Two-stage gravity filtration and separation device for oily wastewater treatment and treatment process

Abstract

The invention discloses a two-stage gravity filtration and separation device for oily wastewater treatment and a treatment process, the two-stage gravity filtration and separation device comprises two gravity filtration mechanisms and a middle pool, the two gravity filtration mechanisms are arranged front and back, the middle pool is arranged on one side of the two gravity filtration mechanisms, and the invention relates to the technical field of sewage treatment. According to the two-stage gravity filtration and separation device for oily wastewater treatment and the treatment process, the middle tank is arranged between the two gravity filtration mechanisms, sewage enters the middle tank after part of pollutants are treated in the front gravity filtration mechanism, and then enters the rear gravity filtration mechanism; the middle tank can be used for treating the sewage to flocculate impurities such as oil dirt in the sewage into large solid impurities, and the sewage is filtered once at the moment, so that residual pollutants are greatly reduced, and the flocculated solid impurities are correspondingly reduced; and the gravity filtering mechanism at the rear part is used for filtering, so that the filtering effect and the filtering efficiency can be ensured.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a two-stage gravity filtration separation device and treatment process for treating oily wastewater. Background Technology

[0002] Wastewater treatment is the process of purifying wastewater to meet the water quality requirements for discharge into a water body or for reuse. Wastewater treatment is widely used in various fields such as construction, agriculture, transportation, energy, petrochemicals, environmental protection, urban landscaping, medical care, and catering, and is increasingly becoming a part of ordinary people's daily lives.

[0003] Rapid sand filters in the water treatment field are an engineering application of gravity filtration. In wastewater treatment, they can treat liquids with low suspended solids concentrations ( / L) through an upward flow operation. Based on the difference in filtration speed, they can be divided into two types: fast (8-10 m / h) and slow (0.1-0.3 m / h).

[0004] However, the structure of general gravity filtration equipment is simple. When filtering oily wastewater with a lot of impurities, it is often impossible to achieve complete filtration in one go. If you want to improve the filtration effect, you need to add flocculants to the wastewater to make the pollutants flocculate into clumps. However, this operation will cause the filter layer in the gravity filtration structure to clog quickly. Not only may the effluent water quality fail to meet the standards, but it will also reduce the efficiency of wastewater treatment. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a two-stage gravity filtration separation device and treatment process for oily wastewater treatment. This solves the problem that conventional gravity filtration equipment, while simple in structure, often cannot achieve complete filtration in one pass when filtering oily wastewater with many impurities. To improve filtration efficiency, flocculants need to be added to the wastewater to cause pollutants to flocculate, but this operation quickly clogs the filter layer in the gravity filtration structure, potentially preventing the effluent quality from meeting standards and reducing wastewater treatment efficiency.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a two-stage gravity filtration separation device for treating oily wastewater, comprising two gravity filtration mechanisms and an intermediate tank. The two gravity filtration mechanisms are arranged one after the other, and the intermediate tank is located on one side of the two gravity filtration mechanisms. The two gravity filtration mechanisms have identical structures. One of the gravity filtration mechanisms includes a filter tank, and a partition is vertically fixedly connected to the middle of the filter tank. The partition divides the interior of the filter tank into two sub-tanks. A horizontal plate is horizontally fixedly connected to the middle of the interior of each of the two sub-tanks. The middle part of the plate protrudes upward to form a conical convex cover. Horizontal meshes are fixedly connected to the interior of the two sub-pools and below the horizontal plate. The upper surface of each of the two horizontal meshes is provided with a filter layer that matches the inner contour of the sub-pool. Vertical through holes are opened on the outer edges of the upper surfaces of the two horizontal plates. The bottom ends of the two through holes are respectively fixedly connected to connecting pipes whose bottom ends extend to the bottom of the two filter layers. A water outlet weir is provided at the top rear of the interior of each of the two sub-pools. A clear water discharge pipe is connected to the rear of each of the two water outlet weirs. A water inlet structure is provided above the front of the filter pool.

[0007] Furthermore, the water inlet structure includes a water inlet pool fixedly connected to the front of the top of the filter tank. Two water inlet weirs are vertically fixedly connected inside the water inlet pool. The two water inlet weirs divide the lower part of the inner cavity of the water inlet pool into a first intermediate cavity and two first side cavities. The bottom ends of the two first side cavities are respectively connected to two water supply pipes. The outer ends of the two water supply pipes penetrate the rear surface of the filter tank and extend to the space between the horizontal plate and the filter layer inside the two partitioned pools. The bottom end of the first intermediate cavity is connected to a water inlet pipe.

[0008] Furthermore, a rinsing water tank is fixedly connected to the bottom center of the rear surface of the filter tank. Two drainage weirs are fixedly connected inside the rinsing water tank. The drainage weirs divide the inner cavity of the rinsing water tank into a second intermediate cavity and two second side cavities. The rear part of the second intermediate cavity is connected to a sewage discharge pipe. The top of the convex cover in each of the two sub-tanks is connected to a siphon pipe. The outer ends of the two siphon pipes extend upward at an angle to the upper rear part of the rear wall of the filter tank, then bend downward and extend into the interior of the two second side cavities respectively.

[0009] Furthermore, the outer surfaces of the top ends of the two siphon tubes are connected to air pipes, and the other ends of the two air pipes extend to the upper surface of the horizontal plate in the two separate pools respectively. The bottom ends of the two air pipes are fixedly connected to hollow cylinders that communicate with their interiors, and the outer surfaces of the two hollow cylinders are provided with multiple air inlets.

[0010] Furthermore, a gantry frame is fixedly connected to the upper surface of the water inlet pool and above the two water inlet weirs. An electrically controlled telescopic rod is vertically fixedly connected to the top of each of the two gantry frames. The bottom ends of the piston rods of the two electrically controlled telescopic rods can slide through the two gantry frames and extend downwards. A baffle is fixedly connected to the bottom ends of the piston rods of the two electrically controlled telescopic rods, and the two baffles correspond to the two water inlet weirs respectively.

[0011] Furthermore, the interior of the intermediate pool is vertically fixed with multiple water-dividing weirs arranged from high to low, from front to back. These weirs divide the interior of the intermediate pool into multiple transition chambers. The two transition chambers at the front end and the rear end are respectively connected to the two clean water drain pipes and water inlet pipes of the gravity filtration mechanism at the front and rear ends.

[0012] Furthermore, the interior of each of the multiple transition chambers in the middle is rotatably connected to a stirring rod, and the outer surface of each of the multiple stirring rods is fixedly connected to a stirring blade. An additive pipe is provided at the front of the intermediate tank.

[0013] Furthermore, a main sewage pipe is provided laterally on the other side of the two gravity filtration mechanisms, and the sewage discharge pipes of the two gravity filtration mechanisms are all connected to the main sewage pipe.

[0014] Furthermore, an equipment box is provided on the outer surface of the rear of the intermediate pool, and a water pump is provided inside the equipment box. The water inlet of the water pump is connected to the transition cavity at the rear end, and the water outlet of the water pump is connected to the water inlet pipe of the gravity filtration mechanism at the rear.

[0015] A two-stage gravity filtration separation process for treating oily wastewater includes the following steps: S1, primary filtration: wastewater is pumped into the inlet pool of the gravity filtration mechanism at the front by a pump, then enters the two first side chambers through the two inlet weirs, and is then sent into the two sub-pools through the two water supply pipes. After passing through the filter layer, the wastewater flows upward along the connecting pipe until it passes through the outlet weir and is discharged through the clear water discharge pipe.

[0016] S2, Intermediate treatment: Wastewater that has passed through the first filtration enters the transition chamber at the front end of the intermediate pool from the clean water drain pipe of the gravity filtration mechanism at the front. Then it flows to the rear of the intermediate pool through multiple water distribution weirs. During this process, a treatment agent is added to the inside and the wastewater is stirred by multiple stirring blades, so that the residual impurities in the wastewater flocculate together to facilitate subsequent treatment.

[0017] S3. Secondary filtration: Wastewater is pumped from the transition chamber at the rear end of the intermediate tank into the gravity filtration mechanism at the rear for a second, repeated filtration process, and finally discharged through the clean water drain pipe of the gravity filtration mechanism at the rear.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] (1) The two-stage gravity filtration separation device and treatment process for oily wastewater treatment uses two gravity filtration mechanisms. The wastewater will first pass through the front gravity filtration mechanism for primary filtration, and then undergo certain treatment before passing through the rear gravity filtration mechanism for secondary filtration. The dual filtration improves the overall filtration effect and ensures that the final discharged water quality meets the standards.

[0020] (2) The oily wastewater treatment uses a two-stage gravity filtration separation device and treatment process. By setting up an intermediate tank, the device sets up an intermediate tank between two gravity filtration mechanisms. When the wastewater passes through the front gravity filtration mechanism, it does not need to undergo flocculation treatment. After some pollutants are removed in the front gravity filtration mechanism, the wastewater enters the intermediate tank and then enters the rear gravity filtration mechanism. The intermediate tank is equipped with stirring blades, and a treatment agent is added to the wastewater. Through this agent, the oil and other impurities in the wastewater are flocculated into large solid impurities. Since the wastewater has been filtered once, the residual pollutants will be greatly reduced, and the flocculated solid impurities will also be reduced accordingly. At this time, the wastewater is then filtered through the rear gravity filtration mechanism, which can ensure both the filtration effect and the filtration efficiency. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0022] Figure 2 This is a schematic diagram of the gravity filtration mechanism in this invention;

[0023] Figure 3 This is a schematic diagram of the water inlet structure of the gravity filtration mechanism in this invention;

[0024] Figure 4 for Figure 3 A magnified view of a portion of area A in the middle.

[0025] In the diagram: 1-Gravity filtration mechanism, 11-Filter tank, 12-Baffle plate, 13-Horizontal plate, 14-Protruding cover, 15-Filter layer, 16-Connecting hole, 17-Inlet pool, 18-Inlet weir, 19-Inlet pipe, 110-Water delivery pipe, 111-Gantry frame, 112-Electrically controlled telescopic rod, 113-Baffle, 114-Outlet weir, 115-Clear water drain pipe, 116-Rinse pool, 117-Drainage weir, 118-Siphon pipe, 119-Sewage drain pipe, 120-Air pipe, 121-Hollow cylinder, 2-Intermediate pool, 3-Divider weir, 4-Agitator rod, 5-Agitator blade, 6-Equipment box, 7-Connecting pipe, 8-Additive pipe, 9-Sewage main pipe. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Please see Figure 1-4 This invention provides a technical solution: a two-stage gravity filtration separation device for treating oily wastewater, comprising two gravity filtration mechanisms 1 and an intermediate tank 2. The two gravity filtration mechanisms 1 are arranged one after the other, and the intermediate tank 2 is located on one side of the two gravity filtration mechanisms 1. The two gravity filtration mechanisms 1 have the same structure. One gravity filtration mechanism 1 includes a filter tank 11. A partition 12 is vertically fixedly connected to the middle of the filter tank 11, dividing the interior of the filter tank 11 into two sub-tanks. A horizontal plate 13 is horizontally fixedly connected to the middle of the interior of each sub-tank, and the middle of the two horizontal plates 13 protrudes upward. A conical convex cover 14 is formed. Horizontal meshes are fixedly connected to the interior of the two sub-pools and below the horizontal plate 13. Filter layers 15, which are adapted to the inner contour of the sub-pools, are provided on the upper surface of the two horizontal meshes. Vertical through holes 16 are provided on the outer edges of the upper surfaces of the two horizontal plates 13. Connecting pipes extending to the bottom of the two connecting holes 16 are fixedly connected to the bottom ends of the two connecting pipes 16, respectively. Water outlet weirs 114 are provided at the top rear of the interior of the two sub-pools. Clear water discharge pipes 115 are connected to the rear of the two water outlet weirs 114. A water inlet structure is provided above the front of the filter tank 11.

[0028] The water inlet structure includes an inlet pool 17 fixedly connected to the front of the top of the filter pool 11. Two inlet weirs 18 are vertically fixedly connected inside the inlet pool 17. The two inlet weirs 18 divide the lower part of the inner cavity of the inlet pool 17 into a first intermediate cavity and two first side cavities. The bottom ends of the two first side cavities are respectively connected to two water supply pipes 110. The outer ends of the two water supply pipes 110 penetrate the rear surface of the filter pool 11 and extend to the space between the horizontal plate 13 and the filter layer 15 inside the two separate pools. The bottom end of the first intermediate cavity is connected to an inlet pipe 19.

[0029] When the gravity filtration mechanism 1 is in use, sewage enters the interior of the first intermediate cavity through the inlet pipe 19, then enters the interior of the two first side cavities through the two inlet weirs 18, and then enters the space between the horizontal plate 13 and the filter layer 15 inside the two sub-pools through the two water supply pipes 110. Under its own gravity, the sewage will permeate through the filter layer 15 and continue to flow downwards, which achieves the filtration effect. When the bottom of the filter layer 15 is filled with water, the filtered water will move upwards through the connecting pipe and enter the space above the horizontal plate 13 of the sub-pool. Then the water level will continue to rise until it exceeds the height of the outlet weir 114. The water will then be discharged through the outlet weir 114 and the clean water drain pipe 115, thus completing the filtration.

[0030] The interior of the intermediate pool 2 is vertically fixed with multiple water-dividing weirs 3 arranged from high to low from front to back. The multiple water-dividing weirs 3 divide the interior of the intermediate pool 2 into multiple transition chambers. The two transition chambers at the front end and the rear end are respectively connected to the two clear water drain pipes 115 and the water inlet pipes 19 of the gravity filtration mechanism 1 at the front and rear.

[0031] The interior of the multiple transition chambers in the middle is connected to a stirring rod 4 that rotates laterally. The outer surface of the multiple stirring rods 4 is fixedly connected to stirring blades 5. An additive pipe 8 is provided at the front of the intermediate tank 2.

[0032] An equipment box 6 is provided on the outer surface of the rear of the intermediate pool 2. A water pump is provided inside the equipment box 6. The water pump inlet is connected to the transition cavity at the rear end, and the water pump outlet is connected to the inlet pipe 19 of the gravity filter mechanism 1 at the rear.

[0033] After being filtered by the gravity filter mechanism 1 at the front, the wastewater enters the transition chamber at the front end of the intermediate tank 2. As the water volume increases, the water level rises. When it exceeds the water distribution weir 3, it enters a transition chamber at the rear. This process is repeated until the water enters the final transition chamber and is pumped into the gravity filter mechanism 1 at the rear. This structure can extend the residence time of the filtered water in the intermediate tank 2, thereby ensuring the treatment effect of the intermediate tank 2.

[0034] After primary filtration, the wastewater undergoes certain treatment inside the intermediate tank 2. By introducing flocculant into the additive pipe 8 and then discharging it into the wastewater, the remaining oil and impurities in the wastewater can be flocculated to form large solid impurities, making subsequent filtration more thorough. Multiple stirring rods 4 are driven by multiple motors to rotate, which in turn drives multiple stirring blades 5 to rotate synchronously, improving the flocculation effect of oil and impurities.

[0035] The outlet of the water pump is connected to the inlet pipe 19 of the gravity filter mechanism 1 at the rear via a connecting pipe 7.

[0036] A rinsing water tank 116 is fixedly connected to the bottom center of the rear surface of the filter tank 11. Two drainage weirs 117 are fixedly connected inside the rinsing water tank 116. The drainage weirs 117 divide the inner cavity of the rinsing water tank 116 into a second intermediate cavity and two second side cavities. The rear part of the second intermediate cavity is connected to a sewage discharge pipe 119. The top of the convex cover 14 in the two sub-tanks is connected to a siphon pipe 118. The outer ends of the two siphon pipes 118 extend upward at an angle to the upper rear part of the rear wall of the filter tank 11, then bend downward and extend into the interior of the two second side cavities respectively.

[0037] The outer surfaces of the top ends of the two siphon tubes 118 are connected to air pipes 120. The other ends of the two air pipes 120 extend to the upper surface of the horizontal plate 13 in the two sub-pools respectively. The bottom ends of the two air pipes 120 are fixedly connected to hollow cylinders 121 that communicate with their interiors. Multiple air inlets are opened through the outer surfaces of the two hollow cylinders 121.

[0038] The end of the siphon pipe 118 is lower than the bottom of the filter tank 11. The filter layer 15 in the gravity filtration mechanism 1 will gradually become clogged during the filtration process until it can no longer filter. When it is clogged, the sewage that enters the inner part of the sub-tank through the water supply pipe 110 cannot flow downward through the filter layer 15. Under the action of water pressure, it will flow upward through the siphon pipe 118. When it exceeds the top of the siphon pipe 118, it will flow downward under the action of gravity, forming a siphon effect. The water in the filter tank 11 will be discharged outward through the siphon pipe 118. In this process, the impurities in the filter layer 15 can be carried away, thereby cleaning the filter layer 15. The sewage discharged through the siphon pipe 118 will enter the inner part of the second intermediate cavity through the drainage weir 117 and then be discharged through the sewage discharge pipe 119.

[0039] When the water level in the filter tank 11 drops below the air inlet of the hollow cylinder 121, external gas will enter the interior of the siphon tube 118 through the hollow cylinder 121 and the air pipe 120, thereby disrupting the siphon effect. At this time, the gravity filtration mechanism 1 will restart the filtration operation, and so on.

[0040] A gantry frame 111 is fixedly connected to the upper surface of the inlet pool 17 and above the two inlet weirs 18. An electrically controlled telescopic rod 112 is fixedly connected vertically to the top of each of the two gantry frames 111. The bottom end of the piston rod of each of the two electrically controlled telescopic rods 112 can slide through the two gantry frames 111 and extend downward. A baffle 113 is fixedly connected to the bottom end of the piston rod of each of the two electrically controlled telescopic rods 112. The two baffles 113 correspond to the two inlet weirs 18 respectively.

[0041] Two electrically controlled telescopic rods 112 drive two baffles 113 to rise and fall. When the baffle 113 falls, it will close with the corresponding inlet weir 18. At this time, sewage cannot enter the first side chamber on the same side through the inlet weir 18 on that side. This makes the filtration of the two sub-tanks asynchronous, ensuring that one sub-tank is always in the filtration state and that both sub-tanks do not enter the siphon backwashing state at the same time.

[0042] The two-stage gravity filtration separation process for treating oily wastewater, as described above, includes the following steps:

[0043] S1. Primary filtration: Wastewater is pumped into the inlet pool 17 of the gravity filter mechanism 1 at the front by a pump, and then enters the two first side chambers through two inlet weirs 18 respectively. Then it is sent into the two sub-pools through two water supply pipes 110 respectively. After passing through the filter layer 15, the wastewater flows upward along the connecting pipe until it passes through the outlet weir 114 and is discharged through the clean water discharge pipe 115.

[0044] S2, Intermediate treatment: The wastewater that has passed through the first filtration enters the transition chamber at the front end of the intermediate tank 2 through the clear water drain pipe 115 of the gravity filter mechanism 1 at the front end. Then it flows to the rear of the intermediate tank 2 through multiple water distribution weirs 3. During this process, treatment agent is added to the inside and stirred by multiple stirring blades 5, so that the residual impurities in the wastewater are flocculated together to facilitate subsequent treatment.

[0045] S3, Secondary Filtration: Wastewater is pumped from the transition chamber at the rear end of the intermediate tank 2 into the gravity filtration mechanism 1 at the rear end for a second repeated filtration operation, and finally discharged through the clean water drain pipe 115 of the gravity filtration mechanism 1 at the rear end.

[0046] During operation, when the gravity filtration mechanism 1 is in use, sewage enters the first intermediate chamber through the inlet pipe 19, then passes through two inlet weirs 18 and enters the two first side chambers respectively. It then enters the space between the horizontal plate 13 and the filter layer 15 inside the two sub-tanks through two water supply pipes 110. Under its own gravity, the sewage permeates through the filter layer 15 and continues to flow downwards, achieving a filtration effect. When the bottom of the filter layer 15 is filled with water, the filtered water moves upwards through the connecting pipe to the area above the horizontal plate 13 of the sub-tank. The water level continues to rise until it exceeds the height of the outlet weir 114, at which point the water is discharged through the outlet weir 114 and the clear water drain pipe 115, thus completing the filtration. After being filtered by the gravity filtration mechanism 1 at the front, the sewage enters the transition chamber at the very front of the intermediate tank 2. As the water volume increases, the water level rises. When it exceeds the diversion weir 3, it enters a transition chamber at the rear. This process is repeated until the water enters the final transition chamber and is pumped into the gravity filtration mechanism 1 at the rear. This structure extends the residence time of the filtered water in the intermediate tank 2, thus ensuring the treatment effect of the intermediate tank 2. After some pollutants are removed in the gravity filtration mechanism 1 at the front, the wastewater enters the intermediate tank and then the gravity filtration mechanism 1 at the rear. The intermediate tank 2 flocculates impurities such as oil in the wastewater into large solid impurities. Since the wastewater has been filtered once, the residual pollutants are greatly reduced, and the flocculated solid impurities are also reduced accordingly. At this point, the wastewater is filtered again by the gravity filtration mechanism 1 at the rear, which ensures both the filtration effect and the filtration efficiency.

[0047] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0048] 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 two-stage gravity filtration and separation device for treating oily wastewater, characterized in that: It includes two gravity filtration mechanisms (1) and an intermediate pool (2), with the two gravity filtration mechanisms (1) arranged one in front of the other, and the intermediate pool (2) arranged on one side of the two gravity filtration mechanisms (1); Both gravity filtration mechanisms (1) have the same structure. One of the gravity filtration mechanisms (1) includes a filter pool (11). A partition (12) is vertically fixedly connected to the middle of the filter pool (11). The partition (12) divides the interior of the filter pool (11) into two sub-pools. A horizontal plate (13) is horizontally fixedly connected to the middle of the interior of each of the two sub-pools. The middle of the two horizontal plates (13) protrudes upward to form a conical convex cover (14). A horizontal mesh is horizontally fixedly connected to the interior of each of the two sub-pools and below the horizontal plate (13). The upper surfaces of the two horizontal meshes are provided with filter layers (15) that are adapted to the contour of the sub-pools. The outer edges of the upper surfaces of the two horizontal plates (13) are vertically connected with connecting holes (16). The bottom ends of the two connecting holes (16) are respectively fixedly connected with connecting pipes that extend to the bottom of the two filter layers (15). The top of the rear of the two sub-pools is provided with a water outlet weir (114). The rear of the two water outlet weirs (114) is connected with a clear water drain pipe (115). The front of the filter pool (11) is provided with a water inlet structure.

2. The two-stage gravity filtration separation device for treating oily wastewater according to claim 1, characterized in that: The water inlet structure includes an inlet pool (17) fixedly connected to the front of the top of the filter pool (11). Two inlet weirs (18) are vertically fixedly connected inside the inlet pool (17). The two inlet weirs (18) divide the lower part of the inner cavity of the inlet pool (17) into a first intermediate cavity and two first side cavities. The bottom ends of the two first side cavities are respectively connected to two water supply pipes (110). The outer ends of the two water supply pipes (110) penetrate the rear surface of the filter pool (11) and extend to the space between the horizontal plate (13) and the filter layer (15) inside the two partitioned pools. The bottom end of the first intermediate cavity is connected to an inlet pipe (19).

3. The two-stage gravity filtration and separation device for treating oily wastewater according to claim 1, characterized in that: A rinsing water tank (116) is fixedly connected to the middle of the bottom end of the rear surface of the filter (11). Two drainage weirs (117) are fixedly connected inside the rinsing water tank (116). The drainage weirs (117) divide the inner cavity of the rinsing water tank (116) into a second intermediate cavity and two second side cavities. The rear part of the second intermediate cavity is connected to a sewage discharge pipe (119). The top of the convex cover (14) in the two separate tanks is connected to a siphon pipe (118). The outer ends of the two siphon pipes (118) extend upward at an angle to the upper rear part of the rear wall of the filter (11) and then bend downward and extend into the interior of the two second side cavities respectively.

4. The two-stage gravity filtration and separation device for treating oily wastewater according to claim 3, characterized in that: The outer surfaces of the top ends of the two siphon tubes (118) are connected to air pipes (120), and the other ends of the two air pipes (120) extend to the upper surface of the horizontal plate (13) in the two sub-pools respectively. The bottom ends of the two air pipes (120) are fixedly connected to hollow cylinders (121) that communicate with their interiors. The outer surfaces of the two hollow cylinders (121) are provided with multiple air inlets.

5. A two-stage gravity filtration and separation device for treating oily wastewater according to claim 2, characterized in that: A gantry frame (111) is fixedly connected to the upper surface of the water inlet pool (17) and above the two water inlet weirs (18). An electrically controlled telescopic rod (112) is fixedly connected vertically to the top of each of the two gantry frames (111). The bottom ends of the piston rods of the two electrically controlled telescopic rods (112) can slide through the two gantry frames (111) and extend downward. A baffle (113) is fixedly connected to the bottom ends of the piston rods of the two electrically controlled telescopic rods (112). The two baffles (113) correspond to the two water inlet weirs (18) respectively.

6. The two-stage gravity filtration separation device for treating oily wastewater according to claim 1, characterized in that: The interior of the intermediate pool (2) is vertically fixed with multiple water-dividing weirs (3) arranged from high to low. The multiple water-dividing weirs (3) divide the interior of the intermediate pool (2) into multiple transition chambers. The two transition chambers at the front end and the rear end are respectively connected to the two clear water drain pipes (115) and the water inlet pipe (19) of the gravity filtration mechanism (1) at the front and rear.

7. A two-stage gravity filtration separation device for treating oily wastewater according to claim 6, characterized in that: The interior of each of the multiple transition chambers in the middle section is rotatably connected with a stirring rod (4), and the outer surface of each of the multiple stirring rods (4) is fixedly connected with a stirring blade (5). An additive pipe (8) is provided at the front of the intermediate tank (2).

8. A two-stage gravity filtration and separation device for treating oily wastewater according to claim 1, characterized in that: A sewage main pipe (9) is arranged laterally on the other side of the two gravity filtration mechanisms (1), and the sewage discharge pipes (119) of the two gravity filtration mechanisms (1) are all connected to the sewage main pipe (9).

9. A two-stage gravity filtration separation device for treating oily wastewater according to claim 6, characterized in that: An equipment box (6) is provided on the outer surface of the rear of the intermediate pool (2). A water pump is provided inside the equipment box (6). The water inlet of the water pump is connected to the transition cavity at the rear end, and the water outlet of the water pump is connected to the water inlet pipe (19) of the gravity filter mechanism (1) at the rear.

10. A two-stage gravity filtration separation process for treating oily wastewater according to claims 1-9, characterized in that: Includes the following steps: S1. Primary filtration: Wastewater is pumped into the inlet pool (17) of the gravity filtration mechanism (1) at the front by a pump, and then enters the two first side chambers through the two inlet weirs (18), and is then sent into the two sub-pools through the two water supply pipes (110). After passing through the filter layer (15), the wastewater flows upward along the connecting pipe until it passes through the outlet weir (114) and is discharged through the clear water drain pipe (115). S2, Intermediate treatment: The wastewater that has been filtered once enters the transition chamber at the front end of the intermediate pool (2) from the clear water drain pipe (115) of the gravity filter mechanism (1) at the front. Then it flows to the rear of the intermediate pool (2) through multiple water distribution weirs (3). During this process, a treatment agent is added to the inside and stirred by multiple stirring blades (5) so that the residual impurities in the wastewater flocculate together to facilitate subsequent treatment. S3, Secondary filtration: Wastewater is pumped from the transition chamber at the rear end of the intermediate tank (2) into the gravity filtration mechanism (1) at the rear end for a second repeated filtration operation, and finally discharged through the clean water drain pipe (115) of the gravity filtration mechanism (1) at the rear end.

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