Multistage filter system based on immobilized microbial carrier and operation method

Abstract

The invention provides a multistage filter system based on an immobilized microbial carrier and an operation method.The system comprises a micro-flocculation water pump, a sedimentation tank, a filter dam and an immobilized microbial filter provided with the microbial carrier which are sequentially communicated, and breeding tail water flows in from the micro-flocculation water pump and flows out from the immobilized microbial filter; the dosage of the microbial carrier in the immobilized microbial filter tank is 5-25% by volume; the microbial carrier comprises an inner hole and a surface layer area, the inner hole is of a macroporous structure with the hole diameter of 0.8-1.2 mm, one or more active chemical groups of-OH,-NH2,-CH (O) CH and CONH2 are distributed on the surface of the inner hole and the surface layer area and chemically bonded with microorganisms, the porosity of the microbial carrier is 97%, and the porosity of the microbial carrier is larger than or equal to 99%. The microbial biomass of the surface layer area is smaller than that of the inner hole of the microbial carrier. According to the invention, the removal efficiency of the sedimentation tank and the filter dam is improved, and the removal of total nitrogen (TN), total phosphorus (TP) and permanganate index (CODMn) is enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of aquaculture tail water treatment, and in particular to a multi-stage filter system based on immobilized microbial carriers and an operation method thereof. Background Art

[0002] The aquaculture tailwater treatment process usually includes steps such as coarse filtration, sedimentation, biological purification and physical purification. First, coarse filtration is carried out through the drainage well network, and then it enters the initial sedimentation tank for sedimentation and filtration treatment. Next, it enters the biological purification tank for further purification treatment, and finally enters the physical purification tank, and is discharged after sedimentation and purification. Commonly used treatment facilities include sedimentation tanks, ecological ditches and ecological purification tanks. Regular cleaning of sludge can be used to reinforce ponds and dams. Large-scale aquatic seedling farms build high-standard treatment facilities on their own, and the treatment facilities of family-type aquatic seedling farms include filtration tanks or microfiltration machines and biochemical tanks, and the treatment facilities can be shared.

[0003] The following problems exist in the actual application of this process: ① It occupies a large area, and the area of ​​treatment facilities accounts for a high proportion of the aquaculture area; ② The treatment efficiency is low, and the sedimentation tank mainly relies on gravity sedimentation, and the efficiency of suspended matter removal is low; ③ The ability to resist shock loads is poor, and farmers usually centrally treat the aquaculture effluent when the water quality of the effluent deteriorates or at the end of the aquaculture period; ④ The construction and operation costs are high. Summary of the invention

[0004] In order to overcome the deficiencies in the prior art, the present invention provides a multi-stage filter system based on immobilized microbial carriers and an operation method.

[0005] To achieve the above object, the present invention provides: a multi-stage filter system based on immobilized microbial carriers, which comprises a micro-flocculation water pump, a sedimentation tank, a filter dam and an immobilized microbial filter provided with microbial carriers, which are connected in sequence, aquaculture tail water flows into the micro-flocculation water pump and flows out of the immobilized microbial filter, and the amount of the microbial carriers in the immobilized microbial filter is 5%-25% by volume;

[0006] The microbial carrier includes an inner pore and a surface area, wherein the inner pore is a macroporous structure with a pore diameter of 0.8-1.2 mm, and one or more active chemical groups of -OH, -NH2, -CH(O)CH and _CONH2 are distributed on the surface of the inner pore and the surface area, chemically bonding with the microorganisms. The porosity of the microbial carrier is 97%, and the microbial biomass of the surface area is smaller than the inner pore of the microbial carrier.

[0007] Preferably, the preparation of the microbial carrier comprises the following steps:

[0008] (1) mixing water, polyether 3010, silicone oil, triethylenediamine, stannous octoate, alkanolamine, halogenated alkyl phosphate, activated carbon and chitosan for foaming;

[0009] (2) cutting the foamed material into particles, reacting with sodium carbonate, and then soaking in an acetic acid solution, washing with water until neutral, and completing the opening of the pores;

[0010] (3) reacting the opened carrier in a 10% chloroacetic acid solution to remember the carrier;

[0011] (4) The carrier is placed into a culture medium containing microorganisms, and a microbial carrier is obtained after sufficient microorganisms have attached.

[0012] Preferably, the microbial load of the microbial carrier is greater than 80 g / L.

[0013] Preferably, the micro-flocculation water pump is provided with a coagulant doser, a tank and a water pump, and the aquaculture tail water is transported by the water pump.

[0014] And the coagulant is added to the aquaculture tail water in the box through the coagulant doser for pretreatment.

[0015] Preferably, the coagulant comprises PAC and / or PFS.

[0016] The present invention provides an operation method of the above-mentioned multi-stage filter system based on immobilized microorganism carriers, which comprises the following steps:

[0017] (1) The aquaculture tail water is introduced into the micro-flocculation water pump for pre-treatment, and then introduced into the sedimentation tank and filter dam;

[0018] (2) The water is then introduced into a fixed microbial filter tank equipped with a microbial carrier. After treatment, part of the water enters the aquaculture pond for recycling, and part of the water meets the discharge standards.

[0019] Preferably, the aeration in the immobilized microbial filter adopts intermittent aeration.

[0020] Preferably, the hydraulic retention time in the immobilized microbial filter is 4-8 hours.

[0021] The beneficial effects of the present invention are as follows:

[0022] The present invention designs a micro-flocculation water pump to achieve the dual purpose of increasing the tailwater head and promoting the flocculation and sedimentation of suspended matter, thereby improving the removal efficiency of the sedimentation tank and the filter dam; the fixed microbial filter is constructed with modified carrier fillers and functional microbial powders to strengthen the total nitrogen (TN), total phosphorus (TP) and permanganate index (COD Mn ) removal; forming aquaculture tailwater treatment process technology with "micro-flocculation water pump-sedimentation tank-filtration dam-immobilized microbial filter" as the main body. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a product picture of a microbial carrier;

[0024] Figure 2 The scanning electron microscope images of the functionalized polyurethane foam carrier and biofilm: (a) 100× carrier without microorganisms; (b) 100× carrier with microorganisms; (c) 4000× carrier with microorganisms;

[0025] Figure 3 The effect of carrier amount and hydraulic retention time on tailwater treatment: (a) TN; (b) TP; (c) COD Mn ; (d) NO3 - ; (e) NO2 - ; (f) NH3-N;

[0026] Figure 4 Aeration time affects tailwater treatment effect;

[0027] Figure 5 The effect of influent concentration on tailwater treatment: (a) TN; (b) TP; (c) COD Mn ; (d) NO3 - ; (e) NO2 - ; (f) NH3-N;

[0028] Figure 6 Effect of coagulant dosage on sedimentation effect (a) PFS; (b) PAC;

[0029] Figure 7 This is a schematic diagram of the structure of the micro-flocculation water pump of the present invention;

[0030] Figure 8 It is an overall schematic diagram of the multi-stage filter system of the immobilized microbial carrier of the present invention. DETAILED DESCRIPTION

[0031] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present application will be further described below in conjunction with specific embodiments.

[0032] The present invention provides a multi-stage filter system based on immobilized microbial carriers, such as Figure 8It includes a micro-flocculation water pump, a sedimentation tank, a filtration dam and an immobilized microbial filter with microbial carriers connected in sequence. Aquaculture tail water flows into the micro-flocculation water pump and flows out of the immobilized microbial filter. The amount of microbial carrier in the immobilized microbial filter is 5%-25% by volume. The microbial carrier includes an inner pore and a surface area. The inner pore is a macroporous structure with a pore size of 0.8-1.2 mm. One or more active chemical groups of -OH, -NH2, -CH(O)CH and _CONH2 are distributed on the surface of the inner pore and the surface area, and chemical bonding occurs with the microorganisms. The porosity of the microbial carrier is 97%, and the microbial biomass of the surface area is smaller than the inner pore of the microbial carrier.

[0033] Furthermore, the micro-flocculation water pump is provided with a coagulant doser, a tank and a water pump, the aquaculture tail water is transported by the water pump, and the coagulant is added to the aquaculture tail water in the tank through the coagulant doser for pre-treatment.

[0034] Example 1: Carrier preparation

[0035] This embodiment provides a method for preparing a microbial carrier in the system of the present invention, which comprises the following steps:

[0036] ① Foaming: Put water, polyether 3010, silicone oil, triethylenediamine, stannous octoate, alkanolamine, halogenated alkyl phosphate, activated carbon and chitosan into a reactor in proportion, stir at high speed for 10 minutes, then add TDI80 and stir at high speed for 2 minutes, pour into a foaming box coated with a release agent, place it in an environment of 40 degrees Celsius for 24 hours, and then take out to obtain a foamed material.

[0037] ② Granulation: Cut the foamed material into 50cm3 particles.

[0038] ③ Opening holes: The above particles are reacted with 10% sodium carbonate solution in a reactor for 6 hours, washed with water until neutral; then soaked in 2% acetic acid solution for 12 hours, washed with water until neutral, and squeezed dry.

[0039] ④ Cross-linking: The porous carrier is reacted in a 10% chloroacetic acid solution at 30°C for 6 hours, squeezed dry, the chloroacetic acid solution is recovered, and the carrier is washed with water until it is neutral to obtain a finished carrier ( Figure 1 ).

[0040] Environmental scanning electron microscopy was used to analyze the morphology of the carrier before and after loading microorganisms and the characteristics of the carrier biofilm. The electron acceleration pressure was 5KV. The results are as follows: Figure 2As shown in Figure 2, the carrier has a macroporous structure with a pore size of about 1 mm. This structure is conducive to the adhesion of bacteria to the carrier and helps the effective mass transfer rate between microorganisms and the matrix, thereby improving the metabolic capacity and impact resistance of microorganisms. This functional carrier is a polymer with micropores and macropores, which is cross-linked and formed by adding chitosan and powdered activated carbon in the synthesis of polyurethane elastic foam plastics. The microstructure can promote effective mass transfer between microorganisms and the matrix, and the microporous surface provides -OH, -NH2, -CH(O)CH and _CONH2. Multiple active chemical groups have good affinity for microbial cell membranes, which is conducive to bonding with microorganisms, adhesion and proliferation of microbial cells, and then make the bacteria adhere to the carrier surface; macroscopic pores contribute to good water permeability and mass transfer process. The inner pores and surface areas of the carrier material are tightly adhered and dispersed by microorganisms, indicating that the microorganisms are successfully adsorbed on the carrier after incubation and denitrification treatment.

[0041] Example 2: Immobilized microorganism acclimatization and attachment

[0042] This embodiment provides the domestication and attachment of immobilized microorganisms to the microbial carrier in the system of the present invention, which includes the following steps: the immobilized carrier of the microbial bacterial liquid (Paraccoccus, Pseudomonas, Diaphorobacter and Pseudoxanthomonas, ratio 4:2:1:1) is put into the culture solution containing microorganisms for cultivation, and the inoculation amount of the bacterial liquid is 20% of the culture solution. After the microorganisms attach to the carrier and grow, the operating conditions of the immobilized microbial filter are investigated.

[0043] Cultivation and acclimatization process: In the acclimatization stage, firstly, the carrier and microbial powder are put into the biofilter. The water quality of the inlet water is shown in Table 2-1 below. On the first day, the inlet and outlet valves are closed, nitrogen is charged to make the dissolved oxygen concentration in the system 0.3-0.8 mg / L, and the biofilter is micro-aerated for one day; then the inlet and outlet valves are opened, and synthetic water is pumped into the filter at a flow rate of 4.17 ml / min (HRT is 12h) by pump, and the continuous flow acclimatization and biofilm cultivation for fourteen days begins. When the biofilm is obviously grown on the carrier and the water quality is stable, it means that the microorganisms have been successfully acclimatized and attached.

[0044] Table 2-1

[0045] name Sodium nitrate Sodium acetate Potassium dihydrogen phosphate Magnesium sulfate Calcium chloride Concentration (mg / L) 121.4 212.6 5.5 10 40

[0046] Determination of carrier biomass: Carefully remove the biofilm carrier and gently rinse it with deionized water several times to remove loose impurities on the carrier surface; place the sample in a 1mol / L NaOH solution and heat it in a water bath at 60°C for 30 minutes; after heating in an alkaline solution, ultrasonicate it at 100W for 30 minutes to remove the biofilm adhering to the carrier as much as possible; finally, filter the detached biofilm mixture through a 0.45μm filter membrane, place the filter paper and the treated carrier in an oven, and weigh them after drying at 80°C for 30 minutes. The biomass attached to the unit mass of the biological carrier can be obtained by calculating the ratio of the mass difference before and after filtration of the filter paper to the mass of the blank carrier. It has been determined that the microbial load of the carrier is about 83g / L.

[0047] Example 3: Study on the operating conditions of the immobilized microbial filter

[0048] This example provides the operating conditions of the immobilized microbial filter in the system of the present invention. The selected operating parameters of the immobilized microbial filter mainly include: carrier dosage, hydraulic retention time, aeration time, influent concentration, etc., aiming to show the influence of various factors on the treatment effect of the immobilized microbial filter on aquaculture tail water. In order to better show the effect, this experiment adopts artificially configured aquaculture tail water, and the water quality is as shown in Table 3-1:

[0049] Table 3-1 Water quality indicators of artificial simulated aquaculture tail water

[0050]

[0051] Acclimation scheme: The denitrifying bacteria used in this experiment were cultured in conical flasks. During the experiment, the nitrogen sources used were KNO3, NH4Cl, and NaNO2; the carbon source used was sodium acetate (CH3COONa), and the C / N ratio was maintained at 4:1. The specific formula of the culture solution is shown in Table 3-2.

[0052] Table 3-2 Culture medium formula

[0053]

[0054] In the acclimation stage, first put the carrier and 2g / L microbial preparation into a conical flask, add the above-prepared culture solution, put it into an air bath constant temperature oscillator and shake it at 30°C to promote aerobic growth of microorganisms. The culture solution in the conical flask is not changed in the first few days of cultivation. The water needs to be changed every day in the subsequent cultivation stage. After a week of continuous cultivation, obvious biofilms appear on the carrier, indicating that the microorganisms have adapted and colonized on the surface of the carrier. After the water quality is stable, the next stage of experimental research can be entered.

[0055] ①Control of carrier dosage and hydraulic retention time

[0056] In five 250ml drying conical flasks, add 5%, 10%, 15%, 20%, and 25% of the volume of the conical flask to the domesticated immobilized microorganisms, add simulated aquaculture tail water after microflocculation treatment to the 200ml mark, and surround the bottle mouth with a sealing film, put it into an air bath constant temperature oscillator and shake it at 30℃. Take the supernatant after 0.5h, 1h, 2h, 4h, and 8h, and use an ultraviolet spectrophotometer to determine its TN, TP, nitrate nitrogen (NO3-), nitrite nitrogen (NO2-), ammonia nitrogen (NH3-N), and use COD reagent to determine its CODMn concentration. The experimental data obtained are organized into charts for comparison to obtain the optimal carrier dosage and hydraulic retention time. The results are as follows Figure 3 , 4 .

[0057] from Figure 3 (a) TN It is not difficult to determine that the increase in hydraulic retention time HRT causes the TN content in the water to decrease continuously, but it tends to be flat between 4h and 8h, indicating that the treatment efficiency of immobilized microorganisms will gradually decrease after 8h. This figure also clearly shows that when the dosage is 20%, the TN removal effect is the best and after 30 minutes of contact with the aquaculture tail water, the TN concentration is lower than other dosages; when the dosage is 5%, the TN concentration is 16.21mg / L, the highest. Figure 3 (b) shows that the TP of most samples decreases with the increase of hydraulic retention time before 4h. However, the TP content of samples with less dosage increases again in the 4h-8h stage. It can also be clearly seen from this figure that when the dosage is 20%, the TP concentration is 4.79mg / L; when the dosage is 5%, the TP removal effect is poor, and the concentration is 8.01mg / L. Figure 3 (c) COD Mn The data show that with the increase of hydraulic retention time, COD Mn The lowest concentration is when the dosage is 20%, the concentration is only 5 mg / L.

[0058] When the hydraulic retention time is 0.5h and the dosage is 5%, the concentration of CODMn is the highest. At 4h-8h, the CODMn concentrations of all sample solutions tend to be stable or increase. Since CODMn is measured using a convenient reagent, the color ratio diagram has fewer values, which leads to unstable values ​​in the picture and problems such as too long treatment and temperature differences. Therefore, the measurement results of CODMn are inconsistent with the expected effects. From the experimental data of NO3- in Figure (d), it can be seen that the content of NO3- in the water is constantly decreasing as the hydraulic retention time gradually increases, but it tends to be flat between 4h and 8h, indicating that the ability of immobilized microorganisms to adsorb NO3- is gradually decreasing after 8h. This figure also shows that when the dosage is 20%, it is the best removal amount of NO3- and after 30 minutes of contact with the aquaculture tail water, the NO3- concentration is significantly lower than other dosages; when the dosage is 5%, the removal effect of NO3- is the worst. Figure 3 (e) The removal effect of NO2- It can be seen that the concentration of NO2- decreases with the increase of hydraulic retention time. When the hydraulic retention time is 0.5h, the sample liquid treated with 20% dosage of immobilized microorganisms has the lowest NO2- concentration and the best removal effect. The sample liquid treated with 5% dosage of immobilized microorganisms has the highest NO2- concentration and the worst removal effect. Within the 8h operation time, it is obvious from the figure that the 20% dosage of immobilized microorganisms is better than other dosages and the NO2- concentration actually increases when the 25% dosage is 4-8h. Figure 3 (f) The removal effect of NH3-N shows that the concentration of NH3-N decreases with the increase of hydraulic retention time. When the hydraulic retention time is 8h, the sample liquid treated with 20% dosage of immobilized microorganisms has the lowest NH3-N concentration and the best removal effect. The sample liquid treated with 25% dosage of immobilized microorganisms has the highest NH3-N concentration and the worst removal effect.

[0059] In summary, when the carrier dosage is 20%, the removal effect is the best, and considering factors such as the pool body, the hydraulic retention time can be selected as 4h.

[0060] ②Control of aeration time

[0061] According to the optimal carrier dosage and hydraulic retention time obtained from the above experiment, the immobilized microorganisms with this dosage were placed in three 250ml conical flasks, and the simulated aquaculture tail water after micro-flocculation treatment was added to the 200ml scale line. The bottle mouth was surrounded by a sealing film, and the bottle was placed in an air bath constant temperature oscillator for constant shaking at 30℃. The aeration time was set to 8h for aeration, 4h for aeration and then 4h for standing, and 8h for standing. After the aeration time, the supernatant was taken and the TN, TP, NO3-, NO2-, and NH3-N were determined by ultraviolet spectrophotometer, and the CODMn concentration was determined by COD reagent. The experimental data obtained were organized into charts for comparison to obtain the optimal aeration time.

[0062] This experiment explored the effect of different aeration times on tailwater treatment. Figure 4 As shown, the solution was prepared according to the concentration of water quality indicators after microflocculation process treatment, and aeration was ensured at room temperature of 30°C. Among the three groups of aeration time, the TN concentration of the group without aeration for 8h was the highest, but the concentration was lower than 22.6mg / L, indicating that the immobilized microorganisms could also remove water quality indicators without aeration. The TN concentration was ranked from high to low as follows: no aeration 8h> aeration 8h> aeration 4h no aeration 4h, with concentrations of 11.02mg / L, 7.86mg / L, and 6.43mg / L, respectively. It can be seen that intermittent aeration has a promoting effect on the optimization of parameter conditions of the immobilized microbial filter. After the aeration, the TP concentrations of the three groups of experiments decreased, and the concentrations were lower than 16.4mg / L. The TP concentrations were ranked from high to low as follows: no aeration 8h> aeration 8h> aeration 4h no aeration 4h, with concentrations of 4.79mg / L, 6.28mg / L, and 3.95mg / L, respectively, which is the same as the experimental results of TN mentioned above. The concentrations of NH3-N, NO3-, and NO2- are all decreasing, and the sum of the three is much lower than the TN concentration of 22.6 mg / L after microflocculation treatment. The removal effect is significant. Figure 5 It can be seen that the concentrations of NO2- and NH3-N are not much different when aeration is performed for 8 hours and when aeration is performed for 4 hours and no aeration is performed for 4 hours. Mn The concentration changes greatly during aeration time. The concentrations are the same when aeration is performed for 8 hours and when aeration is performed for 4 hours without aeration, both of which are 5 mg / L. However, the concentration is higher when aeration is performed for 8 hours, and the contact reaction between microorganisms and tail water is not sufficient. In terms of the overall water quality index concentration reduction rate, intermittent aeration for 4 hours has the best effect. Therefore, intermittent aeration can be selected in subsequent experiments.

[0063] ③Control of influent concentration

[0064] According to the optimal carrier dosage, hydraulic retention time and aeration time obtained from the above experiment, the culture solution concentration uses the tail water concentration after the micro-flocculation process, a 250ml conical bottle containing immobilized microorganisms with the optimal carrier dosage is surrounded by a sealing film, placed in an air bath constant temperature oscillator and shaken at a constant temperature of 30°C. After the optimal hydraulic retention time and the optimal aeration time, the supernatant is taken and the TN, TP, NO3-, NO2-, NH3-N are determined by a UV spectrophotometer, and the CODMn concentration is determined by a COD reagent.

[0065] from Figure 5The comparison of the TN removal effect chart shows that the TN concentrations of the two groups are continuously decreasing. The TN concentration decrease rate of the high-concentration group is slightly higher than that of the other group. The removal efficiency of the low-concentration group increases from 2h to 4h, and both groups tend to be flat after 4h to 8h. After 8h, the treatment efficiency of the immobilized microorganisms will gradually decrease. It can also be clearly seen from this chart that the TN of the low-concentration group at 8h is lower than that of the other group, with a concentration of 5.78mg / L. The low concentration itself may also cause its overall treatment efficiency to be lower than that of the high-concentration group. Figure 5 (b) The removal effect on TP shows that the TN concentrations of the two groups decrease with the increase of hydraulic retention time, and the effect is obvious. However, in the 0.5h-4h stage, the TP concentration in the high-concentration group decreases faster and tends to be flat at 4h-8h. In general, the removal efficiency of the high-concentration group is higher. Figure 5 NH3-N, NO3 in (c)(d)(e) - , NO2 - The concentrations of are all decreasing, and the overall trend is similar to that of TN. All three show that the slope of the curve is large and the concentration removal efficiency is high when the time is 0.5-4h, and the slope of the curve tends to be gentle when the time is 4h-8h. Figure 5 (f) COD Mn It can be seen from the removal effect that the potassium permanganate index of the low concentration group decreased rapidly and the concentration did not change in the remaining time. The high concentration group increased positively with the hydraulic retention time in the first half hour. After 1 hour, COD Mn The value drops to the same level as the low concentration group until the running time ends and no longer changes.

[0066] Example 4: Control of coagulant dosage and sedimentation time

[0067] This embodiment provides a method for pre-treatment of aquaculture tail water by introducing a micro-flocculation pump in the system described in the present invention, and adopts two coagulants, PAC and PFS, for treatment. First, the two coagulants are configured into a 20 / L solution as a stock solution for standby use. Take 400mL of aquaculture tail water in 10 500mL beakers respectively, and add 0.2, 0.4, 0.8, 1.2, and 2mL of 2% PAC solution respectively; add 0.2, 0.4, 0.8, 1.2, and 2mL of 2% PFS solution to one group. Make the concentration of coagulant in the water sample 10, 20, 40, 60, 80, and 100 mg / L respectively. After stirring for 30S, let it stand and settle. Take the supernatant after 5, 10, 20, and 30 minutes to measure the turbidity. The effects of different coagulant dosages and sedimentation times on the coagulation effect are shown in the figure. Figure 6 shown.

[0068] Depend on Figure 6(a) It can be seen that with the increase of PFS dosage, the turbidity shows a trend of first decreasing and then increasing. After 30 minutes of sedimentation, the turbidity is 17.4, 15.9, 17.9, 14.1, 8.1, and 12.6 NTU when the coagulant dosage is 10, 20, 40, 60, 80, and 100 mg / L, respectively. When the dosage increases to 80 mg / L, the turbidity removal rate is the highest and the best effect is achieved. When the dosage is greater than the optimal dosage, it can be seen that the coagulation effect no longer increases and decreases slightly. This is because the dosage of the drug should be determined according to the colloid concentration and the molecular form, charge properties and charge of the hydrolysis products of inorganic metal salts. When the amount of coagulant added is large, the coagulants will affect each other, causing changes in the compression of the double electric layer, adsorption bridging, and net capture capabilities, but not all of the forces are strengthened. When it is greater than its optimal dosage, the effect of adding coagulants will be reduced. As the sedimentation time increases from 5 min to 30 min, the turbidity removal rate gradually increases. When the sedimentation time is 10 min and 30 min, the removal rate is not much different. Considering the subsequent sedimentation tank volume and cost, it is appropriate to choose a sedimentation time of 10 min.

[0069] Figure 6 (b) It can be seen that with the increase of PAC dosage, the turbidity shows an overall downward trend. After 30 minutes of sedimentation, the turbidity is 13.6, 9.5, 4.5, 4.2, 3.3, and 1.5 NTU when the coagulant dosage is 10, 20, 40, 60, 80, and 100 mg / L, respectively. When the PAC dosage reaches 100 mg / L and 40 mg / L, the turbidity removal rate is not much different. Considering the cost, the optimal dosage of PAC is 40 mg / L. Similarly, as the sedimentation time increases from 5 min to 30 min, the turbidity removal rate gradually increases. When the sedimentation time is 10 min and 30 min, the removal rates are 81.56% and 82.35% respectively, and the removal rates are not much different. Considering the subsequent sedimentation tank volume and cost, the sedimentation time is preferably 10 min. Comparing PFS and PAC, it can be seen that the coagulation effect of PAC is better than that of PFS under the same dosage.

[0070] In general, the coagulation effect of PAC is better than that of PFS, so PAC can be given priority as a coagulant in subsequent experiments. When the PAC dosage is 40 mg / L and the sedimentation time is 10 min, the turbidity removal rate is 87.05%.

[0071] According to the above-mentioned coagulant dosage and the influence of sedimentation time, the optimal dosage of PFS is 80 mg / L, the dosage of PAC is 40 mg / L, and the sedimentation time is 10 min. Take the two groups of water samples, and measure the water quality indicators (COD, TN, NH4-N, NO3-N, NO2-N, TP, pH) before and after the addition of coagulants. The results are shown in Table 4-1. Under the optimal dosage conditions, the COD removal rates after adding PFS and PAC were 66.67% and 76.67% respectively, and the TN removal rates were 13.11% and 25.83% respectively. There is no obvious rule in the removal rate of TN by the two coagulants, and the removal rates are relatively low. The removal of nitrogen mainly depends on biological action. The removal of TN in the coagulation process comes from the co-sedimentation of nitrogen-containing substances and coagulants, which may be one of the reasons for the low TN removal rate. The removal rates of the two coagulants for TP were 67.65% and 70.59%, respectively, which are relatively high. The effective ingredient aluminum ion in the PAC agent has a high degree of electrical neutralization and bridging function for colloids and particles in water. It instantly neutralizes the negative charge carried by the colloid particles in water, destabilizes the colloid, and the colloid particles quickly flocculate, and further bridge to form large flocs and quickly precipitate, thereby separating the phosphorus-containing pollutants in the water from the solution. The pH of the water sample was stable at neutral before and after the addition of coagulation.

[0072] In general, after adding coagulants, while reducing turbidity, COD, TN and TP have a certain removal effect. The removal effect of PAC on pollutants is better than that of PFS.

[0073] Table 4-1 Water quality indicators before and after coagulation

[0074]

[0075]

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A multi-stage filter system based on immobilized microbial carriers, characterized in that: The method comprises a micro-flocculation water pump, a sedimentation tank, a filter dam and an immobilized microbial filter provided with a microbial carrier, which are connected in sequence. The aquaculture tail water flows into the micro-flocculation water pump and flows out of the immobilized microbial filter. The amount of the microbial carrier in the immobilized microbial filter is 5% to 25% by volume. The microbial carrier includes an inner pore and a surface area, wherein the inner pore is a macroporous structure with a pore diameter of 0.8-1.2 mm, and one or more active chemical groups of -OH, -NH2, -CH(O)CH and _CONH2 are distributed on the surface of the inner pore and the surface area, chemically bonding with the microorganisms. The porosity of the microbial carrier is 97%, and the microbial biomass of the surface area is smaller than the inner pore of the microbial carrier.

2. The multi-stage filter system based on immobilized microbial carriers according to claim 1, characterized in that: The microbial carrier preparation comprises the following steps: (1) mixing water, polyether 3010, silicone oil, triethylenediamine, stannous octoate, alkanolamine, halogenated alkyl phosphate, activated carbon and chitosan for foaming; (2) cutting the foamed material into particles, reacting with sodium carbonate, and then soaking in an acetic acid solution, washing with water until neutral, and completing the opening of the pores; (3) reacting the opened carrier in a 10% chloroacetic acid solution to remember the carrier; (4) The carrier is placed into a culture medium containing microorganisms, and a microbial carrier is obtained after sufficient microorganisms have attached.

3. The multi-stage filter system based on immobilized microbial carrier according to claim 1, characterized in that: The microbial load of the microbial carrier is greater than 80 g / L.

4. The multi-stage filter system based on immobilized microbial carriers according to claim 1, characterized in that: The micro-flocculation water pump is provided with a coagulant doser, a box body and a water pump. The aquaculture tail water is transported by the water pump, and the coagulant is added to the aquaculture tail water in the box body through the coagulant doser for pretreatment.

5. The multi-stage filter system based on immobilized microbial carriers according to claim 1, characterized in that: The coagulant includes PAC and / or PFS.

6. The method for operating the multi-stage filter system based on immobilized microbial carriers according to any one of claims 1 to 5, characterized in that: The following steps are included: (1) The aquaculture tail water is introduced into the micro-flocculation water pump for pre-treatment, and then introduced into the sedimentation tank and filter dam; (2) The water is then introduced into a fixed microbial filter tank equipped with a microbial carrier. After treatment, part of the water enters the aquaculture pond for recycling, and part of the water meets the discharge standards.

7. The method according to claim 6, characterized in that: The aeration in the immobilized microbial filter adopts intermittent aeration method.

8. The method according to claim 6, characterized in that: The hydraulic retention time in the immobilized microbial filter is 4-8h.

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