CN110697955B - Nanofiltration concentrated solution treatment device and method - Google Patents
Nanofiltration concentrated solution treatment device and method Download PDFInfo
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Abstract
The invention discloses a nanofiltration concentrated solution zero-emission treatment system and method, wherein a membrane treatment unit is used for filtering the nanofiltration concentrated solution to generate a first concentrated water product, the first concentrated water product is sent to a freezing crystallization unit, the freezing crystallization unit is used for performing mass separation crystallization on the first concentrated water product to generate a crystallization product and a crystallization mother solution, a high-grade oxidation unit is used for performing high-grade oxidation treatment on the crystallization mother solution to generate oxidized effluent, and finally the oxidized effluent flows back to the membrane treatment unit. By adopting the method, the nanofiltration concentrated solution in the MBR + NF process is effectively treated, and the membrane operation system has low pressure and low energy consumption. And (3) separating out the sodium sulfate in the first concentrated water product by adopting a freezing crystallization technology and discharging the sodium sulfate out of the system, so that the divalent salt is prevented from accumulating in the system. The adoption is through freezing crystallization mother liquor of advanced oxidation technology processing can effectually reduce the organic matter in the crystallization mother liquor, then flows back the oxidation outlet water behind the advanced oxidation processing to membrane processing unit front end, avoids the accumulation of organic matter in the system.
Description
Technical Field
The invention belongs to the field of landfill leachate treatment, and particularly relates to a nanofiltration concentrated solution treatment device and method.
Background
Because domestic garbage generally adopts a mixed collection and mixed landfill mode, the garbage components are complicated and changeable, and the property change range of garbage leachate in various regions is large. Under the influence of various factors such as the type of landfill, the landfill method, the scale of a landfill site, the landfill period, weather change and the like, particularly in areas with large rainfall, because a large amount of rainwater washes the landfill site during rainfall, pollutants in the landfill site are leached by the rainwater, the quality of leachate is further deteriorated, and the problem of landfill leachate treatment is more severe.
Aiming at the treatment of the landfill leachate, the membrane treatment process technology is mostly adopted to treat the landfill leachate at present, the membrane treatment process technology has good technical effect and large treatment capacity, and the problem of the accumulation of the leachate can be greatly relieved. In many of these areas, the MBR (membrane bioreactor) method is combined with a roll-type Nanofiltration (NF) membrane system to treat the leachate which is difficult to degrade. The recovery rate of a general first-stage NF membrane system can reach about 80 percent, the recovery rate of a second-stage NF membrane system can reach about 85 percent, and the nanofiltration concentrate has high content of divalent salt and organic matters and has larger treatment difficulty.
The patent with publication number CN106242163A in the prior art discloses a treatment method of a membrane-process concentrated solution of landfill leachate, which recycles the concentrated solution treated by combining MBR treatment and a nanofiltration system into a composite softening coagulation sedimentation tank and subsequent operations, and the treatment method can increase the index load of the original inlet water and possibly cause the vicious circle of a biochemical system. The patent with publication number CN109761416A discloses a process for treating landfill leachate, which comprises purifying nanofiltration concentrated water, adding alkali for softening, then treating in an advanced oxidation system, and finally recharging the wastewater into a regulating tank or a refuse dump, wherein the treatment method is easy to cause secondary pollution and is not feasible in the treatment of the stored quantity of landfill leachate.
In view of the above, the method for treating nanofiltration concentrated solution with simple process and good effect is one of the problems to be solved in the field of landfill leachate treatment.
Disclosure of Invention
Under the condition that an MBR + NF + RO process is generally applied to a landfill leachate treatment process, concentrated sulfuric acid is often used for adjusting inlet water of a nanofiltration membrane system, and the inventor of the application finds that a nanofiltration membrane mainly intercepts divalent salts and organic matters and has low rejection rate of monovalent salts, so that a large amount of divalent ions such as sulfate ions and organic matters are contained in nanofiltration concentrated solution, and the nanofiltration concentrated solution is difficult to treat in a subsequent treatment process.
It is an object of the present application to provide a nanofiltration concentrate zero-emission treatment system and method to solve the above-mentioned problems.
According to a first aspect of the invention, a nanofiltration concentrate zero-emission treatment system is disclosed, which comprises a membrane treatment unit, a freezing crystallization unit and an advanced oxidation unit, wherein the membrane treatment unit is used for filtering the nanofiltration concentrate to generate a first concentrated water product, the first concentrated water product is sent to the freezing crystallization unit, the freezing crystallization unit is used for carrying out mass separation crystallization on the first concentrated water product to generate a crystallization product and a crystallization mother liquor, and the advanced oxidation unit is used for carrying out advanced oxidation treatment on the crystallization mother liquor to generate oxidized effluent, and the oxidized effluent is returned to the membrane treatment unit.
In some embodiments, the membrane treatment unit comprises a multi-stage nanofiltration treatment unit comprising a primary nanofiltration treatment unit and a secondary nanofiltration treatment unit, the nanofiltration concentrate being fed to the primary nanofiltration treatment unit to produce a first concentrated water product and a first water product, the first water product being fed to the secondary nanofiltration treatment unit to produce a second water product and a second concentrated water product, the second concentrated water product and the oxidation product water being recycled to the primary nanofiltration treatment unit. The nanofiltration concentrated solution in the MBR and NF is further separated and concentrated through the multistage nanofiltration treatment unit, so that the monovalent salt can effectively permeate while the organic matter and the high-valence salt are efficiently intercepted, and the efficient separation effect is achieved.
In some embodiments, the first nanofiltration treatment unit comprises a disk-and-tube nanofiltration membrane module, and the second nanofiltration treatment unit comprises a micro-tube roll-type nanofiltration membrane module. The dish tubular nanofiltration membrane component produces water and has higher yield, the pollution resistance is better, the microtubule roll-type nanofiltration membrane component can further filter the produced water of the first-level nanofiltration treatment unit, remove the residual COD, ensure the standard discharge of the produced water, effectively discharge the monovalent salt at the same time, avoid the accumulation of the monovalent salt in the system, and ensure that the system can operate under lower pressure.
In some embodiments, the pH of the feed water to the primary nanofiltration treatment unit is controlled to be 6.5 and the conductivity of the first concentrated water product is controlled to be 100 ms/cm. The pH value of the inlet water of the first-stage nanofiltration treatment unit is controlled to prevent inorganic salt scaling of a membrane system, and the conductivity of the first concentrated water product is controlled to ensure that the concentration of sulfate in the concentrated water is high enough, so that subsequent freezing crystallization salt separation is facilitated, and meanwhile, the stable operation of the first-stage nanofiltration treatment unit is ensured.
In some embodiments, the temperature of the freeze crystallization unit ranges from 0 to 5 ℃. According to the difference of different crystallization temperatures of different salts in the wastewater, a freezing crystallization technology is adopted to separate out and discharge sodium sulfate crystals in the first concentrated water product out of the system, so that the accumulation of divalent sulfate in the system is avoided, the freezing point of the sodium sulfate is 0-5 ℃, the theoretical value of the separation rate at zero degree can reach 90%, and the purity is high.
In some embodiments, the advanced oxidation unit treats the crystallization mother liquor by Fenton oxidation or Fenton-like oxidation, and adjusts the pH value to be 9-10.5 by sodium hydroxide when the Fenton oxidation or Fenton-like oxidation is terminated. The method has the advantages that the Fenton oxidation or similar Fenton oxidation treatment technology is adopted to effectively remove organic matters in the crystallization mother liquor, the flocculation effect of the Fenton reaction can be guaranteed by stopping adding sodium hydroxide in the Fenton oxidation or similar Fenton oxidation, part of calcium, magnesium and heavy metals are removed at the same time, accumulation of divalent cations is avoided, advanced oxidation product water flows back to the DTNF water inlet end for retreatment, and zero discharge of concentrated water of leachate is realized.
According to a second aspect of the invention, a nanofiltration concentrate zero-emission treatment method is disclosed, which comprises the following steps:
s1: filtering the nanofiltration concentrated solution to obtain a first concentrated water product;
s2: freezing and crystallizing the first concentrated water product to obtain a crystallized product and a crystallized mother liquor;
s3: carrying out advanced oxidation treatment on the crystallization mother liquor to obtain oxidation water; and
s4: the oxidation product water is returned to step S1 for filtration.
In some embodiments, the step S1 is performed by a multi-stage nanofiltration treatment unit comprising a primary nanofiltration treatment unit and a secondary nanofiltration treatment unit, the nanofiltration concentrate is fed to the primary nanofiltration treatment unit to produce a first concentrated water product and a first water product, the first water product is fed to the secondary nanofiltration treatment unit to produce a second water product and a second concentrated water product, and the second concentrated water product and the oxidation product water are returned to the primary nanofiltration treatment unit. The nanofiltration concentrated solution in the MBR and NF is further separated and concentrated through the multistage nanofiltration treatment unit, so that the monovalent salt can effectively permeate while the organic matter and the high-valence salt are efficiently intercepted, and the efficient separation effect is achieved.
In some embodiments, the first nanofiltration treatment unit comprises a disk-and-tube nanofiltration membrane module, and the second nanofiltration treatment unit comprises a micro-tube roll-type nanofiltration membrane module. The dish tubular nanofiltration membrane component produces water and has higher yield, the pollution resistance is better, the microtubule roll-type nanofiltration membrane component can further filter the produced water of the first-level nanofiltration treatment unit, remove the residual COD, ensure the standard discharge of the produced water, effectively discharge the monovalent salt at the same time, avoid the accumulation of the monovalent salt in the system, and ensure that the system can operate under lower pressure.
In some embodiments, the pH of the feed water to the primary nanofiltration treatment unit is controlled to be 6.5 and the conductivity of the first concentrated water product is controlled to be 100 ms/cm. The pH value of the inlet water of the first-stage nanofiltration treatment unit is controlled to prevent inorganic salt scaling of a membrane system, and the conductivity of the first concentrated water product is controlled to ensure that the concentration of sulfate in the concentrated water is high enough, so that subsequent freezing crystallization salt separation is facilitated, and meanwhile, the stable operation of the first-stage nanofiltration treatment unit is ensured.
In some embodiments, the temperature range for the freezing and crystallizing treatment is 0-5 ℃. According to the difference of different crystallization temperatures of different salts in the wastewater, a freezing crystallization technology is adopted to separate out and discharge sodium sulfate crystals in the first concentrated water product out of the system, so that the accumulation of divalent sulfate in the system is avoided, the freezing point of the sodium sulfate is 0-5 ℃, the theoretical value of the separation rate at zero degree can reach 90%, and the purity is high.
In some embodiments, the advanced oxidation treatment comprises Fenton oxidation or Fenton-like oxidation treatment of the crystallization mother liquor, and the pH value is adjusted to 9-10.5 by sodium hydroxide when the Fenton oxidation or Fenton-like oxidation is terminated. The method has the advantages that the Fenton oxidation or similar Fenton oxidation treatment technology is adopted to effectively remove organic matters in the crystallization mother liquor, the flocculation effect of the Fenton reaction can be guaranteed by stopping adding sodium hydroxide in the Fenton oxidation or similar Fenton oxidation, part of calcium, magnesium and heavy metals are removed at the same time, accumulation of divalent cations is avoided, advanced oxidation product water flows back to the DTNF water inlet end for retreatment, and zero discharge of concentrated water of leachate is realized.
The embodiment of the application provides a nanofiltration concentrated solution zero-emission treatment system and method, wherein a membrane treatment unit is used for filtering the nanofiltration concentrated solution to generate a first concentrated water product, the first concentrated water product is sent to a freezing crystallization unit, the freezing crystallization unit is used for performing mass separation crystallization on the first concentrated water product to generate a crystallization product and a crystallization mother solution, an advanced oxidation unit is used for performing advanced oxidation treatment on the crystallization mother solution to generate oxidized effluent, and finally the oxidized effluent flows back to the membrane treatment unit. The nanofiltration concentrated solution generated in the MBR + NF process is effectively treated in the way, the landfill leachate nanofiltration concentrated solution is treated under the condition of lower energy consumption, the standard-reaching discharge of produced water is ensured, the whole treatment system does not generate membrane concentrated solution, zero discharge is realized, sodium sulfate crystal by-products with higher purity are obtained through freezing crystallization, and the recycling of resources is realized.
Drawings
The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and together with the description serve to explain the principles of the invention. Other embodiments and many of the intended advantages of embodiments will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.
FIG. 1 is a schematic diagram of a nanofiltration concentrate zero-emission treatment system according to an embodiment of the present invention;
FIG. 2 is a flow chart of a nanofiltration concentrate zero-emission treatment method according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the present invention will be described in further detail with reference to the accompanying drawings, and it is apparent that the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention will be described in detail with reference to fig. 1, and an embodiment of the invention discloses a nanofiltration concentrate zero-emission treatment system, which includes a membrane treatment unit 1, a freezing crystallization unit 2 and a high-grade oxidation unit 3, wherein the membrane treatment unit 1 is configured to filter a nanofiltration concentrate to generate a first concentrated water product, the first concentrated water product is sent to the freezing crystallization unit 2, the freezing crystallization unit 2 is configured to perform mass separation crystallization on the first concentrated water product to generate a crystallization product and a crystallization mother liquor, and the high-grade oxidation unit 3 is configured to perform high-grade oxidation treatment on the crystallization mother liquor to generate oxidized effluent, and the oxidized effluent is returned to the membrane treatment unit 1.
In a specific embodiment, membrane treatment unit 1 comprises a multi-stage nanofiltration treatment unit 11, multi-stage nanofiltration treatment unit 11 comprises a primary nanofiltration treatment unit 111 and a secondary nanofiltration treatment unit 112, the nanofiltration concentrate is fed to primary nanofiltration treatment unit 111 to produce a first concentrated water product and a first water product, the first water product is fed to secondary nanofiltration treatment unit 112 to produce a second water product and a second concentrated water product, and the second concentrated water product and the oxidation water product are refluxed to primary nanofiltration treatment unit 111. The nanofiltration concentrated solution in the MBR and NF is further separated and concentrated through the multistage nanofiltration treatment unit 11, so that the monovalent salt can effectively permeate while the organic matter and the high-valence salt are efficiently intercepted, the efficient separation effect is achieved, the treatment efficiency is high, and the energy consumption is low. In a preferred embodiment, the first nanofiltration treatment unit 111 comprises a disk-and-tube nanofiltration membrane module, and the second nanofiltration treatment unit 112 comprises a micro-tube roll nanofiltration membrane module. Because the nanofiltration membrane mainly intercepts divalent salt and has low interception rate of monovalent salt, the primary nanofiltration treatment unit 111 adopts a disc-tube nanofiltration membrane component (DTNF) for treatment, the water yield of the DTNF membrane component is higher and the pollution resistance is better, the interception molecular weight of the DTNF membrane is 300-. In a preferred embodiment, the pH value of the inlet water of the primary nanofiltration treatment unit 111 is controlled to be 6.5, so that inorganic salt scaling, especially calcium carbonate scaling, of the membrane system can be prevented. The conductivity range of the first concentrated water product generated by the first-stage nanofiltration treatment unit 111 is controlled to be 100ms/cm, so that the concentration of sulfate in the first concentrated water product is high enough, the subsequent freezing crystallization salt separation is facilitated, the stable operation of the DTNF membrane module of the first-stage nanofiltration treatment unit 111 is ensured, and when the conductivity is greater than 100ms/cm, the membrane pollution is fast, and the stable operation of the system is not facilitated. In a preferred embodiment, a micro-tube rolling nanofiltration membrane Module (MTNF) can be used as the second-stage nanofiltration treatment unit 112 to further filter the first water product of the first-stage nanofiltration treatment unit 111, so as to remove COD in the first water product, ensure that the second water product can reach the discharge standard, effectively discharge monovalent salt, avoid the accumulation of monovalent salt in the system, and ensure that the system can operate under a lower pressure. The molecular weight of the MTNF membrane component is 200-300 Da, organic matters in the first water product are further intercepted, the COD of the second water product can be effectively guaranteed to reach the standard, the operating pressure of the MTNF membrane component is 10-20 bar, the yield of the produced water is more than 90%, and the second concentrated water product returns to the first-stage nanofiltration treatment unit 111 to play a role in diluting the concentrated water. In other optional implementations, the membrane treatment system 1 may also select the first-stage nanofiltration treatment unit 111 for treatment, and then the final produced water meets the discharge requirement by other means, or the produced water can reach the standard through the first-stage nanofiltration treatment unit 111 under the condition that the conditions are met. In other alternative embodiments, the first nanofiltration treatment unit 111 may also comprise a disk-and-tube nanofiltration membrane module, and the second nanofiltration treatment unit 112 may also comprise a disk-and-tube nanofiltration membrane module, and the nanofiltration concentrate may be treated by a two-stage DTNF membrane module.
In a specific embodiment, the temperature of the freezing and crystallizing unit 2 is in the range of 0 to 5 ℃. The crystallization product is mainly sodium sulfate, the sodium sulfate in the first concentrated water product is crystallized and separated out and discharged out of the system by adopting a freezing crystallization technology according to the difference of different crystallization temperatures of different salts in the wastewater, the accumulation of divalent sulfate in the system is avoided, the freezing point of the sodium sulfate is 0-5 ℃, the theoretical value of the separation rate at zero degree can reach 90%, the purity is high, and the separated sodium sulfate can be used as industrial salt. The physical properties of the sodium chloride and the sodium sulfate are different, and the freezing point of the sodium chloride is below minus 10 ℃, so that the first concentrated water product of the first-stage nanofiltration treatment unit 111 can be further subjected to quality separation crystallization by adopting low-temperature freezing crystallization to separate the sodium sulfate, the accumulation of sulfate radicals in a system is avoided, and the resource recycling can be realized.
In a specific embodiment, the advanced oxidation unit 3 treats the crystallization mother liquor through Fenton oxidation or similar Fenton oxidation, and adjusts the pH value to be 9-10.5 through sodium hydroxide when the Fenton oxidation or similar Fenton oxidation is finished. The Fenton oxidation mechanism is mainly that under the acidic condition, hydrogen peroxide is in Fe2+Under the catalytic action of ions, hydroxyl radicals with strong oxidizing property are formed, organic matters in the wastewater are oxidized and degraded, and after the pH is adjusted to be neutral or alkaline, Fe (OH) is formed3The method has a high-efficiency flocculation effect, can remove partial organic matters and a large amount of suspended matters in the crystallization mother liquor, so as to play a role in clarification, has a removal rate of COD (chemical oxygen demand) of 30-50% by advanced oxidation, and finally packs and discharges sludge generated by Fenton oxidation or similar Fenton oxidation. The principles of Fenton-like oxidation treatment are similar to Fenton oxidation. The method is obtained by experimental verification, theory and literature summarization, Fenton oxidation freezing crystallization mother liquor is adopted, sulfuric acid is adopted to control the reaction pH to be 2-4, the molar ratio of hydrogen peroxide to ferrous sulfate is 2-3, the concentration of the ferrous sulfate is controlled to be 0.03-0.05 mol/L, sodium hydroxide is adopted to adjust the pH to be 9-10.5 when the reaction is stopped according to the theory and hardness removal pH value requirement, the purposes of coagulating sedimentation clarification and hardness removal are achieved, and oxidation effluent flows back to a first-stage nanofiltrationThe water inlet end of the processing unit 111 is processed again, so that the accumulation of organic matters and hardness is avoided. The method has the advantages that the Fenton oxidation or similar Fenton oxidation treatment technology is adopted to effectively remove organic matters in the crystallization mother liquor, the flocculation effect of the Fenton reaction can be guaranteed by stopping adding sodium hydroxide in the Fenton oxidation or similar Fenton oxidation, part of calcium, magnesium and heavy metals are removed at the same time, accumulation of divalent cations is avoided, advanced oxidation product water flows back to the DTNF water inlet end for retreatment, and zero discharge of concentrated water of leachate is realized. In other alternative embodiments, the order of the freezing crystallization unit 2 and the advanced oxidation unit 3 may be interchanged.
Another embodiment of the present application provides a method for zero-emission treatment of nanofiltration concentrate, comprising the steps of:
s1: filtering the nanofiltration concentrated solution to obtain a first concentrated water product;
s2: freezing and crystallizing the first concentrated water product to obtain a crystallized product and a crystallized mother liquor;
s3: carrying out advanced oxidation treatment on the crystallization mother liquor to obtain oxidation water; and
s4: the oxidation product water is returned to step S1 for filtration.
In a specific embodiment, in step S1, the multi-stage nanofiltration treatment unit comprises a first nanofiltration treatment unit and a second nanofiltration treatment unit, the nanofiltration concentrate is fed into the first nanofiltration treatment unit to produce a first concentrated water product and a first water product, the first water product is fed into the second nanofiltration treatment unit to produce a second water product and a second concentrated water product, and the second concentrated water product and the oxidation water are returned to the first nanofiltration treatment unit. The nanofiltration concentrated solution in the MBR and NF is further separated and concentrated through the multistage nanofiltration treatment unit, so that the monovalent salt can effectively permeate while the organic matter and the high-valence salt are efficiently intercepted, and the efficient separation effect is achieved. In a preferred embodiment, the first-stage nanofiltration treatment unit comprises a disc-tube nanofiltration membrane component, and the second-stage nanofiltration treatment unit comprises a micro-tube roll type nanofiltration membrane component. The nanofiltration membrane mainly intercepts divalent salt, so that the interception rate of monovalent salt is low, the primary nanofiltration treatment unit adopts a disc-tube nanofiltration membrane component (DTNF) for treatment, the water yield of the DTNF membrane component is higher, the pollution resistance is better, the interception molecular weight of the DTNF membrane is 300-. In a preferred embodiment, the pH value of the inlet water of the primary nanofiltration treatment unit is controlled to be 6.5, so that inorganic salt scaling, particularly calcium carbonate scaling, of a membrane system can be prevented. The conductivity range of the first concentrated water product generated by the first-stage nanofiltration treatment unit is controlled to be 100ms/cm, so that the concentration of sulfate in the first concentrated water product is high enough, subsequent freezing crystallization salt separation is facilitated, the stable operation of a DTNF membrane module of the first-stage nanofiltration treatment unit is ensured, and when the conductivity is more than 100ms/cm, the membrane pollution is fast, and the stable operation of a system is not facilitated. In a preferred embodiment, a micro-tube roll-type nanofiltration membrane component (MTNF) can be used as a secondary nanofiltration treatment unit to further filter a first water product of the primary nanofiltration treatment unit, so that COD in the first water product is removed, the second water product can be discharged up to the standard, and simultaneously monovalent salt can be effectively discharged, thereby avoiding the accumulation of the monovalent salt in the system and ensuring that the system can operate under lower pressure. The molecular weight of the MTNF membrane component is 200-300 Da, organic matters in the first water product are further intercepted, the COD of the second water product can be effectively guaranteed to reach the standard, the operating pressure of the MTNF membrane component is 10-20 bar, the yield of the produced water is more than 90%, and the second concentrated water product returns to the first-stage nanofiltration treatment unit to play a role in diluting the concentrated water. In other optional implementation, the membrane treatment system can also select a first-stage nanofiltration treatment unit for treatment, and then the final produced water meets the discharge requirement through other means, or the produced water can reach the standard through the first-stage nanofiltration treatment unit under the condition that the condition is met. In other alternative embodiments, the first nanofiltration treatment unit comprises a disk-and-tube nanofiltration membrane module, and the second nanofiltration treatment unit comprises a disk-and-tube nanofiltration membrane module, and nanofiltration concentrated solution is treated by a two-stage DTNF membrane module.
In a specific embodiment, the temperature range for the freezing and crystallizing treatment is controlled to be 0-5 ℃. The crystallization product is mainly sodium sulfate, the sodium sulfate in the first concentrated water product is crystallized and separated out and discharged out of the system by adopting a freezing crystallization technology according to the difference of different crystallization temperatures of different salts in the wastewater, the accumulation of divalent sulfate in the system is avoided, the freezing point of the sodium sulfate is 0-5 ℃, the theoretical value of the separation rate at zero degree can reach 90%, the purity is high, and the separated sodium sulfate can be used as industrial salt. The physical properties of the sodium chloride and the sodium sulfate are different, and the freezing point of the sodium chloride is below minus 10 ℃, so that the first concentrated water product of the first-stage nanofiltration treatment unit 111 can be further subjected to quality separation crystallization by adopting low-temperature freezing crystallization to separate the sodium sulfate, the accumulation of sulfate radicals in a system is avoided, and the resource recycling can be realized.
In a specific embodiment, the high-level oxidation treatment is to crystallize the mother liquor through Fenton oxidation or Fenton-like oxidation treatment, and the pH value is adjusted to be 9-10.5 through sodium hydroxide when the Fenton oxidation or Fenton-like oxidation is finished. The Fenton oxidation mechanism is mainly that under the acidic condition, hydrogen peroxide is in Fe2+Under the catalytic action of ions, hydroxyl radicals with strong oxidizing property are formed, organic matters in the wastewater are oxidized and degraded, and after the pH is adjusted to be neutral or alkaline, Fe (OH) is formed3The method has a high-efficiency flocculation effect, can remove partial organic matters and a large amount of suspended matters in the crystallization mother liquor, so as to play a role in clarification, has a removal rate of COD (chemical oxygen demand) of 30-50% by advanced oxidation, and finally packs and discharges sludge generated by Fenton oxidation or similar Fenton oxidation. The principles of Fenton-like oxidation treatment are similar to Fenton oxidation. The method is obtained by experimental verification, theories and literature summarization, Fenton oxidation freezing crystallization mother liquor is adopted, sulfuric acid is adopted to control the reaction pH to be 2-4, the molar ratio of hydrogen peroxide to ferrous sulfate is 2-3, the concentration of the ferrous sulfate is controlled to be 0.03-0.05 mol/L, sodium hydroxide is adopted to adjust the pH to be 9-10.5 when the reaction is stopped according to theories and hardness removal pH value requirements, the purposes of coagulating sedimentation clarification and hardness removal are achieved, oxidation effluent flows back to the water inlet end of a primary nanofiltration treatment unit 111 for retreatment, and accumulation of organic matters and hardness is avoided. The Fenton oxidation or similar Fenton oxidation treatment technology can effectively remove the organic matters in the crystallization mother liquorThe flocculation effect of the Fenton reaction can be ensured by stopping adding the sodium hydroxide in the Fenton oxidation or similar Fenton oxidation, part of calcium, magnesium and heavy metal are removed, accumulation of divalent cations is avoided, advanced oxidation produced water flows back to the DTNF water inlet end for retreatment, and zero discharge of concentrated water of leachate is realized. In other alternative embodiments, the order of steps S2 and S3 may be interchanged.
Example one
And (3) performing MBR and NF process treatment on the landfill leachate of a certain landfill to generate nanofiltration concentrated solution, wherein the sulfate ion concentration of the nanofiltration concentrated solution is 2000mg/L, and the COD is 6420 mg/L. And (3) introducing the nanofiltration concentrated solution into a nanofiltration concentrated solution zero-emission treatment system, and filtering the nanofiltration concentrated solution by using a disc-tube nanofiltration membrane component to generate a first concentrated water product and a first water product, wherein the sulfate ions of the first water product are 123mg/L, and the COD is 156 mg/L. The yield of the produced water is 80%, and the first produced water product contains the rest COD, so that the first produced water product is further filtered by a micro-tube rolled nanofiltration membrane component to generate a second produced water product and a second concentrated water product, sulfate ions of the second produced water product are 3mg/L, COD is 56mg/L, ammonia nitrogen is 7.3mg/L, and total nitrogen is 8.1mg/L, so that the second concentrated water product can be directly discharged when meeting the standard discharge requirement, the sulfate ions of the second concentrated water product are 1200mg/L, and COD is 1089mg/L, and therefore the second concentrated water product is refluxed to the disc-tube nanofiltration membrane component for further treatment. The sulfate ion in the first concentrated aqueous product was 7552mg/L and the COD was 21400mg/L, and the first concentrated aqueous product was near-frozen for crystallization and yielded sodium sulfate and a crystallization mother liquor. Sulfate ions of the crystallization mother liquor are 3400mg/L, COD is 21300mg/L, so that the crystallization mother liquor is subjected to advanced oxidation treatment to generate oxidation effluent, and the COD is 8000mg/L, so that the oxidation effluent is refluxed to the disc-tube nanofiltration membrane component for treatment, and a nanofiltration concentrate zero-emission treatment system is ensured not to generate membrane concentrate, and the effects of zero emission and resource recovery are achieved.
The embodiment of the application provides a nanofiltration concentrated solution zero-emission treatment system and method, wherein a membrane treatment unit is used for filtering the nanofiltration concentrated solution to generate a first concentrated water product, the first concentrated water product is sent to a freezing crystallization unit, the freezing crystallization unit is used for performing mass separation crystallization on the first concentrated water product to generate a crystallization product and a crystallization mother solution, an advanced oxidation unit is used for performing advanced oxidation treatment on the crystallization mother solution to generate oxidized effluent, and finally the oxidized effluent flows back to the membrane treatment unit. By adopting the method, the nanofiltration concentrated solution generated in the MBR + NF process is effectively treated, and the membrane operation system has low pressure and low energy consumption. And separating out sodium sulfate in the first concentrated water product by adopting a freezing crystallization technology, so that the sodium sulfate is discharged out of the system, and divalent salt is prevented from accumulating in the system. The frozen crystallization mother liquor is treated by the advanced oxidation technology, so that organic matters in the crystallization mother liquor can be effectively reduced, and then oxidation product water after advanced oxidation treatment flows back to the front end of the membrane treatment unit, thereby avoiding the accumulation of the organic matters in the system.
While the principles of the invention have been described in detail in connection with the preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing embodiments are merely illustrative of exemplary implementations of the invention and are not limiting of the scope of the invention. The details of the embodiments are not to be interpreted as limiting the scope of the invention, and any obvious changes, such as equivalent alterations, simple substitutions and the like, based on the technical solution of the invention, can be interpreted without departing from the spirit and scope of the invention.
Claims (8)
1. A nanofiltration concentrate zero-emission treatment system is characterized by comprising a membrane treatment unit, a freezing crystallization unit and an advanced oxidation unit, wherein the membrane treatment unit is used for filtering nanofiltration concentrate to generate a first concentrated water product, the first concentrated water product is fed into the freezing crystallization unit, the freezing crystallization unit is used for performing quality separation crystallization on the first concentrated water product to generate a crystallization product and a crystallization mother liquor, the advanced oxidation unit is used for performing advanced oxidation treatment on the crystallization mother liquor to generate oxidation product water, the oxidation product water is returned to the membrane treatment unit, the membrane treatment unit comprises a multi-stage nanofiltration treatment unit, the multi-stage nanofiltration treatment unit comprises a primary nanofiltration treatment unit and a secondary nanofiltration treatment unit, the nanofiltration concentrate is fed into the primary nanofiltration treatment unit to generate the first concentrated water product and a first product water product, the first water product is sent into the second-stage nanofiltration treatment unit to generate a second water product and a second concentrated water product, the second concentrated water product and the oxidation water product flow back to the first-stage nanofiltration treatment unit, nanofiltration concentrated solution is generated in the process of treating the landfill leachate by MBR and NF processes, the first-stage nanofiltration treatment unit comprises a disc-tube nanofiltration membrane component, the second-stage nanofiltration treatment unit comprises a micro-tube rolling nanofiltration membrane component, and the pH value range of inlet water of the first-stage nanofiltration treatment unit is controlled at 6.5.
2. The nanofiltration concentrate zero-emission treatment system of claim 1, wherein the conductivity of the first concentrated water product is controlled to be in the range of 100 ms/cm.
3. The nanofiltration concentrate zero-emission treatment system according to claim 1, wherein the temperature of the freeze crystallization unit is in the range of 0-5 ℃.
4. The nanofiltration concentrate zero-emission treatment system according to claim 1, wherein the advanced oxidation unit is used for treating the crystallization mother liquor through Fenton oxidation or Fenton-like oxidation, and adjusting the pH value to be 9-10.5 through sodium hydroxide when the Fenton oxidation or Fenton-like oxidation is terminated.
5. A nanofiltration concentrate zero-emission treatment method is characterized by comprising the following steps:
s1: filtering the nanofiltration concentrated solution to obtain a first concentrated water product;
s2: freezing and crystallizing the first concentrated water product to obtain a crystallized product and a crystallized mother liquor;
s3: carrying out advanced oxidation treatment on the crystallization mother liquor to obtain oxidation water; and
s4: returning the oxidation product water to the step S1 for filtration treatment, wherein the step S1 adopts a multi-stage nanofiltration treatment unit for filtration treatment, the multi-stage nanofiltration treatment unit comprises a primary nanofiltration treatment unit and a secondary nanofiltration treatment unit, the nanofiltration concentrate is fed into the primary nanofiltration treatment unit to produce the first concentrated water product and a first water product, the first water product is fed to the secondary nanofiltration treatment unit to produce a second water product and a second concentrated water product, the second concentrated water product and the oxidation product water flow back to the primary nanofiltration treatment unit, the nanofiltration concentrated solution is generated in the process of treating the landfill leachate by MBR + NF technology, the first-stage nanofiltration treatment unit comprises a disc-tube nanofiltration membrane component, the second-stage nanofiltration treatment unit comprises a micro-tube roll type nanofiltration membrane component, and the pH value range of inlet water of the first-stage nanofiltration treatment unit is controlled to be 6.5.
6. The nanofiltration concentrate zero-emission treatment process of claim 5, wherein the conductivity of the first concentrated water product is controlled within a range of 100 ms/cm.
7. The nanofiltration concentrate zero-emission treatment method of claim 5, wherein the temperature control range of the freezing and crystallizing treatment is 0-5 ℃.
8. The nanofiltration concentrate zero-emission treatment method according to claim 5, wherein the advanced oxidation treatment is carried out by Fenton oxidation or Fenton-like oxidation treatment on the crystallization mother liquor, and the pH value is adjusted to 9-10.5 by sodium hydroxide when the Fenton oxidation or Fenton-like oxidation is terminated.
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