Method for treating nitrogen-containing wastewater in chemical industry and preparing inorganic salt

Abstract

The present application belongs to the field of wastewater treatment, and particularly relates to a method for treating nitrogen-containing wastewater in the chemical industry and preparing inorganic salts. The treatment method comprises pretreatment, a nitrification reaction system, concentration, hardness removal, fluorine removal, silicon removal, nanofiltration separation, inorganic salt proportion adjustment, and evaporation system entry for inorganic salt preparation. The method can effectively remove nitrogen-containing organic matter, achieve nitrogen-containing wastewater treatment and inorganic salt preparation, and obtain different resource products as needed, which is economic and efficient. The present application also provides a treatment system for the method.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment, specifically relating to a method for treating nitrogen-containing wastewater from the chemical industry and preparing inorganic salts. It is also applicable to high-nitrogen wastewater from other industries, such as food processing, pharmaceuticals, and aquaculture. Background Technology

[0002] Nitrogenous wastewater (containing ammonia nitrogen and nitrates) generated during chemical production processes has become a major challenge for environmental management due to its high toxicity, recalcitrant nature, and tendency to cause eutrophication. Traditional treatment technologies typically involve two steps: nitrification and denitrification. Ammonia nitrogen is converted into nitrate, which is then reduced back into nitrogen gas by consuming a carbon source and released into the atmosphere. Because the carbon-to-nitrogen ratio in chemical wastewater is often unbalanced, additional carbon sources are frequently required, and this process also results in carbon dioxide emissions. Furthermore, these traditional methods suffer from large land requirements, high civil engineering investment, and high operating costs, and fail to achieve resource utilization of the high-value-added nitrates. Summary of the Invention

[0003] This invention addresses the technical challenges of treating nitrogen-containing wastewater in the chemical industry by proposing an innovative treatment method. This method involves key technical aspects such as a nitrification reaction system, a concentration step, inorganic salt ratio adjustment, and evaporation system for preparing inorganic salts. This technical solution possesses strong adaptability to different water qualities, requires no additional carbon source, and efficiently achieves the treatment of nitrogen-containing wastewater and the synergistic preparation of inorganic salts. This method is not only economical and efficient but also helps reduce carbon emissions, achieving the harmless treatment of pollutants and the resource utilization of high-value-added products. Furthermore, this technology demonstrates significant advantages in terms of civil engineering investment, land area, and operating costs, while simultaneously considering both environmental and economic benefits, showcasing broad application potential.

[0004] A method for treating nitrogen-containing wastewater in the chemical industry and preparing inorganic salts includes the following steps: (1) Pretreatment of nitrogen-containing wastewater from the chemical industry for oil removal, removal of organic pollutants and / or degradation of macromolecular organic matter; (2) The pretreated wastewater undergoes nitrification. (3) The nitrified wastewater is concentrated to obtain concentrated water and product water. The product water can be discharged in compliance with standards or reused. (4) The concentrated water is treated by at least one of the following methods: hardening removal, defluorination and desilicon removal, decarbonization, RO, organic concentration and advanced oxidation, to obtain treated concentrated brine; (5) The concentrated brine is separated by nanofiltration to obtain nanofiltration concentrate and nanofiltration permeate; the nanofiltration concentrate is first evaporated and crystallized or frozen and crystallized to obtain the first crystal containing sodium sulfate, or the nanofiltration concentrate is treated by precipitation and then fed into the nitrification system; the nanofiltration permeate is concentrated by evaporation or membrane concentration to obtain concentrate. (6) Decarbonize and adjust the pH of the concentrate, and then process it in the evaporation system using any of the methods in ai, according to the inorganic salt components and resource utilization requirements of the concentrate; a: The inorganic components are mainly sodium chloride and sodium nitrate. The resource-based product requires sodium chloride and potassium nitrate. Potassium chloride is added to adjust the reaction, and after adjustment, the proportions of each ion satisfy [n(K]]. + )+ n(Cl - )]: [n(Na + )+ n(NO 3- )]=0.8-1.2; then, the evaporation and concentration, evaporation and crystallization are carried out in sequence to obtain the second crystal (sodium chloride product salt), and the freeze crystallization is carried out to obtain the third crystal (agricultural grade potassium nitrate). The optional third crystal is refined to obtain the fourth crystal (industrial grade potassium nitrate). The remaining mother liquor of the third crystal and / or the fourth crystal is evaporated and dried to obtain miscellaneous salt or partially returned to step (4) for further processing. b: The inorganic components are mainly sodium chloride and sodium nitrate, and the resource-based products are required to be sodium chloride and sodium nitrate; the second crystal (sodium chloride product salt) is obtained by evaporation and concentration, evaporation and crystallization, and the third crystal (industrial grade sodium nitrate) is obtained by freeze crystallization. The optional third crystal is refined to obtain the fourth crystal (molten salt grade sodium nitrate). The remaining mother liquor of the third crystal and / or the fourth crystal is evaporated and dried to obtain mixed salt or partially recycled to step (4) for further processing. c: The inorganic components are mainly sodium chloride and potassium chloride. The resource-based product requires sodium chloride and potassium nitrate. Sodium nitrate is added to adjust the reaction, and after adjustment, the proportions of each ion satisfy [n(K + )+ n(Cl - )]: [n(Na + )+ n(NO 3- )]=0.8-1.2; then, the evaporation and concentration, evaporation and crystallization are carried out in sequence to obtain the second crystal (sodium chloride product salt), and the freeze crystallization is carried out to obtain the third crystal (agricultural grade potassium nitrate). The optional third crystal is refined to obtain the fourth crystal (industrial grade potassium nitrate). The remaining mother liquor of the third crystal and / or the fourth crystal is evaporated and dried to obtain miscellaneous salt or partially returned to step (4) for further processing. d: The inorganic components are mainly sodium chloride and potassium chloride, and the resource-based products are required to be sodium chloride and potassium chloride. The product is then subjected to evaporation and concentration, evaporation and crystallization to obtain the second crystal (sodium chloride product salt), and freeze crystallization to obtain the third crystal (industrial grade potassium chloride). The remaining mother liquor of the third crystal is evaporated and dried to obtain mixed salt or partially returned to step (4) for further processing.

[0005] e: The inorganic components are mainly sodium nitrate and potassium nitrate. The resource-based products are required to be sodium nitrate and potassium nitrate. The product is then subjected to evaporation and concentration, evaporation and crystallization to obtain the second crystal (sodium nitrate product salt), and freeze crystallization to obtain the third crystal (industrial grade potassium nitrate). The remaining mother liquor of the third crystal is evaporated and dried to obtain mixed salt or partially returned to step (4) for further processing.

[0006] f: The inorganic components are mainly sodium chloride, potassium chloride, and sodium nitrate. The resource-based products are required to be sodium chloride, potassium chloride, and sodium nitrate. First, the product is concentrated by evaporation and then cooled and crystallized by combined evaporation and crystallization to obtain the second crystal (sodium nitrate product salt). The product is obtained by evaporation and crystallization to obtain a mixed salt of sodium chloride and potassium chloride. The remaining mother liquor of the mixed salt is then processed by method c or method d to obtain resource-based product salt of sodium chloride and potassium chloride. The remaining mother liquor is further processed by evaporation and drying to obtain mixed salt or partially returned to the heavy metal removal step in step (4).

[0007] g: The inorganic components are mainly sodium chloride, potassium chloride, and potassium nitrate. The resource-based products are required to be sodium chloride, potassium chloride, and potassium nitrate. First, the product is evaporated and concentrated, and then cooled and crystallized. The second crystal (potassium nitrate product salt) is obtained by combined evaporation and crystallization. The mixed salt of sodium chloride and potassium chloride is obtained by evaporation and crystallization. The remaining mother liquor of the mixed salt is then processed by method c or method d to obtain resource-based product salt of sodium chloride and potassium chloride. The remaining mother liquor is evaporated and dried to obtain mixed salt or partially returned to the heavy metal removal step in step (4) for further processing.

[0008] h: The inorganic components are mainly sodium chloride, sodium nitrate and potassium nitrate. The resource-based products are required to be sodium chloride, sodium nitrate and potassium nitrate. First, evaporation and concentration are carried out, and then evaporation and crystallization are combined with cooling crystallization to obtain the second crystal (sodium chloride product salt). Cooling crystallization is used to obtain a mixed salt of sodium nitrate and potassium nitrate. The remaining mother liquor of the mixed salt is then processed by method e to obtain resource-based product salts of sodium nitrate and potassium nitrate. The remaining mother liquor is evaporated and dried to obtain mixed salt or partially returned to the heavy metal removal step in step (4) for further processing.

[0009] i: The inorganic components are mainly potassium chloride, sodium nitrate and potassium nitrate. The resource-based products are required to be potassium chloride, sodium nitrate and potassium nitrate. First, evaporation and concentration are carried out, and then evaporation and crystallization are combined with cooling crystallization to obtain the second crystal (potassium chloride product salt). Cooling crystallization is used to obtain a mixed salt of sodium nitrate and potassium nitrate. The remaining mother liquor of the mixed salt is then processed by method e to obtain resource-based product salt of sodium nitrate and potassium nitrate. The remaining mother liquor is evaporated and dried to obtain mixed salt or partially returned to the heavy metal removal step in step (4) for further processing.

[0010] Furthermore, in step (1), one or more of the following methods are used for pretreatment: oil separation, air flotation, and anaerobic digestion.

[0011] Furthermore, in step (1), the COD of the nitrogen-containing wastewater is reduced to 600-1500 mg / L after pretreatment, and the COD removal rate of the pretreatment process is 15-25%.

[0012] Further, in step (1), the nitrogen-containing wastewater in the chemical industry is nitrogen-containing wastewater from the coal chemical industry, wastewater containing ammonia nitrogen and nitrate, concentrated brine containing ammonia nitrogen and nitrate from the industry, or high-nitrogen wastewater from other fields, such as the food processing industry, pharmaceutical industry, and aquaculture industry; COD is 800-2000 mg / L, BOD is 300-1000 mg / L, and ammonia nitrogen content is 200-500 mg / L.

[0013] Further, in step (2), oxygenation is carried out to make the dissolved oxygen concentration in the wastewater 2-6 mg / L, the nitrification reaction time 6-48 hours, the pH 6-8, and the temperature 25-35℃; more preferably, the dissolved oxygen concentration in the wastewater is 2-4 mg / L, the reaction time is 24-48 hours, the pH is 7-8, and the temperature is 30-35℃.

[0014] Furthermore, in step (2), the nitrate nitrogen concentration in the nitrified wastewater is 500-2000 mg / L, and the COD is 100-200 mg / L.

[0015] Furthermore, in step (3), the concentration is achieved by filtration, ultrafiltration (UF), and reverse osmosis (RO).

[0016] Furthermore, in step (3), the produced water is discharged or reused after meeting the standards.

[0017] Furthermore, in step (4), residual organic matter in the product water is removed by advanced oxidation.

[0018] Further, in step (5), the first crystal is obtained by evaporation crystallization at a temperature of 80~120℃ and a pressure of 70-200 KPa (A); or the first crystal is obtained by freeze crystallization at a temperature of -10~30℃ and a pressure of atmospheric pressure.

[0019] Furthermore, in step (5), the concentrated brine is first evaporated and then frozen to separate sodium sulfate and sodium chloride. The mother liquor from the frozen crystallization is diluted and then separated by nanofiltration in step (5). Furthermore, in step (5), the first crystal containing sodium sulfate meets the Class II qualified product standard specified in GB / T 6009-2014, and the sodium sulfate content is above 97.0 wt%.

[0020] Furthermore, in step (6), the typical water quality entering the evaporation system can be: TDS of 60,000-80,000 mg / L, chloride ion concentration of 15,000-20,000 mg / L, sulfate concentration of 10,000-15,000 mg / L, and nitrate concentration of 13,000-16,000 mg / L.

[0021] Further, in step (6), the temperature at which the second crystal (sodium chloride product salt) is obtained by evaporation crystallization is 80-120°C and the pressure is 70-200 KPa (A).

[0022] Furthermore, in step (6), the temperature for obtaining the third crystal (agricultural grade potassium nitrate) by freeze crystallization is 20-40°C, and the pressure is atmospheric pressure.

[0023] Furthermore, in step (6), the temperature for obtaining the third crystal (industrial grade sodium nitrate) by freeze crystallization is 20-40°C, and the pressure is atmospheric pressure; Furthermore, in step (6), the temperature at which the third crystal (industrial grade potassium chloride) is obtained by cooling crystallization is 50-70°C and the pressure is 10-30 kPa.

[0024] Furthermore, in step (6), the method further includes refining the second crystal, and the refined product obtained meets at least the first-grade industrial dry salt standard specified in GB / T5462-2015, with sodium chloride content of 98.5 wt% or higher.

[0025] Furthermore, in step (6), the method further includes refining the third crystal to obtain a refined product, wherein the refined product contains more than 99.0 wt% sodium nitrate or potassium nitrate; more preferably, the refined crystallization uses the product water from step (3).

[0026] Furthermore, in step (6), the condensate generated by the evaporation system is reused or discharged in compliance with the standard if it meets the reuse standard.

[0027] This invention also provides a treatment system for treating nitrogen-containing wastewater and preparing inorganic salts in the chemical industry, comprising: a process one treatment system (mainly for treating nitrogen-containing wastewater) and a process two treatment system (mainly for preparing inorganic salts through an evaporation system). The process one treatment system includes a conditioning pretreatment system, a nitrification reaction system, a wastewater reuse system, a concentrated brine treatment system, a nanofiltration system (NF system), and a sodium sulfate evaporator (or a freeze crystallizer) connected in sequence. The conditioning pretreatment system includes processes such as filtration, oil removal, air flotation, and anaerobic digestion, which are used to remove oil, remove organic pollutants, and / or degrade macromolecular organic matter. The nitrification system is an oxygenated nitrification system in which nitrifying bacteria convert nitrogenous substances into nitrates. The wastewater reuse system includes processes such as filtration, ultrafiltration (UF), and reverse osmosis (RO). Its concentrated water enters the concentrated brine treatment system and its produced water can meet the discharge standards or be reused. The concentrated brine treatment system includes processes such as hardening and desiliconization, decarbonization, reverse osmosis (RO), organic concentration, and optional advanced oxidation. The treated concentrated brine is then fed into a nanofiltration system, and the produced water can meet discharge standards or be reused. The nanofiltration concentrate from the nanofiltration system enters the sodium sulfate evaporator, and the nanofiltration permeate is connected to the process two treatment system. The sodium sulfate evaporator evaporates or freezes nanofiltration concentrate to obtain sodium sulfate product salt (first crystal), or precipitates it to obtain calcium sulfate sludge as ordinary solid waste. The second process system includes, in sequence, a decarbonization and pH adjustment system, an optional reaction adjustment system, an evaporation and concentration system, a sodium chloride evaporation and crystallization system, a potassium nitrate crystallization system (which can be replaced by a sodium nitrate crystallization system or a potassium chloride crystallization system), an optional potassium nitrate refining system (which can be replaced by a sodium nitrate refining system), an evaporation mother liquor tank, a reflux device, and a miscellaneous salt drying device. The reaction regulation system is used to add potassium chloride or sodium nitrate to adjust the ion level. Whether a reaction regulation system is needed depends on the inorganic salt composition of the concentrate and the requirements of the resource-based products. The sodium chloride evaporation crystallization system can obtain sodium chloride product salt (second crystal), and the mother liquor after evaporation enters the potassium nitrate crystallization system (which can be replaced by a sodium nitrate crystallization system or a potassium chloride crystallization system). The potassium nitrate crystallization system can obtain agricultural-grade potassium nitrate. Depending on the needs, it may be necessary to enter an optional potassium nitrate refining system. The mother liquor from the potassium nitrate crystallization system and the optional potassium nitrate refining system enters an evaporation mother liquor tank or a reflux device, which can also yield industrial-grade sodium nitrate and potassium chloride product salts. The agricultural-grade potassium nitrate, industrial-grade sodium nitrate, and potassium chloride product salts can be refined in a nitrate or chloride refining system. The dried salt obtained by the aforementioned salt drying equipment is then transported off-site for disposal. The condensate from the evaporation and concentration system, sodium chloride evaporation and crystallization system, potassium nitrate crystallization system (which can be replaced by a sodium nitrate crystallization system or a potassium chloride purification system), and potassium nitrate refining system (which can be replaced by a sodium nitrate refining system) meets the reuse standards and can be reused.

[0028] Compared with the prior art, the beneficial effects of the present invention include at least the following: 1. By performing pretreatment, nitrification, concentration and crystallization on nitrogen-containing wastewater from the chemical industry, nitrogen-containing organic matter can be effectively removed and a first crystal containing sodium sulfate can be prepared.

[0029] 2. Before entering the evaporation system, by adjusting the ion ratio of inorganic salts in the concentrate, two kinds of inorganic salts can be obtained in the evaporation system through simple evaporation crystallization and freeze crystallization, and different resource-based products can be obtained as needed.

[0030] 3. The produced water, condensate, and mother liquor generated during the preparation process can be recycled, improving economic efficiency.

[0031] 4. This technical solution has strong water quality adaptability, requires no additional carbon source, and can efficiently achieve the treatment of nitrogen-containing wastewater and the synergistic preparation of inorganic salts.

[0032] 5. This method is not only economical and efficient, but also helps to reduce carbon emissions, achieve the harmless treatment of pollutants, and realize the resource utilization of high-value-added nitrate products.

[0033] 6. This technology shows significant advantages in terms of civil engineering investment, land area, and operating costs, while also taking into account both environmental and economic benefits. Attached Figure Description

[0034] Figure 1 This invention relates to a treatment system and process for treating nitrogen-containing wastewater in the chemical industry and preparing inorganic salts. Detailed Implementation

[0035] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Examples of the embodiments are shown in the accompanying drawings. It should be understood that the specific embodiments described in the following embodiments of the invention are merely illustrative examples of specific implementations of the invention and are intended to explain the invention, but do not constitute a limitation thereof.

[0036] The endpoints of the ranges and any values ​​disclosed herein are not limited to the exact ranges or values, which should be understood to include those close to them.

[0037] Example 1 A treatment system for nitrogen-containing wastewater from the chemical industry and for the preparation of inorganic salts, such as... Figure 1 As shown, it includes a process one treatment system (mainly for treating nitrogen-containing wastewater) and a process two treatment system (mainly for preparing inorganic salts through an evaporation system).

[0038] The process system consists of a conditioning pretreatment system, a nitrification reaction system, a wastewater reuse system, a concentrated brine treatment system, a nanofiltration system (NF system), and a sodium sulfate evaporator connected in sequence. The conditioning pretreatment system includes processes such as filtration, oil removal, air flotation, and anaerobic digestion. The nitrification system is an oxygenated nitrification system in which nitrifying bacteria convert nitrogenous substances into nitrates. The wastewater reuse system includes processes such as filtration, ultrafiltration (UF), and reverse osmosis (RO). Its concentrate outlet is connected to the concentrated brine treatment system, and its permeate can be returned to the nitrification reaction system or discharged after meeting the standards. The concentrated brine treatment system includes processes such as hardening and desiliconization, decarbonization, RO, organic concentration and advanced oxidation. Its concentrated brine outlet is connected to the nanofiltration system, and its produced water can be returned to the nitrification reaction system or discharged after meeting the standards. The nanofiltration concentrate from the nanofiltration system enters the sodium sulfate evaporator, and the nanofiltration permeate enters the second process treatment system. The sodium sulfate evaporator nanofiltration of concentrated water yields sodium sulfate product salt (first crystal).

[0039] The second process system includes a decarbonization and pH adjustment system, an optional reaction adjustment system, an evaporation and concentration system, a sodium chloride evaporation and crystallization system, a potassium nitrate crystallization system (which can be replaced by a sodium nitrate crystallization system or a potassium chloride crystallization system), an optional potassium nitrate refining system (which can be replaced by a sodium nitrate refining system), an evaporation mother liquor tank, and a miscellaneous salt drying equipment, all connected in sequence. The reaction regulation system is used to add potassium chloride or sodium nitrate to adjust the ion level. Whether a reaction regulation system is needed depends on the inorganic salt composition of the concentrate and the requirements of the resource-based products. The sodium chloride evaporation crystallization system can obtain sodium chloride product salt (second crystal), and the mother liquor after evaporation enters the potassium nitrate crystallization system (which can be replaced by a sodium nitrate crystallization system or a potassium chloride crystallization system). The potassium nitrate crystallization system can obtain agricultural-grade potassium nitrate. It is determined whether it needs to enter an optional potassium nitrate refining system as needed. The mother liquor from the potassium nitrate crystallization system and the optional potassium nitrate refining system enters an evaporation mother liquor tank or a reflux device. The dried salt obtained by the aforementioned salt drying equipment is then transported off-site for processing. The condensate from the evaporation and concentration system, sodium chloride evaporation and crystallization system, potassium nitrate crystallization system (which can be replaced by a sodium nitrate crystallization system or a potassium chloride purification system), and potassium nitrate refining system (which can be replaced by a sodium nitrate refining system) meets the reuse standards and can be reused.

[0040] like Figure 1 As shown, the processing system for Process 2 differs slightly depending on the inorganic salt components and resource recovery requirements in the concentrate, and can be processed in four ways. Taking Method 1 as an example, the inorganic salt components are mainly sodium chloride and sodium nitrate. In the reaction regulation system, potassium chloride salt is added to adjust the ion ratio. Then, the solution is sequentially passed through evaporation and concentration, sodium chloride evaporation and crystallization, a potassium nitrate crystallization system and an optional potassium nitrate refining system, an evaporation mother liquor tank, and a miscellaneous salt drying device to obtain sodium chloride product salt, agricultural-grade potassium nitrate, industrial-grade potassium nitrate, and dried miscellaneous salt, respectively.

[0041] Example 2 Following the process in Example 1, this example uses organic nitrogen-containing wastewater from the coal chemical industry, with a COD of approximately 850 mg / L, a BOD of approximately 470 mg / L, and an ammonia nitrogen concentration of approximately 250 mg / L. After pretreatment to remove oil, the wastewater enters a nitrification tank for nitrification, converting ammonia nitrogen into nitrate nitrogen. After pretreatment, the COD in the nitrogen-containing wastewater is between 650-680 mg / L, and the COD removal rate of the pretreatment process is 20-25%. The nitrification reaction is carried out at 30-35℃, with a dissolved oxygen concentration of 2-4 mg / L in the nitrification tank, a reaction time of 24-48 hours, and a pH of 7-8. The nitrate nitrogen concentration in the nitrified wastewater is 500-1000 mg / L, and the COD is 100-150 mg / L.

[0042] The nitrified wastewater is concentrated using ultrafiltration and reverse osmosis to obtain concentrated brine and concentrated permeate. The concentrated brine has a TDS of 60,000-80,000 mg / L, a chloride ion concentration of 15,000-20,000 mg / L, a sulfate concentration of 10,000-15,000 mg / L, and a nitrate concentration of 13,000-16,000 mg / L. The concentrated permeate can be reused in the system, for example, as dissolved brine in subsequent purification processes.

[0043] The concentrated brine undergoes post-treatment, including sequential hardening and silica removal, decarbonization, reverse osmosis, concentration, and oxidation. Oxidation removes residual organic matter from the wastewater. The treated concentrated brine is then subjected to nanofiltration using a spiral wound nanofiltration membrane module to obtain nanofiltration concentrate and nanofiltration permeate. The nanofiltration concentrate has a TDS of approximately 110,000 mg / L and a sulfate concentration of approximately 68,000 mg / L. The nanofiltration concentrate is then evaporated and crystallized at 90-110℃ and approximately 100 kPa (A) to obtain a first crystalline solid containing sodium sulfate. The sodium sulfate content in the first crystalline solid is above 97%, meeting the Class II qualified product standards specified in GB / T 6009-2014.

[0044] Nanofiltration permeate is evaporated and concentrated at 80-120℃ to obtain a concentrated solution containing 5-15% sodium chloride. The concentrated solution is then evaporated and crystallized at 80-120℃ and approximately 100 kPa (A) to obtain a second crystalline solid containing sodium chloride and a mother liquor. The mother liquor contains 50-60% sodium nitrate, and the second crystalline solid contains over 95% sodium chloride. The second crystalline solid is refined and dried to obtain the sodium chloride product. The sodium chloride product contains over 98.5% sodium chloride, meeting the Grade II standard for industrial dry salt specified in GB / T 5462-2015.

[0045] The mother liquor from evaporation is freeze-crystallized at 20-40℃ to obtain a third crystalline product containing sodium nitrate, with a sodium nitrate content of over 95%. The third crystalline product is then recrystallized and dried to obtain the sodium nitrate product. Recrystallization utilizes concentrated permeate from the upstream process. The sodium nitrate product contains over 99.5% sodium nitrate, meeting the molten salt type requirements specified in GB / T 4553-2016.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and do not constitute a limitation on the content of the present invention. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including combining various technical features in any other suitable manner. These simple modifications and combinations should also be regarded as the content disclosed in the present invention and all fall within the protection scope of the present invention.

Claims

1. A method for treating nitrogen-containing wastewater in the chemical industry and preparing inorganic salts, characterized in that, Includes the following steps: (1) Pretreatment of nitrogen-containing wastewater from the chemical industry for oil removal, removal of organic pollutants and / or degradation of macromolecular organic matter, wherein the nitrogen-containing wastewater from the chemical industry is nitrogen-containing wastewater from the coal chemical industry, with COD of 800-2000 mg / L, BOD of 300-1000 mg / L, and ammonia nitrogen content of 200-500 mg / L; Pretreatment is carried out using one or more of the following methods: oil separation, air flotation, and anaerobic digestion; the COD of nitrogen-containing wastewater is reduced to 600-1500 mg / L after pretreatment, and the COD removal rate of the pretreatment process is 15-25%. (2) The pretreated wastewater undergoes nitrification. Oxygen is introduced to make the dissolved oxygen concentration in the wastewater 2-6 mg / L. The nitrification reaction time is 6-48 hours, the pH is 6-8, and the temperature is 25-35℃. The nitrate nitrogen concentration in the nitrified wastewater is 500-2000 mg / L, and the COD is 100-200 mg / L. (3) The nitrified wastewater is concentrated to obtain concentrated water and product water. The product water is discharged or reused after meeting the standards. (4) The concentrated water is treated by at least one of the following methods: hardening removal, defluorination and desilicon removal, decarbonization, RO, organic concentration and advanced oxidation, to obtain treated concentrated brine; (5) The concentrated brine is first evaporated and then frozen to separate sodium sulfate and sodium chloride. The mother liquor from the frozen crystallization is diluted and then separated by nanofiltration in step (5) to obtain nanofiltration concentrate and nanofiltration permeate. The nanofiltration concentrate is first evaporated and then frozen to obtain the first crystal containing sodium sulfate, or the nanofiltration concentrate is treated by precipitation and then enters the nitrification system. The nanofiltration permeate is concentrated by evaporation or membrane concentration to obtain a concentrate. The first crystal is obtained by evaporation and crystallization at a temperature of 80~120℃ and a pressure of 70-200 KPa. The first crystal is obtained by freezing and crystallization at a temperature of -10~30℃ and a pressure of atmospheric pressure. (6) The concentrate is decarbonized and pH adjusted. The inorganic components in the concentrate are mainly sodium chloride and sodium nitrate. The resource-based product requires sodium chloride and potassium nitrate. Potassium chloride is added for reaction adjustment. After adjustment, the ratio of each ion meets [n(K + )+n(Cl - )]: [n(Na + )+ n(NO 3- )]=0.8-1.2; then, the second crystallized sodium chloride product salt is obtained by evaporation and concentration, evaporation and crystallization, and the third crystallized agricultural grade potassium nitrate is obtained by freeze crystallization; the remaining mother liquor of the third crystallized product is evaporated and dried to obtain mixed salt, or part of it is returned to step (4) for further processing; In step (6), the temperature for obtaining the second crystal by evaporation crystallization is 80-120℃ and the pressure is 70-200 KPa; the temperature for obtaining the third crystal by freezing crystallization is 20-40℃ and the pressure is atmospheric pressure; the temperature for obtaining the third crystal by cooling crystallization is 50-70℃ and the pressure is 10-30 KPa; step (6) also includes the step of refining the second and third crystals to obtain the refined product; the condensate generated by the evaporation system is reused or discharged in compliance with the standard if it meets the reuse standard.

2. A method for treating nitrogen-containing wastewater in the chemical industry and preparing inorganic salts, characterized in that, Includes the following steps: (1) Pretreatment of nitrogen-containing wastewater from the chemical industry for oil removal, removal of organic pollutants and / or degradation of macromolecular organic matter; the nitrogen-containing wastewater from the chemical industry is nitrogen-containing wastewater from the coal chemical industry, with COD of 800-2000 mg / L, BOD of 300-1000 mg / L, and ammonia nitrogen content of 200-500 mg / L; Pretreatment is carried out using one or more of the following methods: oil separation, air flotation, and anaerobic digestion; the COD of nitrogen-containing wastewater is reduced to 600-1500 mg / L after pretreatment, and the COD removal rate of the pretreatment process is 15-25%. (2) The pretreated wastewater undergoes nitrification; oxygen is introduced to make the dissolved oxygen concentration in the wastewater 2-6 mg / L, the nitrification reaction time is 6-48 hours, the pH is 6-8, and the temperature is 25-35℃; the nitrate nitrogen concentration in the nitrated wastewater is 500-2000 mg / L, and the COD is 100-200 mg / L. (3) The nitrified wastewater is concentrated to obtain concentrated water and product water. The product water is discharged or reused after meeting the standards. (4) The concentrated water is treated by at least one of the following methods: hardening removal, defluorination and desilicon removal, decarbonization, RO, organic concentration and advanced oxidation, to obtain treated concentrated brine; (5) The concentrated brine is first evaporated and then frozen to separate sodium sulfate and sodium chloride. The mother liquor from the frozen crystallization is diluted and then separated by nanofiltration in step (5) to obtain nanofiltration concentrate and nanofiltration permeate. The nanofiltration concentrate is first evaporated and then frozen to obtain the first crystal containing sodium sulfate, or the nanofiltration concentrate is treated by precipitation and then enters the nitrification system. The nanofiltration permeate is concentrated by evaporation or membrane concentration to obtain a concentrate. The first crystal is obtained by evaporation and crystallization at a temperature of 80~120℃ and a pressure of 70-200 KPa. The first crystal is obtained by freezing and crystallization at a temperature of -10~30℃ and a pressure of atmospheric pressure. (6) The concentrate is decarbonized and pH adjusted. The inorganic components in the concentrate are mainly sodium chloride and potassium chloride. The resource-based product requires sodium chloride and potassium nitrate. Sodium nitrate is added for reaction adjustment. After adjustment, the ratio of each ion satisfies [n(K + )+n(Cl - )]: [n(Na + )+ n(NO 3- )]=0.8-1.2; then, the second crystallized sodium chloride product salt is obtained by evaporation and concentration, evaporation and crystallization, and the third crystallized agricultural grade potassium nitrate is obtained by freeze crystallization; the remaining mother liquor of the third crystallized product is evaporated and dried to obtain mixed salt, or part of it is returned to step (4) for further processing; In step (6), the temperature for obtaining the second crystal by evaporation crystallization is 80-120℃ and the pressure is 70-200 KPa; the temperature for obtaining the third crystal by freezing crystallization is 20-40℃ and the pressure is atmospheric pressure; the temperature for obtaining the third crystal by cooling crystallization is 50-70℃ and the pressure is 10-30 KPa; step (6) also includes the step of refining the second and third crystals to obtain the refined product; the condensate generated by the evaporation system is reused or discharged in compliance with the standard if it meets the reuse standard.

3. The method as described in claim 1 or 2, characterized in that, In step (6), the third crystallized agricultural-grade potassium nitrate is refined to obtain the fourth crystallized industrial-grade potassium nitrate. The remaining mother liquor from the third and fourth crystallized products is evaporated and dried to obtain mixed salts, or partially recycled to step (4) for further processing.

4. The method as described in claim 1 or 2, characterized in that, In step (3), concentration is achieved through filtration, ultrafiltration (UF), and reverse osmosis (RO).

5. A processing system for the method of any one of claims 1-4, comprising: Processing system 1 and processing system 2; The process one processing system includes a conditioning pretreatment system, a nitrification reaction system, a wastewater reuse system, a concentrated brine treatment system, a nanofiltration system, and a sodium sulfate evaporation system or a freeze crystallization system connected in sequence. The conditioning pretreatment system includes filtration, oil removal, air flotation, and anaerobic processes. The nitrification system is an oxygenated nitrification system in which nitrifying bacteria convert nitrogenous substances into nitrates. The wastewater reuse system includes filtration, ultrafiltration, and reverse osmosis processes. Its concentrated water enters the concentrated brine treatment system and its produced water is discharged or reused after meeting the standards. The concentrated brine treatment system includes hardening and desiliconization, decarbonization, reverse osmosis, organic concentration and advanced oxidation processes. The treated concentrated brine enters the nanofiltration system, and the produced water meets the discharge standards or is reused. The nanofiltration concentrate from the nanofiltration system enters the sodium sulfate evaporator, and the nanofiltration permeate is connected to the process two treatment system. The sodium sulfate evaporator evaporates or freezes nanofiltration concentrate to obtain sodium sulfate product salt; The second process system includes a decarbonization and pH adjustment system, a reaction adjustment system, an evaporation and concentration system, a sodium chloride evaporation and crystallization system, a nitrate or chloride crystallization system, a nitrate or chloride refining system, an evaporation mother liquor tank, a reflux device, and a miscellaneous salt drying device, connected in sequence. The reaction regulation system is used to add potassium chloride or sodium nitrate to adjust the ion level; The sodium chloride evaporation crystallization system obtains sodium chloride product salt, and the remaining mother liquor after evaporation enters the nitrate or chloride crystallization system. The nitrate or chloride crystallization system can obtain nitrates or chlorides, and the remaining mother liquor after crystallization is sent to an evaporation mother liquor tank or a reflux device. The nitrate or chloride salt is then purified in a nitrate or chloride salt refining system. The mother liquor discharged after evaporation in the evaporation mother liquor tank is either sent to the miscellaneous salt drying equipment or partially returned to the concentrated brine treatment system for further processing, and the dried miscellaneous salt is transported off-site for disposal. The condensate from the evaporation and concentration system, sodium chloride evaporation and crystallization system, nitrate or chloride crystallization system, and nitrate or chloride refining system is reused if it meets the reuse standards.

Images