Large-scale pig farm sewage treatment process for clear effluent

Abstract

The invention discloses a large-scale pig farm sewage treatment process with clear effluent. The large-scale pig farm sewage treatment process comprises the following steps: S1, stacked screw machine treatment; S2, anaerobic fermentation; S3, primary biochemical treatment; according to the method, firstly, the cationic PAM is used as a coagulant aid to be matched with the stacked screw machine for use, meanwhile, the cationic PAM is added in the form of a low-concentration aqueous solution, so that the breeding sewage of the pig farm can be effectively flocculated in a stirring tank of the stacked screw machine, and suspended solids in the sewage of the pig farm can be efficiently removed after the sewage is treated by the stacked screw machine; after primary and secondary biochemical treatment, ozone disinfection and decolorization treatment is combined, so that the water quality indexes of effluent all reach the primary B standard of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant GB18918-2002; and the process disclosed by the invention is low in manufacturing cost, low in operation cost and efficient in treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and particularly to a sewage treatment process for pig farms with large-scale clear effluent. Background Art

[0002] As a major pig-raising country in the world, a large amount of fecal sewage is generated by large-scale farms in China every year. Pig farm wastewater is "three-high" wastewater with high organic matter concentration, high nitrogen and phosphorus content, and a large number of harmful microorganisms. If it is directly discharged into water bodies or stored in inappropriate locations and washed into water bodies by rain, it may cause serious deterioration of surface water or groundwater quality. How to purify pig farm sewage has increasingly become a restricting factor for the sustainable production of large-scale pig farms. Developing recyclable, efficient, and low-cost sewage treatment technologies is an important measure for the sustainable development of large-scale pig breeding.

[0003] In recent years, a new idea of coupling pig farm sewage purification with microalgae biomass production has emerged as a resource treatment method for pig farm sewage. For example, the invention patent with the publication number CN107265725A discloses a method for treating pig farm sewage by ozone for microalgae cultivation. First, the pig farm breeding sewage after multi-stage filtration is sent into a primary ozone processor in the form of spray for decolorization and sterilization treatment with ozone. The effluent is then sent into a secondary ozone aeration processor for secondary ozone aeration treatment, and finally sent into a tertiary air aeration processor to blow off ozone. The water treated by this method can be directly used for microalgae cultivation, but the nitrogen and phosphorus content in it is still relatively high and cannot be directly discharged.

[0004] The invention patent with the publication number CN1167154396A discloses a method for treating pig breeding wastewater. The invention points out that the organic matter in the manure water is degraded into small molecules or residues by the enhanced oxidation method. After flocculation and sedimentation and solid-liquid separation, all indicators can reach the discharge standard after treatment. Moreover, through pretreatment, the pollutant load of the wastewater can be reduced. With the help of anaerobic biochemical treatment, the organic matter in the sewage is decomposed, metabolized, and digested by anaerobic bacteria, resulting in a significant reduction in the organic matter content in the sewage. Aerobic biochemical treatment is used to decompose the organic matter in the wastewater by microorganisms under aerobic conditions and synthesize activated sludge at the same time. Finally, considering the large amount of urine in pig breeding wastewater, the phosphorus element passivation means is used to achieve the purpose of neutralizing and inhibiting the phosphorus element in the pig manure and urine existing in the wastewater. However, the invention does not indicate what the specific substances of the added medicament B, flocculant C, etc. are, nor does it give their addition amounts, and even less does it give the specific treatment effects. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a sewage treatment process for pig farms with large-scale clear effluent that can efficiently treat pig farm sewage and has low cost.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A sewage treatment process for pig farms with large-scale clear effluent, comprising the following steps:

[0008] S1. Treatment by a spiral press filter:

[0009] Send the pig farm breeding sewage into the spiral press filter, add the medicament and stir, then carry out extrusion to obtain solid I and liquid I respectively, and the solid I is subjected to composting treatment; among them,

[0010] The medicament is cationic PAM (polyacrylamide);

[0011] When the suspended solid content in the pig farm breeding sewage sent into the spiral press filter is 20 - 40 g / L, the dosage of the medicament is calculated as adding 0.9 - 1.1 Kg of the medicament per 6 cubic meters of pig farm breeding sewage;

[0012] The medicament is added in the form of a cationic PAM aqueous solution, and the concentration of the cationic PAM aqueous solution is 1 - 2 wt‰;

[0013] S2. Anaerobic fermentation:

[0014] Send the liquid I into a black film anaerobic pond for anaerobic fermentation, control the hydraulic retention time of the black film anaerobic pond to be 20 - 30 days, and the effluent of the black film anaerobic pond enters the regulation pond;

[0015] S3. Primary biochemical treatment:

[0016] Send the sewage in the regulation pond into the primary anoxic pond, and then enter the primary sedimentation tank after passing through the primary aerobic pond; set a reflux between the primary aerobic pond and the primary anoxic pond, and control the reflux ratio from the primary aerobic pond to the primary anoxic pond to be 2 - 5:1;

[0017] Aerobic bacteria or bacterial sludge are put in the primary anoxic pond, aerobic bacteria or bacterial sludge are put in the primary aerobic pond and aeration is required; biological fillers are arranged in the primary anoxic pond and the primary aerobic pond;

[0018] S4. Secondary biochemical treatment:

[0019] The effluent of the primary sedimentation tank passes through the secondary anoxic pond and the secondary aerobic pond and then enters the secondary sedimentation tank. Set a reflux between the secondary aerobic pond and the secondary anoxic pond, and control the reflux ratio from the secondary aerobic pond to the secondary anoxic pond to be 2 - 5:1;

[0020] Aerobic bacteria or bacterial sludge are put in the secondary anoxic pond, aerobic bacteria or bacterial sludge are put in the secondary aerobic pond and aeration is required; biological fillers are arranged in the secondary anoxic pond and the secondary aerobic pond;

[0021] S5. Ozone disinfection and decolorization treatment:

[0022] The effluent from the secondary sedimentation tank is sent to the oxidation tank, and ozone is input from the bottom of the tank in an aeration manner. The ozone input amount is calculated as 1.5 - 3 mg of ozone per liter of the liquid in the tank.

[0023] In the process of the present invention, cationic PAM is creatively used as a coagulant aid in combination with a spiral press, and at the same time, cationic PAM is added in the form of a low-concentration aqueous solution, which can effectively flocculate the pig farm breeding sewage in the stirring tank of the spiral press, so that the removal rate of suspended solids in the effluent treated by the spiral press can reach more than 97%, and the removal rates of BOD and COD also reach more than 35%. The molecular weight of the cationic PAM described in the present invention is between 7 million and 12 million.

[0024] In the process of the present invention, the pig farm breeding sewage sent to the spiral press is obtained by using the existing conventional mechanical manure scraping process or flushing the pig farm with a high-pressure water gun. This sewage is usually collected in a sewage collection tank and then sent to subsequent treatment.

[0025] In step S1 of the above process, further, when the content of suspended solids in the pig farm breeding sewage sent to the spiral press is 29 - 40 g / L, the dosage of the agent is calculated as adding 0.9 - 1.1 Kg of the agent per 6 cubic meters of pig farm breeding sewage; the concentration of the cationic PAM aqueous solution is more preferably 1 - 1.5 wt‰. In order to reduce the working load of the spiral press, solid-liquid separation can also be carried out once by a solid-liquid separator before sending the pig farm breeding sewage into the spiral press, and the effluent is then sent to the spiral press for treatment.

[0026] In step S2 of the above process, the temperature of the sewage in the black film anaerobic pond usually remains at 15 - 35 °C. In winter with lower temperatures, the black film anaerobic pond can be insulated by covering foam boards or carpets around the black film anaerobic pond; in summer with higher temperatures, if necessary, some cold water (such as tap water or groundwater) can be introduced into the black film anaerobic pond to cool the black film anaerobic pond.

[0027] In step S3 of the above process, when aerobic bacteria are selected for dosing in the first-stage anoxic tank or the first-stage aerobic tank, the dosing amount of aerobic bacteria in the first-stage anoxic tank or the first-stage aerobic tank is preferably calculated as 50 - 60 g of aerobic bacteria added per cubic meter of the liquid in the tank. The aerobic bacteria are directly purchased from the market, such as the aerobic bacteria produced by companies like Weifang Fanxing Biotechnology Co., Ltd., Guangzhou Dongling Biotechnology Co., Ltd., Henan Hanxin Water Purification Materials Co., Ltd., etc. When the first-stage anoxic tank or the first-stage aerobic tank selects to dose strain sludge, the dosing amount of strain sludge in the first-stage anoxic tank or the first-stage aerobic tank is preferably calculated as 1 - 3% of the effective volume of the first-stage anoxic tank or the first-stage aerobic tank. This strain sludge is activated sludge, which can be the activated sludge obtained by conducting conventional aerobic cultivation on the aerobic bacteria directly purchased from the market; it can also be the activated sludge purchased from the local sewage treatment plant; or it can be obtained by extracting the activated sludge at the bottom of the sewage sedimentation tank of other pig farms of the same type.

[0028] In step S4 of the above process, the dosing amount of aerobic bacteria in the second-stage anoxic tank and the second-stage aerobic tank is calculated as 50 - 60 g of aerobic bacteria added per cubic meter of the liquid in the tank. The dosing amount of strain sludge in the second-stage anoxic tank and the second-stage aerobic tank is calculated as 1 - 3% of the effective volume of the second-stage aerobic tank. The acquisition methods of aerobic bacteria or strain sludge in the second-stage anoxic tank and the second-stage aerobic tank are the same as those described above.

[0029] In steps S3 and S4 of the above process, by setting biological fillers, the strains in the tank can adhere to them, so as to reduce or even avoid the strains in the tank flowing out with the effluent. The biological fillers are preferably combined fillers. Usually, they are longitudinally arranged in the second-stage anoxic tank and the second-stage aerobic tank, and the distance between adjacent two columns of biological fillers is 15 - 25 cm.

[0030] In steps S3 and S4 of the above process, the aeration volume in the first-stage aerobic tank and the second-stage aerobic tank is 1.5 - 2.5 Kg of air / m 3 / h, that is, it is calculated as 1.5 - 2.5 Kg of air is aerated per cubic meter of the tank volume per hour.

[0031] When the sludge sedimentation in the secondary sedimentation tank is not very good, a sedimentation treatment step can also be set after step S4 and before step S5, that is, step S40 sedimentation treatment. Specifically, the effluent from the secondary sedimentation tank is sent to the final sedimentation tank for re-precipitation, and the effluent from the final sedimentation tank is then subjected to ozone disinfection and decolorization treatment.

[0032] In the above process, when the sludge in the primary sedimentation tank, the secondary sedimentation tank and the final sedimentation tank reaches a certain level, sludge discharge is required. Generally, it is considered that sludge discharge is required when the sedimentation ratio in the tank reaches 25 - 30%. During the normal operation of the system, the daily sludge discharge volume is 1 - 2% of the daily influent volume (volume). The discharged sludge is sent to the pretreatment tank and then enters the spiral press again for solid-liquid separation.

[0033] Compared with the prior art, the features of the present invention are as follows:

[0034] 1. Creatively, the present invention uses cationic PAM as a coagulant aid in combination with a spiral press, and at the same time adds cationic PAM in the form of a low-concentration aqueous solution, which can effectively flocculate the pig farm sewage in the stirring tank of the spiral press, so that the removal rate of suspended solids in the effluent treated by the spiral press can reach more than 97%, and the removal rates of BOD and COD also reach more than 35%.

[0035] 2. The present invention first uses a low-concentration cationic PAM solution in combination with a spiral press, and then combines ozone disinfection and decolorization treatment after primary and secondary biochemical treatments, so that the COD ≤ 80mg / L, BOD ≤ 50mg / L, ammonia nitrogen ≤ 30mg / L, total phosphorus ≤ 8mg / L, suspended solids (SS) ≤ 30mg / L in the effluent, and water quality indicators such as COD, BOD, and SS all meet the standard of Class B of Grade 1 in the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" GB18918-2002. The effluent can be directly discharged or reused, and can also be used for fish farming, irrigation, cleaning, etc.

[0036] 3. The process of the present invention has low construction cost, low operating cost, and high treatment efficiency. Brief Description of the Drawings

[0037] Figure 1 It is a flow chart of a sewage treatment process for a large-scale clear effluent pig farm according to the present invention. Detailed Embodiments

[0038] In order to better explain the technical solution of the present invention, the present invention will be further described in detail below in combination with embodiments, but the embodiments of the present invention are not limited thereto.

[0039] Embodiment 1

[0040] This embodiment is used to treat the sewage of a pig farm in the Zhulinshan Pig Farm in Daxu Town, Lingchuan County, Guilin City, Guilin City (the inventory of the pig farm is 5,000 heads). The flow chart of the treatment process is as Figure 1 shown. According to Figure 1 the said flow chart, the following several pools need to be constructed for sewage treatment:

[0041] 1. Sewage collection pool: Collect the sewage discharged from the pig farm using the mechanical manure scraping process. The size of the sewage collection pool is constructed according to the scale of the pig farm. Usually, the volume of the sewage collection pool needs to be greater than or at least equal to the daily sewage discharge of the pig farm. In this example, the specification of the sewage collection pool is 4m × 4m × 4.5m (length × width × height, the same below).

[0042] 2. Pretreatment Pool: Store the liquid discharged from the solid-liquid separator. In this example, the specifications of the pretreatment pool are 4m × 4m × 4.5m.

[0043] 3. Black Membrane Anaerobic Pond: Used for anaerobic fermentation, where microorganisms degrade or convert organic matters such as macromolecules and large particles into gases, etc. In this example, the specifications of the black membrane anaerobic pond are 32m × 26m × 7m.

[0044] 4. Regulation Pond: Store the water discharged from the black membrane anaerobic pond to reduce the impact load of the influent water in the first-stage anoxic pond. In this example, the specifications of the regulation pond are 3m × 10m × 4.5m.

[0045] 5. First-stage Anoxic Pond: Conduct denitrification reactions to remove ammonia nitrogen, total phosphorus, COD, etc. In this example, the specifications of the first-stage anoxic pond are 3m × 10m × 4.5m.

[0046] 6. First-stage Aerobic Pond: Nitrification reaction, where organic matters are degraded under the action of aerobic bacteria. In this example, the specifications of the first-stage aerobic pond are 9m × 10m × 4.5m.

[0047] 7. Primary Sedimentation Pond: Degradation, sludge discharge, and reduction of the subsequent treatment load. In this example, the specifications of the primary sedimentation pond are 3m × 2.5m × 4.5m.

[0048] 8. Second-stage Anoxic Pond: Conduct denitrification reactions to remove ammonia nitrogen, total phosphorus, COD, etc. In this example, the specifications of the second-stage anoxic pond are 3m × 4.25m × 4.5m.

[0049] 9. Second-stage Aerobic Pond: Nitrification reaction, where organic matters are degraded under the action of aerobic bacteria. In this example, the specifications of the second-stage aerobic pond are 3m × 12.75m × 4.5m.

[0050] 10. Secondary Sedimentation Pond: Degradation, sludge discharge, and reduction of the subsequent treatment load. In this example, the specifications of the secondary sedimentation pond are 3m × 3m × 4.5m.

[0051] 11. Final Sedimentation Pond: Re-sedimentation, increasing the retention time of the sewage, and minimizing the suspended solids in the effluent as much as possible. In this example, the specifications of the final sedimentation pond are 3m × 4.25m × 4.5m.

[0052] 12. Oxidation Pond: Sterilization, decolorization, reduction of COD and BOD, and purification of water quality. In this example, the specifications of the oxidation pond are 1m × 1m × 3m.

[0053] 13. Clear Water Pond: Store the water treated by this process. In this example, the specifications of the clear water pond are 4m × 4m × 4.5m.

[0054] The large-scale clear effluent pig farm sewage treatment process of the present invention includes the following steps:

[0055] S0. Pretreatment:

[0056] The manure and urine in the pig farm are scraped out and flushed by a mechanical manure scraping process, and the discharged sewage is collected in a sewage collection tank.

[0057] The sewage in the sewage collection tank is pumped into a solid-liquid separator for solid-liquid separation. The effluent flows into a pretreatment tank, and the solid part is composted.

[0058] S1. Treatment by a spiral press filter:

[0059] The sewage in the pretreatment tank is pumped into a spiral press filter (the flow rate of the sewage is 6 m 3 / h). After adding a chemical agent and stirring for 15 - 30 s, extrusion is carried out to obtain solid I and liquid I respectively. Liquid I enters a black membrane anaerobic tank, and solid I and the solid part separated by the previous solid-liquid separator are collected together for composting treatment; among them,

[0060] The chemical agent is cationic PAM (molecular weight is 12 million);

[0061] The dosage of the chemical agent is calculated as 1.0 Kg of the chemical agent is added per 6 cubic meters of sewage;

[0062] The chemical agent is added in the form of a cationic PAM aqueous solution. The concentration of the cationic PAM aqueous solution is 1 wt‰, and the flow rate of the cationic PAM aqueous solution is 0.6 m 3 / h.

[0063] S2. Anaerobic fermentation:

[0064] The sewage treated by the spiral press filter flows into a black membrane anaerobic tank for anaerobic fermentation. The temperature of the liquid in the black membrane anaerobic tank is maintained at 20 - 35 °C, the hydraulic retention time of the black membrane anaerobic tank is controlled at 30 days, and the effluent of the black membrane anaerobic tank enters a regulation tank.

[0065] S3. Primary biochemical treatment:

[0066] Combined fillers are arranged in the primary anoxic tank and the primary aerobic tank respectively, adopting a longitudinal arrangement method. The distance between adjacent two columns of biological fillers is 15 - 25 cm; a submersible mixer (the axial thrust of the submersible mixer is 0.15 - 0.2 N / m 3 ) is also installed in the primary anoxic tank.

[0067] The sewage in the regulation tank is pumped into the primary anoxic tank, and aerobic bacteria (Guangzhou Dongling Biology Co., Ltd.) are put into it. The dosage is calculated as 55 g of aerobic bacteria is added per cubic meter of the liquid in the tank. When the removal rates of BOD and COD in the effluent of the primary anoxic tank (relative to the influent of the primary anoxic tank) reach 75%, the cultivation of the strains ends.

[0068] After the cultivation of the bacteria in the first-stage anoxic tank is completed, the effluent of the first-stage anoxic tank can be connected to the first-stage aerobic tank, and aerobic bacteria (Henan Hanxin Water Purification Materials Co., Ltd.) are added to the first-stage aerobic tank. The dosage is calculated as 55 g of aerobic bacteria per cubic meter of the liquid in the tank. At the same time, aeration is carried out in the first-stage aerobic tank, and the aeration volume is 1.5 - 2.5 Kg of air / m 3 / h. When the removal rates of BOD and COD in the effluent of the first-stage aerobic tank (relative to the influent of the first-stage aerobic tank) reach 70%, the effluent of the first-stage aerobic tank is connected to the primary sedimentation tank. A reflux is set between the first-stage aerobic tank and the first-stage anoxic tank, and the reflux ratio from the first-stage aerobic tank to the first-stage anoxic tank is controlled at 4:1.

[0069] S4. Secondary biochemical treatment:

[0070] Combined fillers are arranged in the second-stage anoxic tank and the second-stage aerobic tank respectively, adopting a longitudinal arrangement method. The distance between adjacent two columns of biological fillers is 15 - 25 cm; a submersible mixer is also installed in the second-stage anoxic tank (the axial thrust of the submersible mixer is 0.15 - 0.2 N / m 3 ).

[0071] The effluent of the primary sedimentation tank is connected to the second-stage anoxic tank, and aerobic bacteria (Guangzhou Dongling Biology Co., Ltd.) are added to it. The dosage is calculated as 55 g of aerobic bacteria per cubic meter of the liquid in the tank. When the removal rates of BOD and COD in the effluent of the second-stage anoxic tank (relative to the influent of the second-stage anoxic tank) reach 60%, the cultivation of the bacteria ends.

[0072] After the cultivation of the bacteria in the second-stage anoxic tank is completed, the effluent of the second-stage anoxic tank can be connected to the second-stage aerobic tank, and aerobic bacteria (Henan Hanxin Water Purification Materials Co., Ltd.) are added to the second-stage aerobic tank. The dosage is calculated as 55 g of aerobic bacteria per cubic meter of the liquid in the tank. At the same time, aeration is carried out in the second-stage aerobic tank, and the aeration volume is 1.5 - 2.5 Kg of air / m 3 / h. When the removal rates of BOD and COD in the effluent of the second-stage aerobic tank (relative to the influent of the second-stage aerobic tank) reach 60%, the effluent of the second-stage aerobic tank is connected to the intermediate sedimentation tank. A reflux is set between the second-stage aerobic tank and the second-stage anoxic tank, and the reflux ratio from the second-stage aerobic tank to the second-stage anoxic tank is controlled at 4:1.

[0073] From the time when the sewage in the collection tank enters the solid-liquid separator until the above-mentioned reflux from the second-stage aerobic tank to the second-stage anoxic tank is completed, it takes 55 days. At this time, the whole system starts to operate in a continuous influent mode.

[0074] S40. Sedimentation treatment:

[0075] The effluent of the secondary sedimentation tank is connected to the final sedimentation tank for re-precipitation, and the effluent of the final sedimentation tank is sent to the oxidation tank.

[0076] S5. Ozone disinfection and decolorization treatment:

[0077] The effluent from the secondary sedimentation tank is fed into the oxidation tank, and ozone is input from the bottom of the tank in an aeration manner. The ozone input amount is calculated as 1.5 - 3 mg of ozone per liter of the liquid in the tank. The effluent from the oxidation tank flows into the clear water tank. The hydraulic retention time of the oxidation tank is 3.5 h.

[0078] During the above treatment process, when the sedimentation ratio in the primary sedimentation tank, secondary sedimentation tank and final sedimentation tank reaches 25 - 30%, sludge discharge is required. After the system operates normally, the daily sludge discharge amount is 1 - 2% of the daily influent volume. The discharged sludge is returned to the pretreatment tank and then enters the spiral press again for solid-liquid separation.

[0079] After the continuous flow operation starts, the indexes such as BOD, COD, suspended solids, etc. of the water body or effluent in the sewage collection tank, pretreatment tank, before and after the spiral press treatment, black film anaerobic tank, etc. are detected, and the results are shown in Table 1 below.

[0080] Table 1:

[0081]

[0082]

[0083] The project cost and operation cost of constructing the above system in the present invention are shown in Table 2 below.

[0084] Table 2:

[0085]

[0086] Comparative Example 1

[0087] Repeat Example 1, except that in the spiral press treatment step, cationic PAM is prepared into a concentration of 4 wt‰ and added, and the others remain unchanged. The effluent indexes after the spiral press treatment are detected, and at the same time, the water in the clear water tank is detected, as shown in Table 3 below.

[0088] Comparative Example 2

[0089] Repeat Example 1, except that in the spiral press treatment step, the medicament is changed to anionic PAM (molecular weight of 12 million), and it is also prepared into a concentration of 1 wt‰ and added, and the others remain unchanged. The effluent indexes after the spiral press treatment are detected, and at the same time, the water in the clear water tank is detected, as shown in Table 3 below.

[0090] Comparative Example 3

[0091] Repeat Example 1, except that in the screw press treatment step, the chemicals are changed to the co - use of anionic PAM (molecular weight of 12 million) and polyaluminum chloride (PAC). Among them, the anionic PAM is calculated as 4 Kg added per 6 cubic meters of sewage, and PAC is calculated as 50 Kg added per 6 cubic meters of sewage; both are added in the form of aqueous solutions. The concentration of the anionic PAM aqueous solution is 4 wt‰, and the flow rate is 0.7 m3 / h; the concentration of the PAC aqueous solution is 5 wt%, and the flow rate is 0.9 m3 / h. The effluent indexes after the screw press treatment are detected, and at the same time, the water in the clear water tank is detected, as shown in Table 3 below.

[0092] Table 3:

[0093]

[0094]

[0095] It can be seen that the present invention uses cationic PAM as a coagulant aid in combination with a screw press, and adds the cationic PAM in the form of a low - concentration aqueous solution, which can effectively flocculate the pig farm breeding sewage in the screw press mixing tank, thereby effectively removing the suspended solids in the pig farm sewage.

Claims

1. A sewage treatment process for pig farms with large-scale clear effluent, comprising the following steps: S1. Treatment by a spiral press filter: Feed the pig farm sewage into the spiral press filter, add chemicals and stir, then perform extrusion to obtain solid I and liquid I respectively. Solid I is subjected to composting treatment. Among them, The chemical is cationic PAM; When the suspended solid content in the pig farm sewage fed into the spiral press filter is 20 - 40 g / L, the dosage of the chemical is calculated as adding 0.9 - 1.1 Kg of the chemical per 6 cubic meters of pig farm sewage; The chemical is added in the form of a cationic PAM aqueous solution, and the concentration of the cationic PAM aqueous solution is 1 - 2 wt‰; S2. Anaerobic fermentation: Liquid I is fed into a black membrane anaerobic pond for anaerobic fermentation. Control the hydraulic retention time of the black membrane anaerobic pond to be 20 - 30 days, and the effluent of the black membrane anaerobic pond enters the regulation pond; S3. Primary biochemical treatment: The sewage in the regulation pond is fed into the primary anoxic pond, and then enters the primary sedimentation tank after passing through the primary aerobic pond. A reflux is set between the primary aerobic pond and the primary anoxic pond, and control the reflux ratio from the primary aerobic pond to the primary anoxic pond to be 2 - 5:1; Aerobic bacteria or strain sludge is put in the primary anoxic pond, and aerobic bacteria or strain sludge is put in the primary aerobic pond and aeration is required. Biological fillers are arranged in the primary anoxic pond and the primary aerobic pond; S4. Secondary biochemical treatment: The effluent of the primary sedimentation tank passes through the secondary anoxic pond and the secondary aerobic pond and then enters the secondary sedimentation tank. A reflux is set between the secondary aerobic pond and the secondary anoxic pond, and control the reflux ratio from the secondary aerobic pond to the secondary anoxic pond to be 2 - 5:1; Aerobic bacteria or strain sludge is put in the secondary anoxic pond, and aerobic bacteria or strain sludge is put in the secondary aerobic pond and aeration is required. Biological fillers are arranged in the secondary anoxic pond and the secondary aerobic pond; S5. Ozone disinfection and decolorization treatment: The effluent of the secondary sedimentation tank is fed into the oxidation pond, and ozone is input from the bottom of the pond in an aeration manner. The ozone input amount is calculated as inputting 1.5 - 3 mg of ozone per liter of the liquid in the pond.

2. The large-scale clear effluent pig farm sewage treatment process according to claim 1, characterized in that, In step S1, when the suspended solid content in the pig farm sewage fed into the spiral press filter is 29 - 40 g / L, the dosage of the chemical is calculated as adding 0.9 - 1.1 Kg of the chemical per 6 cubic meters of pig farm sewage.

3. The swine farm sewage treatment process for large-scale clear water discharge according to claim 1, characterized in that, In step S2, the temperature of the sewage in the black membrane anaerobic pond is maintained at 15 - 35 °C.

4. The sewage treatment process for pig farms with large-scale clear effluent according to claim 1, characterized in that, In step S3, the dosage of aerobic bacteria in the primary anoxic pond or the primary aerobic pond is calculated as adding 50 - 60 g of aerobic bacteria per cubic meter of the liquid in the pond.

5. The sewage treatment process for pig farms with large-scale clear effluent according to claim 1, characterized in that, In step S3, the dosage of strain sludge in the primary anoxic pond or the primary aerobic pond is calculated as 1 - 3% of the effective volume of the primary anoxic pond or the primary aerobic pond.

6. The sewage treatment process for pig farms with large-scale clear effluent according to claim 1, characterized in that, In step S4, the dosage of aerobic bacteria in the secondary anoxic pond or the secondary aerobic pond is calculated as adding 50 - 60 g of aerobic bacteria per cubic meter of the liquid in the pond.

7. The large-scale clear effluent pig farm sewage treatment process according to claim 1, characterized in that, In step S4, the dosage of strain sludge in the secondary anoxic pond or the secondary aerobic pond is calculated as 1 - 3% of the effective volume of the secondary aerobic pond.

8. The large-scale clear effluent pig farm sewage treatment process according to claim 1, characterized in that, In steps S3 and S4, the biological filler is a combined filler.

9. The sewage treatment process for pig farms with large-scale clear effluent according to claim 1, characterized in that, The aeration volume in the primary aerobic pond and the secondary aerobic pond is calculated as aerating 1.5 - 2.5 Kg of air per cubic meter of the pond volume per hour.

10. The large-scale clear effluent pig farm sewage treatment process according to claim 1, characterized in that, After step S4 and before step S5, there is also a sedimentation treatment step, specifically sending the effluent from the secondary sedimentation tank to the final sedimentation tank for sedimentation, and then performing ozone disinfection and decolorization treatment on the effluent from the final sedimentation tank.

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