A method for treating high-COD wastewater containing benzene compounds from phenol and acetone production.

Abstract

This invention discloses a method for treating high-COD benzene-containing wastewater from phenol and acetone production, comprising sequential pretreatment and biological treatment. The pretreatment includes a single-effect falling film evaporator, a first-effect evaporator, a second-effect evaporator, and a third-effect evaporator. The biological treatment includes an acidification hydrolysis tank, an oxidation ditch, a primary aerobic tank, a secondary aerobic tank, a primary sedimentation tank, a secondary sedimentation tank, and a sludge thickening tank. This invention achieves chain-breaking degradation and carbon reduction, effectively treating the wastewater and ensuring that the final effluent meets the prescribed discharge requirements.

Description

Technical Field

[0001] This invention relates to a method for treating high-COD wastewater containing benzene compounds in phenol and acetone production, belonging to the field of chemical production technology. Background Technology

[0002] In phenol-acetone production, high-COD benzene-containing wastewater from the phenol-acetone unit flows from the flash preheater to the flash evaporator. The organic waste liquid containing small amounts of acetone and methanol, evaporated from the upper layer of the flash tower, is condensed in the flash condenser and temporarily stored in a collection tank. The saline mother liquor at the bottom of the flash evaporator is pumped into the triple-effect feed tank via the flash discharge pump. The saline wastewater in the triple-effect feed tank is then pumped back through the preheater and flows horizontally into the first, second, and third-effect evaporators for evaporation and concentration, causing sodium sulfate to saturate and precipitate. The salt slurry is then transferred downstream and finally discharged from the triple-effect evaporator. The salt slurry discharged from the evaporation system first undergoes sedimentation separation and then centrifuge separation. The vapor phase from the triple-effect system is condensed and then enters the wastewater treatment system. However, the evaporation capacity of the triple-effect system is relatively low and cannot meet the treatment needs of the upstream high-COD benzene-containing wastewater. Furthermore, the high benzene content after condensation of the vapor phase puts pressure on subsequent processing steps. Summary of the Invention

[0003] At least to address one of the problems existing in the prior art, the present invention provides a method for treating high COD benzene-containing wastewater from phenol and acetone production, which achieves chain-breaking degradation and carbon reduction, effectively treats the wastewater, and ensures that the final effluent meets the prescribed discharge requirements.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a method for treating high COD benzene-containing wastewater in phenol-acetone production, comprising sequential pretreatment and biochemical treatment; The pretreatment includes single-effect falling film evaporators, first-effect evaporators, second-effect evaporators, and third-effect evaporators; The biochemical treatment includes an acidification hydrolysis tank, an oxidation ditch, a primary aerobic tank, a secondary aerobic tank, a primary sedimentation tank, a secondary sedimentation tank, and a sludge thickening tank.

[0005] Preferably, the process also includes advanced treatment, which includes a coagulation-flotation physicochemical tank and a terminal sedimentation tank.

[0006] Preferably, the pretreatment process is as follows: the high-salt, high-COD benzene-containing wastewater from the phenol unit is preheated and then enters a single-effect falling film evaporator for treatment. The concentrated waste liquid from the single-effect falling film evaporator enters a concentrated liquid storage tank and then sequentially enters a first-effect evaporator, a second-effect evaporator, and a third-effect evaporator for treatment. The gas phase from the single-effect falling film evaporator and the third-effect evaporator is condensed by a heat exchange condenser to form pretreated waste liquid, which enters a high-concentration waste liquid tank. The concentrated crystal slurry from the third-effect evaporator enters a settling tank for treatment, and the mother liquor enters an incinerator. The solids from the settling tank are recovered, and the liquid from the settling tank enters a single-effect falling film evaporator.

[0007] Preferably, the biochemical treatment process is as follows: the pretreated waste liquid from the high-concentration waste liquid tank sequentially enters the acidification hydrolysis tank, oxidation ditch, and primary sedimentation tank for treatment; the wastewater from the primary sedimentation tank sequentially enters the secondary aerobic tank and secondary sedimentation tank for treatment; the supernatant from the secondary sedimentation tank enters the deep treatment system; the sludge from the primary sedimentation tank enters the primary aerobic tank and sludge thickening tank for treatment; the wastewater from the sludge thickening tank enters the secondary aerobic tank; and the sludge from the sludge thickening tank is returned to the oxidation ditch or recycled for resource recovery.

[0008] Preferably, the advanced treatment process involves the following steps: the supernatant from the secondary sedimentation tank sequentially enters the coagulation-flotation physicochemical tank and the terminal sedimentation tank for treatment; the water quality from the terminal sedimentation tank meets the discharge standards; and the flocculants from the terminal sedimentation tank enter the oxidation ditch for treatment.

[0009] Preferably, in the pretreatment, the single-effect falling film evaporator utilizes low-pressure steam with a pressure of 0.3~0.35MPa.

[0010] Preferably, in the biochemical treatment, the oxidation ditch consists of an anaerobic zone, an anoxic zone, and an aerobic zone arranged sequentially.

[0011] Preferably, in the biochemical treatment, the secondary aerobic tank is a contact oxidation tank.

[0012] Preferably, in the biochemical treatment, the primary sedimentation tank is a radial flow sedimentation tank. Preferably, in the biochemical treatment, the second sedimentation tank is an inclined plate sedimentation tank.

[0013] Preferably, in the biochemical treatment, the terminal sedimentation tank is an inclined plate sedimentation tank.

[0014] Preferably, the temperature of the pretreated waste liquid is 37~40℃.

[0015] Preferably, the acidification hydrolysis tank treatment conditions are: temperature 30~35℃, pH value 6~7.5 and residence time 4~6h.

[0016] Preferably, the treatment conditions of the oxidation tank are as follows: anaerobic zone: dissolved oxygen concentration less than 0.1 mg / L, temperature 30~35℃, pH value 6~7.5 and residence time 4~6h; anoxic zone: dissolved oxygen concentration 0.2~0.5 mg / L, temperature 30~35℃, pH value 7~8 and residence time 2~4h; aerobic zone: dissolved oxygen concentration 2~3 mg / L, temperature 30~35℃, pH value 6.5~8.5 and residence time 3~5h.

[0017] Preferably, the treatment conditions of the primary aerobic tank are: dissolved oxygen concentration of 2~3 mg / L, temperature of 30~35℃, pH value of 6.5~8.5 and residence time of 2~4h.

[0018] Preferably, the treatment conditions of the secondary aerobic tank are: dissolved oxygen concentration of 3~4 mg / L, combined packing material, air-to-water ratio controlled at 15:1~20:1, temperature of 30~35℃, pH value of 6.5~8.5, and residence time of 3~5h.

[0019] Preferably, the specific surface area of ​​the combined packing is 450~550 m². 2 / m 3 The filling rate is 60-65%.

[0020] Preferably, in the advanced treatment, the coagulation flotation physicochemical tank uses a composite flocculant.

[0021] Preferably, the composite flocculant is composed of polyγ-glutamic acid, sulfated polysaccharide and chitosan.

[0022] Preferably, the composite flocculant comprises, by weight, 2.5 to 5 parts of polyγ-glutamic acid, 2 to 4.5 parts of sulfated polysaccharide, and 7.5 to 15.5 parts of chitosan.

[0023] Preferably, the dosage of the composite flocculant is 15~30 mg / L.

[0024] This invention employs a combined process of pretreatment, biochemical treatment, and advanced treatment for high-COD benzene-containing wastewater from phenol and acetone production. This process achieves chain-breaking degradation and carbon reduction, effectively treating the wastewater and ensuring that the final effluent meets the prescribed discharge requirements. The invention combines a single-effect falling film evaporator with a triple-effect system, increasing the treatment capacity of high-COD benzene-containing wastewater from the phenol and acetone plant from 8 t / h to 16 t / h, while reducing energy consumption and slowing down the scaling rate on the heating surface. The combination of a single-effect falling film evaporator and a triple-effect system effectively reduces the benzene content in the condensate, disrupting stable structures such as benzene rings and breaking chemical bonds, transforming stable aromatic compounds into easily treatable open-chain compounds, thus facilitating subsequent biochemical and advanced treatment. This invention utilizes anaerobic, anoxic, and aerobic processes to further break the chain and open the rings of benzene compounds, significantly reducing the carbon source. 2 The O process and aerobic process ensure good overall biological treatment effect; the invention finally uses a composite flocculant for deep treatment to further reduce COD and impurities in the water, while the flocculants are recycled and reused in the biological treatment process, and promote the treatment effect of biological treatment. Attached Figure Description

[0025] Figure 1 The processing method of the present invention is described. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. The described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply.

[0027] This invention provides a method for treating high-COD benzene-containing wastewater from phenol and acetone production, comprising sequential pretreatment, biochemical treatment, and advanced treatment; the pretreatment includes a single-effect falling film evaporator, a first-effect evaporator, a second-effect evaporator, and a third-effect evaporator; the biochemical treatment includes an acidification hydrolysis tank, an oxidation ditch, a primary aerobic tank, a secondary aerobic tank, a primary sedimentation tank, a secondary sedimentation tank, and a sludge thickening tank; the advanced treatment includes a coagulation-flotation physicochemical treatment tank and a terminal sedimentation tank.

[0028] The specific processing method is shown in the following example.

[0029] Example A method for treating high-COD wastewater containing benzene compounds from phenol and acetone production, such as... Figure 1 The process flow shown is as follows: Pretreatment process: High-salt, high-COD benzene-containing wastewater from the phenol unit is preheated and then enters a single-effect falling film evaporator for treatment. The single-effect falling film evaporator uses low-pressure steam with a pressure of 0.3~0.35MPa. The concentrated waste liquid from the single-effect falling film evaporator enters the concentrated liquid storage tank, and then enters the first-effect evaporator, second-effect evaporator, and third-effect evaporator for treatment in sequence. The gas phase from the single-effect falling film evaporator and the third-effect evaporator is condensed by heat exchange condensers, which destroys the stable structure of benzene rings and breaks its chemical bonds, transforming it from a stable aromatic compound into an easily treated open-chain compound. The condensed waste liquid forms a pretreated waste liquid with a temperature of 37~40℃ and enters a high-concentration waste liquid tank. The concentrated crystal slurry from the third-effect evaporator enters the settling tank for treatment, and the mother liquor enters the incinerator. The solids from the settling tank are recovered, and the liquid from the settling tank enters the single-effect falling film evaporator. Biochemical treatment process: The pretreated wastewater from the high-concentration wastewater tank sequentially enters the acidification hydrolysis tank, oxidation ditch, and primary sedimentation tank for treatment. The acidification hydrolysis tank treatment conditions are controlled as follows: temperature 30-35℃, pH 6-7.5, and residence time 4-6 hours. The oxidation ditch consists of sequentially anaerobic, anoxic, and aerobic zones. The anaerobic zone treatment conditions are controlled as follows: dissolved oxygen concentration less than 0.1 mg / L, temperature 30-35℃, pH 6-7.5, and residence time 4-6 hours. The anoxic zone treatment conditions are: dissolved oxygen concentration 0.2-0.5 mg / L, temperature 30-35℃, and pH 6-7.5. Wastewater from the primary sedimentation tank enters the secondary aerobic tank and then the secondary sedimentation tank for further treatment. The secondary aerobic tank uses a contact oxidation process, and the treatment conditions are controlled as follows: dissolved oxygen concentration 3-4 mg / L, combined packing material, air-to-water ratio 15:1-20:1, temperature 30-35℃, pH 6.5-8.5, and retention time 3-5 hours. The specific surface area of ​​the combined packing material is 450-550 m². 2 / m 3 The filling rate is 60-65%. The secondary sedimentation tank adopts an inclined plate sedimentation tank, and the primary sedimentation tank adopts a radial flow sedimentation tank. The supernatant from the secondary sedimentation tank enters the deep treatment system. The sludge from the primary sedimentation tank enters the primary aerobic tank and sludge thickening tank for treatment. The wastewater from the sludge thickening tank enters the secondary aerobic tank. The sludge from the sludge thickening tank is returned to the oxidation ditch or recycled for resource recovery. The advanced treatment process is as follows: the supernatant from the secondary sedimentation tank enters the coagulation-flotation physicochemical treatment tank and the terminal sedimentation tank for treatment. The coagulation-flotation physicochemical treatment tank uses a composite flocculant. The composite flocculant is composed of polyγ-glutamic acid, sulfated polysaccharide and chitosan. The dosage of the composite flocculant is 25~45mg / L. The terminal sedimentation tank is an inclined plate sedimentation tank. The water quality from the terminal sedimentation tank meets the discharge standards. The flocculants from the terminal sedimentation tank enter the oxidation ditch for treatment.

[0030] The composite flocculant is composed of 2.5 to 5 parts by weight of polyγ-glutamic acid, 2 to 4.5 parts by weight of sulfated polysaccharide, and 7.5 to 15.5 parts by weight of chitosan.

[0031] In the single-effect falling film evaporation treatment of this invention, high-salt, high-COD benzene-containing wastewater exchanges heat with the gas phase of the single-effect falling film evaporator, and then exchanges heat with the steam condensate of the single-effect falling film evaporator to raise its temperature before entering the single-effect falling film evaporator. The high-COD benzene-containing wastewater in the single-effect falling film evaporator is forcibly circulated by a circulation pump and evenly distributed by a distributor at the top of the falling film evaporator, so that the saline wastewater in the evaporator forms a liquid film, which exchanges heat and evaporates with low-pressure steam. The single-effect falling film evaporator heats the circulating wastewater in the single-effect falling film evaporator with 0.35MPa steam. The concentrated liquid and secondary steam are separated. The concentrated waste liquid after evaporation is sent to a triple-effect steam system (first-effect evaporator, second-effect evaporator, and third-effect evaporator) for subsequent treatment; the secondary steam is introduced into the next effect as a heat source.

[0032] In the oxidation ditch of this invention, the anaerobic zone is free of O2 and NO3. - Polyphosphate-accumulating bacteria release phosphorus and absorb easily degradable organic matter in this area; the anoxic zone contains no O2 but has NO3. - Denitrifying bacteria use the remaining organic matter to reduce nitrates in the reflux liquid to nitrogen gas, thus achieving denitrification. The aerobic zone contains O2, and nitrifying bacteria convert ammonia nitrogen into nitrates. The mixed liquid is refluxed to the anoxic zone, where polyphosphate-accumulating bacteria absorb excess phosphorus, and the organic matter is completely oxidized and decomposed.

[0033] According to the treatment method of the above embodiments, the high-salt, high-COD wastewater containing benzene compounds from the phenol unit is first pretreated, and then the pretreated wastewater is subjected to biochemical treatment, or / and the water obtained from the biochemical treatment is further treated to achieve the water quality standard for discharge, as shown in Examples 1 to 6 below.

[0034] The water quality discharge standards are shown in Table 1.

[0035] Water discharge standards

[0036] Example 1 High-salt, high-COD benzene-containing wastewater from the phenol unit enters the pretreatment process at a rate of 16 t / h. The salt content (TDS, total dissolved solids) is 32180 mg / L and the COD content is 18750 mg / L. Pretreatment is performed first, followed by biochemical treatment of the pretreated wastewater. The treatment conditions are as follows: Anaerobic zone: dissolved oxygen concentration less than 0.1 mg / L and retention time 4 h; Anoxic zone: dissolved oxygen concentration 0.5 mg / L and retention time 2 h; Aerobic zone: dissolved oxygen concentration 2 mg / L and retention time 3 h; Primary aerobic tank: dissolved oxygen concentration 2 mg / L and retention time 2 h; Secondary aerobic tank: dissolved oxygen concentration 3 mg / L and specific surface area 480 m². 2 / m 3 The combined packing material with a filling rate of 60%, the air-to-water ratio controlled at 15:1, and the residence time at 3 hours were used. The final water quality test results are shown in Table 2-1, and the water quality meets the discharge standards.

[0037] Table 2-2 Composition content of water in Example 1

[0038] Example 2 High-salt, high-COD benzene-containing wastewater from the phenol unit enters the pretreatment process at a rate of 16 t / h. The salt content (TDS, total dissolved solids) is 31978 mg / L and the COD content is 18895 mg / L. Pretreatment is performed first, followed by biological treatment of the pretreated wastewater. The water obtained from the biological treatment then undergoes further treatment. Specifically: the low-pressure steam pressure in the single-effect falling film evaporator is 0.35 MPa; the retention time in the acidification hydrolysis tank is 4 h; the oxidation tank treatment conditions are: anaerobic zone: dissolved oxygen concentration less than 0.1 mg / L and retention time 4 h; anoxic zone: dissolved oxygen concentration 0.5 mg / L and retention time 2 h; aerobic zone: dissolved oxygen concentration 2 mg / L and retention time 3 h; primary aerobic tank treatment conditions: dissolved oxygen concentration 2 mg / L and retention time 2 h; secondary aerobic tank treatment conditions: dissolved oxygen concentration 3 mg / L and specific surface area 480 m². 2 / m 3 The combined packing material with a filling rate of 60%, the air-to-water ratio controlled at 15:1, and the residence time at 3 hours were used. The dosage of the composite flocculant was 15 mg / L, and it consisted of 2.5 parts polyγ-glutamic acid, 4.5 parts sulfated polysaccharide, and 7.5 parts chitosan by weight. The final water quality discharge test results are shown in Table 2-2. The water quality met the discharge standards, and the flocculants in the terminal sedimentation tank were recycled.

[0039] Table 2-2 Component content of water in Example 2

[0040] Example 3 High-salt, high-COD benzene-containing wastewater from the phenol unit enters the pretreatment process at a rate of 16 t / h. The salt content (TDS, total dissolved solids) is 32145 mg / L and the COD content is 19240 mg / L. Pretreatment is performed first, followed by biological treatment of the pretreated wastewater. The water obtained from the biological treatment then undergoes further treatment. Specifically: the low-pressure steam pressure in the single-effect falling film evaporator is 0.35 MPa; the retention time in the acidification hydrolysis tank is 5 h; the oxidation tank treatment conditions are: anaerobic zone: dissolved oxygen concentration less than 0.1 mg / L and retention time 5 h; anoxic zone: dissolved oxygen concentration 0.4 mg / L and retention time 3 h; aerobic zone: dissolved oxygen concentration 2.5 mg / L and retention time 4 h; primary aerobic tank treatment conditions: dissolved oxygen concentration 2.5 mg / L and retention time 3 h; secondary aerobic tank treatment conditions: dissolved oxygen concentration 3.5 mg / L and specific surface area 480 m². 2 / m 3 The system uses a combination of packing material with a filling rate of 60%, an air-to-water ratio of 17.5:1, and a residence time of 4 hours. The dosage of the composite flocculant is 25 mg / L, and it consists of 3.8 parts by weight of polyγ-glutamic acid, 3.2 parts of sulfated polysaccharide, and 12.8 parts of chitosan. The final water quality discharge test results are shown in Table 2-3. The water quality meets the discharge standards, and the flocculants in the terminal sedimentation tank are recycled.

[0041] Table 2-3 Component content of water in Example 3

[0042] Example 4 High-salt, high-COD benzene-containing wastewater from the phenol unit enters the pretreatment process at a rate of 16 t / h. The wastewater has a total dissolved solids (TDS) content of 32209 mg / L and a COD content of 18928 mg / L. Pretreatment is performed first, followed by biological treatment of the pretreated wastewater. The water obtained from the biological treatment then undergoes further treatment. Specifically: the low-pressure steam pressure in the single-effect falling film evaporator is 0.35 MPa; the retention time in the acidification hydrolysis tank is 6 h; the oxidation tank treatment conditions are: anaerobic zone: dissolved oxygen concentration less than 0.1 mg / L and retention time 6 h; anoxic zone: dissolved oxygen concentration 0.2 mg / L and retention time 4 h; aerobic zone: dissolved oxygen concentration 3 mg / L and retention time 5 h; primary aerobic tank treatment conditions: dissolved oxygen concentration 3 mg / L and retention time 4 h; secondary aerobic tank treatment conditions: dissolved oxygen concentration 4 mg / L and specific surface area 480 m². 2 / m 3The system uses a combination of packing material with a filling rate of 60%, an air-to-water ratio controlled at 120:1, and a residence time of 5 hours. The dosage of the composite flocculant is 30 mg / L, and it consists of 5 parts by weight of polyγ-glutamic acid, 2 parts of sulfated polysaccharide, and 15.5 parts of chitosan. The final water quality discharge test results are shown in Table 2-4. The water quality meets the discharge standards, and the flocculants in the terminal sedimentation tank are recycled.

[0043] Table 2-4 Component content of water in Example 4

[0044] Example 5 High-salt, high-COD benzene-containing wastewater from the phenol unit enters the pretreatment process at a rate of 16 t / h. The salt content (TDS, total dissolved solids) is 31982 mg / L and the COD content is 19080 mg / L. Pretreatment is performed first, followed by biological treatment of the pretreated wastewater. The water obtained from the biological treatment undergoes further treatment, with the flocculants from the terminal sedimentation tanks of Examples 2-4 and 5 applied to the oxidation process. Specifically, the low-temperature evaporator of the single-effect falling film evaporator... The steam pressure is 0.35 MPa; the retention time in the acidification hydrolysis tank is 5 h; the oxidation tank treatment conditions are: anaerobic zone: dissolved oxygen concentration less than 0.1 mg / L and retention time 6 h; anoxic zone: dissolved oxygen concentration 0.4 mg / L and retention time 2.5 h; aerobic zone: dissolved oxygen concentration 3 mg / L and retention time 4.5 h; primary aerobic tank treatment conditions: dissolved oxygen concentration 3 mg / L and retention time 4 h; secondary aerobic tank treatment conditions: dissolved oxygen concentration 4 mg / L and specific surface area 480 m². 2 / m 3 The combined packing material with a filling rate of 60%, the air-to-water ratio controlled at 19:1, and the residence time at 4.5 h were used. The dosage of the composite flocculant was 20 mg / L, and it consisted of 3.5 parts by weight of polyγ-glutamic acid, 3 parts of sulfated polysaccharide, and 12 parts of chitosan. The final water quality test results are shown in Table 2-4, and the water quality met the discharge standards.

[0045] Table 2-5 Component content of water in Example 5

[0046] Example 6 High-salt, high-COD benzene-containing wastewater from the phenol unit enters the pretreatment process at a rate of 16 t / h. The salt content (TDS, total dissolved solids) is 31905 mg / L and the COD content is 18695 mg / L. Pretreatment is performed first, followed by biochemical treatment of the pretreated wastewater. The water obtained from the biochemical treatment is then further treated using polyaluminum sulfate at a dosage of 65 mg / L. The rest is the same as in Example 2. The final water quality test results are shown in Table 2-6. The water quality meets the discharge standards. The flocculants in the terminal sedimentation tank are recycled.

[0047] Table 3-6 Composition content of water in Example 6

[0048] Compared with Example 2, Example 6 uses a larger amount of polyaluminum sulfate, resulting in a poorer flocculation effect on water components.

[0049] Comparative Example 1 High-salt, high-COD benzene-containing wastewater from the phenol unit enters the pretreatment process at a rate of 8 t / h. The salt content (TDS, total dissolved solids) is 32065 mg / L and the COD content is 18784 mg / L. Pretreatment is performed first, and then the pretreated wastewater undergoes biochemical treatment. The pretreatment process does not include a single-effect falling film evaporator. After preheating, the high-salt, high-COD benzene-containing wastewater from the phenol unit enters a triple-effect evaporator from a flash evaporator. The rest is the same as in Example 1. The final water quality test results are shown in Table 3-1. The water quality did not meet the discharge standards.

[0050] Table 3-1 Component content of water in Comparative Example 1

[0051] Comparative Example 2 The high-salt, high-COD benzene-containing wastewater from the phenol unit enters the pretreatment process at a rate of 16 t / h. The salt content (TDS, total dissolved solids) is 32094 mg / L and the COD content is 18925 mg / L. The pretreated wastewater is first pretreated and then subjected to biochemical treatment. The pretreatment process does not include a single-effect falling film evaporator. After preheating, the high-salt, high-COD benzene-containing wastewater from the phenol unit enters a triple-effect evaporator from a flash evaporator. The rest is the same as in Example 1. The final water quality test results are shown in Table 3-1. The water quality did not meet the discharge standards.

[0052] Table 3-2 Component content of water in Comparative Example 2

[0053] Comparative Example 3 High-salt, high-COD benzene-containing wastewater from the phenol unit enters the pretreatment process at a rate of 16 t / h. The salt content (TDS, total dissolved solids) is 31905 mg / L and the COD content is 18695 mg / L. Pretreatment is performed first, followed by biochemical treatment of the pretreated wastewater. The water obtained from the biochemical treatment is then further treated. The flocculants from the terminal sedimentation tanks of Example 6 and Comparative Example 4 are applied to the oxidation hook. The rest is the same as in Example 2, using polyaluminum sulfate at a dosage of 65 mg / L. The final discharge water quality test results are shown in Table 3-3. The water quality did not meet the discharge standards. The flocculants from the terminal sedimentation tank were recycled.

[0054] Table 3-3 Component content of water in Comparative Example 3

[0055] Compared with Example 5, Comparative Example 3 shows that the flocculants formed by polyaluminum sulfate, when applied in the biochemical treatment process, will reduce the removal efficiency of water pollutants, resulting in substandard water discharge.

[0056] Comparative Example 4 High-salt, high-COD benzene-containing wastewater from the phenol unit enters the pretreatment process at a rate of 16 t / h. The salt content (TDS, total dissolved solids) is 31905 mg / L and the COD content is 18695 mg / L. Pretreatment is performed first, followed by biological treatment of the pretreated wastewater, and then further treatment of the water obtained from the biological treatment. The biological treatment process is as follows: the pretreated wastewater from the high-concentration wastewater tank enters the acidification hydrolysis tank, oxidation ditch, primary sedimentation tank, and secondary sedimentation tank for treatment in sequence. The supernatant from the secondary sedimentation tank enters the deep treatment system. The sludge from the primary sedimentation tank and the secondary sedimentation tank enters the primary aerobic tank and sludge thickening tank for treatment. The wastewater from the sludge thickening tank enters the oxidation ditch. The sludge from the sludge thickening tank is returned to the recycling and resource recovery treatment. The rest is the same as in Example 2. The final water quality test results are shown in Tables 3-4. The water quality did not meet the discharge standards.

[0057] Table 3-4 Component content of water in Comparative Example 4

[0058] Compared with Example 2, Comparative Example 4 lacks a secondary oxidation tank in its biochemical treatment, which reduces the treatment effect on wastewater.

[0059] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit and essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0060] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for treating high-COD benzene-containing wastewater from phenol-acetone production, characterized in that, This includes sequential pretreatment and biochemical treatment; The pretreatment includes single-effect falling film evaporators, first-effect evaporators, second-effect evaporators, and third-effect evaporators; The biochemical treatment includes an acidification hydrolysis tank, an oxidation ditch, a primary aerobic tank, a secondary aerobic tank, a primary sedimentation tank, a secondary sedimentation tank, and a sludge thickening tank.

2. The method for treating high-COD benzene-containing wastewater from phenol-acetone production according to claim 1, characterized in that, It also includes advanced treatment, which includes a coagulation-flotation physicochemical tank and a terminal sedimentation tank.

3. The method for treating high-COD benzene-containing wastewater from phenol-acetone production according to claim 2, characterized in that, The pretreatment process is as follows: the high-salt, high-COD benzene-containing wastewater from the phenol unit is preheated and then enters a single-effect falling film evaporator for treatment. The concentrated waste liquid from the single-effect falling film evaporator enters a concentrated liquid storage tank and then sequentially enters a first-effect evaporator, a second-effect evaporator, and a third-effect evaporator for treatment. The gas phase from the single-effect falling film evaporator and the third-effect evaporator is condensed by a heat exchange condenser to form pretreated waste liquid, which enters a high-concentration waste liquid tank. The concentrated crystal slurry from the third-effect evaporator enters a settling tank for treatment, and the mother liquor enters an incinerator. The solids from the settling tank are recovered, and the liquid from the settling tank enters a single-effect falling film evaporator.

4. The method for treating high-COD benzene-containing wastewater from phenol-acetone production according to claim 3, characterized in that, The biochemical treatment process is as follows: the pretreated waste liquid from the high-concentration waste liquid tank enters the acidification and hydrolysis tank, oxidation ditch and primary sedimentation tank for treatment in sequence; the wastewater from the primary sedimentation tank enters the secondary aerobic tank and secondary sedimentation tank for treatment in sequence; the supernatant from the secondary sedimentation tank enters the deep treatment system; the sludge from the primary sedimentation tank enters the primary aerobic tank and sludge thickening tank for treatment; the wastewater from the sludge thickening tank enters the secondary aerobic tank; and the sludge from the sludge thickening tank is returned to the oxidation ditch or recycled for resource recovery. The oxidation ditch consists of an anaerobic zone, an anoxic zone, and an aerobic zone, which proceed sequentially.

5. The method for treating high-COD benzene-containing wastewater from phenol-acetone production according to claim 4, characterized in that, The advanced treatment process is as follows: the supernatant from the secondary sedimentation tank enters the coagulation-flotation physicochemical tank and the terminal sedimentation tank for treatment in sequence, and the water quality from the terminal sedimentation tank reaches the standard for discharge. The flocculent material from the terminal sedimentation tank enters the oxidation ditch for treatment.

6. The method for treating high-COD benzene-containing wastewater from phenol-acetone production according to claim 3, characterized in that, The single-effect falling film evaporator utilizes low-pressure steam, with a pressure of 0.3~0.35MPa.

7. The method for treating high-COD benzene-containing wastewater from phenol-acetone production according to claim 4, characterized in that, The secondary aerobic tank is a contact oxidation tank; the primary sedimentation tank is a radial flow sedimentation tank; and the secondary sedimentation tank is an inclined plate sedimentation tank.

8. A method for treating high-COD benzene-containing wastewater from phenol-acetone production according to claim 7, characterized in that, The acidification hydrolysis tank treatment conditions are: temperature 30~35℃, pH value 6~7.5 and residence time 4~6h; The oxidation tank treatment conditions are as follows: Anaerobic zone: dissolved oxygen concentration less than 0.1 mg / L, temperature 30~35℃, pH value 6~7.5 and retention time 4~6h; Anoxic zone: dissolved oxygen concentration 0.2~0.5 mg / L, temperature 30~35℃, pH value 7~8 and retention time 2~4h; Aerobic zone: dissolved oxygen concentration 2~3 mg / L, temperature 30~35℃, pH value 6.5~8.5 and retention time 3~5h. The treatment conditions for the primary aerobic tank are: dissolved oxygen concentration 2~3 mg / L, temperature 30~35℃, pH value 6.5~8.5 and retention time 2~4 h; The secondary aerobic tank treatment conditions are as follows: dissolved oxygen concentration 3-4 mg / L, combined packing material, air-to-water ratio controlled at 15:1-20:1, temperature 30-35℃, pH value 6.5-8.5, and retention time 3-5 h; the specific surface area of ​​the combined packing material is 450-550 m². 2 / m 3 The filling rate is 60-65%.

9. A method for treating high-COD benzene-containing wastewater from phenol-acetone production according to claim 5, characterized in that, The terminal sedimentation tank adopts an inclined plate sedimentation tank; the coagulation and flotation physicochemical tank adopts a composite flocculant; the composite flocculant is composed of polyγ-glutamic acid, sulfated polysaccharide and chitosan; the dosage of the composite flocculant is 15~30mg / L.

10. The method for treating high COD benzene-containing wastewater in phenol and acetone production according to claim 5, wherein the composite flocculant comprises, by weight, 2.5-5 parts of polyγ-glutamic acid, 2-4.5 parts of sulfated polysaccharide, and 7.5-15.5 parts of chitosan.

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