Continuous Fenton oxidation treatment method for DMAC (dimethylacetamide) wastewater with medium and low concentration

Abstract

The invention discloses a continuous Fenton oxidation treatment method for medium-low-concentration DMAC (dimethylacetamide) wastewater, which comprises the following steps: continuously feeding the medium-low-concentration DMAC wastewater, acid, a ferrous sulfate solution and hydrogen peroxide into a reaction kettle, and carrying out Fenton oxidation in the reaction kettle; continuously feeding the material subjected to Fenton oxidation into a neutralization kettle, and continuously introducing a sodium hydroxide solution into the neutralization kettle at the same time, so that ferrous sulfate reacts with sodium hydroxide to form ferric hydroxide precipitate; and materials reacted in the neutralization kettle enter a precipitation kettle for standing. The method is simple and easy to implement and high in treatment efficiency, the removal rate of DMAC in the wastewater from the precipitation kettle can reach 95% or above, the treated wastewater can be directly subjected to common aerobic or anaerobic biochemical treatment, and the biochemical effect is good.

Description

Technical Field

[0001] The invention relates to a method for treating DMAC wastewater, in particular to a method for continuous Fenton oxidation treatment of medium- and low-concentration DMAC wastewater, and belongs to the technical field of wastewater treatment. Background Art

[0002] DMAC is a commonly used organic solvent, which is used in the chemical and pharmaceutical industries. There are two main methods for treating DMAC wastewater currently produced: the first is high-concentration DMAC wastewater, usually with a DMAC content of more than 1%, and the treatment methods are mainly solvent extraction, adsorption separation, etc., the purpose is to recover DMAC in the wastewater, such as patents CN202311146794.8 and CN114604928B, which use extraction methods to treat DMAC wastewater; the second is low-concentration DMAC wastewater, usually with a DMAC content of less than 1000ppm, which can be treated biochemically by iron-carbon micro-electrolysis or domesticated microorganisms, such as CN210505964 U, which treats DMAC wastewater by biological methods.

[0003] At present, most of the research is on the treatment of high-concentration (above 1%) DMAC wastewater and low-concentration (below 0.1%) DMAC wastewater. There are few introductions to the treatment methods of wastewater with a medium and low concentration range of DMAC concentration of 0.1-1%. When the content of DMAC in wastewater is between 0.1% and 1%, reaching the medium and low concentration range, the extraction efficiency is reduced and the operating cost is relatively increased; the biological toxicity is relatively high and it is difficult to directly treat it biochemically. Therefore, it is of great environmental and economic significance to study the treatment methods suitable for medium and low concentration DMAC wastewater. Summary of the invention

[0004] In view of the shortcomings of few reports on the treatment methods of medium and low concentration DMAC wastewater, low treatment efficiency and high cost of the existing treatment methods, the present invention provides a method for continuous Fenton oxidation treatment of medium and low concentration DMAC wastewater. The method directly uses a continuous Fenton oxidation method to directly destroy and treat DMAC with low recovery value, directly degrade it into small molecular organic matter and ammonia nitrogen, and then directly biochemically treat the wastewater after Fenton oxidation degradation. The operation is simple and reliable.

[0005] The specific technical solutions of the present invention are as follows: A method for continuous Fenton oxidation treatment of medium and low concentration DMAC wastewater, the method comprising the following steps: (1) Low and medium concentration DMAC wastewater, acid, ferrous sulfate solution and hydrogen peroxide are continuously introduced into the reactor, and Fenton oxidation occurs in the reactor; (2) The material after Fenton oxidation is continuously fed into the neutralization kettle, and sodium hydroxide solution is continuously introduced into the neutralization kettle to react with ferrous sulfate and sodium hydroxide to form ferric hydroxide precipitate; (3) The material after the reaction in the neutralization kettle enters the precipitation kettle for standing.

[0006] Furthermore, in step (1), the medium-low concentration DMAC wastewater refers to wastewater with a DMAC content of 0.1-1%, such as 0.1%, 0.5%, and 1%. The wastewater can be industrial wastewater generated in the fields of chemical industry, medicine, pesticide, etc., and the main component of the wastewater except DMAC is water, and the proportion of COD in other trace impurities does not exceed 50%.

[0007] Furthermore, in step (1), the acid may be hydrochloric acid or sulfuric acid. The feed rates of the wastewater and the acid are adjusted so that the pH of the wastewater in the reactor is 3 to 4. The concentration of the acid may be adjusted as required, for example, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, and any range therebetween.

[0008] Furthermore, in step (1), ferrous sulfate is continuously added to the reactor in the form of an aqueous solution, and its concentration can be adjusted as needed, such as 5wt%, 10wt%, 15wt%, 20wt%, and any range value therebetween. The feed rates of wastewater and ferrous sulfate solution are adjusted so that the mass ratio of ferrous sulfate to wastewater in the reactor is (0.1% to 0.2%): 1.

[0009] Furthermore, in step (1), hydrogen peroxide refers to an aqueous solution of hydrogen peroxide, and its concentration can be adjusted as needed, such as 1%, 5%, 10%, 15wt%, 20wt%, 27wt%, and any range value therebetween. The amount of hydrogen peroxide added is related to the DMAC content in the wastewater. The higher the DMAC content, the higher the amount of hydrogen peroxide added should be to ensure that DMAC can be fully oxidized. The feed rates of wastewater and hydrogen peroxide are adjusted so that the mass ratio of hydrogen peroxide in the reactor to DMAC in the wastewater is 0.5-3:1, such as 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 2.7:1, 3:1.

[0010] Furthermore, in step (1), the material is subjected to continuous Fenton oxidation in a reactor, and the temperature in the reactor is 60-70°C.

[0011] Furthermore, in step (1), the residence time of the material in the reactor is 0.5 to 1.0 h. The residence time can be regulated by the volume of the reactor and the feed rate of each material. Preferably, an overflow port is provided on the reactor to control the feed rate of the material. When the material exceeds the overflow port, it will automatically flow into the neutralization kettle to ensure that the material stays in the reactor for the required time.

[0012] Furthermore, in step (1), the flow rates of wastewater, acid, ferrous sulfate, and hydrogen peroxide can be adjusted according to factors such as the volume of the reactor, residence time, material concentration, and raw material mass ratio. For example, when the reactor has a volume of 2.0 L and an overflow port (overflow when reaching 1.8 L), the acid used is 30 wt% hydrochloric acid, the concentration of ferrous sulfate solution is 10 wt%, and the concentration of hydrogen peroxide is 27 wt%, the feed rate of wastewater can be 30 g / min, the feed rate of hydrochloric acid can be 0.029 g / min, the feed rate of ferrous sulfate solution can be 0.3 g / min, and the feed rate of hydrogen peroxide can be 1.5-3 g / min. For another example, when the reactor has a volume of 50 L and is provided with an overflow port (overflows when reaching 45 L), the acid used is 30 wt% hydrochloric acid, the concentration of ferrous sulfate solution is 10 wt%, and the concentration of hydrogen peroxide is 27 wt%, the feed rate of wastewater can be 750 g / min, the feed rate of hydrochloric acid can be 0.73 g / min, the feed rate of ferrous sulfate solution can be 7.5 g / min, and the feed rate of hydrogen peroxide can be 37.5 g / min.

[0013] Further, the material after Fenton oxidation coming out of the reactor continuously enters the neutralization reactor, and at the same time, a sodium hydroxide solution is continuously introduced into the reactor to adjust the pH value of the material to 7.5-8.0. In the reactor, ferrous sulfate and sodium hydroxide in the material react to form ferric hydroxide precipitate. The concentration of the sodium hydroxide solution can be adjusted as needed, for example, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 32wt%, 35wt%, 40wt%, and any range value therebetween.

[0014] Furthermore, in step (2), the residence time of the material in the neutralization kettle is 20 to 60 minutes. The residence time can be regulated by the volume of the neutralization kettle and the feed rate of each material. Preferably, an overflow port is provided on the neutralization kettle to control the feed rate of the material. When the material exceeds the overflow port, it will automatically flow into the precipitation kettle to ensure that the material stays in the neutralization kettle for the required time.

[0015] Furthermore, in step (3), the retention time of the material in the precipitation tank is 1.0 to 2.0 hours. The main function of the precipitation tank is to allow the material to stand still therein, so that the generated iron hydroxide falls to the bottom of the tank in the form of precipitation, thereby clarifying the wastewater. After precipitation in the precipitation tank, the biological toxicity of the wastewater is significantly reduced, and the biodegradability is significantly improved, wherein the DMAC removal rate can reach more than 95%, and more than 60% of the total nitrogen is converted into ammonia nitrogen.

[0016] Furthermore, after precipitation in the precipitation tank, the upper clarified wastewater flows out from the precipitation tank, and the wastewater can be further subjected to biochemical treatment, and the biochemical treatment can be aerobic or anaerobic biochemical treatment.

[0017] The present invention has the following beneficial effects: 1. The present invention performs continuous Fenton oxidation treatment on wastewater, which can quickly destroy DMAC in the treated wastewater and degrade DMAC into small molecules such as formate, acetate, carbon dioxide, and ammonium, thereby meeting the requirements of subsequent direct biochemical treatment. The overall treatment method is simple and effective, and the treatment efficiency is high.

[0018] 2. When the extraction method or distillation method is used to recover high-concentration DMAC, the DMAC in the recovered wastewater can be reduced to less than 1% at most. If the DMAC below 1% is recovered by extraction or other methods, it is likely that the recovery cost will be higher than the value of the recovered DMAC itself; while the microbial biochemical treatment method is suitable for treating wastewater with a DMAC concentration of less than 0.1%. Therefore, the method of the present invention solves the blank interval of high and low concentration DMAC wastewater treatment of 0.1-1% DMAC concentration.

[0019] 3. Compared with iron-carbon + Fenton, electrocatalytic oxidation, biochemical treatment and other treatment methods, the treatment method of the present invention is more efficient and can directly degrade low and medium concentrations of DMAC completely.

[0020] 4. The method of the present invention is simple and easy to implement. It can be added continuously according to the ratio of wastewater and treatment agent. The feeding is continuous and the operation is stable. The effluent meets the treatment requirements.

[0021] 5. The method of the present invention has high treatment efficiency. The removal rate of DMAC in the wastewater from the precipitation tank can reach more than 95%, and more than 60% of the total nitrogen is converted into ammonia nitrogen. The treated wastewater can be directly subjected to ordinary aerobic or anaerobic biochemical treatment with good biochemical effect. The treatment capacity of the equipment of the same volume is higher than that of the intermittent operation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a processing flow chart of low concentration DMAC wastewater in the present invention.

[0023] In the figure, 1. wastewater tank; 2. hydrochloric acid tank; 3. ferrous sulfate solution tank; 4. hydrogen peroxide tank; 5. wastewater metering pump; 6. hydrochloric acid metering pump; 7. ferrous sulfate solution metering pump; 8. hydrogen peroxide metering pump; 9. sodium hydroxide solution tank; 10. sodium hydroxide solution metering pump; 11. reaction kettle; 12. neutralization kettle; 13. precipitation kettle; 14. waste residue; 15. drainage after treatment. DETAILED DESCRIPTION

[0024] The present technology is further described below with specific embodiments. The specific embodiments described herein are only used to explain the present technology, rather than all embodiments. Based on the embodiments in the present technology, all other embodiments obtained by those skilled in the art without making creative work are within the protection scope of the present technology.

[0025] Unless otherwise specified, the following reagents are commercially available and the following concentrations are percentage by mass.

[0026] In the following examples and comparative examples, the DMAC wastewater used is wastewater generated by the agrochemical industry, wherein the DMAC content is 0.5-1% and the total nitrogen content is 800-1600 mg / L.

[0027] In the following examples and comparative examples, the DMAC content was measured by gas chromatography, and the DMAC removal rate was calculated according to the formula w=(w0-w1) / w0, where w0 is the DMAC content before treatment and w1 is the DMAC content after treatment.

[0028] In the following examples and comparative examples, the total nitrogen content was directly measured using Shimadzu TOC-L / TNM-L, the ammonia nitrogen content was measured using Nessler's reagent spectrophotometry, and the ammonia nitrogen conversion rate was calculated using the formula n = n1 / n0, where n0 is the total nitrogen content before treatment and n1 is the ammonia nitrogen content after treatment. (The ammonia nitrogen before treatment is zero, and part of the total nitrogen is converted into ammonia nitrogen after treatment) Example 1 like Figure 1 As shown, a treatment method for low-concentration DMAC wastewater of the present invention is provided, wherein the wastewater tank 1, the hydrochloric acid tank 2, the ferrous sulfate solution tank 3 and the hydrogen peroxide tank 4 are connected to the reactor 11 through the wastewater metering pump 5, the hydrochloric acid metering pump 6, the ferrous sulfate solution metering pump 7, the hydrogen peroxide metering pump 8, respectively, to control the feeding speed of each entering the reactor, the reactor is provided with an overflow port, the overflow port is connected to the neutralization reactor 12, and the neutralization reactor is also connected to the sodium hydroxide solution tank 9 through the sodium hydroxide solution metering pump 10 to control the feeding speed of the sodium hydroxide solution. The neutralization reactor is also provided with an overflow port, the overflow port is connected to the precipitation reactor 13, the material is statically precipitated in the precipitation reactor, and then the waste residue 14 is discharged from the bottom of the precipitation reactor, and after the treatment is completed, the drainage 15 can be directly subjected to biochemical treatment after being discharged from the precipitation reactor.

[0029] Example 2 (1) Use a 2.0L reactor with overflow, add 300g of wastewater with a DMAC content of 0.5% and a total nitrogen content of 800mg / L, add 0.29g of 30% hydrochloric acid, 3.0g of 10% ferrous sulfate solution, start stirring and heat to maintain the temperature at 60-70°C, add 15g of 27% hydrogen peroxide at a rate of 1.5g / min, and the bottom of the reactor is paved; (2) The wastewater feed rate is 30 g / min, the 30% hydrochloric acid feed rate is 0.029 g / min, the 10% ferrous sulfate solution feed rate is 0.3 g / min, and the 27% hydrogen peroxide feed rate is 1.5 g / min. All materials enter the reactor at the same time, and the reactor temperature is maintained at 60-70°C and the pH is 3-4. Feeding is continued. After 1.0 h, the volume of the material in the reactor reaches 1.8 L and overflows from the overflow port on the side of the reactor into the neutralization reactor; (3) When the wastewater enters the neutralization kettle, 32% sodium hydroxide solution is continuously added to the neutralization kettle at a rate of 0.1 g / min. The volume of the neutralization kettle is 1.0 L, the pH of the material in the neutralization kettle is 8.0, and iron hydroxide precipitate is generated in the neutralization kettle. After 0.5 h, the wastewater overflows from the overflow port of the neutralization kettle into the precipitation kettle; (4) The volume of the precipitation tank is 5.0 L. After the material is allowed to settle in the precipitation tank for about 2 h, the waste residue is discharged from the bottom of the precipitation tank, and clear and transparent treated wastewater flows out from the outlet of the precipitation tank. The DMAC content in the discharged wastewater is 0.02%, the DMAC removal rate is 96%, the ammonia nitrogen content is 500 mg / L, and the ammonia nitrogen conversion rate is 62.5%.

[0030] Example 3 (1) Use a 2.0L reactor with overflow, add 300g of wastewater with a DMAC content of 1.0% and a total nitrogen content of 1600mg / L, add 0.29g of 30% hydrochloric acid, 3.0g of 10% ferrous sulfate solution, start stirring and heat to maintain the temperature at 60-70°C, add 30g of 27% hydrogen peroxide at a rate of 1.5g / min, and the bottom of the reactor is paved; (2) The wastewater feed rate is 30 g / min, the 30% hydrochloric acid feed rate is 0.029 g / min, the 10% ferrous sulfate solution feed rate is 0.3 g / min, and the 27% hydrogen peroxide feed rate is 3.0 g / min. All materials enter the reactor at the same time, and the reactor temperature is maintained at 60-70°C and the pH is 3-4. Feeding is continued. After 45 minutes, the wastewater volume in the reactor reaches 1.8 L and overflows from the overflow port on the side of the reactor into the neutralization reactor; (3) When the wastewater enters the neutralization kettle, 32% sodium hydroxide solution is continuously added to the neutralization kettle at a rate of 0.15 g / min. The volume of the neutralization kettle is 1.0 L, the pH of the material in the neutralization kettle is 8.0, and iron hydroxide precipitate is generated in the neutralization kettle. After 23 minutes, the wastewater overflows from the overflow port of the neutralization kettle into the precipitation kettle; (4) The volume of the precipitation kettle is 6.0 L. After the material is allowed to settle in the precipitation kettle for about 2 h, the waste residue is discharged from the bottom of the precipitation kettle, and clear and transparent treated wastewater flows out from the outlet of the precipitation kettle. The DMAC content in the discharged wastewater is 0.05%, the removal rate is 95%, the ammonia nitrogen content is 950 mg / L, and the ammonia nitrogen conversion rate is 59.4%.

[0031] Example 4 (1) Use a 50L reactor with overflow, add 7.5kg of wastewater with a DMAC content of 0.5% and a total nitrogen content of 800mg / L, add 7.3g of 30% hydrochloric acid, 75.0g of 10% ferrous sulfate solution, start stirring and heat to maintain the temperature at 60-70°C, add 375g of 27% hydrogen peroxide at a rate of 37.5g / min, and the bottom of the reactor is completed; (2) The wastewater feed rate is 750 g / min, the 30% hydrochloric acid feed rate is 0.73 g / min, the 10% ferrous sulfate solution feed rate is 7.5 g / min, and the 27% hydrogen peroxide feed rate is 37.5 g / min. All materials enter the reactor at the same time, and the reactor temperature is maintained at 60-70°C and the pH is 3-4. Feeding is continued. After 1.0 h, the wastewater volume in the reactor reaches 45 L and overflows from the overflow port on the side of the reactor and overflows into the neutralization reactor; (3) When the wastewater enters the neutralization kettle, 32% sodium hydroxide solution is continuously added to the neutralization kettle at a rate of 3.75 g / min. The volume of the neutralization kettle is 25 L, the pH of the material in the neutralization kettle is 8.0, and iron hydroxide precipitate is generated in the neutralization kettle. After 0.5 h, the wastewater overflows from the overflow port of the neutralization kettle into the precipitation kettle; (4) The volume of the precipitation tank is 50 L. After the material is allowed to settle in the precipitation tank for about 1.0 h, the waste residue is discharged from the bottom of the precipitation tank, and clear and transparent treated wastewater flows out from the outlet of the precipitation tank. The DMAC content in the discharged wastewater is 0.025%, the removal rate is 95%, the ammonia nitrogen content is 480 mg / L, and the ammonia nitrogen conversion rate is 60%.

[0032] Comparative Example The wastewater was treated according to the method of Example 2, except that: in step (1), 7.5 g of 27% hydrogen peroxide was added at a rate of 1.5 g / min; in step (2), the feeding rate of 27% hydrogen peroxide was 0.75 g / min. The results showed that the DMAC content in the clarified wastewater flowing out of the precipitation tank was 0.25%, the removal rate was 50%, the ammonia nitrogen content was 200 mg / L, and the ammonia nitrogen conversion rate was 25%.

[0033] Comparative Example Compared with Example 2, the amount of hydrogen peroxide added was reduced by half, resulting in a halving of the DMAC removal rate.

Claims

1. A method for continuous Fenton oxidation treatment of medium and low concentration DMAC wastewater, characterized in that The following steps are involved: (1) Low and medium concentration DMAC wastewater, acid, ferrous sulfate solution and hydrogen peroxide are continuously introduced into the reactor, and Fenton oxidation occurs in the reactor; (2) The material after Fenton oxidation is continuously fed into the neutralization kettle, and sodium hydroxide solution is continuously introduced into the neutralization kettle to react with ferrous sulfate and sodium hydroxide to form ferric hydroxide precipitate; (3) The material after the reaction in the neutralization kettle enters the precipitation kettle for standing; Optionally, the upper clarified wastewater flowing out of the settling tank is subjected to biochemical treatment.

2. The method according to claim 1, characterized in that: In step (1), the content of DMAC in the wastewater is 0.1-1%.

3. The method according to claim 1 or 2, characterized in that: In step (1), the feed rates of wastewater and acid are adjusted so that the pH of the wastewater in the reactor is 3-4.

4. The method according to claim 1 or 2, characterized in that: In step (1), the acid is hydrochloric acid or sulfuric acid.

5. The method according to claim 1 or 2, characterized in that: In step (1), the feed rates of wastewater and ferrous sulfate solution are adjusted so that the mass ratio of ferrous sulfate to wastewater is 0.1% to 0.2%:

1.

6. The method according to claim 1 or 2, characterized in that: In step (1), the feed rates of wastewater and hydrogen peroxide are adjusted so that the mass ratio of hydrogen peroxide in the reactor to DMAC in the wastewater is 0.5-3:

1.

7. The method according to claim 1 or 2, characterized in that: In step (1), the temperature in the reactor is 60-70° C., and the residence time of the material in the reactor is 0.5-1.0 h.

8. The method according to claim 1 or 2, characterized in that: In step (2), the feed rates of the Fenton oxidized material and the sodium hydroxide solution are adjusted so that the pH of the material in the neutralization kettle is 7.5 to 8.

0.

9. The method according to claim 1 or 2, characterized in that: In step (2), the residence time of the material in the neutralization kettle is 20 to 60 minutes.

10. The method according to claim 1 or 2, characterized in that: In step (3), the residence time of the material in the precipitation tank is 1.0 to 2.0 h.

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