A method for treating wastewater containing nitrobenzene

Abstract

This invention relates to the field of wastewater treatment technology, specifically to a method for treating nitrobenzene-containing wastewater. The method involves: subjecting the nitrobenzene-containing wastewater to multi-stage cooling crystallization to obtain mixed dinitrobenzene solids and a crystallized filtrate; subjecting the crystallized filtrate to heating and pressurizing oxidation hydrolysis to obtain treated water; the nitrobenzene-containing wastewater comprises 0.5%-1.5% by mass of o-dinitrobenzene, 0.3%-1.0% by mass of m-dinitrobenzene, 0.3%-1.0% by mass of p-dinitrobenzene, and 3%-10% by mass of mononitrobenzene. This treatment method achieves efficient purification and resource utilization of nitrobenzene wastewater while reducing treatment costs and environmental risks, making it a highly efficient, economical, and environmentally friendly method for treating nitrobenzene-containing wastewater. The treated wastewater can directly enter a conventional microbial treatment system without encountering difficulties in microbial degradation.

Description

Technical Field

[0001] This invention relates to a method for treating nitrobenzene-containing wastewater, belonging to the field of wastewater treatment technology. Background Technology

[0002] In the chemical industry, nitrobenzene (usually including mononitrobenzene and dinitrobenzene) is an important raw material widely used in dyes, pesticides, explosives, rubber additives, and other fields. However, the production and use of mixed dinitrobenzene inevitably generates wastewater containing these harmful substances. In the industrial production of mixed dinitrobenzene, the wastewater (raw water) is mainly generated in the post-treatment washing stage of the nitration reaction products: after benzene undergoes a nitration reaction to produce a mixture of mononitrobenzene and dinitrobenzene, it needs to be washed with cold water to remove residual acidic catalysts, unreacted nitrifying agents, and some organic impurities. The nitrobenzene-containing wastewater contains o-dinitrobenzene (0.5%-1.5% by mass), m-dinitrobenzene (0.3%-1.0% by mass), p-dinitrobenzene (0.3%-1.0% by mass), mononitrobenzene (3%-10% by mass), and other pollutants (such as phenol). The suspended solids in the nitrobenzene-containing wastewater are ≤100 mg / L, the COD is 2000-10000 mg / L, the pH is 6.0-7.0, and the temperature of the nitrobenzene-containing wastewater generated during the production process is 80-100℃.

[0003] Existing technology, patent CN102417249B, provides a method for treating nitrobenzene wastewater. This method utilizes nitrobenzene wastewater to prepare coal-water slurry additives, primarily through a series of chemical reactions (sulfonation, acetone sulfonation, polycondensation, etc.) to convert organic matter in the wastewater into coal-water slurry additives. This method is complex, costly, and difficult to control. During the reaction, some byproducts (such as water, alcohols, aldehydes, etc.) may be generated, which may require additional treatment, increasing the complexity and cost of waste treatment.

[0004] Among other conventional wastewater treatment methods, the most common is the use of microorganisms to treat nitrobenzene wastewater. However, nitrobenzene is difficult to degrade, resulting in low microbial degradation efficiency and the potential generation of toxic intermediate products that affect microbial activity. Secondly, microorganisms are sensitive to environmental conditions such as temperature and pH, and are easily affected by fluctuations in the external environment during the treatment process. Furthermore, the treatment cycle is long, requiring a considerable amount of time to achieve the desired effect. In cases of complex wastewater composition, microorganisms may struggle to effectively degrade all pollutants, leading to unstable treatment results.

[0005] The above analysis shows that traditional wastewater treatment methods have problems such as low treatment efficiency, high cost, and secondary pollution, and are not very suitable for the industrial treatment of wastewater containing nitrobenzene. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing a method for treating nitrobenzene-containing wastewater. This method achieves efficient purification and resource utilization of nitrobenzene-containing wastewater while reducing treatment costs and environmental risks. It is an efficient, economical, and environmentally friendly method for treating nitrobenzene-containing wastewater. The treated wastewater can be directly introduced into a conventional microbial treatment system without encountering difficulties in microbial degradation, thus providing a new solution for the treatment of nitrobenzene-containing wastewater.

[0007] The technical solution of this invention to solve the above-mentioned technical problems is as follows: a method for treating nitrobenzene-containing wastewater, wherein the treatment method is as follows:

[0008] S1. The nitrobenzene-containing wastewater is subjected to multi-stage cooling and crystallization, and solid-liquid separation is performed to obtain mixed dinitrobenzene solid and crystallized filtrate.

[0009] S2. The crystallized filtrate is subjected to heating and pressurized oxidative hydrolysis treatment to obtain treated water;

[0010] The nitrobenzene-containing wastewater comprises 0.5%-1.5% by mass of o-dinitrobenzene, 0.3%-1.0% by mass of m-dinitrobenzene, 0.3%-1.0% by mass of p-dinitrobenzene, and 3%-10% by mass of mononitrobenzene. The suspended solids in the nitrobenzene-containing wastewater are ≤100 mg / L, COD is 2000-10000 mg / L, pH is 6.0-7.0, and temperature is 80-100℃.

[0011] Furthermore, in step S1, a two-stage cooling crystallization is adopted, wherein the final crystallization temperature of the first-stage cooling crystallization is 40-45℃; and the final crystallization temperature of the second-stage cooling crystallization is 20-25℃.

[0012] Furthermore, the cooling rate of the first-stage cooling crystallization is 10℃ / min-15℃ / min, the stirring speed is 100-200 rpm, and the isothermal retention time at the final crystallization temperature is 0.5-1.0h.

[0013] The cooling rate for the second-stage cooling crystallization is 5℃ / min-8℃ / min, the stirring speed is 50-100 rpm, and the isothermal retention time at the final crystallization temperature is 1.0-1.5h.

[0014] Furthermore, the specific operation of step S2 is as follows:

[0015] The crystallized filtrate is added to a pressure vessel, the pressure and temperature of the pressure vessel are controlled, and a catalyst and hydrogen peroxide oxidant are added for pressurized oxidation and hydrolysis treatment. Finally, the catalyst is removed to obtain the treated water.

[0016] Furthermore, in step S2, the temperature of the oxidative hydrolysis treatment is 130-180℃, the pressure is 0.1-1.0 MPa, and the oxidative hydrolysis treatment time is 2-12 h.

[0017] Furthermore, the catalyst is at least one of a transition metal salt and a metal oxide.

[0018] Furthermore, the transition metal salt is at least one selected from nickel salt, chromium salt, cobalt salt, manganese salt, copper salt, iron salt, and rhodium salt;

[0019] The metal oxide is at least one of copper oxide, iron oxide, cerium oxide, and zirconium oxide.

[0020] Furthermore, in step S2, the amount of hydrogen peroxide added is 1.5%-4.5% of the mass of the crystallization filtrate; the amount of catalyst added is 0.1%-3.0% of the mass of the crystallization filtrate.

[0021] Furthermore, when the mass content of mononitrobenzene in the crystallization filtrate is not higher than 5%, the amount of hydrogen peroxide added is at least 2% of the mass of the crystallization filtrate;

[0022] For every 1% increase in the mononitrobenzene content in the crystallization filtrate from 5%, the amount of hydrogen peroxide added shall be at least 0.5% of the mass of the crystallization filtrate, based on the 2% mass of the crystallization filtrate.

[0023] Furthermore, the mass content of dinitrate in the treated water is ≤0.01%, and the mass content of mononitrobenzene is ≤0.1%.

[0024] The beneficial effects of this invention are:

[0025] The present invention provides a method for treating nitrobenzene-containing wastewater that addresses the shortcomings of existing nitrobenzene-containing wastewater treatment processes. It is less expensive than direct oxidation methods (energy consumption is significantly reduced; the energy consumption of the treatment method described in this invention is reduced by at least 25% compared to direct oxidation), and shortens the oxidation-hydrolysis treatment cycle (the treatment cycle of the oxidation-hydrolysis treatment method described in this invention is shortened by at least 1 / 2 compared to direct oxidation). Furthermore, the treatment method described in this invention avoids the problems of physical and biological methods being unsuitable for industrial application, is simple to operate, and is more suitable for industrial applications.

[0026] The nitrobenzene-containing wastewater treatment method of the present invention uses a combination of multi-stage cooling crystallization and high-pressure oxidation processes to not only effectively treat nitrobenzene-containing wastewater, but also to achieve continuous treatment of nitrobenzene-containing wastewater, thereby reducing equipment and labor costs.

[0027] The nitrobenzene-containing wastewater treatment method of this invention utilizes multi-stage cooling and crystallization to significantly reduce the content of mixed dinitrobenzene in the wastewater. Furthermore, under high temperature and high pressure, highly oxidizing hydroxyl radicals (-OH) decompose recalcitrant organic compounds such as mononitrobenzene. The entire process can be integrated and continuous. The treated water contains ≤0.01% mixed dinitrobenzene and ≤0.1% mononitrobenzene, allowing for direct final treatment using conventional microbial methods, ultimately achieving compliant wastewater discharge. Moreover, the mixed dinitrobenzene (including o-dinitrobenzene, m-dinitrobenzene, and p-dinitrobenzene) obtained through multi-stage cooling and crystallization meets industrial-grade standards (purity ≥99%), enabling resource reuse.

[0028] Furthermore, in the nitrobenzene-containing wastewater treatment method of the present invention, by reasonably controlling the two-stage cooling crystallization temperature, cooling rate, and stirring speed, the precipitation of mixed dinitrobenzene can be accelerated while avoiding crystal agglomeration leading to equipment blockage and the decrease in purity of mixed dinitrobenzene due to filtrate encapsulation caused by agglomeration. Moreover, the precipitated mixed dinitrobenzene crystals are more uniform, effectively improving the quality of the mixed dinitrobenzene and enabling reuse. In addition, the two-stage cooling crystallization method can save energy while maximizing the recovery of mixed dinitrobenzene, improving the efficiency of subsequent oxidation and hydrolysis treatment, reducing the amount of catalyst and oxidant used, and lowering operating costs.

[0029] In the nitrobenzene-containing wastewater treatment method of the present invention, the combination of cooling crystallization and oxidative hydrolysis treatment makes the overall process simple to operate, low in energy consumption, and achieves efficient wastewater treatment, and also enables the recycling of mixed dinitrobenzene. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a wastewater treatment system containing nitrobenzene.

[0031] In the diagram, 1 is the primary crystallizer; 2 is the integrated heating and cooling unit; 3 is the solid-liquid separation device; 4 is the peristaltic pump; 5 is the secondary crystallizer; 6 is the storage tank; and 7 is the oxidation and hydrolysis treatment device. Detailed Implementation

[0032] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0034] A method for treating nitrobenzene-containing wastewater, the method comprising:

[0035] S1. The nitrobenzene-containing wastewater is subjected to multi-stage cooling and crystallization, and solid-liquid separation is performed to obtain mixed dinitrobenzene solid and crystallized filtrate.

[0036] S2. The crystallized filtrate is subjected to heating and pressurized oxidative hydrolysis treatment to obtain treated water;

[0037] The nitrobenzene-containing wastewater includes o-dinitrobenzene at a mass content of 0.5%-1.5%, m-dinitrobenzene at a mass content of 0.3%-1.0%, p-dinitrobenzene at a mass content of 0.3%-1.0%, and mononitrobenzene at a mass content of 3%-10%. The suspended solids in the nitrobenzene-containing wastewater are ≤100 mg / L, the COD is 2000-10000 mg / L, the pH is 6.0-7.0, and the temperature is 80-100℃.

[0038] Specifically, in step S1, a two-stage cooling crystallization is adopted, wherein the final crystallization temperature of the first-stage cooling crystallization is 40-45℃; and the final crystallization temperature of the second-stage cooling crystallization is 20-25℃.

[0039] Specifically, the cooling rate of the first-stage cooling crystallization is 10℃ / min-15℃ / min, the stirring speed is 100-200 rpm, and the isothermal retention time at the final crystallization temperature is 0.5-1.0h.

[0040] The cooling rate for the second-stage cooling crystallization is 5℃ / min-8℃ / min, the stirring speed is 50-100 rpm, and the isothermal retention time at the final crystallization temperature is 1.0-1.5h.

[0041] During the first stage of cooling crystallization, a relatively fast cooling rate and a relatively fast stirring rate can accelerate the precipitation of mixed dinitrobenzene, avoid crystal agglomeration, and improve crystallization separation efficiency.

[0042] During the second-stage cooling crystallization, a relatively slow cooling rate and a relatively slow stirring rate are used to promote complete crystal growth and reduce the entrainment of fine particles. The purity of the final crystallized mixed dinitrobenzene is ≥99%. Moreover, this two-stage cooling crystallization results in a removal rate of ≥95% of mixed dinitrobenzene from wastewater, which reduces the load on subsequent oxidation and hydrolysis treatments and helps to improve the recovery rate of mixed dinitrobenzene.

[0043] More specifically, during the cooling and crystallization process, a stirring paddle made of tetrafluoroethylene is used for stirring. This material is corrosion-resistant and can reduce the introduction of impurities.

[0044] More specifically, in step S1, after the first stage of cold air crystallization, the solid and liquid are separated at a constant temperature to obtain a portion of mixed dinitrobenzene and a primary filtrate; the primary filtrate is then subjected to a second stage of cooling crystallization, and after the second cooling crystallization, the solid and liquid are separated at a constant temperature again to obtain a second portion of mixed dinitrobenzene and a crystallized filtrate.

[0045] More specifically, solid-liquid separation can be performed using either filtration or centrifugation.

[0046] Specifically, the specific operation of step S2 is as follows:

[0047] The crystallized filtrate is added to a pressure vessel, the pressure and temperature of the pressure vessel are controlled, and a catalyst and hydrogen peroxide oxidant are added for pressurized oxidation and hydrolysis treatment. Finally, the catalyst is removed to obtain the treated water.

[0048] More specifically, the hydrogen peroxide used in this embodiment of the invention has a mass concentration of 27.5%.

[0049] Specifically, in step S2, the temperature of the oxidative hydrolysis treatment is 130-180℃, the pressure is 0.1-1.0 MPa, and the oxidative hydrolysis treatment time is 2-12 hours.

[0050] Preferably, the oxidative hydrolysis treatment time is 2-6 hours.

[0051] Specifically, the catalyst is at least one of a transition metal salt and a metal oxide.

[0052] Specifically, the transition metal salt is at least one selected from nickel salt, chromium salt, cobalt salt, manganese salt, copper salt, iron salt, and rhodium salt;

[0053] The metal oxide is at least one of copper oxide, iron oxide, cerium oxide, and zirconium oxide.

[0054] The nitrobenzene-containing wastewater has a pH of 6-7, which interacts well with transition metal salts (e.g., Fe²⁺ / Cu²⁺). Under these pH conditions, the transition metal salts exhibit high catalytic activity, which helps maintain high catalytic efficiency. Furthermore, it ensures thorough oxidation and hydrolysis treatment, avoiding the formation of intermediate products (such as aniline-based toxic substances), and reducing effluent toxicity by 90%. In the treatment of nitrobenzene-containing wastewater, effluent toxicity is primarily determined by chemical analysis. Chemical analysis directly detects the concentration changes of toxic substances such as anilines (including ammonium nitrobenzene, phenylenediamine, aniline, azoaniline, and other incompletely oxidized products, as well as mononitrobenzene and dinitrobenzene) using HPLC and GC-MS. The concentration of aniline substances before treatment was... C 前 The concentration of aniline compounds after treatment was: C 后 The formula for calculating the toxicity reduction ratio is (1- C后 / C 前 ×100%; "90% reduction in toxicity" refers to the result of comparing the treatment method described in this invention with a control group that did not use transition metal salts (Fe²⁺ / Cu²⁺) catalysis and did not optimize pH conditions. For example, conventional oxidation processes have low catalytic efficiency, resulting in a large amount of aniline intermediates remaining. However, the optimized system completely degrades pollutants through highly efficient catalytic oxidation, reducing the concentration of toxic substances (such as aniline) to 10% of the original level, thereby achieving a significant reduction in toxicity.

[0055] Specifically, in step S2, the amount of hydrogen peroxide added is 1.5%-4.5% of the mass of the crystallization filtrate; the amount of catalyst added is 0.1%-3.0% of the mass of the crystallization filtrate.

[0056] Specifically, when the mass content of mononitrobenzene in the crystallization filtrate is not higher than 5%, the amount of hydrogen peroxide added is at least 2% of the mass of the crystallization filtrate;

[0057] For every 1% increase in the mononitrobenzene content in the crystallization filtrate from 5%, the amount of hydrogen peroxide added shall be at least 0.5% of the mass of the crystallization filtrate, based on the 2% mass of the crystallization filtrate.

[0058] The above dynamic ratio design can avoid the waste of excessive oxidant, while preventing the formation of by-products in the system due to insufficient oxidation, thus reducing processing costs.

[0059] Specifically, the mass content of dinitrate in the treated water is ≤0.01%, and the mass content of mononitrobenzene is ≤0.1%.

[0060] More specifically, the treatment of the nitrobenzene-containing wastewater can use methods such as... Figure 1 The nitrobenzene-containing wastewater treatment system performs continuous treatment, and the specific process is as follows:

[0061] The nitrobenzene-containing wastewater to be treated is discharged into the primary crystallization tank 1. The integrated heating and cooling unit 2 controls the temperature of the primary crystallization tank 1. After the first stage of cooling and crystallization is completed in the primary crystallization tank 1, the primary filtrate, treated by the solid-liquid separation device 3, enters the secondary crystallization tank 5 via a peristaltic pump 4. After the second stage of cooling and crystallization is completed in the secondary crystallization tank 5, the crystallized filtrate, after solid-liquid separation, enters the storage tank 6. The storage tank 6 is connected to the oxidation-hydrolysis treatment device 7 via the peristaltic pump 4. The oxidation-hydrolysis treatment device 7 is equipped with a thermometer and a pressure gauge. The crystallized filtrate undergoes oxidation-hydrolysis treatment in the oxidation-hydrolysis treatment device 7 to obtain treated water. After filtering out the catalyst, the treated water can directly enter the microbial treatment system for microbial decomposition, ultimately yielding water that meets discharge standards.

[0062] Example 1

[0063] The nitrobenzene-containing wastewater includes 1.0% by mass of o-dinitrobenzene, 0.5% by mass of m-dinitrobenzene, 0.8% by mass of p-dinitrobenzene, and 5% by mass of mononitrobenzene. The suspended solids in the nitrobenzene-containing wastewater are ≤100 mg / L, the COD is 5000 mg / L, the pH is 6.0-7.0, and the temperature is 80-100℃.

[0064] A method for treating nitrobenzene-containing wastewater, the method comprising:

[0065] S1. The nitrobenzene-containing wastewater is subjected to two-stage cooling and crystallization:

[0066] The cooling rate for the first-stage cooling crystallization is 10℃ / min, the stirring speed is 100 rpm, the final crystallization temperature is 40℃, and the constant temperature retention time at the final crystallization temperature is 1.0h.

[0067] The cooling rate for the second-stage cooling crystallization is 5℃ / min, the stirring speed is 80 rpm, the final crystallization temperature is 25℃, and the constant temperature retention time at the final crystallization temperature is 1.0h.

[0068] After two-stage cooling crystallization, mixed dinitrobenzene solid and crystallization filtrate were obtained;

[0069] S2. The crystallized filtrate is subjected to heating and pressurized oxidative hydrolysis treatment to obtain treated water;

[0070] The catalyst is copper oxide, the oxidant is hydrogen peroxide, the amount of hydrogen peroxide added is 2% of the mass of the crystallization filtrate, and the amount of catalyst added is 1% of the mass of the crystallization filtrate.

[0071] The oxidation-hydrolysis treatment temperature was 180℃, the pressure was 1.0 MPa, and the oxidation-hydrolysis treatment time was 6 hours.

[0072] Example 2

[0073] The nitrobenzene-containing wastewater includes 0.5% by mass of o-dinitrobenzene, 1.0% by mass of m-dinitrobenzene, 0.3% by mass of p-dinitrobenzene, and 3% by mass of mononitrobenzene. The suspended solids in the nitrobenzene-containing wastewater are ≤100 mg / L, the COD is 3000 mg / L, the pH is 6.0-7.0, and the temperature is 80-100℃.

[0074] A method for treating nitrobenzene-containing wastewater, the method comprising:

[0075] S1. The nitrobenzene-containing wastewater is subjected to two-stage cooling and crystallization:

[0076] The cooling rate for the first-stage cooling crystallization was 15℃ / min, the stirring speed was 200 rpm, the final crystallization temperature was 45℃, and the constant temperature retention time at the final crystallization temperature was 0.5h.

[0077] The cooling rate for the second-stage cooling crystallization was 8℃ / min, the stirring speed was 50 rpm, the final crystallization temperature was 20℃, and the constant temperature retention time at the final crystallization temperature was 1.5h.

[0078] After two-stage cooling crystallization, mixed dinitrobenzene solid and crystallization filtrate were obtained;

[0079] S2. The crystallized filtrate is subjected to heating and pressurized oxidative hydrolysis treatment to obtain treated water;

[0080] The catalyst is copper oxide, the oxidant is hydrogen peroxide, the amount of hydrogen peroxide added is 1.5% of the mass of the crystallization filtrate, and the amount of catalyst added is 0.1% of the mass of the crystallization filtrate.

[0081] The oxidation-hydrolysis treatment temperature was 130℃, the pressure was 1.0 MPa, and the oxidation-hydrolysis treatment time was 12 h.

[0082] Example 3

[0083] The nitrobenzene-containing wastewater includes 1.5% by mass of o-dinitrobenzene, 0.3% by mass of m-dinitrobenzene, 1.0% by mass of p-dinitrobenzene, and 8% by mass of mononitrobenzene. The suspended solids in the nitrobenzene-containing wastewater are ≤100 mg / L, the COD is 6000 mg / L, the pH is 6.0-7.0, and the temperature is 80-100℃.

[0084] A method for treating nitrobenzene-containing wastewater, the method comprising:

[0085] S1. The nitrobenzene-containing wastewater is subjected to two-stage cooling and crystallization:

[0086] The cooling rate for the first-stage cooling crystallization was 15℃ / min, the stirring speed was 150 rpm, the final crystallization temperature was 40℃, and the constant temperature retention time at the final crystallization temperature was 1.0h.

[0087] The cooling rate for the second-stage cooling crystallization was 5℃ / min, the stirring speed was 100 rpm, the final crystallization temperature was 25℃, and the constant temperature retention time at the final crystallization temperature was 1.0h.

[0088] After two-stage cooling crystallization, mixed dinitrobenzene solid and crystallization filtrate were obtained;

[0089] S2. The crystallized filtrate is subjected to heating and pressurized oxidative hydrolysis treatment to obtain treated water;

[0090] The catalyst is iron oxide, the oxidant is hydrogen peroxide, the amount of hydrogen peroxide added is 3.5% of the mass of the crystallization filtrate, and the amount of catalyst added is 3% of the mass of the crystallization filtrate.

[0091] The oxidation-hydrolysis treatment temperature was 160℃, the pressure was 0.6 MPa, and the oxidation-hydrolysis treatment time was 4 hours.

[0092] Example 4

[0093] The nitrobenzene-containing wastewater includes 1.0% by mass of o-dinitrobenzene, 0.5% by mass of m-dinitrobenzene, 0.5% by mass of p-dinitrobenzene, and 10% by mass of mononitrobenzene. The suspended solids in the nitrobenzene-containing wastewater are ≤100 mg / L, the COD is 10000 mg / L, the pH is 6.0-7.0, and the temperature is 80-100℃.

[0094] A method for treating nitrobenzene-containing wastewater, the method comprising:

[0095] S1. The nitrobenzene-containing wastewater is subjected to two-stage cooling and crystallization:

[0096] The cooling rate for the first-stage cooling crystallization was 12℃ / min, the stirring speed was 150 rpm, the final crystallization temperature was 40℃, and the constant temperature retention time at the final crystallization temperature was 1.0h.

[0097] The cooling rate for the second-stage cooling crystallization was 5℃ / min, the stirring speed was 80 rpm, the final crystallization temperature was 20℃, and the constant temperature retention time at the final crystallization temperature was 1.5h.

[0098] After two-stage cooling crystallization, mixed dinitrobenzene solid and crystallization filtrate were obtained;

[0099] S2. The crystallized filtrate is subjected to heating and pressurized oxidative hydrolysis treatment to obtain treated water;

[0100] The catalyst is iron oxide, the oxidant is hydrogen peroxide, the amount of hydrogen peroxide added is 4.5% of the mass of the crystallization filtrate, and the amount of catalyst added is 2% of the mass of the crystallization filtrate.

[0101] The oxidation-hydrolysis treatment temperature was 150℃, the pressure was 0.5 MPa, and the oxidation-hydrolysis treatment time was 4 hours.

[0102] Example 5

[0103] The nitrobenzene-containing wastewater includes 1.0% by mass of o-dinitrobenzene, 0.5% by mass of m-dinitrobenzene, 0.5% by mass of p-dinitrobenzene, and 5% by mass of mononitrobenzene. The suspended solids in the nitrobenzene-containing wastewater are ≤100 mg / L, the COD is 10000 mg / L, the pH is 6.0-7.0, and the temperature is 80-100℃.

[0104] A method for treating nitrobenzene-containing wastewater, the method comprising:

[0105] S1. The nitrobenzene-containing wastewater is subjected to two-stage cooling and crystallization:

[0106] The cooling rate for the first-stage cooling crystallization is 10℃ / min, the stirring speed is 100 rpm, the final crystallization temperature is 40℃, and the constant temperature retention time at the final crystallization temperature is 1.0h.

[0107] The cooling rate for the second-stage cooling crystallization was 5℃ / min, the stirring speed was 50 rpm, the final crystallization temperature was 25℃, and the constant temperature retention time at the final crystallization temperature was 1.5h.

[0108] After two-stage cooling crystallization, mixed dinitrobenzene solid and crystallization filtrate were obtained;

[0109] S2. The crystallized filtrate is subjected to heating and pressurized oxidative hydrolysis treatment to obtain treated water;

[0110] The catalyst is iron oxide, the oxidant is hydrogen peroxide, the amount of hydrogen peroxide added is 2% of the mass of the crystallization filtrate, and the amount of catalyst added is 1% of the mass of the crystallization filtrate.

[0111] The oxidation-hydrolysis treatment temperature was 130℃, the pressure was 0.3 MPa, and the oxidation-hydrolysis treatment time was 2 hours.

[0112] Example 6

[0113] The nitrobenzene-containing wastewater includes 1.0% by mass of o-dinitrobenzene, 0.5% by mass of m-dinitrobenzene, 0.3% by mass of p-dinitrobenzene, and 5% by mass of mononitrobenzene. The suspended solids in the nitrobenzene-containing wastewater are ≤100 mg / L, the COD is 10000 mg / L, the pH is 6.0-7.0, and the temperature is 80-100℃.

[0114] A method for treating nitrobenzene-containing wastewater, the method comprising:

[0115] S1. The nitrobenzene-containing wastewater is subjected to two-stage cooling and crystallization:

[0116] The cooling rate for the first-stage cooling crystallization is 10℃ / min, the stirring speed is 100 rpm, the final crystallization temperature is 40℃, and the constant temperature retention time at the final crystallization temperature is 1.0h.

[0117] The cooling rate for the second-stage cooling crystallization was 5℃ / min, the stirring speed was 50 rpm, the final crystallization temperature was 25℃, and the constant temperature retention time at the final crystallization temperature was 1.5h.

[0118] After two-stage cooling crystallization, mixed dinitrobenzene solid and crystallization filtrate were obtained;

[0119] S2. The crystallized filtrate is subjected to heating and pressurized oxidative hydrolysis treatment to obtain treated water;

[0120] The catalyst is iron oxide, the oxidant is hydrogen peroxide, the amount of hydrogen peroxide added is 2% of the mass of the crystallization filtrate, and the amount of catalyst added is 1% of the mass of the crystallization filtrate.

[0121] The oxidation-hydrolysis treatment temperature was 130℃, the pressure was 0.5 MPa, and the oxidation-hydrolysis treatment time was 2 hours.

[0122] Example 7

[0123] The nitrobenzene-containing wastewater includes 0.5% by mass of o-dinitrobenzene, 1.0% by mass of m-dinitrobenzene, 0.3% by mass of p-dinitrobenzene, and 5% by mass of mononitrobenzene. The suspended solids in the nitrobenzene-containing wastewater are ≤100 mg / L, the COD is 10000 mg / L, the pH is 6.0-7.0, and the temperature is 80-100℃.

[0124] A method for treating nitrobenzene-containing wastewater, the method comprising:

[0125] S1. The nitrobenzene-containing wastewater is subjected to two-stage cooling and crystallization:

[0126] The cooling rate for the first-stage cooling crystallization is 10℃ / min, the stirring speed is 100 rpm, the final crystallization temperature is 40℃, and the constant temperature retention time at the final crystallization temperature is 1.0h.

[0127] The cooling rate for the second-stage cooling crystallization was 5℃ / min, the stirring speed was 50 rpm, the final crystallization temperature was 25℃, and the constant temperature retention time at the final crystallization temperature was 1.5h.

[0128] After two-stage cooling crystallization, mixed dinitrobenzene solid and crystallization filtrate were obtained;

[0129] S2. The crystallized filtrate is subjected to heating and pressurized oxidative hydrolysis treatment to obtain treated water;

[0130] The catalyst is iron oxide, the oxidant is hydrogen peroxide, the amount of hydrogen peroxide added is 2% of the mass of the crystallization filtrate, and the amount of catalyst added is 1% of the mass of the crystallization filtrate.

[0131] The oxidation-hydrolysis treatment temperature was 130℃, the pressure was 0.1 MPa, and the oxidation-hydrolysis treatment time was 2 hours.

[0132] Comparative Example 1

[0133] The same wastewater and method as in Example 1 were used to treat nitrobenzene-containing wastewater, except that step S1 only used primary cooling crystallization (the crystallization conditions were the same as the first-stage cooling crystallization conditions in Example 1). The specific treatment method is as follows:

[0134] S1. The nitrobenzene-containing wastewater is subjected to primary cooling crystallization:

[0135] The cooling rate for crystallization was 10℃ / min, the stirring speed was 100 rpm, the final crystallization temperature was 25℃, and the constant temperature retention time at the final crystallization temperature was 2.0h.

[0136] After primary cooling and crystallization, mixed dinitrobenzene solid and crystallization filtrate were obtained;

[0137] S2. The crystallized filtrate is subjected to heating and pressurized oxidative hydrolysis treatment to obtain treated water;

[0138] The catalyst is copper oxide, the oxidant is hydrogen peroxide, the amount of hydrogen peroxide added is 2% of the mass of the crystallization filtrate, and the amount of catalyst added is 1% of the mass of the crystallization filtrate.

[0139] The oxidation-hydrolysis treatment temperature was 180℃, the pressure was 1.0 MPa, and the oxidation-hydrolysis treatment time was 6 hours.

[0140] Comparative Example 2

[0141] The same wastewater and method as in Example 1 were used to treat nitrobenzene-containing wastewater, except that step S1 only used primary cooling crystallization (the crystallization conditions were the same as the secondary cooling crystallization conditions in Example 1). The specific treatment method is as follows:

[0142] S1. The nitrobenzene-containing wastewater is subjected to primary cooling crystallization:

[0143] The cooling rate for crystallization was 5℃ / min, the stirring speed was 80 rpm, the final crystallization temperature was 25℃, and the constant temperature retention time at the final crystallization temperature was 2.0h.

[0144] After primary cooling and crystallization, mixed dinitrobenzene solid and crystallization filtrate were obtained;

[0145] S2. The crystallized filtrate is subjected to heating and pressurized oxidative hydrolysis treatment to obtain treated water;

[0146] The catalyst is copper oxide, the oxidant is hydrogen peroxide, the amount of hydrogen peroxide added is 2% of the mass of the crystallization filtrate, and the amount of catalyst added is 1% of the mass of the crystallization filtrate.

[0147] The oxidation-hydrolysis treatment temperature was 180℃, the pressure was 1.0 MPa, and the oxidation-hydrolysis treatment time was 6 hours.

[0148] Comparative Example 3

[0149] The same wastewater and method as in Example 1 were used to treat nitrobenzene-containing wastewater, except that the final crystallization temperature of the second-stage cooling crystallization in step S1 was lowered. In Comparative Example 3, the final crystallization temperature of the second-stage cooling crystallization was 10°C. The specific treatment method is as follows:

[0150] S1. The nitrobenzene-containing wastewater is subjected to two-stage cooling and crystallization:

[0151] The cooling rate for the first-stage cooling crystallization is 10℃ / min, the stirring speed is 100 rpm, the final crystallization temperature is 40℃, and the constant temperature retention time at the final crystallization temperature is 1.0h.

[0152] The cooling rate for the second-stage cooling crystallization is 5℃ / min, the stirring speed is 80 rpm, the final crystallization temperature is 10℃, and the constant temperature retention time at the final crystallization temperature is 1.0h.

[0153] After two-stage cooling crystallization, mixed dinitrobenzene solid and crystallization filtrate were obtained;

[0154] S2. The crystallized filtrate is subjected to heating and pressurized oxidative hydrolysis treatment to obtain treated water;

[0155] The catalyst is copper oxide, the oxidant is hydrogen peroxide, the amount of hydrogen peroxide added is 2% of the mass of the crystallization filtrate, and the amount of catalyst added is 1% of the mass of the crystallization filtrate.

[0156] The oxidation-hydrolysis treatment temperature was 180℃, the pressure was 1.0 MPa, and the oxidation-hydrolysis treatment time was 6 hours.

[0157] Comparative Example 4

[0158] The same wastewater and method as in Example 1 were used to treat nitrobenzene-containing wastewater, except that the cooling rate and stirring speed of the second-stage cooling crystallization in step S1 were the same as those in the first-stage cooling crystallization. The specific treatment method is as follows:

[0159] S1. The nitrobenzene-containing wastewater is subjected to two-stage cooling and crystallization:

[0160] The cooling rate for the first-stage cooling crystallization is 10℃ / min, the stirring speed is 100 rpm, the final crystallization temperature is 40℃, and the constant temperature retention time at the final crystallization temperature is 1.0h.

[0161] The cooling rate for the second-stage cooling crystallization was 10℃ / min, the stirring speed was 100 rpm, the final crystallization temperature was 25℃, and the constant temperature retention time at the final crystallization temperature was 1.0h.

[0162] After two-stage cooling crystallization, mixed dinitrobenzene solid and crystallization filtrate were obtained;

[0163] S2. The crystallized filtrate is subjected to heating and pressurized oxidative hydrolysis treatment to obtain treated water;

[0164] The catalyst is copper oxide, the oxidant is hydrogen peroxide, the amount of hydrogen peroxide added is 2% of the mass of the crystallization filtrate, and the amount of catalyst added is 1% of the mass of the crystallization filtrate.

[0165] The oxidation-hydrolysis treatment temperature was 180℃, the pressure was 1.0 MPa, and the oxidation-hydrolysis treatment time was 6 hours.

[0166] Comparative Example 5

[0167] The same wastewater and method as in Example 1 were used to treat nitrobenzene-containing wastewater. The difference was that in Comparative Example 5, only one-stage cooling crystallization was performed. That is, after the first-stage cooling crystallization, no solid-liquid separation was performed. Instead, cooling crystallization continued within the same system under the conditions of the second-stage cooling crystallization. The specific treatment method is as follows:

[0168] S1. Cool and crystallize the nitrobenzene-containing wastewater:

[0169] The cooling rate was controlled at 10℃ / min and the stirring speed at 100 rpm. After the temperature in the system dropped to 40℃, it was kept at the same temperature for 1.0 h. Then the cooling rate was controlled at 5℃ / min and the stirring speed at 80 rpm. The final crystallization temperature was 25℃, and the system was kept at the final crystallization temperature for 1.0 h.

[0170] Finally, solid-liquid separation was performed to obtain mixed dinitrobenzene solid and crystallized filtrate.

[0171] S2. The crystallized filtrate is subjected to heating and pressurized oxidative hydrolysis treatment to obtain treated water;

[0172] The catalyst is copper oxide, the oxidant is hydrogen peroxide, the amount of hydrogen peroxide added is 2% of the mass of the crystallization filtrate, and the amount of catalyst added is 1% of the mass of the crystallization filtrate.

[0173] The oxidation-hydrolysis treatment temperature was 180℃, the pressure was 1.0 MPa, and the oxidation-hydrolysis treatment time was 6 hours.

[0174] Comparative Example 6

[0175] The same wastewater and method as in Example 1 were used to treat nitrobenzene-containing wastewater, except that the amount of hydrogen peroxide added was reduced in Comparative Example 6. The specific treatment method is as follows:

[0176] S1. The nitrobenzene-containing wastewater is subjected to two-stage cooling and crystallization:

[0177] The cooling rate for the first-stage cooling crystallization is 10℃ / min, the stirring speed is 100 rpm, the final crystallization temperature is 40℃, and the constant temperature retention time at the final crystallization temperature is 1.0h.

[0178] The cooling rate for the second-stage cooling crystallization is 5℃ / min, the stirring speed is 80 rpm, the final crystallization temperature is 25℃, and the constant temperature retention time at the final crystallization temperature is 1.0h.

[0179] After two-stage cooling crystallization, mixed dinitrobenzene solid and crystallization filtrate were obtained;

[0180] S2. The crystallized filtrate is subjected to heating and pressurized oxidative hydrolysis treatment to obtain treated water;

[0181] The catalyst is copper oxide, the oxidant is hydrogen peroxide, the amount of hydrogen peroxide added is 1.5% of the mass of the crystallization filtrate, and the amount of catalyst added is 1% of the mass of the crystallization filtrate.

[0182] The oxidation-hydrolysis treatment temperature was 180℃, the pressure was 1.0 MPa, and the oxidation-hydrolysis treatment time was 6 hours.

[0183] Comparative Example 7

[0184] The same wastewater as in Example 1 was used to treat nitrobenzene-containing wastewater, with the difference being that: Comparative Example 7 did not undergo cooling crystallization treatment, but directly performed oxidation hydrolysis treatment (increasing the amount of oxidant and raising the treatment temperature and pressure). The specific treatment method is as follows:

[0185] The wastewater containing nitrobenzene was subjected to heating and pressurized oxidation hydrolysis treatment to obtain treated water.

[0186] The catalyst is copper oxide, the oxidant is hydrogen peroxide, the amount of hydrogen peroxide added is 10% of the mass of the crystallization filtrate, and the amount of catalyst added is 3% of the mass of the crystallization filtrate.

[0187] The oxidation-hydrolysis treatment temperature was 200℃, the pressure was 2.0 MPa, and the oxidation-hydrolysis treatment time was 24 h.

[0188] Comparative Example 8

[0189] The same wastewater and method as in Example 1 were used to treat nitrobenzene-containing wastewater, except that in Comparative Example 8, step S1 only involved the first-stage cooling crystallization. The specific treatment method is as follows:

[0190] S1. Cool and crystallize the nitrobenzene-containing wastewater:

[0191] The cooling rate for crystallization was 10℃ / min, the stirring speed was 100 rpm, the final crystallization temperature was 40℃, and the constant temperature retention time at the final crystallization temperature was 1.0 h.

[0192] After cooling and crystallization, a mixture of dinitrobenzene solids and a crystalline filtrate were obtained.

[0193] S2. The crystallized filtrate is subjected to heating and pressurized oxidative hydrolysis treatment to obtain treated water;

[0194] The catalyst is copper oxide, the oxidant is hydrogen peroxide, the amount of hydrogen peroxide added is 2% of the mass of the crystallization filtrate, and the amount of catalyst added is 1% of the mass of the crystallization filtrate.

[0195] The oxidation-hydrolysis treatment temperature was 180℃, the pressure was 1.0 MPa, and the oxidation-hydrolysis treatment time was 6 hours.

[0196] I. The water treated in the above examples and comparative examples was tested. The contents of mixed dinitrobenzene (ortho, meta, and para isomers) and mononitrobenzene in the treated water were determined by gas chromatography-mass spectrometry (GC-MS, referring to HJ 716-2014 standard). After enriching the target analytes by liquid-liquid extraction, the isomers were separated by chromatographic column and quantified by mass spectrometry. The purity of the recovered mixed dinitrobenzene was evaluated by gas chromatography-flame ionization detection (GC-FID, according to GB / T 9335-2009 standard). The proportion of each isomer and the total purity were calculated based on the peak area normalization method. The specific test results are shown in Table 1 below.

[0197] Table 1 Test Results

[0198]

[0199] As can be seen from the data in the table above: Examples 1-7, using the treatment method described in this invention, treated nitrobenzene-containing wastewater. The mass content of mixed dinitrobenzene in the treated water was ≤0.01%, and the mass content of mononitrobenzene was ≤0.1%. The recovered mixed dinitrobenzene (purity ≥94.5%) can be directly used to prepare high-value-added chemical products such as dye intermediates (e.g., phenylenediamine), pesticide raw materials (e.g., nitrophenol herbicides), rubber additives (antioxidants and vulcanization accelerators), and precursors for energetic materials. Its purity meets the quality requirements of raw materials in the fine chemical industry, achieving resource recycling. Moreover, the recovery rate of mixed dinitrobenzene is high, all reaching over 75%. The processing method described in this invention adopts a step-by-step cooling crystallization operation. In the first-stage cooling crystallization, high-melting-point o-dinitrobenzene (melting point 89℃) can be preferentially precipitated, reducing the co-precipitation of impurities. In the second-stage cooling crystallization process, the temperature is slowly lowered to control the crystal growth rate, thereby obtaining a crystal product with large particle size (D50>50 μm) and high purity (≥98.5%).

[0200] A comparison of the experimental results from Comparative Examples 1, 2, and 1 shows that single-stage cooling crystallization leads to rapid crystal nucleation and growth, resulting in irregular crystal lattices that easily trap unreacted raw materials (such as phenol and nitrifying agent residues) and byproducts (such as nitrophenols). Furthermore, without stepwise crystallization, small crystals redissolve and deposit on the surface of larger crystals due to their high surface energy, burying impurities and reducing the purity of the mixed dinitrobenzene (the purity of the mixed dinitrobenzene in Comparative Examples 1-2 was 85%-88.3%, while the purity of the mixed dinitrobenzene in Example 1 was 98.5%). In addition, the instantaneous large-scale crystallization also causes a sharp increase in the concentration of suspended solids, leading to hydrodynamic blockage, increased equipment pressure drop, and decreased separation efficiency. The recovered mixed dinitrobenzene cannot meet industrial standards, and the equipment is prone to blockage during processing, causing significant inconvenience to production.

[0201] A comparison of the experimental results from Comparative Example 3 and Example 1 shows that when the final crystallization temperature drops to 10°C, other impurities in the wastewater precipitate out (such as dinitrophenol and nitrophenol), leading to a decrease in the purity of the mixed dinitrobenzene. Simultaneously, the crystal growth rate slows down at low temperatures, making it easier to form fine crystals (<10μm), increasing the specific surface area, adsorbing more impurities, and mixing them in the mixed dinitrobenzene, ultimately causing the mixed dinitrobenzene to fail to meet product standards.

[0202] A comparison of the experimental results from Comparative Example 4 and Example 1 shows that when the second stage uses the same cooling rate (10℃ / min) and stirring speed (100rpm) as the first stage, it leads to an imbalance in crystal growth kinetics. The specific reasons are as follows:

[0203] Rapid cooling: When the final temperature of the second stage is 25℃, the supersaturation increases instantaneously (ΔC / Δt is too large), triggering explosive nucleation and forming crystal clusters (agglomeration).

[0204] High-shear stirring: This breaks down crystal clusters into microcrystals (<5 μm). The microcrystals adsorb dissolved organic matter (such as mononitrobenzene) onto their surfaces, and during solid-liquid separation, they penetrate the filter membrane, reducing the recovery rate of mixed dinitrobenzene (63% recovery rate in Comparative Example 4 and 95% recovery rate in Example 1). Therefore, using the first-stage and second-stage cooling crystallization conditions defined in this invention is more conducive to achieving good wastewater treatment while ensuring the acquisition of high-quality mixed dinitrobenzene.

[0205] A comparison of the experimental results of Comparative Example 5 and Example 1 shows that if two-stage crystallization proceeds continuously within the same system and the first-stage crystal is not removed in time, the following problems will occur:

[0206] Crystal redissolution-recrystallization: The primary crystals partially dissolve during the secondary cooling process, and new impurities are introduced during recrystallization, reducing the purity to 83.6%.

[0207] A comparison of the experimental results from Comparative Example 6 and Example 1 shows that when the amount of hydrogen peroxide added decreased from 2% to 1.5%, the amount of hydroxyl radicals (·OH) generated was insufficient (Fenton reaction kinetics), the degradation pathway of mononitrobenzene was blocked, and the toxicity of aniline substances (LC50≈1 mg / L) was much higher than that of nitrobenzene, resulting in increased effluent toxicity (0.33% mononitrobenzene residue in Comparative Example 6, aniline was not detected but was actually present). The dynamic proportion design (adding 0.5% H2O2 for every 1% mononitrobenzene) controlled by stoichiometry (C∶H2O2≈1∶3) ensured sufficient ·OH and complete mineralization into CO2 and H2O.

[0208] A comparison of the experimental results from Comparative Example 7 and Example 1 shows that without crystallization pretreatment (Comparative Example 7), the residue of mixed dinitrobenzene was 0.0667%, and that of mononitrobenzene was 0.667%, far exceeding the results of Example 1. This is because mixed dinitrobenzene (logKow=1.98) has low solubility in high-temperature water (≈0.1 g / L), resulting in high solid-liquid mass transfer resistance and low reaction efficiency during direct oxidation. Furthermore, the competitive consumption of ·OH by multiple components (mixed dinitrobenzene, mononitrobenzene, and phenol) leads to differences in degradation priority and thus increases the residue levels.

[0209] A comparison of the experimental results of Comparative Example 8 and Example 1 shows that if only the first-stage cooling crystallization is carried out in step S1, the yield of mixed dinitrobenzene will decrease significantly, and the wastewater entering step S2 will contain a large amount of mixed dinitrobenzene, ultimately resulting in the treated wastewater still containing a high content of mixed dinitrobenzene and mononitrobenzene.

[0210] II. Microbial treatment suitability analysis

[0211] (1) Feasibility of Examples 1-7

[0212] Data support: The COD content in the wastewater after treatment in Examples 1-7 is 400~600 mg / L, the mixed dinitrobenzene content is ≤0.01%, and the mononitrobenzene content is ≤0.1%, which meets the requirements for influent for microbial treatment (COD<1000 mg / L, nitrobenzene content<2 mg / L).

[0213] Biochemical mechanisms:

[0214] In the aerobic biological treatment of nitrobenzene-containing wastewater, Pseudomonas putida achieves complete degradation of pollutants through a specific enzyme system. The specific process is as follows:

[0215] 1. Hydroxylation and denitration of nitrobenzene:

[0216] A two-component oxygenase system secreted by *Pseudomonas* (containing reductase RedA2, ferroredoxin Fdx1, and oxidase OxB) catalyzes a key reaction. Under dissolved oxygen conditions ≥4 mg / L and 30°C, this enzyme system activates oxygen molecules and inserts them into the nitrobenzene ring, initially generating an unstable cis-dihydroxy intermediate, which is then de-nitro (-NO2) to convert to catechol. This step is energy-dependent by NADH and releases nitrite ions (NO2⁻).

[0217] 2. Ring-opening cleavage of catechol:

[0218] The generated catechol undergoes meta-ring-opening (C2-C3 bond cleavage) catalyzed by catechol 2,3-dioxygenase (C23O). In a weakly alkaline environment at pH 7.0, C23O binds to O2, causing the benzene ring to break, producing 2-hydroxymucosinate semialdehyde, which is then dehydrogenated and hydrolyzed by a hydrolase (HMSD) to convert into the linear chain compound β-ketoadipic acid. This process completely avoids the toxicity accumulation problem associated with the ortho-ring-opening pathway.

[0219] 3. β-Ketoadipic acid mineralization:

[0220] β-Ketoadipic acid is gradually cleaved into acetyl-CoA through a series of enzymatic reactions (succinyl-CoA transfer, decarboxylation, and hydration), and finally enters the tricarboxylic acid (TCA) cycle, where it is completely mineralized into CO2 and H2O, releasing energy (28 ATP molecules are produced per molecule of nitrobenzene).

[0221] Toxicity Control: The wastewater treated by the method described in this invention completely eliminates secondary toxic substances generated during the process: aniline (C6H5NH2), o / m / p-nitroaniline (C6H6N2O2), o / p-toluidine (C7H9N), o / m-phenylenediamine (C6H8N2), and p-chloroaniline (C6H6ClN). These substances are generated from incomplete oxidation due to nitro reduction or free radical recombination (e.g., mononitrobenzene is oxidized to aniline when H2O2 is insufficient). This invention employs a triple blocking mechanism—(1) dynamic H2O2 addition (≥2%) to ensure direct mineralization; (2) transition metals (Cu) at pH 6-7. 2+ / Fe 3+ (3) High-efficiency catalytic ring opening; (4) High temperature of 130-180℃ inhibits side reactions. The above substances were not detected in the wastewater after treatment in Examples 1-7, thus avoiding inhibition of microbial activity (IC50=5 mg / L).

[0222] (2) Causes of failure in comparative examples 7-8

[0223] Data comparison: After treatment, Comparative Example 7 showed 0.0667% dinitrobenzene and >10 mg / L aniline, both far exceeding the tolerance limit of microorganisms. Comparative Example 8, due to its low single-stage crystallization recovery rate, resulted in overload of the oxidation section. Incomplete oxidation led to the generation of highly toxic m-phenylenediamine, which also resulted in nitrobenzene residue, synergistically damaging the metabolic function of microorganisms.

[0224] Toxicity mechanism:

[0225] Cell membrane damage: The wastewater treated in Comparative Examples 7-8 contained aniline. The presence of aniline disrupts the lipid bilayer of the cell membrane (logKow=0.9), leading to leakage of intracellular enzymes (such as dehydrogenases). Consequently, the wastewater treated in Comparative Examples 7-8 cannot be used for the next stage of microbial treatment.

[0226] Metabolic inhibition: The nitrobenzene content in the wastewater after treatment in Comparative Examples 7-8 was relatively high. Nitrobenzene competitively inhibits the activity of NADH dehydrogenase, blocks the electron transport chain (ETC), and hinders ATP synthesis. This also means that the wastewater after treatment in Comparative Examples 7-8 cannot be treated by the next stage of microbial treatment.

[0227] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0228] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for treating nitrobenzene-containing wastewater, characterized in that, The processing method is as follows: S1. The nitrobenzene-containing wastewater is subjected to multi-stage cooling and crystallization to obtain mixed dinitrobenzene solid and crystallization filtrate; S2. The crystallized filtrate is subjected to heating and pressurized oxidative hydrolysis treatment to obtain treated water; The nitrobenzene-containing wastewater includes o-dinitrobenzene at a mass content of 0.5%-1.5%, m-dinitrobenzene at a mass content of 0.3%-1.0%, p-dinitrobenzene at a mass content of 0.3%-1.0%, and mononitrobenzene at a mass content of 3%-10%. The suspended solids in the nitrobenzene-containing wastewater are ≤100 mg / L, the COD is 2000-10000 mg / L, the pH value is 6.0-7.0, and the temperature is 80-100℃. In step S1, two-stage cooling crystallization is used, wherein the final crystallization temperature of the first-stage cooling crystallization is 40-45℃; and the final crystallization temperature of the second-stage cooling crystallization is 20-25℃. The cooling rate of the first-stage cooling crystallization is 10℃ / min-15℃ / min, the stirring speed is 100-200 rpm, and the isothermal retention time at the final crystallization temperature is 0.5-1.0h. The cooling rate for the second-stage cooling crystallization is 5℃ / min-8℃ / min, the stirring speed is 50-100 rpm, and the isothermal retention time at the final crystallization temperature is 1.0-1.5h. The specific operation of step S2 is as follows: the crystallized filtrate is added to a pressure vessel, the pressure and temperature of the pressure vessel are controlled, and a catalyst and hydrogen peroxide oxidant are added for pressurized oxidation and hydrolysis treatment. Finally, the catalyst is removed to obtain the treated water. The amount of hydrogen peroxide added is 1.5%-4.5% of the mass of the crystallization filtrate; the amount of catalyst added is 0.1%-3.0% of the mass of the crystallization filtrate. When the mass content of mononitrobenzene in the crystallization filtrate is not higher than 5%, the amount of hydrogen peroxide added is at least 2% of the mass of the crystallization filtrate. For every 1% increase in the mononitrobenzene mass content of the crystallization filtrate from 5%, the amount of hydrogen peroxide added shall be at least 0.5% of the mass of the crystallization filtrate, based on the 2% mass content of the crystallization filtrate. In step S2, the temperature of the oxidative hydrolysis treatment is 130-180℃, the pressure is 0.1-1.0 MPa, and the oxidative hydrolysis treatment time is 2-12 h.

2. The method for treating nitrobenzene-containing wastewater according to claim 1, characterized in that, The catalyst is at least one of a transition metal salt or a metal oxide.

3. The method for treating nitrobenzene-containing wastewater according to claim 2, characterized in that, The transition metal salt is at least one of nickel salt, chromium salt, cobalt salt, manganese salt, copper salt, iron salt, and rhodium salt; The metal oxide is at least one of copper oxide, iron oxide, cerium oxide, and zirconium oxide.

4. The method for treating nitrobenzene-containing wastewater according to claim 1, characterized in that, The treated water has a dinitrate content of ≤0.01% and a mononitrobenzene content of ≤0.1%.

Images