Ultra-low energy consumption thermal energy internal circulation sewage biochemical treatment system and treatment process

Abstract

The present invention belongs to the technical field of sewage treatment systems, and specifically relates to an ultra-low energy consumption thermal energy internal circulation sewage biochemical treatment system and treatment process. The ultra-low energy consumption thermal energy internal circulation sewage biochemical treatment system includes a water collection well, a first sedimentation tank, an oxidation ditch, an anaerobic tank, and a secondary sedimentation tank. The water collection well is connected to the first sedimentation tank, which is connected to a heating boiler via a primary heat exchanger and a secondary heat exchanger in sequence, and the heating boiler is connected to the anaerobic tank; the outlet of the anaerobic tank is connected to the oxidation ditch via a secondary heat exchanger; the outlet of the oxidation ditch is connected to the secondary sedimentation tank via a primary heat exchanger; the primary heat exchanger or the secondary heat exchanger is a tubular heat exchanger or a tower heat exchanger; a variable frequency heating device is provided between the heating boiler and the anaerobic tank; the ultra-low energy consumption sewage biochemical treatment system provided by the present invention utilizes solar energy and heat preservation and heat exchange treatment of raw sewage to reduce the energy consumption of the entire system; the present invention also provides its treatment process.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment systems, and in particular relates to an ultra-low energy consumption thermal energy internal circulation sewage biochemical treatment system and a treatment process. Background Art

[0002] Anaerobic digestion and biodegradation are economical, effective, safe, and stable methods commonly used in wastewater treatment. The anaerobic process is a complex series of biochemical reactions in which substrates, various intermediates, metabolites, and various groups of microorganisms interact to form a complex microecological system. Microorganisms form symbiotic or commensal relationships through nutrient substrates and metabolic products, and temperature is the most sensitive and important condition for the reproduction and growth of various microorganisms. The optimal temperature for bacteria in anaerobic reactor sludge is between 30-38°C. At 20°C and 10°C, the treatment rates are approximately 33% and 12% of those at 30°C, respectively. This indicates that when the temperature is below 30°C, the wastewater treatment capacity of the wastewater treatment plant decreases, indicating that temperature is directly proportional to the treatment capacity.

[0003] Traditional biochemical sewage treatment typically involves water being retained in an open, open-air settling tank for a period of time (approximately 24 hours). This water continuously exchanges heat with the surrounding environment. When ambient temperatures are low, the water temperature drops even lower, particularly during winter, spring, and autumn in northern China, where temperatures can drop to 3-6°C. Before entering the anaerobic tank, this low-temperature wastewater is heated to 30-38°C (the optimal temperature for microorganisms), consuming significant amounts of heat energy, which is the largest energy cost in sewage treatment plant operating expenses.

[0004] The existing wastewater treatment process in the papermaking industry involves the wastewater first passing through coarse and fine screens, then through a collection well, then through a primary sedimentation tank, then through the supernatant, then through an anaerobic system, then through an oxidation ditch, then through a secondary sedimentation tank. The supernatant then enters an anaerobic pond, where the sludge continues to be concentrated. Existing heat exchangers are unsuitable when the wastewater contains excessive amounts of solid particles and other impurities. These impurities easily adhere to the heat exchange interface, forming deposits that affect heat transfer efficiency and cause blockages.

[0005] Therefore, when treating wastewater in the papermaking industry, it is urgently needed to reduce energy consumption in wastewater treatment. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to transform the traditional high-energy consumption sewage biochemical treatment system into an energy-saving technology, and provide an ultra-low energy consumption sewage biochemical treatment system, which utilizes solar energy and heat insulation and heat exchange treatment of raw sewage to reduce the energy consumption of the entire system; the present invention also provides its treatment process.

[0007] The ultra-low energy consumption thermal energy internal circulation sewage biochemical treatment system of the present invention comprises a water collection well, a first settling tank, an oxidation ditch, an anaerobic tank, and a second settling tank. The water collection well is connected to the first settling tank, which is connected to a heating boiler via a primary heat exchanger and a secondary heat exchanger in sequence, and the heating boiler is connected to the anaerobic tank. The outlet of the anaerobic tank is connected to the oxidation ditch via a secondary heat exchanger. The outlet of the oxidation ditch is connected to the second settling tank via a primary heat exchanger. Both the primary heat exchanger and the secondary heat exchanger are tubular heat exchangers or tower heat exchangers. A variable frequency heating device is provided between the heating boiler and the anaerobic tank.

[0008] The tubular heat exchanger is connected in series in multiple groups, and an external sedimentation and drainage device is installed on the pipeline between the two groups. The external sedimentation and drainage device is a hollow structure with two cones fixed together, and a drainage valve b is installed at the bottom of the external sedimentation and drainage device; the internal sedimentation and drainage device is installed inside the tubular heat exchanger, and a drainage valve a is installed at the bottom of the internal sedimentation and drainage device; the external sedimentation and drainage device is provided with a water inlet and a water outlet, and a filter plate is installed at the water outlet by welding inside, and the filter plate is provided with filter holes;

[0009] One end of the tower heat exchanger is set as a sedimentation cone, and a sewage valve c is set at the bottom of the sedimentation cone;

[0010] The open-air part of a sedimentation tank is provided with an outer enclosure structure a and an inner enclosure structure a;

[0011] A heat-absorbing material is placed in a settling tank or oxidation ditch. The heat-absorbing material is a solar heat-absorbing material and can be a plate, sheet, film, or geometric carrier with a selective heat-absorbing coating. More preferably, it is a hollow sphere structure with a heat-absorbing coating. The heat-absorbing material can be placed between the sun-facing wall and inner enclosure of the settling tank or oxidation ditch and the water surface, or placed on the water surface to float.

[0012] The open-air part of the oxidation ditch is provided with an inner enclosure structure b and an outer enclosure structure b.

[0013] Preferably, a heat exchange tube a is provided inside the tubular heat exchanger, to which a cold medium inlet pipe a and a cold medium outlet pipe a are connected, and a limiting fixing frame a is provided between the heat exchange tubes a; the outermost layer of the tubular heat exchanger is a shell a, and an insulation filling layer a is provided between the shell a and the tubular heat exchanger body; the tubular heat exchanger body is connected to the hot medium inlet a and the hot medium outlet a.

[0014] Preferably, the outermost layer of the tower heat exchanger is the shell b, an insulation filling layer b is provided between the shell b and the tower heat exchanger body, heat exchange tubes b are provided inside the tower heat exchanger, and a limiting fixing frame b is provided between the heat exchange tubes b. The tower heat exchanger body is connected to the heat medium inlet b and the heat medium outlet b; the heat exchange tubes b are connected to the cold medium inlet pipeline b and the cold medium outlet pipeline b.

[0015] Preferably, the open-air portion of a settling tank is provided with an outer enclosure structure a and an inner enclosure structure a using a steel structure. The outer layer of the outer enclosure structure a is provided with a heat-absorbing coating carrier, and the outer enclosure structure a and the inner enclosure structure a form an arched structure, which may also be a triangular or trapezoidal structure. The inner enclosure structure a is a transparent sheet composite plate or membrane material. A heat-absorbing pool wall is provided on the inner side of a settling tank wall of the settling tank; a rotating mechanism is provided within the settling tank. Heat-absorbing material is placed in the settling tank or oxidation ditch.

[0016] Preferably, the open-air part of the oxidation ditch is provided with an inner enclosure structure b and an outer enclosure structure b through a steel structure, and a triangular enclosure structure or an arched enclosure structure is formed between the inner enclosure structure b and the outer enclosure structure b and the oxidation ditch; the oxidation ditch is a parallel strip, and the enclosure method of the inner enclosure structure and the outer enclosure structure for the oxidation ditch is single ditch enclosure or overall enclosure.

[0017] The treatment process of the ultra-low energy consumption thermal energy internal circulation sewage biochemical treatment system includes the following steps:

[0018] (1) After the sewage is discharged into the water collection well, it flows into a sedimentation tank. In the sedimentation tank, the temperature drop caused by the convection between the sewage and the environment is blocked by the outer enclosure structure a and the inner enclosure structure a. In addition, in the sedimentation tank, the temperature of the space between the sewage surface and the enclosure structure is increased by setting the heat-absorbing coating carrier, heat-absorbing material and heat-absorbing tank wall.

[0019] (2) The low-temperature water from the first sedimentation tank enters the primary heat exchanger. After heat exchange with the high-temperature sewage discharged from the oxidation ditch, the temperature of the sewage rises and continues to enter the secondary heat exchanger. After heat exchange with the high-temperature sewage discharged from the anaerobic tank, it enters the heating boiler and is pumped into the anaerobic tank after heating for anaerobic treatment.

[0020] (3) The temperature of the sewage at the outlet of the anaerobic tank is high. The heat is processed by the secondary heat exchanger, and part of the heat is supplied to the sewage at the inlet of the anaerobic tank in step (2) to increase the temperature. The second stage heat exchanger recovers part of the heat discharged from the anaerobic tank, and then sends it to the anaerobic tank after boiler heating and frequency conversion heating. The boiler heating adopts the biogas generated by the anaerobic tank for heating.

[0021] (4) The sewage discharged from the anaerobic tank continues to enter the oxidation ditch. The oxidation ditch uses the inner enclosure structure b and the outer enclosure structure b to isolate the temperature drop caused by the convection between the sewage and the environment, and places heat-absorbing materials in the oxidation ditch to absorb solar heat energy, maintain and increase the temperature of the space between the sewage surface and the enclosure structure; and the sewage discharged from the oxidation ditch has a high temperature, and passes through the first-stage heat exchanger to supply heat to the sewage from the first sedimentation tank in step (1);

[0022] (5) The sewage passing through the oxidation ditch is discharged into the secondary sedimentation tank after heat exchange.

[0023] The anaerobic tank produces its own biogas, which is used to heat the boiler and increase the sewage temperature at the anaerobic tank inlet by 2-5℃.

[0024] The average ambient temperature in December, January, February and March is -2°C. The temperature of the sewage discharged into the collection well in step (1) is 10-20°C. The residence time of the sewage discharged into the first sedimentation tank is 24-48 hours. After being enclosed and absorbing heat in the first sedimentation tank, the temperature of the sewage discharged from the first sedimentation tank is 12-15°C.

[0025] After the first-stage heat exchange in step (2), the sewage temperature rises by 4-6°C. After the second-stage heat exchange, the sewage temperature rises by 7-10°C. Then, the sewage is heated by the self-produced biogas in the anaerobic tank through frequency conversion, so that the temperature reaches the anaerobic required temperature.

[0026] The temperature of the sewage discharged from the anaerobic tank in step (4) is 30-35°C. After the enclosure structure and heat absorption treatment of the oxidation ditch, the temperature of the sewage at the inlet of the oxidation ditch reaches 26-30°C.

[0027] The first process that generates heat loss in the present invention is a settling tank. The settling tank is an open system. Since papermaking wastewater is discharged from the workshop to the water collection well and then flows into the settling tank, it stays in the settling tank for 24 hours. The water in the settling tank exchanges heat with the environment, resulting in a temperature drop. The second process that generates heat loss is the oxidation ditch. The oxidation ditch is also an open system. It has a certain flow time to dissipate heat with the environment, resulting in a temperature drop. The present invention utilizes solar heat by providing an outer protective structure and an inner protective structure for the settling tank and the oxidation ditch, and providing a heat-absorbing coating carrier with a heat-absorbing coating or heat-absorbing plate on the outer protective structure; and placing heat-absorbing materials on the sewage surface within the enclosed structure to further utilize solar heat; and a heat-absorbing pool wall can be provided on the sunny pool wall of the settling tank, that is, the pool wall of the settling tank, to further enhance the utilization of solar heat by the settling tank. The newly added settling tank and oxidation ditch enclosures isolate the wastewater from the surrounding environment, preventing convection and temperature drops. By absorbing solar heat, they convert light energy into heat, raising the temperature of the space between the enclosure and the wastewater. In the oxidation ditch, aerators blow hot air from the enclosure into the water, creating a gas-liquid heat exchange that heats the water.

[0028] The ultra-low energy consumption biochemical sewage treatment system of the present invention is equipped with a two-stage low-temperature heat exchange and recovery device, consisting of a primary heat exchanger and a secondary heat exchanger. The primary heat exchanger exchanges heat between the supernatant from a settling tank and the water from the oxidation ditch outlet, recovering the oxidation ditch's waste heat. The secondary heat exchanger recovers some of the heat discharged from the anaerobic tank, which is then heated by a boiler and heat pump before being fed back into the anaerobic tank. The biogas pipeline of the anaerobic tank can be connected to a biogas boiler, which heats the sewage.

[0029] The present invention realizes ultra-low energy consumption operation through the coordinated efforts of the above enclosure insulation, solar energy collection, and two-stage heat exchange recovery technologies.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The ultra-low energy consumption biochemical sewage treatment system of the present invention is provided with an enclosure structure on a sedimentation tank and an oxidation ditch to prevent the sewage in the tank from exchanging heat with the environment and causing the water temperature to drop. At the same time, a solar heat collection effect is generated to heat the water body, thereby saving energy and reducing consumption.

[0032] (2) The ultra-low energy consumption sewage biochemical treatment system of the present invention adopts a two-stage heat exchange system to achieve internal circulation heat exchange and reduce the input of heat energy.

[0033] (3) The ultra-low energy consumption sewage biochemical treatment system of the present invention places heat-absorbing materials on the water surface of a sedimentation tank and an oxidation ditch, and sets the enclosure structure as heat-absorbing materials, so as to fully realize the conversion of light and heat, save energy and reduce consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the ultra-low energy consumption sewage biochemical treatment system of the present invention.

[0035] Figure 2 Schematic diagram of the structure of a tubular heat exchanger.

[0036] Figure 3 Schematic diagram of the structure of the tower heat exchanger.

[0037] Figure 4 Schematic diagram of the retaining structure of a sedimentation tank.

[0038] Figure 5 This is a top-down structural diagram of a sedimentation tank.

[0039] Figure 6 Schematic diagram of the enclosure structure of the oxidation ditch.

[0040] Figure 7 Schematic diagram of the existing sewage biochemical treatment system.

[0041] In the figure: 1, water collection well; 2, a sedimentation tank; 201, outer enclosure structure a; 202, inner enclosure structure a; 203, heat-absorbing coating carrier; 204, heat-absorbing material; 205, a sedimentation tank wall; 206, heat-absorbing tank wall; 207, rotating mechanism;

[0042] 3. Oxidation ditch; 301. Inner enclosure structure b; 302. Outer enclosure structure b;

[0043] 4. Anaerobic tank; 41. Heating boiler;

[0044] 5. Secondary sedimentation tank; 6. Frequency conversion heating device; 7. Primary heat exchanger; 8. Secondary heat exchanger;

[0045] 9. Tubular heat exchanger; 91. Heat exchange tube a; 92. Internal sedimentation and drainage device; 93. Drain valve a; 94. Limiting bracket a; 95. Shell a; 96. Insulation filling layer a;

[0046] 10. External sedimentation and drainage device; 101. Drain valve b; 102. Water inlet; 103. Water outlet; 104. Filter plate; 105. Filter hole;

[0047] 11. Hot medium inlet a; 12. Hot medium outlet a; 13. Cold medium inlet pipeline a; 14. Cold medium outlet pipeline a;

[0048] 15. Tower heat exchanger; 151. Heat exchange tube b; 152. Shell b; 153. Insulation filling layer b; 154. Sedimentation cone; 155. Limit fixing bracket b; 156. Drain valve c; 157. Cold medium inlet pipeline b; 158. Cold medium outlet pipeline b; 1591. Hot medium inlet b; 1592. Hot medium outlet b. DETAILED DESCRIPTION

[0049] The present invention will be further described below with reference to specific embodiments. In the description of the present invention, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as a limitation on the present invention. The enclosure structures provided for the settling tank 2 and oxidation ditch 3 described in the present invention all adopt support structures, such as existing light steel structures, and their purpose is to support and reinforce. These are all conventional operations in the prior art and will not be discussed further. The heat absorption pool wall 206 described in the present invention is a layer of material with heat absorption function, which can be placed on a settling tank wall 205 in any manner, such as by fixing with rivets, or by external fixing. This operation is also a conventional technique that can be mastered in the prior art and will not be discussed further.

[0050] like Figure 1As shown, the ultra-low energy consumption thermal energy internal circulation sewage biochemical treatment system includes a water collection well 1, a settling tank 2, an oxidation ditch 3, an anaerobic tank 4, and a secondary settling tank 5. The water collection well 1 is connected to the first settling tank 2, and the first settling tank 2 is connected to the heating boiler 41 through a primary heat exchanger 7 and a secondary heat exchanger 8 in sequence, and the heating boiler 41 is connected to the anaerobic tank 4; the outlet of the anaerobic tank 4 is connected to the oxidation ditch 3 through the secondary heat exchanger 8; the outlet of the oxidation ditch 3 is connected to the secondary settling tank 5 through the primary heat exchanger 7; the primary heat exchanger 7 or the secondary heat exchanger 8 is a tubular heat exchanger 9 or a tower heat exchanger 15; a variable frequency heating device 6 is provided between the heating boiler 41 and the anaerobic tank 4.

[0051] like Figure 2 As shown, the tubular heat exchanger 9 is connected in series in multiple groups, and an external sedimentation and sewage discharge device 10 is provided on the pipeline between the two groups. The external sedimentation and sewage discharge device 10 is a hollow structure in which two cones are fixed together. The fixation can be achieved by welding. The external sedimentation and sewage discharge device 10 is a single-layer or double-layer structure. A sewage discharge valve b101 is provided on the external sedimentation and sewage discharge device 10; an internal sedimentation and sewage discharge device 92 is provided inside the tubular heat exchanger 9, and a sewage discharge valve a93 is provided on the internal sedimentation and sewage discharge device 92; the external sedimentation and sewage discharge device 10 is provided with a water inlet 102 and a water outlet 103, and a filter plate 104 is provided at the water outlet 103 by welding inside, and a filter hole 105 is provided on the filter plate 104.

[0052] One end of the tower heat exchanger 15 is provided with a sedimentation cone 154 , and a sewage valve c156 is provided on the sedimentation cone 154 .

[0053] The open-air part of a sedimentation tank 2 is provided with an outer enclosure structure a201 and an inner enclosure structure a202.

[0054] A heat-absorbing material 204 is placed in a settling tank 2 or oxidation ditch 3. The heat-absorbing material is a solar heat-absorbing material and can be a plate, sheet, film, or geometric carrier with a selective heat-absorbing coating. More preferably, it is a hollow sphere with a heat-absorbing coating. The heat-absorbing material 204 can be placed between the sun-facing wall and inner enclosure of the settling tank or oxidation ditch and the water surface, or placed on the water surface to float.

[0055] The open-air part of the oxidation ditch 3 is provided with an inner enclosure structure b301 and an outer enclosure structure b302.

[0056] like Figure 2 As shown, a heat exchange tube a91 is provided inside the tubular heat exchanger 9, to which a cold medium inlet pipe a13 and a cold medium outlet pipe a14 are connected, and a limiting fixing frame a94 is provided between the heat exchange tubes a91; the outermost layer of the tubular heat exchanger 9 is a shell a95, and an insulating filling layer a96 is provided between the shell a95 and the main body of the tubular heat exchanger 9; the main body of the tubular heat exchanger 9 is connected to the hot medium inlet a11 and the hot medium outlet a12.

[0057] like Figure 3 As shown, the outermost layer of the tower heat exchanger 15 is the shell b152. An insulating filling layer b153 is interposed between the shell b152 and the main body of the tower heat exchanger 15. Heat exchange tubes b151 are installed within the tower heat exchanger 15, with retaining brackets b155 positioned between the tubes b151. The main body of the tower heat exchanger 15 is connected to the hot medium inlet b1591 and the hot medium outlet b1592. The heat exchange tubes b151 are connected to the cold medium inlet pipe b157 and the cold medium outlet pipe b158. The heat exchange tubes a91 and b151 are finned tube bellows. The shells a95 and b152 are made of composite insulation material, such as PVC casing. The insulating filling layers a96 and b153 are polyurethane foam filling layers.

[0058] like Figure 4 As shown, the open-air part of a sedimentation tank 2 is provided with an outer enclosure structure a201 and an inner enclosure structure a202 through a steel structure; the outer layer of the outer enclosure structure a201 is provided with a heat-absorbing coating carrier 203, and the outer enclosure structure a201 and the inner enclosure structure a202 form an arch structure, which can also be a triangular structure or a trapezoidal structure. The inner enclosure structure a202 is a transparent sheet composite board or membrane material. Figure 5 As shown, a heat absorbing wall 206 is provided on the inner side of a sedimentation tank wall 205 of a sedimentation tank 2; a rotating mechanism 207 is provided inside the sedimentation tank 2. Heat absorbing materials are placed in a sedimentation tank or oxidation ditch.

[0059] like Figure 6 As shown, the open-air part of the oxidation ditch 3 is provided with an inner enclosure structure b301 and an outer enclosure structure b302 through a steel structure, and a triangular enclosure structure or an arched enclosure structure is formed between the inner enclosure structure b301 and the outer enclosure structure b302 and the oxidation ditch 3; the oxidation ditch 3 is a parallel strip shape, and the enclosure method of the inner enclosure structure b301 and the outer enclosure structure b302 for the oxidation ditch 3 is single ditch enclosure or overall enclosure.

[0060] The treatment process of the ultra-low energy consumption thermal energy internal circulation sewage biochemical treatment system of the present invention comprises the following steps:

[0061] (1) After being discharged into the collection well 1, the sewage flows into a sedimentation tank 2. In the sedimentation tank 2, the outer enclosure structure a201 and the inner enclosure structure a202 are used to isolate the temperature drop caused by convection between the sewage and the environment. In the sedimentation tank 2, the temperature of the space between the sewage surface and the enclosure structure is increased by setting a heat-absorbing coating carrier, heat-absorbing material and heat-absorbing pool wall. The average ambient temperature in December, January, February and March is -2°C. The temperature of the sewage discharged into the collection well is 10-20°C. The residence time of the sewage discharged into the sedimentation tank is 24h-48h. After the enclosure and heat absorption of the sedimentation tank 2, the temperature of the sewage discharged from the sedimentation tank 2 is 12-15°C.

[0062] (2) The low-temperature water from a sedimentation tank enters the primary heat exchanger 7, and after heat exchange with the high-temperature sewage discharged from the oxidation ditch, the temperature of the sewage increases, and the sewage continues to enter the secondary heat exchanger 8, and after heat exchange with the high-temperature sewage discharged from the anaerobic tank, it enters the heating boiler, and after boiler heating and frequency conversion heating, it is pumped into the anaerobic tank for anaerobic treatment; after the primary heat exchange in step (2), the sewage temperature increases by 4-6°C, and after the secondary heat exchange, the sewage temperature increases by 7-10°C, and then it is heated by the anaerobic tank's self-produced biogas boiler and frequency conversion heating to reach the anaerobic required temperature.

[0063] (3) The temperature of the sewage at the outlet of the anaerobic tank is high, and the heat is processed by the secondary heat exchanger 8, and part of the heat is supplied to the sewage at the inlet of the anaerobic tank in step (2) to increase the temperature; the second stage heat exchange recovers part of the heat discharged from the anaerobic tank, and then sends it to the anaerobic tank after boiler heating and frequency conversion heating; the boiler heating adopts the biogas generated by the anaerobic tank for heating.

[0064] (4) The wastewater discharged from the anaerobic tank continues to enter the oxidation ditch. The oxidation ditch uses the inner and outer enclosure structures b to isolate the temperature drop caused by convection between the wastewater and the environment. Heat-absorbing materials are placed in the oxidation ditch to absorb solar heat energy, maintaining and raising the temperature of the space between the wastewater surface and the enclosure structure. The wastewater discharged from the oxidation ditch is at a high temperature. After passing through the primary heat exchanger, the heat is supplied to the wastewater from the first sedimentation tank in step (1). The temperature of the wastewater discharged from the anaerobic tank is 30-35℃. After passing through the enclosure structure and heat absorption treatment of the oxidation ditch, the temperature of the wastewater at the inlet of the oxidation ditch reaches 26-30℃.

[0065] (5) The sewage passing through the oxidation ditch is discharged into the secondary sedimentation tank after heat exchange.

[0066] The wastewater treatment process is carried out using the thermal energy internal circulation wastewater biochemical treatment system of the present invention. The reduction of process energy consumption caused by environmental factors and the like is specifically demonstrated below through specific embodiments.

[0067] Example 1

[0068] A paper mill sewage treatment plant with a daily sewage treatment capacity of 50,000 m 3 , the temperature of sewage discharged from the workshop is 15℃. In December, January, February and March, the ambient temperature is -2℃ on average. The traditional biochemical treatment methods of sewage, such as Figure 7 As shown in the figure, the sewage at 15℃ is discharged into the first sedimentation tank 2 and the residence time is 26h. The first sedimentation tank 2 is open to the environment. The average outflow temperature of the supernatant is 4℃. Before the temperature is heated to 36℃ and enters the anaerobic tank 4, the water temperature is raised by 32℃. It takes 1.16kW·h to raise the temperature of 1 ton of water by 1℃. 3 Raising the water temperature to 32°C requires 1,856,000 kW•h. The average peak and valley electricity price is 0.8 yuan / kW•h, which translates to a cost of up to 1,484,800 yuan.

[0069] The ultra-low energy consumption biochemical sewage treatment system described above in the present invention is also employed. Enclosure structures are installed in a settling tank 2 and an oxidation ditch 3. The open-air portion of the oxidation ditch 3 is provided with an inner enclosure b301 and an outer enclosure b302 via a steel structure, forming a triangular enclosure between the inner enclosure b301 and the outer enclosure b302 and the oxidation ditch 3. The open-air portion of the settling tank 2 is provided with an outer enclosure a201 and an inner enclosure a202 via a steel structure. The outer layer of the outer enclosure a201 is provided with a heat-absorbing coating carrier 203, forming a triangular structure with the inner enclosure a202. The inner enclosure a202 is a transparent sheet composite panel. An upper heat-absorbing pool wall 206 is provided within the settling tank 2. Solar heat-absorbing materials are installed in the inner enclosure a202 of the settling tank 2, and solar heat-absorbing materials are installed in the inner enclosure b301 of the oxidation ditch 3.

[0070] Under the above-mentioned same working conditions, after the implementation of this embodiment, the temperature of the sewage discharged from the workshop is 15°C. In December, January, February and March, the ambient temperature is -2°C on average. The sewage stays in the first sedimentation tank for 26 hours. The average outflow temperature of the supernatant is 13.7°C, which rises to 24°C after heat exchange with the oxidation ditch.

[0071] After heat exchange in the primary heat exchanger 7, the water temperature rises by 5.0°C to 18.7°C. After passing through the secondary heat exchanger 8, the outlet water temperature of the anaerobic tank 4 is 35°C. After heat exchange, the water temperature rises by 9.3°C to 28°C. The biogas produced by the anaerobic tank 4 heats the boiler to raise the water temperature to 29.5°C. Then, it is heated by the heat pump, raising the temperature by 5.5°C from 29.5°C to 36°C, and is pumped into the anaerobic tank 4.

[0072] Compared with the traditional method without the enclosure of the first-stage heat exchanger 7, the second-stage heat exchanger 8, the oxidation ditch 3 and the first sedimentation tank 2, after the low-energy consumption sewage biochemical treatment system transformation of the present invention, the final energy consumption temperature rise is 5.5℃, 50000m 3 The temperature rise is 5.5℃, and the power consumption is 319,000kW·h, which is equivalent to a cost of 255,200 yuan.

[0073] Comparison of energy-saving effects of the present invention and traditional processes:

[0074] Saving heating electricity: 1856000-319000=1537000kW·h, which means energy saving of 82.8%.

[0075] It can be seen that the implementation of this embodiment has a significant effect on energy conservation and emission reduction, providing a good energy-saving technical support for the low-cost operation of sewage treatment plants.

[0076] Example 2

[0077] The daily processing capacity of a sewage treatment plant is 60,000m 3 The first sedimentation tank 2 is designed with a radius of 30m, a depth of 4.5m and an area of ​​2826m 2 , with a volume of 12717m 3 It is a semi-underground structure with a height of 2.0m above the ground. The rotating mechanism 207 is set 1.5m above the pool surface. The outer protective structure a201 and the inner protective structure a202 of the sedimentation tank 2 are designed to be circular arch structures. The design height outside the pool is ±zero. The arch height of the outer protective structure a201 is 6.0m, and the outer protective structure a201 shed is 4.5m high (1.0-2.5m higher than the rotating mechanism 207), and the arch height is 1.5m.

[0078] The supporting structure used is a light steel structure with a designed steel weight of 65kg / m 2 The light steel structure uses hot-dip galvanized rectangular steel, with a design wind load resistance of 13 levels 41m / s, a snow load resistance of 100kg / m2, and an earthquake intensity of 10 degrees.

[0079] The outer protective structure a201 of the first sedimentation tank 2 is made of 3mm PC board with a light transmittance ≥90% and aging resistance ≥15 years; the light-transmitting material of the inner protective structure a202 is EVA0.7mm film with a light transmittance ≥90%. The inner protective EVA film is hung 35cm below and within 30cm inside (vertically) the outer protective PC board, and the vertical support structure is fixed on the outer support structure.

[0080] There is a 30mm rubber-plastic foam thermal insulation bridge material between the outer supporting structure and the light-transmitting material of the external protective structure a201.

[0081] The inner walls of the north, east and west sides of a sedimentation tank 2 are sprayed with nano-metal ion heat-absorbing paint, and hollow spheres with a diameter of 5-10 cm and a heat-absorbing coating, i.e., heat-absorbing material 204, are placed in the pool with a placement density of more than 90%. The plastic balls or metal balls have an absorption rate of ≥90% and an emissivity of ≤8% with the heat-absorbing coating.

[0082] Compared with the conventional method without the enclosure of the primary heat exchanger 7, the secondary heat exchanger 8, the oxidation ditch 3 and the first sedimentation tank 2, the low-energy consumption sewage biochemical treatment system transformation of the present invention has the following effects:

[0083] a. In January, the ambient temperature was -10℃. The temperatures inside the enclosure were measured at 10:00, 12:00 and 16:00 on sunny days, which were 30℃, 49℃ and 28.5℃ respectively. On cloudy nights, the temperature was -15℃ and the temperature inside the enclosure was 12.6℃.

[0084] b. The water temperature of the first sedimentation tank is 14.2℃ and 13.9℃ respectively (the incoming water temperature is 14.5℃).

[0085] c. The water temperature of the traditional open primary sedimentation tank is 4.2-5.1℃.

[0086] Example 3

[0087] A residential area in a certain area is 400 meters away from a sewage treatment plant. Before the present invention was adopted, the first settling tank 2 and the oxidation ditch 3 were open to the open air. In the summer, the surrounding residents could clearly smell the sewage odor. After the first settling tank 2 and the oxidation ditch 3 enclosure structure of the present invention were installed, the sewage odor is no longer odorous. The present invention has the environmental protection of air pollution control.

[0088] Oxidation ditch 3 is 100m long and 70m wide, with 12 parallel single oxidation ditches, averaging 5.8m (including partition walls). The design of the external enclosure structure b302 is triangular or arched. Each ditch has 12 rows, with sealed gables at both ends and drainage gutters. The light steel structure is hot-dip galvanized rectangular steel or round tubes. The arch height is designed to be 1.5-2.0m, the span is 5.8m, and the wind resistance is ≥41m / s and the snow load resistance is ≥150kg / m. 2 , the seismic intensity is set to 10 degrees.

[0089] The inner enclosure structure b301 consists of two layers. The first layer of inner enclosure is 25 cm above the wall of oxidation ditch 3, and the second layer of inner enclosure is installed parallel to it 25 cm below.

[0090] A heat-absorbing film is installed between the water surface and the second-layer inner enclosure, and the heat-absorbing film covers the water surface.

[0091] External light-transmitting enclosure material: 5+12+5 ultra-clear insulating glass; internal light-transmitting enclosure material: PVC or PE 0.75mm thick high-transmittance film; ultra-clear glass transmittance ≥92%; PVC / PE high transmittance ≥90%.

[0092] The solar heat-absorbing film uses 0.75mm thick PVC nano-silicon titanium black heat-absorbing film with an absorptivity of ≥89% and an emissivity of ≥11%.

[0093] When sunlight passes through the enclosing light-transmitting material and radiates onto the heat absorber, the light energy is converted into heat energy, and the air in the space is heated and the temperature is raised through heat exchange with the space. The heated air is sucked into the pool by the aerator, realizing gas-liquid heat exchange, and the water in the oxidation ditch gains heat and the temperature rises.

[0094] After the above design, the effect comparison between the present invention and the traditional one is as follows:

[0095] (1) The average ambient temperature in December, January, February and March was -3°C, the outlet temperature of the anaerobic tank was 36°C, the water temperature in the front section of the oxidation ditch was 35°C, and the water temperature in the back section was 13°C, with a temperature difference of 22°C.

[0096] (2) The water from the oxidation ditch 3 of the present invention is discharged from the anaerobic tank 4 at 36°C and then heat-exchanged in the secondary heat exchanger 8. The water temperature discharged into the oxidation ditch 3 is 30.5°C. The front section of the oxidation ditch is 28°C, and the rear section is 26°C, with a temperature difference of 2°C.

[0097] In winter, spring, and autumn, when ambient temperatures are low and rainy, the combination of snow and rain can significantly drop the temperature of open-air pools, causing temperature fluctuations in the wastewater (especially in the oxidation ditch) and, consequently, biochemical fluctuations. This invention minimizes pool water temperature fluctuations, ensuring a steady growth and reproduction rate for microorganisms, resulting in consistent biochemical treatment results and quality.

[0098] Example 4

[0099] A sewage treatment plant with a daily processing capacity of 40,000m 3 The first-stage heat exchanger 7 and the second-stage heat exchanger 8 of the present invention adopt a tower-type series heat exchanger or a pipeline-type super-long heat exchanger for heat exchange. The incoming water temperature is 14°C, the oxidation ditch drainage temperature is 25-26°C, and the water temperature after heat exchange rises by 4.5°C, reaching 18.5°C.

[0100] The wastewater with a temperature of 18.5°C after heat recovery in the primary heat exchanger 7 is then subjected to a secondary heat exchange with the 35-36°C water discharged from the anaerobic tank 4, and the temperature is raised by 7°C again, so that the sewage inlet temperature reaches 25.5-26.5°C.

[0101] The primary heat exchanger 7 recovers heat by exchanging the supernatant of the first sedimentation tank 2 with the water discharged from the oxidation ditch 3, thereby recovering part of the waste heat discharged from the oxidation ditch 3.

[0102] The large amount of biogas produced by the microorganisms in the anaerobic tank 4 is sent to the biogas gas boiler through the collection pipeline, which heats the incoming sewage at 25.5-26.5℃ to 27-28℃, and then to 36℃ through the variable frequency heating device 6, and then pumped into the anaerobic tank 4 to complete the entire sewage heating process. The final energy consumption will be 40000m 3The heating temperature rises by about 6°C. The final 6°C increase can be achieved by installing solar photovoltaic power generation in non-solar thermal areas of the sewage treatment plant, combined with energy storage, to achieve zero-carbon heating operation.

[0103] The tower heat exchanger 15 and the tubular heat exchanger 9 employed in the primary and secondary heat recovery systems of the present invention share the following characteristics: extended heat exchange time, both media have waste (sediment) removal, and reduced buildup of fixed objects, maintaining excellent heat exchange performance. The heat exchanger's outer shell is constructed of a thermally insulating composite material.

[0104] The tower heat exchanger 15 used in this invention features heat exchange tubes within a conical sedimentation and drainage structure and a drain valve at the bottom. Tower heat exchanger 15 is 20-30 meters tall. The tank is constructed of SUS304 material, 10 mm thick and 3000 mm in diameter. The sedimentation cone is 3000 mm in diameter, with a built-in medium sedimentation diameter of 2000 mm and a cone sedimentation and drainage length of 2000 mm. The built-in medium sedimentation cone is enclosed by 160 Ø57 mm metal finned tubes or bellows, such as aluminum alloy tubes. Large-diameter PVC bellows are fitted around the tank exterior, and polyurethane foam is injected between the tubes. The heat exchange material (aluminum) has a thermal conductivity of ≥280 W / (mK). The high-temperature medium inlet is located at the top of the tank, and the outlet is located at the upper edge of the cone at the bottom. The low-temperature medium inlet is located at the bottom of the tank, and the outlet is located at the top of the tank. The high and low temperature media move relative to each other. The tower heat exchanger 15 of the present invention with a DN3000*30000mm diameter is suitable for a daily processing capacity of 7000m 3 .

[0105] The tubular heat exchanger 9 used in the present invention is an assembled extra-long tubular heat exchanger. The main consideration of the tubular heat exchanger is to increase the heat exchange time. The tubular heat exchanger is composed of multiple sections, and there is an internal sedimentation and sewage discharge device between each section of the tubular heat exchanger. Each section of the tubular heat exchanger has at least one conical external sedimentation and sewage discharge device 10. The diameter range of the tubular heat exchanger is DN500-2000mm. The length of each group is between 8000-20000mm, forming an extra-long tubular heat exchanger of 100-300m, which is suitable for underground installation. The shell of the tubular heat exchanger can be metal, plastic or composite material FRP. The internal heat exchange tube can be a finned tube bellows made of metal or plastic, such as carbon steel pipe, aluminum pipe, copper pipe or PR, PVC, PE and other corrugated pipes. The internal heat exchange tube has a limited fixing frame, and the front and rear ends of the high and low temperature medium inlet are opposite, and the medium moves relative to each other.

[0106] Whether it is a tower heat exchanger 15 or a tubular heat exchanger 9, multiple towers or multiple groups of heat exchangers can be connected in series to ensure sufficient heat exchange time.

[0107] After the ultra-low energy consumption sewage biochemical treatment system of the present invention has been used, the entire system saves energy and reduces consumption. It is a system project integrating insulation, heat collection and energy replenishment, and heat recovery, which saves about 85% energy compared with traditional methods. The incoming water temperature in traditional workshops is about 15°C, and the residence time in a sedimentation tank is about 24 hours. In December, January, February and March, the supernatant water temperature is about 5°C. Since the present invention has installed a protective structure and adopted solar heat collection and energy replenishment, the incoming water temperature can reach 15°C without dropping on sunny days, and about 13.7°C at night on cloudy days, with an average of 14.35°C, which is 9.35°C higher than the traditional water temperature, that is, it saves heat energy of 9.35°C temperature rise.

[0108] Solar thermal energy supplement: Depending on the region and solar energy resources, the second type of light resources, 1630-1860kW·h / m 2 (Based on 1745kW·h / m 2 Calculation), CO2 emission reduction 530kg / m 2 ; Three types of lighting resources, 1390-1630kW·h / m 2 (Based on 1510kW·h / m 2 Calculation), CO2 emission reduction 460kg / m 2 .

[0109] If the total area of ​​a sedimentation tank and oxidation ditch in a sewage treatment plant is 20,000 m 2 For solar thermal collection alone, the second-class lighting resources save 34.9 million kW·h annually and reduce CO2 emissions by 10,600 tons; the third-class lighting resources save 30.2 million kW·h annually and reduce CO2 emissions by 9,200 tons.

[0110] The present invention adopts two-stage heat exchange and heat recovery. The temperature of the first stage heat exchange rises by 5.0℃ (oxidation ditch) to 18.7℃, and the temperature of the second stage heat exchange and heat recovery rises by 9.3℃ to 28℃. That is, only the second stage heat recovery raises the water temperature by 14.3℃.

[0111] The anaerobic tank's own biogas, used to heat the boiler, raises the water temperature by 1.5°C to 29.5°C. Finally, the water is heated by a variable-frequency heating device, raising the temperature from 29.5°C to 36°C before being pumped into the anaerobic tank. This applies to operating conditions in northern China during the months of December, January, February, and March. During the five months from May to September, as ambient temperatures rise and solar radiation increases, ultra-low energy consumption can be achieved through a combination of insulation, heat collection, and heat recovery. Adding solar photovoltaic and solar thermal systems to the sewage treatment plant's site offers the prospect of zero-carbon operations.

[0112] During the five months from May to September, the average ambient temperature is 25°C, and the incoming water temperature is 23°C. After being retained in a sedimentation tank, the temperature rises to 25.5°C, and then undergoes secondary heat exchange and biogas heating, achieving ultra-low energy consumption.

[0113] Biochemical degradation of wastewater is a common and relatively inexpensive method for treating industrial and agricultural wastewater. Existing sewage treatment plants can be retrofitted using the process of this invention by adding the enclosure heat collection and heat recovery equipment of this invention. New plants can also be designed and constructed directly using the process of this invention. This will achieve the ultra-low energy consumption biochemical treatment of wastewater achieved by this invention.

[0114] This invention is a systems engineering project involving multiple composite technologies, including assembly construction, thermal insulation, solar thermal collection, and heat exchange. The resulting effects generate significant economic and social benefits, including environmental protection, energy conservation, and emission reduction. If this invention is promoted in the biochemical sewage treatment industry, it will have significant implications for the development of environmental protection.

[0115] Of course, the above contents are only preferred embodiments of the present invention and should not be considered as limiting the scope of the embodiments of the present invention. The present invention is not limited to the above examples. Equivalent changes and improvements made by ordinary technicians in this technical field within the essential scope of the present invention should all fall within the scope of the patent of the present invention.

Claims

1. An ultra-low energy consumption thermal energy internal circulation wastewater biochemical treatment process, characterized by: The following steps are involved: (1) After the sewage is discharged into the water collection well, it flows into a sedimentation tank. In the sedimentation tank, the temperature drop caused by the convection between the sewage and the environment is blocked by the outer enclosure structure a and the inner enclosure structure a. In addition, in the sedimentation tank, the temperature of the space between the sewage surface and the enclosure structure is increased by setting the heat-absorbing coating carrier, heat-absorbing material and heat-absorbing tank wall. (2) The low-temperature water from the first sedimentation tank enters the primary heat exchanger. After heat exchange with the high-temperature sewage discharged from the oxidation ditch, the temperature of the sewage rises and continues to enter the secondary heat exchanger. After heat exchange with the high-temperature sewage discharged from the anaerobic tank, it enters the heating boiler and is pumped into the anaerobic tank after heating for anaerobic treatment. (3) The temperature of the sewage at the outlet of the anaerobic tank is high. The heat is processed by the secondary heat exchanger, and part of the heat is supplied to the sewage at the inlet of the anaerobic tank in step (2) to increase the temperature. The second stage heat exchanger recovers part of the heat discharged from the anaerobic tank, and then sends it to the anaerobic tank after boiler heating and frequency conversion heating. The boiler heating adopts the biogas generated by the anaerobic tank for heating. (4) The sewage discharged from the anaerobic tank continues to enter the oxidation ditch. The oxidation ditch uses the inner enclosure structure b and the outer enclosure structure b to isolate the temperature drop caused by convection between the sewage and the environment, and places heat-absorbing materials in the oxidation ditch to absorb solar heat energy, thereby maintaining and increasing the temperature of the space between the sewage surface and the enclosure structure; The temperature of the sewage discharged from the oxidation ditch is high, and it passes through the first-stage heat exchanger to supply heat to the sewage from the first sedimentation tank in step (1); (5) The sewage from the oxidation ditch is discharged into the secondary sedimentation tank after heat exchange; An ultra-low energy consumption thermal energy internal circulation sewage biochemical treatment system comprises a water collection well (1), a settling tank (2), an oxidation ditch (3), an anaerobic tank (4), and a secondary settling tank (5). The water collection well (1) is connected to the first settling tank (2), the first settling tank (2) is connected to a heating boiler (41) via a first heat exchanger (7) and a second heat exchanger (8) in sequence, and the heating boiler (41) is connected to the anaerobic tank (4); the outlet of the anaerobic tank (4) is connected to the oxidation ditch (3) via the second heat exchanger (8); the outlet of the oxidation ditch (3) is connected to the secondary settling tank (5) via the first heat exchanger (7); the first heat exchanger (7) or the second heat exchanger (8) is a tubular heat exchanger (9) or a tower heat exchanger (15); a variable frequency heating device (6) is provided between the heating boiler (41) and the anaerobic tank (4); The tubular heat exchanger (9) is connected in series in multiple groups, and an external sedimentation and drainage device (10) is provided on the pipeline between the two groups. The external sedimentation and drainage device (10) is a hollow structure in which two cones are fixed together. A drainage valve b (101) is provided at the bottom of the external sedimentation and drainage device (10); an internal sedimentation and drainage device (92) is provided inside the tubular heat exchanger (9), and a drainage valve a (93) is provided at the bottom of the internal sedimentation and drainage device (92); One end of the tower heat exchanger (15) is provided as a sedimentation cone (154), and a drain valve c (156) is provided at the bottom of the sedimentation cone (154); An open-air portion of a sedimentation tank (2) is provided with an outer enclosure structure a (201) and an inner enclosure structure a (202); A heat absorbing material (204) is placed in a sedimentation tank (2) or an oxidation ditch (3); The open-air portion of the oxidation ditch (3) is provided with an inner enclosure structure b (301) and an outer enclosure structure b (302).

2. The ultra-low energy consumption thermal energy internal circulation sewage biochemical treatment process according to claim 1 is characterized by: The anaerobic tank produces its own biogas, which is used to heat the boiler and increase the sewage temperature at the anaerobic tank inlet by 2-5℃.

3. The ultra-low energy consumption thermal energy internal circulation sewage biochemical treatment process according to claim 1 is characterized by: The average ambient temperature in December, January, February and March is -2°C. The temperature of the sewage discharged into the collection well in step (1) is 10-20°C. The residence time of the sewage discharged into the first sedimentation tank is 24-48 hours. After being enclosed and absorbing heat in the first sedimentation tank, the temperature of the sewage discharged from the first sedimentation tank is 12-15°C.

4. The ultra-low energy consumption thermal energy internal circulation sewage biochemical treatment process according to claim 1 is characterized by: After the first-stage heat exchange in step (2), the sewage temperature rises by 4-6°C. After the second-stage heat exchange, the sewage temperature rises by 7-10°C. Then, the sewage is heated by the self-produced biogas in the anaerobic tank through frequency conversion, so that the temperature reaches the anaerobic required temperature.

5. The ultra-low energy consumption thermal energy internal circulation sewage biochemical treatment process according to claim 1 is characterized by: The temperature of the sewage discharged from the anaerobic tank in step (4) is 30-35°C. After the enclosure structure and heat absorption treatment of the oxidation ditch, the temperature of the sewage at the inlet of the oxidation ditch reaches 26-30°C.

6. The ultra-low energy consumption thermal energy internal circulation sewage biochemical treatment process according to claim 1 is characterized by: A heat exchange tube a (91) is provided inside the tubular heat exchanger (9), a cold medium inlet pipe a (13) and a cold medium outlet pipe a (14) are connected to the heat exchange tube a (91), and a limited fixing frame a (94) is provided between the heat exchange tubes a (91); the outermost layer of the tubular heat exchanger (9) is a shell a (95), and a heat insulation filling layer a (96) is provided between the shell a (95) and the main body of the tubular heat exchanger (9); the main body of the tubular heat exchanger (9) is connected to the hot medium inlet a (11) and the hot medium outlet a (12).

7. The ultra-low energy consumption thermal energy internal circulation wastewater biochemical treatment process according to claim 1 is characterized by: The outermost layer of the tower heat exchanger (15) is a shell b (152), a heat-insulating filling layer b (153) is provided between the shell b (152) and the main body of the tower heat exchanger (15), heat exchange tubes b (151) are provided inside the tower heat exchanger (15), and a limiting fixing frame b (155) is provided between the heat exchange tubes b (151), the main body of the tower heat exchanger (15) is connected to the heat medium inlet b (1591) and the heat medium outlet b (1592); the heat exchange tubes b (151) are connected to the cold medium inlet pipeline b (157) and the cold medium outlet pipeline b (158).

8. The ultra-low energy consumption thermal energy internal circulation wastewater biochemical treatment process according to claim 1 is characterized by: An open-air portion of a sedimentation tank (2) is provided with an outer protective structure a (201) and an inner protective structure a (202) through a steel structure; the outer layer of the outer protective structure a (201) is provided with a heat-absorbing coating carrier (203), and the outer protective structure a (201) and the inner protective structure a (202) form an arch structure; a heat-absorbing tank wall (206) is provided on the inner side of a sedimentation tank wall (205) of the sedimentation tank (2); and a rotating mechanism (207) is provided inside the sedimentation tank (2).

9. The ultra-low energy consumption thermal energy internal circulation wastewater biochemical treatment process according to claim 1 is characterized by: The open-air portion of the oxidation ditch (3) is provided with an inner enclosure structure b (301) and an outer enclosure structure b (302) through a steel structure, and a triangular enclosure structure or an arched enclosure structure is formed between the inner enclosure structure b (301) and the outer enclosure structure b (302) and the oxidation ditch (3); the oxidation ditch (3) is in a parallel strip shape, and the enclosure mode of the inner enclosure structure b (301) and the outer enclosure structure b (302) for the oxidation ditch (3) is single ditch enclosure or overall enclosure.

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