A method for treating phenol-containing wastewater by activated persulfate with biochar-supported zero-valent iron

Abstract

The present application belongs to the technical field of high-concentration coal chemical phenolic wastewater treatment, and discloses a method for treating phenolic wastewater by using biochar loaded sulfidized zero-valent iron to activate persulfate. The method comprises the following steps: mixing biochar powder and polyethylene glycol solution; under an external magnetic field, adding sodium borohydride solution and mixed solution of ferrous sulfate and sulfuration reagent into the obtained solution to obtain biochar loaded sulfidized zero-valent iron, wherein the molar ratio of sulfur to iron in the obtained biochar loaded sulfidized zero-valent iron is 0.05:1; adding biochar loaded sulfidized zero-valent iron and persulfate into phenolic wastewater and fully oscillating to realize the degradation of phenolic compounds in the water body. The method can not only effectively remove polyphenols, but also has a very significant degradation effect on single phenol which is difficult to treat.

Description

Technical Field

[0001] This invention belongs to the field of high-concentration coal chemical phenol-containing wastewater treatment technology, and specifically relates to a method for treating phenol-containing wastewater using biochar-supported zero-valent iron sulfide-activated persulfate. Background Technology

[0002] High-concentration coal chemical phenol-containing wastewater is a type of industrial wastewater with large daily production and high hazards. Because phenols in this wastewater are highly neurotoxic and difficult to biodegrade, they must be treated before discharge. The total phenol concentration in high-concentration coal chemical phenol-containing wastewater is approximately 6000–20000 mg / L, including monophenols and polyphenols. Phenol has the highest content among monophenols, while hydroquinone among polyphenols is difficult to treat due to its low electron cloud density. Therefore, phenol and hydroquinone were used to replace monophenols and polyphenols in the wastewater in experiments. Low-concentration wastewater can be directly treated biologically, while high-concentration coal chemical phenol-containing wastewater generally undergoes oleic acid-phenol recovery to reduce the phenol concentration to at least 500 mg / L before entering the biological treatment stage. However, the total phenol concentration often reaches nearly 1000 ppm. When the wastewater after phenol-amine recovery enters the biological treatment stage, the initial phenol concentration is generally 50-100 ppm, and the polyphenol concentration is 200-800 ppm.

[0003] Currently, the most commonly used biochemical treatment method is the advanced oxidation technology of activating persulfate with iron-based materials, which has advantages such as low cost, safety and stability, and strong oxidation capacity. Among different iron-based materials, sulfide nano-zero valent iron (S-nZVI) has good reactivity due to its large specific surface area and excellent electronic conductivity. However, S-nZVI still has problems in the treatment of phenol-containing wastewater from coal chemical industry. On the one hand, S-nZVI is effective for phenol-containing wastewater with low concentrations, such as surface water, but its degradation effect is insufficient for wastewater with high phenol content, such as coal gasification wastewater. On the other hand, during the synthesis process, the biochar particles loaded with zero valent iron tend to sink to the bottom of the reactor due to mass, and the strong magnetism of iron causes the material to agglomerate, thus preventing the effective loading of S-nZVI in its pore structure. These defects prevent S-nZVI from effectively exerting its degradation capacity, resulting in its ability to remove easily degradable polyphenols, while its degradation effect on monophenols is relatively poor. Summary of the Invention

[0004] In order to overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for treating phenol-containing wastewater by biochar-supported sulfidated zero-valent iron-activated persulfate.

[0005] The objective of this invention is achieved through the following solution:

[0006] A method for treating phenol-containing wastewater using biochar-supported zero-valent iron sulfide-activated persulfate includes the following steps:

[0007] (1) The straw was crushed and pyrolyzed to obtain biochar powder;

[0008] (2) Add polyethylene glycol solution to biochar powder and mix;

[0009] (3) Under an external magnetic field, sodium borohydride solution and ferrous sulfate and sulfidation reagent mixture were added to the solution obtained in step (2), stirred and reacted, and then separated, washed and dried to obtain biochar-supported sulfidated zero-valent iron. The molar ratio of sulfur to iron in the obtained biochar-supported sulfidated zero-valent iron was 0.05:1.

[0010] (4) Add biochar-loaded zero-valent iron sulfide and persulfate to phenol-containing wastewater and shake the reaction to achieve the degradation of phenolic compounds in the water.

[0011] The heating program for pyrolysis in step (1) is as follows: the heating rate is 5-10℃ / min, and after 110 min, it is raised to 600℃. After maintaining this temperature for pyrolysis for 2 hours, it automatically enters the cooling program.

[0012] The atmosphere for pyrolysis in step (1) is nitrogen.

[0013] After pyrolysis in step (1), the resulting solid biochar is ground into powder and passed through a 100-mesh sieve.

[0014] The polyethylene glycol mentioned in step (2) is polyethylene glycol 4000.

[0015] The concentration of the polyethylene glycol solution in step (2) is 5-15 g / L.

[0016] The mass ratio of biochar powder to polyethylene glycol in step (2) is 1 to 3:10.

[0017] The mixing in step (2) specifically involves ultrasonic vibration for 10 to 30 minutes.

[0018] The strength of the external magnetic field in step (3) is 10 to 100 mT.

[0019] The sulfiding agent in step (3) is sodium sulfide.

[0020] The mass ratio of the biochar powder in step (2) to the ferrous sulfate in step (3) is 1:27-28, preferably 1:27.8.

[0021] The molar ratio of sodium borohydride and ferrous sulfate in step (3) is 2 to 3:1.

[0022] The concentration of sodium borohydride in the sodium borohydride solution in step (3) is 0.8–1.2 mol / L; the concentration of sodium sulfide in the mixed solution is 0.02 mol / L.

[0023] The addition and stirring reaction in step (3) are carried out under a nitrogen atmosphere; the stirring reaction time is 30 to 60 minutes.

[0024] The addition in step (3) is by dripping, with a dripping rate of 10 to 30 drops / min.

[0025] Step (3) involves separating, washing, and drying the biochar-supported zero-valent iron sulfide, specifically by using a magnet to separate the black particles from the reaction solution, washing them with deionized water and anhydrous ethanol, and then vacuum drying the washed material at 60-80°C for 8-24 hours for later use.

[0026] The phenol-containing wastewater in step (4) contains monophenols and polyphenols; wherein, monophenols include at least one of phenol and methylphenol; and polyphenols include at least one of hydroquinone, catechol, resorcinol, triphenol or other phenols.

[0027] The concentration of the monophenol in the water body is 100–1000 mg / L, and the concentration of the polyphenol in the water body is 100–1000 mg / L.

[0028] The pH value of the phenol-containing wastewater in step (4) is 4 to 8.5.

[0029] The persulfate mentioned in step (4) includes at least one of perdisulfate and permonosulfate.

[0030] The amount of biochar-supported zero-valent iron added in step (4) satisfies the following condition: the concentration of biochar-supported zero-valent iron in the reaction system is 0.1 to 2.5 g / L.

[0031] The amount of persulfate added in step (4) satisfies the following condition: the concentration of persulfate in the reaction system is 5-60 mmol / L, preferably 40 mmol / L.

[0032] The reaction temperature in step (4) is 25–80°C, and the reaction time is 10–60 min.

[0033] Mechanism of the invention

[0034] This invention first involves the high-temperature pyrolysis and grinding of waste straw to obtain biochar. Then, under a fixed external weak magnetic field, using polyethylene glycol 4000 as a dispersant, zero-valent iron sulfide (ZVFe) is loaded into the porous structure of the biochar using a sodium borohydride reduction method. The external magnetic field and the presence of polyethylene glycol 4000 significantly increase the ZVFe loading on the biochar, successfully preparing a highly loaded biochar ZVFe. The synthesized catalyst and persulfate are then added to high-concentration phenol-containing wastewater from a coal chemical plant after phenol and ammonia recovery treatment, forming a solid-liquid two-phase system in the solution. After a shaking reaction, phenolic compounds in the aqueous phase are removed. This invention not only effectively removes polyphenols but also shows significant degradation effects on difficult-to-treat monophenols. Using environmentally friendly biochar as a loading substrate improves the poor dispersibility of ZVFe; the material remains dispersed in the solution for up to four hours after the reaction. This method has few reaction restrictions, a fast reaction rate, good degradation effect on phenolic substances, easy catalyst particle recovery, and is environmentally friendly. Therefore, this invention has good application potential in the field of phenol-containing wastewater treatment from coal gasification.

[0035] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0036] (1) The present invention modifies zero-valent iron by sulfidation, which reduces the precipitation of iron hydroxide on the surface of the material and makes the material more hydrophobic.

[0037] (2) This invention utilizes biochar loading to improve the defect of zero-valent iron easily agglomerating in water. At the same time, biochar materials are widely available and environmentally friendly.

[0038] (3) In this invention, polyethylene glycol 4000 is used as a dispersant, which enables biochar to be uniformly dispersed and reacted in the solution. At the same time, the external magnetic field makes it difficult for the biochar to settle after being loaded with zero-valent iron, which effectively increases the loading of zero-valent iron on the biochar.

[0039] (4) The present invention has good catalytic degradation effect on both monophenols and polyphenols, and can degrade more than 90% of phenol and hydroquinone in the solution within 1 hour. Attached Figure Description

[0040] Figure 1 This is a scanning electron microscope (SEM) image of the biochar particles obtained in step (1) of Example 1.

[0041] Figure 2 This is a scanning electron microscope (SEM) image of the modified zero-valent iron with an S / Fe molar ratio of 0.05 obtained in Comparative Example 3.

[0042] Figure 3This is a scanning electron microscope (SEM) image of BC-S-nZVI with an S / Fe molar ratio of 0.05 obtained in Example 1.

[0043] Figure 4 The degradation rate of simulated wastewater treated with BC-S-nZVI at a molar ratio of 0.05 (S / Fe) obtained in Example 1 at different times is shown.

[0044] Figure 5 The results are from the degradation of phenol and hydroquinone by BC-S-nZVI with different S / Fe molar ratios.

[0045] Figure 6 This is a comparison chart of phenol degradation by BC-S-nZVI with an S / Fe molar ratio of 0.05 obtained in Example 1 under different temperature conditions.

[0046] Figure 7 This is a comparison chart of the degradation of hydroquinone by BC-S-nZVI with an S / Fe molar ratio of 0.05 obtained in Example 1 under different temperature conditions. Detailed Implementation

[0047] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0048] Unless otherwise specified, all reagents used in the examples are commercially available.

[0049] Example 1: Preparation of zero-valent iron supported on biochar

[0050] (1) The straw was crushed and then placed in a tube furnace for pyrolysis under nitrogen. The setting program of the tube furnace during the pyrolysis process is as follows: the initial temperature is set to 50℃, the heating rate is 5℃ / min, and after 110min, it is raised to the highest temperature of 600℃. After maintaining this temperature for pyrolysis for 2h, it automatically enters the cooling program. The pyrolyzed biochar solid is ground into powder and separated by a 100-mesh sieve to obtain the biochar particles (BC) required for synthesis.

[0051] (2) Take 1.0g of polyethylene glycol 4000 and add it to 100mL of deionized water. Add 0.2g of biochar powder to the solution and sonicate the solution for 15min before pouring it into a four-necked flask. Take 5.56g of ferrous sulfate heptahydrate and 0.24g of sodium sulfide nonahydrate and dissolve them in 50mL of water, then transfer them to a constant pressure dropping funnel. Take 1.52g of sodium borohydride solid and dissolve it in 50mL of water, then transfer the solution to another constant pressure dropping funnel.

[0052] (3) Insert the PTFE stirrer into the solution in the four-necked flask, turn on the stirrer and aerate with high-purity nitrogen (99.999% purity) for 10 minutes to remove dissolved oxygen from the solution; continue to aerate with high-purity nitrogen during the reaction to maintain an oxygen-free state in the reaction system. Fix the magnet block directly above the four-necked flask with a wooden bracket and isolate the reaction system from the outside environment with a perforated plastic cover. Add sodium borohydride solution and a mixture of ferrous sulfate and sodium sulfide solution dropwise using a constant pressure dropping funnel, controlling the dropping rate of the two solutions to be synchronized, preferably 10 drops per minute. After the addition is complete, continue the reaction for 30 minutes to ensure complete reaction. After the reaction is complete, stop stirring, remove the flask, transfer the reaction solution to a beaker, separate the resulting black particles using a strong magnet, and wash them three times with deionized water and anhydrous ethanol, respectively. The washed BC-S-nZVI was placed in a vacuum drying oven and dried under vacuum at 60℃ for 24 hours to obtain BC-S-nZVI powder (S / Fe (S and Fe represent sulfur atoms and iron atoms in BC-S-nZVI powder, respectively) molar ratio of 0.05).

[0053] The BC and BC-S-nZVI prepared in Example 1 were characterized by scanning electron microscopy (SEM). Figure 1 As shown, the surface of biochar particles has many small protrusions and large void structures, providing a large number of attachment sites for zero-valent iron. Figure 2 and Figure 3 The figures show the loading states of zero-valent iron (ZVFe) on a biochar substrate under conditions of no diluent, addition of diluent, and magnetic field. It can be seen that in the undiluent material, ZVFe tends to aggregate and cannot be effectively fixed to the biochar particles. However, after dilution, ZVFe can grow on the surface and within the pore structure of the biochar particles, effectively fixing them and improving the agglomeration defect, thus achieving better catalytic performance. Mapping results show that sulfur is uniformly distributed within the catalyst particles, with the actual sulfur content in the C, O, S, and Fe atoms being less than 2%.

[0054] Example 2: Study on the treatment of simulated coal gasification phenol-containing wastewater by biochar-supported zero-valent iron sulfide

[0055] A 300 mg / L phenol and 300 mg / L hydroquinone solution was used as a simulation (pH = 6). 0.1 g of biochar-supported zero-valent iron sulfide prepared in Example 1 and 8 mmol of sodium persulfate were added to 200 mL of simulated wastewater solution, resulting in a modified zero-valent iron concentration of 0.5 g / L. The experiment was conducted in an electrically heated constant-temperature shaking water bath, with no pH adjustment and the temperature maintained at 30°C. At 5 min, 10 min, 2 min, 40 min, 60 min, and 180 min of reaction time, 5 mL of water samples were collected in test tubes, and the reaction was quenched with 1 mL of methanol. The samples were filtered through a 0.22 μm organic filter membrane, and the filtrate was collected. The concentrations of phenol and hydroquinone were determined using high-performance liquid chromatography (HPLC).

[0056] Test results are as follows Figure 4 .from Figure 4 It can be seen that the reaction is basically completed within one hour, and the degradation rate of hydroquinone is faster, which also indicates that hydroquinone is more easily degraded. After 60 minutes, the degradation efficiency basically does not change. The degradation results after 60 minutes are: phenol degradation rate is 95.6%, and hydroquinone degradation rate is 98.3%.

[0057] Example 3: Degradation effect of catalysts with different S / Fe molar ratios

[0058] (1) Following the steps of Example 1, different amounts of sodium sulfide nonahydrate (0g, 0.24g, 0.48g, 1.44g, 2.4g) were added to prepare modified zero-valent iron with S / Fe molar ratios of 0, 0.05, 0.1, 0.3, and 0.5, respectively.

[0059] (2) Using a phenol solution with a concentration of 300 mg / L and a hydroquinone solution with a concentration of 310 mg / L as a simulation (pH = 6), 0.1 g of modified zero-valent iron with different S / Fe molar ratios was added to 200 mL of simulated wastewater solution. Sodium persulfate was also added, with a sodium persulfate concentration of 40 mmol / L and a modified zero-valent iron concentration of 0.5 g / L. The experiment was conducted in an electrically heated constant-temperature shaking water bath, with no pH adjustment and the temperature maintained at 30 °C. After 60 min of reaction, 5 mL of water sample was taken and placed in a test tube. 1 mL of methanol was added to quench the reaction and terminate it. The solution was filtered using a 0.22 μm organic filter membrane, and the filtrate was collected. The concentrations of phenol and hydroquinone were determined by high-performance liquid chromatography.

[0060] from Figure 5 It can be seen that the S / Fe molar ratio has a significant impact on the degradation performance of the material. The material without sulfur modification has the worst performance. However, more sulfur content is not necessarily better. A small amount of sulfur can promote electron transfer and improve the reaction efficiency, while excessive sulfur may hinder the release of ferrous ions, thereby reducing the reaction effect. Therefore, it is advisable to keep the S / Fe ratio at 0.05 under fixed conditions.

[0061] Example 4: Effects of different catalyst and persulfate dosages on degradation efficiency

[0062] (1) Using a phenol solution with a concentration of 309 mg / L and a hydroquinone solution with a concentration of 323 mg / L as a simulation (pH = 6), sodium persulfate and modified zero-valent iron with an S / Fe molar ratio of 0.05 prepared in Example 1 were added to 200 mL of simulated wastewater solution. The concentration of sodium persulfate in the system was 40 mmol / L. 0.1 g, 0.2 g, and 0.3 g of modified zero-valent iron were added respectively. The experiment was carried out in an electrically heated constant-temperature shaking water bath. The pH value was not adjusted, and the temperature was maintained at 30 °C. After 60 min of reaction, 5 mL of water sample was placed in a test tube, and 1 mL of methanol was added to quench the reaction and terminate it. The solution was filtered using a 0.22 μm organic filter membrane, and the filtrate was collected. The concentrations of phenol and hydroquinone were determined by high performance liquid chromatography. The test results are shown in Table 1. Only a small amount of catalyst material is needed to achieve good catalytic effect. It is advisable to use a carbon-supported sulfide zero-valent iron dosage of 0.1g, that is, the concentration of carbon-supported sulfide zero-valent iron in the system is 0.5g / L.

[0063] (2) Using a phenol solution with a concentration of 300 mg / L and a hydroquinone solution with a concentration of 310 mg / L as a simulation (pH = 6), 0.1 g of modified zero-valent iron with an S / Fe molar ratio of 0.05 prepared in Example 1 was added to 200 mL of simulated wastewater solution. 2 mmol, 4 mmol, 6 mmol, and 8 mmol of sodium persulfate were added respectively. The experiment was conducted in an electrically heated constant-temperature shaking water bath, without adjusting the pH value, and the temperature was maintained at 30 °C. After 20 min of reaction, 5 mL of water sample was taken and placed in a test tube. 1 mL of methanol was added to quench the reaction and terminate it. The solution was filtered using a 0.22 μm organic filter membrane, and the filtrate was collected. The concentrations of phenol and hydroquinone were determined by high-performance liquid chromatography.

[0064] The test results are shown in Table 1. The amount of persulfate added has a significant impact on the system. An appropriate amount of persulfate needs to be added to obtain a good catalytic effect. The appropriate amount of persulfate added is 8 mmol, which means that the concentration of sodium persulfate in the system is 40 mmol / L.

[0065] Table 1. Effects of different catalyst and persulfate addition amounts on degradation efficiency.

[0066]

[0067] Example 5: Effect of initial phenol concentration on the degradation effect of catalyst materials

[0068] Four groups of phenol solutions with different initial concentrations (pH=6) were prepared, with phenol concentrations of 50 and 100 mg / L and hydroquinone concentrations of 200 and 800 mg / L. Sodium persulfate and modified zero-valent iron (S / Fe molar ratio of 0.05 prepared in Example 1) were added to 200 mL of simulated wastewater solution. The concentration of sodium persulfate in the system was 40 mmol / L, and the concentration of modified zero-valent iron was 0.5 g / L. The experiment was conducted in an electrically heated constant-temperature shaking water bath at 30°C without pH adjustment. After 60 min of reaction, 5 mL of water sample was placed in a test tube, and 1 mL of methanol was added to quench the reaction and terminate it. The solution was filtered through a 0.22 μm organic filter membrane, and the filtrate was collected. The concentrations of phenol and hydroquinone were determined by high-performance liquid chromatography (HPLC).

[0069] The test results are shown in Table 2. When the initial phenol concentration is low, the catalyst can effectively remove phenolic substances from the water. When the initial phenol concentration in the water is high, the diphenol is first decomposed into phenol during the reaction, and then the phenol ring-opens. However, the number of free radicals generated by the activation of sodium persulfate by the catalyst is insufficient to completely degrade phenol and hydroquinone, causing the phenol concentration to rise instead. Therefore, more reactants need to be added to improve the degradation effect.

[0070] Table 2. Effect of initial phenol concentration on the degradation efficiency of catalysts.

[0071] Initial phenol concentration (mg / L) Initial concentration of hydroquinone (mg / L) Phenol degradation rate / % Hydroquinone degradation rate / % 50 200 99.9 99.9 50 800 94.6 95.2 100 200 96.0 99.9 100 800 90.5 94.3

[0072] Example 6: Degradation effect of catalysts under different temperature conditions

[0073] A phenol solution with a concentration of 291 mg / L and a hydroquinone solution with a concentration of 330 mg / L was used as a simulation (pH = 6). Sodium persulfate and modified zero-valent iron (S / Fe molar ratio of 0.05 prepared in Example 1) were added to 200 mL of simulated wastewater solution. The concentration of sodium persulfate in the system was 40 mmol / L, and the concentration of modified zero-valent iron was 0.5 g / L. The experiment was conducted in an electrically heated constant-temperature shaking water bath, with no pH adjustment, and the temperatures were 30℃, 40℃, 50℃, and 60℃. At 10 min, 20 min, and 60 min of reaction, 5 mL of water samples were taken and placed in test tubes. The reaction was terminated by adding 1 mL of methanol. The solution was filtered through a 0.22 μm organic filter membrane, and the filtrate was collected. The concentrations of phenol and hydroquinone were determined by high-performance liquid chromatography (HPLC).

[0074] Test results are as follows Figure 6 and Figure 7Increasing the temperature can increase the reaction rate because persulfate also has a thermal activation effect. However, excessively high temperatures can lead to an excessively rapid release rate of sulfate free radicals, which in turn reduces the degradation efficiency of the reaction. At 40℃ for 40 minutes, the degradation rate of phenol can reach 97.7%, and hydroquinone is completely degraded in solution with a degradation rate greater than 99.9%.

[0075] Example 7: Degradation effect of catalysts under different pH conditions

[0076] Using phenol solutions with concentrations of 300 mg / L and hydroquinone solutions with concentrations of 330 mg / L as simulations, sodium persulfate and modified zero-valent iron (with an S / Fe molar ratio of 0.05 prepared in Example 1) were added to 200 mL of simulated wastewater solution. The concentration of sodium persulfate in the system was 40 mmol / L, and the concentration of modified zero-valent iron was 0.5 g / L. The experiment was conducted in an electrically heated constant-temperature shaking water bath at 30 °C, with pH adjusted to 4, 5, 6, 7, and 8. After 60 min of reaction, 5 mL of water samples were taken and placed in test tubes, and the reaction was terminated by adding 1 mL of methanol. The samples were filtered through a 0.22 μm organic filter membrane, and the filtrates were collected. The concentrations of phenol and hydroquinone were determined by high-performance liquid chromatography (HPLC).

[0077] The test results are as follows: pH=4: phenol degradation rate 99.6%, hydroquinone degradation rate 99.9%; pH=5: phenol degradation rate 98.6%, hydroquinone degradation rate 98.9%; pH=6: phenol degradation rate 95.6%, hydroquinone degradation rate 98.3%; pH=7: phenol degradation rate 95.5%, hydroquinone degradation rate 97.8%; pH=8: phenol degradation rate 95.1%, hydroquinone degradation rate 96.2%. The test results show that acidic conditions are more conducive to the degradation reaction.

[0078] Comparative Example 1:

[0079] (1) Following the steps of Example 1, without adding polyethylene glycol 4000, modified zero-valent iron with an S / Fe molar ratio of 0.05 was prepared.

[0080] (2) Using a phenol solution with a concentration of 300 mg / L and a hydroquinone solution with a concentration of 300 mg / L as a simulation (pH = 6), 8 mmol of sodium persulfate and 0.1 g of modified zero-valent iron with an S / Fe molar ratio of 0.05 obtained from Comparative Example 1 were added to 200 mL of simulated wastewater solution. The concentration of sodium persulfate in the system was 40 mmol / L, and the concentration of modified zero-valent iron was 0.5 g / L. The experiment was carried out in an electrically heated constant-temperature shaking water bath, with no pH adjustment and the temperature maintained at 30℃. After 60 min of reaction, 5 mL of water sample was taken and placed in a test tube. 1 mL of methanol was added to quench the reaction and terminate it. The solution was filtered using a 0.22 μm organic filter membrane, and the filtrate was collected and the concentrations of phenol and hydroquinone were determined by high performance liquid chromatography.

[0081] Test results: The degradation rate of phenol was 8.5%, and the degradation rate of hydroquinone was 91.1%. This may be due to the weak external magnetic field strength, which could not effectively keep the bio-carbon-loaded sulfidated zero-valent iron particles suspended.

[0082] Comparative Example 2:

[0083] (1) Following the steps of Example 1, without adding an external magnetic field, modified zero-valent iron with an S / Fe molar ratio of 0.05 was prepared.

[0084] (2) Using a phenol solution with a concentration of 300 mg / L and a hydroquinone solution with a concentration of 300 mg / L as a simulation (pH = 6), 8 mmol of sodium persulfate and 0.1 g of modified zero-valent iron with an S / Fe molar ratio of 0.05 obtained from Comparative Example 2 were added to 200 mL of simulated wastewater solution. The concentration of sodium persulfate in the system was 40 mmol / L, and the concentration of modified zero-valent iron was 0.5 g / L. The experiment was carried out in an electrically heated constant-temperature shaking water bath, with no pH adjustment and the temperature maintained at 30℃. After 60 min of reaction, 5 mL of water sample was taken and placed in a test tube. 1 mL of methanol was added to quench the reaction and terminate it. The solution was filtered using a 0.22 μm organic filter membrane, and the filtrate was collected and the concentrations of phenol and hydroquinone were determined by high performance liquid chromatography.

[0085] Test results: The degradation rate of phenol was 34.6%, and the degradation rate of hydroquinone was 72.5%. This may be due to the decrease in the sedimentation rate of bio-carbon-loaded zero-valent iron particles in polyethylene glycol 4000, but the reaction still cannot be concentrated on the surface of the loaded particles.

[0086] Comparative Example 3:

[0087] (1) Following the steps of Example 1, without adding polyethylene glycol 4000 or an external magnetic field, modified zero-valent iron with an S / Fe molar ratio of 0.05 was prepared.

[0088] (2) Using a phenol solution with a concentration of 300 mg / L and a hydroquinone solution with a concentration of 300 mg / L as a simulation (pH = 6), 8 mmol of sodium persulfate and 0.1 g of modified zero-valent iron with an S / Fe molar ratio of 0.05 obtained from Comparative Example 3 were added to 200 mL of simulated wastewater solution. The concentration of sodium persulfate in the system was 40 mmol / L, and the concentration of modified zero-valent iron was 0.5 g / L. The experiment was carried out in an electrically heated constant-temperature shaking water bath, with no pH adjustment and the temperature maintained at 30℃. After 60 min of reaction, 5 mL of water sample was taken and placed in a test tube. 1 mL of methanol was added to quench the reaction and terminate it. The solution was filtered using a 0.22 μm organic filter membrane, and the filtrate was collected and the concentrations of phenol and hydroquinone were determined by high performance liquid chromatography.

[0089] Test results: The degradation rate of phenol was 7.9%, and the degradation rate of hydroquinone was 92.2%. The test results were consistent with the predicted results. Only in the dispersant solution can the catalyst particles be effectively dispersed. At the same time, a magnetic field must also be present to achieve efficient loading of zero-valent iron sulfide on biocarbon.

[0090] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for treating phenol-containing wastewater using biochar-supported zero-valent iron sulfide-activated persulfate, characterized in that... Includes the following steps: (1) The straw is crushed and pyrolyzed to obtain biochar powder; (2) Add polyethylene glycol solution to biochar powder and mix; (3) Under an external magnetic field, sodium borohydride solution and a mixed solution of ferrous sulfate and sulfiding reagent were added to the solution obtained in step (2), stirred and reacted, and then separated, washed and dried to obtain biochar-supported sulfided zero-valent iron. The molar ratio of sulfur to iron in the obtained biochar-supported sulfided zero-valent iron was 0.05:

1. (4) Add biochar-loaded zero-valent iron sulfide and persulfate to phenol-containing wastewater and shake the reaction thoroughly to achieve the degradation of phenolic compounds in the water. The polyethylene glycol mentioned in step (2) is polyethylene glycol 4000; The concentration of the polyethylene glycol solution in step (2) is 5–15 g / L; In step (2), the mass ratio of biochar powder to polyethylene glycol is 1 to 3:10; The strength of the external magnetic field in step (3) is 10 to 100 mT; The sulfiding agent in step (3) is sodium sulfide; The mass ratio of the biochar powder in step (2) to the ferrous sulfate in step (3) is 1:27~28; the molar ratio of sodium borohydride to ferrous sulfate in step (3) is 2~3:1; In step (3), the concentration of sodium borohydride in the sodium borohydride solution is 0.8~1.2 mol / L; the concentration of sodium sulfide in the mixed solution is 0.02 mol / L.

2. The method for treating phenol-containing wastewater by biochar-supported zero-valent iron sulfide activation of persulfate according to claim 1, characterized in that: The heating program for pyrolysis in step (1) is as follows: the heating rate is 5-10℃ / min, and after 110 min, it is raised to 600℃. After maintaining this temperature for pyrolysis for 2 hours, it automatically enters the cooling program. The atmosphere for pyrolysis in step (1) is nitrogen.

3. The method for treating phenol-containing wastewater by biochar-supported zero-valent iron sulfide activation persulfate according to claim 1, characterized in that: The addition and stirring reaction in step (3) are carried out under a nitrogen atmosphere; the stirring reaction time is 30-60 min. The addition in step (3) is by dripping, with a dripping rate of 10 to 30 drops / min.

4. The method for treating phenol-containing wastewater by biochar-supported zero-valent iron sulfide activation persulfate according to claim 1, characterized in that: The phenol-containing wastewater in step (4) contains monophenols and polyphenols; wherein, monophenols include at least one of phenol and methylphenol; and polyphenols include at least one of hydroquinone, catechol, resorcinol, and triphenols. The concentration of the monophenol in the water body is 100–1000 mg / L, and the concentration of the polyphenol in the water body is 100–1000 mg / L.

5. The method for treating phenol-containing wastewater by biochar-supported zero-valent iron sulfide activation persulfate according to claim 1, characterized in that: The pH value of the phenol-containing wastewater in step (4) is 4 to 8.

5.

6. The method for treating phenol-containing wastewater by biochar-supported zero-valent iron sulfide activation persulfate according to claim 1, characterized in that: The persulfate mentioned in step (4) includes at least one of perdisulfate and permonsulfate; The dosage of biochar-supported zero-valent iron sulfide in step (4) satisfies the following condition: the concentration of biochar-supported zero-valent iron sulfide in the reaction system is 0.1–2.5 g / L; The amount of persulfate added in step (4) satisfies the following condition: the concentration of persulfate in the reaction system is 5-60 mmol / L.

7. The method for treating phenol-containing wastewater by biochar-supported zero-valent iron sulfide activation persulfate according to claim 1, characterized in that: The reaction temperature in step (4) is 25-80℃, and the reaction time is 10-60 min.

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