High-salt high-COD wastewater recovery zero-discharge treatment process and treatment system

Abstract

The invention belongs to the field of sewage treatment, and particularly relates to a high-salt high-COD (Chemical Oxygen Demand) wastewater recovery zero-discharge treatment process and a treatment system. Comprising a pretreatment step, a supercritical water oxidation treatment step, an ultrafiltration membrane unit treatment step, a first-section reverse osmosis membrane unit treatment step, a nanofiltration membrane unit treatment step, a second-section reverse osmosis membrane unit treatment step and a salt separation treatment step. According to the invention, a plurality of sewage treatment means are combined, so that the treatment effect of the high-salt and high-COD wastewater can be effectively improved. Meanwhile, wastewater generated in the sewage treatment process can be utilized to the maximum extent, so that water in the wastewater is recycled, the utilization efficiency of water resources is improved, and the aim of zero emission is finally achieved.

Description

Technical Field

[0001] The present invention belongs to the field of sewage treatment, and in particular relates to a high-salt and high-COD wastewater recovery and zero-discharge treatment process and a treatment system. Background Art

[0002] High salt and high COD have the characteristics of high salt content, complex composition, easy scaling and corrosion, high concentration of organic matter and difficulty in degradation. Conventional physical and chemical methods are difficult to achieve ideal treatment effects and have high energy consumption.

[0003] In the prior art, there are many studies on wastewater treatment, such as a high-concentration organic wastewater wet oxidation treatment system and process disclosed in CN114772823A, including a pressurized high-concentration wastewater storage tank, a high-concentration wastewater pump, a heat exchange reaction device, an oxygen supply unit and a post-reaction wastewater pressure storage tank; the wastewater after the wet oxidation reaction in the heat exchange reaction device is stored in the post-reaction wastewater pressure storage tank for gas-liquid separation, and the CO2-rich reaction gas is passed into the high-concentration wastewater in the pressurized high-concentration wastewater storage tank in the high-concentration wastewater storage device under pressure. The high-concentration wastewater in the pressurized high-concentration wastewater storage tank absorbs the CO2 in the reaction gas, and the high-concentration wastewater is quenched and modified, so that CO2 can be used to significantly enhance the anti-scaling effect of the high-concentration wastewater treatment process, improve the stability and reliability of the process, and at the same time, the reflux of the reaction gas in the post-reaction wastewater pressure storage tank realizes the recycling of the residual pressure energy, which reduces the process energy consumption and treatment cost to a certain extent. However, this treatment process is not ideal for the treatment of wastewater with high salt concentration.

[0004] The applicant has been committed to wastewater treatment and has disclosed relevant technologies in the early stage, such as the zero wastewater sewage treatment system and zero wastewater sewage treatment process disclosed in CN117756334A. However, the patent application technology mainly focuses on how to control the membrane pollution problem in the zero wastewater sewage treatment process, and does not design a targeted process for the treatment of high-salt and high-COD wastewater. This process is used for the treatment of high-salt and high-COD wastewater, and the treatment effect and efficiency need to be further improved. Summary of the invention

[0005] The purpose of the present invention is to solve the above-mentioned problems existing in the current treatment of high-salt and high-COD wastewater, and to provide a high-salt and high-COD wastewater recovery zero-emission process and system for wastewater treatment, especially for the treatment of high-salt and high-COD wastewater, which has significant effects and is less destructive to the treatment system.

[0006] The present invention adopts the following technical solution: In a first aspect of the present invention, a zero-discharge treatment process for high-salt and high-COD wastewater reuse is provided, comprising the following steps: (1) Pre-treating the wastewater, including filtering, softening, etc., to obtain pre-treated water; (2) subjecting the pretreated water to supercritical water oxidation treatment to obtain oxidized water; (3) the oxidized water enters an ultrafiltration membrane unit and a reverse osmosis membrane unit in sequence for concentration and filtration to obtain a first stage of osmotic filtered water and a first stage of osmotic concentrated water; (4) The concentrated permeate water of the first stage enters the nanofiltration membrane unit in turn for treatment to obtain nanofiltration filtered water and nanofiltration concentrated water, and the nanofiltration filtered water is returned to step (3) for cyclic treatment; (5) The nanofiltration concentrate from the nanofiltration membrane unit enters the second-stage reverse osmosis membrane unit for concentration and filtration to obtain second-stage osmosis filtrate water and second-stage osmosis concentrate; (6) The secondary permeate concentrate of the secondary reverse osmosis membrane unit enters the concentrate treatment unit for salt separation, and the treated concentrate flows back to step (2) for circulation treatment; The first stage osmosis filtered water and the second stage osmosis filtered water are recycled water.

[0007] In the above scheme of the present invention, supercritical water oxidation technology is combined with membrane filtration to treat high-salt and high-COD wastewater. Compared with the prior art, this scheme reasonably arranges the order of each step. On the one hand, the wastewater is efficiently treated, and the organic matter and salt in the wastewater can be fully treated. On the other hand, the supercritical water oxidation treatment is arranged after a reverse osmosis membrane treatment, which effectively avoids the influence of high-salt components on supercritical water treatment. The obvious advantage of the present invention is that the treatment effect of high-salt and high-COD wastewater is greatly improved under the premise of ensuring the stable operation of the treatment system.

[0008] Specifically, the treatment process of the present invention first pre-treats the sewage, such as filtering out large particles of impurities and suspended matter, softening, etc., so that the wastewater is more conducive to subsequent treatment processes.

[0009] The pretreated wastewater then enters the supercritical water oxidation unit for water oxidation treatment. The supercritical water oxidation unit uses the high solubility and high diffusivity of supercritical water to fully mix organic pollutants and oxygen in a uniform phase and undergo an oxidation reaction. In the supercritical state, the physical properties of water such as density, viscosity, and dielectric constant change significantly, thereby increasing the oxidation rate and efficiency of organic matter.

[0010] After supercritical water oxidation treatment, it enters the ultrafiltration membrane unit and the reverse osmosis unit in sequence to perform ultrafiltration and reverse osmosis filtration on the oxidized water. The reverse osmosis process removes smaller particles such as ions, dissolved organic matter and microorganisms in the water through the action of a semipermeable membrane, thereby obtaining treated discharge water, which can further improve the purification effect of wastewater.

[0011] After being treated by a reverse osmosis unit, the first reverse osmosis filtered water meets the discharge or reuse standards. The first reverse osmosis concentrated water and ultrafiltration concentrated water need to be further treated. After passing through a nanofiltration membrane unit, the wastewater is filtered more finely by nanofiltration technology to remove smaller particles, microorganisms and colloids, thereby improving the efficiency of wastewater purification. The filtered water after nanofiltration basically meets the discharge or reuse standards. If there is a higher requirement for reuse, the nanofiltration filtered water after nanofiltration can be returned to the first reverse osmosis unit in step (3) for circulation treatment to obtain purified water with a higher degree of purification.

[0012] The concentrated water after nanofiltration enters the second-stage reverse osmosis unit for reverse osmosis filtration. The reverse osmosis effect is used to further purify the water, and the second-stage reverse osmosis filtered water meets the discharge or reuse standards. The concentrated water of the second stage osmosis enters the concentrated water treatment unit for salt separation treatment, and the treated concentrated water is returned to the supercritical water oxidation unit in step (2) for water oxidation treatment for circulation treatment.

[0013] Preferably, during the supercritical water oxidation treatment, the wastewater is contacted with a ceramic adsorbent material.

[0014] For high-salt and high-COD wastewater, conventional methods are used for supercritical water oxidation treatment. During the treatment process, due to the change in the properties of supercritical water, the solubility of inorganic salts in supercritical water is very low, so they are easily deposited in the reactor or pipeline, causing blockage, affecting the stable operation of the reactor, and greatly reducing the oxidation treatment effect.

[0015] In this scheme, in order to solve this problem, with the help of adsorption materials, the deposited inorganic salts are adsorbed in the adsorption materials by contacting the wastewater with the adsorption materials during the supercritical water oxidation process, which not only avoids the adverse effects of the inorganic salts on the supercritical water oxidation treatment, but also removes the inorganic salts during the supercritical water oxidation treatment. After the supercritical conditions are released in the reactor, part of the inorganic salts are redissolved and removed, and the remaining inorganic salts can be regularly recovered and removed by the adsorption materials, and the adsorption materials can be reused.

[0016] Compared with the pre-treated wastewater directly entering the supercritical water oxidation unit for treatment, its treatment efficiency is higher, and because the ion concentration in the wastewater is reduced, a large amount of inorganic salt deposition will not appear in the supercritical water, which reduces the adverse effects on the supercritical water oxidation unit equipment and is conducive to maintaining the stable operation of the equipment.

[0017] Preferably, the ceramic adsorption material is in granular form with a particle size ranging from 0.1 to 5.0 mm.

[0018] Preferably, an inert gas is introduced during the supercritical water oxidation process. In the process of depositing inorganic salts using the adsorbent material, introducing an inert gas is beneficial to further improve the adsorption efficiency of the adsorbent material on the inorganic salts.

[0019] Preferably, the inert gas is introduced simultaneously with the oxygen from the supercritical water oxidation treatment.

[0020] Preferably, the inert gas is nitrogen.

[0021] Preferably, after the pretreatment, the wastewater is subjected to biochemical treatment before entering the supercritical water oxidation treatment. The biochemical treatment is beneficial to the degradation and transformation of organic matter and the removal of nutrients. The supercritical water oxidation treatment process is more efficient than direct treatment.

[0022] Preferably, the supercritical water treatment is carried out under a controlled pressure of 22-26 MPa, a temperature of 370-410° C., and a residence time of 2-15 min.

[0023] The second aspect of the present invention provides a treatment system for implementing the above-mentioned high-salt and high-COD wastewater recovery zero-discharge process, which is used for high-salt and high-COD wastewater treatment.

[0024] The treatment system comprises a pretreatment unit, an ultrafiltration membrane unit, a first-stage reverse osmosis membrane unit, a supercritical water oxidation unit, a nanofiltration membrane unit, a second-stage reverse osmosis membrane unit and a salt separation treatment unit which are sequentially arranged along a treatment path.

[0025] Preferably, the supercritical water oxidation unit comprises a supercritical water oxidation reactor, in which ceramic adsorption material particles are arranged.

[0026] By implementing the above technical solution, the present invention has the following beneficial effects: The present invention can effectively improve the treatment effect of high-salt and high-COD wastewater by combining multiple sewage treatment methods. At the same time, it can maximize the use of wastewater generated in the sewage treatment process, thereby realizing the reuse of water in the wastewater, improving the utilization efficiency of water resources, and ultimately achieving the goal of zero discharge.

[0027] The present invention further optimizes the process, reduces adverse effects on the processing system, and helps maintain stable operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the structure of the high-salt and high-COD wastewater treatment system provided by the present invention. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention are described clearly and completely below through the accompanying drawings. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1 This embodiment provides three types of high-salt and high-COD wastewater treatment systems (treatment system A, treatment system B, and treatment system C), with the same overall unit and structural schematic diagram. Figure 1 It includes a pretreatment unit 100, an ultrafiltration membrane unit 401, a first-stage reverse osmosis membrane unit 200, a supercritical water oxidation unit 300, a nanofiltration membrane unit 402, a second-stage reverse osmosis membrane unit 500 and a salt separation treatment unit 600 which are sequentially arranged along the wastewater treatment direction.

[0031] The specific structure of processing system A is as follows: The pretreatment unit 100 includes a sedimentation tank 102 , a filtration tank 103 and a softening tank 104 . The sedimentation tank 102 is connected to the raw water tank 101 , the filtration tank 103 is connected to the sedimentation tank 102 , and the softening tank 104 is connected to the filtration tank 103 .

[0032] The sedimentation tank 102 performs preliminary sedimentation on the wastewater raw water, and the large particles in it are deposited at the bottom of the tank, and the relatively clear water on the upper layer enters the filter tank 103 for preliminary filtration. This effectively removes the suspended large particles in the tail water after biochemical treatment to prevent them from clogging the subsequent treatment process. In this embodiment, the filter tank 103 adopts sand filtration, and other filtration methods can also be used.

[0033] The softening tank 104 is used to adjust the water quality to make it more suitable for the subsequent supercritical water oxidation treatment, and adjust the pH to an optimum value between 6 and 8.

[0034] The supercritical water oxidation unit 300 comprises a supercritical water oxidation reactor 301, an oxygen storage tank 302 connected thereto, the oxygen storage tank 302 is connected to the oxygen inlet of the supercritical water oxidation reactor 301, the inlet end of the supercritical water oxidation reactor is connected to the water outlet end of the softening tank 104 by a pipeline, and a preheating device can also be set between the soft water tank 104 and the inlet end of the supercritical water oxidation reactor, and the wastewater is first preheated by the preheating device, and then sent to the supercritical water oxidation reactor for oxidation reaction. The outlet end of the supercritical water oxidation reactor is connected to a cooling tank, and the oxidation treatment water after the reaction is completed enters a subsequent ultrafiltration membrane unit 401 and a section of reverse osmosis membrane unit 200 after cooling.

[0035] The ultrafiltration membrane unit 401 adopts an existing ultrafiltration membrane system.

[0036] The first section of the reverse osmosis membrane unit 200 includes a RO reverse osmosis system. The RO reverse osmosis system uses the FR series anti-fouling membrane element FILMTEC BW 30-400FR / 34 of Dow Chemical of the United States. BW30-400FR / 34 is a rolled composite membrane with strong anti-fouling performance. FILMTEC FR / CR anti-fouling elements have many performance advantages and economic advantages: the advanced automatic membrane rolling technology makes the precision reach a level that is far beyond the reach of manual rolling; increasing the number of membranes and shortening the length of the membranes significantly reduces the pressure loss on the water production side, which is more efficient, more uniform in driving pressure, and more uniform in water production flux distribution. The water supply channel of the membrane element is 34mil wide, which is 10-20% wider than other brands of products, which not only reflects its excellent anti-fouling performance, but also reflects its excellent cleaning recovery after pollution. FILMTEC FR anti-fouling membrane has been proven to have anti-bacterial adsorption capabilities, thus greatly extending the cleaning cycle. The bioaccumulation and biofouling rates of FILMTEC FR elements are very low, so the average feed water pressure is very low, which significantly reduces energy consumption.

[0037] The nanofiltration membrane unit 402 adopts an existing nanofiltration membrane system to receive a section of reverse osmosis concentrated water produced by a section of reverse osmosis membrane unit 200 .

[0038] The nanofiltration membrane unit 402 also includes a forward and reverse flushing system for flushing the nanofiltration membrane system. The flushing water can be, for example, a reverse osmosis filtered water obtained from a reverse osmosis membrane unit 200 or filtered water produced by the ultrafiltration membrane unit 401, or filtered water from the nanofiltration membrane unit 400. The waste water after flushing and the concentrated water obtained from the nanofiltration membrane unit 400 are mixed and then enter the supercritical water oxidation unit 300 for further purification.

[0039] The second-stage reverse osmosis membrane unit 500 is the same as the first-stage reverse osmosis unit 200, and also uses the FR series anti-fouling membrane element FILMTEC BW 30-400FR / 34 of Dow Chemical of the United States. BW30-400FR / 34 is a rolled composite membrane. The difference is that the second-stage reverse osmosis membrane unit 500 receives the nanofiltration filtered water obtained by the nanofiltration membrane unit 400, and further purifies the nanofiltration filtered water.

[0040] The salt separation treatment unit 600 performs salt separation treatment on the final secondary permeate concentrate in the final concentrate tank to obtain separated concentrate and separated salt, and the separated concentrate flows back to the supercritical water oxidation unit 300 for further purification. The separated salt is transported out for treatment.

[0041] The difference between treatment system B and treatment system A is that in the reaction chamber of the supercritical water oxidation reactor of treatment system B, ceramic adsorption material particles are arranged, and the particle size ranges from 0.1 to 5.0 mm.

[0042] The difference between treatment system C and treatment system B is that the supercritical water oxidation unit 200 further includes a nitrogen storage tank connected to the oxygen inlet of the supercritical water oxidation reactor.

[0043] Example 2 This embodiment provides a zero-discharge process for recycling high-salt and high-COD wastewater, which is implemented using the treatment systems A, B, and C in Example 1, respectively, and includes the following steps: (1) pre-treating wastewater to obtain pre-treated water; (2) subjecting the pretreated water to supercritical water oxidation treatment at a pressure of 25 MPa, a temperature of 400° C., and a residence time of 10 min to obtain oxidized water; (3) The oxidized water enters the ultrafiltration membrane unit to obtain ultrafiltration filtered water and ultrafiltration concentrated water; (4) The ultrafiltration filtered water enters a reverse osmosis membrane unit for concentration filtration to obtain a section of osmotic filtered water and a section of osmotic concentrated water; (5) The first-stage permeate concentrate and ultrafiltration concentrate enter the nanofiltration membrane unit for treatment to obtain nanofiltration filtered water and nanofiltration concentrate, and the nanofiltration filtered water is returned to step (3) for circulation treatment; (6) The nanofiltration concentrate from the nanofiltration membrane unit enters the second-stage reverse osmosis membrane unit for concentration filtration to obtain second-stage osmosis filtrate water and second-stage osmosis concentrate; (7) The secondary permeate concentrate from the secondary reverse osmosis membrane unit enters the concentrate treatment unit for salt separation, and the treated concentrate flows back to step (2) for circulation treatment.

[0044] The first-stage osmosis filtered water and the second-stage osmosis filtered water are recycled water for reuse.

[0045] Application Examples This application example takes the treatment of printing and dyeing wastewater from a certain factory as an example, and adopts the high-salt and high-COD wastewater reuse zero-discharge process described in Example 2.

[0046] After testing the wastewater, the CODcr of the raw wastewater was 1040 mg / L and the conductivity was 18652 μS / cm.

[0047] The CODcr and conductivity of the water obtained after the key steps were measured respectively. CODcr was determined by potassium dichromate method (GBT11914-89), and conductivity was measured by conductivity analyzer.

[0048] The results are shown in Table 1.

[0049] From the results in Table 1, it can be seen that the three treatment systems in the present invention have good removal effects on organic matter and salt in wastewater. Among them, by comparison, treatment system B, due to the addition of ceramic adsorption material particles in the supercritical water oxidation reactor, has a better removal effect on organic matter and inorganic salts than treatment system A. Treatment system C, on the basis of treatment system B, adds the introduction of inert gas nitrogen, and its removal effect on organic matter and inorganic salts is better than treatment system B, indicating that in this process, the introduction of nitrogen is conducive to improving the treatment efficiency of high-salt and high-COD wastewater.

[0050] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A zero-discharge treatment process for high-salt and high-COD wastewater reuse, characterized in that: The steps include: (1) Pre-treating the wastewater, including filtering, softening, etc., to obtain pre-treated water; (2) subjecting the pretreated water to supercritical water oxidation treatment to obtain oxidized water; (3) The oxidized water enters the ultrafiltration membrane unit and the reverse osmosis membrane unit in sequence for concentration and filtration to obtain a first stage of osmotic filtered water and a first stage of osmotic concentrated water; (4) The concentrated permeate enters the nanofiltration membrane unit for treatment to obtain nanofiltration filtered water and nanofiltration concentrated water, and the nanofiltration filtered water is returned to step (3) for circulation treatment; (5) The nanofiltration concentrated water from the nanofiltration membrane unit enters the second-stage reverse osmosis membrane unit for concentration and filtration to obtain second-stage osmosis filtered water and second-stage osmosis concentrated water; (6) The secondary permeate concentrate of the secondary reverse osmosis membrane unit enters the concentrate treatment unit for salt separation, and the treated concentrate flows back to step (2) for circulation treatment; The first-stage osmotic filter water and the second-stage osmotic filter water are recycled water.

2. A high-salt and high-COD wastewater reuse and zero-discharge treatment process according to claim 1, characterized in that: During the supercritical water oxidation treatment process of step (2), the wastewater comes into contact with the ceramic adsorption material.

3. A high-salt and high-COD wastewater reuse and zero-discharge treatment process according to claim 2, characterized in that: During the supercritical water oxidation treatment in step (2), an inert gas is introduced simultaneously.

4. A high-salt and high-COD wastewater reuse and zero-discharge treatment process according to claim 2, characterized in that: The ceramic adsorption material is in granular form with a particle size ranging from 0.1 to 5.0 mm.

5. A high-salt and high-COD wastewater reuse and zero-discharge treatment process according to claim 3, characterized in that: The inert gas is introduced simultaneously with the oxygen treated by supercritical water oxidation.

6. A high-salt and high-COD wastewater reuse and zero-discharge treatment process according to claim 3, characterized in that: The inert gas is nitrogen.

7. A high-salt and high-COD wastewater reuse and zero-discharge treatment process according to claim 1, characterized in that: The supercritical water treatment is controlled at a pressure of 22-26 MPa, a temperature of 370-410° C., and a residence time of 2-15 min.

8. A treatment system for implementing a high-salt and high-COD wastewater reuse and zero-discharge treatment process as claimed in claim 1, characterized in that: The treatment system comprises a pretreatment unit, an ultrafiltration membrane unit, a first-stage reverse osmosis membrane unit, a supercritical water oxidation unit, a nanofiltration membrane unit, a second-stage reverse osmosis membrane unit and a salt separation treatment unit which are sequentially arranged along a treatment path.

9. A high-salt and high-COD wastewater reuse and zero-discharge treatment system according to claim 8, characterized in that: The supercritical water oxidation unit comprises a supercritical water oxidation reactor, in which ceramic adsorption material particles are arranged.

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