Method for treating organic wastewater by using coconut shell biochar persulfate activator

Abstract

The application provides a method for treating organic wastewater by using coconut shell biochar persulfate activator, which comprises three steps of preparing coconut shell biochar persulfate activator, constructing a reaction system and performing a degradation reaction. When the degradation reaction is performed under the reaction system constructed by the application at a low temperature of 5 DEG C, the degradation treatment efficiency is almost the same as that under a high temperature of 55 DEG C. The method breaks through the temperature restriction of the traditional persulfate activation method for treating wastewater, so that the persulfate activator has a wide application prospect in the treatment of printing and dyeing organic wastewater, especially in winter or high-latitude cold regions.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of environmental remediation materials, and relates to organic pollutant treatment, in particular to a method for treating organic wastewater by using coconut shell biochar persulfate activator. BACKGROUND

[0002] Organic pollution is currently the main type of water environmental pollution, and one of important sources of organic pollution is refractory printing and dyeing wastewater, so it is urgent to seek a fast and efficient printing and dyeing wastewater degradation technology. The methods for treating organic pollution include physical adsorption, biological oxidation and advanced oxidation process, among which, the advanced oxidation process (AOPs) is considered to be an effective method for removing organic pollutants in soil and wastewater remediation, and the principle of the process is that: through reaction, hydroxyl radicals (·OH) and sulfate radicals (SO4 ·- ) with strong oxidation ability are generated, and under the reaction conditions of high temperature and high pressure, electricity, sound, light irradiation, catalyst and the like, macromolecular refractory organic matter is oxidized into low-toxic or non-toxic small molecular organic matter. According to the way of generating free radicals and reaction conditions of AOPs, AOPs can be divided into photochemical oxidation, ozone oxidation, electrochemical oxidation, Fenten oxidation and persulfate oxidation; among them, persulfate is more and more applied in the degradation of organic pollution due to its low cost, high efficiency and stability, and long duration of active free radicals generated in the activation process.

[0003] Generally speaking, the methods for activating persulfate include thermal activation, electric activation, light activation and transition metal activation, however, these methods have some deficiencies. For example: the thermal activation method has high heating cost and low free radical generation rate; the electric activation method has high power consumption cost and is easily hindered by external interference to hinder the propagation of light source; the light activation method has high cost and limited penetration ability; and the transition metal activation method has high cost and potential toxicity of some transition metals (copper, silver, etc.). Therefore, seeking a high-efficiency, environmentally friendly and green persulfate activator is the key to solving the above problems. However, each type of persulfate activator faces the following problems, that is: in special areas and time periods, such as high-latitude cold regions and extremely low temperature weather conditions in winter, the activation kinetics of persulfate is significantly inhibited due to low temperature, thereby limiting the promotion and application of the advanced oxidation technology based on persulfate. SUMMARY

[0004] In view of the defects and deficiencies of the prior art, the purpose of the present application is to provide a method for treating organic wastewater by using coconut shell biochar persulfate activator, which solves the technical problem that the activation effect of persulfate is inhibited due to low environmental temperature in the prior art, and thereby the efficiency of degrading organic pollution wastewater is reduced.

[0005] In order to solve the above technical problems, the present application adopts the following technical solutions:

[0006] A method for treating organic wastewater by using coconut shell biochar persulfate activator, the method specifically comprises the following steps:

[0007] Step one, preparation of coconut shell biochar persulfate activator:

[0008] Step 1.1, preparation of biochar powder (BC):

[0009] Remove the dust and impurities on the surface of the coconut shell, dry and grind and sieve, then pyrolyze, and obtain the biochar powder after pyrolysis.

[0010] Step 1.2, preparation of modified biochar (PGBC):

[0011] Grind the biochar powder prepared in step 1.1 again, then sieve, disperse the sieved powder in a potassium ferrate aqueous solution, remove the supernatant after stirring, and then dry the remaining mixture to obtain the modified biochar.

[0012] Step 1.3, preparation of activator (PGBC-N):

[0013] Calcine the modified biochar prepared in step 1.2, cool the calcined product, and then sequentially wash, centrifuge and dry to obtain the coconut shell biochar persulfate activator.

[0014] Step two, construction of reaction system:

[0015] Add the coconut shell biochar activator (PGBC-N) prepared in step one and persulfate to the organic wastewater containing pollutants to form a reaction system, the concentration of persulfate in the reaction system is 0.3-1.5 mM, and the concentration of the activator is 0.1-1.0 g / L.

[0016] Step three, degradation reaction:

[0017] Stir the reaction system of step two and perform the degradation reaction under stirring, the reaction temperature is 5-55℃, and the reaction time is 45-90 min.

[0018] Specifically, in step two, the pollutant is rhodamine B.

[0019] Specifically, in step two, the concentration of the pollutant is 0.001-0.5 mM.

[0020] Specifically, in step two, the pH value of the reaction system is 1-10.

[0021] Specifically, in step 1.1, the sieve is an 18-mesh sieve.

[0022] Specifically, in step 1.1, the pyrolysis process is as follows: pyrolysis at a temperature of 450-550 DEG C for 2-4 h under a nitrogen atmosphere at a temperature increasing rate of 1-5 DEG C / min.

[0023] Specifically, in step 1.2, the sieve is a 100-mesh sieve.

[0024] Specifically, in step 1.2, 1 g of powder is added to 100 mL of the aqueous potassium ferrate solution.

[0025] Specifically, in step 1.2, the concentration of the aqueous potassium ferrate solution is 0.1 mol / L.

[0026] Specifically, in step 1.3, the calcination process is as follows: calcination at a temperature of 450-600 DEG C for 2-4 h at a temperature increasing rate of 1-5 DEG C / min.

[0027] Compared with the prior art, the present application has the following beneficial technical effects:

[0028] (I) The method for treating organic wastewater by using the coconut shell biochar persulfate activator can significantly reduce the molecular activation energy required for the degradation of persulfate, and accordingly improve the reaction rate. When the degradation reaction is carried out at a low temperature of 5 DEG C in the reaction system constructed by using the method, the degradation treatment efficiency is almost the same as that under a high temperature of 55 DEG C. The method breaks through the temperature restriction in the treatment of wastewater by using the traditional persulfate activation method, and makes the persulfate activator have a wide application prospect in the treatment of printing and dyeing organic wastewater, especially in winter or high-latitude cold regions.

[0029] (II) The method for treating organic wastewater by using the coconut shell biochar persulfate activator has a simple preparation process of the activator and oxidation treatment process, and is easy to operate, so it is easy to be popularized in industry and commerce.

[0030] (III) The raw material for the coconut shell biochar persulfate activator is easy to obtain, and the cost is low. At the same time, the natural waste biomass resources are effectively recycled, which achieves the purpose of treating waste with waste, and meets the demand of green environmental protection. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 SEM images of BC, BC-N, PGBC and PGBC-N prepared in Example 1; wherein a is the SEM image of biochar powder BC, b is the SEM image of the control activator BC-N, c is the SEM image of modified biochar PGBC, and d is the SEM image of coconut shell biochar persulfate activator PGBC-N.

[0032] Figure 2TEM images, XRD patterns, FT-IR patterns, XPS survey patterns, C 1s fine patterns, N 1s fine patterns, O 1s fine patterns of BC, BC-N, PGBC and PGBC-N prepared in Example 1; wherein a is the TEM image of BC, b is the TEM image of BC-N, c is the TEM image of PGBC, d is the TEM image of PGBC-N, e is the high-resolution TEM image of PGBC-N, f is the XRD pattern, g is the FT-IR pattern, h is the XPS survey pattern, i is the C 1s fine pattern, j is the N 1s fine pattern, and k is the O 1s fine pattern.

[0033] Figure 3 Figure is the degradation curve of rhodamine B by coconut shell biochar persulfate activator at different concentrations of coconut shell biochar.

[0034] Figure 4 Figure is the degradation curve of rhodamine B by coconut shell biochar persulfate activator at different pH values.

[0035] Figure 5 Figure is the degradation curve of rhodamine B by coconut shell biochar persulfate activator at different concentrations of persulfate.

[0036] Figure 6 Figure is the comparison chart of degradation efficiency with or without activator in the degradation reaction system at different temperatures.

[0037] Figure 7 Figure is the electron paramagnetic resonance spectrum detection chart of active free radicals generated in the reaction system.

[0038] The technical solutions of the present application are further described below in combination with examples. DETAILED DESCRIPTION

[0039] It should be noted that all the raw materials used in the present application are known in the art unless otherwise specified.

[0040] In accordance with the above technical solutions, the following specific examples of the present application are given. It should be noted that the present application is not limited to the following specific examples, and any equivalent variations made on the basis of the technical solutions of the present application fall within the scope of protection of the present application.

[0041] Example 1:

[0042] The present embodiment provides a preparation method of coconut shell biochar persulfate activator, which specifically comprises the following steps:

[0043] Step 1.1, preparation of biochar powder (BC):

[0044] Remove dust and impurities from the surface of the coconut shell, dry it, grind it and pass it through an 18-mesh sieve. Then, in a tube furnace, slowly pyrolyze the powder at 550°C for 2 hours under a nitrogen atmosphere at a heating rate of 5°C / min to obtain biochar powder.

[0045] Step 1.2, Preparation of modified biochar (PGBC):

[0046] The biochar powder obtained in step 1.1 was ground again and then passed through a 100-mesh sieve to obtain powder with a particle size of less than 0.15 mm. The sieved powder was dispersed in a 0.1 mol / L potassium ferrate aqueous solution at a solid-liquid ratio of 1 g / 100 mL and stirred for 24 h. After removing the supernatant, the remaining mixture was dried at 60 °C to obtain modified biochar.

[0047] Step 1.3, Preparation of activator (PGBC-N):

[0048] The modified biochar obtained in step 1.2 was calcined in a tube furnace at 600°C for 2 hours at a heating rate of 5°C / min. After naturally cooling to room temperature, it was washed alternately with sulfuric acid and deionized water, centrifuged, and dried to obtain coconut shell biochar persulfate activator.

[0049] In this embodiment, a control activator was also prepared using unmodified biochar powder as raw material (i.e., according to steps 1.1 and 1.3 above), denoted as BC-N.

[0050] The material prepared in this embodiment is characterized as follows:

[0051] from Figure 1 (a) The SEM image shows that BC has an irregular small fragment structure. Figure 1 The BC-N, PGBC, and PGBC-N corresponding to b, c, and d in the figure have a structure similar to "dried bean curd sticks" with internal channels. The surface of BC-N is smooth, while the surfaces of PGBC and PGBC-N show tiny textures resulting from chemical treatment.

[0052] from Figure 2 (a) shows that BC maintains its fiber structure. Figure 2 b contains pores of approximately 24 nm on the BC-N surface. Figure 2 In c, PGBC appears as cotton wool, while Figure 2 In image d, the PGBC-N surface exhibits more and smaller pore structures of approximately 10.48 nm. The high-resolution image does not show lattice fringes, indicating an amorphous carbon structure. The porous structure of PGBC-N is suitable for the adsorption of organic pollutants and the binding of PMS.

[0053] Figure 2XRD patterns of (f) are BC, BC-N, PGBC, PGBC-N. Typical amorphous carbon broad peaks are observed for BC, while sharp and high peaks are NaCl (PDF #05-0628) and K3Na(S04)2(PDF #20-0928). The peaks at 23.2° and 43.2° for PGBC-N correspond to (002) and (100) respectively. It indicates that K2Fe04 plays an activation role in the preparation process, which removes impurities together with acid washing, while nitrogen doping strengthens the crystallinity of biochar.

[0054] From Figure 2 FTIR patterns of (g), -OH stretching vibration signals are observed in the range of 3650-3600 cm -1 -1. Signals around 3000 cm -1 and 1380 cm -1 can be attributed to C-H stretching vibration and -CH deformation. For BC and BC-N, 3500 cm -1 , 1590 cm -1 and 815 cm -1 correspond to N-H stretching, deformation and out-of-plane absorption respectively. Signals at 1690 cm -1 show carboxylate. The region of 1300-1200 cm -1 is related to -OH vibration. Strong peaks at 1100 cm -1 are derived from -C-O stretching and -OH deformation vibration. For PGBC and PGBC-N, asymmetric and symmetric stretching vibrations of -CH3 occur at 3500 cm -1 , 2950 cm -1 and 2885 cm -1 .

[0055] In Figure 2 (h) the total spectra from left to right are mainly O 1s (~531.7 eV), N 1s (~400 eV) and C 1s (~285.2 eV). In Figure 2 (i) the C 1s spectra show that biochar is rich in carbon element, the main peak is at 284.8 eV (sp 2 graphitic carbon). The peak at 288.17 eV represents C-O or C-N, while 288 eV corresponds to C=O. In Figure 2 (j), in the N 1s of PGBC-N and BC-N, the highest peak corresponds to pyridine nitrogen, followed by pyrrole nitrogen, pyridine nitrogen oxide and nitrate nitrogen. PGBC does not contain nitrogen element. In Figure 2 (k), the O 1s deconvolution spectra mainly include C=O and -OH structures, and the oxygen content of BC-N and PGBC-N decreases after nitrogen doping.

[0056] Example 2:

[0057] The embodiment provides a method for treating organic wastewater by using coconut shell biochar persulfate activator, and the method specifically comprises the following steps.

[0058] Step one, preparation of coconut shell biochar persulfate activator (PGBC-N):

[0059] In the embodiment, the activator is prepared by the method in the embodiment 1.

[0060] Step two, construction of a reaction system:

[0061] The coconut shell biochar persulfate activator prepared in step one and persulfate are added into the organic wastewater containing 0.02 mM of rhodamine B to form a reaction system, the concentration of the persulfate in the reaction system is 0.86 mM, the concentration of the activator is 0.1 g / L, and the natural pH value of the reaction system is 7.

[0062] Step three, degradation reaction:

[0063] The reaction system in step two is stirred by using a magnetic stirrer at a constant speed under the condition of 25 DEG C, the degradation reaction is started, and the reaction time is 90 min.

[0064] In the embodiment, the concentration of rhodamine B in the reaction system is tested every time interval during the degradation reaction. After the degradation reaction is completed, a curve is drawn by taking time as the horizontal coordinate and the concentration ratio of rhodamine B before and after treatment as the vertical coordinate, as shown in Figure 3 .

[0065] Embodiment 3:

[0066] The embodiment provides a method for treating organic wastewater by using coconut shell biochar persulfate activator, and the method is basically the same as that in the embodiment 2, and the difference is that the concentration of the activator in the reaction system in step two is 0.2 g / L. In the embodiment, the finally drawn rhodamine B degradation curve is as shown in Figure 3 .

[0067] Embodiment 4:

[0068] The embodiment provides a method for treating organic wastewater by using coconut shell biochar persulfate activator, and the method is basically the same as that in the embodiment 2, and the difference is that the concentration of the activator in the reaction system in step two is 0.3 g / L. In the embodiment, the finally drawn rhodamine B degradation curve is as shown in Figure 3 .

[0069] Embodiment 5:

[0070] The embodiment gives a method for treating organic wastewater by using coconut shell biochar persulfate activator. The method is basically the same as that of embodiment 2, and the difference is that the concentration of the activator in the reaction system of step two is 0.5 g / L. In this embodiment, the finally drawn rhodamine B degradation curve is shown in Figure 3 .

[0071] Comparative example 1

[0072] The comparative example gives a method for degrading organic wastewater by using persulfate. The method is basically the same as that of comparative example 2, and the difference is that no activator is added in the reaction system of step two. In this comparative example, the finally drawn rhodamine B degradation curve is shown in Figure 3 .

[0073] Example 6

[0074] The embodiment gives a method for treating organic wastewater by using coconut shell biochar persulfate activator. The method specifically includes the following steps:

[0075] Step one, preparation of coconut shell biochar persulfate activator (PGBC-N):

[0076] In this embodiment, the activator is prepared by the method of embodiment 1.

[0077] Step two, construction of reaction system:

[0078] Coconut shell biochar persulfate activator and persulfate prepared in step one are added to organic wastewater containing 0.02 mM of rhodamine B to form a reaction system, and then dilute H2SO4 is used to adjust the pH value of the reaction system to 1. The concentration of persulfate in the reaction system is 0.86 mM, and the concentration of the activator is 0.5 g / L.

[0079] Step three, degradation reaction:

[0080] Under the condition of 25℃, the reaction system of step two is stirred by a magnetic stirrer at a constant speed to start the degradation reaction, and the reaction time is 60 min.

[0081] In this embodiment, during the degradation reaction, the concentration of rhodamine B in the reaction system is tested every certain period of time. After the degradation reaction, the time is taken as the horizontal coordinate, and the concentration ratio of rhodamine B before and after treatment of the solution is taken as the vertical coordinate, and a curve is drawn, as shown in Figure 4 .

[0082] Example 7

[0083] This example gives a method for treating organic wastewater with coconut shell biochar persulfate activator, which is basically the same as example 6, the difference is only in step two, the pH value of the reaction system is adjusted to 3 with dilute H2SO4. In this example, the final rhodamine B degradation curve drawn is as shown in Figure 4 .

[0084] Example 8:

[0085] This example gives a method for treating organic wastewater with coconut shell biochar persulfate activator, which is basically the same as example 6, the difference is only in step two, the pH value of the reaction system is adjusted to 5 with dilute H2SO4. In this example, the final rhodamine B degradation curve drawn is as shown in Figure 4 .

[0086] Example 9:

[0087] This example gives a method for treating organic wastewater with coconut shell biochar persulfate activator, which is basically the same as example 6, the difference is only in that the pH value of the reaction system is not adjusted, the natural pH value of the reaction system is 7. In this example, the final rhodamine B degradation curve drawn is as shown in Figure 4 .

[0088] Example 10:

[0089] This example gives a method for treating organic wastewater with coconut shell biochar persulfate activator, which is basically the same as example 6, the difference is only in step two, the pH value of the reaction system is adjusted to 9 with NaOH. In this example, the final rhodamine B degradation curve drawn is as shown in Figure 4 .

[0090] Example 11:

[0091] This example gives a method for treating organic wastewater with coconut shell biochar persulfate activator, which is basically the same as example 6, the difference is only in step two, the pH value of the reaction system is adjusted to 10 with NaOH. In this example, the final rhodamine B degradation curve drawn is as shown in Figure 4 .

[0092] Comparative Example 2:

[0093] This comparative example gives a method for treating organic wastewater with coconut shell biochar persulfate activator, which is basically the same as example 6, the difference is only in step two, the pH value of the reaction system is adjusted to 11 with NaOH. In this comparative example, the final rhodamine B degradation curve drawn is as shown in Figure 4 .

[0094] Example 12

[0095] This example gives a method for treating organic wastewater with coconut shell biochar persulfate activator, which specifically comprises the following steps:

[0096] Step one, preparation of coconut shell biochar persulfate activator (PGBC-N):

[0097] In this example, the activator is prepared by the method of Example 1.

[0098] Step two, construction of the reaction system:

[0099] To the organic wastewater containing 0.02 mM of rhodamine B, add the coconut shell biochar persulfate activator prepared in step one and persulfate to form a reaction system, the concentration of persulfate in the reaction system is 0.43 mM, the concentration of the activator is 0.5 g / L, and the natural pH value of the reaction system is 7.

[0100] Step three, degradation reaction:

[0101] Under the condition of 25℃, the reaction system of step two is stirred by a magnetic stirrer at a constant speed, the degradation reaction starts, and the reaction time is 60 min.

[0102] In this example, during the degradation reaction, the concentration of rhodamine B in the reaction system is tested every certain period of time. After the degradation reaction is completed, the time is taken as the horizontal coordinate, and the ratio of the concentration of rhodamine B before and after the solution is taken as the vertical coordinate, to draw a curve, as shown in Figure 5 .

[0103] Example 13

[0104] This example gives a method for treating organic wastewater with coconut shell biochar persulfate activator, which is basically the same as Example 12, the difference is only that in step two, the concentration of persulfate in the reaction system is 0.86 mM. In this example, the final rhodamine B degradation curve is shown in Figure 5 .

[0105] Example 14

[0106] This example gives a method for treating organic wastewater with coconut shell biochar persulfate activator, which is basically the same as Example 12, the difference is only that in step two, the concentration of persulfate in the reaction system is 1.29 mM. In this example, the final rhodamine B degradation curve is shown in Figure 5 .

[0107] Comparative Example 3

[0108] The comparative example gives a method for treating organic wastewater by using coconut shell biochar persulfate activator, which is basically the same as example 12, the only difference is that in step two, no persulfate is added to the reaction system. In the comparative example, the final rhodamine B degradation curve is shown in Figure 5 .

[0109] Comparative example 4:

[0110] The comparative example gives a method for treating organic wastewater by using coconut shell biochar persulfate activator, which is basically the same as example 12, the only difference is that in step two, the concentration of persulfate in the reaction system is 0.215 mM. In the comparative example, the final rhodamine B degradation curve is shown in Figure 5 .

[0111] Example 15:

[0112] The example gives a method for treating organic wastewater by using coconut shell biochar persulfate activator, which specifically includes the following steps:

[0113] Step one, preparation of coconut shell biochar persulfate activator:

[0114] In this example, the activator is prepared by the method of example 1.

[0115] Step two, construction of the reaction system:

[0116] To the organic wastewater containing 0.02 mM of rhodamine B, add the coconut shell biochar persulfate activator prepared in step one and persulfate to form a reaction system, the concentration of persulfate in the reaction system is 0.86 mM, the concentration of the activator is 0.5 g / L, and the natural pH value of the reaction system is 7.

[0117] Step three, degradation reaction:

[0118] The reaction system of step two is stirred by a magnetic stirrer at a constant speed, then the magnetic stirrer is placed in a water bath box, the temperature of the water bath box is kept at 5°C, and the degradation reaction is started, the reaction time is 60 min.

[0119] In this example, during the degradation reaction, samples are taken at regular intervals to test the concentration of rhodamine B in the reaction system. After the degradation reaction, a curve is drawn with time as the horizontal coordinate and the ratio of the concentration of rhodamine B before and after treatment as the vertical coordinate, as shown in Figure 6 (a).

[0120] Example 16:

[0121] This example gives a method for treating organic wastewater with coconut shell biochar persulfate activator, which is basically the same as example 15, the difference is only in step two, the temperature of the water bath box is kept at 15℃. In this example, the final rhodamine B degradation curve drawn is as shown in Figure 6 (a).

[0122] Example 17:

[0123] This example gives a method for treating organic wastewater with coconut shell biochar persulfate activator, which is basically the same as example 15, the difference is only in step two, the temperature of the water bath box is kept at 25℃. In this example, the final rhodamine B degradation curve drawn is as shown in Figure 6 (a).

[0124] Example 18:

[0125] This example gives a method for treating organic wastewater with coconut shell biochar persulfate activator, which is basically the same as example 15, the difference is only in step two, the temperature of the water bath box is kept at 35℃. In this example, the final rhodamine B degradation curve drawn is as shown in Figure 6 (a).

[0126] Example 19:

[0127] This example gives a method for treating organic wastewater with coconut shell biochar persulfate activator, which is basically the same as example 15, the difference is only in step two, the temperature of the water bath box is kept at 45℃. In this example, the final rhodamine B degradation curve drawn is as shown in Figure 6 (a).

[0128] Example 20:

[0129] This example gives a method for treating organic wastewater with coconut shell biochar persulfate activator, which is basically the same as example 15, the difference is only in step two, the temperature of the water bath box is kept at 55℃. In this example, the final rhodamine B degradation curve drawn is as shown in Figure 6 (a).

[0130] Comparative Example 5:

[0131] This comparative example gives a method for degrading organic wastewater with persulfate, which is basically the same as example 15, the difference is only in step two, no coconut shell biochar persulfate activator is added to the reaction system. In this example, the final rhodamine B degradation curve drawn is as shown in Figure 6 (b).

[0132] Comparative Example 6:

[0133] The present comparative example gives a method for degrading organic wastewater by using persulfate salt, which is basically the same as Example 16, with the only difference being that in Step 2, no coconut shell biochar persulfate activator is added to the reaction system. In the present comparative example, the final rhodamine B degradation curve is shown in Figure (b). Figure 6 (b).

[0134] Comparative Example 7:

[0135] The present comparative example gives a method for degrading organic wastewater by using persulfate salt, which is basically the same as Example 17, with the only difference being that in Step 2, no coconut shell biochar persulfate activator is added to the reaction system. In the present comparative example, the final rhodamine B degradation curve is shown in Figure (b). Figure 6 (b).

[0136] Comparative Example 8:

[0137] The present comparative example gives a method for degrading organic wastewater by using persulfate salt, which is basically the same as Example 18, with the only difference being that in Step 2, no coconut shell biochar persulfate activator is added to the reaction system. In the present comparative example, the final rhodamine B degradation curve is shown in Figure (b). Figure 6 (b).

[0138] Comparative Example 9:

[0139] The present comparative example gives a method for degrading organic wastewater by using persulfate salt, which is basically the same as Example 19, with the only difference being that in Step 2, no coconut shell biochar persulfate activator is added to the reaction system. In the present comparative example, the final rhodamine B degradation curve is shown in Figure (b). Figure 6 (b).

[0140] Comparative Example 10:

[0141] The present comparative example gives a method for degrading organic wastewater by using persulfate salt, which is basically the same as Example 20, with the only difference being that in Step 2, no coconut shell biochar persulfate activator is added to the reaction system. In the present comparative example, the final rhodamine B degradation curve is shown in Figure (b). Figure 6 (b).

[0142] From the above examples and comparative examples, the following conclusions can be obtained:

[0143] (A) From Comparative Example 1 and Examples 2 to 5, it can be seen that:

[0144] From the above examples and comparative examples, the following conclusions can be obtained: Figure 6It can be seen that when the concentration of activator (PGBC-N) is 0.1 g / L, 0.2 g / L, 0.3 g / L and 0.5 g / L respectively, the degradation rate of Rhodamine B is 73.38%, 87.00%, 95.14% and close to 100% respectively. The degradation rate of Rhodamine B in the system of persulfate alone without activator is only 48.95%. It can be seen from the results that the oxidation degradation ability of persulfate is significantly improved by the activator, and with the increase of the concentration of the activator, the degradation rate of the pollutants is also improved accordingly.

[0145] (B) It can be seen from Comparative Example 2 and Examples 6 to 11 that:

[0146] It can be seen from Figure 3 that when the pH is 1, 3, 5, 7, 9, 10 and 11 respectively, the degradation rate of Rhodamine B after 60 minutes of reaction is 99%, 100%, 99%, 99%, 99%, 99% and 89% respectively, that is, except under high alkaline conditions (pH = 11), under other different pH conditions, the degradation rate of Rhodamine B in the reaction system is close to 100%, which shows that the reaction system can cope with a wide range of pH values.

[0147] (C) It can be seen from Comparative Examples 3 and 4 and Examples 12 to 14 that:

[0148] It can be seen from Figure 4 that when the concentration of persulfate in the reaction system is 0.00 mM, 0.215 mM, 0.43 mM, 0.86 mM and 1.29 mM respectively, the degradation rate of Rhodamine B in the reaction system is 5%, 78%, 90%, 99% and 99.2% respectively. The results show that with the increase of the concentration of persulfate, the degradation rate of Rhodamine B also increases, and when the concentration reaches 0.86 mM, the increase of the concentration has little effect on the degradation rate, so 0.86 mM is the most appropriate concentration.

[0149] (D) It can be seen from Comparative Examples 5 to 10 and Examples 15 to 20 that:

[0150] It can be seen from Figure 5(a) It can be seen that when coconut shell biochar persulfate activator (PGBC-N) is added to the reaction system, the degradation rates of Rhodamine B in the reaction system at system temperatures of 5℃, 15℃, 25℃, 35℃, 45℃, and 55℃ are 99.5%, 99.4%, 99.3%, 99.2%, 99.1%, and 100%, respectively. When coconut shell biochar persulfate activator is not added to the reaction system, the degradation rates of Rhodamine B in the reaction system at system temperatures of 5℃, 15℃, 25℃, 35℃, 45℃, and 55℃ are 15%, 22%, 31%, 52%, 69%, and 87%, respectively. The higher the reaction system temperature, the faster the reaction rate and the higher the degradation rate of Rhodamine B.

[0151] Depend on Figure 6 (b) It can be seen that when coconut shell biochar persulfate activator (PGBC-N) is added to the reaction system, the activation energy required for the activation of the persulfate reaction decreases from 38.29 kJ / mol to 3.29 kJ / mol. This indicates that under the condition of coconut shell biomass as a persulfate activator, the removal reaction of Rhodamine B is almost not limited by temperature, which is consistent with... Figure 6 The results in (a) are consistent.

[0152] In summary, the analysis above shows that in the presence of coconut shell biochar persulfate activator (PGBC-N), the degradation rate of Rhodamine B in the reaction system remains close to 100%, and temperature changes have almost no effect on the removal rate of pollutants in the wastewater. This overcomes the temperature limitations of the Fenton-like process for degrading organic matter. This indicates that the coconut shell biochar persulfate activator prepared in this invention is applicable to a wide temperature range when used for degrading organic wastewater.

[0153] (E) Based on the results of (A) to (E) above, the optimal reaction system finally determined by this invention is as follows: the concentration of Rhodamine B in the reaction system is 0.02 mM, the concentration of persulfate is 0.86 mM, the concentration of activator is 0.5 g / L, and the reaction pH is 1–10. This reaction system can efficiently degrade Rhodamine B within a temperature range of 5–55 °C.

[0154] (F) To further investigate the reaction mechanism, this invention uses 4-hydroxy-2,2,6,6-tetramethylpiperidine (TMP) and 5,5-dimethyl-1-pyrrolidine-N-oxide (DMPO) as singlet oxygen ( 1 O2) and hydroxyl / sulfate (OH· / SO4) ·- The free radical scavenger was detected by electron paramagnetic resonance (EPR) spectroscopy, and the results are as follows: Figure 6 As shown.

[0155] Depend on Figure 7 Figure 7It was found that the coconut shell biochar persulfate activator (PGBC-N) could effectively activate persulfate, and a large number of active radicals were generated in the system, which ensured the persistence of the degradation efficiency of the system. The existence of a large number of active radicals was the main reason for the rapid degradation of rhodamine B, and the coconut shell biochar persulfate activator in the system was the driving force for the generation of a large number of active radicals.

Claims

1. A method for treating organic wastewater using coconut shell biochar as a persulfate activator, characterized in that, The method specifically includes the following steps: Step 1: Preparation of coconut shell biochar persulfate activator: Step 1.1, Preparation of biochar powder: Remove dust and impurities from the surface of the coconut shell, dry it, grind it and pass it through an 18-mesh sieve. Then, pyrolyze it at a temperature of 450-550°C for 2-4 hours in a nitrogen atmosphere with a heating rate of 1-5°C / min. After pyrolysis, biochar powder is obtained. Step 1.2, Preparation of modified biochar: The biochar powder obtained in step 1.1 was ground again and then passed through a 100-mesh sieve. 1g of the sieved powder was dispersed in 100mL of potassium ferrate aqueous solution with a concentration of 0.1mol / L. After stirring, the supernatant was removed, and the remaining mixture was dried to obtain modified biochar. Step 1.3, Preparation of activator: The modified biochar obtained in step 1.2 was calcined at a temperature of 450-600°C for 2-4 hours at a heating rate of 1-5°C / min. After the calcined product was cooled, it was washed, centrifuged and dried in sequence to obtain coconut shell biochar persulfate activator. Step 2, construct the reaction system: Add the coconut shell biochar persulfate activator and persulfate prepared in step one to the organic wastewater containing Rhodamine B to form a reaction system. The concentration of persulfate in the reaction system is 0.3-1.5 mM and the concentration of activator is 0.1-1.0 g / L. Step 3: Carry out the degradation reaction: The reaction system in step two was stirred and the degradation reaction was carried out under stirring. The temperature of the reaction system was 5℃~55℃ and the reaction time was 45~90min. When coconut shell biochar persulfate activator is added to the reaction system, the activation energy required to activate the persulfate reaction decreases from 38.29 kJ / mol to 3.29 kJ / mol.

2. The method for treating organic wastewater using coconut shell biochar as a persulfate activator as described in claim 1, characterized in that, In step two, the concentration of Rhodamine B is 0.02–0.5 mM.

3. The method for treating organic wastewater using coconut shell biochar as a persulfate activator as described in claim 1, characterized in that, In step two, the pH value of the reaction system is 1 to 10.

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