Process for the treatment of sewage by tubular reactors with enhanced granular sludge cultivation

Abstract

This invention relates to a tubular wastewater treatment method for enhanced granular sludge cultivation, comprising feeding wastewater and activated sludge into a tubular reactor. The tubular reactor includes an above-ground tank and an underground casing. The casing includes an external upflow pipe and an internal downflow pipe. Air is supplied to the upflow pipe to create an upflow and a downflow. After a circulating liquid flow is established in the previous step, air is supplied to the downflow pipe to cultivate aerobic granular sludge. The wastewater and granular sludge treated in the tubular reactor are then fed into a deaeration tank, where turbulence is maintained. The wastewater and granular sludge treated in the deaeration tank are then fed into an upflow selector tank, where the granular sludge settles naturally. Sludge with better settling properties at the bottom of the tank flows back to the tubular reactor along an upflow return pipe. The wastewater and sludge with poor settling properties treated in the upflow selector tank are then fed into a sedimentation tank, where solid-liquid separation is performed, and the treated water is discharged.

Description

Technical Field

[0001] This invention belongs to the field of sludge cultivation and wastewater treatment technology, specifically relating to a tubular wastewater treatment method for enhanced granular sludge cultivation. Background Technology

[0002] Aerobic granular sludge (AGS) refers to granular activated sludge formed through microbial self-aggregation. Compared with ordinary activated sludge, it is less prone to sludge bulking, has strong shock resistance, can withstand high organic loads, and integrates microorganisms with different properties (aerobic, facultative, and anaerobic microorganisms). The technical challenge of aerobic granular sludge lies in cultivating aerobic granular sludge with good settling properties. Existing research shows that cultivating AGS in wastewater with low carbon-to-nitrogen ratios is often difficult, and there is an urgent need in this field for a method to stably cultivate aerobic granular sludge in wastewater with low carbon-to-nitrogen ratios. Summary of the Invention

[0003] To address the above problems, this invention provides a tubular wastewater treatment method with enhanced granular sludge cultivation, including...

[0004] S100: Wastewater and activated sludge are fed into the tubular reactor. The tubular reactor includes an above-ground tank and an underground casing. The casing includes an external riser pipe and an internal downflow pipe. After the casing is filled with wastewater, compressed air is supplied to the riser pipe to form an upward flow. Wastewater enters the downflow pipe through the connecting pipe inside the tank and forms a downward flow in the downflow pipe.

[0005] S200: After a stable circulating liquid flow is formed in step S100, air is introduced into the downflow pipe to maintain the oxygen content in the casing for cultivating aerobic granular sludge.

[0006] S300: Wastewater and granular sludge treated by the tubular reactor are fed into the degassing tank. The granular sludge is kept in a turbulent state in the degassing tank, which promotes the removal of air bubbles from the surface of the granular sludge and restores its true settling performance.

[0007] S400: Wastewater and granular sludge treated in the degassing tank are fed into the upflow selector tank. The granular sludge settles naturally in the upflow selector tank, and the sludge with better settling performance at the bottom of the tank flows back to the tubular reactor along the upflow return pipe.

[0008] S500: Wastewater treated in the upflow selection tank and sludge with poor settling performance are fed into the sedimentation tank. After solid-liquid separation, the produced water is discharged.

[0009] Optionally, the bottom of the tubular reactor is provided with an opening for connecting the top of the riser pipe, the top of the downflow pipe is higher than the top of the riser pipe, and the liquid level in the tank is kept lower than the top opening of the downflow pipe; a horizontal connecting pipe is provided at the top of the downflow pipe, one end of the connecting pipe is connected to the downflow pipe, and the other end is open to the inside of the tank, so that the sewage and sludge inside the tank can enter the downflow pipe through the connecting pipe.

[0010] An air compressor is installed outside the pool. The two parallel pipes of the air compressor extend into the riser pipe and the fallr pipe respectively to provide gas to the riser pipe and the fallr pipe.

[0011] Optionally, in step S100, the depth of the riser pipe is 20-50m, the depth of the pool is 2-3m, and the average particle size of the inoculated sludge is 15-20μm.

[0012] Since the depth of the tank is determined within a formed tubular reactor, the position of the bottom opening of the downflow pipe is determined, and the depth of the upflow pipe is determined, the depth of the downflow pipe is also determined.

[0013] Within the tubular reactor, a circulating liquid flow is formed within the casing, treating wastewater while simultaneously cultivating aerobic granular sludge. Specifically, wastewater and sludge flow downwards in the downflow pipe until they reach the bottom, then enter the upflow pipe and continue rising into the tank. The wastewater in the tank mixes with the newly entering wastewater, then flows back into the downflow pipe through a connecting pipe, flowing downwards again, thus completing the cycle. This tubular reactor of the present invention not only extends the hydraulic retention time but also exhibits strong resistance to fluctuations in influent water quality.

[0014] Optionally, in step S200, compressed air is continuously or intermittently introduced into the riser pipe to maintain the circulating liquid flow of step S100; compressed air is continuously or intermittently introduced into the downflow pipe to maintain the average dissolved oxygen concentration in the casing at 0.5-1 mg / L, so as to provide a suitable dissolved oxygen environment for cultivating granular sludge.

[0015] Further optionally, the diameter ratio of the riser tube to the downflow tube is (1.6-1.9):1.

[0016] In the continuous flow wastewater treatment mode, the formation of AGS is promoted by creating starvation-saturation conditions and autotrophic-heterotrophic synergistic metabolic conditions in the tubular reactor. At the same time, in step S400, the sludge is air-lifted back to the tubular reactor, retaining most of the mature granular sludge.

[0017] The riser and downflow pipes of this invention are relatively deep, resulting in a significant difference in water pressure between the upper and lower sections of the casing. Compressed air introduced into the downflow pipe, as it descends with the circulating liquid, experiences a continuous increase in water pressure, causing its volume to decrease and gradually dissolve into the water. This increases dissolved oxygen levels and promotes COD treatment and nitrification in the wastewater. Then, the water flows upwards through the riser pipe, where the water pressure gradually decreases, and the dissolved air is released. Upon reaching the tank, the oxygen-poor air is released into the atmosphere and enters the next cycle. This creates a relatively anoxic environment in the upper and middle parts of the downflow and riser pipes, and a relatively aerobic environment in the lower and middle parts. Wastewater and sludge circulate between these two environments, undergoing both anoxic and aerobic treatment. Simultaneously, activated sludge, circulating with the wastewater in the tank, riser, and downflow pipes, is cultivated into aerobic granular sludge, which is then fed into the deaeration tank along with the wastewater.

[0018] Because the casing of this invention is an ultra-deep well (20-50 meters), it is beneficial for wastewater treatment and the cultivation of granular sludge. As wastewater carrying granular sludge rises along the upflow pipe, the water pressure decreases, and air is gradually released. Some of the smaller air bubbles adhere to the rough surface of the granular sludge and are discharged from the tubular reactor with the wastewater. The settling performance of the granular sludge with small air bubbles on its surface deteriorates, failing to exhibit its original settling properties. This problem is particularly prominent in the case of the ultra-deep well in this invention. Therefore, in step S300, it is essential to input the wastewater and granular sludge treated by the tubular reactor into the deaeration tank for deaeration. After deaeration, the granular sludge regains its original settling properties and then enters the upflow selection tank. Sludge with good settling properties settles naturally and is then returned to the tubular reactor through the upflow return pipe, greatly reducing the loss rate of mature granular sludge.

[0019] As mentioned above, the main function of the degassing tank is to remove air bubbles attached to the surface of granular sludge, so as to avoid affecting the settling performance of the sludge due to the attachment of surface air bubbles.

[0020] Optionally, in step S300, the dissolved oxygen concentration in the degassing tank is 1-2 mg / L to provide an aerobic environment for continued wastewater treatment and cultivation of granular sludge.

[0021] As described above, the upper part of the downflow pipe is anoxic, the lower part of the downflow pipe and the lower part of the upflow pipe are aerobic, the upper part of the upflow pipe is anoxic, and the deaeration tank is aerobic. This alternating anoxic-aerobic configuration is beneficial for the thorough treatment of pollutants in wastewater. The aeration and stirring deaeration sections in the deaeration tank work together to maintain the turbulent flow of the sludge, preventing sludge settling and degassing the sludge.

[0022] Optionally, the degassing tank has water entering from the lower part of one side and water exiting from the upper part of the other side. The bottom of the degassing tank is equipped with an aeration pipe, which is connected to an external blower to provide upward power for the sewage and sludge in the degassing tank.

[0023] The degassing tank is equipped with a stirring degassing section, including a stirring paddle and concentrically arranged inner and outer stirring layers. Both the inner and outer stirring layers are cylindrical and connected to the stirring paddle at the center. The top of the stirring paddle extends out of the degassing tank and is connected to an external motor to drive the two stirring layers to rotate.

[0024] Further optionally, the sidewalls of the outer and inner stirring layers are both single spirals, and the spiral directions of the two stirring layers can be the same or opposite; the sidewalls of the two stirring layers are hollow, and the spacing between adjacent sidewalls is equal; the height of a solid sidewall of the inner stirring layer corresponds to the height of a hollow section of the sidewall of the outer stirring layer, and the height of a solid sidewall of the outer stirring layer corresponds to the height of a hollow section of the sidewall of the inner stirring layer.

[0025] Further optionally, a rough fiber mesh is evenly laid on the sidewalls of the outer and inner mixing layers. The surface of the fiber mesh is evenly covered with barbs. When the granular sludge collides with the sidewall of the mixing layer, the barbs squeeze and puncture the air bubbles on the surface of the sludge, thus accelerating defoaming.

[0026] Water enters the deaeration tank from the bottom. The rotating deaeration section stirs the water within the tank. The hollow interior of the section creates a negative pressure that draws wastewater in. Aeration pipes at the bottom of the tank further promote the upward movement of wastewater and sludge into the section (between the inner and outer mixing layers). Under centrifugal force, the sludge moves outward and contacts the sidewalls of the inner and outer mixing layers. Because the sidewalls are spiral-shaped, some sludge rolls along them until it detaches. Regardless of whether the sludge rolls, the rough fiber mesh and barbs on the sidewalls help puncture or break the tiny air bubbles on the sludge surface. The fiber mesh, with its thickness, provides cushioning when the sludge collides with it, preventing the granular sludge from being crushed. As the granular sludge moves laterally through the inner and outer mixing layers, it also spirals upward, continuing to degrade pollutants in the wastewater while undergoing thorough defoaming.

[0027] Optionally, in step S400, water enters from one side of the upflow selection tank and exits from the other side; a vertical upflow pipe is provided in the center of the upflow selection tank, the bottom of the upflow pipe is located at the lower part of the upflow selection tank, and the top of the upflow pipe is higher than the liquid level of the upflow selection tank; the bottom of the upflow return pipe extends into the bottom of the upflow pipe, and the upflow return pipe extends out of the upflow selection tank along the upflow pipe and then connects to the tubular reactor;

[0028] An external blower is connected to the riser pipe via an air pipe. The bottom opening of the air pipe is located at the bottom of the riser pipe. Under the action of air stripping, the granular sludge that has settled to the bottom of the riser selection tank rises along the riser return pipe and flows back into the tubular reactor; while the sludge with poor settling performance in the riser selection tank is discharged into the sedimentation tank with the wastewater. The riser pipe prevents disturbance to the sludge settling outside the riser pipe during air stripping.

[0029] Further optionally, in step S400, the sludge return ratio is 180-200%.

[0030] This invention designs an upflow selection tank to screen sludge with strong settling properties and return it to the tubular reactor, where it remains in the system, while sludge with weaker settling properties is discharged through a sedimentation tank.

[0031] Because the tubular reactor of this invention has a relatively deep casing and a wide range of selectable depths, the settling performance of mature granular sludge or recirculated granular sludge is good. The deeper the casing, the less conducive it is to the uniform distribution of granular sludge in the riser and fallr pipes. In particular, granular sludge flowing downwards in the fallr pipe is easier to distribute evenly; granular sludge flowing upwards in the riser pipe is less likely to be distributed evenly.

[0032] Alternatively, the upflow return pipe is located at the end of the tubular reactor and connected to two branch pipes in parallel. Branch pipe one is connected to the upper part of the downflow pipe, and branch pipe two extends into the upflow pipe to divert the returned granular sludge and wastewater into the downflow pipe and the upflow pipe.

[0033] When the depth of the riser pipe is 20-30m, the flow ratio of branch pipe 1 to branch pipe 2 is 1:1; when the depth of the riser pipe is 31-40m, the flow ratio of branch pipe 1 to branch pipe 2 is 1:1.8; when the depth of the riser pipe is 41-50m, the flow ratio of branch pipe 1 to branch pipe 2 is 1:2.3. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the wastewater treatment device in Example 1.

[0035] In the attached diagram, 1-tubular reactor, 2-tank body, 3-upflow pipe, 4-downflow pipe, 5-connecting pipe, 6-degassing tank, 7-upflow selection tank, 8-sedimentation tank, 9-upflow reflux pipe, 10-upflow pipe. Detailed Implementation

[0036] Example 1

[0037] This embodiment provides a tubular wastewater treatment method with enhanced granular sludge cultivation, such as... Figure 1 As shown, including

[0038] S100: Wastewater and activated sludge are fed into the tubular reactor 1. The tubular reactor 1 includes a tank body 2 above ground and a casing underground. The casing includes an external riser pipe 3 and an internal downflow pipe 4. After the casing is filled with wastewater, compressed air is supplied into the riser pipe 3, so that an upward water flow is formed in the riser pipe 3. Wastewater enters the downflow pipe 4 through the connecting pipe 5 in the tank body 2 and forms a downward water flow in the downflow pipe 4.

[0039] S200: After a stable circulating liquid flow is formed in step S100, air is introduced into the downflow pipe 4 to maintain the oxygen content in the casing for cultivating aerobic granular sludge.

[0040] S300: Wastewater and granular sludge treated by tubular reactor 1 are fed into degassing tank 6. The granular sludge is kept in a turbulent state in degassing tank 6 to promote the removal of air bubbles from the surface of the granular sludge and restore its true settling performance.

[0041] S400: Wastewater and granular sludge treated in degassing tank 6 are fed into upflow selection tank 7. Granular sludge settles naturally in upflow selection tank 7. Sludge with better settling performance at the bottom of the tank flows back to tubular reactor 1 along upflow return pipe 9.

[0042] S500: Wastewater treated in the upflow selection tank 7 and sludge with poor settling performance are fed into the sedimentation tank 8. After solid-liquid separation, the produced water is discharged.

[0043] The bottom of the tubular reactor 1 tank body 2 is provided with an opening for connecting to the top of the riser pipe 3. The top of the downflow pipe 4 is higher than the top of the riser pipe 3, and the liquid level in the tank body 2 is kept lower than the top opening of the downflow pipe 4. A horizontal connecting pipe 5 is provided at the upper part of the downflow pipe 4. One end of the connecting pipe 5 is connected to the downflow pipe 4, and the other end is open to the inside of the tank body 2, so that the sewage and sludge inside the tank body 2 can enter the downflow pipe 4 through the connecting pipe 5.

[0044] An air compressor is installed outside the pool body 2. The two parallel pipes of the air compressor extend into the riser pipe 3 and the fallr pipe 4 respectively to provide gas to the riser pipe 3 and the fallr pipe 4.

[0045] The pool body 2 has an inlet on one side and an outlet on the other side, with the open end of the connecting pipe 5 facing the outlet.

[0046] The bottom of the downflow pipe 4 is at the same depth as the bottom of the upflow pipe 3. An opening is provided on the side of the bottom of the downflow pipe 4, allowing sewage and sludge at the bottom of the downflow pipe 4 to enter the bottom of the upflow pipe 3. This downflow pipe 4 is relatively stable. Several connecting rods are provided on the inner wall of the tank body 2 to connect to the upper part of the downflow pipe 4, further improving the stability of the downflow pipe 4.

[0047] In step S100, the depth of the upflow pipe 3 is 20m, the length, width, and height (depth) of the pool body 2 are 2.68m, 0.80m, and 2.28m, respectively, the average particle size of the inoculated sludge is 18μm, and the diameter ratio of the upflow pipe 3 to the downflow pipe 4 is 1.6:1.

[0048] In step S200, compressed air is continuously or intermittently introduced into the riser pipe 3 to maintain the circulating liquid flow of step S100; compressed air is continuously or intermittently introduced into the downflow pipe 4 at an aeration rate of 10 L / min to maintain an average dissolved oxygen concentration of 0.5-1 mg / L in the casing, thus providing a suitable dissolved oxygen environment for cultivating granular sludge.

[0049] In step S300, the dissolved oxygen concentration in degassing tank 6 is 1-2 mg / L, providing an aerobic environment for continued wastewater treatment and cultivation of granular sludge.

[0050] Water enters from the lower part of one side of the degassing tank 6 and exits from the upper part of the other side. The bottom of the degassing tank 6 is equipped with an aeration pipe, which is connected to an external blower to provide upward power for the sewage and sludge in the degassing tank 6.

[0051] The degassing tank 6 is equipped with a stirring degassing section, including a stirring shaft and concentrically arranged inner and outer stirring layers. Both the inner and outer stirring layers are cylindrical and connected to the stirring shaft at the center. The top of the stirring shaft extends out of the degassing tank 6 and is connected to an external motor to drive the two stirring layers to rotate.

[0052] Both the outer and inner stirring layers have single spiral sidewalls, and the spiral directions of the two stirring layers are the same. The sidewalls of both stirring layers are hollow, and the spacing between adjacent sidewalls is equal. The height of a solid sidewall of the inner stirring layer corresponds to the height of a hollow section of the sidewall of the outer stirring layer, and the height of a solid sidewall of the outer stirring layer corresponds to the height of a hollow section of the sidewall of the inner stirring layer.

[0053] The outer and inner mixing layers are uniformly covered with a rough fiber mesh. The surface of the fiber mesh is evenly covered with barbs. When the granular sludge collides with the side wall of the mixing layer, the barbs squeeze and puncture the air bubbles on the surface of the sludge, thus accelerating defoaming.

[0054] In step S400, water enters from one side of the upflow selection tank 7 and exits from the other side; the center of the upflow selection tank 7 is provided with a vertical upflow pipe 3, the bottom of the upflow pipe 3 is located at the lower part of the upflow selection tank 7, and the top of the upflow pipe 3 is higher than the liquid level of the upflow selection tank 7; the bottom of the upflow return pipe 9 extends into the bottom of the upflow pipe 3, and the upflow return pipe 9 extends out of the upflow selection tank 7 along the upflow pipe 3, and then connects to the tube 5 type reactor 1;

[0055] An external blower is connected to three riser pipes via an air pipe. The bottom opening of the air pipe is located at the bottom of the three riser pipes. Under the action of stripping, the granular sludge that has settled to the bottom of the riser selection tank 7 rises along the riser return pipe 9 and flows back into the tubular reactor 1. Meanwhile, the sludge with poor settling performance in the riser selection tank 7 is discharged into the sedimentation tank 8 with the sewage.

[0056] In step S400, the sludge return ratio is 200%.

[0057] The dimensions of the upflow selection tank 7 are 0.8m×0.8m×0.8m, the diameter of the upflow pipe 3 is 90mm, and the diameter of the upflow return pipe 9 is 20mm.

[0058] The upflow return pipe 9 is located at the end of the tubular reactor 1 and is connected to two branch pipes in parallel. Branch pipe one is connected to the upper part of the downflow pipe 4, and branch pipe two extends into the upflow pipe 3, which diverts the returned granular sludge and sewage to the downflow pipe 4 and the upflow pipe 3. The flow ratio of branch pipe one to branch pipe two is 1:1.

[0059] The sedimentation tank 8 is a conventional sedimentation tank 8 in the field, which can separate mud and water. The sludge is discharged from the bottom of the sedimentation tank 8 and then undergoes professional treatment. The overflow of the water is the produced water.

[0060] The ratio of the hydraulic retention times for tubular reactor 1, degassing tank 6, upflow selector tank 7, and sedimentation tank 8 is 3.1:1.1:1:1.2, which are 5.25h, 1.85h, 1.7h, and 2h, respectively.

[0061] In this embodiment, under the operating conditions of low carbon-to-nitrogen ratio (COD / TN less than 4) in the raw wastewater, the wastewater treatment effect is good. Simultaneous nitrification and denitrification occur in the tubular reactor 1, removing nitrogen while removing COD. The permeate discharged from sedimentation tank 8 meets the rural wastewater treatment standards (COD ≤ 50 mg / L, NH4+ ≤ 40 mg / L). 4+ -N≤8mg / L, TN≤20mg / L). After 250 days of cultivation, the average particle size of the aerobic granular sludge reached 140μm, which is 6 times that of traditional MBR sludge, and the SVI sludge settling performance reached 100ml / g.

[0062] Comparative Example 1

[0063] This comparative example provides a tubular wastewater treatment method for enhanced granular sludge cultivation, which is the same as Example 1, except that the tubular reactor does not have a casing, but only a tank body, the volume of which is equal to the volume of the entire tubular reactor in Example 1.

[0064] The quality of the permeate discharged from the sedimentation tank in this comparative example is as follows: COD 52 mg / L, NH4+ 50 mg / L. 4+-N was 19 mg / L and TN was 25 mg / L, indicating significantly poor permeable water quality. The particle size of the cultured aerobic granular sludge was 118 μm.

[0065] Comparative Example 2

[0066] This comparative example provides a tubular wastewater treatment method for enhanced granular sludge cultivation, which is the same as Example 1, except that a degassing tank is not set up, and the wastewater and sludge discharged from the tubular reactor are directly input into the upflow selection tank.

[0067] In this comparative example, the upflow selective tank experienced significant loss of mature sludge, resulting in a higher load on the sedimentation tank.

[0068] Example 2

[0069] This embodiment provides a tubular wastewater treatment method for enhanced granular sludge cultivation, which is the same as that in Embodiment 1, except that no stirring degassing section is installed in the degassing tank.

[0070] In this embodiment, a significant amount of mature sludge is lost from the upflow selection tank, resulting in a high load on the sedimentation tank.

[0071] Example 3

[0072] This embodiment provides a tubular wastewater treatment method for enhanced granular sludge cultivation, which is the same as that in Embodiment 1, except that the diameter ratio of the upflow pipe to the downflow pipe is 1.9:1.

[0073] Example 4

[0074] This embodiment provides a tubular wastewater treatment method for enhanced granular sludge cultivation, which is the same as that in Embodiment 1, except that the diameter ratio of the upflow pipe to the downflow pipe is 2:1.

[0075] Example 5

[0076] This embodiment provides a tubular wastewater treatment method for enhanced granular sludge cultivation, which is the same as that in Embodiment 1, except that when the depth of the upflow pipe is 30m, the flow ratio of branch pipe one to branch pipe two is 1:1.

[0077] Example 6

[0078] This embodiment provides a tubular wastewater treatment method for enhanced granular sludge cultivation, which is the same as that in Embodiment 1, except that when the depth of the upflow pipe is 31m, the flow ratio of branch pipe one to branch pipe two is 1:1.

[0079] Example 7

[0080] This embodiment provides a tubular wastewater treatment method for enhanced granular sludge cultivation, which is the same as that in Embodiment 1, except that when the depth of the upflow pipe is 31m, the flow ratio of branch pipe one to branch pipe two is 1:1.8.

[0081] Example 8

[0082] This embodiment provides a tubular wastewater treatment method for enhanced granular sludge cultivation, which is the same as that in Embodiment 1, except that when the depth of the upflow pipe is 40m, the flow ratio of branch pipe one to branch pipe two is 1:1.8.

[0083] Example 9

[0084] This embodiment provides a tubular wastewater treatment method for enhanced granular sludge cultivation, which is the same as that in Embodiment 1, except that when the depth of the upflow pipe is 41m, the flow ratio of branch pipe one to branch pipe two is 1:1.8.

[0085] Example 10

[0086] This embodiment provides a tubular wastewater treatment method for enhanced granular sludge cultivation, which is the same as that in Embodiment 1, except that when the depth of the upflow pipe is 41m, the flow ratio of branch pipe one to branch pipe two is 1:2.3.

[0087] Example 11

[0088] This embodiment provides a tubular wastewater treatment method for enhanced granular sludge cultivation, which is the same as that in Embodiment 1, except that when the depth of the upflow pipe is 50m, the flow ratio of branch pipe one to branch pipe two is 1:2.3.

[0089] Example 12

[0090] This embodiment provides a tubular wastewater treatment method for enhanced granular sludge cultivation, which is the same as that in Embodiment 1, except that when the depth of the upflow pipe is 19m, the flow ratio of branch pipe one to branch pipe two is 1:1.

[0091] The above embodiments and comparative examples show that the treated raw wastewater volume is 9.6 m³. 3 / d (equivalent to a medium-scale pilot-scale rural wastewater treatment), raw wastewater quality: COD 70.45±28.79 mg / L, NH 4+ -N was 28.33±5.38 mg / L, TN was 32.24±5.08 mg / L, and SS was 78.12±41.22 mg / L.

[0092] Table 1 Comparison of experimental results between Example 1 and Examples 3-12

[0093] project Sludge particle size (μm) COD (mg / L) TN (mg / L) Example 1 140 24 17 Example 3 137 26 16 Example 4 125 25 18 Example 5 138 22 16 Example 6 129 29 20 Example 7 135 20 15 Example 8 137 18 15 Example 9 122 23 18 Example 10 139 17 15 Example 11 136 15 13 Example 12 132 27 19

[0094] The sludge particle size in the table above is the average particle size of the aerobic granular sludge after cultivation; the COD and TN in the table above are the quality of the permeate discharged from the sedimentation tank.

[0095] As can be seen from the table above, the appropriate setting of the upflow pipe and downflow pipe in this invention, combined with the appropriate return flow component (the flow ratio in branch pipe one and branch pipe two), can achieve a better sewage treatment effect, and the particle size of the cultivated aerobic granular sludge is also larger.

Claims

1. A tubular sewage treatment method in which granular sludge cultivation is enhanced, characterized by, include S100: Wastewater and activated sludge are fed into the tubular reactor. The tubular reactor includes an above-ground tank and an underground casing. The casing includes an external riser pipe and an internal downflow pipe. After the casing is filled with wastewater, air is supplied into the riser pipe, which causes an upward flow of water to form in the riser pipe. Wastewater enters the downflow pipe through the connecting pipe in the tank and forms a downward flow of water in the downflow pipe. S200: After a stable circulating liquid flow is formed in step S100, air is supplied into the downflow pipe to maintain the oxygen content in the casing for cultivating aerobic granular sludge. S300: Wastewater and granular sludge treated by the tubular reactor are fed into the degassing tank, where the granular sludge is kept in a turbulent state. S400: Wastewater and granular sludge treated in the degassing tank are fed into the upflow selector tank. The granular sludge settles naturally in the upflow selector tank, and the sludge at the bottom of the tank flows back to the tubular reactor along the upflow return pipe. S500: Wastewater and sludge treated in the upflow selective tank are fed into the sedimentation tank, and after solid-liquid separation, the produced water is discharged. The tubular reactor has an opening at the bottom of the tank body to connect to the top of the riser pipe. The top of the downflow pipe is higher than the top of the riser pipe, and the liquid level in the tank body is kept lower than the top opening of the downflow pipe. A horizontal connecting pipe is provided at the top of the downflow pipe. One end of the connecting pipe is connected to the downflow pipe, and the other end is open to the inside of the tank body, so that the sewage and sludge inside the tank body can enter the downflow pipe through the connecting pipe. An air compressor is installed outside the pool. The two parallel pipes of the air compressor extend into the riser pipe and the fallr pipe respectively to provide gas to the riser pipe and the fallr pipe. The degassing tank has water entering from the lower part of one side and water exiting from the upper part of the other side. The bottom of the degassing tank is equipped with an aeration pipe, which is connected to an external blower to provide upward power for the sewage and sludge in the degassing tank. The degassing tank is equipped with a stirring degassing section, including a stirring paddle and concentrically arranged inner and outer stirring layers. Both the inner and outer stirring layers are cylindrical and connected to the stirring paddle at the center. The top of the stirring paddle extends out of the degassing tank and is connected to an external motor to drive the two stirring layers to rotate. The sidewalls of both the outer and inner stirring layers are single spiral-shaped; the sidewalls of both stirring layers are hollow, and the spacing between adjacent sidewalls is equal; the height of a solid sidewall of the inner stirring layer corresponds to the height of a hollow section of the sidewall of the outer stirring layer, and the height of a solid sidewall of the outer stirring layer corresponds to the height of a hollow section of the sidewall of the inner stirring layer. The outer and inner mixing layers are uniformly covered with a rough fiber mesh. The surface of the fiber mesh is evenly covered with barbs. When the granular sludge collides with the side wall of the mixing layer, the barbs squeeze and puncture the air bubbles on the surface of the sludge, thus accelerating defoaming.

2. The tubular sewage treatment method of cultivating enhanced granular sludge according to claim 1, characterized by, In step S100, the depth of the upflow pipe is 20-50m, the depth of the pool is 2-3m, and the average particle size of the inoculated sludge is 15-20μm; the diameter ratio of the upflow pipe to the downflow pipe is (1.6-1.9):

1.

3. The tubular sewage treatment method of cultivating enhanced granular sludge according to claim 1, characterized by, In step S200, compressed air is continuously or intermittently introduced into the riser pipe to maintain the circulating liquid flow of step S100; compressed air is continuously or intermittently introduced into the downflow pipe to maintain the average dissolved oxygen concentration in the casing at 0.5-1 mg / L, providing a suitable dissolved oxygen environment for cultivating granular sludge.

4. The tubular sewage treatment method of cultivating enhanced granular sludge according to claim 1, characterized by, In step S300, the dissolved oxygen concentration in the degassing tank is 1-2 mg / L, providing an aerobic environment for continued wastewater treatment and granular sludge cultivation.

5. The tubular sewage treatment method of cultivating enhanced granular sludge according to claim 1, characterized by, In step S400, a vertical upflow pipe is provided in the center of the upflow selection tank. The bottom of the upflow pipe is located at the lower part of the upflow selection tank, and the top of the upflow pipe is higher than the liquid level of the upflow selection tank. The bottom of the upflow return pipe extends into the bottom of the upflow pipe, and the upflow return pipe extends out of the upflow selection tank along the upflow pipe and then connects to the tubular reactor. An external blower is connected to the upflow pipe via an air pipe. The bottom opening of the air pipe is located at the bottom of the upflow pipe. Under the action of stripping, the granular sludge that has settled to the bottom of the upflow selection tank rises along the upflow return pipe and flows back into the tubular reactor. In step S400, the sludge return ratio is 180-200%.

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