Low-carbon gradient purification and salt resource recovery method for industrial wastewater containing high-concentration sulfite

Abstract

The invention provides a low-carbon gradient purification and salt resource recovery method for industrial wastewater containing high-concentration sulfite. Aiming at industrial wastewater containing high-concentration sulfite such as catalytic cracking flue gas desulfurization, an air aeration oxidation, ozone oxidation and electrocatalytic oxidation three-stage synergistic gradient oxidation system is invented, and salt resource recovery is realized through cooling crystallization coupling interface concentration circulation purification. The complementation of oxidation technologies with different energy consumption densities is realized by adopting an air aeration, ozone and electro-catalysis gradient integrated process, and the recovery of high-purity sodium sulfate is realized by adopting a cooling crystallization and photo-thermal interface concentration circulating process, so that the method has the characteristics of low energy consumption, small carbon emission, high resource recovery rate and the like; the system is especially suitable for the northwest regions with strong daytime sunlight, large day-night temperature difference and low air humidity in China.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of environmental protection wastewater treatment, and particularly relates to a low-carbon gradient purification and salt resource recovery method for industrial wastewater containing high-concentration sulfite. BACKGROUND

[0002] In the industrial production of papermaking, petroleum chemical industry and textile, wastewater containing high-concentration sulfite is generated, which seriously affects the comprehensive wastewater treatment of enterprises. Taking the flue gas desulfurization wastewater in the heavy oil catalytic cracking in the petroleum refining industry as an example, the typical wastewater is generated in the desulfurization treatment of the flue gas generated by the catalytic cracking device. The sulfite with reducing property is easily oxidized by potassium dichromate in the chemical oxygen demand (COD) test, resulting in a significant high test result, which seriously interferes with the true evaluation of the organic pollutants in the wastewater. In addition, the high-concentration salt will affect the subsequent biological degradation and flocculation precipitation of the wastewater.

[0003] At present, the treatment methods for the wastewater containing high-concentration sulfite mainly include the aeration oxidation method and the ozone oxidation method. However, the aeration oxidation method has the problem of incomplete oxidation, and part of the sodium sulfite is converted into sodium sulfate. Although the ozone oxidation method has high efficiency, the energy consumption cost is high. It is worth noting that the oxidation of sodium sulfite (Na2SO3) to sodium sulfate (Na2SO4) is an important chemical raw material, and if high-purity recovery can be achieved, it can promote the resource utilization of wastewater. However, about 80% of the current sodium sulfate recovery process adopts the heating evaporation crystallization method, which has high energy consumption and cost, and the product is a mixed salt with complex composition and high impurity content, which has limited utilization value. The emerging photothermal interface evaporation technology has attracted much attention, and has significant application potential in the northwest region of China where the sunshine is long and the land resources are abundant.

[0004] Therefore, there is an urgent need in the art for a low-carbon gradient purification and salt resource recovery method for industrial wastewater containing high-concentration sulfite. SUMMARY

[0005] The purpose of the present application is to solve the problems of low efficiency, high energy consumption and resource loss in the wastewater treatment process in the prior art.

[0006] To achieve the purpose of solving the above problems, the technical scheme adopted by the present application is to provide a low-carbon gradient purification and salt resource recovery method for industrial wastewater containing high-concentration sulfite, comprising the following steps:

[0007] Step S1, connecting a microporous aeration head through an air pump, adjusting the aeration amount and controlling the aeration time, and performing air aeration oxidation pretreatment on the wastewater;

[0008] Step S2, generating ozone through an ozone generator, adjusting the ozone aeration amount and the ozone concentration, and performing ozone oxidation treatment on the pretreated wastewater;

[0009] Step S3: By adjusting the current and voltage through electrochemical oxidation, the wastewater after ozone oxidation is electrocatalytically oxidized to simultaneously oxidize the remaining sulfites and mineralized organic matter, thus eliminating the influence of organic matter on subsequent crystallization.

[0010] Step S4: Cool the wastewater after gradient purification by aeration with cold air to crystallize it. After the crystals have completely precipitated, discharge the supernatant to obtain sodium sulfate crystals.

[0011] Step S5: The filtered uncrystallized supernatant is sent to the photothermal interface concentration tank for photothermal interface concentration to concentrate the sodium sulfate concentration of the wastewater to 15% to 20%, and then subjected to secondary cooling crystallization to separate the supernatant from the crystallized salt.

[0012] Step S6: Repeat step S5 continuously until all wastewater evaporates and crystalline sodium salt is obtained.

[0013] Preferably, in step S1, air aeration oxidation is used as a pretreatment to oxidize the sulfite component in a low-energy manner. Hydrochloric acid solution is added to adjust the pH of the wastewater to 4-6, and the air aeration rate is generally 100-300 m³ / h. 3 Air / ton of water, aeration time 4-6 hours.

[0014] Preferably, in step S2, relying on the strong oxidizing properties of ozone, sulfites and organic matter are further oxidized. Sodium hydroxide solution is added to adjust the pH of the wastewater to 9-11, and the ozone aeration rate is generally 30-80 m³ / h. 3 Ozone per ton of water, with an ozone concentration typically between 10 and 20 mg / L, and an aeration time of 15 to 30 minutes.

[0015] Preferably, in step S3, the highly oxidizing activating substances generated at the anode and cathode during the electrocatalytic oxidation process directly or indirectly degrade pollutants, achieving efficient and deep oxidation. The anode material is selected as a boron-doped diamond (BDD) electrode with corrosion resistance, and the cathode is generally selected as a titanium plate, graphite, or other electrodes. The voltage is generally 2–5V, and the current density is generally 40–80 mA / cm². 2 The reaction time is 15–30 min.

[0016] Preferably, in step S4, to prevent scale formation of crystalline salt on the pipe wall and the inner wall of the container, air aeration cooling should be used, with the cold air temperature generally between 2 and 10°C. The aeration pipe is a perforated pipe with an aeration hole diameter of 5 to 10 mm, and the aeration holes are vertically downward to prevent salt crystallization from clogging the aeration holes. The crystallization time is generally 2 to 4 hours.

[0017] Preferably, in step S5, the photothermal interface evaporator is a salt-resistant polyurethane sponge evaporator, which uses 40-50 PPI polyurethane sponge as the matrix, and after cleaning, loads a polyvinyl alcohol-carbon black-PEDOT:PSS composite photothermal layer, and obtains it by glutaraldehyde crosslinking and freeze-drying curing.

[0018] This invention provides a low-carbon gradient purification and salt resource recovery method for industrial wastewater containing high concentrations of sulfite. Specifically targeting industrial wastewater containing high concentrations of sulfite, such as that from catalytic cracking flue gas desulfurization, a three-stage synergistic gradient oxidation system of air aeration oxidation, ozone oxidation, and electrocatalytic oxidation is invented. Salt resource recovery is achieved through a cooling crystallization coupled interface concentration and cyclic purification process. The integrated process of air aeration, ozone, and electrocatalytic gradients achieves complementary oxidation technologies with different energy densities, and the cyclic process of cooling crystallization and photothermal interface concentration achieves the recovery of high-purity sodium sulfate. This method features low energy consumption, low carbon emissions, and high resource recovery rate, making it particularly suitable for the Northwest region of my country, characterized by strong daytime sunshine, large diurnal temperature range, and low air humidity.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. This invention utilizes a three-stage synergistic gradient oxidation system of air aeration oxidation, ozone oxidation, and electrocatalytic oxidation to generate a variety of strong oxidizing substances, achieving complementarity of different oxidation mechanisms, thereby achieving a COD removal rate of over 95%.

[0021] 2. This invention utilizes air aeration pretreatment to reduce the burden of ozone oxidation, reduce reagent consumption, and improve energy utilization efficiency.

[0022] 3. This invention utilizes cold air aeration cooling crystallization and photothermal interface concentration and circulation purification to achieve wastewater concentration and sulfate crystal recovery and utilization, which is particularly suitable for the climate conditions of strong daytime sunshine, large diurnal temperature difference and low air humidity in Northwest my country. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the method for low-carbon gradient purification and salt resource recovery of industrial wastewater containing high concentrations of sulfite according to the present invention.

[0024] Figure 2 The graph shows the solubility of common salts in industrial wastewater containing high concentrations of sulfites as a function of temperature. In (a), the common salt is Na2SO3; and in (b), the common salt is Na2SO4. Detailed Implementation

[0025] To make the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings:

[0026] like Figures 1-2As shown, this invention provides a method for low-carbon gradient purification and salt resource recovery of industrial wastewater containing high concentrations of sulfite, comprising the following steps:

[0027] Step S1: Connect the microporous aeration head to the air pump, adjust the aeration rate and control the aeration time to perform air aeration oxidation pretreatment on the wastewater. Air aeration oxidation is used as a pretreatment method to oxidize sulfite components in a low-energy manner. Hydrochloric acid solution is added to adjust the pH of the wastewater to 4-6. The air aeration rate is generally 100-300 m³ / h. 3 Air / ton of water, aeration time 4-6 hours.

[0028] Step S2: Ozone is generated using an ozone generator. The ozone aeration rate and concentration are adjusted to perform ozone oxidation treatment on the pretreated wastewater. Relying on the strong oxidizing properties of ozone, sulfites and organic matter are further oxidized. Sodium hydroxide solution is added to adjust the pH of the wastewater to 9-11. The ozone aeration rate is generally 30-80 m³ / h. 3 Ozone per ton of water, with an ozone concentration typically between 10 and 20 mg / L, and an aeration time of 15 to 30 minutes.

[0029] Step S3: Using electrochemical oxidation, the current and voltage are adjusted to perform electrocatalytic oxidation treatment on the wastewater after ozone oxidation, simultaneously oxidizing residual sulfites and mineralized organic matter, eliminating the influence of organic matter on subsequent crystallization. The highly oxidizing activating substances generated at the anode and cathode during the electrocatalytic oxidation process directly or indirectly degrade pollutants, achieving efficient and deep oxidation. The anode material is selected as a boron-doped diamond (BDD) electrode with corrosion resistance, while the cathode is generally made of titanium plates, graphite, or similar electrodes. The voltage is typically 2–5V, and the current density is typically 40–80 mA / cm². 2 The reaction time is 15–30 min.

[0030] Step S4: The wastewater after gradient purification is cooled and crystallized by cold air aeration. After the crystals have completely precipitated, the supernatant is discharged to obtain sodium sulfate crystals. To prevent scaling of the crystallized salt on the pipe and container walls, air aeration cooling should be used, with the cold air temperature generally between 2 and 10°C. Based on the solubility curves of sodium sulfate and sodium sulfite as a function of temperature, this cooling process keeps the wastewater temperature far below the saturation point of sodium sulfate, thus creating sufficient supersaturation driving force to promote preferential crystallization of sodium sulfate. The remaining sodium sulfite, due to its high solubility at low temperatures, remains in the mother liquor, ensuring product purity. The aeration pipes are perforated, with aeration holes of 5–10 mm in diameter, and the holes are vertically downward to prevent salt crystallization from clogging the aeration holes. The crystallization time is generally 2–4 hours.

[0031] Step S5: The filtered uncrystallized supernatant is sent to the photothermal interface concentration tank for photothermal interface concentration. The sodium sulfate concentration of the wastewater is concentrated to 15% to 20%. Secondary cooling and crystallization are carried out to separate the supernatant from the crystallized salt. The photothermal interface evaporator is a salt-resistant polyurethane sponge evaporator. It uses 40 to 50 PPI polyurethane sponge as the matrix, and after cleaning, it is loaded with a polyvinyl alcohol-carbon black-PEDOT:PSS composite photothermal layer, which is then crosslinked with glutaraldehyde and freeze-dried to cure the material.

[0032] Step S6: Repeat step S5 continuously until all wastewater evaporates and crystalline sodium salt is obtained.

[0033] Figure 2 The graph shows the solubility of common salts in industrial wastewater containing high concentrations of sulfite as a function of temperature. In (a), the common salt is Na₂SO₃; in (b), it is Na₂SO₄. It can be seen that the solubility of sodium sulfite (Na₂SO₃) and sodium sulfate (Na₂SO₄) is the same at 27.8℃. Below 27.8℃, the solubility of sodium sulfate is much lower than that of sodium sulfite, and decreases sharply with decreasing temperature. Within the crystallization temperature range of 2–10℃, the solubility of sodium sulfate is only about 5–9 g / 100 g water (approximately 50,000 to 90,000 mg / L), a low level that contrasts sharply with the extremely high sodium sulfate concentration in the system. This easily leads to supersaturation and promotes the preferential growth and crystallization of sodium sulfate, while sodium sulfite, due to its high solubility, remains in the mother liquor, achieving efficient separation of the two and recovery of high-purity sodium sulfate.

[0034] Example 1

[0035] The wastewater quality of the heavy oil catalytic cracking flue gas desulfurization wastewater from a petrochemical plant in Xinjiang is as follows: COD 8991.36 mg / L, nitrite 3500 mg / L, sulfite 35000 mg / L, and sulfate 35000 mg / L. Zero discharge of wastewater and recovery of salt resources were achieved using the following method, the specific steps of which are as follows:

[0036] Step S1: Add hydrochloric acid solution to adjust the pH of the water sample to 4, and control the aeration rate to 250 m³ / h. 3 Air per ton of water was subjected to air aeration oxidation treatment for 6 hours. After treatment, the COD removal rate of the water sample was 42.18%, and the sulfate concentration increased to 66958.06 mg / L.

[0037] Step S2: Add sodium hydroxide solution to adjust the pH of the water sample to 10, and control the aeration rate to 80 m³ / h. 3 Ozone per ton of water, with an ozone concentration of 15 mg / L, was used for ozone oxidation treatment for 30 minutes. After treatment, the COD removal rate of the water sample was 85.52%, and the sulfate concentration increased to 94362.27 mg / L.

[0038] Step S3: The anode is a boron-doped diamond (BDD) electrode, the cathode is a titanium plate, and a voltage of 5V and a current density of 60mA / cm are applied. 2 After electrocatalytic oxidation treatment for 30 minutes, the COD removal rate was 98.28%, and the sulfate concentration after gradient oxidation treatment increased to 115821.04 mg / L, achieving the purpose of gradient purification of industrial wastewater containing high concentrations of sulfite.

[0039] Step S4: The wastewater after gradient oxidation is cooled by air aeration at night (10-15℃ in summer; -12--8℃ in winter). The aeration holes are 5mm in diameter and vertically downward. The low temperature causes the sodium sulfate in the solution to reach a supersaturated state due to a sharp decrease in solubility. After 2 hours of cold air aeration, sodium sulfate crystals precipitate out, are filtered and dried to obtain anhydrous sodium sulfate. The recovery rate of sodium sulfate is 58.07%, and the sulfate concentration of the remaining water sample is 52751.7 mg / L.

[0040] Step S5: The filtered, non-crystallized supernatant is sent to a photothermal interface concentration tank. The photothermal interface evaporator is a salt-resistant polyurethane sponge evaporator, using 40-50 PPI polyurethane sponge as the matrix. After cleaning, a polyvinyl alcohol-carbon black-PEDOT:PSS composite photothermal layer is loaded, and then cross-linked with glutaraldehyde and freeze-dried for curing. During the day, under the high temperature of the sun, the interface temperature rises sharply, causing the water to evaporate rapidly, with an evaporation rate of 8.95 kg / (m²). 2 (·h), the sodium sulfate concentration in the wastewater was concentrated by 18.3%, and the sulfate concentration in the concentrated water sample rose to 62405.27 mg / L;

[0041] Step S6: Repeat step S5 until all the wastewater evaporates and crystalline sodium salt is obtained.

[0042] The crystalline sodium salt prepared using this embodiment has a total sodium sulfate recovery rate of 86.7% and a purity of 98.16%, achieving the goal of resource recovery of sodium sulfate from industrial wastewater containing high concentrations of sulfite.

[0043] Example 2

[0044] The wastewater quality of bleaching wastewater from a paper mill in Ningxia is as follows: COD reaches 6542.18 mg / L, sulfite 28500 mg / L, and sulfate 15000 mg / L. The specific steps are as follows:

[0045] Step S1: Add hydrochloric acid solution to adjust the pH of the water sample to 4, and control the aeration rate to 220 m³ / h. 3 Air per ton of water was subjected to air aeration oxidation treatment for 6 hours. After treatment, the COD removal rate of the water sample was 39.82%, and the sulfate concentration increased to 27689.35 mg / L.

[0046] Step S2: Add sodium hydroxide solution to adjust the pH of the water sample to 9, and control the aeration rate to 70 m³ / h. 3 Ozone per ton of water, with an ozone concentration of 20 mg / L, was used for ozone oxidation treatment for 30 minutes. After treatment, the COD removal rate of the water sample was 82.35%, and the sulfate concentration increased to 67152.68 mg / L.

[0047] Step S3: The anode is a boron-doped diamond (BDD) electrode, the cathode is a titanium plate, and a voltage of 5V and a current density of 80mA / cm are applied. 2 After electrocatalytic oxidation treatment for 30 minutes, the COD removal rate was 97.65%, and the sulfate concentration after gradient oxidation treatment was 78926.41 mg / L, achieving the purpose of gradient purification of industrial wastewater containing high concentrations of sulfite.

[0048] Step S4: The wastewater after gradient oxidation is cooled by air aeration at night (10-15℃ in summer; -12--8℃ in winter). The aeration holes are 5mm in diameter and vertically downward. The low temperature causes the sodium sulfate in the solution to reach a supersaturated state due to a sharp decrease in solubility. After 2 hours of cold air aeration, sodium sulfate crystals precipitate out, are filtered and dried to obtain anhydrous sodium sulfate. The recovery rate of sodium sulfate is 55.21%, and the sulfate concentration of the remaining water sample is 35368.27 mg / L.

[0049] Step S5: The filtered, non-crystallized supernatant is sent to a photothermal interface concentration tank. The photothermal interface evaporator is a salt-resistant polyurethane sponge evaporator, using 40-50 PPI polyurethane sponge as the matrix. After cleaning, a polyvinyl alcohol-carbon black-PEDOT:PSS composite photothermal layer is loaded, and then cross-linked with glutaraldehyde and freeze-dried for curing. During the day, under the high temperature of the sun, the interface temperature rises sharply, causing the water to evaporate rapidly, with an evaporation rate of 8.26 kg / (m²). 2 (·h), the sodium sulfate concentration in the wastewater was concentrated by 17.8%, and the sulfate concentration in the concentrated water sample rose to 41663.8 mg / L;

[0050] Step S6: Repeat step S5 until all the wastewater evaporates and crystalline sodium salt is obtained.

[0051] The crystalline sodium salt prepared using this embodiment has a total sodium sulfate recovery rate of 89.64% and a purity of 98.72%, achieving the goal of resource recovery of sodium sulfate from industrial wastewater containing high concentrations of sulfite.

[0052] Example 3

[0053] The wastewater from a dye production plant in Shandong Province has the following characteristics: COD 7856.42 mg / L, sulfite 32800 mg / L, and sulfate 19500 mg / L. The specific steps are as follows:

[0054] Step S1: Add hydrochloric acid solution to adjust the pH of the water sample to 5, and control the aeration rate to 180 m³ / h. 3 Air / ton of water was subjected to air aeration oxidation treatment for 5 hours. After treatment, the COD removal rate of the water sample was 38.94%, and the sulfate concentration increased to 39180.63 mg / L.

[0055] Step S2: Add sodium hydroxide solution to adjust the pH of the water sample to 10, and control the aeration rate to 60 m³ / h. 3 Ozone per ton of water, with an ozone concentration of 15 mg / L, was used for ozone oxidation treatment for 25 minutes. After treatment, the COD removal rate of the water sample was 84.67%, and the sulfate concentration increased to 54924.47 mg / L.

[0056] Step S3: The anode is a boron-doped diamond (BDD) electrode, the cathode is a titanium plate, and a voltage of 4V and a current density of 70mA / cm are applied. 2 After electrocatalytic oxidation treatment for 25 minutes, the COD removal rate was 96.83%, and the sulfate concentration after gradient oxidation treatment was 58123.39 mg / L, achieving the purpose of gradient purification of industrial wastewater containing high concentrations of sulfite.

[0057] Step S4: The wastewater after gradient oxidation is cooled by air aeration at night (10-15℃ in summer; -12--8℃ in winter). The aeration holes are 7mm in diameter and vertically downward. The low temperature causes the sodium sulfate in the solution to reach a supersaturated state due to a sharp decrease in solubility. After 2 hours of cold air aeration, sodium sulfate crystals precipitate out, are filtered and dried to obtain anhydrous sodium sulfate. The recovery rate of sodium sulfate is 52.34%, and the sulfate concentration of the remaining water sample is 27701.6 mg / L.

[0058] Step S5: The filtered, non-crystallized supernatant is fed into a photothermal interface concentration tank. The photothermal interface evaporator is a salt-resistant polyurethane sponge evaporator, using 40-50 PPI polyurethane sponge as the matrix. After cleaning, a polyvinyl alcohol-carbon black-PEDOT:PSS composite photothermal layer is loaded, and then cross-linked with glutaraldehyde and freeze-dried for curing. During the day, under the high temperature of the sun, the interface temperature rises sharply, causing the water to evaporate rapidly, with an evaporation rate of 7.82 kg / (m²). 2 (·h), the sodium sulfate concentration in the wastewater was concentrated by 16.7%, and the sulfate concentration in the concentrated water sample increased to 33255.22 mg / L;

[0059] Step S6: Repeat step S5 until all the wastewater evaporates and crystalline sodium salt is obtained.

[0060] The crystalline sodium salt prepared using this embodiment has a total sodium sulfate recovery rate of 83.45% and a purity of 97.89%, achieving the goal of resource recovery of sodium sulfate from industrial wastewater containing high concentrations of sulfite.

[0061] Example 4

[0062] The wastewater from the bleaching and preservation process at a food processing plant in Fujian Province has the following characteristics: COD 11200.5 mg / L, sulfite 19800 mg / L, and sulfate 8500 mg / L. The specific steps are as follows:

[0063] Step S1: Add hydrochloric acid solution to adjust the pH of the water sample to 4, and control the aeration rate to 180 m³ / h. 3 Air / ton of water was subjected to air aeration oxidation treatment for 6 hours. After treatment, the COD removal rate of the water sample was 38.45%, and the sulfate concentration increased to 20756.63 mg / L.

[0064] Step S2: Add sodium hydroxide solution to adjust the pH of the water sample to 10, and control the aeration rate to 50 m³ / h. 3 Ozone per ton of water, with an ozone concentration of 15 mg / L, was used for ozone oxidation treatment for 30 minutes. After treatment, the COD removal rate of the water sample was 84.12%, and the sulfate concentration increased to 31309.57 mg / L.

[0065] Step S3: The anode is a boron-doped diamond (BDD) electrode, the cathode is a titanium plate, and a voltage of 5V and a current density of 60mA / cm are applied. 2 After electrocatalytic oxidation treatment for 30 minutes, the COD removal rate was 98.51%, and the sulfate concentration after gradient oxidation treatment was 32358.43 mg / L, achieving the purpose of gradient purification of industrial wastewater containing high concentrations of sulfite.

[0066] Step S4: The wastewater after gradient oxidation is cooled by air aeration at night (10-15℃ in summer; -12--8℃ in winter). The aeration holes are 6mm in diameter and vertically downward. The low temperature causes the sodium sulfate in the solution to reach a supersaturated state due to a sharp decrease in solubility. After 3 hours of cold air aeration, sodium sulfate crystals precipitate out, are filtered and dried to obtain anhydrous sodium sulfate. The recovery rate of sodium sulfate is 52.45%, and the sulfate concentration of the remaining water sample is 15386.43 mg / L.

[0067] Step S5: The filtered, non-crystallized supernatant is fed into a photothermal interface concentration tank. The photothermal interface evaporator is a salt-resistant polyurethane sponge evaporator, using 40-50 PPI polyurethane sponge as the matrix. After cleaning, a polyvinyl alcohol-carbon black-PEDOT:PSS composite photothermal layer is loaded, and then cross-linked with glutaraldehyde and freeze-dried for curing. During the day, under the high temperature of the sun, the interface temperature rises sharply, causing the water to evaporate rapidly, with an evaporation rate of 7.85 kg / (m²). 2 (·h), the sodium sulfate concentration in the wastewater was concentrated to 17.5%, and the sulfate concentration in the concentrated water sample rose to 18650.22 mg / L;

[0068] Step S6: Repeat step S5 until all the wastewater evaporates and crystalline sodium salt is obtained.

[0069] The crystalline sodium salt prepared using this embodiment has a total sodium sulfate recovery rate of 85.33% and a purity of 98.91%, achieving the goal of resource recovery of sodium sulfate from industrial wastewater containing high concentrations of sulfite.

[0070] Example 5

[0071] The wastewater from antibiotic production at a pharmaceutical factory in Hubei Province has the following characteristics: COD 9324.67 mg / L, sulfite 29600 mg / L, and sulfate 16800 mg / L. The specific steps are as follows:

[0072] Step S1: Adjust the pH of the water sample to 4 by adding hydrochloric acid solution, and control the aeration rate to 260 m³ / h. 3 Air / ton of water was subjected to air aeration oxidation treatment for 5 hours. After treatment, the COD removal rate of the water sample was 44.25%, and the sulfate concentration increased to 31915.78 mg / L.

[0073] Step S2: Add sodium hydroxide solution to adjust the pH of the water sample to 9, and control the aeration rate to 70 m³ / h. 3 Ozone per ton of water, with an ozone concentration of 15 mg / L, was used for ozone oxidation treatment for 30 minutes. After treatment, the COD removal rate of the water sample was 86.31%, and the sulfate concentration increased to 42806.45 mg / L.

[0074] Step S3: The anode is a boron-doped diamond (BDD) electrode, the cathode is a titanium plate, and a voltage of 4V and a current density of 60mA / cm are applied. 2 After electrocatalytic oxidation treatment for 20 minutes, the COD removal rate was 97.56%, and the sulfate concentration after gradient oxidation treatment was 52438.56 mg / L, achieving the purpose of gradient purification of industrial wastewater containing high concentrations of sulfite.

[0075] Step S4: The wastewater after gradient oxidation is cooled by air aeration at night (10-15℃ in summer; -12--8℃ in winter). The aeration holes are 5mm in diameter and vertically downward. The low temperature causes the sodium sulfate in the solution to reach a supersaturated state due to a sharp decrease in solubility. After 3 hours of cold air aeration, sodium sulfate crystals precipitate out, are filtered and dried to obtain anhydrous sodium sulfate. The recovery rate of sodium sulfate is 56.78%, and the sulfate concentration of the remaining water sample is 22663.93 mg / L.

[0076] Step S5: The filtered, non-crystallized supernatant is fed into a photothermal interface concentration tank. The photothermal interface evaporator is a salt-resistant polyurethane sponge evaporator, using 40-50 PPI polyurethane sponge as the matrix. After cleaning, a polyvinyl alcohol-carbon black-PEDOT:PSS composite photothermal layer is loaded, and then cross-linked with glutaraldehyde and freeze-dried for curing. During the day, under the high temperature of the sun, the interface temperature rises sharply, causing the water to evaporate rapidly, with an evaporation rate of 7.85 kg / (m²). 2 (·h), the sodium sulfate concentration in the wastewater was concentrated by 19.2%, and the sulfate concentration in the concentrated water sample increased to 28049.44 mg / L;

[0077] Step S6: Repeat step S5 until all the wastewater evaporates and crystalline sodium salt is obtained.

[0078] The crystalline sodium salt prepared using this embodiment has a total sodium sulfate recovery rate of 88.92% and a purity of 98.41%, achieving the goal of resource recovery of sodium sulfate from industrial wastewater containing high concentrations of sulfite.

[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make several improvements and additions without departing from the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

[0080] Any modifications, alterations, and variations made by those skilled in the art without departing from the spirit and scope of this invention, based on the disclosed technical content, shall be equivalent embodiments of this invention. Furthermore, any modifications, alterations, and variations made to the above embodiments based on the essential technology of this invention shall still fall within the scope of this invention's technical solution.

Claims

1. A method for low-carbon gradient purification and salt resource recovery of industrial wastewater containing high concentrations of sulfite, characterized in that, Includes the following steps: Step S1: Connect the microporous aeration head to the air pump, adjust the aeration volume and control the aeration time to perform air aeration oxidation pretreatment on the wastewater. Step S2: Ozone is generated by an ozone generator, and the ozone aeration rate and ozone concentration are adjusted to perform ozone oxidation treatment on the pretreated wastewater. Step S3: By adjusting the current and voltage through electrochemical oxidation, the wastewater after ozone oxidation is electrocatalytically oxidized, and the remaining sulfites and mineralized organic matter are oxidized simultaneously. Step S4: The wastewater after gradient purification is cooled and crystallized at low temperature by aeration with cold air. After the crystals have completely precipitated, the supernatant is discharged to obtain sodium sulfate crystals. Step S5: The filtered uncrystallized supernatant is sent to the photothermal interface concentration tank for photothermal interface concentration to concentrate the sodium sulfate concentration of the wastewater to 15% to 20%, and then subjected to secondary cooling crystallization to separate the supernatant from the crystallized salt. Step S6: Repeat step S5 continuously until all wastewater evaporates and crystalline sodium salt is obtained.

2. The method for low-carbon gradient purification and salt resource recovery of industrial wastewater containing high concentrations of sulfite according to claim 1, characterized in that, In step S1, the wastewater is pretreated by air aeration oxidation. Hydrochloric acid solution is added to adjust the pH of the wastewater to 4-6, and the air aeration rate is 100-300 m³ / h. 3 Air / ton of water, aeration time 4-6 hours.

3. The method for low-carbon gradient purification and salt resource recovery of industrial wastewater containing high concentrations of sulfite according to claim 1, characterized in that, In step S2, the pretreated wastewater is subjected to ozone oxidation treatment. Sodium hydroxide solution is added to adjust the pH of the wastewater to 9-11, and the ozone aeration rate is 30-80 m³ / h. 3 Ozone per ton of water, ozone concentration of 10-20 mg / L, aeration time of 15-30 min.

4. The method for low-carbon gradient purification and salt resource recovery of industrial wastewater containing high concentrations of sulfite according to claim 1, characterized in that, In step S3, the highly oxidizing activating substances generated at the anode and cathode during the electrocatalytic oxidation process are used to directly or indirectly degrade pollutants. The anode material is a boron-doped diamond electrode with corrosion resistance, and the cathode is a titanium plate or graphite electrode. The voltage is 2–5V, and the current density is 40–80 mA / cm². 2 The reaction time is 15–30 min.

5. The method for low-carbon gradient purification and salt resource recovery of industrial wastewater containing high concentrations of sulfite according to claim 1, characterized in that, In step S4, air aeration cooling is used, with the cold air temperature being 2-10℃; the aeration pipe is a perforated pipe with an aeration hole diameter of 5-10mm, and the aeration holes are vertically downward to prevent salt crystallization from clogging the aeration holes, and the crystallization time is 2-4 hours.

6. The method for low-carbon gradient purification and salt resource recovery of industrial wastewater containing high concentrations of sulfite according to claim 1, characterized in that, In step S5, the photothermal interface evaporator is a salt-resistant polyurethane sponge evaporator, which uses 40-50 PPI polyurethane sponge as the matrix, and after cleaning, loads a polyvinyl alcohol-carbon black-PEDOT:PSS composite photothermal layer, which is then crosslinked with glutaraldehyde and freeze-dried to cure.

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