane; the current density of the electro-Fenton reactor is 20mA / cm 2 -90mA / cm 2 .

4. The system for treating storage tank cleaning wastewater by electric flocculation coupled with UV synergistic electro-Fenton according to claim 1, characterized in that: The electrocoagulation reactor is provided with an interleaved electrode plate group and / or a parallel electrode plate group, the electrode plate spacing of the electrode plate group is 20 mm-50 mm, and the electrode plate plane forms an angle of 45°-90° with the water flow direction; the electro-Fenton reactor is provided with at least one of an interleaved electrode plate group, a parallel electrode plate group and a tubular electrode plate group, and the electrode plate spacing of the electrode plate group is 20 mm-50 mm.

5. The system for treating storage tank cleaning wastewater by electric flocculation coupled with UV synergistic electro-Fenton according to claim 1, characterized in that: The double-side aeration system and the aeration system are selected from at least one of air blowing aeration, jet aeration and dissolved air aeration.

6. The system for treating storage tank cleaning wastewater by electric flocculation coupled with UV synergistic electro-Fenton according to claim 1, characterized in that: The ultraviolet system is selected from at least one of an external irradiation system and an internal irradiation system.

7. The system for treating storage tank cleaning wastewater by electric flocculation coupled with UV synergistic electro-Fenton according to claim 1, characterized in that: The system further comprises a clarification and precipitation unit arranged between the electrocoagulation treatment unit and the electro-Fenton unit, and the clarification and precipitation unit is selected from at least one of a sedimentation separation unit, a magnetic powder precipitation separation unit, a gas floatation unit and a filtration unit.

8. A method for treating storage tank cleaning wastewater by electric flocculation coupled with ultraviolet synergistic electro-Fenton, characterized in that: The system of any one of claims 1-7 comprises the following steps: passing the storage tank cleaning wastewater into the electrocoagulation treatment unit to perform electrocoagulation treatment, obtaining electrocoagulation treatment effluent, passing the electrocoagulation treatment effluent into the electro-Fenton unit to perform electro-Fenton treatment, and obtaining purified effluent.

9. The method for treating storage tank cleaning wastewater by electric flocculation coupled with UV synergistic electro-Fenton according to claim 8, characterized in that: The pH during the electrocoagulation treatment is 7-9, the aeration rate during the electrocoagulation treatment is 0.05-0.2 L / min, and the electrocoagulation treatment time is 0.5 h-1 h.

10. The method for treating storage tank cleaning wastewater by electric flocculation coupled with UV synergistic electro-Fenton according to claim 8, characterized in that: The pH in the electro-Fenton treatment process is 5-8; the aeration rate in the electro-Fenton treatment process is 0.05-0.2 L / min; the ultraviolet dose in the electro-Fenton treatment process is 500-5000 mJ / cm 2 ; and the electro-Fenton treatment time is 1 h-2 h.

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