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CN-117865407-B - System and method for treating tap water with excessive nitrate

CN117865407BCN 117865407 BCN117865407 BCN 117865407BCN-117865407-B

Abstract

The invention discloses a system and a method for treating tap water with excessive nitrate. The treatment system comprises a nitrate separation device (1), a frequent reverse pole electrodialysis device (2), a nanofiltration salt separation device (3) and a water production tank (5). The treatment method comprises the steps of carrying out nitrate separation treatment on raw water to obtain concentrated water and pre-produced water respectively, introducing the concentrated water into a frequent reverse pole electrodialysis device (2) to obtain low-salt wastewater and high-salt solution respectively, introducing the high-salt solution into a nanofiltration salt separation device (3) to obtain permeate and separation liquid respectively, and mixing the separation liquid with the pre-produced water to obtain the produced water. The invention is mainly used for treating tap water with excessive nitrate in a tap water plant and for subsequent treatment of concentrated water after nitrate removal, and adopts a salt separation reflux mode to reflux divalent ions beneficial to human health and pipe network stability in the concentrated water to tap water, so that the TDS content of the nanofiltration concentrated water after treatment meets the environmental protection requirement.

Inventors

  • ZHONG YANMIN
  • DUAN DONG
  • ZHOU TINGRU
  • RUI MIN
  • LIU ZHIYUAN
  • XU LONG

Assignees

  • 上海市政工程设计研究总院（集团）有限公司
  • 上海水业设计工程有限公司

Dates

Publication Date
20260508
Application Date
20240207

Claims (20)

  1. 1. The treatment system of tap water with excessive nitrate is characterized by comprising a nitrate separation device (1), a frequent reverse electrodialysis device (2), a nanofiltration salt separation device (3) and a water production tank (5); the nitrate separating device (1) is provided with a raw water inlet (11), a concentrated water outlet (12) and a pre-produced water outlet (13) and is used for separating raw water into concentrated water and pre-produced water; The frequent reverse pole electrodialysis device (2) is provided with a concentrated water inlet (21), a high-salt solution outlet (22) and a low-salt wastewater outlet (23) which are used for separating the concentrated water from which nitrate is removed into high-salt solution and low-salt wastewater, wherein the concentrated water inlet (21) is connected with the concentrated water outlet (12); The nanofiltration salt separation device (3) is provided with a high-salt solution inlet (31), a separation solution outlet (33) and a permeate outlet (32) which are used for separating the high-salt solution into a separation solution containing divalent ions and more and a permeate containing monovalent ions, wherein the high-salt solution outlet (22) is connected with the high-salt solution inlet (31), the separation solution outlet (33) and the pre-produced water outlet (13) are respectively connected with the water production tank (5), and the water production tank (5) is used for combining the separation solution with the pre-produced water to serve as produced water; an organic matter removing device (4) is arranged on a connecting pipeline between the separating liquid outlet (33) and the water producing tank (5), and an outer branch is also arranged on a pipeline between the separating liquid outlet (33) and the organic matter removing device (4).
  2. 2. The system for treating tap water with excess nitrate according to claim 1, characterized in that the nitrate separation device (1) is a nanofiltration device or a reverse osmosis device; and/or a nanofiltration membrane is arranged in the nanofiltration salt separation device (3).
  3. 3. The nitrate excess tap water treatment system according to claim 2, characterized in that a pretreatment unit is further provided upstream of the raw water inlet (11); and/or the nanofiltration membrane is made of a poly-piperazine composite film.
  4. 4. The nitrate excess tap water treatment system of claim 3, wherein the pretreatment unit comprises one or more of a sedimentation tank, an air flotation machine, an ozone contact tank, a higher oxidation device, an activated carbon adsorption device, and an ultrafiltration membrane device.
  5. 5. The system for treating excess tap water containing nitrate according to claim 4, wherein the pretreatment unit comprises a sedimentation tank, a high-grade oxidation device, an activated carbon adsorption device and an ultrafiltration membrane device which are connected in sequence.
  6. 6. The nitrate excess tap water treatment system of claim 4, wherein the sedimentation tank is a flocculation sedimentation tank; and/or the activated carbon adsorption device is an upward flow activated carbon adsorption device or a downward flow activated carbon filter; and/or the advanced oxidation device is an ultraviolet-hydrogen peroxide advanced oxidation device; And/or the ultrafiltration membrane device is an immersed ultrafiltration membrane device or a pressure ultrafiltration membrane device.
  7. 7. The system for treating excess nitrate tap water according to claim 1, wherein the organic matter removing device (4) is an ultraviolet light-hydrogen peroxide advanced oxidation device or an activated carbon adsorption device.
  8. 8. A method for treating tap water with excess nitrate, characterized in that the treatment system for tap water with excess nitrate according to any one of claims 1-7 is used, comprising the steps of: Carrying out nitrate separation treatment on raw water to obtain concentrated water and pre-produced water respectively; introducing the concentrated water into a frequent reverse pole electrodialysis device (2) to respectively obtain low-salt wastewater and high-salt solution; introducing the high-salt solution into a nanofiltration salt separating device (3) to obtain a permeate and a separation liquid respectively, removing organic matters of the separation liquid, and mixing with the pre-produced water to obtain the produced water.
  9. 9. The method for treating excess nitrate tap water according to claim 8, wherein the nitrate separation treatment is nanofiltration or reverse osmosis; and/or the water inlet pressure of the frequent reverse pole electrodialysis device (2) is 0.2-0.3MPa; and/or the effective membrane area in the frequent reversed pole electrodialysis device (2) is 250-350m 2 ; And/or the reverse pole period of the frequent reverse pole electrodialysis device (2) is 15-25min; And/or the water inlet pressure of the nanofiltration salt separation device (3) is 0.5-0.8MPa; and/or a nanofiltration membrane is arranged in the nanofiltration salt separation device (3).
  10. 10. The method for treating tap water with excess nitrate according to claim 9, wherein the nitrate separation treatment is preceded by a pretreatment process.
  11. 11. The method of treating nitrate excess tap water according to claim 10, wherein the pretreatment process comprises one or more of precipitation, air flotation, filtration, ozone contact, advanced oxidation, activated carbon adsorption and ultrafiltration.
  12. 12. The method for treating tap water with excess nitrate according to claim 10, wherein the pretreatment process comprises precipitation, advanced oxidation, activated carbon adsorption, ultrafiltration and deep separation in this order.
  13. 13. The method for treating excess nitrate tap water according to claim 11, wherein the advanced oxidation is ultraviolet-hydrogen peroxide advanced oxidation; And/or the conditions of the ultrafiltration meet at least one of the following: ① The membrane flux of the ultrafiltration membrane is 30-40L/h; ② The maximum allowable transmembrane pressure difference of the ultrafiltration membrane is 0.06MPa; ③ The ultrafiltration membrane is made of PVDF; And/or the conditions of reverse osmosis meet at least one of the following: ① The flux of the reverse osmosis is 15-20L/h; ② The water inlet pressure of the reverse osmosis is 1-2MPa; And/or the water inlet pressure of the frequent reverse pole electrodialysis device (2) is 0.25MPa; and/or the effective membrane area in the frequent reverse pole electrodialysis device (2) is 300m 2 ; and/or the reverse pole period of the frequent reverse pole electrodialysis device (2) is 20min; and/or the water inlet pressure of the nanofiltration salt separation device (3) is 0.6MPa; and/or the nanofiltration membrane is made of a poly-piperazine composite film.
  14. 14. The method for treating nitrate-excess tap water according to claim 13, wherein the ultrafiltration membrane has a membrane flux of 35L/h; And/or, the flux of reverse osmosis is 19.98L/h.
  15. 15. The method for treating tap water with excess nitrate according to claim 13, wherein the conditions of the ultraviolet-hydrogen peroxide advanced oxidation satisfy at least one of the following conditions: ① The UV light intensity is 300-500mJ/cm 2 ; ② The ultraviolet transmittance is more than or equal to 85 percent; ③H 2 O 2 The maximum dosage of (C) is 6mg/L.
  16. 16. The method for treating nitrate-excess tap water according to claim 15, wherein the UV light intensity is 400mJ/cm 2 .
  17. 17. The method for treating nitrate excess tap water according to claim 9, wherein the nanofiltration membrane has a maximum pressure drop of 0.1MPa; And/or the membrane flux of the nanofiltration membrane is 15-20L/h.
  18. 18. The method for treating nitrate-excess tap water according to claim 17, wherein the nanofiltration membrane has a membrane flux of 19L/h.
  19. 19. The method for treating nitrate-excess tap water according to claim 8, wherein the ratio of the volumes of the low-salt wastewater and the high-salt solution is 18000 (3100-3200); and/or the volume ratio of the permeate and the separation liquid is 2700 (450-500); And/or, the nitrate content in the raw water exceeds 10.0mg/L; And/or the content of organic matters COD Mn in the raw water is 4.50-5.00mg/L; And/or, in the raw water, the TDS content exceeds 250mg/L; And/or, in the concentrated water, the TDS content is 2500-2700mg/L; and/or, the content of organic matters COD Cr in the concentrated water is 40-60mg/L; and/or, in the pre-produced water, the TDS content is 150-200mg/L; and/or, in the pre-produced water, the content of organic matters COD Mn is 0.9-1.1mg/L; And/or, in the low-salt wastewater, the TDS content is 300-350mg/L; And/or, the content of organic matters COD Cr in the low-salt wastewater is 40-60mg/L; And/or, in the high-salt solution, the TDS content is 15000-16000mg/L; And/or, in the high-salt solution, the content of organic matters COD Cr is 40-60mg/L; and/or, the TDS content in the permeate is 8200-8300mg/L; And/or, the content of organic matters COD Cr in the permeate is not more than 5mg/L; And/or, in the separating liquid, the TDS content is 55000-60000mg/L; and/or, the content of organic matters COD Cr in the separating liquid is 300-400mg/L; And/or, in the produced water, the TDS content is 250-350mg/L; And/or, in the produced water, the content of organic matters COD Mn is less than 3mg/L.
  20. 20. The method for treating nitrate-excess tap water according to claim 19, wherein the volume ratio of the low-salt wastewater to the high-salt solution is 18000:3176; And/or the volume ratio of the permeate and the separation liquid is 2700:476; And/or, the nitrate content in the raw water is 15.0-20.0mg/L; And/or, the content of organic matters COD Mn in the raw water is 4.61mg/L; and/or, the TDS content in the raw water is 350.0-400.0mg/L; and/or, in the raw water, monovalent ions and divalent and above ions account for 48-52% by mass; and/or, in the concentrated water, the TDS content is 2605mg/L; and/or, in the concentrated water, the content of organic matters COD Cr is 50mg/L; And/or, in the pre-produced water, the TDS content is 163mg/L; and/or, in the pre-produced water, the content of organic matters COD Mn is 1mg/L; And/or, in the low-salt wastewater, the TDS content is 306mg/L; and/or, in the low-salt wastewater, the content of organic matters COD Cr is 50mg/L; And/or, in the high-salt solution, the TDS content is 15630mg/L; And/or, in the high-salt solution, the content of organic matters COD Cr is 50mg/L; and/or, in the permeate, the TDS content is 8275mg/L; And/or, the content of organic matters COD Cr in the permeate is 0mg/L; And/or, the TDS content in the separating liquid is 57310mg/L; and/or, the content of organic matters COD Cr in the separating liquid is 333mg/L; And/or, in the produced water, the TDS content is 299mg/L; And/or, in the produced water, the content of organic matter COD Mn is less than 1.8mg/L.

Description

System and method for treating tap water with excessive nitrate Technical Field The invention particularly relates to a system and a method for treating tap water with excessive nitrate. Background Under the condition that the nitrate content of raw water in a running water plant exceeds the standard, inorganic salt cannot be removed by conventional treatment and ozone active carbon advanced treatment, and the nitrate content is required to be removed by adopting a compact nanofiltration membrane or a reverse osmosis process, so that the effluent quality is ensured to reach the standard. Along with the continuous permeation of high-quality produced water produced by the nanofiltration membrane in the nanofiltration process, the inlet water is continuously concentrated, and finally concentrated water (tail water) with high salt content and high organic matter content is formed. If the nanofiltration or reverse osmosis recovery rate is 85% for the purpose of nitrate removal, the TDS content in the concentrated water will be 6-7 times higher than that in the incoming water. The salt content (TDS) in raw water in a part of areas is high, after nanofiltration or reverse osmosis treatment, the TDS content in concentrated water is often higher than 300mg/L, the local environment-friendly emission standard cannot be met, and the contradiction between the requirement for improving the water quality of drinking water and the emission supervision of the environment-friendly industry is caused. The compact nanofiltration membrane or the reverse osmosis system removes nitrate, and simultaneously removes divalent ions which are not removed in water, are beneficial to human health and are related to the chemical stability of the effluent, are not beneficial to the quality of the tap water effluent, and the quality stability of the tap water effluent after the tap water effluent with the excessive ions is excessively removed enters a corresponding pipe network is poor. The TDS in nanofiltration or reverse osmosis concentrated water is removed, industrial wastewater mostly adopts a salt separation crystallization mode, and the crystallization salt can be reused, but the common equipment investment and the energy consumption are higher, and the crystallization salt outlet needs to be solved. For a tap water plant, even if the TDS content of nanofiltration tail water cannot meet the local environment-friendly emission standard, the content of salt in the nanofiltration tail water is much lower than that of industrial wastewater, the energy consumption is high by adopting a salt separation crystallization mode, and the nanofiltration tail water is not applicable, even if concentrated water is treated by adopting salt separation crystallization, the crystallization salt outlet is difficult to solve, so that the concentrated water treated by adopting the salt separation crystallization mode is difficult to popularize in the tap water plant, and the popularization of the nanofiltration process is limited to a certain extent. Disclosure of Invention The invention aims to overcome the defects of the existing method for removing TDS in nanofiltration or reverse osmosis concentrated water, and provides a system and a method for treating tap water with excessive nitrate. The invention is mainly used for the subsequent treatment of concentrated water after nitrate is filtered out in a tap water plant, and divalent ions which are beneficial to human health and pipe network stability in the concentrated water are refluxed to tap water product by adopting a salt-separating reflux mode, so that the TDS content of the nanofiltration concentrated water after the nanofiltration concentrated water is treated meets the environmental protection requirement. The method specifically separates divalent ions such as Ca 2+、Mg2+、SO42-、CO32- and the like in nanofiltration concentrated water which are not required to be removed, returns the divalent ions to running water, separates monovalent ions such as Na +、K+、NO3-、Cl- and the like in the concentrated water and soluble organic matters, is convenient for classification and treatment, and ensures that TDS discharged from nanofiltration links of water plants meets the local environment-friendly emission standard. The invention has the advantages of accurate target, low energy consumption, high economy, high feasibility and the like, and provides a brand new idea for the nanofiltration or reverse osmosis concentrated water treatment of a water works. The aim of the invention is achieved by the following technical scheme. In a first aspect, the invention provides a treatment system for tap water with excessive nitrate, which comprises a nitrate separating device, a frequent reverse pole electrodialysis device, a nanofiltration salt separating device and a water producing tank; the nitrate separating device is provided with a raw water inlet, a concentrated water outlet and a pre-produced water outlet and