Green cyclic resource utilization method for high-salinity wastewater of preserved szechuan pickles

Abstract

The invention relates to a green cyclic resource utilization method of preserved szechuan pickle high-salinity wastewater, which adopts a pretreatment, multi-time low-temperature MVR and pyrolysis combined technology to treat pickling wastewater, efficiently removes impurities, recycles sodium chloride with high yield, improves the yield and quality of solid salt, solves the problems of MVR system blockage and the like, and is suitable for industrial production. And meanwhile, energy consumption and environmental pollution are reduced. The effluent is discharged after reaching the standard or is recycled after being further deeply treated.

Description

Technical Field

[0001] The invention relates to a green recycling resource utilization method for high-salt mustard tuber wastewater, belonging to the technical field of food pickling wastewater treatment. Background Art

[0002] The production of mustard tubers (Zhacai) produces a large amount of pickling wastewater. Its high salt content, high COD content, and high suspended solids content pose significant challenges to its treatment. Traditional methods for desalting pickling wastewater involve repeatedly flushing it with large volumes of clean water to dilute the sodium chloride in the product, and then discharging the resulting dilution. This wastes significant water resources and causes the sodium chloride in the product to be wasted. More importantly, the resulting wastewater places significant pressure on both the company and the environment. Therefore, the development of cost-effective technologies for the treatment and resource utilization of high-salt organic wastewater has become a pressing research challenge for both the preserved food industry and the environmental protection community.

[0003] While there is considerable research on how to purify wastewater to meet discharge standards, there is limited research on resource-recycling methods for the high-salt wastewater produced by mustard tubers. It is noteworthy that, unlike the complex salt composition of wastewater from the chemical industry, the salt content of wastewater from the pickling industry is primarily sodium chloride. Therefore, if the sodium chloride in pickling wastewater could be crystallized, purified, and recycled, it would not only achieve efficient treatment of food pickling wastewater and prevent environmental pollution, but also enable the recycling of pickling salt, reducing resource waste and saving production costs.

[0004] To achieve crystallization recovery of sodium chloride, the MVR process can be used. However, due to the excessive amount of impurities such as suspended solids, colloids, and dissolved organic matter in the wastewater, the impurities will be wrapped and adsorbed in or on the surface of the crystals during the MVR process, resulting in extremely poor quality of the precipitated crystals and causing problems such as blockage of the MVR system.

[0005] In summary, how to efficiently remove impurities from pickling wastewater, realize the recovery and utilization of high-purity salt in high-salt mustard wastewater, and at the same time meet the wastewater discharge requirements is a current problem. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the present invention provides a green recycling resource utilization method for high-salt mustard wastewater.

[0007] This method combines pretreatment, multiple low-temperature MVR cycles, and pyrolysis to treat pickling wastewater. This effectively removes impurities, recovers sodium chloride at a high yield, improves the yield and quality of solid salt, and resolves issues like MVR system clogging, while reducing energy consumption and environmental pollution. The effluent meets discharge standards or can be reused after further advanced treatment.

[0008] The present invention is achieved through the following technical solutions:

[0009] A green recycling resource utilization method for high-salt mustard wastewater comprises the following steps:

[0010] 1) passing the mustard tuber pickling wastewater through a coarse screen and a fine screen in sequence to remove larger impurities in the wastewater, thereby obtaining screened wastewater, and treating the separated impurities as general solid waste;

[0011] 2) After passing through the screen, the wastewater enters the coagulation-sedimentation tank, and coagulation-flocculation reagents are added to the coagulation-sedimentation tank. The colloidal particles and some macromolecular organic matter in the wastewater are removed through the coagulation-sedimentation process. The sediment is treated as general solid waste after centrifugal dehydration.

[0012] 3) The precipitated water enters the filtration device for filtration, and the filter cake is collected and treated as general solid waste to obtain filtered water;

[0013] 4) The filtered water enters a multi-stage low-temperature evaporation crystallization system for multi-stage low-temperature MVR treatment to obtain solid crude salt a;

[0014] 5) The solid crude salt a enters the pyrolysis device, where the organic matter contained in the crude salt is pyrolyzed and converted into gas and solid carbon residue;

[0015] 6) dissolving and filtering the solid matter obtained by pyrolysis in step 5), and the filter residue is a stable biochar having a large specific surface area and abundant pores, which is recycled and used as filler in a subsequent MABR process for desalination wastewater to improve the process water treatment effect;

[0016] 7) The filtrate obtained by filtration in step 6) is placed in an evaporation crystallization system for low-temperature MVR treatment, and solid crude salt b is obtained after evaporation and crystallization;

[0017] 8) dissolving the solid crude salt b, filtering, and placing the filtrate obtained by filtration in an evaporation crystallization system for low-temperature MVR treatment to obtain solid refined salt after evaporation and crystallization;

[0018] 9) Collect the evaporation condensate, mother liquor and remaining wastewater from the evaporation crystallization system in steps 4), 7) and 8), treat them using MABR, and discharge them after testing and meeting the standards.

[0019] According to a preferred embodiment of the present invention, in step 1), particulate matter with a particle size greater than 3 mm is removed through a coarse grid-fine grid.

[0020] According to the preferred embodiment of the present invention, in the step 2), the coagulation-flocculation agent is added to the coagulation sedimentation tank by first adding polyaluminum chloride PAC to the coagulation sedimentation tank, stirring it evenly with a stirrer, and then adding anionic polyacrylamide. The coagulation sedimentation time is 30 minutes to remove colloids, coarse impurities and some soluble macromolecular organic matter.

[0021] Preferably according to the present invention, in step 2), the dosage of polyaluminum chloride (PAC) is 100-300 mg / L, the dosage of anionic polyacrylamide is 3-10 mg / L, and the coagulation pH is 6-8.

[0022] More preferably, when the COD in the wastewater is < 10 g / L, the dosage of polyaluminum chloride (PAC) is 115 mg / L, the dosage of anionic polyacrylamide is 5 mg / L, and the coagulation pH is 6.5; when 10 g / L < COD < 20 g / L in the wastewater, the dosage of polyaluminum chloride (PAC) is 150 mg / L, the dosage of anionic polyacrylamide is 8 mg / L, and the coagulation pH is 6.8.

[0023] Preferably according to the present invention, the filtration device in step 3) is a chamber filter press.

[0024] Preferably according to the present invention, in step 4), the multi-stage low-temperature evaporation crystallization system is a 3-5 stage low-temperature evaporation crystallization system.

[0025] Preferably according to the present invention, in step 4), the low-temperature evaporation crystallization system uses a heat pump low-temperature MVR. The temperature of the heat pump low-temperature MVR system is 50-80 °C, the compression ratio is 1.1-1.6, and the remaining mother liquor amount is 4-10%. More preferably, the temperature of the heat pump low-temperature MVR system is 65-70 °C, the compression ratio is 1.3-1.5, and the remaining mother liquor amount is 5%-6%.

[0026] Preferably according to the present invention, in step 5), the pyrolysis device is a pyrolysis furnace, and nitrogen is passed to keep the inside of the furnace isolated from air.

[0027] Preferably according to the present invention, the temperature of the pyrolysis furnace is 20-700 °C, the heating rate is 5-10 °C / min, and it is maintained for 40-60 min after reaching the highest temperature. More preferably, the temperature of the pyrolysis furnace is 20-600 °C, the heating rate is 10 °C / min, and pyrolysis is carried out at 600 °C for 60 min.

[0028] Preferably according to the present invention, in steps 6) and 8), dissolution and filtration are carried out by low-temperature heating and stirring for dissolution, and filtration is carried out with a fiber filter. The heating temperature is 40-60 °C, and the fiber filter uses a fiber filter element.

[0029] Preferably according to the present invention, in steps 7) and 8), the evaporation crystallization system uses a heat pump low-temperature MVR. The temperature of the heat pump low-temperature MVR system is 50-80 °C, the compression ratio is 1.1-1.6, and the remaining mother liquor amount is 4-10%. More preferably, the temperature of the heat pump low-temperature MVR system is 65-70 °C, the compression ratio is 1.3-1.5, and the remaining mother liquor amount is 5%-6%.

[0030] The present invention adopts MVR low-temperature evaporation crystallization technology to avoid the occurrence of boiling points of different chemical components at high temperature, thereby reducing the impurity concentration in the crystallized salt and improving the quality and yield of the solid salt.

[0031] Inorganic colloids and suspended solids in wastewater can be removed relatively easily and efficiently through coagulation and filtration techniques, but these conventional techniques have limited effectiveness in removing dissolved organic matter. The present invention treats pickling wastewater through a combination of pretreatment, multiple low-temperature MVR cycles, and pyrolysis. This pyrolysis decomposes the dissolved organic matter into gas and water-insoluble solid carbon residue, which is then separated from the salt through a dissolution-filtration process, achieving efficient removal of dissolved organic matter.

[0032] The technical features and advantages of the present invention are as follows:

[0033] 1. The present invention realizes the resource utilization of high-salt wastewater. After crystallization separation, the salt in the wastewater still contains some organic matter and is hazardous waste. After drying and high-temperature pyrolysis, the salt in the waste liquid reaches the standard of industrial salt, turning waste into resources. In addition, the pyrolysis time is long, the quality of the industrial salt produced is stable, the pyrolysis is more thorough, and the tail gas is easy to handle.

[0034] 2. The present invention adopts MVR low-temperature evaporation crystallization technology, which not only improves the yield and quality of solid salt, but also improves the water quality of the remaining mother liquor and condensed water after desalination as much as possible, solves the problem of MVR system blockage, and reduces energy consumption and environmental pollution.

[0035] 3. The present invention realizes the systematic treatment of high-salt and high-organic wastewater. All waste liquids, waste gases and solid wastes generated in the process are treated. All waste liquids are collected and treated by MABR to achieve standard discharge. Solids are hazardous wastes and enter the next stage for drying and pyrolysis to finally obtain refined salt. The gases generated by pyrolysis directly enter the tail gas treatment system.

[0036] 4. Through the addition of drugs for coagulation and centrifugal separation, the fine suspended matter, colloids and some large molecular organic matter in the mustard pickling wastewater are removed, which greatly reduces the frequency of subsequent MVR system operation obstruction and improves the treatment efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is the purity of the recovered salt under different treatment schemes;

[0038] Figure 2 is the TOC of the recovered salt under different treatment schemes;

[0039] Figure 3 is the salt content of wastewater in the wastewater pool under different treatment schemes;

[0040] Figure 4is the COD of wastewater in the wastewater pool under different treatment schemes;

[0041] Figure 1-4 In the figure, the horizontal axes AE represent the results obtained by the implementation schemes of Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, and Example 2, respectively. Specific embodiments

[0042] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings.

[0043] Example 1:

[0044] 1) The high-salt mustard tuber wastewater passes through a screen. The brine contains large suspended solids, sediment, and colloids, such as mustard tuber shreds. Before entering the system, the screen effectively removes most of the suspended solids to prevent clogging of subsequent equipment.

[0045] 2) Wastewater passing through the screen enters the coagulation sedimentation tank. By adjusting the pH and adding appropriate amounts of PAC and PAM, flocculation is carried out, causing colloids and suspended solids in the wastewater to aggregate. The coagulation process is the most basic and extremely important treatment process in industrial water and domestic sewage treatment. By adding certain chemicals (commonly called coagulants and flocculants) to the water, particles that are difficult to settle in the water can aggregate to form colloids. These then combine with impurities in the water to form larger flocs. Flocs have strong adsorption capacity and can absorb not only suspended solids, but also some bacteria and soluble substances. Through adsorption, the flocs increase in volume and sink.

[0046] 3) The sediment in the coagulation sedimentation tank is fed into a centrifuge for centrifugal dehydration. The resulting filter cake is collected and transported to a centralized location for processing, while the precipitated water flows into a chamber filter press for filtration. A chamber filter press is a solid-liquid separation device. A feed pump feeds a solid-liquid mixture into the filter chamber of the chamber filter press. Under pressure, the liquid passes through the filter cloth, along the grooves and channels, and out of the filter. Solids are retained on the filter cloth until they fill the filter chamber and form a filter cake.

[0047] 4) The filtrate after filtration enters a heat pump low-temperature evaporator for evaporation and crystallization. The resulting condensed water and mother liquor are collected for subsequent centralized processing, and the resulting solid crude salt is sent to subsequent equipment. The low-temperature MVR evaporator uses a high-efficiency steam compressor to compress the secondary steam generated by evaporation, thereby increasing the pressure and temperature of the secondary steam. The increased thermal energy of the secondary steam is pumped into a heater to further heat the raw liquid. The heated raw liquid continues to evaporate and generate secondary steam, thus achieving a continuous evaporation state, ultimately evaporating the solution into a concentrate at a relatively low temperature.

[0048] 5) The crude salt obtained by crystallization enters the pyrolysis device, and the temperature of the pyrolysis device is controlled at 20-700°C to pyrolyze the organic matter contained in the crude salt into gas and solid carbon residue (mainly biochar). The gas is connected to the tail gas treatment device for treatment; under high temperature and oxygen-free (or low-oxygen) conditions, the organic solid waste on the crude salt is cracked to produce solid residue and combustible gas.

[0049] 6) The obtained solid enters the dissolution tank, where the solid crude salt is soluble and the solid waste residue is insoluble.

[0050] 7) The liquid in the dissolution tank enters the filter, where the solid waste is separated and collected for use as filler in the subsequent MABR process. Biochar, the primary component of the solid waste, has a large surface area and abundant pores. It also exhibits excellent biological, chemical, and thermodynamic stability, making it less likely to participate in biochemical reactions within the system.

[0051] 8) The obtained filtrate enters the low-temperature MVR evaporator for evaporation and crystallization, and the obtained condensed water and mother liquor are collected for subsequent centralized treatment.

[0052] 9) The solid salt obtained enters the detection system. If its quality meets the Class II standard of "QB / T2830-2015 Mustard Salt", it is directly recycled.

[0053] 10) If the quality of the solid salt does not meet the standards, it will enter the dissolution tank for dissolution.

[0054] 11) The dissolved liquid enters the low-temperature MVR evaporator for secondary evaporation and crystallization. The refined salt obtained after crystallization can be recycled, and the final product salt recovery rate reaches more than 80%.

[0055] 12) The evaporated condensate and mother liquor collected in steps 4), 8) and 11) enter the wastewater mixing tank and are treated by the MABR treatment system before being discharged in compliance with the discharge standards.

[0056] Example 2:

[0057] The system and method in Example 1 were used to treat high-salt and high-organic wastewater from a chemical plant. The steps are as follows:

[0058] 1) 3 L of high-salt mustard tuber wastewater was measured to have a COD of 12,600 mg / L, a SS of 89.1 mg / L, a salinity of 62,000 mg / L, a pH of 5.86, a light green color, and a pungent odor.

[0059] 2) The wastewater passes through a rotary screen machine with a screen aperture of 15 mm, and then enters a spiral screen machine with a screen bar gap of 8 mm.

[0060] 3) The outflowing wastewater enters the coagulation sedimentation tank, and the pH value is adjusted to 6.8 by adding 1 mol / L NaOH solution, and PAC is added at a dosage of 150 mg / L and PAM (anionic type) is added at a dosage of 8 mg / L, and coagulation and sedimentation are carried out for 30 minutes.

[0061] 4) The sediment in the coagulation sedimentation tank is placed in a centrifuge for centrifugal dehydration. The filter cake obtained by centrifugation is collected and transported to a centralized location for treatment. The precipitated water flows into a chamber filter press for filtration. The filtrate obtained is measured to have a COD of 6500 mg / L and a SS of 56.2 mg / L.

[0062] The water becomes clear and the odor is reduced.

[0063] 5) The filtrate obtained after filtration enters the heat pump low-temperature evaporator. The evaporator temperature is adjusted to 65°C, the compression ratio is 1.3, and the residual mother liquor volume is 5%. The resulting condensed water and mother liquor are collected for subsequent centralized treatment. The COD and SS are measured to be 6230 mg / L and 51.3 mg / L.

[0064] 6) The obtained solid crude salt is put into a pyrolysis furnace, nitrogen is passed through the furnace to keep it isolated from the air, the pyrolysis furnace temperature is set to 600°C, the heating rate is 10°C / min, and the pyrolysis is carried out at 600°C for 60 minutes.

[0065] 7) The solid obtained by pyrolysis enters the dissolution tank, is heated and stirred to dissolve, and the heating temperature is maintained at 60°C.

[0066] 8) The liquid in the dissolution tank enters the fiber filter (using a fiber filter element) and is filtered at a temperature of 60°C. The resulting solid residue is collected and used in the subsequent MABR treatment process.

[0067] 9) The filtrate obtained after filtration enters the heat pump low-temperature evaporator, and the evaporator temperature is adjusted to 65° C., the compression ratio is 1.3, and the remaining mother liquor volume is 5%. The obtained condensed water and mother liquor are collected for subsequent centralized treatment.

[0068] 10) 150 g of solid salt was obtained by evaporation and crystallization. The purity was 91.8% and the whiteness was 70. The calculated salt recovery rate was 80.6%. According to the standard "QB / T2830-2015 Mustard Salt", the finished salt can be reused in the production of pickled mustard tubers, so there is no need for secondary evaporation and crystallization.

[0069] 11) The evaporation condensate and mother liquor collected in 5)9) flow into the wastewater mixing tank. After testing, the salt content is 1.3% and the COD is 900 mg / L. It flows into the MABR treatment system for treatment and meets the discharge standards.

[0070] Comparative Example 1

[0071] Take the same high-salt wastewater in Example 2 and process it as follows:

[0072] 1) The wastewater passes through a rotary screen machine with a screen aperture of 15 mm, and then enters a spiral screen machine with a screen bar gap of 8 mm.

[0073] 2) The outflowing wastewater enters the heat pump low-temperature evaporator, and the evaporator temperature is adjusted to 65°C, the compression ratio is 1.3, and the remaining mother liquor volume is 5%. The obtained condensed water and mother liquor are collected for subsequent centralized treatment.

[0074] 3) The obtained solid enters the dissolution tank, is heated and stirred to dissolve, and the heating temperature is maintained at 60°C.

[0075] 4) The resulting solution enters a heat pump low-temperature evaporator, and the evaporator temperature is adjusted to 65° C., the compression ratio is 1.3, and the remaining mother liquor volume is 5%. The resulting condensed water and mother liquor are collected for subsequent centralized treatment, and the resulting solid salt is collected and tested.

[0076] 5) The evaporated condensate and mother liquor collected in 2)4) are flowed into the wastewater mixing tank, where their salt content and COD are tested, and then enter the MABR treatment system for treatment before being discharged in compliance with the standards.

[0077] Comparative Example 2

[0078] Take the same high-salt wastewater in Example 2 and process it as follows:

[0079] 1) The wastewater passes through a rotary screen machine with a screen aperture of 15 mm, and then enters a spiral screen machine with a screen bar gap of 8 mm.

[0080] 2) The outflowing wastewater enters the heat pump low-temperature evaporator, and the evaporator temperature is adjusted to 65°C, the compression ratio is 1.3, and the remaining mother liquor volume is 5%. The obtained condensed water and mother liquor are collected for subsequent centralized treatment.

[0081] 3) The obtained solid crude salt was put into a pyrolysis furnace, nitrogen was passed through the furnace to keep it isolated from the air, the pyrolysis furnace temperature was set to 600°C, the heating rate was 10°C / min, and the pyrolysis was carried out at 600°C for 60 minutes.

[0082] 4) The solid obtained by pyrolysis enters the dissolution tank, is heated and stirred to dissolve, and the heating temperature is maintained at 60°C.

[0083] 5) The liquid in the dissolution tank enters the fiber filter (using a fiber filter element) and is filtered at a temperature of 60°C. The resulting solid residue is collected for subsequent MABR treatment processes.

[0084] 6) The filtrate obtained after filtration enters the heat pump low-temperature evaporator, and the evaporator temperature is adjusted to 65°C, the compression ratio is 1.3, and the remaining mother liquor volume is 5%. The obtained condensed water and mother liquor are collected for subsequent centralized treatment, and the obtained solid salt is collected and tested.

[0085] 7) The evaporation condensate and mother liquor collected in 2)6) are flowed into the wastewater mixing tank, where their salt content and COD are tested, and then enter the MABR treatment system for treatment before being discharged in compliance with the standards.

[0086] Comparative Example 3

[0087] Take the same high-salt wastewater in Example 2 and process it as follows:

[0088] 1) The wastewater passes through a rotary screen machine with a screen aperture of 15 mm, and then enters a spiral screen machine with a screen bar gap of 8 mm.

[0089] 2) The outflowing wastewater enters the coagulation sedimentation tank, and the pH value is adjusted to 6.8 by adding 1 mol / L NaOH solution, and PAC is added at a dosage of 150 mg / L, and coagulation sedimentation is carried out for 30 minutes.

[0090] 3) The sediment in the coagulation sedimentation tank is placed in a centrifuge for centrifugal dehydration. The filter cake obtained by centrifugation is collected and transported to a centralized location for treatment. The precipitated water flows into a chamber filter press for filtration.

[0091] 4) The filtrate enters the heat pump low-temperature evaporator, and the evaporator temperature is adjusted to 65°C, the compression ratio is 1.3, and the remaining mother liquor volume is 5%. The obtained condensed water and mother liquor are collected for subsequent centralized treatment.

[0092] 5) The obtained solid crude salt was put into a pyrolysis furnace, nitrogen was passed through the furnace to keep it isolated from the air, the pyrolysis furnace temperature was set to 600°C, the heating rate was 10°C / min, and the pyrolysis was carried out at 600°C for 60 minutes.

[0093] 6) The solid obtained by pyrolysis enters the dissolution tank, is heated and stirred to dissolve, and the heating temperature is maintained at 60°C.

[0094] 7) The liquid in the dissolution tank enters the fiber filter (using a fiber filter element) and is filtered at a temperature of 60°C. The resulting solid residue is collected for subsequent MABR treatment processes.

[0095] 8) The filtrate obtained after filtration enters the heat pump low-temperature evaporator, and the evaporator temperature is adjusted to 65° C., the compression ratio is 1.3, and the remaining mother liquor volume is 5%. The obtained condensed water and mother liquor are collected for subsequent centralized treatment, and the obtained solid salt is collected and tested.

[0096] 9) The evaporation condensate and mother liquor collected in 4)8) are flowed into the wastewater mixing tank, where their salt content and COD are tested, and then enter the MABR treatment system for treatment before being discharged in compliance with the standards.

[0097] Comparative Example 4

[0098] Take the same high-salt wastewater in Example 2 and process it as follows:

[0099] 1) The wastewater passes through a rotary screen machine with a screen aperture of 15 mm, and then enters a spiral screen machine with a screen bar gap of 8 mm.

[0100] 2) The outflowing wastewater enters the coagulation sedimentation tank, and the pH value is adjusted to 6.8 by adding 1 mol / L NaOH solution, and PAM (anionic type) is added at a dosage of 8 mg / L, and coagulation sedimentation is carried out for 30 minutes.

[0101] 3) The sediment in the coagulation sedimentation tank is placed in a centrifuge for centrifugal dehydration. The filter cake obtained by centrifugation is collected and transported to a centralized location for treatment. The precipitated water flows into a chamber filter press for filtration.

[0102] 4) The filtrate enters the heat pump low-temperature evaporator, and the evaporator temperature is adjusted to 65°C, the compression ratio is 1.3, and the remaining mother liquor volume is 5%. The obtained condensed water and mother liquor are collected for subsequent centralized treatment.

[0103] 5) The obtained solid crude salt was put into a pyrolysis furnace, nitrogen was passed through the furnace to keep it isolated from the air, the pyrolysis furnace temperature was set to 600°C, the heating rate was 10°C / min, and the pyrolysis was carried out at 600°C for 60 minutes.

[0104] 6) The solid obtained by pyrolysis enters the dissolution tank, is heated and stirred to dissolve, and the heating temperature is maintained at 60°C.

[0105] 7) The liquid in the dissolution tank enters the fiber filter (using a fiber filter element) and is filtered at a temperature of 60°C. The resulting solid residue is collected for subsequent MABR treatment processes.

[0106] 8) The filtrate obtained after filtration enters the heat pump low-temperature evaporator, and the evaporator temperature is adjusted to 65° C., the compression ratio is 1.3, and the remaining mother liquor volume is 5%. The obtained condensed water and mother liquor are collected for subsequent centralized treatment, and the obtained solid salt is collected and tested.

[0107] 9) The evaporation condensate and mother liquor collected in 4)8) are flowed into the wastewater mixing tank, where their salt content and COD are tested, and then enter the MABR treatment system for treatment before being discharged in compliance with the standards.

[0108] The test results of Example 2 and Comparative Examples 1-4 are shown in Figures 1-4 By comparison, it is found that Example 2 can significantly increase the purity of the recovered salt, and the salt content in the discharged wastewater is the lowest, and the COD value is also greatly reduced.

[0109] Compared with the traditional direct evaporation crystallization (Comparative Example 1), the combination of multiple low-temperature MVR and pyrolysis (Comparative Example 2) greatly reduces the impurity content in the solid salt, especially the content of impurities such as soluble organic matter.

[0110] Compared with direct evaporation, crystallization and pyrolysis (Comparative Example 2), first performing a complete coagulation and sedimentation treatment (Example 2) can greatly improve the quality of discharged wastewater, reduce the COD and salt content of the wastewater, and is more conducive to the subsequent wastewater treatment process.

[0111] During pretreatment, the effects of a single coagulant (Comparative Example 3) and a coagulant aid (Comparative Example 4) can also effectively improve salt purity and reduce wastewater COD, but when the two are used in combination, the precipitation effect and precipitation speed are better, and the recovered salt quality is better.

[0112] Therefore, the method provided by the present invention combines PAM and PAC coagulation pretreatment for 30 minutes, followed by multiple low-temperature MVR and pyrolysis treatments, to produce high-purity mustard salt and reduce the COD and salt content of the discharged wastewater. Compared with the traditional method of repeatedly rinsing with large amounts of clean water to dilute the sodium chloride in the product and then discharging the diluted solution, this method not only reduces water waste but also achieves the recovery of high-purity sodium chloride and the discharge of low-salt wastewater.

Claims

1. A green circular resource utilization method for high-salt wastewater of pickled mustard tuber, comprising the following steps: 1) Pass the pickled mustard tuber wastewater through a coarse grille - fine grille in sequence to remove larger impurities in the wastewater, obtain the wastewater after passing through the grille, and treat the separated impurities as general solid waste; 2) The wastewater after passing through the grille enters a coagulation - sedimentation tank, and a coagulation - flocculation agent is added to the coagulation - sedimentation tank. Through the coagulation - sedimentation process, colloidal particles and some macromolecular organic matters in the wastewater are removed. After the sediment is centrifugally dehydrated, it is treated as general solid waste; 3) The sedimentation effluent enters a filtration device for filtration, the filter cake is collected and treated as general solid waste to obtain the filtered effluent; 4) The filtered effluent enters a multi - stage low - temperature evaporation crystallization system for multi - stage low - temperature MVR treatment to obtain solid crude salt a; 5) The solid crude salt a enters a pyrolysis device to pyrolyze and convert the organic matters contained in the crude salt into gas and solid carbon slag; 6) Dissolve and filter the solid substance obtained by pyrolysis in step 5). The filter residue is stable biochar, which has a large specific surface area and abundant pores, and is recycled and used as a filler for the subsequent MABR process of desalinated wastewater to improve the water treatment effect of the process; 7) The filtrate obtained by filtration in step 6) is placed in an evaporation crystallization system for low - temperature MVR treatment, and solid crude salt b is obtained after evaporation and crystallization; 8) The solid crude salt b is dissolved and filtered. The filtrate obtained by filtration is placed in an evaporation crystallization system for low - temperature MVR treatment, and solid refined salt is obtained after evaporation and crystallization; 9) Collect the evaporation condensate, mother liquor and remaining wastewater in the evaporation crystallization systems in steps 4), 7) and 8), and treat them with MABR. After being detected to meet the standards, they can be discharged.

2. The method according to claim 1, characterized in that In step 1), particulate matter with a particle size greater than 3 mm is removed through the coarse grille - fine grille.

3. The method according to claim 1, characterized in that In step 2), when adding the coagulation - flocculation agent to the coagulation - sedimentation tank, first add polyaluminum chloride PAC to the coagulation - sedimentation tank, stir evenly with a stirrer, and then add anionic polyacrylamide. The coagulation - sedimentation time is 30 min to remove colloids, coarse impurities and some dissolved macromolecular organic matters.

4. The method according to claim 1, wherein In step 2), the dosage of polyaluminum chloride PAC is 100 - 300 mg / L, the dosage of anionic polyacrylamide is 3 - 10 mg / L, and the coagulation pH is 6 - 8; when the COD in the wastewater < 10 g / L, the dosage of polyaluminum chloride PAC is 115 mg / L, the dosage of anionic polyacrylamide is 5 mg / L, and the coagulation pH is 6.5; when 10 g / L < COD < 20 g / L in the wastewater, the dosage of polyaluminum chloride PAC is 150 mg / L, the dosage of anionic polyacrylamide is 8 mg / L, and the coagulation pH is 6.

8.

5. The method according to claim 1, characterized in that The filtration device in step 3) is a chamber filter press.

6. The method according to claim 1, characterized in that In step 4), the multi - stage low - temperature evaporation crystallization system is a 3 - 5 - stage low - temperature evaporation crystallization system.

7. The method according to claim 1, characterized in that In the step 4), the low-temperature evaporation crystallization system adopts a heat pump low-temperature MVR, the temperature of the heat pump low-temperature MVR system is 50-80°C, the compression ratio is 1.1-1.6, and the residual mother liquor amount is 4-10%; further preferably, the temperature of the heat pump low-temperature MVR system is 65-70°C, the compression ratio is 1.3-1.5, and the residual mother liquor amount is 5%-6%.

8. The method according to claim 1, characterized in that In the step 5), the pyrolysis device is a pyrolysis furnace, nitrogen is passed through the furnace to keep it isolated from the air, the temperature of the pyrolysis furnace is 20-700°C, the heating rate is 5-10°C / min, and after reaching the highest temperature, it is maintained for 40-60 minutes; further preferably, the temperature of the pyrolysis furnace is 20-600°C, the heating rate is 10°C / min, and the pyrolysis is carried out at 600°C for 60 minutes.

9. The method according to claim 1, characterized in that In the steps 6) and 8), the dissolving and filtering are performed by stirring and dissolving with low temperature heating, and filtering with a fiber filter, the heating temperature is 40-60° C., and the fiber filter uses a fiber filter element.

10. The method according to claim 1, characterized in that In the steps 7) and 8), the evaporation crystallization system adopts a heat pump low-temperature MVR, the temperature of the heat pump low-temperature MVR system is 50-80°C, the compression ratio is 1.1-1.6, and the residual mother liquor amount is 4-10%; further preferably, the temperature of the heat pump low-temperature MVR system is 65-70°C, the compression ratio is 1.3-1.5, and the residual mother liquor amount is 5%-6%.

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