A zero-emission process system for sewage treatment

Abstract

The present invention discloses a zero-emission process system for a sewage treatment system, which takes into account the recovery of sodium chloride crystals and the sodium sulfate crystallization recovery system. The entire zero-emission system is organically composed of three parts: reclaimed water external supply, sodium chloride recovery, and sodium sulfate recovery. Each part is further divided into multiple units according to its functions, such as pretreatment, softening, salt separation, sodium chloride concentration and purification, sodium sulfate concentration and purification, and MVR evaporation crystallization. Each unit is further divided into multiple subsystems according to different specific treatment methods. This large-scale zero-emission system can achieve a concentrated water treatment capacity of approximately 38,800 tons per day, of which approximately 30,000 tons of water resources can be recovered, and the total recovery of sodium chloride and sodium sulfate is approximately 540 tons per day. The large-scale application of the zero-emission system truly realizes the reuse of resources, greatly reduces the discharge and treatment of solid-liquid wastes, and makes a more profound contribution to promoting social sustainable development, realizing circular economy, and building an environment-friendly society.

Description

Technical Field

[0001] The present invention relates to the field of sewage treatment systems, and specifically relates to a zero-emission process system for sewage treatment systems. Background Art

[0002] The development of modern society has higher and higher requirements for environmental protection, and thus puts forward higher requirements for the sewage discharge of industries such as pharmaceuticals, papermaking, chemical engineering, dyes, and daily life. Sewage must be treated more deeply before it can meet the discharge standards.

[0003] In existing sewage treatment systems, zero-emission projects generally have deficiencies such as small scale, excessive consumption of fresh water resources, and low efficiency, and cannot meet the current stage requirements.

[0004] The invention patent with the publication number of CN110563213A discloses an industrial wastewater zero-emission process, including a clarification kettle, a softening process, a sedimentation tank, and a reverse osmosis device. Although this method can separate concentrated water and pure water, it fails to further treat the concentrated water, and its treatment scale is small.

[0005] The invention patent with the publication number of CN108128961A discloses a method and system for zero discharge of saline wastewater, including a pretreatment process, a membrane concentration process, and an evaporation crystallization and salt separation process. Through a relatively complex process control system, this invention can better separate sodium chloride and sodium sulfate, but the process flow is long, there are many pre-treatments in the salt separation process, and the degree of automation is low. Although the overall product water and finished salt recovery rates are high, it cannot completely separate and purify sodium chloride and sodium sulfate, there is some mixed salt crystallization output, and no sodium chloride solution output channel is set up. Summary of the Invention

[0006] In order to further recover water resources and inorganic salt resources, while ensuring economic benefits and protecting the environment to achieve the goal of sustainable development, the present invention provides the following technical solutions.

[0007] A zero-emission process system for a sewage treatment system includes a salt separation nanofiltration device, a sodium chloride recovery component, an RO product water tank, and a sodium sulfate recovery component;

[0008] The salt separation nanofiltration device is used for salt separation treatment of sewage, and its output end includes a product water side and a concentrated water side;

[0009] The sodium chloride recovery component includes a low-pressure seawater desalination device, a sodium chloride pretreatment unit, a sodium chloride salt separation unit, a sodium chloride concentration unit, and a sodium chloride crystallization unit that are connected in sequence, and the input end of the low-pressure seawater desalination device is connected to the product water side of the salt separation nanofiltration device;

[0010] The RO product water tank is connected to the product water side of the sodium chloride recovery component;

[0011] The sodium sulfate recovery component includes a sodium sulfate pretreatment unit, a softening unit, a sodium sulfate salt separation unit, and a sodium sulfate concentration, purification, and MVR evaporation crystallization unit, which are connected in sequence. The input end of the sodium sulfate pretreatment unit is communicated with the concentrated water side of the salt separation nanofiltration device. Moreover, the water production side of the sodium sulfate salt separation unit is communicated with the input end of the low-pressure seawater desalination device.

[0012] Further, the sodium chloride crystallization unit is an MVR evaporation crystallization device, and its input end is communicated with the output end of the sodium chloride concentration unit. It is mainly used for the crystallization and purification of sodium chloride, and finally obtains sodium chloride crystals for external supply to users.

[0013] Further, the sodium chloride pretreatment unit includes a chemical silicon removal device, a sand filter tank, and an ultrafiltration device, which are communicated in sequence. The input end of the chemical silicon removal device is communicated with the output end of the low-pressure seawater desalination device, and the output end of the ultrafiltration device is communicated with the input end of the sodium chloride salt separation unit. The chemical silicon removal device reacts chemically with silicon in the wastewater through chemical additives to form a precipitate. The function of the sand filter tank is to filter out the precipitate to remove silicon in the wastewater. The ultrafiltration device is used to remove macromolecular organic matters such as colloids and microorganisms in the water.

[0014] Further, the sodium chloride salt separation unit includes a high-pressure seawater desalination device and an ultra-high-pressure seawater desalination device. The input end of the high-pressure seawater desalination device is communicated with the output end of the sodium chloride pretreatment unit. The input end of the high-pressure seawater desalination device is communicated with the output end of the high-pressure seawater desalination device. The output end of the high-pressure seawater desalination device is communicated with the input end of the sodium chloride concentration unit. It further concentrates sodium chloride, raising the concentration from the initial 3 - 5% to 10 - 15%.

[0015] Further, the sodium chloride concentration unit includes an MVR evaporation concentration device and an electrodialysis device. The input end of the electrodialysis device is communicated with the output end of the high-pressure seawater desalination device. After the output end is communicated with the output end of the ultra-high-pressure seawater desalination device, it is communicated with the input end of the MVR evaporation concentration device. The output end of the MVR evaporation concentration device is communicated with the input end of the sodium chloride crystallization unit. The MVR evaporation concentration device can further increase the sodium chloride concentration to about 30%, and compared with the traditional thermal evaporation system, it can greatly reduce the use of live steam. The electrodialysis device is similar to the MVR evaporation device, but it can only increase the sodium chloride concentration to about 20%. The ultra-high-pressure seawater desalination device has a low investment cost, but its disadvantage is that the increase in sodium chloride concentration can only reach 10 - 15%, while the electrodialysis can reach about 30%, and the disadvantage is that the investment and operation costs are slightly higher. The present invention adopts the form of parallel connection of the two. One is to compare the treatment performance of the two, and the other is to reasonably optimize the investment cost.

[0016] Further, the sodium chloride salt separation unit, the sodium chloride concentration unit, and the sodium chloride crystallization unit all include a water production side communicated with the RO water production pool.

[0017] Further, the sodium sulfate pretreatment unit includes an ozone pool, a sand filter, and an ultrafiltration device connected in sequence. The input end of the ozone pool is communicated with the concentrated water side of the salt separation nanofiltration device, and the output end of the ultrafiltration device is communicated with the input end of the softening unit. The ozone pool is used to reduce the COD and color of the concentrated water. The sand filter removes most of the solids, and the ultrafiltration device removes colloids, microorganisms, etc. in the concentrated water.

[0018] Further, the sodium sulfate salt separation unit includes a medium-pressure nanofiltration device and a high-pressure nanofiltration device. The input end of the medium-pressure nanofiltration device is communicated with the output end of the softening unit, and the output end is communicated with the input end of the high-pressure nanofiltration device. The output end of the high-pressure nanofiltration device is communicated with the sodium sulfate concentration and purification MVR evaporation and crystallization unit. This unit further separates and concentrates the salt in the concentrated water, not only increasing the concentration of sodium sulfate, but also further separating the remaining sodium chloride and transporting it to the sodium chloride recovery component for combined treatment.

[0019] Further, the sodium sulfate concentration and purification MVR evaporation and crystallization unit includes a freezing crystallization device, a nitrate melting tank, and an MVR evaporation and crystallization device connected in sequence. The input end of the freezing crystallization device is communicated with the output end of the sodium sulfate salt separation unit. The function of the freezing crystallization device is to enable sodium sulfate to combine with water molecules and precipitate from the saturated solution in the form of sodium sulfate decahydrate crystals. The role of the nitrate melting tank is to melt the sodium sulfate decahydrate crystals. The MVR evaporation and crystallization device evaporates and crystallizes the molten sodium sulfate decahydrate crystals to finally obtain sodium sulfate crystals for external supply to users.

[0020] The present invention has the following beneficial effects:

[0021] 1. By setting up a sodium chloride recovery component to recover sodium chloride and water resources, and setting up a sodium sulfate recovery component to recover sodium sulfate, large-scale zero-discharge wastewater treatment is achieved, and water resources and inorganic salt resources are recovered.

[0022] 2. The system can provide some produced water for external use and can also be used for the backwashing process of each membrane component unit of the system itself. Therefore, a large amount of fresh water resources can be saved, and the recovery of sodium chloride crystals and sodium sulfate crystals by the system can reduce the discharge of inorganic salt solids.

[0023] 3. Further improve the economic benefits in the wastewater treatment process. Further protect the external natural environment for human survival and achieve the sustainable development of society.

[0024] 5. Large-scale separation and purification of mixed salts have been achieved, enhancing the resource utilization of salts, increasing the added value of industrial salts, and turning waste industrial salts into valuable resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic flow chart of the zero-emission process system in the embodiment of the present invention.

[0026] Figure 2 It is a schematic process flow diagram of the MVR evaporation and concentration device in the embodiment of the present invention.

[0027] Figure 3 It is a schematic process flow diagram of the MVR evaporation and crystallization device in the embodiment of the present invention.

[0028] Figure 4 It is a schematic process flow diagram of the freeze crystallization device in the embodiment of the present invention.

[0029] In the figure: A, sodium sulfate pretreatment unit; B, softening unit; C, sodium chloride salt separation unit; D, sodium sulfate concentration and salt separation unit; E, sodium chloride concentration unit; F, sodium sulfate concentration and purification MVR evaporation and crystallization unit; G, sodium chloride crystallization unit; H, sodium chloride pretreatment unit;

[0030] 1. Salt separation nanofiltration device; 2. Low-pressure seawater desalination device; 3. Chemical silicon removal device; 4. Sand filter tank; 5. Ultrafiltration device; 6. High-pressure seawater desalination device; 7. Ultra-high-pressure seawater desalination device; 8. MVR evaporation and concentration device; 9. Electrodialysis device; 10. MVR evaporation and crystallization device; 11. RO product water tank; 12. Ozone tank; 13. Sand filter tank; 14. Ultrafiltration device; 15. Resin softening device; 16. Medium-pressure nanofiltration device; 17. High-pressure nanofiltration device; 18. Freeze crystallization device; 19. Melting nitrate tank; 20. MVR evaporation and crystallization device. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The present invention will be further described with reference to the accompanying drawings. The embodiments described below are only a part of the embodiments of the present invention and do not represent all embodiments.

[0032] This embodiment provides a zero-emission process system for a sewage treatment system, which includes a salt separation nanofiltration device 1, a sodium chloride recovery component, an RO product water tank 11, and a sodium sulfate recovery component.

[0033] The salt separation nanofiltration device 1 is used for salt separation treatment of sewage. Its output end includes a water production side and a concentrated water side. In this embodiment, the primary concentrated water is subjected to salt separation through the salt separation nanofiltration device 1, and the salt separation of sodium chloride and sodium sulfate is carried out on the concentrated water. The product on the water production side is mainly sodium chloride, and the product on the concentrated water side is mainly sodium sulfate. Then, they enter the sodium chloride recovery component and the sodium sulfate recovery component respectively for treatment. Among them, the nanofiltration membrane composition model of the salt separation nanofiltration device 1 is any one of XC-N, N40-8040, TZD-NF, and PRO-XS2.

[0034] The sodium chloride recovery component is used for treating the product mainly composed of sodium chloride on the water production side of the salt separation nanofiltration device 1 to finally obtain sodium chloride crystals and a sodium chloride crystal solution, and conveying the produced water to the RO water production pool 11 for treatment to obtain reclaimed water for external use.

[0035] Specifically, the sodium chloride recovery component includes a low-pressure seawater desalination device 2, a sodium chloride pretreatment unit H, a sodium chloride salt separation unit C, a sodium chloride concentration unit E, and a sodium chloride crystallization unit G that are connected in sequence, and the input end of the low-pressure seawater desalination device 2 is connected to the water production side of the salt separation nanofiltration device 1. In detail, the sodium chloride pretreatment unit H includes a chemical silicon removal device 3, a sand filter 4, and a first ultrafiltration device 5 connected in sequence. The sodium chloride salt separation unit C includes a high-pressure seawater desalination device 6 and an ultra-high-pressure seawater desalination device 7. The sodium chloride concentration unit E includes an MVR evaporation concentration device 8 and an electrodialysis device 9. The sodium chloride crystallization unit G is an MVR evaporation crystallization device 10. The chemical silicon removal device 3, the sand filter 4, the first ultrafiltration device 5, the high-pressure seawater desalination device 6, the ultra-high-pressure seawater desalination device 7, the MVR evaporation concentration device 8, and the MVR evaporation crystallization device 10 are connected in sequence so that the next device can receive the product transported by the previous device, and the electrodialysis device 9 is connected in parallel with the ultra-high-pressure seawater desalination device 7, that is, the output end of the high-pressure seawater desalination device 6 is divided into two paths, one path is connected to the input end of the ultra-high-pressure seawater desalination device 7, and the other path is connected to the input end of the electrodialysis device 9. The output end of the electrodialysis device 9 converges with the output end of the ultra-high-pressure seawater desalination device 7 and then is connected to the input end of the MVR evaporation concentration device 8.

[0036] The low-pressure seawater desalination device 2, the high-pressure seawater desalination device 6, the ultra-high-pressure seawater desalination device 7, the MVR evaporation concentration device 8, and the MVR evaporation crystallization device 10 all further include a water production side, and the water production sides are all connected to the RO water production pool 11. The low-pressure seawater desalination membrane model of the low-pressure seawater desalination device 2 is any one of TM820V-400 and TM820M-400.

[0037] Please refer to Figure 2, the MVR evaporation and concentration device 8 includes a concentrator, a first heater, a first preheater, and a first steam compressor. The first preheater, the heater, and the concentrator are connected in sequence, and the output end of the concentrator communicates with the input end of the MVR evaporation and crystallization device 10. The feed liquid from the input end of the MVR evaporation and concentration device 8 enters the first preheater for preheating, then enters the first heater for further heating, and finally is transported to the concentrator for evaporation and concentration. The concentrated liquid enters the subsequent MVR evaporation and crystallization device 10 through the outlet. The live steam provides heat for the concentrator, and the steam is cooled into distilled water for further recovery and reuse. The secondary steam generated by the vaporization of the solvent in the concentrator is pressurized, heated up by the first steam compressor, and used as the heat source for the first heater. The high-temperature condensed water formed in the first heater is used as the heat source for the first preheater to preheat the feed liquid.

[0038] In this embodiment, the MVR evaporation and crystallization device 10 utilizes evaporation to remove the solvent to achieve crystal precipitation. Please refer to Figure 3 , the MVR evaporation and crystallization device 10 includes a second preheater, a second heater, a crystallization separator, a first feed liquid pump, a thickener, a first mother liquor tank, a first centrifuge, a second feed liquid pump, a second heater, and a second steam compressor. The second preheater, the second heater, the crystallization separator, the first feed liquid pump, and the thickener are connected in sequence. The bottom outlet of the thickener is connected to the first centrifuge, and the top overflow port of the thickener communicates with the first mother liquor tank. The first mother liquor tank is connected to the second heater through the second feed liquid pump. The feed liquid from the output end of the MVR evaporation and concentration device 8 first enters the second preheater for preheating, then enters the second heater for further heating, and finally is transported to the crystallization separator for evaporation and crystallization. After the crystals in the crystallization separator reach the design requirements, the first feed liquid pump transports the mixture of crystals and mother liquor to the thickener. The crystals in the thickener sink and concentrate due to gravity, and the mother liquor overflows from the top of the thickener to the first mother liquor tank. The concentrated crystals enter the first centrifuge, the crystals are separated out, and are discharged from the crystal discharge port of the first centrifuge, and are sent to the subsequent supporting equipment for drying and packing, and finally supplied externally. The mother liquor enters the second heater through the second feed liquid pump to continue participating in the cyclic evaporation and crystallization. When the salt content in the mother liquor is very low, it can be discharged externally. The live steam provides heat for the crystallization separator, and the steam is cooled into distilled water for further recovery and reuse. The secondary steam generated by the vaporization of the solvent in the crystallization separator is pressurized, heated up by the second steam compressor, and used as the heat source for the second heater. The formed high-temperature condensed water is used as the heat source for the second preheater to preheat the feed liquid.

[0039] In this embodiment, the structure and principle of the MVR evaporation and crystallization device 20 are the same as those of the MVR evaporation and crystallization device 10. Details are not described herein again.

[0040] In this embodiment, the ultrafiltration membrane model of the first ultrafiltration device 5 is HFU-2020N, the high-pressure seawater desalination membrane material model of the high-pressure seawater desalination device 6 is XC-70, and the ultra-high-pressure seawater desalination membrane material model of the ultra-high-pressure seawater desalination device 7 is TZD-HP. The model of the electrodialysis device 9 is AC100-1000. Among them, the maximum designed input flow rate of the ultra-high-pressure seawater desalination device 7 is 60 cubic meters per hour, and the maximum designed input flow rate of the electrodialysis device 9 is 160 cubic meters per hour. The models provided in this embodiment are only specific and implementable examples and do not constitute a limitation.

[0041] The sodium sulfate recovery component is used to treat the product mainly composed of sodium sulfate on the concentrated water side of the salt-splitting nanofiltration device 1 to finally obtain sodium sulfate crystals.

[0042] Specifically, the sodium sulfate recovery component includes a sodium sulfate pretreatment unit A, a softening unit B, a sodium sulfate salt-splitting unit D, and a sodium sulfate concentration and purification MVR evaporation and crystallization unit F, which are connected in sequence. The input end of the sodium sulfate pretreatment unit A is communicated with the concentrated water side of the salt-splitting nanofiltration device 1. Moreover, the water production side of the sodium sulfate salt-splitting unit D is communicated with the input end of the low-pressure seawater desalination device 2.

[0043] In detail, the sodium sulfate pretreatment unit includes an ozone pool 12, a sand filter pool 13, and a second ultrafiltration device 14, which are connected in sequence. The softening unit is a resin softening device 15. The sodium sulfate salt-splitting unit includes a medium-pressure nanofiltration device 16 and a high-pressure nanofiltration device 17. The sodium sulfate concentration and purification MVR evaporation and crystallization unit includes a freezing crystallization device 18, a nitrate melting tank 19, and an MVR evaporation and crystallization device 20, which are connected in sequence. The ozone pool 12, the sand filter pool 13, the second ultrafiltration device 14, the resin softening device 15, the medium-pressure nanofiltration device 16, the high-pressure nanofiltration device 17, the freezing crystallization device 18, the nitrate melting tank 19, and the MVR evaporation and crystallization device 20 are connected in sequence. Moreover, the medium-pressure nanofiltration device 16 and the high-pressure nanofiltration device 17 also include a water production side, and the water production sides are both communicated with the input end of the low-pressure seawater desalination device 2 in the sodium chloride recovery component.

[0044] In this embodiment, the ultrafiltration membrane model of the second ultrafiltration device 14 also adopts HFU-2020N. The nanofiltration membrane of the medium-pressure nanofiltration device 16 adopts the model XC-N, and the nanofiltration membrane of the high-pressure nanofiltration device 17 adopts the model PRO-XS1.

[0045] The principle of the freezing crystallization device 18 is that in a certain temperature range (0 degrees - 40 degrees), the solubility of mirabilite increases significantly with the increase of temperature. By lowering the temperature, it precipitates from the solution. Please refer to Figure 4, the freeze crystallization device 18 includes a forced circulation pump, an external cooler, a crystallizer, a discharge pump, a buffer tank, a second mother liquor tank, and a second centrifuge. The forced circulation pump, the external cooler, and the crystallizer are connected in sequence. The overflow port at the top of the crystallizer communicates with the second mother liquor tank. The bottom outlet of the crystallizer is connected to the buffer tank through the discharge pump, and the overflow port at the top of the buffer tank communicates with the second mother liquor tank. The sodium sulfate feed liquid enters the external cooler through the forced circulation pump. The original liquid that reaches the designed crystallization temperature then enters the crystallizer, where crystals are continuously and stably formed at the bottom of the crystallizer and precipitate to the bottom of the crystallizer. The upper layer liquid in the crystallizer overflows from the top of the crystallizer to the second mother liquor tank. The crystals and a small amount of mother liquor are transported to the buffer tank by the discharge pump, where they precipitate and concentrate again. The upper layer clear liquid in the buffer tank overflows from the top of the buffer tank to the second mother liquor tank. The concentrated crystals enter the second centrifuge to separate the crystals from the mother liquor, obtaining sodium sulfate decahydrate crystals (Glauber's salt). The separated mother liquor enters the mother liquor tank. All the mother liquor recovered by the mother liquor tank is then forced to be transported to the external cooler for continued recycling. When the sodium sulfate content in the mother liquor is very low, it can be directly discharged.

[0046] The recovery process of the sodium chloride recovery component and the recovery process of the sodium sulfate recovery component are specifically described below.

[0047] The sodium chloride recovery process is as follows:

[0048] (a) Sodium chloride on the water production side enters the low-pressure seawater desalination device 2. The produced water output from the water production side of the low-pressure seawater desalination device 2 is introduced into the RO produced water tank 11, and after being processed, it is supplied to users as fresh water, and the concentrated water enters the next step.

[0049] (b) The concentrated water treated by the low-pressure seawater desalination device 2 enters the chemical silicon removal device 3. By chemically reacting the silicon in the wastewater with an additive to form a precipitate, it is then introduced into the sand filter 4 to filter and remove the precipitate, and the concentrated water enters the next step.

[0050] (c) The concentrated water that enters the first ultrafiltration device 5 after being filtered by the sand filter 4 has macromolecular organic matters such as colloids and microorganisms intercepted by the first ultrafiltration device 5, and the concentrated water enters the next step. This device can effectively prevent the reverse osmosis membrane system from being fouled by macromolecules such as colloids and microorganisms, so it plays an important protective role in the subsequent process.

[0051] (d) The concentrated water treated by the first ultrafiltration device 5 enters the high-pressure seawater desalination device 6 to further concentrate the sodium chloride concentrated water. The produced water enters the RO produced water tank 11 for treatment to obtain fresh water and then is supplied to users. A part of the concentrated water (with a maximum input flow rate of 60 m 3 / h) enters the ultra-high-pressure seawater desalination device 7 for further concentration, and a part (with a maximum of 160 m 3The input flow rate ( / h) enters the electrodialysis device 9 for further concentration. Then, the concentrated water from the ultra-high pressure seawater desalination device 7 and the electrodialysis device 9 is combined and enters the MVR evaporation and concentration device 8 for further concentration, and the concentrated water enters the next step.

[0052] Through the low-pressure seawater desalination device 2, the high-pressure seawater desalination device 6, and the ultra-high pressure seawater desalination device 7, the sodium chloride concentration can be concentrated from the initial 3 - 5% to 10 - 15%; and through the low-pressure seawater desalination device 2, the high-pressure seawater desalination device 6, and the electrodialysis device 9, the sodium chloride concentration can be concentrated from the initial 3 - 5% to about 20%; the MVR evaporation and concentration device 8 further increases the sodium chloride concentration to about 30%.

[0053] (e) The sodium chloride concentrated water at about 30% enters the MVR evaporation and crystallization device 10, and finally sodium chloride crystals are obtained.

[0054] So far, the sodium chloride recovery process is completed. The obtained sodium chloride crystals and the sodium chloride solution at about 20% can both be supplied to users externally, achieving the purpose of recycling. And the produced water during the recovery process is transported to the RO product water tank 11 for treatment to obtain usable fresh water.

[0055] Sodium sulfate recovery process:

[0056] (1) The sodium sulfate on the concentrated water side enters the sodium sulfate pretreatment unit, that is, first enters the ozone pool 12 for COD reduction and concentrated water color reduction treatment, then is introduced into the sand filter 13 to filter solid substances, and then passes through the second ultrafiltration device 14 to remove colloids, microorganisms, etc. in the concentrated water, protecting the safe operation of the subsequent membrane system.

[0057] (2) The pretreated concentrated water enters the resin softening device 15 for treatment to reduce the hardness and alkalinity in the concentrated water.

[0058] (2) The concentrated water treated by the resin softening device 15 enters the medium-pressure nanofiltration device 16 to further separate sodium chloride and concentrate sodium sulfate. The concentrated water containing sodium chloride on the product water side of the medium-pressure nanofiltration device 16 is transported to the low-pressure seawater desalination device 2 to recover sodium chloride in the sodium chloride recovery component, improving the recovery rate of sodium chloride in the sewage. The concentrated water on the output side of the medium-pressure nanofiltration device 16 enters the next step.

[0059] (3) The high-pressure nanofiltration device 17 further concentrates sodium sulfate. The concentrated water containing sodium chloride on the product water side of the high-pressure nanofiltration device 17 is further transported to the low-pressure seawater desalination device 2 to recover sodium chloride in the sodium chloride recovery component, further improving the recovery rate of sodium chloride in the sewage. The concentrated water on the output side of the high-pressure nanofiltration device 17 enters the next step. In addition, the produced water from the medium-pressure nanofiltration device 16 and the high-pressure nanofiltration device 17 is transported to the low-pressure seawater desalination device 2, which can also further concentrate the concentrated water and increase the concentration of sodium sulfate.

[0060] (4) The concentrated water on the output side of the high-pressure nanofiltration device 17 enters the freezing crystallization device 18, causing sodium sulfate to crystallize out of the concentrated water in the form of sodium sulfate decahydrate (commonly known as mirabilite) for treatment in the next step.

[0061] (5) Sodium sulfate decahydrate melts in the nitrate melting tank 19 and then enters the MVR evaporation crystallization device 20, finally obtaining sodium sulfate crystals.

[0062] Thus, the sodium sulfate recovery process is completed, obtaining the final product of sodium sulfate crystals for external use.

[0063] The zero-emission process system provided in this embodiment first transports the sewage to the salt separation nanofiltration device 2 for salt separation treatment, producing concentrated water mainly composed of sodium chloride and concentrated water mainly composed of sodium sulfate, and then respectively conducts recovery treatment through the sodium chloride recovery component and the sodium sulfate recovery component.

[0064] During the recovery process of the sodium chloride recovery component, first, after treating the concentrated water mainly composed of sodium chloride to remove silicon, macromolecular organic matters such as colloids / microorganisms, the concentration of sodium chloride in the concentrated water is increased through the high-pressure seawater desalination device 6 and the ultra-high-pressure seawater desalination device 7, and then further concentrated through the MVR evaporation concentration device 8 and the electrodialysis device 9 to increase the concentration of sodium chloride. Finally, sodium chloride crystals are obtained through the MVR evaporation crystallization device, and sodium chloride solution can also be obtained during this recovery process. In addition, the produced water generated during the recovery process can be treated through the RO production water tank 11 to obtain reclaimed water.

[0065] During the recovery process of the sodium sulfate recovery component, first, after reducing the COD, reducing the color of the concentrated water, removing solid substances, colloids, microorganisms, etc. from the concentrated water mainly composed of sodium sulfate, the concentrated water is sent to the medium-pressure nanofiltration device 16 and the high-pressure nanofiltration device 17 for treatment to further separate sodium chloride and sodium sulfate, increase the recovery rate of sodium chloride and the concentration of sodium sulfate. The concentrated water with increased sodium sulfate concentration is sent to the freezing crystallization device 18 for treatment to precipitate crystals. After melting the crystals in the nitrate melting tank 19, they are sent to the MVR evaporation crystallization device 20, and sodium sulfate crystals are obtained after being treated by the MVR evaporation crystallization device 20.

[0066] Therefore, this zero-emission system can effectively separate and purify sodium chloride and sodium sulfate in the sewage, and at the same time can realize the recovery of sodium chloride and sodium sulfate, reduce the discharge of inorganic salt solids, and can also recycle water resources through the RO production water tank. Turning waste into treasure, effectively improving the economic benefits in the wastewater treatment process.

[0067] The large-scale zero-emission system can achieve a concentrated water treatment capacity of approximately 38,800 tons per day, among which the recoverable water resources are approximately 30,000 tons per day, and the total recovery amount of sodium chloride and sodium sulfate is approximately 540 tons per day. The large-scale application of the zero-emission system truly realizes the reuse of resources, greatly reduces the discharge and treatment of solid-liquid wastes, and makes a more profound contribution to promoting social sustainable development, realizing circular economy, and building an environment-friendly society.

[0068] As described above, it is only the preferred embodiment of the present invention, and it does not impose any form of limitation on the present invention. Any equivalent changes, modifications or evolutions made by those skilled in the art to the above embodiments using the technical solutions of the present invention still fall within the scope of the technical solutions of the present invention.

Claims

1. A zero-emission process system for a sewage treatment system, characterized in that: It includes a salt separation nanofiltration device (1), a sodium chloride recovery component, an RO product water tank (11), and a sodium sulfate recovery component; The salt separation nanofiltration device (1) is used for salt separation treatment of sewage, and its output end includes a product water side and a concentrate side; The sodium chloride recovery component includes a low-pressure seawater desalination device (2), a sodium chloride pretreatment unit, a sodium chloride salt separation unit, a sodium chloride concentration unit, and a sodium chloride crystallization unit that are connected in sequence, and the input end of the low-pressure seawater desalination device (2) is connected to the product water side of the salt separation nanofiltration device (1); The RO product water tank (11) is connected to the product water side of the sodium chloride recovery component; The sodium sulfate recovery component includes a sodium sulfate pretreatment unit, a softening unit, a sodium sulfate salt separation unit, and a sodium sulfate concentration and purification MVR evaporation crystallization unit that are connected in sequence, and the input end of the sodium sulfate pretreatment unit is connected to the concentrate side of the salt separation nanofiltration device (1), and furthermore, the product water side of the sodium sulfate salt separation unit is connected to the input end of the low-pressure seawater desalination device (2); The sodium chloride pretreatment unit includes a chemical silicon removal device (3), a sand filter tank (4), and a first ultrafiltration device (5) that are connected in sequence, and the input end of the chemical silicon removal device (3) is connected to the output end of the low-pressure seawater desalination device (2), and the output end of the first ultrafiltration device (5) is connected to the input end of the sodium chloride salt separation unit; The sodium chloride salt separation unit includes a high-pressure seawater desalination device (6) and an ultra-high-pressure seawater desalination device (7), the input end of the high-pressure seawater desalination device (6) is connected to the output end of the sodium chloride pretreatment unit, the input end of the ultra-high-pressure seawater desalination device (7) is connected to the output end of the high-pressure seawater desalination device (6), and the output end of the ultra-high-pressure seawater desalination device (7) is connected to the input end of the sodium chloride concentration unit; The sodium chloride concentration unit includes an MVR evaporation concentration device (8) and an electrodialysis device (9), the input end of the electrodialysis device (9) is connected to the output end of the high-pressure seawater desalination device (6), and the output end is connected to the output end of the ultra-high-pressure seawater desalination device (7) and then connected to the input end of the MVR evaporation concentration device (8), and the output end of the MVR evaporation concentration device (8) is connected to the input end of the sodium chloride crystallization unit; The sodium sulfate pretreatment unit includes an ozone pool (12), a sand filter tank (13), and a second ultrafiltration device (14) that are connected in sequence, and the input end of the ozone pool (12) is connected to the concentrate side of the salt separation nanofiltration device (1), and the output end of the second ultrafiltration device (14) is connected to the input end of the softening unit; The sodium chloride salt separation unit, the sodium chloride concentration unit, and the sodium chloride crystallization unit all include a product water side connected to the RO product water tank (11).

2. The zero - discharge process system for a sewage treatment system according to claim 1, characterized in that: The sodium chloride crystallization unit is an MVR evaporation crystallization device (10), and its input end is connected to the output end of the sodium chloride concentration unit.

3. A zero-emission process system for a sewage treatment system according to claim 1, characterized in that: The sodium sulfate salt separation unit includes a medium-pressure nanofiltration device (16) and a high-pressure nanofiltration device (17). The input end of the medium-pressure nanofiltration device (16) is communicated with the output end of the softening unit, and the output end is communicated with the input end of the high-pressure nanofiltration device (17). The output end of the high-pressure nanofiltration device (17) is communicated with the sodium sulfate concentration and purification MVR evaporation crystallization unit.

4. A zero-emission process system for a sewage treatment system according to claim 1, characterized in that: The sodium sulfate concentration and purification MVR evaporation crystallization unit includes a freezing crystallization device (18), a nitrate melting tank (19) and an MVR evaporation crystallization device (20) that are connected in sequence, and the input end of the freezing crystallization device (18) is communicated with the output end of the sodium sulfate salt separation unit.

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