Improved method and device for treating wastewater by double anode peroxide flocculation

Abstract

The application belongs to the technical field of sewage treatment, and more particularly, an improved double-anode peroxide flocculation sewage treatment method and device are provided.The method and device can remove multiple pollutants in sewage at the same time, improve mineralization efficiency, reduce energy consumption, and reduce sludge production.The application solves the problems of low mineralization efficiency and large iron sludge production in conventional peroxide flocculation water treatment processes.The new sewage treatment device provided by the application comprises an air active diffusion cathode, a modified carbon felt cathode, an aluminum anode, an iron anode, a reaction container, a direct current power supply, and a stirrer.Compared with the conventional peroxide flocculation process, the application can increase the mineralization efficiency of pollutants by nearly 2 times, and the energy consumption and sludge production are reduced by 55% and 40.5% respectively.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sewage treatment, in particular, the present application is a method and device for improved double anode peroxide flocculation sewage treatment. BACKGROUND

[0002] Landfill leachate is complex in water quality, high in color, rich in organic matter, ammonia nitrogen, heavy metals and other pollutants, and poor in biodegradability, which is extremely difficult to treat and poses a great threat to human health and ecological environment. Traditional physical, chemical and biological treatment processes are difficult to effectively treat such sewage, and a single treatment process is also difficult to meet the current requirements for landfill leachate treatment, so it is necessary to reduce and harmlessly treat landfill leachate by means of cooperation and combination of multiple treatment methods.

[0003] Electrochemical method has the advantages of high efficiency, environmental protection, simple operation and good controllability, and has been proved to be able to effectively remove COD, ammonia nitrogen, heavy metals and other pollutants in wastewater, and is widely used in landfill leachate sewage treatment. Among them, electro-Fenton and electro-coagulation show good application prospect. Electro-Fenton process generates strong oxidizing • OH attacks pollutants, which can significantly reduce the concentration of organic pollutants and ammonia nitrogen in landfill leachate. Electro-coagulation process generates a series of coagulants (including single-core, multi-core hydroxyl complexes and hydroxides) through metal anode (aluminum or iron) electrolysis, which removes pollutants by flocculation, adsorption and co-precipitation. However, the narrow pH range of electro-Fenton process and the high cost limit its further application, and the anode of electro-coagulation process is easy to wear, the sludge production is large and the pollutants cannot be fundamentally degraded. In order to overcome the above defects, peroxide flocculation process is applied to the treatment of industrial wastewater. Peroxide flocculation process can be regarded as the combination of electro-Fenton and electro-coagulation processes. In this process, the sacrificial anode continuously provides soluble Fe 2+ ions to the solution and H2O2 generated in situ at the cathode to generate • OH to remove pollutants, at the same time, the oxidation product Fe(III) of Fe(II) hydrolyzes to generate Fe(OH)3, which further removes organic pollutants by coagulation. Through this coupling, peroxide flocculation process achieves better degradation effect, and does not need to add additional reagents, with low operation energy consumption, which can be used as a potential scheme for pretreatment of high-concentration organic pollution wastewater. The reaction equation is as follows:

[0004] Anode: Fe - 2e – → Fe(II)

[0005] Cathode: O2+ 2H + + 2e – → H2O2

[0006] Solution: 4Fe(II) + 4H + + O2→ 4Fe(III) + 2H2O

[0007] Fe(II) + H2O2→ Fe(III) + OH – + • OH

[0008] Fe(III) + 3H2O → Fe(OH)3+ 3H +

[0009] However, the traditional peroxide flocculation process produces a large amount of iron sludge, thereby increasing the subsequent management and disposal costs. Therefore, it is necessary to construct an improved peroxide flocculation wastewater treatment method to improve the treatment efficiency while reducing the sludge production, thereby improving the treatment efficiency. SUMMARY

[0010] In view of the problems of low mineralization rate and high sludge production of the traditional peroxide flocculation process, the application provides a treatment device and method for pretreating high-concentration contaminated wastewater by using an improved aluminum-iron dual-anode peroxide flocculation process. The device comprises an air active diffusion cathode (1), a nitric acid modified carbon felt cathode (2), an iron sacrificial anode (3), an aluminum sacrificial anode (4), a reaction container (5), a stirrer (6), and two direct current power sources (7).

[0011] The method for treating wastewater is based on the following principles: (1) The air active diffusion cathode generates H2O2 in situ without aeration, and the Fe 2+ generated by the electrolysis of the iron sacrificial anode reacts to generate • OH to attack pollutants. The nitric acid modified carbon felt promotes the cyclic regeneration of Fe 2+ to promote homogeneous Fenton reaction, reduces the dependence on anode leaching Fe 2+ , improves the mineralization efficiency while reducing the production of iron sludge. (2) The aluminum-iron dual coagulation mode promotes the generation of dominant hydrolysis species, enhances the mineralization effect, and can effectively improve the precipitation of coagulants, reduce the sludge production, and control the residual coagulants. (3) The synergistic effect between aluminum-iron dual coagulation and oxidation, the presence of active species makes more aluminum / iron ions transform into high-polymer hydrolysis products with higher activity, enhances the flocculation effect, and the formation of high-polymer hydrolysis products in turn strengthens the generation of active species, which together achieve the enhancement of mineralization effect and the reduction of sludge production.

[0012] The application is achieved by the following technical solutions:

[0013] According to one aspect of the present application, the present application provides an improved aluminum-iron dual anode peroxide flocculation sewage treatment device, which comprises an air active diffusion cathode (1) without aeration, a nitric acid modified carbon felt cathode (2), an iron anode (3), an aluminum anode (4), a reaction container (5), a stirrer (6), and two direct current power sources (7);

[0014] Further, the air active diffusion cathode (1) and the aluminum anode (4) are connected by a direct current power source to form a loop; the nitric acid modified carbon felt electrode (2) and the iron anode (3) are connected by another direct current power source to form a loop.

[0015] According to another aspect of the present application, the present application provides a method for treating high-concentration contaminated landfill leachate wastewater by using the improved aluminum-iron dual anode peroxide flocculation sewage treatment device. The key to controlling sludge production lies in regulating the intensity of oxidation and coagulation. Current is crucial in peroxide flocculation. By regulating the current, the intensity of Fenton reaction, as well as the total amount and speed of flocculants produced, can be controlled. Generally, the metal ions dissolved from the anode are proportional to the applied current. Considering anode consumption, sludge production, and economic cost, a small range of current is selected for treatment. The specific steps are as follows:

[0016] A dual anode peroxide flocculation reactor is built, the pH value of the raw water is adjusted to 3-11, and the current density of the air active diffusion cathode / aluminum anode electrode group and the nitric acid modified carbon felt cathode / iron anode electrode group is optimized, respectively. The current range of the former is 2-6 mA / cm 2 , and the current range of the latter is 0.6-2.5 mA / cm 2 .

[0017] The present application has the following outstanding features:

[0018] (1) The sewage treatment device couples the advantages of electrocoagulation and electro-Fenton process, greatly improving the mineralization efficiency of wastewater. The TOC removal rate and removal rate are 1.47-3.52 times and 1.73-4.73 times that of the conventional peroxide flocculation process, respectively.

[0019] (2) The sewage treatment device can simultaneously remove TN, UV 254 , and colority in landfill leachate and other wastewater, with removal rates 1.28-2.3 times, 1.31-1.87 times, and 1.22-2.09 times that of other processes, respectively.

[0020] (3) The sewage treatment device reduces sludge production and energy consumption while improving mineralization rate. The sludge production and energy consumption are reduced by 30%-40.5% and 55%-75.6% compared with the conventional peroxide flocculation process.

[0021] (4) The aluminum-iron dual coagulation mode in the sewage treatment device reduces the content of mononuclear hydrolysis products, increases the content of oligomeric and polymeric hydrolysis products, promotes the conversion of monomeric aluminum / iron to higher polymerization state in the hydrolysis process, and improves the coagulation effect. The content of the advantageous hydrolysis species is 2.71-3.57 times that of the conventional peroxide flocculation process.

[0022] (5) The aluminum-iron dual coagulation mode in the sewage treatment device can strengthen the production of active species, produce more • OH, and vice versa. The generation of active species makes more aluminum / iron ions convert into low / high polymerization state hydrolysis products with higher activity, enhancing flocculation. The synergistic effect between the two produces more • OH, and the H2O2 utilization rate is 3.31-10.51 times that of the conventional peroxide flocculation process.

[0023] (6) The aluminum-iron dual coagulation mode in the sewage treatment device can effectively control the residual coagulant by regulating the hydrolysis state of aluminum / iron. The dissolved metal ion concentration in the solution is 5.8%-27% of that of the conventional peroxide flocculation process. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a schematic diagram of the reaction device of the present application;

[0025] Figure 2 is a comparison chart of TOC removal rates of the reaction device of the present application and the conventional peroxide flocculation device;

[0026] Figure 3 is a comparison chart of TN, UV 254 and color removal rates of the reaction device of the present application and the conventional peroxide flocculation device;

[0027] Figure 4 is a comparison chart of sludge production and energy consumption of the reaction device of the present application and the conventional peroxide flocculation device;

[0028] Figure 5 is a comparison chart of the morphological distribution changes of aluminum / iron hydrolysis products at different times in the reaction device of the present application and the conventional peroxide flocculation device;

[0029] Figure 6 is a comparison chart of H2O2 utilization rates in the reaction device of the present application and the conventional peroxide flocculation device;

[0030] Figure 7 is a comparison chart of total iron ion concentrations in the reaction device of the present application and the conventional peroxide flocculation device;

[0031] Figure 8 is a chart of TOC removal rates of the reaction device of the present application at different pH values;

[0032] Figure 9 TN, UV and color removal rate graph of the reaction device of the present application at different pH values; 254 and color removal rate graph of the reaction device of the present application at different pH values;

[0033] Figure 10 TN, UV and color removal rate graph of the reaction device of the present application at different pH values; DETAILED DESCRIPTION

[0034] Two embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present application, and cannot be understood as limiting the present application.

[0035] The present application proposes an improved dual-anode peroxo-flocculation wastewater treatment device. According to an embodiment of the present application, referring to Figure 1 , the treatment device includes an air active diffusion cathode (1) with an effective area of 6 cm 2 , a modified carbon felt cathode (2) with an effective area of 6 cm 2 , an iron anode (3) with an effective area of 6 cm 2 , an aluminum anode (4) with an effective area of 6 cm 2 , a 120 mL reaction container (5), a stirrer (6), and two direct current power sources (7);

[0036] The air active diffusion cathode (1) and the aluminum anode (4) are connected by a direct current power source to form a loop; the modified carbon felt electrode (2) and the iron anode (3) are connected by another direct current power source to form a loop; the distance between the two groups of cathodes and anodes is 1 cm;

[0037] Embodiment one:

[0038] The improved dual-anode peroxo-flocculation wastewater treatment device greatly improves the mineralization efficiency compared to the traditional peroxo-flocculation. Referring to Figure 2 , when the current density is 3.3 mA / cm 2 (air active diffusion electrode / aluminum) and 1 mA / cm 2 (modified carbon felt cathode / iron) respectively, and pH=6, the TOC removal rate of the system after 180 minutes is 61.8% (318.15 mg / L), which is 1.97 times that of the traditional peroxo-flocculation system, and the removal rate is also 2.26 times that of the traditional peroxo-flocculation system.

[0039] The improved dual-anode peroxo-flocculation wastewater treatment device can remove TN, UV 254 and color in wastewater at the same time as degrading TOC. Referring to Figure 3 , when the current density is 3.3 mA / cm 2 (air active diffusion electrode / aluminum) and 1 mA / cm2 The device removed 47.35% of TN, 95.90% of UV and 97.33% of colority after 180 minutes, which increased by 40.5%, 53.83% and 32.8% respectively compared with the traditional peroxi-flocculation device. 254

[0040] The improved dual-anode peroxi-flocculation device greatly improved the mineralization efficiency and other pollutants removal efficiency, while reducing the power consumption and sludge production. Figure 4 , pH=6, current density of 3.3 mA / cm 2 (Air active diffusion electrode / Al) and 1 mA / cm 2 (modified carbon felt cathode / Fe), the sludge produced by the traditional peroxi-flocculation process reached 2.358 g / L, which was 1.68 times of the improved dual-anode process (1.403 g / L), and the power consumption of the improved dual-anode device (0.754 kWh / kg TOC) was also much lower than that of the traditional peroxi-flocculation process (1.672 kWh / kg TOC), which reduced by about 55%.

[0041] Figure 5 The improved dual-anode peroxi-flocculation device reduced the content of mononuclear hydrolysis products and increased the content of oligomeric and polymeric hydrolysis products compared with the single system, thereby enhancing the mineralization effect. pH=6, current density of 3.3 mA / cm 2 (Air active diffusion electrode / Al) and 1 mA / cm 2 (modified carbon felt cathode / Fe), the content of dominant hydrolysis species in the improved dual-anode process was 2.71 times of that in the traditional peroxi-flocculation process after 30 minutes of reaction. This dual-coagulation can promote the conversion of monomeric aluminum / iron to higher polymerization state during the hydrolysis process, enhance the adsorption and bridging and net capture ability, and greatly improve the mineralization effect.

[0042] Figure 6 The H2O2 utilization rate in the improved dual-anode peroxi-flocculation device was much higher than that in the traditional peroxi-flocculation system. pH=6, current density of 3.3 mA / cm 2 (Air active diffusion electrode / Al) and 1 mA / cm 2 ​​​The H2O2 utilization rate of the dual anode peroxide flocculation system was 3.31 times that of the traditional peroxide flocculation system. On the one hand, aluminum and iron in the system can activate H2O2 as dual active sites to produce more active species; on the other hand, the dual coagulation mode produces more active hydrolysis species and high polymerization hydrolysis products, which can strengthen the generation of active species and the removal of pollutants, and the presence of active species can improve the transformation of more aluminum / iron ions into dominant hydrolysis products, thereby improving the precipitation of flocculation. This transformation not only promotes the mineralization of pollutants but also reduces sludge production. Therefore, the improved dual anode peroxide flocculation process can more thoroughly remove organic pollutants and reduce the risk of secondary pollution.

[0043] Reference Figure 7 The total dissolved metal ion concentration in the improved dual anode peroxide flocculation wastewater treatment device was much lower than that in the traditional peroxide flocculation system. When the current density was 3.3 mA / cm 2 (Air active diffusion electrode / aluminum) and 1 mA / cm 2 (modified carbon felt cathode / iron), the total dissolved metal ion concentration in the solution was 0.7807 mg / L after 180 minutes of reaction, which was only about 5% of that in the traditional peroxide flocculation system. This indicates that the dual coagulation mode of aluminum and iron can effectively control the residual coagulant in the solution, and the co-hydrolysis of aluminum and iron as dual coagulants can effectively improve the precipitation of coagulants, providing a new approach to improving coagulation performance and controlling coagulant residuals.

[0044] Example Two:

[0045] Reference Figure 8 The improved dual anode peroxide flocculation wastewater treatment device showed excellent mineralization effect in the pH range of 3-8.5, and the current density was 5 mA / cm 2 (Air active diffusion electrode / aluminum) and 1.5 mA / cm 2 (modified carbon felt cathode / iron), which can remove 38%-57% of TOC and has good tolerance to pH.

[0046] Reference Figure 9 The improved dual anode peroxide flocculation wastewater treatment device maintained a high removal rate of TN, UV 254 and color in the pH range of 3-8.5, and the current density was 5 mA / cm 2 (Air active diffusion electrode / aluminum) and 1.5 mA / cm 2 (modified carbon felt cathode / iron), which can degrade 35%-47% of TN, 75%-97% of UV 254 and 86%-98% of color, showing potential for application in actual wastewater.

[0047] Reference Figure 10 The improved dual-anode peroxide flocculation wastewater treatment device shows a trend of first decreasing and then increasing in energy consumption and sludge yield in the pH range of 3-8.5, and when the current density is 5 mA / cm 2 (Air active diffusion electrode / aluminum) and 1.5 mA / cm 2 (modified carbon felt cathode / iron), the energy consumption of the device is 1.804-3.004 kWh / kg TOC, and the sludge yield is 1.686-2.336 g / L, and the device maintains low energy consumption and sludge yield in a wider pH range, which is a cost-effective peroxide flocculation wastewater treatment method.

[0048] In summary, the improved dual-anode peroxide flocculation wastewater treatment device and method proposed by the application can simultaneously remove multiple pollutants in actual contaminated wastewater, and the aluminum-iron dual coagulation and oxidation work together, which not only improves the mineralization efficiency but also greatly reduces the energy consumption and sludge yield. At the same time, the dual coagulation mode effectively controls the residual coagulant in the solution after the reaction, reduces the difficulty and cost of subsequent operation, and is a promising pretreatment method for high-concentration and difficult-to-degrade actual wastewater.

Claims

1. A method for improved dual anode peroxide flocculation wastewater treatment, characterized by, The device for improving double anode peroxide flocculation sewage treatment includes air active diffusion cathode (1) without aeration, nitric acid modified carbon felt cathode (2), iron anode (3), aluminum anode (4), reaction container (5), stirrer (6) and two direct current power sources (7); the air active diffusion cathode (1) is connected with the aluminum anode (4) through the direct current power source, and the nitric acid modified carbon felt cathode (2) and the iron anode (3) are connected through another direct current power source; during treatment, the pH value of sewage is adjusted to 3-11, the current of the two groups of electrodes is respectively optimized, the current range of the former is 2-6 mA / cm 2 , and the current range of the latter is 0.6-2.5 mA / cm 2 , and the device is used for organic sewage treatment.

2. The method of claim 1, wherein, Aluminum electrode was used to replace the traditional electrochemical treatment of shape stable anode.

3. The method of claim 1, wherein, There is a synergistic effect between aluminum-iron dual coagulation and oxidation, which improves the utilization rate of H2O2 and strengthens the generation of hydroxyl radicals, achieving enhanced mineralization effect and sludge reduction under low energy consumption.

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