Method for removing organic chloride in wastewater

Abstract

The invention relates to the technical field of water and sewage treatment, in particular to a method for removing organic chlorides in wastewater, which comprises the following steps: firstly, regulating the pH value of the wastewater to 4-6 to create a suitable environment for subsequent reaction, then adding an oxidizing agent, preferably using 0.001% of 1% potassium permanganate solution, into the regulated wastewater, uniformly stirring, carrying out primary oxidation, and finally, carrying out secondary oxidation. Then adding a reducing agent which mainly comprises ferrous sulfate and sodium hydrogen sulfite in a molar ratio of 10: 1, further oxidizing and degrading organic chlorides, then adding sodium hydroxide, adjusting the pH value of the wastewater to 9, keeping stirring to decompose unoxidized chlorides into inorganic chlorides, and finally feeding the treated wastewater into a biochemical system for further treatment. According to the method, the organic chloride in the wastewater can be efficiently removed, the reagent is green and safe, the cost is low, the biodegradability of the treated wastewater is good, the wastewater can reach the discharge standard, and the method has remarkable economic and environmental benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of water and sewage treatment, and particularly to a method for removing organic chlorides from wastewater. Background Art

[0002] In industrial production activities, such as the chemical, pharmaceutical, and printing and dyeing industries, a large amount of wastewater containing organic chlorides is generated. Organic chlorides are organic compounds that contain at least one chlorine atom covalently bonded to other atoms in the molecule. For example, vinyl chloride, chloroform, chloropropane, chlorobenzene, chloroacetic acid, etc. are common organic chlorides. If these wastewaters are directly discharged without effective treatment, they will cause serious pollution to the environment and endanger the ecological balance and human health.

[0003] Currently, there are many problems with traditional wastewater treatment methods when dealing with organic chloride wastewater. Organic chlorides have stable chemical properties and are difficult to be completely degraded by conventional biochemical treatment methods. If such wastewaters are directly discharged into the biochemical system, organic chlorides will inhibit the activity of microorganisms and even cause microbial poisoning and death, thereby paralyzing the biochemical system and making it unable to operate normally.

[0004] In existing oxidation treatment technologies, although there are various oxidants to choose from, each has its own defects. For example, although chlorine dioxide has strong oxidation ability, is less affected by temperature and pH, and does not produce by-products such as trihalomethanes and haloacetic acids, it will generate inorganic disinfection by-products, namely chlorite ions (ClO2 - )and chlorate ions (ClO3 - ); ferrate is a green oxidant, and its oxidation product, ferric ion, can be used as a coagulant to assist in removing pollutants, but it has poor stability and is extremely inconvenient for storage and use; although the redox potential of hydrogen peroxide is as high as 1.77V, it is easily decomposed and its practical application is greatly limited.

[0005] In addition, a single oxidation or reduction treatment method often cannot achieve the ideal treatment effect. In terms of adjusting the pH of wastewater, if the method is improper, it will not only affect the treatment efficiency but also may introduce new impurities. Moreover, existing treatment processes rarely systematically consider the synergistic effects between various treatment links, resulting in high treatment costs and poor effects. Summary of the Invention

[0006] (I) Technical Problems to be Solved In view of the deficiencies of the prior art, the present invention provides a method for removing organic chlorides from wastewater.

[0007] (II) Technical Solutions To achieve the above object, the present invention provides the following technical solutions: A method for removing organic chlorides from wastewater according to the present invention includes the following steps: Step S1: Adjust the pH value of the wastewater to between 4 and 6; Step S2: Add an oxidizing agent to the adjusted wastewater and stir evenly; Step S3: Add a reducing agent to the wastewater and stir evenly; Step S4: Adjust the pH value of the wastewater to 9 to decompose the unoxidized chlorides into inorganic chlorides; Step S5: Enter the biochemical system for further treatment.

[0008] Preferably, in step S1, when adjusting the pH value of the wastewater, an acidic regulator is added to the wastewater.

[0009] More preferably, the acidic regulator includes any one of sulfuric acid, hydrochloric acid, and nitric acid.

[0010] Again preferably, in step S2, the oxidizing agent includes at least one of hydrogen peroxide, potassium permanganate, chlorine, chlorine dioxide, ferrate, and peroxide, preferably potassium permanganate.

[0011] Preferably, in step S2, the usage amount of potassium permanganate is 0.001%, and the mass concentration of the potassium permanganate solution is 1%.

[0012] More preferably, in step S3, the reducing agent is preferably a mixture of ferrous sulfate and sodium bisulfite.

[0013] Again preferably, in step S3, the molar ratio of ferrous sulfate to sodium bisulfite is 10:1, and the usage amount of the reducing agent is 0.2%.

[0014] Preferably, in step S3, the reducing agent further includes at least one of sodium sulfite, sodium sulfide, and sodium thiosulfate.

[0015] More preferably, in step S4, the pH value of the wastewater is adjusted to 9 by adding sodium hydroxide and kept in a stirring state until the unoxidized chlorides are completely converted into inorganic chlorides.

[0016] (III) Beneficial effects Compared with the prior art, the present invention provides a method for removing organic chlorides from wastewater, having the following beneficial effects: Efficiently remove organic chlorides By adjusting the pH of the wastewater to 4 - 6 (step S1), the best conditions are created for the subsequent redox reaction, enabling potassium permanganate (step S2) and the ferrous sulfate - sodium bisulfite mixture (step S3) to act synergistically, significantly enhancing the degradation efficiency of organic chlorides. Experiments show that this method can rapidly reduce the COD of the wastewater by more than 80%, from 25000 mg / L to 5000 - 6000 mg / L, far exceeding traditional treatment methods.

[0017] Environmentally friendly and free of secondary pollution Potassium permanganate is preferably used as the oxidant, and its reaction products are manganese dioxide (or Mn 2+ ), and sulfate radicals, which are non - toxic and harmless and can be removed through subsequent treatment (such as Mn 2+ can be oxidized by aeration to form manganese dioxide precipitation). The ferric hydroxide colloid generated by ferrous sulfate in the reducing agent can also adsorb impurities in the water, further purifying the water quality and avoiding the problem of toxic by - products generated by traditional oxidation methods.

[0018] Low economic cost Both potassium permanganate and ferrous sulfate are common industrial raw materials, with low prices and easy availability. The usage amount of potassium permanganate is only 0.001%, the molar ratio of ferrous sulfate to sodium bisulfite is 10:1, and the total reagent usage is controlled at 0.2%, significantly reducing the treatment cost. At the same time, no additional complex equipment or process transformation is required, and the existing wastewater treatment system can be directly applied.

[0019] Strong process compatibility In step S4, the pH is adjusted to 9, causing the unoxidized chlorides to decompose into inorganic chlorides, significantly improving the biodegradability of the wastewater and creating favorable conditions for subsequent biochemical treatment (step S5). The treated wastewater can directly enter the biochemical system, and finally achieve the discharge standard with a COD less than 500 mg / L, being highly compatible with the existing sewage treatment process.

[0020] Simple operation and high stability The entire treatment process is achieved by step - by - step adjusting the pH, adding oxidants and reducing agents, with simple and controllable operation. The parameters of each step (such as pH value, reagent dosage) have been optimized, the treatment effect is stable, and it has good adaptability to organic chloride wastewater with different concentrations and compositions, and can be widely applied to the wastewater treatment of industries such as chemical engineering and pharmaceuticals. Brief description of the drawings

[0021] Figure 1 It is a schematic diagram of the working process of the present invention; Figure 2 It is a schematic diagram of the removal efficiency and time of the combined use of the oxidant and reducing agent of the present invention; Figure 3 It is a schematic diagram of the removal effect and time of using the oxidant alone in the present invention. Detailed implementation mode

[0022] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0023] Please refer to Figures 1-3 , a method for removing organic chlorides from wastewater of the present invention includes the following steps: Step S1: Adjust the pH value of the wastewater to between 4 and 6; Step S2: Add an oxidant to the adjusted wastewater and stir evenly; Step S3: Add a reducing agent to the wastewater and stir evenly; Step S4: Adjust the pH value of the wastewater to 9 to decompose the unoxidized chlorides into inorganic chlorides; Step S5: Enter the biochemical system for further treatment.

[0024] Principle of adjusting the pH value of wastewater: In the process of treating organic chloride wastewater, a suitable pH environment is crucial for subsequent redox reactions. Adjusting the wastewater pH to between 4 and 6 creates favorable conditions for the oxidant and reducing agent to play their roles. Different redox reactions have the best reaction rates and effects within a specific pH range. In this pH range, the synergistic effect between the oxidant and reducing agent can be enhanced, improving the removal efficiency of organic chlorides. For example, an acidic environment can promote the oxidizing property of potassium permanganate, enabling it to more effectively oxidize organic chlorides. When using acidic regulators such as sulfuric acid, hydrochloric acid, or nitric acid, they ionize hydrogen ions in water to lower the pH value of the wastewater, achieving the purpose of adjusting the acidity and alkalinity.

[0025] Working principle of the oxidant: Taking potassium permanganate as an example, it is a strong oxidant. During the oxidation and degradation of organic matter, the manganese element in potassium permanganate gains electrons and is reduced from +7 valence, while pollutants such as organic chlorides lose electrons and are oxidized. Potassium permanganate does not produce toxic and harmful halogenated disinfection by-products during oxidation, being relatively environmentally friendly. However, its oxidation ability is limited, and the oxidation rate of some structurally stable organic pollutants is slow. But when used in combination with the subsequent added reducing agent, it can significantly improve the treatment effect on organic chlorides. For example, chlorine dioxide has strong oxidation ability, is less affected by temperature and pH, and does not produce by-products such as trihalomethanes and haloacetic acids. However, it will produce inorganic disinfection by-products such as chlorite ions (ClO2 - ) and chlorate ions (ClO3 -); Ferrate is also a green oxidant. Its oxidation product, ferric iron, can also act as a coagulant to enhance the removal of pollutants, but it has poor stability; although hydrogen peroxide has a high redox potential, it is easily decomposed. In contrast, potassium permanganate has relatively prominent comprehensive advantages and is preferably used in this patent.

[0026] Working principle of the reducing agent: A mixture of ferrous sulfate and sodium bisulfite is used as the reducing agent, which has multiple functions. Ferrous sulfate is easily available as a raw material. After dissolving in water, it will generate ferric hydroxide colloid. This colloid has a large specific surface area and can precipitate suspended solids, colloidal particles and some organic matters in water through adsorption and aggregation, thereby improving the clarity of water quality. Ferrous sulfate also has strong reducibility and can reduce heavy metal ions such as hexavalent chromium in wastewater to less toxic valence states, reducing the treatment difficulty. At the same time, ferrous sulfate is an acidic substance and can neutralize alkaline water bodies, further adjusting the wastewater to an appropriate pH value and enhancing the oxidation ability of potassium permanganate under acidic conditions. More importantly, the reaction between bisulfite and potassium permanganate will in-situ generate highly active free ferric manganese (Mn(III)) in a non-complexed state. Free Mn(III) has extremely high oxidation activity and can quickly oxidize and remove various organic pollutants in water, including pollutants that are difficult for potassium permanganate to oxidize originally, greatly improving the oxidation rate. If the reducing agent also contains at least one of sodium sulfite, sodium sulfide, and sodium thiosulfate, they can also utilize their own reducibility to participate in the reaction in the system, synergistically with ferrous sulfate and sodium bisulfite, and further enhance the removal effect of organic chlorides.

[0027] Principle of adjusting pH to 9 to decompose chlorides: After the wastewater undergoes redox reactions, some organic chlorides may not be completely oxidized. Adjusting the pH value to 9, the alkaline environment can promote the hydrolysis and other reactions of the unoxidized chlorides, decomposing them into inorganic chlorides. For example, some organochlorohydrocarbons will undergo nucleophilic substitution reactions under alkaline conditions, the chlorine atoms are replaced by hydroxyl groups, and finally converted into inorganic chlorides and corresponding alcohols or other organic matters. These inorganic chlorides are easier to be treated in the subsequent biochemical system. During the process of adding sodium hydroxide to adjust the pH value, maintaining a stirring state can make sodium hydroxide evenly dispersed in the wastewater, accelerating the reaction rate and ensuring that the unoxidized chlorides are completely converted into inorganic chlorides.

[0028] Principle of further treatment by the biochemical system: After the wastewater is treated through the previous steps, most of the organic chlorides have been removed or converted into inorganic chlorides, and the biodegradability of the wastewater is improved at this time. In the biochemical system, microorganisms use the residual organic matters in the wastewater as carbon sources and energy sources for growth and reproduction. Through a series of metabolic activities, the organic matters are further decomposed into harmless substances such as carbon dioxide, water and the cell substances of the microorganisms themselves, thereby further reducing the COD value of the wastewater and meeting the discharge standards.

[0029] Working principles of various preferred technical solutions Principle of preferred acid regulator: Sulfuric acid, hydrochloric acid, and nitric acid are common strong acids that can completely ionize a large number of hydrogen ions in water, with strong ability and fast speed to adjust the pH value of wastewater. At the same time, they are widely sourced in industry, with relatively low costs, and are easy to obtain and use. Moreover, in the subsequent treatment process, these acid radical ions will not have a negative impact on the treatment effect under appropriate conditions and will not introduce impurities that are difficult to treat. Therefore, they are preferably used as acid regulators for adjusting the pH value of wastewater.

[0030] Principle of preferred potassium permanganate as an oxidant: As mentioned above, compared with other oxidants, potassium permanganate has the advantages of being green and environmentally friendly, easy to operate, convenient for transportation, and low in price. Although it has the disadvantages of limited oxidation ability and slow oxidation rate for some pollutants, by cooperating with specific reducing agents, this deficiency can be effectively compensated. While meeting the treatment effect, it can reduce the treatment cost and risk, and has better comprehensive performance. Therefore, it is preferred among many oxidants.

[0031] Principle of using potassium permanganate in a specific proportion: Controlling the usage amount of potassium permanganate at 0.001% and the solution mass concentration at 1% is obtained through a large number of experimental verifications. This dosage can not only ensure within an acceptable economic cost range but also fully react with the reducing agent to achieve a good removal effect on organic chlorides. If the usage amount is too low, it may not be able to completely oxidize organic chlorides; if the usage amount is too high, it will cause an increase in cost and may lead to difficulties in treating the excess oxidant in subsequent treatment, resulting in new problems.

[0032] Principle of preferred mixture of ferrous sulfate and sodium bisulfite as a reducing agent and specific proportion: Mixing ferrous sulfate and sodium bisulfite in a molar ratio of 10:1 as a reducing agent is because their synergistic effect can exert the greatest efficacy. The iron(III) hydroxide colloid generated by ferrous sulfate can purify water quality, reduce heavy metal ions, and adjust the pH value, while sodium bisulfite can react with potassium permanganate to produce highly active Mn(III). The two cooperate with each other and play multiple roles such as adsorption, reduction, and oxidation in the process of removing organic chlorides, greatly improving the treatment efficiency. The specific molar ratio is to ensure that both can fully play their respective advantages during the reaction and achieve the best synergistic effect.

[0033] Principle of adding sodium hydroxide to adjust the pH to 9 and stirring: Sodium hydroxide is a strong base that can completely ionize hydroxide ions in water, quickly raising the pH value of the wastewater to 9. Stirring can make sodium hydroxide evenly disperse in the wastewater, avoiding local alkalinity being too strong or too weak, ensuring that all unoxidized chlorides can fully contact hydroxide ions, accelerating the reaction speed, and ensuring their complete conversion into inorganic chlorides, providing more favorable conditions for subsequent biochemical treatment.

[0034] Detailed Workflow Step S1: Adjust the pH value of the wastewater to between 4 and 6: Take the wastewater containing organic chlorides and add an acidic regulator to it. The acidic regulator can be any one of sulfuric acid, hydrochloric acid, and nitric acid. By adding the acidic regulator, the hydrogen ions ionized by it in water are used to reduce the pH value of the wastewater, and the pH value of the wastewater is adjusted to between 4 and 6 to create a suitable acidic environment for the subsequent redox reaction. During the adjustment process, the pH value needs to be continuously monitored to ensure that it reaches the target range.

[0035] Step S2: Add an oxidant to the adjusted wastewater and stir evenly: Select at least one of hydrogen peroxide, potassium permanganate, chlorine, chlorine dioxide, ferrate, and peroxide as the oxidant. In this solution, potassium permanganate is preferably used. Take a potassium permanganate solution with a mass concentration of 1% and add it to the wastewater with the adjusted pH value according to the usage amount of 0.001%, and then stir evenly to make the potassium permanganate fully dispersed in the wastewater and come into full contact with the organic chlorides to start the oxidation reaction and initially remove part of the organic chlorides.

[0036] Step S3: Add a reductant to the wastewater and stir evenly: Prepare a mixture of ferrous sulfate and sodium bisulfite in a molar ratio of 10:1 as the reductant. At the same time, the reductant can also contain at least one of sodium sulfite, sodium sulfide, and sodium thiosulfate. The total usage amount of the reductant is 0.2%. Add the prepared reductant to the wastewater containing the oxidant and stir evenly. The iron hydroxide colloid generated by ferrous sulfate adsorbs impurities in the water, and its own reducibility and the highly active Mn(III) generated by the reaction of bisulfite with potassium permanganate act together to further oxidize and remove organic chlorides and improve the treatment effect.

[0037] Step S4: Adjust the pH value of the wastewater to 9 to decompose the unoxidized chlorides into inorganic chlorides: Add sodium hydroxide to the wastewater after the redox reaction while keeping it stirred. Sodium hydroxide ionizes hydroxide ions in water, causing the pH value of the wastewater to gradually rise to 9. Under the alkaline environment and stirring action, the unoxidized chlorides undergo hydrolysis and other reactions and gradually decompose into inorganic chlorides, reducing the treatment difficulty of the wastewater. During the adjustment process, the pH value is continuously monitored to ensure that it is stable at 9, and at the same time, detection means are used to determine that the unoxidized chlorides have been completely converted into inorganic chlorides.

[0038] Step S5: Enter the biochemical system for further treatment: Introduce the wastewater with a pH value of 9 and containing inorganic chlorides after the above treatment into the biochemical system. In the biochemical system, microorganisms use the residual organic matter in the wastewater for metabolic activities, further decompose it into harmless substances, further reduce the COD value of the wastewater, and finally reach the discharge standard to achieve the harmless treatment of the wastewater.

[0039] The reagents used in this technical solution are potassium permanganate, sulfite and bisulfite, all of which are green and safe solid reagents. They are convenient for transportation and low in price, do not require additional treatment units, and do not need to modify the process when applied to the existing process. The reaction product of the oxidant used in this technical solution is manganese dioxide (or Mn 2+ ), and sulfate radical. Manganese dioxide has the functions of adsorption and coagulation aid, which can enhance the removal of pollutants; sulfate radical is non-toxic and harmless and is a background ion in water; Mn 2+ can be oxidized to manganese dioxide by aeration and removed by filtration.

[0040] The excess oxide can react with ferrous sulfate, and the reaction product is ferric ion, which can flocculate and sediment the organic matter in the water body.

[0041] Comparative experiment method: Application cases of this technology: The wastewater containing organic chlorides has a COD of 25000 mg / L, an organic chloride content of 0.2% - 0.5%, and 0.1 - 0.5% of alcohols. The pH value is 7 - 7.5. These alcohols are mainly methanol and ethanol, which are easily degradable and have little impact.

[0042] Take 1000 milliliters of the wastewater, first add 2 milliliters of ferrous sulfate mixed solution (the molar ratio of ferrous sulfate to sodium bisulfite is 10, 10% solution). After mixing, the pH is 5.5 - 6 at this time. Then add 1 milliliter of 1% potassium permanganate solution, mix well and stir for 15 minutes. The COD can quickly drop by 80%. At this time, the COD of the water quality is 5000 - 6000 mg / L.

[0043] The pH value at this time is 7 - 7.5. It is necessary to add sodium hydroxide to adjust the pH to 9 to decompose the unoxidized chlorides into inorganic chlorides and then enter the biochemical system.

[0044] The adjusted water enters the biochemical system and is relatively easy to be further biochemically treated, and finally meets the discharge requirement of COD less than 500 mg / L.

[0045] Removal efficiency and time of jointly using oxidant and reductant

[0046] Removal effect and time of using only oxidant:

[0047] Comparative cases: Case 1: Wastewater containing organic chlorides, with a COD of 25,000 mg / L, an organic chloride content of 0.2% - 0.5%, 0.1 - 0.5% of alcohols, and a pH value of 7 - 7.5. These alcohols are mainly methanol and ethanol, which are easily degradable and have little impact.

[0048] Directly enter the biochemical system, and the changes in the water after biochemical treatment are as follows in the table:

[0049] It can be seen that for the water treated without adding oxidation-reduction agents, the COD degradation rate is very slow. At the same time, the pH in the water quality is decreasing steadily, directly affecting the safety of the equipment. At the same time, it is also becoming increasingly unfavorable for the biochemical system, and the growth of microorganisms is affected.

[0050] Case 2: Wastewater containing organic chlorides, with a COD of 25,000 mg / L, an organic chloride content of 0.2% - 0.5%, 0.1 - 0.5% of alcohols, and a pH value of 7 - 7.5. These alcohols are mainly methanol and ethanol, which are easily degradable and have little impact.

[0051] After the water is treated with the above-mentioned reducing agent and oxidizing agent, the COD is 5000 - 6000 mg / L, the pH is adjusted to 9, and it enters the biochemical system. The changes in the water after biochemical treatment are as follows in the table:

[0052] Thus, it can be seen that for the treated water, the effluent water quality is stable, the treatment efficiency is extremely high, and it is very suitable for subsequent aerobic biochemical treatment. Finally, the effluent water quality is lower than 500 mg / L.

[0053] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for removing organic chlorides from wastewater, characterized in that, It includes the following steps: Step S1: Adjust the pH value of the wastewater to between 4 and 6; Step S2: Add an oxidant to the adjusted wastewater and stir evenly; Step S3: Add a reductant to the wastewater and stir evenly; Step S4: Adjust the pH value of the wastewater to 9 to decompose the unoxidized chlorides into inorganic chlorides; Step S5: Enter the biochemical system for further treatment.

2. The method for removing organochlorides from wastewater according to claim 1, wherein In step S1, when adjusting the pH value of the wastewater, an acidic regulator is added to the wastewater.

3. The method for removing organochlorides from wastewater according to claim 2, characterized in that, The acidic regulator includes any one of sulfuric acid, hydrochloric acid, and nitric acid.

4. A method for removing organic chlorides from wastewater according to claim 3, characterized in that, In step S2, the oxidant includes at least one of hydrogen peroxide, potassium permanganate, chlorine, chlorine dioxide, ferrate, and peroxide, preferably potassium permanganate.

5. A method for removing organic chlorides from wastewater according to claim 4, characterized in that, In step S2, the usage amount of potassium permanganate is 0.001%, and the mass concentration of the potassium permanganate solution is 1%.

6. The method for removing organochlorides from wastewater according to claim 5, characterized in that, In step S3, the reductant is preferably a mixture of ferrous sulfate and sodium bisulfite.

7. A method for removing organochlorides from wastewater according to claim 6, characterized in that, In step S3, the molar ratio of ferrous sulfate to sodium bisulfite is 10:1, and the usage amount of the reductant is 0.2%.

8. A method for removing organic chlorides from wastewater according to claim 6, characterized in that, In step S3, the reductant also includes at least one of sodium sulfite, sodium sulfide, and sodium thiosulfate.

9. A method for removing organochlorides from wastewater according to claim 6, characterized in that, In step S4, the pH value of the wastewater is adjusted to 9 by adding sodium hydroxide and kept in a stirring state until the unoxidized chlorides are completely converted into inorganic chlorides.

Images