A denitrification membrane bioreactor wastewater treatment method

Abstract

The present application relates to sewage treatment technical field, specifically to a kind of denitrification membrane bioreactor sewage treatment method.The present application overcomes the problem of low efficiency of denitrification and phosphorus removal in traditional sewage treatment method.The present application effectively adsorbs and decomposes ammonia nitrogen molecules in sewage by preparing hydrophilic suspended filler;Suitable aeration intensity and adjusting the hydraulic retention time between each unit make organic matter in sewage and sludge decompose deeply, form gradient environment of aerobic, anoxic and anaerobic;Microbial growth promoter as electron donor, supply the carbon source and nitrogen source required for microbial growth and reproduction;Mechanical stirring is carried out in anoxic unit, and suitable swing angle is set in each unit cell, so that sludge and microorganisms are fully contacted, the filtration capacity in denitrification membrane bioreactor is improved, and the time of biofilm formation is shortened;Linkage is formed between anaerobic unit, anoxic unit, membrane separation zone and aerobic unit, and the efficiency of denitrification and phosphorus removal in denitrification membrane bioreactor is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the sewage treatment technical field, specifically to a denitrification membrane bioreactor sewage treatment method. BACKGROUND

[0002] With the acceleration of urbanization and population growth, the degree of water resource tension is increasing. Sewage treatment and recycling can effectively alleviate the water resource pressure; at the same time, sewage treatment can remove harmful substances in sewage and prevent the harmful substances from damaging the ecological environment. Therefore, sewage recycling and treatment is a key measure to realize sustainable resource utilization and environmental protection.

[0003] Traditional sludge treatment methods include activated sludge method and biofilm method. The activated sludge method can adapt to different water quality and quantity of sewage, and has strong impact load capacity; but the method consumes a large amount of energy in the aeration process, and the microbial activity is reduced under low temperature conditions, and the denitrification and phosphorus removal effect is unstable. The volume load of the biofilm method is high, and a large amount of sewage can be treated in a small space; but the anoxic area of the traditional biofilm is small, which is not conducive to the denitrification; at the same time, the carrier is easily blocked by suspended solids and organic matter in the sewage, affecting the growth and metabolism of the biofilm, thereby reducing the denitrification and phosphorus removal efficiency.

[0004] Based on the limitations of the above treatment methods, the present application adopts a denitrification membrane bioreactor treatment method, which combines the advantages of activated sludge method and biofilm method, and can improve the denitrification and phosphorus removal efficiency of domestic sewage under the conditions of energy saving, treatment time and land saving. SUMMARY

[0005] The present application aims to provide a denitrification membrane bioreactor sewage treatment method, which effectively adsorbs and decomposes ammonia nitrogen molecules in sewage by preparing hydrophilic suspended filler; suitable aeration intensity and adjusting the hydraulic retention time between each unit to make the organic matter in sewage and sludge decompose deeply, forming a gradient environment of aerobic, anoxic and anaerobic; the microbial growth promoter as an electron donor supplies the carbon source and nitrogen source required for microbial growth and reproduction; mechanical stirring is carried out in the anoxic unit, and the appropriate swing angle is set in each unit cell to make the sludge and microorganisms fully contact, improve the filtration capacity in the denitrification membrane bioreactor, and shorten the membrane formation time; the linkage between the anaerobic unit, the anoxic unit, the membrane separation zone and the aerobic unit is formed to synergistically improve the denitrification and phosphorus removal efficiency in the denitrification membrane bioreactor.

[0006] In view of the deficiencies of the prior art, the present application provides a denitrification membrane bioreactor wastewater treatment method. The present application sets four reaction zones inside the biological membrane denitrification reactor, and the biological membranes in each reaction zone are cultured separately, which can better form a biological membrane system with specific performance and ensure that each reaction zone can exert denitrification and phosphorus removal performance under suitable conditions.

[0007] To achieve the above object, the present application provides the following technical solutions.

[0008] The present application provides a denitrification membrane bioreactor wastewater treatment method, wherein the denitrification membrane bioreactor comprises, from top to bottom, an anaerobic unit 1, an anoxic unit 2, a membrane separation zone 3 and an aerobic unit 4; the aerobic unit 4, the anoxic unit 2 and the anaerobic unit 1 are each provided with a grid room with a swing angle and a light intensity of 2500 lx.

[0009] The denitrification membrane bioreactor wastewater treatment method is as follows.

[0010] The aerobic unit 4, the anoxic unit 2 and the anaerobic unit 1 of the reaction tank are filled with hydrophilic suspended fillers accounting for 3 / 5 of the total volume of each reaction unit.

[0011] Active sludge with a water content of 95% is loaded onto the hydrophilic suspended fillers in each unit, and each unit is filled; the active sludge is taken from a certain domestic wastewater treatment plant in Nanjing, Jiangsu;

[0012] Wastewater is injected from the bottom of the denitrification membrane bioreactor, and is first injected into the aerobic unit 4 by a water pump; a microbial growth promoter is added to the aerobic unit 4, and the mixture is obtained after 24 h of muffled exposure; then 1 / 3 of the mixture is discharged, and continuous wastewater feeding is started; the aeration intensity of the aerobic unit 4 is set to 3-5 mg / L, and the hydraulic retention time is 8-10 h; the rotational speed of the electric mechanical stirring device 5 in the anoxic unit 2 is set to 20-30 rpm, and the stirring power is 1.5-2.0 kW; the hydraulic retention time ratio of the aerobic unit 4, the anoxic unit 2 and the anaerobic unit 1 is set to 8-10:5-7:4-5.

[0013] Preferably, the volume ratio of the aerobic unit 4, the anoxic unit 2 and the anaerobic unit 1 is 2:1:2.

[0014] Preferably, the aerobic unit 4 and the anaerobic unit 1 are each provided with five compartments; the compartments are staggered in the aerobic unit 4 and the anaerobic unit 1; the sewage is injected into the denitrification membrane bioreactor, and is first injected into the aerobic unit 4 by a water pump, and sequentially passes through the five compartments of the aerobic unit 4; then, under the action of the water pump, the sewage is separated by the membrane separation zone 3 and then enters the anoxic unit 2; the rotational speed of the electromechanical stirring device 5 in the anoxic unit 2 is set to 20-30 rpm, and the stirring power is 1.5-2.0 kW, so as to stir and pump; then, the partition plate between the anoxic unit 2 and the anaerobic unit 1 is opened, so that the sewage sequentially passes through the five compartments of the anaerobic unit 1 and then is discharged; the compartments in the aerobic unit 4 and the anaerobic unit 1 can swing at an angle, and the angle of the compartment swinging is 60°-75° with respect to the vertical direction of the denitrification membrane bioreactor.

[0015] Preferably, a partition plate is arranged between the anoxic unit 2 and the anaerobic unit 1.

[0016] Preferably, the preparation process of the hydrophilic suspended filler is as follows: 50 parts of cultured Arthrospira platensis are subjected to centrifugal concentration treatment, and after the supernatant is removed, the Arthrospira platensis is washed with distilled water, and after two centrifugal treatments, an algal cell solution is obtained; 30 parts of the algal cell solution and 40 parts of a sodium alginate solution with a concentration of 1wt%-3wt% after sterilization treatment are fully mixed to form a mixed solution; the mixed solution is slowly dropped into a ferrous chloride solution with a concentration of 3% after sterilization and stirring to form a cell group with a particle size of 2-3 mm; the cell group is placed in a refrigerator at a temperature of 4-8℃ for 24 h, and after being taken out of the refrigerator, the cell group is washed twice with distilled water to obtain algal cell glue balls; 30 parts of activated carbon and 10 parts of polyethylene are added to the algal cell glue balls to fix the algal cell glue balls and obtain the hydrophilic suspended filler.

[0017] Preferably, the microbial growth promoter includes 30-40 parts of metal salt, 20-30 parts of putrescine, 10-15 parts of glucose, and 7 parts of sodium acetate.

[0018] Preferably, the metal salt is composed of calcium salt CaCl2, copper salt CuCl2, magnesium salt MgSO4, and ferrous salt FeSO4; the ratio of the calcium salt CaCl2, the copper salt CuCl2, the magnesium salt MgSO4, and the ferrous salt FeSO4 is 3:1:2:2.

[0019] Preferably, the internal sewage reflux ratio of the denitrification membrane bioreactor is 300%, and the reflux ratio between the aerobic unit 4 and the anoxic unit 2 is 1.7.

[0020] It should be noted that the "parts" and "parts ratio" mentioned in the present application are "mass parts" and "mass parts ratio".

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] 1. The algae cell glue ball prepared under suitable particle size and temperature conditions, in combination with activated carbon and polyethylene, forms a hydrophilic suspended filler; the hydrophilic suspended filler has a large specific surface area, can effectively adsorb and decompose ammonia nitrogen molecules in the sewage, and provides more attachment sites and a good growth environment for microorganisms, thereby improving the removal efficiency of ammonia nitrogen in the sewage by the denitrification membrane bioreactor, and promoting the denitrification and phosphorus removal process of the denitrification membrane bioreactor.

[0023] 2. Suitable aeration intensity of the aerobic unit, and the hydraulic retention time ratio of the aerobic unit, the anoxic unit and the anaerobic unit, are conducive to the oxidation and decomposition of organic matter in the aerobic unit into small molecules, providing a carbon source for the denitrification of the anoxic unit; the anoxic unit removes nitrate and nitrite through denitrification, and further reduces the chemical oxygen demand; the anaerobic unit carries out anaerobic fermentation and other processes, and deeply degrades the organic matter; thereby forming a gradient environment of oxygen, anoxia and anaerobic, promoting the synergistic effect between microorganisms, and improving the overall chemical oxygen demand removal rate and the efficiency of denitrification and phosphorus removal of the denitrification membrane bioreactor.

[0024] 3. The metal salt, putrescine, glucose and sodium acetate in the microbial growth promoter act as electron donors, provide carbon and nitrogen sources required for microbial growth and reproduction, and the multi-component synergistic effect provides comprehensive nutrition for microorganisms, so that a good positive cycle is formed in the entire denitrification membrane bioreactor, microorganisms are trapped in the reactor, which is conducive to the growth of slowly proliferating microorganisms, and improves the nitrification efficiency in the system; thereby improving the sludge concentration, effluent quality and denitrification and phosphorus removal efficiency in the denitrification membrane bioreactor.

[0025] 4. The electric mechanical stirring device is provided with a suitable rotating speed and power, and a suitable swing angle of each unit cell, so that the sludge can fully contact with the microorganisms, the sewage is filtered more uniformly under more uniform water flow velocity and pressure distribution, the flow smoothness of the sewage from the aerobic unit to the anoxic unit, and from the anoxic unit to the anaerobic unit in the reactor is improved, which helps to create a suitable growth environment for aerobic phosphorus bacteria, denitrifying bacteria and anaerobic phosphorus-releasing bacteria; improves the contact efficiency between pollutants in the sewage and microorganisms, further improves the filtration speed and treatment capacity of the membrane, and further improves the denitrification and phosphorus removal efficiency in the sewage. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The total phosphorus removal rate test results of the wastewater in the embodiments 7-12 and the comparative examples 14-18 of the wastewater treatment method of the denitrification membrane bioreactor of the present application;

[0027] Figure 2 The structural diagram of the denitrification membrane bioreactor of the present application;

[0028] In the figure: 1, anaerobic unit; 2, anoxic unit; 3, membrane separation zone; 4, aerobic unit; 5, electric mechanical stirring device. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0030] Please refer to Figures 1 to 2 The present application provides a denitrification membrane bioreactor wastewater treatment method, and the technical solution is as follows:

[0031] Embodiment 1

[0032] A denitrification membrane bioreactor wastewater treatment method, the denitrification membrane bioreactor is sequentially provided with an anaerobic unit, an anoxic unit, a membrane separation zone and an aerobic unit from top to bottom; the aerobic unit, the anoxic unit and the anaerobic unit are all provided with a grid room with a swing angle and a light intensity of 2500lx; the grid rooms are staggered distributed in each unit;

[0033] The denitrification membrane bioreactor wastewater treatment method is as follows:

[0034] Firstly, 3 / 5 of the total volume of each reaction unit is filled with hydrophilic suspended filler in the aerobic unit, the anoxic unit and the anaerobic unit of the reaction tank;

[0035] Then, the activated sludge with a water content of 95% is loaded on the hydrophilic suspended filler in each unit to fill each unit; the activated sludge is taken from a domestic wastewater treatment plant in Nanjing, Jiangsu;

[0036] The wastewater is injected from the bottom of the denitrification membrane bioreactor, and is first injected into the aerobic unit by a water pump, sequentially passes through the five grid rooms of the aerobic unit, and a microbial growth promoter is added into the aerobic unit, and the mixed liquor is obtained after 24h of muffled exposure; then, 1 / 3 of the mixed liquor is discharged, and the continuous wastewater is started to be injected, and the wastewater sequentially passes through the five grid rooms of the aerobic unit; during this period, the aeration intensity of the aerobic unit is set to 3mg / L, and the hydraulic retention time is 8h; then, under the action of the water pump, the wastewater passes through the membrane separation zone, and then enters the anoxic unit, and the wastewater is stirred and filtered under the electric mechanical stirring device with a rotation speed of 20rpm and a stirring power of 1.5kW, and the hydraulic retention time is 5h; then, the partition plate between the anoxic unit and the anaerobic unit is opened, so that the wastewater sequentially passes through the five grid rooms of the anaerobic unit, and the effluent is discharged after 4h of hydraulic retention; during this period, the grid room swing angle in the aerobic unit and the anaerobic unit is set to 75° back and forth swing with the vertical direction of the denitrification membrane bioreactor.

[0037] The volume ratio of the aerobic unit, the anoxic unit and the anaerobic unit is 2:1:2.

[0038] The internal wastewater reflux ratio of the denitrification membrane bioreactor is 300%; the reflux ratio between the aerobic unit and the anoxic unit is 1.7.

[0039] The preparation process of the hydrophilic suspended filler is as follows: 50 parts of the cultured Arthrospira platensis are subjected to centrifugal concentration treatment, and after the supernatant is removed, the Arthrospira platensis is washed with distilled water, and after two centrifugal treatments, an algal cell solution is obtained; 30 parts of the algal cell solution and 40 parts of a 1wt% sterilized sodium alginate solution are thoroughly mixed to form a mixed solution; the mixed solution is slowly dropped into 3 parts of a 3% sterilized ferrous chloride solution and stirred to form a cell group with a particle size of 2mm; the cell group is placed in a refrigerator at a temperature of 5°C for 24h, and after being taken out of the refrigerator, the cell group is washed twice with distilled water to obtain algal cell beads; 30 parts of activated carbon and 10 parts of polyethylene are added to the algal cell beads to fix the algal cell beads and obtain the hydrophilic suspended filler.

[0040] The microbial growth promoter includes 38 parts of metal salt, 22 parts of putrescine, 11 parts of glucose and 7 parts of sodium acetate.

[0041] The metal salt is composed of calcium salt CaSO4, copper salt CuSO4, magnesium salt MgSO4and ferrous salt FeSO4; the part ratio between the calcium salt CaCl2, the copper salt CuCl2, the magnesium salt MgSO4and the ferrous salt FeSO4is 3:1:2:2.

[0042] Examples 2-6

[0043] Compared with Example 1, the parameters are adjusted, and the specific adjustments are summarized in Table 1; in Table 1, the temperature is the temperature at which the cell group is placed in the refrigerator.

[0044] Table 1: Preparation parameter adjustments of Examples 1-6

[0045]

[0046] Examples 7-12

[0047] Compared with Example 1, the parameters are adjusted, and the specific adjustments are summarized in Table 2; in Table 2, the aeration intensity is the aeration intensity in the aerobic unit; the rotation speed is the rotation speed of the electric mechanical stirring device in the anoxic unit; the stirring power is the stirring power of the electric mechanical stirring device in the anoxic unit; the hydraulic retention time ratio is the hydraulic retention time ratio of the aerobic unit, the anoxic unit and the anaerobic unit; the angle is the swinging angle of the grid with respect to the vertical direction of the denitrification membrane bioreactor.

[0048] Table 2: Preparation parameter adjustments of Examples 7-12

[0049]

[0050] In order to verify the necessity of some technical solutions in the present application to achieve the technical effects of the present application, some comparative examples of the present application will be shown and described below.

[0051] Comparative Example 1

[0052] Referring to Example 1, the difference is that the particle size of the cell group is 0.3 mm in the preparation of the hydrophilic suspended filler.

[0053] Comparative Example 2

[0054] Referring to Example 1, the difference is that the particle size of the cell group is 10 mm in the preparation of the hydrophilic suspended filler.

[0055] Comparative Example 3

[0056] Referring to Example 1, the difference is that the cell group is placed in a -20°C refrigerator for 24 h in the preparation of the hydrophilic suspended filler.

[0057] Comparative Example 4

[0058] Referring to Example 1, the difference is that the cell group is placed in a closed condition at room temperature for 24 h in the preparation of the hydrophilic suspended filler.

[0059] Comparative Example 5

[0060] Referring to Example 1, the difference is that 5 parts of metal salt are added to the microbial growth promoter.

[0061] Comparative Example 6

[0062] Referring to Example 1, the difference is that 70 parts of metal salt are added to the microbial growth promoter.

[0063] Comparative Example 7

[0064] Referring to Example 1, the difference is that 3 parts of putrescine are added to the microbial growth promoter.

[0065] Comparative Example 8

[0066] Referring to Example 1, the difference is that 50 parts of putrescine are added to the microbial growth promoter.

[0067] Comparative Example 9

[0068] Referring to Example 1, the difference is that 1 part of glucose is added to the microbial growth promoter.

[0069] Comparative Example 10

[0070] Referring to Example 1, the difference is that 30 parts of glucose are added to the microbial growth promoter.

[0071] Comparative Example 11

[0072] Referring to Example 1, the difference is that the aeration intensity in the aerobic unit is set to 0.5 mg / L.

[0073] Comparative Example 12

[0074] Referring to Example 1, the difference is that the aeration intensity in the aerobic unit is set to 10 mg / L.

[0075] Comparative Example 13

[0076] Referring to Example 1, the difference is that the hydraulic retention time ratio of the aerobic unit, the anoxic unit and the anaerobic unit is 1:1:1.

[0077] Comparative Example 14

[0078] Referring to Example 1, the difference is that the rotating speed of the electric mechanical stirring device in the anoxic unit is set to 5 rpm.

[0079] Comparative Example 15

[0080] Referring to Example 1, the difference is that the rotating speed of the electric mechanical stirring device in the anoxic unit is set to 50 rpm.

[0081] Comparative Example 16

[0082] Referring to Example 1, the difference is that the stirring power of the electric mechanical stirring device in the anoxic unit is 0.3 kW.

[0083] Comparative Example 17

[0084] Referring to Example 1, the difference is that the stirring power of the electric mechanical stirring device in the anoxic unit is 5 kW.

[0085] Comparative Example 18

[0086] Referring to Example 1, the difference is that the 5 compartments set in the aerobic unit, the anoxic unit and the anaerobic unit in the denitrification membrane bioreactor reaction tank do not have a swing function, and the compartments are 90° to the vertical direction of the denitrification membrane bioreactor.

[0087] Experimental Example 1

[0088] The ammonia nitrogen concentration of the influent and the ammonia nitrogen removal rate were determined by the Nash reagent spectrophotometer method (GB 7479-1987); the specific test results are shown in Table 3.

[0089] Table 3 Ammonia nitrogen removal rate test of wastewater treatment in Examples 1-6 and Comparative Examples 1-4

[0090] No. Influent ammonia nitrogen concentration / mg / L Ammonia nitrogen removal rate / % Example 1 53.74 91.3 Example 2 54.41 91.6 Example 3 52.56 90.4 Example 4 57.85 92.6 Example 5 58.23 93.7 Example 6 53.52 91.1 Comparative Example 1 78.34 69.5 Comparative Example 2 41.43 73.6 Comparative Example 3 97.34 53.3 Comparative Example 4 83.65 60.2

[0091] From the data in Table 3, it can be seen that the wastewater treatment tests were carried out on Examples 1-6, and the influent ammonia nitrogen concentration of wastewater in Examples 1-6 was stable in the range of 52.0-59.0 mg / L, and the ammonia nitrogen removal rate of wastewater was higher than 90%. In Comparative Examples 1-2, during the preparation of the hydrophilic suspended filler, if the cell group formed by mixing the algal cell solution with the sodium alginate solution and the ferrous chloride solution has too large or too small particle size, the adsorption performance of the hydrophilic suspended filler to ammonia nitrogen will decrease, thus leading to the decrease of the ammonia nitrogen removal rate of wastewater. This is because the hydrophilic suspended filler prepared from the cell group with too small particle size has small particle size, and is more likely to be lost with the water flow during the wastewater treatment process. Moreover, the smaller particle size of the hydrophilic suspended filler will correspondingly reduce the area available for the attachment of microorganisms, and the surface energy will be higher, which is more unfavorable for the attachment of microorganisms, and the ammonia nitrogen is retained in the wastewater, thus leading to the significant increase of the influent ammonia nitrogen concentration and the corresponding decrease of the ammonia nitrogen removal efficiency. The cell group with too large particle size will make the effective surface area of the prepared hydrophilic suspended filler small, and the contact area between the hydrophilic suspended filler and the ammonia nitrogen molecules in the wastewater small, thus reducing the adsorption capacity of the hydrophilic suspended filler to ammonia nitrogen. Moreover, the hydrophilic suspended filler prepared from the cell group with too large particle size will hinder the flow of water, thus leading to the uneven distribution of the influent ammonia nitrogen concentration in the denitrification membrane bioreactor, and reducing the ammonia nitrogen removal rate of the denitrification membrane bioreactor to the ammonia nitrogen in the wastewater. In Comparative Examples 3-4, during the preparation of the hydrophilic suspended filler, if the cell group is placed in an environment with too high or too low temperature, the adsorption performance and the binding performance of the prepared hydrophilic suspended filler will obviously decrease, thus reducing the ammonia nitrogen removal rate of wastewater. If the cell group is placed in a low-temperature environment of -20°C for too long, not only the water in the cell group will freeze, but also the sodium alginate in the cell group will become hard, thus affecting the binding capacity of sodium alginate to the Spirulina platensis, leading to the obvious decrease of the binding capacity and the adsorption capacity of the prepared hydrophilic suspended filler to microorganisms, and the hydrophilic suspended filler cannot effectively remove the ammonia nitrogen in the wastewater, thus increasing the influent ammonia nitrogen concentration. If the cell group is placed in a sealed environment at room temperature for 24 h, the bacteria will multiply in large quantities in this environment, thus contaminating the hydrophilic suspended filler. Moreover, in the anoxic environment, the Spirulina platensis will lose activity, thus leading to the decrease of the biodegradation capacity of the hydrophilic suspended filler, the increase of the influent ammonia nitrogen concentration during the wastewater treatment process, and the difficulty in improving the ammonia nitrogen removal rate of wastewater.

[0092] In summary, under the suitable particle size and temperature conditions, the algal cell glue balls are combined with activated carbon and polyethylene to form the hydrophilic suspended filler. The hydrophilic suspended filler has a large specific surface area, can effectively adsorb and decompose the ammonia nitrogen molecules in the wastewater, and can provide more attachment sites and a good growth environment for microorganisms, thus improving the ammonia nitrogen removal efficiency of the denitrification membrane bioreactor to the ammonia nitrogen in the wastewater, and promoting the denitrification and phosphorus removal process of the denitrification membrane bioreactor.

[0093] Experimental Example 2

[0094] The dissolved oxygen concentration of the influent was determined according to the method of "Determination of Dissolved Oxygen in Water-Iodimetry" (HJ 506-2009). The chemical oxygen demand removal rate was determined according to the method of "Determination of Chemical Oxygen Demand in Water-Dichromate Method" (HJ 828-2017). The specific test results are shown in Table 4.

[0095] Table 4. Denitrification Membrane Bioreactor Wastewater Treatment Chemical Oxygen Demand Removal Rate Test for Examples 7-12 and Comparative Examples 11-13

[0096] No. Influent dissolved oxygen concentration / mg / L Chemical oxygen demand removal rate / % Example 7 3.43 78.53 Example 8 3.48 78.37 Example 9 3.56 78.26 Example 10 3.27 79.13 Example 11 3.52 79.21 Example 12 3.37 79.02 Comparative Example 11 1.01 33.52 Comparative Example 12 6.21 54.23 Comparative Example 13 5.80 15.34

[0097] From the data in Table 4, sewage treatment tests were performed on Examples 7-13, in which the influent dissolved oxygen concentration of the sewage in Examples 7-13 was stabilized in the range of 3.20-3.60 mg / L, and the chemical oxygen demand removal rate of the sewage was higher than 78%. If the aeration intensity in the aerobic unit is set too high or too low, it will directly affect the influent dissolved oxygen concentration, and too high or too low influent dissolved oxygen concentration in the reactor will reduce the chemical oxygen demand removal rate of the entire sewage treatment system. When the aeration intensity of the aerobic unit is set to 0.5 mg / L, the air intake in the aerobic unit is low, and the low dissolved oxygen concentration directly affects the activity of microorganisms in the aerobic unit, so that the aerobic microorganisms cannot perform aerobic respiration, thereby reducing the oxidation and decomposition ability of organic matter. At the same time, the organic matter that has not been oxidized and decomposed in the aerobic unit will enter the anoxic unit and the anaerobic unit with the water flow, increasing the difficulty of denitrification and phosphorus removal in the subsequent process, and thereby affecting the chemical oxygen demand removal rate of the entire sewage treatment system. When the aeration intensity is set to 10 mg / L, the dissolved oxygen concentration in the aerobic unit is too high, and the microorganisms excessively oxidize organic matter in the high-oxygen environment, thereby generating a large amount of carbon dioxide and water; the growth and reproduction of nitrifying bacteria in the aerobic unit are inhibited, the activity of nitrifying bacteria is reduced, the amount of nitrite generated by ammonia-oxidizing bacteria under the action of ammonia nitrogen in the sewage is reduced, which further leads to a decrease in the amount of nitrite oxidizing bacteria converting nitrite to nitrate, which is not conducive to the subsequent denitrification; secondly, high aeration intensity will cause part of the dissolved oxygen to diffuse into the anoxic unit and the anaerobic unit, which destroys the microenvironment of the anoxic unit and the anaerobic unit, and is not conducive to the denitrification process, thereby affecting the denitrification and phosphorus removal performance of the entire reactor; furthermore, too high influent dissolved oxygen concentration will promote the growth of filamentous bacteria, leading to sludge bulking, and thereby reducing the chemical oxygen demand removal efficiency of the sewage treatment system. If the hydraulic retention time ratio of the aerobic unit, the anoxic unit and the anaerobic unit is set to 1:1:1 in Comparative Example 13, it will seriously affect the influent dissolved oxygen concentration in each unit, leading to a decrease in the chemical oxygen demand removal rate of the entire sewage treatment system.When the hydraulic retention time ratio of the three units is adjusted to 1:1:1, the hydraulic retention time of the aerobic unit is greatly shortened, the transfer and utilization time of oxygen in the aerobic unit is insufficient, which makes the dissolved oxygen concentration in the aerobic unit decrease, the metabolic activity of aerobic microorganisms is inhibited, which affects the oxidation and decomposition of organic matter and the nitrification of ammonia nitrogen; the sewage from the aerobic unit into the anoxic unit contains high dissolved oxygen, which destroys the microenvironment of the anoxic unit, hinders the anaerobic respiration of denitrifying bacteria in the anoxic unit, reduces the amount of nitrate and nitrite reduced to nitrogen gas in the denitrification process, and further affects the anaerobic decomposition of organic matter in the subsequent anaerobic unit; the synergistic effect between the three units is weakened, the amount of organic matter oxidized and decomposed into small molecular substances in the aerobic unit is reduced, and the denitrification and anaerobic fermentation processes in the anoxic unit and the anaerobic unit are limited, which cannot fully utilize the small molecular organic matter produced in the aerobic unit, resulting in a decrease in the overall removal rate of chemical oxygen demand.

[0098] In summary, appropriate aerobic unit aeration intensity and hydraulic retention time ratio of the aerobic unit, the anoxic unit and the anaerobic unit are conducive to the oxidation and decomposition of organic matter into small molecular substances in the aerobic unit, providing carbon source for denitrification in the anoxic unit; the anoxic unit removes nitrate and nitrite through denitrification, while further reducing chemical oxygen demand; the anaerobic unit carries out anaerobic fermentation and other processes to deeply degrade organic matter; thereby forming a gradient environment of aerobic, anoxic and anaerobic, promoting the synergistic effect between microorganisms, and improving the overall chemical oxygen demand removal rate and the efficiency of denitrification and phosphorus removal of the denitrification membrane bioreactor.

[0099] Experimental Example 3

[0100] The sludge concentration was determined by weight method; the total nitrogen removal rate was determined by "Determination of Total Nitrogen in Water - Alkaline Persulfate Digestion UV Spectrophotometric Method" (HJ 636-2012); the specific test results are shown in Table 5.

[0101] Table 5 Total nitrogen removal rate test of wastewater treatment of denitrification membrane bioreactor of examples 1-6 and comparative examples 5-10

[0102] No. Sludge concentration / mg / L Total nitrogen removal rate / % Example 1 4423 76.26 Example 2 4235 75.84 Example 3 4567 77.63 Example 4 4325 76.56 Example 5 4672 78.67 Example 6 4723 79.42 Comparative Example 5 3423 65.38 Comparative Example 6 2374 53.28 Comparative Example 7 3786 67.43 Comparative Example 8 3834 69.67 Comparative Example 9 3245 56.12 Comparative Example 10 5963 58.43

[0103] As shown in Table 5, sewage treatment tests were conducted on Examples 1-6, and the sludge concentration of the sewage in Examples 1-6 was stabilized in the range of 4200-4800 mg / L, and the total nitrogen removal rate of the sewage was higher than 75%. In Comparative Example 5, when the addition amount of metal salt in the microbial growth promoter was too small, the microbial growth promoter lacked calcium salt, magnesium salt, copper salt, ferrous salt and other important components of microbial cell structure, which could not provide sufficient nutrients and participate in electron transfer for the microorganisms in the reactor, resulting in the decrease of denitrification enzyme activity of the microorganisms, the growth and reproduction of the microorganisms were hindered, and the sludge concentration and total nitrogen removal rate in the reactor were reduced. In Comparative Example 6, when the addition amount of metal salt in the microbial growth promoter was too large, the excessive calcium salt and magnesium salt in the microbial growth promoter would cause the osmotic pressure of the extracellular environment of the microorganisms to be too high, the water in the cells would overflow, and the dehydration of the microbial cells in the activated sludge would occur, thereby reducing the sludge concentration in the reactor; secondly, the excessive calcium salt would combine with the phosphate in the sewage to form a precipitate, reducing the available phosphorus source for the microorganisms; and the excessive copper salt and ferrous salt would damage the cell membrane structure of the microorganisms, affecting the normal physiological function of the cells, producing toxic effects on the denitrifying microorganisms, and inhibiting the progress of nitrification and denitrification stages; the mutual influence among the above would cause the total nitrogen removal rate in the reactor to decrease significantly. Since putrescine can participate in the cell division and protein synthesis of microorganisms, and promote the secretion of extracellular polymers with flocculation function, thereby improving the flocculation of sludge; in Comparative Example 7, when too little putrescine was added to the microbial growth promoter, the growth and reproduction of the microorganisms were limited, the ability of the microorganisms to secrete extracellular polymers was weakened, the sludge in the reactor was difficult to settle and separate, and a large amount of suspended solids would be carried out with the effluent, which would not only affect the effluent quality and the operation efficiency of the sewage treatment system, but also reduce the sludge concentration and total nitrogen removal rate in the reactor. In Comparative Example 8, when too much putrescine was added to the microbial growth promoter, it would interfere with the normal function of the microbial cell membrane, the permeability of the cell membrane would change, some harmful substances to the microorganisms would more easily enter the cells, and the transaminase and metabolic products in the cells would leak, so that the microorganisms lacked sufficient energy in the nitrogen metabolism process, further reducing the total nitrogen removal rate. Glucose is an important carbon source for microbial growth, which provides a large amount of energy for the growth and reproduction of microorganisms. In Comparative Example 9, too little glucose was added to the microbial growth promoter, i.e. the microorganisms lacked sufficient carbon source in the growth and reproduction process, which resulted in slow growth and low concentration of the activated sludge on the hydrophilic suspended filler; in the anoxic unit, the denitrifying bacteria could not effectively reduce nitrate and nitrite to nitrogen, thereby reducing the total nitrogen removal rate in the system.In Comparative Example 10, too much glucose was added to the microbial growth promoter, which caused excessive growth of the microorganisms, resulting in a large amount of filamentous bacteria in the sludge. The overgrown filamentous bacteria made the sludge floc loose and difficult to settle. During the wastewater treatment process, excessive sludge and pollutants accumulated on the membrane separation zone, which reduced the permeability of the membrane and increased the transmembrane pressure difference, thereby reducing the wastewater treatment efficiency of the membrane and further reducing the total nitrogen removal rate and the total phosphorus removal rate in the reactor.

[0104] In summary, the metal salt, putrescine, glucose and sodium acetate in the microbial growth promoter provide the carbon source and nitrogen source required for the growth and reproduction of microorganisms. The multi-component synergistic effect provides comprehensive nutrition for the microorganisms, forms a good positive cycle in the entire denitrification membrane bioreactor, and retains the microorganisms in the reactor, which is conducive to the growth of slowly proliferating microorganisms and improves the nitrification efficiency in the system. Therefore, the sludge concentration, effluent quality and denitrification and phosphorus removal efficiency in the denitrification membrane bioreactor are improved.

[0105] Experimental Example 4

[0106] The total phosphorus removal rate was determined according to "Determination of Total Phosphorus in Water - Ammonium Molybdate Spectrophotometric Method" (GB 11893-1989). The specific test results are shown in Table 6 and Figure 1 Data.

[0107] Table 6 Total phosphorus removal rate test of denitrification membrane bioreactor wastewater treatment in Examples 7-12 and Comparative Examples 14-19

[0108]

[0109]

[0110] Table 6 and Figure 1The data show that the total phosphorus removal rate of wastewater in Examples 7-12 is higher than 86%. In Comparative Examples 1-4, the prepared cell population has a particle size that is too large or too small, and the cell population is placed in a low-temperature or room-temperature environment, which reduces the mass transfer efficiency, inactivates most of the Spirulina platensis, and is not conducive to the adsorption and decomposition performance of the hydrophilic suspended material, thereby affecting the metabolism and removal capacity of the material for phosphorus-containing substances. The function of the electric mechanical stirring device in the anoxic unit is to prevent the phosphorus in the sludge from precipitating too quickly, and to enable the sludge to fully contact the microorganisms through stirring, thereby effectively removing nitrogen and phosphorus elements in the wastewater. In Comparative Example 14 and Comparative Example 16, when the rotating speed of the electric mechanical stirring device in the anoxic unit is set too slowly and the stirring power is too low, the sludge is more likely to produce a large amount of precipitation in the anoxic unit, the nitrate and organic matter are not evenly distributed in the sludge, and part of the microorganisms lack nutrients, grow slowly, or even die, thereby inhibiting the activity of the denitrifying bacteria in the anoxic unit, depositing a large amount of phosphorus compounds in the sludge, and reducing the mass transfer efficiency, which weakens the phosphorus removal effect in the entire reactor. In Comparative Example 15 and Comparative Example 17, when the rotating speed of the electric mechanical stirring device in the anoxic unit is set too fast and the stirring power is too high, the sludge will be subjected to excessive shear force, thereby destroying the microbial community and the aggregates formed by the microorganisms in the sludge, and making the overall structure of the sludge loose, which is quickly pushed to other units under the action of the excessive shear force, thereby affecting the absorption and release of phosphorus by the phosphorus-accumulating bacteria, and further reducing the overall phosphorus removal effect. The swing chamber with a suitable swing angle can make the wastewater be filtered more uniformly under more uniform water flow velocity and pressure distribution, improve the flow smoothness of the wastewater from the aerobic unit to the anoxic unit, and from the anoxic unit to the anaerobic unit, which is conducive to creating a suitable growth environment for the aerobic phosphorus-accumulating bacteria, denitrifying bacteria, and anaerobic phosphorus-releasing bacteria; improves the contact efficiency between the pollutants in the wastewater and the microorganisms, further improves the filtration speed and treatment capacity of the membrane, shortens the membrane formation time, and further improves the nitrogen and phosphorus removal efficiency in the wastewater. In Comparative Example 18, the five chambers provided in the aerobic unit, the anoxic unit, and the anaerobic unit in the denitrification membrane bioreactor do not have a swing function, and the chambers are arranged vertically at an angle of 90° with the denitrification membrane bioreactor; at this time, the flow of the wastewater is relatively single, the distribution of oxygen in the aerobic unit is not as uniform as before, thereby slowing down the growth and metabolism of the nitrifying bacteria, reducing the efficiency of the conversion of ammonia nitrogen to nitrate nitrogen, and increasing the ammonia nitrogen content in the effluent of the aerobic unit; after the wastewater enters the anoxic unit, the denitrification process is carried out under a relatively flat flow state, and the dissolved oxygen concentration is not uniform, thereby reducing the denitrification efficiency and the total nitrogen removal rate; when the chambers cannot swing and are vertically arranged, under the condition of relatively limited flow, a local microbial dead zone will appear in the anaerobic unit, thereby reducing the overall nitrogen and phosphorus removal efficiency of the wastewater.

[0111] In summary, the electric mechanical stirring device sets appropriate rotating speed and power, and appropriate swing angle of each cell chamber, so that the sludge can fully contact with the microorganism, the sewage is filtered more uniformly under more uniform water flow speed and pressure distribution, the flow smoothness of the sewage inside the reactor from the aerobic unit to the anoxic unit and from the anoxic unit to the anaerobic unit is improved, which helps to create suitable growth environment for the bacteria such as aerobic phosphorus accumulating bacteria, denitrifying bacteria and anaerobic phosphorus releasing bacteria; the contact efficiency between the pollutants in the sewage and the microorganism is improved, the filtration speed and the treatment capacity of the membrane are further improved, the membrane formation time is shortened, and the nitrogen and phosphorus removal efficiency in the sewage is further improved.

[0112] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely divergences, modifications, replacements and variations of the embodiments, which can be made by those of ordinary skill in the art without departing from the principles and spirit of the application, and the scope of the application is defined by the appended claims and their equivalents.

Claims

1. A method for wastewater treatment by a denitrifying membrane bioreactor, characterized by: The denitrification membrane bioreactor is sequentially provided with an anaerobic unit, an anoxic unit, a membrane separation zone and an aerobic unit from top to bottom; the aerobic unit and the anaerobic unit are both provided with cells with a swing angle of 60°-75° with respect to the vertical direction of the denitrification membrane bioreactor and a light intensity of 2500lx; The aerobic unit and the anaerobic unit are both provided with five cells; the cells are staggered in the aerobic unit and the anaerobic unit; the cells in the aerobic unit and the anaerobic unit can swing at an angle of 60°-75° with respect to the vertical direction of the denitrification membrane bioreactor; the volume ratio of the aerobic unit, the anoxic unit and the anaerobic unit is 2:1:2; The wastewater treatment method of the denitrification membrane bioreactor is as follows: Load the hydrophilic suspended filler accounting for 3 / 5 of the total volume of each reaction unit; The preparation process of the hydrophilic suspended filler is as follows: centrifugal concentration treatment is performed on 50 parts of cultured Spirulina platensis, and after removing the supernatant, the Spirulina platensis is washed with distilled water, and after two centrifugal treatments, an algal cell solution is obtained; 30 parts of the algal cell solution and 40 parts of a sodium alginate solution with a sterilized concentration of 1wt%-3wt% are thoroughly mixed to form a mixed solution; the mixed solution is slowly dropped into a sterilized ferrous chloride solution with a concentration of 3% and stirred to form a cell group with a particle size of 2-3mm; the cell group is placed in a refrigerator with a temperature of 4-8℃ for 24h, and after being taken out of the refrigerator, the cell group is washed twice with the distilled water to obtain algal cell glue balls; 30 parts of activated carbon and 10 parts of polyethylene are added to the algal cell glue balls to fix the algal cell glue balls to obtain the hydrophilic suspended filler; activated sludge is loaded onto the hydrophilic suspended filler in each unit, and each unit is filled; wastewater is injected from the bottom of the denitrification membrane bioreactor, and the wastewater is first injected into the aerobic unit; a microbial growth promoter is added to the aerobic unit, and the mixture is obtained after 24h of muffled exposure; Then, 1 / 3 of the mixture is discharged, and the continuous wastewater is started; the aeration intensity of the aerobic unit is set to 3-5mg / L, and the hydraulic retention time is 8-10h; the rotational speed of the electric mechanical stirring device in the anoxic unit is set to 20-30rpm, and the stirring power is 1.5-2.0kW; the hydraulic retention time ratio of the aerobic unit, the anoxic unit and the anaerobic unit is set to 8-10:5-7:4-5; The microbial growth promoter comprises 30-40 parts of metal salt, 20-30 parts of putrescine, 10-15 parts of glucose and 7 parts of sodium acetate.

2. The process for wastewater treatment by a denitrifying membrane bioreactor according to claim 1, characterized in that: The wastewater is injected into the denitrification membrane bioreactor, and is first injected into the aerobic unit through the water pump and sequentially passes through the five cells of the aerobic unit; then, under the action of the water pump, the wastewater enters the anoxic unit after being separated by the membrane separation zone; the rotational speed of the electromechanical stirring device in the anoxic unit is set to 20-30 rpm, and the stirring power is 1.5-2.0 kW, so that stirring and suction filtration are performed; then, the partition plate between the anoxic unit and the anaerobic unit is opened, so that the wastewater sequentially passes through the five cells of the anaerobic unit and is discharged.

3. The process as claimed in claim 1, wherein the process is characterized by: The metal salt is composed of calcium salt CaCl2, copper salt CuCl2, magnesium salt MgSO4 and ferrous salt FeSO4; the part ratio between the calcium salt CaCl2, the copper salt CuCl2, the magnesium salt MgSO4 and the ferrous salt FeSO4 is 3:1:2:

2.

4. The process as claimed in claim 1, wherein the process is characterized by: The wastewater reflux ratio in the denitrification membrane bioreactor is 300%; the reflux ratio between the aerobic unit and the anoxic unit is 1.7.

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