Method for removing acetochlor in water by activating persulfate with ferrous ions

Abstract

The invention discloses a method for removing acetochlor in water by using ferrous ion activated persulfate, and belongs to the field of water treatment. Ferrous ions activate persulfate through single electron transfer, sulfate free radicals SO4 <-> with strong oxidizing property are generated, SO4 <-> attacks acetochlor molecules, ring opening and mineralization are achieved through electron transfer, hydrogen extraction or addition reaction, and a good removal effect on acetochlor in water is achieved. The operation method comprises the following steps: adding ferrite, hydroxylamine hydrochloride and persulfate into a pre-acidified water sample containing acetochlor according to a certain concentration, and stirring to react for a certain time, so as to remove acetochlor in the water sample. Compared with the prior art, the method has the characteristics of simplicity in operation, high reaction rate, good removal effect and low cost, the removal rate of 98-99% can be realized by only about 15 minutes for a natural water body with low background concentration of acetochlor, and the acetochlor index in effluent meets the requirements of Standard for Sanitary Drinking Water (GB 5749-2022).

Description

Technical Field

[0001] The invention belongs to the field of water treatment and relates to a method for removing acetochlor from water by activating persulfate with ferrous ions. Background Art

[0002] Pesticides play an important role in controlling agricultural pests and diseases, but due to the low utilization rate of pesticides, about 80% of pesticides enter the environment during use and enter water bodies through circulation, causing water pollution. 14 H 20 ClNO2 is a widely used chloroacetamide pre-emergence herbicide, widely used for its high weed control efficiency and strong selectivity. However, it has a long environmental residual period (up to 45 days), is difficult to volatilize and degrade, and easily remains in soil, water, and agricultural products. Its metabolites pose a threat to human health and the ecological environment. It has been classified by the EPA as a Class B-2 potential carcinogen. The new version of my country's "Standard for Drinking Water Quality" (GB 5749-2022), which came into effect on April 1, 2023, adds acetochlor as an expanded indicator, with a concentration limit of 0.02 mg / L. Therefore, removing acetochlor from water environments is extremely important and urgent.

[0003] Treatment technologies for acetochlor in water can be categorized into three categories: chemical oxidation, physical separation, and biodegradation. Chemical oxidation technologies include ozone oxidation, Fenton oxidation, and photocatalytic oxidation. Ozone oxidation has a low degradation rate for acetochlor. Fenton oxidation has limitations due to the need for hydrogen peroxide, which carries significant safety risks. Photocatalytic oxidation is also less efficient. Current chemical oxidation technologies face challenges balancing efficiency and cost, and by-product control. Physical separation technologies include adsorption and membrane separation. Adsorption utilizes porous materials such as activated carbon to adsorb acetochlor molecules, while membrane separation utilizes nanofiltration or reverse osmosis membranes to intercept acetochlor molecules. However, the fundamental problem with both methods is that acetochlor is not converted, posing the risk of secondary environmental damage. While activated sludge or specific bacterial strain methods have some biodegradation potential for acetochlor, acetochlor inhibits microbial activity, slowing the enrichment of degrading bacteria, lengthening the screening cycle, and leading to low efficiency. Advanced oxidation technology based on persulfate is considered to be one of the most efficient and green methods for degrading some refractory organic matter. However, the effect of acetochlor oxidation by persulfate alone is poor. Activation of persulfate can improve its oxidation performance. Common activation methods include thermal activation, alkali activation, transition metal activation and heterogeneous catalysis. 2+ ) activated persulfate (S2O8 2- ) is an activation method with high efficiency, simple operation and low cost. 2+ With S2O8 2- During the reaction, Fe2+ Transfer electrons to S2O8 2- , which breaks the peroxide bond (-O - O-) in persulfate and produces sulfate radicals (SO 4- ∙), SO 4- ∙It has a high redox potential and can oxidize and decompose acetochlor in water.

[0004] The invention uses ferrous ions to activate persulfate to oxidize and remove acetochlor in water, has high removal efficiency, fast oxidation speed, simple operation, low running cost and one-time investment cost, and is of great significance to protecting the surface water environment and ensuring the safety of drinking water quality. Summary of the Invention

[0005] In view of the current research status of acetochlor removal technology in water, the present invention proposes a method for removing acetochlor by activating persulfate with ferrous ions, which is characterized in that the ferrous ions activate the persulfate to produce SO4 with strong oxidizing properties. - ∙ and a small amount of hydroxyl radicals (∙OH), which can quickly oxidize and remove acetochlor.

[0006] A method for removing acetochlor by activating persulfate with ferrous ions is achieved by the following steps: Step 1: Add the acetochlor to be removed to a reactor containing tap water at room temperature to prepare an acetochlor solution with a concentration not exceeding 5.40 mg / L, and adjust the pH value to 3-5 with 1 mol / L dilute hydrochloric acid; Step 2: Add ferrous sulfate (FeSO4 or FeSO4·7H2O) or ferrous sulfide (FeS) and other ferrous salts to the acetochlor solution described in step 1 at once to make Fe 2+ The concentration reaches 1.12~3.36 mgl / L; Step 3: Add hydroxylamine hydrochloride (NH2OH∙HCl) to the acetochlor solution described in step 1 at one time to make the concentration of hydroxylamine hydrochloride reach 3.00-3.50 mg / L; Step 4: Add persulfate to the reactor to make the concentration of persulfate reach 40~50 μmol / L; Step 5: Start the stirrer in the reactor and stir for 50~60 seconds. -1 The mixture was stirred at a speed gradient of 10-50 min. As the stirring reaction proceeded, the acetochlor in the reactor was removed. The reaction could be terminated at any time by adding methanol (CH3OH).

[0007] Furthermore, the normal temperature in step 1 refers to 20-30° C., and the higher the water temperature, the more conducive it is to increasing the speed of removing acetochlor.

[0008] Furthermore, the acetochlor solution described in step 1 can also be obtained from natural rivers or lakes, but the chemical oxygen demand (COD) of the water sample must be controlled to not exceed 30 mg / L.

[0009] Furthermore, controlling the pH value of the acetochlor solution to 3-5 in step 1 refers to the acidity range, with a preferred value of 3±0.2.

[0010] Furthermore, the operation order of the above steps 2 and 3 can be swapped.

[0011] Furthermore, the persulfate is peroxydisulfate (PDS), and the present invention uses peroxydisulfate represented by potassium persulfate (K2S2O8).

[0012] The reaction principle of the present invention is as follows: (1) In the present invention, persulfate itself has a certain oxidizing property, but its oxidizing ability is relatively weak at room temperature, and its removal efficiency for acetochlor is very low. When activated by ferrous ions, persulfate will produce sulfate radicals and hydroxyl radicals with strong oxidizing properties. The molecular structure of acetochlor contains C—C, C—Cl, CN, CH and other bonds. Sulfate radicals can attack these chemical bonds in the acetochlor molecule, causing these chemical bonds in the acetochlor molecule to break, and gradually oxidize and degrade it into small molecular compounds. (2) In the present invention, hydroxylamine hydrochloride mainly plays the role of a reducing agent in the persulfate activation process. The -OO- in the persulfate has a higher oxidation state, and hydroxylamine hydrochloride can trigger the decomposition reaction of the persulfate through its own reducing property. The N atom in hydroxylamine hydrochloride is in a lower oxidation state, which can provide electrons to promote the breakage of the peroxide bond of the persulfate and generate sulfate radicals with strong oxidizing properties. At the same time, hydroxylamine hydrochloride can also promote the conversion of trivalent iron ions to divalent iron ions. Divalent iron ions will be converted into trivalent iron ions during the persulfate activation process. At this time, the trivalent iron ions are easily reduced to divalent iron ions by hydroxylamine hydrochloride and re-enter the cycle of activating persulfate, thereby improving the activation efficiency; (3) In the present invention, methanol is used as a quencher to react with sulfate radicals at a high reaction rate, rapidly consuming the free radicals in water and preventing acetochlor from being degraded.

[0013] Compared with the prior art, the present invention has the following characteristics: (1) In the present invention, the persulfate advanced oxidation technology is an oxidation technology that produces sulfate radicals as the main free radical, and has the advantages of long free radical life, high oxidation potential, low requirements for the pH value of the reaction system, good selectivity, fast reaction speed, and high removal efficiency of acetochlor; (2) The present invention promotes the circulation of divalent iron ions and trivalent iron ions in the reaction system by adding hydroxylamine hydrochloride, thereby reducing the consumption of ferrous salts and lowering operating costs; (3) The present invention is simple to operate, has a fast reaction speed, a small reactor volume, and low operating costs and initial investment. It has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a comparison chart of the effect of the initial concentration of acetochlor on the efficiency of ferrous ion activated persulfate in removing acetochlor. ACT0 Indicates the initial concentration of acetochlor.

[0015] Figure 2 This is a comparison chart of the effect of the pH value of the reaction system on the efficiency of ferrous ion-activated persulfate in removing acetochlor.

[0016] Figure 3 This is a comparison chart of the effect of the added ferrous ion concentration on the efficiency of ferrous ion activated persulfate in removing acetochlor. Fe2+0 Indicates the concentration of ferrous ions added. DETAILED DESCRIPTION

[0017] Specific embodiment 1: The method for removing acetochlor from water by activating persulfate with ferrous ions described in this embodiment is specifically carried out in the following steps: Step 1: Add the acetochlor to be removed to a reactor containing tap water at a temperature of 20 to 30°C to prepare an acetochlor solution with a concentration not exceeding 5.40 mg / L, and adjust the pH value to 3 to 5 with 1 mol / L dilute hydrochloric acid; Step 2: Add ferrous sulfate to the acetochlor solution in step 1 at one time to make Fe 2+ The concentration reached 1.12~3.36 mg / L; Step 3: adding hydroxylamine hydrochloride to the acetochlor solution described in step 1 at one time to make the concentration of hydroxylamine hydrochloride reach 3.00-3.50 mg / L; Step 4: Add potassium persulfate (K2S2O8) to the reactor to make the concentration of potassium persulfate reach 40~50 μmol / L; Step 5: Start the stirrer in the reactor and stir the reaction for 50-60 seconds. -1 The stirring was carried out at a speed gradient of 10 to 50 minutes. As the stirring reaction proceeded, the acetochlor in the reactor was removed. Methanol was used to terminate the reaction at different reaction times so that samples could be taken to detect the residual concentration of acetochlor and examine its relationship with time.

[0018] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the tap water in step 1 is replaced with a natural surface water sample, but the chemical oxygen demand of the water sample must be controlled to not exceed 30 mg / L. Other aspects are the same as specific embodiment 1.

[0019] Specific embodiment three: This embodiment differs from specific embodiment one in that the ferrous sulfate described in step two is replaced by ferrous sulfide, and the rest is the same as specific embodiment one.

[0020] Specific embodiment 4: This embodiment differs from the specific embodiment 1 in that the stirring reaction described in step 5 is carried out in the following manner: -1 Stir at a speed gradient of 30 s, then at a speed gradient of 50-60 s -1 The mixture is stirred at a speed gradient of 10 to 50 min, and the rest is the same as in the first embodiment. Example

[0021] The effects of the present invention are verified by the following examples:

[0022] Example 1: A method for removing acetochlor from water by activating persulfate with ferrous ions is specifically carried out in the following steps: Step 1: Take a water sample from a river near a rice field. After testing, the acetochlor concentration in the water sample is 0.11 mg / L and the COD concentration in the water sample is 20 mg / L. Adjust the pH value of the water sample to 3±0.2 with 1 mol / L dilute hydrochloric acid. Step 2: Add FeSO4·7H2O to the water sample described in step 1 at once to make Fe 2+ The concentration reached 1.12 mg / L; Step 3: Add hydroxylamine hydrochloride to the water sample described in step 2 at one time to make the concentration of hydroxylamine hydrochloride reach 3.48 mg / L; Step 4: Add potassium persulfate to the reactor to make the concentration of potassium persulfate in the water sample reach 13.50 mg / L; Step 5: Start the stirrer in the reactor and stir for 50~60 seconds. -1 The mixture was stirred at a speed gradient of 100 nm for 50 min, and 10 mL of samples were taken at 5 min, 10 min, 15 min, 20 min, 30 min, 40 min, and 50 min after the start of the reaction. 1 mL of methanol was added to each sample to terminate the reaction. The concentration of acetochlor in the samples was then determined by high performance liquid chromatography. The results are shown in the attached figure. Figure 1 shown.

[0023] Example 2: This example differs from Example 1 in that the concentration of acetochlor in the water sample of step 1 is increased to 0.27 mg / L, 2.7 mg / L, 4.05 mg / L, and 5.4 mg / L, respectively, by adding acetochlor. Other aspects are the same as those of Example 1. The results are shown in the attached figure. Figure 1 shown.

[0024] Example 1 and Example 2 are comparative examples. Figure 1 The results shown in the figure lead to the following conclusions: when the initial acetochlor concentration is not greater than 0.27 mg / L, the removal rate is fast, the removal rate after 15 minutes of reaction is not less than 97%, and the residual acetochlor concentration is about 0.0081 mg / L, which meets the requirement of 0.02 mg / L of acetochlor in the "Sanitary Standard for Drinking Water" (GB 5749-2022). Combined with the concentration of acetochlor in the original natural river water sample in Example 1, it can be seen that the present invention can quickly and effectively remove acetochlor from river water to ensure the safety of drinking water; when the initial acetochlor concentration increases to 2.7 mg / L, a longer reaction time of 30 minutes is required to meet the requirement that the residual acetochlor concentration is not greater than 0.02 mg / L; and when the concentration increases to 5.40 mg / L, even if the reaction time is 50 minutes, the residual acetochlor concentration is not greater than 0.02 mg / L. min; the requirements are still not met; the results of Example 1 and Example 2 show that the lower the initial acetochlor concentration, the better the effect. Considering that the longer the reaction time, the greater the investment required for implementation, when using this invention to remove acetochlor in water, the preferred initial concentration of acetochlor is 0~2.70 mg / L.

[0025] Example 3: This example differs from Example 1 in that the concentration of the original water sample acetochlor in step 1 is adjusted to 2.7 mg / L, and the pH value of the water sample is adjusted to 3±0.2, 5±0.2, 7±0.2 and 9±0.2 respectively with 1 mol / L dilute hydrochloric acid or 1 mol / L NaOH to investigate the effect of pH on the removal effect of acetochlor. Other results are the same as in Example 1. The results are shown in the attached figure. Figure 2 shown.

[0026] Analysis Attachment Figure 2 The results shown lead to the following conclusions: the present invention has a good removal effect on acetochlor under acidic conditions, but has almost no removal effect on acetochlor under alkaline conditions; when the initial acetochlor concentration is 2.7 mg / L, when the pH is about 3, the removal efficiency of acetochlor reaches 98% after 30 minutes of reaction; but when the pH is about 5, the removal rate is only 63% after 50 minutes of reaction; when the pH value is higher, the removal rate decreases significantly or almost disappears; although a lower pH value is conducive to the reaction, considering the problems of economic operation and equipment corrosion, when the present invention is used to remove acetochlor in water, the preferred pH value of the reaction system is 3±0.2.

[0027] Example 4: This example is different from Example 1 in that the concentration of acetochlor in the original water sample in step 1 is adjusted to 2.7 mg / L, and the amount of FeSO4·7H2O added in step 2 is changed to make Fe 2+ The concentrations reached 0.28 mg / L, 0.56 mg / L, 2.24 mg / L and 3.36 mg / L, and the effect of ferrous ion concentration on the removal effect of acetochlor was the same as in Example 1. The results are shown in the attached figure. Figure 3 shown.

[0028] Analysis Attachment Figure 3 The results show that the larger the amount of ferrous salt added to activate persulfate, the more conducive it is to improving the removal rate of acetochlor, shortening the reaction time and saving the first-time investment; under the condition of the initial acetochlor concentration of 2.7 mg / L, when Fe 2+ When the concentration exceeded 1.12 mg / L, the removal rate of acetochlor reached about 98% after 30 min of reaction. 2+ When the concentration is reduced to 0.56 mg / L or below, even after 50 min of reaction, the removal rate of acetochlor does not exceed 70%, and the residual concentration does not meet the requirements; considering that increasing the dosage of ferrous salt will increase the operating cost and bring more difficulties in subsequent iron removal, but considering that the presence of hydroxylamine hydrochloride can reuse ferrous salt, the Fe 2+ The optimal range of dosage concentration is 0.56~1.12 mg / L.

Claims

1. A method for removing acetochlor from water by activating persulfate with ferrous ions, characterized in that Ferrous ions are used to activate persulfate to produce sulfate radicals for the oxidation and removal of acetochlor in water.

2. The method for removing acetochlor from water by activating persulfate with ferrous ions according to claim 1, characterized in that The process of removing acetochlor is carried out in the following steps: Step 1: Add the acetochlor (C 14 H 20 ClNO2), prepare an acetochlor solution with a concentration not exceeding 5.40 mg / L, and adjust its pH to 3-5 with 1 mol / L dilute hydrochloric acid; Step 2: Add ferrous sulfate (FeSO4 or FeSO4·7H2O) or ferrous sulfide (FeS) and other ferrous salts to the acetochlor solution described in step 1 at once to make Fe 2+ The concentration reached 1.12~3.36 mg / L; Step 3: Add hydroxylamine hydrochloride (NH2OH∙HCl) to the acetochlor solution described in step 1 at one time to make the concentration of hydroxylamine hydrochloride reach 3.00-3.50 mg / L; Step 4: Add persulfate to the reactor to make the concentration of persulfate reach 40~50 μmol / L; Step 5: Start the stirrer in the reactor and stir for 50~60 seconds. -1 The mixture was stirred at a speed gradient of 10-50 min. As the stirring reaction proceeded, the acetochlor in the reactor was removed. The reaction could be terminated at any time by adding methanol (CH3OH).

3. The method for removing acetochlor from water by activating persulfate with ferrous ions according to claim 1, characterized in that The normal temperature described in step 1 refers to 20~30℃.

4. The method for removing acetochlor from water by activating persulfate with ferrous ions according to claim 1, characterized in that The preferred concentration of acetochlor in step 1 is 0-2.70 mg / L.

5. The method for removing acetochlor from water by activating persulfate with ferrous ions according to claim 1, characterized in that The pH value of step 1 is 3±0.

2.

6. The method for removing acetochlor from water by activating persulfate with ferrous ions according to claim 1, characterized in that The acetochlor solution described in step 1 may also be a water sample taken from natural surface water, but the chemical oxygen demand (COD) of the water sample is controlled to be no more than 30 mg / L.

7. The method for removing acetochlor from water by activating persulfate with ferrous ions according to claim 1, characterized in that The operation order of the above steps 2 and 3 can be interchanged.

8. The method for removing acetochlor from water by activating persulfate with ferrous ions according to claim 1, characterized in that The persulfate in the above step 4 refers to peroxydisulfate (PDS).

9. The method for removing acetochlor from water by activating persulfate with ferrous ions according to claim 1, characterized in that The stirring method in step 5 above can also be 400~500 s -1 After stirring at a speed gradient of 30 s, the mixture was stirred at a speed gradient of 50-60 s. -1 Stir at a speed gradient of 10 to 50 min.

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