Electrochemical oxidation-reduction synergistic treatment device and method for chlorinated complex organic wastewater

Abstract

This invention discloses an apparatus and method for electrochemical oxidation-reduction synergistic treatment of chlorine-containing complex organic wastewater. The apparatus includes a reaction vessel (1), a chlorine-evolving anode (2) disposed therein, a reduction cathode (3) capable of generating atomic hydrogen in situ, a DC power supply (4), and a stirrer (5). The method includes: introducing wastewater containing chloride ions, ammonia nitrogen, and organic pollutants into the reaction vessel, adjusting the pH value, and adding ferrous salt; during the electrochemical reaction, the active chlorine generated at the anode activates ferrous ions to generate high-valence iron, selectively oxidizing the pollutants; the atomic hydrogen generated at the cathode reduces and dechlorinates the chlorine-containing intermediates, and removes Fe... 3+ The reduction and regeneration process achieves a closed-loop cycle of iron species, while the reduction of nitrates achieves a nitrogen cycle. This invention deeply couples anodic oxidation and cathodic reduction, achieving efficient mineralization of complex pollutants and effectively preventing the accumulation of toxic chlorination byproducts.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection and electrochemical water treatment technology, specifically relating to a method and apparatus for treating chlorine-containing complex organic wastewater using electrochemical oxidation-reduction synergistic treatment. Background Technology

[0002] High-salinity complex organic wastewater (such as coal chemical wastewater) is one of the major challenges in modern industrial water treatment. This type of wastewater typically exhibits characteristics of "complex pollution," characterized by high salinity (rich in chloride ions), the coexistence of recalcitrant organic matter and high concentrations of ammonia nitrogen, resulting in extremely complex water quality. Traditional biological treatment processes are severely limited in their osmotic pressure inhibition effect under high-salinity environments; while physicochemical methods such as thermal evaporation are energy-intensive, expensive to operate, and generate large amounts of hazardous mixed salt waste residue, making sustainable and harmless treatment difficult.

[0003] Against this backdrop, advanced electrochemical oxidation technology has attracted significant attention due to its unique potential in treating high-salinity wastewater. This technology can significantly reduce energy consumption during treatment by utilizing the high ionic conductivity of the wastewater itself; simultaneously, chloride ions in the wastewater can be converted in situ into active chlorine (such as hypochlorous acid, HClO) through an anodic reaction. Active chlorine can act as a strong oxidant to degrade organic pollutants, and can also rapidly convert ammonia nitrogen into nitrogen gas through breakpoint chlorination, thereby greatly improving the overall wastewater treatment efficiency.

[0004] However, for high-salt, complex organic wastewater rich in chloride ions, existing electrochemical treatment technologies face a significant industry bottleneck: a sharp contradiction between the efficient mineralization of pollutants and the accumulation of toxic chlorination byproducts. This manifests in the following three prominent technical problems: First, the large-scale generation of toxic byproducts and secondary pollution. During the electrochemical treatment of chlorinated wastewater, intense electrochemical oxidation inevitably triggers halogenation side reactions, generating large quantities of chlorinated byproducts. These chlorinated byproducts are often more stable and toxic than the parent pollutants, and are highly likely to persist in water bodies, causing serious secondary pollution.

[0005] Second, the mineralization effect is severely limited. High concentrations of chloride ions readily quench highly reactive hydroxyl radicals generated within the electrochemical system. • The oxidation process converts nitrogenous compounds (OH) into weaker free radicals, severely weakening the system's ability to thoroughly mineralize recalcitrant pollutants. Simultaneously, nitrogenous compounds are prone to incomplete transformation during single oxidation processes, leading to nitrate accumulation and hindering complete nitrogen removal.

[0006] Third, the limitations of existing unidirectional oxidation strategies. To suppress the formation of chlorination byproducts, existing technologies attempt to introduce high-valence metal species (such as high-valence iron Fe). IVFe is used as a selective oxidant. While this type of method can reduce the formation of byproducts to some extent, it is essentially a "mitigation" rather than a "complete elimination," and trace amounts of highly persistent toxic chlorinated organic compounds will still remain in the system. Furthermore, traditional Fe... IV The system lacks an efficient iron recycling mechanism, resulting in low steady-state concentrations of active species and the generation of large amounts of iron sludge solid waste.

[0007] In summary, existing single-oxidation systems cannot simultaneously achieve efficient mineralization (deep removal of carbon and nitrogen) of recalcitrant pollutants in chlorinated complex organic wastewater and complete elimination of toxic chlorinated byproducts. Therefore, there is an urgent need in this field to develop a novel wastewater treatment device and method to overcome the bottleneck between oxidative decarbonization and denitrification and chlorinated byproduct control in traditional technologies, achieving efficient degradation of complex pollutants while completely preventing secondary pollution. Summary of the Invention

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: The present invention provides an apparatus for electrochemical oxidation-reduction synergistic treatment of chlorine-containing compound organic wastewater. The apparatus includes: a reaction vessel (1) for adding wastewater and ferrous iron; a chlorine-evolving anode (2) and a reducing cathode (3) capable of generating atomic hydrogen in situ, disposed in the reaction vessel (1); a DC power supply (4) electrically connected to the anode (2) and the cathode (3); and a stirrer (5) provided at the bottom of the reaction vessel (1).

[0009] Furthermore, the anode (2) is a shape-stable anode, a lead dioxide anode, or a boron-doped diamond anode with electro-oxidation chlorine evolution function.

[0010] Furthermore, the reduction cathode (3) is loaded with a catalytic material for in-situ generation of atomic hydrogen, the catalytic material including at least one of palladium metal, palladium alloy and nitrogen and / or phosphorus co-doped carbon-based catalytic material containing a transition metal, wherein the transition metal is selected from at least one of manganese, cobalt, iron, copper and nickel.

[0011] This invention also provides a method for treating chlorine-containing complex organic wastewater using the above-mentioned electrochemical oxidation-reduction synergistic device. The method involves the synergistic treatment of wastewater containing chloride ions, ammonia nitrogen, and organic pollutants through high-valence iron oxidation and atomic hydrogen reduction. The method includes the following steps: The chlorine-containing composite organic wastewater to be treated is introduced into the reaction vessel (1), and the pH value of the wastewater is adjusted to 3.0-7.0. Ferrous salt is added to the wastewater to make the concentration of ferrous ions in the wastewater 0.1-1.0 mM, and the DC power supply (4) is turned on to carry out the electrochemical reaction. During the reaction, the anode (2) oxidizes the chloride ions in the wastewater into active chlorine, and the active chlorine activates the ferrous ions in the wastewater to generate high-valence iron, so as to oxidize the ammonia nitrogen and organic pollutants in the wastewater. At the same time, the reduction cathode (3) generates atomic hydrogen in situ, reduces and dechlorinates the chlorine-containing intermediates generated during the oxidation process in situ, and reduces the iron ions generated in the reaction into ferrous ions, so as to realize the recycling of iron species.

[0012] Furthermore, the DC power supply (4) provides a reactive current density of 7.5-12.5 mA / cm². 2 .

[0013] The technical principle of this invention: This invention constructs a method for treating chlorine-containing composite organic wastewater that integrates anodic selective oxidation and cathodic reduction detoxification. During the electrochemical reaction process, the anode oxidizes chloride ions in the wastewater into active chlorine, which in turn activates the Fe2+ added within the device. 2+ In-situ generation of Fe, which has strong oxidizing properties and high selectivity IV The Fe IV As the dominant oxidant, it can target and deeply mineralize recalcitrant organic matter and synergistically oxidize ammonia nitrogen, significantly inhibiting the formation of toxic chlorinated byproducts from the source. Simultaneously, the device employs a reduction cathode capable of generating H* in situ. The generated H* plays a crucial triple synergistic reduction role within the device: firstly, it rapidly and situ reduces and dechlorinates chlorine-containing intermediates generated during oxidation, completely eliminating byproduct toxicity and lowering the energy barrier for subsequent oxidation; secondly, it rapidly reduces the Fe generated in the reaction... 3+ Reduction and regeneration to Fe 2+ Constructing a highly efficient closed-loop cycle for iron species not only enables the key oxidant Fe within the device to... IV The steady-state concentration is increased several times, fundamentally eliminating the generation of iron sludge solid waste; finally, H* can further reduce nitrate, a byproduct of ammonia nitrogen oxidation, to ammonia nitrogen or nitrogen gas. This invention ingeniously makes "anode Fe" IV The "targeted oxidation" and "cathode H* multi-effect reduction" achieve self-balancing coupling, successfully breaking through the technical bottleneck between efficient mineralization of pollutants and secondary toxicity accumulation in chlorine-containing compound organic wastewater.

[0014] This invention has the following outstanding features: (1) Highly effective blocking of secondary pollution and complete in-situ detoxification: This invention utilizes Fe IVThe deep coupling of targeted oxidation and in-situ reduction dechlorination by cathode H* completely overcomes the bottleneck of conflict between pollutant mineralization and the accumulation of toxic chlorination byproducts in traditional advanced oxidation processes. The total organic chlorine (TOCl) concentration in the final effluent is significantly reduced by 86.7%-97.6% compared to traditional electrochemical devices, effectively preventing the accumulation of persistent chlorination byproducts and eliminating the risk of secondary halogenation pollution.

[0015] (2) Simultaneous deep carbon and nitrogen removal: Utilizing the powerful reduction effect of cathode H* to rapidly accelerate Fe 3+ / Fe 2+ Cycle, making Fe the dominant oxidation IV The steady-state concentration reached the traditional Fe IV The oxidation electrochemical device is about 1.7 times more efficient, ensuring high oxidation efficiency while fundamentally maintaining the activity of soluble iron species and completely eliminating the generation of secondary iron sludge solid waste. At the same time, H* can reduce and eliminate easily accumulated nitrate intermediates to drive the closed-loop nitrogen cycle inside the device, making the TOC and TN removal rates of the device significantly higher than those of traditional devices by 25.97%-70.61% and 29.07%-55.53%, respectively.

[0016] (3) Self-driven and reagent-free, significantly reducing energy consumption and operating costs: This device ingeniously converts the chloride ions naturally present in the wastewater into in-situ active species that drive the reaction, completely eliminating the need for expensive external oxidants. When treating the complex reverse osmosis concentrate from coal chemical plants, the removal rates of TOC, TN, and COD increased by 30.38%-60.51%, 34.63%-61.18%, and 13.74%-50.43%, respectively, while the power consumption was significantly reduced to 17.61 kWh / kg COD, and the overall system energy consumption was significantly reduced by 43.21%-51.03%. The energy consumption is significantly lower than that of traditional advanced oxidation technologies such as ozonolysis and electro-Fenton oxidation. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the reaction apparatus of the present invention; Figure 2 This is a comparison chart of the phenol removal rates using different cathode reduction catalysts in the reaction apparatus of this invention; Figure 3 This is a comparison chart showing the ammonia nitrogen removal rate of the reaction device of the present invention using different cathode reduction catalyst materials; Figure 4 This is a comparison chart of the degradation rate constant, TOC removal rate, and TN removal rate between the reaction device of this invention and a traditional electrochemical treatment device. Figure 5 This is a comparison chart of the concentrations of o-chlorophenol, p-chlorophenol, and chloramine in the reaction device of this invention and in a traditional electrochemical treatment device; Figure 6This is a comparison chart of TOCl concentration between the reaction device of this invention and a traditional electrochemical treatment device; Figure 7 These are the electron paramagnetic resonance (EPR) spectra of active species under different quenchers in this invention; Figure 8 This is the EPR identification spectrum of the DMPO-H* adduct in this invention; Figure 9 The reaction device of this invention differs from that of conventional Fe IV Different valence states of Fe in an oxidative electrochemical treatment device (Fe-DSA device) 2+ Fe 3+ Fe IV Concentration comparison chart; Figure 10 The reaction device of this invention differs from that of a traditional electrochemical treatment device for nitrate ions (NO3). − Concentration comparison chart; Figure 11 This is a diagram of a 60-hour long-term continuous flow degradation experiment of the reaction device of this invention; Figure 12 This is a graph showing the concentration of Mn leaching from recycled materials after 15 consecutive treatments using the reaction apparatus of this invention. Figure 13 This is a comparison chart of the TOC, TN, and COD removal rates and energy consumption of the reaction device of this invention and a traditional electrochemical treatment device for coal chemical reverse osmosis concentrate. Figure 14 This is a comparison chart of the power consumption of the reaction device of the present invention and different advanced oxidation processes. Detailed Implementation

[0018] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. 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.

[0019] This invention proposes a Fe IV A method and apparatus for synergistic treatment of chlorine-containing complex organic wastewater by oxidation and H* reduction (hereinafter referred to as Fe-DSA-oxidation-reduction apparatus). According to embodiments of the present invention, refer to... Figure 1 The device uses a chlorine-evolving electrode as the anode (2) and an electrode that generates H* in situ as the cathode (3). The two electrodes are placed parallel to each other in the reaction vessel (1). The chlorine-containing compound organic wastewater to be treated is introduced into the reaction vessel (1), and the pH value of the wastewater is adjusted. Fe is added. 2+ As an additive; the reaction vessel is placed on a stirrer (5), and a DC power supply (4) provides a stable current input to the entire device.

[0020] refer to Figure 2and Figure 3 The anode (2) adopts a titanium-based stable anode (DSA), and the reduction cathode (3) is based on carbon felt (CF), which is prepared by uniformly loading a catalytic material for in-situ generation of atomic hydrogen on the CF surface. In order to fully verify the catalytic efficiency of the cathode material (i.e., the nitrogen and / or phosphorus co-doped carbon-based catalytic material containing transition metals) described in this invention, this embodiment specifically selected and prepared four specific manganese-based / cobalt-based doped carbon materials (denoted as Mn-NP / C, Co-NP / C, Mn-N / C and Co-N / C, respectively) and coated them on the CF surface for comparative experiments. The initial concentration of phenol in the simulated chlorine-containing compound organic wastewater was set at 50 mg / L, the initial concentration of ammonia nitrogen was 50 mg / L, the concentration of sodium chloride was 100 mM, and FeSO4 additive was added to make the Fe in the wastewater... 2+ The initial concentration was 1.5 mM. This embodiment aims to verify and compare the degradation efficiency of phenol and ammonia nitrogen in the electrochemical redox synergistic device when different catalytic materials are used as reduction cathodes. The results show that in the reduction cathode device using Mn-NP / C supported catalytic material, phenol can be almost 100% completely removed after 20 minutes of reaction, demonstrating a significant advantage in degradation kinetics. After 30 minutes of reaction, the removal rate of ammonia nitrogen by the Mn-NP / C cathode device also significantly outperforms the reaction devices using the other three control catalysts. This excellent pollutant degradation performance confirms that nitrogen and phosphorus co-doped carbon-based catalytic materials containing transition metals, represented by Mn-NP / C, are the optimal cathode material choice in the dual-effect electrochemical device of this invention. This also provides sufficient theoretical support for the application of other transition metals (such as iron, copper, nickel, etc.) and palladium-based materials in this system.

[0021] refer to Figure 4 This embodiment compares the degradation and mineralization efficiency of three different electrochemical treatment devices on simulated chlorine-containing complex organic wastewater. The Fe-DSA-oxidation-reduction device showed an absolute advantage in all indicators. Specifically, the phenol degradation rate constant of the device of this invention is 1.17-2.53 times that of other devices, and the ammonia nitrogen degradation rate constant is 1.29-2.20 times that of other devices. The TOC and TN removal rates are increased by 25.97%-70.61% and 29.07%-55.53% respectively compared with the two control devices. This synergistic effect of "oxidation-reduction" enables the device of this invention to break through the performance bottleneck of traditional single oxidation devices and achieve efficient degradation and deep mineralization of complex pollutants. Figure 5 Thanks to the reductive dechlorination pathway in the device of this invention, the concentrations of toxic intermediates such as o-chlorophenol, p-chlorophenol, and chloramine are significantly suppressed and can be rapidly and completely removed, effectively preventing the accumulation of persistent chlorination byproducts. (Reference) Figure 6The TOCl concentration of the device of the present invention is reduced by 86.7%-97.6% compared with the two traditional electrochemical treatment devices.

[0022] refer to Figure 7 This embodiment utilizes EPR technology combined with DMPO spin trapping agent, and verifies the active species that play a dominant oxidizing role in the device of this invention by comparing the spectral changes after adding different quenchers. When typical [substances] are added to the device... • When the OH-specific quencher tert-butanol (TBA) is used, the intensity of the characteristic signal only decreases slightly, indicating that... • OH is not the primary reactive species. Instead, the addition of OH can quench Fe. IV After treatment with dimethyl sulfoxide (DMSO), this characteristic signal almost completely disappeared. This significant difference under the action of different quenchers conclusively proves that the dominant active species for the efficient oxidative degradation of recalcitrant pollutants in the device of this invention is the in-situ generated Fe. IV rather than traditional • OH. Reference Figure 8 The characteristic peak intensity of DMPO-H* gradually decreased with increasing reaction time, indicating that H* was continuously consumed and participated in the reaction. In the apparatus of this invention, oxidizing and reducing active substances coexist.

[0023] refer to Figure 9 This embodiment compares the Fe in the Fe-DSA redox apparatus and the Fe-DSA apparatus. 2+ Fe 3+ Fe IV The steady-state concentration. Thanks to the efficient reduction effect of H* continuously generated by the cathode of this invention, the Fe accumulated in the device... 3+ Rapidly reduced and regenerated into Fe 2+ This greatly accelerates the closed-loop circulation of iron. Under this highly efficient circulation mechanism, Fe, which plays a crucial role in the degradation of iron in the device of this invention... IV The steady-state concentration was significantly increased, reaching approximately 1.7 times that of the Fe-DSA device.

[0024] refer to Figure 10 This embodiment compares the residual NO3 in three different electrochemical treatment devices. − Concentration. The final accumulated NO3 in the Fe-DSA-redox apparatus of this invention. − The concentration was extremely low, significantly lower than that of traditional Fe-DSA devices. This fully demonstrates that the NO3 concentration generated by traditional oxidation processes is extremely low. − Accumulation, and this invention utilizes H* generated in situ at the cathode to successfully remove NO3 produced by oxidation. − The intermediate undergoes efficient reduction and elimination, converting it into ammonia nitrogen or harmless nitrogen gas.

[0025] refer to Figure 11 To evaluate the industrial application potential of the device of this invention, a long-term continuous flow degradation experiment lasting 60 hours was conducted. The experiment continuously treated five typical pollutants (phenol, ammonia nitrogen, p-cresol, p-nitrophenol, and 1-naphthol) from coal chemical wastewater. Throughout the 60-hour operation, the device exhibited extremely high catalytic stability, with the removal efficiency of the five pollutants consistently remaining above 98.2%, and no significant performance degradation observed. (Reference) Figure 12 The device exhibited extremely strong operational stability, and after 15 consecutive processing cycles, the concentration of metallic Mn leaching from the material was less than 0.045 mg / L.

[0026] refer to Figure 13 In treating actual coal chemical reverse osmosis concentrate, compared to Fe-DSA and DSA units, this device improved TOC removal efficiency by 30.38%-60.51%, TN removal efficiency by 34.63%-61.18%, and COD removal efficiency by 13.74%-50.43%, while reducing power consumption by 43.21%-51.03%. (Reference) Figure 14 Traditional advanced oxidation and electrochemical technologies generally face high energy consumption bottlenecks when treating coal chemical reverse osmosis concentrate. Specifically, the energy consumption of traditional ozone oxidation and UV / chlorine electrochemical processes is as high as 55.01 kWh / kg COD and 283.20 kWh / kg COD, respectively, mainly due to the huge energy consumption caused by ozone generation and continuous UV irradiation. In addition, the typical electro-Fenton process, which relies on continuous and energy-intensive aeration to generate hydrogen peroxide in situ, also consumes 48.54 kWh / kg COD. In contrast, the device of this invention cleverly utilizes the chloride ions naturally present in the wastewater to drive the reaction, completely eliminating the need for external oxidant addition. When treating homogeneous coal chemical reverse osmosis concentrate, the energy consumption of this device is significantly reduced to 17.61 kWh / kg COD. This significant low energy consumption not only greatly reduces operating costs but also completely breaks down the economic barriers in the deep purification of chlorine-containing complex organic wastewater, giving this technology a very prominent advantage for industrial application.

[0027] In summary, this invention ingeniously constructs a dual-effect electrochemical system of "anodic selective oxidation-cathode reduction," utilizing Fe... IV The targeted mineralization and H* reduction detoxification are deeply coupled, successfully breaking through the bottleneck of pollutant mineralization and toxic byproduct accumulation in the treatment of chlorine-containing complex organic wastewater. This invention, through material innovation and a closed-loop iron / nitrogen recycling mechanism, simultaneously overcomes three core challenges: limited reaction kinetics in complex systems, severe secondary pollution, and high operating costs. It provides an efficient, safe, and economical solution for the deep purification and zero discharge of chlorine-containing wastewater from coal chemical and other industries.

Claims

1. A device for the electrochemical oxidation-reduction synergistic treatment of chlorine-containing complex organic wastewater, characterized in that, The device includes: a reaction vessel (1) for adding wastewater and ferrous iron; a chlorine-evolving anode (2) and a cathode (3) capable of generating atomic hydrogen in situ, disposed within the reaction vessel (1); a DC power supply (4) connecting the anode (2) and the cathode (3); and a stirrer (5) provided at the bottom of the reaction vessel (1).

2. The apparatus according to claim 1, characterized in that, The anode (2) is a shape-stable anode with electro-oxidation chlorine evolution function, or a lead dioxide anode or a boron-doped diamond anode.

3. The apparatus according to claim 1, characterized in that, The reduction cathode (3) is loaded with a catalytic material for in-situ generation of atomic hydrogen. The catalytic material includes at least one of palladium metal, palladium alloy, and nitrogen and / or phosphorus co-doped carbon-based catalytic materials containing transition metals, wherein the transition metal is selected from at least one of manganese, cobalt, iron, copper, and nickel.

4. A method for treating chlorine-containing complex organic wastewater using the electrochemical oxidation-reduction synergistic device as described in any one of claims 1 to 3, characterized in that, The process of treating wastewater containing chloride ions, ammonia nitrogen, and organic pollutants by synergistic oxidation of high-valence iron and reduction of atomic hydrogen includes: introducing the chloride-containing complex organic wastewater to be treated into the reaction vessel (1) and adjusting the pH value of the wastewater to 3.0-7.0; adding ferrous salt to the wastewater to make the concentration of ferrous ions in the wastewater 0.1-1.0 mM, and turning on the DC power supply (4) to carry out the electrochemical reaction; during the reaction, the anode (2) oxidizes chloride ions to active chlorine, and the active chlorine activates the ferrous ions in the wastewater to generate high-valence iron, so as to oxidize the ammonia nitrogen and organic pollutants in the wastewater; at the same time, the cathode (3) generates atomic hydrogen in situ, reduces and dechlorinates the chloride-containing intermediates generated in the oxidation process in situ, and reduces the iron ions generated in the reaction to ferrous ions, thereby realizing the recycling of iron species.

5. The method according to claim 4, characterized in that, The DC power supply (4) provides a reactive current density of 7.5-12.5 mA / cm². 2 .

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