Method for removing COD (Chemical Oxygen Demand) in wastewater and application thereof

Abstract

The invention discloses a method for removing COD (Chemical Oxygen Demand) in wastewater and application of the method. The method comprises the steps that a composite oxidizing agent A is added into the wastewater, a first stirring reaction is carried out, and effective components of the composite oxidizing agent A comprise sodium percarbonate and manganese dioxide; a composite oxidizing agent B is added into the reacted wastewater, a second stirring reaction is carried out, and effective components of the composite oxidizing agent B comprise potassium ferrate and hydrogen peroxide. The method realizes efficient treatment of high-concentration organic wastewater, and has both economical efficiency and operability.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a method for removing COD from wastewater and its application. Background Technology

[0002] In recent years, with the increase in industrial wastewater discharge, the treatment of high-concentration organic wastewater has become a challenge in the environmental protection field. Chemical oxygen demand (COD) is an important indicator for measuring the organic matter content in water, and its effective removal is a key step in wastewater treatment. Existing COD removal methods mainly include biological methods, physical methods, and chemical oxidation methods.

[0003] Biological methods are effective in treating low-concentration organic wastewater, but the treatment cycle is long and they are not very tolerant to high concentrations of organic matter. Physical methods, such as adsorption and membrane separation, are costly and prone to secondary pollution. Traditional chemical oxidation methods (such as ozone or hydrogen peroxide oxidation) have problems such as low oxidant utilization, slow reaction rate and incomplete treatment.

[0004] Therefore, developing an efficient and economical COD removal method, especially for the treatment of high-concentration organic wastewater, is of great significance. Summary of the Invention

[0005] This invention proposes a method for removing COD from wastewater, which significantly improves oxidation efficiency, shortens treatment time, and achieves efficient treatment of high-concentration organic wastewater. The method uses readily available raw materials, is cost-effective, and its treatment effect is less affected by factors such as wastewater pH or composition, demonstrating good feasibility.

[0006] The present invention also proposes applications of the method.

[0007] The first aspect of this invention relates to a method for removing COD from wastewater, comprising the following steps:

[0008] S1. Add composite oxidant A to the wastewater and carry out the first stirring reaction. The effective components of the composite oxidant A include sodium percarbonate and manganese dioxide. S2. Add composite oxidant B to the wastewater after the reaction in step S1 and carry out a second stirring reaction. The effective components of the composite oxidant B include potassium ferrate and hydrogen peroxide.

[0009] In this invention, the mechanisms of action of the two oxidants are as follows: Composite oxidant A: Sodium percarbonate decomposes in water to produce hydrogen peroxide and sodium carbonate; manganese dioxide acts as a catalytic center to accelerate the decomposition of hydrogen peroxide to generate reactive oxygen species (such as hydroxyl radicals (·OH) etc.), which further react with carbonate ions to generate carbonate radicals (CO3· -Carbonate radicals have strong oxidizing properties and can break down large organic molecules, which facilitates subsequent oxidation reactions.

[0010] Composite oxidant B: The Fe(VI) in potassium ferrate has strong oxidizing properties. It undergoes a redox reaction with hydrogen peroxide to generate Fe(III) and hydroxyl radicals, further degrading organic pollutants. Hydrogen peroxide plays a dual role as both a proton donor and a free radical initiator, making it irreplaceable in composite oxidant B. If replaced with other peroxides (such as potassium persulfate or ammonium percarbonate), free radical generation cannot be efficient: potassium persulfate has a high oxidation potential, easily leading to electron transfer competition, and the generated sulfate radicals have poor selectivity for oxidizing organic matter and insufficient stability under neutral conditions; ammonium percarbonate decomposes too quickly in water, resulting in poor synchronicity with potassium ferrate and an inability to continuously provide raw materials for hydroxyl radical generation, leading to interruption of the chain oxidation reaction and incomplete oxidation of organic matter.

[0011] The method for removing COD from wastewater according to the first aspect of the present invention has at least the following beneficial effects: This invention achieves highly efficient COD removal through the synergistic effect of composite oxidant A and composite oxidant B. The oxidation process can be divided into two stages: Macromolecular organic matter destabilization stage: Sodium percarbonate in composite oxidant A decomposes under the catalysis of manganese dioxide to produce carbonate free radicals, which can efficiently destroy the benzene ring, double bond and other structures of organic matter, and break down macromolecular organic matter into easily degradable small molecule organic matter, providing more easily degradable target substances for subsequent oxidation reactions.

[0012] Small molecule organic matter mineralization stage: Potassium ferrate in composite oxidant B releases highly oxidizing Fe(VI) in water, and reacts with hydrogen peroxide to generate hydroxyl radicals. These two highly oxidizing components work synergistically to trigger a chain oxidation reaction, mineralizing small molecule organic matter into CO2 and H2O, thus achieving the complete degradation of organic pollutants in wastewater.

[0013] The combined system of two oxidants can operate within a wide pH range without requiring additional pH adjustment of the wastewater, simplifying the operation process and improving the utilization rate of the oxidants and the overall reaction rate. This method can reduce treatment time to less than 30 minutes and produces no bottom sludge, significantly improving wastewater treatment efficiency and solving the problems of long treatment times and low efficiency in traditional COD removal methods.

[0014] The method of this invention is simple to operate, has low operating costs, and is suitable for the treatment of various high-concentration organic wastewaters.

[0015] According to some embodiments of the present invention, in the composite oxidant A, the mass ratio of sodium percarbonate to manganese dioxide is 2.5~3.5:1. When the mass ratio meets the above requirements, the number of catalytic sites of manganese dioxide and the number of hydrogen peroxide molecules generated by the decomposition of sodium percarbonate are optimally matched, maximizing the promotion of carbonate free radical generation. If the proportion of manganese dioxide is too low (e.g., mass ratio 4:1), there are insufficient catalytic sites, resulting in a slower decomposition rate of sodium percarbonate and a sharp decrease in carbonate free radical production; if the proportion of manganese dioxide is too high (e.g., mass ratio 2:1), excess manganese dioxide will adsorb some carbonate free radicals, reducing the utilization rate of free radicals and thus weakening the degradation effect on macromolecular organic matter.

[0016] According to some embodiments of the present invention, in the composite oxidant B, the molar ratio of potassium ferrate to hydrogen peroxide is 1:1.5~2.5. When the molar ratio meets the above requirements, the Gibbs free energy of the reaction is the lowest, the spontaneity of the reaction is the strongest, and the generation rate and yield of hydroxyl radicals reach their peak. If the molar ratio is 1:1, insufficient hydrogen peroxide is added, resulting in incomplete reaction of Fe(VI) and a significant reduction in the yield of hydroxyl radicals. If the molar ratio is 1:3, excess hydrogen peroxide will undergo a quenching reaction with hydroxyl radicals (·OH + H2O2 = HO2· + H2O), reducing the effective concentration of free radicals.

[0017] According to some embodiments of the present invention, the mass ratio of the effective components in composite oxidant A to composite oxidant B is 1~2:1, which can achieve a better synergistic oxidation effect.

[0018] According to some embodiments of the present invention, the effective components in the composite oxidant A and / or the composite oxidant B are pre-dispersed in a dispersant to form a dispersion. Specifically, the dispersant can be water. The present invention does not impose specific limitations on the concentration of the two oxidant dispersions, and appropriate concentrations can be selected as needed. For example, in the dispersion of composite oxidant A, the total mass concentration of the effective components can be controlled at 10% to 20%.

[0019] According to some embodiments of the present invention, the dispersion of the composite oxidant B is prepared by the following method: potassium ferrate is mixed with hydrogen peroxide solution and reacted at 20-40°C for at least 30 minutes to obtain a mixed solution containing hydroxyl radicals. Under these conditions, the reaction between potassium ferrate and hydrogen peroxide is sufficient, generating a large number of hydroxyl radicals, while avoiding self-decomposition caused by excessive potassium ferrate or free radical quenching caused by excessive hydrogen peroxide. The present invention does not impose a specific limitation on the reaction time; a suitable reaction time can be selected according to actual conditions, for example, a reaction time of 30-40 minutes.

[0020] According to some embodiments of the present invention, the dispersion of the composite oxidant A is prepared by the following method: sodium percarbonate and manganese dioxide are mixed, and water is added to dissolve the sodium percarbonate.

[0021] According to some embodiments of the present invention, in step S1, the rotation speed of the first stirring reaction is 150~200 r / min, and the reaction time is 5~10 min.

[0022] According to some embodiments of the present invention, in step S2, the rotation speed of the second stirring reaction is 150~200 r / min, and the reaction time is 15~120 min. Specifically, the reaction time is 15~60 min, and more specifically 15~20 min.

[0023] By controlling the rotation speed and reaction time of the two-step reaction, the COD removal rate and treatment efficiency can be significantly improved.

[0024] According to some embodiments of the present invention, the COD content in the wastewater is ≤10000mg / L, specifically 500~5000mg / L, and further 1000~2000mg / L, which can meet the requirements for efficient treatment of high-concentration organic wastewater.

[0025] According to some embodiments of the present invention, the initial temperature of the wastewater is 20~40℃, within which the oxidant activity is high and the reaction rate is fast. The initial temperature refers to the influent temperature, and the treatment process is generally carried out under normal atmospheric conditions, requiring no special temperature control. The system temperature during the reaction is not significantly different from the initial temperature.

[0026] The second aspect of the present invention relates to the application of the method in the treatment of industrial organic wastewater.

[0027] Specifically, industrial organic wastewater includes shale gas backflow liquid wastewater and chemical wastewater.

[0028] In this article, the effective component refers to the component added in the form of raw materials and that can generate active ingredients (such as hydroxyl radicals and carbonate radicals) to participate in the oxidation reaction and play a role.

[0029] The term "multiple" refers to two or more types, and "more than" includes the stated number.

[0030] The numerical ranges involved all include endpoint values ​​and cover any subranges within that range, such as ranges obtained by any combination of specifically listed numerical values ​​or endpoint values.

[0031] Unless otherwise specified, all solutions mentioned in this article refer to aqueous solutions. Detailed Implementation

[0032] The embodiments of the present invention are described in detail below. These embodiments are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0033] Except for Example 3, the COD concentration of wastewater in other examples and comparative examples is expressed as rounded to the nearest ten digit. For example, the COD concentration is 2000 mg / L, which includes any value that is rounded to the nearest ten digit and is 2000 mg / L, such as 2000 mg / L, 2004 mg / L, etc.

[0034] Example 1 Wastewater: Wastewater from a shale gas flowback, with a COD concentration of 2000 mg / L, a pH of 6, and an initial temperature of 25℃.

[0035] Preparation of composite oxidant A solution: Mix 15g sodium percarbonate and 5g manganese dioxide, add deionized water to dissolve, and prepare a 10% mass concentration solution.

[0036] Preparation of composite oxidant B solution: 0.1 mol potassium ferrate and 0.2 mol hydrogen peroxide (30 wt% solution) were mixed and reacted at 30℃ for 30 min to obtain composite oxidant B solution.

[0037] The wastewater treatment methods are as follows: Step (1): Add composite oxidant A solution to the wastewater. The dosage is 2 g / L based on the total mass of sodium percarbonate and manganese dioxide. Stir the reaction for 5 min at a stirring rate of 150 r / min.

[0038] Step (2): Add the composite oxidant B solution, with an addition amount of 1 g / L based on the total mass of potassium ferrate and hydrogen peroxide. Stir the reaction for 15 min at a stirring rate of 150 r / min.

[0039] Step (3): Measure the COD concentration of the treated liquid.

[0040] The entire treatment process requires no pH adjustment and produces no bottom sludge. After treatment, the COD concentration of the wastewater is reduced to 560 mg / L, with a removal rate of 72%, and the total treatment time is 20 minutes.

[0041] Example 2 Wastewater: Wastewater from a shale gas flowback, with a COD concentration of 1000 mg / L, a pH of 6.5, and an initial temperature of 30℃.

[0042] Preparation of composite oxidant A solution: Mix 15g sodium percarbonate and 5g manganese dioxide, add deionized water to dissolve, and prepare a 20% mass concentration solution.

[0043] Preparation of composite oxidant B solution: 0.2 mol potassium ferrate and 0.4 mol hydrogen peroxide (30 wt% solution) were mixed and reacted at 30℃ for 30 min to obtain composite oxidant B solution.

[0044] The wastewater treatment methods are as follows: Step (1): Add composite oxidant A solution to the wastewater. The dosage is 2 g / L based on the total mass of sodium percarbonate and manganese dioxide. Stir the reaction for 8 min at a stirring rate of 180 r / min.

[0045] Step (2): Add the composite oxidant B solution, with an addition amount of 1 g / L based on the total mass of potassium ferrate and hydrogen peroxide. Stir the reaction for 18 min at a stirring rate of 180 r / min.

[0046] Step (3): Measure the COD concentration of the treated liquid.

[0047] The entire treatment process requires no pH adjustment and produces no bottom sludge. After treatment, the COD concentration of the wastewater is reduced to 190 mg / L, with a removal rate of 81%, and the total treatment time is 26 minutes.

[0048] Example 3 Wastewater: A chemical wastewater with a COD concentration of 510 mg / L, a pH of 4, and an initial temperature of 35℃.

[0049] Preparation of composite oxidant A solution: Mix 15g sodium percarbonate and 5g manganese dioxide, add deionized water to dissolve, and prepare a 15% mass concentration solution.

[0050] Preparation of composite oxidant B solution: 0.05 mol potassium ferrate and 0.1 mol hydrogen peroxide (30 wt% solution) were mixed and reacted at 30℃ for 30 min to obtain composite oxidant B solution.

[0051] The wastewater treatment methods are as follows: Step (1): Add composite oxidant A solution to the wastewater. The dosage is 1 g / L based on the total mass of sodium percarbonate and manganese dioxide. Stir the reaction for 6 min at a stirring rate of 170 r / min.

[0052] Step (2): Add the composite oxidant B solution, with an addition amount of 0.5 g / L based on the total mass of potassium ferrate and hydrogen peroxide. Stir the reaction for 14 min at a stirring rate of 170 r / min.

[0053] Step (3): Measure the COD concentration of the treated liquid.

[0054] The entire treatment process requires no pH adjustment and produces no bottom sludge. After treatment, the COD concentration of the wastewater is reduced to 23.5 mg / L, with a removal rate of 95.4%, and the total treatment time is 20 minutes.

[0055] Comparative Example 1 The wastewater and the composite oxidant A solution are the same as in Example 2.

[0056] The wastewater treatment methods are as follows: Step (1): Add composite oxidant A solution to the wastewater. The dosage is 2 g / L based on the total mass of sodium percarbonate and manganese dioxide. Stir the reaction for 30 min at a stirring rate of 150 r / min.

[0057] Step (2): Measure the COD concentration of the treated liquid.

[0058] After treatment, the COD concentration of the wastewater was reduced to 670 mg / L, with a removal rate of 33%.

[0059] Comparative Example 2 The wastewater and the composite oxidant B solution are the same as in Example 2.

[0060] The wastewater treatment methods are as follows: Step (1): Add composite oxidant B solution to the wastewater. The dosage is 1 g / L based on the total mass of potassium ferrate and hydrogen peroxide. Stir the reaction for 30 min at a stirring rate of 150 r / min.

[0061] Step (2) Measure the COD concentration of the treated liquid.

[0062] After treatment, the COD concentration of the wastewater was reduced to 720 mg / L, with a removal rate of 28%.

[0063] Comparative Example 3 Wastewater: Chemical wastewater, COD concentration of 2000 mg / L, pH of 6, initial temperature of 25℃.

[0064] Preparation of composite oxidant A solution: same as in Example 1.

[0065] Preparation of composite oxidant B solution: Refer to Example 1, except that the hydrogen peroxide solution is replaced with potassium persulfate solution (concentration is not limited, but the appropriate concentration is ensured to completely dissolve the potassium persulfate), and the amount of potassium persulfate added is equal to the original amount of hydrogen peroxide.

[0066] The wastewater treatment steps are carried out in accordance with Example 1. In step (2), the dosage of composite oxidant B is 1 g / L based on the total mass of potassium ferrate and potassium persulfate.

[0067] After treatment, the COD concentration of the wastewater decreased to 920 mg / L, with a removal rate of 54%, which was 18 percentage points lower than that in Example 1.

[0068] Comparative Example 4 The wastewater, composite oxidant A solution, and composite oxidant B solution are the same as in Example 2.

[0069] The wastewater treatment method is the same as in Example 2, except that the order of steps (1) and (2) is reversed.

[0070] The COD concentration of the treated wastewater was 620 mg / L, with a removal rate of 38%, which was 43 percentage points lower than that of Example 2.

[0071] The results of Examples 1-3 show that this method can efficiently remove COD within a wide range of COD concentrations (510-2000 mg / L). The removal rate is higher at lower COD concentrations, demonstrating that this method is applicable to the treatment of organic wastewater with a wide range of COD concentrations.

[0072] The comparison of the treatment effects of Example 2, Comparative Example 1, and Comparative Example 2 shows that when composite oxidant A and composite oxidant B are used in combination, the COD removal rate is significantly higher than that of a single oxidant, indicating that the synergistic effect of the two oxidants effectively improves the COD removal efficiency and shortens the treatment time.

[0073] Comparison of the results of Comparative Example 3 and Example 1 shows that the composite oxidant B using hydrogen peroxide is significantly better than persulfates such as potassium persulfate.

[0074] The comparison between Comparative Example 4 and Example 1 shows that the order of steps has a significant impact on COD removal efficiency. Adding composite oxidant B first causes hydroxyl radicals to preferentially react with small molecules, failing to effectively destroy the macromolecular structure; subsequent addition of composite oxidant A is difficult to effectively degrade organic matter, resulting in a significant decrease in COD removal rate.

[0075] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for removing COD from wastewater, characterized in that, Includes the following steps: S1. Add composite oxidant A to the wastewater and carry out the first stirring reaction. The effective components of the composite oxidant A include sodium percarbonate and manganese dioxide. S2. Add composite oxidant B to the wastewater after the reaction in step S1 and carry out a second stirring reaction. The effective components of the composite oxidant B include potassium ferrate and hydrogen peroxide.

2. The method according to claim 1, characterized in that, In the composite oxidant A, the mass ratio of sodium percarbonate to manganese dioxide is 2.5~3.5:

1.

3. The method according to claim 1, characterized in that, In the composite oxidant B, the molar ratio of potassium ferrate to hydrogen peroxide is 1:1.5~2.

5.

4. The method according to claim 1, characterized in that, The mass ratio of the effective components in composite oxidant A to composite oxidant B is 1~2:

1.

5. The method according to claim 1, characterized in that, The effective components of the composite oxidant A and / or the composite oxidant B are pre-dispersed in a dispersant to form a dispersion.

6. The method according to claim 5, characterized in that, The dispersion of the composite oxidant B is prepared by mixing potassium ferrate with hydrogen peroxide solution and reacting at 20~40℃ for more than 30 minutes.

7. The method according to claim 1, characterized in that, In step S1, the first stirring reaction is carried out at a speed of 150-200 r / min and the reaction time is 5-10 min.

8. The method according to claim 1, characterized in that, In step S2, the second stirring reaction is carried out at a speed of 150-200 r / min and the reaction time is 15-120 min.

9. The method according to claim 1, characterized in that, The COD content in the wastewater is ≤10000mg / L; and / or the initial temperature of the wastewater is 20~40℃.

10. The application of the method according to any one of claims 1-9 in the treatment of industrial organic wastewater.