A method for degrading PAHs in groundwater by activating persulfate with a reversible surfactant

Abstract

The present invention provides a method for degrading PAHs in groundwater by activating persulfate with a reversible surfactant. The main steps of this method are as follows: Add persulfate to the reversible surfactant solution containing PAHs. After充分混合反应后, PAHs in the system can be efficiently removed. The persulfate system can be activated by Br<supgt;‑< / supgt; in the reversible surfactant, which has the same high activation efficiency for persulfate as the similar halogen element chlorine. It can achieve the purpose of循环去除地下水中PAHs without additional activator. The present invention has the advantages of effectively degrading PAHs in groundwater with a small dosage, fast reaction time, simple operation, and can be implemented without additional equipment. It can be used for the degradation of PAHs in groundwater. It should be noted that there are some inaccuracies or unclear expressions in the original Chinese text. The above translation tries to make sense based on the overall context, but for a more accurate translation, the original text may need to be refined. For example, "充分混合反应后" should be something like "after thorough mixing and reaction", and "循环去除地下水中PAHs" should be something like "cyclically removing PAHs in groundwater".

Description

Technical Field

[0001] The invention belongs to the application field of groundwater pollution control, and specifically is a method for degrading PAHs by activating persulfate with a reversible surfactant. Technical Background

[0002] Polycyclic aromatic hydrocarbons (PAHs) are hydrocarbons containing more than two benzene rings in their molecules. The benzene rings in their structural formula are arranged in lines, clusters or angles. The pure substance is a colorless, white or light yellow-green solid. PAHs are persistent, bioaccumulative, and highly toxic (carcinogenic, teratogenic, and mutagenic) in the environment, so they are considered one of the most concerning pollutants. They mostly exist in the soil in an adsorbed or liquid form and are difficult to remove by physical or biological methods. Therefore, the remediation of PAH-contaminated sites is imminent.

[0003] Surfactant synergistic remediation technology refers to the injection of synergistic agents such as surfactants or organic solvents into contaminated soil and groundwater to increase the solubility or mobility of organic pollutants in the soil in the aqueous phase, and then the pollutants are transferred out of the ground through the recovery of the eluent and treated centrally. However, in the later treatment stage, separating pollutants from surfactants often requires specific instruments, equipment and sites, which will lead to cumbersome operation and high energy consumption in the separation process. Therefore, if the solubilized pollutants can be spontaneously released through the special properties of the surfactant itself, and the pollutants can be removed by simple means, the use of surfactants and secondary pollution to the environment can be effectively reduced. Summary of the invention

[0004] The present invention aims to overcome the problems of the prior art and provides a method for degrading PAHs by activating persulfate with a reversible surfactant. The surfactant and PAHs can be separated by ultraviolet light, and the remaining PAHs can be removed by oxidation by adding persulfate. The method has high activation efficiency and PAHs removal rate, small activator dosage, and is environmentally friendly. Using a reversible surfactant to activate persulfate can realize multiple recycling of the activator, thereby reducing the cost of repair.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for degrading PAHs in groundwater by activating persulfate with a reversible surfactant, characterized in that it comprises the following steps: adding persulfate to a reversible surfactant solution rich in PAHs, mixing and reacting for 15-60 minutes (preferably 20-35 minutes, more preferably 30 minutes), and removing PAHs in the system.

[0007] Furthermore, the PAHs is phenanthrene.

[0008] Furthermore, the concentration of the PAHs in the system is about 0 to 5 mg / L.

[0009] Furthermore, the persulfate is a peroxymonosulfate with good stability and solubility.

[0010] Furthermore, the reversible surfactant N 1 ,N 2 -bis[4-[4-[(4-butylphenyl)azo]phenoxy]butyl]-N 1 ,N 2 -Tetramethylethane-1,2-dibromide (N 1 ,N 2 -bis[4-[4-[(4-butylphenyl)azo]phenoxy]butyl]-N 1 ,N 2 -tetramethylethane-1,2-diammonium bromide, referred to as AzoPBT) was added in an amount of 4 to 6 mmol / L.

[0011] Furthermore, the dosage of persulfate in the system is 1-5 mmol / L, preferably 2-4 mmol / L, and more preferably 3 mmol / L.

[0012] Furthermore, based on the effective ingredients, the molar ratio of the reversible surfactant AzoPBT to the persulfate in the system is 1 to 5:1, preferably 2 to 3:1. Too high a persulfate dosage will lead to an aggravation of the self-scavenging effect of free radicals in the system, while too high a surfactant dosage will form a large number of micelles in the solution to encapsulate pollutants, thereby reducing the degradation effect. Too low a surfactant concentration will affect its solubilization ability for PAHs.

[0013] Furthermore, the order of addition is to add the reversible surfactant AzoPBT to solubilize PAHs and then add the persulfate.

[0014] Furthermore, after 30 minutes of reaction, the degradation efficiency is ≥80%.

[0015] The mechanism of the present invention is to add persulfate to the reversible surfactant solution rich in PAHs, and after sufficient mixing and reaction, the PAHs in the system are degraded. The persulfate system can be degraded by the Br in the reversible surfactant. - Activation, like the halogen element chlorine, has a high activation efficiency for persulfate, which can achieve the purpose of removing PAHs from groundwater. The halogen element Br can activate persulfate to produce perbromic acid and further generate singlet oxygen ( 1 O 2), without involving the formation of free radicals. The present invention has the advantages of being able to effectively degrade PAHs at a relatively small dosage, and has a fast action time, a wide pH applicable range, simple operation, and can be implemented without the need to invest in other equipment, and can be used for the degradation of PAHs in groundwater.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] (1) The target substance to be degraded by the present invention is PAHs, which is difficult to remove. The method provided by the present invention can effectively degrade the substance, with a degradation rate of up to 80%, and can be used to remove PAHs in groundwater.

[0018] (2) In the method of the present invention, the dosage of the reversible surfactant AzoPBT and persulfate is relatively small, about one tenth of that of the chlorine / persulfate system with the same degradation effect. The reason is that Br - The process of activating persulfate produces strong oxidizing hypobromous acid (HBrO), which in turn produces a large amount of singlet oxygen ( 1 O 2 Compared with the sulfate radicals (SO 4 ·- ) and hydroxyl radical (·OH), 1 O 2 It is easier to attack groups rich in negative electrons, so it has stronger selectivity for PAHs composed of benzene rings rich in negative electrons, that is, it can achieve better removal effects with less dosage, reduce secondary pollution, save raw materials and reduce costs. At the same time, because reversible surfactants can solubilize PAHs cyclically, the coupling system of reversible surfactant AzoPBT and persulfate can achieve cyclic removal of PAHs in groundwater.

[0019] (3) The persulfate used in the present invention is stable in nature, has high removal efficiency, does not generate secondary pollution, and is environmentally friendly.

[0020] (4) The conditions required for the reaction of the present invention are easy to achieve, the action time is fast, the pH application range is wide, and the removal effect is better in natural groundwater environments. The removal process is simple to operate and does not require other equipment, which is suitable for application and promotion in practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The effects of different molar ratios (persulfate unchanged) of Examples 1 to 3 on the activation of persulfate by the reversible surfactant AzoPBT to degrade phenanthrene;

[0022] Figure 2 The effects of different pH values ​​on the degradation of phenanthrene by persulfate activated by the reversible surfactant AzoPBT are shown in Examples 4 to 8.

[0023] Figure 3 The effects of different water quality backgrounds in Example 1 and Example 9 on the cyclic degradation of phenanthrene by persulfate activated by the reversible surfactant AzoPBT are shown. DETAILED DESCRIPTION

[0024] The present invention provides a method for degrading PAHs in groundwater by activating persulfate with a reversible surfactant, and the method comprises the following steps: adding persulfate to a reversible surfactant solution containing PAHs, and after sufficient mixing and reaction, the PAHs in the system can be efficiently removed. The persulfate system can be activated by Br- in the reversible surfactant, and has a high activation efficiency for persulfate like the similar halogen element chlorine, and can achieve the purpose of cyclically removing PAHs in groundwater without adding an additional activator. The present invention has the advantages of effectively degrading PAHs in groundwater with a relatively small dosage, and has a fast action time, simple operation, and can be implemented without the investment of other equipment, and can be used for the degradation of PAHs in groundwater.

[0025] The present invention is further described in conjunction with the following experiments:

[0026] The first set of experiments

[0027] Example 1

[0028] Take 80mL of a 5mmol / L reversible surfactant AzoPBT solution prepared with ultrapure water into a 100mL reagent bottle, add a certain amount of phenanthrene to the bottle so that the concentration of phenanthrene is 3mg / L, add a certain amount of persulfate so that the concentration in the mixed solution is 3mmol / L, react for 60min, and the molar ratio of the reversible surfactant AzoPBT to the persulfate in the mixed solution is 5:3.

[0029] Example 2

[0030] Compared with Example 1, the only difference is that the molar ratio of the persulfate to the reversible surfactant AzoPBT is 5:1.

[0031] Example 3

[0032] Compared with Example 1, the only difference is that the molar ratio of the persulfate to the reversible surfactant AzoPBT is 1:1.

[0033] In Examples 1 to 3, the obtained residual rate-time relationship diagram of phenanthrene is as follows: Figure 1 As shown in the figure, the ordinate is the residual rate of phenanthrene, and the abscissa is the reaction time. The degradation effect is reflected by the residual rate of phenanthrene. The smaller the residual rate of phenanthrene, the better the degradation effect. The residual rate of phenanthrene is the percentage of the ratio of the phenanthrene concentration in the sample at each time to the initial concentration of phenanthrene.

[0034] Examples 1 to 3 use different ratios of reversible surfactant AzoPBT and persulfate to degrade phenanthrene. Figure 1 It can be seen that the molar ratio of reversible surfactant AzoPBT to persulfate is 5:3, which has the best degradation effect. Increasing the dosage of activator can provide more Br-, increase the contact and collision probability with persulfate, and improve the activation efficiency. Continuously increasing the dosage of activator will inhibit the repair effect, increase the repair cost and increase the risk of secondary pollution.

[0035] The second set of experiments

[0036] Example 4

[0037] Compared with Example 1, the only difference is that sodium hydroxide is used to adjust the pH value to 11 at the beginning.

[0038] Example 5

[0039] Compared with Example 1, the only difference is that sodium hydroxide is used to adjust the pH value to 9 at the beginning.

[0040] Example 6

[0041] Compared with Example 1, the only difference is that dilute sulfuric acid is used to adjust the pH value to 7 at the beginning.

[0042] Example 7

[0043] Compared with Example 1, the only difference is that dilute sulfuric acid is used to adjust the pH value to 5 at the beginning.

[0044] Example 8

[0045] Compared with Example 1, the only difference is that dilute sulfuric acid is used to adjust the pH value to 3 at the beginning.

[0046] The residual rate-time relationship diagram of phenanthrene under different pH conditions obtained in Examples 4 to 8 is as follows: Figure 2 As shown, Figure 2 The degradation effect of persulfate activated by reversible surfactant AzoPBT on phenanthrene under different pH conditions was compared. It can be seen from the figure that the activation effect is best when pH = 7 (Example 6), and it has good activation effect under alkaline and acidic conditions. As the pH of the aqueous solution decreases, a large amount of HBrO is generated in the solution, thereby achieving efficient removal of phenanthrene; and as the pH of the aqueous solution increases, OH - Can activate persulfate to generate 1 O 2 , thus achieving efficient removal of phenanthrene. Since the main active substance type in the reversible surfactant-persulfate system is 1 O 2, which has stronger anti-interference ability and therefore has a wider pH application range than traditional transition metal activated persulfate technology.

[0047] The third experiment

[0048] Example 9

[0049] Compared with Example 1, the difference is that the reversible surfactant AzoPBT solution is prepared using natural groundwater, and an excess of phenanthrene is added to the solution for solubilization. After 24 hours of solubilization, it is irradiated with ultraviolet light to release part of the phenanthrene from the solution, and a certain amount of persulfate is added to the solution to make the concentration of 3 mmol / L. After oxidation for 1 hour, it is irradiated with visible light and then excess phenanthrene is added again for solubilization. This is repeated four times to investigate the recycling ability of this technology.

[0050] The relationship between the residual concentration of phenanthrene in the reversible surfactant AzoPBT solution and the number of cycles under different water quality conditions is obtained in Example 1 and Example 9, as shown in FIG. Figure 3 As shown in the figure, it can be seen that the system still has a strong oxidation ability in the natural groundwater environment, which is mainly due to the good anti-interference ability of the main active substances in the system, which can resist the interference of complex matrices in groundwater. Due to the production of a certain amount of SO 4 2- , which effectively enhances the solubilizing ability of reversible surfactants, significantly improving their solubilizing ability when used for the second time.

[0051] The above description is only a description of the preferred embodiments of the present application, and is not intended to limit the scope of the present application. Any changes or modifications made by any person skilled in the art based on the above disclosed technical contents shall be deemed as equivalent effective embodiments and shall fall within the scope of protection of the technical solution of the present application.

Claims

1. A method for degrading PAHs in groundwater by activating persulfate with a reversible surfactant. It is characterized in that The method comprises the following steps: preparing a reversible surfactant AzoPBT solution using natural groundwater, adding an excess of PAHs to the solution for solubilization, adding persulfate to the reversible surfactant solution rich in PAHs, mixing and reacting for 15-60 minutes, and removing PAHs in the system; The dosage of reversible surfactant AzoPBT is 4-6 mmol / L. 1 ,N 2 -Bis[4-[4-[(4-butylphenyl)azo]phenoxy]butyl]-N 1 ,N 2 -Tetramethylethane-1,2-dibromide.

2. The method according to claim 1, It is characterized in that The PAHs is phenanthrene.

3. The method according to claim 1, It is characterized in that The concentration of the PAHs in the system is 3-5 mg / L.

4. The method according to claim 1, It is characterized in that The persulfate is peroxymonosulfate.

5. The method according to claim 1, It is characterized in that The dosage of persulfate in the system is 1-5 mmol / L.

6. The method according to claim 1, It is characterized in that Calculated on the basis of effective ingredients, the molar ratio of the reversible surfactant AzoPBT to the persulfate in the system is 1 to 5:1.

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