A PVA wastewater treatment system and method

Abstract

The invention discloses a treatment system and method for PVA wastewater, and relates to the technical field of wastewater treatment. A raw water tank containing PVA wastewater is connected to a fiber bundle filter, an outlet of the fiber bundle filter is connected to a heat exchange system, the heat exchange system is connected to an ultrafiltration system, the ultrafiltration system is connected to a fresh water circulation box, the fresh water circulation box is connected to a reverse osmosis system, and a booster pump, a security filter and a high-pressure pump are sequentially arranged between the fresh water circulation box and the reverse osmosis system; an electrodialysis system water inlet is connected to the fresh water circulation box, and the wastewater in the fresh water circulation box is subjected to salt separation and concentration treatment; one end of the concentrated water circulation box is connected to the electrodialysis system, and the other end is connected to a concentrated brine tank, and the concentrated brine tank is connected to a freezing crystallization system. The invention effectively solves the problems of low fresh water reuse rate, low concentrated water concentration multiple, waste of resources, high treatment cost and unstable system operation when washing PVA wastewater.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and in particular to a PVA wastewater treatment system and method. Background Art

[0002] Polyvinyl alcohol fiber (PVA) is a widely used organic synthetic fiber material. It can be used in concrete reinforcement, papermaking, textiles, medicine and other fields because of its excellent properties such as good strength, modulus, acid and alkali resistance, and easy solubility. Polyvinyl alcohol fiber is made of polyvinyl alcohol through dissolution, filtration, degassing, spinning, coagulation, heat treatment and other processes.

[0003] A large amount of wastewater is generated during the production process of polyvinyl alcohol fiber. The washing wastewater contains high concentrations of sodium sulfate and organic pollutants, which are difficult to process and reuse by traditional treatment methods. At present, these wastewaters basically enter the biochemical system of existing sewage treatment plants directly. Since sulfate ions have an inhibitory effect on the biochemical system, the difficulty of biochemical treatment increases, the cost of sewage treatment increases, and the high temperature and high sodium sulfate characteristics of the wastewater can be used as raw materials and resources. In view of this situation, as well as the reuse requirements and water quality characteristics, a special technical plan needs to be formulated to achieve the recycling and treatment of water resources, sodium sulfate salts and thermal energy reuse.

[0004] Chinese patent CN108409022A discloses a method for treating desizing wastewater containing PVA, which uses an acidic regulator to adjust the pH of the desizing wastewater to be treated to 3-5, and then transports the desizing wastewater to an electromagnetic stirring reactor, with the current controlled at 12-14A and the frequency controlled at 25-35HZ, so that the PVA aggregates to form a coagulant, which is then discharged from the electromagnetic stirring reactor, and then filtered to complete the treatment of the pollutant PVA in the desizing wastewater. This patent uses an electromagnetic stirring reactor to filter the pollutant PVA agglomerates, with a low filtration rate, and uses oxidation treatment for the filtered PVA wastewater. There are many uncontrollable factors in the oxidation treatment process, which will have an unstable effect on the final experimental results, that is, the above technical problems still exist. Summary of the invention

[0005] In order to solve the problem that sulfate ions have an inhibitory effect on the biochemical system, which leads to increased difficulty in biochemical treatment and increased sewage treatment costs, the present invention provides a PVA wastewater treatment system and method.

[0006] In order to achieve the purpose of the present invention, the specific technical solution adopted by the present invention is as follows:

[0007] A PVA wastewater treatment system comprises a fiber bundle filter, a heat exchange system, an ultrafiltration system, a reverse osmosis system, a fresh water circulation tank, a concentrated water circulation tank, an electrodialysis system, a concentrated brine tank and a freezing crystallization system;

[0008] The outlet of the raw water tank containing PVA wastewater is connected to the inlet of the fiber bundle filter through a pipeline, the outlet of the fiber bundle filter is connected to the heat exchange system through a pipeline, the heat exchange system is connected to the ultrafiltration system through a pipeline, the ultrafiltration system is connected to the fresh water circulation box through a pipeline, the fresh water circulation box is connected to the reverse osmosis system, and a booster pump, a security filter and a high-pressure pump are sequentially arranged between the fresh water circulation box and the reverse osmosis system;

[0009] The water inlet of the electrodialysis system is connected to the fresh water circulation box and performs salt separation and concentration treatment on the wastewater in the fresh water circulation box; one end of the concentrated water circulation box is connected to the electrodialysis system through a pipeline, and the other end is connected to the concentrated brine tank through a pipeline, and the concentrated brine tank is connected to the freezing crystallization system through a pipeline.

[0010] Furthermore, the fiber bundle filter filters the wastewater in the raw water tank and adopts carbon steel for corrosion protection. The material is polymer modified fiber, the average pore size is 20μm-50μm, the operating pressure is ≤0.6mpa, and the filtration flow rate is 20m / h-40m / h.

[0011] Furthermore, the heat exchange material of the plate heat exchanger of the heat exchange system is SUS304.

[0012] Furthermore, in the ultrafiltration system, the average pore size of the ultrafiltration membrane is 30nm-70nm, the material of the ultrafiltration membrane is hydrophilic PVDF fiber, the filtration form of the ultrafiltration membrane is external pressure type, and the average operating pressure is 0.03mpa-0.1mpa.

[0013] Furthermore, the membrane material in the reverse osmosis system is a polyamide composite membrane, and the average operating pressure is 1.2 MPa-1.6 MPa.

[0014] A method for treating a PVA wastewater treatment system, comprising the steps of:

[0015] Step S1: The booster pump is pumped into the fiber filter, the heat exchange system and the ultrafiltration system in sequence, and the fiber bundle filter and the ultrafiltration system filter the wastewater in the raw water tank, and after the suspended matter in the wastewater is removed, the effluent enters the fresh water circulation tank;

[0016] Step S2: the wastewater in the fresh water circulation tank is pressurized by a booster pump and a high-pressure pump and then enters a reverse osmosis system. After the reverse osmosis system acts, reverse osmosis fresh water and reverse osmosis concentrated water containing a high-concentration sodium sulfate solution are obtained. The reverse osmosis concentrated water is all returned to the fresh water circulation tank, and the original sodium sulfate salt in the wastewater is all retained in the fresh water circulation tank. After the reverse osmosis fresh water enters the heat exchange system for heat exchange, the fresh water is reused;

[0017] Step S3: As the reverse osmosis system runs, when the conductivity of the wastewater in the fresh water circulation box increases to a preset value, the electrodialysis system is turned on to obtain electrodialysis fresh water and electrodialysis concentrated water, the electrodialysis concentrated water is returned to the concentrated water circulation box, the electrodialysis fresh water is returned to the fresh water circulation box, and the sodium sulfate salt migrates to the concentrated water circulation box under the action of the electrodialysis system;

[0018] Step S4: With the operation of the electrodialysis system, in order to maintain the balance of pollutant concentration in the fresh water circulation box, wastewater is discharged from the fresh water circulation box and collected by a drain or a water tank for subsequent treatment;

[0019] Step S5: As the electrodialysis system is running, when the conductivity of the wastewater in the concentrated water circulation box increases to a value greater than a set value, the concentrated water in the concentrated water circulation system is quantitatively discharged to the concentrated brine tank for buffering, and the concentrated brine in the concentrated brine tank is then processed in the freezing crystallization system to precipitate sodium sulfate;

[0020] Step S6: The remaining concentrated brine in the freezing crystallization system is returned to the concentrated water circulation tank, and a small portion of the concentrated brine is discharged and collected by a drain or water tank for subsequent treatment.

[0021] Furthermore, the fresh water circulation box mixes and homogenizes the reverse osmosis concentrated water, the electrodialysis fresh water, and the waste water passing through the ultrafiltration system and performs buffer storage.

[0022] Furthermore, the reverse osmosis system separates the wastewater in the fresh water circulation box from salt water to obtain desalted water and high-salt concentrated water.

[0023] Furthermore, reverse osmosis fresh water contains very small amounts of sodium sulfate salts.

[0024] Furthermore, the concentrated water circulation box mixes and homogenizes the electrodialysis concentrated water and the concentrated brine in the freezing crystallization system and performs buffer storage.

[0025] Furthermore, the concentrated brine tank performs buffer storage on the wastewater in the concentrated water circulation tank.

[0026] Furthermore, the operating voltage in the electrodialysis system is 352V-400V, and the operating current is 99A-112.5A.

[0027] Furthermore, the freezing crystallization device is composed of a crystallizer, an external cooler (external cooler) and an axial flow circulation pump, and is assisted by necessary material turnover pumps and tanks. The operation mode is continuous feeding and continuous discharging, the feed temperature is 30-35°C, and the crystallization temperature is 0°C.

[0028] Furthermore, the sodium sulfate concentration of PVA washing wastewater is 6000 mg / L-12000 mg / L, the sodium sulfate content accounts for more than 85% of the total salt pollutants, the pH is 3-5, and the wastewater temperature is 40-46°C.

[0029] Furthermore, the size of the preset value in step S5 is determined according to the maximum salt concentration tolerable by the design of the reverse osmosis membrane. The stronger the reverse osmosis salt tolerance is, the higher the wastewater conductivity can be, but the reverse osmosis operating pressure is also higher.

[0030] Compared with the prior art, the beneficial effects of the present invention are specifically embodied in:

[0031] (1) The present invention utilizes the high-efficiency salt water separation function of the reverse osmosis membrane and the selective permeability of the electrodialysis ion exchange membrane to remove or enrich and concentrate salt substances and organic matter from the solution to produce a high-concentration sodium sulfate solution;

[0032] (2) The present invention utilizes a heat exchange system to fully exchange heat between wastewater and desalted water, thereby realizing the reuse of wastewater heat and reducing steam consumption. After heat exchange, desalted water is reused, ultimately achieving comprehensive treatment and resource utilization of PVA washing wastewater, which can greatly reduce the production cost of PVA production companies;

[0033] (3) The present invention effectively solves the problems of low fresh water reuse rate, low concentrated water concentration ratio, resource waste, high treatment cost and unstable system operation when treating PVA washing wastewater in conventional technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a structural schematic diagram of the present invention.

[0035] Figure numerals: 1. Raw water tank; 2. Fiber bundle filter; 3. Heat exchange system; 4. Ultrafiltration system; 5. Fresh water circulation tank; 6. Reverse osmosis system; 7. Electrodialysis system; 8. Concentrated water circulation tank; 9. Concentrated brine tank; 10. Freezing crystallization system; 11. Booster pump; 12. High-pressure pump; 13. Safety filter. DETAILED DESCRIPTION

[0036] In order to make the purpose and technical solution of the present invention more clear, the technical solution of the present invention will be clearly and completely described below in conjunction with embodiments.

[0037] Example 1

[0038] according to Figure 1The PVA wastewater treatment system shown in the figure includes a fiber bundle filter 2, a heat exchange system 3, an ultrafiltration system 4, a reverse osmosis system 6, a fresh water circulation tank 5, a concentrated water circulation tank 8, an electrodialysis system 7, a concentrated brine tank 9 and a freezing crystallization system 10; the outlet of the raw water tank 1 containing PVA wastewater is connected to the inlet of the fiber bundle filter 2 through a pipeline, the outlet of the fiber bundle filter 2 is connected to the heat exchange system 3 through a pipeline, the heat exchange system 3 is connected to the ultrafiltration system 4 through a pipeline, the ultrafiltration system 4 is connected to the fresh water circulation tank 5 through a pipeline, and the fresh water circulation tank 5 is connected to the reverse osmosis system 6, and a booster pump 11, a security filter 13 and a high-pressure pump 12 are arranged in sequence between the fresh water circulation box 5 and the reverse osmosis system 6. The security filter 13 is used to filter particles below 5um to protect the subsequent treatment system; the water inlet of the electrodialysis system 7 is connected to the fresh water circulation box 5 and performs salt separation and concentration treatment on the wastewater in the fresh water circulation box 5; one end of the concentrated water circulation box 8 is connected to the electrodialysis system 7 through a pipeline, and the other end is connected to the concentrated brine tank 9 through a pipeline, and the concentrated brine tank 9 is connected to the freezing crystallization system 10 through a pipeline. As far as the fresh water circulation box 5 is concerned, the role of reverse osmosis is to almost retain the sodium sulfate salt in the wastewater in the fresh water circulation box 5, and the role of electrodialysis is to maintain the sodium sulfate concentration in the fresh water circulation box 5. The electrodialysis concentrated water continuously lifts the sodium sulfate in the fresh water circulation box 5 to the rear water tank.

[0039] The fiber bundle filter 2 filters the wastewater in the raw water tank 1, and uses carbon steel for corrosion protection. The filter element uses a fiber bundle, which is made of polymer modified fiber and has an average pore size of 20μm-50μm. The heat exchange system 3 uses a plate heat exchanger, and the heat exchange material is SUS304. The heat exchange system 3 is used to perform heat exchange treatment on high-temperature raw wastewater and low-temperature desalted water, so as to realize the reuse of wastewater heat and reduce steam consumption. The average pore size of the ultrafiltration membrane in the ultrafiltration system 4 is 30nm-70nm, the ultrafiltration membrane material is hydrophilic PVDF fiber, and the ultrafiltration membrane filtration form is external pressure type. The membrane material in the high-pressure pump 12 is a polyamide composite membrane. The fiber bundle filter 2 and the ultrafiltration system 4 are used to filter PVA washing wastewater and remove suspended matter in the wastewater. The fresh water circulation box 5 mixes and homogenizes the reverse osmosis concentrated water, electrodialysis fresh water, and the wastewater passing through the ultrafiltration system 4 and buffers and stores them. The high-pressure pump 12 separates the wastewater in the fresh water circulation box 5 into brine to obtain desalted water and high-salt concentrated water. The concentrated water circulation box 8 mixes and homogenizes the electrodialysis concentrated water and the concentrated brine in the freezing crystallization system 10 and performs buffer storage. The concentrated brine tank 9 performs buffer storage for the wastewater in the concentrated water circulation box 8. The freezing crystallization system 10 is used to perform freeze crystallization treatment on a high-concentration sodium sulfate solution to obtain mirabilite;

[0040] The quality of PVA washing wastewater is as follows: sodium sulfate concentration is 6478 mg / L, sodium sulfate content accounts for 98% of the total salt pollutants, pH is 4, wastewater temperature is 45°C, and the treatment system and method of the present invention are used:

[0041] First, the raw wastewater is filtered at a flow rate of 120m3 / h through the fiber filter, heat exchange system 3 and ultrafiltration system 4 in turn, and the effluent enters the fresh water circulation box 5; the pore size of the fiber filter element is 35μm, and the operating pressure is 0.1mpa; the pore size of the ultrafiltration membrane is 30nm, and the operating pressure is 0.1mpa. The water filtered out of the fiber filter is heat exchanged with the desalted water, and the heat energy recovery rate reaches 58%;

[0042] The wastewater in the fresh water circulation box 5 is pressurized by the booster pump 11 and the high-pressure pump 12 and then enters the high-pressure pump 12. The fresh water recovery rate is 50%, the operating pressure is 1.5 MPa, the total water inlet flow is 234 m3 / h, the total water production flow is 117 m3 / h, the concentrated water flow is 117 m3 / h, and the concentrated water is all returned to the fresh water circulation box 5, so that all the sodium sulfate salts are retained in the fresh water circulation box 5;

[0043] As the high-pressure pump 12 runs, when the conductivity of the wastewater in the fresh water circulation box 5 rises to 15000uS / cm, the electrodialysis is started, and the fresh water recovery rate is about 97%, the operating current is 112.5A, and the operating pressure is 400V; the electrodialysis concentrated water flows back to the concentrated water circulation box 8, and the fresh water flows back to the fresh water circulation box 5. The sodium sulfate salt migrates to the concentrated water circulation box 8 under the action of electrodialysis; in order to maintain the balance of pollutant concentration in the fresh water circulation box 5, the fresh water circulation box 5 needs to discharge 1m3 / h, which is collected by the drainage ditch for subsequent treatment;

[0044] As the electrodialysis system 7 is running, when the conductivity of the wastewater in the concentrated water circulation box 8 increases to more than 120,000uS / cm, 4.35m3 / h of concentrated water is discharged to the concentrated brine tank 9 for buffering. The sodium sulfate content in the concentrated brine tank 9 is about 19.9%. The concentrated brine enters the freezing crystallization system 10 for treatment. The recovery rate of mirabilite is 23%, and the output of precipitated mirabilite is 1440kg / h.

[0045] After the precipitation of mirabilite, the sodium sulfate concentration in the concentrated brine is reduced to 4.3%, of which 3.05m3 / h of wastewater is returned to the concentrated water circulation box 8, and 0.3m3 / h of wastewater is discharged and collected by the drainage ditch for subsequent treatment;

[0046] Finally, the comprehensive treatment rate of this type of PVA washing wastewater was 99%, the effective heat recovery rate was 58%, and the sodium sulfate recovery output was 1440 kg / h.

[0047] The above is only an embodiment of the present invention, and its description is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for treating a PVA wastewater treatment system, characterized in that: A PVA wastewater treatment system is used, the treatment system comprising a fiber bundle filter, a heat exchange system, an ultrafiltration system, a reverse osmosis system, a fresh water circulation tank, a concentrated water circulation tank, an electrodialysis system, a concentrated brine tank and a freezing crystallization system; The outlet of the raw water tank containing PVA wastewater is connected to the inlet of the fiber bundle filter through a pipeline, the outlet of the fiber bundle filter is connected to the heat exchange system through a pipeline, the heat exchange system is connected to the ultrafiltration system through a pipeline, the ultrafiltration system is connected to the fresh water circulation box through a pipeline, the fresh water circulation box is connected to the reverse osmosis system, and a booster pump, a security filter and a high-pressure pump are sequentially arranged between the fresh water circulation box and the reverse osmosis system; The water inlet of the electrodialysis system is connected to the fresh water circulation box and performs salt separation and concentration treatment on the wastewater in the fresh water circulation box; one end of the concentrated water circulation box is connected to the electrodialysis system through a pipeline, and the other end is connected to the concentrated brine tank through a pipeline, and the concentrated brine tank is connected to the freezing crystallization system through a pipeline; The steps include: Step S1: The booster pump is pumped into the fiber filter, the heat exchange system and the ultrafiltration system in sequence, and the fiber bundle filter and the ultrafiltration system filter the wastewater in the raw water tank, and after the suspended matter in the wastewater is removed, the effluent enters the fresh water circulation tank; Step S2: the wastewater in the fresh water circulation tank is pressurized by a booster pump and a high-pressure pump and then enters a reverse osmosis system. After the reverse osmosis system acts, reverse osmosis fresh water and reverse osmosis concentrated water containing a high-concentration sodium sulfate solution are obtained. The reverse osmosis concentrated water is all returned to the fresh water circulation tank, and the sodium sulfate salt in the wastewater is all retained in the fresh water circulation tank. The reverse osmosis fresh water enters a heat exchange system for heat exchange and then is reused as fresh water; Step S3: As the reverse osmosis system runs, when the conductivity of the wastewater in the fresh water circulation box increases to a preset value, the electrodialysis system is turned on to obtain electrodialysis fresh water and electrodialysis concentrated water, the electrodialysis concentrated water is returned to the concentrated water circulation box, the electrodialysis fresh water is returned to the fresh water circulation box, and the sodium sulfate salt migrates to the concentrated water circulation box under the action of the electrodialysis system; Step S4: With the operation of the electrodialysis system, in order to maintain the balance of pollutant concentration in the fresh water circulation box, wastewater is discharged from the fresh water circulation box and collected by a drain or a water tank for subsequent treatment; Step S5: As the electrodialysis system is running, when the conductivity of the wastewater in the concentrated water circulation box increases to a value greater than a set value, the concentrated water in the concentrated water circulation system is quantitatively discharged to the concentrated brine tank for buffering, and the concentrated brine in the concentrated brine tank is then processed in the freezing crystallization system to precipitate sodium sulfate; Step S6: The remaining concentrated brine in the freezing crystallization system is returned to the concentrated water circulation tank, and a small portion of the concentrated brine is discharged and collected by a drain or water tank for subsequent treatment.

2. The processing method according to claim 1, characterized in that: The fresh water circulation box mixes and homogenizes the reverse osmosis concentrated water, the electrodialysis fresh water, and the waste water passing through the ultrafiltration system and performs buffer storage.

3. The processing method according to claim 1, characterized in that: The reverse osmosis system separates the wastewater in the fresh water circulation box into salt water to obtain desalted water and high-salt concentrated water.

4. The processing method according to claim 1, characterized in that: The concentrated water circulation box mixes and homogenizes the electrodialysis concentrated water and the concentrated brine in the freezing crystallization system and performs buffer storage.

5. The processing method according to claim 1, characterized in that: The concentrated brine tank buffers and stores the wastewater in the concentrated water circulation tank.

6. The processing method according to claim 1, characterized in that: The fiber bundle filter filters the wastewater in the raw water tank and adopts carbon steel for corrosion protection. The material is polymer modified fiber with an average pore size of 20μm-50μm.

7. The processing method according to claim 1, characterized in that: The heat exchange system is a plate heat exchanger, and the heat exchange material is SUS304.

8. The processing method according to claim 1, characterized in that: The average pore size of the ultrafiltration membrane in the ultrafiltration system is 30nm-70nm, the ultrafiltration membrane is made of hydrophilic PVDF fiber, and the filtration form of the ultrafiltration membrane is external pressure type.

9. The processing method according to claim 1, characterized in that: The membrane material in the reverse osmosis system is a polyamide composite membrane.

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