A method for processing steviol sugar wastewater

Abstract

The present application relates to the technical field of steviol production, and particularly relates to a steviol wastewater treatment method, which comprises the following steps: collecting, adjusting and treating wastewater, hydrolyzing, blowing off, one-time settling, water distribution, anaerobic reaction, activated sludge pool and two-time settling, so that the organic matters in the wastewater are effectively decomposed, and the wastewater treatment efficiency is improved.

Description

A method for treating stevia wastewater Technical Field

[0001] This invention relates to the field of stevia production technology, and in particular to a method for treating stevia wastewater. Background Technology

[0002] Stevia, also known as stevia glycoside, is a glycoside extracted from the leaves of the plant *Stevia rebaudia* (known as sweet stevia in my country). Currently, the production of stevia glycosides generates a large amount of wastewater, characterized by high COD (Chemical Oxygen Demand) and significant variations in water quality and quantity across different process stages. The wastewater mainly consists of organic matter such as filter residue, lignin, cellulose, hemicellulose, and residual sugars; it also contains high levels of inorganic pollutants such as salts. Therefore, it must be treated to meet discharge standards before being released into the industrial park's wastewater treatment plant. Current technologies primarily treat this wastewater by adding chemical agents. While this method achieves some treatment, it cannot effectively decompose the organic matter in the wastewater, resulting in high COD. Therefore, it is necessary to develop a stevia wastewater treatment method to address these issues. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for treating stevia wastewater, which can effectively treat organic and inorganic substances in wastewater and make the treated wastewater meet the discharge standards.

[0004] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0005] A method for treating stevia wastewater, the method comprising the following steps:

[0006] (1) The acid and alkaline water from the stevia production and the effluent after adsorption by the resin column are collected in the first and second collection tanks respectively, and transported to the interior of the equalization tank by the transfer pump. The pH of the mixed wastewater is adjusted to 6.0-8.0 and then set aside.

[0007] (2) Wastewater in the equalization tank is transported to the hydrolysis tank by a transfer pump. After being treated by anaerobic sludge in the hydrolysis tank, the wastewater enters the stripping tank. After pH adjustment and treatment by anaerobic sludge, it enters the sedimentation tank. After settling and stratification, the wastewater enters the interior of the distribution tank. The sludge enters the interior of the hydrolysis tank through a return pump.

[0008] (3) Adjust the pH and temperature of the wastewater in the distribution tank. The wastewater enters the anaerobic reactor through a transfer pump. After anaerobic sludge treatment, the wastewater enters the anaerobic sedimentation tank. After further anaerobic sludge treatment in the sedimentation tank, the anaerobic sludge is returned to the distribution tank and then returned to the interior of the anaerobic reactor. The wastewater continues to enter the interior of the activated sludge tank for aerobic sludge treatment. The sewage and a small amount of sludge enter the interior of the secondary sedimentation tank. After settling and stratification, the sewage that meets the discharge standards enters the drainage well and is discharged to the park's sewage treatment plant. Part of the sludge after settling and stratification is returned to the interior of the activated sludge tank, and part enters the interior of the sludge thickening tank.

[0009] (4) After the sludge in the sludge thickening tank is thickened, it enters the sludge conditioning tank. After the flocculant is added and mixed, the flocculated sludge enters the sludge dewatering machine for dewatering. The collected filter cake is transported off-site for treatment. The filtrate after dewatering and the wastewater after thickening in the sludge thickening tank enter the water collection well together. The wastewater inside the water collection well enters the interior of the first water collection tank through a transfer pump.

[0010] As an improved technical solution, the sludge concentration in the hydrolysis tank is greater than 5000 mg / L, and the sludge settling ratio is 30-50%; the stripping tank is equipped with an aeration component, which includes an aeration main pipe and multiple aeration branch pipes connected to the aeration main pipe. Multiple aeration heads are provided on the aeration branch pipes, and one end of the aeration main pipe is connected to an induced draft fan; the pH of the wastewater in the stripping tank is adjusted to 6.5-7.0.

[0011] As an improved technical solution, the waste gas from the first collection tank, the second collection tank, the hydrolysis tank, the stripping tank, the primary sedimentation tank, the water distribution tank, the anaerobic reactor, and the anaerobic sedimentation tank is connected to the tail gas treatment system through waste gas pipelines. The tail gas treatment system includes an alkaline spray tower, the exhaust port of which is connected to a deodorization box. The deodorization box includes a box body, an air inlet on one side of the bottom of the box body, an exhaust port on the top of the box body, a Y-shaped filter connected to the air inlet pipe inside the box body, an activated carbon adsorption layer inside the filter, and multiple spray pipes on the upper part of the filter.

[0012] As an improved technical solution, the water distribution tank is equipped with a steam inlet pipe, and the pH of the wastewater in the water distribution tank is adjusted to 6.7-7.5, and the temperature is adjusted to 35±2℃.

[0013] As an improved technical solution, the anaerobic reactor includes a main body, with a gas-liquid separation chamber at the top. Inside the main body, from top to bottom, are sequentially arranged a first treatment chamber, a second treatment chamber, and a mixing chamber, all interconnected. A biogas outlet is located at the top of the gas-liquid separation chamber. Multiple perforated first partition components are located between the first treatment chamber and the gas-liquid separation chamber. Multiple perforated second partition components are located between the first treatment chamber and the second treatment chamber. A perforated third partition component is located between the second treatment chamber and the mixing chamber. A return pipe connected to the mixing chamber and the first treatment chamber is located on one side of the main body. A wastewater inlet and a sludge inlet are located on one side of the mixing chamber. A wastewater outlet is located on the side of the main body corresponding to the upper part of the first partition components. The influent parameters of the anaerobic reactor are controlled as follows: pH 6.7-7.5, COD / SO4. 2- >10; effluent parameters are pH 6.7-7.5, volatile acid <300mg / l, COD <1500mg / l, alkalinity >1500mg / l; operating temperature is 33-37℃.

[0014] As an improved technical solution, both the first and second separating components include an annular body. The annular body contains multiple first and second partitions arranged in a cross-shaped pattern. The multiple first and second partitions are distributed on the body at equal intervals. The cross-section of each first partition is V-shaped, and multiple upper connecting rods perpendicular to each first partition are provided between adjacent first partitions. Multiple lower connecting rods are provided below each upper connecting rod. The upper and lower connecting rods are arranged in an alternating up-and-down manner. The third separating component includes a disc with multiple through holes.

[0015] After adopting the above technical solution, the beneficial effects of the present invention are:

[0016] This invention collects acidic and alkaline wastewater from stevia production, as well as the effluent from the resin column. The pH is adjusted to a slightly acidic level, and the wastewater first enters a hydrolysis tank for anaerobic sludge treatment, then enters a stripping tank for further anaerobic sludge treatment, and finally enters a settling tank for sedimentation. After sedimentation and stratification, the wastewater enters a distribution tank, where the pH and temperature are adjusted before entering an anaerobic reactor. Anaerobic sludge further decomposes the organic matter in the wastewater. The wastewater and a small amount of sludge then enter an anaerobic settling tank for sedimentation and stratification. The sludge is returned to the distribution tank and then re-enters the anaerobic reactor for recycling. The wastewater is pumped into an activated sludge tank for aerobic sludge treatment. After initial treatment, the sludge enters the secondary sedimentation tank for settling. Through the circulation of aerobic and anaerobic sludge, the organic matter in the wastewater is effectively decomposed. Wastewater that meets the discharge standards is discharged into the drainage well. The sludge in the secondary sedimentation tank enters the sludge thickening tank. After settling and stratification, the sludge enters the sludge conditioning tank. Flocculants are added to achieve the sedimentation of inorganic matter in the wastewater. Finally, the sludge is transported to the sludge dewatering machine. The filter cake after dewatering is collected and transported away. The collected filtrate and the wastewater collected after settling and stratification in the sludge thickening tank enter the interior of the collection well and then enter the first collection tank for reprocessing. Using the above treatment method, acidic and alkaline wastewater from stevia production and effluent after resin column adsorption can be treated simultaneously. By controlling the pH and temperature of the wastewater and alternating between primary anaerobic sludge treatment, secondary anaerobic sludge treatment, and tertiary aerobic sludge treatment, the organic matter in the wastewater can be effectively decomposed. The above treatment method greatly improves the wastewater treatment efficiency. In addition, by adding flocculants, inorganic matter in the wastewater can also be flocculated and precipitated, which greatly reduces the COD and ammonia nitrogen content in the wastewater.

[0017] Because the sludge concentration in the hydrolysis tank is greater than 5000 mg / L, and the sludge settling ratio is 30-50%, the stripping tank is equipped with aeration components, including a main aeration pipe and multiple branch aeration pipes connected to it. Multiple aeration heads are installed on the branch pipes, and one end of the main aeration pipe is connected to an induced draft fan. The pH of the wastewater in the stripping tank is adjusted to 6.5-7.0. By controlling the concentration of aerobic sludge and the sludge settling ratio in the hydrolysis tank, effective decomposition of organic matter in the wastewater can be achieved. By installing aeration components in the stripping tank, air enters the tank and is used to purge hydrogen sulfide gas from the wastewater, which is then treated by the exhaust gas treatment system.

[0018] The waste gases from the first collection tank, second collection tank, hydrolysis tank, stripping tank, primary sedimentation tank, water distribution tank, anaerobic reactor, and anaerobic sedimentation tank are connected to the tail gas treatment system via waste gas pipelines. The tail gas treatment system includes an alkaline spray tower, the exhaust port of which is connected to a deodorization box. The deodorization box includes a box body with an air inlet on one side of the bottom and an exhaust port on the top. Inside the box body is a Y-shaped filter connected to the air inlet pipe, and above the filter are multiple layers of spray pipes. The waste gases from each tank enter the alkaline spray tower through pipelines. After alkaline spray absorption treatment, the untreated waste gases enter the deodorization box. First, the activated carbon adsorption layer in the filter absorbs odors, and then the spray liquid absorbs toxic gases, thus reducing the impact on the surrounding environment.

[0019] Because the distribution tank is equipped with a steam inlet pipe, the pH of the wastewater in the tank is adjusted to 6.7-7.5, and the temperature is adjusted to 35-37℃. The temperature and pH of the wastewater required for the anaerobic reactor are thus adjusted through the distribution tank.

[0020] The anaerobic reactor comprises a main body with a gas-liquid separation chamber at its top. Inside the main body, from top to bottom, are interconnected first treatment chambers, second treatment chambers, and a mixing chamber. A biogas outlet is located at the top of the gas-liquid separation chamber. Multiple perforated first partitions separate the first and second treatment chambers, and multiple perforated second partitions separate the second and mixing chambers. A perforated third partition separates the second and mixing chambers. A return pipe connecting the mixing chamber and the first treatment chamber is located on one side of the main body. A wastewater inlet and a sludge inlet are located on one side of the mixing chamber. A wastewater outlet is located on the side of the main body corresponding to the upper part of the first partitions. The influent parameters for the anaerobic reactor are controlled as follows: pH 6.7-7.5, COD / SO4... 2->10; effluent parameters are pH 6.7-7.5, volatile acid <300mg / l, COD <1500mg / l, alkalinity >1500mg / l; operating temperature is 33-37℃. Workers pump anaerobic sludge into the mixing chamber inside the main unit through the sludge inlet, then pump wastewater from the distribution tank into the mixing chamber to mix with the sludge. The wastewater and sludge pass through the third and second separation components, sequentially entering the second and first treatment chambers. The sludge performs anaerobic fermentation on the organic matter in the wastewater, producing a large amount of biogas that passes through the first separation component into the gas-liquid separation chamber, and finally exits from the biogas outlet for collection and utilization. Throughout the treatment process, the wastewater and sludge circulate within the main unit through a return pipe, achieving mixing. When sludge needs to be replaced, it is discharged through the sludge inlet, and fresh sludge is then introduced into the mixing chamber through the sludge inlet. The entire process controls the influent and effluent parameters as well as the operating conditions, facilitating the full decomposition and treatment of organic matter in the wastewater by the anaerobic sludge.

[0021] Since both the first and second partition components include annular bodies, and the interior of the annular body is provided with multiple first partitions and multiple second partitions arranged in a cross shape; the multiple first partitions and multiple second partitions are distributed on the body at equal intervals; the cross-section of the first partition is V-shaped, and multiple upper connecting rods perpendicular to the first partition are provided between two adjacent first partitions, with multiple lower connecting rods below the upper connecting rods; the upper and lower connecting rods are arranged in an alternating up-and-down manner; the third partition component includes a disc body with multiple through holes. After the wastewater and sludge are mixed in the mixing chamber, they pass through the through holes on the disc body (third partition component) into the second treatment chamber for anaerobic fermentation treatment, and then pass through the gap enclosed by the first and second partitions (second partition components) into the first treatment chamber, where the sludge performs anaerobic fermentation treatment on the organic matter in the wastewater. The first, second, and third partition components described above have a simple structure, reasonable design, facilitate wastewater flow, and also achieve sludge retention. Attached Figure Description

[0022] Figure 1 is a process flow diagram of the present invention;

[0023] Figure 2 is a schematic diagram of the anaerobic reactor in this invention;

[0024] Figure 3 is a structural schematic diagram of the first or second partition component in Figure 2;

[0025] Figure 4 is a schematic diagram of the exhaust gas treatment system in this invention;

[0026] Among them, 1-body, 2-gas-water separation chamber, 20-biogas outlet, 21-collection plate, 3-first treatment chamber, 4-second treatment chamber, 5-mixing chamber, 50-wastewater inlet, 51-sludge inlet, 6-first partition component, 60-circular body, 61-first partition, 62-second partition, 63-upper connecting rod, 64-lower connecting rod, 7-second partition component, 8-third partition component, 80-disc body, 81-through hole, 9-return pipe, 10-wastewater conveying pipe, 11-conveying pump, 12-control valve, 13-wastewater outlet, 14-alkali spray tower, 15-deodorization box, 150-filter, 151-activated carbon layer. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] Example 1

[0029] A method for treating stevia wastewater includes the following steps:

[0030] (1) The acid and alkaline water and the effluent after adsorption by the resin column are collected in the first collection tank and the second collection tank respectively, and transported to the inside of the equalization tank by the transfer pump. The mixed wastewater is adjusted to pH 6.0 and then set aside.

[0031] (2) Wastewater in the equalization tank is transported to the hydrolysis tank by a transfer pump (the concentration of anaerobic sludge is greater than 5000 mg / L and the sludge settling ratio is 30-50%). After anaerobic sludge treatment in the hydrolysis tank for 15 hours, the wastewater enters the stripping tank (which is equipped with aeration components, including an aeration main pipe and multiple aeration branch pipes connected to the aeration main pipe, with multiple aeration heads on the aeration branch pipes, and one end of the aeration main pipe is connected to an induced draft fan; the pH of the wastewater in the stripping tank is adjusted to 6.5). After pH adjustment and anaerobic sludge treatment for 8 hours, the wastewater enters the primary sedimentation tank. After 4 hours of settling and stratification, the wastewater enters the distribution tank (which has a steam inlet pipe inside). The sludge enters the hydrolysis tank through a return pump.

[0032] (3) Adjust the pH (6.7) and temperature (33℃) of the wastewater in the distribution tank, and then pump the wastewater into the anaerobic reactor (control the influent parameters of the anaerobic reactor to pH 6.7 and COD / SO4). 2->10; effluent indicators are pH 6.7, volatile acid <300mg / l, COD <1500mg / l, alkalinity >1500mg / l; operating temperature is 33℃). After 10 hours of anaerobic sludge treatment, the wastewater enters the anaerobic sedimentation tank; after another 2 hours of anaerobic sludge treatment in the sedimentation tank, the anaerobic sludge is returned to the distribution tank and then returned to the interior of the anaerobic reactor. The wastewater continues to enter the interior of the activated sludge tank and undergoes aerobic sludge treatment for 18 hours. The wastewater and a small amount of sludge enter the interior of the secondary sedimentation tank. After 8 hours of settling and stratification, the wastewater that meets the discharge standards enters the drainage well and is discharged; part of the sludge after settling and stratification is returned to the interior of the activated sludge tank, and part enters the interior of the sludge thickening tank.

[0033] (4) After the sludge in the sludge thickening tank is thickened, it enters the sludge conditioning tank. Flocculant (polyaluminum chloride, the amount added is 6% of the dry weight of the sludge) is added and stirred for 15 minutes. The flocculated sludge enters the sludge dewatering machine (sludge filter press) for dewatering. The collected filter cake is transported off-site for treatment. The filtrate after dewatering and the wastewater after thickening in the sludge thickening tank enter the collection well together. The wastewater inside the collection well enters the first collection tank through a transfer pump.

[0034] The specific operation of the above treatment method is as follows: Acidic and alkaline wastewater from stevia production, as well as the effluent after passing through the resin column, are collected. The pH is adjusted to a slightly acidic level. The wastewater first enters a hydrolysis tank for anaerobic sludge treatment, then enters a stripping tank for further anaerobic sludge treatment, and then enters a settling tank for sedimentation and stratification. The wastewater then enters a distribution tank, where the pH and temperature are adjusted before entering the anaerobic reactor. Anaerobic sludge further decomposes the organic matter in the wastewater. The wastewater and a small amount of sludge enter an anaerobic settling tank for sedimentation and stratification. The sludge is returned to the distribution tank and then re-enters the anaerobic reactor for recycling. The wastewater is pumped into an activated sludge tank for further treatment. After aerobic sludge treatment, it enters the secondary sedimentation tank for static sedimentation. Through the circulation of aerobic and anaerobic sludge, the organic matter in the wastewater is effectively decomposed, and the wastewater that meets the discharge standards is discharged into the drainage well. The sludge in the secondary sedimentation tank enters the sludge thickening tank. After static stratification, the sludge enters the sludge conditioning tank. After adding flocculant, the inorganic matter in the wastewater is settled. Finally, the sludge is transported to the sludge dewatering machine. After dewatering, the filter cake is collected and transported out. The collected filtrate and the wastewater collected after static stratification in the sludge thickening tank enter the interior of the collection well and then enter the first collection tank for reprocessing.

[0035] The anaerobic reactor, as shown in Figures 2 and 3, includes a main body 1. The top of the main body 1 is equipped with a gas-liquid separation chamber 2. The interior of the main body 1 is provided with a first treatment chamber 3, a second treatment chamber 4, and a mixing chamber 5, which are interconnected from top to bottom. The top of the gas-liquid separation chamber 2 is equipped with a biogas outlet 20. There are multiple hollowed-out first partition components 6 between the first treatment chamber 3 and the gas-liquid separation chamber 2. There are multiple hollowed-out second partition components 7 between the first treatment chamber 3 and the second treatment chamber 4. There is a hollowed-out third partition component 8 between the second treatment chamber 4 and the mixing chamber 5. A return pipe 9 connected to the mixing chamber 5 and the first treatment chamber 3 is provided on one side of the main body 1. There is a wastewater inlet 50 and a sludge inlet 51 on one side of the mixing chamber 5. There is a wastewater outlet 13 on the side of the main body 1 corresponding to the upper part of the first partition component 6. The first dividing component 6 and the second dividing component 7 both include an annular body 60. The annular body 60 contains multiple first partitions 61 and multiple second partitions 62, which are distributed on the main body 1 at equal intervals. The first partition 61 has a V-shaped cross-section. Multiple upper connecting rods 63, perpendicular to the first partition 61, are provided between adjacent first partitions 61. Multiple lower connecting rods 64 are provided below the upper connecting rods 63. The upper connecting rods 63 and lower connecting rods 64 are arranged in an alternating vertical arrangement. The third dividing component 8 includes a disc 80, which has multiple through holes 81.

[0036] In practical applications, anaerobic sludge is pumped into the mixing chamber inside the main body through the sludge inlet. Wastewater from the distribution tank is pumped into the mixing chamber inside the main body through the wastewater inlet to mix with the sludge. The wastewater and anaerobic sludge pass through the through holes on the disc (third partition component) into the second treatment chamber for anaerobic fermentation. Then, they pass through the gap between the first and second partitions (second partition components) and enter the first treatment chamber, where the sludge performs anaerobic fermentation on the organic matter in the wastewater. The large amount of biogas produced passes through the gap between the first and second partitions (first partition components) and enters the gas-liquid separation chamber. Finally, it is discharged from the biogas outlet for collection and utilization. Throughout the entire treatment process, the wastewater and sludge inside the main body circulate through the return pipe, achieving mixing of the wastewater and sludge. When sludge needs to be replaced, it is discharged through the sludge inlet, and fresh sludge is then introduced into the mixing chamber through the sludge inlet. The above-described anaerobic fermentation device for wastewater treatment is reasonably designed, simple in structure, and easy to operate, which greatly improves the efficiency of wastewater treatment. At the same time, it can also utilize the organic matter in the wastewater to produce biogas, and then utilize the biogas, bringing economic benefits to the enterprise.

[0037] One end of the return pipe 9 is connected to the first treatment chamber 3, and the other end of the return pipe 9 is connected to the wastewater inlet via the wastewater delivery pipe 10. A delivery pump 11 is installed on the wastewater delivery pipe 10, and control valves 12 are installed on both the return pipe 9 and the wastewater delivery pipe 10. A large amount of wastewater from the distribution tank is transported into the mixing chamber through the wastewater delivery pipe. The wastewater and sludge circulate freely through the return pipe. The flow of wastewater and sludge is regulated by the control valves. This structural design is reasonable and achieves the circulating flow of wastewater and sludge.

[0038] The gas-liquid separation chamber 2 is internally equipped with multiple inclined collection plates 21, each with multiple through holes. The generated biogas carries some moisture into the chamber, flowing upwards through the through holes and finally exiting through the biogas outlet for collection and reuse. The moisture adheres to the collection plates and flows down them into the first treatment chamber, exiting through the wastewater outlet. This gas-liquid separation chamber design is reasonable and simple, effectively separating biogas and a small amount of moisture.

[0039] The waste gas from the first collection tank, the second collection tank, the hydrolysis tank, the stripping tank, the primary sedimentation tank, the water distribution tank, the anaerobic reactor, and the anaerobic sedimentation tank is connected to the tail gas treatment system through waste gas pipelines. As shown in Figure 4, the tail gas treatment system includes an alkaline spray tower 14 (with an air inlet on one side of the bottom, an exhaust outlet on the top, and multiple layers of packing material inside, with multiple spray pipes above the packing material). The exhaust outlet of the alkaline spray tower is connected to the deodorization box. The deodorization box includes a box body with an air inlet on one side of the bottom and an exhaust outlet on the top. Inside the box body is a Y-shaped filter 150 (made of filter plate) connected to the air inlet pipe. Inside the filter is an activated carbon adsorption layer 151, and multiple spray pipes are located on the upper part of the filter.

[0040] Example 2

[0041] The difference from Example 1 is:

[0042] (1) Adjust the pH of the mixed wastewater to 7.0 and set aside;

[0043] (2) The anaerobic sludge in the hydrolysis tank was treated for 18 hours, and the pH of the wastewater in the stripping tank was adjusted to 6.8 and the anaerobic sludge was treated for 10 hours.

[0044] (3) Adjust the pH (7.0) and temperature (35℃) of the wastewater in the distribution tank. The influent parameters of the anaerobic reactor are pH 7.0 and COD / SO4. 2->10; effluent indicators are pH 7.0, volatile acid <300mg / l, COD <1500mg / l, alkalinity >1500mg / l; operating temperature is 35℃; the anaerobic sludge treatment time for wastewater in the anaerobic reactor is 12.5h; the treatment time in the anaerobic sedimentation tank is 2.5h; the aerobic treatment time in the activated sludge tank is 22h; and the settling time in the secondary sedimentation tank is 10h.

[0045] (4) After adding flocculant to the sludge conditioning tank, stir and mix for 23 minutes. The rest of the operation is the same.

[0046] Example 3

[0047] The difference from Example 1 is:

[0048] (1) Adjust the pH of the mixed wastewater to 8.0 and set aside;

[0049] (2) Adjust the pH of the wastewater in the stripping tank to 7.0;

[0050] (3) Adjust the pH (7.5) and temperature (37℃) of the wastewater in the distribution tank. The influent parameters of the anaerobic reactor are pH 7.5 and COD / SO4. 2- >10; effluent indicators are pH 7.5, volatile acid <300mg / l, COD <1500mg / l, alkalinity >1500mg / l; operating temperature is 37℃; the anaerobic sludge treatment time for wastewater in the anaerobic reactor is 15h; the treatment time in the anaerobic sedimentation tank is 5h; the aerobic treatment time in the activated sludge tank is 25h; and the settling time in the secondary sedimentation tank is 12h.

[0051] (4) After adding flocculant to the sludge conditioning tank, stir and mix for 30 minutes. The rest of the operation is the same.

[0052] The anaerobic and aerobic sludge used in Examples 1-3 were all purchased from the manufacturer. The COD of the wastewater in the equalization tank in step (1) of Examples 1-3 was 8000-10000 mg / L.

[0053] To better demonstrate that the treatment method of the present invention has a better treatment effect, a comparative example 1 is given with reference to Example 3; the treatment methods of Example 1, Example 2 and Example 3 of the present invention and the wastewater treated by Comparative Example 1, and the final wastewater discharge indicators are shown in Table 1.

[0054] Comparative Example 1

[0055] Unlike Example 3, the wastewater after settling in the primary sedimentation tank does not enter the distribution tank or anaerobic reactor for treatment, but instead directly enters the activated sludge tank for treatment; the rest of the operation is the same.

[0056] Table 1

[0057] Example 1 COD (mg / L) Ammonia Nitrogen (mg / L) pH Example 2 15 20.0 17.5 Example 3 13 80.0 17.5 Comparative Example 1 45 0 35 8.8 surface

[0058] The data in Table 1 shows that the treatment method of the present invention significantly improves the efficiency of wastewater treatment and reduces the COD value and ammonia nitrogen content of the wastewater by reducing the cost of steviol glycoside production.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for treating stevia wastewater, characterized in that: The treatment method includes the following steps: (1) Collect the acid and alkaline water from stevia production and the effluent after adsorption by the resin column in the first and second collection tanks respectively, and transport them to the interior of the equalization tank by a transfer pump. Adjust the pH of the mixed wastewater to 6.0-8.0 and set it aside; (2) Transport the wastewater in the equalization tank to the hydrolysis tank by a transfer pump. After the wastewater is treated by anaerobic sludge in the hydrolysis tank, it enters the stripping tank. After the pH is adjusted and the wastewater is treated by anaerobic sludge, it enters the sedimentation tank. After settling and stratification, the wastewater enters the sedimentation tank. Inside the water distribution tank, sludge enters the hydrolysis tank via a return pump; (3) Adjust the pH and temperature of the wastewater in the water distribution tank, and the wastewater enters the anaerobic reactor via a transfer pump. After anaerobic sludge treatment, the wastewater enters the anaerobic sedimentation tank; it continues to be treated by anaerobic sludge in the sedimentation tank, and the anaerobic sludge is returned to the water distribution tank and then returned to the anaerobic reactor. The wastewater continues to enter the activated sludge tank for aerobic sludge treatment. The sewage and a small amount of sludge enter the secondary sedimentation tank, and after settling and stratification, it meets the discharge standards. After entering the drainage well, the wastewater is discharged to the industrial park's wastewater treatment plant. The sludge, after settling and stratification, is partially returned to the activated sludge tank and partially enters the sludge thickening tank. The anaerobic reactor includes a main body with a gas-liquid separation chamber at the top. Inside the main body, from top to bottom, are interconnected first treatment chambers, second treatment chambers, and a mixing chamber. The top of the gas-liquid separation chamber has a biogas outlet. Multiple perforated first partitions are located between the first treatment chamber and the gas-liquid separation chamber. Multiple perforated second partitions are located between the first treatment chamber and the second treatment chamber. A perforated third partition is located between the second treatment chamber and the mixing chamber. A return pipe connected to the mixing chamber and the first treatment chamber is located on one side of the main body. A wastewater inlet and a sludge inlet are located on one side of the mixing chamber. A wastewater outlet is located on the side of the main body corresponding to the upper part of the first partition. The influent parameters of the anaerobic reactor are controlled as follows: pH 6.7-7.5, COD / SO4. 2- >10; effluent parameters are pH 6.7-7.5, volatile acid <300mg / l, COD <1500mg / l, alkalinity >1500mg / l; operating temperature is 33-37℃; both the first and second separating components include an annular body, and the annular body is provided with multiple first partitions and multiple second partitions inside, the first partitions and the second partitions are arranged in a cross shape; the multiple first partitions and the multiple second partitions are distributed on the body at equal intervals; the cross-section of the first partition is V-shaped, and multiple partitions are provided between two adjacent first partitions. The upper connecting rod is perpendicular to the first partition, and multiple lower connecting rods are provided below the upper connecting rod; wherein the upper connecting rod and the lower connecting rod are arranged in an alternating manner; the third partition component includes a disc body, and multiple through holes are provided on the disc body; (4) After the sludge in the sludge thickening tank is thickened, it enters the sludge conditioning tank. After adding flocculant and stirring, the flocculated sludge enters the sludge dewatering machine for dewatering treatment. The collected filter cake is transported off-site for treatment. The filtrate after dewatering treatment and the wastewater after thickening in the sludge thickening tank enter the water collection well together. The wastewater inside the water collection well enters the interior of the first water collection tank through a conveying pump.

2. The method for treating stevia wastewater according to claim 1, characterized in that: The sludge concentration in the hydrolysis tank is greater than 5000 mg / L, and the sludge settling ratio is 30-50%. The stripping tank is equipped with an aeration component, which includes an aeration main pipe and multiple aeration branch pipes connected to the aeration main pipe. Multiple aeration heads are provided on the aeration branch pipes. One end of the aeration main pipe is connected to an induced draft fan. The pH of the wastewater in the stripping tank is adjusted to 6.5-7.

0.

3. The method for treating stevia wastewater according to claim 1, characterized in that: The waste gas from the first collection tank, the second collection tank, the hydrolysis tank, the stripping tank, the primary sedimentation tank, the water distribution tank, the anaerobic reactor, and the anaerobic sedimentation tank is connected to the tail gas treatment system through waste gas pipelines. The tail gas treatment system includes an alkaline spray tower, the exhaust port of which is connected to a deodorization box. The deodorization box includes a box body, an air inlet on one side of the bottom of the box body, an exhaust port on the top of the box body, a Y-shaped filter connected to the air inlet pipe inside the box body, an activated carbon adsorption layer inside the filter, and multiple spray pipes on the upper part of the filter.

4. The method for treating stevia wastewater according to claim 1, characterized in that: The water distribution tank is equipped with a steam inlet pipe. The pH of the wastewater in the water distribution tank is adjusted to 6.7-7.5, and the temperature is adjusted to 35±2℃.

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