A method and device for treating mixed wastewater from lyocell fiber production

Abstract

The present invention relates to a method and device for treating mixed wastewater from lyocell fiber production, belonging to the field of viscose fiber production. The method comprises the following steps: (1) gradually reducing the dilution ratio of the mixed wastewater from lyocell fiber production, slowly increasing the inlet salinity, and repeatedly acclimating anaerobic denitrifying bacteria to obtain acclimated anaerobic denitrifying bacteria; (2) neutralizing the pH value of the mixed wastewater from lyocell fiber production with concentrated sulfuric acid, stirring and adjusting the pH value to neutral, and then performing anaerobic biochemical treatment using the acclimated anaerobic denitrifying bacteria; (3) performing aerobic biochemical treatment on the mixed wastewater from lyocell fiber production after anaerobic biochemical treatment, and finally achieving discharge standards. The present invention realizes biochemical process treatment of the mixed wastewater from lyocell fiber production by acclimating specific anaerobic bacteria in the mixed wastewater from lyocell fiber production. The method has the advantages of low energy consumption, simple equipment configuration, and convenient equipment maintenance.

Description

Technical Field

[0001] The invention relates to a method and a device for treating mixed wastewater from lyocell fiber production, and belongs to the field of viscose fiber production, in particular to the field of treating mixed wastewater from lyocell fiber production in viscose fiber water treatment. Background Art

[0002] The mixed wastewater from lyocell fiber production contains cellulose, NMMO, inorganic salts and other components. The mixed wastewater from lyocell fiber production discharged from the production workshop includes anionic and cationic wastewater. The discharge volume ratio is a mixed solution of anionic:cationic = 1.4. The pH value of the mixed solution is alkaline, the molecular weight is above 1000Da, accounting for about 76%, the B / C is about 20%, and the salt content is about 4%. The aerobic biodegradability of the mixed wastewater from lyocell fiber production is poor, and it is difficult to make it meet the discharge standards using simple aerobic biochemical technology.

[0003] Lyocell fiber production mixed wastewater has a high salt content, and most of the organic molecules contained in the wastewater have long chains, resulting in poor flocculation and strong stability. Currently, most viscose lyocell fiber production mixed wastewater in China is treated using advanced oxidation technology before being discharged to a biochemical process for further treatment. This technology has high operating costs and produces large amounts of solid waste, which can easily cause secondary pollution. Another industry method is to evaporate and concentrate some highly concentrated wastewater to achieve zero wastewater discharge, but this method requires high energy and requires corresponding waste gas treatment capacity. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method and apparatus for treating mixed wastewater from lyocell fiber production. By gradually reducing the dilution factor of the mixed wastewater and slowly increasing the influent salinity, anaerobic denitrifying bacteria adapted to the mixed wastewater are obtained. After anaerobic biochemical treatment by the adapted anaerobic denitrifying bacteria, the mixed wastewater is then subjected to aerobic biochemical treatment, thereby achieving the goal of treating the mixed wastewater to meet discharge standards.

[0005] A technical solution of the present invention to solve the above technical problem is as follows: A method for treating mixed wastewater from lyocell fiber production comprises the following steps:

[0006] (1) By gradually reducing the dilution ratio of the mixed wastewater produced by lyocell fiber and slowly increasing the salinity of the influent, the anaerobic denitrifying bacteria are domesticated multiple times to obtain domesticated anaerobic denitrifying bacteria;

[0007] (2) neutralizing the pH value of the mixed wastewater from lyocell fiber production with concentrated sulfuric acid, stirring it evenly and adjusting it to neutral, and then performing anaerobic biochemical treatment using domesticated anaerobic denitrifying bacteria;

[0008] (3) The mixed wastewater from lyocell fiber production after anaerobic biochemical treatment is then aerobic biochemically treated and finally discharged in compliance with the standards.

[0009] The beneficial effects of the present invention are as follows: the present invention realizes biochemical process treatment of mixed wastewater from lyocell fiber production by domesticating specific anaerobic bacteria species from mixed wastewater from lyocell fiber production, and has the advantages of low energy consumption, simple equipment configuration, and easy equipment maintenance.

[0010] NMMO, a carbocyclic compound containing amines, is found in mixed wastewater from lyocell fiber production. It has a strong solubility for cellulose and produces ammoniacal nitrogen during hydrolysis. This process involves acclimating an anaerobic denitrifying bacterium and applying it to the anaerobic treatment of mixed wastewater from lyocell fiber production. The acclimation process improves the salt tolerance and load-bearing capacity of the anaerobic denitrifying bacteria. The acclimated anaerobic denitrifying bacteria then undergo anaerobic biochemical treatment, degrading large-chain organic molecules in the wastewater and improving its biodegradability. This effluent is then subjected to aerobic biochemical treatment, ultimately ensuring that discharge indicators meet discharge standards. This process has low operating costs and simple acclimation steps, making it suitable for treating mixed wastewater from lyocell fiber production.

[0011] On the basis of the above technical solution, the present invention can also be improved as follows.

[0012] Furthermore, in the step (1), during the multiple domestication of anaerobic denitrifying bacteria, clean water is used for dilution in the early stage and sodium sulfate solution is used for dilution in the later stage. The concentration of the sodium sulfate solution is the same as the salt concentration in the mixed wastewater of lyocell fiber production.

[0013] The beneficial effect of adopting this further solution is that, because the salinity of the mixed wastewater from lyocell fiber production is relatively high, and the main contributor to its salinity is sodium sulfate, this patent uses a sodium sulfate solution with the same salt concentration as the mixed wastewater from lyocell fiber production as the dilution water to dilute the original mixed wastewater during the anaerobic denitrifying bacteria acclimation process. This later dilution process ensures that the salinity of the wastewater remains unchanged, aiming to enable the denitrifying bacteria to be tolerant to salt and high loads during the anaerobic process.

[0014] Furthermore, the step (1) specifically includes the following steps:

[0015] a. Dilute the mixed wastewater from lyocell fiber production with clean water 4 times, adjust the pH value of the wastewater to neutral with 93%-98% concentrated sulfuric acid, and add it to the anaerobic tank equipped with a biochemical filler bed and anaerobic denitrifying bacteria. The concentration of the solution added by anaerobic denitrifying bacteria is 800-1200 mg / L, and the volume load is controlled at 0.8-1 kgCOD / (m 3 d) Acquire acclimated bacteria 1 on the biochemical filler bed in the anaerobic tank with a residence time of 72-96 hours and a temperature control of 35-45°C;

[0016] b. Dilute the mixed wastewater from lyocell fiber production with clean water three times, adjust the pH value of the wastewater to neutral with 93%-98% concentrated sulfuric acid, and add it to the anaerobic tank equipped with a biochemical filler bed and acclimated bacteria. The volume load is controlled at 1.3-2 kg COD / (m 3 d) The residence time is 48-72 hours, and the temperature is controlled at 35-45°C. This step is repeated twice to obtain the second acclimated bacteria on the biochemical filler bed in the anaerobic tank;

[0017] c. Dilute the mixed wastewater from lyocell fiber production with clean water for 2 times, adjust the pH value of the wastewater to neutral with 93%-98% concentrated sulfuric acid, and add it to the anaerobic tank equipped with biochemical filler bed and acclimated bacteria II, and control the volume load at 2-3 kgCOD / (m 3 d) The residence time is 48-72 hours, and the temperature is controlled at 35-45°C. This step is performed once to obtain acclimated bacteria 3 on the biochemical filler bed in the anaerobic tank;

[0018] d. Dilute the mixed wastewater from lyocell fiber production with sodium sulfate solution for 2 times, adjust the pH value of the wastewater to neutral with 93%-98% concentrated sulfuric acid, and add it to the anaerobic tank equipped with biochemical filler bed and acclimated bacteria. The volume load is controlled at 2-3 kg COD / (m 3 d) The residence time is 48-72 hours, and the temperature is controlled at 35-45°C. This step is repeated twice to obtain acclimated bacteria 4 on the biochemical filler bed in the anaerobic tank;

[0019] e. Dilute the mixed wastewater from lyocell fiber production with sodium sulfate solution by 1.8 times, adjust the pH value of the wastewater to neutral with 93%-98% concentrated sulfuric acid, and add it to the anaerobic tank equipped with biochemical filler bed and acclimated bacteria 4, and control the volume load at 4-7kgCOD / (m 3 d) The residence time is 24-36 hours, and the temperature is controlled at 35-45°C. This step is repeated twice to obtain acclimated bacteria 5 on the biochemical filler bed in the anaerobic tank;

[0020] f. Dilute the mixed wastewater from lyocell fiber production with sodium sulfate solution by 1.5 times, adjust the pH value of the wastewater to neutral with 93%-98% concentrated sulfuric acid, and add it to the anaerobic tank equipped with biochemical filler bed and acclimated bacteria 5, and control the volume load at 8-16 kgCOD / (m 3 d), with a residence time of 12-24 hours and a temperature controlled at 35-45°C, this step is repeated three times to obtain acclimated bacteria 6 on the biochemical filler bed of the anaerobic tank, i.e., acclimated anaerobic denitrifying bacteria.

[0021] The beneficial effect of adopting the above further scheme is that after multiple domestication, the domesticated bacteria six are anaerobic denitrifying bacteria domesticated according to the characteristics of the mixed wastewater produced by lyocell fiber. They can be used as anaerobic bacteria in the anaerobic reaction process to treat the mixed wastewater produced by lyocell fiber. This is the key to the successful implementation of the present invention.

[0022] Dilution of the concentration of mixed wastewater from lyocell fiber production has two main effects: one is to reduce the concentration of organic matter in the mixed wastewater from lyocell fiber production; the other is that dilution with clean water in the early stage can reduce the salt concentration of the mixed wastewater from lyocell fiber production, and dilution with sodium sulfate solution in the later stage can increase the salt concentration of the mixed wastewater from lyocell fiber production. The mixed wastewater from lyocell fiber production also needs to be diluted after the strain is domesticated. This is determined by comprehensively considering the equipment load, wastewater retention time, sludge age, and avoiding the occurrence of large amounts of floating sludge during actual operation. The inorganic salt concentration of the mixed wastewater from lyocell fiber production is higher than that of the existing treated viscose staple fiber wastewater. The existing biochemical strains cannot adapt directly to it. It is necessary to gradually domesticate and screen the strains and slowly increase the salt concentration of the influent to prevent the death of biochemical bacteria due to excessive changes in the internal and external osmotic pressure of the biochemical bacteria in a short period of time.

[0023] During the acclimation process, the salinity of the influent is increased. To ensure the successful acclimation of salt-tolerant anaerobic denitrifying bacteria, the dilution water used in step df is a sodium sulfate solution with the same salt concentration as the mixed wastewater from lyocell fiber production. The sodium sulfate solution is used mainly because the main component causing the salinity of lyocell wastewater is sodium sulfate.

[0024] Furthermore, in step (2), the volume load of anaerobic biochemical treatment is controlled at 8-16 kg COD / (m 3 d), residence time 12-24h, temperature controlled at 35-45°C, pH value of treated effluent adjusted to neutral.

[0025] Furthermore, in step (3), the volumetric load of aerobic biochemical treatment is controlled at 1-3 kg COD / (m 3 d) The residence time is 12-24 hours, the temperature is controlled at 25-35°C, and the activated sludge of aerobic biochemical treatment includes nitrite bacteria and nitrate bacteria, with an organic concentration of 1500-3000 mg / L.

[0026] Furthermore, in step (2), anaerobic nutrients are added during the anaerobic biochemical treatment, and the C:N:P mass ratio of the anaerobic nutrients is controlled to be 200:5:1. In step (3), aerobic nutrients are added during the aerobic biochemical treatment, and the C:N:P mass ratio of the aerobic nutrients is controlled to be 100:5:1.

[0027] Another technical solution of the present invention to solve the above technical problem is as follows: a treatment device for implementing the method for treating mixed wastewater from lyocell fiber production, comprising a regulating tank, an anaerobic tank, and an aerobic tank connected in sequence.

[0028] Furthermore, a biochemical filler bed is provided in the anaerobic tank. The filler material of the biochemical filler bed is polyurethane. The temperature of the biochemical filler bed is controlled by steam heating. The aerobic tank has an aeration device and a backwash device.

[0029] The beneficial effect of adopting the above further scheme is that the acclimation process and anaerobic biochemical treatment are both carried out at the biochemical filler bed, which requires corresponding temperature control. The aerobic tank adopts compressed air aeration and is equipped with a backwash device to prevent filler clogging, thereby ensuring biological activity.

[0030] Furthermore, a sedimentation tank is connected between the regulating tank and the anaerobic tank, and the aerobic tank is connected to the secondary sedimentation tank.

[0031] Furthermore, the bottom of the sedimentation tank is connected to a sludge discharge pipe 1, the second sedimentation tank is connected to a drain pipe, the drain pipe is also connected to the sedimentation tank through a return water pipe, and the return ratio is 1:1. The bottom of the second sedimentation tank is connected to a sludge discharge pipe 2, and the sludge discharge pipe 2 is also connected to the aerobic tank through a return sludge pipe, and the return ratio is 1:1. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic structural diagram of the device for treating mixed wastewater from lyocell fiber production according to the present invention.

[0033] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0034] 1. Equalization tank; 2. Sedimentation tank; 3. Anaerobic tank; 4. Aerobic tank; 5. Secondary sedimentation tank; 6. Sludge pump 1; 7. Sludge pump 2; 8. Sludge pump 3; 9. Biochemical filler bed; 10. Transfer pump. DETAILED DESCRIPTION

[0035] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0036] The present invention relates to a method for treating mixed wastewater from lyocell fiber production, comprising the following steps:

[0037] (1) By gradually reducing the dilution ratio of the mixed wastewater produced by lyocell fiber and slowly increasing the salinity of the influent, the anaerobic denitrifying bacteria are domesticated multiple times to obtain domesticated anaerobic denitrifying bacteria;

[0038] (2) neutralizing the pH value of the mixed wastewater from lyocell fiber production with concentrated sulfuric acid, stirring it evenly and adjusting it to neutral, and then performing anaerobic biochemical treatment using domesticated anaerobic denitrifying bacteria;

[0039] (3) The mixed wastewater from lyocell fiber production after anaerobic biochemical treatment is then aerobic biochemically treated and finally discharged in compliance with the standards.

[0040] On the basis of the above technical solution, preferably, in the step (1), during the multiple domestication of anaerobic denitrifying bacteria, clean water is used for dilution in the early stage and sodium sulfate solution is used for dilution in the later stage, and the concentration of the sodium sulfate solution is the same as the salt concentration in the mixed wastewater of lyocell fiber production.

[0041] On the basis of the above technical solution, preferably, the step (1) specifically includes the following steps:

[0042] a. Dilute the mixed wastewater from lyocell fiber production with clean water 4 times, adjust the pH value of the wastewater to neutral with 93%-98% concentrated sulfuric acid, and add it to the anaerobic tank 3 equipped with biochemical filler bed 9 and anaerobic denitrifying bacteria. The concentration of the solution added by anaerobic denitrifying bacteria is 800-1200 mg / L, and the volume load is controlled at 0.8-1 kgCOD / (m 3 d) obtaining acclimated bacteria 1 on the biochemical filler bed 9 of the anaerobic tank 3, with a residence time of 72-96 hours and a temperature controlled at 35-45°C;

[0043] b. Dilute the mixed wastewater from lyocell fiber production with clean water three times, adjust the pH value of the wastewater to neutral with 93%-98% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing the biochemical filler bed 9 and the acclimated bacteria 1. No new bacteria agent is added, and the volume load is controlled at 1.3-2 kgCOD / (m 3 d) The residence time is 48-72 hours, and the temperature is controlled at 35-45°C. This step is repeated twice to obtain the second acclimated bacteria on the biochemical filler bed 9 of the anaerobic tank 3;

[0044] c. Dilute the mixed wastewater from lyocell fiber production with clean water for 2 times, adjust the pH value of the wastewater to neutral with 93%-98% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing the biochemical filler bed 9 and the second acclimated bacteria. No new bacteria agent is added, and the volume load is controlled at 2-3 kg COD / (m 3 d) residence time 48-72 hours, temperature controlled at 35-45°C. This step is performed once to obtain acclimated bacteria 3 on the biochemical filler bed 9 of the anaerobic tank 3;

[0045] d. Dilute the mixed wastewater from lyocell fiber production with sodium sulfate solution for 2 times, adjust the pH value of the wastewater to neutral with 93%-98% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing biochemical filler bed 9 and acclimated bacteria 3. No new bacteria agent is added, and the volume load is controlled at 2-3 kgCOD / (m 3 d) The residence time is 48-72 hours, and the temperature is controlled at 35-45°C. This step is repeated twice to obtain acclimated bacteria 4 on the biochemical filler bed 9 of the anaerobic tank 3;

[0046] e. Dilute the mixed wastewater from lyocell fiber production by 1.8 times with sodium sulfate solution, adjust the pH value of the wastewater to neutral with 93%-98% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing biochemical filler bed 9 and acclimated bacteria 4. No new bacterial agent is added, and the volume load is controlled at 4-7 kg COD / (m 3 d) The residence time is 24-36 hours, and the temperature is controlled at 35-45°C. This step is repeated twice to obtain acclimated bacteria 5 on the biochemical filler bed 9 of the anaerobic tank 3;

[0047] f. Dilute the mixed wastewater from lyocell fiber production with sodium sulfate solution by 1.5 times, adjust the pH value of the wastewater to neutral with 93%-98% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing biochemical filler bed 9 and acclimated bacteria 5. No new bacterial agent is added, and the volume load is controlled at 8-16 kg COD / (m 3 d), with a residence time of 12-24 hours and a temperature controlled at 35-45°C. This step is repeated three times to obtain acclimated bacteria 6 on the biochemical filler bed 9 of the anaerobic tank 3, i.e., acclimated anaerobic denitrifying bacteria.

[0048] The acclimation step is before the formal treatment of the wastewater, but the entire acclimation process also uses a dilution of the mixed wastewater from lyocell fiber production. Through the research of the present invention, even if the wastewater is formally treated, the acclimated bacteria need to dilute the mixed wastewater from lyocell fiber production by 1.5 times to meet the discharge requirements.

[0049] The entire anaerobic denitrification bacteria acclimation process and wastewater formal treatment are all done using Figure 1 The anaerobic tank 3 equipped with the biochemical filler bed 9 shown in FIG is directly used for wastewater treatment after the acclimation period is completed. The effluent quality can also be used to verify whether the acclimated bacteria have taken effect.

[0050] On the basis of the above technical solution, preferably, in step (2), the volume load of anaerobic biochemical treatment is controlled at 8-16 kgCOD / (m 3 d), residence time 12-24h, temperature controlled at 35-45°C, pH value of treated effluent adjusted to neutral.

[0051] On the basis of the above technical solution, preferably, in step (3), the volume load of aerobic biochemical treatment is controlled at 1-3 kgCOD / (m 3 d) a retention time of 12-24 hours, controlled at a temperature of 25-35°C, and aerobic biochemical treatment of the activated sludge, including nitrite and nitrate bacteria, with an organic concentration of 1500-3000 mg / L. According to the method of the present invention, the treated wastewater meets the Class III urban discharge standard and can be directly discharged.

[0052] Based on the above technical solution, preferably, in step (2), anaerobic nutrients are added during the anaerobic biochemical treatment, and the C:N:P mass ratio of the anaerobic nutrients is controlled to be 200:5:1. In step (3), aerobic nutrients are added during the aerobic biochemical treatment, and the C:N:P mass ratio of the aerobic nutrients is controlled to be 100:5:1. The added anaerobic nutrients and aerobic nutrients are generally urea, phosphate fertilizer, etc.

[0053] like Figure 1 As shown, the present invention also relates to a treatment device for implementing the method for treating mixed wastewater from lyocell fiber production, comprising a regulating tank 1, an anaerobic tank 3, and an aerobic tank 4 connected in sequence.

[0054] On the basis of the above technical solution, preferably, a biochemical filler bed 9 is provided in the anaerobic tank 3. The filler material of the biochemical filler bed 9 is polyurethane, which is used to load anaerobic denitrifying bacteria and various domesticated bacteria. The temperature of the biochemical filler bed 9 is controlled by steam heating. The aerobic tank 4 has an aeration device and a backwash device.

[0055] Specifically, the biochemical filler bed 9 is loaded in the middle of the anaerobic tank 3 , the position where wastewater enters the anaerobic tank 3 is located above the biochemical filler bed 9 , and the position where wastewater is discharged is located below the biochemical filler bed 9 .

[0056] The regulating tank 1 also has connections to a lyocell fiber-mixed wastewater inlet pipe and a concentrated sulfuric acid addition pipe, and is equipped with a built-in agitator. The top of the anaerobic tank 3 is also connected to an exhaust gas pipe, which generates exhaust gas that is sent to the exhaust gas treatment process. A delivery pump 10 is also installed on the connecting pipe between the anaerobic tank 3 and the aerobic tank 4 to transport wastewater.

[0057] On the basis of the above technical solution, preferably, a sedimentation tank 2 is further connected between the regulating tank 1 and the anaerobic tank 3 , and the aerobic tank 4 is connected to the secondary sedimentation tank 5 .

[0058] On the basis of the above technical solution, preferably, the secondary sedimentation tank 5 is connected with a drain pipe for discharging qualified water, and the drain pipe is also connected with the sedimentation tank 2 through a return water pipe. Part of the nitrified liquid in the secondary sedimentation tank is returned to the sedimentation tank, and the return ratio is 1:1. The bottom of the sedimentation tank 2 is connected with a sludge discharge pipe 1, and the sludge discharge pipe 1 is provided with a sludge pump 3 8. The bottom of the secondary sedimentation tank 5 is connected with a sludge discharge pipe 2, and the sludge discharge pipe 2 is provided with a sludge pump 2 7. The residual sludge in the sedimentation tank 2 and the secondary sedimentation tank 5 is discharged to the outside of the system in a continuous sludge discharge manner to remove the sludge treatment process. The sludge discharge pipe 2 is also connected with the aerobic tank through a return sludge pipe, and the return ratio is 1:1. The return sludge pipe is provided with a sludge pump 1 6.

[0059] In addition, sludge discharge pipe 2 is connected to anaerobic tank 3 via a return sludge pipe (the connection point with anaerobic tank 3 is located above the biochemical filler bed 9). During the initial startup of anaerobic tank 3, if the bacterial flocs are not yet formed and the bacterial species are lost, the lost bacterial species are returned. However, after normal operation, no return flow is required. After normal operation, the return sludge from secondary sedimentation tank 5 is returned only to aerobic tank 4, ensuring that the sludge concentration in aerobic tank 4 reaches the normal range. The remaining sludge enters the sludge treatment process.

[0060] Example 1

[0061] A method for treating mixed wastewater from lyocell fiber production comprises the following steps:

[0062] (1) By gradually reducing the dilution ratio of the mixed wastewater produced by lyocell fiber and slowly increasing the salinity of the influent, the anaerobic denitrifying bacteria are domesticated multiple times to obtain domesticated anaerobic denitrifying bacteria;

[0063] (2) neutralizing the pH value of the mixed wastewater from lyocell fiber production with concentrated sulfuric acid, stirring it evenly and adjusting it to neutral, and then performing anaerobic biochemical treatment using domesticated anaerobic denitrifying bacteria;

[0064] (3) The mixed wastewater from lyocell fiber production after anaerobic biochemical treatment is then aerobic biochemically treated and finally discharged in compliance with the standards.

[0065] Wherein, the step (1) specifically includes the following steps:

[0066] a. Dilute the mixed wastewater from lyocell fiber production with clean water 4 times, adjust the pH value of the wastewater to neutral with 93% concentrated sulfuric acid, and add it to the anaerobic tank 3 equipped with biochemical filler bed 9 and anaerobic denitrifying bacteria. The concentration of the solution added by anaerobic denitrifying bacteria is 800 mg / L, and the volume load is controlled at 0.8 kg COD / (m 3 d) Acquire acclimated bacteria 1 on biochemical filler bed 9 of anaerobic tank 3 with a residence time of 96 h and a temperature controlled at 35°C;

[0067] b. Dilute the mixed wastewater from lyocell fiber production with clean water three times, adjust the pH value of the wastewater to neutral with 93% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing the biochemical filler bed 9 and the acclimated bacteria 1. No new bacteria agent is added, and the volume load is controlled at 1.3 kg COD / (m 3 d) The residence time is 72 hours, and the temperature is controlled at 35°C. This step is repeated twice to obtain the second acclimated bacteria on the biochemical filler bed 9 of the anaerobic tank 3;

[0068] c. Dilute the mixed wastewater from lyocell fiber production with clean water for 2 times, adjust the pH value of the wastewater to neutral with 93% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing the biochemical filler bed 9 and the second acclimated bacteria. No new bacteria agent is added, and the volume load is controlled at 2 kg COD / (m 3 d) The residence time is 72 hours and the temperature is controlled at 35°C. This step is performed once to obtain the acclimated bacteria 3 on the biochemical filler bed 9 of the anaerobic tank 3;

[0069] d. Dilute the mixed wastewater from lyocell fiber production with sodium sulfate solution for 2 times, adjust the pH value of the wastewater to neutral with 93% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing biochemical filler bed 9 and acclimated bacteria 3. No new bacteria agent is added, and the volume load is controlled at 2 kg COD / (m 3 d) The residence time is 72 hours, and the temperature is controlled at 35°C. This step is repeated twice to obtain acclimated bacteria 4 on the biochemical filler bed 9 of the anaerobic tank 3;

[0070] e. Dilute the mixed wastewater from lyocell fiber production by 1.8 times with sodium sulfate solution, adjust the pH value of the wastewater to neutral with 93% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing biochemical filler bed 9 and acclimated bacteria 4. No new bacterial agent is added, and the volume load is controlled at 4 kg COD / (m 3 d) The residence time is 36 hours and the temperature is controlled at 35°C. This step is repeated twice to obtain acclimated bacteria 5 on the biochemical filler bed 9 of the anaerobic tank 3;

[0071] f. Dilute the mixed wastewater from lyocell fiber production with sodium sulfate solution by 1.5 times, adjust the pH value of the wastewater to neutral with 93% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing biochemical filler bed 9 and acclimated bacteria 5. No new bacterial agent is added, and the volume load is controlled at 8kgCOD / (m 3 d), with a residence time of 24 hours and a temperature controlled at 35° C. This step is repeated three times to obtain acclimated bacteria 6 on the biochemical filler bed 9 of the anaerobic tank 3, i.e., acclimated anaerobic denitrifying bacteria.

[0072] In the step (2), anaerobic nutrients are added during the anaerobic biochemical treatment, the C:N:P mass ratio of the anaerobic nutrients is controlled at 200:5:1, and the volumetric load of the anaerobic biochemical treatment is controlled at 8kgCOD / (m 3 d), residence time 24h, temperature controlled at 35°C, pH value of treated effluent adjusted to 8.0.

[0073] In the step (3), aerobic nutrients are added during the aerobic biochemical treatment, the C:N:P mass ratio of the aerobic nutrients is controlled at 100:5:1, and the volumetric load of the aerobic biochemical treatment is controlled at 1 kgCOD / (m 3 d) The residence time was 24 h, the temperature was controlled at 25°C, and the activated sludge of aerobic biochemical treatment included nitrite bacteria and nitrate bacteria, with an organic concentration of 1500 mg / L.

[0074] Results: The effluent COD removal rate was 96.8%, and the COD of the discharged wastewater reached the third-level urban emission standard.

[0075] Example 2

[0076] A method for treating mixed wastewater from lyocell fiber production comprises the following steps:

[0077] (1) By gradually reducing the dilution ratio of the mixed wastewater produced by lyocell fiber and slowly increasing the salinity of the influent, the anaerobic denitrifying bacteria are domesticated multiple times to obtain domesticated anaerobic denitrifying bacteria;

[0078] (2) neutralizing the pH value of the mixed wastewater from lyocell fiber production with concentrated sulfuric acid, stirring it evenly and adjusting it to neutral, and then performing anaerobic biochemical treatment using domesticated anaerobic denitrifying bacteria;

[0079] (3) The mixed wastewater from lyocell fiber production after anaerobic biochemical treatment is then aerobic biochemically treated and finally discharged in compliance with the standards.

[0080] Wherein, the step (1) specifically includes the following steps:

[0081] a. Dilute the mixed wastewater from lyocell fiber production with clean water 4 times, adjust the pH value of the wastewater to neutral with 95% concentrated sulfuric acid, and add it to the anaerobic tank 3 equipped with biochemical filler bed 9 and anaerobic denitrifying bacteria. The concentration of the solution added by anaerobic denitrifying bacteria is 1000 mg / L, and the volume load is controlled at 0.9 kg COD / (m 3 d) Acquire acclimated bacteria 1 on the biochemical filler bed 9 of the anaerobic tank 3, with a residence time of 84 h and a temperature controlled at 40°C;

[0082] b. Dilute the mixed wastewater from lyocell fiber production with clean water three times, adjust the pH value of the wastewater to neutral with 95% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing the biochemical filler bed 9 and the acclimated bacteria 1. No new bacteria agent is added, and the volume load is controlled at 1.6 kg COD / (m 3 d) The residence time is 60 hours, and the temperature is controlled at 40°C. This step is repeated twice to obtain the second acclimated bacteria on the biochemical filler bed 9 of the anaerobic tank 3;

[0083] c. Dilute the mixed wastewater from lyocell fiber production with clean water for 2 times, adjust the pH value of the wastewater to neutral with 95% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing the biochemical filler bed 9 and the second acclimated bacteria. No new bacterial agent is added, and the volume load is controlled at 2.5 kg COD / (m 3 d) The residence time is 60 hours and the temperature is controlled at 40°C. This step is performed once to obtain the acclimated bacteria 3 on the biochemical filler bed 9 of the anaerobic tank 3;

[0084] d. Dilute the mixed wastewater from lyocell fiber production with sodium sulfate solution for 2 times, adjust the pH value of the wastewater to neutral with 95% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing biochemical filler bed 9 and acclimated bacteria 3. No new bacteria agent is added, and the volume load is controlled at 2.5 kg COD / (m 3 d) The residence time is 60 hours and the temperature is controlled at 40°C. This step is repeated twice to obtain acclimated bacteria 4 on the biochemical filler bed 9 of the anaerobic tank 3;

[0085] e. Dilute the mixed wastewater from lyocell fiber production by 1.8 times with sodium sulfate solution, adjust the pH value of the wastewater to neutral with 95% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing biochemical filler bed 9 and acclimated bacteria 4. No new bacterial agent is added, and the volume load is controlled at 5.5 kg COD / (m 3 d) The residence time is 30 hours and the temperature is controlled at 40°C. This step is repeated twice to obtain acclimated bacteria 5 on the biochemical filler bed 9 of the anaerobic tank 3;

[0086] f. Dilute the mixed wastewater from lyocell fiber production with sodium sulfate solution by 1.5 times, adjust the pH value of the wastewater to neutral with 95% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing biochemical filler bed 9 and acclimated bacteria 5. No new bacterial agent is added, and the volume load is controlled at 12 kg COD / (m 3 d), with a residence time of 18 hours and a temperature controlled at 40° C. This step is repeated three times to obtain acclimated bacteria 6 on the biochemical filler bed 9 of the anaerobic tank 3, i.e., acclimated anaerobic denitrifying bacteria.

[0087] In the step (2), anaerobic nutrients are added during the anaerobic biochemical treatment, the C:N:P mass ratio of the anaerobic nutrients is controlled at 200:5:1, and the volumetric load of the anaerobic biochemical treatment is controlled at 12 kgCOD / (m 3 d), residence time 18 h, temperature controlled at 40°C, and pH value of the treated effluent adjusted to 8.0.

[0088] In the step (3), aerobic nutrients are added during the aerobic biochemical treatment, the C:N:P mass ratio of the aerobic nutrients is controlled at 100:5:1, and the volumetric load of the aerobic biochemical treatment is controlled at 2 kgCOD / (m 3 d), residence time 18 h, temperature controlled at 30°C, aerobic biochemical treatment of activated sludge including nitrite bacteria and nitrate bacteria, organic concentration of 2200 mg / L.

[0089] Results: The effluent COD removal rate was 97.1%, and the COD of the discharged wastewater reached the third-level urban emission standard.

[0090] Example 3

[0091] A method for treating mixed wastewater from lyocell fiber production comprises the following steps:

[0092] (1) By gradually reducing the dilution ratio of the mixed wastewater produced by lyocell fiber and slowly increasing the salinity of the influent, the anaerobic denitrifying bacteria are domesticated multiple times to obtain domesticated anaerobic denitrifying bacteria;

[0093] (2) neutralizing the pH value of the mixed wastewater from lyocell fiber production with concentrated sulfuric acid, stirring it evenly and adjusting it to neutral, and then performing anaerobic biochemical treatment using domesticated anaerobic denitrifying bacteria;

[0094] (3) The mixed wastewater from lyocell fiber production after anaerobic biochemical treatment is then aerobic biochemically treated and finally discharged in compliance with the standards.

[0095] Wherein, the step (1) specifically includes the following steps:

[0096] a. Dilute the mixed wastewater from lyocell fiber production with clean water 4 times, adjust the pH value of the wastewater to neutral with 98% concentrated sulfuric acid, and add it to the anaerobic tank 3 equipped with biochemical filler bed 9 and anaerobic denitrifying bacteria. The concentration of the solution added by anaerobic denitrifying bacteria is 1200 mg / L, and the volume load is controlled at 1 kg COD / (m 3 d) Acquire acclimated bacteria 1 on the biochemical filler bed 9 of the anaerobic tank 3, with a residence time of 72 h and a temperature controlled at 45°C;

[0097] b. Dilute the mixed wastewater from lyocell fiber production with clean water three times, adjust the pH value of the wastewater to neutral with 98% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing the biochemical filler bed 9 and the acclimated bacteria 1. No new bacteria agent is added, and the volume load is controlled at 2 kg COD / (m 3 d) The residence time is 48 hours, and the temperature is controlled at 45°C. This step is repeated twice to obtain the second acclimated bacteria on the biochemical filler bed 9 of the anaerobic tank 3;

[0098] c. Dilute the mixed wastewater from lyocell fiber production with clean water for 2 times, adjust the pH value of the wastewater to neutral with 98% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing the biochemical filler bed 9 and the second acclimated bacteria. No new bacteria agent is added, and the volume load is controlled at 3 kg COD / (m 3 d) The residence time is 48 hours and the temperature is controlled at 45°C. This step is performed once to obtain the acclimated bacteria 3 on the biochemical filler bed 9 of the anaerobic tank 3;

[0099] d. Dilute the mixed wastewater from lyocell fiber production with sodium sulfate solution for 2 times, adjust the pH value of the wastewater to neutral with 98% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing biochemical filler bed 9 and acclimated bacteria 3. No new bacteria agent is added, and the volume load is controlled at 3kgCOD / (m 3 d) The residence time is 48 hours, and the temperature is controlled at 45°C. This step is repeated twice to obtain acclimated bacteria 4 on the biochemical filler bed 9 of the anaerobic tank 3;

[0100] e. Dilute the mixed wastewater from lyocell fiber production by 1.8 times with sodium sulfate solution, adjust the pH value of the wastewater to neutral with 98% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing the biochemical filler bed 9 and the acclimated bacteria 4. No new bacterial agent is added, and the volume load is controlled at 7 kg COD / (m 3 d) The residence time is 24 hours and the temperature is controlled at 45°C. This step is repeated twice to obtain acclimated bacteria 5 on the biochemical filler bed 9 of the anaerobic tank 3;

[0101] f. Dilute the mixed wastewater from lyocell fiber production with sodium sulfate solution by 1.5 times, adjust the pH value of the wastewater to neutral with 98% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing biochemical filler bed 9 and acclimated bacteria 5. No new bacterial agent is added, and the volume load is controlled at 16 kg COD / (m 3 d), with a residence time of 12 hours and a temperature controlled at 45° C. This step is repeated three times to obtain acclimated bacteria 6 on the biochemical filler bed 9 of the anaerobic tank 3, i.e., acclimated anaerobic denitrifying bacteria.

[0102] In the step (2), anaerobic nutrients are added during the anaerobic biochemical treatment, the C:N:P mass ratio of the anaerobic nutrients is controlled at 200:5:1, and the volumetric load of the anaerobic biochemical treatment is controlled at 16 kgCOD / (m 3 d), residence time 24h, temperature controlled at 45°C, and pH value of treated effluent adjusted to 8.0.

[0103] In the step (3), aerobic nutrients are added during the aerobic biochemical treatment, the C:N:P mass ratio of the aerobic nutrients is controlled at 100:5:1, and the volumetric load of the aerobic biochemical treatment is controlled at 3 kgCOD / (m 3 d) The residence time was 24 h, the temperature was controlled at 35°C, and the activated sludge of aerobic biochemical treatment included nitrite bacteria and nitrate bacteria, with an organic concentration of 3000 mg / L.

[0104] Results: The effluent COD removal rate was 96.9%, and the COD of the discharged wastewater reached the third-level urban emission standard.

[0105] Comparative Example 1

[0106] Compared with Example 1, this comparative example is different in that:

[0107] The step (1) specifically includes the following steps:

[0108] a. Dilute the mixed wastewater from lyocell fiber production with clean water 4 times, adjust the pH value of the wastewater to neutral with 93% concentrated sulfuric acid, and add it to the anaerobic tank 3 equipped with biochemical filler bed 9 and anaerobic denitrifying bacteria. The concentration of the solution added by anaerobic denitrifying bacteria is 800 mg / L, and the volume load is controlled at 0.8 kg COD / (m 3 d) Acquire acclimated bacteria 1 on biochemical filler bed 9 of anaerobic tank 3 with a residence time of 96 h and a temperature controlled at 35°C;

[0109] b. Dilute the mixed wastewater from lyocell fiber production with clean water three times, adjust the pH value of the wastewater to neutral with 93% concentrated sulfuric acid, and add it to the anaerobic tank 3 containing the biochemical filler bed 9 and the acclimated bacteria 1. No new bacteria agent is added, and the volume load is controlled at 1.3 kg COD / (m 3 d) The residence time is 72 hours, and the temperature is controlled at 35°C. This step is repeated twice to obtain the second acclimated bacteria on the biochemical filler bed 9 of the anaerobic tank 3;

[0110] Anaerobic biochemical treatment was performed using the second domesticated bacteria as anaerobic denitrifying bacteria domesticated according to the characteristics of the mixed wastewater from lyocell fiber production. Other steps and parameters were the same as those in Example 1.

[0111] Results: The effluent COD removal rate was 90.1%, and the COD of the discharged wastewater did not meet the discharge standard.

[0112] Analysis: Comparing Comparative Example 1 with the Examples reveals that multiple attempts to acclimate the anaerobic denitrifying bacteria are required. As the dilution factor of the lyocell fiber production mixed wastewater is gradually reduced and the influent salinity is slowly increased, the 1.5-fold dilution is required for acclimatization to meet discharge requirements. A dilution of 3-fold does not fully acclimate the anaerobic denitrifying bacteria, resulting in the wastewater treatment failing to meet discharge standards. The dilution factor is crucial to the acclimatization of the anaerobic denitrifying bacteria, and a final dilution factor of 1.5 is the optimal dilution factor.

[0113] Comparative Example 2

[0114] Compared with Example 1, this comparative example is different in that:

[0115] The step (1) specifically includes the following steps:

[0116] The pH value of the mixed wastewater from lyocell fiber production was adjusted to neutral with 93% concentrated sulfuric acid, and the anaerobic biochemical filler bed in step f was used without adding new bacterial agents to obtain acclimated bacteria 6. The volumetric load of the anaerobic biochemical treatment was controlled at 24 kg COD / (m 3 d), residence time 12 h, temperature controlled at 40° C. Other steps and parameters are the same as in Example 1.

[0117] Results: The effluent COD removal rate was 89.3%, and the COD of the discharged wastewater did not meet the discharge standard.

[0118] Analysis: Comparing Comparative Example 2 with the Examples shows that the volumetric load must be controlled within an appropriate range. Further increasing the volumetric load does not further increase the treatment efficiency of the domesticated bacteria, resulting in wastewater treatment failing to meet discharge standards. There is an objectively suitable range for volumetric load. Excessively high volumetric loads result in poor wastewater treatment and failure to meet standards, while excessively low volumetric loads lead to low volumetric utilization and high costs.

[0119] Comparative Example 3

[0120] Compared with Example 1, this comparative example is different in that:

[0121] The anaerobic denitrifying bacteria acclimation step of step (1) was omitted, and step (2) was directly performed. Step (2) specifically comprised the following steps: diluting the mixed wastewater from lyocell fiber production with clean water by 1.5 times, adjusting the pH value of the wastewater to neutral with 93% concentrated sulfuric acid, and adding the wastewater to the anaerobic tank 3 containing the biochemical filler bed 9 and the anaerobic denitrifying bacteria. The concentration of the solution added to the anaerobic denitrifying bacteria was 1000 mg / L, the volumetric load was controlled at 16 kgCOD / (m3·d), the residence time was 12 h, and the temperature was controlled at 40°C. The other steps and parameters were the same as those in Example 1.

[0122] Results: The effluent COD removal rate was 13.1%, and the COD of the discharged wastewater did not meet the discharge standard.

[0123] Analysis: By comparing Comparative Example 3 with the embodiments, it can be seen that if the anaerobic denitrifying bacteria are not domesticated and the existing anaerobic denitrifying bacteria are directly used, the anaerobic biochemical treatment of the mixed wastewater from the lyocell fiber production cannot be performed well, resulting in the wastewater treatment failing to meet the discharge standards.

[0124] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for treating mixed wastewater from lyocell fiber production, characterized in that: The following steps are involved: (1) By gradually reducing the dilution ratio of the mixed wastewater produced by lyocell fiber and slowly increasing the salinity of the influent, the anaerobic denitrifying bacteria are domesticated multiple times to obtain domesticated anaerobic denitrifying bacteria; (2) neutralizing the pH value of the mixed wastewater from lyocell fiber production with concentrated sulfuric acid, stirring it evenly and adjusting it to neutral, and then performing anaerobic biochemical treatment using domesticated anaerobic denitrifying bacteria; (3) The mixed wastewater from lyocell fiber production after anaerobic biochemical treatment is then aerobic biochemically treated and finally discharged in compliance with the standards; In the step (1), during the multiple domestication of anaerobic denitrifying bacteria, dilution is performed using clean water in the early stage and sodium sulfate solution in the later stage, wherein the concentration of the sodium sulfate solution is the same as the salt concentration in the mixed wastewater of lyocell fiber production; The step (1) specifically includes the following steps: a. Dilute the mixed wastewater from lyocell fiber production with clean water 4 times, adjust the pH value of the wastewater to neutral with 93%-98% concentrated sulfuric acid, and add it to the anaerobic tank equipped with a biochemical filler bed and anaerobic denitrifying bacteria. The concentration of the solution added by anaerobic denitrifying bacteria is 800-1200 mg / L, and the volume load is controlled at 0.8-1 kgCOD / (m 3 d) Acquire acclimated bacteria 1 on the biochemical filler bed in the anaerobic tank with a residence time of 72-96 hours and a temperature control of 35-45°C; b. Dilute the mixed wastewater from lyocell fiber production with clean water three times, adjust the pH value of the wastewater to neutral with 93%-98% concentrated sulfuric acid, and add it to the anaerobic tank equipped with a biochemical filler bed and acclimated bacteria. The volume load is controlled at 1.3-2 kg COD / (m 3 d) The residence time is 48-72 hours, and the temperature is controlled at 35-45°C. This step is repeated twice to obtain the second acclimated bacteria on the biochemical filler bed in the anaerobic tank; c. Dilute the mixed wastewater from lyocell fiber production with clean water for 2 times, adjust the pH value of the wastewater to neutral with 93%-98% concentrated sulfuric acid, and add it to the anaerobic tank equipped with biochemical filler bed and acclimated bacteria II, and control the volume load at 2-3 kgCOD / (m 3 d) The residence time is 48-72 hours, and the temperature is controlled at 35-45°C. This step is performed once to obtain acclimated bacteria 3 on the biochemical filler bed in the anaerobic tank; d. Dilute the mixed wastewater from lyocell fiber production with sodium sulfate solution for 2 times, adjust the pH value of the wastewater to neutral with 93%-98% concentrated sulfuric acid, and add it to the anaerobic tank equipped with biochemical filler bed and acclimated bacteria. The volume load is controlled at 2-3 kg COD / (m 3 d) The residence time is 48-72 hours, and the temperature is controlled at 35-45°C. This step is repeated twice to obtain acclimated bacteria 4 on the biochemical filler bed in the anaerobic tank; e. Dilute the mixed wastewater from lyocell fiber production with sodium sulfate solution by 1.8 times, adjust the pH value of the wastewater to neutral with 93%-98% concentrated sulfuric acid, and add it to the anaerobic tank equipped with biochemical filler bed and acclimated bacteria 4, and control the volume load at 4-7kgCOD / (m 3 d) The residence time is 24-36 hours, and the temperature is controlled at 35-45°C. This step is repeated twice to obtain acclimated bacteria 5 on the biochemical filler bed in the anaerobic tank; f. Dilute the mixed wastewater from lyocell fiber production with sodium sulfate solution by 1.5 times, adjust the pH value of the wastewater to neutral with 93%-98% concentrated sulfuric acid, and add it to the anaerobic tank equipped with biochemical filler bed and acclimated bacteria 5, and control the volume load at 8-16 kgCOD / (m 3 d), with a residence time of 12-24 hours and a temperature controlled at 35-45°C, this step is repeated three times to obtain acclimated bacteria 6 on the biochemical filler bed of the anaerobic tank, i.e., acclimated anaerobic denitrifying bacteria.

2. The method for treating mixed wastewater from cellulosic fiber production according to claim 1, characterized in that: In step (2), the volume load of anaerobic biochemical treatment is controlled at 8-16 kg COD / (m 3 d), residence time 12-24h, temperature controlled at 35-45°C, pH value of treated effluent adjusted to neutral.

3. The method for treating mixed wastewater from cellulosic fiber production according to claim 1, characterized in that: In step (3), the volume load of aerobic biochemical treatment is controlled at 1-3 kg COD / (m 3 d) The residence time is 12-24 hours, the temperature is controlled at 25-35°C, and the activated sludge of aerobic biochemical treatment includes nitrite bacteria and nitrate bacteria, with an organic concentration of 1500-3000 mg / L.

4. The method for treating mixed wastewater from cellulosic fiber production according to claim 1, characterized in that: In the step (2), anaerobic nutrients are added during the anaerobic biochemical treatment, and the C:N:P mass ratio of the anaerobic nutrients is controlled at 200:5:

1. In the step (3), aerobic nutrients are added during the aerobic biochemical treatment, and the C:N:P mass ratio of the aerobic nutrients is controlled at 200:5:

1. The N:P mass ratio is controlled at 100:5:

1.

5. A treatment device for implementing the method for treating mixed wastewater from lyocell fiber production according to any one of claims 1 to 4, characterized in that: The invention comprises a regulating tank (1), an anaerobic tank (3) and an aerobic tank (4) which are connected in sequence.

6. The processing device according to claim 5, characterized in that A biochemical filler bed (9) is provided in the anaerobic tank (3). The filler material of the biochemical filler bed (9) is polyurethane. The temperature of the biochemical filler bed (9) is controlled by steam heating. The aerobic tank (4) has an aeration device and a backwash device.

7. The processing device according to claim 5, characterized in that A sedimentation tank (2) is also connected between the regulating tank (1) and the anaerobic tank (3), and the aerobic tank (4) is connected to a secondary sedimentation tank (5).

8. The processing device according to claim 7, characterized in that The bottom of the sedimentation tank (2) is connected to a sludge discharge pipe 1, the secondary sedimentation tank (5) is connected to a drainage pipe, the drainage pipe is also connected to the sedimentation tank (2) through a return water pipe, and the return ratio is 1:

1. The bottom of the secondary sedimentation tank (5) is connected to a sludge discharge pipe 2, the sludge discharge pipe 2 is also connected to the aerobic tank (4) through a return sludge pipe, and the return ratio is 1:1.

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