Silicon carbide production wastewater treatment system and method

Abstract

The invention belongs to the technical field of wastewater treatment, and particularly relates to a silicon carbide production wastewater treatment system and method, high-concentration wastewater and low-concentration wastewater are pretreated respectively and mixed according to the volume ratio of 1 L: (1-15) L, the pH is adjusted to 7-8, and first treated water is obtained; adding a first nutritional agent into the first treated water according to the mass ratio of 10: (1-5) for hydrolytic acidification to obtain second treated water, adding a second nutritional agent into the second treated water according to the mass ratio of 20: (1-2) for primary contact oxidation to obtain third treated water, and adding a third nutritional agent into the third treated water according to the mass ratio of 20: (1-2) for secondary contact oxidation to obtain third treated water; the COD (Chemical Oxygen Demand) of the treated wastewater is less than or equal to 150 mg / L. In the treatment process, the amount of the added nutritional agent corresponds to the COD of the wastewater, and accurate control is carried out, so that the nutritional agent can be saved, the sewage treatment cost is reduced, and the used system is more simplified.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment, and specifically relates to a silicon carbide production wastewater treatment system and method. Background Art

[0002] The cutting, grinding and polishing processes during the manufacture of silicon carbide wafers will generate a large amount of wastewater. The current silicon carbide wastewater treatment process in the factory is cumbersome and the treatment cost is high, especially the treatment of high-concentration wastewater in the factory. In the early stage of high-concentration wastewater treatment, it is first necessary to discharge it into the pretreatment system, add the corresponding reagents for pretreatment, and then enter the anaerobic tower and iron-carbon micro-electrolysis tower for treatment, and then enter the low-concentration biochemical system for treatment. During the process of entering the anaerobic tower and iron-carbon micro-electrolysis tower for treatment, the process is cumbersome, the cost is high, and a large amount of reagents are required, thereby increasing the treatment cost of high-concentration wastewater. Summary of the invention

[0003] In view of this, the present invention provides a silicon carbide production wastewater treatment system and method thereof to solve the technical problem in the prior art that heavily boron-doped single crystal silicon rods have crisscross stripes inside.

[0004] To achieve the above objectives, this application adopts the following scheme:

[0005] A silicon carbide production wastewater treatment system comprises a silicon carbide production system, and also comprises a high-concentration wastewater pretreatment device, a low-concentration wastewater pretreatment device, a mixing tank, a biochemical treatment device and a COD detector: the inlet of the high-concentration wastewater pretreatment device is connected to the high-concentration wastewater outlet of the silicon carbide production system, the inlet of the low-concentration wastewater pretreatment device is connected to the low-concentration wastewater outlet of the silicon carbide production system, the high-concentration wastewater pretreatment device and the low-concentration wastewater pretreatment device are used to pretreat high-concentration wastewater and low-concentration wastewater respectively, and remove large particle impurities and suspended matter in the high-concentration wastewater and the low-concentration wastewater; the outlet of the high-concentration wastewater pretreatment device and the outlet of the low-concentration wastewater pretreatment device are both connected to the inlet of the mixing tank, and the mixing tank is used to mix the pretreated high-concentration wastewater and the low-concentration wastewater according to a certain proportion; the outlet of the mixing tank is connected to the inlet of the biochemical treatment device, and the biochemical treatment device is used to reduce the COD of the wastewater; the mixing tank is connected to the COD detector, and a pH detector is arranged in the mixing tank;

[0006] The biochemical treatment device comprises a hydrolysis acidification tank, a primary contact oxidation tank, a secondary contact oxidation tank, and a sedimentation tank which are connected in sequence, and the hydrolysis acidification tank, the primary contact oxidation tank, the secondary contact oxidation tank, and the sedimentation tank are all connected to a nutrient storage tank.

[0007] Preferably, the sedimentation tank is provided with a drainage pipe, a mud discharge pipe and a return pipe, and the outlet of the return pipe is connected to the inlet of the mixing tank.

[0008] Preferably, the inlets of the high-concentration wastewater pretreatment device and the low-concentration wastewater pretreatment device are both connected to a flocculant liquid storage tank.

[0009] A method for treating silicon carbide production wastewater comprises the following steps:

[0010] S10. The high-concentration wastewater and low-concentration wastewater to be treated are pretreated to remove large particle impurities and suspended solids in the wastewater to ensure the subsequent treatment effect, the COD of the high-concentration wastewater is 20000mg / L to 50000mg / L, and the COD of the low-concentration wastewater is 800mg / L to 1000mg / L;

[0011] S20. The pretreated high-concentration wastewater and the low-concentration wastewater are mixed in a mixing tank at a volume ratio of 1 L: (1 to 15) L, and the pH is adjusted to 7 to 8 to obtain a first treated water;

[0012] S30. Adding a first nutrient to the first treated water for hydrolysis and acidification to obtain a second treated water, wherein the mass ratio of the first treated water to the first nutrient is 10:(1 to 5), and the COD of the second treated water is 2000 mg / L to 3500 mg / L;

[0013] S40. Adding a second nutrient to the second treated water for primary contact oxidation treatment to obtain a third treated water, wherein the COD of the third treated water is 800 mg / L to 1300 mg / L, wherein the mass ratio of the second treated water to the second nutrient is 20:(1 to 2);

[0014] S50. Adding a third nutrient to the third treated water for secondary contact oxidation treatment to obtain a fourth treated water, wherein the mass ratio of the third treated water to the third nutrient is 20:(1 to 2);

[0015] S60. Detect the COD of the fourth treated water. If the COD of the fourth treated water is less than or equal to 150 mg / L, the wastewater treatment is terminated. If the COD of the fourth treated water is greater than 150 mg / L, the wastewater is returned to the mixing tank and steps S30 to S50 are repeated.

[0016] Preferably, the first nutrient, the second nutrient and the third nutrient all include urea and phosphate fertilizer, and the mass ratio of the urea to the phosphate fertilizer is 1:1.

[0017] Preferably, the mass ratio of the first treated water to the nutrient agent is 10:(1 to 5) specifically including:

[0018] When the COD of the first treated water is greater than 20000 mg / L, the mass ratio of the first treated water to the first nutrient is 10:(3 to 5);

[0019] When the COD of the first treated water is 10000 mg / L to 20000 mg / L, the mass ratio of the first treated water to the first nutrient is 10:(2 to 3);

[0020] When the COD of the first treated water is greater than 5000 mg / L and less than 10000 mg / L, the mass ratio of the first treated water to the first nutrient is 10:(1 to 2).

[0021] Preferably, the mass ratio of the second treated water to the second nutrient agent is 20:(1 to 2) specifically including:

[0022] When the COD of the second treated water is 2500 mg / L to 3500 mg / L, the mass ratio of the second treated water to the second nutrient is 20:(1.5 to 2);

[0023] When the COD of the second treated water is greater than 2000 mg / L and less than 2500 mg / L, the mass ratio of the second treated water to the second nutrient is 20:(1 to 1.4).

[0024] Preferably, the mass ratio of the third treated water to the third nutrient is 20:(1 to 2) specifically including:

[0025] When the COD of the third treated water is 1000 mg / L to 1300 mg / L, the mass ratio of the third treated water to the third nutrient is 20:(1.5 to 2);

[0026] When the COD of the third treated water is greater than 800 mg / L and less than 1300 mg / L, the mass ratio of the third treated water to the third nutrient is 20:(1 to 1.4).

[0027] Preferably, the DO value of the fourth treated water is 2 mg / L to 4 mg / L.

[0028] Preferably, pre-treating the high-concentration wastewater and the low-concentration wastewater to be treated comprises: adding a PAC flocculant and a PAM flocculant to the high-concentration wastewater and the low-concentration wastewater, respectively.

[0029] The technical solution adopted in this application can achieve the following beneficial effects:

[0030] The present invention provides a method for treating wastewater from silicon carbide production. Compared with the sewage treatment method in the prior art, the method pre-treats high-concentration wastewater and low-concentration wastewater and mixes them for treatment. The COD of the treated wastewater is less than or equal to 150 mg / L, which meets the wastewater treatment standard. In the treatment process, the amount of added nutrient agent corresponds to the COD of the wastewater and is precisely controlled. Compared with the method of separately treating high-concentration wastewater and low-concentration wastewater in the prior art, the amount of water treated with the same COD can save nutrient agent, reduce the cost of sewage treatment, and the used system is more simplified. DETAILED DESCRIPTION

[0031] In order to facilitate the understanding of the present application, the present application will be described in more detail below. And the preferred embodiments of the present application are given. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thoroughly understood.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0033] A silicon carbide production wastewater treatment system comprises a silicon carbide production system, and also comprises a high-concentration wastewater pretreatment device, a low-concentration wastewater pretreatment device, a mixing tank, a biochemical treatment device and a COD detector: the inlet of the high-concentration wastewater pretreatment device is connected to the high-concentration wastewater outlet of the silicon carbide production system, the inlet of the low-concentration wastewater pretreatment device is connected to the low-concentration wastewater outlet of the silicon carbide production system, the high-concentration wastewater pretreatment device and the low-concentration wastewater pretreatment device are used to pretreat high-concentration wastewater and low-concentration wastewater respectively, and remove large particle impurities and suspended matter in the high-concentration wastewater and the low-concentration wastewater; the outlet of the high-concentration wastewater pretreatment device and the outlet of the low-concentration wastewater pretreatment device are both connected to the inlet of the mixing tank, and the mixing tank is used to mix the pretreated high-concentration wastewater and the low-concentration wastewater according to a certain proportion; the outlet of the mixing tank is connected to the inlet of the biochemical treatment device, and the biochemical treatment device is used to reduce the COD of the wastewater; the mixing tank is connected to the COD detector, and a pH detector is arranged in the mixing tank;

[0034] The biochemical treatment device comprises a hydrolysis acidification tank, a primary contact oxidation tank, a secondary contact oxidation tank, and a sedimentation tank which are connected in sequence, and the hydrolysis acidification tank, the primary contact oxidation tank, the secondary contact oxidation tank, and the sedimentation tank are all connected to a nutrient storage tank.

[0035] In this embodiment, the silicon carbide production wastewater treatment system is arranged at the high-concentration wastewater outlet and the low-concentration wastewater outlet of the silicon carbide production system. When in use, the high-concentration wastewater generated by the silicon carbide production system is passed into the high-concentration wastewater pretreatment device, and the low-concentration wastewater generated by the silicon carbide production system is passed into the low-concentration wastewater pretreatment device. The high-concentration wastewater pretreatment device and the low-concentration wastewater pretreatment device pretreat the high-concentration wastewater and the low-concentration wastewater respectively. The pretreatment includes flocculation precipitation, impurity removal, etc. The high-concentration wastewater and the low-concentration wastewater after pretreatment are The wastewater enters the mixing tank through the first pipe and the second pipe respectively. The first pipe and the second pipe are provided with a meter to control the ratio of high-concentration wastewater and low-concentration wastewater in the mixing tank. The pH detector provided in the mixing tank is used to detect the pH of the wastewater in the mixing tank. When the pH of the wastewater in the mixing tank is 7 to 8, it can enter the biochemical treatment device. Specifically, the wastewater in the mixing tank is passed into the hydrolysis acidification tank, and the wastewater in the hydrolysis acidification tank is passed into the COD detector. The COD detector performs COD detection on the wastewater in the hydrolysis acidification tank to obtain the wastewater. The range of COD is selected, and the amount of nutrient added to the hydrolysis acidification tank is selected according to the COD; then, the water in the hydrolysis acidification tank is passed into the primary contact oxidation tank, and the wastewater in the primary contact oxidation tank is passed into the COD detector, and the COD detector performs COD detection on the wastewater in the primary contact oxidation tank to obtain the range of COD of the wastewater, and the amount of nutrient added to the primary contact oxidation tank is selected according to the COD. After adding the nutrient, the wastewater in the primary contact oxidation tank is passed into the secondary contact oxidation tank, and the secondary The wastewater in the contact oxidation tank is passed into the COD detector, and the COD detector performs COD detection on the wastewater in the secondary contact oxidation tank to obtain the COD range of the wastewater, and selects the amount of nutrient added to the secondary contact oxidation tank according to the COD. After adding the nutrient, the wastewater in the secondary contact oxidation tank is passed into the sedimentation tank, and the sedimentation tank precipitates the wastewater. The precipitated water enters the COD detector. If the COD meets the standard, it is discharged through the drain pipe. If the COD does not meet the standard, it is returned to the mixing tank for reprocessing, and the sediment is discharged through the mud outlet.

[0036] The system provided in this embodiment is simpler than the sewage treatment system existing in the prior art. There is no need to use a high-concentration wastewater treatment system for high-concentration wastewater and a low-concentration wastewater treatment system for low-concentration wastewater. The dosage of nutrients is accurately controlled, which saves nutrients and reduces the cost of sewage treatment.

[0037] Specifically, the inlets of the high-concentration wastewater pretreatment device and the low-concentration wastewater pretreatment device are both connected to a flocculant storage tank, and the flocculant in the flocculant storage tank may be a PAC flocculant or a PAM flocculant.

[0038] It should be noted that, in this system, those skilled in the art can install control valves, flow detectors, and water pumps between the pipelines according to actual conditions.

[0039] A method for treating wastewater from silicon carbide production may adopt any of the above-mentioned wastewater treatment systems from silicon carbide production, and comprises the following steps:

[0040] Step 1: Use the high-concentration pretreatment device and the low-concentration pretreatment device described above to perform flocculation and sedimentation on the high-concentration wastewater and the low-concentration wastewater to be treated, respectively, to remove large particle impurities and suspended matter in the wastewater to ensure the subsequent treatment effect, the COD of the high-concentration wastewater is 20000mg / L to 50000mg / L, and the COD of the low-concentration wastewater is 800mg / L to 1000mg / L;

[0041] Step 2: The high-concentration wastewater and the low-concentration wastewater after flocculation and precipitation are introduced into the mixing tank at a volume ratio of 1L:(1 to 15)L, and the pH of the wastewater in the mixing tank is detected by a pH detector, and the pH of the wastewater in the mixing tank is controlled at 7 to 8 to obtain the first treated water;

[0042] Step 3: passing the first treated water into the hydrolysis acidification tank, adding the first nutrient agent to the hydrolysis acidification for hydrolysis acidification treatment, controlling the mass ratio of the first treated water to the first nutrient agent to be 10:(1 to 5), obtaining the second treated water, the COD of the second treated water being 2000 mg / L to 3500 mg / L, the COD of the second treated water being still very high, and it needs to be treated as follows;

[0043] Step 4: passing the second treated water into a primary contact oxidation tank, adding a second nutrient agent to the second treated water for primary contact oxidation treatment, controlling the mass ratio of the second treated water to the second nutrient agent to be 20:(1 to 2), and obtaining third treated water. The COD of the third treated water after treatment in this step is generally 800 mg / L to 1300 mg / L;

[0044] Step 5: passing the third treated water into a secondary contact oxidation tank, adding a third nutrient to the third treated water for secondary contact oxidation treatment, controlling the mass ratio of the third treated water to the third nutrient to be 20:(1 to 2), and obtaining fourth treated water;

[0045] Step six: the fourth treated water is passed into a sedimentation tank for sedimentation, and the precipitated water enters the COD detector for detection. If the COD of the fourth treated water is less than or equal to 150 mg / L, the water in the sedimentation tank is discharged through the drain port. If the COD of the fourth treated water is greater than 150 mg / L, it flows back to the mixing tank for re-treatment.

[0046] Compared with the sewage treatment methods existing in the prior art, the method provided in this embodiment mixes high-concentration wastewater and low-concentration wastewater after pretreatment for treatment. The COD of the treated wastewater is less than or equal to 150 mg / L, which meets the wastewater treatment standards. During the treatment process, the amount of added nutrient agent is precisely controlled corresponding to the COD of the wastewater. Compared with the method of separately treating high-concentration wastewater and low-concentration wastewater in the prior art, the amount of water with the same COD can save nutrients, reduce the cost of sewage treatment, and the system used is more simplified.

[0047] Wherein, the first nutrient, the second nutrient and the third nutrient all include urea and phosphate fertilizer, and the mass ratio of the urea to the phosphate fertilizer is 1:1.

[0048] In some specific embodiments, the mass ratio of the first treated water to the nutrient agent is 10:(1 to 5) specifically including:

[0049] When the COD of the first treated water is greater than 20000 mg / L, the mass ratio of the first treated water to the first nutrient is 10:(3 to 5);

[0050] When the COD of the first treated water is 10000 mg / L to 20000 mg / L, the mass ratio of the first treated water to the first nutrient is 10:(2 to 3);

[0051] When the COD of the first treated water is greater than 5000 mg / L and less than 10000 mg / L, the mass ratio of the first treated water to the first nutrient agent is 10:(1 to 2).

[0052] In this embodiment, when the volume ratio of the high-concentration wastewater to the low-concentration wastewater is 1:1, and when the COD of the high-concentration wastewater is 50000 mg / L, and the COD of the low-concentration wastewater is 1000 mg / L, according to the formula: (G is high-concentration wastewater; D is low-concentration wastewater; L is the volume sum of high-concentration wastewater and low-concentration wastewater) The COD of the wastewater in the mixing tank is calculated to be 25500 mg / L, so the COD of the second treated water is distributed between 2500 mg / L and 3500 mg / L;

[0053] When the COD of the second treated water is 2500 mg / L to 3500 mg / L, the mass ratio of the second treated water to the second nutrient is 20:(1.5 to 2);

[0054] When the COD of the second treated water is greater than 2000 mg / L and less than 2500 mg / L, the mass ratio of the second treated water to the second nutrient is 20:(1 to 1.4).

[0055] In some preferred embodiments, the mass ratio of the third treated water to the third nutrient is 20:(1 to 2) specifically including:

[0056] The COD of the third treated water obtained by hydrolysis and acidification treatment is 1000 mg / L to 1300 mg / L. The COD is too high and needs to be further treated. The mass ratio of the third treated water to the third nutrient is 20:(1.5 to 2);

[0057] When the COD of the third treated water is greater than 800 mg / L and less than 1300 mg / L, the mass ratio of the third treated water to the third nutrient is 20:(1 to 1.4).

[0058] By testing the COD of each treated water before each step and adding an appropriate amount of nutrients based on the COD, it is possible to reduce the COD in the treated water while saving nutrients, further avoiding waste of nutrients.

[0059] Wherein, the DO value of the fourth treated water is 2 mg / L to 4 mg / L.

[0060] Preferably, pre-treating the high-concentration wastewater and the low-concentration wastewater to be treated comprises: adding a PAC flocculant and a PAM flocculant to the high-concentration wastewater and the low-concentration wastewater, respectively.

[0061] The following specific experimental examples are used to further illustrate the technical solutions and technical effects of the present invention. It should be noted that the following experimental examples are only for further explaining the present invention and do not limit the technical solutions of the present invention.

[0062] 1. Example 1

[0063] The silicon carbide production wastewater treatment system provided in the present application is used to treat the silicon carbide production wastewater according to the method provided in the present application. The flocculant used in this embodiment is a PAC flocculant. The high-concentration wastewater and the low-concentration wastewater are passed into a mixing tank at a volume ratio of 1:1. The wastewater in the mixing tank is tested using a pH detector, and the pH is adjusted to 7 to obtain the first treated water. Then, the wastewater in the mixing tank is passed into a hydrolysis acidification tank, and a first nutrient agent formed by a mixture of urea and phosphate fertilizer is added to obtain a second treated water. The second treated water after hydrolysis and acidification is passed into a primary contact reaction tank, according to the detected COD of the second treated water, adding a second nutrient agent consisting of urea and phosphate fertilizer to the primary contact reaction tank to obtain third treated water, the third treated water is passed into the secondary hydrolysis reaction tank, according to the detected COD of the third treated water, adding a third nutrient agent consisting of urea and phosphate fertilizer to the secondary contact reaction tank to obtain fourth treated water, the fourth treated water enters the sedimentation tank for sedimentation, after the sedimentation is completed, the COD of the wastewater in the sedimentation tank is detected to be less than or equal to 150 mg / L, which meets the standard, and is discharged from the drain outlet;

[0064] After the test, the cost of the reagents (urea and phosphate fertilizer) in Example 1 was calculated, and the results are shown in Table 1:

[0065] Table 1: Water treatment volume in Example 1-2024

[0066] January February March April May June July August September <![CDATA[Low-concentration wastewater (m 3 )]]> 16490 17616 19181 14336 15289 14662 21447 18565 20098 <![CDATA[High-concentration wastewater (m 3 )]]> 2378 2463 2508 1458 1408 1423 2715 1870 2065 Cost of medicine (ten thousand yuan) 12 9.4 10.6 11.65 12.34 13.97 8.17 14.37 12.55

[0067] From the data in Table 1 above, it can be seen that from January to September 2024, a total of 157,684 m 3 High concentration wastewater and 1828m 3 The total cost of chemicals for treating low-concentration wastewater is 1.0505 million yuan, with an average cost of 60 yuan per cubic meter of wastewater.

[0068] 2. Comparative Example 1

[0069] The difference between this comparative example 1 and the above-mentioned embodiment 1 is that the same volume of high-concentration wastewater and low-concentration wastewater are treated respectively by using the system and method in the prior art, and the COD of the treated wastewater is detected to be less than or equal to 150 mg / L;

[0070] After the test, the cost of the reagents (urea and phosphate fertilizer) in Comparative Example 1 was calculated, and the results are shown in Table 2:

[0071] Table 2 Comparative Example 1-2023 Annual Water Treatment Volume

[0072]

[0073]

[0074] From the data in Table 2 above, it can be seen that in 2023, a total of 151,338 m 3 High concentration wastewater and 14519m 3 The total cost of the reagents for treating low-concentration wastewater is 2.5271 million yuan, and the average cost of the reagents per cubic meter of wastewater is 152 yuan, which is nearly doubled compared to the above-mentioned embodiment 1.

[0075] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or substitutions within the technical scope disclosed by the present invention, and these modifications or substitutions should be included in the protection scope of the present invention.

Claims

1. A silicon carbide production wastewater treatment system, comprising a silicon carbide production system, characterized in that: It also includes high-concentration wastewater pretreatment device, low-concentration wastewater pretreatment device, mixing tank, biochemical treatment device and COD detector: The inlet of the high-concentration wastewater pretreatment device is connected to the high-concentration wastewater outlet of the silicon carbide production system, and the inlet of the low-concentration wastewater pretreatment device is connected to the low-concentration wastewater outlet of the silicon carbide production system. The high-concentration wastewater pretreatment device and the low-concentration wastewater pretreatment device are used to pretreat high-concentration wastewater and low-concentration wastewater respectively, and remove large particle impurities and suspended matter in high-concentration wastewater and low-concentration wastewater; the outlet of the high-concentration wastewater pretreatment device and the outlet of the low-concentration wastewater pretreatment device are both connected to the inlet of the mixing tank, and the mixing tank is used to mix the pretreated high-concentration wastewater and low-concentration wastewater in a certain proportion; the outlet of the mixing tank is connected to the inlet of the biochemical treatment device, and the biochemical treatment device is used to reduce the COD of the wastewater; the mixing tank is connected to the COD detector, and a pH detector is provided in the mixing tank; The biochemical treatment device comprises a hydrolysis acidification tank, a primary contact oxidation tank, a secondary contact oxidation tank, and a sedimentation tank which are connected in sequence, and the hydrolysis acidification tank, the primary contact oxidation tank, the secondary contact oxidation tank, and the sedimentation tank are all connected to a nutrient storage tank.

2. The silicon carbide production wastewater treatment system according to claim 1, characterized in that: The sedimentation tank is provided with a drainage pipe, a mud discharge pipe and a return pipe, and the outlet of the return pipe is connected with the inlet of the mixing tank.

3. The silicon carbide production wastewater treatment system according to claim 1, characterized in that: The inlets of the high-concentration wastewater pretreatment device and the low-concentration wastewater pretreatment device are both connected to a flocculant liquid storage tank.

4. A method for treating silicon carbide production wastewater, characterized in that: The steps include: S10. The high-concentration wastewater and low-concentration wastewater to be treated are pretreated to remove large particle impurities and suspended solids in the wastewater to ensure the subsequent treatment effect, the COD of the high-concentration wastewater is 20000 mg / L to 50000 mg / L, and the COD of the low-concentration wastewater is 800 mg / L to 1000 mg / L; S20. The pretreated high-concentration wastewater and the low-concentration wastewater are mixed in a mixing tank at a volume ratio of 1 L: (1 to 15) L, and the pH is adjusted to 7 to 8 to obtain first treated water; S30. Adding a first nutrient to the first treated water for hydrolysis and acidification to obtain a second treated water, wherein the mass ratio of the first treated water to the first nutrient is 10:(1 to 5), and the COD of the second treated water is 2000 mg / L to 3500 mg / L; S40. Adding a second nutrient to the second treated water for primary contact oxidation treatment to obtain a third treated water, wherein the COD of the third treated water is 800 mg / L to 1300 mg / L, wherein the mass ratio of the second treated water to the second nutrient is 20:(1 to 2); S50. Adding a third nutrient to the third treated water for secondary contact oxidation treatment to obtain fourth treated water, wherein the mass ratio of the third treated water to the third nutrient is 20:(1 to 2); S60. Detect the COD of the fourth treated water. If the COD of the fourth treated water is less than or equal to 150 mg / L, the wastewater treatment is terminated. If the COD of the fourth treated water is greater than 150 mg / L, the wastewater is returned to the mixing tank and steps S30 to S50 are repeated.

5. The method for treating silicon carbide production wastewater according to claim 4, characterized in that: The first nutrient, the second nutrient and the third nutrient all include urea and phosphate fertilizer, and the mass ratio of the urea to the phosphate fertilizer is 1:

1.

6. The method for treating silicon carbide production wastewater according to claim 4, characterized in that: The mass ratio of the first treated water to the nutrient agent is 10:(1 to 5) and specifically includes: When the COD of the first treated water is greater than 20000 mg / L, the mass ratio of the first treated water to the first nutrient is 10:(3 to 5); When the COD of the first treated water is 10000 mg / L to 20000 mg / L, the mass ratio of the first treated water to the first nutrient is 10:(2 to 3); When the COD of the first treated water is greater than 5000 mg / L and less than 10000 mg / L, the mass ratio of the first treated water to the first nutrient is 10:(1 to 2).

7. The method for treating silicon carbide production wastewater according to claim 6, characterized in that: The mass ratio of the second treated water to the second nutrient agent is 20:(1 to 2) and specifically includes: When the COD of the second treated water is 2500 mg / L to 3500 mg / L, the mass ratio of the second treated water to the second nutrient is 20:(1.5 to 2); When the COD of the second treated water is greater than 2000 mg / L and less than 2500 mg / L, the mass ratio of the second treated water to the second nutrient is 20:(1 to 1.4).

8. The method for treating silicon carbide production wastewater according to claim 7, characterized in that: The mass ratio of the third treated water to the third nutrient is 20:(1 to 2) and specifically includes: When the COD of the third treated water is 1000 mg / L to 1300 mg / L, the mass ratio of the third treated water to the third nutrient is 20:(1.5 to 2); When the COD of the third treated water is greater than 800 mg / L and less than 1300 mg / L, the mass ratio of the third treated water to the third nutrient is 20:(1 to 1.4).

9. The method for treating silicon carbide production wastewater according to claim 4, characterized in that: The DO value of the fourth treated water is 2 mg / L to 4 mg / L.

10. The method for treating silicon carbide production wastewater according to claim 4, characterized in that: Pre-treating the high-concentration wastewater and the low-concentration wastewater to be treated respectively includes: adding a PAC flocculant and a PAM flocculant to the high-concentration wastewater and the low-concentration wastewater respectively.

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