A multi-stage treatment process for paperboard wastewater

Abstract

The application provides a paperboard wastewater multistage treatment process, and relates to the technical field of wastewater treatment.S1, the paperboard containing ink on the surface is soaked, stirred and broken, and the fiber size in the paperboard recycling wastewater is controlled to be in the range of 0.5-5 mm;S2, the paperboard recycling wastewater is added into a treatment tank, and a deinking agent is added into the treatment tank for a predetermined time;S3, the bubble flotation device is controlled to rotate around the central axis of the treatment tank to generate fine and dense flotation bubbles at each position, and the paperboard recycling wastewater at the bottom position of the treatment tank is lifted to the middle height position through the first flow guide groove, the intermediate flow guide pipeline and the second flow guide groove.The application can reduce the loss of fiber suspensions, automatically promote the mixing of the wastewater at the bottom position of the treatment tank, realize multistage deep treatment of the wastewater at each position in the treatment tank, and greatly reduce the content of ink in the paperboard wastewater, so as to meet the process requirements of paperboard wastewater recycling.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a multi-stage treatment process for cardboard wastewater. Background Technology

[0002] To meet the requirements of environmentally friendly production, waste paperboard materials are recycled and reused for papermaking, which reduces the environmental pollution caused by waste paperboard while replenishing raw materials.

[0003] Waste paper is reformed into pulp through shearing, soaking, and stirring. Since there is a lot of ink material on the surface of waste paperboard, a certain amount of ink capture agent needs to be added to the paperboard recycling wastewater to capture and float the ink in the wastewater, so as to minimize the ink content in the wastewater and meet the requirements of the paperboard recycling process.

[0004] As production scale expands, the existing small-sized paperboard wastewater treatment equipment and processes can no longer meet the treatment needs of large-volume paperboard recycling wastewater. Expanding the treatment tank can accommodate more paperboard recycling wastewater and solve the above problems. However, the increased internal volume of the expanded treatment tank, especially the increased depth of the treatment chamber, leads to excessively long rising distances for the bubbles due to the traditional process of placing the bubble generator at the bottom. Smaller bubbles collide and merge with each other during the rising process to form larger bubbles. These large bubbles not only capture ink but also capture tiny suspended fiber particles in the paperboard recycling wastewater. The suspended fiber particles and ink together form foam residue on the liquid surface, which is then scooped out and discharged, resulting in the loss of suspended fiber particles and affecting the paperboard recycling rate. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a multi-stage treatment process for paperboard wastewater. This invention can reduce the loss of suspended fiber solids and automatically promote the mixing of wastewater at the bottom of the treatment tank, achieving multi-stage deep treatment of wastewater at various locations within the treatment tank. This minimizes the ink content in the paperboard wastewater and meets the process requirements for paperboard wastewater recycling.

[0006] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0007] A multi-stage treatment process for paperboard wastewater includes the following steps: S1, soaking, stirring, and crushing paperboard with ink on its surface, controlling the fiber size in the recycled paperboard wastewater to be within the range of 0.5-5mm; S2, adding the recycled paperboard wastewater to a treatment tank and adding deinking agent to the treatment tank and mixing for a predetermined time; S3, a bubble flotation device is installed at the middle height position in the treatment tank. The bubble flotation device includes a first guide channel, a bubble generator, a middle guide pipe, and a second guide channel arranged sequentially from top to bottom. While controlling the bubble flotation device to rotate directionally around the central axis of the treatment tank to generate fine flotation bubbles at various positions, the recycled paperboard wastewater at the bottom of the treatment tank can be lifted to the middle height position through the first guide channel, the middle guide pipe, and the second guide channel.

[0008] Preferably, the second guide channel and the first guide channel are arranged in opposite directions, and the bubble flotation device is controlled to rotate directionally toward the opening of the second guide channel during the bubble flotation process.

[0009] Preferably, a central adding cylinder is provided in the middle of the treatment tank, a second driving ring is provided on the outside of the central adding cylinder, and the bubble flotation device is fixed on the outside of the second driving ring.

[0010] Preferably, the central adding cylinder is hollow inside and its height is greater than that of the treatment tank. The top of the central adding cylinder is connected to a discharge pipe, and the bottom of the central adding cylinder is provided with a connecting opening. Wastewater is added to the bottom of the treatment tank through the discharge pipe and the central adding cylinder.

[0011] Preferably, the second drive ring is sleeved on the outside of the connecting opening and is relatively sealed and rotatably connected. The second guide groove is provided with an opening and closing valve group on the side near the central adding cylinder. The opening and closing valve group can control the conduction state of the connecting opening.

[0012] Preferably, the valve assembly includes an inlet pipe and a regulating valve, wherein the inlet pipe extends into the interior of the second guide channel and is arranged along the length of the second guide channel.

[0013] With the above structural design, after each opening and closing of the valve assembly, the untreated cardboard recycling wastewater in the central adding cylinder can flow along the transverse channel in the second guide channel to quickly flush the transverse channel. With the above structural design, the newly added cardboard recycling wastewater can be used to flush the fiber suspensions remaining in the corners of the second guide channel, avoiding the residue of the above substances in local positions that may affect the normal recycling and treatment of cardboard recycling wastewater.

[0014] Preferably, during the bubble flotation process, the wastewater is not added to the treatment tank. After the bubble flotation has been completed for a predetermined time, the wastewater is added to the bottom of the treatment tank through the feeding pipe and the central feeding cylinder.

[0015] Preferably, a first drive ring is electrically rotatably connected to the outside of the central adding cylinder, and a scum collection device is fixed to the outside of the first drive ring. A downwardly inclined guide plate is provided below the opening of the scum collection device, and a deflection drive structure is provided between the guide plate and the main body of the scum collection device. The tilt angle of the guide plate is controlled by the deflection drive structure, thereby controlling the height position between the bottom of the scum collection device and the liquid surface.

[0016] Preferably, the top of the central adding cylinder is relatively closed, and wastewater is added into the central adding cylinder before the opening and closing valve group is opened to increase the internal pressure of the central adding cylinder.

[0017] Preferably, after the valve assembly is opened, the second drive ring is controlled to rotate slightly in the opposite direction.

[0018] The beneficial effects of this invention are as follows:

[0019] Compared with existing technologies, by uniformly treating the ink-filled paperboard, controlling the fiber size in the wastewater to within the range of 0.5-5mm can prevent excessively large suspended fiber particles from clogging the treatment equipment and avoid fine bubbles from capturing the suspended fiber particles, thus reducing fiber loss. Simultaneously, the bubble suspension device located in the middle shortens the rising distance of fine bubbles, appropriately reducing their path and preventing excessive contact and collision that could lead to large bubbles, further reducing fiber loss. Furthermore, the combination of the guide channel and guide pipe structure automatically promotes the mixing of wastewater at the bottom of the treatment tank during bubble flotation, achieving multi-stage deep treatment of wastewater from various locations within the tank. This minimizes the ink content in the paperboard wastewater, meeting the process requirements for paperboard wastewater recycling. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the present invention.

[0021] Figure 2 This is a schematic diagram of the three-dimensional structure of the treatment pool of the present invention.

[0022] Figure 3 For the present invention Figure 2 A top-view structural diagram.

[0023] Figure 4 For the present invention Figure 3 A schematic diagram of the AA-direction cross-section structure.

[0024] Figure 5 For the present invention Figure 4 A magnified structural diagram at point B.

[0025] In the diagram: 100, treatment tank; 110, annular overflow trough; 200, central addition cylinder; 210, first drive ring; 220, second drive ring; 300, bubble flotation device; 310, first guide trough; 320, bubble generator; 330, intermediate guide pipe; 340, second guide trough; 341, transverse channel; 400, scum collection device; 500, discharge pipe; 600, on / off valve assembly; 610, liquid inlet pipe; 620, regulating valve. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] To address the problems mentioned in the background art, see Appendix Figure 1 - Appendix Figure 5 A multi-stage treatment process for cardboard wastewater specifically includes the following steps:

[0028] Step 1: The paperboard containing ink on its surface is soaked, stirred, and crushed to control the fiber size in the paperboard recycling wastewater within a predetermined range of 0.5-5mm. This size range prevents excessively fine fibers from being easily carried away by flotation bubbles, while also preventing excessively coarse fibers from affecting subsequent ink separation and pulp recycling efficiency, facilitating subsequent multi-stage processing. Room temperature water is used for soaking, and the soaking time is 30-60 minutes to allow the paperboard to fully swell, ultimately forming paperboard recycling wastewater. Controlling the fiber size in the paperboard recycling wastewater within the predetermined range facilitates subsequent multi-stage processing.

[0029] The mixing and crushing process uses a low-speed mixing paddle to avoid excessive fiber breakage caused by high-speed mixing. After crushing, the fibers larger than 5mm are removed by filtration through a filter screen. The mixing time is 10-15 minutes to ensure that the concentration of solid suspended matter is relatively uniform in various locations in the wastewater, avoid local concentration of solid suspended matter, and improve the effect of subsequent ink separation treatment.

[0030] Step 2: Add the prepared paperboard recycling wastewater to the treatment tank 100 for ink separation treatment. The newly added paperboard recycling wastewater is added to the treatment tank 100 for preliminary stirring to ensure that the concentration of solid suspended matter is relatively uniform in all parts of the wastewater, avoid local concentration of solid suspended matter, and improve the subsequent ink separation treatment effect.

[0031] Step 3: After the initial stirring time, add deinking agent to the treatment tank 100 at a ratio of 0.8-1.5% of the wastewater mass. The deinking agent is a composite formula of NaOH, Na2SiO3, H2O2, and surfactant, with a mass ratio of NaOH:Na2SiO3:H2O2:surfactant = 2:3:1:0.5. After addition, continue stirring at a speed of 30-50 r / min for 15-20 min. During the stirring process, control the wastewater temperature at 45-55℃. Utilize the saponification, emulsification, and oxidation effects of the deinking agent to peel ink particles from the fiber surface and disperse them into small bubbles of 5-20 μm to capture the particle size, thus changing the ink from an attached state to a dispersed and suspended state, making it easier for the subsequent flotation process to carry it away.

[0032] Step 4: After the deinking agent has been added and mixed for a predetermined time, the bubble flotation device 300, located at the middle height in the control treatment tank 100, continuously sprays fine flotation bubbles. For example, the bubble flotation device 300 is set at a height of 1.2-1.8m from the bottom of the tank and 1-1.5m from the liquid surface. As the flotation bubbles rise, they capture the dispersed and suspended ink and float it to the liquid surface, thereby separating the ink from the suspended fiber in the paperboard recycling wastewater and realizing the recycling of waste paper.

[0033] The bubble flotation device 300 continuously sprays out fine flotation bubbles. As the flotation bubbles rise, they capture the dispersed and suspended ink and float it to the liquid surface, thereby separating the ink from the suspended fiber in the paperboard recycling wastewater and realizing the recycling of waste paper.

[0034] The aforementioned treatment tank 100 is a large-sized treatment device. The bubbles generated by the bubble flotation device 300 have a large floating distance. By setting the bubble flotation device 300 at the middle height of the treatment tank 100, the floating distance of the bubbles can be shortened, avoiding the formation of excessively large bubbles during the floating process. This avoids the over-capture of small-sized fiber suspended matter in the paperboard recycling wastewater and prevents the loss of fiber suspended matter.

[0035] The bubble flotation device 300 rotates directionally around the vertical axis of the treatment tank 100, generating fine flotation bubbles at various locations during the rotation, achieving deep flotation across the entire area of ​​the treatment tank 100. The lower end of the bubble flotation device 300 extends downwards, lifting the paperboard recycling wastewater from the bottom of the treatment tank 100 to the middle height of the tank. This promotes the circulation of the paperboard recycling wastewater between the bottom and middle positions, achieving efficient mixing. This not only improves the flotation treatment effect of the paperboard recycling wastewater but also promotes deep circulation and mixing of the wastewater at various locations within the treatment tank 100, achieving deep flotation treatment of the ink within the paperboard recycling wastewater.

[0036] A central adding cylinder 200 is provided in the middle of the treatment tank 100, and a second driving ring 220 is provided on the outside of the central adding cylinder 200. The aforementioned bubble flotation device 300 is fixed on the outside of the second driving ring 220. The second driving ring 220 is driven and controlled by an electronic control structure and can rotate directionally around the surface of the central adding cylinder 200.

[0037] Specifically, the bubble flotation device 300 includes a first guide channel 310, a bubble generator 320, an intermediate guide pipe 330, and a second guide channel 340 arranged sequentially from top to bottom. Dense flotation bubbles can be generated on the surface of the bubble generator 320. The first guide channel 310, the intermediate guide pipe 330, and the second guide channel 340 can lift the paperboard recycling wastewater at the bottom of the treatment tank 100 to the middle position, thereby achieving continuous and efficient recycling of the paperboard recycling wastewater.

[0038] The bubble generator 320 mentioned above is a microporous ceramic aeration head, which can continuously generate dense flotation bubbles on its surface; the intermediate guide pipe 330 is a stainless steel pipe, with 4-6 pipes, which are arranged equidistantly around the bubble generator 320; using the fluid power generated by the rotation of the bubble flotation device 300, the cardboard recycling wastewater at the bottom of the treatment tank 100 can be lifted to the middle position, realizing the continuous and efficient circulation of cardboard recycling wastewater.

[0039] The second guide channel 340 and the first guide channel 310 are arranged in opposite directions. The opening of the second guide channel 340 faces the front of the rotation, while the first guide channel 310 is located in front of the rotation and its opening faces the rear of the rotation. During the overall directional rotation of the bubble flotation device 300 driven by the second drive ring 220, the wastewater at the bottom of the treatment tank 100 enters the second guide channel 340 through the opening on its surface. The pressure inside the second guide channel 340 increases, while the liquid flow velocity at the first guide channel 310 increases and the pressure decreases. The paperboard recycling wastewater in the second guide channel 340 flows upward to the first guide channel 310 through multiple intermediate guide pipes 330, and finally flows from the opening on the surface of the first guide channel 310 towards the rear of the rotation. The outflowing paperboard recycling wastewater flows backward from the surface of the bubble generator 320 and mixes directly with the generated fine bubbles, achieving efficient flotation treatment of the paperboard recycling wastewater.

[0040] It should be noted that, as the wastewater from the bottom of the treatment tank 100 rises to the middle position, the wastewater flowing out from the first guide channel 310 carries fine bubbles and flows synchronously for a certain distance after passing above the bubble generator 320. After the downward flow velocity of the wastewater decreases, the fine bubbles descend to the lowest point and then flow upward. Throughout the process, the bubbles form a J-shaped flow trajectory in three-dimensional space. Without affecting the growth of the bubbles, the flow path of the bubbles is appropriately extended, increasing the contact time with the wastewater and achieving deep flotation treatment of the ink in the wastewater. This minimizes the ink content in the wastewater and improves the quality of the treated wastewater.

[0041] It should also be noted that, in order to improve the mixing rate of the paperboard recycling wastewater flowing upward from the bottom of the treatment tank 100, the second guide channel 340 can be set as a larger funnel opening with an expansion angle of 45-60° to increase the wastewater entry area. The opening size of the first guide channel 310 can be designed to be smaller. During the directional rotation of the bubble flotation device 300, more paperboard recycling wastewater is squeezed into the second guide channel 340 and finally passes through the intermediate guide pipe 330 to be lifted to one side of the first guide channel 310, realizing efficient pumping of paperboard recycling wastewater. With the above structure, there is no need to set up a liquid pumping structure in the bubble flotation device 300, which can realize efficient pumping of paperboard recycling wastewater, especially suitable for wastewater with a lot of suspended matter, such as paperboard recycling wastewater. For processes with pumping rate requirements, a unidirectional pumping structure can be set up in the intermediate guide pipe 330 to realize quantitative unidirectional pumping of paperboard recycling wastewater and ensure the stability of directional transportation of paperboard recycling wastewater.

[0042] A first drive ring 210 is electrically connected to the outside of the central adding cylinder 200. A scum collection device 400 is fixed to the outside of the first drive ring 210. The scum collection device 400 can centrally clean the ink foam scum formed by flotation on the liquid surface, thereby separating the ink foam scum from the paperboard recycling wastewater after flotation treatment and preventing the two from mixing again and affecting the quality of subsequent pulp recycling.

[0043] The scum collection device 400 is located at the top of the treatment tank 100 and is horizontally arranged. The cross-section of the scum collection device 400 is a horizontally arranged U-shape. During the process of the first drive ring 210 driving the scum collection device 400 to rotate horizontally, the ink foam scum on the surface of the liquid in the treatment tank 100 can be collected in a concentrated manner through the scum collection device 400, so as to achieve directional and concentrated capture.

[0044] A downward-sloping guide plate is provided below the opening of the scum collection device 400. The guide plate can concentrate and clean the ink foam on the liquid surface. A deflection drive structure is provided between the guide plate and the main body of the scum collection device 400, which can control the overall tilt angle of the guide plate and thus control the height position between the bottom of the scum collection device 400 and the liquid surface. Finally, the ink is removed and separated. The ink foam can flow upward along the guide plate under pressure and finally enter the scum collection device 400 for centralized collection.

[0045] A separate storage structure can be installed inside the scum collection device 400, which can be cleaned regularly by staff, or a dedicated negative pressure extraction structure can be installed to achieve real-time negative pressure extraction of ink foam scum and real-time transfer of ink foam scum.

[0046] After each bubble flotation cycle at a predetermined time, ink foam residue is formed on the surface of the liquid in the treatment tank 100. During the bubble flotation process, no paperboard recycling wastewater is added to the treatment tank 100. At this time, the liquid level in the treatment tank 100 is relatively constant. The liquid level in the treatment tank 100 is located below the liquid level in the annular overflow tank 110. The paperboard recycling wastewater will not overflow to the outside. At this time, ink foam residue is continuously generated on the surface of the liquid.

[0047] After a certain flotation time, an ink foam residue of a certain thickness is formed on the top of the liquid surface in the treatment tank 100. After a predetermined time of 60-90 minutes for each bubble flotation, an ink foam residue of 20-50 mm thickness is formed on the surface of the liquid in the treatment tank 100. At this time, the guide plate is controlled to tilt downwards, and the ink foam residue is removed as the first drive ring 210 rotates in a directional manner.

[0048] Before the above-mentioned removal process, the thickness of the ink foam residue at the top of the liquid surface can be measured manually or automatically. The thickness of the foam residue is measured in real time by a liquid level sensor. At this time, the above-mentioned guide plate is controlled to tilt downward to 45-60° under the drive of the deflection drive structure. As the first drive ring 210 rotates in a directional manner, the ink foam residue is completely removed, while reducing the loss of treated fiber liquid in the treatment tank 100.

[0049] After one flotation cycle, untreated paperboard recycling wastewater is added to the treatment tank 100 from the bottom, enabling continuous addition of paperboard recycling wastewater. Meanwhile, the paperboard recycling wastewater that has undergone sufficient flotation treatment at the top overflows through the annular overflow trough 110 to the outside and enters the subsequent structure for pulp recycling treatment.

[0050] To ensure a stable and accurate addition of recycled cardboard wastewater to the bottom of the treatment tank 100, the central adding cylinder 200 is hollow. A discharge pipe 500 connects to the top of the central adding cylinder 200. The height of the central adding cylinder 200 is greater than that of the treatment tank 100. The initial state of the recycled cardboard wastewater is added to the central adding cylinder 200 through the discharge pipe 500. A connecting opening is provided at the bottom of the central adding cylinder 200. Utilizing the principle of communicating vessels, continuous addition of recycled cardboard wastewater can be achieved. The recycled cardboard wastewater with higher pressure inside the central adding cylinder 200 can pass through the connecting opening at the bottom and enter the bottom of the treatment tank 100, achieving dynamic equilibrium.

[0051] The inner diameter of the central adding cylinder 200 is smaller than that of the treatment tank 100, which enables the effective addition of paperboard recycling wastewater. During the addition process, it will not have a significant impact on the liquid level of paperboard recycling wastewater in the treatment tank 100, thus ensuring the relative stability of the liquid level in the treatment tank 100, especially at the top of the treatment tank 100.

[0052] The aforementioned second drive ring 220 is sleeved on the outside of the connecting opening and is relatively sealed and rotatably connected. An opening and closing valve group 600 is provided on the side of the second guide groove 340 near the central adding cylinder 200. The opening and closing valve group 600 can control the conduction state of the connecting opening and realize the addition control of paperboard recycling wastewater in the central adding cylinder 200.

[0053] The aforementioned opening and closing valve assembly 600 extends into the interior of the second guide channel 340 and is arranged along the length of the second guide channel 340. Through the above structural design, after each opening and closing valve assembly 600 is opened, the untreated cardboard recycling wastewater in the central adding cylinder 200 can flow along the transverse channel 341 in the second guide channel 340, quickly flushing the transverse channel 341. Through the above structural design, the newly added cardboard recycling wastewater can be used to flush the fiber suspensions remaining in the corners of the second guide channel 340, avoiding the residue of the above substances in local positions that affect the normal recycling and treatment of cardboard recycling wastewater.

[0054] During the opening of the valve assembly 600, the second drive ring 220 can be controlled to rotate slightly in the opposite direction, that is, in the opposite direction to the opening of the second guide channel 340. This appropriately reduces the liquid pressure in the second guide channel 340 and creates local turbulence. Through the above design, the untreated cardboard recycling wastewater pressed in after the inner valve assembly 600 is opened can more effectively flush the internal structure of the second guide channel 340, enhance the flushing effect on fiber suspension, and minimize the residue of fiber suspension.

[0055] The top of the aforementioned central adding cylinder 200 can be relatively closed. Adding excessive liquid into the central adding cylinder 200 through the feeding pipe 500 can increase the liquid flow rate during the opening of the opening and closing valve group 600, which can also improve the flushing effect on the fiber suspension.

[0056] It should be noted that the second guide channel 340 can also intercept and buffer the cardboard recycling wastewater flowing into the side of the opening and closing valve group 600, so as to prevent the cardboard recycling wastewater from flowing in too quickly and affecting the stable bubble flotation of the surrounding liquid, especially the middle and upper layer liquid in the treatment tank 100. The opening and closing valve group 600 mentioned above includes an inlet pipe 610 and a regulating valve 620. The regulating valve 620 is preferably a ball valve, which can stably intercept and control the liquid in the middle position, and can withstand different liquid pressures on both sides to achieve a stable and effective seal.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A multi-stage process for the treatment of paperboard wastewater, characterized in that, Includes the following steps: S1. Soak, stir and crush the paperboard with ink on the surface, and filter it through a filter screen to remove impurity fibers larger than 5mm, controlling the fiber size in the paperboard recycling wastewater within the range of 0.5-5mm; S2. Add the paperboard recycling wastewater into the treatment tank (100) and add deinking agent into the treatment tank (100) and mix for a predetermined time; S3. A bubble flotation device (300) is provided at the middle height position inside the treatment tank (100). The bubble flotation device (300) includes a first guide channel (310), a bubble generator (320), a middle guide pipe (330), and a second guide channel (340) arranged sequentially from top to bottom. While controlling the bubble flotation device (300) to rotate directionally around the central axis of the treatment tank (100) to generate fine flotation bubbles at various positions, the cardboard recycling wastewater at the bottom of the treatment tank (100) can be lifted to the middle height position through the first guide channel (310), the middle guide pipe (330), and the second guide channel (340). The second guide channel (340) and the first guide channel (310) are arranged in opposite directions, and the bubble flotation device (300) is controlled to rotate in the direction of the opening of the second guide channel (340) during the bubble flotation process; The second guide channel opens towards the front of the rotation direction, and the first guide channel is located in front of the rotation direction and its opening direction is towards the rear of the rotation direction. The wastewater from the cardboard recycling process in the second diversion channel flows upward to the first diversion channel through multiple intermediate diversion pipes. A central feeding cylinder (200) is provided in the middle of the treatment tank (100), and a second driving ring (220) is provided on the outside of the central feeding cylinder (200). The bubble flotation device (300) is fixed on the outside of the second driving ring (220).

2. A paperboard wastewater multistage treatment process according to claim 1, characterized in that, The central adding cylinder (200) is hollow inside and its height is greater than that of the treatment tank (100). The top of the central adding cylinder (200) is connected to a discharge pipe (500), and the bottom of the central adding cylinder (200) is provided with a connecting opening. Wastewater is added to the bottom of the treatment tank (100) through the discharge pipe (500) and the central adding cylinder (200).

3. A paperboard wastewater multistage treatment process according to claim 2, characterized in that, The second drive ring (220) is sleeved on the outside of the connecting opening and is relatively sealed and rotatably connected. The second guide groove (340) is provided with an opening and closing valve group (600) on the side near the central adding cylinder (200). The opening and closing valve group (600) can control the conduction state of the connecting opening.

4. A paperboard wastewater multistage treatment process according to claim 3, characterized in that, The valve assembly (600) includes an inlet pipe (610) and a regulating valve (620). The inlet pipe (610) extends into the interior of the second guide channel (340) and is arranged along the length of the second guide channel (340).

5. A paperboard wastewater multistage treatment process according to claim 4, characterized in that, During the bubble flotation process, the wastewater is not added to the treatment tank (100). After the bubble flotation time is set, the wastewater is added to the bottom of the treatment tank (100) through the feeding pipe (500) and the central feeding cylinder (200).

6. A paperboard wastewater multistage treatment process according to claim 5, characterized in that, The outer side of the central adding cylinder (200) is also electrically rotatably connected to a first driving ring (210). A scum collection device (400) is fixed on the outer side of the first driving ring (210). A downwardly inclined guide plate is provided below the opening of the scum collection device (400). A deflection drive structure is provided between the guide plate and the main body of the scum collection device (400). The tilt angle of the guide plate is controlled by the deflection drive structure, thereby controlling the height position between the bottom of the scum collection device (400) and the liquid surface.

7. A paperboard wastewater multistage treatment process according to claim 3, characterized in that, The top of the central adding cylinder (200) is relatively closed. Before opening the opening and closing valve group (600), wastewater is added into the central adding cylinder (200) to increase the internal pressure of the central adding cylinder (200).

8. A paperboard wastewater multi-stage treatment process according to claim 3, characterized in that, After the valve assembly (600) is opened, the second drive ring (220) is controlled to rotate slightly in the opposite direction.

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