A wastewater pre-treatment system

Abstract

The utility model relates to bipolar membrane electrodialysis processing technical field, especially a kind of wastewater front-end treatment system, including the pH adjusting device, air floatation pool, sand filter device, resin treatment device and electrodialysis brine tank connected in turn;The pH adjusting device includes the first mixed reaction tank and the second mixed reaction tank connected in turn;The first mixed reaction tank is communicated with dosing device;The feeding direction of the feed inlet of two mixed reaction tanks is all tangent direction, and the inner wall of mixed reaction tank is all equipped with spiral fairlead;The feed inlet of two mixed reaction tanks is arranged in upper and lower staggered mode.By the system, the problem of unstable pH regulation can be effectively solved, and the processing efficiency and processing effect can be greatly improved.

Description

Technical Field

[0001] This utility model relates to the field of bipolar membrane electrodialysis treatment technology, and in particular to a wastewater pretreatment system. Background Technology

[0002] Bipolar membrane electrodialysis (BMED) is a highly efficient separation and conversion technology based on ion exchange membranes, with wide applications in electrochemical engineering and environmental engineering. The core component of this technology is the bipolar membrane, a special composite membrane structure composed of a cation exchange layer (N-type membrane), an interfacial hydrophilic layer (catalytic layer), and an anion exchange layer (P-type membrane).

[0003] Under the influence of a direct current electric field, the bipolar membrane can decompose water into hydrogen ions (H+). + ) and hydroxide ions (OH) - These two types of ions migrate in opposite directions. When bipolar membranes are used in combination with unipolar membranes (i.e., cation and anion exchange membranes that allow only one type of ion to pass through), salts (such as sodium sulfate, sodium chloride, and other inorganic salts) in solution can be converted into corresponding acids (such as sulfuric acid, hydrochloric acid) and bases (such as sodium hydroxide, sodium hydroxide) without the addition of other chemical reagents. This process not only achieves effective separation of cations and anions in salt solutions but also produces high-purity acid-base products.

[0004] Bipolar membrane electrodialysis technology, due to its high efficiency, energy saving, and environmental friendliness, has significant application potential in many fields such as wastewater treatment, resource recycling, and chemical production. For example, it is being promoted and used as a clean production technology in the production of products such as organic acids, amino acids, and vitamin C. Furthermore, it can be used for the transformation and optimization of various industrial processes, including water treatment of nonwoven fabrics containing ion-functional auxiliaries, desulfurizer regeneration, silica sol production, and sodium phenolate solution treatment.

[0005] Given the unique properties of bipolar membranes, which can convert salt solutions into corresponding acids and alkalis, they are highly compatible with traditional viscose fiber production processes. Viscose's unique processes consume large amounts of sulfuric acid and caustic soda, generating significant amounts of sodium sulfate. Traditional processes can only concentrate the acid bath solution, crystallize the sodium sulfate, and then separate it into sodium sulfate crystals using a centrifuge—a costly and inefficient process. Therefore, a process has been developed that utilizes an electrodialysis device to reconstitute sodium sulfate into sulfuric acid and sodium hydroxide, achieving acid-base recycling.

[0006] Because zinc sulfate was added to the adhesive acid bath, the crystallized sodium sulfate also contained a small amount of zinc sulfate, resulting in zinc ions (Zn) in the solution after dissolution. 2+ Divalent zinc ions bind to the cation exchange membrane of the bipolar membrane, affecting sodium ions (Na).+ Migration of these ions increases the membrane stack resistance, and in severe cases, can lead to membrane burnout. Therefore, when using bipolar membrane electrodialysis to treat sodium sulfate wastewater, pretreatment of the wastewater is necessary to remove as many divalent metal ions as possible, such as zinc, calcium, and magnesium ions, from the solution.

[0007] In the prior art, a Chinese utility model patent document with publication number CN223213961U and publication date of August 12, 2025 has been proposed to solve the above-mentioned technical problems. The technical solution disclosed in this patent document is as follows: a ternary precursor wastewater resource utilization system based on bipolar membrane, including a pretreatment system and a bipolar membrane electrodialysis system. The pretreatment system includes a sand filtration unit, an ultrafiltration unit and a resin unit connected in sequence. The ternary precursor sodium sulfate wastewater passes through the sand filtration unit, the ultrafiltration unit and the resin unit in sequence for sand filtration, and then is adsorbed by the resin unit before being processed into acid and alkali products through the bipolar membrane electrodialysis system.

[0008] The above-mentioned technical solution presents the following problems in practical use: Sodium sulfate wastewater is acidic. If it enters the sand filter unit directly without pH adjustment, the acidic environment easily causes the surface of filter media such as quartz sand to dissolve, releasing silicates and metal impurities. This not only reduces filtration efficiency but may also cause filter bed caking and decreased throughput. Simultaneously, acidic conditions accelerate the corrosion of sand filter equipment, shortening its service life. Furthermore, under low pH conditions, the selective adsorption capacity of subsequent resin adsorption units for target metal ions significantly decreases, and some functional groups may undergo protonation deactivation, leading to reduced adsorption capacity, frequent regeneration, and impacting overall treatment efficiency and operational stability.

[0009] Currently, the pretreatment scheme also includes: adjusting the pH of the wastewater to weakly alkaline (7-8), causing the divalent metal ions in the solution to precipitate as hydroxides, allowing the sediment to stand for 2-4 hours, and then passing the supernatant through a cation chelating resin for further treatment to remove the unprecipitated divalent metal ions in the solution.

[0010] Since the above method involves adjusting the pH value to allow the precipitate to settle naturally, and it is an intermittent operation, the pH value control, treatment efficiency, and treatment effect are unstable. Unstable pH value and insufficient settling time will all have a significant impact on the treatment effect. Summary of the Invention

[0011] To address the aforementioned technical problems, this invention proposes a wastewater pretreatment system, which is particularly suitable for use in bipolar membrane electrodialysis treatment. It can effectively solve the problem of unstable pH control and greatly improve treatment efficiency and effect.

[0012] This utility model is achieved by adopting the following technical solution: A wastewater pretreatment system includes a pH adjustment device, an air flotation tank, a sand filter, a resin treatment device, and an electrodialysis brine tank connected in sequence. The pH adjustment device includes a first mixing reaction tank and a second mixing reaction tank connected in sequence. The first mixing reaction tank is connected to a dosing device. The feed inlets of both mixing reaction tanks are tangential, and the inner walls of both mixing reaction tanks are equipped with spiral guide plates. The feed inlets of the two mixing reaction tanks are arranged in a staggered manner.

[0013] The dosing device includes a PAM dosing tank and a sodium hydroxide dosing tank, which are respectively connected to the first mixing reaction tank via metering pumps; the second mixing reaction tank, which is connected to the flotation tank, is also equipped with a pH detection device.

[0014] The flotation tank includes a flotation tank body; along the water flow direction, the flotation tank body is provided with several baffles to divide the flotation tank body into a scum recovery zone and several buffer zones; one of the buffer zones is also provided with a dissolved air release device; the feed inlets of two adjacent buffer zones are arranged vertically and horizontally; the top of the flotation tank body is also provided with a scum discharge device to send the scum into the scum recovery zone.

[0015] The number of baffles is four, including a first baffle, a second baffle, a third baffle, and a fourth baffle in sequence; the dissolved gas release device is disposed between the first baffle and the second baffle, the tops of the second baffle and the third baffle are inclined upward toward the scum recovery area, and the top of the third baffle is directly connected to the scum recovery area.

[0016] The sand filtration device includes several sand filter tanks arranged in parallel.

[0017] Each sand filter tank is equipped with two inlets and two outlets. The two inlets are connected to the feed pipe and the backwash water inlet pipe, respectively. The two outlets are connected to the filter water outlet pipe and the backwash water outlet pipe, respectively. The feed pipe and the backwash water inlet pipe are also equipped with valves.

[0018] The backwash inlet pipe of the sand filter tank is equipped with two branch pipes at the other end, and each branch pipe is equipped with a valve; one branch pipe is connected to the backwash water pump, and the other branch pipe is connected to the backwash blower.

[0019] The resin treatment device includes several resin towers arranged in parallel.

[0020] Each resin tower is equipped with two feed inlets and two discharge outlets. The two feed inlets are connected to the feed pipe and the backwash water inlet pipe, respectively, and the two discharge outlets are connected to the filter water outlet pipe and the backwash water outlet pipe, respectively. The other end of the backwash water inlet pipe is equipped with two branch pipes, one of which is used to provide backwash water and the other is used to provide backwash acid. Each feed pipe and each branch pipe of the resin tower is equipped with a valve.

[0021] It also includes a zinc sulfate dissolving tank, and the scum recovery area and backwash outlet pipe are respectively connected to the zinc sulfate dissolving tank.

[0022] Compared with the prior art, the beneficial effects of this utility model are as follows: 1. In this utility model, by improving the structure of the mixing reaction tank, the feed inlets of both mixing reaction tanks are set to tangential feed, and a spiral guide plate is set on the inner wall of the mixing reaction tank. This allows the wastewater to form a strong spiral turbulent state under the action of centrifugal force and guide flow after entering the mixing reaction tank, which significantly enhances the mass transfer efficiency between the wastewater and the reagents added by the dosing device, achieves rapid and uniform mixing, effectively shortens the reaction time, and improves the treatment efficiency. It is especially suitable for the continuous treatment of large-flow wastewater.

[0023] Furthermore, the inlets of the first and second mixing reaction tanks are staggered vertically, creating a counter-current flow path within each tank. This extends the overall hydraulic residence time, prevents short-circuiting, and enhances the continuity and stability of the reaction. This two-stage series mixing reaction also enables graded adjustment and fine control of pH: the first stage performs initial neutralization, while the second stage provides fine-tuning, effectively suppressing pH fluctuations and improving the pH stability of the effluent. This provides favorable influent conditions for subsequent steps such as flotation, filtration, and electrodialysis.

[0024] In this invention, the solution after pH adjustment enters the flotation tank, where metal hydroxide precipitates in the wastewater are separated to the upper layer by flotation. The solution after flotation then enters a sand filtration device to further remove precipitates. The solution after sand filtration enters a resin treatment device to remove residual unprecipitated divalent metal ions. The solution treated by the resin treatment device then enters the electrodialysis brine tank. The sodium sulfate solution treated through this process has a high degree of cleanliness, which can improve the operating efficiency of the bipolar membrane stack, extend the membrane stack cleaning cycle, and extend the membrane stack's service life.

[0025] 2. In this utility model, the dosing device includes a PAM dosing tank and a sodium hydroxide dosing tank. By adding PAM and sodium hydroxide into the first mixing reaction tank, not only can the pH value be effectively adjusted, but the added polyacrylamide PAM can also act as a flocculant to promote the aggregation of fine suspended solids and colloidal particles, forming dense and easily floating flocs, which significantly improves the removal efficiency of the flotation tank.

[0026] The pH detection device can monitor the pH value of the wastewater after the reaction in real time. In conjunction with the metering pump, it can realize closed-loop automatic control of sodium hydroxide dosage, ensuring accurate dosing and avoiding over- or under-dosing.

[0027] 3. By setting up several baffles, the dissolved air flotation (DAF) tank is divided into a scum recovery zone and several buffer zones, forming a multi-stage series hydraulic channel. The feed inlets between adjacent buffer zones are staggered vertically, causing the water flow to follow an "up-down-up" or "down-up-down" path between the buffer zones. This significantly extends the hydraulic residence time, avoids short-circuiting and dead zones, enhances the contact efficiency between bubbles and flocs, and significantly improves the separation efficiency, operational stability, and adaptability to water quality fluctuations of the DAF tank.

[0028] 4. The dissolved air release device is located between the first and second baffle plates, at the forefront of the water flow path. After the wastewater to be treated achieves influent buffering and uniform flow velocity distribution, it enters this buffer zone and comes into full contact with the bubbles released by the dissolved air release device. The bubbles adhere to the surface of suspended particles or flocs in the water, forming a "gas-particle" composite with a density less than water, thus enabling it to float. Subsequently, the gas-liquid mixture further stabilizes the combination of bubbles and flocs between the second and third baffle plates, improving the floating efficiency. The scum that floats to the surface is guided by the water flow and the structure of the second and third baffle plates, and is sent to the scum recovery zone by the scum discharge device. The water continues to flow, settling the fine particles that failed to float, further improving the effluent quality, and finally discharged into the sand filter through the outlet.

[0029] In this process, the top of the second baffle plate is inclined upwards towards the scum recovery area, which not only effectively guides air bubbles and impurities to the water surface, but also serves to guide the flow and prevent backflow, thus avoiding scum from being mixed back with the water flow. The top of the third baffle plate is also inclined upwards towards the scum recovery area, and its top is directly connected to the scum recovery area, forming a smooth scum guiding channel, which can directly guide the accumulated scum into the scum recovery area, reducing the risk of retention and blockage.

[0030] This invention achieves a synergistic effect of influent buffering, high-efficiency flotation, scum guidance and deep clarification by rationally arranging baffles, dissolved air release devices and scum guiding structures, which significantly improves the separation efficiency, operational stability and adaptability to water quality fluctuations of the flotation tank.

[0031] 5. The sand filtration device includes several sand filter tanks arranged in parallel, and the resin treatment device includes several resin towers arranged in parallel, which facilitates the improvement of treatment efficiency and makes it more suitable for continuous treatment of large-flow wastewater.

[0032] 6. The sand filter tank in this utility model is equipped with a combined air and water cleaning function, which can perform compressed air flushing (air washing), reverse water flow flushing (backflow washing), and forward water flow flushing; the resin tower can perform backwash water flushing, acid regeneration, and forward water flow flushing, ensuring long-term efficient operation of the filtration and ion exchange units, and is particularly suitable for large-flow, continuous industrial wastewater treatment systems.

[0033] 7. Backwash water / acid recovery enters the zinc sulfate dissolving tank, where the recovered scum (mainly zinc sulfate) is dissolved and recovered, achieving zero discharge of backwash acid water and complete recycling of filter residue. This system separates sodium sulfate wastewater into a clean sodium sulfate solution and a recyclable zinc sulfate solution, achieving both separation and zero discharge.

[0034] 8. This system concentrates divalent metal ions (mainly zinc ions) in wastewater into solids for recycling, greatly reducing the water treatment load and pollutant emissions; it has an excellent effect on treating divalent metal ions in wastewater, and can control the concentration of divalent metal ions in the solution to within 10 ppm. Attached Figure Description

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments, wherein: Figure 1 This is a schematic diagram of the structure of this utility model; Figure 2 This is a cross-sectional structural diagram of region A in this utility model; Figure 3 This is a schematic diagram of the air washing flow direction of the medium sand filter tank of this utility model; Figure 4 This is a schematic diagram of the backwash water flow direction of the medium sand filter tank of this utility model; Figure 5 This is a schematic diagram of the forward wash water flow direction of the medium sand filter tank of this utility model; Figure 6 This is a schematic diagram showing the flow direction of water backwashing or acid regeneration in the resin tower in this utility model; Figure 7 This is a schematic diagram of the flow direction of the washing water in the resin tower in this utility model; Marked in the image: 1. Electrodialysis brine tank; 2. First mixing reaction tank; 3. Second mixing reaction tank; 4. Spiral guide plate; 5. PAM dosing tank; 6. Sodium hydroxide dosing tank; 7. pH detection device; 8. Flotation tank body; 9. Sand filter tank; 10. Dissolved gas release device; 11. Sludge discharge device; 12. First baffle plate; 13. Second baffle plate; 14. Third baffle plate; 15. Fourth baffle plate; 16. Feed pipe; 17. Backwash inlet pipe; 18. Filter outlet pipe; 19. Backwash outlet pipe; 20. Backwash water pump; 21. Backwash blower; 22. Resin tower; 23. Zinc sulfate dissolving tank; 24. Sludge tank; 25. Filter sludge tray. Detailed Implementation

[0036] Example 1 As a basic embodiment of this utility model, the present utility model includes a wastewater pretreatment system, comprising a pH adjustment device, an air flotation tank, a sand filter, a resin treatment device, and an electrodialysis brine tank 1 connected in sequence. The pH adjustment device includes a first mixing reaction tank 2 and a second mixing reaction tank 3 connected in sequence. The first mixing reaction tank 2 is connected to a dosing device. The feed inlets of both mixing reaction tanks are tangential, and the inner walls of both mixing reaction tanks are equipped with spiral guide plates 4. The feed inlets of the two mixing reaction tanks are staggered vertically, that is, the feed inlet and outlet of the same mixing reaction tank are arranged one above the other.

[0037] Since the sodium sulfate wastewater solution is acidic, its pH value can be adjusted to slightly alkaline (7-8) using a pH adjustment device before entering the flotation tank. After pH adjustment, the solution enters the flotation tank, where metal hydroxide precipitates are separated to the upper layer by flotation. The solution after flotation then enters a sand filter to further remove precipitates. The sand-filtered solution then enters a resin treatment unit to remove residual unprecipitated divalent metal ions. The resin-treated solution then enters the electrodialysis brine tank 1. This process results in a high degree of cleanliness in the sodium sulfate solution, which improves the operating efficiency of the bipolar membrane stack, extends the membrane stack cleaning cycle, and prolongs the membrane stack's service life.

[0038] Example 2 In a preferred embodiment of this utility model, the present utility model includes a wastewater pretreatment system, comprising a pH adjustment device, an air flotation tank, a sand filter, a resin treatment device, and an electrodialysis brine tank 1 connected in sequence. The pH adjustment device includes a first mixing reaction tank 2 and a second mixing reaction tank 3 connected in sequence. The first mixing reaction tank 2 is connected to a dosing device. The feed inlets of both mixing reaction tanks are tangential, and the inner walls of both mixing reaction tanks are equipped with spiral guide plates 4. The feed inlets of the two mixing reaction tanks are arranged in a staggered manner.

[0039] The dissolved air flotation (DAF) tank includes a main body 8. Along the water flow direction, the main body 8 is equipped with several baffles to divide it into a scum recovery zone and several buffer zones. One of the buffer zones is also equipped with a dissolved air release device 10. The feed inlets of adjacent buffer zones are staggered vertically. The top of the main body 8 is also equipped with a scum discharge device 11 to send scum into the scum recovery zone.

[0040] Example 3 In another preferred embodiment of this utility model, the present utility model includes a wastewater pretreatment system, comprising a pH adjustment device, an air flotation tank, a sand filter, a resin treatment device, and an electrodialysis brine tank 1 connected in sequence. The pH adjustment device includes a first mixing reaction tank 2 and a second mixing reaction tank 3 connected in sequence. The first mixing reaction tank 2 is connected to a dosing device. The feed inlets of both mixing reaction tanks are tangential, and the inner walls of both mixing reaction tanks are equipped with spiral guide plates 4. The feed inlets of the two mixing reaction tanks are arranged in a staggered manner.

[0041] The sand filtration device includes several sand filter tanks 9 arranged in parallel. Each sand filter tank 9 has two inlets and two outlets. The two inlets are connected to the feed pipe 16 and the backwash water inlet pipe 17, respectively; the two outlets are connected to the filter water outlet pipe 18 and the backwash water outlet pipe 19, respectively. Valves are also provided on the feed pipe 16 and the backwash water inlet pipe 17. Two branch pipes are provided at the other end of the backwash water inlet pipe 17, and each branch pipe is equipped with a valve. One branch pipe is connected to the backwash water pump 20, and the other branch pipe is connected to the backwash blower 21. Through this design, the sand filter tanks 9 can realize sand filtration, air washing, reverse water flow flushing, and forward water flow flushing.

[0042] The resin treatment device includes several resin towers 22 arranged in parallel. Each resin tower 22 has two inlets and two outlets. The two inlets are respectively connected to a feed pipe 16 and a backwash water inlet pipe 17, and the two outlets are respectively connected to a filter water outlet pipe 18 and a backwash water outlet pipe 19. Valves are also provided on the feed pipe 16 and the backwash water inlet pipe 17. Two branch pipes are provided at the other end of the backwash water inlet pipe 17 of the resin tower 22, and each branch pipe is equipped with a valve. One branch pipe is used to provide backwash water, and the other branch pipe is used to provide backwash acid. Through this structural design, the resin tower 22 can perform wastewater treatment, backwash water flushing, acid regeneration, and forward water flushing.

[0043] Example 4 As another preferred embodiment of this utility model, please refer to the appendix to the specification. Figure 1This utility model includes a wastewater pretreatment system, comprising a pH adjustment device, an air flotation tank, a sand filter, a resin treatment device, an electrodialysis brine tank 1, and a zinc sulfate dissolving tank 23 connected in sequence.

[0044] The pH adjustment device includes a first mixing reaction vessel 2 and a second mixing reaction vessel 3 connected in sequence. (Refer to the attached instruction manual.) Figure 2 The feeding directions of the inlets of both mixing reaction vessels are tangential, and the inner walls of both mixing reaction vessels are equipped with spiral guide plates 4. The inlets of the two mixing reaction vessels are arranged in a staggered manner, that is, the inlet and outlet of the first mixing reaction vessel 2 are set one above the other, and the inlet and outlet of the second mixing reaction vessel 3 are set one below the other.

[0045] The first mixing reaction tank 2 is connected to a dosing device. The dosing device includes a PAM dosing tank 5 and a sodium hydroxide dosing tank 6, which are respectively connected to the first mixing reaction tank 2 via metering pumps. The second mixing reaction tank 3, connected to the flotation tank, is also equipped with a pH detection device 7. The pH detection device 7 and the metering pumps can be connected to an existing control system. Based on the detection data from the pH detection device 7 and the set target pH range, the control system dynamically adjusts the output frequency or opening of the metering pump corresponding to the sodium hydroxide dosing tank 6, achieving closed-loop automatic control of the sodium hydroxide dosage. The control system can employ a conventional PID control algorithm. Since PID control is a mature and widely used process control method, a technical means that can be conventionally chosen by those skilled in the art, and this control method is not an innovation of this utility model, this embodiment does not further elaborate on its control details.

[0046] The dissolved air flotation (DAF) tank includes a main body 8, and a sludge discharge device 11 is provided on the top of the main body 8. The sludge discharge device 11 employs conventional techniques in the art, such as a scraper and a drive component for moving the scraper. Along the water flow direction, the main body 8 is provided with several baffles to divide it into a sludge recovery zone and several buffer zones. Specifically, there are four baffles, namely a first baffle 12, a second baffle 13, a third baffle 14, and a fourth baffle 15. The buffer zones are, in sequence, a first buffer zone, a second buffer zone, a third buffer zone, a fourth buffer zone, and a fifth buffer zone. The inlets of adjacent buffer zones are staggered vertically, creating a downward-upward-downward-upward-downward flow path within the main body 8.

[0047] A dissolved gas release device 10 is provided in the second buffer area. The dissolved gas release device 10 can employ conventional techniques in the art, such as a dissolved gas release plate, a dissolved gas tank, and a dissolved gas water pump. The dissolved gas release plate is located at the bottom of the second buffer area. The tops of the second baffle plate 13 and the third baffle plate 14 are inclined upwards towards the scum recovery area. Through this structural design, the second baffle plate 13 not only effectively guides air bubbles and impurities to the water surface but also serves to guide the flow and prevent backflow. The top of the third baffle plate 14 is directly connected to the scum recovery area, forming a smooth scum guiding channel. The scum recovery area is connected in sequence by a scum tank 24 and a filter plate 25 via pipes. The filter plate 25 is connected to a zinc sulfate dissolving tank 23, allowing scum to enter the zinc sulfate dissolving tank 23 for dissolution and recovery.

[0048] The sand filtration device includes several sand filter tanks 9 arranged in parallel. In this embodiment, four sand filter tanks 9 are arranged in parallel. Each sand filter tank 9 has two inlets and two outlets. The two inlets are connected to the feed pipe 16 and the backwash water inlet pipe 17, respectively. The two outlets are connected to the filter water outlet pipe 18 and the backwash water outlet pipe 19, respectively. A drain valve is also provided at the bottom of each sand filter tank 9. Valves are also provided on the feed pipe 16 and the backwash water inlet pipe 17. Two branch pipes are provided at the other end of the backwash water inlet pipe 17, and each branch pipe is provided with a valve; one branch pipe is connected to the backwash water pump 20, and the other branch pipe is connected to the backwash blower 21. The other end of the backwash water outlet pipe 19 connected to the sand filter tank 9 is connected to the zinc sulfate dissolving tank 23.

[0049] Based on this structure, the sand filter tank 9 can also achieve compressed air washing (air washing), reverse water flow washing (backwashing), and forward water flow washing. Before backwashing the sand filter tank 9, the bottom drain valve can be opened to drain some water to facilitate compressed air backwashing. When sand filter air washing is required, the backwash fan 21 starts, and compressed air enters the sand filter tank 9 from the backwash inlet pipe 17 connected to the bottom of the sand filter tank 9, and exhausts from the backwash outlet pipe 19 connected to the top of the sand filter tank 9. The specific flow direction can be found in the instruction manual. Figure 3 The area indicated by the red line is the sand filter. When reverse water flow rinsing of the sand filter is required, the backwash pump 20 starts, and the backwash water enters the sand filter tank 9 from the backwash inlet pipe 17 connected to the bottom of the sand filter tank 9, and exits from the backwash outlet pipe 19 connected to the top of the sand filter tank 9. The backwash water flows to the zinc sulfate dissolving tank 23. For specific flow directions, please refer to the instruction manual. Figure 4 The area indicated by the red line in the diagram. When forward water flushing of the sand filter is required, water enters from the inlet pipe 16 connected to the top of the sand filter tank 9, flows out from the drain valve at the bottom, and enters the zinc sulfate dissolving tank 23. Refer to the instruction manual for the specific flow direction. Figure 5 The area marked with red lines.

[0050] The resin treatment device includes several resin towers 22 arranged in parallel. In this embodiment, four resin towers 22 are arranged in parallel. Each resin tower 22 has two inlets and two outlets. The two inlets are respectively connected to a feed pipe 16 and a backwash water inlet pipe 17, and the two outlets are respectively connected to a filter water outlet pipe 18 and a backwash water outlet pipe 19. Valves are also provided on the feed pipe 16 and the backwash water inlet pipe 17. A drain valve is also provided at the bottom of each resin tower 22. Two branch pipes are provided at the other end of the backwash water inlet pipe 17 of the resin tower 22, and each branch pipe is equipped with a valve; one branch pipe is used to provide backwash water, and the other branch pipe is used to provide backwash acid. The other end of the backwash water outlet pipe 19 connected to the resin tower 22 is connected to a zinc sulfate dissolving tank 23.

[0051] Based on this structure, resin tower 22 can perform backwash water flushing, acid regeneration, and forward water flushing. During backwash water flushing or acid regeneration, the backwash water or acid enters from the backwash inlet pipe 17 connected to the bottom of resin tower 22 and exits from the backwash outlet pipe 19 connected to the top of resin tower 22, entering the zinc sulfate dissolving tank 23. The specific flow direction can be found in the instruction manual. Figure 6 The area indicated by the red line in the diagram. When forward washing of resin tower 22 is required, water enters from the feed pipe 16 connected to the top of resin tower 22, flows out from the drain valve at the bottom, and enters the zinc sulfate dissolving tank 23. Refer to the instruction manual for the specific flow direction. Figure 7 The area marked with red lines.

[0052] Since the sodium sulfate wastewater solution is acidic, its pH value is adjusted to slightly alkaline (7-8) using a pH adjustment device before entering the flotation tank. After pH adjustment, the solution enters the flotation tank, where metal hydroxide precipitates are separated to the upper layer by flotation and scraped into the scum recovery area via the scum discharge device 11. The solution after flotation separation enters the sand filter tank 9 through the feed pipe 16 connected to the top of the sand filter tank 9, further removing precipitates. It then flows through the filter outlet pipe 18 connected to the bottom of the sand filter tank 9 and the feed pipe 16 connected to the top of the resin tower 22, entering the resin tower 22 to remove residual unprecipitated divalent metal ions. The solution treated in the resin tower 22 flows through the filter outlet pipe 18 connected to the bottom of the resin tower 22 into the electrodialysis brine tank 1.

[0053] In the above process, the backwash water / acid is recycled into the zinc sulfate dissolving tank 23, and the filter residue (mainly zinc sulfate) from the filter residue tray 25 is recycled into the zinc sulfate dissolving tank 23 for dissolution, achieving zero discharge of backwash acid water and full recycling of filter residue.

[0054] In summary, any other corresponding modifications made by those skilled in the art based on the technical solution and concept of this utility model without creative mental effort after reading this utility model document are all within the scope of protection of this utility model.

Claims

1. A wastewater pretreatment system, characterized in that: It includes a pH adjustment device, an air flotation tank, a sand filter, a resin treatment device, and an electrodialysis brine tank (1) connected in sequence; the pH adjustment device includes a first mixing reaction tank (2) and a second mixing reaction tank (3) connected in sequence; the first mixing reaction tank (2) is connected to a dosing device; the feeding direction of the inlet of the two mixing reaction tanks is tangential, and the inner wall of the mixing reaction tanks is provided with a spiral guide plate (4); the inlets of the two mixing reaction tanks are arranged in an up-down staggered manner.

2. The wastewater pretreatment system according to claim 1, characterized in that: The dosing device includes a PAM dosing tank (5) and a sodium hydroxide dosing tank (6). The PAM dosing tank (5) and the sodium hydroxide dosing tank (6) are respectively connected to the first mixing reaction tank (2) via metering pumps. The second mixing reaction tank (3) connected to the flotation tank is also equipped with a pH detection device (7).

3. The wastewater pretreatment system according to claim 1, characterized in that: The flotation tank includes a flotation tank body (8); along the water flow direction, the flotation tank body (8) is provided with several baffles to divide the flotation tank body (8) into a scum recovery area and several buffer areas; a dissolved air release device (10) is also provided in one of the buffer areas; the feed inlets of two adjacent buffer areas are arranged vertically and horizontally; a scum discharge device (11) is also provided on the top of the flotation tank body (8) to send the scum into the scum recovery area.

4. The wastewater pretreatment system according to claim 3, characterized in that: The number of baffles is four, including a first baffle (12), a second baffle (13), a third baffle (14) and a fourth baffle (15) in sequence; the dissolved gas release device (10) is set between the first baffle (12) and the second baffle (13), the tops of the second baffle (13) and the third baffle (14) are inclined upward toward the scum recovery area, and the top of the third baffle (14) is directly connected to the scum recovery area.

5. A wastewater pretreatment system according to claim 3 or 4, characterized in that: The sand filtration device includes several sand filter tanks (9) arranged in parallel.

6. The wastewater pretreatment system according to claim 5, characterized in that: Each sand filter tank (9) is provided with two inlets and two outlets. The two inlets are connected to the feed pipe (16) and the backwash water inlet pipe (17) respectively. The two outlets are connected to the filter water outlet pipe (18) and the backwash water outlet pipe (19) respectively. The feed pipe (16) and the backwash water inlet pipe (17) are also provided with valves respectively.

7. A wastewater pretreatment system according to claim 6, characterized in that: The backwash inlet pipe (17) of the sand filter tank (9) has two branch pipes at the other end, each branch pipe is equipped with a valve; one branch pipe is connected to the backwash water pump (20), and the other branch pipe is connected to the backwash blower (21).

8. The wastewater pretreatment system according to claim 4, characterized in that: The resin treatment device includes several resin towers (22) arranged in parallel.

9. A wastewater pretreatment system according to claim 8, characterized in that: Each resin tower (22) is provided with two feed inlets and two discharge outlets. The two feed inlets are connected to the feed pipe (16) and the backwash water inlet pipe (17) respectively, and the two discharge outlets are connected to the filter water outlet pipe (18) and the backwash water outlet pipe (19) respectively. The other end of the backwash water inlet pipe (17) is provided with two branch pipes, one of which is used to provide backwash water and the other is used to provide backwash acid. The feed pipe (16) and each branch pipe of the resin tower (22) are provided with valves respectively.

10. A wastewater pretreatment system according to claim 9, characterized in that: It also includes a zinc sulfate dissolving tank (23), and the scum recovery area and the backwash outlet pipe (19) are respectively connected to the zinc sulfate dissolving tank (23).

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