Chromium-containing industrial wastewater treatment method

Abstract

The invention discloses a chromium-containing industrial wastewater treatment method which comprises the following steps: adding bacillus cereus and pseudomonas aeruginosa into chromium-containing industrial wastewater, stirring at 28-35 DEG C for 3-10 hours, and centrifuging to obtain primary treatment wastewater; adding a composite adsorbent into the primary treatment wastewater, adjusting the pH value to 5-6, stirring, standing at room temperature, and filtering to obtain secondary treatment wastewater; adjusting the pH value of the secondary treatment wastewater to 3-6, adding ethanol, carrying out irradiation treatment with gamma-rays, adjusting the pH value to 8-10, and filtering to obtain tertiary treatment wastewater; barium chloride is added into the wastewater treated for the third time, the pH is adjusted to 8-10, standing is conducted for 10-15 h at the room temperature, then filtering is conducted, polyaluminum chloride PAC is added into filtrate, stirring is conducted for 80-120 min, standing is conducted for 20-45 min, then the pH is adjusted to be neutral, and then discharging is conducted. The treatment method of the chromium-containing industrial wastewater, provided by the invention, is simple in process and high in chromium removal rate.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and particularly to a method for treating chromium-containing industrial wastewater. Background Art

[0002] Chromium is a major pollutant in the environment. With the development of industries such as metallurgy, electroplating, leather making, painting, photography, and printing and dyeing, the amount of chromium-containing wastewater discharged also increases. Chromium has multiple valence states in the water environment, mainly trivalent chromium and hexavalent chromium. Among them, the toxicity of hexavalent chromium is 100 times that of trivalent chromium and has an obvious carcinogenic effect. If this chromium-containing wastewater is directly discharged without treatment, it will cause great harm to the environment. Therefore, removing chromium, especially Cr(VI), from wastewater is of great significance for protecting public health and the ecological environment. Multiple treatment processes for chromium-containing wastewater have been disclosed in the prior art, but there are still deficiencies such as complex processes and low removal rates, which limit their applications. Summary of the Invention

[0003] Based on the technical problems existing in the background art, the present invention proposes a method for treating chromium-containing industrial wastewater, which has a simple process and a high chromium removal rate.

[0004] A method for treating chromium-containing industrial wastewater proposed by the present invention includes the following steps:

[0005] S1. Add Bacillus cereus and Pseudomonas aeruginosa into the chromium-containing industrial wastewater, stir at 28 - 35°C for 3 - 10 h, and centrifuge to obtain the primary treated wastewater;

[0006] S2. Add the composite adsorbent into the primary treated wastewater, adjust the pH to 5 - 6, stir and then let it stand at room temperature, and filter to obtain the secondary treated wastewater;

[0007] S3. Adjust the pH of the secondary treated wastewater to 3 - 6, add ethanol, perform irradiation treatment with γ-rays, adjust the pH to 8 - 10, and filter to obtain the tertiary treated wastewater;

[0008] S4. Add barium chloride into the tertiary treated wastewater, adjust the pH to 8 - 10, let it stand at room temperature for 10 - 15 h and then filter, add polyaluminum chloride PAC to the filtrate, stir for 80 - 120 min, let it stand for 20 - 45 min, and then adjust the pH to neutral and discharge.

[0009] Preferably, in S1, the addition amounts of Bacillus cereus and Pseudomonas aeruginosa in the chromium-containing industrial wastewater are 0.8 - 3 g / L and 0.5 - 2.5 g / L respectively; the stirring speed is 300 - 450 r / min, and the pH of the system is 4 - 6.

[0010] Preferably, in S2, the dosage of the composite adsorbent in the primary treated wastewater is 30 - 55 g / L; the stirring time is 60 - 150 min; the standing time is 1 - 5 h.

[0011] Preferably, in S2, the raw materials of the composite adsorbent by weight include: 50 - 65 parts of bentonite, 20 - 40 parts of modified iron tetroxide, and 3 - 30 parts of corn straw; the preparation process of the modified iron tetroxide includes the following steps: mixing iron tetroxide nanoparticles, ethanol, and water evenly, adding tetraethyl orthosilicate, and adjusting the pH to 8 - 10, stirring at room temperature for 7 - 8.5 h, separating, washing until neutral, and drying to obtain material A; mixing hydroxylated carbon nanotubes, material A, and acetone evenly, adjusting the pH to 2 - 5, dropwise adding epichlorohydrin at room temperature, and then stirring at 55 - 65 °C for 6 - 8 h, obtaining material B after reduced pressure distillation; mixing material B with diethylenetriamine, stirring at 80 - 85 °C for 30 - 90 min, then mixing with triethylamine, stirring at 80 - 85 °C for 150 - 200 min, washing and drying to obtain the modified iron tetroxide.

[0012] Preferably, the mass - volume ratio of the iron tetroxide nanoparticles to tetraethyl orthosilicate is 2 - 4.5:3 - 8 g / ml; the weight ratio of the hydroxylated carbon nanotubes, material A, and epichlorohydrin is 0.1 - 0.45:6 - 10:30 - 45; the mass - volume ratio of material B, diethylenetriamine, and triethylamine is 10 - 15 g:2 - 3 ml:15 - 20 ml.

[0013] Preferably, in S3, the added volume of ethanol is 0.03 - 0.05% of the volume of the secondary treated wastewater; the irradiation dose of the irradiation is 8 - 18 kGy.

[0014] Preferably, in S4, the dosage of barium chloride in the tertiary treated wastewater is 0.05 - 0.12 g / L.

[0015] Preferably, in S4, the amount of polyaluminum chloride added to the filtrate is 200 - 350 mg / L.

[0016] In the treatment method of the chromium - containing industrial wastewater of the present invention, first, Bacillus cereus and Pseudomonas aeruginosa are used to treat the chromium - containing wastewater, and a composite adsorbent is added for adsorption to remove part of the chromium. Then, γ - ray irradiation treatment is carried out to reduce hexavalent chromium to trivalent chromium, improving the chromium removal rate. After that, treatment with barium chloride is carried out, and the pH is adjusted to alkaline so that the remaining hexavalent chromium reacts with barium ions to form barium chromate precipitate, and the remaining trivalent chromium forms Cr(OH) 3Precipitation is carried out to further remove chromium. The present invention combines the advantages of multiple treatment methods at the same time. After multiple purifications, the removal rate of chromium is high. In the preparation process of the modified magnetite, first, magnetite nanoparticles and tetraethyl orthosilicate are used as raw materials, and the reaction conditions are controlled to coat silica on the surface of the magnetite nanoparticles to obtain material A. Then, hydroxylated carbon nanotubes and material A are used as raw materials to react with epichlorohydrin to obtain material B. Then, material B, diethylenetriamine, and triethylamine are used as raw materials, and the reaction conditions are controlled to introduce a large number of amino groups and quaternary ammonium salt structures on its surface. The obtained modified magnetite has a large specific surface area, many adsorption sites, and a large adsorption capacity. When combined with bentonite and corn straw, it is used for the treatment of chromium-containing wastewater, with strong adsorption, fast adsorption speed, and high chromium removal rate. Detailed implementation mode

[0017] Next, the technical solution of the present invention will be described in detail through specific examples.

[0018] Example 1

[0019] A method for treating chromium-containing industrial wastewater includes the following steps:

[0020] S1. Add Bacillus cereus and Pseudomonas aeruginosa to the chromium-containing industrial wastewater, stir at 35°C for 3 h, and centrifuge to obtain the primary treated wastewater.

[0021] S2. Add the composite adsorbent to the primary treated wastewater, adjust the pH to 5, stir and then let it stand at room temperature, and filter to obtain the secondary treated wastewater.

[0022] S3. Adjust the pH of the secondary treated wastewater to 3, add ethanol, irradiate with γ-rays, adjust the pH to 10, and filter to obtain the tertiary treated wastewater.

[0023] S4. Add barium chloride to the tertiary treated wastewater, adjust the pH to 8, let it stand at room temperature for 15 h and then filter, add polyaluminum chloride PAC to the filtrate, stir for 80 min, let it stand for 30 min, and then adjust the pH to neutral and discharge.

[0024] Example 2

[0025] A method for treating chromium-containing industrial wastewater includes the following steps:

[0026] S1. Add Bacillus cereus and Pseudomonas aeruginosa to the chromium-containing industrial wastewater, stir at 28°C for 10 h, and centrifuge to obtain the primary treated wastewater. Among them, the addition amounts of Bacillus cereus and Pseudomonas aeruginosa in the chromium-containing industrial wastewater are 3 g / L and 0.5 g / L respectively; the stirring speed is 450 r / min, and during the stirring process, the pH of the system is 4.

[0027] S2. Add the composite adsorbent to the primary treated wastewater, adjust the pH to 6, stir for 60 min, then let it stand at room temperature for 3 h, and filter to obtain the secondary treated wastewater. Among them, in the primary treated wastewater, the addition amount of the composite adsorbent is 55 g / L. The raw materials of the composite adsorbent include, by weight: 50 parts of bentonite, 40 parts of modified iron tetroxide, and 3 parts of corn straw. The preparation process of the modified iron tetroxide includes the following steps: Mix the iron tetroxide nanoparticles, ethanol, and water evenly, add tetraethyl orthosilicate, and adjust the pH to 8. Stir at room temperature for 8.5 h, perform magnetic separation, then wash until neutral and dry to obtain material A. Mix the hydroxylated carbon nanotubes, material A, and acetone evenly, adjust the pH to 2, dropwise add epichlorohydrin at room temperature, and then stir at 60 °C for 6 h. After reduced pressure distillation, obtain material B. Mix material B with diethylenetriamine, stir at 82 °C for 30 min, then mix with triethylamine, and stir at 85 °C for 150 min. Wash and dry the product to obtain the modified iron tetroxide. Among them, the mass-volume ratio of the iron tetroxide nanoparticles to tetraethyl orthosilicate is 2:8 g / ml; the weight ratio of the hydroxylated carbon nanotubes, material A, and epichlorohydrin is 0.1:7:45; the mass-volume ratio of material B, diethylenetriamine, and triethylamine is 10 g:3 ml:15 ml.

[0028] S3. Adjust the pH of the secondary treated wastewater to 6, add ethanol, perform irradiation treatment with γ-rays, adjust the pH to 8, and filter to obtain the tertiary treated wastewater. Among them, the added volume of the ethanol is 0.03% of the volume of the secondary treated wastewater; the irradiation dose of the irradiation is 8 kGy.

[0029] S4. Add barium chloride to the tertiary treated wastewater, adjust the pH to 10, let it stand at room temperature for 10 h and then filter. Add polyaluminum chloride PAC to the filtrate, stir for 120 min, let it stand for 20 min, and then adjust the pH of the effluent to neutral and discharge. Among them, the addition amount of barium chloride in the tertiary treated wastewater is 0.12 g / L; the amount of polyaluminum chloride added to the filtrate is 200 mg / L.

[0030] Example 3

[0031] A method for treating chromium-containing industrial wastewater includes the following steps:

[0032] S1. Add Bacillus cereus and Pseudomonas aeruginosa to the chromium-containing industrial wastewater, stir at 32 °C for 5 h, and centrifuge to obtain the primary treated wastewater. Among them, the addition amounts of Bacillus cereus and Pseudomonas aeruginosa in the chromium-containing industrial wastewater are 0.8 g / L and 2.5 g / L respectively; the rotation speed of the stirring is 300 r / min, and the pH of the system during the stirring process is 6.

[0033] S2. Add the composite adsorbent to the primary treated wastewater, adjust the pH to 5, stir for 120 min, then let it stand at room temperature for 5 h, and filter to obtain the secondary treated wastewater. Among them, in the primary treated wastewater, the addition amount of the composite adsorbent is 30 g / L. The raw materials of the composite adsorbent include, by weight: 65 parts of bentonite, 20 parts of modified iron tetroxide, and 30 parts of corn straw. The preparation process of the modified iron tetroxide includes the following steps: Mix the iron tetroxide nanoparticles, ethanol and water evenly, add tetraethyl orthosilicate, and adjust the pH to 10. Stir at room temperature for 7 h, separate, wash until neutral, and dry to obtain material A. Mix the hydroxylated carbon nanotubes, material A and acetone evenly, adjust the pH to 3, dropwise add epichlorohydrin at room temperature, and then stir at 65 °C for 7 h. After reduced pressure distillation, obtain material B. Mix material B with diethylenetriamine, stir at 85 °C for 90 min, then mix with triethylamine, stir at 82 °C for 170 min, wash and dry the product to obtain the modified iron tetroxide. Among them, the mass-volume ratio of the iron tetroxide nanoparticles to tetraethyl orthosilicate is 3:5 g / ml; the weight ratio of the hydroxylated carbon nanotubes, material A, and epichlorohydrin is 0.19:10:30; the mass-volume ratio of material B, diethylenetriamine, and triethylamine is 15 g:2 ml:20 ml;

[0034] S3. Adjust the pH of the secondary treated wastewater to 4, add ethanol, and perform irradiation treatment with γ-rays. Adjust the pH to 8 and filter to obtain the tertiary treated wastewater. Among them, the added volume of the ethanol is 0.05% of the volume of the secondary treated wastewater; the irradiation dose of the irradiation is 12 kGy;

[0035] S4. Add barium chloride to the tertiary treated wastewater, adjust the pH to 8, let it stand at room temperature for 12 h and then filter. Add polyaluminum chloride PAC to the filtrate, stir for 90 min, let it stand for 45 min, and then adjust the pH to neutral and discharge. Among them, the addition amount of barium chloride in the tertiary treated wastewater is 0.05 g / L; the amount of polyaluminum chloride added to the filtrate is 350 mg / L.

[0036] Example 4

[0037] A method for treating chromium-containing industrial wastewater, comprising the following steps:

[0038] S1. Add Bacillus cereus and Pseudomonas aeruginosa to the chromium-containing industrial wastewater, stir at 30 °C for 6 h, and centrifuge to obtain the primary treated wastewater;

[0039] S2. Add the composite adsorbent to the primary treated wastewater, adjust the pH to 5, stir and then let it stand at room temperature, and filter to obtain the secondary treated wastewater;

[0040] S3. Adjust the pH of the secondary treated wastewater to 5, add ethanol, irradiate it with γ-rays, adjust the pH to 8.5, and filter to obtain the tertiary treated wastewater;

[0041] S4. Add barium chloride to the tertiary treated wastewater, adjust the pH to 9, let it stand for 13 h at room temperature and then filter. Add polyaluminum chloride PAC to the filtrate, stir for 110 min, let it stand for 35 min, and then adjust the pH to neutral before discharging;

[0042] Among them, in S1, the addition amounts of Bacillus cereus and Pseudomonas aeruginosa in the chromium-containing industrial wastewater are 0.8 g / L and 1 g / L respectively; the rotation speed of the stirring is 400 r / min, and the pH of the system is 5;

[0043] In S2, in the primary treated wastewater, the addition amount of the composite adsorbent is 48 g / L; the stirring time is 150 min; the standing time is 1 h; the raw materials of the composite adsorbent include, by weight: 60 parts of bentonite, 30 parts of modified magnetite, and 10 parts of corn straw; the preparation process of the modified magnetite includes the following steps: Mix the magnetite nanoparticles, ethanol and water evenly, add tetraethyl orthosilicate, and adjust the pH to 9. Stir at room temperature for 8 h, separate and wash until neutral, and dry to obtain material A; Mix the hydroxylated carbon nanotubes, material A and acetone evenly, adjust the pH to 4, dropwise add epichlorohydrin at room temperature, and then stir at 55 °C for 8 h. After vacuum distillation, obtain material B; Mix material B with diethylenetriamine, stir at 80 °C for 60 min, then mix with triethylamine, stir at 80 °C for 180 min, wash and dry to obtain the modified magnetite; Among them, the mass-volume ratio of the magnetite nanoparticles to tetraethyl orthosilicate is 4.5:3 g / ml; the weight ratio of the hydroxylated carbon nanotubes, material A and epichlorohydrin is 0.45:6:39; the mass-volume ratio of material B, diethylenetriamine and triethylamine is 11 g:2.5 ml:17 ml;

[0044] In S3, the added volume of ethanol is 0.04% of the volume of the secondary treated wastewater; the irradiation dose of the irradiation is 15 kGy;

[0045] In S4, the addition amount of barium chloride in the tertiary treated wastewater is 0.07 g / L; the amount of polyaluminum chloride added to the filtrate is 300 mg / L.

[0046] Example 5

[0047] A method for treating chromium-containing industrial wastewater, comprising the following steps:

[0048] S1. Add Bacillus cereus and Pseudomonas aeruginosa into the chromium-containing industrial wastewater, stir at 34 °C for 4 h, and centrifuge to obtain the primary treated wastewater;

[0049] S2. Add the composite adsorbent into the primary treated wastewater, adjust the pH to 5, stir and then let it stand at room temperature, filter to obtain the secondary treated wastewater;

[0050] S3. Adjust the pH of the secondary treated wastewater to 5, add ethanol, irradiate with γ-rays, adjust the pH to 8, filter to obtain the tertiary treated wastewater;

[0051] S4. Add barium chloride into the tertiary treated wastewater, adjust the pH to 8, let it stand at room temperature for 14 h and then filter, add polyaluminum chloride PAC into the filtrate, stir for 90 min, let it stand for 40 min, and then adjust the pH to neutral and discharge;

[0052] Among them, in S1, the addition amounts of Bacillus cereus and Pseudomonas aeruginosa in the chromium-containing industrial wastewater are 2.5 g / L and 1 g / L respectively; the rotation speed of the stirring is 430 r / min, and the pH of the system is 4;

[0053] In S2, in the primary treated wastewater, the addition amount of the composite adsorbent is 38 g / L; the stirring time is 140 min; the standing time is 2 h; the raw materials of the composite adsorbent include, by weight: 58 parts of bentonite, 35 parts of modified magnetite, and 15 parts of corn straw; the preparation process of the modified magnetite includes the following steps: Mix the magnetite nanoparticles, ethanol and water evenly, add tetraethyl orthosilicate, and adjust the pH to 8, stir at room temperature for 7.5 h, separate and wash until neutral, and dry to obtain material A; Mix the hydroxylated carbon nanotubes, material A and acetone evenly, adjust the pH to 4, dropwise add epichlorohydrin at room temperature, and then stir at 58 °C for 7 h, and obtain material B after reduced pressure distillation; Mix material B with diethylenetriamine, stir at 81 °C for 80 min, then mix with triethylamine, stir at 82 °C for 180 min, wash and dry to obtain the modified magnetite; Among them, the mass-volume ratio of the magnetite nanoparticles to tetraethyl orthosilicate is 3:5 g / ml; the weight ratio of the hydroxylated carbon nanotubes, material A, and epichlorohydrin is 0.18:7:39; the mass-volume ratio of material B, diethylenetriamine, and triethylamine is 14 g:2.6 ml:19 ml;

[0054] In S3, the added volume of ethanol is 0.04% of the volume of the secondary treated wastewater; the irradiation dose of the irradiation is 15 kGy;

[0055] In S4, the addition amount of barium chloride in the tertiary treated wastewater is 0.07 g / L; the addition amount of polyaluminum chloride added to the filtrate is 280 mg / L.

[0056] Example 6

[0057] A treatment method for chromium-containing industrial wastewater, comprising the following steps:

[0058] S1. Add Bacillus cereus and Pseudomonas aeruginosa to the chromium-containing industrial wastewater, stir at 29 °C for 8 h, and centrifuge to obtain primary treated wastewater; wherein, the addition amounts of Bacillus cereus and Pseudomonas aeruginosa in the chromium-containing industrial wastewater are 1.2 g / L and 2 g / L respectively; the rotation speed of the stirring is 380 r / min, and the pH of the system during the stirring is 5;

[0059] S2. Add the composite adsorbent to the primary treated wastewater, adjust the pH to 6, stir for 70 min, then stand at room temperature for 4 h, and filter to obtain secondary treated wastewater; wherein, in the primary treated wastewater, the addition amount of the composite adsorbent is 50 g / L; the raw materials of the composite adsorbent include, by weight: 62 parts of bentonite, 28 parts of modified ferric oxide, and 25 parts of corn straw; the preparation process of the modified ferric oxide includes the following steps: Mix ferric oxide nanoparticles, ethanol and water evenly, add tetraethyl orthosilicate, wherein, the mass-volume ratio of the ferric oxide nanoparticles to tetraethyl orthosilicate is 4:7 g / ml, and adjust the pH to 9, stir at room temperature for 8 h, perform magnetic separation, wash to neutrality and dry to obtain material A; Mix hydroxylated carbon nanotubes, material A and acetone evenly, adjust the pH to 3, and dropwise add epichlorohydrin at room temperature, wherein, the weight ratio of the hydroxylated carbon nanotubes, material A and epichlorohydrin is 0.4:8:42, then stir at 60 °C for 6.5 h, perform vacuum distillation to obtain material B; Mix material B with diethylenetriamine, stir at 84 °C for 50 min, then mix with triethylamine, stir at 84 °C for 160 min, wash and dry the product to obtain the modified ferric oxide; wherein, the mass-volume ratio of material B, diethylenetriamine and triethylamine is 12 g:2 ml:17 ml;

[0060] S3. Adjust the pH of the secondary treated wastewater to 4, add ethanol, perform irradiation treatment with γ-rays, adjust the pH to 9, and filter to obtain tertiary treated wastewater; wherein, the added volume of the ethanol is 0.03% of the volume of the secondary treated wastewater; the irradiation dose of the irradiation is 9 kGy;

[0061] S4. Add barium chloride to the tertiary treated wastewater. The dosage of barium chloride added to the tertiary treated wastewater is 0.1 g / L. Adjust the pH to 9, let it stand for 11 h at room temperature, then filter. Add polyaluminum chloride (PAC) to the filtrate. The amount of polyaluminum chloride added to the filtrate is 200 mg / L. Stir for 110 min, let it stand for 25 min, then adjust the pH to neutral and discharge.

[0062] Comparative Example 1

[0063] It is different from Example 6 only in that: it does not contain the S1 step.

[0064] Comparative Example 2

[0065] It is different from Example 6 only in that: it does not contain the S2 step.

[0066] Comparative Example 3

[0067] It is different from Example 6 only in that: it does not contain the S3 step.

[0068] Example 7

[0069] It is different from Example 6 only in that: in S2, the raw materials of the composite adsorbent do not include the modified magnetite mentioned above.

[0070] Example 8

[0071] It is different from Example 6 only in that: in the preparation process of the modified magnetite, hydroxylated carbon nanotubes are not added, but material A is directly mixed evenly with acetone for reaction.

[0072] Example 9

[0073] It is different from Example 6 only in that: in the preparation process of the modified magnetite, triethylamine is not added for reaction, that is, material B is mixed with diethylenetriamine, stirred at 84 °C for 50 min, and then the product is directly washed and dried to obtain the modified magnetite.

[0074] Example 10

[0075] It is different from Example 6 only in that: in the preparation process of the modified magnetite, diethylenetriamine is not added for reaction, that is, the obtained material B is directly mixed with triethylamine, stirred at 84 °C for 160 min, washed and dried to obtain the modified magnetite.

[0076] Example 11

[0077] It is only different from Example 6 in that the preparation process of the modified magnetite includes the following steps: uniformly mixing magnetite nanoparticles, ethanol and water, adding tetraethyl orthosilicate, wherein the mass-volume ratio of the magnetite nanoparticles to tetraethyl orthosilicate is 4:7 g / ml, adjusting the pH to 9, stirring at room temperature for 8 h, performing magnetic separation, washing until neutral, and drying.

[0078] Example 12

[0079] It is only different from Example 6 in that in S2, the magnetite in the raw materials of the composite adsorbent is unmodified magnetite.

[0080] In the chromium-containing wastewater of Examples 1-12 and Comparative Examples 1-3, the total chromium concentration is 200 mg / L; the effluent treated by the methods of Examples 6-12 and Comparative Examples 1-3 of the present invention is detected. Among them, the chromium content in the effluent of Example 6 is 0.16 mg / L, the chromium content in the effluent of Examples 7-12 is 0.48-0.65 mg / L, while the chromium content in the effluent of Comparative Examples 1-3 is ≥1.53 mg / L.

[0081] As mentioned above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A method for treating chromium-containing industrial wastewater, It is characterized in that The following steps are involved: S1. Add Bacillus cereus and Pseudomonas aeruginosa to chromium-containing industrial wastewater, stir for 3-10 hours at 28-35°C, and centrifuge to obtain primary treated wastewater; S2, adding the composite adsorbent to the primary treated wastewater, adjusting the pH to 5-6, stirring and standing at room temperature, and filtering to obtain the secondary treated wastewater; S3, adjusting the pH of the secondary treated wastewater to 3-6, adding ethanol, irradiating with γ-rays, adjusting the pH to 8-10, filtering, and obtaining tertiary treated wastewater; S4. Add barium chloride to the tertiary treated wastewater and adjust the pH to 8-10. Let it stand at room temperature for 10-15 hours and then filter it. Add polyaluminium chloride (PAC) to the filtrate, stir it for 80-120 minutes, let it stand for 20-45 minutes and then adjust the pH to neutral before discharging.

2. The method for treating chromium-containing industrial wastewater according to claim 1, It is characterized in that In S1, the addition amounts of Bacillus cereus and Pseudomonas aeruginosa in the chromium-containing industrial wastewater are 0.8-3 g / L and 0.5-2.5 g / L respectively; the stirring speed is 300-450 r / min, and the pH of the system is 4-6.

3. The method for treating chromium-containing industrial wastewater according to claim 1, It is characterized in that In S2, in the primary treated wastewater, the amount of composite adsorbent added is 30-55 g / L; the stirring time is 60-150 min; and the standing time is 1-5 h.

4. A method for treating chromium-containing industrial wastewater according to any one of claims 1 to 3, It is characterized in that In S2, the raw materials of the composite adsorbent include, by weight, 50-65 parts of bentonite, 20-40 parts of modified ferroferric oxide, and 3-30 parts of corn stalks; the preparation process of the modified ferroferric oxide includes the following steps: uniformly mixing ferroferric oxide nanoparticles, ethanol and water, adding tetraethyl orthosilicate, adjusting the pH to 8-10, stirring at room temperature for 7-8.5 hours, washing to neutrality after separation, and drying to obtain material A; uniformly mixing hydroxylated carbon nanotubes, material A and acetone, adjusting the pH to 2-5, dropping epichlorohydrin at room temperature, and then stirring at 55-65°C for 6-8 hours, and obtaining material B after reduced pressure distillation; mixing material B with diethylenetriamine, stirring at 80-85°C for 30-90 minutes, and then mixing with triethylamine, stirring at 80-85°C for 150-200 minutes, washing, and drying to obtain the modified ferroferric oxide.

5. The method for treating chromium-containing industrial wastewater according to claim 4, It is characterized in that The mass volume ratio of the ferrosilicate nanoparticles and tetraethyl orthosilicate is 2-4.5:3-8 g / ml; the weight ratio of the hydroxylated carbon nanotubes, material A, and epichlorohydrin is 0.1-0.45:6-10:30-45; the mass volume ratio of the material B, diethylenetriamine, and triethylamine is 10-15 g:2-3 ml:15-20 ml.

6. The treatment method of chromium-containing industrial wastewater according to claim 1, characterized in that, in S3, the added volume of ethanol is 0.03-0.05% of the volume of the secondary treated wastewater; the irradiation dose of the irradiation is 8-18 kGy.

7. The treatment method of chromium-containing industrial wastewater according to claim 1, characterized in that, in S4, the added amount of barium chloride in the tertiary treated wastewater is 0.05-0.12 g / L.

8. The treatment method of chromium-containing industrial wastewater according to claim 1, characterized in that, in S4, the amount of polyaluminum chloride added to the filtrate is 200-350 mg / L.